Nanofibers and methods for forming same - Patents.com

Abstract

The present disclosure relates to nanofibers and methods of forming the nanofibers, the method of forming the nanofibers includes providing a 2D material having charge-carrying moieties on its planar surface and at its ends, reacting the charge-carrying moieties on the planar surface with a proton donor, a proton acceptor, an at least partially hydrophobic counterion, or a second 2D material having opposite charge-carrying moieties on its planar surface and at its ends to curl the 2D material, and crosslinking the neutralized charge-carrying moieties on the ends while reacting the charge-carrying moieties on the ends with a proton donor, a proton acceptor, an at least partially hydrophobic counterion, or a second 2D material having opposite charge-carrying moieties on its planar surface and at its ends to cause the 2D materials to interact with each other to form nanofibers.

Description

[Technical field]

[0001] The present invention relates generally to nanofibers and methods of forming the nanofibers. [Background technology]

[0002] Since the advent of graphene in 2004, several methods have been developed to produce scalable, high-quality graphene. These methods can be roughly divided into two categories: 1) top-down and 2) bottom-up. Top-down methods start with graphite and reduce the size of the graphite by reducing the number of layers to one or a few layers. This is the case of the liquid phase exfoliation (LPE) method. Bottom-up approaches start with molecular-sized materials and grow them to larger sizes, as in the case of chemical vapor deposition (CVD). These methods have both advantages and disadvantages. With LPE, micrometer-sized single-crystalline flakes with several layers can be obtained, while with CVD, single-layer polycrystalline macroscopic films are obtained. However, in most cases, graphene requires further improvement to adapt its size, surface, and morphology to technological requirements.

[0003] Besides two-dimensional (2D) graphene, carbon-based nanomaterials can adopt a wide variety of structures, e.g., one-dimensional (1D) morphologies: carbon nanotubes, scrolls, and fibers. The creation of systems with responsive conformational changes (2D⇔1D) is also of great relevance to a wide range of applications, including drug delivery, hydrogen storage, sensors, membranes for filtration, and structures to mimic biological systems such as muscle filaments and microtubules, as well as the aerospace and automotive industries. Graphene fibers have attracted great attention, especially for applications in smart electronic textile devices, fabrics, and as flexible and wearable electronics and sensors. Due to their high aspect ratio, light weight, and resistance, graphene fibers are also very promising as reinforcements for personal protective equipment, thermal management, and the automotive and aerospace industries. The tunable interlayer distance and high electrical conductivity make them attractive for energy applications such as batteries and supercapacitors. Furthermore, their high aspect ratio and ability to intertwine and form cross-linked structures may enable the creation of high performance membranes for air and water purification, as well as aerogels with controlled and reduced pore sizes. In medicine, for example, fibrillar materials can mimic the fibrous nature of the extracellular matrix and serve as excellent tools for tissue engineering and regenerative medicine.

[0004] Graphene fibers with high aspect ratios and nanoscale thicknesses are usually produced by template methods, e.g., carbonization of polypyrrole nanofibers, pyrolysis of bacterial cellulose, or the use of tellurium (Te) nanowires with very high aspect ratios; in this last case, Te@carbon is obtained in the presence of Te nanowires by a hydrothermal carbonization process from glucose, after which the Te core is removed by chemical methods. Thus, it remains a challenge to controllably produce high-aspect-ratio and high-quality 1D graphene fibers from graphene sheets in suspension under mild template-free conditions. Macroscopic graphene fibers with diameters over 60 μm are usually produced by wet-spinning processes similar to those used to produce polymer fibers.

[0005] It would be desirable to overcome or ameliorate at least one of the above problems. Summary of the Invention

[0006] The present invention is based on the understanding that nanofiber assembly can be controlled by short- and long-range interactions such as covalent and hydrogen bonds, hydrophobic interactions, ionic interactions, and π-π stacking. In this regard, it has been found that 2D electrolytes, which are 2D materials with ionic groups attached to their surface that can be deprotonated in liquid media, can undergo morphological transitions in a manner similar to polyelectrolytes, followed by self-assembly and crosslinking in the presence of bifunctional molecules to form long nanofibers. This assembly can also be performed between two different types of 2D electrolytes, called heterostructured nanofibers. Another approach involves the presence of 2D confining electrolytes, which are 2D materials with organic / inorganic salts on the basal plane, and the use of another organic / inorganic salt that leads to ion exchange and destabilization of the system, causing phase separation / solidification resulting in fibers. This catalyst-free and self-templated approach allows the incorporation of 2D electrolytes into composite nanofibers with higher aspect ratios using mild conditions such as aqueous media and room temperature.

[0007] The present invention provides a method of forming nanofibers, comprising the steps of: a) providing a 2D material having charge-carrying portions on its planar surface and at its edges; b) reacting the charge-carrying moieties on the planar surface with a proton donor, a proton acceptor, an at least partially hydrophobic counterion, or a second 2D material having opposite charge-carrying moieties on the planar surface and at its edges to curl the 2D material; and c) reacting the charge-carrying moieties at the ends with a proton donor, a proton acceptor, an at least partially hydrophobic counterion, or a second 2D material having opposite charge-carrying moieties on its planar surface and at its ends, so that the 2D materials of step b) interact with each other to form nanofibers, while simultaneously crosslinking the reacted charge-carrying moieties at the ends.

[0008] It was found that the charge-carrying moieties allow for better dispersion of nanomaterials in aqueous media. For example, graphene can only be dispersed in water after functionalization. The charge-carrying moieties also maintain the 2D material in its planar configuration until it reacts to form nanofibers. The charge-carrying moieties can also induce some conformational changes depending on some specific conditions, such as pH and sonication time. In this sense, the charge-carrying moieties are configured to lose their charge upon neutralization. Furthermore, by providing the charge-carrying moieties on the surface of the nanomaterial, the crosslinking rate can be controlled by varying the reaction conditions, such as pH and bifunctional or multifunctional crosslinkers. In this way, the growth of the nanofibers can be controlled.

[0009] In some embodiments, the charge-carrying moiety is selected from a protonated moiety, a deprotonated moiety, a cationic moiety, or an anionic moiety.

[0010] In some embodiments, the method is carried out in an aqueous medium.

[0011] In some embodiments, the method is carried out at about 10°C to about 50°C.

[0012] In some embodiments, the methods do not rely on a template to form the nanofibers.

[0013] In some embodiments, the two-dimensional material is selected from graphene, graphene oxide, few-layer transition-metal dichalcogenides, hexagonal boron nitride, or combinations thereof.

[0014] In some embodiments, the few-layer transition metal dichalcogenide is selected from MoS2, MoSe2, MoTe2, WS2, or WSe2.

[0015] In some embodiments, the 2D material is at least about 50% functionalized with a charge carrying moiety.

[0016] In some embodiments, the charge-carrying moiety responds by changing the pH.

[0017] In some embodiments, reacting steps b) and / or c) are carried out at a pH of about 3 to about 6.

[0018] In some embodiments, reacting steps b) and / or c) are carried out at a pH of about 4.

[0019] In some embodiments, the at least partially hydrophobic counterion is selected from imidazolium, pyridinium, piperidinium, ammonium, phosphonium, imide, sulfonate, sulfate, borate, phosphate, carboxylate, or derivatives thereof.

[0020] In some embodiments, the 2D material having opposite charge carrying moieties is selected from graphene, graphene oxide few layer transition metal dichalcogenides, hexagonal boron nitride, or combinations thereof.

[0021] In some embodiments, the 2D material having opposite charge carrying moieties is at least about 50% functionalized with the charge carrying moiety.

[0022] In some embodiments, step (b) further comprises cross-linking the reacted charge-carrying moieties on the planar surface.

[0023] In some embodiments, the crosslinking is carried out in the presence of a crosslinking agent.

[0024] In some embodiments, the cross-linking agent comprises at least two cross-linkable moieties.

[0025] In some embodiments, the weight ratio of crosslinker to 2D material is from about 50:1 to about 700:1.

[0026] In some embodiments, at least step b) is performed under sonication and / or stirring.

[0027] In some embodiments, sonication is at about 3° C. to about 10° C. for at least 10 minutes.

[0028] In some embodiments, the method further comprises functionalizing the 2D material with a charge carrying moiety to form a 2D material having a charge carrying moiety of step a).

[0029] In some embodiments, the step of functionalizing the 2D material with a charge-carrying moiety is carried out at a pH of about 5 to about 6.9.

[0030] In some embodiments, the step of functionalizing the 2D material with a charge-carrying moiety is performed under sonication.

[0031] In some embodiments, sonication is at about 3° C. to about 10° C. for at least 10 minutes.

[0032] In some embodiments, sonication is at about 3° C. to about 10° C. for at least 30 minutes.

[0033] In some embodiments, the step of functionalizing the 2D material with a charge-carrying moiety is carried out for at least 2 hours.

[0034] In some embodiments, the step of functionalizing the 2D material with a charge-carrying moiety is carried out for at least 72 hours.

[0035] In some embodiments, the step of functionalizing the 2D material with a charge carrying moiety is carried out at about 20 °C to about 70 °C.

[0036] In some embodiments, when the 2D material is graphene, the step of functionalizing the 2D material with a charge carrying moiety is performed at about 45° C.

[0037] In some embodiments, when the 2D material is MoS2, the step of functionalizing the 2D material with a charge carrying moiety is performed at about 20°C to about 40°C.

[0038] In some embodiments, when the 2D material is graphene, the step of functionalizing the 2D material with a charge carrying moiety is performed under an inert atmosphere.

[0039] In some embodiments, if the pH is maintained and / or the counterions are in excess, the method is self-perpetuating until all the 2D material has reacted.

[0040] In some embodiments, a method of forming nanofibers includes: a) providing a 2D material having protonated or deprotonated moieties on its planar surface and at its edges; b) reacting protonated or deprotonated moieties on the planar surface with proton donors or proton acceptors to curl the 2D material; and c) reacting the protonated or deprotonated moieties at the ends with a proton donor or proton acceptor while simultaneously covalently cross-linking the reacted moieties at the ends so that the 2D materials of step b) interact with each other to form nanofibers.

[0041] In some embodiments, the protonated or deprotonated moiety is a carboxylate moiety.

[0042] In some embodiments, the carboxylate moiety is a carboxyl compound selected from 5-azidopentanoic acid, 6-azido-hexanoic acid, azido-dPEG4-acid, azidopalmitic acid, azidoacetic acid, mercaptopropionic acid, mercaptoacetic acid, 5-mercaptopentanoic acid, or combinations thereof.

[0043] In some embodiments, the charge-carrying moiety is neutralized by changing the pH.

[0044] In some embodiments, steps b) and / or c) are performed at a pH of about 3 to about 6.

[0045] In some embodiments, step b) further comprises covalently crosslinking the reacted protonated or deprotonated moieties on the planar surface.

[0046] In some embodiments, the protonated or deprotonated moiety is covalently crosslinked with a multifunctional or difunctional amino compound.

[0047] In some embodiments, the amino compound comprises at least two amino moieties.

[0048] In some embodiments, the amino compound is triethylenetetramine, triethylenediamine, ethylenediamine, p-phenylenediamine, or a combination thereof.

[0049] In some embodiments, crosslinking is performed in the presence of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) and N-hydroxysuccinimide (NHS).

[0050] In some embodiments, steps b) and c) are carried out at about 3° C. to about 30° C. for at least 1 hour.

[0051] In some embodiments, steps b) and c) are carried out at about 3° C. to about 10° C. for at least 12 hours.

[0052] In some embodiments, steps b) and c) are carried out at about 3° C. to about 10° C. for at least 72 hours.

[0053] In some embodiments, the method involves forming nanofibers in an aqueous medium, the method comprising: a) providing a 2D material having cationic or anionic moieties on its plane and at its edges; b) reacting cationic or anionic moieties on the planar surface with at least partially hydrophobic counterions to curl the 2D material; and c) reacting the cationic or anionic moieties at the ends with at least partially hydrophobic counterions while ionically crosslinking the reacted charge-carrying moieties at the ends so that the 2D materials of step b) interact with each other to form nanofibers.

[0054] In some embodiments, the cationic or anionic moieties are electrostatically bound to the 2D material.

[0055] In some embodiments, the ratio of 2D material to cationic or anionic moieties is from about 1:30 to about 1:80.

[0056] In some embodiments, the ratio of 2D material to cationic or anionic moieties is about 1:50.

[0057] In some embodiments, the cationic or anionic moiety is an organic cationic or anionic moiety.

[0058] In some embodiments, the anionic moiety is bis(trifluoromethane)sulfonimide.

[0059] In some embodiments, the anionic moiety is provided as a salt selected from lithium bis(trifluoromethane)sulfonimide.

[0060] In some embodiments, the charge-bearing moiety reacts with a counterion that has an opposite charge to the cationic or anionic moieties on the 2D material.

[0061] In some embodiments, the counterion is an organic counterion.

[0062] In some embodiments, the counterion is selected from imidazolium, pyridinium, piperidinium, ammonium, phosphonium, imide, sulfonate, sulfate, borate, phosphate, carboxylate, or derivatives thereof.

[0063] In some embodiments, the counterion is 1-butyl-3-methylimidazolium.

[0064] In some embodiments, the counterion is provided by a salt selected from 1-butyl-3-methylimidazolium methanesulfonate.

[0065] In some embodiments, the ratio of 2D materials with cationic or anionic moieties to counterions is about 1:30 to about 1:80.

[0066] In some embodiments, the ratio of 2D materials with cationic or anionic moieties to counterions is about 1:50.

[0067] In some embodiments, step b) further comprises ionically crosslinking the reacted cationic or anionic moieties on the planar surface.

[0068] In some embodiments, at least step b) is performed under sonication.

[0069] In some embodiments, sonication is carried out at about 3° C. to about 10° C. for at least 10 minutes.

[0070] In some embodiments, the method further comprises functionalizing the 2D material with cationic or anionic moieties to form a 2D material having cationic or anionic moieties in step a).

[0071] In some embodiments, the step of functionalizing the 2D material with cationic or anionic moieties is carried out under sonication in the presence of the cationic or anionic moieties.

[0072] In some embodiments, sonication is carried out at about 3° C. to about 10° C. for at least 10 minutes.

[0073] In some embodiments, when the 2D material is graphene, the method further comprises, prior to step a), exfoliating graphite in the presence of cationic or anionic moieties.

[0074] In some embodiments, the graphite and cationic or anionic moieties are dispersed in an aqueous medium and an organic medium mixture in a ratio of about 95: 5. In some embodiments, the aqueous medium and the organic medium are immiscible.

[0075] In some embodiments, the peeling step is performed under high power probe sonication.

[0076] In some embodiments, the method involves forming nanofibers in an aqueous medium, the method comprising: a) providing a 2D material having cationic or anionic moieties on its plane and at its edges; b) reacting cationic or anionic moieties on the planar surface with another 2D material having opposite charge-carrying moieties on the planar surface and at its edges to curl the 2D material; and c) reacting the cationic or anionic moieties at the ends with another 2D material having opposite charge-carrying moieties on its planar surface and at its ends, while ionically crosslinking the reacted charge-carrying moieties at the ends, so that the 2D materials of step b) interact with each other to form nanofibers.

[0077] In some embodiments, the weight ratio of the 2D material to another 2D material is about 1:1.

[0078] In some embodiments, the method includes reacting a 2D material with another 2D material in a flow reactor.

[0079] The present invention also provides a nanofiber, comprising: the nanofibers are characterized by a solid or semi-hollow cross-sectional profile; the nanofibers are characterized by a layered cross-sectional profile of a 2D material that is curled and bonded to one another at its planes and ends; The nanofibers are provided, wherein the 2D material is selected from graphene, graphene oxide, few-layer transition metal dichalcogenides, hexagonal boron nitride, or combinations thereof.

[0080] In some embodiments, the nanofibers are characterized by a diameter of about 5 nm to about 400 nm.

[0081] In some embodiments, the nanofibers are characterized by a diameter of about 10 nm to about 100 nm.

[0082] In some embodiments, the diameter is non-uniform.

[0083] In some embodiments, the nanofibers are characterized by a length of from about 1 μm to about 100 μm.

[0084] In some embodiments, the nanofibers are characterized by a length of about 5 μm to about 50 μm.

[0085] In some embodiments, the nanofibers are characterized by an aspect ratio of about 30 to about 3,000.

[0086] In some embodiments, the nanofibers are semi-crystalline.

[0087] In some embodiments, when the nanofibers are graphene nanofibers, the nanofibers are characterized by an interlayer spacing of about 0.40 nm to 0.5 nm.

[0088] In some embodiments, when the nanofibers are graphene nanofibers, the nanofibers are characterized by an interlayer spacing of about 0.40 nm to 0.45 nm.

[0089] In some embodiments, when the nanofibers are graphene nanofibers, the nanofibers are characterized by amide bonds.

[0090] In some embodiments, when the nanofibers are graphene nanofibers crosslinked by amide moieties, the nanofibers are characterized by an X-ray photoelectron spectrum peak located at about 288 eV to about 290 eV.

[0091] In some embodiments, when the nanofibers are graphene nanofibers crosslinked by amide moieties, the nanofibers have a crosslink length of about 1653 cm -1 and about 1572 cm -1 It is characterized by an FTIR peak located at

[0092] Embodiments of the invention will now be described, by way of non-limiting example, with reference to the drawings, in which: [Brief description of the drawings]

[0093] [Figure 1]Figure 1 is a schematic diagram of the synthesis of 2D electrolyte nanofibers. (a) Functionalization of graphene with lower (G-COOH) and (b) higher (G-COOHhc) functionalization degree. (c) Further functionalization of G-COOH with EDC, NHS, and TETA molecules, and (d) EDC / NHS or (e) a control using only TETA. STEM images of all steps, the structures in light grey background are lacy carbon support films on TEM grids.

[0094] [Diagram 2] Figure 2. XPS characterization of nanofibers. High resolution C1s and N1s XPS comparing graphene, G-COOH, and nanofibers.

[0095] [Diagram 3] Figure 3 Morphological and structural analysis of 2D electrolyte nanofibers. (a, b, c) SEM images and (d, e) HR-STEM of the nanofiber structure, where graphene is located inside the fiber. (f, g, h) SEM images and (i, j) HR-STEM of the nanofiber, where graphene is assembled on the surface of the amorphous phase.

[0096] [Figure 4] Figure 4. Raman characterization of 2D electrolyte nanofibers. (a) and (b) are the intensity maps of the "D", "G" and "2D" bands, respectively. The Raman excitation laser wavelength is 532 nm.

[0097] [Diagram 5] Figure 5 is a theoretical analysis of fiber formation. Chemical bonds are responsible for cross-linking the scrolls (a) along their edges or (b) at their surfaces. C, H, N, and O atoms are represented in gray, white, blue, and red, respectively. The enthalpy of reaction is shown above the arrows. (c) Two random scrolls with too large a size mismatch cannot entangle, and (d) scrolls of comparable size can entangle to form a fiber.

[0098] [Figure 6] FIG. 6 shows an SEM image of the fibers and a particle size distribution histogram.

[0099] [Figure 7] FIG. 7 is a FTIR spectrum comparing graphene (G-COOH and nanofibers) before and after functionalization.

[0100] [Figure 8] FIG. 8 shows SEM images at different stages of the reaction (in all cases the pH is about 6.5).

[0101] [Figure 9] FIG. 9 shows AFM images (a, b) with the respective height profiles of the nanofibers.

[0102] [Figure 10] FIG. 10 compares the XRD diffractograms of graphene and hBN-based fibers with their pure precursor materials.

[0103] [Figure 11] FIG. 11 is Raman spectroscopy of graphene and hBN-based fibers.

[0104] [Figure 12] FIG. 12 shows the morphological and compositional characterization of the graphene and hBN fibrillated systems using: polarized optical microscopy (POM) with cross-polarized light demonstrating the optical anisotropy of the materials, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) demonstrating the fibril morphology of the materials, high-resolution TEM (HRTEM) and selected area electron diffraction (SAED) showing the organization and high crystallinity of the systems; and energy dispersive spectroscopy (EDS) confirming the preservation of the original chemical composition of the 2D materials after fibrillation.

[0105] [Figure 13]Figure 13 shows the characterization of graphene nanofibers: (a) optical, (b) STEM, (c) SEM representative images, and (d) respective particle size distributions.

[0106] [Figure 14] Figure 14: XPS characterization of the synthesized variants. High resolution C1s and N1s XPS comparing graphene, G-COOH-hc, G-COOH-EDC / NHS, and G-COOH-TETA.

[0107] [Figure 15] Figure 15: Characterization of a control sample (no graphene) containing only EDC / NHS / TETA. (a) SEM image and (b) C1s and N1s high-resolution XPS spectra of a sample prepared in the absence of functionalized graphene (no G-COOH).

[0108] [Figure 16] FIG. 16: SEM images of the heterostructured fibers formed after mixing (a) and after sonication for 5 min (b); AFM image with height profile of the heterostructured fibers measured at different positions; and Raman spectrum of the heterostructured fibers acquired using a 532 nm laser (c), showing the presence of both characteristic GO and MoS2 bands. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0109] The present invention provides methods to produce self-assembled ultralong nanofibers via (i) a synthetic method to convert functionalized 2D materials (e.g., 2D electrolytes) into internally (covalently) crosslinked nanofibers, or (ii) a two-step self-assembly method to convert exfoliated pure 2D materials doped with organic salts into internally (ionically) crosslinked nanofibers by confining these salts on the basal plane of the 2D material (2D confining electrolytes). These different template-free approaches are based on the self-assembly of flakes of 2D materials in aqueous suspension and are highly attractive due to their scalability and typically low cost.

[0110] The first method, via 2D electrolytes, involves the addition of anionic groups (e.g., -COO - ) to form cationic 2D electrolytes. + ) and further transformation by 2D electrolyte. Well-defined fiber structures are formed by the scrollification of the 2D electrolyte and structural guidance by the organic fiber network formed simultaneously by the cross-linking reaction of the molecules used for functionalization. By changing the charge content of the dispersion (e.g., by changing the pH), the surface charge density of the 2D material can be electrically shielded, and due to its elasticity and binding energy, it undergoes a conformational change to a 1D-like structure such as scrolls. Further cross-linking at the ends of the 2D material extends the scrolls into nanofibers. This method has the advantage of a controlled functionalization of the material and a living polymerization profile of the fibers, since the fibers continue to grow longitudinally while the precursors (free 2D electrolytes) are available in the liquid medium.

[0111] The second method, via 2D confining electrolyte, may consist of the initial assembly and confinement of an organic / inorganic salt on the basal surface of the 2D material forming the 2D confining electrolyte, and the further addition of another organic / inorganic salt for ion exchange and destabilization of the system causing phase separation / solidification resulting in fibers. When opposite charges are paired and bound to the organic / inorganic salt on the 2D confining electrolyte, they form strong Coulombic interactions between two (or more) paired ionic groups that reduce the binding ability of the organic / inorganic salt with other species and "bridge" the charge-carrying groups. This method has the advantage that it does not involve direct covalent functionalization and does not affect the initial properties of the 2D material used, since the salts that remain in solution and are not directly confined in the 2D lattice can be reused for further use. Furthermore, salts may be applied directly to the exfoliation process, in which case the organic salt acts simultaneously as a surfactant / stabilizer and as a 2D material dopant / modifier.

[0112] As used herein, "2D material" refers to a crystalline solid consisting of a single or few layers of atoms. Such single or few layer materials derived from a single element generally have the suffix -ene in their name (e.g., graphene). Single or few layer materials that are compounds of two or more elements have the suffix -ane or -ide. 2D materials can be generally classified as 2D allotropes of various elements or as compounds (composed of two or more covalently bonded elements).

[0113] As used herein, "2D electrolyte" refers to 2D materials such as graphene, graphene oxide (GO), reduced graphene oxide (rGO), and molybdenum disulfide (MoS2), which have different chemical groups that can be protonated or deprotonated in dispersion, becoming positively charged (2D cations) or negatively charged (2D anions), respectively.

[0114] As used herein, "2D confined electrolyte" refers to 2D materials such as graphene, graphene oxide (GO), reduced graphene oxide (rGO), and molybdenum disulfide (MoS2) in which different organic ions are located on and electrostatically associated with the surface of the 2D material. The organic ions may come from organic salts and may be either organic cations or organic anions. These ions confined on the surface of the 2D material may be exchanged with free ions in the solution.

[0115] Accordingly, the present invention provides a method of forming nanofibers, comprising the steps of: a) providing a 2D material having charge-retaining portions on its planar surface and at its edges; b) reacting charge-carrying moieties on the planar surface with proton donors, proton acceptors, at least partially hydrophobic counterions, or 2D materials having opposite charge-carrying moieties on the planar surface and at their edges to curl the 2D material; c) reacting the charge-carrying moieties at the ends with a proton donor, a proton acceptor, an at least partially hydrophobic counterion, or a 2D material having opposite charge-carrying moieties on its planar surface and at its ends, so that the 2D materials of step b) interact with each other to form nanofibers, while crosslinking the neutralized charge-carrying moieties at the ends.

[0116] It was found that the charge-carrying moieties allow for homogeneous dispersion of nanomaterials in aqueous media. For example, graphene can only be dispersed in water after functionalization. The charge-carrying moieties also maintain the 2D material in its planar configuration until it reacts to form nanofibers. The charge-carrying moieties can also induce some conformational changes depending on some specific conditions, e.g., pH and sonication time. Furthermore, by providing the charge-carrying moieties on the surface of the nanomaterial, the crosslinking rate can be controlled by varying the reaction conditions, e.g., pH and bifunctional or multifunctional crosslinkers.

[0117] The 2D material curls in response to this destabilization because the charge-carrying moieties are configured to lose their charge upon neutralization. The charge-carrying moieties at the ends of the 2D material are relatively more exposed and therefore preferentially interact with other deprotonated or neutralized charge-carrying moieties on other 2D materials to extend the length of the nanofiber. The growth of the nanofibers can be controlled by varying the reaction conditions, e.g., pH and bi- or multi-functional crosslinkers.

[0118] Current 2D materials such as graphene obtained by liquid phase exfoliation usually have reduced lateral size, which can limit their applications. In the method presented here, 2D materials are combined by covalent or ionic bonds, resulting in ultra-long fibers. Once formed, the fibers can continue to grow by self-assembly of small functionalized or salt-doped 2D material flakes.

[0119] This method is simple, versatile, and template-free, and the resulting structures exhibit very high aspect ratios and nanoscale diameters that may be applicable to applications including membranes for filtration, fabrics, batteries, and sensors. In contrast, all previous methods produce materials with lower aspect ratios and diameters greater than 50 μm. Furthermore, all reported methods for producing fibers with nanoscale diameters use templates, which can increase the cost and time of the process.

[0120] Furthermore, most of the methods are carried out in an aqueous medium at room temperature and do not require any special setup.

[0121] This method allows the selection of the crystallinity of the resulting nanofibers and, therefore, the stiffness of the fibers. The method using 2D electrolytes through covalent functionalization of 2D materials partially destroys their lattice crystallinity, while the method using 2D confining electrolytes does not involve direct covalent functionalization and preserves the crystallinity of the initial 2D materials used.

[0122] The method using 2D electrolytes consumes the reactants and leaves little or no residue of the reaction process. Furthermore, the method using 2D confined electrolytes involves the adsorption of organic salts at room temperature onto the 2D material lattice. This is also an environmentally friendly (green) process, as it allows the unadsorbed salts to be recycled into new batches, avoiding the generation of process residues.

[0123] The organic salts are water soluble, allowing for the direct exfoliation of 2D materials in aqueous media and acting as surfactants / stabilizers. Furthermore, the salts can be adsorbed onto the 2D material lattice to generate 2D confined electrolytes, which can be directly applied in the fibrillation process.

[0124] The resulting nanofibers can be applied in a wide variety of applications, including membranes for filtration, systems for gas purification, textiles, electronic textile devices, flexible and wearable electronics, sensors, and energy applications such as batteries and supercapacitors.

[0125] As used herein, a "charge-carrying moiety" refers to a moiety of an organic or inorganic molecule having a moiety that can hold / acquire a positive or negative charge. A charge-carrying moiety can be a functional group that can be protonated or deprotonated to acquire a charge. Examples of protonated and deprotonated moieties include carboxylates (-COO - ), protonated amines (e.g., -NH3 + ), sulfides (e.g., -S - ), and phosphonium (R3P +, optionally functionalized with hydroxyl groups). Alternatively, the charge-carrying moiety can be an organic or inorganic ion. Examples of such cations and anions include H + , hydroxide ion, halide ion, azide, ammonium, nitrate ion, nitride ion, nitrite ion, phosphide ion, oxide ion, sulfide ion, sulfate ion, sulfite ion, selenide ion, triiodide ion, hydrogen difluoride ion, carbonate ion, chlorate ion, chromate ion, dichromate ion, cyclopentadienyl, dihydrogen phosphate ion, hydrogen carbonate ion (bicarbonate ion), hydrogen sulfate ion (bisulfate ion), hydrogen sulfite ion (bisulfite ion), hypochlorite ion, monohydrogen phosphate ion, perchlorate ion, permanganate ion, peroxide ion, phosphate ion, superoxide ion, thiosulfate ion, silicate ion, metasilicate ion, aluminum silicate, acetate ion, formate ion, oxalate ion, and cyanide ion.

[0126] In some embodiments, the charge-carrying moieties are attached to the surface of the 2D material via covalent bonds or via electrostatic interactions.

[0127] In some embodiments, the charge-carrying moiety is selected from a protonated moiety, a deprotonated moiety, a cationic moiety, or an anionic moiety. In other embodiments, the charge-carrying moiety is a protonated moiety or a deprotonated moiety. In other embodiments, the charge-carrying moiety is a cationic moiety or an anionic moiety.

[0128] In some embodiments, each charge-carrying moiety comprises at least one charge. In other embodiments, each charge-carrying moiety comprises at least two charges. For example, a charge-carrying moiety comprises at least two COO - Part or at least two NH3 + The charge-carrying moiety can have a valence of 1, 2, 3, or 4. For example, the charge-carrying moiety can be a divalent or multivalent ion.

[0129] In some embodiments, the method is carried out in an aqueous medium.

[0130] The term "aqueous solution" as used herein refers to an aqueous solvent or solvent system, composed primarily of water. Such solvents can be either polar or non-polar, and / or either protic or aprotic. A solvent system refers to a combination of solvents that results in a final single phase. Both "solvent" and "solvent system" can include, but are not limited to, pentane, cyclopentane, hexane, cyclohexane, benzene, toluene, dioxane, chloroform, diethyl ether, dichloromethane, tetrahydrofuran, ethyl acetate, acetone, dimethylformamide, acetonitrile, dimethylsulfoxide, nitromethane, propylene carbonate, formic acid, butanol, isopropanol, propanol, ethanol, methanol, acetic acid, ethylene glycol, diethylene glycol, or water. An aqueous solvent or solvent system can also include dissolved ions, salts, and molecules, such as amino acids, proteins, sugars, and phospholipids. Such salts may be, but are not limited to, sodium chloride, potassium chloride, ammonium acetate, magnesium acetate, magnesium chloride, magnesium sulfate, potassium acetate, potassium chloride, sodium acetate, sodium citrate, zinc chloride, sodium HEPES, calcium chloride, ferric nitrate, sodium bicarbonate, potassium phosphate, and sodium phosphate. Thus, biological fluids, physiological solutions, and culture media are also included in this definition. In most embodiments, the aqueous solution is water. In some embodiments, the aqueous solution is deionized water. In some embodiments, the aqueous solution is Millipore water.

[0131] In some embodiments, the method is carried out at about 10° C. to about 50° C. In other embodiments, the temperature is about 10° C. to about 45° C., about 10° C. to about 40° C., about 10° C. to about 35° C., about 10° C. to about 30° C., about 15° C. to about 30° C., or about 20° C. to about 30° C. In other embodiments, the method is carried out at ambient temperature.

[0132] In some embodiments, the method is template independent, hi other embodiments, the method is template free.

[0133] In some embodiments, the 2D material is selected from graphene, graphene oxide, few-layer transition metal dichalcogenides, hexagonal boron nitride, or combinations thereof. In other embodiments, the 2D material is selected from graphene, graphene oxide, reduced graphene oxide, few-layer transition metal dichalcogenides, hexagonal boron nitride, or combinations thereof.

[0134] In some embodiments, the few-layer transition metal dichalcogenide is selected from MoS2, MoSe2, MoTe2, WS2, or WSe2.

[0135] In some embodiments, the 2D material is at least about 50% functionalized with charge carrying moieties. In other embodiments, the 2D material is at least about 55%, about 60%, about 65%, about 70%, about 75%, about 80%, about 85%, about 90%, or about 90% functionalized with charge carrying moieties. In other embodiments, the 2D material is about 50% to about 90%, about 60% to about 90%, about 70% to about 90%, or about 80% to about 90% functionalized. Functionalization can be estimated using X-ray photoelectron spectroscopy (XPS).

[0136] In some embodiments, the charge-carrying moiety is neutralized or reacted by controlling the pH. For example, if the charge-carrying moiety is a protonated moiety, the pH can be greater than about 7, greater than about 7.5, greater than about 8, greater than about 8.5, greater than about 9, greater than about 9.5, or greater than about 10. If the charge-carrying moiety is a deprotonated moiety, the pH can be less than about 7, less than about 6.5, less than about 6, less than about 5.5, less than about 5, less than about 4.5, or less than about 4. In other embodiments, the charge-carrying moiety can be paired with an at least partially hydrophobic counterion. For example, if the charge-carrying moiety is a cationic moiety, a salt with an organic anion can be used. If the charge-carrying moiety is an anionic moiety, a salt with an organic cation can be used. The anion and cation can be selected from fully organic salts or inorganic salts with at least one organic counterion. Just a few examples of such salts include imidazolium salts, pyridinium salts, piperidinium salts, ammonium salts, and phosphonium salts as sources of cations, and imide salts, sulfonates, sulfates, borates, phosphates, and carboxylates as sources of anions.

[0137] The phase transition in step b is a morphological transition, i.e., occurs by a dimensional transformation from 2D2D behavior to 1D behavior / 1D behavior to 2D2D behavior, which may be reversible in some cases. This transition was found to be a complex and cooperative competition between elastic, Coulombic and van der Waals interactions. Instead of uncontrolled aggregation, in addition to the 2D material, curling occurs to minimize its surface energy by further destabilizing the edges of the 2D material in a controlled manner (step c). The presence of charges also on the edges of the 2D material allows adjacent 2D materials to connect, which causes the nanomaterial to stretch and form nanofibers.

[0138] In some embodiments, the reacting steps b) and / or c) are carried out at a pH of about 3 to about 6. In other embodiments, the pH is about 3 to about 5. In some embodiments, the neutralization steps b) and / or c) are carried out at a pH of about 4.

[0139] The at least partially hydrophobic counterions are selected from salts with at least one organic counterion, differing in water / organic solvent solubility. It has been found that hydrophobic ion pairing can be used to modulate the solubility of charged hydrophilic 2D materials. When a charged hydrophilic 2D material is ionically paired with an oppositely charged molecule containing a hydrophobic moiety, the resulting uncharged complex tends to be water insoluble and may precipitate in aqueous media. This solubility partitioning can trigger a controlled solidification of the 2D material into nanofibers. Inorganic ions are generally very water soluble and isotropic (and therefore hydrophilic), while organic ions are generally less water soluble and more anisotropic (and therefore at least partially hydrophobic), allowing for a controlled decrease in the stability of the system.

[0140] In some embodiments, when the charge-carrying moiety is at least partially reacted with a hydrophobic counterion, the counterion is an organic counterion. In some embodiments, the counterion is selected from imidazolium, pyridinium, piperidinium, ammonium, phosphonium, imide, sulfonate, sulfate, borate, phosphate, carboxylate, or derivatives thereof. In other embodiments, when the charge-carrying moiety is neutralized with a counterion, the counterion is 1-butyl-3-methylimidazolium. In other embodiments, when the charge-carrying moiety is neutralized with a counterion, the counterion is provided by a salt selected from 1-butyl-3-methylimidazolium methanesulfonate.

[0141] In some embodiments, the charge-carrying moieties on the 2D material react with a 2D material having opposite charge-carrying moieties on its planar surfaces and at its edges. In some embodiments, the 2D material having opposite charge-carrying moieties is selected from graphene, graphene oxide, few-layer transition metal dichalcogenides, hexagonal boron nitride, or combinations thereof. In other embodiments, the 2D material is selected from graphene, graphene oxide, reduced graphene oxide, and few-layer transition metal dichalcogenides, hexagonal boron nitride, or combinations thereof.

[0142] The 2D material with opposite charge carrying moieties may be the same material as the 2D material with charge carrying moieties or a different material. In this regard, in some embodiments, both 2D materials may be independently selected from graphene, graphene oxide, few-layer transition metal dichalcogenides, hexagonal boron nitride, or combinations thereof. Thus, either homostructured or heterostructured nanofibers may be formed.

[0143] Two 2D materials can have opposite charge carrying moieties. For example, if a 2D material has a protonated Bronsted-Lowry base moiety, the other 2D material can have a deprotonated Bronsted-Lowry acid moiety. If a 2D material has a cationic moiety, the other 2D material can have an anionic moiety.

[0144] In some embodiments, the 2D material with opposite charge carrying moieties is at least about 50% functionalized with charge carrying moieties. In other embodiments, the 2D material is at least about 55%, about 60%, about 65%, about 70%, about 75%, about 80%, about 85%, about 90%, or about 90% functionalized with charge carrying moieties. In other embodiments, the 2D material is about 50% to about 90%, about 60% to about 90%, about 70% to about 90%, or about 80% to about 90% functionalized. Functionalization can be estimated using X-ray photoelectron spectroscopy (XPS).

[0145] A 2D material may have charge-carrying moieties on both sides of its surface. As one side is neutralized or reacted and curls to form an inside, the other side is simultaneously neutralized or reacted. This exposed outside can interact with another 2D material to form a layered structure. This results in the nanofiber having a non-uniform diameter over its length.

[0146] In some embodiments, step (b) further comprises cross-linking the charge-carrying moieties on the planar surface. The charge-carrying moieties may be reacted or neutralized to facilitate cross-linking. The rate of nanofiber formation may be further controlled by cross-linking the moieties.

[0147] In some embodiments, crosslinking is carried out in the presence of a crosslinking agent. The crosslinking agent can be a multifunctional or bifunctional molecule or an organic salt. In some embodiments, the crosslinking agent comprises at least two crosslinkable moieties. In some embodiments, the crosslinking agent comprises at least three crosslinkable moieties.

[0148] In some embodiments, when the charge-carrying moiety reacts with an at least partially hydrophobic counterion, the crosslinker is an at least partially hydrophobic counterion. In some embodiments, when the charge-carrying moiety reacts with a 2D material having opposite charge-carrying moieties on its planar surface and at its edges, the 2D material having opposite charge-carrying moieties on its planar surface and at its edges acts as a crosslinker.

[0149] In some embodiments, the weight ratio of crosslinker to 2D material is about 50:1 to about 700:1, in other embodiments, the ratio is about 100:1 to about 700:1, about 150:1 to about 700:1, about 200:1 to about 700:1, about 250:1 to about 700:1, about 300:1 to about 700:1, about 350:1 to about 700:1, about 400:1 to about 700:1, about 450:1 to about 700:1, about 500:1 to about 700:1, about 550:1 to about 700:1, or about 600:1 to about 700:1.

[0150] In some embodiments, the crosslinking steps b) and / or c) are carried out under stirring. In other embodiments, the stirring is carried out at about 3° C. to about 10° C., or at about 10° C. Lower temperatures slow the crosslinking reaction.

[0151] Alternatively, in some embodiments, cross-linking steps b) and / or c) are performed under sonication. In some embodiments, at least step b) is performed under sonication. Sonication is the act of applying sound energy to agitate particles in a sample. Ultrasonic frequencies (>20 kHz) are used for sonication. Sonication can be applied using an ultrasonic bath or an ultrasonic probe (commonly known as a sonicator).

[0152] In some embodiments, the sonication is at about 3° C. to about 10° C., or for at least about 10 minutes at about 10° C. In other embodiments, the duration is at least about 15 minutes, or for about 20 minutes. In some embodiments, the sonication is at about 3° C. to about 10° C. for at least about 30 minutes.

[0153] In some embodiments, the cross-linking step c) is carried out at about 3° C. to about 10° C., or at about 10° C., in the absence of external forces, such as stirring or sonication.

[0154] In some embodiments, the method further comprises functionalizing the 2D material with a charge carrying moiety to form a 2D material having a charge carrying moiety of step a).

[0155] In some embodiments, the weight ratio of the charge-carrying moiety to the 2D material is about 2:1 to about 5:1. In other embodiments, the weight ratio of the charge-carrying moiety to the 2D material is about 3:1.

[0156] In some embodiments, the step of functionalizing the 2D material with a charge-carrying moiety is carried out at a pH of about 5 to about 6.9. In other embodiments, the pH is about 5 to about 6.5, or about 5 to about 6.

[0157] In some embodiments, the step of functionalizing the 2D material with a charge-carrying moiety is performed under sonication.

[0158] In some embodiments, the sonication is for at least about 10 minutes at about 3° C. to about 10° C., or at about 10° C. In other embodiments, the duration is at least about 15 minutes, or about 20 minutes. In some embodiments, the sonication is for at least about 30 minutes at about 3° C. to about 10° C., or at about 10° C.

[0159] In some embodiments, the step of functionalizing the 2D material with a charge-carrying moiety is carried out for at least about 2 hours. In other embodiments, the duration is at least about 4 hours, about 6 hours, about 8 hours, about 12 hours, about 16 hours, about 20 hours, about 24 hours, about 28 hours, about 32 hours, about 36 hours, about 40 hours, about 44 hours, about 48 hours, about 52 hours, about 56 hours, about 60 hours, about 64 hours, or about 68 hours. In some embodiments, the step of functionalizing the 2D material with a charge-carrying moiety is carried out for at least 72 hours.

[0160] In some embodiments, the step of functionalizing the 2D material with a charge carrying moiety is performed at about 20° C. to about 70° C. In other embodiments, the temperature is about 20° C. to about 60° C., about 20° C. to about 50° C., about 25° C. to about 50° C., about 30° C. to about 50° C., about 35° C. to about 50° C., or about 40° C. to about 50° C. In some embodiments, the step of functionalizing the 2D material with a charge carrying moiety is performed at about 45° C. In some embodiments, when the 2D material is graphene, the step of functionalizing the 2D material with a charge carrying moiety is performed at about 45° C. In some embodiments, when the 2D material is MoS2, the step of functionalizing the 2D material with a charge carrying moiety is performed at about 20° C. to about 40° C.

[0161] In some embodiments, when the 2D material is graphene, the step of functionalizing the 2D material with the charge-carrying moiety is carried out under an inert atmosphere. The inert atmosphere can be nitrogen or a noble gas, such as argon. In other embodiments, the step of functionalizing the 2D material with the charge-carrying moiety is carried out under ambient conditions (room temperature and in open air).

[0162] In some embodiments, if the pH is maintained and / or the counterions are in excess, the method is self-perpetuating until all of the 2D material has reacted, in which case the reaction is complete when no unreacted 2D material remains.

[0163] In some embodiments, a method of forming nanofibers includes: a) providing a 2D material having protonated or deprotonated moieties on its planar surface and at its edges; b) reacting protonated or deprotonated moieties on the planar surface with proton donors or proton acceptors to curl the 2D material; and c) reacting the protonated or deprotonated moieties at the ends with a proton donor or a proton acceptor simultaneously to covalently crosslink the reacted moieties at the ends so that the 2D materials of step b) interact with each other to form nanofibers.

[0164] The method of forming the nanofibers can be carried out in an aqueous medium.

[0165] In some embodiments, the protonated or deprotonated moiety is a carboxylate moiety, hi some embodiments, the carboxylate moiety is a carboxyl compound selected from 5-azidopentanoic acid, 6-azido-hexanoic acid, azido-dPEG4-acid, azidopalmitic acid, azidoacetic acid, mercaptopropionic acid, mercaptoacetic acid, 5-mercaptopentanoic acid, or combinations thereof.

[0166] In some embodiments, the charge-carrying moiety is neutralized by changing the pH.

[0167] In some embodiments, steps b) and / or c) are performed at a pH of about 3 to about 6. In other embodiments, the pH is about 3 to about 5. In some embodiments, steps b) and / or c) are performed at a pH of about 4.

[0168] In some embodiments, step b) further comprises covalently crosslinking the protonated or deprotonated moieties on the planar surface. - ) to promote crosslinking (e.g., -OH or OH2 + ) may react.

[0169] In some embodiments, the reacted moieties on the planar surface are covalently crosslinked with a crosslinking agent. Crosslinking is configured to occur in the planar surface, on the 2D material surface and on the inner surface of the nanofiber. The crosslinking agent can be an amino compound. In some embodiments, the amino compound includes at least two or at least three amino moieties. In this regard, the amino compound can be a multifunctional or bifunctional amino compound.

[0170] In some embodiments, the amino compound is triethylenetetramine, triethylenediamine, ethylenediamine, p-phenylenediamine, or a combination thereof.

[0171] In some embodiments, crosslinking is performed in the presence of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) and N-hydroxysuccinimide (NHS). EDC and NHS activate functional groups so that cross-coupling to form amide bonds can occur at lower activation energies. In this way, amino compounds can pair with carboxyl compounds on the 2D material via amide bonds, which then form amide crosslinks with another carboxyl compound depending on the nature of the additional amino moiety on the amino compound.

[0172] In some embodiments, steps b) and c) are carried out for at least 1 hour at about 3° C. to about 30° C. In other embodiments, the duration is at least about 4 hours, about 6 hours, about 8 hours, about 12 hours, about 16 hours, about 20 hours, about 24 hours, about 28 hours, about 32 hours, about 36 hours, about 40 hours, about 44 hours, about 48 hours, about 52 hours, about 56 hours, about 60 hours, about 64 hours, about 68 hours, or about 72 hours. In other embodiments, the temperature is about 3° C. to about 30° C., about 3° C. to about 25° C., about 3° C. to about 20° C., about 3° C. to about 15° C., about 3° C. to about 10° C., or about 10° C.

[0173] In some embodiments, steps b) and c) are carried out for at least 12 hours at about 3° C. to about 10° C. In some embodiments, steps b) and c) are carried out for at least 72 hours at about 3° C. to about 10° C.

[0174] In some embodiments, a method of forming nanofibers includes: a) providing a 2D material having protonated or deprotonated moieties on its planar surface and at its edges; b) reacting a protonated or deprotonated moiety on the planar surface with a proton donor or proton acceptor to form a reacted moiety, and covalently crosslinking the reacted moiety with a crosslinking agent; and c) reacting the protonated or deprotonated moieties at the ends with a proton donor or a proton acceptor simultaneously to covalently crosslink the reacted moieties at the ends so that the 2D materials of step b) interact with each other to form nanofibers.

[0175] In some embodiments, a method of forming nanofibers includes: a) providing a 2D material having deprotonated moieties on its planar surface and at its edges; b) protonating the deprotonated moieties on the planar surface with a proton donor to form reacted moieties, and covalently crosslinking the reacted moieties with a crosslinker; and c) simultaneously protonating the deprotonated moieties at the ends with a proton donor to covalently crosslink the reacted moieties at the ends so that the 2D materials of step b) can interact with each other to form nanofibers.

[0176] In some embodiments, a method of forming nanofibers includes: a) providing a 2D material having deprotonated moieties on its planar surface and at its edges; b) protonating the deprotonated moieties on the planar surface with a proton donor to form reacted moieties, and covalently crosslinking the reacted moieties with a crosslinker; and c) simultaneously protonating the deprotonated moieties at the ends with a proton donor to covalently crosslink the reacted moieties at the ends so that the 2D materials of step b) interact with each other to form nanofibers; The crosslinking agent is a multifunctional crosslinking agent.

[0177] In some embodiments, a method of forming nanofibers includes: a) providing a 2D material having cationic or anionic moieties on its plane and at its edges; b) reacting cationic or anionic moieties on the planar surface with at least partially hydrophobic counterions to curl the 2D material; and c) reacting the cationic or anionic moieties at the ends with at least partially hydrophobic counterions while ionically cross-linking the reacted charge-carrying moieties at the ends so that the 2D materials of step b) interact with each other to form nanofibers.

[0178] The method of forming the nanofibers can be carried out in an aqueous medium.

[0179] In some embodiments, the cationic or anionic moieties are electrostatically bound to the 2D material. In other embodiments, the cationic or anionic moieties are ionically bound to the 2D material. This type of chemical bond involves electrostatic attraction between moieties carrying opposite charges.

[0180] In some embodiments, the ratio of the 2D material to the cationic or anionic moieties is about 1:30 to about 1:80. In other embodiments, the ratio is about 1:30 to about 1:70, about 1:30 to about 1:60, about 1:40 to about 1:60, or about 1:50 to about 1:60. In some embodiments, the ratio of the 2D material to the cationic or anionic moieties is about 1:50.

[0181] Advantageously, excess ionic moieties that do not adsorb onto the 2D material surface remain in solution and can be reused in new batches.

[0182] In some embodiments, the cationic or anionic moiety is an organic cationic or anionic moiety. In other embodiments, the cationic or anionic moiety is selected from sulfonimide, imidazolium, pyridinium, piperidinium, ammonium, phosphonium, imide, sulfonate, sulfate, borate, phosphate, carboxylate, or derivatives thereof. In some embodiments, the cationic or anionic moiety is bis(trifluoromethane)sulfonimide. In some embodiments, the anionic moiety is provided as a salt selected from lithium bis(trifluoromethane)sulfonimide.

[0183] In some embodiments, the charge-bearing moiety reacts with a counterion that has an opposite charge to the cationic or anionic moieties on the 2D material, the counterion being at least partially hydrophobic.

[0184] In some embodiments, the counterion is an organic counterion. In other embodiments, the counterion is selected from imidazolium, pyridinium, piperidinium, ammonium, phosphonium, imide, sulfonate, sulfate, borate, phosphate, carboxylate, or derivatives thereof. In some embodiments, the counterion is 1-butyl-3-methylimidazolium. In some embodiments, the counterion is provided by a salt selected from 1-butyl-3-methylimidazolium methanesulfonate.

[0185] In some embodiments, step b) further comprises ionically crosslinking the reacted cationic or anionic moieties on the planar surface. The crosslinking agent can be the same as the crosslinking agent in step c). The crosslinking agent can be an at least partially hydrophobic counterion.

[0186] In some embodiments, steps b) and c) are performed under sonication or agitation. In some embodiments, at least step b) is performed under sonication or agitation.

[0187] In some embodiments, sonication or agitation is performed at about 3° C. to about 10° C., or at about 10° C. for at least 10 minutes. In other embodiments, the duration is at least about 15 minutes, or about 20 minutes. In some embodiments, sonication or agitation is performed at about 0° C. to about 10° C. for at least about 30 minutes.

[0188] In some embodiments, the method further comprises functionalizing the 2D material with cationic or anionic moieties to form a 2D material having cationic or anionic moieties in step a).

[0189] In some embodiments, the step of functionalizing the 2D material with cationic or anionic moieties is carried out under sonication in the presence of the cationic or anionic moieties.

[0190] In some embodiments, sonication is performed at about 3° C. to about 10° C., or at about 10° C. for at least 10 minutes. In other embodiments, the duration is at least about 15 minutes, or about 20 minutes. In some embodiments, sonication is performed at about 3° C. to about 10° C., or at about 10° C. for at least about 30 minutes.

[0191] In some embodiments, when the 2D material is graphene, the method further comprises, prior to step a), exfoliating graphite in the presence of cationic or anionic moieties.

[0192] In some embodiments, when the 2D material is hexagonal boron nitride, the method further comprises, prior to step a), exfoliating the unexfoliated hexagonal boron nitride in the presence of cationic or anionic moieties.

[0193] In some embodiments, the graphite or non-exfoliated hexagonal boron nitride and the cationic or anionic moieties are dispersed in an aqueous medium and an organic medium mixture in a ratio of about 95:5.

[0194] In some embodiments, the peeling step is performed under high power probe sonication.

[0195] The method can also be applied to a combination of 2D materials to form heterostructured nanofibers. For example, a self-assembly process of 2D electrolytes and 2D confined electrolytes can be applied. Different 2D materials can be functionalized with various ionizable functional groups of opposite charge. For example, graphene oxide (GO) can be functionalized with cationic groups (-NH3 + ) to functionalize molybdenum disulfide (MoS2) with anionic groups (COO -) to allow ionic interactions between oppositely charged nanomaterials. Compared to the 2D electrolyte and 2D confined electrolyte fiber formation disclosed herein, instead of charge reversal, these nanofibers are formed by attractive interactions between both 2D material sheets in a confined aqueous environment. Charge compensation makes these materials less stable in aqueous media and solidifies into nanofibers composed of both materials. The application of a sonication process allows both materials to overcome the energy barrier and continuously assemble and scroll into fibers. As the reaction proceeds, long fiber bundles with branches are formed. This method provides a facile approach for the scale-up synthesis of heterostructured nanofibers with low production costs.

[0196] In some embodiments, a method is for forming nanofibers in an aqueous medium, the method comprising: a) providing a 2D material having cationic or anionic moieties on its plane and at its edges; b) reacting the cationic or anionic moieties on the planar surface with another 2D material having opposite charge carrying moieties on the planar surface and at its edges to curl the 2D material; c) reacting the cationic or anionic moieties at the ends with another 2D material having opposite charge-carrying moieties on its planar surface and at its ends, while ionically cross-linking the reacted charge-carrying moieties at the ends, so that the 2D materials of step b) interact with each other to form nanofibers.

[0197] In some embodiments, a 2D material having opposite charge carrying moieties on its planar surface and at its edges comprises a negative charge carrying moiety when the 2D material comprises positive charge carrying moieties on its planar surface and at its edges, In some embodiments, a 2D material having opposite charge carrying moieties on its planar surface and at its edges comprises a positive charge carrying moiety when the 2D material comprises negative charge carrying moieties on its planar surface and at its edges.

[0198] In some embodiments, the 2D material having opposite charge carrying moieties is selected from graphene, graphene oxide, few layer transition metal dichalcogenides, hexagonal boron nitride, or combinations thereof. In other embodiments, the 2D material is selected from graphene, graphene oxide, reduced graphene oxide, few layer transition metal dichalcogenides, hexagonal boron nitride, or combinations thereof.

[0199] In some embodiments, the 2D material with opposite charge carrying moieties is at least about 50% functionalized with charge carrying moieties. In other embodiments, the 2D material is at least about 55%, about 60%, about 65%, about 70%, about 75%, about 80%, about 85%, about 90%, or about 90% functionalized with charge carrying moieties. In other embodiments, the 2D material is about 50% to about 90%, about 60% to about 90%, about 70% to about 90%, or about 80% to about 90% functionalized. Functionalization can be estimated using X-ray photoelectron spectroscopy (XPS).

[0200] In some embodiments, the 2D material is graphene oxide functionalized with cationic moieties, and another 2D material is molybdenum disulfide (MoS2) functionalized with anionic moieties. In other embodiments, the graphene oxide is -NH3 + MoS2 is functionalized with the -COO moiety. - The moiety is functionalized.

[0201] In some embodiments, the weight ratio of the 2D material to another 2D material is about 1:1, 1:2, and 1:3.

[0202] In some embodiments, the 2D material and / or another 2D material is provided at a concentration of about 0.01 mg / mL to about 1 mg / mL. In other embodiments, the concentration is about 0.01 mg / mL to about 0.9 mg / mL, about 0.01 mg / mL to about 0.8 mg / mL, about 0.01 mg / mL to about 0.7 mg / mL, about 0.01 mg / mL to about 0.6 mg / mL, about 0.01 mg / mL to about 0.5 mg / mL, about 0.01 mg / mL to about 0.4 mg / mL, about 0.01 mg / mL to about 0.3 mg / mL, about 0.01 mg / mL to about 0.2 mg / mL, or about 0.01 mg / mL to about 0.1 mg / mL. In other embodiments, the concentration is about 0.05 mg / mL.

[0203] In some embodiments, the method includes reacting a 2D material with another 2D material in a flow reactor.

[0204] The present invention also provides a nanofiber, comprising: the nanofibers are characterized by a solid or semi-hollow cross-sectional profile; the nanofibers are characterized by a layered cross-sectional profile of a 2D material that is curled and bonded to one another at its planes and ends; The nanofibers are provided, wherein the 2D material is selected from graphene, graphene oxide, few-layer transition metal dichalcogenides, hexagonal boron nitride, or combinations thereof.

[0205] When ionic methods are used, the nanofibers are not completely solid, i.e., there are gaps or spaces along the inner axis (similar to the center of a scrolled or rolled parchment). This longitudinal axis is stabilized by the alkyl chains of the imidazolium salt or residual "free" salt, and therefore is not believed to be actually hollow or contain free space. When covalent methods are used, this space is believed to be filled by an organic phase formed by the crosslinker (amino compound).

[0206] In some embodiments, the nanofibers are characterized by a diameter of about 5 nm to about 400 nm. In other embodiments, the diameter is about 5 nm to about 350 nm, about 5 nm to about 300 nm, about 5 nm to about 250 nm, about 5 nm to about 200 nm, about 5 nm to about 190 nm, about 5 nm to about 180 nm, about 5 nm to about 170 nm, about 5 nm to about 160 nm, about 5 nm to about 150 nm, about 5 nm to about 140 nm, about 5 nm to about 130 nm, about 5 nm to about 120 nm, about 5 nm to about 110 nm, or about 5 nm to about 100 nm. In some embodiments, the nanofibers are characterized by a diameter of about 10 nm to about 100 nm.

[0207] In some embodiments, the diameter is non-uniform. In this regard, the diameter is not fixed throughout the length of the nanofiber, but rather varies along its length. This is a result of the deposition of different amounts of 2D material along the length of the nanofiber.

[0208] In some embodiments, the nanofibers are characterized by a length of about 5 μm to about 100 μm, in other embodiments, the length is about 5 μm to about 90 μm, about 5 μm to about 80 μm, about 5 μm to about 70 μm, about 5 μm to about 60 μm, about 5 μm to about 50 μm, about 5 μm to about 45 μm, about 5 μm to about 40 μm, about 5 μm to about 35 μm, about 5 μm to about 30 μm, about 6 μm to about 30 μm, about 7 μm to about 30 μm, about 8 μm to about 30 μm, about 9 μm to about 30 μm, about 10 μm to about 30 μm, about 12 μm to about 30 μm, about 14 μm to about 30 μm, or about 16 μm to about 30 μm. In some embodiments, the nanofibers are characterized by a length of about 10 μm to about 30 μm.

[0209] In some embodiments, the nanofibers are characterized by an aspect ratio of about 30 to about 3000. In other embodiments, the aspect ratio is about 30 to about 2800, about 30 to about 2600, about 30 to about 2400, about 30 to about 2200, about 30 to about 2000, about 30 to about 1800, about 30 to about 1600, about 30 to about 1400, about 30 to about 1200, about 30 to about 1000, about 50 to about 1000, about 100 to about 1000, about 200 to about 1000, about 300 to about 1000, about 400 to about 1000, about 500 to about 1000, about 600 to about 1000, about 700 to about 1000, or about 800 to about 1000.

[0210] The system behaves similarly to a "living polymerization system" and the limitations on the continued growth of the nanofibers are the supply of building blocks (in this case the functionalized 2D material) and the fiber (meta)stability in the medium. The fiber continues to grow as long as appropriately modified 2D material is added until it reaches a threshold where the fiber is too long to be (partially) stable in the medium and completely phase separates (and growth stops).

[0211] In some embodiments, the nanofibers are semi-crystalline. In this regard, the nanofibers have both crystalline and amorphous properties. The semi-crystalline properties may be due to the spatial orientation of the 2D materials as they bond together to form the nanofibers. The degree of crystallinity may be estimated by various analytical methods, such as calorimetry, X-ray diffraction, Raman spectroscopy, and NMR. In some embodiments, the nanofibers have a crystallinity of about 10% to about 90%, about 10% to about 85%, about 10% to about 80%, about 10% to about 75%, about 10% to about 70%, about 10% to about 65%, about 10% to about 60%, about 10% to about 55%, about 10% to about 50%, about 10% to about 45%, about 10% to about 40%, about 10% to about 35%, about 10% to about 30%, about 10% to about 25%, or about 10% to about 20%.

[0212] In some embodiments, when the nanofibers are graphene nanofibers, the nanofibers are characterized by an interlayer spacing of about 0.40 nm to 0.45 nm. In other embodiments, the interlayer spacing is about 0.40 nm to 0.44 nm, about 0.40 nm to 0.43 nm, about 0.40 nm to 0.42 nm, or about 0.40 nm to 0.41 nm. In some embodiments, when the nanofibers are graphene nanofibers, the nanofibers are characterized by an interlayer spacing of about 0.40 nm to 0.43 nm.

[0213] In some embodiments, when the nanofiber is a graphene nanofiber, the nanofiber is characterized by amide bonds. In some embodiments, when the nanofiber is a graphene nanofiber crosslinked by amide moieties, the nanofiber is characterized by an X-ray photoelectron spectrum peak located at about 288 eV to about 290 eV. In some embodiments, when the nanofiber is a graphene nanofiber crosslinked by amide moieties, the nanofiber is characterized by an X-ray photoelectron spectrum peak located at about 1653 cm -1 and about 1572 cm -1 It is characterized by an FTIR peak located at

[0214] In some embodiments, when the nanofiber is a heterogeneous nanofiber comprising graphene oxide and MoS, the nanofiber has a thickness of about 1350 cm -1 In other embodiments, the nanofibers are characterized by a Raman band located at about 1660 cm -1 In other embodiments, the nanofibers are characterized by a Raman band located at about 380 cm -1 In other embodiments, the nanofibers are characterized by a Raman band located at about 410 cm -1 It is characterized by a Raman band located at EXAMPLES

[0215] Graphene Nanofiber To obtain the 2D electrolyte and assemble them into crosslinked nanofibers, the graphene platelets are first functionalized using 5-azidopentanoic acid via decomposition of azide. Depending on the azide molecule / graphene ratio, different degrees of functionalization and morphological structures are observed. Specifically, an excess of 5-azidopentanoic acid molecules (G-COOH, high concentration, G-COOH-hc) leads to a controlled aggregation process resulting from the formation of fibrous structures (Figure 1b). This type of structure is rarely observed with lower degrees of functionalization (G-COOH) (Figure 1a).

[0216] G-COOH is further functionalized by reacting with a multifunctional molecule, namely triethylenetetramine (TETA), with the carboxyl groups previously activated by EDC / NHS. The initial pH of the G-COOH suspension is adjusted to the acidic range, which favors the scrolling or curling process of the functionalized graphene sheets. Interestingly, the majority of the obtained structures are highly branched nanofibers with high aspect ratios that intertwine with each other (Fig. 1c and Fig. 13). The diameters are in the range of 10-100 nm, while the lengths are more than 10 μm (Fig. 13). This system is referred to herein as nanofibers. It is noteworthy that the highly branched structures can act as gas adsorbents and / or immobilize other types of molecules and structures, such as metal nanoparticles.

[0217] Figure 1 summarizes the fiber formation process. After reaction with EDC / NHS / TETA, the majority of the resulting structures are highly branched nanofibers with high aspect ratios. The diameters are in the range of 10-100 nm, while the lengths are greater than 10 μm (Figure 6). This system is referred to herein as nanofibers. It is noteworthy that the highly branched structures can act as gas adsorbents and / or immobilize other types of molecules and structures, such as metal nanoparticles.

[0218] To clarify the assembly mechanism of the 2D structures, two control experiments are performed: (i) one using only EDC / NHS (G-COOH-EDC / NHS) (Figure 1d) and (ii) one using only TETA (G-COOH-TETA) (Figure 1e). The remaining parameters are kept. In both cases, fibrous structures are observed, but with lower yields compared to the system where EDC / NHS and TETA were applied together (nanofibers).

[0219] The elemental composition of the systems is analyzed and compared step by step by X-ray photoelectron spectroscopy (XPS) (Figure 2). The positions and percentages of the deconvoluted peaks of the C1s spectrum are summarized in Table 1. Deconvolution of the C1s peak shows five major peaks: C=C at 284.4 eV, hydroxyl (CO) at 285.9 eV, epoxy / ether (COC) at 286.7 eV, carbonyl (C=O) at 287.5 eV, and carboxylate (OC=O) at 288.4 eV.

[0220] Table 1. Binding energies of deconvoluted C1s XPS peaks and their relative area percentages (in parentheses).

[0221] [Table 1] For G-COOH with a lower degree of functionalization, a slight relative increase in sp3 and O-containing groups is observed, which further increases after reaction with EDC / NHS / TETA followed by the formation of nanofibers (Figure 2). It is important to note that the relative increase in the peaks around 288-289 eV may be related to the cross-linking reaction between graphene sheets resulting in amide functional groups, which will be discussed later. The peaks at 1653 and 1572 cm in the FTIR spectrum (Figure 7) -1The relative increase in the peaks at 400.3 eV assigned to amide I (C=O stretching vibration) and amide II (NH bending vibration), respectively, confirms the formation of amide groups after the reaction. The reaction with EDC / NHS / TETA results in a relative increase in the total percentage (%) of N, expected due to the presence of TETA molecules. Two major peaks appear: amide (-NH-(C=O)-) or secondary / tertiary amine at 400.3 eV, and protonated amine from TETA (NH3 + ) can be deconvoluted.

[0222] Figure 14 shows high-resolution XPS spectra of C1s and N1s for other derivatives of the reaction previously shown in Figure 1. The graphene spectrum was repeated to facilitate comparison between the spectra. When an excess of 5-azidopentanoic acid (G-COOH-hc) is utilized, a higher degree of functionalization is achieved compared to G-COOH (Figure 2). The alignment of the graphene flakes and the formation of a fibrous structure may result from an intermolecular reaction between the free azide molecules and the carboxylic acids attached to the graphene structure, resulting in a crosslinking process. For the control, G-COOH-EDC / NHS, and G-COOH-TETA, a relative increase in peaks is observed in the regions associated with amide and carboxyl / ester groups, suggesting the formation of crosslinking reactions. Furthermore, for G-COOH-TETA, the broadening of the N1s peak indicates a greater presence of primary amine groups, which is expected due to the presence of TETA molecules.

[0223] It was observed that the reaction could continue until all the small graphene platelets were consumed. Figure 8 shows representative SEM images at different stages at pH 6.5. The small platelets continue to react and self-assemble into existing nanofibers, resulting in longer and thicker structures.

[0224] A closer inspection of the nanofibers using SEM reveals the formation of two different types of structures (Figure 3): (i) those that are more resistant to the electron beam and (ii) those that are less resistant to the electron beam (Figure 3a, b, c). At the same time, some nanofibers are resistant to the electron beam (Figure 3f, g, h), indicating the self-assembly of functionalized graphene sheets on the nanofiber surface. Furthermore, according to our observations, this reaction continues until the graphene platelets are completely consumed. If the reaction is not terminated, the "liberated" platelets maintain a continuous reaction and self-assemble on the existing fibers, resulting in longer and thicker structures depending on the time, indicating spontaneous cross-linking and living polymerization. Electrostatic interactions may also contribute to the assembly process.

[0225] Images obtained by high-resolution scanning transmission electron microscopy (HR-STEM) reveal different locations of the crystalline parts formed by the graphene sheets in the center of the fibers (Fig. 3d, e) or on the surface (Fig. 3i, j). Thus, in Fig. 3a, b, c, the high contrast areas consist mainly of functionalized graphene sheets, thus suggesting their high stability under the electron beam, while the dark areas consist of the amorphous organic phase formed by the reactants (EDC / NHS / TETA).

[0226] Interlayer spacings ranging from 0.40 nm to 0.43 nm were observed, slightly larger than that of graphite (0.34 nm) and almost identical to the scrolls formed by the 2D electrolyte. This result is expected, considering the incorporation of functional groups on the graphene surface. Importantly, neither the crystalline nor amorphous phases are completely homogeneous along the nanofibers. Moreover, fibers with diameters less than 10 nm did not show any obvious crystalline phase.

[0227] This semicrystalline behavior is consistent with the heterogeneous structures observed in the AFM images (Figure 9), which indicate a non-uniform organization resulting from random layer combinations. Furthermore, the diameter of the structures is not uniform along the fiber.

[0228] A bare EDC / NHS / TETA system (without charge-carrying moieties) was also prepared by maintaining the same experimental steps of the reaction as a reference. Fibrous structures were observed in such a system. However, they were more similar to randomly interconnected and low-crosslinking networks (Figure 15a), suggesting the formation of a partially independent network.

[0229] From the high-resolution C1s and N1s XPS spectra (Figure 15b), in the absence of G-COOH, the peaks are assigned to groups such as CO, CN, and C=O. As with the previous sample, there are two major peaks in the N1s region, namely, amide or amine (secondary and tertiary) at 400.3 eV and protonated amine (NH3 + ) can be deconvoluted, both of which originate from TETA and EDC. In the absence of G-COOH, the latter shows a relatively higher intensity and a small shift when compared to the nanofibers, which is associated with a higher concentration of protonated amines. These findings suggest the simultaneous formation of an organic fiber network, but in an organized manner, with the G-COOH building blocks in the scroll morphology of this 2D electrolyte.

[0230] The Raman spectrum (Figure 4) shows the typical bands of carbon structures (D, G and 2D bands) along the nanofiber structure (Figure 4a), with the relative intensity of the Raman bands varying depending on the position along the fiber. The D band, associated with defects and deformations, is much more prominent at positions close to the filament edges, at intersections, or on shorter structures. In the latter, it is difficult to separate the signal from the edge or center of the fiber, since the laser spot (1-2 μm) is larger than the filament diameter. This variation in the relative intensity of the Raman bands along a single structure has also been reported for CNTs, where the enhancement of the D band in scroll-like structures was attributed to curvature-induced irregularities. To better understand the distribution of graphene within the nanofibers, Raman mapping was performed (Figure 4b), which shows that the nanofibers are indeed heterogeneous. However, the D, G and 2D bands dominate along the structure, indicating the successful construction of hybrid nanofibers by the self-assembly technique. Raman mapping of the other systems, G-COOH-hc, G-COOH-EDC / NHS, and G-COOH-TETA, also show D, G, and 2D bands, but with different degrees of discontinuity along the nanofiber. Furthermore, these systems show many "free" graphene flakes, i.e., graphene flakes that are not attached to the nanofiber. As expected, no characteristic D, G, or 2D peaks were detected in the graphene-free systems.

[0231] The underlying mechanism by which such structures are formed is further explored theoretically. We found that functional groups are concentrated at the edges of graphene after functionalization with 5-azidopentanoic acid, as seen in computer simulations (Figure 5a, b). The zigzag sites in the graphene structure are reactive and allow carbene-related reactions such as cycloaddition. Furthermore, oxygen-containing groups on the graphene surface resulting from the liquid-phase exfoliation process are mainly concentrated at the edges and can react with azide molecules. Figure 5(a, b) shows that edge functional groups connect graphene platelets with higher binding energy than surface functional groups. Thus, an efficient regioselectivity of the subsequent reaction steps can be observed, which allows the reaction to continue mainly at the edges, favoring longitudinal fiber growth.

[0232] Considering the steps depicted in Figure 1, we simulate the most likely cross-linking reactions. As can be observed, all mechanisms have similar energies (within <0.4 eV) and can explain not only the nanofiber formation but also the incorporation of G-COOH into or onto the nanofibers. The activation of the carboxyl groups on G-COOH by EDC / NHS and the multifunctional nature of the amine molecules (TETA) can lead to the assembly of graphene sheets, leading to the formation of large 1D structures. However, what we observed experimentally from the "control" reaction and confirmed by computer simulation is that multiple mechanisms can occur simultaneously.

[0233] Furthermore, two random scrolls can only form a self-assembled structure between them if they are composed of platelets with similar sizes; otherwise, regular layer structures are not possible. A model illustrating this effect is shown in Figure 5(c,d). The scroll is an Archimedean spiral represented by (φ) = φd / 2π, where r is the radius vector, φ is the azimuthal angle, and d is the interlayer distance. The scroll shape is determined by balancing the elastic energy that tries to flatten the scroll and the interlayer interactions. Archimedean scrolls made of the same material have the same shape, determined only by the material constants D (bending stiffness) and H (Hamaker constant). So the scrolls are similar in a geometric sense, i.e., they can be represented by the same pair of angles φ0 and φ1, no matter how large the original platelets are (see Figure 5(c,d)). For φ0-φ1≪φ0,φ1, the ratio L / d~φc can be written, where L=2πrc is the linear size of the square platelet, rc is the characteristic scroll radius, and φc is given by φc=2π√6πD / H. For the scrolls to be regularly entangled, the difference between their characteristic radii needs to be of the same order of magnitude as the interlayer distance in the larger sample (i.e., Δrc~d). Since Δrc=ΔL / 2π and d~L / φc, the following condition holds for regular scroll entanglement:

number

[0234] In summary, the experimental evidence suggests that interfacially confined polymerization reactions take place on the G-COOH structures. The chemical environment created by the reaction leads to a scrolling process of G-COOH. Since the G-COOH structures present carboxyl groups on both sides of the sheet, further polymerization takes place in other parts of the scroll structures to form a layered fiber structure. This structure is guided by the organic fiber network that is simultaneously formed by the cross-linking reaction between the EDC / NHS / TETA molecules used for functionalization. Moreover, these reactions take place mainly at the edges of the scrolls / fibers due to both the high regioselective reactivity of the system and the high structural anisotropy, which explains the high aspect ratio obtained. Interestingly, it can be observed that the fibers grow continuously over time via self-assembly and reaction due to the high availability of functional groups at the edges, suggesting a living polymerization profile.

[0235] 2D confined electrolyte assembly in nanofibers The preparation of ionically crosslinked graphene nanofibers can be achieved both (i) directly from the modification of graphene with organic salts or (ii) via the exfoliation of graphite to graphene in the presence of salts. In the two mentioned approaches, only the first step differs, which is explained as follows: 1. If graphene is used, prepare a water dispersion containing 1 part graphene and 50 parts of a salt with a partially hydrophobic organic anion and a hydrophilic inorganic cation, for example lithium bis(trifluoromethane)sulfonimide (LiNTf2). Ideally, the graphene concentration is kept at about 0.5 mg / mL and the dispersion is sonicated (sonic bath) for 20 minutes at 10°C. The dispersion is centrifuged at 6000 rpm for 15 minutes and the supernatant is filtered and washed with water. The remaining water, containing only the salt (LiNTf2), can be reused in a new batch.

[0236] 2. If graphite is used, prepare a water / organic solvent (95 / 5) dispersion containing 1 part graphite and 50 parts salt with partially hydrophobic organic anion and hydrophilic inorganic cation (e.g. LiNTf2). The organic solvent must phase separate with water (e.g. dichloromethane or chloroform) and form a metastable emulsion under ultrasound. Ideally, the graphite concentration is kept at about 0.5 mg / mL and the dispersion is subjected to high power probe ultrasound (20 kHz, 2000 W) for 30 min (divided into three periods of 10 min) at about 10 °C. The formed emulsion is centrifuged at 6000 rpm for 15 min and the supernatant is filtered and washed with water. The remaining water containing only (LiNTf2) can be reused in a new batch.

[0237] For both techniques, the filtered and washed material obtained is redispersed in water, then the new dispersion is vigorously stirred and an equimolar amount (relative to the LiNTf2 previously applied) of a salt with organic and partially hydrophobic cations dissolved in water, for example 1-butyl-3-methylimidazolium methanesulfonate (BMImMes), is added dropwise to the dispersion and left stirring for 1 hour. The mixture is then subjected to ultrasound (ultrasonic bath, 10°C) for 10 minutes and left to stand for 10 minutes. The initially transparent dispersion starts to become turbid and the growth of fibrils is observed. The mixture obtained is left to stand overnight in the refrigerator (approximately 5°C). The fibers obtained are filtered and washed with water.

[0238] The same protocol described above for graphite / graphene can be applied to many other 2D materials by simply choosing the appropriate salts to interact with them during the fibrillation process. Furthermore, the exact same protocol and salts used can be applied to 2D materials such as hexagonal boron nitride (hBN), as shown below.

[0239] The XRD patterns of the bulk and fiber samples are shown in FIG. 10. Typical diffraction lines are observed for the graphite and hBN structures, specifically (002) at 26.46°, (100) at 44.38°, (004) at 54.65°, and (110) at 77.44° for graphite, and (002) at 26.86°, (100) at 41.78°, (101) at 43.77°, and (004) at 55.14° for (bulk) hBN. The remaining diffraction lines seen in all the diffraction patterns of the modified samples correspond to the incorporated salts. The most intense diffraction lines are located at 21.19°, 22.56°, and 23.69°, corresponding to d-spacings of 0.419 nm, 0.394 nm, and 0.376 nm.

[0240] The Raman spectra of the modified graphene and hBN-based fibers are shown in Figure 11. The vibrational modes of the exfoliated materials are 1343 cm for graphite; -1 E2g (G band) and 1574 cm -1 and for hBN, 1359 cm -1 The vibrational bands characteristic of the salt (BMImMes) are all shown without significant shifts. The presence of the 1-butyl-3-methylimidazolium cation is indicated by an excitation at 3029 cm -1 ν in as (CH), 2950cm -1 ν in s (CH), 1574cm -1 , 1408cm -1 , and 1456 cm -1 ν(CC) at 1343cm -1The vibrational band of δ(CH) at 965 cm -1 The bis(trifluoromethylsulfonyl)imide anion corresponds to the breathing vibration of the imidazolium ring at 789 cm -1 ν in as (SN) and ν s (CF), 741cm -1 δ in s (CF3), 558cm -1 δ in s (SO2), and 339cm -1 This is confirmed by the presence of the vibrational mode t(SO2) at

[0241] Polarized optical microscopy (POM, using single and cross polarized light), scanning electron microscopy (SEM), and low- and high-resolution transmission electron microscopy (TEM) and (HRTEM) were used to show the structural order of the fibers, as well as their elemental distribution (using energy dispersive spectroscopy, EDS) and crystallinity (using selected area electron diffraction, SAED), as shown in FIG. 12. The POM images show a highly ordered fiber structure composed of scrolled 2D sheets (graphene or hBN), and their cross polarized images show a clear birefringence effect. The SEM and TEM images show that both graphene and hBN were able to form very long semi-hollow fibers, and the HRTEM of their edges shows the characteristic arrangement of scrolled 2D sheets. The EDS elemental distribution of the fibers confirms that the carbon composition is predominant in the graphene fibers, and the boron and nitrogen composition is predominant in the hBN. Furthermore, HRTEM and SAED demonstrate that much of the original crystallinity of graphene and hBN is preserved throughout the fibrillation process, and there is some directionality of electron diffraction in the direction that the sheets bend and scroll into fibers, as would be expected for curved crystals.

[0242] In summary, we have demonstrated two versatile, facile, and unique approaches to obtain fibers from small graphene flakes through self-assembly. All steps are performed in suspension, most of which are carried out in water at room temperature, which can accelerate the scale-up process and large-scale production. The resulting fibers exhibit high aspect ratios and nanoscale diameters. Such structures are relevant for a wide variety of applications, such as smart electronic textile devices, fabrics, flexible and wearable electronics, sensors, membranes for filtration, batteries, and supercapacitors.

[0243] Self-assembled heterostructure fibers As presented by the SEM image in Figure 16a, after the mixing process of GO(+) and MoS2(-), short nanofibers began to form with open sheets of 2D material around them. Sonication for 5 min was performed after the mixing process to further induce the fiber scroll formation. Long fiber bundles with branches were observed as the main resulting structure (Figure 16b). The fibers exist in a wide range of diameters (within 300 nm) and lengths up to about 100 μm. Based on the height difference in AFM analysis (Figure 16c), the fibers appeared as multi-layer scroll structures, which resulted from the scroll formation of 2D material sheets on the thin fibers (ii and iii), and finally formed thick fibers as shown in (i). Figure 16d shows the Raman characterization of the branched fibers obtained after mixing of TETA-GO and MPA-MoS2. Two main GO characteristic peaks, namely, 1350 cm -1 D band and 1600 cm -1 The G band is observed at 378 cm -1 and 410cm -1 These two bands correspond to the E of MoS2, respectively. 2g Phonon vibration and A 1g This corresponds to the transition, indicating the presence of both GO and MoS2 in the structure.

[0244] Herein, we present a facile aqueous self-assembly approach to synthesize heterostructured fibers from 2D materials. Long branched fiber bundles can be attractive materials for various industries, such as textiles and flexible sensors.

[0245] Experimental Method Functionalization of 2D materials First, graphene is functionalized with 5-azidopentanoic acid (G-COOH). The reaction can be carried out in DMSO under N2 atmosphere at about 45°C for 72 hours. The excess azide molecules are then removed by centrifugation, and graphene shows good stability in water. Another non-limiting example of functionalization is few-layer transition metal dichalcogenides such as MoS2, which can be functionalized at the sulfur vacancies with mercaptopropionic acid (MPA), which also results in a negatively charged surface.

[0246] The structure of the graphene sheets is tuned by modifying the properties of the medium, and the surface charge of the graphene is altered by changing the pH.

[0247] The system is further functionalized with a multifunctional molecule, namely triethylenetetramine (TETA). In this case, 5 mL of G-COOH, 0.04 mg / mL in water is prepared, the pH is adjusted to 4, and the system is sonicated for 20 min at 10 °C. To activate the carboxyl groups, 25 mg of EDC is added and the system is kept under stirring for 15 min, followed by the addition of 50 mg of NHS. After another 15 min, 200 μL of TETA (60%) is added and the system is kept under stirring for 3 h at room temperature. The reaction is then transferred to a refrigerator for 72 h, followed by washing once with ethanol and twice with water.

[0248] Synthesis of TETA-GO (GO(+)) GO was functionalized with triethylenetetramine (TETA) using the 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) / N-hydroxysuccinimide (NHS) crosslinking method. EDC (100 mg) was added to a 0.1 mg / mL GO dispersion, stirred for 15 min at room temperature, and sonicated for 5 min at 10 °C. Next, 200 mg of NHS was added and stirred for 15 min. The reaction mixture was then sonicated for 5 min at 10 °C, and 240 μL of TETA was added. After stirring for 5 h at room temperature, the reaction was stopped and the material was washed with ethanol and deionized water. Just before the synthesis of heterostructured nanofibers, a washing step of the TETA-GO dispersion was performed using dilute hydrochloric acid and water, and the pH was adjusted to about pH 4.5 to protonate the amino groups and generate positive charges on the GO sheets.

[0249] Synthesis of MPA-MoS2 (MoS2(-)) MPA-MoS2 was prepared by adding 50 mg of lithium intercalated MoS2 (LixMoS2) powder into 50 mL of 175 mM 3-mercaptopropionic acid (MPA) aqueous solution. The reaction mixture was sonicated for 30 min at 18 °C, stirred for 2 h, and then subjected to another sonication for 30 min at 18 °C. The functionalized MoS2 was purified by a dialysis process against deionized water for 3 days and freeze-dried. Just before the synthesis of heterostructured nanofibers, the pH of the MoS2 dispersion was adjusted to about pH 8.5 to deprotonate the carboxyl groups and generate negative charges on the MoS2 sheets.

[0250] Synthesis of GO(+) / MoS2(-) heterostructure fibers First, GO(+) and MoS2(-) were prepared using the method described above, i.e., functionalization of GO with molecules that allow the formation of positively charged moieties (e.g., TETA) and functionalization of MoS2 with molecules that allow the formation of negatively charged moieties (e.g., MPA). Then, both functionalized 2D materials were sonicated in an ultrasonic bath for 5 min at 10 °C. Both 2D material dispersions of the same concentration (0.05 mg / mL) were merged at a T-connector to achieve uniform mixing using a dual-channel peristaltic pump operating at a constant flow rate of 0.5 rpm. The dispersion mixture was then transported through a tube connected to the T-connector to allow further mixing along the tube. A vial filled with deionized water was prepared at the end of the tube for sampling. Once both dispersions of 2D materials had completed mixing, the reaction mixture was subjected to an additional 5 min of sonication in an ultrasonic bath (10 °C).

[0251] Characteristic measurements Substrates (Si, Si / SiO2, or Si / Au) are cleaned by immersion in acetone and isopropanol alcohol under sonication (5 min each). The morphology of the nanofiber structures is investigated by electron microscopy techniques. For scanning electron microscopy (SEM), samples are drop-cast directly onto Si, Au-coated, or SiO2-coated Si substrates, and analysis is performed on an FEI Verios 460L field emission scanning electron microscope (FESEM) operating at 2 kV.

[0252] Transmission scanning electron microscopy (STEM) and high-resolution STEM scans are performed on Lacey carbon gold TEM grids (TedPella) using an FEI Verios 460L FESEM and a JEOL JEM-ARM200F atomic resolution analytical microscope, respectively. For size analysis, approximately 150 structures were measured manually using open source image processing ImageJ software. Optical images are obtained on Si / SiO2 substrates using an Olympus optical microscope.

[0253] For XPS, the dispersions are drop-cast directly onto Si substrates and allowed to dry at room temperature. All spectra are calibrated using the Si peak (99.4 eV) from the silicon substrate.

[0254] Shirley-type background, peak fitting, and quantification are performed by CasaXPS software (version 2.1.19). We deconvolute the C1s spectrum to the graphite asymmetric peak (~284.5 eV), and other peaks are fitted using a Gaussian-Lorentzian GL (30) line shape. Atomic force microscopy (AFM) images are acquired on a Bruker Dimension Icon Microscope operated in tapping mode and 512 scan lines, and height profile images are obtained using the open source AFM image processing tool Gwyddion.

[0255] Confocal Raman spectroscopy is performed on a Witec Alpha 300R with an excitation wavelength of 532 nm, a 100x objective, and a numerical aperture of 0.9. For graphene nanofibers, the spectra are normalized to the G-band intensity.

[0256] Calculation method We performed density functional theory calculations using the SIESTA code to determine the enthalpies of reactions involved in the crosslinking process. We used a nonlocal van der Waals density functional. The core electrons were modeled using a pseudopotential of Troullier-Martins type. The basis set of the Kohn-Sham states is a linear combination of numerical atomic orbitals (double zeta polarized basis for all species). The charge density was projected onto a real space grid with an equivalent cutoff energy of 250 Ry to calculate the exchange-correlation and Hartree potentials. Structural relaxation was performed using a combination of conjugate gradient optimizations.

[0257] It will be understood that many further modifications and permutations of various aspects of the described embodiments are possible, and the described aspects are therefore intended to embrace all such alterations, modifications, and variations that fall within the spirit and scope of the appended claims.

[0258] Throughout this specification and the claims that follow, unless the context requires otherwise, the word "comprise" and variations such as "comprises" and "comprising" are understood to mean the inclusion of a stated integer or step or group of integers or steps but not to the exclusion of any other integer or step or group of integers or steps.

[0259] Throughout this specification and the appended claims which follow, unless the context requires otherwise, the phrase "consisting essentially of" and variations such as "consists essentially of" are understood to indicate that the recited elements are essential, i.e., required, elements of the invention. This phrase permits the presence of other unrecited elements that do not materially affect the characteristics of the invention, but excludes additional unrecited elements that may affect the basic and novel characteristics of the defined method.

[0260] Reference in this specification to any prior publication (or information derived therefrom), or to any known matter, is not, and should not be construed as, an acknowledgement or admission, or any form of suggestion, that the prior publication (or information derived therefrom) or known matter forms part of the common general knowledge in the field of endeavor to which this specification pertains.

Claims

1. 1. A method of forming nanofibers, comprising: a) providing a two-dimensional (2D) material having charge-carrying moieties on its planar surfaces and at its edges; b) reacting the charge-carrying moieties on the planar surfaces with a proton donor, a proton acceptor, an at least partially hydrophobic counterion, or a second 2D material having opposite charge-carrying moieties on its planar surfaces and at its edges to curl the 2D material; and c) reacting the charge-carrying moieties at the ends with a proton donor, a proton acceptor, an at least partially hydrophobic counterion, or the second 2D material having opposite charge-carrying moieties on its planar surface and at its ends, while cross-linking the neutralized charge-carrying moieties at the ends, so that the 2D materials of step b) interact with each other to form the nanofibers; A method comprising:

2. The method of claim 1 , wherein the charge-bearing moiety is selected from a protonated moiety, a deprotonated moiety, a cationic moiety, or an anionic moiety.

3. The process is carried out in an aqueous medium, The process is carried out at about 10°C to about 50°C; said reacting steps b) and / or c) being carried out at a pH of about 3 to about 6, or preferably at a pH of about 4; and / or At least step b) is carried out under ultrasonic treatment and / or stirring, and the ultrasonic treatment is carried out at about 3°C to about 10°C for at least 10 minutes; The method of claim 1.

4. the method does not rely on a template to form the nanofibers; and / or If the pH is maintained and / or if counterions are in excess, the method is self-perpetuating until all the 2D material has reacted. The method of claim 1.

5. The 2D material is selected from graphene, graphene oxide, few-layer transition metal dichalcogenide, hexagonal boron nitride, or a combination thereof, and the few-layer transition metal dichalcogenide is MoS ２ , MoSe ２ , MoTe ２ , W.S. ２ , or WSe ２ The method of claim 1 , wherein the compound is selected from the group consisting of:

6. the 2D material is at least about 50% functionalized with the charge-carrying moiety; and / or the second 2D material having opposite charge-carrying moieties is at least about 50% functionalized with the charge-carrying moieties; The method of claim 1.

7. 10. The method of claim 1, wherein the at least partially hydrophobic counterion is selected from imidazolium, pyridinium, piperidinium, ammonium, phosphonium, imide, sulfonate, sulfate, borate, phosphate, carboxylate, or derivatives thereof, and the second 2D material having opposite charge-carrying moieties is selected from graphene, graphene oxide, few-layer transition metal dichalcogenides, hexagonal boron nitride, or combinations thereof.

8. step b) further comprises cross-linking the reacted charge-carrying moieties on the planar surface, wherein the cross-linking is performed in the presence of a cross-linking agent, the cross-linking agent comprising at least two cross-linkable moieties; a weight ratio of the crosslinker to the 2D material of about 50:1 to about 700:1; The method of claim 1.

9. further comprising functionalizing the 2D material with a charge-carrying moiety to form a 2D material having the charge-carrying moiety of step a); wherein the step of functionalizing the 2D material with a charge-carrying moiety is performed at a pH of about 5 to about 6.9, and the step of functionalizing the 2D material with a charge-carrying moiety is performed under sonication, and the sonication is at about 3° C. to about 10° C. for at least 10 minutes, or preferably at about 3° C. to about 10° C. for at least 30 minutes; functionalizing the 2D material with a charge-carrying moiety is carried out for at least 2 hours, or preferably at least 72 hours; functionalizing the 2D material with a charge-carrying moiety is carried out at about 20°C to about 70°C, or preferably at about 45°C; The method of claim 1.

10. The method for forming nanofibers comprises: a) providing a 2D material having protonated or deprotonated moieties on its plane and at its edges; b) reacting the protonated or deprotonated moieties on the planar surface with a proton donor or proton acceptor to curl the 2D material; and c) reacting the protonated or deprotonated moieties of the ends with a proton donor or a proton acceptor, and simultaneously covalently cross-linking the reacted moieties of the ends, so that the 2D materials of step b) interact with each other to form the nanofibers; Including; the protonated moiety or the deprotonated moiety is a carboxylate moiety, and the carboxylate moiety is a carboxylic compound selected from 5-azidopentanoic acid, 6-azido-hexanoic acid, azido-dPEG 4 -acid, azidopalmitic acid, azidoacetic acid, mercaptopropionic acid, mercaptoacetic acid, 5-mercaptopentanoic acid, or a combination thereof; The method of claim 1.

11. 11. The method of claim 10, wherein step b) further comprises covalently cross-linking the reacted protonated or deprotonated moieties on the planar surface.

12. the protonated moiety or the deprotonated moiety is covalently crosslinked by an amino compound, the amino compound comprising at least two amino moieties; the amino compound is triethylenetetramine, triethylenediamine, ethylenediamine, p-phenylenediamine, or a combination thereof; The method of claim 10.

13. 10. The method of claim 1, wherein the nanofibers are formed in an aqueous medium, the method comprising: a) providing a 2D material having cationic or anionic moieties on its planar surface and at its edges; b) reacting the cationic or anionic moieties on the planar surface with at least partially hydrophobic counterions to curl the 2D material; and c) reacting the cationic or anionic moieties of the ends with at least partially hydrophobic counterions while ionically crosslinking the reacted charge-carrying moieties of the ends so that the 2D materials of step b) interact with each other to form the nanofibers; Including; the cationic moiety or the anionic moiety is electrostatically bound to the 2D material; the ratio of 2D material to said cationic moieties or said anionic moieties is from about 1:30 to about 1:80, or preferably about 1:50; the cationic or anionic moiety is an organic cationic or anionic moiety; The method of claim 1.

14. reacting the charge-carrying moiety with a counterion having an opposite charge to the cationic or anionic moieties on the 2D material; the counterion is an organic counterion selected from imidazolium, pyridinium, piperidinium, ammonium, phosphonium, imide, sulfonate, sulfate, borate, phosphate, carboxylate, or derivatives thereof; the ratio of the 2D material having cationic or anionic moieties to said counterions is from about 1:30 to about 1:80, or preferably about 1:50; The method of claim 13.

15. 14. The method of claim 13, wherein step b) further comprises ionically crosslinking the reacted cationic or anionic moieties on the planar surface.

16. further comprising functionalizing the 2D material with cationic or anionic moieties to form a 2D material having cationic or anionic moieties of step a); functionalizing the 2D material with cationic or anionic moieties is carried out in the presence of cationic or anionic moieties under sonication, and the sonication is carried out at about 3° C. to about 10° C. for at least 10 minutes; The method of claim 13.

17. 10. The method of claim 1, wherein the nanofibers are formed in an aqueous medium, the method comprising: a) providing a 2D material having cationic or anionic moieties on its planar surface and at its edges; b) reacting the cationic or anionic moieties on the planar surfaces with another 2D material having opposite charge-carrying moieties on the planar surfaces and at the edges thereof to curl the 2D material; and c) reacting the cationic or anionic moieties at the ends with another 2D material having opposite charge-carrying moieties on its planar surface and at its ends, while ionically crosslinking the reacted charge-carrying moieties at the ends, so that the 2D materials of step b) interact with each other to form the nanofibers; Including; a weight ratio of the 2D material to the other 2D material is about 1:1; The method of claim 1.

18. A nanofiber, the nanofibers are characterized by a solid or semi-hollow cross-sectional profile; the nanofibers are 2D materials characterized by a layered cross-sectional profile of the 2D material that is curled and bonded to one another at its planes and edges; the 2D material is selected from graphene, graphene oxide, few-layer transition metal dichalcogenides, hexagonal boron nitride, or combinations thereof; Nanofiber.

19. the nanofibers are characterized by a diameter of about 5 nm to about 400 nm, or preferably about 10 nm to about 100 nm, and / or a length of about 1 μm to about 100 μm, or preferably about 10 μm to about 30 μm; the nanofibers have a non-uniform diameter; the nanofibers are characterized by an aspect ratio of about 100 to about 3000; the nanofibers are semi-crystalline; The nanofiber of claim 18.

20. When the nanofibers are graphene nanofibers, the nanofibers are characterized by an interlayer spacing of about 0.40 nm to 0.5 nm, or preferably about 0.40 nm to 0.43 nm; When the nanofibers are graphene nanofibers, the nanofibers are characterized by amide bonds, and the nanofibers are characterized by an X-ray photoelectron spectrum peak located at about 288 eV to about 290 eV and / or an FTIR peak located at about 1653 cm −1 and about 1572 cm −1 ; The nanofiber of claim 18.

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