Dispersion and exfoliation of mxenes using high shear and hydrodynamic cavitation

Abstract

Herein we demonstrate a method of high energy delamination called high pressure homogenization (HPH) that combines high shear, cavitation forces, and impact forces to delaminate MXene without any post-process refinement steps or chemical intercalants. HPH-delaminated MXene can be made at scale with high throughput and yield with virtually no waste. We demonstrate the viability of this process by fabricating free-standing films with the material for use as electrodes for energy storage, and as an effective antimicrobial coating with a two-log reduction in pathogenic microbes.

Description

DISPERSION AND EXFOLIATION OF MXENES USING HIGH SHEAR AND HYDRODYNAMIC CAVITATIONCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims priority to and the benefit of United States patent application no. 63 / 509,554, “Dispersion And Exfoliation Of MXenes Using High Shear And Hydrodynamic Cavitation” (filed June 22, 2023). All foregoing applications are incorporated herein by reference in their entireties for any and all purposes.TECHNICAL FIELD

[0002] The present disclosure relates to the field of materials processing.BACKGROUND

[0003] MXenes are a family of two-dimensional (2D) materials that can be solution synthesized from a top-down approach allowing for scalable manufacturing. MXene flakes are produced by etching MAX phase precursors to yield so-called multilayer MXenes. Multilayer MXenes are then further processed by chemical intercalation to produce stable dispersion of 2D flakes in aqueous suspension. The current process of delamination requires multiple time-, energy-, and waste-intensive steps. The resulting material contains impurities from the intercalation step that can affect the final properties and limit the use in certain applications, such as biomedical, where residual ions like lithium are undesired. Chemical intercalation is also limited in scope to the variety of MXenes that it can effectively delaminate, for instance, molten salt etched MXenes.SUMMARY

[0004] Herein we demonstrate a method of high energy delamination called high pressure homogenization (HPH) that combines high shear, cavitation forces, and impact forces to delaminate MXene without any post-process refinement steps or chemical intercalants. HPH-delaminated MXene can be made at scale with high throughput and yield with virtually no waste. We demonstrate the viability of this process by fabricatingfree-standing films with the material for use as electrodes for energy storage, and as an effective antimicrobial coating with a two-log reduction in pathogenic microbes.

[0005] The present disclosure provides, inter alia, a method for delaminating multilayer MXene (ML-MXene) using high pressure homogenization (HPH) and the implementation of HPH-delaminated MXene (HPH-MXene) into applications including energy storage and electrochemical biosensing. The current stage of development is proof- of-concept, having demonstrated the successful delamination of Ti3C2Tx multilayer powder into stable aqueous suspensions of few and single layer flakes through appropriate material characterization (UV-vis spectroscopy, optical imaging). Electrochemical testing has shown HPH-MXene to have good performance as an energy storage material. Additionally, pristine HPH-MXene electrodes have shown potential to be used as electrochemical sensors for the quantification of oxidized-3,3’,5,5’-tetramethylbenzdine (TMB) as indirect detection of foodborne pathogens with improved performance. Preliminary results using Square Wave Voltammetry showed an increase in current response (100X) from oxidized-TMB using HPH-MXene electrodes compared to the standard glassy carbon (GC) electrode.

[0006] Provided is a method of delaminating a multilayer MXene, comprising: subjecting the multilayer MXene to a high-pressure homogenization process sufficient to effect at least partial delamination of the multilayer MXene. The method can be performed free of chemical intercalation.

[0007] Also provided is a method, comprising: effecting cavitation within a multilayered MXene material so as to delaminate at least a portion of the multilayered MXene.

[0008] Further provided is a MXene portion produced according to the present disclosure.

[0009] Also provided is a component, the component comprising a MXene portion according to the present disclosure.

[0010] Further provided is a system, the system configured to delaminate a multilayered MXene, for example a system configured to perform the disclosed methods.BRIEF DESCRIPTION OF THE DRAWINGS

[0011] In the drawings, which are not necessarily drawn to scale, like numerals may describe similar components in different views. Like numerals having different letter suffixes may represent different instances of similar components. The drawings illustrate generally, by way of example, but not by way of limitation, various aspects discussed in the present document. In the drawings:

[0012] Fig. 1 Schematics for high pressure homogenizer (HPH) processing of ml-MXene. a) generalized schematic for the reactor (HPH) cell, b) schematic of HPH delamination of multilayer MXene (ml-MXene) by cavitation pathway, from left to right, ml-MXene flows through small diameter orifice, enters larger diameter orifice where change in pressure cause the formation of bubbles, bubbles nucleate on high energy surface of ml-MXene, back pressure from a constriction in the diameter causes the bubble to implode along the basal plane of ml-MXene, HPH delaminated MXene emerges.

[0013] Fig. 2 a) an aqueous suspension of HPH-MXene. b) a flexible freestanding film made of HPH-MXene made by vacuum filtration, c) Atomic force microscopy of HPH-MXene. d) optical microscopy and SEM (inset) of multilayer MXene (ml-MXene), scale bar for optical is 100 pm, inset scale bar is 2 pm e) MXene processed by high pressure homogenization (HPH-MXene) with SEM (inset), scale bar for optical is 100 pm, inset scale bar is 2 pm.

[0014] Fig. 3 X-ray photoelectron spectroscopy (XPS) of Li -MXene, a) Ti2p and b) Cis c) Ti2p and d) Cis. UV-Vis of Li-MXene and HPH-MXene. e) Raman spectroscopy of ml-MXene, HPH-MXene, and Li-MXene. f) UV-Vis of Li-MXene and HPH-MXene.

[0015] Fig. 4 a) Schematic of -MXene under shear from rheological measurements and b) delaminated MXene under shear during rheological measurements show higher initial viscosity and shear thinning of delaminated flakes, c) Shear rate sweep of -MXene (40 mg mL’1) and HPH-MXene (30 mg mL1). d) oscillation strain sweep of -MXene and HPH-MXene. e) Shear rate sweep of -MXene and HPH-MXene comparing elastic modulus (G’) and viscous modulus (G”)

[0016] Fig. 5 Cyclic voltammetry (CV) of a) So-Li-MXene, b) Li-MXene, and c) HPH-MXene, from 5-1000 mV / s in 3 M H2SO4. d) Rate-dependent gravimetric capacity of So-Li-MXene, Li-MXene, and HPH-MXene.

[0017] Fig. 6 Antimicrobial activities of the MXenes coating against a) nonpathogens b) foodborne pathogens. Bacterial cells were incubated on the MXenes coated (Top) and non-coated (Bottom) stainless disks for 48 hrs (Bottom).DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0018] The present disclosure may be understood more readily by reference to the following detailed description of desired embodiments and the examples included therein.

[0019] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. In case of conflict, the present document, including definitions, will control. Preferred methods and materials are described below, although methods and materials similar or equivalent to those described herein can be used in practice or testing. All publications, patent applications, patents and other references mentioned herein are incorporated by reference in their entirety. The materials, methods, and examples disclosed herein are illustrative only and not intended to be limiting.

[0020] The singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise.

[0021] As used in the specification and in the claims, the term "comprising" can include the embodiments "consisting of' and "consisting essentially of.” The terms “comprise(s),” “include(s),” “having,” “has,” “can,” “contain(s),” and variants thereof, as used herein, are intended to be open-ended transitional phrases, terms, or words that require the presence of the named ingredients / steps and permit the presence of other ingredients / steps. However, such description should be construed as also describing compositions or processes as "consisting of' and "consisting essentially of' the enumerated ingredients / steps, which allows the presence of only the named ingredients / steps, along with any impurities that might result therefrom, and excludes other ingredients / steps.

[0022] As used herein, the terms “about” and “at or about” mean that the amount or value in question can be the value designated some other value approximately or about the same. It is generally understood, as used herein, that it is the nominal value indicated ±10% variation unless otherwise indicated or inferred. The term is intended to convey thatsimilar values promote equivalent results or effects recited in the claims. That is, it is understood that amounts, sizes, formulations, parameters, and other quantities and characteristics are not and need not be exact, but can be approximate and / or larger or smaller, as desired, reflecting tolerances, conversion factors, rounding off, measurement error and the like, and other factors known to those of skill in the art. In general, an amount, size, formulation, parameter or other quantity or characteristic is “about” or “approximate” whether or not expressly stated to be such. It is understood that where “about” is used before a quantitative value, the parameter also includes the specific quantitative value itself, unless specifically stated otherwise.

[0023] Unless indicated to the contrary, the numerical values should be understood to include numerical values which are the same when reduced to the same number of significant figures and numerical values which differ from the stated value by less than the experimental error of conventional measurement technique of the type described in the present application to determine the value.

[0024] All ranges disclosed herein are inclusive of the recited endpoint and independently of the endpoints. The endpoints of the ranges and any values disclosed herein are not limited to the precise range or value; they are sufficiently imprecise to include values approximating these ranges and / or values.

[0025] As used herein, approximating language can be applied to modify any quantitative representation that can vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as “about” and “substantially,” may not be limited to the precise value specified, in some cases. In at least some instances, the approximating language can correspond to the precision of an instrument for measuring the value. The modifier “about” should also be considered as disclosing the range defined by the absolute values of the two endpoints. For example, the expression “from about 2 to about 4” also discloses the range “from 2 to 4.” The term “about” can refer to plus or minus 10% of the indicated number. For example, “about 10%” can indicate a range of 9% to 11%, and “about 1” can mean from 0.9-1.1. Other meanings of “about” can be apparent from the context, such as rounding off, so, for example “about 1” can also mean from 0.5 to 1.4. Further, the term “comprising” should be understood as having its open-ended meaning of “including,” but the term also includes the closed meaning of the term “consisting.” For example, a composition that comprisescomponents A and B can be a composition that includes A, B, and other components, but can also be a composition made of A and B only. Any documents cited herein are incorporated by reference in their entireties for any and all purposes.

[0026] Any embodiment or aspect provided herein is illustrative only and does not limit the scope of the present disclosure or the appended claims. Any part or parts of any one or more embodiments of aspects can be combined with any part or parts of any one or more other embodiments or aspects. MXenes are a family of two-dimensional (2D) materials discovered by Naguib et al.1with attractive electrical,2mechanical,3, and optical4characteristics, which have led to research in a variety of applications.5MXenes are synthesized by selectively etching the A element (e.g., Al, Si, Ga) from the parent layered MAX phase yielding multilayer MXene ( -MXene), where a stack of 2D flakes is held together by van der Waals forces in an accordion morphology.6To take full advantage of many of the properties of MXenes, including versatile surface chemistry and 2D topology, MXenes must be delaminated from the multilayer morphology into single- and few-layer flakes.7Dispersibility of delaminated MXene (t / -MXene) in water allows for simple processing into free-standing films and mechanically robust coatings, which can be used for a variety of applications, including energy storage and antimicrobial / antiviral coatings among others.8,9

[0027] Traditional delamination routes of -MXenes include intercalation of various cations or organic molecules, which expand the interlayer spacing in -MXene and help overcome the residual van der Waals forces between MXene sheets. Positively charged chemical intercalants are typically chosen since they are attracted to the negatively charged surface of MXene and generally can be broken down into organic (e.g., TBAOH, TMAOH6) and inorganic (e.g., LiCl10) intercalants. However, the intercalation approach has several downfalls, including excessive energy input, excessive and toxic waste output, and residual chemicals and impurities. The strong interaction with the MXene surface renders the complete removal of these intercalants practically impossible and affects the final properties of films.11For instance, the cations which were used for the delamination of MXenes were found to be present in the assembled films and structures12and were shown to affect as stability of films under high humidity.12

[0028] Alternatively, shear delamination has been studied for various 2D materials. Graphene,13M0S2, and WS214have been produced by shear exfoliation using arotor stator. Recently, we explored shear delamination of MXenes using a three-roll mill.15While showing potential for scalable delamination of MXenes, this approach has a limited number of parameters for optimization (only shear force) and suffered from comparatively low yield and small flake size.15Hydrodynamic-assisted exfoliation, such as jet cavitation, high pressure homogenization, can help overcome this problem as it combines high shear and cavitation forces to delaminate the material. It has been used previously to exfoliate graphite to few-layer graphene.16 18

[0029] Herein, we demonstrate that -MXene can be delaminated using high pressure homogenization (HPH) without the use of chemical intercalation to dramatically increase the yield and throughput of delamination compared to previous high energy shear delamination techniques and chemical intercalation approaches. We demonstrate that using HPH delaminated MXene (HPH-MXene) suspension can be produced without the need for centrifugation steps to separate the chemical intercalant with increased throughput, which requires only 10 minutes to process 2 g of -MXene, and increased yield of 80% (SI. 1). We show that HPH-MXene can form free-standing films similar to Li+-delaminated MXene and used for the same applications.

[0030] We explore the performance of HPH-MXene in two applications that can benefit from the scalability and high yield of this process, namely as electrodes for supercapacitors and as effective antimicrobial coatings. The electrochemical performance of MXenes has been widely discussed in literature,8,19and HPH-MXene shows comparable capacitance to lithium delaminated films with better rate capability.

[0031] Results and discussion

[0032] Figure 1 shows a schematic of an example high-pressure homogenizer (HPH) cell. The material enters a primary orifice, which induces shear, then experiences the velocity and pressure change upon exiting the primary orifice into the reactors, which induces cavitation (Bernoulli’s principle). The primary orifice and the arrangement / order of different reactors (number, length, orifice diameter) in combination with applied pressures can be used to ultimately drive the shear, cavitation, and impact forces experienced by the material. HPH allows a diverse range of process conditions, such as applied pressure, cavitation, impact, shear, process duration, and temperature.

[0033] To produce -MXene, TisAlC? MAX phase was etched in a mixture of HF and HC1 following previously published protocols.25It is important to limit the amountof residual MAX phase precursor present as it can affect the delamination process and limit the yield. Since the commonly employed etching conditions of 24 hours at 35 °C often provide incomplete etching,26we performed a series of etching experiments for 24 hours at 35 °C, 45 °C and 50 °C . XRD of the etched products showed the appearance of the broad peak at -8.1° indicative of -MXene27and no peaks of residual MAX phase for the sample etched at 50 °C. Due to the lack of residual MAX phase in the sample etched at 50 °C for 24 hours, we used these conditions throughout this work. It is important to note that peaks associated with cubic TiC are present in the -MXene samples throughout the etching conditions which originates from the MAX phase used in this study. The amount of TiC in the MAX phase was estimated to be xxx%, despite the TiC peaks dominating the XRD pattern.

[0034] In a typical HPH delamination experiment, two grams of -MXene were combined with 50 mL of water and the solution was passed through the high-pressure homogenizer for 10 passes to produce delaminated MXene (HPH-MXene). No further processing steps were performed. For comparison, we also prepared MXene delaminated by LiCl according to the previously published protocol (Li-MXene).25HPH-MXene forms a colloidal solution like Li-MXene as shown in Figure 2a. A slightly higher zeta potential of -27.4 ± 0.3 mV, compared to -31.1 ± 0.8 mV for Li-MXene, most likely originates from the inclusion of TiC and lack of Li+ions.

[0035] Similar to Li-MXene, HPH-MXene solution can be used to prepare highly flexible freestanding films by vacuum filtration (Fig. 2b). XRD of the films (Supplementary information 5) showed an expansion and broadening of the (002) peak over Li-MXene. We speculate this increase in interlayer spacing is due to disorder in the film from inclusions of few- to many-layer flakes as well as residual TiC, which will be discussed below. Additional post-processing refinement steps, such as centrifugation, would eliminate these solid phase impurities but would add an additional step and lower the overall yield. While in our previous report on ion-free delamination, we observed an opposite trend for interlayer spacing,15it is noted that we previously used post-processing refinement steps, and it cannot be seen as a direct corollary to this work. The conductivity of the HPH-MXene films was measured to be 1500 S.cm'1. The lower electrical conductivity relative to Li-MXene films, > 13,000 S.cm'1, may be explained by the various factors, such as the non-stoichiometric MAX phase used in this work, the presenceof TiC inclusions and larger interlayer distance discussed above. Because HPH delamination does not require any subsequent washing of the intercalant, it has a yield of 80% and a processing time of 10 minutes for 2 g of -MXene.

[0036] Figure 2 also shows microscopy characterization of MXene flakes. At the individual flake level, atomic force microscopy (AFM) confirms single flake morphology achieved by HPH processing (Fig. 2c). The flake thickness of approximately 3.2 nm exceeds the theoretical monolayer MXene thickness but is in agreement with previously measured values for monolayer MXene flakes.28Optical microscopy of MXene particles show their transformation upon HPH treatment. -MXene appears as large grey particles of different sizes, where each particle exhibits classic accordion morphology (Fig. 2d). Optical microscopy of HPH-MXene exhibits a large change in the morphology with few- and single-layer flakes deposited on the substrate. SEM confirms the presence of single- and few-layer MXene flakes (Fig. 2b), which can explain the lower conductivity measured for the freestanding films of HPH-MXene. Interestingly, the size of individual flakes is in the order of 200 nm, as shown by AFM measurements, however, they tend to aggregate in larger clusters due to the zeta potential being slightly higher than the colloidal stability level of -30 mV.

[0037] HPH processing of multilayer MXene can be controlled in several different ways; pass number, pressure, primary orifice size, reactor setup, and impingement plane can all be manipulated. We isolate the effect that the number of passes has on the HPH processed material and observe different sizes, morphologies, and optical characteristics for different conditions.

[0038] As MXene is delaminated in solution, it greatly expands the surface area as well as increases the anisotropy of the material in solution. The change in morphology can greatly affect the rheological properties of the material, increasing the viscosity, and shear thinning properties, as well as changing the moduli and the ratio of moduli (G7G”) under oscillating conditions (Fig. 4a).31To demonstrate the delamination by HPH, we compared the rheological behavior of solutions of HPH-MXene and -MXene with concentrations of 30 mg.mL'1and 40 mg.mL'1respectively. Although HPH-MXene had a slightly lower concentration, we see a zero point viscosity (0.01 s'1) of 49 Pa.s and a power law exponent of -0.97 compared to -MXene viscosity of 0.37 Pa.s and a power law exponent -0.47. HPH-MXene demonstrates both higher viscosity and more shear thinningindicating delamination has occurred (Fig. 4b). Oscillation tests show higher overall moduli and G7G” ratio for HPH-MXene, these trends match the literature trends comparing delaminated MXene with -MXene.31

[0039] To understand the surface chemistry of the MXenes exfoliated using chemical intercalation and HPH, we performed X-ray Photoelectron Spectroscopy (XPS) analysis of free-standing MXene films. XPS reveals slight changes in the surface chemistry, likely stemming from the presence or lack of cations in the interlayer space that may influence the chemical stability of the resulting MXenes. XPS spectra directly confirm that both samples are TisCkT. MXene based on the binding energy of the peaks which are sensitive to the chemical environment of elements. The F Is, O Is, C Is, and Cl 2p core-level spectra confirm metal bonding with -F, -O, and -Cl as surface terminations, and C as carbide structure (Fig. 3a,b,c,d). Li-MXene shows a slight increase in MXene oxidation state as evidenced in the Ti 2p core-level spectra by the slight shift of the peak near -455.5 eV to higher binding energy (Fig. 3a). The slight increase in the oxide component at -459.4 eV also suggests a higher level of MXene oxidation to bulk titania (6.0% vs. 4.1% respectively for LiCl and HPH). Similarly, the O Is core-level spectra also show a slight increase in the oxide related component at -530.9 eV. Overall quantification indicates very similar compositions: Ti3C1.79O0.97F0.95Cl0.28 for Li-MXene and Ti3C1.93O0.8iF1.02Cl0.28 for HPH-MXene (Supplemental Table 1, Supplemental Table 2). The slight increase in -O and decrease in -F surface terminations may be because of the more open structure in Li-MXene, which promotes the substitution reaction, as Li+bring in more water with them in the form of a hydration shell as they intercalate and strongly interact with the MXene surface. The slight decrease in C content in the Li-MXene sample may result from the increased level of oxidation and carbon vacancy formation. The slightly shifted surface plasmon resonance peak in the UV-Vis absorption spectra for LiCl delaminated MXene supports the XPS results and further indicates that MXene is more oxidized or contains more defects in the carbon lattice (-786 and -775 nm respectively for LiCl and HPH). Thus, we conclude that HPH delamination does not cause the degradation of MXenes and that the quality of materials produced is at least on par with conventionally produced MXenes via chemical intercalation.

[0040] To further analyze HPH-MXene films, Raman spectroscopy was performed to compare the basic lattice and bonding properties of the samples down toseveral hundreds of nanometers from their surface. Figure 3e shows Raman spectra of multilayer and delaminated free-standing MXene films. All the peaks match the results reported before when using a resonant 785 nm laser with Ti3C2Tx samples,29signifying successful synthesis after exploiting both exfoliation methods. The out-of-plane carbon vibration peak shifts from 719.5 cm'1in multilayer MXene to higher wavenumbers in delaminated MXenes, likely representing the increase of the interlayer spacing.29It has been shown that the 725 cm'1Aig(C) peak shifts to the higher wavenumbers with the increase in oxidation30, therefore we could conclude that chemically exfoliated MXene film is slightly more oxidized, which agrees with XPS and UV-Vis data. The lack of any bulk titania peaks, as compared to XPS, could indicate that degradation is happening on the surface (tens of nanometers range). Tx(-230-470 cm'1) region responsible for surface chemistries shows that compared to -MXene the peaks of delaminated MXenes in this region are more pronounced, which could be due to the decreased flake coupling that strengthens surface group vibrations. A 1 cm'1shift in the 123 cm'1resonance peak indicates a small difference in electronic properties, also observed in UV-vis.

[0041] The electrochemical performance of HPH-MXene films was evaluated in 3 M H2SO4 and compared with Li-MXene. To account for the particle size difference, we also prepared sonicated Li-MXene sample (Sonicated-Li-MXene) with the hydrodynamic particle size of 330 ± 8.6 nm, compared to 1700 ± 73 nm and 840 ± 37 nm for Li-MXene and HPH-MXene, respectively (Supplemental Information 6b). As we discussed above, while the DLS size of HPH-MXene is larger, the size of individual flakes is comparable to sonicated Li-MXene. The samples show a pseudocapacitive charge storage behavior (Figure 5a-c), which is governed by the protonation / deprotonation mechanism as demonstrated in our previous studies.32CVs of these three MXenes show dominant pseudocapacitive redox signatures. Interestingly, this redox behavior was quite prominent even at a very high scan rate of 1000 mV s'1for HPH-MXene, which showed a better rate performance compared to Sonicated-Li-MXene and Li-MXene (Fig. 5d). As indicated by XRD (SI. 5), HPH-MXene has a larger interlayer spacing as well as more disordered structure, which provides accessibility of the interlayer spacing and allows for faster insertion and desertion of ions with increased rate capability. Galvanostatic cycling with potential limitation (GCPL) analyses of Sonicated-Li-MXene, Li-MXene, and HPH- MXene at different current densities (1-5 A g'1) (Supporting Information 5a-c) are in linewith the CV observations. At low current density (1 A g'1), Sonicated-Li-MXene shows higher specific capacitance over HPH-MXene, however, upon increasing the current density to 5 A g’1, HPH-MXene shows better capacitance and therefore a higher-rate efficient process over smaller flakes Sonicated-Li-MXene and Li-MXenes (SI. 5d-f). Moreover, HPH-MXene shows a good cyclability - >91% retention of specific capacitance after 10000 continuous cycles with -100% Coulombic efficiency (Supplemental information 6). These observations justify that the HPH-MXene is promising for energy storage applications and could be explored in future studies.

[0042] Antimicrobial coating: Bacterial pathogens intend to attach to the surfaces of food containers, processing equipment, and serving tables to form biofilms, which can cross-contaminate food during storage, processing, and transportation and pose serious threats to human health. Therefore, it is necessary to develop some pathogen-free surface materials. Stainless steel is one of the common materials used in the food industry, retailers, and kitchens. In this study, three major foodborne pathogens and two nonpathogens were investigated for survival on the disk surfaces coated with MXene. The results in Figure 6 show that the coating on the disks has significant antimicrobial activity by reducing 99%~99.9% of the bacterial populations on the coated disk surface (top row) compared with non-coated disks (bottom row).

[0043] We demonstrate that high pressure homogenization can be used to effectively delaminate MXenes without the use of intercalants and with considerable increases in yield over previous methods. The material can be implemented into applications with no further refinement or purification steps, making it an intriguing approach for a large-scale delamination process. We show MXene produced by HPH with post-processing has similar material characteristics to material produced with chemical intercalation and a decreased degree of oxidation from processing. HPH-MXene can be made into free-standing films for use as electrodes showing comparable capacitance to lithium delaminated films with increased rate capability. Finally, we show HPH-MXene can be used as an effective antimicrobial coating on stainless steel, demonstrating a greater than a two-log reduction in pathogens.

[0044] Methods and Materials

[0045] TiiAlC MAX phase etching: TisAlCL MAX phase was sourced fromCarbon Ukraine. Etching was done with the mixed acid method according to theliterature,25however the etching temperature was held at 50 °C for 24 hours to help eliminate residual MAX phase

[0046] LiCl delamination ofml-MXene: Multilayer MXene was chemically delaminated using -MXene obtained by the etching protocol described above. The LiCl chemical delamination was performed per the literature.25

[0047] High-pressure homogenization delamination (HPH): HPH delamination was done with -MXene prepared as described above. A BEE NanoDeBEE homogenizer was used with a primary orifice of 101.6 pm opening and a reactor containing three sets of SP10064 reactors. Pressures exceeded 300 MPa.

[0048] Optical microscopy: Optical microscopy was performed with a Keyence VK-X1050 of dilute MXene suspensions drop cast onto Si / SiCh substrates with a 285 nm oxide layer.

[0049] Scanning electron microscopy (SEM): SEM was performed using a Zeiss Supra 50VP electron microscope with a 3 kV accelerating voltage. Samples were prepared by drop casting dilute MXene solutions onto anodic alumina membranes and ~ 5 nm of platinum was sputtered over the sample.

[0050] Atomic force microscopy (AFM): AFM was performed using a Bruker Multimode 8 instrument in tapping mode in air. Samples were prepared by drop-casting onto Si / SiC>2 wafers with a 285 nm oxide thickness.

[0051] X-ray diffraction (XRD): XRD was performed on free-standing films of delaminated MXene (HPH-MXene and Li -MXene) and powders of Th AIC2 and ml- MXene using a Rigaku SmartLab operating at 40 kV / 30 mA with CuKa. 29 = 3°-70°, step scan of 0.01°, and step time of 1 second.

[0052] Dynamic light scattering (DLS) and zeta potential: Size and zeta potential measurements were performed on dilute solutions using a Malvern Zetasizer Nano ZS. A refractive index of 2.15 was used for Ti3C2Tx.

[0053] UV-Vis: An Evolution 201 UV-Vis spectrometer with a 10 mm optical path was used to collect UV-Vis spectra on samples from 1000 nm - 200 nm in a quartz cuvette.

[0054] X-ray photoelectron spectroscopy (XPS): Free-standing MXene films were mounted on conductive carbon tape and measured using a PHI VersaProbe 5000 spectrometer (Physical Electronics) using a 200 pm, 50 W monochromatic Al Ka X-raysource. The sample was neutralized with a flood gun supplying low-energy electrons and Ar+ions. Samples were analyzed without high-energy ion sputtering to avoid damage to the surface. No binding energy scale correction was needed as the Ti-C peak for reference was -282.0 eV. The pass energy / step size for the survey and core-level spectra, respectively, were set at 117.4 / 0.5 eV and 23.5 / 0.05 eV. Curve fitting and quantification was conducted using the CasaXPS V2.3.25 software, using a spline Shirley background, and symmetric and asymmetric Gaussian-Lorentzian peaks for, respectively, the oxide and MXene related components. Further discussion related to XPS analysis is shown in the SI.

[0055] Raman: We used an inverted reflection mode Renishaw inVia Raman spectrometer instrument in all measurements. All free-standing films were measured using a 785 nm laser with 1200 line / mm grating, the excitation intensity 3.59 mWx10%, the 30 seconds acquisition time, and the *63 objective (NA = 0.7).

[0056] Rheology: Rheological measurements were done with a TA Instruments Discovery HR-3 rheometer with a 20 mm parallel plate at 25 °C at a 0.5 mm gap distance.

[0057] Electrochemical energy storage measurements: Plastic Swagelok cells were used to perform the electrochemical tests. Vacuum filtered free-standing films of MXenes was used as the working electrodes and an Ag wire and activated carbon (AC, YP50F grade) film were incorporated as the reference and counter electrodes, respectively. AC films were prepared using a similar protocol as described earlier33. Glassy carbon electrodes were used as current collectors and Celgard (25 pm thick 3501 polypropylene membrane) was used as the separator. Measurements were recorded at room temperature on a VMP3 electrochemical workstation (BioLogic, France) using cyclic voltammetry (CV) and Galvanostatic cycling with potential limitation (GCPL) techniques. 3 M H2SO4 was used as the electrolyte. Mass loadings for the electrodes are mentioned explicitly in the corresponding figures.

[0058] The gravimetric capacitance (Cg) was calculated from the anodic scan of the CV curve using the following formula:

[0059] where i is the current changed by time 1, and Lis the potential window of the CV scan, and m is the mass of the active material on the working electrode.

[0060] Antimicrobial coating: Fresh cells of pathogens (E. coli O157:H7 20R2R, L. Monocytogenes 19111, and S. typhimurium 53647) and nonpathogens (Listeria innocua 33090 and E. coli K12 23716) was placed on the center of the coated stainless disk (C) and non-coated stainless disk (N). After 48 hrs incubation at 25°C, surviving cells on the disk surfaces were determined for each strain.

[0061] Aspects

[0062] The following Aspects are illustrative only and do not limit the scope of the present disclosure or the appended claims. Any part or parts of any one or more Aspects can be combined with any part or parts of any one or more other Aspects.

[0063] Aspect 1. A method of delaminating a multilayer MXene, comprising: subjecting the multilayer MXene to a high-pressure homogenization process sufficient to effect at least partial delamination of the multilayer MXene. The method can be performed free of chemical intercalation.

[0064] In one embodiment, one can introduce the multilayer MXene to an orifice so as to introduce cavitation; such an approach is shown in FIG. 1. As shown in FIG. 1, one can give rise to bubble formation, bubble nucleation, and bubble cavitation, which in turn gives rise to delaminated MXene. The multilayer MXene can be introduced to a first or primary orifice, which can induce shearing of the multilayer MXene. The velocity and pressure change experienced by the MXene after passage through the first or primary orifice then gives rise to cavitation. The MXene can also experience impact forces, which impact forces can contribute to delamination of the multilayered MXene material.

[0065] Aspect 2. The method of Aspect 1, further comprising collecting MXene portions delaminated from the multilayer MXene. The collection can be accomplished in a variety of ways, for example by filtration and the like.

[0066] Aspect 3. The method of any one of Aspects 1-2, further comprising modulating at least one of a cavitation, a pressure, pass number, a pressure, a primary orifice size, and an impingement plane associated with the process.

[0067] Aspect 4. A method, comprising: effecting cavitation within a multilayered MXene material so as to delaminate at least a portion of the multilayered MXene.

[0068] Aspect 5. The method of Aspect 4, further comprising communicating the multilayered MXene through an orifice.

[0069] Aspect 6. The method of anyone of Aspects 4-5, further comprising communicating the multilayered MXene through a plurality of cavitation zones that give rise to bubble formation within the multilayered MXene.

[0070] Aspect 7. A MXene portion produced according to any one of Aspects 1-6.

[0071] Aspect s. A component, the component comprising a MXene portion according to Aspect 7.

[0072] Aspect 9. The component of Aspect 8, wherein the component comprises a coating.

[0073] Aspect 10. The component of Aspect 8, wherein the component comprises an energy storage device.

[0074] Aspect 11. A system, the system configured to perform the method of any one of Aspects 1 or 4. Such a system can, for example define a fluid pathway through which multilayer MXene can be communicated. As an example, such a fluid pathway can include a first orifice configured to receive multilayer MXene. The fluid pathway can further comprise a cavitation zone downstream from the first orifice; an example such zone is shown in FIG. 1. The diameters of the orifice and the cavitation zone can be selected, along with the flowrate of the multilayer MXene so as to give rise to cavitation within the cavitation zone. As shown, a system can include a plurality of cavitation zones; without being bound to any particular theory, a plurality of zones can give rise to the desired degree of delamination. A multilayered MXene material can undergo one pass through the fluid path, but this is not a requirement, as a multilayered MXene can be passed through the fluid path multiple times.

[0075] Aspect 12. The system of Aspect 11, wherein the system comprises fluid path having a first orifice and a cavitation zone in fluid communication with the first orifice.

[0076] Aspect 13. The system of Aspect 12, therein the system comprises a plurality of cavitation zones in fluid communication with the first orifice.

[0077] Aspect 14. The system of any one of Aspects 11-13, wherein the system is configured to communicate a multilayer MXene along the fluid path a plurality of times.

[0078] Aspect 15. The system of any one of Aspects 11-14, the system being configured to collect delaminated MXene.

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Claims

What is Claimed:

1. A method of delaminating a multilayer MXene, comprising: subjecting the multilayer MXene to a high-pressure homogenization process sufficient to effect at least partial delamination of the multilayer MXene.

2. The method of claim 1, further comprising collecting MXene portions delaminated from the multilayer MXene.

3. The method of any one of claims 1-2, further comprising modulating at least one of a cavitation, a pressure, pass number, a pressure, a primary orifice size, and an impingement plane associated with the process.

4. A method, comprising: effecting cavitation within a multilayered MXene material so as to delaminate at least a portion of the multilayered MXene.

5. The method of claim 4, further comprising communicating the multilayered MXene through an orifice.

6. The method of any one of claims 4-5, further comprising communicating the multilayered MXene through a plurality of cavitation zones that give rise to bubble formation within the multilayered MXene.

7. A MXene portion produced according to any one of claims 1 or 4.

8. A component, the component comprising a MXene portion according to claim 7.

9. The component of claim 8, wherein the component comprises a coating.

10. The component of claim 8, wherein the component comprises an energy storage device.

11. A system, the system configured to perform the method of any one of claims 1 or4.

12. The system of claim 11, wherein the system comprises fluid path having a first orifice and a cavitation zone in fluid communication with the first orifice.

13. The system of claim 12, therein the system comprises a plurality of cavitation zones in fluid communication with the first orifice.

14. The system of any one of claims 11-13, wherein the system is configured to communicate a multilayer MXene along the fluid path a plurality of times.

15. The system of any one of claims 11-13, the system being configured to collect delaminated MXene.

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