Inorganic GELS with 1-dimensional lepidocrocite phase titania-based nanofilaments

Abstract

A gel composition, comprising; a plurality of one-dimensional lepidocrocite (1DL) titanate filaments associated with one another so as to form a gel. A method, comprising: contacting an organic acid to a suspension of 1DL titanate filaments, the contacting being performed under conditions such that the 1DL titanate filaments become associated with one another so as to form a gel. 

Description

INORGANIC GELS WITH 1 -DIMENSIONALLEPIDOCROCITE PHASE TITANIA-BASED NANOFILAMENTSCROSS REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims priority to and the benefit of United States patent application no. 63 / 579,851, “Inorganic Gels From Reaction Of Organic Acids With 1- Dimensional Lepidocrocite Phase Titania-Based Nanofilaments” (filed August 31, 2023). All foregoing applications are incorporated herein by reference in their entireties for any and all purposes.GOVERNMENT RIGHTS

[0002] This invention was made with government support under Contract No. DMR-2211319 awarded by the National Science Foundation. The government has certain rights in the invention.TECHNICAL FIELD

[0003] The present disclosure relates to the field of one-dimensional nanomaterials and to the field of gels.BACKGROUND

[0004] Gel materials have a broad range of uses and applications, but existing gels are not always simple to synthesize and can be limited in their applications. Accordingly, there is a long-felt need in the art for improved gels and related methods.SUMMARY

[0005] In meeting the described long-felt needs, the present disclosure provides a gel composition, comprising; a plurality of one-dimensional lepidocrocite (1DL) titanate filaments associated with one another so as to form a gel.

[0006] Also provided is a method, comprising: contacting an organic acid to a suspension of 1DL titanate filaments, the contacting being performed under conditions such that the 1DL titanate filaments become associated with one another so as to form a gel.BRIEF DESCRIPTION OF THE DRAWINGS

[0007] 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:

[0008] FIGs. 1A-1D provide characterization of 1DL. (FIG. 1 A) SEM micrographs for 1DL displaying the mesophase structure. (FIG. IB) SEM micrograph of 1DL displaying a few nanometers thick filaments. (FIG. 1C) Raman spectra of anatase-TiCh and 1DL. (FIG. ID) XRD patterns for 1DL and anatase-TiCh as a reference.

[0009] FIG. 2 provides a non-limiting schematic for the proposed gelation mechanism of 1DL upon addition of organic acid.

[0010] FIG. 3 provides images of exemplary compositions according to the disclosed technology.

[0011] FIGs. 4A-4B. (FIG. 4A) TGA / DSC thermogram for 1DL powder (FIG. 4B) FTIR of 1DL before (black curve) and after (blue curve) heating to over 500 °C in TGA run.

[0012] FIGs 5A-5C. (FIG. 5A) FTIR spectra of 1DL (red plot) and 1DL gel before (blue plot) and after (black) TMA removal using acrylic acid as gelation inducer. TMA removed by soaking the gel in 10 ml of water twice for a total of 4 days. (FIG. 5B) TGA / DSC for gel after TMA removal. (FIG. 5C) Raman spectra of 1DL (green) and 1DL gel before (red) and after (black) TMA removal. The dashed magenta lines highlight the position of two of the most intense peaks for 1DL.

[0013] FIG. 6A-6C: (FIG. 6A) Compression test for various 1DL gels made using a variety of organic acids as the gelling inducer. (FIG. 6B) A plot of compressive strength of the gels made with acrylic acid as a function of 1DL colloid concentration. Inset shows linear fit parameters. (FIG. C) Stress-strain plot for the gels before and after TMA removal. Inset shows a picture of a gel after TMA removal.

[0014] FIGs. 7A-D. Characterization of compressed 1DL gels. (FIGs. 7A-B) SEM micrographs after compression of the gels in the mechanical test. (FIG. 7C) Raman spectra of gel after compression and of 1DL powder for comparison. (FIG. 7D) XRD patterns for 1DL and 1DL gel after compression.DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0015] The present disclosure may be understood more readily by reference to the following detailed description of desired embodiments and the examples included therein.

[0016] 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.

[0017] The singular forms “a,” “an,’‘ and “the” include plural referents unless the context clearly dictates otherwise.

[0018] 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.

[0019] 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 that similar 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 besuch. 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.

[0020] 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 ty pe described in the present application to determine the value.

[0021] 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.

[0022] 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.

[0023] 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 comprises components 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.

[0024] 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' oneor more embodiments or aspects can be combined with any part or parts of any one or more other embodiments or aspects.

[0025] In the present disclosure, a recently isolated elusive phase of titanate, ID lepidocrocite (1DL), is further studied and the mass percent composition of its organic component, tetramethylammonium (TMA), used for intercalation 1DL filaments was quantified using qNMR and TGA / DSC. The mass % of TMA determined using the qNMR and TGA / DSC methods yielded values of 13.20% and 13.14%, respectively. Furthermore, the 1DL colloid was observed to gel instantly upon addition of organic acid.

[0026] A non-limiting proposed gelation mechanism is discussed, and compression strengths were determined for various samples prepared using different acids and various concentration ranges. The strength of the gels linearly increased as a function of increasing 1DL colloid concentrations. The organic components of the gel (TMA and acid) were completely removed using only two soak cycles to create a completely inorganic gel with superior compression strength to the gel containing TMA. The compression strength of the gels increased by as much as 50% after TMA was completely removed. The amount of TMA removed at each step of the gelling and soaking processes was quantified using the qNMR method. The complete removal of TMA was also validated by using FTIR and TGA / DSC to characterize the xerogels. FTIR showed the disappearance of the bands corresponding to TMA and TGA / DSC showed no thermal events in the range for the decomposition and vaporization of TMA. Raman and XRD results showed that the lepidocrocite polymorphism of 1DL was retained even after gelation and TMA removal. Only after heating at high temperatures above 500 °C, did a phase change to anatase occur. On the other hand, compression of the gels only seemed to convert 1DL filaments to 2D lepidocrocite sheets by evidence of the SEM micrographs.

[0027] Titanium dioxide or titania refers to the metal oxide with the molecular formula TiO2. When the ratio of titanium to oxygen is anything other than 1 :2, these species are formally referred to as titanates. Many titanates exist and usually contain metal cations, organic molecules, protons, and / or hydroxides. Titanates usually have a net negative charge due to the high ratio of oxygen to titanium (greater than 2: 1) which allots the material a large net dipole moment. This classifies titanates as coordination anions that are only weakly attracted to the metal cations. This weak electrostatic attraction is due to the charge being delocalized over the entire coordination species versus on a single atom. Intercalation oftitanates is then easily accomplished using several cations in the interlayers, that due to their weak attraction, can be swapped out for other species.

[0028] The structures of both titanates and titania contain Ti ions that are coordinated to six oxides, forming distorted octahedra. The oxides in turn are coordinated to 3 titanium centers in the three major polymorphs of titania, while titanates can have oxides with multiple coordination numbers, such as two and four-coordinate. The collective crystal structure of all titanium oxides is determined by the spatial arrangement of TiOe octahedra subunits via edge or comer-sharing of oxides. The various sharing of TiOe octahedra subunits via these two systems leads to the formation of crystal structures with various symmetries. For rutile and anatase, tetragonal symmetry is observed, while for brookite, orthorhombic symmetry' is observed. There is a fourth phase of titania known as TiCh(B) w ith a crystal structure that resembles a titanate more than titania. For titanates, several symmetries have been observed, namely, monoclinic, orthorhombic, and tetragonal. Many of these titanate bulk / nano crystal structures are only metastable in comparison to the titania polymorphs, where rutile is the thermodynamically stable form in the bulk, but anatase and brookite can be stable in the nano form.

[0029] Recently, 1 -dimensional (cross section of 5x5 A2) lepidocrocite phase titanate nanofilaments, referred to as 1DL, have been isolated in a minimally intensive and highly scalable synthesis. Badr et al., Matter 2023, 6 (1), 128-141; and Badr et ^.. Materials Today 2022, 54, 8-17, both incorporated herein by reference in their entireties for any and all purposes.

[0030] It has been shown that during 1DL synthesis, the negative surface termination sites of the resulting nanofilaments can be countered, for example with the tetramethylammonium (TMA) cation. Additionally, the use of other bases such as NaOH and KOH, inhibit 1DL formation. Without being bound to any particular theory or embodiment, this may in part be due to the size of the ions that are not large enough for ideal spacing to separate true ID filaments. Instead, 2D self-assembly was observed along the c-axis forming nanosheets. Again w ithout being bound to any particular theory' or embodiment, the unique synthesis procedure for this 1DL titanate may shed some light on the 1-dimensionility observed. Different from the usual hydrothermal and solid-state methods used to make titanates, 1DL can be synthesized using a novel method that utilizes mild conditions at atmospheric pressure. The precursor used can be titanium carbide, nitride, or boride, whichare added to TMAH at temperature ranges of 50 - 90 °C and shaken for up to 6 days. The resulting solid is neutralized by washing with ethanol and centrifuged several times to get a grey powder that is then resuspended in water and sonicated. A stable grey colloid is then formed.

[0031] The foregoing procedure forms the TMA-intercalated 1DL titanate directly, as opposed to all other methods that first form the alkali metal titanate, followed by either protonation and subsequent quaternary’ ammonium intercalation or direct addition of quaternary ammonium hydroxide to get a stable colloidal suspension. In all other cases, the colloidal suspensions are composed of 2D nanosheets that upon acid addition scroll to form nanotubes. 1DL is produced in-situ from the direct reaction of Ti precursors and TMAH so that true ID structures can be realized without self-assembly along the c-axis to form sheets.

[0032] This novel method allows for the formation of a gel upon addition of weak organic acids to produce the protonated 1DL titanate. The gel is formed instantaneously due to the flocculation of 1DL filaments that seem to form braided filaments due to an analogous scrolling phenomenon as seen with titanate nanosheets. The gel is rigid and holds its structure, similar to hydrogels. The lack of elasticity’ in the gel upon small degrees of deformation may be understood to show that the gel is only physically crosslinked. Without being bound to any particular theory’, the gelling in this 1DL may' have relate to its 1- dimensionality that mimics ID organic polymer chains that usually form gels with similar properties.

[0033] Information concerning the formation of 1DL under such mild conditions may be found in understanding the bonding in the Ti precursors and their solubility' in water. All three of the Ti precursors have weaker bonds to titanium than the final product which contains purely Ti — O bonds. These bond energies given as dissociation enthalpies are; Ti — B (272±63 kJ mol1). Ti— N (476±33 kJ mol1), Ti— C (423±30 kJ mol1), and Ti— O (672±9 kJ mol’1). The enthalpy of formation of Ti — O is much higher than all other bonds, thus this thermodynamic factor may be the impetus for driving the reaction towards titanate formation even at such mild conditions. Additionally, the low solubility of all these Ti precursors in very alkaline conditions, means that only a small concentration of Ti4+would be present with an enormous relative concentration of OH’. The instantaneous hydrolysis would occur followed by deprotonation of the hydroxyl groups and capping with TMA via electrostaticattraction. The instant decrease in Ti4+concentration should push this reaction forward, allowing for the grow th of ID titanate nanofilaments in mostly one direction.

[0034] Herein, NMR and TGA / DSC were used to quantify the amount of TMA that is present in 1DL. Additionally, the compression strength of these gels was measured and showed high strength for the first ever reported hydrogel-like composite made from a titanate colloidal system. After the TMA w as fully removed by utilizing two soak cycles in w ater, it can be asserted that the gel is a pure titanate-based gel with no organic species present.

[0035] This gel is the first of its kind and is based on a novel direct method of producing true ID titanates with lepidocrocite structure. The gel is henceforth referred to as a gel composite due to the metal oxide network only trapping w ater in its matrix and not actually holding water as seen in other common organic gels. It is believed that the gel forms a lamellar system upon protonation due to the highly ordered colloid from which it is formed, and this in turn traps w ater in the inter-space betw een aggregated 1DL filaments. Due to this, the gel does not swell in water but actually shrinks slightly, and upon compression water is easily squeezed out of the gel to the point of complete phase separation (liquid water and solid metal oxide components separated) of the gel composite after 80% compression. This correlates well with a lamellar-like structure where interlayer water can easily be pushed out transversely to the applied compression.

[0036] Experimental

[0037] Materials

[0038] Caffeine (USP reference standard), tetramethylammonium hydroxide (TMAH) aqueous solution (25 wt%), deuterated water (99.9 atom % D), propionic acid, formic acid, acry lic acid, trifluororacetic acid, and acetic acid were all purchased from Sigma-Aldrich (St. Louis, MO, USA). Titanium boride Thermo Scientific (Waltham, MA, USA). Ethanol (200 proof) Decon Lab Inc. Ultrapure water, purified using Millipore water deionizing system; resistance: 40 MQ.

[0039] Synthesis of 1DL Titanate

[0040] The 1DL nanofilaments w ere prepared by shaking 0.6 mole equivalents of TiB2 with 1 mole equivalent of TMAH at 80 °C for 5 days in a vented polyethylene bottle using a temperature-controlled shaking incubator (Labnet 21 IDS, 49L. 120V, NJ). Once the reaction was completed, the crude product was filtered and w ashed with ethanol until the filtrate had a pH of approximately 7. After w ashing off the excess TMAH, the w ashed solidwas resuspended in fresh DI water, sonicated for 5 min, and centrifuged at 3,500 rpm for 30 min. Any unreacted TiEh settled to the bottom of the centrifuge tube and the colloidal supernatant was decanted off and filtered to obtain the 1DL colloidal suspension. This resulting colloid was used for all further experiments.

[0041] Formation of the Gel Composite

[0042] The gels were formed directly from the stable 1DL colloidal suspension by adding 225 pl of various organic acids (propionic acid, formic acid, acrylic acid, or acetic acid) to 2 ml of the colloid in a well plate. The colloid transitioned from its sol state to a gel instantly upon addition of the acid. The gels were allowed to sit in the supernatant (residue solvent left after gel formation) for 1 hr before being transferred to clean wells. Any excess supernatant was dabbed off the gel using a Kimwipe before transferring. The gels were then allowed to sit overnight in capped well plates. The next day, all gels were tested for compression strength or processed further for the other tests conducted.

[0043] Mechanical Testing

[0044] The uniaxial compression test of the gels w as conducted on an electromechanical universal test machine (MTS Criterion Model 43) with a 500 N load cell and a crosshead speed of 0.8 mm s '. All tests were conducted at a temperature of 20 °C. A total of 5 gels of each gel type (N = 5) were tested for compression strength unless otherwise stated. The dimensions of each gel fluctuated slightly and the exact dimensions per sample ere used when computing the compression strengths. A typical sample had a diameter of 14 mm, and a height of 10.8 mm. Compression strength was calculated using equation 1.

[0045] Where o is the stress in Pascals (Pa), F is the force or load applied in Newtons (N), and A is the cross-sectional area, defined as the area of a circle in m2.

[0046] qNMR Sample Preparation and Method

[0047] Quantitative 'H NMR (qNMR) experiments were performed on a Varian Unity Inova spectrometer (Palo Alto, CA, USA) operating at 500 MHz and with a Varian triple resonance probe. The temperature was equilibrated at 25 °C for all samples. The gradient shimming feature on the VNMRJ 4.2 NMR software was applied to all samples to attain a lock between 90 and 100, and spinning was turned off for all experiments. For alldata acquired, the same NMR operating parameters were utilized. These parameters were first optimized by determining the longest relaxation time needed for recovery of 99.99 % of magnetization for the quantified signals of interest.

[0048] This was accomplished by running an inversion-recovery sequence to acquire the spin-lattice relaxation time (Ti). Using a 90° pulse length, Ti for all the signals relating to caffeine and TMAH were deduced and the longest relaxation time observed was 8.73 s. A relaxation delay time of 62 s was chosen based on previous works using the equation. 10(Ti -AQ), where AQ is the acquisition time. The remaining parameters were optimized by determining the best values for maximizing the signal to noise ratio (S / N) for the peaks of interest and by following a guideline provided in a reference article. The best digital resolution was seen for acquisition times of 2.5 s. Maximized S / N was achieved using a pulse length of 90°, spectral window of 16 ppm. and 8 scans. The power was kept constant at 58 dB and the receiver gain was set to 16 dB for all runs. Auto phasing and auto baseline corrections using MestreNova software was applied to all NMR plots and provided high quality resolution for the peaks of interest with no interference from13C satellites. The peaks were auto integrated using MestreNova by inputting a recommended integration range of 70 times the full width at half maximum (FWHM).

[0049] The internal standard (ISTD) used in all experiments was a USP caffeine reference standard. A stock solution with a concentration of 19.21 mM was prepared gravimetrically on a pre-calibrated analytical balance with 0.1 mg resolution. 30 pL of both the solution / colloid containing TMA and the caffeine stock solution were added directly to the NMR tube, followed by 600 pL of deuterated water. The NMR tube was capped and vortexed to get all solutions mixed homogenously. If air bubbles were present in the NMR tube, they were bath sonicated to remove them before loading the sample into the NMR.

[0050] For caffeine, four NMR peaks are observed at. 7.77, 3.83, 3.41, and 3.23 ppm. All are sharp singlet peaks that account for the 10 hydrogens found in caffeine. For TMA, one sharp singlet peak is observed at 3.06 ppm and correlates to the 12 hydrogens found in TMA. For the qNMR study, the 3.41 ppm peak was chosen as the ISTD reference peak due to its consistency in yielding a sharp peak, free of any13C satellites, and superior S / N over the other 3 peaks across all concentration ranges used for caffeine. This made the integration simple and reliable. The working concentration of TMA was then determined by using equation 2.

[0051] Where ITMA and Laffeme are the absolute NMR peak integrals of TMA and caffeine, respectively, and Ccaffeine is the working concentration of caffeine in the NMR tube, 8.73 x 10'4M.

[0052] TGA Analysis

[0053] Thermogravimetric analysis (TGA) was performed on a Seiko Instruments Inc. Exstar6000 TG / DTA 6300 (Chiba, Japan). The instrument was calibrated to adjust for major baseline drift. Baseline corrections were carried out before each sample was ran by using empty Pt pans in both the reference and sample balance beams. All samples were accurately weighed using a pre-calibrated analytical balance with 0. 1 mg resolution. The program used for all samples was as follows; equilibrate temperature at 35 °C, ramp at 30 °C min'1to 550 °C, hold for 10 min. All samples were run under inert conditions, using a nitrogen gas flow of 80 ml min'1and the reference in all cases was an empty Pt pan. OriginLab was used to graph and analyze the thermograms.

[0054] DSC Analysis

[0055] Differential scanning calorimetry (DSC) was performed on a TA Instruments DSC Q100 (New Castle, DE, USA) with a refrigerated cooling system. The system was fully calibrated prior to use by utilizing the in-software calibration wizard. The baseline had negligible drift, so no corrections were made. All samples were crimped in aluminum pans and the reference was an empty crimped Al pan. Samples were weighed on a pre-calibrated analytical balance with 0. 1 mg resolution. The heating method used was as follows; equilibrate temperature at 35 °C, ramp at 30 °C min'1to 550 °C. The nitrogen gas flow was kept at 50 ml min'1. OriginLab was used to graph and analyze the thermograms.

[0056] FTIR Analysis

[0057] A PerkinElmer Spectrum One Fourier-transform infrared (FTIR) Spectrometer (Waltham, MA, USA) was used to obtain the FTIR spectra of the samples before and after removal of TMA and TGA / DSC runs. FTIR sampling was performed by attenuated total reflection (ATR) over the range of 500 to 4000 cm'1with a resolution of 4 cm'1. The resulting spectra were processed using the ATR correction feature on the software. The background FTIR spectrum was obtained in atmospheric air for all tests. Each samplewas pressurized to the same magnitude to ensure good contact between the sample and ATR crystal. OriginLab was used to graph and analyze the FTIR spectra of the samples.

[0058] Raman Analysis

[0059] Raman spectra were collected on a Renishaw inVia confocal Raman microscope (Wotton-under-Edge, UK) using a 514 nm laser with a max power of 50 mW, 1800 grooves / mm grating, and a charge-coupled device detector. The instrument was always calibrated before operation using a silicon wafer to center the peak at 520.50 cm’1. Acquisitions were taken in atmospheric conditions. The number of acquisitions and exposure times varied from sample to sample depending on the laser intensity used, which was varied over a range of 1 -100% (increments of 1, 10, 25, 50, and 100%). For all samples tested, a 50x objective was employed to irradiate the laser spot onto the sample. OriginLab was used to graph and analyze the Raman spectra of the samples.

[0060] SEM / EDS Analysis

[0061] Scanning electron microscope (SEM) micrographs were obtained using a ThermoFisher Scientific Apreo 2S LoVac (Waltham, MA, USA) with an In-column ETD (SE) detector as well as a trinity detection system of In-lens detectors; T1 (BSE). T2 (BSE / SE), and T3 (low energy). The beam voltage and cunent were varied to minimize sample charging while maximizing resolution, but generally the ranges used were 1 — 10 kV and 25 — 50 pA. for voltage and current, respectively. Elemental composition was determined using a ThermoFisher Scientific UltraDry 129 eV 60 M energy-dispersive X-ray detector attachment.

[0062] XRD Analysis

[0063] Powder X-ray diffraction, XRD, patterns were acquired using a diffractometer (Rigaku MiniFlex 600 benchtop XRD, Tokyo, Japan) equipped with a Cu Ka radiation source. A 10 mm inlet slit was used and samples were scanned in the range of 3 - 65° 20 with an exposure time of 1.2 s and an incremental step of 0.02 deg s’1. OriginLab was used to graph and analyze the resulting XRD patterns.

[0064] Results and Discussion

[0065] Characterization of 1DL Titanate

[0066] The synthesized 1DL was characterized using Raman. XRD. and SEM. The resulting Raman spectrum (FIG. 1C), XRD pattern (FIG. ID), and micrographs (FIG. 1 A-B) compare well with previous works showing similar spectra and images for 1DL. In FIG. 1C,the XRD pattern clearly shows the presence of two low angle peaks below 20° 20 representative of the intercalated TMA between filaments (peak at ~ 7° 20) and intercalated water or hydronium corresponding to the peak at ~ 15° 20. Additionally, similarities can be seen in the XRD patterns of 1DL and anatase, where both have peaks at about 25°, 37°, 48°, and 62° 20 (magenta dashed lines in Fig. 1A). All of these peaks have also been observ ed in other titanates and are not unique to 1DL or anatase. This is due to the non-basal reflections present in both polymorphs. Moreover, most titanates have several nuance differences in their XRD patterns compared to anatase. For example, the peak center at 24 - 25° 20 for titanates usually is accompanied by a small shoulder to its left and a poorly resolved peak to its right at ~28 - 29° 20. 1DL has a small peak at about 31° 20 which falls close to this range but is shifted enough to be considered unique to 1DL. However, the absence of several other peaks seen in other titanates, such as 33-34, 43-44, and 60 ° 20, categorizes 1DL as a unique titanate never observed based on its XRD pattern alone.

[0067] Notably, anatase has its own distinct differences such as for the peak at 37° and 54° 20 which have triplet and a doublet multiplicities, respectively. XRD reflections for some of the most common titanates used in the literature were compared to 1DL. Excluding the small angle peaks, it can be seen that the closest similarity based on common XRD peaks is with TiCh-B which has a cry stal structure closer to titanates than titania and is commonly referred to as a titanate.

[0068] However, from the Raman spectra in FIG. 1C, 1DL can be confidently discerned from anatase, and even TiCh-B. Anatase has five signature Raman active modes at 143 cm'1(Eg), 197 cm'1(Eg), 397 cm'1(Big), 516 cm'1(Aig), and 637 cm'1(Big). The four peaks at 143, 397, 516, and 637 cm'1are sharp intense peaks and ideal reference peaks to contrast with 1DL. The Raman spectrum for 1DL was completely unique relative to that of anatase, and most notably the 9 peaks at 192, 283. 385, 447, 662. 698, 758. 836, and 950 cm'1were observed. These peaks for 1DL match well with lepidocrocite-ty pe titanate. However, some unique Raman modes were again observed not seen in other titanates at 192, 758, and 950 cm'1. The modes at 758 and 950 cm'1can be attributed to the intercalated TMA vibrations. However, the mode at 192 cm'1is not related to TMA and has not been observed in other titanate spectra. This lends itself to the novelty of this new titanate phase. Moreover, the Raman spectrum of TiCh-B is completely different from 1DL. TiCh-B displays a very busy Raman spectrum with 18 Raman active modes with the most intense peak observed at123 cm'1. This mode is not observed in 1DL as well as many other peaks, thus the two materials can be considered different phases of the metal oxide. Additionally, it was seen that the Raman laser was not capable of generating enough energy / heat to interconvert 1DL to anatase. When the intensity of the laser was varied from 10 - 100% with several exposure times and acquisitions, with no signs of anatase peaks appearing.

[0069] From the SEM image in FIG. IB, several filaments ranging from 27-40 nm in diameter, with an average diameter of 38.31±8.39 nm can be seen. The random arrangement and orientation of the filaments can also be seen in this image. FIG. 1A. shows the mesophase arrangement of the filaments that occurs when they are dried in a vacuum oven overnight. Mesophase agglomerated together were also seen. Without being bound to any particular theory or embodiment, the existence of this phase may be evidence of the anisotropic nature of 1DL and categorize the IDLs as mesogens, or a compound with liquid crystal properties. Gelatin, a common gel-forming biopolymer, exist in these mesophases and is what provides it with its semi-solid or gel-like properties.

[0070] Gelation Mechanism of 1DL Titanate

[0071] An observation was made when small quantities of organic acids were added to colloidal 1DL in well plates. The colloid instantaneously transitioned to a gel from its sol state. Several organic acids, including propionic acid, acetic acid, acrylic acid, formic acid, and trifluoroacetic acid, were used as inducers for forming the gels. All the gels formed were rigid, as long as their corresponding acids possessed pKa values above zero. For trifluoroacetic acid (TFA, pKa: 0) addition, a gel formed that was spherical in contrast to the cylindrical gels formed from other organic acids — the latter being the result of gels taking on the shape of the well. The TFA gels lacked rigidity and quickly lost their form / shape when removed from the well. When pKa values were very low, such as with the dilute mineral acids used, this effect was much more pronounced, and the spherical gels quickly dissolved shortly after forming. The strong acids most likely reacted with the basic TiCh very readily due to their ID morphology forming the corresponding salts as a by-product. It is commonly known that TiCh will dissolve readily in concentrated mineral acids.

[0072] An exemplary’ gelling mechanism is provided in FIG. 2, where after addition of a weak organic acid, the production of hydronium ions exceeds a threshold concentration needed to initiate the instantaneous flocculation of 1DL fdaments. This instantaneous flocculation that effectively makes the gel, was observed to occur in narrow pH ranges of 3 -4. Above a pH of 4, a very7fragile gel would form that could not be easily removed from the well without fracturing it and the gelation time took several hours. On the other hand, when the pH was below 3, the gels would form quickly but sphericalize instantly. When very7low pH’s were used, no gel would form but an exothermic reaction was observed (i.e., high generation of heat) which hinted at the complete neutralization of basic TiO2. This large generation of hydronium ions is responsible for displacing TMA from the colloid and simultaneously initiating the flocculation of filaments. The 1DL gel would still be intercalated, but with hydronium ions that in the gel, act as physical crosslinkers, creating weak crosslinks between adjacent filaments via purely electrostatic interactions, some coordination, and hydrogen bonding to the terminal oxygens present in 1DL.

[0073] The driving force behind this flocculation of filaments is due to the lack of electrostatic repulsion that was present in the colloid from adjacent filaments capped at their surfaces with TMA. This repulsion amongst particles in water is normally how stable colloids are formed and is responsible for the 1DL colloid attained.

[0074] The dark grey gel that is formed is believed to only trap water between its aggregated filament bundles and not actually hold water effectively as common organicbased gels do. This is evident when the gels are compressed, and water quickly squeezes out of the gels even under small degrees of deformation. On the other hand, hydrogels will hold on to water completely when being compressed and not even after failure will water separate from the gels. Brittle gels such as those made from natural polymers (e.g., gelatin), will fail after short compression strains are applied but the gel phase (semi-solid) stays intact.

[0075] The 1DL gel behaves differently than any other gel studied previously, and no gel found in the literature mimicked its complete phase separation upon compression. The 1DL gel does not swell in water, it actually shrinks significantly, further illustrating its ability7to trap water effectively but not hydrophilic enough to absorb additional water. Moreover, once the gel has been completely compressed and the water separated, the gel will not reabsorb any' discernable amount.

[0076] The gels were then air dried overnight to allow the majority7of the water to evaporate. SEM images were then taken of these collapsed network xerogels to observe the type of nano features present. Comparing the SEM images obtained from the 1DL xerogels in FIG. 3 to those of the 1DL powder (FIG. IB), a key distinction between the observed morphologies is that the xerogel samples showed braided filaments (i.e., nano ropes),whereas the randomly oriented loose filaments of 1DL were unbraided and had significantly smaller diameters (38.31±8.39). The diameter of the filament bundles of the nano ropes were measured to be 412 ± 0.078 nm. This corresponds well with the theorized gelling mechanism, where the braided filaments observed are due to physical entanglements after TMA removal and these flocculated bundles form the crosslinked network of the gel.

[0077] 1DL in the colloid may, without being bound to any particular theory7, exist as a series of small nanoparticles that self-assemble linearly into filaments that then further self-assemble into pseudo 2D sheets via adjacent physical bonding of filaments. Knowing this, the braided filaments seen in FIG. 3 may imply that the gelation process proceeds by an intertw ining or twisting of filaments of these well-organized linear filaments in the colloid, and this would explain the braided nano ropes observed in the rigid gel. This high degree of order in the colloid also explains why the filtered films form such orderly stacked structures.

[0078] Determination of the Mass Percent Composition of TMA in 1DL Titanate

[0079] TMA acts as an agonist in muscarinic receptors in post-ganglionic nerve endings of skeletal muscle. This can cause muscular fasciculations, convulsions, and ultimately paralysis. Due to this, it is useful that TMA be removed from the gel, so that it may have potential use in biomedical applications such as in tissue scaffolds. Therefore, the mass percent of TMA in the 1DL colloid was determined using a qNMR method. The method parameters were first optimized by testing several known concentrations of caffeine made using a USP reference standard. The qNMR parameters ere chosen based on getting repeatable results and the best S / N for the 3.41 ppm peak of caffeine and 3.06 ppm peak of TMA. A complete description of the method development and parameters used can be found in the experimental section of this chapter (3.3.5). Once the qNMR method parameters were optimized, it was validated by quantifying several known concentrations of TMA hydroxide (TMAH) solutions. A calibration curve was constructed to compare the linearity of the know n concentrations (determined gravimetrically and by titration) to that of the qNMR determined concentrations.

[0080] Next, the concentrations of the 1DL colloids were measured using the qNMR method. The concentrations measured ranged from 6.6 — 23. 1 mg ml’1and were determined by using a calibrated pipet to dispense a 1 ml aliquot of the colloid into a 10 ml beaker of know weight, and then evaporating off all the w ater overnight in a vacuum oven set to 95 °C. The mass of the dried 1DL film left behind w as then w eighed and this mass to theoriginal volume of the aliquot used, allowed for the determination of the colloidal concentrations listed in Table B.2. The various concentrations of 1DL colloids were then assessed using the qNMR method to quantify the amount of TMA present. The concentrations of TMA determined viaNMR correlated well with the colloid concentrations. These concentrations of TMA were then used to determine the mass percent of TMA present in 1DL. The mass of TMA in the bulk colloids was first calculated using equation 3. mTMA=TMA X F X F x M (3)Where IDTMA is the mass in mg of TMA. CTMA IS the concentration of TMA in the NMR tube, F is the dilution factor (x22 for all samples), V is the volume of the colloid used, and M is the molecular weight of TMA in mg mol'1. The mass percent of TMA was then determined directly for each sample according to equation 4.^'TMAMass % = X 100 (4) m1DLWhere miDL and miMAare the mass in mg of 1DL and TMA, respectively per 1 ml of the colloid. The average mass percent of TMA in the colloids was determined to be 15.57% (std. dev. = 0.32%). The low standard deviation for the mass % of TMA across all concentrations measured indicates that the TMA intercalated in 1DL is an intrinsic property of the material. The composition of 1DL must be established during the synthetic procedure and is due to the experimental conditions chosen.

[0081] TGA and DSC tests were carried out to help validate the qNMR results for the mass percent of TMA in 1DL The 1DL powder samples were first dried under vacuum to remove the majority of the excess water. Three samples were tested, and the mass lost as a percentage using TGA and the thermal characteristics using DSC were analyzed. By coupling both these methods it was possible to elucidate the type of water present in 1DL as well as the mass % of TMA.

[0082] The TGA / DSC thermogram seen in FIG. 4A revealed that the mass loss due to water, occurring between 35 — 230 °C, accounted for -17.00% of the total mass of the sample. This mass lost due to water represents two types of water present in the sample. The first major mass loss occurred at -80 — 100 °C and is due to “free” or weakly adsorbed surface water. This accounted for -6.78% of the total mass lost. The second mass loss occurred just above 200 °C and is representative of the more strongly held water known as “bound” water, which accounted for -10.22% of the total mass lost. These temperatureranges for the loss of both types of water, correlates well with the literature. All the water is fully removed by -230 °C and then another thermal event is seen in the DSC plot that corresponds to a broad peak for the decomposition of TMA under nitrogen atmosphere, followed by complete vaporization of the decomposed byproducts past 340 °C.

[0083] For further validation that TMA is fully decomposed and removed from the sample after TGA, an FTIR was acquired for the solid left after the run. This FTIR can be seen in FIG. 4B, where the vertical red dotted lines at 950 and 1484 cm'1correlate to the skeletal and CH? asymmetric deformation modes, respectively, and are fundamental vibrational modes of TMA. These sharp FTIR bands completely disappear from the spectral profile after TGA was performed at temperatures greater than 500 °C. Therefore, the mass loss at -250 — 410 °C must be due to the decomposition of TMA and was calculated to be -11.31%. When the actual mass of IDL is corrected for the mass due to water in the sample, the TMA mass percentage is calculated to be -12.65%. This number fluctuated slightly for various samples, but an average value of 13.14 mass % (std. dev. = 0.49%) TMA was determined.

[0084] Comparing this value to the results from the qNMR study for the mass % of TMA in the colloids (15.57%), a discrepancy is apparent. This difference in results can be attributed to the slight inaccuracy of the qNMR method at determining the TMA concentration in a colloid. The qNMR method used was optimized for solutions and not for dilute colloids. This caused the TMA peak for the colloids to shift from 3.06 to 3. 14 ppm and broaden. Both these alterations in the NMR spectra, made accurately integrating the peaks difficult and introduced a lot of variability, as evidenced by the higher standard deviation amongst the colloid samples (0.32%) versus the supernatant and soak solutions (0.16 %) discussed in the next section. Additionally, this mass percent value is more accurately determined in the next section using the qNMR method to measure the TMA displaced into soaking solutions where the gels were immersed.

[0085] Removal of Organic Components in the Gel for formation of Inorganic Gel Composite

[0086] After the 1DL gels were formed by the addition of organic acid, TMA was subsequently removed by soaking the gels in ultrapure water for a series of days. The gels were allowed to soak in 10 ml of ultrapure water for 2 days and then swapped into a fresh vessel containing the same volume of water. This cycle was repeated two more times until thegel samples had been swapped into a total of 4 soak solutions for a total soak time of 8 days. It is worth noting, that the gels were soaked for more prolonged periods, as long as 3 months to observe if they would fall apart or revert back to the sol state, but the gel stayed intact with only some noticeable shrinking occurring. Afterwards, the gels that were soaked for 8 days were either tested for their compression strength or dried in the vacuum oven at 90 °C overnight to remove the majority of the water. The gel soak solutions and the gel supernatants (solution left behind after gel formation) were examined for the presence of TMA / acid, and TMA was quantified using the same qNMR method as previously mentioned. The dried gel samples were then tested for the presence of TMA / acid using FTIR and TGA / DSC analysis. From these studies, it was possible to validate that the full removal of all the organic species from the gel was accomplished and the TMA content was more accurately determined. These results were compared to the value previously obtained using TGA / DSC of the 1DL powder.

[0087] Three identical cylindrically shaped gel samples made from the reaction of 2 ml of 1DL colloid with acid were prepared. The gels were subsequently soaked in four different vessels of 10 ml ultrapure water to remove the TMA and acid components. Aliquots of each soak solution and supernatant were ran using caffeine again as the ISTD for qNMR evaluation. The mass % of TMA present in each solution was determined. After 2 soaks, all the TMA and acid seemed to have diffused out of the gel and into the soak solutions. This is evident by the fact that no peaks for the acid nor TMA were seen in the NMR spectra for any of the subsequent soak cycles. To eliminate the possibility of the concentrations being too low and below the limits of detection for the qNMR method, the third and fourth soak solutions were concentrated by evaporating off most of the water. Afterw ards, still no peaks were observed in the NMR spectra. To further confirm the full removal of TMA, an FTIR of the dried gel was obtained after only two soaks and can be seen in FIG. 5A. Notably, the two FTIR bands that correspond to the presence of TMA are completely gone for the twice soaked gels. Furthermore, all the additional IR bands for the acid present in the spectrum of the gel before TMA removal, are not present in the soaked gel spectrum. This can be seen as a further indication that both TMA and the acid were completely removed after only 2 soak cycles for a total of 4 days of soak time.

[0088] The results for the quantification of TMA in all samples are displayed in Table 3. 1 On average, -25% of the total TMA removed was present in the supernatant, which means that it is instantaneously displaced from the colloid upon gel formation. This largeremoval of TMA aligns well with the proposed gelation mechanism of 1DL, where intercalated TMA is pushed out of the interstitial spaces between filaments by hydronium ions, and some terminal oxygens on filaments are simultaneously protonated upon acid addition. This combination causes the flocculation of filaments to form a webbed network held together by physical crosslinks of hydrogen bonding and entangled filaments. The remaining amount of TMA originally present in the colloid is trapped in the gel upon formation due to drastic viscosity changes in the sol to gel transition. However, the TMA can easily diffuse out of the gel once soaked in ultrapure water for several days as evident by the large quantities present in soaking solutions 1 and 2. It was apparent that after 2 soak cycles all the TMA had been removed. As previously mentioned, no NMR peaks for TMA were observed in any of the subsequent soak solutions even when concentrated down.Table 1. Quantity' of TMA in several supernatants and soak solutions, as determined by qNMR analysis.Mass of TMA Present (mg)

[0089] The total amount of TMA removed from the gels in the aqueous solutions in Table 3. 1 relative to the amount determined by the qNMR method for the 1DL colloids was only about 84. 14% on average of the total amount. This discrepancy is due to the quantification of TMA present in the colloid not being optimized for the qNMR method and overestimating the concentration of TMA, for reasons previously mentioned. However, this discrepancy can be reconciled by using the total mass of TMA removed from 1DL in Table 1 as the actual amount of TMA present in the original colloid, instead of the TMA mass determined using the qNMR method for the colloid. The average TMA mass % is thenadjusted to 13.20%. Using TGA / DSC, the mass % of TMA in 1DL was determined to be about 13.14%. Using the total TMA quantified from the soak solutions and supernatants as the basis for the amount of TMA present in the original colloid, then corrects the mass percentage of TMA to a value which agrees with the TGA / DSC results.[0090| The TGA / DSC results in FIG. 5B also agreed with the full removal of TMA in the soaked gels. After removal of TMA, no major thermal events are seen in the DSC curve past 200 °C. However, it was seen that TMA decomposes endothermically at temperatures above 300 °C to give a steep decrease in the mass of the sample as evidenced in the TGA thermogram. The lack of a steep mass loss in the TGA plot nor any endothermic events in the DSC plot past 200 °C, indicates that no TMA is present in the washed gel. A total mass loss of -18.89% is seen in FIG. 5B. It is believed that this is due to hydronium ions strongly bound to the 1DL gel by the high degree of hydrogen bonding present at the surface and interlayers due to hydroxylation of 1DL. This causes a gradual mass loss of strongly adsorbed hydronium via dehydroxylation occurring over the entire temperature range used.

[0091] The Raman spectra were taken for the 1DL gel before and after TMA removal and compared to a 1DL powder sample. The results in FIG. 5C show that the Raman profiles of both gels look very similar to the 1DL powder sample. This infers that both the 1DL gel and the gel after TMA removal, retain the structure of one dimensional lepidocrocite. The phase is stable and does not interconvert to anatase. However, after heating the samples to temperatures of greater than 500 °C used in the TGA / DSC tests, the Raman spectra did show complete conversion to anatase (B. 11).

[0092] Mechanical Strength of the Gel Composite

[0093] The compression strength was tested for the gels made using various organic acids as the gelling inducer and is displayed in FIG. 6A. Specifically, five different organic acids were studied due to their various pKa values; namely, propionic acid, acetic acid, acrylic acid, formic acid, and trifluoroacetic acid. The compression strength was observed to increase with decreasing pKa value of the acid used, with the exception of acr lic acid. Acrylic acid, not being a common organic acid and instead a monomer, may have some unfavorable chemical reactivity that made it an outlier in the general trend observ ed. ANOVA analysis showed that the averages of all samples were significantly different from each other, evident by the P-value obtained well below 0.0005. Since the pH could not be directly measure for the gels, it was theoretically calculated based on the amounts of acidadded, K., values, and the total volume of the gels. Table 3.2 shows the pH values calculated. The same trend as seen with pKa was observed, where compression strength increased as a function of decreasing pH with the exception of acrylic acid. It is worth noting, that the pH of the gels actually would be higher than that theoretically calculated based on the aforementioned information. This is because the pH of the colloid was measured at a value above 10, which means that some acid would be neutralized upon addition and increase the pH of the final gel. The only purpose of calculating the theoretical pH values was to directly compare the strength of the gels based on hydronium concentration and not acid strength (pKa).Table 2. Compression strength of several IDL gels made using various organic acids as the gelling inducer but the same colloid concentration of 15.7 mg ml’1., . , ,, Average Strength Std DevAcid pH pKaz,'1(MPa) (Mpa)The compression strength was then measured for various concentrations of gels made using only acrylic acid as the gelling inducer. FIG. 6B shows that the strength of the gel was highly linearly dependent on the concentration of the colloid used to form the gel when evaluated in the range of 4.28 — 42.6 mg ml’1. This result was quite fascinating, as it implies that the gel compression strength can be easily controlled and tuned by simply vary ing the concentration of the colloid used to form the gel. For comparison, in most hydrogels, the strength of the gel does not usually increase linearly with increasing monomer concentration, which makes predicting the strength based on concentration alone difficult.

[0094] After the gels had been soaked to remove TMA, they were tested for compression strength to compare to the gels prior to soaking (FIG. 6C). It was believed that the gels would lose compression strength after soaking, instead, the opposite was observed.The gels increased in strength by as much as 50%. The strength of 3 gels were measured after soaking for 4 days in 2 soak solutions to remove all the TMA. The average strength for the samples after soaking was 0.128 MPa (std. dev. = 0.0053) versus 0.085 MPa (o = 0.0051) for samples prior to soaking. ANOVA analysis revealed a significant difference amongst the sample sets, indicating that the removal of TMA increases the strength of gels significantly. It is worth noting, that some shrinking in the gels occurred after complete removal of TMA, as much as 25% by volume. This is the opposite of what occurs in hydrogels that swell in water to many times their original volume. When the concentration was corrected for the volume loss due to mostly water, the average strength of the gel measured falls very close to what would be expected for a gel with the corresponding concentration according to the linear fit of FIG. 6B. Hence, the increased strength may be due indirectly to increasing the concentration of 1DL as the gel shrinks and not due completely to the removal of TMA.

[0095] The SEM images taken of the gels after compression (FIG. 7A-B), showed no sign of braided filaments. As can be seen, only flat surface topographies were observed. Originally, it was believed that this was due to mechanical phase conversion of the 1DL to anatase. However, after taking a Raman spectrum of the compressed sample (FIG. 7C), the major peaks corresponding to 1DL are still apparent and no sign of any anatase peaks can be seen. The flat surfaces observed in the SEM images could be due to interconversion of 1 DL titanate to 2DL titanate. This could provide an explanation for the topography observed and the Raman results. XRD results (FIG. 7D) also show that the gel after compression maintains an XRD pattern similar to that of 1DL, which further solidifies the idea that 1DL to anatase phase transition is not possible by compressing the gel, but a morphological change does occur, converting the dimensionality of 1DL from ID to 2D lepidocrocite.

[0096] The gelation of 1DL titanate was demonstrated, a mechanism was proposed, and the compression strength of the gels were determined using different acid inducers and at various concentrations. Strong linearity was observed for the 1DL gels compression strength as a function of increasing 1DL colloid concentration. This is a unique property for the gel that is rarely seen with hydrogels, where increasing monomer concentration does not cause strength to increase linearly. The dimensionality of the gel upon compression seemed to change to a 2D platelet morphology based on inspection of the SEM micrographs. However, the lepidocrocite titanate signature Raman and XRD peaks were maintained. Additionally, the gel shrunk when immersed in water over time by as much as 25% by volume. This maybe the cause of the strength of the gel increasing by as much as 50% when TMA was removed by soaking in water. It was also seen that the gel compression strength generally increased with increasing hydronium concentration. The amount of TMA removed was quantified using an optimized qNMR method that determined the mass % of TMA in 1DL to be 13.20%. Using TGA / DSC, the mass % of TMA was determined to be 13.14%, which agreed very well with the qNMR results. Using the qNMR method, the amount of TMA present in the supernatant and soak solutions was determined. Over 25% of the total TMA in the gel was instantly released upon gelation and left in the supernatant. The remaining amount was diffused out of the gels by soaking them in two containers of water for 2 days each, for a total soak time of 4 days. All the organic species were removed from the gels by these two simple soak cycles to produce a completely inorganic gel composite. The dried gel powder was further characterized using FTIR and TGA / DSC to show that TMA / acid was fully removed from the gel. The gelling process is believed to proceed via a system seen in other titanates, where upon acid addition to produce the protonic titanate, warping of the titanate structure usually occurs forming nanotubes. These other titanates differ from 1DL it terms of dimensionality, where other titanates usually composed of 2D sheets scroll to form the nanotubes. 1DL on the other hand, is truly 1 -dimensional, thus upon protonation using acid, it is believed that a similar warping of the 1DL filaments occurs. This would cause them to intertwine with each other, creating the braided filaments observed in the xerogels that resemble nano ropes.

[0097] Summary

[0098] The gelation of 1DL titanate was demonstrated, a mechanism was proposed, and the compression strength of the gels were determined using different acid inducers and at various concentrations.

[0099] All the organic species were removed from the gels by two simple soak cycles to produce a completely inorganic gel composite.

[0100] The phase of 1DL was retained upon gel formation and compression, with only the morphology converting possibly to 2D sheets.

[0101] The amount of TMA was quantified using an optimized qNMR method and TGA / DSC. the results agreed well, yielding 13.20 and 13. 14%. respectively, in an example, non-limiting embodiment.

[0102] Aspects

[0103] 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.

[0104] Aspect 1. A gel composition, comprising; a plurality of one-dimensional lepidocrocite (1DL) titanate filaments associated with one another so as to form a gel.

[0105] In some embodiments, the gel can include a polymer or other network. Thus, the disclosed gels can comprise a double-network material that includes 1DL titanate filaments as well as a second network, which second network can comprise a polymer or other network material. Such a polymer can have a stiffness less than, equal to, or greater than the associated 1DL titanate filaments. Such a polymer can be biocompatible or even biodegradable; this is not a requirement.

[0106] In this way, a user can select the second network material to arrive at a gel that has a desired set of mechanical properties. The disclosed gels can be double-network in nature in some embodiments; the disclosed gels can in some embodiments be characterized as including interpenetrating networks.

[0107] Aspect 2. The gel composition of Aspect 1, wherein the 1DL titanate filaments comprise a plurality of filament diameters. In some embodiments, the 1DL titanate filaments comprise a monodisperse population of diameters. In some embodiments, the 1DL titanate filaments comprise a polydisperse population of diameters.

[0108] Aspect 3. The gel composition of any one of Aspects 1-2, wherein the gel composition is essentially free of organic species. As described elsewhere herein, organic species can be removed by, for example, soaking, reduced pressure, heating, and other methods.

[0109] Aspect 4. The gel composition of any one of Aspects 1-3, further comprising an amount of water therein. Without being bound to any particular theory or embodiment, the gel can trap water therein. Water can be removed by, for example, heating, compression, reduced pressure, and other methods.

[0110] Aspect 5. The gel composition of any one of Aspects 1-4, wherein the 1DL titanate filaments are characterized as flocculated.

[0111] Aspect 6. The gel composition of Aspect 5, wherein the 1DL titanate filaments are characterized as flocculated into bundles. Without being bound to anyparticular theory or embodiment, such bundles can comprise 1DL filaments that are braided together. An example image of such filaments is provided in panel (d) of FIG. 3.

[0112] Aspect 7. The gel composition of Aspect 6, wherein a 1DL titanate filament has a diameter in the range of from about 20 to about 50 nm, optionally about 40 nm. A 1DL titanate filament can have a diameter of, for example, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, or 50 nm.

[0113] Aspect s. The gel composition of Aspect 6, wherein a bundle has a diameter in the range of from about 300 to about 500 nm. A bundle can have a diameter of, for example, 300 nm, 325 nm, 350 nm, 375 nm, 400 nm, 425 nm, 450 nm, 475 nm, or 500 nm. A gel can include bundles having different diameters.

[0114] Aspect 9. The gel composition of any one of Aspects 1-8, wherein the gel exhibits an average compression strength in the range of from about 0.07 to about 0. 150 MPa.

[0115] Aspect 10. The gel composition of any one of Aspects 1-9, wherein the gel composition comprises a plurality of 2DL titanate sheets.

[0116] Aspect 11. The gel composition of any one of Aspects 1-10, wherein the 1DL titanate filaments are present as a webbed network held together by physical crosslinks of hydrogen bonding and entangled filaments.

[0117] Aspect 12. A method, comprising: contacting an organic acid to a suspension of 1DL titanate filaments, the contacting being performed under conditions such that the 1DL titanate filaments become associated with one another so as to form a gel.

[0118] Aspect 13. The method of Aspect 12, wherein the organic acid has a pKa of greater than 0.

[0119] Aspect 14. The method of any one of Aspects 12-13, wherein the organic acid comprises any one or more of propionic acid, acetic acid, acrylic acid, formic acid, and trifluoroacetic acid.

[0120] Aspect 15. The method of any one of Aspects 12-14, further comprising removing organic species from the gel.

[0121] Aspect 16. The method of any one of Aspects 12-15, wherein the suspension of 1DL titanate filaments comprises water.

[0122] Aspect 17. The method of any one of Aspects 12-16. further comprising removing water from the gel.

[0123] Aspect 18. The method of any one of Aspects 12-17, wherein the 1DL titanate filaments become associated with one another via flocculation.

[0124] Aspect 19. The method of Aspect 18, wherein the flocculation gives rise to bundles of the 1DL titanate filaments.

[0125] Aspect 20. The method of any one of Aspects 12-19, further comprising compressing the gel so as to give rise to 2DL sheets of the 1DL titanate filaments.

Claims

What is Claimed:

1. A gel composition, comprising; a plurality' of one-dimensional lepidocrocite (1DL) titanate filaments associated with one another so as to form a gel.

2. The gel composition of claim 1, wherein the 1DL titanate filaments comprise a plurality' of filament diameters.

3. The gel composition of any one of claims 1-2. wherein the gel composition is essentially free of organic species.

4. The gel composition of any one of claims 1-2, further comprising an amount of water therein.

5. The gel composition of any one of claims 1-2, yvherein the 1DL titanate filaments are characterized as flocculated.

6. The gel composition of claim 5, wherein the 1DL titanate filaments are characterized as flocculated into bundles.

7. The gel composition of claim 6, wherein a 1DL filament has a diameter in the range of from about 20 to about 50 nm, optionally about 40 nm.

8. The gel composition of claim 6, wherein a bundle has a diameter in the range of from about 300 to about 500 nm.

9. The gel composition of any one of claims 1-2, yvherein the gel exhibits an average compression strength in the range of from about 0.07 to about 0.150 MPa.

10. The gel composition of any one of claims 1-2, wherein the gel composition comprises a plurality of 2DL titanate sheets.

11. The gel composition of any one of claims 1-2. wherein the 1DL titanate filaments are present as a webbed network held together by physical crosslinks of hydrogen bonding and entangled filaments.

12. A method, comprising: contacting an organic acid to a suspension of 1DL titanate filaments, the contacting being performed under conditions such that the 1DL titanate filaments become associated with one another so as to form a gel.

13. The method of claim 12, wherein the organic acid has a pKa of greater than 0.

14. The method of any one of claims 12-13, wherein the organic acid comprises any one or more of propionic acid, acetic acid, acrylic acid, formic acid, and trifluoroacetic acid.

15. The method of any one of claims 12-13, further comprising removing organic species from the gel.

16. The method of any one of claims 12-13, wherein the suspension of 1DL titanate filaments comprises water.

17. The method of any one of claims 12-13, further comprising removing water from the gel.

18. The method of any one of claims 12-13, wherein the 1DL titanate filaments become associated with one another via flocculation.

19. The method of claim 18, wherein the flocculation gives rise to bundles of the 1DL titanate filaments.

20. The method of any one of claims 12-13, further comprising compressing the gel so as to give rise to 2DL sheets of the 1DL titanate filaments.

Images