Patent Application
20230391631
Structurally defined materials impart varying stages of complexity and functionality to inorganic solids. The addition of porous structures, as in the case of zeolitic materials, provide the capabilities to perform adsorption processes1 and contribute favorable reaction cavities for catalytic chemical transformations.2 It is therefore of general interest to control the structure and size of the porous cavities, largely targeted by judicious choices of synthesis conditions and parameters. The present disclosure provides zeolites and methods of preparing them which address these needs.
The present disclosure provides in some embodiments, a zeolite having a micropore volume from about 0.001 to about 0.1 cm3/g, comprising Al, Si, O, H, Na, K and Ca; wherein the zeolite comprises:
((K+Na+Ca)/(Al)) (I);
In certain embodiments, the present disclosure provides a method of preparing a zeolite the method comprising:
(2x)/(y+z+(2x))=RC (II);
Synthesis of zeolitic materials is generally performed in basic media in the presence of metal precursors and an organic structure-directing agent (OSDA).3 Silicon and metal precursors dissociate to form amorphous particles4 that organize around structure-directing agents (SDA) during aging stages5,6 prior to crystallization of the desired zeolite topology at elevated temperatures (≥373 K).7 The crystallization mechanism by which SDA-free synthesis takes place, however, is a result of complex phenomena. Metal cations (e.g., Na+, K+, Ca2+) are typically used as a source of counterbalancing charge for the incorporation of Al heteroatoms into the framework during crystallization processes;8 yet they also occupy local cavities and serve as SDAs.9
Phillipsite and tobermorite exemplify synthesis protocols that lead to crystallization of porous, inorganic materials in the absence of an OSDA. Phillipsite precipitates in the presence of sodium,10 potassium,10,11 and/or calcium;12 yet naturally-occurring phillipsite contains predominantly only sodium and potassium.10 Tobermorite, in contrast, is a porous solid that is synthesized at similar synthesis gel molar compositions (e.g., 0.38 Na2O: 0.19 K2O: 0.05 Al2O3: 1 SiO2: 17.57 H2O for phillipsite13 and 0.83 Ca: 1 Si: 18.2 H2O for tobermorite14,15) and temperatures (e.g., 373-393 K) but in growth solutions containing only calcium.
The present disclosure relates to synthesis protocols that advantageously produce zeolites have both phillipsite and tobermorite phases. Zeolite samples were prepared with varying cationic content (i.e., (2×Ca2+)/(K++Na++(2×Ca2+))) in the absence of an organic SDA. Our results indicate that in the absence of calcium, phillipsite is the predominant phase crystallized at 373 and 393 K, whereas tobermorite is the predominant phase crystallized in the absence of sodium and potassium. A monotonic increase in the calcium content reflects a systematic increase in the fraction of tobermorite in the recovered solids, and concomitant increase in the total cationic content occluded in the crystalline solids. The methods and compositions of the disclosure indicate that potassium has a predominant role as an Al counterbalance cation, while sodium and calcium have a predominant role as SDA. The disclosure also highlights the versatility of metal cations as charge balancing agents and inorganic SDAs during zeolite crystallization processes.
Samples are denoted as PHI-TOB-X-Y, where X represents the temperature of the hydrothermal treatment (e.g., 373 K or 393 K) and Y represents the charge ratio, defined as the fraction of calcium in the total cationic content of the synthesis gels ((2×Ca2+)/(K++Na++(2×Ca2+)), see experimental section). Hydrothermal treatments of synthesis gels associated with phillipsite crystallization were performed at 373 and 393 K in the sole presence of sodium and potassium (PHI-TOB-373/393-0), and the structure of the recovered solids was probed using X-ray diffraction (XRD) patterns and nitrogen adsorption isotherms (77 K).
Phillipsite, as a natural and synthetic zeolite, crystallizes in the presence of sodium, potassium, and/or calcium.10-12 To further probe the role of the metal cations in the crystallization processes that lead to phillipsite formation, hydrothermal treatments were performed by replacing the total cationic contributions of sodium and potassium in growth solutions with calcium. Performing hydrothermal syntheses at the same total cationic charge (Na2O+K2O=10.45) but replacing the total metal cations with calcium (CaO=5.23) resulted in XRD patterns (
Metal cations in synthesis gels have varied roles during hydrothermal processes in the absence of OSDAs. An illustration of the roles of metal cations in the microporous cavities of phillipsite after heat treatments (373 K, 168 h) is enclosed in
In synthesis gels of PHI-TOB-373/393-0.0, sodium and potassium account for aluminum counterbalance and as SDA, and we probed their total contribution through elemental analysis. Table 1 contains the elemental composition, collected via induced coupled plasma optical emission spectroscopy (ICP-OES), of the solids recovered for all the syntheses performed in this study. The potassium content is higher than the sodium content in samples prepared at varied temperatures (373 and 393 K), accounting for >50% of the total cations retained with respect to the aluminum content. Although sodium is in excess (2:1 ratio) in synthesis gels when compared to potassium, the sodium content accounts for <40% of the total cations in the solids relative to the retained aluminum.
The total cationic content, defined as the summation of all the metal cations normalized to the aluminum content, is ≤1 for samples prepared in the absence of calcium in growth solutions (PHI-TOB-373/393-0.0, Table 1). The implication of these results, collected after water washing steps intended to remove unreacted species, is that the remaining metal cations are participating as counterbalance cations for aluminum in the framework (assuming that all the aluminum is in a tetrahedral coordination) and those participating in template roles have been selectively removed during washing steps. Consequently, the elemental compositions of PHI-TOB-373/393-0.0, together with the excess of sodium in growth solutions, suggest that the primary role of sodium (Na/Al<40%, Table 1) during hydrothermal treatments is as a SDA and gets removed during washing steps. By extension, our results indicate that potassium (K/Al>50%) has a predominant role as an aluminum counterbalance cation during crystallization of phillipsite zeolites at 373 and 393 K. Zeolites prepared in the sole presence of calcium (PHI-TOB-373-1.0) also contain metal cationic contents that account for less than the total aluminum content (Cat./Al≤1, Table 1), suggesting that the retention of metal cations during tobermorite crystallization procedures are predominantly associated with aluminum heteroatoms. Taken together, these results exemplify the structure-directing role of metal cations in crystallization processes in the absence of SDAs.
Zeolite polymorphism driven by the judicious choice of inorganic SDAs highlights the adaptable capabilities of metal cations in zeolite crystallization protocols.29 Hydrothermal treatments of growth solutions replacing sodium with potassium, for instance, leads to the formation of NU-10 (TON) rather than MFI (523 K, 122 h),30 synthesis gels containing potassium instead of sodium crystallize EDI rather than LTA (468 K, 96 h),31 and synthesis gels containing varying mixtures of sodium and potassium crystallize LTA, SOD, and/or FAU (429 K, 168 h),32 amongst others.29 Here, replacing sodium and potassium with calcium in synthesis gel compositions that typically crystallize phillipsite,13 results in the precipitation of tobermorite, a silicate hydrate of different identity and pore structure. Although the elemental composition of tobermorite prepared at 373 K (PHI-TOB-373-1.0) was expected to occlude more calcium content (i.e., Ca/Al>1) and at higher densities than those measured (Ca/Al<1), the structure of the characterized solid indicates the distinctive features (
The total cationic content is defined as the molar composition in the synthesis gel composed by all metal cations. Systematic substitution of the cationic content with calcium, however, requires accounting for differences between monovalent cations (Na+ and K+) and divalent cations (Ca2+). The role of calcium as a counterbalancing cation for aluminum incorporation is limited by the ability of a framework to accommodate two aluminum heteroatoms in close proximity (Al—O(—Si—O)x—Al, x=1, 2) in order for aluminum incorporation to take place. The calcium content in the synthesis gel was defined by replacing the total molar contributions of sodium and potassium by half to retain the same total cationic charge in the synthesis gel. We define the charge ratio in the synthesis gel as the fraction of the total cationic content composed by calcium (e.g., (2×Ca2+)/(K++Na++(2×Ca2+))).
The transition from phillipsite to tobermorite phases was probed by performing hydrothermal syntheses at varied charge ratio in synthesis growth solutions. XRD patterns of samples prepared at varied charge ratio reflect diffraction peaks centered at 29.4 and 49.9° that in some embodiments, increase concomitantly with increasing calcium content (
Zeolite crystallization mechanisms and polymorphism are generally described by driving forces following the Ostwald rule of stages34,35 or the transformation of crystalline phases guided by their molar density.5,29,36 Crystallization following the Ostwald rule of stages take place after dissolution of synthesis precursors to form amorphous, metastable phases that reorganize over time in stages that form more thermodynamically stable phases (e.g., from structures of less negative to more negative enthalpy of formation).34,35 In other instances, zeolite transformations occur by the formation of metastable phases that transform over time to form a phase with higher framework density (i.e., a framework with a lower molar volume).36 In the phillipsite/tobermorite system studied here, we speculate that silicon and aluminum complexes, available in the synthesis gels after precursor dissolution during aging protocols (ambient, 24 h), nucleate metastable phases around inorganic cations. At the same time, the stabilized structure is dictated by the kinetic diameter or other physicochemical properties of the metal cations in solution (
Distinguishing the ability of various metal cations to arrange within microporous and mesoporous voids allows for the preparation of porous aluminosilicates with varying pore structure. Sodium and potassium contribute to the selective crystallization of phillipsite zeolites in the absence of calcium (at 373 and 393 K). The total cationic content (normalized by Al) on PHI-TOB-373/393-0 samples suggest that the micropores of phillipsite accommodate cations exclusively to counterbalance aluminum heteroatoms. The higher total cationic content (per Al) on samples of varied charge ratio, together with detection of tobermorite phases, however, indicates that tobermorite phases retain metal cations associated with aluminum counterbalance and those that participate of structure-directing processes. The consistently higher total cationic content (per Al) in all the samples prepared at 393 K compared to those synthesized at 373 K, along with XRD features associated with tobermorite becoming prominent at low charge ratios (CR>0.3), corroborate that tobermorite porous structures accommodate metal cations that participate in aluminum counterbalance and template roles. Taken together, this study summarizes guidelines for the preparation of zeolitic phases in the absence of OSDAs and highlights the ubiquitous roles of metal cations during crystallization processes of zeolitic materials.
Synthetic protocols involving zeolite crystallization take place around OSDAs that dictate the resulting topological properties of the precipitates. In the absence of OSDAs, however, inorganic SDAs can selectively nucleate and crystallize aluminosilicates of various framework topologies depending on their identity and synthesis conditions.29
The present disclosure provides methods of controlling the amounts sodium, potassium, and calcium in the crystallization of phillipsite zeolites and/or tobermorite silicate hydrates (at 373 K and 393 K) at the same total molar cationic content. In some embodiments, phillipsite zeolites are selectively crystallized (at 373 K and 393 K) from starting growth solutions that contain solely sodium and potassium, and retain metal cations at molar ratios that account only for roles associated with of aluminum counterbalance during crystallization processes ((Na+K)/Al≤1). In other embodiments, tobermorite samples are selectively crystallized after high temperature treatments (at 373 K and 393 K) of growth solutions containing solely calcium. Aluminosilicates containing tobermorite crystals retained metal cations at molar ratios ((K+Na+Ca)/Al≥1) indicating their ubiquitous roles as both aluminum counterbalance and SDA during crystallization protocols. Syntheses performed (373 K and 393 K) at mixed compositions of metal cations indicate that, in certain embodiments, the partial substitution of sodium and potassium with calcium on synthesis gels (identical total molar compositions) results in the crystallization of mixed phillipsite and tobermorite phases. Without wishing to be bound by theory, we surmise that these results are the consequence of the aluminosilicate complexes stabilized around metal cations during aging stages, leading to nucleation and crystallization of tobermorite when these complexes are encapsulating calcium cations and phillipsite when the complexes are isolating sodium and/or potassium. Taken together, the methods and compositions disclosed herein reveal the roles of metal cations during crystallization processes and highlight the ability of their identity to dictate the topological properties, tailored for specific applications, of the resulting precipitate
aFraction of calcium compared to the total metal cations in the synthesis gel (i.e., (2 × Ca2+)/(K+ + Na+ + (2 × Ca2+))).
bMetal cation content normalized by the aluminum content ((K + Na + Ca)/(Al)).
cSynthesis performed at a lower water content to lower the silicon concentration to 0.2M
dSynthesis performed at reported molar ratios13 with a silicon concentration of 3M
aFraction of calcium with respect to the total metal cations in the synthesis gel (i.e., (2 × Ca2+)/(K+ + Na+ + (2 × Ca2+))).
bSynthesis performed at varied water content to lower the total silicon concentration to 0.2M.
bSynthesis performed at a silicon concentration of 3M.
In certain embodiments, the present disclosure provides a zeolite having a micropore volume from about 0.001 to about 0.1 cm3/g, comprising Al, Si, O, H, Na, K and Ca;
wherein the zeolite comprises:
((K+Na+Ca)/(Al)) (I);
The micropore volume, in some embodiments, is from about 0.002 to about 0.08 cm3/g, or about 0.001 to about 0.003 cm3/g. In more particular embodiments, the micropore volume is about 0.02 to about 0.03 cm3/g, about 0.03 to 0.04 cm3/g, about 0.05 to about 0.06 cm3/g, about to about 0.07 cm3/g, or about 0.07 to about 0.08 cm3/g.
In certain embodiments, the total cation content:aluminum ratio Cat:Al is from about 0.5 to about 30. In more particular embodiments, Cat:Al is about 0.5 to about 0.71, about 1 to about 2, about 2 to about 5, about 5 to about 8, about 8 to about 12, about 12 to about 15, about 15 to about 20, or about 20 to about 30.
In some embodiments, Na:Al is from about 0.1 to about 15, such as about 0.1 to about 1, about 1 to about 5, about 5 to about 10, about 5 to about 15, or about 10 to about 15.
In some embodiments, K:Al is from about 0.05 to about 10, for example about 0.05 to about 1, about 1 to about 2, about 2 to about 5, about 5 to about 7, about 7 to about 10, about to about 5.
In some embodiments, Ca:Al is about 0.02 to about 0.5, for example about 0.5 to about 1, about 1 to about 2, about 2 to about 3, about 3 to about 4, about 4 to about 5.
In some embodiments, the zeolite is characterized by X-Ray powder diffraction peaks at 29.4°±0.2 and 49.9°±0.2. In particular embodiments, the X-Ray powder diffraction peaks 29.4°±0.2 and 49.9°±0.2 increase in strength as Ca:Al increases. In more particular embodiments, the zeolite has an X-Ray powder diffraction pattern as shown in
Other embodiments relate to a method of preparing a zeolite, the method comprising:
(2x)/(y+z+(2x))=RC (II);
In some embodiments, aging the synthesis gel comprises a treatment selected from mechanical agitation, stirring, shaking, swirling, sonication, and any combination thereof. In certain embodiments, aging the synthesis gel does not comprise heating the synthesis gel. In wherein aging the synthesis gel occurs at about 20-30° C.
In some embodiments, heating the synthesis gel comprises heating the synthesis gel to a reaction temperature of from about 350 K to about 410 K, more particularly, from about 350 K to about 400 K and even more particularly from about 370 K to about 395 K, such as about 373 K or about 393 K.
In some embodiments, collecting the zeolite from the product mixture comprises washing the zeolite with water, isolating the zeolite by centrifugation, and drying the zeolite.
In some embodiments, Rc is from about 0.01 to about 0.99, such as about 0.1 to about about 0.2 to about 0.3, about 0.3 to about 0.4, about 0.4 to about 0.5, about 0.5 to about 0.6, about 0.6 to about 0.7, about 0.7 to about 0.8, or about 0.8 to about 0.9.
In some embodiments, a is from about 0.1 to about 3, such as about 0.1 to about 0.2, about 0.2 to about 0.4, about 0.4 to about 0.6, about 0.6 to about 0.8, about 0.8 to about 1, or about 1 to about 1.5.
In some embodiments, b is from about 0.1 to about 1, for example about 0.1 to about 0.2, about 0.2 to about 0.3, about 0.3 to about 0.5, about 0.5 to about 0.6, or about 0.1 to about 2.
In some embodiments, c is from about 0.1 to about 0.2, about 0.2 to about 0.3, about 0.3 to about 0.4, about 0.4 to about 0.5, about 0.5 to about 0.6, about 0.6 to about 0.7, about 0.7 to about 0.8, about 0.8 to about 0.9, or about 0.9 to about 0.1.
In some embodiments, d is from about 0.01 to about 0.4, such as about 0.01 to about about 0.05 to about 0.1, or d is from about 0.1 to about 0.3.
In some embodiments, e is from about 0.5 to about 1.5, such as about 1.
In some embodiments, f is from about 10 to about 40, such as about 10 to about 30, about to about 15, or about 15 to about 20.
Unless otherwise defined herein, scientific and technical terms used in this application shall have the meanings that are commonly understood by those of ordinary skill in the art. Generally, nomenclature used in connection with, and techniques of, chemistry described herein, are those well known and commonly used in the art.
The methods and techniques of the present disclosure are generally performed, unless otherwise indicated, according to conventional methods well known in the art and as described in various general and more specific references that are cited and discussed throughout this specification.
Chemistry terms used herein, unless otherwise defined herein, are used according to conventional usage in the art, as exemplified by “The McGraw-Hill Dictionary of Chemical Terms”, Parker S., Ed., McGraw-Hill, San Francisco, C.A. (1985).
The term “aging” refers to a process of allowing or driving a mixture to reach or approach a desired product or stage. A number of approaches may be used to age a mixture. It may be heated or cooled, treated with mechanical agitation (such as stirring, swirling, shaking, or vibrations), sonicated, or simply allowed to rest for a period of time — or some combination of these treatments, whether applied together or in series, or in any other combination.
All of the above, and any other publications, patents and published patent applications referred to in this application are specifically incorporated by reference herein. In case of conflict, the present specification, including its specific definitions, will control.
The invention now being generally described, it will be more readily understood by reference to the following examples which are included merely for purposes of illustration of certain aspects and embodiments of the present invention, and are not intended to limit the invention.
Phillipsite zeolites (PHI-TOB-373/393-0) were synthesized according to the following procedure.13 In a typical synthesis, potassium hydroxide (KOH, Avantor, 98%) was added to deionized water (18.2 MΩ) and stirred until completely dissolved in a Nalgene wide-mouth HDPE bottle (250 cm3, ThermoFisher Scientific). Then, sodium aluminate was added and the resulting mixture was stirred until completely dissolved. Lastly, sodium silicate was added to the Nalgene container. The resulting gel solution was covered and stirred for 24 h at ambient conditions. The final gel composition was 6.95 Na2O: 3.5 K2O: 1 Al2O3: 18.5 SiO2: 325 H2O. The gel was placed into a Teflon-lined stainless steel autoclave and heated to 373 or 393 K for 7 days under static conditions. The recovered solids were washed thoroughly with water, isolated by centrifugation, and dried overnight at 363 K.
The charge ratio, or the amount of calcium in the synthesis gel, was modified by the following procedure. In a typical synthesis, potassium hydroxide (KOH, 86.6%) was added to deionized water (18.2 MΩ) and stirred until completely dissolved in a Nalgene bottle (250 cm3). Then, sodium hydroxide (NaOH, 98.7%) was added and the resulting mixture was stirred until completely dissolved. Calcium hydroxide (Ca(OH)2, 100%) and aluminum hydroxide (Al(OH)3, 99%) were added individually and the mixture was stirred until complete dissolution. Lastly, Ludox SM30 (30 wt. % in water) was added to the Nalgene container. The resulting gel solution was covered and stirred for 24 h at ambient conditions. The final gel composition was x Na2O: y K2O: z CaO: 1 Al2O3: 18.5 SiO2: 325 H2O, where x, y, and z were modified to attain a given charge ratio (e.g., 0.25-0.80). More details and the specific gel compositions for all the samples in this study are compiled in Table 2. The gel was placed into a Teflon-lined stainless steel autoclave and heated to 373 or 393 K for 7 days under static conditions. The recovered solids were washed thoroughly with water, isolated by centrifugation, and dried overnight at 363 K.
Tobermorite silicate hydrates (PHI-TOB-373/393-1) were synthesized according to the following procedure.14-19 In a typical synthesis, calcium hydroxide (Ca(OH)2, 100%, 10 μm particle size) was added to deionized water (18.2 MΩ) and stirred until completely dissolved in a Nalgene bottle. Then, Ludox SM30 was added and the resulting mixture was stirred until completely dissolved. At 373 K (PHI-TOB-373-1), aluminum hydroxide (Strem Chemicals) was added and the resulting solution was stirred until complete dissolution (0.11 Al2O3: 0.90 CaO: 1 SiO2: 17.59 H2O). The resulting gel solution was covered and stirred for 24 h at ambient conditions. The final gel composition was 0.83 CaO: 1 SiO2: 18.2 H2O. The gel was placed into a Teflon-lined stainless steel autoclave and heated to 373 or 393 K for 7 days under static conditions. The recovered solids were washed thoroughly with water, isolated by centrifugation, and dried overnight at 363 K.
For simplicity, samples are referred to as PHI-TOB-X-Y, where X represents the temperature at which the hydrothermal treatment was performed (e.g., 373 K or 393 K) and Y represents the charge ratio (fraction of calcium in the total cationic content).
Powder X-ray diffraction (XRD) patterns were collected in the range 5-70° of 2θ (scan rate of 0.0765° s−1 and a step size of 0.02°) using a PANalytical X'PertPro X-ray diffractometer with a Cu Kα x-ray source (α=1.54 Å) and an X'Celerator 2 detector.
Vapor-phase N2 (77 K) adsorption isotherms were collected with a Micromeritics TriStar II 3020 instrument. Typically, ˜.0.20 g of zeolite sample, pelleted and sieved to retain particles with size between 180-250 μm, were degassed by heating under vacuum (<0.1 Torr) to 383 K for 24 h prior to adsorption measurements. The micropore volume was determined from semi-log derivative analysis of the isotherm (∂(Vads/g)/∂(log(P/P0) vs. log(P/P0)), where the first maximum represents the micropore filling transition and the subsequent minimum represents the end of micropore filling.
The elemental composition of the recovered solids was measured using an inductively-coupled-plasma optical emission spectrometer (ICP-OES, Varian Vista-MPX). Samples (˜0.03 g) were dissolved overnight in 2 g of HF (48 wt. %, Alfa Aesar) and diluted with ˜50 g of deionized water. In a separate 15 cm3 centrifuge tube, ˜10 g of the resulting solution and 0.1 g of nitric acid were mixed prior to measurements. The Si/Al ratios of PHI-TOB-373/393-0 were calculated using the unit cell formula for the PHI framework topology.
Transmission electron microscope (TEM) images were collected after samples (<20 mg) were dispersed in ethanol for 240 s in an ultrasonic bath. Approximately 4 drops of the dispersion were deposited in a 200 mesh Cu grid with a C film. TEM bright field images were taken with a JEOL JEM-2100F TEM/STEM operated at 200 keV, with spot size 1 and magnifications between 12 and 20 kx.
N2 adsorption isotherms (77 K) are compiled in
Transmission electron microscope (TEM) images were taken on PHI-TOB-373-0 (
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All publications and patents mentioned herein are hereby incorporated by reference in their entirety as if each individual publication or patent was specifically and individually indicated to be incorporated by reference. In case of conflict, the present application, including any definitions herein, will control.
While specific embodiments of the subject invention have been discussed, the above specification is illustrative and not restrictive. Many variations of the invention will become apparent to those skilled in the art upon review of this specification and the claims below. The full scope of the invention should be determined by reference to the claims, along with their full scope of equivalents, and the specification, along with such variations.
This application claims the benefit of priority to U.S. Provisional Patent Application No. 63/344,789, filed May 23, 2022, the contents of which are hereby incorporated by reference in their entirety.
This invention was made with government support under Grant Number DE-AR0001147, awarded by the Department of Energy. The government has certain rights in the invention.
| Number | Date | Country | |
|---|---|---|---|
| 63344789 | May 2022 | US |
