The authors thank undergraduate students Lutao Xie, for physical characterization of the aerogel materials, and Aude Bechu, for testing the draft procedure. We are grateful to the Union College Engineering Laboratory for machining the stainless steel mold. The Union College Aerogel Laboratory has been funded by grants from the National Science Foundation (NSF MRI CTS-0216153, NSF RUI CHE-0514527, NSF MRI CMMI-0722842, NSF RUI CHE-0847901, NSF RUI DMR-1206631, and NSF MRI CBET-1228851). This material is based upon work supported by the NSF under Grant No. CHE-0847901.

Safety Considerations: Safety glasses or goggles should be worn at all times during the preparative work with solutions and the hydraulic hot press. Laboratory gloves should be worn when preparing the chemical reagent solution and when pouring the solution into the mold in the hot press. TMOS, methanol and concentrated ammonia, and solutions containing these reagents, must be handled within a fume hood. The supercritical extraction process releases hot methanol, so it is necessary both to vent the hydraulic hot press, and to ensure that there are no ignition sources within the vent path of the hot press. In addition, we recommend installation of a safety shield around the hot press. In the event of a gasket failure, the shield will help contain the resulting gasket pieces and thereby protect anyone working near the hot press.
1. Prepare Reagents and Other Supplies
<ol>
	<li>Gather the reagents needed for the recipe: tetramethylorthosilicate, methanol, deionized water, and ammonia.</li>
	<li>Make 100.0 ml of a 1.5&#160;M ammonia solution. To do so, dilute 10.1 ml of 14.8 M concentrated ammonia to 100 ml with deionized water.</li>
	<li>Acquire a square stainless steel mold, 12.7 cm x 12.7 cm x 1.9 cm high, with 9 circular wells of 2.2 cm diameter (see Figure 3). Wipe the mold with a clean, damp rag to remove any surface oil or dust. Spray inside of each circular well with high-temperature mold release spray to ease in removal of aerogels from the mold after processing.</li>
	<li>Prepare three sets of sealing gaskets from 1/16 in&#160;(1.6 mm) thick graphite sheet and 0.0005 in&#160;(0.012 mm) thick stainless steel foil. Cut three pieces of each material sufficient to cover the mold completely (&#62;12.7 cm x &#62;12.7cm).</li>
</ol>
2. Prepare Instruments
<ol>
	<li>Program the hot press sealing and extraction programs. First set up a sealing program that will be used to seal the bottom of the open mold. See Table 1 for the necessary program values. Next set up the extraction program with the correct parameters for the silica aerogels using the mold described above. See Table 2 for these parameters.</li>
	<li>Prepare glassware. To avoid contamination, four glass beakers will be needed, one 250&#160;ml beaker labeled &#39;precursor solution,&#39; one 100&#160;ml beaker labeled &#39;methanol,&#39; one 20&#160;ml beaker labeled &#39;DI water,&#39; and one 10&#160;ml beaker labeled &#39;1.5&#160;M ammonia.&#39; Make sure all beakers are clean and dry.</li>
	<li>Prepare pipettes. Digital pipettes should be used for ease. A 10&#160;ml digital pipette and a 1,000&#160;&#956;l&#160;pipette will be used. Make sure multiple pipette tips are available.</li>
	<li>Prepare sonicator by adding water to the fill line.</li>
</ol>
3. Seal Mold Bottom
<ol>
	<li>Place mold and gasket material in hot press. First center a graphite sheet on the lower platen, add a sheet of stainless steel foil and place the mold on top of the stainless steel foil. Add another set of gasket material (stainless steel then graphite) on top of the mold. (Note: used gasket material can be used on the top in this step, but new gasket material must be used on the bottom.)</li>
	<li>Start the hot press sealing program, using the parameters shown in Table 1. This program seals the bottom of the mold to prevent the liquid precursor chemicals from leaking when the mold is filled with precursor solution.</li>
</ol>
4. Make Precursor Solution
The recipe for TMOS-based silica aerogels is shown in Table 3. All solution preparation work is performed in a fume hood.
<ol>
	<li>First pipette aliquots of TMOS totaling 17.0 ml from the reagent bottle into the 250&#160;ml&#160;glass beaker labeled &#39;precursor solution&#39;.</li>
	<li>Pour some methanol into the 100&#160;ml glass beaker and then pipette aliquots of methanol totaling 55.0 ml into the 250&#160;ml glass beaker labeled &#39;precursor solution.&#39;</li>
	<li>Pour some deionized water into the 20&#160;ml beaker labeled &#39;DI water&#39; and from that beaker pipette 7.2 ml of water into the 250&#160;ml beaker.</li>
	<li>Lastly, pour some 1.5&#160;M NH3 into the 10&#160;ml beaker and from that beaker pipette 270 &#181;l&#160;of the solution into the 250&#160;ml beaker.</li>
	<li>Seal the beaker with plastic paraffin film.</li>
	<li>Mix reagents to ensure that hydrolysis occurs by sonicating the precursor solution for at least 5 min. Prior to sonication, two liquid layers are sometimes visible in the precursor mixture. Following 5 min of sonication, the solution should appear to be monophasic. If it does not, sonicate the mixture for an additional 5 min.</li>
</ol>
5. Pour Precursor Solution into the Mold in the Hot Press
<ol>
	<li>At the end of the mold sealing program the hot press platens will open. Remove the top-side gasket material and set aside. Leave the mold as is in the hot press so that the bottom side of the mold remains sealed.</li>
	<li>Fill each well of the mold completely with the precursor solution. (Note: there will be about 10 ml of aerogel precursor solution left over after filling the mold. This can be discarded or processed under ambient conditions to make xerogels.)</li>
	<li>Put fresh gasket material on the top of the mold: the stainless steel foil first and then the graphite on top.</li>
	<li>Run the hot press extraction program (shown in Table 2). This program seals the mold, heats the contents to a supercritical state, performs the supercritical extraction and then cools the mold.</li>
</ol>
6. Remove the Aerogels from the Mold
<ol>
	<li>When the extraction process is complete, remove the mold and gasket material from the hot press.</li>
	<li>Remove the top gasket material from the mold. Set this aside.</li>
	<li>Gently loosen the mold from the bottom gasket material.</li>
	<li>Carefully remove each aerogel from the mold, one at a time, by firmly pushing them through from one side with a gloved finger.</li>
	<li>When the aerogels are removed from the mold, the process is complete.</li>
</ol>

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The authors declare that they have no competing financial interests.

The RSCE method produces consistent batches of monolithic silica aerogels using an automated and simple process. The method as presented here requires an eight-hour processing step. It is possible to speed up the heating and cooling steps to make monolithic aerogels in as little as 3 hr22; however, when an 8 hr procedure is employed, more consistent batches of aerogel monoliths result. Small variations in the process parameters do not affect the physical properties of the resulting aerogels, indicating that th...

Silica aerogel materials have low density, high surface area, and low thermal and electrical conductivity combined with a nanoporous structure with excellent optical properties. The combination of these properties in one material makes aerogels attractive in a large number of applications1. In a recent review article, Gurav et al. describe in detail the current and potential applications of silica aerogel materials, both in scientific research and in development of industrial products2. For example, silica aerogels have been used as absorbents, as sensors, in low-dielectric materials, as storage media for fuels, and for a wide array of thermal insulating applications2.
Aerogels are typically fabricated using a two-step process. The first step involves mixing appropriate chemical precursors, which then undergo condensation and hydrolysis reactions to form a wet gel. To prepare silica gels, the hydrolysis reactions occur between water and a silica-containing precursor, in this case tetramethylorthosilicate (TMOS, Si(OCH3)4), in the presence of acid or base catalyst. 
Si(OCH3)4 + H2O <img alt="arrow" fo:content-width=".2in" src="/files/ftp_upload/51421/arrow.jpg" width="20" /> Si(OCH3)4-n(OH)n + n CH3OH
TMOS is insoluble in water. In order to facilitate hydrolysis, it is necessary to include another solvent, in this case methanol (MeOH, CH3OH), and to stir or sonicate the mixture. Base-catalyzed polycondensation reactions then occur between the hydrolyzed silica species:
R3SiOH + HOSiR3 <img alt="arrow" fo:content-width=".2in" src="/files/ftp_upload/51421/arrow.jpg" width="20" /> R3Si-O-SiR3 + H2O
R3SiOH + CH3OSiR3 <img alt="arrow" fo:content-width=".2in" src="/files/ftp_upload/51421/arrow.jpg" width="20" /> R3Si-O-SiR3 + CH3OH
The polycondensation reactions result in the formation of a wet gel, comprised of a porous SiO2 solid matrix, in which the pores are filled with the solvent byproducts of the reaction, in this case methanol and water. The second step involves drying the wet gel to form an aerogel: removing the solvent from the pores without altering the solid matrix. The drying process is critically important to the formation of the aerogel. If not carried out correctly the fragile nanostructure collapses and a xerogel is formed as illustrated schematically in Figure 1.
There are three basic methods for drying sol-gel materials to produce aerogels: supercritical extraction, freeze drying and ambient pressure drying. The supercritical extraction methods avoid crossing the liquid-vapor phase line so that surface tension effects do not cause the nanostructure of the gel to collapse. Supercritical extraction methods can be performed at high temperature (250-300 &#176;C) and pressure with direct extraction of the alcohol solvent byproduct of the condensation and hydrolysis reactions3-7. Alternatively, one can perform a set of exchanges and replace the alcohol solvent with liquid carbon dioxide, which has a low supercritical temperature (~31 &#176;C). The extraction can then be performed at relatively low temperature8,9, albeit at high pressure. Freeze drying methods10,11 first freeze the wet gel at low temperature and then allow the solvent to sublimate directly to a vapor form, again avoiding crossing the liquid-vapor phase line. The ambient pressure method uses surfactants to reduce the surface tension effects or polymers to strengthen the nanostructure, followed by drying of the wet gel at ambient pressure12-16.
The Union College Rapid Supercritical Extraction (RSCE) process is a one-step (precursor to aerogel) method17-19. The method employs high-temperature supercritical extraction, which allows fabrication of monolithic aerogels in hours, rather than the days to weeks required by other methods. The method utilizes a confined metal mold and a programmable hydraulic hot press. Chemical precursors are mixed and poured directly into the mold, which is placed between the platens of the hydraulic hot press. The hot press is programmed to close and apply a restraining force to seal the mold. The hot press then heats the mold at a specified rate to a temperature, Thigh, above the critical temperature of the solvent (see Figure 2 for a plot of the process). During the heatup period the chemicals react to form a gel and the gel strengthens and ages. As the mold is heated the pressure also rises, eventually reaching a supercritical pressure. Upon reaching Thigh, the hot press dwells at a fixed state while the system equilibrates. Next the hot press force is decreased and the supercritical fluid escapes, leaving behind a hot aerogel. The press then cools the mold and its contents to room temperature. At the end of the process (which can take 3-8 hr) the press opens and monolithic aerogels are removed from the mold.
This RSCE method offers significant advantages over other aerogel fabrication methods. It is fast (&#60;8 hr total) and not very labor intensive, typically requiring only 15-20 min preparation time followed by 3-8 hr processing time. It does not require solvent exchanges, which means that relatively little solvent waste is generated during the process.
In the section that follows, we describe a protocol for preparing a set of cylindrical silica aerogel monoliths via the Union RSCE method from a precursor mixture comprised of TMOS, methanol, and water with aqueous ammonia employed as the catalyst for the hydrolysis and polycondensation reactions (with a TMOS:MeOH:H2O:NH3 molar ratio of 1.0:12:3.6:3.5 x 10-3). We note that the Union RSCE method can be used to prepare aerogels of various different sizes and shapes, depending on the metal mold and hydraulic hot press employed. This RSCE method has also been used to prepare other types of aerogels (titania, alumina, etc.) from different precursor recipes20.

<table><tbody><tr><td>Tetramethylorthosilicate&amp;nbsp; (TMOS)</td><td>Sigma Aldrich</td><td>218472-500G</td><td>98% purity, CAS 681-84-5&amp;nbsp;</td></tr><tr><td>Methanol&amp;nbsp; (MeOH)</td><td>Fisher Scientific</td><td>A412-20</td><td>Certified ACS Reagent Grade, &amp;ge;99.8%</td></tr><tr><td>Ammonium Hydroxide (aqueous ammonia)</td><td>Fisher Scientific</td><td>A669S212</td><td>Certified ACS Plus, about 14.8 N, 28.0-20.0 w/w%</td></tr><tr><td>Deionized Water</td><td>on tap in house</td><td></td><td></td></tr><tr><td>Flexible Graphite Sheet</td><td>Phelps Industrial Products</td><td>7500.062.3</td><td>1/16 in thick</td></tr><tr><td>Stainless Steel Foil</td><td>Various</td><td></td><td>0.0005 in thick, 304 Stainless Steel</td></tr><tr><td>High Temperature Mold Release Spray</td><td>various (for example, CRC Industrial Dry PTFE Lube)</td><td></td><td>Should be able to withstand high temperatures.</td></tr></tbody></table>

preparing silica aerogel monoliths via a rapid supercritical extraction method

A procedure for the fabrication of monolithic silica aerogels in eight hours or less via a rapid supercritical extraction process is described. The procedure requires 15-20 min of preparation time, during which a liquid precursor mixture is prepared and poured into wells of a metal mold that is placed between the platens of a hydraulic hot press, followed by several hours of processing within the hot press. The precursor solution consists of a 1.0:12.0:3.6:3.5 x 10-3 molar ratio of tetramethylorthosilicate (TMOS):methanol:water:ammonia. In each well of the mold, a porous silica sol-gel matrix forms. As the temperature of the mold and its contents is increased, the pressure within the mold rises. After the temperature/pressure conditions surpass the supercritical point for the solvent within the pores of the matrix (in this case, a methanol/water mixture), the supercritical fluid is released, and monolithic aerogel remains within the wells of the mold. With the mold used in this procedure, cylindrical monoliths of 2.2 cm diameter and 1.9 cm height are produced. Aerogels formed by this rapid method have comparable properties (low bulk and skeletal density, high surface area, mesoporous morphology) to those prepared by other methods that involve either additional reaction steps or solvent extractions (lengthier processes that generate more chemical waste).The rapid supercritical extraction method can also be applied to the fabrication of aerogels based on other precursor recipes.

Following the procedure described here results in consistent batches of monolithic silica aerogels. Figure 4 shows images of typical silica aerogels made via this process. Each aerogel takes on the shape and size of the well in the processing mold with no shrinkage. The images show that the silica aerogels are translucent.
The physical properties of these aerogels are summarized in Table 4. They are comparable to those of silica aerogels produced from similar ...

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Preparing Silica Aerogel Monoliths via a Rapid Supercritical Extraction Method

This article describes a rapid supercritical extraction method for fabricating silica aerogels. By utilizing a confined mold and hydraulic hot press, monolithic aerogels can be made in eight hours or less.

A procedure for the fabrication of monolithic silica aerogels in eight hours or less via a rapid supercritical extraction process is described. The ...

preparing-silica-aerogel-monoliths-via-rapid-supercritical-extraction

Research

JoVE Journal

Chemistry

20.2K Views.  Union College. This article describes a rapid supercritical extraction method for fabricating silica aerogels. By utilizing a confined mold and hydraulic hot press, monolithic aerogels can be made in eight hours or less.

Video: Preparing Silica Aerogel Monoliths via a Rapid Supercritical Extraction Method

Preparation of Silica Nanoparticles Through Microwave-assisted Acid-catalysis

Microwave-assisted synthetic techniques were used to quickly and reproducibly produce silica nanoparticle sols using an acid catalyst with nanoparticle diameters ranging from 30-250 nm by varying the reaction conditions. Through the selection of a microwave compatible solvent, silicic acid precursor, catalyst, and microwave irradiation time, these microwave-assisted methods were capable of overcoming the previously reported shortcomings associated with synthesis of silica nanoparticles using microwave reactors. The siloxane precursor was hydrolyzed using the acid catalyst, HCl. Acetone, a low-tan &#948; solvent, mediates the condensation reactions and has minimal interaction with the electromagnetic field. Condensation reactions begin when the silicic acid precursor couples with the microwave radiation, leading to silica nanoparticle sol formation. The silica nanoparticles were characterized by dynamic light scattering data and scanning electron microscopy, which show the materials&#39; morphology and size to be dependent on the reaction conditions. Microwave-assisted reactions produce silica nanoparticles with roughened textured surfaces that are atypical for silica sols produced by St&#246;ber&#39;s methods, which have smooth surfaces.

Silica nanoparticles were prepared using acid-catalysis of a siloxane precursor and microwave-assisted synthetic techniques resulting in the controlled growth of nanomaterials ranging from 30-250 nm in diameter. The growth dynamics can be controlled by varying the initial silicic acid concentration, time of the reaction, and temperature of reaction.

Microwave-assisted synthetic techniques were used to quickly and reproducibly produce silica nanoparticle sols using an acid catalyst with nanoparticle ...

Preparing Adherent Cells for X-ray Fluorescence Imaging by Chemical Fixation

X-ray fluorescence imaging allows us to non-destructively measure the spatial distribution and concentration of multiple elements simultaneously over large or small sample areas. It has been applied in many areas of science, including materials science, geoscience, studying works of cultural heritage, and in chemical biology. In the case of chemical biology, for example, visualizing the metal distributions within cells allows us to study both naturally-occurring metal ions in the cells, as well as exogenously-introduced metals such as drugs and nanoparticles. Due to the fully hydrated nature of nearly all biological samples, cryo-fixation followed by imaging under cryogenic temperature represents the ideal imaging modality currently available. However, under the circumstances that such a combination is not easily accessible or practical, aldehyde based chemical fixation remains useful and sometimes inevitable. This article describes in as much detail as possible in the preparation of adherent mammalian cells by chemical fixation for X-ray fluorescent imaging.

Here, we present a protocol on how to determine the quantity and distribution of metals in a sample using synchrotron X-ray fluorescence. We focus on adherent cells, and describe the chemical fixation method to prepare this sample. We then describe how to mount and image the sample using synchrotron X-rays.

X-ray fluorescence imaging allows us to non-destructively measure the spatial distribution and concentration of multiple elements simultaneously over ...

Preparation of Biopolymer Aerogels Using Green Solvents

Although the first reports on aerogels made by Kistler1 in the 1930s dealt with aerogels from both inorganic oxides (silica and others) and biopolymers (gelatin, agar, cellulose), only recently have biomasses been recognized as an abundant source of chemically diverse macromolecules for functional aerogel materials. Biopolymer aerogels (pectin, alginate, chitosan, cellulose, etc.) exhibit both specific inheritable functions of starting biopolymers and distinctive features of aerogels (80-99% porosity and specific surface up to 800 m2/g). This synergy of properties makes biopolymer aerogels promising candidates for a wide gamut of applications such as thermal insulation, tissue engineering and regenerative medicine, drug delivery systems, functional foods, catalysts, adsorbents and sensors. This work demonstrates the use of pressurized carbon dioxide (5 MPa) for the ionic cross linking of amidated pectin into hydrogels. Initially a biopolymer/salt dispersion is prepared in water. Under pressurized CO2 conditions, the pH of the biopolymer solution is lowered to 3 which releases the crosslinking cations from the salt to bind with the biopolymer yielding hydrogels. Solvent exchange to ethanol and further supercritical CO2 drying (10 - 12 MPa) yield aerogels. Obtained aerogels are ultra-porous with low density (as low as 0.02 g/cm3), high specific surface area (350 - 500 m2/g) and pore volume (3 - 7 cm3/g for pore sizes less than 150 nm).

A new way for the production of biopolymer-based aerogels by carbon dioxide (CO2) induced gelation is shown. The technique utilizes pressurized carbon dioxide (5 MPa) for the production of biopolymer hydrogels and supercritical CO2 (12 MPa) to convert gels into aerogels. The only solvents needed besides CO2 are water and ethanol.

Although the first reports on aerogels made by Kistler1 in the 1930s dealt with aerogels from both inorganic oxides (silica and others) and biopolymers ...

Facile Preparation of Ultrafine Aluminum Hydroxide Particles with or without Mesoporous MCM-41 in Ambient Environments

An aqueous suspension of nanogibbsite was synthesized via the titration of aluminum aqua acid [Al(H2O)6]3+ with L-arginine to pH 4.6. Since the hydrolysis of aqueous aluminum salts is known to produce a wide array of products with a wide range of size distributions, a variety of state-of-the-art instruments (i.e., 27Al/1H NMR, FTIR, ICP-OES, TEM-EDX, XPS, XRD, and BET) were used to characterize the synthesis products and identification of byproducts. The product, which was comprised of nanoparticles (10-30 nm), was isolated using gel permeation chromatography (GPC) column technique. Fourier transform infrared (FTIR) spectroscopy and powder X-ray diffraction (PXRD) identified the purified material as the gibbsite polymorph of aluminum hydroxide. The addition of inorganic salts (e.g., NaCl) induced electrostatic destabilization of the suspension, thereby agglomerating the nanoparticles to yield Al(OH)3 precipitate with large particle sizes. By utilizing the novel synthetic method described here, Al(OH)3 was partially loaded inside the highly ordered mesoporous framework of MCM-41, with average pore dimensions of 2.7 nm, producing an aluminosilicate material with both octahedral and tetrahedral Al (Oh/Td = 1.4). The total Al content, measured using energy-dispersive X-ray spectrometry (EDX), was 11% w/w with a Si/Al molar ratio of 2.9. A comparison of bulk EDX with surface X-ray photoelectron spectroscopy (XPS) elemental analysis provided insight into the distribution of Al within the aluminosilicate material. Furthermore, a higher ratio of Si/Al was observed on the external surface (3.6) as compared to the bulk (2.9). Approximations of O/Al ratios suggest a higher concentration of Al(O)3 and Al(O)4 groups near the core and external surface, respectively. The newly developed synthesis of Al-MCM-41 yields a relatively high Al content while maintaining the integrity of the ordered silica framework and can be used for applications where hydrated or anhydrous Al2O3 nanoparticles are advantageous.

An ultrafine aluminum hydroxide nanoparticle suspension was prepared via the controlled titration of [Al(H2O)]3+ with L-arginine to pH 4.6 with and without cage-effect confinement within mesoporous channels of MCM-41.

An aqueous suspension of nanogibbsite was synthesized via the titration of aluminum aqua acid [Al(H2O)6]3+ with L-arginine to pH 4.6. Since the hydrolysis ...

Fabrication and Testing of Catalytic Aerogels Prepared Via Rapid Supercritical Extraction

Protocols for preparing and testing catalytic aerogels by incorporating metal species into silica and alumina aerogel platforms are presented. Three preparation methods are described: (a) the incorporation of metal salts into silica or alumina wet gels using an impregnation method; (b) the incorporation of metal salts into alumina wet gels using a co-precursor method; and (c) the addition of metal nanoparticles directly into a silica aerogel precursor mixture. The methods utilize a hydraulic hot press, which allows for rapid (&#60;6 h) supercritical extraction and results in aerogels of low density (0.10 g/mL) and high surface area (200-800 m2/g). While the work presented here focuses on the use of copper salts and copper nanoparticles, the approach can be implemented using other metal salts and nanoparticles. A protocol for testing the three-way catalytic ability of these aerogels for automotive pollution mitigation is also presented. This technique uses custom-built equipment, the Union Catalytic Testbed (UCAT), in which a simulated exhaust mixture is passed over an aerogel sample at a controlled temperature and flow rate. The system is capable of measuring the ability of the catalytic aerogels, under both oxidizing and reducing conditions, to convert CO, NO and unburned hydrocarbons (HCs) to less harmful species (CO2, H2O and N2). Example catalytic results are presented for the aerogels described.

Here we present protocols for preparing and testing catalytic aerogels by incorporating metal species into silica and alumina aerogel platforms. Methods for preparing materials using copper salts and copper-containing nanoparticles are featured. Catalytic testing protocols demonstrate the effectiveness of these aerogels for three-way catalysis applications.

Protocols for preparing and testing catalytic aerogels by incorporating metal species into silica and alumina aerogel platforms are presented. Three ...

Preparation of Functional Silica Using a Bioinspired Method

The goal of the protocols described herein is to synthesize bioinspired silica materials, perform enzyme encapsulation therein, and partially or totally purify the same by acid elution. By combining sodium silicate with a polyfunctional bioinspired additive, silica is rapidly formed at ambient conditions upon neutralization. 
The effect of neutralization rate and biomolecule addition point on silica yield are investigated, and biomolecule immobilization efficiency is reported for varying addition point. In contrast to other porous silica synthesis methods, it is shown that the mild conditions required for bioinspired silica synthesis are fully compatible with the encapsulation of delicate biomolecules. Additionally, mild conditions are used across all synthesis and modification steps, making bioinspired silica a promising target for the scale-up and commercialization as both a bare material and active support medium.
The synthesis is shown to be highly sensitive to conditions, i.e., the neutralization rate and final synthesis pH, however tight control over these parameters is demonstrated through the use of auto titration methods, leading to high reproducibility in reaction progression pathway and yield. 
Therefore, bioinspired silica is an excellent active material support choice, showing versatility towards many current applications, not limited to those demonstrated here, and potency in future applications.

Here, we present a protocol to synthesize bioinspired silica materials and immobilize enzymes therein. Silica is synthesized by combining sodium silicate and an amine &#39;additive&#39;, which neutralize at a controlled rate. Material properties and function can be altered either by in situ enzyme immobilization or post-synthetic acid elution of encapsulated additives.

The goal of the protocols described herein is to synthesize bioinspired silica materials, perform enzyme encapsulation therein, and partially or totally ...

A Rapid Synthesis Method for Au, Pd, and Pt Aerogels Via Direct Solution-Based Reduction

Here, a method to synthesize gold, palladium, and platinum aerogels via a rapid, direct solution-based reduction is presented. The combination of various precursor noble metal ions with reducing agents in a 1:1 (v/v) ratio results in the formation of metal gels within seconds to minutes compared to much longer synthesis times for other techniques such as sol-gel. Conducting the reduction step in a microcentrifuge tube or small volume conical tube facilitates a proposed nucleation, growth, densification, fusion, equilibration model for gel formation, with final gel geometry smaller than the initial reaction volume. This method takes advantage of the vigorous hydrogen gas evolution as a by-product of the reduction step, and as a consequence of reagent concentrations. The solvent accessible specific surface area is determined with both electrochemical impedance spectroscopy and cyclic voltammetry. After rinsing and freeze drying, the resulting aerogel structure is examined with scanning electron microscopy, X-ray diffractometry, and nitrogen gas adsorption. The synthesis method and characterization techniques result in a close correspondence of aerogel ligament sizes. This synthesis method for noble metal aerogels demonstrates that high specific surface area monoliths may be achieved with a rapid and direct reduction approach.

A rapid, direct solution-based reduction synthesis method to obtain Au, Pd, and Pt aerogels is presented.

Here, a method to synthesize gold, palladium, and platinum aerogels via a rapid, direct solution-based reduction is presented. The combination of various ...

Encapsulating Cytochrome c in Silica Aerogel Nanoarchitectures without Metal Nanoparticles while Retaining Gas-phase Bioactivity

Applications such as sensors, batteries, and fuel cells have been improved through the use of highly porous aerogels when functional compounds are encapsulated within the aerogels. However, few reports on encapsulating proteins within sol&#8211;gels that are processed to form aerogels exist. A procedure for encapsulating cytochrome c (cyt. c) in silica (SiO2) sol-gels that are supercritically processed to form bioaerogels with gas-phase activity for nitric oxide (NO) is presented. Cyt. c is added to a mixed silica sol under controlled protein concentration and buffer strength conditions. The sol mixture is then gelled and the liquid filling the gel pores is replaced through a series of solvent exchanges with liquid carbon dioxide. The carbon dioxide is brought to its critical point and vented off to form dry aerogels with cyt. c encapsulated inside. These bioaerogels are characterized with UV-visible spectroscopy and circular dichroism spectroscopy and can be used to detect the presence of gas-phase nitric oxide. The success of this procedure depends on regulating the cyt. c concentration and the buffer concentration and does not require other components such as metal nanoparticles. It may be possible to encapsulate other proteins using a similar approach making this procedure important for potential future bioanalytical device development.

Encapsulating Cytochrome c in Silica Aerogel Nanoarchitectures without Metal Nanoparticles while Retaining Gas-phase Bioactivity

This procedure describes how to encapsulate cytochrome c (cyt. c) in silica (SiO2) sol-gels, process these gels to form bioaerogels, and use these bioaerogels to rapidly recognize nitric oxide (NO) through a gas-phase reaction. This type of protocol may aid in the future development of biosensors or other bioanalytical devices.

Applications such as sensors, batteries, and fuel cells have been improved through the use of highly porous aerogels when functional compounds are ...

Bioengineering

Aesthetically Enhanced Silica Aerogel Via Incorporation of Laser Etching and Dyes

A procedure for aesthetically enhancing silica aerogel monoliths by laser etching and incorporation of dyes is described in this manuscript. Using a rapid supercritical extraction method, large silica aerogel monolith (10 cm x 11 cm x 1.5 cm) can be fabricated in about 10 h. Dyes incorporated into the precursor mixture result in yellow-, pink- and orange-tinged aerogels. Text, patterns, and images can be etched onto the surface (or surfaces) of the aerogel monolith without damaging the bulk structure. The laser engraver can be used to cut shapes from the aerogel and form colorful mosaics.

This protocol describes a method for etching text, patterns, and images onto the surface of silica aerogel monoliths in native and dyed form and assembling the aerogels into mosaic designs.

A procedure for aesthetically enhancing silica aerogel monoliths by laser etching and incorporation of dyes is described in this manuscript. Using a rapid ...

Engineering

Impregnation and Grafting of Aminated Compounds onto Silica Substrates

A Synthetic Methodology for Preparing Impregnated and Grafted Amine-Based Silica Composites for Carbon Capture

Recently, there has been a significant effort towards reducing or mitigating CO2 emissions through the use of carbon capture materials for point source or direct air capture (DAC) methods. This work focuses on amine-functionalized CO2 adsorbents for DAC. These materials show promise for CO2 removal because they have low regeneration energy consumption and high adsorption capacity. The incorporation of amine species into a porous substrate combines the advantages of the amine species&#39; affinity to CO2 with the large pore volumes and surface areas of the porous substrate. There are three methods commonly used to prepare amine-based CO2 sorbents, depending on the selection of the amine species, material support, and preparation method. These methods are impregnation, grafting, or chemical synthesis. Silica is a prevalent choice of substrate material because of its adjustable pore size, moisture tolerance, temperature stability, and ability to adsorb CO2 in low concentrations for DAC applications. Typical synthetic procedures and primary attributes of both impregnated and grafted amine-silica composites are described herein.

Author Spotlight: Standardizing the Development of Amine-Based Silica Composites as CO2 Adsorbents for Direct Air Capture 

This work aims to facilitate the development of standardized techniques for impregnating or grafting aminated compounds onto silica substrates, which are often broadly described in the literature. Specific amounts of solvent, substrate, amines, and the values of other important experimental parameters will be discussed in detail.

Recently, there has been a significant effort towards reducing or mitigating CO2 emissions through the use of carbon capture materials for point source or ...

Preparing Silica Aerogel Monoliths via a Rapid Supercritical Extraction Method

Summary

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Chapters in this video

Preparation of Silica Nanoparticles Through Microwave-assisted Acid-catalysis

Preparing Adherent Cells for X-ray Fluorescence Imaging by Chemical Fixation

Preparation of Biopolymer Aerogels Using Green Solvents

Facile Preparation of Ultrafine Aluminum Hydroxide Particles with or without Mesoporous MCM-41 in Ambient Environments

Fabrication and Testing of Catalytic Aerogels Prepared Via Rapid Supercritical Extraction

Preparation of Functional Silica Using a Bioinspired Method

A Rapid Synthesis Method for Au, Pd, and Pt Aerogels Via Direct Solution-Based Reduction

Encapsulating Cytochrome c in Silica Aerogel Nanoarchitectures without Metal Nanoparticles while Retaining Gas-phase Bioactivity

Aesthetically Enhanced Silica Aerogel Via Incorporation of Laser Etching and Dyes

A Synthetic Methodology for Preparing Impregnated and Grafted Amine-Based Silica Composites for Carbon Capture