Restricted Diffusion of Chromium Nitrate Salt Solutions into Porous Sol-Gel-Silica Monoliths

2005 ◽  
Vol 81 (4) ◽  
pp. 877-884 ◽  
Author(s):  
James Kunetz ◽  
Larry Hench
1984 ◽  
Vol 32 ◽  
Author(s):  
Timothy J. Gardner ◽  
D. W. Sproson ◽  
G. L. Messing

ABSTRACTFine-grained, high surface area MgO, NiO and ZnO powders were synthesized by the evaporative decomposition of solutions (EDS) technique at 1000°C from acetate and nitrate salt solutions. The powder characteristics were similar in all cases; however, aggregated powders were obtained from the nitrate salts and aggregate-free powders were obtained from the acetate solutions when reacted in air. This difference is attributed to the oxidation of the acetate radical and/or its residue and that this process acts to disaggregate the salt droplet/particles that are formed during EDS.


2017 ◽  
Vol 121 (10) ◽  
pp. 2166-2171 ◽  
Author(s):  
Karen J. Morenz ◽  
D. James Donaldson

2004 ◽  
Vol 847 ◽  
Author(s):  
Doris Brandhuber ◽  
Nicola Hüsing ◽  
Herwig Peterlik

ABSTRACTHighly porous inorganic-organic hybrid monoliths with mesopores in a macroporous network have been prepared from methyltris(2-hydroxyethoxy)silane (MeGMS) and tetrakis(2-hydroxyethoxy)silane (EGMS) in the presence of an amphiphilic block copolymer. The amount of methyltris(2-hydroxyethoxy)silane (MeGMS) in the gel has been varied from 0 to 100 %. These glycol-modified silanes have the advantage of being water-soluble and thus allowing for a direct templating of liquid-crystalline surfactant mesophases without the presence of a homogenizing organic solvent such as ethanol. The wet gels have been dried by supercritical extraction with carbon dioxide.In the present work, the sol-gel behaviour of these glycol-modified silanes is discussed especially with a focus on the formation of the meso- and macrostructure. In addition, the influences of the varying ratios of methyltris(2-hydroxyethoxy)silane on the structural features of the gels are investigated by various analytical techniques such as small angle X-ray scattering, nitrogen sorption, and scanning electron microscopy.


2019 ◽  
Author(s):  
Ludivine van den Biggelaar ◽  
Patrice Soumillion ◽  
Damien Debecker

<div>Transaminases are immobilized onto macrocellular silica monoliths and used for carrying a continuous flow mode transamination reaction. Monoliths were prepared via an emulsion-templated sol-gel method and functionalized by amino-moieties (APTES) in order to covalently immobilize the enzymes, using glutaraldehyde as a cross-linking agent. In order to obtain higher performance and improved reproducibility, we investigate the key parameters of APTES functionalization and of enzyme grafting. Four functionalization protocols were studied. It is shown that controlling the moisture levels in monolith and in the functionalisation solution led to a 3-fold increase in activity as compared to the previously reported data, and greatly improved the reproducibility. Additionally, we report a strong beneficial effect of running the enzyme immobilization at room temperature instead of 4°C, further enhancing the obtained activity. Finally, the popular method which consists in stabilizing the covalent attachment of the enzyme by reducing the imine bonds formed between the enzyme and the functionalized surface was investigated. We highlight a strong enzyme deactivation caused by cyanoborohydride, making this strategy irrelevant in this case. All in all, the improvements presented here for enzyme immobilization in macrocellular silica monoliths, lead to the preparation of more active materials for continuous flow mode biocatalysis.<br></div>


2019 ◽  
Author(s):  
◽  
Khaleel Idan Hamad

Many synthesis techniques like sol-gel, co-precipitation, hydrothermal, pyrolysis, and many more have been used to synthesize batteries' active electrode materials. High surface area cathode materials with smaller nanoparticles are favored for their higher reactivity compared to materials with particles of larger size. Sol-gel and co-precipitation methods have been primarily adopted because they can produce the desirable particle size easily and on a large scale. This dissertation details an efficient and cost-effective process for using a newly developed sol-gel method that uses glycerol solvent instead of the conventionally used water. Glycerol has three hydroxyl groups (OH) instead of one in water. These can play an important role in nanoparticle formation at earlier stages by speeding up the reaction. One of the main reasons for capacity fade in batteries is cationic mixing between Ni2+ and Li+. This results in blocking of the Li+ path and ultimately poor cyclability. This capacity fade has been successfully minimized in our current work by taking advantage of the high heat released from glycerol to get partially crystalline nanoparticles that could mitigate cationic mixing at high temperatures. The first cathode material synthesized using glycerol solvent was LiMn1/3Ni1/3Co1/3O2 (LMNC) layered oxide cathode material. Temperature's effects on the particles' morphologies, sizes, and electrochemical performances have been studied at four different temperatures. LMN2 was annealed at 900 �C/8hr and shows desirable particles size of ~ 0.3 (�_m), an initial discharge capacity of 177.1 mAh/g in the first cycle, and a superior capacity retention of 83.7% after 100 cycles. The process takes eight hours, rather than >12hr when using other solvents to prepare LMNC material at high temperatures. The results also demonstrate the higher stability and lower cationic mixing after 100 cycles. To increase capacity and voltage, lithium-rich cathode materials with the formula Li1.2Mn0.51Ni0.145+xCo0.145-xO2 (x = 0 (LR2), 0.0725 (LR1)) have been successfully synthesized. In this material, cobalt (Co) content has been decreased by half and the larger produced particles have suppressed the total activation of Li2MnO3 phase in the first charge cycle. The specific discharge capacity retention of LR1 at 1C between 2 and 4.8 V was more than 100% after 100 cycles. Further improvements to LR1 cathode materials have led to an increase in the initial discharge capacity to 248 mAh/g at 0.1C. This is achieved by using an equimolecular combination of acetate and nitrate salt anions (LRACNI) with cornstarch. Cornstarch acts as a capping agent with the nitrate salt anions, and a gelling agent with acetate based anions. LRACNI shows an intermediate particle size with satisfactory capacity retention upon cycling and the lowest cationic mixing. LiNi0.8Co0.15Al0.05O2 (NCA) is one of the most commercialized cathode materials for lithium-ion batteries. It is challenging to have a high Ni content with Li in one combination electrode because cationic mixing increases proportionally. The use of glycerol has diminished the cationic mixing. High capacity retentions of 97% at 1C after 50 cycles, 87.6% at 0.3C after 100 cycles, and 93.6% at 0.1C after 70 cycles have been successfully achieved, which are better than those previously reported.


1994 ◽  
Vol 346 ◽  
Author(s):  
Taipau Chia ◽  
Jon K. West ◽  
Larry L. Hench

ABSTRACTThe infrared vibrational modes of sol-gel derived optical silica monoliths depend upon thermal treatments and chemical environments, as shown by Fourier transform infrared spectroscopy (FTIR). A semi-empirical quantum mechanical theory (PM-3 in MOPAC 6.1) is used to analyze the structural changes responsible for the spectral shifts. Optimized structures of 2-member, 3-, 4-, 5- and 6-member rings of SiO2 are calculated. The force constants for the molecular bonds in the rings are obtained and converted to the associated vibrational spectra for the rings. The peak position of the asymmetric transverse optical (AS1TO) mode of the rings shifts from 1070 cm−1 for 2-member rings to 1100 cm−1 for 3-member rings, 1150 cnr1 for 4-member rings, 1140 cm−1 for 5-member and 1120 cm−1 for 6-member rings. The IR data show a 38 cm”1 shift of the AS1TO mode as the gel-silica density changes from 1.1 g/cc to 2.2 g/cc. Thus, the intensification and shift of the AS1TO mode in the gel-silica to higher wave-numbers corresponds to a change in the distribution to larger silicate size rings.


1998 ◽  
Vol 13 (7) ◽  
pp. 1875-1880 ◽  
Author(s):  
R. Chaim ◽  
M. Hefetz

Amorphous to nanocrystalline ZrO2−3 wt. % Y2O3 powders were formed by chemical precipitation from mixed nitrate salt solutions. The powders were cold pressed and presintered in air for 2 to 6 h within the temperature range of 1100 °C and 1300 °C. Hot isostatic pressing was performed for 2 to 3 h within the temperature range of 1150 °C to 1350 °C in argon pressure of 150 MPa. Fully dense pellets with grain size of 22 nm to 45 nm were formed by application of low presintering temperatures.


2015 ◽  
Vol 44 (30) ◽  
pp. 13592-13601 ◽  
Author(s):  
Xingzhong Guo ◽  
Rui Wang ◽  
Huan Yu ◽  
Yang Zhu ◽  
Kazuki Nakanishi ◽  
...  

Uniform spherical mesopores were successfully prepared by combining polymerization-induced phase separation with an epoxide-mediated sol–gel route.


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