Silica gel

About: Silica gel is a research topic. Over the lifetime, 22313 publications have been published within this topic receiving 325516 citations. The topic is also known as: Amorphous silica & Precipitated amorphous silica.

Effect of formamide additive on the chemistry of silica sol-gels: Part I: NMR of silica hydrolysis

Abstract: Monolithic gels can be more easily obtained when prepared with drying control chemical additives (DCCAs). The influence of formamide DCCA on the hydrolysis and early condensation of tetramethoxysilane has been studied by 29 Si NMR. It was found that formamide decreases the hydrolysis rate by 6 × but increases the polymerization rate slightly. The rate constants for both hydrolysis and condensation reactions depend upon the concentration of formamide and solution pH.

Amphiphobic Nanofibrous Silica Mats with Flexible and High-Heat-Resistant Properties

Abstract: In this study, for the first time, we fabricated flexible, high-heat-resistant, and amphiphobic mats by (fluoroalkyl)silane (FAS) modification of electrospun pure silica nanofibrous mats. The inorganic silica nanofibrous mats were obtained via electrospinning the blend solutions of poly(vinyl alcohol) (PVA) and silica gel, followed by calcination to remove the organic component. The PVA/silica and silica fibers were found to be randomly oriented as nonwoven mats with fiber diameters in the range of 150−500 nm. After the FAS modification, the surface wettability of the silica mats was converted from amphiphilic to amphiphobic. The fluorinated mat with the bead-on-string structure showed the highest water contact angle (WCA) of 154° and oil contact angle (OCA) of 144°. Additionally, the fluorinated inorganic fibrous mats exhibited a high heat resistance; they kept their hydrophobicity (WCA of 138°) and oleophobicity (OCA of 132°) even after the annealing treatment at 450 °C for 30 min. Potential application...

Evaluation of Silica Gel Cartridges Coated In Situ with Acidified 2, 4-Dinitrophenylhydrazine for Sampling Aldehydes and Ketones in Air

Abstract: A procedure for coating in situ silica gel in prepacked cartridges with 2,4-dinitrophenylhydrazine (DNPH) acidified with hydrochloric acid is described. The coated cartridge was compared with a validated DNPH impinger method for sampling organic carbonyl compounds (aldehydes and ketones) in diluted automotive exhaust emissions and in ambient air for subsequent analysis of the DNPH derivatives by high performance liquid chromatography. Qualitative and quantitative data are presented that show that the two sampling devices are equivalent. The coated cartridge is ideal for long-term sampling of carbonyls at sub to low parts-per-billion level in ambient air or for short-term sampling of carbonyls at low ppb to parts-per-million level in diluted automotive exhaust emissions. An unknown degradation product of acrolein has been tentatively identified as x-acrolein. The disappearance of acrolein in the analytical sample matrix correlates quantitatively almost on a mole for mole basis with the growth of x-acrolein. The sum of the concentration of acrolein and x-acrolein appears to be invariant with time.

Great Improvement of Chromatographic Performance Using MCM-41 Spheres as Stationary Phase in HPLC

Abstract: Grafted MCM-41 materials are ordered mesoporous adsorbents suitable for reversed-phase liquid chromatography applications (RP-HPLC): they possess high surface area, which is a great advantage to enhance the thermodynamic behavior of the classical stationary phase by increasing solute retention. Hence, MCM-41s allow the separation of poorly retained solutes which are hard to separate on conventional silica gels. Furthermore, the ordered porosity in MCM-41 enhances the kinetic properties of the classical stationary phase. MCM-41s afford higher and more homogeneous molecular diffusivity, which increases the column efficiency for high flow rates as compared to that of classical silica-based columns. Besides, RP-HPLC provides a meaningful description of the particle size distribution at a macroscopic scale and of the pore ordering by probing the diffusivity of solutes. MCM-41s obtained by pseudomorphic synthesis of silica gel have successfully passed all the chromatographic tests and the results show that thi...