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.

Molecular dynamics simulations of water structure and diffusion in silica nanopores

Abstract: We present molecular dynamics (MD) simulations of water-filled silica nanopores such as those that occur in ordered oxide ceramics (MCM-41, SBA-15), controlled pore glasses (such as Vycor glass), mesoporous silica, bioglasses, and hydrous silica gel coatings of weathered minerals and glasses. Our simulations overlap the range of pore diameters (1–4 nm) where confinement causes the disappearance of bulk-liquid-like water. In ≥2 nm diameter pores, the silica surface carries three statistical monolayers of density-layered water, interfacial water structure is independent of confinement or surface curvature, and bulk-liquid-like water exists at the center of the pore (this last finding contradicts assumptions used in most previous neutron diffraction studies and in several MD simulation studies of silica nanopores). In 1 nm diameter pores, bulk-liquid-like water does not exist and the structural properties of interfacial water are influenced by confinement. Predicted water diffusion coefficients in 1–4 nm dia...

Combination of non-thermal plasma and heterogeneous catalysis for oxidation of volatile organic compounds: Part 2. Ozone decomposition and deactivation of γ-Al2O3

Abstract: The role of ozone was studied for two different configurations combining non-thermal plasma (NTP) and heterogeneous catalysis, namely the use of a gas phase plasma with subsequent exposure of the effluent to a catalyst in a packed-bed reactor (post-plasma treatment) and the placement of the catalyst directly in the discharge zone (in-plasma catalysis). Non-porous and porous alumina and silica were deployed as model catalysts. The oxidation of immobilised hydrocarbons, toluene as a volatile organic compound and CO as an inorganic pollutant were studied in both operational modes. While conversion and selectivity of hydrocarbon oxidation in the case of catalytic post-plasma treatment can be fully explained by the catalytic decomposition of O3 on γ-Al2O3, the conversion processes for in-plasma catalysis are more complex and significant oxidation was also measured for the other three materials (α-Al2O3, quartz and silica gel). It became obvious that additional synergetic effects can be utilised in the case of in-plasma catalysis due to short-lived species formed in the NTP. The capability of porous alumina for ozone decomposition was found to be correlated with its activity for oxidation of carbon-containing agents. It could be clearly shown that the reaction product CO2 poisons the catalytic sites at the γ-Al2O3 surface. The catalytic activity for O3 decomposition can be partially re-established by NTP treatment. However, for practical purposes the additional reaction pathways provided by in-plasma catalytic processes are essential for satisfactory conversion and selectivity.

Adsorption of fluoride, phosphate, and arsenate ions on lanthanum- impregnated silica gel

Abstract: A lanthanum-impregnated silica gel has been developed for the removal of fluoride, phosphate, and arsenate ions by adsorption The interaction between silica gel and lanthanum ion was maximum at a final pH of 6 The removal of fluoride and arsenate ions by adsorption on the lanthanum-impregnated silica gel was more than 99 9% at neutral pH from initial concentration of 055 and 02 mmol/L, respectively The removal of phosphate ion was 95% at an initial concentration of 05 mmol/L at neutral pH Arsenite ion was not adsorbed on the material The rate of adsorption of the anions followed the first-order reaction and fit in the Lagergren equation The adsorption of each anion followed the Langmuir isotherm Other anions such as Cl{sup -}, BR{sup -}, I{sup -}, NO{sub 3}{sup -}, and SO{sub 4}{sup 2-} did not interfere with the adsorption A column study was conducted for the removal of these anions at a fixed flow rate of 05 mL/min at pH approximately 7 These anions were removed by more than 999% at initial first or second fraction, and the column was regenerated at pH 85 The method was applied for the removal of these anions from synthetic and high-tech industrial wastewatersmore » 30 refs, 8 figs, 1 tab« less