Synthesis and characterization of ultramicroporous silica xerogels
Journal of Non-Crystalline Solids(2010)
摘要
Tailoring the porous texture of silica xerogels is of great interest in catalysis, adsorption and sensors. We report the preparation and characterization of xerogels with pore size distribution lower than 0.5nm, synthesized by hydrolysis and condensation of tetraethylorthosilicate (TEOS) at pH 2.5. N2 (77K) and CO2 (273K) adsorption isotherms and immersion calorimetry into liquids with different molecular size (dichloromethane, 0.33nm; trichloromethane, 0.40nm; n-hexane, 0.43nm; cyclohexane, 0.48nm; isooctane, 0.59nm; and carbon tetrachloride, 0.66nm) were used to characterize ultramicroporous xerogels. All the xerogel samples adsorbed CO2 (273K) but not N2 (77K). Pore size distributions from immersion calorimetry showed that hydrolysis and condensation of TEOS at pH 2.5 produced silica xerogels with pore size distributions in the 0.33–0.48nm range. Xerogels synthesized at 333K and a 5.5:1 water:TEOS molar ratio produced xerogels with higher specific surface areas and wider pore size distributions than xerogels obtained at 293K and at 2.5:1 water:TEOS molar ratio.
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关键词
Silica xerogels,Immersion calorimetry,Pore size distribution,Co2 adsorption isotherms
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