Abstract
Gas adsorption properties of microporous silica prepared by selective leaching of metakaolinite were investigated at 25 °C using various adsorbates of different molecular size, shape and polarity, i.e. water, methanol, butan-l-ol, cyclohexane and 2, 2, 4-trimethylpentane. The microporous silica was obtained by chemical treatment of metakaolinite, (derived from the 1: 1 layered clay mineral kaolinite (Al2 (OH) 4Si2 O5) by firing at 600 °C for 24 h) with a 20 mass% H2SO4 solution at 90 °C for 2 h with stirring. The pore size of 0.6 nm previously obtained from the t-plot and Horvath-Kawazoe (HK) methods was examined by comparison of the results obtained from the adsorption isotherms of 2, 2, 4-trimethylpentane on zeolite 4A (pore size 0.42 nm), zeolite ZSM-5 (0.54 nm) and mordenite (0.67 nm). The pore size of the microporous silica was found to be between those of ZSM-5 and mordenite, in good agreement with the value derived from the t-plot and HK methods. The adsorption isotherms of all adsorbates showed a convex curve in the low partial pressure (P/P0) range irrespective of the polarity of adsorbates, indicating micropore filling due to strong interaction between adsorbate and adsorbent in micropores. The increase of adsorption in the low P/N range (P/P0 < 0.05) changed with the shape, size and polarity of the adsorbates due to the steric hindrance and chemical affinity of the adsorbates.
