Preparation of microporous silica from metakaolinite by selective leaching method

Microporous silica was prepared by selective leaching of metakaolinite, derived from the 1:1 layered clay mineral kaolinite (2SiO(2)Al(2)O(3)2H(2)O) by firing at 600 degrees C for 24 h. Treatment with 20 mass% H2SO4 solution at 90 degrees C for 0.5-5 h with stirling. led to a decrease in the Al2O3 content and an increase in the specific surface area (S-A) with increasing leaching time. The adsorption-desorption isotherms of N-2 measured at 77 K show a type I curve, the average pore size, calculated by t-plot method, being about 0.6 nm and the maximum S-A, about 340 m(2)g(-1). The Si-29 MAS NMR spectrum of the 2 h leached sample showed peaks at -101 and -110 ppm, which can be assigned to the layer structure unit (Q(3)) and the SiO4, tetrahedral framework structure unit (Q(4)), respectively. It is suggested that the SiO4, tetrahedral structure of the microporous silica basically maintains the original kaolinite and is different from the general framework structure of silica gel. (C) 1998 Elsevier Science B.V. All rights reserved.