SYNTHESIS OF HIGH-SURFACE-AREA SILICA BY SOLVENT EXCHANGE IN ALKOXY-DERIVED SILICA-GELS

Silica gels have been prepared by the hydrolysis of tetraethyl orthosi licate at pH 9.5 with a high water:TEOS ratio. The gels were exchanged with different solvents such as ethanol, methanol, isopropanol and ac etone. The resultant gels were calcined at 500 degrees C for, 3 h at h eating rate of 3 degrees C min(-1). The surface area and total pore vo lume of the calcined gels measured using nitrogen adsorption show much dependence with the nature of the liquid used for the exchange. The g el washed with ethanol under the conditions of present investigation s hows maximum surface area. The adsorption isotherm of this. gel also s hows the characteristics of Type IV behaviour. Other gels usually show Type II behaviour. Solvents of low vapour pressure and high molecular volume favour the formation of gels with high pore volume. The method of exchange of solvents also influences the characteristics of the fi nal gel precursor in terms of Surface area and pore volume. Repeated w ashing of the gels with solvents and subsequent removal result in high surface area, while evaporating the gels with solvents results in rel atively less porous gels. (C) 1998 Elsevier Science Ltd. All rights re served.