Synthesis of high surface area silica by solvent exchange in alkoxy derived silica gels

Silica gels have been prepared by the hydrolysis of tetraethyl orthosilicate at pH 9.5 with a high water: TEOS ratio. The gels were exchanged with different solvents such as ethanol, methanol, isopropanol and acetone. The resultant gels were calcined at 500°C for 3 h at heating rate of 3°C min−1. The surface area and total pore volume of the calcined gels measured using nitrogen adsorption show much dependence with the nature of the liquid used for the exchange. The gel washed with ethanol under the conditions of present investigation shows maximum surface area. The adsorption isotherm of this gel also shows 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 final gel precursor in terms of surface area and pore volume. Repeated washing of the gels with solvents and subsequent removal result in high surface area, while evaporating the gels with solvents results in relatively less porous gels.