Preparation of sol–gel silica samples modified with drying control chemical additives

Abstract

In this work we investigate the effect of different drying control chemical additives (DCCAs) on the sol–gel processing of silica. Formamide, N,N-dimethylformamide, and propylene carbonate were used as DCCAs in this study. The sols were prepared by the hydrolysis and condensation of tetraethyl orthosilicate in the presence of water, nitric acid, and ethanol. After gelation, the samples were heat treated in air at temperatures from 110 to 1150°C. The structural evolution of these materials was evaluated by Fourier transform infrared spectroscopy (FTIR), nitrogen adsorption tests, and helium pycnometry. The band attributed to silanol groups (≈960cm−1) decreased in intensity and shifted towards larger wavenumbers as reaction time progressed. Bands ascribed to Si–O bonds also shifted towards larger wavenumbers with reaction time. These findings suggest the formation of a more rigid silica framework as time progressed. This behavior was more pronounced for sols prepared using formamide and N,N-dimethylformamide. The heat treatment of DCCA-containing gels at temperatures up to 800°C gave rise to materials with a strong and interconnected framework, showing a high concentration of silanols on the surface. The presence of such groups could enable the chemical modification of these materials upon a post-synthesis treatment.