Investigation of the states of water and OH groups on the surface of silica

The states of water and OH groups on the surface of amorphous nanosilica with heat treatment at different temperature for hours were studied by thermogravimetry (TG), differential scanning calorimetry (DSC) and Fourier-transform infrared (FT-IR) spectroscopy. The physically adsorbed water, OH groups on surface and OH groups below surface were removed mainly at 343, 709, and 1210 K, respectively. With the increasing temperature in DSC curves, the physically adsorbed water was removed firstly; secondly OH groups on surface were dehydrated; lastly were OH groups below the surface. In a wide temperature range, the dehydration of the three kinds of water took place at the same time. According to the surface area and TG results, the H2O density and OH group density on surface were obtained. For the sample without heat treatment, the physically adsorbed water and OH groups on surface were 9.80 and 8.20 nm−2, respectively. And the physically adsorbed water and OH groups of the sample with heat treatment at 1273 K were about 0 and 2.50 nm−2, respectively.