Experimental study on kinetics of water-vapor sorption on surface of silica nano-porous materials

The thermal gravimetrical method was adopted to measure the water-vapor sorption of silica nano-porous materials in the thermal and moisture environment. The water-vapor sorption kinetics was experimentally investigated at environmental temperature 25°C and different relative pressure of vapor from 0.3 to 0.9. The sorption equilibrium data were fitted with different equations. An exponential decay-2 model was proposed based on the experimental data and was compared with the pseudo-first-order and the pseudo-second-order equations. The results show that the correlation coefficients of the Redlich-Peterson equation, the Fritz-Schlünder equation and the BET finite layer equation are higher than those of the other models; the BET model is more reasonable because it can present the monolayer saturation sorption capacity and the sorption layer number, and the sorption equilibrium curve of materials exists an inflection point from monolayer sorption to multilayer sorption. In addition, the kinetics of water-vapor sorption on the surface of silica nano-porous materials can be described by the decay-2 model with correlation coefficients above 0.99, and the decay-2 model fits well with the experimental values in the whole sorption process.