Influence of pore size distribution on water adsorption on silica gels

The influence of pore size distribution on water adsorption has been analysed for a series of partially dehydroxylated silica gels with different pore structure, assessed from the analysis of nitrogen and CO₂ adsorption isotherms. It has been observed that some silica gels show water adsorption mainly in the first range of relative pressures (relative pressure from 0 up to 0.6), while other silica gels also show water adsorption at higher relative pressures. Comparison of the N₂ and water adsorption isotherms points out that only silica gels containing mesoporosity show water adsorption at relative pressures higher than 0.6. Moreover, a good correlation between the initial part of water adsorption isotherms (relative pressure from 0 up to 0.3) and CO₂ adsorption isotherms has been found (the higher the CO₂ adsorption capacity, the higher the water adsorption capacity at low pressure).