CHARGE REGULATION AT THE SURFACE OF POROUS SILICA

The 'charge regulation' model has been used to describe some features of charging the surface of porous solids when overlapping of diffuse e lectric double layers plays a significant part. It has been seen that, because of the charge regulation, the surface tends to be of equal po tential rather than of equal charge density. The distributions of the surface charge density and surface potential over pore sizes have been calculated. The acid-base properties of porous silica gels have been investigated. The total amount of residual silanols has been found to increase with increasing pH due to hydroxylation of the silica surface and subsequent dissolution of silica. A thermodynamic model for silic a dissolution has been put forward that predicts the existence of a si ngular point of the silica solubility curve.