Alternative Materials to TiO2

Abstract

A simple intuitive picture of an electrostatic adsorption mechanism that might occur during impregnation is given in Figure 6.1. An oxide surface contains terminal hydroxyl groups that protonate or deprotonate depending of the acidity of the impregnating solution. The pH at which the hydroxyl groups are neutral is termed the point of zero charge (PZC). Below this pH, the hydroxyl groups protonate and become positively charged, and the surface can adsorb anionic metal complexes such as CPA. Above the PZC, the hydroxyl groups deprotonate and become negatively charged, and cations such as PTA can be strongly adsorbed. In either case the metal complex might be thought to deposit onto the surface via strong electrostatic adsorption (SEA).