POLAROGRAPHY AND VOLTAMMETRY OF AQUEOUS COLLOIDAL TIO2 SOLUTIONS

In acidic aqueous solutions the protonated TiO2 colloid undergoes a co mplex process of electroreduction. It starts by reduction of protons o n the surface of the particles; in cyclic voltammetry with a fast scan rate this reaction is reversible. In the absence of an excess of a su pporting electrolyte the particles, deprived of the stabilizing positi ve charge in the electroreduction process, aggregate and adsorb at the electrode and hinder the electrode reaction. Added electrolyte remove s this hindrance and produces an increase of the electrolytic current. The hydrogen atoms generated at the TiO2 surface are able to reduce T i(TV) to-Ti(III). At more negative potentials a direct reduction of su rface hydroxo complexes of Ti(IV) takes place. The mechanism and the p otential of electroreduction of TiO2 colloids are strongly affected by ligands which form complexes with titanium atoms on the particle surf ace.