Semiconductor photocatalytic reduction is a relatively new technique for the removal of dissolved metal ions in wastewater. In this paper, physical adsorption and photocatalytic reduction of eight environmentally significant metal ions in TiO2 suspensions of Degussa P25 and Hombikat UV100 were investigated. Critical scrutiny of the potential versus pC and pH diagrams reveals that any particular oxidation or reduction reaction can be promoted thermodynamically over other reactions by adding different reactants. In order to elucidate better understanding of the kinetics of the photocatalytic process, operating parameters such as dissolved oxygen, presence of ferric and ferrous ions, organic reductants and their concentrations were examined in detail. It was observed that the presence of dissolved oxygen inhibits while the presence of organic reductants promotes photocatalytic reduction.