Kinetic Studies of Reductive Deposition of Copper(II) Ions Photoassisted by Titanium Dioxide

Photoreduction of copper(II) ions onTiO2 was studied in the presence of sacrificial donors such as HCOONa, Na2C2O4, and Na2H2edta. Formate was the best donor with respect to the reduction rate but an induction period was observed. The induction period increased with an increase in the Cu(II) concentration or with a decrease in the TiO2 weight in suspension. The presence of sulfates, phosphates, and chlorides increased the induction period. The ESR measurements indicate that the Cu(II) ions exist as [Cu(H2O)6]2+ in the formate system while as [Cu(C2O4)2]2- in the oxalate system. The differences in the reduction rates of Cu(II) between the formate and the oxalate system were explained in terms of electrostatic interaction between the Cu(II) complex and the TiO2 surface and a negative shift in the reduction potential by coordination with oxalate. The following rate law was obtained by kinetic analysis:  rate = {k1‘KsNs[CuIIL]IaΦ/(1 + αKs[CuIIL])} × {K[Donor]/(1 + K[Donor])}.