Transmittance change of the TiO2 thin film by photoreductive deposition of Cu(II)

Photoreductive deposition of Cu2+ on TiO2 thin film prepared by sol–gel method has been investigated by measuring a change of transmittance of the film. The transmittance decreased with irradiation time, corresponding to a decrease of the Cu2+ concentration in the solution. Removal percent of Cu2+ ions from the solution was obtained to be 80–98%. On the other hand, the transmittance change (ΔT) was greatly affected by experimental conditions: the ΔT value increased when the thicker films or films fired at higher temperature were used or when the same film was employed repeatedly. With the initial concentrations of Cu2+ more than 100 ppm, induction periods (I.P.) of 45–240 min were observed before the transmittance decreased. When Na2C2O4 was used as a sacrificial donor instead of HCOONa, the decrease rate for Cu2+ concentration in the solution became slightly lower. However, with Na2C2O4, no induction period was observed and the ΔT values were two times as high as those with HCOONa.