Preparation and photocatalytic activity of TiOxNy/CdS heterojunctions

Nitrogen doped titanium oxide (TiOxNy,) thin films were deposited by facing-target sputtering on glass substrates at different nitrogen flow rates (N-R) of 0, 5, 10, 15, and 20 SCCM (SCCM denotes cubic centimeter per minute at STP) at a fixed sputtering pressure of 0.8 Pa to identify the optimum dopant concentration for the efficient photocatalytic activity. X-ray diffraction experiments revealed that the films have anatase phase until N-R of 10 SCCM and become amorphous with further increase in N-R. Higher level nitrogen doping is inhibited due to the difficulty in the replacement of oxygen. CdS thin films were deposited by chemical bath deposition method using the CdCl2 and thiourea as the precursors, and NH3NO4 and KOH as the complexing agent have the optical band gaps of 2.38-2.5 eV for the different thiourea solution concentrations and hexagonal structures. The photocatalytic decomposition of methanol proceeds via formaldehyde and CO as the intermediate species and CO2 is produced after the complete decomposition. The optimum N-R for the nitrogen doping in TiO2 films were found be 5 SCCM. The properties of the films, including the crystallinity, surface morphology, and light absorption capability, are influenced by the nitrogen flow rate, whereas the photocatalytic reaction on TiOxNy thin films is very sensitive to crystallinity and its surface structure. (c) 2007 American Vacuum Society.