Preparation Of ZnO Based Composite Semiconductor Thin Films With Cathodic Deposition And Their Photocatalytic Performance

Coupling of semiconductors is an efficient approach to improve their photocatalytic activity and visible light response. In the present study, ZnO/α-FeOOH, ZnO-α-FeOOH, ZnO/Cu₂O and ZnO/CuO composited films were fabricated on ITO conducting glass substrates with cathodic deposition methods and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and Fourier transform infrared spectroscopy (FT-IR). The photocatalytic activity of the composited semiconductors under UV and visible light illumination was evaluated with photocatalytic degradation of methyl orange (MO) and photocatalytic reduction of Cr(â…¥).ZnO thin films were deposited on ITO from Zn(NO₃)₂, ZnCl2 and ZnCl2 + H₂O₂ aqueous solutions, respectively. The results indicated that the films obtained with NO 3?being used as the oxygen source exhibited higher photocatalytic activity than those with O₂ and H2O₂ used as the oxygen sources.α-FeOOH thin films were fabricated on ITO conducting glass substrates with cathodic deposition methods from Fe(NO₃)₃·9H₂O + EDTA salt aqueous solutions, which showed high photocatalytic activity to reduction of Cr(â…¥) only under UV light illumination. Layer-stacked and mixed ZnO-α-FeOOH composited films were fabricated via a consecutive deposition route and co-depositon route from the corresponding bath solution, respectively. Layer-stacked ZnO/α-FeOOH composited films showed higher visile light induced photocatalytic activity thanα-FeOOH and ZnO alone. The amount ofα-FeOOH on the upper layer has a large effect on the photocatalytic activity of the composited films. The enhancement of photocatalytic activity of the composited films should be attributed to the efficient separation of charge carrier photogenerated through the interface between the two semiconductors. Mixed ZnO-α-FeOOH composited films showed higher photocatalytic activity under both UV and visible light illumination compared with pure ZnO films. The content of Fe in the composited films was an important factor affecting their photocatalytic activity. The improvement of photocatalytic activity for composited films was maily due to the electron-capture sink effect from the Fe present in the composited films. When the content of Fe was 3wt% in the films, the degradation rate for MO and reduction rate for Cr(â…¥) were increased from11% and 25% overv the single ZnO films to 39% and 49% over the mixed composited films in the case of visible light, respectively.Layer-stacked composited films ZnO/Cu₂O and mixed composited films ZnO-CuO were fabricated on ITO conducting glass substrates via a consecutive deposition route and a co-depositon route from the corresponding bath solutions, respectively. The results indicated that the fabrication of mixed composited films ZnO-CuO from the aqueous solutions of Zn(NO3)²⁺ Cu (CH3COO)2 with cathodic deposition was feasible. The visible light induced photocatalytic activity of layer-stacked composited films ZnO/Cu₂O was greatly improved compared with Cu₂O and ZnO alone. It was found that the layer order had an important effect on the photocatalytic activity of layer-stacked composited films. In the case of mixed composited films ZnO-CuO , the efficient separation of charge carrier photogenerated through the interface between the two semiconductors should play a more important role in improving the photocatalytic activity than the electron-capture sink caused by Cu_<sup>2+ present in the composited films. When the content of Cu was 35 wt% in the films, the degradation rate for MO and reduction rate for Cr(â…¥) were increased from11% and 25% over the single ZnO films to 20% and 43% over the mixed composited films in the case of visible light, respectively.