Selective photocatalytic degradation of organic pollutants by CuxS/ZnO/TiO2 heterostructures

Photoactive heterostructures containing CuxS/ZnO/TiO2 have been obtained by spray pyrolysis deposition followed by post-deposition thermal treatment. The ZnO middle layer morphology was tailored by using chemical additives during the deposition. The samples have crystalline structure with average crystallite size around 80 angstrom for metal oxides and 90 angstrom for CuxS. The roughness varies from 27.5 nm for CuxS/dZnO/TiO2 to 33.6 nm for CuxS/pZnO/TiO2 samples. The wettability properties were tested based on the contact angle measurements. The highest surface energy value (106.4 mN/m) corresponding to CuxS/pZnO/TiO2 with 30 min UV irradiation, with a predominant polar component of 85.3 mN/m. The photocatalytic efficiency under UV-Vis light irradiation was evaluated using methylene blue and phenol as pollutants. The highest photocatalytic values (93.4% for methylene blue and 72.3% for phenol) were obtained for CuxS/pZnO/TiO2 heterostructure with successive 30 min UV irradiation at 2 h intervals. The mineralization efficiency was tested using total organic carbon analysis and the results are slightly lower compared with photocatalytic efficiency.