Degradation studies on Paraquat and Malathion using TiO2/ ZnO based photo catalyst

Paraquat, a herbicide and malathion, an insecticide are pesticides that are always polluting our water system. Thus a lot of efforts has been conducted to treat the polluted water. The latest technology proposed is using photo catalyst. In this study, ZnO and TiO2 were used as photo catalysts to degrade the pesticide in the presence of UV light (λ=354 nm). The photodegradation rate was measured using UV-Visible spectrophotometer and TOC analyzer. Malathion showed the absorption peak at λ=210 nm while for paraquat at λ=258 nm. The best coupled photo catalyst for degrading malathion solution is ZnO/ TiO2 with % weight ratio 1:0.05 and the best coupled photo catalyst in degrading paraquat solution is TiO2/ ZnO with % weight ratio 1:0.03. The result shows that Fe2+ ion present in the reaction mixture was better than Fe3+ ion present as a dopant (which is added during the catalyst preparation). The optimum photo catalyst calcination temperature for degrading paraquat and malathion were 550 degree Celsius for TiO2 and 500 degree Celsius for ZnO. The physical properties of the best catalyst were characterized using SEM, XRD, UV-Vis-NIR spectrophotometer and ellipsometers. By increasing the calcination temperature up to 600 degree Celsius, XRD data showed the transformation of TiO2 anatase to rutile phase while for ZnO, the increment of the intensity of ZnO catalyst was observed, indicating that, the quality of ZnO wurtzite crystal was improved. The thicknesses for ZnO, ZnO/ TiO2 1:0.05 and ZnO/ TiO2 doping with Fe3+ thin film were 130.57 nm, 150.68 nm and 153.84 nm respectively. The band gap energy values measured using UV-Vis NIR were in the range of 2.95 to 3.09 eV. (author)