Nanophotocatalytic UV degradation system for organophosphorus pesticides in water samples and analysis by Kubista model

AbstractThe photocatalytic degradation of organophosphorus pesticides like methyl parathion (MP) and parathion (PA), under UV irradiation is studied using synthesized Zinc oxide (ZnO) nanocatalyst. Two cases were considered for removal of organophosphorus (OP) pesticides such as only UV (i.e. direct photolysis) and UV–ZnO nanocrystal. The Langmuir–Hinshelwood (L–H) relationship between the initial rate and the initial concentration indicates that the reaction occurs with the adsorbed substrate. Factors affecting the kinetics of the process such as quantum yield, electrical energy per order (EEO), dosage of nanophotocatalyst and L–H model have been discussed. The optimal conditions for degradation were obtained using 85mgl−1 ZnO, 40% O2 (v/v) with rate constants L–H adsorption equilibrium constant (Kp=0.127 for MP and 0.122 for PA) and rate constant of surface reaction (Kc=0.212 for MP and 0.204 for PA). The kinetics of disappearance of OP pesticides (i.e. MP and PA) in water suspension using ZnO nanophotocatalyst illuminated at λ=253.7nm and examined. The quantum yield values for photodegradation of pesticides by photolysis and UV–ZnO process under the illumination of UV at 253.7nm is calculated as 0.00072, 0.012 for MP; 0.00068 and 0.01 for PA. The EEO values for degradation of pesticide by photolysis for UV–ZnO was found to be 20,006, 1392.4kWhm−3 for MP; 19,089 and 1387.2kWhm−3 for PA