Mineralization of diazinon by low-cost CuO-Kaolin nanocomposite under visible light based RSM methodology: Kinetics, cost analysis, reaction pathway and bioassay

Abstract

A convenient and low-cost co-precipitation method was utilized for stabilization of CuO nanoparticles on Kaolin. The prepared CuO-Kaolin was characterized by XRD, FT-IR, SEM, EDX and pHPZC techniques. In this empirical study, response surface methodology (RSM) based central composite design (CCD) was applied for optimization of operational factors in the photocatalytic removal of Diazinon (DZ). Under optimum conditions, i.e. initial pH=7, initial DZ concentration=30 mg L-1, photocatalyst amount=0.4g L-1 and in the presence of oxalic acid, folic acid and sodium carbonate=5 mg L-1, about 87.23 % DZ removal was achieved by CuO-Kaolin after 180 min of reaction. The ANOVA results of the polynomial model prove that the model is quite meaningful (F-value> 0.001 and P-value< 0.0001). Further, estimated electrical energy per order consumption (EEO) for visible light (VIS)/CuO-Kaolin system was calculated as 213.66 kWh m−3 with operational cost (OC) utilization of 52.053 USD kg−1 that was revealed this process is highly feasible and economic comparing with other photocatalytic processes (VIS/CuO, VIS/Kaolin and VIS). Ten cycle experiments confirmed that the CuO-Kaolin propounded a satisfied stability and recycling potency. By applying the OFAT technique, 96.05 % of DZ degradation and 79.19 % of DZ mineralization could be achieved after 180 min. The five main compounds produced during the VIS/CuO-Kaolin embracing 2-isopropyl-6-methyl-4-pyrimidinol (IMP), diethyl phosphonate, diazoxon, hydroxydiazinon, and diazinon methyl ketone are formed in the path of DZ degradation. The results of toxicity in the photocatalytic removal of DZ by D. magna showed LC50 and TU 48 h equal to 18.79 and 5.32 vol percent.