Sonophotocatalytic degradation and operational parameters optimization of diazinon using magnetic cobalt–graphene nanocomposite as a catalyst

Abstract

Adopting the hydrothermal method, the cobalt ferrite nanocomposite was loaded onto graphene (G–CoFe2O4) and the material thus produced was first characterized and then employed as a sonophotocatalyst to assist in the degradation of diazinon (DZN) at different operational parameters. Further, response surface methodology was used for the optimization and modeling of the operational parameters. From the statistical analysis of the analysis of variance (ANOVA), the quadratic model was observed to give a good fit with the experimental data, barring the catalyst dose (P value = 0.194) and the initial concentration of DZN (P value = 0.20), significantly affected the efficiency of the DZN degradation. Complete DZN degradation was achieved under the conditions of pH 3, time 100 min, DZN concentration 10 mg/L, temperature 50 °C, and the G–CoFe2O4 dose of 0.99 g/L. Reduction in the DZN degradation rate was observed, falling below 10% during the eight consecutive cycles, giving proof of the stability and adequate recyclability of the G–CoFe2O4. Biodegradability related to the five–day biochemical oxygen demand/chemical oxygen demand (BOD5/COD) ratio increased from 0.15 to 0.58, with the corresponding 90.95% total organic carbon (TOC) and 96.41% COD being removed. The toxicity evaluated using the inhibition growth rate of Escherichia coli (E. coli) showed high ability of the suggested treatment system to lower the toxicity, when compared to photocatalysis and photolysis. On using the analytical methods, the presence of the mineral ions such as NH4+, NO3−, SO42−, and PO43− appeared to act as good indicators of mineralization.