Efficient photo-adsorptive eradication of endocrine disrupting pesticides by chitosan co- decorated metal oxide bio-nanocomposite.

Abstract

Extensive consumption, toxicity and bioaccumulation of malathion (MLT) and lindane (γ-HCH) pesticides collectively attract the world's attention. Herein, the nanocomposite of chitosan wrapped NiO@ZnO was synthesized by a green methodology usingAzadirachta indicaleaves extract. Structural and morphological analysis of chitosan-NiO@ZnO showed hollow sphere-flake shaped image adsorbed on a solid chitosan surface with a large surface area of 73 m2g-1. A decrease in values of lattice strain, dislocation density and crystallite size described the imperfection in crystal geometry and new peaks in FT-IR spectra at 698cm-1 and 448cm-1 of Ni-N and Zn-N, which respectively confirm the coupling. Chitosan-NiO@ZnO and individual nanoparticles (NiO and ZnO) were well-characterized and utilized for degradation MLT and γ-HCH under direct sunlight and dark conditions. The highest degradation of pesticides (above 94%) resulted with 2mg L-1 and 10mg L-1 of MLT (π-π) and γ-HCH, respectively with a 20mg catalyst dose, and pH of ~ 7 under daylight exposure (5h). Chitosan-NiO@ZnO substantially suppressed the half-life of the targeted pesticides (MLT: 0.48h; HCH 0.51h) and demonstrated the first-order kinetics with a high adsorption capacity, Xm (MLT: 14.5mgg-1 and γ-HCH 20.7mgg-1), which also confirmed the strong binding with the pesticides, followed by their conversion into safer and smaller metabolites. The charge separation mechanism was elucidated by UV reflectance and photoluminescence data. Hydroxyl radicals were most frequently responsible for the degradation of pesticides as confirmed by scavenger analysis. The synthesized green-nano photocatalyst showed high reusability (up to 10th cycles), sensitivity and stability within the degradation process, presumably making it suitable for industrial applications.