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 using Azadirachta indica leaves 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 698 cm-1 and 448 cm-1 of Ni-N and Zn-N, respectively confirms the coupling. The chitosan- NiO@ZnO nanocomposite with a reduced band gap due to the generation of new energy levels in the vicinity of of conduction and valence band. Chitosan-NiO@ZnO and individuals 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 2 mg L-1 and 10 mg L-1 of MLT (π_π) and γ- HCH, respectively with a 20 mg catalyst dose, and pH of ~7 under daylight exposure (5 h). Chitosan-NiO@ZnO substantially suppressed the half-life of the targeted pesticides (MLT: 0.48 h; HCH 0.51 h) and demonstrated the first- order kinetics with a high adsorption capacity, Xm (MLT: 14.5 mg g-1 and γ- HCH 20.7 mg g-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.

Green synthesis of silver‐doped metal hexacyanoferrates nanostructures for efficient cleanup of endocrine‐disrupting pesticides

“…Through literature surveys, it was observed that Ag doped nanocomposites such as Ag@ZnONSt, 19 Ag/LaTiO 3, 20 CuO/TiO 2 /PANI, 21 Ag‐CuS, 22 Ag/ZnO, 23 and graphene/Ag‐doped TiO 2 24 are synthesized for the removal of selected pesticides shown Table 2. Because of environmental concerns and the implication of green chemistry, there is the trend for the synthesis of doped nanoparticles using plant feedstock (plants, roots, flowers, leaves) which contain several types of phytochemicals such as polyphenols, cellulose, saponins, sugars, flavonoids, and amino acids 25–31 . Therefore, it was envisioned to synthesize silver‐doped metal hexacyanoferrates (Ag@MHCFs) via the green route.…”