Sunlight-mediated efficient remediation of organic pollutants from water by chitosan co-decorated nanocomposites of NiO loaded with WO3: Green synthesis, kinetics, and photoactivity

Azo dyes such as Tropaeolin OOO (TOOO) and Eriochrome black T (EBT) are used in various industrial and laboratory applications. However, their recalcitrant properties make them toxic chemicals and require efficient removal-strategy based on polymer decorated semiconductor nanocomposite. Herein, photodegradation of TOOO and EBT in water was investigated at different reaction parameters through NiO@WO3-chitosan synthesized by green procedure using A. indica. PXRD spectra peaks show semi-crystalline behaviour with spherical morphology and chitosan around metal oxide. In FT-IR, New spectral peaks observed at 1023 cm−1, 870 cm−1, and 540 cm−1 vibration indicated between Ni-O-W, Ni-N, and W-N confirmed effecting coupling. Both dyes (10 mg/L) were found completely colourless within 3 h under sunlight with pH of 7 at 20 mg of catalyst load. Difference in max degradation of 96 % and 92 %, respectively to TOOO and EBT dye credit to structure difference. 1st-order reaction kinetics following early Langmuir adsorption and degradation at optimum condition rate constant k (0.26–0.19-min−1) and half time t1/2(2.68––3.64 min−1). Efficiency of NiO@WO3-chitosan was maintained due to its fine morphology with elevated surface-area (75 m2g−1), large negative zeta potential (−29.5 mV), and lesser value of band distance (2.1 eV). Involvement of •OH, O2–• and holes in photocatalysis mechanism to break complex molecules of TOOO and EBT was revealed in Scavenger analysis. After degradation, small-safer metabolites were confirmed by LC-MS. Reusability up to 8th cycle of NiO@WO3-chitosan without photoactivity reduction makes it a cost-effective cum sustainable composite for industries and wastewater pollutants removal with good surface properties.