Eco-friendly removal of direct orange 26 dye using lignin-ZnO composite: Optimization and application

The study explored a sustainable and greener conversion of wheat straw to lignin for wastewater treatment application. Zinc oxide (ZnO) nanoparticles were incorporated into wheat straw extracted lignin (WSEL) to design WSEL@ZnO composite. X-ray diffraction (XRD) patterns revealed a crystalline structure (25 nm) of WSEL@ZnO composite, with enhanced direct orange 26 (DO26) adsorption and photocatalytic efficiency. Fourier transform infrared spectroscopy (FTIR) confirmed the presence of C=C, C=C-C, Zn-O-H, Zn-O, and O-H functionalities, indicating the successful integration of organic and inorganic components within the composite. As synthesized composite was investigated for industrial wastewater decolorization with maximum adsorption capacity of 45.01 mg/g. Taguchi optimization showed 99.04 % dye removal (C_o: 25 mg/L) from aqueous solution, with 0.125 g composite, 2.14 mmol/L H₂O₂, and solar illumination for 6 h, demonstrating the efficiency of WSEL@ZnO under sustainable conditions. The acquired outcomes were analyzed through established isotherm and kinetic models. Results showed that Langmuir isotherm and pseudo-second-order kinetic were the best fitted models to experimental data. The adsorption assays conducted with real textile industry effluents revealed efficiency of 32 % for color removal by WSEL@ZnO composite that can be easily disposed-off since it is biodegradable, and it can be used as soil conditioning agent.