Effective removal of toxic methylene blue dye using ZnO/nanolignin composite: kinetic, isotherm and thermodynamic study

Lignin nanoparticles (LNp) were prepared by the solvent-non-solvent method from lignin extracted from bagasse. Investigation of particle size revealed that the obtained LNp has size of 282 nm. However, it was used as a bio-template during the synthesis of ZnO to form ZnO/LNp. Characterization of the formed materials was performed by FTIR, XRD, and XPS. A scanning electron microscope is used to study the morphology of both LNp and ZnO/LNp. The prepared nanocomposite is tested as an adsorbent for cationic dye from contaminated water. The results confirmed the efficiency of the nanocomposite to remove methylene blue (MB) from water as ZnO/LNp removed nearly 97% of MB while LNp showed only 93% dye removal. Moreover, the investigation of adsorption kinetics confirmed that the adsorption can be described by pseudo-second-order mechanism. The uptake of MB was increased with elevated temperature, indicating that the adsorption of MB is an endothermic process, and Freundlich isotherm is more applicable than Langmuir isotherm. The low value of Δ H o was found to be lower than 40 kJ/mol. Moreover, Dubinin–Radushkevich (D-R) relations are utilized to determine the nature of adsorption. The parameters of D-R isotherm revealed that the value of E = 3.9 and 4.9 (kJ/mol) which indicated that poor correlation coefficient and confirming that the MB adsorption process occurs via a physical adsorption mechanism.