Chitosan/nano-lignin based composite as a new sorbent for enhanced removal of dye pollution from aqueous solutions

The utilization of renewable and functional group enriched nano-lignin as bio-additve in fabricating composite has become the focus of attention worldwide. Herein, lignin nanoparticles in the form of hollow spheres with the diameter of the order of 138 ± 39 nm were directly prepared from agro-industrial waste (palm kernel shell) using recyclable tetrahydrofuran in an acidified aqueous system without any chemical modification steps. We then fabricated a new chitosan/nano-lignin composite material as highly efficient sorbent, as demonstrated by efficient removal (~83%) of methylene blue (MB) dye under natural pH conditions. The adsorption process obeyed pseudo-second-order kinetics and adequate fitting of the adsorption data using Langmuir model suggested a monolayer adsorption with a maximum adsorption capacity of 74.07 mg g^-1. Moreover, thermodynamic study of the system revealed spontaneous and endothermic nature of the sorption process. Further studies revealed that chitosan composite with nano-lignin showed better performance in dye decontamination compared to native chitosan and chitosan/bulk lignin composite. This could essentially be attributed to synergistic effects of size particularity (nano-effect) and incorporated functionalities due to lignin nanoparticles. Recyclability study performed in four repeated adsorption/regeneration cycles revealed recyclable nature of as-prepared composite, whilst adsorption experiments using spiked real water samples indicated recoveries as high as 89%. Based on this study, as-prepared bio-nanocomposite may thus be considered as an efficient and reusable adsorptive platform for the decontamination of water supplies.