Functionalized lignin-based-adsorbent derived from black liquor in the paper industry for superior adsorption characteristics.

Lignin's availability in large amounts from industrial black liquor as waste from the paper industry is still a problem. On the other hand, its utilization potentials as a green low-cost adsorbent for the effective removal of toxic organic dye from industrial wastewater has become a topic of great interest but remains quite challenging. In this sense, this work aimed to evaluate the feasibility of removing the reactive green dye (RGD) onto the functionalized lignin-based adsorbent (FLA) by the acidic method. The kinetic study suggested the adsorption process confirmed to a pseudo-second-order-kinetic and intra-particle diffusion models. Also, the isotherm results showed that the FLA exhibited multi-layer adsorption. Meanwhile, the results of FTIR and SEM showed that the RG-19 adsorption mechanisms were electrostatic interaction, hydrogen bonding, π-π stacking, and physical adsorption. Thermodynamic parameters were also evaluated and their values indicated that adsorption of RG-19 onto FLA is an exothermic process and spontaneous in nature. As a renewable, low-cost, and natural biomass material, FLA has the potential to be used as a promising sustainable and economic application of biomass and will inspire more scholars to investigate solutions to the problem of contaminated water resources.