A novel modified lignin-based adsorbent for removal of malachite green and Pb2+ ions from wastewater

The development of eco-friendliness and cost-effectiveness featured lignin-based adsorbents is of great interest for the removal of organic dyes and heavy metal ions. In this work, lignin was modified by 5-sulfosalicylic acid using epichlorohydrin and formaldehyde as across-linking agents. Then the prepared lignin product (C-SAL) was applied as an adsorbent for the malachite green (MG) and Pb2+ ions, and the adsorption performances were investigated in detail via a series of experiments. The isotherm and kinetic models indicated that the chem-adsorption for both MG and Pb2+ ions occurred in monolayer, and the thermodynamic models displayed that all processes were endothermic and spontaneous. Based on the calculation, the maximum adsorption capacities (Qmax) of C-SAL could achieve 203.45 and 115.67 mg/g for MG and Pb2+ ions, respectively, which are superior to many other biomass-based adsorbents. Besides, 94.52 % and 88.27 % of initial adsorption capacities could be retained after eight cycles for MG and Pb2+ ions, respectively. Additionally, the adsorption mechanism was also comprehensively investigated by the structural change characterizations, MESP analysis and DFT calculations. The results showed that the adsorption for MG molecules took place through electrostatic, hydrogen bonding and π-π interactions, while that for Pb2+ ions was attributed to the synergistic effect of complexation, hydrogen bonding and electrostatic interactions. In summary, C-SAL has the advantages of satisfied adsorption capacity and good recyclability, which can provide a low-cost and high-efficiency way for adsorptions of pollutants in practical applications.