Functionalized lignin-based magnetic adsorbents with tunable structure for the efficient and selective removal of Pb(II) from aqueous solution

Abstract With the increasing concern in sustainable development and environmental governance, the biomass-based magnetic materials containing sufficient active sites and regular structure can be regarded as the high-performance adsorbents for removal of heavy metal pollutants from wastewater. In this study, we reported the tunable covalent binding of lignin onto amine-functionalized magnetic nanoparticles (AMNP) using cyanuric chloride as a chemoselective cross-linker. The chemical structures, morphologies, and magnetic properties of the synthesized lignin-based magnetic adsorbents (L1@MNP and L2@MNP) were comprehensively characterized. Batch adsorption experiments were conducted to investigate various effecting factors, including pH, contact time, solution concentration and temperature. With the higher component ratio of AMNP/lignin, L1@MNP displayed higher adsorption affinity (qmax = 111.23 mg/g) and selectivity towards Pb(II) than L2@MNP (qmax = 81.97 mg/g). The adsorption kinetics agreed well with the pseudo-second-order kinetic model, and the thermodynamic adsorption behaviors were found to be an endothermic and spontaneous process. In addition, the presence of magnetic cores in the network facilitated the fast recovery of both two magnetic adsorbents after the adsorption process, owing to the good superparamagnetic properties for L1@MNP (40.06 emu/g) and L2@MNP (26.95 emu/g). Furthermore, the core–shell magnetic adsorbents also showed superior stability even in an acidic solution, of which the removal efficiency could well maintain over 85% after 5 cycles. This work provides a facile strategy for the design and synthesis of lignin-based adsorbents with flexible nanoparticles as a building block for the potential application prospects in Pb(II) removal from wastewater.