Functionalized lignin magnetic composites and their absorption capability for methylene blue and methyl orange in aqueous solution

Abstract

A novel lignin-based magnetic composite was synthesized using a facile method, with epichlorohydrin (ECH) serving as a cross-linker to bond amino-functionalized magnetic nanoparticles (AMNP), polyethyleneimine (PEI), and sodium lignosulfonate (LS). The synthesized composite (AMNP/LS-PEI) was subjected to characterization through multiple analytical techniques, namely FTIR, XRD, BET, TG, VSM, XPS, FE-SEM, EDS, HRTEM, and TEM. Following the synthesis, a thorough investigation was conducted into the composite’s adsorption capabilities for methylene blue (MB) and methyl orange (MO) dyes through batch adsorption, taking into account pivotal factors, including pH, contact time, solution concentration, and temperature. The experimental data suggested that the adsorption of MO and MB onto AMNP/LS-PEI was in good accordance with the Langmuir isotherm model. The AMNP/LS-PEI demonstrated maximum adsorption capacities (Q_max) of 482.7 mg g⁻¹ for MO and 375.6 mg g⁻¹ for MB, respectively. The MB and MO-adsorption kinetics onto AMNP/LS-PEI closely fit the pseudo-second-order model. Furthermore, the thermodynamic analysis revealed that the adsorption process of dyes onto AMNP/LS-PEI was an endothermic one. Upon six adsorption–desorption cycles, AMNP/LS-PEI demonstrated sustained adsorption capacity, achieving removal rates of 81.3% for MB and 77.1% for MO, respectively. The potential advantage for practical applications lied in its highly selective adsorption capability for mixed solutions of MB and MO. Specifically, at a pH of 4, MO was preferentially adsorbed, whereas at a pH of 8, MB was favored for adsorption. In addition, the adsorption mechanism of AMNP/LS-PEI toward dyes was explored using FTIR and XPS, and was found to be mainly ascribed to the electrostatic interaction, hydrogen bonding interaction, and cation exchange.

Graphical abstract