Synthesis of Magnetic Lignin-Based Hollow Microspheres: A Highly Adsorptive and Reusable Adsorbent Derived from Renewable Resources

Lignin, a byproduct of the wood-pulping industry, is mostly treated as a noncommercialized waste product. Therefore, it is significant to study its potential for the conversion of this renewable and sustainable resource into high-valued chemicals and materials. In this study, a renewable lignin-based material with high performance in wastewater treatment has been explored on account of its satisfactory properties and being environmentally friendly. Herein, lignin hollow microspheres (LHM) were facilely prepared from esterified organosolv lignin with maleic anhydride (MA) via self-assembly in the mixed tetrahydrofuran–Fe3O4 nanoparticles aqueous media. Moreover, the magnetic lignin spheres (MLS) were also successfully fabricated by introducing Fe3O4 nanoparticles. The structural changes of esterified lignin polymers were identified and morphology and property of obtained LHM and MLS were characterized by means of TEM, SEM, VSM and FT-IR. In addition, the adsorption capacities of MLS for methylene blue and Rhodamine B from aqueous solutions were also comparatively investigated. It was observed from SEM and TEM images that the LHM from larch lignin exhibited uniform spherical and dense surface, but that from poplar lignin was not rigid enough to keep the perfect spherical shape and partially collapsed. The adsorption capacity results showed that the MLS from larch lignin exhibited better adsorption properties for methylene blue (31.23 mg/g) and Rhodamine B (17.62 mg/g) than that from poplar lignin (25.95 and 15.79 mg/g, respectively). Simultaneously, the adsorption kinetics and adsorption isotherm experiments indicated that the data were agreed well with the pseudo-second-order and Langmuir model, respectively. Moreover, after three cycles of desorption, the removal efficiencies of the MLS from larch and poplar lignin could still reach more than 98% and 96%, respectively. Therefore, the developed magnetic lignin-based hollow microspheres has shown a great potential as a low-cost, highly adsorptive and reusable adsorbent for the applications in the wastewater treatments.