Lignin-Based Nanospheres as Environmental Remediation Platforms for Anionic Dye Contaminants

Modern manufacturing of textiles, pharmaceuticals, food, cosmetics, plastics, paper, etc. involves the utilization of anionic and cationic dyes that lead to significant water contamination. Recent research has explored the use of nanomaterials toward developing nanoadsorbents for water decontamination caused by industrial pollution. Here, we report on a novel platform for anionic dye remediation, consisting of a polyethylenimine-functionalized lignin nanosphere (PEI-LNS). The designed nanomaterial shows significant ability to adsorb an anionic dye selected as a proof-of-concept-Sulforhodamine B, from aqueous solutions. The PEI lignin nanoadsorbents (PEI-LNS) showed a better ability to adsorb Sulforhodamine B sodium salt (SBSS) when compared to the raw lignin nanosphere adsorbent (LNS), especially in acidic conditions. The nanomaterial was characterized through transmission electron microscopy, scanning electron microscopy, Brunauer-Emmett-Teller surface area analysis, elemental analysis, zeta potential, thermogravimetric analysis, Fourier transform infrared spectroscopy, and nuclear magnetic resonance. The impacts of ionic strength, contact time, pH, and adsorbent concentration have been evaluated. The ability of PEI-LNS to adsorb SBSS was found to be consistent with Langmuir isotherms and pseudo-second-order kinetic models. The PEI-LNS could be recycled three times, reaching a good (85%) adsorbing capacity even in the third cycle. The study demonstrates that PEI-LNS has a strong affinity as a novel adsorbent for anionic dyes and could be employed in environmental cleanups pertaining to such contaminations.