Humic acid modified lignin-based microspheres to enhance acid Orange 7 dye and tetracycline removal from wastewater

This study investigates the adsorption performance of humic acid-functionalized lignin-based microspheres (HA@LGMS) in eliminating Acid Orange 7 (AO7) and tetracycline (TC) contaminants from wastewater. Lignin, a residual material from pulp manufacturing processes, was utilized to synthesize lignin-based microspheres (LGMS) via reversed-phase suspension polymerization. Subsequently, humic acid was incorporated into LGMS to enhance their adsorption capacity. Comprehensive material characterization involving SEM, FTIR, XPS, etc. revealed the structural features and surface chemistry of the microspheres. Systematic batch adsorption studies examined the adsorption kinetics, isotherms, and thermodynamics of AO7 and TC onto HA@LGMS. Analysis demonstrated chemisorption-driven mechanisms supplemented by boundary layer diffusion and pore penetration phenomena. The adsorption processes were spontaneous and endothermic, with higher temperatures favoring adsorption. HA@LGMS exhibited high adsorption capacities for AO7 (434.81 mg/g) and TC (93.98 mg/g), outperforming many existing adsorbents. The adsorbent also demonstrated excellent reusability and stability in multiple adsorption-desorption cycles. Moreover, HA@LGMS effectively removed AO7 and TC from real water samples, highlighting its potential for practical wastewater treatment applications. This study provides a sustainable and cost-effective solution for the removal of dyes and antibiotics from wastewater using lignin-based materials.