Highly efficient Hg²⁺ removal using sugarcane bagasse-derived biochar/polyaniline nanofiber composite: Adsorption...

In this study, a sustainable sugarcane bagasse-derived biochar/polyaniline nanofiber (SBB/PANI) composite was successfully synthesized via in situ oxidative polymerization and evaluated for efficient Hg²⁺ removal from aqueous solutions. Comprehensive characterization using XRD, FTIR, XPS, SEM, and TEM confirmed the successful integration of polyaniline nanofibers onto the biochar matrix and the presence of abundant surface functional groups. Batch adsorption experiments revealed that the SBB/PANI composite exhibited excellent mercury removal performance, achieving a maximum adsorption capacity of 248.3 mg g^-1 and a removal efficiency of 98.8% under optimal conditions (pH 5, contact time = 60 min, adsorbent dosage = 4 g L^-1). Kinetic data were well described by the pseudo-second-order model, indicating chemisorption-dominated adsorption, while equilibrium data fitted the Langmuir isotherm, suggesting monolayer adsorption on homogeneous active sites. Thermodynamic analysis confirmed that the adsorption process is spontaneous and endothermic. Furthermore, the composite demonstrated excellent selectivity toward Hg²⁺ in the presence of competing metal ions, good regeneration performance over multiple cycles, and high efficiency in treating real industrial wastewater samples. XPS analysis revealed that mercury adsorption is primarily governed by coordination and complexation with nitrogen- and sulfur-containing functional groups, with additional contributions from oxygen-containing groups. These findings highlight the SBB/PANI composite as a promising, low-cost, and environmentally sustainable adsorbent for mercury remediation in water treatment applications.