Waste‐to‐resource conversion of sugar beet pulp into sulfonated biochar for efficient dye adsorption

Abstract This study presents a sustainable “waste‐to‐resource” approach by converting sugar beet pulp into a high‐performance sulfonated biochar (CSBP) through a streamlined chemical carbonization route. By utilizing concentrated sulfuric acid, simultaneous carbonization and surface functionalization were achieved under mild conditions, eliminating the need for high‐temperature pyrolysis. Comprehensive physicochemical characterization revealed a highly porous carbonaceous framework enriched with sulfonic acid groups, yielding a fine‐grained adsorbent (<20 μm) with high thermal stability and a carbon content of approximately 85 wt%. Batch adsorption experiments were systematically performed to evaluate the effects of adsorbent dosage, solution pH, initial dye concentration, contact time, and temperature. The adsorption process exhibited high removal efficiency (>90%) at the natural pH of the dye solution, eliminating the need for pH adjustment. Kinetic analysis demonstrated that the adsorption behavior followed a pseudo‐second‐order model, indicating that chemisorption governs the rate‐controlling step, with an activation energy of 9.01 kJ/mol. Equilibrium data were best described by the Langmuir isotherm, confirming monolayer adsorption on a homogeneous surface, with a maximum adsorption capacity of 2.70 mmol/g at 55°C. Thermodynamic parameters (Δ H ° = +9.301 kJ/mol and negative Δ G ° values) indicated that the adsorption process is endothermic and spontaneous. The adsorption mechanism was attributed to the synergistic contribution of electrostatic interactions, π–π stacking, surface complexation involving sulfonic and oxygen‐containing functional groups, and pore‐filling effects. Overall, this study demonstrates that sulfuric acid‐carbonized sugar beet pulp is a highly effective and environmentally benign adsorbent for cationic dye removal.