The influence of pyrolytic residence time (1–5 h) at 800 °C on the textural properties of Caesalpinia pulcherrima seed biochar (CPSB 1–5 ) was investigated using nitrogen adsorption–desorption isotherms. The biochar produced after 4 h (CPSB 4 ) exhibited the highest surface area (S BET = 1035.26 m 2 g −1 ) and was selected for the removal of crystal violet dye (CVD) and Pb 2+ from simulated textile effluent. CPSB 4 was characterized using BET, SEM, EDX, and FTIR analyses. Under optimal conditions (70 min, 50 mg L −1 , pH 5.4, 30 °C), removal efficiencies of 98.20% for CVD and 94.25% for Pb 2+ were achieved. Equilibrium data followed the Freundlich isotherm (SNE = 1.109) for CVD and the Langmuir isotherm (SNE = 1.182) for Pb 2+ , while the Dubinin–Radushkevich isotherm indicated physisorption with low mean adsorption energies ( 14 kJ/mol, ΔG° > 2.6 kJ/mol, ΔS° > 0.039 kJ/mol· K) confirmed an endothermic process with increased randomness at the solid–solution interface. CPSB 4 retained over 80% removal efficiency after four regeneration cycles. Optimization using RSM with CCD validated the predictive model and demonstrated that CPSB 4 is a reusable and eco-friendly adsorbent for treating textile wastewater containing mixed contaminants. • Caesalpinia pulcherrima seeds were pyrolyzed to produce high-surface-area biochar. • Biochar showed strong adsorption for crystal violet dye and Pb(II) ions. • Adsorption parameters optimized via central composite design of RSM. • Freundlich and Langmuir isotherms confirmed multilayer adsorption behavior. • Biochar retained >80% removal efficiency after four reuse cycles.
Ani et al. (Thu,) studied this question.