Synthesis of nitrogen-doped activated carbon from agricultural wastes of durian peel for Cr (VI) removal from water

Agricultural waste valorization provides a sustainable route for producing low-cost adsorbents for water treatment. In this study, durian peel waste was converted into nitrogen-doped activated carbon (N-doped AC) via post-treatment urea impregnation, yielding materials with nitrogen contents of 6, 9, and 12 wt%. The structural and surface properties were characterized using XRD, BET, CHNS, XPS, and X-ray absorption spectroscopy (XANES/EXAFS). Increasing nitrogen content enhanced the surface area, nitrogen functionalities, and overall adsorption performance. The N(12)-doped AC exhibited the highest Cr(VI) uptake, with a maximum adsorption capacity of 215 mg/g under optimal conditions (pH 2, 0.1 g/L, 120 min). The adsorption followed the Langmuir isotherm (R² = 0.999), indicating monolayer coverage, and the pseudo-second-order model (R² = 0.996), suggesting chemisorption. Spectroscopic analyses confirmed the active role of nitrogen groups in Cr(VI) binding and revealed partial reduction to Cr(III). The N(12)-doped AC maintained approximately 90% removal efficiency after five regeneration cycles, demonstrating good stability. These results highlight the potential of durian peel–derived N-doped AC as an efficient adsorbent for Cr(VI) remediation and provide insights into the influence of nitrogen functionalities on adsorption and reduction mechanisms. • N-doped AC from durian peel achieves high Cr(VI) adsorption of 215 mg/g • Langmuir and pseudo-second-order models best describe the adsorption process. • XANES/EXAFS confirm stable Cr–N bonding and chemisorption mechanism. • Maximum Cr(VI) adsorption capacity: N (12) > N (9) > N (6) > activated carbon. • N (12) doped-AC maintains 95% removal efficiency over five regeneration cycles.