One‐Step Preparation of N‐doped Porous Carbon from Paper Sludge and its Excellent Adsorption Performance for Chromium

Abstract Paper sludge can be directly pyrolyzed into activated carbon, but its adsorption capacity remains limited. This study presents a simple ethylenediamine dihydrochloride‐assisted activation method to transform paper sludge into nitrogen‐doped porous carbon adsorbents for efficient hexavalent chromium (Cr(VI)) removal. Characterization results confirm that ethylenediamine dihydrochloride effectively introduces nitrogen dopants and significantly increases the specific surface area. The best‐performing nitrogen‐doped porous carbon exhibits a large specific surface area (1244 m 2 /g) and a high Cr(VI) adsorption capacity (193.6 mg/g). Adsorption experiments reveal a spontaneous, endothermic chemisorption process following pseudo‐second‐order kinetics and a Langmuir model. X‐ray photoelectron spectroscopy (XPS) analysis further indicates that Cr(VI) is reduced and adsorbed onto nitrogen‐containing functional groups in the porous carbon. This work demonstrates a chemical activation approach for converting paper sludge into high‐performance porous carbon adsorbents, offering a valuable solution for hazardous metal removal and paper sludge valorization.