Nitrogen-doped carbon from cellulose-based palm empty fruit bunches for adsorption of heavy metal chrome (VI) ions in aqueous solution

Wastewater containing hexavalent chromium (Cr(VI)) poses severe environmental and health hazards. Nitrogen-doped carbon (N-doped carbon) from biomass offers a sustainable adsorbent due to its tunable surface chemistry and porosity. Palm empty fruit bunches (PEFB) were here explored for Cr(VI) adsorption. N-doped carbon was synthesized via pyrolysis using PEFB-derived cellulose aerogels and urea as a nitrogen source (2, 4, and 6 g). Characterization (FTIR, BET, SEM–EDS, XRD) confirmed that the 4 g urea sample exhibited the most favorable properties, with a highest of surface area and atom % nitrogen. Batch adsorption revealed optimal performance at pH 6 with 400 ppm initial concentration and 40 min time contact, achieving a highest experimental adsorption capacity (q e ) of 455 mg·g⁻¹ . Adsorption followed the Freundlich isotherm, indicating heterogeneous multilayer adsorption, while kinetics fitted the pseudo-second-order model, suggesting chemisorption. Mechanistic analysis showed that protonated pyridinic nitrogen created positively charged sites enabling electrostatic interaction with HCrO₄⁻, Cr₂O₇²⁻, and CrO₄²⁻. These findings demonstrate the potential of low-cost PEFB-derived N-doped carbon as an efficient and sustainable adsorbent for heavy metal remediation.