Adsorption of chromium from aqueous solution by magnetite modified N-doped carbon based on palm empty fruit bunches

Abstract

Hexavalent chromium (Cr(VI)) is a very hazardous and carcinogenic contaminant frequently present in wastewater from industrial processes. This study aimed to evaluate the performance of Magnetite Modified N-Doped Carbon (N-doped carbon@Fe₃O₄), synthesized from palm empty fruit bunch (PEFB) via sol–gel processing, pyrolysis, and magnetite incorporation, for the reduction of Cr(VI) from aqueous solutions. The adsorbent was completely characterized using FTIR, SEM, and XRD, verifying an effective integration of nitrogen functionalities with Fe₃O₄. Batch adsorption tests at pH 6 and Cr(VI) initial concentration of 400 mg/L showed a maximum adsorption capacity of 547.67 ± 0.299 mg/g, with optimal contact time achieved within 30 min. Kinetic analysis indicated an excellent compatibility with the pseudo-second-order model and adsorption isotherm conformed to the Freundlich model with heterogeneity factor (n) of 0.52. It indicated a heterogeneous adsorption surface with chemisorption. The proposed adsorption mechanism suggests that Cr(VI) removal occurred via a synergistic process involving electrostatic interaction between protonated pyridinic nitrogen and Cr(VI) oxyanions, surface complexation with Fe-OH groups, and partial reduction of Cr(VI) to Cr(III).The formation of Cr₂O₃ detected by XRD after adsorption further confirmed the reduction pathway. The results indicate that N-doped carbon@Fe₃O₄ is an exceptionally effective adsorbent, presenting significant potential for the remediation of Cr(VI) in aquatic environments.

Graphical Abstract