Chromium (VI) adsorption and reduction by humic acid coated nitrogen-doped magnetic porous carbon

A humic acid coated nitrogen-doped magnetic porous carbon (HA-N-MPC) adsorbent was successfully synthesized using lignin isolated from black liquor as the main carbon source. SEM, TEM, FT-IR, XPS and N-2 physisorption measurements showed the HA-N-MPC to possess a high specific surface area, a porous three dimensional structure with magnetic Fe3O4 nanoparticles uniformly embedded in the N-doped porous carbon matrix, and an abundance of surface functional groups for metal ion sorption. Cr (VI) adsorption experiments were subsequently carried out in aqueous solution at pH 2 using HA-NMPC as the adsorbent. Results revealed that HA-N-MPC had a high adsorption capacity of 130.5 mg g(-1) for Cr(VI), with partial reduction of toxic Cr(VI) to nontoxic Cr(III) occurring on adsorption. The adsorption kinetics and equilibrium adsorption isotherm determined for Cr(VI) on HA-N-MPC obeyed the pseudo-second-order model and Langmuir isotherm model, respectively. After magnetic separation from the sorption medium and regeneration, HA-N-MPC retained excellent adsorption performance for Cr(VI). (C) 2019 Elsevier B.V. All rights reserved.