Simultaneous adsorption of Cr(VI) and phenol by biochar-based iron oxide composites in water: Performance, kinetics and mechanism

Highlights: • A novel biochar-based iron oxide composite (FeYBC) was firstly synthesized. • FeYBC exhibited more efficient Cr(VI) and phenol removal than pristine biochar. • Langmuir and pseudo second order models well explain Cr(VI) and phenol adsorption. • Cr(VI) and phenol adsorption were endothermic and exothermic nature, respectively. • The possible removal mechanism of both Cr(VI) and phenol adsorption was proposed. The pollution of heavy metals and organic compounds has received increased attention in recent years. In the current study, a novel biochar-based iron oxide composite (FeYBC) was successfully synthesized using pomelo peel and ferric chloride solution through one-step process at moderate temperature. Results clearly demonstrate that FeYBC exhibited more efficient removal of Cr(VI) and/or phenol compared with the pristine biochar, and the maximum adsorption amounts of Cr(VI) and phenol by FeYBC could reach 24.37 and 39.32 mg g⁻¹, respectively. A series of characterization data suggests that several iron oxides such as Fe₂O₃, Fe⁰, FeOOH and Fe₃O₄ were formed on the FeYBC surface as well as oxygen-containing groups. Thermodynamics study indicates that Cr(VI) and phenol adsorption by FeYBC were endothermic and exothermic processes, respectively. Langmuir adsorption isotherm and pseudo-second order models could better explain the Cr(VI) and phenol adsorption behaviors over FeYBC. The Cr(VI) adsorption might be primarily achieved through the ion exchange and surface complexation and reduction, whereas the π–π interaction and electron donor–acceptor complex mainly contributed to phenol adsorption. The findings indicate that the biochar-based iron oxide composites material was an efficient adsorbent for the remediation of industrial effluents containing Cr(VI) and phenol.