Facile and fast synthesis of nitrogen-doped biocharsupported nanoscale ferrous sulfide composite for efficient removal of aqueous Cr(VI)

In this work, a novel nitrogen-doped biochar-supported nanoscale ferrous sulfide composite (nFeS@NBC) was fabricated by pyrolyzing corn straw pretreated with Mohr’s salt through a one-step carbothermic reduction process, which was applied in the efficient disposal of hexavalent chromium (Cr(VI))-containing wastewater. The key effects of impregnation ratio and pyrolysis temperature on the properties and removal performance of nFeS@NBC for Cr(VI) were subsequently investigated. The properties of nFeS@NBC were characterized through a series of techniques. It indicated that FeS nanoparticles were successfully loaded and −NH₂ functional groups effectively formed on the biochar surface, which enhanced the removal performance of nFeS@NBC for Cr(VI) from wastewater. The removal performance of nFeS@NBC for Cr(VI) was systemically evaluated at different experimental conditions and in the presence of major co-existing ions. Adsorption kinetics was best suited to the pseudo-second-order model. Additionally, Langmuir isotherms model could well explain the adsorption experiment data for the removal of Cr(VI) by nFeS@NBC with the highest adsorption capacity of 373.85 mg·g⁻¹. According to the thermodynamic study, nFeS@NBC dominated the adsorption of Cr(VI) through an endothermic and spontaneous process. The adsorption and reduction served as the main removal mechanisms of nFeS@NBC for aqueous Cr(VI). nFeS@NBC could be used repetitively for its regeneration. Thus, the above results showed that it was feasible and efficient to remove Cr(VI) by nFeS@NBC, providing a potential green material for environmental remediation.