A New Carbon/Ferrous Sulfide/Iron Composite Prepared by an in Situ Carbonization Reduction Method from Hemp (Cannabis sativa L.) Stems and Its Cr(VI) Removal Ability

A facile strategy is developed to prepare carbon/ferrous sulfide/iron (C/FeS/Fe) composites by an in situ carbonization reduction method using agricultural waste hemp stems as the carbon precursor and ferrisulfas as the iron source. Under the reductive atmosphere generated from biomass carbonization, ferrisulphas can be in situ directly decomposed and reduced into FeS/Fe at 800 °C existing in the form of nanoparticles embedded in a carbon matrix; so this synthetic procedure is much simpler compared with traditional multistep methods. The C/FeS/Fe composite, as expected, displays an excellent Cr(VI) removal performance with a maximum capacity of 127 mg/g at pH 5 because of the adsorption on its large surface and simultaneous reducing actions that have been evidenced by XPS analysis. Although the presence of FeS/Fe gives rise to an obvious decline of BET surface area, the strong reducibility can compensate for the loss of surface area and significantly enhance Cr(VI) removal especially at a low pH. The synergy between surface adsorption and FeS/Fe reduction under different pH makes this low-cost composite a potential material for treating contaminated water.