One-step microwave method synthesis of Fe3O4 nanoribbon@ carbon composite for Cr (VI) removal

Cr(VI) is recognized as a non-biodegradable and toxic pollutant, resulting from manufacturing and industrialization processes, which can trigger considerable environmental problems. Herein, a novel nitrogen, sulfur co-doped carbon with Fe3O4 nanoribbons composite was synthesized by microwave method within 150 s and applied for Cr(?) removal. The raw materials are ferrous sulfate heptahydrate, thiourea and glycerin. Among them, thiourea is served as the rich precursor of carbon nitrogen and sulfur elements and can be used to prepare carbon materials co-doped with N and S elements, while ferrous sulfate heptahydrate can provide iron element for catalyzing rapid preparation of carbon-based materials and self-generation of Fe3O4 nanoribbons. Glycerol not only can be used as a solvent but also can efficiently absorb microwave radiation to make the original quickly heated. The result shows that the addition of Fe3O4 nanoribbons would greatly improve the removal of hexavalent chromium. Meanwhile, the adsorption characteristics were investigated by analyzing by the effects of pH, adsorption kinetics and adsorption isotherms. The result indicates that Fe3O4 nanoribbons can be successfully loaded onto the carbon materials. The maximum adsorption capacity of synthesized material (nitrogen and sulfur co-modified carbon/Fe3O4 (N,S-C/Fe3O4-1) composite) for Cr(?) can be reached at pH = 5, probably due to the protonation of functional groups. The adsorption process follows the pseudo-second-order kinetics with the maximum adsorption capacity of 134 mg/g according to Langmuir isotherm model, manifesting that the Cr(?) adsorption process is close to monolayer chemisorption. In this work, a new nitrogen and sulfur co-doped carbon/Fe3O4 composite with high Cr(?) removal capacity can be successfully prepared within three minutes.