Facile synthesis of tea waste/Fe3O4 nanoparticle composite for hexavalent chromium removal from aqueous solution

Abstract

The modification of biomass waste, as a multifunctional composite, has received tremendous attention for resource utilization and recycling. In this study, tea waste, which is a high level generator of biomass waste, was loaded with nano-Fe₃O₄ particles to prepare a magnetic tea waste/Fe₃O₄ (TW/Fe₃O₄) composite through a facile chemical co-precipitation approach. BET, SEM, TEM, XRD, magnetic properties, FTIR, XPS were used to characterize the TW/Fe₃O₄ composite. A superparamagnetic TW/Fe₃O₄ composite (Fe₃O₄: about 20 nm) was successfully synthesized and possessed the advantages of tea waste and nano-Fe₃O₄ particles. A chromium(VI) adsorption experiment showed that this material has a strong adsorption capacity for aqueous chromium ions, which reached 75.76 mg g⁻¹ based on the Langmuir model. The adsorption process could be well fitted by a pseudo-second-order kinetic model and Langmuir, Temkin and Dubinin–Radushkevich (D–R) isotherm models, and was spontaneous and endothermic according to the thermodynamic analysis. The TW/Fe₃O₄ composite revealed good reusability and the removal rate was more than 70% after five recycling cycles. The mechanism of Cr(VI) removal involved electrostatic attraction, reduction process, ion exchange, surface complexation, etc. 70% of Cr(VI) was reduced to Cr(III) in this investigation. This study indicated that a TW/Fe₃O₄ composite could be an attractive option for heavy metal treatment.