Improving the efficiency of Cr(vi) reduction and adsorption by Fe3O4 using ZSM-5 zeolite support prepared through various methods†

Abstract

The study involved the synthesis of magnetite (Fe₃O₄) and zeolite-supported Fe₃O₄ (Fe/Z) using co-precipitation (COP) and hydrothermal (HYD) methods which proved effective for removing Cr(VI) from contaminated water. X-ray diffraction (XRD) analysis showed that the Fe₃O₄ phase had a cubic crystal structure. The COP method resulted in lower crystallinity compared to the HYD method. The different preparation methods also led to variations in the morphologies and sizes of the Fe₃O₄ particles. The HYD-prepared sample exhibited a uniform spherical shape with sizes of 400–500 nm, while the COP-prepared samples showed rod-like and granule shapes with smaller particle sizes of 20–50 nm. The study also investigated the adsorption ability and reducibility of Cr(VI) on the Fe₃O₄ adsorbents. It was found that the crystallinity, shapes, and sizes of Fe₃O₄ significantly influenced the adsorption capacity and stability of the Cr-adsorbed species. Additionally, this work demonstrated that the zeolite supports enhanced the adsorption capabilities of Fe₃O₄, particularly in the HYD-prepared samples, achieving an adsorption capacity of 2.33 mg per g Fe by creating stable Cr-adsorbed species. X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) confirmed the Cr species adsorbed on Fe/Z_HYD, identifying ion-exchange lattice structures of Fe_3−xCr_xO₄ and Fe_1−xCrOOH as the most stable forms. This study provides insights into the potential of Fe₃O₄/ZSM-5 zeolite for Cr(VI) remediation.