Microstructural evolution and catalytic properties of novel high-entropy spinel ferrites MFe2O4 (M= Mg, Co, Ni, Cu, Zn)

Abstract

A novel class of high-entropy (HE) spinel ferrites (Mg0.2Co0.2Ni0.2Cu0.2Zn0.2)Fe2O4, have been successfully synthesized by the solution combustion synthesis method followed by heat-treatment at 500–1500 °C. The resultant spinel ferrites were systematically investigated by various methods including XRD, SEM, TEM, EDS, Raman spectra, etc. It was demonstrated that the entropy drives a reversible transformation between a single-phase state and multiphase. And the entropy predominates the thermodynamic landscape. The as-fabricated high-entropy (Mg0.2Co0.2Ni0.2Cu0.2Zn0.2)Fe2O4 solid solution is single-phase with homogeneous transition-metal element distribution. Moreover, a trade-off between grain growth and crystallization during heat-treatment process; the average grain size of product is only 352.96 nm after being annealed at 1000 °C for 3 h probably due to “sluggish diffusion effect”. The resultant HE spinel ferrites (Mg0.2Co0.2Ni0.2Cu0.2Zn0.2)Fe2O4 were first used as a heterogeneous catalyst of peroxodisulfate (PDS). Compared with basic solution condition, the HE spinel ferrite/PDS system exhibited a higher degradation rate for the removal of rhodamine B (RhB) and tetracycline (TC) at initial pH range of 3.0–5.1. Both the hydroxyl radicals and sulfate radicals played an important role on RhB and TC degradation. The high catalytic efficiency and good stability of high-entropy (Mg0.2Co0.2Ni0.2Cu0.2Zn0.2)Fe2O4 catalyst demonstrates that it is suitable for application in wastewater disposal.