Through rare-earth doping, special attention was paid to improving the photo-electrochemical, optical, magnetic, and structural properties of zinc ferrite

Abstract

• ZF was successfully doped with RE (Sm, Dy, Ho, Er, and Yb) elements. • Er dopant improved the photo-electrochemical and optical properties of ZF. • Ho and Er modify the magnetic characteristics of ZF to become superparamagnetic. • Added RE dopants increased the absorption intensity of ZF. • Reversible and diffusion-controlled processes were dominant at the electrode surface. Over the years, zinc ferrite (ZF) has gained a lot of attention as one of the best visible light-driven magnetic photocatalysts. Nevertheless, its applicability at the industrial scale has been limited because of high electron-hole recombination and the difficulty in separating it from the reaction mixture. Thus, this study focuses on finding the best rare earth element that can be used as a dopant to improve the photo-electrochemical, optical, and magnetic properties of ZF. This was achieved by systematically doping ZF with rare earth elements (RE) (Sm, Dy, Ho, Er, and Yb) using the coprecipitation method. Various characterisation techniques were employed to investigate the impact of added RE dopants on the structural properties of ZF. The formed RE-doped ZF was monodispersed and spherically shaped, with an average particle radius of 10.08 nm, 12.49 nm, 12.55 nm, 12.05 nm, 18.15 nm, and 12.51 nm, for ZF, Sm-ZF, Dy-ZF, Ho-ZF, Er-ZF, and Yb-ZF, respectively. Added RE dopants enhanced the absorption intensity and shifted the ZF band edge to higher wavelengths. Moreover, the band gap was reduced allowing ZF to use both ultraviolet and visible light for photocatalysis application. Cyclic voltammetry scan rate studies showed that both adsorption and diffusion-controlled processes were dominant at the electrode surface. Nyquist plots showed charge transfer capacities of 91.3 Ω, 63.4 Ω, 73.9 Ω, 68.7 Ω, 48.9 Ω, and 55.2 Ω, which correspond to ZF, Sm-ZF, Dy-ZF, Ho-ZF, Er-ZF, and Yb-ZF, respectively. From photoluminescence studies, the order of effective charge separation was found to be in the decreasing order of Er-ZF > Yb-ZF > Sm-ZF > Ho-ZF > Dy-ZF > ZF. Overall, Er was found to be the best dopant for improving the photo-electrochemical and optical properties of ZF. The g-factor and peak-to-peak line width were found to be in the range of (2.0001–2.0938) and (33.32–63.48 mT), respectively. The magnetic field resonance was found to be between 320.07 and 335.62 mT, while the hysteresis loop ranged between 4.06 and 5.23 mT. In summary, the synthesised RE-doped ZF material demonstrated ferromagnetic properties, and the low hysteresis loop values indicate that these particles may possess superparamagnetic capabilities.