The effect of Bi3+ doping on the structural, magnetic, dielectric, optical, and photocatalytic efficiency of Mg-Ni ferrite nanoparticles

Ferrite nanoparticles with the general formula Mg0.7Ni0.3BixFe2-xO4 (MNB) (0 ≤ x ≤ 0.1, Δx = 0.02) were prepared by the citrate combustion method. X-ray diffraction (XRD) results confirmed the spinel single-phase with crystallite size varied from 30.68 ± 9.68E-4 to 43.74 ± 0.00127 nm. Scanning electron microscopes with elemental mapping conformed to the nano-nature of the MNB samples with all the constituents present without secondary elements. The sample Mg0.7Ni0.3Bi0.02Fe1.98O4 has the highest saturation magnetization of 31.06 ± 0.01 emu/g. The sample Mg0.7Ni0.3Bi0.08Fe1.92O4 has the lowest coercivity of 31.06 ± 0.01 emu/g. The high-frequency response of the MNB nanoferrites allows them to be used at frequencies around 6.483–6.872± 0.01 GHz. The nanoferrite MNB6 has notable dielectric parameters at 300 K and 50 Hz: the highest dielectric constant (747.93 with enhancing ratio 371%) and the highest conductivity (26.14 µ(Ω.m)-1 with enhancing ratio 288%). The MNB5 sample has a loss of 8.65 with an enhancing ratio of 56.79% compared to the loss of the pristine MNB1 sample of 15.23. Diffuse reflectance (DR) spectroscopy showed an irregular trend for the band gap values with increasing Bi3+ content, where the nanoferrite MNB6 had the lowest energy gap of 2 eV. The sample MNB6 exhibited the maximum photodegradation efficiency (96.16%) for Rhodamine B (RhB) dye, with outstanding stability after five cycles (96.16, 95.92, 95.71, 95.56, and 95.23%, respectively). The current work has shown the capability to customize ferrite MNB for soft ferrite applications and to eliminate hazardous RhB from water.