Optimization using RSM-CCD in the fabrication of magnesium-doped bismuth ferrite nanoparticles via sol–gel auto-combustion method for enhanced photocatalytic performance

Abstract

Magnesium-doped bismuth ferrite (BiFeO₃ or BFO) nanoparticles were fabricated through the sol–gel auto-combustion method to increase their photocatalytic performance. The synthesis parameters, specifically annealing temperature (400, 500, and 600°C) and Mg doping concentration (5, 10, 15, 20, and 25 %), were varied to investigate their effects on the photocatalytic degradation of Rhodamine B under simulated solar irradiation. The nanoparticles were then characterized using different analytical techniques to assess their structural, optical, and morphological properties. X-ray diffraction (XRD) results found that the existence of high intensity cubic sillenite phase, Bi₂₅FeO₄₀ as a secondary phase in 25 % Mg-doped bismuth ferrite nanoparticles with a crystallite size of 33.9 nm, which would enhance the photocatalytic performance. Besides, the vibrating sample magnetometer (VSM) analysis showed that the doping of Mg in the bismuth ferrite host structure significantly enhances superparamagnetic and soft ferromagnetic behavior as the dopant concentration increases from 5 to 25 % due to increase in saturation magnetization (from 2.28 emu/g to 6.19 emu/g) and reduction in coercivity (from 88.35 Oe to 49.81 Oe). Field emission scanning electron microscopy-energy dispersive X-ray spectroscopy (FESEM-EDX) micrograph shows the particles were fully crystallized with regular shapes, suggesting a uniform surface morphology. Ultraviolet–visible diffuse reflectance spectroscopy (UV–Vis DRS) found that the band gap narrows to 2.0 eV when introducing Mg doping. Based on the photocatalytic degradation activity of Rhodamine B using Mg-doped bismuth ferrite nanoparticle (annealing temperature of 600 °C, 25 % Mg concentration) successfully achieved 80 % at 60 min, which was verified using response surface methodology (RSM)-central composite design (CCD). The photodegradation reaction followed pseudo-first-order kinetics, with the rate constant for the 25 % Mg-doped bismuth ferrite nanoparticles determined to be 0.02699 min⁻¹.