Using egg ovalbumin to synthesize pure α-Fe₂O₃ and cobalt doped α-Fe₂O₃: structural, morphological, optical and photocatalytic properties

Nanoparticles of undoped hematite (α-Fe₂O₃) and Co doped α-Fe₂O₃ were prepared by a simple, green, and cost-efficient process using Co and Fe chlorides and freshly isolated hen egg white. Several techniques of characterization, such as differential thermal and thermogravimetric analysis (DTA/TG), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), EDS analysis, X-ray diffraction analysis (XRD), and Ultra-violet Visible (UV-Vis) analysis were applied. The incorporation of Co particles into the hematite matrix limits the growth of the α-Fe₂O₃ crystalline grain and favours the apparition of γ-Fe₂O₃ phase. SEM analysis reveals that there are no significant morphological differences among α-Fe₂O₃ and Co-α-Fe₂O₃ particles, whereas the XPS analysis confirms the existence of Fe and Co particles in the as-prepared samples. The optical study shows a slight reduction of band gap energy for Co doped α-Fe₂O₃ compared to the non-doped α-Fe₂O₃, which has shown enhanced visible light adsorption performance. On the other hand, the α-Fe₂O₃ and Co-α-Fe₂O₃ nano-photocatalysts with an average crystallite size of 21 and 43 nm respectively, were used to remove the Methylene Blue (MB) dye from aqueous solutions after being exposed to visible light. In a mechanistic study, the radicals OH^• and ^•O₂ ^- were shown to be important in the degradation of MB dye. To optimise the effective parameters on MB dye degradation, the experimental parameters applied in the adsorption experiments, such as pH, photocatalyst dosage, contact time, and temperature, were tested. The optimal conditions were determined as pH = 12, photocatalyst dosage = 0.2 g/L. Degradation efficiency in the optimal conditions is 91.8 % after 120 min of irradiation. The pseudo-first and second orders were used to model the kinetic data. The removal of MB using α-Fe₂O₃ and Co-α-Fe₂O₃ photocatalysts matched well with pseudo-second-order reaction kinetics. Furthermore, the thermodynamic study reveals that MB dye adsorption on the Co-Fe2O3 absorbent was an endothermic and spontaneous process.