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

Abstract

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.