Mechanochemical synthesis, characterization and photocatalytic Properties of M2O3/TiO2 (M = Fe, Mn) nano-composite under visible light

Abstract

Nano-particles of homogeneous solution between TiO2 and M2O3 (M = Fe, Mn; upto 10 wt %) have been prepared by mechanochemical milling of TiO2 and yellow/Red Fe2O3 and Mn2O3 using a planetary ball mill. Photocatalytic activities of TiO2 / M2O3 powders were investigated by photooxidation of different dyes like Rhodamine B (RB), Methyl orange (MO), thymol blue (TB) and Bromocresol green (BG) under visible light (300-W Xe lamp; λ > 420 nm). The results show that the alloy of TiO2 with 5 wt % of Fe2O3 (YFT1) exhibit photocatalytic activity 3-5 times higher than that of P25 TiO2 and 5 wt % of Mn2O3 /TiO2 (MNT1). Therefore, we have mainly discussed on Fe2O3/TiO2 alloy. XRD of powders show that it has anatase structure with no peak of any of Fe2O3/Mn2O3. EDX spectra show that Fe/Mn is uniformly distributed in TiO2. The average particle size and crystallite size of YFT1, MNT1 were found to be 30±5 nm (TEM), 100±5 nm (SEM) and 12 nm (XRD) respectively. Optical adsorption edge of YFT1 is found to be 2.26 eV. EPR and magnetic susceptibility show that Fe3+ is in low spin state corresponding to µB = 1.8 BM. As the band edge is lower than TiO2, which means that Fe3+ is situated in between conduction band and valence band. The optical absorption causes the formation of hole on Fe3+ and liberated electron goes to conduction band. This charge separation is facilitated by visible light rather than UV or near UV light due to lesser energy gap between Fe3+ and bottom of conduction band. The oxidation state of iron has been found to be +3 from redox titration and XPS.