MECHANOCHEMICAL SYNTHESIS, CHARACTEMZATION AND PHOTOCATALYTIC PROPERTIES OF M_2O_3/TiO_2 (M = Fe, Mn) NANO-COMPOSITE UNDER VISIBLE LIGHT

摘要

Nano-particles of homogeneous solution between TiO_2 and M_2O_3 (M = Fe, Mn;;upto 10 wt %) have been prepared by mechanochemical milling of TiO_2 and yellow/Red Fe_2O_3 and Mn_2O_3 using a planetary ball mill. Photocatalytic activities of TiO_2 / M_2O_3 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 TiO_2 with 5 wt % of Fe_2O_3 (YFT1) exhibit photocatalytic activity 3-5 times higher than that of P25 TiO_2 and 5 wt % of Mn_2O_3 /TiO_2 (MNT1). Therefore, we have mainly discussed on Fe_2O_3/TiO_2 alloy. XRD of powders show that it has anatase structure with no peak of any of Fe_2O_3/Mn_2O_3. EDX spectra show that Fe/Mn is uniformly distributed in TiO_2. 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 Fe~(3+) is in low spin state corresponding to μ_B = 1.8 BM. As the band edge is lower than TiO_2, which means that Fe~(3+) is situated in between conduction band and valence band. The optical absorption causes the formation of hole on Fe~(3+) 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 Fe~(3+) and bottom of conduction band. The oxidation state of iron has been found to be +3 from redox titration and XPS.