Photocatalytic performance of nano-photocatalyst from TiO2 and Fe2O3 by mechanochemical synthesis

Nano-particles of homogeneous solid solution between TiO2 and Fe2O3 (up to 10 mol%) have been prepared by mechanochemical milling of TiO2 and yellow Fe2O3/red Fe2O3/precipitated Fe (OH)3 using a planetary ball mill. Such novel solid solution cannot be prepared by conventional co-precipitation technique. A preliminary investigation of photocatalytic activity of mixed oxide (TiO2/Fe2O3) on photo-oxidation of different organic 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) showed that TiO2 having 5 mol% of Fe2O3 (YFT1) is 3–5 times higher photoactive than that of P25 TiO2. The XRD result did not show the peaks assigned to the Fe components (for example Fe2O3, Fe3O4, FeO3, and Fe metal) on the external surface of the anatase structure in the Fe2O3/TiO2 attained through mechanochemical treatment. This meant that Fe components were well incorporated into the TiO2 anatase structure. The average crystallite size and particle size of YFT1 were found to be 12 nm and 30 ± 5 nm respectively measured from XRD and TEM conforming to nanodimensions. Together with the Fe component, they absorbed wavelength of above 387 nm. The band slightly shifted to the right without tail broadness, which was the UV absorption of Fe oxide in the Fe2O3/TiO2 particle attained through mechanochemical method. This meant that Fe components were well inserted into the framework of the TiO2 anatase structure. EPR and magnetic susceptibility show that Fe3+ is in low spin state corresponding to μB = 1.8 BM. The temperature variation of μB shows that Fe3+ is well separated from each other and does not have any antiferromagnetic or ferromagnetic interaction. The evidence of Fe3+ in TiO2/Fe2O3 alloy is also proved by a new method that is redox titration which is again support by the XPS spectrum.

Graphical abstractNano-particles of homogeneous solution between TiO2 and Fe2O3 (up to 5 mol%) have been prepared by mechanochemical milling. The results show that the alloy of TiO2 with 5 mol% of Fe2O3 (YFT1) exhibit photocatalytic activity 3–5 times higher than that of P25 TiO2 for oxidation of various dyes (RB, MO, TB and BG) under visible light irradiation. The average particle size and crystallite size of YFT1 were found to be 30 ± 5 nm and 12 nm measured from TEM and XRD. Optical adsorption edge is found to be 2.26 eV.Figure optionsDownload full-size imageDownload as PowerPoint slideTentative schematic diagram of reaction mechanism of YFT/RFT photocatalysts under visible light irradiation.Highlights► Synthesis of nano-sized homogeneous solid solution between Fe2O3 and TiO2 with high photocatalytic activity for oxidative degradation of different dyes was successfully obtained through mechanochemical synthesis. XRD data shows the formation of solid solution having anatase structure with no free Fe2O3 up to 5 mol% of Fe2O3. Fe2O3/TiO2 catalyst have crystallite size about 12–13 nm measured from XRD and particle size about 30 ± 5 nm measured from TEM. FT-IR of all Fe2O3/TiO2 prepared catalysts is similar to pure TiO2. The maximum solubility of Fe2O3 in TiO2 is 5 mol% of Fe2O3 irrespective of source and this composition has highest photocatalytic activity that is 3–5 times higher than P25 TiO2 for the oxidation of different dyes. We also observed that the rate of degradation of Rhodamine B is faster among all the four dyes under prepared catalyst and visible light.