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

doi:10.1016/j.jallcom.2011.05.069

Journal of Alloys and Compounds

Volume 509, Issue 32, 11 August 2011, Pages 8158-8164

https://doi.org/10.1016/j.jallcom.2011.05.069 Get rights and content

Abstract

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 μ_B = 1.8 BM. The temperature variation of μ_B 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 abstract

Nano-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.

Tentative 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.

Introduction

Photocatalytic oxidation of organic compound by wide band gap semiconductor studies is an important area of investigation. In this regard studies with TiO₂ and modified TiO₂ are area of intense investigation [1], [2], [3], [4], [5], [6], [7], [8], [9], [10].

The photocatalytic property of a multicomponent system is strongly influenced by the composition and the preparation procedure. In recent years, the application of heterogeneous photocatalysis on the removal of contaminants in air and wastewater has fetched some interest [11], [12], [13], [14], [15]. Due to the high photocatalytic activity and stability of titanium dioxide, it is generally used as a photocatalyst for the removal of organic pollutants from water or air [16], [17], [18], [19], [20].

However, TiO₂ follows a relatively high electron–hole recombination rate, which is detrimental to its photoactivity. The doping of TiO₂ with transition metal ions like Ni(II) [21], Cu(II) [22], Nb(V) [23], Cr(III) [24], [25], Fe(III) [26], [27], [28], [29], and metal molybdates [13] were reported to improve the photocatalytic properties with enhanced absorption of visible/ultraviolet light. Binary metal oxides such as TiO₂/WO₃, TiO₂/MoO₃, TiO₂/SiO₂ and TiO₂/ZrO₂ have been widely studied for their unique chemical, physical and photocatalytic properties [30], [31], [32], [33]. Studies with a Fe₂O₃/SrTiO₃ mixed oxide photocatalyst have shown improved photocatalytic activity for photo-oxidizing methanol under visible light irradiation [34]. Adel Ali Ismail has prepared the ternary heterogeneous mixed oxides i.e. Y₂O₃/Fe₂O₃/TiO₂ nanoparticles [35], which showed better photooxidation for EDTA than pure TiO_2. Recently, Fe₂O₃/TiO₂ heterogeneous mixed oxides [36], [37], [38], [39] have shown better photocatalytic activity than pure TiO₂ for oxidation of different organic compounds such as methylene blue, chloroform and formaldehyde but it is inferior to Degussa P 25. In this study a homogeneous solution between Fe₂O₃ and TiO₂ has been made by high energy mechanical milling using various source of Fe³⁺ which shows high photochemical activity and it is more active than Degussa P 25 in visible light for oxidative degradation of various dyes. It is observed that the photocatalytic activity of Fe–Ti oxides alloy largely depends on iron content, preparative condition and sintering temperature having optical adsorption edge around 2.2 eV, which facilitates a strong absorption of visible light. The Fe₂O₃/TiO₂ alloys in different mole ratio were prepared by mechanical milling method (using a ball mill) and their photocatalytic activities were evaluated by the photooxidations 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) irradiation. The alloy of Fe₂O₃ (5 mol%) with TiO₂ (anatase) is a better photoactive material compared to Degussa P25 TiO₂ and other compositions of Fe₂O₃/TiO₂.

Section snippets

Synthesis of Fe₂O₃/TiO₂ photocatalysts

A stoichiometric mixture of TiO₂ (Aldrich, 99.99%) and yellow/red Fe₂O₃ (5, 7 and 10 mol%) (99.9%, Tata-Pigment, India) was prepared by mechanical grinding in a planetary ball mill using small amount of water. This mechanical milling was allowed for 4 h for complete mixing of the oxides forming a solid solution. The milling was performed in Fritsch Pulverisette No. 6 planetary ball mill, using a rotational speed of 250 rpm at a constant rotation direction and a ball to powder weight ratio of 10:1.

XRD analysis

Fig. 1 shows the XRD patterns of TiO₂, YFT1, YFT2, YFT3, YFT4, RFT1, RFT2, YF and RF (abbreviation presented in Table 1) mixed oxides nanopowders after heat treatment at 100 °C for 15 h in air atmosphere. It has been observed that the phases prepared at different molar ratios of mixed oxides TiO₂ and Fe₂O₃ (YFT1, YFT2, YFT4, RFT1 and RFT2) have anatase phase up to 5 mol% of Fe₂O₃ (as per JCPDS no. 84-1285), and YF, RF are hexagonal phases (as per JCPDS no. 86-0550). The XRD pattern of TiO₂ sample

Conclusions

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. The chemical and physical natures of the materials remain same irrespective of source of Fe₂O_3. Fe₂O₃/TiO₂ catalyst have crystallite size about 12–13 nm measured from XRD and

Acknowledgements

This work was supported by the Council of Scientific and Industrial Research, India. The authors are grateful for its financial support.

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

Abstract

Graphical abstract

Highlights

Introduction

Section snippets

Synthesis of Fe2O3/TiO2 photocatalysts

XRD analysis

Conclusions

Acknowledgements

J. Photochem. Photobiol. A: Chem.

Appl. Catal. B: Environ.

Mater. Chem. Phys.

J. Colloid Interface Sci.

Appl. Catal. B: Environ.

J. Mol. Catal. A: Chem.

J. Mol. Catal. A: Chem.

J. Mol. Catal. A: Chem.

J. Hazard. Mater.

Appl. Catal. B: Environ.

J. Photochem. Photobiol. A: Chem.

Mater. Chem. Phys.

Appl. Catal. A: Gen.

Chem. Phys. Lett.

Appl. Catal. B: Environ.

Sol. Energy Mater. Sol. Cells

J. Mol. Catal. A: Chem.

J. Photochem. Photobiol. A: Chem.

Catal. Today

J. Solid State Chem.

J. Phys. Chem. Solids

Appl. Catal. B: Environ.

Mater. Sci. Eng. B

Catal. Today

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

Synthesis of Fe₂O₃/TiO₂ photocatalysts