Photocatalytic decolourisation of RhB and photocorrosion of BiFeO 3
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Photocatalytic decolourisation of RhB and photocorrosion of BiFeO3 Chang Hengky,a and Steve Dunnb a
Biomedical Engineering Group, School of Engineering (Manufacturing), NYP, Singapore,
569830 b
School and Engineering and Materials, Queen Mary University of London, E1 4NS, UK
Email: [email protected] ABSTRACT BiFeO3 nanopowders with a size distribution around 20nm and optical absorption onset at 2eV have been synthesized using self-combustion. These particles were used to photodecolourise RhB under AM1.5 irradiation. XPS showed changes to the oxidation state of the Fe cations. Under AM 1.5 illumination at pH 2 RhB showed >95% decolourisation after 10minutes. INTRODUCTION The use of renewable or low energy sources for the degradation of organic pollutants has generated broad interest. Research on semiconductor photocatalysis came sharply into focus after the discovery that TiO2 photochemical electrodes could split water using ultraviolet light 1. Only 4% of terrestrial radiation is suitable for the photoexcitation of TiO22 rendering the process impractical. Photocorrosion is a well-known problem for many narrow band gap semiconductors such as CdTe. Recently it has been shown that perovskite ferroelectric materials can photocorrode3. BiFeO3 (BFO) has attracted interest due to the multiferroic properties at room temperature4. BFO thin films have been investigated as novel materials for nonvolatile memory5, magnetoelectric switching6, and photovoltaic devices7. In addition, there is increasing interest in these materials for photocatalytic processes under visible-light illumination8. Ferroelectric materials can be highly photoactive with some exceptional properties due to the internal dipole of the material9,10. Selective deposition of metal nano particles has been investigated11,12, 13, 14, 15, 16, 17 and a wide range of different materials including PZT, barium titanate and lithium niobate have been used as a catalyst. Ferroelectrics have also been used to drive photocatalytic reactions such as artificial photo synthesis16,18.
EXPERIMENTAL METHODS Reagent grade Bi(NO3)3·5H2O and Fe(NO3)3·9H2O (purity > 99%, International Laboratory) were used as precursors. 70% HNO3 and de-ionised water dissolved the precursors in a proportion of 1:1M to create a 0.2 M solution. Citric acid >98% purity reagent grade (Sigma Aldrich) was used as the fuel. The solution was heated to 300ºC with a dwell for 30 minutes. The resultant flakes were ground and annealed for 3 hours at 650ºC. The powders were characterized using FESEM, TEM and XRD. Visible absorption was determined using a UV-Vis-NIR spectrophotometer with integrating sphere. Photo decolourisation was performed by mixing 4.8 mg of RhB dye powder in 1 litre of de-ionized water. 300 mg of BFO was loaded into 100 mL of dye solution. X-ray photo-electron spectrometry (XPS) was performed using a Thermo Fisher Scientific Theta Probe. RESULTS AND DISCUSSION An XRD pattern of the as produced material, shown in Figure 1, shows that the majority phase fits JCPDS card no. 71-2494 for
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