Controllable Synthesis of Different Bismuth Ferrites by a PVA Modified Hydrothermal Method and Photocatalytic Characteri
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Controllable Synthesis of Different Bismuth Ferrites by a PVA Modified Hydrothermal Method and Photocatalytic Characterization Tong Tong, Dengren Jin and Jinrong Cheng* School of materials science and engineering, Shanghai University, Shanghai 200072, P.R.China *corresponding author: [email protected]
ABSTRACT Bismuth ferrites crystallites were synthesized by a polyvinyl alcohol (PVA) modified hydrothermal method. X-ray diffraction (XRD) analysis indicated that the pure phase of Bi25FeO40, BiFeO3 and Bi2Fe4O9 were synthesized with initial Bi/Fe ratio of 1:1 at the temperature of 200ഒ for 24 h, using NaOH concentration of 2, 5 and 10 M, respectively. With addition of PVA, the individual Bi-Fe oxides could be existed in a more wide range of processing parameters. The phase evolution of bismuth ferrites in the process of hydrothermal reactions was discussed. Moreover, photocatalytic properties of the bismuth ferrites crystallites were explored. The results showed that they possessed band gaps of about 2.0 eV and performed good degradation effect at visible light region. INTRODUCTION Bismuth ferrites have attracted increasing attention because of their multiferroic property and their potential applications in sensing, actuation, and digital memory [1-4]. Recently, much work has been concerned on their photocatalysis since they have relatively small band gaps that could be responsible to visible light. Among the three different phases of bismuth ferrites, BiFeO3 has a rhombohedrally distorted perovskite structure with a band gap of about 2.18 eV, making it a promising visible light photocatalyst [5]. Bi25FeO40 is a typical sillenite compound with special Bi-O polyhedron structure, high photo-sensitivity and high carrier mobility [6,7], implying its application on catalysis. Mullite-type Bi2Fe4O9 is an important functional which material which has been recommended as an efficient non-platinum catalyst due to high catalytic efficiency for ammonia oxidation to NO [8]. However, it is very difficult to synthesize pure phase of different bismuth ferrites through conventional solid-state procedure. Therefore, various wet chemical methods have been applied, such as co-precipitation [9], sol-gel method [10] and hydrothermal synthesis [11-15]. The prominent advantages of hydrothermal method were high product purity, low reaction temperature and low production costs. Furthermore, it is possible to control the phase or morphology by changing process parameters or adding some special surfactants during hydrothermal treatment [13-15]. In this study, a polyvinyl alcohol (PVA) modified hydrothermal method was used to synthesize the three different phases of bismuth ferrites by varying the concentration of mineralize and adding certain amount of PVA. The mechanism of phase involution of different bismuth ferrites in the hydrothermal procedure was discussed and their
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photocatalytic properties were explored. EXPERIMENTAL The starting chemical reagents were Bi(NO3)3·5H2O, Fe(NO3)3·9H2O, HNO3, NaOH mineralizer and PVA. All the chemic
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