Enhancement of visible light photocatalytic activity of tantalum oxynitride and tantalum nitride by coupling with bismut
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Enhancement of visible light photocatalytic activity of tantalum oxynitride and tantalum nitride by coupling with bismuth oxide; an example of composite photocatalysis Shiba P Adhikari1, 2, Lifeng Zhang3, Michael Gross1, 2 and Abdou Lachgar1, 2 1
Department of Chemistry, Wake Forest University, Winston-Salem, NC 27109
2
Center for Energy, Environment and Sustainability, Wake Forest University, NC 27109
3
Joint School of Nanoscience and Nanoengineering, North Carolina A&T State University, 2907
East Lee Street, Greensboro, NC 27401
ABSTRACT Composite photocatalysts comprised of two semiconducting oxides, with suitable band gaps and band positions, have been reported as an effective approach to enhance photocatalytic activity in the visible region of the electromagnetic spectrum. Here, we report the synthesis, characterization, and photocatalytic evaluations of semiconducting composites made by combing bismuth oxide with either tantalum oxynitride or tantalum nitride. Visible light active composites were synthesized using solution chemistry synthesis method. The composites were characterized by powder X- ray diffraction (PXRD), diffuse reflectance UV-Vis spectroscopy, and photoluminescence (PL). Their photocatalytic activities were evaluated for generation of hydrogen from an aqueous methanol solution under visible light irradiation (λ≥ 420 nm). The asprepared composite catalysts are found to have longer photogenerated charge-carrier life time, resulting in enhanced photocatalytic activities. INTRODUCTION After the discovery of titanium dioxide (TiO2) as an ultraviolet light active photocatalyst for water splitting and degradation of organic compounds in the early 1970s, various photocatalysts have been extensively developed in the field of semiconductor based photocatalysis [1, 2]. In a semiconductor photocatalytic system, photo–induced electron-hole pairs are produced when a photocatalyst is illuminated by light with frequency larger than that of its band gap (hν ≥ Eg). The excited electron-hole pairs can either recombine with no chemical reactivity, or migrate to the surface of the semiconductor where they can be involved in redox processes in which the electron leads to reduction of chemical species available, while the hole participates in the oxidation [3, 4]. The photocatalytic efficiency depends on the number of charge carriers taking part in the redox reactions and on the effective separation of electron-hole pairs generated by the photoexcitation. High rate of recombination of photo-excited carriers and limited efficiency under visible light are the two major limiting factors in the development of efficient semiconductor based photocatalysts. A number of metal oxides and sulfides have been examined as photocatalysts for hydrogen production and decomposition of toxic organic molecules [5, 6]. The majority of binary and ternary semiconducting metal oxides (e.g. TiO2) are primarily active under UV
irradiation, which represents only about 4% of the intensity of the solar spectrum. For better utilization
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