Synthesis and Photocatalytic Activity of M–doped CaBiO2Cl (M = Ag, Co, and Ni) under Visible Light

Abstract

CaBiO2Cl-based photocatalysts doped with M (M = Ag, Co, and Ni) were synthesized by solid state reaction method. The microstructure and morphology of catalysts were characterized by using X-ray diffraction analysis (XRD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDXS) and UV-vis diffuse reflectance spectra techniques. The photocatalytic activities of pure CaBiO2Cl and M-CaBiO2Cl catalysts were further evaluated by degrading methylene blue (MB) under visible-light irradiation. The results suggested that in comparison with pure CaBiO2Cl, the photocatalytic activity of M-CaBiO2Cl composite photocatalysts is greatly improved. The possible mechanism of enhancing the catalytic activity of M-CaBiO2Cl composite photocatalysts was further discussed. Introduction Semiconductor photocatalysts for clean hydrogen energy production and environment decontamination have attracted much interest since the photocatalytic activity of TiO2 was first reported by Fujishima and Honda in 1972. Currently, TiO2-based semiconductors have been considered as one of the efficient and active photocatalysts in practical application due to the intrinsic advantages such as outstanding oxidative power, high stability, and low cost [1-6]. However, TiO2 with larger band gap (about 3.2 eV for anatase TiO2) has no visible-light response. In addition, high recombination rate of photogenerated electron-hole pairs in TiO2 leading to a relatively low quantum yield also hinders its application. It is essential to exploit new visible-light responsive photocatalysts with better photocatalytic performance [7-10]. Recently, many bismuth-based compounds such as BiVO4 [11], Bi2WO6 [12], BiOCl [13], CaBi2O4 [14], Bi2O2CO3 [15] and Bi12TaO20 [16] have been reported as new photocatalytic materials. Moreover, metal doping modification is also considered as an effective way to improve the photocatalytic properties, since metal additives can not only regulate the widths of band gap of semiconductor photocatalysts efficiently to optimize the band structure, but also improve the morphology of photocatalysts obviously [17-18]. CaBiO2Cl is a typical Bi-based oxychloride and belongs to the ideal Sillen X1 structure, in which the fluorite-like [CaBiO2] + layers are separated by the Cl layers as shown in Fig. 1. Recently, CaBiO2Cl has been reported as an active photocatalyst for environmental decontamination under visible-light irradiation and shows exciting photocatalytic activity[19-20]. In this study, the CaBiO2Cl and M-CaBiO2Cl powders were synthesized successfully via a two-step process. The photochemical properties of M-CaBiO2Cl were evaluated by the photocatalytic decomposition of MB under visible-light irradiation. The corresponding visible-light photocatalytic activities of pure CaBiO2Cl and M-CaBiO2Cl composite catalysts were further discussed in detail. International Conference on Material Science and Application (ICMSA 2015) © 2015. The authors Published by Atlantis Press 649 The green, orange, blue, and red spheres are for Ca, Bi, O, and Cl atoms, respectively Fig.1 Crystal structure of CaBiO2Cl Experimental Methods Synthesis All chemicals used in the present experiments were obtained from the commercial sources as analytical reagents. In this paper, the CaBiO2Cl and M-CaBiO2Cl powders were synthesized by a two-step process. Firstly, 0.01mol KCl was dissolved in 50ml deionized water and stirred for 15 min at room temperature to get solution A. While 0.01mol Bi(NO3)3·5H2O was dissolved in 5ml HNO3 of 2 mol/L and stirred for 15min at room temperature to get solution B. White precipitate was obtained immediately after pouring solution A into solution B and the pH value was adjusted to 3 by ammonia and stirring continuously at room temperature for 8h. The precipitate was collected and washed with deionized water and absolute ethanol thoroughly and further dried at 60°C for 12 h in an oven. Secondly, BiOCl and CaCO3 (1:1 molar ratio) were used to synthesize CaBiO2Cl by a solid-state reaction. The reactant powders were mixed completely and ground using a mortar and pestle to create a homogeneous mixture. Furthermore, the precursor was obtained by rejoining a certain amount of Co(NO3)2, AgNO3 and Ni(NO3)2 into the mixture and stirring for 30 min continuously. Then the precursor was transferred into an alumina crucible and heated in air at 900°Cfor 12 h in a chamber furnace. Finally, M-CaBiO2Cl polycrystalline powders were obtained from these reactions.