Solid State Sciences 55 (2016) 58e68
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Ultrasonic-assisted preparation of novel ternary ZnO/Ag3VO4/Ag2CrO4 nanocomposites and their enhanced visible-light activities in degradation of different pollutants Mahsa Pirhashemi, Aziz Habibi-Yangjeh* Department of Chemistry, Faculty of Science, University of Mohaghegh Ardabili, P.O. Box 179, Ardabil, Iran
a r t i c l e i n f o
a b s t r a c t
Article history: Received 14 December 2015 Received in revised form 21 January 2016 Accepted 10 February 2016 Available online 13 February 2016
Novel ternary ZnO/Ag3VO4/Ag2CrO4 nanocomposites were successfully fabricated via preparation of ZnO/ Ag3VO4 followed by coupling of it with Ag2CrO4 through facile ultrasonic-assisted method. The resultant samples were carefully characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy dispersive analysis of X-rays, UVevis diffuse reflectance spectroscopy, Fourier transform-infrared spectroscopy, and photoluminescence techniques. Photocatalytic activity for degradation of organic dyes, including rhodamine B, methylene blue, and methyl orange was examined under visible-light irradiation. Among the prepared samples, the ternary nanocomposite with 20% of Ag2CrO4 demonstrated the superior activity. This nanocomposite showed 10.6, 2.9, and 3.0-folds greater activity compared to ZnO, ZnO/Ag2CrO4, and ZnO/Ag3VO4, respectively. The enhanced activity was attributed to more harvesting of the visible-light irradiation and efficiently separation of the photogenerated charge carriers in the ternary nanocomposites. To understand efficiently separation of the charge carriers, a plausible diagram was proposed based on formation of tandem n-n heterojunctions. © 2016 Elsevier Masson SAS. All rights reserved.
Keywords: ZnO/Ag3VO4/Ag2CrO4 n-n heterojunctions Dye pollutants Visible-light-driven
1. Introduction In the past few decades, it was found that heterogeneous photocatalysts have potential applications in different disciplines especially in degradation of wide range of organic pollutants in water and air [1e5]. Hence, nanomaterials of various semiconductors have been a subject of extensive interest, because of their roles as heterogeneous photocatalysts. Among inorganic semiconductors, TiO2 and ZnO have been extensively applied in photocatalytic processes owing to their appealing properties such as low cost, nontoxicity, and high stability [6e8]. Unfortunately, these photocatalysts can only be activated under UV irradiation, due to the wide band gap of about 3.20 eV [9]. In order to apply the solar energy more effectively in the photocatalytic processes, many efforts have been devoted to prepare visible-light-driven photocatalysts. It has been found that combining TiO2 and ZnO with narrow band gap semiconductors, having appropriate band energy is an effective strategy to prepare the photocatalysts with considerable activity under the solar irradiation [10e17]. Although
* Corresponding author. E-mail address:
[email protected] (A. Habibi-Yangjeh). http://dx.doi.org/10.1016/j.solidstatesciences.2016.02.006 1293-2558/© 2016 Elsevier Masson SAS. All rights reserved.
numerous multi-component photocatalysts have been prepared, there are still some drawbacks of small visible-light harvesting ability and poor charge separation efficiency. To address these issues, the development of novel multi-component photocatalysts is indispensable, which have more visible-light responsive components and more efficient electron-hole separation system. In recent years, many narrow-band gap silver-containing semiconductors such as AgBr, AgI, Ag3PO4, Ag2CO3, and Ag2S have been used to prepare different visible-light-driven photocatalysts [18e24]. Very recently, it was found that Ag3VO4 and Ag2CrO4 have strong absorptions in visible-light region with band gaps of 2.20 and 1.80 eV, respectively [25e30]. Hence, by combination of them with ZnO, visible-light-driven photocatalysts could be prepared. Moreover, ZnO, Ag3VO4, and Ag2CrO4 are n-type semiconductors. Consequently, by combining these semiconductors with each other, n-n heterojunctions will be formed between ZnO and Ag3VO4 in one side and ZnO with Ag2CrO4 in other side, resulting formation of tandem n-n heterojunctions. Formation of nen heterojunctions between counterparts of the nanocomposite could induce internal electric fields between them, leading to highly enhanced photocatalytic activity due to efficiently separation of the photogenerated electron-hole pairs [30e33]. However, to the best of our
