Applied Surface Science 368 (2016) 63–68 Contents lists available at ScienceDirect Applied Surface Science jou rn al h om ep age: www.elsevier.com/locate/apsusc Synthesis, surface and optical properties of Ag 2 Cu(VO 3 ) 4 and Cu(VO 3 ) 2 vanadates Xuebin Qiao a , Yingpeng Wan b , Yuze Li b , Lin Qin c , Hyo Jin Seo c,∗ a Jiangsu Key Laboratory of Advanced Laser Materials and Devices, School of Physics and Electronic Engineering, Jiangsu Normal University, Xuzhou 221116, PR China b College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou 215123, PR China c Department of Physics and Interdisciplinary Program of Biomedical, Mechanical & Electrical Engineering, Pukyong National University, Busan 608-737, Republic of Korea a r t i c l e i n f o Article history: Received 22 October 2015 Received in revised form 20 January 2016 Accepted 25 January 2016 Available online 28 January 2016 Keywords: Inorganic compounds Semiconductors Catalytic properties Optical properties Electronic band structure Photocatalysis a b s t r a c t Ag 2 Cu(VO 3 ) 4 and Cu(VO 3 ) 2 were prepared via the sol–gel chemical synthesis. The phase formation was confirmed by X-ray powder polycrystalline diffraction (XRD) measurements. The surface properties were measured with the scanning electron microscope (SEM), energy dispersive spectra (EDS), transmission electron microscopy (TEM), and nitrogen adsorption–desorption isotherms. The optical properties and the band-gap structures were investigated. The vanadates have efficient optical absorption in the UV to visible wavelength region with an indirect allowed transition. Ag 2 Cu(VO 3 ) 4 has smaller band gap (1.85 eV) than that of Cu(VO 3 ) 2 (2.03 eV). The narrowed band gap is due to the hybridization between the Ag-4d and O-2p in the valence band. The photocatalysis was investigated by photodegradation of methylene blue (MB) solutions excited by the light with wavelength longer than 420 nm. Correspondingly Ag 2 Cu(VO 3 ) 4 has more efficient photocatalytic activity on MB photodegradation than that of Cu(VO 3 ) 2 . The photocat- alytic mechanisms were suggested according to the band positions and the trapping experiments. © 2016 Elsevier B.V. All rights reserved. 1. Introduction The advanced photocatalysts driven by visible light have attracted continuous attention in potential applications such as water splitting, environment pollution solution, and CO 2 reduc- tion etc. In recent years photocatalysts driven by visible-light have been widely developed such as TiO 2 [1–4], ZnO [5,6], g-C 3 N 4 [7–9], BiVO 4 [10], Ag 3 VO 4 [11], Ag 2 O [12], and oxides nanocomposites [13], etc. To develop semiconductors with narrow band gaps is one of the major strategies established to design visible light-driven photocatalysts. Among the wide investigation, Ag-containing vanadates could act as efficient photocatalysts because of the following character- istics. Firstly, there are efficient optical absorption centers (VO 4 3- ) groups in vanadates such as BiVO 4 [14], InVO 4 [15], SrBi 3 VO 8 [16], etc., where photo-induced electrons can be easily induced by the electron transition from oxygen (2p orbital) to V 5+ (vacant 3d orbital) ions [17]. This is important for its excellent photocatalytic activity for photodegradation of dyes or depleting H 2 O. Secondly, ∗ Corresponding author. Tel.: +82 51 629 5568; fax: +82 51 6295549. E-mail address: hjseo@pknu.ac.kr (H.J. Seo). Ag + is a special 4d transition metal ion with its electron configura- tion in the ground state described by [Kr] 4d 10 5s 1 . The mixing of Ag + and O 2- electronic states at the valence band maximum (VBM) is a regarded to be one of the principles for lowing band energy of semiconductors [18]. Kato et al. [19] have concluded that Ag + ions in a compound usually can led a valence band to a more negative posi- tion than O 2p orbital at a more positive level, which is preferable for water oxidation to form O 2 . Usually Ag ions in lattices are important to enhance the photocatalytic propertied [19–21]. Consequently, binary oxides of Ag and V have been studied as efficient photocata- lysts, which show intense absorption bands of visible light due to narrowed band-gap such as - and -AgVO 3 [22], Ag 4 V 2 O 7 [23], Ag 3 VO 4 [24], Ag 2 Sr(VO 3 ) 4 [25]. In this work, Ag 2 Cu(VO 3 ) 4 vanadate was selected to develop a potential photocatalyst, and the reference sample Cu(VO 3 ) 2 was also investigated as a comparison. The motivations are the fol- lowing. Firstly, usually Cu 2+ doping in a host could enhance the Madelung energy and stabilize the silver-based oxides, which are sensitive to photo-corrosion. Secondly, recently Li et al. [25] reported the photocatalisis of Ag 2 Sr(VO 3 ) 4 and Sr(VO 3 ) 2 . Ag 2 Sr(VO 3 ) 4 has the lower O 2 -evolution rates of Ag 2 Sr(VO 3 ) 4 (8.1 mol h -1 ) than that of Sr(VO 3 ) 2 (12 mol h -1 ) [25]. This is due to the bigger Sr 2+ ions inserted into the lattices, which brings out the http://dx.doi.org/10.1016/j.apsusc.2016.01.221 0169-4332/© 2016 Elsevier B.V. All rights reserved.