Contents lists available at ScienceDirect Separation and Purification Technology journal homepage: www.elsevier.com/locate/seppur Silver vanadium oxide materials: Controlled synthesis by hydrothermal method and efficient photocatalytic degradation of atrazine and CV dye Chiing-Chang Chen a , Janah Shaya b , Huan-Jung Fan c , Yi-Kuo Chang d , Han-Ting Chi a , Chung-Shin Lu e, ⁎ a Department of Science Education and Application, National Taichung University of Education, Taichung 403, Taiwan, ROC b Institut de Physique et Chimie des Matériaux (IPCMS), UMR 7504, CNRS-Université de Strasbourg, 23 Rue du Loess, 67034 Strasbourg Cedex 2, France c Department of Environmental Engineering, HungKuang University, Sha-Lu, Taichung 433, Taiwan, ROC d Department of Safety Health and Environmental Engineering, Central Taiwan University of Science and Technology, Taichung 406, Taiwan, ROC e Department of General Education, National Taichung University of Science and Technology, Taichung 404, Taiwan, ROC ARTICLE INFO Keywords: Photocatalysis Silver vanadate Visible light Atrazine Crystal violet Water treatment ABSTRACT Silver vanadium oxides have received remarkable attention in recent years because of their stability, suitable band gaps, and relatively superior photocatalytic abilities. This study reports the synthesis of silver vanadates by the hydrothermal method and the investigation of their photocatalytic abilities for removing crystal violet (CV) and atrazine pollutants under visible-light irradiation. The as-prepared silver vanadates are characterized by X- ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and UV–vis diffuse reflectance spectra (DRS). Crystal violet and atrazine could be successfully degraded in the presence of the silver vanadate catalyst under visible-light irradiation. The obtained results show complete degradation of crystal violet after 24 h of treatment and over 97% degradation of atrazine after 72 h. The as-prepared silver vanadate materials show extremely high catalytic stability and maintain stable activity after three catalytic cycles. The scavenger studies indicate that % O 2 - radicals are the main active species in the degradations of CV and atrazine, while % OH and h + play an assistant role in these processes. Liquid chromatography coupled with electrospray ionization mass spectrometry is used to analyze the samples obtained from the photocatalytic de- gradation of CV and atrazine. The degradation pathways of atrazine are evaluated suggesting two different routes including dechlorination–hydroxylation and alkylic-oxidation–de-alkylation. On the other hand, the de- gradation of the CV takes place via N-de-methylation in a stepwise manner generating the various N-de-me- thylated intermediate CV species. The excellent activity and photostability reveal that silver vanadates (in- cluding Ag 4 V 2 O 7 ) are promising visible-light-responsive photocatalysts for water and wastewater treatment. 1. Introduction Semiconductor photocatalysts have attracted strong attention due to their efficiency in environmental purifications and splitting of water into hydrogen and oxygen gases [1–4] in addition to the importance of catalysis in various domains of research. Silver-based oxides, with the unique hybridized valence bands (O 2p and Ag 4d orbitals), exhibit a narrow band gap (≤3 eV) and highly dispersed valence bands (VB), resulting in useful photoabsorption ability and high mobility of pho- toholes, respectively. Therefore, these materials are prospective can- didates as visible-light-sensitive photocatalysts in interesting applica- tions [5–7]. Among the different silver-based semiconductors, the efficiency of silver vanadium oxide materials (silver vanadates, SVO) in photocatalytic applications using visible irradiation has been documented, owing to their narrow band gap and good crystallization [8–11]. SVO materials are among the most complex metal oxides, with a number of phases present even in the case of a single atomic com- position [12,13]. Moreover, SVO semiconductors exhibit a band gap transition that allows strong absorption in the visible light region [14]. They also have potential uses in rechargeable high-energy density li- thium batteries, solar energy conversions, and sensors [15–18]. Significant effort has been devoted in the past years to synthesize different types of silver vanadates as well as different morphologies [19–21]. Nevertheless, there are few studies that describe the impact of the preparation factors on these vanadates such as the ratio of the silver and vanadium sources, which has not yet been probed, and the effect of the pH on the preparation [22]. Specifically, there exist four main types of silver vanadates: AgVO 3 , Ag 2 V 4 O 11 , Ag 3 VO 4 , and Ag 4 V 2 O 7 . Among https://doi.org/10.1016/j.seppur.2018.06.011 Received 3 February 2018; Received in revised form 18 May 2018; Accepted 3 June 2018 ⁎ Corresponding author at: 129, Sec. 3, San-min Rd., Taichung, Taiwan 40401, Taiwan, ROC. E-mail address: cslu6@nutc.edu.tw (C.-S. Lu). Separation and Purification Technology 206 (2018) 226–238 Available online 04 June 2018 1383-5866/ © 2018 Elsevier B.V. All rights reserved. T