Visible-light photoactive Ag–AgBr/α-Ag3VO4 nanostructures prepared in a water-soluble ionic liquid for degradation of wastewater

Appl Nanosci (2016) 6:1119–1126 DOI 10.1007/s13204-016-0525-z ORIGINAL ARTICLE Visible-light photoactive Ag–AgBr/a-Ag3VO4 nanostructures prepared in a water-soluble ionic liquid for degradation of wastewater Mohsen Padervand1 Received: 14 December 2015 / Accepted: 14 February 2016 / Published online: 2 March 2016 Ó The Author(s) 2016. This article is published with open access at Springerlink.com Abstract Ag–AgBr/a-Ag3VO4 photocatalysts, prepared by an ionic liquid-assisted precipitation method, were used as an efficient visible light-driven photocatalytic system for removal of wastewater and pathogenic bacteria from the aqueous medium. X-ray diffraction powder, diffuse reflectance spectroscopy, Fourier transform infrared, scanning electron microscopy, and nitrogen adsorption– desorption isotherm (BET) analysis methods were used to characterize the nanostructures. Photodegradation mechanism was investigated and the results showed that the prepared samples were too efficient for the degradation of Acid Blue 92 (AB92) azo dye, and E. coli cells under visible light. The photogenerated electron–hole pairs reacted with the species in the solution and produced super active radicals such as OH , HO 2 , and O 2 which are responsible for the degradation of the environmental pollutions. TEM images were used to clarify the antibacterial activity of the products. Finally, as a practical application of the prepared photocatalysts, their ability evaluated for degradation of a real wastewater sample which was provided from the textile industries. Keywords E. coli a-Ag3VO4  Wastewater  Photodegradation  & Mohsen Padervand ; 1 Department of Chemistry, Faculty of Science, University of Maragheh, Maragheh, Tabriz, Iran Introduction Phtocatalytic treatment of water pollution using semiconductor-based materials has been considered as one of the most promising technologies to remove of toxic compounds from the environment. Over the past decades, the development of new visible-light photoactive materials has been pursued to improve the practical capacity of semiconductors under natural solar energy. To achieve this purpose, variant strategies such as doping the elemental impurities, coupling different semiconductors, and the synthesis of new visiblelight photoactive catalysts have been served (Zhang et al. 2010; Lee et al. 2010; Yin et al. 2010; Kudo et al. 1998; Wang et al. 2008, 2010a, b; An et al. 2010). Recently, due to their unique crystal structures and interesting photocatalytic properties, the ability of silverbased compounds such as Ag3VO4 (Konta et al. 2003; Hu and Hu 2007), Ag2CO3 (Dai et al. 2012), and Ag3PO4 (Yi et al. 2010; Bi et al. 2012) have been widely investigated for the degradation of organic pollutions under visible illumination. In spite of having suitable photoactivity, the high rate of electron–hole recombination makes the practical application of such materials limited. Moreover, corrosion of the semiconductor surface can take place during the photoreaction because of the conversion of Ag? ions to metallic Ag particles. To address this issue, recently, much effort has been focused on the development of new series of heterostructure materials, named plasmonic photocatalysts, which can lessen the mentioned limitations (Xiang et al. 2010; Chen et al. 2008). According to the reports the presence of metallic Ag and Au nanoparticles on the surface of Ag-based photocatalysts can improve their stability for repeated using (Kakuta et al. 1999; Wang et al. 2008, 2009). Inspired by these findings, many attempts have been performed to fabricate the highly efficient plasmonic 123 1120 Appl Nanosci (2016) 6:1119–1126 silver-based photocatalysts (Kuai et al. 2010; An et al. 2010; Xu et al. 2009). In this paper we report our new attempts to prepare the visible light Ag–AgBr/a-Ag3VO4 photocatalysts by a facile precipitation method at the presence of a watersoluble ionic liquid which acted as a complexing agent and bromide source. Studying their photocatalytic activity for the degradation of AB92 and E. coli gram-negative bacteria revealed that the plasmonic nanostructures had higher activity than the pure a-Ag3VO4 sample. In addition, cycling experiments were performed to investigate the stability of as-prepared nanostructures after repeated using. product (Ag–AgBr/a-Ag3VO4) was filtered, washed repeatedly with DDW and methanol, and dried at 60 °C overnight. Preparation of pure a-Ag3VO4 was carried out in the same manner without adding any [BMIM]Br. In all the experiments 0.02 g of photocatalysts was used and the used solvent was DDW. The visible illumination source was a 250-W OSRAM lamp. Total concentrations of the dye solution were easily determined using an UV spectrophotometer set at the kmax of AB92 dye (574 nm). Results and discussion Characterization of the nanostructures Experimental The formation process of the nanostructures can be described as follows: Materials, instruments, and methods ðCH3 Þ4 Nþ OH ðH2 OÞ ! ðCH3 Þ4 Nþ ðaqÞ þ OH ðaqÞ ð1Þ Agþ ðaqÞ þ 2OH ðaqÞ ! AgðOHÞ 2 ðaqÞ ð2Þ  2AgðOHÞ 2 ðaqÞ ! Ag2 OðsÞ þ 2OH ðaqÞ þ H2 O ð3Þ 2  VO3 4 þ H2 O ! HVO4 þ OH ð4Þ AgNO3 and NH4VO3 were used as silver and vanadium source, respectively. Tetra methyl ammonium hydroxide (TMAOH) was used as a template agent. During the synthesis procedure, 1-butyl-3-methylimidazolium bromide ([BMIM]Br) ionic liquid acted as the bromide source. All of the chemicals were purchased from Merck Co. and used without further purification. Double distilled water (DDW) was used during the preparation steps. 1.02 g of AgNO3 was dissolved in 20 mL of DDW and the solution added drop by drop to a beaker contains 50 mL of water and 0.5 mL of TMAOH. The obtained yellow suspension was stirred vigorously while the color of precipitation changed to brown and then black. After 2 h of stirring at room temperature, a clear solution containing 0.233 g of NH4VO3 and [BMIM]Br (0.2 mL) in 30 mL of DDW was added slowly to the as-prepared suspension. This resulted in the formation of a yellow precipitation. The reaction medium was stirred for 0.5 h. The final Based on Eqs. 1–7, TMAOH facilitates the formation of Ag(OH)2 intermediate which is a necessary step to complete the formation of the final products. In the next step, unstable Ag(OH)2 species can convert to silver oxide and/or react with HVO-2 4 to form a-Ag3VO4. Besides, the solid Ag2O particles react with TMAOH to prompt the formation of a-Ag3VO4. Fig. 1 The XRD patterns of prepared nanostructures Fig. 2 The FTIR spectrum of prepared Ag–AgBr/a-Ag3VO4 sample 123   HVO2 4 þ 3AgðOHÞ2 ! a  Ag3 VO4 þ 5OH þ H2 O ð5Þ Ag2 OðsÞ þ 3ðCH3 Þ4 Nþ OH þ Agþ þ H2 O þ ! 2AgðOHÞ 2 þ AgOH þ 3ðCH3 Þ4 N ð6Þ AgOH þ OH ! AgðOHÞ 2 ð7Þ Appl Nanosci (2016) 6:1119–1126 1121 Ag3VO4-AgBr Ag3VO4 Absorbance AgBr 360 460 560 660 Wavelenght (nm) 760 Fig. 3 The UV–vis spectra of the prepared photocatalysts Fig. 4 A typical adsorp (...truncated)