Vol.:(0123456789) 1 3 International Journal of Environmental Science and Technology https://doi.org/10.1007/s13762-017-1640-4 ORIGINAL PAPER Improved visible photocatalytic activity of TiO 2 nanoparticles to use in submerged membrane photoreactor for organic pollutant degradation V. Vatanpour 1  · A. Karami 1  · M. Sheydaei 1 Received: 20 August 2017 / Revised: 9 November 2017 / Accepted: 22 December 2017 © Islamic Azad University (IAU) 2018 Abstract In this study, photocatalytic activity of TiO 2 nanoparticles under visible light was improved and the modifed photocatalysts were used in a pilot-scale continuous submerged photocatalytic membrane reactor (SPMR) for decolorization of Reactive Orange 29 (RO29) under visible light irradiation. The Taguchi method was used to optimize the activation of TiO 2 nano- particles. Efect of the activation precursors (urea, thiourea, ammonium thiocyanate and sulfanilic acid), TiO 2 : precursors w/w ratio (1:1–1:6), activation time (1–7 h) and activation temperature (350–500 °C) on the visible photocatalytic efciency of the nanoparticles was investigated to achieve maximum decolorization efciency. X-ray difraction, scanning electron microscopy, Fourier transform infrared and difuse refection spectroscopy analysis were used to characterize the photocata- lysts. The results presented that the doping source and the doping source:TiO 2 ratio had the most and the lowest efect on the TiO 2 activation process, respectively. When urea was applied as an activation precursor with mass ratio of 6:1 to TiO 2 at 450 °C for 5 h, the decolorization efciency of 84.2% was obtained in a continuous SPMR system. The RO29 degradation intermediates were analyzed by gas chromatography coupled with mass spectroscopy technique. Keywords Environmental chemistry · Membranes · Nanotechnology · Photochemistry · Remediation · Reactor confguration Introduction Textile wastewater is one of the main sources of environ- mental contamination. They are not only colorful, but also contain great amounts of suspended organic solids (Dast- khoon et al. 2015). The physicochemical methods such as focculation, oxidation, coagulation, membrane fltration, electrochemical techniques, adsorption, sonocatalyst and photocatalysis are usually utilized for decolorization from industrial wastewaters (Khataee et al. 2009; Madaeni et al. 2011; Zamani et al. 2014; Fakhri et al. 2016; Oskoei et al. 2016; Agarwal et al. 2017; Essandoh et al. 2017). Advanced oxidation processes (AOP), especially the photocatalysts, are the most successful processes for treatment of the dye wastewater. The key advantage of this technique is organic carbon mineralization (Oskoei et al. 2016). This process is based on the creation of highly reactive hydroxyl radicals that can degrade a wide variety of pollution (Sheydaei et al. 2014a, b). The most used photocatalyst is titanium diox- ide (TiO 2 ). Despite the good properties of TiO 2 such as the favorable physical/chemical properties, the low cost, the availability and the stability, this photocatalyst is only active under the UV irradiation (λ < 388 nm) (Khataee et al. 2009; García-Araya et al. 2010; Royaee et al. 2011). Therefore, several attempts have been made in recent years to enhance the visible photocatalytic activity of TiO 2 . Various methods have been used for this purpose such as doping with transi- tion metals (Umebayashi et al. 2002; Rajabi et al. 2013), reduction with hydrogen (Kılıç and Zunger 2002; Palmer et al. 2002), coupling with semiconductors and dye sensiti- zation (Pelaez et al. 2012). The doping with nonmetal elements is one of the most efective and widely used activation methods in which non- metals such as B, C, N, F and S are doped into TiO 2 lattices (Ohno et al. 2004; Kobayakawa et al. 2005; Di Valentin et al. Editorial responsibility: V.K. Gupta * V. Vatanpour vahidvatanpour@khu.ac.ir; vahidvatanpoor@yahoo.com 1 Faculty of Chemistry, Kharazmi University, Tehran 15719-14911, Iran