Visible-light-driven TiO2/Ag2WO4/AgBr heterojunction photocatalyst for deep elimination of Malachite green

In recent decades, almost entire of the earth is facing drinking water scarcity, due to contamination of water and discharge of untreated wastewaters to the environment. Organic dyes, as a significant part of water pollution, is threatening the environment and human health [1]. Accordingly, it is necessary to eliminate these pollutants from the surface waters owing to the degradation-resistant nature, high toxicity, and bioaccumulation potential. Hitherto, plenty of technologies and methods have been tackled to eradicate organic contaminants from the surface waters such as chemical reactions, electrochemical conversion/combustion, flotation, adsorption, biological removal, ion exchange, sedimentation, ozone oxidation, Fenton reaction, filtration, and etc. However, these common techniques possess several disadvantages, like high energy and time-consumption, high operative costs, the inability to completely remove the organic contaminants and just transfer them into another phase, which has seriously prevented their extensive application. Therefore, it is required to discover an efficient strategy to overcome the limitations of traditional techniques [2]. As a green technology, semiconductor-based photocatalysis, has attracted much more interest for degradation of environmental pollutants [3]. Among various semiconductors, titanium dioxide (TiO2) has been the most used photocatalyst in the heterogeneous photocatalytic processes, because of its considerable stability, non-toxicity, and abundant resources. However, the worst drawback of this semiconductor is its poor activity under visible-light irradiation. This is related to the wide band gap of about 3.20 eV and high recombination rate of the photogenerated electron-hole pairs. One effective method to increase visible-light harvesting ability of TiO2 is combination of it with narrow band gap semiconductors [4]. For this reason in this research, TiO₂/Ag₂WO₄/AgBr nanocomposites were prepared by a simple method. The structure, morphology, purity, specific surface area, and electronic properties of the as-prepared samples were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive analysis of X-rays (EDX), UV–vis diffuse reflectance spectroscopy (DRS), Fourier transform-infrared spectroscopy (FT-IR), Brunauer–Emmett–Teller (BET) and photoluminescence (PL) techniques. Photocatalytic activity of the nanocomposites was examined by degradation of Malachite green under visible-light irradiation. Among the ternary nanocomposites, the TiO₂/Ag₂WO₄/AgBr (15%) photocatalyst illustrated the highest photoactivity in degradation of Malachite green, which was approximately 36.5 and 5.5 times higher than the TiO2, and TiO₂/Ag₂WO₄ ( 10%) samples, respectively. The high photocatalytic efficiency of TiO₂/Ag₂WO₄/AgBr (15%) nanocomposite can be attributed to the synergistic catalysis effect between counterparts and formation of tandem n-n heterojunctions, low recombination photo-generated charge carriers, and high surface area. This research provides a feasible method to construct the hetero-structured TiO₂/Ag₂WO₄/AgBr (15%), with dramatically enhanced photocatalytic efficiency.

Keywords:

Water pollution , Photocatalyst , TiO₂/Ag₂WO₄/AgBr (15%) , TiO2