1. IntroductionEnvironmental pollution due to textile industries threatens human lives, and has affected aquatic life very adversely. Dyes are extensively used to produce attractive colours in industries such as textile, paper, pulp, food, cosmetic and leather [1] and [2]. Owing to their high chemical stability, dyes form highly toxic complexes by combining with various heavy metal oxides and should be treated before discharge [3]. Furthermore, the presence of a very small amount of dye in water (<1 mg/L for some dyes) is highly visible and enough to present an aesthetic problem [4]. More than 10,000 different types of dyes are commercially available for industrial applications, and the majority of them cannot be treated or entirely removed by the traditional methods, due to their high stability [5]. In fact, the World Bank estimates that 17–20% of industrial water pollution comes from textile dyeing and treatment [6]. The most commonly used dyes such as rhodamine-B and methylene blue consists of various aromatic amine groups, which are highly carcinogenic and mutagenic. In order to treat these dyes, various physico-chemical methods such as flocculation, coagulation and adsorption and biological methods were previously employed. But these methods suffer with a major drawback of sludge formation and also adsorbent regeneration is relatively difficult, which makes them unsuitable for commercialization. But there is still a demand for an effective method to treat these dyes economically [7], [8] and [9].Photocatalytic degradation resolves these problems, due to its cost effectiveness and ease of operational conditions. Recently, photocatalytic degradation is applied on treatment of various wastewaters and resistant contaminants such as leather industry wastewater [10], dye wastewater [11] and [12], herbicides [13], heterocyclic compounds[14] and others. Photocatalytic materials such as ZnO, TiO2, and Ag based materials were extensively studied [15], [16] and [17]. Materials such as ZnO and TiO2 and some other compounds respond only to in UV region, which makes their practical application very limited. The emerging trend to overcome these problems is to synthesize novel photocatalytic materials which would respond in visible light [18] and [19]. Among the various Bismuth oxyhalides, BiOX (X = Cl, F, Br, I) BiOBr is a vital ternary compound, with a forbidden gap of 2.64 eV, with hybridization between the O 2p and Bi 6s states. The unique layered tetragonal matlockite structure of BiOBr consists of the layered structure of [Bi2O2]2+ sandwiched between the Br atoms. It has a crystal structure of PbFCl type and D4h space group, which brings about an effective separation of the photo induced electrons, and the holes for enhanced photo catalytic activity [20] and [21]. BiOBr is encountered with various morphological structures which are at the peak of research. However its photocatalytic performance has been quite limited due to its high recombination rate which originated from its electron hole pairs. In previous reports, synergistic modifications in BiOBr brought through coupling with BiOCl [22], BiOI [23], AgBr [24], and ZnFe2O4[25] or doping with metals such as Ag [26], Fe [27] improves the photocatalytic ability. The photocatalytic performance of BiOBr can also be further improved by integrating it with any carbonaceous materials [28].Graphene, one of the most widely studied carbonaceous material is considered a promising candidate for various applications including photo catalysis, due to its larger surface area, higher carrier mobility high thermal stability, tunable band gap, high electron mobility and electrical conductivity [29] and [30]. Production of high quality graphene in large scale is difficult due to its poor solubility in water and various organic solvents. On other hand GO which has various oxygen functionalities on basal planes and sheet surface can be produced in large quantities and is highly dispersible in various solvents [31] and [32]. Mainly the fabrication of semiconductor/GO has attracted many researchers’ to obtain an improved photocatalytic activity. Many studies reveal that GO based composites enhances both adsorption rate and the light absorptivity which leads to an efficient charge transportation in photocatalyst [33], [34], [35], [36] and [37].In this present work we report a facile method to prepare GO/BiOBr composite photocatalyst. The photocatalytic performance on the degradation of methylene blue (MB) and rhodamine-B (Rh-B) in aqueous solution was examined with the synthesized composites. Furthermore the influence of the GO loadings on the photocatalytic activity was also investigated. This new hybrid material shows better and faster degradation than bare BiOBr and other commercially available materials reported so far.
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