## 1 Introduction  
In recent years, photocatalytic treatment of refractory organic pollutants has attracted increasing attention in the field of water pollution control due to its many advantages, and TiO\({}_{2}\) has especially been widely used owing to chemical stability, non-toxicity, easy synthesis, high reactivity, and environmental friendliness [1]. However, there are two major bottlenecks for TiO\({}_{2}\) as a photocatalyst: first, the utilization rate of visible light is low, TiO\({}_{2}\) can only absorb ultraviolet light; second, the photo-electron-hole pairs in TiO\({}_{2}\) particles are easy to compound, resulting in low photoquantum efficiency and poor photocatalytic activity [2; 3]. At present, the methods of expanding the TiO\({}_{2}\) photoresponse and suppressing the carrier recombination are mainly to modify TiO\({}_{2}\) by various means [4; 5]. In addition, TiO\({}_{2}\) is loaded on other functional materials to promote the separation of photo-induced charges and prolong the recombination time of photogenerated charge, which is also an effective way to improve TiO\({}_{2}\) photocatalytic performance and improve wastewater treatment effect [6]. Graphene (GR) is a two-dimensional structure consisting of a single layer of hexagonal lattice of carbon atoms, which are covalently bonded to each other. This structure gives excellent electrical conductivity and thermal conductivity, and high mechanical strength and large specific surface area of GR [7; 8] makes GR a promising candidate for use in sensors [9; 10], energy storage and transfer [11; 12], nanoelectronics [13], supercapacitors [14], composite materials [15], and other areas. Graphene oxide (GO), an oxide of GR, still retains the layered structure of GR after oxidization. However, many oxygen-containing functional groups are introduced to the GO monolith of each layer. It is generally considered that hydroxyl and epoxy groups are distributed on GO monolith, while carboxyl and carbonyl groups introduced to the edge of the monolith. The introduction of these oxygen-containing functional groups increases the complexity of single GR structure. Therefore, in addition to some properties of GR, it also has a lot of specific features, such as excellent adsorption properties [16; 17]. If TiO\({}_{2}\) is combined with GO, the composite can effectively promote the separation and migration of photogenerated charges due to excellent electron conduction of GO, and can enrich organic substances within the wastewater to the surface of the composite photocatalyst due to excellent adsorption performance of GO, thus increasing the possibilities of contact with the photocatalyst and achieving better degradation and removal of these contaminants [18; 19].  
In this study, GO was prepared with a modified Hummers method and ultrasonic mechanical delamination, while TiO\({}_{2}\) nanoparticle was prepared with the sol-gel method. Accordingly, the GO/TiO\({}_{2}\) composite photocatalyst with different proportions of GO was prepared by the sol-gel method and was characterized by scanning electron microscope (SEM), x ray diffraction (XRD), and Raman spectroscopy. The methylene blue (MB) synthetic dye wastewater was taken as the target pollutant, in an attempt to study the effect on the treatment of synthetic dye wastewater by photocatalytic treatment process under UV irradiation, especially in terms of organic molecular degradation. Most studies in the past on treatment of MB synthetic wastewater were focused on the probability to treat this kind of water using the composite photocatalyst. In this study, the treatment process of MB synthetic wastewater by the composite photocatalyst under different reaction conditions was studied in detail. At the same time, the reaction mechanism of using the composite photocatalyst to treat MB synthetic wastewater was preliminarily discussed.