Development Of Multiple Composite Photocatalyst With Weak Light Response And Photocatalytic Degradation Of Organic Compounds In Seawater System

With the rapid development of industry and social economy,it has brought many serious environmental pollution problems.The pollution of coastal waters caused by organic pollutant wastewater has seriously affected the overall development of marine-related economic industries such as fisheries and aquaculture in major coastal provinces of China.Seawater system is a typical wastewater containing salt,and there are a large number of biological systems,the traditional treatment of organic wastewater process is difficult to run in the sea water system.Heterogeneous photocatalytic degradation of pollutants,such as Ti02,can provide a new direction for the removal of pollutants in seawater system due to the advantages of stability,safety and low energy consumption.However,in order to degrade organic pollutants effectively in seawater system,photocatalysts are needed to overcome the interference of salt ion.In addition,most of the available light sources in the coastal waters are weak light sources（light intensity is usually below 1 mW/cm2）.So inorder to promote the heterogeneous photocatalytic degradation technology,we also need to develop low-light-responsive photocatalysts.To solve these two difficulties,the author used the oxidation reaction of graphene oxide and tetrabutyl titanate as the raw materials.And the small and high dispersion of TiO₂ particles on the surface of graphene oxide were prepared by adsorption phase reaction technology.（RGO）/TiO₂ composite photocatalyst was obtained by the solvothermal process,which promoted the formation of TiO₂ crystals and reduced the oxidized groups on the surface of the graphene oxide.The photodegradation of phenol in seawater under weak light excitation was investigated,and the photocatalytic activity of several catalysts was evaluated.At the meantime,the mechanism of photodegradation of phenol in seawater was also investigated.Finally,the effects of the preparation conditions and the rare earth metal ions on the structure and photocatalytic activity of the composite photocatalyst were studied by means of multiple characterization methods.The main research contents include the following aspects:1.A series of RGO/TiO₂ composite photocatalysts were prepared by the two-step method of adsorption phase reaction and solvothermal method.The effects of solvothermal temperature and water content on the structure,morphology and photocatalytic properties of TiO₂ were investigated.The results show that the solvothermal reaction temperature 160℃,3 mL preparation of RGO/TiO₂ composite photocatalyst content prepared by the best photocatalytic performance,the pure water system in seawater and total phenol removal rate reached 63.92%and 68.28%respectively.2.The RGO/TiO₂ and SiO2/TiO₂ were prepared under the optimal conditions.The effects of different initial concentrations of phenol on the photocatalytic activity of RGO/TiO₂,SiO2/TiO₂ and commercial P25 photocatalysts in seawater and pure water system were studied respectively.And the mechanism of photodegradation was also discussed.The results showed that the graphene in RGO/TiO₂ has a large amount ofπ-π conjugated double bonds that can selectively adsorb phenol organic molecules by chemical adsorption.The photocatalytic degradation of phenol by RGO/TiO₂ composite photocatalyst is almost free from the interference of salt ions,so the excellent photocatalytic performance could be maintained in seawater system performance.3.Solvothermal reaction technology and two step preparation of X/RGO/TiO₂ nano composite photocatalysts with different amount of rare earth metal elements Yb,In and La doped by adsorption phase reaction（X=Yb,In and La）,were characterized by XRD,TEM,FT-IR and XPS,and studied its photocatalytic performance.The results showed that the rare earth metal elements were present in the catalysts with +3 price,can change the crystal structure of doped Ti02 catalysts,made from anatase into a single mixed crystal of anatase and rutile and can promote the crystallization of TiO₂.The rare earth metal ions,which have not been in the lattice structure,can also be introduced into the shallow energy capture centers,which can enhance the photocatalytic activity of the composite photocatalyst.When the doping amount of In was 0.2%,the photocatalytic activity of In/RGO/TiO₂ composite photocatalyst was the highest,and the degradation rate of phenol could reach as high as 73.8%,which was higher than that of undoped.