Preparation And Applications Of Graphene/tungsten Oxide Nanocomposites

With the rapid development of science and technology,the pace of industrialization in our country has also accelerated substantially in recent years.However,while these advanced industries bring convenience to people,they also bring about a series of pollution problems such as industrial wastewater and organic pollutants emission.Therefore,solving environmental problems is a major challenge at this stage.To design and prepare highly active photocatalysts for solar energy application is one of the most effective way.Tungsten trioxide?WO₃?is a typical metal oxide semiconductor material with a narrower band gap?2.5-2.8 e V?,making it possible to utilize visible light effectively,which accounts for nearly half of the solar radiation energy.However,the photocatalytic activity of WO₃has been limited due to its rapid recombination of photo-induced electrons and holes and low light absorption.Therefore,in order to improve the photocatalytic activity of WO₃,it can be achieved by compositing other materials.Graphene is considered as the best candidate due to its high theoretical surface area and excellent mobility of charge carriers at room temperature.In this paper,one-dimensional WO₃ nanorods and WO₃/graphene nanocomposites?WO₃/GR?were successfully prepared by one-step hydrothermal method.The photocatalytic activity under visible light was studied by analyzing the morphology,structure and composition of the catalyst.The details were shown as follows:First,WO₃was prepared by hydrothermal synthesis using precursor sodium tungstate and sodium sulfate as the structure-directing agent at 160?for 12h,and the phase and microstructure of the prepared samples were analyzed by XRD,SEM and TEM.The result showed that the prepared WO₃ had a standard hexagonal phase structure and was a nanorod in shape with a diameter of about 85 nm and a length of 2.2?m.It was seen from the FFT that the growth direction of the tungsten oxide nanorod was along the?001?plane with an inter-planar distance of 0.3880 nm.The photocatalytic activity of WO₃ under visible light was evaluated by photodegradation of methylene blue?MB?,the results showed that the photocatalytic degradation rate achieved 36.5%.Second,WO₃/graphene nanocomposites were successfully prepared by one-step hydrothermal reaction using sodium tungstate and graphene oxide as precursors,oxalic acid and anhydrous sodium sulfate as additives at 180?for 24h.WO₃/graphene nanocomposites with different graphene oxide contents were prepared.Pure WO₃ nanorods were also obtained through a similar procedure only in the absence of graphene oxide.The results showed that with the increase of graphene oxide content,the WO₃/GR nanocomposites showed stronger light absorption in the visible range and increased the specific surface area of the sample,which improved the photocatalytic activity of the sample.Test results of photocatalytic degradation of MB solution under visible light demonstrated degradation rate of WO₃/GR nanocomposites was 2 times larger than that of pure WO₃.Third,based on the above analysis and research,the photocatalytic degradation mechanism of WO₃/GR was proposed.The main results were shown as follows:Under visible light irradiation,when hv?vis??Eg,the electrons in WO₃ got enough energy to be excited to produce electron-hole pair,the electrons in the WO₃ valence band were transferred into the conduction band of graphene,and the introduction of graphene served as an electron acceptor to enhance the electron separation efficiency and inhibit the recombination ability of photogenerated electron-holes.The results improved the photocatalytic efficiency of the WO₃/GR nanocomposites significantly.