Design And Performance Study Of Tungsten Oxide-based Photocatalyst

With the rapid development of society,environmental pollution is becoming increasingly serious.Printing and dyeing wastewater pollution is a typical industrial pollution,which is difficult to remove completely by traditional treatment methods.Photocatalytic technology can efficiently use solar energy and shows advantages in this field.This technology has the advantages of energy saving and no secondary pollution.The key to developing photocatalysis technology lies in the design and preparation of high-efficiency photocatalysts.Traditional photocatalysts such as titanium dioxide（TiO₂）and zinc oxide（ZnO）are wide-bandgap semiconductors that only respond to ultraviolet light（only about 5%of sunlight）and cannot effectively use about 50%ratio of visible light in sunlight.Therefore,the development of new visible light-responsive photocatalysts is imminent.As an N-type semiconductor catalyst material,WO₃ is widely used in the field of photocatalysis due to its suitable band gap（E_g<3.1 eV）,which can be excited by visible light,showing a strong photocurrent signal and good photosensitivity.However,its photogenerated electrons and holes are easy to recombine,resulting in low photocatalytic performance.In this paper,WO₃ is the main research object,and the research is mainly carried out from the aspects of defect construction,noble metal deposition and compounding with semiconductors.The purpose is designed for the effective adsorption of materials on organic dyes,the absorption capacity of visible light enhancement and the separation efficiency of photo-generated carriers improvement,thus would be beneficial to improve its photocatalytic performance.The main research results of this paper are as follows:（1）To enhance the effective adsorption,WO₃ was prepared by solvothermal method and annealed in Ar/H₂ mixed gas in order to construct an oxygen-deficient WO₃（Ar/H₂）nanosheet.Studies have shown that WO₃ is rich in oxygen defects,which can quickly adsorb organic pollutants with an adsorption capacity up to 63.7 mg/g.Adsorption kinetics studies show that the adsorption process conforms to the pseudo second-order equation model,indicating that is chemical adsorption.Thermodynamic studies have shown that the adsorption process takes place spontaneously at room temperature without consuming energy,which is suitable for wastewater treatment.（2）Although the oxygen-deficient WO₃（Ar/H₂）nanosheets have a large adsorption capacity,they fail to deeply degrade organic pollutants.Therefore,Ag/WO₃ material was successfully constructed by employing the plasma resonance effect of Ag with visible-light adsorption.The optimized Ag/WO₃ material formed by 2 h photo-deposition possesses the best photocatalytic performance,and the degradation efficiency toward Rhodamine B（RhB）reaches 97%within 90 minutes.In addition,through various photoelectrochemical characterizations,it was found that Ag/WO₃ has a stronger visible light absorption capacity and a higher photocurrent response,indicating that the introduction of Ag nanoparticles（diameter about 5 nm）can not only enhance the light absorption capacity,but also can promote the separation of photo-generated carriers,improving the photocatalytic performance.（3）Ag is a precious metal,which is expensive and shows limited application in the treatment of printing and dyeing wastewater.Therefore,a method of semiconductor compounding is sought to modify WO₃ for the photocatalytic performance improvement.Firstly,the WO₃ cube was prepared by hydrothermal method,and then were combined with carbon nitride（CN）by the grinding method to form CN/WO₃composite material.Studies have shown that a tight interface is formed between WO₃and CN,and the energy bands match well with each other to construct a Z type heterostructure.Excited by visible light,the electrons in the WO₃ conduction band combine with the holes in the CN valence band,and the left holes with strong oxidation ability in the WO₃ valence band and the electrons with strong reduction ability in the CN conduction band participate in the oxidation reaction and the reduction reaction,respectively,so that the photogenerated carriers are effectively separated,and the photocatalytic degradation performance based on CN/WO₃ composite is further improved.