In Situ Fabrication And Properties Of Tungsten Oxide Composite Photocatalyst

Photocatalytic technology utilizes photon energy to promote synthesis or degradation of compounds under mild conditions.WO₃ is widely used in photocatalysis,photoelectrocatalysis and other fields due to its unique physical and chemical properties.However,the reduction potential of conduction band of WO₃ is low,which is not enough for reduction reaction,resulting in low quantum efficiency of photocatalysis.Low reduction rate will lead to rapid recombination of photo generated carriers,which limits the photocatalytic oxidation reaction.Therefore,in order to overcome these problems,this paper reasonably designed a multi-component Z-type composite system to improve the photocatalytic performance of single-phase WO₃.The details are as follows:（1）Using Pb²⁺ion as ion exchanger to prepare Z-scheme composite photocatalyst WO₃/PbWO₄ in situ construction by ion exchange.To study whether ion exchange occurs or not and its influence on construction of highly quality carrier transport separation interface.XRD（X-ray diffraction）characterization methods showed that+2 valent metal cations could exchange with precursor H₂WO₄.HR-TEM（High resolution transmission electron microscope）result shows that the highly quality carrier transport separation interface with continuous phase transition can be prepared by ion exchange method.I-T（Transient photocurrent）、EIS（impedance）、PL（Photoluminescence）、TR-PL（Time resolved photoluminescence）and so on found that the photocurrent density increase by 22 times,transmission resistance smaller and longer lifetime than single phase.XPS（X-ray diffraction photoelectron spectroscopy）,ESR（Electron spin resonance）and free radical capture experiments combined with DRS（ultraviolet visible diffuse reflectance）and VB XPS（X-ray diffraction photoelectron valence band spectroscopy）show that the carriers are separated in a Z-scheme pattern between the two phases,which ensures the maximum retention of redox ability of in system.Photocatalytic degradation experiments show that the improvement of carrier separation efficiency can significantly increase the photocatalytic activity of the material,and WO₃/PbWO₄ material has excellent stability.All of these are benefit from the interface of carrier transport and separation constructed by grain boundary and chemical bonding.In addition,compared with the uniform mixing and clear phase interface composite samples,which was found that the highly quality bonded phase interface is one of the key factors for the photocatalytic activity of the composite.（2）Furthermore,using Bi³⁺ion as ion exchanger to prepare Z-scheme composite photocatalyst WO₃/Bi₂WO₆ in situ construction by ion exchange.To study whether ion exchange occurs or not and its influence on construction of highly quality carrier transport separation interface.XRD characterization methods showed that+3 valent metal cations could exchange with precursor H₂WO₄.HR-TEM measurement shows that the ion exchange process can build a highly quality carrier transport and separation interface.I-T,EIS and PL measurements found that the carriers are separated greatly between the two phases,and the composite samples has a high effective carrier concentration.The photodegradation experiment results show that the apparent rate constant k of WO₃/Bi₂WO₆ is 130 times higher than WO₃,which reflects the efficient separation of photogenerated carriers at grain boundaries.The work function and band structure of the materials were determined by UPS,M-S and DRS,combined with free radical capture experiment,XPS,ESR and photoreduction site experiment,the carrier transfer was still the Z-scheme pattern between two phases.Seven times of cyclic degradation experiments showed that WO₃/Bi₂WO₆ samples had excellent photostability,which still benefited from the construction of high-quality carrier transport separation interface.（3）Thirdly,Ag¹⁺was used as the ion-exchange reagent to investigate whether the ion-exchange process could occur,and the photocatalytic activity and mechanism of the samples were studied.The results of XRD show that the ion exchange process takes place and the ternary WO₃/Ag/Ag₂WO₄ composite is obtained.HR-TEM showed a continuous transition between WO₃ and Ag₂WO₄.Combined with the contents of the first two chapters,it is concluded that the design method is universal in this system,and can construct highly quality carrier transport separation interface.The reducibility of Ag makes Ag nanoparticles exist on the composite sample.Therefore,DRS test exhibits the surface plasmon resonance effect,which broadens range of light response.The energy band structure of the sample was determined by DRS,M-S and other tests.meanwhile,combined with free radical capture experiments determined the carrier transfer and separation paths to establish Z-scheme.The effective carrier separation of WO₃/Ag/Ag₂WO₄ shows that composite sample have higher photocurrent density,lower transmission resistance and longer carrier lifetime,and the apparent rate constant of WO₃/Ag/Ag₂WO₄ is 194 times that of Ag₂WO₄.The excellent photostability after seven cycles of degradation benefits from highly quality interface of chemical bonding.