Preparation Of ZnTPyP/WO₃ Z-Scheme Nanomaterials For Enhanced Photocatalytic Hydrogen Generation

Hydrogen energy has the advantages of high combustion value,green products,and extensive sources.It is ideal clean energy to replace fossil fuels in the future.Photocatalytic water splitting is an effective way to produce hydrogen.In order to achieve high-efficiency photocatalytic water splitting to produce hydrogen,researchers have developed different types of photocatalysts.Traditional photocatalysts can be divided into single structure and type II heterojunction photocatalysts in terms of catalyst composition structure.However,in the photocatalytic process,the former photogenerated electron-hole pairs transmutation phase recombines,and the photoresponse region is mostly ultraviolet light;the latter effectively solves the problems of single structure photocatalysts,but the oxidation-reduction capacity has decreased.The researchers were inspired by plant photosynthesis,and proposed and successfully constructed Zscheme photocatalytic system.And photogenerated electrons can be transported along the "Z" path,which not only effectively inhibits the effective recombination of photogenerated electron and holes,but also retains the original redox ability of the catalytic material.However,It also have some limitations: first,the catalyst material must have a matching energy level structure;secondly,The composition of the Z-scheme catalyst can only absorb ultraviolet light,and the light energy utilization efficiency is low.,and some are Sulfurcontaining metal compounds such as Cd S and Mo S2 are highly toxic and cannot be applied on a large scale;finally,the existing Z-scheme photocatalysts has a low hydrogen production efficiency.In order to develop a new and non-toxic Z-scheme photocatalyst with visible light absorption region and more efficient hydrogen production performance,we mainly conducted the following two parts of research:1.We use WO₃ photocatalysts widely used in the field of photocatalysis and new high-efficiency hydrogen production catalyst tetrahydropyridyl zinc porphyrin?ZnTPyP?assembly to construct ZnTPyP assembly/WO₃ direct Z-scheme photocatalyst.Through N-W coordination,the controllable co-assembly of ZnTPyP on WO₃ nanorods was achieved,and the ZnTPyP assembly/WO₃ composite material was prepared.The influence of emulsifier species,p H value of the assembly solution and the input quality of WO₃ nanorods on the morphology of the ZnTPyP/WO₃ composite catalyst was studied by SEM,TEM.HRTEM and element mapping proved the formation of ZnTPyP and WO₃ co-assembly.XRD proved that ZnTPyP exist in the composite material in a hexagonal stacking assembly.The results of UV-diffuse reflectance spectroscopy showed the catalyst has a wide visible light region absorption.FT-IR shows the vibration absorption peak of the chemical bond on the pyridine ring has a red shift,indicating that ZnTPyP and WO₃ have coordination effect.XPS shows binding energy of W and N elements has changed and confirm the coordination between ZnTPyP and WO₃.The results of photocatalytic hydrogen production show that the performance has a close structure-activity relationship with the structure of the composite materials.When the Pt loading is 1 wt%,the side-by-side structure ZnTPyP/WO₃ has a hydrogen production rate as high as 74.53 mmol/g/h,which is 2.62 times that of ZnTPyP assembly.Light deposition Pt experiment showed that the photogenerated electrons appear on ZnTPyP,which shows that the photogenerated electrons are transported along the “Z” path.It allows the photogenerated electrons from WO₃ to directly recombine with the photogenerated holes of ZnTPyP,and effectively improving the separation efficiency of photogenerated electron-hole pairs.This was confirmed by the result of photoelectron lifetime increased 0.35 ns.Finally,the characterization and calculation results of the energy band structure of the material prove that the photogenerated electrons are transported along the “Z” path in the composite material from the theoretical formation of the direct Z-scheme photocatalytic system,indicating that the composite ZnTPyP/WO₃ is a direct Z-scheme photocatalyst.2.In order to further improve the photo-generated electron-hole pairs rate,we introduced Au nanoparticles?NPs?as the electron transport medium at the composite interface of ZnTPyP/WO₃.And the surface plasmon resonance of Au NPs can further improve the mobility of photogenerated carriers in the interface,and further improving the photocatalytic hydrogen production performance of the composite material.UV-diffuse reflectance spectroscopy shows that the introduction of Au NPs enhances the light absorption capacity of the composite.XPS results show that there is Au-N coordination between Au NPs and ZnTPyP.The photocurrent test shows more conducive to the transmission and migration of electrons in the composite catalyst;the photocatalytic hydrogen production results show that the hydrogen production rate of ZnTPyP/Au/WO₃ has been further improved compared to ZnTPyP/WO₃.It is 1.54 times that of ZnTPyP/WO₃ and 4 times that of ZnTPyP assembly,which also shows that the introduction of Au NPs further improves the photocatalytic performance.