Fabrication Of Porphyrin/Au Nanoparticle Composite And Study Of Its Visible-light Photocatalytic Properties

Hydrogen production from visible light photocatalytic water splitting is an effective way to solve energy and environmental problems,and the key to improving the photocatalytic efficiency lies in the preparation of high-efficiency photocatalysts.Due to the surface plasmon resonance effect?SPR?generated by photoexcitation,plasmon materials?gold,silver,graphene,etc.?can effectively enhance the photocatalytic activity of semiconductor materials.Interestingly,the SPR can promote the separation of photogenerated electron-hole pairs,thereby improving the photocatalytic efficiency of semiconductors.However,most of the semiconductors currently used are inorganic semiconductors which absorb spectrum lie in ultraviolet region that cannot fully utilize the energy of sunlight.Otherwise,porphyrin nanoparticles with regular morphology and long-range ordered?-?stacking can enhance optical absorption cross section and the efficiency of intermolecular excited state energy and electron transfer,thus to reduce electron-hole recombination and increase the lifetime of excited electron-holes,and significantly increase the efficiency of visible light photocatalytic water splitting.However,due to relative low energy of photo-generated electrons,usually need add Pt as co-catalyst during reaction.In this work,we chose gold nanoparticles?GNPs?with visible light region excitation and high chemical stability,combined with the advantages of porphyrin assembly,and designed a composite structure of gold nanoparticles?GNPs?and tetrapyridyl zinc porphyrin?ZnTPyP?.We prepared highly efficient visible light photocatalytic hydrogen production catalyst by taking advantage of the synergistic effect of the absorption characteristics in the visible region of the zinc porphyrin assembly and the plasmonic enhanced properties of gold nanoparticle,and explored the relationship between their photocatalytic activity and composite structure.Our work mainly focused on the following two aspects:1.We use electrostatic interactions between gold nanocrystals and assemblies or the coordination of pyridyl with Zn atoms at the center of porphyrins to solve the problem of interface compatibility between gold nanocrystals and porphyrin assembly and prepared ZnTPyP/GNPs composite structure with different interface characteristics.The regular morphology and unique size of gold nanoparticle with different surface ligand has been synthesized via“one-pot synthesis”and“ligand exchange”methods.The TDS-GNPs/ZnTPyP composite material was fabricated through electrostatic interaction,and4-PEM-GNPs/ZnTPyP composite material was fabricated through Zn-N coordination by adjusting the surfactant.The resultant materials have regular morphology,and gold nanoparticle dispersed on the surface of the porphyrin assemblies homogeneously.ZnTPyP/GNPs composites have good crystal structure,and the interface interaction exhibited more compatibility between gold and porphyrin in4-PEM-GNPs/ZnTPyP composite material.2.Investigating the photoelectric properties and photocatalytic performance of composites with different interface properties.The UV-vis absorption,PL intensity,time-resolved fluoresces decay and the i-t test all showed that the ZnTPyP/GNPs exhibited outstanding optoelectronic properties,especially through the Zn-N coordination.The photocatalytic ability was tested in H₂ production from water splitting,the composite materials shows excellent photocatalytic performance without addition of Pt as co-catalyst.Photocatalytic hydrogen production of 4-PEM-GNPs/ZnTPyP composite materials was 8 mmol/g/h twice that of TDS-GNPs/ZnTPyP composites,and was a physical mixture of gold nanoparticles and ZnTPyP self-assembly twenty times,indicating that N-Zn coordination makes gold nanoparticles and ZnTPyP self-assembly interface more compatible and more conducive to photoelectron-hole separation and transmission.Besides,at different wavelengths,the photocatalytic hydrogen production of4-PEM-GNPs/ZnTPyP composites shows that the main electron donor is the ZnTPyP and the role of gold nanoparticles in promoting the separation of electron-hole pairs has a significant effect on the decomposition of hydrogen produced by porphyrins.