Study On Photoelectric Properties Of Porphyrin-based Nanocomposites

Porphyrins exist widely in nature and are known as "life dyes".They are important organic compounds that make up chlorophyll,hemoglobin and other biomolecules.Due to its rigid π-π plane conjugated structure,excellent absorption and emission properties in the visible light range;it plays an important role in the process of photosynthesis where the original electron participates in the multi-step reaction process in the chloroplast.Pigment molecules in nature are the core of energy conversion and electron transfer.Yet owe to the porphyrin and nature of these molecules have an inseparable relationship,their superior electronic,optical,catalytic,biochemical properties,caused it to become a promising organic semiconductor materials.In recent years,the platform for solar energy conversion and photocatalysis need to be developed rapidly,the reasonable design of high efficiency,stable light capture is the inevitable requirement,thus constructing efficient light-harvesting the performance of the porphyrin based nanocomposites,and the study of its electron transfer and charge separation within the structure have become a research hotspot.In this paper,the porphyrin molecules as the core,from porphyrin aggregates,metal porphyrin ligand coordination effect,and different metal porphyrins,performance study three aspects to carbon materials,precious metals and TiO₂ nanorods as the auxiliary,intended to build efficient light-harvesting system,combined with ultraviolet visible light source and Scanning Electrochemical microscopy（UV-vis/SECM）platform,from the perspective of micro interface dynamics porphyrin based nanocomposites studied the photoelectric performance.This work mainly has the following three aspects,the specific research content is as follows: 1.New Insight into Enhanced Photocatalytic Activity of Morphology-dependent TCPP-AGG/RGO/Pt Composites.The porphyrin aggregate is recognized as an attractive candidate for developing artificial light-harvesting systems.Using 5,10,15,20-tetrakis-（4-carboxyphenyl）porphyrin（TCPP）,the porphyrin aggregates with different morphologies（sphere,rod and flake）are controllably prepared by the surfactant-assisted self-assembly reaction,and then synthesize the ternary bionic-system（e.g.porphyrin composites）.These composites are characterized by scanning-electron microscopy（SEM）,atomic force microscope（AFM）and spectroscopic technology.The combinatorial technique consisted of ultraviolet–visible spectroscopy and scanning electrochemical microscopy（UV-vis/SECM）is used to record SECM approach curves of porphyrin photocatalysis under visible light illumination at the specific zones,where morphology-dependent porphyrin composite is recognized to be distributed evenly on ITO surface.Heterogeneous photoelectron transfer rates（keff）are given by simulating SECM approach curves.It is suggested that rod-like porphyrin aggregate composite has highest photocatalytic efficiency with the kinetics rate to be 8.624×10-2 cm s-1,the largest keff of which is obtained at the excitation wavelength of 469 nm.These findings are also proved by photocatalytic decomposition test of pollutants（methyl orange）.It is indicated that one-dimensional nanostructure is advantageous for separation of electrons and holes and directional transmission of photoelectron.2.Preparation and Photoelectrochemical Study of Supramolecular Light harvesting Bodies: Surface-Modified TiO₂ NR with Metal Ligand Coordination Fixation Sensitizer.Continuous photoinduced electron transfer（PET）dynamics of metal porphyrin bound to TiO₂ nanorod（TiO₂ NR）surfaces via the metal-ligand axial coordination approach have been investigated using the self-construction UV-vis/scanning electrochemical microscopy（UV-vis/SECM）platform.The employed metal porphyrins covered absorption at different portions of the visible and near-IR region of the spectrum with LUMO energy levels are-3.0 e V and-3.2 e V,respectively,that is,having energy higher than the TiO₂ conduction band edge（-4.4 e V）.Phenylimidazole has been employed to visualize electronic coupling between the porphyrin and metal oxide surface for optimal PET dynamics.In agreement with the previously reported photocurrent generation of dye sensitized solar cells constructed using this self-assembly approach（J.Am.Chem.Soc.2009,131,14646）,interfacial electron transfer evidence indicates that PET is obtained from the excited metal porphyrin to TiO₂ NR.Heterogeneous photoelectron transfer rates（keff）are given by simulating SECM approach curves.It is suggested that zinc metalated meso-tetraarylporphyrins having halogen substituents on the peripheral aryl groups has highest PET dynamics with the rate to be 11.94×10-2 cm s-1 under visible light illumination,the largest keff of which is obtained at the excitation wavelength of 531 nm and an illumination intensity of 80 %.The efficient PET system constructed in this study will,we believe,provide useful information to help people investigate the mechanism of the charge transfer process of artificial photosynthesis.3.Studying of the Interfacial Light-induced Electron Transfer Behavior of N/Si Co-Doped TiO₂ NR/MTCPPs.Metal porphyrins（MTCPPs）are the class of molecules closely related to life processes.Therefore,studying the influence of different coordination metal ions on the physical and chemical properties such as light and electricity will help people understand the biological activity and mechanism of porphyrin natural compounds in vivo.Chemical modification of single-crystal TiO₂ NR by N/Si co-doping method improves the photoelectrochemical（PEC）activity under visible light,and further fixe the MTCPPs material on the N/Si co-doped TiO₂ NR conductive substrate.The N/Si co-doped TiO₂ NR/MTCPPs nanocomposites based on the in situ,real-time UV-vis/SECM technique and the traditional electrochemical methods were used to investigate the interface photoinduced electron transfer behaviors controlled by different metal ions in the porphyrin core.The reaction of electron transfer between I3-/I-and N/Si co-doped titania nanowires sensitized by MTCPPs（M = Fe,Co,Ni）was studied.The results showed that the photo-induced electron transfer behavior at the interface of the hybrid TiO₂ NR/MTCPPs was further controlled by transition metal ions in the porphyrin core.