Assembly And Electron Transfer Mechanisms On Visible Light Responsive 5,10,15,20,-meso-tetra- (4-caboxvphenvl/4-hvdroxvphenyl)porphyrin/ Transition Metal Oxides Composite For Photocatalytic Hydrogen Production

Solar energy and hydrogen energy are the two most promising new energy sources in twenty-first century. Converting solar energy into hydrogen energy or electric energy by photocatalytic technology is one of the most promising ways to solve energy crisis and environmental problems at present. It was found that visible light absorption and photocatalytic activity for hydrogen production over metal oxide semiconductors can be improved by dye sensitization. Porphyrins and their derivatives possess highly conjugated planar structure, luminescent and chromogenic groups and high thermostability, and they are a class of photosensitive materials with excellent performances. In addition, it is also possible to achieve hybrid materials with excellent performances (such as photoelectricity,photocatalysis and sensor) by changing the functional groups surrounding the porphyrin,.Based on the structural variability and excellent visible light absorption properties of porphyrin, in this paper, four carboxyphenyl/hydroxyphenyl porphyrin sensitized transition metal oxides, such as cuprous oxide, nickel oxide, were constructed through non-covalent interactions. Furthermore, the assembly mechanism, photoelectric properties, photocatalytic activity for hydrogen production, and the mechanisms of photoinduced electron transfer and photocatalytic hydrogen production were studied. The main contents are summarized as the followed:The excited state and oxidation state of the meso-tetra (4-carboxyphenyl)-porphyrin (TCPP)have good regeneration ability. Moreover, it is easy to be binded onto the surface of metal oxide. Based on this, with TCPP and cuprous oxide nanoparticle as main reactants, a novel composite (TCPP/Cu2O) was prepared via a facile method. The assembly mechanism of TCPP and Cu2O was investigated by UV-vis spectroscopy and FTIR. The results indicated that not only peripheries of TCPP but also the central of TCPP macrocycle interacted with Cu2O. Furthermore, with the obtained composite as the photocatalyst, the photocatalytic activity for hydrogen production was investigated. The composite showed more excellent performance for hydrogen production than that of pure TCPP or pure Cu2O, and also higher than that of 5,10,15,20-meso-tetraphenylporphyrin (TPP)/Cu2O composite. By means of fluorescence spectra, electrochemical impedance spectra and photoelectronic performance measurement, the mechanism of electron transfer in the composite was explored. The results showed that the introduction of TCPP can enhance the light absorption of Cu2O, and the strong interaction between TCPP and Cu2O can quicken the transfer of photo-generated electrons. It hoped that this work can open up a new perspective for the assembly and application of dye-functionalized semiconductor nanoparticles.With meso-tetra (4-hydroxyphenyl)porphyrin (THPP) and hexagonal nickel oxide nanosheets as the main reactants, a series of THPP/NiO nanocomposites with various mass ratio were prepared. The assembly mechanism of THPP and NiO was studied by UV-vis spectroscopy and fluorescence spectroscopy. Furthermore, the photocatalytic hydrogen production performance, photoelectric properties and electron transfer mechanism of THPP/NiO nanosheet composites were investigated. It was indicated that the photocatalytic activity for hydrogen production can be adjusted by modifying the binding mode between the porphyrin and metal oxide semiconductors. In addtion, the studies about the assembly and electron transfer mechanisms for the THPP/NiO nanocomposites will provide a new idea for preparing the catalysts with highly efficient photocatalytic activity for hydrogen production.Four TCPP self-assemblies with different structures and morphologies were prepared by adjusting the pH value of TCPP ethanol solution. The self-assembly mechanism of TCPP molecules at various pH values was investigated by UV-vis spectroscopy, FTIR and fluorescence spectroscopy. It was found that J-type assemblies of TCPP molecules can be formed at pH = 1, and H-type assemblies can be formed at pH = 12. Electrostatic interaction,hydrogen bond and ?-? conjugation interaction were the main driving force for the assembly of TCPP molecule. Moreover, the photocatalytic activity and photoelectrochemical properties of those TCPP self-assemblies prepared at various pH values were studied. The results showed that the acidity of the solution have a great influence on the photoactivity of hydrogen production of the TCPP assemblies. The J-type TCPP assembly showed a more favorable photocatalytic performance for hydrogen evolution.Based on the above results in this paper, it is demonstrated that the non-covalent interaction is a simple, rapid and effective method for the preparation of the porphyrin-based hybrids.Importantly, the assembly, electron transfer and photocatalytic performance of porphyrin/transition metal oxide hybrids can be controlled by changing the reaction conditions or the structure of the porphyrins. It provides a new theoretical and experimental basis for designing and preparing highly efficient photocatalysts for photocatalytic hydrogen production.