Fabrication Of Porphyrin Metal Complexes/Carbon Nanotube Composite For Photocatalytic Hydrogen Evolution Under Visible Light

With the development of society,the demand for energy is increasing,and the energy issues have become one of the major challenges for human society.To solve this problem,scientists turn their attention to the field of new energy.Hydrogen is favored because of its high calorific value,green production and rich raw material in the existing new energy.Solar energy is inexhaustible,therefore,water photolysis becomes an efficient and large-scale hydrogen production,and has great application prospects.However,the problem of water photolysis is the catalyst.Water can not produce hydrogen with light only,so developing efficient catalyst for photocatalytic hydrogen production is necessary.In nature,green plants are mainly photosynthetic by chlorophyll,whose main component is magnesium porphyrin.The porphyrin has a wide range of light absorption in the range of 400-500 nm,and the range can be wider by modification.It has a large porphyrin ring conjugate structure,strong chemical stability,and molecular modification easily.So it has great application prospects in the field of photocatalysis.In addition,most porphyrins are in the form of assembly.By assembling the porphyrin molecules into ordered nanostructures,the photosynthesis of plants can be better simulated,and the efficiency of photocatalytic hydrogen production can be further improved.In this paper,we studied the preparation and photocatalytic hydrogen production properties of supermolecular aggregates based on porphyrin coordination polymers and their composites with carbon nanotubes.The main research contents are divided into the following two parts:1.In this paper,porphyrin-metal complexes were prepared through the reaction of 5,10,15,20-tetra(4-carboxypheny)porphine(TCPP)with metal salts by one-step solvothermal method,which improved the degree of conjugation and excited fluorescence resonance energy transfer(FRET)between porphyrin molecules,thus stabilizing the excited state electrons,extending the carrier lifetime.The result showed that the average hydrogen production rate reached 7.82 mmol/g in 8 h without platinum loaded.2.The porphyrin metal complexes/carbon nanotubes composites were prepared by a simple solvothermal reaction of TCPP with metal salts and carbon nanotubes.The study showed that the porphyrin-metal complexes were further compounded with carbon nanotubes,and it improved the ability of electron transport in the excited state,which further improved the lifetime of electron-hole pairs and enhanced the photocatalytic hydrogen production performance under visible light.The average hydrogen production rate reached 18.67 mmol/g in 5 h.The EDS,UV-Vis,FTIR,XPS and other characterization methods showed that Sn entered into the center of the porphyrin macrocycle to metallize the porphyrin TCPP,and at the same time the carboxyl group around the porphyrin was coordinated with the metal in the porphyrin ring and solution generating a space-like conjugate structure.The metallized porphyrin metal complex is closely coated on the surface of the carbon nanotubes to form a porphyrin-metal complex / carbon nanotube composite,and the UV visible absorption of the porphyrin metal complexes and composites was widened and redshift in the visible region,which can favor the absorption of light in the visible region.The results showed that the degree of metallization of porphyrin has a great influence on the photocatalytic water decomposition performance.The higher the degree of metallization,the stronger the photocatalytic water decomposition performance.