The Assembly And Photocatalytic Hydrogen Evolution Of Graphene/Conjugated Organic Hybrids Induced By Rare Earth Ions/Compounds

The increase of serious energy shortage and the excessive use of fossil energy have brought many problems to the social and economic development and living environment.The development of clean energy represented by hydrogen energy is an effective way to solve these problems.Photocatalytic hydrogen evolution can convert solar energy into renewable energy,and the product of hydrogen combustion is water.Therefore,by photocatalytic hydrogen evolution,the environment can be protected,and energy shortage could be solved.The efficiency of photocatalytic hydrogen evolution is closely related to the composition and microstructure of the photocatalyst.In this paper,a series of high-efficient photocatalysts for hydrogen evolution were prepared with graphene as the main substance.By being induced with rare earth ions/compounds,the assemblies of conjugated organic compounds?such as ethylnylpyridine and porphyrin?and graphene can be modified.Subsequently,a series of composite photocatalysts for highly efficient hydrogen evolution were achieved.Furthermore,the assembly and electron transfer mechanisms were investigated in detail.The main points of the reseach are as follows:With rare earth ions?Ln?as interfacial linkers,novel three-dimensional assemblies composed by 1,2-di?pyridine-4-ly?ethyne?DPyE?and graphene oxide?GO?were fabricated by means of electrostatic interaction and coordination interaction.The microstructure,morphology and assembly mechanism of the composites were investigated by means of transmission electron microscopy,UV-visible spectroscopy,infrared spectroscopy,Raman spectroscopy and X-ray powder diffraction.Further,the photocatalytic activity for hydrogen evolution over the GO-Ln-DPyE composite was investigated.It was found that the photocatalytic activity of GO-Ln-DPyE was significantly higher than that of GO-DPyE composite without bridging agent?rare earth ion?,indicating that the Ln played a key role in regulating the microstructure and photocatalytic activity of the GO-Ln-DPyE composite.Moreover,the results of photocurrent response and electrochemical impedance spectroscopy showed that,as the interfacial linker between GO and DPyE,earth ions can provide a definite way for photoelectron transfer,which is beneficial to improve the separation of electrons and holes as well as photocatalytic activity for hydrogen production.Compared with 1,2-di?4-pyridyl?ethyne,the porphyrin was easy to be prepared and possessed various structures and high visible molar extinction coefficient.Therefore,by means of the bridging of rare earth ions?Ln?,a novel nanohybrid?GO-Ln-DPDPP?constructedbygrapheneoxide?GO?pillaredwith5,15-diphenyl-10,20-di?4-pyridyl?porphyrin?DPDPP?was prepared by electrostatic interaction combined with coordination interaction.It was found that the riveted Ln at the GO interface had an important effect on the morphology and structure of GO-DPDPP.Meanwhile,photo-produced electron transfer in the hybrid can be effectively promoted by the Ln implanted in the GO.Photocatalytic H₂ production and electron transfer mechanism were further explored.It showed that,based on the bridging of the Ln,lower interfacial resistance and higher separation of electron and hole caused by the strong interaction between DPDPP and GO were very responsible for the increased photocatalytic activity of H₂ production.These results indicate the key role of the interfacial modulation in the architectures in order to achieve an efficient photocatalyst for substantial improvement in photocatalytic activity.By in-situ hydrothermal method,the GO-C₃N₄-LaVO₄ composite with high dispersion,small size and mixed phase LaVO₄ in the GO-C₃N₄ was prepared.The GO-C₃N₄-LaVO₄ composite showed high photocatalytic activity for hydrogen evolution.Based on the results of photocatalytic hydrogen evolution,fluorescence spectrum,photocurrent response and electrochemical impedance,it was confirmed that the LaVO₄ implanted in the composite could not only improve the light absorption of the GO-C₃N₄ composite,but also effectively inhibit the combination of photo-produced electron-hole.In addition,the crystallization of the LaVO₄ could be regulated by GO and C₃N₄.The LaVO₄ with mixed tetragonal phase and the monocline phase in the composite were beneficial to the separation of photogenerated electrons and holes.Therefore,the photocatalytic performance for hydrogen evolution over the composite was significantly improved.Obviously,the introduction of the mixed phase LaVO₄ in the interface of GO-C₃N₄ can not only improve the light absorption of the composite and promote electron transfer,but also avoid the oxidation with metal nanoparticles as a cocatalyst,providing a new idea for the construction of a new,stable,efficient and cheap organic composite semiconductor photocatalyst.The research in this paper provides a new idea for constructing graphene-based composite photocatalysts with novel structure and excellent performance,and also provides experimental basis and theoretical guidance for photo-produced electron transfer involved in the process of converting solar energy into hydrogen energy.