Preparation Of Hybrid Materials Based On Covalent Organic Framework And Application Of Photohydrolyzed Hydrogen Production

With the increasing challenges in energy demands and environmental concerns,the development of sustainable and clean energy to replace existing fossil fuels has attracted considerable attentions.Among various renewable energy projects,hydrogen is considered to be the best alternative to fossil energy due to its environmental-friendly and high-energy-density advantages,photocatalytic water splitting reaction is regarded as one of the most promising routes to obtain hydrogen energy and the investigation of photocatalysts that can efficiently split water by harvesting solar energy is the critical technique of photocatalytic hydrogen evolution.In recent years,COFs have shown great potential in the field of photocatalytic water splitting due to their excellent visible light absorption and orderly pore structure.However,the extremely high photoelectron-hole recombination rate existed in COFs limits further improvement of their photocatalyst performance.To improve the immigration of photogenerated electrons in COFs photocatalysts and hydrogen evolution activity of COF-based photocatalysts,two types of covalently connected heterostructures photocatalysts,TiPa-1-COF and MOF-808-Tp Pa-1-COF,were designed and synthesized in this research.The main contents are as follows:（1）The Ti O₂ nanosheets were synthesized via the solvothermal method,and modified with 3-aminopropyltriethoxysilane and 2,4,6-trihydroxy-1,3,5-benze-netrialdehyde.The final covalently bonded TiPa-1-COF hybrid materials with diverse mass ratios were synthesized by adding CHO-Ti O₂ into the synthetic reaction system of Tp Pa-1-COF.The results of UV-vis diffuse reflection spectra,Fourier transform infrared spectra and X-ray photoelectron spectroscopy spectrum confirm the successful two-step modification of Ti O₂ and the covalent connection between Ti O₂and Tp Pa-1-COF components in hybrid materials.DRS and Mott–Schottky（MS）measurements suggest that TiPa-1-COF hybrid material shows the type II heterojunction.As a result,the photocatalytic activity of TiPa-1-COF（1:3）hybrid material is 11.19 mmol?g^-1?h^-1,approximately 3 and 4.6 times higher than that of TiPa-1-COF（1:3）and physical mixture（1:3）,respectively.The results of photocurrent-time profiles,electrochemical impedance spectrum,photoluminescence spectrum and surface photovoltage spectroscopy confirm that covalent connection between two components in hybrid material can effectively suppresse the recombination of electron–hole in hybrid materials.（2）The MOF-808 was synthesized by the stirring method.Subsequently the as-prepared MOF-808 were functionalized with para aminobenzoic acid（PABA）by post synthetic modification.The MOF-808-Tp Pa-1-COF was synthesized by addingMOF-808 into the synthetic reaction system of Tp Pa-1-COF.UV-vis diffuse reflection spectra and Fourier transform infrared spectra confirm the covalent connection between MOF-808 and Tp Pa-1-COF components in hybrid materials.DRS and Mott–Schottky（MS）measurements suggest that MOF-808-Tp Pa-1-COF hybrid material shows the type II heterojunction.The photocatalytic activity of MOF-808-Tp Pa-1-COF（6/4）hybrid material is 11.88 mmol?g^-1?h^-1,which is approximately 2.9 and 2.6times higher than that of MOF-808/Tp Pa-1-COF（6/4）and physical mixture（6/4）,respectively.Further analysis via EIS,PL spectrum and SPS showed that the covalent connection between two components in hybrid material can really serve as a bridge to improve the separation of electron hole pairs in the photocatalytic process.