Preparation And Application Of Noble-Metal-Free Photocatalysts Based On Tp-Covalent Organic Framework

The excessive utilization of fossil fuel is the key factors contributing to the energy shortage and environmental pollution,and it is imperative to develop green and alternative energy sources.Therefore,photocatalytic water splitting driven by solar energy would seemingly provide a potential option to obtain hydrogen energy.Thus,searching for high efficient,stable,visible-light responsible photocatalysts is still the kernel in photocatalysis field.Covalent Organic Frameworks（COFs）are an emerging class of photocatalysts with excellent hydrogen production performance due to their porous structure,large surface area,tunable band and structure.However,due to the serious recombination of photo-generated carriers of pure COFs,which requires noble metal Pt as co-catalyst to realize high hydrogen production activity.Nevertheless,the use of noble metal restricts the practical application of COFs photocatalysts.Therefore,this paper choose the classic Schiff base Tp Pa-COF as a model.Regulating the separation of photogenerated charges and the active centers by compounding non-noble metal Cu-based co-catalysts and constructing heterojunctions to realize the efficient hydrogen production activity of noble-metal-free photocatalysts based on COFs.The main contents are as follows:Firstly,the Cu₂O/Tp Pa-2-COF composite materials were constructed and explored its H₂ production performance and the active sites in photocatalytic water splitting.The Cu₂O was synthesized by a wet chemical reduction method.By adding Cu₂O into the synthesis system of Tp Pa-2-COF in situ,a series of Cu₂O/Tp Pa-2-COF composite materials with different proportions were prepared.X-ray powder diffraction,FT-IR spectras,SEM images,TEM images and other characterizations determined the successful synthesis and core-shell structure of Cu₂O/Tp Pa-2-COF hybrid materials.The characterizations of energy band structure of UV-vis DRS spectras and Mott-Schottky plots demonstrated that composite materials meet the thermodynamic requirements of photocatalytic H₂ evolution.The Cu₂O/Tp Pa-2-COF（1:9）manifests better photocatalytic activity of 5.24 mmol·g^-1·h^-1,which is about10 times higher than that of Tp Pa-2-COF.X-ray photoelectron spectroscopy spectrum（XPS）analyses were carried out to study the chemical states of Cu element,further determining the Cu as active sites in photocatalytic process.Photocurrent-time responses,EIS nyquist plots,LSV curves,PL emission spectras and other photo-electrochemical characterizations reveal that the Cu cocatalyst and heterojunction structure can realize the effective separation of photo-generated charges,thereby improving the H₂ production rate.Then the Cu-NH₂-MIL-125/Tp Pa-2-COF composite materials coordinated with single-site were prepared and explored its H₂ production performance and the active sites in photocatalytic water splitting.The NH₂-MIL-125 was synthesized by solvothermal method.The Cu-NH₂-MIL-125 was obtained by coordinating Cu ions.A series of Cu-NH₂-MIL-125/Tp Pa-2-COF hybrid materials with were prepared by adding Cu-NH₂-MIL-125 into the reaction system of Tp Pa-2-COF.The structure and morphology characterizations determined the successful synthesis and core-shell structure of composite materials.The energy band structure characterizations demonstrated the composite materials meet the thermodynamic requirements of photocatalytic H₂ evolution.The Cu-NH₂-MIL-125/Tp Pa-2-COF（4:6）sample exhibits the average H₂ evolution rate of 9.21 mmol·g^-1·h^-1,which is approximately 17.7 times higher than that of the parent Tp Pa-2-COF.The AQE was calculated to be 8.6%at500 nm.X-ray photoelectron spectroscopy spectrum（XPS）analyses were carried out to study the chemical states of Cu element,further determining the Cu²⁺/Cu⁺as active sites.The photo-electrochemical characterizations further proved that the heterojunction and Cu²⁺/Cu⁺active sites can effectively improve the separation efficiency of photo-generated charges.The performance testing of benzylamine oxidation proved that Cu-based co-catalyst can promote the interfacial charge transfer.Cu-based co-catalyst can not only provide the active sites,but also promote charge separation and improve the activity and stability of photocatalysts,which also explores a feasible path for the industrial application of photocatalytic hydrogen production technology.