| Developing sustainable and clean new energy is the primary way to solve the problem of energy shortage and environmental pollution caused by the excessive reliance on fossil energy.Hydrogen obtained by photocatalytic water splitting is undoubtedly the most ideal method to solve the above problems.Covalent organic frameworks?COFs?,as an emerging class of crystalline and porous materials connected by covalent bonds,has become a newly-developing photocatalyst in recent years because of its suitable band energy and wide visible light adsorption in more recent years.However COFs as photocatalyst is still constrained by the fast recombination of photo-generated electrons and holes,which makes it difficult to achieve ideal hydrogen production performance.Until now,Pt and other precious metal co-catalysts are used to realize the separation of photo-generated electrons and holes.It is difficult to realize large-scale practical application because of high cost and rare.Hence,in this work,two kind of transition metal inorganic semiconductors loading on COFs,so as to solve fast recombination of photo-generated electrons and holes.Thus,the photocatalytic activity of hydrogen production can be achieved without the precious metal as co-catalyst.The main contents are as follows:?1?Preparation of Ni2P/TpPa-2-COF composites.TpPa-2-COF,synthesized by solvothermal method,grinded with Ni Cl2.6H2O and Na H2PO2?H2O.The Ni2P/TpPa-2-COF composites were synthesized by phosphating at high temperature in a tube furnace.The structural integrity of TpPa-2-COF and introduced Ni2P successfully in composite were confirmed by X-ray diffraction and X-ray photoelectron spectroscopy.Morphology was confirmed by scanning electron microscope and transmission electron microscope.Band gap was investigated by UV-vis diffuse reflectance spectroscopy and Mott-Schottky,in order to determine the capacity of photocatalytic water splitting.Transient photocurrent responses,impedance spectra,linear sweep voltammetry,photoluminescence spectrum and surface photovoltage spectroscopy show that loading Ni2P as a co-catalyst suppress the recombination of photogenerated charges.These characterizations all indicate Ni2P/TpPa-2-COF have huge potential for photocatalytic hydrogen production.Then the photocatalytic hydrogen production of a series of composites was tested.The results of photocatalytic H2evolution under visible light irradiation show that 5 wt%Ni2P loading on the TpPa-2-COF shows optimal H2production activity with a rate as high as 5.58 mmol?h-1?g-1which is 11 times as high as that of the pure TpPa-2-COF.?2?Preparation of MoS2/TpPa-1-COF composites.MoS2is synthesized through hydrothermal synthesis method,afterthat exfoliated in N,N-dimethylformamide?DMF?by sonication.Triformylphloroglucinol and paraphenylenediamine were added to synthesize MoS2/TpPa-1-COF composites by solvothermal method.TpPa-1-COF was synthesized successfully in DMF was confirmed by powder X-ray diffraction and Fourier transform infrared.X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy results show MoS2was synthesized and loaded successfully.And we also confirm the band energy of TpPa-1-COF and composites by UV-vis diffuse reflectance spectroscopy and Mott-Schottky.Transient photocurrent responses,impedance spectra,linear sweep voltammetry,photoluminescence spectrum and surface photovoltage spectroscopy show that loading MoS2as a co-catalyst facilitate the transport of photogenerated electrons and effectively suppress the recombination of photogenerated charges.The results of photocatalytic H2evolution under visible light irradiation show that 3 wt%MoS2loading on the TpPa-1-COF shows optimal H2production activity with a rate as high as 5.58 mmol?h-1?g-1which is 32 times as high as that of the pure TpPa-1-COF.And H2production activity also can be comparable to the same Pt loading(5.48 mmol?g-1?h-1),which achieved the goal of replacing noble-metal as co-catalyst. |
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