Research On Photocatalytic Performance Of G-C₃N₄-based Cu-MOF Derived Coprous Selenide Composite Materials

The global energy crisis can be solved by the use of solar energy.The photocatalytic decomposition of water for hydrogen production under sunlight with appropriate photocatalyst is a promising solution to the global energy crisis.Graphite carbon nitride（g-C₃N₄）is a potential photocatalytic semiconductor material due to its advantages such as no metal elements,easy synthesis,strong visible light response and excellent physical and chemical stability.The modification of g-C₃N₄ to further improve its photocatalytic activity has become the focus of current research.In this paper,g-C₃N₄ was modified by loading efficient co-catalyst and introducing pore channels to enhance electron transport performance.The morphology and pore structure of the calcined Cu_2-xSe and Cu₂Se@C samples obtained under different conditions of Cu-MOF calcination were analyzed,and the effect of Cu_2-xSe and Cu₂Se@C on the photocatalytic hydrogen production activity of g-C₃N₄ was discussed.Cu_2-xSe particles with a size of about 200 nm were obtained by calcination of Cu-MOF in air and selenization in nitrogen.Cu_2-xSe/g-C₃N₄ composites were prepared by calcining Cu_2-xSe and melamine.The BET test shows that the microporous structure of Cu-MOF is transformed into the mesoporous and macroporous structure of Cu_2-xSe during calcination.UV-Vis DRS test showed that the absorption range and absorption intensity of the composite samples were significantly improved.The photocatalytic hydrogen production and conditional experiments show that Cu_2-xSe/g-C₃N₄-4 has the best photocatalytic hydrogen production efficiency of 87.2μmol·h^-1·g^-1 without the addition of precious metal Pt,which is about 12 times that of pure g-C₃N₄.It shows excellent hydrogen production activity.This is because Cu_2-xSe has good electron transport capacity,which can effectively reduce the recombination rate of photoelectron holes and improve the separation effect of photoelectron holes.In order to further improve the electron transfer capacity of the co-catalyst and form a more uniform three-dimensional pore,Cu-MOF was calcined in nitrogen and then selenized in nitrogen to obtain Cu₂Se@C.Finally,Cu₂Se@C/g-C₃N₄ composite was prepared by calcining Cu₂Se@C and melamine.The morphology of Cu₂Se@C was characterized by SEM,TEM and Raman as Cu₂Se particles wrapped in a regular octahedral amorphous carbon skeleton.The BET test shows that the microporous structure of MOF is transformed into three-dimensional ordered mesoporous structure of Cu₂Se@C during calcination,which can further improve the charge transfer rate.UV-Vis DRS test showed that the absorption range and absorption intensity of the composite samples were significantly improved.Cu₂Se@C/g-C₃N₄-2wt%showed excellent photocatalytic activity.The hydrogen production efficiency of the sample was 178.0μmol·h^-1·g^-1,which was about 23 times that of pure g-C₃N₄and 1.5 times that of g-C₃N₄ loaded with 0.5wt%Pt.The high fluorescence lifetime of excitons in PL time-resolved fluorescence spectra and the weak fluorescence intensity in fluorescence emission spectra,as well as the strong photocurrent response and the low interfacial resistance all prove that the Cu₂Se@C composite co-catalyst has a good electron transport capacity,which can greatly improve the separation efficiency of photogenerated electron holes in the sample.Therefore,the composite catalyst has excellent photocatalytic activity.