Synthesis Of Mesoporous Ni_xCo_1-xS₂/S-g-C₃N₄ Composites And Photocatalysis For Hydrogen Production

Since 2009,Professor Xinchen Wang first reported that graphene phase carbon nitride（g-C₃N₄）can photocatalytic decomposition of water under visible light.It quickly became a star material in the field of photocatalysis,because of its advantages such as simple preparation,low price,stable chemical properties,and suitable band structure.However,the conventional methods prepared g-C₃N₄ has low specific surface area,high electron-hole pair recombination rate,slow surface reaction kinetics,and high hydrogen overpotential,which makes g-C₃N₄show low photocatalytic efficiency.These disadvantages limit the practical application of g-C₃N₄.In this paper,we first use the effective mass transfer effect of mesoporous materials to improve the contact and transfer between H₂O and the catalyst.At the same time,use the transition metal element and S coordination atom layer as the transition connection layer between metal sulfide and S-doped g-C₃N₄（S-g-C₃N₄）to ensure the efficient transport of photogenerated carriers between S-g-C₃N₄ and sulfide.Finally,the transition metal sulfide is used as a co-catalyst to reduce the hydrogen evolution overpotential and promote the electrocatalytic reduction of H⁺.As the results,the photocatalytic hydrogen production performance of g-C₃N₄ was effectively improved.The main contents of this article are as follows:（1）Using mesoporous SiO₂ as a hard template,and CH₄N₂S and Ni（CH₄N₂S）₄ as precursors,a mesoporous S-g-C₃N₄ supported Ni S₂ composite photocatalyst was successfully prepared by one-step annealing.XRD,SEM,TEM,UV-vis DRS,FT-IR,XPS and other material testing methods were used to characterize the morphology and structure of the photocatalysts,and then its photocatalytic hydrogen production performance was tested.The results show that under visible light（λ≥420 nm）,the hydrogen production rate of the 100-Ni SCN sample can reach 141.33μmol?g^-1?h^-1,which is 46 times high than that of pure g-C₃N₄.Then we used steady state/transient fluorescence spectrum,electrochemical impedance spectroscopy,linear voltammetry curve,transient photocurrent and other tests to further explore the photocatalytic mechanism.（2）A mesoporous S-g-C₃N₄ supported CoS₂ composite photocatalyst was successfully prepared by a simple annealing using mesoporous SiO₂as a hard template and CH₄N₂S and Co（CH₄N₂S）₄ as precursors.XRD,SEM,TEM,UV-vis DRS,FT-IR,XPS and other material testing methods were used to characterize the morphology and structure of the photocatalysts,and then its photocatalytic hydrogen production performance was tested.The results show that under visible light（λ≥420 nm）,the hydrogen production rate of 100-CoSCN samples can reach394.18μmol?g^-1?h^-1,which is 108 times higher than that of pure g-C₃N₄.Then we used steady state/transient fluorescence spectrum,electrochemical impedance spectroscopy,linear voltammetry curve,transient photocurrent and other tests to further explore the photocatalytic mechanism.Comparing the three methods of mechanical mixing,ordinary loading and one-step annealing preparation in this paper,the one-step annealing preparation method ensures good contact between CoS₂ and S-g-C₃N₄,making it show the highest photocatalytic hydrogen production performance,further proves Co-S coordination atomic layer can effectively improve carrier transport as a transition connection layer between S-g-C₃N₄ and CoS₂.（3）Using mesoporous SiO₂ as a hard template,and CH₄N₂S and Ni_xCo_1-x（CH₄N₂S）₄and as precursors,Ni_xCo_1-xS_2-SCN（0≤x≤1）nanocomposites were prepared in situ by thermal polycondensation.Its morphology and structure were characterized by XRD,SEM,TEM,UV-vis DRS,FT-IR,XPS and other material testing methods,and then its photocatalytic hydrogen production performance was tested.The results show that in visible light（λ≥420 nm）,the hydrogen production rate of Ni_0.1Co_0.9S₂-SCN samples reaches 716.08μmol?g^-1?h^-1,which is1.8 times and 5.1 times higher than that of CoS₂-SCN and Ni S₂-SCN.Then we used steady state/transient fluorescence spectrum,electrochemical impedance spectroscopy,linear voltammetry curve,transient photocurrent and other tests to further explore the photocatalytic mechanism.