Photocatalyst Design And Hydrogen Evolution Based On Enhanced Charge Transport Of Molybdenum-based Materials And MOFs Derivatives

In this paper,the problems of low photo-generated carrier separation efficiency and weak light absorption ability in the photocatalytic water splitting technology of molybdenum-based materials and metal-organic framework derivatives were modified to construct high-efficiency photocatalytic hydrogen production catalysts.By constructing a heterojunction in the dye-sensitized system and introducing transition metal phosphide as a cocatalyst,the light absorption capacity of the photocatalyst and the separation efficiency of photogenerated carriers were improved,and the hydrogen production mechanism was further explored.The main contents are as follows:（1）The p-n heterojunction is constructed by using the p-type semiconductor Co₃O₄and the Mo Se₂ to provide an additional built-in electric field to enhance the separation and transfer of carriers.The Mo Se₂/Co₃O₄ with good photocatalytic properties were prepared by a simple hydrothermal method and physical mixing method.The Mott-Schottky test confirms that Mo Se₂ is a typical n-type semiconductor,and Co₃O₄ is a p-type semiconductor.By optimizing the loading of Co₃O₄,the optimal hydrogen production can reach 7029.2μmol g^-1 h^-1,which is 2.34 times that of pure Mo Se₂.Among them,the fluorescence properties and photoelectrochemical characterization experiments further prove that the close contact interface and built-in electric field formed by Mo Se₂ and Co₃O₄ achieve the purpose of directional regulation of the separation and transfer of carriers.In addition,combined with the characterization results of XRD,XPS,SEM,BET,etc.,the possible hydrogen production mechanism is proposed.（2）Three-dimensional（3D）nanoflower-like Mo S_x and In₂O₃ build a stepped heterojunction（S-scheme）to accelerate the separation and transfer of photogenerated carriers.The Mo S_x was prepared by a hydrothermal method,and the stacked nanosheet structure exposed more edge active sites,which facilitated the adsorption of dye molecules.In situ growth of nanoflowers on the surface of In₂O₃ avoids the agglomeration of nanoflowers,and the contact interface after successful coupling promotes the concentration of electrons to the active center of Mo S_x for hydrogen evolution reaction.In addition,the construction of the S-scheme heterojunction between the 3D morphology of Mo S_x and In₂O₃ provides a channel for the separation and transport of electrons.（3）Ni-based metal-organic framework and Bi VO₄ construct S-scheme heterojunction while deriving Ni₂P as electron capture center to improve the charge separation efficiency of photocatalysts.The Ni-MOF-74/Bi VO₄/P with excellent performance was prepared by high temperature calcination.Ni₂P nanoparticles with good electrical conductivity were derived from phosphating metal-organic framework materials,while maintaining the rhombic basic morphology of Ni-MOF-74 as the loading space for Bi VO₄ and Ni₂P,which effectively avoided the accumulation of nanoparticles.The hydrogen production of Ni-MOF-74/Bi VO₄/P can reach 226.13μmol within 5 h,which is 22 times that of pure Ni-MOF-74.By constructing an S-scheme heterojunction between Ni-MOF-74 and Bi VO₄,the directional transfer of charge carriers is achieved,maintaining the redox ability of the photocatalyst.At the same time,the band structures and density of states of Ni₂P and Bi VO₄ were studied by density functional theory calculations,which further provided strong evidence for the photocatalytic mechanism.（4）The transition metal Fe₂P with good electrical conductivity was derived from the iron-based metal-organic framework material by phosphating as a cocatalyst to modify the porous perovskite material to improve the transfer rate of photogenerated carriers.The results show that the hydrogen production performance of Ni Ti O₃/Fe₂P within 5 h is significantly improved,which is 3.68 times that of pure Fe₂P.The advantage of metal-organic frameworks provides space for the growth of Ni Ti O₃ and Fe₂P and the adsorption of dye molecules.In addition,Fe₂P acts as a cocatalyst anchored on the surface of Ni Ti O₃ as an electron capture center for the hydrogen evolution reaction.The construction of hollow nanorods and dye-sensitized system is the reason for the enhanced light absorption ability of the composites.