Construction Of The MoS₂/MS?M=Zn/Cd? Heterojunction From Metal-Organic Frameworks For Photocatalytic Hydrogen Evolution

Solar-driven water splitting for hydrogen is part of the most attractive methods for hydrogen fuel now.Transition metal sulfides are a class of ideal photocatalytic hydrogen production catalytic materials due to their suitable bandgap and wide range of visible-light absorption.However,there are some problems in photocatalytic hydrogen production of the single-component sulfide semiconductors,such as photochemical stability,energy mismatch,and recombination of the photoinduced carriers.Therefore,it is necessary to construct a highly efficient sulfide composite photocatalyst by semiconductor modification.Compared with traditional inorganic semiconductors,metal-organic frameworks?MOFs?are easily derivatized due to that the metal nodes in the skeleton are highly ordered by organic ligands.Combing with their inherently excellent physicochemical properties,MOF-based porous materials have a broader application prospect in photocatalytic hydrogen evolution reaction.Using MOFs as a precursor,a novel composite photocatalytic material with adjustable and variable functionality can be designed and constructed at the molecular level simply and efficiently.Moreover,such MOFs-based porous derivative materials have a large specific surface area,a fully exposed active site,a regulatable band structure and a heterojunction interface,which facilitates sufficient contact between the photogenerated carriers and the reactants through the pore structure.Thereby,the recombination rate of photoinduced carriers are effectively reduced,and the photocatalytic hydrogen evolution performance is enhanced.In this paper,a simple and efficient,molecularly controllable MOFs precursor method was used to design and construct a novel sulfide composite photocatalytic material for photocatalytic hydrogen production.In the first part:a new type of CdS/MoS₂ heterojunction was constructed by vulcanization from the precursor of the core-shell MoS₂@Cd-MOF material.Due to the controllable thickness of the Cd-MOF shell,the highly ordered Cd²⁺ions,which are completely separated by the organic ligand,can be directly converted into CdS nanoparticles after vulcanization,thus achieving a uniform loading on the MoS₂flowers.Compared with the MoS₂-CdS hybrid prepared by physical mixing and deposition-precipitation,this heterojunction photocatalytic material has a large specific surface area,a tightly bonded and controllable heterojunction interface,and thus exhibits a higher photocatalytic hydrogen production performance.Optimizing the CdS loading,the highest average hydrogen production rate can reach 5587?mol g^-1 h^-1.Subsequently,the electron transfer pathway in the CdS/MoS₂ heterojunction was illustrated by PL spectrum,Mote-Schottky curve,photocurrent curve and EIS curve.In the second part,a novel MoS₂/ZnS-CdS composite photocatalytic material was constructed by the vulcanization process of Zn-MOF/Cd-MOF composite combining with photo-assisted deposition technique.Due to the small atomic radius of Cd,it is easy to ion exchange with Zn-MOF,so that Zn and Cd elements can be uniformly dispersed to achieve a certain degree of atomic-scale mixing,forming a certain composition of Zn_xCd_1-xS solid solution interface.By this method,an interface structure having a tunable lattice constant and an energy band structure is embedded to enhance the interface state between the semiconductors,thereby accelerating the separation and migration of carriers.The Zn/Cd ratio in ZnS-CdS composite photocatalytic material was optimized,and the highest average hydrogen production rate in the Na₂S-Na₂SO₃ sacrificial system was 5294?mol g^-1 h^-1 under visible light irradiation.After photodeposition of MoS₂,the performance and stability of the catalyst are improved.