Effects Of Mo-based Cocatalysts On The Photocatalytic Hydrogen Evoluction Performance Of CdS In Reforming Lactic Acid

Energy shortage and environmental pollution are two major problems that affect the sustainable development of human society,and the development and utilization of efficient and clean hydrogen（H2）energy is considered to be an effective approach to solve these two problems.Using solar energy as power,the photocatalytic technology is considered to be a "green" and promising route to produce H2 by reforming renewable biomass under mild conditions.However,the single-component photocatalysts,such as CdS,TiO₂ and etc.,still suffer the technical bottleneck of low light absorption capacity and quantum efficiency severely,which seriously limit their practical applications.In recent years,Mo-based nanomaterials（with abundant earth richness and low price）have been proved to be a kind of efficient cocatalysts for photocatalytic hydrogen evolution（PHE）.Further regulating the composition,phase structure and morphology of Mo-based cocatalyst to construct the high-efficient photocatalytic system,have been the focus of the PHE research filed.In this paper,several novel Mo-based nanomaterials are designed and developed to solve the shortcomings of CdS in the PHE process of reforming Lactic Acid（LA）,such as low photocatalytic activity and severe photocorrosion.The main research contents of this paper are as follows:（1）Using Mo-organic coordination intermediate Mo3O10（C6H8N）2·2H2O as precursor,one-dimensionalMoO₂-C cocatalyst was synthesized by calcining method.Then,mixingMoO₂-C cocatalyst with CdS nanorods under ultrasonication to prepare theMoO₂-C/CdS（MOCCS）ternary heterogeneous photocatalyst.It was found there is a disordered region（MoOx）at the interface betweenMoO₂ and C,which can act as a hydrogen-evolution active center to reduce the PHE overpotential.Moreover,at the heterogeneous interface betweenMoO₂-C and CdS,some complex interfacial structure,such as Mo-S bond and metallic Cd,were also formed to help the interfacial transfer of the photogenerated charge carriers.The synergies between the unique microstructures and heterogeneous interfaces can achieve effective separation and reaction of photogenerated carriers in the system,thereby effectively improving the LA reforming PHE activity of MOCCS ternary heterogeneous photocatalyst（up to 16.08 mmol·h-1·g-1,about 33 times the hydrogen production performance of pure CdS）.（2）Herein,NH4HCO3 was used to regulate the crystal phase and morphology of MoO₂,to grow the vertical multiphasic MoO₂ nanosheets on the CdS nanorods（CdS@VM-MoO₂）by a simple hydrothermal method.It was found that the vertical-standing MoO₂ nanosheets can not only expose more catalytic active centers,but also ensure the CdS nanorods can use the excitation light more effectivly.Simultaneously,1T-MoO₂ in the cocatalyst can promote the interfacical migration of photogenerated electrons between the main catalyst and cocatalyst,and act as an electron aggregation center and active center to promote the efficiency of H2 evolution reaction.The prepared CdS@VM-MoO₂ composite photocatalyst exhibits a very high PHE performance of reforming LA（40.1 mmol·h-1·g-1）,and an enhanced photostability.（3）The CdS@Cd MoO4-MoOx core-shell photocatalyst was prepared by a photochemical deposition method.Then,by using the hydrothermal ion exchange method,the CdMoO4-MoOx shell layer was further sulfided and transformed into "cicada wings like" Cd MoS4-MoO₂.It was found that the close coated CdMoO4-MoOx shell would inhibit CdS to use the excitation light effectively,while the "cicada wing like" Cd MoS4-MoO₂ nanosheets cannot only allow the effective light utilization,but also be benefit for the transfer and reaction of photogenerated electrons.The LA reforming PHE activities of the as-synthesized CdS@Cd MoO4-MoOx and CdS@Cd MoS4-MoO₂ composites are tested to be 2.4 mmol·h-1·g-1 and 40.3 mmol·h-1·g-1,respectively.The results demonstrate that the composition and morphology of Mo-based cocatalysts have an important influence on the light-utilization efficiency,carrier migration and separation efficiency,hydrogen production activity and synergistic mechanism of the composite photocatalyst system.