Design And Synthesis Of UiO-66 Metal-Organic Frameworks-based Hybrid Photocatalysts For Visible-Light-Response Hydrogen Generation

Energy shortage and environmental pollution are two major problems in today's society when facing sustainable development.Therefore,using solar energy to produce hydrogen to solve the energy crisis and environmental pollution is a promising research subject.Hydrogen is a kind of clean energy with large burning value and easy storage and transportation.However,the design and synthesis of photocatalytic materials and their catalytic performance and efficiency are the core issues in the process of using solar energy to decompose water to produce hydrogen.As a new type of photocatalytic material,metal-organic frameworks?MOFs?materials have attracted much attention of researchers in recent years.Metal-organic frameworks are a class of porous solid materials composed of metal ion centers.They have the advantages of designable structures,tunable pores and ultra-high specific surface area.Therefore,it can be easily synthesized by physical or chemical methods with other compounds to design and synthesize a novel and efficient photocatalyst based on the metal-organic framework material.The research content of this paper is mainly based on MOFs materials to build composite photocatalytic materials,and its visible light photocatalytic hydrogen production performance,the specific research are as follows:1.All solid state Z-Scheme in UiO-66-NH₂@Au@CdS three-component system for enhanced photocatalytic hydrogen evolution under visible-light irradiation:Firstly,UiO-66-NH₂ with octahedral morphology was prepared by hydrothermal method,and then Au nanoparticles were loaded on the surface by double solvent method.Finally,Au nanoparticles were coated by CdS and hydrothermally formed on the surface of MOFs a "core-shell" structure of all solid Z-Scheme photocatalyst.The prepared UiO-66-NH₂@Au@CdS compounds were characterized by X-ray powder diffraction?XRD?,Fourier transform infrared spectroscopy?FT-IR?,UV-visible absorption spectroscopy?UV-vis?,scanning electron microscopy?SEM?,transmission electron microscopy?TEM?and photoluminescence spectroscopy?PL?to study their morphology,structures and properties.Using 0.1 M L-ascorbic acid as electron sacrificial agent and Pt as cocatalyst,the activity of UiO-66-NH₂ @ Au @ CdS composite photocatalyst hydrogen evolution was measured under visible light???420 nm?irradiation.The experimental results reveal that the prepared UiO-66-NH₂ @ Au@ CdS composite photocatalysts show remarkably active hydrogen evolution.The mainly reason is that the Au nanoparticles act as the electron mediator between the MOFs and the semiconductor CdS so that the electrons on the conduction band of the UiO-66-NH₂ can be transferred to the valence band of the semiconductor CdS through the Au nanoparticles and then contact with the holes,which makes the photogenerated electrons mainly concentrate on the conduction band of the semiconductor CdS,while the holes mainly remain in the valence band of the UiO-66-NH₂,which not only effectively prevents the recombination of photogenerated electron-hole pairs at the same time also greatly enhance the photogenerated electronic reduction ability.2.Synergetic effect of N12P co-catalysts and dye sensitization for increased photocatalytic H2 generation by UiO-66 MOFs under visible-light-driven exposure:The nickel phosphide?Ni₂P?nanoparticles were loaded on a Zr-containing MOFs UiO-66 octahedrons surface by hydrothermal and phosphidation method as a noble-metal-free cocatalyst for boosting H2 generation from Erythrosin B dye sensitization under visible-light irradiation.The UiO-66/Ni₂P hybrid with optimum Ni₂P amount of 0.69 wt.%offers the highest H2 evolution rate of 65 ?mol h-1.This value is near 19 times higher than the reference sample of no Ni₂P presence.The strong-interaction of benzene rings between Erythrosin B dye and UiO-66 MOFs ensures the efficient electron transfer from the photoexcited dyes to UiO-66 MOFs,and finally across the interfaces of UiO-66 and Ni₂P to Ni₂P nanoparticles.This efficient charge transfer process ensures the enhanced H,genenration.The present results show the great potential of Ni₂P as a low cost and active co-catalysts for enhancing photocatalytic H2 generation of MOFs.