Preparation Of Transition Metal Organic Frame Derivatives Composites For Catalytic Reaction

With the rapid development of modern society and economy,the excessive consumption of fossil energy and global environmental pollution are particularly prominent,the sustainable development of human society is facing a severe ordeal.As a clean alternative of conventional fuels,hydrogen energy has attracted wide attention because of its characteristics of zero pollution,storage and high energy conversion efficiency,which makes it an ideal choice to solve the problem of energy shortage.Considering from the perspective of environment and cost,the production method of photolysis water reaction is environmentally friendly,and the raw material,water,is abundant and cheap,which is an ideal preparation method.However,due to the limitation of bandgap width and light absorption range,the utilization rate of solar energy of the catalyst is much lower than expected.At the same time,the rapid recombination of photogenic carriers in the material is also an important factor affecting the performance of hydrogen production.Therefore,the design and construction of excellent corrosion resistance catalyst is the key factor to improve the reaction performance.In addition,electrochemical catalytic hydrolysis is an efficient and recyclable way to prepare renewable hydrogen energy.Electrolytic water reaction can be divided into two half processes:oxygen evolution reaction（OER）and hydrogen evolution reaction（HER）,where the OER reaction involves four electron transfers to form O-O bonds,which is speed control steps for water decomposition.Rhodium-based compounds and precious metal platinum-based materials are currently the best electrocatalysts for OER and HER reactions respectively,but their high cost and low reserves limit its practical production applications.It is an important way to develop efficient and cheap non-noble metal-based catalysts.Metal-organic framework（MOFs）is a kind of porous frame material composed of ions/clusters and organic ligands by coordination has the characteristics of high designability,high specific surface area and regular pore structure.However,low stability,poor conductivity and slow kinetic reaction are common problems of MOFs materials,which hinder their further development in the field of catalysis.Therefore,starting from the synthesis of MOFs materials,this work obtains the derivatives of MOFs by the methods of low temperature vulcanization,multi-dimensional composite and metal element doping.To a great extent,while inheriting the characteristics of MOFs materials such as high specific surface area and controllable morphology,the catalytic and stability of derived materials can be improved.During the experiment,the materials were analyzed and characterized from the aspects of morphology and phase structure（SEM,TEM,XRD）,optical properties（UV-vis）,elemental valence state（XPS）and pore structure（BET）.The specific work content is as follows:（1）Two dimensional metal-organic frameworks-derived leaf-like Co₄S₃/CdS composite for enhancing photocatalytic water evolutionThe 2D CoMOF precursor was synthesized at room temperature and refluxed in low temperature oil bath.2D Co₄S₃ nanosheets material was obtained by calcining and annealing.During the process of vulcanization,the precursor material gradually changes into sheet metal sulfide,and a large number of irregular porous structures are generated by the high-temperature calcining reaction.The two-dimensional lamellar materials prepared have large specific surface area and abundant reactive sites,which can effectively promote electron-hole separation.Co₄S₃/CdS composites with different loads were prepared by one-step hydrothermal reaction.The characterization results showed that the morphology of the composites changed with different degrees.Compared with pure CdS material,the light absorption range of the composite is significantly larger,and the solar energy utilization efficiency is higher.In addition,the morphology of Co₄S₃/CdS（0.2）sample is regular,and the cadmium sulfide nanosphere is evenly dispersed on the surface of the nanometer sheet,showing the most outstanding catalytic performance in the reaction.From the band position relation of the composite material,it can be seen that the catalyst forms a typical Type-II of heterogeneous structure,which is beneficial to the rapid separation of electron-holes and reduce the recombination rate of carriers.（2）Well-designed cobalt-nickel sulfide microspheres with unique peapod-like structure for overall water splittingThree-dimensional transition metal hydroxide microspheres formed by self-assembly of nanorods were synthesized by hydrothermal method on nickel foam substrate,and introduced the organic ligand to produce small-size ZIF-67 particles.The samples have multi-dimensional advantages,such as large specific surface area,dispersed active sites and open internal spatial structure.After vulcanization,the peapod-like 3D microspheres have exposed cobalt sulfide nanoparticles,abundant electron transfer channels and adequate gas release platform.Therefore,the peapod-like composite catalyst shows excellent reaction performance.（3）Hollow cobalt-nickel phosphide nanoflakes with triangular nanowall architecture for enhanced water splitting propertyHollow CoNiP/NF nanoflakes catalysts doped with nickel and phosphating were prepared using 2D CoMOF as the precursor/self-sacrificial template.During the reflux process,ion exchange and etching reactions occur,forming a hollow and porous lamellar structure,which can effectively promote the penetration of electrolyte and accelerate the evolution/release of gas.Ion exchange is an effective way to form hierarchically hollow structure.After phosphating reaction,a triangular porous CoNiP/NF material was prepared by assembling small-sized microspheres.The unique nanomaterial not only has a large specific surface area and more electron transport channels,but also provides ample reaction sites for catalytic reactions.Combining with the theoretical calculation and analysis of DFT,the doping of nickel element can adjust the intrinsic electronic structure of catalyst,reduce the potential barrier of catalytic reaction,accelerate the electron transfer rate,and significantly enhance the catalytic performance.