Construction Of Functional Catalytic Materials Based On Surfactant-encapsulating Polyoxometalates Self-assembly

Environmental pollution and energy shortage have become two major problems that need to be solved urgently in the world nowadays.At present,researchers have found that reducing nitrobenzene to multifunctional aniline by using noble metal nanoparticle catalysts is one of the simplest and most effective methods to deal with nitrobenzene water pollution.Based on cost and catalytic efficiency considerations,the ideal noble metal nanoparticles should have the smallest possible size and good dispersibility to increase the effective contact area with the reactants.Therefore,it is of great significance to search for a carrier that can disperse and fix the noble metal nanoparticles.Surfactant-encapsulating polyoxometalates（SEPs）have both the redox characteristics of the polyoxometalate itself,and the negatively charged polyoxometalate units are arranged in an orderly manner at a certain distance,which is conducive to the firm attachment of noble metal cations and in-situ reduction into dispersed small-size noble metal nanoparticles.It can be seen that SEPs are expected to become reducing agents and dispersion carriers for noble metal nanoparticles.On the other hand,electrolysis of water is an advanced technology for producing hydrogen,and the key to its large-scale promotion is to find efficient and inexpensive electrocatalysts.In this regard,researchers have developed highly active electrocatalysts such as transition metal sulfides,carbides and nitrides.Taking transition metal sulfides as an example,most of the current synthesis methods require complicated reaction conditions and low yields,which are not conducive to large-scale industrial applications.Therefore,it is necessary to find a suitable precursor to simplify the reaction conditions and increase the yield of transition metal sulfides.There are a large number of transition metal-oxygen bonds in the polyoxometalate unit of SEPs self-assembly,which can obtain high-yield transition metal sulfides through the exchange of sulfur atoms and oxygen atoms at a lower temperature,and is based on the morphology structure of the SEPs self-assembly can avoid stacking of transition metal sulfides.Therefore,this type of SEPs self-assembly has the potential to become an ideal precursor for large-scale synthesis of transition metal sulfides under low temperature conditions.At the same time,SEPs can obtain a rich morphology and structure by changing the types of surfactants or adjusting the polarity of solvents to self-assemble,and the carrier/precursor can be easily functionalized.Based on the SEPs,this thesis explored the phenomenon and mechanism of its self-assembly,obtained different self-assembly structures,and explored its properties and applications.The main research work of this paper is as follows:1、We have constructed the SEPs DODA-PMo₁₂ through the electrostatic interaction of dodecyldimethylammonium bromide（DODA）and molybdophosphate(H₃PMo₁₂O₄₀,PMo₁₂).By adjusting the polarity of the organic mixed solution of chloroform and n-butanol,DODA-PMo₁₂ self-assembled into two-dimensional ultra-thin（1.8 nm）circular nanosheets with a diameter of about 800 nm,which can be used as a universal carrier for silver nanoparticles.Under the coordinated protection of well-arranged PMo₁₂ units and hydrophobic oleic acid（OA）,molybdophosphate is reduced under light irradiation,and Ag nanoparticles（5±2 nm）obtained by reduction of silver oleate（Ag OA）are monodispersed in DODA-PMo₁₂nanosheet self-assemblies to form Ag_x/DODA-PMo₁₂composite material.The optimized Ag_4.89/DODA-PMo₁₂ composite material shows high catalytic activity and good stability in the degradation of4-nitrophenol（4-NP）.The reaction rate constant is 6.49×10^-3 s^-1,and there was no obvious deterioration after three cycles.This kind of SEPs self-assembly carrier has universal applicability to other noble metal nanoparticles.2、We prepared CTAB-PMo₁₂ nanowires self-assembly（1.5±0.5μm in length and 150±50 nm in diameter）with phosphomolybdic acid(H₃PMo₁₂O₄₀)and cetyltrimethylammonium bromide（CTAB）in the acetone/n-butanol mixed solvent system,which was used as the template precursor to obtain the hollow molybdenum disulfide nanorods at a temperature below 200°C.The hollow nanorods are assembled from molybdenum disulfide nanosheets.At the same time,Ru/MoS₂,a composite material doped with ruthenium on MoS₂hollow nanorods,was designed and prepared as an effective catalyst for electrocatalytic hydrogen evolution reaction,achieving an initial overpotential of 105 m V and a Tafel slope of64 m V dec^-1.Ruthenium doping greatly increases the active sites for electrocatalytic hydrogen production,and the electronic synergy between zero-valent Ru and MoS₂ hollow nanorods makes the composite material exhibit higher activity.Through the research in this thesis,we have prepared surfactant-encapsulating polyoxometalates（SEPs）self-assemblies and used them as a carrier for the dispersion and reduction of nobel metals and a template precursor for large-scale hydrothermal synthesis of MoS₂ at lower temperatures.The synthesized composite material has certain industrial application value for the treatment of nitrobenzene water pollution and electrocatalytic hydrogen production.At the same time,it provides a new direction for the application of SEPs.