| Over recent decades,with the rapid development of nanoscience and nanotechnology,nanomaterials exhibit a broad application potential in various fields,such as catalysis,electronic,renewable energy,etc.The research focus in the dimension and characterization means of nanomaterials issue has evolved from the microstructure to molecular level,or even atomic level,from steady-state analysis to real-time dynamic monitoring.It has been a hot topic that how to understand the formation mechanism and the evolution process of nanomaterials in operando condition at the atomic level.Synchrotron Radiation(SR)techniques have many unique advantages,such as continuously tunable wavelength,high brightness,broad wavelength,and time structure,etc.Synchrotron radiation-based X-ray absorption spectroscopy(XAS)technique,as one of the multi-disciplinary research tools,could be applied to track the formation process of nanomaterials,the evolution process of the electronic structure and local structure of nanomaterials in the real condition,deeply understand the correlation between electronic/local structure and properties of nanomaterials at the atom level,thus improve the performance of nanomaterials.Noble metal nanomaterials(Pt,Au,Pd,etc.)have many unparalleled physical and chemical properties,especially platinum-based nanomaterials which have extensive potentials in many application areas,such as catalysis in organic synthesis and clean energy conversion.Since platinum with the scarce resource,expensive and large-scale demand in the market has become a bottleneck hindering widespread commercial application.Due to the performance of platinum-based nanomaterials correlating to their component,size,and shape,it is a key issue that how to improve efficiency,reduce usage of platinum or even explore non-platinum catalyst.In addition,the deep understanding of the nucleation kinetics and growth mechanism is of great significance in tailoring the ideal size and shape as well as the desired physical and chemical properties of metal nanocrystals to promote the potential for practical applications.Despite many studies involving precision-controlled synthesis of highly dispersed metal nanocrystals,the nucleation and growth mechanism of noble metal nanocrystals in aqueous solution is still a controversial issue due to the short lifetime of nucleation and growth of metal nanocrystals and the limits of the characterization methods available for real-time monitoring of the nucleation and growth processes.In the thesis,based on X-ray absorption spectroscopy(XAS)technique,the systematic studies have been focused on platinum-based nanomaterials including the nucleation and growth mechanism of platinum nanocrystals,the electronic structure and short-range environment of platinum catalysts with different nanostructures,the evolution prcocess of electronic structure of uniform FePt nanoparticles under different environments and the catalytic performance of supported platinum catalyst prepared by microwave-assisted polyol preparation.In addition,the luminescence channel of blue fluorescence materials and scintillating crystal have been discussed by the combination of soft X-ray absorption spectroscopy and X-ray excited optical luminescence(XEOL),which is sensitive to their luminescence channel.1.Based on in-situ XAS techniques,the nucleation and growth in the formation of colloidal platinum nanocrystal have been investigated.Colloidal Pt nanocrystals were synthesized by the reduction of H2PtCl6 solution using ascorbic acid(AA)as the reducing agent in the presence of polyvinyl pyrrolidone(PVP)by means of adjusting the injection rate of reducing agent,which has been monitored by in-situ XAFS method.These results show the two reduction pathways from H2PtCl6 precursor: one-time reduction,the precursor ions were sharply reduced into the zero-valence Pt atoms and grew via breaking Pt-Cl bonds;the precursor ions were gradually reduced,aggregated into PtnClx and the formation via breaking the Pt-Cl bonds.These results experimentally demonstrate that two reduction pathways coexist in LaMer crystal theory,and the reduction pathways were controlled by the synthetic condition,guiding to study the nucleation and growth mechanism as well as controlled synthesis of nanocrystals.2.The shape-activity correlation of platinum catalysts with different nanostructures was investigated.The as-synthesized three platinum catalysts(Pt NWs,Pt NRs,and Pt NPs)show different performance in the formation of azobenzene,and these findings show that the performance of Pt NWs is superior to these of Pt NPs and Pt NRs.Compared to Pt NPs and Pt NRs,the Pt NWs show low oxidation state,low coordination number and contracted Pt-Pt bond distance that have rich defects offering available sites in the formation of azobenzene.Moreover,to confirm the catalytic mechanism for the formation of azobenzene by quasi in-situ XAS techniques,-OH as radical,Pt NWs could form weak Pt-OH bond in the base and also offer the active site for cracking the H-H bond,prompting the formation of azobenzene and in-depth understanding of the formation mechanism of azobenzene.3.Due to the “synergistic effect” of FePt catalyst,their performance is superior to these of their counterpart.The evolution process of electronic structure of their counterpart of FePt catalyst was investigated in the real condition by in-situ XAS technique,such as temperature and environment.The sensitivity of iron component is higher than to that of platinum component.However,the behaviour tendency of two components is greatly different when temperature change,the platinum is more stable than iron.The evolution process of their counterparts was studied,which contribute to comprehend their “synergistic effect” action.4.By means of microwave-assisted polyol preparation with energy-efficient,largescale platinum catalysts could be efficiently synthesized.Various materials(Vulan XC-72 Carbon Black,and Carbon Nanotube)supported platinum or platinum alloy was synthesized by microwave-assisted polyol preparation.The as-synthesized catalysts were characterized by Transmission Electron Microscope(TEM),X-ray Powder Diffraction(XRD),which show these catalysts were uniformly dispersed.These catalysts show superior performance that was conducted in some catalytic reaction models.The controlled shapes of platinum or platinum alloy with high performance will be synthesized by microwave-assisted preparation via adjusting corresponding parameters.5.Combined soft x-ray absorption spectroscopy(XAS)and x-ray excited optical luminescence(XEOL)technique,the luminescence channel of fluorescence materials and luminescence mechanism of scintillation crystals have been studied.As-synthesized di[4-(4-diphenylaminophenyl)phenyl] sulfone(DAPSF)as blue fluorescence materials in the organic light emitting device(OLED)exhibit a broad application potential.The correlation between luminescence channel and electronic structure of each element in the DAPSF molecule was studied,and these results show luminescence channel is mainly originated from SO3-groups.In addition,the luminescence mechanism of scintillation crystals has been studied by time-resolved XEOL(TR-XEOL). |
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