Study On Two-Dimension Materials:Controllable Synthesis By The Oriented Anchoring Strategy And Their Optical And Electrochemical Properties

Synthesis of two-dimensional(2D)materials is often explored through a lot of experimental experience to obtain the synthesis strategy and design system in the traditional energy storage and energy catalysis process.The complex preliminary exploration process has limits on economy,efficiency and environmental friendliness.Meanwhile,due to the limited theoretical cognition,the limitations in subsequent exploration on energy storage mechanism and active site of 2D materials appear.Therefore,the development of efficient,directional and controllable 2D material design strategy from the view of micro-structure is very important on realizing the accurate synthesis of materials and efficient utilization in the field of energy storage and energy catalysis.To prepare 2D nano-materials with target composition,size,crystal phase and surface structure accurately,directional anchor synthesis strategies become an effective method.The directional and precise synthesis of two-dimensional nano-materials is beneficial to further study their physical,chemical,electrochemical and optical properties,which can help to explore the application potential of different forms of 2D nano-materials in many fields.By summary,the directional anchoring synthesis strategy of 2D nano-materials includes interface,crystal surface matching anchoring,covalent bond anchoring,and surface atomic dispersion anchoring.These synthesis strategies are widely used in the field of energy storage and energy catalysis,optimizing the controllable design and synthesis of 2D materials,which could improve the performances of 2D materials.In this dissertation,2D nano-composites are prepared by the directional anchor synthesis strategies,moreover,the optimization mechanism and optical,electrochemical properties are roundly studied,which mainly include the following parts:(1)Large-grain-size α-CsPbI3 nano-crystals are synthesized through crystal surface directed anchoring strategy by the irradiation of moderate UV(ultraviolet)light,which achieves a phase stability and improved optical property.Quasi-in situ high-angle annular dark-field scanning transmission electron microscopy(HAADF-STEM)is used to explore the oriented anchoring process of α-CsPbI3 under UV light.The results exhibit that under moderate UV light irradiation,the edges ofα-CsPbI3 quantum dots(QDs)are destroyed initially,which induces the exposure of(110)and(111)facets.The ligand covered(100)facets with higher surface energy drive QDs to merge along(110)facets due to the relatively low surface energy.Finally,stable α-CsPbI3 nanoparticles with high crystallinity,less crystal boundary and larger size are obtained.However,with illumination under high-wattage UV light,theα-CsPbI3 QDs quickly transform into orthogonal phase,and subsequently destroyed into small particles of δ-CsPbI3 and PbI2.With optical performance characterizations,it is confirmed that the moderate UV light can improve the optical performance and stability of α-CsPbI3,reversely,the optical activity of α-CsPbI3 under high-wattage UV light illumination is quickly disappeared.(2)The density functional theory(DFT)calculations are firstly used here to predict the possible property of SnO2 materials with different exposed facets:(211)facet is found to have the relatively high surface energy and a lower energy barrier towards Li+when compared with other planes.Then the graphene-SnO2 nanorods with highly exposed(211)facets(GSn-211)is fabricated by utilizing a crystalline-spacing-matching method.When tested as anode for LIBs,GSn-211 indeed shows a great electrochemical property:Ultra stable cycling stability and an outstanding rate capability.The Li ions anisotropic transport and the atomic-scale ledged behaviors of GSn-211 along(211)are further visualized via an in situ TEM at atomic level,in which the Sn/O atoms-peeling-off through(211)facet is observed.This indicates(211)planes hold high active sites towards Li-ions insertion,leading to a fast Li+storage.Combined with theoretical calculations,their atomistic mechanical properties during lithiation are explored:the decrease of bulk modulus means the GSn-211 is softened after the initial lithiated state leads to better structural stability.(3)Two types of catalysts via a cation-deficient anchorage strategy:single-atom Pd1-TiO2 and dual-atom Pd1Cu1-TiO2 nanosheets.Multiple structural characterizations prove that Pd and PdCu are uniformly distributed on TiO2 nanosheets.An ultrahigh urea production rate of 10 mmol h-1 g-1 with the corresponding 22.54%Faradaic efficiency at-0.5 V vs.reversible hydrogen electrode(RHE)is achieved over Pd1Cu1-TiO2,which is much higher than that of Pd1-TiO2.Various characterization including an isotope-labeled nuclear magnetic resonance(NMR)and theoretical calculations demonstrate that the synergistic effect of the Pd1Cu1 dual-atom and oxygen vacancy active centers plays key role in the direct C-N coupling,that promotes the coupling of CO2 and N2 over above two active sites as well as stabilizes the formed*NCON*intermediate over the Pd1Cu1 sites.By contrast,it is much hard to activate N2 for Pd1-TiO2 over the oxygen vacancy active center,resulting in a tough C-N coupling.