| Tungsten trioxide(WO3),as a wide band gap semiconductor(2.4-3.0eV),has become a promising multifunctional semiconductor material and attracted much attention for the potential applications in electrochromic devices,gas sensing sensor,lithium ion batteries,and photocatalysts for splitting water.With the development and wide application of new material measuring technologies,the deep understanding for semiconductor photocatalyst materials has been brought up.However,the experimental results can't reflect the in-situ information of the photocatalytic reactions,which restricts the cognition for micro-reaction mechanisms.Therefore,it is particularly important to understand the crystal structures and micro-action mechanisms through theoretical simulations.In this thesis,the crystal structures and basic properties of WO3 with different phases and the adsorption and dissociation of water molecules on surfaces of h-WO3 were studied through the first-principles calculations aiming to provide a theoretical guidance for its practical applications.Firstly,based on the analysis of structures and relative energies,we noted that the distortion of W06 octahedron was mainly responsible for the enhanced crystal stability of ?-,?,?-and ?-WO3,while the titling of WO6 octahedron played a secondary effect.The results of the calculated dipole moment indicated that the phase transformation from?to?-WO3 induced the change of antiferroelectricitv-ferroelectricity,which was contributed to the octahedral distortion along x and y directions.The calculation of band structures presented that the increasing of the band gaps were contributed to the decreasing valence band width due to the expanded octahedral volume.Importantly,the distortion of the W06 octahedron lifted the level of 5dxy states at bottommost of the conduction band,which much enlarged the band gaps of ?-.?-and ?-WO3.The lattice dynamic properties presented unstable structures of c-.h-and ?-WO3,and stable structures of ?-,?-,and ?-WO3.The instability mainly originated from the stretching vibrations of O-W-O bonds with few contributions by the blending vibrations of W-O bonds.Secondly,the mechanism of surface state/surface structure of h-WO3 low index effecting on the adsorption and dissociation of water molecules was discussed.For the adsorption and dissociation of H2O molecules on the perfect surface,their activities followed the rules from the perspective of thermodynamics and kinetics:(110)surface>(001)surface>(100)surface.The adsorption and dissociation configurations at surface(110)showed great structural relaxation,providing appropriate adsorption and dissociation sites.The exothermic reaction process and the lower reaction barrier were more conducive to the reaction.On the defect surface,H2O was adsorbed stably on the oxygen vacancy in the form of molecules,and the oxygen defect caused the redistribution of charge.Therefore,compared with the perfect surface,the reduced positive charge and acidity of metal atoms resulted in the decrease of the adsorption stability of adsorbent atoms.Finally,the synergistic effect of loaded Aun cluster and surface structures on the adsorption and dissociation of H2O on h-WO3(100)surface was studied by the first-principles method.The results showed that the stable adsorption and dissociation sites of water molecules were still on the surface of WO3.The size and morphology of gold clusters had an impact on H2O adsorption and O-H bond activation.The synergistic effect of Aun clusters,surface structures and H2O molecules led to the structural changes of Aun clusters and surface structures,which improved the adsorption ability.Meanwhile,more adsorption sites are introduced to make the H2O adsorption and dissociation reaction processing easier.At the end of this paper,the main conclusions were summarized and the innovation points were enumerated in sequence;meanwhile,the following researches of this project were introduced. |
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