Surface modification with metal oxide nanoclusters has emerged as a candidate for the enhancement of the photocatalytic activity of titanium dioxide. An increase in visible light absorption and the suppression of char...Surface modification with metal oxide nanoclusters has emerged as a candidate for the enhancement of the photocatalytic activity of titanium dioxide. An increase in visible light absorption and the suppression of charge carrier recombination are necessary to improve the efficiency. We have studied Mg4O4 and Sn4O4 nanoclusters modifying the（101） surface of anatase TiO2 using density functional theory corrected for on-site Coulomb interactions（DFT ＋ U）. Such studies typically focus on the pristine surface, free of the point defects and surface hydroxyls present in real surfaces. We have also examined the impact of partial hydroxylation of the anatase surface on a variety of outcomes such as nanocluster adsorption, light absorption, charge separation and reducibility. Our results indicate that the modifiers adsorb strongly at the surface, irrespective of the presence of hydroxyl groups, and that modification extends light absorption into the visible range while enhancing UV activity. Our model for the excited state of the heterostructures demonstrates that photoexcited electrons and holes are separated onto the TiO2 surface and metal oxide nanocluster respectively. Comparisons with bare TiO2 and other TiO2-based photocatalyst materials are presented throughout.展开更多
Oxygen vacancy formation and migration in La0.9Sr0.1Ga0.8Mg0.2O3-5 （LSGM） with various crystal symmetries （cubic, rhombohedral, orthorhombic, and monoclinic） are studied by employing first-principles calculations ...Oxygen vacancy formation and migration in La0.9Sr0.1Ga0.8Mg0.2O3-5 （LSGM） with various crystal symmetries （cubic, rhombohedral, orthorhombic, and monoclinic） are studied by employing first-principles calculations based on density functional theory （DFT）. It is shown that the cubic LSGM has the smallest band gap, oxygen vacancy formation energy, and migration barrier, while the other three structures give rise to much larger values for these quantities, implying the best oxygen ion conductivity of the cubic LSGM among the four crystal structures. In out calculations, one oxygen vacancy migration pathway is considered in the cubic and rhombohedral structures due to all the oxygen sites being equivalent in them, while two vacancy migration pathways with different migration barriers are found in the orthorhombic and monoclinic symmetries owing to the existence of nonequivalent O1 and 02 oxygen sites. The migration energies along the migration pathway linking the two 02 sites are obviously lower than those along the pathway linking the O1 and 02 sites. Considering the phase transitions at high temperatures, the results obtained in this paper can not only explain the experimentally observed different behaviours of the oxygen ionic conductivity of LSGM with different symmetries, but also predict the rational crystal structures of LSGM for solid oxide fuel cell applications.展开更多
基金support from Science Foundation Ireland through the US-Ireland R&D Partnership Program (No. SFI 14/US/ E2915)the European Commission through COST Action CM1104 "Reducible Metal Oxides, Structure and Function"+1 种基金funded by SFIby the SFI and Higher Education Authority funded Irish Centre for High End Computing
文摘Surface modification with metal oxide nanoclusters has emerged as a candidate for the enhancement of the photocatalytic activity of titanium dioxide. An increase in visible light absorption and the suppression of charge carrier recombination are necessary to improve the efficiency. We have studied Mg4O4 and Sn4O4 nanoclusters modifying the（101） surface of anatase TiO2 using density functional theory corrected for on-site Coulomb interactions（DFT ＋ U）. Such studies typically focus on the pristine surface, free of the point defects and surface hydroxyls present in real surfaces. We have also examined the impact of partial hydroxylation of the anatase surface on a variety of outcomes such as nanocluster adsorption, light absorption, charge separation and reducibility. Our results indicate that the modifiers adsorb strongly at the surface, irrespective of the presence of hydroxyl groups, and that modification extends light absorption into the visible range while enhancing UV activity. Our model for the excited state of the heterostructures demonstrates that photoexcited electrons and holes are separated onto the TiO2 surface and metal oxide nanocluster respectively. Comparisons with bare TiO2 and other TiO2-based photocatalyst materials are presented throughout.
基金supported by the National Natural Science Foundation of China (Grant No.10974183)
文摘Oxygen vacancy formation and migration in La0.9Sr0.1Ga0.8Mg0.2O3-5 （LSGM） with various crystal symmetries （cubic, rhombohedral, orthorhombic, and monoclinic） are studied by employing first-principles calculations based on density functional theory （DFT）. It is shown that the cubic LSGM has the smallest band gap, oxygen vacancy formation energy, and migration barrier, while the other three structures give rise to much larger values for these quantities, implying the best oxygen ion conductivity of the cubic LSGM among the four crystal structures. In out calculations, one oxygen vacancy migration pathway is considered in the cubic and rhombohedral structures due to all the oxygen sites being equivalent in them, while two vacancy migration pathways with different migration barriers are found in the orthorhombic and monoclinic symmetries owing to the existence of nonequivalent O1 and 02 oxygen sites. The migration energies along the migration pathway linking the two 02 sites are obviously lower than those along the pathway linking the O1 and 02 sites. Considering the phase transitions at high temperatures, the results obtained in this paper can not only explain the experimentally observed different behaviours of the oxygen ionic conductivity of LSGM with different symmetries, but also predict the rational crystal structures of LSGM for solid oxide fuel cell applications.
