Controllable Preparation And Photocatalytic Hydrogen Production Of Single Crystalline Tantalum Oxides Microcubes

Micro-nano single crystal materials is more like ideal crystal structure. It has a complete conservation of crystal anisotropy and symmetry in the whole bulk. For such reason, it has no crystal boundaries to scatter the electron to disturb the charge transfer. In many aspects, single crystal has potential applying for the nice electric properties. Other wise, so many chemical reactions are sensitive to surface structure, facet engineering is one of major methods of properties improvement for micro/nano crystal materials. To gain micro/nano crystal with new facet configuration especially the high energy facet normal means evolution on such research region.Oxides containing tantalum is an important function material in dielectric, coating, catalysis, etc. However, most reported tantalum oxides are amorphous and/or polycrystals due to the rapid hydrolysis of tantalum precursors and the high crystalline temperature of tantalum oxides. In order to obtain single crystal structure tantalum oxides, which is benefit for studying properties of its crystal planes, we have developed a strong acid-weak acid mixed system to regulate the hydrolysis of Ta5+ ions and established a quasi-equilibrium environment to prepare TaO2.18Cl0.64 microcubes(TaO2.18Cl0.64 MCs) with a new composition in the solvothermal process. The composition of the MCs has been characterized by XRD?XPS and XRF. The crystal lattice structure of TaO2.18Cl0.64 MCs is a super structure with long-range order due to the substitute of oxygen atoms by chloride atoms. The formation mechanism of TaO2.18Cl0.64 MCs has been clearly elucidated. Simultaneously, the light absorption properties and photocatalytic activity for hydrogen production have been also investigated. The results show that the as-prepared TaO2.18Cl0.64 MCs exhibit an improved light harvest, a rapid charge transfer and a much higher photocatalytic activity than those of commercial Ta2O5 and hierarchical structure composed of single-crystal Ta2O5 nanorods.Based on the DFT calculation results on surface energies of facets, the {0 0 1} facets(the facet with d value being 3.9 ?) of beta phase tantalum oxide have the highest surface energy in {0 0 1}, {0 1 0} and {1 0 0}. In order to obtain a high proportion of the {0 0 1} facets, Ta2O5 MCs have been prepared by calcinating the TaO2.18Cl0.64 MCs. The proportion of the {0 0 1} facets in the as-prepared Ta2O5 MCs is about 33.3 %, which is larger than that of the reported Ta2O5. The strategy of the thermal transformation to obtain the new facet configuration is correlated to the lattice similarity of Ta2O5 and TaO2.18Cl0.64. In the calcination process, facet layers with d value of 3.9 ?(this facet is vertical to c axis) have been reserved in the phase transition, leading to exposing high proportion of the {0 0 1} facets. The special surface activity for photocatalytic hydrogen production of the as-prepared Ta2O5 MCs is much higher than that of single-crystal Ta2O5 nanorods because of the high proportion of the {0 0 1} facets.