Controlled Synthesis And Properties Of Tantalum-based Oxide Nanomaterials

Semiconductor tatalates has been increasingly researched due to its unique properties of luminescence and photocatalytic water splitting. This dissertation is focused on the solvothermal and sol-gel fabrication of YTaO4, NaTaO3, CoxNi1-xTa2O6nano-materials. Our investigations are based on the aspects including fabrication, formation mechanism and the property characterization. The contents comprise phase transformation induced growth mode change of solvothermal-fabricated YTaO4nanostructures, Surfactant-free fabrication of high surface area NaTaO3nanocrystals and their photocatalytic water splitting, and sol-gel fabricated porous CoxNi1-xTa2O6microspheres and their visible light driven water splitting. By using the mild liquid phase synthetic procedure, the structure, sizes, surface area and morphology of the products are well controlled, and the formation mechanism under different condition of all the products is investigated in this paper. This work is not only enriched the investigation area of tantalate semiconductor nanomaterials, but also provided fundamental research and technique support to the potencial applications of tantalate photocatalytic nanomaterials.1. Phase transformation induced growth mode change of solvothermal-fabricated YTaO4nanostructuresYttrium tantalate (YTaO4) nanostructures were solvothermally prepared at240℃without any additives. The quasi-square plate-like products were constructed by50-70nm cores and80-100nm nanorods with diameter of-15nm. The central part was formed by nanoparticle aggregation. The YTaO4nanorods were formed by dissolution-recrystallizition. Due to the difference of the crystal growth behavior between Y10Ta4O25intermediate and YTaO4, the YioTa4O25-YTaO4phase transformation was considered to be responsible for the formation of such exquisite structure. Nanorods grew on four perpendicular directions influenced by imperfect Oriented-attachment. The luminescent emission of as-prepared YTaO4with the luminescence quantum efficiency of17.4%was distinctly red-shifted.2. Surfactant-free fabrication of high surface area NaTaO3nanocrystals and their photocatalytic water splittingUniform NaTaO3ca.15nm and ca.70nm nanocrystals were synthesized via a novel surfactant-free solvothermal reaction. The acidic alkoxide hydrolyzation leads to small size and high surface area particles. The different size of the nanocrystals was controlled by altering concentration. The alkoxide-based synthetic route leads to small particle size and high surface area, which improved the charge separation and migration of photogenerated carriers and benefitted the surface chemical reaction of catalysts. As a result, the high total yield of photocatalytic water splitting hydrogen generation was obtained, which was as high as3.106mmol·h-1·g-1.3. Sol-gel fabrication of porous CoxNi1-xTa2O6mocrospheres and their visible light driven water splittingContinuous CoxNi1-xTa2O6porous microspheres were synthesized by using simple inorganic salts in aqueous solution. The stabilizing effect of H2O2to Ta(V) is a key factor in the forming of aqueous tantalum sol. After the XRD investigation, the sintering temperature was determined as800℃. The particle size of porous CoxNi1-xTa2O6microspheres slightly increased with the increase of Co doping amount. The porous CoxNi1-xTa2O6microspheres showed high phothcatalytic water splitting efficiency, with the highest of1366.7μmol·h-1·g-1by Co0.8Ni0.2Ta2O6. The catalytic efficiency of porous CoxNi1-xTa2O6microspheres was significatntly affected by lattice distortion. This result indicated the band structure, lattice distortion, surface area are important factors for the water splitting photocatalysts.