Layered Snnb <sub> 2 </ Sub> O <sub> 6 </ Sub> Preparation And Photoelectrochemical Properties

Using and transforming of solar energy is a significant way to solve the world-wideenergy crisis and environment problems, and realize sustainable development. In this present work, simple methods to synthesize SnNb₂O₆ nanomaterials via molten salt process and co-precipitation technique were successfully developed. The photoelectrochemical properties of SnNb₂O₆ nanomaterials were improved by doping of transition metal ions and surface modification of metal oxide.SnNb-2O₆ nanoplates were successfully synthesized by the molten salt method using SnO and Nb₂O₅ as raw materials, and NaCl and KCl as the solvent at 600℃for 2 h. The as-prepared SnNb₂O₆ was found to be a single-crystalline feature of the whole nanoplate which is of hexagonal geometry with very smooth edges and homogeneous size distribution, with around 80 nm in thickness and around 500 nm along their longest edge. From the Photoelectrochemical measurements, longer relaxation time and higher photovoltage have been found for the SnNb₂O₆ nanoplates than those for the SnNb₂O₆ particles obtained by solid-state reaction.A simple co-precipitation technique was successfully used to synthesize fine powders of tin niobates. In a typical synesthes, Nb₂O₅ powder used as Nb source was dissolved in hot HF. Then an acquous solution containing Sn slat was added in the resulting solution, and the pH value was controled. After calcining the precursor at 700°C for 6 h, the nanoscale tin niobates were obtained. The Sn-Nb molar ratio affected the synthesis product. SnNb₂O₆ (or Sn₂Nb₂O₇) powders could be obtained when Sn/Nb molar ratio was 1/2 (or 1/1). The average particle sizes of SnNb₂O₆ and Sn₂Nb₂O₇ were about 80 nm and 50 nm, respectively according to XRD analysis and TEM images. Photocatalytic properties of the powders were investigated by measuring degradation of methyl orange in aqueous solution under light irradiation. The SnNb₂O₆ powder showed a relatively high photocatalytic activity, while the Sn₂Nb₂O₇ powder had almost no photocatalytic activity.NiO nanoparticles, which were used as the trap of electron and hole, were loaded on the surface of SnNb₂O₆ particles by impregnation method. The SnNb₂O₆: NiO/Ni electrode had much higher photocurrent than the SnNb₂O₆/Ni electrode, which was about 2μA. SnNb₂O₆ doped with transition metals was synthesized by the solid state reaction. The Cr (or Co) -doped SnNb₂O₆: NiO/Ni electrode had much higher photovoltage (photo-induced open circuit voltage) than the SnNb₂O₆ doping with other metal ions. And according to the decay constant measurement, the decay constant 'b' of Cr (or Co)-doped SnNb₂O₆:NiO/Ni electrode was also found to be smaller. Furthermore, the Cr (or Co)-doped SnNb₂O₆:NiO/Ni electrode also had relative higher photocurrent density than the SnNb₂O₆ doping with other metal ions. Thus, it is concluded that the SnNb₂O₆ doping with Cr or Co could be improved more efficient in photoelectrochemical properties.