Invited Paper EH-ThM5
Effect of Different Synthesis Routes of NaTaO₃ and the Presence of Metal-Based Nanoparticles as Co-Catalyst on the Hydrogen Production

Thursday, December 11, 2014, 9:20 am, Room Lehua

Significant attention has been paid on the investigations of new photocatalysts metal-oxides because of their ability to harness the sun energy to drive fuel-producing reactions, such as water splitting. The compound NaTaO₃ has been studied in the last 10 years as photocatalyst in this reaction. According to the results obtained by several authors, high activity on this reaction was found by using NaTaO₃ material prepared by solid state route. This result is associated with the high crystallinity of the powder. However, there are other factors that also influence the physicochemical properties of semiconductor material such as specific surface area, microestructure, optoelectronic properties among others. Therefore the synthesis of metal-oxides can be carry out by soft chemical methods in order to modify and control the morphology, which allows to increase sites for hydrogen evolution. In our research group we have explored the performance of sodium tantalate, NaTaO₃ and RuO₂/La:NaTaO₃ prepared by several synthesis methods such as solid state reaction, sol-gel, hydrothermal, ultrasonic, solvo-combustion on photoinduced reactions. The sodium tantalate phase with perosvkite structure has been synthesized by solvo-combustion path at low temperature (180°C) and using nanoparticles of RuO₂ as co-catalyst. This material showed considerably high photocatalytic activity for hydrogen production around 9,800 µmol.h^-1g^-1, twice greater than those results obtained when the material was prepared by solid state method. The activity is associated with the material high crystallinity and the presence of the second phase, Na₂Ta₄O₁₁ in small concentration after annealed at 600°C. The formation of nanosteps between NaTaO₃ nanoparticles also contributed to the reaction efficiency. In addition, it was found that the crystalline structure formed by chains enhances mobility among linked octahedra and separation of hole-electron pairs, which increases the photoactivity of the material in these processes. From photoelectrochemical study was proposed the reaction mechanism that occurs during the water splitting on NaTaO₃ single and doped phase. Additionally, experiments of the electrochemical impedance spectroscopy were realized in order to obtain Mott-Schottky plots to determine the flat band potential of NaTaO₃, RuO₂/La:NaTaO₃.