Colloidal Synthesis of Tantalum (Oxy)Nitride Clusters

The development of water splitting photocatalysts for hydrogen production is potentially an important component of the complex strategy that will be required to meet our energy needs.

Tantalum (oxy)nitrides have been suggested by Domen et al. as novel visible light-driven photocatalysts (lambda< 600nm) for water splitting. Traditionally Ta₃N₅ and TaON are synthesized as bulk powders through high temperature (1000 C) nitriding processes using ammonia. Our strategy focuses on the low temperature (< 300 C) synthesis of colloidal Ta₃N₅ nanocrystals(NCs) and sol-gel derived TaO_xN_y. Our Ta₃N₅ NCs made by a colloidal synthesis method are highly crystalline with particle sizes from 2 to 10 nm. However, these materials are air sensitive and easily oxidized possibly during synthesis as opposed to post-situ oxidation. TaO_xN_y was synthesized through a wet-chemical sol-gel route.

To complement our experiments, density functional theory calculations provide some insight as to active sites and desired size range for photocatalytic NCs. We have found that (100) and (110) surfaces are the most stable faces of Ta₃N₅. We also examined the adsorption and dissociation of O₂ and H₂O on these surfaces to understand the mechanism of oxidation of Ta₃N₅.