| Abstract
| - The conduction and valence band edges for electronic band gaps and Fermi levels are determined for Ta2O5,TaON, and Ta3N5 by ultraviolet photoelectron spectroscopy (UPS) and electrochemical analyses. Reasonableagreement between the results of the two methods is obtained at the pH at which the ζ potentials of theparticles are zero. The tops of the valence bands are found to be shifted to higher potential energies on theorder Ta2O5< TaON < Ta3N5, whereas the bottoms of the conduction bands are very similar in the range−0.3 to −0.5 V (vs NHE at pH = 0). From the results, it is concluded that TaON and Ta3N5 are promixingcatalysts for the reduction and oxidation of water using visible light in the ranges λ < 520 nm and λ < 600nm, respectively. It is also demonstrated that the proposed UPS technique is a reliable alternative toelectrochemical analyses for determining the absolute band gap positions for materials in aqueous solutionsthat would otherwise be difficult to measure using electrochemical methods.
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