Go Hitoki

An oxynitride, TaON, as an efficient water oxidation photocatalyst under visible light irradiation (λ≤ 500 nm)

Under visible light irradiation (λ n= 420–500 nm), a tantalum oxynitride, TaON, functions as a stable and very efficient photocatalyst for oxidation of water into O2 with a sacrificial electron acceptor (Ag+).

TaON and Ta3N5 as new visible light driven photocatalysts

Abstract TaON and Ta3N5, Ta5+-based (oxy)nitrides, were studied as visible light driven photocatalysts. Under visible light irradiation (λ≥420xa0nm), the (oxy)nitrides oxidize water to O2 and reduce H+ to H2 in the presence of sacrificial reagents (Ag+ and methanol). TaON oxidizes water into O2 efficiently, with a maximum quantum yield of 10%. The photocatalytic reactions proceed via the bandgap transitions (Eg, TaON: 2.5xa0eV, Ta3N5: 2.1xa0eV) without any noticeable degradation of the catalysts. The small energy gaps of TaON and Ta3N5 are ascribed to the valence band structures consisting of N 2p orbitals.

Visible-light-driven photocatalytic behavior of tantalum-oxynitride and nitride

Tantalum oxynitride (TaON) and tantalum nitride (Ta3N5) are investigated in detail as visible-light-responsive photocatalysts. It is found that TaON and Ta3N5 evolve H2 or O2via bandgap excitation in the presence of a sacrificial electron donor or acceptor, respectively. These materials exhibit high stability against photo-corrosion under the reaction conditions for H2 and O2 evolution. Structural and physical properties of these photocatalysts were also investigated in detail.

MECHANO-CATALYTIC OVERALL WATER SPLITTING

Mechano-catalysis, a novel and simple method to decompose water into H2 and O2 in which mechanical energy is directly converted into chemical energy, is demonstrated.

Mechano-catalytic overall water splitting on some mixed oxides

Abstract Simple transition metal oxides such as NiO, Co3O4, Fe3O4 and Cu2O were found to catalytically decompose water into H2 and O2 by mechanical energy. The reaction is regarded as “mechano-catalytic” overall water splitting” and is a quite novel catalytic reaction. In this paper, some general aspects on the mechano-catalytic overall water splitting are reviewed on simple oxides. In addition, recent results on the mechano-catalytic activity of a groups of mixed oxides, wolramite-type oxides with a formula of ABO4 (A=Fe, Co, Ni and Cu, etc., B=W, Mo), are shown. AWO4 (A=Fe, Co, Ni and Cu) decomposed water into H2 and O2 under the supply of mechanical energy, indicating that mechano-catalytic overall water splitting proceeded on wolframite-type compounds containing 3d-transition metals. AMoO4 (A=Fe, Co, Ni) also decomposed water into H2 and O2 under supply of mechanical energy. The reaction properties on wolframite-type oxides are discussed.

30 Ta3N5 and TaON as novel photocatalysts responding to visible light

Abstract TaON and Ta 3 N 5 , Ta 5+ -based (oxy)nitrides, were studied as visible light driven photocatalysts. Under visible light irradiation (λ≥420 nm), the (oxy)nitrides oxidize water to O 2 and reduce H + to H 2 in the presence of sacrificial reagents (Ag + and methanol). TaON oxidizes water into O 2 efficiently, with a maximum quantum yield of 34%. The photocatalytic reactions proceed via the bandgap transitions (Eg, TaON: 2.5 eV, Ta 3 N 5 : 2.1 eV) without any noticeable degradation of the catalysts.