Design of nitrogen-doped layered tantalates for non-sacrificial and selective hydrogen evolution from water under visible light

Nitrogen doping into a series of layered tantalates (ALaTa 2 O 7 , where A = Li, Na, K, Rb, or Cs) was attempted in order to produce materials capable of catalyzing non-sacrificial and endergonic water reduction under visible light. Heating of KLaTa 2 O 7 and RbLaTa 2 O 7 in an NH 3 stream at 1073 K led to successful nitrogen doping, accompanied by a significant shift in the absorption edge of the material toward the visible-light region, while similar treatment of the other tantalates resulted in the collapse of the layered structure or partial anion substitution at the surface. Although the NH 3 heating of a conventional RbLaTa 2 O 7 precursor prepared with nearly stoichiometric Rb (Rb/La = 1.2) resulted in the formation of impurities such as Ta 3 N 5 and amorphous tantalum nitrides, the use of a Rb-rich precursor prepared with excess Rb (Rb/La = 2.4) effectively suppressed this impurity formation. The Rb + cations in the prepared pure nitrogen-doped sample were exchanged with H + to facilitate the intercalation of water, and a cationic Pt precursor was then selectively introduced into the interlayers and photocatalytically reduced to Pt metal particles. The internally platinized H + /RbLaTa 2 O 7− x N y showed stable H 2 evolution in the presence of I − as an electron donor under visible light, accompanied by the generation of I 3 − . Although the externally platinized H + /RbLaTa 2 O 7− x N y sample and other bulk-type photocatalysts such as Ta 3 N 5 generated H 2 in the presence of a sacrificial electron donor, H 2 evolution was negligible in the presence of I − . The stable H 2 evolution over the internally platinized H + /RbLaTa 2 O 7− x N y sample is due to the suppressed backward reduction of I 3 − to I − at selective reduction sites in the interlayer spaces, which are accessible only to cationic species and water. Nitrogen doping into a series of layered tantalates (ALaTa 2 O 7 , where A = Li, Na, K, Rb, or Cs) was attempted in order to produce materials capable of catalyzing non-sacrificial and endergonic water reduction under visible light.