Relationship between interlayer hydration and photocatalytic water splitting of A'1-xNaxCa2Ta3O10 • nH2O(A' = K and Li)

Partial replacement of alkaline metals in anhydrous KCa2Ta3O10 and LiCa2Ta3O10 was studied to control interlayer hydration and photocatalytic activity for water splitting under UV irradiation. A'1-xNaxCa2Ta3O10 center dot nH(2)O (A''= K and Li) samples were synthesized by ion exchange of CsCa2Ta3O10 in mixed molten nitrates at 400 degrees C. In K1-xNaxCa2Ta3O10 center dot nH(2)O, two phases with the orthorhombic (C222) and tetragonal (14/mmm) structures were formed at x <= 0.7 and x >= 0.5, respectively. Upon replacement by Na+ having a larger enthalpy of hydration (Delta H-h(0)), the interlayer hydration occurred at x >= 0.3 and the hydration number (n) was increased monotonically with an increase of x. Li1-xNaxCa2Ta3O10 center dot nH(2)O showed a similar hydration behavior, but the phase was changed from I4/mmm (x < 0.5, n similar to 0) via P4/mmm (x similar to 0.5, n similar to 1) to 14/mmm (x similar to 1.0, n similar to 2). The photocatalytic activities of these systems after loading 0.5 wt% Ni were quite different each other. K1-xNaxCa2Ta3O10 center dot nH(2)O exhibited the activity increasing in consistent with n, whereas Li1-xNaxCa2Ta3O10 center dot nH(2)O exhibited the activity maximum at x = 0.77, where the rates of H-2/O-2 evolution were nearly doubled compared with those for end-member compositions (x = 0 and 1). (c) 2008 Elsevier Inc. All rights reserved.