Calcium niobate nanosheets prepared by the polymerized complex method as catalytic materials for photochemical hydrogen evolution

The Dion-Jacobson phase niobate perovskite, KCa ₂Nb ₃O ₁₀, was prepared by the polymerized complex (PC) method. The corresponding proton-exchanged material, HCa ₂Nb ₃O ₁₀, was then exfoliated by reaction with tetra(η-butyl)ammonium hydroxide (TBA ⁺OH ^-), yielding unilamellar colloidal nanosheets whose lateral dimensions increased with the final calcination temperature in the PC synthesis. By restacking the TBA ⁺-stabilized nanosheets with hydrochloric acid, aggregates of HCa ₂Nb ₃O ₁₀ nanosheets were obtained and tested as photocatalytic materials. The rate of H ₂ production from aqueous methanol solution under band gap irradiation (λ > 300 nm) was dependent on the calcination temperature. The best materials, prepared by the PC method at the intermediate calcination temperature of 1273 K, had higher activity than those made by a conventional solid state reaction. In contrast, the rate of visible-light hydrogen evolution (1 = 450 ± 20 nm) from aqueous ethylenediaminetetraacetic acid (EDTA) solution with materials sensitized by [Ru(bpy) ₂(4,4'(PO ₃H ₂) ₂bpy)](PF ₆) ₂ (abbreviated RuP ²⁺ ) was essentially insensitive to the preparation conditions. These results suggest that increasing the crystallinity of the nanosheets enhances their activity under band gap irradiation, where catalytic reactions compete with electron-hole recombination within the nanosheet. In contrast, the quantum yield for sensitized H ₂ production is primarily governed by electron injection efficiency from the excited-state sensitizer into the nanosheet.