Optimization of Methods for Synthesis and Protonation of Layered Perovskite-Structured Photocatalysts APb2Nb3O10 (A = Rb, Cs)

Synthesis of layered perovskite-like niobates APb₂Nb₃O₁₀ (A = Rb, Cs), being promising visible light active photocatalysts, has been conducted by the ceramic method under variable conditions to obtain the samples with the highest possible phase purity. The oxides prepared were shown practically not to undergo protonation and hydration of the interlayer space upon keeping in water. Both phases APb₂Nb₃O₁₀ were used to yield corresponding protonated hydrated forms H_xA_1 − xPb₂Nb₃O₁₀∙yH₂O via acid treatment. It was found that the propensity of the samples to the substitution of interlayer cations by protons depends clearly on the A⁺ cation: while the Rb-containing niobate is capable of complete protonation (x = 1) upon a single treatment with 6 M nitric acid, the Cs-containing counterpart gives a high enough protonation degree (x ≥ 0.9) only after several renewals of the acid solution. The protonated niobates obtained were exposed to an additional water treatment under hydrothermal conditions, which allowed producing new hydrated derivatives with the enhanced thermal stability towards interlayer dehydration as compared with the protonated precursors.