La_1.33-xNa_3xTi₂O₆/Na_{3La2(BO3)3 heterostructure transformed from La2Ti2O7 plates for enhanced photocatalytic H2 evolution}

Perovskite-type oxide semiconductors, as promising photocatalysts, possess flexible structures with cornershared BO6 octahedrons and A cations, but are limited by the broad band gaps and severe photo-induced carrier recombination. Herein, a series of La1.33-xNa3xTi2O6/Na3La2(BO3)(3) composites were synthesized by annealing the layered La2Ti2O7 with NaBH4. The doping of Na+ ions in perovskite's A-site promotes the transformation of La2Ti2O7 into La1.33-xNa3xTi2O6 phase, meanwhile, substituted La species turn into Na3La2(BO3)(3) phase. The crystalline degree of perovskite structure evolves with the ratio of Na+ ions in the A site, and La2Ti2O7 undergoes amorphization, recrystallization, and further decomposition as the Na species increases. In wellcrystallized La1.17Na0.48Ti2O6/Na3La2(BO3)(3), intimate interfacial contacts induce extended optical absorption and optimized charge transfer. Under visible light irradiation, the sample exhibits significantly enhanced photocatalytic H2 evolution activity, with hydrogen production rate reaching 660 mu mol.g(-1).h(-1), whereas La2Ti2O7 has almost no catalytic activity. This work presents a novel strategy to transform the perovskite oxides at a relatively low temperature by exchanging cations with reductive NaBH4. It demonstrates applications in the development of visible light-driven perovskite-based heterogeneous photocatalysts.