Synthesis and Photocatalytic Properties of Manganese-Substituted Layered Perovskite-like Titanates A′₂La₂Mn_xTi_3−xO₁₀ (A′ = Na, H)

Abstract

The search for effective and reliable methods of photosensitization of oxide-based semiconductor materials is of great significance for their use in photocatalytic reactions of hydrogen production and environmental remediation under natural sunlight. The present study is focused on partial substitution of titanium with manganese in the structure of layered perovskite-like titanate Na2La2Ti3O10, which was employed to yield a series of photocatalytically active materials, Na2La2MnxTi3−xO10 (x = 0.002–1.0), as well as their protonated forms H2La2MnxTi3−xO10 and nanosheets. It was established that the manganese cations Mn4+ are embedded in the middle sublayer of oxygen octahedra in the perovskite slabs La2MnxTi3−xO102− and that the maximum achievable manganese content x in the products is ≈0.9. The partial cationic substitution in the perovskite sublattice led to a pronounced contraction of the optical band gap from 3.20 to 1.35 eV (depending on x) and, therefore, allowed the corresponding photocatalysts to utilize not only ultraviolet, but also visible and near-infrared light with wavelengths up to ≈920 nm. The materials obtained were tested as photocatalysts of hydrogen evolution from aqueous methanol, and the greatest activity in this reaction was demonstrated by the samples with low manganese contents (x = 0.002–0.01). However, the materials with greater substitution degrees may be of high interest for use in other photocatalytic processes and, especially, in thermophotocatalysis due to their improved ability to absorb the near-infrared part of solar radiation.

Keywords

• layered perovskite
• photosensitization
• cationic substitution
• protonation
• exfoliation
• nanosheets