Perovskite-like La_xSr_2−xTi_1−x/2Cu_x/2O₄ (x = 0.2, 0.3, 0.5) oxides with the K₂NiF₄-type structure active in visible light range: new members of the photocatalyst family

A layered perovskite-like oxides La_xSr_2−xTi_1−x/2Cu_x/2O₄ (x = 0.2, 0.3, 0.5) with a K₂NiF₄-type structure were obtained. The introduction of copper into the titanium sublattice reduces the band gap. Copper in these materials serve as a photoactivity regulator and is presented in two oxidation states in accordance with optical, voltammetric and EPR data. La_xSr_2−xTi_1−x/2Cu_x/2O₄ (x = 0.2) exhibits the greatest photoactivity in the oxidation of phenolic compounds and As(III) under the influence of UV and blue light; with increasing degree of substitution x, the photoactivity of La_xSr_2−xTi_1−x/2Cu_x/2O₄ decreases. This is explained by the formation of a magnetic polaron, which is observed in La_xSr_2−xTi_1−x/2Cu_x/2O₄ (x = 0.5) in the temperature range from 50 to 200 K and is proven by ESR method. The expansion of the spectral range of La_xSr_2−xTi_1−x/2Cu_x/2O₄ to the visible region is explained by the formation of acceptor levels \(\left( {{\text{Cu}}^{2 + } + {\text{e}}^{ - } \to {\text{Cu}}^{ + } / {\text{Cu}}^{ + } + {\text{h}}^{ + } \to {\text{Cu}}^{2 + } } \right)\) $\left({\text{Cu}}^{2+}+{\text{e}}^{-}\to {\text{Cu}}^{+}/{\text{Cu}}^{+}+{\text{h}}^{+}\to {\text{Cu}}^{2+}\right)$ in the band gap of Sr₂TiO₄, which increases the efficiency of separation of photogenerated electron–hole pairs. The presence of Cu (I) в La_xSr_2−xTi_1−x/2Cu_x/2O₄ enhance photoactivity through the formation of active superoxygen radical on its surface ( \({\text{Cu}}^{ + } {\text{ + O}}_{{{2}\left( {{\text{ad}}} \right)}} \to {\text{Cu}}^{{2 + }} +\cdot{{\text{O}}}_{{2}}^{ - }\) ${\text{Cu}}^{+}{\text{+ O}}_{2\left(\text{ad}\right)}\to {\text{Cu}}^{2+}+·{\text{O}}_2^{-}$ ).