Rational tailoring of the electronic structure for the Sr_xNaTa_yO₃ semiconductor: Insights into its enhanced photoactivity and optical property

NaTaO₃ (NTO), as a popular photocatalyst with the prominent redox ability, largely straddles across the conduction band minimum (CBM) and valence band maximum (VBM) edge over Fermi level. Pristine NTO exhibits the poor light-harvesting ability and the rapid recombination of electron-hole pairs. We proposed an effective method to improve the photocatalytic property of NTO (ABO₃-type) by substituting B site with Sr. The Sr_xNaTa_yO₃ (SNTO) exhibited the boosted photocatalytic activity toward tetracycline oxidation under solar light irradiation. The rate constant for S_0.5NTO (molar ratio of Sr: Ta = 1 : 2) was 5.1 times higher than the pure NTO. DFT results indicated that the Sr 3d orbital combining the O 2p and Ta 5d hybrid orbitals, widened the VB of SNTO. The band gap was narrowed from 3.86 to 2.82 eV after Sr substitution, which enhanced its light-harvesting ability. The VBM moved upward for 1.42 V and the CBM moved upward for 0.38 V. The shifts of the CBM and VBM, together with the more stretched Ta-O-Ta configuration, highly facilitated the electron-hole pair separation in SNTO. These electronic structure changes accounted for the significant photocatalytic performance enhancement of NaTaO₃ via Sr substitution for B-site-Ta.