Exploring the Photocatalytic Mechanism of BiTi₄GaO₁₁: Insights from the Electronic Structure and Chemical Bonding

Photocatalytic water splitting and CO₂ reduction offer sustainable solutions to energy and environmental issues, but efficient semiconductor photocatalysts are still limited. Oxide photocatalysts with d⁰ and/or d¹⁰ metals often have wide bandgaps, and incorporating d¹⁰ns² metals can raise the valence band maximum (VBM) and narrow the bandgap. Here, we synthesized BiTi₄GaO₁₁ (BTGO), a new photocatalyst containing d¹⁰6s², d⁰, and d¹⁰ metals. Structural analysis via powder X-ray and neutron diffraction confirmed BTGO crystallizes in the space group <i>Cmcm</i>, with Ga cooccupying all three Ti sites. Density functional theory calculations revealed that the conduction band minimum (CBM) of BTGO is primarily composed of Ti t_2g - O 2p antibonding orbitals. Hybridization between Bi 6s and O 2p orbitals leads to the formation of antibonding orbitals, which further interact with Bi 6p orbitals to form the VBM. This interaction shifts the VBM upward, narrows the bandgap (<i>E</i>_g = 2.82 eV), and enables the visible-light absorption. Experimental results demonstrated that BTGO efficiently catalyzes photocatalytic H₂ production and CO₂ reduction. Furthermore, the incorporation of cocatalysts suppressed the recombination of photogenerated charge carriers, enhancing photocatalytic activity. This work highlights the importance of electronic structure and bonding analysis in understanding the fundamental mechanisms of photocatalysis.