Local structure analysis and structure mining for design of photocatalytic metal oxychloride intergrowths

In this work, the local structures of durable, high-activity Bi₄TaO₈Cl-Bi₂GdO₄Cl intergrowth photocatalysts that were prepared in a molten flux are determined by pair distribution function analysis of X-ray total scattering data and correlated to their photocatalytic performance. This system gives understanding to how the local structure of photocatalysts can be manipulated controllably through incorporation of rigid and flexible layers via intergrowth formation to achieve high activity. This analysis revealed that the local symmetry and distortion of the [TaO₆] octahedra introduced through intergrowth formation and dictated by intergrowth stoichiometry correlate with their photocatalytic activity. That is, the greater the Ta-O-Ta bond angles, the higher the photocatalytic activity of a given intergrowth for the oxygen evolution reaction. Moreover, greater tilting of the [TaO₆] octahedra is associated with a larger band gap. This analysis was coupled with a structure mining approach to model the intergrowth structure by building supercells for refinement of the X-ray diffraction data. This analysis found that Ta- and Gd-domains are separated within the intergrowths, with large Gd-domains separated by small Ta-domains at high Gd% and the opposite for high Ta%. Taken together with Williamson-Hall analysis, our results highlight that the local structure of layered materials can be modulated through strain engineering enabled by the selection of rigid and flexible intergrowth layers, providing a new design pathway to high performance photocatalysts.