Influence of Composition and Structure on the Optoelectronic Properties of Photocatalytic BiNbOCl-BiGdOCl Intergrowths.

Mixed metal oxyhalides are an exciting class of photocatalysts, capable of the sustainable generation of fuels and remediation of pollutants with solar energy. Bismuth oxyhalides of the types BiMOX (M = Nb and Ta; X = Cl and Br) and BiAOX (A = most lanthanides; X = Cl, Br, and I) have an electronic structure that imparts photostability, as their valence band maxima (VBM) are composed of O 2p orbitals rather than X p orbitals that typify many other bismuth oxyhalides. Here, flux-based synthesis of intergrowth BiNbOCl-BiGdOCl is reported, testing the hypothesis that both intergrowth stoichiometry and M identity serve as levers toward tunable optoelectronic properties. X-ray scattering and atomically resolved electron microscopy verify intergrowth formation. Facile manipulation of the BiNbOCl-to-BiGdOCl ratio is achieved with the specific ratio influencing both the crystal and electronic structures of the intergrowths. This compositional flexibility and crystal structure engineering can be leveraged for photocatalytic applications, with comparisons to the previously reported BiTaOCl-BiGdOCl intergrowth revealing how subtle structural and compositional features can impact photocatalytic materials.