To elucidate and understand the fundamental processes that promote heterogeneous catalysis, structure-property relationships must be studied. Recently, we demonstrated Bi4TaO8Cl-Bi2GdO4Cl intergrowths as emerging durable and efficient photocatalysts for overall solar water splitting. In this study, we investigate the nanoscale structure of this emerging multimetal oxyhalide intergrowth oxychloride: Bi4TaO8Cl-Bi2GdO4Cl material. We varied the amount of Bi4TaO8Cl in the intergrowths to rationalize the effect changes in the nanoscale and electronic structure. The modulation of the Bi4TaO8Cl and Bi2GdO4Cl layers and rotation of the [TaO6] octahedral resulted in coupled effects in the crystal structure of the nanomaterials. Atomic-resolution imaging in transmission electron microscopy (TEM) and Scanning TEM (STEM) is often a purely two-dimensional projection of the sample and misses atomic position modulation along the incident electron beam. Such modulations can be measured by the azimuthal variation in the intensity of the High Order Laue Zone (HOLZ) rings in a convergent beam electron diffraction (CBED) pattern. HOLZ rings have components of the diffraction vector along the beam direction, revealing information about the 3D atomic structure. Consequently, the ordering of Bi4TaO8Cl and Bi2GdO4Cl layers and rotation of the [TaO6] octahedral can be inferred. We observed a more intense outer HOLZ ring for high Ta% intergrowths. This effect can be related to a higher amount of distortion along the &lt;001&gt; direction. This distortion variation has direct implications on the electronic structure, such as conduction and valence band energy levels. Combining Ultraviolet Photoelectron Spectroscopy (UPS), UV-Visible Diffuse Reflectance Spectroscopy (DRS), and Electron Energy Loss Spectroscopy (EELS) techniques, the electronic structure of the oxyhalide intergrowths was investigated. The low-loss energy region of the EEL spectrum (&lt;50 eV) can provide information about the composition and electronic structure, as well as optical properties. We obtained the band gap of the intergrowths by looking at the onset of the low-loss region. We found strong correlations between the band gaps obtained via bulk measurements (DRS and UPS) and nanoscale measurements (EELS). We believe our approach opens up opportunities for understanding the atomic-scale structure-property phenomena for designing next-generation novel photocatalytic systems.

Nanoscale structure investigations of emerging multimetal oxychloride intergrowth photocatalysts

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