Synthesis of New Intergrowth and Nanostructured Metal Oxyhalide Photocatalysts

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Nontechnical summaryThere is a critical need for materials that absorb visible light so that such energy can be used to drive reactions at their surfaces, such a solar water splitting which promises to provide hydrogen as a clean fuel. Metal oxyhalides are an exciting class of such photocatalytic materials but often they will be converted to their corresponding metal oxide upon use, making them ineffective long-term. Recently, a subset of bismuth-containing metal oxyhalides was identified to be both visible light absorbing as well as durable during their use as photocatalysts. With this project, supported by the Solid State and Materials Chemistry program in the Division of Materials Research, Professor Sara Skrabalak and her research group at Indiana University will develop new materials that combine different bismuth-containing metal oxyhalides for uses in solar water splitting. The atomic level structure of these new materials are also characterized in detail to understand how their structure provides both visible light absorption and critical durability. These materials are also being synthesized as crystals with defined shapes so that the best crystal faces are expressed to facilitate the water splitting reaction. This work provides fundamental insight into the properties of materials, with potential to address material durability challenges associated with harnessing solar energy. The research is paired with broad educational and outreach activities that foster understanding about material science and solar energy to the general public.Technical summaryThis project, supported by the Solid State and Materials Chemistry program in the Division of Materials Research, will develop synthetic methods for the growth of new metal oxyhalide intergrowths of the form Bi4MO8X-Bi2LnO4X. The fundamental hypothesis of this work involves the idea that intergrowth formation and modulation of their stoichiometry enables engineering of their electronic structure and internal electric fields toward enhanced photocatalytic efficiency and photostability compared to the parent compounds. This synthetic work is coupled with detailed structural characterization by high resolution electron microscopy and X-ray total scattering experiments so that robust structure-property correlations are established. A final aim focuses on the synthesis of shape-controlled Bi4MO8X nanocrystals and the study of their faceting on photocatalytic performance. Collectively, this research advances the synthesis and design of durable metal oxyhalides by elucidating the roles of local and nanoscale structure on the optoelectronic properties and photocatalytic performance of these promising heteroanionic materials. The project will also support educational and outreach activities that introduce energy concepts to non-scientists through partnerships with Wonderlab (a children’s science museum in Bloomington, Indiana) and Indiana University’s ScienceFest.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.