Oxynitride materials can serve as photocatalysts for the water splitting reaction on account of their narrow band gaps which are suitable for visible light absorption as well as high oxidative stability. As such, they offer an excellent opportunity to shift the global energy landscape from a fossil fuel-dependent paradigm to sustainable and carbon-neutral solar fuels. Unfortunately, most synthetic methods for making these materials rely on high temperature solid state reactions. Though these methods provide a means of exploring complex compositions, the extremely high temperatures they employ bypass many of the metastable states necessary to access size and shape controlled crystallites of such materials. Ultrasonic spray synthesis (USS) is one synthetic technique that allows access to these metastable states. In USS, an ultrasonic nebulizer generates aerosol droplets of a precursor solution, which are transported into a tube furnace via a gas. Reactions then take place in the heated aerosol droplets. Multi-domain microspheres of an amorphous La-Ti-O phase are produced by traditional USS and can be converted to polycrystalline LaTiON microspheres via ammonolysis. A moderate surface area suitable for catalysis applications is maintained. Introducing a molten flux into the USS system can provide control over crystallite size and shape for a variety of compositions, including those requiring high temperature preparations. These methods are also applied to achieve La-Ti-O phases for conversion to LaTiON. The mechanism for product formation is analyzed by thermal analysis, alongside extensive structural characterization of the product particles. These materials are promising platforms for visible light solar water splitting.

Ultrasonic spray synthesis as a route to shape controlled LaTiON nanoparticles

250th National Meeting (2015)

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