Ball Mill Beatdown: Mechanochemical Synthesis of TaON Nanocrystals

Semiconductor photocatalysts play a key role in advancing sustainable fuel production, air purification, and water treatment. The rapid growth of heterogeneous photocatalysis is further supported by the development of flow-based photoreactors, which have paved the way toward pilot- and commercial-scale photocatalysis. However, their operation often relies on stable suspensions of the catalyst in solution, posing a significant barrier to entry for many promising photocatalysts. Specifically, oxynitride semiconductors, some of the leading contenders in photochemical water splitting, tend to undergo rapid sedimentation. To address this challenge, we investigate mechanochemical methods of synthesizing dispersible TaON nanocrystals. We show that it is possible to prepare <20 nm TaON nanocrystals from both pre- and postnitridation ball milling, with the latter method enabling particle size control. TaON nanocrystals prepared by both methods form significantly more stable suspensions than do their bulk counterparts. We demonstrate that TaON nanocrystals prepared by both routes display similar photocatalytic activity to their bulk forms while exhibiting remarkable stability under neutral and acidic conditions. Further, we demonstrate that Ag and C electrodes modified with TaON nanocrystals achieve a substantial decrease of more than 0.8 V in cathodic peak potentials for CO₂ electroreduction. These combined results indicate that ball milling produces stable, dispersible, and catalytically active oxynitride nanocrystals, extending their potential applications from laboratory to large-scale catalysis.