Photochemistry of Plasmonic Titanium Nitride Nanocrystals

Titanium nitride (TiN) offers advantages compared to standardly used plasmonic materials such as gold and silver in terms of thermal stability, cost, and sustainability. While gold and silver nanostructures have played an important role in the rapidly growing field of plasmonic catalysis, the potential of TiN in this application is still underexplored. Here we provide evidence of plasmon-driven chemical activity in TiN by using the photoreduction of platinum ions under visible-near-infrared (vis-NIR) illumination as probe reaction. An aqueous solution of TiN, methanol, and chloroplatinic acid (H2PtCl6) was exposed to vis-NIR radiation (600-900 nm). Scanning transmission electron microscopy (STEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS) show nanostructures composed of similar to 2 nm metallic platinum clusters decorating similar to 10 nm TiN nanoparticles, confirming the plasmon-driven reduction of the Pt4+ ions to their metallic state. At the same time, the evolution of CO2 resulting from the photooxidation of methanol is monitored via gas chromatography. The molar Pt deposition-to-CO2 evolution ratio is in good agreement with the theoretical expectation based on the redox reaction charge balance. We have found that both Pt deposition and CO2 evolution are self-limiting. We attribute this to the increasing plasmon dephasing rate during the photoreduction process, likely due to the high optical losses of Pt in the vis-NIR region. In addition, density functional theory (DFT) simulations of a Pt(111)-TiN(111) junction suggest the existence of an energy barrier limiting electron transfer. This work confirms that plasmonic TiN nanoparticles can use visible light to drive photochemical reactions and highlights the potential of TiN as a cost-effective alternative to gold and silver.