Decoding Plasmonic Enhancement Pathways in Group 4 Metal Nitride-TiO2 Composites: Rhodamine B Dye Degradation Case Study

Traditional photocatalysis uses TiO2 for its low-cost, chemical stability, and non-toxicity. However, its wide bandgap (>3 eV) limits solar absorption to under 5%, reducing efficiency under sunlight. Plasmonic materials address this by extending light absorption into the visible and near-infrared range, enhancing catalytic activity through localized electromagnetic fields, hot carriers, and photothermal effects. Transition metal nitrides like TiN, ZrN, and HfN emerge as promising, cost-effective alternatives to noble metals due to their strong broadband absorption and chemical stability. While earlier studies attribute their photocatalytic enhancement mainly to hot carrier injection, more detailed assessment is needed to properly understand the enhancement pathway. This study synthesizes composites of TiN, ZrN, and HfN with commercial P25 TiO2 and evaluates their photocatalytic performance via Rhodamine B dye degradation. Under 100 mW cm-2 illumination, the 1 wt% ZrN/TiO2 composite achieves over 99% dye degradation in 50 minutes, outperforming TiN and HfN, which require 10 wt% loading for similar results. By analyzing reaction temperature profiles and degradation kinetics under different light intensities, the study finds hot carrier effects dominate in TiN/TiO2 and ZrN/TiO2 systems, while photothermal effects play a larger role in HfN/TiO2 composites. This highlights the distinct mechanisms by which plasmonic nitrides enhance photocatalytic efficiency.