Heterojunction-Engineered Cu ₃ Mo ₂ O ₉ /MoO ₃ Nanocomposites for Highly Selective Trimethylamine Sensing

One-dimensional MoO3 nanobelts are promising materials for trimethylamine (TMA) detection due to their abundant surface acid sites and favorable electronic transport properties. However, the adsorption of TMA on MoO3 is limited by steric hindrance between methyl groups and terminal oxygen atoms, which constrains both selectivity and detection limit in gas sensing applications. To overcome this challenge, Cu3Mo2O9/MoO3 heterojunction nanocomposites are constructed through interfacial engineering to regulate adsorption and electronic interactions. Structural and surface analyses confirm the uniform decoration of Cu3Mo2O9 nanoparticles on MoO3 nanobelts and the formation of well-defined heterojunctions. Benefiting from exposed Cu-enriched interfacial active sites, the sensor exhibits markedly enhanced sensing performance toward TMA, achieving an ultralow detection limit of 10 ppb and a high response of 62.5−10 ppm TMA at an operating temperature of 170 °C, representing a six-fold improvement over pure MoO3. In addition, excellent selectivity against structurally similar amines and other interfering gases is demonstrated. Density functional theory calculations (DFT), together with temperature-programmed reduction (TPR) and in situ FTIR analyses, reveal that the heterojunction alleviates steric hindrance and promotes interfacial charge transfer, thereby facilitating preferential adsorption and catalytic oxidation of TMA. Furthermore, a micro-electro-mechanical systems (MEMS) sensor based on the Cu3Mo2O9/MoO3 nanocomposites enables rapid (34 s) and real-time monitoring of TMA evolution during storage, demonstrating the feasibility of this platform for miniaturized electronic sensing devices and portable gas monitoring systems.