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

One-dimensional MoO 3 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 MoO 3 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, Cu 3 Mo 2 O 9 /MoO 3 heterojunction nanocomposites are constructed through interfacial engineering to regulate adsorption and electronic interactions. Structural and surface analyses confirm the uniform decoration of Cu 3 Mo 2 O 9 nanoparticles on MoO 3 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 MoO 3 . 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 Cu 3 Mo 2 O 9 /MoO 3 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.