Oxygen Vacancy Mediated-Bismuth Molybdate/Graphitic Carbon Nitride Type II Heterojunction Chemiresistor for Efficient NH₃ Detection at Room Temperature

Metal oxide-based chemiresistive gas sensors are expected to play a significant role in assessing human health and evaluating food spoilage. However, the high operating temperature, insufficient limit of detection (LOD), and long response/recovery time restrict their broad application. Herein, 3D Bi₂MoO₆/2D Eg-C₃N₄ heterocomposites are developed for advanced NH₃ gas sensors with RT operational mode. Utilizing the synergetic engineering of micro-nanostructure, surface oxygen vacancies, and well-defined Type II n-n heterojunctions, BMOCN3 demonstrated superior NH₃ sensing properties at 23 °C, including the high response (S = 13.6 at 10 ppm), fast response/recovery speed (8/30 s), excellent selectivity, and low LOD (166 ppb). Based on the experimental, DFT, and MD studies, the improved sensing performance can be ascribed to accelerated charge transfer, superior redox capacity, and improved adsorption/desorption kinetics. Moreover, the practical application in rapid exhaled NH₃ biomarker detection of the as-fabricated gas sensor was preliminarily verified. This work highlights that the novel synergetic engineering can effectively modulate the electronic structure and charge transfer, offering a rational solution for room temperature chemiresistive gas sensors.