UV illumination-enhanced ultrasensitive ammonia gas sensor based on (001)TiO2/MXene heterostructure for food spoilage detection

Ammonia has been used as an important marker to indicate the extent of food spoilage. However, current gas sensors for ammonia suffer from either insufficient sensitivity and selectivity or unsatisfactory levels of automation, impeding their practical application for on-site and real-time monitoring of food quality. To overcome these limitations, we propose here the design of a sensing material by in-situ growing (001)TiO2 onto a two-dimensional transition-metal carbide (Ti3C2Tx, MXene). In this design, TiO2 with a highly active (001) crystal plane provides efficient photogeneration under UV irradiation, while Ti3C2Tx can store holes through Schottky junction formed at the interface with TiO2, which greatly promotes the separation of electron-hole pairs, thereby enhancing ammonia sensing performance. By further introducing UV light for electron excitation, the (001)TiO2/Ti3C2Tx based sensor shows 34 times higher sensitivity for ammonia (30 ppm) than that of Ti3C2Tx. The density functional theory further revealed that the (001) plane of TiO2 and Ti3C2Tx composite configuration exhibited the highest adsorption affinity towards ammonia. Finally, an integrated circuit alarm system including near-field communication and a micro-controller system was designed to detect the decay process of fresh pork, fish, and shrimp. We believe such a sensing technology holds great promise in food quality monitoring.