MoS ₂ –ZnO p–n heterojunctions are employed to sensitively detect trace NO ₂ gas under UV illumination at room temperature.

In recent decades, chemiresistive gas sensors (CGS) have been widely studied due to their unique advantages of expedient miniaturization, simple fabrication, easy operation, and low cost. As one ubiquitous interference factor, humidity dramatically affects the performance of CGS, which has been neglected for a long time. With the rapid development of technologies based on gas sensors, including the internet of things (IoT), healthcare, environment monitoring, and food quality assessing, the humidity interference on gas sensors has been attracting increasing attention. Inspiringly, various anti-humidity strategies have been proposed to alleviate the humidity interference in this field; however, comprehensive summaries of these strategies are rarely reported. Therefore, this review aims to summarize the latest research advances on humidity-independent CGS. First, we discussed the humidity interference mechanism on gas sensors. Then, the anti-humidity strategies mainly including surface engineering, physical isolation, working parameters modulation, humidity compensation, and developing novel gas-sensing materials were successively introduced in detail. Finally, challenges and perspectives of improving the humidity tolerance of gas sensors were proposed for future research.

Nitrogen dioxide (NO₂) plays a key role in environmental protection and human health. Recently, molybdenum disulfide (MoS₂) representative of novel 2D materials has been utilized to detect NO₂ gas, still hindered by the weak response, high operation temperature, as well as poor recovery characteristics. Herein, we report a UV light-assisted, room-temperature, recoverable, sensitive and selective NO₂ gas sensing based on few-layer MoS₂ nanosheet-Au nanoparticle composites serving as the sensing layer. In the dark condition, the as-prepared MoS₂-Au sensor showed a response of 10% toward 2.5 ppm NO₂ more than two times larger than MoS₂ one, arising from more reaction sites (spillover effect and produced interfaces) and smaller baseline resistance after Au incorporation. Undesirably, all sensors exhibited an incomplete recovery. When MoS₂-Au sensors were exposed to NO₂ gas under UV illumination, better performance in terms of three-time enhanced response, full recovery and favorable repeatability was achieved in comparison with that in the dark case. Two aspects were responsible for these phenomena. On one hand, additional photoinduced charge carriers ensured sufficient gas-solid interactions between sensing layer and target molecules, thereby resulting in a larger response. The other aspect lay in effective separation of these charge carriers at MoS₂/Au interfaces, contributing to recoverable and repeatable reactions. MoS₂-Au composites were adopted for NO₂ detection under UV illumination and exhibited a promising capacity of UV photodetector as well as an inspiring room-temperature gas detection, which provided an alternative strategy to design a single optoelectronic device with multi-functions.