Strategy and Future Prospects to Develop Room-Temperature-Recoverable NO2 Gas Sensor Based on Two-Dimensional Molybdenum Disulfide

Nitrogen dioxide(NO2),a hazardous gas with acidic nature,is continuously being liberated in the atmosphere due to human activity.The NO2 sensors based on traditional materials have limitations of high-temperature requirements,slow recovery,and performance degradation under harsh environmental conditions.These limitations of traditional materials are forcing the scientific community to discover future alternative NO2 sensitive materials.Molybdenum disulfide(MoS2)has emerged as a potential candidate for developing next-generation NO2 gas sensors.MoS2 has a large surface area for NO2 molecules adsorption with controllable morphologies,facile integration with other materials and compatibility with internet of things(IoT)devices.The aim of this review is to provide a detailed overview of the fabrication of MoS2 chemiresistance sensors in terms of devices(resistor and transistor),layer thickness,morphology control,defect tailoring,heterostructure,metal nanoparticle doping,and through light illumination.Moreover,the experimental and theoretical aspects used in designing MoS2-based NO2 sensors are also discussed extensively.Finally,the review concludes the challenges and future perspectives to further enhance the gas-sensing performance of MoS2.Understanding and addressing these issues are expected to yield the development of highly reliable and industry standard chemiresistance NO2 gas sensors for environmental monitoring.

Highly sensitive and rapidly responding room-temperature NO2 gas sensors based on W03 nanorods/sulfonated graphene nanocomposites

Metal oxide/graphene nanocomposites are emerging as promising materials for developing room-temperature gas sensors. However, the unsatisfactory performances owing to the relatively low sensitivity, slow response, and recovery kinetics limit their applications. Herein, a highly sensitive and rapidly responding room-temperature NO2 gas sensor based on WO3 nanorods/sulfonated reduced graphene oxide （S-rGO） was prepared via a simple and cost-effective hydrothermal method. The optimal sensor response of the WO3/S-rGO sensor toward 20 ppm NO2 is 149% in 6 s, which is 4.7 times higher and 100 times faster than that of the corresponding WO3/rGO sensors. In addition, the sensor exhibits excellent reproducibility, selectivity, and extremely fast recovery kinetics. The mechanism of the WOJS-rGO nanocomposite gas sensor is investigated in detail. In addition to the high transport capability of S-rGO as well as its excellent NO2 adsorption ability, the superior sensing performance of the S-rGO/WO3 sensor can be attributed to the favorable charge transfer occurring at the S-rGO/WO3 interfaces. We believe that the strategy of compositing a metal oxide with functionalized graphene provides a new insight for the future development of room-temoerature gas sensors.

Parametric Analysis of NO2 Gas Sensor Based on Carbon Nanotubes

Two types of carbon nanotubes [single walled nanotubes （SWCNTs） and multi walled carbon nanotubes （MWCNTs）] are deposited on porous silicon by the drop casting technique. Upon exposure to test gas mixing ratio 3% NO2, the sensitivity response results show that the SWCNTs＇ sensitivity reaches to 79.8%, where MWCNTs＇ is 59.6%. The study shows that sensitivity response of the films increases with an increase in the operating temperature up to 200℃ and 150℃ for MWCNTs and SWCNTs. The response and recovery time is about 19s and 54s at 200℃ for MWCNTs, respectively, and 20s and 56s at 150℃ for SWCNTs.

Cu_xO self-assembled mesoporous microspheres with effective surface oxygen vacancy and their room temperature NO_2 gas sensing performance

A series of CuxO self-assembled mesoporous microspheres （SMMs）, with different and controlled mor- phology （virus-like, urchin-like, spherical）, were synthesized by facile liquid phase approach. The morphology of the as- prepared CuxO SMMs was evolved from spherical to virus-like shape by controlling the ratio of DI water in solution. It can also realize the transformation from loose assembly to dense assembly by extending the reaction time. These CuxO SMMs exhibited good response to NO2 gas at room temperature, benefiting from their 3D self-assembly structure. Among these the resulting virus-like CuxO SNMMs-based sensor exhibits largely enhanced response to 1 ppm NO2 gas at room temperature. The enhanced response of the virus-like Cn2O SMMs-based sensor can be ascribed to the high surface area, hier- archical 3D nanostructures, micropores for effective gas diffusion, the heterojunctions formed between CuO and Cu2O, and the existence of abundant surface oxygen vacancies.