Functionalized MWCNTs@ZnO nanocomposites via spray printing for NO2 gas sensing

The accurate and timely detection of nitrogen dioxide gas (NO₂) is of utmost relevance in environmental monitoring and industrial applications. This study examines the process of functionalizing multi-walled carbon nanotubes (FMWCNTs) by treating them with a combination of sulfuric acid and nitric acid. The proposed treatment method improves the chemical reactivity of carbon nanotubes by the addition of hydroxyl and carboxylic functional groups. The FMWCNTs combined with zinc oxide (ZnO) are synthesized via a hydrothermal process, forming FMWCNTs@ZnO composites. The synthesized materials underwent various material characterizations. The composites are then printed over a silicon wafer substrate with lithographically patterned interdigitated electrodes in a square shape. 10 mg FMWCNTs in Zn(NO₃)₂·6H₂O (CNTZ2) showed the best gas-sensing capability. The sensor exhibits good gas response and fast response/recovery times at room temperature (RT) with values of 80% and 131/156 s at 100 ppm, respectively, as well as lifetime testing for 40 days. The spray printing method is simple and economical which can be utilized for coating on various substrates. Moreover, the proposed functionalization process allows good gas-sensing properties even at RT. This work paves the way towards new opportunities and fostering an optimistic outlook for the future of gas-sensing technology.