High performance langasite based SAW NO₂ gas sensor using 2D g-C₃N₄@TiO₂ hybrid nanocomposite

Nitrogen dioxide (NO₂) gas has emerged as a severe air pollutant that causes damages to the environment, human life and global ecosystems etc. However, the currently available NO₂ gas sensors suffers from insufficient selectivity, sensitivity and long response times that impeding their practical applicability for room temperature (RT) gas sensing. Herein, we report a high performance langasite (LGS) based surface acoustic wave (SAW) RT NO₂ gas sensor using 2-dimensional (2D) g-C₃N₄@TiO₂ nanoplates (NP) with {001} facets hybrid nanocomposite as a chemical interface. The g-C₃N₄@TiO₂ NP/LGS SAW device showed a significant negative frequency shift (∆f) of ~19.8 kHz which is 2.4 fold higher than that of the pristine TiO₂ NP/LGS SAW sensor toward 100 ppm of NO₂ at RT. In addition, the hybrid SAW device fascinatingly exhibited a fast response/recovery time with a low detection limit, high selectivity, and an effective long term stability toward NO₂ gas. It also exhibited an enhanced and robust negative frequency shifts under various relative humidity conditions ranging from 20% to 80% for 100 ppm of NO₂ gas. The high performance of the g-C₃N₄ @TiO₂ NP/LGS SAW gas sensor can be attributed to the enhanced mass loading effect which was assisted by the large surface area, oxygen vacancies, OH and amine functional groups of the n-n hybrid heterojunction of g-C₃N₄@TiO₂ NP that provide abundant active sites for the adsorption and diffusion of NO₂ gas molecules. These results emphasize the significance of the integration of 2D materials with metal oxides for SAW based RT gas sensing technology holds great promise in environmental protection.