High performance langasite based SAW NO 2 gas sensor using 2D g-C 3 N 4 @TiO 2 hybrid nanocomposite.

Nitrogen dioxide (NO ₂ ) gas has emerged as a severe air pollutant that causes damages to the environment, human life and global ecosystems etc. However, the currently available NO ₂ 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 NO ₂ gas sensor using 2-dimensional (2D) g-C ₃ N ₄ @TiO ₂ nanoplates (NP) with {001} facets hybrid nanocomposite as a chemical interface. The g-C ₃ N ₄ @TiO ₂ 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 TiO ₂ NP/LGS SAW sensor toward 100 ppm of NO ₂ 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 NO ₂ 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 NO ₂ gas. The high performance of the g-C ₃ N ₄ @TiO ₂ 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-C ₃ N ₄ @TiO ₂ NP that provide abundant active sites for the adsorption and diffusion of NO ₂ 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.
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