Highly sensitive g-C3N4 nanosheets as a potential candidate for the effective detection of NO2 gas via langasite-based surface acoustic wave gas sensor

Abstract

In view of the fact, the poor stability and inadequate chemical properties of conductive polymers inhibit their use in gas sensor applications. Moreover, the elegant two-dimensional (2D) polymeric graphitic carbon nitride (g-C3N4) has attracted great attention for room-temperature (RT) gas sensing applications due to its intrinsic porous structure and lone pair electrons on nitrogen atoms. Herein, we report surface acoustic wave (SAW) NO2 gas sensors using 2D g-C3N4 nanosheets deposited on langasite (LGS) SAW device. Furthermore, the thickness effect on gas sensing performances was manifested and it was noticed that 220 nm thickness of g-C3N4-coated LGS SAW sensors showed better sensing performances. The g-C3N4/LGS SAW sensor showed a significant negative differential frequency shift (Delta f) of similar to 3.1 kHz at room temperature (RT similar to 27 degrees C) for 100 ppm of NO2 gas with a quick response/recovery time (42/22 s). Furthermore, our experimental results indicated that the effect of temperature remarkably influences NO2 sensing responses, which escalated from similar to 3.1 kHz to similar to 23.3 kHz in the temperature range of 27 degrees C to 200 degrees C for 100 ppm of NO2. Moreover, the device showed immense sensitivity towards NO2 (100 ppm) under various relative humidity (RH) conditions (20-80%) at RT. Besides, the g-C3N4/LGS SAW sensor showed low detection limit (similar to 158 ppb), excellent long-term stability, high sensitivity and selectivity to NO2 gas, which could be ascribed to the enhancement in mass loading effect resulting from the absorption of NO2 gas molecules. Finally, using resistive gas sensor, we deliberately discuss the underlying gas sensing mechanism associated with the 2D g-C3N4 nanosheet-deposited LGS SAW device.