Boron doped g-C3N4 quantum dots based highly sensitive surface acoustic wave NO2 sensor with faster gas kinetics under UV light illumination

Abstract

The elegant two-dimensional (2D) graphitic carbon nitride (GCN) holds great promise in the detection of hazardous toxic gases especially NO2, for environmental protection and public health safety. However, the poor sensitivity and low surface area of bulk 2D GCN restrains its practical applicability of room temperature (RT) NO2 sensing. Herein, we present the fabrication of boron-doped GCN quantum dots (B@GCN QD) coated langasite (LGS) based surface acoustic wave (SAW) sensor for the RT NO2 gas detection, and applied UV activation energy (365 nm) as an effective strategy to further enhance the NO2 sensing. Fascinatingly, under UV light, the B@GCN QD/LGS SAW sensor showed an enhanced gas sensing performance to the NO2 gas (500 ppb - 50 ppm) with high sensitivity (Δf=35.97 kHz/50 ppm), good selectivity, ultra-low detection limit (DL∼7.9 ppb), fast response/recovery times (35 s/43 s), excellent long-term stability as compared to dark condition. This could be attributed to the generation of abundant photoinduced charge carriers under UV activation, which leads to the significant enhancement in conductivity and enlarged mass loading effect, also, the device showed robust sensitivity responses to NO2 gas at various temperatures (RT-200 °C) and relative humidity (20–80%) conditions. Moreover, the effective doping of B to the GCN QD exhibited a typical p-type behavior which is good in agreement with density functional theory predictions that can induce structural defects, vacancies, and amine functional groups leading to a high specific surface area, which can remarkably enhance the sensitivity and selectivity of NO2 gas. This work may provide insights into the design and development of 2D GCN nanostructure-based SAW RT gas sensors for environmental monitoring.