Highly sensitive graphene ammonia sensor enhanced by concentrated nitric acid treatment

• After concentrated HNO 3 treatment, the response of graphene sensor increased by 3.02∼3.34 times for low concentration NH 3 test. • The response of the sensor is 40.9% and 3.08% under the ammonia concentration of 100 ppm and 0.5 ppm, respectively. • The theoretical detection limit of the graphene sensor towards NH 3 is 27 ppb. • HNO 3 treatment is a simple and low-cost but effective method to improve graphene sensor’s NH 3 -sensing performance. The ammonia (NH 3 )-sensing performance of graphene gas sensor treated with concentrated nitric acid (HNO 3 ) was systematically studied in this paper. The performance of graphene gas sensor has been significantly improved after simple immersion in concentrated HNO 3 (65 wt%) at a certain temperature (52 °C). In the test concentration range (20 ∼ 100 ppm), the NH 3 -response of the treated graphene gas sensor is increased by 3.02 ∼ 3.358 times, and the theoretical limit of detection (LOD) is 0.027 ppm (27 ppb). The treated sensor also shows good repeatability, stability and ultra-high selectivity. In the same concentration test, the response of NH 3 is dozens of times higher than others. XPS, FTIR and Raman spectra analysis revealed that the nondestructive introduction of oxygen-containing functional groups (NO 2 – ) onto graphene surface by concentrated HNO 3 treatment is considered to be the key to improve the NH 3 -sensing performance of graphene gas sensors. NO 2 – groups are supposed to provide abundant O atoms as effective adsorption sites to assist graphene to adsorb NH 3 , thus improving the NH 3 -response of graphene. A simple, effective and low-cost method is proposed to improve the NH 3 -sensing performance of graphene in this work, which is of great significance to promote the practical application of graphene gas sensor.