▎ 摘　　要

The ammonia (NH3)-sensing performance of graphene gas sensor treated with concentrated nitric acid (HNO3) was systematically studied in this paper. The performance of graphene gas sensor has been significantly improved after simple immersion in concentrated HNO3 (65 wt%) at a certain temperature (52 ?). In the test concentration range (20 -100 ppm), the NH3-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 NH3 is dozens of times higher than others. XPS, FTIR and Raman spectra analysis revealed that the nondestructive introduction of oxygen-containing functional groups (NO2-) onto graphene surface by concentrated HNO3 treatment is considered to be the key to improve the NH3-sensing performance of graphene gas sensors. NO2- groups are supposed to provide abundant O atoms as effective adsorption sites to assist graphene to adsorb NH3, thus improving the NH3-response of graphene. A simple, effective and low-cost method is proposed to improve the NH3-sensing performance of graphene in this work, which is of great significance to promote the practical application of graphene gas sensor.