Revealing the Role of Surface Co-modification in Boosting the Gas Sensing Performance of Graphene Using Experimental and Theoretical Evidences

Silver nanoparticles (NPs) and 6-Mercaptohexanoic acid (MHA) co-modified reduced graphene oxide (RGO-Ag-MHA) is rationally designed for ultrasensitive and highly reversible NO₂ sensing at room temperature (RT). Due to the enhanced adsorption of NO₂ on the abundant active sites provided by Ag NPs and MHA, both the NO₂ adsorption and charge transfer processes are promoted. Consequently, the RGO-Ag-MHA exhibits orders of magnitude higher sensitivity and much lower limit of detection (LOD) toward NO₂ than the unmodified RGO. These experimental observations are supported by theoretical simulations, as density functional theory simulation reveals that the binding energy of NO₂ on Ag NPs and MHA is 2.03 and 10.9 times higher than that on RGO, respectively. Furthermore, molecular dynamics simulation indicates the adsorbed NO₂ density on RGO-Ag-MHA is twofold higher than that on RGO. The RGO-Ag-MHA NO₂ sensor displays very competitive performance, including ultrahigh sensitivity (53 ppm^-1), exceptional low theoretical LOD (3.5 ppb), excellent selectivity, linearity and repeatability. This work not only unveils the role of surface co-modification in dictating the chemical sensing performance of graphene, but also provides a feasible route to fabricate high-performance, RT NO₂ sensors for various applications.