Selective passivation of 2D MoS₂ nanosheets surface defects by spontaneous growth of Au nanoparticles for full response-recovery NO₂ detection at room temperature

Full recovery at room temperature (RT) is quite challengng for two dimensional transition metal dichalcogenides chemiresistive gas sensors. The main reason for the incomplete recovery is the strong bonding of gas molecules onto sensing layer defects. Here, we show that the recovery rate of MoS₂ chemiresistive NO₂ sensors can be improved by selective passivation of MoS₂ nanosheets (NSs) defects with Au nanoparticles (NPs) via a simple spontaneous reduction method. MoS₂ NSs were produced by liquid shear exfoliation. Pristine and Au NPs functionalized MoS₂ were characterized using ς-potential, UV–Visible spectroscopy, TEM, SEM, AFM, EDS, XRD, XPS and Raman spectroscopy. The analyses confirm the presence of Au NPs on the edges of MoS₂ NSs at defective sites with NP sizes of 1–4 nm and 5–30 nm. Both pristine MoS₂ and Au-decorated MoS₂ NSs were employed to fabricate NO₂ chemiresistive devices. Au-decorated MoS₂ sensors showed an improved performance (for 1 ppm NO₂, Au-MoS₂ sensor exhibited a response of 5.6 % instead of 2.2 % for MoS₂ sensor), and gave faster response and better recovery time. Concurrently, the functionalization is independent of the adsorption and desorption of NO₂. Most importantly, the functionalization of MoS₂ NSs helps to full response-recovery within one hour, without either thermal or UV irradiation treatment.