Decoration of Ag nanoparticles on reduced graphene oxide and their application to gas sensors

Abstract

We fabricated functionalized RGO that demonstrates excellent sensitivity to H2S gas. The functionalization process used GO suspensions mixed with AgNO3, NaOH, and DI water. X-ray diffraction (XRD) and transmission electron microscopy indicated that the functionalizing structures were composed of cubic Ag and silver oxide (AgxOy) phases. Nanoparticles and nanorods with a cubic Ag phase were attached to the surface of the RGO. Raman spectra revealed that the structural disorder of the functionalized RGO was higher than that of pristine GO. The decrease of resistance by the introduction of H2S gas indicated that the functionalized RGO was an n-type sensor. Accordingly, we suggested that the n-type AgxOy, whose presence was confirmed by XRD, should be a main current path for the sensor. A H2S gas sensing test revealed that the sensor response at 50 ppm was about 1.65. With respect to H2S sensing mechanisms, we propose that the following four reasons could explain the significant enhanced sensitivity by the functionalization: (i) reduction of the conduction volume by the conduction through the AgxOy structure rather than RGO, (ii) generation of silver sulfide structures, (iii) generation of an n-AgxOy/p-RGO heterointerface, and (iv) larger surface area of Ag/AgxOy structures. The Ag catalyst is not only the source of the AgxOy, but also provides the spillover effect.