Effective Tuning of Silver Decorated Graphene Sensing Properties by Adjusting the Ag NPs Coverage Density

Noble-metal decorated graphene nanohybrids are expected to be a new type of sensing material with high sensitivity and excellent selectivity, since the metal nanoparticles can act as a mediator in the interaction between analytes and graphene, determining peculiar mechanisms of charge transfer according to chemical or electronic sensitization. In particular, the decoration by silver nanoparticles (Ag NPs) can improve the sensing behavior of carbon nanostructures towards ammonia. In this work, graphene/Ag nanoparticles (GR/AgNPs) hybrids were prepared by a one-step microwave-assisted reduction method by irradiating a water/isopropyl alcohol solution of pristine graphene and AgNO₃. Two different concentrations of silver precursor were tested obtaining graphene hybrids with different surface coverage. The effect of the metal decoration was investigated by probing the sensing properties of the chemiresistive layers towards NO₂ and NH₃ at concentrations, respectively, of sub-ppm and hundreds of ppm in air, which are considered as standard marker levels of environmental pollution. The results show that the high specificity of bare graphene towards NO₂ in ppb levels was reversed towards NH₃ by addition of Ag NPs. Noteworthy, a low areal density of Ag NPs allowed the material to gain sensitivity towards ammonia while still retaining sensitivity to NO₂. At higher surface coverage an almost complete reversal of the sensitivity occurred and the silver decorated material appeared highly sensitive towards ammonia.