Galvanic replacement of colloidal monolayer crystal on a QCM device for selective detection of mercury vapor

Abstract

Bimetallic nanostructures formed through galvanic replacement (GR) reaction have extraordinary activity in various applications such as catalysis, optics, electronics and bio/chemical sensing, just to name a few. However, the homogenous decoration of metal nanoparticles on less noble metal thin-film substrates to produce long range ordered surfaces for sensing applications using this simple, one step reaction has proved to be a challenge. Here, we demonstrate the formation of polystyrene-based (PS-based) monodispersed nanosphere monolayer (PS-MNM), homogeneously decorated with bi-metallic Pd–Au nanostructures through GR reaction. Furthermore, the size of the Au nanoparticles decorated on the Pd-MNM colloids was controlled for gas sensing applications during GR reaction. Upon transferring the developed materials onto a sensor transducer, namely the quartz crystal microbalance (QCM), it was found that the 1mM Au GR solution produced the best performing sensitive layer for elemental mercury (Hg0) vapor sensing application. The sensor had more than 26 times higher response magnitude at 30°C as well as enhanced sensitivity and selectivity over the control Pd-MNM counterpart at 75°C. The homogeneous decoration concept developed here can be transferred to other bimetallic systems.