AuNPs/TiO2NF: a promising combination for low cost and effective sensor devices for GEM monitoring in the framework of GMOS

In the framework of on going research projects and programmes (i.e., GMOS, UNEP F&T) aiming to develop advanced sensors for major atmospheric pollutants, and having as overarching goal to assure a full operational capability of global observing systems for persistent pollutants such as mercury a novel sensors with promising sensing features for environmental applications have been designed and tested. The aim of this paper is to present a novel sensor based on nanostructured hybrid materials capable of entrapping and detecting Gaseous Elemental Mercury (GEM) at trace levels once the photocatalysis is activated with UV light irradiation. This nanostructured hybrid material is obtained by combining composite nanofibrous electrospun scaffolds of titania and gold nanoparticles. The size and the shape of these nanostructures have been demonstrated to be key parameters in defining the properties of the resulting sensors, because of the strict relationship between the surface and the bulk of the sensing material which is extremely reduced in size. The increase in the number of binding sites has been confirmed to be a successful strategy to ensure sensitivity at trace level. SEM, AFM, TEM and HR-TEM analyses have been performed to characterise the morphology and the nano-sized structure of these composite materials. Different electrical and sensing features of the resulting chemosensors have been achieved by tuning fibres roughness and gold nanoparticle size. A suitable measuring chamber for mercury detection have been designed and developed in order to improve the sensing feature of the sensor. Thus few minutes of air sampling were sufficient to detect the concentration of mercury in the air without using traps (LOD ? 1 ppb). Longer measurements allowed the sensor to detect lower concentrations of GEM (tens of ppt). A short thermal treatment (450°C, 3min) was necessary to completely desorb mercury from AuNPs. The resulting chemosensors are expected to be very stable over time, robust and resistant to the interference that may be caused by common solvents and by VOCs commonly present in ambient air.