A selective global elemental mercury passive sampler based on TiO2NPs photocatalytically decorated with AuNPs

Several international initiatives and programs are making a great effort in identifying and quantifying Hg pollution across the globe aimed at reducing risk of exposure to this neurotoxic pollutant. Passive sampling systems sound to be a low cost strategy to quantify Hg levels in air over different environmental locations, remote as the Polar Regions, rural and urban locations. Passive samplers have to be compact, portable, unobtrusive, and inexpensive. They are able to give information about the average pollution levels over time periods of few hours to weeks/months. For this reason novel passive samplers (PASs) of mercury based on nanostructured materials (nanoparticles of titanium oxide properly functionalized with gold nanoparticles), have been designed and developed. These structures were expected to be very promising candidates for mercury samplers due to both the strong affinity of gold with Hg and the wide adsorbing surface. They consisted of an adsorbent membrane made of titania nanoparticles (<=25nm diameter) that after a suspension in an aqueous solution of PVP/HAuCl4 and UV-irradiation changed the color from white to blue-violet, resulting from a fine decoration with gold nanoparticles (6-20 nm). Such a functionalization occurred for the photocatalytic properties of TiO2 (anatase). The nanostructured suspension was deposited on a thin quartz slices (500 ?m thick, 20 mm length), dried to 550°C and then incorporated into an axial sampler in order to be exposed firstly to air polluted with well-known amounts of Hg0 for calibration and characterization and secondly to the atmosphere. The adsorbed mercury was thermally desorbed (550°C) and then measured by a mercury vapor analyzer (Tekran2537A). UV-Vis spectra showed a blue shift of the membrane when exposed to Hg0 mercury vapors. Such a sampling systems reported an efficiency of adsorption equal to ~ 95%. Temperature and relative humidity only mildly affected the membrane performances. The morphological characteristics of sample were studied by HRTEM (High-Resolution - Transmission Electron Microscopy), AFM and optical microscopy.