A TITANIA NANOFIBROUS SMART SCAFFOLD FOR ELEMENTAL MERCURY VAPOUR SENSORS

Electrospun titania nanofibres combine large surface area with intrinsic semiconducting properties, thus providing great potential to such material for various applications. Anatase is the most photoactive phase of titania, and is then eligible for sensor, optoelectronic and catalytic devices, playing also a crucial role in disinfection applications and environmental remediation processes. As n-type semiconductor, titania nanofibres have been widely investigated and used for detecting several atmospheric pollutants at both high and room temperature, after the addition of organic and inorganic dopants [1]. Recently, Au/TiO2 nanocomposite layers have been investigated by the authors as potential conductive sensors to detect elemental mercury at room temperature in the atmosphere [2]. Because of their high sensitivity combined with low maintenance, easy of handling and low fabrication costs, such sensors resulted as promising candidates to detect mercury in proximity of polluted areas. In that study, the photocatalytic properties of titania allowed gold nanoparticles to selectively grow on the nanofibrous scaffold from HAuCl4 (tetrachloroauric acid) as a precursor, under UV-light irradiation. The results obtained in that study, however, were far enough from commercial analytical devices, which detect traces of mercury (< 0.1 ng/m3) in a few minutes (~5min). A great exposure time was necessary, indeed, to trap enough mercury in order to get observable electrical signals. In the present study, the amazing properties of titania were further employed in distinct strategies to improve the sensing features of the material and the resulting sensors. In the former strategy, rougher nanofibrous layers of titania were created, in order to greatly increase the number of gold nucleation sites. This finding was achieved by adding an aliquot of a non-ionic surfactant (Triton X) in the freshly prepared electrospun solution. SEM, AFM, TEM and HR-TEM analyses were carried out to characterise the morphology and the nano-sized structures of such composite nanofibres. It is known that the sensor response depends on the number of mercury atoms adsorbed on its sensitive surface. The increase in the global number of binding sites on the electrospun fabric was, then, expected to be successful in improving the sensor performances. In the latter strategy, UV-light (365 nm) was applied on the nanocomposite material in order to enable titania to cooperate with gold in mercury entrapment [3] and then enlarge the properties of the sensing layer. Optical and electrical features of both rough and UV-treated Au/TiO2 layers are here reported and discussed.