(CdSe)ZnS QDs DECORATION OF NANOFIBROUS TITANIA TO REVEAL TOXIC GAS TRACES IN THE ATMOSPHERE

Electrospinning technology has been proven to be an intriguing strategy to create highly performing nanostructured sensors [1] able to reveal toxic gases and VOCs in the environment. Therefore various nanocomposite fibrous layers have been synthesized and investigated for their applications as active materials for gas sensors [2]. The design of nanocomposite layers for sensor applications takes in consideration several factors, such as the arrangement of both materials within the fibres, their interfacial characteristics, electrical and optical performances, thermal and mechanical stability, etc., all of which depending significantly on each materials features and deposition process parameters. In the present study, titania nanofibrous layers were decorated with fluorescent nanoparticles (QDs) and then investigated as potential chemical sensors, at solid state, for detecting toxic gases. TiO2 sounds a suitable scaffold since it is a photoactive semiconductor material easily tuning by incorporating dye molecules and semiconductor nanocrystals [3,4]. Therefore first, fluorescent (CdSe)ZnS core-shell quantum dots were synthesized, according to literature, by decomposing organometallic precursors at high temperature in a suitable coordinating solvent [5] and then functionalized with a stabilizing organic shell, trioctylphosphine oxide (TOPO). Second, the resulting QDs (~6nm) were deposited on electrospun titania nanofibres (anatase) both by dipping (physical interaction) and by in situ chemical functionalization of the fibres with bi-functional linkers (containing -COOH and -SH), capable of immobilizing the nanoparticles. Their different arrangements over the fibres were characterized by AFM (Atomic Force Microscopy) and HR-TEM (High-Resolution Transmission Electron Microscopy), and their optical performances were investigated by spectrophotometry and spectrofluorometry as well as fluorescence microscopy. Since fibres were grown on the transducers (interdigitated electrodes of Pt/Ti) and the following functionalization occurred in situ, the resulting fibres were simultaneously investigated as potential optical sensors due to the quenching of their fluorescence after gas interaction and as photoconductive sensors at room temperature due to the changes of their photoconductivity (UV-LED 365 nm) under known concentrations of a toxic gas (NH3).