Pi-Guey Su

Fabrication and NO2 gas-sensing properties of reduced graphene oxide/WO3 nanocomposite films

One-pot polyol process was combined with the metal organic decomposition (MOD) method to fabricate a room-temperature NO2 gas sensor based on tungsten oxide and reduced graphene oxide (RGO/WO3) nanocomposite films. Fourier Transform infrared spectrometer (FTIR), X-ray diffractometry (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to analyze the microstructure and morphology of the fabricated films. The electrical and NO2 gas-sensing properties of WO3 to which various amounts of RGO were added were measured in detail as a function of concentration of NO2 gas at room temperature, to elucidate the contribution of RGO to the NO2 gas-sensing capacity. The NO2 gas-sensing mechanism of the RGO/WO3 nanocomposite films were explained by considering their composition and microstructures. The sensor that was based on a nanocomposite film of RGO/WO3 exhibited a strong response to low concentrations of NO2 gas at room temperature, satisfactory linearity and favorable long-term stability.

Flexible NH3 sensors fabricated by in situ self-assembly of polypyrrole

Novel flexible NH(3) gas sensors were formed by the in situ self-assembly of polypyrrole (PPy) on plastic substrates. A negatively charged substrate was prepared by the formation of an organic monolayer (3-mercapto-1-propanesulfonic acid sodium salt-MPS) on a polyester (PET) substrate using a pair of comb-like Au electrodes. Two-cycle poly(4-styrenesulfonic acid) sodium salt/poly(allylamine hydrochloride) (PSS/PAH) bilayers (precursor layer) were then layer-by-layer (LBL) deposited on an MPS-modified substrate. Finally, a monolayer of PPy self-assembled in situ and PPy multilayer thin films self-assembled LBL in situ on a (PSS/PAH)(2)/MPS/Au/Cr/PET substrate. The thin films were analyzed by atomic force microscopy (AFM). The effects of the precursor layer (PSS), the deposition time of the monolayer of PPy and the number of PPy multilayers on the gas sensing properties (response) and the flexibility of the sensors were investigated to optimize the fabrication of the film. Additionally, other sensing properties such as sensing linearity, reproducibility, response and recovery times, as well as cross-sensitivity effects were studied. The flexible NH(3) gas sensor exhibited a strong response that was comparable to or even greater than that of sensors that were fabricated on rigid substrate at room temperature.

Novel low humidity sensor made of TiO2 nanowires/poly(2-acrylamido-2-methylpropane sulfonate) composite material film combined with quartz crystal microbalance

A novel ceramic nanowires of TiO(2) and poly(2-acrylamido-2-methylpropane sulfonate) (TiO(2) NWs/PAMPS) composite material films coated on quartz crystal microbalance (QCM) was prepared as a low humidity sensor. The 50wt.% of TiO(2) NWs/PAMPS composite material films showed excellent sensitivity (2.63-DeltaHz/Deltappm(v)) at 31.5ppm(v)), linearity (R(2)=0.9959) and acceptable response time (64s at 34.6ppm(v)). The low humidity sensing mechanism was discussed in terms of surface texture and nanostructured morphology of the composite materials. Moreover, the adsorption dynamic analysis, molecular mechanics calculation (association constant), was used to elucidate the effect of adding 50wt.% TiO(2) NWs into PAMPS in the increased sensitivity of low humidity sensing.

In situ prepared polypyrrole for low humidity QCM sensor and related theoretical calculation

In situ preparation of polypyrrole (Ppy) by photo-polymerization coated on a quartz crystal microbalance (QCM) as a low humidity sensor was reported. Different concentrations of Ppy films say 0wt.% (as blank), 0.1, 1, and 10wt.% were investigated to measure humidity concentrations between 14.7 and 5412.5ppm(v). The adsorption/desorption behavior was also examined at humidity concentration 510.2ppm(v). The sensitivities of 0, 0.1 and 1wt.% Ppy films at 51.5ppm(v) were 0.143, 0.219 and 0.427, respectively. For 1wt.% Ppy, the highest sensitivity was obtained. The slope and correlation coefficients (R(2)) for 1wt.% Ppy at the ranges of 14.7-898.6ppm(v) were 0.0646 and 0.9909, respectively. A series of molecular simulations have been carried out to calculate bond energy for the water molecule interaction with Ppy, which was found to be approximately 3kcal/mol indicating the existence of hydrogen bonding during the sorption process. Based on Langmuir isotherm adsorption assumption, for 0.1 and 1wt.% Ppy films, the association constants were 2606.30 and 5792.98, respectively. This larger association constant for 1wt.% Ppy film explains higher sensitivity.

P1.4.2 Effect of polycations used in multi-walled carbon nanotubes thin films prepared by layerby-layer technique on flexibility and gas sensing properties

In the current work, layer-by-layer self-assembled surface-oxidized multi-walled nanotubes (MWCNTs) and cationic polyelectrolyte (poly(allylamine hydrochloride)) (PAH) or poly(diallyldimethylammonium chloride) (PDDA) were synthesized on a polyester (PET) substrate for sensing NH3 gas. The electrical and gas sensing properties (response) and flexibility characteristics of the fabricated sensors depended strongly on the amounts of adsorbed MWCNTs and polycations type. The structural configuration of MWCNTs network in MWCNTs/PDDA multilayered thin film was more compact than that of MWCNTs/PAH. The conductivity of the MWCNTs/PDDA multilayered thin film was much higher than that of MWCNTs/PAH. The MWCNTs/PAH multilayered thin film showed a higher response and flexibility than that of MWCNTs/PDDA.