Improvement of H2S sensing properties of SnO2-based thick film gas sensors promoted with MoO3 and NiO.

The effects of the SnO2 pore size and metal oxide promoters on the sensing properties of SnO2-based thick film gas sensors were investigated to improve the detection of very low H2S concentrations (<1 ppm). SnO2 sensors and SnO2-based thick-film gas sensors promoted with NiO, ZnO, MoO3, CuO or Fe2O3 were prepared, and their sensing properties were examined in a flow system. The SnO2 materials were prepared by calcining SnO2 at 600, 800, 1,000 and 1,200 °C to give materials identified as SnO2(600), SnO2(800), SnO2(1000), and SnO2(1200), respectively. The Sn(12)Mo5Ni3 sensor, which was prepared by physically mixing 5 wt% MoO3 (Mo5), 3 wt% NiO (Ni3) and SnO2(1200) with a large pore size of 312 nm, exhibited a high sensor response of approximately 75% for the detection of 1 ppm H2S at 350 °C with excellent recovery properties. Unlike the SnO2 sensors, its response was maintained during multiple cycles without deactivation. This was attributed to the promoter effect of MoO3. In particular, the Sn(12)Mo5Ni3 sensor developed in this study showed twice the response of the Sn(6)Mo5Ni3 sensor, which was prepared by SnO2(600) with the smaller pore size than SnO2(1200). The excellent sensor response and recovery properties of Sn(12)Mo5Ni3 are believed to be due to the combined promoter effects of MoO3 and NiO and the diffusion effect of H2S as a result of the large pore size of SnO2.

Effects of textural properties on the response of a SnO2-based gas sensor for the detection of chemical warfare agents.

The sensing behavior of SnO(2)-based thick film gas sensors in a flow system in the presence of a very low concentration (ppb level) of chemical agent simulants such as acetonitrile, dipropylene glycol methyl ether (DPGME), dimethyl methylphosphonate (DMMP), and dichloromethane (DCM) was investigated. Commercial SnO(2) [SnO(2)(C)] and nano-SnO(2) prepared by the precipitation method [SnO(2)(P)] were used to prepare the SnO(2) sensor in this study. In the case of DCM and acetonitrile, the SnO(2)(P) sensor showed higher sensor response as compared with the SnO(2)(C) sensors. In the case of DMMP and DPGME, however, the SnO(2)(C) sensor showed higher responses than those of the SnO(2)(P) sensors. In particular, the response of the SnO(2)(P) sensor increased as the calcination temperature increased from 400 °C to 800 °C. These results can be explained by the fact that the response of the SnO(2)-based gas sensor depends on the textural properties of tin oxide and the molecular size of the chemical agent simulant in the detection of the simulant gases (0.1-0.5 ppm).

Electrospun carbon nanotubes-gold nanoparticles embedded nanowebs: prosperous multi-functional nanomaterials.

Electrospinning was employed to prepare new multi-functional nanowebs. Cyclodextrin based inclusion complex (CD-IC) was used to disperse multiwalled carbon nanotubes (MWNT) within electrospun polyvinylidene fluoride nanofibrous membranes (PVdF-NFM). Subsequently, MWNT(CD-IC)/PVdF-NFM was loaded with gold (Au) particles. The morphology, structure and thermal properties of Au/MWNT(CD-IC)/PVdF-NFM were investigated by transmission electron microscopy, field emission scanning electron microscopy, FT-IR spectroscopy, x-ray diffraction spectroscopy and differential scanning calorimetry. The new Au/MWNT(CD-IC)/PVdF-NFM is electroactive and shows excellent electrocatalytic activity towards oxidation of ascorbic acid.

Effects of Thin-Film Thickness on Sensing Properties of SnO2-Based Gas Sensors for the Detection of H2S Gas at ppm Levels.

SnO2 thin-film gas sensors were easily created using the ion sputtering technique. The as-deposited SnO2 thin films consist of a tetragonal SnO2 phase and densely packed nanosized grains with diameters of approximately 20-80 nm, which are separated by microcracks. The as-deposited SnO2 thin film is well crystallized, with a dense columnar nanostructure grown directly onto the alumina material and the Pt electrodes. The grain size and thickness of SnO2 thin films are easily controlled by varying the sputtering time of the ion coater. The responses of the SnO2 thin-film sensors decrease as the SnO2 film thickness is increased, indicating that a negative association exists between the sensor response and the SnO2 film thickness due to gas diffusion from the surface. The SnO2 thin-film sensor, which was created by ion sputtering for 10 min, shows an excellent sensor response (Ra/Rg where Ra is the electric resistance under air and Rg is the electric resistance under the test gas) for detecting 1 ppm H2S at 350°C.

Fabrication and properties of poly(vinylidenefluoride)/PbS/Au heterogeneous nanostructures.

We report on the fabrication of polyvinylidenefluoride (PVdF) PVdF/PbS and PVdF/PbS/Au heterogeneous nanostructures by the processes, electrospinning and chemical treatment. Initially electrospinning a solution consisting of PVdF and lead acetate was used to form PVdF nanofibers loaded with Pb ions. Exposure of Pb ions loaded PVdF fibers to H2S resulted in PVdF/PbS nanostructures. The deposition of gold nanoparticles onto PVdF/PbS nanostructures results in PVdF/PbS/Au heterogeneous structure. The existence of PbS particles with an average diameter of 11 nm is evident from field emission transmission electron microscopy (FETEM) image of PVdF/PbS. The results from X-ray diffraction of PVdF/PbS also predict the size of PbS particles as in accordance with FETEM. A blue shift in the optical transition of PbS is noticed in the UV-visible spectrum of PVdF/PbS as a result of quantum confinement effect. The band gap of PbS is influenced by the presence of Au nanoparticles over the PbS particles. An equal atomic weight % of Au and PbS is found in the PVdF/PbS/Au nanostructure as inferred from energy dispersive X-ray spectroscopy (EDX). Photoluminescence (PL) spectra of PVdF/PbS and PVdF/PbS/Au are compared. Emission peaks are noticed at 400 nm and 480 nm for PVdF/PbS and PVdF/PbS/Au nanostructures respectively for an excitation wavelength of 254 nm. The presence of Au nanoclusters in PVdF/PbS/Au diminishes the intensity of photo emission of PbS.

Spectrofluorimetric study of the interaction between europium(III) and moxifloxacin in micellar solution and its analytical application.

A sensitive spectrofluorimetric method has been developed for the determination of moxifloxacin (MOX) using europium(III)-MOX complex as a fluorescence probe in the presence of an anionic surfactant, sodium dodecyl benzene sulfonate (SDBS). The fluorescence (FL) intensity of Eu(3+) was enhanced by complexation with MOX at 614 nm after excitation at 373 nm. The FL intensity of the Eu(3+)-MOX complex was significantly intensified in the presence of SDBS. Under the optimum conditions, it was found that the enhanced FL intensity of the system showed a good linear relationship with the concentration of MOX over the range of 1.8 × 10(-11)-7.3 × 10(-9) g mL(-1) with a correlation coefficient of 0.9998. The limit of detection of MOX was found to be 2.8 × 10(-12) g mL(-1) with relative standard deviation (RSD) of 1.25% for 5 replicate determination of 1.5 × 10(-8) g mL(-1) MOX. The proposed method is simple, offers higher sensitivity with wide linear range and can be successfully applied to determine MOX in pharmaceutical and biological samples with good reproducibility. The luminescence mechanism is also discussed in detail with ultraviolet absorption spectra.

Development of a stable cholesterol biosensor based on multi-walled carbon nanotubes-gold nanoparticles composite covered with a layer of chitosan-room-temperature ionic liquid network.

A novel amperometric biosensor was fabricated based on the immobilization of cholesterol oxidase (ChOx) into a cross-linked matrix of chitosan (Chi)-room-temperature ionic liquid (IL) (1-butyl-3-methylimidazolium tetrafluoroborate). Initially, the surface of bare electrode (indium tin oxide coated glass) was modified with the electrodeposition of Au particles onto thiol (-SH) functionalized multi-walled carbon nanotubes (MWNTs). The biosensor electrode is designated as MWNT(SH)-Au/Chi-IL/ChOx. Scanning electron microscopy image of MWNT(SH)-Au/Chi-IL/ChOx reveals that Chi-IL exists as the interconnected wires covering the Au particles on the surface of MWNT(SH)-Au. Cyclic voltammetry and chronoamperometry were used for the electrochemical determination of cholesterol at the biosensor electrode, MWNT(SH)-Au/Chi-IL/ChOx. The presence of Au particles in the matrix of CNTs provides an environment for the enhanced electrocatalytic activities. The MWNT(SH)-Au/Chi-IL/ChOx biosensor exhibited a linear response to cholesterol in the concentration range of 0.5-5mM with a correlation coefficient of 0.998, good sensitivity (200 microAM(-1)), a low response time ( approximately 7s), repeatability (R.S.D value of 1.9%) and long term stability (20 days with a decrease of 5% response). The synergistic influence of MWNT(SH), Au particles, Chi and IL contributes to the excellent performance for the biosensor.

An electrochemical glucose biosensor exploiting a polyaniline grafted multiwalled carbon nanotube/perfluorosulfonate ionomer-silica nanocomposite.

A glucose biosensor was fabricated with loading of glucose oxidase (GOx) into a new organic-inorganic hybrid nanocomposite. The preparation involves formation of silica network into a Nafion (perfluorosulfonate ionomer) and subsequent loading of polyaniline grafted multiwalled carbon nanotubes (MWNT-g-PANI) onto Nafion-silica nanocomposite. Field emission scanning electron microscopy (FE-SEM) of Nafion-silica/MWNT-g-PANI composite reveals the presence of spherical silica particles (sizes in the range 250 nm-1 microm) and tubular MWNT-g-PANI particles. Chronoamperometry and cyclic voltammetry were used to evaluate the performance of biosensor towards glucose. The Nafion-silica/MWCNT-g-PANI/GOx biosensor exhibited a linear response to glucose in the concentration range of 1-10 mm with a correlation coefficient of 0.9972, good sensitivity (5.01 microA/mm), a low response time (approximately 6s), repeatability (R.S.D value of 2.2%) and along-term stability. The presence of silica network within Nafion and MWNT-g-PANI synergistically contributes to the performance of the biosensor towards the electrochemical detection of glucose.