Fast Response Recovery Characteristics Research Articles

A flexible nonenzymatic sweat glucose sensor based on Au nanoflowers coated carbon cloth

A flexible sensor which can be integrated with clothes and collect sweat is a promising technology for wearable sweat glucose monitoring. Herein, we demonstrate a flexible nonenzymatic glucose-sensing device based on carbon cloth (CC), in which the three electrodes are integrated with gauze spacer through sewing, and the sensing electrode is functionalized by Au nanoflowers (Au NFs). The Au NFs is optimized by synthesis time regulation, and the optimal Au NFs@CC electrode exhibits high electrocatalytic performance for glucose due to the hydrous gold oxide on the electrode surface. The as-developed Au NFs@CC based device can actively absorb solution and only 240 μL of solution is required to realize the detection. It also offers high selectivity, wide linear interval, and fast response recovery characteristics, as well as it can detect glucose under neutral conditions. Noticeably, the integrated cloth material based flexible nonenzymatic glucose sensor demonstrates excellent ability to monitor the glucose level in sweat, which can be used for mobile medical and diabetic patients.

Enhance methanol-sensing properties based on Ag functionalized monolayer LDH nanosheet: A combined experimental and theoretical calculation investigation

Layered double hydroxides has been greatly explored for gas sensor applications due to their highly tunable chemical composition and unique layer structure. In this work, an investigation combined experimental and theoretical on Ag functionalized monolayer ZnAl-LDH (Ag/LDH) is performed for excellent methanol sensing performance. The monolayer ZnAl-LDH nanosheets was firstly prepared via an inverse-microemulsion method to reduce the stacking of LDHs. Then Ag nanoparticles (NPs) were successfully introduced on the surface of monolayer LDH by glucose reduction method. The Ag/LDH nanocomposite shows Ag NPs uniformly attached on the monolayer LDH nanosheet with large specific surface area. Benefiting from the unique microstructure of monolayer LDH and Ag functionalization, the Ag/LDH gas sensor exhibits about 23-fold enhancement in response value to 25 ppm methanol at room temperature compared with multilayer LDHs sensor. Meanwhile, the as-prepared sensor can detect 500 ppb methanol and exhibits extremely fast response-recovery characteristics upon 10–200 ppm methanol. Further gas adsorption calculations based on first principles were performed to clarify the key contribution of Ag NPs to methanol adsorption and the corresponding gas mechanism is also proposed. Above all, the present work indicates that the functionalization of Ag NPs is highly potential for enhancing the response LDH towards methanol vapor. • Combination of experiment and first-principles calculations. • Monolayer LDH nanosheets with uniformly attached Ag NPs were prepared. • The Ag/LDH sensor shows rapid response and recovery characteristic to methanol at room temperature. • The as-fabricated gas sensor could detect as low as 500 ppb methanol with a response of 3.35% at room temperature.

Trace level toxic ammonia gas sensing of single-walled carbon nanotubes wrapped polyaniline nanofibers

This paper presents a two-step enhancement and a comprehensive analysis of single-walled carbon nanotubes (SWCNTs) wrapped polyaniline nanofiber (NPANI) ammonia (NH3) gas sensor at room temperature. SWCNT-PANI composites are successfully synthesized using an efficient and cost-effective rapid in situ chemical polymerization method. The structural morphology and modification of the samples are characterized using field-emission scanning electron microscopy and HRTEM. FTIR and Raman spectroscopic studies are also performed to gain a better insight into the chemical environmental interaction in the as-prepared nanocomposite. The analysis confirms the successful formation of the nanocomposite. The observed NH3 gas-sensing response at 10 ppm of SWCNT, f-SWCNT (functionalised SWCNT), and SWCNT-PANI composite sensors are 5%–6%, 18%–20%, and 24%–25%, respectively. The SWCNT-PANI composite sensors have shown higher repeatability, selectivity, long-term stability, and fast response-recovery characteristics as compared to f-SWCNTs and pristine SWCNT sensors. Concentration and temperature dependent gas-sensing studies are also analyzed. The sensor response also shows a linear relationship with NH3 gas concentration and an inverse relationship with increasing temperature.

Single-step hydrothermally grown nanosheet-assembled tungsten oxide thin films for sensitive and selective NO2 gas detection

A well-organized tungsten oxide (WO3) nanosheet-assembled microbricks have been synthesized by the hydrothermal route at 180 °C with the help of peroxy-tungstic acid sol. The as-synthesized thin films have been characterized for structural, morphological and compositional studies by using X-ray diffraction, scanning electron microscopy and FT-Raman spectroscopy. The deposited WO3 thin films have been found to be polycrystalline in nature with the monoclinic crystal structure. The SEM micrographs revealed the formation of microbrick-like structure which was made up of two-dimensional (2D) nanosheets. The 2D nanosheets act as a nanobuilding blocks for the formation of microbricks. The gas-sensing performance of WO3 thin films was carried out for different gases, and it is observed that sensor exhibited maximum gas response towards Nitrogen dioxide (NO2) gas which is seven times higher than that of other gases at an operating temperature of 300 °C over the concentration range of 5–100 ppm. WO3 microbricks sensor showed higher response about 11.5 and fast response–recovery characteristics towards NO2 gas, especially a much quicker gas response time of 16 s and recovery time of 260 s at 100 ppm.

A europium (III) based nano-flake MOF film for efficient fluorescent sensing of picric acid

The authors describe a fast response-recovery characteristics of optical sensing platform based on a luminescent thin film composed of a nano-flake metal organic framework (MOF) of the type [Eu4(NDC)6(H2O)5]·3H2O (referred to as Eu-NDC), where NDC stands for naphthalene-2,6-dicarboxylate. The film can be prepared within 20 s and shows strong luminescence (with excitation/emission maxima at 355/614 nm) that is characteristic for Eu(III) ion sensitized by the electron-rich ligands. The structure of the MOF films is confirmed by powder X-ray diffraction, and their surface morphology is examined by scanning electron microscopy. The luminescence of the sensor film is strongly quenched by picric acid (PA), and this finding is exploited in a sensing scheme for PA with good selectivity over other nitroaromatic explosives. The limit of detection for PA is 0.67 μM. The luminescence quenching mechanisms were also investigated. The sensor is easily prepared, stable, and can be recycled by rinsing with water. It was also applied to the determination of PA in Pearl River water that was spiked with PA.

KOH post-etching-induced rough silicon nanowire array for H2 gas sensing application

The limited surface area and compacted configuration of silicon nanowires (SiNWs), which are made by one-step metal-assisted chemical etching (MACE) go against target gas diffusion and adsorbtion for gas sensing application. To harvest suitable gas sensitivity and fast response–recovery characteristics, an aligned, rough SiNW array with loose configuration and high surface area was fabricated by a two-step etching process. The MACE technique was first employed to fabricate a smooth SiNW array, and then a KOH post-etching method was developed to roughen the NW surface further. The influence of the KOH post-etching time on the array density and surface roughness of the SiNWs was investigated, and the H2-sensing properties of the sensor based on the as-fabricated rough SiNW array were evaluated systematically at room temperature. It was revealed that the post-etching of KOH roughens the NW surface effectively, and also decreases the wire diameter and array density considerably. The resulting configuration of the SiNW array with high active surface and loose geometry is favorable for gas sensing. Consequently, the rough SiNW array-based sensor exhibited a linear response to H2 with a wide range of concentrations (50–10 000 ppm) at room temperature. Good stability and selectivity, satisfying response–recovery characteristics were also achieved. However, over-etching of SiNWs by KOH solution results in a considerable decrease in surface roughness and then in the H2-sensing response of the NWs.

Hydrothermally grown ZnO nanorods arrays for selective NO2 gas sensing: Effect of anion generating agents

Vertically aligned ZnO nanorods (ZNRs) arrays with various aspect ratios were deposited by using a simple and inexpensive hydrothermal route at relatively low temperature of 90°C. The influence of hydroxide anion generating agents in the solution on the growth of ZNRs arrays was studied. Hexamethylenetetramine (HMTA) and ammonia were used as hydroxide anion generating agents while polyethyleneimine (PEI) as structure directing agent. The combined effect of these three agents plays a crucial role in the growth of ZNRs arrays with respect to their rod length and diameter, which controls the aspect ratio. The deposited ZNRs exhibited hexagonal wurtize crystal structure with preferred orientation along (002) plane. The highly crystalline nature and pure phase formation of ZNRs was confirmed from FT-Raman studies. The maximum gas response (Rg/Ra) of 67.5 was observed for high aspect ratio ZNRs, deposited with combination of HMTA, ammonia as well as PEI. The enhancement in gas response can be attributed to high surface area (45 cm2/g) and desirable surface accessibility in high aspect ratio ZNRs. Fast response–recovery characteristics, especially a much quicker gas response time of 32s and recovery time of 530s were observed at 100ppm NO2 gas concentration.

Fast-response hydrogen sensors based on discrete Pt/Pd bimetallic ultra-thin films

This study presents the fast response-recovery characteristics of an ultra-thin discrete platinum/palladium (Pt/Pd) bimetallic film-based hydrogen (H2) sensor. Pt/Pd bimetallic nanoparticles (NPs) with a size of 2–11nm were deposited on an alumina (Al2O3) substrate using a pulsed laser deposition (PLD) method. The metal loading and the composition of the Pt/Pd NPs were carefully controlled by varying the deposition conditions of the PLD system. The resultant discrete Pt/Pd bimetallic ultra-thin film was applied as a new H2 detection material, in which the fabricated Pt (3nm)/Pd (3nm) film showed noteworthy advantages, such as a large detection range of 10–40,000ppm, high response magnitude, and fast response-recovery time. For a 10,000ppm (1vol.%) H2 concentration at 150°C, a maximum sensor response of 13.56% and a response-recovery time of 4/5s were observed. The observed fast response-recovery time characteristics can be attributed to the enhanced hydrogen-induced changes in the work function of the Pt/Pd ultra-thin film. The fabricated sensor also exhibits good reproducibility and a negligible humidity effect within the entire detection range.

Controllable synthesis of ultrathin vanadium oxide nanobelts via an EDTA-mediated hydrothermal process**Project supported by the National Natural Science Foundation of China (Grant Nos. 61274074, 61271070, and 61574100).

Ultrathin VO2 nanobelts with rough alignment features are prepared on the induction layer-coated substrates by an ethylenediaminetetraacetic acid (EDTA)-mediated hydrothermal process. EDTA acts as a chelating reagent and capping agent to facilitate the one-dimensional (1D) preferential growth of ultrathin VO2 nanobelts with high crystallinities and good uniformities. The annealed induction layer and concentration of EDTA are found to play crucial roles in the formation of aligned and ultrathin nanobelts. Variation in EDTA concentration can change the VO2 morphology of ultrathin nanobelts into that of thick nanoplates. Mild annealing of ultrathin VO2 nanobelts at 350 °C in air results in the formation of V2O5 nanobelts with a nearly unchanged ultrathin structure. The nucleation and growth mechanism involved in the formations of nanobelts and nanoplates are proposed. The ethanol gas sensing properties of the V2O5 nanobelt networks-based sensor are investigated in a temperature range from 100 °C to 300 °C over ethanol concentrations ranging from 3 ppm to 500 ppm. The results indicate that the V2O5 nanobelt network sensor exhibits high sensitivity, good reversibility, and fast response-recovery characteristics with an optimal working temperature of 250 °C.

Thermal-oxidative growth of aligned W18O49 nanowire arrays for high performance gas sensor

Gas sensors based on aligned arrays of W18O49 nanowires were formed directly via a novel route of in situ thermal oxidation of sputtered W film on the substrate attached patterned Pt electrodes. The well-developed nanowires have diameter of 10–20nm and show roughly aligned morphology. It is found that the duration of oxygen exposure during thermal annealing plays a crucial role to harvest a pure phase of W18O49 nanowire with desired length. The roughly aligned W18O49 nanowires show favourable microstructure for gas adsorption and rapid gas diffusion. The NO2-sensing properties of aligned W18O49 nanowires sensor were evaluated at 50°C up to 200°C over NO2 concentration ranging from 250ppb to 2.5ppm. The results indicate that the W18O49 nanowire arrays sensor exhibits good NO2-sensing performances at its optimal operating temperature of 150°C, especially perfect stability and fast response–recovery characteristics. The reliable interface performance and fast gas adsorption–desorption properties of the directly assembled vertically aligned nanowire array attribute to the superior stability and quick response/recovery. The growth mechanism of aligned W18O49 nanowires is proposed based on the direct SEM observations on the intermediate products, and meanwhile the sensing mechanism of the corresponding sensor is analyzed.

NO sensing by single crystalline WO3 nanowires

Single crystalline WO3 nanowires were directly grown on FTO substrates by a hydrothermal approach. After calcination at 400°C, the nanowires assumed an orthorhombic structure and their diameters were mostly in the range of 15–20nm. The sensor based on the WO3 nanowires exhibited a markedly high response and fast response–recovery characteristics to NO gas at 300°C. XPS and DRIFT studies demonstrated that the chemisorption of NO and the oxidation of NO by defect-like oxygen anions on the nanowire surfaces were key to the sensing performance.

One-pot synthesis of 3D hierarchical SnO2 nanostructures and their application for gas sensor

3D hierarchical SnO2 nanostructures, constructed by well-defined 1D SnO2 nanorod units, were synthesized by a facile, one-step hydrothermal route, only using simple inorganic compounds SnCl4·5H2O and NaOH as starting materials, without using any surfactants and templates. The prepared 3D SnO2 hierarchical nanostructures were applied to fabricate a gas sensor for selectively detecting n-butanol. The gas sensing results demonstrated that the 3D SnO2 hierarchical nanostructure sensor exhibited excellent gas sensing performances to ppm-level n-butanol in terms of high response, good reproducibility, fast response–recovery characteristics and superior selectivity, and significantly enhanced response compared with the commercial SnO2 nanopowder sensor. The enhanced gas sensing performances could be attributed to the facilitated molecular absorption, gas diffusion and mass transport induced by the unique 3D loose and porous structure, and the high surface-to-volume ratio resulted from the 1D rod-like nanostructure which could provide more active sites for gas absorption. It was believed that the 3D hierarchical SnO2 nanostructures could also further offer a potential opportunity for other applications such as lithium-ion batteries, catalysis and dye-sensitized solar cells.

Mesoporous three-dimensional network of crystalline WO3 nanowires for gas sensing application

Mesoporous three-dimensional (3D) network of crystalline WO3 nanowires was prepared by nanocasting method using 3D SBA-15 silica with hexagonally ordered mesopores as hard template. After impregnation, mineralization and template removal, a mesoporous 3D framework of ordered crystalline WO3 nanowires with high specific surface area and stable mesopore channels was formed through the randomly distributed bridging between the neighboring nanowires. The mesostructure of the product was confirmed by low-angle X-ray diffraction (XRD) and nitrogen physisorption measurements. High resolution transmission electron microscopy (HRTEM) images indicate the single crystal structure with different crystal orientation for mesoporous particles. The gas sensing properties of the mesoporous 3D WO3 nanowires replica were investigated at 50°C up to 200°C over NO2 concentration ranging from 15 to 500ppb. The results indicate that the mesoporous 3D WO3 nanowires exhibits high response, good selectivity and fast response–recovery characteristics in the detection of sub-ppm and ppb level NO2 at the optimal operating temperature of 125°C due to the stable mesopore channels, large surface area and perfect single-crystal structure.

Porous WO3 from anodized sputtered tungsten thin films for NO2 detection

In this paper, porous WO3 films were prepared by anodic oxidation of metallic tungsten (W) films deposited on alumina substrates. The structural and morphological properties of the porous WO3 films were investigated using field emission scanning electron microscope (FESEM) and X-ray diffraction (XRD). A large number of cracks appeared on the surface of films after anodization, which makes the films porous. The porous WO3 sensors achieved their maximum response values to NO2 at a low operating temperature of 150°C. The porous WO3 sensors showed high response values, great stability and fast response–recovery characteristics to different concentration of NO2 gas due to the high specific surface area and special structural and morphological properties.

An organic–inorganic hybrid ultrathin film: preparation and characterization of copper phthalocyanine derivative–ferric oxide nanoparticles

A nanoparticulate ferric oxide–copper tris(2,4-di-tert-amylphenoxy)-8-quinolinolylphthalocyanine hybrid ultrathin film was constructed from alternate layers by the Langmuir–Blodgett technique. The composition, morphology and structure of the film were studied by X-ray photoelectron spectroscopy (XPS), transmission electron microscopy, atomic force microscopy, small-angle X-ray diffraction, visible spectroscopy and polarized UV-Vis spectroscopy. All the above analyses suggest that the thin film is a kind of one-dimensional superlattice, composed of organic and inorganic components. The XPS data reveal that the nanoparticulate ferric oxide exists as an α-Fe2O3 phase in the films. Gas-sensing measurements show that the hybrid LB film has very fast response-recovery characteristics towards 2 ppm C2H5OH vapor.