Qianqian Jia

Rapid and selective detection of acetone using hierarchical ZnO gas sensor for hazardous odor markers application

Hierarchical nanostructured ZnO dandelion-like spheres were synthesized via solvothermal reaction at 200°C for 4h. The products were pure hexagonal ZnO with large exposure of (002) polar facet. Side-heating gas sensor based on hierarchical ZnO spheres was prepared to evaluate the acetone gas sensing properties. The detection limit to acetone for the ZnO sensor is 0.25ppm. The response (Ra/Rg) toward 100ppm acetone was 33 operated at 230°C and the response time was as short as 3s. The sensor exhibited remarkable acetone selectivity with negligible response toward other hazardous gases and water vapor. The high proportion of electron depletion region and oxygen vacancies contributed to high gas response sensitivity. The hollow and porous structure of dandelion-like ZnO spheres facilitated the diffusion of gas molecules, leading to a rapid response speed. The largely exposed (002) polar facets could adsorb acetone gas molecules easily and efficiently, resulting in a rapid response speed and good selectivity of hierarchical ZnO spheres gas sensor at low operating temperature.

Exposed facets induced enhanced acetone selective sensing property of nanostructured tungsten oxide

WO3 nanorods with exposed (100) and (002) facets were fabricated via a hydrothermal route using different directing agents. Microspheres that were assembled randomly by WO3 nanorods with exposed (002) facets were porous with a specific surface area of 62.2 m2 g−1. Acetone gas sensing properties of the as-prepared sensors were investigated for the breath diagnosis of diabetes. The acetone detection limit of WO3 microspheres was 0.25 ppm, and the response (Ra/Rg) to 1 ppm acetone was 3.53 operated at 230 °C with a response and recovery time of 9 and 14 s, respectively. WO3 samples with exposed (002) facets exhibited better acetone sensitivity and selectivity than those with (100) facets. The sensing mechanism was discussed in detail. Because of the asymmetric distribution of unsaturated coordinated O atoms in the O-terminated (002) facets, the surface had an extent of polarization. Induced local electric dipole moment contributed to easy adsorption and reaction between the (002) facets and acetone molecules with a large dipole moment at low working temperatures. Room temperature PL spectra clearly displayed that the WO3 samples exposed with (002) facets had numerous oxygen vacancies and defects, resulting in excellent acetone sensing properties.

A CuO–ZnO nanostructured p–n junction sensor for enhanced N-butanol detection

Herein, a novel CuO–ZnO nanostructured p–n junction composite is prepared via the hydrothermal method. It is composed of a ZnO two dimensional (2-D) porous nanosheet assembly and leaf-like 2-D CuO nanoplates. Then, its gas sensing performance toward n-butanol is studied. The 2-D/2-D CuO–ZnO composite sensor shows 2.7 times higher sensitivity than that of pure ZnO at 220 °C. Moreover, its response to n-butanol is 3.5–84 times higher than those for other target gases. This reveals an excellent selectivity toward n-butanol. Its detection limit for n-butanol is calculated to be 0.4 ppm, indicating a potential advantage in low concentration detection. The significant enhancement of the composites sensing performance can be firstly attributed to the p–n junction, which brings electronic sensitization for the composite sensor. Moreover, the porous structure and the open 2-D/2-D heterostructure also contribute to the sensing performance of the composite. These allow the gas molecules to diffuse rapidly, making chemisorption and surface reactions on the p–n junction more easy.

A simple sol–gel route for preparing the Barium Strontium Calcium Titanate-Magnesium Oxide composite powders and the sintering/dielectric properties of the ceramics

In the present work, sol–gel method based on the citric acid (CA)-ethylene glycol (EG) system was employed to prepare the Ba0.55Sr0.40Ca0.05TiO3-MgO (BSCT-MgOsg for short, the footnote “sg” was the description of the sol–gel method) powders [(MgO/BSCT)mass = 40/60]. The BSCT-MgOsg powders were spheroidal with particle size of 50–150 nm, estimated from the scanning electronic microscope (SEM) images. Fine crystallized BSCT and MgO phases were detected in the X-ray diffraction (XRD) pattern of the BSCT-MgOsg powders. The Ba0.55Sr0.40Ca0.05TiO3-MgO (BSCT-MgOsg) ceramics, of which the relative density was 93.73–97.78 % after being sintered at 1,000–1,100 °C for 2 h, had much denser and more homogeneous microstructure, compared with the BSCT-MgOss ceramics which were prepared by solid state method. The solid solubility of Mg2+ in the BSCT lattice was much lower in the BSCT-MgOsg ceramics than that in the BSCT-MgOss ceramics, according to the result in the Energy dispersive spectrum (EDS) spectrograms. The suitable permittivity and super-low dielectric loss of the BSCT-MgOsg ceramics were 65 and 0.00078, respectively, which were tested at 2 MHz, room temperature (RT). The BSCT-MgOsg ceramics could be expected as a promising candidate for applying in microwave electric components, such as phase shifters or resonators, by possessing preferable sintering properties and suitable dielectric properties.

Semiconducting Nano-structured SmFeO3-based Thin Films Prepared by Novel Sol-gel Method for Acetone Gas Sensors

SmFe1−xCuxO3 (x = 0, 0.05, 0.10, 0.15) thin films were prepared on Al2O3 substrates by a novel sol-gel technique using citric acid (CA) as chelating agent and ethylene glycol (EG) as cross-linking agent. The as-growth thin films were well-crystallized and the grain size was about 40 nm after annealed at 750°C. After doped with Cu2+, the temperature dependence of resistance of SmFeO3-based thin films were flattened and stable. The measuring temperature of SmFeO3-based thin films were optimized to 450°C. The SmFeO3-based thin film The SmFe0.95Cu0.05O3 thin film responsed selectively to the acetone and ethanol gas, becoming a new candidate for the applications of medical diagnostics, food industry and so on.

The Phase Transformation, Morphology Evolution and Visible-Light Photocatalytic Activity of V-Doped TiO2 Thin Films

V-doped TiO2 thin films had been fabricated on glass substrates via sol–gel method. These films were characterised by simultaneous thermogravimetry and differential scanning calorimetry (TG-DSC), X-ray diffraction (XRD) and scanning electron microscopy (SEM). It was found that the nanoparticle shape of the TiO2 films changed from spindle shape to sphere-like shape with the increase of V doping. The anatase-to-rutile transformation was accelerated by the presence of vanadium doping. The 10 mol% V-doped TiO2 films with a mixed phase of anatase and rutile exhibited better visible light photocatalytic performance.