Zhixuan Cheng

The template-free synthesis of square-shaped SnO2 nanowires: the temperature effect and acetone gas sensors

Square-shaped single-crystalline SnO(2) nanowires and their sphere-like hierarchical structures were synthesized successfully with a template-free hydrothermal approach. It was found that an intermediate phase-Na(2)Sn(OH)(6)-is first produced because it is slow to dissolve in ethanol/water media. The intermediate phase gradually decomposes and converts into SnO(2) at temperatures higher than 200 °C. The reaction temperature also affects the microstructure of SnO(2) nanomaterials. Uniform square-shaped SnO(2) nanowires, which form sphere-like hierarchical structures in 100% structure yield, can be produced at 285 °C on a large scale. The diameter of the nanowires shows a decrease accompanying the increase of the reaction temperature. The temperature effect could be a result of the faster and oriented growth of SnO(2) nanowires along their [Formula: see text] direction at higher temperature. Chemical sensors constructed with square-shaped SnO(2) nanowires exhibit excellent stability, good sensitivity and selectivity, as well as a quick response and short recovery times under exposure to acetone gas in practical applications.

A new route for preparing corundum-type In2O3 nanorods used as gas-sensing materials

Corundum-type In2O3 nanorods were synthesized under ambient pressure by annealing, at 600 ◦ C, orthorhombic InOOH nanorods obtained by solvothermal reaction. The samples were characterized by x-ray diffraction (XRD) and transmission electronic microscopy (TEM), and their gas sensitivities were obtained. The results of XRD and TEM experiments show that solvent and surfactants have significant effects on the formation and morphology of the metastable phase during the synthesis of the precursor. The gas-sensitivity results show that hexagonal In2O3 nanorods are very sensitive to dilute ethanol and H2S. (Some figures in this article are in colour only in the electronic version)

Porous corundum-type In2O3 nanoflowers: controllable synthesis, enhanced ethanol-sensing properties and response mechanism

Porous rhombohedral In2O3 (corundum-type In2O3, rh-In2O3) with a morphology of uniform nanoflowers was fabricated by using a mild, facile solvent-thermal method. The formation mechanism and transformation of phase were studied. The results revealed that the precursors were transformed from In(OH)3 to InOOH with an increase in reaction time. The phase transformation was attributed to the stability of the InOOH phase at small crystal volume, less water molecules and small pH value, which in turn led to the formation of metastable rh-In2O3. The optimal working temperature of the sensor based on porous rh-In2O3 nanoflowers was proved to be 280 °C, corresponding to chemisorbed oxygen analysis based on a temperature changeable XPS, further demonstrating the surface resistance controlled gas sensing mechanism of In2O3. The sensor exhibited an enhanced response and rapid response/recovery toward ethanol vapour, which was ascribed to hierarchical porous structures and more active defects.

CdSnO3 micro-cubes with porous architecture: synthesis and gas-sensing properties

CdSnO3 micro-cubes with porous architecture were obtained exclusively via a simple co-precipitation method at 80 °C for 6 hours, with which a good response to ethanol vapor in ppb was observed.

Mesoporous In 2 O 3 : effect of material structure on the gas sensing

We present a semiconductor gas sensor based on mesoporous In2O3 (m-In2O3). The m-In2O3 was successfully fabricated by a simple sol-gel process, using block copolymer PE6800 as a soft template. The results of gas sensing reveal that the m-In2O3 prepared at room temperature shows higher resistance, which plays the key role in its greater sensitivity. The pore structure of material has an influence on gas adsorption on the material surface, which further affects response-recovery time of gas sensor.

Controllable Evolution of Dual Defect Zni and VO Associate-Rich ZnO Nanodishes with (0001) Exposed Facet and Its Multiple Sensitization Effect for Ethanol Detection

Building an effective way for finding the role of surface defects in gas sensing property remains a big challenge. In the present work, we synthesized the ZnO nanodishes (NDs) and first explored the formation process of rich electron donor surface defects by means of studying mechanism for the ZnO NDs synthesis. The test results revealed that ZnO-6, added by 6 mmol Zn powder, had the best gas-sensing properties with the excellent selectivity to ethanol than the others. Specially, the ZnO-6 sensor exhibited the best response (about 49) to 100 ppm ethanol at 230 °C among four as-synthesized samples, while noncustomized ZnO was only 28. It was mainly caused by the following two reasons: the exposure of target (0001) crystal facet and rich electron donor surface defects zinc interstitial (Zni) and oxygen vacancy (VO). As a guide, the formation process of surface defects was revealed by an ideal defect model. By the small-angle XRD and TEM patterns, we could conclude that ZnO NDs, changing stoichiometric ratio, increased the content of Zni by adding Zn powder, while excessive Zn powder promoted the growth of c axis of ZnO NDs in the self-assembly engineering. Besides, a depletion model has been provided to explain how the surface defects work on the sensors and the complex mechanism of gas sensing performance. These findings will develop the application of ZnO-based gas sensor in health and security.

Superhydrophobic Polymerized n-Octadecylsilane Surface for BTEX Sensing and Stable Toluene/Water Selective Detection Based on QCM Sensor

The present study reports a facile and low-cost route to produce a superhydrophobic polymerized n-octadecylsilane surface with micronano hierarchical structure on the surface of quartz crystal microbalance (QCM). The surface is used as a novel functional sensing material to detect benzene, toluene, ethylbenzene, and xylene (BTEX) vapor on the basis of QCM platform. The composites were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, and contact angle measurements. The type of solvent used to dissolve N-octadecyltrichlorosilane has a big impact on the morphology, wettability, and sensing performance of the polymer material. Further systematic studies suggest that surface wettability (contact angle) and molecular polarity of the detected analytes are effective factors in selective detection toward BTEX using resonator-type gas sensors. Gas sensing results toward toluene in different relative humidities show that the new-style sensor has stable toluene/water selective detection performance and that the disturbance of water is negligible. Besides, the limit of detection toward toluene of the sensor is lower than the odor threshold value.