Qingyi Pan

Grain size control and gas sensing properties of ZnO gas sensor

Nanometer ZnO gas sensing material with different particle size were made by chemical precipitation, emulsion and microemulsion, respectively. Crystal structure and ceramic microstructure of powders were determined by XRD and TEM. The mean grain size and lattice distortion of the materials were calculated with the Cauchy–Cauchy and Debye–Scherrer methods, respectively. Gas sensitivity of ZnO to H2, SF6, C4H10, gasoline, C2H5OH was measured. It can be shown from experimental results that grain size of ZnO gas-sensitive materials can be controlled by means of different processes or surfactants. The gas sensitivity of ZnO gas sensor depends upon its grain size.

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.

Self-assemblies of Pd nanoparticles on the surfaces of single crystal ZnO nanowires for chemical sensors with enhanced performances

Single-crystalline ZnO nanowires were synthesized, and further modified with Pd nanoparticles through self-assemblies. The self-assembly strategy shows advantages of tailoring the surface modification of ZnO nanowires with monodispersed Pd nanoparticles and further tuning of the functionalities of nano-architectures. It was found that poly(vinylpyrrolidone) (PVP) plays a key role in loading Pd nanoparticles onto the surfaces of ZnO nanowires. Having been turned into chemical sensors, the nano-architectures constructed from ZnO nanowires and Pd nanoparticles exhibit a highly enhanced response to H2S gas, compared to the devices from pure ZnO nanowires.

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)

Sensing characteristics of double layer film of ZnO

Abstract Pure ZnO powder was made by chemical precipitation. ZnO-based gas sensing materials and Al 2 O 3 -based catalysts doped with a noble metal were prepared with impregnation. Gas sensitivity of ZnO single layer and double layer film gas sensors was measured in static state. It can be shown from experimental results that the gas sensitivity and selectivity of ZnO gas sensor can be improved by doping noble metal and using noble metal catalyst coating.

Gas-sensitive properties of nanometer-sized SnO2

Abstract Nanometer-sized SnO 2 particles were prepared by a sol–gel method using inorganic salt as a precursor material. The investigated results indicate that well-crystallized nano-sized SnO 2 with size around 15 nm was obtained at annealing temperature 600°C. The activation energy for the growth of nano-SnO 2 was calculated to be 26.55 kJ mol −1 when the annealing temperature was higher than 500°C. The measurements also show that there is a peculiar resistance change as a function of temperature for nano-SnO 2 . It has relevance to the increase of surface adsorbed oxygen. The selective detection for C 4 H 10 and petrol can be increased when ruthenium ion was doped in nano-SnO 2 as a catalyst. The gas sensitivity to CO, CH 4 , H 2 , etc., can be increased when rhodium ion was doped in nano-SnO 2 as a catalyst and the detection to the several reducing gas can be realized ranging in temperature from 260°C to 400°C.

Synthesis and chlorine sensing properties of nanocrystalline hierarchical porous SnO2 by a phenol formaldehyde resin-assisted process

Nanocrystalline tin dioxide (SnO2) materials with very interesting architectures (well-defined pores, hierarchical pores) were synthesized by a suitable heat treatment of SnO2/phenol formaldehyde resin (PFR) nanocomposite. The composite was obtained through a facile hydrothermal approach by using tin(IV) tetrachloride pentahydrate (SnCl4·5H2O) as a raw material, hexamethylenetetramine (HMT) as a pore-forming agent and monomer (HCHO) source for polymerization with phenol. Compared with the fine porous SnO2 sensor, the hierarchical porous SnO2 sensor showed a higher response. Owing to the hierarchical porous structure, the as-prepared materials exhibit satisfactory selectivity to chlorine along with high-sensitivity (249.3 at 10 ppm), fast response (7 s), very short recovery time (15 s), long-term stability as well as low power. The excellent sensing performance was discussed concerning the architectures of the materials.

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.

STUDY ON STABILITY AND RHEOLOGY OF PEG6000/NANO-Ni(OH)2 SOL

The PEG6000/nano-Ni(OH)2 sol was prepared by modified sol–gel method. The effect of Ac- on Ni(OH)2 colloidal particles and the structure of PEG6000/nano-Ni(OH)2 was investigated. The results show that hydrogen bonds or other weak interaction forces between PEG6000 and Ni(OH)2 can change the zeta potential of the Ni(OH)2 surface and enhance the colloidal stability of Ni(OH)2. The stable region of the PEG6000/Ni(OH)2 sol was determined by measuring the viscosity. The ratio of PEG6000 to Ni(OH)2 is the principal factor that influences the flow patterns of the sol. Surfaces of the thin films prepared from Newtonian sol by sol–gel spin-coating method are smooth while those from pseudoplastic sol are rough. The results establish the theoretical foundation for preparing the nano-NiO thin films by spin-coating method.