| ZnO is a new-type semiconductor with the direct band gap of 3.37 ev and the exciting binding energy of 60 mev so that it is easy to be adopted. Further, it is cheap, enviromentally friendly and biocompatible, which leads that ZnO has many widely application such as solar-cells, purple light detector, transparent electrode, gas sensors and so on. As so far, there has been many methods and modified technique to fabricate diverse Zn O nanostructure with different size and shape. Further, different morphology affects the application of the Zn O gas sensor. In this paper, we used zinc acete(Zn(CH3COO)2·2H2O) and ammonia water as raw material, polyvinyl pyrrolidone(PVP) as surfactant, ethanol and deionized water as solvent, then accroding to the certain mole ratio, the prepared solution was annealed for 1.5 h at 500°C in the furnace, so that the mesoscopic structure of ZnO nanorods have been prepared. The preparation of the nanorods is the first part of our work and the basis work in this paper. Based on the preparation of nanorods, we have further modified the mophology of ZnO though changing the annealing time and the precursor, then the gas sensing properties of the prepared samples are studied by analyzing the experimental data, and then we emphasis on the analysis about the reasons for the enhancement of gas sensing property and proving the retionality of the experimental data by the theory. The main research contents and results are as follows:1. The mesoscopic ZnO nanorods with the length of 1 μm and the diameter of about 90 nm have been well prepared by the solution-calcination method and analyzed the morphology and structure by XRD, SEM and TEM. The results show that the fabricated sample is wurtzite hexagonal phase of ZnO, the morphology presents typical one-dimensional(1D) nanodords, and the lattice spacing is about 0.259 nm corresponding to(001) plane. During the growth process, two chemicals(PVP and NH3·H2O) greatly affect the morphology growth. The gas sensor based on this structure performs the perfect acetone gas sensing property at the optimal working temperature of 420°C. The good sensitivity and fast response to lower concentration of acetone are applied well in the acetone sensor.2. On the basis of ZnO 1D nanorods, the three samples have been prepared with the annealing time of 1.5 h, 2.0 h and 2.5 h, respectively. The samples present 1D nanorods, 3D nanoflower and caddice clew-like ZnO feature, respectively. The sensitivity, selectivity and working temperature of these samples have been tested. The results show that the nanoflower ZnO material with the annealing time of 2.0 h is more sensitive and decreases the optimal working temperature to 360°C towards ethanol, meanwhile it has the shortest response/recovery time(9 s/ 12 s) and excellent selectivity to ethanol. These superior ethanol sensing properties is owing to 3D hierarchical architecture which produces more active sites, so that the reaction speed of the target gas and the absorbed oxygen is enhanced. Meanwhile, the specific surface area of 3D hierarchical architecture is the biggest after the BET tests. The BET surface area of flower-like is 35.66 m2/g, and that of the nanorods and caddice clew-like ZnO structure are 20.19 and 4.31 m2/g.3. Based on the nanorods, the 1D nanorods are optimized to the porous honeycomb like feature using zinc nitrate instead of zinc acetate. This structure self-assembled layer-by-layer by numerous irregular nanoparticles and holes, which is benefit for gas adsorption and desorption. After the gas sensing tests, the sensor based on this architecture shows the high response, fast response/recovery time(14/ 9 s), good selectivity, long-term stability and reproducibility toward glacial acetic acid(CH3COOH) at 370°C, thus it is used for the CH3 COOH detection. In addition, the enhanced gas sensing property is attributed to the porous honeycomb-like structure which provides more active center and gas diffusion ways and increases the specific surface area. |
PDF Full Text Request