Guanying Cao

High performance of 1-D ZnO microwire with curve-side hexagon as ethanol gas sensor

Abstract ZnO microwires of two different cross-sectional profiles were synthesized by chemical vapor deposition, and their morphologies were characterized by scanning electron microscopy. Their cross-sectional hexagonal profile could be tuned from straight to curved sides, by regulating the ZnO:graphite powder ratio used during synthesis. The ZnO microwires had hexagonal profiles with curved sides at a higher graphite ratio, and hexagonal profiles with straight sides at a lower graphite ratio. The higher graphite ratio was speculated to lower the growth rate from center to hexagonal sides, relative to the corners. The ZnO microwires were fabricated into gas sensors, and their sensing characteristics towards ethanol gas were investigated. The sensor based on a ZnO microwire with curved sides exhibited superior ethanol sensing performance than that based on a microwire with straight sides, which was attributed to the higher surface-to-volume ratio of the curved-side microwire. The sensor based on a ZnO microwire with curved sides was stable, and exhibited rapid response and recovery times. The straight-forward and economical fabrication of the gas sensor at room temperature makes it attractive for practical application.

Mid- and long-waveband infrared imaging system design

A dual-waveband infrared re-imaging system has been designed with less lens number and short system length. The properties of re-imaging system to correct chromatic aberration have been researched. The main parameters of this system include F number, focal length, diameter, dual waveband, and imaging plane size are 2,000 mm, 200 mm, 3-5 μm /8-12 μm, and 9.3 mm × 12.4 mm, respectively. After design the average modulation value of all fields of view is 0.60 at 10lp/mm, and the difference between limited diffractive system and actual system is less than 0.3. The ray aberration has been corrected at the center wavelength 5 μm. The focal length varies with wavelength around 400 mm, and gets 400 mm exactly at 4 μm and 10 μm.

Investigation of oxygen vacancies on Pt- or Au-modified CeO2 materials for CO oxidation

Metal (Au or Pt)-modified CeO2 materials with excellent redox ability for the oxidation of CO to CO2 were prepared by a redox precipitation method to investigate the role of surface oxygen vacancies. It was found that most of the Au or Pt was encapsulated by CeO2. Both Au and Pt can effectively improve the reducibility of CeO2 to form more oxygen vacancies at lower temperatures. The surface oxygen vacancies were thoroughly studied by UV-Vis spectroscopy, CO adsorption FTIR, H2-TPR and CO pulse oxidation techniques. During the reaction cycle of CO oxidation, the oxygen vacancies were affected by the modified metals but played different roles in the performance of CO oxidation. There were more oxygen vacancies on Pt-CeO2, which facilitated the formation of more carbonates. A certain amount (4.2%) of oxygen vacancies was necessary to improve the CO oxidation on this material. Comparatively, the rather fewer oxygen vacancies and the lower adsorption strength of carbonates did not affect the final elimination efficiency of CO on Au-CeO2.