Study On Preparation And Their Gas Sensing Properties Of CuO And Doped ZnO Porous Microspheres

As an important p-type semiconductor, CuO has been recently attracted a great deal of attention for gas sensor applications due to the well-known surface conductivity of CuO. However, p-type CuO usually has lower responses to analytical gases than frequently-used n-type semiconductor materials, such as SnO2and ZnO. Although the utilization of ZnO in the field of sensing gases has a long history, it has been, somewhat limited in the real applications, due to low sensitivity, poor selectivity and high working temperature. Ions doping and morphology control are regarded as two promising strategies to improve the gas-sensing properties. The responses to meso-macroporous CuO microspheres towards ethanol were improved by the way of morphology control in this paper. And the responses to mesoporous ZnO microspheres towards ethanol and n-butanol were improved with Co and Fe as dopants, respectively. The main contexts are as follows:(1) The meso-macroporous CuO microspheres composed of nanosheets were prepared by the solvothermal method. CuO microspheres had a specific surface area of42.0m2/g, a pore volume of0.224cm3/g, and a main pore size of8-58nm, as well as the platelet-like building blocks had a thickness of about50nm. The response of CuO microspheres to100ppm ethanol was13.7at a working temperature of150℃. The enhancement of the response was attributed to the larger specific surface area、the larger pore volume and thinner platelet-like building blocks.(2) Co-doped Mesoporous ZnO microspheres were prepared by the hydrothermal method. The3mol%Co-doped ZnO sample had a specific surface area of59.5m2/g, a pore volume of0.110cm3/g, and a main pore size of2-12nm. Co species existed as a form of divalent state in the sample and substituted Zn2+sites in ZnO crystal lattice. The sensor showed the highest response value of78.1to100ppm ethanol at350℃, which were5folds higher than that of the pure ZnO sensor. The recovery time of the3mol%Co-doped ZnO sensor to100ppm ethanol was9s. The maximal deviations of the responses to ethanol are less than10%in 90days. The improvement of the response was contributed to higher donor defects contents combined with larger specific surface area.(3) Fe-doped Mesoporous ZnO microspheres were prepared by the hydrothermal method. The4mol%Fe-doped ZnO sample had a specific surface area of56.2m/g, a pore volume of0.125cm/g, and a main pore size of5-33nm. Fe-doped ZnO sensors could detect n-butanol down to ppb level. The4mol%Fe-doped ZnO sensor showed the best response to ppb-level n-butanol at300℃. The sensor had a response value of230.4to100ppm n-butanol, which was11.5folds as high as that of the pure ZnO sensor. The sensor had a response value of1.6to10ppb n-butanol with a detection limit of n-butanol below10ppb.And the sensor exhibited good selectivity to n-butanol. The improvement of the response was contributed to higher donor defects contents combined with larger specific surface area.