ZnO Nano-powders as Chemical Sensor to Malathion Vapor

Thick films of zinc oxide (ZnO) nanopowders have been prepared by high energy ball-milling for various spans of mill time (3-18 h). The morphology and crystal structure of the prepared ZnO powder were characterized by scanning electron microscope and X-ray diffraction. The ZnO thick films were then used to construct a gas sensor for O,O-dimethyl dithiophosphate of diethyl mercaptosuccinate (malathion) at different operating temperatures. The sensor response at 100 ppm of malathion was found to reach a maximum as large as 80 at 6 h of high energy ball-milling, four times larger than that found for ethanol. Scanning electron microscope observation of the granular state and pore size distribution analyses indicated that increasing high energy ball-milling time gave rise especially to an increase in the volume of pores in the pore size range of 6-35 nm. It is suggested that such a change in nanostructure is responsible for the marked promotion of the response to malathion.