Solvothermal synthesis of ZnO nanostructures and their morphology-dependent gas-sensing properties.

Single-crystalline ZnO nanostructures were synthesized by solvothermal method using methanol as solvent. The effect of counterions of zinc salts (nitrate, acetate, and chloride) on the morphology of ZnO nanostructures was investigated. ZnO nanorods (NRs) were formed for all kinds of zinc salts except zinc chloride, where nanoparticles (NPs) were formed. The length and width of ZnO NRs were 100-150 nm and 20-25 nm, respectively, whereas NPs were 20-25 nm in diameter. Replacing methanol to ethanol generated only NRs for all kinds of zinc salts and they were about 10 times larger than those in methanol. The effect of morphology on sensing property was investigated by comparing their response. ZnO NRs showed very high response as compared to ZnO NPs for NO2 and vice versa for CO, although the surface area of ZnO NPs (42.83 m(2)/g) was much higher than those of ZnO NRs (17.6 m(2)/g). The response of ZnO NRs was 30 times higher than those of NPs for NO2 gas, whereas 4 times lower for CO gas. The maximum response of as prepared ZnO NRs was 44.2 to 50 ppm of NO2 gas at 300 °C. A relationship between morphology and interelectrode gap was established. It was demonstrated that the number of grains present between interelectrode gaps has significantly affected the response.