Microstructure Design, Preparation And Gas Sensing Properties Of Nano-ZnO

Metal-oxide semiconductor gas sensor has been attracted wide attention due toits advantages of high sensitivity, fast response, small size, low energy consumptionand costs, and easy to operate. Metal-oxide semiconductor with pecial hierarchicalstructure and exposing polar crystal face is benefical to improve gas sensingproperties. In this study, different hierarchical structured and exposing polar crystalface ZnO were prepared by hydrothermal and solvothermal methods. Thehydrothermal and solvothermal process and gas sensing properties were discussed,especially, the sensor’s selectivity to acetone.We synthesized0-3hollowspheres,1-3dandelion-like,2-3plate-like hierarchicalZnO by adopting zinc nitrate or zinc acetate as raw material, a certain amount ofsurfactant under certain temperature and hydrothermal time. By selecting the suitablethe molar ratio of carbon source to metal salt, zinc source, carbon source, we obtainedthe0-3hollowspheres ZnO with uniform size and high specific surface area andderived its forming process and acetone gas sensitive properties. The1-3dandelion-like ZnO were synthesized by adjusting the reaction time, the concentrationof reactant, reaction solvent.The possible formation mechanism and gas sensingproperties were investigated. The influence of the concentration of complexing agent,pH value of2-3plate-like ZnO and the acetone gas sensitive performance werediscussed.The gas response, selectivity and the reason for different gas sensing propertieswere analysised from the structure characteristics of three different morphologies.When the concentration of acetone is low (from0.25to40ppm), the sensitivity of0-3hollowspheres ZnO is best among the three sensors and the sensitivity of2-3plate-like ZnO is lowest. When the concentration of acetone is large (from40to100ppm), sensitivity to acetone of1-3dandelion-like ZnO was obviously higher than thatof other two kinds of ZnO.0-3hollowspheres ZnO shows have certain selectivity toacetone.1-3dandelion-like ZnO shows similar response to ethanol and acetone,which indicates higher selectivity to acetone.2-3plate-like ZnO manifests the highestselectivity to acetone. In a word, with the improvement of crystal orientation, that isto say increase the proportion of the exposed (0001) crystal plane, the selectivity toacetone gas increases gradually.The sensitivity mainly depends on the microstructure of materials such asspecific surface area and hierarchical structure, etc. The selectivity to acetone dependson the exposed (0001) crystal plane. Compared with other gases, when the acetoneabsorbs on the polar (0001) and the strength of absorbtion is high, the surfacereconstruction and charge transfer would happen, which will change the band gap of ZnO. Then the conductivity of ZnO would change, which shows high reponse andhigh selectivity to acetone. Therefore, the specific surface area and the proportion ofexposed (0001) crystal plane with structure defect restricted each other. Only if thespecific surface area and the proportion of exposed (0001) crystal plane reach aparticular restriction ratio, does the sensor show better gas sensing performance.