Study On The Fabrication And Gas Sensing Properties Of ZnO/TiO₂Hybrid Nanofibers

As the economy and industry of our nation developing rapidly, our living standardis getting better and better. People concerned about the environment where they livemore and more. The gas sensor is a kind of device that monitor the change ofconcentration of certain gas, semiconductor gas sensor is with a lot of advantages forapplication such as easy to manufacture at relatively low cost and high sensitivity. It iswidely used in the modern life. In this paper, we introduce a fast and easy way toachieve a gas sensor with high response and great selectivity.To achieve TiO₂based brush like ZnO-TiO₂heterojunction nanofibers, we makecombination of two techniques which are very popular today, electrospinning andhydrothermal process.For the first part of this paper, we fabricated the TiO₂nanofibers and study thesensing properties of them. Precursor was made of Ti（OBu）4, PVP, ethanol and glacialacetic acid. By calcining the polymer nanofibers which made from the precursor, thepure TiO₂nanofibers were achieved. The XRD analysis demonstrated that the samplethat we made were anatase type TiO₂, no other impurity was detected. The SEMimages showed the nanofibers have a uniform diameter distribution of about100nmand possess a relatively smooth surface. After fabricated a gas sensor with thismaterial, the gas sensing properties was conducted. The result showed that theresponse to the ethanol gas at20ppm,50ppm,100ppm,200ppm and500ppm was2.04,3.01,4.2,5.5and6.6, respectively. The sensor also got a very satisfied response and recovery time which were about5-10seconds. The most outstanding feature wasthe very high selectivity to the ethanol, almost no response to the other gases we test,such as H₂S, CH₄, C₃H₆O, CO, CH₃OH and C₂H₂.For the second part of this paper, we conducted the as prepared TiO₂nanofiberswith hydrothermal process, which achieved the three dimensional ZnO-TiO₂hierarchical nanostructures. The SEM images revealed that high density of thesecondary ZnO nanorods were dispersed on the primary TiO₂backbones. The XRDanalysis demonstrated that the sample that we made were anatase type TiO₂andhexagonal wurtzite ZnO, no other impurity was detected. After fabricated a gas sensorwith this material, the gas sensing properties was conducted. The result showed thatthe response to the ethanol gas at20ppm,50ppm,100ppm,200ppm and500ppmwas4.1,10.6,13.2,26.1and50.6, respectively. These results indicated that theZnO-TiO₂sensor displayed about2-3and3-8fold enhancement in sensitivitycompared to the pure ones. And still, the gas sensor got fast response and recoverytime which were about5-10seconds. For systematic analysis, the sensitivity values tovarious gases （C2H5OH, H₂S, CH₄, C₃H₆O, CO, CH₃OH and C₂H₂） at500ppm weremeasured and it indicated that the hierarchical ZnO-TiO₂heterostructure was hardlyaffected by the other gases （H₂S, CH₄, C₃H₆O, CO, CH₃OH and C₂H₂） except for theC₂H₅OH.