Preparation And Gas Sensing Properties Of SnO₂-based Nanomaterials

Semiconducting metal oxides as gas sensing materials have been widely used in detection of toxic gases and vapors.However,the major problems associated with these gas sensors are their unsatisfactory selectivity,high working temperature and long-term stability.So the development of a high selectivity and low power consumption gas sensor based on semiconducting metal oxides has become a main subject in the fields.SnO₂ as a kind of n-type semiconductor materials with a wide band gap has been a commercial gas sensitive element owing to their low cost,long service life.However,the sensitivity and selectivity of SnO₂ gas sensing materials also need to be further improved to meet the higher and higher requirements of the gas detection.This paper has synthesized successfully the solid and hollow SnO₂ nanowires as a base of gas sensitive material,and subsequently,ZnO/SnO₂ and CuO/SnO₂ composited nanostructure materials were obtained through the hydrothermal approach.Then,the influence of annealing time and the proportion of PVP and salt on the formation of hydrothermal composite nanostructure morphology and gas sensitive performance were studied.The specific research work can be divided into four aspects:1.The preparation of solid SnO₂ nanowires by electrospinning method.In the aspect,the effect of the relative air humidity?HR?to the morphology and uniform diameter of SnO₂ nanowires was studied.The dependent of gas response of SnO₂ nanofibers to working temperature was further investigated.It showed that the optimum working temperature of SnO₂ nanofibers was about 375 ?,which had better selectivity to alcohol.2.Preparated the ZnO / SnO₂ hierarchical nanostructures by two step hydrothermal method.First,the ZnO seed layer was grown on SnO₂ nanofibers,and then the ZnO nanowire arrays were grown on the surface of SnO₂ nanofibers by hydrothermal method.The effects of different hydrothermal time on the growth of ZnO / SnO₂ hierarchical nanostructures were also studied by means of XRD,SEM and gas sensing test.It was found that the seed layer treated with 250 ? was most favorable for the growth of SnO₂ / ZnO hierarchical nanostructures.And the ZnO nanometer arrays are dense when the hydrothermal time increases from 2h to 6h.The optimum operating temperature of ZnO / SnO₂ hierarchical nanostructures is 300 ?,the sensitivity to 100 ppm acetone was 20.8.3.The preparation of hollow SnO₂ nanowires by electrospinning method.We explored the mechanism of the formation of hollow SnO₂ nanowires.Different annealing temperature and the proportion of PVP and tin salt have great influence toform good morphology of hollow SnO₂ nanowires,with a 10 ? / min heating rate and the molar ratio of 4:6 PVP and tin salt can prepare the best of morphology and performance of hollow SnO₂ nanowires,and its gas sensitive performance is superior.4.The preparation of CuO/ SnO₂ hollow composited nanostructures.We preparated the CuO/ SnO₂ hollow composited nanostructures and made a gas sensor employed them as sensitive materials successfully.We found that the CuO/ SnO₂ hollow composited nanostructures have high sensitivity at the temperature range from30 to 150 ? for 10 ppm of H₂S gas,and have few sensitivity to 100 ppm of H₂,CO,ethanol,methanol,and acetone gas at the same working condition.The superiority of gas-sensing properties of CuO / SnO₂ hollow nanomaterials is related to their specific heterostructures.Owing to their much larger specific surface area,CuO/SnO₂ hollow composited nanomaterials can provide more surface active sites.