The Synthesis And Gas/Humidity Sensing Performance Of ZnO Composite Hierarchical Structure

With the rapid development of nanotechnology and the maturation of nanomaterial preparation processing,gas and humidity sensors based on ZnO nanocomposites have attracted much attention.The method to enhance the sensing property has been a new research hotspot of this field.In this paper,we focused on the controlled synthesis,modification and compositing of two-dimensional ZnO,and synthesized three kinds of ZnO nanosheets composite hierarchical structures.The gas and humidity sensing performances of the obtained ZnO structures were studied,and the enhancing mechanisms of sensing performance were analyzed further.The major research achievements we obtained are as follows:1.Graphene quantum dots(GQDs)-ZnO nanocomposites with different proportions were synthesized by using a simple two-step method,and their morphologies and structures were characterized.The results showed that the GQDs-ZnO nanocomposites had uniform size and good dispersion.The gas sensing performance was studied by fabricating the gas sensors with nanocomposites,and the results showed that the sensor based on 1.0%GQDs-ZnO nanocomposite exhibited a high sensitivity to dimethylamine at the lower optimum operating temperature.The sensitivity to 200 ppm dimethylamine at 160℃ reached196.03,which was approximately 3.2 times as that of pure ZnO-based gas sensor under the same conditions.The enhancement of gas sensing performance toward dimethylamine can be attributed to the additional resistance modulation from the modification of GQDs,the located p-n heterojunctions and the additional active sites for gas adsorption on the GQDs-ZnO interface.2.2D ZnO@3D CF nanocomposite was synthesized by growing two-dimensional ZnO nanoarray on three-dimensional foamy carbon basis with hydrothermal method.The gas sensing performance of the nanocomposite and the impact from heating treatment temperature were investigated.The testing results showed that the 2D ZnO@3D CF-250 nanocomposite calcinated at 250℃ exhibited best gas sensing performance.At the optimum operating temperature 120℃,it possessed relatively high sensitivity,short response-recovery time,good selectivity and stability to ethanol.The gas sensing performance enhancement of2 D ZnO@3D CF nanocomposite is mainly due to the large specific surface area,the high porosity of the material and the enhancement of the migration rate of free electrons in the nanocomposites with CF as the supporting material,which could provide a theoretical support to the design of gas sensors operating at low and room temperatures.3.CuO and ZnO nanosheets were synthesized with hydrothermal method,and achieved a 2D CuO-2D ZnO nanocomposite by mixing them with various molar ratios.The structure and the humidity sensing characteristics of the composite were investigated.Compared with the pure phase CuO and ZnO,the humidity sensors based on CuO-ZnO exhibit highersensitivity,shorter response and recovery time,smaller hysteresis,and better reproducibility in the relative humidity range of 12%-97%.The composite CuO:ZnO with 1:8 molar ratio showed the best response.The impedance decreased by about 4 orders of magnitude along with the relative humidity increasing from 12% to 97%,and the response time was only 3 s.The CuO-ZnO p-n heterojunctions were considered to be the main reason for enhancing the humidity sensing property.