| As a common reagent,acetone is widely used in industry and experiments.Prolonged exposure to high concentrations of acetone can cause anesthesia in the central nervous system and irritate the eyes,nose,and throat.In addition,acetone gas in exhaled breath is a potential biomarker for detecting diabetes.Therefore,acetone gas monitoring is of great significance to human health.ZnO,an n-type semiconductor with advantages of a wide band gap（3.37 e V）,a large exciton binding energy（60 me V）,a high electron mobility,and a high chemical and thermal stability,has been used as the basic for acetone sensing material.However,there are still many limiting factors for the development and application of ZnO-based sensors,such as high operating temperature,low sensitivity,and poor selectivity.Therefore,it is necessary to further improve the acetone sensing properties of ZnO nanomaterials to meet practical application requirements.In this paper,ZnO nanostructures in different morphologies,Pr6O11modified ZnO nanorods,and Co3O4 modified flower-like ZnO hierarchical structures were synthesized by a hydrothermal method,and the effects of morphology,microstructure,and metal oxide surface modification on the acetone sensing performance of ZnO nanomaterials were explored.The acetone sensing characteristics of ZnO disk pairs,flower-like and walnut-like hierarchical structures,the optimal ratio of Pr6O11 and Co3O4 surface modification are given,and the enhanced sensing mechanism is analyzed from the perspectives of gas diffusion,surface reaction and internal conduction.The main conclusions are as follows:（1）ZnO disk pairs,flower-like,and walnut-like hierarchical architectures were prepared by varying the relative amount of citric acid,Na OH,and zinc acetate dihydrate during the hydrothermal process.At the lowest prime working temperature（210℃）,the ZnO flowers exhibited the highest gas response（23.5-100 ppm）,stability,and selectivity towards acetone due to the highest degree of（001）facet exposure and Schottky barrier height,largest BET specific surface area and BJH average pore size.At the same temperature,the ZnO walnuts displayed the shortest response/recovery time（3/7 s）and lowest limit of detection（49.5 ppb）due to the highest content of surface oxygen vacancy and high reactivity of adsorbed O2-ions;the ZnO disk pairs showed unique selectivity towards ethylene glycol monomethyl ether due to the highest degree of（100）facet exposure and smallest BJH average pore size.Replacing Zinc acetate dehydrate by Zinc nitrate hexahydrate improved the acetone sensing performance of the ZnO flowers in terms of response value,stability,and selectivity at the expense of a higher LOD and slower recovery speed.（2）Pr6O11 nanoparticles modified ZnO nanorods were prepared by a hydrothermal method.Among all sensors with the mole ratios of Pr/Zn as 0,0.03,0.05,and 0.1 the Pr6O11-loaded ZnO sensor with Pr/Zn as 0.05 exhibited the highest gas response（47.7）to 100ppm acetone with relatively high repeatability,stability and selectivity at the prime working temperature of 190°C.The improved sensing performance can be ascribed to the larger electron depletion region and higher Schottky barrier height in the ZnO nanorods caused by the electron transfer from ZnO to Pr6O11 across the Pr6O11/ZnO interface.（3）The flower-like ZnO hierarchical structure was modified by Co3O4 nanoparticles by different degrees through hydrothermal synthesis.Co3O4 nanoparticle modification reduces the optimal operating temperature of ZnO sensors.Among the sensors with 0,0.03,0.05,and0.1 Co molar content in metal ions,the sensor with 0.03 mol Co had the largest gas response（48.6）to 100 ppm acetone at the optimal operating temperature（160°C）.The enhanced acetone response is attributed to the p-n heterojunction effect between Co3O4 and ZnO,the catalytic and high oxygen adsorption ability of Co3O4. |
