空间有序异质分级结构ZnO/CuO气敏材料的可控制备及性能研究

Hierarchically structured metal oxides with synergistic effect of the multi-stage, multi-component, multi-dimensional morphology have great advantages in improving the gas sensing performance. But its detection level is on the order of ppm, which cannot satisfy the requirement of toxic gas detection on a scale of <100 ppb in the atmosphere. The factors that are affecting gas sensitivity are as follows:1) high potential barrier between nanostructures and low utilization rate of surface active sites; 2) the positive charge accumulated in the gas sensing reactions obstructing the movement of free electrons to the surface of nanostructures. In this project, the controllable preparation of ZnO/CuO hierarchical structure with p-n heterogeneous and spatial ordered structure is realized based on mechanoelectrospinning. Then the structure and morphology of ZnO/CuO hierarchical structure are optimized, and the gas sensing performance of ZnO/CuO is analyzed. The structure-activity relationship between the structural characteristics and gas sensing performance is revealed. The improvement of gas sensing sensitivity is achieved based on the following two points: 1) The point junctions between spatial ordered structures are increased, and the potential barrier is reduced and the utilization rate of surface active sites increases; 2) The built-in electric field of the p-n heterojunction attracts the accumulated positive charge, which weakens the obstruction during the movement for the free electrons from conduction band to the surface of nanostructures. The results aim to achieve the accurate detection of ppb-scale toxic gas with the hierarchically structured oxide, and provide a reference for the preparation of gas sensor with high sensitivity based on hierarchically structured oxide.

分级结构氧化物以独特形貌形成的多级次、多组分、多维度的耦合协同效应在改善气敏性能方面具有很大优势，但其灵敏度测定气体浓度范围(ppm量级)难以满足大气中有毒气体含量(<100 ppb)的测定要求。原因在于以下问题影响着其气敏灵敏度：1)纳米结构之间的势垒高、表面活性位点利用率低；2)气敏反应中积累的空穴电荷对电子向表面运动具有阻碍作用。本项目拟基于电流体直写工艺实现空间有p-n异质分级结构ZnO/CuO的可控制备，进而优化其结构形貌，测试分析其气敏性能，揭示结构与气敏特性之间的构效关系，基于以下两点提高灵敏度：1)空间有序使顶点接触结构增多，势垒降低，表面活性位点利用率增大；2)p-n结的内建电场可牵制积累的空穴，减弱其对电子向表面运动的阻碍作用。研究成果有望实现分级结构氧化物材料对ppb量级有毒气体的精确测定，为制备高灵敏度分级结构氧化物气体传感器提供可借鉴的思路。

分级结构氧化物材料以其独特的结构形貌形成多级次、多组分、多维度的耦合和协同效应，可极大改善材料气敏性能，已成为纳米氧化物半导体气体传感器中最具优势的一类气敏功能材料。但分级结构氧化物材料气敏性能还没能实现对低浓度(<0.1ppm)有毒气体的测定，其原因在于材料空间分布无序性、高势垒接触位点多、结构表面活性位点利用率低、气敏传感信号的转换功能低等原因限制了其气敏性能的耦合/协同优化效应。本项目通过逐级生长法实现了CuO-ZnO有序异质分级结构的调控制备，建立了材料气敏特性与分级结构特征的关系，揭示了异质分级结构的耦合/协同效应对材料气敏性能的优化原理，实现气敏性能的导向优化，有效减小分级结构之间的势垒，增大纳米结构间顶点接触的形成机率，提高纳米结构表面活性位点利用率。同时在分级结构中引入p-n异质结，利用其内建电场对气敏反应过程中逐渐积累的空穴电荷的牵制作用，减小自由电子向表面运动的阻力，有效提高了材料的气敏性能。最终实现了室温下对超低浓度(<0.01ppm)有害气体(H2S)的超高响应值和优异选择性。本项目的研究成果为分级结构材料的气敏性能的优化提供了实验依据和改善思路。