气敏和光催化功能氧化钨纳米材料的改性设计及机制

Tungsten oxide is an n-type semiconductor with small band gap, which exhibits high sensing response for toxic gases. Tungsten oxide as a visible-light-driven photocatalyst is used for the degradation of organic pollutants. However, pure WO3 is not an efficient photocatalyst due to its high electron-hole recombination rate and the difficulty in reduction of oxygen, but the nanostructural tungsten oxide after modification has grateful potentials for enhancement of gas sensing and photocatalytic activity. Thus, this project focused on the design and modification of the material, and the intrinsic mechanism of the modification to improve the gas sensing and enhance photocatalytic activity, the modified techniques are described as following: The nanostructural WO3 are synthesized by the facial and mild solution-based techniques to control morphology and size of the materials, and enhance the surface to volume ratio, leading to the increase of surface active sites for gas adsorption and reaction; Through doping metal ions or surface modification of other metal oxides to control and change the crystalline structure for enhancement of gas adsorption and reaction; Coupling of WO3 with other metal oxide semiconductors, such as TiO2 or ZnO using different preparation methods efficiently suppressed recombination of the photogenerated electron-hole pairs, making charge separation more efficient, results in enhancement of gas sensing and catalytic activity; The WO3 nanoparticles are synthesized on the surface of grapheme sheets or fabricated into organic polymer/WO3 composites, which reduced the recombination of the electron-hole pairs and enhanced electrons transport due to the synergistic effects of two components, leading to improved photo-conversion efficiency.

n-型半导体氧化钨具有本征非化学计量性和较窄禁带，经改性后提高气敏和光催化活性的潜能巨大。本项目着重研究纳米结构WO3晶体的性能对结构敏感性、改性设计及其机制。采用低温水热和常温超声法合成不同形貌、高比表面的纳米结构WO3；通过掺杂或表面修饰调控其晶体结构，增加表面对气体的吸附和反应活性；在石墨烯骨架上负载或并入WO3，加速电荷迁移；以两种半导体藕合的异质结构调控能带，提高光生电子和空穴的分离；合成有机导电高聚物和WO3的复合材料，发挥有机和无机组分的叠加或协同效应，实现WO3功能材料的最优化应用。采用L-H 反应机理对暂态气敏数据进行模拟，研究传感器的应答和恢复可逆性及传感速率随气体浓度的变化规律；利用基于密度泛函的第一性原理计算材料改性前后的能带结构、态密度和电子布居变化，以揭示WO3气敏和光催化作用机理及其改性的机制，进而用于材料研制过程中的性能预测及结果分析。

n型半导体氧化钨具有本征非化学计量性和较窄禁带，对环境有毒气体(如二氧化氮)有气敏响应并作为光催化和光电催化剂具有巨大潜力，但是，单一的金属氧化物气敏温度高并选择性差，不能满足当前实际需要。本项目采用设备简单、条件温和的溶液基方法，采用硅球、介孔分子筛和金属有机骨架为模板来可控合成不同结构、形貌、大比表面、多孔和结构稳定的三维分级微/纳米结构的金属氧化物，达到“结构优化”，增强气体的吸附、扩散和反应活性；另一方面，对基质材料进行修饰、采用掺杂不同金属元素和与其他半导体金属氧化物进行复合，构建具有n-n 和p-n异质结的复合材料，进一步“功能化”来提高材料对二氧化氮和VOCs气敏性能。为了提高材料的比表面和导电性能，本项目也采用石墨烯与半导体金属氧化物进行杂化提高其气敏性能。.为了研制节能、安全和长寿命的室温气体传感器，采用溶液基的原位化学氧化聚合制备导电高分子，聚苯胺、聚吡咯和聚噻吩及其衍生物；利用各种不同溶液基方法制备半导体金属氧化物，将导电高分子-无机金属氧化物进行杂化，并且用柔性的有机PET薄膜做基质将杂化物负载在基质上构成不同的p-n异质结气敏材料，并研制灵巧的气体传感器能在室温下操作，不仅对环境中有毒气体NO2和挥发性有机化合物在室温下具有高的灵敏度，好的选择性和低的检测极限，而且传感器具有柔性、透明、轻巧、低成本和可携带的特点，为当前发展的可穿戴电子元件打开窗口。对传感器的气敏机制进行了深入讨论，如对n型金属氧化物半导体从空气中氧分子的吸附和在混合气体中吸附氧和目标气体的反应来讨论耗尽层的变化；对p型半导体主要从材料表面孔隙累积层厚度的变化进行讨论；对无机-有机复合气敏材料从他们间的协同效应，p-n异质结界面形成能带弯曲和主载流子耗尽层的变化来讨论其敏感机制。