理论与实验研究典型VOCs在Au/TiO2@CNTs上的吸附、可见光催化降解及其协同机理

This project aims to develop a novel environmental-friendly Au/titanium dioxide@carbon nanotubes (Au/TiO2/CNTs) composite photocatalyst capable of effective adsorption and subsequently rapid degradation as well as mineralization of low concentration atmospheric volatile organic compounds (VOCs). CNTs have relatively high adsorption capacities and will adsorb and concentrate atmospheric VOCs even in the extremely low concentration, and Au/TiO2 has the visible hight photocatalytic capability to decompose VOCs. The adsorption characteristic of VOCs onto the interface of CNTs as well as Au/TiO2@CNTs photocatalyst, the surface combination morphology as well as the interfacial transfer and the adsorption mechanism of VOCs onto the composite photocatalyst surface will be systematically probed by using temperature-programmed desorption of VOCs, in situ analysis by Fourier transform -infrared spectrometer (FT-IR) and the theoretical modeling. Furthermore, the photocatalytic degradation kinetics of VOCs onto the Au/TiO2@CNTs surface will be investigated, and both the theoretically calculated values and the degradation intermediates obtained from GC-MS will be collectively utilized to illustrate the mechanistic aspects of visible light photocatalytic degradation process. The relationship between the structure of photocatalyst, the adsorption capacity of the catalyst and the photocatalytic degradation efficiency, as well as the nature why the photocatalytic degradation efficiency of VOCs is enhanced by combining Au/TiO2 with CNTs together will be also investigated. The outcome of this project will certainly advance the fundamental knowledge of related disciplines. It will significantly help us to full insight into the role of VOCs in the global climate change and the environmental geochemical cycle, as well as the role in the processes of the adsorption, transformation and degradation of VOCs onto the environmental mineral surfaces in field sites. Particularly, the success of the proposed project will also bring considerable socioeconomic benefit to human beings since the project concerns a vitally important field - waste gas treatment.

本项目将碳纳米管(CNTs)对低浓度挥发性有机物(VOCs)有效吸附富集作用和Au/TiO2可见光催化降解矿化作用相结合,研制一种适合于低浓度VOCs降解的高效环境友好型Au/TiO2@CNTs复合光催化剂。采用典型VOCs程序升温吸附-脱附法、原位傅立叶-红外分析与理论计算模拟相结合的手段，研究典型VOCs在CNTs和Au/TiO2@CNTs上的界面吸附、催化剂表面结合形态和界面迁移等；探讨典型VOCs在Au/TiO2/CNTs上吸附和降解动力学，研究其吸附机理与降解反应途径，并结合理论模拟数据对其吸附与降解动力学及其机理进行验证；探讨催化剂结构特征、吸附和光催化降解效率之间关系，阐明CNTs负载对VOCs降解效率提高的本质原因。项目的成功实施对于了解VOCs在全球气候变化和环境地球化学过程中活性矿物界面吸附、迁移转化及降解过程及脱毒机制、提高人体健康水平，均具有重要理论与现实意义。

大气环境中VOCs污染问题越来越受到人们的关注。本项目主要成果如下：①(a)结合浸湿包覆、水热法生长和光还原方法，将Au纳米粒子负载在TiO2纳米线包覆的多孔层次碳纤维纸上，制得三元复合材料(Au/TiO2 NWs@CFP)。苯乙烯气体的光催化降解实验显示：可见光照射时，Au/TiO2 NWs@CFP表现出优良的光催化活性和光催化稳定性。(b)以微纳米气泡为软模板，利用原位自组装和原位光还原的方法获得了稳定复合结构的Au/TiO2@CNTs三元光催化材料。基于响应面的实验结果分析表明，各试验参数中反应温度是影响复合催化剂降解苯乙烯的效率和矿化率的关键的因素，较高的反应温度有利于获得稳定高效的苯乙烯降解效率和矿化率。②(a)采用理论计算研究了苯乙烯在(TiO2)n分子簇表面的吸附机理和•OH介导的光催化降解机理。发现苯乙烯更易以侧链乙烯基吸附在分子簇表面。吸附的苯乙烯容易被•OH攻击生成乙烯基-OH-加成产物。(b)理论计算研究了典型挥发性有机物苯乙烯在矿物颗粒物表面非均相反应，结果表明苯乙烯以范德华力和氢键相互作用吸附在SiO2周期表面和分子簇上。苯乙烯和矿物颗粒Si(OH)4上的•OH的反应机理在气相中是基本相同的。(c)开展了典型含羰基类VOCs在锐钛矿(001)表面的吸附的理论化学研究，发现含羰基类VOCs，如乙醛，丙酮与乙酸甲酯等很容易通过羰基与催化剂表面Ti5c原子作用吸附到锐钛矿(001)表面。(d)开展了•OH引发的苯乙烯氧化反应形成二次有机气溶胶可行性的理论研究，发现•OH与苯乙烯的大气反应过程中存在OH加成和H提取反应通道，而加成反应更容易发生。在NO含量较高的区域，大气中的过氧自由基IMOO将很快与高浓度NO反应产生硝酸酯类，而硝酸酯类是SOA的组成部分。目前相关研究内容发表SCI论文22篇。本项目的成功实施可以促进了解VOCs 在全球气候变化和环境地球化学过程中活性矿物界面吸附、迁移转化及降解过程及脱毒机制、提高人体健康水平，均具有重要理论与现实意义。