聚苯胺/TiO2/粘土矿物稳定的Pickering乳液光催化体系的构建及其烯丙位光催化氧化性能研究

Allylic oxidation of olefins plays an important role in the drug development and chemical industry. The traditional method for allylic oxidation often results in severe environmental pollution and energy problems. Photocatalytic oxidation, on the other hand, is a green oxidation method for allylic oxidation of olefins. However, several issues with this method remain to be solved, including the limitation of mass transportation of substrate to the photocatalyst surface, low utilization of solar energy, poor selectivity towards target product, rigorous preparation conditions, difficulty in catalyst recycling, etc. To address these issues, it is proposed in this project to photocatalytic allylic oxidation of olefins in Pickering emulsion stabilized by heterogeneous polyaniline/crystalline TiO2/clay minerals. The heterogeneous polyaniline/crystalline TiO2/clay minerals are facilely constructed at low temperature by using clay minerals as support. The polyaniline/crystalline TiO2/clay minerals-stabilized Pickering emulsion photocatalytic oxidation system has the following advantages: 1) the unique properties inherent in Pickering emulsions will ensure a large active area, the separation of the product from the reactants and the fast and simple procedures employed for demulsifying/re-emulsifying during the photocatalytic allylic oxidation process; 2) growing crystalline TiO2 on clay minerals at low-temperature will guarante intact contour and the crystallinity structure of clay minerals and avoid the growth of TiO2 crystallites; 3) the photocatalytic oxidation range of the polyaniline/crystalline TiO2/clay minerals can be extended to visible light area and the stability of the Pickering emulsion can be adjustable by taking advantage of the visible light absorption and polarity tunability properties of polyaniline; 4) the clay minerals are economically accessible natural materials, which essentially make the Pickering emulsion-based photocatalytic oxidation system technically simple and thus practically applicable. The proposed approach breaks through the limitation of traditional synthesis approach of photocatalytic oxidation catalyst. Furthermore, the photocatalytic allylic oxidation activity of the polyaniline/crystalline TiO2/clay minerals-stabilized Pickering emulsion photocatalytic system are investigated systematically, including the influence of the stability of Pickering emulsion, the clay mineral structure, TiO2 crystal form, polyaniline content and polyaniline polarity to reveal the synergistic photocatalytic oxidation relationship among polyaniline, TiO2 and clay minerals and the photocatalytic allylic oxidation mechanism of the Pickering emulsion based photocatalytic system. This work will provide theoretical and scientific foundation for the construction of novel and efficient polyaniline/TiO2/clay mineral-stabilized Pickering emulsion photocatalytic oxidation system and the study of its photocatalytic allylic oxidation mechanism.

烯丙位氧化在原药开发发挥重要作用，传统的氧化方法存在严重环境污染和能源问题。光催化是烯丙位氧化的绿色工艺，但存在传质困难、目标产物选择性差、太阳能利用率低、催化剂制备条件苛刻、回收困难等问题。针对上述存在的问题，本项目拟结合Pickering乳液固有特性、结晶TiO2低温合成技术和聚苯胺的可见光吸收、极性可调性质，以丰富的粘土矿物为载体，低温制备聚苯胺/结晶TiO2/粘土矿物复合结构，并以此为固体乳化剂，构建烯丙位氧化的Pickering乳液型光催化体系。通过考察粘土矿物结构、TiO2晶型、聚苯胺含量/极性与烯丙位光催化氧化性能之间的关系，揭示聚苯胺、TiO2、粘土矿物的协同光催化氧化规律，并进一步阐明Pickering乳液光催化体系烯丙位光催化氧化机理。本项目将为新型高效的聚苯胺/TiO2/粘土矿物稳定的Pickering乳液光催化体系的研制及其烯丙位光催化氧化机理的研究提供理论基础。

烯烃的烯丙位氧化产物在原药开发中发挥重要作用。针对TiO2在烯烃烯丙位光催化氧化普遍存在的问题，本项目以廉价易得的粘土矿物-埃洛石纳米管和刻蚀疏水性改性粘土纳米管为载体，结合TiO2液相低温合成技术，一步制备聚苯胺/结晶TiO2/粘土纳米管（刻蚀疏水性改性粘土纳米管）。通过反应物比例、反应体系pH值、掺杂酸种类和聚苯胺的掺杂/脱掺杂调控聚苯胺/结晶TiO2/粘土矿物光催化剂中TiO2的晶型/晶粒大小和聚苯胺掺杂态。结果表明： pH为0.5，盐酸为掺杂酸/pH调节剂下制备的聚苯胺/结晶TiO2/粘土纳米管中TiO2的晶型为锐钛矿/金红石混晶结构，聚苯胺为翠绿亚胺型和具有较高的掺杂度；pH为1.5，磷酸为掺杂酸/pH调节剂下制备的复合纳米管中TiO2的晶型为锐钛矿，聚苯胺为醌式结构为主的聚苯胺和具有较低的掺杂度。通过不同浓度的掺杂酸和碱对所制备的聚苯胺/结晶TiO2/粘土纳米管进行“掺杂”和 “脱掺杂”，结果表明：1 M HCl再掺杂的聚苯胺/结晶TiO2/粘土纳米管具有较高的掺杂度。以上述制备的聚苯胺/结晶TiO2/粘土纳米管（刻蚀疏水性改性粘土纳米管）作为固体乳化剂，构建Pickering乳液。结果表明：当以 P-TH/0.5/1%-HCl和C18-H/7.5 h/PT/0.5/1%-HCl（pH 0.5，HCl为掺杂酸/pH调节剂，1%ANI/TTIP体积比下制备的复合纳米管）为固体乳化剂和2:1水/油比下制备的Pickering乳液较稳定。系统地考察了上述构建的聚苯胺/结晶TiO2/粘土复合纳米管（刻蚀疏水性改性粘土纳米管）稳定的Pickering乳液的环己烯光催化氧化性能。结果表明：最佳的催化剂为P-TH/0.5/1%-HCl；最佳的反应条件为2:1 H2O2/环己烯体积比、48h反应时间和和无溶剂。在此最佳催化剂和反应条件下，紫外光和模拟太阳光照射下，环己烯转化率分别为97.62%和95.09%，4,4’-联环己烯醇的选择性分别为95.64%和90.68%。根据上述结果，提出此催化体系高效的烯丙位氧化活性源自聚苯胺/结晶TiO2/粘土纳米管的异质结结构和Pickering乳液光催化体系的协同作用。本项目将为新型高效的聚苯胺/TiO2/粘土矿物稳定的Pickering乳液的研制及其烯丙位光催化氧化机理的研究提供理论基础。