分子体系中光调控下的分子裁剪研究

The polyolefins in waste plastics and the polyaromatic hydrocarbons (PAHs) generated by burning coal and oil are regarded as the two important factors leading to the current environment pollution. The controllable degradation of the polyolefins and the PAHs would be the best approaches used to completely control the pollution and recycle the resources. Light, as a manipulation means with high selectivity and less pollution, has been applied to control many physical and chemical processes. Here our project is focused on the polyolefins and the PAHs, and their controllable degradation under the manipulation of light will be studied theoretically and experimentally. The research contents mainly include: i) Study the mechanisms of the polyolefins degradation and the optical manipulation, consider the influences of light wavelength and intensity on the production distribution, and suggest a feasible method of the effective and controllable degradation for the polyolefins; ii) Study the generation mechanism of the conjugation-lost states of the PAHs and the optical manipulation, and further achieve the controllable molecular tailoring of the PAHs under the control of laser. The researches of the project are beneficial to deep understanding of the degradation of the polyolefins and the PAHs, and the mechanism of the optical manipulation, which will provide the theoretical and experimental guidance for bringing under control the environment pollution caused by the polyolefins and the PAHs, and also realizing the recycling of the carbon-related resources.

废塑料中的聚烯烃和煤、石油等燃烧产生的稠环芳烃是当前环境污染的两大重要因素。实现聚烯烃和稠环芳烃的可控降解是彻底根治污染、绿色利用资源的最佳途径。光作为调控手段，具有选择性高和无污染的优点，已经被应用于许多物理化学过程的调控。因此，本项目拟选择聚烯烃和稠环芳烃为研究对象，理论和实验研究聚烯烃和稠环芳烃在光调控下的可控降解，主要内容包括：（1）研究聚烯烃的降解机理和光调控机制，考虑波长和光强等对产物结构分布的影响，提出聚烯烃高效可控降解的可行方法；（2）研究多种稠环芳烃失共轭态的产生机理和光调控机制，实现激光调控下稠环芳烃的可控分子裁剪。本项目的研究工作有利于深入理解聚烯烃和稠环芳烃等分子的降解机理和光调控机制，为根治聚烯烃和稠环芳烃导致的环境污染和实现碳资源的循环利用提供指导。

按照本项目提出的研究课题，开展了一系列研究，基本完成了本项目所提出的研究内容。主要的研究成果包括以下三个方面：（1）基于聚烯烃光催化降解机理和控制机制，通过理论和实验结合研究了聚烯烃光催化降解的产物分布及其控制机制。结果表明：聚烯烃裂解产物的主要成分以直链烷烃为主，长链中间碳氢键的断裂能小于端基碳氢键的，因此部分自由基会容易发生分子内H转移，环化和质子转移形成环烷烃，很少一部分会发生β断裂形成烯烃，产物中少部分异构烯烃也可能会经过自由基转移、环烷烃脱氢形成少量芳烃。（2）基于稠环芳烃的失共轭机理和分子裁剪机制，研究了苯和不同稠环芳烃的失共轭态。结果表明苯的基态和第三、四激发态叠加时苯处于失共轭状态，渺位缩合和迫位缩合稠环芳烃外环的芳香共轭性也可以通过态叠加控制。（3）基于超软赝势理论，研究了光催化剂表面调控及其缺陷、复合调控机理和控制机制。研究结果发现，过渡金属对催化剂表面改性与其外层d电子数目存在竞争协调机制；Aun吸附于催化剂载体表面时催化活性增加，且载体金属电负性的差异会导致团簇显示出截然不同的光催化活性；二维层状催化剂的表面缺陷对产物选择性存在先增后减的竞争协调规律。基于本项目的研究成果，我们将继续研究光催化剂改性以及大气灰霾和水污染物的可见光催化降解等，这些研究结果为我们的后续研究奠定了基础。