有序介孔二氧化硅在构建环境pH值响应离子传输通道中的应用及其机制研究

The fabrication of porous scaffolds containing highly ordered and monodispersed nanochannels is attracting increasing interest as an effective route to achieve controlled transport of molecular species in nanoconfined environments. In particular, the generation of interfaces discriminating the transport of ionic species through which the passage of ions can be triggered or inhibited using pH as a chemical trigger has received increasing attention from the mesoporous materials science community. Functional hybrids of polyionic brushes and mesoporous silicas are able to discriminate and modulate the transport of ions while inhibiting the passage of contra-ions over a wide pH range. This methodology is based on grafting porous substrates with ion conducting polymers, thus resulting in the creation of matrices with ion conductive properties and excellent mechanical properties. However, one important drawback of this powerful approach concerns on the framework stability and the macromolecular controllability of the polyelectrolyte confined in the pore. In this study, we describe a feasible approach to fabricate ion conducting hybrid based on the surface-initiated polymerization of pH-sensitive polyionic brushes from ordered mesoporous silica frameworks using reversible addition-fragmentation chain transfer polymerization (RAFT) technology. The RAFT technology can be easily performed in mild and "green" conditions, being compatible with a huge variety of functional monomers and providing an excellent control of the grafted macromolecular characteristics. In the case of pH-sensitive trigger, the pH value and range at which this transition occurs could be tuned by choosing the chemical nature of the polymer. Moreover, we will research the hydrodynamic volume changes of the polyionic chains responding to the electrostatic repulsions of the generated charges (anions or cations). This is the key element of the system. The fabricated polyionic polymers/ordered mesoporous silicas hybrids display proton or hydroxyl ion conductivities. The morphological aspects, chemical stability, and performance of the hybrid assemblies are characterized by a set of techniques including transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, nuclear magnetic resonance and impedance spectroscopy, among others. Versatility and relative ease of preparation are two key aspects that make this approach an attractive alternative for the molecular design and preparation of ion conducting systems.

在保证有序介孔二氧化硅结构完整的前提下，研究如何得到结构稳定和厚度均一的离子型聚合物接枝层，利用离子型聚合物提高特殊类型离子传输效率，构建化学结构稳定、环境pH值响应灵敏、传输效率高、离子迁移机制明晰的智能响应型离子传输通道，是介孔二氧化硅应用领域有待解决的重要科学问题之一。本研究拟利用可逆-加成-链转移可控自由基聚合(RAFT)方法，首先在有序介孔二氧化硅内壁接枝具有不同化学极性、链结构和链长的大分子链，构建pH值响应灵敏的离子高效传输通道。然后以质子和氢氧根离子作为模型阳离子和阴离子，深入研究在不同pH值环境下孔道内接枝聚合物链的结构、介孔孔道形貌和表面化学性质对智能响应、模型离子迁移效率的影响规律，建立理论模型，为解决"如何实现不同离子在微米-纳米级通道中的选择性和高效传输"这一问题提出一种可靠和可行的有机聚合物-无机介孔材料纳米复合材料解决方案。

近年来，有序介孔SiO2以其高比表面积、高反应活性、结构规整和稳定的优异特性，在化学物质的传输、分离和催化等方面应用广泛。其中，在保证有序介孔SiO2结构完整的前提下，赋予其环境响应灵敏、机制明晰、传输可控的化学物质传输功能，作为一个基础理论问题受到研究者重点关注；如何有效构建化学物质的可控传输，在诸如药物控释、生命体监测、智能传感器、离子交换膜等前沿应用中具有重大的研究价值。本项目采用有机/无机复合的方式，在介孔SiO2孔道表面化学接枝具有环境响应特性的聚合物层，赋予介孔SiO2材料pH值和温度双响应功能，构建环境响应灵敏、传输效率高、化学结构稳定、离子迁移机制明晰的金属离子传输通道。.根据研究计划，本项目采用可逆-加成-链转移聚合(RAFT)方法，将在有序介孔SiO2内壁接枝具有不同化学极性、链结构和链长的大分子链，得到结构稳定和厚度均一的离子型聚合物接枝层，利用离子型聚合物提高金属离子传输效率；同时通过选择聚合物单体结构，赋予复合材料本身环境pH值和温度双响应特性，拓宽该类离子传输通道的“开关”应用范围。本项目进一步研究在不同pH值环境下离子通道内接枝聚合物链的结构、介孔孔道尺寸对模型离子迁移效果的影响规律，初步建立理论模型，为“如何实现不同离子在微米-纳米级通道中的选择性和高效传输”这一问题，提出了一类可靠的有机聚合物-无机介孔材料纳米复合离子传输通道解决方案。本项目按计划顺利完成研究内容。