A Post-Synthetic Method for the Construction of Titanium-Based Metal Organic Frameworks and Their Applications

Abstract

Titanium-based metal organic frameworks (Ti-MOFs) have become a hot topic in current materials research due to their excellent photocatalytic activity. However, due to the extremely high reactivity and oxygenophilic properties of Ti ions, oxides and other competing by-products are easily formed during the reaction process, making the synthesis of Ti-MOFs extremely challenging. The research on Ti-MOFs was carried out simultaneously at the early stage of MOFs development, however, after more than two decades of development, only tens of Ti-MOFs have been reported, accounting for an extremely limited proportion of the tens of thousands of MOFs. In order to avoid or reduce the occurrence of titanium ion side reactions, Ti-MOFs are usually synthesized by introducing metal Ti ions into the framework of known MOFs to orientate the synthesis of Ti-MOFs, which is called post-synthetic method (PSM) and is also an effective method to construct Ti-MOF framework. The examples of PSM for constructing Ti-MOFs are systematically investigated and summarized in a timely manner. Firstly, based on the different ways and positions of titanium ion introduction, three routes are classified as ion exchange, ion insertion (introduction of titanium ion at the position of metal nodes or cluster units) and ligand modification (introduction of titanium ion at the position of organic ligands), and the Ti-MOFs constructed by each route are introduced by examples. Subsequently, the design and application of Ti-MOFs constructed by PSM and their composites are discussed. Finally, the current status of PSM-constructed Ti-MOFs is summarized and the future development direction is foreseen. Keywords metal organic framework; post-synthetic method (PSM); titanium; photocatalysis 1 引言 金属有机框架(MOFs)是由金属离子/簇单元通过有 机配体连接形成的一类晶态多孔材料, 具有超高的孔隙 率/比表面积、 孔尺寸和孔环境高度可调节及结构可设计 和可预测性强等优点. 在吸附分离 [1][2][3] 、催化 [4][5][6] 、电子 传输 [7] 和抗菌 [8] 等诸多方面具有潜在的应用前景. 其中, 钛离子具有光活性、低毒性及丰富储量, 使得钛基金属 有机框架(Ti-MOFs)成为 MOFs 的一个重要分支和当前 研究的热点领域之一 [9][10][11][12] .