Shim Chul Hwan, Oh Sojin, Lee Sujeong, Lee Gihyun, Oh Moonhyun
Department of Chemistry, Yonsei University 50 Yonsei-ro, Seodaemun-gu Seoul 03722 Republic of Korea
RSC Adv. 2023 Mar 13;13(12):8220-8226. doi: 10.1039/d3ra01222k. eCollection 2023 Mar 8.
Numerous open metal sites and well-developed micropores are the two most significant characteristics that should be imparted to design metal-organic frameworks (MOFs) as effective catalysts. However, the construction of the best MOF catalyst with both these characteristics is challenging because the creation of numerous open metal sites generally triggers some structural collapse of the MOF. Herein, we report the construction of well-structured but defected MOFs through the growth of defected MOFs, where some of the original organic linkers were replaced with analog organic linkers, on the surface of a crystalline MOF template (MOF-on-MOF growth). Additional open metal sites within the MOF-74 structure were generated by replacing some of the 2,5-dihydroxy-1,4-bezenedicarboxylic acid presenting in MOF-74 with 1,4-benzenedicarboxylic acid due to the missing hydroxyl groups. And the resulting additional open metal sites within the MOF-74 structure resulted in enhanced catalytic activity for the cyanosilylation of aldehydes. However, the collapse of some of the well-developed MOF-74 structure was also followed by structural defects. Whereas, the growth of defected MOF-74 (D-MOF-74) on the well-crystallized MOF-74 template led to the production of relatively well-crystallized D-MOF-74. Core-shell type MOF-74@D-MOF-74 having abundant open metal sites with a preserved crystallinity exhibited the efficient catalytic cyanosilylation of several aldehydes. Additionally, MOF-74@D-MOF-74 displayed excellent recyclability during the consecutive catalytic cycles.
大量的开放金属位点和发达的微孔是设计作为有效催化剂的金属有机框架（MOF）时应具备的两个最重要特征。然而，构建同时具备这两个特征的最佳MOF催化剂具有挑战性，因为大量开放金属位点的产生通常会引发MOF的一些结构坍塌。在此，我们报告了通过在结晶MOF模板表面生长缺陷型MOF（其中一些原始有机连接体被类似有机连接体取代）来构建结构良好但有缺陷的MOF（MOF-on-MOF生长）。由于缺少羟基，用1,4-苯二甲酸取代MOF-74中存在的一些2,5-二羟基-1,4-苯二甲酸，在MOF-74结构内产生了额外的开放金属位点。MOF-74结构内产生的额外开放金属位点提高了醛的氰基硅烷化催化活性。然而，一些发达的MOF-74结构的坍塌也伴随着结构缺陷。而在结晶良好的MOF-74模板上生长缺陷型MOF-74（D-MOF-74）导致产生了结晶度相对较好的D-MOF-74。具有丰富开放金属位点且保留结晶度的核壳型MOF-74@D-MOF-74对几种醛表现出高效的催化氰基硅烷化作用。此外，MOF-74@D-MOF-74在连续催化循环中表现出优异的可回收性。
