Tuning the properties of the metal–organic framework UiO-67-bpy via post-synthetic N-quaternization of pyridine sites

Abstract

A new UiO-67-type zirconium metal organic framework (MOF) material UiO-67-bpy-Me (bpy = 2,2-bipyridine-4,4'-dicarboxylic acid, Me = methyl) was prepared by N-quaternization of the pyridine sites in UiO-67-bpy. After N-quaternization, the pristine neutral framework turned cationic while its high thermal and chemical stabilities were primarily preserved. Fast and enhanced anionic dye adsorption was observed in UiO-67-bpy-Me. In addition, despite the decrease in surface area and pore volume, UiO-67-bpy-Me exhibited an evident increase in CO2 uptake compared to UiO-67-bpy. The enhancement was ascribed to the strong interactions between CO2 and the N-quaternized framework. More importantly, as the N-quaternization has changed the electronic structure of the organic linker. UiO-67-bpy-Me showed optical absorption up to ca. 800 nm with a large red shift of 450 nm compared to the pristine UiO-67-bpy (ca. 350 nm). The extended optical absorption may lead to more efficiency in light utilization. A proof-of-concept demonstration showed that UiO-67-bpy-Me could more efficiently catalyze methyl-orange degradation under UV-Vis light irradiation than the pristine UiO-67-bpy. These findings demonstrate that N-quaternization could serve as a facile post-synthetic modification method to tune the chemical/physical properties of free pyridyl-containing MOFs.

Synthetic Strategies and Structural Arrangements of Isoreticular Mixed‐Component Metal–Organic Frameworks

“…By employing mixed‐component strategies, new degrees of freedom in controlling of MOF properties are gained. The incorporation of an additional linker or metal may result in changes of the material properties, like adsorption properties, acid‐base behavior, thermal, and chemical stability, conductivity, flexibility or the emission and absorption of light …”

Rational Design of Catalytic Centers in Crystalline Frameworks

“…It provides a rapid synthetic pathway to introduce new functionalities and can even lead to functionalities otherwise inaccessible. Some recent studies on Zr‐UiO‐based MOFs have highlighted the feasibility of postsynthetic modification on 2,2‐bypyridine units to impart/optimize their properties and functionalities . Du and co‐workers applied a nondestructive postsynthetic modification method through N‐quaternination of pyridine sites to tune the physical and chemical properties of UiO‐67‐bpy MOF .…”

“…Some recent studies on Zr‐UiO‐based MOFs have highlighted the feasibility of postsynthetic modification on 2,2‐bypyridine units to impart/optimize their properties and functionalities . Du and co‐workers applied a nondestructive postsynthetic modification method through N‐quaternination of pyridine sites to tune the physical and chemical properties of UiO‐67‐bpy MOF . Postsynthetic N‐quaternination of pyridine site can be accomplished by heating UiO‐67‐bpy in THF and iodomethane at 100 °C for 72 h. The successful methylation of the N‐pyridine sites in UiO‐67‐bpy was revealed by 1 H NMR and FT‐IR measurements.…”

Secondary amine-functionalised metal–organic frameworks: direct syntheses versus tandem post-synthetic modifications

“…Many functional groups, however, cannot be incorporated directly into MOFs, as they are incompatible with the synthetic conditions. 24 In addition, conversions of azides to triazoles, 25 aldehydes to alcohols 26 and hydrazones, 27 nitro groups to amines, 28 sulfides to sulfones, 29 and halides to nitriles 30 have all been documented, as have methylations, 31 activations of aryl CH groups, 32 thermolysis reactions 33,34 and photolysis reactions. 7,8 PSM involves carrying out a reaction on a pre-formed MOF, converting it into a different MOF.…”