Nanochannel Engineering in Metal–Organic Frameworks by Grafting Sulfonic Groups for Boosting Proton Conductivity

Abstract

Constructing highly proton-conducting metal−organic frameworks (MOFs) remains a difficult challenge. Hence, we developed an effective nanochannel engineering strategy by grafting sulfonic-abundant benzene-1,3,5-trisulfonic acid (BTSA) onto the Zr 6 -clusters of PCN-222 to act as a proton-conducting intensifier. Although the introduced BTSA dramatically reduced the pore volume, the resultant MOF (PCN-222-BTSA) exhibited strong water affinity and thus significantly enhanced water uptake at low RH values, reaching up to an almost equivalent water adsorption capacity at a high RH value compared with the capacity of pristine PCN-222. Benefiting from the enhanced water adsorption behavior and the proton-donating capability of sulfonic groups, PCN-222-BTSA displayed 2−3 orders of magnitude higher proton conductivity than pristine PCN-222. Our work is the first to report on postsynthetic modification in the nanochannel of MOFs for proton conduction, which demonstrates a strategy to design functional MOFs with abundant sulfonic groups and provides a bright avenue for constructing proton-conducting materials.

A Porous Sulfonated 2D Zirconium Metal–Organic Framework as a Robust Platform for Proton Conduction

“…Except for the amino acid linker containing NH 3 + acidic group [24] and the terephthalate functionalized with COOH groups, [25,26] the rest of such MOFs contains sulfonated terephthalates, [19,20,[26][27][28] or sulfonated naphthalene-2,6-dicarboxylates, [29][30][31] or else postsynthetically incorporated sulfonic acid. [32] It is worthy of note, however, that there are not any 2D Zr-MOFs among them, and none of the mentioned 3D Zr-MOFs is proton conductive under anhydrous conditions, either. The only examples of anhydrous conduction among Zr-MOFs were reported for UiO-66 based composites with graphene oxide or chitosan [33,34] and for UiO-67 infiltrated with imidazole.…”

“…In the literature there are just a few recent reports of successful incorporation of terminal acidic groups into zirconium‐based backbones followed by studies of their proton conduction (Table S1, Supporting Information). Except for the amino acid linker containing NH 3 + acidic group [24] and the terephthalate functionalized with COOH groups, [25,26] the rest of such MOFs contains sulfonated terephthalates, [19,20,26–28] or sulfonated naphthalene‐2,6‐dicarboxylates, [29–31] or else post‐synthetically incorporated sulfonic acid [32] . It is worthy of note, however, that there are not any 2D Zr‐MOFs among them, and none of the mentioned 3D Zr‐MOFs is proton conductive under anhydrous conditions, either.…”

A Multifunctional Co-Based Metal–Organic Framework as a Platform for Proton Conduction and Ni trophenols Reduction

“…Metal–organic frameworks (MOFs) have the well-defined structural information, rich adjustable porosity, and modifiable features of functional pore cages/channels, and thus MOFs have been developed as one of the most promising candidates as proton conduction materials. − Especially, the advantages of MOFs can help us to understand deeply the proton conduction mechanism and provide theoretical guidance for the design of novel MOF proton conductors. − At present, there are two main strategies that can be adopted to improve the proton conductivity of MOFs. − The first method is to introduce acid functional groups (e.g., free carboxylate or sulfonic groups) into the MOF skeletons, , and the second strategy is to load functional guest molecules (e.g., triazole, imidazole, and ammonium cation) as proton carriers into the pores of MOFs . As a class of excellent proton carrier, the encapsulation imidazole (Im) molecule into MOFs can promote the proton conductivity of MOFs .…”

“…20−22 At present, there are two main strategies that can be adopted to improve the proton conductivity of MOFs. 23−25 The first method is to introduce acid functional groups (e.g., free carboxylate or sulfonic groups) into the MOF skeletons, 26,27 and the second strategy is to load functional guest molecules (e.g., triazole, imidazole, and ammonium cation) as proton carriers into the pores of MOFs. 28 As a class of excellent proton carrier, the encapsulation imidazole (Im) molecule into MOFs can promote the proton conductivity of MOFs.…”

Post-synthesis functionalization of ZIF-90 with sulfonate groups for high proton conduction

“…However, the acidic groups are particularly prone to deprotonation and participate in the coordination with metal ions, resulting in a significant change in acidity, and the proton conductivity of obtained MOF is much lower than expected. 5 Therefore, only a few examples of MOFs containing free –SO 3 H groups have been reported until now, 6 although the –SO 3 H group is considered to be one of the best for proton conduction.…”