Enhanced proton conductivity by guest molecule exchange in an acylamide-functionalized metal-organic framework

Proton Conducting Metal-Organic Frameworks (MOFs) via Post Synthetic Transmetallation and Water Induced Structural Transformations

Post Synthetic Modification (PSM) of Metal-Organic Frameworks (MOFs) is a crucial strategy for developing new MOFs with enhanced functional properties compared to their parent one. PSM can be accomplished through various methods:1) modification of organic linkers; 2) exchange of metal ions or nodes; and 3) inclusion or exchange of solvent/guest molecules. Herein, PSM of bimetallic and monometallic MOFs containing biphenyl dinitro-tetra-carboxylates (NCA) are demonstrated. The tetra carboxylate NCA, produces monometallic Cd-MOF-1 and Cu-MOF-1 and bimetallic CoZn-MOF in solvothermal reactions with the corresponding metal salts. The CoZn-MOF undergoes post-synthetic transmetallation with Cd(NO3)2 and Cu(NO3)2 in aqueous solution to yield Cd-MOF-2 and Cu-MOF-2, respectively. Additionally, green crystals of Cu-MOF-1 found to undergo a single-crystal-to-single-crystal (SCSC) transformation to blue crystals of Cu-MOF-3 upon dipped into water at room temperature. These MOFs demonstrate notable proton conductivities ranging from 10-3 to 10-4 S cm-1 under variable temperatures and humidity levels. Among them, Cu-MOF-3 achieves the highest proton conductivity of 1.36×10-3 S cm-1 at 90 °C and 98 % relative humidity, attributed to its continuous and extensive hydrogen bonding network, which provides effective proton conduction pathways within the MOF. This work highlights a convenient strategy for designing proton-conducting MOFs via post-synthetic modification.

A stable Mn(II) coordination polymer demonstrating proton conductivity and quantitative sensing of oxytetracycline in aquaculture

The construction and investigation of dual-functional coordination polymers (CPs) with proton conduction and luminescence sensing is of great significance in clean energy and agricultural monitoring fields. In this work, an Mn-based coordination polymer (Mn-CP), namely, [Mn0.5(HL)] (H2L = HOOCC6H4C6H4CH2PO(OH)OCH3), was hydrothermally synthesized. Mn-CP has a one-dimensional (1D) chain structure, in which uncoordinated -COOH groups can serve as potential sites for fluorescence sensing. Moreover, Mn-CP shows good water and pH stabilities, offering the feasibility for proton conduction and sensing applications. Mn-CP displays comparatively high proton conductivity of 1.07 × 10-4 S cm-1 at 368 K and 95% relative humidity (RH), which is promising for proton conduction materials. Moreover, it can serve as a repeatable, highly selective, and visualized fluorescence sensor for detecting oxytetracycline (OTC). More importantly, Mn-CP reveals an amazing quantitative sensing of OTC in actual samples such as seawater, aquaculture freshwater, soil infiltration solutions, and tap water. This work proves the excellent application potential of dual-functional CPs in the field of clean energy and environmental protection, especially for the fluorescence detection of antibiotics in aquaculture systems.