Enhancement of Intrinsic Proton Conductivity and Aniline Sensitivity by Introducing Dye Molecules into the MOF Channel

Abstract

The encapsulation of dyes into metal–organic frameworks (MOFs) has generated a variety of platforms for luminescence, but little attention has been paid to their application in proton conduction. Here, a cationic MOF {{[In3OL1.5(H2O)3]­(NO3)}·(DMA)3·(CH3CN)6·(H2O)30} n (FJU-10, H4L = 4,4′,4″,4‴-(1,4-phenylenbis­(pyridine-4,2,6-triyl))-tetrabenzoic acid, DMA = N,N-dimethylacetamide) was synthesized, and the dye molecule 8-hydroxy-1,3,6-pyrenetrisulfonic acid trisodium salt (HPTS) was further added to the MOF growth solution, but during the reaction, HPTS was nitrated and nitrated HPTS was encapsulated into the FJU-10 to obtain dye@FJU-10. As a result, the intrinsic proton conductivity of dye@FJU-10 is nearly 5 times higher than that of FJU-10 at 90 °C. Dye@FJU-10 exhibits more sensitive fluorescence quenching toward aniline than FJU-10 in DMF solution (the detection limits of FJU-10 and dye@FJU-10 are as low as 0.58 and 0.62 μM, respectively). Here, it is demonstrated for the first time that intrinsic proton conductivity can be effectively improved by encapsulating a nitrated HPTS dye into an MOF.

Applications of MOFs as Luminescent Sensors for Environmental Pollutants

“…Notably, the combination of these guests and LMOFs can further generate the multiple-emitting luminescence, which can be even directly observed by the naked eye in some reports. [33,34] For target detection, the large surface area and inherently porous structures in LMOFs can increase the contact area to enrich the analytes. LMOFs can achieve target sensing when the porosity configuration is matching with the size and shape of the analytes.…”

Metal–Organic Frameworks as a Versatile Platform for Proton Conductors

“…The high surface areas, rich structural tunability, and functional pore surface of MOFs provide great opportunities to load a variety of guest molecules as proton carriers and to systemically modify the proton concentration and mobility within the available spaces ( Scheme ). [ 27–33 ] In addition, the crystalline nature of MOFs endows an opportunity to investigate the proton transport pathway and mechanism, which will provide theoretical guidance for the design and synthesis of novel proton‐conducting materials. Until now, generally including four types (types I to IV) of strategies have been proposed to regulate the proton conductivity of crystalline porous materials.…”

Proton Conductive Zr-Phosphonate UPG-1—Aminoacid Insertion as Proton Carrier Stabilizer

“…Their chemical, thermal and mechanical stability in symbiosis with their intrinsic structural properties (e.g., easy tunable composition and topology and high regular porosity-up to S BET = 7000 m 2 ·g −1 [ 21 , 22 ], allowing the hosting of chemical species) offer the chance to create defined and efficient conductive pathways toward high proton conductivities. Thus, two main strategies have been reported to prepare high proton-conducting MOFs—(i) an intrinsic conductivity coming from the hybrid framework by using phosphonate-, sulfonate- or carboxylate-based coordinating ligands with or without additional free functional groups bearing acidic protons, responsible to tune the p K a values (R = -NH 2 , -SO 3 H, -OH, -CO 2 H) [ 23 , 24 , 25 , 26 ]; and (ii) insertion of proton carriers into the porous network such as counterions and/or neutral acids and dyes (e.g., NH 4 + , H 2 SO 4 , H 3 PO 4 , imidazole, 1 H -1,2,4-triazole and adipic acid, among others) [ 27 , 28 , 29 , 30 , 31 , 32 , 33 ].…”

“…7 orders of magnitude from 10 −10 to 10 −3 S·cm −1 ) by tuning the water adsorption through the insertion of a series of guest molecules into the MOF’s porosity (e.g., dimethylformamide, diethylamine, nitrobenzene, 1,4-dinitrobenzene, pyridine and 1 H -1,2,4-triazole). Recently, Liu and co-workers also assessed the influence of the encapsulation of a dye (8-hydroxy-1,3,6-pyrenetrisulfonic acid trisodium salt) into the microporous cationic indium carboxylate FJU-10, on its proton conductivity [ 29 ]. Both FJU-10 and dye@FJU-10 confine abundant water into their channels, favoring proton conduction.…”