Sulfonate-Grafted Metal–Organic Framework─A Porous Alternative to Nafion for Electrochemical Sensors

Abstract

Nafion, a polymer containing negatively charged sulfonate groups, is commonly used as a thin film cast on the electrode to adjust the selectivity of complicated electrochemical reactions involving charged reactants or analytes in the electrochemical sensing and electrolytic systems. Herein, a highly porous and chemically stable metal–organic framework (MOF) with enriched sulfonate groups in its pores is synthesized by performing the postsynthetic immobilization of the sulfonate-based ligand within a zirconium-based MOF, MOF-808, and the resulting sulfonate-grafted MOF (SO3-MOF-808) is proposed as a “porous Nafion”an appealing alternative to the conventional Nafion coating for modulating the selectivity of electrochemical reactions. As a demonstration, the electrochemical sensing of dopamine (DA), which usually suffers from interference caused by the oxidation of the coexisting negatively charged ascorbic acid (AA) and uric acid (UA), is implemented. With the use of the SO3-MOF-808 thin film deposited on the active electrode surface, both the current signal for DA oxidation and the selectivity toward the oxidation of DA against those of AA and UA remarkably outperform those achieved by the Nafion thin film with an optimized film thickness. Findings here suggest the new role of such sulfonate-grafted MOFs as an advanced alternative to Nafion in a range of electrochemical sensing systems and other complicated electrochemical reactions.

Sulfonate-Functionalized Two-Dimensional Metal–Organic Framework as a “Dispersant” for Polyaniline to Boost Its Electrochemical Capacitive Performance

“…ZrBTB was synthesized by serving benzoic acid as the modulator, , followed by the removal of coordinated benzoate from the 2D Zr-MOF by using the DMSO/HCl mixture. , The details of synthetic procedures can be found in our recent work . The procedure for installing sulfoacetic acid on the ZrBTB sheets was slightly modified from that reported recently for another Zr-MOF . First, 200 mg of ZrBTB, 169 mg of sulfoacetic acid, and 20 mL of DMF were placed in a sealed vial.…”

“…After sonication for 5 min, the mixture was heated in an oven at 60 °C for 18 h. After cooling the mixture to room temperature (RT), 30 mL of fresh DMF was used to wash the solid three times to remove the unreacted chemicals. Afterward, the solvent-exchange process with acetone and the activation process were performed, similar to those reported previously; , the resulting solid was designated as “ZrBTB–SO 3 .…”

“…In this study, the sulfonate-based ligand, sulfoacetic acid, was installed on the hexa-zirconium nodes of the 2D ZrBTB via solvent-assisted ligand incorporation (SALI), , and the resulting 2D MOF (ZrBTB–SO 3 ) was utilized as the “dispersant” during the in situ polymerization of AN (see Figure ). The use of SALI to immobilize sulfoacetic acid within another 3D Zr-MOF has been reported in our recent work . During the polymerization performed in the acidic aqueous solution, the AN monomer can be acidified to form the positively charged anilinium, and the sulfoacetate ligand immobilized on 2D MOF sheets can be deprotonated to generate the negatively charged sulfonate group .…”

Stable and Electrochemically “Inactive” Metal−Organic Frameworks for Electrocatalysis

“…Very recently, our group also utilized the similar ion-gating effect of Zr-MOFs to modulate the reaction rates and selectivity of electrochemical sensing reactions. [30] The idea is illustrated in Figure 3. The anionic sulfonate group was immobilized into the entire porous structure of another Zr-MOF with a larger pore size, MOF-808, and such a MOF thin film was coated on the surface of the graphene oxide-based electrode that can electrocatalyze the oxidation of dopamine (DA).…”

Synthesis of Phosphovanadate-Based Porous Inorganic Frameworks with High Proton Conductivity

“…The performance and durability of these fuel cells greatly rely on the proton exchange membranes employed. Although Nafion is commonly used as a proton exchange membrane material and exhibits excellent performance, its high price, complicated manufacturing process, and fluorine content hinder rapid advancement. − In addition, the ambiguity of Nafion’s structural properties makes it difficult to deeply understand the proton conduction mechanism . Consequently, there is a growing research focus on the exploration of crystalline proton-conducting materials with well-defined structures and high efficiency.…”