Conductive Metal–Organic Frameworks as Ion-to-Electron Transducers in Potentiometric Sensors

Abstract

This paper describes an unexplored property of conductive metal-organic frameworks (MOFs) as ion-to-electron transducers in the context of potentiometric detection. Several conductive two-dimensional MOF analogues were drop-cast onto a glassy carbon electrode and then covered with an ion-selective membrane to form a potentiometric sensor. The resulting devices exhibited excellent sensing properties toward anions and cations, characterized by a near-Nernstian response and over 4 orders of magnitude linear range. Impedance and chronopotentiometric measurements revealed the presence of large bulk capacitance (204 ± 2 μF) and good potential stability (drift of 11.1 ± 0.5 μA/h). Potentiometric water test and contact angle measurements showed that this class of materials exhibited hydrophobicity and inhibited the formation of water layer at the electrode/membrane interface, resulting in a highly stable sensing response with a potential drift as low as 11.1 μA/h. The property of ion-to-electron transduction of conductive MOFs may form the basis for the development of this class of materials as promising components within ion-selective electrodes.

Origin of the Chemiresistive Response of Ultrathin Films of Conductive Metal–Organic Frameworks

“…The rise of electrically conductive metal–organic frameworks (MOFs) has positioned these coordination frameworks, traditionally considered insulating, as promising alternatives to classical conductive materials for the development of electronic devices . The combination of high crystallinity, chemical versatility, and porosity with electrical conductivity makes them appealing candidates for energy storage platforms, field‐effect transistors (FETs), Schottky barrier diodes, thermoelectrics, resistive random‐access memories, rectifiers, or ion‐to‐electron transducers . Besides the search for new materials, research efforts have centered in gaining chemical control over their design to optimize the electrical conductivity.…”

Conductive Metal–Organic Frameworks: Design, Synthesis, and Applications

“…There have been many reports about MOFs‐modified GCEs for electrochemical sensing. [ 186–190 ] For example, Hosseini et al fabricated a hydrazine electrochemical sensor by immobilizing AuSHSiO 2 nanoparticles (NPs) on CuMOF. [ 186 ] The sensor exhibited good electrocatalytic activity toward the oxidation of hydrazine in a buffer solution at pH = 7.0.…”

“…Recently, the application of 2D conductive MOFs in potentiometric detection was illustrated by Mirica’s group, as shown in Figure a,b. [ 188 ] They achieved potentiometric determination of K + and NO 3 − ions by integrating several 2D conductive MOFs (Ni 3 HHTP 2 , Cu 3 HHTP 2 , and Co 3 HHTP 2 ) into solid‐state potentiometric devices (coated with ion‐selective membrane). The sensors exhibited excellent performances including near‐Nernstian behavior (54.1–58.2 mV s −1 ) and high sensitivity to K + and NO 3 − of 6.31 ± 0.01 × 10 −7 m and 5.01 ± 0.01 × 10 −7 m , respectively (Figure 15c).…”

Solid-Contact Ion-Selective Electrodes: Response Mechanisms, Transducer Materials and Wearable Sensors

“…The oxygen vacancy increased the electronic conductivity and the EDL capacitance, leading to high stability. In addition to the high surface area carbon materials, metal-organic frameworks (MOFs) [73] with high porous characteristic were first implemented as ion-to-electron transducer by Mirica and coworkers ( Figure 7F). The material was synthesized by interconnection of 2,3,6,7,10,11-hexahydroxytriphenylene-HHTP and Ni, Cu, or Co nodes in a Kagome lattice.…”