Exploiting the Balance Between Conductivity and Adsorption Capacity/Redox Electrocatalytic Ability In MIL-Based Porous Crystalline Materials for the Electrochemical Response

Abstract

MIL-53(Fe), MIL-101(Cr), and MIL-53(Al) were successfully prepared and selected as promising modifying materials on electrode surface. With the difference in porous textural parameters and metal nodes, the physical characteristics, electrochemical behaviors, and performances towards chloramphenicol (CAP) detecting at each modified electrode were systematically evaluated through cyclic voltammetry (CV) and differential pulse voltammetry (DPV) measurements. Results pointed out that both MIL-53(Fe)/SPE and MIL-101(Cr)/SPE exhibited excellent electrochemical performance through the enhancement of the EASA value, electrocatalytic ability, adsorption capacity (Γ), diffusion ability, and interaction with the CAP molecules, promising to be great materials in fabricating electrode. In which, MIL-101(Cr)/SPE with a huge BET, large pore volume, and good redox electrocatalytic ability of Cr3+ metal nodes significantly enhanced electrochemical response of CAP, despite it was still limited by poor adsorption capacity and diffusion due to the strong water-molecule interaction force of the Cr3+ centers and steric effect of the cramped microporous system. While, MIL-53(Fe) with a much smaller specific surface area and pore volume, it still showed good electrocatalytic activity of Fe3+ ions, along with high interact-ability and large adsorption capacity with CAP through hydrogen bonding and weak interaction force with water. In contrast, MIL-53(Al)/SPE showed poor electrochemical performance due to weak electron conductivity and the lack of electrocatalytic active sites. Obviously, in addition to conductivity, the merits of high adsorption capacity and excellent electrocatalytic activity of unsaturated metal centers need to be maximumly taken advantage of. A perfect balance in terms of the conductivity and adsorption capacity, as well as the electrocatalytic ability in MIL materials still needs to be further preferred in electrochemical sensors.