Highly Electroconductive Metal-Organic Framework: Tunable by Metal Ion Sorption Quantity.

Abstract

This study has developed a simple and innovative approach to design a metal-organic framework (MOF) with tunable conductivity. The in situ amine functionalized TMU-60 [Zn(OBA)(L*)·DMF] has the potential of converting to a conductor due to the selective and fast sorption of cadmium ion. In order to precisely monitor the cadmium penetration to the framework pores, in addition to full kinetic and thermodynamic studies of sorption, the time-dependent effects of Cd(II) penetration to MOF pores was taken by fluorescence and electrochemical methods. The results obviously prove that the conductivity of the structure can be adjusted by changing the Cd exposure time and the quantity of ion sorption. The presence of cadmium ions can enhance the ability of the framework to pass electrons through its constituents. Even though the porosity of the structure remains to a certain extent, the achieved tunable and highly stable electrical conductivity is provided by sorption of metal ions. More importantly, the conductivity has been improved from 53 × 10-6 to 1.8 × 10-2 S·cm-1 for TMU-60 and TMU-60-Cd compressed pellet (room temperature), respectively. The mechanism of charge transport through the pellet is proposed to be a hopping mechanism between metal nodes and localized Cd(II) after sorption, which is supported by chronoamperometry measurement. A fit of the time-dependent data to the Cottrell equation gave a charge-transport diffusion coefficient of 1.6 × 10-10 cm2/s throughout the structure. This novel approach not only enhances the conductivity of the MOF but also allows adjusting the conductivity according to the desired applications.