A Metal–Organic Framework-Based Material for Electrochemical Sensing of Carbon Dioxide

Abstract

The free primary hydroxyl groups in the metal-organic framework of CDMOF-2, an extended cubic structure containing units of six γ-cyclodextrin tori linked together in cube-like fashion by rubidium ions, has been shown to react with gaseous CO2 to form alkyl carbonate functions. The dynamic covalent carbon-oxygen bond, associated with this chemisorption process, releases CO2 at low activation energies. As a result of this dynamic covalent chemistry going on inside a metal-organic framework, CO2 can be detected selectively in the atmosphere by electrochemical impedance spectroscopy. The "as-synthesized" CDMOF-2 which exhibits high proton conductivity in pore-filling methanolic media, displays a ∼550-fold decrease in its ionic conductivity on binding CO2. This fundamental property has been exploited to create a sensor capable of measuring CO2 concentrations quantitatively even in the presence of ambient oxygen.

Biologically derived metal organic frameworks

“…[203] It is shown that the diffusion of CO2 into the extended framework of CD-MOF-2 resulted in the formation of alkyl carbonic acid functions on the γ-CD, by covalent bonding to non-coordinated free primary hydroxyl groups, affording CA-CDMOF-2. [204] While there has been a lot of data on CO2 sequestration, there has been only one report using colorimetric sensing, and no reports of electrochemical sensing of CO2 by bioMOFs and also in MOFs. [204] The authors employed electrochemical impedance spectroscopy to measure the changes in proton conductivity, and after observing a large drop in conductivity (approximately 550 fold) following infusion of CO2 in CDMOF-2, associated this with the impediment in motility of free protons.…”

“…[204] While there has been a lot of data on CO2 sequestration, there has been only one report using colorimetric sensing, and no reports of electrochemical sensing of CO2 by bioMOFs and also in MOFs. [204] The authors employed electrochemical impedance spectroscopy to measure the changes in proton conductivity, and after observing a large drop in conductivity (approximately 550 fold) following infusion of CO2 in CDMOF-2, associated this with the impediment in motility of free protons. [204] Decrease in the conductivity of CA-CDMOF-2 can be attributed to the loss of coordinated hydroxide that catalyzes the deprotonation of the methanolic medium, blocking of hydrophilic triangular shaped β-windows, therefore decreasing the mass transfer of the intermedium molecules.…”

“…[204] The authors employed electrochemical impedance spectroscopy to measure the changes in proton conductivity, and after observing a large drop in conductivity (approximately 550 fold) following infusion of CO2 in CDMOF-2, associated this with the impediment in motility of free protons. [204] Decrease in the conductivity of CA-CDMOF-2 can be attributed to the loss of coordinated hydroxide that catalyzes the deprotonation of the methanolic medium, blocking of hydrophilic triangular shaped β-windows, therefore decreasing the mass transfer of the intermedium molecules. [204] Carboxylation occurs primarily in these windows as they are the only location of uncomplexed, primary alcohol functions.…”

“…[204] Decrease in the conductivity of CA-CDMOF-2 can be attributed to the loss of coordinated hydroxide that catalyzes the deprotonation of the methanolic medium, blocking of hydrophilic triangular shaped β-windows, therefore decreasing the mass transfer of the intermedium molecules. [204] Carboxylation occurs primarily in these windows as they are the only location of uncomplexed, primary alcohol functions. [204] CDMOF-2 was reported as having a high degree of reversibility, which occurs rapidly under mild conditions, liberating sequestered CO2.…”

Smart organometallic polymer platforms for redox sensing and as metal nanopatricle foundry

“…The CO 2 sensors that were fabricated based on this principle were capable of measuring CO 2 concentrations quantitatively. 161 Figure 2.25 also shows the cyclic change of conductivity of the CD-MOF with sequential CO 2 absorption and desorption. The plot of average conductivity value vs. CO 2 concentration shows that the sensitivity of the conductivity change is relatively high at low CO 2 concentrations.…”