Two Highly Stable Proton Conductive Cobalt(II)–Organic Frameworks as Impedance Sensors for Formic Acid

Metal–organic frameworks (MOFs) have been extensively explored as advanced chemical sensors in recent years. However, there are few studies on MOFs as acidic gas sensors, especially proton conductive MOFs. In this work, two new proton‐conducting 3D MOFs, {[Co3(p‐CPhHIDC)2(4,4′‐bipy)(H2O)]⋅2 H2O}n (1...

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Published in:Chemistry : a European journal 2019-11, Vol.25 (62), p.14108-14116
Main Authors: Liu, Rui‐Lan, Shi, Zhi‐Qiang, Wang, Xin‐Yue, Li, Zi‐Feng, Li, Gang
Format: Article
Language:English
Subjects:
Acids
Carboxylic acids
Chemical bonds
Chemical sensors
Chemistry
Cobalt
Conductivity
Dicarboxylic acids
Formic acid
formic acid sensors
Gas sensors
Humidity
Imidazole
imidazole multicarboxylate-based MOF
Impedance
Metal-organic frameworks
mild temperatures
Organic chemistry
proton conduction
Protons
Relative humidity
Selectivity
Sensitivity analysis
Sensors
Structural analysis
Temperature dependence
Vapors
Water chemistry
Water vapor
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Summary:Metal–organic frameworks (MOFs) have been extensively explored as advanced chemical sensors in recent years. However, there are few studies on MOFs as acidic gas sensors, especially proton conductive MOFs. In this work, two new proton‐conducting 3D MOFs, {[Co3(p‐CPhHIDC)2(4,4′‐bipy)(H2O)]⋅2 H2O}n (1) (p‐CPhH4IDC=2‐(4‐carboxylphenyl)‐1 H‐imidazole‐4,5‐dicarboxylic acid; 4,4′‐bipy=4,4′‐bipyridine) and {[Co3(p‐CPhHIDC)2(bpe)(H2O)]⋅3 H2O}n (2) (bpe=trans‐1,2‐bis(4‐pyridyl)ethylene) have been solvothermally prepared and investigated their formic acid sensing properties. Both MOFs 1 and 2 show temperature‐ and humidity‐dependent proton conductive properties and exhibit optimized proton conductivities of 1.04×10−3 and 7.02×10−4 S cm at 98 % relative humidity (RH) and 100 °C, respectively. The large number of uncoordinated carboxylic acid sites, free and coordination water molecules, and hydrogen‐bonding networks inside the frameworks are favorable to the proton transfer. By measuring the impedance values after exposure to formic acid vapor at 98 % or 68 % RH and 25 °C, both MOFs indicate reproducibly high sensitivity to the analyte. The detection limit of formic acid vapor is as low as 35 ppm for 1 and 70 ppm for 2. Meanwhile, both MOFs also show commendable selectivity towards formic acid among interfering solutions. The proton conducting and formic acid sensing mechanisms have been suggested according to the structural analysis, Ea calculations, N2 and water vapor absorptions, PXRD and SEM measurements. This work will open a new avenue for proton‐conductive MOF‐based impedance sensors and promote the potential application of these MOFs for indirectly monitoring the concentrations of formic acid vapors. Detecting formic acid: The proton conductive and formic acid vapor sensing properties for two imidazole multicarboxylate‐based metal–organic frameworks (MOFs) have been investigated. By measuring the resistance and stability when exposed to formic acid vapor under ambient conditions, both materials show remarkable stability and reproducibly high sensitivity to the analyte at low concentrations. The detection limit is as low as 35 ppm (1) and 70 ppm (2). Both materials also showed commendable selectivity towards formic acid vapor among interfering vapors.
ISSN:0947-6539
1521-3765
DOI:10.1002/chem.201902169