期刊
CHEMISTRY-A EUROPEAN JOURNAL
卷 25, 期 62, 页码 14108-14116出版社
WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.201902169
关键词
formic acid sensors; imidazole multicarboxylate-based MOF; metal-organic frameworks; mild temperatures; proton conduction
资金
- the National Science Foundation of China [21571156] Funding Source: Medline
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, {[Co-3(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 {[Co-3(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 1.04x10(-3) and 7.02x10(-4) S cm at 98 % relative humidity (RH) and 100 degrees 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 degrees 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, E-a calculations, N-2 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.
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