Fabrication of capacitive sensor based on Cu-BTC (MOF-199) nanoporous film for detection of ethanol and methanol vapors

• Using IL [C8 mim][Cl] (1-methyl-3-octylimidazolium chloride) for the first time as conducting salt in the electrochemical synthesis of Cu-BTC layer.
• Application of fabricated nanosensor for VOC detection at room temperature.
• Fabrication of capacitive nanosensor by using electrochemical synthesized Cu-BTC film for the first time.
• Detection of ethanol and methanol by a capacitive nanosensor which its dielectric layer (Cu-BTC film) was prepared through an electrochemical method.

Metal–organic framework (MOF), a nanoporous compound, has been used as sensing material to fabricate capacitive nanosensor. The proposed nanosensor was fabricated by growing a Cu-BTC (MOF-199) film on a copper substrate using electrochemical method. 1-Methyl-3-octylimidazolium chloride, an ionic liquid (IL), was used as conducting salt in the electrochemical cell. Scanning electron microscopy (SEM), FTIR spectroscopy, X-ray diffraction analysis, and BET techniques were used to characterize the prepared MOF which shows a thin film (about 5 μm) of Cu-BTC layer with particle size of 2–3 μm. In order to fabricate the upper electrode of capacitor some interconnected Ag paste dots were patterned on the MOF layer which was coated on the copper surface as back electrode. This fabricated sensor was used for investigation of the capacitance variations in the presence of different amounts of introduced ethanol and methanol vapors. The capacitive sensing parameters were measured by a LCR meter. Relative capacitance variations were measured to verify the potential of the Cu-BTC films for using as dielectric layer in this capacitive sensor. The linear range of the signal vs. concentration is 0–1000 ppm for ethanol and methanol. Limit of detection of the fabricated sensors were 130.0 ppm and 39.1 ppm for ethanol and methanol, respectively. The selectivity of the sensor for polar and nonpolar VOCs was examined by introducing n-hexane in sensing chamber.

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