Detection of formic acid and acetic acid gases by QCM sensor coated with acidified multi-walled carbon nanotube membrane.

In this paper, the acidified multi-walled carbon nanotubes (MWCNTs) film was coated on the quartz crystal microbalance (QCM) to prepare a high performance sensor for real-time detection of organic acid gases. The material characteristics of the thin films were analyzed by field emission scanning electro microscopy (FESEM), Raman spectra and X-ray photoelectron spectroscopy (XPS). The organic acid vapors sensing results indicated that acidized-MWCNTs thin film exhibited good frequency response, repeatability, reversibility and stability. There is a clear linear relationship between the frequency offset and the organic acid vapors with concentration below 5.0 ppm, and the detection limit of 0.77 ppm and 0.73 ppm for formic and acetic acid vapors, respectively. The sensor shows the highest response to formic acid vapor than acetic acid vapor which may be ascribed to the molecular polarity. Furthermore, a sensing mechanism model was introduced to understand the adsorption reaction between organic acid molecules and acidized-MWCNTs. This paper proves that acidized-MWCNTs is a potential and suitable material for organic acid vapors detection when combined with a QCM sensor.