Electrospun nanofibrous polyelectrolytes membranes as high sensitive coatings for QCM-based gas sensors

Electrospun nanofibrous polyelectrolytes (polyacrylic acid (PAA) and polyethyleneimine (PEI)) membranes are studied as sensing materials coated on quartz crystal microbalance (QCM) for detection of NH3 and H2S at ppb level. The submicron fibers, as small as tens of nanometers, with different morphologies can be deposited on the electrode of QCM by electrospinning the homogenous solutions of polyelectrolytes or blend solutions of polyelectrolytes and template polymer poly(vinyl alcohol) (PVA) under various processing parameters. A series of nanofibrous membranes with various weight percentage of PAA or PEI to PVA are fabricated and characterized regarding their morphology, sensitivity, and selectivity. Sensing experiments are examined by measuring the resonance frequency shifts of QCM which are due to the additional mass loading. The ultrahigh sensitivity of QCM sensors can accurately detect mass uptake on the order of nanograms. The results of sensing experiments indicate that the sensitivity of nanofibrous membranes coated QCM (NFM-QCM) sensors is much higher than that of continuous films coated QCM sensors. Meanwhile, the PAA fibrous membranes coated QCM (FMQCM) sensors exhibit high sensitivity towards low concentration of NH3, as low as 130 ppb at the relative humidity of 40%. And, a good stability is displayed in the preliminary study of the stability of PAA FM-QCM sensors within 10 days. Additionally, the PEI/PVA NFM-QCM sensors show relatively good selectivity to the sulfide gases. The pre-sorbed water in nanofibrous membranes is proved to be the key factor to affect the sensitivity of NFM-QCM sensors for target gases. The sensor performance has been found to depend on the morphology of nanofibrous membranes, content ofpolyelectrolytes component in nanofibrous membranes, concentrations of target gases, coating load of nanofibrous membranes on QCM, ambient temperature, and relative humidity.