Nanofibrous polyethyleneimine membranes as sensitive coatings for quartz crystal microbalance-based formaldehyde sensors

A novel formaldehyde sensor was fabricated by electrospinning deposition of nanofibrous polyethyleneimine (PEI)/poly(vinyl alcohol) (PVA) membranes as sensitive coatings on quartz crystal microbalance (QCM). The morphology of the porous three-dimensional PEI/PVA membranes comprising fibers with diameter of 40 nm to 1.8 μm was controllable by tuning the compositions of polymers and solvents in PEI/PVA solutions. The resultant sensors showed a fast response to formaldehyde and a linear relationship upon increasing the formaldehyde concentrations due to the reversible interaction between formaldehyde molecules and amine groups of PEI. The sensor responses were reversible and reproducible towards formaldehyde in the concentration range of 10–255 ppm at room temperature. The sensitivity of fibrous membrane coated QCM sensors formed from the cosolvent of water and ethanol was three times higher than that of corresponded flat membrane coated QCM sensors when exposed to 255 ppm of formaldehyde. Relative humidity in testing chamber was proved to be the key parameter to affect the sensor sensitivity. Additionally, the fibrous PEI/PVA membrane coated QCM sensors exhibited a good selectivity to formaldehyde when tested with competing vapors.