Integrated sensing layer of bacterial cellulose and polyethyleneimine to achieve high sensitivity of ST-cut quartz surface acoustic wave formaldehyde gas sensor

Abstract

Surface acoustic wave (SAW)-based formaldehyde gas sensor using bi-layer nanofilms of bacterial cellulose (BC) and polyethyleneimine (PEI) was developed on an ST-cut quartz substrate using sol-gel and spin coating processes. BC nanofilms significantly improve the sensitivity of PEI films to formaldehyde gas, and reduces response and recovery times. The BC films have superfine filamentary and fibrous network structures, which provide a large number of attachment sites for the PEI particles. Measurement results obtained using in situ diffuse reflectance Fourier transform infrared spectroscopy showed that the primary amino groups of PEI strongly adsorb formaldehyde molecules through nucleophilic reactions, thus resulting in a negative frequency shift of the SAW sensor due to the mass loading effect. In addition, experimental results showed that the frequency shifts of the SAW devices are determined by thickness of PEI film, concentration of formaldehyde and relative humidity. The PEI/BC sensor coated with three layers of PEI as the sensing layer showed the optimal sensing performance, which had a frequency shift of 35.6 kHz for 10 ppm formaldehyde gas, measured at room temperature and 30% RH. The sensor also showed good selectivity and stability, with a low limit of detection down to 100 ppb.

Hydrophobic Metal Organic Framework Enhanced Acoustic Wave Formaldehyde Sensor Based on Polyethyleneimine and Bacterial Cellulose Nanofilms

“…The hydrogen bonds formed between the hydroxyl group on the surface of BC and the amine group of PEI prevent the aggregation of PEI particles, which ensure the uniform distribution of PEI on the BC lm and enhance the adsorption of formaldehyde gas molecules. This has been reported in our previous work [15]. In addition, for 10 ppm formaldehyde gas, the frequency shift of the SAW sensor coated with ZIF-8@PEI/BC lms is 13% higher than that of PEI/BC lms.…”

“…The response performance of ZIF-8@PEI nano lms, PEI/BC bi-layer nano lms [15] and ZIF-8@PEI/BC composite nano lms to different low concentrations of formaldehyde gas under 25oC and 30% RH.…”

“…Based on our previous work, the volume V liquid of the formaldehyde solution required to set the concentration of formaldehyde gas can be obtained using Eq. 1 [15], where C (ppm) is the required concentration of formaldehyde gas, and T (K) is the temperature of the test environment. A eld emission scanning electron microscope (FE-SEM, FEI-INSPECT F50) was used to characterize the surface morphology of the sensing lm.…”

“…The hydrophobic composite sensing layer uses BC lm as the structural substrate, PEI particles to provide reaction sites, and ZIF-8 shell as the hydrophobic layer. The fermentation process of BC solution and the preparation process of PEI/BC bi-layer lms have been introduced in detail in our previous work [15]. The BC hydrosol (1 wt‰) and PEI hydrosol (1.25 wt‰) were sequentially coated onto the ST-cut quartz substrate with the spinning speeds of 6000 and 7000 rpm, respectively, then dried in an oven at 60℃ for 10 minutes to make a PEI/BC bi-layer on the SAWR.…”

“…Previously, we developed a surface acoustic wave (SAW) formaldehyde gas sensor based on a bi-layer nano lm of bacterial cellulose (BC) and polyethyleneimine (PEI) [15]. The BC nano layer signi cantly improves the sensitivity of the PEI lm and reduces the response and recovery time for the low concentrations of formaldehyde.…”