Hydrophobic metal organic framework for enhancing performance of acoustic wave formaldehyde sensor based on polyethyleneimine and bacterial cellulose nanofilms

A surface acoustic wave (SAW) formaldehyde gas sensor was fabricated on a 42 degrees 75 ' ST-cut quartz substrate, with a composite sensing layer of zeolitic imidazolate framework (ZIF)-8 on polyethyleneimine (PEI)/bacterial cellulose (BC) nanofilms. The addition of snowflake-like ZIF-8 structure on the PEI/BC sensitive film significantly improves the hydrophobicity of the SAW sensor and increases its sensitivity to formaldehyde gas. It also significantly increases surface roughness of the sensitive film. The hydrophobic nature of ZIF-8 prevents water molecules from entering into the internal pores of the BC film, thereby avoiding a significant mass loading caused by humidity when the sensor is used to detect low-concentration formaldehyde gas. The Zn2+ sites at the surface of ZIF-8 improves the sensor's response to formaldehyde gas through enhanced physical adsorptions of gas molecules. Experimental results show that the ZIF-8@PEI/BC SAW sensor has a response (e.g., frequency shift) of 40.3 kHz to 10 ppm formaldehyde gas at 25 degrees C and 30% relative humidity (RH). When the relative humidity is increased from 30 to 93%, the response of the sensor only varies similar to 5%, and the change in response is negligible at medium humidity levels (similar to 50 to 60% RH).

Automated summary

A surface acoustic wave formaldehyde gas sensor was developed with a composite sensing layer of ZIF-8 on PEI/BC nanofilms, showing enhanced sensitivity and hydrophobicity. The addition of ZIF-8 increased the sensor's ability to detect low-concentration formaldehyde gas by preventing water interference and improving gas molecule adsorption. Experimental results demonstrated the sensor's stable response to changes in relative humidity, making it suitable for various environmental conditions.