A Metal–Organic Framework Based Gas Sensor for Real-Time Formaldehyde Detection: Metal(III/IV) Pyrazole Carboxylates as a Case Study

This study examines the gas-sensing properties of two pyrazole-based metal–organic framework (MOF) films coated on interdigitated electrode (IDE) and quartz crystal microbalance (QCM) sensors for the detection of formaldehyde. The microporous metal(III/IV) MOFs of Al-3,5-PDA and Zr-3,5-PDA (PDA: pyrazole dicarboxylate) were assessed for their sensitivity and selectivity for formaldehyde in comparison to other common volatile organic compounds (VOCs), including water, acetaldehyde, toluene, and hexane. The findings demonstrated that Al-3,5-PDA exhibits better selectivity for formaldehyde, facilitated by robust physisorption and chemisorption mechanisms, with water augmenting the adsorption energy and electron transfer processes. IDE sensors exhibited increased sensitivity to variations in dielectric characteristics at low humidity, whereas QCM sensors predominantly reacted to mass alterations, displaying less sensitivity to humidity interference. The sensing property of these MOFs paves the way for their deployment as practical sensors for various applications such as air purification, industrial emission control, and environmental monitoring.