Highly Sensitive QCM Humidity Sensor Based on MOFs-Derived SnO₂/Chitosan Hybrid Film

Abstract

This paper demonstrated an accurate and reliable QCM humidity sensor based on metal-organic frameworks (MOFs)-derived SnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /chitosan (CS) nanostructure. MOF-SnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> nanoparticles with uniform size were derived from Sn-based MOFs. The morphologies and nanostructures of the MOF-SnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /CS composite were characterized by multiple characterization techniques. The MOF-SnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /CS composite based QCM humidity sensor exhibits high sensitivity (43.14 Hz/%RH), short response/recovery time (8 s/3 s), excellent selectivity, and fine long-term stability. Besides, the tests of finger approaching/sliding and human breathing based on MOF-SnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /CS QCM humidity sensor were performed in this work, showing its potential applications in identifying humidity change and analyzing aspiration status. The resonant behavior of MOF-SnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /CS QCM humidity sensor was analyzed by conductance spectrum. The adsorption and desorption processes of water molecules were analyzed by a bimodal exponential model, which reveals the adsorption and desorption dynamics of water molecules on the MOF-SnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /CS composite.