Formaldehyde detection using quartz crystal microbalance (QCM) nanosensor coated by nanoporous MIL-101(Cr) film

Abstract

Herein is reported a novel sensitive quartz crystal microbalance (QCM) gas sensor based on metal organic framework (MOF) as a sensitive coating material for detection of formaldehyde vapors in ambient condition. MIL-101(Cr) is selected from MOFs family due to the high porosity and huge surface area. The synthesized MIL-101(Cr) is characterized by SEM, FTIR, XRD etc. to identify size, morphology, chemical structure, crystallinity, and surface area. This MOF is deposited onto the surface of crystal by drop-casting method. The response of the sensor to the vapors of formaldehyde under N2 atmosphere at ambient condition is investigated. The frequency of the crystal changes during the adsorption of gas molecules onto the MOF layer. The frequency variations as the sensor response are followed vs formaldehyde concentrations. The developed formaldehyde sensor demonstrates fast and short response/recovery time, low detection limit of 1.79 ppm, complete reversibility and repeatability in the concentrations range of 2–700 ppm which can be attributed to the almost weak sorption of the formaldehyde vapors into the MOF pores and high stability of the device. Furthermore, the sensor sensitivity to formaldehyde can achieve up to 1.67 Hz/ppm and the sensor has good stability of response values after two months. Surprisingly, the MIL-101(Cr) based QCM sensor shows specific selectivity when it is tested against a range of volatile organic compounds (VOCs), such as acetone, methanol, ethanol etc. The adsorption/desorption process via hydrogen bonding between carboxylate groups of MOF and formaldehyde molecules may be the sensing mechanism for formaldehyde sensing.