A Highly Sensitive Toluene and Xylene QCM Nanosensor Using Nanoporous MIL-101(Cr) as a Sensing Layer

This study reports a facile method to fabricate a metal-organic framework (MOF) MIL-101(Cr) based quartz crystal microbalance (QCM) for the detection of volatile organic compounds (VOCs) at room temperature. MIL-101(Cr) as a novel superior material with an extremely large surface area of 2612 m(2)/g and pore volume of 1.26 cm(3)/g, can have higher adsorption capacity in comparison with zeolites, carbon nanotubes, and many porous polymers. It was chosen as a sensing thin film coated onto the surface of the QCM electrode by using the drop-casting method. The synthesized MOF was characterized by scanning electron microscopy, Fourier-transform infrared spectroscopy, X-ray diffraction, and so on. The frequency of the crystal changes during the adsorption of gas molecules onto the MOF layer. Adsorption/desorption behaviors of toluene and o-xylene vapors in different concentrations vs time are considered and sensing properties such as sensor response, response/recovery time, sensitivity, and limit of detection are measured. The sensor exhibits a short response/recovery time, as well as a fully reversible and repeatable sensor response that reflects the high stability of the sensor. The most prominent advantage of this research in comparison with other works is the high sensitivity of the sensor to o-xylene and toluene with a sensitivity of 26.912 and 11.604 Hz/ppm and the very low detection limits of 1.960, 4.102 ppm for o-xylene and toluene respectively which are very lower than the reported threshold limit values. pi-pi stacking interaction between benzenedicarboxylate groups of MIL-101(Cr) and aromatic rings may be the effective factor in selective detection among other analytes like methanol, ethanol, acetone, n-hexane, dichloromethane, tetrahydrofuran (THF).