Surface-Mounted Metal-Organic Framework for the Adsorption and Sensing of Monoaromatic Pollutants in Water Using Quartz Crystal Microbalance

Abstract Environmental pollution from industrial and anthropogenic activities pose a threat to this access to clean water. Advanced chemical sensors that are simple-to-operate can offer high spatial and temporal resolution, increasing the understanding of the source, fate and distribution of pollutants. One class of highly water-soluble pollutants are benzene, toluene, ethylbenzene and xylene isomers (collectively referred to as BTEX). These compounds are prevalent specifically in fossil fuels and are therefore often found in areas surrounding processing and storage facilities. Selective sensing of chemicals in water is challenging due to the cross-reactivity toward water. Porous metal-organic frameworks have shown promise as analyte-receptors due to the possibility to tune their structure for selective adsorption. It is hypothesized that a hydrophobic MOF with pore dimensions similar to the BTEX molecules will selectively partition these analytes from water. In this study, it is have specifically investigated UHMOF-100, a material previously shown to be highly water-repellent with narrow pores hypothesized to selectively adsorb non-polar compounds. Bulk adsorption experiments confirmed the ability of UHMOF-100 to rapidly adsorb BTEX from water, demonstrating high mass capacities influenced by a complex interplay of water solubility, molecular size, and guest–host interactions. Building upon this, UHMOF-100 thin films on quartz crystal microbalance (QCM) resonators using a layer-by-layer technique is fabricated. The functionalized QCM sensors successfully detected individual BTEX species in water within a 0–50 mg L−1 range, with quantifiable responses as low as 5 mg L−1. The sensors showed low cross-sensitivity toward polar contaminants and demonstrated both chemical stability and mechanical robustness under continuous flow. This work presents, to the knowledge, the first example of a MOF-based QCM sensor for BTEX detection in water, demonstrating the potential of suitably designed porous materials for challenging aqueous sensing applications.