Tailored UiO-66-X on quartz crystal microbalance for PPB-level toluene detection

Metal–organic frameworks (MOFs) are ideal for fabricating sensors due to their well-defined and highly tailored nano-porous architectures. Herein, a series of zirconium-based MOFs (UiO-66 and UiO-66-X, X = NH 2 , Br, NO 2 ) with functionalized ligands and uniform morphology were synthesized by incorporating L-histidine as a structural modulator. Subtle changes in responses are achieved by altering the MOFs guest adsorption affinities through the incorporation of functional groups into its linkers. The UiO-66 and UiO-66-X material, used in a quartz crystal microbalance (QCM) gravimetric sensor, enables the ultrasensitive detection of toluene at room temperature (25 °C) and fixed humidity (55 % RH). Compared with UiO-66, UiO-66-Br and UiO-66-NO 2 , UiO-66-NH 2 exhibited superior selectivity toward toluene vapor owing to the presence of proper molecular size and π–π stacking/hydrogen bonding between the microporous framework of UiO-66-NH 2 and toluene molecules. Furthermore, the UiO-66-NH 2 based QCM sensor demonstrated exceptional sensitivity (190 Hz @ 10 ppm) and short response/recovery time (less than 6/21 s), achieving detection limit as low as 50 ppb for toluene under air ambient conditions. This work provides valuable insights into the rational design of ligand-functionalized MOFs for gas sensing applications.