Metal-organic frameworks (MOFs) have been proved to be outstanding candidates for humidity sensors, however, pure MOFs are still limited in hysteresis, integration, and intelligence. In this investigation, inspired by a single-site-ion strategy for catalysis, UiO-66-NH 2 is first grafted by 2, 6-DPA (2, 6-dipicolinic acid) molecules (named as U-DPA) and then combined by Zn (II) ions (noted as U-DPA-Zn). Taking advantage of electrolyte and MOF, U-DPA-Zn exhibits significantly enhanced humidity sensing performance than UiO-66-NH 2 and U-DPA. U-DPA-Zn possesses the highest sensitivity (S r = 8.07 × 10 3 ), the best linearity (R 2 = 0.994), the shortest response-recovery time (τ res = 2 s, τ rec = 105 s), the smallest hysteresis (ΔH = 1.81%), as well as good repeatability in a wide relative humidity (RH) range (11%-97%). Thanks to its excellent properties, U-DPA-Zn shows great potential in the field of monitoring human respiration (breath detection) and water evaporation on human skin (finger detection). Additionally, the humidity sensing mechanism is discussed based on complex impedance analysis, revealing the single Zn (II) make giant contribution to MOFs. This work provides an optional material for humidity sensors and further a new strategy to improve the humidity sensitivity of pure MOFs.
The abnormal concentration of anthrax spore biomarker 2,6-pyridinedicarboxylic acid (2,6-DPA) will seriously affect public health. Therefore, a sensitive and rapid assay for 2,6-DPA monitoring is of vital importance. In this work, novel nano-sized amorphous Eu-NH 2 BDC (amEu-NH 2 BDC) and amorphous Tb-NH 2 BDC (amTb-NH 2 BDC) metal organic frameworks are prepared by adjusting the ratio of metal and ligand, respectively. Both of them exhibit highly sensitive and selective ratiometric fluorescence detection for 2,6-DPA with wider linear range and lower detection limit in aqueous solutions and human serum. Attributed to the coordination effect of 2,6-DPA in triggering the characteristic fluorescence emissions of Eu 3+ or Tb 3+ by replacing coordinated solvent molecules, as evidenced by ultraviolet–visible spectroscopy, the fluorescence lifetimes analysis, thermal gravimetric analysis , Fourier-transform infrared spectroscopy, density functional theory (DFT) simulations and X-ray photoelectron spectroscopy. In addition, the amEu-NH 2 BDC or amTb-NH 2 BDC loaded paper-based microsensors are constructed for real-time and sensitive detection of 2,6-DPA and coupled with a smartphone-assisted visual portable device.
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