A Tb-based-metal–organic framework prepared under ultrasound for detection of organic amines in aqueous solution through fluorescence quenching

Dual Stimulus Responsive GO-Modified Tb-MOF toward a Smart Coating for Corrosion Detection

Smart-sensing coatings that exhibit multistimulus response, rapid indication, and reusability are in urgent need to effectively enhance the practicability of coatings while accurately detecting metal corrosion. In this work, a reusable corrosion self-reporting coating with multiple pH and Fe3+ stimulus responses was first constructed by the integration of a composite fluorescent probe into the resin matrix. This composite sensor was constructed by combining a lanthanide metal-organic framework (Ln-MOF) based on terbium and trimeric acid (H3BTC) with graphene oxide (GO) nanosheets (GO@Tb-BTC). The incorporation of GO formed a sea-urchin-like structure, thereby increasing the specific surface area and active sites of the probe. The coatings were characterized by using electrochemical impedance spectroscopy (EIS), visual observation, and fluorescence spectrophotometry. The surface morphology, wettability, and adhesion of the coating samples were analyzed using SEM, XPS, hydrostatic contact angle test, and an adhesion test. EIS measurements in 3.5 wt % NaCl solution for 72 h demonstrated the superior corrosion protection performance of the 0.3 wt %/GO@Tb-BTC/WEP coating compared to blank coating, with the charge-transfer resistance reaching 4.33 × 107 Ω·cm2, which was 9.5 times higher than that of the pure coating. The bright green fluorescence of GO@Tb-BTC/WEP coating exhibited a turn-off response when there was an excess of OH-/H+, but it demonstrated a reversible turn-on fluorescence when the ambient pH returned to neutral. Furthermore, such Fe3+-triggered fluorescence quenching responded to concentrations as low as 1 × 10-6 M. The fluorescence quenching rate of both intact and damaged coatings surpassed that of visual and EIS detection methods. Significantly, the fluorescence in scratches was effectively quenched within 25 min using 0.3 wt %/GO@Tb-BTC/WPU coating for visual observation. GO@Tb-BTC demonstrated exceptional corrosion self-reporting capabilities in both epoxy and polyurethane systems, making it a versatile option beyond single-coating applications.

Solvent- and pH-Stable Eu(III)-Based Metal-Organic Framework with Phosphate-Ratio Fluorescence Sensing and Significant Proton Conduction

Lanthanide-based metal-organic frameworks show good potential for applications due to their unique structures and functional properties. A highly thermally and acid-base stable Eu-MOF was synthesized by a solvothermal method with the molecular formula {[(CH3)2NH2]2[Eu2(NDDP)2(H2O)2]·H2O}n (Eu-MOF, H4NDDP = 5,5'-(naphthalene-2,6-diyl)diisophthalic acid). Eu-MOF takes a three-dimensional (4,4,8)-connected topology. The water molecules involved in the coordination, free water molecules, and [(CH3)2NH2]+ cations in the pore can be used as proton carriers. The proton conductivity attains 1.25 × 10-4 S cm-1 at room temperature and 2.42 × 10-3 S cm-1 at 70 °C and 98% relative humidity. Combined with the dual-emission properties from the ligands and Eu(III) ions enables Eu-MOF to be used as a ratiometric fluorescent sensor for phosphate efficiently and rapidly, with a limit of detection of 0.12 μM in the Tris-HCl buffer solution. These results provide a new approach for the construction of MOFs with high proton conductivity and a ratiometric fluorescence response.

Humidity Sensors Based on Metal-Organic Frameworks

Humidity sensors are important in industrial fields and human activities. Metal-organic frameworks (MOFs) and their derivatives are a class of promising humidity-sensing materials with the characteristics of a large specific surface area, high porosity, modifiable frameworks, and high stability. The drawbacks of MOFs, such as poor film formation, low electrical conductivity, and limited hydrophilicity, have been gradually overcome with the development of material science. Currently, it is moving towards a critical development stage of MOF-based humidity sensors from usability to ease of use, of which great challenges remain unsolved. In order to better understand the related challenges and point out the direction for the future development of MOF-based humidity sensors, we reviewed the development of such sensors based on related published work, focusing on six primary types (impedance, capacitive, resistive, fluorescent, quartz crystal microbalance (QCM), and others) and analyzed the sensing mechanism, material design, and sensing performance involved, and presented our thoughts on the possible future research directions.

A novel 2D metal–organic framework probe: a highly sensitive and visual fluorescent sensor for Al3+, Cr3+ and Fe3+ ions

A novel 2D MOF Tb-DBA was constructed. Tb-DBA could detect Al3+, Cr3+ and Fe3+ ions rapidly, sensitively, selectively, reversibly and visually. Tb-DBA represents a promising material for the quick detection of metal ions in aqueous solution.