We
present the optical sensing of phthalate esters (PAEs), a group of
endocrine-disrupting chemicals. The sensing takes place as changes
in the fluorescence emission intensity of aminopyrene covalently bound
to the organic ligands of the metal–organic framework compound
ZIF-8. In the presence of PAEs, a quenching of the fluorescence emission
is observed. We evaluated strategies to engineer colloidal size distribution
of the sensing particles to optimize the sensory response to PAEs.
A thorough characterization of the modified ZIF-8 nanoparticles included
powder X-ray diffractometry, transmission electron microscopy, high-performance
liquid chromatography, and photophysical characterization. The presented
capability of the fluorophore-functionalized ZIF-8 to sense PAEs complements
established methods such as chromatography-based procedures, which
cannot be used on-site and paves the way for future developments such
as hand-held quick sensing devices.
Metal-organic frameworks (MOFs) are promising nanoporous materials with many practical applications. This owes largely to their remarkable porosity and the presence of specific chemical functionalities, such as exposed metal sites (EMS). The MOF-74 structure is known for exhibiting one of the highest EMS densities among porous materials. Moreover, the inclusion of structural defects has been proposed to enhance activity further. This was previously achieved by mixing the original linker together with a second one, having lower topology. The presence of structural defects was evidenced by the resulting crystalline properties and thermal stability. In this work, different mixtures of tetratopic 2,5-dihydroxyterephthalic acid with up to 60% of the tritopic hydroxyterephtalic acid were used to synthesize crystalline Co-MOF-74-like materials. Materials synthesized from higher proportions than 30% of hydroxyterephtalic acid in the synthesis media collapse upon partial removal of the solvent molecules. This indicates the presence of structural defects and the importance of the solvent molecules in stabilizing the crystalline structures. Electron microscope images show that crystal size reduces with inclusion of hydroxyterephtalic acid as the second linker. The presence of coordinated solvent molecules at the EMS was evaluated by Fourier-transform infrared spectra (FTIR) spectroscopy, so that a higher degree of solvent-exchange was observed during washing for defective structures. Furthermore, TG analysis suggests defective structures exhibit lower desolvation temperatures than the defect-free structures. Finally, N 2 adsorption-desorption analyses at −196 • C showed an enhanced accessibility of the gas to the inner porosity of the defective structures and therefore, the EMS of the material. All these finding make this pathway interesting to enhance the potential interest of these materials for an industrial application because of both a facilitated activation and a better access to the active sites.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.