ZnO@MOF-5 as a Fluorescence “Turn-Off” Sensor for Ultrasensitive Detection as well as Probing of Copper(II) Ions

Recently, the synthesis, characterization, and structural evaluation of metal–organic framework (MOF) nanocomposites gain more attention due to the versatility in their applications. In the present work, the fluorescent active ZnO@MOF-5 composite was synthesized by encapsulating ZnO nanoparticles into the zinc terephthalate metal–organic framework (MOF-5). ZnO nanoparticles were prepared by a green method using the leaf extract of Annona muricata. Incorporation of ZnO nanoparticles onto the framework structure (ZnO@MOF-5) was done by a solvothermal method. The new composite material was characterized by Fourier transform infrared spectroscopy, Powder X-ray diffraction, Ultraviolet–visible spectroscopy, Transmission Electron Microscopy, X-ray photoelectron spectroscopy, Brunauer–Emmett–Teller analysis, Dynamic light scattering, Thermogravimetry-Differential Thermal analysis, and Photoluminescence spectroscopy. The material displayed blue fluorescence with a peak at 402 nm upon excitation at 282.46 nm. ZnO@MOF-5 showed a good fluorescence sensing efficiency toward the detection as well as probing of Cu(II) ions in aqueous solution. Sensing experiments performed revealed that as the concentration of copper ions in the solution increases, the quenching efficiency of the composite also increases. A quenching efficiency of 96.20% was achieved on reaching a concentration of 5 μM. The limit of detection for the sensing of Cu2+ ions was calculated to be 0.185 μM.