Green synthesis of fluorescent PEG-ZnS QDs encapsulated into Co-MOFs as an effective sensor for ultrasensitive detection of copper ions in tap water.

In this work, a novel and highly fluorescent (FL) metal-organic framework (MOF)-based host-guest hybrid system was developed through encapsulation of polyethylene glycol (PEG)-capped ZnS quantum dots (QDs) into zeolitic imidazolate framework (ZIF)-67 at ambient temperature. This new composite material was characterized by FT-IR, XRD, TEM, UV-Vis absorption and FL spectroscopy, and then exploited as fluorescence sensor for highly sensitive and selective detection of Cu (II) ions in water samples. The as-prepared PEG-ZnS QDs@ZIF-67 nanohybrids took advantages of both accumulation effect in ZIF-67 and FL sensitivity and selectivity in ZnS QDs toward analyte-Cu2+. In this regard, ZIF-67 was treated as absorbents to capture and enrich Cu (II) ions, and ZnS QDs were exploited as tentacle to selectively and sensitively sense the bonding interactions between ZIF-67 and Cu (II) ions, and further transduce these chemical events to the detectable fluorescence signals. By this approach, Cu2+ could be detected in a wide concentration range of 3 to 500 nM with a LOD as low as 0.96 nM. The proposed FL-sensor can be promising in the field of preparation of various QDs@MOFs platforms for application in high-performance optical sensing.