Luminescent Zn-MOF@COF hybrid for selective decontamination of Cu(II) ions and methylene blue dye in aqueous media

Metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) have attained great attraction from researchers nowadays because of their diverse applications owing to their tunable porosity and controllable functions. This work reports an interlinked hybrid composite of Zn-based MOF and imine-base COF (Zn-MOF@COF) based on the ZnN bond. The resulting mesoporous hybrid material shows excellent capability for detecting and removing Cu2+ ions and methylene blue (MB) from water. The adsorption process followed pseudo-first-order kinetics, and the Langmuir model fits for Cu2+ adsorption and the Freundlich isotherm model for MB adsorption. The thermodynamic studies showed that the reaction process between Zn-MOF@COF composite and adsorbates is endothermic. Further, negative ΔS0 show a decrease in randomness and an increase in the order of adsorbent on solid/liquid interface, and positive ΔG0 suggests non-spontaneous behaviour of the reaction process. The composite material detected Cu2+ ions via luminescence quenching with a high Ksv value and low detection limit, showing strong interactions with Cu2+. The maximum adsorption efficiency of Zn-MOF@COF towards Cu2+ and MB is 99.8 and 97.6 %, respectively. The hybrid composite shows the best performance for decontaminating Cu2+ ions and MB among various COF- and MOF-based chemosensors.