A new NCDs@ZIF-90-based sensor: fluorescent "turn-on" detection of Al³⁺ ions with high selectivity and sensitivity

A new NCDs@ZIF-90 composite as fluorescence sensor was designed and prepared by encapsulation of N-doped carbon dots (NCDs) in metal-organic framework (MOF) ZIF-90 in one-pot synthesis. NCDs@ZIF-90 retained the crystal structure and high thermal stability of ZIF-90; meanwhile, it also displayed the good chemical stability. NCDs@ZIF-90 dispersion in ethanol exhibited selective "turn-on" fluorescence response towards Al³⁺. The other coexisting competing metal ions had no obvious influence on the sensing performance of NCDs@ZIF-90 for Al³⁺. The fluorescence intensity at 447 nm of NCDs@ZIF-90 dispersion in ethanol had good linear relation with the concentrations of Al³⁺ with a low detection limit of 3.196 μM. The fluorescence enhancement after the addition of Al³⁺ was attributed to the release of NCDs from the inside of ZIF-90 to ethanol solution. In addition, NCDs@ZIF-90 displayed good recovery in detection of Al³⁺ in water samples indicating its practical application capability. The high selectivity and sensitivity indicate that NCDs@ZIF-90 is a good candidate as a "turn-on" fluorescence chemosensor to identify and detect Al³⁺.