Nanoscale zeolitic imidazole framework-90: selective, sensitive and dual-excitation ratiometric fluorescent detection of hazardous Cr(vi) anions in aqueous media

Abstract

The development of selective and sensitive sensing systems for Cr(VI) anions (CrO₄²⁻/Cr₂O₇²⁻) has been a growing interest because Cr(VI) anions are potent carcinogenic and mutagenic ions that have become serious potential threats to public health and safety. Herein, the selective and highly sensitive detection of toxic Cr(VI) anions in aqueous solution has been achieved by virtue of nanoscale zeolitic imidazole framework-90 (NZIF-90). NZIF-90 is the first individual MOF-based material which can selectively sense Cr(VI) anions from Fe³⁺ cations, and it also has the lowest detection limits among the reported fluorescent MOF-based probes for Cr(VI) anions: 1.41 μM (0.16 ppm) for CrO₄²⁻ and 1.78 μM (0.38 ppm) for Cr₂O₇²⁻. The detailed sensing mechanism study uncovered that the excellent sensing performance of NZIF-90 for Cr(VI) anions is based on the synergistic effect of the competitive energy absorption process and the electrostatic interaction between NZIF-90 and Cr(VI) anions. Moreover, as for a further potential application of this probe, the Förster resonance energy transfer (FRET)-based dual-excitation ratiometric fluorescent detection of Cr(VI) anions was also realized by Rhodamine B (RhB) encapsulated into NZIF-90 (RhB@NZIF-90).