Zr4+-based metal organic gel as a fluorescent “Turn on–off” sensing platform for the selective detection and adsorption of CrO42−

Abstract

The recognition and adsorption of heavy metal ions in aqueous media remains a serious challenge. Herein, a rapid synthesis method of Zr⁴⁺-based metal–organic gels (Zr-MOG-1 and Zr-MOG-2) was first developed. Arginine (ARG), which is the linker of Zr-MOG-2, can trigger the MOG to emit an obvious fluorescent “turn-on” signal through ligand to metal charge transfer (LMCT). Remarkably, Zr-MOG-2 not only achieves a good fluorescent signal, but also provides a recognition platform for CrO₄²⁻. Therefore, Zr-MOG-2 with excellent fluorescence can be used for the selective detection of CrO₄²⁻ in aqueous media. CrO₄²⁻ dilutes the LMCT between ARG and Zr⁴⁺ and induces a “turn-off” effect on the fluorescence of Zr-MOG-2. The sensing mechanism of CrO₄²⁻ is demonstrated to be a fluorescence resonance energy transfer (FRET) process. The detection linear range for CrO₄²⁻ is 0.5–10.2 μM, and the detection limit is as low as 5.2 ppb. The sensing effect for CrO₄²⁻ in simulated water samples was also investigated. In addition, the Zr-MOG-2 xerogel has good adsorption capacity for CrO₄²⁻ in water including excess other ions. This novel fluorescent switch sensing platform lays a solid foundation for the multifunctional utilization of MOGs.