Zinc adeninate metal–organic framework-coated optical fibers for enhanced luminescence-based detection of rare earth elements

Abstract

Luminescent sensing platforms for metal ions show significant promise due to their low cost, portability, and ease-of-use. Here, we demonstrate a portable system for monitoring visible light-emitting rare earth elements by immobilizing a zinc adeninate metal–organic framework using a sol–gel method onto a fiber optic tip, which is then integrated with a compact lab-built spectrometer. The sensor is capable of sensitizing emission from terbium, europium, dysprosium and samarium down to part-per-billion concentrations. Unlike conventional solution-based luminescent approaches, immobilization of the sensing material provides a straightforward method for removing solvent molecules after exposure to rare earth element-containing solutions, thus reducing vibrational quenching and enhancing signal while also facilitating recovery, regeneration, and reuse of the sensing material over at least 10 sensing cycles. When the sensor system is applied to a simulated rare earth element process stream, good qualitative agreement with results obtained by inductively-coupled plasma mass spectrometry is exhibited. The sensor system is also capable of detecting sub-part-per-million concentrations of Tb and Eu in a spiked acid mine drainage sample. This work therefore demonstrates immobilization of luminescent sensing material films on fiber optics as a promising strategy for improving metal ion detection in complex environments.