Aqueous contaminant detection via UiO-66 thin film optical fiber sensor platform with fast Fourier transform based spectrum analysis

Abstract

Routine water quality monitoring is required in drinking and waste water management. A particular interest is to measure concentrations of a range of diverse contaminants on-site or remotely in real time. Here we present metal organic framework (MOF) integrated optical fiber sensor that allows for rapid optical measurement based on fast Fourier transform (FFT) spectrum analysis. The end-face of these glass optical fibers was modified with UiO-66(Zr) MOF thin film by in situ hydrothermal synthesis for the detection of the model contaminants, Rhodamine-B and 4-Aminopyridine, in water. The sensing mechanism is based on the change in the optical path length of the thin film induced by the adsorption of chemical molecules by UiO-66. Using FFT analysis, various modes of interaction (physical and chemical) became apparent, showing both irreversible changes upon contact with the contaminant, as well as reversible changes according to actual concentration. This was indicated by the second harmonic elevation to a certain level translating to high sensitivity detection.

Physical and chemical reaction sensing in a mixed aqueous solution via metal‐organic framework thin‐film coated optical fiber

“…The frequency domain spectra (normalized FFT amplitude vs frequency) are shown in Figure where the fresh water (“water 1st trial”) has the fundamental harmonic peak at 514 Hz. Upon introduction of RhB, the second peak at 1472 Hz (RhB characteristic peak) obtained an apparent increase which was related to partial filling of the UiO‐66 surface micropores with RhB . However, after placing the sensor again in DI water (“water 2nd trial”) or lower strength RhB, the amplitude of the second peak showed some irreversible effects which may relate to the strong attachment of RhB to UiO‐66.…”

“…UiO‐66 crystals were synthesized using the previously reported protocol, while the optical fiber UiO‐66 thin‐film was obtained after immersing the fiber into the precursor solution. In Figure C, the optical fiber with a deposited thin layer of UiO‐66 on its tip (end face) is compared with its bare situation in Figure B.…”

“…To evaluate the sensing capability of the fabricated device, rhodamine‐B (RhB) and methyl viologen (MV) were used as the model pollutants. Subsequently, their interactions with UiO‐66 and water were studied using UV‐Vis technique as described in Reference and Appendix.…”

“…MOFs have attracted significant interests for water purification purposes due to their specific high porosity, tunable pore size, large surface area, and versatile surface functionality . Here, we made up a new sensor by coating UiO‐66 MOF at the tip (end face) of an SMF‐28 in order to in situ detect specific substances of water . To the best of our knowledge, there are no other reports of physical and chemical reaction sensing in a mixed aqueous solution via MOF thin‐film coated optical fiber.…”

“…Also, glass optical fibers can tolerate high temperatures, which enable them to operate under extremely harsh conditions . An optical fiber with the water‐stable UiO‐66 MOF thin‐film at its tip (end face) can potentially form an effective sensing system for chemical species . The existence of certain chemical contaminants in water can be adsorbed/reacted by the MOF or water modulated by the properties of light, such as intensity, phase, refractive index, or polarization.…”