Metal–Organic\nFramework-Based Fiber Optic Sensor\nfor Chromium(VI) Detection

Abstract

This study demonstrates a novel fiber optic sensing strategy\nfor\nselective adsorption and rapid detection of Cr(VI) ions by exploiting\na suitable metal–organic framework matrix and the characteristic\nspectral absorption of Cr(VI) at 395 nm wavelength, respectively.\nU-bent fiber optic sensor (U-FOS) probes that exhibit remarkably high\nevanescent wave-based absorbance sensitivity were employed to efficiently\ndetect the Cr(VI) ions that are adsorbed to a stable zeolitic imidazolate\nframework (ZIF-67) matrix immobilized on the probe surface. A facile\ntechnique was developed for the fabrication of ZIF-67-coated U-FOS\nprobes (FOS/ZIF-67) involving an <i>in situ</i> deposition\nprocess followed by heat treatment. Selectivity of the FOS/ZIF-67\nprobes to Cr(VI) was confirmed by optical absorption spectral investigations\nwith 14 other heavy metals and interfering ions. The sensor performance\nwas evaluated with a compact light-emitting diode-photodetector-based\nsetup. FOS/ZIF-67 probes demonstrate an ability to detect Cr(VI) ions\nwith a limit of detection of 1 ppb and a wide linear dynamic range\nfrom 0.005 to 100 ppm within a short response time of 5 to 10 min.\nThese sensors show good recovery rates with real water samples and\na shelf-life of at least 4 weeks under ambient conditions, thereby\ndemonstrating their viability for real-world application.