Rapid recognition of fatal cyanide in water in a wide pH range by a trifluoroacetamido based metal–organic framework

Abstract

A new metal–organic-framework (MOF) called UiO-66-NH-COCF₃ was prepared using a trifluoroacetamido-functionalized terephthalic acid ligand. Powder X-ray diffraction (PXRD), infrared (IR) spectroscopy, thermogravimetric analysis (TGA) and a Brunauer Emmett–Teller (BET) experiment were carried out to investigate the phase purity, functionality, thermal stability and surface area, respectively, of the newly synthesized MOF material. The solvent-free MOF material (1′) was obtained by stirring the as-synthesized material in methanol for 24 h and then heated at 100 °C in vacuum. A systematic fluorescence study of 1′ showed an ultrafast, highly selective turn-on response towards the lethal cyanide (CN⁻) ion. A 300-fold increment in fluorescence intensity was observed, which has not previously been reported for any probe for cyanide sensing. To check the selectivity of 1′ towards CN⁻ over other interfering anions, fluorescence sensing experiments were performed with 1′ in the presence of a wide range of anions, none of which caused significant interference. The detection time for the probe 1′ towards CN⁻ was only 1 min, with a very low limit of detection (LOD) (0.28 μM). A fluorescence study was carried out in different pH media to check its usefulness towards the sensing of CN⁻ in a wide pH range. Naked-eye detection of CN⁻ was achieved by a paper strip coated with MOF material, which showed promise for more realistic applications. The reversibility of the CN⁻ sensor was demonstrated using trifluoroacetic acid as the proton source. Furthermore, we could utilize the probe to detect CN⁻ in food and real water samples.