A fluorescent zirconium organic framework displaying rapid and nanomolar level detection of Hg(ii) and nitroantibiotics

Abstract

The solvothermal reaction of ZrCl₄ with a benzo[1,2-b:4,5-b′]dithiophene-2,6-dicarboxylic acid (L1) linker molecule in the presence of a trifluoro acetic acid modulator afforded a UiO-66 type of metal organic framework (MOF) (IITG-5, IITG = Indian Institute of Technology, Guwahati). The synthesized MOF material was characterized in detail with the help of PXRD, FE-SEM, FT-IR, EDX and elemental analyses. The material showed high thermal stability up to 390 °C in air atmosphere. This porous material (surface area = 1228 m² g⁻¹) also displayed significant chemical stability in various solvents. The thermally activated compound (IITG-5a) exhibited excellent detectability towards Hg²⁺ in aqueous medium and various nitro-antibiotics (nitrofurazone and nitrofurantoin) in MeOH. Besides the fast response (1 min for all analytes), very low limits of detection (LODs) were observed for the sensing of all the targeted analytes (LOD for Hg²⁺, nitrofurazone and nitrofurantoin were 5, 156.7 and 96.3 nM, respectively). A paper strip-based sensing technique was developed for all the three analytes. Interestingly, for the sensing of all the above-mentioned analytes, IITG-5a featured excellent reusability of up to five consecutive cycles without loss of its sensing efficiency. Mechanisms for all the sensing actvities were elaborately explored by means of DFT calculations and analytical methods.