Diamino group-functionalized Zr-based metal–organic framework for fluorescence sensing of free chlorine in the aqueous phase and Knoevenagel condensation

Abstract

We developed a porous diamino group-functionalized Zr(IV) metal–organic framework (MOF). The synthesized MOF has a similar structure to DUT-52 (DUT = Dresden University of Technology), which has a face-centered cubic structure with an Fmm space group. The synthesized material (DUT-52-(NH₂)₂-1) was solvent exchanged with methanol (MeOH) and activated at 100 °C overnight. Both the as-synthesized and activated materials (DUT-52-(NH₂)₂-1′) are thermally stable until 300 °C. The Brunauer–Emmett–Teller (BET) surface area of DUT-52-(NH₂)₂-1′ was found to be 413 m² g⁻¹. DUT-52-(NH₂)₂-1′ showed a significant quenching of fluorescence response after coming in contact with free chlorine (ClO⁻) in an aqueous medium. The selectivity of DUT-52-(NH₂)₂-1′ towards ClO⁻ was not significantly hampered in the presence of any competitive ion. The limit of detection (LOD) value was found to be 0.08 μM in phosphate-buffered saline (PBS, pH = 7.4). DUT-52-(NH₂)₂-1′ is recyclable and very sensitive towards ClO⁻. Moreover, the paper strip method was developed for onsite identification of ClO⁻. Furthermore, the catalytic activity of DUT-52-(NH₂)₂-1′ was tested in the Knoevenagel condensation between benzaldehyde and cyanoacetamide. The experimental results clearly indicate that DUT-52-(NH₂)₂-1′ exhibits high activity with very high selectivity towards condensation products. The solid was reusable three times with no decay in its activity, as evidenced by powder X-ray diffraction (PXRD), field emission scanning electron microscopy (FE-SEM) and fourier transform infrared (FT-IR).