A bifunctional imidazolium-based porous organic polymer for efficient detection of Cr2O72− and adsorptive separation of Cr2O72− and MO in water

Abstract

The presence of heavy metal ions and organic dyes in aqueous solutions has a significant impact on the ecological environment and human health. Herein, a novel bifunctional imidazolium-based porous organic polymer (IMSPF-Br-C=C) was prepared successfully via quaternization reaction of spirobifluorene and 1,4-dibromo-2-butene. The synthesized material was characterized by scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), Fourier transform infra-red spectra (FTIR), Thermogravimetric analysis (TGA), X-ray diffraction (XRD), N2 adsorption-desorption analysis and solid-state 13C CP/MAS NMR spectroscopy, confirming its structure and stability. Owing to the conjugated structure of spirobifluorene, IMSPF-Br-C=C showed excellent recognition performance for dichromate anion (Cr2O72−) with the limit of detection (LOD) of 1.58 μmol/L. In addition, IMSPF-Br-C=C with the abundant imidazolium cations showed the outstanding adsorption performance in the removal of Cr2O72− and methyl orange (MO). Removal efficiencies and adsorption capacities of IMSPF-Br-C=C were 98.3 % and 99.4 %, 452.8 and 1304.2 mg/g in 6 min, respectively. The results show that the electrostatic interactions and π-π stacking play crucial roles in the fluorescence detection of Cr2O72− and adsorptive separation of Cr2O72− and MO. Furthermore, physico-chemical techniques, density functional theory (DFT) calculation and frontier molecular orbital theory (FMO) were used to explain action mechanism. This work provides a cost-effective IMSPF-Br-C=C as a bifunctional platform for sensing Cr2O72− and adsorptive separation of Cr2O72− and MO in aqueous solution.