Selective and efficient removal of ReO4- from aqueous solution by imidazolium-based porous organic polymers

In this paper, imidazolium-functionalized porous organic polymers (IM-Br-2OH) are prepared successfully via a quaternization reaction of tetrakis[4-(1-imidazolyl)phenyl]methane (TIPM) and 1,4-dibromo-2,3-butanediol (2,3-BDO). The as-synthesized IM-Br-2OH are characterized by various tools such as Fourier transform infrared spectroscopy (FTIR), Scanning electron microscope and energy dispersive spectrum (SEM-EDS mapping), Thermogravimetric analysis (TGA), N2 adsorption-desorption isotherms, X-ray photoelectron spectroscopy (XPS) and solid-state 13C CP/MAS NMR spectroscopy. The IM-Br-2OH exhibits the maximum adsorption capacity of perrhenate (ReO4-) was 658.4 mg/g with removal efficiency of 98.0 ± 0.2% at 35 ºC. Experimental results showed that the IM-Br-2OH presents a higher adsorption capacity for ReO4- than the previously reported adsorbents. In addition, excellent adsorption selectivity of IM-Br-2OH for ReO4- was observed in the presence of competing anions such as CO32-, Cl-, SO42-, NO3-, and PO43-. Adsorption process of ReO4- from solutions onto IM-Br-2OH follows a pseudo-second-order mode well and the adsorption data are in accordance well with the Langmuir isotherm equations. Adsorption mechanism is confirmed with the help of Zeta potentials, FTIR and XPS, indicating that anion-exchange interactions between N+ and ReO4- contribute to the ReO4- adsorption from aqueous solution. The conclusions imply that IM-Br-2OH has potential application in the removal of radioactive pollutants from effluents.