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), N 2 adsorption-desorption isotherms, X-ray photoelectron spectroscopy (XPS) and solid-state 13 C CP/MAS NMR spectroscopy. The IM-Br-2OH exhibits the maximum adsorption capacity of perrhenate (ReO 4 - ) 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 ReO 4 - than the previously reported adsorbents. In addition, excellent adsorption selectivity of IM-Br-2OH for ReO 4 - was observed in the presence of competing anions such as CO 3 2- , Cl - , SO 4 2- , NO 3 - , and PO 4 3- . Adsorption process of ReO 4 - 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 ReO 4 - contribute to the ReO 4 - adsorption from aqueous solution. The conclusions imply that IM-Br-2OH has potential application in the removal of radioactive pollutants from effluents.