Microwave synthesis of metal-organic frameworks absorbents (DUT-5-2) for the removal of PFOS and PFOA from aqueous solutions

Abstract

Perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) are new persistent pollutants that are difficult to degrade. In this work, DUT-5-2 and other six metal-organic frameworks were prepared to remove PFOS and PFOA; their adsorption amount, micropore and adsorption performances (kinetics, isotherms, pH, ions and renewability) were determined. DUT-5-2 had the highest adsorption amount (PFOS: 145.4 mg/g; PFOA: 98.2 mg/g), its microporous characteristic (specific surface area: 1840 m2/g, pore volume: 0.93 cm3/g, pore size: 0.85 nm) and single tooth coordination mode were verified by N2 isotherms and Fourier-transform infrared (FT-IR) spectroscopy. The results of adsorption kinetics and adsorption isotherms revealed that adsorption process of DUT-5-2 involves with a physical monolayer adsorption and the maximum adsorption capacities of PFOS and PFOA were 1015 mg/g and 473.7 mg/g, respectively. The removal rate for PFOS and PFOA would be somewhat affected by the pH and anions; when pH = 3, DUT-5-2 had the highest removal rate for PFOS (96.6%) and PFOA (60.9%). A slight negative effect on the removal rate was found at Cl− (PFOS: 95.6–93.6%, PFOA: 60.6–58.9%) and SO42− (PFOS: 90.9–88.9%, PFOA: 58.0–56.9%) with the concentration of 25–100 mg/L. After four cycles, the regeneration efficiency of DUT-5-2 for PFOS and PFOA was 92.5% and 93.0%, respectively. This study provides a new method for the microwave synthesis of DUT-5-2 to remove PFOS and PFOA from an aqueous environment.