Exceptional adsorption of arsenic by zirconium metal-organic frameworks: Engineering exploration and mechanism insight

Abstract

Highly stable zirconium metal-organic frameworks (UiO-66 and UiO-66(NH2)) had been synthesized and investigated to remove arsenic (As) from contaminated water. The As(III, V) removal performance was studied by batch experiments and adsorption kinetics. At the pH of 9.2 ± 0.1, UiO-66 had exceptional removal capacities of 205.0 and 68.21 mg/g for As(III) and As(V), respectively. The As removal processes were exothermic and verified as chemisorption reactions according to the calculation of Gibbs free energy and Dubinin-Radushkevich (D-R) isotherm model. Fixed-bed reactor removal experiments indicated that the number of effective treatment volumes reached 2270 and 1775 BVs for As(III) and As(V), respectively, until the most stringent As regulation level of 10 μg/L (initial As concentration at 100 μg/L) was reached. FTIR and XPS study indicated that ZrO bonds of zirconium metal-organic frameworks played a vital role in As adsorption. XANES revealed the As adsorption on UiO-66 without the change of oxidation state. More intriguingly, EXAFS spectra demonstrated the main formation of bidentate mononuclear complexes for As(V), and bidentate binuclear complexes for As(III) on the hexanuclear Zr cluster of UiO-66. The advantages of nontoxicity, high stability, high As adsorption capacity, low-cost and easy availability confirm the highly promising application of zirconium metal-organic frameworks in As-contaminated wastewater remediation.