Adsorptive removal of uranium(vi) from wastewater using a crosslinked amidoxime-functionalized β-cyclodextrin polymer

Abstract

In this work, a crosslinked amidoxime-functionalized β-cyclodextrin polymer (β-CDP-AO) was synthesized, characterized, and applied to adsorptive removal of U(VI) from wastewater. β-Cyclodextrin polymer (β-CDP) was firstly synthesized by using β-cyclodextrin as the monomer and tetrafluorophenonitrile as the crosslinking agent. And then β-CDP-AO was prepared by reaction with hydroxylamine hydrochloride using triethylamine as an attractant to introduce amidoxime groups. The prepared polymers were characterized by scanning electron microscopy, energy-dispersive spectrometry, infrared spectroscopy, Brunauer–Emmett–Teller and X-ray photoelectron spectroscopy and so on, and the results demonstrated that β-CDP-AO was successfully obtained. The results of batch adsorption experiments showed that β-CDP-AO had better adsorption capacity and removal efficiency than β-CDP, although the specific surface area of the polymer was significantly reduced after amidoximation. The introduction of amidoxime groups can enhance the adsorption performance and accelerate the U(VI) adsorption process significantly. The obtained amidoxime-functionalized β-CDP-AO can achieve equilibrium in 120 min and the maximum adsorption capacity for U(VI) was 221.54 mg g⁻¹ at pH = 6.0. Meanwhile, the adsorption process conformed to a pseudo-second-order kinetics model and Langmuir model, indicating that the chemisorption of the monolayer was dominant, and the adsorption process was spontaneous and endothermic. More importantly, the removal efficiency of β-CDP-AO to U(VI) was only 4% lower after 5 cycles of regeneration, which can effectively reduce costs in practical applications, and the removal efficiency still achieved 83.26% by adding 7 coexisting ions, indicating that β-CDP-AO had good selectivity to absorb U(VI) in complex wastewater. And the possible mechanism of uranium adsorption by β-CDP-AO was investigated by XPS methods. Results showed that the absorption process was a comprehensive outcome of the synergistic action of cyclodextrin and amidoxime.