Highly efficient removal of Sr2+ from aqueous solutions using a polyacrylic acid/crown-ether/graphene oxide hydrogel composite

Abstract

With the development of nuclear power, efficiently treating nuclear wastes generated during operation has attracted extensive attention. Hydrogels are common adsorbent materials in the treatment of wastewater due to their high swelling rate and easy post-treatment. In this work, a novel polyacrylic acid/crown-ether/graphene oxide (PAA/DB18C6/GO) hydrogel composite was synthesized by a radical cross-linking copolymerization method and characterized using various analytical tools such as SEM, FT-IR, TGA and XPS. The effects of time, pH, initial Sr²⁺ concentration, and temperature on Sr²⁺ adsorption onto the PAA/DB18C6/GO were studied. The PAA/DB18C6/GO shows a high adsorption capacity of 379.35 mg g⁻¹ at an initial Sr²⁺ concentration of 772 mg L⁻¹ due to the unique structure of dibenzo-18-crown-ether-6 and high swelling. The composite has a high selectivity for Sr²⁺ with a removal rate of 82.4% when concentrations of Na⁺ and K⁺ were 10 times higher than that of Sr²⁺. The pH and temperature have no apparent impact on adsorption performance of the PAA/DB18C6/GO under the experimental conditions. The composite shows excellent reusability with more than 92% removal rate for Sr²⁺ after five continuous cycles. In addition, the mechanism of Sr²⁺ adsorption by PAA/DB18C6/GO was analyzed by fitting the adsorption data to the theoretical models and XPS data.