Photothermal composite polyamidoxime-graphene oxide/polyacrylamide hydrogel for efficient and selective uranium extraction from seawater

Abstract

Uranium extraction from seawater is considered to be one of the seven separation technologies that will revolutionize the world. Although adsorbents containing amidoxime (AO) groups have shown promising results, their capacity and selectivity still pose challenges. In this study, polyamidoxime-graphene oxide/polyacrylamide (PAO-GO/PAM) photothermal composite hydrogels were prepared using an ultraviolet photoinitiation strategy. The three-dimensional (3D) hydrophilic network at the molecular level by radical polymerization of acrylamide retains a large amount of PAO, facilitating the easy migration of uranyl ions (UO₂²⁺) to the interior of the adsorbent to chelate with AO groups. In addition, GO was introduced to provide the hydrogel with excellent photothermal conversion ability, causing a rapid temperature increase upon exposure to simulated sunlight. Based on the heat-absorbing properties of UO₂²⁺ chelated with AO groups, the temperature increase of the hydrogel inevitably leads to a right-shift of the thermodynamic equilibrium, providing the prepared hydrogel with a high adsorption capacity under light conditions. Adsorption experiments showed that the PAO₅₀-GO_1.5/PAM hydrogel achieves a maximum adsorption capacity of 396.82 mg·g⁻¹ at pH = 6 with an improvement of 63.4 % in the K_U/K_V ratio. After five cycles, the elution rate remained at 87.1 %. These results demonstrate the promising applications of the adsorbent in large-scale uranium extraction from seawater.