Preparation and adsorption performance of 5-azacytosine-functionalized hydrothermal carbon for selective solid-phase extraction of uranium

► Hydrothermal carbon (HTC) was chosen as matrix of solid-phase extractant. ► A multidentate N-donor ligand, 5-azacytosine, was first grafted on HTC matrix. ► The adsorbent shows high capacity (408 mg g−1) and distinct selectivity for U(VI). ► Ionic strength up to 5.0 mol L−1 NaNO3 had only slight effect on the adsorption. ► The process is fast, endothermic, spontaneous, and pseudo-second-order chemisorption.