A new solid-phase extraction adsorbent was prepared by employing a two-step "grafting from" approach to anchor a multidentate N-donor ligand, 5-azacytosine onto hydrothermal carbon (HTC) microspheres for highly selective separation of U(VI) from multi-ion system. Fourier-transform infrared and X-ray photoelectron spectroscopies were used to analyze the chemical structure and properties of resultant HTC-based materials. The adsorption behavior of U(VI) onto the adsorbent was investigated as functions of pH, contact time, ionic strength, temperature, and initial U(VI) concentration using batch adsorption experiments. The U(VI) adsorption was of pH dependent. The adsorption achieved equilibrium within 30 min and followed a pseudo-second-order equation. The adsorption amount of U(VI) increased with raising the temperature from 283.15 to 333.15 K. Remarkably, high ionic strength up to 5.0 mol L-1 NaNO3 had only slight effect on the adsorption. The maximum U(VI) adsorption capacity reached 408.36 mg g(-1) at 333.15 K and pH 4.5. Results from batch experiments in a simulated nuclear industrial effluent, containing 13 co-existing cations including uranyl ion, showed a high adsorption capacity and selectivity of the adsorbent for uranium (0.63 mmol U g(-1), accounting for about 67% of the total adsorption amount). (C) 2012 Elsevier Inc. All rights reserved.