Improved U(VI) electrosorption performance of hierarchical porous heteroatom-doped electrode based on double-template method

As an indispensable element in the field of nuclear energy, uranium (U(VI)) is widely concerned because it is abundant and easy to obtain from seawater. Herein, we report a promising dual-template strategy to prepare heteroatom-doped carbon materials with hierarchical micro−/meso−/macroporous from low-cost biomass precursors. The carbon materials with hierarchical porosity nitrogen/oxygen are synthesized through freeze-drying, high-temperature thermal treatment and subsequent HF etching treatment by in-situ growth of SiO2 on the precursor with ethyl silicate as silicon source and introduction of ZnCl2 as hard template and starch/ammonia as carbon and nitrogen source. Based on the advantages of three-dimensional interconnected hierarchical porous heteroatom doping, the electrosorption capacity reaches 67.25 mg/g, and the removal efficiency is as high as 98.45%, when the initial UO2(NO3)2 concentration is 80 mg/L in capacitive deionization. The isothermal adsorption of nitrogen doped hierarchical porous carbon (NHPC) is consistent with the Langmuir model, with a maximum electrosorption capacity of 152.43 mg/g, good cycle stability and high charge efficiency (energy consumption is only 0.77 kg-U kWh−1). Fascinatingly, the initial UO2(NO3)2 concentration is 80 mg/L and it also has a high adsorption capacity in 3.5 wt% NaCl solution, and the U(VI) removal efficiency could reach 42.5% after 8 h of continuous adsorption, with high selectivity. The prepared adsorbent NHPC shows good selectivity for U(VI) in the solution of 11 metal ions co-existing, and the effective selectivity Kd value of U(VI) is 1620.84 mL/g. Finally, X-ray photoelectron spectroscopy analysis reveals that in addition to Coulomb interaction and chelation during the adsorption process, there is also a synergistic effect of the conversion of U(VI) to UO2 under electric drive to improve the adsorption capacity of U(VI).