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

Abstract

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).