Electrosorption of uranium (VI) by sulfonic acid‑decorated FeOOH nanorods

The capacitive deionization (CDI) technology for the removal of U(VI) has been the focus of attention because of its superiorities in operation cost, energy consumption, and environmental friendliness. In this report, electrode materials based on sulfonic acid‑decorated FeOOH were applied to CDI and flow electrode capacitive deionization (FCDI) for the first time. The sulfonic acid‑decorated FeOOH nanorods presented a high electrosorption capability of U(VI) in the CDI system (709.4 mg g−1 at 1.2 V and pH = 4.0, based on Langmuir model), which may result from the coordinative surfaces as well as the mesoporous structures of FeOOH. The thermodynamic and kinetic behaviors of the electrosorption process can be well-fitted using the Freundlich and pseudo-second-order model. The effective electrosorption in the presence of Na+ competitive ions and recycling of adsorbents in the CDI system further demonstrated the potential application of sulfonic acid‑decorated FeOOH nanorods for the electrosorptive removal of U(VI) from radioactive wastewater. The electrosorption mechanism was determined to be a combined process that is composed of diffusion of the uranyl ions into the EDL and adsorption onto the surface of FeOOH via the coordination interaction from Fe-OH and sulfonic acid groups (-SO3H). Further, continuous FCDI batch experiments in low concentration of feed water (60 mg L− 1 U) show that removal efficiency of U remained over 99% in 10 times continuous cycles, endowing it more possibilities for capacitive deionization from research to practical application.