Efficient nitrate removal by nitrogen-doped carbon spheres electrodes with interconnected architecture in novel stirring capacitive deionization: Dual promoting effect of facile mass transfer and additional active centers

Nitrate contamination in the water environment has become an increasingly serious problem. Capacitive deionization (CDI), an emerging electrochemical water treatment technique, possesses a promising potential for efficient nitrate removal. Herein, we prepared nitrogen-doped carbon spheres (NCS) by controlled self-assembly using nano-SiO2 as a sacrificial template and constructed a novel stirring CDI (SCDI) using NCS as nitrate capture electrodes. The interconnected framework and controllable mesoporous structure of NCS-900 enhance the transfer and diffusion of nitrate ions. In addition, the defects caused by the nitrogen-doped increase the active sites of NCS-900, resulting in outstanding specific capacitive properties. SCDI system promotes mass transfer and allows them to be more uniformly distributed in solution. As a consequence, the concentration of ions near the electrode is elevated, which enhances the removal capacity and reaction rate of the process. Importantly, the SCDI system using NCS-900 as the electrode achieved an ultrahigh nitrate electrosorption capacity of 149.35 mg/ g with a rapid removal rate of 7.46 mg/g/min at 1.2 V condition in 5 mM NaNO3 solution, which was much higher than that of reported nitrate capture electrodes. The superior nitrate removal performance can be ascribed to the synergy between the novel electrode material NCS with high adsorption capacity and the reaction device SCDI with improved system dynamics. In addition, the stability and selectivity of nitrate electrosorption were maintained well in the comprehensive conditions and actual sewage. This work opens a new path for efficient nitrate removal by CDI technology.

Automated summary

This study demonstrates the efficient removal of nitrate from water using a novel stirring capacitive deionization (CDI) system with nitrogen-doped carbon spheres (NCS) as the electrode material. The NCS-900 electrodes exhibited an interconnected framework and controllable mesoporous structure, which enhanced the transfer and diffusion of nitrate ions and resulted in excellent specific capacitive properties. The CDI system achieved an ultrahigh nitrate electrosorption capacity and rapid removal rate, surpassing previously reported nitrate capture electrodes. Furthermore, the stability and selectivity of nitrate electrosorption were well maintained in comprehensive conditions and actual sewage.