Selective pseudocapacitive separation of zinc ions via silk cocoon derived N-doped porous carbon

Abstract

Selective separation of zinc(II) ions is vital not only for the removal of toxic heavy metal pollution in drinking water, but also the recovery of resource in sustainable supply. In this work, nitrogen-doped porous carbon (NPC) derived from silk cocoon was developed for symmetric capacitive deionization towards Zn2+ separation. The high specific surface area, hierarchical porous structure with rich micro-meso-pores and the considerable N-doping content, endow the NPC with the outstanding pseudocapacitive capacity towards Zn2+ ions capture as 33.1 mg g−1 at optimized voltage of 1.0 V. Quantitative analysis of electrochemical kinetics demonstrated that the Zn-ion removal was dominated by surface-dominated charge storage process. Moreover, DFT calculations illustrated the benefits of nitrogen doping and the ascendency of the pyrrolic and pyridinic nitrogen over the quaternary nitrogen dopant for selectively adsorption of Zn2+ ion. The highest selectivity coefficient (& = 90.5) of Zn2+ removal was obtained in Zn-Na ions mixed solution with a molar ratio of 1:100. Moreover, the related electrochemical measurements revealed the supportive explanation for intrinsic pseudocapacitive selective behavior of Zn2+ ion. Our work would present new insights in effects of N-doping and selective separation towards Zn2+ ion for carbon materials.