Green double organic salt activation strategy for one-step synthesis of N-doped 3D hierarchical porous carbon for capacitive deionization

Abstract

Exploiting a sustainable and effective strategy for fabricating 3D N-doped hierarchical porous carbon (3DNHPC) for capacitive deionization (CDI) is a huge challenge for desalination. The traditional methods often adopt expensive precursors, complex routes and strong corrosive activators that are harmful for its practical application. Herein, a novel green double organic salt activation strategy is developed that utilizes lotus stem (LS) with a regular 3D macroarray structure to acquire 3DNHPCx. Different from single C6H5K3O7 or Na2EDTA activation, 3DNHPCx obtained under double organic salt co-activation exhibits a suitable micro-meso-macro porous structure with a high BET surface area (SBET) of 2256.2 m2/g, a large pore volume of 1.02 cm3/g, a remarkable mesoporous volume of 0.41 cm3/g and 1.31 % N content. Its unique tertiary pore structure and copious surface-exposed active sites facilitate the ions rapid insertion and extraction from the micropores. The assembled CDI cells achieve a superior salt removal capability of 25.36 mg/g as well as a splendid volumetric adsorption capacity (VAC) of 6.21 mg/cm3 and an ultrafast average salt removal rate of 7.84 mg/g/min. Meanwhile, 3DNHPC11 maintain 89.4 % adsorption capacity after 50 cycles. Besides, 3DNHPC11 obtains a high water recovery (WR) of 82.2 % and high productivity of 290 gNaCl/gC/(h m2) or 108.1 gNaCl/cm3C/(h m2). This work sheds light on one way to design economical and eco-friendly 3DNHPCs for high-performance CDI desalination.