High-yield green synthesis of N-doped hierarchical porous carbon by Nitrate-Mediated organic salt activation strategy for capacitive Deionization: Universality and commerciality

Abstract

Developing a green and facile strategy for high-yield preparing N-doped hierarchical porous carbon (NHPC) for capacitive deionization (CDI) is a huge challenge for desalination. So far, there are limited reports on high-yield NHPC synthesis. Herein, a novel nitrate (NaNO3, KNO3, Zn(NO3)2 and NH4NO3)-mediated-organic salt activation strategy was exploited to construct NHPCXy (X = Na, K, Zn, NH4; Y(nitrate ratio) = 1, 3, 5). Thereinto, C6H5K3O7 served as activator and nitrate acted as assisted-activator and foaming agent. Compared with C6H5K3O7 activation, NHPCNa3 acquired by NaNO3-C6H5K3O7 co-activation achieved 35.5% high yield and depicted 3D macroarray structures with high specific surface area (SBET) of 1912.2 m2/g, large pore volume (Vpore) of 1.56 cm3/g and 1.21 % N content. Its tertiary pore structure and rich surface-exposed active sites favored the ions rapid insertion and extraction from the micropores. The final NHPCNa3 delivered an excellent salt adsorption capacity (SAC) of 19.74 mg/g. Moreover, it exhibited 14.61 mg/g high SAC at 15.5 mg/cm2 and only showed 9.4% SAC drop after 50 cycles. While using diverse biomass precursors, it obtained an optimal SAC of 23.16 mg/g. NHPCK3, NHPCZn3 and NHPC(NH4)3 also presented the feature of high-yield-high-performance. The high yield came from the foaming effect of nitrate and the property difference may be ascribed to the different cations. This work provides one span-new green universality strategy to design high-yield-high-performance NHPCs in commercial-grade CDI applications.