Hierarchical Porous Carbon for High-Performance Capacitive Desalination of Brackish Water

Capacitive deionization (CDI), as an energy-efficient and promising brackish water desalination technique, has certain advantages over conventional methods such as thermal distillation, ultrafiltration, and reverse osmosis. However, CDI technology is as yet not widely applied as it can only treat low salinity water due to the limitation of salt adsorption capacity of the electrode. The complexity and high cost of the preparation of such materials with excellent salt removal capability also hinder the commercialization of CDI technology. To surmount these barriers in CDI technology, we hereby developed a hierarchical porous carbon (h-PC) which was prepared via a facile, economic, and green calcination of biomass mixed with an activator. Our prepared h-PC electrodes demonstrate an outstanding salt adsorption capacity (SAC) of 83.0 mg/g when the NaCl concentration is 1000 mg/L for batch mode CDI. This SAC is significantly higher than those reported elsewhere (normally between 15–25 mg/g), and the ultrahigh SAC may be due to the high specific surface area (SSA) and favorable hierarchical pore structure of h-PC. The as-prepared h-PC can also effectively remove heavy metals and desalinate brackish water with a wide range of salinity up to 10000 mg/L. Furthermore, the h-PC-800 electrode shows outstanding cycling stability with no decline of salt adsorption capacity or its corresponding charge efficiency in the long term continuous mode CDI process (over 200 cycles). Our study of this work may be helpful in the design of practical and economical material for high-performance CDI application of the desalination of brackish water with various salinity.