While traditional seawater desalination technologies including reverse osmosis (RO), low-temperature multi-effect distillation (LT-MED), and multi-stage flash (MSF) have made great developments in the past decades , emerging desalination technologies based on new concepts have also been continuously developed rapidly. Among them, capacitive deionization (CDI) has attracted the attention of many researchers in recent years due to its energy-efficient and environmentally friendly.
The hollow carbon sphere (HCS) coated with polypyrrole (PPy) layer was synthesized using β-cyclodextrin as the precursor compound with ion-doped (Cl-, DBS-) polypyrrole for the capacitive removal of salt ions from brackish water. HCS derived from β-cyclodextrin was firstly prepared using Pluronic F-127 as the soft template. The combination of HCS and ion-doped PPy effectively exerts the advantages of both to achieve a win-win effect. The supporting effect of HCS alleviates the agglomeration of PPy and enables the composite material to have a larger specific surface area.
The electrochemical tests show that the HCS@PPy-Cl and HCS@PPy-DBS composites have
improved electrochemical performance. The desalination tests indicate that the HCS@PPyCl||HCS@PPy-DBS (H-PC||H-PD) asymmetric cell exhibits a high electrosorption capacity of 31.77 mg g− 1,
which is much higher than that of the HCS||HCS (H||H) symmetric cell (26.35 mg g− 1) in 500 mg L-1 NaCl
The composite material containing ion-doped PPy molecular chains and hollow carbon spheres can effectively facilitate ion transport and enhance ionic affinity and electrical conductivity.
 Zhao, Y., Cai, Y., Wang, Y., Xu, S. (2021) A win-win strategy of β-cyclodextrin and ion-doped polypyrrole composite nanomaterials for asymmetric capacitive deionization. Separation and Purification Technology