A win-win strategy of β-cyclodextrin and ion-doped polypyrrole composite nanomaterials for asymmetric capacitive deionization

Abstract

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, with specific capacitances of 65.4F g−1 and 101.9F g−1, which are 1.62 times and 2.52 times that of HCS, respectively. Furthermore, the desalination tests indicate that the HCS@PPy-Cl||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 solution. And the charge efficiency of H-PC||H-PD cell can reach 76.2%, which means a great improvement compared to 60.5% of the H||H cell. The improved performances indicate that ion-doped PPy can effectively improve the adsorption capacity of the composite material by providing pseudo-capacitance and suppressing the co-ion effect, while the total specific surface area can effectively increase by HCS and thereby improving the adsorption site.