Capacitive deionization and methyl orange removal of holey graphene hydrogels

Abstract

In this study, we designed a new strategy to synthesize holey graphene hydrogel (r-HGH) using a one-step hydrothermal method by simultaneous reduction and etching. Based on this simple method, the holies on the graphene layers successfully inhibit the collapse of the graphene structure after the drying. Therefore, the r-HGH can form three-dimensional network structure with hierarchical holey. Using as a binderless supercapacitor electrode, the r-HGH exhibits a high specific capacitance of 451 F g−1 and low internal resistance of ~1.6 Ω. The capacitance can maintain 95.6% after 2000 cycles. Applying for capacitive deionization (CDI) for desalination and methyl orange removal, the r-HGH displays a desalination capacity as high as 44.44 mg·g−1 at voltage of 1.2 V with the initial NaCl conductivity of 1600 μS·cm−1, with the short adsorption/desorption equilibrium time of 200 s. Further, the r-HGH has obvious advantages for the electrosorption of charged organic ions. The electrosorption capacity for methyl orange is 57 mg·g−1, and the adsorption/desorption equilibrium time are within 200 s and 100 s, respectively. Thus, the high electrosorption capacity and rate for NaCl and methyl orang enables the r-HGH to be a promising electrode material for capacitive deionization and wastewater treatment.