| In recent years, capacitive deionization (CDI) emerged as an environmental friendly water treatment technology. The ions in the aqueous solution are absorbed to the opposite electrodes with the applied voltage and then the double layer is formed to store energy. Compared with electrodialysis, ion-exchange, distillation and reverse osmosis, CDI is an economical and effective method, which has many advantages, such as low cost, long service life, easy recycling, energy conservation, and no secondary pollution. Therefore, the CDI in water treatment has potential value. The physical and chemical properties of the electrode materials have great effect on the performance of CDI.3D graphene nanocomposites not only main the 2D graphene’ mechanical property and electrochemical property but also have 3D materials’highly developed pore structure. Due to it has the inert surface and poor dispersibility in common used solvents, strongly limiting the application in many fields. The modified graphene composite materials and the presence of heteroatoms (N, O, S, B, P) have been widely used to make carbon materials have a range of applications in the field of electrochemistry.We synthesise the nitrogen-enriched carbon aerogel material through a facile polycondensation reaction. Melamine (M), resorcinol (R), formaldehyde (F), graphene oxide (GO) as raw materials and sodium carbonate (C) as catalyst. The organic-gels were pyrolyzed at 700℃ for 2 h with the heating rate of 5℃ min-1 under the nitrogen-flow to obtain the nitrogen-enriched carbon aerogel material (GO-MRF-x). With the varying molar ratio of M with R, the nitrogen contents of the nanocomposites are different. The results demonstrated that N atom can substite C through high temperature pyrolysis. With the increasing temperature of the pyrolysis, the nitrogen contents of the nanocomposites decreased. The specific surface area decreased sharply with the increasing molar ratio of M with R, for the instability of melamine-formaldehyde has been collapsed during the pyrolysis process. GO-MRF-0.8 showed excellent specific capacitance, lowest charge transfer resistance and ion transport resistance. All of these can contribute to its higher adsorption capacity in the CDI process. In CDI, at the constant current operation of 25 mA, the GO-MRF-0.8 reached a 16.72 mg g-1 electrosorption capacity with lower energy consumption. According to the experiments of the adsorption of different ions during the electrosorption process, the electrode materials had a selective electrosorption of Na+ and PO43- ions; According to the competitive electrosorption between ions, the adsorption capacities of Mg2+ and PO43- are higher.Considering the above obtained nitrogen-enriched carbon aerogel material with a smaller specific surface area. We use KOH as an activator, the activation temperature is 800℃ and the mass of KOH with carbon material is 3:1. The activation process had a great impact on the pore structure and specific surface area of the nanocomposites. With mass contents as a variable factor, the A-N-GRF-1 got a high specific surface area of 1199 m2 g-1 and possessed a surface nitrogen content of 1.95 at% after activation process. The A-N-GRF-1 exhibited the superior specific capacitance (317 F g-1), low charge transfer resistance and outstanding cycle stability (93.03% retention after 2000 cycles). The electrosorption capacity of the A-N-GRF-1 for NaCl was 24.63 mg g-1 with the initial concentration around 800 mg L-1. These results suggested that the A-N-GRF-1 had a great potential as supercapacitor and capacitive deionization for NaCl electrode material. |
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