Enhanced capacitive deionization of a low-concentration brackish water with protonated carbon nitride-decorated graphene oxide electrode

Freshwater resources are one of the core elements that affect the harmonious development of mankind and society. Capacitive deionization (CDI) technology is one of the effective methods to transform brackish water into fresh water. The choice of material for a CDI electrode is critical to its electrosorption performance, which directly affects the electrosorption performance through interface optimization. Herein, protonated carbon nitride (H-C3N4)-modified graphene oxide (H-C3N4-mGO1/8) is fabricated by a simultaneous nucleophilic addition and amide reaction in order to enhance capacitive deionization of a very low concentration brackish water. Using activated carbon (AC) as the positive electrode and H-C3N4-mGO1/8 as the negative electrode, H-C3N4-mGO1/8 || AC asymmetric CDI devices are used to remove ions from a NaCl aqueous solution. The CDI test results indicate that the system has a high electrosorption capacity of 8.36 mg g-1 in the 50 mg L-1 NaCl solution with a low applied voltage of 1.2 V, which is 1.40 times than AC || AC symmetric. Moreover, the CDI device performs faster adsorption rate of 0.1879 mg (g·min)-1 and an excellent regeneration efficiency of 100%. The salt electrosorption capacity, electrosorption rate of the H-C3N4-mGO1/8 || AC asymmetric electrodes improve with increasing applied voltage due to the stronger Coulombic interaction between the electrode and charged ions with the formation of a more sufficient electric double layer principle.