Efficiency Improvement of a Capacitive Deionization (CDI) System by Modifying 3D SWCNT/RVC Electrodes Using Microwave-Irradiated Graphene Oxide (mwGO) for Effective Desalination

Abstract

This work is aimed at improving the electrosorption capacity of carbon nanotube/reticulated vitreous carbon- (CNT/RVC-) based 3D electrodes and decreasing the duration of electrosorption-desorption cycles by facilitating the ions’ adsorption and desorption on the electrode surface. This was achieved by preparing composites of microwave-irradiated graphene oxide (mwGO) with CNT. All composite materials were coated on RVC by the dip-coating method. The highest loading level was 50 mg. This is because it exhibited the maximum electrosorption capacity when tested in terms of geometric volume. The results showed that the 9-CNT/mwGO/RVC electrode exhibited 100% capacitive deionization (CDI) cyclic stability within its 1st five cycles. Moreover, 27.78% time was saved for one adsorption-desorption cycle using this electrode compared to the CNT/RVC electrode. In addition, the ion removal capacity of NaCl by the 9-CNT/mwGO/RVC electrode with respect to the mass of the electrode (3.82 mg/g) has increased by 18.27% compared to the CNT/RVC electrode (3.23 mg/g) when measured at the optimum conditions. In a complete desalination process, the water production per day for the 9-CNT/mwGO/RVC electrode was increased by 67.78% compared to the CNT/RVC electrode when measured within the same CDI cell using NaCl solution of concentration less than 1 mg/L. When considered volume of 1 m3, this optimum 9-CNT/mwGO/RVC electrode produces water 29,958 L per day. The highest electrosorption capacity, when measured experimentally at 500 mg/L NaCl feed concentration, was 10.84 mg/g for this optimum electrode, whereas Langmuir isotherm gave the theoretically calculated highest value as 16.59 mg/g. The results for the 9-CNT/mwGO/RVC composite electrode demonstrate that it can be an important electrode material for desalination in CDI technology.