Novel Graphene-Like Electrodes for Capacitive Deionization

Abstract

Capacitive deionization (CDI) is a novel technology that has been developed for removal of charged ionic species from salty water, such as salt ions. The basic concept of CDI, as well as electrosorption, is to force charged ions toward oppositely polarized electrodes through imposing a direct electric field to form a strong electrical double layer and hold the ions. Once the electric field disappears, the ions are instantly released back to the bulk solution. CDI is an alternative low-energy consumption desalination technology. Graphene-like nanoflakes (GNFs) with relatively high specific surface area have been prepared and used as electrodes for capacitive deionization. The GNFs were synthesized by a modified Hummers' method using hydrazine for reduction. They were characterized by atomic force microscopy, N2 adsorption at 77 K and electrochemical workstation. It was found that the ratio of nitric acid and sulfuric acid plays a vital role in determining the specific surface area of GNFs. Its electrosorption performance was much better than commercial activated carbon (AC), suggesting a great potential in capacitive deionisation application. Further, the electrosorptive performance of GNFs electrodes with different bias potentials, flow rates and ionic strengths were measured and the electrosorption isotherm and kinetics were investigated. The results showed that GNFs prepared by this process had the specific surface area of 222.01 m²/g. The specific electrosorptive capacity of the GNFs was 23.18 µmol/g for sodium ions (Na+) when the initial concentration was at 25 mg/L, which was higher than that of previously reported data using graphene and AC under the same experimental condition. In addition, the equilibrium electrosorption capacity was determined as 73.47 µmol/g at 2.0 V by fitting data through the Langmuir isotherm, and the rate constant was found to be 1.01 min⁻¹ by fitting data through pseudo first-order adsorption. The results suggested that the chemically synthesized GNFs can be used as effective electrode materials in CDI process for brackish water desalination.

Functional graphene nanocomposite as an electrode for the capacitive removal of FeCl3 from water

“…32 This suggested that the monolayer adsorption was the primary adsorption mechanism during the electrosorption process. Furthermore, the parameter Q m defined as the maximum adsorption capacity is 69.52 mg g À1 , which is much higher than the reported data, 32 implying that the RGO-RF has great potential in the electrosorption of FeCl 3 .…”

“…To explore the impact of anions on the electrosorption performance of the RGO-RF electrode, batch mode experiments were performed in FeCl 3 , Fe(NO 3 ) 3 and Fe 2 (SO 4 ) 3 solutions with the same experimental conditions. It is known that electrosorption in liquid is strongly related to the size and potential of the ions and the solubility of the solute.…”

“…Fig. 6 illustrates the electrosorption of different anions onto the RGO-RF electrode at a flow rate of 20 mL min À1 and applied voltage of 2.0 V. The electrosorptive capacity of Fe 2 (SO 4 ) 3 , Fe(NO 3 ) 3 and FeCl 3 are 3.69, 3.58 and 3.41 mg g À1 , respectively. The order of the anions removal efficiency was SO 4 2À > NO 3 À > Cl À .…”

“…Up to now, the graphene has been successfully proposed and developed as a CDI electrode for the removal of salty ions from brackish water. 3,24 However, it is found that the specific surface area of as prepared graphene is much less than its theoretical value, which is attributed to the serious aggregation during the preparation. Hence, in the present paper, we proposed a reduced graphene and resol (RGO-RF) nanocomposite as a CDI electrode for the electrosorption of ferric ions.…”

“…[1][2][3][4][5] So there are scientists who have dedicated themselves to alleviating the stresses on freshwater supply. Taking ferric ions as an example, which are common hazardous pollutants in wastewater and are often released by metallurgical, electroplating, circuits printing, fertilizer manufacturing and refinery industries in their effluent.…”