Electro-enhanced removal of copper ions from aqueous solutions by capacitive deionization
Introduction
Copper ion (Cu2+) is considered a hazardous pollutant and has been introduced in large quantities into the aqueous environment by the wastewater of several industries such as mining, metallurgy, plating, and printing circuits. The permissible limits given by the World Health Organization for Cu2+ discharged into inland surface water and in drinking water are 3.0 mg/L and 0.05 mg/L, respectively [1]. The excess Cu2+ consumption can cause gastrointestinal symptoms and liver toxicity. Therefore, it is of great importance to remove Cu2+ from water. Various treatment technologies have been suggested for the removal of Cu2+ from wastewater, such as chemical precipitation, ion exchange, membrane filtration, and electrochemical methods [2]. To date, these processes, however, are usually limited due to technical or economic constraint, especially at the lower concentrations of Cu2+. The efforts dedicated to exploring advanced, clean, energy efficient techniques still continue to grow for separating small amounts of Cu2+ from aqueous solutions.
The electrosorption process, also called capacitive deionization technology (CDI), appears to be a promising method for the removal of low level dissolved ions in water due to its environmental friendliness, reduced energy consumption, and low fouling potential [3], [4]. In CDI, ions are extracted from water by applying an electric voltage difference between a pair of highly porous carbon electrodes, in which the ions are temporarily stored via the formation of an electrical double-layer (EDL) inside the pores. In addition, by reducing the cell difference, electrosorption is reversible, and the electrode can be regenerated by desorption. Hence, the electrosorption process offers flexibility in operation and delivers high-quality purified water as the product. On the materials side, nanoporous carbons are employed as a key component in the electrosorption process due to their good electrical conductivity, high surface area, and remarkable sorption capacity, including carbon aerogels [5], [6], activated carbons [7], [8], carbon nanofibers [9], carbon nanotubes [10], [11], mesoporous carbon [12], [13], graphene [14], and mixture of these materials [15], [16]. Most recently, graphene-coated hollow mesoporous carbon spheres have been used as promising electrode materials in CDI due to their hierarchically porous structures [17]. Among these porous carbons, activated carbons possessing the main feature of large pore volume, micropores, and mesopores along with a high specific surface area are the most cost-efficient adsorbent materials. Advantageously, activated carbon is one of the most common materials used for electrosorption because of its strong mechanical stability, high electrochemical stability, and low manufacturing cost. Many studies have indicated that the electrosorption process by activated carbon electrodes has succeeded effectively in removing various unwanted ions such us sodium, magnesium, calcium, chloride, nitrate, and sulfate from water [7], [18], [19], [20], [21].
Currently, research to explore the electrosorptive removal of metal ions from aqueous solutions remains limited. The first study by Farmer et al. [22] successfully employed electrosorption using carbon aerogel electrodes to remediate groundwater contaminated with chromium Cr(VI). Oda and Nakagawa [23] investigated the removal characteristics of Cu2+ and Zn2+ using activated carbon electrodes by applying a direct voltage of 1 V. Zhan et al. [24] fabricated carbon nanotube and nanofiber film electrodes for the electrosorption of Cu2+ at various voltages (0–2 V). Huang and Su [25] reported that modified activated carbon cloth had a much higher electrosorptive capacity at 0.3 V than that at open circuit. Moreover, the electrosorption of Cu2+ was performed using a carbon nanotube–chitosan composite electrode [26] and mesoporous carbon electrode [27]. Hence, the electrosorptive removal of Cu2+ from aqueous solutions by various carbon electrodes has recently received attention. In addition, the electrosorption selectivity that determines the CDI performance for the actual applications has not been clearly elucidated. Most of the relative studies were focused on the electrosorption preference in a single-ionic solution. Several researchers showed that the electrosorption selectivity of ions could be determined by the hydrated size, ionic charge, and initial molar concentration in multi-ionic solutions [6], [28]. To the best of our knowledge, the ion selectivity of Cu2+ in the carbon-based CDI process has not been reported.
The objective of this study is to evaluate the feasibility of electrosorptive removal of Cu2+ from aqueous solutions using activated carbon electrodes in the CDI process. To elucidate the interaction between Cu2+ and the carbon electrode surface, a systematic investigation was performed using cyclic voltammetry and surface characterization. The applicability of the CDI process in Cu2+ removal was examined using batch-mode experiments in a continuous recycling system. More specifically, the electrosorption selectivity of Cu2+ in a competitive environment was investigated in the presence of sodium chloride (NaCl), natural organic matter (NOM), and dissolved reactive silica.
Section snippets
Activated carbon electrode materials
The carbon sheets for the electrodes were made by mixing activated carbon powder (Filtrasorb 400, Chemviron Carbon Inc.) and polyvinylidene fluoride (PVDF, M.W. = 534,000, Sigma-Aldrich) binder, as described in our previous work [8]. The weight ratio of the material was 9:1. N,N-dimethylacetamide (DMAc, 99%, Alfa Aesar) was used as the solvent. The mixture was dropped onto a titanium plate, dried at 120 °C for 2 h, and finally dried in an 80 °C vacuum oven for 2 h to remove all the organic solvents.
Electrochemical characteristics
The activated carbon electrode fabricated in this study had a BET specific surface area of 964 m2/g and a total pore volume of 0.50 cm3/g. This large surface area was proposed to be crucial to the high removal capacity. The average pore diameter based on the pore distribution curve was 2.1 nm. The micropore surface area was estimated to be 513 m2/g. Previously, we confirmed that the activated carbon electrodes exhibit excellent electrical double-layer capacitive behavior, and thus can be considered
Conclusions
The results described in this study provide the fundamental aspects of electro-enhanced removal of Cu2+ ions from aqueous solutions using activated carbon electrodes. At a relatively low voltage, the occurrence of copper electrodeposition is restricted, and therefore, Cu2+ ions are removed from the solution onto the electrode surface by pure electrostatic interaction in terms of the electrical double-layer formation in the nanoporous region. It is evident that the electrosorptive removal of Cu2+
Acknowledgments
This work was supported by the National Science Council of Taiwan under Grant no. NSC-101-2622-E-002-022-CC3.
References (35)
- et al.
Waste biomass adsorbents for copper removal from industrial wastewater—a review
J. Hazard. Mater.
(2013) - et al.
Capacitive deionization as an electrochemical means of saving energy and delivering clean water. Comparison to present desalination practices: Will it compete?
Electrochim. Acta
(2010) - et al.
Review on the science and technology of water desalination by capacitive deionization
Prog. Mater. Sci.
(2013) Fabrication of a carbon electrode using activated carbon powder and application to the capacitive deionization process
Sep. Purif. Technol.
(2010)- et al.
Preparation of activated carbon sheet electrode assisted electrosorption process
J. Taiwan Inst. Chem. Eng.
(2012) - et al.
Salty water desalination using carbon nanotube sheets
Desalination
(2010) - et al.
Single-walled carbon nanotubes and polyaniline composites for capacitive deionization
Desalination
(2012) - et al.
Using mesoporous carbon electrodes for brackish water desalination
Water Res.
(2008) - et al.
Fabrication and characterization of a porous carbon electrode for desalination of brackish water
Desalination
(2009) - et al.
A study of the capacitive deionisation performance under various operational conditions
J. Hazard. Mater.
(2012)
Microwave-assisted ionothermal synthesis of nanostructured anatase titanium dioxide/activated carbon composite as electrode material for capacitive deionization
Electrochim. Acta
Removal of ionic substances from dilute solution using activated carbon electrodes
Carbon
Removal of copper ions from wastewater by adsorption/electrosorption on modified activated carbon cloths
J. Hazard. Mater.
Carbon nanotube–chitosan composite electrodes for electrochemical removal of Cu(II) ions
J. Alloys Compd.
Electrosorptive removal of copper ions from wastewater by using ordered mesoporous carbon electrodes
Chem. Eng. J.
A comparative study of electrosorption selectivity of ions by activated carbon electrodes in capacitive deionization
Desalination
Removal of copper from aqueous solution by electrodeposition in cathode chamber of microbial fuel cell
J. Hazard. Mater.
Cited by (148)
Mg Fe- layered double hydroxides (LDHs) modified electrode enhanced capacitive deionization for simultaneous phosphorus recovery and copper ions removal
2024, Journal of Environmental Chemical EngineeringHighly efficient capacitive deionization of copper(Ⅱ) ions from wastewater in symmetric Ti<inf>3</inf>C<inf>2</inf>T<inf>x</inf> MXene-based electrode: Performance, optimization and deionization mechanism
2024, Journal of Environmental Chemical EngineeringCopper hexacyanoferrate/carbon sheet combination with high selectivity and capacity for copper removal by pseudocapacitance
2024, Journal of Colloid and Interface ScienceThree-dimensional cross-linked sugarcane bagasse carbon material: A substitute for graphene with excellent performance in capacitive deionization and highly efficient Cu<sup>2+</sup> removal
2024, Colloids and Surfaces A: Physicochemical and Engineering AspectsProgress in the treatment of copper(II)-containing wastewater and wastewater treatment systems based on combined technologies: A review
2024, Journal of Water Process Engineering