Combining Electrochemistry and Carbon Nanotubes for Water Treatment

By Susha Cheriyedath, M.Sc.Reviewed by Lexie CornerMay 14 2025

Rapid industrialization, agricultural expansion, and population growth have placed increasing pressure on global freshwater resources.

According to the United Nations’ 2023 report, between 2 and 3 billion people experience water scarcity, with 2 billion lacking access to safe drinking water and 3.6 billion without safely managed sanitation.

These figures highlight the urgent need for effective water treatment technologies to prevent pollution and support long-term environmental and socioeconomic stability.¹

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Traditional water treatment techniques, including reverse osmosis, forward osmosis (FO), and ultrafiltration (UF), can be costly and energy-intensive. In contrast, electrochemical (EC) techniques offer several advantages, including lower operational costs, chemical selectivity, and compact system design.

Among several carbon nanomaterials, carbon nanotubes (CNTs) have facilitated the development of active EC filtration systems that can absorb chemical pollutants and promote the electro-oxidation of contaminants.

The integration of CNTs with EC treatment presents a promising strategy for improving water purification efficiency.^1,2

Carbon Nanotubes in Electrochemical Water Treatment

CNTs are cylindrical carbon-based macromolecules with a hexagonal lattice structure. They are known for their exceptional mechanical strength, electrical conductivity, flexibility, and chemical resistance.

Depending on the number of concentric carbon layers, CNTs are classified as either single-walled (SWCNTs) or multi-walled (MWCNTs).

In water treatment, CNT-based EC filters absorb and electrochemically oxidize target compounds. They are composed of densely packed CNTs held together by van der Waals forces, offering high specific surface area and electrical conductivity.

Compared to conventional methods, EC-CNT systems provide enhanced contaminant removal, thanks to several fundamental processes that contribute to their performance.

These systems operate through key electrochemical mechanisms including temperature-dependent adsorption and desorption, voltage-mediated electron transfer, and hydrodynamics-assisted mass transport.²

Electrooxidation of Organic Compounds

Organic contaminants, including pharmaceuticals, salts, and perfluorinated chemicals, are adsorbed and electro-oxidized on the anodic CNT filters. This process requires the anode’s redox potential to exceed that of the target compound. Oxidation occurs via direct electron transfer between the compound and the electrode.²

Electrosorption of Heavy Metals

Heavy metals like chromium (Cr), copper (Cu), and arsenic (As) that contaminate water can be captured by CNT filters. The adsorption efficiency is further enhanced by the incorporation of functional groups like lactone, phenyl, and carboxyl. Additionally, titanium dioxide (TiO₂) coatings on CNT filters have been shown to improve arsenic sorption.

In one system, a cathode composed of unaligned CNTs suspended in alcohol can selectively separate metals such as copper, depending on the difference in reduction potential.³

Generation of Reactive Oxygen Species

Reactive oxygen species (ROS) are produced through one-electron oxygen reduction. The initial reduction forms superoxide anion, which can then be further reduced to hydrogen peroxide (H₂O₂). While H₂O₂ is effective for contaminant breakdown, its high cost, narrow effective pH range, and handling hazards limit its practical use.

CNTs, as next-generation oxygen reduction catalysts, can act as cathodes in electro-Fenton systems. Here, in situ-generated H₂O₂ reacts with iron(II) (Fe²⁺) to form hydroxyl radicals capable of degrading organic pollutants. This in situ generation reduces safety concerns associated with external H₂O₂ handling.²

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The Dual Role of CNTs

CNTs serve a dual function: as both a structural filter and an active electrode. As filter membranes, they enhance water permeability and flux. When functionalized with carboxyl groups, CNTs also act as efficient electrodes for copper ion adsorption in an aqueous solution.

One example includes a CNT-encapsulated α-ferric oxide (Fe₂O₃) cathode, which enables efficient degradation of tetracycline and supports two-electron reduction reactions. This synergy between targeted degradation and efficient transport pathways highlights the efficacy of the CNT-based electrode.⁴

Key Factors Influencing CNT-EC Filter Performance

The efficiency of CNT-based electrochemical water treatment systems depends on a combination of electrical, material, chemical, and design parameters. Optimizing these variables is essential to achieve consistent and effective contaminant removal.

Electrical Parameters

Voltage, current density, and pulse types influence filter efficiency. CNT tips become electrochemically active at higher potentials (≥ 0.3 V), while sp² conjugated sidewalls are prevalent at lower potentials (≤ 0.2 V). However, applying excessively high voltages can degrade the CNT structure.

Current density increases with anode potential. Compared to direct current capacitive deionization (CDI), CNT systems powered by pulsed voltage supplies offer improved desalination performance for saline water.²

CNT Properties

The physical and chemical characteristics of CNTs influence overall filtration efficiency. MWCNTs have a high specific surface area, reducing cathodic impedance, enhancing anode potential, and boosting current density, which results in more effective adsorption.

Vertically aligned MWCNTs exhibit higher water flux due to reduced internal gaps. Additionally, doping CNTs with nitrogen or boron modifies their work function, improving their electrochemical filtration capability.

Surface modification of CNTs with biomolecules (e.g., aptamers, antibodies) or inorganic compounds like magnetite further enhances filter selectivity and performance.⁵

Water Chemistry

CNT filters operate optimally at neutral pH. Their efficiency is influenced by the chemical nature of the electrolyte and the presence of interfering ions.

For example, variations in the ionic strength of sodium sulfate do not affect the oxidation of ferrocyanide, whereas changes in sodium chloride concentration do. Similarly, phosphate recovery is suppressed in the presence of competing anions like sulfate, nitrate, and chloride, indicating high selectivity of CNT filters toward phosphate.^2,6

Reactor Design

Reactor configuration plays a significant role in treatment efficiency. Flow-through systems outperform batch systems, which are limited by slower diffusion and lower recovery rates. Internal convection in flow-through designs supports more efficient mass transport.

Electrode spacing also impacts electrosorption. Greater distances between electrodes reduce the removal efficiency of compounds such as perfluorooctanoate. Effective electrochemical treatment depends on reactors with high surface-area-to-volume ratios and optimized flow rates, both of which enhance current efficiency and oxidation performance.²

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Case Studies and Recent Innovations

Recent research has highlighted the growing potential of CNT-based systems in advanced water treatment applications, particularly in the removal of organic micropollutants and heavy metals.

One study explored the effectiveness of CNTs synthesized via chemical vapor deposition in removing pharmaceutical pollutants from wastewater through electrochemical treatment. The CNTs, characterized using a range of techniques, showed high contaminant removal efficiency.⁷

In a separate pilot-scale investigation, a graphene–CNT composite adsorbent was used to reduce o-cresol concentrations in wastewater to below 1.12 mg/kg. The study found the composite to function as an effective and reversible adsorbent for pollutant removal.⁸

Researchers at Donghua University and the Harbin Institute of Technology investigated the development of a catalytic CNT membrane designed for permanganate activation. Their results showed that the permanganate/CNT system significantly improved micropollutant degradation and could offer a sustainable solution for treating contaminated wastewater.⁹

Additionally, a review by the Swiss Federal Institute of Aquatic Science and Technology (Eawag) examined current challenges in quantifying CNTs in environmental matrices. The authors highlighted the lack of standardized methods for CNT detection, underscoring the need for more robust monitoring of CNT discharge into natural water systems, alongside comprehensive toxicity assessments.¹⁰

Together, these studies reflect the rapid innovation in CNT-enabled water treatment and point to the broader role of advanced materials in addressing global water challenges. To explore related technologies, see the articles below:

• Next-Generation Materials for Water Purification
• Using AFM to Study Membranes in Water Treatment Facilities
• Graphene Membranes: Applications in Modern Water Purification
• How is Nanocellulose Used in Water Purification?
• The Instrumental Role of MEMS Pressure Sensors in Water Conservation

References and Further Reading

1. United Nations Educational, Scientific and Cultural Organization (UNESCO). (2023). United Nations World Water Development Report 2023: Partnerships and cooperation for water. UNESCO Publishing. DOI: 10.18356/9789210026463. https://unesdoc.unesco.org/ark:/48223/pf0000384655
2. Jame, S. A. et al. (2016). Electrochemical carbon nanotube filters for water and wastewater treatment. Nanotechnol. Rev., 5(1), 41–50. DOI:10.1515/ntrev-2015-0056. https://www.degruyterbrill.com/document/doi/10.1515/ntrev-2015-0056/html?lang=en
3. O'Connor, M. P. et al. (2018). Electrochemical deposition for the separation and recovery of metals using carbon nanotube-enabled filters. Environ. Sci.: Water Res. Technol., 4, 58–66.
4. Chen, W. et al. (2025). Efficient degradation of tetracycline contaminants by a flow-through Electro-Fenton system: Carbon nanotube-encapsulated α-Fe₂O₃ under nanoconfinement. Chem. Eng. J., 507, 160449. DOI:10.1016/j.cej.2025.160449. https://www.sciencedirect.com/science/article/abs/pii/S1385894725012549
5. Gao, G. et al. (2012). Doped Carbon Nanotube Networks for Electrochemical Filtration of Aqueous Phenol: Electrolyte Precipitation and Phenol Polymerization. ACS Appl. Mater. Interfaces, 4(3), 1478–1489. DOI:10.1021/am2017267.
6. Schnoor, M. H. et al. (2013). Quantitative examination of aqueous ferrocyanide oxidation in a carbon nanotube electrochemical filter: Effects of flow rate, ionic strength, and cathode material. J. Phys. Chem. C, 117, 6,2855–2867. 10.1021/jp3112099.
7. Gangadhar, A. et al. (2023). Fabrication of carbon nanotubes coated electrode to remove pharmaceutical pollutant in treated effluent. Chem. Pap., 77, 3855–3866.
8. Yin, Z. et al. (2021). High-performance graphene/carbon nanotube-based adsorbents for treating diluted o-cresol in water in a pilot-plant scale demo. ACS Appl. Mater. Interfaces, 13(36), 43266–43272. DOI:10.1021/acsami.1c11410
   https://pubs.acs.org/doi/10.1021/acsami.1c11410
9. Wang, X. et al. (2023). Insights into the electron transfer mechanisms of permanganate activation by carbon nanotube membrane for enhanced micropollutants degradation. Front. Environ. Sci. Eng., 17(9), 106. DOI:10.1007/s11783-023-1706-0. https://journal.hep.com.cn/fese/EN/10.1007/s11783-023-1706-0
10. Elijah J.P., et al. Quantification of Carbon Nanotubes in Environmental Matrices: Current Capabilities, Case Studies, and Future Prospects. Environmental Science & Technology (2016) 50 (9), 4587-4605. DOI: 10.1021/acs.est.5b05647 https://pubs.acs.org/doi/10.1021/acs.est.5b05647

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