Determination of humic acid (HA) and sodium alginate in water using Fe₂O₃ and CuO nanoparticle-modified glassy carbon electrode

ABSTRACT

This study reported the determination of humic acid (HA) and sodium alginate (Na-Alg) at glassy carbon electrode (GCE) modified with iron oxide (Fe₂O₃) and copper oxide (CuO) nanoparticles (NPs), respectively. The synthesised NPs were characterised using spectroscopic and microscopic techniques. Successful modification of the electrode with NPs was confirmed with 1 mM Ferri/Ferro ([Fe(CN)₆]^3−/4−) redox probe using cyclic voltammetry and electrochemical impedance spectroscopy (EIS). Results indicated that GCE-Fe₂O₃ and GCE-CuO have higher current responses with lower charge transfer resistance (Rct) compared with the bare GCE. Electrocatalytic oxidation of HA and Na-Alg at the modified electrode showed a current drop due to adsorption of the analyte or electrode fouling effect. GCE-CuO showed better resistance to the analyte fouling effect with 17.7% and 31.1% current drops after second scan in HA and Na-Alg, respectively. The limit of detection values were 5.42 μM (HA), 5.06 μM (Na-Alg) at GCE-Fe₂O₃ electrode and 4.88 μM (HA), 3.82 μM (Na-Alg) at GCE-CuO electrode using LSV technique. The adsorption equilibrium constant β at the electrodes ranged from 3.03 to 60.50 × 10⁴ M⁻¹, while free energy due to adsorption ΔG^o ranged from −25.57 to −32.99 kJmol⁻¹. The developed sensors can be used for detection and monitoring of HA and sodium alginate in treated and untreated water samples.

KEYWORDS:

• Adsorption
• electrochemical impedance
• electrochemical sensor
• humic acid
• Langmuir isotherm

Acknowledgments

The authors acknowledged the support of Nanotechnology and Water Sustainability Research Unit (NanoWS), College of Science, Engineering and Technology, University of South Africa, Johannesburg, South Africa. ASA thanks University of South Africa (UNISA) for the Visiting Researcher Support Programme (VRSP) and Obafemi Awolowo University Nigeria for the Sabbatical leave visit.

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplementary material

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Additional information

Funding

This project was supported by Nanotechnology and Water Sustainability Research Unit (NanoWS), College of Science, Engineering and Technology, University of South Africa (UNISA), Johannesburg, South Africa.