Abstract
A self-supported CuO/Cu nanowire electrode (CuO/CuNWE), which was prepared by annealing Cu nanowires to form a porous Cu nanowire electrode (CuNWE) and then anodizing the as-prepared CuNWE in alkaline medium to generate Cu(OH)2 nanowires followed by calcination, was employed for chemical oxygen demand (COD) determination using cyclic voltammetry (CV). The structure and electrochemical behavior of the CuO/CuNWE were investigated by scanning electron microscopy, X-ray diffraction, and CV. The results indicated that the as-synthesized CuO/CuNWE, in which CuO nanowires with a length of several micrometers and a diameter of 100 to 300 nm could be found, was stable in alkaline medium and more electrocatalytically active for oxidizing a wide range of organic compounds in comparison with the CuNWE. Under optimized alkaline concentration and scan rate, the CuO/CuNWE exhibited a good performance for COD measurement, with a linear range of 5 to 1153 mg L−1, a sensitivity of 2.46× 10−2 mA /(mg L−1), and a detection limit of about 2.3 mg L−1. In addition, an excellent correlation was observed in COD values obtained by our method and the classic dichromate method (r = 0.9995, p < 0.01, n = 11). Finally, our method was successfully used to measure the COD values in real water samples, showing great potential for practical application in water pollution control.
Highlights
Chemical oxygen demand (COD), an important indicator in environmental monitoring, is widely employed to evaluate the amount of organic compounds in wastewater and surface water [1,2].The standard method for COD determination is defined as a measurement of the amount of oxygen equivalently consumed in the oxidation of organic compounds to carbon dioxide, ammonia, and water by strong oxidants under acidic conditions, as in the case of dichromate titration [3]
We feel that use of the Cu nanowire electrode (CuNWE) as substrate for decoration or growth of CuO should be a good choice for generating a CuO/Cu sensor for COD detection because a porous CuNWE is more highly conductive compared to GCE, and has a higher specific surface area than both GCE and Cu rod or foil
In order to prepare a self-supported CuO/CuNWE electrode that can benefit from the high electrical conductivity of Cu, the grown CuO nanowires shouldn’t be too long, so that the porous Cu nanowires (CuNWs) substrate should not be heavily destroyed by anodization (Note: CuO nanowires that are too long will lead to a high charge transfer resistance because of the low electrical conductivity of CuO)
Summary
Chemical oxygen demand (COD), an important indicator in environmental monitoring, is widely employed to evaluate the amount of organic compounds in wastewater and surface water [1,2]. Silva et al used a Cu rod electrode as the sensor and found that it exhibited a wide COD linear range (53.0–2801.4 mg/L) but a high detection limit (20.3 mg/L) despite having a good ability to produce active species CuO(OH) [7]. We have found that thermal annealing of Cu nanowires (CuNWs) can produce a self-supported porous Cu nanowire electrode (CuNWE) with high surface area [25,26,27]. We feel that use of the CuNWE as substrate for decoration or growth of CuO should be a good choice for generating a CuO/Cu sensor for COD detection because a porous CuNWE is more highly conductive compared to GCE, and has a higher specific surface area than both GCE and Cu rod or foil. The CuO/CuNWE-based electrochemical sensor was used to determine the COD values of real water samples collected from industries and surface waters
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