Abstract
This manuscript reports the use of nanoparticle-modified voltammetric sensors for the rapid and green determination of chemical oxygen demand in river waters and waters from agricultural waste. Four different variants of modified electrodes have been prepared: CuO nanoparticles electrogenerated over Cu and covered with Nafion film (CuO/Cu-Nf), and graphite–epoxy composites modified with Cu, CuO, and Cu–Ni alloy nanoparticles. The response features of these electrodes were assessed by calibrating them vs. glucose, glycine, ethyleneglycol, and hydrogenphtalate in alkaline media, as samples providing different difficulty in their (bio)degradation characteristics. The most sensitive electrode was demonstrated to be the (CuO/Cu-Nf) electrode, with an LOD of 12.3 mg O2·L−1. The joint information provided by the sensor array showed the ability of estimating both the organic load and the type of sample in terms of difficulty of degradation, in what can be named an intelligent sensor assembly.
Highlights
Accompanied with the development of the modern industry, the protection of water resources from being polluted by waste effluents is becoming more relevant
Chemical oxygen demand (COD) is an important parameter for evaluating the degree of water pollution by generic organic compounds, being a faster variant to ascertain the actual requirements for its biodegradation, the biochemical oxygen demand (BOD), which has precise long estimation times
COD is defined as the equivalent amount of molecular oxygen required to decompose by chemical oxidation all the organic compounds contained in 1 L of aqueous solution to carbon dioxide and water
Summary
Accompanied with the development of the modern industry, the protection of water resources from being polluted by waste effluents is becoming more relevant. There is a well-established and standardized method in many countries for measuring COD using potassium dichromate as the oxidizer in sulfuric acid media This method is very time-consuming, has high costs, and it is environmentally hazardous, as there is a reflux (2–4 h) in the process, and some expensive (Ag), corrosive (H2 SO4 and Cr2 O7 2− ), and highly toxic (Hg and Cr (VI)) reagents are needed throughout the procedure [1]. In spite of the fact that it is almost impossible to decompose all the organic contaminants, getting close to it is a necessary step to improve the accuracy and precision in the COD electrochemical determination In addition to this information, whether a certain organic compound is decomposed or this is difficult contributes some important additional information to the organic load of a sample. The PCA technique applied to the profiles shown in the voltammograms was used to evaluate the main component of a polluted water sample, which was able to indicate whether this is easy or difficult to be degraded
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