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Chemistry LibreTexts

Introduction

The detection of phenol and other phenolic related compounds in water samples is of great importance due to their toxicity and high solubility. These compounds are contaminants in environmental matrices, food, and medicine products that can easily be absorbed through humans and animals’ skin or mucous membranes. This absorption affects vital organs and tissues (1 - 4). This lab focuses on the ability to enhance phenol detection by further modifying the surface of bare sonogel-carbon electrodes with ZrO2.

This research can be challenging for students since it requires the synthesis of a sonogel-carbon electrode modified with zirconium oxide and operation of a potentiostat. The analysis for the laboratory exercise includes a comparison of a modified electrode’s cyclic voltammogram with that of a bare sonogel-carbon electrode. Cyclic voltammetry is a widely used method in teaching electrochemistry. The current at the working electrode is plotted against the potential applied. When the potential is sufficiently “negative” or “positive”, the component in solution being analyzed got reduced or oxidized at the electrode surface, respectively. A jump of current is observed when the component is electrolyzed (oxidized or reduced) corresponding to a peak on the graph. The most important parameters of a cyclic voltammogram are the magnitudes of the peak currents (anode and cathode) as well as the potentials at which the peaks occur. Reversibility is a vital concept in analyzing a cyclic voltammogram. For a reversible couple, the separation of peak potential is independent of the scan rate. However, an irreversible couple’s peak separation depends on the scan rate (5). The graph of cyclic voltammogram can have one of three shapes: reversible, quasi-reversible, or irreversible. When the anode and cathode peak currents’ height ratio is very close to 1, the process is reversible. Similarly, when the peak height ratio is less than or greater than 1, the process is quasi-reversible. In an irreversible process, only one peak (either oxidation or reduction) is observed. Both quasi-reversible and irreversible cyclic voltammogram exhibit an irreversible couple, because as the scan rate increases or decreases, a quasi-reversible plot will become irreversible. This experiment is designed to fit into two lab sessions, where each lab session is approximately five hours long. This lab has been created for Project REEL (Research Experiences to Enhance Learning). The project goal is to help undergraduate students develop problems solving and analyzing techniques by incorporating research-intensive programs. These research modules (programs) were introduced during into introductive chemistry courses and carried out through the senior level, which encourages students to pursue further scientifically oriented training and increase graduation in science related fields. Further details can be found at www.ohio-reel.osu.edu/project.php