Optimization of Boron-Doped Diamond Thin-Layer Cell for Chemical Oxygen Demand Sensor Based on Anodic Oxidation of Organics

Abstract

The advanced electrochemical oxidation process (AEOPs) has been considered as an appealing approach to overcome problems associated with the conventional water treatment methods. The use of expensive and toxic chemical oxidizing reagents in chemical oxygen demand, for example, can lead to environmental concerns of the production of secondary pollution. Anodic oxidation, one of the most popular AEOPs, offers a rapid and straightforward COD determination by removing the need for chemical oxidants. The process mainly relies on the anode material to degrade the organic molecules; thus, choosing the appropriate material is one of the keys to a successful electrochemical oxidation.Numerous electrochemical applications utilize boron-doped diamond as the anode material due to its unique properties such as wide potential window, low background current, and resistance to fouling. The employment of BDD for anodic oxidation of organics enables complete oxidation of organics via physically adsorbed hydroxyl radicals (●OH). The species offers a high standard redox potential of E° (●OH/H2O) = 2.80 V/SHE, high reactivity, and short lifetime, makes it possible to be used for the on-site electrochemical oxidation process.The objective of this study is to develop and optimize an electrochemical system for chemical oxygen demand determination based on a photoelectrochemical degradation principle. The degradation of phenols takes place in a specially designed BDD thin-layer electrode, and the amount of electrons transferred at the electrode can be measured to define the equivalent COD value. A 60μm thick films are used as a spacer, resulting in a contact area of 3 cm2. At 2.54 V vs. SHE, a sample containing 50 mg/L analytes required less than 3 mins to degrade, and the assay time for organics decay increases for a higher concentration of phenols. Incorporating the BDD electrode with cathode materials, such as Pt-coated indium tin oxide (ITO), will be employed as an attempt to improve the degradation efficiency by minimizing the voltage drop between the electrodes. Sandwiching the BDD-cathode using Nafion® membrane will be studied to remove the need for additional supporting electrolytes. The major experimental conditions of the anodic oxidation of organic molecules by BDD, such as applied potential bias, supporting electrolyte concentration, pH, and dissolved oxygen concentration, will be varied to obtain the optimum conditions.