Amperometric sensing of chemical oxygen demand at glassy carbon and silicon electrodes modified with boron-doped diamond

A boron-doped diamond (BDD) sensor is proposed for effective detection of chemical oxygen demand (COD) by means of amperometric technique. Boron-doped diamond thin films, acting as active sensors, were deposited on both silicon wafer and glassy carbon (GC) substrates by microwave plasma assisted chemical vapour deposition. SEM micrographs showed that BDD–Si displays triangle-faceted crystallites ca. 0.5–3 μm in size, while BDD–GC has triangle-faceted crystallites ranging from 0.5 to 3 μm and also a small amount of square-faceted grains 0.5–1 μm in size. The structure of BDD was confirmed by broad Raman bands centred at 483 cm−1 and 1216 cm−1. Cyclic voltammograms were measured in tetrabutylammonium perchlorate/dimethyl sulfoxide solution to determine chemical oxygen demand by amperometric technique. The reduction of oxygen at boron-doped diamond predominantly involves the one electron reduction of oxygen to superoxide. The reduction of oxygen on BDD–Si and BDD–GC was found to be quasi-reversible (ΔE = 59 − 100 mV). The lowest detection limit was about 0.9 mg l−1. Two different types of electrochemical behaviour were observed at BDD–Si and BDD–GC electrodes which indicates a complexity of electroreduction of oxygen on the BDD surface.