Evaluation of the surface activity of silicon in electrolytic media under the influence of hydroxyl radicals

Abstract

The purpose of this study is to evaluate the surface activity of silicon by evaluating a voltammetric profile of the substrate in an electrolytic medium. Since the electrical current flowing through the circuit is a measure of the rate at which a redox process occurs at the interface, higher current values will indicate more active substrates. For this study, hydroxyl radicals were generated by photochemical decomposition of H₂O₂. For this purpose, a H₂O₂ solution was irradiated with a UV lamp. The experimental conditions that were varied in the process were: illumination time, H₂O₂ concentration. The presence of the hydroxyl radicals generated through the methodology employed was qualitatively confirmed by fluorescence, using for this purpose (i) a 2′,7′-dichlorodihydrofluorescein diacetate (DCFH-DA) probe and (ii) a “radical scavenger”, which corresponds to an antioxidant species, in this case ascorbic acid. On the other hand, for the voltammetric measurements of the semiconducting substrate after interaction with hydroxyl radicals, a 0,1 M KCl solution was used as electrolyte solution. The experimental conditions studied were: influence of the pH of the medium and influence of different chemical treatments applied to the substrates used after interaction with hydroxyl radicals. From the results obtained, an increase in both_H2O2 concentration and immersion time produces an increase in current in the interphase electrode processes, indicating an activation of the semiconductor electrode surface. Indeed, in the anodic hemicycle, the signal of substrate oxidation appears at −0,75 V, and then from −0,45 V onwards, the oxidation of water. This is an indication that the semiconductor/electrolyte interface is ohmic, since in the absence of illumination (absence of minority carriers, h⁺) there are oxidation processes. On the other hand, for pH values in the intervals between 2 > pH > 5 and 7 > pH > 13, the slopes are approximately 0 mV/pH and for the interval between 5 > pH > 7, of the order of 60 mV/pH, this being an indication of a change in the nature of the surface functional groups of silicon.