Electrostatic boosting of ionic dye pollutant removal from aquatic environment using a single electrode photoreactor

Abstract

A green advanced oxidation (AO) strategy to destroy dye pollutants and remove them from aquatic environments is to utilize sunlight and employ thin-film semiconducting photo-reactors. In this light-driving AO method, besides the type of dye and semiconductor material, attention to the electrostatic interactions between dye and electrode is of great importance. In this paper, a couple of nanostructured, narrow-bandgap, semiconducting photoelectrodes, i.e., hematite (n-type) and pyrite (p-type) were fabricated electrochemically and employed for the elimination of two cationic (malachite green) and anionic (methyl orange) dyes inside a single-electrode photoreactor. It was shown that without applying a faradic potential bias and consuming electricity or changing the pH of medium, the decolorization ability of the fabricated photoelectrodes can be substantially boosted just by their connection to an electrostatic (non-faradic) bias source. Regardless of the type of photoelectrode, in the case of cationic dye, the application of a negative polarity and for the anionic dye, a positive polarity remarkably promoted the reactor activity. These observations were discussed in detail through electrostatic attractive/repulsive forces between ionic dyes and charged photoelectrodes, and finally a mechanistic perspective was put forward for the photo-electrostatic dye removal process.