6:2 fluorotelomer sulfonate (6:2 FTS) is being widely used as an anti-foam agent in the electroplating process. As such, it is a common co-contaminant in electroplating wastewater streams beside chromate (i.e., Cr(VI)). Conventional methods for the removal of Cr(VI) from electroplating wastewaters include adsorption, reduction, and precipitation. However, these methods are unlikely effective at removing 6:2 FTS since this compound is relatively hydrophilic and highly resistant to reductive degradation. Recent studies have shown that 6:2 FTS can be destroyed by reactive species such as hydroxyl and sulfate radicals. As such, we hypothesize that 6:2 FTS and Cr(VI) can be removed using a treatment system that couples reduction of Cr(VI) with the oxidation of 6:2 FTS. Specifically, we hypothesize that the simultaneous reduction of Cr(VI) and oxidation of 6:2 FTS can be achieved using wide-band-gap photocatalysts that upon UV-light irradiation will generate strong reductants (e.g., conduction band electron) and oxidants (e.g., valence band hole, hydroxyl radical). We also hypothesize that the removals of Cr(VI) and 6:2 FTS will be enhanced by the presence of each other, since they will retard the recombination of electrons and holes in the photocatalyst. To test these hypotheses, the removal of 6:2 FTS and Cr(VI) was investigated using two wide-band-gap photocatalysts, namely In2O3 (Eg = 2.9 eV) and Ga2O3 (Eg = 4.8 eV), and a commercial TiO2 photocatalyst. Under UV-C irradiation, Ga2O3 appeared to be significantly more effective than In2O3 and TiO2, with over 90% of [6:2 FTS]0 = 100 μg/L oxidized and a complete reduction of 1 mg/L Cr(VI) into Cr(III) within 2 hours (a fluence of 19 J/cm2). The oxidation of 6:2 FTS was twice slower in the absence of Cr(VI), confirming the synergistic effect between the co-contaminants. A detailed mechanism of contaminant removal is proposed.

Simultaneous photocatalytic removal of 6:2 fluorotelomer sulfonate and hexavalent chromium by gallium oxide under ultraviolet irradiation

ACS Spring Meeting 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.