The oligomer approach: An effective strategy to assess phenylene vinylene systems as organic heterogeneous photocatalysts in the degradation of aqueous indigo carmine dye

Abstract

Four oligo-phenylenevinylenes (OPVs) were synthesized by the Mizoroki-Heck cross-coupling reaction to provide a deeper understanding of the mechanism and fate of phenylenevinylene systems when applied to the heterogeneous photocatalytic degradation of indigo carmine (IC) dye in aqueous media. OPVs displayed visible light absorption near 500 nm and appreciable emission properties. The stability, mechanism, and photodegradation activity of the OPV systems over aqueous indigo carmine were investigated using radical scavengers, a singlet oxygen (1O2) trap, and ESI-IT-MS. It was confirmed that superoxide radical (O2·−), 1O2, and direct oxidation are responsible for dye degradation. Hydroxide radical formation, under neutral pH conditions, does not occur, and it was corroborated by the HOMO and LUMO levels of the photocatalysts. Additionally, the use of oxalic acid as an electron sacrificial donor was demonstrated as an effective approach to enhance the OPVs photocatalytic activity. However, a significant decrease in activity during the first three irradiation cycles was observed, indicating that the enhancement in photo- and chemical stability is required for further dye-contaminated water treatment applications.