Stability and Performance Enhancement of an Oligo (phenylene vinylene) Photocatalyst via Surface Grafting onto TiO₂ for Visible‐Light Indigo Carmine Degradation

Abstract

The chemical immobilization of a dibenzoic acid oligo (phenylene vinylene) (OPV) derivative for TiO2 sensitization was evaluated as a strategy to enhance both the stability and photocatalytic performance of this π‐conjugated moiety when applied to the photodegradation of indigo carmine dye (IC) as model pollutant. The results show that the electron injection from the photoexcited OPV to the TiO2 conduction band remarkably boosts the IC degradation ability under visible light illumination. The use of SiO2 as non‐photoactive support was also investigated to simultaneously determine the role of the inorganic support in the photocatalytic process. The spectroscopic, thermal, and surface characterization validated the successful grafting of the OPV to the inorganic supports. Moreover, superoxide radical and singlet oxygen were established as the active species involved in the dye degradation identifying an additional direct reducing pathway. Interestingly, the use of electron donors proved to be an ineffective approach to increase the system performance, entailing that the OPV regeneration proceeds chiefly via back electron transfer processes. Finally, the reusability tests confirmed that TiO2/OPV material retains up to 86 % of their photocatalytic activity during the first five cycles, demonstrating a critical enhancement in the organic conjugated framework stability.

Tunable Generation of Reactive Oxygen Species in SnO2/SnS2 Nanostructures: Mechanistic Insights into Indigo Carmine Photodegradation

“…Knowing that the efficiency of IC degradation increases with increasing SnS 2 content (Figure ) and how ROS speciation and generation efficiency change across all the samples with their changing composition, the IC photodegradation pathways can be proposed (Figure ) in line with the representative literature. − Indigo carmine is classified as a donor–acceptor dye type, where heterocyclic amines (−NH– groups) are electron donors, and carbonyl groups (−CO) are electron acceptors. The color of IC in aqueous solutions (absorbance maximum at 610 nm , ) is related to the structural unit consisting of two −NH– and −CO groups that are “cross-conjugated” through >CC< bridge (H-chromophore). , Under light illumination, dye molecules can be converted into a higher-energy excited state (IC*). One of the five possible resonance structures is shown in Figure .…”

“…74−82 Indigo carmine is classified as a donor− acceptor dye type, where heterocyclic amines (−NH− groups) are electron donors, and carbonyl groups (−C�O) are electron acceptors. The color of IC in aqueous solutions (absorbance maximum at 610 nm 77,78 ) is related to the structural unit consisting of two −NH− and −C�O groups that are "cross-conjugated" through >C�C< bridge (Hchromophore). 77,83 Under light illumination, dye molecules can be converted into a higher-energy excited state (IC*).…”