Alginate–oligothiophene aerogels as photocatalysts for the degradation of emerging organic contaminants in water

Abstract

V-shaped oligothiophenes bearing a benzothiophene (BT) core and S-oxide or S,S-dioxide moieties are herein proposed as photocatalysts for the degradation of three selected water emerging contaminants. Photocatalyst molecules were designed in order to minimize aggregation in the solid state (V-shape structure), lower the HOMO–LUMO gap (S,S-dioxide moiety functionalization) with respect to conventional oligothiophenes and enhance the photocatalytic performance. The targeted BT molecules were synthesized by the Stille cross-coupling reaction and their ability to generate reactive oxygen species (ROS) upon blue-light irradiation was demonstrated. For practical exploitation, BTs were embedded into an alginate matrix by ionotropic gelation–freeze drying processes to obtain porous aerogels that were dispersed in water and used for the degradation of emerging contaminants. Degradation performance of up to 99% after 2 h on ofloxacin (antibiotic), rhodamine B (dye) and bisphenol A (plastic additive), was observed. In addition, regenerated photocatalysts showed unchanged performance after five reuse cycles. The relationship between the BT molecular structure and ROS production, investigated by QM calculations, highlighted the role of the S,S-dioxide moiety in ROS generation, with ofloxacin antibiotic degradation performance reaching up to 99% for BTO₂-T2. Remarkably, ecotoxicity studies showed no toxicity of the photodegradation products toward the Aliivibrio fischeri bioluminescent bacterium, highlighting the potential of BT molecules for water purification.