Symbiotic coupling of ZnO nanoparticles and coumarin photosensitizer in soft polyurethane matrices for boosting visible-light photocatalytic performance

Photocatalysis provides a practical and efficient solution to eliminate harmful substances from the environment by using light energy to activate the catalysts, and the development of sustainable photocatalysts easily recoverable and highly efficient in visible light remains a significant challenge. To address this issue, herein we present a facile approach to immobilize silane-functionalized ZnO NPs in polyurethanes with coumarin chromophore, resulting in highly active recyclable and reusable hybrid materials as photocatalytic systems for the degradation of organic dyes. Characterization of ZnO NPs revealed that the attachment of silane units to nanoparticles' surface decreased band gap values (up to 2.83 eV) and reduced the rate of charge carrier recombination. The performed investigations showed that incorporation of ZnO NPs into macromolecular chains via quaternization near to coumarin units promoted efficient photoinduced charge transfer between semiconductor nanoparticles and photosensitizer molecules. The band gap energy for hybrid films ranged between 2.73 eV and 2.32 eV, and the best photodegradation results for malachite green (MG) under visible-light irradiation were attained after 17 min (k = 17.7 x 10-2 min-1). The photocatalytic mechanism was clarified using scavenger tests and the photocatalytic efficiency of the best performing sample was tested for the degradation of other dyes (brilliant blue R, sunset yellow, congo red, rhodamine B, s.o.) and for the removal of MG from binary dye mixtures. The stability and integrity evaluation after 7 catalysis cycles reveals that the photocatalytic potential is retained without substantial structural changes.