Ultra-fast photocatalytic degradation of Rhodamine B exploiting oleate-stabilized zinc oxide nanoparticles

Rhodamine B (RhB) is a harmful dye released by industrial wastewaters, thus necessitating its urgent removal. Advanced oxidation processes constitute promising strategies to purify polluted water. Among others, photocatalysis relies on reac- tive oxygen species (ROS) produced by photocatalytic particles, typically semiconductors like titania or zinc oxide (ZnO), excited by solar or UV–Vis light. However, their wide band gap limits their catalytic capabilities within the absorption of the UV spectrum and causes fast electron–hole recombination. This study presents novel strategies to overcome these limitations: (i) doping semiconductors to increase photocatalytic efficiency; (ii) sensitization-mediated photocatalysis for visible light activation using chemical moieties to trap dye molecules; (iii) nanosizing the photocatalysts to enhance the surface area. ZnO nanoparticles, doped with iron or gadolinium and capped with oleic acid are here synthesized and tested in RhB dye solutions. Remarkably, the results demonstrate an ultra-fast RhB degradation, driven by oleic acid hav- ing crucial role in dye adsorption. The degradation mechanisms, including ROS-induced N-deethylation and xanthene group cleavage, are also unraveled. These findings underscore the efficacy of the proposed semiconductor photocatalyst design, highlighting a significant advancement with extensive potential applications in wastewater remediation. This innovative approach paves the way for more efficient and practical solutions to combat industrial dye pollution.