Enhanced photodegradation of tartrazine using 5- (hydroxyphenyl)-10, 15, 20-tris- (pentafluoro) porphyrinato palladium chloride and ZnO nanocomposites under visible light

Abstract

The persistence of synthetic dyes such as tartrazine (TAR) in aquatic environments poses significant ecological risks. This study explores the visible light-driven photocatalytic degradation of TAR using zinc oxide (ZnO) and porphyrin-based systems. Comparative analysis was performed between ZnO, free-base porphyrin (H 2 P), palladium-metallated porphyrin (HPd), ZnO-H 2 P, and ZnO–HPd composites, where the composite was synthesized through the physical adsorption method for the photodegradation of tartrazine. Comprehensive characterization channelling between the materials was carried out using Transmission Electron Microscope (TEM), Scanning Electron Microscope (SEM), Energy Dispersive Spectroscopy (EDS) and other spectroscopic techniques, where SEM and TEM analyses revealed well defined hexagonal ZnO nanoparticles that become rougher and more aggregated upon porphyrin functionalization, with EDS confirming the presence C, N, Pd, indicating the successful conjugation and metalation. The ZnO–HPd composite demonstrated the highest photocatalytic performance, 98.8% degradation within 70 minutes under visible light irradiation, furthermore, under the same optimal conditions (10 mg catalyst, pH 7, visible light), ZnO-H 2 P achieved degradation efficiency of 63%, and ZnO was 14% The superior activity of ZnO-HPd was attributed to enhanced light absorption, efficient charge separation, and synergistic charge carrier channelling between ZnO and HPd. Furthermore, under the same optimal conditions (10 mg catalyst, pH 7, visible light), the ZnO-HPd composite also exhibited good reusability, maintaining 53.2% of its photocatalytic activity after four consecutive cycles, with FTIR analysis confirming no significant structural changes after reuse. The effectiveness of this composite under visible light suggests promising real-world applications that use natural light for water purification.