Comparative photocatalytic degradation of acid fuchsin and basic fuchsin: insights into the role of sulfonate groups, degradation pathways, and toxicity to brine shrimp
摘要
Photocatalytic degradation of acid fuchsin (AF) and basic fuchsin (BF) dyes on anatase titania nanoparticles (TiO₂ NPs) activated under 365 nm light was systematically investigated to elucidate the role of sulfonate groups in the degradation of triphenylmethane textile dyes. The photocatalytic degradation rate, kinetics, rate-limiting steps, and thermodynamics parameters were evaluated by analyzing experimental data using the Langmuir–Hinshelwood, Weber-Morris, Arrhenius, and Eyring models. The results showed that, up to 180 min of irradiation, the average degradation rate of AF was 0.268 ± 0.012 μM min–1, approximately twofold higher than that of BF (0.138 ± 0.010 μM min–1), while other aspects of the photocatalytic degradation of AF and BF dyes were comparable. The higher degradation rate of AF, compared with BF, was attributed to the presence of its additional sulfonate groups, which together with amino groups induced a push-full effect, enhancing charge delocalization and intermolecular interactions with surface atoms of the photocatalyst. LC–MS and FTIR analyses revealed that the degradation pathways involved radical-induced breakdown of the triphenylmethane structure, followed by hydroxylation, desulfonation, ring opening, demethylation, and dealkylation, ultimately forming smaller aromatic compounds. Both AF and BF dyes produced several identical photocatalytic degradation products, which were further mineralized upon prolonged irradiation. Brine shrimp lethality assays indicated that the photocatalytic degradation products were essentially non-toxic and therefore less harmful to the aquatic environment than their parent fuchsin dyes.
Graphical abstract