TiO₂/UV-assisted rhodamine B degradation: putative pathway and identification of intermediates by UPLC/MS

The present study was designed to evaluate the photocatalytic degradation of Rhodamine B (Rh-B) in a self-assembled TiO₂-assisted system under UV light irradiation. Chemical oxygen demand, total organic carbon and high-performance liquid chromatography analyses confirmed the elevated Rh-B degradation level. A stepwise meticulous breakdown pathway based on the ultra-performance liquid chromatography coupled with electrospray ionization mass spectrometry is proposed. Results demonstrated that the degradation of Rh-B mainly occurred via N-de-ethylation process, and N-de-ethylated intermediate products were further oxidized into acids and alcohols. Reduction in toxicity of the dye by the formation of metabolites was measured using human cell lines (MTT assay) and toxicity tests based on shrimp Artemia salina. Noticeably, the degraded intermediates of Rh-B revealed low or non-toxicity than the original dye molecule. Therefore, it can be inferred that the TiO₂-assisted photocatalysis could be beneficial for the degradation of recalcitrant compounds and textile wastewater effluents, and for the elimination of toxicity therein.