Degradation of methylene blue and methyl orange by palladium-doped TiO2 photocatalysis for water reuse: Efficiency and degradation pathways

In this work, methylene blue (MB, a thiazine dye) and methyl orange (MO, an azo dye), which have similar molecular weights but different structures, are selected as model pollutants. The Pd-doped TiO2 catalysts are prepared using a facile sol-gel method for enhanced photocatalysis because this process achieves not only decolorization but also complete mineralization. The intermediates produced during photocatalysis of single dyes are identified by an ultra-performance liquid chromatography-tandem mass spectrometry (UPLC®-MS/MS, Waters), and consequently the degradation pathways are proposed and discussed.266