Rutile TiO2 is one of the best potocatalysist present, and the photocatalysis depends on the absorbance maxima of the dye and its concentration in solvent and the band gap of your TiO2.

The photocatalytic degradation efficiency of organic dyes such as Malachite Green (MG), Methylene Blue (MB), Methyl Orange (MO), and Rhodamine B (RhB) using pure rutile TiO₂ varies significantly due to differences in their molecular structures, adsorption behaviors, and degradation pathways. Among these dyes, Methylene Blue generally demonstrates the highest photocatalytic activity when degraded by rutile TiO₂, primarily because of its strong cationic nature that promotes excellent adsorption onto the slightly negatively charged surface of rutile TiO₂ (pH > PZC ~5–6). This strong adsorption facilitates efficient charge transfer and oxidation by photogenerated holes (h⁺) and hydroxyl radicals (•OH), leading to rapid degradation. Malachite Green, another cationic dye, also shows good degradation performance, though it may form slightly more stable intermediates compared to MB, resulting in marginally slower kinetics. In contrast, Rhodamine B exhibits weaker adsorption due to its pH-dependent zwitterionic form, and its degradation is further complicated by stepwise N-deethylation processes that generate persistent intermediates before complete mineralization occurs. Methyl Orange, being an anionic dye, faces the greatest challenges due to electrostatic repulsion from the rutile surface, which severely limits its adsorption and subsequent degradation. Since rutile TiO₂ generates fewer •OH radicals compared to anatase, MO's reliance on •OH-mediated oxidation further reduces its degradation efficiency. Experimental studies consistently report the following order of photocatalytic activity for these dyes on rutile TiO₂: MB > MG > RhB > MO. To enhance the degradation of less efficiently removed dyes like MO and RhB, modifications such as doping rutile TiO₂ with metals or creating heterojunctions with other semiconductors may be necessary to improve adsorption and charge separation. Overall, the superior performance of MB makes it an ideal model pollutant for evaluating the photocatalytic activity of rutile TiO₂, while the other dyes require tailored approaches for effective degradation.

Under the same experimental conditions, Methylene Blue (MB) shows slightly better degradation.