Synergic Effects of pH, Reaction Temperature, and Various Light Sources on the Photodegradation of Methylene Blue Without Photocatalyst: A Relatively High Degradation Efficiency

This study investigates the influences of synergic effects the wide range pH values (4–11) and different light sources such as UV-lamp, LED-lamp, Solar light, and halogen lamp on the photodegradation of MB without photocatalyst. So, this is the first comprehensive study about photodegradation of the MB without photocatalyst under various light irradiation with relatively higher photocatalytic activity. Comparatively, the highest photocatalytic degradation efficiencies (η) of MB were obtained as 99.24 and 99.84% for the 90 and 120 min under the halogen and solar light radiation, respectively. Further, remarkable MB η of 85.53 and 98.56% were obtained for 30 and 60 min under the halogen light radiation, reflecting a high sensitivity of the MB to visible light. Furthermore, the photodegradation of MB was pH-sensitive. Comparatively, in the alkaline medium, the higher η values were obtained than those of the acidic and neutral media suggesting the base medium where OH⁻ could be directly reacted with a hole to produce hydroxyl radical, OH*. Moreover, the impact of the reaction temperature cannot be ignored. The observed high sensitivities were attributed to synergic effects of the pH, visible light (the convenient energy difference between the LUMO and HUMO energy states of π–π* of MB, which highly matched with the energy of the visible region of the solar and halogen light spectra) and reaction temperature.