Photo Decoloration of Methylene Blue with Ribose under Optimum Conditions by Visible Radiation

Photo decoloration of the methylene blue (MB) with reducing sugar, ribose (RH), was investigated on an especially designed optical processor using monochromatic radiation of 661 nm through a red filter. The dye molecule gets excited into triplet transient species (MB_T) during flushing with lifetime of 10.1 µs into acetate buffered aqueous alcoholic medium, which later on reduces to protonated leuco dye (MBH). Photolysis of the aqueous alcholic medium generated highly reactive oxygen radical (O^?·) with the production of 2e^?, which led to probable oxidation of the ribose into respective acid while hydrogen abstraction and 2e^? reduced the dye (MB) into MBH by following reaction MBr⁺+RCHO→MBH+RCOOH. Influences of different operational parameters suggest the imperative role of acidity, reductant and temperature where positive relations with quantum yield (π) were established under the optimum conditions while elevated concentration of dye resulted in the decrease in the absorption of number of photon consequently, and no change in the π was observed. A highly solvated transient complex was reported in the reduction of MB and RH through thermodynamics activation parameters. A mechanism of MB_T formation and its reduction into MBH has been discussed.