Photodegradation of methylene blue, rhodamine 6G and methyl orange under sunlight/H2O2 irradiation

Abstract This study investigates the photodegradation of the organic dyes, methylene blue (MB), rhodamine 6G (R6G) and methyl orange (MO), using a hydrogen peroxide (H 2 O 2 )-based system, which instead UV, like most reports in literature, is activated by natural sunlight. The degradation efficiency was evaluated by varying the H 2 O 2 volume (0, 50, 100 and 500 μL) in dye solutions (100 mL) exposed to sunlight for 8h. The dye degradation process was followed by UV–Vis absorbance spectroscopy and photoluminescence measurements of the dye solutions. The results revealed high removal efficiencies of 99% for MB, 98% for R6G and 87% for MO. Degradation kinetic analysis demonstrated that MB degradation followed a second-order model, whereas R6G and MO adhered to a first-order model. Photoluminescence and FTIR studies provided further insight into structural changes during degradation, identifying intermediate fluorescent species and assigning specific spectral bands to monomers, aggregates, and degradation byproducts. These findings elucidate the underlying photochemical mechanisms and highlight the H 2 O 2 /sunlight system as an efficient, sustainable approach for degrading organic pollutants in aqueous environments.