Methylene blue (MB) is a synthetic dye widely used in textile industries. This work describes the application of solar radiation to direct photolysis degradation of methylene blue in aqueous solution. Experiments were conducted at room temperature to study the effects of exposure time, solution volume and MB concentration on dye degradation rates. The results show that the maximum amount of methylene blue removed is 6.8 mg/L, obtained at an initial concentration of 10 mg/L, volume of 50 mL and exposure to solar radiation for 5 hours. These results also point to an increased efficacy of direct photolysis of methylene blue as the dye concentration increases. Kinetic model analysis indicates that the absorption of methylene blue follows a first-order kinetics, with a constant velocity k = 1,3 × 10⁻³ min⁻¹. Direct photolysis by solar radiation is an effective method for degrading or even eliminating methylene blue in water.
