Photo-Degradation of Dexamethasone through Radical-Based Advanced Oxidation Processes Using UV/H2O2 and Fe2+/UV/H2O2 Systems

We report on the effective degradation of dexamethasone (DEX) using systems that generate ·OH radicals based on advanced oxidation processes, specifically UV/H2O2 and photo-Fenton systems. The effects of such parameters as pH (3–11), H2O2 concentration (0.85–68 mg/L) and initial DEX concentration (20–80 mg/L) on degradation were investigated at the temperature range 5–30°C. The efficiency of degradation degree in UV/H2O2 system was found to be 90.92% under the optimal conditions: pH 7, after 8 min, DEX concentration of 40 mg/L, H2O2 concentration of 0.85 mg/L, UV radiation of 1000 W and at the temperature of 25°C. Usage of hydrogen peroxide as an oxidant becomes an additional source of ·OH radicals and reinforces oxidation of the considered drugs. Advanced oxidation technologies, including UV/H2O2, sa-tisfy a pseudo second-order reaction kinetics model, the values of the constant are between 0.386 and 1.249 L/(mg min). The degradation process of DEX in the photo-Fenton system was studied at different Fe2+/H2O2 ratios, between 1 : 10 and 1 : 80, the optimal ratio was found to be 1 : 50 under the following conditions: H2O2 concentration of 2.5 × 10–3 mg/L, DEX concentration of 40 mg/L, at pH 4, Fe2+ concentration of 0.5 × 10–4 mg/L, at a temperature of 25°C. The addition of Fe2+ ions as a catalyst allowed to increase the degradation degree of DEX in the photo-Fenton system up to 99.87%.