Oxidative degradation of 1,5-naphthalenedisulfonic acid in aqueous solutions by microwave irradiation in the presence of H₂O₂

Sulfonated aromatic pollutants such as Armstrong's acid, or 1,5-naphthalenedisulfonic acid (NDS), are recalcitrant to environmental breakdown and microbial treatment. This study investigated the effects of H₂O₂ concentration, pH, microwave (MW) power and irradiation time on the oxidative degradation of NDS in aqueous solutions. The formation of hydroxyl radicals as the active oxidant was confirmed by electron paramagnetic resonance spin trapping. A combination of both H₂O₂ and MW heating proved essential for NDS degradation. Degradation factors of f ≥ 70% were obtained after about 20 min of irradiation at [H₂O₂]:[NDS] ratios = 10. Acidic conditions were found to be more favorable to the degradation of NDS, and the process follows pseudo-first-order kinetics. Attempts to scale-up the process using a conventional MW reactor provided less striking results.