Removal of emerging pollutants by Ru/TiO2-catalyzed permanganate oxidation

Abstract

TiO2 supported ruthenium nanoparticles, Ru/TiO2 (0.94‰ as Ru), was synthesized to catalyze permanganate oxidation for degrading emerging pollutants (EPs) with diverse organic moieties. The presence of 1.0 g L−1 Ru/TiO2 increased the second order reaction rate constants of bisphenol A, diclofenac, acetaminophen, sulfamethoxazole, benzotriazole, carbamazepine, butylparaben, diclofenac, ciprofloxacin and aniline at mg L−1 level (5.0 μM) by permanganate oxidation at pH 7.0 by 0.3–119 times. The second order reaction rate constants of EPs with permanganate or Ru/TiO2-catalyzed permanganate oxidation obtained at EPs concentration of mg L−1 level (5.0 μM) underestimated those obtained at EPs concentration of μg L−1 level (0.050 μM). Ru/TiO2-catalyzed permanganate could decompose a mixture of nine EPs at μg L−1 level efficiently and the second order rate constant for each EP was not decreased due to the competition of other EPs. The toxicity tests revealed that Ru/TiO2-catalyzed permanganate oxidation was effective not only for elimination of EPs but also for detoxification. The removal rates of sulfamethoxazole by Ru/TiO2-catalyzed permanganate oxidation in ten successive cycles remained almost constant in ultrapure water and slightly decreased in Songhua river water since the sixth run, indicating the satisfactory stability of Ru/TiO2. Ru/TiO2-catalyzed permanganate oxidation was selective and could remove selected EPs spiked in real waters more efficiently than chlorination. Therefore, Ru/TiO2-catalyzed permanganate oxidation is promising for removing EPs with electron-rich moieties.