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

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 1.0gL^-1 Ru/TiO₂ increased the second order reaction rate constants of bisphenol A, diclofenac, acetaminophen, sulfamethoxazole, benzotriazole, carbamazepine, butylparaben, diclofenac, ciprofloxacin and aniline at mgL^-1 level (5.0μM) 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 mgL^-1 level (5.0μM) underestimated those obtained at EPs concentration of μgL^-1 level (0.050μM). Ru/TiO₂-catalyzed permanganate could decompose a mixture of nine EPs at μgL^-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.