Catalytic remediation of toxic oxyanions ($ClO_4^{-}$, $NO_3^{-}$) from Water

Abstract

As the growing concern about contamination of ground water and industrial wastewater, a number of inor-ganic oxyanion contaminants such as perchlorate ($ClO_4^{-}$) and nitrate ($NO_3^{-}$) become also severely issued due to the toxic effect on human even at low level concentrations. In order to remove these anions from contam-inated water, various technologies have been investigated, including ion-exchange, biological denitrification, and catalytic reduction. However, each method has its own advantages and disadvantages in field applica-tions. Here synergistic integrated technology combining adsorption and catalytic decomposition were demonstrated for complete removal of oxyanions ($ClO_4^{-}$, $NO_3^{-}$) from water. In the process, various metal supported adsor-bents are synthesized as adsorption/catalysis bifunctional materials. After the adsorbents were saturated with each oxyanions in an adsorption mode, the adsorbed anions were fully decomposed into nontoxic product by the catalytic function of the catalysts under $H_2$ atmosphere. In the case of $ClO_4^{-}$, Pd supported $ClO_4^{-}$-selective ion-exchange resin showed >90% decomposition rate of the adsorbed ClO4- within 24 h at 10 bar H2 and 373 K in the presence of ethanol. Also, complete decomposition of $NO_3^{-}$ into $N_2$ without the formation of harmful $NH_4^{+}$ was demonstrated by PdCu supported $NO_3^{-}$-selective ion-exchange resin under $H_2$/$CO_2$ (1/1, v/v) conditions. The adsorption-catalytic decomposition cycle in column could be repeated up to five times without loss of adsorption capacity and selectivity of $ClO_4^{-}$ or $NO_3^{-}$.