Takehiko Sakamoto

Metal-induced decomposition of perchlorate in pressurized hot water.

Decomposition of perchlorate (ClO(4)(-)) in pressurized hot water (PHW) was investigated. Although ClO(4)(-) demonstrated little reactivity in pure PHW up to 300°C, addition of zerovalent metals to the reaction system enhanced the decomposition of ClO(4)(-) to Cl(-) with an increasing order of activity of (no metal)≈Al < Cu < Zn < Ni << Fe: the addition of iron powder led to the most efficient decomposition of ClO(4)(-). When the iron powder was added to an aqueous ClO(4)(-) solution (104 μM) and the mixture was heated at 150°C, ClO(4)(-) concentration fell below 0.58 μM (58 μg L(-1), detection limit of ion chromatography) in 1 h, and Cl(-) was formed with the yield of 85% after 6 h. The decomposition was accompanied by transformation of the zerovalent iron to Fe(3)O(4). This method was successfully used in the decomposition of ClO(4)(-) in a water sample contaminated with this compound, following fireworks display at Albany, New York, USA.

Efficient decomposition of a new fluorochemical surfactant: perfluoroalkane disulfonate to fluoride ions in subcritical and supercritical water.

Decomposition of (-)O3SC3F6SO3(-) in subcritical and supercritical water was investigated, and the results were compared with the results for C3F7SO3(-). This is the first report on the decomposition of perfluoroalkane disulfonates, which are being introduced in electronics industry as greener alternatives to environmentally persistent and bioaccumulative perfluoroalkyl surfactants. Addition of zerovalent iron to the reaction system dramatically increased the yield of F(-) in the reaction solution: when the reaction of (-)O3SC3F6SO3(-) was carried out in subcritical water at 350°C for 6h, the F(-) yield was 70%, which was 23times the yield without zerovalent iron. Prolonged reaction increased the F(-) formation: after 18h, the F(-) yield from the reaction of (-)O3SC3F6SO3(-) reached 81%, which was 2.1times the F(-) yield from the reaction of C3F7SO3(-). Although the reactivity of FeO toward these substrates was lower than zerovalent iron in subcritical water, the reactivity was enhanced when the reaction temperature was elevated to supercritical state, at which temperature FeO underwent in situ disproportionation to form zerovalent iron, which acted as the reducing agent. When the reaction of (-)O3SC3F6SO3(-) was carried out in the presence of FeO in supercritical water at 380°C for 18h, the F(-) yield reached 92%, which was the highest yield among tested.