Efficient Decomposition of Environmentally Persistent Perfluorooctanesulfonate and Related Fluorochemicals Using Zerovalent Iron in Subcritical Water

Abstract

Decomposition of perfluorooctanesulfonate (PFOS) and related chemicals in subcritical water was investigated. Although PFOS demonstrated little reactivity in pure subcritical water, addition of zerovalent metals to the reaction system enhanced the PFOS decomposition to form F-ions, with an increasing order of activity of no metal approximately equal Al < Cu < Zn << Fe. Use of iron led to the most efficient PFOS decomposition: When iron powder was added to an aqueous solution of PFOS (93-372 microM) and the mixture was heated at 350 degrees C for 6 h, PFOS concentration in the reaction solution fell below 2.2 microM (detection limit of HPLC with conductometric detection), with formation of F-ions with yields [i.e., (moles of F- formed)/(moles of fluorine content in initial PFOS) x 100] of 46.2-51.4% and without any formation of perfluorocarboxylic acids. A small amount of CHF3 was detected in the gas phase with a yield [i.e., (moles of CHF3)/(moles of carbon content in initial PFOS) x 100] of 0.7%, after the reaction of PFOS (372 microM) with iron at 350 degree C for 6 h. Spectroscopic measurements indicated that PFOS in water markedly adsorbed on the iron surface even at room temperature, and the adsorbed fluorinated species on the iron surface decomposed with rising temperature, with prominent release of F- ions to the solution phase above 250 degrees C. This method was also effective in decomposing other perfluoroalkylsulfonates bearing shorter chain (C2-C6) perfluoroalkyl groups and was successfully applied to the decomposition of PFOS contained in an antireflective coating agent used in semiconductor manufacturing.

An integrated two-stage process for effective dechlorination of polychlorinated biphenyls in subcritical water in the presence of hydrogen donors

“…This indicates that lower temperature at first stage might favor the following dechlorination at 330°C. Apparently, the corrosion and passivation of Ni/Fe particles would be completed rapidly in subcritical water owing to the high temperature above 250°C in previous reports [2,3]. Low temperature at first stage in this study might retard the corrosion of Fe 0 and formation of insoluble iron oxides, which hence enhanced the utility efficiency of Fe 0 and yield of hydrogen species used for dechlorination.…”

“…As hydrogen donor, water under subcritical state can supply more available H 3 O + and energy for accelerating rate constant as compared to ambient water during this process [1][2][3][4][5]. Meanwhile, the solubility of organics is enhanced greatly in subcritical water, and therefore the limits of mass transfer between water phase and organic phase decline remarkably.…”

Perfluoroalkyl and polyfluoroalkyl substances: current and future perspectives

“…Several laboratory scale studies have also reported methods to decompose PFASs in water. [34] Integration of filtration and sorption techniques into the existing wastewater treatment processes will help reduce environmental release of these compounds. Perhaps one of the most promising research areas would be to exploit the known proteinophilic character of the perfluorinated acids for removal from wastewater streams.…”

Reductive degradation of perfluorinated compounds in water using Mg-aminoclay coated nanoscale zero valent iron

“…Other studies have also found that persulfate and Fenton reagent can effectively degrade perfluorocarboxylic acids (PFCAs) to fluoride ions, carbon dioxide and shorter chain PFCAs [11][12][13]. Regarding the use of microsized ZVI, Hori et al [14] reported that PFOS can partially be degraded by elemental iron, Fe(0), in water under subcritical water conditions (> 250 o C) and high pressure (20 MPa). Moreover, Lee at al.…”