[ { "id": "authors:94e7p-ztt48", "collection": "authors", "collection_id": "94e7p-ztt48", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20111221-134214410", "type": "article", "title": "Reductive degradation of perfluoroalkyl compounds with aquated electrons generated from iodide photolysis at 254 nm", "author": [ { "family_name": "Park", "given_name": "Hyunwoong", "orcid": "0000-0002-4938-6907", "clpid": "Park-Hyunwoong" }, { "family_name": "Vecitis", "given_name": "Chad D.", "clpid": "Vecitis-C-D" }, { "family_name": "Cheng", "given_name": "Jie", "clpid": "Cheng-Jie" }, { "family_name": "Dalleska", "given_name": "Nathan F.", "orcid": "0000-0002-2059-1587", "clpid": "Dalleska-N-F" }, { "family_name": "Mader", "given_name": "Brian T.", "clpid": "Mader-B-T" }, { "family_name": "Hoffmann", "given_name": "Michael R.", "orcid": "0000-0001-6495-1946", "clpid": "Hoffmann-M-R" } ], "abstract": "The perfluoroalkyl compounds (PFCs), perfluoroalkyl sulfonates (PFXS) and perfluoroalkyl carboxylates (PFXA) are environmentally persistent and recalcitrant towards most conventional water treatment technologies. Here, we complete an in depth examination of the UV-254 nm production of aquated electrons during iodide photolysis for the reductive defluorination of six aquated perfluoroalkyl compounds (PFCs) of various headgroup and perfluorocarbon tail length. Cyclic voltammograms (CV) show that a potential of +2.0 V (vs. NHE) is required to induce PFC oxidation and \u22121.0 V is required to induce PFC reduction indicating that PFC reduction is the thermodynamically preferred process. However, PFCs are observed to degrade faster during UV(254 nm)/persulfate (S2O82\u2212) photolysis yielding sulfate radicals (E\u00b0 = +2.4 V) as compared to UV(254 nm)/iodide (I\u2212) photolysis yielding aquated electrons (E\u00b0 = \u22122.9 V). Aquated electron scavenging by photoproduced triiodide (I3\u2212), which achieved a steady-state concentration proportional to [PFOS]0, reduces the efficacy of the UV/iodide system towards PFC degradation. PFC photoreduction kinetics are observed to be dependent on PFC headgroup, perfluorocarbon chain length, initial PFC concentration, and iodide concentration. From 2 to 12, pH had no observable effect on PFC photoreduction kinetics, suggesting that the aquated electron was the predominant reductant with negligible contribution from the H-atom. A large number of gaseous fluorocarbon intermediates were semi-quantitatively identified and determined to account for [similar]25% of the initial PFOS carbon and fluorine. Reaction mechanisms that are consistent with kinetic observations are discussed.", "doi": "10.1039/c1pp05270e", "issn": "1474-905X", "publisher": "Royal Society of Chemistry", "publication": "Photochemical and Photobiological Sciences", "publication_date": "2011-10-25", "series_number": "12", "volume": "10", "issue": "12", "pages": "1945-1953" }, { "id": "authors:3afyz-d4851", "collection": "authors", "collection_id": "3afyz-d4851", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20110405-110946196", "type": "article", "title": "Sorption of Perfluorochemicals to Granular Activated Carbon in the Presence of Ultrasound", "author": [ { "family_name": "Zhao", "given_name": "Deming", "clpid": "Zhao-Deming" }, { "family_name": "Cheng", "given_name": "Jie", "clpid": "Cheng-Jie" }, { "family_name": "Vecitis", "given_name": "Chad D.", "clpid": "Vecitis-C-D" }, { "family_name": "Hoffmann", "given_name": "Michael R.", "orcid": "0000-0001-6495-1946", "clpid": "Hoffmann-M-R" } ], "abstract": "Perfluorochemicals (PFCs) are emerging pollutants of increasing public health and environmental concern due to their worldwide distribution, environmental persistence, and bioaccumulation potential. Activated carbon adsorption is an effective method to remove PFCs from water. Herein, we report on the sorption of four PFCs: perfluorooctane sulfonate (PFOS), perfluorooctanoate (PFOA), perfluorobutane sulfonate (PFBS), and perfluorobutanoate (PFBA), from deionized water (MQ) and landfill groundwater (GW) by granular activated carbon (GAC) in the absence and presence of 20 kHz ultrasound. In all cases, the adsorption kinetics were found to be well-represented by a pseudosecond-order model, with maximum monolayer sorption capacity and initial sorption rate values following the orders q_(e)^(PFOS) > q_(e)^(PFOA) > q_(e)^(PFBS) > q_(e)^(PFBA) and v_(0)^(PFOS) > v_(0)^(PFBS) > v_(0)^(PFOA) > v_(0)^(PFBA), respectively. The equilibrium adsorption was quantified by the BET multilayer absorption isotherm, and the monolayer sorption capacity increased with increasing PFC chain length: q_(m)^(PFOS) > q_(m)^(PFOA) > q_(m)^(PFBS) > q_(m)^(PFBA). The equilibrium PFC sorption constants, q_e and q_m, and the sorption kinetic constants, v_0 and k_2, were greater in Milli-Q water than in landfill groundwater with or without pretreatment, indicating competition for sorption sites by natural and cocontaminant groundwater organics. Ultrasonic irradiation significantly increased the PFC\u2212GAC sorption kinetics, 250\u2212900%, and slightly increased the extent of PFC equilibrium adsorption, 5\u221250%. The ultrasonic PFC\u2212GAC sorption kinetics enhancement increased with increasing PFC chain length, suggesting ultrasound acts to increase the PFC diffusion rate into GAC nanopores.", "doi": "10.1021/jp111784k", "issn": "1089-5639", "publisher": "American Chemical Society", "publication": "Journal of Physical Chemistry A", "publication_date": "2011-03-24", "series_number": "11", "volume": "115", "issue": "11", "pages": "2250-2257" }, { "id": "authors:f9g7x-dkr49", "collection": "authors", "collection_id": "f9g7x-dkr49", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20110324-085340982", "type": "article", "title": "Kinetics of microwave-enhanced oxidation of phenol by hydrogen peroxide", "author": [ { "family_name": "Zhao", "given_name": "Deming", "clpid": "Zhao-Deming" }, { "family_name": "Cheng", "given_name": "Jie", "clpid": "Cheng-Jie" }, { "family_name": "Hoffmann", "given_name": "Michael R.", "orcid": "0000-0001-6495-1946", "clpid": "Hoffmann-M-R" } ], "abstract": "Aqueous solutions of phenol were oxidized by\nhydrogen peroxide assisted by microwave (MW) irradiation.\nA simple kinetic model for the overall degradation of\nphenol in the presence of excess H_2O_2 is proposed in\nwhich the degradation rate of phenol is expressed as a\nlinear function of the concentrations of phenol and H_2O_2.\nA detailed parametric study showed that the degradation\nrate of phenol increased with increasing [H_2O_2] until\nsaturation was observed. Phenol degradation followed\napparent zero-order kinetics under MW radiation or H_2O_2\noxidation. However, after 90 min of irradiation, the\nobserved kinetics shifted to pseudo first order. The overall\nreaction rates were significantly enhanced in the combined\nMW/H_2O_2 system, mainly because microwave could\naccelerate H_2O_2 to generate hydroxyl radical (\u2022OH) and\nother reactive oxygen intermediates. The observed synergetic\neffects of the MW/H_2O_2 process resulted in an\nincreased in the net reaction rate by a factor of 5.75. When\nhydrogen peroxide is present in a large stoichiometric\nexcess, the time required to achieve complete mineralization\nis reduced significantly.", "doi": "10.1007/s11783-010-0251-9", "issn": "1673-7415", "publisher": "Springer Verlag", "publication": "Frontiers of Environmental Science and Engineering in China", "publication_date": "2011-03", "series_number": "1", "volume": "5", "issue": "1", "pages": "57-64" }, { "id": "authors:a1ftp-dbd72", "collection": "authors", "collection_id": "a1ftp-dbd72", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20100202-112053909", "type": "article", "title": "Sonochemical Degradation of Perfluorooctane Sulfonate (PFOS) and Perfluorooctanoate (PFOA) in Groundwater: Kinetic Effects of Matrix Inorganics", "author": [ { "family_name": "Cheng", "given_name": "Jie", "clpid": "Cheng-Jie" }, { "family_name": "Vecitis", "given_name": "Chad D.", "clpid": "Vecitis-C-D" }, { "family_name": "Park", "given_name": "Hyunwoong", "orcid": "0000-0002-4938-6907", "clpid": "Park-Hyunwoong" }, { "family_name": "Mader", "given_name": "Brian T.", "clpid": "Mader-B-T" }, { "family_name": "Hoffmann", "given_name": "Michael R.", "orcid": "0000-0001-6495-1946", "clpid": "Hoffmann-M-R" } ], "abstract": "Ultrasonic irradiation has been shown to effectively degrade perfluorinated chemicals (PFCs) such as perfluorooctane sulfonate (PFOS) and perfluorooctanoate (PFOA) in aqueous solution. Reduced PFC sonochemical degradation rates in organic-rich groundwater taken from beneath a landfill, however, testify to the negative kinetic effects of the organic groundwater constituents. In this study, the PFOX (X = S or A) sonochemical degradation rates in a groundwater sample with organic concentrations about 10 times lower than those in the groundwater taken from beneath a landfill are found to be 29.7% and 20.5% lower, respectively, than the rates in Milli-Q water, suggesting that inorganic groundwater constituents also negatively affect PFC sonochemical kinetics. To determine the source of the groundwater matrix effects, we evaluate the effects of various inorganic species on PFOX sonochemical kinetics. Anions over the range of 1\u221210 mM show Hofmeister effects on the sonochemical degradation rates of PFOX, k_(ClO_4)^(\u2212PFOX) > k_(NO_3)^(\u2212PFOX) ~ k_(Cl^\u2212)^(\u2212PFOX) \u2265 k_(MQ)^(\u2212PFOX) > k_(HCO_3)^(\u2212PFOX) ~ k_(SO_(4)^(2\u2212)^(\u2212PFOX). In contrast, common cations at 5 mM have negligible effects. Initial solution pH enhances the degradation rates of PFOX at 3, but has negligible effects over the range of 4 to 11. The observed inorganic effects on sonochemical kinetics are hypothesized to be due to ions' partitioning to and interaction with the bubble\u2212water interface. Finally, it is shown that the rate reduction in the groundwater in this study is primarily due to the presence of bicarbonate and thus can be fully rectified by pH adjustment prior to sonolysis.", "doi": "10.1021/es902651g", "issn": "0013-936X", "publisher": "American Chemical Society", "publication": "Environmental Science and Technology", "publication_date": "2010-01-01", "series_number": "1", "volume": "44", "issue": "1", "pages": "445-450" }, { "id": "authors:t92r9-xfx17", "collection": "authors", "collection_id": "t92r9-xfx17", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20100129-140507678", "type": "article", "title": "Sonochemical Degradation of Perfluorooctanesulfonate in Aqueous Film-Forming Foams", "author": [ { "family_name": "Vecitis", "given_name": "Chad D.", "clpid": "Vecitis-C-D" }, { "family_name": "Wang", "given_name": "Yajuan", "clpid": "Wang-Yajuan" }, { "family_name": "Cheng", "given_name": "Jie", "clpid": "Cheng-Jie" }, { "family_name": "Park", "given_name": "Hyunwoong", "orcid": "0000-0002-4938-6907", "clpid": "Park-Hyunwoong" }, { "family_name": "Mader", "given_name": "Brian T.", "clpid": "Mader-B-T" }, { "family_name": "Hoffmann", "given_name": "Michael R.", "orcid": "0000-0001-6495-1946", "clpid": "Hoffmann-M-R" } ], "abstract": "Aqueous film-forming foams (AFFFs) are fire extinguishing agents developed by the Navy to quickly and effectively combat fires occurring close to explosive materials and are utilized today at car races, airports, oil refineries, and military locations. Fluorochemical (FC) surfactants represent 1\u22125% of the AFFF composition, which impart properties such as high spreadability, negligible fuel diffusion, and thermal stability to the foam. FC's are oxidatively recalcitrant, persistent in the environment, and have been detected in groundwater at AFFF training sites. Ultrasonic irradiation of aqueous FCs has been reported to degrade and subsequently mineralize the FC surfactants perfluorooctanoate (PFOA) and perfluorooctanesulfonate (PFOS). Here we present results of the sonochemical degradation of aqueous dilutions of FC-600, a mixture of hydrocarbon (HC) and fluorochemical components including cosolvents, anionic hydrocarbon surfactants, fluorinated amphiphilic surfactants, anionic fluorinated surfactants, and thickeners such as starch. The primary FC surfactant in FC-600, PFOS, was sonolytically degraded over a range of FC-600 aqueous dilutions, 65 ppb < [PFOS]_i < 13100 ppb. Sonochemical PFOS\u2212AFFF decomposition rates, R_(AFFF)^(\u2212PFOS), are similar to PFOS\u2212Milli-Q rates, R_(MQ)^(\u2212PFOS), indicating that the AFFF matrix only had a minor effect on the sonochemical degradation rate, 0.5 < R_(AFFF)^(\u2212PFOS)/R_(MQ)^(\u2212PFOS) < 2.0, even though the total organic concentration was 50 times the PFOS concentration, [Org]_(tot)/[PFOS] ~50, consistent with the superior FC surfactant properties. Sonochemical sulfate production is quantitative, \u0394[SO_4^(2\u2212)]/\u0394[PFOS] \u2265 1, indicating that bubble-water interfacial pyrolytic cleavage of the C\u2212S bond in PFOS is the initial degradation step, in agreement with previous studies done in Milli-Q water. Sonochemical fluoride production is significantly below quantitative expectations, \u0394[F^\u2212]/\u0394[PFOS] ~4 vs 17, suggesting that in the AFFF matrix, PFOS' fluorochemical tail is not completely degraded, whereas Milli-Q studies yielded quantitative F\u2212 production. Measurements of time-dependent methylene blue active substances and total organic carbon indicate that the other FC-600 components were also sonolytically decomposed.", "doi": "10.1021/es902444r", "issn": "0013-936X", "publisher": "American Chemical Society", "publication": "Environmental Science and Technology", "publication_date": "2010-01-01", "series_number": "1", "volume": "44", "issue": "1", "pages": "432-438" }, { "id": "authors:snn11-h4136", "collection": "authors", "collection_id": "snn11-h4136", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20100520-152149454", "type": "article", "title": "Confocal Fluorescence Microscopy of the Morphology and Composition of Interstitial Fluids in Freezing Electrolyte Solutions", "author": [ { "family_name": "Cheng", "given_name": "Jie", "clpid": "Cheng-Jie" }, { "family_name": "Soetjipto", "given_name": "Cherrie", "clpid": "Soetjipto-C" }, { "family_name": "Hoffmann", "given_name": "Michael R.", "orcid": "0000-0001-6495-1946", "clpid": "Hoffmann-M-R" }, { "family_name": "Colussi", "given_name": "A. J.", "orcid": "0000-0002-3400-4101", "clpid": "Colussi-A-J" } ], "abstract": "Ice rheology, the integrity of polar ice core records, and ice\u2212atmosphere interactions are among the phenomena controlled by the morphology and composition of interstitial fluids threading polycrystalline ice. Herein, we investigate how ionic impurities affect such features via time-resolved confocal fluorescence microscopy of freezing electrolyte solutions doped with a pH probe. We find that the 10 \u03bcM probe accumulates into 12 \u03bcm thick glassy channels in frozen water, but it is incorporated into randomly distributed <1 \u03bcm diameter inclusions in freezing 1 mM NaCl. We infer that morphology is largely determined by the dynamic instabilities generated upon advancing ice by the rejected solute, rather than by thermodynamics. The protracted alkalinization of the fluid inclusions reveals that the excess negative charge generated by the preferential incorporation of Cl^\u2212 over Na^+ in ice is neutralized by the seepage of the OH^\u2212 slowly produced via H_2O \u2192 H^+ + OH^\u2212 thermal dissociation.", "doi": "10.1021/jz9000888", "issn": "1948-7185", "publisher": "American Chemical Society", "publication": "Journal of Physical Chemistry Letters", "publication_date": "2010-01", "series_number": "1", "volume": "1", "issue": "1", "pages": "374-378" }, { "id": "authors:jbsv1-k1124", "collection": "authors", "collection_id": "jbsv1-k1124", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20090817-144816269", "type": "article", "title": "Enrichment Factors of Perfluoroalkyl Oxoanions at the Air/Water Interface", "author": [ { "family_name": "Psillakis", "given_name": "Elefteria", "orcid": "0000-0002-5867-3940", "clpid": "Psillakis-E" }, { "family_name": "Cheng", "given_name": "Jie", "clpid": "Cheng-Jie" }, { "family_name": "Hoffmann", "given_name": "M. R.", "orcid": "0000-0001-6495-1946", "clpid": "Hoffmann-M-R" }, { "family_name": "Colussi", "given_name": "A. J.", "orcid": "0000-0002-3400-4101", "clpid": "Colussi-A-J" } ], "abstract": "The refractory, water-bound perfluoro-n-alkyl carboxylate F(CF_2)_nCO_2^\u2212 and sulfonate F(CF_2)_nSO_3^\u2212 surfactant anions reach remote locations by mechanisms that are not well understood. Here we report experiments in which the relative concentrations of these anions on the surface of microdroplets produced by nebulizing their aqueous solutions are measured via electrospray ionization mass spectrometry. Enrichment factors f (relative to Br^\u2212: f(Br^\u2212) \u2261 1) increase with n, asymptotically reaching f[F(CF_2)_nSO_3^\u2212] ~2f[F(CF_2)_nCO_2^\u2212] ~200 f(Br^\u2212) values above n ~ 8. The larger f values for F(CF_2)_nSO_3^\u2212 over their F(CF_2)_nCO_2^\u2212 congeners are consistent with a closer approach of the bulkier, less hydrated \u2212SO_3^\u2212 headgroup to the air/water interface. A hyperbolic, rather than the predicted linear log f[F(CF_2)_nCO_2^\u2212] vs n dependence suggests the onset of conformational restrictions to interfacial enrichment above n ~4. Marine aerosols produced from contaminated ocean surface waters are therefore expected to be highly enriched in F(CF_2)_nCO_2^\u2212/F(CF_2)_nSO_3^\u2212 species.", "doi": "10.1021/jp902795m", "issn": "1089-5639", "publisher": "American Chemical Society", "publication": "Journal of Physical Chemistry A", "publication_date": "2009-08-06", "series_number": "31", "volume": "113", "issue": "31", "pages": "8826-8829" }, { "id": "authors:s4pry-qfx86", "collection": "authors", "collection_id": "s4pry-qfx86", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20090814-140047629", "type": "article", "title": "Acid dissociation versus molecular association of perfluoroalkyl oxoacids: environmental implications", "author": [ { "family_name": "Cheng", "given_name": "Jie", "clpid": "Cheng-Jie" }, { "family_name": "Psillakis", "given_name": "Elefteria", "orcid": "0000-0002-5867-3940", "clpid": "Psillakis-E" }, { "family_name": "Hoffmann", "given_name": "M. R.", "orcid": "0000-0001-6495-1946", "clpid": "Hoffmann-M-R" }, { "family_name": "Colussi", "given_name": "A. J.", "orcid": "0000-0002-3400-4101", "clpid": "Colussi-A-J" } ], "abstract": "Perfluorooctanoate (PFO) and perfluorooctanesulfonate (PFOS) surfactant anions, once released, may rapidly\nreach remote regions. This phenomenon is puzzling because the water-bound anions of strong F-alkyl acids\nshould be largely transported by slow oceanic currents. Herein, we investigate whether these hydrophobic\nF-alkyl oxoanions would behave anomalously under environmental conditions, as suggested elsewhere. Negative\nelectrospray ionization mass spectra of micromolar aqueous PFO or PFOS solutions from pH 1.0 to 6.0 show\n(1) m/z ) 499 (PFOS) signals that are independent of pH and (2) m/z ) 413 (PFO) and 369 (PFO - CO_2)\nsignals, plus m/z ) 213 (C_3F_7CO_2\n-) and 169 (C_3F_7\n-) signals at higher collision energies, and, below pH ~\n4, m/z ) 827 signals from a remarkably stable (PFO)_2H- cluster that increase with decreasing pH. Since the\nsum of the m/z ) 369, 413, and 827 signal intensities is independent of pH, that is, effectively encompasses\nall major species, we infer that pK_a(PFOSA) < 1.0 and pK_a(PFOA) < 1.0. We also derive K_2 \u2264 4 \u00d7 10^7 M^(-2)\nfor the clustering equilibrium 2PFO + H^+ \u21cc (PFO)_2H. Thus, although (PFO)_2H is held together by an\nexceptionally strong homonuclear covalent hydrogen bond, neither PFOS nor PFO will associate or protonate\nsignificantly at environmentally relevant subnanomolar concentrations above pH ~ 1.", "doi": "10.1021/jp9051352", "issn": "1089-5639", "publisher": "American Chemical Society", "publication": "Journal of Physical Chemistry A", "publication_date": "2009-07-23", "series_number": "29", "volume": "113", "issue": "29", "pages": "8152-8156" }, { "id": "authors:q3c53-08x43", "collection": "authors", "collection_id": "q3c53-08x43", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20091022-115846361", "type": "article", "title": "Treatment technologies for aqueous perfluorooctanesulfonate (PFOS) and perfluorooctanoate (PFOA)", "author": [ { "family_name": "Vecitis", "given_name": "Chad D.", "clpid": "Vecitis-C-D" }, { "family_name": "Park", "given_name": "Hyunwoong", "orcid": "0000-0002-4938-6907", "clpid": "Park-Hyunwoong" }, { "family_name": "Cheng", "given_name": "Jie", "clpid": "Cheng-Jie" }, { "family_name": "Mader", "given_name": "Brian T.", "clpid": "Mader-B-T" }, { "family_name": "Hoffmann", "given_name": "Michael R.", "orcid": "0000-0001-6495-1946", "clpid": "Hoffmann-M-R" } ], "abstract": "Fluorochemicals (FCs) are oxidatively recalcitrant, environmentally persistent, and resistant to most conventional treatment technologies. FCs have unique physiochemical properties derived from fluorine which is the most electronegative element. Perfluorooctanesulfonate (PFOS), and perfluorooctanoate (PFOA) have been detected globally in the hydrosphere, atmosphere and biosphere. Reducing treatment technologies such as reverses osmosis, nano-filtration and activated carbon can remove FCs from water. However, incineration of the concentrated waste is required for complete FC destruction. Recently, a number of alternative technologies for FC decomposition have been reported. The FC degradation technologies span a wide range of chemical processes including direct photolysis, photocatalytic oxidation, photochemical oxidation, photochemical reduction, thermally-induced reduction, and sonochemical pyrolysis. This paper reviews these FC degradation technologies in terms of kinetics, mechanism, energetic cost, and applicability. The optimal PFOS/PFOA treatment method is strongly dependent upon the FC concentration, background organic and metal concentration, and available degradation time.", "doi": "10.1007/s11783-009-0022-7", "issn": "1673-7520", "publisher": "Springer", "publication": "Frontiers of Environmental Science and Engineering in China", "publication_date": "2009-06", "series_number": "2", "volume": "3", "issue": "2", "pages": "129-151" }, { "id": "authors:w2a7j-mbv69", "collection": "authors", "collection_id": "w2a7j-mbv69", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20090410-134802114", "type": "article", "title": "Reductive defluorination of aqueous perfluorinated alkyl surfactants : effects of ionic headgroup and chain length", "author": [ { "family_name": "Park", "given_name": "Hyunwoong", "orcid": "0000-0002-4938-6907", "clpid": "Park-Hyunwoong" }, { "family_name": "Vecitis", "given_name": "Chad D.", "clpid": "Vecitis-C-D" }, { "family_name": "Cheng", "given_name": "Jie", "clpid": "Cheng-Jie" }, { "family_name": "Choi", "given_name": "Wonyong", "clpid": "Choi-Wonyong" }, { "family_name": "Mader", "given_name": "Brian T.", "clpid": "Mader-B-T" }, { "family_name": "Hoffmann", "given_name": "Michael R.", "orcid": "0000-0001-6495-1946", "clpid": "Hoffmann-M-R" } ], "abstract": "Perfluorinated chemicals (PFCs) are distributed throughout the environment. In the case of perfluorinated alkyl carboxylates and sulfonates, they can be classified as persistent organic pollutants since they are resistant to environmentally relevant reduction, oxidation, and hydrolytic processes. With this in mind, we report on the reductive defluorination of perfluorobutanoate, PFBA (C_3F_7CO_2\u2212), perfluorohexanoate, PFHA (C_5F_(11)CO_2\u2212), perfluorooctanoate, PFOA (C_7F_(15)CO_2\u2212), perfluorobutane sulfonate, PFBS (C_4F_9SO_3\u2212), perfluorohexane sulfonate, PFHS (C_6F_(13)SO_3\u2212), and perfluorooctane sulfonate, PFOS (C_8F_(17)SO_3\u2212) by aquated electrons, eaq\u2212, that are generated from the UV photolysis (\u03bb = 254 nm) of iodide. The ionic headgroup (-SO_3\u2212 vs -CO_2\u2212) has a significant effect on the reduction kinetics and extent of defluorination (F index = \u2212[F\u2212]_(produced)/[PFC]_(degraded)). Perfluoroalkylsulfonate reduction kinetics and the F index increase linearly with increasing chain length. In contrast, perfluoroalkylcarboxylate chain length appears to have a negligible effect on the observed kinetics and the F index. H/F ratios in the gaseous fluoro-organic products are consistent with measured F indexes. Incomplete defluorination of the gaseous products suggests a reductive cleavage of the ionic headgroup occurs before complete defluorination. Detailed mechanisms involving initiation by aquated electrons are proposed.", "doi": "10.1021/jp807116q", "issn": "1089-5639", "publisher": "American Chemical Society", "publication": "Journal of Physical Chemistry A", "publication_date": "2009-01-29", "series_number": "4", "volume": "113", "issue": "4", "pages": "690-696" }, { "id": "authors:43e86-bhn18", "collection": "authors", "collection_id": "43e86-bhn18", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200518-070742483", "type": "article", "title": "Sonochemical Degradation of Perfluorooctane Sulfonate (PFOS) and Perfluorooctanoate (PFOA) in Landfill Groundwater: Environmental Matrix Effects", "author": [ { "family_name": "Cheng", "given_name": "Jie", "clpid": "Cheng-Jie" }, { "family_name": "Vecitis", "given_name": "Chad D.", "clpid": "Vecitis-C-D" }, { "family_name": "Park", "given_name": "Hyunwoong", "orcid": "0000-0002-4938-6907", "clpid": "Park-Hyunwoong" }, { "family_name": "Mader", "given_name": "Brian T.", "clpid": "Mader-B-T" }, { "family_name": "Hoffmann", "given_name": "Michael R.", "orcid": "0000-0001-6495-1946", "clpid": "Hoffmann-M-R" } ], "abstract": "Perfluorinated chemicals such as perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) are environmentally persistent and recalcitrant to most conventional chemical and microbial treatment technologies. In this paper, we show that sonolysis is able to decompose PFOS and PFOA present in groundwater beneath a landfill. However, the pseudo first-order rate constant for the sonochemical degradation in the landfill groundwater is reduced by 61 and 56% relative to MilliQ water for PFOS and PFOA, respectively, primarily due to the presence of other organic constituents. In this study, we evaluate the effect of various organic compounds on the sonochemical decomposition rates of PFOS and PFOA. Organic components in environmental matrices may reduce the sonochemical degradation rates of PFOS and PFOA by competitive adsorption onto the bubble\u2212water interface or by lowering the average interfacial temperatures during transient bubble collapse events. The effect of individual organic compounds depends on the Langmuir adsorption constant, the Henry's law constant, the specific heat capacity, and the overall endothermic heat of dissociation. Volatile organic compounds (VOCs) are identified as the primary cause of the sonochemical rate reduction for PFOS and PFOA in landfill groundwater, whereas the effect of dissolved natural organic matter (DOM) is not significant. Finally, a combined process of ozonation and sonolysis is shown to substantially recover the rate loss for PFOS and PFOA in landfill groundwater.", "doi": "10.1021/es8013858", "issn": "0013-936X", "publisher": "American Chemical Society", "publication": "Environmental Science and Technology", "publication_date": "2008-11-01", "series_number": "21", "volume": "42", "issue": "21", "pages": "8057-8063" }, { "id": "authors:9bb5n-cg913", "collection": "authors", "collection_id": "9bb5n-cg913", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:CHEest08", "type": "article", "title": "Sonochemical Degradation of Perfluorooctane Sulfonate (PFOS) and Perfluorooctanoate (PFOA) in Landfill Groundwater: Environmental Matrix Effects", "author": [ { "family_name": "Cheng", "given_name": "Jie", "clpid": "Cheng-Jie" }, { "family_name": "Vecitis", "given_name": "Chad D.", "clpid": "Vecitis-C-D" }, { "family_name": "Park", "given_name": "Hyunwoong", "orcid": "0000-0002-4938-6907", "clpid": "Park-Hyunwoong" }, { "family_name": "Mader", "given_name": "Brian T.", "clpid": "Mader-B-T" }, { "family_name": "Hoffmann", "given_name": "Michael R.", "orcid": "0000-0001-6495-1946", "clpid": "Hoffmann-M-R" } ], "abstract": "Perfluorinated chemicals such as perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) are environmentally persistent and recalcitrant to most conventional chemical and microbial treatment technologies. In this paper, we show that sonolysis is able to decompose PFOS and PFOA present in groundwater beneath a landfill. However, the pseudo first-order rate constant for the sonochemical degradation in the landfill groundwater is reduced by 61 and 56% relative to MilliQ water for PFOS and PFOA, respectively, primarily due to the presence of other organic constituents. In this study, we evaluate the effect of various organic compounds on the sonochemical decomposition rates of PFOS and PFOA. Organic components in environmental matrices may reduce the sonochemical degradation rates of PFOS and PFOA by competitive adsorption onto the bubble\u2212water interface or by lowering the average interfacial temperatures during transient bubble collapse events. The effect of individual organic compounds depends on the Langmuir adsorption constant, the Henry's law constant, the specific heat capacity, and the overall endothermic heat of dissociation. Volatile organic compounds (VOCs) are identified as the primary cause of the sonochemical rate reduction for PFOS and PFOA in landfill groundwater, whereas the effect of dissolved natural organic matter (DOM) is not significant. Finally, a combined process of ozonation and sonolysis is shown to substantially recover the rate loss for PFOS and PFOA in landfill groundwater.", "doi": "10.1021/es8013858", "issn": "0013-936X", "publisher": "American Chemical Society", "publication": "Environmental Science and Technology", "publication_date": "2008-11-01", "series_number": "21", "volume": "42", "issue": "21", "pages": "8057-8063" }, { "id": "authors:g0002-3z667", "collection": "authors", "collection_id": "g0002-3z667", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20090507-100656322", "type": "article", "title": "Enhancement of perfluorooctanoate and perfluorooctanesulfonate activity at acoustic cavitation bubble interfaces", "author": [ { "family_name": "Vecitis", "given_name": "C. D.", "clpid": "Vecitis-C-D" }, { "family_name": "Park", "given_name": "H.", "orcid": "0000-0002-4938-6907", "clpid": "Park-Hyunwoong" }, { "family_name": "Cheng", "given_name": "J.", "clpid": "Cheng-Jie" }, { "family_name": "Mader", "given_name": "B. T.", "clpid": "Mader-B-T" }, { "family_name": "Hoffmann", "given_name": "M. R.", "orcid": "0000-0001-6495-1946", "clpid": "Hoffmann-M-R" } ], "abstract": "Acoustic cavitation driven by ultrasonic irradiation decomposes and mineralizes the recalcitrant perfluorinated surfactants perfluorooctanesulfonate (PFOS) and perfluorooctanoate (PFOA). Pyrolytic cleavage of the ionic headgroup is the rate-determining step. In this study, we examine the sonochemical adsorption of PFOX, where X = S for PFOS and A for PFOA, by determining kinetic order and absolute rates over an initial PFOX concentration range of 20 nM to 200 \u03bcM. Sonochemical PFOX kinetics transition from pseudo-first-order at low initial concentrations, [PFOX]_i < 20 \u03bcM to zero-order kinetics at high initial concentrations, [PFOX]_i > 40 \u03bcM, as the bubble interface sites are saturated. At PFOX concentrations below 100 \u03bcM, concentration-dependent rates were modeled with Langmuir\u2212Hinshelwood (LH) kinetics. Empirically determined rate maximums, V_(Max)^(\u2212PFOA) = 2230 \u00b1 560 nM min^\u22121 and V_(Max)^(\u2212PFOS) = 230 \u00b1 60 nM min^\u22121, were used in the LH model, and sonochemical surface activities were estimated to be K_(Sono)^(PFOS) = 120000 M^\u22121 and K_(Sono)^(PFOA) = 28500 M^\u22121, 60 and 80 times greater than equilibrium surface activities, K_(Eq)^(PFOS) and K_(Eq)^(PFOA). These results suggest enhanced sonochemical degradation rates for PFOX when the bubble interface is undersaturated. The present results are compared to previously reported sonochemical kinetics of nonvolatile surfactants.", "doi": "10.1021/jp804050p", "issn": "1932-7447", "publisher": "American Chemical Society", "publication": "Journal of Physical Chemistry C", "publication_date": "2008-10-30", "series_number": "43", "volume": "112", "issue": "43", "pages": "16850-16857" }, { "id": "authors:28gze-n4z55", "collection": "authors", "collection_id": "28gze-n4z55", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150623-154751053", "type": "article", "title": "Anion Fractionation and Reactivity at Air/Water:Methanol Interfaces. Implications for the Origin of Hofmeister Effects", "author": [ { "family_name": "Cheng", "given_name": "Jie", "clpid": "Cheng-Jie" }, { "family_name": "Hoffmann", "given_name": "Michael R.", "orcid": "0000-0001-6495-1946", "clpid": "Hoffmann-M-R" }, { "family_name": "Colussi", "given_name": "A. J.", "orcid": "0000-0002-3400-4101", "clpid": "Colussi-A-J" } ], "abstract": "Anions are selectively enriched in interfacial layers. This universal phenomenon, first identified in connection with protein precipitation 120 years ago, underlies fundamental processes. Its physical causes, however, remain conjectural. It has been speculated that the more polarizable anions should have larger affinities for air/liquid interfaces, and that their reactivities toward gaseous species would be affected by whether the liquid is capped by hydroxyl groups, as in water itself, or by hydrophobic layers of organic contaminants. These issues are particularly relevant to the composition and fate of atmospheric aerosols. Recently, we found that fractionation factors, f_(X^\u2212), of simple anions at the air/water interface increase exponentially with ion radius, a_(X^\u2212). In this paper, we report new experimental results on a set of anions that include the large PF_6^\u2212 and the highly polarizable IO_3^\u2212 species. A strict ln\u2009f_(X^\u2212) \u221d a_(X^\u2212) correlation is confirmed. Experiments performed in {x_wH_2O + (1 \u2212 x_w)MeOH} mixtures show that f_(X^\u2212) is almost independent of x_w. Furthermore, O_3(g) oxidizes I^\u2212 at virtually identical rates on H_2O and MeOH.", "doi": "10.1021/jp803184r", "issn": "1520-6106", "publisher": "American Chemical Society", "publication": "Journal of Physical Chemistry B", "publication_date": "2008-06-19", "series_number": "24", "volume": "112", "issue": "24", "pages": "7157-7161" }, { "id": "authors:06sw6-8qm81", "collection": "authors", "collection_id": "06sw6-8qm81", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150805-151834195", "type": "article", "title": "Kinetics and Mechanism of the Sonolytic Conversion of the Aqueous Perfluorinated Surfactants, Perfluorooctanoate (PFOA), and Perfluorooctane Sulfonate (PFOS) into Inorganic Products", "author": [ { "family_name": "Vecitis", "given_name": "Chad D.", "clpid": "Vecitis-C-D" }, { "family_name": "Park", "given_name": "Hyunwoong", "orcid": "0000-0002-4938-6907", "clpid": "Park-Hyunwoong" }, { "family_name": "Cheng", "given_name": "Jie", "clpid": "Cheng-Jie" }, { "family_name": "Mader", "given_name": "Brian T.", "clpid": "Mader-B-T" }, { "family_name": "Hoffmann", "given_name": "Michael R.", "orcid": "0000-0001-6495-1946", "clpid": "Hoffmann-M-R" } ], "abstract": "The perfluorinated surfactants perfluorooctane sulfonate (PFOS) and perfluorooctanoate (PFOA) are recognized as widespread in the environment as well as recalcitrant toward most conventional water treatment technologies. In this study, acoustic cavitation as driven by high-frequency ultrasound is shown to be effective in the degradation of aqueous solutions of PFOS and PFOA and effective over a wide range of concentrations from 10 nM to 10 \u03bcM for a given compound. Sulfur, fluorine, and carbon mass balances indicate that mineralization occurs immediately following the degradation of the initial perfluorinated surfactant. Near complete conversion of PFOS and PFOA to CO, CO_2, F^-, and SO_4^(2-) occurs due to pyrolytic reactions at the surface and vapor phase of transiently collapsing cavitation bubbles. The initial PFOS or PFOA pyrolytic degradation occurs at the bubble\u2212water interface and involves the loss of the ionic functional group leading to the formation of the corresponding 1H-fluoroalkane or perfluoroolefin. The fluorochemical intermediates undergo a series of pyrolytic reactions in the bubble vapor leading to C_1 fluoro-radicals. Secondary vapor-phase bimolecular reactions coupled with concomitant hydrolysis converts the C_1 fluoro-radicals to carbon monoxide, carbon dioxide, and HF, forming a proton and fluoride upon dissolution. Sonochemical half-lives, which are calculated from high-temperature gas-phase kinetics, are consistent with kinetic observations and suggest that mineralization occurs shortly after initial perfluorinated surfactant interfacial pyrolysis.", "doi": "10.1021/jp801081y", "issn": "1089-5639", "publisher": "American Chemical Society", "publication": "Journal of Physical Chemistry A", "publication_date": "2008-05-08", "series_number": "18", "volume": "112", "issue": "18", "pages": "4261-4270" }, { "id": "authors:58ymn-01f90", "collection": "authors", "collection_id": "58ymn-01f90", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150623-154751358", "type": "article", "title": "Mass spectrometry of interfacial layers during fast aqueous aerosol/ozone gas reactions of atmospheric interest", "author": [ { "family_name": "Enami", "given_name": "S.", "orcid": "0000-0002-2790-7361", "clpid": "Enami-Shinichi" }, { "family_name": "Vecitis", "given_name": "C. D.", "clpid": "Vecitis-C-D" }, { "family_name": "Cheng", "given_name": "J.", "clpid": "Cheng-Jie" }, { "family_name": "Hoffmann", "given_name": "M. R.", "orcid": "0000-0001-6495-1946", "clpid": "Hoffmann-M-R" }, { "family_name": "Colussi", "given_name": "A. J.", "orcid": "0000-0002-3400-4101", "clpid": "Colussi-A-J" } ], "abstract": "The oxidations of sulfite and iodide in the interfacial layers of aqueous microdroplets exposed to O_3(g) for 1 ms are investigated by online mass spectrometry of the electrostatically ejected anions. S(IV) oxidation losses in Na_2SO_3 microdroplets are proportional to [S(IV)] [O_3(g)] up to \u223c90% conversion. I^\u2212 is more abundant than HSO_3^- in the interfacial layers of equimolar (Na_2SO_3 + NaI) microdroplets and \u223c3 times more reactive than image toward O_3(aq) in bulk solution, but it is converted with minimal loss to I_3^- and IO_3^- plus a persistent ISO_3^- intermediate. These observations reveal unanticipated interfacial gradients, reactivity patterns and transport phenomena that had not been taken into account in previous treatments of fast gas\u2013liquid reactions.", "doi": "10.1016/j.cplett.2008.02.075", "issn": "0009-2614", "publisher": "Elsevier", "publication": "Chemical Physics Letters", "publication_date": "2008-04-10", "series_number": "4-6", "volume": "455", "issue": "4-6", "pages": "316-320" }, { "id": "authors:txxaa-4ka94", "collection": "authors", "collection_id": "txxaa-4ka94", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150623-154751968", "type": "article", "title": "Electrospray Mass Spectrometric Detection of Products and Short-Lived Intermediates in Aqueous Aerosol Microdroplets Exposed to a Reactive Gas", "author": [ { "family_name": "Enami", "given_name": "S.", "orcid": "0000-0002-2790-7361", "clpid": "Enami-Shinichi" }, { "family_name": "Vecitis", "given_name": "C. D.", "clpid": "Vecitis-C-D" }, { "family_name": "Cheng", "given_name": "J.", "clpid": "Cheng-Jie" }, { "family_name": "Hoffmann", "given_name": "M. R.", "orcid": "0000-0001-6495-1946", "clpid": "Hoffmann-M-R" }, { "family_name": "Colussi", "given_name": "A. J.", "orcid": "0000-0002-3400-4101", "clpid": "Colussi-A-J" } ], "abstract": "The intermediates ISO_3^- (m/z = 207) and IS2O3- (m/z = 239) generated in aqueous (NaI/Na_2S2O_3) microdroplets traversing dilute O_3 gas plumes are detected via online electrospray mass spectrometry within \u223c1 ms, and their stabilities gauged by collisionally induced dissociation. The simultaneous detection of anionic reactants and the S_2O_6^(2-), HSO_4^-, IO_3^-, and I_3^- products as a function of experimental conditions provides evidence of genuinely interfacial reaction kinetics. Although O_3(aq) reacts about 3 times faster with I- than with S_2O_3^(2-) in bulk solution, only S_2O_3^(2-) is significantly depleted in the interfacial layers of [I^-]/[S_2O_3^(2-)] = 10 microdroplets below [O_3(g)] \u223c 50 ppm.", "doi": "10.1021/jp075505r", "issn": "1089-5639", "publisher": "American Chemical Society", "publication": "Journal of Physical Chemistry A", "publication_date": "2007-12-20", "series_number": "50", "volume": "111", "issue": "50", "pages": "13032-13037" }, { "id": "authors:3cgaz-78g07", "collection": "authors", "collection_id": "3cgaz-78g07", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150623-154752216", "type": "article", "title": "Global Inorganic Source of Atmospheric Bromine", "author": [ { "family_name": "Enami", "given_name": "S.", "orcid": "0000-0002-2790-7361", "clpid": "Enami-Shinichi" }, { "family_name": "Vecitis", "given_name": "C. D.", "clpid": "Vecitis-C-D" }, { "family_name": "Cheng", "given_name": "J.", "clpid": "Cheng-Jie" }, { "family_name": "Hoffmann", "given_name": "M. R.", "orcid": "0000-0001-6495-1946", "clpid": "Hoffmann-M-R" }, { "family_name": "Colussi", "given_name": "A. J.", "orcid": "0000-0002-3400-4101", "clpid": "Colussi-A-J" } ], "abstract": "A few bromine molecules per trillion (ppt) causes the complete destruction of ozone in the lower troposphere during polar spring and about half of the losses associated with the \"ozone hole\" in the stratosphere. Recent field and aerial measurements of the proxy BrO in the free troposphere suggest an even more pervasive global role for bromine. Models, which quantify ozone trends by assuming atmospheric inorganic bromine (Br_y) stems exclusively from long-lived bromoalkane gases, significantly underpredict BrO measurements. This discrepancy effectively implies a ubiquitous tropospheric background level of \u223c4 ppt Br_y of unknown origin. Here, we report that I^- efficiently catalyzes the oxidation of Br^- and Cl^- in aqueous nanodroplets exposed to ozone, the everpresent atmospheric oxidizer, under conditions resembling those encountered in marine aerosols. Br^- and Cl^-, which are rather unreactive toward O_3 and were previously deemed unlikely direct precursors of atmospheric halogens, are readily converted into IBr_2^- and ICl_2^- en route to Br_2(g) and Cl_2(g) in the presence of I^-. Fine sea salt aerosol particles, which are predictably and demonstrably enriched in I^- and Br^-, are thus expected to globally release photoactive halogen compounds into the atmosphere, even in the absence of sunlight.", "doi": "10.1021/jp074903r", "issn": "1089-5639", "publisher": "American Chemical Society", "publication": "Journal of Physical Chemistry A", "publication_date": "2007-09-13", "series_number": "36", "volume": "111", "issue": "36", "pages": "8749-8752" }, { "id": "authors:0e5dd-4yv63", "collection": "authors", "collection_id": "0e5dd-4yv63", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150623-154752779", "type": "article", "title": "Experimental Anion Affinities for the Air/Water Interface", "author": [ { "family_name": "Cheng", "given_name": "Jie", "clpid": "Cheng-Jie" }, { "family_name": "Vecitis", "given_name": "Chad D.", "clpid": "Vecitis-C-D" }, { "family_name": "Hoffmann", "given_name": "M. R.", "orcid": "0000-0001-6495-1946", "clpid": "Hoffmann-M-R" }, { "family_name": "Colussi", "given_name": "A. J.", "orcid": "0000-0002-3400-4101", "clpid": "Colussi-A-J" } ], "abstract": "Anion affinities, \u03b3_(X^\u2212), for the aerial interface of aqueous (Br^- + NO_3^- + I^- + SCN^- + BF_4^- + ClO_4^-) solutions are determined by electrospray ionization mass spectrometry. The composition of the ions ejected from the surface of fissioning nanodroplets shows that \u03b3_X(\u2212^ )increase (decrease) exponentially with anionic radii, a_(X\u2212(dehydration free energies, ^dG_(X^\u2212)), and selectively respond to the presence of surfactants. BF_4^-, the least hydrated and polarizable anion of the set, has one of the largest \u03b3_(X^\u2212) values. Non-ionic surfactants decrease \u03b3_(I^\u2212) and \u03b3_(SCN^\u2212) but increase \u03b3_(BF_4^\u2212). Cetyltrimethyl ammonium markedly enhances the \u03b3_(X^\u2212) of smaller anions. A similar but weaker effect is observed upon lowering the pH of the bulk solutions from 8.2 to 3.0. Dodecyl sulfate has a negligible effect on \u03b3_(X^\u2212). Considering that (i) universal many-body electrodynamic interactions will progressively stabilize the interfacial layer as its dielectric permittivity falls relative to that of the bulk solution and (ii) water permittivity is uniformly depressed by increasing concentrations of these anions, we infer that the observed Hofmeister correlation, ln \u03b3_(X^\u2212) \u221d - ^dG_(X^\u2212), is consistent with the optimal depression of the permittivity of the drier interfacial layer by the least hydrated ions. Interfacial ion\u2212ion interactions can significantly influence \u03b3_(X^\u2212) in environmental aqueous media.", "doi": "10.1021/jp066197k", "issn": "1520-6106", "publisher": "American Chemical Society", "publication": "Journal of Physical Chemistry B", "publication_date": "2006-12-28", "series_number": "51", "volume": "110", "issue": "51", "pages": "25598-25602" } ]