Efficient Mineralization of Lithium Bis(pentafluoroethanesulfonyl)imide and Related Electrolyte Fluorochemicals Using Superheated Water.

Lithium bis(pentafluoroethanesulfonyl)imide, Li[N(SO2C2F5)2], a typical fluorochemical aimed at better electrochemical performance of battery electrolytes, in superheated water was studied for its waste treatment. When Li[N(SO2C2F5)2] was reacted in pure superheated water at 300 °C, little F- ions were produced. In contrast, complete mineralization of the fluorine, sulfur, and nitrogen atoms in Li[N(SO2C2F5)2] was achieved when the reaction was performed in the presence of KMnO4. Specifically, when Li[N(SO2C2F5)2] was treated for 18 h with 158 mM of KMnO4, the F- and SO42- yields were 101 and 99%, respectively, and the sum of the NO3- and NO2- yields was 101%. In the gas phase, trace CO2 was detected and no CHF3, which has high global warming potential, was formed. Furthermore, the fluorine, sulfur, and nitrogen atoms in the analogues K[N(SO2C4F9)2] and K[N(SO2CF2)2CF2] also underwent complete mineralization using the same approach.

Efficient Mineralization of Fluoroelastomers Using Superheated Water in the Presence of Potassium Hydroxide.

The mineralization of fluoroelastomers (FKMs) in superheated water in the presence of potassium hydroxide (KOH) was investigated with the aim of developing a methodology for recycling the fluorine element. Two FKMs-an "uncrosslinked FKM", representing a poly(vinylidene fluoride-co-hexafluoropropylene) (poly(VDF-co-HFP)) copolymer with a VDF/HFP molar ratio of 78/22 and a "crosslinked FKM" consisting of this copolymer (cured by peroxide) and carbon black-were treated. The fluorine content of these FKMs was efficiently transformed into F- ions in the reaction solution using low KOH concentrations (0.10-0.50 M) at 200-250 °C. When the uncrosslinked or crosslinked FKMs reacted with aqueous KOH (0.20 M) at a rather low temperature (200 °C) for 18 h, the fluorine content of these FKMs was completely mineralized (both F- yields were 100%). Although the crosslinked FKM contained carbon black, the fluorine mineralization of the FKM was not inhibited. The addition of Ca(OH)2 to the reaction solutions after the superheated water treatment at 250 °C for 6 h with aqueous KOH (0.50 M) led to the production of pure CaF2, identified using X-ray spectroscopy, with 100% and 93% yields for the uncrosslinked and crosslinked FKMs, respectively.

Recycling and the end of life assessment of fluoropolymers: recent developments, challenges and future trends.

Herein, we present the state of the art technology on the recycling, reuse, thermal decomposition (by thermolysis, thermal processing, flash pyrolysis, smoldering, open burning, open-air detonation, and incineration), and the life cycle assessment of fluoropolymers (FPs, ranging from poly(tetrafluoroethylene), PTFE, and poly(vinylidene fluoride), PVDF, to various fluorinated copolymers based on VDF and TFE). FPs are niche specialty polymers endowed with exceptional properties and have found many applications in high-tech industries. However, compared to other polymers, the reuse of FPs is still not well-established and is in its infancy. Accordingly, their recycling has attracted increasing interest, even reaching the pilot stage. In addition, recently, several studies have been reported on vitrimers, which are regarded as polymers ranking between thermosets and thermoplastics. In this case, although many articles have reported to date on the thermal degradation of these technical polymers, intensive efforts have been devoted to avoiding the release of low molar mass oligomers and per- and poly-fluoroalkyl substances (PFAS, and especially polymerisation aids such as perfluorooctanoic acid (PFOA) and its alternatives), while various reports demonstrated the complete decomposition of PTFE, leading to the formation of TFE (and hexafluoropropylene or octafluorocyclobutane to a lesser extent). Incineration is one of only a few technologies that can potentially degrade FPs and completely degrade PTFE and other PFAS from 850 °C. Recent studies on the mineralisation of FPs under subcritical water represent an interesting approach to close the loop of the fluorine chemistry cycle. Because of the high molar masses (several million for PTFE) and thermal, chemical, photochemical, and hydrolytic inertness and biological stability of FPs, it has been clearly evidenced that they satisfy the 13 accepted regulatory assessment criteria to be considered as polymers of low concern.

A degradable fluorinated surfactant for emulsion polymerization of vinylidene fluoride.

An original degradable fluorinated surfactant, 3-hydroxy-2-(trifluoromethyl)propanoic acid (MAF-OH), was applied for the emulsion polymerization of vinylidene fluoride (VDF) to yield a latex of PVDF, consisting of typically 100 nm particle diameters. This surfactant was shown to be easily decomposed in subcritical water, releasing fluoride anions. The % reversed head-to head (H-H) addition is greatly minimized (2.4%) in the PVDF, prepared in the presence of MAF-OH surfactant.

Efficient decomposition of perchlorate to chloride ions in subcritical water by use of steel slag.

Decomposition of perchlorate (ClO4-) in subcritical water in the presence of steel slag, a by-product of the steel industry, was investigated. Reactivity of ClO4- was low in pure subcritical water state up to 300 °C, whereas adding steel slag efficiently accelerated the decomposition of ClO4- to Cl-, with no leaching of heavy metals such as chromium and other environmentally undesirable elements (boron and fluorine). When the reaction was performed in subcritical water at a relatively low temperature (250 °C) for 6 h, virtually all ClO4- ions were removed from the reaction solution. The concentration of Cl- after the reaction was well accounted for by the sum of the amount of Cl- ascribed to the decomposition of ClO4- and the amount of Cl- leached from the slag. This method was successfully applied to decompose ClO4- in water samples collected from a man-made reflection pond following a fireworks display, even though these samples contained much higher concentrations of Cl- and SO42- than ClO4-.

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.

Visible light-induced decomposition of a fluorotelomer unsaturated carboxylic acid in water with a combination of tungsten trioxide and persulfate.

Photochemical decomposition of a fluorotelomer unsaturated carboxylic acid, C3F7CFCHCOOH (1), in the presence of WO3 and an electron acceptor (S2O8(2-) or H2O2) in water under visible-light irradiation was investigated. Under an O2 atmosphere, 1 was not decomposed either by TiO2 (P25) or WO3 alone. A combination of WO3 and H2O2 also resulted in almost no decomposition of 1. In contrast, irradiation in the presence of a combination of WO3 and S2O8(2-) (potassium salt) efficiently decomposed 1 to F(-), CO2, C3F7COOH, and C2F5COOH. The decomposition of 1 was affected by the counter cation of S2O8(2-): the decomposition extent was higher with K2S2O8 than with (NH4)2S2O8. The decomposition of 1 was further enhanced when the reaction in the presence of WO3 and K2S2O8 was carried out under an argon atmosphere. Under O2, the amount of H2O2 formed in the reaction solution was an order of magnitude higher than the amount formed under argon. This fact suggests that the decrease in the decomposition of 1 under O2 can be ascribed to the formation of H2O2, which consumed S2O8(2-) and SO4(-).

First radical homopolymerisation of 2-trifluoromethacrylic acid in water and study of the degradation of the resulting homopolymers.

The radical homopolymerisation of 2-trifluoromethacrylic acid (MAF) initiated by Na2S2O8 in water, under the influence of pH, led to original water soluble surfactants, the decomposition of which was investigated. The value of the square of the propagation rate constant to the termination rate constant, kp(2)/kte, of MAF was 4 × 10(-3) l mol(-1) s(-1) at 80 °C.

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.

Photocatalytic mineralization of hydroperfluorocarboxylic acids with heteropolyacid H4SiW12O40 in water.

The decomposition of hydroperfluorocarboxylic acids [H-PFCAs; HC(n)F(2)(n)COOH (n=4 and 6)] induced by heteropolyacid photocatalyst H(4)SiW(12)O(40) in water was investigated, and the results are compared with the results for the corresponding perfluorocarboxylic acids (PFCAs; C(n)F(2)(n)(+1)COOH). This is the first report on the photochemical decomposition of H-PFCAs, which are being developed as alternative surfactants to environmentally persistent and bioaccumulative PFCAs. H-PFCAs were not decomposed by irradiation with UV-Visible light (>290 nm) in the absence of H(4)SiW(12)O(40). In contrast, UV-Visible light irradiation of H-PFCAs in the presence of H(4)SiW(12)O(40) efficiently decomposed H-PFCAs to F(-) and CO(2). The decomposition reactions showed pseudo-first-order kinetics, and the decomposition rate constants were 1.8-2.5 times higher than those for the corresponding PFCAs. The reaction mechanism can be explained by elimination of H(+) from the ω-H atom of the H-PFCAs by the excited catalyst, followed by formation of perfluorodicarboxylic acids.

Oxygen-induced efficient mineralization of perfluoroalkylether sulfonates in subcritical water.

The decomposition of perfluoroalkylether sulfonates C(2)F(5)OC(2)F(4)SO(3)(-) and C(3)F(7)OC(2)F(4)SO(3)(-) in subcritical water was investigated, and the results were compared with those for perfluorobutanesulfonate (C(4)F(9)SO(3)(-)), which has no ether linkage. This is the first report on the use of subcritical water to decompose perfluoroalkylether sulfonates, which are being developed as alternative surfactants to environmentally persistent and bioaccumulative perfluoroalkylsulfonates. Whereas C(4)F(9)SO(3)(-) showed little reactivity in subcritical water, C(2)F(5)OC(2)F(4)SO(3)(-) decomposed efficiently in subcritical water ( approximately 350 degrees C) in the presence of oxygen gas to form F(-) and SO(4)(2-) in the aqueous phase and CO(2) in the gas phase as major products. Trifluoroacetic acid (CF(3)COOH, TFA) and trifluoromethane (CF(3)H) were also detected as minor products in the aqueous and gas phases, respectively. Similar decomposition behavior was observed for C(3)F(7)OC(2)F(4)SO(3)(-), which decomposed at a rate that was somewhat higher than that of C(2)F(5)OC(2)F(4)SO(3)(-). When argon was used in place of oxygen gas, the time profile of the decrease in the amount of C(2)F(5)OC(2)F(4)SO(3)(-) remained almost unchanged, but the product distribution changed markedly: the amounts of F(-), SO(4)(2-), and CO(2) dramatically decreased, the amounts of TFA and CF(3)H increased, and a new product, HCF(2)SO(3)(-), was detected. These results clearly indicate that treatment with subcritical water in the presence of oxygen gas effectively mineralized perfluoroalkylether sulfonates to F(-), SO(4)(2-), and CO(2). On the basis of a product analysis, we propose a decomposition mechanism.

Efficient decomposition of perfluorocarboxylic acids and alternative fluorochemical surfactants in hot water.

Decomposition of C5-C9 perfluorocarboxylic acids (PFCAs) and perfluoroether carboxylic acids (alternatives to PFCA-based surfactants) in hot water in a sealed reactor was investigated. Although PFCAs showed almost no decomposition in hot water at 80 degrees C in the absence of persulfate (S2O8(2-)), the addition of S2O8(2-) to the reaction system led to efficient decomposition, even at this relatively low temperature. The major products in the aqueous and gas phases were F- ions and CO2, respectively, and short-chain PFCAs were also detected in the aqueous phase. For example, when an aqueous solution containing perfluorooctanoic acid (PFOA, 374 microM) and S2O8(2-) (50.0 mM) was heated at 80 degrees C for 6 h, PFOA concentration in the aqueous phase fell below 1.52 microM (detection limit of HPLC with conductometric detection), and the yields of F- ions [i.e., (moles of F- formed) /(moles of fluorine content in initial PFOA)] and CO2 [i.e, (moles of CO2 formed) /(moles of carbon content in initial PFOA)] were 77.5% and 70.2%, respectively. This method was also effective in decomposing perfluoroether carboxylic acids, such as CF3OC2F4OCF2COOH, CF3OC2F4OC2F4OCF2COOH, and C2F5OC2F4OCF2COOH, which are alternatives to PFCA-based surfactants, producing F- and CO2 with yields of 82.9-88.9% and 87.7-100%, respectively, after reactions at 80 degrees C for 6 h. In addition, the method was successfully used to decompose perfluorononanoic acid in a floor wax solution. When PFOAwastreated at a higher temperature (150 degrees C), other decomposition reactions occurred: the formation of F- and CO2 was dramatically decreased, and 1H-perfluoroalkanes (C(n)F(2n+1)H, n = 4-7) formed in large amounts. This result clearly indicates that treatment with high-temperature water was not suitable for the decomposition of PFCAs to F-: surprisingly, the relatively low temperature of 80 degrees C was preferable.

Iron-induced decomposition of perfluorohexanesulfonate in sub- and supercritical water.

Decomposition of perfluorohexanesulfonate (PFHS), a bioaccumulative analogue of perfluorooctanesulfonate (PFOS), in sub- and supercritical water was investigated. Although PFHS was only slightly reactive in pure subcritical water at 350 degrees C, it decomposed to F(-) and SO(4)(2-) ions when the temperature was increased to 380 degrees C, at which temperature the water became supercritical state. Addition of zerovalent iron to the reaction system dramatically accelerated PFHS decomposition to F(-) ions in both sub- and supercritical water: for example, when the initial PFHS concentration was 741microM, the F(-) yields at 350 degrees C were 4.13-16.0 times as high as those in the absence of iron, depending on the amount and the particle size of the iron powder. After the reactions, small amounts of CO(2) and CF(3)H were also detected in the gas phase; these increased with temperature, and the amount of CF(3)H increased markedly when the reaction was carried out in supercritical water. Increasing the specific surface area of the iron powder markedly increased PFHS consumption and F(-) formation in the aqueous phase, which indicates that the reactions occurred on the iron surface and that the increased specific surface area was a key factor in accelerating the decomposition of PFHS to F(-) ions.

Persulfate-induced photochemical decomposition of a fluorotelomer unsaturated carboxylic acid in water.

The persulfate (S(2)O(8)(2-))-induced photochemical decomposition of C(3)F(7)CF=CHCOOH in water was investigated to develop a method to neutralize stationary sources of fluorotelomer unsaturated carboxylic acids (FTUCAs), which have recently been detected in the environment, and are considered to be more toxic than the environmentally persistent perfluorocarboxylic acids (PFCAs). Photolysis of S(2)O(8)(2-) produced highly oxidative sulfate radical anions (SO(4)(-)), which efficiently decomposed C(3)F(7)CF=CHCOOH to F(-) and CO(2) via C(3)F(7)COOH. With an initial S(2)O(8)(2-) concentration of 12.5mM and irradiation from a 200-W xenon-mercury lamp, C(3)F(7)CF=CHCOOH at a concentration of 680 microM was completely decomposed within 5 min. When 8.00 mM S(2)O(8)(2-) was used, the initial rate of C(3)F(7)CF=CHCOOH decomposition induced by 254-nm light irradiation was 45 times as high as that with photolysis alone. The apparent quantum yield for the C(3)F(7)CF=CHCOOH decomposition with 6.25 mM S(2)O(8)(2-) and 254-nm light was 2.4, indicating that virtually all SO(4)(-) anions produced by the photolysis of S(2)O(8)(2-) contribute to the decomposition of C(3)F(7)CF=CHCOOH.

Photochemical decomposition of environmentally persistent short-chain perfluorocarboxylic acids in water mediated by iron(II)/(III) redox reactions.

The photochemical decomposition of short-chain (C(3)-C(5)) perfluorocarboxylic acids (PFCAs) was investigated. Direct photolysis in water proceeded slowly with the 220- to 460-nm light emission from a xenon-mercury lamp to form F(-), CO(2), and shorter-chain PFCAs. Addition of a small amount of Fe(3+) to the aqueous solutions of the PFCAs dramatically enhanced their photochemical decomposition under an oxygen atmosphere: when the (initial PFCA)/(initial Fe(3+)) molar ratio was 13.5 (initial PFCA concentration=67.3mM), the pseudo-first-order rate constants for the PFCA decomposition were 3.6-5.3 times those with photolysis alone, and the turnover number for the catalytic PFCA decomposition [i.e., (moles of decomposed PFCA)/(moles of initial Fe(3+))] reached 6.71-8.68 after 24h of irradiation. The catalysis can be explained by photoredox reactions between PFCA, Fe(3+)/Fe(2+) and oxygen via photo-induced complexation of Fe(3+) with the PFCAs.

TiO2-induced heterogeneous photodegradation of a fluorotelomer alcohol in air.

Degradation of C4F9C2H4OH in air over TiO2 particles was examined in this first report of gas-solid heterogeneous photochemical degradation of fluorotelomer alcohols (FTOHs), which may be precursors of perfluorocarboxylic acids (PFCAs) in the environment. Photoirradiation (>290 nm) of C4F9C2H4OH in air flowing over TiO2 produced CO2, via C4F9CH2CHO, C4F9CHO, CnF(2n+1)COF (n=2 and/or 3), and COF2, in that order. X-ray photoelectron spectroscopy of the Ti02 surface showed a decrease in the amount of fluorine bonded to carbon and an increase in the amount of F- as the degradation of C4F9C2H4OH in air proceeded. Of the carbon content in the initial C4F9C2H4OH (78.8 ppmv), 90.7% was transformed to CO2, and the predominant fluorine species produced on the TiO2 surface was F-. Fluorotelomer unsaturated acids, which are considered to be toxic and have been observed in the biodegradation of FTOHs, did notform. Increased relative humidity in the air accelerated the decomposition of the reaction intermediates, which led to increased CO2 and F- formation. This result indicates that humidity is a key factor for counteracting FTOHs in indoor air. Although perfluoroalkyl substances such as PFCAs in water reportedly undergo little photodegradation over TiO2, our data show that mineralization of C4F9C2H4OH in air can be achieved with TiO2.

Efficient decomposition of environmentally persistent perfluorooctanesulfonate and related fluorochemicals using zerovalent iron in subcritical water.

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.

Efficient photochemical decomposition of long-chain perfluorocarboxylic acids by means of an aqueous/liquid CO2 biphasic system.

Photochemical decomposition of persistent and bioaccumulative long-chain (C9-C11) perfluorocarboxylic acids (PFCAs) with persulfate ion (S2O8(2-)) in an aqueous/liquid CO2 biphasic system was examined to develop a technique to neutralize stationary sources of the long-chain PFCAs. The long-chain PFCAs, namely, perfluorononanoic acid (PFNA), perfluorodecanoic acid (PFDA), and perfluoroundecanoic acid (PFUA), which are used as emulsifying agents and as surface treatment agents in industry, are relatively insoluble in water but are soluble in liquid CO2; therefore, introduction of liquid CO2 to the aqueous photoreaction system reduces the interference of colloidal PFCA particles. When the biphasic system was used to decompose these PFCAs, the extent of reaction was 6.4-51 times as high as that achieved in the absence of CO2. In the biphasic system, PFNA, PFDA, and PFUA (33.5-33.6 micromol) in 25.0 mL of water were 100%, 100%, and 77.1% decomposed, respectively, after 12 h of irradiation with a 200-W xenon-mercury lamp; F- ions were produced as a major product, and short-chain PFCAs, which are less bioaccumulative than the original PFCAs, were minor products. All of the initial S2O8(2-) was transformed to SO42-. The system also efficiently decomposed PFCAs at lower concentrations (e.g., 4.28-16.7 micromol of PFDA in 25.0 mL) and was successfully applied to decompose PFNA in floor wax.

Efficient decomposition of environmentally persistent perfluorocarboxylic acids by use of persulfate as a photochemical oxidant.

Photochemical decomposition of persistent perfluorocarboxylic acids (PFCAs) in water by use of persulfate ion (S2O8(2-)) was examined to develop a technique to neutralize stationary sources of PFCAs. Photolysis of S2O8(2-) produced highly oxidative sulfate radical anions (SO4-), which efficiently decomposed perfluorooctanoic acid (PFOA) and other PFCAs bearing C4-C8 perfluoroalkyl groups. The major products were F- and CO2; also, small amounts of PFCAs with shorter than initial chain lengths were detected in the reaction solution. PFOA at a concentration of 1.35 mM (typical of that in untreated wastewater after an emulsifying process in fluoropolymer manufacture) was completely decomposed by a photochemical system with 50 mM S2O8(2-) and 4 h of irradiation from a 200-W xenon-mercury lamp. The initial PFOA decomposition rate was 11 times higherthan with photolysis alone. All sulfur-containing species in the reaction solution were eventually transformed to sulfate ions by this method. This method was successfully applied to the decomposition of perfluorononanoic acid contained in a floor wax solution.

Decomposition of environmentally persistent perfluorooctanoic acid in water by photochemical approaches.

The decomposition of persistent and bioaccumulative perfluorooctanoic acid (PFOA) in water by UV-visible light irradiation, by H202 with UV-visible light irradiation, and by a tungstic heteropolyacid photocatalyst was examined to develop a technique to counteract stationary sources of PFOA. Direct photolysis proceeded slowly to produce CO2, F-, and short-chain perfluorocarboxylic acids. Compared to the direct photolysis, H2O2 was less effective in PFOA decomposition. On the other hand, the heteropolyacid photocatalyst led to efficient PFOA decomposition and the production of F- ions and CO2. The photocatalyst also suppressed the accumulation of short-chain perfluorocarboxylic acids in the reaction solution. PFOA in the concentrations of 0.34-3.35 mM, typical of those in wastewaters after an emulsifying process in fluoropolymer manufacture, was completely decomposed by the catalyst within 24 h of irradiation from a 200-W xenon-mercury lamp, with no accompanying catalyst degradation, permitting the catalyst to be reused in consecutive runs. Gas chromatography/mass spectrometry (GC/MS) measurements showed no trace of environmentally undesirable species such as CF4, which has a very high global-warming potential. When the (initial PFOA)/(initial catalyst) molar ratio was 10: 1, the turnover number for PFOA decomposition reached 4.33 over 24 h of irradiation.