Efficient Decomposition of Environmentally Persistent Perfluorocarboxylic Acids by U of Persulfate as a Photochemical Oxidant
H I S A O H O R I,*A R I Y A M A M O T O,
E T S U K O H A Y A K A W A,S A C H I T A N I Y A S U,
N O B U Y O S H I Y A M A S H I T A,A N D
S H U Z O K U T S U N A
National Institute of Advanced Industrial Science and Technology,AIST Tsukuba West,16-1Onogawa,
Tsukuba305-8569,Japan
H I R O S H I K I A T A G A W A A N D
R Y U I C H I A R A K A W A
Department of Applied Chemistry,Faculty of Engineering, Kansai University,3-3-35Yamate-cho,Suita564-8680,Japan
Photochemical decomposition of persistent perfluorocar-boxylic acids(PFCAs)in water by u of persulfate ion(S2O82-) was examined to develop a technique to neutralize stationary sources of PFCAs.Photolysis of S2O82-produced highly oxidative sulfate radical anions(SO4•-),which efficiently decompod perfluorooctanoic acid(PFOA)and other PFCAs bearing C4-C8perfluoroalkyl 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 of1.35 mM(typical of that in untreated wastewater after an emulsifying process in fluoropolymer manufacture)was completely decompod by a photochemical system with 50mM S2O82-and4h of irradiation from a200-W xenon-mercury lamp.The initial PFOA decomposition rate was 11times higher than 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
natalie imbrugliaacid contained in a floor wax solution.
Introduction
Perfluorocarboxylic acids(PFCAs)and perfluorosulfonic acids and their salts have been widely ud
as emulsifying agents in polymer synthesis and as surface treatment agents in photolithography,paper coatings,and waxes and polishes (1-3).As the u of the perfluorinated acids has incread, some of them,such as perfluorooctanoic acid(C7F15COOH; PFOA)and perfluorooctanesulfonate(C8F17SO3-;PFOS),have recently been detected in environmental waters,wildlife,and humans(4-8).Analytical studies have revealed their bio-accumulation,with longer-chain compounds being more bioaccumulative(9-11),and their toxicological properties are being clarified(9-14).Recently,PFCAs bearing C8-C10 perfluoroalkyl groups,which are more bioaccumulative than PFOA,were detected in wildlife at higher concentrations than PFOA(15).The anthropogenic compounds,who high stability is ascribed to their C-F bonds,have no known natural decomposition process.When the compounds are boiled in nitric acid or sulfuric acid,no sign of C-F bond cleavage is obrved(1,2).To thermally decompo them, high temperatures(∼1200°C)are required(3).Therefore, the development of techniques for decomposing them(as waste,especially in wastewater)to harmless species under mild conditions is desirable as a measure against stationary ,manufacturing,processing,and waste sites)(7, 14).Ideally,the method would involve cleavage of the C-F bonds to form F-ions,becau F-ions readily combine with Ca2+to form environmentally harmless CaF2.
The heterogeneous photocatalyst TiO2has been widely studied for the decomposition of air and water pollutants (16,17).However,the reactivity of TiO2toward PFCAs is estimated to be very low,becau OH•radicals in aqueous solution are hardly reactive to PFCAs such as trifluoroacetic acid(18,19).So far,heteropolyacid H3PW12O40has been the only photocatalyst reported to decompo PFCAs(20-23).
Persulfate ion(S2O82-)is not a photocatalyst.However, it is an attractive candidate to photochemically decompo PFCAs becau photolysis of S2O82-produces two sulfate radical anions(SO4•-)with quantum efficiency of unity(eq 1),and the formed SO4•-can act as a strong oxidant in aqueous systems(24,25):
There have been a few examples of photochemical systems using S2O82-to help decompo environmentally harmful compounds(26-28).However,in such systems,S2O82-was mostly ud as an electron-trapping agent to suppress hole-electron recombination in the TiO2photocatalytic system; substantially,the reactivity of SO4•-toward substrate was ignored.
Here we show the effective photochemical decomposition of PFOA and other PFCAs bearing C4-C9perfluoroalkyl groups using S2O82-.By u of this system,PFCAs were effectively decompod to
F-and CO2,and all of the initial S2O82-was transformed to SO42-,for which there is a well-established waste treatment process.Finally,we applied this method to the decomposition of perfluorononanoic acid (C8F17COOH;PFNA)contained in a floor wax solution as an example of wastewater treatment.
Experimental Section
Materials.Potassium persulfate(>99.0%)was purchad from Wako Pure Chemical Industries(Osaka,Japan)and ud as received.Trifluoroacetic acid(CF3COOH,>99.0%),pen-tafluoropropionic acid(C2F5COOH,>98%),heptafluorobu-tyric acid(C3F7COOH,>99%),nonafluoropentanoic acid (C4F9COOH,>98%),undecafluorohexanoic acid(C5F11COOH, >98%),and PFNA(>95%)were purchad from Tokyo Kai
Kogyo Co.(Tokyo,Japan).Tridecafluoroheptanoic acid(C6F13-COOH,>96%)and PFOA(>95%)were obtained from Wako Pure Chemical Industries.
Photochemical Procedures.A cylindrical pressure-resistant Inconel reactor(176-mL volume,5.9-cm i.d.;Nitto Koatsu Co.,Tsukuba,Japan)equipped with a sapphire window(4.0-cm i.d.)was ud.The inner wall of the reactor was coated with poly(tetrafluoroethylene).A gold vesl(105 mL,5.5-cm i.d.),
which is stable to highly acidic solutions, was introduced into the reactor.In a typical run,an acidic (pH3.0-3.1)aqueous solution(22mL)containing PFOA
*Corresponding author phone:+81-298-61-8161;fax:+81-298-61-8258;e-mail:jp.S2O82-+hνf2SO4•-(1)
Environ.Sci.Technol.2005,39,2383-
2388
10.1021/es0484754CCC:$30.25©2005American Chemical Society VOL.39,NO.7,2005/ENVIRONMENTAL SCIENCE&TECHNOLOGY92383 Published on Web02/18/2005
(29.6µmol;1.35mM)and K2S2O8(0.14-1.10mmol;6.4-50.0 mM)was poured into the gold vesl.The initial PFOA concentration was in the concentration range prent in untreated wastewater after an emulsifying process in fluoro-polymer manufacture.After the reactor was bubbled and then pressurized to0.48MPa with oxygen gas,the solution was irradiated with UV-visible light from a xeno
n-mercury lamp(200W,L20001-01L,San-Ei Electric Co.,Osaka,Japan). For the light irradiation,a water filter and an optical-quartz glass fiber were ud.In all runs,the reaction temperature was held constant at25°C.After irradiation,the pressure was relead,and gas was collected in a sampling bag and subjected to gas chromatography/mass spectrometry(GC/ MS)and GC measurements.Gas volume was measured by an integrating flowmeter.The reaction solution was analyzed by ion chromatography,ion-exclusion chromatography, high-performance liquid chromatography(HPLC),and elec-trospray ionization(ESI)mass spectrometry.
Analytical Procedures.An ion-chromatography system (IC-2001,Tosoh Corp.,Tokyo,Japan)consisting of an automatic sample injector(30-µL injection volume),a degasr,a pump,a guard column(TSKguard column Super IC-A,4.6-mm i.d.,1.0-cm length;Tosoh Corp.),a paration column(TSKgel Super IC-Anion,4.6-mm i.d.,15-cm length), a column oven(40°C),and a conductivity detector with a suppressor device was ud to measure the F-and SO42-concentrations.The mobile pha was an aqueous solution containing Na2B4O7(6mM),H3BO3(15mM),and NaHCO3 (0.2mM),and the flow rate was0.8mL min-1.The limits of detection(LODs),which were calculated from a signal-to-noi(S/N)ratio of3,were0.74and2.62µg L-1for F-and SO42-,respectively.
An ion-exclusion chromatograph system consisting of a guard column(TSKgel OApak-P,7.8-mm i.d.,
1.0-cm length; Tosoh Corp.),a paration column(TSKgel OApak-A,7.8-mm i.d.,30-cm length;Tosoh Corp.),a pump,a column oven (40°C),and a conductivity detector was ud to measure the concentrations of short-chain PFCAs(CF3COOH to C3F7-COOH).The mobile pha was phthalic acid(10mM)with a flow rate of0.6mL min-1,and typical sample injection volume was5µL.The LODs(S/N)3)(injected at5µL)were 0.27,0.28,and0.81mg L-1for CF3COOH,C2F5COOH,and C3F7COOH,respectively.
The concentrations of longer-chain PFCAs(C4F9COOH to PFNA)were measured by an HPLC system with conduc-tometric detection(IC-2001,Tosoh Corp.);the column was a Tosoh TSKgel Super-ODS(4.6-mm i.d.,10-cm length×2), and the mobile pha was a mixture of methanol and aqueous NaH2PO4(20mM,adjusted to pH3.0with H3PO4)at veral mixing ratios with a flow rate of0.4mL min-1.When the sample injection volume was30µL,the LODs(milligrams per liter,S/N)3)were as follows:0.30and0.63for C4F9-COOH and C5F11COOH[mobile pha55:45(v/v)methanol/ aqueous NaH2PO4];0.18,0.15,0.63,and0.57for C5F11COOH, C6F13COOH,PFOA,and PFNA[65:35(v/v)methanol/aqueous NaH2PO4];and0.14,0.20,and0.33for C6F13COOH,PFOA, and PFNA[70:30(v/v)methanol/aqueous NaH2PO4],re-spectively.Details of the HPLC method are described elwhere(29).
ESI mass spectrometry was ud to identify the products in the reaction solution.The system ud(Kansai University) was a triple-stage quadrupole mass spectrometer(TSQ700, Finnigan MAT,San Jo,CA).Analys were carried out in negative ion mode.The electrospray potential was-4.5kV against the counter electrode of a heated capillary.The capillary was ud to aid desolvation of electrosprayed droplets.Ions entered the vacuum system through a skimmer cone.The cone voltage was20V.The capillary temperature was t to150°C,becau the loss of CO2from C7F15COO-was markedly obrved at higher temperatures such as250°C.Reaction samples were diluted with acetonitrile(1000-fold by volume)and were electrosprayed at a flow rate of 10µL min-1.
A GC/MS system consisting of a gas chromatograph (HP5890,Hewlett-Packard,Wilmington,DE)with a column (Poraplot Q,0.32-mm i.d.,25-m length,Chrompack,Bergen op Zoom,The Netherlands),a mass spectrometer(HP5972A), and a workstation(HP G1034CJ)was ud to identify the products in the gas pha.The carrier gas was He.The oven temperature was held constant at30°C.The sample gas (30µL)was introduced into the GC/MS system in splitless mode.The injector temperature was held constant at120°C, and the electron impact(EI)source was operated at70eV.
Quantification of CO2was carried out by a GC system(GC 323,GL Sciences,Tokyo,Japan)with an active carbon column (60/80mesh,2.17-mm i.d.,2-m length,110°C)and a thermal conductivity detecto
r.The sample injection mode was splitless,and the injection volume was0.4mL.The LOD (S/N)3)for CO2was94.1ppmv.
Quantification of PFNA in floor wax was performed by HPLC with conductometric detection and LC/MS/MS(MS/ MS)electrospray/tandem mass spectrometry).Conditions for LC/MS/MS were identical with that reported elwhere (29),except for the ammonium acetate(2mM)/methanol mobile-pha gradient:10%methanol,incread to30%at 0.1min,75%at7min,and100%at10min,maintained until 12min,and returned to the original conditions at20min. PFNA was determined by monitoring product ion of m/z419 from primary ion m/z463.
Wax Sample Treatment.The decomposition of PFNA contained in floor wax solution was examined as an example of PFCA decomposition in wastewater.The colloidal white-colored wax contained not only PFNA but also many other compounds and diments;therefore,solid-pha extraction by InertSep RP-1cartridges(250mg/6mL;GL Sciences, Tokyo,Japan)was performed to clean up and concentrate PFNA prior to HPLC analysis.
To quantify PFNA in the wax itlf,the wax(0.50g)was diluted to50mL with water.The cartridges were precon-ditioned with methanol(10mL),followed by water(10mL). After preconditioning,the aqueous w
ax solution was pasd through the cartridge at a rate of1mL min-1.The PFNA was then eluted from the cartridge with methanol(5mL).The eluted solution was concentrated under argon to1mL and then subjected to HPLC with conductometric detection.In this manner,the PFNA concentration in the wax(before dilution)was determined to be75.4mg L-1.The above procedure was also taken for aqueous solution(0.50mL)of PFNA(112mg L-1)instead of the wax,and good recovery was obtained(101%,n)4,relative standard deviation) 3.7%).Quantification of PFNA in the wax was also performed by LC/MS/MS and u of different solid-pha extraction media(Oasis HLB cartridges,200mg/6mL;Waters Corp., Milford,MA),and a similar value,74.5mg L-1,was obtained.
To decompo PFNA in the wax photochemically,an aqueous solution(22mL)containing the wax(0.44g)and K2S2O8(1.10mmol;50.0mM)was introduced into the reactor. The concentration of PFNA in the reaction solution was1.51 mg L-1(3.25µM).Then the solution was irradiated for12h in the same manner as described above.After irradiation, the precipitate that formed was removed by centrifugation (3000rpm,10min).A portion of the liquid pha(15mL) was diluted to50mL with water.The diluted solution was pasd through the preconditioned InertSep RP-1cartridge, eluted by methanol,and concentrated to1mL in the manner described above.Finally,the concentrated solution was analyzed by HPLC,and PFNA was quantified.
23849ENVIRONMENTAL SCIENCE&TECHNOLOGY/VOL.39,NO.7,2005
Results and Discussion
Decomposition of PFOA.In our reaction conditions,an aqueous solution containing PFOA and S2O82-was irradiated with UV-visible light from a xenon-mercury lamp through a water filter.Figure1shows wavelength distribution for absorption of PFOA and of S2O82-and emission from the lamp.Under the conditions,the lamp emits mainly220-460-nm light.Since PFOA absorbs from the deep-UV region to220nm and has a weak,broad absorption to∼270nm, whereas S2O82-absorbs from the deep-UV region to350nm, we obrved S2O82-to be the dominant absorbing species in our reaction conditions.
We determined the irradiation-time dependence of the photoreaction using a37-fold molar excess of S2O82-over PFOA(Figure2).The amount of PFOA decread with irradiation,and F-and CO2were found as products in the liquid and gas phas,respectively.After4h of irradiation, PFOA disappeared on the HPLC chromatogram(LOD was 0.20mg L-1)0.48µM;1.06×10-8mol in the22mL reaction solution).On the other hand,the production of F-and CO2 still continued after4h,indicating that species other than PFOA continued to produce F-and CO2.After12h of irradiation,the yield of F-[(mol
es of F-formed)/(moles of initial PFOA×15)]reached73.8%.We detected not only F-ions but also small amounts of shorter-chain PFCAs such as the one CF2unit-shortened PFCA(C6F13COOH)in the liquid pha(Figure3A).The formation of C6F13COOH was followed by more CF2unit-shortened species,C5F11COOH,C4F9COOH, and C3F7COOH.The amounts of the shorter-chain PFCAs reached maxima at2h.The total recovery of , molar ratio of total fluorine content in F-and short-chain PFCAs formed and in unchanged PFOA to that in the PFOA before irradiation)was99.1%at2h of irradiation.Likewi, total carbon ,molar ratio of total carbon content in CO2and short-chain PFCAs formed and in unchanged PFOA to that in the PFOA before irradiation)was97.7%. Hence,the initial fluorine and carbon in PFOA can be almost completely accounted for by unchanged PFOA,F-,CO2,and short-chain PFCAs formed.
The formation of shorter-chain PFCAs was also confirmed by ESI mass spectral measurements,showing peaks corre-sponding to[C6F13COO]-(m/z363)and[C5F11COO]-(m/z 313)(Figure4).Further irradiation decread the amounts of the shorter-chain PFCAs and incread formation of further shorter PFCAs(C2F5COOH and CF3COOH;Figure3B). The obrvations indicate that short-chain PFCAs form in a stepwi manner from longer-chain PFCAs.
GC/MS analysis of the gas pha indicated that this system produced no environmentally undesirabl
infinitel
e species such as CF4and CF3H,which are stable species that have high global-warming potentials(at least3900and9400times as high as CO2,respectively;30).In contrast,CF4is often obrved in the decomposition of perfluorinated compounds by ex-tremely high energy techniques such as electron beam irradiation(31).
FIGURE 1.Wavelength distribution for absorption of PFOA (1.35mM in water)and of S2O82-(50.0mM in water)and emission from the xenon-mercury lamp.The concentrations of PFOA and S2O82-were the same as in subquent photochemical reactions (Figure2).The path length for measurement of the absorption spectra was1.0cm.
FIGURE2.Irradiation-time dependence of PFOA decomposition with S2O82-:detected molar amounts of PFOA,CO2,and F-.An aqueous solution(22mL)containing S2O82-(1.10mmol;50.0mM) and PFOA(29.6µmol;1.35mM)was irradiated with a xenon-mercury lamp under oxygen(0.48MPa).FIGURE3.Irradiation-time dependence of PFOA decomposition with S2O82-:detected molar amounts of PFCAs bearing(A)C3-C6 and(B)C1-C2perfluoroalkyl groups.Reaction conditions were the same as in Figure2.
VOL.39,NO.7,2005/ENVIRONMENTAL SCIENCE&TECHNOLOGY9
2385
We determined the reaction yields for various combina-tions of S 2O 82-,light irradiation,and reaction
atmosphere (Table 1).In the abnce of light irradiation,no reaction occurred (entry 2).When light was irradiated in the abnce of S 2O 82-(direct photolysis),PFOA decomposition,F -for-mation,and CO 2formation all markedly decread (entry 3)compared to tho in the prence of S 2O 82-(entry 1).This obrvation clearly indicates that SO 4•-reacts with PFOA:
On the other hand,when the reaction was carried out in the prence of S 2O 82-under argon (entry 4),the reaction yields of PFOA decomposition,F -formation,and CO 2formation were similar to tho of reactions under oxygen (entry 1);also,no significant differences were obrved in the formation of shorter-chain PFCAs (Table 2).Thus,the oxygen gas in the reaction system does not play a significant role in the PFOA decomposition system.
Effect of S 2O 82-Concentration.The amount of PFOA decread linearly with respect to irradiation time during a short initial period after irradiation started.We ud the initial PFOA decomposition rate,the slope taken from this period,as a measure for the photochemical reactivity.We measured the effect of initial S 2O 82-amount on the initial PFOA decomposition rate (Figure 5).The photochemical reactivity incread when the initial amount of S 2O 82-was incread.When 0.59mmol of S 2O 82-(26.8mM)was ud,the decomposition rate was 11times that for direct photolysis.
hauntHowever,further increa in the initial S 2O 82-resulted in saturation,that is,no further increa in the PFOA decom-position rate.When the initial amount of S 2O 82-was 0.59mmol (26.8mM),the transmittance of the initial reaction solution in the reactor at 254nm (a maximum emission line of the lamp)was 35.8%,as calculated for an optical path of 0.9cm in the reactor.Therefore,the saturation of the PFOA decomposition rate obrved above 0.59mmol of S 2O 82-cannot be ascribed to the saturation of the light absorption ability.It was reported that SO 4•-radical anions,produced by photolysis of S 2O 82-,react with S 2O 82-to form SO 42-and S 2O 8•-with a rate constant (k 3)of 5.5×105M -1s -1under acidic conditions (pH 2)(32):
In addition,SO 4•-radical anions react with water with a rate constant k 4[H 2O]of 460s -1(32):
For our reaction conditions,the k 3[S 2O 82-]value was 1.47×104s -1,calculated from an initial S 2O 82-amount of 0.59mmol (26.8mM).This value was much larger than k 4[H 2O](460s -1);therefore the reaction of SO 4•-with water (eq 4)is negligible.Hence,the tendency of the PFOA decomposition rate to saturate at higher S 2O 82-concentra-tions can be explained by the fact that the reaction of SO 4•-with S 2O 82-(eq 3)occurs at higher S 2O 82-concentrations,resulting in saturation of SO 4•-concentration.
FIGURE 4.Typical ESI mass spectrum of the photochemical reaction solution.An aqueous solution (22mL)containing S 2O 82-(1.10mmol;50.0mM)and PFOA (29.6µmol;1.35mM)was irradiated with a xenon -mercury lamp under oxygen (0.48MPa)for 2h.The anions [C 7F 15]-and [C 6F 13]-were fragment species derived from [C 7F 15COO]-and [C 6F 13COO]-,respectively.
TABLE 1.Reaction Yields for Various Combinations between S 2O 82-,Light Irradiation,and Reaction Atmosphere a
entry S 2O 82-light irradiation atmos-phere b PFOA decomposition (%)F -yield c (%)CO 2
yield d
(%)1prent e prent
O 210059.149.82prent e none O 20003none prent O 216.89.0 6.64
prent e
prent
Ar
96.6
52.3
43.3
a
Reaction time was 4h,initial amount of PFOA was 29.6µmol,and the reaction solution volume was 22mL.b Pressure was 0.48MPa.c F -yield )[(moles of F -formed)/(moles of initial PFOA ×15)]×100.d CO 2yield )[(moles of CO 2formed)/(moles of initial PFOA ×8)]×100.e Amount of initial S 2O 8
2-was 1.10mmol.TABLE 2.Effect of Reaction Atmosphere on Photochemical Decomposition of PFOA with S 2O 82-:Detection of Short-Chain PFCAs as Minor Products a
entry atmos-phere b C 6F 13COOH (µmol)C 5F 11COOH (µmol)C 4F 9COOH (µmol)C 3F 7COOH (µmol)1O 2 2.07 3.75 2.39 2.702
millionsofAr
2.42
3.86
3.37
3.48
ctcsa Reaction time was 4h.Initial amounts of PFOA and S 2O 8
2-were 29.6µmol and 1.10mmol,respectively.Reaction solution volume was 22mL.b Gas pressure was 0.48MPa.
FIGURE 5.Effect of initial amount of S 2O 82-on the initial
decomposition rate of PFOA.An aqueous solution (22mL)containing S 2O 82-(0-1.10mmol;0-50.0mM)and PFOA (29.6µmol;1.35mM)was irradiated with a xenon -mercury lamp under oxygen (0.48MPa).The initial decomposition rate of PFOA was taken from the initial period of irradiation when the decomposition amount of PFOA incread linearly with respect to time.
SO 4•-+S 2O 82-f SO 42-+S 2O 8•-
(3)
SO 4•-+H 2O T HSO 4-+OH •T SO 42-+H ++OH •(4)
SO 4•-+PFOA f SO 42-+PFOA •+
(2)
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2005
In the photochemical PFOA decomposition system with heteropolyacid H 3PW 12O 40(23),the PFOA decomposition rate (the initial PFOA concentration was the same as our condition)was 2.9times that for direct photolysis.Hence,the u of S 2O 82-(11times that for direct photolysis)was more efficient,although our method is not a photocatalytic system.
Fate of Sulfur Species.In our photochemical reaction system,SO 4•-radical anions are formed from photolysis of S 2O 82-(eq 1),which then react with PFOA.In such a system,SO 42-forms by one-elect
ron transfer from PFOA to SO 4•-(eq 2).
The irradiation-time dependence of the amounts of SO 42-detected during photochemical decomposition of PFOA (same experimental conditions as in Figures 2and 3)was determined (Figure 6).As expected,SO 42-accumulated in the liquid pha and the amount incread with irradiation time,while PFOA decomposition and F -and CO 2formation also occurred.After 12h of irradiation,the amount of SO 42-reached 2.26mmol.The initial amount of S 2O 82-was 1.10mmol;therefore,the recovery of sulfur content was 103%.Thus,although S 2O 82-radical anions may form at higher S 2O 82-concentration (eq 3),all sulfur species ud in this reaction were eventually transformed into SO 42-.The fate of PFOA •+after an electron transfer with SO 4•-(eq 2)is not clear;however,on the basis of the reported experimental results and on data from the literature (33,34),it is possible to propo a mechanism.The first bond to be cleaved is the C -C bond between C 7F 15and COOH.The C 7F 15radicals in
water form the thermally unstable alcohol C 7F 15OH,which undergoes HF elimination to form C 6F 13COF (33).This acid fluoride undergoes hydrolysis (34),resulting in the formation of the one CF 2unit-shortened species C 6F 13COOH.
Other PFCAs and Wax Solution.We applied our method to other PFCAs bearing C 4-C 8perfluoroalkyl groups at a constant irradiation time of 12h.The results are summarized in Table 3,together with the data for direct photolysis.In each ca,F -and shorter-chain PFCAs were detected in the liquid pha,and CO 2was detected in the gas pha.When S 2O 82-was ud,the decomposition yield of each substrate reached 100%(except for C 4F 9COOH,98.6%).The effective-ness of S 2O 82-is clear for each substrate.The amount of F -formed by the reaction with S 2O 82-for each substrate bearing C 4-C 6perfluoroalkyl groups was 14-34times higher than that obtained by the corresponding direct photolysis at the same initial substrate concentration and light intensity (entries 1-6).
As for PFNA decomposition in the wax solution,the concentration of PFNA in the reaction solution was 1.51mg L -1(3.25µM)before irradiation.After 12h of irradiation in the prence of S 2O 82-(50.0mM),the PFNA concentration in the reaction solution was determined to be 89µg L -1(0.19µM)by HPLC with sample concentration by solid-pha extraction.Therefore,almost all (94%)of the initial PFNA was effectively removed from the reaction solution,despite the prence of other chemical species (resin,etc.)in the initial solution.label
Our system is a simple photochemical system that allows effective decomposition of PFOA and othe
r PFCAs in water,bad on the high reactivity of SO 4•-radical anions toward PFCAs.The SO 4•-radical anions exist in aqueous-pha atmosphere such as in cloud droplets (35).Therefore,the high reactivity of SO 4•-toward PFCAs in water may indicate the possibility for SO 4•-rving as a tropospheric sink for PFCAs [gaous reaction with OH •radicals is a minor fate (36)].Of cour,such possibility should be evaluated by the reaction rate and tropospheric concentration levels of SO 4•-and PFCAs.
Acknowledgments
This work was supported in part by a Grant-in-Aid for Scientific Rearch (15310066)from the Japan Society for the Promotion of Science (JSPS).
Literature Cited
(1)Renner,R.Growing concern over perfluorinated chemicals.
Environ.Sci.Technol .2001,35,154A -160A.
(2)Giesy,J.P.;Kannan,K.Perfluorochemical surfactants in the
environment.Environ.Sci.Technol .2002,36,146A -152A.
TABLE 3.Photochemical Decomposition of PFCAs Bearing C 4-C 8Perfluoroalkyl Groups a
entry substrate (initial,µmol)initial S 2O 82-(mmol)decompod substrate (µmol)[yield,%]b F -(µmol)CO 2(µmol)short-chain PFCAs (µmol)
1C 6F 13COOH (29.3) 1.1029.3[100]260121C 5F 11COOH (1.96),C 4F 9COOH (2.78),C 3F 7COOH (8.69),C 2F 5COOH (4.48),CF 3COOH (2.42)2C 6F 13COOH (29.7)0 5.56[18.7]16.737.4C 5F 11COOH (3.00),C 4F 9COOH (1.10)
3C 5F 11COOH (29.4) 1.1029.4[100]241118C 4F 9COOH (1.87),C 3F 7COOH (3.20),C 2F 5COOH (6.98),CF 3COOH (2.81)
4C 5F 11COOH (29.7)0 3.55[12.0]7.120.0C 4F 9COOH (3.06),C 3F 7COOH (1.10),C 2F 5COOH (0.27)5C 4F 9COOH (29.3) 1.1028.9[98.6]20098.7C 3F 7COOH (1.87),C 2F 5COOH (3.33),CF 3COOH (3.11)6C 4F 9COOH (29.7)0 4.63[15.6]14.716.0C 3F 7COOH (3.31),C 2F 5COOH (1.40)
7c PFNA (14.8) 1.1014.8[100]187104C 5F 11COOH (0.14),C 4F 9COOH (0.25),C 3F 7COOH (0.24),C 2F 5COOH (0.22),CF 3COOH (0.81)
8c
PFNA (15.0)
9.67[64.5]
68.5
50.8
PFOA (3.86),C 6F 13COOH (0.95),C 5F 11COOH (0.52),C 4F 9COOH (0.29)
a
An aqueous solution (22mL)of substrate was irradiated with a xenon -mercury lamp under oxygen (0.48MPa)for 12h.b [(Moles of decompod substrate)/(moles of initial substrate)]×100.c The light intensity of the lamp was different from that for entries 1-6.
FIGURE 6.Irradiation-time dependence of the amounts of SO 42-detected during photochemical decomposition of PFOA with S 2O 82-.Reaction conditions were the same as in Figure 2.
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