DECOMPOSITION OF PERFLUOROOCTANOIC ACID PHOTOCATALYZED BY TIO2:

CHEMICAL MODIFICATION OF THE CATALYST SURFACE INDUCED BY FLUORIDE IONS

M. Sansotera1,2,3, S. Gatto*1,3, F. Persico*2,3, C. Pirola1,3, W. Navarrini2,3, C. L. Bianchi1,3 1 Università degli Studi di Milano, Dipartimento di Chimica , via Golgi, 19 – 20133 Milano (Italy)

2Politecnico di Milano, Dipartimento di Chimica, Chimica Industriale e Ingegneria Chimica “Giulio Natta”, via Mancinelli, 7 – 20131 Milano (Italy) 3Consorzio INSTM, via G. Giusti, 9 – 50121 Firenze (Italy)

(*) corresponding authors: sara.gatto@unimi.it fpersico@chem.polimi.it

PERFLUOROOCTANOIC ACID

Perfluorooctanoic acid (PFOA) is one of the most largely employed

industrial surfactant [1]. Recent studies have shown the presence of

high levels of this compound in the environment, particularly in seas

and rivers.

PFOA is listed as persistent organic pollutant and nowadays US-EPA

(Environmental Protection Agency) and EEA (European Environment

Agency) are taking action to minimize the emission of PFOA in the

environment [3].

XPS ANALYSIS

Ti 2p region XPS spectra of titanium dioxide

catalyst: after 4 h (A); after 9 h reaction (B); after

9 h reaction and after suspension in fluorinated

solvent (C).

EXPERIMENTAL APPARATUS

FT-IR spectra of titanium dioxide catalyst at

different reaction times (*) C−F stretching; (+)

COO symmetric stretching.

FT-IR ANALYSIS

0

5

10

15

20

25

0 50 100 150 200 250 300 350 400

F-yi

eld

(%

)Time (min)

F- yield (%) changing [PFOA]

[PFOA] = 4.0 mM

[PFOA] = 7.8 mM

[PFOA] = 12.0 mM

0

5

10

15

20

25

0 50 100 150 200 250 300 350 400

F-yi

eld

(%

)

Time (min)

F- yield (%) changing [TiO2]

[TiO2] = 0.66 g/l

[TiO2] = 1.00 g/l

0

5

10

15

20

25

30

35

0 50 100 150 200 250 300 350 400

F-yi

eld

(%

)

Time (min)

F- yield (%) changing light intensity

W = 75 W/m2

W = 95 W/m2

Ionic Chromatography analyses - Kinetic curves of [F-]

growth related to PFOA degradation.

FLUORIDE IONS BALANCE

TiO2 Evonik® P25

hν CB

VB

TiIIIOH

TiIVOH TiIVOH

TiIVOH∙+ Organic compound

Mineralized products {HO2∙, HO2-, H2O2, OH-} O2

-∙

O2 H2O

PFOA degradation through photocatalytic TiO2

Cn → Cn-1 mechanism [5]

Magnetic Stirrer

Cooling Water Inlet

Cooling Water Outlet

UV Lampλ = 310-400 nmW = 75-95 W/m2

Samples Collectionat 0, 30, 60, 120, 180, 300 min. Sample centrifuged and filtered through a 0.45 μm polycarbonate membrane before analyses

PFOA Aqueous Solution[PFOA] = 4.0 mM[PFOA] = 7.8 mM

[PFOA] = 12.0 mM

TiO2 Slurry[TiO2] = 0.66 g/l [TiO2] = 1.00 g/l

T = 30±5 °C

ThPFOA degradation.

REFERENCES [1] E. Smulders, W. Von Rybinski, A. Nordskog, Laundry Detergents, in: Ullmann’s Encyclopedia of Industrial Chemistry 2011, seventh ed., Wiley-VCH, Weinheim.

[2] A. Zaggia, B. Ameduri, Curr. Opin. Colloid Interface Sci. 17 (2012) 188-195.

[3] US-EPA, 2010/2015 PFOA Stewardship Program, Pollution Prevention & Toxics, 2009.

[4] F. Persico, M. Sansotera, M.V. Diamanti, L. Magagnin, F. Venturini, W. Navarrini, Effect of Amorphous Fluorinated Coatings on Photocatalytic Properties of Anodized

Titanium Surface, Thin Solid Films (2013) accepted.

[5] M. Sansotera, W. Navarrini, M. Gola, C.L. Bianchi, P Wormald, A. Famulari, M. Avataneo, J. Fluorine Chem. 132 (2011) 1254-1261.

[6] R. Dillert, D. Bahenemann, H. Hidaka, Chemosphere 67 (2007) 785-792.

TiO2 P25 SEM image:

Mag= 250.00 K X

CF3(CF2)6COO- hν

CF3(CF2)6COO∙

CO2

CF3(CF2)5CF2∙

CF3(CF2)5CF2OO∙

CF3(CF2)12CF3

CF3(CF2)5CF2OO∙ 2 CF3(CF2)5CF2O∙

CF3(CF2)5CF2OH + OH-

H2O

CF3(CF2)5C(O)F

TiO2*

H2O CF3(CF2)5COOH

CF3(CF2)4CF2∙

COF2

O2

HF

CF3(CF2)6COOH

H+

1

CONCLUSIONS

A plateau in F- yield (%) was reached, working at the

optimal degradation reaction conditions; this

phenomenon could be related to the chemical

modifications of the TiO2 surface

PFOA and its by-products were present on the

catalyst surface in the first hours of

photodegradation, while after longer reaction times

the intensity of FT-IR peaks was evidently decreased.

Formation of highly fluorinated and hydroxylated

TiO(2-x/2-y/2)OHyFx species on the catalyst surface.

These chemical modifications could limit the

photocatalytic activity of TiO2

Highest PFOA degradation rates with:

[PFOA] < CMC (Critical Micelle Concentration)

[TiO2] = 1.00 g/L

High radiation power, W = 95 W/m2

ηF- = [F-]

15 ∙ [PFOA]0

PFOA has been found to be bioaccumulative, carcinogen, liver and

immune system toxicant and able to exert hormonal effects [2].

A

[4]

t

F- yield (%) at different light intensity

F- yield (%) at different [TiO2]

F- yield (%) at different [PFOA]

u.a

. u

.a.

u.a

.

Organic compound Mineralized products

Perfluoroalkyl radials are further degraded following the mechanism at step A [6] 1 2

2

u.a

. u

.a.

u.a

.

A

B

C