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DECOMPOSITION OF PERFLUOROOCTANOIC ACID PHOTOCATALYZED BY TIO 2 : CHEMICAL MODIFICATION OF THE CATALYST SURFACE INDUCED BY FLUORIDE IONS M. Sansotera 1,2,3 , S. Gatto *1,3 , F. Persico *2,3 , C. Pirola 1,3 , W. Navarrini 2,3 , C. L. Bianchi 1,3 1 Università degli Studi di Milano, Dipartimento di Chimica , via Golgi, 19 – 20133 Milano (Italy) 2 Politecnico di Milano, Dipartimento di Chimica, Chimica Industriale e Ingegneria Chimica “Giulio Natta”, via Mancinelli, 7 – 20131 Milano (Italy) 3 Consorzio INSTM, via G. Giusti, 9 – 50121 Firenze (Italy) (*) corresponding authors: [email protected] [email protected] 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 - yield (%) 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 - yield (%) Time (min) [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 - yield (%) Time (min) W = 75 W/m2 W = 95 W/m2 Ionic Chromatography analyses - Kinetic curves of [F - ] growth related to PFOA degradation. FLUORIDE IONS BALANCE TiO 2 Evonik ® P25 hν CB VB Ti III OH Ti IV OH Ti IV OH Ti IV OH∙ + Organic compound Mineralized products {HO 2 ∙, HO 2 - , H 2 O 2 , OH - } O 2 - ∙ O 2 H 2 O PFOA degradation through photocatalytic TiO 2 C n → C n-1 mechanism [5] Magnetic Stirrer Cooling Water Inlet Cooling Water Outlet UV Lamp λ = 310-400 nm W = 75-95 W/m 2 Samples Collection at 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 TiO 2 Slurry [TiO 2 ] = 0.66 g/l [TiO 2 ] = 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. TiO 2 P25 SEM image: Mag= 250.00 K X CF 3 (CF 2 ) 6 COO - hν CF 3 (CF 2 ) 6 COO∙ CO 2 CF 3 (CF 2 ) 5 CF 2 ∙ CF 3 (CF 2 ) 5 CF 2 OO∙ CF 3 (CF 2 ) 12 CF 3 CF 3 (CF 2 ) 5 CF 2 OO∙ 2 CF 3 (CF 2 ) 5 CF 2 O∙ CF 3 (CF 2 ) 5 CF 2 OH + OH - H 2 O CF 3 (CF 2 ) 5 C(O)F TiO 2 * H 2 O CF 3 (CF 2 ) 5 COOH CF 3 (CF 2 ) 4 CF 2 ∙ COF 2 O 2 HF CF 3 (CF 2 ) 6 COOH 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 TiO 2 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) OH y F x species on the catalyst surface. These chemical modifications could limit the photocatalytic activity of TiO 2 Highest PFOA degradation rates with: [PFOA] < CMC (Critical Micelle Concentration) [TiO 2 ] = 1.00 g/L High radiation power, W = 95 W/m 2 η F - = [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 [TiO 2 ] 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
