Degradation of Perfluorooctanoic Acid by UV/Chloride Process†

doi:10.7503/cjcu20160156

Abstract

Abstract:

Based on the characteristic of perfluorooctanoic acid(PFOA) that it is vulnerable to be nucleophile attacked, we developed a new method for the degradation of PFOA in aqueous phase with chloride as a mediator. In this study, 185 nm ultraviolet photolysis of chloride leads to the generation of hydrated electrons, which contribute to the defluorination of PFOA. Chloride, ultraviolet, and anaerobic environment are all the necessary factors to ensure the effective degradation of PFOA. In this system, when the concentration of PFOA is 0.03 mmol/L, the optimal reaction conditions are $c C l -$ /c_PFOA=10.0, pH=10.0, with temperature being 25 ℃. Under these conditions, the degradation and defluorination rates of PFOA after 23 h’s reaction are 99.6% and 65.0%, respectively. Kinetic analysis indicated that the decomposition of PFOA fits the first order model with a rate constant of 6.3×10^-3 min^-1. The degradation products are fluorinion, perfluorinated carboxylic acid with short-carbon-chains, formic acid, and acetic acid. According to the degradation products, we proposed two major degradation pathways of PFOA: direct cleavage of C—F bonds and C—C bonds due to the attack by hydrated electrons; and decarboxylating by ultraviolet irradiation and defluorinate by hydrolysis. This method is of great significance to eliminate the PFOA in wastewater.

Key words: Perfluorooctanoic acid, Hydrated electron, Chloride, 185 nm Ultraviolet

CLC Number:

O644

TrendMD:

GUO Rui,ZHANG Chaojie,ZHANG Geng,ZHOU Qi. Degradation of Perfluorooctanoic Acid by UV/Chloride Process^†[J]. Chem. J. Chinese Universities, 2016, 37(8): 1499.

Figures/Tables 9

Fig.1 Equipment diagram 1. UV light; 2. quartz tube; 3. aerator pipe; 4. seal cover; 5. circulating water inlet valve; 6. circulating water outlet valve; 7. sampling place; 8. temperature probe; 9. magnetic stirring apparatus.

Table 1 Reaction conditions of three systems*

System	c_NaCl/(mmol·L^-1)	Time(He)/min	pH	UV185
PFOA+He+NaCl+UV185	0.3	30	10.0	Irradiate
PFOA+He+UV185	0	30	10.0	Irradiate
PFOA+He+NaCl	0.3	30	10.0	None

Fig.2 Degradation(A) and defluorination(B) rates of PFOA under different conditions a. PFOA+He+NaCl+UV185; b. PFOA+He+UV185; c. PFOA+He+NaCl.

Fig.3 Degradation kinetics of PFOA

Table 2 Degradations of PFOA in different reaction systems

System	Reaction kinetic	10³k_obs/min^-1	Half-life/h	Reference
PFOA+NaCl+He+UV185	First-order	6.3	1.77	This study
PFOA+KI+N₂+UV254	First-order	7.0	1.58	[30]
PFOA+K₂S₂O₈+O₂+UV185	First-order	1.4	8.19	[31]
PFOA+N₂+UV185	First-order	1.9		[27]

Fig.4 Degradation(A) and defluorination(B) rates of PFOA with different cCl -/cPFOA cCl -/cPFOA: a. 0; b. 1.0; c. 10.0; d. 122.0.

Fig.5 Degradation(A) and defluorination(B) rates of PFOA with different initial pH values pH: a. 5; b. 6; c. 7; d. 8; e. 9; f. 10.

Fig.6 Concentration of PFOA and intermediate products during the degradation

Fig.7 C-balance(A) and F-balance(B) after different reaction time

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