Sorption of Perfluoroalkyl Acids to Fresh and Aged Nanoscale

Sorption of Perfluoroalkyl Acids to Fresh and Aged Nanoscale Zerovalent Iron Particles. Yanyan Zhang , Yue Zhi , Jinxia Liu , and Subhasis Ghoshal. En...
1 downloads 4 Views 504KB Size
Subscriber access provided by Kaohsiung Medical University

Environmental Processes

Sorption of Perfluoroalkyl Acids to Fresh and Aged Nanoscale Zerovalent Iron Particles Yanyan Zhang, Yue Zhi, Jinxia Liu, and Subhasis Ghoshal Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.8b00487 • Publication Date (Web): 30 Apr 2018 Downloaded from http://pubs.acs.org on May 3, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 24

Environmental Science & Technology

1

Sorption of Perfluoroalkyl Acids to Fresh and Aged Nanoscale Zerovalent

2

Iron Particles

3 4

Yanyan Zhang, Yue Zhi, Jinxia Liu, Subhasis Ghoshal*

5 6

Department of Civil Engineering, McGill University, Montreal, Quebec H3A 0C3, Canada

7

*Corresponding Author: Phone: (1)-514-398-6867; fax: (1)-514-398-7361; e-mail: [email protected]

8 9 10

Total word counting: 7991

11

Main text: 5491

12

Table: 1

13

Figures: 4

14 15 16 17 18 19 20 21 22 23 1

ACS Paragon Plus Environment

Environmental Science & Technology

24

TOC/Abstract Art

25 nZVI Injection for TCE

Fuel fire AFFFs Iron oxy(hydr)oxides

log KF = 4.88

Fe0 Iron sulfides log KF = 4.82

Fe0

log KF = 3.96

H2O

Fe0

log KF = 5.00

HS–

Fe0

log KF = 4.84 log KF = 4.73

Fe3O4

γ-Fe2O3

26 27

ABSTRACT

28

The sorption of perfluoroalkyl acids (PFAAs), particularly perfluorooctanesulfonic acid (PFOS), to

29

freshly-synthesized nanoscale zerovalent iron (nZVI) and aged (oxidized) and sulfidated nZVI, was

30

investigated under anaerobic conditions. The of sorption of PFAAs to nZVI was 2–4 orders of

31

magnitude higher than what has been reported for sediments, soils, and iron oxides. The

32

hydrophobicity of the perfluorocarbon chain dominated the sorption, although FTIR spectra indicated

33

specific interactions between sulfonate and carboxylate head groups and nZVI. The contributions from

34

electrostatic interactions depended on the surface charge and pH. Humic acids influenced sorption

35

only at concentrations above 50 mg/L. nZVI aged in deoxygenated water up to 95 days showed similar

36

sorption isotherms for PFOS to fresh nZVI, because Fe(OH)2 was the predominant phase on the nZVI

37

surface independent of aging time. Sulfidation of nZVI reduced sorption of PFOS by 1 log unit owing

38

to the FeS deposited, but the sorption affinity was restored after aging because of formation of

39

Fe(OH)2. Oxidation of nZVI by water and dissolved oxygen also resulted in similar sorption of PFOS

40

as fresh nZVI at environmentally-relevant concentrations. The results suggest that injection of nZVI

41

could reduce PFAA concentrations in groundwater despite changes to its surface chemistry with aging.

42

INTRODUCTION

43

Since its first development in 1960s, significant amounts of aqueous film-forming foams (AFFFs)

44

have been applied during military training and fire-fighting activities.1,2 At many AFFF-impacted sites,

2

ACS Paragon Plus Environment

Page 2 of 24

Page 3 of 24

Environmental Science & Technology

45

this has resulted in groundwater contamination by per- and polyfluoroalkyl substances (PFASs),3

46

which are the key fire extinguishing components in AFFFs. Many of these PFASs can chemically or

47

biologically transform to perfluoroalkyl acids (PFAAs) in the natural environment.2,4–7 PFAAs are

48

highly persistent, and have relatively high water solubility and thus migrate in groundwater.8 For

49

example, up to milligrams per liter levels of PFAAs were detected in the groundwater at military bases

50

where fire-fighting activities were conducted.3 Food web analyses have shown that long-chain PFAAs

51

are bioaccumulative.9 Exposure to some PFAAs can cause adverse effects including hepatotoxicity,

52

tumor induction, and endocrine disruption.10

53

Chlorinated solvents such as trichloroethene are common pollutants in groundwater and are often

54

encountered together with PFAAs at the AFFF-impacted sites because of their use in formulation of

55

ignition fluids during fire-training exercises.11,12 Nanoscale zerovalent iron (nZVI) has been proposed

56

as an in situ remediation agent for chlorinated solvent contaminated groundwater.13 It is necessary to

57

investigate the interactions between PFAAs and nZVI at sites where nZVI-based remediation is

58

attempted and how the treatments may influence the concentration and composition of PFAAs in

59

groundwater.

60

PFAAs are strong acids (pKa < 0) that dissociate in most natural environments, thus sorption of PFAAs

61

to charged solids such as nZVI is expected to be influenced by the pH and ionic strength of the

62

aqueous phase and surface charge.14 Long-chain PFAAs can overcome the electrostatic repulsion and

63

sorb to negatively-charged mineral surfaces and natural organic matter because of their hydrophobicity.

64

nZVI particles have a core-shell structure comprised of an Fe0 core and iron(hydr)oxide shell. Aging or

65

prolonged exposure of nZVI in water leads to corrosion of Fe0, resulting in increased iron(hydr)oxides

66

on the surface, change in particle morphology, and reduction in Fe0 content.15,16 nZVI can also interact

67

with dissolved organic matter,17,18 and react with groundwater ions, in particular, bisulfide formed by

68

microbial sulfate reduction, resulting in deposits of iron sulfides on the nZVI surface.19,20 This

69

sulfidation process can significantly enhance the reactivity of nZVI towards chlorinated solvents and

70

sulfidated nZVI is considered as a more feasible agent for in situ remediation.17,21–23 The change in

71

composition and morphology of nZVI during aging in groundwater is expected to affect its 3

ACS Paragon Plus Environment

Environmental Science & Technology

72

interactions with PFAAs.

73

In this study, the sorption of PFAAs to nZVI was characterized by developing sorption isotherms.

74

FTIR was used to identify the specific interactions between PFAAs and nZVI. Sorption of

75

perfluorooctanesulfonic acid (PFOS) to nZVI was also investigated at different solution pH and ionic

76

strength, and in the presence of dissolved organic matter. PFOS is one of the most common PFAAs

77

detected in groundwater,3 and is listed as a Persistent Organic Pollutant under the Stockholm

78

Convention.24 The effect of nZVI aging on sorption of PFOS was further tested under anaerobic aging

79

(oxidation of nZVI during reduction of water to H2), sulfidation, and aerobic aging (oxidation by water

80

and dissolved oxygen) scenarios. Sorption isotherms of PFOS were also developed for the synthesized

81

nanoscale iron species generated during aging and sulfidation of nZVI, including Fe(OH)2, γ-Fe2O3,

82

Fe3O4, γ-FeOOH, and FeS. To our knowledge, this is the first study on sorption of PFAAs to nZVI.

83

EXPERIMENTAL SECTION

84

Materials

85

PFOS potassium salt (PFOS-K, ≥ 98%), perfluorohexanesulfonic acid potassium salt (PFHxS-K, ≥

86

98%), perfluorobutanesulfonic acid (PFBS, 97%), perfluorodecanoic acid (PFDA, 98%),

87

perfluorononanoic acid (PFNA, 97%), and perfluorooctanoic acid (PFOA) (96%) used for sorption

88

experiments were purchased from Sigma-Aldrich (Table S1). Standards of PFAAs and

89

isotope-labelled PFAAs used for quantification were purchased from Wellington Laboratories.

90

FeSO4·7H2O (> 99%) and FeCl3·6H2O (≥ 99%) were purchased from MP Biomedical, and Acros

91

Organics, respectively. Carboxymethyl cellulose sodium salt (CMC, MW 700 000 g/mol), humic acid

92

sodium salt (HA, technical grade), NaBH4 (99.99%), Na2S, and CaCl2 were purchased from

93

Sigma-Aldrich. Ammonium hydroxide (30%, w/w), FeCl2·4H2O (99–102%), NaCl, and NaOH were

94

purchased from Fisher Scientific. Plasma pure HCl (37%, w/w) and HNO3 (70%, w/w) were

95

purchased from SCP Science. Acetonitrile and methanol were HPLC grade and were purchased from

96

Fisher Scientific. ASTM Type I water was used in all experiments.

4

ACS Paragon Plus Environment

Page 4 of 24

Page 5 of 24

Environmental Science & Technology

97

nZVI Synthesis and Aging

98

nZVI particles were synthesized by NaBH4 reduction23 in an anaerobic glove chamber (Coy

99

Laboratories) containing high purity mix of 2–4% H2 in N2. Briefly, NaBH4 (0.75 g in 15 mL) was

100

added dropwise to a continuously mixed solution of FeSO4·7H2O (2.0 g in 100 mL of 30% methanol)

101

at 3 mL/min using a syringe pump, followed by a mixing time of 1 h. A glass-coated magnetic stir bar

102

was used to achieve efficient stirring (700 rpm). The resulting nZVI particles were separated by a

103

magnet, washed five times with water and three times with methanol, and dried inside the chamber.

104

Water and solvents were deoxygenated by purging with N2 for 45 min before bringing into the

105

chamber.

106

Sulfidated nZVI (S-nZVI) particles were prepared inside the anaerobic chamber by adding a Na2S

107

solution to an aqueous suspension of nZVI with a prescribed S/Fe molar ratio and then sonicating for

108

10 min.23 The resulting S-nZVI particles were washed five times with water to remove any unbound

109

bisulfide ions before use.

110

Anaerobic aging of nZVI was conducted in 22 mL glass vials with 10 mL of 2.0 g/L nZVI suspension.

111

The suspensions were prepared inside the anaerobic chamber with deoxygenated water, and the vials

112

were fitted with butyl rubber stoppers and crimp sealed and shaken at 175 rpm at 25 °C for 20, 50, and

113

95 days. The resulting particles were referred to as nZVI-20 d, nZVI-50 d, and nZVI-95 d, respectively.

114

Aerobic aging of nZVI was conducted in a 120 mL glass vial with 100 mL of 8.0 g/L nZVI suspension;

115

the suspension was stirred at 300 rpm for 72 h in open air. The resulting particles were referred to as

116

O-nZVI-72 h. Synthesis methods for other nanosized iron species formed after aging, including

117

Fe(OH)2, FeS, γ-Fe2O3, Fe3O4, and γ-FeOOH, are provided as Supporting Information (SI-2).

118

Sorption Experiments

119

All sorption experiments were conducted in triplicates inside the anaerobic chamber. Sorption

120

isotherms were obtained by single-solute batch sorption experiments in 15 mL polypropylene tubes

121

mounted on an end-over-end rotator for seven days at room temperature (~22 °C). Preliminary tests

122

showed seven days was sufficient to reach sorption equilibrium (Figure S1). The freshly-synthesized

5

ACS Paragon Plus Environment

Environmental Science & Technology

123

nZVI and the other iron nanoparticles were dispersed by sonication in the sealed vial, and the

124

suspension (2.0 g/L) was added into the tubes to a final concentration of 0.1 g/L using NaCl (5 mM) as

125

background electrolyte.

126

PFAA aqueous stock solution was spiked to obtain an initial concentration range of 1–20 000 µg/L in

127

10 mL of test solution. pH was not adjusted and the pH of the suspension after sorption was close (