Adsorption of Perfluorooctane Sulfonate and Perfluorooctanoic Acid

Article pubs.acs.org/jced

Adsorption of Perfluorooctane Sulfonate and Perfluorooctanoic Acid on Magnetic Mesoporous Carbon Nitride Tingting Yan,† Huan Chen,† Fang Jiang,*,† and Xin Wang‡ †

Key Laboratory of Jiangsu Province for Chemical Pollution Control and Resources Reuse, School of Environmental and Biological Engineering, Nanjing University of Science and Technology, Nanjing 210094, China ‡ Key Laboratory of Soft Chemistry and Functional Materials, Nanjing University of Science and Technology, Ministry of Education, Nanjing 210094, China

ABSTRACT: A novel magnetic mesoporous carbon nitride (MMCN) adsorbent with large surface area has been synthesized by a chemical precipitation method, and characterized by X-ray diffraction pattern, transmission electron microscope, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, zeta potential, and magnetic hysteresis loop measurements. Kinetic results revealed that the adsorption equilibrium of perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) on MMCN was achieved within 180 min, and the adsorption process followed the pseudo-second-order kinetic model. Adsorption isotherms fit well to the Langmuir model, and the maximum adsorption amounts of PFOS and PFOA on MMCN were 454.55 and 370.37 mg g−1, indicative of a more favorable adsorption of PFOS by MMCN than PFOA. The difference of adsorption amount of PFOS and PFOA on MMCN was ascribed to the different functional groups of PFOS and PFOA. Moreover, adsorption of PFOS and PFOA on MMCN was spontaneous and endothermic in nature. The adsorption mechanisms of PFOS and PFOA on MMCN could be attributed to electrostatic attraction and hydrophobic interaction. Furthermore, MMCN was readily recovered in an external magnetic field and still maintained high adsorption capacity after five-times recycling tests.

1. INTRODUCTION

traditional technologies such as biological degradation, oxidation, and reduction. Although some special techniques including sonochemical degradation,11 photochemical oxidation,12,13 and ozonation under alkaline conditions14 have been used for PFOS and PFOA degradation, the specific conditions and the high energy consumption are still big challenges. Adsorption has been proven to be one of the most effective methods to remove PFOS and PFOA pollutants from aqueous solution due to its low energy cost, simple procedure, high adsorption capacity, and environmental friendliness. In recent years, various adsorbents such as boehmite,15 alumina,2 activated carbon,16 carbon nanotubes,3 activated sludge,17 and quaternized cotton18 have been used for the removal of PFOS and PFOA. However, these adsorbents are not very efficient for

Perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) are the most typical perfluorinated compounds (PFCs), and their chemical structures are shown in Figure 1.1,2 Because of the unique chemical and physical properties like both hydrophobicity and oleophobicity, PFOS and PFOA have been widely used in many industries as surfactants, fire retardants, lubricants, and polymer additives.3,4 The wide use and relatively inefficient removal have led to the ubiquitous presence in the environment. So far, PFOS and PFOA have been detected in air, water, sediment, soil, livers of human beings, and wildlife species.5−8 Considering that PFOS and PFOA are environmentally persistent, bioaccumulate, and potentially toxic to living organisms,9,10 it is very urgent to develop effective techniques to remove PFOS and PFOA from the aqueous environment. PFOS and PFOA, with extraordinary chemical stability due to the strong C−F bonds, are difficult to decompose using © 2014 American Chemical Society

Received: November 8, 2013 Accepted: January 14, 2014 Published: January 21, 2014 508

dx.doi.org/10.1021/je400974z | J. Chem. Eng. Data 2014, 59, 508−515

Journal of Chemical & Engineering Data

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2.2. Characterization of MMCN. The powder X-ray diffraction (XRD) pattern of MMCN was obtained on a Bruker D8 Advanced diffractometer. The Brunauer−Emmett−Teller (BET) specific surface area was measured by N2 adsorption− desorption measurement using a Micromeritics ASAP 2200 adsorption analyzer. The pore structure was analyzed by transmission electron microscope (TEM) using a JEOL JEM2100 microscope. X-ray photoelectron spectroscopy (XPS) measurement was carried out in a PHI Quantera II instrument equipped with a monochromatized Mg Kα excitation source (hν = 1253.6 eV). The zeta potential was analyzed with a Brookhaven zeta PALS. The Fourier transform infrared (FTIR) spectra were recorded using a Nicolet iS10 FT-IR spectrometer. The magnetic property of MMCN was studied by a Lake Shore 7410 vibrating sample magnetometer. 2.3. Adsorption Experiments. The adsorption kinetics were performed by batch adsorption experiments at an initial concentration of PFOS or PFOA of 280 mg L−1 at pH 3.25. Typically, 0.15 mg of MMCN was added into a 500 mL flask containing 250 mL of PFOS or PFOA solution, which was strongly stirred at 298 K. During the adsorption process, 1 mL of sample was withdrawn from the flask at preset time intervals. After magnetic separation, the PFOS/PFOA concentration in the solution was determined and the adsorption amount was calculated according to

Figure 1. Chemical structures of PFOS and PFOA.

PFOS/PFOA removal because of their low adsorption capacities or long equilibrium time. Therefore, it is necessary to explore novel and efficient adsorbents with increased capacities and high sorption rate. Mesoporous carbon nitride (MCN) is a well-known and fascinating material due to its versatile properties such as large surface areas, intercalation abilities and surface functionalization.19−23 Because of the incorporation of nitrogen atoms in the carbon, MCN presents the basic sites on its surface, which allows it to be used as a good adsorbent for the selective removal of acidic toxic molecules. For example, Haque et al.24 reported that the adsorption capacity of phenol on MCN was much higher than that of ordered mesoporous carbon (CMK3) and activated carbon. Our previous work25 showed that MCN exhibited a high adsorption capacity for PFOS. It should be noted that the separation of the used adsorbent from the treated water is an important step, which is conventionally performed by filtration or centrifugation. As an alternative, magnetic separation is considered as a quick and effective technique.26 Thus, the introduction of magnetic nanoparticles into MCN is proposed. To the best of our knowledge, the adsorption of PFOS and PFOA using magnetic MCN as an adsorbent have never been reported in the literature. Herein, magnetic mesoporous carbon nitride (MMCN) was prepared by a chemical precipitation method under N2, and the adsorption behaviors of PFOS and PFOA on MMCN including adsorption kinetics, adsorption isotherm as well as the influence of solution temperature were investigated. The possible adsorption mechanisms of PFOS and PFOA on MMCN were also discussed. The reusability of MMCN was tested using the repeating consecutive adsorption−desorption regeneration experiment.

qt =

(C0 − Ct )V M

(1)

where qt is the adsorption amount at time t (mg g−1), C0 is the initial concentration of PFOS or PFOA solution (mg L−1), Ct is the concentration of PFOS or PFOA solution at time t (mg L−1), V is the volume of PFOS or PFOA solution (L), and M is the mass of MMCN adsorbent (g). The adsorption isotherms of PFOS/PFOA were conducted in 50 mL Erlenmeyer flasks on an incubator with a speed of 180 rev min−1 at initial pH 3.25. In a typical run, 0.015 g of MMCN was added into flasks containing 25 mL of PFOS with an initial concentration ranging from 0 mg L−1 to 800 mg L−1 or a PFOA ranging from 0 mg L−1 to 900 mg L−1. The flasks were transferred into an incubator and shaken at 298 K for 180 min. The equilibrium adsorption amount of PFOS or PFOA on MMCN was calculated by using the following eq qe =

(C0 − Ce)V M

(2)

where qe is the equilibrium adsorption amount (mg g−1), Ce is the equilibrium concentration of PFOS or PFOA (mg L−1), and other parameters are defined in eq 1. The effect of solution temperature on adsorption was also investigated. Briefly, a series of 50 mL Erlenmeyer flasks containing 0.015 g of MMCN and 25 mL of 280 mg L−1 PFOS or PFOA solution were shaken at a preset temperature for 180 min. The solution temperature was controlled at (278, 288, 298, 308, and 318) K, respectively. All of the experiments were conducted in three replicates, and the average values were reported here. 2.4. Regeneration and Reuse of MMCNs. For the regeneration study, 0.015 g of MMCN was initially added to 25 mL of 280 mg L−1 PFOS or PFOA solution in 50 mL Erlenmeyer flasks The flasks were shaken at 298 K for 180 min. After the adsorption equilibrium, the PFOS-adsorbed or PFOA-adsorbed MMCN was separated and regenerated in

2. EXPERIMENTAL SECTION 2.1. Synthesis of MMCN. MCN was prepared by a modified method reported by Vinu et al.19 The synthesis of MMCN was as follows: 1.25 g of MCN was suspended in 100 mL of mixed solution containing 0.425 g of ammonium ferrous sulfate and 0.6275 g of ammonium ferric sulfate (nFe2+/nFe3+ = 1:2) with the aid of ultrasonic stirring for 10 min. Then the reaction mixture was adjusted to a pH ranging from 10 to 11 using 8 M NH4OH solution and allowed to crystallize for 30 min at 323 K under N2 atmosphere. After the completion of the reaction, the suspension was allowed to cool to room temperature and washed with distilled water until neutral. The MMCN was separated from the mixture by a permanent magnet and dried in a vacuum oven at 373 K. 509



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agglomerates of the magnetic nanoparticles are also observed. In the HR-TEM image of magnetic nanoparticles, distinct fringes at about 0.22 nm are observed, which is in good agreement with the lattice fringes of the (110) plane for Fe.29,30 The textural parameters such as the BET surface area, pore volume, and pore size of MMCN are given in Table 1. The

100 mL of 0.1 M NaOH solution on a rotary shaker at 180 rev min−1 for 24 h. Then, MMCN was separated by magnet and washed to neutral by distilled water. The regenerated MMCN was dried in a vacuum oven at 373 K and reused in the next cycle of adsorption experiments. Five sequential cycles of adsorption−desorption experiments were carried out. 2.5. PFOS and PFOA Determination. After the adsorption experiments, the mixture were filtered with a 0.22 μm nylon membrane. The concentration of PFOS or PFOA was determined using an e2695-HPLC with a 432 conductivity detector from Waters (USA). The XBridge-C18 column (4.6 mm × 250 mm) from Agilent Technologies (USA) was adopted and the mixture of methanol/0.02 M NaH2PO4 (75/ 25, v/v) was used as the mobile phase at 1.0 mL min−1 flow rate. The sample volume injected was 50 μL.

Table 1. Textural Properties of MMCN BET surface area 2

−1

samples

m g

MMCN

404

pore volume 3

cm g

−1

0.44

pore size nm 3.7

BET surface area of MMCN is found to be 404 m2 g−1, and the pore volume of MMCN is 0.44 cm3 g−1, which are lower than that of MCN.25 The decreased BET surface area and pore volume of MMCN compared to MCN may result from the fact that the introduced γ-Fe2O3 occupies a partial surface area of MMCN. Figure 3 displays the XPS spectra of MMCN. The XPS survey spectrum of MMCN confirms that MMCN is mainly composed of carbon, nitrogen, oxygen, and iron. The existence of oxygen mainly comes from the precursor of carbon nitride or iron. From Figure 3b, the C1s peak is deconvolved into three peaks with binding energies of (284.3, 285.7, and 289.1) eV, which are assigned to pure graphitic sites in the amorphous CN matrix, the characteristic of sp2 carbon atoms bonded to nitrogen atoms inside the aromatic structure, and the sp2 hybridized carbon in the aromatic ring attached to the NH2 groups, respectively.19,21,23 Figure 3c reveals the deconvolved N1s spectra of MMCN with two peaks at about 398.5 eV and 400.1 eV. The lower binding energy peak at 398.5 eV is attributed to sp2 hybridized aromatic nitrogen bonded to the graphitic carbon atoms, and the higher binding energy peak at 400.1 eV is assigned to the nitrogen atoms trigonally coordinated with all the sp2 carbons.21,23,24 Figure 3d shows the XPS spectra of Fe 2p and the binding energies of Fe 2p3/2 and Fe 2p1/2 are observed at 710.1 eV and 724.1 eV, respectively, indicative of the presence of Fe3+ in the MMCN.31,32 3.2. Adsorption Kinetics. Figure 4a shows the adsorption kinetics of PFOS and PFOA on MMCN. It is found that the adsorption of PFOS and PFOA on MMCN is time dependent and their kinetics profiles are similar. The adsorption amounts of PFOS and PFOA increase rapidly with the increase of contact time during the first 10 min and then reach the adsorption equilibrium within 180 min. Pseudo-second-order kinetics is based on the adsorption capacity of the adsorbent, which usually gives a good description of the adsorption process.33 Therefore, the adsorption of PFOS and PFOA on MMCN was simulated using pseudo-second-order kinetic models in this study. A pseudo-second-order kinetic model can be expressed as eq 3,34 t 1 t = + qt qe k 2qe2 (3)

3. RESULTS AND DISCUSSION 3.1. Characterization of MMCN. Figure 2a shows the XRD patterns of MMCN. As shown in the small-angle XRD

Figure 2. (a) XRD patterns of MMCN (Inset: small-angle XRD patterns of MMCN); (b) TEM image of MMCN; (c) HR-TEM image of MMCN.

patterns (inset in Figure 2a), MMCN exhibits the (100) reflection peak, indicating that the 2D-hexagonal pore structure from SBA-15 template is preserved. In the wide-angle XRD patterns, MMCN presents the broad peak around 2θ of 25.7°, which is similar to the characteristic (002) basal plane diffraction peak in many carbon-based materials.19 In addition, peaks at the 2θ of 30.2° (220), 35.6° (311), 43.3° (400), 57.2° (511), and 62.8° (440) have appeared, suggesting the presence of γ-Fe2O3 (JCPDS: 39-1346).27,28 The microstructure of MMCN was observed using TEM and the results are shown in Figure 2b and Figure 2c. MMCN displays an ordered mesoporous structure with a linear array of mesopores, which is similar to MCN.19,20 As expected, magnetic nanoparticles are found covering the surface of MCN or embedding in MCN. In addition, some big

where qe is the equilibrium adsorption amount (mg g−1), qt is the adsorption amount at time t (mg g−1), and k2 is the pseudosecond-order rate constant (g mg−1 min−1). The parameters of k2 and qe can be calculated from the slope and intercept of the plot obtained by plotting t/qt versus t. It was found that the pseudo-second-order kinetic model fits the 510



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Figure 3. XPS spectra of MMCN: (a) survey spectra, (b) C1s, (c) N1s, and (d) Fe 2p.

amount of PFOS (309.17 mg g−1) is about 1.5 times as large as that of PFOA (189.33 mg g−1). It is supposed that the difference of the adsorption amount between PFOS and PFOA could be attributed to the different functional groups of them, which will be further investigated in the subsequent sections. 3.3. Adsorption Isotherm. The adsorption isotherms of PFOS and PFOA on MMCN are compared in Figure 4b. Two commonly used models, the Langmuir and Freundlich isotherm models are applied to describe the experimental data, which can be expressed respectively as35

qe =

Q 0bCe 1 + bCe

(4)

qe = kFCen

(5) −1

where Q0 is the maximum adsorption amount (mg g ), b is the equilibrium adsorption constant (L mg−1), and kF and n are Freundlich constants, respectively. The theoretical parameters of adsorption isotherm by two isotherm models are summarized in Table 2. It can be seen that Table 2. Constants of Langmuir and Freundlich Models for the Adsorption of PFOS and PFOA on MMCN Langmuir constant

Figure 4. (a) Adsorption kinetics of PFOS and PFOA on MMCN and modeling using the pseudo-second-order equation; (b) Adsorption isotherms of PFOS and PFOA on MMCN and modeling using the Langmuir equation.

Freundlich constant 2

adsorbate

Q0

b

R

PFOS PFOA

454.55 370.37

0. 0271 0.0068

0.9992 0.9951

KF

n

R2

46.24 6.27

2.64 1.57

0.9352 0.9498

the experimental data fit the Langmuir model (R2 > 0.99) better than the Freundlich model. According to the Langmuir fitting, the maximum adsorption amounts of PFOS and PFOA on MMCN are 454.55 mg g−1 and 370.37 mg g−1, respectively, reflecting the more favorable adsorption of PFOS on MMCN. Given the similar −CF2− chain length and same number of

experimental data well with R2 > 0.999. According to the pseudo-second-order model, the equilibrium adsorption 511



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ΔG° = −RT ln K C

carbons, the distinct difference of adsorption amount is presumably due to the different functional groups of PFOS and PFOA. It is known that PFOS has a sulfonate group and PFOA with a carboxylate group. On the basis of the concept of hard and soft acids/bases, the carboxylate group is a soft base while the sulfonate group is a relatively hard one, and a hard base is more readily adsorbed on oxide surfaces.2,16 Thus, PFOS is more easily adsorbed than PFOA on the surfaces of MMCN. Additionally, the hydrophobicity of PFOS is the slightly stronger than that of PFOA due to the larger molecular size of PFOS, which also resulted in the more favorable adsorption of PFOS.17 3.4. Effect of Adsorption Temperature. The effect of temperature on the adsorption of PFOS and PFOA over MMCN is also investigated, and the results are shown in Figure 5a. It is found that the adsorption amounts of PFOS and PFOA on MMCN increase with increasing temperatures from 278 K to 318 K.

ln K C =

(7)

ΔS° ΔH ° − R RT

(8)

where KC is an equilibrium constant between the adsorbed equilibrium concentration and the aqueous equilibrium concentration (L g−1), R is the gas constant (8.314 J mol−1 K−1), T is the adsorption temperature (K). Values of ΔH° and ΔS° are obtained from the slope and the intercept of lnKC versus 1/T which are shown in Figure 5b, and the thermodynamic parameters (ΔG°, ΔH°, and ΔS°) are listed in Table 3. The ΔG° values at tested temperatures are all negative, demonstrating that the adsorption of PFOS and PFOA onto MMCN occurs spontaneously. In addition, the decrease of ΔG° values with the increase of adsorption temperature suggests that PFOS and PFOA adsorption is favorable at high temperature. The positive values of ΔH° demonstrate that the adsorption process is endothermic in nature, illustrating that the adsorption amounts of PFOS or PFOA on MMCN increase with the adsorption temperatures. Similar results were also observed by Qu et al.37 The ΔS° value of PFOS or PFOA adsorption is positive which reflects an increased randomness due to the displacement of water molecules from the interface by PFOS or PFOA molecules. 3.5. Adsorption Mechanism. Zeta potentials of MMCN as a function of solution pH are presented in Figure 6a. It can be seen that zeta potentials continuously decreased with solution pH and the points of zero charge (pHpzc) of MMCN is found to be 4.62. Under the solution pH values lower than 4.62, the surfaces of the MMCN are positively charged due to the protonation. Since the pKa values of PFOS and PFOA are around −3.27 and −0.1,18 respectively, they mainly exist in anionic forms at the studied pH of 3.25. Therefore, PFOS and PFOA strongly interact with MMCN by electrostatic interaction. Additionally, as the perfluorinated chain of PFOS and PFOA is hydrophobic and oleophobic, it is favorable that PFOS and PFOA molecules are adsorbed on the surface of MMCN via a hydrophobic interaction. To further illustrate the adsorption mechanisms of PFOS and PFOA on MMCN, the FT-IR study is performed on asprepared MMCN, PFOS-adsorbed MMCN, and PFOAadsorbed MMCN. As seen in Figure 6b, the FT-IR spectrum of MMCN exhibits three major bands centered around (1310.1, 1600.7, and 3415.4) cm−1, which are attributed to aromatic C− N stretching vibration, aromatic ring mode and the stretching mode of N−H groups with the O−H vibration mode attached to the aromatic ring, respectively.21 Compared with MMCN, the FT-IR spectra of PFOS-adsorbed MMCN and PFOAadsorbed MMCN show some changes. The peaks at (1150.1, 1214.9, and 1242.5) cm−1 after the PFOS adsorption or the peaks at (1148.0, 1206.7, and 1240.9) cm−1 after the PFOA adsorption match up with CF2 and CF3 groups, which implies that PFOS or PFOA has been adsorbed on the surface of MMCN. In FT-IR spectra of PFOS-adsorbed MMCN, the bands shown in the range of 600 cm−1 to 700 cm−1 can be

Figure 5. (a) Effect of temperature on the adsorption of PFOS and PFOA by MMCN; (b) plots of ln KC versus 1/T.

To quantify the effect of adsorption temperature, the thermodynamic parameters such as standard free energy (ΔG°), standard enthalpy (ΔH°) and standard entropy (ΔS°) are calculated using the following formulas:36 q KC = e Ce (6)

Table 3. Thermodynamic Parameters for the Adsorption of PFOS and PFOA on MMCN ΔG°/(kJ mol−1)

ΔS°

adsorbate

278 K

288 K

298 K

308 K

318 K

PFOS PFOA

−1.60 −0.09

−2.35 −0.14

−2.83 −0.30

−3.16 −0.52

−3.60 −0.80

512

−1

(J mol

ΔH° −1

K )

48.75 18.07

(kJ mol−1) 11.82 5.02



Article

Figure 6. (a) Zeta potential of MMCN at different solution pH values; (b) FT-IR spectra of MMCN, PFOS-adsorbed MMCN, and PFOA-adsorbed MMCN.

assigned to the vibrations of organic sulfonate group (−SO3−).38 Meanwhile, the characteristic peak of C−N at 1310.1 cm−1 is not observed, and the intensity of a broad peak representing N−H groups decreases after the adsorption of PFOS or PFOA, which implies that certain chemical bonds are formed between MMCN and PFOS (PFOA). 3.6. Regeneration and Magnetic Property of MMCN. After the MMCN adsorbent was saturated with PFOS or PFOA and separated from the mixture solution using the magnet, the PFOS-adsorbed or PFOA-adsorbed MMCN was regenerated using 0.1 M NaOH solution. The adsorption performance of regenerated MMCN was investigated by the repeating consecutive adsorption−desorption process, and the results are shown in Figure 7a. After five cycles of adsorption− desorption regeneration, the adsorption amounts of PFOS and PFOA on MMCN decrease from 303.96 mg g−1 to 296.71 mg g−1 and 187.47 mg g−1 to 180.70 mg g−1, respectively, showing that MMCN can still maintain a high adsorption capacity for PFOS and PFOA after five cycles of adsorption−desorption regeneration. Figure 7b shows the magnetization curves of as-prepared MMCN and MMCN after five cycles of adsorption−desorption regeneration. The saturation magnetizations of as-prepared MMCN and MMCN after five cycles are 4.82 emu g−1 and 4.23 emu g−1, respectively, implying a relatively strong magnetic response to the magnetic field. The slight decrease of saturation magnetization of MMCN after five cycles might be ascribed to the little loss of magnetic nanoparticles in the process of adsorption−desorption regeneration. In addition, as seen in the inset of Figure 7b, MMCN can homogeneously disperse in aqueous solution and is completely and fleetly separated within 5 min by applying a permanent magnet near the glass bottle.

Figure 7. (a) Regeneration studies of MMCN after five cycles; (b) magnetization curves of MMCN before adsorption and after five times of adsorption−desorption regeneration tests. Inset: photograph of MMCN dispersed in water (left) and the response of MMCN to a permanent magnet after 5 min (right).

4. CONCLUSIONS In the present study, a novel MMCN adsorbent with BET surface area of 404 m2 g−1 was synthesized, and the adsorption behaviors of PFOS and PFOA on MMCN were investigated by batch adsorption experiments. The characterization results showed that MMCN possessed a highly ordered mesoporous structure and ferromagnetic characteristic, which allow MMCN to be easily separated from the aqueous solution by an external magnetic field. The adsorption equilibrium of PFOS and PFOA on MMCN was reached within 180 min and followed the pseudo-second-order kinetic model. Adsorption isotherm data fitted well to Langmuir model with high correlation coefficients and the maximum adsorption capacities of MMCN for PFOS

and PFOA were 454.55 mg g−1 and 370.37 mg g−1, respectively, suggesting the favorable adsorption of PFOS on MMCN. The thermodynamic parameters indicated that adsorption of PFOS and PFOA on MMCN was a spontaneous and endothermic process in nature. Meanwhile, the adsorption of PFOS and PFOA on MCN was mainly controlled by electrostatic attraction as well as hydrophobic interaction. Additionally, MMCN can maintain high adsorption capacity after five cycles of adsorption−desorption regeneration tests. Therefore, it is expected that MMCN can be potentially used as an excellent and recoverable adsorbent to remove organic pollutants from water. 513



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AUTHOR INFORMATION

Corresponding Author

*Tel.: +86-25-84311819. Fax: +86-25-84315352. E-mail: [email protected]. Funding

The authors thank the NNSF of China (Nos. 51178223, 21171094 and 51208257), NSAF (No.U1230125), China Postdoctoral Science Foundation (2013M541677), the Natural Science Foundation of Jiangsu Province (SBK201240759), the Jiangsu Planned Projects for Postdoctoral Research Funds (1202007B), the project from Environmental Protection Department of Jiangsu Province (No. 2012008) for financial support. Notes

The authors declare no competing financial interest.

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Adsorption of Perfluorooctane Sulfonate and Perfluorooctanoic Acid

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