Rapid and efficient removal of organic micropollutants ...

Chemical Engineering Journal 343 (2018) 61–68

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Chemical Engineering Journal journal homepage: www.elsevier.com/locate/cej

Rapid and efficient removal of organic micropollutants from environmental water using a magnetic nanoparticles-attached fluorographene-based sorbent

T

Wenjing Wanga,1, Zhenlan Xub,1, Xiaoxia Zhanga, Andreas Wimmerc, En Shia, Yang Qina, ⁎ Xueping Zhaob, Baocheng Zhoua, Lingxiangyu Lia, a

Department of Chemistry, School of Sciences, Zhejiang Sci-Tech University, Hangzhou 310018, China Agricultural Ministry Key Laboratory for Pesticide Residue Detection, Institute of Quality and Standard of Agro-Products, Zhejiang Academy of Agricultural Sciences, Hangzhou 310021, China c Department of Chemistry, Technical University of Munich, Garching 85748, Germany b

H I G H L I G H T S

G RA P H I C A L AB S T R A C T

nanoparticles-attached • Magnetic fluorographene-based sorbent was facilely fabricated.

MNPs@FG sorbent showed su• The perior adsorption of OMPs compared to activated carbon.

efficient removal of OMPs from • Highly water could be achieved within 2–10 min.

organic matter showed little • Natural effect on OMPs removal by the MNPs@FG sorbent.

MNPs@FG sorbent showed ex• The cellent readsorption capacity of OMPs.

A R T I C L E I N F O

A B S T R A C T

Keywords: Organic micropollutants Environmental water Adsorption Magnetic separation Regeneration

Organic micropollutants (OMPs), including both regulated and emerging contaminants, have been extensively detected in ground and surface waters, posing hazards to organisms and humans. Rapid and efficient removal of OMPs from environmental water by novel sorbents is still faced with severe challenges. Here we developed a magnetic nanoparticles-attached fluorographene-based (MNPs@FG) sorbent with high affinity to OMPs such as perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) compared to powdered activated carbon, the most widespread sorbent for OMPs removal. The removal efficiencies of PFOA and PFOS using the MNPs@ FG sorbent were systematically examined at room temperature. The MNPs@FG sorbent showed 92–95% and 94–97% removal efficiencies of PFOA (180 μg/L) and PFOS (180 μg/L) in 2 min respectively, with relatively high sorption capacities for PFOA (50.4 mg/g) and PFOS (17.2 mg/g). The adsorption performance was stable even in the presence of natural organic matter. Moreover, the MNPs@FG sorbent could notably reduce PFOA and PFOS from ∼5 μg/L (an environmentally relevant concentration) to < 50 ng/L in environmental water, lower than the U.S. Environmental Protection Agency health advisory level (70 ng/L). Besides PFOA and PFOS, the MNPs@FG sorbent also showed high removal efficiencies (97–99%) of difloxacin hydrochloride (DIF), acetochlor (ACE) and chlorantraniliprole (CHL) in short time (e.g. 10 min). The used MNPs@FG sorbent was facilely regenerated by

⁎

1

Corresponding author. E-mail address: [email protected] (L. Li). These authors contributed equally to this work.

https://doi.org/10.1016/j.cej.2018.02.101 Received 26 January 2018; Received in revised form 22 February 2018; Accepted 23 February 2018 Available online 24 February 2018 1385-8947/ © 2018 Elsevier B.V. All rights reserved.


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methanol washing and reused five times without reduction in PFOA/PFOS removal and magnetic performance. Thus, this study provided a novel sorbent for rapid and effective removal of OMPs from environmental water.

1. Introduction

environmental water. OMPs such as PFOA, perfluorooctane sulfonate (PFOS), ACE, difloxacin hydrochloride (DIF) and chlorantraniliprole (CHL) were selected as the target substances for removal in the present study. The removal of PFOA and PFOS from water by the MNPs@FG sorbent was compared with the powdered AC to show the superior performance of the novel sorbent. Moreover, the stability, reusability and applicability of the novel sorbent were evaluated.

The extensive occurrence of organic micropollutants (OMPs), including both regulated and emerging contaminants (e.g. perflourinated compounds, pharmaceuticals, pesticides and herbicides), in many ground and surface waters has attracted much attention over the past years [1–6]. A large number of studies documented that exposure to OMPs would pose high risks to human health [7–9]. For example, residents exposed to perfluorooctanoic acid (PFOA) in drinking water due to chemical plant emissions would likely suffer from kidney and testicular cancer [10]. Additionally, the data collected by the European Union (E.U.) showed that some pesticides like acetochlor (ACE) would act as endocrine disruptors, being part of the EU-list of priority substances of concern in water [11]. Thus it is necessary to develop effective and economic techniques to remove OMPs from water. Compared to photodegradation and electrochemical oxidation, adsorption is an effective and economic method to remove OMPs from water, in particular when some OMPs (e.g. PFOA) resist oxidation or degradation [12–19]. Although carbon based materials (e.g., carbon nanofibres, multi-wall carbon nanotubes and activated carbon) may possess different properties of sorption activity [20], most of these materials have been applied to environmental remediation. Currently, powdered activated carbon (AC) is widely used as a leading sorbent to remove OMPs in water because of its reasonable adsorption capacity but inexpensive cost. However, it takes some time (e.g. hours ∼ days) for AC to adsorb/remove OMPs, while high AC doses are present [21,22]. Moreover, adsorption by AC would be drastically affected by environmental matrices such as natural organic matter (NOM) particularly if OMPs are at environmentally relevant concentrations (μg/ L ∼ ng/L) [23–25]. In addition, regeneration of used AC consumes massive energy and likely produces by-products of unknown toxicity during thermal processes [26–28]. Therefore, there is a critical need to develop novel sorbents with rapid adsorption kinetics, excellent removal performance of OMPs from water even in the presence of environmental matrices, and easy regeneration. Yan et al. [29] reported that good extraction efficiency (> 80%) of perfluorinated compounds could be achieved within 6 min by using fluorine functionalized magnetic nanoparticles. In recent, a tetrafluoroterephthalonitrile-doped βcyclodextrin-based polymer designed and developed by Helbling and Dichtel [30], showing rapid (∼2 min) removal (efficiency: ∼90%) of OMPs from water, whereas synthesis and fabrication of the sorbent was a very complex and time-cost procedure, with involvement of toxic agents (e.g. CH2Cl2). Later, Helbling and Dichtel [31] modified agents and further developed a decafluorobiphenyl-doped β-cyclodextrinbased sorbent, yet > 95% removal efficiency of PFOA at environmentally relevant concentrations needed at least 13.5 h. Fluorographene (FG), as an important derivative of graphene, can quickly form strong hydrogen bonding with chemical compounds due to the high electronegativity of F atoms [32,33], and has a high specific surface area, being a potential sorbent for OMPs removal. Yet, FG is highly hydrophobic and difficult to disperse in water because of its extreme low surface free energy [34,35], restricting its adsorption of OMPs in water. Attaching hydrophilic magnetic nanoparticles (MNPs) into FG may achieve dispersion in water, and this would allow a sorbent magnetic separation as well, which can improve the recovery and reuse potential of sorbent. However, fabrication and application of MNPsattached FG-based (denoted as MNPs@FG) sorbents to remove OMPs in environmental water appears unreported. The aim of this study was to develop a novel sorbent constructed by MNPs-attached FG for rapid and efficient removal of OMPs in the

2. Materials and methods 2.1. Fabrication of MNPs@FG sorbents MNPs@FG sorbents were prepared through a simple and facile strategy. Firstly, FG was exfoliated from commercial fluorographite (FGi) by using the method as developed in previous studies [36,37]. In brief, 1.25 g FGi (XFNANO, Nanjing, China) reacted with 250 mL of Nmethyl-2-pyrrolidone (NMP, Aladdin, Shanghai, China) at 60 °C for 2 h, NMP molecules easily diffused into the interlayers of FGi due to strong π-π interactions [36], which makes FGi sheets much easier to be exfoliated by low power sonication, generating FG nanosheets. After centrifugation (9500 rpm, 30 min) and solvent removal, FG was dried at 70 °C in an oven. Secondly, MNPs were prepared according to a published method [38]. In brief, 3.0g FeCl2·4H2O and 6.1g FeCl3·6H2O were dissolved in 100 mL of ultrapure water (UPW). The iron solution was heated to 90 °C in a round-bottom flask (250 mL) equipped with a reflux condenser. Afterward, 10 mL of 25% ammonium hydroxide was added into the iron solution rapidly, followed by incubation at 90 °C for 30 min. The solid products were washed with UPW and dried in a vacuum oven at 40 °C for 24 h. The prepared MNPs and FG were mixed in ethanol according to the desired mass ratios of 1:1, 3:5 and 1:3 (total 200 mg), denoted as 1-, 2- and 3-MNPs@FG respectively (Supplementary Material, Table S1), and sonicated for 2 h to embed MNPs onto the surface of FG [39,40], followed by centrifugation and purification. 2.2. Characterization of sorbents In the present study, the morphology of MNPs, FG and MNPs@FG was observed through a JEOL JEM-2100F high-resolution transmission electron microscope (HRTEM) at 200 kV, and the elemental composition of the imaged objects was analyzed by using an energy-dispersive X-ray (EDS) detector (Oxford Inca, UK). The X-ray diffraction (XRD) pattern of samples was characterized through a PANalytical X'Pert PRO diffractometer with Cu Kα radiation, with the diffraction angle from 10° to 70° at 0.05° per step. Infrared spectrometer (IR) was performed on a Thermo Nicolet iS10 with a diamond attenuated total reflectance (ATR) attachment to qualitative estimation of functional groups on the surface of solid products (e.g. MNPs, FG and MNPs@FG). The specific surface area and porosity of solid products were determined by using a surface area analyzer (ASAP2020, Micromeritics, USA) based on N2 adsorption principal, and calculated by using the Brunauer-Emmet-Teller (BET) equation. The X-ray photoelectron spectroscopy (XPS) spectra of the samples were measured using a Kratos Axis Ultra DLD spectrometer (Kratos). 2.3. Batch adsorption experiments Adsorption experiments were conducted in 50 mL polypropylene tubes fixed in an orbital shaker at room temperature. In the investigation of adsorption kinetics of OMPs such as PFOA, PFOS, ACE, DIF and CHL, 20 mL of OMPs (at desired concentrations) aqueous solution with 62


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with 220 rpm for 30 min. Then, concentrations of residual PFOA and PFOS in water were measured by using HPLC-MS/MS. In the investigation of PFOA and PFOS removal from environmental water, 10 mg of 2-MNPs@FG sorbent was added into 25 mL of three types of environmental water (e.g. lake water, river water and tap water). The basic properties of the environmental water are shown in Table S2. Before adding the sorbent, PFOA and PFOS were spiked into each water to achieve ∼5 μg/L of each chemical.

sorbents (e.g. 1-MNPs@FG, 2-MNPs@FG, 3-MNPs@FG, MNPs, FG and powdered AC) was stirred with 220 rpm, and 1.5 mL aliquots of the solution was taken at certain intervals, followed by separation immediately. The residual concentrations of OMPs in the supernatant were determined by using high performance liquid chromatography mass spectrometry mass spectrometry (HPLC-MS/MS) (see below the Section 2.6). It should be noted that a parallel group of controls without any sorbent was set up, showing negligible change during the batch adsorption experiments. All experiments in this study were performed in triplicate. The effect of NOM on the PFOA and PFOS removal by the novel sorbents was examined. A NOM stock solution with the determined content of 100 mg/L dissolved organic carbon (DOC) was prepared dissolving the dry powder (2R101N, International Humic Substance Society, USA) in UPW, followed by filtration through a 0.45 μm membrane syringe. NOM stock solution was added into the water with PFOA (180 μg/L) and PFOS (180 μg/L) to achieve 2 mg/L of DOC. Afterward, the novel sorbents were added into the mixture, followed by stirring

2.4. Flow-through experiments Here flow-through experiments were conducted using the method as described in a previous study [30]. In brief, 6 mg of the MNPs@FG sorbent was stirred in 5 mL UPW for 1 min, and then suspension was pushed by a syringe through a 0.22 μm membrane filter, forming a thin layer of the sorbent on the surface of the filter. 15 mL of aqueous solution with OMPs at a desired concentration was pushed through the filter at a flow rate of ∼5 mL/min. The filtrate was collected and

Fig. 1. Characterization of MNPs@FG sorbents. (a) TEM image of the 2-MNPs@FG sorbent. (b) EDS image of the 2-MNPs@FG sorbent. (c) XRD. (d) FTIR. (e) XPS.

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2.6. Quantification of OMPs

measured by HPLC-MS/MS to show the residual concentration of OMPs.

Native standards (i.e. compounds that were not mass-labeled, PFOA and PFOS) and mass-labeled standards (13C8 PFOA and 13C8 PFOS) were obtained from Wellington Laboratories (Guelph, Canada). 13C8 PFOA and 13C8 PFOS were used as injection internal standards (ISs), which were added just prior to injection. After solid-liquid separation, supernatant is collected and diluted with methanol (HPLC grade, JT Baker) before analysis. PFOA, PFOS, CHL, DIF and ACE were measured using an ultra-fast liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS, LCMS 8050, Shimadzu, Japan). The mass system was equipped with an electro spray ionization (ESI) source. The LC was equipped with a Waters Acquity UPLC BEH C18 column (2.1 mm × 100 mm, 1.7 μm particle size, Milford, MA, USA). The

2.5. Sorbent regeneration A 30 mL of PFOA (180 μg/L) and PFOS (180 μg/L) aqueous solution with 12 mg of 2-MNPs@FG sorbent was stirred at 220 rpm for 30 min, followed by sorbent separation. The residual PFOA and PFOS in the water were determined by HPLC-MS/MS. The used 2-MNPs@FG sorbent was regenerated by sonication in methanol (5 mL) for 30 min and recovered by magnetic separation. The adsorption and desorption cycle was conducted 5 times to show the excellent performance of reusability, which was also conducted in past studies [30,31].

Fig. 2. Removal efficiencies of OMPs by using different sorbents in batch ([sorbent]: 400 mg/L) and flow-through (sorbent mass: 6.0 mg) adsorption experiments. Error bars: standard deviation of three experiments. (a) Structures and relevance of each tested OMP. (b) Batch experiment: [PFOA]0: 180 μg/L. (c) Batch experiment: [PFOS]0: 180 μg/L. (d) Flow-through experiment: removal efficiencies of PFOA and PFOS obtained by rapidly (∼5 mL/min) flowing the PFOA/PFOS solution (15 mL) through a thin layer of sorbent (6.0 mg). (e) PFOA and PFOS adsorption isotherms by the 2-MNPs@FG sorbent ([PFOA]0: 500–40,000 μg/L, [PFOS]0: 500–40,000 μg/L, [2-MNPs@FG]: 250 mg/L, 220 rpm, 30 min). Lines show fits to Langmuir (magenta line) and Freundlich (black line) models. (f) Removal efficiencies obtained by stirring (220 rpm, 10 min) OMPs ([CHL]0: 200 μg/L, [ACE]0: 200 μg/L, [DIF]0: 200 μg/L) solution with different sorbents (400 mg/L).

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stretch [44]. Also, a broad peak at 3418 cm−1 was observed in MNPs and MNPs@FG, suggesting the O-H stretching vibration due to the FeOOH in MNPs, which is well consistent with the finding through XRD analysis. The XPS also showed a strong peak of F-C-F bond in MNPs@ FG (Fig. 1e), suggesting that MNPs@FG sorbents still kept a high degree of fluorination, as preserved in the FG. With these unique properties, MNPs@FG sorbents would disperse in water, and still kept the potential to adsorb OMPs.

column and sample manager were kept at 40 and 4 °C, respectively. The injection volume was 2 μL. The nebulizer and drying gas were 99.95% nitrogen, and their flow rates were 3.0 and 10.0 L/min, respectively. The heating gas was 99.95% air with a flow rate of 10.0 L/min. The collision gas was 99.99% argon with a pressure of 270 kPa. Other parameters were as follows: interface voltage 4.0 kV, interface temperature 300 °C, DL temperature 250 °C, heat block temperature 400 °C, and detector voltage 1.82 kV. Mobile phase for measurement of PFOA and PFOS: the mobile phase was composed of 5 mM ammonium acetate (HPLC grade, SigmaAldrich) in UPW and methanol (HPLC grade, JT Baker) as solvents A and B, respectively, with a flow rate of 0.2 mL/min. The gradient elution program was as follows: 0–0.5 min, 60–95% B; 0.5–2.5 min, retain 95% B; 2.51 min, change to 60% B; 2.51–6.0 min, retain 60% B, equilibration of the column. Mobile phase for measurement of CHL, DIF and ACE: the mobile phase was composed of 0.1% (v/v) formic acid (HPLC grade, SigmaAldrich) in UPW and acetonitrile (HPLC grade, JT Baker) as solvents A and B, respectively, with a flow rate of 0.2 mL/min. The gradient elution program is as follows: 0–0.3 min, 10% B; 0.3–1.3 min, retain 10–95% B; 1.3–3.0 min, retain 95% B, 3.01 min, change to 10% B; 3.01–5.0 min, retain 10% B, equilibration of the column. In the experiment of removing PFOA and PFOS at environmentally relevant concentrations, 30 mL of supernatant after sorbent separation was collected for the determination of PFOA and PFOS. HLB cartridges (3 cc, 60 mg, Milford, MA, USA) were used for accumulation of PFOA and PFOS. The supernatant was loaded onto the HLB cartridges preconditioned with 3 mL of methanol and 3 mL of UPW. The cartridge was allowed to run dry. Finally, target analytes were eluted with 5 mL of methanol. The eluate was then reduced to 200 μL under a gentle stream of N2, and transferred to HPLC vial for measurement. Data were collected in the multiple reaction monitoring (MRM) mode. MRM transitions were showed in Table S3. The limit of detection (LOD) was defined as a value corresponding to a signal-to-noise ratio of 3 (S/N = 3), and the limit of quantification (LOQ) equaled a value corresponding to S/N of 10. The LODs and LOQs are also listed in Table S3.

3.2. Adsorption kinetics and isotherm of PFOA and PFOS PFOA and PFOS are emerging persistent OMPs (Fig. 2a), showing significantly negative effects on organisms compared to regulated OMPs. We thus firstly adopted PFOA and PFOS as model OMPs to evaluate the adsorption capacity of the MNPs@FG sorbents. The PFOA and PFOS removal efficiencies of different sorbents with equal mass concentrations (400 mg/L) were investigated in batch experiments using both high (5400 μg/L) and low (180 μg/L) levels of PFOA/PFOS (Figs. 2b,c and S3). Each MNPs@FG sorbent could eventually remove 91–97% of PFOA and PFOS from the 180 μg/L aqueous solution, while both powdered AC and MNPs removed only 4–9% of PFOA and PFOS in water, even though BET surface areas of powdered AC (148.94 m2/g) and MNPs (159.47 m2/g) were comparable to those of the MNPs@FG sorbents (169.85–225.42 m2/g). A similar phenomenon was also observed in the batch experiment with 5400 μg/L PFOA and PFOS (Fig. S3): PFOA and PFOS removal efficiencies by powdered AC, MNPs and FG were significantly lower than those of the MNPs@FG sorbents. These data clearly suggested that the MNPs@FG sorbents had superior adsorption of PFOA and PFOS compared with powdered AC, MNPs and FG. The mass ratio of MNPs to FG showed an important effect on the PFOA and PFOS removal: PFOA and PFOS removal efficiencies of 1MNPs@FG were 10–20% lower than those of 2- and 3-MNPs@FG sorbents (Figs. 2b,c and S3), which might be attributed to more MNPs in the 1-MNPs@FG because MNPs had a lower adsorption for PFOA and PFOS than FG (Fig. S3). More importantly, both 2- and 3-MNPs@FG sorbents could achieve adsorption equilibrium within 2 min, being much faster than the 1-MNPs@FG sorbent which reached equilibrium in 10 min (Fig. 2b,c). The highly efficient removal of PFOA and PFOS from water by 2- and 3-MNPs@FG sorbents could be maximized within 2 min, which is 120 times as fast as a magnetic fluorinated vermiculite for PFOS removal (4 h) [45]. Given the rapid adsorption kinetics observed in the batch experiment, we further evaluated the PFOA and PFOS removal efficiencies of the MNPs@FG sorbents by using flow-through experiments. The 1MNPs@FG sorbent removed 61 and 77% of PFOA and PFOS respectively, while the 2- and 3-MNPs@FG sorbents could remove 90–93% of PFOA and 96–97% of PFOS under the same conditions (Fig. 2d), being comparable to the removal efficiencies observed in the batch experiments (Fig. 2b,c). Although both 2- and 3-MNPs@FG sorbents showed comparable removal efficiencies and rates of PFOA and PFOS, the 2-MNPs@FG outclassed 3-MNPs@FG as an effective sorbent with regard to the economic cost because the latter consumed more FG compared to the former (Table S4). Thus, we further examined the adsorption isotherms of PFOA and PFOS on the 2-MNPs@FG [250 mg/L] by using [PFOA] and [PFOS] from 500 to 40,000 μg/L (Fig. 2e). The Freundlich and Langmuir models fitted the adsorption isotherms well, while the Langmuir model may be more appropriate for the PFOA and PFOS adsorption of 2-MNPs@FG on the basis of data (Table 1). The maximum PFOA adsorption capacity of the 2-MNPs@FG sorbent was 50.4 mg/g, much higher than recently reported decafluorobiphenyl-doped β-cyclodextrin-based polymer (adsorption capacity: 34 mg/g) [31] and βcyclodextrin-ionic liquid polyurethane-modified magnetic sorbent (adsorption capacity: 2.5 mg/g) [46] for PFOA removal (Table S5).

3. Results and discussion 3.1. Preparation and characterization of MNPs@FG sorbents In the present study, FGi sheets were exfoliated through sonication very well, as reported in previous studies [36,37], generating FG nanosheets (Supplementary Material, Fig. S1a). Moreover, EDS analysis showed that the ratio of F to C atoms in FG was 1.15: 1 (Fig. S1a), suggesting that FG was nearly fully fluorinated. The prepared MNPs were round in shape (Fig. S1b), with an average size of ∼22 nm (on the basis of size measurement through TEM images, n = 198). Moreover, the main diffraction peaks shown in Fig. 1c at 21.0° and 35.7°, 43.5°, 57.1°, 62.9° display characteristics typical of FeOOH and Fe3O4, respectively [41]. Here it should be noted that the prepared mixture of FeOOH and Fe3O4 was denoted as MNPs in this study. The MNPs were embedded into the FG surfaces through sonication regardless of MNPs/FG mass ratio (Figs. 1a,b and S2), suggesting that MNPs-attached FG sorbents could be facilely fabricated. The sonicationdependent fabrication was also applied to develop a TiO2-attached graphene sorbent in past studies [39]. Compared to FG, the new peaks appearing in the XRD of MNPs@FG sorbents could be assigned to the MNPs (Fig. 1c), and the disappearance of a peak at 12.7° for MNPs@FG sorbents was ascribed to the attaching MNPs between the layers of FG, which may destroy the regular layer stacking of FG [42]. A similar phenomena was also observed when Ouyang et al. [43] fabricated Fe3O4/graphene oxide hybrids. In addition, both FG and MNPs@FG exhibited sharp peaks at 1208 and 1347 cm−1 in the FTIR (Fig. 1d), which is attributed to the specific absorption of the C-F and F-C-F 65


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Table 1 Freundlich and Langmuir parameters derived from plots of the PFOA and PFOS binding isotherm in Fig. 2e. OMPs

PFOA PFOS

Freundlich

Table 2 Application of the 2-MNPs@FG sorbent to remove PFOA and PFOS at environmentally relevant concentrations in environmental water.

Langmuir

Concentration (ng/L)

KF (mg/g) (L/mg)1/n

n

R2

KL (L/mg)

Qmax mg/g

R2

2.15 3.33

0.68 0.42

0.97 0.96

0.026 0.120

50.4 17.2

0.99 0.97

Initial Residual Total redisual

Lake water

River water

Tap water

PFOA

PFOS

PFOA

PFOS

PFOA

PFOS

4230 11 39a

6990 28

4390 16 38[a]

6670 22

3910 31 49a

5650 18

a The U.S. Environmental Protection Agency assigned a health advisory level of 70 ng/ L for the combined concentration of PFOA and PFOS in drinking water. Here the total residual of PFOA and PFOS is lower than the assigned concentration through the 2MNPs@FG sorbent adsorption.

3.3. Applicability and reusability of the novel sorbent In addition to perflourinated compounds (PFOA and PFOS), we also evaluated the ability of the 2-MNPs@FG sorbent to remove regulated OMPs including pharmaceuticals, herbicides and pesticides (Fig. 2a): DIF, a model of broad-spectrum antibiotic that has been extensively detected in surface and groundwater; ACE, one of the most common herbicides that is listed in the EU-report for priority substances in water due to potential endocrine disruption; CHL, a pesticide that has been widely used in the world. The 2-MNPs@FG sorbent also showed impressive removal efficiencies (97–99%) of DIF, ACE and CHL within short time, and it also outperformed powdered AC and MNPs for all of the tested regulated OMPs (Fig. 2f). The performance of most of the reported sorbents was affected by environmental matrices in particular NOM because binding sites for adsorption on the surface of sorbents would be occupied due to fouling [47–49]. Fig. 3 shows that NOM exerts ignorable influence on the adsorption of PFOA (180 μg/L) and PFOS (180 μg/L) onto the MNPs@FG sorbents, indicating good applicability of the novel sorbents. Accordingly, the rapid and effective removal of OMPs by the 2-MNPs@FG sorbent was further examined at environmentally relevant concentrations of PFOA and PFOS [50–52] in different types of environmental water. The 2-MNPs@FG sorbent (400 mg/L) reduced PFOA and PFOS concentrations from 3910–6990 to 11–31 ng/L within 10 min (Table 2), showing higher than 99.2% of removal efficiencies. More importantly, after the impressive adsorption by the 2-MNPs@FG sorbent, the total residual concentration (39–49 ng/L) of combined PFOA and PFOS in water was much lower than the health advisory level (70 ng/L) assigned by U.S. Environmental Protection Agency (EPA), providing a potential sorbent to ensure drinking water safety. Besides good applicability, the MNPs@FG sorbents showed an impressive reusability (Fig. 4); PFOA and PFOS could be easily removed from the used sorbents through sonication with methanol for 30 min at room temperature, achieving a complete 2-MNPs@FG sorbent regeneration. Five consecutive PFOA and PFOS adsorption and desorption cycles were conducted and the regenerated 2-MNPs@FG sorbent exhibited almost no significant decrease in the PFOA and PFOS removal

efficiencies and magnetic performance compared to the as-fabricated 2MNPs@FG sorbent. After the 5 cycles, we further did another 7 times of adsorption and desorption cycle, showing good removal efficiencies of PFOA (> 79%) and PFOS (> 83%) for the case of 12th cycle. Moreover, the change in morphology of sorbent was negligible (Fig. S4), although some separated magnetic NPs were observed. 4. Conclusions In conclusion, we showed an easy way to prepare a MNPs-attached FG-based material and demonstrated its excellent application as a rapid, effective and regenerable sorbent for the removal of OMPs from environmental water to replace the powdered AC, ensuring the safety of water. The fabricated MNPs@FG sorbents showed > 95% removal efficiencies of PFOA, PFOS, DIF, ACE and CHL within short time, which represents a one order of magnitude improvement compared to powdered AC. Given its superior performance, pilot-scale studies with the MNPs@FG sorbent and carbon-based materials like powder AC would be further operated respectively, showing differences in regards to removal efficiency of OMPs, running costs and technical bottlenecks, which would pave a way for environmental application in future. Furthermore, the novel sorbent could be easily regenerated and reused multiple cycles without significant reduction in performance after sonication with methanol. Also, the 2-MNPs@FG sorbent could reduce PFOA and PFOS from environmentally relevant concentrations (μg/L) in environmental water to tens ng/L levels, well below U.S. EPA health advisor limits. Therefore, the novel sorbent fabricated in this study showed the great potential for rapid and effective removal of OMPs from environmental water. Acknowledgements This work was financially supported by Zhejiang Province of

Fig. 3. Effect of NOM at a DOC content of 2 mg/L on the removal efficiencies of PFOA and PFOS by using MNPs@FG sorbents (400 mg/L) in batch experiments (220 rpm, 30 min). (a) PFOA ([PFOA]0: 180 μg/L). (b) PFOS ([PFOS]0: 180 μg/L).

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Fig. 4. Regeneration and reusability of the 2-MNPs@FG sorbent by washing with MeOH. Removal experiments: [PFOA]0: 180 μg/L, [PFOS]0: 180 μg/L, [2-MNPs@FG]: 400 mg/L, stirring at 220 rpm for 30 min. Desorption experiments: the used 2-MNPs@FG sorbent was sonicated in MeOH for 30 min. (a) Removal efficiency of PFOA. (b) Removal efficiency of PFOS. (c) TEM of the fresh 2-MNPs@FG sorbent. (d) EDS image of the fresh 2-MNPs@FG sorbent (inlet: photo of magnetic separation). (e) TEM of the regenerated 2-MNPs@FG sorbent after 5 cycles. (f) EDS image of the regenerated 2-MNPs@FG sorbent (inlet: photo of magnetic separation).

Natural Science Foundation (LY18B070011, LQ16B070003, 2015C32039) and Science Foundation of Zhejiang Sci-Tech University (17062003-Y). We would like to acknowledge Fanglan Geng (Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences) for her significant contribution on the HRTEM and EDS analysis. We also thank the anonymous reviewers for their valuable comments and suggestions on this work.

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