Free-Standing Graphene Oxide-Palygorskite Nanohybrid Membrane

Subscriber access provided by GAZI UNIV

Article

Free-Standing Graphene Oxide-Palygorskite Nanohybrid Membrane for Oil/Water Separation Xueting Zhao, Yan-Lei Su, Yanan Liu, Yafei Li, and Zhongyi Jiang ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.5b12876 • Publication Date (Web): 08 Mar 2016 Downloaded from http://pubs.acs.org on March 8, 2016

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 free 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 accessible to all readers and 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.

ACS Applied Materials & Interfaces 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 27

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces

Free-Standing Graphene Oxide-Palygorskite Nanohybrid Membrane for Oil/Water Separation Xueting Zhaoa,b,c, Yanlei Sua,b, Yanan Liua,b, Yafei Lia,b, Zhongyi Jianga,b,∗ a

Key Laboratory for Green Chemical Technology of Ministry of Education, School of Chemical

Engineering and Technology, Tianjin University, Tianjin 300072, China b

Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), Tianjin 300072,

China c

Center for Membrane and Water Science & Technology, Ocean College, Zhejiang University of

Technology, Hangzhou 310014, China

Abstract Graphene oxide (GO) is an emerging kind of building block for advanced membranes with tunable passageway for water molecules. To synergistically manipulate the channel and surface structures/properties of GO-based membranes, the different building blocks are combined and the specific interfacial interactions are designed in this study. With vacuum-assisted filtration self-assembly, palygorskite nanorods are intercalated into adjacent GO nanosheets, and GO nanosheets are assembled into laminate structures through π-π stacking and cation crosslinking. The palygorskite nanorods in the free-standing GOP nanohybrid membranes take a threefold role, rendering enlarged mass transfer channels, elevating hydration capacity and creating hierarchical

∗ Corresponding author. School of Chemical Engineering and Technology, Tianjin University, No. 92, Weijin Road, Nankai District, Tianjin 300072, China Tel: 86-22-27406646. Fax: 86-22-23500086. E-mail address: [email protected] (Z.Y. Jiang) 1 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 27

nanostructures of membrane surfaces. Accordingly, the permeate fluxes from 267 L/(m2h) for GO membrane to 1867 L/(m2h) for GOP membrane. The hydration capacity and hierarchical nanostructures synergistically endow GOP membranes with underwater superoleophobic and low oil-adhesive water/membrane interfaces. Moreover, by rationally imparting

chemical and physical

joint defense mechanisms, the GOP membranes exhibit outstanding separation performance and antifouling properties for various oil-in-water emulsion system (with different concentration, pH or oil species). The high water permeability, high separation efficiency as well as superior anti-oil-fouling properties of GOP membranes enlighten the great prospects of graphene-based nanostructured materials in water purification and wastewater treatment.

Keywords: graphene oxide nanosheets, palygorskite nanorods, intercalation, free-standing nanohybrid membranes, oil/water separation

2 ACS Paragon Plus Environment

Page 3 of 27

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1. Introduction Graphene oxide (GO) nanosheets are derived from the nanometer-thick sp2 hybridized graphene, functionalized with oxidative groups, and structured with nanoscale wrinkles and defects.1-3 GO nanosheets have sparked enormous interest owing to the unique properties such as high surface area,4 high flexibility,5 high Young’s modulus,6 accessible interface designs,7 and ultrafast transport properties.8 Ruoff et al.9 first highlighted the potential of using paper-like GO-based membrane material for selective permeation in 2007. Since then, GO nanosheets have been exploited into diverse kinds of membrane materials either as fillers of polymeric matrix or as bulk building blocks of self-assembled membrane (SAM).10-13 In general, the oxidation and exfoliation of graphite into GO nanosheets can enlarge the adjacent interlayer distance of GO nanosheets from 0.34 nm to 0.65 nm,14,15 therefore, GO-based SAMs with laminate 2D nanochannels between adjacent GO nanosheets have become one of the most popular membrane materials in water treatment applications.16-24 The laminate 2D nanochannels as well as the wrinkled interlayer space throughout GO-based SAMs can render efficient passageway for water molecules and block other the species larger than the space between adjacent GO nanosheets.24,25 The capillary driven force, ultralow friction and boundary slip factors offered by hydrophobic walls of unoxidized graphene regions also ensure the fast water transport when water molecules permeate through GO-based SAMs.20-22,26 The morphology and alignment of GO nanosheets are closely related to the nanochannel structures within GO-based SAMs and the structure-property relationships in water treatment applications. GO nanosheets with nanoscale defects are demonstrated to exhibit shorter effective lateral length, and the channel length of GO-based SAMs can be regulated by rendering shorter pathways for water transport.27-29 GO nanosheets with intercalated structure are demonstrated to exhibit larger interlayer distance, and the channel width of GO-based SAMs can be regulated by broadening the water transport pathways.30-34 Considering that practical separation systems in water treatment contained



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

different types of foultants, membrane fouling still remains a grand challenge. Hence, to further enlarge the application fields of GO-based SAMs (such as oily water treatment, biological separation, desalination, photocatalytic degradation, etc.), the nanochannel structures within GO-based SAMs must be delicately regulated and optimally integrated with functional surfaces/interfaces for deterring membrane fouling. With the attributes in variable building blocks and accessible interface designs, GO nanosheets with intercalated structure should be a preferred choice. The synergy of nanochannel structures and functional surfaces/interfaces may be readily achieved by intercalating nanomaterials into GO laminate structures. The nano-units assembled into adjacent GO nanosheets are expected to create intercalated framework with larger nanochannels for rapid water permeation. Moreover, the nano-units assembled onto external GO nanosheets are utilized to impart membrane surface with diverse chemico-physical structures for target surface properties, such as antifouling, antimicrobial and photocatalytic properties. For water treatment applications, antifouling properties have been commonly recognized as the critical surface properties of membranes. The primary design criteria to obtain desired antifouling properties are to suppress the unfavorable interactions between foulants and membrane surfaces. Inspired from natural antifouling surfaces, i.e., the scales or skins of underwater organisms, both physical and chemical defense mechanisms play vital roles in antifouling properties.35,36 Manipulating the physical topography of membrane surfaces aims at coordinating the hierarchical nanostructures, which will disturb the flow regime near water/membrane interface and lead to nonequilibrium attachment of foulants.37,38 Manipulating the chemical composition of membrane surfaces aims at coordinating the hydration capacity, which will resist foulants out of hydration barrier layers.39-43 Therefore, both hierarchical nanostructures and high hydration capacity are required to prevent membrane fouling in practical applications.44-47 As for GO-based SAMs with intercalated structure, the rational design of the channel structures and surface properties is indispensable to tailor membranes with both high water permeability and antifouling capacity, which


Page 4 of 27

Page 5 of 27

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


is undoubtedly beneficial to efficient and long-term water treatment operations. A major objective of this study is to synergistically tune the channel structures and surface properties of GO-based SAMs for high water permeability and antifouling capacity by combining the favorable attributes of both GO nanosheets and intercalated nano-units. PGS nanorods are chosen for this study, owing to the robust 1D nanostructure, high surface area, hydrophilic surface and high water retention capacity. Herein, a free-standing SAMs are fabricated based on GO nanosheets and palygorskite (PGS) nanorods through vacuum-assisted filtration self-assembly process. The intercalation of PGS nanorods into adjacent GO nanosheets can simultaneously tailor the channel structure and surface topography of the as-prepared GOP membranes, endowing membranes with hierarchical nanostructures and enhanced water transport performance. The synergistic effect of the hierarchical nanostructures and outstanding hydration capacity endows membranes with robust underwater superoleophobic and low oil-adhesive water/membrane interface. The separation performance and anti-oil-fouling properties of GOP membranes are successfully demonstrated via oil-in-water emulsion separation test. The current study proposes a facile method for controllable construction of GO-based SAMs with elevated water permeability, high separation efficiency, and superior underwater superoleophobicity, and extends their applications to broader fields besides water treatment.

2. Materials and methods 2.1. Materials

GO nanosheets (thickness: 1.2 nm, size: 300~500 nm) were prepared from graphite powders according to the typical Hummers method. PGS nanorods were prepared from raw palygorskite clay by a series of purification. The chemical exfoliation process of graphite and the purification process of palygorskite clay could be found in the Supporting Information. All the other chemicals used for GO synthesis, membrane fabrication and performance evaluation were purchased from Guangfu Fine



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Chemical Research Institute (Tianjin, China) and used as received. Ultrapure water (>18 MΩ/cm) purified by Milli-Q system was used throughout the experiments. 2.2. Fabrication of GO and GOP membranes

The GO membrane and GOP membranes with different PGS/GO mass ratios were fabricated by vacuum-assisted filtration self-assembly process. The GO nanosheets (20 µg) or mixture of GO nanosheets and PGS nanorods (GO: 20 µg, PGS: 40~200 µg) were dispersed into 50 mL with water, followed by ultra-sonicating for 30 min. The PGS/GO mass ratio varied from 2 to 10. The resulting GO-PGS dispersions were vacuum-filtrated on cellulose acetate membrane (pore size 220 nm). The as-prepared GO and GOP membranes were dried at 50 oC overnight. Free-standing GO and GOP membranes were obtained by dissolving cellulose acetate membrane in acetone, and then transferred onto non-woven fabric (3M) for performance evaluation. 2.3. Characterization

Scanning electron microscopy (SEM) was performed on a Nova Nanosem 430 field-emission scanning electron microscope equipment. Transmission electron microscopy (TEM) was performed on a JEM-2100F transmission electron microscope equipment. Atomic force microscopy (AFM) was performed on a Bruker multimode 8 atomic force microscope system to determine the surface morphology and Young’s moduli of membranes (each membrane was transferred onto a polycarbonate microfiltration membrane substrate for measurement). X-ray diffraction (XRD) was performed on a Rigaku D/max-2500 X-ray diffraction equipment. Raman spectra were recorded on a Renishaw InVia Reflex spectrometer using a 532 nm laser. Apparent contact angles and contact angle hysteresis were measured by a JC2000C contact angle goniometer. The dynamic underwater superoleophobicity was determined by the approach-compress-detach process of a hexadecane droplet (10 µL). 2.4. Permeation performance and antifouling property evaluation

The permeation performances of GO and GOP membranes were tested in a dead-end ultrafiltration


Page 6 of 27

Page 7 of 27

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


cell (Millipore Model 8003) with effective membrane area of 0.9 cm2. The transmembrane pressure was applied by pressurized nitrogen gas. Each membrane was first pre-compacted at specific operating pressure with ultrapure water until a stable permeate flux, and then underwent 10 min filtration of ultrapure water. The permeate fluxes J (L/(m2h)) were calculated according to Equation (1): J =

V A∆T

(1)

where V (L) was the volume of permeated water, A (m2) was the effective membrane area, and ∆T (h) was the permeate time. The antifouling properties of GO and GOP membranes were evaluated by water-oil-water three stage filtration process. The initial permeate fluxes of ultrapure water (Jinitial), stable permeate fluxes of oil-in-water emulsion (Joil), and the recovered permeate fluxes of ultrapure water (Jrecovery) after 10 minutes rinsing were calculated. Higher flux recovery ratio (FRR=Jrecovery/Jinitial) and lower flux decline ratio (FDR=1-Joil/Jinitial) indicated better antifouling properties. Several kinds of oil-in-water emulsions were employed: 100 mg or 1 g hexadecane, 100 mg pump oil, or 100 mg soybean oil and a certain amount of sodium dodecylsulfate were added into 100 mL ultrapure water, and then ultra-sonicated for 30 min. The pH values were adjusted by NaOH and HCl. These oil-in-water emulsions were stable for at least 48 hours without obvious stratification. The size and distribution of emulsified oil droplets were performed on a Brookhaven 90Plus PALS particle size analyzer.

3. Results and discussion 3.1. Membrane preparation and morphology characterization The fabrication of GOP membranes via vacuum-assisted filtration self-assembly was schematically depicted in Figure 1. The epoxy, hydroxyl, carbonyl and carboxyl groups on GO nanosheets acted as anchoring sites for the attachment of intercalated nanomaterials.48 PGS nanorods with plentiful hydroxyl groups on the external surfaces can attach onto GO nanosheets via hydrogen 7 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

bond interaction.49 Moreover, the strong π-π stacking interaction among the π-conjugated aromatic domains (unoxidized benzene rings in the basal plane) of adjacent GO nanosheets energetically favored the parallel orientation with the largest faces opposite each other.50-52 The alkoxide bonds or dative bonds between the oxygen functional groups of GO nanosheets and PGS leaching cations (Mg2+, Al3+) also help cross-link neighboring GO nanosheets together.3,17 The engagement of stacked GO nanosheets resulted in the intercalation of PGS nanorods within the interlayers of GO nanosheets. Combining the unique merits of GO nanosheets and PGS nanorods would rationally tune both surface topography and channel structure of the GOP membranes.

Figure 1. Schematic diagram of the process to fabricating of GOP membranes via vacuum-assisted filtration self-assembly. The surface morphologies of GO and GOP membranes with different PGS/GO mass ratios were shown in Figure 2. GO membrane was quite smooth and possessed wrinkled corrugations. Upon the intercalation of PGS nanorods within the interlayers of GO nanosheets, the surfaces of GOP membranes were evenly distributed with 1D interpenetrating nanostructure. No obvious corrugation could be observed on the surface of GOP membranes resulting from the presence of PGS nanorods. The AFM image also indicated the uniform distribution of PGS nanorods on the surface of GOP membranes (Figure 2h). Moreover, the larger roughness of GOP membrane compared with that of 8 ACS Paragon Plus Environment

Page 8 of 27

Page 9 of 27

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


the GO membrane was confirmed (Table 1). The resulting hierarchical roughness could enhance the potential underwater superoleophobicity of water/membrane interfaces.53

Figure 2. SEM images of (a) GO membrane, (b) GOP (PGS/GO=2) membrane, (c) GOP (PGS/GO=4) membrane, (d) GOP (PGS/GO=6) membrane, (e) GOP (PGS/GO=8) membrane, and (f) GOP (PGS/GO=10) membrane. (g) Photographs of free-standing GOP (PGS/GO=4) membrane. (h) AFM image of GO membrane and GOP (PGS/GO=4) membrane. (i) XRD patterns of GO 9 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 27

membrane and GOP (PGS/GO=4) membrane. (j) Raman spectra of GO and GOP membranes. The ultrathin GOP membrane was totally free-standing, transparent, intact and defect-free after being released from substrate membrane (Figure 2g). The average thickness of GO and GOP membranes was in the range 38~85 nm (Figure S3). The intercalation of PGS increased the thickness of membranes. The free-standing feature of GOP membranes indicated the robust crosslinking interactions within GO nanosheets or at PGS/GO interfaces. The mechanical properties of GO and GOP membranes were also critical to keep the free-standing feature of GOP membranes, which were assessed by AFM force measurements (Figure S4, Table 1). Upon PGS intercalation, the Young’s moduli of membranes were increased from 1.26 GPa for GO membrane to 1.79 GPa for GOP (PGS/GO=8) membrane. The increase in mechanical properties suggested the reinforcement effect of PGS intercalation. Table 1. Surface roughness, Young’s modulus, interlayer distance, thickness and the relative intensities of the D and G peaks in Raman spectra of GO membrane and GOP membranes. RMS

Young’s modulu

Interlayer distance

Thickness

(nm)

(GPa)

(nm)

(nm)

GO

25.8

1.26

0.82

38

1.57

GOP (PGS/GO=4)

52.4

1.56

1.13

67

1.81

GOP (PGS/GO=8)

61.3

1.79

N.A.

85

2.04

Membrane

ID/IG

The structural evolution upon PGS nanorod intercalation is reflected by XRD and Raman analyses. As shown in Figure 2i and Table 1, stacked GO nanosheets of GO membrane showed typical broad diffraction peak at 2θ = 10.7o,54 and PGS nanorods of GOP membrane showed diffraction peaks at 2θ =5.7o and 8.3o.55 Notably, interlayer distance (d-spacing) increased from 0.82 nm (2θ =10.7o) for GO membrane to 1.13 nm (2θ =7.8o) for GOP membrane. This shifting revealed the successful intercalation of PGS nanorods into the interlayers of GO nanosheets. Furthermore, the Raman spectra (Figure 2j) also confirmed the intercalation of PGS nanorods. Raman spectrum of GO and 10 ACS Paragon Plus Environment

Page 11 of 27

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


GOP membranes revealed G band at 1600 cm-1 and D band at 1360 cm-1, which was attributed to the crystallinity of sp2 hybrid carbon regions and the carbon lattice distortion, respectively. This result indicated that the π-stacking structures of adjacent GO nanosheets could be well-preserved with PGS nanorod intercalation. The intensity ratio ID/IG increased from 1.57 for GO membrane to 1.81 for GOP (PGS/GO=4) membrane and 2.04 for GOP (PGS/GO=8) membrane (Table 1). This increase indicated that more defects were formed during the intercalation process. The enlarged intercalated channels imparted more structural disorder into the GO laminate structures. The increased interlayer distance and structural disorder are promising in rendering more efficient water transport pathways for better separation performance of GOP membranes. As PGS nanorod intercalation brought the increased interlayer distance and structural disorder into GOP membranes, the changes in GO laminate structures might have negative effect on GOP membrane stability. Fortunately, GOP membranes were found to have enhanced stability compared with GO membrane after oscillation in water. Figure S5a,b showed the GO and GOP membranes before and after oscillation at 100 rpm for 48 h in water. Slight peeling of GO layer was observed on the GO membrane while no visible structural destruction were observed on the GOP membrane under the same oscillation condition. This indicated the better stability of GOP membranes due to intercalation. We proposed that intercalated PGS nanorods and leached cations (Mg2+, Al3+) were effective in crosslinking GO laminate structures via hydrogen bonds, alkoxide bonds or dative bonds, and intensified the stability of membranes.3,17 3.2. Permeation performance The water fluxes of GOP membranes were tested to evaluate permeation performance of membrane according to different PGS/GO mass ratios and transmembrane pressure. A series of GOP membranes were fabricated with 15.9 mg/m2 GO nanosheets and different loadings of PGS nanorods ranging from 31.7 to 158.7 mg/m2, and the fluxes were shown in Figure 3a. The flux of GO membrane was 267 L/(m2h). The fluxes of GOP membranes were first increased and then decreased



with the increase of PGS/GO mass ratio. The highest flux about 1867 L/(m2h) was obtained when the loading amount of PGS nanorods was four times the amount of GO nanosheets. In the initial stage, the increasing flux was caused by the generation of nanorod intercalated channels within the interlayers of GO nanosheets.30, 33 As PGS nanorods were intercalated into adjacent GO layers, the interlayer distance (d-spacing) was increased to 1.13 nm for GOP (PGS/GO=4) membrane, which was considerably enlarged compared with that of GO membrane (~0.82 nm). Higher interlayer distance indicated higher membrane permeability according to Hagen-Poiseuille equation.22 However, when the PGS/GO mass ratio was further increased, the fluxes of GOP membranes were decreased. The GOP membranes suffered from undesirable loss in mass transfer channels due to the agglomeration of PGS nanorods and the functional incapacitation of GO nanosheets sheltered by PGS nanorods.31,49 The dependence of the fluxes of GOP membranes to the applied transmembrane pressure was also evaluated, as shown in Figure 3b. The as-prepared GOP membrane with the PGS/GO mass ratio about 4 was able to withstand a transmembrane pressure up to 0.15 MPa. A gradual increase in the fluxes of GOP membranes was observed with the increase of applied transmembrane pressure. It was worth noting that increasing rate of flux was reduced. It was implied that the nanorod intercalated channels underwent compression to some extent with the increasing transmembrane pressure. (b)

(a)

4000

50000

30000

2

Flux (L/m h)

1200 800

2000

2

2

40000

3000

1600

20000 1000 10000

400 0

0

0

1

2

3

4

5

6

7

8

9

0.00

10

δ(Flux) (L/m h MPa)

2000

Flux (L/m h)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 12 of 27

0.03

0.06

0.09

0.12

0.15

0

P (Mpa)

PGS/GO (wt/wt)

Figure 3. (a) Permeate fluxes of GOP membranes with different PGS/GO mass ratios, (b) permeate fluxes of GOP (PGS/GO=4) membrane under different applied transmembrane pressure. 12 ACS Paragon Plus Environment

Page 13 of 27

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


3.3. Wetting behavior To evaluate the wetting behavior of GOP membranes, both apparent water contact angles in air and apparent oil contact angles under water were measured. As shown in Figure 4a, upon PGS nanorod intercalation, a decrease in the apparent water contact angles of GOP membranes was notable compared with that of GO membrane. The highly hydrophilic nature of PGS nanorods with plentiful hydroxyl groups on the surface contributed surface hydrophilicity, which elevated hydration capacity of GOP membrane surfaces.56, 57 Moreover, the architecture of the palygorskite contributed hierarchical nanostructures and higher water contact angle hysteresis (Figure S6a). It could be deduced that the entrapped water within the nanoscale topography of GOP membranes would endow membranes with robust hydration layer at water/membrane interfaces (Figure S6b).53, 58-60 We also suggested that the surface hydrophilicity and hierarchical nanostructures of membrane surfaces synergistically enhanced the underwater superoleophobicity of water/membrane interfaces. As shown in Figure 4b, with the enhancement in surface hydration capacity, an increase in underwater apparent oil contact angles from 153o for GO membrane to 165o for GOP membranes was observed. When an oil droplet contacted with hierarchical membrane surface, the trapped water in the hierarchical nanostructures served as a protective hydration structure to prevent oil droplet completely contacting with solid membrane surface. Consequently, oil/water/membrane three-phase contact interfaces became discontinuous, and thus the effective contact area between oil droplet and membrane surface was significantly decreased.44, 61, 62 The discontinuous oil/water/membrane contact interface would prevent oil wetting and maintain spherical droplet without deformation (Figure 4c). Therefore, the GOP membranes showed enhanced underwater superoleophobicity in the oil/water/membrane three-phase interfaces.



(a) O

Water contact angle ( )

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 27

70 60 50 40 30 20 10 0

0

2

4

6

8

10

PGS/GO (wt/wt)

Figure 4. (a) Apparent water contact angles in air and (b) apparent oil contact angle under water of GOP membranes with different PGS/GO mass ratios. (c) Schematic of the oil/water/membrane interfaces of GO and GOP membranes. The

underwater

oil-adhesion

test

of

GOP

membranes

was

investigated

via

an

approach-compress-detach process (Figure 5). Oil droplets of 10 µL were trapped on the needle tip of microsyringe and forced to contact with GO and GOP membranes. As the oil droplets were compressed on membrane surfaces, oil droplets were deformed from spherical to ellipsoidal form. As the oil droplets were removed downwards, oil droplets could overcome the adhesion force with GO and GOP membrane surfaces and detach from membrane surfaces. Particularly, almost no obvious deformation was found when the oil droplet detached from GOP membrane surface, revealing lower oil adhesiveness of GOP membrane than GO membrane. When an oil droplet was removed downwards, the adhesion force between the oil droplet and membrane surface generated vertical tensile stress and promoted the deformation. For hierarchical GOP membrane, the compact hydration layer at water/membrane interface prevented the direct contact of oil droplets, significantly lowered the oil-adhesion force (or vertical tensile stress) and suppressed the oil deformation,44, 14 ACS Paragon Plus Environment

63-65

Page 15 of 27

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


suggesting dynamic underwater superoleophobicity.

Figure 5. Dynamic approach-compress-detach oil-adhesion test of (a) GO membrane and (b) GOP (PGS/GO=4) membrane. 3.4. Oil/water separation performance and anti-oil-fouling properties Anti-oil-fouling performance of membranes was also crucial for membrane implementation during oil-in-water emulsion separation. The GOP membrane showed excellent anti-oil-fouling properties as compared to GO membrane (Figure 6a). The oil/water separation process performed under a transmembrane pressure of 0.05 MPa and a near-surface stirring speed of 200 rpm. During hexadecane-in-water emulsion separation, the flux recovery ratios of GOP membranes were gradually increased to above 90% with the increase of PGS/GO mass ratio from 0 to 6. Oil rejection ratios of all membranes were above 99.9% as determined by UV-vis spectrophotometer. In particular, the initial flux of GOP (PGS/GO=4) membrane was from 1933 L/(m2h) and declined to 1200 L/(m2h) for hexadecane-in-water emulsion filtration, while the flux could recover to 1800 L/(m2h) by simple water rinsing. The flux recovery ratio of 93% and flux decline ratio of 38% revealed excellent anti-oil-fouling properties of GOP (PGS/GO=4) membrane even under high flux. These results were in a good agreement with the underwater superoleophobic and low oil-adhesive water/membrane interface of GOP (PGS/GO=4) membrane. As the PGS/GO mass ratio increased to 8, the anti-oil-fouling properties of GOP membrane were slightly decreased, probably resulting from the 15 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

agglomeration of PGS nanorods. The GOP (PGS/GO=4) membrane with highest water permeability is thus chosen to systematically study the universality and anti-oil-fouling properties of GOP membranes during oil/water separation. Hexadecane-in-water emulsions with concentration of 1 g/L and 10 g/L were employed to evaluate the anti-oil-fouling properties of GOP membrane (Figure 6b). The flux of 10 g/L hexadecane-in-water emulsion was lower than that of 1 g/L hexadecane-in-water emulsion. This result could be attributed to preferred surface oil coalescence at higher oil concentration. However, the flux recovery ratio after rinsing were both higher than 85%, indicating the extensive anti-oil-fouling properties of GOP membrane for emulsions with different concentration. The rejection ratios of both emulsions were higher than 99.9% as determined by UV-vis spectrophotometer (Figure S7a). Hexadecane-in-water emulsions with pH of 1.0, 7.0, and 11.0 were employed to evaluate the anti-oil-fouling properties of GOP membrane (Figure 6c). The GOP membrane showed flux recovery ratio of 91 % at pH 1.0, 93% at pH 7.0, and 92% at pH 11.0. Although GOP membrane exhibited slightly lower flux recovery ratio at pH 1.0 and pH 11.0, the anti-oil-fouling properties of GOP membrane were also competitive under harsh acid or base environment. Even higher pH might induce the changes in the chemico-physical structures of GO nanosheets. The rejection ratios of emulsions at different pH were higher than 99.9% as determined by UV-vis spectrophotometer (Figure S7b). Three kinds of oil-in-water emulsions (hexadecane-in-water, pump oil-in-water, or soybean oil-in-water) were also employed to evaluate the anti-oil-fouling properties of GOP membranes. GOP membrane was efficient in the different oil-in-water emulsion separation with rejection ratio higher than 99.9% as determined by UV-vis spectrophotometer (Figure S7c). The initial water fluxes, emulsion fluxes and recovered water fluxes after water rinsing were shown in Figure 6d. The GOP membrane showed flux recovery ratio of 93% for hexadecane-in-water separation. Again, the GOP


Page 16 of 27

Page 17 of 27

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


membrane also exhibited high flux recovery ratio in other emulsion systems: 85% for pump oil-in-water emulsion separation, and 81% for soybean oil-in-water emulsion separation, respectively. All these results demonstrate that the PGS nanorod intercalation not only enhance the water permeability of GOP membranes but also favor the anti-oil-fouling properties of the membrane. The anti-oil-fouling properties of GOP membranes were believed to be closely related to the chemical and physical defense mechanisms. Both the chemical composition and surface topography would influence the attaching of oil droplets and the fouling of surfaces. The chemical defense mechanism was derived from the surface hydration capacity. The oxidative groups on GOP membrane surfaces induced strong electrostatic and hydrogen bonding of water molecules, and the resulting hydration layer at water/membrane interfaces created strong repulsive barrier to resist the fouling from oil droplets. The physical defense mechanism was derived from the surface hierarchical nanostructures. On one hand, the trapped water within the nanoscale topographies strengthened hydration barrier layers and led to underwater superoleophobic and low oil-adhesive water/membrane interfaces; on the other hand, the nanoscale topographies would also allow an increase in flow disturbance of hydraulic shear near water/membrane interfaces, which depressed the coalescence and spreading of oil droplets. The synergistic chemical and physical defense mechanisms have offered a powerful strategy to pursue the excellent anti-oil-fouling properties of GOP membranes. As a result, we suggested that the GOP membranes with both anti-oil-fouling properties and well-defined channel structures can be employed for diverse applications in oil-associated water treatment.



Jinitial

Joil

Jrecovery

Jinitial

100

2000

60

Flux(L/m2h)

800

FFR

80 1200 70

800

50 400

0

2

4

6

30

8

(c) Jinitial

2000

Joil

Jrecovery

FFR

60

400

40

0

50

10 g/L

1 g/L

(d)

100

2000

Jinitial

Joil

Jrecovery

FFR

90

90 1600

70

800 400

pH=1

pH=7

pH=11

FFR(%)

80

1200

Flux(L/m2h)

1600

0

100

80

1200

70

800

60

400

50

0

FFR(%)

0

100 90

FFR(%)

70

Jrecovery

1600

80 1200

Joil

2000

90

1600

Flux(L/m2h)

(b)

110 FFR

FFR(%)

(a)

Flux(L/m2h)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 27

60

hexadecane/water

pump oil/water

soybean oil/water

50

Figure 6. permeate fluxes and flux recovery ratios of GOP membranes in water-emulsion-water three stage oil-in-water emulsion filtration (a) with different PGS/GO mass ratios, (b) with different oil concentration, (c) with different pH, and (d) with different type of emulsion.

4. Conclusions Facile fabrication of free-standing GOP nanohybrid membranes with high water permeability, high separation efficiency, and anti-oil-fouling properties was demonstrated through the controlled assembly of PGS nanorods into the interlayers of stacked GO nanosheets. The intercalated structure of GOP membranes combined the benefit of both GO nanosheets and PGS nanorods in a synergistic way. The GO nanosheets take dual roles, creating laminate structures and constructing efficient passageway for water molecules. The palygorskite nanorods take a threefold role, rendering enlarged mass transfer channels, elevating the hydration capacity and creating hierarchical nanostructures of membrane surfaces. All these attributes endow GOP membranes with optimized channel structures


Page 19 of 27

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


and antifouling properties. Upon the intercalation of PGS nanorods within the interlayers of GO nanosheets, the GOP membranes exhibited a drastic increase in permeate fluxes from 267 L/(m2h) for GO membrane to 1867 L/(m2h) for GOP membrane. Upon the combination of high hydration capacity with hierarchically nanostructured membrane surfaces, the GOP membranes acquired underwater superoleophobic and low oil-adhesive water/membrane interfaces. Upon the integration of chemical and physical defense mechanisms, the GOP membranes exhibited excellent and universal anti-oil-fouling properties during oil-in-water emulsion separation in various conditions (different concentration, pH or oil species). These results may contribute a novel design of GO-based membranes to pursue the synergistic enhancement in separation performance and antifouling properties. This study may also provide new insight into the cooperative construction of GO composite materials toward remarkably enhanced or newly derived functionalities/characteristics.

Acknowledgment. This study was supported by National Science Fund for Distinguished Young Scholars (21125627) and Tianjin Natural Science Foundation (14JCZDJC37400, 13JCYBJC20500).

Supporting Information Available. Preparation and characterization of graphene oxide nanosheets and palygorskite nanorods; supplementary figures of cross-section SEM, AFM force-mapping contact angle hysteresis, and underwater captive air contact angles; evaluation of membrane stability; size and distribution of different emulsified oil droplets. This material is available free of charge via the Internet at http://pubs.acs.org.

References (1) Lerf, A.; He, H.; Forster, M.; Klinowski, J. Structure of Graphite Oxide Revisited. J. Phys. Chem.

B 1998, 102, 4477-4482.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(2) Dreyer, D. R.; Park, S.; Bielawski, C. W.; Ruoff, R. S. The Chemistry of Graphene Oxide. Chem.

Soc. Rev. 2010, 39, 228-240. (3) Park, S.; Lee, K.-S.; Bozoklu, G.; Cai, W.; Nguyen, S. T.; Ruoff, R. S. Graphene Oxide Papers Modified by Divalent Ions-Enhancing Mechanical Properties via Chemical Cross-Linking. ACS

Nano 2008, 2, 572-578. (4) Dong, Z.; Wang, D.; Liu, X.; Pei, X.; Chen, L.; Jin, J. Bio-Inspired Surface-Functionalization of Graphene Oxide for the Adsorption of Organic Dyes and Heavy Metal Ions with a Superhigh Capacity. J. Mater. Chem. A 2014, 2, 5034-5040. (5) Pei, S.; Zhao, J.; Du, J.; Ren, W.; Cheng, H.-M. Direct Reduction of Graphene Oxide Films into Highly Conductive and flexible Graphene Films by Hydrohalic Acids. Carbon 2010, 48, 4466-4474. (6) Gong, T.; Lam, D. V.; Liu, R.; Won, S.; Hwangbo, Y.; Kwon, S.; Kim, J.; Sun, K.; Kim, J.-H.; Lee, S.-M.; Lee, C. Thickness Dependence of the Mechanical Properties of Free-Standing Graphene Oxide Papers. Adv.Funct.Mater. 2015, 25, 3756-3763. (7) Cheng, Q.; Duan, J.; Zhang, Q.; Jiang, L. Learning from Nature: Constructing Integrated Graphene-Based Artificial Nacre. ACS Nano 2015, 9, 2231-2234. (8) Smith, Z. P.; Freeman, B. D. Graphene Oxide: A New Platform for High-Performance Gas- and Liquid-Separation Membranes. Angew. Chem. Int. Ed. 2014, 53, 10286-10288. (9) Dikin, D. A.; Stankovich, S.; Zimney, E. J.; Piner, R. D.; Dommett, G. H. B.; Evmenenko, G.; Nguyen, S. T.; Ruoff, R. S. Preparation and Characterization of Graphene Oxide Paper. Nature 2007,

448, 457-460. (10) Hegab, H. M.; Zou, L. Graphene Oxide-Assisted Membranes: Fabrication and Potential Applications in Desalination and Water Purification. J. Membr. Sci. 2015, 484, 95-106. (11) Mahmoud, K. A.; Mansoor, B.; Mansour, A.; Khraisheh, M. Functional Graphene Nanosheets: The Next Generation Membranes for Water Desalination. Desalination 2015, 356, 208-225.


Page 20 of 27

Page 21 of 27

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(12) Huang, H.; Ying, Y.; Peng, X. Graphene Oxide Nanosheet: An Emerging Star Material for Novel Separation Membranes. J. Mater. Chem. A 2014, 2, 13772-13782. (13) Shao, J.-J.; Lv, W.; Yang, Q.-H. Self-Assembly of Graphene Oxide at Interfaces. Adv. Mater. 2014, 26, 5586-5612. (14) Compton, O. C.; Nguyen, S. T. Graphene Oxide, Highly Reduced Graphene Oxide, and Graphene: Versatile Building Blocks for Carbon-Based Materials. Small 2010, 6, 711-723. (15) Perreault, F.; Fonseca de Faria, A.; Elimelech, M. Environmental Applications of Graphene-Based Nanomaterials. Chem. Soc. Rev. 2015, 44, 5861-5896. (16) Sun, P.; Zhu, M.; Wang, K.; Zhong, M.; Wei, J.; Wu, D.; Xu, Z.; Zhu, H. Selective Ion Penetration of Graphene Oxide Membranes. ACS Nano 2013, 7, 428-437. (17) Yeh, C.-N.; Raidongia, K.; Shao, J.; Yang, Q.-H.; Huang, J. On the Origin of the Stability of Graphene Oxide Membranes in Water. Nat. Chem. 2015, 7, 166-170. (18) Huang, H.; Mao, Y.; Ying, Y.; Liu, Y.; Sun, L.; Peng, X. Salt Concentration, pH and Pressure Controlled Separation of Small Molecules through Lamellar Graphene Oxide Membranes. Chem.

Commun. 2013, 49, 5963-5965. (19) Wang, Y.; Chen, S.; Qiu, L.; Wang, K.; Wang, H.; Simon, G. P.; Li, D. Graphene-Directed Supramolecular Assembly of Multifunctional Polymer Hydrogel Membranes. Adv.Funct.Mater. 2015,

25, 126-133. (20) Nair, R. R.; Wu, H. A.; Jayaram, P. N.; Grigorieva, I. V.; Geim, A. K. Unimpeded Permeation of Water Through Helium-Leak-Tight Graphene-Based Membranes. Science 2012, 335, 442-444. (21) Liu, H.; Wang, H.; Zhang, X. Facile Fabrication of Freestanding Ultrathin Reduced Graphene Oxide Membranes for Water Purification. Adv. Mater. 2015, 27, 249-254. (22) Han, Y.; Xu, Z.; Gao, C. Ultrathin Graphene Nanofiltration Membrane for Water Purification.

Adv.Funct.Mater. 2013, 23, 3693-3700.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(23) Huang, Y.; Li, H.; Wang, L.; Qiao, Y.; Tang, C.; Jung, C.; Yoon, Y.; Li, S.; Yu, M. Ultrafiltration Membranes with Structure-Optimized Graphene-Oxide Coatings for Antifouling Oil/Water Separation. Adv. Mater. Interfaces 2015, 2, 1400433 (24) Joshi, R. K.; Carbone, P.; Wang, F. C.; Kravets, V. G.; Su, Y.; Grigorieva, I. V.; Wu, H. A.; Geim, A. K.; Nair, R. R. Precise and Ultrafast Molecular Sieving Through Graphene Oxide Membranes.

Science 2014, 343, 752-754. (25) Mi, B. Graphene Oxide Membranes for Ionic and Molecular Sieving. Science 2014, 343, 740-742. (26) Wei, N.; Peng, X.; Xu, Z. Understanding Water Permeation in Graphene Oxide Membranes. ACS

Appl. Mater. Interfaces 2014, 6, 5877-5883. (27) Ying, Y.; Sun, L.; Wang, Q.; Fan, Z.; Peng, X. In-Plane Mesoporous Graphene Oxide Nanosheet Assembled Membranes for Molecular Separation. RSC Adv. 2014, 4, 21425-21428. (28) Cohen-Tanugi, D.; Grossman, J. C. Water Desalination across Nanoporous Graphene. Nano Lett. 2012, 12, 3602-3608. (29) Li, H.; Huang, Y.; Mao, Y.; Xu, W. L.; Ploehn, H. J.; Yu, M. Tuning the Underwater Oleophobicity of Graphene Oxide Coatings via UV Irradiation. Chem. Commun. 2014, 50, 9849-9851. (30) Gao, S. J.; Qin, H.; Liu, P.; Jin, J. SWCNT-Intercalated GO Ultrathin Films for Ultrafast Separation of Molecules. J. Mater. Chem. A 2015, 3, 6649-6654. (31) Xu, C.; Xu, Y.; Zhu, J. Photocatalytic Antifouling Graphene Oxide-Mediated Hierarchical Filtration Membranes with Potential Applications on Water Purification. ACS Appl. Mater. Interfaces 2014, 6, 16117-16123. (32) Huang, H.; Song, Z.; Wei, N.; Shi, L.; Mao, Y.; Ying, Y.; Sun, L.; Xu, Z.; Peng, X. Ultrafast Viscous Water Flow through Nanostrand-Channelled Graphene Oxide Membranes. Nat. Commun. 2013, 4, 2979.


Page 22 of 27

Page 23 of 27

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(33) Han, Y.; Jiang, Y.; Gao, C. High-flux Graphene Oxide Nanofiltration Membrane Intercalated by Carbon Nanotubes. ACS Appl. Mater. Interfaces 2015, 7, 8147-8155. (34) Xu, C.; Cui, A.; Xu, Y.; Fu, X. Graphene Oxide-TiO2 Composite Filtration Membranes and Their Potential Application for Water Purification. Carbon 2013, 62, 465-471. (35) Darmanin, T.; Guittard, F. Superhydrophobic and Superoleophobic Properties in Nature. Mater.

Today 2015, 18, 273-285. (36) Liu, K.; Jiang, L. Bio-Inspired Self-Cleaning Surfaces. Annu. Rev. Mater. Res. 2012, 42, 231-263. (37) Lejars, M.; Margaillan, A.; Bressy, C. Fouling Release Coatings: A Nontoxic Alternative to Biocidal Antifouling Coatings. Chem. Rev. 2012, 112, 4347-4390. (38) Ma, S.; Ye, Q.; Pei, X.; Wang, D.; Zhou, F. Antifouling on Gecko's Feet Inspired Fibrillar Surfaces: Evolving from Land to Marine and from Liquid Repellency to Algae Resistance. Adv.

Mater. Interfaces 2015, 1500257. (39) Tang, Y. P.; Chan, J. X.; Chung, T. S.; Weber, M.; Staudt, C.; Maletzko, C. Simultaneously Covalent and Ionic Bridging towards Antifouling of GO-Imbedded Nanocomposite Hollow Fiber Membranes. J. Mater. Chem. A 2015, 3, 10573-10584. (40) Zhao, X.; Su, Y.; Cao, J.; Li, Y.; Zhang, R.; Liu, Y.; Jiang, Z. Fabrication of Antifouling Polymer-Inorganic Hybrid Membranes through the Synergy of Biomimetic Mineralization and Nonsolvent Induced Phase Separation. J. Mater. Chem. A 2015, 3, 7287-7295. (41) Leng, C.; Hung, H.-C.; Sun, S.; Wang, D.; Li, Y.; Jiang, S.; Chen, Z. Probing the Surface Hydration of Nonfouling Zwitterionic and PEG Materials in Contact with Proteins. ACS Appl. Mater.

Interfaces 2015, 7, 16881-16888. (42) Jiang, S.; Cao, Z. Ultralow-Fouling, Functionalizable, and Hydrolyzable Zwitterionic Materials and Their Derivatives for Biological Applications. Adv. Mater. 2009, 22, 920-932.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(43) Li, Y.; Lu, Q.; Liu, H.; Wang, J.; Zhang, P.; Liang, H.; Jiang, L.; Wang, S. Antibody-Modified Reduced Graphene Oxide Films with Extreme Sensitivity to Circulating Tumor Cells. Adv. Mater. 2015, 27, 6848-6854. (44)Xue, Z.; Cao, Y.; Liu, N.; Feng, L.; Jiang, L. Special Wettable Materials for Oil/Water Separation.

J. Mater. Chem. A 2014, 2, 2445-2460. (45) Xue, Z.; Wang, S.; Lin, L.; Chen, L.; Liu, M.; Feng, L.; Jiang, L. A Novel Superhydrophilic and Underwater Superoleophobic Hydrogel-Coated Mesh for Oil/Water Separation. Adv. Mater. 2011, 23, 4270-4273. (46) Gao, X.; Xu, L.-P.; Xue, Z.; Feng, L.; Peng, J.; Wen, Y.; Wang, S.; Zhang, X. Dual-Scaled Porous Nitrocellulose Membranes with Underwater Superoleophobicity for Highly Efficient Oil/Water Separation. Adv. Mater. 2014, 26, 1771-1775. (47) Fan, J.-B.; Song, Y.; Wang, S.; Meng, J.; Yang, G.; Guo, X.; Feng, L.; Jiang, L. Directly Coating Hydrogel on Filter Paper for Effective Oil-Water Separation in Highly Acidic, Alkaline, and Salty Environment. Adv.Funct.Mater. 2015, 25, 5368-5375. (48) Chen, S.; Zhu, J.; Wu, X.; Han, Q.; Wang, X. Graphene Oxide-MnO2 Nanocomposites for Supercapacitors. ACS Nano 2010, 4, 2822-2830. (49) Wang, R.; Li, Z.; Liu, W.; Jiao, W.; Hao, L.; Yang, F. Attapulgite-Graphene Oxide Hybrids as Thermal and Mechanical Reinforcements for Epoxy Composites. Compos. Sci. Technol. 2013, 87, 29-35. (50) Li, Z.; Liu, Z.; Sun, H.; Gao, C. Superstructured Assembly of Nanocarbons: Fullerenes, Nanotubes, and Graphene. Chem. Rev. 2015, 115, 7046-7117. (51) Kim, J.; Cote, L. J.; Kim, F.; Yuan, W.; Shull, K. R.; Huang, J. Graphene Oxide Sheets at Interfaces. J. Am. Chem. Soc. 2010, 132, 8180-8186.


Page 24 of 27

Page 25 of 27

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(52) Qiu, L.; Yang, X.; Gou, X.; Yang, W.; Ma, Z.-F.; Wallace, G. G.; Li, D. Dispersing Carbon Nanotubes with Graphene Oxide in Water and Synergistic Effects between Graphene Derivatives.

Chem. Eur. J. 2010, 16, 10653-10658. (53) Wang, S.; Liu, K.; Yao, X.; Jiang, L. Bioinspired Surfaces with Superwettability: New Insight on Theory, Design, and Applications. Chem. Rev. 2015, 115, 8230-8293. (54) Liu, Y.; Zhou, J.; Zhu, E.; Tang, J.; Liu, X.; Tang, W. Covalently Intercalated Graphene Oxide for Oil-Water Separation. Carbon 2015, 82, 264-272. (55) Wang, W.; Wang, A. Nanocomposite of Carboxymethyl Cellulose and Attapulgite as A Novel pH-Sensitive Superabsorbent: Synthesis, Characterization and Properties. Carbohydr. Polym. 2010,

82, 83-91. (56) Li, J.; Yan, L.; Li, H.; Li, W.; Zha, F.; Lei, Z. Underwater Superoleophobic Palygorskite Coated Meshes for Efficient Oil/Water Separation. J. Mater. Chem. A 2015, 3, 14696-14702. (57) Zhang, Y.; Zhao, J.; Chu, H.; Zhou, X.; Wei, Y. Effect of Modified Attapulgite Addition on the Performance of a PVDF Ultrafiltration Membrane. Desalination 2014, 344, 71-78. (58) Liu, C.; Yang, J.; Tang, Y.; Yin, L.; Tang, H.; Li, C. Versatile Fabrication of the Magnetic Polymer-Based Graphene Foam and Applications for Oil-Water Separation. Colloid Surface A 2015,

468, 10-16. (59) Li, J.; Yan, L.; Hu, W.; Li, D.; Zha, F.; Lei, Z. Facile Fabrication of Underwater Superoleophobic TiO2 Coated Mesh for Highly Efficient Oil/Water Separation. Colloid Surface A 2016, 489, 441-446. (60) Xu, L.-P.; Dai, B.; Fan, J.; Wen, Y.; Zhang, X.; Wang, S. Capillary-Driven Spontaneous Oil/Water Separation by Superwettable Twines. Nanoscale 2015, 7, 13164-13167. (61) Yong, J.; Chen, F.; Yang, Q.; Zhang, D.; Farooq, U.; Du, G.; Hou, X. Bioinspired Underwater Superoleophobic Surface with Ultralow Oil-Adhesion Achieved by Femtosecond Laser Microfabrication. J. Mater. Chem. A 2014, 2, 8790-8795.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(62) Palama, I. E.; D'Amone, S.; Arcadio, V.; Caschera, D.; Toro, R. G.; Gigli, G.; Cortese, B. Underwater Wenzel and Cassie Oleophobic Behaviour. J. Mater. Chem. A 2015, 3, 3854-3861. (63) Jiang, T.; Guo, Z.; Liu, W. Biomimetic Superoleophobic Surfaces: Focusing on Their Fabrication and Applications. J. Mater. Chem. A 2015, 3, 1811-1827. (64) Zhu, Y.; Zhang, F.; Wang, D.; Pei, X. F.; Zhang, W.; Jin, J. A Novel Zwitterionic Polyelectrolyte Grafted PVDF Membrane for Thoroughly Separating Oil from Water with Ultrahigh Efficiency. J.

Mater. Chem. A 2013, 1, 5758-5765. (65) Wang, B.; Liang, W.; Guo, Z.; Liu, W. Biomimetic Super-Lyophobic and Super-Lyophilic Materials Applied for Oil/Water Separation: A New Strategy Beyond Nature. Chem. Soc. Rev. 2015,

44, 336-361.


Page 26 of 27

Page 27 of 27

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


TOC graphic


Free-Standing Graphene Oxide-Palygorskite Nanohybrid Membrane

Recommend Documents