Comparison of Hydrophilicity and Mechanical Properties of

Subscriber access provided by Binghamton University | Libraries

Article

Comparison of hydrophilicity and mechanical properties of nanocomposite membranes with cellulose nanocrystals (CNCs) and carbon nanotubes (CNTs) Langming Bai, Nathan Bossa, Fangshu Qu, Judy Winglee, Guibai Li, Kai Sun, Heng Liang, and Mark R. Wiesner Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.6b04280 • Publication Date (Web): 30 Nov 2016 Downloaded from http://pubs.acs.org on December 3, 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.

Environmental Science & Technology 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 31

Environmental Science & Technology

1

Comparison of hydrophilicity and mechanical properties of

2

nanocomposite membranes with cellulose nanocrystals (CNCs) and

3

carbon nanotubes (CNTs)

4

Langming Bai,†,‡,§ Nathan Bossa,‡,§ Fangshu Qu,† Judy Winglee,‡,§ Guibai Li,† Kai Sun,†,║ Heng

5

Liang,*† Mark R. Wiesner* ‡,§

6

†

7

of Technology, 73 Huanghe Road, Nangang District, Harbin, 150090, P.R. China

8

‡

9

27708, United States

,

State Key Laboratory of Urban Water Resource and Environment (SKLUWRE), Harbin Institute

Department of Civil and Environmental Engineering, Duke University, Durham, North Carolina

10

§

11

North Carolina 27708, United States

12

║

13

Technology, 73 Huanghe Road, Nangang District, Harbin, 150090, P.R. China

Center for the Environmental Implications of NanoTechnology (CEINT), Duke University, Durham,

Nanotechnology Innovation Center for environment and ecosystem, (NICE2), Harbin Institute of

14 15 16 17 18

*Corresponding author: Tel.: +86 451 86282252; fax: +86 451 86282252; e-mail:

19

[email protected]

20

*Corresponding author: Phone: 919-660-5292; fax: 919-660-5219; e-mail: [email protected].

21

ACS Paragon Plus Environment


22

23

1


Page 2 of 31

Page 3 of 31


24

ABSTRACT

25

The inherent properties of hydrophilicity and mechanical strength of cellulose nanocrystals (CNCs)

26

make them a possible alternative to carbon nanotubes (CNTs) that may present fewer objections to

27

application water treatment membranes. In this work, the hydrophilicity and mechanical properties

28

of CNCs and CNTs nanocomposite polyethersulfone (PES) membranes were characterized and

29

compared. Membrane pore geometry was analyzed by scanning electron microscopy (SEM).

30

Overall porosity and mean pore radius were calculated based on a wet-dry method. Results

31

showed that PES polymers were loosely packed in the top layer of both the CNC- and CNT-

32

composite membranes (CNC-M) and (CNT-M). The porosity of the CNC-M was greater than that

33

of the CNT-M. Membrane hydrophilicity, measured by water contact angle, free energy of

34

cohesion and water flux was increased through the addition of either CNCs or functionalized

35

CNTs to an otherwise hydrophobic polymer membrane. The hydrophilicity of the CNC-M was

36

greater than the CNT-M. In addition, the Young’s modulus and tensile strength was enhanced for

37

both the CNC-M and CNT-M. While smaller concentrations of CNTs were required to achieve an

38

equal increase in Young’s modulus compared with the CNCs, the elasticity of the CNC-composite

39

membranes was greater.

2



40

INTRODUTION

41

Membrane technologies have been broadly applied in water treatment to achieve disinfection, salt

42

removal, organic removal, liquid-solid separation and gas transfer.1,2 Pressure-driven membrane

43

process can be highly automated, require a small plant footprint and are readily adaptable to

44

modular configurations at various system scales.3 They have been widely applied for water and

45

wastewater treatment4, reuse and desalination throughout the world.5

46

Nanomaterials, in particular carbon nanotubes (CNTs), have been incorporated into membranes to

47

improve membrane permeability and selectivity as well as to increase durability of the

48

membranes.6 CNTs exhibit high tensile strength with a reported Young’s modulus of 1 TPa and a

49

strength of 300 GPa.7 Both multi-walled (MW) and single-walled (SW) CNTs can be used as

50

reinforcing fillers for polymeric membranes by capitalizing on the load transfer to CNTs within

51

the composite.8-10 Increases in the Young’s modulus of 140% over that of pure polysulfone (PSf)

52

membrane have been reported at 2.0 wt % content of MWCNTs in the composite.11 Kumar et al.12

53

reported that the tensile strength of a Poly(p-phenylene benzobisoxazole (PBO)/SWCNTs

54

composite was about 50% higher than pure PBO. CNTs are often been functionalized, to improve

55

the distribution of CNTs in the composite and/or to impart specific properties such as reactivity or

56

hydrophilicity. Common functional groups include carboxylate (COOH), hydroxyl (OH), amine

57

(NH2) and polyethylene glycol (PEG). Functionalized CNTs maintain the strength characteristics

58

of pristine CNTs,13 while imparting the desired characteristic to the composite materials.

59

Functionalized MWCNTs incorporated in PES membranes increased the membrane hydrophilicity,

60

pure water flux,14 anti-fouling properties and salt rejection.15 However, some studies have reported

61

that CNTs exposure increases the risk of fibrosis, genotoxicity, cytotoxicity, and oxidative stress in 3


Page 4 of 31

Page 5 of 31


62

the lung.16,17 These possible health effects have led to concern about the use of CNTs in water

63

treatment membranes where some have speculated that CNTs might be released over time. In

64

addition, the energy requirements for CNT production and the some of the feed stacks involved

65

suggest that CNTs might not be desirable materials to use from the standpoint of an environmental

66

life cycle assessment.

67

Cellulose nanomaterials (CNs) may be an environmentally preferable alternative to CNT for

68

environmental engineering applications. They are made from renewable and sustainable resources,

69

such as wood, cotton, hemp, wheat, and straw,

70

have lower environmental, health and safety footprints.19 Cellulose nanomaterials have desirable

71

mechanical properties, hydrophilic properties and can be produced at low cost. These attributes

72

make CNs an attractive alternative as additives for improving water filtration membranes.20

73

Generally, CNs can be categorized as cellulose nanocrystals (CNCs) or cellulose nanofibrils

74

(CNFs). CNCs are highly crystalline with fewer amorphous regions compared to CNFs. CNCs

75

exhibit excellent mechanical properties with a maximum Young’s modulus and strength reported

76

to be approximately 150 and 6 GPa, respectively.20-22 CNCs-based nanocomposite membranes

77

have been reported to enhance mechanical properties, specifically the Young’ modulus,23 tensile

78

strength,24 elongation25 and toughness.26 It is also reported that electrospun membranes coated

79

with CNCs can significantly reduce biofouling and biofilm formation.27 Chitosan ultrafiltration

80

membranes blended with CNCs show great efficiency for the removal of dyes28. In addition, at an

81

approximate cost of $1/g, CNCs are potentially less expensive fillers than CNTs which may cost

82

from $8 to $15/g.

83

It is necessary to investigate the possibility for CNCs being an alternative to CNTs in composite

18

are biodegradable, non-petroleum based and

4



84

membranes. A direct comparison between the CNCs and CNTs nanocomposite membranes has not

85

been conducted to date. Previous studies usually emphasize improvements to membrane

86

performance, as measured by parameters such as water flux, organic removal, anti-fouling

87

properties and salt rejection with and without a given nano-filler. With respect to water treatment

88

membranes, insufficient attention has been devoted to the relative effects of CNCs and CNTs on

89

polymer-nanomaterials interactions, membrane morphologies, membrane hydrophilicity and

90

mechanical properties. The current study addresses the need for a direct comparison between

91

membranes fabricated using either CNTs or CNCs as nano-fillers.

92 93

MATERIALS AND METHODS

94

In this study, we compare CNCs and CNTs nanocomposite membranes that are fabricated and

95

evaluated under the similar conditions. SEM and atomic force microscopy (AFM) were used to

96

characterize and compare membrane morphologies of the CNC-M and CNT-M. The overall

97

porosities and mean pore radius of CNC-M and CNT-M were calculated and compared.

98

Hydrophilicity of membranes were evaluated and compared by testing contact angle, surface free

99

energy of cohesion and pure water flux. Mechanical properties including Young’s modulus, tensile

100

strength, elongation and toughness were investigated.

101

Materials

102

PES with a molecular weight of 58,000 g/mol was supplied from Goodfellow Cambridge Ltd.

103

(Huntingdon, England). Dimethyl formamide (DMF, Sigma-Aldrich Chemical Company, USA)

104

was used as a solvent for the polymers. Polyvinylpyrrolidone (PVP) with a molecular weight of

105

360,000 g/mol, purchased from Sigma-Aldrich, was used as an additive to increase hydrophilicity 5


Page 6 of 31

Page 7 of 31


106

and permeability of the membranes. CNCs, as slurries of 6.2 wt% solids, were obtained from the

107

Process Development Center of the University of Maine (Maine, USA). According to the

108

manufacture’s specifications, the CNCs were made from wood pulp with dimensions of

109

approximately 5 nm in diameter and 150 to 200 nm length. Multi-wall carbon nanotubes

110

(MWCNTs) with –OH groups were supplied from Cheap Tubes Inc. (Vermont, USA) with an

111

outer diameter of 20 to 30 nm and lengths ranging from 10 to 30 µm. According to the

112

manufacture’s specifications, functionalized CNTs were produced by catalyzed chemical vapor

113

deposition. Acid chemistry was used to purify or functionalize CNTs.

114

Characterization of CNCs and CNTs

115

CNCs and CNTs were characterized by XRD, FTIR, and TEM. Equipment information and

116

measurement procedures were described in Supporting Information (SI).

117

Fabrication and characterization of the membranes

118

Membrane fabrication

119

Membranes were fabricated via phase inversion in a water coagulation bath. The composition of

120

casting solution was listed in Table S1 and details of fabrication procedures were described in SI.

121

The resultant membranes were named according to their weight concentration of CNCs or CNTs.

122

For example, the 0.5 CNC-M was fabricated with 0.5 wt% of CNCs. A control PES membrane

123

(named Control-M) with no CNCs or CNTs was also fabricated via the same procedures. The

124

weight percentages of the membrane additives are based relative to the mass of PES.

125

Morphologies of the membranes

126

Morphologies of the membranes were examined by scanning electron microscope (SEM, FEI

127

XL30 SEM-FEG) with an accelerating voltage set at 10 KV. To obtain top views, membrane 6



Page 8 of 31

128

samples were dried at room temperature. To obtain the cross-sectional views, membrane samples

129

were fractured after freezing using liquid nitrogen. All the membrane specimens were sputtered

130

with gold (Hummer 6.2 Vacuum Sputter) before the tests. Surface roughness of the membranes

131

was tested using AFM. Details are described in supporting information.

132

Porosity and pore size of the membranes

133

The overall porosity (ε) was determined by the gravimetric method using equation (1).29

134

ԑ=

135

Where W1 is the weight of the wet membrane (g), W2 is the weight of the dry membrane (g), V is

136

the volume of the membrane (cm3) and dw is the pure water density (0.998 g/cm3). The presented

137

data are the means of triplicate measurements.

138

The mean pore radius of the membrane (rm) was estimated using the filtration velocity method

139

where radius is calculated using Guerout–Elford–Ferry equation (2).30

140

=

141

In this equation, ԑ is the overall porosity (%), ƞ is the water viscosity, 1.0016×10-3 Pa∙s, Ɩ is the

142

membrane thickness (2×10-4 m), Q is the volume of the permeate water per second in m3/s, A is

143

the effective area of the membrane in m2 and P is the working pressure (105 Pa).

144

The specific measure of surface porosity (%) was calculated by the analysis of the top surface

145

SEM images using ImageJ software (Version 1.49, National Institute of Health, USA). The images

146

were processed by first conducting a segmentation procedure to isolate the voids from the

147

membrane polymer. The output of this pore segmentation is a binary image where the pores and

148

the solid matrix are imaged as white (binary value = 1) and black (binary value = 0) pixels,

149

respectively. The porosity corresponds to the percentage of void pixel in the image. The data

W1 - W2

(1)

V × dw

2.9-1.75ԑ8ƞlQ

(2)

ԑ ×A×P

7


Page 9 of 31


150

reported are the means from five images measurements.

151

Hydrophilicity of the membranes

152

Contact angle

153

The hydrophilicity of the membranes was quantified by contact angle measurements using a

154

contact angle goniometer (Kruss EasyDrop Goniometer, Hamburg, Germany) by placing a drop of

155

DI water (2 µL) on the membrane surface. The measurement range of the contact angle

156

goniometer is 0-180° and the deviation is the measured value ± 0.1°. At least 10 contact angle

157

measurements were performed and recorded for each type of membrane analyzed. The highest and

158

lowest values were discarded and the mean value of the 8 remaining angles was reported.

159

Interfacial free energy of cohesion

160

Quantification of the total interfacial free energy of cohesion (GTOT ) reflects the free energy due

161

to the non-electrostatic interactions of the solute in the water and the membrane phase.31,32 It is

162

another method for determining the hydrophilicity/hydrophobicity of the membrane. In this study,

163

GTOT is composed of Lifshitz-van der Waals force (LW) and acid–base (AB) components of

164

interfacial free energy, as can be described in equation (3).33

165

GTOT =GLW +GAB

166

Positive values of GTOT indicate that the membrane is hydrophilic and negative values indicate

167

that the membrane is hydrophobic.33,34 The values of G

168

equation (4) and (5), respectively.34

169

GLW = -2 γLW -γLW l

170

GAB =2γ+l (2γ − γl ) + 2γl (2γ+ -γ+l ) − 4γ+ γ

171

Where γLW , γ+ and γ- are surface tension parameters calculated using Young-Dupré equation

-

(3)

LW

AB

and G can be calculated by

2

(4) -

-

-

8


(5)


Page 10 of 31

172

(6)31 by measuring the contact angles of three probe liquids of known surface tension. In this study,

173

DI water, diiodomethane and formamide were used to calculate GTOT.

174

1+ cos θγTOT =2 γLW γLW +γ+ γl +γ γ+l l

175

Where θ is the contact angle of the three probe liquids, γ+ is electron acceptor and γ- is electron

176

donor, γTOT is the total surface tension and can be calculated by the three probe liquids with

177

known surface tension parameters by equation (7) and (8).

178

γTOT =γLW +γAB

(7)

179

γAB =2γ+ γ-

(8)

180

Membrane permeability

181

To evaluate the permeability of the fabricated membranes, dead-end filtration tests were

182

performed in a cell (Sterlitech™ HP4750, Sterlitech, USA) with an effective volume of 300 mL.

183

The permeate volume was automatically weighed and recorded via a data acquisition system at

184

interval of 1 second over a range of applied pressures of 0.1, 0.2, 0.3, 0.4 and 0.5 MPa. The water

185

flux was calculated as in equation (9).

186

J=V/(A×∆t)

187

Where J is the permeation flux (L/m2 h) (LMH), V is the volume of the permeate (L), A is the

188

membrane area (m2) and ∆t is the permeate collection interval (h).

189

Mechanical properties of the membranes

190

Mechanical properties of membranes were measured using a Micro-Strain Analyzer (TA

191

instruments RSA III, USA). The maximum force of the Micro-strain analyzer is 35 N with force

192

and strain resolution 0.0001 N and 1 nm, respectively. The specimens were cut into 10 mm wide

193

and 25 mm length rectangular strips. Maximum force applied was 500 gm and speed of test was

(6)

(9)

9


Page 11 of 31


194

set at a rate of 0.2 mm/min at 22 °C. Each test was replicated at least 10 times. Four properties

195

including Young’s modulus, tensile strength, elongation at break, and toughness were determined

196

from strain-stress relationships.

197

RESULTS AND DISCUSSIONS

198

CNCs and CNTs characterization

199

To characterize functional groups of CNCs and CNTs, FTIR analysis was performed and present

200

in Figure 1a. In the case of CNCs, the peaks at around 3341 and 2900 cm-1 are corresponded to O–

201

H and C–H stretching vibrations, respectively.35 The peaks observed at 1060 and 1645 cm-1 are the

202

pyranose ring ether band of cellulose and O–H stretching vibration of absorbed water.36 The

203

spectra of CNTs showed characteristic band at 1578 cm-1, which is attributed to the vibration of

204

the carbon skeleton. The presence of CH2/CH3 groups was indicated by peaks of 2850 and 2920

205

cm-1, which likely originated from defects generated in the graphitic structure.37 In addition, the

206

peaks at 3343 and 1090 cm-1 are related to the O–H and C–C–O stretching vibration,

207

respectively.38 FTIR results indicated hydrophilicity for both CNCs and CNTs.

208

TEM images showed the morphology of CNCs (Figure 1b, c) and CNTs (Figure 1d). A single

209

CNC particle showed rod-like structure with dimensions ranging from 200 to 300 nm in length

210

and around 15 to 30 nm in width. CNTs exhibited tube-like structure with diameter at around 20 to

211

30 nm and length in micro level.

10



212

b

c

d

213

100 nm

50 nm

100 nm

214

Figure 1. FTIR of CNCs and CNTs (a); TEM of CNCs (b) and (c); TEM of CNTs (d).

215 216

Membrane characterization

217

The morphological and structural characterization of fabricated membranes was based on SEM,

218

AFM, porosity and pore size investigation.

219

Membrane morphologies

220

To analyze the addition of CNCs and CNTs on the membrane microstructure, SEM images of the

221

top surfaces and cross-sections of the investigated membranes were compared. In top surface

222

images, the Control-M (Figure 2a) exhibited a smooth surface with pores uniformly distributed on

223

the membrane surface. In the cases of 0.5 CNC-M (Figure 2d) and 0.5 CNT-M (Figure 2g),

224

homogeneous surfaces with more pores could be found on the membrane surfaces. Well dispersed

225

CNCs and CNTs leading to homogeneous casting solution are responsible for the phenomenon. In 11


Page 12 of 31

Page 13 of 31


226

cross-sectional images (Figure 2b, e and h), all the membranes showed a typical asymmetric

227

porous structure, with a skin layer as the selective barrier, a finger-like substructure and a

228

sponge-like bottom support. It is generally considered that the resistance mass transfer of a porous

229

UF membrane is mainly determined by the characteristics of the top layer, i.e. its pore structure,

230

thickness and surface porosity. To better understand the pore structure of the top layer of the

231

fabricated membranes, enlarged images of top layer were captured. As can be seen in Figure 2c,

232

the Control-M exhibited a dense structure of its skin layer, probably due to the large amount of

233

water intake during preevaporation.39 However, the 0.5 CNC-M (Figure 2f) and the 0.5 CNT-M

234

(Figure 2i) showed a loose top layer with more porous structures. Magnified images of active

235

layer of the Control-M (Figure 2j) and 0.5 CNC-M (Figure 2k) were compared. The PES polymer

236

of the Control-M was densely packed, and few voids were observed; while the polymer of the 0.5

237

CNC-M was loosely arranged and many pores were seen. Visually, no distinct difference was

238

found in the pore structure of the top layer of the CNC-M and the CNT-M. Additionally, in both

239

membrane types, there was no relationship between the visual appearance of the top layer

240

structure and the additive concentration (Figure S2).

a

10 µm

500 nm

241

e

d

242

c

b

500 nm

f

10 µm

500 nm 12


500 nm


g

h

i

500 nm

243

Page 14 of 31

10 µm

j

500 nm

k

100 nm

100 nm

244 245 246 247 248 249

Figure 2. SEM images of Control-M (a-c); 0.5 CNC-M (d-f) and 0.5 CNT-M (g-i). In each row, the first image is the top membrane surface; the second image is the cross-section of membrane; and the third image zooms in the active layer. Higher Magnification was used to observe the active layer of Control-M (j) and 0.5 CNC-M (k).

250

Porosity and pore size of the membranes

251

Table 1 shows the porosity and mean pore radius data for the membranes. The Control-M

252

exhibited the lowest overall porosity, mean pore radius and surface porosity, respectively.

253

Increasing amounts of both CNCs and CNTs led to greater membrane pore size and porosity at the

254

surface (binary segmentation images in Figure S3) as well as in the bulk. This result is consistent

255

with the cross-sectional SEM images (Figure 2) which present a loosely packed active layer with

256

more pore structures of the CNC-M and CNT-M.

257

The difference in morphologies between the nanocomposite membranes and the Control-M can be

258

explained by the effects of hydrophilic CNCs and CNTs on the rate of exchange between solvent

259

and non-solvent during phase inversion. During phase inversion, the casting solution is rapidly

260

solidified at the interface between solvent and non-solvent due to concentration gradient of the 13


Page 15 of 31


261

components. Hydrophilic additives can generate weak points due to immitigable stresses produced

262

by shrinkage or syneresis and lead to formation of fracture points, which eventually develop into

263

pores.40 The addition of hydrophilic CNCs and CNTs could increase the demixing rate by

264

enhancing the thermodynamic instability, leading to the membranes with higher porosity, mean

265

pore radius and surface porosity.15 Similar results have been shown in a PES/ZnO UF membrane41

266

and a graphene oxide (GO)/PSf membrane bioreactor (MBR).42 In addition, with the same

267

addition content of nanomaterials, the porosity and pore size of the CNC-M were higher than the

268

CNT-M. This point might be attributed to an accelerated demixing process due to the more

269

hydrophilic CNC with abundant -OH groups.

270

Table 1. Porosity and mean pore radius of Control-M and Nanocomposite-M Polymer Solution

Overall porosity (%)

Surface porosity (%)

Mean pore radius (nm)

Control-M Nanocomposite-M Loading 0.5% 1.0% 2.0%

65 ± 1.0

15.1 ± 0.1

54.2 ± 0.7

CNC/CNT 76 ± 0.5/71 ± 1.0 77 ± 0.5/75 ± 0.3 79 ± 0.3/78 ± 0.3

CNC/CNT 17.7 ± 0.2/15.5 ± 0.1 19.6 ± 0.3/17.9 ± 0.1 20.5 ± 0.2/18.9 ± 0.2

CNC/CNT 60.9 ± 0.4/56.3 ± 0.7 81.2 ± 0.7/67.1 ± 0.3 81.5 ± 0.3/71.1 ± 0.2

271

Surface roughness

272

Membrane surface roughness was characterized by three-dimensional (3D) AFM images (Figure

273

S4). For better evaluation of the surface variations, mathematical analysis of the AFM images was

274

performed; the parameters are tabulated in Table S2. Parameters Rq, Ra, and Rmax represent the root

275

mean square of the height deviations, average plane roughness and the maximum roughness,

276

respectively. As evident from the results in Table S2, the Control-M exhibited the lowest surface

277

roughness with the Ra value of 4.9 nm. Membranes with higher concentrations of CNCs and CNTs

278

had greater surface roughness due to the enhancement of solvent and non-solvent exchange by

279

well dispersed hydrophilic CNCs and CNTs.14,43 With the same addition concentration, CNC-M 14



280

were smoother than the CNT-M. As mentioned above, the length of the CNC rod is orders of

281

magnitude smaller than that of the CNTs, leading to the better miscibility of CNCs in casting

282

solution. Hence, the difference between surface roughness of CNC-M and CNT-M may be due to

283

better miscibility and dispersion between the CNCs and the solvent, resulting in a more

284

homogeneous casting solution. It should be noted that surface roughness has an effect on the

285

contact angle measurement and thus influences the evaluation of hydrophilicity of the membrane

286

surface.44 However, the surface roughness of the CNC-M and CNT-M only increased slightly, and

287

as a result, the effect of surface roughness on the hydrophilicity of the membranes was not

288

investigated in this study.

289

Hydrophilicity of the membranes

290

Contact angle

291

The hydrophilicity of the membrane surface can be evaluated by water contact angle

292

measurements. The contact angle was measured immediately after placing a drop of DI water onto

293

the membrane surface. Lower contact angle measurements indicate that the membrane is

294

hydrophilic while higher contact angle merriments indicate that the membrane is hydrophobic. As

295

can be seen in Figure 3a, the Control-M showed the highest contact angle of 56.7 °, indicating it is

296

the most hydrophobic of all the investigated membranes. Compared with the Control-M, water

297

contact angles of the CNC-M and the CNT-M declined which suggested more hydrophilic surfaces

298

of the composite membranes due to the hydrophilic –OH groups of CNC and CNT, which is

299

confirmed by FTIR results. The increase in hydrophilicity may be due to the migration of

300

nanomaterials to the membrane surface during the phase inversion process.29 It can be found that

301

the contact angles of both the CNC-M and the CNT-M decreased as the increasing of 15


Page 16 of 31

Page 17 of 31


302

nanomaterials content; and with the same addition content, the CNC-M showed a more

303

hydrophilic surface than the CNT-M.

304

Addition of 0.5 wt% of nanomaterials decreased the contact angle of the 0.5 CNC-M and the 0.5

305

CNT-M from 56.7 ° to 50.8 ° and 56.1 °, respectively. The considerable decrease in contact angle

306

of the 0.5 CNC-M indicated that in low concentrations, CNCs were more effective in increasing

307

the membrane hydrophobicity. However, with the addition of 1.0 wt%, contact angle of the

308

CNT-M was comparable with that of the CNC-M. The large increase in hydrophilicity of the 1.0

309

CNT-M was probably due to the increased amount of CNT which were sufficient to anchor more

310

hydrophilic PVP of the membranes during the phase inversion process.45 In the case of 2.0 wt%

311

nanomaterials addition, the contact angle of the 2.0 CNC-M was less than that of the 2.0 CNT-M,

312

probably due to the greater hydrophilic of CNCs. In addition, possible agglomeration of CNTs in

313

high concentrations may have decreased the effective surface of CNTs, leading to the reduction of

314

functional groups of membrane surface.46

315 316 317 318 319

Figure 3. (a) Contact angle of Control-M and Nanocomposite-M (error bars represent the standard deviations from the means) (n=8). (b) Pure water flux of Control-M and Nanocomposite-M at different TMP levels (error bars represent the standard deviations from the means) (n=3).

320

Interfacial free energy of cohesion

321

The interfacial free energy of cohesion is the interaction free energy when two surfaces of the 16



322

same material are immersed in water and brought into contact.47 The values of free energy can

323

provide a quantitative insight in terms of hydrophilicity/hydrophobicity of the membranes. A

324

negative value for G131 represents the thermodynamically unstable state, while positive value

325

represents a stable state.48 Table 2 lists the surface energy parameters and the interfacial free

326

energy of cohesion derived from multiple contact angle measurements. As can be seen, the

327

2 G 131 of the Control-M (-27.64 mJ/m ) was negative, indicating its hydrophobic surface nature.

328

By contrast, the G 131 of the nanocomposite membranes exhibited positive values, indicating

329

their hydrophilic characteristics due to the addition of hydrophilic CNCs and CNTs. Similar

330

results were reported for a PES UF membrane blended with cellulose fibrils43 and a CNT/PES

331

composite membrane.49 The free energy values of both types of nanocomposite membranes were

332

greater as the he loading content of the nanomaterials increased (Table 2). A comparison between

333

the G 131 values with the same amount of nanomaterial shows that, the G131 of CNC-Ms

334

was greater than that of CNT-Ms, suggesting higher hydrophilicity of the CNC-M. The free energy

335

results were in good agreement with water contact angle data shown in Figure 3a, demonstrating a

336

more hydrophilic surface of the CNC-Ms.

17


Page 18 of 31

Page 19 of 31


Table 2. Surface energy parameters and interfacial free energy of cohesion (unit: mJ/m2) Surface Control-M Nanocomposite-M Loading 0.5% 1.0% 2.0%

γLW

γ+

γ-

γAB

γTot

GLW 131

GAB 131

G 131

43.16

2.18

13.08

10.67

53.83

-7.22

-20.42

-27.64

CNC/CNT 49.41/45.97 48.78/48.37 46.74/46.88

CNC/CNT 0.63/0.23 0.86/0.29 1.26/0.04

CNC/CNT 36.68/33.06 41.67/37.05 50.35/38.19

CNC/CNT 9.58/5.55 11.99/6.6 15.92/2.48

CNC/CNT 58.99/51.52 60.77/54.97 62.66/49.36

CNC/CNT -5.38/-8.91 -10.71/-10.44 -9.38/-9.48

CNC/CNT 17.16/12.79 23.17/18.71 32.14/21.92

CNC/CNT 11.78/3.88 12.46/8.27 22.86/12.44

18



337

Pure water flux

338

The variation of pure water flux under different transmembrane-pressure (TMP) levels of the

339

Control-M and the Nanocomposite-M is presented in Figure 3b. The flux increased linearly with

340

the TMP (details in Figure S5) indicating that the membrane pores were not compressed or

341

narrowed during the filtration process. The flux of the Control-M increased from around 242 to

342

1240 LMH as TMP rise from 0.1 to 0.5 MPa. The flux of the nanocomposite membranes was

343

greater for membranes with higher CNC or CNT contents. The maximum fluxes were 3524 and

344

2833 LMH at TMP of 0.5 MPa with the 2.0 CNC-M and 2.0 CNT-M, respectively. The increase in

345

flux of the CNC-M and the CNT-M was due to the enhanced porous structure and improved

346

hydrophilicity due to the addition of the nanomaterials. A comparison of membranes with the same

347

amount of added nanomaterials shows that, the pure water flux of a CNC-M was greater than that

348

of a CNT-M. This finding is consistent with the results of pore structure analysis (Table 1) and

349

hydrophilicity evaluation (Figure 3a and Table 2). Interestingly, even though 2.0 CNC-M

350

presented greater hydrophilic than the 1.0 CNC-M, the fluxes of the two membranes were similar.

351

As mentioned above, the permeability of membranes depends on both pore structure and

352

hydrophilicity of the membranes. As tableted in Table 1, the mean pore radius of the 1.0 CNC-M

353

and the 2.0 CNC-M was quite narrow, 81.2 and 81.5 nm, respectively. Consequently, it can be

354

deduced that in this case, pore structure played a major role influencing the flux enhancement. In

355

summary, the flux of the investigated membranes showed apparent regularity with CNC-M >

356

CNT-M > Control-M, in accordance with membrane pore structure and hydrophilicity

357

measurements.

19


Page 20 of 31

Page 21 of 31


358

Mechanical properties of the membranes

359

Evaluation of mechanical properties of the investigated membranes was conducted by

360

micro-tensile tests as shown in Figure 4a. Under applied stress, membranes first underwent

361

reversible elastic deformation, as shown in the initial linear part of the stress-strain curves.

362

Subsequently, membranes endured irreversible inelastic deformation with the increased applied

363

stress, as shown in the curvature portion of the curves. Eventually, membranes attained their

364

fracture strength, resulting in breakage. In practical operation, inelastic deformation caused by

365

excessive stress leads to the fatigue damage of the membranes, resulting in membrane failure for

366

the purposes of industrial application. For better comparison the mechanical properties of the

367

CNC-M and CNT-M, Young’s modulus, tensile strength, elongation and toughness were extracted

368

from strength-strain curves and investigated specifically.

369

370 20



371 372 373

Figure 4. (a) Stress-strain curves of the membranes. Mechanical properties of the membranes: (b) Young’s modulus; (b) Tensile strength (d) Elongation; and Toughness (e).

374 375

Young’s modulus and tensile strength

376

Young’s modulus is used as an indication of stiffness of the onset at elastic deformation, which is

377

calculated from the initial slope of linear portion (approximately initial 2.0 % of strain) of the

378

stress-strain isotherm. The values of Young’s modulus of the investigated membranes are shown in

379

Figure 4b. Young’s modulus of the Control-M is the lowest of all the membranes with a value of

380

44.7 MPa. CNC-M and CNT-M exhibited an increasing trend of Young’s modulus for membranes

381

with higher nanomaterials contents. The Young’s modulus of the 2.0 CNC-M and the 2.0 CNT-M

382

is 150% and 185% of the Control-M, respectively, indicating enhanced stiffness of the CNC-M

383

and CNT-M. Similar trends were reported in a distillation polyvinylidene fluoride (PVDF) hollow

384

fiber (HF) membrane incorporating 2.0 wt % of CNCs, and a proton exchange membrane (PEM)

385

with functionalized CNTs, where the Young’s modulus increased to 145.8% and 195% of the

386

control membrane, respectively.23,50 The tensile strength is the maximum stress that membrane

387

samples can withstand while being stretched before breaking and can be used as a parameter to

388

evaluate strength of the membrane. As shown in Figure 4c, tensile strength of the Control-M is the

389

lowest among the investigated membranes with a value of 1.70 MPa. The tensile strength of the 21


Page 22 of 31

Page 23 of 31


390

CNC-M and the CNT-M increased in membranes with higher concentration of nanomaterials.

391

Specifically, tensile strength was reinforced to 150 and 156% of the Control-M for the 2.0 CNC-M

392

and the 2.0 CNT-M, respectively. Similar behaviors have been reported in a CNC/Chitosan

393

nanocomposite membrane and an aramid nanofibers (ANFs)/CNT membrane.51,52

394

The increase of stiffness and strength of the nanocomposite membranes can be explained by the

395

properties of CNCs and CNTs materials themselves and their dispersion ability in casting solution.

396

The Young’s modulus and tensile strength of individual CNCs particle are reported to range from

397

20 to 150 GPa53 and 2 to 6 GPa20, respectively. The Young’s modulus of CNTs is reported to be 1

398

TPa54 which is orders of magnitude greater that the CNCs, and tensile strength of individual CNTs

399

was reported as 11 to 63 GPa.20 Dispersion of nanomaterials is the most significant factor for

400

nanocomposites exploiting mechanical properties of CNCs and CNTs55. The well-dispersed CNCs

401

and CNTs in casting solution can overcome surface interactions including Van der Waals

402

interaction, the hydration force, depletion, et al.56 In addition, CNTs can nucleate the

403

crystallization of the polymer55, leading to strengthening and load transfer from nanomaterials to

404

composite membranes. Evidence can be found in recent publications, which investigated complete

405

and incomplete cracked surfaces of nanocomposite membranes. CNCs were observed at the

406

cracked edge of the membrane,57 acting as the final barrier maintaining the membrane integrity.

407

Unbroken CNT fibers were seen in the cracked part of the membrane, indicating not only

408

polymers but also CNTs underwent stretched, breakage and pull-out during crack growth.52

409

Figure 4b and c also show that, with the same weight percentage of nanomaterials, the Young’s

410

modulus and tensile strength of the CNT-M was greater than the CNC-M due to the stronger

411

properties of CNTs. However, Young’s modulus of the 1.0 CNC-M and the 0.5 CNT-M was quite 22



412

comparable, 52.7 and 52.5MPa, respectively. Additionally, Young’s modulus of the 2.0 CNC-M

413

and the 1.0 CNT-M were in the same range with values of 67.0 and 66.7 MPa, respectively.

414

Similar phenomenon can be also found in tensile strength results where the 1.0 CNC-M and the

415

0.5 CNT-M exhibited similar tensile strengths with a mean value of 2.27 MPa. The tensile strength

416

of the 2.0 CNC-M (2.55 MPa) was higher than that of the 1.0 CNT-M (2.38 MPa). Therefore, it

417

can be deduced that in our study, Young’s modulus and tensile strength of a CNT-M are

418

approximately those of a CNC-M having half the nano-filler content.

419

It should be noted that the CNC-M and CNT-M had Young’s moduli and tensile strengths that fall

420

far below those of the individual building blocks (CNCs and CNTs). Young’s modulus and tensile

421

strength were insufficient to capture the full mechanical behavior of the composite membranes.58

422

This may be attributed to the relatively low concentrations of nano-filler and the intrinsic

423

mechanical properties of the PES polymer which are comparatively weak.

424

Elongation

425

The elongation at break, corresponding to the expansion percentage of the initial span of a

426

membrane sample, is used as an indication of ductility of membrane. As shown in Figure 4d, the

427

elongation of the Control-M was 31.4%. The elongation of the CNC-M exhibited a modest

428

increasing tendency as the increase of CNCs and reached to 33.9% of the 2.0 CNC-M. By contrast,

429

the elongation of the CNT-M decreased for membranes with higher weight loading percentages.

430

The elongation of the 2.0 CNT-M decreased to only 16.0%. Similar behavior can be found in a

431

poly (vinyl alcohol)/CNC membrane24 and an aromatic polyamide (PA)/CNT membrane.59

432

The difference of intrinsic properties of the CNCs and CNTs are responsible for the opposite

433

results of elongation. The elongation of individual CNCs was investigated by Sinko et al. using a 23


Page 24 of 31

Page 25 of 31


434

potential of mean force (PMF) method.26 From the stress-strain curve of their study, the elongation

435

at break of the CNC was ca. 40%. However, CNTs are generally considered to be hard and stiff,

436

but brittle as well. The elongation at break of individual CNT was reported as ca. 12% by a

437

nanostressing stage combining SEM and AFM.7 Well-dispersed of CNCs and CNTs resulted in the

438

composite membranes following the elongation properties of the nanomaterials, leading to the

439

different elongation trends of the CNC-M and the CNT-M.

440

Toughness

441

Toughness is defined as the amount of energy a material absorbs before it fails,60 expressed as

442

follow:

443

U= 0 σ dԑ

444

Where U is the energy per volume absorbed, σ is the stress, and ԑ is the failure stain. The value for

445

toughness of the investigated membranes was determined by integrating the area under

446

stress-strain curve from zero load to maximum extension. As shown in Figure 4e, the toughness of

447

the Control-M was about 0.438 MJ/m3. The toughness of the CNC-M increased with increasing

448

CNC content and attained a value of 0.688 MJ/m3 of the 2.0 CNC-M. However, the toughness of

449

the CNT-M showed an opposite trend, decreasing to 0.342 MJ/m3 of the 2.0 CNT-M. The CNC-M

450

was stronger and more stretchable because of the enhanced tensile strength and elongation

451

captured from CNCs, resulting in the improvement of toughness. However, the strength of the

452

CNT-M was increased accompanied with the decreasing of elongation, lead to a drop of the

453

toughness of the CNT-M. The better performance in toughness of the CNC-M indicated that they

454

can endure more energy or work required for rupture.

ԑ

(11)

24



Page 26 of 31

455

IMPLICATIONS

456

In this study, the hydrophilicity and mechanical properties of nanocomposite membranes were

457

investigated to compare the effects of CNCs and CNTs. The porosity, hydrophilicity and pure

458

water flux of the CNC-M was greater than the CNT-M. The most promising finding was that the

459

CNC-M could attain same level in Young’s modulus and tensile strength as the CNT-M by

460

doubling the CNCs content. Considering the advantages of CNCs compared to CNTs of abundant

461

existence, environmental friendly, biocompatible, biodegradable, renewable

462

hydrophilic,18-20 the enhancement of mechanical properties of the CNC-M is promising for

463

environmental application of nanocomposite membranes with CNCs. Since the cost of CNCs and

464

CNTs are $1/g and $8 to $15/g, respectively,20 even when doubling the concentration of CNCs, the

465

cost of the CNC-M is still lower than the CNT-M. This reveals that it is achievable to widely

466

utilize CNC in environmental engineering applications, especially water filtration membranes. To

467

better understand and utilize CNCs and CNTs in membrane application, different membrane types

468

for specific aims need to be further explored.

469

ASSOCIATED CONTENT

470

Supporting Information

471

Equipment information and measurement procedures of TEM, FTIR and XRD for CNTs and

472

CNCs characterization; composition of casting solution for the Control-M and Nanocomposite-M

473

(Table S1); methods of AFM characterization for Control-M and Nanocomposite-M; XRD of

474

CNCs and CNTs (Figure S1); SEM images of 1.0 CNC-M, 2.0 CNC-M, 1.0 CNT-M and 2.0

475

CNT-M (Figure S2); SEM images after binary segmentation of the Control-M and

476

Nanocomposite-M (Figure S3); AFM images of the Control-M and Nanocomposite-M (Figure S4); 25


and more

Page 27 of 31


477

Surface roughness parameters of Control-M and the Nanocomposite-M (Table S2); Linear

478

relationship between pure water flux (LMH) and TMP (MPa) of the Control-M and

479

Nanocomposite-M (Figure S5).

480

ACKNOWLEDGEMENTS

481

This work was partially funded through the Center for the Environmental Implications of

482

NanoTechnology (CEINT). We gratefully acknowledge the valuable help of Dr. Jingjing Li and Dr.

483

Marielle DuToit in the experimental analysis and discussion. This research was jointly supported

484

by the National Natural Science Foundation of China (51378140), the National Science

485

Foundation for the Outstanding Youngster Fund (51522804), Program for New Century Excellent

486

Talents in University (NCET-13-0169), HIT Environment and Ecology Innovation Special Funds

487

(HSCJ201603). The first author also thanks China Scholarship Council (CSC) for providing the

488

living cost during his study at Duke University.

489

26



490

References:

491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532

(1) Pendergast, M. M.; Hoek, E. M., A review of water treatment membrane nanotechnologies. Energ.

Environ. Sci. 2011, 4, (6), 1946-1971. (2) Khin, M. M.; Nair, A. S.; Babu, V. J.; Murugan, R.; Ramakrishna, S., A review on nanomaterials for environmental remediation. Energ. Environ. Sci. 2012, 5, (8), 8075-8109. (3) Mallevialle, J.; Odendaal, P. E.; Wiesner, M. R., Water treatment membrane processes. American Water Works Association: 1996. (4) Nassar, I. M., Highly Efficient Nano-Structured Polymer-Based Membrane/Sorbent for Oil Adsorption from O/W Emulsion Conducted of Petroleum Wastewater. J. Disper. Sci. Technol. 2015,

36, (1), 118-128(11). (5) Wiesner, M. R.; Chellam, S., Peer reviewed: the promise of membrane technology. Environ. Sci.

Technol. 1999, 33, (17), 360A-366A. (6) Qu, X.; Alvarez, P. J. J.; Li, Q., Applications of nanotechnology in water and wastewater treatment. Water Res. 2013, 47, (12), 3931-3946. (7) Yu, M.; Lourie, O.; Dyer, M. J.; Moloni, K.; Kelly, T. F.; Ruoff, R. S., Strength and Breaking Mechanism of Multiwalled Carbon Nanotubes Under Tensile Load. Science 2000, 287, 637. (8) Falvo, M. R.; Clary, G. J.; Taylor, R. M.; Chi, V.; Brooks, F. P.; Washburn, S.; Superfine, R., Bending and buckling of carbon nanotubes under large strain. Nature 1997, 389, (6651), 582-584. (9) Baughman, R. H.; Zakhidov, A. A.; de Heer, W. A., Carbon Nanotubes--the Route Toward Applications. Science 2002, 297, (5582), 787-792. (10) Coleman, J. N.; Khan, U.; Blau, W. J.; Gun Ko, Y. K., Small but strong: A review of the mechanical properties of carbon nanotube–polymer composites. Carbon 2006, 44, (9), 1624-1652. (11) de Lannoy, C.; Soyer, E.; Wiesner, M. R., Optimizing carbon nanotube-reinforced polysulfone ultrafiltration membranes through carboxylic acid functionalization. J. Membrane Sci. 2013, 447, (0), 395-402. (12) Kumar, S.; Dang, T. D.; Arnold, F. E.; Bhattacharyya, A. R.; Min, B. G.; Zhang, X.; Vaia, R. A.; Park, C.; Adams, W. W.; Hauge, R. H.; Smalley, R. E.; Ramesh, S.; Willis, P. A., Synthesis, Structure, and Properties of PBO/SWNT Composites&. Macromolecules 2002, 35, (24), 9039-9043. (13) Tasis, D.; Tagmatarchis, N.; Bianco, A.; Prato, M., Chemistry of Carbon Nanotubes. Chem. Rev.

2006, 106, (3), 1105-1136. (14) Celik, E.; Park, H.; Choi, H.; Choi, H., Carbon nanotube blended polyethersulfone membranes for fouling control in water treatment. Water Res. 2011, 45, (1), 274-282. (15) Vatanpour, V.; Madaeni, S. S.; Moradian, R.; Zinadini, S.; Astinchap, B., Fabrication and characterization of novel antifouling nanofiltration membrane prepared from oxidized multiwalled carbon nanotube/polyethersulfone nanocomposite. J. Membrane Sci. 2011, 375, (1–2), 284-294. (16) Li, R.; Wang, X.; Ji, Z.; Sun, B.; Zhang, H.; Chang, C. H.; Lin, S.; Meng, H.; Liao, Y.; Wang, M.; Li, Z.; Hwang, A. A.; Song, T.; Xu, R.; Yang, Y.; Zink, J. I.; Nel, A. E.; Xia, T., Surface Charge and Cellular Processing of Covalently Functionalized Multiwall Carbon Nanotubes Determine Pulmonary Toxicity. ACS Nano 2013, 7, (3), 2352-2368. (17) Nel, A.; Xia, T.; Meng, H.; Wang, X.; Lin, S.; Ji, Z.; Zhang, H., Nanomaterial Toxicity Testing in the 21st Century: Use of a Predictive Toxicological Approach and High-Throughput Screening.

Accounts Chem. Res. 2013, 46, (3), 607-621. 27


Page 28 of 31

Page 29 of 31


533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576

(18) Klemm, D.; Kramer, F.; Moritz, S.; Lindström, T.; Ankerfors, M.; Gray, D.; Dorris, A., Nanocelluloses: A New Family of Nature-Based Materials. Angewandte Chemie International Edition

2011, 50, (24), 5438-5466. (19) Moon, R. J.; Martini, A.; Nairn, J.; Simonsen, J.; Youngblood, J., Cellulose nanomaterials review: structure, properties and nanocomposites. Chem. Soc. Rev. 2011, 40, (7), 3941-3994. (20) Carpenter, A. W.; de Lannoy, C.; Wiesner, M. R., Cellulose Nanomaterials in Water Treatment Technologies. Environ. Sci. Technol. 2015, 49, (9), 5277-5287. (21) Iwamoto, S.; Kai, W.; Isogai, A.; Iwata, T., Elastic Modulus of Single Cellulose Microfibrils from Tunicate Measured by Atomic Force Microscopy. Biomacromolecules 2009, 10, (9), 2571-2576. (22) Habibi, Y.; Lucia, L. A.; Rojas, O. J., Cellulose Nanocrystals: Chemistry, Self-Assembly, and Applications. Chem. Rev. 2010, 110, (6), 3479-3500. (23) Lalia, B. S.; Guillen, E.; Arafat, H. A.; Hashaikeh, R., Nanocrystalline cellulose reinforced PVDF-HFP membranes for membrane distillation application. Desalination 2014, 332, (1), 134-141. (24) Paralikar, S. A.; Simonsen, J.; Lombardi, J., Poly(vinyl alcohol)/cellulose nanocrystal barrier membranes. J. Membrane Sci. 2008, 320, (1–2), 248-258. (25) Ping, L. A. Y. H., Cellulose nanocrystal-filled poly(acrylic acid) nanocomposite fibrous membranes. Nanotechnology 2009, 20, (41), 415604. (26) Sinko, R.; Mishra, S.; Ruiz, L.; Brandis, N.; Keten, S., Dimensions of Biological Cellulose Nanocrystals Maximize Fracture Strength. ACS Macro Lett. 2014, 3, (1), 64-69. (27) Goetz, L. A.; Jalvo, B.; Rosal, R.; Mathew, A. P., Superhydrophilic anti-fouling electrospun cellulose acetate membranes coated with chitin nanocrystals for water filtration. J. Membrane Sci. 2016,

510, 238-248. (28) Karim, Z.; Mathew, A. P.; Grahn, M.; Mouzon, J.; Oksman, K., Nanoporous membranes with cellulose nanocrystals as functional entity in chitosan: Removal of dyes from water. Carbohyd. Polym.

2014, 112, 668-676. (29) Zinadini, S.; Zinatizadeh, A. A.; Rahimi, M.; Vatanpour, V.; Zangeneh, H., Preparation of a novel antifouling mixed matrix PES membrane by embedding graphene oxide nanoplates. J. Membrane

Sci. 2014, 453, 292-301. (30) Yu, L.; Xu, Z.; Shen, H.; Yang, H., Preparation and characterization of PVDF–SiO2 composite hollow fiber UF membrane by sol–gel method. J. Membrane Sci. 2009, 337, (1–2), 257-265. (31) van Oss, C. J., Development and applications of the interfacial tension between water and organic or biological surfaces. Colloids and Surfaces B: Biointerfaces 2007, 54, (1), 2-9. (32) Botton, S.; Verliefde, A. R. D.; Quach, N. T.; Cornelissen, E. R., Influence of biofouling on pharmaceuticals rejection in NF membrane filtration. Water Res. 2012, 46, (18), 5848-5860. (33) Li, L.; Wang, Z.; Rietveld, L. C.; Gao, N.; Hu, J.; Yin, D.; Yu, S., Comparison of the Effects of Extracellular and Intracellular Organic Matter Extracted From Microcystis aeruginosa on Ultrafiltration Membrane Fouling: Dynamics and Mechanisms. Environ. Sci. Technol. 2014, 48, (24), 14549-14557. (34) Hurwitz, G.; Guillen, G. R.; Hoek, E. M. V., Probing polyamide membrane surface charge, zeta potential, wettability, and hydrophilicity with contact angle measurements. J. Membrane Sci. 2010, 349, (1–2), 349-357. (35) Mtibe, A.; Linganiso, L. Z.; Mathew, A. P.; Oksman, K.; John, M. J.; Anandjiwala, R. D., A comparative study on properties of micro and nanopapers produced from cellulose and cellulose nanofibres. Carbohyd. Polym. 2015, 118, 1-8. (36) Pei, A.; Zhou, Q.; Berglund, L. A., Functionalized cellulose nanocrystals as biobased nucleation 28



577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620

agents in poly(l-lactide) (PLLA) – Crystallization and mechanical property effects. Compos. Sci.

Technol. 2010, 70, (5), 815-821. (37) Gunawan, P.; Guan, C.; Song, X.; Zhang, Q.; Leong, S. S. J.; Tang, C.; Chen, Y.; Chan-Park, M. B.; Chang, M. W.; Wang, K.; Xu, R., Hollow Fiber Membrane Decorated with Ag/MWNTs: Toward Effective Water Disinfection and Biofouling Control. ACS Nano 2011, 5, (12), 10033-10040. (38) Fajardo, A. R.; Lopes, L. C.; Rubira, A. F.; Muniz, E. C., Development and application of chitosan/poly(vinyl alcohol) films for removal and recovery of Pb(II). Chem. Eng. J. 2012, 183, 253-260. (39) Zhao, S.; Wang, Z.; Wei, X.; Tian, X.; Wang, J.; Yang, S.; Wang, S., Comparison study of the effect of PVP and PANI nanofibers additives on membrane formation mechanism, structure and performance. J. Membrane Sci. 2011, 385–386, 110-122. (40) Strathmann, H.; Kock, K., The formation mechanism of phase inversion membranes.

Desalination 1977, 21, (3), 241-255. (41) Zhao, S.; Yan, W.; Shi, M.; Wang, Z.; Wang, J.; Wang, S., Improving permeability and antifouling performance of polyethersulfone ultrafiltration membrane by incorporation of ZnO-DMF dispersion containing nano-ZnO and polyvinylpyrrolidone. J. Membrane Sci. 2015, 478, (0), 105-116. (42) Lee, J.; Chae, H.; Won, Y. J.; Lee, K.; Lee, C.; Lee, H. H.; Kim, I.; Lee, J., Graphene oxide nanoplatelets composite membrane with hydrophilic and antifouling properties for wastewater treatment. J. Membrane Sci. 2013, 448, (0), 223-230. (43) Qu, P.; Tang, H.; Gao, Y.; Zhang, L.; Wang, S., Polyethersulfone composite membrane blended with cellulose fibrils. BioResources 2010, 5, (4), 2323-2336. (44) Subhi, N.; Verliefde, A. R. D.; Chen, V.; Le-Clech, P., Assessment of physicochemical interactions in hollow fibre ultrafiltration membrane by contact angle analysis. J. Membrane Sci. 2012,

403–404, 32-40. (45) Irfan, M.; Idris, A.; Yusof, N. M.; Khairuddin, N. F. M.; Akhmal, H., Surface modification and performance enhancement of nano-hybrid f-MWCNT/PVP90/PES hemodialysis membranes. J.

Membrane Sci. 2014, 467, 73-84. (46) Wu, H.; Tang, B.; Wu, P., Optimization, characterization and nanofiltration properties test of MWNTs/polyester thin film nanocomposite membrane. J. Membrane Sci. 2013, 428, (0), 425-433. (47) Chen, L.; Tian, Y.; Cao, C.; Zhang, J.; Li, Z., Interaction energy evaluation of soluble microbial products (SMP) on different membrane surfaces: Role of the reconstructed membrane topology. Water

Res. 2012, 46, (8), 2693-2704. (48) Lee, S.; Kim, S.; Cho, J.; Hoek, E. M., Natural organic matter fouling due to foulant-membrane physicochemical interactions. Desalination 2007, 202, (1), 377-384. (49) Celik, E.; Liu, L.; Choi, H., Protein fouling behavior of carbon nanotube/polyethersulfone composite membranes during water filtration. Water Res. 2011, 45, (16), 5287-5294. (50) Gahlot, S.; Kulshrestha, V., Dramatic Improvement in Water Retention and Proton Conductivity in Electrically Aligned Functionalized CNT/SPEEK Nanohybrid PEM. ACS Appl. Mater. Inter. 2015, 7, (1), 264-272. (51) Khan, A.; Khan, R. A.; Salmieri, S.; Le Tien, C.; Riedl, B.; Bouchard, J.; Chauve, G.; Tan, V.; Kamal, M. R.; Lacroix, M., Mechanical and barrier properties of nanocrystalline cellulose reinforced chitosan based nanocomposite films. Carbohyd. Polym. 2012, 90, (4), 1601-1608. (52) Zhu, J.; Cao, W.; Yue, M.; Hou, Y.; Han, J.; Yang, M., Strong and Stiff Aramid Nanofiber/Carbon Nanotube Nanocomposites. ACS Nano 2015, 9, (3), 2489-2501. 29


Page 30 of 31

Page 31 of 31


621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641

(53) Usov, I.; Nyström, G.; Adamcik, J.; Handschin, S.; Schütz, C.; Fall, A.; Bergström, L.; Mezzenga, R., Understanding nanocellulose chirality and structure–properties relationship at the single fibril level. 2015, 6, 7564. (54) Wong, E. W.; Sheehan, P. E.; Lieber, C. M., Nanobeam Mechanics: Elasticity, Strength, and Toughness of Nanorods and Nanotubes. Science 1997, 277, (5334), 1971-1975. (55) Spitalsky, Z.; Tasis, D.; Papagelis, K.; Galiotis, C., Carbon nanotube–polymer composites: Chemistry, processing, mechanical and electrical properties. Prog. Polym. Sci. 2010, 35, (3), 357-401. (56) Sengur, R.; de Lannoy, C.; Turken, T.; Wiesner, M.; Koyuncu, I., Fabrication and characterization of hydroxylated and carboxylated multiwalled carbon nanotube/polyethersulfone (PES) nanocomposite hollow fiber membranes. Desalination 2015, 359, 123-140. (57) Wang, B.; Walther, A., Self-Assembled, Iridescent, Crustacean-Mimetic Nanocomposites with Tailored Periodicity and Layered Cuticular Structure. ACS Nano 2015, 9, (11), 10637-10646. (58) Chung, J. Y.; Lee, J.; Beers, K. L.; Stafford, C. M., Stiffness, Strength, and Ductility of Nanoscale Thin Films and Membranes: A Combined Wrinkling–Cracking Methodology. Nano Lett.

2011, 11, (8), 3361-3365. (59) Shawky, H. A.; Chae, S.; Lin, S.; Wiesner, M. R., Synthesis and characterization of a carbon nanotube/polymer nanocomposite membrane for water treatment. Desalination 2011, 272, (1–3), 46-50. (60) Meyers, M. A.; McKittrick, J.; Chen, P., Structural Biological Materials: Critical Mechanics-Materials Connections. Science 2013, 339, (6121), 773-779.

30


Comparison of Hydrophilicity and Mechanical Properties of

Recommend Documents