Preparation and Characterization of Thin-Film Nanocomposite

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Materials and Interfaces

Preparation and characterization of thin film nanocomposite membrane with high flux and antibacterial performance for forward osmosis Enling Tian, Xingzu Wang, Xiao Wang, Yiwei Ren, Yuntao Zhao, and Xiaochan An Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.8b04476 • Publication Date (Web): 18 Dec 2018 Downloaded from http://pubs.acs.org on December 20, 2018

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Industrial & Engineering Chemistry Research

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Submitted to Industrial & Engineering Chemistry Research:

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Date: 2018-12-10

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Preparation and characterization of thin film nanocomposite membrane

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with high flux and antibacterial performance for forward osmosis

5 6

Enling Tian a,*, Xingzu Wang a , Xiao Wang a , Yiwei Ren a, Yuntao Zhao a

7

and Xiaochan An b

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aKey

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Intelligent Technology, Chinese Academy of Sciences, Chongqing 400714, China

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Laboratory of Reservoir Aquatic Environment, Chongqing Institute of Green and

bState

Key Laboratory of Separation Membranes and Membrane Processes, School

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of Materials Science and Engineering, Tianjin Polytechnic University, Tianjin 300387,

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China

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*Corresponding Author at: No.266 Fangzheng Avenue, Shuitu Hi-tech Industrial Park,

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Beibei District, Chongqing, 400714, China.

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Phone: +86 023-65935805; Fax: +86 023-65935806

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E-mail addresses: [email protected]; [email protected] (E.L. Tian)

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ACS Paragon Plus Environment

Industrial & Engineering Chemistry Research 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

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Abstract

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In this work, thin film nanocomposite (TFN) forward osmosis (FO)

24

membranes have been prepared by electrospinning technology and

25

interfacial polymerization technology. Scanning electron microscope and

26

fourier transform infrared spectroscopy analysis confirmed that graphene

27

oxide (GO) has been successfully added into polyamide (PA) selective layer.

28

The reduced roughness of membrane’s surface was verified by atomic force

29

microscopy. Together with the hydrophilic/hydrophobic interpenetrating

30

network composite nanofibers (HH-IPN-CNF) structure of the substrate, the

31

incorporation of hydrophilic GO into selective layer of FO membrane also

32

enhanced water permeability. The superior FO separation performance of

33

the modified FO membrane was obtained under circumstance of 0.05 wt%

34

GO with average water flux of 29.88, 44.02 LMH in FO mode and pressure

35

retarded osmosis (PRO) mode, respectively. This most permeable modified

36

FO membrane had a water flux about 50% and 40% higher than the pristine

37

FO membrane with a negligible variation in reverse salt flux. The GO

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modifying also significantly enhanced the antibacterial property of the FO

39

membrane. The existence of the GO effectively inhibited the growth of the

40

biofilm formed by Escherichia coli on the surface of the FO membrane. This

2


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concept provides a simple efficient method to develop high performance FO

42

membranes.

43

Key words: graphene oxide; HH-IPN-CNF; forward osmosis; interfacial

44

polymerization; high flux

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1. Introduction

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Osmosis driven membrane separation process has potential in resolving

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global water resourse scarcity and acquiring clean water 1. On account of its

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low operation hydraulic pressure, superior impediment of contaminants and

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low energy consumption, forward osmosis (FO) technology has been

50

becoming popularity recently 2-4. Polyamide (PA) thin film composite (TFC)

51

membrane is extensively utilized in FO owing to the more flexibility of

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tuning active layer and support layer separately

53

hydrophobicity of PA surface is prone to adsorb foulants and hence

54

aggravates membrane fouling 6. Although FO experiences lower irreversible

55

membrane fouling propensity than pressure-driven membrane processes

56

such as ultrafiltration, nanofiltration and reverse osmosis, organic and

57

biological foulants are two major limiting factors in this emerging

58

technology applications

59

solutes after dilution is another limiting factor to hinder the real application

7, 10-13.

5.

However, the

7-9

And how to economically re-generate draw

3



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of FO technology. Hence strategies for mitigating FO membrane fouling are

61

indispensible to promote the successful implementation of FO technology.

62

In addition, in order to ensure FO membrane to be commercially available in

63

large scales, the permeation flux also need improvement.

64

Numerous studies have been conducted to regulate and alleviate FO

65

membrane fouling. For instance, optimizing FO operation conditions,

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fabricating double-skinned FO membrane by layer by layer (LbL) assembly

67

method, cleaning FO membrane using different methods, pretreating the

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feed effluent and membrane surface modification

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methods aforementioned are valuable, surface modification of TFC

70

membrane is an effective and easy way to mitigate organic and biofouling.

71

Since membrane surface properties of wetting, adhesion and adsorption

72

greatly influence the interaction between foulant and membrane 18.

14-17.

Although all the

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Recently, nanoparticles have been added into PA active layer of TFC

74

membranes to enhance the permselectivity, hydrophilicity, antimicrobial

75

activity, fouling resistance and mechanical stability

76

carbon-based nanomaterial-graphene oxide (GO) has been focused on as a

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very useful antifouling material in terms of its high specific surface area,

78

hydrophilicity, charge properties, smooth, and strong antibacterial activity 13, 4


19-25.

Most notably,

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79

26-29.

GO contains a single atomic layer of sp2–bonded carbon decorated with

80

a mass of oxygen functional groups 30. The antibacterial activity arises from

81

the physical damage by direct contact interactions between GO and the

82

bacteria cell membrane 31, 32. GO has been demonstrated to have the highest

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antibacterial activity among reduced graphene oxide (rGO), graphite (Gt)

84

and graphite oxide (GtO) under the same condition

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functionalized with GO of TFC PA active layer has been reported by several

86

studies to improve membrane antimicrobial activity

87

GO nanoparticles were covalently bound to the PA active layer of TFC

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membrane, the synthesis of mediated activators and functionalization

89

procedure were fairly complex. What’s more, the water permeability

90

performance of GO functionalized TFC FO membrane was not enhanced

91

compared to the pristine TFC FO membrane 13, 34, 35.

33.

Therefore, surface

13, 34, 35.

However, since

92

In this study, hydrophilic/hydrophobic interpenetrating network

93

composite nanofibers (HH-IPN-CNF) as substrate was prepared by

94

electrospinning technology. The novelties of this work are as follows: (1)

95

The hydrophilic property and the water-transferring function of the HH-IPN-

96

CNF structure is beneficial to provide available channels for water

97

transmitting through support layer. (2) GO was used to modify the active

98

layer of FO flat sheet membrane by interfacial polymerization method. And 5



99

the combination of the two aspects has not yet been reported. Therefore, the

100

significance of this paper could not only enhance water permeability of FO

101

membrane, but also improve the antibacterial property.

102

The effect of different contents of GO on the structure, morphology,

103

separation and antibacterial properties of thin film nanocomposite (TFN) FO

104

membranes were characterized and evaluated, respectively. It has been

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proved that the resultant TFN FO membrane was effective in enhancing

106

water flux and inhibiting biofilm growth. This method is cost-effective and

107

efficient, which could be potentially applied in TFN FO membrane

108

manufacture technology on a large scale.

109

2. Experimental

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2.1 Materials and chemicals

111

Polyethylene terephthalate (PET) was provided by Far Eastern Industry and

112

polyvinyl alcohol (PVA) was supplied by Yili Chemicals Co. Ltd.. Sodium

113

chloride (NaCl) was supplied by National Medicine Group. Glutaraldehyde,

114

trifluoracetic acid and n-hexane were purchased from Chengdu Kelon.

115

Graphene oxide nanoparticles (GO, with diameters of 500 nm ~ 3 μm) were

116

supplied by Chengdu Organic Chemicals Co. Ltd., Chinese Academy of

117

Sciences. Trimesoyl chloride (TMC, 98%) and 1,3-phenylenediamine (MPD, 6


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118

99%) from TCI were utilized as monomers for interfacial polymerization.

119

Deionized (DI) water was acquired from an ultra pure water equipment.

120

2.2 Membrane preparation

121

2.2.1 Electrospinning of PVA/PET composite nanofibers substrate

122

The same content of PVA and PET nanofibers were fabricated as substrate,

123

which was designed and produced by electrospinning. The preparation of

124

PVA/PET composite nanofibers substrate and postprocessing methods could

125

consult our published paper 36.

126

2.2.2 TFN FO membranes preparation

127

The ultrathin PA selective layer was prepared above PVA/PET composite

128

nanofibers substrate by interfacial polymerization, which was introduced

129

from our published paper with some changes 36. The process was described

130

below: firstly 3.4 wt% MPD aqueous solution was poured onto the surface

131

of composite nanofibers substrate for 5 min. Afterwards, the residual MPD

132

droplets were removed by nitrogen. After exposed to the air for 2 min, the

133

organic phase solution (0.10 wt% TMC in n-hexane) was poured onto the

134

saturated substrate for 1 min. The nascent FO membrane was stored in an

135

oven under 95 oC for 8 min. Finally, the TFC FO membrane was kept in DI

136

water until it was tested. 7



137

In view of the hydrophilic performance of GO, aqueous solution was

138

selected to disperse GO nanoparticles. The GO modified TFC FO

139

membranes were acquired by dispersing 0.05-1.00 wt% of GO nanoparticles

140

(on account of the total weight of MPD and TMC monomers) in the MPD

141

solution. The GO nanoparticles size distribution in the aqueous solution was

142

measured by Malvern zeta potentiometer (Zetasizer Nano ZS, England). The

143

TFN FO membranes were fabricated similarly to TFC FO membranes,

144

except that the GO nanoparticles were dispersed in aqueous phase

145

beforehand. Varied amount (0.05, 0.10, 0.50, 1.00 wt%) of GO nanoparticles

146

were dispersed in DI water using a probe sonicator (JY98-IIIN, Shanghai

147

Jingxin Industrial Development Co., Ltd., China) for 60 min in ice bath and

148

then magnetically stirred for 24 h before interfacial polymerization. The

149

resultant membranes were denoted as TFN 0.05, TFN 0.10, TFN 0.50 and

150

TFN 1.00, respectively, where the number corresponds to GO content.

151

2.3 TFN FO membranes characterizations

152

Field Emission Scanning Electron Microscope (FESEM, JSM-7800F, Japan)

153

was used to qualitatively investigate the surface and cross-sectional structure

154

of the pristine and GO modified FO membranes. All the samples were dried

155

and then coated with platinum before observation. 8


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156

Nanoscope IIIa Atomic Force Microscopy (AFM) from Digital

157

Instruments (Dimension Edge™, Germany) was utilized to evaluate the

158

surface roughness of membranes. The dried membranes with an area of 0.5

159

cm2 were adhered to a metal substrate. An area of 10 μm × 10 μm was

160

scanned under tapping mode at 0.5 Hz.

161

The surface chemical compositions of the pristine and GO modified

162

TFC FO membranes were analyzed by Attenuated Total Reflectance Fourier

163

Transform

164

spectrometer with diamond ATR accessory (Agilent Cary 630, America).

Infrared

Spectroscopy

(ATR-FTIR),

using

a

infrared

165

The water contact angle of pristine and GO modified TFC FO

166

membranes was measured using an optical goniometer (DSA100, KRUSS,

167

Germany). 5 µL of DI water was used by the sessile drop method at 25 oC ±

168

1. The contact angle was calculated by a matched computer software (VCA

169

Optima XE). Three independent samples and five random locations for each

170

sample were tested to obtain the average values.

171

The zeta potential of TFN FO membranes with different GO loading

172

was tested utilizing Anton Paar SurPASSTM 2 electrokinetic analyzer

173

(Anton Paar, Austria). 1.0 mM KCl was adopted as the test solution and the

9



174

pH value was adjusted of 7. Four random points of each membrane were

175

tested to acquire the average value.

176

2.4 Separation properties of TFN FO membranes

177

The water flux and reverse salt flux of pristine and GO modified FO

178

membranes were investigated on a lab-scale FO system, as illustrated in Fig.

179

1. The membrane test cell has rectangle configuration (size of 100 mm

180

length ×45 mm width×2 mm depth). Both the feed solution (FS, DI water)

181

and draw solution (DS, 0.5 M NaCl) were circulated at a fixed flow rate of

182

107 mL/min (cross flow velocity is about 0.02 m s-1). Each membrane was

183

assessed in two different modes: (1) pressure retarded osmosis (PRO mode)

184

where the PA selective layer faced the DS; (2) FO mode where the support

185

layer faced the DS. A constant temperature of 25 oC ± 1 for FS and DS was

186

maintained by means of submerged stainless steel heat exchange coils within

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two water baths (XMTD-204, HH-S, Jintan Medical Instrument Factory,

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China). A digital analytical balance (BSA6202S-CW, China) connected to a

189

computer recorded the weight changes of DS every 2 min. The reverse salt

190

flux through the membrane was ascertained by measuring the conductivity

191

of the FS using a conductivity meter (DDSJ-308A, China).

10


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192 193

194

195 196

197 198

199


The water flux (Jw, L m-2 h-1 abbreviated as LMH) was calculated according to the Eq. (1). 𝐽𝑤 =

∆𝑚 ∆𝑡

1

(1)

× 𝐴𝑚

Where Δm (g) is the weight change of the DS over a interval time Δt (h); Am (m2) is the test membrane area. The reverse salt flux (Js, g m-2 h-1 abbreviated as gMH) was evaluated using the Eq. (2). 𝐽𝑠 =

(𝐶𝑡𝑉𝑡) ― (𝐶0𝑉0) ∆𝑡

1

(2)

× 𝐴𝑚

200

Where Ct (mol·L-1) and Vt (L) are the salt concentration and the volume

201

of the FS over Δt (h), while Co (mol·L-1) and Vo (L) are the initial salt

202

concentration and the volume of the FS. Am (m2) is the effective membrane

203

surface.

204

In addition, the intrinsic separation properties, water permeability

205

coefficient A and salt permeability coefficient B of the developed TFN FO

206

membranes were evaluated according to a standard testing method reported

207

by Tiraferri et al.37

208 11



209 210 211 212 213 214 215 216 217 218 219

Fig.1. The diagram of the FO test system. 1 feed solution; 2 peristaltic pump; 3 FO membrane cell; 4 flow meter; 5 temperature control system; 6 conductivity meter; 7 draw solution; 8 balance; 9 PC.

220

221

2.5 Antibacterial activity tests of TFN FO membranes

222

The antibacterial activity of the pristine and GO modified TFC FO

223

membranes was also evaluated. As the molecular probe of viable cell, green

224

fluorescent protein was used to observe the biological living cells in real-

225

time. Escherichia coli (E. coli) marked by green fluorescent protein was

226

inoculated and acclimated in 100 mL Luria-Bertani nutrient medium. The

227

initial concentration of the E. coli was 106 CFU/mL. Every membrane

228

sample was soaked in the nutrient medium equidistantly. The E. coli was

229

domesticated for 21 h at 33 oC with the membranes in the medium. Then the

230

membranes were drawn from the medium for further research. A FV1200 12


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231

confocal laser scanning microscope (CLSM, Japan) was applied to

232

investigate the morphology features of the E. coli on the membranes surface.

233

3. Results and discussion

234

3.1 Characterization of PVA/PET composite nanofibers substrate

235

As illustrated in Fig.2, the thinner and hydrophilic PVA nanofibers, as well

236

as the thicker and hydrophobic PET nanofibers presented interlaced

237

distribution. HH-IPN-CNF structure has formed among the pores of the

238

composite nanofibers. The enhancement of hydrophilicity and the water-

239

transferring function of the HH-IPN-CNF was conductive to provide

240

available channels for water transmitting through support layer. And it was

241

in favor of improving the water flux of TFN FO membrane.

242

243

244

245 Fig.2. SEM image for the PVA/PET HH-IPN-CNF substrate.

246

247

13



248

3.2 Characterization of TFN FO membranes

249

The existence of GO in the PA active layer of prepared TFC FO membrane

250

was inferred by FTIR (Fig. 3). For the pristine FO membrane, the FTIR

251

spectrum in Fig. 3B precisely exhibited the typical absorption band of an

252

aromatic polyamide active layer. AmideⅠband C=O stretching vibration at

253

1662 cm-1; AmideⅡband N-H deformation vibration at 1542 cm-1; Amide

254

Ⅲ band C-N stretching vibration band at 1241 cm-1. The characteristic

255

bands at 1486, 1575, and 1610 cm-1 were assigned to the vibration of carbon

256

skeleton in aromatic rings. The incomplete react C-Cl stretching vibration

257

appeared a strong absorption band at 557 cm-1.

258

In comparison with pristine FO membrane, the GO modified TFC FO

259

membrane exhibited several characteristic bands attributable to OH and

260

epoxide groups. Besides the distinct characteristic peaks of formed aromatic

261

polyamide groups by interfacial polymerization, new peak at 2964 cm-1 (Fig.

262

3A) may be ascribed to the hydrogen bond formed between GO

263

nanoparticles and polymer functional groups. The band at 3318 cm-1 (Fig.

264

3A) was due to O-H stretching vibration. Additionally, new bands at 1361

265

cm-1, 1385 cm-1 and 1168 cm-1 appeared, which could be attributed to the C-

266

O stretching vibration in epoxy groups and alkoxy groups 38, 39. These results 14


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267

verified the presence of GO nanoparticles on the surface of the pristine FO

268

membrane by interfacial polymerization.

269 270 271 272 273 274 275 A

276

B

Fig.3. FTIR spectra of the pristine and GO modified TFC FO membranes. (A) Full spectra of the

277

membranes in the scope of 400-4000 cm-1; (B) Detailed spectra of the membranes in the scope of 4001800 cm-1.

278

279

The morphology of active layer of the prepared TFN FO membranes

280

was evaluated by SEM. As can be seen from Fig. 4, PA active layer

281

exhibited flake nodules. The ridge-and-valley structure has been observed,

282

which is the typical morphology of PA TFC membranes 40. Although there

283

was similar surface morphology for pristine and TFN FO membranes, the

284

TFN FO membranes presented finely and denser dispersed nodular structure.

285

According to SEM images, the surface roughness of the TFC FO membranes

286

decreased consistently with the increase of GO content. It meant that the 15



287

TFN FO membranes became smoother with GO content increasing, which

288

was further confirmed by AFM analysis following. What’s more, a detailed

289

explanation of the mechanism for the smoother membrane surface with the

290

addition of GO is given in the following AFM analysis.

291

292

293 294 295 296 297

A 15,000×

A 30,000×

B 15,000×

B 30,000×

298 299 300 301 302 303 304 305 306 307 308 309 16


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310 311 312 313 314 315 316

C 15,000×

C 30,000×

317 318 319 320 321 322 323 324

D 15,000×

D 30,000×

325 326 327 328 329 330 331

E 15,000×

E 30,000×

332 333

Fig. 4. Surface SEM images of the TFN FO membranes at magnifications of 15,000 × and 30,000 ×. (A)

334

pristine FO, (B) 0.05% GO modified FO, (C) 0.10% GO modified FO, (D) 0.50% GO modified FO and

335

(E) 1.00% GO modified FO.

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336

The SEM images of the cross-section of prepared TFN FO membranes

337

were shown in Fig. 5. From the SEM images, it was easy to recognize that a

338

thin PA selective layer was successfully fabricated on the HH-IPN-CNF

339

substrate.

340 341 342 343 344 345 346

A

347

B

348 349 350 351 352 353 354 355 356 357 358

D

C

E

Fig. 5. Cross-sectional SEM images of the TFN FO membranes at magnification of 10,000 ×. (A) pristine FO, (B) 0.05% GO modified FO, (C) 0.10% GO modified FO, (D) 0.50% GO modified FO and (E) 1.00% GO modified FO.

359

FTIR spectra for the resultant TFN FO membranes were shown in Fig.

360

6. The characteristic band at ~1241 cm-1 corresponds to the Amide Ⅲ (-C18


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361

N- stretching vibration) in the PA active layer. The appearance of

362

characteristic band at ~973 cm-1 attributed to ester group (-COO-) in the HH-

363

IPN-CNF substrate was also observed, demonstrating that the beam

364

penetrated the PA layer into the support layer in ATR-FTIR measurement.

365

Herein, the proportion of amide absorption peak intensity to ester groups in

366

FTIR spectrum of each TFN FO membrane was introduced as a quantitative

367

index for the PA layer thickness, and the ratios were shown in Table 1. The

368

higher intensity ratio of (-C-N-)/ (-COO-) indicated a thicker PA layer 41. As

369

Table 1 showed, the resultant PA active layer thickness decreased with the

370

increase of the GO content. This may be attributed to the smoother surface

371

and the lower ridge heights of the PA layer as the GO increasing.

372 373 374 375 376 377 378 379 380 381

Fig. 6. FTIR spectra of TFN FO membranes by baseline correction.

382 383 19



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384 Table 1 The intensity ratio of (-C-N-)/(-COO-) for different TFN FO membranes.

membranes

pristine

TFN0.05

TFN 0.10

TFN 0.50

TFN 1.00

I(-C-N-)/I(-COO-)

12.12±0.09

11.94±0.35

9.53±0.36

8.38±1.33

7.05±0.08

385

386

Three-dimensional images and roughness parameters of the TFN FO

387

membranes were presented in Fig. 7. It was clearly found that the roughness

388

of the surface was influenced by adding GO nanoparticles in PA layer. The

389

results revealed the broad asperities on pristine FO membrane surface, with

390

mean roughness Ra = 118±1 nm, root mean square Z value Rms = 147±1 nm,

391

and maximum vertical distance between the highest peak and lowest valley

392

Rmax = 1040±20 nm (Table 2). Meanwhile, addition of GO resulted in

393

sharper and denser asperities on surface of TFN FO membranes than that of

394

pristine FO membrane. In addition, based on the Ra, Rms and Rmax values, the

395

roughness parameters of TFN FO membranes gradually decreased with GO

396

loading increased till to 1.00 wt%. As mentioned above, the roughness

397

decline may be ascribed to the hydrogen bonds between PA selective layer

398

and GO nanoparticles

399

substrate was removed vertically from GO/MPD aqueous solution, the GO

400

nanoparticles tended to orient horizontally along the membrane surface on

42.

On the other hand, while the HH-IPN-CNF

20


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401

account of the Langmuir-Blodgett film deposition

402

oriented GO nanoparticles would retard MPD diffusing into the organic

403

solvent, which restricted further growth of the ridge. According to the

404

literature

405

diffusion and bring a smoother surface in the end.

43,

28.

The horizontally

the smaller substrate pore size would also retard the MPD

406

407

408

409 B

A

410 411 412 413 414 415 416 417 418

C

D

E

419

Fig. 7. Three-dimensional AFM images of the TFN FO membranes. (A) pristine FO, (B) 0.05% GO

420

modified FO, (C) 0.10% GO modified FO, (D) 0.50% GO modified FO and (E) 1.00% GO modified FO.

421 422 21



423

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Table 2 Surface roughness of TFN FO membranes with different GO contents.

424 GO loading (%) 0.00 0.05 0.10 0.50 1.00

Ra (nm) 118±1 72.3±0.3 55.1±0.1 49±0.5 42.9±0.2

Rq (nm) 147±1 91.8±0.35 69.8±0.15 63±0.05 54.8±0.2

Rmax (nm) 1040±20 607±3 536±2.5 625±1 473±2.5

425 426

Contact angle measurement was performed to study the influence of

427

GO on the hydrophilicity of prepared TFC FO membranes. As depicted in

428

Table 3, the contact angle of TFN FO membranes decreased overall by

429

addition of GO nanoparticles. This might play a favorable role in improving

430

water flux of GO modified FO membranes. When GO loading was 0.05 wt%,

431

the lowest contact angle value of TFN FO membrane reached about 75

432

degree which corresponded to reduction by almost 30% compared to that of

433

the pristine FO membrane. At low concentration, the better dispersion of GO

434

nanoparticles made the oxygenous functional groups such as hydroxyl,

435

carboxyl and epoxy groups fully exposed on the membrane surface, which

436

definitely played their role in improving the membrane hydrophilicity.

437

However, it was also observed that the contact angle increased slightly at a

438

certain extent when GO content ranged from 0.05 wt% to 1.00 wt%. Fig.8

439

presented the GO nanoparticles size distribution in the MPD aqueous

440

solution with different GO content. As illustrated in Fig.8, as the GO content 22


Page 23 of 80 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


441

in the aqueous solution was 0.05 wt%, the nanoparticles size was in the

442

range of 70-100 nm. Only several particles size surpassed 100 nm while 0.1

443

wt% GO dispersed in the MPD solution. As the GO content increased to 0.5

444

wt%, the GO nanoparticles size distribution was extended the scope of 40 to

445

500 nm. A wider size distribution range was observed and some particles

446

size was up to 5 μm with the GO content increasing to 1.0 wt%. It indicated

447

that the high content of additives were not evenly distributed in aqueous

448

solution due to agglomeration, which reduced effective area of GO

449

nanoparticles and the hydrophilic functional groups on the membrane

450

surface. Additionally, from Chae 28, the subsequent increase in contact angle

451

might be understood in light of the decrease of the surface roughness.

452

Wenzel Robert N. investigated the impact of solid surface on the water

453

contact angle and established the Wenzel the Eq. (3) 44.

454

cos θ2

r = roughness actor = cos θ1

455

Where θ1 and θ2 are the contact angles of the actual surface

456

and projection surface; and “r” is defined as the ratio of the actual surface

457

area to the projection area. From Eq. (3), as the contact angle is less than 90o,

458

the contact angle should increase with the decrease of solid surface

459

roughness. 23



Page 24 of 80

460

Hence, the variation in contact angle could be caused by the trade-off

461

between the oxygen content and the surface roughness with GO content

462

altering.

463

Table 3 Contact angle of TFN FO membranes as a function of GO contents in MPD aqueous solution.

GO content 0.00

0.05

0.10

0.50

1.00

106.86±1.08

75.05±1.21

81.9±0.98

90.57±1.09

94.62±1.61

(%) Contact angle (degree)

464

465

466

467

468

A

B

C

D

469

470

471

472

24


Page 25 of 80 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


473 Fig. 8. Particle size distribution on GO dispersion in aqueous solution with different GO content.

474

(A) 0.05% GO , (B) 0.10% GO, (C) 0.50% GO and (D) 1.00% GO.

475

3.3 Separation properties of TFN FO membranes

476

The TFN FO membranes with different GO contents were tested using

477

0.5 M NaCl DS and DI water as FS. The water flux and reverse salt flux

478

were evaluated under FO and PRO modes to determine the effect of GO on

479

the separation performance of the prepared FO membranes. As shown in Fig.

480

9A, the water fluxes of all the TFN FO membranes were superior to that of

481

the pristine FO membrane. The average water flux reached to its maximum

482

value at 0.05 wt% (29.88, 44.02 LMH), which was approximately 50% and

483

40% higher than that of the pristine FO membrane (15.09, 26.56 LMH) in

484

FO mode and PRO mode, respectively. The observed trend on water flux

485

was in accordance with the trend of contact angle. Based on the solution–

486

diffusion theory 45, an increase in hydrophilicity of the FO membrane could

487

enhance water molecules movement and facilitate their diffuse through the

488

membrane, thus improve water permeability. And the addition of GO

489

reduced the thickness of PA active layer, in the benefit of lowing water

490

molecules transport resistance. Finally, the interfacial gap between GO

491

nanoparticles and PA active layer provided additional water molecules 25



492

transport channels 46. However, it should be noted that the higher amount of

493

GO from 0.05 wt% to 1.00 wt% in the aqueous solution led to a slight

494

decline in water flux. This may be ascribed to the following two aspects. GO

495

nanoparticles at high concentration were prone to aggregate and hence

496

blocked the pore in PA layer, which hindered water molecules transmission.

497

In the mean time, a decrease of membrane surface roughness decreased

498

water permeability

499

exhibited lower than that in PRO mode, which may be attributed to internal

500

concentration polarization (ICP).

43, 47.

It was also found that the water fluxes in FO mode

501

As can be seen from Fig. 9B, compared to the pristine sample, there

502

was a slight increase of the reverse salt flux. This may be explained that a

503

higher water flux tended to promote salt passage. Nonetheless, the respective

504

salt leakage could be controlled underneath 5.00 gMH in FO mode and 8.10

505

gMH in PRO mode. Therefore, GO modified TFC FO membranes produced

506

promising FO separation performance on the whole.

507

508

509

26


Page 26 of 80

Page 27 of 80 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


510 511 512 513 514 515 516 517

A

B

Fig.9. (A) The water flux and (B) reverse salt flux of pristine and GO modified TFC FO membranes as different GO contents.

518 519

() Table 4 lists the intrinsic transport properties (A and B) of the resultant

520

TFN FO membranes. As can be seen from Table 4, the A values of all the

521

GO modified FO membranes exceeds that of the pristine membrane. And the

522

change tendency of A value was in accordance with the trend of water flux.

523

The B values of the TFN FO membranes abide by the same changing trend

524

as that of the reverse salt flux.

525

Table 4 Intrinsic separation properties of TFN FO membranes.

membranes

A-value (LMH/bar)

B-value (LMH)

Pristine

1.72±0.15

0.23±0.03

TFN 0.05

3.18±0.32

0.37±0.04

TFN 0.10

2.09±0.23

0.26±0.05

TFN 0.50

2.27±0.12

0.29±0.06

TFN 1.00

2.06±0.18

0.33±0.02

526

27



527

The separation properties of the prepared FO membrane in this work

528

(TFN0.05) were compared with the commercialized HTI-TFC FO

529

membrane and recently developed FO membranes, as shown in Table 5.

530

Under the same test conditions, the water flux of the prepared TFN0.05

531

membrane in this work is much higher than that of the commercialized HTI-

532

TFC FO membrane in both operation modes whereas the reverse salt flux is

533

comparable.

534

Herein, the reverse flux selectivity, Js/ Jw, was introduced to evaluate

535

the overall efficiency of the FO membranes 48. It also can be seen that the Js/

536

Jw of our TFN0.05 FO membrane in FO mode is lower than that of the other

537

modified FO membranes reported in the literatures despite Js/ Jw value is

538

comparative in PRO mode

539

modifying PA active layer of TFC FO membrane in this study is a simple

540

and economically efficient approach than other modified methods.

49-53.

Based on the above comparison, the GO

541 542 543

28


Page 28 of 80

Page 29 of 80 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


544 545

Table 5 Comparison among the property of the TFN FO membrane in this work, commercialized

546

TFC FO membrane and representative FO membranes recently reported in the literatures.

547 548

Membrane code TFN0.05 HTI-TFC PA- PSf/GO a

549

PACaCO3/PSf b PAGO/PANc PAPVDF/PFSAd PATAEA/PSf e

DS 0.5 M NaCl 0.5 M NaCl 0.5 M NaCl 2M NaCl 0.5 M NaCl 1M NaCl 2M NaCl

FS DI DI DI DI DI DI DI

Water flux (Jw)(LMH) 29.88 44.02 8.67 15.62 19.77 41.0 17.0 27.6 25.0 34.7 27.0 54.4 26.9 51.7

Reverse Salt Flux (Js) (gMH) 4.35 7.41 4.81 7.79 3.2 6.3 45.0 50.0 4.2 4.7 8.4 10.9 9.3 15.5

Js/ Jw (g/L)

Orientation mode

0.15 0.17 0.55 0.50 0.16 0.15 2.65 1.81 0.17 0.14 0.31 0.20 0.35 0.30

FO PRO FO PRO FO PRO FO PRO FO PRO FO PRO FO PRO

Refs. This work Selftesting (49) (50) (51) (52) (53)

550 551

Polyamide active layer was formed on the polysulfone (PSf) substrate containing GO nanosheets. This membrane was denoted as GOT-0.25 in Ref. (49).

552 553

Polyamide active layer was formed on the polysulfone (PSf) substrate containing CaCO3 nanoparticles. This membrane was designated as TFC21 in Ref. (50).

554 555

GO nanosheets was incorporated into the polyamide selective layer formed on the hydrolyzed polyacrylonitrile (HPAN) substrate. This membrane was denoted as TFC-600 in Ref. (51).

556 557

Polyamide layer was formed on the polyvinylidene fluoride (PVDF) substrate containing Perfluorosulfonic acid (PFSA) . This membrane was designated as MT-3 in Ref. (52).

558 559

Tris(2-aminoethyl)amine (TAEA) was incorporated into the polyamide selective layer formed on the PSf substrate. This membrane was denoted as MPD/TAEA+TMC on PSF in Ref. (53).

560 561

a

b

c

d

e

3.4 Antibacterial activity of TFN FO membranes

562

The antibacterial activity of GO modified TFC FO membranes was

563

clearly revealed by the CLSM images in Fig. 10. It was observed that the 29



Page 30 of 80

564

thickness of biofilm that was formed by viable E. coli decreased with an

565

increase of GO content in the PA active layer. Only a few cluster of sparse E.

566

coli microorganism attached on the surface of FO membrane without

567

forming intact biofilm in the case where the GO content was 1.0 wt% (Fig.

568

10E). The enhanced antibacterial property of TFN FO membranes with

569

increasing GO content could be attributed to the superior hydrophilicity and

570

surface smoothness. The hydrophilic surface would reduce hydrophobic

571

bacteria adsorption and the smooth surface would result in less adhesion

572

sites on the membrane surface. Besides, according to the literatures 54, 55, the

573

GO modified membrane surface possesses negative charge. Meanwhile,

574

Table 6 shows the zeta potentials of the pristine and GO modified TFC FO

575

membranes. As can be observed from Table 6, the zeta potentials of TFN FO

576

membranes exhibit an upward trend with the increase of GO content. It

577

implies that the membrane surfaces are more negatively charged as GO

578

content increases. This should induce enhanced electrostatic repulsion

579

between the negative charged E. coli and membrane surface, thus hampering

580

the surface attachment of E. coli. What’s more, the GO could induce E. coli

581

cell damage by extracting phospholipid molecules from the outer cell

582

membrane by direct contact or by generation of reactive oxygen species or

583

through direct oxidation of E. coli cellular components 30


32, 33, 56.

The dead

Page 31 of 80 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


584

cells induced by GO also make for the reduced biofilm formation on the

585

surface of TFN FO membranes 34.

586

587

588

589 A

B

590

591 592 593 594 595 596 597 598 599

C

D

E

Fig.10. CLSM images of biofilm formed by attached microorganism on surface of TFN FO membranes with various GO contents. (A) pristine FO, (B) 0.05% GO modified FO, (C) 0.10% GO modified FO, (D) 0.50% GO modified FO and (E) 1.00% GO modified FO.

600 601 602 603 604 31



605 606

Page 32 of 80

Table 6 The zeta potentials of TFN FO membranes with different GO loading.

GO content (%)

0.00

0.05

0.10

0.50

1.00

Zeta potential (mV)

14.27±2.03

18.72±0.57

19.09±1.62

21.72±2.08

23.12±0.90

607 608 609

4. Conclusions

610

In summary, TFN FO membranes were successfully fabricated with

611

GO nanoparticles incorporated in the PA selective layer by interfacial

612

polymerization method. This easy method of preparation resulted in a more

613

efficient and convenient approach than other modification methods. A

614

variety of characterizations were employed to illustrate the changes in the

615

chemical and morphology of TFN membranes. It was found that the

616

introduction of GO significantly enhanced the properties of the TFC FO

617

membranes in terms of water permeability and antibacterial performance.

618

The antibacterial property against E. coli improved with the GO content

619

increasing. Results revealed that an optimal amount of GO addition (0.05

620

wt%) led to the highest water flux, moderate reverse salt flux. It could be

621

expected that the stable GO based FO membrane is poised to be applied in

622

the complex wastewater reclamation such as landfill leachate, printing and

623

dyeing wastewater, and so on. 32


Page 33 of 80 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

624


Acknowledgements The authors would acknowledge the supports from the Natural Science

625 626

Foundation

of

Chongqing,

China

627

No.cstc2018jcyjAX0312) and the National Natural Science Foundation of

628

China (51503205) for funding this research project.

629

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(47) Hirose, M.; Ito, H.; Kamiyama, Y. Effect of skin layer surface

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structures on the flux behaviour of RO membranes. J. Membr. Sci. 1996, 121,

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Permeation in Forward Osmosis: Modeling and Experiments. Environ. Sci.

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polysulfone substrate for the fabrication of flat-sheet thin-film composite

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forward osmosis membranes. J. Membr. Sci. 2015, 493, 496-507.

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Investigation of internal concentration polarization reduction in forward

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osmosis membrane using nano-CaCO3 particles as sacrificial component. J.

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Membr. Sci. 2016, 497, 485-493.

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composite membranes for forward osmosis applications. Chem. Eng. Sci.

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osmosis process, J. Membr. Sci. 2017, 535, 188-199.

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thin-film composite membranes for forward osmosis applications, J. Membr.

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3186.

property

of

polysulfone

ultrafiltration

806 807 808 809 810 811 812 813 814 815 816 817 42


membrane

by

Page 43 of 80 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


Graphical Abstract

818

819 820

821

Brief Summary

822

Forward osmosis (FO) membranes with graphene oxide (GO) nanoparticles

823

modified polyamide selective layer by interfacial polymerization method on

824

electrospun hydrophilic/hydrophobic interpenetrating network composite

825

nanofibers substrate have been fabricated. The results demonstrated that GO

826

modified FO membranes exhibited superior separation property and

827

antibacterial performance.

43


Industrial & Engineering Chemistry Research 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

Page 44 of 80

GO Live bacteria

Dead bacteria Interfacial polymerization

Nanofiber support layer

MPD

TMC

NaCl

Water GO modified FO membrane


Page 45 of 80 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


5

4

3

5

4

7

2

6

2

1 8


9


Fig.2. SEM image for the PVA/PET HH-IPN-CNF substrate. 126x88mm (256 x 256 DPI)


Page 46 of 80

Page 47 of 80

2 2 0

G O

m o d ifie d T F C F O

m e m b ra n e

2 0 0 1 8 0

2 9 6 4 T r a n s m itta n c e ( % )

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


1 6 0 1 4 0 1 2 0

p r is tin e F O

m e m b ra n e

1 0 0 8 0 6 0 4 0 5 0 0

1 0 0 0

1 5 0 0

2 0 0 0

2 5 0 0

W ACSa v Paragon e n u Plus m Environment b e rs (c m

3 0 0 0 -1

)

3 5 0 0

4 0 0 0


2 2 0

G O

m o d ifie d T F C F O

m e m b ra n e

1 3 8 5

2 0 0 1 8 0

T r a n s m itta n c e ( % )

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

Page 48 of 80

1 6 0

1 3 6 1

1 4 0

1 1 6 8

1 2 0

p r is tin e F O

1 0 0

m e m b ra n e

8 0 6 0 4 0 4 0 0

6 0 0

8 0 0

1 0 0 0

1 2 0 0

W ACSa v Paragon e n u Plus m Environment b e rs (c m

1 4 0 0 -1

)

1 6 0 0

1 8 0 0

Page 49 of 80 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


Fig. 4(A) Surface SEM image of the pristine FO membrane at magnification of 15,000 ×. 119x89mm (271 x 271 DPI)



Fig. 4(A) Surface SEM image of the pristine FO membrane at magnification of 30,000 ×. 119x89mm (271 x 271 DPI)


Page 50 of 80

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Fig. 4(B) Surface SEM image of the 0.05% GO modified FO membrane at magnification of 15,000 ×. 119x89mm (271 x 271 DPI)



Fig. 4(B) Surface SEM image of the 0.05% GO modified FO membrane at magnification of 30,000 ×. 119x89mm (271 x 271 DPI)


Page 52 of 80

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Fig. 4(C) Surface SEM image of the 0.10% GO modified FO membrane at magnification of 15,000 ×. 119x89mm (271 x 271 DPI)



Fig. 4(C) Surface SEM image of the 0.10% GO modified FO membrane at magnification of 30,000 ×. 119x89mm (271 x 271 DPI)


Page 54 of 80

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Fig. 4(D) Surface SEM image of the 0.50% GO modified FO membrane at magnification of 15,000 ×. 120x88mm (270 x 270 DPI)



Fig. 4(D) Surface SEM image of the 0.50% GO modified FO membrane at magnification of 30,000 ×. 119x89mm (271 x 271 DPI)


Page 56 of 80

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Fig. 4(E) Surface SEM image of the 1.00% GO modified FO membrane at magnification of 15,000 ×. 119x89mm (271 x 271 DPI)



Fig. 4(E) Surface SEM image of the 1.00% GO modified FO membrane at magnification of 30,000 ×. 119x89mm (271 x 271 DPI)


Page 58 of 80

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Fig. 5(A) Cross-sectional SEM image of the pristine FO membrane at magnification of 10,000 ×. 119x89mm (271 x 271 DPI)



Fig. 5(B) Cross-sectional SEM image of the 0.05% GO modified FO membrane at magnification of 10,000 ×. 119x89mm (271 x 271 DPI)


Page 60 of 80

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Fig. 5(C) Cross-sectional SEM image of the 0.10% GO modified FO membrane at magnification of 10,000 ×. 119x89mm (271 x 271 DPI)



Fig. 5(D) Cross-sectional SEM image of the 0.50% GO modified FO membrane at magnification of 10,000 ×. 119x89mm (271 x 271 DPI)


Page 62 of 80

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Fig. 5(E) Cross-sectional SEM image of the 1.00% GO modified FO membrane at magnification of 10,000 ×. 119x89mm (271 x 271 DPI)



Fig. 6. FTIR spectra of TFN FO membranes by baseline correction. 279x215mm (300 x 300 DPI)


Page 64 of 80

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Fig. 7(A) Three-dimensional AFM image of the pristine FO membrane. 201x201mm (96 x 96 DPI)



Fig. 7(B) Three-dimensional AFM image of the 0.05% GO modified FO membrane. 201x201mm (96 x 96 DPI)


Page 66 of 80

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Fig. 7(C) Three-dimensional AFM image of the 0.10% GO modified FO membrane. 201x201mm (96 x 96 DPI)



Fig. 7(D) Three-dimensional AFM image of the 0.50% GO modified FO membrane. 201x201mm (96 x 96 DPI)


Page 68 of 80

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Fig. 7(E) Three-dimensional AFM image of the 1.00% GO modified FO membrane. 201x201mm (96 x 96 DPI)



Fig. 8(A) Particle size distribution on GO dispersion in aqueous solution with 0.05% GO content. 288x200mm (300 x 300 DPI)


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Fig. 8(B) Particle size distribution on GO dispersion in aqueous solution with 0.10% GO content. 288x200mm (300 x 300 DPI)



Fig. 8(C) Particle size distribution on GO dispersion in aqueous solution with 0.50% GO content. 288x200mm (300 x 300 DPI)


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Fig. 8(D) Particle size distribution on GO dispersion in aqueous solution with 1.00% GO content. 288x200mm (300 x 300 DPI)



5 0

F O

m o d e P R O m o d e

4 5 4 0 3 5

W a te r F lu x ( 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

Page 74 of 80

3 0 2 5 2 0 1 5 1 0 5 0

0 .0 5 0 G O

0 .1

0 .5

c o n t e n t ACS i n Paragon t h e Plus a q Environment u e o u s s o lu tio n ( w t% )

1 .0

Page 75 of 80

1 0

F O

m o d e P R O m o d e

9 8 7

R e v e r s e S a lt F lu x ( g 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


6 5 4 3 2 1 0

0

0 .0 5 G O

0 .1

0 .5

c o n t e n t ACS i n Paragon a q u Plus e o Environment u s s o lu tio n ( w t% )

1 .0


Fig.10(A) CLSM image of biofilm formed by attached microorganism on surface of pristine FO membrane.


Page 76 of 80

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Fig.10(B) CLSM image of biofilm formed by attached microorganism on surface of 0.05% GO modified FO membrane.



Fig.10(C) CLSM image of biofilm formed by attached microorganism on surface of 0.10% GO modified FO membrane.


Page 78 of 80

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Fig.10(D) CLSM image of biofilm formed by attached microorganism on surface of 0.50% GO modified FO membrane.



Fig.10(E) CLSM image of biofilm formed by attached microorganism on surface of 1.00% GO modified FO membrane.


Page 80 of 80

Preparation and Characterization of Thin-Film Nanocomposite

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