Effect of ultrasonication parameters on forward osmosis performance of thin film composite polyamide membranes prepared with ultrasound-assisted interfacial polymerization

Effect of ultrasonication parameters on forward osmosis performance of thin film composite polyamide membranes prepared with ultrasound-assisted interfacial polymerization

Journal Pre-proof Effect of ultrasonication parameters on forward osmosis performance of thin film composite polyamide membranes prepared with ultraso...

4MB Sizes 0 Downloads 245 Views

Journal Pre-proof Effect of ultrasonication parameters on forward osmosis performance of thin film composite polyamide membranes prepared with ultrasound-assisted interfacial polymerization Liang Shen, Wei-song Hung, Jian Zuo, Lian Tian, Ming Yi, Chun Ding, Yan Wang PII:

S0376-7388(19)32868-6

DOI:

https://doi.org/10.1016/j.memsci.2020.117834

Reference:

MEMSCI 117834

To appear in:

Journal of Membrane Science

Received Date: 14 September 2019 Revised Date:

9 January 2020

Accepted Date: 10 January 2020

Please cite this article as: L. Shen, W.-s. Hung, J. Zuo, L. Tian, M. Yi, C. Ding, Y. Wang, Effect of ultrasonication parameters on forward osmosis performance of thin film composite polyamide membranes prepared with ultrasound-assisted interfacial polymerization, Journal of Membrane Science (2020), doi: https://doi.org/10.1016/j.memsci.2020.117834. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2020 Published by Elsevier B.V.

Author Statement

Liang Shen: Conceptualization, Methodology, Validation, Formal analysis, Investigation, Data Curation, Writing Original Draft, Writing-Review&Editing, Visualization Wei-song Hung: Investigation Jian Zuo: Investigation Lian Tian: Investigation Ming Yi: Investigation Chun Ding: Investigation Yan Wang: Conceptualization, Methodology, Validation, Writing-Review&Editing, Supervision, Project administration, Funding acquisition

Graphic Abstract for Effect of Ultrasonication Parameters on Forward Osmosis Performance of Thin Film Composite Polyamide Membranes Prepared with Ultrasound-Assisted Interfacial Polymerization” Liang Shen, Wei-song Hung, Jian Zuo, Lian Tian, Ming Yi, Chun Ding, and Yan Wang a,b*

Ultrasound power: 360 W

Ultrasound frequency: 60 KHz

480-600 W

40 KHz

Ultrasound power: 360 W Ultrasound frequency: 40 KHz

Ultrasound time: Short

Modification efficiency Balance

Ultrasound frequency: 40 KHz 60 KHz

Ultrasound time: Long

Weak Strong

Morphology change Thinner PA layer with smoother surface & smaller free volume

Thicker PA layer with rougher surface & larger free volume

1

Effect of Ultrasonication Parameters on Forward Osmosis Performance of Thin

2

Film Composite Polyamide Membranes Prepared with Ultrasound-Assisted

3

Interfacial Polymerization

4 5

Liang Shen a,b, Wei-song Hung c,d, Jian Zuo e, Lian Tian a,b, Ming Yi a,b, Chun Ding a,b

6

and Yan Wang a,b*

7 a

8

Key Laboratory of Material Chemistry for Energy Conversion and Storage

9

(Huazhong University of Science and Technology), Ministry of Education, Wuhan,

10

430074, China b

11

Hubei Key Laboratory of Material Chemistry and Service Failure, School of

12

Chemistry and Chemical Engineering, Huazhong University of Science and

13

Technology, Wuhan, 430074, P.R. China c

14

Graduate Institute of Applied Science and Technology, National Taiwan University of Science and Technology, Taipei, 10607, Taiwan

15 16

d

R&D Centre for Membrane Technology, Chung Yuan Christian University, Taoyuan, 32023, Taiwan

17 18

e

Singapore Institute of technology, 10 Dover Drive, Singapore 138683, Singapore

19 20 21

* Corresponding author. Tel.: 86 027-87543032; fax: 86 027-87543632.

22

E-mail address: [email protected] (Yan Wang)

1

23

ABSTRACT

24 25

High-performance thin-film composite (TFC) membranes with a high water

26

permeability and high salt rejection are requisites for the successful development of

27

the forward osmosis technology. Based on our previous work on high-performance

28

TFC membranes obtained by a novel ultrasound-assisted interfacial polymerization

29

with different ultrasonication powers, this work conducts a comprehensive

30

investigation of the effects of various ultrasonication parameters including

31

ultrasonication power, frequency, and time on the membrane performance. The effects

32

of the ultrasonication parameters on the chemical and surface properties, morphology,

33

free volume, and the corresponding separation performance characteristics were

34

investigated systematically. The modified TFC membrane obtained at the optimized

35

ultrasonication conditions shows a water flux of 120.1±2.1 LMH (2.6 times higher

36

than that of the control membrane) and a reverse salt flux of 12.1±0.7 gMH (34.2%

37

reduction relative to that of the control membrane) in the pressure retarded osmosis

38

mode with the draw solution of 2 M NaCl and the feed solution of deionized water.

39 40

Keywords:

Ultrasound-assisted

interfacial

41

Thin-film composite membrane; Polyamide; Ultrasonication parameters

42

2

polymerization;

Forward

osmosis;

43

1. Introduction

44 45

Due to their ultrathin selective layer, thin-film composite (TFC) membranes with

46

nanometer or sub-nanometer scale pores have emerged as mainstream candidates for

47

use in a wide variety of separation fields, including nanofiltration [1-4], reverse

48

osmosis [5-7] and forward osmosis (FO) [8-10]. Commonly, the polyamide (PA)

49

selective layer is formed by aromatic amine and acyl halide via interfacial

50

polymerization (IP), and is highly-crosslinked and inherently hydrophobic, leading to

51

the low water flux. Additionally, the permeability-rejection trade-off relationship also

52

limits the improvement in the membrane separation properties.

53

It is well-known that the bulk properties of the PA layer are important factors for

54

determining the separation performance of TFC membranes, and are controlled by the

55

interplay between the diffusion and reaction of both monomers [11, 12]. Since the IP

56

reaction generally occurs in the organic phase due to the solubility differences

57

between the two monomers [11, 12], the morphology and microstructure of the

58

resultant PA layer and the separation performance of the TFC membranes are mainly

59

affected by the absolute IP reaction rate, that is governed by the diffusion of the amine

60

monomers into the organic phase [13].

61

Massive efforts have been made to optimize and alter the IP reaction by various

62

modifications to improve the overall separation performance of TFC membranes. One

63

widely-used strategy is to utilize additives (such as the phase transfer catalyst) in one

64

of the two phases to facilitate the penetration of amine monomers into the reaction

65

zone [14], or reduce (accelerate) the IP reaction rate with an inhibitor [15] (catalyst

66

[16]), resulting in the optimized separation properties. Another strategy is to use a

67

co-solvent (such as dimethyl sulfoxide, acetone, or alcohols) in the aqueous phase to 3

68

form a transition layer between the two phases to enhance the phase miscibility,

69

increasing the amount of diffused amine monomer, and resulting in the formation of a

70

rougher PA layer [17]. Furthermore, the addition of nanomaterials into the monomer

71

solution may also affect the IP process, giving rise to the formation of a thinner and

72

smoother PA layer, and hence the improved separation performance [18, 19].

73

Moreover, the molecular layer-by-layer method that utilizes a single toluene solvent to

74

dissolve both monomers has been reported recently for the fabrication of the PA layer

75

of TFC membranes [20]. This method can control the thickness and roughness of the

76

resulting PA layer by overcoming the kinetic and mass transfer limitations of the

77

traditional IP, contributing to the optimized separation properties of the resultant TFC

78

membranes [20].

79

Recently, we developed a novel green method called ultrasound-assisted

80

interfacial polymerization (UAIP) for fabricating TFC membranes with excellent

81

separation properties [21]. The effect of the ultrasonication power on the bulk

82

properties and separation performance of the obtained TFC membranes was also

83

studied. The sonochemical effect of the ultrasonication not only enlarges the mixing

84

interface to increase the polymerization area, but also promotes the diffusion of amine

85

monomers, resulting in the better mixing efficiency of the two monomers, and thus a

86

more complete IP reaction. Additionally, the introduced ultrasound waves also

87

disrupted the PA chain packing, generated more nanobubbles, and increased the

88

amount of the amine penetrating into the organic phase, giving rise to the formation of

89

a looser PA layer with a larger free volume [22, 23]. With the increased

90

ultrasonication power, the resultant membrane exhibits a rougher and thicker PA layer

91

with a larger free volume, achieving greatly improved separation performance.

92

This study is a continuation of our previous work and investigates the effects of 4

93

different ultrasonication parameters (including power, frequency, and time) on the

94

bulk and separation properties of the resultant TFC membranes. Theoretically, when a

95

higher ultrasonication frequency is applied, more ultrasound waves with relatively

96

lower energy can be generated [24], exerting more frequent but less intense effects on

97

the formation of the PA layer during the IP process. Meanwhile, a longer

98

ultrasonication time may facilitate the diffusion of more amine monomers into the

99

organic phase, increasing the amount of the amine monomer involved in the IP

100

reaction and therefore obtaining a rougher, thicker and looser PA layer. As a

101

continuation of our previous work [21], here we comprehensively explore the

102

interplay between the ultrasonication power and frequency, as well as its impacts on

103

the morphology and microstructure, and the separation performance of the obtained

104

TFC membranes. Moreover, the effect of the ultrasonication time on these properties

105

is also studied systematically. Therefore, the aim of this work is to comprehensively

106

explore and optimize the ultrasonication parameters in order to develop a TFC

107

membrane with the desirable morphology, microstructure, and improved separation

108

performance.

109 110

2. Materials and methods

111 112

2.1 Materials and chemicals

113 114

Polysulfone (PSF, Mw: 800 kDa), N-methyl pyrrolidone (NMP, ≥99.5%) and

115

polyethylene glycol 400 (PEG-400, 99%) were applied for fabricating the substrate

116

membrane. M-phenylenediamine (MPD, 99.5%), trimesoyl chloride (TMC, 98%), and

117

n-hexane (≥99%) were used for preparing the PA layer. Sodium chloride (NaCl, 5

118

≥99.5%) was employed in FO and reverse osmosis (RO) tests.

119 120

2.2 Preparation of TFC membranes

121 122

PSF substrates and PA active layers were prepared by the phase inversion and IP

123

methods, respectively. The detailed procedures can be referred to our previous works

124

[25-29]. A brief description about the fabrication of the PA layer under ultrasonication

125

is shown as below [21]. First, the substrate washed by ultrapure water was immersed

126

in 2.0 wt% MPD aqueous solution 2 min. After the removal of excessive amine

127

solution, 0.1 wt% TMC/hexane solution was brought to contact with the substrate for

128

1 min under an ultrasonication circumstance. After the organic solution discarded, the

129

obtained TFC membrane was stored in deionized (DI) water. The ultrasonication

130

powers and frequencies applied in this work were 360, 480, 600 W, and 40, 60 kHz,

131

respectively. These obtained membranes were denoted as PA-p-f, which p and f

132

represent the ultrasonication power and frequency, respectively. Meanwhile, these

133

modified membranes formed with different ultrasonication time (0 - 60 seconds) (here

134

the ultrasonication power and frequency were fixed at 360 W and 40 kHz) were

135

denoted as PA-T, which T stands for the ultrasonication time. For example, PA-15s

136

refers to the membrane formed under UAIP for 15 seconds.

137 138

2.3 Membrane characterizations

139 140

Surface and bulk properties of obtained TFC membranes were examined by

141

various characterization techniques, and a detailed description can be found in the

142

Supporting Information. Specifically, the crosslinking degree (CD) value of the PA 6

143

network (Fig. 1) can be calculated from the X-ray Photoelectron Spectroscopy (XPS)

144

results based on Eqs. (1) and (2). Here x and y refer to the repeat unit numbers of

145

fully-crosslinked and linearly-crosslinked parts in the PA network, respectively.

146

147



=

(1)



CD =



× 100% =

×

(2)

× 100%

148

149 150 151

Fully-crosslinked PA network

Linearly-crosslinked PA network

Fig. 1. Molecular structures of fully and linearly crosslinked PA networks

152 153

2.4 Evaluation of separation and antifouling properties of TFC membranes

154 155

The intrinsic transport properties of the TFC membranes were determined by RO

156

tests using a RO system. The FO performance and antifouling capacity were

157

evaluated by FO tests using a lab-scale FO set-up. The detailed descriptions also can

158

be found in the Supporting Information.

159 160

3. Results and discussion

161 162

3.1 Effect of ultrasonication power and frequency

163 7

164

In this work, two ultrasonication frequencies (40 and 60 kHz) are used for the

165

preparation of TFC membranes by the UAIP process. On the one hand, ultrasound

166

waves generated at a low frequency are generally energetic, and may destroy the

167

nascent PA layer easily at a high power density [21]. On the other hand, at a

168

high-frequency condition, the sound is readily attenuated, so that the cavitation

169

bubbles are smaller and collapse less energetically with lower temperature and

170

pressures [30], resulting in the weaker cavitation effect. This is due to the rarefaction

171

cycles are too short to allow the growth of developed cavitation bubbles to the

172

equilibrium size [30, 31]. When the applied power density is low, the generated sound

173

waves have low energy, particularly for the high-frequency condition with more

174

sound waves where a lower amount of effective sound waves leads to a weaker

175

sonochemical effect in the IP process. On the other hand, when the power density

176

increases, the sonochemical effect is enhanced because both the number of the

177

cavitation bubbles and the size of the cavitation zone increase with the higher pressure

178

amplitude of the sound waves [30, 32]. Moreover, hydrodynamic turbulence also

179

increases with the higher power density, as the result of the combined effects of the

180

higher bubble implosion density, larger number of bubbles, and greater absorption of

181

the acoustic energy by the medium [30, 32]. Therefore, for a sufficiently high power

182

density, more sound waves will be energetic and effective. Accordingly, the

183

sonochemical effect in the high-frequency condition is more pronounced than that in

184

the low-frequency condition due to more effective cavitation bubbles.

185

Additionally, ultrasonication power in the range of 360-600 W is applied in this

186

work due to the relatively better sonochemical effect of ultrasonication in this power

187

range as found in our previous work [21]. According to the above analysis, for the

188

ultrasonication power of 360 W, the modification effect of the ultrasonication with a 8

189

higher frequency is expected to be weaker. By contrast, when the applied power

190

density increases to 480-600 W, the modification effect of the ultrasonication with a

191

higher frequency is expected to be stronger than that of the lower-frequency condition.

192

The different modification effects are verified by the examination of the variations in

193

the chemical properties, micro-morphology, and the separation properties of the

194

resultant TFC membranes as described below.

195

The chemical changes in the PA layers due to the use of ultrasonication are

196

examined by XPS, and the corresponding results are displayed in Figs. 2 and S1 and

197

Table S1. Fig. 2 shows that the O/N ratios of the modified membranes increase

198

compared to that of the control membrane, suggesting the higher crosslinking degrees

199

(CDs) of the modified PA layers, particularly under a higher ultrasonication power.

200

This behavior is resulted from the more complete IP reaction achieved by

201

ultrasonication assistance, as discussed in our previous work [21]. It is also observed

202

that with the exception of the PA-360-60 membrane, the O/N ratios of the modified

203

membranes formed with a frequency of 60 kHz are lower than those of the modified

204

membranes formed with a frequency of 40 kHz. This is ascribed to the more efficient

205

monomer mixing under the higher ultrasonication frequency condition with a

206

relatively high ultrasonication power, as discussed above.

207

The micro-structural changes introduced to the resultant PA layers by

208

ultrasonication are further examined by Positron Annihilation Lifetime Spectra (PALS)

209

characterization. Figs. 3a and S2-a show that the S values of the modified membranes

210

increase compared to that of the control one, suggesting the formation of a looser PA

211

layer. This is believed to be due to the looser PA chain packing [21], greater

212

generation of nanovoids [22], and greater MPD penetration [23] obtained with the

213

assistance of ultrasonication in the IP process. With the exception of the membranes 9

214 215 216

217 218

Fig. 2. O/N ratios and crosslinking degrees (CD) of the control membrane and

219

modified ones formed with different ultrasonication powers and frequencies

220 221

formed at the ultrasonication power of 360 W, the S values of all modified membranes

222

formed under ultrasonication at 60 kHz are higher than those of the membranes

223

formed under ultrasonication at 40 kHz with the same ultrasonication power, as

224

shown in Fig. 3a. The larger S values indicate the looser structure of the PA layers

225

formed under a higher frequency that is most likely due to the greater amount of free

226

volume cavities generated with a larger pore size as derived from the orth-positron

227

(o-Ps) lifetime results. The smaller S value of the PA-360-60 membrane compared to

228

that of the PA-360-40 membrane is believed to be due to the less energetic cavitation

229

effect.

10

230

The lifetime results presented in Figs. 3b and 3c further reveal the free volume

231

properties of the obtained PA layers. Fig. 3b shows that the free volume pore radii (R)

232

of the modified PA layers (2.932-3.063 Å) are all larger than that of the control one

233

(2.878 Å). Additionally, the order of the pore radius (R) values is consistent with the

234

order of the S values, that is, PA-0 < PA-600-40 < PA-360-60 < PA-480-40 <

235

PA-360-40 < PA-600-60 < PA-480-60. Moreover, as observed from Fig. 3c, despite

236

the different sequence of the free volume intensity (I3) values, i.e., PA-0 < PA-360-60

237

< PA-600-40 < PA-480-40 < PA-360-40 < PA-600-60 < PA-480-60, the fractional free

238

volume (FFV) result is still consistent with the S value result that is positively related

239

to the free volume pore radius and amount (density). With an intermediate

240

ultrasonication power density (360 W), the modification efficiency for a lower

241

ultrasonication frequency (40 kHz) is higher than that with a higher frequency (60

242

kHz). This may be ascribed to the greater impact of the acoustical cavitation on the

243

above-described factors. By contrast, a high ultrasonication power density (480-600

244

W) coupled with a high frequency favors stronger sonochemical effects that are most

245

likely due to enhanced acoustical cavitation.

246 247

(a)

(b)

248 249

(c) 11

250 251

Fig. 3. (a) S values at 2 keV, (b) o-Ps lifetime distribution, and (c) free volume pore

252

parameters of the control membrane and modified ones formed with various

253

ultrasonication powers and frequencies

254 255

The more efficient monomer mixing under ultrasonication is expected to benefit

256

the formation of a thicker and rougher PA layer. As observed from Fig. 4a that

257

compared to the control membrane, the ridge-and-valley structural feature becomes

258

more pronounced on the surface of the modified membranes, which also can be

259

confirmed by AFM images (Fig. S3). Additionally, rougher and thicker PA layers are

260

formed at a higher ultrasonication frequency compared to those formed at a lower

261

frequency (except for the PA-360-60 membrane). This is ascribed to the more

262

efficient monomer mixing and a larger reaction interface for the interfacial

263

polymerization. Specifically, for the PA-600-40 membrane, unlike for the PA-600-60

264

membrane, the roughness and thickness of the PA layer is even lower than that of the

12

265

PA-480-40 membrane. This phenomenon could be due to the fact that the

266

ultrasonication power (600 W) is very strong and provides the energy for the

267

destruction of the nascent formed PA layer, leading to the defective PA layer with

268

non-uniformly distributed ridge-and-valley structures [21]. Due to the higher surface

269

roughness, the WCA values of the membranes formed by UAIP are lower than that of

270

the membrane formed by the traditional IP as displayed in Fig. 4b, indicating the

271

improved surface hydrophilicity. Except for the PA-360-60 membrane, better surface

272

hydrophilicity of the formed TFC membrane can be obtained with a higher

273

ultrasonication frequency of 60 kHz employed in UAIP.

274 275

(a)

276 277

(b)

13

278 279

Fig. 4. (a) SEM images, (b) average roughness (Ra) and WCAs of the control

280

membrane and modified membranes formed with various ultrasonication powers and

281

frequencies

282 283

The RO results of these membranes prepared under different ultrasonication

284

powers and frequencies are shown in Fig. 5a. It is observed that the water permeances

285

(A) of the modified membranes increase compared to that of the control one due to the

286

better surface hydrophilicity, larger FFV, and rougher surface. Additionally, it is

287

interesting to note that the water permeances of the modified membranes formed

288

under ultrasonication at 60 kHz show non-monotonic changes with increasing power,

289

while those of the modified membranes formed under ultrasonication at 40 kHz

290

decrease monotonically. With the further increase in the ultrasonication power, a

291

reduction in the water fluxes is observed for both the PA-480-40 and PA-600-60

292

membranes, caused by the thicker PA layer and the smoother surface, respectively.

293

Furthermore, with the exception of the PA-360-60 membrane, the water permeances 14

294

of the modified membranes under ultrasonication at 60 kHz are all larger than those of

295

the modified membranes obtained under ultrasonication at 40 kHz, due to the further

296

improved membrane hydrophilicity, surface roughness, and FFV.

297

On the other hand, modified membranes with a thicker PA layer also show higher

298

salt rejections (Rs), except for the PA-600-40 membrane due to the formation of a

299

defect-containing PA layer [21]. In addition, with the exception of the PA-360-60

300

membrane, modified membranes formed under ultrasonication at 60 kHz exhibit

301

higher salt rejections than those of the modified membranes formed under

302

ultrasonication at 40 kHz with the same ultrasonication power, which is consistent

303

with the variation of the PA layer thickness. Moreover, the salt rejections of the

304

modified membranes obtained under both ultrasonication frequencies increase with

305

increasing power (with the exception of the PA-600-40 membrane) because of the

306

formed thicker PA layer. Additionally, except for the PA-600-60 membrane, the salt

307

permeability (B) of the control membrane is lower than or comparable to those of

308

modified ones. Accordingly, the B/A ratio of the control membrane is lower than those

309

of the modified ones (with the exception of the PA-600-40 membrane), indicating the

310

improved permselectivity.

311

The FO performance characteristics of these membranes are also evaluated (Fig.

312

5b). In accordance with their intrinsic transport properties, the water flux of the

313

control membrane is lower than those of the modified membranes, as the result of the

314

lower surface hydrophilicity, smoother surface, and smaller FFV. Accordingly, except

315

for the PA-360-60 membrane, the modified membranes formed under ultrasonication

316

at 60 kHz exhibit increased water fluxes compared to those of the modified ones

317

formed under ultrasonication at 40 kHz with the same power condition. In addition,

318

with the exception of the PA-600-40 membrane, the reverse salt fluxes of the 15

319 320

(a)

321 322

(b)

323 324

Fig. 5. (a) Intrinsic transport properties and (b) FO separation performance of the 16

325

control membrane and modified ones formed with different ultrasonication powers

326

and frequencies

327 328

modified membranes with thicker PA layers decrease compared to that of the control

329

one, and decrease with increasing ultrasonication power. Moreover, with the

330

exception of the PA-360-60 membrane, the reverse salt fluxes of the modified

331

membranes obtained under ultrasonication at 60 kHz are lower than those of the

332

modified ones obtained under ultrasonication at 40 kHz at the same power condition.

333 334

3.2 Effect of ultrasonication time

335 336

In theory, with a longer ultrasonication time, more amine monomers can diffuse

337

into the organic phase due to the longer duration of the sonochemical effect on the IP

338

process, resulting in a higher IP reaction degree, and therefore the formation of a

339

thicker, rougher, and looser PA layer.

340

XPS results in Fig. S4 reveals that the O/N ratios of the obtained membranes

341

decrease with increasing ultrasonication time, indicating a higher crosslinking degree

342

(20.59-48.96%) due to the more complete IP reaction. Additionally, Fig. 6a shows

343

that the roughness and thickness of these membranes increase monotonically with

344

increasing ultrasonication time. Correspondingly, the WCA values of the obtained

345

membranes decrease with increasing ultrasonication time, as displayed in Fig. 6b,

346

indicating the improved surface hydrophilicity due to the rougher surface.

347

PALS characterizations of the PA layers formed under ultrasonication for different

348

time are performed to study the microstructure changes. As displayed in Fig. 7, the S

349

values, free volume pore radii, and FFVs of the modified membranes increase with 17

350

increasing ultrasonication time, indicating the formation of an increasingly loose PA

351

layer with the longer ultrasonication time.

352 353

(a)

354 355

(b)

356 357

Fig. 6. (a) SEM images, (b) average roughness (Ra) and WCAs of as-fabricated

358

membranes with different ultrasonication time

18

359

(a)

(b)

360

(c)

361

362 363

Fig. 7. (a) S values and (b) free volume pore parameters of as-fabricated membranes

364

formed with different ultrasonication time

365 366

Accordingly, the FO performance characteristics of the obtained TFC membranes

367

are studied as shown in Fig. 8. It can be found that the water fluxes of the membranes

368

increase monotonically with increasing ultrasonication time, while the reverse salt 19

369

fluxes present non-monotonic changes with increasing ultrasonication time. Due to

370

the increased free volume pore size, the reverse salt fluxes of the membranes formed

371

by UAIP with a shorter ultrasonication time (15-30 s) increase compared to that of the

372

control one. By contrast, with a further increase in the ultrasonication time (45-60 s),

373

the thicker PA layer contributes to the lower reverse salt flux of the modified

374

membranes. The RO performance results (Table S2) are consistent with the FO

375

performance results. The water permeances of the resultant membranes increase with

376

longer ultrasonication time. Meanwhile, the salt rejection (Rs) values of the modified

377

membranes first tend to decrease and then increase with the longer ultrasonication

378

time. Moreover, the salt permeabilities (B) of the resultant membranes decrease

379

monotonically with the increase in the ultrasonication time. Accordingly, the B/A

380

results of as-fabricated membranes are opposite to their Rs results.

381

382 383

Fig. 8. FO performance of TFC membranes formed with various ultrasonication time

384 385

To further explore the relationship between the pore size and the separation

386

performance, Fig. 9 presents the results for the water flux and salt rejection of the 20

387

as-fabricated membranes as a function of the mean free volume pore radius. It is

388

observed that the water flux presents a rough rising trend with the increase of free

389

volume pore radius. Generally, a membrane with a larger free volume should have a

390

high water flux because the flux is proportional to the size and density of the free

391

volume in the PA layer [23, 33]. However, since both the free volume pore density

392

and surface roughness are also important factors that determine the membrane

393

permeability, the water flux of a membrane with a large free volume pore size but a

394

low pore density and/or smooth surface may not follow the trend strictly. By contrast,

395

salt rejection is not directly affected by the changes in the free volume pore radius,

396

because it is mainly governed by the amount of the free volume pores larger than the

397

hydrated salt [23] and the PA layer thickness rather than by the mean free volume pore

398

radius.

399

400 401 402

Fig. 9. Water flux and salt rejection of obtained TFC membranes as a function of mean free volume pore radius

403 404

3.3 Antifouling properties of TFC membranes

405 21

406

The effects of the ultrasonication introduced in the IP on the antifouling properties

407

are also studied using the PA-0 membrane (smoothest surface, lowest crosslinking

408

degree and hydrophilicty) and the PA-600-60 membrane (roughest surface, highest

409

crosslinking degree and hydrophilicty) against three foulant systems, namely

410

inorganic gypsum foulant, organic sodium alginate (SA) foulant, and mixed foulant

411

containing both SA and Ca2+ ions.

412

The inorganic fouling test results are presented in Fig. 10a and show that in

413

comparison with the PA-0 membrane, the PA-600-60 membrane exhibits a lower flux

414

drop and a higher flux recovery. This implies that the modified membrane has

415

improved anti-scaling property that is mainly attributed to its highly-crosslinked PA

416

layer with fewer carboxylate groups. The gypsum scale fouling on PA-based

417

membranes is predominantly governed by the surface chemistry of the PA layer, i.e.,

418

the carboxylate groups [34-36]. It was reported in previous studies that the gypsum

419

fouling on the PA layer is mainly caused by surface heterogeneous crystallization that

420

proceeds through the stages of prenucleation cluster, amorphous nanoparticle, and

421

polycrystal [34]. The complexion of negatively-charged carboxylate groups with Ca2+

422

ions increases the Ca2+ ion concentration on the PA layer surface, inducing the

423

occurrence of the gypsum prenucleation [34, 36]. Therefore, a greater amount of

424

carboxylate groups in the PA-600-60 membrane leads to the more severe gypsum

425

fouling [34, 36].

426

The organic fouling results presented in Fig. 10b reveal that the PA-600-60

427

membrane exhibits a greater water flux decrease and less water flux recovery than

428

those of the PA-0 membrane. This is due to the rougher surface of the PA layer with

429

less negative charges. The SA fouling layer growth on the membrane surface

430

undergoes two stages, namely the stage driven by the membrane - foulant interaction 22

431

(a)

432 433

(b)

434 435

(c)

436 437

Fig. 10 Dynamic fouling testing results of the PA-0 and PA-600-60 membranes: (a)

438

inorganic fouling using gypsum as foulant, (b) organic fouling using SA as foulant, (c)

439

organic fouling using SA and Ca2+ ions as foulant

440 441

and the stage driven by the foulant - foulant interaction [37]. The formation of an 23

442

initial SA gel layer in the first stage is the necessary step for the SA membrane fouling

443

[37]. Generally, a rough PA surface is prone to the accumulation of SA molecules due

444

to its large surface area [37, 38] and uneven flux distribution [37, 39]. Additionally, a

445

PA layer with a greater amount of negatively-charged carboxylate groups can

446

electrostatically repel the negatively-charged SA molecules. Accordingly, the initial

447

formation of the SA layer in the modified PA layer with larger roughness and fewer

448

negative charges is easier, enhancing the further growth of the SA gel layer caused by

449

the foulant – foulant interaction.

450

The combined fouling results are presented in Fig. 10c, and show that both

451

membranes exhibit a more severe water flux reduction and less water flux recovery

452

compared to the SA-only fouling, because the presence of the Ca2+ ions in the SA

453

foulant solution aggravates the fouling behavior through its “bridge” effect for the

454

crosslinking of SA molecules that leads to the formation of a denser SA gel layer [37,

455

40]. However, unlike the organic fouling caused by SA, the PA-600-60 membrane

456

exhibits a slightly better antifouling capacity than that of the PA-0 membrane. This

457

may be resulted from the formation of a relatively looser SA gel layer in the

458

membrane-foulant interaction stage.

459 460

3.4 Benchmarking

461 462

Table 1 summarizes the separation performance benchmarking of the TFC

463

membrane developed in this work and some other TFC membranes recently reported

464

[41-50]. An examination of the listed data reveals that compared to the other TFC

465

membranes obtained using various modification approaches, the PA-480-60

466

membrane shows a much higher water flux and a comparable reverse salt flux. 24

467

Accordingly, the specific reverse salt flux (Js/Jv) of the PA-480-60 membrane is much

468

lower than those of most other reported membranes, indicating its much better

469

membrane permselectivity. The superior separation performance of the PA-480-60

470

membrane is attributed to the optimized microstructure and morphology of the PA

471

layer prepared via the UAIP process with optimized parameters.

472 473

Table 1 FO performance benchmarking of TFC membranes Membrane code

Jv Js Js/Jv Feed (LMH) (gMH) (g/L) solution 120.10

12.10

0.10

73.87

7.90

0.11

PA-PSF/LDH

34.60

12.70

0.37

PA-PES/SPES

35.10

9.90

0.28

PA-PSf/HNT

26.01

14.20

0.55

PA-AMPES/3

56.30

9.50

0.17

PA-PSf/zeolite

~85.00

~55.00

0.65

PA-PVDF nanofiber

30.40

6.40

0.21

PA-PSF/BP

74.40

11.88

0.16

PA-PVDF/SiO2 @MWCNT

22.10

4.10

0.19

PA-PSf/TiO2

31.20

6.66

0.21

PA-PSf/LDH /GO

13.5

5.5

0.41

PA-PSf/GO

19.77

3.36

0.17

PA-480-60

Draw solution

Operation mode

DI water

2M NaCl

PRO

DI water DI water DI water DI water DI water DI water DI water DI water DI water DI water DI water

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

Ref.

FO

This work

PRO

[41]

PRO

[42]

PRO

[43]

PRO

[44]

PRO

[45]

PRO

[46]

PRO

[47]

FO

[51]

FO

[48]

FO

[49]

FO

[50]

474 475

4. Conclusion

476 477

The present study is a continuation of our previous study for the development of 25

478

high-performance TFC membranes by the UAIP method with different ultrasonication

479

parameters (power, frequency, and time). The introduction of ultrasonication in the IP

480

process promotes efficient monomer mixing, resulting in the more complete IP

481

reaction. With a relatively high ultrasonication power (480-600 W), a high

482

ultrasonication frequency (60 kHz) with greater amount of effective cavitation

483

bubbles favors the efficient modification of the TFC membrane, resulting in the

484

higher crosslinking, larger free volume pore size, and rougher and thicker PA layer,

485

and therefore the superior separation performance of this membrane compared to

486

those of the TFC membrane formed under low-frequency (40 kHz) ultrasonication.

487

However, with a low power intensity at 360 W, the modification at the lower

488

ultrasonication frequency (40 kHz) is more effective than that at the higher frequency

489

(60 kHz), due to the stronger sonochemical effect of acoustical cavitation. As a result,

490

compared to the PA-360-40 membrane, the PA-360-60 membrane shows a lower

491

crosslinking degree, smaller free volume pore size, smoother and thinner PA layer,

492

and inferior separation performance. On the other hand, the crosslinking degree, S

493

value, FFV, roughness, thickness, and hydrophilicity of the PA layer in the resultant

494

TFC membrane increase with increasing ultrasonication time. Consequently, the

495

water fluxes of the resultant membranes increase monotonically with longer

496

ultrasonication time, while reverse salt fluxes present non-monotonic changes.

497

Moreover, despite the formation of a rougher PA layer under ultrasonication, the

498

modified membrane with fewer carboxylate groups exhibits improved antifouling

499

capacities against gypsum scaling and mixed SA/Ca2+ foulants, but poor resistance to

500

organic foulants of SA.

501 502 26

503

Acknowledgment

504 505

We thank the financial support from National Natural Science Foundation of

506

China (no. 21306058), and the Free Exploring Fundamental Research Project from

507

Shenzhen Research Council, China (no.JCYJ20160408173516757). We are indebted

508

to Prof. Tai-Shung Chung’s group in the National University of Singapore for his help

509

with PALS characterization. Special thanks are also given to the Analysis and Testing

510

Center, the Analysis and Testing Center of Chemistry and Chemical Engineering

511

School, and the State Key Laboratory of Materials Processing and Die & Mould

512

Technology, in Huazhong University of Science and Technology for their help with

513

material characterizations.

514 515

27

516

List of abbreviations and nomenclatures

517 518

Abbreviations

519 520

AFM

: atomic force microscopy

521

CD

: crosslinking degree

522

DI

: deionized

523

FFV

: fractional free volume

524

FO

: forward osmosis

525

IP

: interfacial polymerization

526

mLBL

: molecular layer-by-layer

527

MPD

: m-phenylenediamine

528

NaCl

: sodium chloride

529

NMP

: N-Methyl pyrrolidone

530

o-Ps

: orth-positron

531

PA

: polyamide

532

PALS

: position annihilation lifetime spectroscopy

533

PDF

: probability density function

534

PEG

: polyethylene glycol

535

PRO

: pressure retarded osmosis

536

PSf

: polysulfone

537

RO

: reverse osmosis

538

SEM

: scan electron microscopy

539

TFC

: thin-film composite

540

TMC

: 1,3,5-trimesoyl chloride 28

541

UAIP

: ultrasound-assisted interfacial polymerization

542

WCA

: water contact angle

543

XPS

: X-ray photoelectron spectroscopy

544 545

Nomenclatures

546 547

A

: water permeance

548

Am,FO

: effective membrane area in FO process

549

Am,RO

: effective membrane area in RO process

550

B

: salt permeability

551

Cf

: feed concentration

552

Cp

: permeate

553

Ct

: salt concentration

554

I3

: free volume intensity

555

J

: pure water flux

556

Js

: reverse salt flux

557

Js/Jv

: specific reverse salt flux

558

Jv

: water flux

559

LMH

: L·m-2·h-1

560

gMH

: g·m-2·h-1

561

R

: free volume pore size radius

562

Ra

: average roughness

563

Rs

: salt rejection

564

S

: ratio of total annihilation counts at 511 keV

565

∆P

: hydraulic pressure

concentration

29

566

∆t

: test time

567

∆V

: volume change

568

∆π

: osmotic pressure

569

τ3

: orth-positron lifetime

570

30

571

References

572 573

[1] T.-D. Lu, B.-Z. Chen, J. Wang, T.-Z. Jia, X.-L. Cao, Y. Wang, W. Xing, C.H. Lau,

574

S.-P. Sun, Electrospun nanofiber substrates that enhance polar solvent separation from

575

organic compounds in thin-film composites, Journal of Materials Chemistry A, 6

576

(2018) 15047-15056.

577

[2] X.Q. Cheng, L. Shao, C.H. Lau, High flux polyethylene glycol based

578

nanofiltration membranes for water environmental remediation, Journal of membrane

579

science, 476 (2015) 95-104.

580

[3] S. Karan, Z. Jiang, A.G. Livingston, Sub–10 nm polyamide nanofilms with

581

ultrafast solvent transport for molecular separation, Science, 348 (2015) 1347-1351.

582

[4] D. Wu, J. Martin, J.R. Du, Y. Zhang, D. Lawless, X. Feng, Effects of chlorine

583

exposure on nanofiltration performance of polyamide membranes, Journal of

584

membrane science, 487 (2015) 256-270.

585

[5] L.F. Greenlee, D.F. Lawler, B.D. Freeman, B. Marrot, P. Moulin, Reverse osmosis

586

desalination: water sources, technology, and today's challenges, Water research, 43

587

(2009) 2317-2348.

588

[6] C.Y. Tang, Q.S. Fu, A. Robertson, C.S. Criddle, J.O. Leckie, Use of reverse

589

osmosis membranes to remove perfluorooctane sulfonate (PFOS) from semiconductor

590

wastewater, Environmental science & technology, 40 (2006) 7343-7349.

591

[7] S. Qi, R. Wang, G.K.M. Chaitra, J. Torres, X. Hu, A.G. Fane, Aquaporin-based

592

biomimetic reverse osmosis membranes: Stability and long term performance, Journal

593

of Membrane Science, 508 (2016) 94-103.

594

[8] N.L. Le, N. Bettahalli, S. Nunes, T.-S. Chung, Outer-selective thin film composite

595

(TFC) hollow fiber membranes for osmotic power generation, Journal of Membrane 31

596

Science, 505 (2016) 157-166.

597

[9] Y.-H. Chiao, A. Sengupta, S.-T. Chen, S.-H. Huang, C.-C. Hu, W.-S. Hung, Y.

598

Chang, X. Qian, S.R. Wickramasinghe, K.-R. Lee, Zwitterion augmented polyamide

599

membrane for improved forward osmosis performance with significant antifouling

600

characteristics, Separation and Purification Technology, 212 (2019) 316-325.

601

[10] X. Li, C.H. Loh, R. Wang, W. Widjajanti, J. Torres, Fabrication of a robust

602

high-performance FO membrane by optimizing substrate structure and incorporating

603

aquaporin into selective layer, Journal of Membrane Science, 525 (2017) 257-268.

604

[11] V. Freger, Kinetics of Film Formation by Interfacial Polycondensation,

605

Langmuir : the ACS journal of surfaces and colloids, 21 (2005) 1884-1894.

606

[12] P.W. Morgan, S.L. Kwolek, Interfacial polycondensation. II. Fundamentals of

607

polymer formation at liquid interfaces, Journal of Polymer Science Part A: Polymer

608

Chemistry, 34 (1996) 531-559.

609

[13] A.K. Ghosh, B.-H. Jeong, X. Huang, E.M.V. Hoek, Impacts of reaction and

610

curing conditions on polyamide composite reverse osmosis membrane properties,

611

Journal of Membrane Science, 311 (2008) 34-45.

612

[14] J. Xiang, Z. Xie, M. Hoang, D. Ng, K. Zhang, Effect of ammonium salts on the

613

properties of poly(piperazineamide) thin film composite nanofiltration membrane,

614

Journal of Membrane Science, 465 (2014) 34-40.

615

[15] Z. Tan, S. Chen, X. Peng, L. Zhang, C. Gao, Polyamide membranes with

616

nanoscale Turing structures for water purification, Science, 360 (2018) 518.

617

[16] L. Shen, L. Tian, J. Zuo, X. Zhang, S. Sun, Y. Wang, Developing

618

high-performance thin-film composite forward osmosis membranes by various

619

tertiary amine catalysts for desalination, Advanced Composites and Hybrid Materials,

620

2 (2019) 51-69. 32

621

[17] S.-Y. Kwak, S.G. Jung, S.H. Kim, Structure-Motion-Performance Relationship of

622

Flux-Enhanced Reverse Osmosis (RO) Membranes Composed of Aromatic

623

Polyamide Thin Films, Environmental science & technology, 35 (2001) 4334-4340.

624

[18] L. Shen, S. Xiong, Y. Wang, Graphene oxide incorporated thin-film composite

625

membranes for forward osmosis applications, Chemical Engineering Science, 143

626

(2016) 194-205.

627

[19] S. Sorribas, P. Gorgojo, C. Tellez, J. Coronas, A.G. Livingston, High flux thin

628

film nanocomposite membranes based on metal-organic frameworks for organic

629

solvent nanofiltration, Journal of the American Chemical Society, 135 (2013)

630

15201-15208.

631

[20] J.-E. Gu, S. Lee, C.M. Stafford, J.S. Lee, W. Choi, B.-Y. Kim, K.-Y. Baek, E.P.

632

Chan, J.Y. Chung, J. Bang, J.-H. Lee, Molecular Layer-by-Layer Assembled

633

Thin-Film Composite Membranes for Water Desalination, Advanced materials, 25

634

(2013) 4778-4782.

635

[21] L. Shen, W.-s. Hung, J. Zuo, X. Zhang, J.-Y. Lai, Y. Wang, High-performance

636

thin-film composite polyamide membranes developed with green ultrasound-assisted

637

interfacial polymerization, Journal of Membrane Science, 570-571 (2019) 112-119.

638

[22] X.-H. Ma, Z.-K. Yao, Z. Yang, H. Guo, Z.-L. Xu, C.Y. Tang, M. Elimelech,

639

Nanofoaming of polyamide desalination membranes to tune permeability and

640

selectivity, Environmental Science & Technology Letters, 5 (2018) 123-130.

641

[23] S.H. Kim, S.-Y. Kwak, T. Suzuki, Positron annihilation spectroscopic evidence to

642

demonstrate

643

thin-film-composite (TFC) membrane, Environmental science & technology, 39 (2005)

644

1764-1770.

645

[24] M. Lamminen, Mechanisms and factors influencing the ultrasonic cleaning of

the

flux-enhancement

mechanism

33

in

morphology-controlled

646

particle-fouled ceramic membranes, Journal of Membrane Science, 237 (2004)

647

213-223.

648

[25] L. Shen, J. Zuo, Y. Wang, Tris(2-aminoethyl)amine in-situ modified thin-film

649

composite membranes for forward osmosis applications, Journal of Membrane

650

Science, 537 (2017) 186-201.

651

[26] L. Shen, F. Wang, L. Tian, X. Zhang, C. Ding, Y. Wang, High-performance

652

thin-film composite membranes with surface functionalization by organic phosphonic

653

acids, Journal of Membrane Science, 563 (2018) 284-297.

654

[27] L. Shen, X. Zhang, J. Zuo, Y. Wang, Performance enhancement of TFC FO

655

membranes with polyethyleneimine modification and post-treatment, Journal of

656

Membrane Science, 534 (2017) 46-58.

657

[28] L. Shen, Y. Wang, Efficient surface modification of thin-film composite

658

membranes with self-catalyzed tris(2-aminoethyl)amine for forward osmosis

659

separation, Chemical Engineering Science, 178 (2018) 82-92.

660

[29] L. Shen, M. Yi, L. Tian, F. Wang, C. Ding, S. Sun, A. Lu, L. Su, Y. Wang,

661

Efficient surface ionization and metallization of TFC membranes with superior

662

separation performance, antifouling and anti-bacterial properties, Journal of

663

Membrane Science, 586 (2019) 84-97.

664

[30] H.M. Kyllönen, P. Pirkonen, M. Nyström, Membrane filtration enhanced by

665

ultrasound: a review, Desalination, 181 (2005) 319-335.

666

[31] E. Heikkola, M. Laitinen, Model-based optimization of ultrasonic transducers,

667

Ultrasonics sonochemistry, 12 (2005) 53-57.

668

[32] M.O. Lamminen, H.W. Walker, L.K. Weavers, Mechanisms and factors

669

influencing the ultrasonic cleaning of particle-fouled ceramic membranes, Journal of

670

membrane science, 237 (2004) 213-223. 34

671

[33] Q. An, W.-S. Hung, S.-C. Lo, Y.-H. Li, M. De Guzman, C.-C. Hu, K.-R. Lee,

672

Y.-C. Jean, J.-Y. Lai, Comparison between Free Volume Characteristics of Composite

673

Membranes Fabricated through Static and Dynamic Interfacial Polymerization

674

Processes, Macromolecules, 45 (2012) 3428-3435.

675

[34] B. Mi, M. Elimelech, Gypsum scaling and cleaning in forward osmosis:

676

measurements and mechanisms, Environmental science & technology, 44 (2010)

677

2022-2028.

678

[35] S. Shirazi, C.-J. Lin, D. Chen, Inorganic fouling of pressure-driven membrane

679

processes — A critical review, Desalination, 250 (2010) 236-248.

680

[36] M. Xie, S.R. Gray, Gypsum scaling in forward osmosis: Role of membrane

681

surface chemistry, Journal of Membrane Science, 513 (2016) 250-259.

682

[37] X. Lu, S. Romero-Vargas Castrillon, D.L. Shaffer, J. Ma, M. Elimelech, In situ

683

surface chemical modification of thin-film composite forward osmosis membranes for

684

enhanced organic fouling resistance, Environmental science & technology, 47 (2013)

685

12219-12228.

686

[38] E.M. Vrijenhoek, S. Hong, M. Elimelech, Influence of membrane surface

687

properties on initial rate of colloidal fouling of reverse osmosis and nanofiltration

688

membranes, Journal of Membrane Science, 188 (2001) 115-128.

689

[39] S. Lee, C. Boo, M. Elimelech, S. Hong, Comparison of fouling behavior in

690

forward osmosis (FO) and reverse osmosis (RO), Journal of Membrane Science, 365

691

(2010) 34-39.

692

[40] A. Tiraferri, Y. Kang, E.P. Giannelis, M. Elimelech, Superhydrophilic thin-film

693

composite forward osmosis membranes for organic fouling control: fouling behavior

694

and antifouling mechanisms, Environmental science & technology, 46 (2012)

695

11135-11144. 35

696

[41] P. Lu, S. Liang, L. Qiu, Y. Gao, Q. Wang, Thin film nanocomposite forward

697

osmosis membranes based on layered double hydroxide nanoparticles blended

698

substrates, Journal of membrane science, 504 (2016) 196-205.

699

[42] S. Sahebi, S. Phuntsho, Y.C. Woo, M.J. Park, L.D. Tijing, S. Hong, H.K. Shon,

700

Effect of sulphonated polyethersulfone substrate for thin film composite forward

701

osmosis membrane, Desalination, 389 (2016) 129-136.

702

[43] M. Ghanbari, D. Emadzadeh, W. Lau, H. Riazi, D. Almasi, A. Ismail, Minimizing

703

structural parameter of thin film composite forward osmosis membranes using

704

polysulfone/halloysite nanotubes as membrane substrates, Desalination, 377 (2016)

705

152-162.

706

[44] M. Qiu, J. Wang, C. He, A stable and hydrophilic substrate for thin-film

707

composite forward osmosis membrane revealed by in-situ cross-linked polymerization,

708

Desalination, 433 (2018) 1-9.

709

[45] N. Ma, J. Wei, S. Qi, Y. Zhao, Y. Gao, C.Y. Tang, Nanocomposite substrates for

710

controlling internal concentration polarization in forward osmosis membranes,

711

Journal of Membrane Science, 441 (2013) 54-62.

712

[46] M. Tian, C. Qiu, Y. Liao, S. Chou, R. Wang, Preparation of polyamide thin film

713

composite forward osmosis membranes using electrospun polyvinylidene fluoride

714

(PVDF) nanofibers as substrates, Separation and Purification Technology, 118 (2013)

715

727-736.

716

[47] X. Zhang, J. Tian, Z. Ren, W. Shi, Z. Zhang, Y. Xu, S. Gao, F. Cui, High

717

performance thin-film composite (TFC) forward osmosis (FO) membrane fabricated

718

on novel hydrophilic disulfonated poly (arylene ether sulfone) multiblock

719

copolymer/polysulfone substrate, Journal of Membrane Science, 520 (2016) 529-539.

720

[48] D. Emadzadeh, W.J. Lau, T. Matsuura, M. Rahbari-Sisakht, A.F. Ismail, A novel 36

721

thin film composite forward osmosis membrane prepared from PSf–TiO2

722

nanocomposite substrate for water desalination, Chemical Engineering Journal, 237

723

(2014) 70-80.

724

[49] P. Lu, S. Liang, T. Zhou, X. Mei, Y. Zhang, C. Zhang, A. Umar, Q. Wang,

725

Layered double hydroxide/graphene oxide hybrid incorporated polysulfone substrate

726

for thin-film nanocomposite forward osmosis membranes, RSC Advances, 6 (2016)

727

56599-56609.

728

[50] M.J. Park, S. Phuntsho, T. He, G.M. Nisola, L.D. Tijing, X.-M. Li, G. Chen, W.-J.

729

Chung, H.K. Shon, Graphene oxide incorporated polysulfone substrate for the

730

fabrication of flat-sheet thin-film composite forward osmosis membranes, Journal of

731

Membrane Science, 493 (2015) 496-507.

732

[51] X. Zhang, L. Shen, C.-Y. Guan, C.-X. Liu, W.-Z. Lang, Y. Wang, Construction of

733

SiO2@MWNTs incorporated PVDF substrate for reducing internal concentration

734

polarization in forward osmosis, Journal of Membrane Science, 564 (2018) 328-341.

735

37

Research Highlights for the manuscript “Effect of Ultrasonication Parameters on Forward Osmosis Performance of Thin Film Composite Polyamide Membranes Prepared with Ultrasound-Assisted Interfacial Polymerization” by Liang Shen, Wei-song Hung, Jian Zuo, Lian Tian, Ming Yi, Chun Ding, and Yan Wang a,b*

Effects of ultrasonication parameters on the PA layer formation were studied Modification efficiency varies with the ultrasonication power and frequency conditions Higher modification efficiency benefits the rougher, thicker and looser PA layer Longer ultrasonication time favors the high separation performance of TFC membranes Optimized ultrasonication condition benefits the high water permeance and salt rejection

Declaration of interests ☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. ☒The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:

No financial interest/personal relationship is considered as potential competing interests.