Regenerable Polyelectrolyte Membrane for Ultimate Fouling Control in

Subscriber access provided by UNIV OF CALIFORNIA SAN DIEGO LIBRARIES

Article

Regenerable Polyelectrolyte Membrane for Ultimate Fouling Control in Forward Osmosis Yan Kang, Sunxiang Zheng, Casey Finnerty, Michael J. Lee, and Baoxia Mi Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.6b05665 • Publication Date (Web): 16 Feb 2017 Downloaded from http://pubs.acs.org on February 24, 2017

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Environmental Science & Technology is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 27

Environmental Science & Technology

1 2

Regenerable Polyelectrolyte Membrane for Ultimate Fouling

3

Control in Forward Osmosis

4

Second revision submitted to

5 6


7 8

February 14, 2017

9 10

Yan Kanga, Sunxiang Zhengb, Casey Finnertyb, Michael J. Leea, Baoxia Mib*

11 12

a

13

Department of Civil and Environmental Engineering

University of Maryland, College Park, Maryland 20742, United States

14

b

15

Department of Civil and Environmental Engineering

University of California, Berkeley, California 94720, United States

16 17 18 19 *

The author to whom correspondence should be addressed. fax: +1-510-643-5264

e-mail: [email protected]; tel.: +1-510-664-7446,

ACS Paragon Plus Environment


Page 2 of 27

20

ABSTRACT

21

This study demonstrated the feasibility of using regenerable polyelectrolyte membranes to

22

ultimately control the irreversible membrane fouling in a forward osmosis (FO) process.

23

regenerable membrane was fabricated by assembling multiple polyethyleneimine (PEI) and

24

poly(acrylic acid) (PAA) bilayers on a polydopamine-functionalized polysulfone support.

25

resulting membrane exhibited higher water flux and lower solute flux in FO mode (with the

26

active layer facing feed solution) than in PRO mode (with the active layer facing draw solution)

27

using trisodium citrate as draw solution, most likely due to the unique swelling behavior of the

28

polyelectrolyte membrane.

29

existing PEI-PAA bilayers using strong acid and then reassembling fresh PEI-PAA bilayers on

30

the membrane support.

31

PEI layer and some realigned PAA remained on the membrane support, acting as a beneficial

32

barrier that prevented the acid-foulant mixture from penetrating into the porous support during

33

acid treatment.

34

the original membrane regardless of alginate fouling, suggesting an ultimate solution to

35

eliminating the irreversible membrane fouling in an FO process.

36

the typical membrane cleaning protocol, in-situ membrane regeneration is not expected to

37

noticeably increase the membrane operational burden but can satisfactorily avoid the expensive

38

replacement of the entire membrane module after irreversible fouling, thereby hopefully

39

reducing the overall cost of the membrane-based water treatment system.

The

The

Membrane regeneration was conducted by first dissembling the

It was found that, after the acid treatment, the first covalently bonded

Water and solute flux of the regenerated membrane was very similar to that of

40

1


With a procedure similar to

Page 3 of 27

41


Table of Contents (TOC) and Abstract Art

42

43

2



Page 4 of 27

44

INTRODUCTION

45

Membrane processes, including the traditional nanofiltration (NF) and reverse osmosis (RO) as

46

well as the emerging forward osmosis (FO), are among the most effective approaches to treating

47

water, especially that from non-traditional sources.1, 2 The semipermeable membranes commonly

48

used in these processes are mostly of thin-film composite polyamide and cellulose triacetate

49

types due to their good separation capability and reasonable chemical resistance.3-5

50

membrane fouling aggravates the long-term membrane separation efficiency

51

significantly increases the capital costs associated with fouling-preventive pretreatment as well

52

as membrane cleaning and replacement.

53

FO membrane alleviates its fouling problem to some extent,10-13 irreversible fouling (i.e.,

54

accumulation of foulants that cannot be removed from the active layer by physical cleaning) still

55

poses a major obstacle to the sustainable application of FO technology.

56

6-9

However,

and as a result

Although the lack of fouling layer compaction for an

Membrane surface characteristics (e.g., hydrophilicity, charge, and chemistry) play a key

57

role in the foulant deposition and fouling layer formation.

58

characteristics via appropriate surface modification provides an effective route to improving the

59

membrane resistance to various types of fouling.14, 15 Typical surface modification strategies

60

include decreasing membrane surface roughness, increasing membrane surface hydrophilicity,

61

and introducing anti-adhesive monomers, polymers, or particles onto membrane surface.14-19

62

Recent advances in nanotechnology, polymer science, and biomimetic surface engineering have

63

greatly accelerated the development of antifouling strategies for membrane surface modification,

64

covering the following emerging areas: (1) bio-inspired engineered topography, where various

65

biomimetic surface patterns are designed to deter fouling;20 (2) nano-structured amphiphilic

3


Hence, optimizing these

Page 5 of 27


66

coating, where hydrophobic and hydrophilic segments are combined to create a nano-scaled,

67

chemically heterogeneous surface to repel foulants;21-23 (3) super-hydrophilic zwitterionic

68

polymerization, where an electrostatically induced strong zwitterionic hydration layer created by

69

zwitterions effectively repels the attachment of proteins and cells;

70

strategies leading to, for example, phase-segregating copolymers,26 super-hydrophobic surfaces,

71

27

24, 25

and (4) many other

and nanocomposite materials. 28-30

72

Although the above antifouling strategies have proven effective for controlling

73

individual types of membrane fouling, they usually become inadequate when various types of

74

foulants are present simultaneously and may even interact with one another to further complicate

75

the fouling problem.31 Moreover, after an extended period of operation, irreversible membrane

76

fouling may eventually occur but cannot be effectively mitigated using the membrane cleaning

77

protocols, causing the costly replacement of membrane modules.32 Therefore, an ultimate

78

approach to irreversible fouling control is to make a new type of antifouling membrane that

79

allows for the releasing of the severely fouled membrane active layer and regeneration of a fresh

80

one.

81

A promising candidate membrane material for such ultimate fouling control is the layer-

82

by-layer (LbL) assembled polyelectrolyte.

83

been developed by adjusting fabrication conditions, altering surface charge and functionality,

84

and/or selecting different polyelectrolyte species.33-37 These membranes showed satisfactory

85

separation

86

polyelectrolyte layer can be released under controlled conditions,41, 42 a unique property that

87

enables the possibility of (i) removing the polyelectrolyte active layer of the membrane as a

performance

Various polyelectrolyte membranes have recently

under diverse circumstances.36,

4


38-40

More important,

the


Page 6 of 27

88

sacrificial layer along with the irreversible foulants and then (ii) assembling in-situ a new

89

polyelectrolyte layer to restore the membrane functionality.

90

polyelectrolytes were used in the synthesis of regenerable NF membranes, and strong acids or

91

bases were employed to detach the polyelectrolyte active layer from these membranes.43-45

In previous studies, weak

92

However, the fouling behavior of polyelectrolyte membranes or their regenerability for

93

fouling control in an osmotically driven FO process, for which the fouling behavior and

94

mechanisms can be considerably different from those for a pressure-driven NF process,46 has not

95

been investigated.

96

nor the fouling layer formed on top would experience hydraulic pressure-induced compression in

97

an FO process,11 thus potentially resulting in different separation behavior and regeneration

98

capability.

99

by electrostatic interaction, which could be significantly affected by the high ionic strength of the

For example, unlike in an NF/RO process, neither the polyelectrolyte layer

In addition, the structure and integrity of a polyelectrolyte membrane are maintained

100

draw solution used in an FO process.

101

examine the feasibility of developing a regenerable polyelectrolyte membrane for FO

102

applications and in the meantime to fundamentally understand the corresponding mechanisms.

103

Therefore, research is definitely needed to thoroughly

This paper reports the regenerability of a polyelectrolyte membrane in the FO process,

104

without and with alginate fouling, respectively.

This membrane was fabricated by the LbL

105

assembly of a polyelectrolyte layer on top of a porous support.

106

polyelectrolyte membrane were measured in FO and pressure-retarded osmosis (PRO) modes,

107

respectively, and the effect of polyelectrolyte layer thickness on such performances was

108

examined.

109

and deposit a fresh one.

Water and solute fluxes of the

Membrane regeneration was carried out to release the existing polyelectrolyte layer The structure and properties of polyelectrolyte layers before, during,

5


Page 7 of 27


110

and after membrane regeneration were characterized.

The effect of alginate fouling on

111

membrane regeneration was investigated.

112

MATERIALS AND METHODS

113

Membrane Synthesis.

114

purchased from Sigma-Aldrich (St. Louis, MO) and were used as received.

115

support was made of polysulfone (PSf, with a molecular weight Mw of 22,000) using a

116

conventional phase-inversion method with polyvinylpyrrolidone (PVP, Mw 55,000) as a pore-

117

forming agent.

118

PSf/PVP/NMP weight ratio of 16/4/80, and kept in vacuum for 48 h. Next, the solution was

119

cast on a glass plate to form a 125-µm-thick film using a stainless steel casting knife, and the

120

glass plate was immediately immersed into a water bath for 10 min.

121

support was then peeled off from the glass plate and transferred to another water bath, which was

122

refreshed several times to rinse out any residual solvent.

123

a refrigerator and ready for use.

Unless specified otherwise, all materials and chemicals were The membrane

PSf and PVP were fully dissolved in N-Methyl-2-pyrrolidone (NMP), with a

The thus formed PSf

Finally, the PSf support was stored in

124

To synthesize the polyelectrolyte membrane, the PSf support was first soaked in a

125

freshly prepared dopamine solution (2 mg/mL dopamine in 10mM Tris-HCl, pH 8.5) for 5 h.

126

Then, the polydopamine-coated PSf was alternately immersed in 1 g/L polyethyleneimine (PEI,

127

Mw 750,000) and 1 g/L poly(acrylic acid) (PAA, Mw 450,000) solutions for a specified number of

128

cycles.

129

Deionized (DI) water was used to rinse the membrane between any two dipping steps.

130

LbL assembly process created the polyelectrolyte membrane with a desired number of PEI-PAA

131

bilayers on the polydopamine-coated PSf support.

Each dipping step lasted 20 min except that the first PEI dipping step took 1 h.

6


This


Page 8 of 27

132

Membrane Fouling, Regeneration, and Performance Tests. The membrane fouling

133

tests used a mixture of 200 mg/L alginate and feed solution that contained 50 mM NaCl and 0.5

134

mM CaCl2.7

135

sufficient deposition of foulants, followed by the disassembly of the fouled polyelectrolyte layer,

136

regeneration of a fresh polyelectrolyte layer, and evaluation of the membrane performance.

137

tests were repeated multiple times to ensure the reliability of data.

Each fouling test typically lasted 18 h with about 2 L of filtrate to allow for

The

138

To disassemble the polyelectrolyte layer, the membrane was immersed in HCl solution

139

(pH 1) for 30 min, rinsed with DI water for several times, and then stabilized in DI water for 1 h.

140

The effectiveness of disassembly by HCl solution at higher pH (2 to 3) was also evaluated.

141

Regeneration of the fresh polyelectrolyte layer followed a procedure similar to that for

142

membrane synthesis — the acid-treated membrane was alternately soaked in the PEI and PAA

143

solutions to deposit a desired number of new PEI-PAA bilayers.

144

Membrane performances before and after the regeneration of the fresh polyelectrolyte

145

layer were evaluated using a lab-scale FO system.47 The membrane was installed in a cross-flow

146

cell at a constant flow rate of 8.5 cm/s and then tested in FO mode (with the membrane top

147

surface facing feed solution) and PRO mode (with the membrane top surface facing draw

148

solution), respectively.

149

used as a draw solution.

150

reached a steady state (typically in 30 min) was monitored for 2 h using a conductivity meter

151

(Accumet Excel XL30, Thermo Scientific, Marietta, OH).

152

concentrations (1 to 100 mM) of TSC were first used to establish a standard curve, which was

153

then employed to convert the conductivity measurements to solute concentrations so that the

0.5 M trisodium citrate (TSC, Fisher Scientific, Pittsburgh, PA) was The change in the conductivity of feed solution after the water flux

7


Solutions with known

Page 9 of 27


154

reverse solute flux could be calculated.

155

Membrane Characterization.

156

Fourier transform infrared (FTIR) spectroscopy (Nicolet 6700, Thermo Scientific, Marietta, OH),

157

scanning electron microscopy (SEM, SU-70, Hitachi High Technologies America, Gaithersburg,

158

MD), and quartz crystal microbalance with dissipation (QCM-D, Q-sense E4 system, Sweden).

159

For the FTIR and SEM analyses, the samples were dried overnight at room temperature and

160

placed in an oven at 60 °C for 30 min to remove moisture content before characterization.

161

SEM samples were sputtered with a thin (~2 nm) layer of gold nanoparticles on top to eliminate

162

the electron-charging effect.

163

procedure as that for membrane synthesis.

164

used to monitor the changes in vibration frequency and energy dissipation, which were modeled

165

using the Q-Tools software (Q-sense, Sweden) to calculate the amount of mass deposited on or

166

released from the sensor surface.

167

Lincoln, NE) was coupled with the QCM-D to measure the thickness of the polyelectrolyte

168

layers deposited on the QCM-D sensor.

169

JEM 2100, Peabody, MA) was also employed to examine the structural change in the

170

polyelectrolyte layer due to acid treatment.

171

PEI and PAA solutions following the steps for membrane synthesis excluding the step of

172

polydopamine functionalization.

173

RESULTS AND DISCUSSION

174

LbL Membrane Synthesis.

175

deposited on the PSf support, respectively.

The polyelectrolyte membrane was characterized by the

The

The QCM-D sensors were prepared using the same LbL assembly A flow chamber at a flow rate of 0.1 mL/min was

An ellipsometer (FS-1 Multi-wavelength, Film Sense,

The transmission electron microscopy (TEM, JEOL

A TEM copper grid was alternately dipped into the

Different numbers (2, 4, and 6) of PEI-PAA bilayers were The top surface (Figure 1(a)) of the PSf support,

8



Page 10 of 27

176

facing the ambient water when formed during phase inversion synthesis, was denser (i.e., less

177

porous) than the bottom surface (Figure 1(b)), which was attached to the glass plate during the

178

support synthesis.

179

surface roughness of PSf (Figure 1(c)), the subsequent polyelectrolyte deposition, either with

180

only two PEI-PAA bilayers (Figure 1(d-e)) or more bilayers (Figure S1), created relatively

181

smooth and featureless surfaces .

182

Although the pretreatment by polydopamine significantly increased the top

The successful LbL deposition of PEI-PAA bilayers was also confirmed by FTIR spectra

183

(Figure 1(f)).

Compared with the control PSf support, the polyelectrolyte membranes showed a

184

small characteristic peak of carboxylates near 1700 cm-1.

185

increased, two new broad peaks were predominant at around 1550 cm-1 and 1410 cm-1,

186

representing the asymmetric carboxylate stretching due to PEI-PAA binding.48

187

the characteristic peaks of PSf in the range of 1250 cm-1 to 700 cm-1 became less intensive as the

188

number of PEI-PAA bilayers increased.

189

As the number of PEI-PAA bilayers

In the meantime,

FIGURE 1

190

Membrane Transport Behavior.

191

membrane using 0.5 M TSC as draw solution. The water flux and reverse solute flux were

192

measured in FO and PRO modes, respectively.

193

modes, as the number of PEI-PAA bilayers increased (i.e., the membrane active layer became

194

thicker), the membrane resistance to water permeation was enhanced and thus the water flux

195

decreased.

196

transport, the reverse solute flux may not necessarily decrease in inverse proportion to the active

197

layer thickness.

The polyelectrolyte membrane was tested as an FO

As shown in Figure 2(a), in both FO and PRO

In contrast, although a thicker membrane also generates a higher resistance to solute

As shown in Figure 2(b), although the thinnest 2-bilayer membrane had the

9


Page 11 of 27


198

highest reverse solute flux, the 6-bilayer membrane turned out to have a slightly higher solute

199

flux than the 4-bilayer membrane.

200

membrane helps reduce the resistance to solute transport, thereby counteracting with the original

201

resistance increase for the thicker membrane.

202

was compared in Fig. 2 (a-b) with that of a citrate triacetate (CTA) FO membrane commercially

203

available from Hydration Technology Innovations (Albany, OR).

204

bilayer membrane exhibited high water flux of ~22 L/m2/h (more than three times that of the

205

CTA membrane) and reasonable reverse solute flux of ~0.06 mole/m2/h (about twice that of the

206

CTA membrane), while both 4 and 6-bilayer membranes demonstrated moderately higher water

207

flux but slower solute flux than the CTA membrane. Therefore, the 2-bilayer membrane was

208

selected as a representative polyelectrolyte membrane for the subsequent regeneration tests.

209

This is because the lowered water flux of a thicker

The performance of PEI-PAA bilayer membranes

Tested in FO mode, the 2-

It is interesting to observe in Figure 2(a) that the water flux of a polyelectrolyte

210

membrane in PRO mode was significantly lower than that in FO mode.

211

dramatically differs from the behavior of a traditional FO membrane, which typically has a lower

212

water flux in FO mode than in PRO mode due to the membrane’s asymmetric structure that leads

213

to a lesser degree of internal concentration polarization in PRO mode.49, 50 Such a unique flux

214

behavior of the polyelectrolyte membrane was most likely attributed to the swelling of the

215

polyelectrolyte layer in a high ionic strength solution (0.5 M TSC), and this active layer could be

216

further loosened under the impact of water flow.

217

has a dense active layer on top of its support only, both top and bottom surfaces of the

218

asymmetric PSf support in this study were coated with polyelectrolyte layers, with the top layer

219

being denser and thicker than the bottom one.

220

contributed to solute rejection because relatively large pores (> 400 nm) of the PSf support were

10

This observation

In contrast to a traditional FO membrane that

The bottom polyelectrolyte layer unlikely



Page 12 of 27

221

not fully covered by the polyelectrolyte layer (Figure 1(e)).

222

illustrated in Figure 2(c), when the polyelectrolyte membrane was operated in FO mode, its top

223

surface facing the feed solution (with low ionic strength) was relatively dense and acted as an

224

effective osmotic barrier to generate high water flux and low reverse solute flux.

225

when the membrane was operated in PRO mode, its top polyelectrolyte layer swelled due to

226

exposure to 0.5 M TSC solution (with high ionic strength) and hence became less effective as an

227

osmotic barrier, leading to lower water flux and higher solute flux.

228

the swelling of a 2-bilayer polyelectrolyte film under high ionic strength was confirmed by the

229

change in the film thickness, which increased from 23 nm in DI water to 45 nm in 0.5 M TSC

230

solution.

231

Therefore, as schematically

In comparison,

As shown in Figure 2(d),

FIGURE 2

232

Acid Treatment and Regeneration of Membrane.

233

membrane, the first step is to dissemble the existing polyelectrolyte layer from the original

234

membrane so that a fresh layer can be deposited.

235

disassembly approach is to treat the polyelectrolyte membrane with a strong acid that can the

236

protonate carboxylate groups and neutralize the negative charge of PAA, thereby destroying the

237

electrostatic binding between PEI and PAA.

238

a fresh PSf support (Figure S2) with the 2-bilayer membrane (Figure 3(b, d)) and 6-bilayer

239

membrane (Figure 3(c, e)) before and after pH 1 HCl treatment, respectively, demonstrated the

240

effectiveness in detaching the existing PEI-PAA bilayers by strong acid.

241

residual polyelectrolytes could still remain after acid treatment, especially for membranes with a

242

relatively thick polyelectrolyte layer.

To regenerate a polyelectrolyte

As illustrated in Figure 3(a), an effective

Comparison of the cross-sectional SEM images of

Note that some

For example, acid treatment reduced the thickness of the

11


Page 13 of 27


243

polyelectrolyte layer of the 6-bilayer membrane from ~2 µm (Figure 3(c)) to ~0.5 µm (Figure

244

3(e)).

245

FIGURE 3

246

In order to more accurately characterize the membrane regeneration, QCM-D was

247

employed to monitor the mass change during the LbL assembly and acid treatment of the 2-

248

bilayer membrane.

249

membrane pretreatment and then deposited with two PEI-PAA bilayers.

250

3(f) that the mass of the second PEI-PAA bilayer was much larger than that of the first bilayer.

251

This is because the first PEI layer was covalently bonded to polydopamine through nucleophilic

252

addition,51, 52 resulting in a low degree of PEI attachment.

253

bilayer increased the number of charged sites on the exposed membrane surface, attracting more

254

polyelectrolyte and thus increasing the mass for the subsequent bilayer deposition.

255

The QCM-D sensor was first coated with polydopamine to simulate the It is observed in Figure

Besides, deposition of a PEI-PAA

As shown in Figure 3(g), the mass changes associated with the process of regenerating

256

the 2-bilayer thin film are normalized by its original mass.

257

treatment removed about 70% of the total mass of the 2-bilayer thin film.

258

observed in Figure 3(f), the masses of the first and second bilayers are approximately equal to 30%

259

and 70%, respectively, of the total mass, indicating that acid treatment mainly removed the outer

260

second bilayer while leaving the inner first bilayer intact.

261

treatment, only one new bilayer was deposited on the QCM-D sensor in order to maintain a

262

relatively constant mass of the 2-bilayer membrane.

263

regeneration cycle, the normalized mass of the regenerated membrane is close to unity,

264

indicating that its thickness was similar to that of the original 2-bilayer membrane.

12

It is observed that the first acid Note that, as

For this reason, after each acid

Figure 3(g) shows that, after each



Page 14 of 27

265

The nearly 30% residual mass after each acid treatment, as observed in Figure 3(g), was

266

most likely associated with the first PEI layer, which was covalently attached to polydopamine,

267

as well as some undetached PAA due to the partial protonation of its carboxylate groups.

268

is because, although the theoretical pKa of carboxylate groups in PAA is around 4.5 and thus

269

would be fully protonated at pH 1, the effective pKa can be very different when these functional

270

groups are localized and constrained instead of moving freely on a surface.53

271

much lower than 4.5 was confirmed by the non-effective acid treatment at higher pH (Figure S3)

272

— the fact that polyelectrolyte layers were almost unaffected by acid treatment at pH 2 to 3

273

indicated an effective pKa of less than 2.

This

An effective pKa

274

The residual polyelectrolyte layer after acid treatment was actually beneficial for the

275

membrane regeneration because it helped prevent the acid-foulant mixture from penetrating into

276

the membrane support during the acid treatment.

277

attached PEI layer unlikely changes during regeneration, the amount of residual mass after each

278

regeneration cycle mainly depends on the effectiveness of acid treatment in breaking the

279

electrostatic interactions between polyelectrolytes.

280

membrane before and after acid treatment (Figure S4) are similar, indicating that no chemical

281

reaction or change in the polyelectrolyte chemistry was introduced by acid treatment.

282

Since the mass of the first chemically

Besides, the FTIR spectra of the 2-bilayer

TEM characterization as shown in Figure 4 reveals that acid treatment caused some

283

structural changes in the residual polyelectrolyte layer.

284

exhibited a smooth, featureless surface, as similarly observed in the SEM image (Figure 1(d)).

285

After the pH 1 acid treatment, the residual polyelectrolyte layer led to a rougher surface (Figure

286

4(d)) with aligned features at a few spots (Figure 4(e)), indicating that the acid treatment did not

13

The as-prepared 2-bilayer sample


Page 15 of 27


287

evenly or entirely dissemble the existing polyelectrolyte layer.

Besides, the TEM diffraction

288

patterns show that the acid-treated sample had a bright ring compared with the as-prepared

289

sample, indicating the existence of some aligned polyelectrolytes.

290

likely caused by the realignment of partially protonated PAA as pH decreased. Note that a

291

similar pH effect on the structure of polyelectrolyte layers was also reported in the literature.54

Such a structural change was

292

The TEM-EDX analysis (Figure S5) showed an almost complete PEI removal by acid

293

treatment, as no nitrogen (N) peak was detected for the acid-treated 2-bilayer sample. Note that

294

because the TEM sample holder was not pre-treated with polydopamine, PEI was not covalently

295

attached to the TEM sample holder.

296

electrostatically deposited PEI and only left the first layer of covalently bonded PEI and some

297

partially protonated, well aligned PAA in the residual polyelectrolyte layer.

In summary, acid treatment was able to remove almost all

298

FIGURE 4

299

Membrane Performance in FO Process. The performances of both the original 2-bilayer

300

membrane and the membrane after each cycle of acid treatment and regeneration were tested in

301

FO mode.

302

water flux, obviously because the decrease in the polyelectrolyte layer thickness lowered the

303

water resistance. Note that the water flux after each membrane regeneration was lower than

304

that of the original membrane due to the existence of a residual polyelectrolyte layer (after acid

305

treatment) that increased the water resistance.

306

general not significantly affected by acid treatment or regeneration, indicating the residual

307

polyelectrolyte layer, mainly composed of the first PEI-PAA bilayer based on mass analysis, was

308

also a somewhat effective solute barrier.

Figure 5(a) shows that the acid treatment in each cycle increased the membrane

As shown in Figure 5(b), the solute flux was in

However, the solute flux dramatically increased after

14



Page 16 of 27

309

the third acid treatment.

310

after each acid treatment (Figure 5(a)), is consistent with our previous understanding that acid

311

treatment alone did not evenly or entirely dissemble the existing polyelectrolyte layer.

312

demonstrated by the TEM image in Figure 4(d), the acid treatment resulted in a heterogeneous

313

structure with realignment of residual PAA, thus potentially leading to defects that result in

314

increased solute passage. Although such defects are fully sealed by the subsequent bilayer

315

deposition in the next regeneration cycle, it is predicted that the efficiency of polyelectrolyte

316

layer removal and regeneration could be further improved by employing useful membrane

317

cleaning strategies such as surfactant and back wash.

318

319

This observation, along with the noticeable variations in water flux

As

FIGURE 5

The regenerability of the polyelectrolyte membrane fouled by alginate was also tested in

320

the FO membrane system.

The flux decline curves of the original and regenerated membranes

321

obtained from the alginate fouling experiments are shown in Figure 5(c).

322

water flux of the original membrane declined by more than 30% due to alginate fouling,

323

indicating a thick fouling layer was formed on the membrane surface.

324

treatment and regeneration, the regenerated membrane regained an initial water flux that was

325

almost the same as that of the original clean membrane.

It is observed that

After each cycle of acid

326

Such effective membrane regeneration after significant fouling offers a great opportunity

327

to ultimately control the irreversible membrane fouling, a long-standing problem that

328

considerably deteriorates membrane performance and shortens membrane lifetime.

329

conventional fouling control procedures such as physical and chemical cleaning for which the

330

fouling-control effectiveness depends on foulant types and attachment mechanisms, membrane

15


Unlike the

Page 17 of 27


331

regeneration breaks the electrostatic interactions between the polyelectrolyte layers and thus

332

removes the bilayers together with various foreign substances attached to them, including

333

irreversible foulants.

334

that is not affected by the type of foulants or level of their attachment to the membrane.

335

the procedure for dissembling and regenerating the polyelectrolyte layer of the present

336

membrane is quite similar to a typical membrane cleaning protocol, it is reasonable to believe

337

that the in-situ membrane regeneration may not significantly increase the membrane operation

338

cost but can satisfactorily avoid the expensive replacement of the entire membrane module due

339

to irreversible fouling, thereby potentially reducing the overall cost of the membrane-based water

340

treatment system.

341

cost-effectiveness of the proposed membrane technology.

342

out of the scope of the present study.

Therefore, membrane regeneration offers a universal cleaning strategy Since

Indeed, a thorough cost-benefit analysis is warranted to assess the long-term However, research in this direction is

343

344

ASSOCIATED CONTENT

345

Supporting Information. SEM images of the top surfaces of polyelectrolyte membranes

346

made with 2, 4, and 6 PEI-PAA bilayers, respectively (Figure S1); cross-sectional SEM image of

347

the PSf support (Figure S2); changes in sensor frequency from the QCM-D measurement of a 2-

348

bilayer film after subsequent acid treatments at pH 2-3 (Figure S3); FTIR spectra of 2-bilayer

349

and 4-bilayer membranes before and after pH 1 acid treatment (Figure S4); and TEM-EDX

350

analysis of a 2-bilayer film on a TEM copper grid after pH 1 acid treatment (Figure S5).

351

16



352

ACKNOWLEDGEMENTS

353

The material is based upon work supported by the U.S. National Science Foundation under

354

Award Number CBET-1565452 and the U.S. Department of Energy under Award Number DE-

355

IA0000018.

356

reflect those of the sponsors.

Page 18 of 27

The opinions expressed herein are those of the authors and do not necessarily

357

17


Page 19 of 27


358

359 360 361

Figure 1. SEM images of the (a) top surface and (b) bottom surface of the PSf support, (c) top

362

surface of the polydopamine-coated PSf support, (d) top surface and (e) bottom surface of the 2-

363

bilayer membrane, and (f) FTIR spectra of the PSf support before and after being deposited with

364

different numbers of PEI-PAA bilayers.

365

18



Page 20 of 27

366 367 (a)

(b) 30

0.6

Water Flux (L/m2/h)

Solute Flux (mol/m2/h)

FO Mode PRO Mode

25 20 15 10 5 0

FO Mode PRO Mode 0.4

0.2

0.0 CTA

2-bilayer 4-bilayer 6-bilayer

CTA

2-bilayer 4-bilayer 6-bilayer

368 369

370 371

Figure 2. (a) Water flux and (b) reverse solute flux of polyelectrolyte membranes made with

372

different numbers of PEI-PAA bilayers, using 0.5 M TSC draw solution. (c) Schematic

373

illustration of the swelling of the polyelectrolyte layers on the draw side in FO and PRO modes,

374

respectively, making the membrane less effective for rejecting solutes. (d) Thickness of

375

polyelectrolyte layer in DI water and 0.5 M TSC solution, as measured by ellipsometer.

376

19


Page 21 of 27


377

378

379 380 381

Figure 3.

382

from the membrane; cross-sectional SEM images of (b) original 2-bilayer membrane, (c) original

383

6-bilayer membrane, (d) acid-treated 2-bilayer membrane, and (e) acid-treated 6-bilayer

384

membrane; and QCM-D measurements of (f) the PEI-PAA bilayer deposition and (g) repeated

385

cycles of acid treatment and regeneration of a 2-bilayer membrane. Note that the masses in (g)

386

were normalized by the mass of the original 2-bilayer membrane.

(a) Schematic illustration of acid treatment for the disassembly of PEI-PAA bilayers

387 388

20



389

390 391 392

Figure 4. TEM surface images and diffraction patterns of a 2-bilayer sample (a-c) before and (d-

393

f) after the pH 1 acid treatment.

394

21


Page 22 of 27

Page 23 of 27


(a)

30

After acid treatment After regeneration

Water Flux (L/m2/h)

25 20 15 10 5 0

Original

1st 3rd 2nd Membrane Regeneration Stage

395 (b) 0.35 After acid treatment After regeneration

Solute Flux (mol/m2/h)

0.30 0.25 0.20 0.15 0.10 0.05 0.00

396

(c)

Original

30 25

Water Flux (L/m2/h)

1st 3rd 2nd Membrane Regeneration Stage

Original membrane

20

Regenerated membrane

15 10 Alginate fouling

5 0

0

200

400 Time(min)

600

800

397 398

Figure 5.

399

declines of the original 2-bilayer membrane and membrane after each cycle of acid treatment and

400

regeneration.

401

solution, 20 mM NaCl and 0.5 M CaCl2 as feed solution, and 200 mg/L alginate for fouling

402

experiments.

(a) Pure water fluxes, (b) reverse solute fluxes, and (c) fouling-induced water flux

The experiments were conducted in FO mode, 0.5 M TSC was used as draw

The blue-colored data points in (c) represent the initial water flux measured 22



403

without foulants.

404

REFERENCES

405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444

1. Shannon, M. A.; Bohn, P. W.; Elimelech, M.; Georgiadis, J. G.; Marinas, B. J.; Mayes, A. M., Science and technology for water purification in the coming decades. Nature 2008, 452, (7185), 301-310. 2. Elimelech, M.; Phillip, W. A., The future of seawater desalination: Energy, technology, and the environment. Science 2011, 333, (6043), 712-717. 3. Gu, Y. S.; Wang, Y. N.; Wei, J.; Tang, C. Y. Y., Organic fouling of thin-film composite polyamide and cellulose triacetate forward osmosis membranes by oppositely charged macromolecules. Water Res 2013, 47, (5), 1867-1874. 4. Yip, N. Y.; Tiraferri, A.; Phillip, W. A.; Schiffman, J. D.; Elimelech, M., High performance thin-film composite forward osmosis membrane. Environ Sci Technol 2010, 44, (10), 3812-3818. 5. Tiraferri, A.; Yip, N. Y.; Phillip, W. A.; Schiffman, J. D.; Elimelech, M., Relating performance of thin-film composite forward osmosis membranes to support layer formation and structure. J Membrane Sci 2011, 367, (1-2), 340-352. 6. Shaffer, D. L.; Arias Chavez, L. H.; Ben-Sasson, M.; Romero-Vargas Castrillon, S. R.; Yip, N. Y.; Elimelech, M., Desalination and reuse of high-salinity shale gas produced water: Drivers, technologies, and future directions. Environ Sci Technol 2013, 47, (17), 9569-9583. 7. Mi, B.; Elimelech, M., Chemical and physical aspects of organic fouling of forward osmosis membranes. J Membrane Sci 2008, 320, (1-2), 292-302. 8. Le-Clech, P.; Chen, V.; Fane, T. A. G., Fouling in membrane bioreactors used in wastewater treatment. J Membrane Sci 2006, 284, (1-2), 17-53. 9. Padaki, M.; Murali, R. S.; Abdullah, M. S.; Misdan, N.; Moslehyani, A.; Kassim, M. A.; Hilal, N.; Ismail, A. F., Membrane technology enhancement in oil-water separation. A review. Desalination 2015, 357, 197-207. 10. Mi, B.; Elimelech, M., Gypsum scaling and cleaning in forward osmosis: Measurements and mechanisms. Environ Sci Technol 2010, 44, (6), 2022-2028. 11. Mi, B.; Elimelech, M., Organic fouling of forward osmosis membranes: Fouling reversibility and cleaning without chemical reagents. J Membrane Sci 2010, 348, (1-2), 337-345. 12. Mi, B.; Elimelech, M., Silica scaling and scaling reversibility in forward osmosis. Desalination 2013, 312, 75-81. 13. Liu, Y.; Mi, B., Effects of organic macromolecular conditioning on gypsum scaling of forward osmosis membranes. J Membrane Sci 2014, 450, 153-161. 14. Zhou, M.; Liu, H.; Kilduff, J.; Langer, R.; Anderson, D.; Belfort, G., High-throughput membrane surface modification to control NOM fouling. Environ Sci Technol 2009, 43, (10), 3865-3871. 15. Zhou, Y.; Yu, S.; Gao, C.; Feng, X., Surface modification of thin film composite polyamide membranes by electrostatic self deposition of polycations for improved fouling resistance. Sep Purif Technol 2009, 66, (2), 287-294. 16. Mo, Y. H.; Tiraferri, A.; Yip, N. Y.; Adout, A.; Huang, X.; Elimelech, M., Improved antifouling properties of polyamide nanofiltration membranes by reducing the density of surface

23


Page 24 of 27

Page 25 of 27

445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490


carboxyl groups. Environ Sci Technol 2012, 46, (24), 13253-13261. 17. Tiraferri, A.; Kang, Y.; Giannelis, E. P.; Elimelech, M., Superhydrophilic thin-film composite forward osmosis membranes for organic fouling control: Fouling behavior and antifouling mechanisms. Environ Sci Technol 2012, 46, (20), 11135-11144. 18. Diagne, F.; Malaisamy, R.; Boddie, V.; Holbrook, R. D.; Eribo, B.; Jones, K. L., Polyelectrolyte and silver nanoparticle modification of microfiltration membranes to mitigate organic and bacterial fouling. Environ Sci Technol 2012, 46, (7), 4025-4033. 19. Li, X.; Cai, T.; Chung, T. S., Anti-fouling behavior of hyperbranched polyglycerolgrafted poly(ether sulfone) hollow fiber membranes for osmotic power generation. Environ Sci Technol 2014, 48, (16), 9898-9907. 20. Kirschner, C. M.; Brennan, A. B., Bio-inspired antifouling strategies. Annu Rev Mater Res 2012, 42, 211-229. 21. Kristalyn, C. B.; Lu, X. L.; Weinman, C. J.; Ober, C. K.; Kramer, E. J.; Chen, Z., Surface structures of an amphiphilic tri-block copolymer in air and in water probed using sum frequency generation vibrational spectroscopy. Langmuir 2010, 26, (13), 11337-11343. 22. Li, Y.; Liu, C. M.; Yang, J. Y.; Gao, Y. H.; Li, X. S.; Que, G. H.; Lu, J. R., Antibiofouling properties of amphiphilic phosphorylcholine polymer films. Colloid Surface B 2011, 85, (2), 125-130. 23. Weinman, C. J.; Finlay, J. A.; Park, D.; Paik, M. Y.; Krishnan, S.; Sundaram, H. S.; Dimitriou, M.; Sohn, K. E.; Callow, M. E.; Callow, J. A.; Handlin, D. L.; Willis, C. L.; Kramer, E. J.; Ober, C. K., ABC triblock surface active block copolymer with grafted ethoxylated fluoroalkyl amphiphilic side chains for marine antifouling/fouling-release applications. Langmuir 2009, 25, (20), 12266-12274. 24. Yu, H. Y.; Kang, Y.; Liu, Y. L.; Mi, B., Grafting polyzwitterions onto polyamide by click chemistry and nucleophilic substitution on nitrogen: A novel approach to enhance membrane fouling resistance. J Membrane Sci 2014, 449, 50-57. 25. Zheng, S.; Yang, Q.; Mi, B., Novel antifouling surface with improved hemocompatibility by immobilization of polyzwitterions onto silicon via click chemistry. Applied Surface Science 2016, 363, 619-626. 26. Lowe, A. B.; Vamvakaki, M.; Wassall, M. A.; Wong, L.; Billingham, N. C.; Armes, S. P.; Lloyd, A. W., Well-defined sulfobetaine-based statistical copolymers as potential antibioadherent coatings. J Biomed Mater Res 2000, 52, (1), 88-94. 27. Chapman, J.; Regan, F., Nanofunctionalized superhydrophobic antifouling coatings for environmental sensor applicationsuadvancing deployment with answers from nature. Adv Eng Mater 2012, 14, (4), B175-B184. 28. Yang, Q.; Mi, B., Nanomaterials for membrane fouling control: Accomplishments and challenges. Advances in Chronic Kidney Disease 2013, 20, (6), 536-555. 29. Hu, M.; Zheng, S.; Mi, B., Organic fouling of graphene oxide membranes and its implications for membrane fouling control in engineered osmosis. Environ Sci Technol 2016, 50, (2), 685-693. 30. Liu, Y.; Rosenfield, E.; Hu, M.; Mi, B., Direct observation of bacterial deposition on and detachment from nanocomposite membranes embedded with silver nanoparticles. Water Res 2013, 47, (9), 2949-2958. 31. Liu, Y.; Mi, B., Combined fouling of forward osmosis membranes: Synergistic foulant interaction and direct observation of fouling layer formation. J Membrane Sci 2012, 407, 136144.

24



491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536

Page 26 of 27

32. Ang, W. S.; Yip, N. Y.; Tiraferri, A.; Elimelech, M., Chemical cleaning of ro membranes fouled by wastewater effluent: Achieving higher efficiency with dual-step cleaning. J Membrane Sci 2011, 382, (1-2), 100-106. 33. Duong, P. H. H.; Zuo, J.; Chung, T. S., Highly crosslinked layer-by-layer polyelectrolyte fo membranes: Understanding effects of salt concentration and deposition time on fo performance. J Membrane Sci 2013, 427, 411-421. 34. Kang, Y.; Emdadi, L.; Lee, M. J.; Liu, D. X.; Mi, B. X., Layer-by-layer assembly of zeolite/polyelectrolyte nanocomposite membranes with high zeolite loading. Environ Sci Tech Let 2014, 1, (12), 504-509. 35. Liu, C.; Shi, L.; Wang, R., Crosslinked layer-by-layer polyelectrolyte nanofiltration hollow fiber membrane for low-pressure water softening with the presence of so42- in feed water. J Membrane Sci 2015, 486, 169-176. 36. Stanton, B. W.; Harris, J. J.; Miller, M. D.; Bruening, M. L., Ultrathin, multilayered polyelectrolyte films as nanofiltration membranes. Langmuir 2003, 19, (17), 7038-7042. 37. Hong, S. U.; Lu, O. Y.; Bruening, M. L., Recovery of phosphate using multilayer polyelectrolyte nanofiltration membranes. J Membrane Sci 2009, 327, (1-2), 2-5. 38. Pardeshi, P.; Mungray, A. A., Synthesis, characterization and application of novel high flux FO membrane by layer-by-layer self-assembled polyelectrolyte. J Membrane Sci 2014, 453, 202-211. 39. Saren, Q.; Qiu, C. Q.; Tang, C. Y. , Synthesis and characterization of novel forward osmosis membranes based on layer-by-layer assembly. Environ Sci Technol 2011, 45, (12), 52015208. 40. Jin, W. Q.; Toutianoush, A.; Tieke, B., Use of polyelectrolyte layer-by-layer assemblies as nanofiltration and reverse osmosis membranes. Langmuir 2003, 19, (7), 2550-2553. 41. Dubas, S. T.; Schlenoff, J. B., Polyelectrolyte multilayers containing a weak polyacid: Construction and deconstruction. Macromolecules 2001, 34, (11), 3736-3740. 42. Sukhishvili, S. A.; Granick, S., Layered, erasable, ultrathin polymer films. J Am Chem Soc 2000, 122, (39), 9550-9551. 43. Irigoyen, J.; Politakos, N.; Murray, R.; Moya, S. E., Design and fabrication of regenerable polyelectrolyte multilayers for applications in foulant removal. Macromol Chem Phys 2014, 215, (16), 1543-1550. 44. Ahmadiannamini, P.; Bruening, M. L.; Tarabara, V. V., Sacrificial polyelectrolyte multilayer coatings as an approach to membrane fouling control: Disassembly and regeneration mechanisms. J Membrane Sci 2015, 491, 149-158. 45. Ilyas, S.; de Grooth, J.; Nijmeijer, K.; de Vos, W. M., Multifunctional polyelectrolyte multilayers as nanofiltration membranes and as sacrificial layers for easy membrane cleaning. Journal of Colloid and Interface Science 2015, 446, 386-393. 46. Lee, S.; Boo, C.; Elimelech, M.; Hong, S., Comparison of fouling behavior in forward osmosis (FO) and reverse osmosis (RO). J Membrane Sci 2010, 365, (1-2), 34-39. 47. Liu, Y. L.; Mi, B. X., Combined fouling of forward osmosis membranes: Synergistic foulant interaction and direct observation of fouling layer formation. J Membrane Sci 2012, 407, 136-144. 48. Socrates, G.; Socrates, G., Infrared and raman characteristic group frequencies : Tables and charts. 3rd ed.; Wiley: Chichester ; New York, 2001; p xv, 347 p. 49. Cath, T. Y.; Childress, A. E.; Elimelech, M., Forward osmosis: Principles, applications, and recent developments. J Membrane Sci 2006, 281, (1-2), 70-87.

25


Page 27 of 27

537 538 539 540 541 542 543 544 545 546 547 548 549 550


50. Alsvik, I. L.; Hagg, M. B., Pressure retarded osmosis and forward osmosis membranes: Materials and methods. Polymers-Basel 2013, 5, (1), 303-327. 51. Gu, J. E.; Lee, S.; Stafford, C. M.; Lee, J. S.; Choi, W.; Kim, B. Y.; Baek, K. Y.; Chan, E. P.; Chung, J. Y.; Bang, J.; Lee, J. H., Molecular layer-by-layer assembled thin-film composite membranes for water desalination. Adv Mater 2013, 25, (34), 4778-4782. 52. LaVoie, M. J.; Ostaszewski, B. L.; Weihofen, A.; Schlossmacher, M. G.; Selkoe, D. J., Dopamine covalently modifies and functionally inactivates parkin. Nat Med 2005, 11, (11), 1214-1221. 53. Burke, S. E.; Barrett, C. J., Acid-base equilibria of weak polyelectrolytes in multilayer thin films. Langmuir 2003, 19, (8), 3297-3303. 54. Lutkenhaus, J. L.; McEnnis, K.; Hammond, P. T., Nano- and microporous layer-by-layer assemblies containing linear poly(ethylenimine) and poly(acrylic acid). Macromolecules 2008, 41, (16), 6047-6054.

551

552

553

26


Regenerable Polyelectrolyte Membrane for Ultimate Fouling Control in

Recommend Documents