Rightsizing Nanochannels in Reduced-Graphene Oxide Membranes

Subscriber access provided by Kaohsiung Medical University

Remediation and Control Technologies

Rightsizing Nanochannels in Reduced-Graphene Oxide Membranes by Solvating for Dye Desalination Liang Huang, Suting Huang, Surendar R. Venna, and Haiqing Lin Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.8b03661 • Publication Date (Web): 26 Sep 2018 Downloaded from http://pubs.acs.org on September 27, 2018

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 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 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.

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 19

Environmental Science & Technology

1

Rightsizing Nanochannels in Reduced-Graphene

2

Oxide Membranes by Solvating for Dye

3

Desalination

4

Liang Huang,† Suting Huang,† Surendar R. Venna,‡ and Haiqing Lin*, †

5

† Department of Chemical and Biological Engineering, University at Buffalo, The State

6

University of New York, Buffalo, NY 14260

7

‡ National Energy Technology Laboratory/AECOM, 626 Cochrans Mill Rd., Pittsburgh, PA

8

15236

9

1 ACS Paragon Plus Environment


Page 2 of 19

10

ABSTRACT

11

Membranes with high water permeance, near-zero rejection to inorganic salts (such as NaCl

12

and Na2SO4), and almost 100% rejection to organic dyes are of great interest for the dye

13

desalination (the separation of dyes and salts) of textile wastewater. Herein, we prepared

14

reduced graphene oxide membranes in a solvation state (S-rGO) with nanochannel sizes

15

rightly between the salt ions and dye molecules. The S-rGO membrane rejects >99.0% of

16

Direct Red 80 (DR 80) and has almost zero rejection for Na2SO4. By contrast, conventional

17

GO or rGO membranes often have the channel sizes smaller than divalent ions (such as SO42-)

18

and thus high rejection for Na2SO4. More interestingly, high salinity in typical dye solutions

19

decreases the channel size in the S-rGO membranes, and thus increase the dye rejection, while

20

the Na2SO4 rejection decreases because of the negatively charged surface on GO and the salt

21

screening effect. The membranes also show pure water permeance as high as 80 L m−2 h−1

22

bar−1, which is about eight times that of commercial NF 90 membrane and two times that of a

23

commercial ultrafiltration membrane (with a molecular weight cutoff of 2000 Dalton),

24

rendering their promise for practical dye desalination.

25 26

1. INTRODUCTION

27

Desalination of aqueous dye solutions is critical to the dye production, where the salts (e.g.,

28

NaCl and Na2SO4) are byproducts, and to the dye recovery from textile wastewater after the

29

dyeing processes because the salts are often added to enhance the dye uptake by textiles.1,2

30

Nanofiltration (NF)1,3-9 and ultrafiltration (UF)10,11 membranes with pores smaller than dye

31

molecules have attracted significant interests for dye desalination because of their high

32

energy-efficiency. However, conventional polyamide-based NF membranes have high

33

rejection for divalent salts (like Na2SO4) and moderate rejection for monovalent salts (such as 2 ACS Paragon Plus Environment

Page 3 of 19


34

NaCl), resulting in low salt removal efficiency.6 More importantly, dye solutions usually have

35

high salinity (such as ~6.0 wt% NaCl and ~5.6 wt% Na2SO4) and thus very high osmotic

36

pressure. The high pressure required to overcome the significant osmotic pressure difference

37

across the membranes can make the process cost-prohibitive. Recently, novel loose NF

38

hollow fiber membranes were developed with high water permeance (7.0−71 L m−2 h−1 bar−1

39

or LMH/bar), high rejection to dyes (95.5−99.9%), and less than 10% rejection to Na2SO4.8

40

UF membranes usually have high water permeances and low rejections for the salts, while

41

their rejections to the dyes are often too low to achieve satisfactory dye recovery. Tight UF

42

membranes were developed with low rejection to Na2SO4 and more than 98% rejection for the

43

dyes.10,12,13 Nevertheless, membranes with high water permeance, nearly 100% rejection for

44

the organic dyes, and negligible rejection to multivalent salts like Na2SO4, are of great interest

45

for this application.

46

Graphene oxide (GO)-based membranes with tunable two-dimensional (2D) nanochannels

47

formed by stacking GO nanosheets in parallel present a new opportunity for dye

48

desalination.3,14-17 Graphene comprises a single layer of carbon atoms connected to a

49

hexagonal network by sp2 bonds, which can be oxidized to form GO sheets with hydrophilic

50

functional groups (such as hydroxyl, epoxy, and carboxyl), making them highly dispersible in

51

water.18 The 2D GO sheets with electrostatic repulsion between the ionized carboxyl groups

52

can be easily assembled in parallel into a layered structure.19,20 The sub-nanometer gap

53

between the sheets can be tuned for molecular separations, such as gas separation,21-23 solvent

54

nanofiltration,20,24,25 and water purification3,26-28. Current research is often focused on

55

reducing the channel size to enhance the salt rejections for desalination,4,17,27-37 which makes

56

them unsuitable for dye desalination. Particularly, to improve the stability for long-term

57

underwater operation, the hydrophilic GO films are often reduced to enhance the π–π

58

interactions between the GO sheets.3,20,24,36,38,39 The reduced GO (rGO) films become more

59

hydrophobic and have smaller interlayer distance, significantly decreasing the water 3 ACS Paragon Plus Environment


Page 4 of 19

60

permeance and increasing the salt rejection.17,40,41 To maintain the channel size during the

61

reduction, hybrids of GO and nanocrystals such as metal organic frameworks42 and

62

nanotubes17 were prepared, which, however, is complex. On the other hand, if the rGO films

63

were deliberately kept in the solvated state (i.e., S-rGO films) after the reduction, they were

64

demonstrated to retain the channel size and high permeance of organic solvents for organic

65

solvent nanofiltration (OSN).24 However, these S-rGO membranes have not been evaluated

66

for dye desalination performance, particularly in the high-concentration salt solutions.

67

Herein, we demonstrate that the nanochannels of the S-rGO films can be facilely rightsized

68

between the organic dye molecules and hydrated ions (such as Na+, SO42-, and Cl-) by

69

deliberate solvation to achieve superior desalination performance of the dye solutions.

70

Specifically, we deposited ultrathin layers of S-rGO onto commercial microfiltration (MF)

71

membranes, which were kept in the swollen state to control the channel size. The obtained S-

72

rGO membranes can reject ~99% of Direct Red 80 (DR 80) with almost no rejection for NaCl

73

and Na2SO4. Furthermore, the channel size in S-rGO membranes is decreased by the high

74

salinity in the typical dye solutions, as evidenced by the measurement of the molecular weight

75

cutoff (MWCO) of the membranes. The resulted S-rGO membranes exhibit higher dye

76

rejection and still negligible salt rejection, which makes them particularly suitable for dye

77

desalination. By contrast to the conventional studies of GO membranes to decrease channel

78

size and increase salt rejection, this study demonstrates the versatility of the rGO membranes

79

with channels manipulated to achieve high water and salt permeance and >99% rejection of

80

the organic dyes.

81 82

2. MATERIALS AND METHODS

83

2.1 Preparation of rGO Dispersion. GO aqueous dispersion was prepared from natural

84

graphite powder by a modified Hummers method43 as described in the supporting

85

information. The GO dispersion (0.10 mg/mL) was then reduced to rGO by hydrazine in an 4 ACS Paragon Plus Environment

Page 5 of 19


86

aqueous ammonia solution with a pH value of 10, where the solution was vigorously shaken

87

in an oil bath at 60 oC for 3 h.44

88

2.2 Fabrication of S-rGO Films. S-rGO membranes were prepared by vacuum filtration of

89

the diluted rGO dispersions through Nylon microfiltration membranes (47 mm in diameter,

90

0.65 µm pore size). The rGO mass loading is 100 mg/m2 in our experiments, resulting in a

91

thickness of ~50 nm. Thinner rGO membranes leads to higher water permeance and higher

92

possibility of forming defects (or lower dye rejection rates). Once the filtration was

93

completed, a certain amount of water was immediately poured on the surface of the as-formed

94

S-rGO coating to immerse it in water and keep it in the solvated state. The amount of water is

95

not critical as long as the S-rGO membrane is fully immersed in water. The as-prepared S-

96

rGO membranes were always soaked in water before and during the permeation tests, which

97

is critical to retain high water and salt permeance. Conventional dry rGO (D-rGO)

98

membranes14,15 were usually prepared by drying the membranes in the air at room

99

temperature.

100

2.3 Evaluation of the Membrane Separation Performance. Permeation experiments were

101

performed using a plastic dead-end filtration cell with a stirring rate of 700 rpm. The rejection

102

of the dyes (including MB, CB, CR and DR 80) and Na2SO4 at concentrations ranging from

103

0.2 to 2.0 g/L was determined at ~21 oC. The concentration of the dyes and Na2SO4 was

104

determined using a UV-vis spectrophotometer and a conductivity meter, respectively. At least

105

three different membranes were tested, and the values of the water permeance and rejection

106

are the average of these tests.

107 108 109

Water permeance (AW) with a unit of liters per square meter per hour per bar (LMH/bar) was calculated using equation (1): AW = V/(A × t × ∆P)

(1)

110

where V is the volume of the permeated water (liter) with a time of t (h), A is the effective

111

membrane area (m2), and ∆P is the effective pressure difference across the membrane (bar). 5 ACS Paragon Plus Environment


112

Because the Na2SO4 rejection is very low for the S-rGO membranes and PES 2K, the osmotic

113

pressure difference across the membrane is negligible compared with the ΔP.

114

The rejection (R) of the dyes or salts was calculated using equation (2):

115

R = (1−CP/CF) × 100%

(2)

116

where CP and CF are the concentrations of the dyes or salts in the permeate and feed solutions,

117

respectively. The steady state CP values were used for the calculation.

118

2.4 Characterizations. SEM images were taken using a Carl Zeiss AURIGA CrossBeam

119

Focused Ion Beam (FIB) Electron Microscope (Carl Zeiss, Germany). The SEM tests of S-

120

rGO composite membrane were taken after being dried in the air. X-ray diffraction (XRD)

121

was performed using a Rigaku Ultima IV diffractometer with Cu Kα radiation (λ = 0.15418

122

nm, Rigaku, Japan). Atomic force microscope (AFM) images were recorded by a Bruker

123

Dimension Icon Atomic Force Microscope (Bruker, Germany). Raman spectra were obtained

124

using a Renishaw inVia Raman Microscope (Renishaw plc, UK) with a 514-nm laser. X-ray

125

photoelectron spectroscopy (XPS) spectra were collected using a PHI 5600ci photoelectron

126

spectrometer (Physical Electronics, Inc., Chanhassen, MN, USA). UV-Vis spectra were

127

collected by a UV-2600 spectrophotometer (Shimadzu, Kyoto, Japan) and Vernier UV-Vis

128

spectrophotometer (Vernier Software & Technology, Beaverton, OR, USA). Total organic

129

carbon (TOC) was measured using a TOC-L TOC analyzer (Shimadzu).

130 131

3. RESULTS AND DISCUSSION

132

3.1 Structure of S-rGO Membranes. The as-prepared GO sheets have a lateral size of

133

about 1 µm and a thickness of about 0.8 nm (Figure 1a), which are typical for single-layer GO

134

sheets.18 The chemical composition of GO and rGO were analyzed by XPS. The C/O atomic

135

ratio is 2.2 for GO and 3.2 for rGO (Figure S1a and Table S1), confirming the decreased

136

amount of the oxygen-containing functional groups after the reduction. The removal of these

137

oxygen-containing groups can also be confirmed by Fourier transfer infrared (FTIR) 6 ACS Paragon Plus Environment

Page 6 of 19

Page 7 of 19


138

spectroscopy (Figure S1b). Figures 1b and 1c further confirm the reduction using XPS. The

139

C1s peak can be divided into four peaks corresponding to four types of carbon bonds: C‒

140

C/C=C (284.6 eV), C‒OH/C‒O‒C (286.5 eV), C=O (287.8 eV), and HO‒C=O (289.0 eV).44

141

The percentage of C‒OH/C‒O‒C peak area in the C1s spectrum reduces from 40% for GO to

142

28% for rGO, while most of the carboxyl groups remain during the reduction.

143 144 145 146

Figure 1. (a) AFM image of the GO sheets and the corresponding height profile. Highresolution C1s XPS spectra of (b) GO and (c) rGO. (d) Photos (inset) and UV-vis spectra of the GO and rGO dispersion. (e) Raman spectra of the GO and rGO sheets.

147 148

The inset of Figure 1d demonstrates that the as-prepared rGO can be stably dispersed in

149

alkaline water solution (pH = 10) due to the electrostatic repulsion between the ionized

150

carboxyl groups.18 The UV-vis spectra show that the absorption peak of the GO dispersion at

151

230 nm redshifts to 263 nm and the absorption in the whole spectral region increases after the

152

reduction, confirming that the reduction partially restores the electronic conjugation within

153

the GO sheets and creates new graphitic domains.18 The structural change from GO to rGO is

154

also validated by their Raman spectra (Figure 1e). The GO spectrum has two prominent peaks

155

at 1348 and 1603 cm-1, corresponding to the D- and G-band of carbon, respectively.44 The D-

156

band is associated with the structural defects of graphitic domains, and the G-band is related

157

to graphitic carbon. The rGO has a slightly higher D/G intensity ratio than the GO, indicating 7 ACS Paragon Plus Environment


Page 8 of 19

158

that the average size of the sp2 domains slightly decreases upon the reduction,44 because the

159

newly created graphitic domains in rGO are smaller than those in GO. On the other hand,

160

these newly created graphitic domains increase the hydrophobicity of the rGO sheets and thus

161

the long-term stability during the underwater operation.

162

Figure 2a shows a schematic of a thin film composite (TFC) membrane comprising an S-

163

rGO selective layer on a Nylon MF membrane. The membrane was fabricated by filtrating the

164

as-prepared rGO dispersion through the MF membrane with a pore size of ~0.65 µm (Figure

165

2b), smaller than the average lateral dimension of the rGO sheets (~1 µm). As a result, the

166

rGO sheets were deposited onto the Nylon surface and formed a uniform coating (Figure 2c).

167

As shown in the X-ray diffraction (XRD) patterns in Figure 2d, the S-rGO film does not show

168

any diffraction peaks related to the stacked rGO sheets at 2θ = 5−16o, indicating that the peak

169

should be at 2θ < 5o, and the interlayer distance is larger than 1.8 nm. After drying in the air,

170

the S-rGO membrane transforms into the D-rGO membrane and exhibits a distinct layered

171

structure in the cross-sectional SEM image (Figure S2). The D-rGO film exhibits a distinct

172

diffraction peak at 2θ = 13.5o, corresponding to an interlayer distance of 0.66 nm. When the

173

D-rGO film is soaked in water, its interlayer distance expands to 0.98 nm (2θ = 9.0o),45,46

174

which, however, is still much smaller than that in the S-rGO film. Once the rGO film is

175

completely dried, the channel size decreases irreversibly.

176


Page 9 of 19


177 178 179 180 181

Figure 2. (a) Schematic illustration of the structure of the S-rGO composite membrane and its separation of dye molecules and salts. Surface SEM images of (b) a Nylon MF membrane and (c) the S-rGO coating of 100 mg/m2 (about 50 nm) on the MF membrane. (d) Comparison of the XRD patterns of the S-rGO, D-rGO, and re-hydrated D-rGO films.

182 183

3.2 The Water Permeance of S-rGO Membranes. Figure 3a compares the pure water flux

184

of the D-rGO and S-rGO membranes at various applied pressures, which are also

185

benchmarked with PES 2K (Alfa Laval Inc.) with a molecular weight cutoff (MWCO) of

186

2000 Dalton. The water flux in the S-rGO membrane increases linearly with the pressure and

187

then deviates from the linear relationship at pressures of above 2 bar. The deviation at high

188

pressures can be ascribed to the compression of both S-rGO (consistent with that reported in

189

the literature29) and Nylon layer. Figure S3 shows that the water flux of Nylon films increases

190

linearly with the pressure before slightly deviating from the linear relationship at 3 bar, while

191

the degree of deviation is less than that in the S-rGO membrane suggesting the additional

192

contribution from the compression of S-rGO layer. Nevertheless, the S-rGO membrane

193

exhibits a water permeance of 80 LMH/bar at 2 bar, which is almost eight times that of D-

194

rGO membrane because of the fully solvated structure in S-rGO. The pure water permeance in



Page 10 of 19

195

S-rGO membrane is also twice that of commercial PES 2K, demonstrating their potential for

196

water purification.

197 198 199 200 201 202 203 204

Figure 3. (a) Comparison of water fluxes of the S-rGO membranes, D-rGO membranes, NF 90 and PES 2K at various applied pressures. (b) Rejection of the S-rGO membranes for different dye molecules, including methyl blue (MB), Columbia blue (CB), Congo red (CR), and DR 80. The insets are photographs of dye solutions before and after the filtration. (c) The DR 80 rejection and water permeance at different DR 80 concentration for the S-rGO membrane and PES 2K. (d) The Na2SO4 rejection and water permeance at different Na2SO4 concentrations for the S-rGO membrane and PES 2K.

205 206

3.3 The Dye Rejection of S-rGO Membranes. We systematically explored the potential of

207

the S-rGO membranes for dye desalination applications. First, a series of dye molecules with

208

different sizes were selected to test the dye rejection performance of the S-rGO membranes.

209

The chemical structure and molecular model of these dye molecules are illustrated in Figure

210

S4. Graphene-based materials are known to have high adsorption capability for dye

211

molecules.33,41 So to exclude the effect of physical adsorption, we used a relatively high

212

concentration of 0.2 g/L for all dyes in the feed solution and calculated the rejections when 10 ACS Paragon Plus Environment

Page 11 of 19


213

the concentration of the permeate solution became stable. As shown in Figure 3b and Figure

214

S5, the S-rGO membrane exhibits high rejection for these dyes, 97.6 ± 1.0% for methyl blue

215

(MB), 99.5 ± 0.2% for Columbia blue (CB), 99.9 ± 0.2% for Congo red (CR), and 99.4 ±

216

0.3% for DR 80. Because the S-rGO is negatively charged in water, the high rejections of the

217

S-rGO for these negatively charged dye molecules can be attributed to both size exclusion and

218

electrostatic repulsion.4,24,33 The CB, CR, and DR 80 exhibit similar rejection, which is

219

slightly higher than the MB, presumably because of the smaller molecular size and the less

220

negative charge due to the presence of the positively charged –NH- groups in MB (Figure

221

S4).

222

Textile wastewater usually has a high dye concentration, so the effect of dye concentration

223

on rejection and water permeance was evaluated. As shown in Figure 3c, the high DR 80

224

rejections in the S-rGO membrane is essentially independent of the DR 80 concentrations in

225

the feed solution. On the other hand, increasing the DR 80 concentration decreases the water

226

permeances for all the membranes investigated (Figure 3c and Figure S6), presumably

227

because the DR 80 molecules adsorb on the rGO and block the pores on the membrane

228

surface. Considering the relatively low molar concentration of DR 80, the osmotic pressure of

229

the solution (~0.02 bar) is negligible. Nevertheless, the S-rGO membrane exhibits much

230

higher water permeance than PES 2K and NF 90. For example, with 2.0 g/L DR 80, the S-

231

rGO membrane shows a water permeance of 42 ± 3 LMH/bar, which is more than four times

232

that of PES 2K (9.1 ± 0.8 LMH/bar) and about five times that of NF 90 (8.0 ± 0.1 LMH/bar).

233

3.4 The Salt Rejection of S-rGO Membranes. For dye desalination, the membrane should

234

not only have a high rejection for dye molecules but also have high salt permeance or salt

235

rejection as low as possible, especially at high salt concentrations.6 Na2SO4 was chosen as a

236

marker because Na2SO4 often has higher rejection than NaCl due to the larger SO42- ions, and

237

it also has the size similar to the organic dyes (Figure S4 and Table S2). As shown in Figure

238

3d, when the concentration of Na2SO4 is 2 g/L, the S-rGO membrane shows very low Na2SO4 11 ACS Paragon Plus Environment


Page 12 of 19

239

rejection (8.9%), which is much lower than NF 90 (96.4%, Figure S6) and almost same as

240

PES 2K (9.4%). More importantly, increasing the Na2SO4 content further decreases its

241

rejection. For example, as the Na2SO4 content increases from 2 g/L to 60 g/L, the rejection

242

decreases from 8.9% to almost zero because GO is negatively charged and increasing the salt

243

content decreases the Donnan potential, increases the co-ion sorption (SO42- in this case), and

244

thus increasing the salt permeability.47,48 This behavior is consistent with NF90, which shows

245

decreased rejection with increasing salt content (Figure S6b) and has negatively charged

246

surface. This attribute of the S-rGO films is very desirable because the waste dye/salt streams

247

usually have very high salinity (such as ~6.0 wt% NaCl and ~5.6 wt% Na2SO4). Additionally,

248

even at a Na2SO4 concentration of 60 g/L, the S-rGO membrane still exhibits water

249

permeance of 65 ± 1 LMH/bar, more than two times that of PES 2K (26 ± 1 LMH/bar).

250

3.5 The Molecular Weight Cutoff (MWCO) of S-rGO Membranes. Figure 3d also

251

shows that the water permeance in the S-rGO membrane decreases with increasing the

252

Na2SO4 content. We hypothesize that the nanochannels in the S-rGO are narrowed with

253

increasing the salt content, leading to the distinct decrease in water permeance. To prove this

254

assumption, we determined the MWCO of the membranes using a series of polyethylene

255

glycol (PEG) molecules with different molecular weight dissolved in water or 60 g/L Na2SO4

256

solution, which are shown in Figures 4a and 4b. The Stokes diameter (d, nm) of PEG can be

257

calculated using d = 33.46 × 10-3 M0.557, where M is the PEG molecular weight (g/mol). The

258

S-rGO exhibits a channel gap size between 3.4 and 5.7 nm, which corresponds to the PEG

259

molecular weight of 4,000 and 10,000 g/mol. This MWCO result is consistent with the XRD

260

patterns (Figure 2d), which indicates that the channel size should be more than 1.8 nm.

261

Interestingly, the PES 2K also shows the pore size between 3.4 and 5.7 nm and a MWCO of

262

10 K, which is much larger than the 2K provided by the manufacturer.

263

Figure 4b shows that the PEG rejection by PES 2K film is lower in the salt solution than in

264

water because the PEG molecules are more compactly coiled and thus have smaller sizes in 12 ACS Paragon Plus Environment

Page 13 of 19


265

the solution with higher salinity.49,50 However, the rejections of PEG by the S-rGO membrane

266

are higher in the salt solution than in water (Figure 4a), indicating that the channel size of the

267

S-rGO in the salt solution is smaller than that in water. The ionic strength may cause the

268

screening effect, reduce the repelling force between the carboxyl groups on the rGO, and thus

269

decrease the channel sizes.29,51

270 271 272 273 274 275 276 277

Figure 4. The MWCO curves of (a) an S-rGO membrane and (b) PES 2K in water and 60 g/L Na2SO4 using 1 g/L PEG with various molecular weights. Separation of DR 80 and Na2SO4 in (c) the S-rGO membrane and (d) PES 2K. The concentration of Na2SO4 is 60 g/L in all feed solutions. (e) Comparison of the dye desalination performance in the S-rGO membrane with those reported in the literature, including GO-based membranes,4,17,28,29,31,33,34 polymeric loose NF membranes,1,6-8 and polymeric tight UF membranes10. The details are shown in Table S3. (f) The long-term stability and fouling behavior of the membranes by alternately filtrating 13 ACS Paragon Plus Environment


278 279 280 281

pure water and the salty dye solution for three cycles. The dye solution contains 0.2 g/L DR 80 and 60 g/L Na2SO4. The black filled data points refer to the cycles using pure water and the red data points correspond to the periods filtrating the salty dye solution. Water flux recovery is the ratio of water flux to the initial water flux of the first pure water cycle.

282 283

3.6 Separation of Salt/Dye Mixture Solution and Low-Fouling Behavior of the S-rGO

284

Membranes. Figures 4c and 4d demonstrate the desalination of the dye solutions containing

285

60 g/L Na2SO4 and various concentrations of DR 80 in the S-rGO membranes and PES 2K,

286

respectively. The S-rGO membrane exhibits rejection of almost 100% for DR 80 and 0% for

287

Na2SO4. Increasing the dye concentration decreases the water permeance, which is consistent

288

with that in the dye solutions without Na2SO4. At the DR 80 concentration of 1.2 g/L, the

289

water permeance is 27 ± 1 LMH/bar, more than five times that of PES 2K (5.2 ± 0.2

290

LMH/bar). PES 2K still shows a Na2SO4 rejection of 4.5% at the DR 80 concentration of 1.2

291

g/L.

292

Figure 4e compares the dye desalination performance of the S-rGO membranes with other

293

membranes reported in the literature. The separation factor (α) is defined as the ratio of the

294

salt permeation rate to the dye permeation rate and calculated using α = (1-Rsalt)/(1-Rdye),

295

representing the salt removal efficiency of membranes.7 The higher the separation factor, the

296

better the salt removal efficiency. The S-rGO membrane shows both higher separation factor

297

and higher water permeance than the previously reported GO-based membranes,4,17,28,29,31,33,34

298

polymeric loose NF membranes,1,6-8 and polymeric tight UF membranes,10 indicating an

299

excellent desalination performance. In addition, the S-rGO membrane exhibits excellent long-

300

term stability and low-fouling behavior with the salty dye solutions. The water flux remains

301

stable during the filtration of pure water, and it decreased by almost 60% when the feed

302

solution was changed to the salty dye solution (Figure 4f). As discussed in Section 3.3 and

303

3.5, this can be attributed to the narrowing of nanochannels in S-rGO membrane at high salt

304

concentration and the partial blocking of pores by dye molecules. However, the water flux can

305

be fully recovered after changing the feed solution back to pure water (Figure 4f). This means 14 ACS Paragon Plus Environment

Page 14 of 19

Page 15 of 19


306

that the structural change of S-rGO membrane caused by high-concentration salt is

307

completely restored, and the blocking of pores by dye molecules is not permanent and can be

308

reversed. After alternately filtrating pure water and the salty dye solution for three cycles, the

309

water flux recovery is still 100% (Figure 4f), demonstrating the good stability of the S-rGO

310

membrane.

311 312

ASSOCIATED CONTENT

313

Supporting Information

314

The Supporting Information is available free of charge on the ACS publications website.

315

Details on the preparation of GO, the chemical structures of the dyes, the dye and salt

316

rejection of NF 90, and supplementary figures and tables (PDF).

317

AUTHOR INFORMATION

318

Corresponding Author

319

*E-mail: [email protected]

320

Notes

321

The authors declare no conflict of interest.

322 323

ACKNOWLEDGMENT

324

We gratefully acknowledge the support from the U.S. National Science Foundation (NSF)

325

under CAREER award number 1554236. This work was also partially supported by the

326

U.S. NSF Division of Civil, Mechanical, and Manufacturing Innovation (CMMI) with a

327

grant number of 1635026.

328

REFERENCES 15 ACS Paragon Plus Environment


329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377

Page 16 of 19

(1) Lin, J.; Ye, W.; Zeng, H.; Yang, H.; Shen, J.; Darvishmanesh, S.; Luis, P.; Sotto, A.; Van der Bruggen, B. Fractionation of direct dyes and salts in aqueous solution using loose nanofiltration membranes. J. Membr. Sci. 2015, 477, 183-193. (2) Kim, T. H.; Park, C.; Kim, S. Water recycling from desalination and purification process of reactive dye manufacturing industry by combined membrane filtration. J. Cleaner Prod. 2005, 13, 779-786. (3) Morelos-Gomez, A.; Cruz-Silva, R.; Muramatsu, H.; Ortiz-Medina, J.; Araki, T.; Fukuyo, T.; Tejima, S.; Takeuchi, K.; Hayashi, T.; Terrones, M.; Endo, M. Effective NaCl and dye rejection of hybrid graphene oxide/graphene layered membranes. Nat. Nanotech. 2017, 12, 1083-1088. (4) Han, Y.; Xu, Z.; Gao, C. Ultrathin graphene nanofiltration membrane for water purification. Adv. Funct. Mater. 2013, 23, 3693-3700. (5) Lin, J.; Tang, C. Y.; Ye, W.; Sun, S.-P.; Hamdan, S. H.; Volodin, A.; Haesendonck, C. V.; Sotto, A.; Luis, P.; Van der Bruggen, B. Unraveling flux behavior of superhydrophilic loose nanofiltration membranes during textile wastewater treatment. J. Membr. Sci. 2015, 493, 690-702. (6) Xu, Y.; Lin, J.; Gao, C.; Van der Bruggen, B.; Shen, Q.; Shao, H.; Shen, J. Preparation of high-flux nanoporous solvent resistant polyacrylonitrile membrane with potential fractionation of dyes and Na2SO4. Ind. Eng. Chem. Res. 2017, 56, 11967-11976. (7) Hong, S. U.; Miller, M. D.; Bruening, M. L. Removal of dyes, sugars, and amino acids from NaCl solutions using multilayer polyelectrolyte nanofiltration membranes. Ind. Eng. Chem. Res. 2006, 45, 6284-6288. (8) Han, G.; Chung, T. S.; Weber, M.; Maletzko, C. Low-pressure nanofiltration hollow fiber membranes for effective fractionation of dyes and inorganic salts in textile wastewater. Environ. Sci. Technol. 2018, 52, 3676-3684. (9) Ye, W.; Lin, J.; Borrego, R.; Chen, D.; Sotto, A.; Luis, P.; Liu, M.; Zhao, S.; Tang, C. Y.; Van der Bruggen, B. Advanced desalination of dye/NaCl mixtures by a loose nanofiltration membrane for digital ink-jet printing. Sep. Purif. Technol. 2018, 197, 27-35. (10) Lin, J.; Ye, W.; Baltaru, M.-C.; Tang, Y. P.; Bernstein, N. J.; Gao, P.; Balta, S.; Vlad, M.; Volodin, A.; Sotto, A.; Luis, P.; Zydney, A. L.; Van der Bruggen, B. Tight ultrafiltration membranes for enhanced separation of dyes and Na2SO4 during textile wastewater treatment. J. Membr. Sci. 2016, 514, 217-228. (11) Han, G.; Feng, Y.; Chung, T.-S.; Weber, M.; Maletzko, C. Phase inversion directly induced tight ultrafiltration (UF) hollow fiber membranes for effective removal of textile dyes. Environ. Sci. Technol. 2017, 51, 14254-14261. (12) Jiang, M.; Ye, K.; Deng, J.; Lin, J.; Ye, W.; Zhao, S.; Van der Bruggen, B. Conventional ultrafiltration as effective strategy for dye/salt fractionation in textile wastewater treatment. Environ. Sci. Technol. 2018, DOI: 10.1021/acs.est.1028b02984. (13) Jiang, M.; Ye, K.; Lin, J.; Zhang, X.; Ye, W.; Zhao, S.; Van der Bruggen, B. Effective dye purification using tight ceramic ultrafiltration membrane. J. Membr. Sci. 2018, 566, 151160. (14) Zhu, J.; Hou, J.; Uliana, A.; Zhang, Y.; Tian, M.; Van der Bruggen, B. The rapid emergence of two-dimensional nanomaterials for high-performance separation membranes. J Mater Chem A 2018, 6, 3773-3792. (15) Liu, G. P.; Jin, W. Q.; Xu, N. P. Two-dimensional-material membranes: A new family of high-performance separation membranes. Angew. Chem. Int. Ed. 2016, 55, 13384-13397. (16) Park, H. B.; Kamcev, J.; Robeson, L. M.; Elimelech, M.; Freeman, B. D. Maximizing the right stuff: The trade-off between membrane permeability and selectivity. Science 2017, 356, eaab0530.


Page 17 of 19

378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428


(17) Zhu, L.; Wang, H.; Bai, J.; Liu, J.; Zhang, Y. A porous graphene composite membrane intercalated by halloysite nanotubes for efficient dye desalination. Desalination 2017, 420, 145-157. (18) Li, D.; Müller, M. B.; Gilje, S.; Kaner, R. B.; Wallace, G. G. Processable aqueous dispersions of graphene nanosheets. Nat. Nanotech. 2008, 3, 101-105. (19) Dikin, D. A.; Stankovich, S.; Zimney, E. J.; Piner, R. D.; Dommett, G. H. B.; Evmenenko, G.; Nguyen, S. T.; Ruoff, R. S. Preparation and characterization of graphene oxide paper. Nature 2007, 448, 457-460. (20) Huang, L.; Li, Y. R.; Zhou, Q. Q.; Yuan, W. J.; Shi, G. Q. Graphene oxide membranes with tunable semipermeability in organic solvents. Adv. Mater. 2015, 27, 3797-3802. (21) Kim, H. W.; Yoon, H. W.; Yoon, S. M.; Yoo, B. M.; Ahn, B. K.; Cho, Y. H.; Shin, H. J.; Yang, H.; Paik, U.; Kwon, S.; Choi, J. Y.; Park, H. B. Selective gas transport through fewlayered graphene and graphene oxide membranes. Science 2013, 342, 91-95. (22) Li, H.; Song, Z.; Zhang, X.; Huang, Y.; Li, S.; Mao, Y.; Ploehn, H. J.; Bao, Y.; Yu, M. Ultrathin, molecular-sieving graphene oxide membranes for selective hydrogen separation. Science 2013, 342, 95-98. (23) Wang, S. F.; Wu, Y. Z.; Zhang, N.; He, G. W.; Xin, Q. P.; Wu, X. Y.; Wu, H.; Cao, X. Z.; Guiver, M. D.; Jiang, Z. Y. A highly permeable graphene oxide membrane with fast and selective transport nanochannels for efficient carbon capture. Energy Environ. Sci. 2016, 9, 3107-3112. (24) Huang, L.; Chen, J.; Gao, T.; Zhang, M.; Li, Y.; Dai, L.; Qu, L.; Shi, G. Reduced graphene oxide membranes for ultrafast organic solvent nanofiltration. Adv. Mater. 2016, 28, 8669-8674. (25) Zhang, Y.; Chung, T. S. Graphene oxide membranes for nanofiltration. Curr. Opin. Chem. Eng. 2017, 16, 9-15. (26) Mi, B. Materials science. Graphene oxide membranes for ionic and molecular sieving. Science 2014, 343, 740-742. (27) Chen, L.; Shi, G.; Shen, J.; Peng, B.; Zhang, B.; Wang, Y.; Bian, F.; Wang, J.; Li, D.; Qian, Z.; Xu, G.; Liu, G.; Zeng, J.; Zhang, L.; Yang, Y.; Zhou, G.; Wu, M.; Jin, W.; Li, J.; Fang, H. Ion sieving in graphene oxide membranes via cationic control of interlayer spacing. Nature 2017, 550, 380-383. (28) Hu, M.; Mi, B. Enabling graphene oxide nanosheets as water separation membranes. Environ. Sci. Technol. 2013, 47, 3715-3723. (29) Huang, H.; Mao, Y.; Ying, Y.; Liu, Y.; Sun, L.; Peng, X. Salt concentration, pH and pressure controlled separation of small molecules through lamellar graphene oxide membranes. Chem. Commun. 2013, 49, 5963-5965. (30) Huang, H.; Song, Z.; Wei, N.; Shi, L.; Mao, Y.; Ying, Y.; Sun, L.; Xu, Z.; Peng, X. Ultrafast viscous water flow through nanostrand-channelled graphene oxide membranes. Nat. Commun. 2013, 4, 2979. (31) Han, Y.; Jiang, Y.; Gao, C. High-flux graphene oxide nanofiltration membrane intercalated by carbon nanotubes. ACS Appl. Mater. Interfaces 2015, 7, 8147-8155. (32) Zhang, Y.; Zhang, S.; Chung, T. S. Nanometric graphene oxide framework membranes with enhanced heavy metal removal via nanofiltration. Environ. Sci. Technol. 2015, 49, 10235-10242. (33) Akbari, A.; Sheath, P.; Martin, S. T.; Shinde, D. B.; Shaibani, M.; Banerjee, P. C.; Tkacz, R.; Bhattacharyya, D.; Majumder, M. Large-area graphene-based nanofiltration membranes by shear alignment of discotic nematic liquid crystals of graphene oxide. Nat. Commun. 2016, 7, 10891. (34) Chen, L.; Moon, J.-H.; Ma, X.; Zhang, L.; Chen, Q.; Chen, L.; Peng, R.; Si, P.; Feng, J.; Li, Y.; Lou, J.; Ci, L. High performance graphene oxide nanofiltration membrane prepared by electrospraying for wastewater purification. Carbon 2018, 130, 487-494. 17 ACS Paragon Plus Environment


429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478

Page 18 of 19

(35) Xi, Y.-H.; Liu, Z.; Ji, J.; Wang, Y.; Faraj, Y.; Zhu, Y.; Xie, R.; Ju, X.-J.; Wang, W.; Lu, X.; Chu, L.-Y. Graphene-based membranes with uniform 2d nanochannels for precise sieving of mono-/multi-valent metal ions. J. Membr. Sci. 2018, 550, 208-218. (36) Oh, Y.; Armstrong, D. L.; Finnerty, C.; Zheng, S.; Hu, M.; Torrents, A.; Mi, B. Understanding the pH-responsive behavior of graphene oxide membrane in removing ions and organic micropollulants. J. Membr. Sci. 2017, 541, 235-243. (37) Yang, Q.; Su, Y.; Chi, C.; Cherian, C. T.; Huang, K.; Kravets, V. G.; Wang, F. C.; Zhang, J. C.; Pratt, A.; Grigorenko, A. N.; Guinea, F.; Geim, A. K.; Nair, R. R. Ultrathin graphene-based membrane with precise molecular sieving and ultrafast solvent permeation. Nat. Mater. 2017, 16, 1198-1202. (38) Yeh, C.-N.; Raidongia, K.; Shao, J.; Yang, Q.-H.; Huang, J. On the origin of the stability of graphene oxide membranes in water. Nat. Chem. 2015, 7, 166-170. (39) Qiu, L.; Zhang, X.; Yang, W.; Wang, Y.; Simon, G. P.; Li, D. Controllable corrugation of chemically converted graphene sheets in water and potential application for nanofiltration. Chem. Commun. 2011, 47, 5810-5812. (40) Nair, R. R.; Wu, H. A.; Jayaram, P. N.; Grigorieva, I. V.; Geim, A. K. Unimpeded permeation of water through helium-leak-tight graphene-based membranes. Science 2012, 335, 442-444. (41) Huang, L.; Zhang, M.; Li, C.; Shi, G. Q. Graphene-based membranes for molecular separation. J. Phys. Chem. Lett. 2015, 6, 2806-2815. (42) Guan, K. C.; Zhao, D.; Zhang, M. C.; Shen, J.; Zhou, G. Y.; Liu, G. P.; Jin, W. Q. 3d nanoporous crystals enabled 2D channels in graphene membrane with enhanced water purification performance. J. Membr. Sci. 2017, 542, 41-51. (43) William S. Hummers, J.; Offeman, R. E. Preparation of graphitic oxide. J. Am. Chem. Soc. 1958, 80, 1339-1339. (44) Stankovich, S.; Dikin, D. A.; Piner, R. D.; Kohlhaas, K. A.; Kleinhammes, A.; Jia, Y.; Wu, Y.; Nguyen, S. T.; Ruoff, R. S. Synthesis of graphene-based nanosheets via chemical reduction of exfoliated graphite oxide. Carbon 2007, 45, 1558-1565. (45) Zheng, S.; Tu, Q.; Urban, J. J.; Li, S.; Mi, B. Swelling of graphene oxide membranes in aqueous solution: Characterization of interlayer spacing and insight into water transport mechanisms. ACS Nano 2017, 11, 6440-6450. (46) Cho, Y. H.; Kim, H. W.; Lee, H. D.; Shin, J. E.; Yoo, B. M.; Park, H. B. Water and ion sorption, diffusion, and transport in graphene oxide membranes revisited. J. Membr. Sci. 2017, 544, 425-435. (47) Kamcev, J.; Galizia, M.; Benedetti, F. M.; Jang, E. S.; Paul, D. R.; Freeman, B. D.; Manning, G. S. Partitioning of mobile ions between ion exchange polymers and aqueous salt solutions: Importance of counter-ion condensation. Phys. Chem. Chem. Phys. 2016, 18, 60216031. (48) Kamcev, J.; Paul, D. R.; Manning, G. S.; Freeman, B. D. Predicting salt permeability coefficients in highly swollen, highly charged ion exchange membranes. ACS Appl. Mater. Interfaces 2017, 9, 4044-4056. (49) Heeb, R.; Lee, S.; Venkataraman, N. V.; Spencer, N. D. Influence of salt on the aqueous lubrication properties of end-grafted, ethylene glycol-based self-assembled monolayers. ACS Appl. Mater. Interfaces 2009, 1, 1105-1112. (50) Brunchi, C. E.; Ghimici, L. PEG in aqueous salt solutions. Viscosity and separation ability in a tio2 suspension. Rev. Roum. Chim. 2013, 58, 183-188. (51) Yang, X. W.; Qiu, L.; Cheng, C.; Wu, Y. Z.; Ma, Z. F.; Li, D. Ordered gelation of chemically converted graphene for next-generation electroconductive hydrogel films. Angew. Chem. Int. Ed. 2011, 50, 7325-7328.


Page 19 of 19

479


Table of Contents Graphic

480 481


Rightsizing Nanochannels in Reduced-Graphene Oxide Membranes

Recommend Documents