Subscriber access provided by University of Newcastle, Australia
Article
Mitigation of Thin Film Composite Membrane Biofouling via Immobilizing Nano-Sized Biocidal Reservoirs in the Membrane Active Layer Alireza Zirehpour, Ahmad Rahimpour, Ahmad Arabi Shamsabadi, Mohammad Sharifian Gh., and Masoud Soroush Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.7b00782 • Publication Date (Web): 17 Apr 2017 Downloaded from http://pubs.acs.org on April 18, 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 30
Environmental Science & Technology
1
Mitigation of Thin Film Composite Membrane Biofouling
2
via Immobilizing Nano-Sized Biocidal Reservoirs in the
3
Membrane Active Layer
4 5 6
Alireza Zirehpour1, Ahmad Rahimpour1*, Ahmad Arabi Shamsabadi2,
7
Mohammad Sharifian Gh.3, Masoud Soroush2*
8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
Key Words: Thin-film composite membrane, metal-organic framework, biofouling
24
mitigation, forward osmosis, biocidal reservoir
April 10, 2017
THIRD REVISED VERSION
Submitted for Publication in ACS Environmental Science and Technology
25 26 27 28 29 30 31 32 33 34 35
1
Department of Chemical Engineering, Babol Noushirvani University of Technology, Shariati Ave., Babol, Iran 2 Department of Chemical and Biological Engineering, Drexel University, Philadelphia, PA 19104, USA 3 Department of Chemistry, Temple University, Philadelphia, PA 19122, USA *Corresponding authors: Rahimpour:
[email protected],
[email protected], 98-11-32334204 (tel/fax) Soroush:
[email protected], 1-215-895-1710 (tel), 1-215-895-5837 (fax)
ACS Paragon Plus Environment
Environmental Science & Technology
36
ABSTRACT
37
This work investigates the use of a silver-based metal-organic framework (MOF) for
38
mitigating biofouling in forward-osmosis thin-film composite (TFC) membranes. This is the
39
first study of the use of MOFs for biofouling control in membranes. MOF nanocrystals were
40
immobilized in the active layer of the membranes via dispersing them in the organic solution
41
used for interfacial polymerization. Field emission scanning electron microscopy (FE-SEM)
42
and X-ray photoelectron spectroscope (XPS) characterization results showed the presence of
43
the MOF nanocrystals in the active layer of the membranes. The immobilization improved
44
the membrane active layer in terms of hydrophilicity and transport properties, without
45
adversely affecting the selectivity. It imparted antibacterial activity to the membranes; the
46
number of live bacteria attached to the membrane surface was over 90% less than that of
47
control membranes. Additionally, the MOF nanocrystals provided biocidal activity that lasted
48
for 6 months. The immobilization improved biofouling resistance in the membranes, whose
49
flux had a decline of 8% after 24 hours of operation in biofouling experiments, while that of
50
the control membranes had a greater decline of ~21%. Investigating of the membranes using
51
showed that the improvement in the biofouling resistance is due to simultaneous
52
improvement of anti-adhesive and antimicrobial properties of the membranes. Fluorescence
53
microscopy and FE-SEM indicated simultaneous improvement in anti-adhesive and
54
antimicrobial properties of the TFN membranes, resulting in a limited biofilm formation.
55 56 57 58 59 60
1 ACS Paragon Plus Environment
Page 2 of 30
Page 3 of 30
Environmental Science & Technology
61
INTRODUCTION
62
The demand for water sources has been increasing with the world population. The decreasing
63
water supply in arid and semiarid areas has motivated more use of unconventional water
64
sources (for example, brackish and seawater desalination, and wastewater treatment) 1.
65
Membrane-based technologies can play a major role in addressing the increasing water
66
demand. In these technologies, membrane fouling is a major issue, as it lowers membrane
67
performance, increases operational costs, and shortens membrane life 1-3.
68
Forward osmosis (FO) is a high water-recovery and low-cost membrane-based
69
technology that has potential applications in desalination 4 and wastewater treatment
70
advantage of FO (beneficial for fouling control) over pressure-driven membrane technologies
71
is that it does not need hydraulic pressure to operate 6-12. Nevertheless, biofouling has limited
72
the use of FO, in particular, for feeds containing microorganisms 9, 12-13.
73
2, 5
. An
There are four main types of membrane fouling: organic, inorganic, colloidal, and 14-17
74
microbial (biofouling)
. Compared to organic and inorganic fouling, biofouling is much
75
more complex, because in biofouling, the foulants are microorganisms in the feed solution.
76
The microorganisms attach to the membrane surface, propagate, and produce sticky
77
extracellular polymeric substances (EPSs), leading to the formation of aggregated biofilms 18-
78
20
79
filtration process consumes more energy
80
entire membrane surfaces. Therefore, a small amount of them in the feed solution can result
81
in severe biofouling 18. Furthermore, EPS matrices enhance the adhesion of microorganisms
82
on the membrane surface and prevent the biofilms from being treated by oxidizing agents,
83
biocides, and antibiotics 23-24.
. Once the biofilms are stabilized on membrane surfaces, water flux decreases and the 21-22
. Microorganisms are capable of colonizing
84
Thin film composite (TFC) membranes based on polyamide materials have been used
85
predominantly as osmotic membranes in water and energy applications 25-29. Biofouling poses
2 ACS Paragon Plus Environment
Environmental Science & Technology
Page 4 of 30
86
a unique challenge to these membranes, because the membranes cannot tolerate oxidants such
87
as chlorine that is inexpensive and widely used
88
mitigation strategies are needed.
30-31
.
Therefore, effective biofouling
89
Surface modification of TFC membranes by directly incorporating or anchoring
90
biocide agents is a promising approach to improving membrane properties (such as
91
biofouling resistance). The appeal of this approach is mainly due to the ability of biocidal
92
agents on membrane surfaces to deactivate bacteria upon a contact. Metal/metal oxide
93
nanoparticle systems are commonly used to prepare antimicrobial membranes. For instance,
94
different types of biocidal nanomaterials including silver (Ag) nanoparticles and silver-based
95
compounds 32-35, copper (Cu) nanoparticles 35-36, titanium dioxides (TiO2) 37, and zinc oxides
96
(ZnO) 38 have been used to develop antibacterial membranes. Applying silver-based materials
97
has been recognized as an effective approach to decreasing membrane biofouling
98
these materials have strong and broad biocidal activity against bacteria, fungi, and viruses 41.
99
Nevertheless, the direct blending method has some disadvantages. First, the biofouling
100
mitigation does not last long, as the particles have weak resistance to washing (they are easily
101
released), causing the membranes to quickly lose their antimicrobial function 36, 42-44. Second,
102
membrane performance (membrane selectivity) deteriorates as a result of low compatibility
103
between the inorganic nanomaterials and organic membrane
104
32-33, 39-40
;
44-45
.
Recent studies have generally focused on forming nanomaterial agents on membrane
105
surface to endow membranes with direct, effective and long-lasting biofouling mitigation
106
39-40, 46-48
107
(NaBH4), which is not environmentally friendly, has been recommended
108
permeability loss during membrane modification is still a major problem 18.
36,
. Among these studies, the use of toxic reductants such as sodium borohydride 39, 48
. Moreover,
109
In recent years, metal-organic frameworks (MOFs), which are compounds consisting
110
of metal ions or clusters coordinated to organic ligands, have been studied for their great
3 ACS Paragon Plus Environment
Page 5 of 30
Environmental Science & Technology
49-52
111
potential in bactericidal applications
. MOFs are promising antibacterial materials,
112
because their inorganic and organic components can provide platforms to generate strong
113
bactericidal activity and biocompatibility 52-56. A major advantage of MOFs is their ability to
114
act as a reservoir of metal ions that are inherent parts of their molecular structure. The metal
115
ions are stabilized by the formation of chemical bonds to the organic linker that are
116
sufficiently strong to make the MOF structure adequately robust without blocking their
117
antibacterial activity. Another advantage of MOFs is their uniform distribution of metal
118
active sites. Thus, MOFs provide a long-lasting antibacterial effect and prevent metal
119
agglomeration and oxidation 50.
120
In this work, we investigate the use of silver-based MOF nanocrystals to mitigate the
121
biofouling in FO membranes. The MOF nanocrystals have a good compatibility with the
122
polyamide layer because of their organic ligand. Consequently, the membrane active layer is
123
improved without detrimental effects on the layer selectivity. Results presented in this paper
124
highlight the great potential of MOF compounds in improving the biofouling resistance of
125
membranes. To best of our knowledge, this work is the first study of MOFs for biofouling
126
control in membranes.
127 128
MATERIALS AND METHODS
129
MOF nanocrystal synthesis and characterization. The synthesis protocol was adapted
130
from typical conditions reported in the literature 57. The MOF nanocrystals were synthesized
131
under ultrasonic irradiation at a frequency of 24 KHz (Heilscher UP400s, Germany) for a
132
reaction time of 60 min. The output and pulse of ultrasonic waves were kept at 80W and 0.6,
133
respectively.
134
dissolved in 40 ml dimethylformamide (DMF) as solvent, and then mixed with 40 ml solution
135
of silver nitrate [AgNO3, (1 g)] in DMF. Afterwards, the product was centrifuged, and the
In a typical synthesis, 1,3,5-benzenetricarboxylic acid [BTC, (1 g)] was
4 ACS Paragon Plus Environment
Environmental Science & Technology
136
precipitate was washed with a mixture of water and ethanol (1:1), and then dried at 60°C for
137
24 h. The morphology of MOF nanocrystals was observed using transmission electron
138
microscopy (TEM, Zeiss EM900), operated at 20 kV. Chemical and functional groups of the
139
MOF nanocrystals were determined using a Bruker-IFS 48 FTIR spectrometer (Ettlingen,
140
Germany) with a horizontal ATR device. X-ray powder diffraction (XRD) patterns for the
141
MOF nanomaterial were recorded at 298 K using a XPERT-PRO X-ray diffractometer. The
142
chemical characterization of MOF block was investigated via energy-dispersive X-ray (EDX)
143
spectroscopy. Size distributions of MOF nanocrystals were measured in n-hexane organic
144
solution via dynamic light scattering (DLS, Nano ZS ZEN 3600).
145
Immobilization of MOF nanocrystals in the active layer of FO membranes. The
146
selective layer of FO membranes was prepared via interfacial polymerization (IP) on
147
polyethersulfone (PES) substrates. Further information on the PES substrate synthesis and the
148
membranes characterization are given in the Supporting Information (SI). Thin film
149
nanocomposite (TFN) membranes were prepared by immobilizing the silver-based MOF
150
nanocrystals within their selective layer during IP process. The PES substrate was immersed
151
in a 2.0 wt.% 1,3-phenylendiamine (MPD) solution for 2 min. The excess MPD solution was
152
carefully removed from the membrane surface by an air-knife. The MPD-soaked membrane
153
was then dipped in a 0.1 wt./v% trimesoylchloride (TMC) in a n-hexane solution for 30 sec.
154
The MOF nanocrystals were loaded in a TMC-n-hexane solution (0.02 wt./v%) and dispersed
155
by ultrasonicating for 30 min. The reaction of MPD and TMC at the interface resulted in the
156
formation of an ultrathin polyamide rejection layer on the PES substrates. Afterward, the
157
membranes were cured in an oven at 80 °C for 5 min. The prepared membranes were stored
158
in 20 °C deionized water before being tested.
159
Statistical Analysis. To confirm any observed difference is due to the MOF
160
modification but not an experimental error, significant differences (α = 0.05) were
5 ACS Paragon Plus Environment
Page 6 of 30
Page 7 of 30
Environmental Science & Technology
161
determined via Student’s t-test with two-tailed distribution and reported as p-values.
162
Microsoft Excel® software was used for the calculations. P-values less than 0.05 suggest that
163
the differences are statistically significant.
164 165
REDULTS AND DISCUSSIONS
166
Characterization of the MOF nanocrystals. The silver-based MOF was characterized using
167
TEM, IR and EDX. The TEM image in Fig. 1a shows the morphology of the MOF
168
nanocrystals prepared by the ultrasonic method. The chemical composition of the MOF was
169
characterized via energy-dispersive X-ray (EDX) analysis, as presented in Fig. 1b. The EDX
170
analysis indicates that oxygen-to-silver atom ratio in the MOF building block is 2.52. The IR
171
spectrum of the MOF nanocrystals (Fig. 1c) shows the characteristic peaks for C–H (690-760
172
cm-1), C–O (1090 cm-1), and C=C bonds (1620 cm-1), and also oxygenated C=O (1735 cm-1)
173
and O–H (3300-3600 cm-1) groups. The absorption bands of the carboxylate group and the
174
aromatic benzene ring are consistent with the nature of the organic ligand
175
measurement indicated that the size distribution of nanocrystals has a sharp and narrow peak
176
with an approximately 33 nm mean size (Fig. 1d), which is in the range of the MOF size
177
measured from the TEM image. The organic ligands and the small size of the MOFs lead to
178
no defects in the membrane active layer when MOFs are present in the active layer. The
179
XRD pattern of the MOF nanocrystals presented in the SI (Fig. S1) had three diffraction
180
peaks for silver: Ag (111), Ag (200), and Ag (220)
181
and intense peaks at 6.6°, 9.8°, 11.2° and 13.1°, confirming the crystalline structure in the
182
synthesized nanomaterial.
58
. The DLS
35, 59
. In addition, there were other sharp
183
Characterization of the TFN membranes. Loading MOF nanocrystals alter
184
polyamide-layer specifications of the TFN membrane. Fig. 2 shows the surface micrographs
185
of the TFC and TFN membranes obtained using different detectors of field emission scanning
6 ACS Paragon Plus Environment
Environmental Science & Technology
186
electron microscopy (FE-SEM). The left-side images were taken using a common secondary
187
detector, while the right-side images using a backscattered imaging detector. The bright areas
188
in each of the modes have a different meaning. In the secondary imaging mode, the bright
189
areas represent a projection or a hill on the membrane surface. Instead, the bright points in
190
the backscattered imaging mode indicate the existence of a high-atomic-number element on
191
the sample surface. Heavy elements (such as silver in this case) backscatter electrons more
192
strongly than light elements (such as carbon, nitrogen and oxygen in the polyamide layer),
193
and thus they appear brighter in the image
194
changes in the overall morphology of the membrane surface (“ridge and valley”). The
195
backscattered images showed bright spots on the surface of the TFN membranes, which can
196
be attributed to the silver, as characteristic element of MOF nanocrystals used (Fig. 2b, right-
197
side). This observation clearly identified the MOF nanocrystals in the active layer of TFN
198
membrane.
60-61
. Loading MOF nanocrystals did not cause
199
A higher magnification of the FE-SEM images of the TFN membrane surfaces is
200
shown in Fig. 2c. The images indicate that MOF nanocrystals exist within the thin selective
201
layer of the TFN membranes and on their surfaces as well. It seems that the MOF
202
nanocrystals have been completely surrounded by the thin-film polyamide matrix (orange
203
arrows). This agrees well with the good compatibility of the MOF nanocrystals and
204
polyamide network, causing the two phases to match well (without any gaps between the two
205
phases). In addition, the EDX spectrum was obtained for different bright points on the TFN
206
membrane surface, and the results again revealed that these points were associated with the
207
MOF nanocrystals (Fig. 2c).
208
Fig. 3 illustrates cross-section FE-SEM micrographs of the TFC and TFN membranes.
209
As can be seen, both membranes have identical active-layer thicknesses (Figs. 3a and 3b).
210
The atomic force microscopy (AFM) results shown in Fig. 3d also indicate no considerable
7 ACS Paragon Plus Environment
Page 8 of 30
Page 9 of 30
Environmental Science & Technology
211
alteration in surface roughness of the membranes after immobilizing MOF nanocrystals. The
212
results presented in Figs. 2 and 3 suggest that MOF nanocrystals do not significantly affect
213
overall morphology of TFN membrane surface, as its thin-film polyamide features were
214
similar to those of the TFC membranes.
215
Fig. 3f compares the water contact-angle of the TFN membrane to that of the control
216
TFC membrane. A statistical analysis of the contact angle results indicate that the presented
217
results are statistically significant (P-value < 0.05). The contact angle results demonstrate that
218
the surface of TFN membrane become more hydrophilic by immobilizing the MOF
219
nanocrystals. The enhanced hydrophilicity of the TFN membrane is due to the hydrophilic
220
property of the MOF nanocrystals coming from the functional groups of the nanocrystals
221
(Fig. 1c).
222
The polyamide active layers of the FO membranes were analyzed for the elemental
223
composition, chemical bonding, and cross-linking degree through X-ray photoelectron
224
spectroscope (XPS). The XPS surveys spectra of TFC and TFN membranes presented in Fig.
225
4 confirm the presence of oxygen (O 1s), nitrogen (N 1s), and carbon (C 1s) elements at the
226
membranes surface (~ 10 nm depth). Signals at around 368 eV and 374 eV, attributed to Ag
227
3d orbitals, appeared in the spectrum of the TFN membrane, prove the existence of the MOF
228
nanocrystals in the top 10 nm depth of TFN membrane surface.
229
The element ratios of O/N, important properties of the polyamide layer which reflect
230
the layer cross-linking degree, were calculated from the XPS spectra. These results are
231
summarized in Table 1. Theoretically, O/N ratio varies between 1.0 and 2.0. A value of 1.0
232
indicates that the polyamide layer is fully cross-linked, while a value of 2.0 corresponds to a
233
fully linear structure
234
MOF nanocrystals into the polyamide layer increases O/N ratio of the TFN membranes. This
235
behavior can be due to the formation of a less-cross-linked structure in the polyamide
62-63
. The elemental-composition analysis shows that immobilizing the
8 ACS Paragon Plus Environment
Environmental Science & Technology
Page 10 of 30
236
network or the existence additional oxygen sources of the MOF organic block in the
237
membrane. Atomic concentrations determined from the MOF EDX analysis (Fig. 1b) and
238
XPS analysis (Table 1) were used to estimate the oxygen percent added from the MOF. The
239
concentration values allow one to determine if an increase in the O/N ratio is due to a smaller
240
cross-linking degree or the existence of additional oxygen sources in the MOF. Table 1
241
shows two kinds of O/N ratios (X and Y). The O/N ratio denoted by X was determined
242
directly from the XPS results, while the ratio denoted by Y was calculated after eliminating
243
the oxygen content added by the MOF. As shown in Table 1, the O/N ratio of the TFC
244
membrane was 1.02, indicating 97% cross-linking in its selective layer. Loading the MOF
245
nanocrystals to the TMC organic solution increased the O/N ratios of the TFN membrane to
246
1.04 (ratio denoted by Y), indicating 93% cross-linking. The change in cross-linking is due to
247
the interrupting polymer chains in the polyamide network (caused by the presence of MOF
248
nanocrystals).
249
High-resolution XPS spectra of carbon (1s) are presented in Figs. 4b and 4c for the
250
TFC and TFN membranes, respectively. Peak fitting was carried out to provide information
251
of the chemical bonding. The carbon (1s) spectrum of TFC membrane shows two peaks (Fig.
252
4b): a major peak at 284.8 eV corresponds to carbons without adjacent electron withdrawing
253
groups (such as carbons in aliphatic and aromatic C–C or C–H bonds)
254
peak at 287.9 eV. The peak with the 3.1 eV shift corresponds to carbons in a strong electron-
255
withdrawing environment (most likely those in carboxylic O=C–O and amide O=C–N
256
groups)
257
peak at 285.9 with an intermediate binding energy shift (Fig. 4c), which is likely associated
258
with carbons in a weak electron withdrawing environment (most likely carbons in C–O
259
bonds). This exclusive peak is likely to a sign of the organic building block of the MOF
260
nanocrystals in the active layer of TFN membrane. The results indicate that loading MOF
62, 64-65
, and a minor
62-63, 66
. Compared to the TFC membranes, the TFN membranes have an additional
9 ACS Paragon Plus Environment
Page 11 of 30
Environmental Science & Technology
261
nanocrystals alters the physiochemical properties of the polyamide layer of the TFN
262
membrane. These alterations are expected to modify the transport properties of the resultant
263
membrane.
264
Effects of MOF nanocrystals on transport through the active layer of TFN
265
membranes. The effects of immobilizing MOF nanocrystals on the transport properties of
266
the membranes were investigated, and the results are summarized in Table 2. The intrinsic
267
water and solute permeability coefficients (denoted by A and B, respectively) of the
268
membranes were calculated based on the mean of each three independent FO experimental
269
data and using the four-step FO characterization protocol described in Ref. 67. As can be seen
270
in Table 2, immobilizing the MOF nanocrystals enhanced the water permeability by about
271
55%. Likewise, the solute permeability coefficient (B) of the TFN membrane is slightly
272
higher than that of the TFC membrane. Immobilizing the MOF nanocrystals reduces the
273
solute permeability/water permeability ratio (B/A) in the TFN membrane, pointing to an
274
improved permselectivity of the membrane (Table 2). Generally, a low B/A ratio is desired to
275
enhance selectivity and decrease fouling tendency, thus improving the FO process stability 68-
276
70
277
membrane. This verifies that there is no gap between the incorporated nanomaterials and the
278
polyamide network. The results suggest the presence of a lower transport resistance in the
279
selective layer of TFN membrane, which can be attributed to the following factors. First,
280
loading the MOF nanocrystals in the TMC organic solution may affect the IP process, which
281
increases the fractional free-volume in the polyamide matrix due to the disrupted polymer
282
chain packing
283
have a lower cross linking degree of polyamide layer compared to the TFC membranes
284
(Table 1). Second, the more hydrophilic surface of the TFN membrane can attract water
285
molecules, initiating a faster overall flow of water molecules through the layer. In summary,
. Moreover, the TFN membrane provided a slightly higher salt rejection than the TFC
71
. This is supported by the XPS results, showing that the TFN membranes
10 ACS Paragon Plus Environment
Environmental Science & Technology
286
these results indicate that immobilizing the MOF nanocrystals facilitate the transport across
287
the selective layer of TFN membrane, while preserving the membrane selectivity.
288
Effects of MOF nanocrystals on the biocidal activity of the TFN membranes. The
289
bactericidal activity of the membranes was assessed for two model bacteria: E. coli and S.
290
aureus, as detailed in the SI. Fig. 5 shows the results of antibacterial assays of the TFN
291
membrane, normalized by the number of attached live bacteria on the TFC membrane. As
292
can be seen, the presence of the MOF nanocrystals significantly reduced the number of viable
293
bacteria attached to the TFN membrane, demonstrating antimicrobial activity of the TFN
294
membrane surface. One-hour incubation tests of the TFN membranes achieved bacterial
295
inactivation rates of over 96% and 90% for E. coli and S. aureus, respectively, relative to
296
those of the TFC membranes. A statistical analysis indicated that the presented results of the
297
membranes' biocidal activity are statistically significant, with the P-value less than 0.05
298
(shown by the stars above the bars). This bactericidal activity was achieved with a very low
299
loading (0.02%) of the MOF nanocrystals. This loading level is much less than the loading
300
levels of silver compounds used in previous studies35,
301
antibacterial activity. This can be attributed to the minimal aggregation of MOF nanocrystals,
302
leading to an effective distribution of biocidal agents over the membrane surface. This
303
finding is in agreement with previous studied49, 73 that silver-based MOFs have much better
304
antibacterial activities than many commonly-used silver-based compounds at low
305
concentrations, and that they have long-term efficiency for biocidal capability. In summary,
306
the MOF nanocrystals are still active when immobilized into the membrane selective layer
307
and impart biocidal properties to the surface of TFN membranes.
72
to provide membranes with
308
To evaluate the stability of the biocidal activity of the TFN membranes, the
309
membranes were stored in a water container for two different durations: 24 days and six
310
months. The stored membranes were then evaluated for their antibacterial properties again. 11 ACS Paragon Plus Environment
Page 12 of 30
Page 13 of 30
Environmental Science & Technology
311
After 24 days of membranes being in water, there was a slight increase in the number of
312
attached live bacteria to the membranes, indicating no significant change in their bactericidal
313
activity (Fig. 5). Likewise, there was no considerable change in biocidal activity of the TFN
314
membranes after six months of being in water. These results point to another very appealing
315
feature of MOF nanocrystals; that is, imparting a stable antibacterial activity to the TFN
316
membranes for long-term applications.
317
The MOF nanocrystals activity against bacteria comes from one or more biocidal
318
agent in their structure. The silver sites in the framework can be active against bacteria.
319
Furthermore, the organic ligand used in the framework may have antimicrobial action owing
320
to its functional groups. Leaching of Ag+ from the MOF nanocrystals may be the cause of
321
bacterial cell inactivation. The released Ag+ may interact with the thiol groups of proteins and
322
disrupt integrity of bacterial membrane 74-75. Also, functional groups of organic ligand in the
323
framework can bond with cations in cell, causing modification and fragmentation of DNA 76.
324
Ultimately, these leads to cytoplasm outflow and death of the bacteria.
325
As the dynamics of Ag+ release from the MOF nanocrystals immobilized in TFN
326
membrane active layer control the duration of its biocidal activity, we examined the silver-
327
ion release from the TFN membrane in batch experiments. As Fig. 6 shows, the silver-ion
328
release from the TFN membrane decreased sharply from the initial value of about 0.07
329
µg.cm-2.day-1 during the first 2 days. The release rate then decreased very slowly afterwards.
330
This Ag+-release rate demonstrates the long-term durability of biocidal activity exhibited by
331
the TFN membranes. This implies that the MOF can work as an Ag+ reservoir immobilized in
332
the membrane active layer, providing a controlled sustained Ag+ release
333
indicate that the MOF imparts a long-lasting antibacterial activity to the membrane surface to
334
mitigate biofouling in a prolonged period of the membrane operation. This attractive
335
performance is much better than those reported in previous studies where other silver
12 ACS Paragon Plus Environment
50, 77
.
These results
Environmental Science & Technology
Page 14 of 30
336
compounds, such as silver nanoparticles, were used and the resulting membranes had
337
antibacterial activity only over a short period of time 39-40, 48.
338
Effects of MOF nanocrystals on the biofouling resistance of the TFN
339
membranes. To determine how the TFN membrane surface inhibits the biofilm formation,
340
the membranes were examined in biofouling experiments according to the protocol described
341
in ref.14,
342
biofouling experiments were performed twice independently. Fig. 7 shows the corresponding
343
results. During the experiments, a gradual decline in the water flux was observed. The decline
344
is due to the adhesion of bacteria and hence biofouling on the membrane surface. The
345
presence of E. coli in the feed solution affected the flux of the TFC membrane considerably.
346
Over the course of 24 h, the FO water flux through the TFC membrane dropped about 20-
347
24%, indicating that the membrane easily fouled under the conditions. In contrast, the TFN
348
membrane showed only a 6-10% decline in water flux, indicating much better biofouling
349
resistance. Cross-flow cleaning yielded more than 90% recovery in FO water flux for both
350
membranes (higher level of recovery for the TFN membrane) (Fig. 7c).
78
and detailed in the SI. To show that the observed trends are reproducible, the
351
To understand the role of MOF nanocrystals in biofouling mitigation, attached
352
bacteria on the biofouled membranes were further investigated. Fig. 8 shows representative
353
images of the TFN and TFC membranes using FESEM and fluorescence microscopy. As can
354
be seen, less bacteria were found on the surface of the TFN membranes than on the surface of
355
the TFC membranes (Figs. 8a and 8b). The quantitative analysis presented in Fig. 8e
356
supported this issue so that considerably fewer numbers of bacteria were attached to TFN
357
membrane surface (~ 48 %) than to the TFC membrane surface. This is in agreement with the
358
anti-adhesion properties of the TFN membrane surface against the bacteria
359
live/dead staining experiment revealed that a large portion of the bacteria on the TFC
360
membranes appeared in green (seemed alive) (Fig. 8c). In contrast, the cells on the TFN
13 ACS Paragon Plus Environment
18, 79-80
. The
Page 15 of 30
Environmental Science & Technology
361
membranes appeared in red, indicating the strong capability of these membranes to kill the
362
bacteria (Fig. 8d). This observation is in good agreement with the biocidal activity results
363
shown in Fig. 5.
364
This study showed that biocidal activity imparted by MOF nanocrystals contribute to
365
the mitigation of biofouling on TFN membranes. It demonstrated that it is possible to
366
improve both the biocidal activity and the hydrophilicity of the membrane active layer,
367
without any adverse effects on the membrane selectivity. MOFs are very attractive materials
368
for developing high-performance FO membranes. They have great potential in improving the
369
biofouling resistance of FO membranes that require both antibacterial and anti-adhesion
370
features.
371
Supporting Information
372
Additional Materials and Methods, FO performance results (Table S1), and XRD pattern of
373
the MOF nanocrystals (Fig. S1) are available free of charge via the Internet at
374
http://pubs.acs.org.
375
Acknowledgment
376
The authors would like to express their thanks to Prof. Joel B. Sheffield, Department of
377
Biology, Temple University, for permitting them to use his fluorescence microscope for this
378
work.
379 380 381
14 ACS Paragon Plus Environment
Environmental Science & Technology
382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429
REFERANCES (1) Elimelech, M.; Phillip, W. A., The future of seawater desalination: energy, technology, and the environment. science 2011, 333 (6043), 712-717. (2) Lutchmiah, K.; Verliefde, A. R. D.; Roest, K.; Rietveld, L. C.; Cornelissen, E. R., Forward osmosis for application in wastewater treatment: a review. Water Res. 2014, 58, 179-197. (3) Yin, J.; Deng, B., Polymer-matrix nanocomposite membranes for water treatment. J. Membr. Sci. 2015, 479, 256-275. (4) Shaffer, D. L.; Yip, N. Y.; Gilron, J.; Elimelech, M., Seawater desalination for agriculture by integrated forward and reverse osmosis: Improved product water quality for potentially less energy. J. Membr. Sci. 2012, 415, 1-8. (5) Chung, T.-S.; Zhang, S.; Wang, K. Y.; Su, J.; Ling, M. M., Forward osmosis processes: yesterday, today and tomorrow. Desalination 2012, 287, 78-81. (6) Cath, T. Y.; Childress, A. E.; Elimelech, M., Forward osmosis: principles, applications, and recent developments. J. Membr. Sci. 2006, 281 (1), 70-87. (7) Hoover, L. A.; Phillip, W. A.; Tiraferri, A.; Yip, N. Y.; Elimelech, M., Forward with osmosis: emerging applications for greater sustainability. Environ. Sci. Technol. 2011, 45 (23), 9824-9830. (8) Zhao, S.; Zou, L.; Tang, C. Y.; Mulcahy, D., Recent developments in forward osmosis: opportunities and challenges. J. Membr. Sci. 2012, 396, 1-21. (9) Achilli, A.; Cath, T. Y.; Marchand, E. A.; Childress, A. E., The forward osmosis membrane bioreactor: a low fouling alternative to MBR processes. Desalination 2009, 239 (1), 10-21. (10) Lee, S.; Boo, C.; Elimelech, M.; Hong, S., Comparison of fouling behavior in forward osmosis (FO) and reverse osmosis (RO). J. Membr. Sci. 2010, 365 (1), 34-39. (11) Li, Z.-Y.; Yangali-Quintanilla, V.; Valladares-Linares, R.; Li, Q.; Zhan, T.; Amy, G., Flux patterns and membrane fouling propensity during desalination of seawater by forward osmosis. Water Res. 2012, 46 (1), 195-204. (12) Mi, B.; Elimelech, M., Organic fouling of forward osmosis membranes: fouling reversibility and cleaning without chemical reagents. J. Membr. Sci. 2010, 348 (1), 337-345. (13) McGinnis, R. L.; Elimelech, M., Energy requirements of ammonia–carbon dioxide forward osmosis desalination. Desalination 2007, 207 (1), 370-382. (14) Kwan, S. E.; Bar-Zeev, E.; Elimelech, M., Biofouling in forward osmosis and reverse osmosis: Measurements and mechanisms. J. Membr. Sci. 2015, 493, 703-708. (15) Kumar, M.; Adham, S. S.; Pearce, W. R., Investigation of seawater reverse osmosis fouling and its relationship to pretreatment type. Environ. Sci. Technol. 2006, 40 (6), 20372044. (16) Herzberg, M.; Elimelech, M., Biofouling of reverse osmosis membranes: role of biofilmenhanced osmotic pressure. J. Membr. Sci. 2007, 295 (1), 11-20. (17) Arkhangelsky, E.; Wicaksana, F.; Tang, C.; Al-Rabiah, A. A.; Al-Zahrani, S. M.; Wang, R., Combined organic–inorganic fouling of forward osmosis hollow fiber membranes. Water Res. 2012, 46 (19), 6329-6338. (18) Kochkodan, V.; Hilal, N., A comprehensive review on surface modified polymer membranes for biofouling mitigation. Desalination 2015, 356, 187-207. (19) Yoon, H.; Baek, Y.; Yu, J.; Yoon, J., Biofouling occurrence process and its control in the forward osmosis. Desalination 2013, 325, 30-36. (20) O'Toole, G.; Kaplan, H. B.; Kolter, R., Biofilm formation as microbial development. Annu. Rev. Microbiol. 2000, 54 (1), 49-79.
15 ACS Paragon Plus Environment
Page 16 of 30
Page 17 of 30
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
Environmental Science & Technology
(21) Habimana, O.; Semião, A. J. C.; Casey, E., The role of cell-surface interactions in bacterial initial adhesion and consequent biofilm formation on nanofiltration/reverse osmosis membranes. J. Membr. Sci. 2014, 454, 82-96. (22) Hegab, H. M.; ElMekawy, A.; Barclay, T. G.; Michelmore, A.; Zou, L.; Saint, C. P.; Ginic-Markovic, M., Fine-Tuning the Surface of Forward Osmosis Membranes via Grafting Graphene Oxide: Performance Patterns and Biofouling Propensity. ACS Appl. Mater. Interfaces 2015, 7 (32), 18004-18016. (23) Flemming, H.-C.; Wingender, J., The biofilm matrix. Nat. Rev. Microbiol. 2010, 8 (9), 623-633. (24) Al-Juboori, R. A.; Yusaf, T., Biofouling in RO system: mechanisms, monitoring and controlling. Desalination 2012, 302, 1-23. (25) Yip, N. Y.; Tiraferri, A.; Phillip, W. A.; Schiffman, J. D.; Hoover, L. A.; Kim, Y. C.; Elimelech, M., Thin-film composite pressure retarded osmosis membranes for sustainable power generation from salinity gradients. Environ. Sci. Technol. 2011, 45 (10), 4360-4369. (26) Wei, J.; Qiu, C.; Wang, Y.-N.; Wang, R.; Tang, C. Y., Comparison of NF-like and ROlike thin film composite osmotically-driven membranes—implications for membrane selection and process optimization. J. Membr. Sci. 2013, 427, 460-471. (27) Bui, N.-N.; McCutcheon, J. R., Nanofiber supported thin-film composite membrane for pressure-retarded osmosis. Environ. Sci. Technol. 2014, 48 (7), 4129-4136. (28) Tiraferri, A.; Kang, Y.; Giannelis, E. P.; Elimelech, M., Highly hydrophilic thin-film composite forward osmosis membranes functionalized with surface-tailored nanoparticles. ACS Appl. Mater. Interfaces 2012, 4 (9), 5044-5053. (29) Sukitpaneenit, P.; Chung, T.-S., High performance thin-film composite forward osmosis hollow fiber membranes with macrovoid-free and highly porous structure for sustainable water production. Environ. Sci. Technol. 2012, 46 (13), 7358-7365. (30) Glater, J.; Hong, S.-k.; Elimelech, M., The search for a chlorine-resistant reverse osmosis membrane. Desalination 1994, 95 (3), 325-345. (31) Shemer, H.; Semiat, R., Impact of halogen based disinfectants in seawater on polyamide RO membranes. Desalination 2011, 273 (1), 179-183. (32) Zhang, M.; Zhang, K.; De Gusseme, B.; Verstraete, W.; Field, R., The antibacterial and anti-biofouling performance of biogenic silver nanoparticles by Lactobacillus fermentum. Biofouling 2014, 30 (3), 347-357. (33) 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. (34) Park, S.-H.; Ko, Y.-S.; Park, S.-J.; Lee, J. S.; Cho, J.; Baek, K.-Y.; Kim, I. T.; Woo, K.; Lee, J.-H., Immobilization of silver nanoparticle-decorated silica particles on polyamide thin film composite membranes for antibacterial properties. J. Membr. Sci. 2016, 499, 80-91. (35) Kim, E.-S.; Hwang, G.; El-Din, M. G.; Liu, Y., Development of nanosilver and multiwalled carbon nanotubes thin-film nanocomposite membrane for enhanced water treatment. J. Membr. Sci. 2012, 394, 37-48. (36) Ben-Sasson, M.; Zodrow, K. R.; Genggeng, Q.; Kang, Y.; Giannelis, E. P.; Elimelech, M., Surface functionalization of thin-film composite membranes with copper nanoparticles for antimicrobial surface properties. Environ. Sci. Technol. 2013, 48 (1), 384-393. (37) Leong, S.; Razmjou, A.; Wang, K.; Hapgood, K.; Zhang, X.; Wang, H., TiO 2 based photocatalytic membranes: a review. J. Membr. Sci. 2014, 472, 167-184. (38) Li, Q.; Chen, S. L.; Jiang, W. C., Durability of nano ZnO antibacterial cotton fabric to sweat. J. Appl. Polym. Sci. 2007, 103 (1), 412-416.
16 ACS Paragon Plus Environment
Environmental Science & Technology
478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525
(39) Ben-Sasson, M.; Lu, X.; Bar-Zeev, E.; Zodrow, K. R.; Nejati, S.; Qi, G.; Giannelis, E. P.; Elimelech, M., In situ formation of silver nanoparticles on thin-film composite reverse osmosis membranes for biofouling mitigation. Water Res. 2014, 62, 260-270. (40) Yin, J.; Yang, Y.; Hu, Z.; Deng, B., Attachment of silver nanoparticles (AgNPs) onto thin-film composite (TFC) membranes through covalent bonding to reduce membrane biofouling. J. Membr. Sci. 2013, 441, 73-82. (41) Rai, M.; Yadav, A.; Gade, A., Silver nanoparticles as a new generation of antimicrobials. Biotechnol. Adv. 2009, 27 (1), 76-83. (42) Miller, D. J.; Araújo, P. A.; Correia, P. B.; Ramsey, M. M.; Kruithof, J. C.; van Loosdrecht, M. C. M.; Freeman, B. D.; Paul, D. R.; Whiteley, M.; Vrouwenvelder, J. S., Short-term adhesion and long-term biofouling testing of polydopamine and poly (ethylene glycol) surface modifications of membranes and feed spacers for biofouling control. Water Res. 2012, 46 (12), 3737-3753. (43) Yu, D. G.; Teng, M. Y.; Chou, W. L.; Yang, M. C., Characterization and inhibitory effect of antibacterial PAN-based hollow fiber loaded with silver nitrate. J. Membr. Sci. 2003, 225 (1), 115-123. (44) Ong, C. S.; Goh, P. S.; Lau, W. J.; Misdan, N.; Ismail, A. F., Nanomaterials for biofouling and scaling mitigation of thin film composite membrane: A review. Desalination 2016, 393, 2-15. (45) Daer, S.; Kharraz, J.; Giwa, A.; Hasan, S. W., Recent applications of nanomaterials in water desalination: a critical review and future opportunities. Desalination 2015, 367, 37-48. (46) Zhang, S.; Qiu, G.; Ting, Y. P.; Chung, T.-S., Silver–PEGylated dendrimer nanocomposite coating for anti-fouling thin film composite membranes for water treatment. Colloids Surf., A 2013, 436, 207-214. (47) Rahaman, M. S.; Thérien-Aubin, H.; Ben-Sasson, M.; Ober, C. K.; Nielsen, M.; Elimelech, M., Control of biofouling on reverse osmosis polyamide membranes modified with biocidal nanoparticles and antifouling polymer brushes. J. Mater. Chem. B 2014, 2 (12), 1724-1732. (48) Soroush, A.; Ma, W.; Silvino, Y.; Rahaman, M. S., Surface modification of thin film composite forward osmosis membrane by silver-decorated graphene-oxide nanosheets. Environmental Science: Nano 2015, 2 (4), 395-405. (49) Lu, X.; Ye, J.; Zhang, D.; Xie, R.; Bogale, R. F.; Sun, Y.; Zhao, L.; Zhao, Q.; Ning, G., Silver carboxylate metal–organic frameworks with highly antibacterial activity and biocompatibility. J. Inorg. Biochem. 2014, 138, 114-121. (50) Wyszogrodzka, G.; Marszałek, B.; Gil, B.; Dorożyński, P., Metal-organic frameworks: mechanisms of antibacterial action and potential applications. Drug Discov. Today 2016, 21 (6), 1009-1018. (51) Rodríguez, H. S.; Hinestroza, J. P.; Ochoa‐Puentes, C.; Sierra, C. A.; Soto, C. Y., Antibacterial activity against Escherichia coli of Cu‐BTC (MOF‐199) metal‐organic framework immobilized onto cellulosic fibers. J. Appl. Polym. Sci. 2014, 131 (19), 4081540819. (52) Zhuang, W.; Yuan, D.; Li, J. R.; Luo, Z.; Zhou, H. C.; Bashir, S.; Liu, J., Highly Potent Bactericidal Activity of Porous Metal‐Organic Frameworks. Adv. Healthc. Mater. 2012, 1 (2), 225-238. (53) Cavicchioli, M.; Massabni, A. C.; Heinrich, T. A.; Costa-Neto, C. M.; Abrão, E. P.; Fonseca, B. A. L.; Castellano, E. E.; Corbi, P. P.; Lustri, W. R.; Leite, C. Q. F., Pt (II) and Ag (I) complexes with acesulfame: Crystal structure and a study of their antitumoral, antimicrobial and antiviral activities. J. Inorg. Biochem. 2010, 104 (5), 533-540.
17 ACS Paragon Plus Environment
Page 18 of 30
Page 19 of 30
526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575
Environmental Science & Technology
(54) Wang, K.; Ma, X.; Shao, D.; Geng, Z.; Zhang, Z.; Wang, Z., Coordination-induced assembly of coordination polymer submicrospheres: promising antibacterial and in vitro anticancer activities. Cryst. Growth Des. 2012, 12 (7), 3786-3791. (55) Ng, N. S.; Leverett, P.; Hibbs, D. E.; Yang, Q.; Bulanadi, J. C.; Wu, M. J.; AldrichWright, J. R., The antimicrobial properties of some copper (II) and platinum (II) 1, 10phenanthroline complexes. Dalton Trans. 2013, 42 (9), 3196-3209. (56) Horcajada, P.; Chalati, T.; Serre, C.; Gillet, B.; Sebrie, C.; Baati, T.; Eubank, J. F.; Heurtaux, D.; Clayette, P.; Kreuz, C., Porous metal-organic-framework nanoscale carriers as a potential platform for drug delivery and imaging. Nat. Mater. 2010, 9 (2), 172-178. (57) Israr, F.; Chun, D.; Kim, Y.; Kim, D. K., High yield synthesis of Ni-BTC metal–organic framework with ultrasonic irradiation: Role of polar aprotic DMF solvent. Ultrason. Sonochem. 2016, 31, 93-101. (58) Autie-Castro, G.; Autie, M. A.; Rodríguez-Castellón, E.; Aguirre, C.; Reguera, E., CuBTC and Fe-BTC metal-organic frameworks: Role of the materials structural features on their performance for volatile hydrocarbons separation. Colloids Surf., A 2015, 481, 351-357. (59) Akhavan, O., Lasting antibacterial activities of Ag–TiO 2/Ag/a-TiO 2 nanocomposite thin film photocatalysts under solar light irradiation. J. Colloid Interface Sci. 2009, 336 (1), 117-124. (60) Echlin, P.; Fiori, C. E.; Goldstein, J.; Joy, D. C.; Newbury, D. E., Advanced scanning electron microscopy and X-ray microanalysis. Springer Science & Business Media: 2013. (61) Goldstein, J.; Newbury, D. E.; Echlin, P.; Joy, D. C.; Romig Jr, A. D.; Lyman, C. E.; Fiori, C.; Lifshin, E., Scanning electron microscopy and X-ray microanalysis. Springer Science & Business Media: 2012. (62) Tang, C. Y.; Kwon, Y.-N.; Leckie, J. O., Probing the nano-and micro-scales of reverse osmosis membranes—a comprehensive characterization of physiochemical properties of uncoated and coated membranes by XPS, TEM, ATR-FTIR, and streaming potential measurements. J. Membr. Sci. 2007, 287 (1), 146-156. (63) Tang, C. Y.; Kwon, Y.-N.; Leckie, J. O., Effect of membrane chemistry and coating layer on physiochemical properties of thin film composite polyamide RO and NF membranes: I. FTIR and XPS characterization of polyamide and coating layer chemistry. Desalination 2009, 242 (1), 149-167. (64) Boussu, K.; De Baerdemaeker, J.; Dauwe, C.; Weber, M.; Lynn, K. G.; Depla, D.; Aldea, S.; Vankelecom, I. F. J.; Vandecasteele, C.; Van der Bruggen, B., Physico‐Chemical Characterization of Nanofiltration Membranes. ChemPhysChem 2007, 8 (3), 370-379. (65) Benavente, J.; Vázquez, M. I., Effect of age and chemical treatments on characteristic parameters for active and porous sublayers of polymeric composite membranes. J. Colloid Interface Sci. 2004, 273 (2), 547-555. (66) Wagner, C. D.; Muilenberg, G. E., Handbook of X-ray photoelectron spectroscopy. Perkin-Elmer: 1979. (67) Tiraferri, A.; Yip, N. Y.; Straub, A. P.; Castrillon, S. R.-V.; Elimelech, M., A method for the simultaneous determination of transport and structural parameters of forward osmosis membranes. J. Membr. Sci. 2013, 444, 523-538. (68) Wei, J.; Qiu, C.; Tang, C. Y.; Wang, R.; Fane, A. G., Synthesis and characterization of flat-sheet thin film composite forward osmosis membranes. J. Membr. Sci. 2011, 372 (1), 292-302. (69) Phillip, W. A.; Yong, J. S.; Elimelech, M., Reverse draw solute permeation in forward osmosis: modeling and experiments. Environ. Sci. Technol. 2010, 44 (13), 5170-5176. (70) Zirehpour, A.; Rahimpour, A.; Seyedpour, F.; Jahanshahi, M., Developing new CTA/CA-based membrane containing hydrophilic nanoparticles to enhance the forward osmosis desalination. Desalination 2015, 371, 46-57. 18 ACS Paragon Plus Environment
Environmental Science & Technology
576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604
(71) Moaddeb, M.; Koros, W. J., Gas transport properties of thin polymeric membranes in the presence of silicon dioxide particles. J. Membr. Sci. 1997, 125 (1), 143-163. (72) Lee, S. Y.; Kim, H. J.; Patel, R.; Im, S. J.; Kim, J. H.; Min, B. R., Silver nanoparticles immobilized on thin film composite polyamide membrane: characterization, nanofiltration, antifouling properties. Polym. Adv. Technol. 2007, 18 (7), 562-568. (73) Chamakura, K.; Perez-Ballestero, R.; Luo, Z.; Bashir, S.; Liu, J., Comparison of bactericidal activities of silver nanoparticles with common chemical disinfectants. Colloids Surf., B 2011, 84 (1), 88-96. (74) Matsumura, Y.; Yoshikata, K.; Kunisaki, S.-i.; Tsuchido, T., Mode of bactericidal action of silver zeolite and its comparison with that of silver nitrate. Appl. Environ. Microbiol. 2003, 69 (7), 4278-4281. (75) Feng, Q. L.; Wu, J.; Chen, G. Q.; Cui, F. Z.; Kim, T. N.; Kim, J. O., A mechanistic study of the antibacterial effect of silver ions on Escherichia coli and Staphylococcus aureus. Journal of biomedical materials research 2000, 52 (4), 662-668. (76) Pulido, M. D.; Parrish, A. R., Metal-induced apoptosis: mechanisms. Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis 2003, 533 (1), 227-241. (77) Berchel, M.; Le Gall, T.; Denis, C.; Le Hir, S.; Quentel, F.; Elléouet, C.; Montier, T.; Rueff, J.-M.; Salaün, J.-Y.; Haelters, J.-P., A silver-based metal–organic framework material as a ‘reservoir’of bactericidal metal ions. New J. Chem. 2011, 35 (5), 1000-1003. (78) Perreault, F.; Jaramillo, H.; Xie, M.; Ude, M.; Elimelech, M., Biofouling Mitigation in Forward Osmosis using Graphene Oxide Functionalized Thin-Film Composite Membranes. Environ. Sci. Technol. 2016, 50 (11), 5840-5848. (79) Yang, H.-L.; Chun-Te Lin, J.; Huang, C., Application of nanosilver surface modification to RO membrane and spacer for mitigating biofouling in seawater desalination. Water Res. 2009, 43 (15), 3777-3786. (80) Zhu, X.; Bai, R.; Wee, K.-H.; Liu, C.; Tang, S.-L., Membrane surfaces immobilized with ionic or reduced silver and their anti-biofouling performances. J. Membr. Sci. 2010, 363 (1), 278-286.
605 606 607 608 609 610 611 612 613 614
19 ACS Paragon Plus Environment
Page 20 of 30
Page 21 of 30
Environmental Science & Technology
615 616 617 618 619
Table 1. Elemental compositions, O/N ratio, and the degree of cross-linking of the polyamide selective layer. O/N Ratio
Atomic concentration (%)
Cross-linking degreec (%)
Membrane
620 621 622 623
a
b
C (1s)
O (1s)
N (1s)
Ag (3d)
X
Y
TFC
74.18
13.02
12.81
0
1.021
1.021
97
TFN
75.44
12.55
11.89
0.12
1.054
1.042
93
a
The ratio was calculated directly from atomic concentrations determined using XPS results. The ratio was estimated after eliminating the oxygen content added by the organic block of the MOF. c The degree was calculated from the Y O/N ratios.
b
624 625 626 627
Table 2. Transport parameters of the FO membranes (calculated using the protocol described in Ref. 67). They
628
were estimated from the flux means and standard deviations reported in Table S1. The solute rejection results (R
629
values) are from experiments with a 2000 ppm NaCl feed and at 2.5 bar in the RO mode. A = water
630
permeability coefficient, B = solute permeability coefficient, = water flux coefficient of determination,
631
= solute flux coefficient of determination, and R = solute rejection.
A
B
B/A
(L/(m2.h.bar))
(L/(m2.h))
(1/bar)
TFC
2.10±0.14
0.27±0.02
TFN
3.25±0.18
0.36±0.02
R (%)
0.129±0.018
96.1
0.975
0.992
0.111±0.012
96.8
0.988
0.991
Membrane
632 633 634 635 20 ACS Paragon Plus Environment
Environmental Science & Technology
636 637 638 639 640
641 642
Fig. 1. Characterization of MOF nanocrystals. (a) TEM micrograph, (b) Element concentration determined via
643
EDX analysis, (c) IR spectrum, identifying the functional groups of MOF, (d) DLS measurement, representing
644
size distribution of the nanocrystals in n-hexane organic solution.
645 646
21 ACS Paragon Plus Environment
Page 22 of 30
Page 23 of 30
Environmental Science & Technology
647 648
Fig. 2. FE-SEM images of the membranes using different imaging detectors. (a) TFC membrane, (b) TFN
649
membrane, (c) A higher-magnification image of the TFN membrane surface. The left-hand images were taken
650
using a secondary detector, while the right-hand image were taken using a backscattered imaging detector. The
651
backscattered image of TFN membrane shows numerous bright spots on the surface, attributed to the silver
652
element as a MOF nanocrystal characteristic. The orange arrows in the right-side image show the positions of
653
some of the bright spots in the backscattered image. EDX results of three different spectra, revealing the
654
presence of silver as the characteristic element of the MOF nanocrystals used.
22 ACS Paragon Plus Environment
Environmental Science & Technology
655 656
Fig. 3. Thin film polyamide layer characterization of TFC and TFN membranes, (a) Cross-section FE-SEM
657
image of a TFC membrane, (b) Cross-section FE-SEM image of a TFN membrane, (c) AFM image of a TFC
658
membrane, (d) AFM image of a TFN membrane, (e) Surface roughness parameters of TFC and TFN membranes
659
[the mean roughness (Ra), the root mean square of the Z data (Rq), and the mean difference between the five
660
highest peaks and lowest valleys (Rm)], (f) water contact angles of TFC and TFN membrane surfaces (each bar
661
represents the standard deviation of the trials. Asterisks above the bars represent the statistical significance (P-
662
value < 0.05), determined by a student’s t-test).
663 23 ACS Paragon Plus Environment
Page 24 of 30
Page 25 of 30
Environmental Science & Technology
664 665
666 667
Fig. 4. XPS analysis of the elemental composition and chemical bonding. (a) Survey spectra of TFC and TFN
668
membranes, (b) high-resolution XPS spectra of carbon (1s) for a TFC membrane, and (c) high-resolution XPS
669
spectra of carbon (1s) for a TFN membrane.
670 671 24 ACS Paragon Plus Environment
Environmental Science & Technology
672 673
674 675
Fig. 5. Biocidal activity of TFC and TFN membranes, the normalized number of attached live bacteria on the
676
TFC and TFN membranes for E. coli and S. aureus bacteria. The values were normalized by the number of
677
attached live bacteria on the TFC. The orange and violet bars illustrate the antibacterial activity of the TFN
678
membranes after 24 days and 6 months of storing the TFN membranes in water, respectively. Each bar indicates
679
the standard deviation of three independent test, each with a fresh membrane. Asterisks above the bars represent
680
the statistical significance (P-value < 0.05), determined by a student’s t-test.
681 682 683 684 685 686 687 688 25 ACS Paragon Plus Environment
Page 26 of 30
Page 27 of 30
Environmental Science & Technology
689 690
691 692
Fig. 6. Release rate of Ag+ from the TFN membrane.
693 694 695 696 697 698 699 700 701 702
26 ACS Paragon Plus Environment
Environmental Science & Technology
703 704
Fig. 7. Normalized water fluxes of TFC and TFN membranes vs. time in biofouling experiments using E. coli
705
(experimental conditions: initial water flux = 27 L/m2h, velocity = 8.5 cm/s, T = 25 °C). (a) First run, (b)
706
Repeated run (Each one represents the biofouling experiment obtained from independent runs with a fresh
707
membrane), and (c) FO water flux recovery ratio after cross-flow cleaning.
27 ACS Paragon Plus Environment
Page 28 of 30
Page 29 of 30
Environmental Science & Technology
708
709 710
Fig. 8. Bacterial inactivation properties of the membrane surface after biofouling experiment with E. coli. FE-
711
SEM image of (a) TFC membrane, and (b) TFN membrane. Fluorescence microscopy image of (c) TFC
712
membrane surface, and (d) TFN membrane surface, (e) quantitative analysis of the number of attached bacteria
713
to the membranes surface, determined via observing different areas of the membranes. The images c and d were
714
taken using the live/dead staining experiment.
28 ACS Paragon Plus Environment
Environmental Science & Technology
ACS Paragon Plus Environment
Page 30 of 30