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Facile synthesis of highly dispersed Ag doped Graphene Oxide/Titanate nanotubes as visible light photocatalytic membrane for water treatment Gonggang Liu, Kai Han, Yonghua Zhou, Hongqi Ye, Xiang Zhang, Jinbo Hu, and Xianjun Li ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.8b00029 • Publication Date (Web): 29 Mar 2018 Downloaded from http://pubs.acs.org on March 30, 2018

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ACS Sustainable Chemistry & Engineering

1

Facile synthesis of highly dispersed Ag doped Graphene

2

Oxide/Titanate nanotubes as visible light photocatalytic

3

membrane for water treatment

4

Gonggang Liua#, Kai Hanb#, Yonghua Zhoub, Hongqi Yeb, Xiang Zhanga, Jinbo Hua,c*, Xianjun Lia,c*

5

a

6

. College of Materials Science and Engineering, Central South University of Forestry and Technology, Changsha 410004, China

b

7

. College of Chemistry and Chemical Engineering, Central South University, Changsha 410083, China

c

. Hunan Provincial Collaborative Innovation Center for High-efficiency Utilization of Wood and Bamboo Resources, Central South

8 9

University of Forestry and Technology, Changsha 410004, China

#

Thesis two authors contributed equally.

10

*Corresponding authors. Email: [email protected], [email protected].

11

ABSTRACT

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Graphene oxide (GO) membranes have attracted extensive interest due to their

13

ultrathin, high-flux, pore size tunable, superior flexibility and energy-efficient

14

properties for transporting ions and molecules through the unique 2D channels.

15

Nevertheless, membrane fouling leading to membrane blocking and poor water flux

16

of GO membranes during long-term use resulting from the membrane fouling is one

17

of the major obstacles for water treatment or desalination application. In this work, Ag

18

doped GO/Titanate nanotubes (Ag/GO/TNTs) membranes with enhanced visible light

19

degradation ability were fabricated by a single-step procedure to resolve the fouling

20

problem via integration of photocatalysis with membrane filtration. The results show

21

that the Ag nanoparticles could be highly dispersed on the surface of GO and TNTs.

22

And the as-prepared Ag/GO/TNTs membranes exhibited reasonable ability on

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photocatalytic degradation of Methylene Blue under visible light. 90% of MB could

2

be effectively degraded after 120 min irradiation with 8 mg of photocatalyst. More

3

importantly, the membrane fouling could be effectively alleviated with visible light

4

irradiation. In coupling photocatalysis and membrane separation process, the flux of

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Ag/GO/TNTs membranes with GO and TNT ratio at 1: 3 and Ag content of 6% could

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keep at 34.7 L/m2h which doubles that of membrane filtration without visible light

7

irradiation. In addition, Ag/GO/TNTs membranes possess high acid-alkali resistance

8

stability and good compressive strength. These results have provided a simple

9

preparation strategy to obtain highly dispersed nanoparticles and valuable insight of

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endowing membranes with visible-light degradation ability for solving GO based

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membrane fouling.

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Keywords: Graphene oxide membranes; membrane fouling; visible light;

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photocatalytic degradation; Ag; Titanate nanotubes

14 15

INTRODUCTION

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Due to a rising water pollution problem, affordable and safe drinking water is an

17

on-going global challenge. Especially, contamination of dyes and other organism is

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one of the main problems in water treatment [1-3]. Membrane separation technology

19

has been a promising approach due to high efficiency, low energy consuming and easy

20

operation [4, 5]. Recently, graphene oxide (GO) and GO based membranes as a

21

perfect molecular level separating unit have exhibited extraordinary separation

22

performance in respect of water flux and pollutant molecular/ions rejection [6-14].


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And it has been an emerging field of research which has drawn extensive attentions

2

[15-18]. However, when treating organic pollutants, GO based membranes is easy to

3

suffer from membrane fouling resulting in flux decline due to strong adsorption

4

ability for organic dye molecules [19-21], and it is intractable to remove attached

5

pollutants which restricts their large scale application. Aiming at decreasing

6

membrane pollution, endowing GO membranes with UV photocatalysis function have

7

been proposed in our previous work [19, 21]. But to the best of our knowledge, few

8

reports were found to synthesize and study GO based membrane with visible light

9

photocatalytic ability for water decontamination and resolving membrane fouling

10

under visible light irradiation.

11

On the other hand, the fabrication of GO-based hybrid photocatalysts with a

12

remarkable photocatalytic performance is currently a hot topic attracting global

13

attentions [22-25]. GO could effectively reduce the electron-hole recombination rate

14

and red-shift the response edge of TiO2 from UV to visible region [26]. And compared

15

with

16

photocatalytic activity as nanowires structure have larger specific surface and more

17

contact area between TiO2 and graphene [27, 28]. Besides, nanoparticles of noble

18

metals (i.e. Ag, Au, Pt) strongly absorb visible light due to their surface plasmon

19

resonance (SPR) which could further significantly enhance visible light photocatalytic

20

performance of GO-based hybrid photocatalysts [29, 30]. Sun [31] synthesized

21

multifunctional nanocomposites (Ag/GO/TiO2) integrating 2D GO sheets, 1D TiO2

22

nanorods and 0D Ag nanoparticles via a facile two-phase method. The Ag/GO/TiO2

GO/TiO2

nanoparticle

composites,

GO/TiO2


nanowires

show

higher


1

nanocomposites demonstrate remarkably enhanced photocatalytic activities in

2

degrading organic dye (AO7) and phenol under solar irradiation compared with

3

GO/TiO2 and Ag/GO.

4

In the present work, single-step solvothermal synthesis of Ag/GO/TNTs was used. In

5

a single-step synthetic procedure, the reduction of AgNO3 and graphene oxide and Ag

6

loading on GO/TNTs were spontaneously performed by TEOA which act as reductant.

7

Highly dispersed Ag nanoparticles on GO and TNTs were obtained. Meanwhile, the

8

Ag/GO/TNTs membranes were fabricated by vacuum filtration of the Ag/GO/TNTs

9

suspension, which could be directly used for water filtration treatment. In addition,

10

crossflow filtration which is more approximated to real industrial process was applied

11

to evaluate the separation performance. The results show that the as-prepared

12

Ag/GO/TNTs membranes exhibited reasonable photocatalytic degradation of

13

methylene blue (MB) dyes under visible light, which is superior to GO/TNTs and

14

Ag/GO/P25 membranes. Moreover, the membrane fouling of Ag/GO/TNTs

15

membranes could be effectively alleviated via a synergistic visible-light illumination

16

compared with single membrane separation process. Besides, the Ag/GO/TNTs

17

membranes possess high acid-alkali resistance stability and good compressive

18

strength due to carbon-based material and support of embedded TNTs between GO

19

layers respectively.

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EXPERIMENTAL SECTION

21

Chemicals and materials. GO was prepared by the modified Hummers method, as

22

shown in our previous work [32]. Titanate nanotubes (average diameters size of 10


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1

nm) were purchased from Klamar Chemical Reagent Co. Ltd. (Shanghai, China) and

2

used as received.

3

Synthesis of Ag doped GO/TNTs composites. Ag doped GO/TNTs composites were

4

obtained via a simple solvothermal process. Typically, 0.18 g of TNTs with 40 mL GO

5

dispersion (1.5 mg/mL) was under ultrasonic dispersion for 2 h, and the mixture was

6

fully dispersed. Subsequently, 20 mL AgNO3 (1.2 mg/mL) were slowly added into the

7

uniform suspension following with ultrasonic treatment for 1 h. Next, 10 mL of

8

triethanolamine (TEOA) was dripped slowly into the mixture and stirred at a

9

temperature of 80℃ for 3h. After several cycles of centrifugation and washing, Ag

10

doped GO/TNTs composites was obtained. And it was finally diluted to a 0.15% w/w

11

(1.5 mg/mL) aqueous suspension for storage and use, denoted Ag/GO/TNTs. The

12

preparation of Ag/GO, GO/TNTs and Ag/GO/P25 composites adopted similar method.

13

Fabrication of Ag/GO/TNTs composite membranes. Ag/GO/TNTs composite

14

membranes were fabricated by vacuum filtration of the as-prepared Ag/GO/TNTs

15

suspension through a porous cellulose filter membrane (200 mm in diameter, 0.45 µm

16

pore size). Typically, about 8.3 mL Ag/GO/TNTs composites were dispersed in 50 mL

17

distilled water under ultrasonic treatment for 10min. Then Ag/GO/TNTs membranes

18

were prepared by vacuum filtration of the aforesaid dispersion through a porous

19

cellulose filter membrane (200 mm in diameter, 0.45 µm pore size), and it was

20

stabilized for 30 min under a pressure of 0.3 MPa by nitrogen filling. The preparation

21

of other GO composite membranes adopted similar method.

22

Test of membrane flux, rejection and photocatalytic properties. Water flux and



1

rejection performance of Ag/GO/TNTs composite membranes were investigated using

2

a flat sheet crossflow membrane filtration system as shown in the Fig. S1 similar with

3

our previous [21]. It consists of a feed tank, peristaltic pump, flat sheet filter and a

4

xenon lamp (with a UV-cutoff filter, λ>400 nm) just above the filter. When studying

5

membrane separation performance separately, the xenon lamp was turned off. And

6

photocatalysis-membrane filtration integrated process was investigated keeping the

7

xenon lamp on. Methylene Blue (MB) solution (10 mg/L) was used to simulated

8

dye-containing wastewater, and the dye concentration of the feed was determined by a

9

UV-vis spectrometer (752N) at a wavelength of 662 nm. Permeate flux was calculated

10

on the basis of permeate volume divided by effective surface area and filtration time,

11

unit is L/(m2h).

12

When the separate photodegradation activity of as-prepared membranes was studied,

13

the membranes were stripped from porous cellulose filter membranes. The

14

membranes (8 mg) were put in 100 mL MB solution (10 mg/L), and before UV-light

15

irradiation, the suspensions were kept in the dark for 30min to establish an

16

adsorption-desorption equilibrium. The 752N UV-vis spectrometer was used to

17

analyze the sampled suspension. The changes in maximum absorption versus

18

irradiation time (C/C0 versus t) were obtained which reflected the decrease in the MB

19

concentration.

20

Characterization. X-ray diffraction (XRD) was analyzed using a Japan Rigaku

21

D/MAX-2500 instrument with a Cu Ka radiation and a scanning rate of 5℃/min.

22

Morphology of the membranes was observed by a scanning electronic microscope


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1

(Nova, Nano SEM230, USA) and Transmission electron microscopy (JEM-2100F).

2

The light absorption abilities of the as-prepared membranes were tested using UV-Vis

3

spectrometer (UV-2550, Shimadzu, Japan). The pore structure and specific surface

4

area were measured at 77 K with a Quantachrome NOVA 2200e instrument

5

(America).

6

RESULTS AND DISCUSSION

7

Morphologies of the as-prepared membranes were characterized by SEM as shown in

8

Fig. 1. As shown in Fig. 1a, GO membranes have a typical corrugated surface

9

structure which offers filtering channels for molecule or ions [19]. Compared with the

10

surface of pure GO and Ag/GO membranes (Fig. 1b), the surface of Ag/GO/TNTs

11

membranes (Fig. 1c) are more rough and have much more corrugations. These

12

corrugations could provide more transportation corridors for small molecules. As

13

shown in Fig. 1d, the structure of TNTs and lots of highly dispersed nanoparticles are

14

observed on the surface of GO sheets. The cross section SEM images of Ag/GO/TNTs

15

membranes (12.5 mg) are shown in Fig. 1e and f. It shows a typical thickness of about

16

10 µm. Moreover, TNTs are not well dispersed on the surface of GO. Instead, they

17

aggregates into porous particles and are clearly encapsulated by GO sheets forming

18

layer structure of Ag/GO/TNTs membranes. The pores from porous particles are in

19

favour of molecular sieving. The clearer SEM image of porous particles in the

20

membrane is shown in Fig. S2. Meanwhile, in order to further study the Ag/GO/TNTs

21

membrane structure, the nitrogen adsorption-desorption isotherms and the pore size

22

distribution (calculated by BJH model) was provided, and the results are as shown in



1

Fig S3. The isotherm of Ag/GO/TNTs membrane is a typical IV-type curve with a

2

clear H3-type hysteretic loop, which was characteristic of mesoporous materials

3

suggesting that slit-shaped pores in agreement with graphene layers structure and

4

non-rigid aggregates of one-dimensional TNTs [33]. The BET specific surface area is

5

106.35 m2/g, and pore volume was 0.49 cm3/g. The pore size distribution was

6

centered at 4-15 nm.

7

In order to study the observed dispersed nanoparticles, the morphologies of GO/TNTs

8

and Ag/GO/TNTs membranes were further characterized by TEM. As shown in Fig.

9

2a and b, TNTs are chaotically stacked on GO sheets in both the GO/TNTs and

10

Ag/GO/TNTs membranes. For Ag/GO/TNTs membranes (as shown in Fig. 2b, c, d),

11

Ag nanoparticles (with a uniform size of about 3 nm) are highly dispersed on the

12

surface of both GO and TNTs.


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1 2

Fig. 1 SEM images of (a) pure GO, (b) Ag/GO and (c~f) Ag/GO/TNTs membranes

3



1

Fig. 2 TEM images of (a) GO/TNTs and (b, c, d) Ag/GO/TNTs membranes

2 3

The XRD patterns of TNTs, Ag/GO and Ag/GO/TNTs composite membranes with

4

different mass ratio of GO and TNTs (1:0.5, 1:1, 1:2, 1:3 and 1:4) were shown in Fig.

5

3. For TNTs, the characteristic peaks of H2Ti2O5·H2O (47-0124 JCPDS file) are

6

observed at 9.78°, 24.06°, 27.82° and 48.02°, respectively. For the Ag/GO composite

7

membranes, there are strong characteristic peaks of metallic Ag at 38.11°, 44.30°,

8

32.23°, 38.70° and 40.78°. However, there are no observable peaks of graphene oxide,

9

which is probably due to the partial reduction of GO by TEOA [34]. As for

10

Ag/GO/TNTs composite membranes, the characteristic peaks of both metallic Ag and

11

H2Ti2O5·H2O can be observed. This demonstrates the highly dispersed nanoparticles

12

on GO and TNTs are metallic Ag. Moreover, with the increased content of TNTs, the

13

peak intensity of TNTs becomes stronger, while the peak intensity of Ag is weakened.

14

Therefore, combined with the results of SEM and TEM, highly dispersed Ag

15

nanoparticles could be obtained by a simple procedure which Ag+ first was adsorbed

16

on the active sites of GO/TNTs and then grew up in situ.


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1 2

Fig.3 XRD patterns of TNTs, Ag/GO and Ag/GO/TNTs composite membranes with different mass

3

ratio of GO and TNTs (1:0.5, 1:1, 1:2, 1:3 and 1:4)

4 5

The optical absorbance spectra obtained by the diffuse reflections of TNTs, GO/TNTs

6

and Ag/GO/TNTs are shown in Fig. 4. The absorption edge and bandgap of TNTs are

7

375 nm and 3.1 eV, which are close to TiO2 [31]. However, an obvious red shift of the

8

absorption edge and decreased bandgap are observed for GO/TNTs. This is mainly

9

caused by graphene which could reduce the bandgap of TNTs due to the direct

10

interaction between C and Ti atoms on TNTs surface during solvothermal treatment

11

[35]. And after Ag doping, a red shift of the absorption edge and decreased bandgap

12

are also observed for Ag/GO/TNTs. The improved visible light absorption abilities are

13

potent to explain for the enhanced visible light photocatalytic properties of the

14

Ag/GO/TNTs composite, which will be discussed later.



1 2

Fig.4 (a) The UV-Vis DRS spectra of TNTs, GO/TNTs and Ag/GO/TNTs membranes, (b)

3

corresponding bandgaps

4 5

The photocatalytic activities of TNTs, GO/TNTs, Ag/GO/P25 and Ag/GO/TNTs were

6

studied via MB degradation under visible light. The results are shown in Fig. 5. In

7

30min dark condition, MB molecules were adsorbed onto all samples. Obviously, GO

8

shows strong adsorption ability for MB, but almost has no catalytic activity. However,

9

the strong adsorption ability easily leads to membrane fouling resulting in a

10

significant decline in membrane flux, and the contaminant is difficult to be eliminated

11

via regular cleaning method due to strong interactions. On the other hand, TNTs also

12

has impressive adsorption ability for MB due to its high specific surface area and

13

abundant hydroxyl group. In addition, it has good photocatalytic degradation ability

14

for MB. It reveals that membrane fouling could be alleviated by photocatalysis. As a

15

consequence, Ag/GO/TNTs membranes exhibit a better adsorption and photocatalytic

16

ability than Ag/GO/P25. 90% of MB could be degraded after 120 min irradiation. In

17

order to distinguish the catalytic effects of different materials, the kinetic degradation


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1

curves simulated by first-order degradation equation were obtained as shown in Fig.

2

S4. The rate constants of Ag/GO/TNTs, GO/TNTs and Ag/GO/P25 membranes are

3

calculated to be 0.74 h 1, 0.23 h 1 and 0.31 h 1, respectively. Obviously, Ag loading and

4

TNTs benefit the enhancement of photocatalytic dye degradation.

5

Beyond that, the photocatalytic activities of Ag/GO/TNTs membranes with different

6

ratio of GO: TNTs (1: 0, 1: 0.5, 1: 1, 1: 2, 1: 3, 1: 4) and Ag content (0%, 1.5%, 3%,

7

6%, 7%) were also investigated to optimize preparation parameters for obtaining the

8

Ag/GO/TNTs membrane with improved photocatalytic ability. As shown in Fig. 6a,

9

with increase of TNTs content in the composite membranes, the removal ability of

10

MB increased at first and then decreased. And the Ag/GO/TNTs membranes show

11

higher removal ability when the ratio of GO: TNTs reaches to 1: 3 via

12

adsorption-photocatalysis synergistic effect. It could be interpreted by the variation of

13

adsorption abilities of Ag/GO/TNTs membranes. With the rising TNTs content,

14

plentiful corrugations and bulges on the surface of Ag/GO/TNTs membranes as shown

15

in Fig. S5 and they are formed by the intercalation of TNTs as shown in Fig. S6, and

16

the pores from porous TNTs particles benefit to adsorption of MB. However, because

17

of GO with a stronger adsorption ability than TNTs (Fig. 5), excessive content of

18

TNTs is unfavorable to increase the adsorption ability of Ag/GO/TNTs membranes.

19

On the other hand, excessive amounts of Ag are also not in favor of MB removal as

20

shown in Fig. 6b. And the Ag/GO/TNTs membranes with Ag content of 6% show

21

higher removal ability. It is mainly because the excessive metal loading leads to the

22

limitation of the amount of light reaching to the surface of the catalyst, and therefore

−

−

−



1

results in decreasing photogenerated charge carriers [36].

2 3

Fig. 5 Photocatalytic activities of GO, TNTs, GO/TNTs and Ag/GO/TNTs for degradation of MB

4

under visible light illumination

5

6 7

Fig. 6 The photocatalytic activities of Ag/GO/TNTs membranes with different ratio of (a) GO:

8

TNTs (1: 0, 1: 0.5, 1: 1, 1: 2, 1: 3, 1: 4) and (b) Ag content (0%, 1.5%, 3%, 6%, 7%) for

9

degradation of MB under visible light.

10 11

In order to investigate the photocatalytic mechanism of Ag/GO/TNTs for degradation

12

of MB, 1mL tert-butyl alcohol (TBA) and TEOA which act as radical and hole


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1

scavenger were added into photocatalytic reaction system, respectively. The

2

photocatalytic activities are as shown in Fig. S7. In presence of TBA, the

3

photocatalytic activity of Ag/GO/TNTs significantly decreases, while it almost

4

remains invariable with addition of TEOA. It indicates radical plays an important role

5

on photodegraded MB molecule for Ag/GO/TNTs catalyst. Here, a possible

6

photocatalytic mechanism is proposed on the basis of the literature [30, 31], as shown

7

in Fig. 7. Due to Ag doping and GO composite, Ag/GO/TNTs could adsorb visible

8

light and produce photoinduced electrons. On account of high electronic mobility of

9

graphene, these photoinduced electrons could easily transfer from TNTs and Ag to

10

GO sheets. It could effectively suppress the recombination of photoinduced electrons

11

and holes, thus enhance the photocatalytic activity of Ag/GO/TNTs. Then, these

12

electrons could react with adsorbed oxidants to produce reactive oxygen radicals (•O2

13

−

14

molecule could be photodegraded by these active radicals eventually.

15 16

−

), while the holes react with H2O/OH to generate hydroxyl radicals (•OH). MB

Fig. 7 Schematic of photocatalytic mechanism of Ag/GO/TNTs membranes under visible light

17

18

The compressive strength of Ag/GO/TNTs membranes was further evaluated via

19

water fluxes variation with 10 cycles changed pressure (0.01-0.07 MPa). The results



1

are as shown in Fig. 8. The water fluxes of Ag/GO/TNTs membranes were improved

2

with the increasing pressure from 0.01-0.07 MPa, and it presented a fine linear

3

relationship and even after 10 cycles. It indicates the pore of Ag/GO/TNTs

4

membranes was without severe compressive deformation due to the influence of

5

higher pressure according to Hagen-Poiseuille equation [37]. The results reveal

6

Ag/GO/TNTs membranes have a good compressive strength at a range of 0.01-0.07

7

MPa.

8

Meanwhile, the acid and alkali resistance of Ag/GO/TNTs membranes were

9

researched by a soaked process in HCl and NaOH solution with a concentration of 0.1

10

mol/L respectively as shown in Fig. 9. The results show free standing Ag/GO/TNTs

11

membranes have no any disintegration, and they are exhibit high acid-alkali resistance

12

stability within even for one month. Besides, Ag/GO/TNTs membranes have good

13

transparency which is beneficial to ensure their photocatalysis reaction efficiency. In

14

order to further confirm their acid-alkali resistance, the membranes were used to filter

15

0.1 mol/L HCl and NaOH solution for 6h respectively, and the fluxes were tested. The

16

results are as shown in Fig. S8. It can be seen the fluxes of HCl or NaOH solution

17

have no significant change indicating that the membrane structure and pores haven’t

18

been destroyed seriously. It is mainly due to acid-alkali resistance of carbon based

19

materials.


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1 2

Fig. 8 The water fluxes of Ag/GO/TNTs membranes with 10 cycles changed pressure (0.01-0.07

3

MPa)

4 5

Fig. 9 Ag/GO/TNTs membranes were soaked at 0.1 mol/L HCl or NaOH solution with different

6

time

7

Photocatalysis-membrane filtration integrated process of as-prepared Ag/GO/TNTs

8

membranes with GO and TNT ratio at 1: 3 and Ag content of 6% was investigated by

9

a flat-sheet crossflow filtration unit, and the fluxes and rejection rates for MB solution

10

were tested. Meanwhile the antifouling ability of Ag/GO/TNTs membranes was

11

evaluated from the flux change with and without visible light irradiation, and the

12

results are shown in Fig. 10. As shown in Fig. 10a, the fluxes dramatically decreased

13

for the Ag/GO/TNTs membranes with and without visible light due to membrane



1

fouling. Without light irradiation, the water fluxes decreased quickly from 70.2 to

2

20.0 L/m2h in the first 100 min. And in this period, the adsorption of the membrane

3

for MB was main filtration resistance which caused membrane fouling. Then the

4

fluxes decreased slowly to equilibrium (17.8 L/m2h) until 6h. As comparison, when

5

the membrane separation process was operated under visible light irradiation, the

6

fluxes decreased slower and maintained at a higher equilibrium value (34.7 L/m2h).

7

The fluxes of GO membrane for MB solution with and without visible light were also

8

shown in Fig. S9. It is found that the initial flux of GO membrane is less than

9

Ag/GO/TNTs membrane. In addition, visible light has no effect on the flux

10

recoverability of GO membrane. On the other hand, the results of rejection rates of

11

Ag/GO/TNTs membrane for MB are as shown in Fig. 10b. For membrane separation

12

process with visible light, MB removal rate decreased until 64% due to saturation of

13

adsorption capacity and the process of membrane separation. However, it’s higher

14

than that without light irradiation. This improvement could be attributed to the

15

synergetic function of adsorption and photocatalysis in Ag/GO/TNTs membranes. In

16

order to intuitively investigate anti-fouling ability of Ag/GO/TNTs membrane under

17

visible light, contaminated membranes under 6h cross-flow filtration were cut into a

18

piece with diameter of 4 cm and put in a watchglasses with water under visible light

19

irradiation. The results are as shown in Fig. S10. Obviously, the color of MB

20

contaminated membrane is dark blue. Then the color has bleach out with a period of

21

visible light irradiation, and large amounts of bubbles are observed at the same time.

22

It indicates MB molecules on surface of membrane are photodegraded under light


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1

irradiation. In this sense, visible light irradiation could effectively alleviate the

2

membrane fouling via photocatalysis during membrane separation process.

3 4

Fig. 10 (a) The fluxes and (b) the rejection rates of Ag/GO/TNTs membranes through cross-flow

5

filtration with and without visible light illumination

6 7

CONCLUSIONS

8

Ag doped GO/TNT have been successfully synthesized by a single step solvothermal

9

reaction, and Ag nanoparticles with a size of about 3 nm were obtained and highly

10

dispersed on the surface of GO and TNTs. As-prepared Ag/GO/TNT membranes with

11

visible light photocatalytic ability were used in crossflow filtration process. They

12

exhibited reasonable ability on photocatalytic degradation of Methylene Blue under

13

visible light, and the membrane fouling could be effectively alleviated via integrating

14

visible photocatalytic-membrane filtration. In addition, the as-prepared Ag/GO/TNTs

15

membranes possess high acid-alkali resistance stability and good compressive

16

strength. Our research could provide a valuable reference value for synthesis of highly

17

dispersed nanoparticles and using Ag/GO/TNTs membranes to alleviate membrane



1

fouling under visible light.

2

SUPPORTING INFORMATION

3

The Supporting Information is available free of charge on the ACS Publications

4

website.

5

Schematic of the membrane filtration system, SEM images and nitrogen

6

adsorption-desorption results of various samples, the kinetic degradation curves, the

7

photocatalytic activities, the membrane fluxes under various conditions, the photos of

8

contaminated membranes under visible light with different time.

9

ACKNOWLEDGEMENTS

10

Gonggang Liu received funding from PhD research startup foundation of Central

11

South University of Forestry and Technology (104-0456). Kai Han received funding

12

from the National Natural Science Foundation of China (No. 21706292), China

13

Postdoctoral Science Foundation (2015M582343, 2016T90758) and Hunan Provincial

14

Natural Science Foundation of China (No. 2017JJ3376). Yonghua Zhou received

15

funding from the National Natural Science Foundation of China (NO. 21676303).

16

Jinbo Hu received funding from Hunan Provincial Natural Science Foundation of

17

China (No. 2017JJ1038).

18

REFERENCES

19 20 21 22 23 24 25 26

[1] Balaban, M. Growth of Desalination and Water Treatment. Desalin. Water Treat. 2012, 50 (1-3), DOI org/10.1080/19443994.2012.754537. [2] Hillie, T.; Hlophe M. Nanotechnology and the challenge of clean water. Nat. Nanotechnol. 2007, 2 (11), DOI 10.1038/nnano.2007.350. [3] Pan, D.; Jiao, J.; Li, Z.; Guo, Y.; Feng, C.; Liu, Y.; Wang, L.; Wu, M. Efficient separation of electron-hole pairs in graphene quantum dots by TiO2 heterojunctions for dye degradation. ACS Sustain. Chem. Eng. 2015, 8 (9), DOI 10.1021/acssuschemeng.5b00771. [4] Bowen, W.R.; Welfoot, J.S. Modelling the performance of membrane nanofiltration-critical assessment and


Page 20 of 24

Page 21 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44

model development. Chem. Eng. Sci. 2002, 57 (7), DOI org/10.1016/S0009-2509(01)00413-4. [5] Owen, G.; Bandi, M.; Howell, J.A.; Churchouse, S.J. Economic assessment of membrane processes for water and waste water treatment. J. Membr. Sci. 1995, 102 (15), DOI org/10.1016/0376-7388(94)00261-V. [6] Liang, C.; Guosheng, S.; Jie, S.; 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 (7676), DOI 10.1038/nature24044. [7] 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 (53), DOI 10.1039/c3cc41953c. [8] Joshi, R.K.; Carbone, P.; Wang, F.C.; Kravets, V.G.; Su, Y.; Grigorieva I.V. Precise and ultrafast molecular sieving through graphene oxide membranes. Science 2014, 343 (6172), DOI 10.1126/science.1245711. [9] 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

(4),

DOI

10.1038/ncomms3979. [10] Jin, J.; Gao, J.S.; Qin, H.; Liu, P. SWCNT-intercalated GO ultrathin films for ultrafast separation of molecules. J. Mater. Chem. A 2015, 3 (12), DOI 10.1039/C5TA00366K. [11] Xu, K.; Feng, B.; Zhou, C.; Huang, A. Synthesis of highly stable graphene oxide membranes on polydopamine functionalized supports for seawater desalination. Chem. Eng. Sci. 2016, 146, DOI org/10.1016/j.ces.2016.03.003. [12] Huang, K.; Liu, G.; Lou, Y.; Dong, Z.; Shen, J.; Jin, W. A graphene oxide membrane with highly selective molecular separation of aqueous organic solution. Angew. Chem. Int. Edit. 2014, 53 (27), DOI 10.1002/anie.201401061. [13] Ding, R.; Zhang, H.; Li, Y.; Wang, J.; Shi, B.; Mao, H. Graphene oxide-embedded nanocomposite membrane for solvent resistant nanofiltration with enhanced rejection ability. Chem. Eng. Sci. 2015, 138, DOI org/10.1016/j.ces.2015.08.019. [14] Liu, G.; Ye, H.; Li, A.; Zhu, C.; Jiang, H.; Liu, Y.; Han, K.; Zhou, Y. Graphene oxide for high-efficiency separation

membranes:

Role

of

electrostatic

interactions.

Carbon

2016,

110,

DOI

org/10.1016/j.carbon.2016.09.005. [15] Joshi, R.K.; Alwarappan, S.; Yoshimura, M.; Sahajwalla, V.; Nishina, Y. Graphene oxide: the new membrane material. Applied Materials Today 2015, 1 (1), DOI org/10.1016/j.apmt.2015.06.002. [16] Mahmoud, K.A.; Mansoor, B.; Mansour, A.; Khraisheh, M. Functional graphene nanosheets: The next generation membranes for water desalination. Desalination 2015, 356, DOI org/10.1016/j.desal.2014.10.022. [17] Huang, H.; Ying, Y., Peng, X. Graphene oxide nanosheet: an emerging star material for novel separation membranes. J. Mater. Chem. A 2014, 2 (34), DOI 10.1039/C4TA02359E. [18] Hegab, H.M.; Zou, L. Graphene oxide-assisted membranes: Fabrication and potential applications in desalination and water purification. J. Membr. Sci. 2015, 484, DOI org/10.1016/j.memsci.2015.03.011. [19] Liu, G.; Han, K.; Ye, H.; Zhu, C.; Gao, Y.; Liu, Y.; Zhou, Y. Graphene oxide/triethanolamine modified titanate nanowires

as

photocatalytic

membrane

for

water

treatment.

Chem.

Eng.

J.

2017,

320,

DOI

org/10.1016/j.cej.2017.03.024. [20] Hu, M.; Zheng, S.; Mi, B. Organic fouling of graphene oxide membranes and its implications for membrane fouling control in engineered osmosis. Environ. Sci. Technol. 2016, 50 (2), DOI 10.1021/acs.est.5b03916. [21] Zhu, C.; Liu, G.; Han, K.; Ye, H.; Wei, S.; Zhou, Y. One-step facile synthesis of graphene oxide/TiO2 composite as efficient photocatalytic membrane for water treatment: Crossflow filtration operation and membrane fouling analysis. Chem. Eng. Process. 2017, 120, DOI 10.1016/j.cep.2017.06.012.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44

[22] Qian, W.; Greaney, P.A.; Fowler, S.; Chiu, S.K.; Goforth, A.M.; Jiao, J. Low-temperature nitrogen doping in ammonia solution for production of n-doped TiO2-hybridized graphene as a highly efficient photocatalyst for water treatment. ACS Sustain. Chem. Eng. 2014, 2 (7), DOI 10.1021/sc5001176. [23] Wang, W.S.; Wang, D.H.; Qu, W.G.; Lu, L.Q.; Xu, A.W. Large ultrathin anatase TiO2 nanosheets with exposed {001} facets on graphene for enhanced visible light photocatalytic activity. J. Phys. Chem. C 2012, 116 (37), DOI 10.1021/jp306498b. [24] Rokhsat, E.; Akhavan, O. Improving the photocatalytic activity of graphene oxide/ZnO nanorod films by UV irradiation. Appl. Surf. Sci. 2016, 371, DOI org/10.1016/j.apsusc.2016.02.222. [25] Qamar, M.; Merzougui, B.; Ahmed, M.I.; Yamani, Z.H. Broad solar spectrum-responsive and highly efficient photoanode of nonstoichiometric TiO2 nanoplates/reduced graphene oxide. ACS Sustain. Chem. Eng. 2018, 6 (2), DOI 10.1021/acssuschemeng.7b03535. [26] Yoo, D.H.; Cuong, T.V.; Pham, V.H.; Chung, J.S.; Khoa, N.T.; Kim, E.J.; Hahn, S.H. Enhanced photocatalytic activity of graphene oxide decorated on TiO2, films under UV and visible irradiation. Curr. Appl. Phys. 2011, 11 (3), DOI org/10.1016/j.cap.2010.11.077. [27] Perera, S.D.; Mariano, R.G.; Vu, K.; Nour, N.; Seitz, O.; Chabal, Y.; Balkus Jr, K.J. Hydrothermal synthesis of graphene-TiO2 nanotube composites with enhanced photocatalytic activity. ACS Catal. 2012, 2 (6), DOI 10.1021/cs200621c. [28] Pan, X.; Zhao, Y.; Liu, S.; Korzeniewski C.L.; Wang, S.; Fan, Z. Comparing graphene-TiO2 nanowire and graphene-TiO2 nanoparticle composite photocatalysts. ACS Appl. Mater. Inter. 2012, 4 (8), DOI 10.1021/am300772t. [29] Sher Shah, M.S.; Zhang, K.; Park, A.R.; Kim, K.S.; Park, N.G.; Park, J.H.; Yoo, P.J. Single-step solvothermal synthesis of mesoporous Ag-TiO2-reduced graphene oxide ternary composites with enhanced photocatalytic activity. Nanoscale 2013, 5 (11), DOI 10.1039/c3nr00579h. [30] Ullah, K.; Zhu, L.; Meng, Z.D.; Ye, S.; Sun, Q.; Oh, W.C. A facile and fast synthesis of novel composite Pt-graphene/TiO2, with enhanced photocatalytic activity under UV/Visible light. Chem. Eng. J. 2013, 231 (9), DOI org/10.1016/j.cej.2013.07.014. [31] Vasilaki, E.; Georgaki, I.; Vernardou, D.; Vamvakaki, M.; Katsarakis, N. Ag-loaded TiO2/reduced graphene oxide nanocomposites for enhanced visible-light photocatalytic activity. Appl. Surf. Sci. 2015, 353, DOI org/10.1016/j.apsusc.2015.07.056. [32] Han, K.; Liu, Z.; Shen, J.; Lin, Y.; Dai, F.; Ye, H. A free-standing and ultralong-life lithium-selenium battery cathode enabled by 3D mesoporous carbon/graphene hierarchical architecture. Adv. Funct. Mater. 2015, 25 (3), DOI 10.1002/adfm.201402815. [33] Xing, Z.; Asiri, A.M.; Obaid, A.Y.; Sun, X.; Ge, X. Carbon nanofiber-templated mesoporous TiO2 nanotubes as a high-capacity anode material for lithium-ion batteries. RSC Adv. 2014, 4 (18), DOI 10.1039/C3RA47239F. [34] Liu, G.; Gui, S.; Zhou, H.; Zeng, F.; Zhou, Y.; Ye, H. A strong adsorbent for Cu2+: graphene oxide modified with triethanolamine. Dalton T. 2014, 43 (19), DOI 10.1039/c4dt00063c. [35] Lee, E.; Hong, J.Y.; Kang, H.; Jiang, J. Synthesis of TiO2 nanorod-decorated graphene sheets and their highly efficient photocatalytic activities under visible-light irradiation. J. Hazard. Mater. 2012, 219-220 (12), DOI 10.1016/j.jhazmat.2011.12.033. [36] Carp, O.; Huisman, C.L.; Reller, A. Photoinduced reactivity of titanium oxide. Prog. Solid State Ch. 2004, 32 (1), DOI org/10.1016/j.progsolidstchem.2004.08.001. [37] Jeon, G.; Jee, M.; Yang, S.Y.; Lee, B.Y.; Jang, S.K.; Kim, J.K. Hierarchically self-organized monolithic nanoporous membrane for excellent virus enrichment. ACS Appl. Mater. Inter. 2014, 6 (2), DOI 10.1021/am4049404.


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1 2 3 4

GRAPHIC ABSTRACT: Ag doped GO/Titanate nanotubes membranes endowing GO

membranes with enhanced visible light degradation ability could alleviate their membrane fouling problem for long term water treatment and achieve sustainable use.



graphical abstract 87x32mm (600 x 600 DPI)


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Facile synthesis of highly dispersed Ag doped ... - ACS Publications

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