Facile Fabrication and Application of Superhydrophilic Stainless Steel

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Facile fabrication and application of superhydrophilic stainless steel hollow fiber microfiltration membranes Ming Wang, Yue Cao, Zhen-Liang Xu, Yu-Xuan Li, and Shuang-Mei Xue ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.7b02300 • Publication Date (Web): 18 Sep 2017 Downloaded from http://pubs.acs.org on September 24, 2017

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ACS Sustainable Chemistry & Engineering

Facile fabrication and application of superhydrophilic stainless steel hollow fiber microfiltration membranes Ming Wang, Yue Cao, Zhen-Liang Xu∗, Yu-Xuan Li, Shuang-Mei Xue State Key Laboratory of Chemical Engineering, Membrane Science and Engineering R&D Lab, Chemical Engineering Research Center, East China University of Science and Technology, 130 Meilong Road, Shanghai 200237, China ABSTRACT: Superhydrophilic stainless steel hollow fiber microfiltration membranes (SSHF-MF) were

developed through a facile dip-coating method followed by sintered at a low temperature of 500℃. A novel mediating additive was explored to mediate the coating suspensions. The additive which could form hydrogen bonds with TiO2 agglomerations facilitated the formation of a continuous TiO2 layer on the rough surface of stainless steel hollow fiber (SSHF). The fabricated SSHF-MF exhibited superhydrophilic and under water superoleophobicity wettability, which enabled SSHF-MF to be applied to antifouling fields. The fouling resistance of SSHF-MF for oil/water emulsion, cake layer foulant (sodium alginate, SA) and adhesive foulant (bovine serum albumin, BSA) were investigated systematically. SSHF-MF exhibited superior antifouling properties and high rejections of 99% and 90% for oil/water emulsion and SA foulant solution, respectively. For adhesive BSA solution, SSHF-MF still showed good antifouling property after washing with a dilute alkaline solution and superior separation performance (90%). Meanwhile, SSHF-MF exhibited an excellent separation performance for polystyrene microspheres (100nm) with a rejection of 100%. In conclusion, SSHF-MF showed great potentials not only in traditional microfiltration fields such as solid-liquid separation but also in the antifouling field such as oil/water separation. The facile fabrication conditions and superior wettability further improved the sustainability of SSHF-MF in practical applications. KEYWORDS: hydrogen bond, super-wettability, microfiltration, oil/water separation, antifouling

∗

To whom all correspondence should be addressed. Email: [email protected]; Tel: 86-21-64253670; Fax: 86-21-64252989.

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INTRODUCTION

SSHF with narrow pore size distribution. The composite

Crude oil leakage accident and oily wastewater are

membranes usually include a functional ceramic layer and

destroying our marine environment severely, which is one

SS substrates. As is well known, it is easier to handle

of the top environmental concerns1. Meanwhile, it is

submicron ceramic particles than SSP with the same size

highly desired to reclaim the pure oil from their

which enable finer microstructures and well-defined pore

wastewater.

handling

size17. The combination of both advantages of ceramic and

countermeasures such as skimming, coagulation, in situ

SS membranes overcomes the insufficient of individual SS

burning, and flocculation techniques are expensive,

membranes efficiently. Commonly preferred ceramic

ineffective and even non-environmental-friendly2-4. In

particles are metallic oxide such as ZrO2, Al2O3 and TiO2,

contrast, membrane process as a green and low cost

among which TiO2 grains have drawn considerable

technology has drawn extensive attention for oil/water

attention because of their numerous characteristics

separation. For the water in oil system, various

including hydrophily, catalysis, semiconductivity, low

superhydrophobic membranes with superior separation

melting temperature (compared with ZrO2, Al2O3) and

efficiency for water droplet and antifouling property have

good adhesive ability with metal substrates10.

been developed5-7. For the oil in water system, membrane

Up to now, dip-coating18, 19, wet powder spraying10, 17, slip

pores are inclined to be blocked by oil droplets due to their

casting20,

distortion and high viscosity. However superhydrophilic

are commonly used to functionalize these materials.

microfiltration (MF) membranes could ease the membrane

Among these methods, dip-coating is a conventional and

fouling phenomenon due to the lower oil adhesion to the

facile technique to form a ceramic layer. Although

membrane surface

separation

sometimes the fine particles would penetrate into the

efficiency for oil droplet, antifouling property and even

support pores resulting in the sacrifice of original

Nevertheless,

conventional

and exhibit superior 2, 8, 9

21

and electrophoretic deposition22,

23

technique

. As we all know, inorganic MF

permeability of supports, the particles penetration could

membranes could realize high thermal stability, good

improve the binding strength and thermal stability between

chemical stability and superior cleaning ability through

the ceramic layer and metal substrates.

chemical, high pressure or backflushing where organic

Asymmetric TiO2 microfiltration membranes supported on

antibacterial activity

10

membranes suffer from their limited long-term stability .

SS tubes or flat sheets have been commercialized for years

Therefore, the exploitation of superhydrophilic inorganic

by the corporations such as: GKN, Mott, Graver

MF membranes still needs significant efforts.

Technologies, Pall, and Hyflux and so on. However, since

In recent years, stainless steel hollow fibers (SSHF) with

Forschungszentrum

different configurations have been developed due to their

microfiltration membranes with the mean pore size of

typical properties such as high mechanical strength, good

0.11µm on planar SS substrates by wet powder spraying

thermal shock resistance and easy integration into modules

technique10, 17, the reports on stainless steel microfiltration

by welding11. However, the interests of recent researches

membranes (SS-MF) are limited especially on their

12-16

on SSHF mainly focused on their preparation

process;

application

fields.

Juelich

developed

Therefore,

the

graded

preparation

TiO2

and

direct practical application of SSHF is unavailable due to

application of SS-MF still show great potentials to

their drawbacks of rough surface and large pore size

optimize and explore.

distribution. As it is a high energy-consuming task to

In the present study, superhydrophilic SSHF-MF are

obtain finer stainless steel powders (SSP), the composite

fabricated through dip-coating TiO2 suspensions on SS

membranes seem to be a promising alternative to acquire

substrates followed by sintered at a low temperature (500


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℃). A novel additive which could form hydrogen bonds

pressed out through the spinneret under pressure of

with TiO2 agglomerations facilitated the formation of a

0.1MPa. And then the precursors were immersed in

continuous TiO2 layer. Corresponding experiments and

deionized water for 24h to remove the residual solvent.

characterization have verified the positive effect of

Lastly, the precursors were dried naturally and sintered in

hydrogen bonds. It is well known that the more

an atmosphere furnace. The temperature was raised up to

hydrophilic the surface is, the better antifouling property it

350℃ with the heating rate of 1℃/min and hold for 1h to

3, 24

presents

. According to the intrinsic superhydrophilic

burnout the polymer. Then the fibers were sintered at 1100

property of TiO2 layer, a series of antifouling and

℃for 2h with the heating rate of 5℃/min to acquire the

separation experiments have been conducted. Bovine

mechanical strength. SSHF-MF: TiO2 coating suspension

serum albumin (BSA), sodium alginate (SA) and oil/water

with 10wt% particle content was obtained by dispersing

emulsion are used to evaluate SSHF-MF’s antifouling

TiO2 nanoparticles in deionized water. Three kinds of

properties. Additionally, the morphology, wettability, and

monomers (PIP, PEI and ethylenediamine) as additive

pore size distribution of SSHF-MF are characterized

were added to mediate the coating suspension. SSHF with

systematically.

both ends wrapped up by Teflon tapes were pulled up from suspension with a speed of 50cm/min after dipped for 30s,

EXPERIMENTAL SECTION

and then were dried in ambient temperature for 24h.

Materials. BSA, SA and vacuum pump oil were supplied by Shanghai Lianguan Biochemical Engineering Co. Ltd, Sinopharm Chemical Reagent Co., Ltd and Shanghai VACDO Vacuum equipment Co. Ltd, respectively. TiO2 particles (nominal particle size: 25nm) were provided by Xuan Cheng Jing Rui New Material Co., Ltd. Polystyrene microspheres (PS, nominal particle size: 100nm) were provided by Suzhou SmartyNano Technology Co., Ltd. Surfactant sodium dodecylsulfate (SDS), piperazine (PIP), ethylenediamine and dichloromethane (CH2Cl2) were provided by Sinopharm Chemical Reagent Co., Ltd. Polyethyleneimine (PEI) was provided by Aladdin.

Preparation of SSHF and SSHF-MF. SSHF supports: the preparation technique was referred to in our previous In

brief,

polyacrylonitrile

(PAN)

and

polyvinylpyrrolidone (PVP) firstly mixed in N, Ndimethylacetamide (DMAc) and then SSP were added to form the uniform casting solution with the mass ratio of SSP:PAN:DMAc:PVP=80:3.2:16.6:0.2.

for 2h to assure the coalescence of TiO2 particles. SSHFMF prepared from four different TiO2 suspensions (without additive, with PIP, with PEI and with ethylenediamine) were abbreviated as SSHF-MF0, SSHFMF1, SSHF-MF2 and SSHF-MF3, respectively. Characterization. The morphology of SSHF-MF was examined by scanning electron microscopy (SEM, JEOL Model JSM-6380 LV, Japan). SSHF-MF were fixed to a copper holder and sputtered with gold under vacuum. Attenuated total reflectance Fourier transform infrared spectrums (ATR-FTIR) of different coating solutions were

Deionized water was made in our own lab.

work25.

Lastly, SSHF-MF were obtained after calcined at 500℃

Then,

the

suspension was poured into a tubular vessel and vacuum degassed for 30min. Subsequently, the suspension was

measured by the spectrometer (Nicolet 6700, USA) to analyze the existence of hydrogen bonds in coating solutions. The pore size distribution of pristine SSHF and SSHF-MF

were

measured

by

the

capillary

flow

porosimetry (Beishide instrument 3H-2000PB, China). The effective pore size was evaluated by the rejection of PS microspheres. The particle sizes of PS microspheres were measured by dynamic light scattering (DLS, Zetasizer Nano ZS, UK). Water and oil contact angles were

3 ACS Paragon Plus Environment


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measured

via

an

equipment

(JC2000A,

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Shanghai

under the pressure of 0.1MPa but at 0.05MPa in case the

Zhongcheng Digital Equipment Co. Ltd., China) to

oil droplet transformation. The membranes were washed

investigate the surface wettability.

with deionized water for 30min after emulsion filtration

Antifouling properties of SSHF-MF. Mass transfer

test. Jw2 of the cleaned membrane was obtained after a

property of SSHF-MF was characterized based on pure

stable operation at 0.05MPa for 30min. Flux recovery ratio

water flux (Jw1). The filtration test module was referred to

(FRR) and decay ratio (DR) were used to evaluate the

11

in our previous work . Jw1 was obtained after a stable

antifouling properties of SSHF-MF. The calculation

operation at 0.1MPa for 30min. The calculation method

methods of FRR and DR were showed in Eq. (2) and Eq.

was showed in Eq. (1):

(3), respectively.

Jw 1 =

Q A × t × ∆P

(1)

FRR =

Herein, Q represented the volume of permeate (L), A represented the effective outer surface area (m2), t

DR =

Jw 2 Jw1

(2)

Jw1 − J p Jw1

(3)

represented the collecting time (s) and ∆P represented the transmembrane pressure (0.1MPa).

The concentration of pump oil, SA and BSA were

Antifouling properties of SSHF-MF were evaluated

determined

through the separation and recovery experiments of three

SHIMADZU, Japan) with wavelengths of 290 nm, 220 nm

kinds of common model foulant: pump oil, SA and BSA.

and 280 nm, respectively. The rejection (R) was obtained

The concentration of SA and BSA feed solutions were

in Eq. (4):

by

UV-VIS

absorbance

(UV-1800,

both 300 ppm. For pump oil system, a high concentration (5000ppm) of oil in water emulsion was prepared as follows. 2.5g pump oil and 0.1g SDS were added into 500ml distilled water. The mixture was blended through a high speed stirrer (Gong Yi Yu Hua Instrument Co., Ltd,

R =

CF − Cp CF

(4)

Herein, CF and CP were the concentration of feed and permeate, respectively.

China) for 4h to form the stable oil in water emulsion. The resultant emulsion was used within 24h. The droplet sizes

RESULTS AND DISCUSSION

of emulsion were measured by Malvern Instrument

Characterization of SSHF-MF. It is well known that

(MASTERSIZER 3000, UK). To be specific, the permeate

nanoparticles in suspension tend to agglomerate due to

flux of SA and BSA solutions were measured every 10

their large surface energy. The agglomeration segments

minutes under the pressure of 0.1MPa and the stable

were always isolated with others. These segments were

permeate flux (Jp) was obtained after 1h filtration test. The

unable to form a continuous layer on the rough surface

membranes were subsequently washed with deionized

directly by dip-coating process. Accidentally, we found

water and 5‰ NaOH solution for SA and BSA polluted

that the addition of PIP in suspension had a beneficial

membranes for 30min, respectively. The pure water flux

effect on the formation of a continuous layer. The possible

(Jw2) of the cleaned membranes were obtained after a

function mechanism was illustrated in Figure 1.

stable operation at 0.1MPa for 30min. In similar, Jp of oil in water emulsion was measured every 10 minutes not


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Figure 2. SEM images of SSHF and SSHF-MF1. A: surface of SSHF, B: cross section of SSHF, C: pore size Figure 1. Schematic diagram of function mechanism of

distribution of SSHF, D: surface of SSHF-MF1, E: cross

hydrogen bondsbetween PIP and TiO2 particles

section of SSHF-MF1, F: pore size distribution of SSHF-

The secondary diamines of PIP formed hydrogen bonds (blue dotted line) with the surface hydroxyl groups of TiO2. These hydrogen bonds connected the isolated segments forming a random and fluctuating three-

MF1. Table 1 A summary of fundamental properties of SSHF and SSHF-MF1 Membrane

Mean pore size

Contact

Tensile

Pure

N2 permeance

No.

(µm)

angle (°)

strength

water flux

( ×10-5

dimensional network in suspension which were analogous

(MPa)

In our previous report, the positive effect of PIP has been demonstrated

in

zeolite

seeds

dispersion

(L/(m h

mol/(m2 s pa))

bar))

to the network in water26. The mutual connecting segments were easily coated on the rough surface of pristine SSHF.

2

SSHF

1.43±0.27

--

20±3

1900±300

32.0±3.8

SSHF-MF1

0.24±0.05

18±2

53±4

680±97

6.1±1.1

aspect27.

Therefore, with the assistance of PIP, a continuous TiO2

Figure 3 exhibited SEM images of SSHF and SSHF-MF1

layer could be formed only through a dip-coating method.

with different coating suspensions. Figure 3 (A and B)

The following experiments demonstrated the function

were the magnified images of pristine SSHF. The surfaces

mechanism of hydrogen bonds. The morphology and pore

of metal crystals were smooth and the crystal boundary

size of SSHF and SSHF-MF1 were showed in Fig. 2. It

was well-defined. Figure 3 (C and D) were the magnified

could be seen that the pristine HF exhibited rough surface

images of SSHF-MF0 whose coating suspension was

and large pore size. Large areas of finger-like region gave

absence of PIP. It can be seen that TiO2 particles stuck to

rise to a high Jw1 of pristine HF. The surface of SSHF-MF1

the crystal surfaces rather than forming a continuous layer.

was continuous and the thickness of TiO2 layer was about

The crystal boundary was still distinct. Figure 3 (E and F)

3µm. Some fundamental properties of SSHF and SSHF-

were the magnified images of SSHF-MF1 whose coating

MF1 were summarized in Table 1. In particular, tensile

suspension comprised of PIP. It can be found that most of

strength of SSHF-MF1 was more than two times larger

surface area was continuous and some large particles were

than that of SSHF. To verify the effect of PIP, a

still visible. And there were no obvious defects on the

comparative experiment had been performed.

surface. A photograph of SSHF, SSHF-MF0 and SSHFMF1 was showed in Figure S1. The appearance of SSHF and SSHF-MF0 was similar. However, SSHF-MF1 showed



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a distinguished appearance. In short, both figures demonstrated the positive effect of PIP.

Figure 4. ATR-FTIR spectra of A: PIP solution, B: TiO2 suspension with PIP

Figure 3. SEM images of SSHF, SSHF-MF0 and SSHFMF1. A and B: surfaces of SSHF, C and D: surfaces of SSHF-MF0, E and F: surfaces of SSHF-MF1. Figure 4 illustrated the ATR-FTIR spectrum of PIP solution (spectrum A) and TiO2 suspension containing PIP (spectrum B). The peak of spectrum A at 3414 cm-1 was corresponded to OH stretching vibrations in water. After

Figure 5. SEM images of SSHF-MF2 (A: surface, C: cross-section) and SSHF-MF3 (B: surface, D: crosssection)

the addition TiO2 into PIP solution, the OH vibration band broadened inhomogeneously and the peak offset to 3421

To further confirm the universal effect of hydrogen bonds,

cm-1 in spectrum B due to the hydrogen bonds between

different additives (PEI and ethylenediamine) which could

PIP molecules and TiO2 agglomerations which affected the

form hydrogen bonds with surface hydroxyl groups were

transition frequency of the individual OH stretching

investigated. Figure 5 showed SEM images of SSHF-MF2

vibrations26. The peak of spectrum A at 1560 cm-1 was

and SSHF-MF3 whose coating suspensions contained

corresponded to N-H deformation vibrations which were

different additives. It can be seen that most of surface areas

usually weak28,

. In spectrum B, the weak N-H

of the two membranes were continuous, proving that the

deformation vibrations were covered by the strong peak at

hydrogen bonds were in favor of the formation of

1642 cm-1 due to the offset of vibration band. The change

continuous layers.

29

of O-H and N-H vibrations demonstrated the hypothesis presented in Figure 1.


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indicating a good separation efficiency for oil in water emulsion.

Figure 6. Photographs of the whole process of underwater

Figure 7. Droplet size distribution of oil in water emulsion and photograph of emulsion and permeate.

oil contact angles measurement. Water contact angle and underwater oil contact process were showed in Figure S2 and Figure 6. Figure S2 illustrated that the initial water contact angle was 18° and the water droplet disappeared in 5s. Figure 6 illustrated the low oil adhesion of SSHF-MF1. Oil (dichloromethane) droplet approached to the surface and was compressed to skew the needle. When the needle gradually lifted up, the

Figure 8. Left: time-dependent flux and rejection of

oil droplet detached from the surface without oil adhesion.

SSHF-MF1 in oil in water emulsion filtration process. Each

Both results revealed the properties of superhydrophilic

cycle contains four steps: pure water flux of fresh

and under water superoleophobicity, which enabled the

membrane, oil in water emulsion separation, water

antifouling property of SSHF-MF1.

cleaning for 30min (not shown), and pure water flux of

Oil/water emulsion antifouling property and separation

refreshed membrane. Operating pressure 0.05MPa and the

performance of SSHF-MF. In oil/water separation

concentration of oil in water emulsion was 5000ppm.

process, a water film forming on the membrane surface

Right: the changes of DR and FRR for different cycles.

prevented the direct contact between the oil droplet and the

The quantative separation efficiency and the antifouling

membrane

with

property of SSHF-MF1 were showed in Figure 8. Three

superhydrophilic and under water superoleophobicity

cycles were conducted to verify its antifouling property for

characteristics are propitious to mitigate the membrane

separation high concentration of oil in water emulsion.

fouling phenomenon and maintain a high oil/water

SSHF-MF1 exhibited a significant rejection (99%) for oil

surface.

In

general,

membranes

emulsion separation efficiency4. Therefore, SSFH-MF1

in the whole test process. FRR was more than 90% in the

could be applied to oil/water separation because of its

first cycle indicating a good flux recovery property. In the

aforementioned superior wettability. Figure 7 showed the

following two cycles, FRR reached up to 99% meaning an

pore size distribution of pump oil in water emulsion and a

almost fully recovery of flux. The oil droplets deposited on

photograph of emulsion and permeate. The oil in water

the membrane surface were washed away easily resulting

emulsion belonged to micro-emulsion system. The

in the high FRR. DR in three cycles were below 10%

permeate became transparent after the separation test



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Page 8 of 24

resulting from the slight concentration polarization3. In

into some large pores irreversibly in the first cycle.

conclusion, it is the superhydrophilic and under water

However, this process reached to the balance in the

superoleophobicity surface that rendered SSHF-MF1 with

following two cycles. To some extent, the concentration

superior separation performance and antifouling property

polarization phenomenon in SA separation process

for oil in water emulsion. Although some polymer-based

affected the flux. Therefore, DR in all three cycles were

fibers also exhibited superior separation performance for

between 40% and 50%. Moreover, the deposition of cake

oil in water emulsion, SSHF-MF could withstand harsh

layer also reduced the flux. Even so, the stable flux in SA

operation

without

separation process was still as high as 305 L/(m2 h) after

sacrificing its separation performance. This is where the

three cycles. In conclusion, SSHF-MF1 exhibited superior

superiority of SSHF-MF is, and therefore SSHF-MF

separation performance and antifouling property for SA

showed the potential in practical applications.

solutions.

conditions

and

tough

cleaning

SA and BSA antifouling properties and separation performance of SSHF-MF. For SA and BSA separation processes, pore size and wettability determined the separation performance and antifouling properties30. The pore size (244nm) of SSHF-MF1 had been measured by the capillary flow porosimetry. This device could measure the size of through-holes in theory. However, the shape of pores which affected the practical rejection can’t be measured by the device. Hence, to confirm the effective pore size of SSHF-MF1, PS microspheres with particles size ranging from 100-200nm (Figure S3) were employed to characterize the effective pore size. The rejection of PS microspheres was 100% indicating the effective pore size

Figure 9. Left: time-dependent flux and rejection of SSHF-MF1 in SA filtration process. Each cycle contains four steps: pure water flux of fresh membrane, SA solution separation, water cleaning for 30min (not shown), and pure water flux of refreshed membrane. Operating pressure 0.1MPa and the concentration of SA solution was 300ppm. Right: the changes of DR and FRR for different cycles.

below 100nm. This result may be attributed to the shape of pore and the stacking of PS particles in the filtration process. In addition, the membrane and the PS particles were both negatively charged, so the membrane repelled also much smaller particles as the real pore size. According to this result, SSHF-MF1 got the potential to separate sub-micro sized SA molecules. SA as a colloidal

Figure 10. Left: time-dependent flux and rejection of

pollutant is a natural polysaccharide which tends to form a

SSHF-MF1 in BSA filtration process. Each cycle contains

cake layer on membrane surface due to its strong gel

four steps: pure water flux of fresh membrane, BSA

ability31. Antifouling property and separation performance

solution separation, 5‰ NaOH solution cleaning for

were displayed in Figure 9. It can be seen that the rejection

30min (not shown), and pure water flux of refreshed

of SA was around 90% in the whole test process indicating

membrane.

a good separation performance. FRR was 85% in the first

concentration of BSA solution was 300ppm. Right: The

cycle and were improved to 95% in the following two

changes of DR and FRR for different cycles.

Operating

cycles. This may be because that some SA cakes deposited


pressure

0.1MPa

and

the

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Unlike SA pollutant, BSA as a common foulant had the

eventually reached the saturation state with the flux

molecule size of only a few nanometers and the property

fluctuation around 60 L/(m2 h) in the following time.

of electrification in different pH solutions31. The

However the diffusion of BSA molecules reached a steady

adsorption of BSA onto TiO2 particles has been studied in

state until 66 hours’ operation. After that period, the

32

previous report . In our preliminary experiments, it was

rejection also maintained the value of 75%. In other words,

found that the flux was completely unable to recover by

for BSA separation process, the adsorption and diffusion

water washing in BSA filtration process. Depending on the

of BSA molecules determined the ultimate separation

protein denaturation feature, dilute NaOH solution was

performance. In terms of the performance in the first 6

used to desorb BSA from TiO2 particles. Figure 10 showed

hours, SSHF-MF were qualified for the separation of BSA

the antifouling property and separation performance of

with the flux and rejection of 93 L/(m2 h) and 88%,

SSHF-MF1 for BSA solution. The rejection of BSA was

respectively. However, with the prolonged operation time,

around 90% in the whole testing process indicating a good

the separation performance had a discount. Fortunately, the

separation performance. However, the nano-sized BSA

separation performance could recover to a great extent

molecules were easily stuck into pores leading to an

with dilute alkaline solution washing.

irreversible reduction of flux and the effective pore size. This was why SSHF-MF1 still exhibited good rejection of nano-sized BSA molecules and FRR was only 65% in the first cycle33. FRR were gradually improved in the following two cycles. That is to say, the irreversible flux decay was weakened with the increase of cycle times. DR were more than 80% in three cycles. Two possible reasons could account for the high flux decay in filtration process. One was that the absorption of BSA enhanced the concentration polarization. The other was that small BSA molecules were stuck into some pores and blocked some

Figure 11. Time-dependent flux and rejection of SSHF-

channels. To further figure out the effect of BSA

MF1 in BSA long-term filtration process. Insert image

adsorption, long-term running operation for BSA solution

represents the variation of flux and rejection in the first 6

was conducted as shown in Figure 11. After three days

hours.

operation, SSHF-MF1 reached a steady state with the flux and rejection of 60 L/(m2 h) and 75%, respectively. In the

CONCLUSION

first 6 hours, the rejection of BSA was around 90% and the

A novel superhydrophilic and under water superoleophobic

flux decreased gradually. In this period, the adsorption of

stainless steel hollow fiber microfiltration membrane

BSA was the key factor to affect its separation

(SSHF-MF) was prepared successfully via a facile dip-

performance. After 18 hours’ operation, the rejection had

coating method followed by sintered at a low temperature

an obvious decline which may be induced by the diffusion

(500 ℃ ). Piperazine (PIP) as an additive mediated the

of BSA molecules across the channel under the pressure.

interparticle relations contributing to the formation of a

Meanwhile, the adsorption of BSA was also close to the

continuous and uniform TiO2 layer on the rough surface of

saturation state. After another 12h, the adsorption process

SSHF. SSHF-MF exhibited superior antifouling properties



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

and separation performance. For oil in water emulsion, 2

SSHF-MF showed the proper flux of 230 L/(m

Page 10 of 24

(1) Ma, Q.; Cheng, H.; Fane, A. G.; Wang, R.; Zhang, H.,

h)

Recent development of advanced materials with special

operating at 0.05MPa and a high rejection of 99% even if

wettability for selective oil/water separation. Small 2016,

the membranes were reused for three cycles. Flux recovery

12 (16), 2186-2202.

ratio maintained more than 90% in three cycles. For SA

(2) Chang, Q.; Zhou, J. E.; Wang, Y.; Liang, J.; Zhang, X.;

2

solution, SSHF-MF showed a high flux of 305 L/(m h)

Cerneaux, S.; Wang, X.; Zhu, Z.; Dong, Y., Application of

and a good rejection of 90% after three cycles. Flux

ceramic microfiltration membrane modified by nano-TiO2

recovery ratio reached up to 95% after three cycles. For

coating in separation of a stable oil-in-water emulsion. J.

2

BSA solution, SSHF-MF showed a flux of 73 L/(m h) and

Membr. Sci. 2014, 456 (8), 128-133.

a rejection of 91% after three cycles. In a sum, SSHF-MF

(3) Chen, W.; Su, Y.; Zheng, L.; Wang, L.; Jiang, Z., The

displayed excellent antifouling properties and separation

improved oil/water separation performance of cellulose

performance for non-adsorption solutions. Moreover,

acetate-graft-polyacrylonitrile membranes. J. Membr. Sci.

SSHF-MF also displayed superior separation performance

2009, 337 (1-2), 98-105.

and good antifouling property for adsorption solutions

(4) Cheng, Q.; Ye, D.; Chang, C.; Zhang, L., Facile

(BSA) on the premise of washing with dilute alkaline

fabrication of superhydrophilic membranes consisted of

solution.

fibrous tunicate cellulose nanocrystals for highly efficient oil/water separation. J. Membr. Sci. 2017, 525, 1-8.

ASSOCIATED CONTENT

(5) Lin, X.; Choi, M.; Heo, J.; Jeong, H.; Park, S.; Hong,

Supporting information Photograph of SSHF, SSHF-MF0

J., Cobweb-inspired superhydrophobic multiscaled gating and SSHF-MF1;

photographs of the whole process of water contact angles measurement; particle size distribution of PS microspheres.

membrane with embedded network structure for robust water-in-oil emulsion separation. ACS Sustain. Chem. Eng. 2017, 5 (4), 3448-3455. (6) Shi, Z.; Zhang, W.; Zhang, F.; Liu, X.; Wang, D.; Jin,

AUTHOR INFORMATION

J.; Jiang, L., Ultrafast separation of emulsified oil/water

Corresponding Author * Email: [email protected]; Tel: 86-21-64253670;

mixtures by ultrathin free-standing single-walled carbon nanotube network films. Adv. Mater. 2013, 25 (17), 2422-

Fax: 86-21-64252989.

2427.

Notes

(7) Wang, C.-F.; Chen, L.-T., Preparation of superwetting

The authors declare no competing financial interest.

porous materials for ultrafast separation of water-in-oil emulsions. Langmuir 2017, 33 (8), 1969-1973.

ACKNOWLEDGEMENTS

(8) Zhao, Y.; Zhang, M.; Wang, Z., Underwater

The authors are thankful for the financial support received

superoleophobic membrane with enhanced oil-water

from the National Natural Science Foundation of China

separation, antimicrobial, and antifouling activities. Adv.

(20076009, 21176067, 21276075 and 21406060), Project

Mater. Interfaces 2016, 3 (13), 1500664.

of National Energy Administration of China (2011-1635

(9) Peng, Y.; Guo, Z., Recent advances in biomimetic thin

and 2013-117), and the Open Project of State Key

membranes applied in emulsified oil/water separation. J.

Laboratory of Chemical Engineering (SKL-ChE-14C03).

Mater. Chem. A 2016, 4 (41), 15749-15770.

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(29) Rao, P. S.; Smitha, B.; Sridhar, S.; Krishnaiah, A., Effect of blending ratio on pervaporative separation of 1, 4-dioxane/water mixtures through PVA-PEI membranes. Vacuum 2006, 81 (3), 299-306. (30) Fang, L.-F.; Jeon, S.; Kakihana, Y.; Kakehi, J.-i.; Zhu, B.-K.; Matsuyama, H.; Zhao, S., Improved antifouling properties of polyvinyl chloride blend membranes by novel phosphate based-zwitterionic polymer additive. J. Membr. Sci. 2017, 528, 326-335. (31) Zhao, X.; Liu, C., One-step fabricated bionic PVDF ultrafiltration membranes exhibiting innovative antifouling ability to the cake fouling. J. Membr. Sci. 2016, 515, 29-35. (32) Giacomelli, C. E.; Avena, M. J.; Pauli, C. P. D., Adsorption of bovine serum albumin onto TiO2 particles. J. Colloid Interf. Sci. 1997, 188, 387-395. (33) Padaki, M.; Murali, R. S.; Abdullah, M.; Misdan, N.; Moslehyani, A.; Kassim, M.; Hilal, N.; Ismail, A., Membrane

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Table of Contents graphic

Schematic diagram of function mechanism of hydrogen bonds between PIP and TiO2 particles and its antifouling applications in different aspects



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Figure 1. Schematic diagram of function mechanism of hydrogen bonds between PIP and TiO2 particles

125x87mm (300 x 300 DPI)


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SEM images of SSHF and SSHF-MF1. A: surface of SSHF, B: cross section of SSHF, C: pore size distribution of SSHF, D: surface of SSHF-MF1, E: cross section of SSHF-MF1, F: pore size distribution of SSHF-MF1. 338x178mm (150 x 150 DPI)



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Figure 3. SEM images of SSHF, SSHF-MF0 and SSHF-MF1. A and B: surfaces of SSHF, C and D: surfaces of SSHF-MF0, E and F: surfaces of SSHF-MF1.


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ATR-FTIR spectra of A: PIP solution, B: TiO2 suspension with PIP 272x190mm (150 x 150 DPI)



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Figure 5. SEM images of SSHF-MF2 (A: surface, C: cross-section) and SSHF-MF3 (B: surface, D: cross-section)

50x42mm (300 x 300 DPI)


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Figure 6. Photographs of the whole process of underwater oil contact angles measurement. 137x93mm (300 x 300 DPI)



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Droplet size distribution of oil in water emulsion and photograph of emulsion and permeate. 226x102mm (150 x 150 DPI)


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Left: time-dependent flux and rejection of SSHF-MF1 in oil in water emulsion filtration process. Each cycle contains four steps: pure water flux of fresh membrane, oil in water emulsion separation, water cleaning for 30min (not shown), and pure water flux of refreshed membrane. Operating pressure 0.05MPa and the concentration of oil in water emulsion was 5000ppm. Right: the changes of DR and FRR for different cycles. 579x202mm (150 x 150 DPI)



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Left: time-dependent flux and rejection of SSHF-MF1 in SA filtration process. Each cycle contains four steps: pure water flux of fresh membrane, SA solution separation, water cleaning for 30min (not shown), and pure water flux of refreshed membrane. Operating pressure 0.1MPa and the concentration of SA solution was 300ppm. Right: the changes of DR and FRR for different cycles. 579x202mm (150 x 150 DPI)


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Left: time-dependent flux and rejection of SSHF-MF1 in BSA filtration process. Each cycle contains four steps: pure water flux of fresh membrane, BSA solution separation, 5‰ NaOH solution cleaning for 30min (not shown), and pure water flux of refreshed membrane. Operating pressure 0.1MPa and the concentration of BSA solution was 300ppm. Right: The changes of DR and FRR for different cycles. 579x202mm (150 x 150 DPI)



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Figure.11 Time-dependent flux and rejection of SSHF-MF1 in BSA long-term filtration process. Insert image represents the variation of flux and rejection in the first 6 hours. 289x202mm (150 x 150 DPI)


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Facile Fabrication and Application of Superhydrophilic Stainless Steel

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