Improving pressure durability and fractionation property via reinforced PES loose nanofiltration hollow fiber membranes for textile wastewater treatment

ARTICLE IN PRESS

JID: JTICE

[m5G;January 7, 2020;22:26]

Journal of the Taiwan Institute of Chemical Engineers xxx (xxxx) xxx

Contents lists available at ScienceDirect

Journal of the Taiwan Institute of Chemical Engineers journal homepage: www.elsevier.com/locate/jtice

Improving pressure durability and fractionation property via reinforced PES loose nanofiltration hollow fiber membranes for textile wastewater treatment Zhiyong Chu a, Kaikai Chen a,b, Changfa Xiao a,b,∗, Dawei Ji a, Haoyang Ling b, Muyang Li b, Hailiang Liu b a

School of Textiles Science and Engineering, and State Key Laboratory of Separation Membranes and Membrane Processes, Tiangong University, Tianjin 300387, China b National Center for International Joint Research on Separation Membranes, Tiangong University, Tianjin 300387, China

a r t i c l e

i n f o

Article history: Received 1 August 2019 Revised 19 November 2019 Accepted 18 December 2019 Available online xxx Keywords: Loose nanofiltration Twisted fiber bundle Hollow fiber membrane Permeation stability Textile wastewater treatment

a b s t r a c t Loose nanofiltration (NF) hollow fiber membranes with excellent dye rejection and high inorganic salt transmission are promising for textile wastewater treatment. Herein, a novel kind of reinforced PES loose NF hollow fiber membranes with robust twisted fiber bundle was fabricated by a facile dry-wet spinning process. The SEM results indicate that the favorable interfacial bonding layer was formed between the separation and supporting layer for the sake of endowing the membranes with high longitudinal strength and lateral pressure resistance. For one thing, the tensile strength of the PST membranes was up to 185.7 MPa, a considerably higher than FEP hollow fiber membrane prepared by melt spinning process (18.5 MPa). Moreover, the PST-1 membranes show almost no deformation, compared to sever deformation of FEP hollow fiber membrane after 100 h at high pressure operation. For another, the prepared PST membranes display stable pure water flux of 52.3 L·m−2 ·h−1 under 0.6 MPa. Specifically, the PST membranes exhibit excellent fractionation efficiency of dye/salt mixtures, along with high dye rejection of 99.9% and low salt rejection (<7%). These results indicate that the robust reinforced PES loose NF hollow fiber membranes with permeation stability have great potential application for practical textile wastewater treatment. © 2019 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

1. Introduction With the development of the world economy, the water resources are over exploited, wasted and polluted, causing a global water crisis [1–3]. The discharge of textile wastewater is one of the important causes of global water pollution. Moreover, the human health and environment would be damaged by a large amount of textile wastewater without being treated [4,5]. Generally, the textile wastewater contains various dyes and high content inorganic salt, which could be reused and recycled [6,7]. Therefore, how to fractionate dye/salt mixtures has attracted extensive attention worldwide. Nanofiltration (NF) is considered to be a process between ultrafiltration and reverse osmosis, and become a rapidly growing technology in membrane field [8–11]. NF can usually block the passage of small molecules and salt, ∗ Corresponding author at: School of Textiles Science and Engineering, and State Key Laboratory of Separation Membranes and Membrane Processes, Tiangong University, Tianjin 300387, China. E-mail address: [email protected] (C. Xiao).

allowing water molecules to pass smoothly due to the sieve effect and Donna exclusion effect [12–17]. Although NF membrane owns high rejection to dye and salt, it is difficult for high-efficient dye desalination to fractionate the dye/salt mixtures because of their similar size, so a relatively loose NF membrane is necessarily designed with high dye rejection and low salt rejection. In general, it is well-known that hollow fiber membranes are usually prepared by the traditional wet spinning process with the characteristics of nature technology and excellent membrane separation. However, these hollow fiber membranes accompanied by poor mechanical property with inferior permeation stability might be insufficient to satisfy the practical application. In fact, the membrane filaments were subjected to long-time high-pressure flow, then the high-speed water flow and frequent cleaning could cause great damage to the membrane and even break [18–20]. In our previous work, the novel hollow fiber NF membranes were successfully prepared with dense-loose structure by one-step non-solvent induced phase separation method without post treatment [21]. The optimized membrane showed a high dye rejection of 99.9% for treating the simulated textile wastewater, whereas

https://doi.org/10.1016/j.jtice.2019.12.009 1876-1070/© 2019 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

Please cite this article as: Z. Chu, K. Chen and C. Xiao et al., Improving pressure durability and fractionation property via reinforced PES loose nanofiltration hollow fiber membranes for textile wastewater treatment, Journal of the Taiwan Institute of Chemical Engineers, https://doi.org/10.1016/j.jtice.2019.12.009

JID: JTICE 2

ARTICLE IN PRESS

[m5G;January 7, 2020;22:26]

Z. Chu, K. Chen and C. Xiao et al. / Journal of the Taiwan Institute of Chemical Engineers xxx (xxxx) xxx

these kinds of membranes were easily broken and compacted, sequentially affected the permeation stability of membrane. Currently, introducing the supporting reinforcement is one of the methods to enhance the mechanical property of hollow fiber membranes with great permeation stability. A number of detailed review papers have been devoted to the preparation of reinforced hollow fiber membranes. Liu et al. [22] fabricated homogeneousreinforced polyvinyl choride (PVC) hollow fiber membranes consisting of coating layer and matrix via coating process; Fan et al. [23] reported homogeneous braid reinforced cellulose acetate (CA) hollow fibers which consisted of CA separation layer and CA hollow tubular braids; Liu et al. [24] developed a polyester (PET) threads reinforced Polyvinylidene Fluoride (PVDF) hollow fiber membrane. These reports showed the mechanical properties of the membrane were improved along with good permeability. Nevertheless, its lateral pressure resistance of hollow fiber membrane is still a challenge owing to the membrane being easily bent and compacted under high operating pressure. Hence, it is important to explore a novel kind of method to enhance the lateral pressure resistance, so as to ensure permeation stability of membrane. In our previous study [18], the twisted fiber bundle could be regard as a new type of supporting reinforcement, which could boost effectively the mechanical properties of the membrane in terms of longitudinal strength and lateral pressure resistance, compared to the first two fiber reinforcement. Traditionally, PET fibers could be widely used because of its low-cost, great mechanical property and thermal stability. According to the molecular structure of PET, it is well-known that, the degree of PET fiber expansion in water or its hygroscopicity are poor on account of high crystallinity and closely dense arrangement of molecular without hydrophilic group except for the terminal group. Besides, there is no specific dyeing group on the PET molecular chain resulting in poor dyeability. Herein, the robust PET twisted fiber bundle reinforced PES loose NF hollow fiber membranes were prepared by a facile dry-wet spinning process. The main objective of this study was the enhancement of permeation stability of the loose NF hollow fiber membranes with thin separation layer as well as high dye rejection and low salt rejection. Moreover, the surface and cross-section morphologies of the prepared loose NF hollow fiber membranes were observed by SEM and CSM. The mechanical properties and the separation performance of the prepared membranes were investigated in detail. This work would provide a new insight to design the structure of membrane and offer a facile method to fabricate loose NF hollow fiber membranes with high separation efficiency and long-term permeation stability for textile wastewater treatment. 2. Experimental section 2.1. Materials Polyethersulfone (PES Ultras on E6020P, Mw=58,0 0 0 g·mol−1 ) was provided by Tianjin Motian Membrane Engineering & Technology Co., Ltd. (Tianjin, China). N-dimethylacetamide (DMAc, ≥99.5%), Polyvinyl pyrrolidone (PVP, K-30), Polyethylene glycol (PEG, Mw = 400 g/mol), sodium chloride (NaCl) and sodium sulfate (Na2 SO4 ) were all purchased from Tianjin Yuyuan Technology Co. LTD. Polyester (PET) fibers (35 Tex) were obtained from Suzhou Zhaoda Specially Fiber Technical Co. Ltd. Congo red was bought from Tianjin No.9 Dyestuff Chemical Factory. 2.2. Membrane preparation 2.2.1. Preparation of PET twisted fiber bundle The PET twisted fiber bundle was prepared by twister. Firstly, the two bundles of PET fiber were twisted into a bundle of fibers

Table 1 The compositions of the PST membranes. Membrane code

PES (wt%)

PEG-400 (wt%)

PVP-K30 (wt%)

DMAc (wt%)

PST-0 PST-1 PST-2 PST-3

13 15 18 20

21 21 21 21

5 5 5 5

61 59 56 54

Table 2 Spinning parameters of PST membranes. Spinning conditions

Value

Spinning temperature (°C) Coagulation bath Coagulation temperature (°C) Air gap (mm) Take-up speed (m·min−1 )

70 ± 3 deionized water 15 ± 2 5 1.50 ± 0.05

in the “S” direction. Then, using the four bundles of preceding fiber to twist a bundle in the “Z” direction, would help PET fibers hold together better from “S” to “Z” (similar to natural tangles without real twist). The speed and the twist were 20 m·min−1 and 20 T·10 cm−1 through this process, respectively. 2.2.2. Preparation of the reinforced PES loose NF hollow fiber membranes The robust PET twisted fiber bundle reinforced PES loose NF hollow fiber membranes were prepared by a facile dry-wet process. Before the process, PES was dried in vacuum oven at 70 °C for 24 h. The dry-wet spinning process was shown in Fig. 1. The compositions of dope solution were shown in Table 1, and the four kinds of membranes with different PES content were named PST-0, PST-1, PST-2 and PST-3, respectively. The spinning parameters were shown in Table 2. In this process, the PET twisted fiber bundle was coated with PES dope solution and guided through a coagulation bath (100% water at 15 ± 2 °C), where the loose NF hollow fiber membranes were formed initially. Then the fresh membranes were stored in deionized water for more than 24 h to remove the solvent and other water-soluble additives. 2.3. Membrane characterization The viscosity of dope solution was tested by Haake Rheomix. The shear rate (γ ) was ranged from 0–10 0 0 s−1 at 25 °C. The surface characteristics in regard to the functional groups of PET fiber and the prepared membranes were observed by Fourier Transform-Infrared Spectroscopy (FTIR, Thermo Fisher Scientific, Nicolet IS50). The surface zeta potentials of the prepared membranes were tested by electrokinetic analyzer (SurPASS 3, Anton Paar, Austria) at different pH values. The morphologies of the prepared membranes were characterized by scanning electron microscope (SEM, Hitachi S-4800, Japan), confocal scanning microscopy (CSM, Zeiss CSM700, Germany) and atomic force microscopy (AFM, Agilent S5500, USA). To prepare the samples for measurements, the samples were all freeze dried for about 12 h. Then they were sputter-coated with gold before SEM analysis In order to evaluate pore size distribution of membrane, the pore size of the optimal membrane was analyzed by N2 adsorption-desorption isotherms curves via density function theory (DFT) method by a fully automatic absorption apparatus (Autosob-iQ-C, Quantachrome, USA). The molecular weight cut off (MWCO) of the membrane was conducted by filtrating a series of polyethylene glycols (PEGs) with average molecular weight of 20 0 0, 40 0 0, 60 0 0, 80 0 0 and 10,0 0 0 Da at a concentration of 0.1 g·L−1 and 0.6 MPa. The

Please cite this article as: Z. Chu, K. Chen and C. Xiao et al., Improving pressure durability and fractionation property via reinforced PES loose nanofiltration hollow fiber membranes for textile wastewater treatment, Journal of the Taiwan Institute of Chemical Engineers, https://doi.org/10.1016/j.jtice.2019.12.009

ARTICLE IN PRESS

JID: JTICE

[m5G;January 7, 2020;22:26]

Z. Chu, K. Chen and C. Xiao et al. / Journal of the Taiwan Institute of Chemical Engineers xxx (xxxx) xxx

3

Fig. 1. Schematic of the PST loose NF hollow fiber membrane fabrication process.

concentration of PEGs was measured by the total organic carbon (TOC). The MWCO of membrane has been defined as the molecular weight of PEG which has 90% rejection rate, and the mean effective pore size (μp ) has been defined as the Stokes radius (ds ) of a neutral solute at 50% rejection rate. The Stokes radius of PEG could be calculated on the basis of its average molecular weight: .557 ds = 16.73 × 10−12 × M0PEG

(1)

The relationship between pore size distribution and solute Stokes radius was mathematically fitted by an exponential probability density function on the hypothesis that there are no hydrodynamic and electrostatic interactions between neutral solutes and membrane pores.



 dR(r p ) (ln r p − ln μ p )2 1 = exp − √ 2 dr p r p ln σ p 2π 2(ln σ p )

(2)

where rp is the pore radius and μp is the mean effective pore size, and σ p is the geometric standard deviation, which is the ratio of rp at 84.13% rejection rate over that at 50%. The static water contact angles (WCAs) of the prepared membranes were measured by water contact angle instrument (DCAT11, Dataphysics, Germany) at room temperature. The samples were all dried in the air. The mechanical properties of the prepared membranes were measured by electronic single yarn tensile tester (YG061, China) with the tensile rate of 10 mm·min−1 at room temperature. 2.4. Membrane filtration measurements The filtration performances of the loose NF hollow fiber membranes were measured by a cross-flow permeation apparatus at an effective membrane area of 12.56 cm2 . All test temperature was at 20 ± 2 °C. Pure water flux was measured at different pressure from 0.2 to 1.0 MPa. The Fig. S1 displays the schematic of filtration process and concentration testing devices. In the preliminary test, the filtration experiments were first carried out with a single-component salt (NaCl) and dye (Congo red) at various concentrations under 0.6 MPa, respectively. Then the fractionation of dye/salt mixtures was used by Congo red (0.1 g·L−1 ) and salt (1.0 g·L−1 ) as feed solution under various operating pressure (from

0.2 to 1.0 MPa). Subsequently, the optimal membrane was selected for the next filtration experiment based on the previous experimental results. Under circumstance of various concentrations of dye/NaCl mixtures and operating pressures, the fractionation of dye/NaCl mixtures was implemented to evaluate the optimal membrane filtration properties. In addition, the long-term stability of the membrane was also tested under 0.6 MPa. After fractionation of dye/NaCl mixtures, the fouled membrane was cleaned by flowing deionized water for 60 min after every 180 min operating measurement. The water flux (J) and rejection (R) were calculated through the following Eq. (3) and Eq. (4):

J=

V A×t

(3)

Where J is the water flux (L·m−2 ·h−1 ). V is the volume of permeate water (L). A is the effective area (m2 ) of the membrane and t is the operating time (h).

R=

C f − Cp × 100% Cf

(4)

Where Cf is the concentration of feed solution and where Cp is the concentration of permeate solution. The concentrations of dye and salt solution were obtained by UV–Vis spectrophotometer and conductivity meter, respectively. The flux recovery ratio (FRR) was calculated using the following Eq. (5):

F RR =

Jr × 100% Ji

(5)

Where Ji is the initial permeate water flux, the Jr is the permeate water flux after being cleaned by flowing deionized water. 3. Results and discussion 3.1. Surface characteristic Viscosity is the resistance of a fluid to flow which determines the diffusion rate of dope solution and the membrane formation. Fig. 2a and b depicts the change of shear stress and apparent viscosity with an increasing shear rate. As the shear rate increases, it’s

Please cite this article as: Z. Chu, K. Chen and C. Xiao et al., Improving pressure durability and fractionation property via reinforced PES loose nanofiltration hollow fiber membranes for textile wastewater treatment, Journal of the Taiwan Institute of Chemical Engineers, https://doi.org/10.1016/j.jtice.2019.12.009

JID: JTICE 4

ARTICLE IN PRESS

[m5G;January 7, 2020;22:26]

Z. Chu, K. Chen and C. Xiao et al. / Journal of the Taiwan Institute of Chemical Engineers xxx (xxxx) xxx

Fig. 2. Shear stress (a) and viscosity (b) as a function of shear rate with different PES content, FTIR spectrum of the prepared membranes (c), zeta potential of the PES membrane (d).

found that the shear stress of dope solution increased, and the viscosity dropped down. It is worth noting that PST-0 and PST-1 dope solution exhibited no obvious change in viscosity with an increasing shear rate. In general, a Newtonian fluid is a fluid in which the shear stress arising from its flow are linearly proportional to the shear rate [25,26]. According to above results, it could be believed that the PST-0 and PST-1 dope solution is almost a Newtonian fluid, and the others are non-Newtonian pseudoplastic fluids. As the PES content increases, it was difficult for the relative slip of polymer molecular chains with more polymers, which hindered the movement of molecular chains, causing the increase of solution viscosity in the macroscopic view [27]. Certainly, the solution viscosity would affect deeply on the morphologies and interfacial bonding layer, so as to decide the permeation stability of PST membrane. In order to observe the surface structure of the prepared membranes and PET fibers, the FTIR measurements were carried out. As shown in Fig. 2c, the absorption peak at 1711 cm−1 is assigned to the stretching vibration of C=O in ester groups, which is a typical characteristic absorption peak of PET [28]. The absorption peaks located at 1236 cm−1 and 1146 cm−1 are observed from the surface of the prepared membranes, which are attributed to asymmetric and symmetric the S=O stretching vibration of PES characteristic absorption peak, respectively [29]. Also, the Fig. S3 shows that the surface of the membrane is smooth and the fibers are not visible on the outer surface. The results reveal that the PET fibers of supporting layer were completely wrapped by the PES separation layer, avoiding the formation of macropores and flaw on the membrane surface. The surface potential of the PST membrane was investigated by the zeta potential measurement. Fig. 2d shows the surface zeta potential of the prepared membrane under various pH values from 3 to 10. It could be seen that the surface potential of the

membrane increased with the decreasing pH and kept a negative potential, which are consistent with previous work [30–32]. Especially, it would facilitate dye separation process on account of the electrostatic repulsion between the membrane surface and negatively charged dyes [33,34]. 3.2. Membrane morphology and structure The cross-section morphologies of the PST membranes are shown in Fig. 3. As could be seen, the cross-section structure of all PST membranes is composed of the PES separation layer, the interfacial bonding layer and the PET twisted fiber bundle reinforced supporting layer. Obviously, with an increasing content in the dope solutions, the cross-section structures were changed from large and short pores to narrow and long finger-like pores. Due to the penetration of the PES dope solution, the introduction of twisted fiber bundle into axis of hollow fiber membrane allowed forming a special interfacial bonding layer between the separation layer and the supporting layer on account of using fiber bundle compared to other membrane substrate or tubular braid. Under lower PES content, it is easy to find hole flaws at the interfacial joint, and the interfacial bonding layer became thicker. Besides, the interfacial bonding layer was combined better as the PES content increased. Moreover, the sponge skin layers became thicker and denser from 0.56 to 3.01 μm with an increasing PES content in Fig. 3 a3–d3. The results could be attributed to the kinetic mechanism and diffusion rate between solvent and non-solvent with the increasing viscosity of PES dope solution. Based on the kinetic mechanism in case of low viscosity, the diffusion rate between solvent and nonsolvent would slow down, which delayed the speed of instantaneous phase separation, resulting in finger-like pores and thicker outer layer [29]. Also, the membrane structure diagram and morphologies of hollow fiber membrane are showed in Fig. S2. The

Please cite this article as: Z. Chu, K. Chen and C. Xiao et al., Improving pressure durability and fractionation property via reinforced PES loose nanofiltration hollow fiber membranes for textile wastewater treatment, Journal of the Taiwan Institute of Chemical Engineers, https://doi.org/10.1016/j.jtice.2019.12.009

JID: JTICE

ARTICLE IN PRESS

[m5G;January 7, 2020;22:26]

Z. Chu, K. Chen and C. Xiao et al. / Journal of the Taiwan Institute of Chemical Engineers xxx (xxxx) xxx

5

Fig. 3. SEM images of cross-section morphology of the PST membranes. (a PST-0; b PST-1; c PST-2; d PST-3; 1 full morphology; 2–3 partial enlargement morphologies).

advantages of introducing twisted fiber bundle into membrane include possibility to enhance the mechanical properties of the PST membranes in terms of longitude strength and lateral pressure resistance without significantly altering the nature, pore structure, and charge of membrane. The dope solution solidifies into membrane on the surface of the twisted fiber bundle which is mainly as a support, and there is only a physical combination between them. It does not change the chemical character and surface properties of the PST membranes with less impact on the membrane pore structure except for low PES concentration, which was easy to form hole flaws (see Fig. 3a). Meanwhile, the interspace between the PET fibers could provide permeate water channels for stable permeability. In order to further investigate the surface change of the PST membranes, SEM, CSM and AFM outer surface morphologies of the prepared membranes are observed in Fig. 4. As shown in Fig. 4A, it is quite clear that the surface of the membrane is rough with many wrinkles and humps, especially in low content. Meanwhile, the membranes become smoother with an increasing PES content. Similarly, the 3D morphologies and Ra value were investigated by CSM so as to show the surface changes of the PST membranes. As shown in Fig. 4B, the CSM images presents arched 3D

morphologies with similar color. The color changes gradually deepened from the sides to the top of the arch without significant difference. It reveals that the twisted fiber bundle was completely wrapped inside the membrane. In addition, the uniform distribution of color on the surface illustrates that the membrane surface is smooth without clear flaw. As the Ra tested, the Ra of the membrane surface (PST-0 to PST-3) are 0.474, 0.415, 0.358, 0.242 μm, respectively. Compared with the CSM, the AFM has higher resolution and the measured membrane surface morphologies are more precise. In the AFM images (see Fig. 4C), the membrane surfaces are observed more clearly (area: 5 × 5 μm) and the PST membranes has a decreased Ra roughness from 16.1 to 5.6 nm with the increase of PES content. In short, the results of CSM and AFM indicate that the surface roughness of the membrane decreased as the PES content increased, and the membrane surfaces do not have obvious flaw. These results are consistent with the observation of SEM morphologies. The PST-3 membrane displays smoother and denser outer surface. These phenomena might be due to the similar aforementioned reasons: the PES content had effects on the viscosity of the dope solution, which further affected the diffusion rate between the solvent and non-solvent during the phase separation process.

Please cite this article as: Z. Chu, K. Chen and C. Xiao et al., Improving pressure durability and fractionation property via reinforced PES loose nanofiltration hollow fiber membranes for textile wastewater treatment, Journal of the Taiwan Institute of Chemical Engineers, https://doi.org/10.1016/j.jtice.2019.12.009

JID: JTICE 6

ARTICLE IN PRESS

[m5G;January 7, 2020;22:26]

Z. Chu, K. Chen and C. Xiao et al. / Journal of the Taiwan Institute of Chemical Engineers xxx (xxxx) xxx

Fig. 4. SEM (A), CSM (B) and AFM (C) of outer surface morphology of the PST membranes. (a PST-0; b PST-1; c PST-2; d PST-3).

Fig. 5. DFT pore size distribution of the PST-1 membrane (a). WCAs of the PST membrane samples (b). Pure water flux of the PST membranes under different operating pressure (c).

3.3. Pore size distribution and water permeability It is well-known that pore-size distribution could decide the key performance indicators of selectivity and permeability of membrane. In order to further illustrate the dense-loose NF structure, the pore size distribution of PST-1 membrane was measured by N2 adsorption-desorption isotherms curves via DFT method. As shown in Fig. 5a, the curve exhibits many pore size peaks ranged from 1.3 to 38.1 nm. The small pore size of 1–3 nm is belonging to the dense outer membrane surface as shown in Fig. 4A, whereas the larger pore size is attributed to the inner surface pores of the cross-section. These kinds of pore structure and pore size distribution were consistent with the dense-loose structure. Furthermore, Fig. S4 shows that the MWCO of the PST-1 membrane is 9353 Da and mean effective pore size is 1.702 nm, respectively, which suggests the PST-1 membrane is a loose nanofiltration. Moreover, the relatively dense-loose structure is necessarily designed with high dye rejection and low salt rejection [35,36]. The great surface wettability of membrane is beneficial to boost the water permeation and reduce the membrane fouling due to the hydration layer by hydrogen bonds between the water molecules and membrane surface. But simultaneously, it is also affected by surface structure of membrane. The static WCAs of the prepared

membranes are shown in Fig. 5b. The WCAs of the prepared membranes increases slightly in the order of PST-0 < PST-1 < PST-2 < PST-3. This increasing WCAs are possibly caused by the surface structure of membranes. The wettability of membrane surface could be related to its roughness which the rougher hydrophilic surface has greater wettability to water leading to lower WCAs [37–39]. According to the aforementioned results (Fig. 4), the membrane surface was smoother with increasing PES content which posed the higher WCAs. The pure water fluxes of the prepared membranes were also measured. As shown in Fig. 5c, the pure water fluxes are 254.6, 63.0, 59.4, 7.3 L·m−2 ·h−1 under 0.6 MPa from PST-0 to PST-3, respectively. In general, the commercial and other reported hollow fiber membrane could be squashed when the external pressure operation was up to 0.8 MPa [24,40]. In this study, it could be found that the pure water flux of PST membranes kept increasing as the operating pressure increased. Noticeably, the presence of the PET twisted fiber bundle supporting layer enhanced the pressure resistance of the hollow fiber membrane, so as to bring the permeation stability. Furthermore, the pure water flux with the lowest content (PST-0) increased the most, while the water flux of the highest content (PST-3) raised slightly. It is mainly due to the formation of many micropores which facilitated passage of water

Please cite this article as: Z. Chu, K. Chen and C. Xiao et al., Improving pressure durability and fractionation property via reinforced PES loose nanofiltration hollow fiber membranes for textile wastewater treatment, Journal of the Taiwan Institute of Chemical Engineers, https://doi.org/10.1016/j.jtice.2019.12.009

JID: JTICE

ARTICLE IN PRESS

[m5G;January 7, 2020;22:26]

Z. Chu, K. Chen and C. Xiao et al. / Journal of the Taiwan Institute of Chemical Engineers xxx (xxxx) xxx

7

Fig. 6. The mechanical performance of the prepared membranes (a, b). Cross section morphologies of membrane: FEP hollow fiber membrane before operation (c), FEP hollow fiber membrane after operation (d), PST-1 membrane after operation (e). Operating condition: deionized water at 20 °C and 0.6 MPa for 100 h.

molecules, but the thicker and denser spongy layer would block the smooth passage of water molecules [41,42]. The results are consistent with the morphology and structure of the membranes aforementioned. 3.4. Mechanical properties of the PST membranes In general, the service life of membrane can be usually decided by its mechanical properties. Fig. 6a depicts that the tensile strength increased from 140.4 MPa for PST-0 membrane to 185.7 MPa for PST-3 membrane, and the breaking elongation increased with the increasing PES content. Generally, the hollow fiber membrane by NIPS method exhibits poor mechanical properties [43,44], while the hollow fiber membrane by melt spinning process possess of good mechanical properties. Therefore, the fluorinated ethylene-propylene (FEP) hollow fiber membrane that prepared by melt spinning process was utilized to as a comparison sample. The Fig. 6b shows that the FEP hollow fiber membrane showed lower tensile strength (18.5 MPa) than the PST membranes [45]. The mainly reason for these results is due to the wrapped PET twisted fiber bundle by PES separation layer. In fact, the separation layer of the PST membranes had first break prior to the PET fiber, losing its efficacy before final effect [23]. The variation trend of mechanical performances for the prepared membranes is attributed to the penetration of the dope solution. This penetration was mainly depended on solution viscosity and DMAc concentration. Lower PES content dope solution with high concentration of DMAc had lower viscosity and were more permeable into the PET fiber bundle, which might affect the structure of PET and bring about the reduced tensile strength of the membranes. Moreover, from the observation in Fig. 6c,d, FEP hollow fiber membrane produced sever deformation on account of the creation of defects after 100 h operation at 0.6 MPa. However, the PST-1 membrane shows almost no deformation at the same condition (Fig. 6e). Consequently, it illustrates that introducing PET twisted fiber bundle enhanced the longitudinal strength and lateral pressure in favor of long-term permeation stability. Next, the prepared membranes needed to be deeply assessed by filtration performance and longterm permeation stability measurement so as to demonstrate the advantages of introducing PET twisted fiber bundle as reinforced supporting layer.

3.5. Filtration performance of the PST membranes 3.5.1. Filtration of salt and dye solutions Removal of dye from dye/salt mixture solutions for dye desalination in the textile industry is an important application for loose NF membrane. The filtration performances of the PET twisted fiber bundle reinforced PES loose NF hollow fiber membranes for pure salt or dye as a function of concentration were investigated. As shown in Fig. 7a, the water flux of PST-0 membrane dramatically decreases and others slightly reduce with the increasing Congo red concentration under 0.6 MPa. The membranes possess of higher rejection of Congo red in higher dye concentration except for the PST-0 membrane. On the one hand, the sponge skin layer (dense skin) of the PST membranes were thicker (see Fig. 3) and the interconnectivity between the pores decreased as the concentration of the PES polymer increased, which led to an increase in the blockage of water molecules through the membrane. On the other hand, the more dye molecules accumulated on the membrane surface would form a cake layer causing concentration during the filtration, and it would strengthen the filtration resistance of dyes and weak driving force of the water permeation. Furthermore, the Fig. 7b displays the water flux and salt rejection with the increasing NaCl concentration under 0.6 MPa. It could be observed that water permeation flux has no obvious decrease in higher content, but the rejection of NaCl decreases to less than 3%, and even the salt was almost completely through the membrane. This is because large pore size of the loose NF hollow membrane could destroy the electrostatic repulsion force between the membrane surface and ions, and an increasing salt concentration suppressed the Debye screening length, which is beneficial to the penetration of the salt [46]. Therefore, the low rejection of salt and high dye rejection are conductive to the fractionation of dye/salt mixtures with a stable water permeation. 3.5.2. Filtration performance at different operating pressures 3.5.2.1. Effect of the PES concentration at different operating pressures. The fractionations of Congo red and NaCl mixtures were carried out under various operating pressure, and the filtration behaviors of the PST membranes are shown in Fig. 8. Obviously, with increasing operating pressure at lower PES content, the water flux increases markedly, whereas the membrane has low rejection

Please cite this article as: Z. Chu, K. Chen and C. Xiao et al., Improving pressure durability and fractionation property via reinforced PES loose nanofiltration hollow fiber membranes for textile wastewater treatment, Journal of the Taiwan Institute of Chemical Engineers, https://doi.org/10.1016/j.jtice.2019.12.009

JID: JTICE 8

ARTICLE IN PRESS

[m5G;January 7, 2020;22:26]

Z. Chu, K. Chen and C. Xiao et al. / Journal of the Taiwan Institute of Chemical Engineers xxx (xxxx) xxx

Fig. 7. Filtration of salt and dye solution for the PST membranes. Effect of Congo red concentration (a); Effect of NaCl concentration (b).

Fig. 8. Permeation water flux (a) and rejection (b) of the PST membranes for the stimulated textile wastewater (Congo red:0.1 g·L−1 , NaCl: 1 g·L−1 ) at various operating pressures.

(48%) of Congo red along with comparatively low rejection of NaCl. Others exhibit lower water flux with high dye rejection and low salt rejection. These results are attributed to the following reasons. Firstly, the larger pores of the membrane could contribute to the passage of water molecules, and the salt and a very small amount of dye molecule were also transmitted through the membrane. Secondly, an increasing operating pressure promoted the flow rate of water molecule, however, the concentration polarization was enhanced which weakened the separation effect of dye/salt mixture solution. Besides, the size effect and Donnan exclusion of membrane plays important role in the rejection of dye (shown in Fig. S5). As mentioned above, the small pore size of 1–3 nm is endowed to the membrane with dense outer surface, which shows a fine size effect for the dye. At the same time, the effective Donna exclusion is kept with great zeta potential between the outer surface and the mixture solution. Combined with aforementioned results of fractionation of dye/NaCl mixture solution, an operating pressure of 0.6 MPa and PES content of 15% (PST-1)

were considered as the preferential parameters for the following filtration measurements. 3.5.2.2. Effect of dye and salt concentrations at different operating pressures. As mentioned above, the membrane filtration performance could be affected deeply by dye and salt concentrations when operating in practical textile wastewater treatment [47,48]. The filtration measurements for the PST-1 membranes were chose to be tested with different concentrations of dye and salt under various pressure via aforementioned results. Firstly, the Congo red concentration was changed from 0.1 to 1 g·L−1 with the constant NaCl concentration of 1 g·L−1 in the stimulated textile wastewater. As shown in Fig. 9a, the increasing Congo red concentration poses that the water flux of dye/ NaCl mixture solution for membrane declines, and the Congo red rejection slightly increases with the stable salt rejection. This is mainly due to the increasing osmotic pressure difference between the inside and outside of the loose NF hollow fiber membranes, which weakened the driving force

Please cite this article as: Z. Chu, K. Chen and C. Xiao et al., Improving pressure durability and fractionation property via reinforced PES loose nanofiltration hollow fiber membranes for textile wastewater treatment, Journal of the Taiwan Institute of Chemical Engineers, https://doi.org/10.1016/j.jtice.2019.12.009

JID: JTICE

ARTICLE IN PRESS

[m5G;January 7, 2020;22:26]

Z. Chu, K. Chen and C. Xiao et al. / Journal of the Taiwan Institute of Chemical Engineers xxx (xxxx) xxx

9

Fig. 9. Filtration performance of the PST-1 membranes at various operating pressure. Effect of Congo red concentration (1 g·L−1 NaCl) (a), effect of salt concentration (0.1 g·L−1 Congo red) (b).

for water permeation under higher dye concentration, leading to a decreasing water flux. Meanwhile, the aggregated dye molecules could expand their effective size and destroy themselves diffusion coefficient for enhancing the dye rejection of the membrane [6]. Moreover, the higher water fluxes of the prepared membranes were obtained with an increasing in operating pressure, and the Congo red rejection declined. It could be attributed to the aggregation behavior of Congo red on the membrane surface leading to membrane fouling and concentration polarization, which reduced water fluxes and Congo red rejection [49,50]. Then, the NaCl concentration was changed from 1 to 10 g·L−1 with the constant Congo red concentration of 0.1 g·L−1 in the stimulated textile wastewater. As shown in Fig. 9b, the water flux and rejection of the loose NF hollow fiber membranes in the Congo red/NaCl mixtures both decreases with the increase of NaCl concentration. As the operating pressure increased, an increasing water flux was obtained, whereas the rejection of Congo red had no obvious change. It’s because of the formation of cake layer on the membrane surface which was against the back diffusion of salt, facilitating the concentration polarization. Therefore, the enhanced osmotic pressure undermined the driving force for permeation water resulting in the lower water flux. In general, the surface charge of the membrane might be affected by the salt which is unfavorable for fractionation of dye/salt mixtures. The aggregation of dye on the membrane surface might enlarge dye size and inhibit the dye through membrane. However, the existed screen effect during the filtration process could play negative influences on the rejection of dye. On the one hand, the sodium ions in the salt were neutralized by the negative charge on the surface of the membrane, which reduced the surface free charge and made the dye more permeable [51,52]. On the other hand, the presence of high salt concentration allowed the dye to be more evenly distributed with increasing deposition of dye into the membrane pores for reducing membrane permeability [53]. Besides, the flow rate of water might be increased by higher operating pressure to dilute the solute in the permeation solution for relieving previous

negative effects. Furthermore, the Fig. S6 shows that the PST-1 membranes keep high rejection of Congo red with low rejection of Na2 SO4 . All in all, the filtration performances at different operating pressures were in order to achieve the optimal operating pressure. Especially, the objective of designing PST membranes is also breaking the limit of operation pressure to improve operating efficiency, thereby saving time and reducing costs in practical textile wastewater treatment. 3.5.3. Permeation stability The permeation stabilities of the PST membranes for dye desalination of stimulated Congo red/NaCl mixture solution as functions of operating time are displayed in Fig. 10a. It could be observed that the water flux shows a slight degradation from 65.5 to 52.3 L·m−2 ·h−1 with increasing dye rejection from 90.3 to 99.9%, along with a stable NaCl rejection (<7%). It’s due to the compacting of the membrane pores and membrane fouling. The aggregation of dye with larger size and cake layer might be beneficial to the rejection of dye [54]. Moreover, the antifouling properties of the prepared membranes were also measured. During this process, the fouled membrane was cleaned by flowing deionized water for 60 min after 180 min operation. Fig. 10b shows that the membrane was endowed with high flux recovery of 97% and 95% after two cycles. Meanwhile, it is particularly gratifying that the membrane kept high Congo red rejection and low NaCl rejection. These results illustrate that the membranes are endowed with excellent longterm permeation stability and antifouling property. Furthermore, the comparative filtration performance of the PST-1 membrane with other reported membranes was summarized in Table S1-2. The prepared PST-1 membranes exhibit higher water flux, excellent dye rejection, lower salt rejection, long-term stability and antifouling property as well as great mechanical performance. This indicates that the PST membranes with permeation stability exhibits great potential for the practical application in textile wastewater treatment.

Please cite this article as: Z. Chu, K. Chen and C. Xiao et al., Improving pressure durability and fractionation property via reinforced PES loose nanofiltration hollow fiber membranes for textile wastewater treatment, Journal of the Taiwan Institute of Chemical Engineers, https://doi.org/10.1016/j.jtice.2019.12.009

ARTICLE IN PRESS

JID: JTICE 10

[m5G;January 7, 2020;22:26]

Z. Chu, K. Chen and C. Xiao et al. / Journal of the Taiwan Institute of Chemical Engineers xxx (xxxx) xxx

Fig. 10. Long-term stability of the PST-1 membrane for the application of textile wastewater treatment (a). Anti-fouling and recycling properties of the PST-1 membrane (b).

4. Conclusions

References

In this work, PET twisted fiber bundle reinforced PES loose NF hollow fiber membranes was prepared by a facile dry-wet spinning process. The surface analysis illustrate that the PES had completely wrapped PET twisted fiber bundle with the dense-loose structure. Besides, the cross-section morphologies of PST membranes show favorable interfacial bonding between the PES separation layer and PET twisted fiber bundle supporting layer. The mechanical properties of the PST membranes were up to 185.7 MPa due to the introducing PET twisted fiber bundle and the formation of reinforcement structure. Furthermore, the membranes exhibit almost no deformation compared to FEP hollow fiber membrane, which indicates that better pressure resistance was obtained through introduction of the PET twisted fiber bundle supporting layer. Especially, the PST-1 membrane in this work shows relatively high pure water flux of 63 L·m−2 ·h−1 under 0.6 MPa, high rejection for dye (above 99%) and lower rejection for salt (almost complete permeation). The PST-1 hollow fiber loose NF membrane shows high fractionation efficiency for dye/salt mixture solution with high rejection for dye (stable rejection 99%), low rejection for salt (<7%) and high permeate flux (52.3 L·m−2 ·h−1 ). Also, there are excellent longterm permeation stability and antifouling property with over 96% flux recovery ratio. Therefore, these kinds of reinforced loose NF hollow fiber membranes provide a superior idea to realize stable and high-efficient dye desalination, which breaks the limit of operation pressure to improve operating efficiency, thereby saving time and reducing costs in practical application. In a word, the robust twisted fiber bundle reinforced PES loose NF hollow fiber membranes with permeation stability have great potential application for practical textile wastewater treatment.

[1] Vorosmarty CJ, McIntyre PB, Gessner MO, Dudgeon D, Prusevich A, Green P, Glidden S, Bunn SE, Sullivan CA, Liermann CR, Davies PM. Global threats to human water security and river biodiversity. Nature 2010;468:334. [2] Gleick PH. Water in crisis: paths to sustainable water use. Ecol Appl 1998;8:571–9. [3] Srinivasan V, Lambin EF, Gorelick SM, Thompson BH, Rozelle S. The nature and causes of the global water crisis: syndromes from a meta-analysis of coupled human-water studies. Water Resour Res 2012;48:1–16. [4] Zhou L, Zhou HJ. Evaluation of textile industry wastewater treatment and reuse in China. Desalin Water Treat 2019;144:330–8. [5] Tavangar T, Jalali K, Shahmirzadi MAA, Karimi M. Toward real textile wastewater treatment: membrane fouling control and effective fractionation of dyes/inorganic salts using a hybrid electrocoagulation - Nanofiltration process. Sep Purif Technol 2019;216:115–25. [6] Van der Bruggen B, Daems B, Wilms D, Vandecasteele C. Mechanisms of retention and flux decline for the nanofiltration of dye baths from the textile industry. Sep Purif Technol 2001;22-3:519–28. [7] Koyuncu I, Topacik D, Yuksel E. Reuse of reactive dyehouse wastewater by nanofiltration: process water quality and economical implications. Sep Purif Technol 2004;36:77–85. [8] Anand A, Unnikrishnan B, Mao JY, Lin HJ, Huang CC. Graphene-based nanofiltration nanofiltration membranes for improving salt rejection, water flux and antifouling-A review. Desalination 2018;429:119–33. [9] Lv Y, Du Y, Chen ZX, Qiu WZ, Xu ZK. Nanocomposite membranes of polydopamine/electropositive nanoparticles/polyethyleneimine for nanofiltration. J Membr Sci 2018;545:99–106. [10] Abdel-Fatah MA. Nanofiltration systems and applications in wastewater treatment: review article. Ain Shams Eng J 2018;9:3077–92. [11] Arki P, Hecker C, Tomandl G, Joseph Y. Streaming potential properties of ceramic nanofiltration membranes - Importance of surface charge on the ion rejection. Sep Purif Technol 2019;212:660–9. [12] Van der Bruggen B, Schaep J, Wilms D, Vandecasteele C. Influence of molecular size, polarity and charge on the retention of organic molecules by nanofiltration. J Membr Sci 1999;156:29–41. [13] Oatley-Radcliffe DL, Walters M, Ainscough TJ, Williams PM, Mohammad AW, Hilal N. Nanofiltration membranes and processes: a review of research trends over the past decade. J Water Process Eng 2017;19:164–71. [14] Schafer AI, Waite TD, Fane AG. Nanofiltration-principles and applications. Elsevier, Oxford; 2005. p. 121–2. [15] Chakraborty S, Purkait MK, DasGupta S, De S, Basu JK. Nanofiltration of textile plant effluent for color removal and reduction in COD. Sep Purif Technol 2003;31:141–51. [16] Ye WY, Liu HW, Lin F, Lin JY, Zhao SF, Yang SS, Hou JW, Zhou SG, Van der Bruggen B. High-flux nanofiltration membranes tailored by bio-inspired co-deposition of hydrophilic g-C3 N4 nanosheets for enhanced selectivity towards organics and salts. Environ Sci: Nano 2019;6:2958–67. [17] Ye WY, Lin JY, Borreg R, Chen D, Sotto A, Luis P, Liu MH, Zhao SF, Tang CY, Van der Bruggen B. Advanced desalination of dye/NaCl mixtures by a loose nanofiltration membrane for digital ink-jet printing. Sep Purif Technol 2018;197:27–35. [18] Chen KK, Xiao CF, Liu HL, Ling HY, Chu ZY, Hu ZH. Design of robust twisted fiber bundle-reinforced cellulose triacetate hollow fiber reverse osmosis membrane with thin separation layer for seawater desalination. J Membr Sci 2019;578:1–9. [19] Chou SR, Wang R, Fane AG. Robust and high performance hollow fiber membranes for energy harvesting from salinity gradients by pressure retarded osmosis. J Membr Sci 2013;448:44–54. [20] Zhang XL, Xiao CF, Hu XY, Bai QQ. Preparation and properties of homogeneous-reinforced polyvinylidene fluoride hollow fiber membrane. Appl Surf Sci 2013;264:801–10.

Declaration of Competing Interest The authors declare no conflict of interest. Acknowledgments This work was supported by the National Natural Science Foundation of China (51673149, 51603146), and the Science and Technology Plans of Tianjin (No. 18PTSYJC00170). Supplementary materials Supplementary material associated with this article can be found, in the online version, at doi:10.1016/j.jtice.2019.12.009.

Please cite this article as: Z. Chu, K. Chen and C. Xiao et al., Improving pressure durability and fractionation property via reinforced PES loose nanofiltration hollow fiber membranes for textile wastewater treatment, Journal of the Taiwan Institute of Chemical Engineers, https://doi.org/10.1016/j.jtice.2019.12.009

JID: JTICE

ARTICLE IN PRESS Z. Chu, K. Chen and C. Xiao et al. / Journal of the Taiwan Institute of Chemical Engineers xxx (xxxx) xxx

[21] Ji DW, Xiao CF, An SL, Zhao J, Hao JQ, Chen KK. Preparation of high-flux psf/go loose nanofiltration hollow fiber membranes with dense-loose structure for treating textile wastewater. Chem Eng J 2019;363:33–42. [22] Liu HL, Xiao CF, Huang QL, Hu XY. Structure design and performance study on homogeneous-reinforced polyvinyl chloride hollow fiber membranes. Desalination 2013;331:35–45. [23] Fan ZW, Xiao CF, Liu HL, Huang QL. Preparation and performance of homogeneous braid reinforced cellulose acetate hollow fiber membranes. Cellulose 2015;22:695–707. [24] Liu J, Li PL, Li YD, Xie LX, Wang SC, Wang Z. Preparation of PET threads reinforced PVDF hollow fiber membrane. Desalination 2009;249:453–7. [25] Panton RL, Andreopoulos Y. Incompressible flow. Phys Today 1996;49:89–90. [26] Batchelor GK. An introduction to fluid dynamic. Phys Today 1959;12:36–8. [27] Zhang ZH, An QF, Ji YL, Qian JW, Gao CJ. Effect of zero shear viscosity of the casting solution on the morphology and permeability of polysulfone membrane prepared via the phase-inversion process. Desalination 2010;260:43–50. [28] Farah S, Tsach T, Bentolila A, Domb AJ. Morphological, spectral and chromatography analysis and forensic comparison of PET fibers. Talanta 2014;123:54–62. [29] Abdel-Karim A, Leaper S, Alberto M, Vijayaraghavan A, Fan XL, Holmes SM, Souaya ER, Badawy MI, Gorgojo P. High flux and fouling resistant flat sheet polyethersulfone membranes incorporated with graphene oxide for ultrafiltration applications. Chem Eng J 2018;334:789–99. [30] Low ZX, Ji J, Blumenstock D, Chew YM, Wolverson D, Mattia D. Fouling resistant 2D boron nitride nanosheet - PES nanofiltration membranes. J Membr Sci 2018;563:949–56. [31] Peydayesh M, Mohammadi T, Bakhtiari O. Effective treatment of dye wastewater via positively charged TETA-MWCNT/PES hybrid nanofiltration membranes. Sep Purif Technol 2018;194:488–502. [32] Thong ZW, Gao J, Lim JXZ, Wang KY, Chung TS. Fabrication of loose outer-selective nanofiltration (NF) polyethersulfone (PES) hollow fibers via single-step spinning process for dye removal. Sep Purif Technol 2018;192:483–90. [33] An AK, Guo JX, Jeong S, Lee EJ, Tabatabai SAA, Leiknes T. High flux and antifouling properties of negatively charged membrane for dyeing wastewater treatment by membrane distillation. Water Res 2016;103:362–71. [34] Xing LX, Guo NN, Zhang YT, Zhang HQ, Liu JD. A negatively charged loose nanofiltration membrane by blending with poly (sodium 4-styrene sulfonate) grafted SiO2 via SI-ATRP for dye purification. Sep Purif Technol 2015;146:50–9. [35] Laakso T, Pihlajamaki A, Manttari M. Effect of polycation structure on the fabrication of polyelectrolyte multilayer hollow fiber membranes for loose nanofiltration applications. Sep Purif Technol 2018;194:141–8. [36] Zhang N, Jiang B, Zhang LH, Huang ZH, Sun YL, Zong Y, Zhang HM. Low-pressure electroneutral loose nanofiltration membranes with polyphenol-inspired coatings for effective dye/divalent salt separation. Chem Eng J 2019;359:1442–52. [37] Gu HY, Wang C, Gong SJ, Mei Y, Li H, Ma WM. Investigation on contact angle measurement methods and wettability transition of porous surfaces. Surf Coat Tech 2016;292:72–7. [38] Tang YL, Sun J, Li SF, Ran ZL, Xiang YX. Effect of ethanol in the coagulation bath on the structure and performance of PVDF-G-PEGMA/PVDF membrane. J Appl Polym Sci 2019;136:1–10.

[m5G;January 7, 2020;22:26] 11

[39] Cassie ABD, Baxter S. Wettability of porous surfaces. Trans Faraday Soc 1944;40:546–51. [40] Quan Q, Xiao CF, Liu HL, Huang QL, Zhao W, Hu XY, Huan GL. Preparation and characterization of braided tube reinforced polyacrylonitrile hollow fiber membranes. J Appl Polym Sci 2015;132:1–10. [41] Xu ZL, Qusay FA. Polyethersulfone (PES) hollow fiber ultrafiltration membranes prepared by PES/non-solvent/NMP solution. J Membr Sci 2004;233:101–11. [42] Alsalhy QF, Salih HA, Simone S, Zablouk M, Drioli E, Figoli A. Poly(ether sulfone) (PES) hollow-fiber membranes prepared from various spinning parameters. Desalination 2014;345:21–35. [43] An R, Song J, Li Y, Tan XY, Sunarso J, Zhang C, Wang SB, Liu SM. Bundling strategy to simultaneously improve the mechanical strength and oxygen permeation flux of the individual perovskite hollow fiber membranes. J Membr Sci 2017;527:137–42. [44] Childress AE, Le-Clech P, Daugherty JL, Chen C, Leslie GL. Mechanical analysis of hollow fiber membrane integrity in water reuse applications. Desalination 2005;180:5–14. [45] Huang Y, Liu H, Xiao C, Wang C, Chen D, Sun K. Robust preparation and multiple pore structure design of poly (tetrafluoroethylene-co-hexafluoropropylene) hollow fiber membrane by melt spinning and post-treatment. J Taiwan Inst Chem Eng 2019;97:441–9. [46] Jiang M, Ye KF, Lin JY, Zhang XY, Ye WY, Zhao SF, Van der Bruggen B. Effective dye purification using tight ceramic ultrafiltration membrane. J Membr Sci 2018;566:151–60. [47] Wei X, Kong X, Sun C, Chen J. Characterization and application of a thin-film composite nanofiltration hollow fiber membrane for dye desalination and concentration. Chem Eng J 2013;223:172–82. [48] Wang L, Wang NX, Zhang GJ, Ji SL. Covalent crosslinked assembly of tubular ceramic-based multilayer nanofiltration membranes for dye desalination. AICHE J 2013;59:3834–42. [49] Liu S, Wang Z, Ban M, Song P, Khan B. Chelation–assisted in situ self-assembly route to prepare the loose PAN–based nanocomposite membrane for dye desalination. J Membr Sci 2018;566:168–80. [50] Yu L, Zhang Y, Wang Y, Zhang H, Liu J. High flux, positively charged loose nanofiltration membrane by blending with poly (ionic liquid) brushes grafted silica spheres. J Hazard Mater 2015;287:373–83. [51] Lin JY, Ye WY, Zeng HM, Yang H, Shen JN, Darvishmanesh S, Luis P, Sotto A, Van der Bruggen B. Fractionation of direct dyes and salts in aqueous solution using loose nanofiltration membranes. J Membr Sci 2015;477:183–93. [52] Lin JY, Tang CYY, Ye WY, Sun SP, Hamdan SH, Volodin A, Van Haesendonck C, Sotto A, Luis P, Van der Bruggen B. Unraveling flux behavior of superhydrophilic loose nanofiltration membranes during textile wastewater treatment. J Membr Sci 2015;493:690–702. [53] Chen PL, Ma X, Zhong ZX, Zhang F, Xing WH, Fan YQ. Performance of ceramic nanofiltration membrane for desalination of dye solutions containing NaCl and Na2 SO4 . Desalination 2017;404:102–11. [54] Alventosa-DeLara E, Barredo-Damas S, Zuriaga-Agusti E, Alcaina-Miranda MI, Iborra-Clar MI. Ultrafiltration ceramic membrane performance during the treatment of model solutions containing dye and salt. Sep Purif Technol 2014;129:96–105.

Please cite this article as: Z. Chu, K. Chen and C. Xiao et al., Improving pressure durability and fractionation property via reinforced PES loose nanofiltration hollow fiber membranes for textile wastewater treatment, Journal of the Taiwan Institute of Chemical Engineers, https://doi.org/10.1016/j.jtice.2019.12.009