- Email: [email protected]
Superhydrophobic ceramic hollow fiber membrane planted by ZnO nanorod-array for high-salinity water desalination
ARTICLE IN PRESS
JID: JTICE
[m5G;October 26, 2019;6:3]
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
Superhydrophobic ceramic hollow fiber membrane planted by ZnO nanorod-array for high-salinity water desalination Tao Wang a, Yanbin Yun a,∗, Manxiang Wang b,∗, Chunli Li c, Guicheng Liu b,d, Woochul Yang b a
College of Environmental Science and Engineering, Beijing Forestry University, Beijing, 100083, PR China Department of Physics, Dongguk University, Seoul 04620, Republic of Korea c New Technique Centre, Institute of Microbiology, Chinese Academy of Sciences, Beijing 100101, PR China d State Key Laboratory for Modification of Chemical Fibers and Polymer Materials, Donghua University, Shanghai 200092, PR China b
a r t i c l e
i n f o
Article history: Received 8 July 2019 Revised 25 September 2019 Accepted 12 October 2019 Available online xxx Keywords: Ceramic hollow fiber membrane ZnO nanorods Superhydrophobic surface Vacuum membrane distillation Antifouling
a b s t r a c t To solve the problems of membrane material tolerance and membrane fouling, a micro/nano hierarchial structure with low surface energy was constructed above the exterior surface of a ceramic hollow fiber membrane using ZnO nanorod arrays and 1H,1H,2H,2H-perfluorodecyltriethoxysilane (PDTS) coatings, which make it superhydrophobic and self-cleaning. The surface morphology, chemical functional groups, and water contact angel of the modified membranes were identified. The results show that large quantity of ZnO nanorods possess desirable characteristics (i.e. superhydrophobicity, exceptional thermal and mechanical stability, and water contact angle of 160.12°) were detected on the ceramic membrane. The novel membrane shows excellent self-cleaning performance and good desalination ability in the utilization of vacuum membrane distillation (VMD) system for high-salinity water desalination. © 2019 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
1. Introduction Technology advancement on water treatment for wastewater recycling and production of clean water is gaining increasing attention due to the ever-growing of pollution in the water environment and shortage of clean water resource [1,2]. In recent years, membrane distillation technology has been widely used in water and wastewater treatment [3–9]. At present, the existing membranes available in the market are mostly organic polymer membranes which have low thermal and mechanical stability will restraint their performance under extreme conditions [10,11]. In contrast, ceramic membranes that are mostly derived from metal oxides (e.g. silica, alumina, zirconia and so on) show better performance in terms of their mechanical and thermal stability. However, due to the existence of hydroxyl (-OH) groups on the surface of the ceramic membrane that lead to its hydrophilic nature [12], the ceramic membrane is unfavourable to be used directly in membrane distillation. Frequent membrane cleaning and membrane replacement caused by membrane fouling are other difficulties that limit the application of membrane distillation [13]. Therefore, the development of a ceramic membrane with superhydrophobicity and
∗
Corresponding authors. E-mail addresses: [email protected] (Y. Yun), [email protected] (M. Wang).
anti-pollution ability is of great significance to the development of membrane distillation technology. Larbot et al. [14] first applied fluorosilane hydrophobic modified alumina and zirconia ceramic membrane to the membrane distillation process, which proves the feasibility of modified ceramic membrane used in membrane distillation. Many superhydrophobic surfaces such as sacred lotus leaves [15], water strider’s legs [16], cicada orni’s wings (Lee et al.) [17] exist in nature whose water contact angles are greater than 150°. There is a large number of micro/nano scale protrusions on these surfaces. Studies have shown that the combination of micron and nano-scale rough surfaces, as well as small surface energy materials resulted in water contact, angles greater than 150° and self-cleaning effects [18]. At the same time, the micro/nano hierarchical structured surface associated with small free energy can effectively promote the liquid from Wenzel state to Cassie state spontaneously [19,20]. Therefore, constructing a micro/nanoscale hierarchical structured nanorod arrays with small surface energy coatings on the membrane surface represents a more competent and ideality avenue for modifying the ceramic hollow fiber membrane. Recently, a large number of nanomaterials, such as PbI2 , NiO and ZnO, have been applied in different fields [21-23]. Among these, due to the advantages such as simple preparation technique, rich morphology, stable chemical, mechanical and thermal properties, ZnO nanophase materials have been used to fabricate superhydrophobic surfaces in many fields. Meanwhile, the hydrothermal method has been widely used in the
https://doi.org/10.1016/j.jtice.2019.10.009 1876-1070/© 2019 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
Please cite this article as: T. Wang, Y. Yun and M. Wang et al., Superhydrophobic ceramic hollow fiber membrane planted by ZnO nanorod-array for high-salinity water desalination, Journal of the Taiwan Institute of Chemical Engineers, https://doi.org/10.1016/j.jtice. 2019.10.009
JID: JTICE 2
ARTICLE IN PRESS
[m5G;October 26, 2019;6:3]
T. Wang, Y. Yun and M. Wang et al. / Journal of the Taiwan Institute of Chemical Engineers xxx (xxxx) xxx
growth of metal oxide nanorods because of its low reaction temperature and mild reaction conditions [24–27]. Duan et al. [28] developed a ceramic spheres layered with nanorod. Growth of ZnO nanorods was performed via sintering treatment at 350 °C and hydrothermal reaction. Then, the substrate of balls was cleaned with deionized water multiple times and dried prior for calcination at 450 °C in air followed by cooling to room temperature and finally ZnO nanorods grown on ceramic balls were obtained. Wang et al. [29,30] sintered zinc nitrate hexahydrate solution on the surface of PDMS at 300 °C and obtained a novel superhydrophobic anti-ice and de-icing material by hydrothermal growth of ZnO nanorods. Wang et al. [31] treated the hydrophobicity of PVDF membrane by using micro/nano structure to improve the fouling and wetting resistance of PVDF membrane. Fang et al. [32] used fluorinated silane hydrophobic modified ceramic hollow fiber membrane. The dried ceramic hollow fiber membrane was immersed into 2 wt% 1H, 1H, 2H, 2H- perfluorooctyltriethoxysilane (FAS) in ethanol solution at room temperature for 24 h. Hydrophobic modified ceramic hollow fiber membranes were obtained after drying. Due to the low surface energy and excellent thermal stability of 1H,1H,2H,2H-perfluorodecyltriethoxysilane (PDTS), Krajewski et al. [33]. used PDTS chloroform solution of 0.01 mol L − 1 as a graft solution. The membranes produced were detected with the contact angle ranging from 142°–148°, thus indicating the hydrophobic nature of the fluoroalkylsilanes grafted ceramic zirconia membrane. In previous studies, the hydrophobicity and antifouling ability of the membrane can be effectively improved by combining the growth of micron/nano materials on the membrane surface to change the roughness of the membrane surface and the coating of fluorosilane to reduce the surface energy of the membrane. To the best of our knowledge, there has yet to be any research reported on the growth of ZnO nanorods particles and coating of fluorosilane on modification of ceramic hollow fiber membranes for use in the vacuum membrane distillation (VMD) field. In this paper, a superhydrophobic ceramic hollow fiber membrane has been developed for desalination of high concentration brine via membrane distillation. The hydrophobic surface with micro/nanoscale hierarchical structure was constructed on alumina ceramic hollow fiber membrane by ZnO nanorod array and PDTS coating. The preparation of ZnO seeds layer by a pyrolysis−adhesion approach at 350 °C represents the key step in order to construct a three-dimensional structure ZnO nanorods to adhere on the membrane surface. The preparation process of the membrane was described in detail in the following, while the membrane fouling, VMD properties, chemical composition, mechanical and thermal stability, surface structure, hydrophobicity, N2 permeance and clean water flux of the membrane were also presented and discussed extensively. 2. Experimental section Fig. 1 shows the modification steps of the ZnO nanorods and PDTS ceramic hollow fiber membrane. Firstly, before seeding and growth processes, the virgin ceramic hollow fiber membrane was cleaned with deionized water and ethanol in an ultrasonic bath for 10 min to remove surface contaminants. Secondly, preparation and adhesion of the ZnO seeds on the ceramic hollow fiber membrane. This process involves two effective in-situ reactions: Zn(CH3 COO)2 + 2NaOH → Zn(OH)2 ↓ + 2NaCH3 COO (neutralization, pH = 9.05) and Zn(OH)2 ↓ → ZnO↓ + H2 O↑ (pyrolysis). Among these, The in-situ reactions on the surface of ceramic hollow fiber membranes were carried out using the pyrolysisadhesion method at 350 °C to solve the technical difficulty of ZnO seeds layer preparation [34]. Thirdly, ZnO nanorod arrays were grown by classical hydrothermal reaction. Finally, the hydrophobic-
ity of the ZN–CHF membrane was layered by combining with the PDTS. 2.1. Planting of ZnO seeds on ceramic hollow fiber membrane After immersing into a 0.07 mol L−1 zinc acetate ethanol solution for 5 min, the ceramic hollow fiber membrane was gently taken out at a uniform velocity and placed in the muffle furnace at 350 °C for 30 min. Subsequently, the dried ceramic hollow fiber membrane was soaked into a 0.1 mol L−1 sodium hydroxide ethanol solution for 1 min followed by a second time of drying at the same condition. Finally, the ZnO seeds that adhered on the ceramic hollow fiber membrane (labelled as ZS-CHF membrane) was obtained by scouring the inner and outer surfaces of the resulting membrane with deionized water and dried in a muffle furnace at 350 °C for 30 min again. 2.2. Growth of ZnO nanorods on the ZS-CHF membrane A formulated mixture of zinc nitrate (0.05 mol L − 1 ) and hexamethylenetaetramine (HMTA) (0.05 mol L − 1 ) stirred by a magnetic stirrer was used as a growth solution of ZnO nanorods on the ZS-CHF membrane. The ZS-CHF membrane and the growth solution were transferred into a closed stainless-steel reaction vessel. The sealed stainless-steel reaction vessel was initially heated at 65 °C for 2 h and then increased the temperature to 95 °C and maintained for 18 h. After washing the obtained membrane with deionized water and drying at 350 °C for 1 h, the final product i.e. ZnO nanorod array grown ceramic hollow fiber membrane (marked as ZN–CHF membrane) was obtain. 2.3. Hydrophobicity treatment for original ceramic hollow fiber and ZN-CHF membrane The fluorosilane coating method was employed for hydrophobicity modification on the alumina ceramic hollow fiber membrane. The membrane was immersed in a 1 vol% PDTS ethanol solution for 24 h followed by drying at 120 °C for 2 h to obtain the PDTS-coated alumina ceramic hollow fiber membrane (labelled as P-CHF membrane). The same method was used to modify the ZN–CHF membrane to obtain the PDTS-coating ZN–CHF membrane (labelled as P-ZN–CHF membrane). 2.4. VMD performances of the P-ZN-CHF membrane The VMD properties of the P-ZN–CHF membranes were analyzed using a custom-made VMD system feeding by a 1000 mL of 200 g L − 1 NaCl solution, and the effective area of the membrane in the module was 27.65 cm2 . The feed was continuously fed the vacuum membrane distillation process, the concentration increased throughout the test. The changes of membrane permeation and the ionic conductivity of the permeated liquid were tabulated at different operation conditions (e.g. temperature, vacuum pressure, and flow velocity) of the feed solution. The permeation flux and conductivity of the P-ZN–CHF membrane and the P-CHF membrane for 3 h of continuous operation in the VMD system were compared. 3. Results and discussion 3.1. Properties of the ceramic hollow fiber membranes Fig. 2 shows the surface diversification of ceramic hollow fiber membranes after modification. The surface of hydrophilic virgin ceramic hollow fiber membrane used in the experiment was composed of irregular block structure (Fig. 2a and b). However, the surface of the membrane is relatively smooth without apparent bulges. As shown in Fig. 2c and d, it is evident that there is
Please cite this article as: T. Wang, Y. Yun and M. Wang et al., Superhydrophobic ceramic hollow fiber membrane planted by ZnO nanorod-array for high-salinity water desalination, Journal of the Taiwan Institute of Chemical Engineers, https://doi.org/10.1016/j.jtice. 2019.10.009
JID: JTICE
ARTICLE IN PRESS
[m5G;October 26, 2019;6:3]
T. Wang, Y. Yun and M. Wang et al. / Journal of the Taiwan Institute of Chemical Engineers xxx (xxxx) xxx
3
Fig. 1. Structural evolution for the formation of superhydrophobic ceramic hollow fiber membrane. Notes: ZnO seeds planted ceramic hollow fiber membrane (ZS-CHF membrane), ZnO nanorod array grown ceramic hollow fiber membrane (ZN–CHF membrane), and PDTS-coated ZN–CHF membrane (P-ZN–CHF membrane).
a dense protrusion like a stone fragment on the surface of the ceramic hollow fiber membrane, whose diameter between 400– 550 nm. The seeds layer of ZnO formed above the membrane substrate by pyrolysis-adhesion approach at 350 °C is an indispensable condition for the growth of three-dimensional ZnO nanorods. ZnO nanorod arrays were grown on ZS-CHF membrane treated by hydrothermal method with milder temperature conditions instead of a few two-dimensional sheet ZnO layers as in Fig. 2c and d. As observed in Fig. 2e and f, there are many uniforms and ordered nanorod arrays with a diameter of ∼288 nm and a length of ∼ 650 nm on the ZN–CHF membrane. Also, as shown in Fig. 2e, f, g and h, no significant differences were observed on the surface morphology between ZN–CHF and P-ZN–CHF membranes. In Fig. 3, due to the deposition of ZnO nanorod-array on surface of ceramic film, Zn-O stretching vibration absorption peaks of ZN–CHF and P-ZN–CHF are shown at 480 cm−1 . PDTS is composed of the hydrophilic triethoxy silane segment and the hydrophobic carbon chain. And the C-F peak in 1262 cm−1 is from the PDTS. The triethoxy silane segment, touching with water, is easy to be hydrolyzed to form trisilicon alcohol. Then, the hydroxyl group of the trisilicon alcohol reacts with ZnO to form hydrogen bond and Si-O-Zn covalent bond (as shown in 974 cm−1 of P-ZN–CHF). Under appropriate conditions (for example, favorable distance and direction), cross-linking among trisilicon alcohol molecules occurred to form a 2D network with the formation of Si-O-Si bond (in 1147 cm−1 of P-ZN–CHF). Finally, due to the heating treatment at 120 °C, the density of the Si-OH bond significantly reduced, which is conducive to the formation of Si-O-Zn bonds. And the above peaks reveal that PDTS had been coated on the surface of the ZnO nanorods. Hence, the hydrophobization treatment performed on the ZN–CHF membrane shows a negligible effect to its morphology in which similar observation was reported in the literatures [35,36]. The surface roughness of ceramic membranes varies greatly during hydrophobic modification. Compared to the smooth surface of the original ceramic membrane (Fig. 4a, 5 μm × 5 μm), the roughness of ZS-CHF film surface increases obviously (Fig. 4b, 5 μm × 5 μm). Moreover, as shown in Figs. 4c (5 μm × 5 μm) and 4d (10 μm × 10 μm), the surface roughness of P-ZN–CHF membrane is the highest, among the three samples due to the existence of ZnO nanorod arrays. In the process of ceramic membrane modification, the roughness of the membrane surface is increasing
Table 1 Information about the liquid entry pressure, pore parameter, thickness, diameter and length of the CHF, P-CHF and P-ZN–CHF membranes. Information
CNF
P-ZN–CHF
P-CHF
LEP/MPA Porosity (%) Median pore diameter (volume)/nm Median pore diameter (area)/nm Average pore diameter (4 V/A)/nm Thickness (mm) Internal diameter (mm) External diameter (mm) Length (cm)
– 26.83564369.5 3962.8 3406.4 2.01 9.51 11.52 15
0.175 15.9009 4434.1 3778.1 3104.3 2.01 9.51 11.52 15
0.11 26.643 4364.8 3924.5 3333.0 2.01 9.51 11.52 15
step by step, and the hydrophobicity of the membrane is also improving with the improvement of the roughness. As shown in Table 1 and Fig. 5a, pore distribution (median pore diameter, average pore diameter) and porosity of the original alumina ceramic hollow fiber (marked as CHF membrane), P-CHF and P-ZN–CHF membranes were measured by mercury porosimetry. In Fig. 5a, a main peak was observed in the pore diameter distribution of the three ceramic hollow fiber membranes (CHF, P-CHF and P-ZN–CHF membranes). Among them, there is no difference between CHF and P-CHF membranes, which also proves that the hydrophobic modification of PDTS has little effect on the membrane morphology. Compared with CHF and P-CHF membranes, the median pore size, average pore size and porosity of P-ZN–CHF membranes decreased in varying degrees, and the porosity of P-ZN–CHF membranes decreased by about 40%. This may be caused by the density of the micro/nanostrcuture of the ZnO nanorods modified membrane [37,38]. Overall, the ceramic hollow fiber membrane shows superhydrophobic micro/nanoscale hierarchical structures after growing with the ZnO nanorods on its surface and PDTS coating, which can be used in membrane distillation applications. At the same time, it retained the original internal structure, including micropores, thickness and so on. Fig. 5b and 5c present the gas and liquid (clean water flux) permeation properties of the ceramic hollow fiber membranes. As observed from Fig. 5b that the membrane maintained high permeability to nitrogen gas (1.99 × 106 L m2 h−1 MPa−1 ) after modification with ZnO nanorods, which were lower than that for the CHF membrane (4.53 × 106 L m−2 h−1 MPa−1 ) and P-CHF mem-
Please cite this article as: T. Wang, Y. Yun and M. Wang et al., Superhydrophobic ceramic hollow fiber membrane planted by ZnO nanorod-array for high-salinity water desalination, Journal of the Taiwan Institute of Chemical Engineers, https://doi.org/10.1016/j.jtice. 2019.10.009
JID: JTICE 4
ARTICLE IN PRESS
[m5G;October 26, 2019;6:3]
T. Wang, Y. Yun and M. Wang et al. / Journal of the Taiwan Institute of Chemical Engineers xxx (xxxx) xxx
Fig. 2. SEM morphologies of ZnO nanorod decorated ceramic membranes. (a, b) Virgin ceramic hollow fiber membrane, (c, d) ZS-CHF, (e, f) ZN–CHF, and (g, h) P-ZN–CHF membranes.
Please cite this article as: T. Wang, Y. Yun and M. Wang et al., Superhydrophobic ceramic hollow fiber membrane planted by ZnO nanorod-array for high-salinity water desalination, Journal of the Taiwan Institute of Chemical Engineers, https://doi.org/10.1016/j.jtice. 2019.10.009
JID: JTICE
ARTICLE IN PRESS
[m5G;October 26, 2019;6:3]
T. Wang, Y. Yun and M. Wang et al. / Journal of the Taiwan Institute of Chemical Engineers xxx (xxxx) xxx
5
Fig. 3. FT-IR curve of the virgin ceramic hollow fiber, ZN–CHF, P-ZN–CHF membranes.
Fig. 4. AFM morphologies of ZnO nanorod decorated ceramic membranes. (a) Virgin ceramic hollow fiber membrane, (b) ZS-CHF, and (c, d) P-ZN–CHF membranes.
brane (2.76 × 106 L m2 h−1 MPa−1 ). This was due to the decrease of porosity of ceramic hollow fiber membrane modified by ZnO nanorods. However, it still maintained good gas permeation properties. The modifications of ZnO and PDTS on the membrane have increased the surface hydrophobicity which subsequently decreased the permeability of clean water. The clean water can be passed through the un-modified hydrophilic CHF membrane at a faster rate of 46.2 × 103 kg m−2 h−1 MPa−1 (Fig. 5c). For the modified P-ZN–CHF membrane, the permeation of clean water was
observed only at a pressure above 0.175 MPa. Thus, it was indicated that the P-ZN–CHF membrane (175 kPa) possesses a higher liquid entry pressure (also refers to critical pressure value) than the CHF membrane (0 kPa) and P-CHF membrane (110 kPa). So, the P-ZN–CHF membrane, which has low water permeability, was suitable for the application of vacuum membrane distillation. Water contact angle (WCA) is an important parameter reflecting the hydrophobicity of a material. And the membrane material with strong hydrophobicity is needed in the application of
Please cite this article as: T. Wang, Y. Yun and M. Wang et al., Superhydrophobic ceramic hollow fiber membrane planted by ZnO nanorod-array for high-salinity water desalination, Journal of the Taiwan Institute of Chemical Engineers, https://doi.org/10.1016/j.jtice. 2019.10.009
JID: JTICE 6
ARTICLE IN PRESS
[m5G;October 26, 2019;6:3]
T. Wang, Y. Yun and M. Wang et al. / Journal of the Taiwan Institute of Chemical Engineers xxx (xxxx) xxx
Fig. 5. (a) Pore size distributions, (b) N2 permeance, and (c) clean water flux (CWF) of the CHF, P-CHF and P-ZN–CHF membranes.
membrane distillation. Only vapour can pass through the membrane, which must be hydrophobic and not wetted by the liquid. The higher the hydrophobicity performance better in the property. The superhydrophobic membrane not only can prevent the membrane pore from being wet, but also improve the liquid entry pressure, antifouling and long-term stability of the membrane. To prove that ZnO nanorod arrays and PDTS coating modified ceramic hollow fiber membranes were suitable for membrane distillation,
the hydrophobicity, thermal stability and mechanical stability of modified membranes were measured at different temperatures and condition. As shown in Fig. 6, the difference of WCA between different membranes during the modification process was intuitively introduced. It was found that the original ceramic hollow fiber membrane used in the study is superhydrophilic and its contact angle was approximately 0°. The ZN–CHF membrane shows an inferior hydrophobicity with the WCA of 94.34°. Due to its low
Please cite this article as: T. Wang, Y. Yun and M. Wang et al., Superhydrophobic ceramic hollow fiber membrane planted by ZnO nanorod-array for high-salinity water desalination, Journal of the Taiwan Institute of Chemical Engineers, https://doi.org/10.1016/j.jtice. 2019.10.009
JID: JTICE
ARTICLE IN PRESS
[m5G;October 26, 2019;6:3]
T. Wang, Y. Yun and M. Wang et al. / Journal of the Taiwan Institute of Chemical Engineers xxx (xxxx) xxx
Fig. 6. Surface contact angles of the CHF, ZN–CHF, P-ZN–CHF and P-CHF membranes.
surface energy, the PDTS was coated on the ZnO surface to reduce the wash and erosion of the ZnO substrate by distillate. Surface contact angle is up to 160.12°, which is the quantitative and direct evidence. The WCA of the P-ZN–CHF membrane modified by ZnO
7
nanorods and PDTS shows the highest value of 160.12°, indicating the superhydrophobic nature of P-ZN–CHF membrane. According to Fowkes method, the solid surface energy of P-ZN–CHF membrane in water is 6.46344 × 10−5 J m−2 . The hydrophobic properties of PZN–CHF membrane were enhanced by two aspects: First, the PDTS layer can make the membrane surface hydrophobic, owing to the lower surface energy of methyl fluoride (- CF3 ) group [39], which also makes the WCA of the P-CHF membrane be 142.96°. Second, the micro/nanoscale structure produced by the modification of ZnO nanorods is a super hydrophobic structure. It is observed that the WCA of the P-ZN–CHF membrane is greater than the P-CHF membrane without modification by ZnO nanorods. This can be explained by the micro/nanoscale hierarchical structure present on the P-ZN–CHF membrane surface can store abundant air pockets in the troughs between the individual nanorods. Consequently, the contact area and the adhesion/binding force between the membrane surface and the droplets was decreased by the high aspect ratio of the ZnO nanorods. According to the Cassie-Baxter theory [40], it is a significant characteristic to tailor the surface with superhydrophobicity. In vacuum membrane distillation (VMD) applications, the membrane materials should maintain its hydrophobicity throughout the
Fig. 7. Effect of the (a) ultrasonic treatment time and (b) 80 °C-immersion time on the water contact angles of the CHF, P-CHF and P-ZN–CHF membranes.
Please cite this article as: T. Wang, Y. Yun and M. Wang et al., Superhydrophobic ceramic hollow fiber membrane planted by ZnO nanorod-array for high-salinity water desalination, Journal of the Taiwan Institute of Chemical Engineers, https://doi.org/10.1016/j.jtice. 2019.10.009
JID: JTICE 8
ARTICLE IN PRESS
[m5G;October 26, 2019;6:3]
T. Wang, Y. Yun and M. Wang et al. / Journal of the Taiwan Institute of Chemical Engineers xxx (xxxx) xxx
Fig. 8. Variation of the permeate fluxes of P-ZN–CHF membrane with increasing (a) feed temperature, (b) vacuum pressure, and (c) feed velocity.
Please cite this article as: T. Wang, Y. Yun and M. Wang et al., Superhydrophobic ceramic hollow fiber membrane planted by ZnO nanorod-array for high-salinity water desalination, Journal of the Taiwan Institute of Chemical Engineers, https://doi.org/10.1016/j.jtice. 2019.10.009
JID: JTICE
ARTICLE IN PRESS
[m5G;October 26, 2019;6:3]
T. Wang, Y. Yun and M. Wang et al. / Journal of the Taiwan Institute of Chemical Engineers xxx (xxxx) xxx
9
Fig. 9. Permeate fluxes and ionic conductivity of the P-CHF and P-ZN–CHF membranes during a 180-min-continuous-VMD operation with a 200 g L−1 NaCl feed solution, 0.085 MPa vacuum pressure and 0.032 m s−1 velocity, at 61 °C.
range of running temperature and distinguished thermal stability and excellent mechanical stability to accommodate to different process conditions, including high running temperature, different vacuum pressure and strong liquid flow velocity. To evaluate the mechanical stability and thermal stability of modified membranes in membrane distillation applications. In this study, modified membranes were placed in a hot water bath and ultrasonic environment to simulate the scour of the feed liquid on the membrane [41–43]. The change of contact angle on the membranes can reflect the hydrophobicity of the membrane [41]. Fig. 7a shows the changes of the contact angle of P-ZN–CHF, P-CHF and CHF membranes after an ultrasonic treatment for 1 h in deionized water at room temperature. The contact angle of P-ZN–CHF membrane is about 149° after 60 min, while the minimum contact angle of P-CHF membrane is only 134°, indicating that P-ZN–CHF membrane has excellent mechanical stability. Meanwhile, the PZN–CHF membrane has distinguished thermal stability. Fig. 7b depicts the contact angle of P-ZN–CHF membrane were measured after processed in deionized water at 80 °C for 60 min. The contact angle of P-CHF membrane decreased to 135°, while that of P-ZN–CHF membrane only decreased by 6° and reached to 154°, indicating that P-ZN–CHF membrane has distinguished thermal stability. The reasons why the P-ZN–CHF membrane emerges the excellent mechanical stability and significant thermal stability are presented as followed: On the one hand, ZnO nanorods have been strong fastened on the ceramic hollow fiber membrane-based material by ZnO seed layer. The water molecule was hardly to be permeated into the gaps between the ZnO nanorods that has a higher density. On the other hand, there is Si-O-Zn covalent bond formed between PDTS and ZnO nanorods makes the film surface form a stable hydrophobic layer and not easy to fall off. Therefore, the effect of ultrasonic vibration and hot water on P-ZN–CHF membrane was weakened. 3.2. Application of the P-ZN-CHF membrane in vacuum membrane distillation In this paper, P-ZN–CHF membrane was used for vacuum membrane distillation to desalination high concentration brine. A homemade VMD system was used to investigate the effects of high salinity of NaCl solution (200 g L−1 ) on the permeation fluxes of P-ZN–CHF membrane at different feed temperature, vacuum and feed velocity. Due to the increase of temperature and velocity of
feed liquid and vacuum degree, the driving force on both sides of P-ZN–CHF membrane enhances while the thermal boundary layer on the film surface decreases. Therefore, in Fig. 8, when the temperature and velocity of feed liquid and vacuum pressure are increased, the permeation fluxes of the membrane increased in varying degrees. The most obvious one is the effect of feed temperature on the permeate fluxes of P-ZN–CHF membrane; when vacuum pressure and feed velocity were fixed to 0.085 MPa and 0.032 m s−1 , the feed temperature is 80 °C, permeate fluxes is 70.82 kg m−2 h−1 , and it is only 12.73 kg m−2 h−1 at 55 °C. The Fig. 8b was the effect of vacuum pressure on the membrane permeate fluxes of P-ZN–CHF when feed temperature and feed velocity were fixed to 60 °C and 0.032 m s − 1 , vacuum pressure was 0.07 MPa permeate fluxes was 16.71 kg m−2 h−1 , and it is 28.25 kg m−2 h−1 at 0.09 MPa. Vacuum pressure has a great influence on permeate fluxes, although it is not as big as temperature. It is noteworthy that, the adjustment of the feed velocity shows a negligible effect on the P-ZN–CHF membrane when feed temperature and vacuum pressure were fixed to 60 °C and 0.085 MPa respectively (Fig. 8c), the feed velocity was 0.016 m s−1 , permeate fluxes was 21.09 kg m−2 h−1 , and it was 22.76 kg m−2 h−1 at 0.048 m s−1 . The results show that the P-ZN–CHF membrane has high resistivity towards the shear force on the surface of the membrane. In this study, the NaCl solution with a concentration of 200 g L−1 was used to simulate the wastewater of perchlor-alkali industrial resin regeneration with high salt content, which was used to verify the self-cleaning properties of the membranes. A continuous operation method was used to verify the high permeate fluxes performance and anti-pollution capacity and assess the desalination performance of P-ZN–CHF membrane by comparing the VMD system of P-ZN–CHF membrane and P-CHF membrane running continuously for 3 h at 61 °C, 0.032 m s−1 and 0.085 MPa. Fig. 9 reveals that the permeate fluxes of the P-ZN–CHF and PCHF membrane were gradually reduced when the operation time was increased and the ionic conductivity (IC) of the permeated liquid was gradually increased. After 3 h of testing, the permeate flux of the P-ZN–CHF membrane reduced from 27.35–23.66 kg m−2 h−1 and the IC of the permeated liquid increased from 5.13–14.32 μS cm−1 . And the WCA of P-ZN–CHF membrane remained 144.62°, which proves that PDTS did not diffuse during practice application. The P-CHF membrane has obvious differences with it, that the IC increased from 106.65 to 184.65 μS cm−1 and the permeate flux reduced from 44.06–33.55 kg m−2 h−1 . The NaCl rejection
Please cite this article as: T. Wang, Y. Yun and M. Wang et al., Superhydrophobic ceramic hollow fiber membrane planted by ZnO nanorod-array for high-salinity water desalination, Journal of the Taiwan Institute of Chemical Engineers, https://doi.org/10.1016/j.jtice. 2019.10.009
ARTICLE IN PRESS
JID: JTICE 10
[m5G;October 26, 2019;6:3]
T. Wang, Y. Yun and M. Wang et al. / Journal of the Taiwan Institute of Chemical Engineers xxx (xxxx) xxx
Table 2 MD performance for organic and ceramic membranes published recently [40–45]. Reference
Application
Membrane material
Membrane morphology
Feed solution
Water permeation flux (kg m−2 h−1 )
[45] [46] [47] [48] [49] [50] P-CHF P-ZN-CHF
VMD DCMD VMD DCMD VMD VMD VMD VMD
PTFE PVDF PP β -Sialon Zeolite/Al2 O3 Si3 N4 Al2 O3 Al2 O3
Hollow fiber Hollow fiber Disk Hollow fiber Tubular Hollow fiber Hollow fiber Hollow fiber
4 mol L−1 NaCl solution, 60 °C 4 mol L−1 NaCl solution, 60 °C 100 g L−1 NaCl solution, 55 °C 2wt% NaCl solution, 50 °C 3.5 wt% NaCl solution, 60 °C 4 wt% NaCl solution, 70 °C 200 g L−1 NaCl solution, 61 °C 200 g L−1 NaCl solution, 61 °C
7.30 ∼ 8.67 14.0 14.41 2.5 12 22.2 33.6 ∼ 44.1 23.7 ∼ 27.4
Conductivity (μS cm−1 ) 90 ∼ 100 15.6 2.49 — — — 106.6 ∼ 184.6 5.1 ∼ 14.3
Fig. 10. SEM images of the surface of used (a–c) P-ZN–CHF and (d–f) P-CHF membrane surfaces after 3 h of continuous VMD operation.
rate of P-ZN–CHF membrane is always greater than 99.99%, while the average rejection rate of P-CHF membrane is 99.94%. Compared with the P-CHF membrane, the permeation water quality of the modified membrane was much higher and kept a relatively stable state. The permeation flux and the rate of permeation flux reduction were lower than P-CHF membrane. The permeation flux of P-ZN–CHF membrane was still higher than that of other membrane distillation studies, although it was lower than P-CHF membrane. As shown in Table 2, P-ZN–CHF has higher permeation flux and maintains higher water quality than other organic and ceramic membranes. The P-ZN–CHF membrane modified by ZnO nanorods and PDTS has good performance in the application of membrane distillation. The VMD properties of P-ZN–CHF membrane indicate that the fouling and wetting situation of P-ZN–CHF membrane are more optimistic. To support this view, some direct evidence was provided by examining the P-ZN–CHF membrane tested with SEM images. In Fig. 10a–c, it shows that there are only a few NaCl crystal on the surface of P-ZN–CHF membrane, and the superhydrophobic structure on the surface of the film is not destroyed. However, the surface of P-CHF membrane contains a large amount of NaCl crystal, which have entered and blocked the membrane pore (Fig. 10d– f). It is obvious that the P-ZN–CHF membrane has good abilities of anti-fouling and self-cleaning. Water droplets are unstable on the surface of the superhydrophobic membrane and will leave the surface of the membranes quickly when disturbed slightly by the environment. The contaminants on the surface of the membranes can be removed by the droplets during the rolling process. Therefore, the superhydrophobic membrane has the function of self-cleaning. In the non-working state, the entering of water into the pore structure of the membrane is unfavourable because the hydrophobic ZnO nanorod prevents the feed liquid adhered on the surface of the
modified membrane. Even under the vacuum force in working condition, the entering of feed solution into the pore structure was still prevented due to the presence of hydrophobic ZnO nanorods that had improved the membrane surface to a superhydrophobic characteristic meanwhile also reduced the porosity of the pore opening, and thus resulting in a smaller bulge of the feed liquid. Other team also reported and discussed the same working mechanism [44]. 4. Conclusions In this paper, the ZnO seeds layer was planted on alumina ceramic hollow fiber membrane at 350 °C by the pyrolysis-adhesion method. On this basis, new ZnO nanorods modified ceramic hollow fiber membrane with micro/nanoscale hierarchical structured was fabricated by the hydrothermal method. Finally, a novel superhydrophobic membrane structure was created by coating PDTS and applied to the VMD desalination of concentrated brine. The new membrane containing with the hydrophobic ZnO nanorods can hold up abundant air molecule and turn the droplets to become Cassie’s state, this results in the membrane with superhydrophobic surface plus a water contact angle of 160°. Also, the strong bonding between ZnO nanorods and ceramic hollow fiber membranes combined with the low surface energy of PDTS coating, the new P-ZN–CHF membrane showed several properties that are necessary for utilization in the membrane distillation. This includes stable superhydrophobicity at various temperatures with distinguished thermal stability, excellent mechanical stability, maintained good gas permeation properties and higher liquid entry pressure. The new membrane was detected with a lower IC of permeated liquid after 3 h distillation of NaCl solution (200 g L−1 ) performed using a custom-made VMD system at 61 °C, due to the presence of microns gaps between the feed and membrane endow with unique an-
Please cite this article as: T. Wang, Y. Yun and M. Wang et al., Superhydrophobic ceramic hollow fiber membrane planted by ZnO nanorod-array for high-salinity water desalination, Journal of the Taiwan Institute of Chemical Engineers, https://doi.org/10.1016/j.jtice. 2019.10.009
JID: JTICE
ARTICLE IN PRESS T. Wang, Y. Yun and M. Wang et al. / Journal of the Taiwan Institute of Chemical Engineers xxx (xxxx) xxx
tifouling and antiwetting properties. Compared with other organic and inorganic membranes, P-ZN–CHF membranes have higher permeation flux. P-ZN–CHF membrane is suitable for membrane distillation applications. Acknowledgments This work was supported by the National Key Research and Development Program of China (No. 2018YFB060430203), the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (Nos. 2019R1C1C1006310 and 2019R1A2C1002844), the Ministry of Education, Korea (No. 2016R1A6A1A03012877), Brain Pool program funded by the Ministry of Science and ICT through the National Research Foundation of Korea (No. 2019H1D3A2A02100593), and State Key Laboratory for Modification of Chemical Fibers and Polymer Materials, Donghua University. Supplementary material Supplementary material associated with this article can be found, in the online version, at doi:10.1016/j.jtice.2019.10.009. References [1] Pendergast MM, Hoek EM. A review of water treatment membrane nanotechnologies. Energy Environ Sci 2011;4(6):1946–71. [2] Quist-Jensen CA, Ali A, Drioli E, Macedonio F. Perspectives on mining from sea and other alternative strategies for minerals and water recovery–The development of novel membrane operations. J Taiwan Inst Chem Eng 2019;94:129–34. [3] Li Y, Jin C, Peng Y, An Q, Chen Z, Zhang J, Ge L, Wang S. Fabrication of PVDF hollow fiber membranes via integrated phase separation for membrane distillation. J Taiwan Inst Chem Eng 2019;95:487–94. [4] Hitsov I, Eykens L, De Schepper W, De Sitter K, Dotremont C, Nopens I. Full-scale direct contact membrane distillation (DCMD) model including membrane compaction effects. J Membr Sci 2017;524:245–56. [5] Chen TH, Huang YH. Dehydration of diethylene glycol using a vacuum membrane distillation process. J Taiwan Inst Chem Eng 2017;74:233–7. [6] Li Y, Zhu L. Preparation and characterization of novel poly (vinylidene fluoride) membranes using flower-like Bi2WO6 for membrane distillation. J Taiwan Inst Chem Eng 2017;80:867–74. [7] Suzuki T, Tanaka R, Tahara M, Isamu Y, Niinae M, Lin L, Wang J, Luh J, Coronell O. Relationship between performance deterioration of a polyamide reverse osmosis membrane used in a seawater desalination plant and changes in its physicochemical properties. Water Res 2016;100:326–36. [8] Duong PH, Chung TS, Wei S, Irish L. Highly permeable double-skinned forward osmosis membranes for anti-fouling in the emulsified oil–water separation process. Environ Sci Technol 2014;48(8):4537–45. [9] Fu W, Wang X, Zheng J, Liu M, Wang Z. Antifouling performance and mechanisms in an electrochemical ceramic membrane reactor for wastewater treatment. J Membr Sci 2019;570:355–61. [10] Zhu L, Chen M, Dong Y, Tang CY, Huang A, Li L. A low-cost mullite-titania composite ceramic hollow fiber microfiltration membrane for highly efficient separation of oil-in-water emulsion. Water Res 2016;90:277–85. [11] Qi H, Niu S, Jiang X, Xu N. Enhanced performance of a macroporous ceramic support for nanofiltration by using α -Al2 O3 with narrow size distribution. Ceram Int 2013;39(3):2463–71. [12] Picard C, Larbot A, Sarrazin J, Janknecht P, Wilderer P. Ceramic membranes for ozonation in wastewater treatment. Annales De Chimie Science Des Matériaux 2001;26(2):13–22. [13] Yin J. Membrane fouling in membrane bioreactors. Technigues Equipment Environ.Pollut.Cont 2001;3. [14] Larbot A, Gazagnes L, Krajewski S, Bukowska M, Kujawski W. Water desalination using ceramic membrane distillation. Desalination 2004;168:367–72. [15] S Sun T, Feng L, Gao X, Jiang L. Bioinspired surfaces with special wettability. Acc Chem Res 2005;38(8):644–52. [16] Gao X, Jiang L. Biophysics: water-repellent legs of water striders. Nature 2004;432(7013):36. [17] Lee W, Jin MK, Yoo WC, Lee JK. Nanostructuring of a polymeric substrate with well-defined nanometer-scale topography and tailored surface wettability. Langmuir 2004;20(18):7665–9. [18] Nakajima A, Hashimoto K, Watanabe T. Recent studies on super-hydrophobic films. Molecular materials and functional polymers. Vienna: Springer; 2001. p. 31–41. [19] Wenzel RN. Resistance of solid surfaces to wetting by water. Ind Eng Chem 1936;28(8):988–94. [20] Cassie AB. Contact angles. Discuss Faraday Soc 1948;3:11–16. [21] Kaviyarasu K, Sajan D, Selvakumar MS. A facile hydrothermal route to synthesize novel pbi2 nanorods. J Phys Chem Solids 2012;73(11):1396–400.
[m5G;October 26, 2019;6:3] 11
[22] Kaviyarasu K, Manikandan E, Kennedy J, Jayachandran M, Gomes UUD. Synthesis and characterization studies of nio nanorods for enhancing solar cell efficiency using photon upconversion materials. Ceram Int 2016;42(7):8385–94. [23] Kaviyarasu K, Mola GT, Oseni SO, Kanimozhi K, Magdalane CM. ZnO doped single wall carbon nanotube as an active medium for gas sensor and solar absorber. J Mater Sci Mater Electron 2019;30(1):147–58. [24] Liu G, Wang H, Wang M, Liu W, Ardhi RE, Zou D, Lee JK. Study on a stretchable, fiber-shaped, and Tio2 nanowire array-based dye-sensitized solar cell with electrochemical impedance spectroscopy method. Electrochim Acta 2018;267:34–40. [25] Li X, Liu G, Shi M, Li J, Li J, Guo C, Lee JK, Zheng J. Using tio2 mesoflower interlayer in tubular porous titanium membranes for enhanced electrocatalytic filtration. Electrochim Acta 2016;218:318–24. [26] Li X, Liu G, Shi M, Zou D, Wang C, Zheng J. A novel electro-catalytic ozonation process for treating rhodamine b using mesoflower-structured Tio2-coated porous titanium gas diffuser anode. Sep Purif Technol 2016;165:154–9. [27] Liu G, Gao X, Wang H, Kim AY, Zhao Z, Lee JK, Zou D. A novel photoanode with high flexibility for fiber-shaped dye sensitized solar cells. J Mater Chem A 2016;4(16):5925–31. [28] Duan YQ, Yang SP, Yu JL, Yuan ZH. Photocatalytic degradation of gaseous formaldehyde by Fe-doped ZnO nanorods grown on ceramic spheres. Chin J Inorg Chem 2014(7):27. [29] Wang M, Yu W, Zhang Y, Woo JY, Chen Y, Wang B, Yun Y, Liu G, Lee JK, Wang L. A novel flexible micro-ratchet/ZnO nano-rods surface with rapid recovery icephobic performance. J Ind Eng Chem 2018;62:52–7. [30] Chen Y, Liu G, Jiang L, Kim JY, Ye F, Lee JK, Wang L, Wang B. Icephobic performance on the aluminum foil-based micro-/nanostructured surface. Chin Phys 2017;26(4):351–5. [31] Wang M, Liu G, Yu H, Lee SH, Wang L, Zheng J, Wang T, Yun Y, Lee JK. ZnO nanorod array modified PVDF membrane with superhydrophobic surface for vacuum membrane distillation application. ACS Appl Mater Inter 2018;10(16):13452–61. [32] Fang H, Gao JF, Wang HT, Chen CS. Hydrophobic porous alumina hollow fiber for water desalination via membrane distillation process. J Membr Sci 2012;403:41–6. [33] Krajewski SR, Kujawski W, Bukowska M, Picard C, Larbot A. Application of fluoroalkylsilanes (FAS) grafted ceramic membranes in membrane distillation process of Nacl solutions. J Membr Sci 2006;281(1–2):253–9. [34] Manekkathodi A, Lu MY, Wang CW, Chen LJ. Direct growth of aligned zinc oxide nanorods on paper substrates for low-cost flexible electronics. Adv Mater 2010;22(36):4059–63. [35] Wang L, Yu L, Yi L, Yuan B, Hou Y, Meng X, Liu J. Long time and distance self-propelling of a PVC sphere on a water surface with an embedded ZnO micro-/nano-structured hollow sphere. Chem Comm 2017;53(15):2347–50. [36] Zhang M, Wang L, Feng S, Zheng Y. A strategy of antifogging: air-trapped hollow microsphere nanocomposites. Chem Mater 2017;29(7):2899–905. [37] Kaviyarasu K, Maria MC, Kanimozhi K, Kennedy J, Letsholathebe D. Elucidation of photocatalysis, photoluminescence and antibacterial studies of ZnO thin films by spin coating method. J Photochem Photobiol B Biol 2017;173:466–75. [38] Saravanakkumar D, Oualid HA, Brahmi Y, Ayeshamariam A, Kaviyarasu K. Synthesis and characterization of Cuo/ZnO/Cnts thin films on copper substrate and its photocatalytic applications. OpenNano 2019;4:100025. [39] Li L, Li B, Dong J, Zhang J. Roles of silanes and silicones in forming superhydrophobic and superoleophobic materials. J Mater Chem A 2016;4(36):13677–725. [40] Fujii S, Yusa SI, Nakamura Y. Stimuli-Responsive liquid marbles: controlling structure, shape, stability, and motion. Adv Funct Mater 2016;26(40):7206–23. [41] Guo P, Zheng Y, Wen M, Song C, Lin Y, Jiang L. Icephobic/anti-icing properties of micro/nanostructured surfaces. Adv Mater 2012;24(19):2642–8. [42] Benzinger WD, Parekh BS, Eichelberger JL. High temperature ultrafiltration with Kynar® poly (vinylidene fluoride) membranes. Sep Sci Technol 1980;15(4):1193–204. [43] Razmjou A, Arifin E, Dong G, Mansouri J, Chen V. Superhydrophobic modification of Tio2 nanocomposite PVDF membranes for applications in membrane distillation. J Membr Sci 2012;415:850–63. [44] Yang C, Tian M, Xie Y, Li XM, Zhao B, He T, Liu J. Effective evaporation of CF4 plasma modified PVDF membranes in direct contact membrane distillation. J Membr Sci 2015;482:25–32. [45] Jang E, Nam SH, Hwang TM, Lee S, Choi Y. Effect of operating parameters on temperature and concentration polarization in vacuum membrane distillation process. Desalin Water Treat 2015;54(4–5):871–80. [46] Edwie F, Chung TS. Development of hollow fiber membranes for water and salt recovery from highly concentrated brine via direct contact membrane distillation and crystallization. J Membr Sci 2012;421:111–23. [47] Safavi M, Mohammadi T. High-salinity water desalination using VMD. Chem Eng J 2009;149(1–3):191–5. [48] Wang JW, Li L, Zhang JW, Xu X, Chen CS. β -Sialon ceramic hollow fiber membranes with high strength and low thermal conductivity for membrane distillation. J Eur Ceram Soc 2016;36(1):59–65. [49] Garofalo A, Donato L, Drioli E, Criscuoli A, Carnevale MC, Alharbi O, Aljlil SA, Algieri C. Supported mfi zeolite membranes by cross flow filtration for water treatment. Sep Purif Technol 2014;137:28–35. [50] Zhang JW, Fang H, Hao LY, Xu X, Chen CS. Preparation of silicon nitride hollow Fibre membrane for desalination. Mater Lett 2012;68:457–9.
Please cite this article as: T. Wang, Y. Yun and M. Wang et al., Superhydrophobic ceramic hollow fiber membrane planted by ZnO nanorod-array for high-salinity water desalination, Journal of the Taiwan Institute of Chemical Engineers, https://doi.org/10.1016/j.jtice. 2019.10.009
JID: JTICE
[m5G;October 26, 2019;6:3]
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
Superhydrophobic ceramic hollow fiber membrane planted by ZnO nanorod-array for high-salinity water desalination Tao Wang a, Yanbin Yun a,∗, Manxiang Wang b,∗, Chunli Li c, Guicheng Liu b,d, Woochul Yang b a
College of Environmental Science and Engineering, Beijing Forestry University, Beijing, 100083, PR China Department of Physics, Dongguk University, Seoul 04620, Republic of Korea c New Technique Centre, Institute of Microbiology, Chinese Academy of Sciences, Beijing 100101, PR China d State Key Laboratory for Modification of Chemical Fibers and Polymer Materials, Donghua University, Shanghai 200092, PR China b
a r t i c l e
i n f o
Article history: Received 8 July 2019 Revised 25 September 2019 Accepted 12 October 2019 Available online xxx Keywords: Ceramic hollow fiber membrane ZnO nanorods Superhydrophobic surface Vacuum membrane distillation Antifouling
a b s t r a c t To solve the problems of membrane material tolerance and membrane fouling, a micro/nano hierarchial structure with low surface energy was constructed above the exterior surface of a ceramic hollow fiber membrane using ZnO nanorod arrays and 1H,1H,2H,2H-perfluorodecyltriethoxysilane (PDTS) coatings, which make it superhydrophobic and self-cleaning. The surface morphology, chemical functional groups, and water contact angel of the modified membranes were identified. The results show that large quantity of ZnO nanorods possess desirable characteristics (i.e. superhydrophobicity, exceptional thermal and mechanical stability, and water contact angle of 160.12°) were detected on the ceramic membrane. The novel membrane shows excellent self-cleaning performance and good desalination ability in the utilization of vacuum membrane distillation (VMD) system for high-salinity water desalination. © 2019 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
1. Introduction Technology advancement on water treatment for wastewater recycling and production of clean water is gaining increasing attention due to the ever-growing of pollution in the water environment and shortage of clean water resource [1,2]. In recent years, membrane distillation technology has been widely used in water and wastewater treatment [3–9]. At present, the existing membranes available in the market are mostly organic polymer membranes which have low thermal and mechanical stability will restraint their performance under extreme conditions [10,11]. In contrast, ceramic membranes that are mostly derived from metal oxides (e.g. silica, alumina, zirconia and so on) show better performance in terms of their mechanical and thermal stability. However, due to the existence of hydroxyl (-OH) groups on the surface of the ceramic membrane that lead to its hydrophilic nature [12], the ceramic membrane is unfavourable to be used directly in membrane distillation. Frequent membrane cleaning and membrane replacement caused by membrane fouling are other difficulties that limit the application of membrane distillation [13]. Therefore, the development of a ceramic membrane with superhydrophobicity and
∗
Corresponding authors. E-mail addresses: [email protected] (Y. Yun), [email protected] (M. Wang).
anti-pollution ability is of great significance to the development of membrane distillation technology. Larbot et al. [14] first applied fluorosilane hydrophobic modified alumina and zirconia ceramic membrane to the membrane distillation process, which proves the feasibility of modified ceramic membrane used in membrane distillation. Many superhydrophobic surfaces such as sacred lotus leaves [15], water strider’s legs [16], cicada orni’s wings (Lee et al.) [17] exist in nature whose water contact angles are greater than 150°. There is a large number of micro/nano scale protrusions on these surfaces. Studies have shown that the combination of micron and nano-scale rough surfaces, as well as small surface energy materials resulted in water contact, angles greater than 150° and self-cleaning effects [18]. At the same time, the micro/nano hierarchical structured surface associated with small free energy can effectively promote the liquid from Wenzel state to Cassie state spontaneously [19,20]. Therefore, constructing a micro/nanoscale hierarchical structured nanorod arrays with small surface energy coatings on the membrane surface represents a more competent and ideality avenue for modifying the ceramic hollow fiber membrane. Recently, a large number of nanomaterials, such as PbI2 , NiO and ZnO, have been applied in different fields [21-23]. Among these, due to the advantages such as simple preparation technique, rich morphology, stable chemical, mechanical and thermal properties, ZnO nanophase materials have been used to fabricate superhydrophobic surfaces in many fields. Meanwhile, the hydrothermal method has been widely used in the
https://doi.org/10.1016/j.jtice.2019.10.009 1876-1070/© 2019 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
Please cite this article as: T. Wang, Y. Yun and M. Wang et al., Superhydrophobic ceramic hollow fiber membrane planted by ZnO nanorod-array for high-salinity water desalination, Journal of the Taiwan Institute of Chemical Engineers, https://doi.org/10.1016/j.jtice. 2019.10.009
JID: JTICE 2
ARTICLE IN PRESS
[m5G;October 26, 2019;6:3]
T. Wang, Y. Yun and M. Wang et al. / Journal of the Taiwan Institute of Chemical Engineers xxx (xxxx) xxx
growth of metal oxide nanorods because of its low reaction temperature and mild reaction conditions [24–27]. Duan et al. [28] developed a ceramic spheres layered with nanorod. Growth of ZnO nanorods was performed via sintering treatment at 350 °C and hydrothermal reaction. Then, the substrate of balls was cleaned with deionized water multiple times and dried prior for calcination at 450 °C in air followed by cooling to room temperature and finally ZnO nanorods grown on ceramic balls were obtained. Wang et al. [29,30] sintered zinc nitrate hexahydrate solution on the surface of PDMS at 300 °C and obtained a novel superhydrophobic anti-ice and de-icing material by hydrothermal growth of ZnO nanorods. Wang et al. [31] treated the hydrophobicity of PVDF membrane by using micro/nano structure to improve the fouling and wetting resistance of PVDF membrane. Fang et al. [32] used fluorinated silane hydrophobic modified ceramic hollow fiber membrane. The dried ceramic hollow fiber membrane was immersed into 2 wt% 1H, 1H, 2H, 2H- perfluorooctyltriethoxysilane (FAS) in ethanol solution at room temperature for 24 h. Hydrophobic modified ceramic hollow fiber membranes were obtained after drying. Due to the low surface energy and excellent thermal stability of 1H,1H,2H,2H-perfluorodecyltriethoxysilane (PDTS), Krajewski et al. [33]. used PDTS chloroform solution of 0.01 mol L − 1 as a graft solution. The membranes produced were detected with the contact angle ranging from 142°–148°, thus indicating the hydrophobic nature of the fluoroalkylsilanes grafted ceramic zirconia membrane. In previous studies, the hydrophobicity and antifouling ability of the membrane can be effectively improved by combining the growth of micron/nano materials on the membrane surface to change the roughness of the membrane surface and the coating of fluorosilane to reduce the surface energy of the membrane. To the best of our knowledge, there has yet to be any research reported on the growth of ZnO nanorods particles and coating of fluorosilane on modification of ceramic hollow fiber membranes for use in the vacuum membrane distillation (VMD) field. In this paper, a superhydrophobic ceramic hollow fiber membrane has been developed for desalination of high concentration brine via membrane distillation. The hydrophobic surface with micro/nanoscale hierarchical structure was constructed on alumina ceramic hollow fiber membrane by ZnO nanorod array and PDTS coating. The preparation of ZnO seeds layer by a pyrolysis−adhesion approach at 350 °C represents the key step in order to construct a three-dimensional structure ZnO nanorods to adhere on the membrane surface. The preparation process of the membrane was described in detail in the following, while the membrane fouling, VMD properties, chemical composition, mechanical and thermal stability, surface structure, hydrophobicity, N2 permeance and clean water flux of the membrane were also presented and discussed extensively. 2. Experimental section Fig. 1 shows the modification steps of the ZnO nanorods and PDTS ceramic hollow fiber membrane. Firstly, before seeding and growth processes, the virgin ceramic hollow fiber membrane was cleaned with deionized water and ethanol in an ultrasonic bath for 10 min to remove surface contaminants. Secondly, preparation and adhesion of the ZnO seeds on the ceramic hollow fiber membrane. This process involves two effective in-situ reactions: Zn(CH3 COO)2 + 2NaOH → Zn(OH)2 ↓ + 2NaCH3 COO (neutralization, pH = 9.05) and Zn(OH)2 ↓ → ZnO↓ + H2 O↑ (pyrolysis). Among these, The in-situ reactions on the surface of ceramic hollow fiber membranes were carried out using the pyrolysisadhesion method at 350 °C to solve the technical difficulty of ZnO seeds layer preparation [34]. Thirdly, ZnO nanorod arrays were grown by classical hydrothermal reaction. Finally, the hydrophobic-
ity of the ZN–CHF membrane was layered by combining with the PDTS. 2.1. Planting of ZnO seeds on ceramic hollow fiber membrane After immersing into a 0.07 mol L−1 zinc acetate ethanol solution for 5 min, the ceramic hollow fiber membrane was gently taken out at a uniform velocity and placed in the muffle furnace at 350 °C for 30 min. Subsequently, the dried ceramic hollow fiber membrane was soaked into a 0.1 mol L−1 sodium hydroxide ethanol solution for 1 min followed by a second time of drying at the same condition. Finally, the ZnO seeds that adhered on the ceramic hollow fiber membrane (labelled as ZS-CHF membrane) was obtained by scouring the inner and outer surfaces of the resulting membrane with deionized water and dried in a muffle furnace at 350 °C for 30 min again. 2.2. Growth of ZnO nanorods on the ZS-CHF membrane A formulated mixture of zinc nitrate (0.05 mol L − 1 ) and hexamethylenetaetramine (HMTA) (0.05 mol L − 1 ) stirred by a magnetic stirrer was used as a growth solution of ZnO nanorods on the ZS-CHF membrane. The ZS-CHF membrane and the growth solution were transferred into a closed stainless-steel reaction vessel. The sealed stainless-steel reaction vessel was initially heated at 65 °C for 2 h and then increased the temperature to 95 °C and maintained for 18 h. After washing the obtained membrane with deionized water and drying at 350 °C for 1 h, the final product i.e. ZnO nanorod array grown ceramic hollow fiber membrane (marked as ZN–CHF membrane) was obtain. 2.3. Hydrophobicity treatment for original ceramic hollow fiber and ZN-CHF membrane The fluorosilane coating method was employed for hydrophobicity modification on the alumina ceramic hollow fiber membrane. The membrane was immersed in a 1 vol% PDTS ethanol solution for 24 h followed by drying at 120 °C for 2 h to obtain the PDTS-coated alumina ceramic hollow fiber membrane (labelled as P-CHF membrane). The same method was used to modify the ZN–CHF membrane to obtain the PDTS-coating ZN–CHF membrane (labelled as P-ZN–CHF membrane). 2.4. VMD performances of the P-ZN-CHF membrane The VMD properties of the P-ZN–CHF membranes were analyzed using a custom-made VMD system feeding by a 1000 mL of 200 g L − 1 NaCl solution, and the effective area of the membrane in the module was 27.65 cm2 . The feed was continuously fed the vacuum membrane distillation process, the concentration increased throughout the test. The changes of membrane permeation and the ionic conductivity of the permeated liquid were tabulated at different operation conditions (e.g. temperature, vacuum pressure, and flow velocity) of the feed solution. The permeation flux and conductivity of the P-ZN–CHF membrane and the P-CHF membrane for 3 h of continuous operation in the VMD system were compared. 3. Results and discussion 3.1. Properties of the ceramic hollow fiber membranes Fig. 2 shows the surface diversification of ceramic hollow fiber membranes after modification. The surface of hydrophilic virgin ceramic hollow fiber membrane used in the experiment was composed of irregular block structure (Fig. 2a and b). However, the surface of the membrane is relatively smooth without apparent bulges. As shown in Fig. 2c and d, it is evident that there is
Please cite this article as: T. Wang, Y. Yun and M. Wang et al., Superhydrophobic ceramic hollow fiber membrane planted by ZnO nanorod-array for high-salinity water desalination, Journal of the Taiwan Institute of Chemical Engineers, https://doi.org/10.1016/j.jtice. 2019.10.009
JID: JTICE
ARTICLE IN PRESS
[m5G;October 26, 2019;6:3]
T. Wang, Y. Yun and M. Wang et al. / Journal of the Taiwan Institute of Chemical Engineers xxx (xxxx) xxx
3
Fig. 1. Structural evolution for the formation of superhydrophobic ceramic hollow fiber membrane. Notes: ZnO seeds planted ceramic hollow fiber membrane (ZS-CHF membrane), ZnO nanorod array grown ceramic hollow fiber membrane (ZN–CHF membrane), and PDTS-coated ZN–CHF membrane (P-ZN–CHF membrane).
a dense protrusion like a stone fragment on the surface of the ceramic hollow fiber membrane, whose diameter between 400– 550 nm. The seeds layer of ZnO formed above the membrane substrate by pyrolysis-adhesion approach at 350 °C is an indispensable condition for the growth of three-dimensional ZnO nanorods. ZnO nanorod arrays were grown on ZS-CHF membrane treated by hydrothermal method with milder temperature conditions instead of a few two-dimensional sheet ZnO layers as in Fig. 2c and d. As observed in Fig. 2e and f, there are many uniforms and ordered nanorod arrays with a diameter of ∼288 nm and a length of ∼ 650 nm on the ZN–CHF membrane. Also, as shown in Fig. 2e, f, g and h, no significant differences were observed on the surface morphology between ZN–CHF and P-ZN–CHF membranes. In Fig. 3, due to the deposition of ZnO nanorod-array on surface of ceramic film, Zn-O stretching vibration absorption peaks of ZN–CHF and P-ZN–CHF are shown at 480 cm−1 . PDTS is composed of the hydrophilic triethoxy silane segment and the hydrophobic carbon chain. And the C-F peak in 1262 cm−1 is from the PDTS. The triethoxy silane segment, touching with water, is easy to be hydrolyzed to form trisilicon alcohol. Then, the hydroxyl group of the trisilicon alcohol reacts with ZnO to form hydrogen bond and Si-O-Zn covalent bond (as shown in 974 cm−1 of P-ZN–CHF). Under appropriate conditions (for example, favorable distance and direction), cross-linking among trisilicon alcohol molecules occurred to form a 2D network with the formation of Si-O-Si bond (in 1147 cm−1 of P-ZN–CHF). Finally, due to the heating treatment at 120 °C, the density of the Si-OH bond significantly reduced, which is conducive to the formation of Si-O-Zn bonds. And the above peaks reveal that PDTS had been coated on the surface of the ZnO nanorods. Hence, the hydrophobization treatment performed on the ZN–CHF membrane shows a negligible effect to its morphology in which similar observation was reported in the literatures [35,36]. The surface roughness of ceramic membranes varies greatly during hydrophobic modification. Compared to the smooth surface of the original ceramic membrane (Fig. 4a, 5 μm × 5 μm), the roughness of ZS-CHF film surface increases obviously (Fig. 4b, 5 μm × 5 μm). Moreover, as shown in Figs. 4c (5 μm × 5 μm) and 4d (10 μm × 10 μm), the surface roughness of P-ZN–CHF membrane is the highest, among the three samples due to the existence of ZnO nanorod arrays. In the process of ceramic membrane modification, the roughness of the membrane surface is increasing
Table 1 Information about the liquid entry pressure, pore parameter, thickness, diameter and length of the CHF, P-CHF and P-ZN–CHF membranes. Information
CNF
P-ZN–CHF
P-CHF
LEP/MPA Porosity (%) Median pore diameter (volume)/nm Median pore diameter (area)/nm Average pore diameter (4 V/A)/nm Thickness (mm) Internal diameter (mm) External diameter (mm) Length (cm)
– 26.83564369.5 3962.8 3406.4 2.01 9.51 11.52 15
0.175 15.9009 4434.1 3778.1 3104.3 2.01 9.51 11.52 15
0.11 26.643 4364.8 3924.5 3333.0 2.01 9.51 11.52 15
step by step, and the hydrophobicity of the membrane is also improving with the improvement of the roughness. As shown in Table 1 and Fig. 5a, pore distribution (median pore diameter, average pore diameter) and porosity of the original alumina ceramic hollow fiber (marked as CHF membrane), P-CHF and P-ZN–CHF membranes were measured by mercury porosimetry. In Fig. 5a, a main peak was observed in the pore diameter distribution of the three ceramic hollow fiber membranes (CHF, P-CHF and P-ZN–CHF membranes). Among them, there is no difference between CHF and P-CHF membranes, which also proves that the hydrophobic modification of PDTS has little effect on the membrane morphology. Compared with CHF and P-CHF membranes, the median pore size, average pore size and porosity of P-ZN–CHF membranes decreased in varying degrees, and the porosity of P-ZN–CHF membranes decreased by about 40%. This may be caused by the density of the micro/nanostrcuture of the ZnO nanorods modified membrane [37,38]. Overall, the ceramic hollow fiber membrane shows superhydrophobic micro/nanoscale hierarchical structures after growing with the ZnO nanorods on its surface and PDTS coating, which can be used in membrane distillation applications. At the same time, it retained the original internal structure, including micropores, thickness and so on. Fig. 5b and 5c present the gas and liquid (clean water flux) permeation properties of the ceramic hollow fiber membranes. As observed from Fig. 5b that the membrane maintained high permeability to nitrogen gas (1.99 × 106 L m2 h−1 MPa−1 ) after modification with ZnO nanorods, which were lower than that for the CHF membrane (4.53 × 106 L m−2 h−1 MPa−1 ) and P-CHF mem-
Please cite this article as: T. Wang, Y. Yun and M. Wang et al., Superhydrophobic ceramic hollow fiber membrane planted by ZnO nanorod-array for high-salinity water desalination, Journal of the Taiwan Institute of Chemical Engineers, https://doi.org/10.1016/j.jtice. 2019.10.009
JID: JTICE 4
ARTICLE IN PRESS
[m5G;October 26, 2019;6:3]
T. Wang, Y. Yun and M. Wang et al. / Journal of the Taiwan Institute of Chemical Engineers xxx (xxxx) xxx
Fig. 2. SEM morphologies of ZnO nanorod decorated ceramic membranes. (a, b) Virgin ceramic hollow fiber membrane, (c, d) ZS-CHF, (e, f) ZN–CHF, and (g, h) P-ZN–CHF membranes.
Please cite this article as: T. Wang, Y. Yun and M. Wang et al., Superhydrophobic ceramic hollow fiber membrane planted by ZnO nanorod-array for high-salinity water desalination, Journal of the Taiwan Institute of Chemical Engineers, https://doi.org/10.1016/j.jtice. 2019.10.009
JID: JTICE
ARTICLE IN PRESS
[m5G;October 26, 2019;6:3]
T. Wang, Y. Yun and M. Wang et al. / Journal of the Taiwan Institute of Chemical Engineers xxx (xxxx) xxx
5
Fig. 3. FT-IR curve of the virgin ceramic hollow fiber, ZN–CHF, P-ZN–CHF membranes.
Fig. 4. AFM morphologies of ZnO nanorod decorated ceramic membranes. (a) Virgin ceramic hollow fiber membrane, (b) ZS-CHF, and (c, d) P-ZN–CHF membranes.
brane (2.76 × 106 L m2 h−1 MPa−1 ). This was due to the decrease of porosity of ceramic hollow fiber membrane modified by ZnO nanorods. However, it still maintained good gas permeation properties. The modifications of ZnO and PDTS on the membrane have increased the surface hydrophobicity which subsequently decreased the permeability of clean water. The clean water can be passed through the un-modified hydrophilic CHF membrane at a faster rate of 46.2 × 103 kg m−2 h−1 MPa−1 (Fig. 5c). For the modified P-ZN–CHF membrane, the permeation of clean water was
observed only at a pressure above 0.175 MPa. Thus, it was indicated that the P-ZN–CHF membrane (175 kPa) possesses a higher liquid entry pressure (also refers to critical pressure value) than the CHF membrane (0 kPa) and P-CHF membrane (110 kPa). So, the P-ZN–CHF membrane, which has low water permeability, was suitable for the application of vacuum membrane distillation. Water contact angle (WCA) is an important parameter reflecting the hydrophobicity of a material. And the membrane material with strong hydrophobicity is needed in the application of
Please cite this article as: T. Wang, Y. Yun and M. Wang et al., Superhydrophobic ceramic hollow fiber membrane planted by ZnO nanorod-array for high-salinity water desalination, Journal of the Taiwan Institute of Chemical Engineers, https://doi.org/10.1016/j.jtice. 2019.10.009
JID: JTICE 6
ARTICLE IN PRESS
[m5G;October 26, 2019;6:3]
T. Wang, Y. Yun and M. Wang et al. / Journal of the Taiwan Institute of Chemical Engineers xxx (xxxx) xxx
Fig. 5. (a) Pore size distributions, (b) N2 permeance, and (c) clean water flux (CWF) of the CHF, P-CHF and P-ZN–CHF membranes.
membrane distillation. Only vapour can pass through the membrane, which must be hydrophobic and not wetted by the liquid. The higher the hydrophobicity performance better in the property. The superhydrophobic membrane not only can prevent the membrane pore from being wet, but also improve the liquid entry pressure, antifouling and long-term stability of the membrane. To prove that ZnO nanorod arrays and PDTS coating modified ceramic hollow fiber membranes were suitable for membrane distillation,
the hydrophobicity, thermal stability and mechanical stability of modified membranes were measured at different temperatures and condition. As shown in Fig. 6, the difference of WCA between different membranes during the modification process was intuitively introduced. It was found that the original ceramic hollow fiber membrane used in the study is superhydrophilic and its contact angle was approximately 0°. The ZN–CHF membrane shows an inferior hydrophobicity with the WCA of 94.34°. Due to its low
Please cite this article as: T. Wang, Y. Yun and M. Wang et al., Superhydrophobic ceramic hollow fiber membrane planted by ZnO nanorod-array for high-salinity water desalination, Journal of the Taiwan Institute of Chemical Engineers, https://doi.org/10.1016/j.jtice. 2019.10.009
JID: JTICE
ARTICLE IN PRESS
[m5G;October 26, 2019;6:3]
T. Wang, Y. Yun and M. Wang et al. / Journal of the Taiwan Institute of Chemical Engineers xxx (xxxx) xxx
Fig. 6. Surface contact angles of the CHF, ZN–CHF, P-ZN–CHF and P-CHF membranes.
surface energy, the PDTS was coated on the ZnO surface to reduce the wash and erosion of the ZnO substrate by distillate. Surface contact angle is up to 160.12°, which is the quantitative and direct evidence. The WCA of the P-ZN–CHF membrane modified by ZnO
7
nanorods and PDTS shows the highest value of 160.12°, indicating the superhydrophobic nature of P-ZN–CHF membrane. According to Fowkes method, the solid surface energy of P-ZN–CHF membrane in water is 6.46344 × 10−5 J m−2 . The hydrophobic properties of PZN–CHF membrane were enhanced by two aspects: First, the PDTS layer can make the membrane surface hydrophobic, owing to the lower surface energy of methyl fluoride (- CF3 ) group [39], which also makes the WCA of the P-CHF membrane be 142.96°. Second, the micro/nanoscale structure produced by the modification of ZnO nanorods is a super hydrophobic structure. It is observed that the WCA of the P-ZN–CHF membrane is greater than the P-CHF membrane without modification by ZnO nanorods. This can be explained by the micro/nanoscale hierarchical structure present on the P-ZN–CHF membrane surface can store abundant air pockets in the troughs between the individual nanorods. Consequently, the contact area and the adhesion/binding force between the membrane surface and the droplets was decreased by the high aspect ratio of the ZnO nanorods. According to the Cassie-Baxter theory [40], it is a significant characteristic to tailor the surface with superhydrophobicity. In vacuum membrane distillation (VMD) applications, the membrane materials should maintain its hydrophobicity throughout the
Fig. 7. Effect of the (a) ultrasonic treatment time and (b) 80 °C-immersion time on the water contact angles of the CHF, P-CHF and P-ZN–CHF membranes.
Please cite this article as: T. Wang, Y. Yun and M. Wang et al., Superhydrophobic ceramic hollow fiber membrane planted by ZnO nanorod-array for high-salinity water desalination, Journal of the Taiwan Institute of Chemical Engineers, https://doi.org/10.1016/j.jtice. 2019.10.009
JID: JTICE 8
ARTICLE IN PRESS
[m5G;October 26, 2019;6:3]
T. Wang, Y. Yun and M. Wang et al. / Journal of the Taiwan Institute of Chemical Engineers xxx (xxxx) xxx
Fig. 8. Variation of the permeate fluxes of P-ZN–CHF membrane with increasing (a) feed temperature, (b) vacuum pressure, and (c) feed velocity.
Please cite this article as: T. Wang, Y. Yun and M. Wang et al., Superhydrophobic ceramic hollow fiber membrane planted by ZnO nanorod-array for high-salinity water desalination, Journal of the Taiwan Institute of Chemical Engineers, https://doi.org/10.1016/j.jtice. 2019.10.009
JID: JTICE
ARTICLE IN PRESS
[m5G;October 26, 2019;6:3]
T. Wang, Y. Yun and M. Wang et al. / Journal of the Taiwan Institute of Chemical Engineers xxx (xxxx) xxx
9
Fig. 9. Permeate fluxes and ionic conductivity of the P-CHF and P-ZN–CHF membranes during a 180-min-continuous-VMD operation with a 200 g L−1 NaCl feed solution, 0.085 MPa vacuum pressure and 0.032 m s−1 velocity, at 61 °C.
range of running temperature and distinguished thermal stability and excellent mechanical stability to accommodate to different process conditions, including high running temperature, different vacuum pressure and strong liquid flow velocity. To evaluate the mechanical stability and thermal stability of modified membranes in membrane distillation applications. In this study, modified membranes were placed in a hot water bath and ultrasonic environment to simulate the scour of the feed liquid on the membrane [41–43]. The change of contact angle on the membranes can reflect the hydrophobicity of the membrane [41]. Fig. 7a shows the changes of the contact angle of P-ZN–CHF, P-CHF and CHF membranes after an ultrasonic treatment for 1 h in deionized water at room temperature. The contact angle of P-ZN–CHF membrane is about 149° after 60 min, while the minimum contact angle of P-CHF membrane is only 134°, indicating that P-ZN–CHF membrane has excellent mechanical stability. Meanwhile, the PZN–CHF membrane has distinguished thermal stability. Fig. 7b depicts the contact angle of P-ZN–CHF membrane were measured after processed in deionized water at 80 °C for 60 min. The contact angle of P-CHF membrane decreased to 135°, while that of P-ZN–CHF membrane only decreased by 6° and reached to 154°, indicating that P-ZN–CHF membrane has distinguished thermal stability. The reasons why the P-ZN–CHF membrane emerges the excellent mechanical stability and significant thermal stability are presented as followed: On the one hand, ZnO nanorods have been strong fastened on the ceramic hollow fiber membrane-based material by ZnO seed layer. The water molecule was hardly to be permeated into the gaps between the ZnO nanorods that has a higher density. On the other hand, there is Si-O-Zn covalent bond formed between PDTS and ZnO nanorods makes the film surface form a stable hydrophobic layer and not easy to fall off. Therefore, the effect of ultrasonic vibration and hot water on P-ZN–CHF membrane was weakened. 3.2. Application of the P-ZN-CHF membrane in vacuum membrane distillation In this paper, P-ZN–CHF membrane was used for vacuum membrane distillation to desalination high concentration brine. A homemade VMD system was used to investigate the effects of high salinity of NaCl solution (200 g L−1 ) on the permeation fluxes of P-ZN–CHF membrane at different feed temperature, vacuum and feed velocity. Due to the increase of temperature and velocity of
feed liquid and vacuum degree, the driving force on both sides of P-ZN–CHF membrane enhances while the thermal boundary layer on the film surface decreases. Therefore, in Fig. 8, when the temperature and velocity of feed liquid and vacuum pressure are increased, the permeation fluxes of the membrane increased in varying degrees. The most obvious one is the effect of feed temperature on the permeate fluxes of P-ZN–CHF membrane; when vacuum pressure and feed velocity were fixed to 0.085 MPa and 0.032 m s−1 , the feed temperature is 80 °C, permeate fluxes is 70.82 kg m−2 h−1 , and it is only 12.73 kg m−2 h−1 at 55 °C. The Fig. 8b was the effect of vacuum pressure on the membrane permeate fluxes of P-ZN–CHF when feed temperature and feed velocity were fixed to 60 °C and 0.032 m s − 1 , vacuum pressure was 0.07 MPa permeate fluxes was 16.71 kg m−2 h−1 , and it is 28.25 kg m−2 h−1 at 0.09 MPa. Vacuum pressure has a great influence on permeate fluxes, although it is not as big as temperature. It is noteworthy that, the adjustment of the feed velocity shows a negligible effect on the P-ZN–CHF membrane when feed temperature and vacuum pressure were fixed to 60 °C and 0.085 MPa respectively (Fig. 8c), the feed velocity was 0.016 m s−1 , permeate fluxes was 21.09 kg m−2 h−1 , and it was 22.76 kg m−2 h−1 at 0.048 m s−1 . The results show that the P-ZN–CHF membrane has high resistivity towards the shear force on the surface of the membrane. In this study, the NaCl solution with a concentration of 200 g L−1 was used to simulate the wastewater of perchlor-alkali industrial resin regeneration with high salt content, which was used to verify the self-cleaning properties of the membranes. A continuous operation method was used to verify the high permeate fluxes performance and anti-pollution capacity and assess the desalination performance of P-ZN–CHF membrane by comparing the VMD system of P-ZN–CHF membrane and P-CHF membrane running continuously for 3 h at 61 °C, 0.032 m s−1 and 0.085 MPa. Fig. 9 reveals that the permeate fluxes of the P-ZN–CHF and PCHF membrane were gradually reduced when the operation time was increased and the ionic conductivity (IC) of the permeated liquid was gradually increased. After 3 h of testing, the permeate flux of the P-ZN–CHF membrane reduced from 27.35–23.66 kg m−2 h−1 and the IC of the permeated liquid increased from 5.13–14.32 μS cm−1 . And the WCA of P-ZN–CHF membrane remained 144.62°, which proves that PDTS did not diffuse during practice application. The P-CHF membrane has obvious differences with it, that the IC increased from 106.65 to 184.65 μS cm−1 and the permeate flux reduced from 44.06–33.55 kg m−2 h−1 . The NaCl rejection
Please cite this article as: T. Wang, Y. Yun and M. Wang et al., Superhydrophobic ceramic hollow fiber membrane planted by ZnO nanorod-array for high-salinity water desalination, Journal of the Taiwan Institute of Chemical Engineers, https://doi.org/10.1016/j.jtice. 2019.10.009
ARTICLE IN PRESS
JID: JTICE 10
[m5G;October 26, 2019;6:3]
T. Wang, Y. Yun and M. Wang et al. / Journal of the Taiwan Institute of Chemical Engineers xxx (xxxx) xxx
Table 2 MD performance for organic and ceramic membranes published recently [40–45]. Reference
Application
Membrane material
Membrane morphology
Feed solution
Water permeation flux (kg m−2 h−1 )
[45] [46] [47] [48] [49] [50] P-CHF P-ZN-CHF
VMD DCMD VMD DCMD VMD VMD VMD VMD
PTFE PVDF PP β -Sialon Zeolite/Al2 O3 Si3 N4 Al2 O3 Al2 O3
Hollow fiber Hollow fiber Disk Hollow fiber Tubular Hollow fiber Hollow fiber Hollow fiber
4 mol L−1 NaCl solution, 60 °C 4 mol L−1 NaCl solution, 60 °C 100 g L−1 NaCl solution, 55 °C 2wt% NaCl solution, 50 °C 3.5 wt% NaCl solution, 60 °C 4 wt% NaCl solution, 70 °C 200 g L−1 NaCl solution, 61 °C 200 g L−1 NaCl solution, 61 °C
7.30 ∼ 8.67 14.0 14.41 2.5 12 22.2 33.6 ∼ 44.1 23.7 ∼ 27.4
Conductivity (μS cm−1 ) 90 ∼ 100 15.6 2.49 — — — 106.6 ∼ 184.6 5.1 ∼ 14.3
Fig. 10. SEM images of the surface of used (a–c) P-ZN–CHF and (d–f) P-CHF membrane surfaces after 3 h of continuous VMD operation.
rate of P-ZN–CHF membrane is always greater than 99.99%, while the average rejection rate of P-CHF membrane is 99.94%. Compared with the P-CHF membrane, the permeation water quality of the modified membrane was much higher and kept a relatively stable state. The permeation flux and the rate of permeation flux reduction were lower than P-CHF membrane. The permeation flux of P-ZN–CHF membrane was still higher than that of other membrane distillation studies, although it was lower than P-CHF membrane. As shown in Table 2, P-ZN–CHF has higher permeation flux and maintains higher water quality than other organic and ceramic membranes. The P-ZN–CHF membrane modified by ZnO nanorods and PDTS has good performance in the application of membrane distillation. The VMD properties of P-ZN–CHF membrane indicate that the fouling and wetting situation of P-ZN–CHF membrane are more optimistic. To support this view, some direct evidence was provided by examining the P-ZN–CHF membrane tested with SEM images. In Fig. 10a–c, it shows that there are only a few NaCl crystal on the surface of P-ZN–CHF membrane, and the superhydrophobic structure on the surface of the film is not destroyed. However, the surface of P-CHF membrane contains a large amount of NaCl crystal, which have entered and blocked the membrane pore (Fig. 10d– f). It is obvious that the P-ZN–CHF membrane has good abilities of anti-fouling and self-cleaning. Water droplets are unstable on the surface of the superhydrophobic membrane and will leave the surface of the membranes quickly when disturbed slightly by the environment. The contaminants on the surface of the membranes can be removed by the droplets during the rolling process. Therefore, the superhydrophobic membrane has the function of self-cleaning. In the non-working state, the entering of water into the pore structure of the membrane is unfavourable because the hydrophobic ZnO nanorod prevents the feed liquid adhered on the surface of the
modified membrane. Even under the vacuum force in working condition, the entering of feed solution into the pore structure was still prevented due to the presence of hydrophobic ZnO nanorods that had improved the membrane surface to a superhydrophobic characteristic meanwhile also reduced the porosity of the pore opening, and thus resulting in a smaller bulge of the feed liquid. Other team also reported and discussed the same working mechanism [44]. 4. Conclusions In this paper, the ZnO seeds layer was planted on alumina ceramic hollow fiber membrane at 350 °C by the pyrolysis-adhesion method. On this basis, new ZnO nanorods modified ceramic hollow fiber membrane with micro/nanoscale hierarchical structured was fabricated by the hydrothermal method. Finally, a novel superhydrophobic membrane structure was created by coating PDTS and applied to the VMD desalination of concentrated brine. The new membrane containing with the hydrophobic ZnO nanorods can hold up abundant air molecule and turn the droplets to become Cassie’s state, this results in the membrane with superhydrophobic surface plus a water contact angle of 160°. Also, the strong bonding between ZnO nanorods and ceramic hollow fiber membranes combined with the low surface energy of PDTS coating, the new P-ZN–CHF membrane showed several properties that are necessary for utilization in the membrane distillation. This includes stable superhydrophobicity at various temperatures with distinguished thermal stability, excellent mechanical stability, maintained good gas permeation properties and higher liquid entry pressure. The new membrane was detected with a lower IC of permeated liquid after 3 h distillation of NaCl solution (200 g L−1 ) performed using a custom-made VMD system at 61 °C, due to the presence of microns gaps between the feed and membrane endow with unique an-
Please cite this article as: T. Wang, Y. Yun and M. Wang et al., Superhydrophobic ceramic hollow fiber membrane planted by ZnO nanorod-array for high-salinity water desalination, Journal of the Taiwan Institute of Chemical Engineers, https://doi.org/10.1016/j.jtice. 2019.10.009
JID: JTICE
ARTICLE IN PRESS T. Wang, Y. Yun and M. Wang et al. / Journal of the Taiwan Institute of Chemical Engineers xxx (xxxx) xxx
tifouling and antiwetting properties. Compared with other organic and inorganic membranes, P-ZN–CHF membranes have higher permeation flux. P-ZN–CHF membrane is suitable for membrane distillation applications. Acknowledgments This work was supported by the National Key Research and Development Program of China (No. 2018YFB060430203), the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (Nos. 2019R1C1C1006310 and 2019R1A2C1002844), the Ministry of Education, Korea (No. 2016R1A6A1A03012877), Brain Pool program funded by the Ministry of Science and ICT through the National Research Foundation of Korea (No. 2019H1D3A2A02100593), and State Key Laboratory for Modification of Chemical Fibers and Polymer Materials, Donghua University. Supplementary material Supplementary material associated with this article can be found, in the online version, at doi:10.1016/j.jtice.2019.10.009. References [1] Pendergast MM, Hoek EM. A review of water treatment membrane nanotechnologies. Energy Environ Sci 2011;4(6):1946–71. [2] Quist-Jensen CA, Ali A, Drioli E, Macedonio F. Perspectives on mining from sea and other alternative strategies for minerals and water recovery–The development of novel membrane operations. J Taiwan Inst Chem Eng 2019;94:129–34. [3] Li Y, Jin C, Peng Y, An Q, Chen Z, Zhang J, Ge L, Wang S. Fabrication of PVDF hollow fiber membranes via integrated phase separation for membrane distillation. J Taiwan Inst Chem Eng 2019;95:487–94. [4] Hitsov I, Eykens L, De Schepper W, De Sitter K, Dotremont C, Nopens I. Full-scale direct contact membrane distillation (DCMD) model including membrane compaction effects. J Membr Sci 2017;524:245–56. [5] Chen TH, Huang YH. Dehydration of diethylene glycol using a vacuum membrane distillation process. J Taiwan Inst Chem Eng 2017;74:233–7. [6] Li Y, Zhu L. Preparation and characterization of novel poly (vinylidene fluoride) membranes using flower-like Bi2WO6 for membrane distillation. J Taiwan Inst Chem Eng 2017;80:867–74. [7] Suzuki T, Tanaka R, Tahara M, Isamu Y, Niinae M, Lin L, Wang J, Luh J, Coronell O. Relationship between performance deterioration of a polyamide reverse osmosis membrane used in a seawater desalination plant and changes in its physicochemical properties. Water Res 2016;100:326–36. [8] Duong PH, Chung TS, Wei S, Irish L. Highly permeable double-skinned forward osmosis membranes for anti-fouling in the emulsified oil–water separation process. Environ Sci Technol 2014;48(8):4537–45. [9] Fu W, Wang X, Zheng J, Liu M, Wang Z. Antifouling performance and mechanisms in an electrochemical ceramic membrane reactor for wastewater treatment. J Membr Sci 2019;570:355–61. [10] Zhu L, Chen M, Dong Y, Tang CY, Huang A, Li L. A low-cost mullite-titania composite ceramic hollow fiber microfiltration membrane for highly efficient separation of oil-in-water emulsion. Water Res 2016;90:277–85. [11] Qi H, Niu S, Jiang X, Xu N. Enhanced performance of a macroporous ceramic support for nanofiltration by using α -Al2 O3 with narrow size distribution. Ceram Int 2013;39(3):2463–71. [12] Picard C, Larbot A, Sarrazin J, Janknecht P, Wilderer P. Ceramic membranes for ozonation in wastewater treatment. Annales De Chimie Science Des Matériaux 2001;26(2):13–22. [13] Yin J. Membrane fouling in membrane bioreactors. Technigues Equipment Environ.Pollut.Cont 2001;3. [14] Larbot A, Gazagnes L, Krajewski S, Bukowska M, Kujawski W. Water desalination using ceramic membrane distillation. Desalination 2004;168:367–72. [15] S Sun T, Feng L, Gao X, Jiang L. Bioinspired surfaces with special wettability. Acc Chem Res 2005;38(8):644–52. [16] Gao X, Jiang L. Biophysics: water-repellent legs of water striders. Nature 2004;432(7013):36. [17] Lee W, Jin MK, Yoo WC, Lee JK. Nanostructuring of a polymeric substrate with well-defined nanometer-scale topography and tailored surface wettability. Langmuir 2004;20(18):7665–9. [18] Nakajima A, Hashimoto K, Watanabe T. Recent studies on super-hydrophobic films. Molecular materials and functional polymers. Vienna: Springer; 2001. p. 31–41. [19] Wenzel RN. Resistance of solid surfaces to wetting by water. Ind Eng Chem 1936;28(8):988–94. [20] Cassie AB. Contact angles. Discuss Faraday Soc 1948;3:11–16. [21] Kaviyarasu K, Sajan D, Selvakumar MS. A facile hydrothermal route to synthesize novel pbi2 nanorods. J Phys Chem Solids 2012;73(11):1396–400.
[m5G;October 26, 2019;6:3] 11
[22] Kaviyarasu K, Manikandan E, Kennedy J, Jayachandran M, Gomes UUD. Synthesis and characterization studies of nio nanorods for enhancing solar cell efficiency using photon upconversion materials. Ceram Int 2016;42(7):8385–94. [23] Kaviyarasu K, Mola GT, Oseni SO, Kanimozhi K, Magdalane CM. ZnO doped single wall carbon nanotube as an active medium for gas sensor and solar absorber. J Mater Sci Mater Electron 2019;30(1):147–58. [24] Liu G, Wang H, Wang M, Liu W, Ardhi RE, Zou D, Lee JK. Study on a stretchable, fiber-shaped, and Tio2 nanowire array-based dye-sensitized solar cell with electrochemical impedance spectroscopy method. Electrochim Acta 2018;267:34–40. [25] Li X, Liu G, Shi M, Li J, Li J, Guo C, Lee JK, Zheng J. Using tio2 mesoflower interlayer in tubular porous titanium membranes for enhanced electrocatalytic filtration. Electrochim Acta 2016;218:318–24. [26] Li X, Liu G, Shi M, Zou D, Wang C, Zheng J. A novel electro-catalytic ozonation process for treating rhodamine b using mesoflower-structured Tio2-coated porous titanium gas diffuser anode. Sep Purif Technol 2016;165:154–9. [27] Liu G, Gao X, Wang H, Kim AY, Zhao Z, Lee JK, Zou D. A novel photoanode with high flexibility for fiber-shaped dye sensitized solar cells. J Mater Chem A 2016;4(16):5925–31. [28] Duan YQ, Yang SP, Yu JL, Yuan ZH. Photocatalytic degradation of gaseous formaldehyde by Fe-doped ZnO nanorods grown on ceramic spheres. Chin J Inorg Chem 2014(7):27. [29] Wang M, Yu W, Zhang Y, Woo JY, Chen Y, Wang B, Yun Y, Liu G, Lee JK, Wang L. A novel flexible micro-ratchet/ZnO nano-rods surface with rapid recovery icephobic performance. J Ind Eng Chem 2018;62:52–7. [30] Chen Y, Liu G, Jiang L, Kim JY, Ye F, Lee JK, Wang L, Wang B. Icephobic performance on the aluminum foil-based micro-/nanostructured surface. Chin Phys 2017;26(4):351–5. [31] Wang M, Liu G, Yu H, Lee SH, Wang L, Zheng J, Wang T, Yun Y, Lee JK. ZnO nanorod array modified PVDF membrane with superhydrophobic surface for vacuum membrane distillation application. ACS Appl Mater Inter 2018;10(16):13452–61. [32] Fang H, Gao JF, Wang HT, Chen CS. Hydrophobic porous alumina hollow fiber for water desalination via membrane distillation process. J Membr Sci 2012;403:41–6. [33] Krajewski SR, Kujawski W, Bukowska M, Picard C, Larbot A. Application of fluoroalkylsilanes (FAS) grafted ceramic membranes in membrane distillation process of Nacl solutions. J Membr Sci 2006;281(1–2):253–9. [34] Manekkathodi A, Lu MY, Wang CW, Chen LJ. Direct growth of aligned zinc oxide nanorods on paper substrates for low-cost flexible electronics. Adv Mater 2010;22(36):4059–63. [35] Wang L, Yu L, Yi L, Yuan B, Hou Y, Meng X, Liu J. Long time and distance self-propelling of a PVC sphere on a water surface with an embedded ZnO micro-/nano-structured hollow sphere. Chem Comm 2017;53(15):2347–50. [36] Zhang M, Wang L, Feng S, Zheng Y. A strategy of antifogging: air-trapped hollow microsphere nanocomposites. Chem Mater 2017;29(7):2899–905. [37] Kaviyarasu K, Maria MC, Kanimozhi K, Kennedy J, Letsholathebe D. Elucidation of photocatalysis, photoluminescence and antibacterial studies of ZnO thin films by spin coating method. J Photochem Photobiol B Biol 2017;173:466–75. [38] Saravanakkumar D, Oualid HA, Brahmi Y, Ayeshamariam A, Kaviyarasu K. Synthesis and characterization of Cuo/ZnO/Cnts thin films on copper substrate and its photocatalytic applications. OpenNano 2019;4:100025. [39] Li L, Li B, Dong J, Zhang J. Roles of silanes and silicones in forming superhydrophobic and superoleophobic materials. J Mater Chem A 2016;4(36):13677–725. [40] Fujii S, Yusa SI, Nakamura Y. Stimuli-Responsive liquid marbles: controlling structure, shape, stability, and motion. Adv Funct Mater 2016;26(40):7206–23. [41] Guo P, Zheng Y, Wen M, Song C, Lin Y, Jiang L. Icephobic/anti-icing properties of micro/nanostructured surfaces. Adv Mater 2012;24(19):2642–8. [42] Benzinger WD, Parekh BS, Eichelberger JL. High temperature ultrafiltration with Kynar® poly (vinylidene fluoride) membranes. Sep Sci Technol 1980;15(4):1193–204. [43] Razmjou A, Arifin E, Dong G, Mansouri J, Chen V. Superhydrophobic modification of Tio2 nanocomposite PVDF membranes for applications in membrane distillation. J Membr Sci 2012;415:850–63. [44] Yang C, Tian M, Xie Y, Li XM, Zhao B, He T, Liu J. Effective evaporation of CF4 plasma modified PVDF membranes in direct contact membrane distillation. J Membr Sci 2015;482:25–32. [45] Jang E, Nam SH, Hwang TM, Lee S, Choi Y. Effect of operating parameters on temperature and concentration polarization in vacuum membrane distillation process. Desalin Water Treat 2015;54(4–5):871–80. [46] Edwie F, Chung TS. Development of hollow fiber membranes for water and salt recovery from highly concentrated brine via direct contact membrane distillation and crystallization. J Membr Sci 2012;421:111–23. [47] Safavi M, Mohammadi T. High-salinity water desalination using VMD. Chem Eng J 2009;149(1–3):191–5. [48] Wang JW, Li L, Zhang JW, Xu X, Chen CS. β -Sialon ceramic hollow fiber membranes with high strength and low thermal conductivity for membrane distillation. J Eur Ceram Soc 2016;36(1):59–65. [49] Garofalo A, Donato L, Drioli E, Criscuoli A, Carnevale MC, Alharbi O, Aljlil SA, Algieri C. Supported mfi zeolite membranes by cross flow filtration for water treatment. Sep Purif Technol 2014;137:28–35. [50] Zhang JW, Fang H, Hao LY, Xu X, Chen CS. Preparation of silicon nitride hollow Fibre membrane for desalination. Mater Lett 2012;68:457–9.
Please cite this article as: T. Wang, Y. Yun and M. Wang et al., Superhydrophobic ceramic hollow fiber membrane planted by ZnO nanorod-array for high-salinity water desalination, Journal of the Taiwan Institute of Chemical Engineers, https://doi.org/10.1016/j.jtice. 2019.10.009