F-SiO₂-embedded PLA-based superhydrophobic nanofiber membrane for highly efficient membrane distillation

Abstract

Obtaining a superhydrophobic surface is key for constructing membrane distillation systems for desalination. Although perfluoroalkyl materials have been proven to be good candidates for membrane distillation, the lack of a friendly approach to treat waste perfluoroalkyl-based membranes has attracted significant concern. Herein, we propose a simple strategy for the preparation of superhydrophobic polylactic acid (PLA) nanofibre membranes. PLA nanofibres were coated with polydimethylsiloxane (PDMS) via coaxial electrostatic spinning technique, and 0.1% fluorine-modified silica (F-SiO₂) nanoparticles were embedded in the nanofibres to form nanoscale projections, which can increase roughness. Results showed that the coating of the low-surface-energy material PDMS and the nanoscale projections of F-SiO₂ endowed the membrane with excellent superhydrophobicity. The presence of the biodegradable material PLA and only 0.1% fluorine-containing substances made the membrane environment friendly. In addition, a large-pore-size high-flux support layer could maximize transmembrane vapor transfer while a small-pore-size high-rejection selective layer could avoid brine wetting and exhibited excellent salt rejection. The flux of the membrane reached 6.87 L m⁻² h⁻¹ and rejection was higher than 99%. Therefore, the PPF-AS membrane, as a superhydrophobic membrane, has wide potential for application in the field of MD.

---

Water impact

In recent years, membrane distillation (MD) has attracted great interest as a promising desalination technology. Although perfluoroalkyl materials have been proven to be good candidates for membrane distillation, the lack of a friendly approach to treat waste perfluoroalkyl-based membranes has attracted significant concern. We focused on polylactic acid (PLA) nanofibers coated with a polydimethylsiloxane (PDMS) layer with low surface energy and embedded with fluorine-modified silica (F-SiO₂) nanoparticles for constructing superhydrophobic membrane surfaces. The construction of MD membranes using PLA, a biodegradable material, and very small amounts of fluorinated substances is a sustainable strategy and its future development potential is highlighted.

1. Introduction

Water scarcity is a severe global problem.^1–4 Among the current desalination technologies, membrane processes dominate the global market owing to their high energy efficiency and small footprint.^5,6 Traditional membrane process desalination technologies, such as reverse osmosis (RO)^7,8 and nanofiltration (NF),⁹ are primarily pressure-driven processes and involve high energy expenditure.¹⁰ In recent years, membrane distillation (MD) has attracted great concern as a promising desalination technology.^11,12 MD is a steam-driven thermal desalination process based on hydrophobic membranes. Considering the transmembrane temperature gradient, only steam molecules can pass through the hydrophobic membrane, driven by a partial steam pressure difference, and then condense on the cold permeable side.^13–15 However, the long-standing problem of insufficient wettability, which leads to the penetration of feed solution into the distillate, has hindered the widespread application of MD technology. Therefore, the design of superhydrophobic membranes with wettability and the use of environmentally friendly materials are essential for the high performance and sustainability of MD.¹⁶

Superhydrophobic MD membranes prepared using conventional methods, such as phase transformation, thermally induced phase separation and sintering, mostly suffer from drawbacks caused by their poor porosity and internally disconnected microporous structures.^17,18 It is worth noting that electrostatic spinning is considered a simple and versatile method for the preparation of nanofibre membranes with high porosity and tunable structures by varying solution properties, electric field strength, and the spinning distance to better control the structure of the resulting membrane.^19,20 The construction of microstructures by employing an electrostatic spinning technique using low-surface-energy materials to achieve superhydrophobic surfaces is an effective solution. Polydimethylsiloxane (PDMS) is a convenient superhydrophobic modifier.²¹ Cao et al.²² used PDMS to modify cotton fabrics superhydrophobically. Upon contact with water, it showed superhydrophobic activity. However, there are limitations to the alterations of membrane superhydrophobicity by simply introducing PDMS. The introduction of nanoparticles can achieve superior superhydrophobic surfaces by altering film roughness.²³ Song et al.²⁴ crosslinked polydimethylsiloxane (PDMS) on the feed side of polytetrafluoroethylene (PTFE) membranes by preparing PDMS to reduce the surface energy of the membranes and improve their resistance to wetting. However, membranes containing fluorinated functional groups are generally not environmentally friendly during production²⁵ and there is a lack of friendly methods to dispose of perfluoroalkyl-based waste membranes.

Herein, we present a simple strategy for the MD process. In our method, utilizing a coaxial electrostatic spinning technique, low-surface-energy PDMS is coated on the surface of polylactic acid (PLA) nanofibers and embedded with fluorine-modified silica (F-SiO₂) nanoparticles to construct MD membranes with superhydrophobic surfaces. In addition, the large-pore-size high-flux support layer maximizes transmembrane vapor transfer while the small-pore-size high-rejection selective layer avoids brine wetting and exhibits excellent salt-rejection characteristics.²⁶ The results show that the MD membrane had a good structure and excellent superhydrophobicity, with an improved contact angle of 150.5° as well as superhydrophobicity under oil. Good flux and rejection performances were also demonstrated in the MD process. Most importantly, PLA is mainly derived from starch and other fermentation products and is a non-toxic, inexpensive, biodegradable, and compatible polymer material. Only 0.1% amount of fluorine-containing substances were used in the membrane preparation process, which reduces the hazards from the fluorinated substances and makes the modified membranes environmentally friendly, with wide ranging potential in the MD field.^27–29

2. Experimental section

2.1 PLA membrane preparation

The 10% polylactic acid (PLA) and a solvent mixture of N-methyl pyrrolidone (NMP) and dioxane (DX) (1 : 1 mass ratio) were mixed in a three-necked round-bottom flask and stirred in a 70 °C water bath for 10 h until dissolved, and then defoamed and set aside (solution A). The solution was then transferred into a syringe with a needle for electrostatic spinning. The following are the specific operating parameters: voltage, 27 kV (25 kV positive and 2000 V negative); scanning rate, 0.4 cm s⁻¹; distance between the spinning needle and the receiver, 15 cm; and the collector spinning rate, 237 rpm min⁻¹ drum. After 6 h, the spinning was finished, and the membrane was placed in a 100 °C oven for 2 h for heat treatment. The membrane was denoted as PLA membrane.

2.2 PLA-P membrane preparation

The preparation process followed a method reported in previous research.³⁰ First, 10% poly-dimethylsiloxane (PDMS) was dissolved in THF and stirred overnight at room temperature to obtain PDMS (solution B). Coaxial electrostatic spinning of solution A as the core solution and solution B as the shell solution was performed, and then the obtained membrane was placed in an oven for heat treatment for 2 h. The membrane was denoted as PLA-P membrane.

2.3 F-SiO₂ nanoparticles preparation

The preparation process followed a method reported in previous research.²⁹ First, 0.3 g trifluoro (1H,1H,2H,2H-tridecafluoro-n-octyl) silane, 0.2 g tetraethyl orthosilicate (TEOS), SiO₂ (0.1 g), and n-hexane (8.5 g) were mixed and centrifuged at room temperature with magnetic stirring to achieve thorough mixing for 10 h. The mixture was then placed in a 100 °C oven for 1 h.

2.4 PP-AS and PPF-AS membranes preparation

PLA (15%) and a solvent mixture of NMP and DX (1 : 1 mass ratio) were mixed in a three-necked round-bottom flask and stirred in a 70 °C water bath for 10 h until dissolved, then defoamed and set aside (solution C). Coaxial electrostatic spinning with solution C as the core solution and solution B as the shell solution was performed to obtain a large-pore-size support layer, while the coaxial electrostatic spinning of solution A and solution B for 2 h obtained the small-pore-size selective layer. The membrane was denoted as PP-AS membrane. The PPF-AS membranes were prepared in a similar way to the PP-AS membrane, but with the addition of F-SiO₂ nanoparticles to solution A and the membrane was denoted PP-AS membrane.

3. Results and discussion

3.1 Morphology and properties of the membranes' surfaces

We designed four kinds of nanofibre membranes to test our hypothesis (Fig. 1). These were the symmetrically structured PLA nanofiber membrane (PLA membrane), PDMS-coated symmetrically structured PLA nanofiber membrane (PLA-P membrane), PDMS-coated asymmetrically structured PLA nanofiber membrane (PP-AS membrane), and F-SiO₂ nanoparticles-embedded PDMS-coated asymmetrically structured PLA nanofiber membrane (PPF-AS membrane). The above selected layers were prepared at the indicated concentrations for comparison. The nanofibers ordering in the PLA nanofiber membranes was more sparse with the presence of bead-like structures, as shown in Fig. 2a. The diameter of the nanofibers increased with increasing the PLA concentration and the bead-like structure decreased (Fig. S1 and S2†). This was probably because of the higher polymer solution viscosity at high concentrations and the entanglement of the polymer chains, leading to the solvent molecules being uniformly distributed on the entangled polymer molecules to form smooth nanofibers, while increasing the diameters of the nanofibers.³¹ Moreover, increasing the solution viscosity or decreasing the surface tension could reduce the formation of bead-like structures.³² The bead-like structure tended to be aggregated for the PP-AS membranes (Fig. 2b). This was due to the high steam pressure of tetrahydrofuran (THF), which is easily volatilized during the electrostatic spinning process while the PDMS will encapsulate the surface of the PLA nanofibers and bead-like structures, which leads to agglomeration of the bead-like structures and reduces the surface energy of the nanofibers.³³ As a result, the average diameter of nanofibers was reduced from 200 nm to 150 nm (Fig. 2d and e). As the concentration of PDMS increased, the volume of the bead-like structure on the membrane surface became more extensive and polymer attachment occurred (Fig. S3†), with bead-like-to-bead-like, nanofibers-to-nanofibers, and bead-like-to-nanofibers structures interlocking and entangling with each other.

Fig. 1 Preparation of the membrane and membrane distillation process.

Fig. 2 Surface morphology of (a) PLA membrane, (b) PP-AS membrane and (c) PPF-AS membrane. Diameter distribution of nanofiber membranes of (d) the PLA membrane, (e) PP-AS membrane and (f) PPF-AS membrane. (g) TEM of the F-SiO₂ distribution in the nanofibers. EDS images of the PPF-AS membrane: (h) F element and (i) Si element.

To improve the superhydrophobicity and the desalination performance of the prepared membranes, we added F-SiO₂ nanoparticles in the PLA solution. The size of the nanoparticles before and after modification remained at about 25 nm, with regular square shapes, a round contour, and consistent size (Fig. S4†). It can be seen that the surface morphology of the PPF-AS membrane in Fig. 2c was similar to that in Fig. 2b. Interestingly, the average diameter of the nanofibers increased to 400 nm after adding F-SiO₂, resulting in small pore sizes (Fig. 2e). This is because F-SiO₂ nanoparticles reduce the surface tension of the PLA solution, resulting in fewer and smaller bead-like structures in the presence of higher charge density and lower surface tension.³⁴ The embedding of F-SiO₂ nanoparticles into the PLA nanofibers was observed from the transmission electron microscopy (TEM) image, which showed nanoscale raised structures, which may help to increase the roughness of the PLA membrane and improve the membrane wettability (Fig. 2f). In addition, as shown in Fig. S5,† the SEM images showed that the volume and number of bead like structures decreased gradually with the increase in F-SiO₂ concentration, and when the concentration was increased to 0.5%, the bead-like structures on the membrane surface became stretched and the polymers appeared to be agglomerated. In comparison with the pore size of the PLA membrane (2.94 μm), the introduction of PDMS reduced the pore size to 1.02 μm. The pore size of the PP-AS membrane was increased to 2.44 μm by the construction of a large-pore-size supporting layer and a small-pore-size selective layer. The introduction of F-SiO₂ nanoparticles further reduced the pore size of PPF-AS to 2.17 μm (Fig. S6†).

Moreover, based on the energy dispersive X-ray spectrometry (EDS) images, it could be observed that the five elements C, O, F, Si, and Cl were distributed on the PPF-AS membrane surface. The C and O elements were mainly distributed in the bead-like structure (Fig. S7b and c†). The F element was mainly distributed in the nanofibers and a few were distributed in the bead-like structure (Fig. 2h). The Si element was distributed on the whole surface of the membrane (Fig. 2i). F and Cl (Fig. S7d†) mainly came from FTOS while Si mainly came from PDMS and F-SiO₂. So it could be seen that the low-surface-energy PDMS was evenly coated on the bead-like structure and nanofibers.

3.2 Chemical analysis of the membranes

The X-ray photoelectron spectroscopy (XPS) patterns illustrated that the PLA membrane contained mainly C and O elements, while the PPF-AS membrane contained mostly C, O, and Si elements (Fig. 3a). The Si element was mainly from both the PDMS and F-SiO₂ nanoparticles. Further split-peak fitting of the C 1s spectrum showed that the C–C bond, O–C=O bond, and C–O bond were responsible for the characteristic absorption peaks of PLA, and the C–F bond was attributed to the F-SiO₂ nanoparticles; thus it could be tentatively inferred that the F-SiO₂ nanoparticles had been successfully doped (Fig. 3b).

Fig. 3 XPS spectroscopy of PPF-AS membranes: (a) full spectrum scan and (b) C 1s peaks.

3.3 Surface hydrophilicity of the membranes

In the case of hydrophobicity, the PLA, PLA-P, PP-AS, and PPF-AS membranes showed water contact angles of 135°, 150°, 150.5°, and 152°, respectively (Fig. 4a). The PLA membrane presented the smallest contact angle due to its chemical properties and insufficient surface roughness. It can be seen from Fig. 4b that the water droplets exhibited an approximately spherical shape on the surfaces of the PP-AS and PPF-AS membranes. All four membranes exhibited hydrophobic behavior in the presence of oil and lower adhesion to water in an oily environment, as shown in Fig. 4c, while the oil–water roll angle was 2.7° for the PP-AS membrane and 2.5° for the PPF-AS membrane (Fig. 4d). PPF-AS exhibited the most superhydrophobic surface, mainly because the PDMS coated in the outer layer of PLA nanofibers acted as a nonpolar layer and reduced the membrane surface energy. Moreover, the F-SiO₂ nanoparticles embedded in the nanofibers formed a raised structure, leading to an increase in roughness, which further supported the superhydrophobic structure. It was thus proven that the surface morphology and surface energy were significant for the superhydrophobic performance of PPF-AS.

Fig. 4 (a) PLA, PLA-P, PP-AS and PPF-AS membranes' water contact angles. (b) Optical photographs of water droplets on the PLA, PLA-P, PP-AS and PPF-AS membranes' surfaces. (c) Under-the-oil contact angles for the PLA, PLA-P, PP-AS and PPF-AS membranes. (d) Oil water rolling angles for the PP-AS and PPF-AS membranes. (e) Effect of the concentration of PLA on the contact angle. (f) Effect of the concentration of PDMS on the contact angle. (g) Effect of the concentration of F-SiO₂ on the contact angle.

PLA membranes are poorly hydrophobic, and the contact angle of the PLA membranes at different concentrations did not exceed 140° (Fig. 4e). In Fig. 4f, PDMS was coated on the outer layer of the PLA nanofiber membrane, which changed the hydrophobicity of the membrane by decreasing its surface energy. As the concentration of PDMS increased from 8% to 10%, the contact angle increased to 154°; however, when continuing to increase the concentration of PDMS, PDMS agglomerated to form a smooth surface and the contact angle decreased to 139°. With the introduction of F-SiO₂ nanoparticles, it could be seen that the contact angles were all above 150°, reaching a maximum contact angle of 156° when the concentration was 0.1%, along with superior superhydrophobicity (Fig. 4g).

3.4 Membrane distillation performance

To achieve high separation performance in the MD membrane, constructing a large-pore-size high-flux support layer allowed maximizing transmembrane vapor transfer while the small-pore-size high-rejection selective layer could avoid brine wetting and exhibit excellent salt-rejection performance (ESI,† S2 and S3). According to Fig. 5a, considering the flux and rejection of the membrane, 15% PLA solution was finally selected as the support layer and 10% PLA solution as the selective layer. When the PDMS concentration was 8%, some defects were observed on the surface of the membrane, which led to a lower rejection. At 12% PDMS concentration, the PDMS molecules aggregated to form a smooth surface, reducing the membrane's superhydrophobicity. Therefore, the optimum PDMS concentration of 10% was finally selected, at which the flux of the membrane was 3.28 L m⁻² h⁻¹ (Fig. 5b). The flux and rejection performance with adding F-SiO₂ nanoparticles were based on coaxial electrostatic spinning. The membrane with 0.1% F-SiO₂ nanoparticle concentration showed a considerable increase in flux (6.87 L m⁻² h⁻¹) and the rejection remained almost the same compared to the membrane without nanoparticle addition (Fig. 5c). When the F-SiO₂ nanoparticles concentration exceeded 0.1%, the original pores of the membrane were filled, which reduced the ability of the micro- and nanostructures on the membrane surface to form air gaps.³⁵

Fig. 5 Impact on MD film performance of (a) PLA concentration, (b) PDMS concentration, (c) F-SiO₂ nanoparticle concentration. (d) Effect of feed solution temperature on the flux and rejection rate of the PPF-AS membrane. (f) Effect of NaCl concentration on flux and rejection of PPF-AS membranes. (e) Effect of the feed liquid flow rate on the flux and rejection of the PPF-AS membranes.

The temperature of the feed liquid has a great influence on the flux of the MD process. During the experiment, we maintained the permeation side temperature at 10 °C. With the increase in feed solution temperature, the flux of the PPF-AS membrane increased, and the rejection remained above 99% (Fig. 5d). This was mainly because the higher the average temperature differential between the feed side and the permeate side, the higher the stream pressure on the membrane surface, and the flux increased. However, too high a temperature difference could lead to differential temperature polarization, which may result in membrane fouling or wetting, and higher energy consumption.³⁶ Therefore, a feed solution temperature of 50 °C was chosen for the MD experiments, achieving the highest energy utilization with a mild temperature difference.³⁷

The flux described in Fig. 5e decreased with the feed concentration, probably due to the higher concentration of sodium chloride (NaCl) solution causing concentration polarization on the feed side and increasing the mass-transfer resistance. At the same time, the increased concentration of NaCl can cause NaCl crystallization on the surface of the membrane, resulting in pore clogging.^38,39 As the concentration of membrane surface feed increased, the water activity decreased, and the membrane surface temperature and saturated steam pressure decreased.⁴⁰ However, the effect was relatively small. Thus, the flux remained high, although the increase in concentration resulted in a decrease in the flux. The rejection varied insignificantly and roughly showed an increasing trend with increasing the feed concentration. This may be due to the formation of a polarized layer on the surface of the membrane, further increasing the rejection rate.⁴¹

The rejection rates were maintained above 99.6% when the feed liquid flow rate was increased from 15 mL min⁻¹ to 75 mL min⁻¹, and the flux was increased from 3.9 L m⁻² h⁻¹ to 12.43 L m⁻² h⁻¹ (Fig. 4f). The flux of the PPF-AS membrane increased gradually with the increase in the feed flow rate, yet the rejection decreased slightly when the feed flow rate was too high. This was due to the superhydrophobic membrane interface only allowing water steam to pass through, while inorganic salt ions were retained by the membrane surface and formed an ion interfacial layer and so the partial pressure of water steam decreased, making the flux decrease and increasing the feed liquid flow rate, which then disturbed the ion interface layer, reduced the thickness of the ion layer, and reduced the concentration polarization phenomenon. Consequently, the pressure at the interface of the liquid membrane increased, making the rejection lower.⁴⁰ After comprehensively considering the flux, rejection stability, and comprehensive energy utilization, we chose a feed liquid flow rate of 45 mL min⁻¹.

4. Conclusion

We propose a simple strategy to construct a multistage structured PPF-AS membrane approach for efficient high-concentration brine membrane distillation. The coaxial electrostatic spinning technique was applied to introduce low-surface-energy silane-coated nanofibers as well as the doping of F-SiO₂ nanoparticles, which successfully endowed the PLA nanofiber membrane with superhydrophobic properties. The superhydrophobic contact angle was as high as 150.5°, the oil-in-water contact angle reached 153°, and the oil-in-water roll angle was 4°. In addition, a membrane flux of 6.87 L m⁻² h⁻¹ was achieved with a rejection rate higher than 99% by constructing a large-pore-size high-flux support layer, which could maximize transmembrane vapor transfer, and a small-pore-size high-rejection selective layer, which could avoid brine wetting and exhibited excellent salt-rejection performance. It is worth noting that the presence of the biodegradable material PLA and only a 0.1% amount of fluorine-containing substances endowed the membrane with environmental friendliness. Thus the PPF-AS membrane shows great potential as a superhydrophobic membrane in the field of membrane distillation.

Data availability

All the data generated or analyzed during this study are included in this published article and its ESI.†

Author contributions

Yuqian He: conceptualization, data curation, investigation, methodology, writing-original draft. Yanyan Ye: methodology, investigation. Mi Zhou: investigation. Linlin Yan: supervision. Yingjie Zhang: formal analysis. Enrico Drioli: validation. Jun Ma: supervision. Li Yonggang: supervision. Xiquan Cheng: validation, funding acquisition, formal analysis, visualization, writing – review &editing.

Conflicts of interest

There are no conflicts to declare.

Acknowledgements

This work was supported by the Key R&D Program of Shandong Province, China (Grant No. 2023CXPT068), the State Key Laboratory of Urban Water Resource and Environment (Harbin Institute of Technology) (No. 2022TS43), the Science and Technology Project of the Hebei Academy of Sciences (24702), and the Fundamental Research Funds for the Central Universities (HIT.OCEF.2024031), and the Guangxi First-class Disciplines (Agricultural Resources and Environment).

Notes and references

1. L. D. Tijing, J. Choi, S. Lee, S. Kim and H. K. Shon, Recent progress of membrane distillation using electrospun nanofibrous membrane, J. Membr. Sci., 2014, 453, 435–462.
2. B. Nazari and M. Keshavarz, Water population density: Global and regional analysis, Theor. Appl. Climatol., 2023, 153, 431–445.
3. S. W. Cooley, J. C. Ryan and L. C. Smith, Human alteration of global surface water storage variability, Nature, 2021, 591, 78.
4. M. Rodell, J. S. Famiglietti, D. N. Wiese, J. T. Reager, H. K. Beaudoing, F. W. Landerer and M. H. Lo, Emerging trends in global freshwater availability, Nature, 2018, 557, 650.
5. P. J. J. Alvarez, C. K. Chan, M. Elimelech, N. J. Halas and D. Villagan, Emerging opportunities for nanotechnology to enhance water security, Nat. Nanotechnol., 2018, 13, 634–641.
6. P. Wang and T. Chung, Recent advances in membrane distillation processes: Membrane development, configuration design and application exploring, J. Membr. Sci., 2015, 474, 39–56.
7. S. Park, Y. Ko, S. Park, J. S. Lee, J. Cho, K. Baek, I. T. Kim, K. Woo and J. Lee, Immobilization of silver nanoparticle-decorated silica particles on polyamide thin film composite membranes for antibacterial properties, J. Membr. Sci., 2016, 499, 80–91.
8. S. S. Shenvi, A. M. Isloor and A. F. Ismail, A review on RO membrane technology: Developments and challenges, Desalination, 2015, 368, 10–26.
9. X. Zhu, X. Cheng, X. Luo, Y. Liu, D. Xu, X. Tang, Z. Gan, L. Yang, G. Li and H. Liang, Ultrathin Thin-Film Composite Polyamide Membranes Constructed on Hydrophilic Poly (vinyl alcohol) Decorated Support Toward Enhanced Nanofiltration Performance, Environ. Sci. Technol., 2020, 54, 6365–6374.
10. Z. Wang, D. Hou and S. Lin, Composite Membrane with Underwater-Oleophobic Surface for Anti-oil-fouling membrane distillation, Environ. Sci. Technol., 2016, 50, 3866–3874.
11. W. Suwaileh, D. Johnson, D. Jones and N. Hilal, An integrated fertilizer driven forward osmosis- renewables powered membrane distillation system for brackish water desalination: A combined experimental and theoretical approach, Desalination, 2019, 471, 114126.
12. S. M. Alawad and A. E. Khalifa, Analysis of water gap membrane distillation process for water desalination, Desalination, 2019, 470, 114088.
13. A. V. Dudchenko, C. Chen, A. Cardenas, J. Rolf and D. Jassby, Frequency-dependent stability of CNT Joule heaters in ionizable media and desalination processes, Nat. Nanotechnol., 2017, 12, 557–563.
14. M. Bhadra, S. Roy and S. Mitra, Flux enhancement in direct contact membrane distillation by implementing carbon nanotube immobilized PTFE membrane, Sep. Purif. Technol., 2016, 161, 136–143.
15. B. Van der Bruggen, Integrated membrane separation processes for recycling of valuable wastewater streams: nanofiltration, membrane distillation, and membrane crystallizers revisited, Ind. Eng. Chem. Res., 2013, 52, 10335–10341.
16. J. Lee, C. Boo, W. Ryu, A. D. Taylor and M. Elimelech, Development of omniphobic desalination membranes using a charged electrospun nanofiber scaffold, ACS Appl. Mater. Interfaces, 2016, 8, 11154–11161.
17. X. Li, X. Yu, C. Cheng, L. Deng, M. Wang and X. Wang, Electrospun superhydrophobic organic/inorganic composite nanofibrous membranes for membrane distillation, ACS Appl. Mater. Interfaces, 2015, 7, 21919–21930.
18. A. He, Z. Jiang, Y. Wu, H. Hussain, J. Rawle, M. E. Briggs, M. A. Little, A. G. Livingston and A. Cooper, A smart and responsive crystalline porous organic cage membrane with switchable pore apertures for graded molecular sieving, Nat. Mater., 2022, 21, 463.
19. C. Bavatharani, E. Muthusankar, S. M. Wabaidur, Z. A. Alothman, K. M. Alsheetan, M. M. AL-Anazy and D. Ragupathy, Electrospinning technique for production of polyaniline nanocomposites/nanofibres for multi-functional applications: A review, Synth. Met., 2021, 271, 116609.
20. E. Lee, A. K. An, T. He, Y. C. Woo and H. K. Shon, Electrospun nanofiber membranes incorporating fluorosilane-coated TiO 2 nanocomposite for direct contact membrane distillation, J. Membr. Sci., 2016, 520, 145–154.
21. A. K. An, J. Guo, E. Lee, S. Jeong, Y. Zhao, Z. Wang and T. Leiknes, PDMS/PVDF hybrid electrospun membrane with superhydrophobic property and drop impact dynamics for dyeing wastewater treatment using membrane distillation, J. Membr. Sci., 2017, 525, 57–67.
22. C. Cao, M. Ge, J. Huang, S. Li, S. Deng, S. Zhang, Z. Chen, K. Zhang, S. S. Al-Deyab and Y. Lai, Robust fluorine-free superhydrophobic PDMS-ormosil@fabrics for highly effective self-cleaning and efficient oil-water separation, J. Mater. Chem. A, 2016, 4, 12179–12187.
23. F. Yu, Z. Yu, X. Huang, A. Gu, J. Du, S. Xie, R. Liu, D. Zou, S. Fang, M. Xie, J. Lin and W. Ye, Effective membrane distillation of landfill leachate concentrate using a superhydrophobic SiO₂/PVDF membrane for resource recovery, ACS ES&T Water, 2024, 4, 1711–1719.
24. H. Xu, Q. Zhang, N. Song, J. Chen, M. Ding, C. Mei, Y. Zong, X. Chen and L. Gao, Membrane distillation by novel Janus-enhanced membrane featuring hydrophobic-hydrophilic dual-surface for freshwater recovery, Sep. Purif. Technol., 2022, 302, 122036.
25. M. M. Damtie, Y. C. Woo, B. Kim, R. H. Hailemariam, K. Park, H. K. Shon, C. Park and J. Choi, Removal of fluoride in membrane-based water and wastewater treatment technologies: performance review, J. Environ. Manage., 2019, 251, 109524.
26. Y. Hou, P. Shah, V. Constantoudis, E. Gogolides, M. Kappl and H. J. Butt, A super liquid-repellent hierarchical porous membrane for enhanced membrane distillation, Nat. Commun., 2023, 14 6886.
27. E. Castro-Aguirre, F. Iniguez-Franco, H. Samsudin, X. Fang and R. Auras, Poly (lactic acid)- Mass production, processing, industrial applications, and end of life, Adv. Drug Delivery Rev., 2016, 107, 333–366.
28. I. Armentano, N. Bitinis, E. Fortunati, S. Mattioli, N. Rescignano, R. Verdejo, M. A. Lopez-Manchado and J. M. Kenny, Multifunctional nanostructured PLA materials for packaging and tissue engineering, Prog. Polym. Sci., 2013, 38, 1720–1747.
29. D. Garlotta, A literature review of poly (lactic acid), J. Polym. Environ., 2001, 9, 63–84.
30. Y. Ye, T. Li, Y. Zhao, J. Liu, D. Lu, J. Wang, K. Wang, Y. Zhang, J. Ma, E. Drioli and X. Cheng, Engineering environmentally friendly nanofiber membranes with superhydrophobic surface and intrapore interfaces for ultrafast Oil-water separation, Sep. Purif. Technol., 2023, 317, 123885.
31. C. Mit-uppatham, M. Nithitanakul and P. Supaphol, Ultratine electrospun polyamide-6 fibers: Effect of solution conditions on morphology and average fiber diameter, Macromol. Chem. Phys., 2004, 205, 2327–2338.
32. Q. Su, J. Zhang and L. Zhang, Fouling resistance improvement with a new superhydrophobic electrospun PVDF membrane for seawater desalination, Desalination, 2020, 476, 114246.
33. B. J. Deka, E. Lee, J. Guo, J. Kharraz and A. K. An, Electrospun nanofiber membranes incorporating PDMS-aerogel superhydrophobic coating with enhanced flux and improved antiwettability in membrane distillation, Environ. Sci. Technol., 2019, 53, 4948–4958.
34. Q. Su, J. Zhang and L. Zhang, Fouling resistance improvement with a new superhydrophobic electrospun PVDF membrane for seawater desalination, Desalination, 2020, 476, 114246.
35. Y. Shen, K. Li, H. Chen, Z. Wu and Z. Wang, Superhydrophobic F-SiO₂@PDMS composite coatings prepared by a two-step spraying method for the interface erosion mechanism and anti-corrosive applications, Chem. Eng. J., 2021, 413, 127455.
36. A. Khalifa, H. Ahmad, M. Antar, T. Laoui and M. Khayet, Experimental and theoretical investigations on water desalination using direct contact membrane distillation, Desalination, 2017, 404, 22–34.
37. A. A. Khan, M. I. Siyal and J. Kim, Fluorinated silica - modified anti - oil-fouling omniphobic F-SiO₂@PES robust membrane for multiple foulants feed in membrane distillation, Chemosphere, 2021, 263, 128140.
38. A. Razmjou, E. Arifin, G. Dong, J. Mansouri and V. Chen, Superhydrophobic modification of TiO₂ nanocomposite PVDF membranes for applications in membrane distillation, J. Membr. Sci., 2012, 415–416, 850–863.
39. C. Li, W. Liu, J. Mao, L. Hu, Y. Yun and B. Li, Superhydrophobic PVDF membrane modified by dopamine self-polymerized nanoparticles for vacuum membrane distillation, Sep. Purif. Technol., 2023, 304, 122182.
40. Y. Yang, Q. Liu, H. Wang, F. Ding, G. Jin, C. Li and H. Meng, Superhydrophobic modification of ceramic membranes for vacuum membrane distillation, Chin. J. Chem. Eng., 2017, 25, 1395–1401.
41. S. T. Hsu, K. T. Cheng and J. S. Chiou, Seawater desalination by direct contact membrane distillation, Desalination, 2002, 143, 279–287.

---

Footnote

† Electronic supplementary information (ESI) available: Materials and methods, Fig. S1–S6. See DOI: https://doi.org/10.1039/d4ew00611a

---