Self-Healing Hydrophilic Porous Photothermal Membranes for Durable and Highly Efficient Solar-Driven Interfacial Water Evaporation

Abstract

Open AccessCCS ChemistryRESEARCH ARTICLE14 Jul 2022Self-Healing Hydrophilic Porous Photothermal Membranes for Durable and Highly Efficient Solar-Driven Interfacial Water Evaporation Fuchang Xu, Dehui Weng, Xiang Li, Yang Li and Junqi Sun Fuchang Xu State Key Laboratory of Supramolecular Structure and Materials, College of Chemistry, Jilin University, Changchun 130012 Google Scholar More articles by this author , Dehui Weng State Key Laboratory of Supramolecular Structure and Materials, College of Chemistry, Jilin University, Changchun 130012 Google Scholar More articles by this author , Xiang Li State Key Laboratory of Supramolecular Structure and Materials, College of Chemistry, Jilin University, Changchun 130012 Google Scholar More articles by this author , Yang Li *Corresponding author: E-mail Address: [email protected] State Key Laboratory of Supramolecular Structure and Materials, College of Chemistry, Jilin University, Changchun 130012 Google Scholar More articles by this author and Junqi Sun State Key Laboratory of Supramolecular Structure and Materials, College of Chemistry, Jilin University, Changchun 130012 Google Scholar More articles by this author https://doi.org/10.31635/ccschem.021.202101111 SectionsSupplemental MaterialAboutAbstractPDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareFacebookTwitterLinked InEmail It is highly desirable to develop a solar-driven interfacial water evaporator with a self-healing ability and high-efficiency water evaporation performance for water distillation and desalination; however, this process is considerably challenging. Herein, by exploiting the advantages of a self-healing hydrophilic polymer, a self-healing hydrophilic porous photothermal (SHPP) membrane was fabricated by curing a mixture of the polymer, carbon black, and NaCl, followed by removal of the NaCl from water. Since the SHPP membrane could serve as a photothermal layer and water transportation channel simultaneously, a solar-driven interfacial evaporator could be fabricated readily by assembling the SHPP membrane with polyethylene foam. We have shown that the SHPP membrane-based evaporator exhibited a water evaporation rate of 1.68 kg m−2 h−1 and an energy efficiency of 97.3%. These values are superior to those obtained using solar-driven interfacial evaporators with self-healing capability. Notably, by hydrogen bonds reformation between the fracture surfaces, the SHPP membrane could regain its structural integrity after breaking, making the SHPP membrane-based evaporator the first to heal entirely and repeatedly from physical damage to sustain its water evaporation capacity. Therefore, the potential of using SHPP membranes to develop stable, long-lasting, and high-efficiency solar-driven interfacial water evaporators is highlighted. Download figure Download PowerPoint Introduction Fresh water, accounting for only 3% of the total water resources on earth, is vital to human survival and social development. However, with increased population, as well as persistent environmental pollution, the shortage of fresh water has become a key global issue. Therefore, it is imperative to develop effective technologies to generate fresh water from seawater or sewage.1–3 Among all the water treatment technologies, solar-driven evaporation has attracted extensive research attention due to the environment-friendly and renewable characteristics of solar energy.4 Recently, solar-driven interfacial water evaporation, which minimizes thermal dissipation and applies most of the heat to the liquid–vapor phase transition by concentrating heat at the water–air interface, has been developed to improve the water evaporation efficiency.5–17 Generally, most of the reported solar-driven interfacial evaporators comprise three parts18,19 (Scheme 1a1: (1) a photothermal layer with broadband light absorption and high photothermal conversion, (2) a floatable supporting layer with low thermal conductivity, and (3) a hydrophilic water channel either on the outside or in the middle of the supporting layer that ensures a continuous water supply to the photothermal layer. Although many high-efficiency solar-driven interfacial evaporators have been developed, in practical applications, the photothermal layer or water channel can be damaged by scratching or corrosion, thereby deteriorating the water evaporation efficiency (Scheme 1a2). Hence, to satisfy the requirements for practical applications, it is critical to develop solar-driven interfacial evaporators with a stable water evaporation efficiency. In particular, it is crucial to develop solar-driven interfacial evaporators that can maintain their water evaporation performance after damage. Scheme 1 | (a) Schemes of (1) the composition of a typical solar-driven interfacial evaporator and (2) the loss of its water evaporation capacity due to damage to the water transportation channel. (b) Schematics of (1) the composition of the SHPP membrane-based solar-driven interfacial evaporator and (2) its ability to restore the water evaporation ability via self-healing after physical damage. Download figure Download PowerPoint With the progress in supramolecular chemistry and synthetic chemistry, various self-healing polymers capable of healing damage by themselves to restore the mechanical and/or chemical properties have been synthesized successfully.20–23 In addition, by combining self-healing polymers with functional materials, plenty of self-healing functional materials with superhydrophobicity,24–27 antifouling,28–30 electrical conductivity,31–34 sensing,35–41 and other functions42–50 have been fabricated, decreasing maintenance costs and promoting safety, reliability, and service life significantly. The design and fabrication of self-healing materials with photothermal and water transportation capabilities, able to repair their functions upon damage, would be a judicious solution to increase the stability and service life of solar-driven interfacial evaporators. Although our group and a few other researchers have reported the fabrication of self-healing photothermal membranes for solar-driven water evaporation, these membranes can only heal chemical damage.51,52 Furthermore, the water evaporation rates of these self-healing photothermal membranes were not ideal (<1.31 kg m−2 h−1), related to their hydrophobic/superhydrophobic nature that hindered water transportation and evaporation. Previously, our group reported that self-healing superhydrophobic porous materials with a photothermal conversion ability capable of healing physical damage could be obtained using a self-healing hydrophobic polymer and carbon nanotubes as the main materials using NaCl as the template.53 Based on the experience in self-healing porous materials fabrication, along with the widely available knowledge in hydrophilic self-healing polymer synthesis, a rational selection of the material composition was made that led to self-healing hydrophilic photothermal membranes with long-term advantages of high-efficiency evaporation capability for solar-driven interfacial evaporators. As a proof of concept, for the first time, we are reporting a self-healing hydrophilic porous photothermal (SHPP) membrane for highly efficient solar-driven interfacial water evaporation based on a carefully designed and synthesis of a self-healing hydrophilic polymer. The SHPP membrane was fabricated by curing a mixture of self-healing hydrophilic polymer with carbon black (CB) and NaCl, followed by removing the NaCl from water. By tuning the hydrophilicity of the self-healing polymer and the mass ratios of the feed materials, the water content of the SHPP membrane that considerably affects the water evaporation performance could be controlled. From the self-healing perspective, the self-healing polymer permitted the coalescence of the cut SHPP membrane via the reformation of hydrogen bonds between the fracture surfaces, leading to the healing of structural integrity. As the SHPP membrane could simultaneously serve as the photothermal layer and water transportation channel, a highly efficient solar-driven interfacial evaporator can be readily fabricated by assembling the SHPP membrane with a polyethylene (PE) foam (Scheme 1b1). By floating such a designed evaporator on the water surface, the evaporation rates of lake water and seawater reached 1.67 and 1.61 kg m−2 h−1, respectively. When the water evaporation capacity of the evaporator was lost by cutting the SHPP membrane, it was able to self-heal at room temperature, and the water evaporation performance of the evaporator was fully restored (Scheme 1b2). Moreover, the SHPP membrane was capable of healing damage caused at the exact location repeatedly without losing the water evaporation performance. The simple structure of the SHPP membrane-based evaporator benefits its integration into conventional solar distillation devices. In this study, we fabricated a prototype distillation device comprising an SHPP membrane-based evaporator to demonstrate the applicability of the SHPP membrane for sewage purification and seawater desalination. Experimental Methods Materials PE glycol (PEG; Mw = 1000) and polyvinyl alcohol (PVA; Mw = 85,000–124,000, 87–89% hydrolyzed) were purchased from Sigma-Aldrich (Shanghai, China). Polytetramethylene ether glycol (PTMG; Mw = 1000) was purchased from Aladdin (Shanghai, China). Dicyclohexylmethane 4,4-diisocyanate (DMDI; purity < 90%) was purchased from TCI Development Co., Ltd. (Shanghai, China). Dibutyltin dilaurate (DBTDL; purity < 97.5%) was purchased from J&K Scientific Ltd. (Beijing, China). Tetrahydrofuran (THF) was purchased from Innochem Science & Technology Co., Ltd. (Beijing, China). CB was purchased from Alfa Aesar Chemical Co., Ltd. (Shanghai, China). Anhydrous ethanol and NaCl were purchased from Beijing Chemical Reagents Company (Beijing, China). All of the chemicals were used without further purification. Synthesis of PUx A series of PUx with different molar ratios of PEG and PTMG were synthesized by the step-growth polymerization of PEG, PTMG, and DMDI. Taking PU50 as an example, PEG (5.00 g, 5 mmol) and PTMG (5.00 g, 5 mmol) were added into a 250 mL three-neck round-bottom flask equipped with mechanical agitation, nitrogen inlet, and condensation reflux. The reaction was allowed to proceed under vacuum for 2 h at 100 °C; then the system was cooled to 60 °C and filled with nitrogen gas. Subsequently, THF (100 mL), DMDI (3.15 g, 12 mmol), and DBTDL (0.05 g, 0.08 mmol) were added into the three-neck round-bottom flask. After 48 h of stirring at 60 °C under nitrogen, the reaction solution was purified by dialysis using a dialysis membrane [molecular weight cutoff (MWCO), 8000–14,000 Da] with anhydrous ethanol. Finally, PU50 was obtained after ethanol evaporation. PU0, PU10, PU20, PU30, and PU40 were synthesized separately in accordance with the method described above. Fabrication of PUx/CBm/NaCln membranes CB and NaCl with different mass ratios were mixed for 30 min using a ball mill machine. Next, CB and NaCl blends were added to 15 mL THF solutions of PUx (the concentration of PUx depended on the composition of PUx/CBm/NaCln), followed by mechanical stirring at 500 rpm for 1 h to ensure that CB and NaCl were well dispersed in the PUx solutions. The resulting solution mixtures were poured into Teflon molds and cured at room temperature. After complete removal of THF, the exteriors of the solidified composite blocks were rubbed with sandpaper and immersed in water baths renewed every 6 h over 2 days to remove the NaCl completely with the resultant PUx/CBm/NaCln porous membranes. The water-soaked PUx/CBm/NaCln porous membranes were wiped with filter papers and then dried at room temperature. Characterization The Mw and PDI of PUx were characterized on a Shimadzu gel-permeation chromatography (GPC; Shimadzu, Japan) system. THF was used as the moving phase, and the flow rate was 1.0 mL min−1. Fourier transform infrared (FT-IR) spectra were taken on a Bruker VERTEX 80 V FT-IR spectrometer (Bruker, Germany). The differential scanning calorimetry (DSC) curves of PUx were obtained on a TA instrument Q200 (TA, USA) at the heating/cooling rate of 10 °C min−1 in a N2 atmosphere. Simulated solar light was provided by a PL-XQ500W xenon lamp (Beijing Springs Technology Co., Ltd., Beijing, China), and the light intensity was kept at 1000 W m−2. Temperature values and IR images of the samples were captured using a HIKVISION H10 thermal imager (HIKVISION, Hangzhou, China). The distance between the sample and the thermal imager was fixed at 20 cm. The accuracy in temperature of the thermal imager is ±2 °C. The reflection and transmission spectra of the samples were characterized by a UV-3600 spectrophotometer (Shimadzu, Kyoto, Japan). The optical images and videos were captured using a Canon PowerShot SX40 HS camera (Canon, China). The scanning electron microscopy (SEM) images were obtained using a JEOL JSM 6700F field emission scanning electron microscope (JEOL, Japan). The optical microscopy images were obtained using an Olympus DP72 optical microscope (Olympus, China). The porosity (ρ) of the PUx/CBm/NaCln porous membrane was calculated by the following equation: ρ = ( M wet − M dry ) / ( M wet − M sub ) (1)where Mdry is the dry mass of the membrane, Mwet is the mass of the prewetted membrane measured in air, and Msub is the mass of the membranes soaked in water. The solar thermal conversion efficiency (η) of the PUx/CBm/NaCln porous membrane was calculated by the following equation: η = H e × ( ν Total − ν Dark ) / Q s , (2)where He is the heat of water evaporation (2260 kJ kg−1), Qs is the incidence light power, νTotal is the evaporation rate of the PUx/CBm/NaCln porous membrane at stable state under one sun irradiation, and νDark is the evaporation rate of the PUx/CBm/NaCln porous membrane in dark environment. To test its water transport capacity, a piece of PUx/CBm/NaCln porous membrane (0.1 cm × 1 cm × 5 cm) was partially immersed in a beaker containing 50 mL of deionized (DI) water, and a piece of filter paper was used to absorb water from the upper end of the membrane continuously. The filter paper was replaced after it was saturated with water. The water flux (F) of the PUx/CBm/NaCln membrane was calculated by the following equation: F = M water / ( S * t ) , (3)where Mwater is the mass change of the DI water in the beaker, S is the cross-sectional area of the membrane, and t is the test time. Results and Discussion The self-healing hydrophilic polymer that was key for fabricating the SHPP membrane with a stable, highly efficient solar-driven interface water evaporation capability was synthesized by the step-growth polymerization of PEG, PTMG, and DMDI, as shown in Figure 1a. The resulting polymers were denoted as PUx, where x referred to the molar percentage of PEG in the total monomers. A peak characteristic of –N=C=O at 2268 cm−1 was not observable in the FT-IR spectra of PUx ( Supporting Information Figure S1). Meanwhile, peaks corresponding to the C=O stretching vibration, as well as N–H stretching and bending vibrations, were observed around 1720 and 1533 cm−1, respectively, confirming the successful synthesis of PUx. GPC was employed to estimate the weight-average molecular weight (Mw) and polydispersity index (PDI) of PUx. Supporting Information Table S1 lists the results. Although the molar ratios of PEG and PTMG were different, all of the PUx exhibited similar Mw and PDI. In this study, hydrophobic PTMG and hydrophilic PEG were used rationally by adjusting the molar ratio of the two monomers due to the regulation of hydrophilicity of PUx. With an increase in the PEG content, the water uptake of PUx increased, indicating that the hydrophilicity of PUx increases with an increase in the molar ratio of PEG ( Supporting Information Figure S2). Figure 1 | (a) Synthetic route of PUx. (b) Photographs of the PU20 film after being cut and being healed at room temperature for 6 h. (c) Microscopy images of the cut PU20 membrane before and after healing for 6 h at room temperature. (d) Stress–strain curves of the pristine PU20 film and the cut PU20 film after healing for different times at room temperatures. The stretching speed was 50 mm min−1. Download figure Download PowerPoint Taking PU20 as a representative, the self-healing ability of PUx was examined. A piece of the PU20 film (0.6 cm × 3.5 cm) was cut in half with a knife, and the two parts were subsequently reattached closely (Figure 1b). After placing the PU20 film under ambient conditions for 6 h, the separated PU20 film was conglutinated together, restoring its structural integrity. In addition, an optical microscopy image confirmed that the cut was healed completely (Figure 1c). The self-healing ability of PU20 was attributed to its abundant reversible hydrogen bonds and low glass transition temperature (−51.3 °C, Supporting Information Figure S3). When the fracture surfaces were brought into close contact, the polymer chains migrated gradually into the voids, and the hydrogen bonds reformed with one another, leading to healing of the cut.54 Tensile tests were employed to characterize the healing ability of PU20 further. As the healing time increased, the fracture stress of the healed PU20 film increased gradually and recovered to 4.26 MPa after 6 h of healing at room temperature (Figure 1d). Accordingly, the healing efficiency of PU20, defined as the proportion of the restored fracture stress to the original stress, was calculated to be 98.4%, indicating a satisfactory self-healing ability. In addition, the self-healing abilities of PUx with different PEG contents were examined. Supporting Information Table S2 lists the results. With an increase in the PEG content, the healing efficiency of PUx increased due to the reduction in Young’s modulus of the resulting polymer via an increase in the PEG segments ( Supporting Information Table S2). With the successful synthesis of PUx, SHPP membranes were fabricated using PUx, CB, and NaCl. CB was used due to its good photothermal conversion ability and low costs,55,56 while NaCl was used as a sacrificial template. The self-healing hydrophilic porous PUx/CBm/NaCln membranes, where m and n represent the mass ratios of CB and NaCl to PUx, respectively, were fabricated by casting a dispersion of PUx, CB, and NaCl in THF into a Teflon (R) mold, followed by solvent evaporation and NaCl removal in water (Figure 2a). Owing to the simple fabrication, a piece of PU20/CB0.5/NaCl5 membrane with dimensions of 11 cm × 11 cm was obtained readily (Figure 2b). The SEM image in Figure 2c reveals that the PU20/CB0.5/NaCl5 membrane exhibits a three-dimensional interconnected hierarchical porous structure, comprising a CB-reinforced PU20 skeleton and macropores with diameters ranging from 9.7 to 109.8 μm. Based on Archimedes’ method (eq 1), the porosity of the PU20/CB0.5/NaCl5 membrane was 59.8%. Figure 2 | (a) Schematic of the fabrication processes of the PUx/CBm/NaCln membranes. (b) Photographs of the PU20/CB0.5/NaCl5 membrane. (c) Cross-section SEM image of the PU20/CB0.5/NaCl5 membrane. (d) Photograph showing that the PU20/CB0.5/NaCl5 membrane transported water to a height of 5 cm in 3 min. (e) Photograph of the PU20/CB0.5/NaCl5 membrane-based solar-driven interfacial evaporator. (f) Temperature changes of DI water and the PU20/CB0.5/NaCl5 membrane-based evaporator floating on the DI water under simulated solar light irradiation. (g) Time-sequence IR images of the DI water-filled glass containers without (left) and with (right) the PU20/CB0.5/NaCl5 membrane-based evaporator under simulated solar light irradiation for (1) 1 min and (2) 60 min. (h) The mass changes of the DI water with and without the PU20/CB0.5/NaCl5 membrane-based evaporator under simulated solar light irradiation. Download figure Download PowerPoint The combination of the hydrophilicity of PU20 and the porous structure permitted a 5 cm vertical transport of water by the PU20/CB0.5/NaCl5 membrane due to capillary force (Figure 2d), qualifying it to be a water transportation channel. In addition, the average transmittances and reflections of the PU20/CB0.5/NaCl5 membrane were close to zero in the wavelength range from 200 to 2500 nm ( Supporting Information Figure S4). The intense light absorption of the PU20/CB0.5/NaCl5 membrane was related to the excellent light absorption performance of the CB in a broad wavelength range and the porous structure. This further improved the solar-energy harvesting efficiency via a reduction in light reflection.57 Next, the photothermal ability of the PU20/CB0.5/NaCl5 membrane was investigated by irradiating the membrane with a simulated solar light (1000 W m−2), then an IR camera was used to monitor the temperature of the membrane in air. Under light irradiation, the temperature of the PU20/CB0.5/NaCl5 membrane increased rapidly to 57 °C in 1 min and then reached a steady-state temperature of 70 °C by 5 min ( Supporting Information Figure S5), demonstrating an excellent photothermal ability. As the PU20/CB0.5/NaCl5 membrane simultaneously exhibited excellent water transport and photothermal abilities, we envisioned that a simple yet efficient solar-driven interfacial water evaporator could be assembled readily by adhering the PU20/CB0.5/NaCl5 membrane onto a PE foam to serve as a support and an insulation layer simultaneously (Figure 2e). The water evaporation performance of the PU20/CB0.5/NaCl5 membrane-based evaporator floating on the water surface was measured by placing the evaporator in a DI water-filled glass container placed on an electronic balance. Simulated light with an intensity of 1000 W m−2 was shone directly on the PU20/CB0.5/NaCl5 membrane surface, and the real-time water mass change was monitored. Under light irradiation, the PU20/CB0.5/NaCl5 membrane absorbed light and self-heated the water inside. The temperature of the PU20/CB0.5/NaCl5 membrane rapidly increased to 35 °C in 1 min and reached a steady-state temperature of 43 °C by 5 min (Figure 2f and 2g1). Since the PU20/CB0.5/NaCl5 membrane transported water from the glass container to the top of the evaporator continuously (Scheme 1b1), this membrane-based evaporator exhibited a steady water evaporation rate of 1.68 kg m−2 h−1 (Figure 2h). According to eq 2 provided in the Experimental Section, the solar thermal conversion efficiency of the PU20/CB0.5/NaCl5 membrane-based evaporator was 97.3%. Thus, we proposed that such a high solar thermal conversion efficiency for the evaporator was related to the fact that most of the heat was used to evaporate the water at the top of the evaporator and that only a small part of the heat was transferred to the bulk water inside the glass container. As proof, after 1 h of simulated light irradiation, the temperature of the water under the evaporator only increased by 5 °C (Figure 2g2). In contrast, the temperature of water in the glass container without the PU20/CB0.5/NaCl5 membrane-based evaporator increased slowly by 9 °C after 1 h of simulated light irradiation (Figure 2g2). Owing to the low light absorption capacity of water and overall water heating, the evaporation rate of water in the glass container without the evaporator was only 0.32 kg m−2 h−1 (Figure 2h). Thus, with the assistance of the PU20/CB0.5/NaCl5 membrane-based evaporator, the evaporation rate of water increased 5.3 times. Subsequently, the effect of the composition of the PUx/CBm/NaCln membranes on the water-evaporation performance of the PUx/CBm/NaCln membrane-based evaporators was examined. First, the PUx/CB0.5/NaCl5 membranes with x being 0–50 were prepared. As mentioned earlier, with an increase in PEG content, the hydrophilicity of PUx increased. Thus, when the PUx/CB0.5/NaCl5 membrane-based evaporators were floating on the water, the inner PUx/CB0.5/NaCl5 membrane water content increased with increasing PEG content of PUx (Figure 3a). By contrast, since an increase in PUx hydrophilicity hindered water flow inside the membrane, the water flux of the PUx/CB0.5/NaCl5 membrane decreased, as the PEG content increased. Notably, with an increase in the PEG content, the water evaporation rate of the PUx/CB0.5/NaCl5 membrane-based evaporators increased initially and then decreased. At water content and water flux of 2.05 g−1 and 378 kg m−2 h−1, the water evaporation rate reached a maximum of 1.68 kg m−2 h−1 (Figure 3a). Next, the water evaporation rates of the PU20/CB0.5/NaCln membrane-based evaporators were examined (Figure 3b). As the NaCl content was increased, the water content and water flux of the PU20/CB0.5/NaCln membrane increased. This result was reasonable as increased NaCl content increased the membrane porosity ( Supporting Information Figure S6), with an ultimate increase in water content and water flux. At a NaCl to PU20 mass ratio of 5, the PU20/CB0.5/NaCl5 membrane-based evaporator exhibited the highest water evaporation rate. Finally, the effect of the CB content on the performance of the PU20/CBm/NaCl5 membrane-based evaporators was examined (Figure 3c). We observed that the PU20/CB0.5/NaCl5 membrane exhibited the highest water content and water flux; thus, confirming that the PU20/CB0.5/NaCl5 membrane-based evaporator had the highest water evaporation rate. This is because, at an extremely low CB content, the pores in the resulting PU20/CB0.3/NaCl5 membrane collapsed ( Supporting Information Figure S7a), thereby leading to a dramatic decrease in porosity ( Supporting Information Figure S7b), water content, and water flux (Figure 3c). On the other hand, owing to its hydrophobicity, excess CB also led to a decrease in the water content and water flux of the membrane (Figure 3c). Collectively, our experimental results showed that when PU20 was used, the mass ratios of CB to PU20 and NaCl to PU20 were set at 0.5 and 5, respectively, and the PU20/CB0.5/NaCl5 membrane-based evaporator exhibited the maximum water evaporation rate of 1.68 kg m−2 h−1. Therefore, in the following study, the PU20/CB0.5/NaCl5 membranes were used to construct the self-healing solar-driven water evaporator. Figure 3 | Evaporation rate, water flux, and water content of the PUx/CBm/NaCln membrane as a function of (a) the molar ratio of PEG, (b) the mass ratio of NaCl, and (c) the mass ratio of CB. (d) Mass changes of the simulated seawater and lake water with PU20/CB0.5/NaCl5 membrane-based evaporators under simulated solar light irradiation. Download figure Download PowerPoint The water evaporation rates of the PU20/CB0.5/NaCl5 membrane-based evaporator floating on lake water and simulated seawater (3.5 wt % NaCl), apart from DI water, were examined. With the assistance of the evaporator, the evaporation rates of the lake water and simulated seawater were 1.67 and 1.61 kg m−2 h−1, respectively (Figure 3d). The corresponding solar thermal conversion efficiencies were 96.7% and 94.2%. Salt accumulation is a challenge that all solar-driven evaporators encounter during seawater desalination. Benefiting from the good corrosion resistance of the PU20/CB0.5/NaCl5 membrane, the seawater evaporation rate of the PU20/CB0.5/NaCl5 membrane-based evaporator was maintained at 1.34 kg m−2 h−1 after 8 h of seawater evaporation, which was still 4.5 times higher than that of bare simulated seawater ( Supporting Information Figure S8). Moreover, the seawater evaporation of the evaporator was recovered by applying 10 mL of seawater onto the PU20/CB0.5/NaCl5 membrane ( Supporting Information Figure S8). These results indicate that the PU20/CB0.5/NaCl5 membranes demonstrated potential applications in sewage purification and seawater desalination. Further, the stability of the PU20/CB0.5/NaCl5 membranes was examined. We found that the porosity of the PU20/CB0.5/NaCl5 membranes was unchanged after immersion in aqueous CH3COOH (1 wt %, pH 2.8), Na2CO3 (1 wt %, pH 11.7), and NaCl (3.5 wt %) solutions for 10 days, indicating that the membranes exhibited satisfactory corrosion resistance (Figures 4a–4c). Moreover, the porosity of the PU20/CB0.5/NaCl5 membranes was well maintained after placing in the air or immersing in hot water at 50 °C for 10 days ( Supporting Information Figure S9 and Figure 4d), indicating that the porous structure in the membranes was highly stable. These results revealed th