Co2.67S4-Based Photothermal Membrane with High Mechanical

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Co2.67S4‑Based Photothermal Membrane with High Mechanical Properties for Efficient Solar Water Evaporation and Photothermal Antibacterial Applications Le Zhao,† Qingzhu Yang,‡ Wei Guo,*,† Haixia Liu,† Tianyue Ma,† and Fengyu Qu*,† †

Key Laboratory of Photochemical Biomaterials and Energy Storage Materials, Heilongjiang Province and College of Chemistry and Chemical Engineering, Harbin Normal University, Harbin 150025, P. R. China ‡ School of Life Science and Technology, Harbin Institute of Technology, Harbin 150080, P. R. China

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ABSTRACT: The lack of freshwater resources, or the freshwater crisis, is an important issue in the resource field. One potential green and sustainable method to solve this problem is to implement solar energy-driven water evaporation to collect freshwater. Capitalizing on the low cost, high production yield, and simplified fabrication process properties of nonstoichiometric Co2.67S4 nanoparticles, we strategically designed and synthesized a Co2.67S4-deposited Teflon (PTFE) membrane for realizing efficient solar water evaporation and photothermal antibacterial properties under light irradiation. Compared with previously reported cellulose acetate and poly(vinylidene fluoride) membranes, the PTFE membrane displayed significantly enhanced mechanical properties. Additionally, a Co2.67S4-deposited PTFE membrane with a hydrophobic treatment (termed as the Final-PTFE membrane) exhibited excellent durability. The light-to-heat conversion efficiency (η) of water evaporation reached a value of 82% for our as-prepared Final-PTFE membrane under two sun irradiation conditions. Moreover, the antibacterial mechanism observed by scanning electron microscopy was attributed to the thermal effect, which damaged the cell wall of bacteria. Our work highlights the great potentials of the Final-PTFE membrane as a versatile system for implementing solar energy-driven photothermal water evaporation and water purification. KEYWORDS: excellent mechanical properties, Co2.67S4, photothermal conversion, solar vapor generation, photothermal antibacterial application

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INTRODUCTION The freshwater crisis remains one of the world’s most serious resource problems due to the rapid development of modern industry, environmental pollution, and expansion of the human population.1 One smart strategy to combat this is to harvest freshwater from wastewater and seawater using renewable energy.2 Solar energy is an abundant, sustainable, and clean energy that exhibits great potential in numerous areas including solar cells,3 photocatalysis,4−6 and water evaporation.7 Therefore, solar energy-driven water evaporation has been frequently used in clean-water regeneration and water recovery systems due to its low cost, environment-friendly characteristics, and adaptability.8,9 However, the natural mechanism of solar energy-driven water evaporation is often compromised by several frequently encountered concerns such as a low evaporation rate, low temperature increase, and the absorption mismatch of water and the solar spectrum.10 To address the above challenges, localized heating on the interface of a water vapor−liquid interface has been explored as an effective strategy for enhanced water evaporation, usually by employing light-absorbing agents accumulated on a porous membrane being exposed to solar irradiation. In recent years, many such new light-absorbing agents have been developed, © XXXX American Chemical Society

including plasmonic metal particles, carbon-based nanomaterials, black metal oxides, two-dimensional materials, semimetallic nanoparticles (NPs), and so on.11−26 Wang et al. fabricated highly monodispersed silver nanoparticles that have a great potential for efficient solar energy collection and conversion in a fast and consecutive manner.27 Ye et al. developed black TiOx nanoparticles through Mg reduction of TiO2 nanocrystals for solar water evaporation. The as-prepared TiOx nanoparticles have multiple advantages, including tunable light absorption, low toxicity, superhydrophobicity, and chemical stability.28 Despite their high evaporation efficiency, the practicality and large-scale applications of most nanomaterials are limited, mainly because of the expensive material costs, low production yields, and complicated fabrication processes.29−33 Moreover, the mechanical properties of such a porous membrane need to be taken into account because the actual environment of water evaporation may be relatively harsh. Recently, cellulose acetate (CA) and poly(vinylidene fluoride) (PVDF) commercial membranes with vesicular structures have Received: March 12, 2019 Accepted: May 21, 2019 Published: May 22, 2019 A

DOI: 10.1021/acsami.9b04452 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

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ACS Applied Materials & Interfaces

Scheme 1. Schematic Illustration of the Synthetic Method, Efficient Solar Water Evaporation, and Thermal Antibacterial Property

shown great potential for water evaporation.34,35 However, finding novel membranes with excellent mechanical properties for water evaporation applications is still a challenge for the field. In this work, we demonstrated a novel Co2.67S4-based photothermal membrane with excellent mechanical properties created using a vacuum filtration method and evaluated its potential as a multifunctional platform for efficient solar water evaporation and photothermal antibacterial applications (Scheme 1). The nonstoichiometric Co2.67S4 nanoparticles (NPs), with their low cost, high production yield, and simplified fabrication process properties, possess strong optical absorbance in a broad wavelength region that greatly matches the spectrum of sunlight. Teflon (PTFE) has been proposed as a new generation of membrane material for water evaporation due to its advantages of excellent mechanical properties, corrosion resistance, thermostability, and nontoxicity. Combining the above excellent advantages, a Co2.67S4-deposited PTFE membrane not only effectively strengthens the solar vaporgeneration efficiency but also enhances the elimination rate of bacteria for water purification. Moreover, it is worth noting that the performance in terms of solar vapor generation did not change after 10 repetitions in a pH range of 5.4−8.5. Therefore, we believe that the results presented here should stimulate advances in the use of Co2.67S4-coated PTFE membranes for highly effective solar vapor applications.

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Preparation and Hydrophobic Treatment of Co 2.67 S 4 Membranes. Co2.67S4-deposited membranes were prepared by filtering 10 mL of Co2.67S4 solution (2.5, 5, and 10 mg mL−1) through the PTFE membrane under vacuum. Then, the hydrophobic Co2.67S4-deposited membrane (Final-PTFE membrane) was obtained using a chloroalkylsiane modification method. Briefly, the Co2.67S4 NP-deposited PTFE membrane was placed in a vacuum desiccator and 200 μL of MTS was added into a small beaker in the desiccator. Then, the desiccator was hooked up to a vacuum pump and placed at room temperature for 12 h under vacuum. Characterization. Transmission electron microscopy (TEM) images were obtained on an FEI Tecnai G2 F20 microscope at an acceleration voltage of 200 kV. The phase composition of the sample was determined by X-ray diffraction analysis (XRD, Bruker AXS D8 Advance). The chemical valence of Co ions was measured by X-ray photoelectron spectroscopy (XPS, Perkin Elmer PHI 5600). The optical properties were measured using a spectrophotometer (U-4100. Hitachi). Contact angles were measured on a commercial contact angle system (JY-82B). Temperature changes and thermal distribution images were obtained using an infrared camera (FLIR ONE PRO). Water evaporation measurement was performed using a 300 W Xe lamp (HSX-UV300). The mechanical properties were measured using a universal electronic testing machine (CMT6103). Water Evaporation Performance Tests. Water evaporation was measured based on the mass loss of water using an electronic balance (WT30002). Briefly, a Co2.67S4-deposited membrane with a diameter of 3.0 cm was floated on the surface of water (25 mL) in a 30 mL beaker. A Xe light (2 kW m−2) at the top of the beaker was employed to simulate sunlight. Then, the surface temperature was recorded using an infrared camera for 60 min at intervals of 5 min. The temperature and humidity for the water evaporation tests were 22.3 °C and 17%, respectively. The emissivities of water, the Final-PTFE membrane, and the glass sidewall of the beaker were determined by an emissivity measuring instrument (IR-2), and their emissivities were 0.95, 0.96, and 0.92, respectively. The IR camera used had the function of emissivity calibration (FLIR ONE PRO), and all of the obtained results were approximately corrected before testing. Photothermal Antibacterial Test. The Escherichia coli O157:H7 strain was incubated with shaking at 180 rpm in Luria-Bertani broth at 37 °C for 12 h. After overnight incubation, the concentration of bacteria reached ∼5.0 × 109 CFU mL−1. Bacteria at a concentration of 1.0 × 105 CFU mL−1 were achieved by dilution with phosphatebuffered saline (PBS, 10 mM, pH = 7.4), and 25 mL of the obtained bacterial solution was poured into the beaker. Next, a Final-PTFE membrane was placed on the surface of the bacteria solution, and then a Xe lamp was employed to irradiate the membrane for 60 min (the bacteria solution in the beaker was under magnetic stirring during the irradiation). An untreated bacteria solution was used as a control, whereas a Final-PTFE membrane without irradiation and pure

EXPERIMENTAL SECTION

Materials. Sodium sulfide (Na2S·9H2O), cobalt chloride (CoCl2· 6H2O), ethylene glycol (EG), and methyltrichlorosilane (MTS) were purchased from Aladdin. All commercial membranes (CA, polyethersulfone (PES), PVDF, polypropylene (PP), and PTFE, aperture: 0.22 μm) were provided by Haining Taoyuan Medical Chemical Co. Ltd (Zhejiang, China). Synthesis of Co2.67S4 Nanoparticles. Co2.67S4 nanoparticles were prepared using a solvothermal method. First, 1 mmol of CoCl2· 6H2O was dissolved in 20 mL of EG with a magnetic stir bar, forming a peach-colored solution. Then, 20 mL of Na2S·9H2O (2.2 mmol) was added to the above solution. The two solutions were mixed by stirring at room temperature for 30 min, forming a homogeneous solution. The resulting solution was then transferred to a Teflon-lined autoclave with 100 mL internal volume, and the solution was heated at 180 °C for 10 h. After the reaction, the resulting black powders were centrifuged and washed with water and then with ethanol. The products were then dried at room temperature for 24 h. B


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Figure 1. (a) TEM image of Co2.67S4 nanoparticles, (b) SEM image of Co2.67S4 agglomerations, (c) XRD pattern of Co2.67S4 nanoparticles, (d, e) fitted Co and S 2p XPS spectra of Co2.67S4 nanoparticles, and (f) UV−vis−NIR spectra of Co2.67S4 powder sample.

Figure 2. (a) Cross-sectional SEM images of different commercial membranes; (b−f) various mechanical performance indexes of different commercial membranes. fixed with 4% paraformaldehyde containing PBS for 30 min at room temperature. Then, the bacteria were dehydrated by sequential treatments with 30, 50, 70, 85, 95, and 100% ethanol each for 5 min. Finally, the dried bacteria were sputter-coated with gold for SEM.

bacteria solution with irradiation were used as the additional controls. After irradiation, 1 mL of the collected bacteria solution from each group was centrifuged, washed twice with PBS, and then redispersed in PBS for further use. For the colony-counting experiments, 100 μL of the above bacteria solution from each group was diluted 100 times with PBS. Then, 50 μL of the diluted bacteria solution was spread on 60 mm agar culture plates and incubated at 37 °C for 18 h. Finally, a camera was used to record the results. For fluorescence staining tests, 100 μL of the above bacteria solution from each group was diluted 100 times with PBS. Next, 3 mL of this diluted bacteria solution was added into a dye solution containing 0.39 μM SYTO-9 and 2.35 μM propidium iodide (PI). The stained bacteria were measured using an Olympus BX53 fluorescence microscope. The living and dead bacteria were stained green and red by SYTO-9 and PI, respectively. Morphological Observation of Bacteria. The four typical groups of bacterial suspensions were dropped on silicon wafers and

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RESULTS AND DISCUSSION The one-step synthesis of Co2.67S4 nanoparticles was carried out through a solvothermal method at 180 °C as shown in Figure 1. As can be seen in the transmission electron microscopy (TEM) image, the size of these Co 2.67 S 4 nanoparticles was in the range of 8−15 nm (Figure 1a). Interestingly, these small nanoparticles very easily agglomerated into larger nanoparticles, which displayed a size of about 200−300 nm (Figures 1b and S1). X-ray diffraction (XRD) was employed to explore the crystal phase and purity of the asC


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Figure 3. (a, b) SEM images of a PTFE membrane, (c) SEM image of a Co2.67S4-deposited PTFE membrane, (d) reflection/transmission/ reflection spectra of a Co2.67S4p-deposited PTFE membrane, and (e) schematic illustration of the preparation of different membranes and their corresponding water contact angles.

research subject, and their cross-sectional SEM images are shown in the Figure 2a. The average thicknesses of CA, PES, PVDF, PP, and PTFE membranes were 70, 78, 49, 185, and 74 μm, respectively. From Figures S3 and S4, the average apertures of CA, PVDF, PES, and PTFE membranes were 1.03, 0.61, 1.25, and 0.40 μm, respectively. Unfortunately, we could not accurately determine the aperture of the PP membrane, which consisted of many thick and disorganized microwires (Figure S3). As can be seen in Figure 2b−f, the main mechanical properties of different commercial membranes per unit thickness such as the elongation at break, elasticity modulus, maximum force, tensile yield stress, and tensile strength were measured, and the performance indexes gradually increased from the CA membrane to the PTFE membrane. Among the five films tested, the PTFE membrane displayed the best overall mechanical performance. For example, compared with those of the CA and PVDF membranes, the elongation at break of a PTFE membrane per unit thickness was increased by nearly 10 times and 3 times, respectively. Consequently, we selected a PTFE membrane with the best mechanical performance for subsequent experiments. A Co2.67S4-deposited PTFE membrane was fabricated via a vacuum filtration method. As depicted in Figure 3a,b, the average aperture of the PTFE membrane was about 0.40 μm (Figure S4). After the deposition of Co2.67S4 nanoparticles, the surface of the membrane became rough and full of stacking gaps (∼1.37 μm) that contribute to water evaporation (Figures 3c and S5). As shown in Figure 3d, the photoabsorption band of a Co2.67S4-deposited PTFE membrane with broad and strong properties largely matched the solar spectra (gray curve), which is typified by limited reflection and negligible light transmittance in the 200−2500 nm region. Surface hydrophobicity can give a membrane self-floating capacity on a water surface, which is a necessary condition for interface heating. Therefore, we carried out a hydrophobic treatment by chloroalkylsiane modification on a Co2.67S4-deposited PTFE membrane. As can be seen from Figure 3e, we observed that the water contact angle increased from 0° for a pure PTFE membrane or a Co2.67S4-deposited PTFE membrane to 133°

fabricated Co2.67S4 nanoparticles. From Figure 1c, it can be clearly seen that all of the peaks corresponded to the characteristics of cubic-phase Co2.67S4 (PDF#97-010-9368). The X-ray photoelectron spectroscopy (XPS) assay results displayed in Figure 1d,e were further used to investigate the chemical states of cobalt and sulfur in the Co2.67S4 nanoparticles. Figure 1d reveals the Co 2p XPS spectra of the Co2.67S4 nanoparticles. The two main peaks were located at 792.9 eV (Co 2p1/2) and 777.9 eV (Co 2p3/2), which could be assigned to the spin-orbit coupling of Co3+ ions.36−38 The peaks observed at 796.5 eV (Co 2p1/2) and 780.3 eV (Co 2p3/2) in the second doublet exhibit the binding energy of Co2+ ions.39,40 Moreover, there were two typical peaks situated at 802.2 and 784.8 eV for the satellite peaks of Co 2p, which have been widely reported.41 For the S 2p signal (Figure 1e), the peaks at 160.8 and 161.6 eV were assigned to the spin-orbit coupling of S− ions, whereas the peak at 162.2 eV was attributed to the spin-orbit coupling of S2− ions.36,42 The peak at 167.8 eV is contributed by the shake-up satellite (sat.) structure.43 Meanwhile, the characteristic peak at 165.5 eV could be assigned to Co−S−thiolate bonds.44 We further quantified the molar ratio of S and Co in the Co2.67S4 nanoparticles by the inductively coupled plasma optical emission spectrometry (ICP-OES) method, which is calculated to be 1.5. Thus, it is nearly the same as that in the proposed Co2.67S4 (1.498) phase. Then, we checked the photoabsorption of a Co 2.67 S 4 powder sample using a UV−vis−NIR spectrophotometer. As can be seen from Figure 1f, nonstoichiometric Co2.67S4 displays high absorption in the full region from 200 to 2500 nm, meaning that it should be an impressive NIR-absorbing material for solar water evaporation. Since the mechanical properties of a porous membrane are an important index for determining its service life, the mechanical properties of membranes that are used in water evaporation should be studied in detail. Although CA and PVDF membranes have been employed for water evaporation, their mechanical properties have received little attention. In this section, we selected five different commercial membranes (including CA, PVDF, PES, PP, and PTFE membranes) as our D


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Figure 4. (a) Top-view IR images of beakers under light irradiation for varied times; (b) side-view IR thermal images of beakers under light irradiation for varied times; (c) plot of the maximum temperature attained by the PTFE membrane, Final-PTFE membrane, and H2O; (d) time course of water evaporation for different samples; (e) time course of water evaporation and (f) the corresponding evaporation rate for water with different treatments; (g) solar vapor-generation cycle performance of the Final-PTFE membrane immersed in aqueous solutions at different pH values; (h) concentration changes of Na+, K+, Ca2+, Mg2+, and B3+ in seawater samples (from the Bohai Sea, China) before and after desalination, which are compared with the standard of drinking water quality (there is presently no specific standard value for K+).

This hot-zone allowed water to evaporate quickly at the interface, leading to a high water evaporation efficiency. Subsequently, the water evaporation performance of the assynthetized Final-PTFE membrane was quantitatively examined by recording the weight change of water as a function of the light irradiation time. As displayed in Figure 4d, water evaporation at 60 min was 2.62 kg m−2 for the 5 mg mL−1 group under two sun irradiations, which is higher than that of the 2.5 mg mL−1 group. As the concentrations of the Co2.67S4 NPs were increased to 10 mg mL−1, the water evaporation at 60 min was slightly reduced, which may be due to the blocking of water transport channels by excessive materials. Based on the above results, we believed that a photothermal membrane with optimal performance was obtained when the material concentration was 5 mg mL−1. As can be seen in Figure 4e, obvious time-dependent water evaporation increases for the pure water, PTFE, and Final-PTFE groups were found under light irradiation, whereas the pure water, PTFE, and Co2.67S4deposited PTFE groups without light irradiation showed negligible change. Water evaporation at 60 min was 2.62 kg m−2 for the Final-PTFE membrane under two sun irradiations, which is more than twice as much as those of the water or PTFE groups under similar light irradiation conditions. Meanwhile, the Final-PTFE group combined with light irradiation also exhibited the highest water evaporation rate of

for the Final-PTFE membrane, implying that the hydrophobic treatment was successful. Since good photothermal conversion performance is an important condition for determining whether a membrane can be used for water evaporation, we next examined the photothermal abilities of the as-prepared Final-PTFE membrane. An infrared camera was employed to record the thermal distribution of different membranes floating on the water surface over a period of light irradiation. As shown in Figure 4a, under light irradiation, the rises in the temperature of pure water and of a bare PTFE membrane were 14.0 and 15.4 °C, respectively. By contrast, the temperature of the Final-PTFE membrane quickly rose from 20.2 to 62.5 °C after 60 min of light irradiation, suggesting that it had an outstanding photothermal conversion ability and light-harvesting efficiency (Figure S6). To confirm the light utilization rate of this FinalPTFE membrane, side-view IR thermal images of beakers under light irradiation for varied times were recorded. From Figure 4b,c, one can observe that the pure water and the FinalPTFE membrane groups had different heating modes under light irradiation. The pure water group exhibited an overall heating characteristic, meaning that the water temperature will rise slowly, whereas the Final-PTFE membrane group had the characteristic of interfacial heating, meaning that there was a “hot-zone” at the interface between water and air (Scheme 1). E


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ACS Applied Materials & Interfaces 2.62 kg m−2 h−1 at 60 min (Figure 4f). It is worth mentioning that when the solar light power density was 2 kW m−2 (2 sun), the light-to-heat conversion efficiency (η) of water evaporation reached a value of 82% for the Final-PTFE group, which was calculated by the following equation η=

dm dt × S

× He

Qs

× 100%

where m is the mass of evaporated water, t is the time, S is the surface area of the Final-PTFE group, He is the heat of evaporation of water (∼2260 kJ kg−1), and Qs is the power density of the light source (2 kW m−2).45 Table S1 summarizes some of the representative evaporation rates and photo-tothermal conversion efficiencies of the current work and previous works. Obviously, the evaporation rate and phototo-thermal conversion efficiency of the Final-PTFE membrane reported in this work were 2.62 kg m−2 h−1 and 82% under two sun irradiations, respectively, which arrayed highly in these related research works. In addition to the water evaporation properties of a membrane, the cycle life of the final membrane is an important indicator for its practical application in water evaporation processes. The device may be immersed in acidic and alkaline aqueous solutions while dealing with wastewater during practical usage. Therefore, its durability in aqueous solutions in a wide range of pH values should be evaluated. The vapor-generation experiments with the Final-PTFE membrane were performed for 10 cycles. As displayed in Figure 4g, the Final-PTFE membrane still maintained a relative evaporation rate of more than 90% after 10 cycles in a pH range of 5.4−8.5, suggesting an excellent durability under the above-mentioned acidic or alkaline conditions. Unfortunately, the relative evaporation rate significantly decreased with the increase of cycle numbers for the pH = 4.0 or pH = 10.0 groups, implying that the Final-PTFE membrane had an excellent durability in aqueous solutions in a pH range of 5.4− 8.5. We further evaluated the desalination performance of the Final-PTFE membrane by measuring the concentrations of main elements in seawater. By using the ICP-OES analysis, the final concentrations of Na+, K+, Ca2+, Mg2+, and B3+ in seawater were significantly reduced after desalination (Figure 4h). The concentrations of Na+, K+, Ca2+, Mg2+, and B3+ in the collected water were 80.01, 40.08, 2.502, 3.523, and 0.1987 mg L−1, respectively, which were within the standards of drinkingwater quality.46,47 Therefore, the as-prepared Final-PTFE membrane has potential in solar energy-driven seawater desalination. The water obtained by water evaporation can easily cause diseases such as cholera, typhoid fever, and dysentery if it contains pathogenic bacteria. Therefore, an ideal photothermal membrane used for water evaporation should not only have excellent water evaporation efficiency, but also have strong photothermal antibacterial properties. To detect the antibacterial properties of the membrane we prepared, we used E. coli O157:H7, a bacterial strain that is widely distributed in wastewater and contaminated water, as a model bacterium. It has been reported that thermal inactivation is an effective method of sterilization, and most pathogenic bacteria will die when the temperature is above 60 °C for more than 30 min. First, the colony-counting method was used to determine the antibacterial ability of the Final-PTFE membrane. As shown in Figure 5a, compared with the control group, the Final-PTFE group without irradiation or the light group showed no

Figure 5. (a) Photographs of bacterial colonies formed by E. coli for different groups; (b) fluorescence images of E. coli after different treatments; (c) SEM images of E. coli after different treatments.

significant antibacterial effect, indicating that the Final-PTFE membrane without irradiation or light itself did not kill E. coli in 60 min. In sharp contrast, the Final-PTFE membrane combined with light irradiation could effectively kill all E. coli, which may have been due to the hot-zone formed at the air− water interface and the adequate sterilization time. To further substantiate this, we also determined the antibacterial effects of the Final-PTFE membrane by fluorescence staining. Propidium iodide (PI) with red fluorescence and SYTO-9 with green fluorescence were utilized as staining agents for dead bacteria and live bacteria, respectively (Figure 5b). In the case of the control group, the Final-PTFE group, and the Light group, all of the bacteria showed green fluorescence, suggesting that nearly all of the bacteria were alive. By contrast, the FinalPTFE group displayed remarkable and considerable red fluorescence, implying that nearly all of the bacteria were dead, which was consistent with our previously mentioned colony-counting results. To explore the antibacterial mechanism of the Final-PTFE membrane, we also performed SEM on bacteria from the above four experimental groups. In Figure 5c, nearly all of the E. coli cells from the control group, the Final-PTFE group without irradiation, and the Light group are bacilliform and have good morphology with a smooth surface. In the case of the Final-PTFE membrane irradiated by light, most of the bacteria became smaller and the cell walls of the bacteria appear to be severely damaged, leading to the dissolution of substances inside the bacteria, which may have caused the bacteria irreversible damage. Therefore, the antibacterial mechanism of the as-prepared Final-PTFE membrane with the light irradiation is related to the destruction of the cell wall by thermal effects.

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CONCLUSIONS In this study, we established a photothermal membrane with excellent mechanical properties based on nonstoichiometric Co2.67S4, which was an excellent solar-harvesting material to simultaneously realize efficient solar water evaporation and photothermal antibacterial treatment under light excitation. The as-prepared Final-PTFE membrane not only possessed a high water evaporation rate (2.62 kg m−2 h−1) and a high lightto-heat conversion efficiency (82% under two sun irradiations) but also exhibited strong hydrophobic properties and excellent F


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ACS Applied Materials & Interfaces cycle durability. Both colony counting and fluorescence staining revealed that the Final-PTFE membrane combined with the light irradiation could greatly inhibit bacterial growth and even completely inactivate bacteria. The antibacterial mechanism was confirmed to be a thermal effect that caused damage to the cell wall of bacteria. These results highlight that the combination of photothermal conversion and photothermal antibacterial properties has endowed the Final-PTFE membrane with high potential as a material for solar energydriven photothermal water evaporation and water purification.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.9b04452. SEM images and electron diffraction data of Co2.67S4 nanoparticles; SEM images and aperture distribution of different membranes; design of the seawater desalination device; summary of representative evaporation rates and photo-to-thermal conversion efficiencies (PDF)

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected] (W.G.). *E-mail: [email protected] (F.Q.). ORCID

Wei Guo: 0000-0001-5445-7872 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China (No. 21471041). REFERENCES

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Co2.67S4-Based Photothermal Membrane with High Mechanical

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