Polylactic Acid Fiber

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Melt Electrospun Reduced Tungsten oxide /Polylactic acid Fiber Membranes as Photothermal Material for Light-driven Interfacial Water Evaporation Tolesa Fita Chala, Chang-Mou Wu, Min Hui Chou, and Zhen Lin Guo ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b07434 • Publication Date (Web): 27 Jul 2018 Downloaded from http://pubs.acs.org on July 28, 2018

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ACS Applied Materials & Interfaces

Melt Electrospun Reduced Tungsten oxide /Polylactic acid Fiber Membranes as Photothermal Material for Light-driven Interfacial Water Evaporation Tolesa Fita Chala, Chang Mou Wu*, Min Hui Chou, Zhen-Lin Guo Department of Materials Science and Engineering, National Taiwan University of Science and Technology, Taipei 10607, Taiwan, R.O.C. * Corresponding author: E-mail: [email protected] , Tel.: +886-2-2737-6530

Abstract The development of efficient photothermal materials is the most important issue in solar water evaporation. In this work, melt electrospun reduced tungsten oxide-Polylactic acid (WO2.72/PLA) fiber membranes were successfully prepared with improved near-infrared (NIR) photothermal conversion properties owing to strong NIR photoabsorption by the metal oxide. WO2.72 powder nanoparticles were incorporated into PLA matrix by melt processing, following which the composites were extruded into wires using a single screw extruder. Subsequently, fiber membranes were prepared from the extruded wire of the WO2.72/PLA composite by melt electrospinning, which is a cost-effective technique that can produce fiber membranes without the addition of environmentally unfriendly chemicals. The melt electrospun WO2.72/PLA fiber membranes, floatable on water due to surface hydrophobicity, was systematically designed for, and applied to, vapour generation based on the interfacial concept of solar heating. With the photothermal WO2.72/PLA fiber membrane containing 7 wt% of WO 2.72 nanoparticles, the water evaporation efficiency was reached 81.39 %, which is higher than that for the pure PLA fiber membrane and bulk water. Thus, this work contributes to the development of novel photothermal fiber membranes in order to enhance light-driven water evaporation performance for potential applications in the fields of water treatment and desalination. Keywords: Tungsten trioxide (WO3), Polylactic acid (PLA), Melt electrospinning, Photothermal conversion, water evaporation.

1 ACS Paragon Plus Environment

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1. Introduction Solar energy conversion is the most important aspect of solar energy harvesting technologies, enabling the effective utilization of renewable, clean, and sustainable energy for the development of human society.1-6 Water evaporation is an interfacial process, an essential part of the global water cycle, and can be accelerated using solar radiation as a source of heat, which is free and abundantly available on the earth. It is also an endothermic process, in which heat energy is absorbed. 7-8 Recently, utilization of efficient solar energy for production of other forms energy is a critical factor for variety of application, such as solar photothermal autoclave for sterilization, desalination and power generation.9-10 A material that absorbs light energy and converts it to thermal energy in a process also known as photothermal conversion, can be employed for water evaporation. 11-12 Photothermal materials can be harnessed for water evaporation to generate heat under light

irradiation, further improve the efficiency of water

evaporation without affecting water quality.2, 13 Among several active photothermal nanomaterials, those tungsten oxide based are of particular interest owing to their strong local surface plasma resonances, which give rise to strong photoabsorption in a broad wavelength range of the NIR region. 14-15 They are also suitable for solar energy collectors, heat-ray shielding, smart windows, and energy economization. 16 Hua, Z et al., reported NIR and Visible (Vis) light absorbing materials are desirable for solar water evaporation application, because NIR and Vis lights compose nearly 40% of total solar energy. NIR light responsive photothermal materials are attracting a great attention because the wavelength of NIR is larger than most water drops in cloud and thus avoid the blocking of cloud much easier than visible light. As a result, the energy harvesting from NIR light is promising for steam generation. 2, 17 In addition, Wang et al. employed Cu7S4 nanocrystals for water evaporation application under an infrared light irradiation, because of excellent photothermal conversion properties of Cu7S4 nanocrystals in NIR region.10 Hence, the development of appropriate NIR-absorbing solar radiation materials is considered to be a rational strategy to efficiently harvest solar energy for vapour generation via heat localization.18 Currently, a novel technique called “air-water interface solar heating” has attracted immense interest for water evaporation. In this process, light-absorbing materials float on water and heat only the surface while avoiding homogenously heating the bulk water. Target heating at the air-water interface can generate a sharper localized temperature and realize a more efficient water evaporation efficiency whereas bulk water


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heating system delivers poor effeciencies.19-23 The physicochemical stability and increasing availability of transition metal oxide nanostructures has also attracted great attention. In particular, there is interest in oxygen-deficient non-stoichiometric metal oxides such as WO3-x MoO3-x, and TiOx whose strong photoabsorption properties in a broad wavelength region make them suitable for converting light energy to thermal energy to generate steam power.4, 24-25 Thus, the WO2.72/PLA composite fiber membrane is a suitable candidate for the process of photothermal water evaporation because of its efficient light-to-heat conversion, strong NIR absorption ability, and floatability on water due to surface hydrophobicity. 26 Previously, numerous photothermal materials with strong light absorbance in the solar spectrum range, including noble metal nanoparticles,13,

27-29

conducting polymers of polypyrrole,30-31 carbon-based

materials, graphene oxide, carbon fibers, carbon nanotubes (CNT),32-35 MXene,36 black metal oxides37 and plasmonic absorbers38-39 have been intensively studied and found to exhibit greater evaporation rate than that of bulk water under irradiation. However, to the best of our knowledge melt electrospun WO2.72/PLA fiber membrane photothermal material has not yet been reported for light-driven water evaporation. Fibers are currently used in a variety of engineering applications in which a fibrous structure and a large surface area are required.40 A variety of materials, such as hybrid, inorganic-organic, or polymer composites with nanofibers, have been prepared using electrospinning techniques. 41-42 Electrospinning techniques is an attractive method for producing ultrathin fibers with diameters ranging from the micro to the nanoscale.43-44 There are two types of electrospinning methods. Melt electrospinning and solution electrospinning, in which both microscale and nanoscale fibers are produced respectively.4546

Solution electrospinning requires a solvent to dissolve a given polymer type, whereas melt

electrospinning involves the heating of the polymer to its melting point to produce a viscous fluid which can be drawn into fibers.47-48 Melt electrospinning holds some benefits over solution electrospinning in tissue engineering applications49 because this technique is free of toxic solvents, safer, more environmentally friendly, economical, and is a controllable method for producing higher efficiency nano/micro fibers, compared to solution electrospinning. 50-53 Therefore, melt electrospinning has recently been gaining more attention and a limited number of research studies have been conducted using this technique.



In this work, reduced tungsten oxide (WO2.72) nanoparticles were incorporated into polylactic acid (PLA) by a melt compounding process and extruded into a wire using a single screw extruder. Subsequently, novel fiber membranes were fabricated from the extruded wire of WO2.72/PLA by melt electrospinning. Tungsten oxide nanoparticles were rationally selected as photothermal material because of its strong absorption ability in the NIR region due to unusual oxygen defect structure and light to heat conversion properties whereas PLA polymer is used as matrix for fabrication of fiber membrane, because PLA is an eco-friendly polymer and can be easily electrospun in to fiber membrane by melt possessing. The prepared photothermal melt electrospun WO2.72/PLA fiber membrane was employed for light-driven water evaporation via air-water interface solar heating.

In addition, photothermal conversion and thermal

properties, like thermal conductivity, thermal resistivity, and thermal absorptivity of the fiber membranes were discussed in this study.

2. Materials and Methods Tungsten trioxide (WO3) was obtained from Advanced Ceramics Nanotech Co. Ltd, Taiwan (molecular weight = 231.84 g/mol). Polylactic acid (PLA) pellets (PLA 6210D, Nature Works®, USA) were used in this study. 2.1. Preparation of melt electrospun WO2.72/PLA fiber membrane The preparation and characterization of WO 2.72 nanoparticles were reported in our previous work.54 To prepare the melt electrospinning WO 2.72/PLA fiber membrane first, PLA pellets were dried in a vacuum oven at 80 °C overnight to remove moisture prior to blending. Then, 4 and 7 wt% WO2.72 powders were melt-blended with PLA using a twin-screw extruder (T-BEG-02042, Taiwan). The extruder temperature was set to 190 °C with a screw rotation speed of 17 rpm, and the melt-compounded sample was cooled in a water bath and pelletized. Subsequently, the pelletized composite samples were also dried in a vacuum oven at 80 °C for 12 h and WO2.72/PLA wires were obtained using a single-screw extruder (FS-50J, Taiwan). Finally, using melt electrospinning, the WO 2.72/PLA wires were fabricated into fiber membranes under the following electrospinning conditions: nozzle temperature: 260 °C, electric field: 4 kV/cm, drum rotation speed: 100 rpm, and extrusion rate: 0.013 g/min. The diagram of the melt electrospinning system


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developed in this work is shown in Figure 1.55 The as spun fiber membranes were heat treated at 80 oC for 10 min to release the residual stress caused by the stretching during fiber spinning and shows some shrinkage. Then, the thermal treated fiber membranes become stable and never shrinkage under infrared light irradiation. 2.2. Water evaporation performance measurement The measurement of water evaporation performance was carried out under infrared light irradiation at a room temperature of 25 °C and a relative humidity of about 50 %. Firstly, the membrane sample with a diameter of 5 cm and an areal density of 57.1 g/m2 was placed on the surface of the water in a 100 mL beaker and was irradiated by infrared light vertically from above with a light intensity of 0.294 Wcm-2. In order to reduce the thermal loses, the beaker was wrapped by polystyrene foam as a heat-insulating materials.56-57 The temperature distribution of the fiber membrane floating on water was recorded using an IR camera, and the weight loss of water due to evaporation was recorded using an electronic analytical balance (XS 105 Dual Range). Finally, the evaporation rate of water was determined by recording the mass change as a function of time. 2.3. Characterization The morphology of the melt electrospun fiber membranes was analyzed by scanning electron microscopy (SEM; JSM-6390, Japan) and transmission electron microscopy (TEM, JEOLJEM2010). To prepare the TEM samples, the fiber membrane was embedded in epoxy resin, and after curing, the prepared samples were cut with an ultramicrotome for imaging (Leica EM UCT6 and EM FC6 and EM KMR2, Germany). The optical responses were measured in the wavelength range 300-2500 nm with a UV-VIS-NIR-Spectrophotometer (JASCO V-670, Keith Link Technology, Taiwan). The photothermal conversion properties of the fiber membrane were investigated under irradiation of 150 W infrared lamp, and temperature profile was monitored using an IR thermographic camera (FLIR P384A3-20, CTCT, Co. Ltd, Taiwan), which is shown in Figure S1. Contact angles of the fabricated melt electrospun fiber membrane were measured using a contact angle measuring device (Contact Angle Goniometer, Sindatek Model 100SB, Taiwan) at ambient temperature. Thermal properties such as thermal conductivity, thermal



absorptivity, and thermal resistivity of the fiber membrane were also evaluated using an Alambeta device (Sensora Instruments, Czech Republic).

3. Results and Discussion 3.1. Morphology of the melt electrospun WO2.72/PLA fiber membranes Representative images of the morphology of melt electrospun WO 2.72/PLA fiber membrane, containing 0, 4, and 7 wt% of WO2.72 nanoparticles, are shown in Figures 2a, b, and c, respectively. Figure 2a is an image of the pure PLA fibers, which are cylindrical and uniform with a diameter of ~8-13 µm. The diameter of the melt electrospun fibers containing WO 2.72 was unaffected by the addition of WO2.72 nanoparticles. The energy dispersive spectroscopy (EDS) scan shown in Figure 2d also indicates the presence of elements W, O, and C in the WO 2.72/PLA composites, confirming the incorporation of tungsten oxide nanoparticles in the PLA matrix. Moreover, the incorporation of WO 2.72 nanoparticles into the PLA matrix was also investigated using TEM. The TEM image shows that WO 2.72 nanoparticles are uniformly dispersed and distributed in the PLA matrix (Figure 3a). The high-resolution TEM image in Figure 3b shows a well-defined lattice fringe with a spacing of 0.37 nm, corresponding to the interplanar spacing of the (010) lattice plane of monoclinic WO 2.72 nanoparticles. 3.2.

Optical and NIR photothermal conversion properties

Figure 4 shows the UV-Visible-Near-Infrared absorbance spectra of WO 2.72/PLA containing 0, 4, and 7 wt% of WO 2.72 nanoparticles. The WO2.72/PLA material exhibits a strong broad absorption in the wavelength region of 300-2500 nm, particularly in the NIR light region ranging from 780-2500 nm. The absorbance for pure PLA is limited in the NIR region; however, after the addition of WO2.72 nanoparticles, the absorbance in this region significantly increases. Furthermore, for water evaporation application the most important requirements for photothermal materials is their light absorption ability in the entire region.58 As shown in Figure 4 WO2.72/PLA containing 7wt% of WO2.72 nanoparticles exhibits a short wavelength absorption band-edge at ≈ 550 nm, with its band gap of Eg = 2.65 eV (Figure S3). Moreover, they also exhibit an increased photoabsorption in the NIR region. The reasons why tungsten oxides (WO 3-x) gives strong and wide absorption in the


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NIR region are originated from intervalence charge transfers, local surface plasma resonance (LSPRs) of free electrons, and small polaron absorption. 15,

59-61

In addition, the presences of

narrow band gap with strong NIR light absorption of metal oxide may convert NIR light energy into heat. Light is absorbed by metal oxides like, MoO 3-x, Fe3O4, WO 3-x, Cu2-xS, and TiO x to induce electron-hole pairs. These electron-hole pairs would further recombine to generate heat.4, 17, 24, 6263

Therefore, the prepared material is suitable for light-driven water evaporation application.

The photothermal conversion performance of the fabricated melt electrospinning fiber membranes was investigated under infrared light illumination. Figure 5 shows the temperature elevation of WO2.72/PLA containing 0, 4 and 7 wt% of WO 2.72 nanoparticles. The results indicate that higher weight fractions of WO 2.72 nanoparticles facilitate quicker and higher temperature increments. The temperature increment (T) reached T = 85.4 °C for 7 wt% and T = 71.7 °C for 4 wt% after 3 min of irradiation. This shows that the prepared WO2.72/PLA melt electrospun fiber membrane can efficiently and rapidly convert absorbed light energy into local heat. For comparison, the temperature change using pure PLA melt electrospun fiber membrane was only T = 15.1 °C after 3 min of irradiation. Furthermore, the temperature of the WO2.72/PLA fiber membrane containing 7 wt% of WO 2.72 nanoparticles increased dramatically, reaching T = 56.7 °C after 10 s and T = 67.5 °C after 30 s, then remained constant upon further prolonging the irradiation time to 180 s. This phenomenon can be attributed to faster heat loss at higher temperatures. 59,

64

In

addition, when the source of illumination was turned off after 180 s, the temperature of the WO2.72/PLA melt electrospun fiber membrane quickly returned to ambient temperature. This explains why the higher-temperature photothermal material undergoes rapid cooling. Such a quick response results from the strong light-to-heat converting ability of the WO 2.72/PLA fiber membrane, and enables a quick start of the water evaporation process 8, 65. Thermal-related properties including thermal conductivity, absorptivity, and resistance of the WO2.72/PLA fiber membrane were measured by an Alambeta instrument. Table 1 presents the thermal characteristics of the WO 2.72/PLA fiber membranes with 0, 4, and 7 wt% of WO 2.72 nanoparticles. The thermal conductivity and absorption of the melt electrospun fiber membrane slightly increases as the weight fraction increases from 0 to 7 wt%. The incorporation of a lower



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weight fraction of 4 wt% WO 2.72 yields no obvious changes in either thermal conductivity or absorption of the WO 2.72/PLA fiber membrane compared with pure PLA melt electrospun fiber. Thus, the WO2.72/PLA composite melt electrospun fiber membrane does not show significant improvement in thermal properties compared to the pure PLA melt electrospun fiber membrane. This is due either to the open pore structure and irregular pore network of the fiber membrane or to the air trapped inside the fiber membrane. The resistance to heat flow or thermal resistance of the WO2.72/PLA fiber membrane with different WO 2.72 nanoparticle weight fractions was also examined under similar conditions. The results in Table 1 show that the thermal resistivity of the WO2.72/PLA melt electrospun fiber membrane decreases with increasing WO 2.72 weight fraction. Table 1. Thermal properties of WO 2.72/PLA melt electrospun fiber membrane prepared with (0-7 wt%) WO2.72 nanoparticles Weight fraction of WO2.72 (wt %)

0

4

7

Thermal conductivity (mWm-1K-1)

29.00

29.50

33.00

Thermal Absorption (Ws1/2m−2K−1)

57.13

59.80

63.13

Thermal Resistance (m 2mkW −1)

37.10

26.40

24.00

For water evaporation process the photothermal material should be floatable on water to generate localized heat at the water-air interface to enhance evaporation rate. Hence, investigating the hydrophobicity of the surface of the photothermal WO 2.72/PLA fiber membrane is important to confirm its floatability on water. The hydrophobicity of the WO 2.72/PLA fiber membranes was determined by measuring contact angle. Figure 6 shows the water contact angle of the WO2.72/PLA fiber membrane containing 7 wt% of WO 2.72 nanoparticles. The membrane exhibits a strong hydrophobic character with a large contact angle of 136.7°. Therefore, due to its hydrophobicity and low density, the WO 2.72/PLA fiber membrane can easily float on water (as shown in Figure S1), enabling interfacial solar heating to increase the evaporation rate of water. 3.3. Water evaporation performance Having confirmed the photothermal conversion properties, the WO 2.72/PLA fiber membrane was evaluated for water evaporation performance by floating it on water under infrared light irradiation.


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Figure 7a shows a schematic of the experimental setup used for this measurement. Temperature variation and thermal images were captured by an IR thermographic camera. Figures 7b and 7c show surface temperatures and IR thermal images, respectively, of the WO 2.72/PLA fiber membrane containing 0, 4, and 7 wt% WO 2.72 nanoparticles floating on water, and pure water without a floating fiber membrane. For the pure PLA fiber membrane, there was only a slow and small temperature rise of ΔT= 19.4 °C. In contrast, the WO 2.72/PLA fiber membranes containing 4 and 7 wt% WO 2.72 nanoparticles exhibited a rapid rise in temperature, which then remained constant over 5 min of irradiation. Temperature variation for the membrane containing 7 wt% WO2.72 reached ΔT= 75.3 °C and that for the 4 wt% sample reached ΔT= 44.7 °C. The rapid temperature rises for WO 2.72/PLA fiber membranes indicates good photothermal conversion performance for the reduced tungsten oxide (WO 2.72) nanoparticles, attributed to its strong optical absorption characteristics in the NIR wavelength region. The temperature rise for bulk water without a membrane was significantly smaller ΔT = 14.0 °C under similar condition. To determine the potential applications of the prepared photothermal WO 2.72/PLA melt electrospun fiber membrane, we investigated its water evaporation performance by floating it on water in a beaker under light irradiation. A 100 ml beaker containing sample membrane was kept on an electronic balance to measure the real-time mass loss of water. Infrared light with an intensity of 0.294 Wcm-2 was shone directly on the WO 2.72/PLA fiber membrane. For comparison, water evaporation performance without a membrane was measured under similar conditions. Figure 8a shows the weight loss of evaporated water as a function of the irradiation time. The results show the evaporation of water increased linearly with irradiation time. With 7 wt% WO2.72 nanoparticles, water evaporation mass loss reached 1.340 kgm -2 after 35 min of irradiation. Without a fiber membrane, evaporation was 0.640 kgm -2 under similar conditions. Figure 8b shows the corresponding evaporation rate V, estimated by equation (1) V =

dm dt × s

(1)

Where t is time, m is the mass of evaporated water, and S is the surface area of the fiber membrane. The evaporation rates for 0, 4, and 7 wt% (WO 2.72/PLA) fiber membranes after 35 min



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reached 2.45, 3.07, and 3.81 kgm -2h-1, respectively, under infrared irradiation. By comparison, the evaporation rate for pure water reached only 1.830 kgm -2h-1 under the same conditions. These results clearly indicate that water evaporation is strongly enhanced in the presence of a photothermal fiber membrane, and the evaporation rate gradually increased with an increasing content of WO 2.72 nanoparticles. This is attributable to an enhancement in photothermal performance of the WO 2.72/PLA fiber membrane, contributed by the reduced tungsten oxide nanoparticles. Finally, the steam generation efficiency (η) of melt electrospun WO 2.72/PLA fiber membranes was estimated by equation (2)8, 66 η=

𝑄𝑒 𝑄𝑠

(2)

where Qs is the incident light power of 0.294 Wcm-2 and Qe is the power of evaporation of water which can estimated by equation (3) Q 𝑒 = V x H𝑒

(3)

where, He is heat of evaporization of water (≈ 2260 kJ kg -1), and V is the water evaporation rate estimated from equation (1). The corresponding water evaporation efficiency (η) is shown in Figure 8c. The calculation shows that the water evaporation efficiency (η) of the WO 2.72/PLA fiber membrane containing 7 wt% WO 2.72 nanoparticles reached 81.39%, which is significantly higher than that of pure water 39.09%. As result, the water evaporation efficiency of the WO 2.72/PLA fiber membrane is significantly improved in the presence of photothermal reduced tungsten oxide nanoparticles. Thus, this photothermal material could have large-scale practical applications in areas such as steam generation, sterilization of waste, and seawater desalination. Cycling test was conducted to demonstrate the durability and stability of the WO2.72/PLA fiber membranes under infrared light irradiation. Figure 8d shows that the water weight loss was identical at each cycle tests, conforming that the WO2.72/PLA fiber membranes possesses the high photothermal stability and durability. Thus, the WO2.72/PLA fiber membranes can be an ideal option for practical vapor generation application.


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4. Conclusion In conclusion, melt electrospun WO 2.72/PLA fiber membranes with strong NIR absorption capability were developed for the first time for highly efficient interfacial water evaporation. The photothermal conversion characteristics of the WO 2.72/PLA fiber membranes were investigated under

infrared

irradiation.

The

composite

WO 2.72/PLA

fiber

membranes

exhibit

higher

photothermal conversion than pure PLA fiber membranes. The as-prepared WO 2.72/PLA fiber membrane also exhibits strong hydrophobic behavior with a large contact angle, and easily floats on water. The evaporation rate for the WO 2.72/PLA fiber membrane with 7 wt% WO 2.72 nanoparticles calculated to be 3.81 kgm-2h-1, which is significantly higher than that of without a fiber membrane 1.83 kgm-2h-1. The main reason for the enhancement of evaporation is a significant temperature increment of the WO 2.72/PLA fiber membrane on irradiation due to strong broad band light absorption. Thus, it is expected that this fabricated melt electrospun fiber membrane has great potential for applications in photo-thermal energy conversion, such as water distillation, desalination, and evaporation.

Associated Content Supporting Information Photothermal experimental investigation of melt electrospun fiber, floatability of prepared melt electrospun fiber membrane on water

Author Information * Corresponding author: E-mail: [email protected] , Tel.: +886-2-2737-6530

Conflicts of interest The authors declare no conflict of interest

Acknowledgements



The authors would like to thank the Ministry of Science and Technology of Taiwan, ROC, financial support part of this work, under contract numbers: MOST 106-2221-E-011-138 and 106-2218-E-011-018.

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Table of Content (TOC)



Figures

Figure 1. Image of melt electrospun system (inset: processed fiber membrane).


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Figure 2. FESEM images of (a) Neat PLA, (b) WO 2.72/PLA with 4 wt% WO 2.72, (c) WO 2.72/PLA with 7 wt% WO 2.72 nanoparticles, and (d) energy dispersive spectroscopy (EDS) map of WO 2.72/PLA with 7 wt% WO 2.72 nanoparticles

Figure 3. (a) TEM image, and (b) HRTEM image of WO 2.72/PLA nanofiber with 7 wt% WO2.72 nanoparticles



Figure 4. UV-Vis-Absorption spectra of WO2.72/PLA with (0-7 wt%) WO2.72 nanoparticles


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Figure 5. Photothermal response of WO2.72/PLA electrospun fiber membrane with (0-7 wt %) WO2.72 in the presence and absence of infrared light

Figure 6. Water contact angle of WO2.72/PLA fiber membrane containing 7 wt % WO2.72 nanoparticles



Figure 7. (a) Schematic of water evaporation measurement with WO2.72/PLA fiber membrane floating on air-water interface, b) Temperature of WO2.72/PLA fiber membrane containing 0, 4, and 7 wt% WO 2.72 nanoparticles floating on water, and that of pure water without the fiber membrane at ambient temperature, c). IR thermal images of WO2.72/PLA fiber membrane containing 0, 4, and 7 wt% WO2.72 nanoparticles and pure water without the fiber membrane, under infrared light.


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Figure 8. a) Mass loss through water evaporation under infrared illumination as a function of the irradiation time for WO2.72/PLA fiber membranes containing 0, 4, and 7 wt% WO 2.72 nanoparticles and pure water without the fiber membrane, b) corresponding water evaporation rates, c) evaporation efficiency and d) Mass loss through water evaporation under infrared light irradiation for 35 min over six cycles showing the stability of melt electrospun WO2.72/PLA fiber membrane containing 7 wt% of nanoparticles.


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Polylactic Acid Fiber

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