A Simple, Low-dose, Durable and Carbon Nanotubes Based Floating

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A Simple, Low-dose, Durable and Carbon Nanotubes Based Floating Solar Still for Efficient Desalination and Purification Qimao Gan, Tuqiao Zhang, Rong Chen, Xun Wang, and Miaomiao Ye ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.8b05036 • Publication Date (Web): 14 Jan 2019 Downloaded from http://pubs.acs.org on January 15, 2019

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ACS Sustainable Chemistry & Engineering

A Simple, Low-dose, Durable and Carbon Nanotubes Based Floating Solar Still for Efficient Desalination and Purification Qimao Gan, Tuqiao Zhang, Rong Chen, Xun Wang, and Miaomiao Ye* Zhejiang Key Laboratory of Drinking Water Safety and Distribution Technology, College of Civil Engineering and Architecture, Zhejiang University, Hangzhou 310058, PR China Corresponding author. Tel.: +86-571-88206759; Fax: +86-571-88208721. Email address: [email protected](M.M. Ye) ABSTRACT A simple, low-dose, durable and carbon nanotubes (CNTs) based floating solar still (CNTs-FSS) has been prepared for seawater desalination based on interfacial solar heating. The CNTs-FSS is composed of a surface layer of CNTs to absorb solar light, a thermal barrier layer of polyurethane sponge (PUS) to avoid the heat transfer into the underneath bulk water, and a water transport channel of air-laid paper to deliver sufficient water to the CNTs layer. The water evaporation efficiency (k) of the CNTs-FSS can be optimized by tuning the thickness of the CNTs layer and the PUS layer. The optimized CNTs dose is only 4 g/m2, far less than that of other reported carbon-based photothermal materials. The k values of the CNTs-FSS are 0.88 kg/m2·h, 1.58 kg/m2·h, and 4.64 kg/m2·h under 1 sun, 2 sun and 4 sun irradiance respectively, which are correspondingly 2.8, 3.4 and 5.3 times higher than that of the control case of pure water. The excellent durability of the CNTs-FSS has been proved by monitoring the water evaporation efficiency during at least 20 cycles of use within 30 days. Finally, we have demonstrated that the organic and inorganic contaminants in condensed freshwater can be well reduced by the CNTs-FSS. KEYWORDS: Solar desalination, Carbon nanotubes, Floating solar still, Interfacial 1 `

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solar heating, Purification INTRODUCTION Although 75% of the earth's surface is covered by water, of which freshwater resources account for only 0.5%, resulting in a serious shortage of freshwater in the world.1,2 In addition, the population growth, water pollution, industrial expansion, and agricultural activities make the water scarcity even more worse. Today, there are more than one-third of the global population lives under strained freshwater resources, this figure is expected to reach nearly two-thirds by 2025.3 Seawater desalination, water recycling, and long-distance water transfer are considered as the three effective methods capable to tackle the global water crisis. Of these, seawater desalination has been considered to be the best way to solve the crisis of water shortage not only because it can offer abundant high-quality fresh water but also because more than 70% of the world's population lives within 70 km from the coast.4,5 In practice, distillation methods and membrane-based separation methods are the mainly two methods that widely applied for seawater desalination. However, these two types of seawater desalination technologies are also plagued by the high energy consumption, advanced supporting infrastructure and large centralized installations,6 which is not feasible in remote, poor and arid or semi-arid areas of the world.7 As water evaporation only occurs at the interface between air and water, absorbing solar light and efficiently converting the energy into heat for heating the water surface is a key factor for accelerating steam generation.8,9 This interfacial heating concept was started in the early 2010s,8,10,11 and has recently triggered worldwide research interests toward solar desalination.12 To date, many efforts have been devoted to synthesize new photothermal materials such as plasmonic metal nanoparticles,13-16 carbon-based materials,8,17-21 and metallic oxides12,22,23 for solar 2 `


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desalination. Among them, carbon-based materials such as hollow carbon spheres,8,17 carbon black,9 graphene,24-26 and graphite27 have attracted more attentions due to their high solar-thermal conversion efficiency, good chemical stability, light weight and low cost. Some comparative studies have pointed out that the carbon-based materials have clearly convincing advantages over expensive plasmonic metal nanoparticles in terms of solar photothermal conversion efficiency.21 In the interfacial heating system, the generated heat will dissipate into the bulk water if the photothermal materials are directly floated on the water surface.28,29 To localize the heat on air-water interface, thermal barriers are usually introduced to separate the photothermal layer and the bulk water. Recently, macroporous silica substrate,30 solid polystyrene foam,25 gauze,9 and wood,31 have been combined with different photothermal materials to fabricate solar stills for steam generation. However, either the poor chemical stability of the thermal barriers or the high cost of the photothermal materials make these solar stills impossible scaling up use in remote and poor areas. Some thermal barriers even may block the water transport channel results in the insufficient water supply to the surface absorbance layer. In this work, we report the fabrication of a simple, low-dose, durable and carbon nanotube based floating solar still (CNTs-FSS) for seawater desalination based on the interfacial solar heating. Carbon nanotubes (CNTs) were selected as the photothermal materials due to their high absorbance in the entire solar spectrum, excellent mechanical strength, porous network structure and good thermal transport properties. More importantly, the carbon nanotubes have advantages over other photothermal materials as they can be used for water and vapor purification during the solar evaporation process due to their excellent adsorption properties.32 Because the organic contaminants especially the volatile organic compounds (VOCs) in many impaired 3 `



source waters would evaporate along and be collected together with water during solar distillation. Very small amount of CNTs, which will reduce the cost of the solar still, were deposited on an air-laid paper (ALP) to form a thin film with controllable thickness by vacuum filtration. A polyurethane sponge (PUS) was used as a floatable thermal barrier layer to localize the heat only at the heating area, which was realized by minimizing heat transfer from the air-water interface to the underlying bulk water . The PUS was wrapped in the above air-laid paper with CNTs layer on its just top. Here, the PUS also plays an important role in the solar still because it not only can prevent heat diffusion but also can serve as the floating support. In addition to PUS covering, the hydrophilic air-laid paper also serve as the water transport channel to deliver water directly to the CNTs layer via capillary action. As a result, the water evaporation efficiency of this floating solar still can be significantly enhanced. Furthermore, we demonstrated that the model organic contaminants such as naproxen, carbamazepine and nitrobenzene in water can be removed by the this CNTs-based floating solar still during the solar distillation process. Finally, this CNTs-based floating solar still was also used for real seawater desalination. The salinity, cations, anions and total organic compounds (TOC) in the condensed fresh water can be significantly reduced. EXPERIMENTAL Materials. All chemicals were of a analytical grade and used as received without any further purification. Multi-walled carbon nanotubes (MW-CNTs assay: 70%-80% (Carbon content, TGA)) with BET surface areas of 277.78 m2/g and average pore size of 16.1 nm (Figure S1a, Supporting Information) were purchased from Sigma-Aldrich, USA. Air-laid paper (length × widths: 110 mm × 210 mm) with BET surface area of 0.74 m2/g (Figure S1b, Supporting Information) was obtained from Kimtech, USA. 4 `


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Polyurethane sponge with density of 12 kg/m3 and BET surface area of 1.06 m2/g (Figure S1b, Supporting Information) was purchased from Nantong Dagong Sponge Co., China. Preparation of the CNTs-Based Floating Solar Still. 1 mg, 5 mg, 10 mg, and 15 mg of MW-CNTs was dispersed in 40 mL of ultra-pure water by ultrasonic crush at a biosafer 650-92 Ultrasonic Cell Shredder at an ultrasonic power of 650 W for 1 h to form a black slurry. The CNTs slurry was deposited onto an air-laid paper to form a heating layer with diameter of 4 cm through vacuum filtration at the vacuum of 0.07MPa.

Here,

we

denote

them

as

ALP-CNTs-1mg,

ALP-CNTs-5mg,

ALP-CNTs-10mg, and ALP-CNTs-15mg, respectively. The above synthesized samples then were directly wrapped over a cylindrical polyurethane sponge (PUS, with diameter of 4 cm and height range from 0.5-3.0 cm) with the black CNTs layer on its just top. Finally, the as-prepared carbon nanotubes based floating solar stills (CNTs-FSS) were dried at room temperature. We denote the final products as CNTs-FSS-1mg,

CNTs-FSS-5mg,

CNTs-FSS-10mg,

and

CNTs-FSS-15mg,

respectively. Water Evaporation. The water evaporation experiments were conducted at humidity of 60% ± 10% and temperature of 22 oC ± 1 oC. The floating solar still was placed in a 50 mL beaker with 40 mL ultra-pure water. To simulate the solar-irradiance, a 300 W xenon lamp (CEL-S500, 20A) obtained from Beijing Jin Yuan Science and Technology Co., China was used with an AM 1.5 filter. The weights of the evaporated water were recorded at different time intervals using an electronic balance (FA2104, Shanghai Shun Yuheng Scientific Instruments Co., China.). To evaluate the quality of the condensed fresh water, a self-designed condensation device was used for the collection of the condensed fresh water (see Figure S2, Supporting Information). 5 `



Characterization of CNTs-FSS and Water Quality Detection. The morphology and the thickness of the CNTs layer in the floating solar still was examined using a JEM-2010 microscope at an accelerating voltage of 10 kV. The Ultraviolet Visible Near Infrared (UV–Vis–NIR) diffuse reflectance spectra of air-laid paper with and without CNTs were measured on a U-4100 UV–Vis–NIR spectrophotometer (Hitachi, Japan) equipped with an integrating sphere accessory. BaSO4 powder was used as a 100% reflectance standard. The temperature distribution of the floating solar still surface was measured by a S65 thermal infrared imager (FLIR, USA). The concentration of model organic contaminants such as naproxen carbamazepine, and nitrobenzene were determined by an Agilent 1200 HPLC equipped with a UV-Vis detector (Agilent, USA). The concentrations of anions and cations in the condensed fresh water were tested by a Dionex ICS-2000 ion chromatograph (Dionex, USA) and a PE NexION 300Q inductively coupled plasma mass spectrometry (Perkin Elmer, USA), respectively. The conductivity (salinity) was determined by a HQ14d conductivity meter (HACH, America). The total organic carbon (TOC) was measured by a TOC-VCPHTOC analyzer (Shimadzu, Japan). The turbidity was tested by a 2100Q01 portable turbidimeter (HACH, America). The solution pH value was measured by a FE28-Standard pH meter (FiveEasy Plus, China). RESULTS AND DISCUSSION Characterization of the CNTs-Based Floating Solar Still. As one of the important properties of the photothermal conversion materials, the optical absorption properties of the air-laid paper (ALP) with and without carbon nanotubes (CNTs) deposition were primarily investigated. Before CNTs deposition, the CNTs were dispersed in pure water by ultrasonic crush method (Figure S3, Supporting Information). After CNTs deposition, the color of the ALP obviously grows black with increasing 6 `


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deposition amounts of CNTs (as shown in Figure 1a-d). The darkened colors of the ALP-CNTs means the increase of optical absorption. Figure 1e shows the optical absorption spectra spanning from the ultraviolet to infrared region of the ALP and ALP-CNTs with different amounts of CNTs deposition. Obviously, deposition of a thin CNTs layer significantly increases the intensity of the absorption spectrum. Here, the proportion of optical absorption in different spectrum regions at the wavelength range from 300 to 2000 nm can be calculated by the MATLAB software for mathematical integral that we have reported previously.6,22 As calculated, the optical absorption of ALP and ALP-CNTs with different CNTs depositions range from 1-15 mg are 4%, 95.79% ± 0.58%, 97.33% ± 0.39%, 97.11% ± 0.39%, and 97.01% ± 0.31%, respectively. The detailed optical absorption in UV (300-400 nm) to visible (400-760 nm) and infrared (760-2000 nm) regions of all samples are displayed in Table S1, Supporting Information. The results demonstrate that the optical absorption of ALP-CNTs can be controlled by depositing different amounts of CNTs to facilitate efficient solar absorption. Besides, the deposition dose of CNTs also determine the thickness of the CNTs absorbance layer, which in the next step will affect the vapor deliver pathway. Without CNTs deposition, the fiber of the air-laid paper (ALP) can be seen clearly in the SEM image (Figure 2a). After deposition a thin layer of CNTs, the paper fiber image becomes fuzzy and a large quantity of small particles can be found on top or inside of the fiber gaps (Figure 2b). The small particles are composed of numerous carbon nanotubes, as shown in the high-magnification SEM images in Figure S4, Supporting Information. The paper fibers can be completely covered by the CNTs with further increase of the deposition dose of CNTs (Figure 2c-e). The thickness of the CNTs absorbance layer was also monitored by observation of the cross-section of the ALP-CNTs, and the results are shown in Figure 2f-j. Obviously, 7 `



the thickness of the CNTs absorbance layer increases with the increase of the CNTs deposition dose.

Figure 1. Digital photos of the air-laid paper deposited with (a) 1 mg, (b) 5 mg, (c) 10 mg, and (d) 15 mg of carbon nanotubes. (e) Solar spectrum and UV-Vis-NIR absorption spectra of air-laid paper with and without CNTs deposition.

Figure 2. SEM images of the air-laid paper deposited with (a, f) 0 mg, (b, g) 1 mg, (c, h) 5 mg, (d, i) 10 mg, and (e, j) 15 mg of carbon nanotubes. Besides the optical absorption property, water transport property of the carbon nanotubes based floating solar still (CNTs-FSS) is another important basis for the solar evaporation. Here, the air-laid paper (ALP) also serve as the water transport channel to deliver sufficient water directly to the CNTs absorbance layer via capillary action. To evaluate water-uptake behavior, the CNTs-FSS-5mg was placed directly in water to visualize liquid movement. It only takes 20 seconds for the air-laid paper 8 `


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with effective areas of ~0.0020 m2 to be fully wetted by water (Figure S5 and Video 1, Supporting Information), meaning the excellent water wettability of the air-laid paper. Here, the water sorption rate can be calculated to 128.4 kg/m2·h, which is significantly higher than the water evaporation rate. Such high sorption rate effectively ensures that the floating solar still has sufficient water supply and can not be dried out during the evaporation process. Water Evaporation. The water evaporation performance of the carbon nanotubes based floating solar still (CNTs-FSS) was evaluated by measuring the mass of the evaporated water. As a reference, the water evaporation experiments by pure water, polyurethane sponge (PUS) covered by air-laid paper (PUS-ALP), and carbon nanotubes deposited on air-laid paper (ALP-CNTs) were also carried out. As shown in Figure 3a, all water evaporation processes can be easily modeled by the zero-order kinetics and described by the Equation (1): m - m0 = -kt

(1)

where m and m0 are the actual water mass at time t and the initial water mass respectively, and k is the water evaporation efficiency. Thus, the water evaporation efficiency of the CNTs-FSS-5mg can be calculated to 1.58 kg/m2·h under solar irradiance with intensity of 2 kW/m2 (2 sun), which is 1.4, 2.3 and 3.4 times higher than that of the control cases of water covered by ALP-CNTs-5mg, water covered by PUS-ALP, and pure water, respectively. The enhanced water evaporation efficiency demonstrates that the CNTs-FSS can achieve efficient interfacial solar heating and promote water evaporation. Compare with the case of PUS-ALP, the CNTs-FSS-5mg has a CNTs absorbance layer on its just top, which results in an increase of 2.3 times the evaporation efficiency. In addition, compare with the case of ALP-CNT-5mg, the CNTs-FSS-5mg has a 1.4 times better performance on water evaporation due to the 9 `



addition of the polyurethane sponge that acts as a thermal barrier layer to localize the heat only at the interfacial region.

Figure 3. (a) The mass of the evaporated water as a function of their irradiation time in pure water, water with PUS-ALP, water with ALP-CNTs-5mg, and water with CNTs-FSS-5mg. The effects of (b) CNTs dose, (c) PUS thickness, and (d) solar intensity on the water evaporation efficiency. The interfacial heating behavior was further proved by measuring the air-water interface temperature change via a thermal infrared imager. As a reference, the water surface temperature in the evaporation processes of pure water and water covered by ALP-CNTs-5mg were also recorded by the IR imager. Before solar irradiance, the air-water interface temperatures with and without CNTs-FSS are 21.2 oC and 22.2 oC respectively (see Figure 4a and d). After solar irradiance for 60 seconds, the air-water 10 `


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interface temperature with CNTs-FSS quickly reaches to 46.4 oC, while only reaches to 22.5 oC in the case without CNTs-FSS. The rapid temperature response is due to the CNTs absorbance layer, which can absorb the light and convert it to heat instantly. After solar irradiance for 60 minutes, the air-water interface temperature is 52.4 oC, which is 20.8 oC higher than that the control case of pure water (as shown in Figure 4c and f). The high temperature difference between the two air-water interfaces with and without CNTs-FSS strongly confirms the interfacial heating behavior. In addition, after solar irradiance for 60 minutes, although the air-water interface temperature of the ALP-CNTs-5mg reaches to 44.6 oC, it is still 7.8 oC lower than that of the case of the CNTs-FSS-5mg, indicating the thermal barrier effect that only heating the interfacial region while minimizing heat transfer from the air-water interface to the underlying bulk water. The water surface temperature changes over time of the pure water, water covered by the ALP-CNTs-5mg and water covered by the CNTs-FSS-5mg were recorded throughout the evaporation process, and the result is shown in Figure S6, Supporting Information.

11 `



Figure 4. IR thermal images of (a, b, c) the sample of pure water, (d, e, f) the sample of water covered by CNTs-FSS-5mg and (g, h, i) the sample of water covered by ALP-CNTs-5mg after light irradiation for 0, 60 seconds and 60 minutes. To optimize the solar evaporation conditions, the effects of absorbance layer thickness, thermal barrier thickness, and the solar irradiance intensity on the water evaporation efficiencies were investigated. As shown in Figure 3b, the water evaporation efficiency increases significantly from 0.47 kg/m2·h to 1.58 kg/m2·h with increase of CNTs deposition dose at a range from 0 to 5 mg (0 to 4 g/m2). However, over deposit of CNTs results in the deterioration of evaporation efficiency due to the hindered heat exchange velocity.8,10,33 Similarly, the increase of PUS thickness is only clearly noticed up to a value of 2 cm, above this height, the increase of the PUS thickness do not yield any further increase of the water evaporation efficiency (Figure 3c). As shown in Figure 3d, the water evaporation efficiency is 0.88 kg/m2·h under 1 12 `


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sun irradiance and reaches to 4.64 kg/m2·h under 4 sun irradiance, which shows reveals the strong light intensity effect. Remarkably, the solar irradiance intensity expand 4 times while the evaporation efficiency correspondingly enhanced 5.3 times, indicating which means that a relatively high solar irradiance intensity is more conducive to the improvement of water evaporation efficiency. In addition, when the solar irradiance intensity is increased by 4 times, the evaporation efficiency by ALP-CNTs-5mg increases 5.3 times while the evaporation efficiency by PUS-ALP only increases 3.1 times. The results indicate that the enhanced evaporation efficiency is due to the absorption effect by CNTs rather than the insulation effect by PUS. For comparison, Table 1 summaries figures-of-merit of some reported carbon-based photothermal materials. The water evaporation efficiency of the as-prepared CNTs-FSS is better than a variety of the reported carbon-based photothermal materials. We believe that the enhanced water evaporation efficiency of the CNTs-FSS can be attributed to the high solar absorption of the CNTs surface layer, the efficient thermal isolation of the PUS layer, and rapid water transport channel of the ALP. More importantly, the dosage of the photothermal material used in our solar still is only 4 g/m2, far less than that of the reported works. As a result, the cost of the CNTs-FSS will be significantly reduced and can be potentially used in poor or remote areas. Table 1 Summary of figures-of-merit of various photothermal materials under solar irradiance Solar Photothermal material

Dosage

WERw

WERPM

(g/m2)

(kg/m2·h)

(kg/m2·h)

intensity (sun)

WERPM/ WERw

Hollow carbon beads8

1

714

0.54

1.28

2.4

Carbon-black-based super

3

509

1.02

3.06

3.0

13 `



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hydrophobic gauze9 Hollow carbon spheres17

1

1033

0.58

1.45

2.5

Carbon fabric34

1

1350

0.40

0.90

1.8

Reduced graphene oxide film25

1

126

0.42

1.31

3.1

Reduced graphene oxide35

4

18

0.89

4.02

4.5

1

4

0.32

0.88

2.8

2

4

0.47

1.58

3.4

4

4

0.88

4.64

5.3

Our work

WERw: Water evaporation rate of pure water WERPE: Water evaporation rate of carbon-based photothermal material

Stability and Durability. The stability and durability are important properties for further commercial applications of the CNTs-FSS because they can be reused to reduce the cost. Figure 5 shows the water evaporation efficiency after storage in pure water and real seawater (obtained from the East China Sea) for different periods including 10 days, 15 days, 25 days and 30 days. Obviously, no water evaporation efficiency is lost over the whole measured period both in pure water and real seawater, which undoubtedly reveals the good stability and durability of the CNTs-FSS.

Figure 5. Water evaporation efficiency of CNTs-FSS-5mg in (a) pure water in 30 days and (b) real seawater in 25 days under 2 sun solar irradiance. Condensed Fresh Water Quality Control. Water pollution is a ubiquitous and 14 `


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difficult problem in the world. A growing number of contaminants, especially synthetic organic compounds such as pharmaceuticals and personal care products (PPCPs), endocrine disrupting compounds (EDCs) and etc, are being detected in seawater in the past several decades. 36,37 Therefore, the quality of the condensed fresh water must be examined when the polluted seawater was used for solar evaporation. However, up to now, little attention has been paid to the control of organic contaminants in the condensed fresh water. Here, CNTs have advantages over other photothermal materials as they can remove organic contaminants by adsorption. 38 To explore the contaminant removal activity of the CNTs-FSS, carbamazepin, nitrobenzene, and naproxen were selected as the model pollutants. The initial concentrations of carbamazepin, nitrobenzene, and naproxen are 472.5 µg/L, 400.0 µg/L, and 460.5 µg/L, respectively. After solar evaporation without CNTs-FSS for 5 hours, the concentrations of carbamazepin, nitrobenzene, and naproxen in the condensed fresh water are reduced to 139.1 µg/L, 169.7 µg/L and 19.7 µg/L respectively (Figure 6), which strongly confirms that the organic contaminants can be volatilized result in the disqualification of the condensed fresh water. Therefore, we believe that more attention should be paid to the quality of condensate in future research. By contrast, the concentrations of the carbamazepin, nitrobenzene, and naproxen in the condensed fresh water by solar evaporation with CNTs-FSS decreases significantly, which means that the organic contaminants can be effectively removed by the CNTs-FSS during solar evaporation. Take naproxen for an example, no naproxen can be detected in the condensed fresh water (Figure 6c), indicating the complete removal of some selected organic contaminants of the CNTs-FSS. Therefore, we believe that our CNTs-FSS is an ideal solar still for both water quality and quantity generation. 15 `



Figure 6. The concentrations of (a) carbamazepine, (b) nitrobenzene and (c) naproxen in condensed fresh water by solar distillation with and without CNTs-FSS. P1: Before distillation; P2: Distillation without CNTs-FSS; P3: Distillation with CNTs-FSS-1mg; P4: Distillation with CNTs-FSS-5mg; P5: Distillation with CNTs-FSS-10mg; P6: Distillation with CNTs-FSS-15mg To further evaluate the potential application of the CNTs-FSS in practice, a real seawater sample obtained from the East China Sea was used for solar evaporation. The conductivity (salinity) of the seawater significantly reduces from 40400 to 13.52 µs/cm (Figure 7a), which is much lower than the value defined by the World Health Organization (WHO).39 The concentration of the total organic compounds (TOC) reduces from 6.69 mg/L to 3.81 mg/L (Figure 7b), which is below the value defined by the Standards for drinking water quality in China (GB5749-2006).40 In addition, boron ion, which is not easily removed in the two-stage reverse osmosis process, can be well removed in the solar desalination process (Figure 7c). Other typical water-quality parameters (such as pH, turbidity, cations and anions) of the seawater before and after desalination are shown in Table S2, Supporting Information. After desalination, the concentrations of cations (Na+, K+, Ca2+, Mg2+), anions (F-, Cl-, Br-, NO3-, SO42-) originally present in the seawater decrease to 0.002-2.38 mg/L, which are below the values defined by the World Health Organization (WHO)39, the US Environmental Protection Agency (EPA) standards,41 and the Standards for drinking water quality in China40. 16 `


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Figure 7. (a) The conductivity, (b) TOC and (c) boron ion concentration in seawater and in condensed fresh water. CONCLUSION In summary, we have demonstrated the preparation of a carbon nanotubes based floating solar still (CNTs-FSS) and its application for seawater desalination and purification based on interfacial solar heating. The enhanced water evaporation efficiency is due to the high solar absorption of the CNTs surface layer, the efficient thermal isolation of the PUS layer, and rapid water transport channel of the air-laid paper. No water evaporation efficiency was lost during 20 cycles of use in 30 days, which undoubtedly reveals the good stability and durability of the CNTs-FSS. The concentrations of the organic and inorganic contaminants in condensed fresh water can be well reduced by the CNTs-FSS. We believe that the simple structure, low-dose, low-cost, good stability and durability, as well as the well-controlled condensed fresh water quality make the as-designed CNTs-FSS potentially useful in practical settings of solar desalination in remote and poor areas. ASSOCIATED CONTENT Supporting Information N2 adsorption-desorption, SEM image, digital photographs, temperature change curve, light absorption in different spectrum regions, water-quality of condensed water. AUTHOR INFORMATION Corresponding Author 17 `



E-mail address: [email protected] ORCID Miaomiao Ye: 0000-0002-5546-1133 Notes The authors declare no competing financial interest. ACKNOWLEDGMENTS The present work was financially supported by the Public Welfare Technology Application Research Project of Zhejiang Province (No. LGG18E080002), the Funds for International Cooperation and Exchange of the National Natural Science Foundation of China (No.51761145022), the National Science and Technology Major Protects for Water Pollution Control and Treatment (No. 2017ZX07201004), and the Fundamental Research Funds for the Central Universities (No. 2018FZA4017). REFERENCES (1) Surwade, S. P.; Smirnov, S. N.; Vlassiouk, I. V.; Unocic, R. R.; Veith, G. M.; Dai, S.; Mahurin, S. M. Water Desalination Using Nanoporous Single-Layer Graphene. Nat. Nanotechnol. 2015, 10 (5), 459. (2) Muthu Manokar, A.; Kalidasa Murugavel, K.; Esakkimuthu, G. Different Parameters Affecting the Rate of Evaporation and Condensation on Passive Solar Still – A review. Renew Sust. Energ. Rev. 2014, 38, 309–322. (3) Elimelech, M.; Phillip, W. A. The Future of Seawater Desalination: Energy, Technology, and the Environment. Science 2011, 333 (6043), 712–717. (4) Karagiannis, I. C.; Soldatos, P. G. Water Desalination Cost Literature: Review and Assessment. Desalination 2008, 223 (1–3), 448–456. (5) Golsefatan, H. R.; Fazeli, M.; Mehrabadi, A. R.; Ghomi, H. Enhancement of Corrosion Resistance in Thermal Desalination Plants by Diamond like Carbon 18 `


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TOC/Abstract Graphic

Synopsis Renewable and sustainable solar energy was used for desalination and purification to continuously obtain abundant high-quality fresh water.

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A Simple, Low-dose, Durable and Carbon Nanotubes Based Floating

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