KR102131313B1 - Composite structure for solar desalination, and apparatus and method for desalination - Google Patents

Abstract

The composite structure according to the present invention includes a pillar-shaped support having a plurality of pores connected to each other on a surface and an interior, and a light absorber layer formed on one underside of the support, to an apparatus and method for desalination of seawater using sunlight Can be used.

Description

Complex structure, desalination device and method for solar desalination {COMPOSITE STRUCTURE FOR SOLAR DESALINATION, AND APPARATUS AND METHOD FOR DESALINATION}

The present invention relates to a complex structure for desalination of seawater using sunlight, a desalination device comprising the same, and a desalination method using the same.

Currently, global population growth and environmental pollution problems continue to grow and some countries face water shortages, and technologies for producing clean water are getting more and more attention. In particular, the technology for desalination using semi-permanent solar energy and seawater constituting 97.6% of the water on the earth is very inexpensive and is capable of producing clean water without additional energy resources.

Early solar desalination devices had a problem of low photothermal conversion due to high heat loss and unable to absorb broadband sunlight. However, according to a recent study, it was possible to realize an ideal solar desalination device that maximizes the absorption rate while minimizing heat loss to the seawater channel. These devices have a high absorption rate over a wide wavelength range to produce enormous heat. In addition, the heat-insulating material having a vertical flow path is suspended in the seawater to concentrate heat at the water-air interface to rapidly absorb from the bottom to the top. Water can be transported.

For example, the conventional floating solar desalination device is limited to the area of the air-water interface, thereby limiting the heat generated by absorbed energy, thereby maximizing the solar-to-heat conversion rate and minimizing heat loss to the seawater. (Jiang, Q. et al., Journal of Materials Chemistry A 2017, 5, 18397-18402). However, materials having a very good absorbance for the broadband spectrum are being developed one after another, and there is room for further increasing the surface area required for evaporation of moisture and further improving insulation performance in a conventional solar desalination device.

Meanwhile, 3D structuring technology is being used as an approach to significantly improve the desired performance in various fields such as photoelectrochemical water splitting systems, batteries, supercapacitors and surface-enhanced Raman spectroscopy. Indeed, by expanding the surface of the active material from 2D to 3D, the surface area can be increased to operate devices in various fields more efficiently. For example, a 3D cell used in an energy storage device has excellent structural characteristics, and can improve cycle stability by buffering stress caused by a volume change occurring in a cycle process. In addition, in a chemical sensor based on surface-enhanced Raman spectroscopy (SERS), it is possible to increase specific surface area and light scattering property by 3D structuring, thereby increasing interaction due to light irradiation. In addition, a conventional solar desalination device can also improve solar-steam conversion efficiency by 3D structuring.

Jiang, Q. et al., Journal of Materials Chemistry A 2017, 5, 18397-18402

In the conventional solar desalination device, since the evaporation is performed only on the surface of the absorber, the efficiency of solar-steam conversion was not so high, and it was necessary to further reduce heat loss to the seawater.

Accordingly, the present inventors, unlike attempts to support the solar desalination device in seawater in many recent studies, by designing in a columnar shape that can stand in shallow seawater by a new 3D structure design, the evaporation efficiency can be significantly improved. In addition, it was found that the heat insulation properties can be increased.

Accordingly, an object of the present invention is to provide a structure suitable for desalination of seawater by sunlight due to improved evaporation efficiency and heat insulation, a desalination device including the same, and a desalination method using the same.

The present invention is a columnar support having a plurality of pores connected to each other on the surface and the inside; And a light absorber layer formed on one bottom surface of the support.

In addition, the present invention provides a desalination device comprising the composite structure.

In addition, the present invention provides a method of desalination, comprising placing the composite structure in the seawater so that the bottom surface on which the light absorber layer is formed faces upwards and is exposed at least 1 cm above the water surface.

According to the present invention, the evaporation region of seawater for solar desalination can be extended from 2D to 3D by simple structure design exposing the side surface of the support on which the light absorber layer is formed on one bottom surface, so that the absorption at the top In addition to photothermal evaporation by the body layer, additional steam generation is possible at night due to the non-photothermal evaporation region on the side.

Accordingly, the desalination device of the present invention can exhibit not only full-day-working performance, but also high steam generation efficiency under inexpensive and eco-friendly solar lighting. In addition, due to exposure to the air above the water surface of the support, thermal insulation due to physical distance between the light absorber layer and seawater can be effectively performed to minimize heat loss. Therefore, the desalination device of the present invention is expected to be able to supply clean water worldwide in the near future.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.
The meanings of the abbreviations described in the brief description of the drawings are as defined in the specific examples.
FIG. 1 is a conceptual view of (a) a conventional floating PF (1.5 cm height) and a standing LCPF (5 cm height) solar seawater desalination device (insertion is a SEM image of an enlarged area near the upper region of the LCPF), (b ) Photo showing rapid transport of water to the top of the 5 cm thick LCPF by strong capillary force, (c) Irradiated with floating PF (1.5 cm height) and standing LCPF (5 cm height) for 1 hour after solar irradiation It shows the image of heat dissipation.
FIG. 2 shows (a) high porosity internal structure of PF, (b) rGO on PF confirmed by SEM, (c) XPS wide area scan results of rGO and PF, (d) fitting curve of C1s spectrum of PF, ( e) It shows the fitting curve of the C1s spectrum of rGO.
3 is (a) rGO and PF solar absorption spectrum, (b) and (c) temperature change and thermal image of the upper surface upon exposure to sunlight for 1 hour, (d) sunlight for 1 hour Mass change of floating PF (1.5 cm) and standing LCPF (5 cm) with or without rGO under exposed and steam generating conditions, (e) rGO of various heights under conditions of generating steam in dark conditions It shows the thermal image of the side of rGO/LCPF of various heights when the mass change of PF and (f) exposure to sunlight for 1 hour.
FIG. 4 shows (a) a device manufactured by forming rGO on LCPFs of various heights, exposed to sunlight for 1 hour, and changes in mass when generating steam, (b) and (c) rGO/LCPF (5 cm). The long-term durability evaluation and cycle characteristics of (d) are shown by comparing the salinity before and after desalination using an rGO/LCPF (5 cm) device.
5(a) to 5(c) are pictures in which PF, wood, and paper are suspended, and black arrows indicate the positions of the absorbers, and blue arrows indicate the water surface.
6 is a result of measuring the surface area of (a) rGO and (b) pore size distribution.
FIG. 7 shows a fitting curve of (a) wide scan XPS spectrum and contact angle image of water droplets, and (b) C1s spectrum of GO.
8(a) and 8(b) compare mass changes for LCPFs of various heights under sunlight and dark conditions, respectively, and (c) and (d) show LCPFs or PFs of various heights under sunlight. This is a comparison of mass changes for the base structure.
FIG. 9(a) is a photograph of LCPFs of various heights (1.5 cm, 3 cm, 4 cm, and 5 cm) when placed in 3 cm of sea water, and (b) generates rGO/LCPF vapors under sunlight. Is a photograph of a device designed to measure, and (c) and (d) are images of rGO and rGO/PF observed by SEM, respectively.
10 is an FT-IR spectrum of rGO and PF.
11(a) and 11(b) are photographs showing steam generation when rGO/LCPF5 is exposed to a sealed container under dark conditions and sunlight conditions for 1 hour, respectively.
12 shows the mass change according to various temperature conditions of the surrounding environment when the humidity is fixed at 18% and exposed for 1 hour under sunlight.
13(a) and 13(b) show the results of evaluating long-term stability when rGO/PF and rGO/LCPF3 are exposed to sunlight, respectively.

Hereinafter, the present invention will be described in detail.

Complex structure

According to an aspect of the present invention, a pillar-shaped support having a plurality of pores connected to each other on a surface and an interior; And a light absorber layer formed on one underside of the support.

Support

The support acts as a transport material for water and as a heat insulating material.

The support has a number of pores connected to each other on the surface and inside. Accordingly, water absorbed from the lower surface of the support may be evaporated through the pores connected to the inside and through the pores of the upper side and upper surface. The individual sizes of the pores may range from 1 μm to 20 μm, or from 100 μm to 500 μm.

For example, the support may be a porous foam formed of a polymer material. At this time, the polymer material may be phenol, urethane, ethylene glycol, or a composite material thereof.

Specifically, the support may include a porous phenolic foam. The porous phenolic foam is suitable as a support because of its large area and hydrophilicity, strong capillary force, and excellent thermal insulation with a thermal conductivity of about 0.04 W/m·K.

Alternatively, the support may be a porous material formed of paper such as a non-woven fabric.

The support has a column shape. For example, the support may have a column shape having a circular or polygonal bottom surface.

In addition, the support may have a column shape having a height higher than the diameter of the bottom surface. At this time, when the bottom surface is a polygon, the diameter of the bottom surface may be an average value of the longest diameter and the shortest diameter.

As an example, the support may have a cylindrical shape having a height higher than the diameter of the bottom surface. Specifically, the ratio (h/d) of the height (h) to the diameter (d) of the underside of the support may be in the range of 1.1 to 10, or in the range of 1.5 to 3. When having the structure as described above, it is possible to widen the area of the side surface exposed to the outside and evaporation occurs.

The height of the support needs to be higher than the depth of the seawater to which the composite structure will be applied. For example, the height of the support and the composite structure may be 0.5 cm or more, 1 cm or more, or 2 cm or more higher than the depth of the seawater. Specifically, the difference between the height of the support and the water depth of the seawater may range from 0.2 to 2.5 cm or 0.5 to 2 cm. When within the above range, the composite structure is erected in sea water, and an evaporation effect on the side surface of the support exposed outside the water surface may be increased.

The composite structure may be used in seawater having a shallow water depth, and accordingly, the height of the support may be higher than that of a shallow water depth. For example, the height of the support may be 3.5 cm or more, 4 cm or more, 4.5 cm or more, or 5 cm or more. Specifically, the height of the support may be in the range of 3.5-10 cm or 3.5-5.5 cm.

It is advantageous in terms of evaporation efficiency of water that the support has high hydrophilicity. For example, the contact angle of the support with water may be 30° or less, 20° or less, 10° or less, or 5° or less.

In addition, it is advantageous in terms of thermal insulation that the support has low thermal conductivity. For example, the thermal conductivity of the support may be 1 W/m·K or less, 0.5 W/m·K or less, 0.1 W/m·K or less, or 0.05 W/m·K or less.

As an example, the support may have a contact angle of 10° or less with respect to water and a thermal conductivity of 0.1 W/m·K or less. As another example, the support may have a contact angle of 5° or less with respect to water and a thermal conductivity of 0.05 W/m·K or less.

Absorber layer

The absorber layer is exposed to sunlight to generate photo-thermal energy conversion, thereby causing water evaporation under light conditions.

The absorber layer is formed on one bottom surface of the support.

The absorber layer preferably includes a material having a high absorbance at a wide band wavelength. Examples of such materials include carbon-based materials, for example, graphene-based or graphite-based materials.

Specifically, the absorber layer may include a graphene oxide-based material, and more specifically, may include reduced graphene oxide (rGO). The reduced graphene oxide (rGO) is useful as a light absorber for effective steam generation because it has a high absorption rate for light of a wide band wavelength and excellent workability.

For example, the absorber layer may have an absorbance of 75% or more, 80% or more, or 85% or more in all bands of 250 to 2500 nm.

The thickness of the light absorber layer may range from 10 μm to 50 μm or from 10 μm to 100 μm. When within the above range, it is possible to secure a high light absorption rate due to sufficient light absorption without transmitting light, while maintaining the porosity so that the steam generated inside the structure can easily escape into the air, thereby achieving high photothermal conversion efficiency and effective steam generation rate. It can be advantageous in terms.

Characteristics of composite structures

The composite structure has an evaporation rate under light conditions equal to or higher than that of the prior art. For example, the composite structure has a water evaporation rate of 1.5 kg/m 2 ·h or more, 2.0 kg/m 2 ·h or more, 2.3 kg/m 2 ·h or more, or 2.5 kg/h under light conditions of 1 kW/m 2 intensity. It may be ㎡·h or more.

In addition, the composite structure has a relatively high water evaporation rate even in dark conditions. For example, the composite structure may have a water evaporation rate in the dark condition of 0.3 kg/m 2 ·h or more, 0.5 kg/m 2 ·h or more, or 1.0 kg/m 2 ·h or more.

As an example, the composite structure may exhibit a water evaporation rate of at least 2.0 kg/m 2 ·h in a light condition of 1 kW/m 2 intensity, and a water evaporation rate of at least 0.5 kg/m 2 ·h in a dark condition. As another example, the composite structure may exhibit a water evaporation rate of at least 2.3 kg/m 2 ·h in a light condition of 1 kW/m 2 intensity, and a water evaporation rate of at least 1.0 kg/m 2 ·h in a dark condition.

In addition, the composite structure has a high light-vapor conversion efficiency. For example, the composite structure may exhibit 80% or more in the light-steam conversion efficiency (η) calculated by Equation 1 below:

[Equation 1]

In Equation 1, A is the cross-sectional area (m 2) of illumination, C _opt is the optical density, Q _s is the light irradiation intensity (1 kW/m 2 ), Q _e is calculated by Equation 2 below,

[Equation 2]

In Equation 2, m is the evaporation rate (kg/m 2 ·h) of water by photothermal conversion energy, λ is latent heat (2255.2 J/g) when the phase changes to water vapor, C is the specific heat capacity of water ( 4.2 J/g·K), and ΔT is the temperature increment (K) of the vapor produced.

In addition, the light-steam conversion efficiency (η) of the composite structure may be 90% or more, 100% or more, 120% or more, or 150% or more, specifically, 80 to 200%, 80 to 150%, 80 to 100 %, or 150-200%.

Use of complex structures

The composite structure may be useful in fields where desalination or desalination of brine is required. For example, the composite structure may be used for seawater desalination using sunlight. Specifically, the composite structure is built so that the bottom of the absorber layer is formed in the seawater at a depth lower than the height of the composite structure, and can be used for desalination of seawater using sunlight.

According to a specific example of the present invention, the support is a porous phenolic foam, the absorber layer includes a reduced graphene oxide, and the composite structure, the base on which the absorber layer is formed faces upward, at least 1 cm above the water surface It is built in seawater to be exposed and can be used for desalination of seawater using sunlight.

Desalination device

According to another aspect of the invention, there is provided a desalination device comprising the composite structure.

The composite structure included in the desalination device has substantially the same configuration and properties as the composite structure described above.

The desalination device can be used to perform desalination by standing on seawater.

To this end, desalination may be performed by standing the desalination device directly on the sea, but there is a fear that the desalination device may easily fall under the influence of the waves. Therefore, when the desalination device is utilized directly in the sea, it is preferable to additionally include a fixing means that allows the composite structure to be erected.

Preferably, the desalination device may further include a water tank for containing sea water. Accordingly, after adding seawater to the water tank, the desalination device may be placed and desalination may be performed. In this way, a more controlled working environment can be provided when using the water tank.

In addition, the desalination device may further include a means for condensing water evaporated from the composite structure. In addition, the desalination device may further include a means for collecting the condensed water.

As an example, the desalination device includes the complex structure, the first water tank in which the seawater and the complex structure are introduced, a second water tank having a bottom surface larger than the first water tank, and the first water tank disposed therein, and the first water tank And it may include a cover having a transparency covering the second tank as a whole. Accordingly, seawater contained in the first water tank is evaporated by the composite structure, and condensed on the wall surface of the cover to be collected in the second water tank.

The desalination device can perform desalination in dark conditions as well as light conditions. That is, the desalination device, under light conditions, causes active evaporation by the photo-thermal energy conversion action of the light absorber layer on the top of the composite structure, and can evaporate through the pores on the side exposed above the water surface in the support even in dark conditions. . Accordingly, the desalination device can exhibit all-day-working performance.

Desalination method

According to another aspect of the present invention, there is provided a method of desalination, comprising placing the composite structure in seawater so that the bottom surface on which the light absorber layer is formed faces upward and is exposed at least 1 cm above the water surface.

For example, the composite structure may be placed so as to be exposed to 1 cm or more, 2 cm or more, 3 cm or more, 5 cm, or 10 cm or more above the water surface.

As a specific example of the desalination method, (1) placing the composite structure in sea water so as to be exposed at least 1 cm above the water surface; (2) generating steam from seawater using the composite structure; And (3) condensing and collecting the steam.

At this time, the step of generating the steam may be performed under light conditions and/or dark conditions. As a specific example, the step of generating the steam may be performed for the entire day (ie day and night).

[Example]

The present invention will be described in more detail through the following examples. However, the scope of the present invention is not limited to these examples.

The meanings of the abbreviations used in the examples below are as follows.

-GO: graphene oxide

-rGO: reduced graphene oxide

-PF: phenolic foam

-LCPF: long cylindrical phenolic foam

-PFn: PF with height n(cm)-LCPFn: LCPF with height n(cm)

-rGO/PF: Composite structure with rGO sheet formed on the upper surface of PF (floating type)

-rGO/LCPF: Composite structure with rGO sheet formed on the top surface of LCPF (standing type)

The materials used in the following examples are as follows:

-Phenol foam for the production of PF and LCPF was purchased from Oasis Economy.

-Graphite powder and sodium chloride (NaCl) are used for Bay Carbon Inc. And Samjeon Chemical Company, respectively.

-All chemicals were used without further purification.

The measuring devices used in the following examples are as follows:

-Scanning electron microscopy (SEM): Hitach High-Technologies S-4800

-Transmission electron microscopy (TEM): JEM-2100 from JEOL

-Raman spectroscopy: alpha300R from WITec

-X-ray photoelectron spectroscopy (XPS): Kalpha from Thermo Fisher

-UV-Vis spectroscopy: Agilent's Cary 5000

-Ion chromatography: cation-ICP 1600, anion-ICP 2100

In the examples below, the temperature and mass changes due to evaporation of water were measured under simulated solar lighting (Sol2A class ABA 94062A, 1000W Xenon lamp, Newport, Inc.) with a power density of 1 kW/m 2.

In addition, the temperature of the upper surface was measured using a thermal imaging camera, and the mass change due to evaporation was measured every 1 minute using an electronic fine balance having an error of 0.1 mg. For the experiment control, 1 cm thick polystyrene was used as the outer heat insulating layer (see Fig. 9 (b)).

Example 1: Preparation of a composite structure (rGO/LCPF)

A long cylindrical phenolic foam (LCPF) was produced by cutting a phenolic foam into a cylindrical shape with a diameter of 2 cm having various heights (3 cm, 4 cm and 5 cm) using a punch.

Graphene oxide (GO) was prepared from the graphite powder by a Humer method. The graphene oxide was washed with 1% by weight HCl and filtered with sufficient distilled water. Then, the graphene oxide was centrifuged several times with distilled water until the pH of the solution became neutral and freeze-dried.

After the ultrasonic treatment at 200 W power, a chemical reduction reaction was performed while stirring vigorously at 95° C. for 3 hours using a hydrazine hydrate solution and an ammonia solution.

Then, a reduced graphene oxide (rGO) sheet is deposited by drop casting on an LCPF by precipitation of an aqueous solution in which the reduced graphene oxide (rGO) is dispersed (20 mg, about 20 μm). Stacked.

Comparative Example 1: Preparation of a composite structure (rGO/PF)

Phenol foam (PF) was produced in a cylindrical shape with a diameter of 2 cm having various heights (1.5 cm, 2 cm and 2.5 cm). The reduced graphene oxide (rGO) sheet was deposited on the PF in the same manner as in Example 1.

Experimental Example 1: Comparison of floating type and standing type

In (a) of FIG. 1, a standing composite structure in which rGO is deposited on LCPF (5 cm in height) according to the method of Example 1, and rGO is deposited on PF (1.5 cm in height) according to the method of Comparative Example 1 Compared with the floating floating composite structure.

When a 1.5 cm high PF is suspended in a 3 cm deep water beaker, it is slightly exposed above the water surface (approximately 2 mm is exposed to the outside) as soon as it is immersed, while a 5 cm deep beaker contains 5 When the LCPF was raised with a height of 2 cm, the top 2 cm of the cylinder was exposed outside the water surface.

At this time, the floating phenolic foam corresponds to a steam generator having only rGO (region I) deposited on the top surface, and the standing phenolic foam (LCPF) is rGO (region I: photothermal evaporation region) deposited on the top and additionally external Corresponds to a steam generator having two exposed regions of a cylindrical porous side exposed to (region II: non-thermal evaporation region even under illumination).

Indeed, the side of the LCPF provides a significant vapor generating region (2πrh, where h is the height of the exposed region, r is the radius of the LCPF), so that a large amount of water can be evaporated with or without illumination.

The porous structure of the LCPF and the strong capillary force due to the hydrophilic surface make it easy to transport water by a process similar to distillation.

As shown in FIG. 1(b), when the 5 cm-high LCPF is standing still in a beaker containing 3 cm-high water, water is transported to all surfaces of the top and sides of the LCPF in just 1 minute, thereby quickly overall. It could be wetted, and after the seawater was completely absorbed by the LCPF, 3 cm deep water became 1 cm deep.

In addition, as shown in Figure 1 (c), it was confirmed that the heat transport from the top to the seawater is completely blocked, the standing LCPF acts as a high heat insulating material.

The heat loss from the absorber to the seawater can be reduced by placing an insulating material such as wood, cellulose membrane, polyurethane foam, etc. between the absorber and the seawater. However, since the floating insulating material is immersed in a large part of sea water, it is almost close between the absorber and the sea water, and heat loss cannot be effectively reduced.

5 is a photograph of floating materials (PF, wood, paper) when placed in water. The black arrow indicates the position of the absorber, and the blue arrow indicates the water surface. The suspended materials exhibit thermal insulation as much as the distance between the position of the light absorber and the surface of the water absorber, but heat loss may occur because the distance is very close to approximately 2 mm.

In the left thermal image of FIG. 1(c), the water-immersed area of the floating PF appeared orange, so it was possible to clearly confirm the low thermal insulation properties.

In addition, in the right thermal image of FIG. 1 (c), since the external exposure area of the standing LCPF was dark blue, it was possible to confirm the thermal insulation effect due to the separation between the light absorber and the seawater, and the water absorbed heat in this area. It was found that it evaporated.

That is, as the evaporation region expanded from the 2D plane to the 3D cylinder, it was possible to secure the insulation between the absorber and the seawater, and to generate additional steam in terms of LCPF.

Experimental Example 2: Structural Analysis

2(a) is an image of the porous structure of the PF, and many pores less than tens of microns are observed in a pore frame having a size of several hundred microns, and water can be easily transported through the 3D network passage. Since the PF having pores having a micron size has a very large surface area, the transported seawater evaporates, and thus a wide area in which vapor can be released into the air in the form of steam.

Figure 2 (b) is a shape image of the rGO on the porous PF. The rGO was well deposited along the frame structure of the PF and maintained the pore structure of the PF.

6 is a result of measuring the surface area of (a) rGO and (b) pore size distribution. The surface area and pore size distribution of the rGO were measured by BET (Brunauer-Emmett-Teller) and BJH (Barrett-Joyner-Hallender) methods, respectively. It can be seen from FIG. 6 that the rGO has a surface area of about 90.6 cm 2 /g due to many fine pores, and these pores activate evaporation at the air-water interface to generate steam and discharge it to the outside. .

The hydrophilicity of water transport materials and absorbers is important for efficient steam generation. The broad spectrum according to the X-ray photoelectron spectroscopy (XPS) of PF and rGO shows two different peaks (peak O1s and C1s peaks) at about 532 eV and about 285 eV (see Fig. 2(c)), from which The hydrophilicity by the functional group of the material can be confirmed.

2(d) and (e) show the fitting curve of C1s, which is deconvolution with 4 carbon peaks, specifically the CC (aromatic) peak at about 284.2 eV, at about 285.7 eV CO (hydroxyl and epoxy), and OC=O (carboxyl) at about 288.5 eV.

It is the surface properties of the hydrophilic rGO and PF that occupy a large proportion of the oxygen-containing groups. When water droplets were dropped on the rGO and PF, they disappeared immediately and exhibited a contact angle of almost 0° (refer to the insert images in Figs. 2(d) and (e)), which means that the hydrophilicity of these surfaces is very high, It is also consistent with XPS results.

Experimental Example 3: Steam generation evaluation

In order to effectively generate steam from seawater through photothermal evaporation, the absorbance and photo-thermal energy conversion of the absorber material of the solar desalination device must be high.

In order to find out the optical properties of the absorbing material, the absorption spectra of rGO and PF for the broadband solar spectrum (wavelength 300 to 2500 nm) were measured with a spectrometer and shown in FIG. 3(a).

While PF showed an average absorption of 69% in the visible and near-infrared bands, the rGO sheet exhibited a high absorption of about 90% in all wavelength bands of the spectrum.

In order to evaluate the solar desalination performance, first, the previously prepared desalination device is placed at a humidity condition of less than about 20C and less than 20%, so that the absorber at the top is sufficiently wet by evaporation, and then this is a solar simulator (AM 1.5, 1000 W). Xenon lamp, Newport). The water depth was adjusted to 3 cm.

After exposure to 1 hour under sunlight, the desalination device was measured at the top temperature and shown in FIG. 3(b). The highest temperature (22°C to 41.9°C) was measured in the rGO/PF sample, which is presumed to be a combination of the high absorbance of rGO and the heat collecting properties on the top of the floating PF. The rGO/LCPF showed a slightly lower heat rise (22°C to 37.6°C) compared to rGO/PF.

The low heat rise of rGO/LCPF is attributed to the endothermic evaporation occurring on the side of the LCPF. However, the LCPF-based structures (rGO/LCPF and LCPF) showed a high heat rise for the first 5 minutes compared to the PF-based structures (rGO/PF and PF), during which time cooling by endothermic evaporation of the LCPF side It seems that the heat coagulation effect at the top was greater than the effect. However, after 5 minutes, due to the cooling effect due to the continuous side evaporation, the temperature at the top of the LCPF gradually decreased.

The temperature of the top of the PF and LCPF without rGO was increased to 34.5°C and 30.7°C, and this trend was the same as that of the RF-formed PF and LCPF, and the absorbance of PF was shown in FIG. 3(a). As you can see, it is relatively high at about 69%. On the other hand, when only water was present, the photothermal conversion was not involved, so the temperature was maintained at 26.8°C.

FIG. 3(c) is a thermal image comparing the surface temperature after exposure to sunlight for 1 hour with or without rGO formed on floating PF (1.5 cm thick) and standing LCPF (5 cm thick). It is an image. The rGO/PF composite structure showed the highest temperature, and the LCPF structure without forming the light absorber showed the lowest temperature.

FIG. 3(d) shows a change in mass according to steam generation when 20 mg of rGO is deposited on PF or LCPF and placed under sunlight. The intensity of light incident on the rGO surface was adjusted to 1 kW/m 2.

When using rGO/LCPF, it showed a mass change rate of about 2.38 kg/m 2 ·h, which is 6.43 times higher than the mass change rate due to natural evaporation of brine (about 0.37 kg/m 2 ·h). It is also about 1.53 times the theoretical maximum mass change rate, and this improvement was achieved by converting sunlight into thermal energy. The steam generation performance of rGO/LCPF was much better than that of rGO/PF, due to the large evaporation area on the side of the LCPF.

In general, as the temperature increases, the photothermal evaporation effect may increase. However, when the temperature change in FIG. 3(b) for rGO/PF and rGO/LCPF (except for the first 5 minutes) and the photothermal vapor generation rate in FIG. 3(d) were not observed, this general trend was not observed. .

This is because the heat converted from the upper surface is not discarded as seawater, but is used for endothermic evaporation through the porous side of the LCPF. Accordingly, although the temperature of the upper surface is slightly decreased in the process of non-thermal heat evaporation from the side, the total amount of water evaporation can be increased.

In addition, the distance between the top and the sea level of the rGO/LCPF (2 cm) was much larger than the distance (2 mm) in the case of the rGO/PF, and thus higher thermal insulation properties could be exhibited.

In addition, as noted above, the LCPF-based structure can generate steam even in a condition where there is little lighting, such as a night time or a cloudy day, by utilizing the heat remaining in the surroundings (see FIG. 11(a) ).

In order to determine the evaporation rate through the side surface of the LCPF in the absence of sunlight, rGO was formed in LCPFs of different heights, and mass change was measured in dark conditions, and the results are shown in FIG. 3(e).

Considering evaporation by capillary force, the maximum height of PF is expected to be 5.8 cm in seawater at a depth of 3 cm, so the height of rGO/LCPF was designed to about 5 cm in this example.

FIG. 9(a) is a photograph when LCPFs of various heights are placed in 3 cm depth of seawater. As shown in FIG. 9(a), as a result of floating 1.5 cm high PF in 3 cm deep sea water, the side was exposed 2 mm and the remaining 1.3 cm sank below the water surface. In addition, 3 cm, 3 cm, 4 cm, and 5 cm tall rGO/LCPF (referred to as rGO/LCPF3, rGO/LCPF4, rGO/LCPF5, respectively) resulted in 0 cm, 1 cm, 2 sides respectively cm was exposed.

As the height of the LCPF increased, the area of the side surface increased to improve the performance of generating non-thermal heat, and reached 0.57 kg/m 2 ·h for rGO/LCPF and 1.02 kg/m 2 ·h for rGO/LCPF5. From this, it can be seen that the non-photothermal evaporation performance can be remarkably improved by a simple method of expanding the evaporation region on the side surface.

Considering that the rate of mass change under sunlight is 2.38 kg/m 2 ·h, it can be seen that the amount of steam generated by rGO/LCPF5 at night is about 43% of the daytime.

3(f) is a thermal image obtained by exposing the rGO/PF of various heights to sunlight for 1 hour and observing the side surface thereof.

In view of this, it can be seen that as the area of the side exposed above the water surface increases, it exhibits high thermal insulation properties under illumination. Specifically, the side temperature was measured in the order of rGO/LCPF5 <rGO/LCPF4 <rGO/PF <rGO/LCPF3.

This result is consistent with the mass change in dark conditions, which means that non-thermal heat evaporation actually improves the adiabatic properties as well as increases the mass change by evaporation of water under light conditions.

Experimental Example 4: Desalination performance evaluation

A structure (rGO/LCPF) in which an LCGO compound having a high absorbance and an LCPF with minimal heat loss due to low thermal conductivity (rGO/LCPF) can be usefully used for solar steam generation.

In order to evaluate the steam generation performance of LCPF under solar irradiance (1 kW/m 2 ), the mass change of 3.5% brine, long-term durability, cycle stability, and salinity change after desalination were measured, and the results are shown in FIG. 4. . LCPF-based structures had a larger mass change as the external exposure area increased, and reached up to 2.38 kg/m 2 ·h for rGO/LCPF5.

The mass change of rGO/PF was larger than that of rGO/LCPF3, which was 2 mm exposed for non-thermal evaporation in the case of rGO/PF, while rGO/LCPF3 was built in 3 cm of salt water and all sides This is because it is submerged below the surface.

The light-steam conversion efficiency (η) was calculated by the following equation.

(

)

(

)

In the above formula, A is the cross-sectional area (m 2) of illumination, C _opt is the optical density, Q _s is the light irradiation intensity (1 kW/m 2 ), and m is the evaporation rate of water (kg/m 2 ·h) by photothermal conversion energy ), λ is the latent heat at the phase change of water to steam (2255.2 J/g), C is the specific heat capacity of water (4.2 J/g·K), and △T is the temperature increment (K) of the generated steam. .

As a result of calculation according to the above formula, the light-steam conversion efficiency (η) of brine and rGO/LCPF5 under light conditions of 1 kW/m 2 showed a significant difference of 8.85% and 86.2%, respectively. In addition, it was confirmed that the amount of vapor on the side of the LCPF is proportional to the height exposed on the side of the LCPF.

Durability is very important when actually performing desalination using LCPF. Existing desalination devices have had many problems such as corrosion of the absorber and occlusion. However, the LCPF according to the above embodiment can prevent corrosion because it is separated by a certain distance between seawater and the absorber.

In addition, since the pores of the phenolic foam are more than a few microns, the flow path is not blocked even when operating in sunlight for 6 hours, and as shown in FIG. 4(b), a high steam generation rate can be maintained.

FIG. 4(c) shows the results of evaluating the cycle characteristics of rGO/LCPF5 under sunlight (20 cycles per hour). The evaporation rate was kept high at about 2.24 kg/m 2 ·h, which means that rGO/LCPF can be recycled with high performance.

In order to more specifically check the desalination performance, the salinity change between steam generated by rGO/LCPF and seawater was measured by an inductively coupled plasma mass-spectroscopy (ICP-MS) device and shown in FIG. 4(d). . The concentrations of sodium and chlorine ions in the vapor generated by rGO/LCPF were significantly reduced compared to those in seawater.

The salinity of steam obtained through desalination was lower than the salinity, which is a safety standard for drinking water according to WHO (World Health Organization) and EPA (US Environmental Protection Agency) standards.

Through the above experimental examples, the LCPF according to the embodiment of the present invention achieved a high steam generation rate of about 2.38 kg/m 2 ·h that exceeds (153%) the maximum amount of conventional solar steam generation by the 3D porous surface. Could know. This is because, in addition to photothermal evaporation (1.36 kg/m 2 ·h) at the top of the LCPF, which occurs primarily under the sun, the rate of steam generated by non-thermal heat action reaches 1.02 kg/m 2 ·h day and night in terms of LCPF. .

In addition, by exposing the side surfaces of the LCPF foam, a large gap was provided between the absorber and the sea level, a non-thermal heat evaporation area that was endothermic, and heat loss to the sea water could be minimized. In addition, when a more effective absorbing material is applied to the LCPF according to the embodiment, it is expected that the photothermal evaporation performance can be further improved. Therefore, it is expected that the 3D steam generating device according to the above embodiment can solve the serious water shortage problem worldwide.

Claims (14)

A pillar-shaped support having a plurality of pores connected to the surface and the inside and having a height higher than the diameter of the bottom surface; And
A composite structure comprising a light absorber layer formed on one bottom surface of the support,
The composite structure is used for desalination of seawater using sunlight by being built in seawater at a depth lower than the height of the composite structure so that the side surface on which the absorber layer is formed faces upward and the side surface is exposed at least 1 cm above the water surface, 1 kW/㎡ A composite structure exhibiting a water evaporation rate of at least 2.0 kg/m 2 ·h in light conditions of an intensity and a water evaporation rate of at least 0.5 kg/m 2 ·h in dark conditions.
delete delete According to claim 1,
The composite structure has a height of 1 cm or more higher than the depth of the sea water, the composite structure.
According to claim 1,
A composite structure in which the support has a contact angle of 10° or less with respect to water and a thermal conductivity of 0.1 W/m·K or less.
According to claim 1,
A composite structure, wherein the support comprises a porous phenolic foam.
According to claim 1,
A composite structure in which the absorber layer has an absorbance of 85% or more in all bands having a wavelength of 250 to 2500 nm.
According to claim 1,
A composite structure in which the light absorber layer contains reduced graphene oxide.
According to claim 1,
The composite structure, wherein the light absorber layer has a thickness in the range of 10 μm to 100 μm.
delete According to claim 1,
The support is a porous phenolic foam,
A composite structure in which the light absorber layer contains reduced graphene oxide.
According to claim 1,
The composite structure shows 80% or more in the light-steam conversion efficiency (η) calculated by the following equation (1):
[Equation 1]

In Equation 1, A is the cross-sectional area (m 2) of illumination, C _opt is the optical density, Q _s is the light irradiation intensity (1 kW/m 2 ), Q _e is calculated by Equation 2 below,
[Equation 2]

In Equation 2, m is the evaporation rate of water (kg/m 2 ·h) by photothermal conversion energy, λ is the latent heat (2255.2 J/g) when the phase changes to water vapor, and C is the specific heat capacity of water ( 4.2 J/g·K), and ΔT is the temperature increment (K) of the vapor produced.
A desalination device comprising the composite structure of claim 1.
A method of desalination comprising the step of placing the composite structure of claim 1 in sea water so that the side surface on which the light absorber layer is formed faces upward and the side surface is exposed at least 1 cm above the water surface.

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