CN113072119A

CN113072119A - Heat-gathering solar seawater desalination structure and method based on hydrophobic oxidized foamy copper

Info

Publication number: CN113072119A
Application number: CN202110488871.2A
Authority: CN
Inventors: 祁志福; 厉宸希; 骆周扬; 申震; 徐翼苏; 杜长庆; 鲍华
Original assignee: Shanghai Jiaotong University; Zhejiang Energy Group Research Institute Co Ltd
Current assignee: Shanghai Jiaotong University; Zhejiang Energy Group Research Institute Co Ltd
Priority date: 2021-04-28
Filing date: 2021-04-28
Publication date: 2021-07-06

Abstract

The invention relates to a heat-gathering solar seawater desalination structure based on hydrophobic oxidized foamy copper, which comprises the following components: the water absorption layer, the heat insulation layer, the light absorption layer and the heat accumulation layer; the two ends of the water absorption layer penetrate through the heat insulation layer and then are immersed in the water body, the light absorption layer and the heat accumulation layer are positioned above the heat insulation layer, and the middle of the water absorption layer is positioned between the heat insulation layer and the light absorption layer and between the heat accumulation layer; the heat insulation layer is filled with the water storage device to isolate water and air, so that a heat insulation effect is achieved; the light absorption layer and the heat accumulation layer are made of foam copper oxide with hydrophobic surfaces and GeNPs coatings attached. The invention has the beneficial effects that: the heat-gathering solar seawater desalination structure based on the hydrophobic oxidized foam copper is adopted to realize the interface solar evaporation with high evaporation rate and relatively large evaporation area; the oxidized foam copper with the hydrophobic surface and the GeNPs coating is used as the light absorption layer and the heat accumulation layer, and can absorb more than 95% of AM1.5G solar spectrum; the evaporation temperature of the CF is greatly increased and thus the evaporation rate is increased.

Description

Heat-gathering solar seawater desalination structure and method based on hydrophobic oxidized foamy copper

Technical Field

The invention belongs to the field of seawater desalination, and particularly relates to a heat-gathering solar seawater desalination structure and method based on hydrophobic oxidized foamy copper.

Background

Water is essential for the growth and reproduction of all the living things of the earth, and particularly most mammals including human beings can only live in fresh water, and the fresh water resources on the earth account for less than 3% of the total water resources. The demand and pressure for fresh water in humans continues to rise due to climate change and population growth. Although the cost of converting seawater or sewage into fresh water is generally expensive, many arid areas can be treated for water shortage. While conventional reverse osmosis techniques typically require intensive energy and require pretreatment of seawater or sewage, solar distillation is a low cost, environmentally friendly and large scale manner of fresh water production.

A typical solar distillation process is similar to the way solar energy drives the circulation of natural water on earth by using solar energy to heat seawater in a closed system and collecting condensed water. With conventional solar distillers, the entire bulk of the water in the container is heated by absorbing sunlight, which inevitably results in significant heat loss. For the interface sunlight evaporation, the photothermal effect is limited to the interface of water and air, and the evaporation layer is kept in heat insulation with the bulk water below, so that the design has great potential in realizing evaporation with high speed and high conversion efficiency. In general, high efficiency interfacial solar evaporators have several important structural features including broad spectrum high efficiency light absorbing materials, pores through which water vapor can escape, water transport channels through capillary forces, and low thermal conductivity thermal insulation to prevent heat loss to the underlying bulk water and to enable the absorber to float on the water surface.

Photothermal materials can be classified into various types according to the photothermal conversion mechanism to realize interfacial solar evaporation. For example, plasmonic nanoparticles are combined with porous templates, such as Au nanoparticle thin films deposited on dust-free paper and on alumina scaffolds, Ag nanoparticles deposited on diatomaceous earth and Al nanoparticles self-assembled into three-dimensional porous membranes; they show significant efficiency of photothermal conversion due to plasmon resonance, but their widespread use is hindered by higher cost. Carbon-based materials such as carbon black, graphite flakes, functionalized graphene and carbon nanotube composites have shown good broadband light absorption capabilities while being inexpensive and durable. In addition, various inorganic nanomaterials with unique optical properties, e.g. Cu_2-xS nanowire of Ti₂O₃Nanoparticles, black TiO₂Nano cage, MoO_3-xQuantum dots and Fe₃O₄The magnetic microspheres all show unique advantages in the field of interface solar evaporation application.

Although solar energy is a green energy source and has the characteristics of cleanness and inexhaustibility, compared with other energy sources, the main problem of the solar energy is that the energy density is lower. Therefore, in solar steam generation, optical concentration systems are often used to enhance solar flux in order to produce more steam in a relatively short time. Typical optical concentrating systems include parabolic trough collectors, heliostat field collectors, linear fresnel reflectors, and parabolic dish collectors. While solar flux can increase by a factor of ten or even thousands, optical concentration systems are generally quite expensive. Recently, an economical and efficient heat collecting method has been proposed, in which heat generated from solar energy can be concentrated into an evaporation tank through a copper sheet, and when heat radiation loss, heat convection loss and heat conduction loss are greatly suppressed, steam of 100 ℃ can be generated in the evaporation tank without an optical concentration system. However, in this design, the evaporation area is relatively small, which limits its practical application to high rate steam generation.

The main by-product of seawater desalination is concentrated seawater, which can adversely affect the marine ecosystem if discharged directly into the sea, and in addition, concentrated seawater contains a large amount of mineral resources, such as chloride, sodium, magnesium, sulfur, etc., and is wasted if discharged directly. Traditionally, salt can be extracted from brine by a salt pan method, but the method is greatly influenced by weather, and needs to occupy a large amount of land resources, so that the development is restricted. Nowadays, salt is usually separated from seawater by electrodialysis. However, the process of separating salt from seawater by electrodialysis has a high energy requirement, concentrated seawater usually requires pretreatment, and neither of these two methods is environmentally friendly.

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disclosure of Invention

The invention aims to overcome the defects in the prior art and provides a heat-gathering solar seawater desalination structure and method based on hydrophobic oxidized foamy copper.

A heat-gathering solar seawater desalination structure based on hydrophobic oxidized foamy copper comprises: the water absorption layer, the heat insulation layer, the light absorption layer and the heat accumulation layer; wherein both ends of the water absorption layer penetrate through the heat insulation layer and then are immersed in the water body, the light absorption layer and the heat accumulation layer are positioned above the heat insulation layer, and the middle part of the water absorption layer is positioned between the heat insulation layer and the light absorption layer as well as between the heat accumulation layer; the heat insulation layer is filled with the water storage device to isolate water and air, so that a heat insulation effect is achieved; the light absorption layer and the heat accumulation layer are made of foam copper oxide with hydrophobic surfaces and GeNPs coatings attached.

Preferably, the lower part of the middle part of the water absorption layer is tightly attached to the heat insulation layer, and the upper part of the middle part of the water absorption layer is tightly attached to the light absorption layer and the heat collection layer; the water absorbing layer is made of filter paper or cloth material with better water absorption; the heat insulation layer is made of polystyrene foam.

A heat-gathering solar seawater desalination structure based on hydrophobic oxidized foamy copper comprises: the water absorption layer, the heat insulation layer, the light absorption layer, the heat accumulation layer and the covering device; wherein both ends of the water absorption layer penetrate through the heat insulation layer and then are immersed in the water body, the light absorption layer and the heat accumulation layer are positioned above the heat insulation layer, and the middle part of the water absorption layer is positioned between the heat insulation layer and the light absorption layer as well as between the heat accumulation layer; the heat insulation layer is positioned on the surface of the water body and plays a role in heat insulation, the surface area of the heat insulation layer is smaller than that of the water body, and part of the water body is exposed; the top of the water storage device is provided with a covering device which completely covers the water storage device; the light absorption layer and the heat accumulation layer are made of foam copper oxide with hydrophobic surfaces and GeNPs coatings attached.

Preferably, the lower part of the middle part of the water absorption layer is tightly attached to the heat insulation layer, and the upper part of the middle part of the water absorption layer is tightly attached to the light absorption layer and the heat collection layer; the water absorbing layer is made of filter paper or cloth material with better water absorption; the heat insulation layer is polystyrene foam; the covering means is a glass plate or a PMMA lid.

Preferably, the covering means is placed at an oblique angle.

A heat-gathering solar seawater desalination structure desalination method based on hydrophobic oxidized foamy copper comprises the following steps:

step 1, using oxidized foam copper with a hydrophobic surface and a GeNPs coating as a light absorption layer and a heat accumulation layer, and concentrating heat generated at the periphery of an evaporation area to the evaporation area at the center of the light absorption layer and the heat accumulation layer when the light absorption area is larger than the water evaporation area; the preparation method of the copper oxide foam with the hydrophobic surface and the GeNPs coating is as follows: firstly, oxidizing the surface of the foam copper into black CuO, then adhering GeNPs (germanium nanoparticles) sol on the surface of the black CuO to enhance infrared absorption, and finally treating the foam copper subjected to surface oxidation and sol adhesion by trichloro (1H,1H,2H, 2H-perfluorooctyl) silane to make the surface hydrophobic;

step 2, after the light absorption layer and the heat accumulation layer absorb the heat of sunlight, transferring the heat to the water absorption layer to generate steam, and discharging the steam through mutually communicated holes in the foam copper in the light absorption layer and the heat accumulation layer;

and 3, collecting the steam by using a collecting device to obtain condensed fresh water.

Preferably, in step 1, the light absorption area is the size of the copper oxide foam with the hydrophobic surface and the GeNPs coating attached, and the water evaporation area is the size of the water absorption layer.

and 3, condensing the steam to form condensed fresh water after the steam reaches the covering device, collecting part of the condensed fresh water through a collecting device, and refluxing the rest of the condensed fresh water to the water body along the inclined direction of the covering device.

Preferably, the inclination angle of the covering means in step 3 is 10 °

The invention has the beneficial effects that: according to the invention, the heat-gathering solar seawater desalination structure based on the hydrophobic oxidized foamy copper is adopted, so that the interface solar evaporation with high evaporation rate and relatively large evaporation area is realized; the oxidized foam copper with the hydrophobic surface and the GeNPs coating is used as the light absorption layer and the heat accumulation layer, and can absorb more than 95% of AM1.5G solar spectrum; the evaporation temperature of CF and thus the evaporation rate can be greatly increased.

Drawings

FIG. 1(A) is a schematic cross-sectional view of a heat-gathering solar seawater desalination structure based on hydrophobic oxidized foam copper; FIG. 1(B) is a schematic cross-sectional view of a heat-concentrating solar seawater desalination structure based on hydrophobic oxidized foam copper, wherein the top of a container is covered with a glass sheet;

FIG. 2(A) is a square copper foam, FIG. 2(B) is a circular copper foam, and FIG. 2(C) is a schematic view of a solar evaporator with a PMMA cover on top of the circular copper foam;

FIG. 3(A) is a Transmission Electron Microscope (TEM) image of germanium nanoparticles (GeNPs) at different magnifications; FIG. 3(B) is a Dynamic Light Scattering (DLS) particle size distribution plot of germanium nanoparticles (GeNPs) dispersed in Tetrahydrofuran (THF) solvent; FIG. 3(C) is an X-ray powder diffraction (XRD) pattern of germanium nanoparticle (GeNPs) powder; FIG. 3(D) is a Fourier Transform Infrared (FTIR) microscopy spectrum of germanium nanoparticle (GeNPs) powder; FIG. 3(E) is a molar extinction coefficient spectrum (dark curve) of a germanium nanoparticle suspension in tetrahydrofuran and an absorption spectrum (light curve) of a dry germanium nanoparticle powder, with the inset being a plot of the behavior of germanium nanoparticles in tetrahydrofuran solvent at room temperature;

FIGS. 4(A) to 4(I) are clean (after water bath sonication), NaOH/K, respectively₂S₂O₈Scanning Electron Microscope (SEM) images of copper foam with 267- μm, 195- μm, and 51- μm pore sizes after oxidation, GeNPs dip coating, and TCPFOS treatment; FIG. 4(J) and FIG. 4(K) are NaOH/K, respectively₂S₂O₈High-power scanning electron microscope images of the foamy copper after oxidation, GeNPs dip coating and TCPFOS treatment; FIGS. 4(L) to 4(N) are clean, NaOH/K, respectively₂S₂O₈The energy dispersion X-ray analysis result schematic diagram of the foamed copper with the aperture of 267-mu m after oxidation, GeNPs dip coating and TCPFOS treatment;

FIGS. 5(A) to 5(C) are NaOH/K after cleaning, respectively₂S₂O₈Absorption spectrograms of the foam copper with the aperture of 267-mu m, 195-mu m and 51-mu m respectively after oxidation and GeNPs and TCPFOS treatment; FIGS. 5(D) to 5(F) are NaOH/K after cleaning, respectively₂S₂O₈Pictures of foamed copper with apertures of 267-mum, 195-mum and 51-mum respectively after oxidation and treatment by GeNPs and TCPFOS under indoor light;

FIGS. 6(A) to 6(I) are graphs showing the water evaporation quality of oxidized copper foam having a pore size of 267 μm, a pore size of 195 μm, and a pore size of 51 μm, which is hydrophobic on the surface and to which GeNPs are attached, with time in a dark environment and under sunlight, respectively; fig. 6(a) to 6(C) show a square of 2cm × 2cm in copper oxide foam, fig. 6(D) to 6(F) show a circular shape of 6cm in diameter, fig. 6(G) to 6(I) show a circular shape of 6cm in diameter and a PMMA lid is provided above the container, and the filter paper is fixed to a size of 2cm × 2 cm; fig. 6(a) to 6(I) are insert diagrams showing infrared thermography of the solar steam generator, in which the number is the center temperature; fig. 6(J) to 6(L) are evaporation rate curves and light-vapor conversion efficiency curves under different conditions calculated from the mass change curves in fig. 6(a) to 6(I), respectively;

FIG. 7(A) is a water evaporation mass change curve of oxidized CF having a diameter of 6cm and a pore diameter of 195 μm, a surface of which is hydrophobic and to which GeNPs are attached, as an absorption layer and a heat accumulating layer, respectively corresponding to filter papers (i.e., water absorbing layers) of different sizes, including 1cm × 1cm, 2cm × 2cm, 3cm × 3cm and 4cm × 4 cm; FIG. 7(A) is an inset of a calculated water evaporation rate versus time based on the water evaporation mass profile; FIG. 7(B) is a graph of the corresponding horizontal mean evaporation rate and dry salt accumulation rate of FIG. 7(A) over a 5 hour period, the inset in FIG. 7(B) showing the ratio between the dry salt accumulation rate and the horizontal mean evaporation rate; FIG. 7(C) is a state diagram of CF in FIG. 7(A) every hour during evaporation; FIG. 7(D) is an infrared thermography of the CF in FIG. 7(A) during the second hour of the evaporation process;

FIG. 8(A) is a graph showing changes with time of NaCl solutions having initial concentrations of 10 wt%, 5 wt% and 1 wt% under solar irradiation, using oxidized CF as a light absorbing layer and a heat accumulating layer; FIG. 8(B) is a state diagram of CF before and after the salt extraction process;

FIG. 9 is a flow chart of surface passivation of GeNPs using 10-UD-ol;

FIG. 10 is an absorption spectrum of a suspension obtained by dispersing GeNPs at various concentrations in tetrahydrofuran;

FIG. 11 is a Raman spectrum of oxidized CF with a 267 μm pore size;

FIG. 12 is a FTIR reflectance spectrum of CF having a 267 μm pore size after oxidation, GeNPs dip coating, and TCPFOS hydrophobic treatment;

FIG. 13(A), FIG. 13(B), FIG. 13(C) are schematic contact angle diagrams of oxidized CF with GeNPs attached and the surface of 267 μm, 195 μm and 51 μm pore size, respectively, is hydrophobic;

FIGS. 14(A) to 14(I) are respectively a 267 μm pore size, a 195 μm pore size and a 51 μm pore size CF after cleaning, NaOH/K₂S₂O₈Schematic diagrams of transmission spectra (T), reflection spectra (R) and absorption spectra (a) after oxidation, GeNPs dip coating and TCPFOS treatment; t + R + a ═ 1;

FIGS. 15(A) to 15(C) are absorption curves of the solar spectrum corresponding to the calculated CF with an aperture of 267 μm, an aperture of 195 μm and an aperture of 51 μm, respectively;

FIG. 16 is a graph showing the water evaporation quality of hydrophilic CF having an aperture of 195 μm and a size of 2cm × 2cm in a dark environment under one solar irradiation with time; the inset in fig. 16 is an infrared thermography of a solar evaporation device, centered on the center temperature of the hydrophilic CF;

FIGS. 17(A) to 17(C) are experimental values M obtained by fitting the three curves of FIG. 8(A), respectively_s(t) corresponding fitted equation graphs;

fig. 18 is an XRD pattern of Ge wafer.

Description of reference numerals:

the water-absorbing layer 1, the water body 2, the heat-insulating layer 3, the light-absorbing layer and the heat-collecting layer 4, the covering device 5 and the water storage device 6.

Detailed Description

The present invention will be further described with reference to the following examples. The following examples are set forth merely to aid in the understanding of the invention. It should be noted that, for a person skilled in the art, several modifications can be made to the invention without departing from the principle of the invention, and these modifications and modifications also fall within the protection scope of the claims of the present invention.

Example 1:

step 1, using oxidized foam copper with a hydrophobic surface and a GeNPs coating as a light absorption layer and a heat accumulation layer 4, and concentrating heat generated at the periphery of an evaporation area to the evaporation area at the center of the light absorption layer and the heat accumulation layer 4 when the light absorption area is larger than the water evaporation area; the preparation method of the copper oxide foam with the hydrophobic surface and the GeNPs coating is as follows: firstly, oxidizing the surface of the foam copper into black CuO, then adhering GeNPs (germanium nanoparticles) sol on the surface of the black CuO to enhance infrared absorption, and finally treating the foam copper subjected to surface oxidation and sol adhesion by trichloro (1H,1H,2H, 2H-perfluorooctyl) silane to make the surface hydrophobic;

step 2, after the light absorption layer and the heat accumulation layer 4 absorb the heat of sunlight, the heat is transferred to the water absorption layer 1 to generate steam, and the steam is discharged through mutually communicated holes in the copper foam in the light absorption layer and the heat accumulation layer 4;

The heat-gathering solar seawater desalination structure based on the hydrophobic oxidized foam copper comprises: a water absorption layer 1, a heat insulation layer 3, a light absorption layer and a heat collection layer 4; wherein both ends of the water absorption layer 1 penetrate through the heat insulation layer 3 and then are immersed in the water body 2, the light absorption layer and the heat accumulation layer 4 are positioned above the heat insulation layer 3, and the middle part of the water absorption layer 1 is positioned between the heat insulation layer 3 and the light absorption layer and the heat accumulation layer 4; the heat insulation layer 3 is filled with the water storage device 6 to isolate the water body 2 from air, so that the heat insulation effect is achieved; the light absorption layer and the heat collection layer 4 are made of oxidized foam copper with hydrophobic surfaces and GeNPs coatings, the heat insulation layer 3 is tightly attached to the lower part of the middle part of the water absorption layer 1, and the light absorption layer and the heat collection layer 4 are tightly attached to the upper part of the middle part of the water absorption layer 1; the water absorbing layer 1 is made of filter paper or cloth material with better water absorption; the thermal insulation layer 3 is polystyrene foam.

Example 2:

on the basis of example 1, interfacial solar evaporation with a high evaporation rate and a relatively large evaporation area was first achieved using a heat-concentrating method in which copper oxide foam (CF) having germanium nanoparticles (GeNPs) attached thereto, the surface of which is hydrophobic, was used as a light-absorbing layer and a heat-concentrating layer (as shown in fig. 1 (a)). Firstly, oxidizing the CF surface into black CuO, then adhering and covering with GeNPs sol to enhance infrared absorption, and finally treating with trichloro (1H,1H,2H, 2H-perfluorooctyl) silane to make the surface hydrophobic, wherein the prepared photo-thermal material can absorb more than 95% of AM1.5G solar spectrum, the generated heat is transferred to the filter paper absorbing water below to generate steam (cloth materials with better water absorption can be adopted in large-scale solar distillation), and the steam is discharged through the mutually communicated holes of the foamy copper. Both ends of the filter paper are immersed in the bulk water, continuously absorbing the water by capillary force and transporting the water. The polystyrene foam is located under the hydrophobic CF and hydrophilic filter paper to provide thermal insulation. In addition, due to the high thermal conductivity and surface hydrophobic properties of copper foam, when the light absorption area (i.e., CF size) is larger than the water evaporation area (i.e., filter paper size), the heat generated at the periphery of the evaporation area can be concentrated to the evaporation area at the center. By this means the evaporation temperature of the CF and thus the evaporation rate can be greatly increased.

Next, a salt extraction experiment (fig. 1(B)) was performed under a heat accumulation condition of the NaCl solution using a similar apparatus as shown in fig. 1(a), except that the container was covered with a glass plate and the glass plate was tilted by about 10 ° to facilitate the backflow of the condensed water into the solution, as shown in fig. 1 (a). Due to the high rate of evaporation generated under the coalescing structure, and the hydrophobic surface of the CF, dry salt crystals remain on the CF surface as the brine evaporates. In addition, due to the backflow of condensed water, the total water amount is unchanged, and the salinity of the salt solution is gradually reduced to realize desalination. Compared with the traditional salt field method and the current electrodialysis method, the salt extraction method shown in the embodiment utilizes solar energy for driving, can easily extract dry salt from salt solution, and does not need to evaporate the whole water body.

Fig. 1(a) is a schematic cross-sectional view of a thermal-concentrating interfacial solar steam generator, in which a layer of thin water is formed between a hydrophobic copper foam and a hydrophilic filter paper, and polystyrene foam is used as a thermal insulation layer to insulate the hydrophobic copper foam and the hydrophilic filter paper from water lumps below, wherein the surface of the thermal-concentrating interfacial solar steam generator is hydrophobic and the oxidized copper foam with a GeNPs coating is used as a light absorption layer and a thermal-concentrating layer; the container in fig. 1(B) is covered with a glass plate that is slightly tilted about 10 ° to facilitate the back flow of condensed water into the salt solution.

The experimental results are as follows:

synthesis and characterization of GeNPs

The synthesis of GeNPs was based on a previously developed high energy ball milling process with some modifications (as shown in FIG. 9):

firstly, isopropanol and zirconia beads are added into a grinding tank, then a sample germanium wafer is put in the grinding tank, and GeNPs are obtained after long-time high-energy ball milling (synthesis of 10-UD-ol passivated GeNP: 24 hours, and industrial grinding time is 2-200 hours). The GeNPs were then treated with dilute HF (GeNP treated with approximately 5% HF) to remove surface oxides forming Ge-H bonds, followed by thermally induced hydrosilylation with undecenol (10-UD-ol) in an oxygen-free environment. GeNPs subjected to 10-UD-ol passivation treatment were stored in Tetrahydrofuran (THF) solvent to form a uniform and stable suspension for subsequent experiments. And (A) crushing the Ge single crystal wafer into GeNPs by high-energy ball milling. Treating GeNPs with diluted HF to remove surface oxides and generate Ge-H ends, and thermally inducing hydrosilylation reaction with 10-UD-ol in an oxygen-free environment, wherein chloroplatinic acid is used as a catalyst. The 10-UD-ol passivated GeNPs were then washed with copious amounts of THF to remove excess reactants and then uniformly dispersed in THF for subsequent experiments.

Wherein, the synthesis of 10-UD-ol passivated GeNPs: ge wafers (about 0.6g) with an n-type crystal orientation of (111) were placed in a zirconia milling jar containing about 80g of zirconia beads and 25mL of isopropanol. In a high energy ball mill (MITR QM-QX0.4L), Ge wafers were first crushed to a coarse powder using zirconia beads 10 mm in diameter by 4 hour ball milling, followed by crushing of Ge wafers to nanoparticles (GeNPs) using 3 mm zirconia beads by 20 hour ball milling. Next, the GeNPs were treated with about 5% HF to remove surface oxides and generate Ge-H bonds, mixed with a small amount of chloroplatinic acid, dispersed in deoxyundecenol (10-UD-ol) while heating to 130 ℃ for thermally induced hydrosilylation, and after more than 20 hours, the 10-UD-ol passivated GeNPs were washed with a large amount of Tetrahydrofuran (THF) by repeated centrifugal precipitation and sonication to remove excess reactants, and finally dispersed in THF solvent for subsequent experiments. The GeNPs suspension (8 mg mL-1 in THF) can be kept uniform and stable for several months.

As can be seen from a Transmission Electron Microscope (TEM) image (see FIG. 3(A)) and a Dynamic Light Scattering (DLS) particle size distribution diagram (see FIG. 3 (B)), the GeNPs are irregular flakes, and the particle sizes are mainly distributed in the range of 100-400 nm. Further, an X-ray powder diffraction (XRD) pattern (see fig. 3(C)) shows that GeNPs are polycrystalline, while the raw material germanium wafer is single-crystalline (fig. 18). This transition in crystallinity may be due to surface strain induced by high energy ball milling. At Ti₂O₃Similar phenomena are also found in nanoparticles and Si nanoparticles.

Fourier transformationThe surface chemistry of GeNPs was characterized by a Fourier Transform Infrared (FTIR) microscopy spectrogram (FIG. 3(D)) in which the absorption peak of the Ge-O-Ge group appeared at 746cm^-1This is similar to the Si-O-Si stretching vibration (1100 cm) found in Si nanoparticles and Si quantum dots^-1) Ge-C swinging vibration mode (848 cm)^-1)，CH₂Bending vibration mode (1450 cm)^-1) And CH₂Telescopic vibrating die (2860 cm)^-1，2930cm^-1) Surface passivation of GeNPs after 10-UD-ol ligation was demonstrated. The wave numbers highlighted from left to right in FIG. 3(D) correspond to CH, respectively₂Asymmetric telescoping (2930 cm)^-1)，CH₂Symmetric expansion (2860 cm)^-1)， CH₂Bending (1450 cm)^-1) Ge-C swing (848 cm)^-1) And Ge-O-Ge symmetric expansion (746 cm)^-1)；

The molar extinction coefficient spectra (dark curve in fig. 3 (E)) can be calculated from the absorption spectra (fig. 10) of the GeNPs suspensions at different concentrations:

according to Lambert-Beer law, a ═ epsilon bC, where a is absorbance, epsilon is molar extinction coefficient, b is optical path length in cm, and C is nanoparticle concentration in solution. In this experiment, b is 1cm, which is the width of the cuvette used. C is calculated by the formula:

where ρ is_sIs the solution density (g/L), V_NIs the volume (cm) of a nanoparticle³) Here we consider the germanium nanoparticles as spheres with a particle size of 140nm, ρ_NIs a germanium density (5.35 g/cm)³)，N_AIs the Avogastron constant (6X 10)²³). According to the absorbance of GeNP suspension liquid with different concentrations at a certain specific wavelength, the slope can be obtained through linear regression fitting, and the slope is the molar extinction coefficient.

GeNPs have a high molar extinction coefficient in THF, an extinction coefficient in the visible range of greater than 5X 10¹⁰ M^-1cm^-1Extinction coefficient in the Near Infrared (NIR) range greater than 2X 10¹⁰M^-1cm^-1. Phase (C)In contrast, the molar extinction coefficient of 34nm diameter citrate terminated plasmonic material gold nanoparticles at the surface plasmon resonance wavelength (506nm) is equal to 6.1 × 10⁹M^-1cm^-1. In addition, in the embodiment, the GeNPs are coated on the surface of the CF and dried, the drying temperature is 50 ℃, the drying time is 2 hours, and the industrial drying time is 2-20 hours. The light absorption capacity of the dried GeNPs powder needs to be characterized, and the light colored curve in fig. 3(E) is the absorption spectrum of the dried GeNPs powder, with a similar trend to the molar extinction coefficient spectrum. In particular, the spectra show an absorption peak at a wavelength greater than the bandgap of germanium (0.67eV, 1.85 μm) due to defects in the bandgap of the surface or dangling bonds.

Secondly, preparing and characterizing oxidized CFs with hydrophobic surfaces and GeNPs

In this example, three different structural features of CFs were used, each having a different thickness (mm) and pore density (PPI, average pore size per inch length), including a CF having a thickness of 5mm, 95-PPI (average pore size 267 μm), a CF having a thickness of 2mm, 130-PPI (average pore size 195 μm), and a CF having a thickness of 1mm, 500-PPI (average pore size 51 μm). And the densities of CF with an aperture of 267 μm, 195 μm and 51 μm are equal to 0.415, 0.320 and 3.276g cm, respectively^-3Corresponding to porosities of 95%, 96% and 63%, respectively. A brief preparation of oxidized CF with hydrophobic surface and attached GeNPs is as follows: firstly, sequentially carrying out water bath ultrasound on CF in acetone, isopropanol and 1M HCl to clean the surface, wherein the ultrasound time is 5-50 minutes in each step, and then placing the cleaned CF in 2.5M NaOH and 0.1M K₂S₂O₈Oxidizing in the mixed solution to form black CuO on the surface of the CF; the experimental time is 0.5-4 hours, and the industrial time is 0.5-40 hours. Next, the oxidized CF was immersed in a THF suspension of GeNPs (concentration 8mg mL)^-1) And taking out the surface of the CF for a while, and soaking the surface of the CF with 10-UD-ol passivated GeNPs. Finally, treating the GeNPs-coated oxidized CF with trichloro (1H,1H,2H, 2H-perfluorooctyl) silane (TCPFOS) to make the surface hydrophobic by immersing the oxidized CF with the GeNPs attached in 2.8 wt% trichloro (1H,1H,2H, 2H-all-trichloro)Fluorooctyl) silane (TCPFOS) for 1 hour (hexane as solvent), the procedure was performed in a nitrogen-filled glove box to prevent the TCPFOS from reacting with moisture. After TCPFOS treatment, CF was rinsed thoroughly with hexane and placed in a glove box to air dry. Finally, the hydrophobic oxidized CFs coated with the GeNPs were stored in an oven at 50 ℃. TCPFOS can be attached to GeNPs surface-coated with CuO by coupling between trichlorosilane and the hydroxyl termini of 10-UD-ol.

Wherein the preparation process of the oxidized CF comprises the following steps: in this example, three different structures of CF, 95-PPI (average pore diameter 267 μm), porosity 95%, CF with a thickness of 5mm, 130-PPI (average pore diameter 195 μm), porosity 96%, CF with a thickness of 2mm, 500-PPI (average pore diameter 51 μm), porosity 63% and CF with a thickness of 1mm were used. First, CF was ultrasonically cleaned in water baths of acetone, isopropanol, and 1M HCl in sequence, each step lasting 5 minutes. Subsequently, the cleaned CF was immersed in 2.5M NaOH and 0.1M K₂S₂O₈In the mixed solution of (2) until the entire CF surface becomes black, NaOH/K₂S₂O₈The solution gradually changed from colorless to dark blue. After oxidation, the CF was thoroughly rinsed with deionized water and ethanol, respectively, then blown dry with nitrogen, and the oxidized CF was stored in an oven at 50 ℃.

Preparation of oxidized CF with hydrophobic surface and GeNPs coating: the oxidized CF was immersed in a GeNPs suspension (8 mg mL in THF)^-1) Then taken out and dried in an oven at 50 ℃. The oxidized CF with the GeNPs attached was then immersed in 2.8 wt% trichloro (1H,1H,2H, 2H-perfluorooctyl) silane (TCPFOS) for 1 hour (hexane as solvent) in a nitrogen-filled glove box to prevent the TCPFOS from reacting with moisture. After TCPFOS treatment, CF was rinsed thoroughly with hexane and placed in a glove box to air dry. Finally, the hydrophobic oxidized CF with the GeNPs coating was stored in an oven at 50 ℃.

From Scanning Electron Microscope (SEM) images and energy dispersive X-ray (EDX) analysis, clean CF has high purity copper and a smooth microscopic surface, but clean CF with a 51 μm pore size has a relatively pronounced grain structure (FIG. 4)(A) Fig. 4(C) and 4 (L)). In the presence of NaOH/K₂S₂O₈After oxidation, the concentration of oxygen element increases (fig. 4(M)), and the CF microscopic surface becomes a highly porous structure, and the submicron-order close-packed petaloid structure covers the entire CF surface (fig. 4(M) to fig. 4 (F) and fig. 4 (J)). Raman spectroscopy of oxidized CF (fig. 11) further confirmed that the surface porous structure is composed of CuO. After the GeNPs dip coating and TCPFOS treatment, the concentrations of F, Ge, and C elements increased (fig. 4(N)), while the CF surface roughness slightly decreased (fig. 4(G) to fig. 4 (I)). At high magnification, the GeNPs sheet clusters deposited on top of the porous surface of CuO are clearly visible (fig. 4 (K)).

The CF after GeNPs dip-coating and TCPFOS treatment showed additional FTIR absorption peaks, including CH, compared to oxidized CF₂Stretching vibration (2860 and 2930 cm)^-1) And CF₂Stretching vibration (1150 and 1200 cm)^-1) They belong to the 10-UD-ol hydrocarbon chain and to the perfluoroalkyl chain of TCPFOS, respectively (FIG. 12). Furthermore, the CF surface became highly hydrophobic by modification of the perfluoroalkyl chains of TCPFOS, the contact angles of CF with a pore size of 267 μm, 195 μm and 51 μm were as high as 130 °, 117 ° and 116 °, respectively (FIG. 13), and the surface was hardly wetted by water droplets (SI Video S1A). In contrast, only through NaOH/K₂S₂O₈The oxidized CF surface is hydrophilic and the water droplets are rapidly absorbed by its surface (SI Video S1B).

The absorption spectra of the CFs for the different structural and surface features are shown in fig. 5, where the absorption is 1-transmittance-reflectance. The transmission and reflection spectra were measured by an ultraviolet-visible near-infrared spectrophotometer with an integrating sphere as shown in fig. 14. The absorption band of the cleaned CF was mainly below 600nm (dark curves in fig. 5(a) to 5 (C)), and the cleaned CF also appeared yellowish brown at room temperature (left panels of fig. 5(D) to 5 (F)). In the presence of NaOH/K₂S₂O₈After oxidation, porous CuO is formed on the surface of CF, the absorptivity of the oxidized CF with three structural characteristics is more than 95% in the range of 200nm to 800nm, the absorptivity of the oxidized CF with three structural characteristics is more than 85% in the NIR range (the curve with the lightest color in the graphs from 5(A) to 5 (C)), and the absorption curve is in a step transition between the two areas, wherein the step transition is formed by the step curve and the clean CFThe step-shaped curves in the absorption curves correspond to each other. Since oxidized CF is almost completely absorbed in the visible range, it appears as a carbon black under indoor light (middle graph of fig. 5(D) to 5 (C)). Also, similar spectral features of other oxidized CFs are observed in the reference. The oxidized CF after GeNPs dip coating and TCPFOS treatment, the color of the CF slightly grayed out under room light (right panels in fig. 5(D) to 5 (F)), the absorption spectrum in the visible range of which remained almost unchanged (lighter color curves in fig. 5(a) to 5 (C)), and the light absorption capacity in the NIR range of which was further improved, which was most evident on the absorption spectrum of CF with an aperture of 195 μm. The absorption of the am1.5g solar spectrum of oxidized CF with hydrophobic surface and attached GeNPs was calculated to be above 95% regardless of pore size, thickness and porosity (fig. 15).

And (3) characterization: TEM images were measured with the instrument JEOL JEM-2100. The DLS particle size distribution plot was obtained by Malvern Panalytical Zetasizer Nano S. The XRD pattern was obtained by Bruker D8 ADVANCE. FTIR microscope spectra were obtained from Thermo Fisher Nicolet iN10 MX. Raman spectra were obtained from Bruker Senterra R200-L. The reflected FTIR spectrum was obtained by Nicolet 6700 with an integrating sphere attachment. Absorption, reflection and transmission spectra of CF were obtained by Perkin Elmer Lamda 950. SEM images and EDX analysis were obtained by FEI Nova Nanosem 450. Contact angle analysis by

And (4) obtaining. For solar steam generation and salt extraction experiments, one solar irradiance was calibrated using the beijing zhongjin source solar simulator CEL-S500 and using the beijing zhongjin source optical power meter CEL-FZ-A. The change in mass was recorded by analytical balance Sartorius BSA 2245-CW.

Three, heat-collecting type solar evaporation

This example characterizes the generation of solar steam in a thermal concentrating configuration by using the device shown in fig. 1(a) with oxidized CF having GeNPs attached to it, the surface of which is hydrophobic, having different structural characteristics (fig. 6). During the entire evaporation process, the liquid water, although in direct contact with the CF, stays only in the filter paper, and the generated vapor is vented through the interconnected pores inside the CF. The evaporation rate and the light-vapor conversion efficiency were calculated by subtracting the evaporation in the dark environment:

efficiency of light-vapor conversion (. eta.) through

Calculated, where R is the evaporation rate (kg m) subtracted in a non-illuminated environment^-2s^-1)，A_paperIs the area of the filter paper (m)²)，h_LVIs latent heat of vaporization (2406 to 2333kJ kg at 40 ℃ to 70 ℃)^-1)，A_CFIs the light absorption area, i.e. the area (m) of CF²)，q_solarIs a solar irradiance (1kW m-²)。

When the size of oxidized CF with the surface hydrophobic and the attached GeNPs is the same as that of the filter paper, i.e., 2 cm. times.2 cm (FIG. 2 (A)), the evaporation rate and conversion efficiency under one solar light irradiation are 0.97, 1.09, and 0.98kg m for 267 μm, 195- μm, and 51- μm pore size CF, respectively^-2h^-1And 65%, 72%, and 65% (fig. 6(a) to 6(C) and fig. 6(J) to 6(J) in fig. 6 (L)), the evaporation temperature was around 46 ℃, with the evaporation rate of the 195 μm pore size CF being slightly higher because of its larger pore size and smaller thickness, facilitating the discharge of vapor. In contrast, with the same area and pore size but only through NaOH/K₂S₂O₈The hydrophilic CF oxidized without subsequent surface treatment showed a higher evaporation rate of 1.35 kg m^-2h^-1And higher conversion of 89%, and lower surface temperature (fig. 16). The results indicate that hydrophilic CFs transfer heat more efficiently to water than hydrophobic CFs, although the hydrophobic surface characteristics of the CFs can achieve heat accumulation and salt extraction.

When the CF area is enlarged to a circle of 6cm in diameter while the size of the underlying filter paper is maintained (fig. 2(B)), heat generated at the peripheral area of the CF may be continuously concentrated to the central area since the evaporation area at the center of the CF absorbs heat during evaporation. The experimental results show that the surface temperature of the CF at the center can reach more than 60 ℃, the pore diameter is 267 mu m, and the evaporation rates of the CF at 195 mu m and 51 mu m are respectively improved to 2.78, 2.30 and 2.79kg m^-2h^-1(ii in fig. 6(D) to 6(F) and 6(J) to 6 (L)). The evaporation rate increased by a factor of 2 to 3 compared to the no heat accumulation condition (fig. 6(a) to 6 (C)). However, higher temperatures at the CF surface also result in more heat loss, especially thermal convection and radiation losses. The light-vapor conversion efficiency thereof falls to the range between 20% and 30%. Notably, the 51- μm pore size CF has a higher thermal conductivity (65.3W m) than the other two structures (CF)^-1K^-1) And therefore has a greater heat gathering capacity, with a temperature difference of only 1 ℃ between the central region and the peripheral region. In contrast, CF with a pore size of 195 μm is relatively low due to thermal conductivity (8.1W m)^-1K^-1) Thinner (resulting in a smaller cross-section) and unable to transfer heat efficiently to the surface, the temperature difference between its central and peripheral regions being up to 10 ℃.

To reduce the heat convection loss, a 1mm thick Polymethylmethacrylate (PMMA) plate with a 2cm by 2cm hole in the center aligned with the outer contour of the filter paper was mounted on top of the CF with a 5mm gap between it (FIG. 2 (C)). After adding the PMMA plate, the central temperature of CF with the aperture of 267 μm, 195 μm and 51 μm was increased to 69.3 ℃, 64.8 ℃ and 74.3 ℃, and the evaporation rate was further increased to 2.96, 2.63 and 3.19kg m^-2h^-1At the same time, the conversion efficiency is also improved to 30% (iii in fig. 6(G) to 6(I) and 6(J) to 6 (L)). In the previously designed concentrating solar evaporator, the conversion efficiency calculated by simulation was about 30% when the steam temperature reached 80 ℃, and in this experiment, the case of a 51- μm pore size CF plus PMMA plate was compared, with a conversion efficiency equal to 29.1%, and the temperature of the central region of the CF should be close to the steam temperature, equal to 74.3 ℃.

It is noteworthy that if the PMMA plate is placed directly on the CF surface without leaving air gaps, condensation water adhesion within the PMMA plate during steam generation occurs, especially for CF of 267 μm pore size. This phenomenon indicates that the steam can not only be discharged vertically, but also spread horizontally through the interconnected pores inside the CF and then escape from the peripheral region of the CF. Therefore, it is important to maintain a proper air gap so that the lateral air flow can carry away the vapor between the PMMA plate and the CF while mitigating the vertical heat convection losses in the peripheral region of the CF.

Salt extraction experiment under heat accumulation condition

Based on the previous experiment with oxidized CF with hydrophobic surface and attached GeNPs as the absorption layer and the heat accumulation layer, the salt extraction experiment was designed in this example, and the relationship between the heat accumulation structure and the salt accumulation was first characterized (fig. 7), and then the salt extraction experiment with different salinity solutions was further explored by using the obtained experimental results (fig. 8).

First, a 3.5% by mass NaCl solution was used for the experiment. In a typical seawater evaporation experiment, as the salt water evaporates, although the salt is temporarily deposited on the surface of the evaporator, it will eventually diffuse back into the original bulk water for the purpose of removing the salt. However, in the examples, due to the heat accumulation effect, the salt cannot diffuse back into the bulk water in time and accumulates on the filter paper, and as the salt gradually accumulates, it will permeate through the pores of the CF and eventually become a dry salt on the CF surface. In the experiment, the CF size was fixed to a 6cm circle, and as the filter paper size was decreased from 4 cm. times.4 cm to 1 cm. times.1 cm, the average evaporation rate of water was increased from 1.49kg to 7.92 kg m^-2h^-1The rate of accumulation of dry salt increased from 0.026kg to 0.208kg m^-2h^-1(FIGS. 7(A) and 7(B)), and the ratio of the dry salt accumulation rate to the average evaporation rate of water also increased from 1.72 wt% to 2.63 wt% (inset in FIG. 7 (B)). The initial NaCl concentration of the experiment was 3.5 wt%, assuming that the theoretical maximum value of the ratio of dry salt accumulation rate to average evaporation rate of water was 3.5/(100-3.5) — 3.63 wt% during evaporation if no salt diffused from the rate paper back into the bulk solution.

The salt accumulated on the surface of the traditional interface solar evaporator can block the absorption of light, and the salt scale can block the water channel, so that the evaporation rate is reduced, different from the traditional interface solar evaporator, the dry salt generated by the embodiment can not reduce the generation efficiency of solar steam, and the reason is that: (1) due to the hydrophobic nature of the CF surface, the entire CF remains completely dry during evaporation, so dry salt is only present on the CF surface (SI Figure S6 and SI Video S1A). In contrast, wet salt (i.e., a high concentration of solute) is present on the filter paper, which can diffuse back into the bulk water. (2) The dry salt is generally formed in the central portion of the CF, does not affect the light absorbing ability of the rest of the CF, and the generated heat can be efficiently transferred to the evaporation site due to the high thermal conductivity of the CF (fig. 6 (E)). (3) Although the dry salt may block the exit passage of the vapor above the filter paper, the vapor may still pass horizontally through the interconnected pores inside the CF and escape elsewhere.

Experiments have shown that the evaporation rate remains relatively stable or even increases when dry salt is grown on CF surfaces (inset in fig. 7 (a)). At relatively high accumulation rates, the rapidly accumulating wet salt will spread laterally between the polystyrene foam and the filter paper while stacking upward, resulting in an effective evaporation area larger than the filter paper size. Therefore, during the evaporation, when the filter paper size is small (especially 1cm × 1cm), the evaporation rate gradually increases (blue and green curves in fig. 7 (a)). In addition, dry salt is initially formed in the edge area of the filter paper, where the evaporation rate is relatively high and the corresponding CF temperature is also relatively high (fig. 7(C) and 7(D)), which is most apparent when the filter paper has a size of 4cm × 4cm, and dry salt on CF corresponds to the periphery of the filter paper. The formation of dry salt started in the second hour of the evaporation process when using filter papers of 1cm × 1cm and 2cm × 2cm, and was observed in the fourth hour when using filter papers of 4cm × 4 cm. The observed results are consistent with the calculated dry salt accumulation rate as a function of filter paper size by weighing (dark curve in fig. 7 (B)).

By using the irreversible process of dry salt formation as described above, we performed a salt extraction experiment by using the apparatus shown in fig. 1(B), and the experimental results are shown in fig. 8. As shown in fig. 1(B), the glass sheet was covered on top of the vessel and the steam was confined in a closed system with the glass sheet tilted about 10 ° so that the condensed water refluxed into the solution. Under the irradiation of the solar simulator, dry salt forms and accumulates on the CF surface, and the salinity of the solution gradually decreases as the total water amount remains constant. In the experiment, oxidized CF having a pore size of 195 μm and a diameter of 6cm, which is hydrophobic on the surface and to which GeNPs are attached, was used as a light absorbing layer and a heat accumulating layer, and the size of the water absorbing layer filter paper was fixed at 2cm × 2cm, and the salinity of NaCl solution (70g) was reduced from the initial 10 wt%, 5 wt% and 1 wt% to 8.1 wt%, 4.3 wt% and 0.8 wt% under one sunlight irradiation for 7.5 hours continuously. Furthermore, the salinity decline over time can be well fitted to an exponential function (fig. 17).

By comparing the mass of CF before and after the salt extraction experiment, the mass of the dried salt evaporated from NaCl solutions with initial concentrations of 10 wt%, 5 wt% and 1 wt%, respectively, were 1.321, 0.331 and 0.045g, respectively (FIG. 8 (B)).

For the salt extraction device shown in fig. 1(B), assuming that diffusion of salt from the filter paper to the lower solution is negligible and that condensed water adhering to the inner surface of the glass sheet is negligible compared to the lower square-shaped solution, then

At t 0, the initial salt concentration is equal to 10 wt%, at 5 wt% and 1 wt%, the theoretical value of a is equal to 11.11(═ 10/90 × 100), 5.26 (═ 5/95 × 100) and 1.01(═ 1/99 × 100), respectively, close to the value of a (experimental value) shown in the fitted equation. In addition, fitting equations based on exponential form and m in the experiment_wThe initial salt concentration was 10 wt%, 5 wt% and 1 wt%, the mass of salt was 70 x 0.90, 70 x 0.95 and 70 x 0.99g, respectively, and the R-value (i.e. evaporation rate) was calculated to be 1.70, 1.40 and 2.01gh^-1This is compared with the average evaporation rate R of 1.42gh of water obtained when the filter paper size is 2cm × 2cm and the initial salt concentration is 3.5 wt%^-1Close (blue curve in fig. 7 (B)); dividing the mass of dry salt by the mass of the total solution (70g) (the total water volume remains constant during evaporation due to the reflux of the condensed water) is almost the same as the reduced salinity as measured by the salinity meter in fig. 8(a), and there is a slight deviation attributable to the accumulation of salt on the filter paper, which solutes do not account for the dry salt mass.

Conclusion

This example presents a novel absorber and collector based on CF for solar evaporation and salt extraction. In the experiment, the CF surface was first oxidized to black CuO, then dip-coated with colloidal GeNPs to enhance infrared absorption, and finally treated with TCPFOS to make its surface hydrophobic. GeNPs are synthesized by a high-energy ball milling method, surface passivation modification is carried out by 10-UD-ol, uniform colloidal suspension is formed in THF, the GeNPs have an irregular flaky polycrystalline structure, and the grain diameter is mainly distributed between 100nm and 400 nm. Oxidized CF of different thickness and pore size used in this project, surface hydrophobic and attached with GeNPs, can absorb over 95% of am1.5g solar irradiance spectrum, the absorbed light is converted into heat energy, heating the underlying water absorbing filter paper, thereby generating steam, which is then vented through the interconnected pores inside the CF. In addition, the CF area is about 7 times the area of the filter paper due to the hydrophobicity and high thermal conductivity of CF (the thermal conductivity of CF with a pore size of 51 μm is 65.3W m^-1K^-1) The heat generated at the periphery of the CF may be concentrated to the central evaporated region. After the PMMA plate is covered to reduce the heat convection loss, the central temperature of CF with the aperture of 51 mu m can reach 74.3 ℃ under the irradiation of 1 sun, and the evaporation rate is as high as 3.2kg m^-2h^-1The light-to-steam conversion efficiency was 29.1%, which is similar to the efficiency of previously studied thermal solar evaporators with steam temperatures of about 80 ℃. Furthermore, when the salt solution is evaporated in a closed system with recycled condensed water, dry salt crystals may form and accumulate on the CF surface due to the high evaporation rate and hydrophobic surface of the CF caused by the heat-concentrating structure. Because the total water quantity is kept unchanged, the solution gradually realizes desalination. When the experiment used oxidized CF having a pore size of 195 μm and a diameter of 6cm, which was hydrophobic on the surface and to which GeNPs were attached, as a light absorbing layer and a heat accumulating layer, and the size of the water absorbing layer filter paper was fixed at 2 cm. times.2 cm, 70g of NaCl solution was irradiated with one sun for 7.5 hours, the salinity of the solution was reduced from the initial 10 wt% to 8.1 wt%, and 1.321 g of dry salt could be obtained. In contrast to the electrodialysis and traditional salt field methods of today, the salt extraction method proposed in this example is solar driven and can easily extract dry salt from a salt solution without having to evaporate all of the water.

Claims

1. A heat-gathering solar seawater desalination structure based on hydrophobic oxidized foamy copper is characterized by comprising: a water absorption layer (1), a heat insulation layer (3), a light absorption layer and a heat accumulation layer (4); wherein both ends of the water absorbing layer (1) penetrate through the heat insulating layer (3) and then are immersed in the water body (2), the light absorbing layer and the heat accumulating layer (4) are positioned above the heat insulating layer (3), and the middle part of the water absorbing layer (1) is positioned between the heat insulating layer (3) and the light absorbing layer and the heat accumulating layer (4); the heat insulation layer (3) is filled with the water storage device (6) to isolate the water body (2) and the air; the light absorbing layer and the heat accumulating layer (4) are made of oxidized foam copper with a surface hydrophobic and a GeNPs coating attached.

2. The heat-concentrating solar seawater desalination structure based on hydrophobic oxidized foam copper as claimed in claim 1, wherein: the lower part of the middle part of the water absorption layer (1) is tightly attached to the heat insulation layer (3), and the upper part of the middle part of the water absorption layer (1) is tightly attached to the light absorption layer and the heat accumulation layer (4); the water absorbing layer (1) is made of filter paper or cloth material with better water absorption; the heat insulation layer (3) is made of polystyrene foam.

3. A heat-gathering solar seawater desalination structure based on hydrophobic oxidized foamy copper is characterized by comprising: a water absorption layer (1), a heat insulation layer (3), a light absorption layer, a heat accumulation layer (4) and a covering device (5); wherein both ends of the water absorbing layer (1) penetrate through the heat insulating layer (3) and then are immersed in the water body (2), the light absorbing layer and the heat accumulating layer (4) are positioned above the heat insulating layer (3), and the middle part of the water absorbing layer (1) is positioned between the heat insulating layer (3) and the light absorbing layer and the heat accumulating layer (4); the heat insulation layer (3) is positioned on the surface of the water body (2), the surface area of the heat insulation layer (3) is smaller than that of the water body (2), and part of the water body (2) is exposed; the top of the water storage device (6) is provided with a covering device (5), and the covering device (5) completely covers the water storage device (6); the light absorbing layer and the heat accumulating layer (4) are made of oxidized foam copper with a surface hydrophobic and a GeNPs coating attached.

4. The heat-concentrating solar seawater desalination structure based on hydrophobic oxidized foam copper as claimed in claim 3, characterized in that: the lower part of the middle part of the water absorption layer (1) is tightly attached to the heat insulation layer (3), and the upper part of the middle part of the water absorption layer (1) is tightly attached to the light absorption layer and the heat accumulation layer (4); the water absorbing layer (1) is made of filter paper or cloth material with better water absorption; the heat insulation layer (3) is polystyrene foam; the covering device (5) is a glass sheet or a PMMA cover.

5. The heat-concentrating solar seawater desalination structure based on hydrophobic oxidized foam copper as claimed in claim 3, characterized in that: the covering device (5) is placed in an inclined angle.

6. The method for desalinating the heat-concentrating solar seawater desalination structure based on the hydrophobic oxidized foam copper according to claim 1, characterized by comprising the following steps:

step 1, using copper foam oxide with a hydrophobic surface and a GeNPs coating as a light absorption layer and a heat accumulation layer (4), and concentrating heat generated at the periphery of an evaporation area to the evaporation area at the center of the light absorption layer and the heat accumulation layer (4) when the light absorption area is larger than the water evaporation area; the preparation method of the copper oxide foam with the hydrophobic surface and the GeNPs coating is as follows: firstly, oxidizing the surface of the foam copper into black CuO, then adhering and covering the surface of the black CuO with GeNPs sol, and finally treating the foam copper subjected to surface oxidation and sol adhesion with trichlorosilane to make the surface hydrophobic;

step 2, after the light absorption layer and the heat accumulation layer (4) absorb the solar heat, transferring the heat to the water absorption layer (1) to generate steam, and discharging the steam through mutually communicated holes in the copper foam in the light absorption layer and the heat accumulation layer (4);

7. The heat-concentrating solar seawater desalination method based on hydrophobic oxidized foam copper as claimed in claim 6, characterized in that: in the step 1, the light absorption area is the size of the oxidized foamy copper with the hydrophobic surface and the GeNPs coating, and the water evaporation area is the size of the water absorption layer (1).

8. A method for desalinating a heat-concentrating solar seawater desalination structure based on hydrophobic copper oxide foam according to claim 3, characterized by comprising the following steps:

and 3, condensing the steam after the steam reaches the covering device (5) to form condensed fresh water, collecting part of the condensed fresh water through a collecting device, and refluxing the rest of the condensed fresh water to the water body (2) along the inclined direction of the covering device (5).

9. The desalination method of the heat-concentrating solar seawater desalination structure based on hydrophobic oxidized foam copper, which is characterized by comprising the following steps of: the inclination angle of the covering device (5) in the step 3 is 10 degrees.