A photothermal evaporator based on nickel-cobalt bimetallic oxide

Abstract

The present invention discloses a photothermal evaporator based on nickel-cobalt bimetallic oxide, comprising a paraffin heat storage layer, a gel water conductive layer and a photothermal conversion layer; further comprising a polyethylene foam shell, wherein the paraffin heat storage layer, the gel water conductive layer and the photothermal conversion layer are sequentially placed in the polyethylene foam shell with an opening at the top; the photothermal conversion layer is adhered to the gel water conductive layer, a through hole I extending longitudinally is provided in the paraffin heat storage layer, and a through hole II corresponding to the through hole I is provided at the bottom of the polyethylene foam shell; further comprising a water transmission medium, wherein one end of the water transmission medium contacts the gel water conductive layer, and the other end of the water transmission medium sequentially passes through the through hole I and the through hole II and extends out of the through hole II. When the photothermal evaporator floats on the liquid surface, the other end of the water transmission medium sequentially passes through the through hole I and the through hole II and extends into the water body.

Description

Technical Field

[0001] The invention relates to a photothermal evaporator based on nickel-cobalt bimetallic oxide. Background Art

[0002] The shortage of fresh water resources has led to the emergence of many new methods and equipment for producing fresh water in recent years. Among them, the most common technologies include distillation and reverse osmosis, which are often used to obtain pure water from seawater or even sewage. However, traditional seawater desalination technology has problems such as high energy consumption and high cost. In order to obtain water resources more economically and efficiently, a promising solar desalination technology that uses sustainable energy for large-scale water purification has emerged. Solar-driven evaporation, which converts solar energy into thermal energy at the air / liquid interface, is considered to be one of the most promising sustainable solutions to water shortages. With its excellent photothermal conversion efficiency and evaporation rate, photothermal desalination devices have attracted great interest from researchers in the fields of seawater desalination, power generation, carbon dioxide capture, heavy metal recovery, steam sterilization, oil-water separation, etc.

[0003] In solar-driven water evaporation, the design of photothermal materials, such as semiconductors, polymers, carbon-based materials, and plasmonic materials, is crucial for improving heat conversion efficiency. Metal oxide semiconductors (MOS) hold great promise as photothermal materials in solar desalination research. These materials possess excellent photothermal conversion capabilities and broadband light absorption, benefiting from their high environmental stability, tunable band gap, non-toxicity, and low cost. They are frequently used in solar evaporation research. However, during continuous seawater evaporation, salt deposition can occur on the surface of the evaporator, impairing light absorption and hindering water transport, leading to a sharp decline in evaporation performance. Furthermore, current photoabsorbers are highly sensitive to solar radiation intensity, and interfacial evaporation systems suffer from poor energy management under intermittent solar radiation, reducing overall photothermal conversion efficiency and hindering their practical application. With diminished solar radiation intensity, the heat is insufficient to maintain an efficient evaporation process, resulting in a significant decrease in evaporation performance. Even under abundant sunlight, this heat is inevitably lost to the environment or water, resulting in energy waste. Summary of the Invention

[0004] Purpose of the invention: The purpose of the present invention is to provide a photothermal evaporator that is not affected by intermittent light intensity and can continuously perform interfacial evaporation under no light conditions.

[0005] Technical solution: The photothermal evaporator based on nickel-cobalt bimetallic oxide described in the present invention includes a paraffin heat storage layer, a gel water conductive layer and a photothermal conversion layer; it also includes a polyethylene foam shell, and the paraffin heat storage layer, the gel water conductive layer and the photothermal conversion layer are placed in the polyethylene foam shell with an open top in sequence; the photothermal conversion layer is adhered to the gel water conductive layer, and the paraffin heat storage layer is provided with a through hole I extending in the longitudinal direction, and the bottom of the polyethylene foam shell is provided with a through hole II corresponding to the through hole I; it also includes a water transfer medium (water conductive core), one end of the water transfer medium is in contact with the gel water conductive layer, and the other end of the water transfer medium passes through the through hole I and the through hole II in sequence and extends out of the through hole II. When the photothermal evaporator floats on the liquid surface, the other end of the water transfer medium passes through the through hole I and the through hole II in sequence and extends into the water body.

[0006] Wherein, the aperture of the through hole I is not less than 3 mm.

[0007] Wherein, the water transport medium is cotton or dust-free paper.

[0008] The thickness of the paraffin heat storage layer is 1 cm, and its phase change temperature is 52-54°C.

[0009] Among them, the photothermal conversion layer is prepared by the following method, specifically: weighing nickel chloride, cobalt chloride, ammonium chloride and sodium hydroxide and dissolving them in deionized water, sealing the mixed solution and placing it in an oven for heating; after heating, naturally cooling to room temperature, washing with deionized water and ethanol, and then freeze-drying to obtain nickel cobalt bimetallic hydroxide; calcining the nickel cobalt bimetallic hydroxide at high temperature in air to obtain black nickel cobalt bimetallic oxide powder; loading the nickel cobalt bimetallic oxide powder on dust-free paper, and drying it in a vacuum drying oven to obtain the photothermal conversion layer.

[0010] The black nickel-cobalt bimetallic oxide prepared by the present invention has a regular nanoflower structure in its microscopic morphology. The nanoflower structure facilitates the refraction and reabsorption of sunlight therein. When the size of the nanostructure matches the wavelength of the incident light, the refractive index properties change, and the light is trapped in the nanostructure and then reflected and absorbed multiple times, thereby improving the light absorption efficiency and further improving the photothermal conversion efficiency.

[0011] Among them, the mass ratio of nickel chloride, cobalt chloride, ammonium chloride and sodium hydroxide is 35.5-35.6:142.7-142.8:214:55.

[0012] The reaction temperature in the oven was 55° C., and the reaction time was 15 hours.

[0013] The nickel-cobalt double hydroxide was calcined at a high temperature in an air environment at a heating rate of 5°C / min, a calcination temperature of 350°C, and a reaction time of 2h.

[0014] The gel water-conducting layer is a calcium alginate hydrogel, which is prepared by the following method: dissolving sodium alginate in deionized water to form a sodium alginate solution, completely soaking the melamine sponge in the sodium alginate solution, and freezing it at -10°C; soaking the frozen sodium alginate sponge in a calcium chloride solution with a concentration of 5 mg / mL overnight to form a calcium alginate hydrogel. The sodium alginate sponge is soaked in the calcium chloride solution, and the Na in the sodium alginate is + Ca + Replaced, and then the calcium alginate molecule is replaced by Ca + The melamine sponge acts as a skeleton support in the system. The thickness of the calcium alginate hydrogel is 4 to 5 mm.

[0015] The photothermal conversion layer of the present invention uses a nickel-cobalt bimetallic oxide with a regular nanoflower structure in its microscopic morphology. The flower-like lamellar structure refracts and repeatedly absorbs incident light multiple times, giving the photothermal conversion layer excellent light absorption and photothermal conversion capabilities. Calcium alginate hydrogel has excellent hydrophilicity and a rich pore structure. The calcium alginate hydrogel utilizes the capillary action of its rich pore structure to continuously transport water and reduce the evaporation enthalpy, thereby greatly promoting water evaporation. While transporting water to the evaporation interface of the photothermal layer through the capillary force of the gel, it intercepts salt, thereby effectively avoiding the deposition of salt on the photothermal evaporation surface during the interfacial evaporation process.

[0016] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: the evaporator of the present invention can be used for seawater desalination, and the evaporator of the present invention effectively enhances its photothermal absorption capacity through the synergistic effect of the multi-layer structure, thereby improving the evaporation efficiency, and can also effectively prevent the accumulation of salt in seawater on the photothermal evaporation surface, so that it has stable cyclic evaporation performance; finally, the three-layer structure with phase change heat storage material can also store a large amount of photothermal energy from solar illumination as latent heat, and release it in the absence of sunlight, reducing the adverse effects of intermittent photothermal energy and ensuring sustainable interface evaporation under no light conditions; the evaporator of the present invention has good photothermal evaporation performance and can ensure the continuous evaporation of seawater. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 (a) is a scanning electron microscope image of the Co / Ni bimetallic oxide synthesized with a Ni:Co molar ratio of 1:4; (b) is an X-ray diffraction pattern; (c) is a transmission energy spectrum;

[0018] Figure 2 Schematic diagram of the structure of the photothermal evaporator of the present invention;

[0019] Figure 3 This is the contact angle test of the nickel-cobalt bimetallic oxide photothermal film in Example 1;

[0020] Figure 4 This is a graph showing the mass change of a nickel-cobalt bimetallic oxide evaporator with or without a heat storage layer under the same solar illumination intensity during a light and dark evaporation cycle test.

[0021] Figure 5 This is a comparison of the salt deposition resistance performance of nickel-cobalt bimetallic oxide evaporators with and without a gel water-conducting layer; the upper figure is the evaporator of Example 1, and the lower figure is the evaporator without a gel water-conducting layer;

[0022] Figure 6 The scanning electron microscope images of the metal oxides obtained in Examples 1 to 6 are shown;

[0023] Figure 7 is the light absorption capacity of the metal oxides obtained in Examples 1 to 6 in the solar spectrum range (200 to 2500 nm). DETAILED DESCRIPTION

[0024] like Figure 2 As shown, the present invention is a photothermal evaporator based on nickel-cobalt bimetallic oxide, comprising a paraffin heat storage layer, a gel water conductive layer and a photothermal conversion layer; the evaporator also includes a polyethylene foam shell, the paraffin heat storage layer, the gel water conductive layer and the photothermal conversion layer are sequentially placed in the polyethylene foam shell with an open top, and the photothermal conversion layer is located on the top of the polyethylene foam shell; the photothermal conversion layer is adhered to the gel water conductive layer, the paraffin heat storage layer is provided with a through hole I extending longitudinally, and the bottom of the polyethylene foam shell is provided with a through hole II corresponding to the through hole I; it also includes a water transfer medium (water conductive core), one end of the water transfer medium is in contact with the gel water conductive layer, and the other end of the water transfer medium sequentially passes through through hole I and through hole II and extends out of through hole II. When the photothermal evaporator floats on the liquid surface, the other end of the water transfer medium sequentially passes through through hole I and through hole II and extends into the water body. To ensure the water supply effect, the aperture of through hole I and through hole II is 3mm; the water transfer medium can be cotton or dust-free paper. Based on capillary action, the water transfer medium acts as a water transfer channel to absorb water into the gel water conductive layer and then transfer it to the photothermal conversion layer.

[0025] The thickness of the paraffin heat storage layer is 1 cm, and its phase change temperature is 52-54°C. The phase change temperature of the paraffin heat storage layer is slightly higher than the interface evaporation temperature. This can ensure that sufficient energy can be stored on the one hand, and the overall structure will not collapse on the other hand.

[0026] Example 1

[0027] The preparation method of the photothermal evaporator based on nickel-cobalt bimetallic oxide of the present invention comprises the following steps:

[0028] (1) Preparation of light-to-heat conversion layer:

[0029] (1.1) Weigh 550 mg of sodium hydroxide and dissolve it in 200 mL of deionized water to obtain a sodium hydroxide solution.

[0030] (1.2) Weigh 355 mg of nickel chloride, 1427.58 mg of cobalt chloride, and 2140 mg of ammonium chloride, dissolve them in the prepared sodium hydroxide solution, and stir for 10 min. Seal the mixture and place in an oven at 55°C for 15 h.

[0031] (1.3) After cooling naturally to room temperature, washing with deionized water and ethanol, and then freeze-drying at -60°C for 48 hours to obtain nickel-cobalt double hydroxide;

[0032] (1.4) The nickel-cobalt double hydroxide was heated to 350°C in a tube furnace at a rate of 5°C / min and maintained at this temperature for 2 hours. After calcination, the temperature was naturally cooled to obtain a black nickel-cobalt double hydroxide powder;

[0033] (1.5) Loading nickel-cobalt bimetallic oxide powder on dust-free paper and drying in a vacuum drying oven at 60° C. for 2 h (vacuum drying fixes the nickel-cobalt bimetallic oxide powder on the dust-free paper) to obtain a light-to-heat conversion layer;

[0034] (2) Preparation of calcium alginate hydrogel water-conducting layer:

[0035] (2.1) Weigh 50 mg of sodium alginate and add it to 10 mL of deionized water. Stir for 1 hour to form a sodium alginate solution.

[0036] (2.2) Completely immerse the melamine sponge in sodium alginate solution and freeze it into a cylinder at -10°C;

[0037] (2.3) Soak the frozen sodium alginate sponge in a 5 mg / mL calcium chloride solution overnight to form a calcium alginate hydrogel;

[0038] (3) Adhere one side of the moistened light-to-heat conversion layer dust-free paper to the upper surface of the calcium alginate hydrogel;

[0039] (4) After the paraffin wax is melted, it is placed in a mold for solidification to form a cylinder with the same bottom area as the photothermal conversion layer, and a through hole is opened at the center of the paraffin heat storage layer. The paraffin heat storage layer, the gel water conductive layer and the photothermal conversion layer are stacked in a polyethylene shell in order from bottom to top to obtain a photothermal evaporator.

[0040] The seawater desalination performance of the evaporator obtained in Example 1 was analyzed. Under one illumination condition, the photothermal evaporation temperature could reach 74.1°C (the evaporator has a three-layer structure, with interface evaporation at the top, the top temperature is the highest, and the bottom and middle temperatures do not reach the phase transition temperature of paraffin wax), and the evaporation rate reached 1.51 kg m-2 h -1 , the solar-steam energy conversion efficiency reached 96.02%.

[0041] The obtained nickel-cobalt bimetallic oxide was analyzed by X-ray energy dispersive spectrometer, and the element composition thereof was: Co: 39.75 wt %, Ni: 10.24 wt %, and O: 27.67 wt %.

[0042] from Figure 1 In a, it can be shown that the nickel-cobalt bimetallic oxide is a regular nanoflower structure; Figure 1 b is the X-ray diffraction pattern of the nickel-cobalt bimetallic oxide obtained in Example 1. After calcination, the peak positions of the nickel-cobalt bimetallic oxide are located at 31.0°, 36.6°, 44.5°, 58.9°, and 64.8°, corresponding to the (220), (311), (400), (511), and (440) crystal planes, respectively, proving that the obtained sample is a nickel-cobalt bimetallic oxide with good crystallinity. Figure 1 c is the transmission energy spectrum, where green represents the Co element, red represents the Ni element, and blue represents the O element, which proves that the elements in the nickel-cobalt bimetallic oxide are evenly distributed, and further proves that the oxide material is fully oxidized and has good thermal stability.

[0043] Figure 3 The contact angle test of the nickel-cobalt bimetallic oxide photothermal film prepared in Example 1 shows that the liquid droplets are completely absorbed within 1.7 seconds after contacting the surface of the photothermal evaporation film, proving that the photothermal evaporation film has good hydrophilicity, which is conducive to the rapid diffusion of water on the surface of the material and the escape of vapor.

[0044] The photothermal evaporation performance test of the evaporator of Example 1 was carried out. Figure 4 The graph shows the mass change of the dark evaporation cycle test under one solar illumination intensity for evaporators with and without a heat storage layer. The photothermal evaporation performance of the evaporator in Example 1 far exceeds that of water, indicating that the evaporator of the present invention has excellent photothermal seawater evaporation performance. The evaporation rate of the evaporator without a heat storage layer is 0.45 kg m -2 h -1 After adding the heat storage layer, the evaporation rate of the evaporator can reach 0.62 kg m -2 h -1 , the performance is improved by 37.76%; compared with pure water 0.08kg m -2 h -1 The evaporation rate increased by 68.25%.

[0045] Figure 5This chart compares the salt deposition resistance of an evaporator consisting solely of a nickel-cobalt bimetallic oxide photothermal film and a heat storage layer (without a gel water-conducting layer) and the evaporator of Example 1. Under a given light intensity, salt deposits formed on the surface of the nickel-cobalt bimetallic oxide photothermal film of the evaporator without a gel water-conducting layer within four hours, while no salt deposits remained on the surface of the nickel-cobalt bimetallic oxide photothermal film of Example 1. This demonstrates the excellent salt deposition resistance of the evaporator of the present invention. The heat storage photothermal evaporator of the present invention can be well integrated with interface evaporation materials to ensure full utilization of heat.

[0046] Example 2

[0047] The preparation method of the photothermal evaporator in Example 2 is the same as that in Example 1, with the only difference being that when preparing the photothermal conversion layer, the metal oxide is prepared by using nickel and cobalt in a molar ratio of 5:0.

[0048] Example 3

[0049] The preparation method of the photothermal evaporator in Example 3 is the same as that in Example 1, with the only difference being that when preparing the photothermal conversion layer, a nickel-cobalt bimetallic oxide is prepared with a molar ratio of nickel to cobalt of 4:1.

[0050] Example 4

[0051] The preparation method of the photothermal evaporator in Example 4 is the same as that in Example 1, with the only difference being that when preparing the photothermal conversion layer, a nickel-cobalt bimetallic oxide is prepared with a nickel-cobalt molar ratio of 3:2.

[0052] Example 5

[0053] The preparation method of the photothermal evaporator in Example 5 is the same as that in Example 1, with the only difference being that when preparing the photothermal conversion layer, a nickel-cobalt bimetallic oxide is prepared with a nickel-cobalt molar ratio of 2:3.

[0054] Example 6

[0055] The preparation method of the photothermal evaporator in Example 6 is the same as that in Example 1, with the only difference being that when preparing the photothermal conversion layer, the metal oxide is prepared by using a nickel:cobalt molar ratio of 0:5.

[0056] pass Figure 6 It can be seen that flower-shaped samples can only be obtained when the molar ratio of nickel chloride to cobalt chloride is 1:4.

[0057] pass Figure 7 It can be seen that the flower-shaped sample with a molar ratio of nickel chloride to cobalt chloride of 1:4 exhibits excellent light absorption ability in the solar spectrum range (200-2500nm), with an average light absorption rate exceeding 95%.

[0058] The evaporator of the present invention combines a photothermal conversion layer with good photothermal conversion performance and wide light band absorption with a calcium alginate hydrogel with a porous structure. Water is transported to the evaporation interface of the photothermal layer through the capillary force of the gel, while intercepting salt while supplying water to avoid the occurrence of salt deposition. At the same time, combined with the phase change heat storage material paraffin, a unique three-layer structure is formed, which enables the entire device to continuously and efficiently produce clean water under unstable solar radiation.

Claims

1. A photothermal evaporator based on nickel-cobalt bimetallic oxide, characterized by: It includes a paraffin heat storage layer, a gel water conductive layer and a photothermal conversion layer; it also includes a polyethylene foam shell, wherein the paraffin heat storage layer, the gel water conductive layer and the photothermal conversion layer are sequentially placed in the polyethylene foam shell with an opening at the top; the photothermal conversion layer is adhered to the gel water conductive layer, the paraffin heat storage layer is provided with a through hole I extending in the longitudinal direction, and the bottom of the polyethylene foam shell is provided with a through hole II corresponding to the through hole I; it also includes a water transmission medium, one end of the water transmission medium contacts the gel water conductive layer, and the other end of the water transmission medium sequentially passes through the through hole I and through hole II and extends out of the through hole II. When the photothermal evaporator floats on the liquid surface, the other end of the water transmission medium sequentially passes through the through hole I and through hole II and then extends into the water body; the gel water conductive layer is a calcium alginate hydrogel; The photothermal conversion layer is prepared by the following method: nickel chloride, cobalt chloride, ammonium chloride, and sodium hydroxide are weighed and dissolved in deionized water, the mixed solution is sealed and placed in an oven for heating; after heating, it is naturally cooled to room temperature, washed with deionized water and ethanol, and then freeze-dried to obtain nickel-cobalt bimetallic hydroxide; the nickel-cobalt bimetallic hydroxide is calcined at high temperature in air to obtain nickel-cobalt bimetallic oxide powder; the nickel-cobalt bimetallic oxide powder is loaded on dust-free paper, and dried in a vacuum drying oven to obtain the photothermal conversion layer; Among them, the mass ratio of nickel chloride, cobalt chloride, ammonium chloride and sodium hydroxide is 35.5~35.6:142.7~142.8:214:55; the reaction temperature heated in the oven is 55°C, and the reaction time is 15 hours; nickel cobalt double hydroxide is calcined at high temperature in an air environment, with a heating rate of 5°C / min, a calcination temperature of 350°C, and a reaction time of 2 hours.

2. The photothermal evaporator based on nickel-cobalt bimetallic oxide according to claim 1, characterized in that: The aperture of the through hole I is not less than 3 mm.

3. The photothermal evaporator based on nickel-cobalt bimetallic oxide according to claim 1, characterized in that: The water transport medium is cotton or dust-free paper.

4. The photothermal evaporator based on nickel-cobalt bimetallic oxide according to claim 1, characterized in that: The thickness of the paraffin heat storage layer is 1 cm, and its phase change temperature is 52-54°C.

5. The photothermal evaporator based on nickel-cobalt bimetallic oxide according to claim 1, characterized in that: The calcium alginate hydrogel is prepared by the following method: sodium alginate is dissolved in deionized water to form a sodium alginate solution, a melamine sponge is completely immersed in the sodium alginate solution, and then frozen at -10°C; the frozen sodium alginate sponge is soaked in a calcium chloride solution with a concentration of 5 mg / mL overnight to form a calcium alginate hydrogel.

6. The photothermal evaporator based on nickel-cobalt bimetallic oxide according to claim 5, characterized in that: The thickness of calcium alginate hydrogel is 4~5mm.

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