Porous carbon hydrogels for efficient solar interfacial evaporation

Abstract

The present invention relates to the field of solar evaporators, and specifically to a porous carbon hydrogel for efficient solar interface evaporation. The evaporator is composed of a hydrogel and oxygen-rich porous carbon. The hydrogel forms a cross-linked network structure with glucomannan and polyvinyl alcohol. The oxygen-rich porous carbon is uniformly incorporated into the cross-linked network structure of the hydrogel. The cross-linked network structure of the hydrogel provides continuous and interconnected capillary water transport channels, and the oxygen-rich porous carbon also provides additional water transport channels. The present invention can absorb and utilize more sunlight to convert it into thermal energy, reduce energy loss, and improve energy utilization efficiency. The present invention reduces the energy required for the evaporation of water molecules. The present invention forms a salt concentration gradient in the vertical direction during the evaporation process, promotes the absorption and diffusion of salt ions, and achieves discharge balance, thereby achieving salt resistance and maintaining the evaporation performance of the evaporator.

Description

Technical Field

[0001] The invention relates to the field of solar evaporators, in particular to porous carbon hydrogels for efficient solar interface evaporation. Background Art

[0002] However, traditional seawater desalination technologies such as reverse osmosis, multi-stage flash evaporation, and multi-effect evaporation have problems such as high fossil energy consumption, high greenhouse gas emissions, and complex system structures [3]. There is an urgent need to develop low-carbon, environmentally friendly, and simple water purification technologies to solve the problem of water shortage. In recent years, the research on seawater desalination by solar-coupled interfacial evaporation has been widely developed by scientific research teams due to its advantages of zero cost, low energy consumption, and no pollution, and is used to produce environmentally friendly and pure distilled water.

[0003] In recent years, the advantage of interfacial heating in solar interfacial evaporation over water heating is that the absorber concentrates heat at the evaporation interface, which is used more for evaporating water rather than heating it, thus reducing heat loss to the water and lowering the solar energy consumption required for evaporation. Achieving efficient solar interfacial evaporation relies primarily on excellent energy management, a low evaporation energy barrier, and rapid material transport. However, existing methods, such as carbon-based solar evaporators, nanomaterial-coated evaporators, and dip-coated thin-film evaporators, generally suffer from insufficient energy management, high evaporation energy barriers, and low material transport efficiency. Furthermore, they require external insulation and floating devices to suppress heat loss to the water and control the evaporator to interface heating, resulting in a relatively complex structure. Therefore, developing efficient and economical solar evaporators is the current goal of many research teams. Summary of the Invention

[0004] Based on this, it is necessary to provide a porous carbon hydrogel for efficient solar interfacial evaporation to address the existing technical problems.

[0005] In order to solve the problems of the prior art, the technical solution adopted by the present invention is:

[0006] A porous carbon hydrogel for efficient solar interfacial evaporation, wherein the porous carbon hydrogel is composed of a hydrogel matrix and oxygen-rich porous carbon, wherein the hydrogel matrix is formed into a cross-linked network structure by glucomannan and polyvinyl alcohol, and the oxygen-rich porous carbon is uniformly doped in the cross-linked network structure of the hydrogel matrix;

[0007] The cross-linked network structure of the porous carbon hydrogel provides continuous and interconnected capillary water transport channels, and the oxygen-enriched porous carbon provides additional water transport channels;

[0008] The hydrophilic groups in the oxygen-enriched porous carbon, deacetylated glucomannan and polyvinyl alcohol form strong hydrogen bonds with some water molecules, thereby weakening the hydrogen bonds between free water molecules and reducing the energy required for water evaporation;

[0009] The oxygen-rich porous carbon absorbs free water in the hydrogel through its abundant pore structure and evaporates it into water vapor through photothermal conversion and diffuses it;

[0010] The water transfer channel in the evaporator forms a salt concentration gradient in the vertical direction.

[0011] Furthermore, the preparation method of the oxygen-rich porous carbon is as follows:

[0012] S1, taking 100 ml of 100 g / L Chlorella solution and mixing it with 33.3 ml of methanolic choline chloride DES solution, hydrothermally pretreated at 160 ° C for 10 min, taking the solid phase to obtain algal residue and freeze-drying it;

[0013] S2, adding activator KOH in a ratio of 1:1 to freeze-dried algae residue and placing it in a tube furnace, heating it to 600 °C under an inert gas atmosphere and pyrolyzing it for 2 hours to obtain algae residue biochar;

[0014] S3, adding an appropriate amount of hydrochloric acid to the algae residue biochar and washing it until it becomes neutral to obtain oxygen-rich porous carbon.

[0015] Furthermore, the preparation method of the deacetylated glucomannan is as follows:

[0016] S1, 30 g of KGM powder and 200 ml of 50% ethanol solution were mixed, and the mixed suspension was stirred and swelled at 50 °C for 30 min (150 r / min);

[0017] S2, then add Na2CO3 solution and react at 40℃ for 24 hours. After deacetylation, wash with ethanol aqueous solution (50%, 75% and 95%) three times to remove excess Na2CO3, and finally wash with anhydrous ethanol;

[0018] S3, evaporate the excess ethanol in a fume hood and then dry under vacuum at 40 °C for 6 h to obtain powdered deacetylated KGM.

[0019] Furthermore, the preparation method of the porous carbon hydrogel is as follows:

[0020] 4 g of polyvinyl alcohol, 0.5 g of deacetylated glucomannan, 0.1 g of oxygen-enriched porous carbon, and 0.52 ml of glutaraldehyde crosslinker were added to a beaker and placed in an ultrasonic machine for 4 hours to form a homogeneous solution, which was then allowed to stand in an oven at 70°C overnight to obtain a porous carbon hydrogel.

[0021] Furthermore, the transparent steam collecting device is an acrylic plate.

[0022] Furthermore, the hydrophobic coating is a silicon dioxide coating.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] Firstly, the present invention can absorb and utilize more sunlight to convert it into heat energy, reduce energy loss, and improve energy utilization efficiency;

[0025] Secondly, the present invention reduces the energy required for evaporation of water molecules, so that solar energy with low heat flux density can evaporate more water;

[0026] Thirdly, the present invention forms multi-level pores and continuous water channels in horizontal and vertical directions, so that a salt concentration gradient is formed in the vertical direction of the evaporator during the evaporation process, thereby promoting the absorption and diffusion of salt ions to achieve discharge balance, achieving salt resistance and maintaining the evaporation performance of the evaporator. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic diagram of the structural principle of the present invention;

[0028] The numbers in the figure are: 1-oxygen-rich porous carbon; 2-continuous water channels; 3-cross-linked network. DETAILED DESCRIPTION

[0029] In order to further understand the features, technical means, specific objectives and functions achieved by the present invention, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0030] The porous carbon hydrogel for efficient solar interface evaporation of the present invention is Figure 1 As shown, the porous carbon hydrogel is composed of a hydrogel matrix and oxygen-rich porous carbon. The hydrogel matrix is composed of glucomannan and polyvinyl alcohol to form a cross-linked network structure, and the oxygen-rich porous carbon is uniformly incorporated into the cross-linked network structure of the hydrogel matrix.

[0031] The cross-linked network structure of the hydrogel provides continuous and interconnected capillary water transport channels, and the oxygen-rich porous carbon also provides additional water transport channels;

[0032] The hydrophilic groups in the oxygen-enriched porous carbon, deacetylated glucomannan and polyvinyl alcohol form strong hydrogen bonds with some water molecules, thereby weakening the hydrogen bonds between free water molecules and reducing the energy required for water evaporation;

[0033] The oxygen-rich porous carbon absorbs free water in the hydrogel through its abundant pore structure and evaporates it into water vapor through photothermal conversion and diffuses it;

[0034] An acrylic plate made of an organic material with strong weather resistance, good processing performance and the highest light transmittance is placed above the porous carbon hydrogel as a steam condensation device. It is coated with a silica hydrophobic coating to allow steam to flow back to the bottom without blurring the light-transmitting layer. At the same time, a certain greenhouse effect is generated inside the device to heat the volume of water, fully improving energy utilization efficiency.

[0035] The interconnected capillary channels formed by the polymer network inside the hydrogel are excellent water transport structures for solar evaporators. The continuous water channels form a salt concentration gradient in the vertical direction and transport salt ions downward to achieve salt resistance. The polymer network structure limits the convective heat transfer of water molecules, reducing their heat flux and thus achieving stable energy management. At the same time, the hydrophilic polymer chains can accelerate the evaporation of water in the hydrogel, but their low absorbance prevents the hydrogel from generating enough steam when receiving solar energy.

[0036] Existing studies have mostly incorporated materials such as polypyrrole, graphene oxide, and carbon nanotubes into hydrogels as solar absorbers. However, their high cost and hydrophobic properties lead to a decrease in evaporator efficiency. The high porosity of microalgae-based oxygen-rich porous carbon is conducive to fully capturing solar energy, and its abundant hydrophilic groups can accelerate the evaporation of water molecules. At the same time, its multi-level pores can provide additional water transport channels for hydrogels, forming continuous water channels with the hydrogel polymer network.

[0037] Therefore, the present invention forms a porous carbon hydrogel solar evaporator by dispersing oxygen-rich porous carbon into a hydrogel polymer network. The hydrogel network characteristics provide continuous and interconnected capillary water transport channels and low heat flux, and the oxygen-rich porous carbon provides high absorbance and additional water transport channels. The two work together to reduce enthalpy while the salt gradient diffusion effect in the vertical direction of the continuous water channels jointly improves its evaporation rate and service life.

[0038] The preparation method of the porous carbon hydrogel is as follows:

[0039] 4 g of polyvinyl alcohol, 0.5 g of deacetylated glucomannan, 0.1 g of oxygen-enriched porous carbon, and 0.52 ml of glutaraldehyde crosslinker were added to a beaker and placed in an ultrasonic machine for 4 hours to form a homogeneous solution, which was then allowed to stand in an oven at 70°C overnight to obtain a porous carbon hydrogel.

[0040] The preparation method of the oxygen-rich porous carbon is as follows:

[0041] S1, taking 100 ml of 100 g / L Chlorella solution and mixing it with 33.3 ml of methanolic choline chloride DES solution, hydrothermally pretreated at 160 ° C for 10 min, taking the solid phase to obtain algal residue and freeze-drying it;

[0042] S2, adding activator KOH in a ratio of 1:1 to freeze-dried algae residue and placing it in a tube furnace, heating it to 600 °C under an inert gas atmosphere and pyrolyzing it for 2 hours to obtain algae residue biochar;

[0043] S3, adding an appropriate amount of hydrochloric acid to the algae residue biochar and washing it until it becomes neutral to obtain oxygen-rich porous carbon.

[0044] Porous carbon, as a carbon-based solar absorber, can extend the propagation path of light by increasing the porosity of the porous carbon, allowing more sunlight to be reflected and reabsorbed multiple times inside the porous carbon, thereby improving the absorption performance of the solar absorber; at the same time, natural Chlorella, which is rich in nitrogen and oxygen functional groups, can retain more nitrogen and oxygen functional groups during carbonization after being treated with deep eutectic solvents, thereby improving water transport performance and reducing the evaporation enthalpy of water.

[0045] The preparation method of the deacetylated glucomannan is as follows:

[0046] S1, 30 g of KGM powder and 200 ml of 50% ethanol solution were mixed, and the mixed suspension was stirred and swelled at 50 °C for 30 min (150 r / min);

[0047] S2, then add Na2CO3 solution and react at 40℃ for 24 hours. After deacetylation, wash with ethanol aqueous solution (50%, 75% and 95%) three times to remove excess Na2CO3, and finally wash with anhydrous ethanol;

[0048] S3, evaporate the excess ethanol in a fume hood and then dry under vacuum at 40 °C for 6 h to obtain powdered deacetylated KGM.

[0049] Glucomannan, which is naturally abundant and low-cost, has a large number of hydroxyl hydrophilic groups and a small number of acetyl groups. After the deacetylation alcoholysis reaction, the hydrophobic acetyl groups are replaced by hydrophilic hydroxyl groups, which increases the water content inside the hydrogel while reducing the evaporation enthalpy of water.

[0050] Polyvinyl alcohol, as the skeleton of the polymer network, is rich in hydroxyl groups and has multiple cross-linking points. After chemical cross-linking with deacetylated glucomannan, a strong cross-linked network is formed. The rich hydroxyl groups of both can reduce the evaporation enthalpy of water, and the swelling change of the polymer network during the evaporation process is extremely small, thereby ensuring continuous evaporation.

[0051] Porous carbon embedded in a porous interconnected polymer cross-linked network to form an integrated hydrogel solar evaporator:

[0052] 1) It has the water transport properties of hydrogel and can capture solar energy and convert it into thermal energy;

[0053] 2) Both have the ability to reduce the enthalpy of water evaporation, synergistically forming a stronger enthalpy reduction effect;

[0054] 3) The continuous water channels and multi-level pore structure formed by the integrated hydrogel facilitate the vertical downward diffusion of salt ions, ensuring that salt ions do not crystallize on the surface of the solar evaporator, thereby enabling the long-term use of the solar evaporator.

[0055] Working principle:

[0056] When sunlight is incident on the surface of the porous carbon hydrogel, due to the rich pore structure, the sunlight is reflected multiple times on the surface, causing more carbon-based molecules to vibrate thermally, fully capturing the sunlight and converting it into heat energy. Due to the low thermal conductivity of the hydrogel, the heat energy is localized around the porous carbon without being dissipated into the bulk water, thereby improving energy utilization efficiency. The water molecules around the porous carbon hydrogel enter the interior of the gel through the multi-level pores therein, and the capillary effect and hydrophilic groups inside the porous carbon hydrogel transport the water molecules from bottom to top, thereby maintaining the continuous replenishment and evaporation of water molecules at the evaporation interface. Since the porous carbon is surrounded by a polymer network, when the water molecules in the polymer network reach the periphery of the porous carbon, the free water directly absorbs the heat energy converted by the photothermal conversion of the porous carbon and evaporates, and the steam is transported to the atmosphere through the rich pores of the porous carbon hydrogel.

[0057] The abundant hydrophilic groups in the polyvinyl alcohol, deacetylated glucomannan, and oxygen-enriched porous carbon in the hydrogel form strong hydrogen bonds with some water molecules, thereby weakening the hydrogen bonds between free water molecules and reducing the energy required for water evaporation. The porous carbon embedded in the hydrogel polymer network provides more water transport channels for the hydrogel, increasing the water transport rate. The hydrogel also allows the porous carbon to be firmly embedded and not easily detached, extending the service life of the hydrogel solar evaporator. The resulting porous carbon hydrogel solar evaporator, due to its continuous water channels and multi-layered pore structure, forms a salt concentration gradient in the vertical direction, promoting salt ion absorption and diffusion to achieve discharge equilibrium, ensuring that salt ions on the solar evaporator surface do not crystallize, achieving salt tolerance and maintaining the evaporation performance of the evaporator.

[0058] After the steam passes through the porous carbon hydrogel, it is transferred to the condensation interface of the upper acrylic plate and condensed on the interface. Because it is coated with a hydrophobic coating, the water molecules flow back to the water collection device along the inclined acrylic plate, realizing water desalination.

[0059] Effect:

[0060] 1) Simulated solar evaporation experiment: Prepare simulated seawater with a mass fraction of 3.5wt% (the average salinity of seawater in the world). Use a solar light simulation lamp to simulate the light intensity of one sun. After preheating for 10 minutes, start the measurement. After recording the total mass of the device, measure the mass every 60 minutes. The average evaporation rate is calculated to be 2.74kg / (m 2 ·h).

[0061] 2) Natural sunlight evaporation experiment: The device was installed on the roof of the School of Electrical Engineering of Guizhou University and compared with pure water evaporation. The evaporation experiment was carried out on May 4, 2022 (average temperature 24°C, humidity 64%, cloudy). After three hours of evaporation experiment from 14:00 to 17:00, it can be directly observed through the steam condensation area on the condensation interface that the evaporation amount of porous carbon hydrogel is much higher than that of pure water. The evaporation rate of porous carbon hydrogel was measured to be 0.92 kg / (m 2 ·h), compared with the evaporation rate of pure water of 0.29kg / (m 2 h) is improved by about 3.2 times.

[0062] Benefit Analysis:

[0063] The benefits of porous carbon hydrogels were compared and analyzed in three aspects: practical application, energy saving and emission reduction benefits, and cost-effectiveness.

[0064] Practical application: Based on the above evaporation rate measurement, and assuming that the daily exposure time is 12 hours and the exposure intensity is one solar hour, only 0.216m 2 The porous carbon hydrogel solar evaporator can meet the daily drinking water needs of a typical family of three (about 2.7 liters per day for women, about 3.7 liters per day for men, and about 0.8 liters per day for children).

[0065] Economic benefits: Compared with traditional seawater desalination devices, the construction cost of porous carbon hydrogel solar evaporator is greatly reduced. According to the market price of drinking water, it is about 500 yuan / ton. 2 The porous carbon hydrogel material costs about 87.3 yuan. It can produce 32.88 liters of fresh water worth 16.44 yuan by working under one sun for 12 hours a day. Therefore, the investment recovery period is 5-6 days, which has extremely high economic benefits.

[0066] Table 1 Comparison with traditional seawater desalination equipment

[0067]

[0068]

[0069] Energy saving and emission reduction benefits: Compared with traditional seawater desalination devices, the evaporation process of porous carbon hydrogel only consumes solar energy (excluding energy consumption) and does not emit any greenhouse gases. The calculated minimal energy consumption is only used for the water pump to pump water into the evaporator to produce 1m 3 Fresh water can save at least 1.61kg of standard coal and reduce 3.97kg of CO2 emissions, with extremely high energy-saving and emission-reduction benefits.

[0070] This system has the advantages of low production cost, simple structure and maintenance, and high evaporation efficiency. Compared with traditional seawater desalination technology, it achieves low energy consumption and reduces greenhouse gas emissions, with significant energy-saving and emission-reduction effects. It is a solar seawater desalination device with both social, economic and ecological benefits.

[0071] The above embodiments merely represent one or several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make various modifications and improvements without departing from the spirit of the present invention, and these modifications and improvements fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A porous carbon hydrogel for efficient solar interfacial evaporation, characterized in that: The porous carbon hydrogel is composed of a hydrogel matrix and oxygen-rich porous carbon, wherein the hydrogel matrix is formed by a cross-linked network structure of deacetylated glucomannan and polyvinyl alcohol, and the oxygen-rich porous carbon is uniformly doped in the cross-linked network structure of the hydrogel matrix; The cross-linked network structure of the porous carbon hydrogel provides continuous and interconnected capillary water transport channels, and the oxygen-enriched porous carbon provides additional water transport channels; The hydrophilic groups in the oxygen-enriched porous carbon, deacetylated glucomannan and polyvinyl alcohol form strong hydrogen bonds with some water molecules, thereby weakening the hydrogen bonds between free water molecules and reducing the energy required for water evaporation; The oxygen-rich porous carbon absorbs free water in the hydrogel through its abundant pore structure and evaporates it into water vapor through photothermal conversion and diffuses it; The water transport channel in the porous carbon hydrogel forms a salt concentration gradient in the vertical direction; The preparation method of the oxygen-rich porous carbon is as follows: S1, taking 100 ml of 100 g / L Chlorella solution and mixing it with 33.3 ml of methanolic choline chloride DES solution, hydrothermally pretreated at 160 ° C for 10 min, taking the solid phase to obtain algal residue and freeze-drying it; S2, adding activator KOH in a ratio of 1:1 to freeze-dried algae residue and placing it in a tube furnace, heating it to 600 °C under an inert gas atmosphere and pyrolyzing it for 2 hours to obtain algae residue biochar; S3, adding an appropriate amount of hydrochloric acid to the algae residue biochar and washing it until it becomes neutral to obtain oxygen-rich porous carbon.

2. The porous carbon hydrogel for efficient solar interfacial evaporation according to claim 1, characterized in that: The preparation method of the deacetylated glucomannan is as follows: S1, 30 g KGM powder was mixed with 200 ml 50% ethanol solution, and the mixed suspension was stirred and swelled at 50 °C for 30 min; S2, then add Na2CO3 solution and react at 40℃ for 24 hours, after deacetylation, wash with ethanol aqueous solution three times to remove excess Na2CO3, and finally wash with anhydrous ethanol; S3, evaporate the excess ethanol in a fume hood and then dry under vacuum at 40 °C for 6 h to obtain powdered deacetylated KGM.

3. The porous carbon hydrogel for efficient solar interfacial evaporation according to claim 1, characterized in that: The preparation method of the porous carbon hydrogel is as follows: 4 g of polyvinyl alcohol, 0.5 g of deacetylated glucomannan, 0.1 g of oxygen-enriched porous carbon, and 0.52 ml of glutaraldehyde crosslinker were added to a beaker and placed in an ultrasonic machine for 4 hours to form a homogeneous solution, which was then allowed to stand in an oven at 70°C overnight to obtain a porous carbon hydrogel.

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