Coal-based carbon / carboxymethyl cellulose photothermal sponge, preparation method and application thereof

Abstract

This invention belongs to the field of high-salinity mine water recovery and treatment, and discloses a coal-based carbon / carboxymethyl cellulose photothermal sponge, its preparation method, and its application. Coal-based carbon material with photothermal conversion function is uniformly distributed within the carboxymethyl cellulose sponge to form a porous structure. The method first prepares the coal-based carbon material, and then uses the coal-based carbon material as a precursor to prepare the coal-based carbon / carboxymethyl cellulose photothermal sponge. This invention utilizes the coal-based carbon material to significantly improve the light absorption performance of the carboxymethyl cellulose sponge, enabling the sponge to possess photothermal conversion capabilities, thus solving the problems of high cost and low efficiency of traditional treatment methods.

Description

Technical Field

[0001] This invention belongs to the field of high-mineralization mine water recycling and treatment, and relates to a high-efficiency carbonaceous photothermal conversion material and its preparation method, as well as its application in the interfacial evaporation treatment of high-mineralization mine water. Background Technology

[0002] Mine water is formed during coal mining when groundwater or surface water seeps into or surges into the tunnels through water-conducting fissures near the coal seam. High-mineralized mine water generally refers to mine water with a total dissolved solids (TDS) greater than 1000 mg / L. Its salts mainly come from sulfates and carbonates in the coal seam, and the water quality is mostly neutral or slightly alkaline. Statistics show that about 30% of mine water in my country is high-mineralized, while the proportion exceeds 50% in Northwest China. The characteristics of mine water vary significantly across different regions. Geological conditions, coal seam characteristics, mining methods, and the surrounding environment all affect the composition of mine water. In the Yellow River basin of Northwest China, coal mine water tends to be strongly alkaline, generally alkaline or weakly alkaline, with a pH between 7 and 9. In northern regions, coal-bearing strata contain small amounts of fluoride minerals, resulting in high concentrations of fluoride in the mine water. In some coal mines in Shaanxi Province and Inner Mongolia Autonomous Region, the sodium content in the mine water is high. + and Ca 2+ High concentration of SO4 in mine water of Guandi Coal Mine in Xishan Mining Area, Shanxi Province 2- and HCO3 - The concentration is relatively high; the Shendong mining area contains high-fluoride mine water, all of which is sodium-type.

[0003] Due to high evaporation rates in arid regions, the concentration of groundwater salts leads to further increases in salinity. Many arid and semi-arid areas in western China suffer from fragile ecosystems, scarce water resources, and a lack of receiving water bodies. The continuous increase in coal production has resulted in a corresponding increase in mine water volume. Direct discharge of highly mineralized mine water would cause soil salinization, ecological damage, and water waste. Therefore, the effective treatment and resource reuse of highly mineralized mine water is a serious challenge facing the coal industry, and some local environmental protection departments have already mandated that mine water cannot be discharged. Currently, typical processes for treating highly mineralized mine water include pretreatment, membrane concentration, and concentrated brine evaporation and crystallization. Membrane concentration and volume reduction processes include reverse osmosis and electrodialysis; however, membrane concentration systems often suffer from long processing times and high energy consumption per ton of water, making long-term stable operation difficult. Evaporation and crystallization technologies commonly include mechanical steam recompression evaporation and multi-effect evaporation, but these technologies still suffer from high costs, high energy consumption, and equipment corrosion.

[0004] Photothermal desalination technology utilizes photothermal conversion materials to convert light energy into heat energy to evaporate high-concentration brine. This technology has low energy consumption, wide applicability, and promising application prospects. Interfacial evaporation involves floating photothermal materials on the water surface, concentrating the heat generated by photothermal conversion at the interface to achieve a similar light-concentrating effect. This significantly improves the evaporation rate and energy utilization efficiency, effectively addressing the problems of slow evaporation rates and low energy utilization efficiency in traditional methods.

[0005] Chinese patent application 202211626810.9 discloses a method for preparing a photothermal coating composite material for solar interfacial evaporation. The method involves dissolving pyrrole in ethanol to obtain a pyrrole solution; dissolving tannic acid in Tris-HCl buffer solution to obtain a tannic acid solution; and uniformly mixing the obtained pyrrole solution and tannic acid solution to obtain a tannic acid-pyrrole mixed solution. A porous substrate is then immersed in the prepared tannic acid-pyrrole mixed solution, followed by immersion in a prepared ferric chloride solution, followed by washing and drying to obtain the tannic acid-polypyrrole photothermal coating composite material. The material exhibits excellent photothermal response performance and rapid water diffusion, but its evaporation efficiency is not high.

[0006] Chinese patent application 202311721523.0 discloses a polypyrrole / diatomite-porous foam composite photothermal material, its preparation method, and its application. The photothermal agent, polypyrrole, is obtained by oxidative polymerization of pyrrole monomer and an oxidant under acidic conditions. The pyrrole monomer is dissolved in deionized water, and a certain amount of diatomite and dilute hydrochloric acid are added to prepare a pyrrole / diatomite dispersion. This dispersion is then coated onto a polymer porous foam, and in-situ oxidative polymerization is performed. The mixture is then dried in a forced-air drying oven to obtain the polypyrrole / diatomite-porous foam composite photothermal material. The resulting composite photothermal material exhibits stable structure, excellent photothermal conversion performance, and salt resistance. It is a promising photothermal conversion material for large-scale production and can be applied to applications such as high-salinity seawater desalination.

[0007] Chinese patent application 202310575769.5 discloses a method for preparing a photothermal sponge for solar-driven evaporation and auxiliary wastewater purification. The method involves processing bamboo segments to obtain flocculent, lignin-free bamboo fibers; then mixing biochar with N,N-dimethylformamide, zirconium chloride, and 2-aminoterephthalic acid, heating in a reaction vessel, centrifuging, washing, and drying to obtain C@MOF powder; adding the lignin-free bamboo fibers and chitosan to an acetic acid aqueous solution and stirring, followed by the addition of C@MOF powder to obtain a black non-Newtonian flow; transferring this flow to a silicone mold and unidirectionally freezing to form a polymer network structure for the photothermal sponge; freeze-drying; and then immersing in NaOH solution for cross-linking treatment to obtain the photothermal sponge CS / BFs / C@MOF. The material exhibits good water transport and self-cleaning properties, but this study only simulated the purification effect on polluted water bodies and did not demonstrate effective performance for water with high salt content, such as high-mineralized mine water. Summary of the Invention

[0008] To address the problems existing in the prior art, this invention is based on solar interface evaporation technology and aims to provide a coal-based carbon / carboxymethyl cellulose photothermal sponge material CMC@MC and its application in the efficient removal of highly mineralized mine water.

[0009] In a first aspect, the present invention provides a coal-based carbon / carboxymethyl cellulose photothermal sponge material (CMC@MC), wherein the coal-based carbon material MC with photothermal conversion function is uniformly distributed inside the carboxymethyl cellulose sponge CMC to form a porous structure material.

[0010] Preferably, multiple porous structural materials are disposed on the foam substrate.

[0011] Specifically, foam substrate refers to polystyrene foam board.

[0012] Secondly, the present invention provides a method for preparing the coal-based carbon / carboxymethyl cellulose photothermal sponge material described in the first aspect, comprising the following steps:

[0013] (3) Coal slime is dried, crushed, calcined under nitrogen, acid washed, dried and ground to obtain coal-based carbon materials;

[0014] (4) Sodium carboxymethyl cellulose, α-cellulose, polyacrylic acid and coal-based carbon materials are added to water in a mass ratio of 10:10:1 to 6:4 and stirred evenly. The resulting precursor solution is frozen into a solid state, then freeze-dried under vacuum, and finally cross-linked under vacuum at 100°C for 20 to 30 hours to obtain CMC@MC.

[0015] Preferably, in step (1), the calcination is carried out at 800°C for 2 hours under nitrogen.

[0016] Preferably, in step (2), it is freeze-dried under vacuum at -45℃ to -35℃ for 30 to 40 hours.

[0017] Thirdly, the present invention provides an application of the coal-based carbon / carboxymethyl cellulose photothermal sponge material described in the first aspect in the solar interface evaporation treatment of highly salinized mine water.

[0018] Furthermore, the salts contained in high-mineralization mine water are sodium chloride, with a salt content of 3.5–20 wt%.

[0019] Compared with the prior art, the present invention has the following advantages:

[0020] (1) The coal-based carbon material of the present invention is derived from coal slime, a by-product of coal processing. The present invention utilizes coal slime as a resource, has a simple preparation process, and low cost. When added to a sponge, it effectively improves the light absorption and photothermal conversion performance of the material. Among similar biomass-based carbon materials, it has a simpler carbonization process and greater application potential.

[0021] (2) The carboxymethyl cellulose sponge of the present invention has a controllable 3D porous structure with strong hydrophilicity, which is beneficial to the scattering of light inside its pores and improves the light absorption and photothermal conversion capabilities of coal-based carbon materials. The sponge-like polymer is synthesized by the esterification reaction of polyacrylic acid and sodium carboxymethyl cellulose at high temperature. The pore size of the sponge can be controlled by changing the amount of polyacrylic acid added. At the same time, the carboxymethyl cellulose sponge also has high portability and high flexibility, and can adapt to various complex application conditions.

[0022] (3) The 3D solar interface evaporator of this invention uses a coal-based carbon / carboxymethyl cellulose photothermal sponge as its core component. This sponge possesses strong upward capillary water transport capabilities, continuously transferring the aqueous solution from the bottom to the top, resulting in an evaporation point far exceeding that of traditional film-type interface evaporation devices. The coal-based carbon / carboxymethyl cellulose photothermal sponge exhibits excellent heat retention and salt resistance; after repeated use, the evaporation rate does not significantly decrease. The salt ion concentration in the condensate after evaporation decreases significantly.

[0023] (4) Combining the above-mentioned technical advantages, the sponge significantly improves the evaporation rate of highly mineralized mine water. For example, under one solar equivalent, in a solar evaporation experiment on a 20wt% NaCl solution, the CMC@MC photothermal evaporation device achieved a maximum evaporation rate of 3.72 kg·m³. -2 ·h -1 . Attached Figure Description

[0024] Figure 1 This is a schematic diagram of a solar-driven interface evaporator device with coal-based carbon / carboxymethyl cellulose photothermal sponge as its core.

[0025] Figure 2 This is a flowchart illustrating the preparation process of the coal-based carbon / carboxymethyl cellulose photothermal sponge described in this invention.

[0026] Figure 3 The present invention relates to coal-based carbon materials (a) and CMC. 10 / 4 @MC Scanning electron microscope images at low magnification (b) and high magnification (c).

[0027] Figure 4 To test CMC 10 / 4 The graphs show the light absorption, photothermal conversion, and evaporation performance of CMC and other control samples; where (a) is the CMC. 10 / 4 @MC and CMC 10 / 4 (a) UV-Vis-NIR absorption spectrum; (b) CMC 10 / 4 @MC、CMC 10 / 4 Surface temperature changes of MC@cellulose membrane over 30 min; (c) is 1 kW·m -2 CMC under illumination 10 / 4 @MC shows the liquid mass change graph, which is monitored and recorded in real time by computer, when evaporating a 20wt% NaCl solution; (d) is the evaporation rate graph obtained based on the liquid mass change.

[0028] Figure 5 To test CMC 10 / 4 The salt tolerance effect diagram of @MC, where (a) is CMC 10 / 4 @MC evaporation of NaCl solutions of different concentrations, real-time monitoring and recording of liquid mass changes by computer; (b) evaporation rate graph obtained based on liquid mass changes; (c) 1kW·m -2 CMC under illumination 10 / 4 @MC was used in 10 cycles in a 20wt% NaCl solution. Evaporation rate graph; (d) shows the CMC. 10 / 4 @MC Evaporation rate graph for 3 consecutive days, 8 hours of evaporation per day. Detailed Implementation

[0029] To further understand the technical solution of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and embodiments.

[0030] The concept of this invention is as follows: A composite material based on solar-driven interfacial evaporation technology is pre-prepared, and using this material as the core, a solar-driven interfacial evaporator device is constructed for evaporating and concentrating high-mineralization mine water. The composite material is coal-based carbon / carboxymethyl cellulose photothermal sponge, where the coal-based carbon is the photothermal material and the carboxymethyl cellulose sponge is the carrier of the coal-based carbon material. The material is placed on a foam substrate and floated on the surface of high-mineralization mine water. The entire assembly is then placed in a transparent container with a sloping top. Under the radiation of sunlight, water vapor condenses at the top, forming water droplets that accumulate along the slope of the container and are collected at the bottom, thus achieving the treatment and recycling of high-mineralization mine water. Figure 1 This is a schematic diagram of a solar-driven interface evaporator device with coal-based carbon / carboxymethyl cellulose photothermal sponge as its core.

[0031] Example 1

[0032] Combination Figure 2 This embodiment provides the preparation process of the coal-based carbon / carboxymethyl cellulose photothermal sponge.

[0033] Coal slime obtained from a coal mine was dried in a 60℃ oven. After complete drying, it was thoroughly crushed using a crusher. A certain amount of the crushed coal slime was placed in a tube furnace and heated to 800℃ under a N2 atmosphere. The resulting calcined product was acid-washed three times with 1mol / L HCl, then washed with ultrapure water until neutral, filtered, and dried overnight in a 100℃ oven. After grinding, a coal-based carbon material, denoted as MC, was obtained. 2.5g of sodium carboxymethyl cellulose, 2.5g of α-cellulose, a certain amount of polyacrylic acid, and 1g of the coal-based carbon material were dispersed in 100mL of deionized water and mechanically stirred for 1.5h to obtain a homogeneous precursor solution. After aging, the precursor dispersion was poured into a cylindrical mold and then frozen for 12h. The completely frozen precursor solution was freeze-dried under vacuum at -40℃ for 36h, and then crosslinked in a vacuum oven at 100℃ for 24h to obtain a coal-based carbon / carboxymethyl cellulose photothermal sponge. To find the optimal porosity of carboxymethyl cellulose (CMC) sponges and fully utilize the photothermal conversion performance of coal-based carbon materials, the amount of polyacrylic acid was adjusted. Sodium CMC and polyacrylic acid were prepared in six ratios: 10:1, 10:2, 10:3, 10:4, 10:5, and 10:6. These six coal-based carbon / carboxymethyl cellulose photothermal sponges were subsequently named CMC. 10 / 1 @MC、CMC 10 / 2 @MC、CMC 10 / 3 @MC、CMC 10 / 4 @MC、CMC 10 / 5 @MC、CMC 10 / 6 @MC.

[0034] Under equivalent sunlight irradiation, the evaporation performance of these six coal-based carbon / carboxymethyl cellulose photothermal sponges on a 20 wt% NaCl solution was recorded. The test lasted for two hours, and the mass change of the liquid was monitored and recorded in real time by computer to calculate the evaporation rate of the sponge. As shown in Table 1, the evaporation performance of these six coal-based carbon / carboxymethyl cellulose photothermal sponges on a 20 wt% NaCl solution was recorded in detail.

[0035] Table 1. Evaporation performance of six coal-based carbon / carboxymethyl cellulose photothermal sponges on 20 wt% NaCl solution.

[0036]

[0037] As shown in Table 1, changing the amount of polyacrylic acid added will change the evaporation rate of the coal-based carbon / carboxymethyl cellulose photothermal sponge, among which CMC... 10 / 4 @MC indicates that the sponge exhibits the optimal evaporation rate when the ratio of sodium carboxymethyl cellulose to polyacrylic acid is 10:4; therefore, CMC is selected. 10 / 4 @MC will explore this further.

[0038] Figure 3 (a) is a SEM image of coal-based carbon material MC. Coal-based carbon consists of multiple layers that are tightly packed together, exhibiting a uniform and compact state. Figure 3 (b) in the text is CMC 10 / 4 The SEM image of the CMC surface shows the CMC. 10 / 4 The @MC surface has a porous structure with a large pore size distribution, and the maximum pore diameter can reach 100μm. Figure 3 (c) in the text refers to CMC. 10 / 4 The morphology of @MC under a high-power scanning electron microscope shows that sheet-like coal-based carbon is uniformly distributed on the sponge skeleton, proving that coal-based carbon has been successfully incorporated into the carboxymethyl cellulose sponge.

[0039] Example 2

[0040] To verify that adding coal-based carbon materials to carboxymethyl cellulose (CMC) sponges enables the sponges to convert light energy into heat energy, and that the 3D porous structure of the CMC sponges is beneficial for the photothermal conversion of coal-based carbon materials, the CMC from Example 1 was used. 10 / 4 @MC、CMC 10 / 4 A control experiment was conducted on a carboxymethyl cellulose sponge prepared by mixing sodium carboxymethyl cellulose and polyacrylic acid in a ratio of 10:4 without adding coal-based carbon materials and a MC@cellulose membrane (coal-based carbon material MC was loaded onto a cellulose membrane by vacuum filtration, wherein the cellulose membrane was a polyvinylidene fluoride membrane).

[0041] Test CMC separately 10 / 4 @MC and CMC10 / 4 Its light absorption capacity over a wide spectral range (200–2500 nm) was characterized using a UV-Vis-NIR spectrophotometer, and the results are as follows: Figure 4 As shown in (a) of CMC. 10 / 4 Its light absorption rate is only 42.15%, but after being combined with coal-based carbon materials, CMC... 10 / 4 @MC light absorption rate reaches 96.46%. Photothermal conversion performance is as follows: Figure 4 As shown in (b), under 1 solar equivalent irradiation, CMC 10 / 4 @MC's surface temperature can reach 68℃, while CMC's... 10 / 4 It can only reach 46°C. Furthermore, MC@cellulose membranes, under one solar equivalent, can only reach a temperature of 53°C. This illustrates the limitations of CMC. 10 / 4 @MC's 3D porous structure facilitates light scattering within its pores, thereby enhancing light absorption and photothermal conversion, demonstrating the significant advantages of 3D solar interface evaporators over 2D evaporators.

[0042] Furthermore, to improve the utilization rate of the land area, the variation of water evaporation rate in coal-based carbon / carboxymethyl cellulose photothermal sponges at different heights was studied. Under one solar equivalent, the CMC was changed... 10 / 4 At the height of @MC, a solar evaporation experiment was conducted on a 20wt% NaCl solution. Figure 4 (c) in the figure represents the changes in liquid mass monitored and recorded by the computer in real time. Figure 4 In the figure, (d) represents the evaporation rate obtained from the change in liquid mass, which increases with CMC. 10 / 4 The effective height of the MC increased from 1cm to 2.5cm, and the water evaporation rate increased from 3.09kg·m. -2 ·h -1 Increased to 4.08 kg·m -2 ·h -1 Increasing the height of the sponge can increase the rate of water evaporation. When the height is increased to 3cm, the evaporation rate decreases. A sponge with a height of 2.5cm exhibits the best evaporation performance, but after evaporation for more than two hours, salt deposits will appear on the surface. For long-term efficient operation, a height of 2cm is optimal.

[0043] Example 3

[0044] Salt resistance is one of the most important indicators for evaluating the application value of solar interfacial evaporators. Therefore, tests were conducted at 1kW·m -2 Under illumination, CMC 10 / 4 @MC evaporation performance for different NaCl concentrations (3.5wt%, 10wt%, and 20wt%). Figure 5(a) in the figure represents the changes in liquid mass monitored and recorded by the computer in real time. Figure 5 (b) shows the evaporation rate obtained based on changes in liquid mass. When the NaCl concentration is 3.5 wt% (approximately seawater salinity), the evaporation rate relative to pure water remains almost constant. With further increases in NaCl concentration, the evaporation rate shows a slight decrease, but at 20 wt% NaCl (approximately the salinity of high-mineralization mine water reverse osmosis concentrate), the evaporation rate can still reach 3.76 kg·m³. -2 ·h -1 The material exhibits good stability under high salt conditions. For example... Figure 5 As shown in (c) in the figure, at 1kW·m -2 Under illumination, CMC 10 / 4 After 10 cycles of use in a 20wt% NaCl solution, the evaporation rate of @MC did not decrease significantly. Furthermore, as... Figure 5 As shown in (d), under evaporation for three consecutive days with eight hours of evaporation each day, the CMC 10 / 4 The fact that @MC can still maintain high evaporation performance indicates that the sponge has good cycle stability, laying a good foundation for subsequent practical applications.

Claims

1. A coal-based carbon / carboxymethyl cellulose photothermal sponge, characterized in that, Coal-based carbon materials with photothermal conversion function are uniformly distributed inside the carboxymethyl cellulose sponge and form a porous structure material. Prepared by the following steps: (1) Coal slime is dried, crushed, calcined under nitrogen, acid washed, dried and ground to obtain coal-based carbon materials; (2) Sodium carboxymethyl cellulose, α-cellulose, polyacrylic acid and coal-based carbon materials are added to water in a mass ratio of 10:10:1~6:4 and stirred evenly. The resulting precursor solution is frozen into a solid state, then freeze-dried under vacuum, and finally cross-linked under vacuum at 100℃ for 20~30 h to obtain coal-based carbon / carboxymethyl cellulose photothermal sponge.

2. The coal-based carbon / carboxymethyl cellulose photothermal sponge as described in claim 1, characterized in that, Multiple porous structural materials are disposed on the surface of the foam substrate.

3. The coal-based carbon / carboxymethyl cellulose photothermal sponge as described in claim 2, characterized in that, Foam base refers to polystyrene foam board.

4. A method for preparing a coal-based carbon / carboxymethyl cellulose photothermal sponge material as described in any one of claims 1-3, characterized in that, Includes the following steps: (1) Coal slime is dried, crushed, calcined under nitrogen, acid washed, dried and ground to obtain coal-based carbon materials; (2) Sodium carboxymethyl cellulose, α-cellulose, polyacrylic acid and coal-based carbon materials are added to water in a mass ratio of 10:10:1~6:4 and stirred evenly. The resulting precursor solution is frozen into a solid state, then freeze-dried under vacuum, and finally cross-linked under vacuum at 100℃ for 20~30 h to obtain coal-based carbon / carboxymethyl cellulose photothermal sponge.

5. The method as described in claim 4, characterized in that, In step (1), calcination is carried out at 600~800℃ for 2~4 h under nitrogen.

6. The method as described in claim 4, characterized in that, In step (2), it is freeze-dried under vacuum at -45℃ to -35℃ for 30 to 40 hours.

7. An application of the coal-based carbon / carboxymethyl cellulose photothermal sponge material as described in any one of claims 1-3 in the solar interface evaporation treatment of highly salinized mine water.

8. The application as described in claim 7, characterized in that, The salts contained in highly mineralized mine water are sodium chloride, with a salt content of 3.5~20wt%.

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