High-stability carbon dot modified heavy metal ion adsorption composite material and application thereof

Abstract

The application discloses a heavy metal ion adsorption composite material based on high-stability carbon dots and application thereof, and belongs to the technical field of environmental protection.The composite material is prepared by the following steps: firstly, using citric acid, urea and acrylamide as carbon source and nitrogen source, carbon dots are prepared through a one-step hydrothermal method; secondly, the carbon dots are modified by using a quaternary ammonium salt to obtain high-stability carbon dots; and finally, the high-stability carbon dots and montmorillonite are mixed and stirred, and then cation exchange is performed to obtain high-stability carbon dot-montmorillonite composite material.The nitrogen-doped high-stability carbon dots in the composite material have adsorption effect on heavy metal ions, the high-stability carbon dot-montmorillonite composite material can effectively complex metal ions through amino groups, carbonyl groups and hydroxyl groups, and due to the properties of the carbon dot nanomaterial (i.e., high specific surface area), the adsorption performance on heavy metal ions is further improved, the biocompatibility of the composite material is improved, and environmental pollution is reduced.

Description

Technical Field

[0001] This invention relates to the field of polymer composite materials technology, and in particular to a heavy metal ion adsorption composite material based on highly stable carbon dot modification and its application. Background Technology

[0002] The threat of toxic heavy metals in wastewater is gradually becoming a global problem, making the effective removal of these metals a challenging task. Polymer heavy metal ion adsorbents have become a commonly used agent for treating heavy metal wastewater. At room temperature and within a wide pH range, they can rapidly react with various heavy metal ions in wastewater, such as Hg, Cd, Cu, Pb, Mn, Ni, Zn, and Cr, forming water-insoluble flocculent precipitates. These precipitates are fast, easy to filter, highly stable, and highly sensitive, thus achieving the purpose of adsorbing and removing heavy metal ions. They have been widely used in industries such as electroplating, electronics, and circuit boards. However, there are still some drawbacks in the preparation of polymer heavy metal ion adsorbents. For example, the preparation and treatment costs may be high, especially in large-scale production, which may limit their application range; some polymer materials may release harmful substances during preparation or use, causing environmental pollution or impact; some polymer materials may require specific operating conditions to achieve optimal adsorption effects, such as specific pH values, temperatures, or ion concentrations, which may increase the complexity and cost of operation. In the field of heavy metal ion adsorbent research, developing low-cost, easily synthesized adsorbent materials to remove heavy metal ions through adsorption is one of the most promising methods.

[0003] Currently, commonly used adsorbent materials mainly include montmorillonite, activated carbon, zeolite, inorganic oxides, modified silica, and biomimetic materials. Compared with traditional adsorbents, nanoscale adsorbent materials can significantly improve their metal removal performance. Carbon quantum dots, as a novel fluorescent nano-semiconductor material, have received widespread attention and research, especially the interaction between carbon dots and metal ions, which makes carbon dots a promising adsorbent material for heavy metal adsorption. Patent CN202211073614.3, "A carbon dot-functionalized resin material and its preparation method and application," firstly uses glycidyl acrylate as a functional monomer and prepares macroporous resin microspheres with epoxy groups on the surface using a seed swelling method. Then, it uses atom transfer radical polymerization technology to graft a polymer brush with alkyne groups onto the surface of the macroporous resin microspheres. Finally, it introduces thiol-based carbon dots into the surface of the macroporous resin microspheres through a photo-initiated click chemistry reaction, obtaining a carbon dot-functionalized resin material that can be applied to metal ion detection and / or adsorption. Although this method prepares a composite resin for heavy metal ion adsorption, its preparation is complex and unsuitable for large-scale application. Furthermore, the composite resin exhibits poor adsorption performance, indicating poor stability of the carbon dots and their inability to stably adsorb heavy metal ions. Patent CN201610365980.4, "A Preparation Method and Application of Montmorillonite and Carbon Composite Material," modifies the surface of the composite material through steps such as montmorillonite purification and sodium conversion, hydrothermal treatment of montmorillonite and glucose, and functionalization of the composite material, thereby preparing carbon-modified montmorillonite for water treatment. However, this method involves a high amount of glucose monohydrate and only tests the adsorption of lead as a heavy metal ion, failing to test the adsorption performance of the composite material for other heavy metal ions. Therefore, ensuring that the composite material exhibits excellent adsorption performance for multiple heavy metal ions while simplifying the preparation process is of great significance for the promotion of heavy metal ion adsorption technology. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a heavy metal ion adsorption composite material based on highly stable carbon dot modification and its application. This composite material has high stability and excellent adsorption performance, and can be widely used in the removal and treatment of heavy metal pollution in wastewater treatment.

[0005] To achieve its objectives, the present invention employs the following technical solution:

[0006] This invention first provides a heavy metal ion adsorption composite material based on high-stability carbon dots modification. The composite material is obtained by loading high-stability carbon dots onto the surface of montmorillonite. The high-stability carbon dots are obtained by a one-step hydrothermal method using citric acid, urea and acrylamide as reaction precursors, followed by quaternization modification of the carbon dots.

[0007] This invention further provides a method for preparing the aforementioned heavy metal ion adsorption composite material based on highly stable carbon dots. The method involves: firstly, obtaining carbon dots via a one-step hydrothermal method using citric acid, urea, and acrylamide; then, modifying the carbon dots with quaternary ammonium salts to obtain highly stable carbon dots; finally, mixing and stirring the highly stable carbon dots and montmorillonite, and then performing cation exchange to obtain a highly stable carbon dot-montmorillonite composite material. The composite adsorption material provided by this invention exhibits adsorption properties because both carbon dots and montmorillonite possess large specific surface areas, providing abundant adsorption sites and enabling effective adsorption of heavy metal ions from the surrounding environment. The composite adsorption material of this invention has a convenient preparation process and can effectively adsorb various heavy metal ions in aqueous solutions.

[0008] The preparation method of the present invention specifically includes the following steps:

[0009] (1) Add citric acid, urea and acrylamide to water and sonicate to obtain an aqueous solution in which the raw materials are uniformly dispersed; put the aqueous solution in which the raw materials are uniformly dispersed into a high-pressure hydrothermal reactor lined with polytetrafluoroethylene and heat it in an oven. After the reaction is completed, let the reactants cool naturally to room temperature, centrifuge to take the supernatant, dialyze the supernatant, freeze dry it to obtain carbon dots.

[0010] (2) The carbon dots were added to water and then ultrasonically dispersed and dissolved. Then, quaternary ammonium salt was added, and the reaction was stirred at room temperature. After stirring, the reaction was heated. After the reaction was completed, the reaction solution was centrifuged, the solid was collected and washed with ethanol, and then dried under vacuum to obtain highly stable carbon dots.

[0011] (3) Add the high-stability carbon dots to pure water and sonicate them to dissolve them completely; add montmorillonite to pure water and stir to form a suspension; then add the high-stability carbon dot aqueous solution to the montmorillonite suspension and stir continuously to carry out cation exchange; finally, filter the mixed sample, freeze dry it, and grind it to obtain the heavy metal ion adsorption composite material modified by high-stability carbon dots.

[0012] Preferably, in step (1), the mass ratio of citric acid, urea, acrylamide and water is 1:2:2:25 to 100, and the heating temperature in the oven is 150 to 200°C and the reaction time is 4 to 6 hours.

[0013] Preferably, in step (1), the molecular weight cutoff of the dialysis bag for dialysis is 1 to 14 kDa.

[0014] Preferably, in step (1), the particle size of the carbon dots is 2 to 8 nm.

[0015] Preferably, in step (2), the mass ratio of the carbon dots to the quaternary ammonium salt is 1:1 to 3.

[0016] Preferably, in step (2), the quaternary ammonium salt is one of 2,3-epoxypropyltrimethylammonium chloride (GDTMAC), dimethyl diallyl ammonium chloride (DDA), and benzalkonium chloride (BKC).

[0017] Preferably, in step (3), the montmorillonite is one of calcium-based, sodium-based, sodium-calcium-based, or magnesium-based montmorillonite.

[0018] Preferably, in step (3), the mass ratio of the highly stable carbon dots to montmorillonite is 1:5 to 20.

[0019] The highly stable carbon dot-montmorillonite composite material prepared by the above method can be directly used for heavy metal ion adsorption in soil remediation and wastewater treatment, thereby improving the environment and reducing heavy metal pollution. The heavy metal ions adsorbed by the composite material include mercury ions, lead ions, iron ions, copper ions, and chromium ions.

[0020] The carbon dots provided by this invention are prepared by a one-step hydrothermal method using citric acid, urea, and acrylamide as carbon and nitrogen sources, respectively. Then, quaternary ammonium salts are used to modify the carbon dots to obtain highly stable carbon dots. Finally, the highly stable carbon dots and montmorillonite are mixed and stirred, and then subjected to cation exchange to obtain a highly stable carbon dot-montmorillonite composite material. This highly stable carbon dot-montmorillonite composite material is used for heavy metal ion adsorption. Specifically, compared with existing technologies, the beneficial effects of this invention are reflected in:

[0021] 1. This invention first prepares highly stable carbon dots by using citric acid, urea, and acrylamide as carbon and nitrogen sources respectively via a one-step hydrothermal method, followed by GDTMAC quaternization modification. Then, the highly stable carbon dots are mixed with montmorillonite to obtain a composite material. The nitrogen-doped highly stable carbon dots in the composite material provided by this invention exhibit adsorption properties for heavy metal ions. Furthermore, the highly stable carbon dot-montmorillonite composite material effectively complexes metal ions through amino, carbonyl, and hydroxyl groups. Due to the properties of carbon dot nanomaterials (i.e., high specific surface area), the adsorption performance for heavy metal ions is further improved, and the biocompatibility of the composite material is enhanced, reducing environmental pollution.

[0022] 2. In the composite material of the present invention, the highly stable carbon dots and montmorillonite undergo cation exchange, and there are electrostatic adsorption, hydrogen bonding and complexation to promote the combination of the two, which improves the stability between carbon dots and montmorillonite, so that carbon dots can be more stably loaded in montmorillonite.

[0023] 3. The composite material of the present invention has fewer synthesis steps, is easy to operate, has low preparation cost, and is suitable for large-scale production. Attached Figure Description

[0024] Figure 1 This is a SEM image of the carbon dots prepared in Example 1 of the present invention.

[0025] Figure 2 These are TEM images of the carbon dots prepared in Example 1 of the present invention, where (a), (b), (c), and (d) correspond to different magnifications.

[0026] Figure 3 This is an elemental analysis chart of montmorillonite and the prepared high-stability carbon dot-montmorillonite composite material in Example 1 of the present invention.

[0027] Figure 4 The adsorption efficiency of different heavy metal ions for the highly stable carbon dot-montmorillonite composite materials prepared in Examples 1-5 of this invention. Detailed Implementation

[0028] The embodiments of the present invention are described in detail below. These embodiments are implemented based on the technical solution of the present invention, and provide detailed implementation methods and specific operation processes. However, the scope of protection of the present invention is not limited to the following embodiments.

[0029] Example 1

[0030] This embodiment provides a method for preparing a heavy metal ion adsorption composite material based on highly stable carbon dot modification and its application, including the following steps:

[0031] 1. Add 1g of citric acid (Shanghai Titan Technology Co., Ltd.), 2g of urea (Shanghai Titan Technology Co., Ltd.), and 2g of acrylamide (Shanghai Titan Technology Co., Ltd.) to 25mL of ultrapure water, and sonicate for 10min to obtain a uniformly dispersed aqueous solution. Place the uniformly dispersed aqueous solution into a polytetrafluoroethylene-lined high-pressure hydrothermal reactor. Preheat the oven to 200℃, and after preheating, place the reactor inside and react for 6h. After the reaction is complete, cool the oven to room temperature, remove the reactor, and centrifuge the reaction solution (8000rpm, 10min). Collect the supernatant, and then dialyze the reaction product using a dialysis bag (molecular weight cutoff of 1000Da). After dialysis, freeze-dry to obtain carbon dot powder.

[0032] 2. Take 1 part of carbon dots and add them to water, then disperse and dissolve them by ultrasonication. Then add 2 parts of 2,3-epoxypropyltrimethylammonium chloride (GDTMAC), stir the reaction at room temperature for 2 hours, and then heat and stir at 80°C for 6 hours. After the reaction is completed, centrifuge the reaction solution (8000 rpm, 10 min), collect the obtained solid and wash it with ethanol. Dry it under vacuum at 70°C for 12 hours to obtain highly stable carbon dots.

[0033] 3. Add 1 part of high-stability carbon dots to ultrapure water and sonicate for 15 minutes to completely dissolve them; add 20 parts of magnesium-based montmorillonite (Zhejiang Fenghong New Material Co., Ltd.) to ultrapure water and stir for 15 minutes to form a suspension; then add the high-stability carbon dot aqueous solution to the montmorillonite suspension and stir continuously for 30 minutes; finally, filter the mixed sample, freeze-dry it, grind it, and pass it through a 200-mesh sieve to obtain the high-stability carbon dot-montmorillonite composite material.

[0034] Example 2

[0035] This embodiment provides a method for preparing a heavy metal ion adsorption composite material based on highly stable carbon dot modification and its application, including the following steps:

[0036] 1. Add 1g of citric acid (Shanghai Titan Technology Co., Ltd.), 2g of urea (Shanghai Titan Technology Co., Ltd.), and 2g of acrylamide (Shanghai Titan Technology Co., Ltd.) to 25mL of ultrapure water, and sonicate for 10min to obtain a uniformly dispersed aqueous solution. Place the uniformly dispersed aqueous solution into a polytetrafluoroethylene-lined high-pressure hydrothermal reactor. Preheat the oven to 200℃, and after preheating, place the reactor inside and react for 6h. After the reaction is complete, cool the oven to room temperature, remove the reactor, and centrifuge the reaction solution (8000rpm, 10min). Collect the supernatant, and then dialyze the reaction product using a dialysis bag (molecular weight cutoff of 1000Da). After dialysis, freeze-dry to obtain carbon dot powder.

[0037] 2. Take 1 part of carbon dots and add them to water, then disperse and dissolve them by ultrasonication. Then add 2 parts of benzalkonium chloride (BKC), stir and react at room temperature for 2 hours, then heat to 80°C and stir for 6 hours. After the reaction is completed, centrifuge the reaction solution (8000 rpm, 10 min), collect the obtained solid and wash it with ethanol. Dry it under vacuum at 70°C for 12 hours to obtain highly stable carbon dots.

[0038] 3. Add 1 part of high-stability carbon dots to ultrapure water and sonicate for 15 minutes to completely dissolve them; add 15 parts of magnesium-based montmorillonite (Zhejiang Fenghong New Material Co., Ltd.) to ultrapure water and stir for 15 minutes to form a suspension; then add the high-stability carbon dot aqueous solution to the montmorillonite suspension and stir continuously for 30 minutes; finally, filter the mixed sample, freeze-dry it, grind it, and pass it through a 200-mesh sieve to obtain the high-stability carbon dot-montmorillonite composite material.

[0039] Example 3

[0040] This embodiment provides a method for preparing a heavy metal ion adsorption composite material based on highly stable carbon dot modification and its application, including the following steps:

[0041] One part of the highly stable carbon dots prepared in Example 1 was added to ultrapure water and ultrasonically vibrated for 15 min to completely dissolve them; 15 parts of magnesium-based montmorillonite (Zhejiang Fenghong New Material Co., Ltd.) were added to ultrapure water and stirred for 15 min to form a suspension; then the aqueous solution of highly stable carbon dots was added to the montmorillonite suspension and stirred continuously for 30 min; finally, the mixed sample was filtered, freeze-dried, ground, and passed through a 200-mesh sieve to obtain the highly stable carbon dots-montmorillonite composite material.

[0042] Example 4

[0043] This embodiment provides a method for preparing a heavy metal ion adsorption composite material based on highly stable carbon dot modification and its application, including the following steps:

[0044] One part of the highly stable carbon dots prepared in Example 1 was added to ultrapure water and ultrasonically vibrated for 15 minutes to completely dissolve them; 10 parts of magnesium-based montmorillonite (Zhejiang Fenghong New Material Co., Ltd.) were added to ultrapure water and stirred for 15 minutes to form a suspension; then the aqueous solution of highly stable carbon dots was added to the montmorillonite suspension and stirred continuously for 30 minutes; finally, the mixed sample was filtered, freeze-dried, ground, and passed through a 200-mesh sieve to obtain the highly stable carbon dots-montmorillonite composite material.

[0045] Example 5

[0046] This embodiment provides a method for preparing a heavy metal ion adsorption composite material based on highly stable carbon dot modification and its application, including the following steps:

[0047] One part of the highly stable carbon dots prepared in Example 1 was added to ultrapure water and dissolved, and ultrasonically vibrated for 15 min to completely dissolve them; five parts of magnesium-based montmorillonite (Zhejiang Fenghong New Material Co., Ltd.) were added to ultrapure water and stirred for 15 min to form a suspension; then the aqueous solution of highly stable carbon dots was added to the montmorillonite suspension and stirred continuously for 30 min; finally, the mixed sample was filtered, freeze-dried, ground, and passed through a 200-mesh sieve to obtain the highly stable carbon dots-montmorillonite composite material.

[0048] Performance Testing: 500 mL of a 300 mg / L aqueous solution of heavy metal ions was prepared, and 300 mg of the highly stable carbon dot-montmorillonite composite material was added. The solution was shaken at 150 rpm for 24 hours until complete precipitation. The precipitate was then removed by filtration. The adsorption capacity of the treated aqueous solution was measured, and the adsorption efficiency of the highly stable carbon dot-montmorillonite composite material for heavy metal ions was calculated. The adsorption capacity and adsorption efficiency of the highly stable carbon dot-montmorillonite composite material for heavy metal ions were calculated using the following formula:

[0049]

[0050]

[0051] q e (mg / g) represents the equilibrium adsorption capacity of the highly stable carbon dot-montmorillonite composite material; C1 (mg / L) and C2 (mg / L) are the initial and residual concentrations of metal ions in the solution, respectively; M (mg) is the weight of the highly stable carbon dot-montmorillonite composite material; V (L) is the volume of the aqueous solution; SE (%) is the adsorption efficiency of the highly stable carbon dot-montmorillonite composite material.

[0052] Table 1. Equilibrium adsorption capacity of high-stability carbon dot-montmorillonite composite materials for different metal ions.

[0053]

[0054] Table 1 shows that the high-stability carbon dot-montmorillonite composite material of Example 3 exhibits the best adsorption effect for heavy metal ions. Specifically, the equilibrium adsorption capacity of the high-stability carbon dot-montmorillonite composite material of Example 3 is 421.8 mg / g for mercury ions, 411.4 mg / g for lead ions, 378.4 mg / g for iron ions, 407.8 mg / g for copper ions, and 368.6 mg / g for chromium ions. This is attributed to the higher carbon dot content, which increases the specific surface area and the number of loading sites on the montmorillonite surface, thus increasing the adsorption capacity for heavy metal ions. However, excessively high carbon dot content leads to aggregation, reducing the adsorption capacity for heavy metal ions. Secondly, when the quaternary ammonium salt is 2,3-epoxypropyltrimethylammonium chloride, the adsorption capacity for heavy metal ions is even higher. This is because the rigid benzene ring in benzalkonium chloride has steric hindrance, reducing its adsorption capacity.

[0055] From Table 1 and Figure 4 It can be seen that the highly stable carbon dot-montmorillonite composite material exhibits a large adsorption capacity for mercury and lead ions at adsorption equilibrium. This is mainly because mercury and lead are elements in the sixth period, and their coordination numbers are greater than those of copper, iron, and chromium, which are in the fourth period.

[0056] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and not a limitation on the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a heavy metal ion adsorption composite material based on highly stable carbon dot modification, characterized in that, Includes the following steps: (1) Add citric acid, urea and acrylamide to water and sonicate to obtain a uniformly dispersed aqueous solution of raw materials; place the uniformly dispersed aqueous solution of raw materials into a high-pressure hydrothermal reactor lined with polytetrafluoroethylene, heat it in an oven, and after the reaction is completed, allow the reactants to cool naturally to room temperature, centrifuge to collect the supernatant, dialyze the supernatant, freeze dry it to obtain carbon dots; the mass ratio of citric acid, urea, acrylamide and water is 1:2:2:25~100, the heating temperature in the oven is 150~200 ℃ and the reaction time is 4~6 h; (2) The carbon dots are added to water, then ultrasonically dispersed and dissolved, then quaternary ammonium salt is added, the reaction is stirred at room temperature, then heated and stirred. After the reaction is completed, the reaction solution is centrifuged, the obtained solid is collected and washed with ethanol, and then vacuum dried to obtain highly stable carbon dots; the mass ratio of the carbon dots to the quaternary ammonium salt is 1:1~3. (3) The highly stable carbon dots are added to pure water and ultrasonically vibrated to dissolve them completely; montmorillonite is added to pure water and stirred to form a suspension; then the highly stable carbon dots aqueous solution is added to the montmorillonite suspension and cation exchange is carried out by continuous stirring; finally, the mixed sample is filtered, freeze-dried, and ground to obtain the heavy metal ion adsorption composite material modified by highly stable carbon dots; the mass ratio of the highly stable carbon dots to montmorillonite is 1:5~20.

2. The preparation method according to claim 1, characterized in that: In step (1), the molecular weight cutoff of the dialysis bag for dialysis is 1~14 kDa.

3. The preparation method according to claim 1, characterized in that: In step (2), the quaternary ammonium salt is one of 2,3-epoxypropyltrimethylammonium chloride, dimethyldiallylammonium chloride, and benzalkonium chloride.

4. The preparation method according to claim 1, characterized in that: In step (3), the montmorillonite is one of calcium-based, sodium-based, sodium-calcium-based, or magnesium-based montmorillonite.

5. The application of a heavy metal ion adsorption composite material based on highly stable carbon dot modification prepared by the preparation method of claim 1 in soil remediation and wastewater treatment.

6. The application according to claim 5, characterized in that: the heavy metal ions adsorbed by the heavy metal ion adsorption composite material include mercury ions, lead ions, iron ions, copper ions and chromium ions.

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