Composite material for adsorbing heavy metal thallium and preparation method thereof

Abstract

The invention relates to a composite material for adsorbing heavy metal thallium and a preparation method thereof, which are applied to the technical field of environmental functional materials. The composite material comprises a porous carrier, an organic ligand which is grafted on the porous carrier and has a specific binding effect on Tl < + >, and loaded metal sulfide nanoparticles. The preparation method is characterized in that the surface of the carrier is modified with a bifunctional coupling agent, a first functional group of the coupling agent is covalently bonded with an organic ligand, and a second functional group of the coupling agent is an active group capable of being coordinated with metal ions; the metal sulfide nanoparticles are generated in situ under the guidance of coordination of active groups. The preparation method comprises the steps of carrier coupling, capture unit grafting, metal ion coordination and enrichment, sulfur source introduction, selective in-situ vulcanization and the like. According to the method, high-selectivity adsorption and deep in-situ mineralization solidification of trace thallium ions in water are achieved, the synergistic effect is remarkable, secondary pollution can be effectively eradicated, the condition is mild, and the method is suitable for treatment of various types of thallium-containing wastewater.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of environmental functional materials, in particular, to a composite material for adsorbing heavy metal thallium and a preparation method thereof. BACKGROUND

[0002] Thallium (Tl) is a highly toxic heavy metal, and trace pollution in water environment poses a serious threat to the ecosystem and human health. Existing thallium removal technologies mainly fall into two categories:

[0003] One is adsorption method, such as using Prussian blue (PB) and its analogues, modified biochar, metal oxides, etc. These materials can enrich thallium, but the enrichment phase formed usually through physical adsorption or weak chemical bonding, which is not stable enough, and there is a risk of thallium ion leaching when environmental conditions such as pH and ionic strength change, which essentially realizes the transfer of pollutants rather than elimination.

[0004] The second is solidification / stabilization method, such as sealing thallium in glass or ceramic network through high-temperature melting or sintering technology. This method has a long-lasting solidification effect, but usually has extremely high energy consumption and complex process, making it difficult to be directly applied to large-scale water phase pollutant treatment.

[0005] Therefore, it is of great technical value and environmental significance to develop a material that can simultaneously achieve high selectivity capture of thallium ions and convert them into stable mineral phases under normal temperature and near-neutral aqueous conditions, achieving the goal of one-step completion from "separation" to "harmless". SUMMARY

[0006] The present application aims to overcome the defects of existing adsorption materials, such as insufficient solidification ability of thallium, risk of secondary pollution, and difficulty of solidification / stabilization technology in direct application to water treatment, and provides a composite material that can simultaneously achieve selective capture and in-situ stabilization of thallium ions under mild aqueous conditions, and a preparation method thereof.

[0007] To achieve the above-mentioned purpose, in a first aspect, the present application provides a composite material for adsorbing heavy metal thallium, comprising: a porous carrier; organic ligands grafted on the porous carrier, which have specific bonding with monovalent thallium ions (Tl + ); and metal sulfide nanoparticles loaded on the porous carrier.

[0008] The surface of the porous carrier is modified with a bifunctional coupling agent, the first functional group of the coupling agent is covalently bonded with the organic ligands, and the second functional group is an active group capable of coordinating with metal ions; the metal sulfide nanoparticles are generated in-situ by the coordination of the active group.

[0009] Further, the bifunctional coupling agent is a silane coupling agent, which has a general formula of X 3 Si-R-Y, wherein X is a hydrolysable group, R is an alkylene chain, and Y is a mercapto group (-SH).

[0010] Further, the bifunctional coupling agent is a silane coupling agent, which has a general formula of X 3 Si-R-Y, wherein X is a hydrolysable group, R is an alkylene chain, and Y is a mercapto group (-SH).

[0011] Further, the organic ligand is a compound containing a thiacrown ether structure.

[0012] Further, the organic ligand is a compound containing a thiacrown ether structure.

[0013] Further, the metal sulfide nanoparticles are ferrous sulfide (FeS) or manganese sulfide (MnS).

[0014] Further, the porous carrier is an amino-functionalized mesoporous silica microsphere.

[0015] In a second aspect, the present application provides a method for preparing the composite material for adsorbing thallium, comprising the following steps:

[0016] S1, carrier coupling: the porous carrier is surface-modified by a bifunctional coupling agent to obtain a coupled carrier with active groups on the surface;

[0017] S2, grafting of capture units: the coupled carrier is grafted with an organic ligand specific to Tl + The organic ligand reacts with the first functional group of the bifunctional coupling agent to form a specific complex.

[0018] S3, in-situ synthesis of solidification units: first, the carrier grafted with the organic ligand is contacted with a solution of a soluble metal salt, so that the metal ions are coordinated with the active groups and enriched at the sites of the active groups; then, a sulfur source is introduced, so that the enriched metal ions react with the sulfur source at the sites of the active groups, thereby selectively generating metal sulfide nanoparticles in-situ.

[0019] Further, in step S3, the soluble metal salt is ferrous sulfate heptahydrate, and the sulfur source is thioacetamide; the reaction is carried out in a hydrothermal environment at 100-120°C under the protection of an inert atmosphere.

[0020] In addition, the composite material provided by the present application is particularly suitable for treating acid mine wastewater, thallium-containing wastewater in the electronic industry, and thallium-contaminated surface water in actual water environments.

[0021] Compared with the prior art, the present application has the following beneficial effects:

[0022] 1. Due to the grafting of thiacrown ether-based organic ligands based on "soft acid-soft base" specific interactions, the composite material in the present application can still maintain high adsorption capacity for trace Tl + (1 mg / L) in simulated wastewater containing high concentrations of alkali metal or alkaline earth metal competitive ions (such as Na + , K + , Ca 2+ , Mg 2+ each 1000 mg / L), and the capacity is significantly higher than that of materials without this specific ligand. This indicates that the organic ligand effectively improves the capture ability of the material for Tl + in complex water quality.

[0023] 2. The present application constructs a synergistic system with spatial proximity between "capture units" (organic ligands) and "solidification units" (metal sulfide precursor sites) through the process of "bifunctional coupling agent" bridging and "mercapto-directed in-situ synthesis". This structure not only provides abundant effective sites, making the composite material have high adsorption capacity for Tl + , but more importantly, enables the enriched Tl + to be quickly converted into stable mineral phases such as thallium sulfide with a very low solubility product. Long-term leaching experiments have verified that the leaching concentration of thallium in the treated solid phase under acidic conditions can be lower than 0.1 μg / L, achieving deep fixation of pollutants and significantly reducing the risk of secondary pollution.

[0024] 3. The entire adsorption and solidification process can be completed in one step at room temperature in a near-neutral aqueous environment, without the need for subsequent high-temperature sintering or harsh chemical treatment, resulting in low energy consumption, simple process, and ease of large-scale application in actual water treatment engineering.

[0025] 4. Due to the use of "bifunctional coupling agent" in the present application, the "capture units" and "solidification units" form a synergistic system with spatial proximity on a nanoscale through chemical bonding. This structure greatly shortens the mass transfer path of thallium ions from the recognition site to the mineral conversion site, not only significantly accelerating the solidification reaction kinetics, but also greatly improving the final solidification capacity and stability through local high concentration effect.

[0026] 5. The preparation method in the present application ensures that metal sulfide nanoparticles can selectively and repeatedly grow on the pre-designed active sites through strict step sequence and condition control, especially the key step of "coordination enrichment first, then sulfidation", thereby reliably and consistently achieving the structure and performance of the composite material. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 is the process flowchart of the present application;

[0028] Figure 2The XRD patterns of the composite material prepared in Example 1 before and after adsorbing thallium are shown in the following figure.

[0029] Figure 3 The adsorption capacity of the material of Example and Comparative Example to Tl + is shown in the following figure. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application will be described in detail below with examples. The following examples are only used to illustrate the present application, but not to limit the scope of the present application. The experimental methods not specified in the examples are usually carried out according to the conventional conditions in the art or according to the suggested conditions of the manufacturers. The reagents and instruments used are conventional products available in the market, unless otherwise specified.

[0031] Example 1

[0032] Step 1, synthesis and template removal of mesoporous silica microspheres (SiO2):

[0033] 2.00 g of cetyltrimethylammonium bromide (CTAB) was dissolved in 480 mL of deionized water and 32 mL of a mixture of 25% ammonia water. Under the conditions of 35℃ water bath and 500 rpm mechanical stirring, 10.0 mL of tetraethyl orthosilicate (TEOS) was added dropwise at a rate of 2 mL / min using a constant pressure dropping funnel. After the addition was completed, the reaction was continued at a constant speed under stirring at 35℃ for 2 hours. After the reaction was completed, the white suspension was centrifuged (8000 rpm, 10 min), and washed with deionized water and anhydrous ethanol each for three times until the filtrate was clear. The product was dried in an oven at 60℃ for 12 hours, then placed in a muffle furnace, and heated to 550℃ at a rate of 2℃ / min, and kept in air atmosphere for 6 hours to completely remove the CTAB template, to obtain pure mesoporous silica microspheres (SiO2).

[0034] Step 2, preparation of amino-functionalized mesoporous silica microspheres (NH2-SiO2):

[0035] 1.00 g of SiO2 microspheres obtained in Step 1 was dispersed in 100 mL of anhydrous toluene, and ultrasonically treated for 30 minutes to make it fully dispersed. 2.0 mL of 3-aminopropyltriethoxysilane (APTES, purity ≥98%) was added, and the reaction was carried out under reflux condensation at 110℃ oil bath under nitrogen protection for 12 hours. After the reaction was completed, the product was washed with toluene and ethanol each for three times, and dried at 60℃ under vacuum to obtain the amino-functionalized carrier (NH2-SiO2).

[0036] Step 3, carrier coupling (S1):

[0037] NH2-SiO2, 1.00 g, was dispersed in 100 mL of anhydrous toluene and ultrasonically dispersed for 30 min. 2.0 mL of 3-mercaptopropyltrimethoxysilane (MPTMS, purity ≥ 97%) was added, and the reaction was carried out under reflux in an oil bath at 110°C for 12 h under nitrogen protection. After the reaction was completed, the product was washed with toluene and ethanol three times, respectively, and dried at 60°C under vacuum to obtain a thiol-functionalized carrier (SH-SiO2).

[0038] Step 4, grafting of the capture unit (S2):

[0039] SH-SiO2, 0.80 g, was dispersed in 80 mL of anhydrous N,N-dimethylformamide (DMF). 0.50 g of 3,3’-(1,10-dithia-4,7-dioxadodecane-1,10-diyl)dipropionic acid (thiacrown ether derivative, purity ≥ 95%), 0.60 g of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC·HCl), and 0.36 g of N-hydroxysuccinimide (NHS) were added, and the reaction was carried out at room temperature (25 ± 2°C) under stirring at 300 rpm for 24 h under nitrogen atmosphere. After the reaction, the product was washed with DMF and ethanol four times alternately, and dried at 60°C under vacuum to obtain a ligand-functionalized carrier (L-SiO2).

[0040] Step 5, in-situ synthesis of the solidification unit (S3):

[0041] L-SiO2, 0.50 g, was dispersed in 50 mL of deionized water which was strictly deoxygenated by bubbling high-purity nitrogen for 30 min. 0.278 g of ferrous sulfate heptahydrate (FeSO4·7H2O, 1.0 mmol) was added, and the reaction was carried out under stirring at 300 rpm for 2 h at room temperature under nitrogen protection, so that Fe 2+ was fully located and enriched on the surface of the thiol groups of the carrier. Subsequently, 0.075 g of thioacetamide (TAA, 1.0 mmol) was added, and the whole system was transferred into a 100 mL polytetrafluoroethylene-lined high-pressure reaction kettle, which was sealed and placed in a blast drying oven at 120°C for 6 h. After the reaction was completed, the product was naturally cooled to room temperature, washed with deoxygenated deionized water and ethanol three times, and dried at 60°C under vacuum to obtain the final target composite, which was denoted as L-SiO2@FeS.

[0042] Example 2

[0043] The preparation steps were the same as in Example 1, except that in Step 5, ferrous sulfate heptahydrate was replaced by an equimolar amount (1.0 mmol) of manganese chloride (MnCl2·4H2O), and the final composite was prepared, which was denoted as L-SiO2@MnS.

[0044] Comparative Example 1

[0045] The ligand-grafted support (L-Si02) was prepared according to the procedure of Example 1, steps 1, 2, 3, 4, without performing step 5 (in situ synthesis of the immobilized unit).

[0046] Comparative Example 2

[0047] The thiol-functionalized support (SH-Si02) was prepared according to the procedure of Example 1, steps 1, 2, 3. Then, step 4 (grafting of the capture unit) was skipped and step 5 of Example 1 was performed directly on SH-Si02, resulting in a material loaded with FeS only, noted FeS-Si02.

[0048] Comparative Example 3

[0049] The L-Si02from Comparative Example 1 and the FeS-Si02from Comparative Example 2 were physically mixed by simple milling for 30 minutes in a ratio of 1 : 1 by mass of support, resulting in a physically mixed material.

[0050] Comparative Example 4

[0051] The NH2-Si02support was prepared according to the procedure of Example 1, steps 1, 2.

[0052] Instead of coupling the NH2-Si02with MPTMS, 1.00 g of NH2-Si02was directly amidated with 0.50 g of the above thiacrown ether derivative in the presence of EDC-HCl and NHS in DMF (conditions as in Example 1, step 4), resulting in a support (L-Si02-noSH) grafted with the ligand but without thiol directing sites.

[0053] FeS was loaded on L-Si02-noSH by a conventional co-precipitation method: 0.50 g of L-Si02-noSH was dispersed in 50 mL of deoxygenated deionized water, and 0.278 g of FeS04-7H20 and 0.240 g of Na2S-9H20 were added (molar ratio 1 : 1) while stirring at room temperature under nitrogen for 12 hours. The product was washed and dried, resulting in a material noted Random-L-Si02@FeS.

[0054] Comparative Example 5

[0055] The ligand-functionalized support (L-Si02) was prepared according to the procedure of Example 1, steps 1-4. Subsequently, in step 5, the following modification was performed: instead of first coordinating metal ions, 0.50 g of L-Si02was dispersed in 50 mL of deoxygenated deionized water and 0.278 g of FeS04-7H20 and 0.075 g of thioacetamide (TAA) were added simultaneously to the suspension. It was immediately transferred to a high-pressure reactor and reacted for 6 hours under the same conditions (nitrogen atmosphere, 120 °C). The product was washed and dried in the same way, resulting in a material noted One-Pot-L-Si02@FeS.

[0056] Performance test experiment

[0057] 1. Selective adsorption and capacity test experiment, this experiment aims to simulate high-salt background wastewater, to evaluate the adsorption performance and selective trend of the composite material for Tl + in the presence of high-concentration competitive ions, the specific steps are as follows:

[0058] Prepare a simulated wastewater containing 1000 mg / L of Na + , K + , Ca 2+ , Mg 2+ (as NaCl, KCl, CaCl2, MgCl2) as competitive ions, and Tl + (initial concentration 1.0 mg / L added as TlNO3) with pH adjusted to 6.5±0.2 by dilute HNO3 or NaOH solution. Take 50.0 mg of each example and comparative example material (solid-liquid ratio 1:2 g / L) and add to 100.0 mL of the above solution, and place in a constant temperature oscillator (25°C, 150 rpm) to avoid light oscillation for 24 hours to reach adsorption equilibrium. Take samples, filter through a 0.22 μm water filter membrane, and determine the residual Tl + concentration in the filtrate by inductively coupled plasma mass spectrometry, and calculate the equilibrium adsorption capacity of the material. The results are shown in Figure 3 and Table 1. The equilibrium adsorption capacity of Example 1 (L-SiO2@FeS) for Tl + is 38.5 mg / g. Especially in an environment containing a large amount of competitive ions, its adsorption capacity is much higher than that of Comparative Example 2 (FeS-SiO2, 5.1 mg / g) without specific ligand, which indicates that the grafted thiacrown ether ligand has obvious preferential adsorption for Tl + .

[0059] 2. In-situ solidification verification experiment:

[0060] After the above adsorption experiment is performed and saturation is reached, the material of Example 1 is separated, washed twice with deionized water, and dried at 60°C under vacuum. X-ray diffractometer is used to analyze the phase of the material before and after adsorption. The results are shown in Figure 2 After adsorption saturation, the XRD pattern of the material shows obvious characteristic diffraction peaks of thallium sulfide (Tl2S) at 2θ≈23.5°, 27.8°, 32.5°, etc., while no such crystal phase is detected in the spectrum of the material before adsorption and all the comparative example materials after adsorption saturation, which directly proves that the material of the present application can realize in-situ mineralization solidification of thallium.

[0061] 3. Long-term stability (leaching) experiment:

[0062] The saturated adsorption materials were separated and dried. Referring to the acid condition of "Solid Waste - Leaching Toxicity Leaching Method - Sulfuric Acid Nitric Acid Method" (HJ / T 299-2007), 0.100 g of thallium-containing solid waste was mixed with 20.0 mL of nitric acid leaching agent (prepared with concentrated nitric acid) with pH = 2.00 ± 0.05, and was placed on a rolling oscillator at a speed of 30 ± 2 rpm for 24 ± 0.5 hours at room temperature. The leaching solution was filtered through a 0.45 μm filter membrane, and the thallium concentration was determined by ICP-MS. The results are shown in Table 1.

[0063] 4. Metal sulfide type verification experiment:

[0064] To verify the applicability of different metal sulfides, the same adsorption and leaching tests as in Example 1 were performed on Example 2 (L-SiO2@MnS). Under the same competitive ion conditions, its equilibrium adsorption capacity for Tl + was 36.8 mg / g, and the acid leaching concentration after adsorption saturation was 0.08 μg / L. This indicates that using MnS as the solidification unit, efficient adsorption and deep solidification of Tl + can also be achieved, verifying the feasibility of the selection of metal sulfides in the present application.

[0065] Table 1: Performance test data of each example and comparative example

[0066] Material No. Tl + equilibrium adsorption capacity (mg / g) Acid leaching concentration after adsorption saturation (μg / L) Example 1 38.5 ＜0.05 Example 2 36.8 0.08 Comparative Example 1 35.2 ＞1200 Comparative Example 2 5.1 15.3 Comparative Example 3 22.7 85.0 Comparative Example 4 18.9 320.0 Comparative Example 5 25.4 210.0

[0067] Conclusion

[0068] The comparative data of the above examples and comparative examples clearly show that:

[0069] The composite material provided by the present application (Example 1) successfully constructs a "capture-solidification" spatially proximal synergistic system through the unique design of "dual-functional coupling agent bridging" and "thiol-directed in-situ vulcanization". Its adsorption capacity (38.5 mg / g) is higher than that of a single adsorption material (Comparative Example 1, 35.2 mg / g), and its leaching concentration (<0.05 μg / L) is much lower than that of all comparative examples, proving the deep solidification effect.

[0070] The comparison between Comparative Example 3 (physical mixing) and Example 1 proves that the structural integration design is the key to the synergistic effect, and physical mixing cannot achieve the same solidification stability.

[0071] The comparison between Comparative Example 4 (no guided loading) and Example 1 verifies the substantial contribution of the "thiol-directed" structural feature to the selective growth of nanoparticles and the excellent performance obtained.

[0072] Comparative Example 5 (one-pot method) and Example 1 are compared to further confirm that the specific preparation process of "coordination enrichment first and sulfuration later" plays a decisive role in achieving the above-mentioned structure and deep curing effect.

[0073] In addition, the comparison between Example 2 and Example 1 shows that excellent results can also be achieved by using manganese sulfide (MnS) as a curing unit, which verifies the universality of the technical solutions of the present application.

[0074] In summary, the present application successfully provides a composite material capable of realizing high-selective adsorption and deep in-situ mineralization curing of trace heavy metal thallium in water and an efficient preparation method thereof.

[0075] The above is only an example and description of the concept of the present application. Those skilled in the art can make various modifications or supplements to the described specific examples or use similar ways to replace them, as long as they do not deviate from the scope defined by the concept of the present application, which shall belong to the protection scope of the present application.

Claims

1. A composite material for adsorbing the heavy metal thallium, characterized in that, The application relates to a porous carrier, an organic ligand with specific binding to monovalent thallium ions grafted on the porous carrier, and metal sulfide nanoparticles loaded on the porous carrier. The porous carrier is surface-modified with a bifunctional coupling agent, the first functional group of which is covalently bonded to the organic ligand, and the second functional group is an active group capable of coordinating with metal ions; the metal sulfide nanoparticles are generated in situ by the coordination of the active group. The bifunctional coupling agent is a silane coupling agent with a general formula of X3Si-R-Y, wherein X is a hydrolysable group, R is an alkylene chain, and Y is a mercapto group. The silane coupling agent is 3-mercaptopropyl trimethoxysilane. The organic ligand is a compound containing a thiacrown ether structure.

2. The composite material for adsorbing heavy metal thallium according to claim 1, wherein The organic ligand is 3,3'- (1,10-dithia-4,7-dioxacyclododecane-1,10-diyl) dipropionic acid, which is covalently bonded to the first functional group of the bifunctional coupling agent through an amide bond.

3. The composite material for adsorbing heavy metal thallium according to claim 2, wherein The metal sulfide nanoparticles are ferrous sulfide or manganese sulfide.

4. The composite material for adsorbing heavy metal thallium according to claim 1, wherein The porous carrier is an amino-functionalized mesoporous silica microsphere.

5. The composite material for adsorbing heavy metal thallium according to claim 4, wherein The application also discloses a preparation method of the porous carrier.

6. The composite material for adsorbing heavy metal thallium according to claim 1, wherein The application comprises the following steps:

7. The composite material for adsorbing heavy metal thallium according to claim 1, wherein S1, carrier coupling: surface-modifying the porous carrier with a bifunctional coupling agent to obtain a coupling carrier with active groups on the surface; 8. A method of preparing a composite material for adsorbing the heavy metal thallium as claimed in any one of claims 1 to 7, characterized in that, S2, capture unit grafting: reacting the coupling carrier with an organic ligand with specific binding to monovalent thallium ions, so that the organic ligand is covalently bonded to the first functional group of the bifunctional coupling agent; S3, in-situ synthesis of solidification unit: firstly, contacting the carrier grafted with the organic ligand with a soluble metal salt solution, so that the metal ions are coordinated with the active groups and enriched at the sites of the active groups; Subsequently, a sulfur source is introduced, so that the enriched metal ions react with the sulfur source at the sites of the active groups, thereby selectively generating metal sulfide nanoparticles in situ. In step S3, the soluble metal salt is ferrous sulfate heptahydrate, and the sulfur source is thioacetamide; the reaction is carried out in a hydrothermal environment at 100-120 DEG C under the protection of an inert atmosphere. ​ 9. The method of claim 8, wherein, ​

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