A highly selective magnetic covalent triazine organic polymer adsorbent, its preparation method and application

Abstract

This invention discloses a highly selective magnetic covalent triazine organic polymer adsorbent, its preparation method, and its applications, belonging to the technical field of magnetic solid adsorbent compositions. This invention prepares a highly selective magnetic covalent triazine organic polymer adsorbent in an aqueous solution via a green and mild redox reaction. This method has advantages such as low cost, simplicity, rapid reaction, mild reaction conditions, and a green and environmentally friendly process that does not consume harmful organic solvents. The prepared adsorbent is rich in triazine and thiol functional groups, has a large specific surface area, high porosity, and is easily magnetically separated. It can achieve highly selective adsorption of heavy metal mercury ions over a wide pH range, with fast adsorption kinetics and high adsorption capacity. Furthermore, the highly selective magnetic covalent triazine organic polymer adsorbent can meet the needs of multiple fields and has good applicability, showing broad application prospects in the adsorption removal, extraction separation, enrichment, and detection of heavy metal mercury ions in water.

Description

Technical Field

[0001] This invention relates to the field of magnetic solid adsorbent composition technology, and in particular to a highly selective magnetic covalent triazine organic polymer adsorbent, its preparation method, and its application. Background Technology

[0002] Mercury (Hg), a well-known highly toxic heavy metal, is widely used in metallurgy, electrolysis, pharmaceuticals, and electronics. Mercury-polluted water not only harms aquatic plants and animals but also poses serious risks to humans and ecosystems through the food chain. Therefore, efficiently removing excess mercury from water and accurately and sensitively measuring trace amounts of mercury in water are crucial for ensuring water safety and environmental water quality monitoring.

[0003] Inductively coupled plasma mass spectrometry (ICP-MS) is a commonly used analytical instrument for detecting mercury in water, offering advantages such as high sensitivity and wide linearity. However, in practical sample analysis, it often faces challenges due to sample matrix interference and low concentrations of target substances. To improve detection sensitivity and reduce interference, highly efficient solid adsorbents and solid-phase extraction (SPE) techniques are typically used before instrumental analysis to achieve pre-separation of the sample matrix and pre-enrichment of the target element.

[0004] In recent years, novel solid adsorbents such as carbon-based materials, magnetic materials, mesoporous materials, metal-organic frameworks, and porous organic polymers have been continuously developed for water treatment and purification. Among them, porous organic polymers (POPs) are polymer network porous materials formed by the covalent linkage of organic monomers composed of lightweight elements. Due to their advantages such as large specific surface area, high porosity, and tunable structure, they are widely used for the adsorption of metal ions. However, POPs have low density, and their use in water treatment inevitably requires cumbersome operations such as filtration and centrifugation, making solid-liquid two-phase separation time-consuming and inefficient. The separation and recovery process of solid POPs adsorbents is also cumbersome, increasing operational complexity. Introducing magnetic nanomaterials into POPs can produce magnetic POPs that can achieve rapid magnetic separation using an external magnetic field, thus simplifying the separation operation. However, existing magnetic POPs often require harsh synthesis conditions or the use of toxic and harmful organic solvents or expensive precious metal catalysts.Trac-Trends in Analytical Chemistry (2020, 132, 116048.), limiting its large-scale application. Therefore, developing a green and mild new method for preparing magnetic POPs is of great practical significance.

[0005] Trisodium trithiocyanate is a newly developed, low-cost, environmentally friendly heavy metal ion removal agent in recent years. It can react with sulfophilic heavy metal ions in water, such as Hg. 2+ Pb 2+ Plasma forms stable compounds and precipitates out, thereby achieving the purpose of removing heavy metal ions. However, trisodium trithiocyanate, as a homogeneous adsorbent, is difficult to recover and reuse after use. Modifying trithiocyanate or trisodium trithiocyanate onto some biomass solid materials can produce solid adsorbents that achieve highly efficient adsorption of metal ions, and the materials can be reused. For example, Chinese invention patent CN109012604A discloses a corn husk adsorbent material modified with trithiocyanate, its preparation method, and its application. This material utilizes trithiocyanate-modified corn husk adsorbent to improve the adsorption rate of trace mercury ions. Another example is Chinese invention patent CN110280219A, which discloses a method for preparing a sunflower stem pith adsorbent modified with trithiocyanate. After pretreating the natural polymer sunflower stem pith, trithiocyanate-modified magnetic reed is used as an adsorbent to adsorb and separate gold, giving it the characteristics of a natural polymer and the selectivity of special active groups. However, all of the above preparation methods use toxic and harmful organic solvents or expensive organic monomers, which are environmentally unfriendly and increase production and wastewater treatment costs. Furthermore, when these solid adsorbents are used in water treatment, cumbersome steps such as filtration and centrifugation are required to recover the adsorbent, resulting in low efficiency.

[0006] In summary, developing new, green, and mild methods using low-cost raw materials to prepare adsorbents that are easy to separate and can be recycled multiple times is of great practical significance for reducing the cost of heavy metal pollution control and achieving efficient separation and detection of heavy metal ions from the sample matrix in water samples. Summary of the Invention

[0007] In view of the above-mentioned deficiencies of the prior art, in a first aspect of the present invention, a method for preparing a low-cost, green, mild, efficient, and convenient highly selective magnetic covalent triazine organic polymer adsorbent is provided, comprising the following steps:

[0008] (1) Prepare a solution of trithiocyanuric acid monosodium salt (TMS);

[0009] (2) Add a dispersion of core-shell Fe3O4@SiO2 magnetic nanoparticles and a solution of 1,3,5-triazine-2,4,6-trithiocyanuric acid trisodium salt (TTS) to a solution of monosodium trithiocyanate, and then add a mixed solution of iodine and potassium iodide to carry out a redox reaction. After the reaction is completed, the product is recovered and purified to obtain a highly selective magnetic covalent triazine organic polymer adsorbent.

[0010] In the preparation method of this invention, core-shell Fe3O4@SiO2 magnetic nanoparticles are used as the core, and TMS and tri-TTS are used as functional monomers. Through the oxidation of elemental iodine, TMS and TTS are reduced to form a polymer linked by disulfide bonds, thereby introducing a covalent triazine organic polymer onto the surface of the magnetic nanoparticles. Based on this principle, magnetic poly(trithiocyanic acid) polymers (MPTAPs), i.e., highly selective magnetic covalent triazine organic polymer adsorbents, are synthesized in an aqueous solution.

[0011] Sodium trithiocyanate can be purchased commercially available reagents or produced temporarily by reacting trithiocyanate with sodium hydroxide. Considering that the cost of finished sodium trithiocyanate is higher than that of trithiocyanate and sodium hydroxide alone, it is appropriate to prepare the sodium trithiocyanate solution by reacting trithiocyanate with sodium hydroxide, while still achieving the purpose of this invention.

[0012] Preferably, in step (1), the sodium trithiocyanate solution is temporarily generated by the reaction of trithiocyanate (TA) and sodium hydroxide in a solution environment, and its preparation method includes the following steps:

[0013] Trithiocyanate was ultrasonically dispersed in water to obtain a trithiocyanate dispersion; sodium hydroxide aqueous solution was added to the trithiocyanate dispersion, mixed and reacted to obtain a monosodium trithiocyanate solution.

[0014] More preferably, the amount of trithiocyanate added is 1-2 mmol; the amount of water used is 50-100 mL; and the concentration of the sodium hydroxide aqueous solution is 0.10-0.11 mol L. -1 The dosage is 10-20 mL.

[0015] More preferably, the sodium hydroxide aqueous solution is added dropwise at a rate of 50-60 drops / min; the mixing stirring rate is 400-500 rpm; the reaction time is 2-3 h; and the reaction temperature is room temperature.

[0016] Preferably, in step (2), the dispersion of core-shell Fe3O4@SiO2 magnetic nanoparticles is prepared by adding 100-300 mg of core-shell Fe3O4@SiO2 magnetic nanoparticles to 25-30 mL of water and then dispersing by ultrasonication; the 1,3,5-triazine-2,4,6-trithione trisodium salt solution is prepared by dissolving 0.5-1 mmol of 1,3,5-triazine-2,4,6-trithione trisodium salt in 25-30 mL of water; and the mixed solution of iodine and potassium iodide is prepared by mixing 1 mmol of elemental iodine with 5 mL of solution containing 0.2-0.5 g / mL potassium iodide. -1 It is prepared by mixing potassium iodide aqueous solution.

[0017] The core-shell structured Fe3O4@SiO2 magnetic nanoparticles used in the steps can be obtained directly from existing materials, commercially available products, or through self-production. This invention is suitable for preparing these particles using co-precipitation and sol-gel hydrolysis methods. Co-precipitation can obtain chemically homogeneous nanoparticles through chemical reactions in solution, meaning that metal ions can be uniformly distributed during precipitation, ensuring a stable composition ratio for each nanoparticle. Sol-gel hydrolysis achieves highly uniform mixing of materials through liquid-phase reactions, which can also improve the uniformity of nanoparticles. Sol-gel hydrolysis can be carried out at lower temperatures, helping to save energy and reduce costs.

[0018] More preferably, the core-shell structured Fe3O4@SiO2 magnetic nanoparticles are prepared by co-precipitation and sol-gel hydrolysis, including the following steps:

[0019] S1. Under an inert gas atmosphere, the chloride salts of Fe(III) and Fe(II) were dissolved in water, heated to 80-90℃ and maintained for 50-60 min; then concentrated ammonia was added and the reaction continued at this temperature for 30-40 min; after the reaction was completed, the mixture was cooled to room temperature, the product was recovered and purified, and Fe3O4 magnetic nanoparticles were obtained.

[0020] S2. The Fe3O4 magnetic nanoparticles are dispersed in a mixture of water and ethanol, concentrated ammonia and tetraethyl orthosilicate are added, and a SiO2 layer is formed on the surface of the Fe3O4 magnetic nanoparticles by hydrolysis of tetraethyl orthosilicate (TEOS). After reacting at 25-30 °C for 10-12 h, the product is recovered and purified to obtain core-shell structured Fe3O4@SiO2 magnetic nanoparticles.

[0021] In the preparation of core-shell structured Fe3O4@SiO2 magnetic nanoparticles, the chloride salts of Fe(III) and Fe(II) can be ferric chloride, ferrous chloride, or their corresponding hydrates, depending on the actual conditions.

[0022] More preferably, in S1, the amount of Fe(III) chloride is 20 mmol, the molar ratio of Fe(III) chloride to Fe(II) chloride is 2:1-1.1, and the amount of water is 100-150 mL; in S2, the volume ratio of water to ethanol in the mixture is 1:3-4, the amount of the mixture is 150-200 mL, the amount of concentrated ammonia is 2-2.5 mL, and the amount of tetraethyl orthosilicate is 2-2.5 mL.

[0023] Preferably, in step (2), the addition of raw materials and the redox reaction are carried out under a stirring environment with a stirring rate of 400-500 rpm; when adding the mixed solution of iodine and potassium iodide, the temperature of the reaction system is 0-10 ℃ to avoid the volatilization of iodine; the mixed solution of iodine and potassium iodide is added dropwise at a rate of 50-60 drops / min; after the mixed solution of iodine and potassium iodide is added, the mixture is allowed to naturally warm to room temperature.

[0024] Preferably, in step (2), the redox reaction is carried out at room temperature for 10-12 hours.

[0025] In a second aspect of the present invention, a highly selective magnetic covalent triazine organic polymer adsorbent is provided, which is easy to recycle and separate, has strong anti-interference ability, and has a high-efficiency adsorption and removal effect on heavy metal mercury ions, and is prepared by the method of the first aspect of the present invention.

[0026] According to the preparation method provided in the first aspect of the present invention, the structure of the highly selective magnetic covalent triazine organic polymer adsorbent comprises a magnetic Fe3O4 core, a SiO2 layer sequentially wrapped around the Fe3O4 core, and a covalent triazine organic polymer layer based on trithiocyanate. Functionally, it achieves the characteristics of easy recovery and separation, strong anti-interference ability, and highly efficient adsorption and removal of heavy metal mercury ions.

[0027] In a third aspect of the invention, an application of the highly selective magnetic covalent triazine organic polymer adsorbent of the second aspect of the invention is provided, specifically as an adsorbent material for the adsorption, removal, extraction, separation, enrichment, and detection of heavy metal mercury ions in water.

[0028] Based on the above technical solutions, the inventive concept of this invention lies in using monosodium trithiocyanate and trisodium trithiocyanate organic monomers as reducing agents and iodine as an oxidizing agent, utilizing a mild redox reaction under mild conditions to synthesize a porous polythiocyanate organic polymer on the surface of magnetic nanomaterials. This yields a magnetic covalent triazine organic polymer (MPTAPs) with highly efficient and selective adsorption and removal of heavy metal mercury ions. The preparation method provided by this invention has advantages such as being green, mild, efficient, convenient, low-cost, easy to prepare, and reusable. The prepared material has advantages such as large specific surface area, wide applicable pH range for adsorption, fast adsorption kinetics, high adsorption capacity, and easy dispersion and magnetic separation. Furthermore, this material can achieve rapid adsorption and desorption of heavy metal mercury ions, and can withstand interference from high concentrations of coexisting salts. It can achieve rapid extraction and separation under an external magnetic field, and can be used for the efficient removal of mercury ions from acidic or neutral industrial wastewater, as well as for low concentrations of Hg. 2+ This method enables extraction and enrichment, improving detection sensitivity and thus achieving sensitive detection of mercury ions in environmental water samples and laboratory wastewater. It can provide information on the content of heavy metal ions for water environment monitoring and has good application prospects in the fields of wastewater treatment and water quality analysis.

[0029] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0030] This invention provides a method for preparing a highly selective magnetic covalent triazine organic polymer adsorbent, which has the advantages of high efficiency, convenience, greenness, and mild reaction conditions.

[0031] This invention provides a highly selective magnetic covalent triazine organic polymer adsorbent, which consists of core-shell Fe3O4@SiO2 magnetic nanoparticles and a covalent triazine organic polymer layer based on trithiocyanate. It features easy recovery and separation, strong anti-interference ability, and highly efficient and selective adsorption and removal of heavy metal mercury ions.

[0032] This invention provides an application of a highly selective magnetic covalent triazine organic polymer adsorbent that can meet the needs of multiple fields and has good applicability. It has broad application prospects in multiple fields such as adsorption removal, extraction separation, enrichment and detection of heavy metal mercury ions in water. Attached Figure Description

[0033] Figure 1 A schematic diagram of the synthesis of MPTAPs;

[0034] Figure 2(a) and (b) are transmission electron microscope (TEM) images of core-shell Fe3O4@SiO2 magnetic nanoparticles at different magnifications, and (c) and (d) are TEM images of MPTAPs at different magnifications.

[0035] Figure 3 (a)-(d) show the infrared spectroscopy (IR), magnetic intensity, thermogravimetric analysis and X-ray diffraction (XRD) characterization results of core-shell Fe3O4@SiO2 magnetic nanoparticles and MPTAPs, respectively.

[0036] Figure 4 Nitrogen adsorption / desorption isotherms and pore distribution diagrams of MPTAPs;

[0037] Figure 5 pH value for the adsorption of Hg by MPTAPs 2+ The influence of common coexisting metal ions;

[0038] Figure 6 (a) and (b) show the effect of adsorption time on the adsorption of Hg by MPTAPs, respectively. 2+ The influence of the pseudo-second-order adsorption kinetics and the fitting curve of the pseudo-second-order adsorption kinetics;

[0039] Figure 7 (a) and (b) represent the effects of initial mercury ion concentrations on the adsorption of Hg by MPTAPs, respectively. 2+ The influence of Langmuir adsorption isotherm fitting curves;

[0040] Figure 8 (a)-(d) represent the effects of thiourea content, hydrochloric acid concentration, elution volume, and elution time on the extraction of Hg from MPTAPs, in that order. 2+ The impact of recovery rate.

[0041] Figure 9 (a)-(c) represent the effects of sample volume, adsorption time, and adsorbent dosage on the extraction of Hg from MPTAPs, in that order. 2+ The impact of recovery rate;

[0042] Figure 10 To evaluate the reusability performance of MPTAPs. Detailed Implementation

[0043] The present invention is further illustrated below by way of embodiments, but the invention is not limited to the scope of the embodiments described herein. Experimental methods in the following embodiments that do not specify specific conditions were performed according to conventional methods and conditions, or as selected according to the product instructions.

[0044] In the following embodiments, the core-shell structured Fe3O4@SiO2 magnetic nanoparticles were prepared in-house, and the steps are as follows:

[0045] S1. Under nitrogen protection, weigh 5.41 g FeCl3·6H2O and 1.99 g FeCl2·4H2O into a 250 mL three-necked flask, add 100 mL of high-purity water, and start mechanical stirring to dissolve the iron salt. Then, under constant temperature water bath and mechanical stirring, heat to 85 ℃ and maintain for 1 h. Subsequently, increase the nitrogen flow rate and stirring speed, add 20 mL of concentrated ammonia water, and the color of the mixture changes from orange-yellow to black. Continue to stir the reaction at constant temperature for 30 min, then stop heating, cool to room temperature, stop mechanical stirring, remove nitrogen protection, and remove the supernatant from the obtained solid-liquid mixture by magnetic separation. The magnetic solid is washed 3-4 times each with high-purity water and ethanol to obtain Fe3O4 magnetic nanoparticles, which are stored in 100 mL of ethanol.

[0046] S2. Add Fe3O4 magnetic nanoparticles to a mixed solution of 200 mL of high-purity water and ethanol (1:3, v / v), and disperse evenly by ultrasonication. Under mechanical stirring, add 2 mL of concentrated ammonia water, then add 2 mL of TEOS. Stir the mixed solution for 12 h under constant temperature water bath heating at 30 ℃. After the reaction is completed, wash the obtained solid material with high-purity water and ethanol 3-4 times each, and dry it under vacuum at 60 ℃ for 24 h to obtain core-shell structured Fe3O4@SiO2 magnetic nanoparticles.

[0047] Example 1

[0048] A method for preparing a highly selective magnetic covalent triazine organic polymer adsorbent, such as... Figure 1 As shown, the steps are as follows:

[0049] (1) Weigh 177 mg TA (i.e., 1 mmol) and ultrasonically disperse it in 60 mL of high-purity water. Add it to a 250 mL three-necked flask, turn on the mechanical stirrer at 400 rpm, and then add 10 mL of 0.1 mol / L solution dropwise at a rate of 60 drops / min. -1 A sodium hydroxide aqueous solution was added to a TA solution and stirred in a water bath at room temperature for 2 h to prepare a TMS solution.

[0050] During the stirring reaction, 200 mg of core-shell Fe3O4@SiO2 magnetic nanoparticles were weighed and ultrasonically dispersed in 25 mL of high-purity water to obtain a dispersion of core-shell Fe3O4@SiO2 magnetic nanoparticles; simultaneously, 243 mg (1 mmol) of TTS was weighed and ultrasonically dispersed in 25 mL of high-purity water to obtain a TTS solution; and 508 mg (2 mmol) of elemental iodine was weighed and placed in 5 mL of 0.2 g / mL water. -1 A mixed solution of iodine and potassium iodide is prepared by mixing potassium iodide solutions.

[0051] (2) In the prepared TMS solution, while maintaining the aforementioned mechanical stirring rate, a dispersion of core-shell Fe3O4@SiO2 magnetic nanoparticles and a TTS solution were added. Then, an appropriate amount of ice was added to the water bath to maintain the ice-water bath temperature at 0-10℃. A mixed solution of elemental iodine and potassium iodide was then added dropwise at a rate of 60 drops / min. After the solution was added, no more ice was added to maintain the 0-10℃ temperature. The water bath heating was not turned on, and the ice-water bath was allowed to naturally warm up to room temperature. The reaction was stirred for 12 h at room temperature. After the reaction, the crude product was washed with water 2-3 times, and then treated with 0.1 mol L... -1 The product was washed 3-4 times with a mixed solution of dilute hydrochloric acid and ethanol (1:1, v / v), and then washed with water until neutral. The resulting solid product was freeze-dried to obtain highly selective magnetic covalent triazine organic polymer adsorbents (MPTAPs). The yield of MPTAPs was calculated to be approximately 93% based on the weight of MPTAPs and the amounts of TMS, TTS monomers, and Fe3O4@SiO2 magnetic nanoparticles.

[0052] Example 2

[0053] This embodiment investigated the effect of the TA to TTS molar ratio during the preparation of MPTAPs. The specific implementation scheme is as follows:

[0054] The amount of TA was kept basically the same as in Example 1 (i.e., 1 mmol TA corresponds to approximately 1 mmol of TMS), and the amount of TTS was changed to 2 mmol and 3 mmol, respectively. The molar ratio of TMS to TTS was 1:2 and 1:3, respectively. Other preparation conditions were kept the same as in Example 1, and two types of MPTAPs were prepared.

[0055] The yields of the obtained solid products were weighed and calculated. It was found that when the molar ratios of TMS and TTS were 1:2 and 1:3, the yields of MPTAPs were 79% and 62%, respectively. Compared with the MPTAPs prepared in Example 1 (TMS and TTS molar ratio of 1:1, yield of 93%), the yields were significantly lower.

[0056] The likely reason is that the reaction is more complete when the molar ratio of TMS to TTS is 1:1, which is related to the structures of TMS and TTS. TMS molecules contain one sodium sulfide salt site (sulfide anion active site), while TTS monomer molecules contain three sodium sulfide salt sites (sulfide anion active sites). In the presence of zero-valent iodine, iodine acts as an oxidant, promoting the oxidation of two divalent sulfide anions to form a monovalent disulfide bond. This allows two adjacent TMS or TTS molecules containing sulfide anions to connect and form a disulfide bond. Simultaneously, iodine is reduced to produce monovalent iodide anions. Since TTS molecules have three sulfide anion active sites, two adjacent TTS molecules can each consume one sulfide anion active site to form a disulfide bond. This process can be repeated to form long polymer chains from multiple TTS molecules. Similarly, one sulfide anion active site on TMS can connect with the remaining sulfide anion active sites on TTS, thus enabling the successful interconnection of TMS and TTS. According to the oxidation state equilibrium, 1 mmol of elemental iodine can oxidize 2 mmol of sulfide anions. In Example 1, when both TMS and TTS were used at 1 mmol, the total amount of sulfide anions was 4 mmol. If all sulfide anions were to undergo a complete oxidation reaction to form disulfide bonds, the amount of elemental iodine should be 2 mmol. Therefore, a TMS / TTS molar ratio of 1:1 results in a more complete reaction. If the TMS / TTS molar ratio is 1:2 or 1:3, it means that there is an excess of TTS reaction sites. Under the condition that the amount of iodine oxidant remains constant, some TTS will not be able to undergo a redox reaction to form disulfide bonds, resulting in an excess of monomers and a lower yield of MPTAPs.

[0057] To improve product yield and reduce costs and reagent consumption, the molar ratio of TMS to TTS was fixed at 1:1 in subsequent examples.

[0058] Example 3

[0059] This embodiment investigated the effect of the amount of core-shell Fe3O4@SiO2 magnetic nanoparticles used in the preparation of MPTAPs. The specific implementation scheme is as follows:

[0060] The amounts of TMS and TTS were kept basically the same as in Example 1 (i.e., 1 mmol TA produces 1 mmol TMS and 1 mmol TTS). The amounts of Fe3O4@SiO2 magnetic nanoparticles with different core-shell structures were changed to 100 mg and 300 mg, respectively. Other steps were the same as in Example 1. The yield of the obtained solid products was weighed and calculated, and the magnetic properties of different products were compared.

[0061] When the amount of core-shell Fe3O4@SiO2 magnetic nanoparticles was 100 mg and 300 mg, the yields of MPTAPs were 86% and 95%, respectively, both around 90%. However, the fewer the magnetic cores, the weaker the magnetism of the resulting product. When the amount of core-shell Fe3O4@SiO2 magnetic nanoparticles was 100 mg, the magnetism of the resulting product was significantly weakened, and the magnetic separation sedimentation time after the MPTAPs were dispersed in water required more than 10 minutes, indicating a significant increase in magnetic separation time. When the amount of magnetic cores increased to 300 mg, the resulting product had strong magnetism and rapid magnetic separation, but the proportion of organic polymers per unit mass of MPTAPs adsorbent decreased, resulting in fewer adsorption sites. In Example 1, when the amount of magnetic cores was 200 mg, the resulting product had strong magnetism and a fast magnetic separation speed, and compared to the product prepared with 300 mg of magnetic cores, it had a higher proportion of organic polymers and stronger adsorption capacity.

[0062] Therefore, in subsequent embodiments, the amount of core-shell Fe3O4@SiO2 magnetic nanoparticles used is fixed at 200 mg.

[0063] Example 4

[0064] In this embodiment, the core-shell structured Fe3O4@SiO2 magnetic nanoparticles and the MPTAPs of Example 1 were characterized for various material properties.

[0065] First, TEM was used to characterize the core-shell structured Fe3O4@SiO2 magnetic nanoparticles and MPTAPs to study the structural characteristics of the magnetic hydroxyazobenzene porous organic polymer adsorbent. The corresponding results are as follows: Figure 2 As shown.

[0066] from Figure 2 It can be seen that Fe3O4@SiO2 has a core-shell structure, while MPTAPs have a porous network structure with a large amount of polymer coating with low contrast on the outer layer, indicating that porous organic polymers have been successfully prepared and coated on the surface of core-shell Fe3O4@SiO2.

[0067] The core-shell structures of Fe3O4@SiO2 and MPTAPs were characterized using Fourier transform infrared spectroscopy, thermogravimetric analysis using a vibrating sample magnetometer, and X-ray powder diffraction. The corresponding results are as follows: Figure 3 As shown.

[0068] from Figure 3 (a) It can be seen that Fe3O4@SiO2 has Si-O (1092 cm⁻¹) -1 ), Fe-O (580 cm) -1The characteristic absorption peaks of the stretching vibration of TA and Fe3O4@SiO2 indicate that core-shell structured Fe3O4@SiO2 magnetic nanoparticles have been successfully prepared. Characteristic absorption peaks of TA and Fe3O4@SiO2 appeared in the infrared spectrum of MPTAPs, including the C=N stretching vibration absorption peak on the TA triazine ring (1450 cm⁻¹). -1 1251 cm -1 and 829 cm -1 (nearby), and Si-O on Fe3O4@SiO2 (1089 cm) -1 ), Fe-O (582 cm) -1 The characteristic absorption peaks of stretching vibrations indicate that the magnetic covalent triazine organic polymer based on trithiocyanate has been successfully prepared.

[0069] Figure 3 (b) shows the magnetic intensity characterization of core-shell Fe3O4@SiO2 magnetic nanoparticles and MPTAPs, with saturation magnetic intensities of 49.6 and 28.4 emu·g, respectively. -1 The magnetic strength of MPTAPs is less than that of Fe3O4@SiO2, indicating that a large amount of organic polymer coating has been successfully applied to the surface of Fe3O4@SiO2. Although the magnetic strength is reduced, it is still sufficient for magnetic solid phase extraction separation.

[0070] Figure 3 (c) shows the thermogravimetric analysis (TGA) of core-shell Fe3O4@SiO2 magnetic nanoparticles and MPTAPs. Within the measured temperature range, the weight loss percentage of Fe3O4@SiO2 is approximately 5%, indicating that the magnetic nanoparticles have high thermal stability and are difficult to thermally decompose. However, MPTAPs have a higher weight loss percentage, approximately 64%. The small weight loss of MPTAPs between 100-300 °C may be caused by the evaporation of volatile molecules, while the large weight loss between 300-800 °C may be due to the thermal decomposition of the hydrocarbon organic polymer components on the MPTAPs, decomposing into carbon dioxide and water. The TGA results indicate that MPTAPs were successfully prepared, and compared to core-shell Fe3O4@SiO2 magnetic nanoparticles, the hydrocarbon organic polymer components on MPTAPs account for a higher proportion.

[0071] Depend on Figure 3(d) It can be seen that the core-shell structured Fe3O4@SiO2 magnetic nanoparticles and MPTAPs have six characteristic diffraction peaks with almost identical diffraction angles, appearing at 2θ positions of 29.95°, 35.41°, 43.13°, 54.04°, 57.12°, and 63.07°, respectively. These characteristic peaks are all characteristic diffraction peaks of Fe3O4, indicating that the core structure of magnetic Fe3O4 was not changed during the synthesis of MPTAPs. No additional XRD peaks were detected in MPTAPs, indicating that the organic polymer network outside MPTAPs belongs to an amorphous polymer.

[0072] To further verify the porosity of MPTAPs, N2 adsorption / desorption experiments were also conducted, and the corresponding results are as follows: Figure 4 As shown. Figure 4 The adsorption / desorption isotherms exhibit hysteresis loops within a relative pressure range of 0.70–0.95, indicating the coexistence of mesopores and macropores in MPTAPs. N2 adsorption / desorption experiments revealed that the pore volume and BET surface area of ​​MPTAPs were 0.63 cm³. 3 ·g -1 and 124 m 2 ·g -1 These values ​​are much higher than the pore volume and BET surface area (0.17 cm²) of Fe3O4@SiO2. 3 ·g -1 and 35 m 2 ·g -1 This also demonstrates that porous organic polymers have been successfully prepared on the surface of core-shell Fe3O4@SiO2 magnetic nanoparticles.

[0073] Example 5

[0074] This embodiment studies the adsorption performance of the MPTAPs prepared in Example 1 on heavy metal ions in an application.

[0075] The effects of the MPTAPs prepared in Example 1 on eight heavy metal ions (Cd) were investigated within a pH range of 2-8. 2+ Co 2+ Cr 3 + Cu 2+ Hg 2+ Ni 2+ Pb 2+ and Zn 2+ The adsorption properties of the mixed solution are shown in the following results: Figure 5 As shown in (a), MPTAPs have a high susceptibility to Hg in the pH range of 2–8. 2+The adsorption rates of all MPTAPs were above 90%, while the adsorption rates for the other seven coexisting metal ions were significantly lower. This result indicates that MPTAPs can adsorb Hg over a wide pH range (even in acidic environments with pH 2-3). 2+ The high selectivity of MPTAPs reveals their ability to adsorb Hg over a wide pH range (acidic or neutral solutions). 2+ The applicability of selective separation of MPTAPs to Hg. 2+ The high selectivity may be due to the thiol groups and Hg in MPTAPs. 2+ The strong binding ability is related to this, which can be explained by Pearson's hard-soft acid-base theory: soft ligands, such as -SH, readily bind to Hg. 2+ It forms complexes with soft metal ions, rather than with boundary acids (such as Pb). 2+ ) or hard acids (such as Co) 2+ In addition, from Figure 5 (a) It can be seen that MPTAPs affect Cu 2+ and Pb 2+ The adsorption rate of these MPTAPs gradually increases with increasing pH, reaching adsorption equilibrium at approximately pH 6. 2+ and Pb 2+ pH-dependent trends of MPTAPs on Hg 2+ The wide pH adaptability of HgS exhibits significant adsorption differences. This difference is related to the chelation constants of different metal ions with sulfur, as the Ksp of HgS remains stable at different pH levels (4 × 10⁻⁶). -53 The Ksp of CuS and PbS is easily affected by acidic environments, while the Ksp of PbS is lower in neutral environments. Cu (6×10) -36 ) and Ksp PbS (1×10) -28 The values ​​are relatively high, but they decrease to 6×10 in acidic environments. -15 and 1×10 -6 Under strongly acidic conditions (pH=2-3), the Hg in MPTAPs 2+ The strong adsorption force between MPTAPs and thiol groups enables them to remove Hg from industrial acidic wastewater. 2+ This is very beneficial for controlling mercury pollution.

[0076] To further investigate the effect of MPTAPs on Cu 2+ and Pb 2+ The potential adsorption potential of Hg, at pH 6, was observed with and without Hg. 2+ In this case, MPTAPs were used to treat Cu 2+ and Pb 2+ Adsorption experiments. For example... Figure 5 As shown in (b), when Cu 2+ and Pb 2+ Ions and Hg 2+ When ions coexist, Hg 2+ Ions can be completely adsorbed by MPTAPs, while Cu 2+ and Pb 2+ The adsorption rate was relatively low, further confirming the poor adsorption capacity of MPTAPs for Cu. 2+ and Pb 2+ High selectivity. However, in the absence of Hg 2+ In the case of ions, MPTAPs for Cu 2+ The adsorption rate is as high as 96.7%, for Pb 2+ The adsorption rate was 87.4%, indicating that MPTAPs are effective against Hg-free substances. 2+ The solution of ions has the ability to remove Cu 2+ and Pb 2+ Therefore, MPTAPs adsorbents have the ability to [achieve Hg-free adsorption]. 2+ Treatment of Cu-containing compounds in a near-neutral environment 2+ and Pb 2+ Wastewater treatment also shows great promise. 50 mL of Cu-containing... 2+ and Pb 2+ Industrial wastewater (pH pre-adjusted to 6) was mixed with 10 mg of MPTAPs for adsorption feasibility testing. The results showed that this material effectively adsorbed Cu... 2+ and Pb 2+ The adsorption rates of MPTAP all exceeded 85%, verifying that MPTAP can be used in Hg-free environments. 2+ Removal of Cu from wastewater 2+ and Pb 2+ The feasibility of this.

[0077] The above adsorption experiments confirmed that MPTAPs contain a large number of thiol groups, which also indirectly verified the successful modification of the Fe3O4@SiO2 surface with a covalent triazine organic polymer based on trithiocyanate. It is noteworthy that MPTAPs exhibit Hg-reactive properties over a wide pH range. 2+ The ions exhibit high adsorption selectivity, which is beneficial for Hg adsorption under different sample conditions. 2+ Selective separation of ions. Considering that the pH of daily drinking water is close to neutral and that metal ions are easily hydrolyzed under alkaline conditions, subsequent adsorption studies were conducted at pH=6.

[0078] To further explore the effects of MPTAPs on Hg 2+ The adsorption capacity was determined at a fixed MPTAPs dosage of 10 mg and an initial Hg. 2 +Under a concentration of 100 mg L⁻¹, the effects of MPTAPs on Hg were investigated by varying adsorption times of 1 min, 3 min, 5 min, 7 min, 10 min, 15 min, and 20 min. 2+ Adsorption kinetics experiment Figure 6 (a) Hg at different adsorption times 2+ Adsorption capacity on MPTAPs (Qt, mg g) -1 The adsorption rate increased rapidly within the first 5 minutes, then reached adsorption equilibrium at approximately 10 minutes. This indicates that MPTAPs are effective against Hg. 2+ The adsorption process is rapid, which can be attributed to the abundance of highly active thiol binding sites and hierarchical pores (micropores and macropores) on MPTAPs. These characteristics are conducive to the rapid adsorption and removal of Hg. 2+ Ions. To achieve efficient adsorption, MPTAPs were used with Hg in subsequent experiments. 2+ The adsorption contact time was fixed at 10 min. From Figure 6 The adsorption data in (a) can be used to calculate the effect of MPTAPs on Hg. 2+ The maximum adsorption capacity is 209 mg g. -1 This indicates that MPTAPs are effective against Hg. 2+ The adsorption capacity of MPTAPs is very strong. Further data fitting revealed that MPTAPs have a strong adsorption capacity for Hg. 2+ The adsorption of MPTAPs conforms to the pseudo-second-order adsorption kinetic model, indicating that MPTAPs have a positive effect on Hg. 2+ The adsorption of MPTAPs is mainly driven by chemisorption and exhibits high selectivity. Furthermore, the effects of MPTAPs on Hg under acidic conditions (pH=2) were also investigated. 2+ Similar results were obtained from the adsorption kinetics of MPTAPs for Hg. Under acidic conditions, MPTAPs showed similar adsorption kinetics for Hg. 2+ The maximum adsorption capacity is 187 mg g -1 Adsorption equilibrium was reached in approximately 10 minutes. This result verifies that Hg under acidic conditions... 2+ The stability of the sulfur chelation constant indicates the effectiveness of MPTAPs in removing Hg from industrial acidic wastewater. 2+ The immense application potential of MPTAPs was demonstrated. The results were validated using actual industrial acidic mercury-containing wastewater, achieving a satisfactory mercury removal rate (92%), confirming the effectiveness of MPTAPs in removing Hg from industrial acidic wastewater. 2+ Feasibility of ions.

[0079] To further investigate the adsorption mechanism, under adsorption equilibrium conditions, 10 mg of MPTAPs and Hg were used. 2+ The solutions were mixed for 10 min, and the initial concentrations (5-100 mg / L) were investigated. -1 Hg 2+The effect of adsorption. For example, Figure 7 As shown in (a), Hg 2+ The adsorption capacity varies with the initial concentration from 5 mg / L -1 Increase to 50 mg L -1 And increase, then at 60-100 mg L -1 The levels tend to stabilize between these values. Calculations showed that MPTAPs had a significant effect on Hg levels. 2+ The maximum adsorption capacity is 211 mg g -1 Further data fitting revealed that MPTAPs have a positive effect on Hg. 2+ The adsorption conforms to the Langmuir adsorption isotherm model, indicating that MPTAPs have a positive effect on Hg. 2+ The adsorption is a monolayer adsorption.

[0080] Example 6

[0081] This embodiment uses actual industrial acidic wastewater for verification, and studies the extraction of Hg by MPTAPs in application. 2+ Feasibility and optimal extraction conditions.

[0082] According to Example 5, MPTAPs adsorb Hg 2+ The pH range was 2-8. Considering that the pH of domestic water is close to neutral, and in order to reduce the hydrolysis of metal ions under alkaline conditions, MPTAPs extraction of Hg was performed at pH 6. 2+ Feasibility study. Specifically, the procedure involves Hg at pH=6. 2+ A certain amount of MPTAPs was added to the solution, and the mixture was shaken on a shaker for 10 minutes to allow Hg to rise. 2 + Adsorbed onto MPTAPs, followed by magnetic separation, the supernatant was then taken out for Hg measurement. 2+ The content, and then to the adsorbed Hg 2+ A certain volume of acidic thiourea solution was added to the MPTAPs material as an eluent, and vortex desorption was performed for 10 min to desorb Hg. 2+ After magnetic separation, the supernatant was collected for Hg measurement. 2+ Content. From Figure 8 (a) It can be seen that when the concentration of HCl in the acidic thiourea solution is specified as 1 mol L... -1 When the thiourea content exceeds 0.2%, Hg 2+ Ions could be quantitatively eluted. To ensure a high elution rate, the thiourea content was set at 0.4% in subsequent studies. The effect of HCl concentration in the acidic thiourea solution was then investigated. Figure 8 (b) It can be seen that when the HCl concentration in the acidic thiourea solution exceeds 0.4 mol / L... -1 At that time, Hg 2+The recovery rate was above 90%. To ensure complete elution, the subsequent eluent composition was set to 0.5 mol / L containing 0.4% thiourea. -1 HCl solution. Then other elution conditions were investigated, including elution volume and elution time. According to... Figure 8 (c) and Figure 8 The data from (d) indicate that the optimal elution conditions were 0.4 mL of 0.5 mol / L HCl containing 0.4% thiourea. -1 Elute with HCl solution by vortexing for 3 min.

[0083] Based on the optimized conditions described above, the effects of sample solution volume, extraction and adsorption time, and material dosage on the extraction of Hg by MPTAPs were investigated. 2+ The impact of recovery rate. According to Figure 9 According to the data results, when the volume of the test solution is 100 mL, the extraction and adsorption time is 10 min, and the amount of material used is 10 mg, Hg 2+ It can be quantitatively adsorbed and quantitatively eluted and recovered by quantitative MPTAPs. Dividing the 100 mL sample volume by the 0.4 mL elution volume yields a theoretical enrichment factor of 250-fold. This indicates that MPTAPs can be used to extract Hg from large-volume water samples. 2+ Extraction and separation, even for trace amounts of Hg 2+ After elution with a small volume of eluent, Hg 2+ The concentration can be increased, which is beneficial for trace Hg. 2+ Ultra-sensitive detection.

[0084] Example 7

[0085] This embodiment studies the application of MPTAPs to extract Hg. 2+ Its tolerance to coexisting salt interference and reusability.

[0086] In a solution containing 10 ng Hg 2+ Introduce different concentrations of various common ions (such as K+) into the solution + Na + Fe 3+ Al 3+ and Cl - (etc.). Subsequently, the extraction process was carried out using the previously optimized magnetic solid phase extraction (MSPE) conditions to evaluate the effect of different concentration levels of these common coexisting ions on the extraction of Hg from MPTAPs. 2+ The effects are shown in Table 1.

[0087] Table 1: Trace Hg extracted by MPTAPs 2+ Maximum tolerance concentration of coexisting interfering ions

[0088]

[0089] The experimental results in Table 1 show that the highest tolerable concentration of these coexisting ions can reach 12000 mg / L. -1 The presence of these high concentrations of coexisting ions affects the extraction of Hg by MPTAPs. 2+ It has almost no effect. Furthermore, the maximum tolerated concentration of these coexisting ions is higher than the target Hg. 2+ The concentrations of ions were several thousand times higher, which highlights the strong anti-interference ability of the prepared MPTAPs.

[0090] In addition, the regenerability and reusability of the MPTAPs adsorbent were investigated. After one round of extraction, the MPTAPs were used with 0.4 mL of 0.4% thiourea in 0.5 mol L⁻¹ solution. -1 HCl solution removes the small amount of Hg remaining on MPTAPs 2+ The elution process fully exposes the selective adsorption sites. The mixture is then washed with high-purity water until neutral and treated with 0.1 mol L⁻¹. -1 After activation with ammonium acetate solution, MPTAPs can be regenerated and reused, allowing for repeated adsorption and desorption steps. For example... Figure 10 As shown, MPTAPs were repeatedly used in the order of adsorption, desorption, washing, and activation. The results showed that even after 10 repetitions, MPTAPs did not significantly reduce Hg levels. 2+ The recovery rate did not decrease significantly, indicating that MPTAPs have good stability and regeneration performance.

[0091] Example 8

[0092] This embodiment studies MPTAPs in Hg 2+ Applications in separation, enrichment, and detection.

[0093] The MPTAPs prepared in Example 1 were used to couple MSPE and ICP-MS to establish an MSPE-ICP-MS detection method for Hg. 2+ The analytical performance of the novel MSPE-ICP-MS method based on MPTAPs proposed in this invention was investigated under the optimized extraction conditions of Example 6, and the results are shown in Table 2.

[0094] Table 2: Analytical performance of the MSPE-ICP-MS method based on MPTAPs

[0095]

[0096] This new method is effective for Hg. 2+ The detection limits were 0.61 ng / L. -1The linear range is 2-3000 ng L. -1 The intra-batch (n=7) and inter-batch relative standard deviations (n=5) were 5.7% and 8.5%, respectively, with an actual enrichment factor of 232-fold. This is comparable to the ICP-MS instrument's performance on Hg. 2+ The detection limit of 73 ng / L -1 After extraction with MSPE, the detection limit decreased significantly and the detection sensitivity increased significantly.

[0097] Analysis of Hg in standard water samples (pre-diluted 10 times) according to GSB 07-3173-2014 "Water Quality Mercury Standard Samples" 2+ The accuracy of the MSPE-ICP-MS method was verified, and the results are shown in Table 3.

[0098] Table 3: Hg in standard substances 2+ Content determination results (n=3)

[0099]

[0100] The results showed that the measured values ​​obtained by the MSPE-ICP-MS method were very close to the standard values, indicating that this MSPE-ICP-MS method based on MPTAPs has high accuracy.

[0101] Under optimal conditions, the established method was applied to the Hg levels in the Huanggang section of the Yangtze River, Yiai Lake, laboratory tap water, and laboratory wastewater. 2+ The results of the determination are shown in Table 4.

[0102] Table 4: Hg in actual water samples detected by MSPE-ICP-MS 2+ Content (n=3)

[0103]

[0104] In the table, " / " indicates that there is no data available for testing.

[0105] The table above shows that Hg in laboratory tap water... 2+ Hg was not detected in river water, lake water, or laboratory wastewater. 2+ Different levels of detection were observed, with spiked recoveries ranging from 88.2% to 111%. This demonstrates that the method of this invention has good anti-interference capabilities and can be used for trace Hg in actual water samples. 2+ Separation, enrichment, and detection.

[0106] The above research results show that, compared with simple porous organic polymers, the MPTAPs prepared by this invention not only have the advantages of high porosity and abundant adsorption sites of porous organic polymers, but also can achieve rapid separation under an external magnetic field, avoiding cumbersome phase separation operations such as centrifugation and filtration, improving separation and enrichment efficiency, and overcoming the disadvantage of porous organic polymers being difficult to separate quickly, making the application of this novel porous material more convenient and efficient.

[0107] The MPTAPs prepared in this invention, compared to other solid adsorbents based on trithiocyanate, offer advantages such as a green, mild, efficient, convenient, low-cost, easy-to-prepare, easy-to-separate and recyclable preparation method, and the ability to reuse the material multiple times. This novel adsorbent can selectively adsorb heavy metal ions (Hg) from water over a wide pH range. 2+ Even in acidic wastewater, Hg can be removed. 2+ It exhibits highly efficient removal, high adsorption capacity, and rapid adsorption kinetics, enabling the removal of high concentrations of heavy metal ions (Hg) in wastewater at different pH levels. 2+ Highly efficient and selective rapid removal, especially for products without Hg. 2+ neutral Cu 2+ Pb 2+ The prepared magnetic adsorbents also showed good adsorption and removal effects on the wastewater, and these experiments fully demonstrate that MPTAPs have good application prospects in the treatment of heavy metal wastewater.

[0108] The MPTAPs prepared by this invention can also achieve the detection of low concentrations of heavy metal ions (Hg) in complex water samples. 2+ Extraction, thereby achieving trace amounts of Hg 2+ Separation from complex sample matrices can reduce the influence of the sample matrix on the detection results when used with modern instruments. By optimizing adsorption and desorption conditions, trace amounts of Hg can also be detected. 2+ Enrichment enhances detection sensitivity. This magnetic solid-phase extraction technique, based on a magnetic covalent triazine organic polymer adsorbent, provides enrichment for trace Hg, improving detection sensitivity. 2+ This provides a new approach to detection.

[0109] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A method for preparing a highly selective magnetic covalent triazine organic polymer adsorbent, characterized in that, Includes the following steps: (1) Prepare a sodium trithiocyanate solution; (2) Add a dispersion of core-shell structured Fe3O4@SiO2 magnetic nanoparticles and a solution of 1,3,5-triazine-2,4,6-trithionine trisodium salt to a solution of monosodium trithiocyanate, and then add a mixed solution of iodine and potassium iodide to carry out a redox reaction. After the reaction is completed, the product is recovered and purified to obtain a highly selective magnetic covalent triazine organic polymer adsorbent.

2. The method for preparing the highly selective magnetic covalent triazine organic polymer adsorbent according to claim 1, characterized in that, In step (1), the sodium trithiocyanate solution is temporarily generated by the reaction of trithiocyanate and sodium hydroxide in a solution environment. Its preparation method includes the following steps: Trithiocyanate was ultrasonically dispersed in water to obtain a trithiocyanate dispersion; sodium hydroxide aqueous solution was added to the trithiocyanate dispersion, mixed and reacted to obtain a monosodium trithiocyanate solution.

3. The method for preparing the highly selective magnetic covalent triazine organic polymer adsorbent according to claim 2, characterized in that: The amount of trithiocyanate added is 1-2 mmol; the amount of water used is 50-100 mL; and the concentration of the sodium hydroxide aqueous solution is 0.10-0.11 mol / L. -1 The amount used is 10-20 mL; the sodium hydroxide aqueous solution is added dropwise at a rate of 50-60 drops / min; the stirring rate is 400-500 rpm; the reaction time is 2-3 h; and the reaction temperature is room temperature.

4. The method for preparing the highly selective magnetic covalent triazine organic polymer adsorbent according to claim 1, characterized in that: In step (2), the dispersion of core-shell Fe3O4@SiO2 magnetic nanoparticles is prepared by adding 100-300 mg of core-shell Fe3O4@SiO2 magnetic nanoparticles to 25-30 mL of water and then dispersing them by ultrasonication; the 1,3,5-triazine-2,4,6-trithione trisodium salt solution is prepared by dissolving 1-3 mmol of 1,3,5-triazine-2,4,6-trithione trisodium salt in 25-30 mL of water; and the mixed solution of iodine and potassium iodide is prepared by mixing 1 mmol of elemental iodine with 5 mL of solution containing 0.2-0.5 g / mL potassium iodide. -1 It is prepared by mixing potassium iodide aqueous solution.

5. The method for preparing the highly selective magnetic covalent triazine organic polymer adsorbent according to claim 4, characterized in that, The core-shell structured Fe3O4@SiO2 magnetic nanoparticles were prepared by co-precipitation and sol-gel hydrolysis, including the following steps: S1. Under an inert gas atmosphere, the chloride salts of Fe(III) and Fe(II) were dissolved in water, heated to 80-90 °C and maintained for 50-60 min; then concentrated ammonia was added and the reaction continued at this temperature for 30-40 min; after the reaction was completed, the mixture was cooled to room temperature, the product was recovered and purified, and Fe3O4 magnetic nanoparticles were obtained. S2. The Fe3O4 magnetic nanoparticles are dispersed in a mixture of water and ethanol, concentrated ammonia and tetraethyl orthosilicate are added, and a SiO2 layer is formed on the surface of the Fe3O4 magnetic nanoparticles by hydrolysis of tetraethyl orthosilicate. After reacting at 25-30 °C for 10-12 h, the product is recovered and purified to obtain core-shell structured Fe3O4@SiO2 magnetic nanoparticles.

6. The method for preparing the highly selective magnetic covalent triazine organic polymer adsorbent according to claim 5, characterized in that: In step S1, the amount of Fe(III) chloride is 20 mmol, the molar ratio of Fe(III) chloride to Fe(II) chloride is 2:1-1.1, and the amount of water is 100-150 mL; in step S2, the volume ratio of water to ethanol in the mixture is 1:3-4, the amount of the mixture is 150-200 mL, the amount of concentrated ammonia is 2-2.5 mL, and the amount of tetraethyl orthosilicate is 2-2.5 mL.

7. The method for preparing the highly selective magnetic covalent triazine organic polymer adsorbent according to claim 1, characterized in that: In step (2), the addition of raw materials and the redox reaction are carried out under a stirring environment at a stirring rate of 400-500 rpm. When adding the mixed solution of iodine and potassium iodide, the temperature of the reaction system is 0-10 ℃ to avoid the volatilization of iodine. The mixed solution of iodine and potassium iodide is added dropwise at a rate of 50-60 drops / min. After the mixed solution of iodine and potassium iodide is added, the mixture is allowed to naturally warm to room temperature.

8. The method for preparing the highly selective magnetic covalent triazine organic polymer adsorbent according to claim 1, characterized in that: In step (2), the redox reaction is carried out at room temperature for 10-12 hours.

9. A highly selective magnetic covalent triazine organic polymer adsorbent, characterized in that: It is prepared by the preparation method described in any one of claims 1-8.

10. The application of a highly selective magnetic covalent triazine organic polymer adsorbent as described in claim 9, characterized in that: Applications of mercury as an adsorbent material for the adsorption, removal, extraction, separation, enrichment, and detection of heavy metal mercury ions in water.

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