Preparation method of mesoporous silica pore channel confinement ferrous sulfide and application of mesoporous silica pore channel confinement ferrous sulfide in mercury pollution remediation

Abstract

The invention relates to a preparation method of mesoporous silica pore channel confinement ferrous sulfide and application of the mesoporous silica pore channel confinement ferrous sulfide in mercury pollution remediation, ferrous sulfide is precipitated among pore channels of mesoporous silica nanoparticles by using a double-solvent method, and nano confinement ferrous sulfide is prepared. The mesoporous silica pore channel confinement ferrous sulfide can be used for removing mercury in environmental pollution, and has higher mercury saturation adsorption capacity and stronger mercury methylation inhibition effect. The confined ferrous sulfide can maintain good dispersibility due to the support of the mesoporous silicon pore skeleton, so that efficient fixation of mercury ions and effective control of methyl mercury pollution are maintained.

Description

Technical Field

[0001] The present invention belongs to the technical field of water treatment, and particularly relates to a preparation method of mesoporous silica pore-confined iron sulfide and its application in mercury pollution remediation. Background Art

[0002] Mercury is a highly toxic heavy metal that can be emitted into the environment through natural sources (volcanic eruptions) and anthropogenic sources (metal smelting, fossil fuel combustion). Among various environmental media, sediments are important sinks in the global mercury biogeochemical cycle. The mercury fluxes in lake and peat sediments show the same trend as atmospheric mercury deposition. During the process of mercury emission from land to the ocean, a large amount of mercury is retained in estuarine and marine sediments. The unique environmental conditions of sediments, especially marine sediments, make them not only hotspots of mercury pollution but also hotspots of mercury methylation. Methylmercury has high neurotoxicity and is prone to bioaccumulation in the food web once formed, posing a great threat to human health. Since heavy metals cannot be removed from the environment and can only undergo speciation transformation, it is of great significance to reduce the bioavailability of mercury in sediments and simultaneously inhibit the production of methylmercury to eliminate the risk of mercury pollution.

[0003] In-situ immobilization by adsorbing or precipitating mercury in pore water is a common method for remediating mercury-contaminated sites. Nano-sulfide minerals have a strong affinity for mercury, which is the result of soft Lewis acid-base interactions. Among them, nano-ferrous sulfide has attracted attention due to its strong immobilization ability, low cost, and environmental friendliness. Nano-ferrous sulfide can simultaneously immobilize mercury through chemical precipitation, ion exchange, and surface complexation. The formed mercury sulfide is considered one of the safest forms of mercury because it is very stable in the environment.

[0004] Although nano-ferrous sulfide shows good ability to remove mercury, the complex hydrochemical conditions of sediments often limit its application. For example, in coastal sediments with high ionic strength, nano-ferrous sulfide will aggregate, and the limited surface area reduces the amount of mercury removed; sediments often contain various organic / inorganic ligands, which strongly interfere with the reactivity of the material towards mercury. Some studies have solved the above problems through methods such as carboxymethyl cellulose modification. Although it can effectively reduce the concentration of dissolved mercury, the immobilized material often forms a mercury-rich interface or mercury-containing nanoparticles. Since methylating bacteria can still directly contact this part of mercury (usually considered to have a higher methylation potential), the risk of methylmercury production still exists. Summary of the Invention

[0005] To solve the above technical problems, the present invention provides a preparation method of mesoporous silica pore-confined iron sulfide and its application in mercury pollution remediation.

[0006] The technical solution adopted by the present invention is as follows: A preparation method of mesoporous silica-confined iron sulfide, in which iron sulfide is precipitated between the pores of mesoporous silica nanoparticles by a double-solvent method to obtain nano-confined iron sulfide.

[0007] Preferably, the mesoporous silica is dispersed in a hydrophobic organic solution, and an FeSO4 solution and an Na2S solution are successively added dropwise thereto under anaerobic conditions. After stirring and reacting, mesoporous silica-confined iron sulfide is obtained.

[0008] Preferably, the molar ratio of FeSO4 to Na2S is 1:1.

[0009] Preferably, the total volume of the FeSO4 and Na2S solutions is less than the total pore volume of the mesoporous silica material.

[0010] Preferably, the hydrophobic organic solvent is n-hexane, cyclohexane or dichloromethane.

[0011] Preferably, after the reaction, the precipitate is collected and washed successively with toluene, absolute ethanol and ultrapure water.

[0012] Mesoporous silica-confined iron sulfide prepared by the preparation method of mesoporous silica-confined iron sulfide.

[0013] Preferably, the mesoporous silica-confined iron sulfide is stored under anaerobic conditions.

[0014] Application of mesoporous silica-confined iron sulfide in the remediation of mercury-polluted environment.

[0015] Preferably, the mesoporous silica-confined iron sulfide or a suspension containing mesoporous silica-confined iron sulfide is put into the mercury-polluted environment.

[0016] The advantages and positive effects of the present invention are as follows: Iron sulfide is precipitated between the pores of mesoporous silica nanoparticles. Due to the effect of nano-confinement, the synthesized iron sulfide has a smaller particle size. Nano-confined iron sulfide has higher mercury sequestration performance, stronger complexation with mercury, and still maintains good removal ability under different ionic strengths, pH values and the presence of ligands. After nano-confined iron sulfide binds to mercury, the formed mercury sulfide precipitate is sealed between the pores, isolating the contact between bacteria and mercury, and can reduce the subsequent environmental risks brought by microbial transformation to the greatest extent. Description of the Drawings

[0017] Figure 1 Schematic diagram of the synthesis process of mesoporous silica-confined iron sulfide material;

[0018] Figure 2 SEM image of the synthesized mesoporous silica nanoparticles;

[0019] Figure 3 TEM images of synthesized mesoporous silica nanoparticles;

[0020] Figure 4 TEM images of the mesoporous silica pore-confined iron sulfide material; A is the SEM image of FeS@MSNs; B and C are the TEM images of FeS@MSNs;

[0021] Figure 5 XRD patterns of mesoporous silica nanoparticles and the mesoporous silica pore-confined iron sulfide material;

[0022] Figure 6 Adsorption kinetic curves of FeS and FeS@MSNs for adsorbing and immobilizing dissolved inorganic divalent mercury (fitted using the pseudo-second-order kinetic model);

[0023] Figure 7 Adsorption isotherms of FeS and FeS@MSNs for adsorbing and immobilizing dissolved inorganic divalent mercury (fitted using the Langmuir model);

[0024] Figure 8 Effect of ionic strength on the adsorption and immobilization of dissolved inorganic divalent mercury by the two materials;

[0025] Figure 9 Effect of pH on the adsorption and immobilization of dissolved inorganic divalent mercury by the two materials;

[0026] Figure 10 Effect of common ligands in the aquatic environment on the adsorption and immobilization of dissolved inorganic divalent mercury by the two materials;

[0027] Figure 11 Risk assessment of mercury methylation after FeS@MSNs immobilize mercury; (a) The amount of methylmercury generated in the reaction system after the dissolved inorganic divalent mercury and the two materials adsorbing and immobilizing the dissolved inorganic divalent mercury react with the culture of sulfate-reducing bacterium P.mercurii ND132 under different ionic strengths; (b) The amount of methylmercury generated in the reaction system after the dissolved mercury and the solid-phase mercury adsorbed by the two materials react with the culture of sulfate-reducing bacterium P.mercurii ND132. Detailed implementation manners

[0028] The embodiments of the present invention will be described below with reference to the accompanying drawings.

[0029] The present invention relates to a preparation method of mesoporous silica-confined iron sulfide and its application in mercury pollution remediation. The iron sulfide is precipitated between the pores of mesoporous silica nanoparticles by using a dual-solvent method to prepare nano-confined iron sulfide. The mesoporous silica-confined iron sulfide can be used for the removal of mercury in polluted environments, having a higher mercury saturation adsorption capacity and a stronger inhibitory effect on mercury methylation. Due to the support of the mesoporous silica pore framework, the confined iron sulfide can maintain good dispersion, thus maintaining efficient fixation of mercury pollution and effective control of methylmercury pollution.

[0030] Encapsulating or confining materials in a nanoscale space to form nano-confinement, this confined space provides a specific microenvironment for the nucleation, growth, and stability of products, enabling nanomaterials to obtain unique properties. Limiting the mercury removal reaction process within a nanoscale space and physically isolating the contact between methylating bacteria and mercury can eliminate the risk of methylmercury generation.

[0031] In certain embodiments of the present invention, the preparation method of mesoporous silica-confined iron sulfide includes the following steps:

[0032] Step 1: Synthesis of mesoporous silica material; under the condition of an 80 °C oil bath, triethanolamine is added to ultrapure water and stirred vigorously; cetyltrimethylammonium bromide (CTAB) and sodium salicylate are added, and stirring is continued; finally, tetraethyl orthosilicate is added, and stirring is continued for 5 - 6 h. After the reaction ends, the white product formed by the reaction is collected by centrifugation, and the residual reactants are removed by washing with absolute ethanol to obtain mesoporous silica MSNs.

[0033] Step 2: Synthesis of mesoporous silica-confined iron sulfide material; as Figure 1 shown in the synthesis schematic diagram, 1 g of mesoporous silica is dispersed into 200 ml of a hydrophobic organic solvent; under anaerobic conditions, while stirring, an FeSO4 solution is dropped into the suspension, and after sufficient stirring, an Na2S solution with the same volume and the same concentration is added dropwise, and the reaction is continuously stirred for 5 - 8 h under anaerobic conditions. After the reaction ends, the product is collected by centrifugation under anaerobic conditions and washed successively with toluene, absolute ethanol, and ultrapure water. The obtained product is mesoporous silica-confined iron sulfide FeS@MSNs, freeze-dried, and then the dried powder is vacuum-packed and stored in an anaerobic operation box. During the reaction process, the hydrophobic organic solvent wraps around the material surface, which can promote the hydrophilic precursor solution to enter the pores. The total volume of the added FeSO4 and Na2S solutions is less than the total pore volume of the mesoporous silica material, which is to ensure that the precipitation process mainly occurs between the pores; first, the pore volume of the mesoporous silica is detected, and then the dosages of the required FeSO4 solution and Na2S solution are set according to the pore volume. Among them, the hydrophobic organic solvent is n-hexane, cyclohexane, or dichloromethane.

[0034] In certain embodiments of the present invention, commercially available mesoporous silica materials can be used to directly synthesize mesoporous silica pore-confined iron sulfide FeS@MSNs through Step 2.

[0035] The double-solvent method was used to precipitate iron sulfide between the pores of mesoporous silica nanoparticles, and nano-confined iron sulfide was successfully prepared. Due to the effect of nano-confinement, the synthesized iron sulfide has a smaller particle size. Batch experiments confirmed that nano-confined iron sulfide has higher mercury sequestration performance and still maintains good removal ability in the presence of different ionic strengths, pH values, and ligands. A series of characterizations of the reaction products showed that nano-confined iron sulfide has a stronger complexation with mercury, and the formed mercury sulfide precipitate is sealed between the pores, isolating the contact between bacteria and mercury. The methylmercury produced after co-culturing the reaction product of nano-confined iron sulfide sequestering mercury with mercury-methylating model bacteria can be ignored. The fixed heavy metals are restricted in the nano-space, which can largely reduce the subsequent environmental risks brought by microbial transformation. Mesoporous silica pore-confined iron sulfide can be used to remove mercury in the water environment and serve as a mercury pollution remediation material.

[0036] When in use, nano-confined iron sulfide can be directly put into the mercury-polluted environment, or the material can be first dispersed in water to prepare a suspension and then added to the polluted environment. The specific dosage can be designed according to the specific situation.

[0037] Under the confinement of mesoporous-sized pores, iron sulfide nanoparticles with a particle size less than 10 nm were in-situ formed between the pores. Compared with the flaky iron sulfide generated by homogeneous co-precipitation, such nanoparticles have a higher mercury saturation adsorption capacity and a stronger mercury methylation inhibition effect. Due to the small particle size of the iron sulfide particles in nano-confined iron sulfide and the large number of surface active sites, a higher adsorption capacity can be brought. The stronger mercury methylation inhibition effect is due to two reasons. On the one hand, the confined iron sulfide has a higher complexation degree with mercury and is more likely to form stable mercury sulfide precipitates that are not easily utilized by microorganisms. On the other hand, the pore size physically isolates the iron sulfide nanoparticles adsorbed with mercury from microorganisms, effectively reducing the interfacial interaction and fundamentally inhibiting the mercury methylation process of mercury-containing particles.

[0038] In addition, the change in water environment conditions (increase in ionic strength) significantly reduces the adsorption performance of co-precipitated iron sulfide and increases the methylation risk of its reaction product with mercury. However, confined iron sulfide can maintain good dispersion due to the support of the mesoporous silica pore framework, thus maintaining efficient fixation of mercury pollution and effective control of methylmercury pollution.

[0039] The following is an explanation of the solution of the present invention in conjunction with the accompanying drawings. Among them, for the experimental methods without specific operation steps, they are all carried out in accordance with the corresponding product manuals. The instruments, reagents, and consumables used in the examples can be purchased from commercial companies without special instructions.

[0040] Example 1: Synthesis of mesoporous silica-confined iron sulfide material

[0041] 1.1 Synthesis of mesoporous silica material

[0042] Under the condition of an 80 °C oil bath, 0.068 g of triethanolamine was added to 25 mL of ultrapure water. After stirring vigorously for 30 minutes, 0.38 g of cetyltrimethylammonium bromide (CTAB) and 0.084 g of sodium salicylate were added, and stirring was continued for 60 minutes. Finally, 3.8 mL of tetraethyl orthosilicate was added, and stirring was continued for 5 hours and 30 minutes. After the reaction ended, the white product formed by the reaction was collected by centrifugation at 10,000 rpm for 10 minutes, and washed 3 times with anhydrous ethanol to remove the residual reactants. The specific operation was as follows: After centrifugation, pour off the supernatant, add anhydrous ethanol and invert and mix well to make the material evenly dispersed in anhydrous ethanol, centrifuge again to collect the material, and repeat 3 times.

[0043] In order to completely remove the possible residual template agent in the reaction product, the material was suspended in acidic ethanol (3 mL of concentrated HCl dissolved in 50 mL of anhydrous ethanol), and the material was evenly dispersed in the solution. At the same time, under the condition of heating in a 60 °C water bath and stirring vigorously for 12 hours, after centrifugation, pour off the supernatant to collect the material, add acidic ethanol again, and extract again, repeating 3 times. The eluted material was centrifuged at 10,000 rpm for 10 minutes to collect the product, washed 3 times with anhydrous ethanol and ultrapure water respectively, and the washed product was freeze-dried to obtain the mesoporous silica material. Subsequently, the dried powder was vacuum-packed and stored in an anaerobic operation box. The SEM image of the synthesized mesoporous silica nanoparticles is as Figure 2 shown, and the TEM image is as Figure 3 shown. It can be seen that the silica nanoparticles have regular pores.

[0044] 1.2 Synthesis of mesoporous silica-confined iron sulfide material

[0045] Add 0.1 g of the mesoporous silica nanoparticles MSNs prepared in Step 1.1 to 20 mL of n - hexane and sonicate until evenly dispersed. Transfer the suspension to an anaerobic glove box, dropwise add 1.5 mol / L FeSO4 solution, seal it, and vigorously stir for 2 hours under anaerobic conditions. Subsequently, dropwise add the same volume of 1.5 mol / L Na2S solution, seal it, and continue to vigorously stir for 6 hours under anaerobic conditions. The hydrophobic n - hexane wrapped on the material surface can promote the hydrophilic precursor solution to enter the pores. The total volume of the added FeSO4 and Na2S solutions is less than the total pore volume of the mesoporous silica material to ensure that the precipitation process mainly occurs between the pores. After the reaction, centrifuge at 10000 rpm for 10 minutes to collect the product, and wash it 3 times with toluene, absolute ethanol, and ultrapure water respectively. The specific operation is as follows: After centrifugation, pour out the supernatant, add toluene or absolute ethanol or deoxygenated water and invert to mix evenly to disperse the material uniformly, centrifuge again to collect the material, and repeat 3 times. Pay attention to maintaining anaerobic conditions during the centrifugation and washing operations. Finally, freeze - dry the washed material (i.e., FeS@MSNs), and then vacuum - pack and store the dried powder anaerobically. The characterization results of FeS@MSNs are as Figure 4 shown. It can be seen that FeS is distributed in the pores in the prepared product, and the exposed crystal plane of FeS in the pores is (101).

[0046] Compare the structures of the mesoporous silica nanoparticles and the mesoporous silica - confined iron sulfide material FeS@MSNs. The XRD patterns of the two are as Figure 5 shown. The characteristic peak of mesoporous silica at 2° represents its ordered pore structure. After in - situ formation of FeS in the pores, the characteristic peak of the material at this position disappears, indicating that FeS precipitates between the pores.

[0047] Example 2: Application of mesoporous silica - confined iron sulfide FeS@MSNs in mercury ion adsorption

[0048] Take a 20 - mL glass bottle equipped with a PTFE gasket as the reaction vessel. First, add Hg(NO3)2 stock solution to a 10 mmol / L NaNO3 background solution, and the total mercury addition concentration is 0.5 mg / L. Subsequently, use 1 mol / L NaOH solution and 1 mol / L HNO3 solution to adjust the pH of the reaction system to 7.0 ± 0.4.

[0049] Add the FeS@MSNs suspension to the above - mentioned reaction system so that the concentration of the FeS@MSNs solid material is 5 mg / L. Seal the reaction vessel and take it out of the anaerobic glove box, place it on a rotary mixer, and continuously rotate at a speed of 60 rpm to ensure full mixing of the system.

[0050] 2.1 Adsorption kinetics experiment

[0051] 100 mL of a Na2S solution with a concentration of 0.4 mol / L was added dropwise to 100 mL of a FeSO4 solution with a concentration of 0.4 mol / L, and vigorous stirring was maintained during the dropping process. After the dropping was completed, the pH value of the system was measured, and if necessary, 1 mol / L NaOH solution and 1 mol / L HNO3 solution were used for adjustment to ensure that the reaction system was maintained under neutral conditions (pH = 7.0 ± 0.4). Stirring was continued for 6 hours, and the entire reaction was carried out in an anaerobic operation box. Subsequently, the product was collected by centrifugation at 10,000 rpm for 10 minutes and washed 3 times with deoxygenated water. Attention was paid to maintaining anaerobic conditions during the centrifugation and washing operations. The washed FeS material was freeze-dried, and then the dried powder was vacuum-packed and stored in an anaerobic operation box.

[0052] FeS was used to replace FeS@MSNs, and Hg(NO3)2 stock solution and FeS were added to the reaction system as a control group. At each sampling time point (0, 10, 20, 30, 60, 90, 120, 150 minutes), the experimental group and the control group were sampled by the sacrifice sampling method. Each group contained at least three parallel samples. Samples of each group were taken with a disposable syringe, filtered through a hydrophilic polytetrafluoroethylene needle filter with a pore size of 0.22 μm, and the filtrate was stored in a 2% (v / v) HCl solution. The total mercury concentration in the filtrate was determined by atomic fluorescence spectrometry (AFS), and the total mercury amount in the solid phase (i.e., the total mercury removal amount in the system) was calculated by the mass balance method.

[0053] The experimental results are as Figure 6 shown. Compared with pure FeS, the FeS@MSNs adsorbent showed higher adsorption efficiency and larger adsorption capacity for mercury ions. When the initial mercury concentration was 0.5 mg / L, the fixed amount of Hg(Ⅱ) by the adsorbent was normalized by the mass of ferrous sulfide, and the nanoconfined ferrous sulfide had faster removal kinetics ( Figure 6 ), as shown in Table 1, and the pseudo-second-order adsorption rate constant was 2.8 times that of ferrous sulfide.

[0054] Table 1 Fitting results of the pseudo-second-order kinetic model for the adsorption kinetic curves of FeS and FeS@MSNs for the adsorption and fixation of dissolved inorganic divalent mercury

[0055]

[0056]

[0057] Note: Q t (mg / g FeS) is the content of solid-phase Hg(Ⅱ) at the start of the reaction t (min), Q e (mg / g FeS) is the content of solid-phase Hg(Ⅱ) at adsorption equilibrium, K1 (min-1 ) is the pseudo-second-order adsorption rate constant, R 2 is the correlation coefficient.

[0058] 2.2 Adsorption Isotherm Experiment

[0059] Using a 20 mL glass bottle equipped with a PTFE gasket as the reaction vessel, first add the Hg(NO3)2 stock solution to the 10 mmol / L NaNO3 background solution. The added concentrations of total mercury are 0.025, 0.05, 0.1, 0.25, 0.5, 0.75, 1, and 2 mg / L, respectively. Subsequently, use 1 mol / L NaOH solution and 1 mol / L HNO3 solution to adjust the pH of the reaction system, and add the material particle suspension to the reaction system to carry out the adsorption reaction under the conditions of a solid material concentration of 5 mg / L and pH = 7.0 ± 0.4. Seal the reaction vessel and take it out of the anaerobic operation box, place it on a rotary mixer, and continuously rotate at a speed of 60 rpm to ensure sufficient mixing of the system.

[0060] Replace FeS@MSNs with FeS, and add the Hg(NO3)2 stock solution and FeS to the reaction system as the control group. After the adsorption equilibrium is reached after 4 hours of reaction, samples are taken from the experimental group and the control group. The adsorption of FeS and FeS@MSNs is as shown in Figure 7 and Table 2. Compared with FeS, the FeS@MSNs material shows better adsorption effect on mercury. At the initial mercury concentration of 0–2 mg / L, the adsorption and fixation amount of mercury by the FeS@MSNs material is significantly higher than that of the FeS material, which can be attributed to the in-situ generation of smaller and more dispersed nanoparticles in the confined space.

[0061] Table 2 Fitting results of the Freundlich adsorption model for the adsorption isotherms of FeS and FeS@MSNs for the adsorption and fixation of dissolved inorganic divalent mercury

[0062]

[0063] Note: K f ((mg g -1 FeS) / (mg L -1 ) n ) is the Freundlich adsorption constant, n is the Freundlich index, R 2 is the correlation coefficient

[0064] Example 3: Effects of various factors in the water environment on the removal and fixation of mercury by two iron sulfide materials 3.1 Test on the effect of ionic strength on the removal and fixation of mercury by materials

[0065] The ionic strength range used in the test was selected according to the conditions of typical natural waters, covering the common ionic strengths of fresh water and seawater from low to high. Solutions with different ionic strengths were prepared in reaction vessels (20 mL glass bottles equipped with PTFE gaskets). Hg(NO3)2 stock solution was first added to NaNO3 background solutions with different concentrations. The concentrations of the NaNO3 solutions were 0, 1, 10, 50, 100, 500, and 1000 mmol / L respectively, and the added concentration of total mercury was 0.025 mg / L. Subsequently, 1 mol / L NaOH solution and 1 mol / L HNO3 solution were used to adjust the pH of the reaction system to 7.0 ± 0.4. Under anaerobic conditions, the FeS@MSNs suspension prepared in Example 1 was added to the reaction system, and the adsorption reaction was carried out at a solid material concentration of 5 mg / L. After sealing the reaction vessel, it was taken out of the anaerobic operation box and placed on a rotary mixer, and continuously rotated at a speed of 60 rpm to ensure full mixing of the system. FeS was used to replace FeS@MSNs, and the addition of Hg(NO3)2 stock solution and FeS to the reaction system was used as the control group. After the reaction reached adsorption equilibrium after 4 hours, samples were taken from the experimental group and the control group. The results are as Figure 8 shown that the FeS@MSNs material maintained good removal ability under various ionic strengths.

[0066] 3.2 Test on the effect of pH on the removal of fixed mercury by the material

[0067] The reaction vessel was a 20 mL glass bottle equipped with a PTFE gasket. Hg(NO3)2 stock solution was first added to the 10 mmol / L NaNO3 background solution, and the pH of the reaction system was adjusted to 4, 5, 6, 7, 8, 9, and 10 in turn using 1 mol / L NaOH solution and 1 mol / L HNO3 solution. The added concentration of total mercury was 0.025 mg / L. Subsequently, under anaerobic conditions, the FeS@MSNs suspension was added to the reaction system, and the adsorption reaction was carried out at a solid material concentration of 5 mg / L. After sealing the reaction vessel, it was taken out of the anaerobic operation box and placed on a rotary mixer, and continuously rotated at a speed of 60 rpm to ensure full mixing of the system. FeS was used to replace FeS@MSNs, and the addition of Hg(NO3)2 stock solution and FeS to the reaction system was used as the control group. After the reaction reached adsorption equilibrium after 4 hours, samples were taken from the experimental group and the control group. The results are as Figure 9 shown that the FeS@MSNs material maintained good removal ability under various pH conditions.

[0068] 3.3 Test on the effect of common ligands in the environment on the removal of fixed mercury by the material

[0069] Investigate the effects of common ligands in the environment on the process of mercury immobilization. Sodium chloride (NaCl), cysteine (CYS), glutathione (GSH), Suwannee River humic acid (SRHA), and Suwannee River fulvic acid (SRFA) were added. The concentration settings of each ligand in the reaction system referred to the common concentrations in the environment.

[0070] The reaction vessel was a 20 mL glass bottle equipped with a polytetrafluoroethylene gasket. First, a Hg(NO3)2 stock solution was added to a 10 mmol / L NaNO3 background solution, and the added concentration of total mercury was 0.025 mg / L. Subsequently, stock solutions of sodium chloride (NaCl), cysteine (CYS), glutathione (GSH), Suwannee River humic acid (SRHA), and Suwannee River fulvic acid (SRFA) were added respectively, so that the corresponding concentrations in the reaction system were 1 mmol / L NaCl, 1 μmol / L CYS, 1 μmol / L GSH, 1 mg-C / L SRHA, and 1 mg-C / L SRFA. Under anaerobic conditions, an FeS@MSNs suspension was added to the reaction system to carry out the adsorption reaction at a solid material concentration of 5 mg / L. Subsequently, a 1 mol / L NaOH solution and a 1 mol / L HNO3 solution were used to adjust the pH of the reaction system to pH = 7.0 ± 0.4. The reaction vessel was sealed and taken out of the anaerobic operation box, placed on a rotary shaker, and continuously rotated at a speed of 60 rpm to ensure full mixing of the system. FeS was used to replace FeS@MSNs, and adding a Hg(NO3)2 stock solution and FeS to the reaction system was used as the control group. After 4 hours of reaction to reach the adsorption equilibrium, samples were taken from the experimental group and the control group. The results are as Figure 10 shown. Compared with FeS, FeS@MSNs showed better adaptability to various ligands and had a higher adsorption effect on mercury ions.

[0071] In the range of ionic strength from 0–1000 mmol / L NaNO3 and pH from 4–10, the FeS@MSNs material showed a higher mercury removal efficiency than the FeS material, and for common ligands in the environment that may affect the speciation of mercury and the adsorption reaction on the solid surface, including inorganic Cl -For organic CYS, GSH, SRHA, and SRFA, the FeS@MSNs material exhibits stronger anti-interference ability, while the mercury removal ability of the FeS material decreases in the presence of ligands. Notably, with the increase in ionic strength, the mercury removal rate of the FeS material decreases significantly, while the FeS@MSNs material still maintains good mercury removal performance (removal rate > 98%). This is not only because the synthesized ferrous sulfide under the confined space has a smaller particle size and a higher specific surface area, but also because the support of the mesoporous silica channels enables the ferrous sulfide nanoparticles in the confined space to always have high dispersibility under different ionic strengths, while the FeS material agglomerates violently under high ionic strength, and its mercury removal ability drops rapidly.

[0072] Example 4: Risk assessment of mercury methylation after mercury immobilization by FeS@MSNs

[0073] The sulfate-reducing strain P.mercurii ND132 was used as the model strain for mercury methylation. The P.mercurii ND132 bacterial cells grown to the late logarithmic phase were centrifuged at 1200×g for 10 minutes, and the collected bacterial cells were washed with PBS buffer at pH = 7.4. After washing, the cell density in the cell suspension was measured using a flow cytometer, and the cell suspension was diluted with PBS to a cell density of 10 8 cells / mL. Subsequently, 1 mmol / L sodium pyruvate and 1 mmol / L sodium fumarate were added to the diluted cell suspension as the electron donor and electron acceptor required for bacterial growth, respectively.

[0074] The adsorption experiment was carried out according to the method of Example 2, with the adsorption reaction carried out under the conditions of a total mercury addition concentration of 0.025 mg / L, an FeS@MSNs solid material concentration of 5 mg / L, and pH = 7.0 ± 0.4, and the concentrations of the NaNO3 background solution were 10, 100, and 1000 mmol / L, respectively. The particle suspension after reaching adsorption equilibrium after 4 hours of reaction was ultrasonically dispersed evenly, and the particle suspension was added to the bacterial culture system using a disposable sterile syringe, with the total mercury addition concentration being 8 nmol / L. In addition to the experimental group, three control groups were set up: a non-biological control group, which refers to adding a Hg(NO3)2 solution with the same total mercury concentration to PBS without adding bacterial cells; a blank control group, which refers to adding only bacterial cells to PBS without adding mercury; a positive control group, which refers to adding a Hg(NO3)2 solution with the same total mercury concentration to PBS with added bacterial cells. Each group contains at least three parallel samples. At each sampling time point (0, 3, 6, 9 hours), the sacrifice sampling method was used to sample the experimental group and the control groups.

[0075] The results are as Figure 11As shown in Figure a, nano-confined iron sulfide can further reduce the risk of subsequent methylmercury production. After 9 hours of exposure to P.mercurii ND132 cells, the methylation rate of dissolved mercury ions was 8-9%. Both materials can inhibit the production of methylmercury. However, as the ionic strength increased from 10 to 1000, the inhibitory effect of FeS decreased significantly, which may be due to particle aggregation leading to a decrease in the ability of FeS to immobilize dissolved mercury ions. In the presence of FeS@MSNs, the production of methylmercury was negligible regardless of the ionic strength.

[0076] To investigate the mercury methylation potential of the solid-phase reaction products after FeS@MSNs adsorbed and immobilized mercury, a set of mercury methylation experiments without dissolved mercury after the adsorption reaction were designed. The adsorption experiment was carried out according to the method of Example 2, with the adsorption reaction carried out under the conditions of a total mercury addition concentration of 0.025 mg / L, a solid material concentration of 100 mg / L, pH = 7.0 ± 0.4, and a NaNO3 background solution concentration of 10 mmol / L. The particle suspension after 4 hours of reaction to reach adsorption equilibrium was ultrasonically dispersed evenly, and the particle suspension was added to the bacterial culture system with a disposable sterile syringe, and the total mercury addition concentration was 8 nmol / L. The rest of the operations were the same as above.

[0077] The results are as Figure 11 shown, where the grey markers indicate the experimental results of the positive control group. Since the blank control group and the abiotic control group did not produce methylmercury, their data were not shown; from the data comparison in the figure, it can be seen that the amount of methylmercury produced after FeS@MSNs adsorbed and immobilized mercury and reacted with the culture of sulfate-reducing bacterium P.mercurii ND132 remained at a very low level.

[0078] To further confirm the effect of nano-confined blocking on methylmercury production, the solid-liquid ratio of the two materials for adsorbing and immobilizing mercury ions was increased so that all mercury ions were present in the solid phase. The solid-phase reaction products after adsorbing and immobilizing mercury were exposed to P.mercurii ND132, with the dissolved mercury of the same concentration as the control. The results showed that the solid-phase mercury after FeS@MSNs material immobilized mercury had a lower methylation risk. The methylation efficiency of the mercury immobilized by FeS material was 1.74%, and the methylation efficiency of the mercury immobilized by FeS@MSNs material was 0.77%. There was a significant difference in the methylation ability of the solid-phase mercury formed after the two materials reacted with mercury.

[0079] The above has described the embodiments of the present invention in detail, but the content described is only the preferred embodiments of the present invention and cannot be considered as limiting the scope of implementation of the present invention. All equivalent changes and improvements made according to the scope of the present invention application should still fall within the scope covered by the patent of the present invention.

Claims

1. A method for preparing mesoporous silica channel confined ferrous sulfide, characterized in that: Ferrous sulfide is precipitated between the pores of mesoporous silica nanoparticles by a double solvent method to prepare nano-confined ferrous sulfide.

2. The method for preparing mesoporous silica channel confined ferrous sulfide according to claim 1, characterized in that: Mesoporous silica is dispersed in a hydrophobic organic solution, and FeSO4 solution and Na2S solution are added dropwise thereto under anaerobic conditions. After stirring and reacting, mesoporous silica pore-confined ferrous sulfide is obtained.

3. The method for preparing mesoporous silica channel confined ferrous sulfide according to claim 2, characterized in that: The molar ratio of FeSO4 and Na2S is 1:

1.

4. The method for preparing mesoporous silica channel confined ferrous sulfide according to claim 3, characterized in that: The total volume of FeSO4 and Na2S solution is smaller than the total pore volume of mesoporous silica material.

5. The method for preparing mesoporous silica channel confined ferrous sulfide according to claim 2, characterized in that: The hydrophobic organic solvent is n-hexane, cyclohexane or dichloromethane.

6. The method for preparing mesoporous silica channel confined ferrous sulfide according to any one of claims 1 to 5, characterized in that: After the reaction, the precipitate was collected and washed with toluene, anhydrous ethanol and ultrapure water in sequence.

7. Mesoporous silica channel confined ferrous sulfide prepared by the method for preparing mesoporous silica channel confined ferrous sulfide as described in any one of claims 1 to 6.

8. The mesoporous silica channel confined ferrous sulfide according to claim 7, characterized in that: Ferrous sulfide confined in mesoporous silica pores is stored under anaerobic conditions.

9. Use of the mesoporous silica channel confined ferrous sulfide according to claim 7 or 8 in the remediation of a mercury-contaminated environment.

10. The use according to claim 9, characterized in that: The mesoporous silica channel confined ferrous sulfide or a suspension containing the mesoporous silica channel confined ferrous sulfide is placed in a mercury-contaminated environment.

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