PH heavy metal ion double-response type biological nano-selenium soil remediation agent and preparation method thereof

Abstract

The invention discloses a pH heavy metal ion double-response type biological nano-selenium soil remediation agent and a preparation method thereof, and belongs to the technical field of soil remediation. The preparation method comprises the following steps: slowly stirring and reacting biological nano-selenium, a sodium citrate buffer solution and succinic anhydride, and centrifugally washing to obtain carboxylation modified biological nano-selenium; the preparation method comprises the following steps: mixing a sodium alginate solution, a carboxymethyl chitosan solution and ethylenediamine tetraacetic acid dianhydride for reaction to obtain a mixed solution A; mixing carboxylation modified biological nano-selenium and the mixed solution, and performing ultrasonic dispersion in an ice bath to obtain a mixed solution B; dropwise adding the mixed solution B into a calcium chloride solution, filtering and drying to obtain the biological nano-selenium soil remediation agent. The successfully developed pH / heavy metal ion double-response type core-shell structure biological nano-selenium repairing agent can intelligently release and efficiently passivate soil heavy metals in a targeted manner, so that the cadmium content of rice grains is reduced by over 65 percent and is lower than the national standard, the repairing agent is long-acting and stable, and precise and intelligent treatment on heavy metal pollution of farmland is realized.

Description

Technical Field

[0001] This invention belongs to the field of building decoration materials technology, specifically relating to a pH- and heavy metal ion-responsive bio-nano selenium soil remediation agent and its preparation method. Background Technology

[0002] Heavy metal pollution in soil has become a global environmental problem, seriously threatening agricultural product safety and ecosystem health. Common remediation technologies include physical soil replacement, chemical leaching, and bioremediation. In recent years, passivation remediation technology has attracted much attention due to its low cost and ease of operation. Its core principle is to add passivating materials to the soil to convert bioavailable heavy metals into stable forms, thereby reducing their bioavailability.

[0003] Among numerous passivation materials, nano-selenium, especially biosynthesized nano-selenium, shows application potential due to its environmental friendliness, high specific surface area, and strong reactivity. Existing technologies mainly involve: 1) direct application of bio-nano-selenium suspensions; and 2) simple loading of bio-nano-selenium onto porous carriers before application. However, these methods have significant limitations: First, nano-selenium particles are prone to aggregation and oxidation in complex soil media, leading to a sharp reduction in active surface area; second, its release and action process is entirely passive diffusion, unable to intelligently respond to spatiotemporal differences in pollution levels, resulting in material waste in low-pollution areas and incomplete remediation in highly polluted core areas due to insufficient local dosage; third, fluctuations in key environmental factors such as soil pH significantly affect the stability and passivation efficiency of nano-selenium, especially under acidic conditions, raising questions about the long-term stability of its immobilized products. Furthermore, existing technologies often focus on a single chemical immobilization mechanism, with insufficient consideration for the interaction between the material and the soil microenvironment and ecological compatibility.

[0004] Therefore, developing a novel bio-nano selenium material that can adapt to changes in the soil environment, achieve targeted passivation of heavy metals, and possess long-term stability has become a key technological bottleneck that urgently needs to be overcome in the field. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a pH- and heavy metal ion-responsive bio-nano selenium soil remediation agent and its preparation method. The bio-nano selenium remediation agent of this invention can intelligently target and release and efficiently passivate heavy metals in the soil, thus achieving precise and intelligent treatment of heavy metal pollution in farmland.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] This invention provides a method for preparing a pH- and heavy metal ion-responsive bio-nano selenium soil remediation agent, comprising the following steps: S1. Bio-nano selenium, sodium citrate buffer, and succinic anhydride were reacted under slow stirring, followed by centrifugation and washing to obtain carboxyl-modified bio-nano selenium; S2. Mix sodium alginate solution, carboxymethyl chitosan solution, and ethylenediaminetetraacetic anhydride to obtain mixture A; S3. The carboxyl-modified bio-nano selenium and the mixture were mixed and then ultrasonically dispersed in an ice bath to obtain mixture B; S4. Add mixture B dropwise into calcium chloride solution, filter and dry to obtain bio-nano selenium soil remediation agent.

[0008] Preferably, the mass ratio of bio-nano selenium, sodium citrate buffer, and succinic anhydride in S1 is (0.02-0.05):1:(0.02-0.05).

[0009] Preferably, the temperature of the stirring reaction in S1 is 20-25°C and the time is 4 hours.

[0010] Preferably, the volume-to-mass ratio of sodium alginate solution, carboxymethyl chitosan solution, and ethylenediaminetetraacetic anhydride in S2 is (30-40) mL: (10-15) mL: (0.01-0.03) g.

[0011] Preferably, the sodium alginate solution has a concentration of 2-4% w / v; and the carboxymethyl chitosan solution has a concentration of 1-3% w / v.

[0012] Preferably, the temperature of the S2 mixing reaction is 40-50℃ and the time is 1-3h.

[0013] Preferably, the volume-to-mass ratio of the carboxyl-modified bio-nano selenium in S3 to the mixed solution is (0.1-3:1).

[0014] Preferably, the concentration of the calcium chloride solution in S4 is 4%wt.

[0015] Preferably, the particle size of the bio-nano selenium soil remediation agent is 0.8-1.5 mm.

[0016] The present invention also provides a pH- and heavy metal ion-responsive bio-nano selenium soil remediation agent, which is prepared by the above-described preparation method.

[0017] It contains at least the following beneficial technical effects: The intelligent responsive bio-nano selenium soil remediation agent provided by this invention demonstrates outstanding efficacy in controlling heavy metal pollution. Its core technology lies in a dual-response mechanism of pH and heavy metal ions. Experiments show that the remediation agent releases nearly 80% of its active selenium within 72 hours, while the release rate in clean soil is less than 20%, achieving on-demand remediation and significantly improving material utilization. In pot experiments, this remediation agent reduced available cadmium in the soil by 68.6% and lowered the cadmium content in rice grains to 0.18 mg / kg, a reduction of 65.4%, significantly outperforming ordinary bio-nano selenium and commercially available passivating agents. Simultaneously, the stable selenium compounds it forms are resistant to leaching and aging, maintaining a passivation effect of over 82% after 180 days, exhibiting excellent long-term effectiveness. This technology fundamentally changes the extensive approach of traditional passivating agents, providing a precise, efficient, and environmentally friendly intelligent solution for heavy metal pollution in farmland. Detailed Implementation

[0018] Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this invention. The invention will now be described with reference to specific embodiments. It should be noted that these embodiments are merely descriptive and do not limit the invention in any way.

[0019] Bio-nano selenium is obtained by fermentation of selenium-converting microorganisms. The following examples specifically use bio-nano selenium obtained by fermentation of Bacillus vesiculosus N-8. Other raw materials are commercially available.

[0020] Example 1 S1. Preparation of carboxyl-modified bio-selenium nanoparticles: Weigh 0.02 g of bio-nano selenium powder and add it to 1.0 g of 0.1 M, pH 6.0 sodium citrate buffer solution, and disperse it evenly by ultrasonication. Then add 0.02 g of succinic anhydride and stir slowly at 200 rpm for 4 hours at 20℃. After the reaction is complete, centrifuge the mixture at 12000 rpm for 15 minutes at 4℃, discard the supernatant, and wash the precipitate three times with deionized water to obtain carboxyl-modified bio-nano selenium, which is then redispersed in 1 mL of deionized water to obtain Se@BC suspension.

[0021] S2. Preparation of intelligent responsive shell prepolymer: Prepare 2% (w / v) sodium alginate (SA) solution and 1% (w / v) carboxymethyl chitosan (CMCS) solution, respectively. Measure 30 mL of SA solution and 10 mL of CMCS solution into a three-necked flask and mix. Add 0.01 g of ethylenediaminetetraacetic dianhydride (EDTAD) while stirring. Place the mixture in a 40°C water bath and stir at 300 rpm for 1 hour to obtain a homogeneous mixture A.

[0022] S3. Preparation of core-shell precursor mixture: Measure 0.1 mL of the Se@BC suspension prepared in step S1 and mix it with 1.0 mL of the mixture A prepared in step S2 in a 5 mL glass vial. Place the vial in an ice-water bath and sonicate it for 10 minutes using an ultrasonic cell disruptor (200W power, 2 seconds on, 2 seconds off) to uniformly disperse the nano-selenium in the polymer solution, thus obtaining mixture B.

[0023] S4. Preparation of repair agent microspheres: Prepare 200 mL of a 4% (wt) calcium chloride aqueous solution and place it in a 250 mL beaker. Using a syringe with an inner diameter of 0.5 mm, add mixture B dropwise into the calcium chloride solution. The droplets gel upon contact, forming microspheres. After standing and solidifying for 30 minutes, filter the microspheres through a sieve and rinse three times with deionized water to remove residual Ca from the surface. 2+ The wet gel microspheres were pre-frozen at -40℃ for 12 hours, then transferred to a freeze dryer and freeze-dried at -50℃ and 0.1 Pa for 24 hours to obtain dried soil remediation agent microspheres. After sieving, the particle size was mainly distributed in the range of 0.8-1.0 mm.

[0024] Example 2 S1. Preparation of carboxyl-modified bio-selenium nanoparticles: Weigh 0.035 g of bio-nano selenium powder and add it to 1.0 g of 0.1 M, pH 6.0 sodium citrate buffer solution, and disperse it evenly by ultrasonication. Then add 0.035 g of succinic anhydride and react slowly at 200 rpm for 4 hours at 22°C. Subsequent centrifugation, washing, and resuspension steps are the same as in Example 1 to obtain Se@BC suspension.

[0025] S2. Preparation of intelligent responsive shell prepolymer: Prepare 3% (w / v) sodium alginate (SA) solution and 2% (w / v) carboxymethyl chitosan (CMCS) solution, respectively. Mix 35 mL of SA solution with 12.5 mL of CMCS solution, and add 0.02 g of EDTAD while stirring. Place the mixture in a 45°C water bath and stir at 300 rpm for 2 hours to obtain mixture A.

[0026] S3. Preparation of core-shell precursor mixture: Measure 1.55 mL of the Se@BC suspension prepared in step S1 and mix it with 1.0 mL of mixture A. Disperse the mixture under ultrasonication in an ice bath as in Example 1 to obtain mixture B.

[0027] S4. Preparation of repair agent microspheres: Drop granulation was performed using a 4% (wt) calcium chloride solution, and the curing and washing steps were the same as in Example 1. The repair agent microspheres obtained after freeze-drying were sieved, and their particle size was mainly distributed in the range of 1.0-1.3 mm.

[0028] Example 3 S1. Preparation of carboxyl-modified bio-selenium nanoparticles: Weigh 0.05 g of bio-nano selenium powder and add it to 1.0 g of 0.1 M, pH 6.0 sodium citrate buffer solution, and disperse it evenly by ultrasonication. Then add 0.05 g of succinic anhydride and stir slowly at 200 rpm for 4 hours at 25°C. Subsequent centrifugation, washing, and resuspension steps are the same as in Example 1 to obtain Se@BC suspension.

[0029] S2. Preparation of intelligent responsive shell prepolymer: Prepare 4% (w / v) sodium alginate (SA) solution and 3% (w / v) carboxymethyl chitosan (CMCS) solution, respectively. Mix 40 mL of SA solution with 15 mL of CMCS solution, and add 0.03 g of EDTAD while stirring. Place the mixture in a 50°C water bath and stir at 300 rpm for 3 hours to obtain mixture A.

[0030] S3. Preparation of core-shell precursor mixture: Measure 3.0 mL of the Se@BC suspension prepared in step S1 and mix it with 1.0 mL of mixture A prepared in step S2. Disperse the mixture under ultrasonication in an ice bath as in Example 1 to obtain mixture B.

[0031] S4. Preparation of repair agent microspheres: Drop granulation was performed using a 4% (wt) calcium chloride solution, and the curing and washing steps were the same as in Example 1. The repair agent microspheres obtained after freeze-drying were sieved, and their particle size was mainly distributed in the range of 1.2-1.5 mm.

[0032] Experimental Example 1 1. Characterization and verification of the intelligent response performance of the repair agent material Experimental methods: pH-responsive release experiment: Under conditions free from heavy metal ion interference, equal volumes of the remediation agent were placed in buffer solutions at pH 4.0, 5.5, 7.0, and 8.5, respectively, and the solutions were kept at a constant temperature of 25°C with shaking. Samples were taken at predetermined time points (1h, 6h, 24h, 72h), centrifuged, and the selenium concentration in the supernatant was determined using hydride generation-atomic fluorescence spectrometry (HG-AFS). The cumulative release rate of nano-selenium was calculated.

[0033] Cd2+ Ion response release experiment: In a buffer solution with a fixed pH of 5.5, different Cd values ​​were set... 2+ Concentration gradients (0, 5, 20, 50 mg / L). Add equal volumes of the remediation agent and repeat the above procedure to determine different Cd values. 2+ Release kinetics of nano-selenium at different concentrations.

[0034] 1.3 Experimental Results: pH response results: Under acidic conditions of pH 4.0 and 5.5, the cumulative release rate of nano-selenium reached 85.2% and 62.7% after 72 hours, respectively; while under neutral and alkaline conditions of pH 7.0 and 8.5, the release rate was only 12.4% and 8.1%, respectively. This proves that the remediation agent is significantly activated in an acidic environment, as shown in Table 1.

[0035] Table 1. Cumulative release rate of nano-selenium in the remediation agent under different pH conditions.

[0036] Cd 2+ Ion response results: at pH 5.5, Cd 2+ At a concentration of 0 mg / L, the release rate was 15.3%; when Cd 2+ When the concentration increased to 50 mg / L, the release rate rapidly increased to 78.9%, and the release rate increased with increasing Cd concentration. 2+ The rate increases with increasing concentration. This proves that Cd... 2+ It can specifically trigger the release of nano-selenium, as shown in Table 2.

[0037] Table 2 Different Cd values ​​under pH 5.5 conditions 2+ Effect of concentration on cumulative release rate of nano selenium

[0038] Conclusion: The experiment successfully confirmed that the prepared repair agent has a core-shell structure and exhibits intelligent release behavior that responds to both pH and heavy metal ion concentration, which is fully consistent with the purpose of the invention.

[0039] 2. Verification of the effect of potted plant remediation on contaminated soil Experimental methods: Test soil and design: A typical acidic Cd-contaminated paddy soil was collected (pH=5.6, total Cd 1.8 mg / kg, DTPA-extractable Cd 1.05 mg / kg).

[0040] Set up 4 processes: T1: Apply the remediation agent prepared in Example 1 at a rate of 75 kg / ha (calculated as potted plant dosage based on topsoil quality).

[0041] T2: Ordinary biological nano-selenium powder with the same amount of selenium applied (prepared from the same strain, without shell encapsulation).

[0042] T3: Apply an equivalent commercially available lime-based passivating agent.

[0043] CK: No repair agents added.

[0044] Each treatment had 6 replicates. Each pot contained 2.0 kg of soil, and after the remediation agent was mixed with the soil, rice seedlings of uniform growth were transplanted.

[0045] Sample collection and testing: Cultivate for 90 days until rice matures.

[0046] Soil: Rhizosphere soil was collected, and the pH value and DTPA-extractable Cd content were measured.

[0047] Plants: Rice roots, stems, leaves and grains (brown rice) were collected separately, and after digestion, the Cd content of each part was determined by inductively coupled plasma mass spectrometry (ICP-MS).

[0048] The test results are shown in Table 3. Table 3

[0049] Results analysis: The treatment of this invention (T1) achieved a passivation rate of up to 68.6% for available Cd in the soil, which is significantly better than that of ordinary bio-nano selenium (T2, 43.1%) and commercially available passivating agents (T3, 40.2%), demonstrating its high efficiency.

[0050] The Cd content in rice grains treated with T1 decreased to 0.18 mg / kg, below the national food safety limit (0.2 mg / kg), representing a reduction of 65.4%, and the effect was significantly better than other treatments. This indicates that the nano-selenium released by the intelligent response can more effectively act on sites with high heavy metal activity, inhibiting their migration to edible parts, demonstrating the advantage of targeted treatment.

[0051] Comprehensive regulation: While passivating Cd, T1 gently raised the soil pH from 5.62 to 6.18, creating environmental conditions that were less conducive to the activation of heavy metals, demonstrating multiple synergistic effects.

[0052] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a pH- and heavy metal ion-responsive bio-nano selenium soil remediation agent, characterized in that, Includes the following steps: S1. Bio-nano selenium, sodium citrate buffer, and succinic anhydride were reacted under slow stirring, followed by centrifugation and washing to obtain carboxyl-modified bio-nano selenium; S2. Mix sodium alginate solution, carboxymethyl chitosan solution, and ethylenediaminetetraacetic anhydride to obtain mixture A; S3. The carboxyl-modified bio-nano selenium and the mixture were mixed and then ultrasonically dispersed in an ice bath to obtain mixture B; S4. Add mixture B dropwise into calcium chloride solution, filter and dry to obtain bio-nano selenium soil remediation agent.

2. The preparation method according to claim 1, characterized in that, The mass ratio of bio-nano selenium, sodium citrate buffer, and succinic anhydride in S1 is (0.02-0.05):1:(0.02-0.05).

3. The preparation method according to claim 1, characterized in that, The stirring reaction in S1 is carried out at a temperature of 20-25℃ for 4 hours.

4. The preparation method according to claim 1, characterized in that, The volume-to-mass ratio of sodium alginate solution, carboxymethyl chitosan solution, and ethylenediaminetetraacetic dianhydride in S2 is (30-40) mL: (10-15) mL: (0.01-0.03) g.

5. The preparation method according to claim 4, characterized in that, The sodium alginate solution has a concentration of 2-4% w / v; the carboxymethyl chitosan solution has a concentration of 1-3% w / v.

6. The preparation method according to claim 1, characterized in that, The temperature of the S2 mixing reaction is 40-50℃, and the time is 1-3h.

7. The preparation method according to claim 1, characterized in that, The volume-to-mass ratio of the carboxyl-modified bio-nano selenium in S3 to the mixed solution is (0.1-3:1).

8. The preparation method according to claim 1, characterized in that, The concentration of calcium chloride solution in S4 is 4%wt.

9. The preparation method according to claim 1, characterized in that, The particle size of the bio-nano selenium soil remediation agent is 0.8-1.5 mm.

10. A pH- and heavy metal ion-responsive bio-nano selenium soil remediation agent, characterized in that, It is prepared by the preparation method according to any one of claims 1-9.

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