Nano-enzyme composite material, preparation method thereof and application of nano-enzyme composite material in remediation of organic chemical pesticide pollution of soil

Abstract

The invention relates to the field of soil remediation materials, in particular to a nano-enzyme composite material, a preparation method of the nano-enzyme composite material and application of the nano-enzyme composite material in remediation of organic chemical pesticide pollution of soil, and the preparation method of the nano-enzyme composite material comprises the following steps: S1, sequentially coating the surfaces of Fe3O4 nano particles with a compact SiO2 layer and a mesoporous SiO2 layer to form an SFe3O4atMSN composite material; s2, the surfaces of the CaO2 nanoparticles are coated with a compact SiO2 layer, and an SCaO2 composite material is formed; s3, preparing a chitosan ferrous complex solution Cs-Fe, and uniformly dispersing the SFe3O4 (at) MSN composite material in the Cs-Fe solution to form a dispersion liquid containing the SFe3O4 (at) MSN (at) Cs-Fe composite material; and S4, adjusting the pH value of the dispersion liquid containing the SFe3O4 (at) MSN (at) Cs-Fe composite material to 7-10, and dispersing SCaO2 in the solution to obtain the SFe3O4 (at) MSN (at) SCaO2 (at) Cs-Fe. The nano-enzyme composite material disclosed by the invention is applied to acid soil, and organic chemical pesticide pollutants in the acid soil can be effectively degraded.

Description

Technical Field

[0001] The present invention relates to the field of soil remediation materials, and in particular to a nanoenzyme composite material, a preparation method thereof, and an application thereof in remediation of soil contaminated by organic chemical pesticides. Background Art

[0002] In modern agricultural production, the widespread use of organic chemical pesticides has greatly ensured crop yield and quality. However, the long-term and irrational application of organic chemical pesticides has resulted in large amounts of pesticide residues in the soil, causing serious soil pollution. These residual organic pesticides not only alter the physical and chemical properties of the soil and affect the structure and function of the soil microbial flora, but can also migrate through the soil-plant system, threatening agricultural product safety and human health. Therefore, the problem of soil pollution caused by organic chemical pesticides needs to be addressed urgently.

[0003] Currently, extensive research has focused on the remediation of soil contaminated by organic chemical pesticides. These include physical methods such as soil washing to remove organic chemical pesticides, chemical remediation methods such as adding strong oxidants or reducing agents to degrade organic chemical pesticides, and bioremediation methods that introduce environmentally friendly engineered bacteria into the soil to degrade organic chemical pesticides. However, these methods are often costly, prone to secondary pollution, or inefficient, making them difficult to meet practical needs.

[0004] Nanozymes are a class of nanomaterials with catalytic activity similar to that of natural enzymes. In recent years, they have demonstrated significant advantages in many fields due to their unique physicochemical properties. Compared with traditional biological enzymes, nanozymes have great advantages in terms of stability and efficiency. In terms of stability: they have strong tolerance to extreme environments, can be stored for a long time and remain active after multiple cycles, and have strong resistance to biodegradation. In terms of efficiency: the high specific surface area and active site density contribute to their high catalytic activity. By adjusting the size, shape, surface modification and composition of the nanozyme, its catalytic performance can be precisely optimized. A single nanozyme can simultaneously simulate the activities of multiple natural enzymes (such as peroxidase, superoxide dismutase, oxidase, etc.) to achieve cascade catalytic reactions. In addition, nanozymes can be prepared on a large scale through chemical synthesis, which is far lower than the production cost of biological enzymes. In summary, nanozymes have greater potential in practical applications due to their good catalytic activity, simple preparation, low cost, and easy storage and transportation.

[0005] There have been many related studies on the degradation of organic chemical pesticides by nanozymes. For example, Professor Zhang Zhen of Jiangsu University and Professor Yang Zhugen of Cranfield University collaborated to develop a bionic nanozyme (MOF-808-Apt) for the selective and efficient degradation of organophosphorus pesticides (OPs). The degradation rates of various typical OPs such as profenofos, paraoxon, and chlorpyrifos have been significantly improved. Another example is that Shi Shuxian et al. disclosed a composite nanozyme and a method for detecting and removing organophosphorus using the composite nanozyme in Chinese Patent CN118308096A. By compounding gold nanoclusters (AuNCs) on the metal-organic framework material UiO, gold composite particles UiO@AuNCs were obtained, and manganese dioxide nanosheets were in-situ loaded on UiO@AuNCs to obtain the composite nanozyme UiO@AuNCs / MnO2. This composite nanozyme can achieve the rapid and accurate detection of organophosphorus agents and can absorb and degrade organophosphorus agents.

[0006] The application of metal oxide nanozymes, such as iron oxide (Fe3O4) nanozymes, cupric peroxide (CuO2) nanozymes, etc., in the degradation of organic chemical pesticides has also been widely studied. As early as 2010, Fang Guodong of Anhui Agricultural University studied the degradation of 2,4-D and atrazine by nano iron oxide in his master's research paper, proving that iron oxide nanozymes have a degradation effect on 2,4-D and atrazine in water and soil. Wang Jianlong et al.from Tsinghua University disclosed a method for treating chlorinated organic wastewater by heterogeneous Fenton-like reaction in Chinese Patent CN102295341A. Using nano FeO, nano Fe3O4 or a mixture of nano FeO / Fe3O4 as Fenton-like catalysts, in the presence of the above Fenton-like catalysts and H2O2, they react with chlorinated organic wastewater (organochlorine pesticides) to degrade the chlorinated organic compounds in the wastewater. Another example is the citric acid-modified cupric peroxide nanozyme and its preparation method and use disclosed by Yang Dongchen et al. in Chinese Patent CN115382573A. A new type of copper-based Fenton-like nanozyme was prepared, realizing self-supply of H2O2 and driving the Fenton-like reaction to generate ·OH. It can efficiently degrade organic pollutants such as pesticides in water and soil within a wide pH range, achieving in-situ remediation of water and soil environments.

[0007] It can be seen that relatively mature research has been conducted on the degradation of organic chemical pesticide pollutants by metal oxide nanozymes. However, when applying metal oxide nanozymes to the in-situ remediation of soils polluted by organic chemical pesticides, it is often difficult to achieve the expected results. The reasons are as follows: (1) Metal oxide nanozymes are prone to agglomeration in soils, reducing their effective specific surface area and exposing insufficient active sites, thereby decreasing the catalytic degradation efficiency; (2) Metal oxide nanozymes often need to be activated to exert their catalytic effects. For example, iron oxide (Fe₃O₄), copper peroxide (CuO₂), etc. catalyze the oxidation reaction of substrates in the presence of hydrogen peroxide, while titanium dioxide (TiO₂), manganese dioxide (MnO₂), etc. generate reactive oxygen species (ROS) with strong oxidizing properties under light conditions; (3) The properties of different types of soils vary greatly, such as pH value, which has a significant impact on the stable and long-term exertion of the catalytic activity of metal oxide nanozymes.

[0008] Therefore, developing a nanozyme composite material that enables metal oxide nanozymes to stably play a degradation role in soils polluted by organic chemical pesticides has important practical significance and broad application prospects. Summary of the Invention

[0009] The purpose of the present invention is to provide a nanozyme composite material, its preparation method, and its application in the remediation of soils polluted by organic chemical pesticides. When applied to acidic soils, it can effectively degrade organic chemical pesticide pollutants in acidic soils, thereby achieving the remediation of soils polluted by organic chemical pesticides.

[0010] To achieve the above purpose, the present invention provides the following technical solutions:

[0011] A preparation method of a nanozyme composite material, comprising the following steps:

[0012] S1 Preparation of SFe₃O₄@MSN: Sequentially coat a dense SiO₂ layer and a mesoporous SiO₂ layer on the surface of Fe₃O₄ nanoparticles to form an SFe₃O₄@MSN composite material;

[0013] S2 Preparation of SCaO₂: Coat a dense SiO₂ layer on the surface of CaO₂ nanoparticles to form an SCaO₂ composite material;

[0014] S3 Preparation of SFe₃O₄@MSN@Cs-Fe: Dissolve chitosan under acidic conditions to prepare a chitosan-ferrous complex solution, denoted as Cs-Fe solution; uniformly disperse the SFe₃O₄@MSN composite material prepared in step S1 in the above Cs-Fe solution, so that the chitosan-ferrous complex is coated on the surface of the SFe₃O₄@MSN composite material to form a dispersion containing the SFe₃O₄@MSN@Cs-Fe composite material;

[0015] Preparation of SFe3O4@MSN@SCaO2@Cs-Fe in S4: Adjust the pH value of the dispersion liquid containing the SFe3O4@MSN@Cs-Fe composite material obtained in step S3 to 7 - 10, stir and react for 0.5 - 1 h, and then slowly and uniformly disperse the SCaO2 prepared in step S2 in the above dispersion liquid under stirring. After the reaction, centrifuge, wash, and dry at a low temperature below 100 °C to obtain the nanzyme composite material, denoted as SFe3O4@MSN@SCaO2@Cs-Fe.

[0016] First of all, the present invention uses Fe3O4 nanozyme as the core material. The Fe3O4 nanozyme is applied to degrade organic chemical pesticides in soil. Its core mechanism of action is to carry out Fenton oxidation reaction in soil, that is: through the chemical reaction between iron ions and H2O2, finally generate hydroxyl radicals (·OH) with super strong oxidation activity, thereby promoting the accelerated decomposition of organic chemical pesticides in soil. The specific reaction process of Fe3O4 generating hydroxyl radicals is as follows:

[0017] Fe 2+ +H2O2→Fe 3+ +·OH+OH - (1)

[0018] Fe 3+ +H2O2→Fe 2+ +HO2·+H + (2)

[0019] After research, the core conditions for the continuous progress of the above reactions include: (1) continuous supply of H2O2; (2) continuous generation of Fe 2+ ; However, in the actual soil application environment, the content of H2O2 is extremely limited, and the reaction rate of the above reaction (2) Fe 3+ reacting with H2O2 to obtain Fe 2+ is relatively low. Even in many cases, due to the large amount of soil OH - , Fe 3+ hydrolyzes to form Fe(OH)3, making reaction (2) difficult to proceed. Therefore, in actual soil applications, Fe3O4 nanozyme is difficult to continuously and stably play a catalytic role.

[0020] The present invention is committed to being able to continuously supply H2O2 and Fe 2+ in soil to promote the continuous progress of the Fenton reaction in the soil environment. This is the design goal, and the nanzyme composite material of the present invention is designed. Specifically:

[0021] (1) First, the present invention introduces CaO2 with a peroxide bond (-O-O-) into the composite material to self - supply H2O2 during use. H2O2 is an essential component for the Fenton reaction to occur. Since H2O2 is liquid at room temperature and extremely unstable, it is easy to react when mixed with Fe3O4, so it is difficult to store the two simultaneously. To overcome this problem, the present invention selects a substance that can generate H2O2 under the use conditions and does not react with Fe3O4 under the storage conditions to introduce H2O2 into the system. CaO2 will gradually convert to H2O2 under acidic conditions and is relatively stable under alkaline conditions. Therefore, the present application selects CaO2 as the activator to achieve self - supply of H2O2 under acidic soil conditions.

[0022] (2) Whether it is the active substance Fe3O4 nanozyme or the activator CaO2 nanoparticles of the present application, there is a problem of easy agglomeration. In actual agricultural soil use, if the two are directly added to the soil, it is very easy to form aggregates and cannot be well dispersed in the soil. Based on this, the present invention coats SiO2 on the surfaces of both Fe3O4 nanozymes and CaO2 nanoparticles. Due to the good dispersibility of SiO2, the extremely easy - to - agglomerate Fe3O4 nanoparticles and CaO2 can have good dispersibility, avoiding their agglomeration in the soil. At the same time, the porosity of SiO2 does not affect the release of the coated substances to participate in the reaction.

[0023] (3) On this basis, the present invention further designs an activation system for activating the Fenton reaction in an acidic soil environment, that is: by designing a coating material that dissolves under acidic conditions to coat the Fe3O4 nanozyme, so as to achieve the release of Fe3O4 nanozyme under acidic soil conditions and then activate its catalytic reaction. Specifically, the present invention selects chitosan as the coating material. On the one hand, chitosan, as a synergist widely used in agriculture, has good effects on soil micro - environment restoration, crop quality improvement, etc. On the other hand, chitosan itself has acid - responsive properties. Under acidic conditions, the amino ions on its surface are protonated and it will dissolve, thereby releasing the internally encapsulated Fe3O4 nanozyme. Further, the surface - coated chitosan can also avoid the strong adsorption of metal ions by biomass materials in the soil, ensuring that the Fe3O4 nanozyme can be effectively dispersed in the soil.

[0024] (4) The present invention further coats mesoporous silica on the surface of the SiO2 - coated Fe3O4 nanozyme (SFe3O4). Utilizing the porosity and easy functionalization modification and other characteristics of mesoporous silica, the SFe3O4 can be more stably combined with the subsequent coated chitosan layer, ensuring the coating stability of the coating shell under storage conditions.

[0025] (5) In step S3, the present invention prepares a chitosan-ferrous complex solution by dissolving chitosan under acidic conditions, and creatively chelates Fe 2+ on the coating shell material to achieve the purpose of stably carrying Fe 2+ into the soil. In the acidic environment of the soil, as chitosan dissolves, Fe 2+ will be continuously released, thereby providing the Fe 2+ required for the Fenton reaction.

[0026] (6) It should be noted that CaO2 nanoparticles are extremely unstable under acidic conditions, and chitosan needs to be dissolved under acidic conditions. How to effectively coat both Fe3O4 nanozymes and CaO2 nanoparticles within the chitosan shell layer is the core design of the present invention.

[0027] For this reason, the present invention sets the conditions to uniformly disperse the chitosan-ferrous complex chelated with Fe 2+ and SFe3O4@MSN under acidic conditions, and then adjusts the pH value to an alkaline state. During the change of pH value from alkaline to acidic, the mesopores on the surface of the chitosan-ferrous complex and SFe3O .

[0028] 4@MSN stably bind to form a stable coating layer, namely SFe3O4@MSN@Cs-Fe, achieving the purpose that Fe3O4 nanozymes can be released only under acidic conditions.

[0029] In the alkaline state, chitosan is in a gel state. At this time, SCaO2 is dispersed in the gel-like SFe3O4@MSN@Cs-Fe under stirring. The chitosan-ferrous complex that is not wrapped on the surface of SFe3O4@MSN will further wrap SCaO2 on the surface of SFe3O4@MSN@Cs-Fe, and a small part of SCaO2 is only mixed with SFe3O4@MSN@Cs-Fe, finally forming a complex aggregate. The present invention designates this complex aggregate as SFe3O4@MSN@SCaO2@Cs-Fe.

[0029] The present invention creatively wraps Fe3O4 nanozymes and CaO2 nanoparticles into the chitosan shell layer by the above method, and carries them into the soil together with chitosan. Under the acidic conditions of the soil, chitosan dissolves and releases the internal Fe3O4 nanozymes and CaO2 nanoparticles; and under acidic conditions, CaO2 nanoparticles will gradually dissolve to form H2O2 and Ca 2+ , Fe 2+ will also detach from the surface of chitosan under acidic conditions; thereby providing the H2O2 and Fe 2+ required for the Fenton reaction, promoting the continuous progress of the Fenton reaction, continuously generating hydroxyl radicals, and promoting the decomposition of organic chemical pesticides and other organic substances in the soil.

[0030] Preferably, the particle size of the Fe3O4 nanoparticles in step S1 is less than 50 nm; the particle size of the CaO2 nanoparticles in step S2 is less than 50 nm.

[0031] Nano-scale particles are selected, which have many active sites on their surface. Once these nanoparticles are dispersed in the soil under the carrier of the composite material, the multiple active sites on their surface will enable them to exert strong catalytic activity, which is also the key to their enzyme-like activity.

[0032] As a preference, in step S3, the amount of SFe3O4@MSN composite material and Cs-Fe is based on the ratio of Fe3O4 and Fe 2+ The molar ratio is: n(Fe3O4): n(Fe 2+ )=1:1~1.5. Meanwhile, in step S4, the amount of SCaO2 added satisfies: n(CaO2)=1~1.5(n(Fe3O4)+n(Fe 2+ )).

[0033] The present invention limits the dosage of Fe3O4, chitosan ferrous complex and CaO2 to ensure that the reaction can continue to proceed in the direction of generating hydroxyl radicals in an acidic soil system, thereby avoiding the large-scale generation of Fe(OH)3 precipitation and also avoiding the quenching of hydroxyl radicals.

[0034] Preferably, the Fe3O4 nanoparticles in step S1 are prepared by a coprecipitation method, a thermal decomposition method, or a sol-gel method. In practice, the Fe3O4 nanoparticles can be prepared in-house or purchased directly.

[0035] Preferably, the CaO2 nanoparticles in step S2 are prepared by reacting Ca(OH)2 and H2O2. Similarly, in practice, the CaO2 nanoparticles can be made in-house or purchased directly.

[0036] Most preferably, the specific method for preparing SFe3O4@MSN in step S1 includes:

[0037] 0.5 g to 0.7 g of Fe3O4 nanoparticles with a particle size of less than 50 nm were weighed and ultrasonically dispersed in 180 mL to 220 mL of ethanol solvent for 20 min to 30 min, and then 80 mL to 120 mL of deionized water was added and ultrasonic dispersion was continued for 10 min to 20 min. Ammonia was added to adjust the pH value to 10-11 and the mixture was stirred evenly. 0.4 g to 0.6 g of TEOS was slowly added dropwise and the mixture was stirred at room temperature for 3 to 4 h. After the reaction was completed, the black precipitate was separated from the suspension by magnetic separation, and then washed twice with anhydrous ethanol and three times with deionized water to obtain a Fe3O4 composite material densely coated with silica, which was recorded as SFe3O4.

[0038] The above-mentioned SFe3O4 composite material was added to 280 mL to 320 mL of an ethanol-water mixed solvent with a volume ratio of 2:1 and ultrasonically dispersed for 20 min to 30 min. 0.2 g to 0.35 g of CTAB was slowly added to the above solution and stirred until completely dissolved. Ammonia water was added to adjust the pH value to 9.5 to 10.5. 0.6 g to 0.8 g of TEOS was slowly added dropwise to the solution at 40 °C to 60 °C, and the mixture was stirred and reacted for 20 h to 28 h. After the reaction, the solid product was collected by centrifugation, and then CTAB was removed. After washing and drying, a composite material with mesoporous silica coated on the surface of SFe3O4 was obtained, denoted as SFe3O4@MSN.

[0039] Further preferably, in step S1, the method for removing CTAB is selected from any one of the following: (1) extracting and removing CTAB with a 1 mol / L HCl / ethanol solution; (2) calcining at 500 °C - 600 °C to remove CTAB.

[0040] Preferably, the specific method for preparing SCaO2 in step S2 includes: weighing 0.15 g to 0.25 g of CaO2 nanoparticles with a particle size less than 50 nm and ultrasonically dispersing them in 180 mL to 220 mL of a PVP solvent for 20 min to 30 min. Then, 80 mL to 120 mL of deionized water was added and ultrasonically dispersed for another 10 min to 20 min. Ammonia water was added to adjust the pH value to 10 - 11, and the mixture was stirred evenly; 0.35 g to 0.45 g of TEOS was slowly added dropwise, and the mixture was continuously stirred and reacted at room temperature for 3 to 4 h. After the reaction, the solid phase was separated by centrifugation, and then it was washed twice with absolute ethanol and rinsed three times with deionized water, and dried at a low temperature below 100 °C to obtain a composite material of CaO2 densely coated with silica, denoted as SCaO2.

[0041] Preferably, the specific method for preparing SFe3O4@MSN@Cs-Fe in step S3 includes: weighing chitosan with a deacetylation degree ≥ 80% and dissolving it in 400 mL to 500 mL of 0.01 mol / L acetic acid solution and stirring to form a chitosan solution; slowly adding dropwise a ferrous ammonium sulfate solution with a concentration of 1.5 mol / L to 2.5 mol / L to the chitosan solution; stirring and reacting at 40 °C to 50 °C for 30 min to 50 min to form a chitosan-iron(II) complex solution, denoted as Cs-Fe solution; the weight ratio of ferrous ammonium sulfate to chitosan satisfies 2.5 to 3.5:1;

[0042] Preferably, the SFe3O4@MSN prepared in step S1 was slowly and uniformly dispersed in the above Cs-Fe solution in proportion, and the mixture was continuously stirred and reacted for 10 h to 18 h; a dispersion containing the SFe3O4@MSN@Cs-Fe composite material was prepared.

[0043] Preferably, the specific method for preparing SFe3O4@MSN@SCaO2@Cs-Fe in step S4 includes: adjusting the pH value of the solution containing the SFe3O4@MSN@Cs-Fe composite material obtained in step S3 to 7.0 - 8.0 with a 0.045 mol / L - 0.065 mol / L sodium hydroxide solution, stirring and reacting for 0.5 - 1 h, and then slowly and uniformly dispersing the SCaO2 prepared in step S2 in the above solution in a stirred state in proportion, continuing to stir and disperse for 5 h - 10 h. After the reaction, the solid phase is separated by centrifugation, and then rinsed 3 times with deionized water and dried at a low temperature below 100 °C to obtain the nanozyme composite material, denoted as SFe3O4@MSN@SCaO2@Cs-Fe.

[0044] The present invention also provides a nanozyme composite material prepared by the above preparation method.

[0045] The present invention also provides the application of the above nanozyme composite material in the repair of soil organic chemical pesticides. It is applied to acidic soil, specifically, to acidic soil with a pH value ≤ 5.5, preferably to acidic soil with a pH value ≤ 5.0; in actual use, it can be applied alone or mixed with any neutral or alkaline solid fertilizer and then applied.

[0046] The present invention has the following beneficial effects compared with the prior art:

[0047] (1) The nanozyme composite material prepared by the preparation method of the present invention can realize the in-situ degradation of organic chemical pesticides in acidic soil, and has a high degradation rate and strong persistence, effectively repairing the soil chemical pesticide pollution and avoiding the impact of pesticide pollution on the quality of crops.

[0048] (2) The nanozyme composite material prepared by the preparation method of the present invention can realize the degradation of other organic substances (such as organic phosphorus and organic nitrogen) in acidic soil in addition to organic chemical pesticides, so as to promote the conversion of nutrient elements in the soil into nutrient forms that crops can absorb, thereby improving the soil fertility, promoting crop growth, and increasing the crop yield and quality.

[0049] (3) The nanozyme composite material of the present invention, while degrading soil organic chemical pesticides, also introduces small molecule organic acids such as chitosan and calcium elements that are relatively lacking in acidic soil, which can improve the soil microenvironment and promote crop growth. Description of the Drawings

[0050] Figure 1 is the preparation flow chart of the nanozyme composite material of Examples 1 - 3 of the present invention;

[0051] Figure 2It is the trend chart of the concentration change of hexachlorocyclohexane in the soil samples of each experimental group in Experimental Example 1;

[0052] Figure 3 It is the trend chart of the concentration change of DDT in the soil samples of each experimental group in Experimental Example 1. Detailed implementation manners

[0053] To further understand the present invention, the preferred implementation manners of the present invention will be described below in conjunction with embodiments. However, it should be understood that these descriptions are only for further explaining the features and advantages of the present invention, rather than limiting the claims of the present invention.

[0054] The preparation methods of Fe3O4 nanoenzymes in the following Embodiments 1-3 and Comparative Examples 1-2 are as follows:

[0055] Weigh FeSO4·7H2O and FeCl3·6H2O according to the molar ratio of Fe 2+ / Fe 3+ of 0.5, dissolve them in deionized water, and ultrasonically stir until completely dissolved to obtain a mixed solution. Subsequently, heat the mixed solution with stirring to 50 °C, keep it warm for 20 min. After the heating is completed, immediately slowly add an ammonia water solution with a concentration of 13 mol / L to the solution to adjust the pH value to 10-11, and then continue to react at 50 °C for 1 h to obtain a suspension; after the reaction is completed, separate the black precipitate from the suspension by magnetic separation method, then wash it twice with absolute ethanol and three times with deionized water, and dry it at low temperature to prepare Fe3O4 nanoenzyme.

[0056] The preparation methods of CaO2 nanoparticles in the following Embodiments 1-3 and Comparative Examples 1-2 are as follows:

[0057] Dissolve PVP in ultrapure water, ultrasonically disperse for 20 min, then add Ca(OH)2 and continue to ultrasonically disperse for 20 min. Slowly add H2O2 to the above dispersion for reaction, the reaction time is 2-4 h, control the reaction process at 5-10 °C. After the reaction is completed, centrifuge, filter, wash three times with ultrapure water, and dry at 50 °C at low temperature. In the above reaction: the mass ratio of Ca(OH)2 to PVP is 1:15; the mass ratio of Ca(OH)2 to H2O2 is 1:15.

[0058] Embodiment 1

[0059] This embodiment provides a nanoenzyme composite material and its preparation method, wherein: the preparation method includes the following steps:

[0060] S1 Prepare SFe3O4@MSN

[0061] Weigh 0.6 g of Fe3O4 nanoparticles with a particle size less than 50 nm and ultrasonically disperse them in 200 mL of ethanol solvent for 20 min. Then add 100 mL of water and continue ultrasonic dispersion for 10 min. Add ammonia water to adjust the pH value to 10 and stir evenly. Slowly add 0.5 g of TEOS and continue stirring and reacting at room temperature for 4 h. After the reaction, use magnetic separation to separate the black precipitate from the suspension. Subsequently, wash it twice with absolute ethanol and three times with deionized water to obtain a Fe3O4 composite material densely coated with silica, denoted as SFe3O4;

[0062] Add the above SFe3O4 composite material to 300 mL of an ethanol-water mixed solvent with a volume ratio of 2:1 and ultrasonically disperse it for 20 - 30 min. Slowly add 0.25 g of CTAB to the above solution and stir until it is completely dissolved. Add ammonia water to adjust the pH to 10.5. Slowly add 0.6 g of TEOS to the solution at 60 °C and stir and react for 24 h. After the reaction, centrifuge to collect the solid-phase product, then extract CTAB with 1 mol / L HCl / ethanol solution, wash it with absolute ethanol again, and finally dry it at a low temperature below 100 °C to obtain a composite material with mesoporous silica coated on the surface of SFe3O4, denoted as SFe3O4@MSN.

[0063] S2 Preparation of SCaO2

[0064] Weigh 0.2 g of CaO2 nanoparticles with a particle size less than 50 nm and ultrasonically disperse them in 200 mL of PVP solvent for 20 min. Then add 100 mL of water and continue ultrasonic dispersion for 10 min. Add ammonia water to adjust the pH value to 11 and stir evenly. Slowly add 0.4 g of TEOS and continue stirring and reacting at room temperature for 4 h. After the reaction, centrifuge to separate the solid phase. Subsequently, wash it twice with absolute ethanol and three times with deionized water, and dry it at a low temperature below 100 °C to obtain a CaO2 composite material densely coated with silica, denoted as SCaO2;

[0065] S3 Preparation of SFe3O4@MSN@Cs-Fe

[0066] Weigh chitosan (degree of deacetylation ≥ 80%) and dissolve it in 500 mL of 0.01 mol / L acetic acid solution, and stir to form a chitosan solution; slowly dropwise add a solution of ammonium ferrous sulfate with a concentration of 2 mol / L to the chitosan solution; the weight ratio of ammonium ferrous sulfate to chitosan satisfies 3:1, and stir and react at 50 °C for 30 min to form a chitosan-ferrous complex solution, denoted as Cs-Fe solution; uniformly disperse the SFe3O4@MSN prepared in step S1 in the above Cs-Fe solution, and continue to stir and react for 18 h; prepare a dispersion containing the SFe3O4@MSN@Cs-Fe composite material; the dosages of the SFe3O4@MSN composite material and Cs-Fe are based on Fe3O4 and Fe 2+ to satisfy: n(Fe3O4):n(Fe 2+ ) = 1:1.1;

[0067] S4 Preparation of SFe3O4@MSN@SCaO2@Cs-Fe

[0068] Adjust the pH value of the solution containing the SFe3O4@MSN@Cs-Fe composite material obtained in step S3 to 7.0 with 0.05 mol / L sodium hydroxide solution, stir and react for 0.5 h, and then slowly and uniformly disperse the SCaO2 prepared in step S2 in the above solution under stirring, continue to stir and disperse for 5 h. After the reaction is completed, centrifuge to separate the solid phase, then rinse it 3 times with deionized water, and dry it at a low temperature below 100 °C to obtain the nanozyme composite material

[0069] SFe3O4@MSN@SCaO2@Cs-Fe, where the addition amount of SCaO2 satisfies: n(CaO2) = 1.2(n(Fe3O4) + n(Fe 2 + ));

[0070] The nanozyme composite material prepared in this example is denoted as nanozyme 1.

[0071] Example 2

[0072] This example provides a nanozyme composite material and its preparation method. The difference from Example 1 is that:

[0073] In step S3, the dosages of the SFe3O4@MSN composite material and Cs-Fe are based on Fe3O4 and Fe 2+ to satisfy: n(Fe3O4):n(Fe 2+ ) = 1:1.5;

[0074] In step S4, the addition amount of SCaO2 satisfies: n(CaO2) = 1(n(Fe3O4) + n(Fe 2+ ));

[0075] The nanozyme composite material prepared in this example is denoted as nanozyme 2.

[0076] Example 3

[0077] This example provides a nanozyme composite material and its preparation method. The difference from Example 1 is as follows:

[0078] In step S3, the dosages of SFe3O4@MSN composite material and Cs-Fe are such that the amounts of Fe3O4 and Fe 2+ counting satisfy: n(Fe3O4):n(Fe 2+ ) = 1:1.

[0079] In step S4, the addition amount of SCaO2 satisfies: n(CaO2) = 1.5(n(Fe3O4)+n(Fe 2+ ))).

[0080] The nanozyme composite material prepared in this example is denoted as nanozyme 3.

[0081] Comparative Example 1

[0082] This comparative example provides a nanozyme composite material and its preparation method, wherein: the preparation method includes the following steps:

[0083] S1 Prepare SFe3O4@MSN

[0084] Weigh 0.6 g of Fe3O4 nanoparticles with a particle size less than 50 nm and ultrasonically disperse them in 200 mL of ethanol solvent for 20 min. Then add 100 mL of water and continue to ultrasonically disperse for 10 min. Add ammonia water to adjust the pH value to 10 and stir evenly; slowly drop 0.5 g of TEOS and continue to stir and react at room temperature for 4 h. After the reaction is completed, use magnetic separation to separate the black precipitate from the suspension. Subsequently, wash it with absolute ethanol twice and rinse it with deionized water three times to obtain a Fe3O4 composite material with a dense silica coating, denoted as SFe3O4;

[0085] Add the above SFe3O4 composite material to 300 mL of an ethanol-water mixed solvent with a volume ratio of 2:1 and ultrasonically disperse it for 30 min. Slowly add 0.25 g of CTAB to the above solution and stir until it is completely dissolved. Add ammonia water to adjust the pH to 10.5, and slowly drop 0.6 g of TEOS into the solution at 60 °C and stir and react for 24 h. After the reaction is completed, centrifuge to collect the solid-phase product, then extract CTAB with 1 mol / L HCl / ethanol solution, wash it with absolute ethanol again, and finally dry it at a low temperature below 100 °C to obtain a composite material with mesoporous silica coated on the surface of SFe3O4, denoted as SFe3O4@MSN.

[0086] Preparation of SCaO2

[0087] Weigh 0.2 g of CaO2 nanoparticles with a particle size less than 50 nm and ultrasonically disperse them in 200 mL of PVP solvent for 20 min. Then add 100 mL of water and continue ultrasonic dispersion for 10 min. Add ammonia water to adjust the pH value to 11 and stir evenly. Slowly drop 0.4 g of TEOS and continue stirring and reacting at room temperature for 4 h. After the reaction, centrifuge to separate the solid SCaO2 nanoparticles, and then wash them twice with absolute ethanol and three times with deionized water, and dry them at a low temperature below 100 °C to obtain a CaO2 composite material densely coated with silica, denoted as SCaO2;

[0088] Preparation of SFe3O4@MSN@Cs

[0089] Weigh chitosan (degree of deacetylation ≥ 80%) and dissolve it in 500 mL of 0.01 mol / L acetic acid solution and stir to form a chitosan solution; uniformly disperse the SFe3O4@MSN prepared in step S1 in the above chitosan solution and continue stirring and reacting for 18 h; obtain a solution containing the SFe3O4@MSN@Cs composite material; among them, the dosages of the SFe3O4@MSN composite material and Cs, calculated based on Fe3O4 and chitosan, satisfy: n(Fe3O4):n(chitosan) = 1:0.37.

[0090] Preparation of SFe3O4@MSN@SCaO2@Cs

[0091] Adjust the pH value of the solution containing the SFe3O4@MSN@Cs composite material obtained in step S3 to 7.0 with 0.05 mol / L sodium hydroxide solution, stir and react for 0.5 h, and then slowly and uniformly disperse the SCaO2 prepared in step S2 in the above solution under stirring, and continue stirring and dispersing for 5 h. After the reaction, centrifuge to separate the solid phase, and then wash it three times with deionized water and dry it at a low temperature below 100 °C to obtain the nanozyme composite material SFe3O4@MSN@SCaO2@Cs, where the addition amount of SCaO2 satisfies: n(CaO2) = 4.2n(Fe3O4).

[0092] The nanozyme composite material prepared in this comparative example is denoted as nanozyme 4.

[0093] Comparative Example 2

[0094] This comparative example provides a nanozyme composite material and a preparation method thereof, where: the preparation method includes the following steps:

[0095] Preparation of SFe3O4@MSN

[0096] Weigh 0.6 g of Fe3O4 nanoparticles with a particle size less than 50 nm and ultrasonically disperse them in 200 mL of ethanol solvent for 20 min. Then add 100 mL of water and continue ultrasonic dispersion for 10 min. Add ammonia water to adjust the pH value to 10 and stir evenly. Slowly drop 0.5 g of TEOS and continue stirring and reacting at room temperature for 4 h. After the reaction is completed, use magnetic separation to separate the black precipitate from the suspension. Subsequently, wash it twice with absolute ethanol and three times with deionized water to obtain a Fe3O4 composite material densely coated with silica, denoted as SFe3O4;

[0097] Add the above SFe3O4 composite material to 300 mL of an ethanol-water mixed solvent with a volume ratio of 2:1 and ultrasonically disperse it for 30 min. Slowly add 0.25 g of CTAB to the above solution and stir until it is completely dissolved. Add ammonia water to adjust the pH to 10.5. Slowly drop 0.6 g of TEOS into the solution at 60 °C and stir and react for 24 h. After the reaction is completed, centrifuge to collect the solid-phase product, then extract CTAB with 1 mol / L HCl / ethanol solution, wash it with absolute ethanol again, and finally dry it at a low temperature below 100 °C to obtain a composite material with mesoporous silica coated on the surface of SFe3O4, denoted as SFe3O4@MSN.

[0098] S2 Preparation of SFe3O4@MSN@Cs-Fe

[0099] Weigh chitosan (deacetylation degree ≥ 80%) and dissolve it in 500 mL of 0.01 mol / L acetic acid solution and stir to form a chitosan solution; slowly drop a 2 mol / L ammonium ferrous sulfate solution into the chitosan solution; the weight ratio of ammonium ferrous sulfate to chitosan satisfies 3:1, and stir and react at 50 °C for 30 min to form a chitosan-ferrous complex solution, denoted as Cs-Fe solution; uniformly disperse the SFe3O4@MSN prepared in step S1 in the above Cs-Fe solution and continue stirring and reacting for 18 h; prepare a solution containing the SFe3O4@MSN@Cs-Fe composite material; the dosage of the SFe3O4@MSN composite material and Cs-Fe is based on Fe3O4 and Fe 2+ to satisfy: n(Fe3O4):n(Fe 2+ ) = 1:1.1;

[0100] Use 0.05 mol / L sodium hydroxide solution to adjust the pH value of the solution containing the SFe3O4@MSN@Cs-Fe composite material obtained in step S3 to 7.0, continue stirring and dispersing for 1 h. After the reaction is completed, centrifuge to separate the solid phase, then wash it three times with deionized water and dry it at a low temperature below 100 °C to obtain the nanozyme composite material SFe3O4@MSN@Cs-Fe.

[0101] The nanozyme composite material prepared in this comparative example is denoted as nanozyme 5.

[0102] Experimental Example 1: Degradation of Organic Chemical Pesticides in Soil by Nanozyme Composite Material

[0103] Preparation of soil sample: A soil sample with severely excessive organochlorine pesticides was taken from the leafy vegetable planting base in Huangshui Town, Shuangliu District, Chengdu City, Sichuan Province. The pH value of the soil sample was 4.8. The contents of hexachlorocyclohexane and DDT in the soil were measured to be 1.75 mg / kg and 2.31 mg / kg respectively by the method of "Determination of Organochlorine Pesticides in Soil and Sediments - Gas Chromatography" (HJ 921-2017).

[0104] The above soil sample was filled into an experimental soil column with a total height of 20 cm. The experimental soil column was formed by stacking 2 soil columns with a diameter of 10 cm and a height of 10 cm. Among them, the lower soil column was filled with a soil sample with a height of 10 cm, and the upper soil column was filled with a soil sample with a height of 5 cm. The filling density of the soil sample was 1.35 g / cm 3 , and water was added to make the soil moisture content 35% ± 1%, and 10 mL of water was regularly supplemented every day;

[0105] Six experimental groups were set up, and 3 parallel experiments were set up for each experimental group. The six experimental groups included experimental groups 1-5 that respectively applied the nanozyme composite materials of Examples 1-3 and Comparative Examples 1-2, and experimental group 6 that did not apply any material as a control group. The addition amount of the nanozyme composite material in each parallel test of each experimental group was 0.5 g; 0.5 g of nanozyme was evenly sprinkled 3 cm away from the soil sample surface, and soil samples at 5 cm from the soil sample surface were taken every 5 days. The contents of hexachlorocyclohexane and DDT in the soil were measured by the method of "Determination of Organochlorine Pesticides in Soil and Sediments - Gas Chromatography" (HJ 921-2017); the changes in the contents of hexachlorocyclohexane and DDT in the soil samples of each experimental group over time are as Figure 1 and Figure 2 shown.

[0106] From Figure 1 and Figure 2 the data, it can be known that the nanozyme composite material prepared in Example 1 of the present invention can continuously degrade the organic chemical pesticides in the soil at a relatively stable rate, and finally completely degrade hexachlorocyclohexane and DDT in the soil in 35 d and 40 d respectively; the nanozyme composite materials of Example 2 and Example 3 can degrade hexachlorocyclohexane and DDT in the soil more rapidly in the early stage, but the degradation rate decreases in the later stage, and even cannot completely degrade hexachlorocyclohexane and DDT in the soil; the nanozyme composite materials of Comparative Example 1 and Comparative Example 2 can degrade the organic pesticides in the soil when they are just added to the soil, but cannot continuously and stably degrade the organic chemical pesticides in the soil.

[0107] This is because, in the nanozyme composite material of Example 1, chitosan can dissolve under acidic conditions to release the internal Fe3O4 nanozyme and CaO2 inside, and CaO2 can decompose under acidic conditions to generate H2O2, which can then promote the Fenton reaction. At the same time, Fe chelated on the surface of chitosan 2+ is gradually released under acidic conditions to provide the Fe required for the continuous progress of the Fenton reaction 2+ , which can then ensure the continuous progress of the Fenton reaction and continuously decompose organic pesticides;

[0108] In the nanozyme composite materials of Example 2 and Example 3, due to the excessive content of H2O2 or Fe 2+ in them, hydroxyl radicals can be rapidly generated in the early stage. However, at the same time, due to the excess of H2O2 or Fe 2+ , the hydroxyl radicals will continue to react with H2O2 to generate HO2·, resulting in the quenching of hydroxyl radicals; or the concentration of Fe 3+ is too high, and excessive hydrolysis produces too much Fe(OH)3, which in turn affects the degradation of organic chemical pesticides.

[0109] Although Comparative Example 1 can degrade organic pesticides through the action of the Fenton reaction, due to the limitation of its Fe 2+ content, the rate of the Fenton reaction is limited, and thus hydroxyl radicals cannot be generated at a high rate, and organic chemical pesticides cannot be continuously and rapidly decomposed; while in Comparative Example 2, due to the limited content of peroxy bonds in the soil itself, in the absence of external H2O2 supplementation, even with the supplementation of Fe 2+ , the subsequent Fenton reaction hardly occurs anymore, and no more hydroxyl radicals are generated.

[0110] In summary, the nanozyme composite material prepared by the present invention can continuously and stably degrade organic chemical pesticides in acidic soil, and various components in the composite material of the present invention have good improvement effects on the soil microenvironment, and have application prospects in the remediation of organic chemical pesticide pollution in farmland soil.

Claims

1. A preparation method of a nanozyme composite material, characterized in that, It includes the following steps: S1 Prepare SFe3O4@MSN: Coating a dense SiO2 layer and a mesoporous SiO2 layer on the surface of Fe3O4 nanoparticles in sequence to form an SFe3O4@MSN composite material; S2 Prepare SCaO2: Coating a dense SiO2 layer on the surface of CaO2 nanoparticles to form an SCaO2 composite material; S3 Prepare SFe3O4@MSN@Cs-Fe: Dissolve chitosan under acidic conditions to prepare a chitosan-ferrous complex solution, denoted as Cs-Fe solution; uniformly disperse the SFe3O4@MSN composite material prepared in step S1 in the above Cs-Fe solution so that the chitosan-ferrous complex is coated on the surface of the SFe3O4@MSN composite material to form a dispersion containing the SFe3O4@MSN@Cs-Fe composite material; S4 Prepare SFe3O4@MSN@SCaO2@Cs-Fe: Adjust the pH value of the dispersion containing the SFe3O4@MSN@Cs-Fe composite material obtained in step S3 to 7-10, stir and react for 0.5-1 h, and then slowly and uniformly disperse the SCaO2 prepared in step S2 in the above solution under stirring. After the reaction, centrifuge, wash, and dry at a low temperature below 100 °C to obtain the nanozyme composite material, denoted as SFe3O4@MSN@SCaO2@Cs-Fe.

2. The preparation method of the nanozyme composite material according to claim 1, characterized in that The particle size of the Fe3O4 nanoparticles in step S1 is less than 50 nm; the particle size of the CaO2 nanoparticles in step S2 is less than 50 nm.

3. The preparation method of the nanozyme composite material according to claim 1, wherein, In step S3, the dosages of the SFe3O4@MSN composite material and Cs-Fe, calculated based on Fe3O4 and Fe 2+ meet the requirement: n(Fe3O4):n(Fe 2+ ) = 1:1 to 1.

5.

4. The preparation method of the nanozyme composite material according to claim 1, wherein, In step S4, the addition amount of SCaO2 in terms of CaO2 satisfies: n(CaO2) = 1 - 1.5(n(Fe3O4) + n(Fe 2+ )) 5. The preparation method of the nanozyme composite material according to any one of claims 1 to 4, characterized in that, The specific method for preparing SFe3O4@MSN in step S1 includes: Weigh 0.5 g - 0.7 g of Fe3O4 nanoparticles with a particle size less than 50 nm, ultrasonically disperse them in 180 mL - 220 mL of ethanol solvent for 20 min - 30 min, then add 80 mL - 120 mL of deionized water and continue to ultrasonically disperse for 10 min - 20 min. Add ammonia water to adjust the pH value to 10-11, and stir evenly; slowly dropwise add 0.4 g - 0.6 g of TEOS, and continue to stir and react at room temperature for 3 - 4 h. After the reaction, use magnetic separation to separate the black precipitate from the suspension, and then wash it with absolute ethanol twice and rinse it with deionized water three times to obtain an Fe3O4 composite material with a dense SiO2 coating on the surface, denoted as SFe3O4; Add the above SFe3O4 composite material to 280 mL - 320 mL of an ethanol-water mixed solvent with a volume ratio of 2:1, ultrasonically disperse it for 20 min - 30 min, slowly add 0.2 g - 0.35 g of CTAB to the above solution and stir until it is completely dissolved. Add ammonia water to adjust the pH value to 9.5 - 10.5, and slowly dropwise add 0.6 g - 0.8 g of TEOS to the solution at 40 °C - 60 °C, stir and react for 20 h - 28 h. After the reaction, centrifuge to collect the solid-phase product, then remove CTAB, wash and dry to obtain a composite material with mesoporous silica coated on the surface of SFe3O4, denoted as SFe3O4@MSN.

6. The preparation method of the nanozyme composite material according to any one of claims 1 to 4, characterized in that, The specific method for preparing SCaO2 in step S2 includes: Weigh 0.15 g to 0.25 g of CaO2 nanoparticles with a particle size less than 50 nm and ultrasonically disperse them in 180 mL to 220 mL of PVP solvent for 20 min to 30 min. Then add 80 mL to 120 mL of deionized water and continue ultrasonic dispersion for 10 min to 20 min. Add ammonia water to adjust the pH value to 10 - 11 and stir evenly. Slowly add dropwise 0.35 g to 0.45 g of TEOS and continue stirring and reacting at room temperature for 3 to 4 h. After the reaction is completed, centrifuge to separate the solid phase, then wash it twice with absolute ethanol and three times with deionized water, and dry it at a low temperature below 100 °C to obtain a CaO2 composite material with a dense SiO2 coating on the surface, denoted as SCaO2.

7. The preparation method of the nanozyme composite material according to any one of claims 1 to 4, characterized in that, The specific method for preparing SFe3O4@MSN@Cs-Fe in step S3 includes: Weigh chitosan with a deacetylation degree ≥ 80% and dissolve it in 400 mL to 500 mL of 0.01 mol / L acetic acid solution and stir to form a chitosan solution; slowly add dropwise a ferrous ammonium sulfate solution with a concentration of 1.5 mol / L to 2.5 mol / L to the chitosan solution; stir and react at 40 °C to 50 °C for 30 min to 50 min to form a chitosan ferrous complex solution, denoted as Cs-Fe solution; the weight ratio of the ferrous ammonium sulfate to the chitosan satisfies 2.5 to 3.5:1; Weigh SFe3O4@MSN prepared in step S1 according to the proportion and slowly and evenly disperse it in the above Cs-Fe solution, and continue stirring and reacting for 10 to 18 h; a dispersion liquid containing the SFe3O4@MSN@Cs-Fe composite material is prepared.

8. The preparation method of the nanozyme composite material according to any one of claims 1 to 4, characterized in that, The specific method for preparing SFe3O4@MSN@SCaO2@Cs-Fe in step S4 includes: Use a 0.045 mol / L to 0.065 mol / L sodium hydroxide solution to adjust the pH value of the dispersion liquid containing the SFe3O4@MSN@Cs-Fe composite material obtained in step S3 to 7.0 to 8.

0. Then, under stirring, slowly and evenly disperse SCaO2 prepared in step S2 in the above solution according to the proportion, and continue stirring and dispersing for 5 h to 10 h. After the reaction is completed, centrifuge to separate the solid phase, then wash it three times with deionized water, and dry it at a low temperature below 100 °C to obtain the nanozyme composite material, denoted as SFe3O4@MSN@SCaO2@Cs-Fe.

9. A nanozyme composite material, characterized in that, Prepared by the preparation method of the nanozyme composite material according to any one of claims 1 to 8.

10. Use of the nanozyme composite material prepared by the preparation method of the nanozyme composite material according to any one of claims 1 to 8 in the remediation of soil organic chemical pesticide pollution, characterized in that, The pH value of the soil ≤ 5.5.

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