A slow-release oxidant with a multi-layer loading structure, and a preparation method and application thereof

Abstract

This invention discloses a slow-release oxidant with a multilayered loading structure, its preparation method, and its application. The preparation method includes: adding ammonia and hydrogen peroxide to a calcium chloride solution to obtain nano-sized calcium dioxide; dispersing the nano-sized calcium dioxide in ethanol to obtain a suspension; adding ammonia to the suspension and then adding tetraethyl orthosilicate solution dropwise to obtain calcium dioxide loaded with silica; ultrasonically dispersing the silica-loaded calcium dioxide in ethanol to obtain dispersion one; adding sodium tripolyphosphate dropwise to a chitosan solution to obtain dispersion two; and then adding dispersion two dropwise to dispersion one to obtain a slow-release oxidant with a multilayered loading structure. This invention is the first to use a multilayered loading design composed of silica and chitosan for slow-release calcium peroxide, enabling long-term stable release of hydrogen peroxide under various water quality conditions. Furthermore, the slow-release oxidant poses no risk of releasing harmful components into the environment, is environmentally friendly and safe, and is easy to operate, making it highly valuable for application.

Description

Technical Field

[0001] This application relates to the field of pollution control technology, specifically to a slow-release oxidant with a multilayered loading structure, its preparation method, and its application. Background Technology

[0002] In recent years, with the rapid development of industrialization, the problems of soil and deep groundwater pollution have become increasingly widespread and severe. In particular, the long-term retention of recalcitrant organic pollutants (such as phenols) poses a serious threat to the ecological environment. For in-situ remediation of groundwater under complex geological conditions, traditional ex-situ excavation or pumping and storage technologies are often costly and extremely difficult to implement.

[0003] Therefore, directly injecting oxidizing liquid or solid environmental remediation materials into underground aquifers to degrade pollutants through in-situ free radical generation has become the most economical and efficient mainstream remediation strategy. Developing injectable oxidant materials that are easy to pump and can effectively diffuse with groundwater flow is the core technology in this field.

[0004] However, existing injectable oxidants face challenges in release control during practical applications. Traditional liquid hydrogen peroxide or exposed oxygen-generating solid materials often experience uncontrollable "burst release" after being injected into groundwater, meaning that the local hydrogen peroxide concentration becomes excessively high instantaneously, leading to ineffective decomposition and consumption of the oxidant, and consequently resulting in a very small effective radius of action for the material.

[0005] Furthermore, the complex conditions in groundwater, including the coexisting ions and organic matter, can deplete active ingredients, leading to rapid material deactivation. Lacking effective slow-release mechanisms, these traditional oxidants not only result in significant performance and cost waste but also fail to maintain long-term active concentrations in contaminated sites, making it difficult to meet the long-term, stable in-situ remediation requirements.

[0006] Besides the issues of effectiveness and longevity, the environmental safety of existing injectable materials is another major concern. While many composite oxidants improve degradation efficiency, their material composition or residual skeletons after failure may cause secondary pollution to groundwater ecosystems. For example, some synthetic polymer-coated materials are difficult to degrade naturally in groundwater, or their byproducts can cause drastic changes in groundwater quality (such as pH and hardness).

[0007] Therefore, there is an urgent need in the field for a remediation material that can achieve long-term sustained release of oxidants while ensuring that their degradation products are completely harmless to the environment and do not cause secondary pollution. Summary of the Invention

[0008] To address the shortcomings of existing technologies, this invention provides a slow-release oxidant with a multilayered supported structure, its preparation method, and its application, thereby solving the problems existing in the prior art. The slow-release oxidant with the multilayered supported structure described in this invention can slow down the release of hydrogen peroxide while avoiding secondary pollution.

[0009] The present invention adopts the following technical solution.

[0010] The first aspect of this invention discloses a method for preparing a slow-release oxidant having a multilayer supported structure, comprising the following steps: Step 1: Add ammonia and hydrogen peroxide to calcium chloride solution according to the set ratio, stir the reaction, centrifuge to collect the precipitate, wash with ethanol, and dry to obtain nano-sized calcium dioxide (CaO2). Step 2: Disperse the obtained nano-sized calcium dioxide (CaO2) in ethanol to obtain a suspension. Add ammonia water to the suspension and add tetraethyl orthosilicate solution dropwise. After stirring and reacting, collect the precipitate by centrifugation and wash it with ethanol. After drying, obtain calcium dioxide (SiO2@CaO2) loaded with silicon dioxide. Step 3: The calcium dioxide SiO2@CaO2 loaded with silica obtained in Step 2 is ultrasonically dispersed in ethanol to obtain dispersion one. Sodium tripolyphosphate is added dropwise to chitosan solution at a set flow rate and allowed to react fully to obtain dispersion two. Dispersion two is then added dropwise to dispersion one at a set flow rate. After stirring and reacting, the precipitate is collected by centrifugation and washed with ethanol. After drying, a multilayer loaded slow-release oxidant Chitosan@SiO2@CaO2 is obtained.

[0011] Preferably, the proportions set in step 1 are as follows: the volume ratio of calcium chloride, ammonia, and hydrogen peroxide is 3~5:1:1, the concentration of ammonia is 25~28%, the concentration of hydrogen peroxide is 30~35%, the concentration of calcium chloride is 6 g / L, and the average particle size of nano-sized calcium dioxide is 25~40 nm.

[0012] Preferably, step 2 includes: Step 2.1: After washing and centrifuging the nano-sized calcium dioxide (CaO2) obtained in Step 1 with ethanol, add ethanol to disperse and obtain a suspension with a concentration of 15-40 g / L. Step 2.2: Add ammonia to the suspension obtained in step 2.1, and add tetraethyl orthosilicate solution dropwise at the set flow rate. After stirring the reaction thoroughly, centrifuge to collect the precipitate and wash it with ethanol. After drying, obtain calcium dioxide SiO2@CaO2 loaded with silica.

[0013] Preferably, in step 2.2, the volume ratio of the suspension to ammonia and tetraethyl orthosilicate solution is 1:1:4~6, and the dripping flow rate is set to 0.03-0.05 mL / min.

[0014] Preferably, in step 2, the tetraethyl orthosilicate solution is prepared using ethanol, and its volume fraction is 5% to 20%.

[0015] Preferably, in step 3, the concentration of the first dispersion is 15~40 g / L, the concentration of the chitosan solution is 0.1~1 g / L, the concentration of the sodium tripolyphosphate solution is 1 g / L, and the volume ratio of the chitosan solution to the sodium tripolyphosphate solution is 5:1.

[0016] Preferably, in step 3, the set dripping flow rate is 1 mL / min, and after the sodium tripolyphosphate is dripped into the chitosan solution, the reaction is allowed to proceed for 10 minutes, and after the dispersion is dripped into the solution, the reaction is allowed to proceed for another hour.

[0017] Preferably, the stirring is magnetic stirring with a speed of 400-600 rpm, and each centrifugal washing is repeated 3 times. The drying temperature and time are 50-60 ℃ and 8 hours respectively.

[0018] The second aspect of the present invention discloses a slow-release oxidant having a multilayered supported structure, obtained according to the preparation method of the slow-release oxidant having a multilayered supported structure described in the first aspect.

[0019] The third aspect of the present invention discloses the application of a slow-release oxidant with a multilayered loading structure as described in the second aspect in groundwater treatment.

[0020] Compared with the prior art, the beneficial effects of the present invention include at least the following: This invention is the first to construct an easily injectable, slow-release calcium dioxide oxidant with a multilayered loading structure of silica and chitosan. This overcomes the problem of explosive release and self-consumption caused by traditional exposed calcium peroxide and achieves stable hydrogen peroxide release over a long period. This invention introduces silica as a rigid porous layer to precisely control the diffusion paths of water molecule infiltration and hydrogen peroxide overflow, while combining it with an outer chitosan layer as a flexible permeable layer to respond to the aquatic environment. This multi-interface assembly not only constructs a microscopic programmed release reactor but also cleverly transforms the release mechanism of the active substance from instantaneous matrix dissolution to controlled pore diffusion, thereby ensuring long-term stable release kinetics.

[0021] This invention is highly adaptable to various water conditions (including different concentrations of common anions, natural organic matter, and varying pH levels), and performs exceptionally well in complex real-world water bodies such as rivers and groundwater. Its microscopic principle lies in the fact that the outermost chitosan layer not only provides sustained-release resistance but also constructs a natural protective barrier on the material surface. This polymer layer effectively shields and resists the ineffective consumption and interference of complex coexisting anions and natural macromolecular organic matter (such as humic acid) in groundwater on the internal core oxidant, ensuring high efficiency in in-situ remediation under complex matrices.

[0022] This invention requires no additional activator and is green and safe throughout its entire life cycle. This is thanks to the material's unique microenvironment acid-base self-regulation and all-natural fate mechanism: First, the strongly alkaline product (calcium hydroxide) left after the core reaction of calcium peroxide is neutralized by the deprotonation of chitosan and the weak acid (metasilicic acid) generated by the slow hydrolysis of silica. The three work together to construct a self-limiting acid-base buffer system, preventing extreme alkalization of the water body. Second, the degradation path of the residual material perfectly matches the natural material cycle: the outermost chitosan can be naturally decomposed by enzymes secreted by environmental microorganisms and enter the carbon cycle; the middle layer of silica is slowly hydrolyzed into non-toxic silicates widely present in the background of groundwater; and the remaining calcium ions in the core combine with the abundant carbonate ions in the environment to form stable calcium carbonate minerals that fill the pores.

[0023] Furthermore, the chemical raw materials (such as calcium salts, silicates, and biopolymers) and equipment required by the method provided in this application are readily available, the operation process is simple, and the pain point of secondary pollution of traditional in-situ chemical oxidation technology is completely eliminated, which has extremely high engineering application value and promotion potential. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of this disclosure or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this disclosure. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a schematic diagram of the CSC material synthesis method; Figure 2 These are powder X-ray diffraction patterns of CaO2, SiO2@CaO2, and CSC materials; Figure 3 These are the infrared spectra of CaO2, SiO2@CaO2, and CSC materials; Figure 4 This represents the zeta potential of CSC materials with different chitosan loading ratios. Figure 5The performance of materials under different loading conditions in releasing hydrogen peroxide; Figure 6 This describes the performance of CSC materials in releasing hydrogen peroxide at different pH levels. Figure 7 This refers to the ability of CSC materials to slowly release hydrogen peroxide in the presence of humic acid; Figure 8 This refers to the performance of CSC materials in the slow release of hydrogen peroxide in natural water bodies; Figure 9 It refers to the performance of CSC materials and pyrite in degrading phenol. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of this invention. The embodiments described in this application are merely some embodiments of this invention, and not all embodiments. Based on the spirit of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of this invention.

[0027] like Figure 1 As shown, the present invention provides a method for preparing a slow-release oxidant with a multilayer supported structure, comprising the following steps: Step 1: Add ammonia and hydrogen peroxide to calcium chloride solution according to the set ratio, stir the reaction thoroughly, centrifuge to collect the precipitate, wash with ethanol, and dry to obtain nano-sized calcium dioxide (CaO2).

[0028] In a preferred but non-limiting embodiment of the present invention, the set ratio is that the volume ratio of calcium chloride, ammonia, and hydrogen peroxide is 3~5:1:1, wherein the concentration of ammonia is 25~28%, the concentration of hydrogen peroxide is 30~35%, the concentration of calcium chloride is 6g / L, and the average particle size of nano-sized calcium dioxide is 25~40 nm.

[0029] More preferably, the volume ratio of calcium chloride, ammonia, and hydrogen peroxide is 10:3:3.

[0030] Step 2: The obtained nano-sized calcium dioxide is ultrasonically dispersed in ethanol to obtain a suspension. Ammonia water is added to the suspension, and tetraethyl orthosilicate solution is added dropwise at a set flow rate. After stirring the reaction thoroughly, the precipitate is collected by centrifugation and washed with ethanol. After drying, calcium dioxide loaded with silicon dioxide (SiO2@CaO2) is obtained.

[0031] In a preferred but non-limiting embodiment of the present invention, step 2 specifically involves: Step 2.1: After washing and centrifuging the nano-sized calcium dioxide obtained in Step 1 with ethanol, add ethanol and disperse to obtain a suspension with a concentration of 15-40 g / L. More preferably, the concentration of the suspension is 15 g / L. The preferred parameter is taken as a low value in the range to ensure that the material load is sufficient and uniform while avoiding waste.

[0032] Step 2.2: Add ammonia to the suspension obtained in step 2.1, and add tetraethyl orthosilicate solution dropwise at the set flow rate. After stirring the reaction thoroughly, centrifuge to collect the precipitate, wash it with ethanol, and dry it to obtain calcium dioxide loaded with silicon dioxide (SiO2@CaO2).

[0033] The volume ratio of the suspension to ammonia and tetraethyl orthosilicate solution is 1:1:4~6.

[0034] Specifically, 150 mg of nano-sized calcium dioxide solid can be taken, and 6 mL of ethanol can be added to ultrasonically disperse to obtain a suspension. 2 mL of the suspension can be mixed with 2 mL of ammonia water, and then 9 mL of tetraethyl orthosilicate solution can be added dropwise. After the reaction is complete, the precipitate can be collected by centrifugation and washed with ethanol. After drying, calcium dioxide loaded with silicon dioxide (SiO2@CaO2) can be obtained.

[0035] More preferably, the tetraethyl orthosilicate solution is prepared using ethanol, and its volume fraction is 5% to 20%, preferably 10%.

[0036] It is worth noting that by adjusting the ratio of tetraethyl orthosilicate to ethanol solution, different silica loading amounts can be controlled. The inventors' team discovered through numerous experiments that a moderate loading amount can ensure the sustained-release effect without excessively hindering the release.

[0037] Specifically, the material exhibits the best performance when the volume concentration of the prepared 9 mL tetraethyl orthosilicate solution is 10%; a volume concentration of 5% may result in insufficient long-term stability due to excessively rapid release; and a volume concentration of 20% may prevent the oxidant from being fully released due to an overly dense silica layer.

[0038] More preferably, the set dripping flow rate is 0.03-0.05 mL / min, preferably 0.04 mL / min, and the reaction is continued for 12 hours after the dripping is completed, with the reaction container sealed throughout the process to prevent excessive ethanol evaporation.

[0039] This invention achieves a longer-lasting and more stable sustained-release effect of hydrogen peroxide by setting a dripping flow rate to slowly add tetraethyl orthosilicate solution, thereby loading a more uniform and dense silica layer on the surface of calcium peroxide. It also maintains a stable upward trend in hydrogen peroxide concentration for at least 10 days.

[0040] Step 3: The calcium dioxide loaded with silica obtained in Step 2 is ultrasonically dispersed in ethanol to obtain dispersion one. Sodium tripolyphosphate is added to the chitosan solution at a set droplet flow rate and allowed to react fully to obtain dispersion two. Dispersion two is then added to dispersion one at a set droplet flow rate. After stirring and reacting fully, the precipitate is collected by centrifugation and washed with ethanol. After drying, the calcium dioxide Chitosan@SiO2@CaO2 material loaded with chitosan and silica is obtained, hereinafter referred to as CSC material, which is a multilayer loaded structure slow-release oxidant.

[0041] In a preferred but non-limiting embodiment of the present invention, the first dispersion is made by taking 150-240 mg of the calcium dioxide material loaded with silica obtained in step 2 and adding 6-10 mL of ethanol, wherein the concentration is 15-40 g / L, more preferably 15 g / L. The chitosan solution concentration is 0.5 g / L (can be 0.1~1 g / L), the sodium tripolyphosphate solution concentration is 1 g / L, and the volume ratio of chitosan solution to sodium tripolyphosphate solution is 5:1.

[0042] More preferably, the set dripping flow rate is 1 mL / min, and after the sodium tripolyphosphate is completely added to the chitosan solution, the reaction continues for 10 minutes, and after the dispersion is completely added, the reaction continues for 1 hour.

[0043] In a preferred but non-limiting embodiment of the present invention, the stirring in the above steps is magnetic stirring with a speed of 400-600 rpm, each centrifugal washing is repeated 3 times, and the drying temperature and time are 50-60 ℃ and 8 hours respectively.

[0044] The present invention also provides a multilayer supported slow-release oxidant, which is obtained based on the above preparation method, namely calcium peroxide Chitosan@SiO2@CaO2 (CSC) encapsulated with silica and chitosan.

[0045] This invention verifies the successful synthesis of the material through the following three comparative examples, specifically: Comparative Example 1 This comparative test examined the presence of calcium dioxide in the materials, and the results are as follows: Figure 2 As shown in the figure. The results indicate that after loading silica and chitosan, the characteristic peaks of calcium dioxide in the powder X-ray diffraction pattern still exist, namely the peaks at approximately 35.6° (110 crystal plane, relatively strong) and 30.3° (002 crystal plane, relatively weak). For SiO2@CaO2 and CSC materials, the peak intensities are significantly lower than those of CaO2 before loading, indicating that the silica and chitosan have successfully coated the outer layer, thus masking the characteristic signals of calcium dioxide.

[0046] Comparative Example 2 This comparative example tested the presence of silica in the material, and the results are as follows: Figure 3 As shown in the figure. The results indicate that after loading silica, characteristic peaks of silica, namely 1000–1100 cm⁻¹, appeared in the infrared spectrum. –1 The peak of the antisymmetric stretching vibration of the silicon-oxygen bond is observed. For SiO2@CaO2 and CSC materials, the peak intensity is significantly higher than that of CaO2 before loading, indicating successful loading of silicon dioxide.

[0047] Comparative Example 3 This comparative test examined the presence of chitosan in the material, and the results were as follows: Figure 4 As shown in the figure. The results indicate that the higher the proportion of chitosan loaded, the more significantly the zeta potential of the material shifts to a positive value. Under strong acidity (pH 3), the zeta potentials of CSC materials with different chitosan loading ratios are significantly higher than those of SiO2@CaO2 without chitosan loading, which demonstrates the successful loading of chitosan.

[0048] The present invention also provides an application of a slow-release oxidant with a multilayered loading structure. By adding the CSC material to the water to be treated and allowing it to stand in the dark, the concentration of hydrogen peroxide in the aqueous solution to be treated can maintain an upward trend for at least ten days.

[0049] In a preferred but non-limiting embodiment of the present invention, the specific components include: Step 1: Add CSC material to water and leave it in the dark to simulate a groundwater environment.

[0050] Preferably, in step 1, the material concentration is 1 g / L.

[0051] Step 2: Extract the solution sample, dilute it with pure water, and then perform color development using 0.4 mol / L potassium iodide and 0.1 mol / L potassium hydrogen phthalate.

[0052] Preferably, in step 2, the sample is diluted 10 times (0.1 mL sample + 0.9 mL pure water), and 1 mL of colorimetric reagent is added.

[0053] In step 2, color development is for the purpose of OD... 350 The concentration of hydrogen peroxide in the solution was quantitatively obtained by detection, so as to obtain the result that the CSC material continuously and stably increases the concentration of hydrogen peroxide within a certain time range, which confirms the conclusion that the CSC material can slowly release hydrogen peroxide in water within a certain time.

[0054] Step 3: Allow the sample to stand for 1 hour to ensure a complete colorimetric reaction, and then measure the absorbance (OD) at 350 nm using a UV-Vis spectrophotometer. 350 ).

[0055] The absorbance measurement is used to quantitatively determine the concentration of hydrogen peroxide in the solution, because hydrogen peroxide reacts with potassium iodide to form elemental iodine, and its absorption spectrum has a significant peak at 350 nm. Therefore, the OD value is conventionally taken as the concentration. 350 The data is used for quantitative testing. In addition, potassium hydrogen phthalate provides an acidic environment for the reaction and acts as a buffer to keep the pH stable, so that the results of quantitative detection after color development are more accurate.

[0056] This invention also provides an application of a multilayer supported slow-release oxidant, comprising the following steps: Step 1: Add CSC material to water containing phenol, and add iron-containing minerals at the same time to simulate the catalytic environment in real groundwater.

[0057] Preferably, in step 1, pyrite (FeS2) is used as the iron-bearing mineral.

[0058] Step 2: Extract the solution sample over time and filter it through a 0.22 μm fiber filter.

[0059] Preferably, in step 2, sodium thiosulfate is used as a quenching agent. The filter head is used to prevent solid particles from affecting the injection of high performance liquid chromatography. The instrument is precise, and solid particles may clog the pipeline and damage the instrument.

[0060] Step 3: Use high performance liquid chromatography to determine the concentration of phenol in the sample.

[0061] By detecting the phenol concentration, the trend of phenol concentration change with reaction time was obtained. Thus, by obtaining data showing that the phenol concentration decreases monotonically over time, the conclusion that CSC materials have certain pollutant degradation performance in nature is supported.

[0062] Preferably, in step 3, high performance liquid chromatography, pure water and acetonitrile are used as the mobile phase (volume ratio of 6:4).

[0063] Through the above applications, it is further demonstrated that, in addition to releasing hydrogen peroxide, the hydrogen peroxide released by CSC materials can be activated by iron-containing minerals (such as pyrite) that are widely available in nature, thereby producing the effect of degrading typical pollutants (such as phenol).

[0064] Example 1 This embodiment evaluates the basic sustained-release capacity of the material, and the results are as follows: Figure 5 As shown in the figure, the released concentration of hydrogen peroxide showed a continuous upward trend over 10 days. The greater the loading of the material coating layer, the more ideal the slow-release control effect. In a pure water environment, the final cumulative release concentration of hydrogen peroxide released by the CSC material can reach approximately 1 mM.

[0065] Example 2 This embodiment investigates the slow-release behavior of CSC materials in water bodies with initial pH values ​​of 3, 5, 7, and 9. The results are as follows: Figure 6 As shown in the figure. The results indicate that an acidic environment has a slight promoting effect on the release of hydrogen peroxide, while an alkaline environment has almost no effect on the slow-release rate of CSC materials, demonstrating excellent pH adaptability of CSC materials.

[0066] Example 3 This embodiment tests the sustained-release performance of CSC materials when the concentrations of humic acid (HA) in the water are 0.1, 1.0, and 5.0 mg / L, respectively. The results are as follows: Figure 7 As shown in the figure. The results indicate that the weakly acidic microenvironment introduced by HA has a slight promoting effect on the release process, but the overall sustained-release performance of the CSC material is almost unaffected by the HA concentration.

[0067] Example 4 This embodiment examines the performance of CSC materials in actual river water and groundwater samples, and the results are as follows: Figure 8 As shown in the figure. The results indicate that, compared to the pure water environment in the laboratory, the complex coexisting matrix and ions in natural water bodies can further promote the effective release of hydrogen peroxide, demonstrating the potential of CSC materials for practical applications.

[0068] Example 5 This embodiment verifies the effectiveness of the material combined with pyrite in constructing a Fenton-like system for degrading organic pollutants. The results are as follows: Figure 9 As shown in the figure. Tests show that when 0.5 mg / L of CSC material and 0.5 mg / L of pyrite (FeS2) catalyst are added to the system simultaneously, the system can efficiently degrade phenol at a concentration of 5 mg / L within 60 minutes.

[0069] This invention is the first to construct an easily injectable, slow-release calcium dioxide oxidant with a multilayered loading structure of silica and chitosan. This overcomes the problem of explosive release and self-consumption caused by traditional exposed calcium peroxide and achieves stable hydrogen peroxide release over a long period. Furthermore, this invention is highly adaptable to various aquatic conditions and performs excellently in complex real-world water bodies such as rivers and groundwater.

[0070] Furthermore, this invention requires no additional activator and is green and safe throughout its entire life cycle. At the same time, the chemical raw materials and equipment required by this invention are readily available, the operation process is simple, and it completely eliminates the pain point of secondary pollution in traditional in-situ chemical oxidation technology. It has extremely high engineering application value and promotion potential.

[0071] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the claims of the present invention.

Claims

1. A method for producing a sustained-release oxidant having a multilayer load structure, characterized by, Includes the following steps: Step 1: Add ammonia and hydrogen peroxide to calcium chloride solution according to the set ratio, stir the reaction, centrifuge to collect the precipitate, wash with ethanol, and dry to obtain nano-sized calcium dioxide (CaO2). Step 2: Disperse the obtained nano-sized calcium dioxide (CaO2) in ethanol to obtain a suspension. Add ammonia water to the suspension and add tetraethyl orthosilicate solution dropwise. After stirring and reacting, collect the precipitate by centrifugation and wash it with ethanol. After drying, obtain calcium dioxide (SiO2@CaO2) loaded with silicon dioxide. Step 3: The calcium dioxide SiO2@CaO2 loaded with silica obtained in Step 2 is ultrasonically dispersed in ethanol to obtain dispersion one. Sodium tripolyphosphate is added dropwise to chitosan solution at a set flow rate and allowed to react fully to obtain dispersion two. Dispersion two is then added dropwise to dispersion one at a set flow rate. After stirring and reacting, the precipitate is collected by centrifugation and washed with ethanol. After drying, a multilayer loaded slow-release oxidant Chitosan@SiO2@CaO2 is obtained.

2. The method for preparing a slow-release oxidant with a multilayer supported structure according to claim 1, characterized in that, The set ratio in step 1 is as follows: the volume ratio of calcium chloride, ammonia, and hydrogen peroxide is 3~5:1:1, the concentration of ammonia is 25~28%, the concentration of hydrogen peroxide is 30~35%, the concentration of calcium chloride is 6 g / L, and the average particle size of nano-sized calcium dioxide (CaO2) is 25~40 nm.

3. The method for preparing a slow-release oxidant with a multilayered supported structure according to claim 1, characterized in that, Step 2 includes: Step 2.1: After washing and centrifuging the nano-sized calcium dioxide (CaO2) obtained in Step 1 with ethanol, add ethanol to disperse and obtain a suspension with a concentration of 15-40 g / L. Step 2.2: Add ammonia to the suspension obtained in step 2.1, and add tetraethyl orthosilicate solution dropwise at the set flow rate. After stirring the reaction thoroughly, centrifuge to collect the precipitate and wash it with ethanol. After drying, obtain calcium dioxide SiO2@CaO2 loaded with silica.

4. The method for preparing a slow-release oxidant with a multilayer supported structure according to claim 3, characterized in that, In step 2.2, the volume ratio of the suspension to ammonia and tetraethyl orthosilicate solution is 1:1:4~6, and the dripping flow rate is set to 0.03-0.05 mL / min.

5. The method for preparing a slow-release oxidant with a multilayer supported structure according to claim 1, characterized in that, In step 2, the tetraethyl orthosilicate solution is prepared using ethanol, with a volume fraction of 5% to 20%.

6. The method for preparing a slow-release oxidant with a multilayer supported structure according to claim 1, characterized in that, In step 3, the concentration of dispersion one is 15~40 g / L, the concentration of chitosan solution is 0.1~1 g / L, the concentration of sodium tripolyphosphate solution is 1 g / L, and the volume ratio of chitosan solution to sodium tripolyphosphate solution is 5:

1.

7. The preparation method of the slow-release oxidant with a multi-layer loading structure according to claim 1, characterized in that, In step 3, the dropwise flow rate is set to 1 mL / min, sodium tripolyphosphate is dropped into the chitosan solution, and after the dropping is completed, the dispersion is reacted for 10 minutes, and after the dropping is completed, the dispersion is reacted for 1 hour.

8. The preparation method of the slow-release oxidant with a multi-layer loading structure according to claim 1, characterized in that, The stirring is magnetic stirring, the stirring speed is 400-600 rpm, each centrifugal washing is repeated for 3 times, and the drying temperature and time are both 50-60 ℃ and 8 hours.

9. A slow-release oxidizing agent having a multi-layered load structure, characterized by, The preparation method of the slow-release oxidant with a multi-layer loading structure according to any one of claims 1-8.

10. The application of the slow-release oxidant with a multi-layer loading structure according to claim 9 in groundwater treatment.

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