Slow-release type self-adjusting pH response microcapsule, preparation method thereof and application of microcapsule in control of endogenous phosphorus in river and lake bottom mud

Abstract

The invention provides a slow-release self-adjusting pH response microcapsule, a preparation method thereof and an application of the microcapsule in control of endogenous phosphorus in river and lake bottom mud, and belongs to the field of environmental remediation materials. The preparation method comprises the following steps: reacting CaCl2 with H2O2 in an alkaline environment, and obtaining active nano CaO2 through a high-speed oscillation method; mixing the active nano CaO2 and attapulgite in an acid solution to obtain a mixed solution; dropwise adding the obtained mixed solution into a sodium hydroxide solution at a constant speed by adopting a dripping method to obtain microcapsules with uniform particle sizes, carrying out dehydration treatment by utilizing ethanol and tert-butyl alcohol solutions, and then carrying out freeze drying to obtain the slow-release type self-adjusting pH response microcapsules. The capsule wall material used in the invention is environment-friendly natural organic matter chitosan. The method is simple in process, convenient to operate, mild in reaction, low in energy consumption and free of harmful waste.

Description

Technical Field

[0001] This invention relates to the field of environmental remediation materials technology, and in particular to a slow-release, self-regulating pH-responsive microcapsule, its preparation method, and its application in the control of endogenous phosphorus in river and lake sediments. Background Technology

[0002] Eutrophication is a prominent water environment problem. With the gradual control of exogenous pollution, the release of endogenous substances from sediments has become a key driver of persistent eutrophication. Phosphorus is a major limiting factor for eutrophication, and controlling its re-release from sediments is a core aspect of water management. In-situ passivation is an important method for managing high-phosphorus sediments. Studies have shown that a considerable portion of reactive phosphorus is stored in sediments, and under certain conditions, such as low dissolved oxygen (DO), high pH, ​​and high temperature, it can be released from the sediments. For example, the annual static release flux of endogenous phosphorus in the Huayang River-Lake Group is approximately 12.92 t, and the dynamic resuspension release is approximately 1.129 × 10⁻⁶ t. 4 ~1.684×10 4 During resuspension, the dynamic release of endogenous phosphorus contributes up to 75% to the total phosphorus (TP) concentration in the water. The short-term and long-term phosphorus release rates in Chaohu Lake are related to the input of exogenous phosphorus (3.56 mg / m³). 2 ·d -1 All of these are within the same order of magnitude. Among them, the long-term release of endogenous phosphorus from sediments in West Chaohu Lake has a severe impact on eutrophication, with a long-term release of 698 tons / year, accounting for approximately 69% of the exogenous phosphorus input. These findings highlight the importance of controlling the internal phosphorus load in sediments as a key strategy to reverse eutrophication in natural water bodies once external phosphorus loading decreases.

[0003] Endogenous phosphorus treatment methods include: (1) sediment dredging, which reduces the amount of phosphorus by regularly excavating and cleaning the sediment. Its technical advantage is that it is direct and efficient and can quickly cut off endogenous pollution. However, the dredging project is costly, and the suspension of some sediment during the dredging process has a great impact on the surrounding ecological environment. It may also lead to a large amount of phosphorus being released back into the water in the short term. (2) aeration and oxygen supply, which regulates the redox conditions of sediment-water interface by supplying O2 or air into the water, enhances the adsorption and fixation of phosphorus in the sediment, and inhibits the release of endogenous phosphorus. Aeration and oxygen supply technology does not require the addition of any chemical agents and is simple to operate. However, it has a strong energy consumption dependence and high long-term operating costs. (3) physical cover, which uses uncontaminated sand or soil to cover the surface of contaminated sediments to build one or more physical isolation layers, directly blocking the migration of phosphorus in the sediments to the overlying water. However, the selection and laying technology of the cover material are highly demanding, and the long-term effect is unstable. (4) aquatic plant remediation: using aquatic plants to absorb phosphorus in the sediment and water. However, the growth of aquatic plants is greatly affected by factors such as season, climate and water quality, and the purification effect is unstable. Moreover, phosphorus may be released again after the plants die and decompose. (5) Adding chemical agents: such as adding aluminum salts, iron salts, etc., which combine with active phosphorus to form precipitates. However, the large-scale use of chemical agents may change the chemical properties of the water body and bottom sediment, be toxic to aquatic organisms, and may also cause secondary pollution.

[0004] Capsules are widely used for administering drugs and nutrients to humans and animals; however, their application in river and lake management is rarely studied. Calcium peroxide is an excellent phosphorus passivating material, possessing both oxygen release and phosphorus fixation functions. However, its sustained effectiveness is limited by its tendency to agglomerate and fail during use, unstable oxygen release rates, and drastic pH fluctuations. Therefore, this invention proposes a method for preparing calcium peroxide-based microcapsules to prolong the action time of calcium peroxide and mitigate its damaging effects on environmental pH. Summary of the Invention

[0005] To address the above technical problems, this invention provides a sustained-release, self-regulating pH-responsive microcapsule, its preparation method, and its application in controlling endogenous phosphorus in river and lake sediments. A sustained-release microcapsule formulation was successfully synthesized by uniformly embedding nano-sized calcium peroxide, which possesses both oxygen-releasing and phosphorus-fixing functions, within the pH-responsive chitosan outer wall. This microcapsule retains the oxygen-releasing and phosphorus-fixing properties of calcium peroxide, prolonging its action time and overcoming the shortcomings of calcium peroxide powder, such as rapid action, easy agglomeration and inactivation, and significant impact on environmental pH. The capsule wall material used in this invention is the environmentally friendly natural organic chitosan. This invention features a simple process, convenient operation, mild reaction, low energy consumption, and no harmful waste generation.

[0006] The first objective of this invention is to provide a method for preparing sustained-release, self-regulating pH-responsive microcapsules, comprising the following steps: (1) CaCl2 and H2O2 react in an alkaline environment to obtain active nano-CaO2 by high-speed shaking method; the active nano-CaO2 and attapulgite are mixed in an acid solution to obtain a mixed solution; the mixed solution is rapidly injected into a chitosan solution; (2) The mixed solution obtained in step (1) is uniformly dropped into a strong alkaline solution by the dripping method to obtain microcapsules with uniform particle size. The microcapsules are then dehydrated using ethanol and tert-butanol solutions and then freeze-dried to obtain the sustained-release self-regulating pH-responsive microcapsules.

[0007] In some embodiments of the present invention, in step (1), the pH of the alkaline environment is 10-12; the mass-to-volume ratio of CaCl2 to H2O2 is (11.1-44.1):(20-60) g / mL; and the concentration of H2O2 is 30%.

[0008] In some embodiments of the present invention, in step (1), the degree of deacetylation of chitosan in the chitosan solution is 85-95%.

[0009] In some embodiments of the present invention, in step (1), the acid in the acid solution includes acetic acid or hydrochloric acid; the concentration of the acid solution is 1~5wt%.

[0010] In some embodiments of the present invention, the mass ratio of active nano-calcium peroxide, attapulgite, and chitosan is (2:1:8) to (16:1:8). In some embodiments of the present invention, in step (2), the mixed solution is added at a rate of 0.5 to 1 drop / s.

[0011] In some embodiments of the present invention, in step (2), the concentration of the strong alkali solution is 0.8~1.2 mol / L; the strong alkali solution includes sodium hydroxide, potassium hydroxide, etc. In the present invention, the amino groups in the chitosan structure are deprotonated by a strong alkali, forming gel microspheres.

[0012] The second objective of this invention is to provide a sustained-release, self-regulating pH-responsive microcapsule prepared by the aforementioned preparation method.

[0013] In some embodiments of the present invention, the particle size of the sustained-release self-regulating pH-responsive microcapsules is 3-6 mm.

[0014] A third objective of this invention is to provide the application of the aforementioned slow-release, self-regulating pH-responsive microcapsules in the control of endogenous phosphorus in river and lake sediments.

[0015] Furthermore, the phosphorus control refers to the removal of reactive phosphorus. This invention utilizes the precipitation effect of calcium ions released from the hydrolysis of calcium peroxide on phosphorus, and the released oxygen improves the redox conditions on the sediment surface, thereby inhibiting phosphorus release under anaerobic conditions. The physical isolation provided by the microcapsules placed on the sediment surface further hinders the upward release of phosphorus from the sediment.

[0016] Furthermore, the dosage relationship between the slow-release self-regulating pH-responsive microcapsules and the river and lake sediment is as follows: 0.6-1.2 kg of slow-release self-regulating pH-responsive microcapsules are added per square meter of sediment.

[0017] The technical solution of the present invention has the following advantages compared with the prior art: This invention combines pH response with long-term sustained release: Chitosan is used as the microcapsule shell structure. Under neutral pH conditions, the microcapsules dissolve moderately, releasing calcium peroxide. As calcium peroxide is released, the surrounding pH increases, causing the microcapsules to contract, thus enhancing their barrier effect and slowing down the release of calcium peroxide. In summary, the microcapsules can dynamically respond to changes in the surrounding pH during hydrolysis, autonomously regulating the release rate of calcium peroxide, ensuring a sustained release effect while avoiding drastic disturbances to the environmental pH. Furthermore, the chitosan shell material of this invention has good biocompatibility and biodegradability. Its natural antibacterial properties also help inhibit the excessive growth of harmful microorganisms in eutrophic water bodies, reducing the risk of secondary pollution. Attached Figure Description

[0018] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings, wherein... Figure 1 These are the XRD (a) and SEM (b) spectra of nano-calcium peroxide obtained in Example 1 of this invention.

[0019] Figure 2 The morphology (a) and particle size (b) distribution of the sustained-release pH-responsive microcapsules obtained in Example 1 of this invention are shown.

[0020] Figure 3 The sustained-release pH-responsive microcapsules obtained in Example 1 of this invention release Ca 2+ pH responsiveness (a) 30d phosphorus fixation effect (b) Detailed Implementation

[0021] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0022] Example 1 This embodiment provides a method for preparing nano-calcium peroxide, as detailed below: 14.7 g of CaCl₂·2H₂O was dissolved in 25 mL of pure water, and 30 mL of concentrated ammonia solution was added. 20 mL of 30% hydrogen peroxide was slowly injected into the solution at a flow rate of 5 mL / min. The mixture was continuously stirred at high speed at 25 °C for 20 min, and finally transferred to a centrifuge tube for centrifugation. The obtained precipitate was washed twice with pure water and twice with ethanol, and dried in an oven at 80 °C for 2 h to obtain the nano-calcium peroxide. The obtained nano-calcium peroxide was characterized, and the results are shown in the figure. Figure 1 From XRD patterns ( Figure 1 The results in (a) show that the precipitate obtained is calcium peroxide, and the SEM images show that the particle size of calcium peroxide is approximately 20 nm. Figure 1 (b)

[0023] Example 2 This embodiment provides a method for preparing sustained-release pH-responsive microcapsules, as detailed below: (1) Dissolve 4g of chitosan with a degree of deacetylation of 85% in 100 mL of 3% acetic acid solution to prepare a 4% chitosan solution. Take 20 mL of this chitosan solution into a 100 mL beaker and keep shaking at high speed.

[0024] (2) Weigh 1200 mg of nano calcium peroxide and 100 mg of attapulgite obtained in Example 1 and mix them evenly in 6 mL of 3wt% acetic acid solution to prepare a uniform mixed solution.

[0025] (3) The mixed solution of nano-calcium peroxide and attapulgite was quickly poured into a chitosan solution under high-speed shaking to obtain a uniformly mixed solution. A 10 mL syringe was used to extract the mixed solution, which was then added dropwise at a rate of 1 drop / s to a 1 mol / L sodium hydroxide solution to obtain uniformly sized microcapsules. The formed spherical microcapsules were left in the sodium hydroxide solution for 15 min, and then washed in ethanol and tert-butanol solutions respectively. Finally, the microcapsules were pre-frozen at -80℃ for 2 h and then dried in a freeze dryer for 24 h to obtain dried microcapsules (nCaO2-CSM, where n indicates nanometer and has no other special meaning). The morphology of the obtained nCaO2-CSM is as follows: Figure 2 As shown in Figure a, they appear as smooth, white, small spheres, with the particle size mainly concentrated between 4.5 and 5.5 mm. Figure 2 (As shown in b).

[0026] Performance testing This test example demonstrates the sustained-release performance of a sustained-release pH-responsive microcapsule, as shown below: Dry nCaO2-SCM was prepared according to the method in Example 2. The Ca release from the nCaO2-SCM was then measured in an environment with pH 7–9. 2+ The ability. For example... Figure 3 As shown in Figure a, nCaO2-SCM exhibits significant pH responsiveness, displaying different CaO2 content at different pH levels. 2+ Release rate. Ca 2+ The release rate slows down as pH increases.

[0027] Application examples Phosphorus removal performance of sustained-release pH-responsive microcapsules: A laboratory simulation device was constructed by collecting sediments and overlying water from the polluted water body, and a 30-day passivation experiment was conducted. The results are shown below. Figure 3 Experimental results show that the application of nCaO2-SCM can reduce the active phosphorus (SRP) in the overlying water by 92.61%.

[0028] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing sustained-release, self-regulating pH-responsive microcapsules, characterized in that, Includes the following steps: (1) CaCl2 and H2O2 react in an alkaline environment to obtain active nano-CaO2 by high-speed shaking method; the active nano-CaO2 and attapulgite are mixed in an acid solution to obtain a mixed solution; the mixed solution is rapidly injected into a chitosan solution; (2) The mixed solution obtained in step (1) is uniformly dropped into a strong alkaline solution by the dripping method to obtain microcapsules with uniform particle size. The microcapsules are then dehydrated using ethanol and tert-butanol solutions and then freeze-dried to obtain the sustained-release self-regulating pH-responsive microcapsules.

2. The preparation method according to claim 1, characterized in that, In step (1), the pH of the alkaline environment is 10-12; the mass-to-volume ratio of CaCl2 to H2O2 is (11.1-44.1):(20-60) g / mL; and the concentration of H2O2 is 30%.

3. The preparation method according to claim 1, characterized in that, In step (1), the degree of deacetylation of chitosan in the chitosan solution is 85-95%.

4. The preparation method according to claim 1, characterized in that, In step (1), the acid in the acid solution includes acetic acid or hydrochloric acid; the concentration of the acid solution is 1~5wt%.

5. The preparation method according to claim 1, characterized in that, The mass ratio of active nano-calcium peroxide, attapulgite, and chitosan is (2:1:8) to (16:1:8). According to the preparation method of claim 1, the mixed solution is added at a rate of 0.5 to 1 drop / s in step (2).

6. The preparation method according to claim 1, characterized in that, In step (2), the concentration of the strong alkali solution is 0.8~1.2 mol / L; the strong alkali in the strong alkali solution includes sodium hydroxide and / or potassium hydroxide.

7. A sustained-release, self-regulating pH-responsive microcapsule, characterized in that, Prepared by the preparation method according to any one of claims 1 to 7.

8. The sustained-release, self-regulating pH-responsive microcapsule according to claim 8, characterized in that, The sustained-release, self-regulating pH-responsive microcapsules have a particle size of 3–6 mm.

9. The application of the slow-release, self-regulating pH-responsive microcapsules as described in claim 8 or 9 in the control of endogenous phosphorus in river and lake sediments.

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