Buoyancy capsule based on slow release of 3-hydroxydecanoic acid as well as preparation method and application of buoyancy capsule

Abstract

The invention discloses a buoyancy capsule based on slow release of 3-hydroxydecanoic acid as well as a preparation method and application of the buoyancy capsule. The capsule comprises an air / inert gas core, a biodegradable polymer shell layer and 3-hydroxydecanoic acid loaded in the shell layer, the apparent density of the capsule is lower than or close to that of water, and the capsule can suspend on the surface layer of a water body for a long time and continuously release 3-hydroxydecanoic acid, so that the concentration of 3-hydroxydecanoic acid is maintained at an effective window of 1-2 ppm, thereby inhibiting growth of blue-green algae for a long time and reducing recurrence. The preparation method adopts coaxial gas-liquid injection to form gas-nucleus liquid drops and solidify the gas-nucleus liquid drops, and has the advantages of monodisperse particle size, adjustable hollow rate, greenness, no residue and the like. The buoyancy capsule prepared by the invention can inhibit the growth of blue-green algae in a water body for a long time, is suitable for water environments such as lakes, reservoirs, landscape water bodies and the like in which the blue-green algae are easy to gather on the surface layer, and is particularly used for inhibiting the proliferation and water bloom formation of dominant blue-green algae such as synechococcus, synechocystis and microcystis aeruginosa.

Description

Technical Field

[0001] This invention belongs to the field of water ecological restoration and harmful algae control technology, specifically involving a buoyancy capsule based on 3-hydroxydecanoic acid slow release, its preparation method and application. Background Technology

[0002] In recent years, influenced by factors such as climate warming, eutrophication, and changes in hydrodynamic conditions, cyanobacterial blooms have become increasingly frequent in lakes, reservoirs, and urban landscape water bodies. During a cyanobacterial bloom, large amounts of algae accumulate on the water surface, forming a distinct floating layer. This not only leads to decreased water transparency, fluctuations in dissolved oxygen, and ecological imbalance, but may also produce harmful metabolites such as microcystins, further threatening drinking water safety, fisheries production, and the health of aquatic ecosystems. Therefore, developing safe, effective, and long-term technologies and materials for controlling cyanobacterial blooms is of significant environmental and social importance.

[0003] Currently, conventional methods for controlling cyanobacteria mainly include chemical algaecides, flocculation and sedimentation, physical removal, and ecological regulation. Among these, chemical algaecides are widely used due to their rapid effectiveness and ease of operation. However, existing chemical algaecides usually require high dosages to achieve significant algae suppression effects, and can easily produce toxic or stressful effects on non-target organisms such as zooplankton, fish, aquatic plants, and microbial communities. Furthermore, some algaecides introduce residual ions or byproducts into the water, posing a risk of secondary pollution. Due to water dilution, photolysis, redox reactions, and microbial degradation, the effective duration of chemical algaecides is often short, requiring frequent application in practice. This not only increases treatment costs but also exacerbates disturbance to the aquatic ecosystem.

[0004] In contrast, using allelochemicals to regulate algal growth is considered a more eco-friendly approach to algae suppression. Allelochemicals are usually secondary metabolites released by aquatic plants, algae, or microorganisms during their growth. They can inhibit photosynthesis, cell division, membrane structure stability, or metabolic enzyme activity of algae within a certain concentration range, thereby affecting the growth competition of algal populations. Currently, a wide range of allelochemicals with algae-suppressing activity have been reported, including but not limited to: (1) fatty acids and their derivatives, which interfere with algal cell membrane permeability and the photosynthetic system; (2) phenolic acids and polyphenolic compounds, such as p-hydroxybenzoic acid, ferulic acid, vanillic acid, and catechols, which can suppress algae by inducing oxidative stress, inhibiting the activity of key metabolic enzymes, or disrupting the photosystem II function; (3) terpenes, quinones, and alkaloids, which are commonly found in the metabolites of submerged plants or microorganisms and have an inhibitory effect on algal respiration and energy metabolism; (4) extracellular polypeptides, lipopeptides, or other microbial-derived algae-suppressing metabolites, which can cause damage to algal cell structure or inhibit quorum sensing-related pathways. The algae-suppressing effects of the aforementioned allelochemicals have been verified to some extent at the laboratory scale and are considered to have the advantages of "natural source, ecological regulation, and potential selective algae suppression".

[0005] However, existing allelochemical algaecides still have the following common limitations in engineering applications: First, most reported allelochemicals have relatively high effective algae-inhibiting concentrations, often requiring concentrations of ten to several hundred mg / L to achieve significant inhibition; second, allelochemicals are easily deactivated in real water bodies due to factors such as photooxidation, microbial degradation, and changes in pH and ionic strength, resulting in insufficient stability; third, allelochemicals are usually small molecules or easily diffused components, which, after direct addition, will rapidly diffuse, dilute, and migrate in the water, making it difficult to maintain an effective concentration window in the surface area where cyanobacteria mainly accumulate for a long time, resulting in short inhibition time and limited recurrence control capabilities.

[0006] Therefore, how to transform the algicidal activity of allelochemicals into a material form that can maintain a stable effect in natural water bodies over a long period remains a key technical problem that urgently needs to be solved in this field. Current technologies lack an algicidal material that can remain on the surface of water bodies where cyanobacteria easily accumulate for a long time and continuously release allelochemicals at an effective concentration, making it difficult to achieve long-term, low-dose, and eco-friendly stable control of cyanobacterial blooms. Summary of the Invention

[0007] This invention aims to address the common problems in existing cyanobacterial bloom control, such as high dosage, short-term effects, and ecological risks, by providing a buoyancy capsule based on sustained-release 3-hydroxydecanoic acid, its preparation method, and its application.

[0008] 3-Hydroxydecanoic acid (3-HHDC) is a novel allelochemical that can significantly inhibit the growth of various cyanobacteria even at low concentrations (1–2 mg / L). However, when free 3-HHDC is directly added to water, its effective concentration is difficult to maintain long-term due to factors such as dissolution, diffusion, and environmental degradation, and its inhibitory effect easily decays over time, failing to meet the needs of long-term control of cyanobacterial bloom recurrence in actual water bodies. By preparing it into buoyant capsules, it has a low apparent density, allowing it to remain suspended or slowly float in the upper layer of water for extended periods, continuously releasing 3-HHDC. This enables it to maintain an effective algal-inhibiting concentration in the local water body for a long time, thereby achieving long-term inhibition of cyanobacterial growth and control of algal bloom recurrence.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, this invention provides a buoyancy capsule based on sustained-release 3-hydroxydecanoic acid, characterized by a gas core cavity formed by air or nitrogen within the capsule, which significantly reduces the apparent density of the capsule and imparts buoyancy; the gas core is coated with a biodegradable polymer shell to carry the active substance and achieve synergistic diffusion-degradation sustained release; 3-hydroxydecanoic acid is loaded within the shell material and / or shell pores, and can be dissolved, dispersed, or adsorbed within the shell, thereby continuously releasing it in water. The apparent density of the capsule is not higher than 1.05 g / cm³. 3 This allows it to remain suspended in the upper layer of the water for a long time or float slowly in the surface area, in order to match the spatial distribution of the main activities and aggregation of cyanobacteria.

[0010] To further optimize buoyancy, slow-release cycle, and algae-suppressing effect, the shell material can be one or more biodegradable polymers such as PLGA, PLA, PCL, and PHB. The gas core can be air or nitrogen. The capsule particle size can be controlled within the range of 100 nm–500 μm, preferably 1–100 μm. The 3-hydroxydecanoic acid loading can be 10–30 wt% relative to the shell material weight, and the effective release period of the capsule in water can reach 60 days.

[0011] Secondly, the present invention provides a green and controllable preparation method for the buoyancy capsule. The method adopts a coaxial gas-oil-water three-coaxial gas-liquid injection technology, which makes the obtained capsule have monodisperse particle size, adjustable hollow rate, and designable shell thickness and release cycle, and has good repeatability and engineering scale-up potential.

[0012] The preparation method includes the following steps: First, the biodegradable polymer is dissolved in an organic solvent and 3-hydroxydecanoic acid is added to obtain a homogeneous shell organic phase, wherein the polymer concentration is 5–20 wt%, the organic solvent can be ethyl acetate or dichloromethane, and the 3-hydroxydecanoic acid content is 10–30 wt% relative to the shell material weight.

[0013] Subsequently, an external aqueous phase containing polyvinyl alcohol (PVA) was prepared as the continuous phase and interface stabilizer, with a PVA concentration of 0.1–1 wt%. Next, the polymer organic phase and nitrogen or air were introduced into the coaxial channel of a coaxial gas-liquid jet device. Under the shearing action of the external aqueous phase, stable gas-nucleated droplets were formed and introduced into the external aqueous phase collection tank. Stirring for 50–90 minutes allowed the organic solvent to diffuse and evaporate, promoting the gradual solidification of the shell and locking in a stable hollow structure. Finally, drying yielded the finished buoyancy-controlled release capsule.

[0014] During the preparation process, the flow rate ratio Q g (Gas): Q o (Shell phase) is a key parameter controlling the hollowness and buoyancy, with a ratio of 5 to 25:1. The hollowness and buoyancy increase with Q. g / Q o Increased concentration leads to a thicker shell, resulting in greater diffusion resistance, slower release rate, and longer duration. PVA in the external aqueous phase is more conducive to obtaining stable monodisperse gas-nucleus droplets and hollow capsules; the required volume of the external aqueous phase must be sufficient to completely submerge and disperse the capsules. By comprehensively adjusting particle size, hollowness, and shell thickness, the apparent density of the capsules can be made close to or slightly less than that of water, thus ensuring their long-term residence on the water surface and continuous algae-suppressing effect.

[0015] Thirdly, the present invention also provides the application of the buoyancy capsule in the long-term inhibition of cyanobacterial growth in water bodies, which is suitable for water environments such as lakes, reservoirs, and landscape water bodies where cyanobacteria are prone to accumulate on the surface, especially for inhibiting the proliferation and algal blooms of dominant cyanobacteria such as Synechococcus, Synechococcus, and Microcystis aeruginosa.

[0016] Compared with existing technologies, this invention has the following advantages: the first discovery that 3-hydroxydecanoic acid can significantly inhibit cyanobacterial growth at 1–2 mg / L achieves effective algae suppression with low dosage and significantly reduces the total dosage; due to the presence of the gas core, the capsule density is significantly reduced, allowing it to remain suspended or float in the surface waters where cyanobacteria are mainly active for a long time, enhancing targeting; the shell diffusion and degradation coupled release achieve long-term inhibition of cyanobacterial proliferation and reduce the probability of recurrence; the shell material is biodegradable, making it more green and eco-friendly; the coaxial jetting droplet forming process makes the capsule particle size controllable, ensures good batch consistency, and has the potential for scale-up, facilitating its application in actual water bodies. Attached Figure Description

[0017] Figure 1 A scanning electron microscope image of the buoyancy capsule prepared in Example 3; Figure 2 The image shows the color comparison of Microcystis aeruginosa after 7 days of treatment with buoyancy capsules and the untreated group. Detailed Implementation

[0018] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following embodiments are only for illustrating the present invention and should not be regarded as limiting the scope of the present invention.

[0019] 3-Hydroxydecanoic acid (CAS: 5561-87-5) was used in the examples; all other compounds were commercially available products. Unless otherwise specified, conditions were performed according to standard procedures or the manufacturer's recommendations. Reagents or instruments used in the examples, unless otherwise specified, were commercially available products.

[0020] Example 1: Preparation of PLGA-shelled 3-hydroxydecanoic acid sustained-release buoyancy capsules Raw materials: polylactic acid-glycolic acid copolymer (PLGA) (lactic acid / glycolic acid molar ratio of 75:25, molecular weight 50kDa), 3-hydroxydecanoic acid, dichloromethane, polyvinyl alcohol (PVA, 87–89% degree of hydrolysis), nitrogen.

[0021] Preparation steps: Preparation of the shell organic phase: Weigh 0.7 g PLGA and dissolve it in 10 mL dichloromethane, add 0.3 g 3-hydroxydecanoic acid, and stir magnetically for 15 min to obtain a homogeneous polymer organic phase; Preparation of external aqueous phase: Prepare 200 mL of 0.5 wt% PVA aqueous solution, stir at 60 °C until completely dissolved, and cool to room temperature for later use; Gas nucleus droplet formation: 10 mL of organic phase and high-purity nitrogen were connected to a coaxial gas-liquid jet apparatus, with the organic phase serving as the outer shell channel and the gas as the inner core channel. The gas flow rate was adjusted to 25 mL / min and the organic phase flow rate to 5 mL / min, forming stable gas-nucleus droplets in an outer aqueous phase (200 mL, stirred at 600 rpm) as the continuous phase. Under these conditions, microcapsules with a shell thickness of approximately 400–600 nm were prepared.

[0022] Curing and molding: The capsule is stirred in the external aqueous phase for about 50 minutes to solidify the PLGA shell and form a hollow buoyancy capsule with a nitrogen core.

[0023] Washing and drying: The particles were washed three times by centrifugation with 100 mL of deionized water (3000 rpm, 5 min), and then vacuum dried at 60℃ for 24 h to obtain particles with an average size of 15 μm and an apparent density of 0.98 g / cm³. 3 Buoyancy capsules.

[0024] Example 2: Preparation of nanoscale buoyancy capsules with PLA shells Raw materials: PLA (molecular weight 80 kDa), 3-hydroxydecanoic acid, ethyl acetate, PVA.

[0025] Preparation steps: Preparation of the polymer organic phase: Dissolve 0.50 g PLA in 8 mL of ethyl acetate, add 0.10 g of 3-hydroxydecanoic acid, and stir to obtain a clear and homogeneous solution.

[0026] External aqueous phase: Prepare 100 mL of 0.1 wt% PVA solution.

[0027] Gas nucleus droplet formation: A coaxial gas-liquid jet method equipped with a nano-nozzle is used, with a nitrogen flow rate of 5 mL / min (core channel) and an organic phase flow rate of 0.5 mL / min (outer channel), forming nanoscale gas nucleus droplets in an outer aqueous phase as the continuous phase (100 mL, stirred at 600 rpm).

[0028] Curing and molding: The above-mentioned nano-sized gas nuclei droplets were continuously stirred in the external aqueous phase for 1 h to complete the curing and ethyl acetate removal.

[0029] Washing and drying: Wash three times with 100 mL of deionized water (10,000 rpm, 5 min), and vacuum dry at 40℃ to obtain hollow capsules with an average particle size of 800 nm and an apparent density of 0.95 g / cm³. 3 .

[0030] Example 3: Hollow Buoyancy Capsule with PCL / PHB Composite Shell Raw materials: PCL (molecular weight 80 kDa), PHB (molecular weight 150 kDa), 3-hydroxydecanoic acid, dichloromethane, polyvinyl alcohol (PVA) (molecular weight 13,000–23,000, degree of hydrolysis 87-89%).

[0031] Preparation steps: Preparation of shell material solution: 0.8 g PCL and 0.6 g PHB were dissolved together in 12 mL dichloromethane, and 0.14 g 3-hydroxydecanoic acid was added. The mixture was stirred magnetically for 30 min to obtain a homogeneous solution.

[0032] Preparation of external aqueous phase: Prepare 300 mL of 1 wt% PVA solution, stir until completely dissolved, and set aside.

[0033] Gas-nucleus droplet generation: A coaxial gas-liquid jet apparatus was used, with a nitrogen flow rate of 40 mL / min (core channel) and an organic phase flow rate of 1.6 mL / min (outer channel). Under these conditions, stable gas-nucleus droplets of approximately 200 μm were formed in the outer aqueous phase.

[0034] Curing and molding: The droplets are stirred in the external aqueous phase for 1.5 h to promote the curing of the polymer shell.

[0035] Washing and drying: The obtained buoyancy capsules were washed three times with 150 ml of deionized water by centrifugation (3000 rpm, 5 min) to remove residual organic solvents. Then, the washed capsules were vacuum dried at 40°C for 24 h.

[0036] The capsules prepared by this method have a particle size distribution mainly concentrated at 200 μm and an apparent density of 0.93 g / cm³. 3 It has a distinct hollow structure (see Figure 1 ).

[0037] Example 4: Test of the sustained-release and degradation performance of three types of buoyancy capsules in water for 60 days. 100 mg of the three types of buoyancy capsules prepared in Examples 1-3 were added to 1 L of tap water and allowed to stand at 25 °C for 60 days. The concentration of 3-hydroxydecanoic acid in the supernatant was determined by HPLC differential refractive index at preset time points (0, 10, 20, 30, 45, and 60 days), and the cumulative release rate (%) was calculated. Residual capsules were collected, dried, and weighed at 0, 10, 20, 30, 45, and 60 days, and the residual mass (relative to the initial mass, %) was calculated. The results are shown in Table 1.

[0038] Table 1. Comparison of the sustained-release and degradation performance of 3-hydroxydecanoic acid in three types of buoyancy capsules over 60 days.

[0039] Table 1 shows that all three types of capsules were essentially fully released and largely degraded within 60 days. Comparatively, PLGA had the fastest release rate, while PCL / PHB were more difficult to degrade.

[0040] Example 5: Long-term inhibitory effect of buoyancy capsules on Synechococcus, Synechococcus pyogenes and Microcystis aeruginosa Algal species: Synechococcus Synechocystis sp. (FACHB-805), Synechocystis ( Synechocystis sp. FACHB-898, Microcystis aeruginosa Microcystis aeruginosa (FACHB-930) were all purchased from the Freshwater Algae Culture Bank of the Institute of Hydrobiology, Chinese Academy of Sciences.

[0041] Culture medium: Commercially available BG-11 cyanobacteria culture medium, prepared with deionized water, with the initial pH adjusted to 8.0 ± 0.2, and sterilized at 121℃ for 20 min before use.

[0042] Initial algal density: The algal density in the stock solution was measured using a hemocytometer, the dilution ratio was calculated, and the algae were inoculated into the culture medium to achieve an algal density of 1 × 10⁻⁶. 4 cells / mL.

[0043] Temperature and light intensity: 25±1 ℃, light intensity 60 μmol·m -2 ·s -1 , 12 h / 12 ​​h light and dark.

[0044] Each concentration was set up with 3 parallel groups, and the mixture was shaken 4-5 times a day.

[0045] After culturing the algal strain in 200 ml of culture medium, the following steps were performed: Control group: No buoyancy capsules added; Treatment group: PLGA buoyancy capsules (prepared in Example 1) were added at 10 mg / L.

[0046] Comparative example: 3-hydroxydecanoic acid was added at a total concentration of 3 mg / L.

[0047] The formula for calculating the algae density inhibition rate is: Algae density inhibition rate = (Control − Treatment) / Control × 100%; The formula for calculating the chlorophyll a inhibition rate is: Chl-a inhibition rate = (control − treatment) / control × 100%.

[0048] The algal density was measured using a hemocytometer, and the chlorophyll a content was determined according to the method in the "National Environmental Protection Standard of the People's Republic of China" HJ 897-2017.

[0049] The data results are shown in Table 2-4.

[0050] Table 2. Inhibition rate of buoyancy capsules on the density and chlorophyll content of Synechococcus.

[0051] Table 2 shows that 10 mg / L buoyancy capsules maintained an algal density inhibition rate of approximately 60–67% and a chlorophyll inhibition rate of approximately 60–85% against Synechococcus for 60 days, demonstrating a stable and long-lasting algal control ability. The control group also showed good inhibition at 15 days (81.2%), but the effect was only 15.2% at 30 days and almost disappeared after 45 days. This indicates that 3-hydroxydecanoic acid itself cannot maintain a long-term algal inhibitory effect due to dissipation and degradation in the water.

[0052] Table 3. Inhibition rate of buoyancy capsules on algal density and chlorophyll in Synechocystis.

[0053] Table 3 shows that Synechocystis is also sensitive to the buoyancy capsules of this invention, with the algal density inhibition rate remaining at 63–68% for 60 days, indicating that 10 mg / L can achieve long-term effective control. Meanwhile, the buoyancy capsules showed a higher inhibition rate on chlorophyll, indicating that they affect chlorophyll synthesis in algae.

[0054] Table 4. Inhibition rate of buoyancy capsules on algal density and chlorophyll content of Microcystis aeruginosa

[0055] The results in Table 4 show that *Microcystis aeruginosa* is less sensitive to the buoyancy capsules of this invention than *Synechococcus* and *Synostemma pentaphyllum*. Within 60 days, the algal density inhibition rate was approximately 42–47%, significantly lower than the 60–70% of the other two algal species. The chlorophyll a inhibition rate during the same period was approximately 44–63%, indicating a relatively limited inhibitory effect on photosynthetic pigment synthesis. Although the overall inhibition rate is low, it still exerts continuous pressure on the growth of *Microcystis aeruginosa*, reducing the risk of cyanobacterial blooms. Figure 2 The image shows the color comparison of Microcystis aeruginosa after 7 days of treatment with buoyancy capsules with the untreated group, revealing that its chlorophyll content was severely inhibited.

[0056] 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 buoyancy capsule based on sustained-release 3-hydroxydecanoic acid, characterized in that, The buoyancy capsule comprises a gas core, a biodegradable polymer shell encapsulating the gas core, and 3-hydroxydecanoic acid loaded in the polymer shell; the particle size of the buoyancy capsule is 100 nm–500 μm, and the apparent density of the buoyancy capsule is ≤1.05 g / cm³. 3 .

2. The buoyancy capsule according to claim 1, characterized in that, The gas core is a cavity formed by air or nitrogen.

3. The buoyancy capsule according to claim 1, characterized in that, The biodegradable polymer shell material is selected from one or more of polylactic acid-hydroxyacetic acid copolymer, polylactic acid, polycaprolactone, and polyhydroxybutyrate.

4. The buoyancy capsule according to claim 1, characterized in that, The loading of the 3-hydroxydecanoic acid is 10–30% of the mass of the polymer shell material.

5. A method for preparing a buoyancy capsule according to claims 1-4, characterized in that, Includes the following steps: (1) Preparation of shell organic phase: Dissolve the biodegradable polymer in ethyl acetate or dichloromethane to obtain a polymer solution with a concentration of 5-20 wt%, and add 3-hydroxydecanoic acid with a polymer content of 10-30 wt%, stir for 10-30 min to obtain a polymer organic phase containing 3-hydroxydecanoic acid; (2) Preparation of external aqueous phase: Prepare a polyvinyl alcohol aqueous solution with a concentration of 0.1~1 wt%; (3) Synchronously and continuously introduce the polymer organic phase and nitrogen or air described in step (1) into the coaxial channel of the coaxial gas-liquid jet device to form stable gas core droplets under the shearing action of the external aqueous phase prepared in step (2); (4) Stir the gas core droplets described in step (3) in the outer aqueous phase for 50-90 minutes. After the shell solidifies, a hollow buoyancy capsule with an air or nitrogen core is formed. (5) The buoyancy capsule was prepared by centrifuging and washing three times with deionized water and drying for 24 hours.

6. The preparation method according to claim 5, characterized in that, In step (3), the specific method for forming stable gas nuclei and liquid droplets using a coaxial gas-liquid jet device is as follows: the flow rate ratio of nitrogen or air to organic phase is 5~25:

1.

7. The application of the buoyancy capsule according to claims 1-4 in the long-term inhibition of cyanobacteria growth in water.

8. The application according to claim 7, characterized in that, The cyanobacteria mentioned are specifically Synechococcus, Synechococcus, and Microcystis aeruginosa.

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