A method for preparing a slow-release material, the prepared slow-release material and application thereof

Abstract

This invention discloses a method for preparing a sustained-release material, the prepared sustained-release material, and its application. The method includes: (1) dispersing a first starch in water, then adding a first active substance, activated carbon, and sodium alginate and mixing evenly to obtain product I; (2) dispersing a second starch in water, then adding a second active substance and mixing evenly to obtain product II; (3) mixing product I obtained in step (1), product II obtained in step (2), a strength agent, a matrix, and a solvent, molding, and drying to obtain a sustained-release material; in step (1), the activated carbon is modified biochar; the preparation method of the modified biochar includes a modification step of impregnating the biochar in an acidic solution containing organic alcohols. The sustained-release material prepared by this method has the characteristics of being environmentally friendly and having a long-term release, and can be used for the sustained-release of materials, especially for the remediation of organic pollutants in soil and groundwater, where it can achieve long-term and efficient remediation.

Description

Technical Field

[0001] This invention belongs to the field of sustained-release materials technology, specifically relating to a method for preparing a sustained-release material, the prepared sustained-release material, and its application. Background Technology

[0002] Among numerous remediation technologies, oxidative remediation is a mainstream soil and groundwater remediation technology, boasting advantages such as simple operation and high remediation efficiency. However, due to the short residence time of the reagents underground, the oxidative remediation process immediately terminates once the injection of the oxidant stops, failing to achieve long-term remediation. Therefore, further improvements to oxidative remediation reagents are needed.

[0003] Sustained-release agents (SRAs) can continuously release their contained agents at a relatively low release rate, extending the drug's residence time underground and achieving long-term removal of pollutants. The principle is mainly based on using poorly soluble binders mixed with or coated with the target drug. The binder acts as a slow solvent in water, thus slowing down the release rate of the target drug. The material can also have a matrix material with a certain mechanical strength added to improve its resistance to mechanical shock, or other auxiliary materials added to regulate the release rate.

[0004] CN115385750A discloses a porous coal gangue-loaded humic acid type slow-release soil conditioner and its preparation method. Modified coal gangue is prepared by mixing coal gangue powder and organic acid. Biochemical humic acid, potassium humate, urea, and phosphatidylcholine dihydrogen phosphate are then loaded onto the modified coal gangue, followed by extrusion granulation to produce a porous coal gangue-loaded humic acid type slow-release soil conditioner. This slow-release material is only for soil improvement and cannot remediate contaminated groundwater. Furthermore, since coal gangue is a waste that requires proper disposal, adding it to the land can easily introduce secondary pollution. CN102491425A discloses a slow-release potassium permanganate oxidant for in-situ chemical remediation of groundwater. This research involves dispersing KMnO4 into molten paraffin wax, then cooling and solidifying it in a mold to produce slow-release KMnO4 oxidants of different shapes, thereby achieving the purpose of slow-release KMnO4 oxidant. However, this study used paraffin, a harmful organic compound, as one of the raw materials, posing a significant risk of secondary pollution.

[0005] CN107188361A discloses a slow-release sulfiding agent, its preparation method, and a method for using the slow-release sulfiding agent to purify heavy metals and arsenic in acidic solutions. This research is conducted on Fe-containing... 2+ Mn 2+ and Zn 2+A slow-release sulfiding agent, a nano- to micron-sized metal sulfide sol, is obtained by reacting a sulfur source and surfactant in a solution. This agent is used to remove heavy metals and arsenic from acidic solutions, exhibiting advantages such as high removal efficiency, low sulfiding agent usage, and low hydrogen sulfide release. However, this agent is only effective against heavy metal pollutants and cannot remediate organically contaminated groundwater, and it is difficult to achieve long-term remediation.

[0006] In summary, existing slow-release remediation materials and methods are either only suitable for heavy metal contaminated sites and have limited effectiveness in remediating organic pollutants, or their matrix materials are unsuitable for long-term release and have short release cycles, thus failing to achieve the goal of slow release and long-term remediation. Therefore, there is an urgent need to develop an environmentally friendly, long-term release slow-release material. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a method for preparing a slow-release material, the prepared slow-release material, and its applications. The slow-release material prepared by this method is environmentally friendly and has long-term release characteristics, making it suitable for slow-release applications, particularly for the long-term and efficient remediation of organic pollutants in soil and groundwater.

[0008] The first aspect of this invention provides a method for preparing a sustained-release material. The method includes:

[0009] (1) Disperse the first starch in water, then add the first active substance, activated carbon, and sodium alginate and mix evenly to obtain product I;

[0010] (2) Disperse the second starch in water, then add the second active substance and mix well to obtain product II;

[0011] (3) Mix product I obtained in step (1), product II obtained in step (2), strength agent, matrix and solvent, mold and dry to obtain sustained-release material.

[0012] According to the present invention, in step (1), the activated carbon is modified biochar. The preparation method of the modified biochar includes a modification step of impregnating the biochar in an acidic solution containing organic alcohols.

[0013] According to the present invention, the modified biochar in step (1) has a particle diameter of 40-60 mesh. Macropores (pore size > 50 nm) account for more than 8% of the total pore volume, preferably 8%-10%.

[0014] According to the present invention, in step (1), the modified biochar preparation method uses commercially available products or self-made biochar. Preferably, the biochar preparation method includes: drying, pulverizing, sieving, and heating under an anaerobic atmosphere to obtain biochar. The drying conditions are drying at 40-60°C for 20-48 hours. The sieving is a 20-40 mesh sieve. The heating conditions are heating at 450-650°C for 3-6 hours. The anaerobic atmosphere is a nitrogen atmosphere. Preferably, the obtained biochar is placed in air for at least 30 days, preferably 30-90 days.

[0015] According to the present invention, in step (1), the method for preparing the modified biochar includes at least one of methanol, ethanol, propanol, isopropanol, and ethylene glycol. The acid includes at least one of hydrochloric acid, sulfuric acid, and nitric acid, preferably hydrochloric acid. The concentration of the acid in the acidic solution containing the organic alcohol is 0.05–0.15 mol / L. -1 The volume concentration of the organic alcohol is 95%–99%.

[0016] According to the present invention, in step (1), in the method for preparing the modified biochar, the solid-liquid ratio of the mixture of biochar and acidic solution containing organic alcohol is 1:(10-20) by mass. The impregnation time is 4-8 hours.

[0017] According to the present invention, in step (1), the modified biochar is prepared by impregnation, followed by washing and drying. The washing solution is at least one of water and an acidic solution. The number of water washes is 10 to 20. The total amount of water used for washing is 20 to 26 times the mass of the modified biochar. The acidic solution is preferably hydrochloric acid solution. The concentration of the hydrochloric acid solution is 0.1 to 0.5 mol / L. -1 An acidic solution can remove unreacted methanol. The drying conditions are: room temperature (10–30°C) for 72–80 hours. Compared with the original biochar, the modified biochar exhibits improved surface pore structure and surface functional groups. The number of surface ester and hydroxyl groups is significantly increased, while the number of carbonyl groups is reduced. This leads to the formation of more covalent hydrogen bonds between the modified biochar and starch, enhancing the adsorption capacity for starch and thus allowing the biochar to load more active substances. Simultaneously, the proportion of large pores (pore size > 50 nm) within the modified biochar is also increased compared to the unmodified form, further enhancing the adsorption capacity of starch particles.

[0018] According to the present invention, the first starch in step (1) and / or the second starch in step (2) are modified porous starches. The first starch in step (1) and the second starch in step (2) can be the same starch or different starches.

[0019] According to the present invention, the method for preparing the modified porous starch includes:

[0020] Porous starch was dispersed in water, and octenyl succinic anhydride was added to carry out the reaction. The solid was filtered and dried to obtain modified porous starch.

[0021] According to the present invention, in the method for preparing the modified porous starch, the porous starch is dispersed in water to obtain an emulsion, and the mass content of the porous starch is 25wt% to 40wt%.

[0022] According to the present invention, in the preparation method of the modified porous starch, the mass ratio of octenyl succinic anhydride to porous starch is 1:(30-55).

[0023] According to the present invention, in the method for preparing the modified porous starch, the reaction conditions are as follows: reaction temperature of 40–55°C, pH of the reaction solution controlled at 8.5–10.5, and reaction time of 2–6 h. Further, the reaction is terminated by adjusting the pH of the reaction solution to below 6. After termination of the reaction, the product is washed, filtered, and dried. The drying conditions are as follows: temperature of 45–55°C, and time of 10–16 h.

[0024] According to the present invention, in the preparation method of the modified porous starch, the porous starch can be commercially available or homemade. The median pore size of the porous starch is 4.5–6.5 μm. The modified porous starch possesses both hydrophilic and ester-philic properties. After adsorption and binding with activated carbon, it can both help the activated carbon to firmly bind with active substances and enhance the hydrophilicity of the activated carbon itself, promoting the entry of polluted water into the pores and facilitating the efficient degradation of pollutants.

[0025] According to the present invention, preferably, the porous starch can be prepared using conventional methods. Further, the method for preparing the porous starch includes: adding α-amylase and saccharifying enzyme to a starch-water suspension, reacting, filtering, and drying the resulting residue to obtain porous starch.

[0026] According to the present invention, in the method for preparing porous starch, the starch includes one or more of corn starch, potato starch, and cassava starch.

[0027] According to the present invention, in the method for preparing porous starch, the starch content in the suspension is 15wt% to 30wt%.

[0028] According to the present invention, in the method for preparing porous starch, the pH of the suspension is 4.5 to 6.5.

[0029] According to the present invention, in the method for preparing porous starch, the suspension is preheated before adding α-amylase and saccharifying enzyme. The preheating temperature is 15-20°C, and the preheating time is 20-30 minutes.

[0030] According to the present invention, in the method for preparing porous starch, the reaction conditions are: temperature 30-40°C, time 33-35 minutes.

[0031] According to the present invention, in the method for preparing porous starch, the mass ratio of α-amylase to saccharifying enzyme is 1:(3.5-5.5).

[0032] According to the present invention, in the method for preparing porous starch, the total amount of α-amylase and saccharifying enzyme added accounts for 0.03‰ to 0.11‰ of the mass of the suspension.

[0033] According to the present invention, in the method for preparing porous starch, the drying conditions are: drying at 45-55°C for 16-24 hours.

[0034] According to the present invention, the first active substance in step (1) includes one or more of sodium persulfate, potassium persulfate, ammonium persulfate, calcium persulfate, potassium permanganate, sodium permanganate, sodium sulfite, and microbial nutrients, preferably one or more of sodium persulfate, potassium persulfate, and ammonium persulfate. Further, the microbial nutrient includes at least one of glucose, lignin, nitrate, and ferrous salt. The first active substance does not produce harmful substances or cause secondary pollution of groundwater after oxidation-reduction or biological utilization.

[0035] According to the present invention, in step (1), the materials are fed in the following ratio: water, sodium alginate, first starch, first active substance, and activated carbon at a mass ratio of 100:(1-3):(5-15):(35-50):(30-45). The product prepared within this ratio range can maximize the loading of the first starch particles carrying the first active substance into the pores of the activated carbon.

[0036] According to the present invention, in step (1), after dispersing the first starch in water, it should be stirred thoroughly. Then, the first active substance, activated carbon, and finally sodium alginate are added in sequence. Each time a material is added, it should be mixed evenly. Preferably, stirring should be performed after adding activated carbon, preferably mechanical stirring. The mechanical stirring device can be a magnetic stirrer. Preferably, the mechanical stirring time is 1 to 2.5 hours. More preferably, sodium alginate is added during the stirring process.

[0037] According to the present invention, in step (1), product I is shaken in a shaker. The shaking time is 30-50 min, so that the starch carrying the active substance is fully loaded into the activated carbon. The resulting product I is an activated carbon composite material loaded with the first active substance.

[0038] According to the present invention, product I in step (1) can be filtered, washed and dried. The drying can be natural drying, for example, drying at room temperature (10-25°C) for 10-48 hours.

[0039] According to the present invention, the second active substance in step (2) includes one or more of sodium persulfate, potassium persulfate, ammonium persulfate, calcium persulfate, potassium permanganate, sodium permanganate, sodium sulfite, and microbial nutrients, preferably one or more of sodium persulfate, potassium persulfate, and ammonium persulfate. Further, the microbial nutrient includes at least one of glucose, lignin, nitrate, and ferrous salt. The second active substance does not produce harmful substances or cause secondary pollution of groundwater after oxidation-reduction or biological utilization. The first and second active substances can be the same or different.

[0040] According to the present invention, in step (2), the mass ratio of water, second starch and second active substance is 100:(20-30):(50-60).

[0041] According to the present invention, the strength agent in step (3) includes at least one of quartz sand and glass fiber. The strength agent provides mechanical strength to the sustained-release material and simultaneously creates large pores, increasing the drug release rate. The matrix includes one or more of polytetrafluoroethylene (PTFE), polystyrene (PS), polyethylene (PE), and polypropylene (PP). The matrix serves as the matrix skeleton material of the sustained-release material, providing support and bonding. The solvent includes at least one of dichloromethane and n-hexane. Preferably, the solvent includes dichloromethane and n-hexane. Preferably, the volume ratio of dichloromethane to n-hexane is 1:(0.5-1). The solvent evaporates and dissipates after the material is formed and is not present in the material.

[0042] According to the present invention, in step (3), the mass ratio of product I, product II, strength agent, matrix, and solvent is (80-95):(75-85):(1-3):100:(50-70). This feeding ratio allows it to form a layered encapsulated structure, with the matrix material encapsulating the second active substance as the outer shell and the activated carbon composite material loaded with the first active substance as the inner core. In sustained-release applications, this further creates a staged release effect, prolonging the drug release time and increasing the oxidation cycle.

[0043] According to the present invention, preferably, the mixing method of product I, product II, strength agent, matrix, and solvent in step (3) includes:

[0044] (31) Mix the matrix with the solvent;

[0045] (32) The mixture obtained in step (31) is mixed evenly with product I;

[0046] (33) Mix the mixture obtained in step (32), product II and strength agent evenly.

[0047] According to the present invention, the slow-release material in step (3) has a shape including at least one of cylindrical, spherical, strip-shaped and tablet-shaped.

[0048] According to the present invention, the drying conditions in step (3) are: temperature 30-45°C and time 30-60 hours.

[0049] A second aspect of the present invention provides a sustained-release material prepared by the above method.

[0050] The third aspect of this invention provides the application of the sustained-release material prepared by the above method in sustained-release applications.

[0051] According to the present invention, the application includes the use of slow-release materials in the remediation of organic pollutants in groundwater.

[0052] According to the present invention, the application involves using the aforementioned slow-release material as a filler, filling it into permeable reactive barriers, groundwater remediation wells, and other remediation structures to carry out in-situ chemical oxidation, in-situ chemical reduction, and in-situ bioremediation of contaminated groundwater. During the in-situ chemical oxidation and reduction processes, when groundwater carrying pollutants flows through the filler, it undergoes oxidation-reduction reactions with the active substances released by the slow-release material, resulting in the removal of pollutants and purification of the groundwater. During the in-situ bioremediation process, the carbon source, nitrogen source, electron acceptor, and other nutrients released by the slow-release material prepared by the above method provide sustained support for microbial agents, thereby accelerating the degradation of pollutants by microorganisms and achieving groundwater remediation.

[0053] Compared with the prior art, the present invention has achieved significant and outstanding technical effects:

[0054] (1) In the method of the present invention, the method adopts a sequential batch mixing method to form a multi-core structure of the sustained-release material with multiple layers. After the outer shell is decomposed, multiple dispersed cores in the inner layer can release the active substance from the inner layer to the outer layer in turn, achieving the effect of multi-level release in layers, thereby realizing the long-term stable drug release.

[0055] Furthermore, in the method, starch is modified with octenyl succinic anhydride to give it both hydrophilic and ester-philic properties. When combined with activated carbon adsorption, it can not only help activated carbon to firmly bind with inorganic oxidants, but also improve the hydrophilicity of activated carbon itself to promote the entry of polluted water into the pores, thus improving the contact efficiency of pollutants and slow-release materials.

[0056] Furthermore, in the method, the biochar is modified to significantly increase the number of ester and hydroxyl functional groups on its surface and reduce the number of carbonyl groups. This results in more covalent hydrogen bonds forming between the modified biochar and starch, enhancing the adsorption capacity for starch and allowing the biochar to be loaded with more active substances, thus prolonging the release time. At the same time, the proportion of macropores (pore size > 50 nm) inside the modified biochar is also increased compared to the unmodified version, further increasing the adsorption capacity of starch particles.

[0057] (2) The unique material ratio scheme in the product of this invention ensures the loading of active substances while achieving close integration of active substances with other materials, develops a high-strength skeleton structure, avoids material breakage and disintegration in water, and prolongs the grading speed of finished material in water.

[0058] (3) The slow-release material prepared by the method of the present invention can effectively prolong the release cycle of the agent and stabilize the release rate. In particular, when applied to the remediation of pollutants in groundwater, it can improve the removal efficiency of pollutants and the stability of technical operation, reduce the amount of agent added, and prevent pollution rebound. Attached Figure Description

[0059] Figure 1 This is a graph showing the sustained-release performance test results of Example 1;

[0060] Figure 2 This is a graph showing the sustained-release performance test results of Example 2;

[0061] Figure 3 This is a graph showing the sustained-release performance test results of Example 3;

[0062] Figure 4 The graph shows the sustained-release performance test results of Comparative Example 1;

[0063] Figure 5 A simplified diagram of a contaminated groundwater treatment device for an application example;

[0064] Figure 6 The image shows the effect of slow-release materials on the remediation of petroleum hydrocarbon (TPH) contaminated groundwater as an application example. Detailed Implementation

[0065] The present invention will be further illustrated by the following embodiments, but the scope of protection of the present invention is not limited by the embodiments.

[0066] In this invention, the method for testing the sustained-release performance is as follows: 10g of the sustained-release material is placed in 1L of deionized water. The content of active substances in the water is measured at regular intervals, and the level of organic matter in the water is also measured simultaneously to detect whether the sustained-release material will cause secondary pollution of the water body. The testing interval increases with the testing time. For example, in the initial stage, it can be every 1 day; in the middle stage, it can be every 2-5 days; and in the final stage, it can be every 10 days. After each test, the deionized water used for testing is replaced with 1L of fresh deionized water. The above steps are repeated periodically until no active substances can be detected in the deionized water. In this invention, the content of active substances in the water is tested using spectrophotometry. For example, when persulfate is used as the active substance, the persulfate content is tested using the potassium iodide-ultraviolet spectrophotometric method. When ferrous salt is used as the active substance, the iron content is tested using the o-phenanthroline spectrophotometric method. When glucose is used as the active substance, the glucose content is determined by high-performance liquid chromatography.

[0067] In this invention, the method for testing organic matter in water is the method specified in "Determination of Volatile Organic Compounds in Water by Purge-Trap-Gas Chromatography (HJ 686-2014)".

[0068] In this invention, the loading of active substances in the prepared sustained-release materials was determined using an elemental analyzer. In this invention, the release period is the time from when the sustained-release material is added to water until the active substance is no longer detectable in the water; the cumulative release rate of the sustained-release material is the sum of the masses of active substances measured each time within the release period, divided by the loading of active substances in the sustained-release material; the average release rate is the sum of the masses of active substances measured each time within the release period, divided by the release period.

[0069] Example 1

[0070] (1) Preparation of modified biochar:

[0071] The sawdust was dried at 50°C for 48 hours, then pulverized and passed through a 20-40 mesh sieve. Under a nitrogen atmosphere, in the absence of oxygen, it was heated at 550°C for 4.5 hours to obtain biochar. The biochar was then exposed to air indoors for 60 days before modification operations began.

[0072] Biochar was impregnated in a mixed solution of methanol and HCl for 6 hours. The methanol concentration in the mixed solution was 99% by volume, and the HCl concentration was 0.15 mol / L. -1 The mass ratio of biochar to the mixed solution was 1:20. After impregnation, the mixture was repeatedly cooled and washed 20 times with ultrapure water to terminate the modification reaction. The total amount of water used for washing was 26 times the mass of the modified biochar. After washing, 0.1 mol / L of... -1The biochar was washed with HCl solution to remove unreacted methanol. After washing, it was dried at room temperature (20°C) for 72 hours and then passed through a 40-60 mesh sieve to obtain modified biochar. Measurements showed that macropores (pore size > 50 nm) accounted for 10% of the total pore volume of the modified biochar.

[0073] The preparation method of modified porous starch is as follows:

[0074] Preparation of porous starch: Corn starch was added to water and stirred until homogeneous to prepare a 30 wt% starch suspension with a pH of 5.5. The suspension was preheated in a water bath at 30°C for 30 minutes. Then, a mixture of α-amylase and saccharifying enzyme at a mass ratio of 1:5.5 was added to the starch suspension, with the total amount of α-amylase and saccharifying enzyme being 0.11‰ of the suspension mass. The suspension was kept at a constant temperature of 40°C in a water bath for 33 minutes. After filtration to remove water, the mixture was dried in a 45°C oven for 24 hours to obtain porous starch. The median pore size of the porous starch was 6.5 μm.

[0075] Preparation of modified porous starch: Using the porous starch prepared above as raw material, water was added to make a 40 wt% starch emulsion. Octenyl succinic anhydride was added, with a mass ratio of octenyl succinic anhydride to porous starch in the starch emulsion of 1:55. The reaction was maintained at a constant temperature of 55℃ in a water bath for 3 hours, and the pH of the reaction solution was controlled at 9. Then, hydrochloric acid was added to adjust the pH to 6 to end the reaction. The reaction product was washed, filtered, and dried at 50℃ for 13 hours to obtain modified porous starch.

[0076] In this example, the first starch and the second starch are modified porous starches as described above.

[0077] 15g of starch was added to 100g of water and stirred thoroughly to form an emulsion. Then, 50g of sodium persulfate was added to the emulsion and dissolved and mixed. After stirring evenly, 45g of modified biochar was added to the mixture. The mixture was then stirred thoroughly in a magnetic stirrer for 2 hours. Then, while stirring, 3g of sodium alginate was added to form a colloid. The colloid was placed in a shaker and shaken for 45 minutes to ensure that the starch containing active substances was fully loaded into the modified biochar. The adsorbed activated carbon was then filtered, washed, and air-dried at 25°C for 48 hours to obtain product I.

[0078] (2) Weigh some of the above-mentioned modified porous starch again as the second starch, and sodium persulfate. Mix the starch and sodium persulfate in water to obtain product II. The mass ratio of the feed is water:starch:sodium persulfate = 100:30:60.

[0079] (3) Mix product I obtained in step (1), product II obtained in step (2), strength agent, matrix, and solvent, and then mold and dry to obtain a sustained-release material. The specific steps are as follows:

[0080] (31) Mix the matrix polytetrafluoroethylene powder with a solvent (dichloromethane and n-hexane in a volume ratio of 1:1);

[0081] (32) The mixture obtained in step (31) is mixed evenly with product I;

[0082] (33) The mixture obtained in step (32), product II, and the strength agent quartz sand are thoroughly mixed. The product I: product II: quartz sand: polytetrafluoroethylene: solvent = 95:85:3:100:70. After thorough mixing, the material is extruded into strips and dried at 45°C for 48 hours to obtain cylindrical granular slow-release material A.

[0083] The mass fraction of sulfur in the controlled-release material A in this example was determined to be 6.1 wt%, therefore the sodium persulfate loading in controlled-release material A can be calculated to be 23.17 wt%. The controlled-release performance test results of this example are as follows: Figure 1 As shown, the release of the active substance can be divided into two stages: the first stage, from day 0 to day 9, is the decomposition and release stage of the outer shell, characterized by a rapid change in release rate and a steep release curve; the second stage, from day 10 to day 165, is the slow-release stage of the inner core, characterized by a stable release rate and a smooth curve. The relay release of the first and second stages achieves a layered, multi-stage slow-release effect. The final test results show that the release period of slow-release material A is 165 days. The cumulative release rate of sodium persulfate during the release period is 98.85 wt%, with an average release rate of 1.41 mg / (gd). Throughout the entire slow-release period, no organic matter was detected in the water, and the slow-release material particles remained intact and did not disintegrate.

[0084] Meanwhile, the inventors replaced the modified activated carbon in this example with 60-mesh wood-based activated carbon (with macropores accounting for 5.3% of the total pore volume) and conducted parallel comparative experiments to prepare the sustained-release material DA. The mass fraction of sulfur in the sustained-release material DA was determined to be 5.93 wt%, thus the sodium persulfate loading in DA was calculated to be 22.07 wt%. The sustained-release performance test results of this example show that the release period of sustained-release material DA is 135 days. The cumulative release rate of sodium persulfate during the release period is 97.9 wt%, and the average release rate is 1.7 mg / (gd). Comparing the test results of sustained-release material A and sustained-release material DA demonstrates that using modified activated carbon as a raw material further extends the release period of the agent and results in a more stable release rate.

[0085] Example 2

[0086] (1) Preparation of modified biochar:

[0087] The sawdust was dried at 60°C for 35 hours, then pulverized and passed through a 20-40 mesh sieve. Under a nitrogen atmosphere, in the absence of oxygen, it was heated at 450°C for 6 hours to obtain biochar. The biochar was then exposed to air indoors for 90 days before modification operations began.

[0088] Biochar was impregnated in a mixed solution of methanol and HCl for 8 hours. The methanol concentration in the mixed solution was 95% by volume, and the HCl concentration was 0.05 mol / L. -1 The mass ratio of biochar to the mixed solution was 1:10. After impregnation, it was treated with 0.5 mol / L... -1 The biochar was washed 10 times with an HCl solution to terminate the modification reaction. The total amount of water used for washing was 20 times the mass of the modified biochar. After washing, the biochar was washed again with ultrapure water to remove unreacted methanol. After washing, the biochar was dried at 30°C for 80 hours and then passed through a 40-60 mesh sieve to obtain the modified biochar. Measurements showed that macropores (pore size > 50 nm) accounted for 9% of the total pore volume of the modified biochar.

[0089] The preparation method of modified porous starch is as follows:

[0090] Preparation of porous starch: Potato starch was added to water and stirred until homogeneous to prepare a 15 wt% starch suspension with a pH of 4.5. The suspension was preheated in a water bath at 25°C for 20 minutes. Then, a mixture of α-amylase and saccharifying enzyme at a mass ratio of 1:3.5 was added to the starch suspension, with the total amount of α-amylase and saccharifying enzyme being 0.07‰ of the suspension mass. The suspension was kept at a constant temperature of 35°C in a water bath for 33 minutes. After filtration to remove water, the mixture was dried in a 55°C oven for 20 hours to obtain porous starch. The median pore size of the porous starch was 4.5 μm.

[0091] Preparation of modified porous starch: Using the porous starch prepared above as raw material, water was added to make a 25 wt% starch emulsion. Octenyl succinic anhydride was added, with a mass ratio of octenyl succinic anhydride to porous starch in the starch emulsion of 1:30. The reaction was maintained at a constant temperature of 50℃ in a water bath for 3 hours, and the pH of the reaction solution was controlled at 10.5. Then, hydrochloric acid was added to adjust the pH to 6 to end the reaction. The reaction product was washed, filtered, and dried at 55℃ for 10 hours to obtain modified porous starch.

[0092] In this example, the first starch and the second starch are modified porous starches as described above.

[0093] 5g of starch was added to 100g of water and stirred thoroughly to form an emulsion. Then, 35g of potassium persulfate was added to the emulsion and dissolved and mixed. After stirring evenly, 30g of modified biochar was added to the mixture. The mixture was then stirred thoroughly in a magnetic stirrer for 1 hour. Then, while stirring, 1g of sodium alginate was added to form a colloid. The colloid was placed in a shaker and shaken for 30 minutes to ensure that the starch containing active substances was fully loaded into the modified biochar. The adsorbed activated carbon was then filtered, washed, and air-dried at 25°C for 24 hours to obtain product I, i.e., the activated carbon composite material.

[0094] (2) Weigh some of the above-mentioned modified starch again as the second starch, and calcium persulfate. Mix the starch and calcium persulfate in water to obtain product II. The feed ratio is water:starch:calcium persulfate = 100:20:50.

[0095] (3) Mix product I obtained in step (1), product II obtained in step (2), strength agent, matrix, and solvent, and then mold and dry to obtain a sustained-release material. The specific steps are as follows:

[0096] (31) Mix the matrix polytetrafluoroethylene powder with a solvent (dichloromethane and n-hexane in a volume ratio of 1:0.5);

[0097] (32) The mixture obtained in step (31) is mixed evenly with product I;

[0098] (33) The mixture obtained in step (32), product II, and the strength agent quartz sand are thoroughly mixed. The product I: product II: quartz sand: polytetrafluoroethylene: solvent = 80:75:1:100:50. After thorough mixing, the material is extruded into strips and dried at 40°C for 60 hours to obtain cylindrical granular slow-release material B.

[0099] The mass fraction of sulfur in the controlled-release material B in this example was determined to be 5.98 wt%. Therefore, the calculated loading of the active substances (potassium persulfate and calcium persulfate) in controlled-release material B is 22.88 wt%. The controlled-release performance test results of this example are as follows: Figure 2 As shown, the release of the active substance can be divided into two stages: the first stage, from day 0 to 10, is the decomposition and release stage of the outer shell, characterized by a rapid change in release rate and a steep release curve; the second stage, from day 11 to 160, is the slow-release stage of the inner core, characterized by a stable release rate and a smooth curve. The relay release of the first and second stages achieves a multi-stage slow-release effect. The final test results show that the release period of slow-release material B is 160 days. The cumulative release rate of sodium persulfate during the release period is 97.9 wt%, with an average release rate of 1.43 mg / (gd). Throughout the entire slow-release period, no organic matter was detected in the water, and the slow-release material particles remained intact and did not disintegrate.

[0100] Example 3

[0101] (1) Preparation of modified biochar:

[0102] The sawdust was dried at 40°C for 20 hours, then pulverized and passed through a 20-40 mesh sieve. Under a nitrogen atmosphere, in the absence of oxygen, it was heated at 650°C for 3 hours to obtain biochar. The biochar was then exposed to air indoors for 30 days before modification operations began.

[0103] Biochar was impregnated in a mixed solution of methanol and HCl for 4 hours. The methanol concentration in the mixed solution was 97% by volume, and the HCl concentration was 0.1 mol / L. -1 The mass ratio of biochar to the mixed solution was 1:15. After impregnation, it was treated with 0.5 mol / L... -1 The biochar was washed 15 times with an HCl solution to terminate the modification reaction. The total amount of water used for washing was 23 times the mass of the modified biochar. After washing, the biochar was washed again with ultrapure water to remove unreacted methanol. After washing, the biochar was dried at 30°C for 80 hours and then passed through a 40-60 mesh sieve to obtain the modified biochar. Measurements showed that macropores (pore size > 50 nm) accounted for 8% of the total pore volume of the modified biochar.

[0104] The preparation method of modified porous starch is as follows:

[0105] Preparation of porous starch: Cassava starch was added to water and stirred until homogeneous to prepare a 25 wt% starch suspension with a pH of 6.5. The suspension was preheated in a water bath at 28°C for 25 minutes. Then, a mixture of α-amylase and saccharifying enzyme at a mass ratio of 1:4.5 was added to the starch suspension, with the total amount of α-amylase and saccharifying enzyme being 0.03‰ of the suspension mass. The suspension was kept at a constant temperature of 30°C in a water bath for 35 minutes. After filtration to remove water, the mixture was dried in a 50°C oven for 24 hours to obtain porous starch. The median pore size of the porous starch was 5.5 μm.

[0106] Preparation of modified porous starch: Using the porous starch prepared above as raw material, water was added to make a 35 wt% starch emulsion. Octenyl succinic anhydride was added, with a mass ratio of octenyl succinic anhydride to porous starch in the starch emulsion of 1:45. The reaction was maintained at a constant temperature of 40℃ in a water bath for 3 hours, and the pH of the reaction solution was controlled at 8.5. Then, hydrochloric acid was added to adjust the pH to 6 to end the reaction. The reaction product was washed, filtered, and dried at 45℃ for 16 hours to obtain modified porous starch.

[0107] In this example, the first starch and the second starch are modified porous starches as described above.

[0108] 10g of starch was added to 100g of water and stirred thoroughly to form an emulsion. Then, 40g of ferrous sulfate was added to the emulsion and dissolved and mixed. After stirring evenly, 40g of modified biochar was added to the mixture. The mixture was then stirred thoroughly in a magnetic stirrer for 1.5h. Then, while stirring, 2g of sodium alginate was added to form a colloid. The colloid was placed in a shaker and shaken for 50min to ensure that the starch containing active substances was fully loaded into the modified biochar. The adsorbed activated carbon was then filtered, washed, and air-dried at 25℃ for 48h to obtain product I, i.e., the activated carbon composite material.

[0109] (2) Weigh some of the modified starch again as the second starch, and ferrous sulfate. Mix the starch and ferrous sulfate in water to obtain product II. The mass ratio of the feed is water:starch:ferrous sulfate = 100:25:55.

[0110] (3) Mix product I obtained in step (1), product II obtained in step (2), strength agent, matrix, and solvent, and then mold and dry to obtain a sustained-release material. The specific steps are as follows:

[0111] (31) Mix the matrix polytetrafluoroethylene powder with a solvent (dichloromethane and n-hexane in a volume ratio of 1:0.8);

[0112] (32) The mixture obtained in step (31) is mixed evenly with product I;

[0113] (33) The mixture obtained in step (32), product II, and the strength agent quartz sand are thoroughly mixed. The product I: product II: quartz sand: polytetrafluoroethylene: solvent = 85:80:2:100:60. After thorough mixing, the material is extruded into strips and dried at 45°C for 60 hours to obtain cylindrical granular slow-release material C.

[0114] The mass fraction of iron in the controlled-release material C in this example was determined to be 9.4 wt%, therefore the ferrous sulfate loading in the controlled-release material C can be calculated to be 25.51 wt%. The controlled-release performance test results of this example are as follows: Figure 3 As shown, the release of the active substance can be divided into two stages: the first stage, from day 0 to 12, is the decomposition and release stage of the outer shell, characterized by a rapid change in release rate and a steep release curve; the second stage, from day 13 to 162, is the slow-release stage of the inner core, characterized by a stable release rate and a smooth curve. The relay release of the first and second stages achieves a multi-stage slow-release effect. The final test results show that the release period of the slow-release material C is 162 days. The cumulative release rate of sodium persulfate during the release period is 97.5 wt%, with an average release rate of 1.52 mg / (gd). Throughout the entire slow-release period, no organic matter was detected in the water, and the slow-release material particles remained intact and did not disintegrate.

[0115] Example 4

[0116] The difference from Example 1 is that the active substance in steps (1) and (2) is glucose, while the rest is the same as in Example 1.

[0117] The glucose loading in sustained-release material D in this example was determined to be 30.11 wt%. The sustained-release performance test results of this sustained-release material are as follows: Figure 1 As shown, the release of the active substance can be divided into two stages: the first stage, from day 0 to day 8, is the decomposition and release stage of the outer shell, characterized by a rapid change in release rate and a steep release curve; the second stage, from day 9 to day 165, is the slow-release stage of the inner core, characterized by a stable release rate and a smooth curve. The relay release of the first and second stages achieves a layered, multi-stage slow-release effect. The final test results show that the release period of the slow-release material D is 165 days. The cumulative release rate of sodium persulfate during the release period is 97 wt%, with an average release rate of 1.55 mg / (gd). Throughout the entire slow-release period, no organic matter was detected in the water, and the slow-release material particles remained intact and did not disintegrate.

[0118] Comparative Example 1

[0119] The difference between this example and Example 1 is that the active substance, sodium persulfate, is not added in steps, but all at once. That is, all the materials from steps (1) and (2) of Example 1 are added at once in step (1) of Example 1. The amount of materials added and other operating steps are the same as in Example 1.

[0120] The sustained-release performance test results of the sustained-release material in this example are as follows: Figure 4 As shown, the results indicate that the release period of the slow-release material is only 9 days, which does not achieve the effect of slow release.

[0121] Application examples

[0122] The principle of using slow-release materials to remediate contaminated groundwater is as follows: Figure 5As shown, the slow-release material A from Example 1 of this invention was used as filler material and filled into a permeable reactive wall. The permeable reactive wall was then placed in the flow path of organically contaminated groundwater. The contaminated groundwater permeated through the wall, and the organic pollutants were oxidized and degraded by the active substances released by the slow-release material, thus removing the pollutants. The pollution removal rate could be calculated by testing the pollutant concentrations in the groundwater upstream and downstream of the permeable reactive wall. In this application example, groundwater contaminated with petroleum hydrocarbons (TPH) was selected, with an influent TPH concentration of (130±5) mg / L. The wall dimensions were set at 10m*0.6m*5.8m, and 2 tons of slow-release material were filled at one time as wall filler material. A pollution remediation application was carried out for 175 days. During this period, the TPH concentrations in the groundwater upstream and downstream of the permeable reactive wall were measured at regular intervals, and the pollution removal rate was calculated. The pollution remediation effect is as follows: Figure 6 As shown, during the first 165 days, the TPH removal rate remained above 90 wt%, reaching a maximum of 97 wt%. After day 165, most of the oxidant in the slow-release material had been released, and the pollution removal rate decreased. This result indicates that the slow-release material has stable slow-release performance and can be continuously released during the slow-release period, successfully remediating contaminated groundwater.

Claims

1. A method for preparing a sustained-release material, characterized in that, The method includes: (1) Disperse the first starch in water, then add the first active substance, activated carbon, and sodium alginate and mix evenly to obtain product I; (2) Disperse the second starch in water, then add the second active substance and mix well to obtain product II; (3) Mix product I obtained in step (1), product II obtained in step (2), strength agent, matrix and solvent, mold and dry to obtain sustained-release material; In step (1), the activated carbon is modified biochar; the preparation method of the modified biochar includes a modification step of impregnating the biochar in an acidic solution containing organic alcohols. In step (1), the first starch and / or in step (2), the second starch is modified porous starch; The method for preparing the modified porous starch includes: dispersing porous starch in water, adding octenyl succinic anhydride and reacting, filtering to obtain a solid, and drying to obtain the modified porous starch. The method for preparing porous starch includes: adding α-amylase and saccharifying enzyme to a starch-water suspension, filtering the mixture after reaction, and drying the filter residue to obtain porous starch. The first active substance in step (1) and the second active substance in step (2) each independently include one or more of the following: sodium persulfate, potassium persulfate, ammonium persulfate, calcium persulfate, potassium permanganate, sodium permanganate, sodium sulfite, and microbial nutrients. The strength agent mentioned in step (3) includes at least one of quartz sand and glass fiber; the matrix includes one or more of polytetrafluoroethylene, polystyrene, polyethylene, and polypropylene; and the solvent includes at least one of dichloromethane and n-hexane.

2. The method according to claim 1, characterized in that, The modified biochar in step (1) has a particle diameter of 40-60 mesh; the macropores with a pore size > 50 nm account for more than 8% of the total pore volume.

3. The method according to claim 2, characterized in that, In the modified biochar described in step (1), the macropores with a pore size > 50 nm account for 8% to 10% of the total pore volume.

4. The method according to claim 1, characterized in that, In the method for preparing the modified biochar, the organic alcohol includes at least one of methanol, ethanol, propanol, isopropanol, and ethylene glycol. And / or, the acid includes at least one of hydrochloric acid, sulfuric acid, and nitric acid; And / or, in the acidic solution containing organic alcohol, the concentration of acid is 0.05~0.15 mol / L and the volume concentration of organic alcohol is 95%~99%.

5. The method according to claim 4, characterized in that, The acid is hydrochloric acid.

6. The method according to claim 1, characterized in that, In step (1), in the method for preparing modified biochar, the solid-liquid ratio of the mixture of biochar and acidic solution containing organic alcohol is 1:(10~20) by mass. And / or, the soaking time is 4~8 hours.

7. The method according to claim 1, characterized in that, In the preparation method of the modified porous starch, the mass ratio of octenyl succinic anhydride to porous starch is 1:(30~55).

8. The method according to claim 1, characterized in that, In the method for preparing the modified porous starch, the reaction conditions are: a reaction temperature of 40~55℃; and / or, controlling the pH of the reaction solution to be 8.5~10.5; and / or, a reaction time of 2~6 h.

9. The method according to claim 1, characterized in that, The porous starch has a median pore size of 4.5~6.5μm.

10. The method according to claim 1, characterized in that, In the method for preparing porous starch, the reaction conditions are: temperature 30~40℃, time 33~35 minutes; And / or, the mass ratio of α-amylase to glucoamylase is 1:(3.5~5.5); And / or, the total amount of α-amylase and glucoamylase added accounts for 0.03‰~0.11‰ of the suspension mass; And / or, the starch content in the suspension is 15wt%~30wt%.

11. The method according to claim 1, characterized in that, The first active substance in step (1) and the second active substance in step (2) each independently include one or more of sodium persulfate, potassium persulfate, and ammonium persulfate.

12. The method according to claim 1, characterized in that, The microbial nutrient includes at least one of glucose, lignin, nitrate, and ferrous salt.

13. The method according to claim 1, characterized in that, In step (1), the following feeding ratio is adopted for each material, namely, the mass ratio of water, sodium alginate, first starch, first active substance and activated carbon is 100: (1~3): (5~15): (35~50): (30~45).

14. The method according to claim 1, characterized in that, In step (2), the mass ratio of water, second starch, and second active substance is 100:(20~30):(50~60).

15. The method according to claim 1, characterized in that, In step (3), the mass ratio of product I, product II, strength agent, matrix and solvent is (80~95): (75~85): (1~3): 100: (50~70).

16. A sustained-release material prepared by the method according to any one of claims 1 to 15.

17. The application of a sustained-release material prepared by the method according to any one of claims 1 to 15 in the field of sustained-release materials.

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