Preparation method of sustained-release material, prepared sustained-release material and application of sustained-release material

Abstract

The invention discloses a preparation method of a sustained-release material, the prepared sustained-release material and application of the sustained-release material. The method comprises the following steps: (1) dispersing first starch in water, then adding a first active substance, activated carbon and sodium alginate, and uniformly mixing to obtain a product I; (2) dispersing second starch in water, then adding a second active substance, and uniformly mixing to obtain a product II; and (3) mixing the product I obtained in the step (1), the product II obtained in the step (2), a strength agent, a matrix and a solvent, molding, and drying to obtain the sustained-release material. In the step (1), the activated carbon is modified charcoal; the preparation method of the modified biochar comprises a modification step of dipping biochar in an acid solution containing organic alcohol. The slow-release material prepared by the method has the characteristics of environmental friendliness and long-term release, can be used in the aspect of slow release of the slow-release material, and particularly can realize long-term and efficient remediation when being used for remediation of organic pollutants in soil and underground water.

Description

Technical Field

[0001] The present invention belongs to the technical field of sustained-release materials, and in particular relates to a method for preparing a sustained-release material, the prepared sustained-release material and applications thereof. Background Art

[0002] As the country pays more and more attention to ecological and environmental protection, the remediation of soil and groundwater pollution has attracted more and more attention. Among the many remediation technologies, oxidation remediation is the mainstream soil and groundwater remediation technology, which has the advantages of simple operation and high remediation efficiency. However, due to the short residence time of the agent in the ground, once the injection of the oxidant stops, the oxidation remediation will be terminated immediately, and long-term remediation cannot be achieved. Therefore, further improvement of the oxidation remediation agent is needed.

[0003] Sustained release agent (SRA) can continuously release the contained drugs at a lower release rate, which can prolong the residence time of drugs in the ground and achieve long-term removal of pollutants. Its principle is mainly to use insoluble adhesive materials to mix or encapsulate with target drugs, and slow down the release rate of target drugs through the slow solvent of adhesive materials in water. The material can also add a matrix material with a certain mechanical strength to improve the material's mechanical impact resistance, or add other auxiliary materials to regulate the release rate.

[0004] CN115385750A discloses a porous gangue-loaded humic acid type slow-release soil conditioner and a preparation method thereof. The modified gangue is prepared by mixing gangue powder and organic acid, and biochemical humic acid, potassium humate, urea and phosphoamine diamine are loaded on the modified gangue respectively, and extruded and granulated to prepare a porous gangue-loaded humic acid type slow-release soil conditioner. This slow-release material is only for soil improvement and cannot repair contaminated groundwater. Moreover, since gangue is a waste that needs to be properly disposed of, it is easy to introduce secondary pollution when added to the land. CN102491425A discloses a slow-release potassium permanganate oxidant for in-situ chemical remediation of groundwater. This study is to use KMnO 4 Dispersed into molten paraffin, and then cooled and solidified in a mold to make sustained-release KMnO in different shapes 4 Oxidant, in order to achieve slow release of KMnO 4 The purpose of slow release of oxidants. However, in this study, harmful organic paraffin was used as one of the raw materials, which poses a great risk of secondary pollution.

[0005] CN107188361A discloses a slow-release sulfiding agent and a preparation method thereof, and a method for using the slow-release sulfiding agent to purify heavy metals and arsenic in an acidic solution. 2+ , Mn 2+ and Zn 2+A sulfur source and a surfactant are added to a solution to react, obtaining a nano-micron metal sulfide sol sustained-release sulfur agent, which is used for the removal of heavy metals and arsenic in acidic solutions. It has the advantages of high removal efficiency, low usage amount of the sulfur agent, and low hydrogen sulfide release amount. However, this agent is only effective for heavy metal pollutants, cannot repair organic-polluted groundwater, and it is difficult to achieve long-term repair.

[0006] In summary, the sustained-release repair materials and repair methods disclosed in the prior art either are only developed for heavy metal polluted sites and have limitations in the repair effect of organic pollutants, or the matrix materials are not suitable for long-term release and the sustained-release period is short, resulting in the inability to achieve the purpose of slow release and long-term repair of the sustained-release materials. Therefore, there is an urgent need to develop an environmentally friendly sustained-release material with long-term release. Summary of the Invention

[0007] Aiming at the defects existing in the prior art, the present invention provides a preparation method of a sustained-release material, the prepared sustained-release material and its application. The sustained-release material prepared by this method has the characteristics of environmental friendliness and long-term release, and can be used for the slow release of the sustained-release material. Especially when used for repairing organic pollutants in soil and groundwater, it can achieve long-term and efficient repair.

[0008] The first aspect of the present invention provides a preparation method of a sustained-release material. The method includes:

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

[0010] (2) Dispersing the second starch in water, and then adding the second active substance and mixing evenly to obtain product II;

[0011] (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 the 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 alcohol.

[0013] According to the present invention, the particle diameter of the modified biochar in step (1) is 40-60 mesh. The pore volume occupied by macropores (pore diameter > 50 nm) is more than 8% of the total pore volume, preferably 8%-10%.

[0014] According to the present invention, in step (1), in the method for preparing modified biochar, the biochar can be a commercial product or homemade. Preferably, the method for preparing biochar comprises: drying, crushing, sieving, and heating sawdust in a non-oxygen atmosphere to obtain biochar. The drying condition is drying at 40 to 60°C for 20 to 48 hours. The sieving is a 20 to 40 mesh sieve. The heating condition is heating at 450 to 650°C for 3 to 6 hours. The non-oxygen atmosphere is a nitrogen atmosphere. Preferably, the obtained biochar is placed in the air for at least 30 days, preferably 30 to 90 days.

[0015] According to the present invention, in step (1), in the preparation method of the modified biochar, the organic alcohol 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 acid concentration in the acidic solution containing the organic alcohol is 0.05 to 0.15 mol.L -1 , the volume concentration of organic alcohol is 95% to 99%.

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

[0017] According to the present invention, in step (1), in the preparation method of the modified biochar, after immersion, washing and drying are performed. The washing liquid for washing is at least one of water and an acidic solution. The number of washing times for water washing is 10 to 20 times. The total amount of water used for water washing is 20 to 26 times the mass of the modified biochar. The acidic solution is preferably a hydrochloric acid solution. The concentration of the hydrochloric acid solution is 0.1 to 0.5 mol.L -1 . The acidic solution can remove unreacted methanol. The drying conditions are: room temperature 10-30°C, 72-80h. Compared with the original biochar, the surface pore structure and surface functional groups of the modified biochar are improved. The number of surface ester groups and hydroxyl groups will be greatly increased, and the number of carbonyl groups will be reduced, which will form more covalent hydrogen bonds between the modified biochar and starch, enhance the adsorption capacity of starch, and thus make the biochar load more active substances; at the same time, the proportion of large pores (pore diameter > 50nm) inside the modified biochar is also increased compared with that before modification, further increasing 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 starch. 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 preparation method of the modified porous starch comprises:

[0020] The porous starch is dispersed in water, octenyl succinic anhydride is added to react, the solid is filtered and dried to obtain the modified porous starch.

[0021] According to the present invention, in the preparation method of 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 method for preparing 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 preparation method of the modified porous starch, the reaction conditions are: the reaction temperature is 40-55°C, the pH value of the reaction solution is controlled to be 8.5-10.5, and the reaction time is 2-6h. Further, the reaction is terminated by adjusting the pH value of the reaction solution to below 6. After the reaction is terminated, the product is washed, filtered and dried. The drying conditions are: temperature 45-55°C, time 10-16h.

[0024] According to the present invention, in the preparation method of the modified porous starch, the porous starch can be commercially available porous starch or homemade. In the porous starch, the median pore size is 4.5 to 6.5 μm. The modified porous starch has both hydrophilic and lipophilic properties. After being combined with activated carbon adsorption, it can not only help the activated carbon to be firmly combined with the active substance, but also improve the hydrophilicity of the activated carbon itself to promote the entry of polluted water into the pores, helping to efficiently degrade pollutants.

[0025] According to the present invention, preferably, the porous starch preparation method can be prepared by conventional methods. Further, the porous starch preparation method comprises: adding α-amylase and saccharifying enzyme to a suspension of starch and water, filtering the obtained filter residue after reaction, and drying to obtain porous starch.

[0026] According to the present invention, in the method for preparing the 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 mass 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 4.5-6.5.

[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 the 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 the porous starch, the mass ratio of α - amylase to glucoamylase is 1:(3.5 - 5.5).

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

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

[0034] According to the present invention, in step (1), the first active substance includes one or more of sodium persulfate, potassium persulfate, ammonium persulfate, calcium persulfate, potassium permanganate, sodium permanganate, sodium sulfite, and microbial nutrient agents, preferably one or more of sodium persulfate, potassium persulfate, and ammonium persulfate. Further, the microbial nutrient agent includes at least one of glucose, lignin, nitrate, and ferrous salt. No harmful substances are produced after the first active substance is redox - reacted or biologically utilized, and no secondary pollution of groundwater is caused.

[0035] According to the present invention, in step (1), the following feeding ratios of each material are used, that is, the mass ratio of water, sodium alginate, the first starch, the first active substance, and activated carbon is 100:(1 - 3):(5 - 15):(35 - 50):(30 - 45). The product prepared within this ratio range can maximize the promotion of 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 fully stirred. Then, the first active substance and activated carbon are added in sequence, and finally sodium alginate is added. After each addition of a material, it should be mixed evenly. Preferably, after adding the activated carbon, stirring is carried out, preferably mechanical stirring. The device for mechanical stirring can be a magnetic stirrer. Preferably, the mechanical stirring time is 1 - 2.5 h. More preferably, sodium alginate is added during the stirring process.

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

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

[0039] According to the present invention, in step (2), the second active substance 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 after being oxidized, reduced, or biologically utilized, and does not cause secondary pollution of groundwater. The first active substance and the second active substance may be the same or different.

[0040] According to the present invention, in step (2), the mass ratio of water, the second starch and the 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 can provide mechanical strength for the sustained-release material, while creating a large pore size and increasing the release rate of the drug. The matrix includes one or more of polytetrafluoroethylene (PTFE), polystyrene (PS), polyethylene (PE), and polypropylene (PP). The matrix serves as a skeleton material for the sustained-release material matrix and plays a supporting and bonding role. 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 will evaporate after the material is formed and will not be 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 feed ratio can form a layered wrapped structure, with the matrix material wrapped with 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 the sustained-release application, a graded release effect is formed, which prolongs the release time of the drug and increases the oxidation cycle.

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

[0044] (31) mixing a matrix with a solvent;

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

[0046] (33) The mixture obtained in step (32), product II and a strength agent are mixed uniformly.

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

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

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

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

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

[0052] According to the present invention, the application is to use the above-mentioned slow-release material as filler, fill it into permeable reaction walls, groundwater remediation wells and other remediation structures, and carry out in-situ chemical oxidation, in-situ chemical reduction and in-situ biological remediation of polluted groundwater. In the process of in-situ chemical oxidation and in-situ chemical reduction, when groundwater carries pollutants through the filler, it undergoes redox reaction with the active substances released by the above-mentioned slow-release material, so that the pollutants are removed and the groundwater is purified; in the process of in-situ biological remediation, the carbon source, nitrogen source, electron acceptor and other nutrients released by the slow-release material prepared by the above method provide continuous 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 remarkable technical effects:

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

[0055] Furthermore, in the method, the starch is modified with octenylsuccinic anhydride to make it have both hydrophilic and lipophilic properties. After being adsorbed and combined with activated carbon, it can not only help the activated carbon to firmly combine with the inorganic oxidant, but also improve the hydrophilicity of the activated carbon itself to promote the entry of polluted water into the pores, thereby helping the contact efficiency between high-efficiency pollutants and slow-release materials.

[0056] Furthermore, in the method, the biochar is modified so that the number of ester groups and hydroxyl functional groups on its surface is greatly increased and the number of carbonyl groups is reduced, which will form more covalent hydrogen bonds between the modified biochar and starch, enhance the adsorption capacity of starch, and thus allow the biochar to load more active substances and extend the release time; at the same time, the proportion of macropores (pore diameter > 50nm) inside the modified biochar is also increased compared to before modification, further increasing the adsorption capacity of starch particles.

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

[0058] (3) The sustained-release material prepared by the method of the present invention can effectively prolong the release period of the agent and stabilize the release rate during application. 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 dosage of the agent, and prevent pollution rebound. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1 This is a diagram showing the sustained release performance test effect of Example 1;

[0060] Figure 2 This is a diagram showing the sustained release performance test effect of Example 2;

[0061] Figure 3 This is a diagram showing the sustained release performance test effect of Example 3;

[0062] Figure 4 This is a graph showing the sustained release performance test effect of Comparative Example 1;

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

[0064] Figure 6 This is an application example of the remediation effect of slow-release materials on groundwater contaminated by petroleum hydrocarbons (TPH). DETAILED DESCRIPTION

[0065] The present invention will be further described below by way of examples, but the protection scope of the present invention is not limited by the examples.

[0066] In the present invention, the method for testing the sustained-release performance is: weigh 10g of the sustained-release material and place it in 1L of deionized water, and measure the content of the active substance in the water at regular intervals, and at the same time measure the level of organic matter in the water to detect whether the sustained-release material will cause secondary pollution of the water body. The test interval increases with the test time. For example, the test can be performed every 1 day in the initial stage, every 2 to 5 days in the middle stage, and every 10 days in the final stage. After each test, the deionized water that has been tested is replaced with fresh 1L of deionized water. Repeat the above steps regularly until the active substance cannot be detected in the deionized water. In the present invention, the content of the active substance in the water is tested by spectrophotometry. For example, in each case, when persulfate is used as the active substance, the test method for the persulfate content adopts the potassium iodide-ultraviolet spectrophotometry method. When ferrous salt is used as the active substance, the test method for the iron content adopts the o-phenanthroline spectrophotometry method. When glucose is used as the active substance, the glucose determination method is sampled by high-performance liquid chromatography.

[0067] In the present invention, the test method for organic matter in water adopts the method of "Determination of Volatile Organic Matter in Water Quality - Purge and Trap-Gas Chromatography (HJ 686-2014)".

[0068] In the present invention, the loading amount of active substances in the sustained-release materials prepared in each example is determined by an element analyzer. In the present invention, the release period is the time from the addition of the sustained-release material to the water until the active substances can no longer be detected in the water; the cumulative release rate of the sustained-release material is the sum of the mass of active substances measured each time during the release period, divided by the loading amount of active substances in the sustained-release material; the average release rate is the sum of the mass of active substances measured each time during 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 crushed through a 20-40 mesh sieve, isolated from oxygen in a nitrogen atmosphere, and heated at 550°C for 4.5 hours to obtain biochar. The biochar was exposed to air indoors for 60 days before the modification operation began.

[0072] The biochar was immersed in a mixed solution of methanol and HCl for 6 hours. In the mixed solution of methanol and HCl, the volume concentration of methanol was 99% and the concentration of HCl was 0.15 mol.L -1 The mass ratio of biochar to mixed solution was 1:20. After immersion, ultrapure water was used to cool and wash 20 times 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 -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 passed through a 40-60 mesh sieve to obtain modified biochar. It was determined that the pore volume of the modified biochar was 10% of the total pore volume of macropores (pore diameter>50nm).

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

[0074] Preparation of porous starch: Add corn starch to water and stir evenly to prepare a 30wt% starch suspension with a pH of 5.5. Preheat the suspension in a water bath for 30 minutes at a temperature of 30°C. Then, add a mixture of α-amylase and saccharifying enzyme in a mass ratio of 1:5.5 to the starch suspension, and the total amount of α-amylase and saccharifying enzyme added accounts for 0.11‰ of the mass of the suspension. Keep the suspension in a water bath at a constant temperature of 40°C and keep the reaction for 33 minutes. After filtering the reacted mixture to remove water, place it in a 45°C oven and dry it for 24 hours to obtain porous starch. The median pore size of the porous starch is 6.5μm.

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

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

[0077] 15 g of the first starch was added to 100 g of water, and the mixture was stirred to form an emulsion. Then 50 g of sodium persulfate was added to the emulsion to dissolve and mix. After stirring evenly, 45 g of modified biochar was added to the mixture. The mixture was placed in a magnetic stirrer and stirred for 2 h. Then 3 g of sodium alginate was added while stirring to form a colloid. The colloid was placed in a shaker and shaken for 45 min to allow the starch with active substances to be fully loaded into the modified biochar. The activated carbon after adsorption was then filtered, washed, and air-dried at 25 ° C for 48 h to obtain product I.

[0078] (2) Re-weigh some of the modified porous starch 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 materials is water: starch: sodium persulfate = 100:30:60.

[0079] (3) Mixing the product I obtained in step (1), the product II obtained in step (2), a strength agent, a matrix, and a solvent, and forming and drying them to obtain a sustained-release material. The specific steps are:

[0080] (31) mixing 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 uniformly mixed with product I;

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

[0083] It was determined that the mass fraction of sulfur in the slow-release material A in this example was 6.1 wt %, and the loading amount of sodium persulfate in the slow-release material A was calculated to be 23.17 wt %. The slow-release performance test results of the slow-release material in this example are as follows: Figure 1 As shown, it can be seen that the release of active substances can be divided into two stages: the first stage is from 0 to 9 days, which is the decomposition and release stage of the outer shell, characterized by a faster change in release rate and a steeper release curve; the second stage is from 10 to 165 days, which is the sustained 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 the effect of layered multi-level sustained release. The final test results show that the release period of sustained-release material A is 165 days. The cumulative release rate of sodium persulfate during the release period is 98.85wt%, and the average release rate is 1.41mg / (gd). During the entire sustained-release period, no organic matter was detected in the water, and the particles of the sustained-release material were never broken or disintegrated.

[0084] At the same time, the inventor replaced the modified activated carbon in this example with 60-mesh wood activated carbon (the pore volume occupied by macropores is 5.3% of the total pore volume), and conducted a parallel comparison experiment to prepare a slow-release material DA. It was determined that the mass fraction of sulfur in the slow-release material DA in this example was 5.93wt%, and the calculated loading amount of sodium persulfate in the slow-release material DA was 22.07wt%. The slow-release performance test results of the slow-release material in this example showed that the release period of the slow-release material DA was 135 days. The cumulative release rate of sodium persulfate during the release period was 97.9wt%, and the average release rate was 1.7mg / (gd). The test results of the slow-release material A compared with the slow-release material DA show that the use of modified activated carbon as a raw material further extends the release period of the agent and the release rate is more stable.

[0085] Example 2

[0086] (1) Preparation of modified biochar:

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

[0088] The biochar was immersed in a mixed solution of methanol and HCl for 8 hours. In the mixed solution of methanol and HCl, the volume concentration of methanol was 95% and the concentration of HCl was 0.05 mol.L -1 The mass ratio of biochar to mixed solution was 1:10. After impregnation, 0.5 mol.L -1 The modified biochar was washed with HCl solution for 10 times 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 with ultrapure water to remove unreacted methanol. After washing, it was dried at 30°C for 80 hours and passed through a 40-60 mesh sieve to obtain the modified biochar. It was determined that the pore volume of the modified biochar (pore size>50nm) accounted for 9% of the total pore volume.

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

[0090] Preparation of porous starch: Add potato starch to water and stir evenly to prepare a 15wt% starch suspension with a pH of 4.5. Preheat the suspension in a water bath for 20 minutes at a temperature of 25°C. Then, add a mixture of α-amylase and saccharifying enzyme in a mass ratio of 1:3.5 to the starch suspension, and the total amount of α-amylase and saccharifying enzyme added accounts for 0.07‰ of the mass of the suspension. Keep the suspension in a water bath at a constant temperature of 35°C and keep the reaction for 33 minutes. After filtering the reaction mixture to remove water, place it in a 55°C oven and dry it for 20 hours to obtain porous starch. The median pore size of the porous starch is 4.5μm.

[0091] Preparation of modified porous starch: Using the porous starch prepared above as raw material, add water to prepare a 25wt% starch emulsion, add octenyl succinic anhydride, the mass ratio of octenyl succinic anhydride to the porous starch in the starch emulsion is 1:30, keep the reaction at a constant temperature of 50°C in a water bath for 3 hours, and control the pH of the reaction solution to 10.5. Then, add hydrochloric acid to adjust the pH to 6 to terminate the reaction. Wash the reaction product, filter it, and dry it at 55°C for 10 hours to obtain modified porous starch.

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

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

[0094] (2) Re-weigh some of the modified starch 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) Mixing the product I obtained in step (1), the product II obtained in step (2), a strength agent, a matrix, and a solvent, and forming and drying them to obtain a sustained-release material. The specific steps are:

[0096] (31) mixing 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 uniformly mixed with product I;

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

[0099] It was determined that the mass fraction of sulfur in the sustained-release material B in this example was 5.98wt%, and the loading amount of active substances (potassium persulfate and calcium persulfate) in the sustained-release material B was calculated to be 22.88wt%. The sustained-release performance test results of the sustained-release material in this example are as follows: Figure 2 As shown, it can be seen that the release of active substances can be divided into two stages: the first stage is from 0 to 10 days, which is the decomposition and release stage of the outer shell, characterized by a faster change in release rate and a steeper release curve; the second stage is from 11 to 160 days, which is the sustained 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 the effect of layered multi-level sustained release. The final test results show that the release period of sustained-release material B is 160 days. The cumulative release rate of sodium persulfate during the release period is 97.9wt%, and the average release rate is 1.43mg / (gd). During the entire sustained-release period, no organic matter was detected in the water, and the particles of the sustained-release material were never broken or disintegrated.

[0100] Example 3

[0101] (1) Preparation of modified biochar:

[0102] The sawdust was dried at 40°C for 20 hours, then crushed through a 20-40 mesh sieve, isolated from oxygen in a nitrogen atmosphere, and heated at 650°C for 3 hours to obtain biochar. The biochar was exposed to air in a room for 30 days before the modification operation began.

[0103] The biochar was immersed in a mixed solution of methanol and HCl for 4 hours. In the mixed solution of methanol and HCl, the volume concentration of methanol was 97% and the concentration of HCl was 0.1 mol.L -1 The mass ratio of biochar to mixed solution was 1:15. After impregnation, 0.5 mol.L -1 The modified biochar was washed with HCl solution for 15 times 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 with ultrapure water to remove unreacted methanol. After washing, it was dried at 30°C for 80 hours and passed through a 40-60 mesh sieve to obtain the modified biochar. It was determined that the pore volume of the modified biochar (pore size>50nm) accounted for 8% of the total pore volume.

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

[0105] Preparation of porous starch: Add cassava starch to water and stir evenly to make a 25wt% starch suspension with a pH of 6.5. Preheat the suspension in a water bath for 25 minutes at a temperature of 28°C. Then, add a mixture of α-amylase and saccharifying enzyme in a mass ratio of 1:4.5 to the starch suspension, and the total amount of α-amylase and saccharifying enzyme added accounts for 0.03‰ of the mass of the suspension. Keep the suspension in a water bath at a constant temperature of 30°C and keep the reaction for 35 minutes. After filtering the reacted mixture to remove water, place it in a 50°C oven and dry it for 24 hours to obtain porous starch. The median pore size of the porous starch is 5.5μm.

[0106] Preparation of modified porous starch: Using the porous starch prepared above as raw material, add water to prepare a 35wt% starch emulsion, add octenyl succinic anhydride, the mass ratio of octenyl succinic anhydride to the porous starch in the starch emulsion is 1:45, keep the reaction at a constant temperature of 40°C in a water bath for 3h, and control the pH of the reaction solution to 8.5. Then, add hydrochloric acid to adjust the pH to 6 to terminate the reaction. Wash the reaction product, filter it, and dry it at 45°C for 16h to obtain the modified porous starch.

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

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

[0109] (2) Re-weigh some of the modified starch 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 materials is water: starch: ferrous sulfate = 100: 25: 55.

[0110] (3) Mixing the product I obtained in step (1), the product II obtained in step (2), a strength agent, a matrix, and a solvent, and forming and drying them to obtain a sustained-release material. The specific steps are:

[0111] (31) mixing 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 uniformly mixed with product I;

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

[0114] It was determined that the mass fraction of iron in the sustained-release material C in this example was 9.4 wt %, and the loading amount of ferrous sulfate in the sustained-release material C was calculated to be 25.51 wt %. The sustained-release performance test results of the sustained-release material in this example are shown in FIG. Figure 3 As shown, it can be seen that the release of active substances can be divided into two stages: the first stage is from 0 to 12 days, which 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 is from 13 to 162 days, which is the sustained 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 the effect of layered multi-level sustained release. The final test results show that the release period of sustained-release material C is 162 days. The cumulative release rate of sodium persulfate during the release period is 97.5wt%, and the average release rate is 1.52mg / (gd). During the entire sustained-release period, no organic matter was detected in the water, and the particles of the sustained-release material were never broken or disintegrated.

[0115] Example 4

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

[0117] The measured results show that the glucose loading in the sustained-release material D is 30.11 wt %. Figure 1 As shown, it can be seen that the release of active substances can be divided into two stages: the first stage is from 0 to 8 days, which is the decomposition and release stage of the outer shell, characterized by a faster change in release rate and a steeper release curve; the second stage is from 9 to 165 days, which is the sustained 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 the effect of layered multi-level sustained release. The final test results show that the release period of sustained-release material D is 165 days. The cumulative release rate of sodium persulfate during the release period is 97wt%, and the average release rate is 1.55mg / (gd). During the entire sustained-release period, no organic matter was detected in the water, and the particles of the sustained-release material were never broken or disintegrated.

[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 in steps (1) and (2) of Example 1 are added at once in step (1) of Example 1. The material feeding amount and other operation steps are the same as in Example 1.

[0120] After determination, the sustained release performance test results of this example sustained release material are as follows Figure 4 As shown, the results showed that the release period of the sustained-release material was only 9 days, and the slow-release effect was not achieved.

[0121] Application Examples

[0122] The principle of using slow-release materials to repair contaminated groundwater is as follows Figure 5As shown, the slow-release material A of Example 1 of the present invention is used as a filler and filled into a permeable reaction wall, and the permeable reaction wall is arranged in the flow path of organic contaminated groundwater. The contaminated groundwater penetrates through the wall, and the organic pollutants are oxidized and degraded by the active substances released by the slow-release material, and the pollutants are removed. The pollution removal rate can be calculated by testing the pollutant concentrations in the groundwater upstream and downstream of the permeable reaction wall respectively. In this application example, groundwater contaminated by petroleum hydrocarbons (TPH) was selected, and the concentration of influent petroleum hydrocarbons was (130±5) mg / L. The wall size was set to 10m*0.6m*5.8m, and 2 tons of slow-release material was filled as the wall filler at one time, and a pollution remediation application lasting 175 days was carried out. During this period, the TPH concentrations in the groundwater upstream and downstream of the permeable reaction wall were measured at regular intervals, and the pollution removal rate was calculated. The pollution remediation effect is shown in the figure. Figure 6 As shown. Within the 0th to 165th day, the TPH removal rate was maintained above 90wt%, and the highest was 97wt%. After the 165th day, most of the oxidants in the slow-release material had been released, and the pollution removal rate changed from high to low. This result shows that the slow-release performance of the slow-release material is stable, and the material can be continuously released within the slow-release period, successfully repairing the contaminated groundwater.

Claims

1. A method for preparing a sustained-release material, It is characterized in that The method includes: (1) dispersing the first starch in water, then adding the first active substance, activated carbon, and sodium alginate and mixing them evenly to obtain a product I; (2) dispersing the second starch in water, and then adding the second active substance and mixing evenly to obtain product II; (3) mixing the product I obtained in step (1), the 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 immersing the biochar in an acidic solution containing an organic alcohol.

2. The method according to claim 1, It is characterized in that The particle diameter of the modified biochar in step (1) is 40-60 mesh; the pore volume occupied by macropores (pore diameter>50nm) is more than 8% of the total pore volume, preferably 8%-10%.

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

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

5. The method according to any one of claims 1 to 4, It is characterized in that The first starch in step (1) and / or the first starch in step (2) is a modified porous starch; Furthermore, the preparation method of the modified porous starch comprises: dispersing the porous starch in water, adding octenyl succinic anhydride to react, filtering to obtain a solid, and drying to obtain the modified porous starch.

6. The method according to claim 5, It is 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).

7. The method according to claim 5, It is characterized in that In the preparation method of the modified porous starch, the reaction conditions are: the reaction temperature is 40 to 55° C.; and / or the pH value of the reaction solution is controlled to be 8.5 to 10.5; and / or the reaction time is 2 to 6 hours.

8. The method according to claim 5, It is characterized in that In the porous starch, the median pore diameter is 4.5 to 6.5 μm.

9. The method according to claim 5, It is characterized in that The method for preparing porous starch comprises: adding α-amylase and saccharifying enzyme to a suspension of starch and water, filtering and drying the filter residue obtained after the reaction, and obtaining porous starch.

10. The method according to claim 5, It is characterized in that In the method for preparing porous starch, the reaction conditions are: temperature 30-40° C., time 33-35 minutes; and / or, the mass ratio of α-amylase to saccharifying enzyme is 1:(3.5-5.5); and / or, the total amount of α-amylase and saccharifying enzyme added accounts for 0.03‰ to 0.11‰ of the mass of the suspension; And / or, the starch content in the suspension is 15wt% to 30wt%.

11. The method according to claim 1, It is 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, 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; Furthermore, the microbial nutrient includes at least one of glucose, lignin, nitrate and ferrous salt.

12. The method according to claim 1, It is characterized in that In step (1), the materials are fed in the following ratio, i.e., the mass ratio of water, sodium alginate, the first starch, the first active substance, and activated carbon is 100: (1-3): (5-15): (35-50): (30-45).

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

14. The method according to claim 1, It is 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).

15. A sustained-release material prepared by the method according to any one of claims 1 to 14.

16. Use of a sustained-release material prepared by the method according to any one of claims 1 to 14 in sustained-release of materials.

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