Composite pollution repairing agent as well as preparation method and application thereof

Abstract

The invention provides a composite pollution repairing agent as well as a preparation method and application thereof, and belongs to the technical field of environmental functional materials. The composite pollution repairing agent comprises biochar, nano zero-valent iron (nZVI) loaded on the biochar, cyclodextrin and heteroatoms, and at least part of the nZVI is wrapped in the cyclodextrin. According to the prepared composite pollution repairing agent, solid waste resource utilization can be effectively achieved, the removal rate of micro-plastics reaches 90% or above, and the removal rate of heavy metal is 100%. The composite pollution repairing agent has excellent performance and good application prospect, provides a feasible solution for micro-plastic and heavy metal composite pollution treatment, and shows remarkable practical application value.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of environmental functional materials, in particular to a composite pollution remediation agent, a preparation method thereof and application thereof in composite pollution removal. BACKGROUND

[0002] Microplastics, as a new environmental pollutant, are widely distributed in water, soil and atmosphere. Due to its high chemical stability and non-degradability, traditional physical adsorption and biological degradation methods have low removal efficiency, high cost and easy secondary pollution. For example, activated carbon adsorption method can only enrich microplastics but cannot completely degrade them, microbial degradation has a long cycle and is limited by environmental conditions, and advanced oxidation technology (such as Fenton method and persulfate advanced oxidation method) may produce toxic intermediates and has high processing cost. Especially for microplastics with a particle size of less than 100 μm, the removal efficiency of related remediation technologies is generally low. At the same time, microplastics coexist with heavy metals, forming composite pollution which poses a serious threat to the ecological environment and human health. This composite pollution changes the environmental behavior and toxicity effect of single pollutants, and causes more serious damage to the ecological system than single pollution. Therefore, it is of great significance to develop remediation technology for composite pollution of microplastics and heavy metals and to develop remediation materials.

[0003] Nanoscale zero-valent iron (nZVI) has great potential in the field of environmental pollution remediation due to its high specific surface area, strong reducing property and low cost. nZVI can degrade organic pollutants through adsorption, catalytic reduction and free radical oxidation mechanisms, but it still faces problems such as easy aggregation and easy oxidation inactivation in practical application. SUMMARY

[0004] Therefore, in order to at least partially solve at least one of the above-mentioned technical problems, the present application provides a composite pollution remediation agent, a preparation method thereof and application thereof.

[0005] According to an embodiment of one aspect of the present application, a composite pollution remediation agent is provided, comprising: biochar, and nZVI, cyclodextrin and heteroatom loaded on the biochar, at least part of the nZVI being wrapped in the cyclodextrin.

[0006] According to an embodiment of another aspect of the present application, a preparation method of a composite pollution remediation agent is provided, comprising: mixing biochar in a mixed solution containing iron salt, cyclodextrin and heteroatom-containing reagent, adding a reducing agent under the protection of an inert atmosphere, stirring and reacting, and separating the composite pollution remediation agent by magnetic separation.

[0007] According to an embodiment of the application, the application provides a composite pollution remediation agent, which comprises nZVI, biochar, beta-cyclodextrin and a heteroatom dopant.

[0008] The composite pollution remediation agent of the application is based on nZVI, and the nZVI is loaded on biochar to increase its dispersibility, thereby reducing agglomeration and improving the reaction activity of the nZVI. The beta-cyclodextrin introduced as a steric hindrance agent can also prevent the agglomeration of the nZVI, and the microplastics and heavy metals adsorbed on the surface of the composite pollution remediation agent are enriched on the surface of the nZVI to improve the reaction activity. The kirkendall effect is enhanced by the heteroatom doping, the formation of nano-cracks on the surface of the nZVI is promoted, the long-term slow release of the active ingredient nZVI is achieved, the passivation of the nZVI is delayed, and the problem of easy deactivation of the traditional nZVI is solved. The Fe-P-C ternary active interface is formed, the oxidation resistance and electron transfer capacity of the composite pollution remediation agent are improved, and the removal effect on the composite pollution is improved.

[0009] The preparation process of the composite pollution remediation agent of the application is simple, and the resource utilization of solid waste can be effectively realized. The removal efficiency of the microplastics is as high as 90% or more, and the removal rate of the heavy metals is 100%. The composite pollution remediation agent has excellent performance and good application prospect, provides a feasible solution for the treatment of the composite pollution of the microplastics and the heavy metals, and has significant practical application value. BRIEF DESCRIPTION OF DRAWINGS

[0010] Figure 1 The figure is a flowchart of the preparation method of the composite pollution remediation agent in the embodiment of the application.

[0011] Figure 2 The figure is a removal effect diagram of different composite pollution remediation agents on PVC microplastics in the embodiment of the application.

[0012] Figure 3 The figure is a removal effect diagram of different composite pollution remediation agents on heavy metal Cd in the embodiment of the application.

[0013] Figure 4 The figure is a result diagram of the amount of chloride ion precipitated in the composite pollution remediation agent / PVC microplastic system in the embodiment of the application.

[0014] Figure 5 The figure is a result diagram of the chloride ion precipitation rate constant in the composite pollution remediation agent / PVC microplastic system in the embodiment of the application.

[0015] Figure 6N2 adsorption / desorption curve and total pore size distribution results of different composite pollution remediation agents in the embodiments of the present application;

[0016] Figure 7 N2 adsorption / desorption curve and total pore size distribution results of different composite pollution remediation agents in the embodiments of the present application;

[0017] Figure 8 SEM image of the composite pollution remediation agent prepared in Embodiment 3 of the present application;

[0018] Figure 9 SEM image of the composite pollution remediation agent prepared in Embodiment 3 of the present application after 25 days of reaction;

[0019] Figure 10 EDS image of the composite pollution remediation agent prepared in Embodiment 3 of the present application;

[0020] Figure 11 Statistical chart of the content of elements contained in the composite pollution remediation agent prepared in Embodiment 3 of the present application by energy dispersive X-ray spectrometer. DETAILED DESCRIPTION

[0021] Hereinafter, embodiments of the present application will be described with reference to the accompanying drawings. It should be understood, however, that the description which follows is merely illustrative and is not intended to limit the scope of the present application. In the following detailed description of embodiments of the present application, numerous specific details are set forth in order to provide a thorough understanding of the present application. However, it will be apparent to one skilled in the art that one or more embodiments of the present application can be practiced without these specific details. In other instances, well-known structures and functions have not been described in detail in order to avoid obscuring the concepts of the present application.

[0022] The terms used herein are merely used to describe specific embodiments and are not intended to limit the present application. The term "include" used herein indicates the presence of a feature, step, operation, but does not exclude the presence or addition of one or more other features.

[0023] In the process of realizing the inventive concept, it is found that nZVI has great potential in environmental pollution remediation due to its high specific surface area, strong reducing property and low cost, but it still faces problems such as easy aggregation and easy oxidation inactivation in practical application. Although bimetallic modification can significantly enhance the reducing effect of nZVI and provide some special reaction mechanisms, the problem of easy aggregation also limits its application in pollutant removal. Therefore, the present application selects biochar to load nZVI, which can increase the dispersity of nZVI and thus provide more active sites for the reduction of pollutants. β-cyclodextrin can enrich microplastics and heavy metals adsorbed on the surface of the composite pollution remediation agent to the surface of nZVI to improve its reactivity. Heteroatom doping can also effectively improve the hydrophobicity of nZVI, thereby reducing the hydrogen evolution reaction of nZVI with water and promoting the transfer of electrons from nZVI to pollutants, and improving the electron selectivity of nZVI.

[0024] Specifically, according to an embodiment of one aspect of the present application, a composite pollution remediation agent is provided, comprising: biochar, and nZVI, cyclodextrin and heteroatom loaded on the biochar, at least part of the nZVI being wrapped in the cyclodextrin.

[0025] According to an embodiment of the present application, by combining biochar, nZVI, cyclodextrin and heteroatom, a "adsorption-enrichment-degradation" synergistic system is constructed, i.e. biochar adsorbs heavy metals, β-cyclodextrin captures microplastics, heteroatom prolongs nZVI passivation, and nZVI degrades microplastics and heavy metals through reduction and dechlorination processes, providing a solution with high efficiency, economy and sustainability for the remediation of microplastic and heavy metal composite pollution.

[0026] According to an embodiment of the present application, nZVI can remove various pollutants in the environment through mechanisms such as catalytic reduction, adsorption and free radical oxidation. Its reducing property can directly or indirectly reduce pollutants through electron transfer, converting them into low-toxicity or easily removable forms. For example: high-valence ions of many heavy metals (such as Cd, Pb, Hg, Ag, etc.) have oxidizing property and can be reduced to low-valence or elemental state by nZVI, and then removed by precipitation, adsorption, etc. nZVI can also break the C-Cl bond in chlorinated organic matter through electron transfer to achieve dechlorination reduction, generating low-chlorine or chlorine-free small molecule organic matter, significantly reducing its toxicity. nZVI is easy to oxidize in water environment, generating Fe 2+ , Fe 3+Plasma, further forming iron oxides (such as FeO, Fe2O3), hydroxides (such as Fe(OH)2, Fe(OH)3) or oxyhydroxides (such as FeOOH). These oxidation products have high specific surface area and abundant surface functional groups (such as -OH), which can remove pollutants by adsorption and separate them from the water body, achieving the effect of purifying the water environment. Under aerobic conditions, the corrosion process of nZVI may be accompanied by the generation of reactive oxygen species (ROS) (such as ·OH, O2 - ·etc.), which have strong oxidizing properties and can indirectly oxidize phenolic, dye and other pollutants.

[0027] According to the embodiment of the present application, the biochar can increase the dispersibility of nZVI to provide more active sites for the reduction of organic matter. In addition to improving the dispersibility of nZVI, the introduction of biochar can also enhance the hydrophobicity of nZVI, accelerate electron transfer, enhance the adsorption of pollutants, and form a micro-electrolysis system, thereby improving the ability of nZVI to repair composite pollution.

[0028] According to the embodiment of the present application, the cyclodextrin is selected from at least one of α-cyclodextrin, β-cyclodextrin, γ-cyclodextrin, α-cyclodextrin polymer, β-cyclodextrin polymer, γ-cyclodextrin polymer, and preferably β-cyclodextrin.

[0029] According to the embodiment of the present application, the biochar and cyclodextrin are used to load nZVI, and the cyclodextrin acts as a molecular interface modifier. By virtue of its unique hydrophobic cavity and hydrophilic outer wall structure, the cyclodextrin preferentially includes hydrophobic pollutants such as microplastics, and through the "molecular enrichment effect", the target pollutants are transported to the active sites of nZVI. At the same time, the cyclodextrin also wraps nZVI, which can inhibit the side reactions (Fe 0 + 2H2O → Fe 2+ + H2↑ + 2OH - , 2Fe 0 + O2 + 2H2O → 2Fe 2+ + 4OH - ) of nZVI with oxygen and water, and enhances the reaction activity and long-acting property of nZVI. The cyclodextrin can also act as a steric hindrance agent to prevent the aggregation of nZVI and improve the reaction activity of nZVI.

[0030] According to the embodiment of the present application, the heteroatom is selected from at least one of nitrogen, phosphorus and sulfur atoms, and preferably a phosphorus atom.

[0031] According to an embodiment of the present application, the heteroatom enhances the kirkendall effect by electronic structure regulation of the composite pollution remediation agent, promotes the formation of nano cracks, greatly increases the density of active sites, can release the active ingredient nZVI for a long time, prolongs the passivation of nZVI, solves the problem of easy deactivation of traditional nZVI. In addition, the nano cracks can also enhance the electron transfer ability and antioxidant stability of nZVI, while optimizing the pollutant enrichment efficiency of cyclodextrin, realizing the synergistic improvement of material activity and service life, and making the composite pollution remediation agent have high efficient degradation and controlled release functions.

[0032] Figure 1 The flowchart of the preparation method of the composite pollution remediation agent in the embodiment of the present application is shown.

[0033] According to an embodiment of another aspect of the present application, a preparation method of a composite pollution remediation agent is provided, as shown in Figure 1 The method comprises steps S1-S3.

[0034] Step S1: The biochar is placed in a mixed solution containing iron salt, cyclodextrin and heteroatom-containing reagent for mixing.

[0035] Step S2: Add a reducing agent under the protection of an inert atmosphere and stir the reaction.

[0036] Step S3: The composite pollution remediation agent is obtained by magnetic separation.

[0037] According to an embodiment of the present application, a long-acting composite pollution remediation agent based on controlled release technology is constructed by one-pot method on the basis of liquid phase reduction method. Through in-situ compounding, the loss of physical and chemical properties of components (such as oxidation and agglomeration) in multi-step preparation can be reduced, and the synergistic efficiency of each component can be improved. Compared with step-by-step preparation, one-pot method can reduce energy consumption and raw material loss, and is suitable for large-scale production. The preparation method of the present application can be efficiently operated under normal temperature and pressure conditions, and the process operation is simple and easy to control. The composite pollution remediation agent obtained after reaction can be quickly recovered by magnetic separation, and has high removal efficiency and long-acting advantages for microplastics and heavy metals, and has significant engineering application value.

[0038] According to the embodiment of the present application, before step S1, the preparation method of the biochar comprises: ball milling the cleaned and dried crab shells to obtain crab shell powder; and pyrolyzing the crab shell powder under an inert gas atmosphere to obtain the biochar. Specifically, the discarded crab shells are repeatedly washed with deionized water until neutral, so as to remove the surface salt, protein residues and attached pollutants, and the ultrasonic cleaning is assisted to remove the deep impurities. Then, the crab shells are placed in a 60°C oven for 12-14h to constant weight. The dried crab shells are added into a ball mill for ball milling treatment, and are prepared through a 20-mesh sieve. The grinding body used for the ball milling treatment is a zirconia ball, and the weight ratio of the zirconia ball to the added amount of the crab shells is 30-60:1, for example, which can be 30:1, 35:1, 45:1, 50:1 or 60:1; the ball milling speed is 200-600 rpm, for example, which can be 200 rpm, 300 rpm, 400 rpm, 500 rpm or 600 rpm, and the ball milling time is 8-16h, for example, which can be 8h, 10h, 12h, 14h or 16h. The sieved crab shell powder is placed into a crucible, compacted and then placed in a tube furnace for pyrolysis under an inert gas N2 atmosphere at a high temperature of 500-900°C for 2-6h to obtain the crab shell-based biochar. The pyrolysis time is preferably 4h, and the pyrolysis temperature can be, for example, 500°C, 700°C or 900°C.

[0039] According to the embodiment of the present application, a low-cost preparation process of an environmentally friendly biochar material is developed by using discarded crab shells as raw materials, which has the characteristics of low cost and environmental friendliness. A porous biochar (specific surface area >70 m 2 / g) is prepared by a high-temperature pyrolysis method, and the three-dimensional hierarchical porous structure thereof is used as a carrier and an electronic medium of nZVI, which not only solves the problem of solid waste disposal, realizes the high-value utilization of biochar resources, significantly reduces the preparation cost of the composite pollution remediation agent, and improves the possibility of field application. At the same time, the defects of easy oxidation of traditional nZVI are overcome, the abundant oxygen-containing functional groups (such as carboxyl and hydroxyl) and defect sites of the crab shell biochar not only effectively inhibit the agglomeration of nZVI particles, significantly improve the adsorption capacity for heavy metals, but also enhance the reaction activity of the composite pollution remediation agent through electron transfer.

[0040] According to the embodiment of the present application, as Figure 1As shown, in step S1, the iron salt is selected from any one of a divalent iron salt or a trivalent iron salt, for example, can be ferrous nitrate, ferrous sulfate, ferric nitrate, ferric sulfate, preferably ferrous sulfate heptahydrate, the mass ratio of the iron salt to the biochar is 0.2-5:1, for example, can be: 0.2:1, 0.8:1, 1:1, 2:1, 3:1, 4:1, 5:1, preferably 1:1; the mass ratio of the biochar to the cyclodextrin is 0.08-0.8:1, for example, can be: 0.08:1, 0.2:1, 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1.

[0041] According to an embodiment of the present application, in step S1, the heteroatom-containing reagent is selected from at least one of a nitrogen-containing reagent, a phosphorus-containing reagent or a sulfur-containing reagent, for example, can be at least one or a combination of multiple of: potassium dihydrogen phosphate, urea, phosphoric acid, dipotassium hydrogen phosphate, phytic acid, thiourea, preferably the phosphorus-containing reagent potassium dihydrogen phosphate solution, the mass ratio of the biochar to the heteroatom-containing reagent is 0.2-2:1, for example, can be: 0.2:1, 0.4:1, 0.6:1, 0.8:1, 1:1, 1.2:1, 1.5:1, 1.8:1, 2:1.

[0042] According to an embodiment of the present application, in step S1, the phosphorus-containing reagent as a dopant has better effects in terms of material performance improvement and pollutant removal efficiency. Specifically, (1) the phosphorus atom-containing dopant can enhance electron transfer efficiency and reduce passivation: nZVI sulfidation usually forms a FeS shell layer, which can improve electron transfer, but may still be passivated due to thickening of the iron oxide shell after long-term reaction. Phosphidation of nZVI forms FePO4 or Fe-P bonding structure, which not only promotes electron conduction, but also induces a Kirkendall effect during the reaction process to form a nano-crack structure, continuously exposing fresh active sites and delaying passivation. (2) The phosphorus atom-containing dopant can increase the specific surface area and active site density: phosphidation modification can optimize the surface chemical properties of the composite pollution remediation agent, increase the number of hydroxyl (-OH) and phosphate (-PO4) functional groups, and enhance the coordination adsorption capacity for heavy metals. Compared with sulfidation nZVI, the nano-crack structure of phosphidation nZVI can provide more exposed Fe 0 active sites, improving reaction kinetics. (3) The phosphorus atom-containing dopant can enhance pH adaptability and stability: sulfidation nZVI is easily dissolved in acidic conditions (FeS + 2H + → Fe 2+ + H2S), while the FePO4 structure of phosphidation nZVI is more stable in a wide pH range (pH 4-10) and is suitable for complex water body environments. (4) Sulfidation nZVI mainly removes Cd(II) through adsorption-reduction-co-precipitation, but there is competitive adsorption (such as competition for active sites with Pb(II)), which limits the removal rate of Cd(II). The phosphate groups (PO4 3-) preferentially bind Cd 2+ , forming stable Cd3(PO4)2precipitates, reducing the effect of competitive adsorption. Therefore, the present application introduces P doping to form a Fe-P-C ternary active interface, which can improve the material's oxidation resistance and electron transfer ability, and improve the removal effect of composite pollution.

[0043] According to an embodiment of the present application, in step S2, the reducing agent is selected from any one of NaBH4 or KBH4, preferably NaBH4, the molar ratio of the dropwise addition amount of the reducing agent to the amount of iron salt added is 1-5:1, preferably 3:1; the stirring reaction time is 0.5-1.0h, and the reaction temperature is 15-28℃, preferably 25℃.

[0044] According to an embodiment of the present application, in step S2, NaBH4 is used as a strong reducing agent to release hydrogen anions (H - ) in an aqueous solution, reducing Fe 2+ to Fe 0 , while being oxidized to sodium metaborate (BO2 - ) itself. The reducing agent releases heat when it comes into contact with water, so it needs to be added slowly and at a low temperature (15-28℃). To prevent nZVI oxidation, N2 needs to be continuously introduced during the dropwise addition process.

[0045] According to an embodiment of the present application, in step S3, the reaction solution is subjected to magnetic separation and freeze-drying to obtain a composite pollution remediation agent. The freeze-drying time is 12-24h, for example, it can be 12h, 14h, 18h, 20h, or 24h; the temperature is -50~-80℃, for example, it can be -50℃, -60℃, -70℃, or -80℃.

[0046] According to an embodiment of the present application, in step S3, nZVI has strong ferromagnetism and can be quickly adsorbed and separated by an external magnetic field, while impurities such as reducing agents, unreacted Fe 2+ / Fe 3+ , and NaBH4 decomposition products remain in the liquid phase due to the lack of magnetism. Freeze-drying is a key step to remove the reaction solvent, obtain a dry composite pollution remediation agent, and maximize its dispersibility and activity.

[0047] According to an embodiment of another aspect of the present application, an application of a composite pollution remediation agent is provided, which includes using the composite pollution remediation agent to remove microplastic and heavy metal composite pollution; the microplastic includes at least one of polystyrene microplastic, polyethylene microplastic, and polyvinyl chloride microplastic; and the heavy metal includes at least one of Cd, As, and Pb.

[0048] According to the embodiment of the present application, the composite pollution remediation agent can effectively remove microplastics and heavy metal composite pollution, and provides a solution with high efficiency, economy and sustainability for composite pollution treatment.

[0049] According to the embodiment of the present application, the composite pollution remediation agent has a dosage of 0.5-5 g / L in removing composite pollution, for example, 0.5 g / L, 1 g / L, 2 g / L, 3 g / L, 4 g / L, 5 g / L; the reaction time is 10-30 d, for example, 10 d, 20 d, 30 d; the microplastic addition amount is 0.1%-1%, for example, 0.1%, 0.5%, 1%; and the heavy metal concentration is 20-100 mg / L, for example, 20 mg / L, 50 mg / L, 80 mg / L, 100 mg / L.

[0050] The present application will be further described in detail with reference to the specific embodiments, and the embodiments are only for illustrating the present application, but not for limiting the scope of the present application. The embodiments provided below can be used as a guide for further improvement by those skilled in the art, and do not constitute any limitation on the present application.

[0051] The experimental methods in the following embodiments are all conventional methods, and are carried out according to the techniques or conditions described in the literature in the art or according to the product instructions, unless otherwise specified. The materials, reagents and the like used in the following embodiments can be obtained from commercial channels, unless otherwise specified.

[0052] Preparation Example:

[0053] The preparation method of the biochar is shown in steps (1)-(3):

[0054] (1) The discarded crab shells are repeatedly washed with deionized water until neutral, assisted by ultrasonic cleaning, and then placed in a 60℃ oven for 12 h to constant weight;

[0055] (2) The dried crab shells in step (1) are added to a ball mill for ball milling treatment, and then passed through a 20-mesh sieve to obtain crab shell powder.

[0056] (3) The sieved crab shell powder in step (2) is placed in a crucible, compacted, and then placed in a tube furnace and pyrolyzed at 500℃, 700℃, and 900℃ under N2 for 4 h, respectively, to obtain respective corresponding biochar.

[0057] Example 1

[0058] (1) Composite pollution remediation agent CBC 500Preparation of P-nZVI@ -CD: 2.482 g of FeS04-7H20, 0.5 g of biochar (crab shell powder pyrolyzed at 500 °C), 1.5 g of β-cyclodextrin ( -CD) and 0.659 g of KH2P04 were weighed into 500 mL of ultrapure water and mixed, and then transferred to a 1000 mL three-necked flask and stirred for 2 h under N2 atmosphere to fully mix. At the same time, a NaBH4 solution was prepared (1.445 g dissolved in 300 mL of ultrapure water, three times the molar mass of Fe to ensure that Fe is fully reduced), and the pH was adjusted to 11 with 0.5 M NaOH. A peristaltic pump was used to slowly add the NaBH4 solution to the three-necked flask at a low speed of 10 rpm to fully reduce the iron salt to nZVI, and after the dropwise addition was completed, the stirring was continued for 30 min for aging. Subsequently, the black precipitate was separated by magnetic separation, washed with ultrapure water and ethanol several times, and freeze-dried for 12 h to obtain the composite pollution remediation agent CBC 500 P-nZVI@ -CD (phosphorus-nZVI coated with -cyclodextrin using 500 °C biochar as a carrier) was stored in an anaerobic box for standby use.

[0059] (2) CBC 500 P-nZVI@ -CD degradation of polyvinyl chloride (PVC) microplastics: PVC microplastics were selected as the characteristic pollutants for material adsorption and degradation performance tests. The PVC microplastic removal and degradation experiment was carried out in a 100 mL headspace bottle, and 100 mL of ultrapure water was added. The specific steps are as follows: first, 0.2% (w / w) of PVC microplastics (m0) was added to 100 mL of ultrapure water. Subsequently, 200 mg (2 g / L) of CBC 500 P-nZVI@ -CD, the jaws were covered with a polytetrafluoroethylene (PTFE) liner, and the reaction was carried out in a horizontal shaking box (180 rpm) at 25 ± 2 °C. Samples were taken from the reaction mixture at specific times (0, 1, 2, 4, 7, 10, 15, 20, 25 d), and nZVI was separated using magnetic separation technology. Subsequently, 1.5 mL of supernatant was collected and filtered using a 0.45 μm polytetrafluoroethylene (PTFE) membrane, and the filtered sample was placed in a 1.5 mL chromatographic sample bottle to detect the Cl - concentration released in the system.

[0060] At the 25th d, all supernatant was collected by magnetic separation technology, and the water sample was vacuum filtered, the filter membrane was washed with ultrapure water for 3 times, and the filter membrane was transferred to a glass culture dish and dried at 40°C for standby. The dried sample was mixed with the floatation liquid (NaI) at a ratio of 1:3, and shaken for 30 minutes. Then it was placed for 30 minutes, and the PVC particles floated to the liquid surface, and the supernatant was sucked with a glass syringe and vacuum filtered. The filter membrane was washed with ultrapure water for 3 times, and the filter membrane was transferred to a glass culture dish and dried at 40°C for standby. The dried sample was weighed (m), and the removal efficiency of PVC microplastics was calculated ).

[0061] (3) CBC 500 Degradation of heavy metal Cd by P-nZVI@β-CD: Select heavy metal Cd as the characteristic pollutant, and test the adsorption and degradation performance of the material. The heavy metal Cd adsorption experiment was carried out in a 100 mL headspace bottle, and the specific steps were as follows: 50 mg·L -1 of Cd 2+ solution was prepared, 100 ml was transferred to a 100 mL headspace bottle, CBC 500 -P-nZVI@β-CD (2 g·L -1 ) was added, it was covered with a polytetrafluoroethylene (PTFE) lined jaw cover, and was placed in a horizontal shaking box (180 rpm) at 25±2°C for reaction. At a certain time (0, 0.25, 0.5, 1, 2, 4, 6 h), the repair material was separated by magnetic separation technology. Then, 1.5 mL of supernatant was collected, filtered with a 0.45 μm polytetrafluoroethylene (PTFE) membrane, and the filtered sample was placed in a 1.5 mL chromatographic sample bottle to determine the residual concentration of Cd 2+ .

[0062] Example 2

[0063] The preparation method and pollutant removal method of Example 1 are consistent, except that the pyrolysis temperature of biochar is 700°C, and the composite pollution repair agent CBC 700 -P-nZVI@β-CD is obtained.

[0064] Example 3

[0065] The preparation method and pollutant removal method of Example 1 are consistent, except that the pyrolysis temperature of biochar is 900°C, and the composite pollution repair agent CBC 900 -P-nZVI@β-CD is obtained.

[0066] Example 4

[0067] The preparation method and the pollutant removal method of Example 3 are consistent, except that Na2S2O4 (0.329 g) is selected as the dopant containing impurity atoms to obtain the composite pollution remediation agent CBC 900 -S-nZVI@β-CD.

[0068] Figure 10 The energy dispersive X-ray spectrum (EDS) of the composite pollution remediation agent prepared in Example 3 of the application is shown in the figure; Figure 11 The figure shows the element content statistics of the composite pollution remediation agent prepared in Example 3 of the application by an energy dispersive X-ray spectrometer.

[0069] According to Figure 10 It can be seen that the CBC 900 -P-nZVI@β-CD has successfully realized P doping, and the doping amount is 12.14 wt% ( Figure 11 ).

[0070] The removal rates of heavy metal Cd, PVC microplastics, Cl- release amount and release rate constant in Examples 1-4 are shown in Table 1:

[0071] Table 1

[0072]

[0073] Figure 2 The figure shows the removal effect of different composite pollution remediation agents on PVC microplastics in the examples of the application; Figure 3 The figure shows the removal effect of different composite pollution remediation agents on heavy metal Cd in the examples of the application; Figure 4 The figure shows the Cl- release amount in the composite pollution remediation agent / PVC microplastic system in the examples of the application; Figure 5 The figure shows the Cl- release rate constant in the composite pollution remediation agent / PVC microplastic system in the examples of the application; Figure 7 The figure shows the N2 adsorption / desorption curve and total pore size distribution of different composite pollution remediation agents in the examples of the application.

[0074] As shown in Table 1, the removal rates of different composite pollution remediation agents prepared in Examples 1-4 on PVC microplastics all reach more than 80% ( Figure 2 ), and the removal rates of heavy metal Cd are all 100% ( Figure 3 ). The Cl - release amount in the system of Example 3 is the highest ( Figure 4 ), and the release rate constant is the largest ( Figure 5 ), which indicates that the high-temperature carbonization temperature of biochar is a key factor affecting the degradation ability of the composite material. The 900℃ carbonized biochar has a highly graphitized structure and abundant mesopores ( Figure 7), significantly enhancing the electron transfer efficiency and storing the dechlorination reaction of PVC. At the same time, P-doping has better comprehensive performance than S-doping by enhancing electron transfer, optimizing interface reaction and improving stability.

[0075] Comparative Example 1

[0076] (1) Preparation of nZVI: 2.482 g of FeSO4·7H2O was dissolved in 500 mL of ultrapure water and transferred to a 1000 mL three-necked flask, and stirred for 1 h under N2atmosphere. At the same time, NaBH4solution was prepared (1.445 g dissolved in 300 mL of ultrapure water, three times the molar mass of Fe, to ensure that Fe is fully reduced), and the pH was adjusted to 11 with 0.5 M NaOH. A peristaltic pump was used to slowly add the NaBH4solution to the three-necked flask at a low speed of 10 rpm to fully reduce the iron salt to nZVI, and after the dropwise addition was completed, the stirring was continued for 30 min. Subsequently, the black precipitate was separated by magnetic separation, washed with ultrapure water and ethanol several times, and freeze-dried for 12 h to obtain the nZVI material, which was stored in an anaerobic box for use.

[0077] (2) The pollutant removal method of Comparative Example 1 was consistent with that of Example 1.

[0078] Comparative Example 2

[0079] The preparation method and pollutant removal method of Example 3 were consistent, except that no β-cyclodextrin and KH2PO4were added during the preparation process, and CBC 900 -nZVI was obtained.

[0080] Comparative Example 3

[0081] The preparation method and pollutant removal method of Example 3 were consistent, except that no KH2PO4was added during the preparation process, and CBC 900 -nZVI@β-CD was obtained.

[0082] Comparative Example 4

[0083] The preparation method and pollutant removal method of Example 3 were consistent, except that no β-cyclodextrin was added during the preparation process, and CBC 900 -P-nZVI was obtained.

[0084] The removal rates of heavy metals Cd, PVC microplastics, Cl - precipitation rates and constants of Example 3 and Comparative Examples 1-4 are shown in Table 2:

[0085] Table 2

[0086]

[0087] Figure 6 N2 adsorption / desorption curves and total pore size distribution results of different composite pollution remediation agents in the embodiments of the present application; Figure 8 SEM image of the composite pollution remediation agent prepared in Example 3 of the present application; Figure 9 SEM image of the composite pollution remediation agent prepared in Example 3 of the present application after 25 days of reaction.

[0088] As can be seen from Table 2, compared with Comparative Examples 1-4, the removal efficiency of PVC in Example 3 is the highest, Figure 2 ), and the Cl - release amount is the highest, Figure 4 , which indicates that the biochar, β-CD and P doping all play a key role in the degradation process. The biochar pyrolyzed at 900℃ provides a highly graphitized conductive network and abundant mesoporous structure, Figure 6 , which significantly improves the electron transfer efficiency and pollutant adsorption capacity. β-CD selectively enriches PVC microplastics through molecular encapsulation and transports them to the active sites of nZVI. P doping enhances the co-kendall effect and promotes the formation of nano-cracks, Figure 8 , which maintains the stability of the material after 25 days of reaction, Figure 9 , and significantly enhances the oxidation stability of nZVI. The synergistic effect of biochar, β-CD and P doping can promote the efficient removal of PVC and maximize the release of Cl - , and enhance the stability and activity of nZVI, and improve the environmental adaptability of nZVI.

[0089] The above specific embodiments further illustrate the purpose, technical solutions and beneficial effects of the present application. It should be understood that the above description is only for specific embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A composite pollution remediation agent, characterized by, Comprise: biochar, and nano zero-valent iron, cyclodextrin and heteroatom supported on the biochar, at least part of the nano zero-valent iron is wrapped in the cyclodextrin.

2. The composite pollution remediation agent according to claim 1, characterized in that: the cyclodextrin is selected from at least one of α-cyclodextrin, β-cyclodextrin, γ-cyclodextrin, α-cyclodextrin polymer, β-cyclodextrin polymer, γ-cyclodextrin polymer; the heteroatom is selected from at least one of nitrogen, phosphorus, sulfur atoms.

3. A method for preparing the composite pollution remediation agent according to claim 1 or 2, characterized by, Comprise: Mixing the biochar in a mixed solution containing iron salt, cyclodextrin and heteroatom-containing reagent, adding reducing agent under the protection of inert atmosphere, stirring reaction, and separating the composite pollution remediation agent by magnetic separation.

4. The preparation method according to claim 3, characterized in that: the reducing agent is selected from any one of NaBH4 or KBH4; the stirring reaction time is 0.5-1.0 h, and the reaction temperature is 15-28℃.

5. The preparation method according to claim 3, characterized in that, The preparation method of the biochar comprises: ball milling the cleaned and dried crab shells to obtain crab shell powder; pyrolyzing the crab shell powder under an inert gas atmosphere to obtain biochar.

6. The preparation method according to claim 5, characterized in that, The inert gas used in the pyrolysis process is N2, the pyrolysis time is 2-6 h, and the pyrolysis temperature is 500-900℃.

7. The preparation method according to claim 3, characterized in that, The iron salt is selected from any one of divalent iron salt or trivalent iron salt; The heteroatom-containing reagent is selected from at least one of nitrogen-containing reagent, phosphorus-containing reagent or sulfur-containing reagent.

8. The preparation method according to claim 3, characterized in that: the mass ratio of the iron salt to the biochar is 0.2-5:1; the molar ratio of the reducing agent to the iron salt is 1-5:1; the mass ratio of the biochar to the cyclodextrin is 0.08-0.8:1; the mass ratio between the biochar and the heteroatom-containing reagent is 0.2-2:

1.

9. The preparation method according to claim 3 or 7, characterized in that: the heteroatom-containing reagent is selected from at least one of potassium dihydrogen phosphate, urea, phosphoric acid, dipotassium hydrogen phosphate, phytic acid, thiourea, or a combination of one or more thereof.

10. Use of the composite pollution remediation agent according to claim 1, wherein: the use comprises using the composite pollution remediation agent to remove microplastic and heavy metal composite pollution; the microplastic comprises at least one of polystyrene microplastic, polyethylene microplastic and polyvinyl chloride microplastic, and the heavy metal comprises at least one of Cd, As and Pb.

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