Slow-release nano calcium peroxide, preparation method thereof, and intelligent permeable reaction wall and application thereof

Abstract

This invention provides a slow-release nano-calcium peroxide, its preparation method, and an intelligent permeable reactive barrier and its application, relating to the field of water treatment technology. In this invention, sodium hydroxide is added under pH ≥ 11 conditions to hydrolyze polyvinylpyrrolidone, exposing a large number of unsaturated functional groups; subsequently, calcium salt and Na+ are added. + The displacement reaction forms a relatively stable primary encapsulation layer; polyvinylpyrrolidone is added again for secondary encapsulation to maximize the slow-release effect of the core and shell. The slow-release nano-calcium peroxide has pH self-regulation and promotes iron ion microcirculation. This invention also provides an intelligent permeable reactive barrier, a spatiotemporally ordered three-stage intelligent reactive barrier of "reduction-oxidation-purification," which can autonomously maintain the optimal reaction pH, autonomously drive iron circulation, and autonomously arrange the sequence of reduction and oxidation reactions through the synergistic effect of its internal components, ultimately forming a highly efficient, durable, stable, and truly "passive" groundwater remediation system.

Description

Technical Field

[0001] This invention relates to the field of water treatment technology, and in particular to a slow-release nano-calcium peroxide and its preparation method, and an intelligent permeable reactive barrier and its application. Background Technology

[0002] Permeable Reactive Barrier (PRB) technology is one of the core technologies in the field of in-situ groundwater remediation. Its basic principle is to construct a wall composed of active reactive media along the groundwater flow path. When contaminated groundwater flows through this wall driven by a hydraulic gradient, the pollutants react with the wall filler material through physical, chemical, or biological reactions (such as adsorption, precipitation, redox, and degradation), thereby being removed or transformed into harmless substances, achieving the interception and purification of the pollution plume. Among various PRB fillers, nano-zero-valent iron (nZVI) has become the most widely used active medium due to its wide availability, low cost, strong reducing power, and environmental friendliness. The remediation mechanism of nZVI is mainly based on its strong reducing properties (standard electrode potential E). 0 With a voltage of -0.44 V, nano-zero-valent iron (nZVI) can reduce and degrade highly toxic pollutants in groundwater (such as tetrachloroethylene (PCE) and trichloroethylene (TCE)) into less toxic intermediate products (such as dichloroethylene (DC) and vinyl chloride (VC)) through direct electron transfer or the generation of reduced hydrogen. However, nano-zero-valent iron (nZVI) faces challenges in its application, including easy oxidation and deactivation, and a narrow applicability to a limited range of pollutants (only applicable to electron-gaining pollutants such as halogenated hydrocarbons, heavy metals, and nitro compounds).

[0003] To overcome the limitations of single nZVI-PRB in treating complex pollutants (especially oxidizing or recalcitrant organic compounds), research trends are shifting towards constructing multifunctional synergistic composite PRB systems. For example, nZVI is mixed with adsorbents, catalysts, or oxidants to achieve synergistic effects of multiple reaction mechanisms. For instance, related technologies disclose PRBs using "Hangjin No. 2 soil loaded with nano-zero-valent iron" as filler, with magnets on both sides of the wall to form an external magnetic field. The core principle is to utilize the external magnetic field to enhance the reactivity of nZVI, inhibit its passivation, and oxidize and degrade pollutants by generating sulfate radicals through the reaction of nZVI with persulfate. However, it is difficult to achieve the desired transition metal ion Fe in the nZVI / persulfate system. 2+ / Fe 3+The effective cycle of this method cannot achieve a sustained self-driven oxidation system. Furthermore, it relies on an external physical field (magnetic field) to enhance the reaction, requiring additional energy input. Related technologies disclose a method for degrading organic pollutants by combining persulfate and calcium peroxide. The principle is that the dual oxidants can simultaneously generate sulfate radicals and hydroxyl radicals, expanding the degradation range of pollutants. Although theoretically, the superoxide radical anions in the calcium peroxide-based Fenton system can reduce Fe in the reaction system to a certain extent... 3+ For Fe 2+ This allows for the continuous production of sulfate and hydroxyl radicals in the reaction system. However, the decomposition of calcium peroxide to produce calcium hydroxide and other substances rapidly increases the pH of the reaction system. Under high pH conditions, Fe... 2+ It rapidly transforms into Fe(OH)2 / Fe(OH)3 precipitate and becomes inactive, completely inhibiting the formation pathway of ·OH. Simultaneously, the strongly alkaline environment and the precipitation of iron oxides / hydroxides form a denser and thicker passivation layer on the nZVI surface, not only causing the loss of its oxidative catalytic function but also drastically diminishing its core reductive dechlorination function due to blocked electron transfer. This necessitates the artificial adjustment and maintenance of pH at neutral or slightly acidic levels, which is clearly unsuitable for remediation work in actual contaminated sites. Another related technology discloses a spherical slow-release oxidant material consisting of a core and an outer shell. The core is rich in oxidants (such as CaO2), while the outer shell is composed of plastic binder minerals (such as cement), pH buffers (such as fly ash and tourmaline), and highly permeable materials (such as quartz sand). The release rate of the oxidant is controlled through the physical barrier effect of the outer shell, and the pH buffer mitigates alkaline shocks. This technology attempts to mitigate the pH rise caused by CaO2 hydrolysis by adding a pH buffer. However, while this external pH buffer can alleviate the pH increase, the appropriate amount is difficult to control precisely. Furthermore, in conventional groundwater remediation processes, pH buffers and oxidants often fail to maintain the same migration rate, meaning that pH increases caused by CaO2 remediation are still unavoidable, leading to low remediation efficiency. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a slow-release nano-calcium peroxide, its preparation method, and an intelligent permeable reactive barrier and its application. The slow-release nano-calcium peroxide provided by this invention can autonomously maintain the optimal reaction pH and autonomously drive the iron cycle, forming a highly efficient, durable, stable, and truly "passive" oxidation system during water remediation.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing sustained-release nano-calcium peroxide, comprising the following steps: (1) Polyvinylpyrrolidone, water and sodium hydroxide are mixed and hydrolyzed to obtain the first solution; (2) The first solution is mixed with an aqueous solution of calcium salt to carry out an ion exchange reaction to obtain a second solution; the hydrolysis reaction and the ion exchange reaction are both carried out under the condition of pH value ≥ 11; (3) The second solution was mixed with hydrogen peroxide to carry out a metathesis reaction to obtain primary slow-release nano calcium peroxide; (4) The primary slow-release nano calcium peroxide, alcohol solvent and polyvinylpyrrolidone are mixed and self-assembled to obtain the slow-release nano calcium peroxide.

[0006] Preferably, the hydrolysis reaction takes 2 to 5 hours.

[0007] Preferably, the mass ratio of polyvinylpyrrolidone to calcium salt in the calcium salt aqueous solution used to prepare the first solution is (0~25):6, and the mass ratio is not 0:6; the time of the ion replacement reaction is 2~5 h.

[0008] Preferably, the metathesis reaction takes 2 to 4 hours.

[0009] Preferably, in step (4), the mass ratio of polyvinylpyrrolidone to the calcium salt used to prepare the primary slow-release nano calcium peroxide is (0~25):6, and the mass ratio is not 0:6; the self-assembly time is 20~24 h, and the self-assembly is carried out under stirring conditions.

[0010] This invention provides a slow-release nano-calcium peroxide prepared by the preparation method described in the above technical solution.

[0011] This invention provides a smart Fenton-like system, comprising a ferrous ion source and the slow-release nano-calcium peroxide described in the above technical solutions.

[0012] This invention provides an intelligent permeable reactive wall, comprising a first reactive wall, a second reactive wall, and a third reactive wall arranged sequentially and at intervals along the water flow direction. The active filler of the first reactive wall is nano-zero valent iron, the active filler of the second reactive wall is the slow-release nano-calcium peroxide described in the above technical solution, and the active filler of the third reactive wall is a natural adsorbent material.

[0013] Preferably, the natural adsorbent material includes natural zeolite and / or attapulgite.

[0014] This invention provides the application of the intelligent Fenton-like system or the intelligent permeable reactive barrier described in the above technical solutions in water pollution treatment.

[0015] This invention provides a method for preparing sustained-release nano-calcium peroxide. The method involves adding sodium hydroxide and, under conditions of pH ≥ 11, hydrolyzing the amide groups in polyvinylpyrrolidone to carboxyl groups, exposing a large number of unsaturated functional groups to form sodium carboxylate. Subsequently, calcium salt is added to... 2+ More likely to be associated with Na + A displacement reaction occurs, forming a relatively stable primary encapsulation layer. To further enhance the sustained-release effect of polyvinylpyrrolidone (PVP) on nano-calcium peroxide (nCaO2), PPVP is added again for secondary encapsulation, forming a closed core-shell structure, thereby maximizing the sustained-release effect of the core-shell. Compared with the prior art, this invention has the following beneficial effects: In the Fenton-like system, the H2O2 generated by the slow-release nano-calcium peroxide prepared in this invention encounters ferrous ions (Fe(II)) and undergoes a Fenton reaction, generating reactive species such as ·OH that degrade organic matter. Simultaneously, the polyvinylpyrrolidone core-shell mechanism initiates micro-regulation, controlling the slow release of H2O2 from the core-shell, effectively avoiding ineffective decomposition and ineffective consumption of Fe(II) due to excessively high oxidant concentration. Furthermore, it inhibits the rapid rise in environmental pH caused by calcium peroxide decomposition, stabilizing the pH of the reaction system within a milder, weakly alkaline range (~9.0). In addition, the unsaturated functional groups on the surface of polyvinylpyrrolidone coordinate with Fe(II), enhancing the electron-gaining and losing ability of ferric ions. This strengthens the electron-losing ability of Fe(II), accelerating the Fenton reaction and driving the large-scale generation of reactive oxygen species, achieving efficient operation of the reaction system. Simultaneously, the unsaturated functional groups on the surface also coordinate with Fe... 3+ (Fe(III)) enhances its electron-accepting ability and promotes the absorption of Fe(III) by residual H2O2 or superoxide radicals (·O2) generated from its decomposition in the system. - The polyvinylpyrrolidone (PVP) is reduced to Fe(II), which then undergoes the Fenton reaction again and enters the next cycle, constructing a cyclic structure: "polyvinylpyrrolidone-Fe(II)→(H₂O₂)→polyvinylpyrrolidone-Fe(III)→(·O₂)". - The closed-loop microcycle of "→polyvinylpyrrolidone-Fe(II)" promotes catalyst regeneration and allows the oxidation reaction to proceed continuously. The slow-release nano-calcium peroxide provided by this invention can autonomously maintain the optimal reaction pH and autonomously drive the iron cycle, forming a highly efficient, durable, stable, and truly "passive" operating system during water remediation.

[0016] This invention provides an intelligent permeable reactive barrier, comprising a first reactive barrier, a second reactive barrier, and a third reactive barrier arranged sequentially and at intervals along the water flow direction. The active filler of the first reactive barrier is nano-zero-valent iron, the active filler of the second reactive barrier is the slow-release nano-calcium peroxide described in the above technical solution, and the active filler of the third reactive barrier is a natural adsorbent material. This invention provides a spatiotemporally ordered three-stage intelligent reactive barrier of "reduction-oxidation-purification." This invention breaks the vicious cycle of "pH imbalance-iron cycle interruption-reaction mechanism antagonism" in existing nZVI-oxidant composite PRB technology, and develops a composite filler and PRB structure with "chemical intelligence." It can autonomously maintain the optimal reaction pH, autonomously drive the iron cycle, and autonomously arrange the order of reduction and oxidation reactions through the synergistic effect of internal components, ultimately forming a highly efficient, durable, stable, and truly "passive" groundwater remediation system. Specifically, a three-stage PRB structure of "reduction-oxidation-purification" is achieved by sequentially arranging a first, second, and third reaction wall along the water flow direction, realizing the sequential treatment of pollutants "first reduction, then oxidation, and then purification," thus avoiding internal antagonism between the reducing agent and the oxidizing agent; the pre-treatment zone (first reaction wall) provides the necessary catalyst Fe to the core zone (second reaction wall). 2+ The core zone (second reactive wall) utilizes the intelligent properties of slow-release nano-calcium peroxide to efficiently degrade pollutants and achieve iron recycling under stable pH conditions; the terminal zone (third reactive wall) ensures the safety of the effluent. This invention achieves broad-spectrum and long-lasting remediation through the synergy of the first, second, and third reactive walls, which is impossible with a single technology. Attached Figure Description

[0017] Figure 1 The particle size distribution diagram of the slow-release nano-calcium peroxide prepared in Example 1 with a mass ratio of polyvinylpyrrolidone to calcium chloride of 20:6 is shown. Figure 2 This is a SEM image of the sustained-release nano-calcium peroxide prepared in Example 1 with a mass ratio of polyvinylpyrrolidone to calcium chloride of 20:6. Figure 3 Thermogravimetric analysis (TGA) diagrams of pure nano-calcium peroxide (nCaO2), initially encapsulated slow-release nano-calcium peroxide nanoparticles, and secondarily encapsulated slow-release nano-calcium peroxide nanoparticles in Example 1 are shown. Figure 4 XPS analysis of the C1s layer on the surface of the sustained-release nano-calcium peroxide prepared in Example 1; Figure 5 XPS analysis image of N1s on the surface of the sustained-release nano-calcium peroxide prepared in Example 1; Figure 6A graph showing the time relationship between the release of nano-calcium peroxide, the initially encapsulated sustained-release nano-calcium peroxide prepared in Example 1, and the secondarily encapsulated sustained-release nano-calcium peroxide. Figure 7 pH change graphs for the release of nano-calcium peroxide, the initially encapsulated sustained-release nano-calcium peroxide prepared in Example 1, and the secondarily encapsulated sustained-release nano-calcium peroxide. Figure 8 Identification of active species in the sustained-release nano-calcium peroxide-based Fenton system prepared in Example 1; Figure 9 To determine the electron gain and loss capabilities of Fe(II) and Fe(III); Figure 10 Determination of the electron gain and loss capabilities of polyvinylpyrrolidone-Fe(II) and polyvinylpyrrolidone-Fe(III); Figure 11 This is a schematic diagram of the structure of the intelligent permeable reactive wall provided by the present invention; Figure 12 The operation flow diagram of the intelligent permeable reactive wall for in-situ remediation of polluted water bodies provided by the present invention; Figure 13 This is a two-dimensional sandbox model of experimental group C1 constructed in Example 2; Figure 14 This is a two-dimensional sandbox model of experimental group C2 constructed in Example 2; Figure 15 This is a two-dimensional sandbox model of experimental group C3 constructed in Example 2; Figure 16 The sustained-release results of the sustained-release nano-calcium peroxide obtained in different experimental groups of Example 1 and Comparative Examples 1-2 are shown. Figure 17 Results of TCE degradation in different experimental groups; Figure 18 The change in pH before and after the reaction in different experimental groups. Detailed Implementation

[0018] This invention provides a method for preparing sustained-release nano-calcium peroxide, comprising the following steps: (1) Polyvinylpyrrolidone, water and sodium hydroxide are mixed and hydrolyzed to obtain the first solution; (2) The first solution is mixed with an aqueous solution of calcium salt to carry out an ion exchange reaction to obtain a second solution; the hydrolysis reaction and the ion exchange reaction are both carried out under the condition of pH value ≥ 11; (3) The second solution was mixed with hydrogen peroxide to carry out a metathesis reaction to obtain primary slow-release nano calcium peroxide; (4) The primary slow-release nano calcium peroxide, alcohol solvent and polyvinylpyrrolidone are mixed and self-assembled to obtain the slow-release nano calcium peroxide.

[0019] Unless otherwise specified, all raw materials involved in this invention are commercially available products well known in the art.

[0020] In this invention, polyvinylpyrrolidone, water, and sodium hydroxide are mixed and subjected to a hydrolysis reaction to obtain a first solution.

[0021] In this invention, the polyvinylpyrrolidone is preferably K30, and the water is preferably ultrapure water. There are no particular requirements for the amount of water used, as long as it is sufficient to fully disperse the polyvinylpyrrolidone. In this invention, the hydrolysis reaction is carried out under conditions where the pH value is ≥11. Preferably, the polyvinylpyrrolidone is dispersed in water, and then the pH value of the solution is adjusted to above 11 using sodium hydroxide before the hydrolysis reaction. In this invention, the hydrolysis reaction time is preferably 2-5 hours, and the hydrolysis reaction can be carried out at room temperature (25°C). In this invention, the hydrolysis reaction specifically involves: under strongly alkaline conditions, the amide groups on the surface of polyvinylpyrrolidone are fully hydrolyzed, exposing a large number of carboxylate ions, which then react with Na+ in the aqueous solution. + They combine to form the -R-COONa structure.

[0022] After obtaining the first solution, the present invention mixes the first solution with an aqueous solution of calcium salt to carry out an ion exchange reaction to obtain the second solution.

[0023] In this invention, the calcium salt aqueous solution is preferably obtained by dissolving the calcium salt in ultrapure water, and the calcium salt is preferably calcium chloride. This invention does not have particular requirements on the amount of water used, as long as it is sufficient to fully dissolve the calcium salt. In this invention, the preferred mass ratio of polyvinylpyrrolidone to calcium salt in the calcium salt aqueous solution used to prepare the first solution is (0~25):6 (and the mass ratio is not 0:6), and can be 5:6, 10:6, 15:6, 20:6, or 25:6.

[0024] In this invention, the ion exchange reaction is carried out under conditions where the pH value is ≥11. Preferably, the first solution is mixed with a calcium salt aqueous solution, stirred thoroughly, and then the pH value of the resulting mixture is adjusted to ≥11 to carry out the ion exchange reaction; the reagent used to adjust the pH value of the mixture is preferably sodium hydroxide. In this invention, the ion exchange reaction time is preferably 2-5 hours, and the ion exchange reaction can be carried out at room temperature. In this invention, the process of the ion exchange reaction is as follows: Ca in an alkaline environment... 2+ Na+ bound to carboxylate + An ion substitution reaction occurs, forming a [-R-COO]2Ca cross-linked structure.

[0025] After obtaining the second solution, the present invention mixes the second solution with hydrogen peroxide to carry out a metathesis reaction to obtain primary slow-release nano calcium peroxide.

[0026] In this invention, excess hydrogen peroxide is added to the second solution according to the ratio of calcium ions to hydrogen peroxide undergoing a metathesis reaction. In this invention, the metathesis reaction time is preferably 2-4 hours, calculated from the time the hydrogen peroxide is completely added. The metathesis reaction can be carried out at room temperature; preferably, it is carried out under stirring. In this invention, the metathesis reaction process is as follows: after the addition of hydrogen peroxide, calcium ions in the system combine with the peroxide ions of hydrogen peroxide to form a calcium peroxide precipitate with lower solubility. The surface of the newly formed calcium peroxide crystals has a large number of unsaturated coordinated calcium ions. These surface calcium ions have a strong coordination tendency and will recombine with carboxylate ions in the solution or nearby to form a "surface calcium carboxylate complex".

[0027] After the metathesis reaction is completed, the present invention preferably performs solid-liquid separation and drying on the obtained reaction solution to obtain a powdered solid, namely the primary slow-release nano-calcium peroxide. In the present invention, the solid-liquid separation can be performed by centrifugation, and the drying is preferably vacuum drying, and the vacuum drying time is preferably 8 hours.

[0028] After obtaining the primary slow-release nano-calcium peroxide, the present invention mixes the primary slow-release nano-calcium peroxide, an alcohol solvent, and polyvinylpyrrolidone for self-assembly to obtain the slow-release nano-calcium peroxide.

[0029] In this invention, the alcohol solvent is preferably anhydrous ethanol. There are no particular requirements on the amount of alcohol solvent used, as long as the primary slow-release nano-calcium peroxide is sufficiently dispersed. In this invention, the mass ratio of polyvinylpyrrolidone to the calcium salt used in preparing the primary slow-release nano-calcium peroxide is preferably (0~25):6 (and the mass ratio is not 0:6), and can be 5:6, 10:6, 15:6, 20:6, or 25:6, preferably consistent with the mass ratio of polyvinylpyrrolidone to calcium salt in the calcium salt solution used in preparing the first solution as described in the above technical solutions.

[0030] In this invention, the preferred method for mixing the primary slow-release nano-calcium peroxide, alcohol solvent, and polyvinylpyrrolidone is to disperse the primary slow-release nano-calcium peroxide in an alcohol solvent and then add polyvinylpyrrolidone thereto.

[0031] In this invention, the self-assembly time is preferably 20-24 hours, and the self-assembly is preferably carried out at room temperature with stirring. After self-assembly, a thick white solution is obtained. Preferably, the thick white solution is subjected to precipitation, solid-liquid separation, washing, and drying sequentially to obtain the slow-release nano-calcium peroxide. In this invention, the solid-liquid separation can be performed by centrifugation; the washing is preferably performed three times with ethanol; the drying is preferably carried out in a vacuum dryer, and the drying time is preferably 24 hours.

[0032] This invention involves adding sodium hydroxide to hydrolyze the amide groups in polyvinylpyrrolidone to carboxyl groups under pH ≥ 11 conditions, forming sodium carboxylate salts and exposing a large number of unsaturated functional groups. Subsequently, calcium salts are added to... 2+ More likely to be associated with Na + A displacement reaction occurs, forming a relatively stable primary encapsulation layer. To further enhance the sustained-release effect of polyvinylpyrrolidone (PVP) on nano-calcium peroxide (nCaO2), PPVP is added again for secondary encapsulation via self-assembly. (PVP reacts with the CaO in the primary sustained-release nano-calcium peroxide through the negative charge of its amide groups.) 2+ Electrostatic attraction is generated to adhere to the surface of the primary slow-release nano-calcium peroxide, thereby maximizing the slow-release effect of the core and shell. In this embodiment of the invention, the primary slow-release nano-calcium peroxide is referred to as primary encapsulated slow-release nano-calcium peroxide, and the finally obtained slow-release nano-calcium peroxide nanoparticles are referred to as secondary encapsulated slow-release nano-calcium peroxide.

[0033] This invention first performs a hydrolysis reaction under conditions of sodium hydroxide addition and pH value ≥11 to enhance the hydrolysis of polyvinylpyrrolidone and expose a large number of unsaturated functional groups. This is beneficial on the one hand to the formation of cross-links, and on the other hand to the subsequent Fe in the Fenton system. 2+ The electron transfer rate. In this invention, if the hydrolysis reaction is not carried out under the conditions of adding sodium hydroxide and pH value ≥11, or if the pH is adjusted only with weak alkaline ammonia, on the one hand, polyvinylpyrrolidone cannot be hydrolyzed, which prevents the subsequent formation of the [-R-COO]2Ca cross-linked structure, and can only form a form similar to physical coating; on the other hand, the core and shell will not have a large number of unsaturated carboxylate functional groups exposed, and cannot cross-link with iron ions in the Fenton-like system, so it cannot effectively accelerate the electron transfer rate of iron ions.

[0034] This invention provides a sustained-release nano-calcium peroxide prepared by the preparation method described above. In this invention, the sustained-release nano-calcium peroxide has a core-shell structure, comprising nano-calcium peroxide and a polyvinylpyrrolidone sustained-release layer coating the nano-calcium peroxide. Preferably, the particle size of the sustained-release nano-calcium peroxide is 400-450 nm.

[0035] The slow-release nano-calcium peroxide provided by this invention is a filler with pH self-regulation and iron ion microcirculation promotion functions. Specifically, in a Fenton-like system, ferrous ions (Fe(II)) encounter H2O2 generated by the slow-release nano-calcium peroxide, undergoing a Fenton-like reaction to generate active species such as ·OH that degrade organic matter. Simultaneously, the polyvinylpyrrolidone core-shell amide group initiates micro-regulation, controlling the slow release of H2O2 from the core and shell, effectively avoiding self-decomposition reactions caused by excessively high oxidant concentrations and the ineffective consumption of Fe(II). Furthermore, it inhibits the rapid rise in environmental pH caused by calcium peroxide decomposition, stabilizing the pH of the reaction system within a milder, weakly alkaline range (~9.0). Furthermore, the unsaturated functional groups on the surface of polyvinylpyrrolidone coordinate with Fe(II), enhancing the electron-gaining and loss capabilities of iron ions. On one hand, this strengthens the electron-loss capability of Fe(II), accelerating the Fenton reaction and driving the large-scale generation of reactive oxygen species, thus achieving efficient operation of the reaction system. On the other hand, the unsaturated functional groups on the surface also coordinate with Fe(III), enhancing its electron-gaining capability and promoting the absorption of Fe(III) by residual H2O2 or superoxide radicals (·O2) generated from its decomposition in the system. - The polyvinylpyrrolidone (PVP) is reduced to Fe(II), which then undergoes the Fenton reaction again and enters the next cycle, constructing a cyclic structure: "polyvinylpyrrolidone-Fe(II)→(H₂O₂)→polyvinylpyrrolidone-Fe(III)→(·O₂)". - The closed-loop microcycle of “→polyvinylpyrrolidone-Fe(Ⅱ)” promotes catalyst regeneration and allows the oxidation reaction to proceed continuously.

[0036] This invention provides a smart Fenton-like system, comprising a ferrous ion source and the slow-release nano-calcium peroxide described in the above technical solutions.

[0037] The present invention does not have any special requirements for the ferrous ion source, as long as it can generate ferrous ions.

[0038] Existing in-situ remediation technologies for polluted water bodies face a progressive triple dilemma: The first dilemma: Single reducing technologies (such as nZVI) have remediation blind spots, failing to achieve complete mineralization of pollutants; the second dilemma (simple mixed systems): Oxidizing components (CaO2) introduced to address the first dilemma, due to their incompatibility with the system's fundamental chemical properties, actually disrupt the remediation environment, leading to the failure of both "reduction" and "oxidation"; the third dilemma (limited material functionality): Existing CaO2 slow-release technologies only focus on "slow release" and cannot "regulate," failing to address key system parameters such as pH and Fe. 2+ / Fe 3+The rapid cycle is powerless to break the vicious cycle described above. However, the slow-release nano-calcium peroxide described in this invention can intelligently regulate the reaction microenvironment, and the Fenton-like system composed of it can ensure that the reducing and oxidizing abilities can be synergistically, effectively, and stably exerted.

[0039] This invention provides an intelligent permeable reactive wall, comprising a first reactive wall, a second reactive wall, and a third reactive wall arranged sequentially and at intervals along the water flow direction. The active filler of the first reactive wall is nano-zero valent iron, the active filler of the second reactive wall is the slow-release nano-calcium peroxide described in the above technical solution, and the active filler of the third reactive wall is a natural adsorbent material.

[0040] Figure 11 This is a structural schematic diagram of the intelligent permeable reactive wall provided by the present invention. The following is in conjunction with... Figure 11 Provide a detailed explanation ( Figure 11 In this context, the PRB reactive wall nZVI filler layer, the PRB reactive wall slow-release nano calcium peroxide filler layer, and the PRB reactive wall natural adsorbent material filler layer are respectively the first reactive wall, the second reactive wall, and the third reactive wall.

[0041] In this invention, the active filler of the first reactive wall is nano-zero-valent iron (nZVI). To improve its stability and dispersibility, the nZVI can be loaded onto conventional and inexpensive carriers such as granular activated carbon or Hangjin clay. In this invention, no oxidant is added to the first reactive wall to ensure a strongly reducing environment.

[0042] The present invention preferably sets up background value monitoring wells in uncontaminated plots. Figure 11 S1), used to determine the environmental background value of uncontaminated sites, aims to restore the water quality of contaminated sites to the same level as the background value of uncontaminated sites. The invention also preferably includes a pollutant concentration monitoring well (S1) within the pollution plume (before the first reaction wall). Figure 11 (S2).

[0043] In this invention, the first reaction wall is the first zone (pre-reduction zone), whose function is to preferentially remove electron-derived pollutants such as heavy metals and dehalogenated hydrocarbons, and to provide Fe(II) as an initiator for downstream reactions. Its basic working principle is as follows: the pollutant plume first enters this zone under the action of groundwater flow, where electron-derived pollutants such as Cr(VI), Ni(II), As(III) and TCE in the groundwater are rapidly reduced by nZVI. At the same time, the corrosion reaction of nZVI (Fe(O) + 2H2O → Fe(II) + H2 + 2OH) - This generates a large amount of ferrous ions (Fe(II)), which are essential catalysts for downstream Fenton-like reactions.

[0044] In this invention, the active filler of the second reactive wall is the slow-release nano-calcium peroxide described in the above technical solution; in order to ensure permeability, the slow-release nano-calcium peroxide can be uniformly mixed with coarse quartz sand, and the volume ratio of the slow-release nano-calcium peroxide to coarse quartz sand is preferably 1:2~5.

[0045] In this invention, the second reaction wall is the second zone (core catalytic oxidation zone), and its function is to utilize the Fe generated in the first zone. 2+ The slow-release nano-calcium peroxide is activated to generate strong oxidizing free radicals, which thoroughly degrade electron-losing pollutants (such as benzene, phenol, and petroleum hydrocarbons) and achieve efficient microcirculation of iron ions.

[0046] In this invention, the working principle (intelligent collaborative process) of the second zone is as follows: After water (such as groundwater) from the first zone flows into this zone, it activates the slow-release nano-calcium peroxide particles to gradually release H2O2. Simultaneously, Fe(II) provided by the first zone encounters H2O2 in the reaction system, undergoing a Fenton-like reaction to generate active species such as ·OH that degrade organic matter. At the same time, the polyvinylpyrrolidone core-shell amide group initiates micro-regulation, controlling the slow release of H2O2 from the core and shell, effectively avoiding self-decomposition reactions caused by excessively high oxidant concentrations and the ineffective consumption of Fe(II) in the first zone. Furthermore, it inhibits the rapid rise in environmental pH caused by calcium peroxide decomposition, stabilizing the pH of the reaction system within a milder, weakly alkaline range (~9.0). Furthermore, the unsaturated functional groups on the surface of polyvinylpyrrolidone coordinate with Fe(II) generated in the first region, enhancing the electron-gaining and losing ability of iron ions in the reaction zone. On the one hand, this strengthens the electron-losing ability of Fe(II), accelerating the Fenton reaction and driving the large-scale generation of reactive oxygen species in the core reaction zone, thus achieving efficient operation of the reaction system. On the other hand, the unsaturated functional groups on the surface also coordinate with Fe. 3+ This enhances its electron-acquiring ability and promotes the absorption of Fe(III) by residual H2O2 or superoxide radicals (·O2) generated from its decomposition in the system. - The polyvinylpyrrolidone (PVP) is reduced to Fe(II), which then undergoes the Fenton reaction again and enters the next cycle. This means that a cycle of "polyvinylpyrrolidone-Fe(II)→(H2O2)→polyvinylpyrrolidone-Fe(III)→(·O2)" is formed within this region. - The closed-loop microcycle of “→polyvinylpyrrolidone-Fe(Ⅱ)” promotes catalyst regeneration and allows the oxidation reaction to proceed continuously.

[0047] In this invention, the active filler of the third reaction wall is a natural adsorbent material, preferably including natural zeolite and / or attapulgite. These mineral materials are inexpensive and environmentally friendly, and have excellent ion exchange capacity and adsorption performance.

[0048] In this invention, the third reaction wall is the third zone (end-of-pipe buffer purification zone), which functions to: intercept trace amounts of iron flocs that may escape, adsorb incompletely degraded intermediate products, and adjust the pH of the effluent to near neutral to ensure environmental safety.

[0049] In this invention, the working principle of the third zone is as follows: after the groundwater from the second zone flows into this zone, it uses natural zeolite and other adsorbents in the purification zone to adsorb a large amount of residual organic pollutants and capture iron ions, calcium ions and other substances in the water to prevent secondary pollution.

[0050] In this invention, the spaces between the first and second reaction walls, as well as between the second and third reaction walls, are preferably filled with gravel fill layers. The gravel fill layers serve two purposes: firstly, they separate the reduction zone, oxidation zone, and final purification zone, preventing interference between the functions of each zone; secondly, the presence of the gravel fill layer helps prevent the generation and blockage of the byproduct Ca(OH)2 after the calcium peroxide reaction. In this invention, the distance between adjacent reaction walls must be less than the thickness of the corresponding reaction wall.

[0051] The present invention also preferably includes an effluent water quality monitoring well located downstream of the third reaction wall. Figure 11 In section S3, a water quality monitoring well is equipped with a water quality sensor to manually adjust the pH of the groundwater in the third zone in real time, ensuring that the pH rise caused by calcium peroxide decomposition in the second zone does not affect the regional groundwater system. In addition, the water quality sensor also monitors the concentration of relevant pollutants in the groundwater in real time, ensuring that the water quality after PRB treatment does not differ significantly from the environmental background value (S1 well). If there is a significant difference between the water quality and the environmental background value, the water is extracted through a collection well and directly injected into the first pre-treatment zone, circulating back and forth until the water quality after treatment in the third zone does not differ significantly from the environmental background value. This process is called monitoring reflux treatment.

[0052] This invention provides a spatiotemporally ordered three-stage intelligent reactive barrier (PRB) of reduction, oxidation, and purification. It abandons the traditional approach of simply mixing or partitioning nZVI and nCaO2, instead constructing an intelligent PRB system with functional gradient changes along the water flow direction and reaction sequence coupling. The core of this system lies in utilizing the invention's unique slow-release nano-calcium peroxide filler to autonomously create a microenvironment within the PRB optimal for the sequential occurrence of nZVI reduction and Fenton-like oxidation reactions. The entire PRB wall consists of three functionally distinct but closely synergistic reaction zones, arranged sequentially along the groundwater flow direction: ① pre-reduction zone; ② core catalytic oxidation zone; ③ end-buffer purification zone; ④ monitoring and reflux treatment zone.

[0053] This invention breaks the vicious cycle of "pH imbalance - iron cycle interruption - reaction mechanism antagonism" in existing nZVI-oxidant composite PRB technology. It develops a composite filler and PRB structure with "chemical intelligence," which can autonomously maintain the optimal reaction pH, autonomously drive the iron cycle, and autonomously arrange the order of reduction and oxidation reactions through the synergistic effect of its internal components, ultimately forming a highly efficient, durable, stable, and truly "passive" groundwater remediation system. Details are as follows: (1) Solving the problem of "pH conflict" and catalyst deactivation within the redox system The essence of the problem: In a composite system with nZVI as the core reducing agent and calcium peroxide (nCaO2) as an oxidizing agent, there exists an inherent chemical contradiction. The hydrolysis of nCaO2 produces OH-. - This leads to a sharp increase in the system's pH (strong alkalinity), and the optimal pH environment for both ZVI corrosion producing active hydrogen species and Fenton / Fenton-like reactions generating free radicals is acidic or neutral. The increase in pH directly results in: thickening of the passivation film on the nZVI surface, and a decrease in electron transfer ability; Fe... 2+ / Fe 3+ Hydroxide precipitates form, losing catalytic activity and terminating the Fenton-like reaction. While methods to mitigate pH elevation rely on artificial adjustment or the addition of external pH buffers, artificial adjustment is impractical in real-world underground environments. pH buffers also suffer from drawbacks such as asynchronous migration rates with the oxidant, limited buffering capacity, and difficulty in precise control.

[0054] The breakthrough of this invention lies in its design of an internally generated pH regulation mechanism that matches the reaction process. The goal is not simply to "resist" alkalinity, but to dynamically stabilize the pH within the range most suitable for nZVI activity and Fenton-like reactions through internal chemical reactions, thereby achieving a shift from "external regulation" to "endogenous intelligent control."

[0055] (2) Achieving iron cycle (Fe 3+ / Fe 2+ Its high efficiency and long-lasting self-driving capability overcomes the drawback of "one-time" consumption of oxidants. The essence of the problem: In the nZVI / persulfate or nZVI / nCaO2 system, nZVI provides the initial Fe. 2+ It was then quickly oxidized to Fe. 3+ If Fe 3+ It cannot be effectively and continuously reduced back to Fe. 2+If the free radical generation reaction stops rapidly, a large amount of oxidants (such as persulfate and hydrogen peroxide) will remain and cannot be effectively activated, leading to a sharp drop in repair efficiency and low material utilization. Methods that rely on external magnetic fields to enhance iron cycling exist, but this requires additional energy input and equipment maintenance, contradicting the "passive repair" principle of PRB technology. Other systems lack effective and continuous Fe... 3+ Restoration path.

[0056] The breakthrough of this invention lies in its ingenious utilization of the continuous corrosion of nZVI and the intermediate products of nCaO2 decomposition to construct a closed-loop iron-cycling microenvironment. The core idea is: on the one hand, to utilize nZVI as an electron pool, continuously providing electrons to directly or indirectly reduce Fe. 3+ On the other hand, the superoxide radicals (·O2) generated by the decomposition of nCaO2 under specific conditions are utilized. - Reducing species such as Fe will 3+ Reduced to Fe 2+ Simultaneously, by fully utilizing the slow-release core-shell and iron species adsorption phases, the electron-gaining and losing ability of iron ions in the reaction system is altered, thereby promoting the Fe reaction in the system. 2+ / Fe 3+ The continuous cycle.

[0057] (3) Construct a spatiotemporally coupled "reduction-oxidation" synergistic barrier to achieve broad-spectrum, sequential removal of complex pollution plumes. The essence of the problem: Real-world contaminated sites often contain both electron-gaining pollutants (such as Cr(VI) and chlorinated hydrocarbons) and electron-lossing pollutants (such as benzene compounds and petroleum hydrocarbons). Single reducing or oxidizing PRBs are insufficient for effective simultaneous treatment. Simply physically mixing reducing and oxidizing agents may lead to them "killing each other," with the oxidizing agent prematurely consuming nZVI or the reducing agent quenching free radicals, reducing overall efficiency. Existing composite PRBs often focus on the simple superposition of mechanisms, failing to finely design the spatial distribution and reaction sequence of reactants within the PRB wall, potentially leading to internal antagonism.

[0058] The breakthrough of this invention lies in its ability to achieve an intelligent process of "reduction followed by oxidation" or "zonal synergy" for pollutant removal through the structural design of the packing material (such as core-shell structure or layered packing). Specifically, the pollutant plume first flows through a reduction zone dominated by nZVI, preferentially removing easily reduced pollutants such as heavy metals and dehalogenated hydrocarbons; subsequently, at specific downstream reaction sites, Fe generated by nZVI corrosion is utilized... 2+ The activation of H2O2 produced by nCaO2 initiates a Fenton-like oxidation reaction, efficiently degrading the remaining recalcitrant oxidizing organic matter. This spatiotemporally ordered synergistic mechanism is key to achieving broad-spectrum and efficient remediation.

[0059] This invention constructs a complete technical system from material intelligence to system intelligence. The core lies in utilizing slow-release nano-calcium peroxide with pH self-regulation and iron cycle promotion functions as a "chemical intelligence hub," maximizing its efficiency through a spatiotemporally ordered partitioned PRB structure. ① Key material—Multifunctional core-shell structured slow-release nano-calcium peroxide; slow-release function, pH regulation function, and iron cycle promotion function. ② Key system—Spatiotemporally ordered "reduction-oxidation-purification" three-level PRB structure; temporal coupling (achieving sequential treatment of pollutants "first reduction, then oxidation, then purification," avoiding internal antagonism between reducing agents and oxidizing agents), and functional synergy (the pre-zone provides the core zone with the necessary catalyst Fe). 2+ The core zone utilizes the intelligent properties of slow-release nano-calcium peroxide to efficiently degrade pollutants and achieve iron cycling under stable pH conditions; the terminal zone ensures the safety of the effluent; these three elements work synergistically to achieve broad-spectrum and long-lasting remediation that cannot be achieved by a single technology. ③ Key Mechanism—A Shift from “External Regulation” to “Endogenous Intelligence”: The pH regulation and iron cycling catalysis of the entire system no longer rely on external energy input (such as magnetic fields), human intervention (such as artificial pH control), or physically mixed buffers, but are autonomously achieved through the inherent chemical properties of the packing material itself (the core-shell structure of slow-release nano-calcium peroxide and the functional groups of polyvinylpyrrolidone). This is a fundamental technological paradigm shift, achieving truly “passive” intelligent remediation.

[0060] This invention provides the application of the intelligent Fenton-like system or the intelligent permeable reactive barrier described in the above technical solutions in water pollution remediation.

[0061] Figure 12 The present invention provides an operational process for the in-situ remediation of contaminated water bodies (such as groundwater) using an intelligent permeable reactive barrier. Before remediation, the flow direction of groundwater in the contaminated area is first determined, and the concentration is monitored at the pollutant monitoring well. Figure 11 (S2) Determine the concentration of groundwater pollutants, assess the scale of pollution, and calculate the dosage of each PRB reactive barrier based on this background; then, install PRB reactive barriers downstream of the pollution plume (see S2). Figure 11 The invention utilizes an intelligent permeable reactive barrier to construct an in-situ remediation system for the effective remediation of organic pollutants in groundwater. Groundwater quality samples are collected from the third zone of the PRB reactive barrier. If the water quality differs significantly from the environmental background value, it is extracted through a collection well and directly injected into the first zone, circulating repeatedly until the water quality after treatment in the third zone shows no significant difference from the environmental background value. The pH of the groundwater in the third zone is manually adjusted in real time to ensure the safety of the effluent.

[0062] To further illustrate the present invention, the following detailed descriptions, in conjunction with examples, illustrate the slow-release nano-calcium peroxide and its preparation method, as well as the intelligent permeable reactive wall and its applications. However, these descriptions should not be construed as limiting the scope of protection of the present invention.

[0063] Example 1 The preparation steps for sustained-release nano-calcium peroxide are as follows: (1) In a beaker, calcium chloride is dispersed in ultrapure water (the mass ratio of calcium chloride to water is 1:10), and the resulting solution is labeled as A1.

[0064] Polyvinylpyrrolidone (K30) was dispersed in ultrapure water (the mass ratio of polyvinylpyrrolidone to water was 1:5), and the pH of the solution was adjusted to 11 with NaOH. The reaction was carried out for 2 hours, and the resulting solution was labeled as A2.

[0065] (2) Mix A1 and A2 thoroughly. The mass ratio of polyvinylpyrrolidone in A2 to calcium chloride in A1 is 0:6, 10:6, 15:6, 20:6, and 25:6. Then add sodium hydroxide to adjust the pH of the mixed solution to 11 and carry out the ion exchange reaction. The reaction time is 2 hours. The resulting solution is labeled as A3.

[0066] (3) Add excess hydrogen peroxide to A3 according to the ratio of calcium ions to hydrogen peroxide undergoing metathesis reaction, and stir continuously for 2 hours; then centrifuge the sample, dry it in a vacuum drying oven for 8 hours, take out the powder solid and label it as B1 (i.e. the first-time embedded slow-release nano calcium peroxide).

[0067] (4) Disperse B1 in anhydrous ethanol (the mass ratio of B1 to anhydrous ethanol is 1:10), then add polyvinylpyrrolidone (k30, the amount of polyvinylpyrrolidone added is the same as in step (2)) and stir thoroughly at room temperature for 24 hours until a thick white solution is obtained. After precipitation, separate by centrifugation and wash three times with ethanol. Then dry in a vacuum dryer for 24 hours to obtain the slow-release nano calcium peroxide (i.e., the secondary encapsulated slow-release nano calcium peroxide).

[0068] The sustained-release performance of the finally obtained sustained-release nano-calcium peroxide in Example 1 was tested under the following conditions: room temperature 25℃, ultrapure water, pH=7.0±0.2. Test results: The sustained-release times of the sustained-release nano-calcium peroxide prepared in Example 1 with polyvinylpyrrolidone to calcium chloride mass ratios of 0:6, 10:6, 15:6, 20:6, and 25:6 were 3, 65, 140, 240, and 225 min, respectively.

[0069] The sustained-release nano-calcium peroxide prepared in Example 1 with a mass ratio of polyvinylpyrrolidone to calcium chloride of 20:6 is characterized below: (1) Figure 1 and Figure 2 The images show the particle size distribution and SEM image of the sustained-release nano-calcium peroxide prepared in Example 1 using a polyvinylpyrrolidone to calcium chloride mass ratio of 20:6. The average particle size of the calcium peroxide nanoparticles after polyvinylpyrrolidone encapsulation is approximately 426 nm. The SEM image shows that the encapsulated sustained-release nano-calcium peroxide is a regular spherical shape.

[0070] (2) TGA and DTG analyses further confirmed the polymer core-shell on nCaO2 in the temperature range of 25.0℃ to 800.0℃. Figure 3 Thermogravimetric analysis (TGA) charts are shown for pure nano-calcium peroxide (nCaO2), initially encapsulated slow-release nano-calcium peroxide, and secondarily encapsulated slow-release nano-calcium peroxide. After calcination at 800℃, the mass losses of pure nCaO2, initially encapsulated slow-release nano-calcium peroxide nanoparticles, and secondarily encapsulated slow-release nano-calcium peroxide nanoparticles were 28.5%, 32.3%, and 38.9%, respectively. Figure 3 Clearly, with the increase of coating thickness, the nanoparticles exhibit greater mass loss, which further verifies that the polyvinylpyrrolidone core-shell has been successfully coated onto the nCaO2 surface.

[0071] (3) XPS was used to analyze the surface chemical composition and chemical state of the slow-release nano-calcium peroxide nanoparticle sample. Figure 4 The image shows the XPS analysis of the C1s layer on the surface of the prepared sustained-release nano-calcium peroxide. Figure 5 XPS analysis of the N1s layer on the surface of the prepared sustained-release nano-calcium peroxide. Figure 4 The C1s nuclear level spectrum was displayed and can be fitted to three main peaks: CC (248.8 eV), CO / CN (286.8 eV), and C=O (289.2 eV). Figure 5 The N1s nuclear level spectrum was deconvoluted into three peaks at 399.6 eV, 400.2 eV, and 401.5 eV, which were attributed to amide groups (O=C-NH-), primary amines (-R-NH2), and ammonium groups (-NH3), respectively. + These results confirm that polyvinylpyrrolidone has been coated on the surface of nano-calcium peroxide and has a large number of functional groups exposed.

[0072] (4) Release experiments were conducted on nano-calcium peroxide (nCaO2), primary encapsulated slow-release nano-calcium peroxide and secondary encapsulated slow-release nano-calcium peroxide (experimental conditions: room temperature 25℃, ultrapure water, pH=7.0±0.2). Figure 6 This is a graph showing the time relationship between the release of nano-calcium peroxide, primary encapsulated sustained-release nano-calcium peroxide, and secondary encapsulated sustained-release nano-calcium peroxide. Figure 7The figure shows the pH changes during the release of hydrogen peroxide from nano-calcium peroxide, primary-encapsulated slow-release nano-calcium peroxide, and secondary-encapsulated slow-release nano-calcium peroxide. Release experiments showed that the release time of hydrogen peroxide from the encapsulated slow-release nano-calcium peroxide increased from 3 min to 240 min, and the pH of the reaction solution rebounded from 11.6 to 8.6 after the release was completed.

[0073] (5) A slow-release nano-calcium peroxide-like Fenton system was further constructed using ferrous ions. Specifically, 100 mL of ultrapure water was placed in a 150 mL conical flask, and 0.1 mol of ferrous sulfate heptahydrate and 0.1 g of slow-release nano-calcium peroxide were added to the conical flask. Figure 8 To identify the active species in a sustained-release nano-calcium peroxide-based Fenton system. The main active species in the reaction system include ·OH and ·O2. - and 1 O2 indicates that the Fenton-like system constructed from the prepared slow-release nano-calcium peroxide possesses the ability to oxidize and degrade organic pollutants in groundwater. Simultaneously, the electron-gaining and losing ability of iron ions in the reaction system was measured. Figure 9 For the determination of the electron gain and loss ability of Fe(II) and Fe(III), Figure 10 The electron-gaining and loss capabilities of polyvinylpyrrolidone-Fe(II) and polyvinylpyrrolidone-Fe(III) were determined. It was observed that the electron-loss capability of Fe(II) and the electron-gaining capability of Fe(III) in the reaction system were enhanced to varying degrees. This is attributed to the fact that when Fe(II) combines with the core-shell unsaturated functional groups of polyvinylpyrrolidone, the coordination of iron ions affects its electronic structure, leading to a redistribution of its electron cloud and a change in electron density. This is mainly manifested in the unsaturated functional group (carboxyl group) attracting electrons from Fe(II) through coordination, causing Fe(II) to lose some electrons. This electron pull enhances the electron-loss capability of Fe(II) to some extent, thus making its oxidation reaction more likely. Similarly, Fe(III) exhibits a stronger electron-attracting ability after combining with polyvinylpyrrolidone. When coordinated with unsaturated functional groups, Fe(III) gains electrons from the unsaturated bond oxygen atoms through its strong electron-attracting effect, thereby enhancing its electron-gaining capability. Clearly, both from the perspective of controlled-release nano-calcium peroxide and from the perspective of accelerating the electron transfer rate of catalysts, the polyvinylpyrrolidone core-shell structure is beneficial to the degradation of organic pollutants in groundwater by the calcium peroxide-based Fenton system oxidation reaction.

[0074] Example 2 like Figures 13-15A two-dimensional sandbox model was constructed, with three experimental groups designated C1, C2, and C3. Group C1 served as a blank control group without a reaction wall. Group C2 had a reaction wall composed only of an nZVI filler layer. Group C3 had a first, second, and third reaction wall spaced sequentially along the water flow direction. The active filler for the first reaction wall was nano-zero-valent iron. The active filler for the second reaction wall was slow-release nano-calcium peroxide prepared in Example 1 with a polyvinylpyrrolidone to calcium chloride mass ratio of 20:6, mixed with coarse quartz sand at a volume ratio of 1:2. The active filler for the third reaction wall was a natural adsorbent material (natural zeolite). The spaces between the first and second reaction walls, and between the second and third reaction walls, were filled with a gravel filler layer (5 cm thick). Contaminated groundwater was simulated entering the two-dimensional sandbox model from left to right, with an outlet located at the right end of the model. The groundwater pollutant in the simulation experiment was set as TCE, with a concentration of 10 mg·L⁻¹. -1 The TOC concentration was 1.72 mg·L⁻¹. -1 After 24 hours of operation, the pollutant concentration and TOC removal rate of the blank control group (experimental group C1) remained basically unchanged; the TCE removal rate of experimental group C2 was about 72.0%, but the TOC removal rate remained basically unchanged, which was attributed to the reduction effect of zero-valent iron in the first zone; the TCE removal rate of experimental group C3 reached 99.3%, and the TOC removal rate reached 89.7%, which was attributed to the reduction of zero-valent iron in the first zone (first reaction wall) and the catalytic oxidation in the second zone (second reaction wall).

[0075] Comparative Example 1 The preparation steps for sustained-release nano-calcium peroxide are as follows: (1) In a 500 mL beaker, calcium chloride is dispersed in ultrapure water (the mass ratio of calcium chloride to water is 1:10), and the resulting solution is labeled as A1.

[0076] Polyvinylpyrrolidone (K30) was dispersed in ultrapure water (the mass ratio of polyvinylpyrrolidone to water was 1:5), and the solution was labeled as A2.

[0077] (2) Mix A1 and A2 thoroughly (the mass ratio of polyvinylpyrrolidone in A2 to calcium chloride in A1 is 20:6), and add ammonia water to adjust the pH of the mixed solution to 11. React for 2 hours, and the resulting solution is labeled as A3.

[0078] (3) Add excess hydrogen peroxide to A3 according to the ratio of calcium ions to hydrogen peroxide undergoing a metathesis reaction, and stir continuously for 2 hours. Then, centrifuge the sample, dry it in a vacuum drying oven for 8 hours, and take out the powdered solid and label it as B1.

[0079] (4) Disperse B1 in anhydrous ethanol (the mass ratio of B1 to anhydrous ethanol is 1:10), then add polyvinylpyrrolidone (the amount of polyvinylpyrrolidone added is the same as in step (2)) and stir thoroughly at room temperature for 24 hours until a thick white solution is obtained. After precipitation, separate by centrifugation and wash three times with ethanol. Then dry in a vacuum dryer for 24 hours to obtain slow-release nano calcium peroxide.

[0080] Comparative Example 2 The preparation steps for sustained-release nano-calcium peroxide are as follows: (1) In a 500 mL beaker, calcium chloride is dispersed in ultrapure water (the mass ratio of calcium chloride to water is 1:10), and the resulting solution is labeled as A1.

[0081] Polyvinylpyrrolidone (K30) was dispersed in ultrapure water (the mass ratio of polyvinylpyrrolidone to water was 1:5), and the solution was labeled as A2.

[0082] (2) Mix A1 and A2 thoroughly (the mass ratio of polyvinylpyrrolidone in A2 to calcium chloride in A1 is 20:6), react for 2 hours, and label the resulting mixture as A3.

[0083] (3) Add excess hydrogen peroxide to solution A3 according to the ratio of calcium ions to hydrogen peroxide undergoing a metathesis reaction, and stir continuously for 2 hours. Then, centrifuge to separate the sample, vacuum dry it, and take out the powdered solid and label it as B1.

[0084] (4) Disperse B1 in anhydrous ethanol (the mass ratio of B1 to anhydrous ethanol is 1:10), then add polyvinylpyrrolidone (k30, the amount of polyvinylpyrrolidone added is the same as in step (2)) and stir thoroughly at room temperature for 24 hours until a thick white solution is obtained. After precipitation, separate by centrifugation and wash three times with ethanol. Then dry in a vacuum dryer for 24 hours to obtain slow-release nano calcium peroxide.

[0085] Release experiments were conducted on slow-release nano-calcium peroxide prepared by different methods (experimental conditions: room temperature 25℃, ultrapure water, pH=7.0±0.2). Figure 16 The results of sustained-release nano-calcium peroxide obtained in different experimental groups of Example 1 and Comparative Examples 1-2 are as follows. Figure 16Experimental group 1 was the slow-release nano-calcium peroxide prepared in Example 1 with a mass ratio of polyvinylpyrrolidone to calcium chloride of 20:6 (i.e., slow-release nano-calcium peroxide prepared by NaOH hydrolysis). Experimental group 2 was the slow-release nano-calcium peroxide prepared in Comparative Example 1 with only ammonia added for adjustment. Experimental group 3 was the slow-release nano-calcium peroxide prepared in Comparative Example 2 without adjustment. Experimental results: The release times of the slow-release nano-calcium peroxide prepared by the three different methods in experimental groups 1-3 were 240, 150, and 120 min, respectively. This shows that the exposure of a large number of unsaturated functional groups is conducive to the formation of cross-links, which in turn is more conducive to the slow release of nano-calcium peroxide.

[0086] In addition, the degradation performance of three slow-release nano-calcium peroxide-based Fenton systems in experimental groups 1-3 on organic pollutants was compared, using 10 mg·L⁻¹. -1 TCE was used as the target pollutant, and 100 mL of 10 mg·L⁻¹ was used. -1 TCE solution was placed in a 150mL Erlenmeyer flask. 0.1g of the three types of slow-release nano-calcium peroxide and 0.1mM ferrous sulfate heptahydrate were added to each flask. After 3 hours of reaction, the degradation rates of TCE in experimental groups 1, 2, and 3 were 98.5%, 82.9%, and 81.5%, respectively. Figure 17 (Results of TCE degradation in different experimental groups). Clearly, polyvinylpyrrolidone hydrolyzed with NaOH is more conducive to the degradation of the target pollutant. This is mainly attributed to three aspects: Firstly, the slow-release nano-calcium peroxide prepared after NaOH hydrolysis has a longer slow-release lifespan, which avoids the self-consumption reaction of short-term explosive release of H2O2 by the nano-calcium peroxide, thus enhancing the utilization efficiency of the oxidant. Secondly, the particle sizes of the slow-release nano-calcium peroxide prepared in the three experimental groups were 376 nm (Comparative Example 1), 361 nm (Comparative Example 2), and 426 nm (Example 1), respectively. The larger particle size of the slow-release nano-calcium peroxide prepared after NaOH hydrolysis means that the amount of polyvinylpyrrolidone embedded shell also increases, resulting in a smaller pH change in the reaction system (see...). Figure 18 , Figure 18 The change in pH before and after the reaction in different experimental groups (this represents the amount of pH change before and after the reaction) facilitated the subsequent Fenton-like reaction. Furthermore, Figure 9 , 10 It has been confirmed that the unsaturated functional groups on the surface of polyvinylpyrrolidone can effectively accelerate the electron transfer rate of iron ions, which provides a favorable environment for the generation of active species in Fenton-like reactions.

[0087] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing sustained-release nano-calcium peroxide, characterized in that, Includes the following steps: (1) Polyvinylpyrrolidone, water and sodium hydroxide are mixed and hydrolyzed to obtain the first solution; (2) The first solution is mixed with an aqueous solution of calcium salt to carry out an ion exchange reaction to obtain a second solution; the hydrolysis reaction and the ion exchange reaction are both carried out under the condition of pH value ≥ 11; (3) The second solution was mixed with hydrogen peroxide to carry out a metathesis reaction to obtain primary slow-release nano calcium peroxide; (4) The primary slow-release nano calcium peroxide, alcohol solvent and polyvinylpyrrolidone are mixed and self-assembled to obtain the slow-release nano calcium peroxide.

2. The preparation method according to claim 1, characterized in that, The hydrolysis reaction takes 2 to 5 hours.

3. The preparation method according to claim 1, characterized in that, The mass ratio of polyvinylpyrrolidone to calcium salt in the aqueous solution of calcium salt used to prepare the first solution is (0~25):6, and the mass ratio is not 0:6; the time of the ion exchange reaction is 2~5 h.

4. The preparation method according to claim 1, characterized in that, The time for the metathesis reaction is 2-4 hours.

5. The preparation method according to claim 1, characterized in that, In step (4), the mass ratio of polyvinylpyrrolidone to the calcium salt used to prepare the primary slow-release nano calcium peroxide is (0~25):6, and the mass ratio is not 0:6; the self-assembly time is 20~24 h, and the self-assembly is carried out under stirring conditions.

6. The sustained-release nano-calcium peroxide prepared by the preparation method according to any one of claims 1 to 5.

7. An intelligent Fenton-like system, characterized in that, It includes a ferrous ion source and the slow-release nano-calcium peroxide as described in claim 6.

8. A smart permeable reactive barrier, characterized in that, It includes a first reaction wall, a second reaction wall, and a third reaction wall arranged sequentially at intervals along the water flow direction. The active filler of the first reaction wall is nano-zero valent iron, the active filler of the second reaction wall is the slow-release nano-calcium peroxide as described in claim 6, and the active filler of the third reaction wall is a natural adsorbent material.

9. The intelligent permeable reactive wall according to claim 8, characterized in that, The natural adsorbent material includes natural zeolite and / or attapulgite.

10. The application of the intelligent Fenton-like system of claim 7 or the intelligent permeable reactive barrier of claim 8 or 9 in water pollution remediation.

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