Underground water in-situ remediation method based on slow-release nano-catalyst

Abstract

The invention relates to the technical field of underground water chemical remediation, and discloses an underground water in-situ remediation method based on a slow-release nano-catalyst, which comprises the following steps: preparing a nano-catalyst coated with a polymer with a lower critical solution temperature on the surface, and configuring a molecular recognition group and a co-catalysis area on the surface of the nano-catalyst, according to the method, a target pollutant is selectively enriched by using a molecular recognition group, and a polymer is triggered to generate conformation phase change by virtue of heat generated by reaction of the molecular recognition group and a co-catalysis region, so that a catalytic active site is exposed to degrade the pollutant. The active state of the catalyst is directly coupled with existence facts of pollutants, so that the problem of mismatching of a preset slow release strategy and a dynamic pollution environment is solved, surface self-cleaning and activity regeneration are realized by utilizing a phase change process, and the effective life of a repair system is prolonged.

Description

TECHNICAL FIELD

[0001] The application relates to an in-situ groundwater remediation method based on slow-release nanocatalysts and belongs to the technical field of groundwater chemical remediation. BACKGROUND

[0002] In an in-situ groundwater remediation project, in order to degrade persistent organic pollutants, a technology of injecting nanocatalysts (for example, nanometer zero-valent iron) into a contaminated aquifer is generally used. In order to avoid the rapid failure of the material due to the too fast reaction, the industry usually adopts a slow-release technology, that is, the surface of the nanometer particles is modified to continuously release the active sites of the catalyst at a preset relatively constant rate. This way aims to prolong the effective action time of the remediation material.

[0003] However, the above-mentioned slow-release strategy based on time programming is based on a relatively stable remediation environment. When this strategy is applied to a real dynamic groundwater system, its applicability is restricted. The groundwater system is an open system, and the pollutant concentration will present a complex dynamic of long-time low concentration and short-time concentration pulse alternately due to factors such as rainfall water level fluctuation. Under this real working condition, there is a mismatch between the static and preset slow-release rate and the dynamic and pulsed pollutant flux. Simply adjusting the preset release rate cannot solve this fundamental mismatch. In essence, it is only a choice between two failure modes. Setting a higher release rate can cope with the pollution pulse, but it will cause a large waste of catalyst and premature failure during the long low-concentration period. Conversely, setting a lower release rate can prolong the overall life, but it will cause the pollution to migrate downstream when the pollution pulse appears because the remediation capacity is much lower than the pollutant flux.

[0004] Specifically, the prior art mainly has the following deficiencies: 1. The active release of the catalyst is disconnected in time with its working object, that is, the actual existence of the pollutant, which leads to the fact that the chemical potential energy of the catalyst cannot be effectively utilized; 2. The remediation system lacks a self-perception and response mechanism for pollution events. Its operation logic is a passive preset program and cannot adapt to the nonlinear dynamic changes of the groundwater chemical environment; 3. In order to maintain long-term remediation effect, excessive addition or late injection of remediation materials is often needed in engineering practice, which not only increases the overall cost of the project, but also brings potential secondary pollution risk. Therefore, how to establish a control mechanism that can directly link the active state of the catalyst to the real-time concentration of the target pollutant at the remediation site, avoid the use of a preset time program release mode, and enable the catalyst to be activated autonomously when the concentration of the pollutant increases and to return to a dormant state after the pollutant is degraded, has become a technical problem to be solved by the present application. SUMMARY

[0005] The application provides a groundwater in-situ remediation method based on slow-release nanocatalysts, which mainly aims to solve the problem that the active release rate of the catalysts in the existing slow-release technology cannot match the dynamically changing pollutant concentration in the groundwater environment.

[0006] To achieve the above-mentioned purpose, the application provides a groundwater in-situ remediation method based on slow-release nanocatalysts, which comprises the following steps: Step a: providing a particle group composed of a catalytic core and a first temperature-sensitive polymer layer with a lower critical solution temperature coated outside the catalytic core, and setting the background temperature of the target groundwater environment to be higher than the background temperature Step b: dispersing and arranging the particle group in the groundwater environment, and under the background temperature , the first temperature-sensitive polymer layer is in a swelling and stretching state to shield the active sites of the catalytic core; Step c: in the vicinity of the catalytic core, a molecular recognition group capable of specifically combining with the target pollutant is fixed, and a cocatalytic area thermally coupled with the catalytic core is arranged; Step d: when the molecular recognition group selectively enriches the target pollutant and triggers the exothermic reaction of the cocatalytic area, the heat released by the exothermic reaction is used as an initial heat source to make the local temperature on the surface of the particle cross the critical solution temperature ; Step e: in response to the local temperature crossing the critical solution temperature , the first temperature-sensitive polymer layer undergoes a conformational phase transition from the swelling and stretching state to the dehydrated and contracted state, the conformational phase transition exposes the active sites to catalyze the degradation of the target pollutant, and the mechanical shearing action generated by the conformational phase transition peels off the attachments from the surface of the catalytic core; Step f: when the target pollutant is completely degraded, the local temperature falls below the critical solution temperature , the first temperature-sensitive polymer layer automatically restores to the swelling and stretching state and re-shields the active sites.

[0007] Preferably, in step e, the conformational phase transition of one particle releases heat, which triggers the conformational phase transition of adjacent particles within the thermal diffusion length range thereof in sequence, forming a self-amplifying cascade activation process, so that a macroscopic in-situ reaction zone is automatically formed in the area where the target pollutant exists.

[0008] Preferably, in step a, the surface of the particle group is further modified with a second temperature-sensitive polymer, the conformation of the second temperature-sensitive polymer can respond to the seasonal fluctuations of the background temperature , and by changing the local ionic strength in the vicinity of the first temperature-sensitive polymer layer, the value of the critical solution temperature is adjusted to change with the changing background temperature. Next, maintain the initial temperature rise threshold required to activate the method Satisfy the condition Wherein, The adjusted lower critical solution temperature.

[0009] Preferably, the co-catalytic zone comprises at least one selected from the group consisting of nano-palladium and nano-platinum, which is configured to generate a higher unit reaction exothermic enthalpy change than the catalytic core when reacting with the target pollutant.

[0010] Preferably, the molecular recognition group is a cyclodextrin or a molecular sieve with a specific pore size, which is selectively fixed on the surface or nanoscale adjacent region of the co-catalytic zone, to construct a mass transfer channel based on host-guest interaction between the co-catalytic zone and the target pollutant.

[0011] Preferably, the attachment in step e is a natural organic matter or inorganic salt deposition layer adsorbed on the surface of the particles in the groundwater environment, and the severe stretching of the first temperature-sensitive polymer layer chain in the conformational phase transition generates shear force at the interface between the deposition layer and the catalytic core, to achieve physical peeling of the deposition layer and online regeneration of the catalytic core activity.

[0012] Preferably, in step b, the first temperature-sensitive polymer layer in a swollen and stretched state forms a steric repulsion force between the particles, prompting the formation of a reversible flocculation aggregate structure, which further stabilizes the shielding state of the active sites while enhancing the retention capacity of the particle group in the groundwater porous medium.

[0013] Preferably, the method further comprises an online diagnosis of the activity of the particle group, which comprises: step g, applying an alternating magnetic field with a preset frequency and field strength to the groundwater area where the particle group is located; step h, measuring the temperature rise rate caused by the heat induced in the catalytic core by the alternating magnetic field; step i, comparing the measured temperature rise rate with a reference temperature rise rate representing the initial health state of the particle group, to determine the current activity state of the particle group.

[0014] Preferably, in step i, when the measured temperature rise rate is 20% to 50% lower than the reference temperature rise rate, it is determined that the particle group has been deeply deactivated by irreversible mineral crust, biofilm or hard agglomeration.

[0015] Preferably, the catalytic core is nano zero-valent iron, and the first temperature-sensitive polymer layer is poly N-isopropyl acrylamide or a copolymer thereof; and in step a, by adjusting the monomer types and proportions of the copolymer, Set to be in the range of 2 degrees Celsius to 10 degrees Celsius higher than the annual average background temperature of the target groundwater environment.

[0016] Compared with the prior art, the application has the following beneficial effects: 1. By setting the lower critical solution temperature of the temperature-sensitive polymer modified on the surface of the nanometer catalyst to be higher than the background temperature of the underground water, and using the heat generated when the catalytic degradation reaction occurs to make the local temperature of the catalyst surface exceed the critical temperature, a direct coupling relationship between the catalyst activity and the catalytic reaction is established; this relationship makes the activation of the catalyst no longer dependent on the external preset time program, but determined by the presence or absence of the pollutants, avoiding the irreversible deactivation of the catalyst due to continuous release when the concentration of the pollutants is low, and avoiding the problem of missing the treatment opportunity due to the preset low release rate when the concentration of the pollutants is pulsed.

[0017] 2. In the preparation of the temperature-sensitive gate nanometer catalyst, a promoter and a molecular recognition group capable of specifically interacting with the target pollutants are also arranged on the surface or adjacent area of the temperature-sensitive gate nanometer catalyst, and a multi-stage activation triggering mechanism is constructed; wherein, the molecular recognition group first selectively enriches the target pollutants, and then the enriched pollutants react with the promoter to generate a heat source with higher intensity than the initial heat source of the main catalyst, and the heat source triggers the conformational change of the temperature-sensitive polymer; this series of continuous and interrelated steps not only meet the thermodynamic conditions, but also meet the precondition of chemical recognition, solving the problem of false triggering and catalyst waste caused by non-target substances such as dissolved oxygen or nitrate in complex underground water chemical environment.

[0018] 3. By using the physical process of hydrophilic-hydrophobic transition and chain conformational change of the temperature-sensitive polymer at the critical temperature, the natural organic matter or inorganic salt deposited on the surface of the catalyst is physically removed in each activation cycle triggered by the pollutants; in addition, the magnetocaloric response characteristics of the nanometer catalyst itself make the temperature rise rate under the action of the external alternating magnetic field can be used to characterize the surface cleanliness and dispersion state of the catalyst; the combination of the two mechanisms makes the remediation system not only has the ability to respond to pollutants and self-cleaning, but also provides a way for external diagnosis of long-term running activity remotely and non-destructively, and turns the one-time injected remediation material into an underground engineering system with state-known activity and recoverable activity. BRIEF DESCRIPTION OF DRAWINGS

[0019] Fig. 1 The logical flow chart of the catalyst activity gate and state diagnosis of the application; Fig. 2 The degradation efficiency comparison curve of the method of the application and the conventional method under the simulation of pollutant pulse; Fig. 3 The structure composition and response mechanism diagram of the temperature-sensitive gate nanometer catalyst of the application. DETAILED DESCRIPTION

[0020] In order to make the technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific examples described herein are intended to explain the present application, but not to limit the present application.

[0021] The core of the disclosed groundwater in-situ remediation method based on slow-release nanocatalyst is to construct a closed-loop self-activated catalyst activity regulation system driven by the existence of target pollutants. The operation process mainly includes three interrelated stages: first, preparation of functional nanocatalyst particles and calibration of key parameters; second, spontaneous formation of dynamic dormant state of particle groups after injection into the groundwater environment; and finally, cascade activation of self-cleaning and pollutant degradation triggered by the heat of catalytic reaction when pollutants appear, and automatic recovery to the dormant state after pollutant degradation.

[0022] In groundwater remediation projects, a common application layer objective obstacle is the mismatch between the activity release rate of the remediation material and the dynamically changing pollutant flux it should deal with. To address this challenge, the present method first performs step a, which provides a particle group composed of a catalytic core and a first temperature-sensitive polymer layer with a lower critical solution temperature coated outside the catalytic core. The catalytic core is preferably nanoscale zero-valent iron, which is not only a high-efficiency catalytic degradation functional main body but also provides a physical basis for subsequent remote non-destructive diagnosis due to its magnetism. The first temperature-sensitive polymer layer is preferably poly-N-isopropyl acrylamide or its copolymer. The functional role of this polymer layer is to realize reversible shielding and exposure of the active sites of the catalytic core through its temperature-sensitive conformational phase transition, thereby acting as a molecular switch. A key parameter calibration procedure is to set the value of higher than the background temperature of the target groundwater environment This setting is based on the need to build an activation threshold triggered by an external heat source. By adjusting the types and proportions of hydrophilic or hydrophobic monomers in the poly-N-isopropyl acrylamide copolymer, the value of can be adjusted. A preferred working window is to set in the range of 2 to 10 degrees Celsius higher than the annual average background temperature of the target groundwater environment. For example, if the annual average background temperature of the groundwater at a site is 15 degrees Celsius, the value of Set between 17 degrees Celsius to 25 degrees Celsius, so that the particle group can maintain the effective shielding of catalytic activity in the conventional groundwater environment, and establish the conditions for subsequent on-demand activation; then, the method of the present application performs step b, and the prepared and calibrated particle group is dispersed in the groundwater environment, because the current environmental temperature (T ) is lower than the of the polymer, the first temperature-sensitive polymer layer is in a hydrophilic swollen and stretched state, and the high molecular chains form a structure similar to the villi on the surface of the particle, effectively shielding the active sites of the internal catalytic core; in other words, the stretched polymer chains will produce steric repulsion between particles, and this colloid chemical effect promotes the formation of a reversible flocculation aggregate structure in the porous medium, which further stabilizes the shielding state of the active site at the physical level, and enhances the retention capacity of the particle group in the groundwater environment, avoiding its rapid migration and loss, thereby forming a dynamic dormant area with abundant energy but isolated from the outside in the injection area.

[0023] The complexity of the groundwater chemical environment, especially the coexistence of non-target substances such as dissolved oxygen or nitrate, may cause ineffective consumption of the catalyst, which constitutes another application layer objective obstacle, therefore, the method of the present application sets a pre-chemical recognition logic in step c for the activation process, i.e. in the vicinity of the catalytic core, there are molecular recognition groups that can specifically bind to target pollutants, and a co-catalytic area is set in thermal coupling with the catalytic core; the molecular recognition group here plays the role of a recognition unit for pollutants, preferably cyclodextrin or molecular sieve with a specific pore size, for example, for hydrophobic organic pollutants such as trichloroethylene, beta-cyclodextrin can be selected, its hydrophobic internal cavity structure can selectively capture and enrich target pollutants through host-guest interaction, while excluding inorganic ions such as nitrate; the co-catalytic area is configured as the initial heat source of the system, preferably containing at least one of nano-palladium and nano-platinum, which is selectively fixed in the nanoscale vicinity of the molecular recognition group to build an efficient mass transfer channel, and when the co-catalytic area reacts with the target pollutant, it is configured to generate a higher unit reaction heat enthalpy than the main catalytic core, thereby ensuring that an initial heat source with sufficient strength can be generated to overcome the heat dissipation of the water flow in the initial stage; through the above configuration, only when the target pollutant passes the screening of the molecular recognition group and reacts in the co-catalytic area, can the subsequent thermodynamic activation process be triggered, which solves the problem of false triggering caused by non-target substances.

[0024] When the aforementioned chemical recognition preconditions are met, i.e., the target pollutant appears and is enriched, the method of the present invention proceeds to steps d and e, executing a self-excited cascade activation and degradation process. When the target pollutant enriched by the molecular recognition group undergoes an exothermic reaction with the co-catalytic zone, the heat released by this reaction serves as the initial heat source, causing the local temperature on the surface of a single or a few particles to rise instantaneously, exceeding the preset threshold. Threshold; in response, the first thermosensitive polymer layer undergoes a conformational phase transition from a swollen and stretched state to a dehydrated and contracted state, like turning on a switch, instantly exposing all the catalytically active sites of the particle, and causing a larger-scale catalytic degradation reaction with the surrounding pollutants; this process releases more heat, and through heat diffusion, it triggers the same conformational phase transition in adjacent particles within the heat diffusion length range, forming a positive feedback, self-amplifying cascade activation process, and finally automatically forming a macroscopic in-situ reaction zone in the area where the target pollutant exists.

[0025] In groundwater environments, catalyst surfaces can become passivated due to the slow adsorption and deposition of natural organic matter or inorganic salts, which limits their long-term effectiveness. To address this issue, the present invention utilizes the conformational phase transition process of the first temperature-sensitive polymer layer in step e to achieve surface self-cleaning. During each activation cycle triggered by contaminants, the movement of polymer chains from full swelling to rapid dehydration and contraction generates mechanical shear forces at the interface between the catalyst core and surface deposits (such as inorganic salt deposits). These shear forces are sufficient to physically peel off these deposits, restoring the catalyst surface to cleanliness and exposing a highly active surface each time activation occurs. This self-cleaning mechanism transforms the one-time injected remediation material into a system with recoverable activity. Finally, once the contamination pulse has passed and the target contaminant has been degraded, the catalytic reaction stops, the heat source disappears, and the present invention proceeds to step f, where the local temperature of the particle surface automatically drops back to the ambient background temperature. Below, i.e., below At this point, the first temperature-sensitive polymer layer will spontaneously absorb water and swell, returning to its extended state and re-shielding the active sites of the catalytic core, allowing the entire remediation system to automatically return to a dynamic dormant state, awaiting the arrival of the next pollution event, thus forming a complete remediation cycle driven by pollutants.

[0026] To cope with groundwater background temperature To mitigate potential seasonal fluctuations, a preferred embodiment involves, in step a, further modifying the particle surface with a second thermosensitive polymer; this second thermosensitive polymer is configured to respond to... The seasonal fluctuations are dynamically adjusted by changing the local ion intensity in the neighborhood of the first temperature-sensitive polymer layer. The actual value is determined by the goal of maintaining the initial temperature rise threshold required to activate the method regardless of seasonal changes. () satisfies condition 1 degree Celsius ≤ ( The temperature is ≤5 degrees Celsius, thus ensuring that the system maintains response sensitivity and stability in different seasons. In addition, to achieve remote non-destructive diagnosis of the long-term operational activity of the underground remediation system, the method of the present invention also includes an online diagnostic step, which includes: step g, applying an alternating magnetic field with a preset frequency and field strength value to the groundwater area where the particle group is located from the surface; step h, using a temperature sensor such as an optical fiber to measure the rate of temperature rise caused by the heat induced by the alternating magnetic field in a magnetic catalytic core (such as nano-zero valent iron); step i, comparing the measured rate of temperature rise with a reference rate of temperature rise characterizing the initial health state of the particle group to determine the current activity state of the particle group; for example, when the measured rate of temperature rise is 20% to 50% lower than the reference rate of temperature rise, it can be determined that the surface of the particle group has deep passivation caused by irreversible mineral crust or biofilm, or irreversible hard agglomeration has occurred.

[0027] Example 1: This example illustrates the specific application of the disclosed in-situ groundwater remediation method based on slow-release nanocatalysts in the pollution control of a specific industrial site. At a former chlorinated solvent production site where the main pollution source had been removed, a long-term, low-concentration trailing plume of trichloroethylene formed in the aquifer. The site's hydrogeological conditions exhibited typical seasonal characteristics: during the eight-month dry season, the groundwater level remained stable, and the trichloroethylene concentration remained below 0.1 mg / L; however, during the rainy season, concentrated surface runoff would flush residual pollutants from the soil into the aquifer within a few days, causing the trichloroethylene concentration in the monitoring well to rise above 5 mg / L within 48 hours, forming a brief but high-flux pollution pulse. For this condition, a batch of prepared particles was injected into the core region of the pollution plume in a single injection. The catalyst core was nano-zero-valent iron, the first temperature-sensitive polymer layer was poly(N-isopropylacrylamide) copolymer, the molecular recognition group was β-cyclodextrin, and the co-catalytic zone was nano-palladium. Based on the site's annual average groundwater background temperature... Based on survey data of 16 degrees Celsius, the lower critical dissolution temperature of the first temperature-sensitive polymer layer of the particles was adjusted by regulating the copolymer monomer ratio. The temperature was set at 19 degrees Celsius. During the entire dry season after injection, monitoring data showed that there was no significant release of catalyst activity in the remediation area, and the trichloroethylene concentration in the downstream monitoring well was no different from the background value. The entire remediation system was in a dynamic dormant state.

[0028] When the site enters the rainy season, 24 hours after the first heavy rainfall event, the upstream monitoring well data shows that the concentration of trichloroethylene begins to rise. When the pollution pulse reaches the remediation area, the molecular recognition group on the surface of the particle, i.e. β-cyclodextrin, uses its host-guest interaction to selectively capture and enrich trichloroethylene molecules from the water body, while excluding high concentrations of sulfate and nitrate ions in the water body. This selective enrichment provides a high-purity reactant microenvironment for the subsequent initial heat source generation; the enriched trichloroethylene molecules immediately undergo dechlorination with the adjacent catalytic area, i.e. nano-palladium. Due to the high unit reaction exothermic enthalpy, a transient high-intensity local temperature rise occurs on the surface of the particle, causing the temperature of the micro-area to exceed 19 degrees Celsius in a short time Once the local temperature exceeds , the first temperature-sensitive polymer layer in this area immediately undergoes a conformational phase transition, completely exposing the nano-zero-valent iron catalytic core as the main force. The exposed active sites undergo a violent redox degradation reaction with the high concentration of trichloroethylene around them, releasing more heat, which further triggers the same conformational phase transition in adjacent particles, forming a self-amplifying cascade activation process. In the core area where the pollution pulse flows through, an in-situ reaction zone is quickly formed; during the conformational phase transition of the polymer layer, the stretching and contraction of its segments generate mechanical shear forces on the surface of the catalytic core, stripping a small amount of naturally occurring organic matter slowly deposited on the surface of the particle during the dry season, so that the exposed active sites are in a clean state, thereby coping with the high-throughput pollutant degradation task; after the pollution pulse passes, the trichloroethylene in the remediation area is completely degraded, the heat source of the catalytic reaction disappears, and the local temperature on the surface of the particle quickly falls back to the environmental background temperature of 16 degrees Celsius. The first temperature-sensitive polymer layer below automatically returns to the swollen and stretched state, re-shielding the active sites of the catalytic core, and the entire system returns to a dynamic dormant state, with its activity release behavior changing from a pre-set time program to an event-triggered mode directly coupled to the presence of pollutants.

[0029] To further verify the essential advantages brought by the event-triggered mode of the present method compared to existing conventional slow-release technology from the perspective of field application effect, the following Comparative Example 1 is set up.

[0030] Comparative Example 1: This comparative example aims to simulate the remediation effect that can be achieved by using a conventional and time-programmed release based slow-release material in the same site and hydrogeological conditions as Example 1. Except for the remediation material, all other conditions of this comparative example, including the selection of the remediation site, hydrogeological parameters, pollutant type (trichloroethylene), pollution plume characteristics (low concentration tailing in dry season and high concentration pulse in rainy season), material injection method, injection amount, and monitoring well layout and sampling analysis method, are strictly consistent with Example 1. The remediation material used in this comparative example is a conventional slow-release nano zero-valent iron. The specific preparation method of this material refers to the prior art. The same batch of nano zero-valent iron as Example 1 is mechanically mixed with sodium carboxymethyl cellulose (CMC-Na) as a slow-release agent at a mass ratio of 1:1, so as to achieve the sustained and slow release of the active sites of nano zero-valent iron through the slow dissolution of CMC-Na in groundwater. After the above conventional slow-release nano zero-valent iron material is injected into the core area of the pollution plume, it is continuously monitored for 360 days. The key performance data are recorded in Table 1.

[0031] Table 1: Comparison of key performance of Comparative Example 1 and Example 1 in the period of 360 days.

[0032] As can be seen from the data in Table 1, in Comparative Example 1 using the conventional CMC-Na slow-release technology, the effective activity of the catalyst is irreversibly lost during the low-concentration period of up to 240 days in the dry season due to sustained and unnecessary slow release, and has decreased to 31.8% of the initial activity before the arrival of the pollution pulse. When the high-concentration (more than 5 mg / L) pollution pulse arrives in the rainy season, the system has insufficient effective activity and the release rate cannot be dynamically increased, so that the instantaneous degradation rate is only 25.4%, resulting in a serious pollutant breakthrough of up to 3.75 mg / L in the downstream monitoring well. The test results show that the conventional slow-release strategy based on time-programmed release cannot match the dynamic flux change of groundwater pollutants, and has the defects of early activity waste and insufficient response capability in the later period in real application scenarios.

[0033] Example 2: To objectively verify the response behavior and remediation efficiency of the method of the present application in response to dynamic pollutant flux, the following column simulation test is set up. The test platform is composed of a glass column with an inner diameter of 2.5 cm and a length of 30 cm, which is filled with 100-200 mesh quartz sand as a porous medium to simulate a sandy aquifer. The test solution is injected at a constant rate of 5 mL / min by a peristaltic pump to simulate the common seepage velocity in the groundwater environment. The entire column is placed in a constant temperature water bath with a temperature control accuracy of ±0.1 degrees Celsius to maintain a stable environmental background temperature In the region of the column filled with catalyst, three fiber optic temperature sensors are equidistantly arranged along the axial direction. The temperature measurement accuracy is 0.1 degrees Celsius and the sampling frequency is 1 Hz. These sensors are used to monitor the temperature change of the catalyst bed in real time. The water outlet of the column is connected to an ultraviolet-visible spectrophotometer to continuously monitor the concentration of the target pollutant trichloroethylene in the water through online colorimetry.

[0034] This experiment included a control group and an experimental group. The control group used a conventional slow-release nano-zero-valent iron material, prepared by mixing nano-zero-valent iron with sodium carboxymethyl cellulose at a mass ratio of 1:1, aiming to achieve continuous release of active sites through the slow dissolution of the polymer. The experimental group used a particle group prepared by the method of this invention, with nano-zero-valent iron as the catalytic core and surface modified with poly(N-isopropylacrylamide) copolymer as the first temperature-sensitive polymer layer, β-cyclodextrin as the molecular recognition group, and nano-palladium as the co-catalytic region. The lower critical dissolution temperature of the experimental group particle group was... The ambient background temperature was set at 19.0 degrees Celsius throughout the experiment. The temperature was set to 16.0 degrees Celsius. This parameter was designed to ensure that the test group could operate without external heat source stimulation. Always lower The system was placed under preset dormancy conditions. The experiment was divided into three stages: the first stage was the background period (0-12h), during which a background solution with a trichloroethylene concentration of 0.1 mg / L was continuously injected into both columns; the second stage was the pulse period (12-24h), during which the injected solution was switched to a high-concentration pulse solution with a trichloroethylene concentration of 5.0 mg / L; and the third stage was the recovery period (24-36h), during which the injected solution was switched back to the background solution with a concentration of 0.1 mg / L. Throughout the experiment, the concentration of trichloroethylene in the effluent and the temperature of the catalyst bed in both columns were continuously monitored. Key data are shown in Table 2.

[0035] Table 2: Performance comparison data of the control group and the experimental group at different stages.

[0036] According to the data in Table 2, during the background period (0-12h), the control group showed a stable degradation rate of approximately 20.0%, indicating continuous release of its active sites. In contrast, the experimental group's degradation rate was only 10.0%, with the bed temperature maintained at a background level of 16.0°C, indicating effective masking of its active sites. During the pulse period (12-24h), the degradation rate of the control group did not increase. Faced with a high influent concentration of 5.0 mg / L, its effluent concentration was 3.95 mg / L, indicating pollutant breakthrough. Simultaneously, the effluent concentration of the experimental group rapidly decreased to 0.15 mg / L, and the degradation rate rose to 97.0%. The catalyst bed temperature simultaneously increased from 16.0°C to 22.5°C, exceeding its previous set limit of 19.0°C. After entering the recovery period (24-36h), the bed temperature and degradation rate of the experimental group returned to the background level, indicating that it returned to a dormant state after the pollutant was degraded. The experimental data confirmed that the particle group using the method of the present invention has a direct response relationship with the pollutant concentration. It can maintain dormancy to preserve activity when the pollutant concentration is low, and autonomously activate to show high degradation efficiency when the pollutant concentration increases.

[0037] Example 3: This example combines Figs. 1 to 3 The following describes a method for in-situ remediation of groundwater based on slow-release nanocatalysts, such as... Fig. 1 As shown, the process begins with the system entering a dynamic dormant state after being deployed in groundwater. When the target pollutant appears, it triggers molecular recognition and selective enrichment steps, where the molecular recognition groups selectively enrich the target pollutant. Subsequently, it enters a co-catalytic exothermic and initial activation stage, where the co-catalytic zone reacts with the pollutant, releasing initial heat. This heat induces a conformational phase change and exposure of active sites, meaning the local temperature exceeds [a certain threshold]. The polymer shrinks, exposing active sites. This conformational phase transition process is accompanied by a parallel surface self-cleaning and active regeneration mechanism. The surface adhering substances are peeled off by the mechanical shearing action of the phase transition process. After the active sites are exposed, the system performs catalytic degradation and cascade activation. The active sites degrade pollutants, and heat diffusion triggers a chain activation. The system then enters a judgment loop to determine whether the pollutants have been completely degraded. If not, it returns to continue the catalytic degradation and cascade activation steps. If so, it enters the system reset and dormancy recovery stage. At this time, the heat source disappears, the temperature drops, and the polymer returns to its swollen state. In addition, the method also includes an independent online diagnostic particle group activity module. This module includes three consecutive steps: step g: applying an alternating magnetic field, step h: measuring the temperature rise rate, and step i: comparison and judgment, which are used to determine the current activity state of the particle group.

[0038] like Fig. 2As shown, the horizontal axis represents time in hours (h), and the vertical axis represents the degradation rate of the target pollutant in percentage (%). The graph contains two curves: one is a dashed line marked with a circle, representing the degradation rate of the control group, and the other is a solid line marked with a triangle, representing the degradation rate of the experimental group. During the background period of the experiment, i.e., the interval from 0 to 12 hours, the degradation rate of the control group remained at 20%, while the degradation rate of the experimental group remained at 10%. During the pulse period of the experiment, i.e., the interval from 12 hours to 24 hours, when the pollutant concentration increased, the degradation rate of the experimental group rapidly climbed to nearly 100%, while the degradation rate of the control group only fluctuated slightly, remaining at 22%. During the recovery period of the experiment, i.e., starting from 24 hours, when the pollutant concentration returned to the background level, the degradation rate of the experimental group quickly dropped back to the initial level of 10%, while the degradation rate of the control group remained basically unchanged.

[0039] like Fig. 3 As shown, this structure is based on a catalytic core nanoparticle of zero-valent iron, whose surface is modified with a co-catalytic region (nanopalladium / platinum) as an initial heat source and cyclodextrin, a molecular recognition group for selectively capturing pollutants. These functional units are encapsulated within a first thermosensitive polymer layer of poly(N-isopropylacrylamide). It is adjustable and follows a temperature response mechanism, that is, when the ambient temperature... < At that time, it is in a dormant state of swelling and stretching, while when < When the temperature is high, dehydration and shrinkage occur, and the system is activated. This state transition is driven by a cascade activation process. A second temperature-sensitive polymer can also be configured on the outermost layer of the structure as an optional component for seasonal adjustment of the system.

[0040] Example 4: To determine the lower critical dissolution temperature of the first temperature-sensitive polymer layer of the particle group in the method of the present invention. So that it has a specific annual average background temperature The contaminated site possesses pre-defined response characteristics, and the following standardized engineering calibration procedure is performed. This procedure is conducted in a laboratory environment with predefined initial conditions, including a water bath reactor with a temperature control accuracy of ±0.1 degrees Celsius and a UV-Vis spectrophotometer for measuring solution turbidity. The calibrated samples are a series of poly(N-isopropylacrylamide)-co-acrylamide copolymers, aiming to establish the relationship between the molar fraction of acrylamide monomer in the copolymer and the final copolymer. quantitative relationship between the two; the calibration process first prepares a set of poly (N-isopropylacrylamide-co-acrylamide) copolymers with acrylamide molar fraction of 0%, 2%, 4%, 6%, 8% and 10% respectively under the same reaction conditions through free radical polymerization; then, each copolymer is prepared into an aqueous solution with a concentration of 1.0 g / L and placed in a sample cell of a UV-visible spectrophotometer; a program is set to raise the temperature from 15.0 degrees Celsius to 35.0 degrees Celsius at a rate of 0.2 degrees Celsius / min, and the transmittance of the solution at a wavelength of 500 nm is continuously monitored during the process; the temperature corresponding to the transmittance dropping to 50% of the initial value is defined as the activation temperature of the copolymer sample. By measuring six groups of samples, a set of data points of acrylamide molar fraction and activation temperature is obtained, and linear fitting is performed on the set of data to obtain the calibration curve under the specific polymerization system.

[0041] In one specific application, if the annual average background temperature of the target remediation site is 16.0 degrees Celsius, and the activation temperature threshold is set to 3.0 degrees Celsius, i.e., the target is 19.0 degrees Celsius, then according to the calibration curve established by the above experiment, the molar fraction of acrylamide monomer required to achieve a 19.0 degrees Celsius activation temperature is calculated to be 7.5%; this calculation result can be used to guide the feeding ratio of reactants NIPAM and AAm in subsequent production to prepare a particle group that meets the requirements of the specific site and has a determined response temperature. Example 5: This embodiment discloses a procedure for pre-deployment calibration of the particle group in the method of the present application to establish its online diagnostic function reference parameters; in a site where the remediation scheme design has been completed, before a batch of particles prepared according to the preparation is injected on a large scale, the reference temperature rise rate of the specific batch of particles needs to be established; to establish the reference, first take out a representative sample with a mass of 1.0 g from the particles to be injected, and mix it uniformly with 100 g of saturated quartz sand taken from the aquifer of the target remediation area, then fill the mixture in an adiabatic test container; place the container in the center of a Helmholtz coil capable of generating a standardized alternating magnetic field, set the field strength value of the alternating magnetic field to 30 kA / m, set the frequency to 200 kHz, and insert an optical fiber thermometer with a measurement accuracy of 0.01 degrees Celsius into the center of the mixture to record the temperature change.

[0042]

[0043] After the calibration procedure is initiated, a standardized alternating magnetic field is applied to the test container, and temperature data is continuously recorded for 300 seconds. An initial temperature rise rate is calculated by performing linear regression analysis on the first 60 seconds of the temperature rise curve. For this batch of particles, the reference temperature rise rate in the specific site medium was measured. The value is 0.50 degrees Celsius per minute; this value is recorded as the initial baseline value for the site remediation system, and the following activity status judgment logic is established: when the subsequent on-site measurement of the temperature rise rate is... Meet the conditions When the system activity is normal, it is determined that the system activity is normal; when the conditions are met... When, the system is determined to have partial passivation; when If this occurs, the system is determined to have undergone deep passivation.

[0044] Example 6: This example discloses a procedure for preparing particle groups with adaptive background temperature adjustment capability to cope with the significant seasonal temperature fluctuations in the groundwater environment; in a remediation site in a temperate region, the groundwater background temperature... Temperatures range from as low as 12 degrees Celsius in winter to as high as 17 degrees Celsius in summer. This wide temperature range is suitable for applications using a fixed lower critical melting temperature. The presence of large particle clusters poses an application challenge, as they may trigger false activation in summer due to small temperature differences, or fail to respond in winter due to excessively high required activation temperatures. To address these issues, in step a, the surface chemical modification of the particles is adjusted by employing a layered graft polymerization method to construct a dual polymer shell on the surface of the nano-zero-valent iron catalytic core. The inner layer is a first temperature-sensitive polymer layer, namely poly(N-isopropylacrylamide), which serves as the core gating unit. The temperature is set to 18 degrees Celsius; the outer layer is a second temperature-sensitive polymer, namely a regulating polymer, which is a polymer with a high critical dissolution temperature. During its polymerization process, sodium chloride is loaded as an ion regulator through electrostatic adsorption.

[0045] The cooperative operation mechanism of the dual polymer shell is as follows: In winter, when When the temperature drops to 12 degrees Celsius, the outer regulating polymer enters a contracted state due to the temperature being below its higher critical solution temperature. This conformation releases the loaded sodium chloride ions into the microenvironment of the inner gated polymer, and the increased local ionic strength leads to the gating polymer... The temperature is automatically lowered from 18 degrees Celsius to 14.5 degrees Celsius, thus maintaining the activation temperature rise threshold at 2.5 degrees Celsius; in summer, when When the temperature rises to 17 degrees Celsius, the outer regulating polymer, due to the temperature exceeding its high critical solution temperature, enters a swollen and stretched state. The resulting polymer network recaptures and fixes sodium chloride ions, reducing the ionic strength within the gated polymer microenvironment, thereby... From 18 degrees Celsius to 20 degrees Celsius automatically, the activation temperature rise threshold is maintained at 3.0 degrees Celsius; the particle group obtained by this preparation method is not a static parameter, but can respond to changes in ambient temperature and independently adjust the activation temperature rise threshold ) in a fixed working window, ensuring that the repair method has consistent response sensitivity and operational stability in long-term and variable real environments.

[0046] It is obvious to those skilled in the art that the present application is not limited to the details of the above exemplary embodiments, and can be implemented in other specific forms without departing from the spirit or essential characteristics of the present application.

[0047] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application and are not limiting. Although the present application has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that the technical solutions of the present application can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present application.

Claims

1. A method for in-situ remediation of groundwater based on slow-release nanocatalysts, characterized in that, The method comprises the following steps: Step a, providing a population of particles consisting of a catalytic core coated with a first temperature-sensitive polymer layer having a lower critical solution temperature set to be higher than the background temperature of the target groundwater environment ;​ Step b, dispersing the population of particles in the groundwater environment at background temperature The first temperature-sensitive polymer layer is in a swollen, extended state to shield the active sites of the catalytic core. Step c, fixing molecular recognition groups capable of specific binding with target pollutants in the vicinity of the catalytic core, and setting a co-catalytic region thermally coupled with the catalytic core; Step d, when the molecular recognition group selectively enriches the target pollutant and triggers the exothermic reaction in the co-catalytic zone, using the heat released by the exothermic reaction as the initial heat source, so that the local temperature of the particle surface crosses the critical solubility temperature ; Step e, in response to the local temperature crossing the critical dissolution temperature , the first temperature-sensitive polymer layer undergoes a conformational phase transition from a swollen extended state to a dehydrated contracted state, which exposes active sites to catalyze the degradation of target pollutants, and the mechanical shearing effect generated by the conformational phase transition peels off the attachments from the surface of the catalytic core; Step f. When the target pollutant is degraded, the local temperature falls back to the critical solution temperature The first temperature-sensitive polymer layer automatically reverts to the swollen stretched state and re-masks the active sites.

2. The method for in-situ remediation of groundwater based on slow-release nanocatalysts according to claim 1, characterized in that, In step e, the conformational phase transition of one particle triggers the conformational phase transition of adjacent particles within its thermal diffusion length range in turn, forming a self-amplifying cascade activation process.

3. The method for in-situ remediation of groundwater based on slow-release nanocatalysts according to claim 1, characterized in that, In step a, the surface of the population of particles is further modified with a second temperature-sensitive polymer, the conformation of which is capable of responding to seasonal fluctuations in the background temperature and adjusting the value of by changing the local ionic strength in the vicinity of the first temperature-sensitive polymer layer, to maintain the initial temperature rise threshold required to activate the method under varying background temperatures satisfies the condition wherein is the adjusted lower critical solution temperature.

4. The method for in-situ remediation of groundwater based on slow-release nanocatalysts according to claim 1, characterized in that, The co-catalytic region contains at least one selected from the group consisting of nano-palladium and nano-platinum, which is configured to produce higher unit reaction exothermic enthalpy change than the catalytic core when reacting with the target pollutants.

5. The method for in-situ remediation of groundwater based on slow-release nanocatalysts according to claim 1, characterized in that, The molecular recognition group is a cyclodextrin or a molecular sieve with a specific pore size, which is selectively fixed on the surface of the co-catalytic region or its nanoscale vicinity.

6. The method for in-situ groundwater remediation based on slow-release nanocatalysts according to claim 1, characterized in that, The attachment in step e is a natural organic matter or an inorganic salt deposition layer adsorbed on the surface of the particle in the groundwater environment, and the dramatic stretching of the first temperature-sensitive polymer layer chain in the conformational phase transition process generates shear force at the interface between the deposition layer and the catalytic core.

7. The method for in-situ groundwater remediation based on slow-release nanocatalysts according to claim 1, characterized in that, In step b, the first temperature-sensitive polymer layer in the swollen and stretched state forms a steric repulsion force between particles, which promotes the formation of a reversible flocculation aggregate structure, which further stabilizes the shielding state of the active site while enhancing the retention capacity of the particle group in the groundwater porous medium.

8. The method for in-situ groundwater remediation based on slow-release nanocatalysts according to claim 1, characterized in that, The method further comprises a step of diagnosing the activity of the particle group online, which comprises: step g, applying an alternating magnetic field with a preset frequency and field strength to the groundwater area where the particle group is located; step h, measuring the temperature rise rate caused by the heat induced in the catalytic core by the alternating magnetic field; step i, comparing the measured temperature rise rate with a reference temperature rise rate representing the initial health status of the particle group.

9. The method for in-situ remediation of groundwater based on slow-release nanocatalysts according to claim 8, characterized in that, In step i, when the measured temperature rise rate is 20% to 50% lower than the reference temperature rise rate, it is determined that the particle group has been deeply inactivated by irreversible mineral crust, biofilm or hard agglomeration.

10. The method for in-situ remediation of groundwater based on slow-release nanocatalysts according to claim 1, characterized in that, The catalytic core is nano zero-valent iron, and the first temperature-sensitive polymer layer is poly N-isopropyl acrylamide or its copolymer; and In step a, by regulating the monomer kind and ratio of the copolymer, the is set to a range of 2 degrees Celsius to 10 degrees Celsius higher than the annual average background temperature of the target groundwater environment.

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