Iron-based composite materials, their preparation methods and applications

Abstract

The present invention relates to the fields of material preparation and organic pollution control, and discloses an iron-based composite material, its preparation method, and application. The iron-based composite material comprises micron-sized zero-valent iron particles, a modified shell formed on the surface of the micron-sized zero-valent iron particles, and a carbon material dispersed around the periphery of the micron-sized zero-valent iron particles, wherein the modified shell is formed by electrolyzing a metal sulfide and a citrate to react with the micron-sized zero-valent iron particles. The iron-based composite material modifies the zero-valent iron with metal sulfide and citrate and uses the carbon material for loading, thereby improving the dispersibility of the zero-valent iron while further enhancing the lifespan and degradation ability of the iron-based composite material.

Description

Technical Field

[0001] This invention relates to the field of material preparation and organic pollution control, specifically to an iron-based composite material, its preparation method, and its application. Background Technology

[0002] With economic and social development and the accelerating pace of industrialization, organic pollution of soil and groundwater has become a global environmental problem. Due to the complexity of the soil and groundwater environment, once polluted, it can take years or even decades to remove the contaminants, seriously threatening the surrounding environment, residents' health, and land reuse. Therefore, the remediation of polluted soil and groundwater has become an environmental, economic, and social issue that must be addressed.

[0003] Currently, halogenated hydrocarbons are among the most common organic pollutants in groundwater, with trichloroethylene (TCE), carbon tetrachloride (CT), and tetrachloroethylene (PCE) being the most prevalent. Traditional groundwater remediation technologies include groundwater extraction and treatment, in-situ thermal desorption, surfactant leaching, and zero-valent iron chemical reduction. Zero-valent iron, in particular, is widely used due to its simple preparation, long lifespan, and lack of secondary pollution from the reaction products.

[0004] In recent years, nano-zero-valent iron has been widely used as a highly efficient modifier for in-situ remediation of water pollution due to its superior adsorption performance, reduction activity, reaction rate, and good environmental compatibility. It has found broad applications in wastewater treatment, contaminated soil remediation, and groundwater remediation. Laboratory-synthesized nano-zero-valent iron has a spherical structure with a core-shell dual structure. The core is a robust zero-valent iron crystal with a diffused ring structure resembling a metallic iron body-centered cubic crystal, surrounded by a thin oxide shell. However, its large specific surface area and surface energy result in a fast reaction rate and short lifespan. The high reaction rate and surface energy contribute to the short reaction lifespan of traditional zero-valent iron. Furthermore, its magnetic properties make it prone to aggregation in aqueous solutions, reducing its mobility and thus affecting its applications.

[0005] Currently, to address the issue of poor stability and rapid reaction with water and air of traditional zero-valent iron (ZVFe), reduced graphene oxide, carbon materials, carboxymethyl cellulose, and water-in-oil emulsions are commonly used as stabilizers. Among these, carbon materials, as inexpensive and readily available substrates with a large specific surface area and abundant microporous structure, have been successfully used to stabilize and control the aggregation of ZVFe, thereby enhancing its performance in environmental remediation. However, current preparation methods mostly involve stepwise high-temperature pyrolysis, and the raw materials often use chemical reagents such as ferric chloride, ferrous sulfate, and sodium borohydride. These processes are complex and expensive, limiting the large-scale application of these materials. Summary of the Invention

[0006] The purpose of this invention is to overcome the problems of poor dispersibility and easy agglomeration of zero-valent iron catalysts in the existing technology, and the need for further improvement in the remediation performance of remediation materials for groundwater pollutants. This invention provides an iron-based composite material, its preparation method and application. The iron-based composite material modifies zero-valent iron with metal sulfides and citrates, and uses carbon materials for loading. This can improve the dispersibility of zero-valent iron and further improve the lifespan and degradation capacity of the iron-based composite material.

[0007] To achieve the above objectives, the present invention provides an iron-based composite material comprising micron-sized zero-valent iron particles, a modified shell layer formed on the surface of the micron-sized zero-valent iron particles, and carbon material dispersed on the periphery of the micron-sized zero-valent iron particles, wherein the modified shell layer is formed by electrolysis of metal sulfides and citrates with the micron-sized zero-valent iron particles.

[0008] Preferably, the particle size of the micron-sized zero-valent iron particles is 2-15 μm.

[0009] Preferably, the D of the micron-sized zero-valent iron particles 50 The particle size is 6-12 μm.

[0010] Preferably, the iron-based composite material has a weight of 100 wt%, the modified shell has a content of 3.5-5.5 wt%, the micron-sized part has an iron content of 77-88 wt%, and the carbon material has a content of 8.5-17.5 wt%.

[0011] A second aspect of the present invention provides a method for preparing an iron-based composite material, the method comprising the following steps:

[0012] (1) Mix micron-sized zero-valent iron with a carbon source, and then calcine it;

[0013] (2) Remove the passivation film on the surface of the product obtained in step (1), and then use it as the working electrode, the inert electrode as the counter electrode, and the solution containing metal sulfide and citrate as the electrolyte. Perform constant voltage electrolysis to obtain iron-based composite material.

[0014] Preferably, step (2) includes the following process:

[0015] S1. The passivation film on the surface of the product obtained in step (1) is removed by electrolysis;

[0016] S2. Using a solution containing metal sulfide and citrate as the electrolyte, the product obtained in step S1 is used as the anode and an inert material is used as the cathode to perform constant voltage electrolysis to obtain an iron-based composite material.

[0017] Preferably, in step S1, the electrolysis is performed by alternating between the first stage of electrolysis and the second stage of electrolysis.

[0018] In this process, the product obtained in step (1) is used as the working electrode, the inert material is used as the counter electrode, and water is used as the electrolyte. The first stage of electrolysis is constant voltage electrolysis with the inert electrode as the cathode, and the second stage of electrolysis is constant voltage electrolysis with the inert electrode as the anode.

[0019] Preferably, in step S1, the conditions for the first stage of electrolysis include: a voltage of 2.5-4V and a time of 30-90s;

[0020] Preferably, the conditions for the second stage of electrolysis include: a voltage of 2.5-4V and a time of 30-90s.

[0021] Preferably, in step S2, the constant voltage electrolysis conditions include: voltage of 1-2V and time of 2-5h.

[0022] Preferably, in step S1, the electrolysis time is 2-4 hours.

[0023] Preferably, the weight ratio of micron-sized zero-valent iron particles, metal sulfides, and citrate is 14-20:1:1.5-7.

[0024] Preferably, the particle size of the micron-sized zero-valent iron particles is 2-15 μm.

[0025] Preferably, the weight ratio of the micron-sized zero-valent iron particles to the carbon source is 1:0.05-0.5.

[0026] Preferably, the calcination conditions include: a temperature of 200-250℃ and a time of 5-20 minutes.

[0027] A third aspect of the present invention provides an iron-based composite material prepared by the above-described preparation method.

[0028] A fourth aspect of the present invention provides an application of the above-mentioned iron-based composite material in the remediation of groundwater pollutants.

[0029] Preferably, the groundwater pollutant is selected from one or more of carbon tetrachloride, tetrachloroethylene, trichloroethylene, dichloroethylene, tetrachloropropane, and trichloropropane.

[0030] The iron-based composite material of this invention disperses carbon material around micron-sized zero-valent iron particles, preventing magnetic attraction between zero-valent iron particles and improving the dispersibility and stability of these particles. Furthermore, the micron-sized zero-valent iron particles are further modified with metal sulfides and citric acid via electrochemical methods, further enhancing their degradation capacity for groundwater pollutants. Additionally, the sulfides on the surface of the sulfide-type zero-valent iron cause electron transfer to favor pollutants rather than water molecules, while simultaneously inhibiting passivation, significantly improving the lifespan and degradation capacity of the iron-based composite material and extending its effective lifespan.

[0031] This invention employs an electrochemical method to prepare iron-based composite materials. Through repeated alternating electrolysis at the anode and cathode, micron-sized zero-valent iron particles are modified by sulfidation and citric acid treatment, resulting in more uniform modification and higher activity. Furthermore, the preparation method described in this invention does not require the addition of strong acids or bases as catalysts, resulting in a simple process, low cost, recyclability, and suitability for large-scale production. More importantly, the iron-based composite materials prepared using the method described in this application exhibit superior degradation effects on groundwater pollutants, demonstrating significant application potential. Detailed Implementation

[0032] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0033] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0034] In this invention, the passivation film on the surface of the product obtained in step (1) specifically refers to the iron oxide film generated by the reaction on the surface of zero-valent iron.

[0035] In this invention, the iron-based composite material comprises micron-sized zero-valent iron particles, a modified shell layer formed on the surface of the micron-sized zero-valent iron particles, and carbon material dispersed on the periphery of the micron-sized zero-valent iron particles. The modified shell layer is formed by electrolysis of metal sulfides and citrates with the micron-sized zero-valent iron particles.

[0036] In this invention, the carbon material dispersed around the micron-sized zero-valent iron particles is tightly bonded to the micron-sized zero-valent iron particles by chemical bonds, making it difficult for them to detach. Dispersing the carbon material around the micron-sized zero-valent iron increases the dispersibility and stability of the modified zero-valent iron, preventing aggregation between the modified zero-valent iron particles that would lead to decreased activity, and stabilizing and controlling the agglomeration of zero-valent iron. Furthermore, the co-modification with metal sulfides and citric acid makes electron transfer more inclined towards contaminants rather than water molecules, while simultaneously inhibiting passivation of the material, significantly improving the lifetime and degradation ability of the zero-valent iron. In this invention, the carbon material and the modified shell synergistically enhance the degradation ability of the iron-based composite material.

[0037] In this invention, the carbon material can be a carbon material commonly used in the art for loading metal particles.

[0038] In a preferred embodiment, the particle size of the micron-sized zero-valent iron particles is 2-15 μm. By using micron-sized zero-valent iron as the active component in this invention, the specific surface area of ​​the micron-sized zero-valent iron is larger, resulting in stronger stability compared to nano-sized zero-valent iron used in the prior art. Consequently, the material exhibits a longer remediation cycle and superior pollutant degradation ability during groundwater remediation.

[0039] In a preferred embodiment, the D of the micron-sized zero-valent iron particles 50 The particle size is 6-12 μm.

[0040] In a preferred embodiment, the iron-based composite material has a weight of 100 wt%, the modified shell has a content of 3.5-5.5 wt%, the micron-sized part has an iron content of 77-88 wt%, and the carbon material has a content of 8.5-17.5 wt%.

[0041] In this invention, micron-sized zero-valent iron is modified by electrolysis using metal sulfides and citrates, which results in more uniform modification and higher activity in the iron-based composite material prepared later.

[0042] In this invention, during the electrolysis process, since the carbon material is an inert material and cannot react with metal sulfides and citrates, the distribution of the carbon material and the modified shell layer does not overlap. The carbon material and the modified shell layer can either completely encapsulate the micron-sized zero-valent iron or only partially encapsulate it. Furthermore, by controlling the content of the modified shell layer and the carbon material, the activity of the iron-based composite material is made more superior, thus extending the effective lifespan of the iron-based composite material.

[0043] This invention further provides a method for preparing an iron-based composite material, the method comprising the following steps:

[0044] (1) Mix micron-sized zero-valent iron particles with a carbon source, and then calcine them;

[0045] (2) Remove the passivation film on the surface of the product obtained in step (1), and then use it as the working electrode, the inert electrode as the counter electrode, and the solution containing metal sulfide and citrate as the electrolyte. Perform constant voltage electrolysis to obtain iron-based composite material.

[0046] In a specific implementation, in step (1), carbon material is dispersed around the zero-valent iron by mixing and calcining the zero-valent iron with a carbon source to improve the dispersion and stability of the zero-valent iron and prevent the aggregation of the zero-valent iron.

[0047] In a specific implementation, the zero-valent iron can be a commercial product or can be prepared by conventional methods in the art.

[0048] In specific embodiments, the carbon source used can be a common carbon source in the art, or a commercially available product commonly used in the art. Preferably, in order to further improve the degradation performance of the prepared iron-based composite material, the carbon source is selected from one or more of gelatin, carrageenan, sodium caseinate, and sodium alginate.

[0049] In a preferred embodiment, in order to further improve the degradation performance of the prepared iron-based composite material, the selected micron-sized zero-valent iron has a particle size of 2-15 μm.

[0050] In a preferred embodiment, the D of the micron-sized zero-valent iron 50 The particle size is 6-12 μm.

[0051] In a specific implementation, in step (1), when mixing zero-valent iron with a carbon source, the carbon source can be dissolved in water first, and then zero-valent iron can be added, mixed evenly, and then dried and calcined.

[0052] In a specific implementation, the drying conditions for the material after mixing zero-valent iron with carbon source in step (1) include: a temperature of 100-120°C and a time of 30-60 min.

[0053] In a specific implementation, in step (1), the zero-valent iron and the carbon source can be mixed by mechanical stirring at a speed of 200-900 rpm, preferably 500-700 rpm.

[0054] In a preferred embodiment, to further improve the degradation performance of the prepared iron-based composite material, the weight ratio of zero-valent iron to carbon source is controlled to be 1:0.05-0.5, preferably 1:0.1-0.3. Specifically, the weight ratio of zero-valent iron to carbon source can be 1:0.05, 1:0.1, 1:0.2, 1:0.3, 1:0.4, or 1:0.5.

[0055] In a preferred embodiment, in step (1), the calcination conditions include: a temperature of 200-250°C and a time of 5-20 minutes. Specifically, the calcination temperature can be 200°C, 210°C, 220°C, 230°C, 240°C, or 250°C; and the calcination time can be 5 minutes, 10 minutes, 15 minutes, or 20 minutes.

[0056] In this invention, zero-valent iron is modified with metal sulfides and citric acid using an electrochemical method to further enhance the degree of modification, thereby improving the degree of modification of zero-valent iron in the iron-based composite material and further enhancing the degradation ability of the iron-based composite material for pollutants.

[0057] In a specific implementation, before electrochemical modification in step (2), the passivation film on the surface of zero-valent iron in the product obtained in step (1) needs to be removed to increase the number of active sites and reactivity of zero-valent iron, so as to facilitate the subsequent modification of zero-valent iron with metal sulfides and citrates.

[0058] In this invention, the method of removing the passivation film on the surface of the product obtained in step (1) is not limited; it is only necessary to remove the passivation film on the surface of the material.

[0059] In a preferred embodiment, step (2) includes the following process:

[0060] S1. The passivation film on the surface of the product obtained in step (1) is removed by electrolysis;

[0061] S2. Using a solution containing metal sulfide and citrate as the electrolyte, the product obtained in step S1 is used as the anode and an inert material is used as the cathode to perform constant voltage electrolysis to obtain an iron-based composite material.

[0062] In a preferred embodiment, in order to improve the removal rate of the passivation film on the surface of the product prepared in step (1) and ensure the uniformity of subsequent modification, an electrolytic method can be used for removal.

[0063] In a preferred embodiment, in step S1, the electrolysis is performed by alternating between the first stage of electrolysis and the second stage of electrolysis.

[0064] In this process, the product obtained in step (1) is used as the working electrode, the inert material is used as the counter electrode, and water is used as the electrolyte. The first stage of electrolysis is constant voltage electrolysis with the inert electrode as the cathode, and the second stage of electrolysis is constant voltage electrolysis with the inert electrode as the anode.

[0065] In a preferred embodiment, the product obtained in step (1) can be used as the working electrode, and then the passivation film on the surface of the product obtained in step (1) can be removed by repeated alternating electrolysis of the anode and cathode, so that the modification of zero-valent iron in the later stage is more uniform and the degradation performance of the prepared iron-based composite material is further improved.

[0066] In a specific implementation, in step S1, the choice of the first electrolysis is not limited when alternating between the first stage electrolysis and the second stage electrolysis. It can be understood that during the alternating electrolysis process, the first electrolysis is not limited to either the first stage electrolysis or the second stage electrolysis, as long as the subsequent alternation between the first stage electrolysis and the second stage electrolysis is satisfied.

[0067] In this invention, during the first stage of electrolysis, oxygen is generated by electrolyzing water in the anode region, gradually destroying the passivation film on the surface of zero-valent iron through mechanical means. Simultaneously, H2O generated in the electrolyte in the anode region... + This process further promotes the dissolution of the passivation film, further removing the passivation film layer on the surface of zero-valent iron. In the second stage of electrolysis, the electrolysis of water in the cathode area generates a large amount of hydrogen gas, which further and gradually mechanically destroys the passivation film layer. By alternating between the first and second stages of electrolysis, the passivation film layer on the surface of zero-valent iron is removed as much as possible. Furthermore, removing the passivation film layer by electrolysis avoids the solvent pollution problems caused by the use of strong acids and alkalis to remove the passivation film layer commonly used in existing technologies, and is suitable for large-scale production, as the preparation process does not introduce secondary pollution.

[0068] In this invention, the conditions for the first stage of electrolysis in step S1 include: a voltage of 2.5-4V, preferably 2.6-3.5V, and a time of 30-90s, preferably 40-60s. Specifically, the voltage for the first stage of electrolysis can be 2.5V, 3V, 3.5V, or 4V; the time for the first stage of electrolysis can be 30s, 40s, 50s, 60s, 70s, 80s, or 90s.

[0069] In this invention, the conditions for the second-stage electrolysis in step S1 include: a voltage of 2.5-4V, preferably 2.6-3.5V, and a time of 30-90s, preferably 40-60s. Specifically, the voltage for the second-stage electrolysis can be 2.5V, 3V, 3.5V, or 4V; and the time for the second-stage electrolysis can be 30s, 40s, 50s, 60s, 70s, 80s, or 90s.

[0070] In a specific implementation, the voltage and electrolysis time set for the first stage of electrolysis can be the same as or different from those set for the second stage of electrolysis. Preferably, the voltage and electrolysis time set for the first stage of electrolysis are the same as those set for the second stage of electrolysis.

[0071] In a specific implementation, in step S1, the total time for alternating the first stage electrolysis and the second stage electrolysis is not limited. It is only necessary to remove the passivation film on the surface of the product obtained in step (1) by alternating the first stage electrolysis and the second stage electrolysis.

[0072] In a preferred embodiment, to further ensure complete removal of the passivation film on the surface of the product obtained in step (1), the electrolysis time in step S1 is 2-4 hours. Specifically, the electrolysis time can be 2 hours, 3 hours, or 4 hours. The electrolysis time in step S1 refers to the total electrolysis time for alternating between the first and second stage electrolysis.

[0073] In a specific implementation, after electrolysis in step S1, in order to further save preparation time, it is possible to choose not to replace the electrolytic cell and directly add metal sulfide and citrate to the electrolytic cell used in step S1 to obtain the electrolyte required in step S2.

[0074] In this invention, in step S2, the product obtained after electrolysis in step S1 is used as the anode, and zero-valent iron is modified during electrolysis by adding metal sulfide and citrate to the original electrolyte (water). The zero-valent iron modified by the method described in this invention is more uniformly modified, and the resulting product has better degradation ability.

[0075] In this invention, during step S2, the pH value of the electrolyte needs to be monitored continuously to maintain an alkaline environment, ensuring that sodium sulfide and sodium citrate exist in the electrolyte in anionic form. When the pH value of the electrolyte reaches 7-8, the electrolysis is stopped to obtain the iron-based composite material.

[0076] In a preferred embodiment, in step S2, the conditions for constant voltage electrolysis include: a voltage of 1-2V and a time of 2-5h. Specifically, the voltage for constant voltage electrolysis is 1V, 1.5V, or 2V; and the time for constant voltage electrolysis is 2h, 3h, 4h, or 5h.

[0077] In a preferred embodiment, the weight ratio of micron-sized zero-valent iron particles, metal sulfide, and citrate is 14-20:1:1.5-7, more preferably 14-20:1:2-6.

[0078] In a preferred embodiment, in step S2, the metal sulfide is sodium sulfide and / or potassium sulfide, and the citrate is selected from one or more of sodium citrate, potassium citrate, magnesium citrate, and ferric citrate.

[0079] In a preferred embodiment, the concentration of metal sulfide in the electrolyte is controlled to be 0.6-1.5 mol / L, and the concentration of citrate in the electrolyte is controlled to be 0.6-1.5 mol / L.

[0080] In a specific implementation, in step (2), after electrolysis, the obtained product needs to be washed with pure water 2-5 times and then dried at low temperature under an inert atmosphere to obtain an iron-based composite material.

[0081] In this invention, during the first stage electrolysis, the second stage electrolysis, and the constant voltage electrolysis in step S2, the selected electrolytic cell can be a common electrolytic cell in the art that has a cathode region and an anode region. The cathode region and the anode region are separated by a diaphragm to avoid the substances obtained by electrolysis in the cathode region and the anode region from affecting each other.

[0082] In a specific implementation, in steps S1 and S2, when modifying the product obtained in step (1) as a working electrode, the product obtained in step (1), carbon black and Nafion binder can be mixed evenly, and then the slurry is coated on a graphite plate and dried to serve as a working electrode.

[0083] The present invention may further provide an application of the above-mentioned iron-based composite material in the remediation of groundwater pollutants.

[0084] In this invention, the iron-based composite material can be directly injected into groundwater to treat pollutants, or it can be used as a reducing agent in a permeable reactive wall to treat pollutants directly.

[0085] In specific embodiments, when the iron-based composite material is used to treat groundwater pollutants, the type of groundwater being treated is not limited. The iron-based composite material of this invention is particularly suitable for groundwater with high dissolved oxygen and nitrate content, and can rapidly reduce the redox potential of the groundwater, forming a reducing environment and ensuring that the zero-valent iron surface loses as little reducing capacity as possible due to oxidation by oxygen and nitrates.

[0086] In a preferred embodiment, the groundwater pollutant is selected from one or more of carbon tetrachloride, tetrachloroethylene, trichloroethylene, dichloroethylene, tetrachloropropane, and trichloropropane. The iron-based composite material described in this invention exhibits excellent degradation ability against these pollutants.

[0087] The present invention will be described in detail below through embodiments, but the scope of protection of the present invention is not limited thereto. The embodiments are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operating procedures, but the scope of protection of the present invention is not limited to the following embodiments.

[0088] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods in the art. Unless otherwise specified, the experimental materials used in the following embodiments are commercially available.

[0089] In the following examples and comparative examples, in step (2), the preparation process of the working electrode is as follows: the product obtained in step (1), carbon black, and Nafion binder are mixed evenly in a weight ratio of 8:1:1 to form a slurry, and then the slurry is coated on a 1×1cm plate. 2 After drying on a graphite plate, it is used as a working electrode.

[0090] Example 1

[0091] (1) Dissolve carrageenan in water, then add zero-valent iron granules (the weight ratio of carrageenan to zero-valent iron granules is 0.1:1, and the D of the zero-valent iron granules is...). 50 The particles (7μm in diameter) were mechanically stirred (stirring speed 600rpm) until uniformly mixed, then dried at 110℃ for 40min. The dried material was then placed in a muffle furnace for calcination at 220℃ for 8min.

[0092] (2) The product obtained in step (1) is subjected to a first-stage electrolysis and a second-stage electrolysis alternately, with a total electrolysis time of 2 hours. The product obtained in step (1) is used as the working electrode, the carbon rod as the counter electrode, and water as the electrolyte. The first-stage electrolysis is a constant-voltage electrolysis with the carbon rod electrode as the cathode, with a voltage of 2.5V and a time of 60s. The second-stage electrolysis is a constant-voltage electrolysis with the carbon rod as the anode, with a voltage of 2.5V and a time of 60s.

[0093] (3) Add 1 mol / L sodium sulfide and 1 mol / L sodium citrate to the electrolyte (the weight ratio of zero-valent iron particles, sodium sulfide and sodium citrate is 20:1:2). Then, use the product obtained in step (2) as the anode and the carbon rod as the cathode for constant voltage electrolysis at a voltage of 1.5V for 2 hours. After the electrolysis is completed, wash with pure water 2-5 times and dry to obtain iron-based composite material. XPS detection shows that the content of modified shell in the iron-based composite material is 4.9 wt%, the content of micron-sized zero-valent iron is 85.8 wt%, and the content of carbon material is 9.3 wt%.

[0094] Example 2

[0095] (1) Dissolve sodium alginate in water, then add zero-valent iron granules (the weight ratio of sodium alginate to zero-valent iron granules is 0.15:1, and the D of the zero-valent iron granules is...). 50 The particles (with a particle size of 8 μm) were mechanically stirred (stirring speed 700 rpm) until uniformly mixed, then dried at 110℃ for 30 min. The dried material was then placed in a muffle furnace for calcination at 210℃ for 10 min.

[0096] (2) The product obtained in step (1) is subjected to a first-stage electrolysis and a second-stage electrolysis alternately, with a total electrolysis time of 2.5 h; wherein, the product obtained in step (1) is used as the working electrode, the carbon rod is used as the counter electrode, and water is used as the electrolyte; the first-stage electrolysis is a constant-voltage electrolysis with the carbon rod electrode as the cathode, the voltage is 2.8 V, and the time is 60 s; the second-stage electrolysis is a constant-voltage electrolysis with the carbon rod as the anode, the voltage is 2.8 V, and the time is 60 s.

[0097] (3) Add 1.1 mol / L sodium sulfide and 1.1 mol / L sodium citrate to the electrolyte (the weight ratio of zero-valent iron particles, sodium sulfide and sodium citrate is 16.6:1:3). Then, use the product obtained in step (2) as the anode and the carbon rod as the cathode for constant voltage electrolysis at a voltage of 1.6V for 2.5h. After the electrolysis is completed, wash with pure water 2-5 times and dry to obtain iron-based composite material. XPS detection shows that the content of modified shell in the iron-based composite material is 5.1wt%, the content of micron-sized zero-valent iron is 83.2wt%, and the content of carbon material is 11.7wt%.

[0098] Example 3

[0099] (1) Dissolve sodium caseinate in water, then add zero-valent iron granules (the weight ratio of sodium caseinate to zero-valent iron is 0.2:1, and the D of the zero-valent iron granules is...). 50 The particles (with a particle size of 6μm) were mechanically stirred (stirring speed 700rpm) until uniformly mixed, then dried at 120℃ for 40min. The dried material was then placed in a muffle furnace for calcination at 220℃ for 8min.

[0100] (2) The product obtained in step (1) is subjected to a first stage of electrolysis and a second stage of electrolysis alternately, with a total electrolysis time of 3 hours. The product obtained in step (1) is used as the working electrode, the carbon rod is used as the counter electrode, and water is used as the electrolyte. The first stage of electrolysis is a constant voltage electrolysis with the carbon rod electrode as the cathode, with a voltage of 3V and a time of 45s. The second stage of electrolysis is a constant voltage electrolysis with the carbon rod as the anode, with a voltage of 3V and a time of 45s.

[0101] (3) Add 1.2 mol / L sodium sulfide and 1.2 mol / L sodium citrate to the electrolyte (the weight ratio of zero-valent iron particles, sodium sulfide and sodium citrate is 16.6:1:6). Then, use the product obtained in step (2) as the anode and the carbon rod as the cathode to perform constant voltage electrolysis. The voltage is 1.7V and the electrolysis time is 3h. After the electrolysis is completed, wash with pure water 2-5 times and then dry to obtain iron-based composite material. XPS detection shows that the content of modified shell in iron-based composite material is 5wt%, the content of micron-sized zero-valent iron is 81.8wt%, and the content of carbon material is 13.2wt%.

[0102] Example 4

[0103] (1) Dissolve carrageenan in water, then add zero-valent iron granules (the weight ratio of carrageenan to zero-valent iron granules is 0.25:1, and the D of the zero-valent iron granules is...). 50 The particles (with a particle size of 5 μm) were mechanically stirred (stirring speed 700 rpm) until uniformly mixed, then dried at 120℃ for 30 min. The dried material was then placed in a muffle furnace for calcination at 230℃ for 10 min.

[0104] (2) The product obtained in step (1) is subjected to a first-stage electrolysis and a second-stage electrolysis alternately, with a total electrolysis time of 3.5 h; wherein, the product obtained in step (1) is used as the working electrode, the carbon rod is used as the counter electrode, and water is used as the electrolyte; the first-stage electrolysis is a constant-voltage electrolysis with the carbon rod electrode as the cathode, the voltage is 3.2 V, and the time is 45 s; the second-stage electrolysis is a constant-voltage electrolysis with the carbon rod as the anode, the voltage is 3.2 V, and the time is 45 s.

[0105] (3) Add 0.8 mol / L sodium sulfide and 0.8 mol / L sodium citrate to the electrolyte (the weight ratio of zero-valent iron particles, sodium sulfide and sodium citrate is 16.6:1:4). Then, use the product obtained in step (2) as the anode and the carbon rod as the cathode for constant voltage electrolysis at a voltage of 1.8V for 3.5h. After the electrolysis is completed, wash with pure water 2-5 times and dry to obtain iron-based composite material. XPS detection shows that the content of modified shell in the iron-based composite material is 4.8wt%, the content of micron-sized zero-valent iron is 79.2wt%, and the content of carbon material is 16wt%.

[0106] Example 5

[0107] (1) Dissolve gelatin in water, then add zero-valent iron granules (the weight ratio of gelatin to zero-valent iron is 0.3:1, and the D of the zero-valent iron granules is...). 50The particles (with a particle size of 8 μm) were mechanically stirred (stirring speed 700 rpm) until uniformly mixed, then dried at 120℃ for 40 min. The dried material was then placed in a muffle furnace for calcination at 220℃ for 10 min.

[0108] (2) The product obtained in step (1) is subjected to alternating first-stage electrolysis and second-stage electrolysis for a total electrolysis time of 4 hours. The product obtained in step (1) is used as the working electrode, the carbon rod as the counter electrode, and water as the electrolyte. The first-stage electrolysis is performed by constant voltage electrolysis with the carbon rod electrode as the cathode at a voltage of 3.5V for 50 seconds. The second-stage electrolysis is performed by constant voltage electrolysis with the carbon rod as the anode at a voltage of 3.5V for 50 seconds.

[0109] (3) Add 1.5 mol / L sodium sulfide and 1.5 mol / L sodium citrate to the electrolyte (the weight ratio of zero-valent iron particles, sodium sulfide and sodium citrate is 14.2:1:5). Then, use the product obtained in step (2) as the anode and the carbon rod as the cathode for constant voltage electrolysis at 2V for 4 hours. After the electrolysis is completed, wash with pure water 2-5 times and dry to obtain iron-based composite material. XPS detection shows that the content of modified shell in the iron-based composite material is 4.5 wt%, the content of micron-sized zero-valent iron is 81.2 wt%, and the content of carbon material is 14.3 wt%.

[0110] Example 6

[0111] (1) Dissolve carrageenan in water, then add zero-valent iron granules (the weight ratio of carrageenan to zero-valent iron granules is 0.6:1, and the D of the zero-valent iron granules is...). 50 The particles (7μm in diameter) were mechanically stirred (stirring speed 600rpm) until uniformly mixed, then dried at 110℃ for 40min. The dried material was then placed in a muffle furnace for calcination at 220℃ for 8min.

[0112] (2) The product obtained in step (1) is subjected to a first-stage electrolysis and a second-stage electrolysis alternately, with a total electrolysis time of 2 hours. The product obtained in step (1) is used as the working electrode, the carbon rod as the counter electrode, and water as the electrolyte. The first-stage electrolysis is a constant-voltage electrolysis with the carbon rod electrode as the cathode, with a voltage of 2.5V and a time of 60s. The second-stage electrolysis is a constant-voltage electrolysis with the carbon rod as the anode, with a voltage of 2.5V and a time of 60s.

[0113] (3) Add 1 mol / L sodium sulfide and 1 mol / L sodium citrate to the electrolyte (the weight ratio of zero-valent iron particles, sodium sulfide and sodium citrate is 20:1:2). Then, use the product obtained in step (2) as the anode and the carbon rod as the cathode for constant voltage electrolysis at a voltage of 1.5V for 2 hours. After the electrolysis is completed, wash with pure water 2-5 times and dry to obtain iron-based composite material. XPS detection shows that the content of modified shell in the iron-based composite material is 1.8wt%, the content of micron-sized zero-valent iron is 79.3wt%, and the content of carbon material is 18.9wt%.

[0114] Example 7

[0115] (1) Dissolve carrageenan in water, then add zero-valent iron granules (the weight ratio of carrageenan to zero-valent iron granules is 0.1:1, and the D of the zero-valent iron granules is...). 50 The particles (7μm in diameter) were mechanically stirred (stirring speed 600rpm) until uniformly mixed, then dried at 110℃ for 40min. The dried material was then placed in a muffle furnace for calcination at 220℃ for 8min.

[0116] (2) The product obtained in step (1) is subjected to a first-stage electrolysis and a second-stage electrolysis alternately, with a total electrolysis time of 2 hours. The product obtained in step (1) is used as the working electrode, the carbon rod as the counter electrode, and water as the electrolyte. The first-stage electrolysis is a constant-voltage electrolysis with the carbon rod electrode as the cathode, with a voltage of 2.5V and a time of 60s. The second-stage electrolysis is a constant-voltage electrolysis with the carbon rod as the anode, with a voltage of 2.5V and a time of 60s.

[0117] (3) Add 1 mol / L sodium sulfide and 1 mol / L sodium citrate to the electrolyte (the weight ratio of zero-valent iron particles, sodium sulfide and sodium citrate is 20:1:2). Then, use the product obtained in step (2) as the anode and the carbon rod as the cathode for constant voltage electrolysis at a voltage of 2.5V for 2 hours. After the electrolysis is completed, wash with pure water 2-5 times and dry to obtain iron-based composite material. XPS detection shows that the content of modified shell in the iron-based composite material is 5.8 wt%, the content of micron-sized zero-valent iron is 84.2 wt%, and the content of carbon material is 10 wt%.

[0118] Example 8

[0119] (1) Dissolve carrageenan in water, then add zero-valent iron granules (the weight ratio of carrageenan to zero-valent iron granules is 0.1:1, and the D of the zero-valent iron granules is...). 50 The particles (7μm in diameter) were mechanically stirred (stirring speed 600rpm) until uniformly mixed, then dried at 110℃ for 40min. The dried material was then placed in a muffle furnace for calcination at 220℃ for 8min.

[0120] (2) The product obtained in step (1) is subjected to a first-stage electrolysis and a second-stage electrolysis alternately, with a total electrolysis time of 2 hours. The product obtained in step (1) is used as the working electrode, the carbon rod as the counter electrode, and water as the electrolyte. The first-stage electrolysis is a constant-voltage electrolysis with the carbon rod electrode as the cathode, with a voltage of 2.5V and a time of 60s. The second-stage electrolysis is a constant-voltage electrolysis with the carbon rod as the anode, with a voltage of 2.5V and a time of 60s.

[0121] (3) Add 1 mol / L sodium sulfide and 1 mol / L sodium citrate to the electrolyte (the weight ratio of zero-valent iron particles, sodium sulfide and sodium citrate is 20:1:10). Then, use the product obtained in step (2) as the anode and the carbon rod as the cathode for constant voltage electrolysis at a voltage of 1.5V for 2 hours. After the electrolysis is completed, wash with pure water 2-5 times and dry to obtain iron-based composite material. XPS detection shows that the content of modified shell in the iron-based composite material is 7.1 wt%, the content of micron-sized zero-valent iron is 75.6 wt%, and the content of carbon material is 17.3 wt%.

[0122] Example 9

[0123] (1) Dissolve carrageenan in water, then add zero-valent iron granules (the weight ratio of carrageenan to zero-valent iron granules is 0.1:1, and the D of the zero-valent iron granules is...). 50 The particles (7μm in diameter) were mechanically stirred (stirring speed 600rpm) until uniformly mixed, then dried at 110℃ for 40min. The dried material was then placed in a muffle furnace for calcination at 220℃ for 8min.

[0124] (2) The product obtained in step (1) is subjected to a first-stage electrolysis and a second-stage electrolysis alternately, with a total electrolysis time of 2 hours. The product obtained in step (1) is used as the working electrode, the carbon rod as the counter electrode, and water as the electrolyte. The first-stage electrolysis is a constant-voltage electrolysis with the carbon rod electrode as the cathode, with a voltage of 2.5V and a time of 60s. The second-stage electrolysis is a constant-voltage electrolysis with the carbon rod as the anode, with a voltage of 2.5V and a time of 60s.

[0125] (3) Add 1 mol / L sodium sulfide and 1 mol / L sodium citrate to the electrolyte (the weight ratio of zero-valent iron particles, sodium sulfide and sodium citrate is 25:1:2). Then, use the product obtained in step (2) as the anode and the carbon rod as the cathode for constant voltage electrolysis at a voltage of 1.5V for 2 hours. After the electrolysis is completed, wash with pure water 2-5 times and dry to obtain iron-based composite material. XPS detection shows that the content of modified shell in the iron-based composite material is 3.3wt%, the content of micron-sized zero-valent iron is 89.3wt%, and the content of carbon material is 7.4wt%.

[0126] Example 10

[0127] (1) Dissolve carrageenan in water, then add zero-valent iron granules (the weight ratio of carrageenan to zero-valent iron granules is 0.1:1, and the D of the zero-valent iron granules is...). 50 The particles (7μm in diameter) were mechanically stirred (stirring speed 600rpm) until uniformly mixed, then dried at 110℃ for 40min. The dried material was then placed in a muffle furnace for calcination at 220℃ for 8min.

[0128] (2) Soak the product obtained in step (1) in 1 mol / L HCl solution for 15 min. After soaking, take it out and wash it with water.

[0129] (3) Add 1 mol / L sodium sulfide and 1 mol / L sodium citrate to the electrolyte (the weight ratio of zero-valent iron particles, sodium sulfide and sodium citrate is 20:1:2). Then, use the product obtained in step (2) as the anode and the carbon rod as the cathode for constant voltage electrolysis at a voltage of 1.5V for 2 hours. After the electrolysis is completed, wash with pure water 2-5 times and dry to obtain iron-based composite material. XPS detection shows that the content of modified shell in the iron-based composite material is 2.1wt%, the content of micron-sized zero-valent iron is 85.4wt%, and the content of carbon material is 12.5wt%.

[0130] Comparative Example 1

[0131] Dissolve sodium caseinate in water, then add ferrous oxide granules (sodium caseinate to ferrous oxide by weight ratio of 0.2:1, ferrous oxide granules D...). 50 The particles (with a particle size of 9 μm) were mechanically stirred (stirring speed 700 rpm) until uniformly mixed, then dried at 120℃ for 40 min. The dried material was then placed in a muffle furnace for calcination at 220℃ for 8 min to obtain the product.

[0132] Comparative Example 2

[0133] (1) Zero-valent iron particles (the D of zero-valent iron particles) 50 Electrolysis was carried out alternately in two stages (with a particle size of 7 μm), with a total electrolysis time of 3 hours. Zero-valent iron particles were used as the working electrode, carbon rods as the counter electrode, and water as the electrolyte. The first stage of electrolysis was performed at a constant voltage of 2.5 V for 60 seconds, with the carbon rod electrode as the cathode. The second stage of electrolysis was performed at a constant voltage of 2.5 V for 60 seconds, with the carbon rod electrode as the anode.

[0134] (2) Add 1 mol / L sodium sulfide and 1 mol / L sodium citrate to the electrolyte (the weight ratio of zero-valent iron particles, sodium sulfide and sodium citrate is 20:1:2). Then, use the product obtained in step (1) as the anode and the carbon rod as the cathode to perform constant voltage electrolysis. The voltage is 1.5V and the electrolysis time is 2h. After the electrolysis is completed, wash with pure water 2-5 times and then dry to obtain the product.

[0135] Test case

[0136] Test Example 1

[0137] The particle size distribution of the iron-based composite materials prepared in Examples 1-5 was tested using a laser particle size analyzer, and it was found that the particle size of the iron-based composite materials was 3-18 μm.

[0138] Test Example 2

[0139] The iron-based composite materials prepared in Examples 1-5 and the product prepared in Comparative Example 1 were tested using XRD. According to the XRD results, the iron in the iron-based composite materials prepared in Examples 1-5 is elemental iron and there is no iron oxide. This indicates that the passivation film on the surface of the product prepared in this invention is completely removed. The product prepared in Comparative Example 1 contains not only elemental iron but also iron oxide.

[0140] Furthermore, after the iron-based composite materials prepared in Examples 1-5 were left to stand for 12 months, XRD was tested again. It was found that the characteristic peaks of zero-valent iron were still present in the XRD spectra of the products prepared in Examples 1-5. This indicates that the iron-based composite materials prepared by the method described in this invention have strong stability, relatively uniform modification of zero-valent iron, and reduced the probability of zero-valent iron oxidation passivation.

[0141] The XRD test of the product prepared in Comparative Example 1 after standing for 3 months showed that the intensity of the characteristic peak of iron oxide in the spectrum increased, indicating that the product prepared in Comparative Example 1 had poor stability.

[0142] According to the full elemental scan of XPS, the products prepared in Examples 1-10 contain Na, S and C elements in addition to Fe. The product prepared in Comparative Example 1 does not contain Na and S elements, and the product prepared in Comparative Example 2 does not contain C elements. This indicates that zero-valent iron was successfully modified by electrochemical means in this invention.

[0143] Test Example 3

[0144] Static sustained-release tests were conducted on the products prepared in Examples 1-10 and Comparative Examples 1-2.

[0145] Test method: Take 1g of the sample to be tested and place it in 100mL of boiled and cooled water. Let it stand for 12 months, and then perform XRD test. Analyze the obtained XRD spectrum to obtain the content of elemental iron in the sample. The results are shown in Table 1.

[0146] Test Example 4

[0147] The degradation capabilities of the products prepared in Examples 1-10 and Comparative Examples 1-2 for chlorinated hydrocarbon pollutants were tested.

[0148] Test method: The products prepared in Examples 1-10 and Comparative Examples 1-2 were mixed with simulated chlorinated hydrocarbon-contaminated groundwater samples (the types and concentrations of pollutants in the simulated samples are shown in Table 1) and reacted. The reaction temperature was 15-20℃ and the reaction time was 12h. The concentration of chlorinated hydrocarbons after the reaction was tested, and the degradation rate of chlorinated hydrocarbons was calculated. The calculation formula was: (chlorinated hydrocarbon concentration before reaction - chlorinated hydrocarbon concentration after reaction) ÷ chlorinated hydrocarbon concentration before reaction × 100%. The results are shown in Table 1.

[0149] Table 1

[0150]

[0151]

[0152] As can be seen from the results in Table 1, the iron-based composite material described in this invention exhibits excellent degradation performance against chlorinated hydrocarbons, with a longer repair cycle. Furthermore, the preparation method is simple, green, and pollution-free, demonstrating great application potential.

[0153] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. An iron-based composite material, characterized in that, The iron-based composite material comprises micron-sized zero-valent iron particles, a modified shell layer formed on the surface of the micron-sized zero-valent iron particles, and carbon material dispersed around the micron-sized zero-valent iron particles. The modified shell layer is formed by electrolysis of metal sulfides and citrates with the micron-sized zero-valent iron particles. The content of the modified shell layer is 3.5-5.5 wt%, the content of the micron-sized zero-valent iron particles is 77-88 wt%, and the content of the carbon material is 8.5-17.5 wt%, with the iron-based composite material weighing 100 wt%.

2. The iron-based composite material according to claim 1, characterized in that, The particle size of the micron-sized zero-valent iron particles is 2-15 μm.

3. The iron-based composite material according to claim 1 or 2, characterized in that, The D of the micron-sized zero-valent iron particles 50 The particle size is 6-12 μm.

4. A method for preparing an iron-based composite material, characterized in that, The preparation method includes the following steps: (1) Micron-sized zero-valent iron particles are mixed with a carbon source and then calcined; (2) Remove the passivation film on the surface of the product obtained in step (1), and then use it as the working electrode, the inert electrode as the counter electrode, and the solution containing metal sulfide and citrate as the electrolyte. Perform constant voltage electrolysis to obtain iron-based composite material.

5. The method for preparing the iron-based composite material according to claim 4, characterized in that, The process of step (2) includes: S1. The passivation film on the surface of the product obtained in step (1) is removed by electrolysis; S2. Using a solution containing metal sulfide and citrate as the electrolyte, the product obtained in step S1 is used as the anode and an inert material is used as the cathode to perform constant voltage electrolysis to obtain an iron-based composite material.

6. The method for preparing the iron-based composite material according to claim 5, characterized in that, In step S1, the electrolysis is performed by alternating between the first stage of electrolysis and the second stage of electrolysis. In this process, the product obtained in step (1) is used as the working electrode, the inert material is used as the counter electrode, and water is used as the electrolyte. The first stage of electrolysis is constant voltage electrolysis with the inert electrode as the cathode, and the second stage of electrolysis is constant voltage electrolysis with the inert electrode as the anode.

7. The method for preparing the iron-based composite material according to claim 6, characterized in that, In step S1, the conditions for the first stage of electrolysis include: a voltage of 2.5-4V and a time of 30-90s.

8. The method for preparing the iron-based composite material according to claim 6 or 7, characterized in that, The conditions for the second stage of electrolysis include: a voltage of 2.5-4V and a time of 30-90s.

9. The method for preparing the iron-based composite material according to claim 5, characterized in that, In step S2, the conditions for constant voltage electrolysis include: voltage of 1-2V and time of 2-5h.

10. The method for preparing the iron-based composite material according to claim 5, characterized in that, In step S1, the electrolysis time is 2-4 hours.

11. The method for preparing the iron-based composite material according to claim 4 or 5, characterized in that, The weight ratio of micron-sized zero-valent iron particles, metal sulfides, and citrate is 14-20:1:1.5-7.

12. The method for preparing the iron-based composite material according to claim 4, characterized in that, The particle size of the micron-sized zero-valent iron particles is 2-15 μm.

13. The method for preparing the iron-based composite material according to claim 4, characterized in that, The weight ratio of the micron-sized zero-valent iron particles to the carbon source is 1:0.05-0.

5.

14. The method for preparing the iron-based composite material according to claim 4, characterized in that, The calcination conditions include: a temperature of 200-250℃ and a time of 5-20 minutes.

15. The iron-based composite material prepared by the method for preparing iron-based composite materials according to any one of claims 4-14.

16. The application of the iron-based composite material according to any one of claims 1-3 or the iron-based composite material according to claim 15 in the remediation of groundwater pollutants.

17. The application according to claim 16, characterized in that, The groundwater pollutants are selected from one or more of carbon tetrachloride, tetrachloroethylene, trichloroethylene, dichloroethylene, tetrachloropropane, and trichloropropane.

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