Carbon-based composite catalytic material, preparation method and application thereof

Abstract

This invention discloses a carbon-based composite catalytic material, its preparation method, and its applications. The invention employs a one-step carbonization process involving molten salt confinement, a non-urea nitrogen source, and no ball milling: a dinuclear iron precursor, nitrogen-containing organic matter (as both a non-urea nitrogen source and a carbon source), ZnCl2, and a molten salt system are mixed. After high-temperature pyrolysis under an inert atmosphere, the mixture is sequentially washed with hot water to dissolve the molten salt, followed by washing with HCl solution and drying. The entire process eliminates the need for complex mechanical treatments such as ball milling, simplifying the steps and providing milder conditions, making it more suitable for scale-up preparation and engineering applications. The above-mentioned carbon-based composite catalytic material is applied to the degradation of chlorinated organic pollutants in soil, particularly in conjunction with persulfate oxidants to construct an advanced oxidation system. The highly coordinated dinuclear M2N6 reaction center efficiently activates persulfate, generating sulfate radicals, hydroxyl radicals, and / or non-radical active species, achieving rapid degradation of recalcitrant chlorinated organic pollutants.

Description

Technical Field

[0001] This invention relates to a carbon-based composite catalytic material, its preparation method, and its application, particularly to a carbon-based composite catalytic material based on a binuclear high coordination reaction center, its preparation method, and its application in the removal of organochlorine pollutants in soil, belonging to the field of environmental remediation and catalytic materials technology. Background Technology

[0002] In the remediation of recalcitrant organic pollutants (especially chlorinated organics) in soil, chemical oxidation / activation systems such as Fenton / Fenton-like agents, persulfate oxidation, electrochemical oxidation, photocatalytic oxidation, and carbon-based composite catalysis have been widely studied and applied. However, in the dense, heterogeneous pore structure of soil, the mass transfer between oxidants and pollutants is severely limited. Active species are easily and ineffectively consumed by inorganic anions, natural organic matter, and mineral surfaces, resulting in low effective concentrations of free radicals, numerous non-selective side reactions, and difficulty in simultaneously achieving high agent utilization and remediation efficiency.

[0003] To improve the activation efficiency and stability of oxidants, researchers have proposed various carbon-based / metal-carbon composite catalytic materials, such as single-atom / dual-atom MNC catalysts, Fe / Co-doped biochar, and carbon / metal oxide composites. These materials rely on the carbon framework to provide specific surface area and electron transport channels, showing certain advantages in persulfate activation. However, in complex soil environments, traditional particulate or blocky catalytic materials still suffer from insufficient mass transfer performance, ineffective consumption of active species, and limited degradation efficiency. Furthermore, the single-atom MNC structure is prone to MN bond breakage and metal loss under strong oxidation and pH fluctuation conditions. The single metal center bears an excessively high electron load during multiple redox cycles, easily leading to localized charge accumulation and uneven electron cloud distribution, thereby inducing non-selective attacks of free radicals on non-target functional groups, affecting structural stability and reaction selectivity.

[0004] In recent years, diatomic / dual-nuclear (DAC) systems have demonstrated superior performance compared to single-atom sites in terms of oxidant adsorption and activation, intermediate transformation, and structural stability due to electronic coupling and multiple electron transfer channels between adjacent metals. Therefore, there is an urgent need to develop novel carbon-based composite catalytic materials with high activity, high selectivity, and high stability in chlorinated organic soil systems. This would improve oxidant utilization efficiency, enhance the deep mineralization capacity of chlorinated organic compounds in soil, reduce the risk of secondary pollution, and thus meet the engineering application needs of remediation of contaminated sites. Summary of the Invention

[0005] Objective of the Invention: To address the aforementioned deficiencies in existing technologies, the primary objective of this invention is to provide a carbon-based composite catalytic material based on a binuclear high-coordination reaction center. Another objective is to provide a molten salt-confined one-step carbonization method for preparing the aforementioned carbon-based composite catalytic material. A final objective is to provide the application of the aforementioned carbon-based composite catalytic material based on a binuclear high-coordination reaction center in the removal of recalcitrant organic pollutants from soil, particularly its application in the remediation of chlorinated organic compounds in soil.

[0006] Technical solution: The present invention provides a method for preparing a carbon-based composite catalytic material, comprising the following steps:

[0007] (1) Mix the dinuclear iron precursor, nitrogen-containing organic matter and ZnCl2, add it to the pre-dried NaCl / KCl molten salt system, so that the metal source, carbon source and nitrogen source are uniformly dispersed in the solid molten salt medium, and dry to obtain composite powder;

[0008] (2) The above composite powder is loaded into a covered crucible, and the surface is covered with the same molten salt to keep it in a confined space. It is then pyrolyzed at high temperature under the protection of an inert gas. After cooling, the pyrolysis product is taken out.

[0009] (3) The pyrolysis products are washed with hot water to dissolve the molten salt, then washed with HCl solution and dried.

[0010] Further, in step (1), the dinuclear iron precursor is a μ-oxo type dinuclear iron porphyrin compound with Fe-O-Fe bridging bonds, preferably [Fe(TPP)]2O or a porphyrin derivative with the same Fe-O-Fe bridging structure and capable of forming a dinuclear coordination center. The nitrogen-containing organic matter contains non-urea nitrogen and carbon sources, preferably dicyandiamine and / or melamine. In the NaCl / KCl molten salt system, the molar ratio of NaCl to KCl is (0.5-2):1, and the mass ratio of the dinuclear iron precursor, nitrogen-containing organic matter, ZnCl2 to the NaCl / KCl molten salt system is 1:(2-5):(0.1-0.5):(30-100). In step (2), the inert gas is nitrogen, argon, and / or helium. The heating rate during high-temperature pyrolysis is 2-10 °C, the pyrolysis temperature is 850-950 °C, and the pyrolysis time is 60-180 min. It can be removed after cooling to below 200 °C. In step (3), the hot water temperature is above 60-100 °C, and the immersion is repeated 2-6 times for 5-60 min. The concentration of the HCl solution is 0.1-2 M, and the immersion time is above 5-60 min. The drying temperature is 50-100 °C.

[0011] The carbon-based composite catalytic material obtained by the preparation method described in this invention.

[0012] The application of the carbon-based composite catalytic material described in this invention in the removal of recalcitrant organic pollutants from soil.

[0013] Furthermore, the recalcitrant organic pollutants are chlorinated organic compounds, which may be 2,4,6-trichlorophenol, p-nitrochlorobenzene, and / or chlorobenzene.

[0014] This invention addresses common problems in the remediation of recalcitrant organic pollutants (especially chlorinated organic pollutants) in soil, such as limited mass transfer within pore water films, easy deactivation and metal loss of single-atom MNC sites under strong oxidation and pH fluctuations, and low utilization rates due to ineffective consumption of oxidants such as persulfate. It provides a carbon-based composite catalytic material based on binuclear highly coordinated reaction centers and its application in soil remediation. This material achieves efficient enrichment, selective oxidation, and catalytic site stabilization of pollutants and oxidants by constructing stable binuclear highly coordinated M2N6 active centers within a porous carbon framework, thereby improving oxidant utilization efficiency and soil remediation effectiveness.

[0015] (1) Material structure and configuration characteristics

[0016] The carbon-based composite catalytic material uses a porous carbon framework as a carrier, with a binuclear, highly coordinated M2N6 reaction center anchored in situ within the carbon framework. M is one or more transition metals (preferably iron). The porous carbon framework provides interconnected channels and a high specific surface area, which serves two purposes: firstly, to simultaneously enrich chlorinated organic pollutants and persulfate oxidants in soil pore water films; and secondly, to form short-range diffusion channels to increase the effective contact probability between reactants and active sites. The binuclear, highly coordinated structure forms a stable coordination environment through close coupling between adjacent metal centers, enabling the active center to possess both high activation capacity and structural durability.

[0017] (2) Mechanism of action and reaction pathway

[0018] In soil systems, the mechanism of action of the material of this invention can be summarized as a coupled process of "enrichment and enhanced mass transfer + dual-nuclear synergistic activation of persulfate + parallel oxidation by free radicals / non-free radicals":

[0019] Enrichment and mass transfer enhancement: The interconnected channels and high specific surface area of ​​the porous carbon skeleton make it easier for pollutants and oxidants to be adsorbed / enriched and migrate to active sites in the pore water film environment, thereby alleviating the mass transfer limitation caused by the heterogeneous structure of the soil and improving the apparent reaction rate.

[0020] Dual-core synergy and stabilization: There is electronic coupling and synergistic transfer between adjacent metal centers in the dual-core high-coordination M2N6 sites, which can share the multi-step electron transfer load and maintain a more balanced local charge distribution, thereby inhibiting MN breakage and metal loss, and improving structural stability under strong oxidizing environment and pH fluctuation conditions.

[0021] Oxidizing agent activation and selective oxidation: Persulfate undergoes adsorption / internal coordination activation at binuclear sites, promoting the breaking of peroxy bonds and generating sulfate radicals (SO4). •⁻ ), hydroxyl radical (•OH) and / or non-radical activity ( 1 O2 species enable rapid bond breaking and deep oxidation of aromatic rings and C-Cl bonds; at the same time, the material can mediate the interfacial electron transfer process, so that pollutants act as electron donors and persulfates act as electron acceptors to undergo non-radical oxidation, thereby reducing ineffective side reactions and improving oxidant utilization and reaction selectivity in complex soil matrices.

[0022] (3) Preparation logic: molten salt confinement + non-urea nitrogen source + one-step carbonization without ball milling

[0023] This invention employs a one-step heat treatment process confined by molten salt: a metal precursor, a non-urea nitrogen-containing organic compound (which also serves as a carbon / nitrogen source), and a molten salt system are mixed and directly pyrolyzed under an inert atmosphere. This allows the organic components to carbonize in situ and be nitrogen-doped within the confined environment, while simultaneously inducing the self-assembly of metal species within the carbon framework to form binuclear, highly coordinated M2N6 centers and construct interconnected channels. The molten salt plays a role in spatial confinement, pore structure regulation, and high metal dispersion and fixation during heat treatment. The non-urea nitrogen source avoids the excessive gas / secondary phase problems associated with traditional urea systems, making it easier to obtain binuclear centers with controllable coordination environment and stable structure. The entire process eliminates the need for ball milling, simplifying the steps and facilitating scale-up and engineering applications.

[0024] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0025] (1) The molten salt system of the present invention provides a fluid confined environment during heat treatment, so that carbonization, nitrogen doping and the nucleation process of binucleate sites can be carried out simultaneously, thereby obtaining a stable binucleate high coordination structure and a well-developed micro / mesoporous system, which is superior to the traditional ball milling-pyrolysis or urea melting and flaking technology.

[0026] (2) The present invention enables the rapid migration and enrichment of pollutants in the soil pore water film through the open channels and short-range diffusion channels constructed by porous materials, which significantly increases the contact probability between pollutants and active sites, thereby enhancing the overall reaction rate.

[0027] (3) The porous carbon framework of the present invention can enrich pollutants and persulfate, shortening the mass transfer distance; the binucleate high coordination center can activate persulfate more efficiently, significantly improving the generation rate and utilization rate of active species and reducing the ineffective consumption of oxidant. Attached Figure Description

[0028] Figure 1 This is a comparison chart of the degradation efficiency of the binuclear high coordination reaction center catalytic material provided in Example 2 and the comparative material in the degradation of 2,4,6-trichlorophenol;

[0029] Figure 2 This is a comparison chart of the degradation efficiency of the binuclear high coordination reaction center catalytic material provided in Example 3 and the comparative material in the degradation of p-nitrophenol;

[0030] Figure 3 This is a comparison chart of the degradation efficiency of the binuclear high-coordination reaction center catalytic material provided in Example 4 and the comparative material in the degradation of triclosan. Detailed Implementation

[0031] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0032] Example 1

[0033] (1) Mix 0.10 g of dinuclear iron precursor [Fe(TPP)]2O, 0.30 g of dicyandiamine, and 0.03 g of ZnCl2 in a mortar; add 1-2 mL of ethanol to moisten, and continue grinding until a uniform wet powder is formed, and allow the ethanol to evaporate at room temperature.

[0034] (2) Add 5.0 g of pre-dried molten salt (NaCl:KCl=1:1 (molar ratio)), mix thoroughly, dry the composite powder at 60℃, and then pass it through a 100-mesh sieve to obtain a uniform composite powder.

[0035] (3) Put the composite powder into a covered crucible, cover the surface of the composite powder with another layer of molten salt with the same formula as in step (2) (≥5mm thick), cover the crucible tightly, and place it in a quartz boat.

[0036] (4) Place the quartz boat in the tube furnace and purge it continuously in a nitrogen atmosphere for 20 minutes.

[0037] (5) Heat the temperature from room temperature to 900 ℃ at a rate of 5 ℃ / min and keep it at that temperature for 100 minutes; then let it cool naturally to <200 ℃ before taking it out.

[0038] (6) Pour out the contents of the cooled crucible, rinse and stir with 70 °C hot deionized water for 10 min, centrifuge to remove the supernatant, and repeat 3 times.

[0039] (7) Add 0.5 M HCl and wash for 15 minutes (to remove residual metal salts / oxides), then wash with deionized water / ethanol alternately until neutral. Then dry under vacuum at 70 °C overnight to obtain a black powder material, which is the binuclear high coordination reaction center catalyst material, denoted as Fe-Fe DACs.

[0040] Comparative Example 1: Preparation of Fe SACs Catalytic Materials

[0041] The experimental procedure was the same as in Example 1, except that the amount of dicyandiamine used was different, as detailed below:

[0042] (1) Mix 0.10 g of dinuclear iron precursor [Fe(TPP)]2O, 0.60 g of dicyandiamine, and 0.03 g of ZnCl2 in a mortar; add 1-2 mL of ethanol to moisten, and continue grinding until a uniform wet powder is formed, and allow the ethanol to evaporate at room temperature.

[0043] (2) Add 5.0 g of pre-dried molten salt (NaCl:KCl=1:1 (molar ratio)), mix thoroughly, dry the composite powder at 60℃, and then pass it through a 100-mesh sieve to obtain a uniform composite powder.

[0044] (3) Put the composite powder into a covered crucible, cover the surface of the composite powder with another layer of molten salt with the same formula as in step (2) (≥5mm thick), cover the crucible tightly, and place it in a quartz boat.

[0045] (4) Place the quartz boat in the tube furnace and purge it continuously in a nitrogen atmosphere for 20 minutes.

[0046] (5) Heat the temperature from room temperature to 900 ℃ at a rate of 5 ℃ / min and keep it at that temperature for 100 minutes; then let it cool naturally to <200 ℃ before taking it out.

[0047] (6) Pour out the contents of the cooled crucible, rinse and stir with 70 °C hot deionized water for 10 min, centrifuge to remove the supernatant, and repeat 3 times.

[0048] (7) Add 0.5 M HCl and wash for 15 minutes (to remove residual metal salts / oxides), then wash with deionized water / ethanol alternately until neutral. Then dry under vacuum at 70 °C overnight to obtain Fe SACs catalyst material.

[0049] Comparative Example 2: Preparation of NC (no Fe) Catalytic Material

[0050] The experimental procedure is the same as in Example 1, except that iron is not added. The details are as follows:

[0051] (1) Mix 0.30 g dicyandiamine and 0.03 g ZnCl2 in a mortar, add 1-2 mL of ethanol to moisten, continue grinding until uniform wet powder is formed, and allow the ethanol to evaporate at room temperature.

[0052] (2) Add 5.0 g of pre-dried molten salt (NaCl:KCl=1:1 (molar ratio)), mix thoroughly, dry the composite powder at 60℃, and then pass it through a 100-mesh sieve to obtain a uniform composite powder.

[0053] (3) Put the composite powder into a covered crucible, cover the surface of the composite powder with another layer of molten salt with the same formula as in step (2) (≥5mm thick), cover the crucible tightly, and place it in a quartz boat.

[0054] (4) Place the quartz boat in the tube furnace and purge it continuously in a nitrogen atmosphere for 20 minutes.

[0055] (5) Heat the temperature from room temperature to 900 ℃ at a rate of 5 ℃ / min and keep it at that temperature for 100 minutes; then let it cool naturally to <200 ℃ before taking it out.

[0056] (6) Pour out the contents of the cooled crucible, rinse and stir with 70 °C hot deionized water for 10 min, centrifuge to remove the supernatant, and repeat 3 times.

[0057] (7) Add 0.5 M HCl and rinse for 15 minutes (to remove residual metal salts / oxides), then rinse with deionized water / ethanol alternately until neutral. Then dry under vacuum at 70 °C overnight to obtain N-doped carbon (NC, Fe-free) material, denoted as NC (no Fe).

[0058] Example 2 Performance Testing

[0059] The degradation performance of the catalysts prepared in Example 1, Comparative Example 1, and Comparative Example 2 on recalcitrant organic pollutants was evaluated using 2,4,6-trichlorophenol in soil systems contaminated with nitrochlorobenzene and chlorobenzene. Specific test methods are as follows:

[0060] 1. Performance evaluation of degradation of 2,4,6-trichlorophenol

[0061] (1) Remove plant roots, stones and other impurities from the uncontaminated soil and air dry at room temperature. Grind and pass through a 2 mm sieve for later use.

[0062] (2) Dissolve 2,4,6-trichlorophenol in methanol solvent and add it dropwise to a predetermined mass of soil at a target concentration of 500 mg / kg (based on dry soil mass). After thorough mixing, age the soil for two weeks under dark conditions to allow the pollutants to be fully adsorbed and evenly distributed in the soil, thus obtaining simulated contaminated soil.

[0063] (3) Add 2.0 g of simulated contaminated soil to a brown sieve bottle and add 1.6 mL of deionized water. Then add 10 mg of the catalyst material prepared in Example 1 and Comparative Examples 1-2 to the soil, so that the catalyst material dosage is 5 mg / g dry soil. After sealing with a stopper, place on a rotary mixer and premix at 70 r / min for 30 min at room temperature to ensure that the catalyst material is in full contact with the contaminated soil and water.

[0064] (4) Add 0.4 mL of 20 mM potassium persulfate (PMS) aqueous solution to the mixture in step (3) to make the initial concentration of oxidant 5 mM. After sealing the reaction flask, place it in a rotary mixer and react at 70 r / min for 120 min at room temperature. Then immediately add excess sodium thiosulfate to the system to terminate the reaction and shake thoroughly to avoid continuous oxidation after sampling, which may lead to deviation in the results.

[0065] (5) Add 10 mL of extraction solvent (methanol / water = 80 / 20 (v / v)) to the reaction system of step (4). Then place the mixture in an ultrasonic cleaner and sonicate for 30 min to enhance the extraction of 2,4,6-trichlorophenol. After sonication, place the brown filament bottle back on a rotary mixer and continue to rotate and mix at 70 r / min for 30 min to ensure sufficient extraction of contaminants. After extraction, centrifuge at 5000 rpm for 5 min, take the supernatant as the sample to be tested, repeat the above operation, and combine the supernatants. To further remove suspended particles, filter the supernatant through a 0.22 μm microporous membrane and determine the residual concentration of 2,4,6-trichlorophenol using high performance liquid chromatography. The high-performance liquid chromatography (HPLC) detection conditions were as follows: a C18 reversed-phase column (Poroshell 120 EC-C18, 4.6 * 150 mm, 4 pm, with column ID), methanol / 0.1% acetic acid (70:30, V / V) as the mobile phase, flow rate 1.0 mL / min, column temperature 30 ℃, and detection wavelength 290 nm.

[0066] (6) The degradation effect of the catalytic material / PMS system on 2,4,6-trichlorophenol in soil was evaluated by calculating the concentration of 2,4,6-trichlorophenol, and systems with only PMS, Fe-Fe DACs, Fe SACs, or NC (no Fe) were set as controls for comparison. The results are as follows: Figure 1 As shown. Figure 1 The results showed that, without the participation of the oxidant PMS, the degradation efficiencies of Fe-Fe DACs, Fe SACs, and NC (no Fe) for 2,4,6-trichlorophenol were 8.03%, 5.69%, and 4.41%, respectively. However, under the conditions of 5 mM PMS oxidant, 5 mg / g catalyst in simulated contaminated soil, and an initial pollutant concentration of 500 mg / kg, the Fe-Fe DACs / PMS system in Example 1 significantly reduced the content of 2,4,6-trichlorophenol in the soil, achieving a degradation efficiency of 79.07%, which was significantly better than the Fe SACs / PMS (58.67%) and NC (no Fe) / PMS (29.28%) control systems.

[0067] The Fe-Fe DACs catalytic material with Fe2N6 binuclear high-coordination reaction centers described in this invention synergistically removes recalcitrant organic pollutants in soil systems in conjunction with PMS. Its mechanism of action can be understood as a coupled process of "enrichment and enhanced mass transfer + binuclear synergistic activation of PMS + parallel oxidation by free radicals / non-free radicals". The Fe-Fe DACs catalytic material possesses interconnected pores and a high specific surface area, enabling it to simultaneously enrich pollutants and PMS in the soil pore water film and shorten the diffusion distance, thereby increasing the contact probability between pollutants, oxidants, and active sites and alleviating the mass transfer limitation problem commonly found in soil systems. Furthermore, PMS can undergo internal coordination adsorption at the Fe2N6 binuclear centers to form surface-activated complexes. Compared to Fe SACs sites, binuclear sites possess electron coupling and synergistic transfer capabilities between adjacent metals, can share the multi-step electron transfer load, and maintain a more balanced local charge distribution, thus being more conducive to the effective activation of PMS. Simultaneously, it inhibits MN bond breaking and metal loss, and improves structural stability and durability under strong oxidation and pH fluctuation conditions. Under the electron-supply / feedback effect of binuclear Fe sites, the peroxy bonds in PMS are more prone to breakage, generating SO4. •⁻ Active species; SO4 •⁻ In the aqueous phase, hydroxyl radicals (•OH) can be further transformed / generated in parallel, both of which have strong oxidative bond-breaking capabilities for aromatic rings and C–Cl bonds. In addition to the radical pathway, Fe-NC materials in the PMS system may also undergo catalyst-mediated electron transfer: pollutants (electron donors) undergo interfacial electron migration at the carbon skeleton / Fe2N6 sites, transferring electrons to the PMS (electron acceptor) via the catalyst, thereby triggering a non-radical oxidation process; under certain conditions, it may also be accompanied by the generation of non-radical reactive species such as singlet oxygen, exhibiting stronger selectivity and higher oxidant utilization efficiency.

[0068] 2. Evaluation of the performance in degrading p-nitrophenol

[0069] (1) The preparation of simulated contaminated soil is the same as steps (1) and (2) in this embodiment, except that the pollutant 2,4,6-trichlorophenol is replaced with p-nitrophenol and the organic solvent methanol is replaced with acetonitrile.

[0070] (2) The degradation reaction process is the same as the operation in Example 1 of this embodiment.

[0071] (3) The extraction and purification process is the same as in Example 1, except that the high performance liquid chromatography detection conditions are as follows: a C18 reversed phase column is used, methanol / water (60:40, V / V) is used as the mobile phase, the flow rate is 1.0 mL / min, the column temperature is 30 ℃, and the detection wavelength is 320 nm.

[0072] (4) The degradation effect of the catalytic material / PMS system on p-nitrophenol in soil was evaluated by calculating the p-nitrophenol concentration. The results are as follows: Figure 2 As shown. Figure 2 The results showed that, without the participation of the oxidant PMS, the degradation efficiencies of Fe-Fe DACs, FeSACs, and NC (no Fe) for p-nitrophenol were 8.93%, 5.37%, and 4.88%, respectively. However, under the conditions of 5 mM PMS oxidant, 5 mg / g catalyst in simulated contaminated soil, and an initial pollutant concentration of 500 mg / kg, the Fe-Fe DACs / PMS system significantly reduced the p-nitrophenol content in the soil, achieving a degradation efficiency of 65.13%, which was significantly better than the Fe SACs / PMS (48.69%) and NC (no Fe) / PMS (24.28%) control systems. The mechanism of action can be understood as a coupled process of "enhanced mass transfer enrichment + dual-nuclear synergistic activation of PMS + parallel oxidation by free radicals / non-free radicals".

[0073] 3. Evaluation of Triclosan Degradation Performance

[0074] (1) The configuration of simulated contaminated soil is the same as steps (1) and (2) in this embodiment, except that the pollutant 2,4,6-trichlorophenol is replaced with triclosan.

[0075] (2) The degradation reaction process is the same as the operation in Example 1 of this embodiment.

[0076] (3) The extraction and purification process is the same as in Example 1, except that the high performance liquid chromatography detection conditions are as follows: a C18 reversed phase column is used, with methanol / 0.01% acetic acid water (85:15, V / V) as the mobile phase, a flow rate of 1.0 mL / min, a column temperature of 30 ℃, and a detection wavelength of 280 nm.

[0077] (4) The degradation effect of the catalytic material / PMS system on triclosan in soil was evaluated by calculating the triclosan concentration. The results are as follows: Figure 3 As shown. Figure 3The results showed that, without the participation of the oxidant PMS, the degradation efficiencies of Fe-FeDACs, Fe SACs, and NC(no Fe) for triclosan were 5.87%, 6.57%, and 5.66%, respectively. However, under the conditions of 5 mM PMS oxidant, 5 mg / g catalyst in simulated contaminated soil, and an initial pollutant concentration of 500 mg / kg, the Fe-FeDACs / PMS system significantly reduced the triclosan content in the soil, achieving a degradation efficiency of 61.39%, which was significantly better than the FeSACs / PMS (43.26%) and NC(no Fe) / PMS (21.41%) control systems. The mechanism of action can be understood as a coupled process of "enhanced mass transfer through enrichment + dual-nuclear synergistic activation of PMS + parallel oxidation by free radicals / non-free radicals".

[0078] In summary, this invention successfully prepared Fe-Fe DACs catalytic materials with a Fe2N6 binuclear high-coordination structure through a one-step carbonization process using molten salt confinement and a non-urea nitrogen source. When applied to the degradation experiments of 2,4,6-trichlorophenol, p-nitrophenol, and triclosan in soil, this material exhibited excellent catalytic degradation performance under conditions of 5 mM oxidant, 5 mg / g catalyst (based on dry soil mass), and an initial pollutant concentration of 500 mg / kg.

Claims

1. A method for preparing a carbon-based composite catalytic material, characterized in that, Includes the following steps: (1) Mix the dinuclear iron precursor, nitrogen-containing organic matter and ZnCl2, add it to the pre-dried NaCl / KCl molten salt system, so that the metal source, carbon source and nitrogen source are uniformly dispersed in the solid molten salt medium, and dry to obtain composite powder; (2) The above composite powder is loaded into a covered crucible, and the surface is covered with the same molten salt to keep it in a confined space. It is then pyrolyzed at high temperature under the protection of an inert gas. After cooling, the pyrolysis product is taken out. (3) The pyrolysis products are washed with hot water to dissolve the molten salt, then washed with HCl solution and dried.

2. The method for preparing the carbon-based composite catalytic material according to claim 1, characterized in that, In step (1), the dinuclear iron precursor is a μ-oxo type dinuclear iron porphyrin compound with Fe–O–Fe bridging bonds. The nitrogen-containing organic matter contains non-urea nitrogen source and carbon source, selected from dicyandiamine or melamine.

3. The method for preparing the carbon-based composite catalytic material according to claim 1, characterized in that, In step (1), the molar ratio of NaCl to KCl in the NaCl / KCl molten salt system is (0.5-2):1, and the mass ratio of the dinuclear iron precursor, nitrogen-containing organic matter, ZnCl2 to the NaCl / KCl molten salt system is 1:(2-5):(0.1-0.5):(30-100).

4. The method for preparing the carbon-based composite catalytic material according to claim 1, characterized in that, In step (2), the inert gas is nitrogen, argon or helium, the heating rate during high-temperature pyrolysis is 2-10 ℃, the temperature of high-temperature pyrolysis is 850-950 ℃, and the time of high-temperature pyrolysis is 60-180 min.

5. The method for preparing the carbon-based composite catalytic material according to claim 1, characterized in that, In step (2), the product can be removed once it has cooled to below 200°C.

6. The method for preparing the carbon-based composite catalytic material according to claim 1, characterized in that, In step (3), the temperature of the hot water is 60-100 ℃, the soaking time is 5-60 min, and the soaking is repeated 2-6 times to dissolve the molten salt; the concentration of the HCl solution is 0.1-2 M, and the soaking time is 5-60 min.

7. The method for preparing the carbon-based composite catalytic material according to claim 1, characterized in that, In step (3), the drying temperature is 50-100 ℃ and the drying time is 6-24 h.

8. The carbon-based composite catalytic material obtained by the preparation method according to any one of claims 1-7.

9. The application of the carbon-based composite catalytic material according to claim 8 in the removal of recalcitrant organic pollutants from soil.

10. The application according to claim 9, characterized in that, The recalcitrant organic pollutants are 2,4,6-trichlorophenol, p-nitrochlorobenzene, and / or triclosan.

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