Preparation method and application of a polymer iron phthalocyanine single-atom carbon-based catalyst with abundant defects

Abstract

This invention provides a method for preparing a polymeric iron phthalocyanine single-atom carbon-based catalyst with abundant defects and its application. The catalyst prepared by this method is used to activate persulfate treatment of recalcitrant organic pollutants in wastewater. The preparation method assembles a mixture of 1,2,4,5-tetracyanobenzene (BTC) and 1,2-dicyanobenzene (DCB) with iron centers into a fully encapsulated conjugated covalent organic framework. Because the introduction of DCB replaces some bridging-based BTC unit portions, it eliminates excess cyano groups within the framework, thereby providing defect sites along the polymer backbone in the resulting conjugated covalent organic framework. Simultaneously, this invention introduces nitrogen-doped carbon nanotubes as a stable scaffold. The resulting catalyst possesses abundant defect sites and high catalytic activity. Experimental results show that the catalyst prepared by this invention has good degradation effects on low-concentration organic pollutants such as bisphenol A-contaminated water.

Description

Technical Field

[0001] This invention relates to a polymer iron phthalocyanine single-atom carbon-based catalyst with abundant defects, its preparation method, and its application in activating persulfate to treat recalcitrant organic pollutant wastewater. Background Technology

[0002] Organic pollutants (EOCs) are a class of anthropogenic chemical substances that have become widespread in aquatic environments in recent years, accumulating at low concentrations (ng / L to μg / L). Therefore, micro-advanced oxidation processes (AOPs) have become the most commonly used method for treating EOCs in water. These pollutants have harmful effects on the environment and human health, and have become an urgent part of global environmental problems that need to be addressed.

[0003] Sulfate-based active oxygen compounds (AOPs) (SR-AOPs) have attracted much attention due to their high redox potential (E0(SO4.- / SO42-) = 2.5-3.1V), long lifetime (30-40 μs), and applicability to a wide range of sulfate pH values. Peroxymonosulfate (PMS) is a commonly used oxidant in SR-AOPs. Previous studies have shown that transition metals (such as Fe, Co, and Mn) are effective catalysts for activating persulfates. However, although transition metal-based materials have proven to be excellent heterogeneous persulfate activators, capable of dissociating OO bonds to generate active radicals, the high energy consumption and secondary pollution caused by metal leaching limit their practical application. Therefore, developing synergistic, efficient, environmentally friendly, and high-performance PMS activation strategies is crucial.

[0004] In recent years, Fe single-atom catalysts (SACs) have been widely used as a novel catalyst in the PMS catalytic oxidation process on porous carbon matrices, where Fe-N4 active sites are dispersed on the carbon matrix. SACs are widely recognized for their high activity, long-lasting stability, and maximum atom utilization. Their unique advantages, including maximum atom utilization, tunable electronic structure, and high metal center performance, make them an ideal choice for PMS-activated catalytic oxidation of organic pollutants in aqueous phases. However, SAC technology currently faces many challenges. For example, during synthesis and catalysis, metal atoms exhibit a strong tendency to migrate and aggregate, leading to a rapid decline in catalytic activity. Therefore, developing a suitable support material that can firmly immobilize individual atoms while maintaining high catalytic activity remains a significant challenge. Summary of the Invention

[0005] The purpose of this invention is to address the problem of poor performance of existing conventional wastewater treatment for low-concentration emerging organic pollutants (including bisphenol A-contaminated water bodies) in the environment. It provides an advanced oxidation technology for persulfate treatment using a polymer iron phthalocyanine single-atom carbon-based catalyst (D-FeN5-x) material rich in defects, and describes the preparation method and application conditions of the polymer iron phthalocyanine single-atom catalyst material rich in defects.

[0006] In a first aspect, the present invention provides a method for preparing a polymeric iron phthalocyanine single-atom carbon-based catalyst with abundant defects, comprising the following steps:

[0007] Step 1: Disperse the mixture of 1,2,4,5-benzenetetracarbonitrile (BTC), 1,2-dicyanobenzene (DCB), and ferric salt in an organic solvent; sonicate the resulting mixture. The molar ratio of 1,2,4,5-benzenetetracarbonitrile (BTC) to 1,2-dicyanobenzene is (1-3):(1-3).

[0008] Step 2: Introduce the polymerization catalyst into the mixture obtained in Step 1 and react it under a nitrogen atmosphere.

[0009] Step 3: Disperse nitrogen-doped carbon nanotubes into the product obtained in Step 2.

[0010] Step 4: Perform a hydrothermal reaction on the product obtained in Step 3, and collect the solid product after cooling to obtain a polymer iron phthalocyanine single-atom carbon-based catalyst with abundant defects.

[0011] Preferably, in step one, the molar ratio of 1,2,4,5-benzenetetracarbonyl nitrile, 1,2-dicyanobenzene, and the ferric salt is 1:1:0.6. The ferric salt is anhydrous ferric chloride.

[0012] Preferably, in step one, the organic solvent is a mixed solution of ethylene glycol and DMF (N,N-dimethylformamide). The volume ratio of ethylene glycol to N,N-dimethylformamide (DMF) is 9:1.

[0013] Preferably, the polymerization catalyst in step two is 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU).

[0014] Preferably, the reaction time in step two under a nitrogen atmosphere is 30 min to 60 min.

[0015] Preferably, the hydrothermal reaction conditions in step three are: a reaction at 180℃~200℃ for 72h~80h.

[0016] Preferably, the product obtained in step four is washed sequentially with 1M hydrochloric acid, anhydrous ethanol, and deionized water.

[0017] Preferably, the product obtained in step four is washed and then vacuum dried at 70°C for 48 hours to obtain a polymer iron phthalocyanine single-atom carbon-based catalyst (D-FeN5-x) containing abundant defects.

[0018] Preferably, in steps three and four, nitrogen-doped carbon nanotubes provide a stable scaffold for the single Fe-NC center in the defective conjugated phthalocyanine structure, resulting in the obtained polymer iron phthalocyanine single-atom carbon-based catalyst material exhibiting a rod-like morphology.

[0019] Secondly, this invention provides the application of the catalyst prepared by the aforementioned method in the catalytic oxidation degradation treatment of organic polluted wastewater. The specific process for the catalytic oxidation degradation treatment of organic polluted wastewater is as follows: a single-atom carbon-based polymer iron phthalocyanine catalyst containing abundant defects is added to the wastewater to be treated, it is dispersed by ultrasonication, then an oxidant is added, and the reaction is stirred.

[0020] Preferably, the organic polluted wastewater is phenol-containing polluted water. The pollutants in the phenol-containing polluted water can be bisphenol A or other phenol-containing organic compounds.

[0021] Preferably, the oxidant is persulfate.

[0022] Preferably, the persulfate is potassium monopersulfate; the amount of persulfate relative to the wastewater being treated is 0.14 mM.

[0023] Preferably, the amount of the polymeric iron phthalocyanine single-atom carbon-based catalyst (D-FeN5-x) containing abundant defects is 0.05 g / L relative to the wastewater being treated.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] 1. This invention provides a single-atom carbon-based catalyst (D-FeN5-x) of polymeric iron phthalocyanine containing abundant defects. This catalyst is assembled with an iron center using a specific ratio of 1,2,4,5-benzenetetracarbononitrile (BTC) and 1,2-dicyanobenzene (DCB) as monomers to form a fully encapsulated conjugated covalent organic framework. By introducing DCB to replace part of the bridging-based BTC unit, excess cyano groups within the framework are eliminated, thereby forming defect sites in the resulting conjugated covalent organic framework. This method disrupts the π-π bonding integrity of the polymeric iron phthalocyanine, optimizing the charge state of adjacent carbon atoms. Edge carbon atoms typically exhibit a slightly higher charge density than the basal plane, resulting in better electronic activity. By utilizing the electronegativity difference between the metal atom and the carbon atom, charge enrichment at the edge sites allows sufficient charge transfer, enhancing the catalytic activity of the defective iron phthalocyanine sites.

[0026] 2. This invention introduces nitrogen-doped carbon nanotubes as part of the precursor mixture, providing a stable scaffold for the single Fe-NC centers in the defect-conjugated phthalocyanine structure. The polymeric iron phthalocyanine single-atom carbon-based catalyst (D-FeN5-x) material containing abundant defects exhibits a rod-like morphology.

[0027] 3. The polymeric iron phthalocyanine single-atom carbon-based catalyst (D-FeN5-x) synthesized in this invention, containing abundant defects, possesses unique planar symmetric Fe-N4 sites. By combining nitrogen-doped carbon nanotubes with iron atoms in phthalocyanine iron to form Fe-N5 sites, a higher iron site density and better conductivity can be provided, maximizing the utilization of metal sites and improving catalytic efficiency.

[0028] 4. This invention introduces nitrogen-doped carbon nanotubes into the precursor mixture to prevent the aggregation of defective phthalocyanine iron molecules during pyrolysis and to improve the conductivity of the resulting catalyst. The carbon nanotube-supported polymeric iron phthalocyanine single-atom carbon-based catalyst, rich in defects, can separate and stabilize atomically dispersed metals. Its unique surface morphology promotes metal loading, thereby facilitating the catalytic process.

[0029] 5. The heterogeneous Fenton catalyst provided by this invention exhibits excellent performance in the degradation of bisphenol A wastewater, demonstrating a high removal efficiency. Furthermore, the catalyst of this invention possesses acid and alkali resistance and a long service life. This catalyst utilizes persulfate as an oxidant to oxidize and degrade recalcitrant organic pollutants, achieving a high removal efficiency and effectively avoiding the problems of narrow effective pH range, low hydrogen peroxide utilization, and secondary iron ion pollution inherent in the traditional Fenton process. Attached Figure Description

[0030] Figure 1 This is a SEM image of the catalyst prepared in Example 1 of the present invention.

[0031] Figure 2a This is a schematic diagram of the molecular structure of the catalyst prepared in Example 1 of the present invention.

[0032] Figure 2b This is a schematic diagram of the molecular structure of the catalyst prepared in Example 2 of the present invention.

[0033] Figure 2c This is a schematic diagram of the molecular structure of the catalyst prepared in Example 3 of the present invention.

[0034] Figure 2d This is a schematic diagram of the molecular structure of the catalyst prepared in Comparative Example 1 of the present invention.

[0035] Figure 3 The images show the XRD patterns of the catalysts prepared in Examples 1-3 and Comparative Example 1 of this invention.

[0036] Figure 4 The graphs show the degradation curves of organic pollutants of the catalysts prepared in Examples 1-3 of this invention.

[0037] Figure 5 This is a degradation curve of different organic pollutants in Example 1 of the present invention. Detailed Implementation

[0038] The present invention is further described below through specific embodiments, but the scope of protection of the present invention is not limited to the materials, reagents, etc. used in the following examples, which are all commercially available unless otherwise specified.

[0039] Example 1

[0040] A method for preparing a polymeric iron phthalocyanine single-atom carbon-based catalyst (D-FeN5-x) containing abundant defects includes the following steps:

[0041] Step 1: Disperse 0.10 g (i.e. 0.7 mmol) of 1,2,4,5-benzenetetracarboxynitrile, 0.108 g (i.e. 0.7 mmol) of 1,2-dicyanobenzene in a molar ratio of 1:1 and 0.14 g (i.e. 0.085 mmol) of anhydrous ferric chloride in a solution of 54 mL of ethylene glycol and 6 mL of LDMF (N,N-dimethylformamide), and sonicate for 30 min to completely dissolve the powder to obtain a mixed solution.

[0042] Step 2: 0.23 g (i.e. 0.15 mmol) of 1,8-diazabicyclo[5.4.0]undec-7-ene (i.e. 1,8-diazabicyclo[5.4.0]undec-7-ene, DBU) was introduced into the mixed solution as a catalyst and reacted under a nitrogen atmosphere for 30 minutes to produce iron phthalocyanine with irregular defects.

[0043] Step 3: Add 100 mg of nitrogen-doped carbon nanotubes to the liquid system obtained in Step 2; transfer the liquid system to a 250 mL beaker with a built-in rotor, turn on the magnetic stirrer, and stir vigorously for 24 h; so that the carbon nanotubes and the solution in Step 2 are mixed evenly.

[0044] Step 4: Transfer the obtained mixture to a high-pressure reactor and heat at 180°C for 72 hours, then slowly cool to room temperature. Collect the precipitated solid by centrifugation and wash successively with 1M hydrochloric acid, anhydrous ethanol, and deionized water. Dry the resulting product under vacuum at 70°C for 48 hours to obtain a polymeric iron phthalocyanine single-atom carbon-based catalyst (D-FeN5-50) containing abundant defects.

[0045] The morphology of the obtained polymeric iron phthalocyanine single-atom carbon-based catalyst (D-FeN5-50) containing abundant defects is as follows: Figure 1As shown, the catalyst as a whole consists of rod-shaped carbon nanotubes covered with defective phthalocyanine iron.

[0046] The molecular structure of D-FeN5-50 obtained in this embodiment is as follows: Figure 2a As shown.

[0047] Example 2

[0048] A method for preparing a single-atom carbon-based polymeric iron phthalocyanine catalyst (D-FeN5-25) with abundant defects is disclosed in this embodiment, which differs from Example 1 in that the molar ratio of 1,2,4,5-benzenetetracarbonyl nitrile and 1,2-dicyanobenzene in step one is 3:1 (specifically, 10.5 mmol of 1,2,4,5-benzenetetracarbonyl nitrile and 3.5 mmol of 1,2-dicyanobenzene). Other steps and parameters are the same as in Example 1.

[0049] The molecular structure of D-FeN5-25 obtained in this embodiment is as follows: Figure 2b As shown.

[0050] Example 3

[0051] A method for preparing a single-atom carbon-based polymeric iron phthalocyanine catalyst (D-FeN5-75) with abundant defects is disclosed in this embodiment, which differs from Example 1 in that the molar ratio of 1,2,4,5-benzenetetracarbonyl nitrile and 1,2-dicyanobenzene in step one is 1:3 (specifically, 3.5 mmol of 1,2,4,5-benzenetetracarbonyl nitrile and 10.5 mmol of 1,2-dicyanobenzene). Other steps and parameters are the same as in Example 1.

[0052] The molecular structure of D-FeN5-75 obtained in this embodiment is as follows: Figure 2c As shown.

[0053] Comparative Example 1

[0054] A method for preparing a defect-free polymeric iron phthalocyanine single-atom carbon-based catalyst (D-FeN5-0) is disclosed. The difference between this embodiment and Example 1 is that the molar ratio of 1,2,4,5-benzenetetracarbononitrile and 1,2-dicyanobenzene in step one is 1:0. Other steps and parameters are the same as in Example 1.

[0055] The molecular structure of D-FeN5-0 obtained in this embodiment is as follows: Figure 2d As shown.

[0056] contrast Figures 2a-2d It can be seen that the introduction of 1,2-dicyanobenzene into the system can lead to the formation of defect structures in the phthalocyanine iron polymer, and the amount of 1,2-dicyanobenzene introduced will affect the number of defect structures.

[0057] The XRD results of the products obtained in Examples 1-3 and Comparative Example 1 are as follows: Figure 3 As shown; from Figure 3 As can be seen, the main diffraction peaks of the crystals obtained in Examples 1-3 and Comparative Example 1 remain generally unchanged, and no diffraction peaks related to FePc are found. The sharp X-ray diffraction (XRD) pattern of monomeric FEPC indicates its high crystallinity, while the XRD mode of D-FeN5-x material indicates that it is in an amorphous state.

[0058] Comparative experiments were conducted using the products obtained in Examples 1-3 and Comparative Example 1 to treat wastewater containing bisphenol A compounds. The procedures were as follows: 40 mL of 100 mg / L BPA solution and 160 mL of deionized water were placed in a 200 mL beaker with a built-in magnetic rotor. Then, 10 mg of catalyst was added, followed by the addition of persulfate monosulfate (PMS) as an oxidant. The water temperature was controlled at 25°C, and the reaction was carried out on a magnetic stirrer at 700 rpm. The reaction time was set to 30 min. At the set time point, 1 mL of the reaction solution was taken out, and the precipitate was separated using a 0.22 μm filter. The experiment was repeated twice.

[0059] Three experimental groups and five control groups were set up, as follows:

[0060] Experimental group 1 used the product obtained in Example 1 as a catalyst (corresponding to...) Figure 4 (D-FeN5-50 curve);

[0061] Experimental group 2 used the product obtained in Example 2 as a catalyst (corresponding to...) Figure 4 (D-FeN5-25 curve);

[0062] Experimental group 3 used the product obtained in Example 3 as a catalyst (corresponding to...) Figure 4 (D-FeN5-75 curve);

[0063] Control group 1 used the product obtained from Comparative Example 1 as a catalyst (corresponding to...) Figure 4 (D-FeN5-0 curve);

[0064] Control group 2 used nitrogen-doped carbon nanotubes as a catalyst (corresponding to Figure 4 (CNT curve);

[0065] In control group 3, no PMS was added, but only the product obtained in Example 1 was added as an adsorbent (corresponding to...). Figure 4 (Curve of D-FeN5-50 only);

[0066] In control group 4, no catalyst was added, only PMS (corresponding to) was added. Figure 4 (PMS only curve);

[0067] In control group 5, no PMS was added, but nitrogen-doped carbon nanotubes were added as adsorbents (corresponding to...). Figure 4 (CNT-only curve).

[0068] The above experiments demonstrate that the defective structure in the D-FeN5-x materials prepared in Examples 1-3 facilitates significant charge transfer of Fe atoms to the carbon matrix, activating PMS to generate ROS that attacks pollutants, thus achieving the degradation of bisphenol A (BPA) in environmental water. Furthermore, the product obtained in Example 1 exhibits the best reactivity, achieving a 100% removal rate of BPA. It can serve as a high-performance catalyst for removing BPA from environmental water. Figure 4 As can be seen, almost no BPA is removed through adsorption by CNTs and D-FeN5-x, and the reactivity of PMS in BPA degradation is negligible. When D-FeN5-0, D-FeN5-25, and D-FeN5-75 are used as catalysts, PMS degrades less than 65%, 68%, and 80% of BPA within 30 minutes, respectively. The enhanced activity of the D-FeN5-50 / PMS system compared to other D-FeN5-x catalysts can be attributed to structural defects within the framework. Excessive (D-FeN5-75) or insufficient (D-FeN5-25) structural defects lead to reduced BPA removal efficiency, highlighting the importance of degree of polymerization control.

[0069] Example 4

[0070] A method for degrading organic pollutants in groundwater, specifically comprising adding the catalysts provided in Examples 1-3 to the water body to be treated. The organic pollutants in the water body to be treated are bisphenol A (BPA), carbamazepine (CBZ), 4-chlorophenol (4-CP), and 2,4-dichlorophenol (2,4-D).

[0071] The following is a comparative experiment using the catalyst (D-FeN5-50) obtained in Example 1 to decompose common micropollutants (bisphenol A, carbamazepine, 4-chlorophenol, 2,4-dichlorophenol) in different water bodies:

[0072] Take 40 mL of a 100 mg / L micropollutant solution and 160 mL of deionized water into a 200 mL beaker with a built-in magnetic stirrer, then add 10 mg of the test material, followed by the addition of persulfate monosulfate (PMS) oxidant. Maintain the water temperature at 25 °C and place the beaker on a magnetic stirrer at 700 rpm for the reaction. Set the reaction time to 30 min. At each set time point, remove 1 mL of the reaction solution and separate the precipitate using a 0.22 μm filter. Repeat the experiment twice.

[0073] Experimental results are as follows Figure 5 As shown; from Figure 5It can be seen that the polymer iron phthalocyanine single-atom carbon-based catalyst (D-FeN5-50) with abundant defects provided in Example 1 has a good degradation effect on different pollutants.

Claims

1. A method for preparing a polymeric iron phthalocyanine single-atom carbon-based catalyst with abundant defects, characterized in that: Includes the following steps: Step 1: Disperse the mixture of 1,2,4,5-benzenetetracarbonitrile, 1,2-dicyanobenzene and ferric salt in an organic solvent; sonicate the resulting mixture; the molar ratio of 1,2,4,5-benzenetetracarbonitrile to 1,2-dicyanobenzene is (1-3):(1-3); Step 2: Introduce the polymerization catalyst into the mixture obtained in Step 1 and react under a nitrogen atmosphere; Step 3: Disperse nitrogen-doped carbon nanotubes into the product obtained in Step 2; Step 4: The product obtained in Step 3 is subjected to a hydrothermal reaction. After cooling, the solid product is collected to obtain a polymer iron phthalocyanine single-atom carbon-based catalyst with abundant defects. The hydrothermal reaction conditions are 180℃~200℃ for 72h~80h. Nitrogen-doped carbon nanotubes provide a stable scaffold for the single Fe-NC center in the defect conjugated phthalocyanine structure, so that the obtained polymer iron phthalocyanine single-atom carbon-based catalyst material has a rod-like morphology.

2. The preparation method according to claim 1, characterized in that: In step one, the molar ratio of 1,2,4,5-benzenetetracarbonyl nitrile, 1,2-dicyanobenzene and ferric salt is 1:1:0.6; the ferric salt is anhydrous ferric chloride.

3. The preparation method according to claim 1, characterized in that: The polymerization catalyst mentioned in step two is 1,8-diazabicyclo[5.4.0]undec-7-ene.

4. The preparation method according to claim 1, characterized in that: The reaction time in step two under a nitrogen atmosphere is 30 min to 60 min.

5. The preparation method according to claim 1, characterized in that: The product obtained in step four was washed sequentially with 1M hydrochloric acid, anhydrous ethanol, and deionized water.

6. A polymeric iron phthalocyanine single-atom carbon-based catalyst with abundant defects, characterized in that: It has a rod-like morphology and is prepared by the preparation method described in any one of claims 1-5.

7. The application of the polymer iron phthalocyanine single-atom carbon-based catalyst with abundant defects as described in claim 6 in the catalytic oxidation degradation treatment of organic polluted wastewater.

8. The application according to claim 7, characterized in that: The organic polluted wastewater mentioned above is a phenol-containing polluted water body.

9. The application according to claim 7, characterized in that: The oxidant used in the catalytic oxidation degradation process is persulfate.

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