Confined range type iron monatomic catalyst as well as preparation method and application thereof

Abstract

The invention discloses a preparation method of a confinement type iron monatomic catalyst (Fe SAC), the confinement type iron monatomic catalyst (Fe SAC) is applied to a Fenton reaction, and the confinement type iron monatomic catalyst (Fe SAC) is characterized in that iron monatomic atoms are confined in a limited space of a ZSM-5 substrate containing micropore channels, so that generated hydroxyl free radicals (. OH) are protected, and therefore, the confinement type iron monatomic catalyst (Fe SAC) not only has good. OH cumulative yield (1.68-2.64 mmol / L), but also has good catalytic activity. OH can be continuously generated for 24 hours, and the degradation effect on parachlorophenol in water can reach 12 hours. The results show that the Fe SAC continuously generates and effectively utilizes. OH by activating hydrogen peroxide, the long-term effect of the Fenton reaction is improved, and the Fe SAC has a good application prospect in the aspect of removal of micropollutants in advanced sewage treatment.

Description

Technical Field

[0001] The present invention belongs to the field of catalysts, and in particular relates to a confined iron single-atom catalyst and a preparation method and application thereof. Background Art

[0002] Fenton catalytic oxidation is an advanced oxidation process (AOP) in wastewater treatment. It catalytically activates hydrogen peroxide (H2O2) to produce a product with a very high oxidation potential (2.6-3.1V vs NHE), a fast reaction (reaction rate constant with benzene ring organic matter is up to 10 9 ) and hydroxyl radicals (•OH) without secondary pollution (their own decomposition products are H2O and O2), which can effectively oxidize and degrade organic pollutants in wastewater. In recent years, the use of heterogeneous catalysts to replace the soluble homogeneous phase (ferrous ions) in the traditional Fenton process has been widely studied. This method is easy to separate and recycle the catalyst, which can reduce the generation of iron-containing sludge. However, the short lifespan (10 -3 The low utilization of H₂O₂ is hampered by the self-quenching of •OH in the short (microsecond) timeframe and the indiscriminate side reactions of •OH with organic matter and ions. Currently, there is an urgent need for breakthroughs in the construction of novel Fenton catalysts that can continuously generate and effectively utilize •OH.

[0003] Previous studies have reported optimizing the coordination environment of catalysts by modulating the electronic structure of active sites, promoting H2O2 activation and the sustainable generation of •OH. Furthermore, nanoconfinement can be exploited to spatially confine short-lived free radicals and reactants within the critical diffusion length, effectively utilizing •OH. In particular, single-atom catalysts (SACs), which inherit the advantages of both homogeneous and heterogeneous catalysts, offer high atom utilization, high reactivity, high selectivity, and strong stability. Iron is inexpensive and abundant in nature. Iron single-atom catalysts (Fe SACs) possess uniquely tunable, uniform, and single active sites, promoting the cracking of H2O2 and the generation and utilization of •OH. Zeolites, with their rich pore structures and strong adsorption capacity, are ideal supports for designing confined Fe single-atom catalysts. Confining single Fe atoms with a tunable coordination environment within the nanoscale pores of zeolites is expected to achieve the continuous generation and efficient utilization of •OH, overcoming the challenges of traditional Fenton catalytic oxidation and providing a promising advanced oxidation technology solution for advanced wastewater treatment. Summary of the Invention

[0004] The purpose of the present invention is to address the deficiencies of the prior art and provide a confined iron single-atom catalyst and a preparation method and application thereof.

[0005] The object of the present invention is achieved through the following technical solutions: In a first aspect, the present invention provides a method for preparing a confined iron single-atom catalyst, comprising the following steps: (1) Place 0.6-0.8 g of ferrocene on a watch glass and spread it flat. Dry it in an oven at 35-45°C for 0.5-1.5 h to obtain dried ferrocene. (2) 0.6-0.8 g of dried ferrocene is placed in a first alumina crucible, so that the dried ferrocene is evenly distributed on the bottom of the first alumina crucible and the surface is flat; and 0.9-1.1 g of ZSM-5 is placed in a second alumina crucible, so that the ZSM-5 is evenly distributed on the bottom of the second alumina crucible and the surface is flat; (3) Then, the first alumina crucible and the second alumina crucible are placed close together in the center of the quartz tube of the tube furnace, with the first alumina crucible placed upstream of the air flow and the second alumina crucible placed downstream of the air flow; (4) Heat to 50-70°C in an argon atmosphere at a flow rate of 10-20 mL / min, purge for 30-50 min to remove the air in the quartz tube, and then heat to 90-110°C at a heating rate of 1-3°C / min, with a purge time of 5-90 min; (5) Heating to 140-160°C for 3.5-4.5 h in an argon atmosphere at a flow rate of 10-20 mL / min, and obtaining a confined iron single atom catalyst in a second alumina crucible, which is designated as Fe1-ZSM-5(1); Alternatively, the catalyst is heated to 490-510°C in an argon atmosphere at a flow rate of 10-20 mL / min for 3.5-4.5 h, and a confined iron single atom catalyst is obtained in a second alumina crucible, which is recorded as Fe1-ZSM-5(2).

[0006] In a second aspect, the present invention provides a confined iron single-atom catalyst.

[0007] In a third aspect, the present invention provides an application of a confined iron single-atom catalyst for long-term removal of para-chlorophenol in water, comprising the following steps: adding a confined iron single-atom catalyst and hydrogen peroxide to water to complete the removal of para-chlorophenol in the water; the dosage of the confined iron single-atom catalyst is 0.5~2g / L; the dosage of the hydrogen peroxide is 6~10mmol / L; the concentration of para-chlorophenol in the water body is 0.01~0.1 mmol / L.

[0008] The beneficial effects of the present invention are: 1) The zeolite ZSM-5 selected in the present invention has a rich microporous structure, and the easily sublimated ferrocene can enter the pores, ensuring that the iron atoms in the catalyst are confined to a nanoscale space; 2) The present invention utilizes the characteristic of gradual thermal decomposition of ferrocene. By adjusting the heating temperature, the degree of ferrocene decomposition is controlled, and the coordination structure of the iron atom is adjusted to obtain iron single-atom catalysts with two coordination configurations. 3) The two confined iron single-atom catalysts prepared in this invention can activate H2O2 and protect the generated ·OH in the pores, thereby improving the long-term effectiveness of the Fenton reaction. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 The reaction temperature and crucible placement diagram of the confined iron single atom catalyst Fe1-ZSM-5 (1) prepared in Example 1 and the confined iron single atom catalyst Fe1-ZSM-5 (2) prepared in Example 2; Figure 2 is an X-ray absorption spectrum and coordination environment comparison diagram of Fe2O3, FeO, Fe foil, the confined iron single atom catalyst Fe1-ZSM-5 (1) prepared in Example 1 and the confined iron single atom catalyst Fe1-ZSM-5 (2) prepared in Example 2, wherein Figure 2 (a) is an X-ray absorption spectrum of Fe2O3, FeO, Fe foil, the confined iron single atom catalyst Fe1-ZSM-5 (1) prepared in Example 1 and the confined iron single atom catalyst Fe1-ZSM-5 (2) prepared in Example 2, and Figure 2 (b) is a coordination environment comparison diagram of Fe2O3, FeO, Fe foil, the confined iron single atom catalyst Fe1-ZSM-5 (1) prepared in Example 1 and the confined iron single atom catalyst Fe1-ZSM-5 (2) prepared in Example 2; Figure 3 This is a comparison chart of the pore size and pore volume changes of the confined iron single-atom catalyst Fe1-ZSM-5 (1) prepared in Example 1, the confined iron single-atom catalyst Fe1-ZSM-5 (2) prepared in Example 2, and the zeolite ZSM-5.

[0010] Figure 4 This is a spherical aberration-corrected high-angle annular dark-field scanning transmission electron micrograph of the confined iron single-atom catalyst Fe1-ZSM-5 (2) prepared in Example 2; Figure 5 The confined iron single atom catalyst Fe1-ZSM-5 (1) prepared in Example 1 and the confined iron single atom catalyst Fe1-ZSM-5 (2) prepared in Example 2 and Fe 2+ Electron paramagnetic resonance spectra of hydroxyl radicals generated by activated hydrogen peroxide; Figure 6 Fe 2+, a schematic diagram of the cumulative concentration of hydroxyl radicals generated by the activation of hydrogen peroxide by the confined iron single-atom catalyst Fe1-ZSM-5 (1) prepared in Example 1 and the confined iron single-atom catalyst Fe1-ZSM-5 (2) prepared in Example 2; Figure 7 The confined iron single atom catalyst Fe1-ZSM-5 (1) prepared in Example 1 and the confined iron single atom catalyst Fe1-ZSM-5 (2) prepared in Example 2 and Fe 2+ Schematic diagram of the removal of para-chlorophenol in water by activating hydrogen peroxide to generate long-lasting hydroxyl radicals; Figure 8 This is an electron microscope iron element spectrum scanning image of the confined iron single atom catalyst prepared in Example 2-5; Figure 9 This is a comparison of the X-ray absorption spectra of the confined iron single-atom catalysts prepared in Examples 2-5; Figure 10 Schematic diagram of the linear relationship between the reaction rate difference and the cumulative concentration of ·OH of the confined iron single-atom catalysts prepared in Examples 2-5. DETAILED DESCRIPTION

[0011] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to illustrate the present invention, rather than to represent all embodiments. All other embodiments obtained by persons of ordinary skill in the art based on the embodiments of the present invention without creative work are within the scope of protection of the present invention.

[0012] The present invention uses a gas diffusion scheme to prepare a confined iron single-atom catalyst. This method utilizes the easy sublimation of ferrocene and the adsorption effect of ZSM-5 to confine the former in the pores of the latter through a purge process using an inert gas as a carrier gas, thereby obtaining a confined iron single-atom catalyst. The gradual thermal decomposition of ferrocene at different temperatures allows it to interact with the hydroxyl groups within the ZSM-5 to adjust the coordination environment of the confined iron single-atom catalyst. After different purge times, the diffusion degree of gaseous ferrocene entering the micropores of ZSM-5 varies, resulting in confined iron single-atom catalysts with different degrees of single-atom dispersion within the pores.

[0013] The present invention provides a method for preparing a confined iron single-atom catalyst, comprising the following steps: (1) Place 0.6-0.8 g of ferrocene on a watch glass and spread it flat. Dry it in an oven at 35-45°C for 0.5-1.5 h to obtain dried ferrocene. (2) 0.6-0.8 g of dried ferrocene is placed in a first alumina crucible, so that the dried ferrocene is evenly distributed on the bottom of the first alumina crucible and the surface is flat; and 0.9-1.1 g of ZSM-5 is placed in a second alumina crucible, so that the ZSM-5 is evenly distributed on the bottom of the second alumina crucible and the surface is flat; (3) Then, the first alumina crucible and the second alumina crucible are placed close together in the center of the quartz tube of the tube furnace, with the first alumina crucible placed upstream of the air flow and the second alumina crucible placed downstream of the air flow; (4) Heat to 50-70°C in an argon atmosphere at a flow rate of 10-20 mL / min, purge for 30-50 min to remove the air in the quartz tube, and then heat to 90-110°C at a heating rate of 1-3°C / min, with a purge time of 5-90 min; (5) Heating to 140-160°C for 3.5-4.5 h in an argon atmosphere at a flow rate of 10-20 mL / min, and obtaining a confined iron single atom catalyst in a second alumina crucible, which is designated as Fe1-ZSM-5(1); Alternatively, the catalyst is heated to 490-510°C in an argon atmosphere at a flow rate of 10-20 mL / min for 3.5-4.5 h, and a confined iron single atom catalyst is obtained in a second alumina crucible, which is recorded as Fe1-ZSM-5(2).

[0014] Example 1: (1) 0.7 g of ferrocene was placed flat on a dry surface dish and dried in an oven at 40°C for 1 h to obtain dried ferrocene; (2) Place 0.7 g of dried ferrocene in a clean first alumina crucible, so that the dried ferrocene is evenly distributed on the bottom of the first alumina crucible and the surface is flat; and place 1.0 g of ZSM-5 in a clean second alumina crucible, so that the ZSM-5 is evenly distributed on the bottom of the second alumina crucible and the surface is flat; (3) Then, the first alumina crucible and the second alumina crucible are placed close together in the center of the quartz tube of the tube furnace, with the first alumina crucible placed upstream of the air flow and the second alumina crucible placed downstream of the air flow; (4) Heat to 60°C under an argon atmosphere at a flow rate of 15 mL / min, purge for 40 min to remove the air in the quartz tube, and then heat to 100°C at a heating rate of 2°C / min, and purge for 60 min; (5) The mixture was heated to 150°C for 4 h in an argon atmosphere at a flow rate of 15 mL / min, and a confined iron single atom catalyst was obtained in a second alumina crucible, which was recorded as Fe1-ZSM-5(1).

[0015] Example 2: (1) 0.7 g of ferrocene was placed flat on a dry surface dish and dried in an oven at 40°C for 1 h to obtain dried ferrocene; (2) Place 0.7 g of dried ferrocene in a clean first alumina crucible, so that the dried ferrocene is evenly distributed on the bottom of the first alumina crucible and the surface is flat; and place 1.0 g of ZSM-5 in a clean second alumina crucible, so that the ZSM-5 is evenly distributed on the bottom of the second alumina crucible and the surface is flat; (3) Then, the first alumina crucible and the second alumina crucible are placed close together in the center of the quartz tube of the tube furnace, with the first alumina crucible placed upstream of the air flow and the second alumina crucible placed downstream of the air flow; (4) Heat to 60°C under an argon atmosphere at a flow rate of 15 mL / min, purge for 40 min to remove the air in the quartz tube, and then heat to 100°C at a heating rate of 2°C / min, and purge for 60 min; (5) The mixture was heated to 500°C for 4 h in an argon atmosphere at a flow rate of 15 mL / min, and a confined iron single atom catalyst was obtained in a second alumina crucible, which was recorded as Fe1-ZSM-5(2).

[0016] Example 3: (1) 0.7 g of ferrocene was placed on a dry surface dish and spread flatly, and dried in an oven at 40°C for 1 h to obtain dried ferrocene; (2) Place 0.7 g of dried ferrocene in a clean first alumina crucible, so that the dried ferrocene is evenly distributed on the bottom of the first alumina crucible and the surface is flat; and place 1.0 g of ZSM-5 in a clean second alumina crucible, so that the ZSM-5 is evenly distributed on the bottom of the second alumina crucible and the surface is flat; (3) Then, the first alumina crucible and the second alumina crucible are placed close together in the center of the quartz tube of the tube furnace, with the first alumina crucible placed upstream of the air flow and the second alumina crucible placed downstream of the air flow; (4) Heat to 60°C under an argon atmosphere at a flow rate of 15 mL / min, purge for 40 min to remove the air in the quartz tube, and then heat to 100°C at a heating rate of 2°C / min, with a purge time of 5 min; (5) The mixture was heated to 500 °C for 4 h in an argon atmosphere at a flow rate of 15 mL / min, and a confined iron single atom catalyst was obtained in a second alumina crucible, which was recorded as Fe1-ZSM-5(2)-5.

[0017] Example 4: (1) 0.7 g of ferrocene was placed on a dry surface dish and spread flatly, and dried in an oven at 40°C for 1 h to obtain dried ferrocene; (2) Place 0.7 g of dried ferrocene in a clean first alumina crucible, so that the dried ferrocene is evenly distributed on the bottom of the first alumina crucible and the surface is flat; and place 1.0 g of ZSM-5 in a clean second alumina crucible, so that the ZSM-5 is evenly distributed on the bottom of the second alumina crucible and the surface is flat; (3) Then, the first alumina crucible and the second alumina crucible are placed close together in the center of the quartz tube of the tube furnace, with the first alumina crucible placed upstream of the air flow and the second alumina crucible placed downstream of the air flow; (4) Heat to 60°C under an argon atmosphere at a flow rate of 15 mL / min, purge for 40 min to remove the air in the quartz tube, and then heat to 100°C at a heating rate of 2°C / min, and purge for 45 min; (5) The mixture was heated to 500 °C for 4 h in an argon atmosphere at a flow rate of 15 mL / min, and a confined iron single atom catalyst was obtained in a second alumina crucible, which was recorded as Fe1-ZSM-5(2)-45.

[0018] Example 5: (1) 0.7 g of ferrocene was placed on a dry surface dish and spread flat, and dried in an oven at 40°C for 1 h to obtain dried ferrocene; (2) Place 0.7 g of dried ferrocene in a clean first alumina crucible, so that the dried ferrocene is evenly distributed on the bottom of the first alumina crucible and the surface is flat; and place 1.0 g of ZSM-5 in a clean second alumina crucible, so that the ZSM-5 is evenly distributed on the bottom of the second alumina crucible and the surface is flat; (3) Then, the first alumina crucible and the second alumina crucible are placed close together in the center of the quartz tube of the tube furnace, with the first alumina crucible placed upstream of the air flow and the second alumina crucible placed downstream of the air flow; (4) Heat to 60°C under an argon atmosphere at a flow rate of 15 mL / min, purge for 40 min to remove the air in the quartz tube, and then heat to 100°C at a heating rate of 2°C / min, and purge for 120 min; (5) The mixture was heated to 500 °C for 4 h in an argon atmosphere at a flow rate of 15 mL / min, and a confined iron single atom catalyst was obtained in a second alumina crucible, which was recorded as Fe1-ZSM-5(2)-90.

[0019] Application Example 1: (1) The confined iron single-atom catalyst prepared in Example 1 was added to water to a concentration of 2 g / L, dispersed with ultrasound assistance, and stirred on a magnetic stirrer. Parachlorophenol was added to an initial concentration of 0.1 mmol / L. The oxidant H2O2 was added to an initial concentration of 6 mmol / L.

[0020] (2) Start timing after adding the oxidant, and use a syringe to take samples at 0, 15, 30, 60, 120 and 180 minutes respectively. After separating the catalyst with a 0.22 micron water filter membrane, add it to a liquid phase vial containing a 10% by volume methanol solution.

[0021] (3) The concentration of parachlorophenol in the solution was determined using high performance liquid chromatography.

[0022] Application Example 2: (1) The confined iron single atom catalyst prepared in Example 1 was added to water to a concentration of 2 g / L, dispersed with ultrasound assistance, and placed on a magnetic stirrer for stirring.

[0023] (2) Add the oxidant H2O2 to an initial concentration of 6 mmol / L and activate for 9 hours.

[0024] (3) Add parachlorophenol to an initial concentration of 0.1 mmol / L. Use a syringe to take samples at 0, 15, 30, 60, 120, and 180 min, separate the catalyst with a 0.22 μm water filter, and add it to a liquid phase vial containing a 10% by volume methanol solution.

[0025] (4) The concentration of parachlorophenol in the solution was determined using high performance liquid chromatography.

[0026] Application Example 3: (1) The confined iron single-atom catalyst prepared in Example 2 was added to water to a concentration of 2 g / L, dispersed with ultrasound assistance, and stirred on a magnetic stirrer. Parachlorophenol was added to an initial concentration of 0.1 mmol / L. The oxidant H2O2 was added to an initial concentration of 6 mmol / L.

[0027] (2) Start timing after adding the oxidant, and use a syringe to take samples at 0, 15, 30, 60, 120 and 180 minutes respectively. After separating the catalyst with a 0.22 micron water filter membrane, add it to a liquid phase vial containing a 10% by volume methanol solution.

[0028] (3) The concentration of parachlorophenol in the solution was determined using high performance liquid chromatography.

[0029] Application Example 4: (1) The confined iron single atom catalyst prepared in Example 2 was added to water to a concentration of 2 g / L, dispersed with ultrasound assistance, and placed on a magnetic stirrer for stirring.

[0030] (2) Add the oxidant H2O2 to an initial concentration of 6 mmol / L and activate for 9 hours.

[0031] (3) Add parachlorophenol to an initial concentration of 0.1 mmol / L. Use a syringe to take samples at 0, 15, 30, 60, 120, and 180 min, separate the catalyst with a 0.22 μm water filter, and add it to a liquid phase vial containing a 10% by volume methanol solution.

[0032] (4) The concentration of parachlorophenol in the solution was determined using high performance liquid chromatography.

[0033] Application Example 5: (1) The confined iron single-atom catalysts prepared in Examples 3-5 were added to water to a concentration of 2 g / L, dispersed with ultrasound assistance, and stirred on a magnetic stirrer. Parachlorophenol was added to an initial concentration of 0.1 mmol / L. The oxidant H2O2 was added to an initial concentration of 6 mmol / L.

[0034] (2) Start timing after adding the oxidant, and use a syringe to take samples at 0, 15, 30, 60, 120 and 180 minutes respectively. After separating the catalyst with a 0.22 micron water filter membrane, add it to a liquid phase vial containing a 10% by volume methanol solution.

[0035] (3) Use high performance liquid chromatography to determine the concentration of parachlorophenol in the solution and calculate the reaction rate constant based on it.

[0036] Application Example 6: (1) Add the confined iron single-atom catalyst prepared in Examples 3-5 to water to a concentration of 2 g / L, disperse with the aid of ultrasound, and place on a magnetic stirrer for stirring.

[0037] (2) Add oxidant H2O2 at a concentration of 6 mmol / L and activate for 9 hours.

[0038] (3) Add parachlorophenol to an initial concentration of 0.1 mmol / L. Use a syringe to take samples at 0, 15, 30, 60, 120, and 180 min, separate the catalyst with a 0.22 μm water filter, and add it to a liquid phase vial containing a 10% by volume methanol solution.

[0039] (4) Use high performance liquid chromatography to determine the concentration of parachlorophenol in the solution and calculate the reaction rate constant based on it.

[0040] Figure 1The reaction temperature and crucible placement diagram of the confined iron single atom catalyst Fe1-ZSM-5(1) prepared in Example 1 and the confined iron single atom catalyst Fe1-ZSM-5(2) prepared in Example 2 are shown in FIG2(a). The X-ray absorption spectra of Fe2O3, FeO, Fe foil (iron foil), Fe1-ZSM-5(1) and Fe1-ZSM-5(2) are shown in FIG2(a). As shown in FIG2(a), compared with the Fe foil, Fe1-ZSM-5(1) and Fe1-ZSM-5(2) have no iron-iron bonds, indicating that the iron components have not agglomerated and exist in the form of single atoms. By comparing the structures of the two catalysts through coordination environment fitting, it is found that the iron in Fe1-ZSM-5(1) is coordinated with two oxygen atoms and one pentadiene ring, while the iron in Fe1-ZSM-5(2) is coordinated with four oxygen atoms. The iron valence state of the former is lower than that of the latter. Figure 3 The comparison diagram of the pore size and pore volume changes of the confined iron single-atom catalyst Fe1-ZSM-5 (1) prepared in Example 1 and the confined iron single-atom catalyst Fe1-ZSM-5 (2) prepared in Example 2, as well as the zeolite ZSM-5, preliminarily proves that after the gas diffusion scheme, the iron enters the micropore channels of ZSM-5.

[0041] Figure 4 This is a spherical aberration-corrected high-angle annular dark-field scanning transmission electron microscopy image of the confined iron single-atom catalyst prepared in Example 2. The metal atom bright spots in the ZSM-5 lattice fringes can be clearly seen, indicating that the iron component is successfully confined in the micropores in the form of single atoms.

[0042] like Figure 5 As shown, using electron paramagnetic resonance to detect ·OH, the confined iron single atom catalyst Fe1-ZSM-5 (1) prepared in Example 1 and the confined iron single atom catalyst Fe1-ZSM-5 (2) prepared in Example 2 are compared with the iron ions (Fe 2+ ), which can activate H2O2 to generate •OH for 24 hours.

[0043] Figure 6 Quantification of Fe 2+The cumulative concentration of hydroxyl radicals produced by the activation of hydrogen peroxide by the confined iron single-atom catalyst Fe1-ZSM-5 (1) prepared in Example 1 and the confined iron single-atom catalyst Fe1-ZSM-5 (2) prepared in Example 2 over 24 hours was significantly greater than that of the traditional Fenton reaction at the same concentration, demonstrating the advantage of the confined iron single-atom catalyst in continuously producing •OH. The reason for this is that the iron single-atom catalyst forms a spatial constraint on •OH, which can prolong the survival time of •OH in water. The confined iron single-atom catalyst Fe1-ZSM-5 (1) prepared in Example 1 has a lower iron valence state, which is conducive to the valence state cycle in the reaction and can thus produce more •OH, resulting in a higher cumulative concentration. Figure 7 The confined iron single atom catalyst Fe1-ZSM-5 (1) prepared in Example 1 and the confined iron single atom catalyst Fe1-ZSM-5 (2) prepared in Example 2 and the Fe 2+ The removal rate of chlorophenol, such as Figure 7 As shown in the figure, H2O was added for 29 hours to fully activate it and all ·OH was produced. Then, para-chlorophenol was added and it could still be degraded by relying on the ·OH retained in the catalyst. This proves that the confined iron single-atom catalyst shortens the mass transfer distance with the pollutants by limiting the iron single-atom active sites in the micropores, realizes the long-term utilization of ·OH, and finally successfully improves the degradation durability of the Fenton reaction.

[0044] Figure 8 The iron element energy spectrum scanning diagrams under an electron microscope of the confined iron single-atom catalysts Fe1-ZSM-5(2), Fe1-ZSM-5(2)-5, Fe1-ZSM-5(2)-45, and Fe1-ZSM-5(2)-90 prepared at different purge times in Examples 2-5 show that as the purge time increases, the iron element distribution becomes more uniform, and when the time reaches 90 minutes, iron element agglomeration occurs. Figure 9 Further comparison of the coordination structure of confined iron single atom catalyst under different purge times by X-ray absorption spectra revealed that Figure 8The conclusions are consistent. As the purge time increases, the iron single atom signal becomes stronger, and when it reaches 90 minutes, iron-iron bonds appear, indicating that iron clusters may have appeared. Therefore, the confined iron single atom catalyst Fe1-ZSM-5(2) obtained when the purge time is 60 min in Example 2 has the best dispersibility of the iron single atom structure. The ·OH produced by the activation of hydrogen peroxide by the confined iron single atom catalysts Fe1-ZSM-5(2), Fe1-ZSM-5(2)-5, Fe1-ZSM-5(2)-45, and Fe1-ZSM-5(2)-90 prepared in Examples 2-5 was quantified. It was found that the ·OH produced by the activation of hydrogen peroxide by the confined iron single atom catalysts Fe1-ZSM-5(2), Fe1-ZSM-5(2)-5, Fe1-ZSM-5(2)-45, and Fe1-ZSM-5(2)-90 prepared in Examples 2-5 increased with the extension of the purge time, and the cumulative concentration of ·OH of Fe1-ZSM-5(2)-90 with iron agglomeration was the lowest. The difference in the reaction rate constants between Application Example 5 and Application Example 6 was used to represent the degree of improvement in the long-term effectiveness of the Fenton reaction. It was found that, consistent with the above conclusions, Fe1-ZSM-5(2) had the best effect in improving the long-term effectiveness of the Fenton reaction. Figure 10 The fitting results show that the reaction rate differences of the confined iron single-atom catalysts Fe1-ZSM-5(2), Fe1-ZSM-5(2)-5, Fe1-ZSM-5(2)-45, and Fe1-ZSM-5(2)-90 prepared in Examples 2-5 have a good linear correlation with the cumulative concentration of ·OH, further proving that the confined iron single-atom catalysts achieve the continuous generation and effective utilization of ·OH, thereby improving the long-term effectiveness of the Fenton reaction.

[0045] The present invention adopts a gas diffusion scheme to prepare a confined iron single-atom catalyst. This method utilizes the easy sublimation of ferrocene and the adsorption effect of ZSM-5, and confines the former in the pores of the latter through a purge process using an inert gas as a carrier gas, thereby obtaining a confined iron single-atom catalyst; then, through the characteristics of ferrocene gradually thermally decomposing at different temperatures, the coordination environment of the confined iron single-atom catalyst is adjusted by interacting with the hydroxyl groups in ZSM-5; after a purge process of different times, the diffusion degree of the gaseous ferrocene entering the micropores of ZSM-5 is different, thereby obtaining a confined iron single-atom catalyst with different degrees of single-atom dispersion in the pores. The molecular size of ferrocene matches the pore diameter of the zeolite micropores, and the internal hydroxyl groups are evenly dispersed, ensuring that the decomposed iron atoms are evenly confined in the pores after a period of purge process, thereby successfully preparing a confined iron single-atom catalyst. The advantages of the confined iron single-atom catalyst of this invention are as follows: 1. The zeolite ZSM-5 selected in this invention has a rich microporous structure and hydroxyl groups within the micropores, ensuring that the iron atoms in the catalyst are confined to a nanoscale space; 2. The iron-containing organic complex selected in this invention is ferrocene, which has the characteristics of easy sublimation and gradual thermal decomposition, ensuring gas diffusion of the iron component and regulation of the coordination environment; 3. The confined iron single-atom catalyst prepared in this invention can activate H2O2, protecting the generated ·OH within the pores, thereby improving the long-term effectiveness of the Fenton reaction. This provides a new solution for the preparation of a novel Fenton catalyst that continuously generates and effectively utilizes ·OH, and has great application potential in industrial production and advanced wastewater treatment.

[0046] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a confined iron single-atom catalyst, characterized in that: The following steps are involved: (1) Place 0.6-0.8 g of ferrocene on a watch glass and spread it flat. Dry it in an oven at 35-45°C for 0.5-1.5 h to obtain dried ferrocene. (2) 0.6-0.8 g of dried ferrocene is placed in a first alumina crucible, so that the dried ferrocene is evenly distributed on the bottom of the first alumina crucible and the surface is flat; and 0.9-1.1 g of ZSM-5 is placed in a second alumina crucible, so that the ZSM-5 is evenly distributed on the bottom of the second alumina crucible and the surface is flat; (3) Then, the first alumina crucible and the second alumina crucible are placed close together in the center of the quartz tube of the tube furnace, with the first alumina crucible placed upstream of the air flow and the second alumina crucible placed downstream of the air flow; (4) Heat to 50-70°C in an argon atmosphere at a flow rate of 10-20 mL / min, purge for 30-50 min to remove the air in the quartz tube, and then heat to 90-110°C at a heating rate of 1-3°C / min, with a purge time of 5-90 min; (5) Heating to 140-160°C for 3.5-4.5 h in an argon atmosphere at a flow rate of 10-20 mL / min, and obtaining a confined iron single atom catalyst in a second alumina crucible, which is designated as Fe1-ZSM-5(1); Alternatively, the catalyst is heated to 490-510°C in an argon atmosphere at a flow rate of 10-20 mL / min for 3.5-4.5 h, and a confined iron single atom catalyst is obtained in a second alumina crucible, which is recorded as Fe1-ZSM-5(2).

2. A confined iron single-atom catalyst prepared by any method of claim 1.

3. The use of a confined iron single-atom catalyst for long-term removal of para-chlorophenol in water according to claim 2, characterized in that: The following steps are involved: A confined iron single-atom catalyst and hydrogen peroxide are added to water to complete the removal of para-chlorophenol in the water; the addition amount of the confined iron single-atom catalyst is 0.5-2 g / L; the addition amount of the hydrogen peroxide is 6-10 mmol / L; and the concentration of para-chlorophenol in the water is 0.01-0.1 mmol / L.

Images