Preparation method of space-limited composite catalyst for inhibiting iron atom aggregation

Abstract

This invention provides a method for preparing spatially confined composite catalysts that suppress iron atom aggregation, belonging to the field of catalyst preparation technology. The method of this invention constructs a three-step process: "plasma activation—spatial confinement coating—high-energy pulsed laser thermal migration." The core advantage of this method lies in utilizing the instantaneous local ultra-high temperature field generated by nanosecond-level high-energy pulsed lasers to directionally drive and forcibly anchor iron atoms in a spatially confined environment. This transforms the preparation concept from "passively relying on pyrolysis" to "actively manipulating atoms," physically avoiding the inevitable aggregation under long-term thermal conditions. This not only ensures higher single-atom density and structural uniformity but also endows the process with unprecedented precision control and repeatability, providing a new technological paradigm for the preparation of high-performance single-atom catalysts.

Description

Technical Field

[0001] This invention belongs to the field of catalyst preparation technology, specifically to a method for preparing a spatially confined composite catalyst that inhibits iron atom aggregation. Background Technology

[0002] In the field of single-atom catalysts, especially carbon-based single-atom catalysts based on non-precious metals (such as iron and cobalt), traditional methods mainly rely on high-temperature pyrolysis.

[0003] Although patent CN113529103B uses MOF spatial confinement to bind peptone / carbon nitride anchoring, it still relies on long-term global high-temperature pyrolysis and fails to fundamentally solve the problem of atomic migration and aggregation.

[0004] While patent CN118022803B employs ball milling pretreatment combined with long-term (3-6 hours) global high-temperature pyrolysis (600℃), it still relies on a slow heat transfer process, making it difficult to completely avoid the risk of atomic migration and aggregation under long-term thermal conditions.

[0005] Although patent CN116832810A also focuses on the singlet oxygen pathway, its preparation method relies on nitrogen-containing polymer coordination and long-term (4 hours) global high-temperature pyrolysis (900°C), which still does not get rid of the potential risk of atomic migration and aggregation in the traditional pyrolysis process.

[0006] Although high-temperature pyrolysis can produce materials with high catalytic activity, its inherent technical defects severely restrict further improvement of catalyst performance, batch repeatability, and large-scale industrial application.

[0007] The core challenge of existing technologies lies in the fact that the physical field they rely on—the slow, global, and long-duration high-temperature pyrolysis—is inherently incompatible with the rapid, localized, and directional atomic anchoring process required to achieve atomic-level dispersion. Therefore, developing a new method capable of overcoming this thermodynamic equilibrium constraint and achieving directional migration and precise anchoring of metal atoms has become an urgent and critical technical challenge in this field.

[0008] In view of this, the present invention is hereby proposed. Summary of the Invention

[0009] The purpose of this invention is to provide a method for preparing a spatially confined composite catalyst that inhibits iron atom aggregation. By combining low-temperature plasma activation, nano-space confinement coating, and high-energy pulsed laser thermal migration, the method achieves directional anchoring and atomic-level dispersion of iron atoms, thus avoiding the aggregation problem caused by traditional high-temperature heat treatment.

[0010] To achieve the above-mentioned objectives of this invention, the following technical solution is adopted:

[0011] A method for preparing a spatially confined composite catalyst for inhibiting iron atom aggregation includes the following steps:

[0012] S1. Dissolve the nitrogen-containing iron source in concentrated sulfuric acid and stir to form solution A; at the same time, reflux multi-walled carbon nanotubes (MWCNTs) in mixed acid and then wash until neutral to obtain activated multi-walled carbon nanotubes.

[0013] S2. The activated multi-walled carbon nanotubes are dispersed in N,N-dimethylformamide (DMF) to form a suspension, then solution A is added, and the mixture is sonicated to obtain a mixed suspension; the mixed suspension is then placed in a low-temperature plasma reaction chamber for treatment to obtain a composite centrifuge.

[0014] S3. Wash the composite centrifuge material and perform spatial confinement coating to obtain a confinement shell layer;

[0015] S4. Use a heat source to scan the product in S3;

[0016] S5. Selectively etch away the confined shell, wash, collect, and dry to obtain the final product;

[0017] The iron source in S1 is either an inorganic iron salt or an organic iron salt.

[0018] Preferably, in S1, the concentration of concentrated sulfuric acid is 98 wt%;

[0019] Preferably, the multi-walled carbon nanotubes have a diameter of 10nm-20nm and a length of 1μm-10μm;

[0020] Preferably, the nitrogen-containing iron source is iron phthalocyanine (II) (FePc) or a mixture of inorganic iron salts and urea;

[0021] Preferably, the purity of phthalocyanine iron(II) is ≥99.9%;

[0022] Preferably, the volume ratio of ferrophthalocyanine (II) to concentrated sulfuric acid is 1:(50-100).

[0023] Preferably, the inorganic iron salt is FeCl3·6H2O;

[0024] Preferably, the mixed acid is prepared by mixing concentrated nitric acid with a concentration of 65 wt% and concentrated sulfuric acid with a concentration of 98 wt% in a volume ratio of 1:3.

[0025] Preferably, in step S3, the specific steps of spatial confinement coating are: processing the composite centrifuge and reacting it with the spatial confinement template to grow a shell layer on the surface of the composite centrifuge.

[0026] Preferably, in step S1, the reflux temperature is 80℃-100℃, and the reflux time is 4h-6h;

[0027] Preferably, the reflux temperature is 80°C and the reflux time is 4 hours;

[0028] Preferably, the mass-to-volume ratio of multi-walled carbon nanotubes to mixed acid is 1g:100mL.

[0029] Preferably, in S2, the mass ratio of FePc to MWCNTs is 1:(10-20).

[0030] Preferably, in S2, the mass ratio of FePc to MWCNTs is 1:20.

[0031] Preferably, in S2, the gas in the low-temperature argon-hydrogen plasma reaction chamber is a mixture of argon and hydrogen, or N2 plasma;

[0032] Preferably, the volume ratio of argon to hydrogen is 4:1;

[0033] Preferably, the pressure is 50Pa-100Pa, the power is 100W-300W, and the processing time is 10min-30min;

[0034] Preferably, the pressure is 50 Pa, the power is 200 W, and the processing time is 20 min.

[0035] Preferably, in step S2, the concentration of the suspension is 1 mg / mL to 5 mg / mL;

[0036] Preferably, in step S2, the concentration of the suspension is 2 mg / mL.

[0037] Preferably, in S3, the spatially confined template is tetraethyl orthosilicate (TEOS) or zeolite imidazole ester skeleton-8 (ZIF-8).

[0038] Preferably, the zeolite imidazole ester framework-8 is a zinc-based metal-organic framework material;

[0039] Preferably, the mass ratio of the spatial confinement template to the composite centrifuge is (1-2):1;

[0040] Preferably, the pH is 9-10.

[0041] Preferably, when the spatially confined template is tetraethyl orthosilicate (TEOS), the specific steps of S3 are as follows:

[0042] The complex was collected by centrifugation, washed with DMF and ethanol, and then dispersed in hexadecyltrimethylammonium bromide (CTAB) and sonicated to form a homogeneous dispersion.

[0043] The dispersion was mixed with tetraethyl orthosilicate at a mass ratio of 1:(1-2), and hydrolyzed under alkaline conditions to form a mesoporous silica shell.

[0044] Preferably, when the spatial confinement template is ZIF-8, the specific steps of S3 are as follows:

[0045] The complex was collected by centrifugation and dispersed in a methanol solution containing 2-methylimidazole. Zinc nitrate was then added, and the mixture was stirred at room temperature to form a ZIF-8 shell.

[0046] Preferably, in step S3, washing is performed using DMF or ethanol;

[0047] Preferably, in S3, the concentration of hexadecyltrimethylammonium bromide is 2 wt%, and the volume ratio of the centrifuged complex to hexadecyltrimethylammonium bromide is 1:50.

[0048] Preferably, the ultrasonic treatment time in S3 is 1 hour.

[0049] Preferably, the mass ratio of the spatial confinement template to the composite centrifuge is 1:1.

[0050] Preferably, in step S4, the heat source is a high-energy pulsed laser or a flash lamp;

[0051] Preferably, the specific parameters of the high-energy pulsed laser are as follows:

[0052] Pulse energy: 100mJ / pulse - 500mJ / pulse;

[0053] Pulse width 10ns-100ns;

[0054] The repetition frequency is 10Hz-50Hz;

[0055] Scanning speed: 5mm / s-20mm / s;

[0056] Preferably, the specific parameters of the flash unit are as follows:

[0057] Pulse width 1ms-3ms;

[0058] Energy density 13 J / cm³ 2 -17J / cm 2 .

[0059] Preferably, in step S5, hydrofluoric acid with a concentration of 5 wt% or NaOH with a concentration of 1 M is used to selectively etch away the shell.

[0060] Preferably, in step S5, the etching conditions are stirring at room temperature for 2 hours, followed by washing with deionized water until neutral.

[0061] Preferably, in step S5, the collection speed is 10,000 rpm and the collection time is 10 minutes.

[0062] Preferably, in step S5, the drying conditions are vacuum drying at 60°C for 12 hours.

[0063] The present invention also provides a composite catalyst prepared by the above-described method for preparing a spatially confined composite catalyst that inhibits iron atom aggregation.

[0064] The present invention also provides an application of the above-mentioned spatially confined composite catalyst for inhibiting iron atom aggregation in wastewater treatment.

[0065] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0066] The method of this invention constructs a three-step process of "plasma activation—spatial confinement coating—high-energy pulsed laser thermal migration". The core advantage of this method lies in utilizing the instantaneous localized ultra-high temperature field generated by nanosecond-level pulsed lasers to directionally drive and forcibly anchor iron atoms in a spatially confined environment. This transforms the preparation concept from "passively relying on pyrolysis" to "actively manipulating atoms," physically avoiding the inevitable aggregation under prolonged thermal conditions. This not only ensures higher single-atom density and structural uniformity but also endows the process with unprecedented precision control and repeatability, providing a completely new technological paradigm for the preparation of high-performance single-atom catalysts.

[0067] More specifically, the present invention has the following innovations and advantages:

[0068] Firstly, the synergy between high-energy pulsed laser thermal migration anchoring and spatial confinement effects. In a spatially confined environment (such as a mesoporous silica shell), a high-energy pulsed laser is used to instantaneously irradiate a support loaded with a metal precursor. The resulting localized ultra-high temperature enables the directional thermal migration of metal species, which are then stably anchored by the support, thus preparing single-atom catalysts and fundamentally solving the key problem of atomic aggregation. High-energy pulsed lasers provide instantaneous, localized ultra-high energy that is impossible with traditional pyrolysis, driving high-speed atomic migration; while the spatially confined shell restricts this migration to the nanoscale, forcing atoms to bind only to the nearest anchoring point on the support, thereby achieving directional anchoring rather than random aggregation.

[0069] Secondly, plasma-assisted ligand exchange and loading serve as a pre-activation step. Prior to the spatial confinement coating step, a mixture of organometallic precursors (such as iron phthalocyanine) and functionalized supports (such as activated carbon nanotubes) is treated with low-temperature plasma (especially argon-hydrogen plasma) to achieve the activation, dissociation, and preliminary bonding of the precursors with the functional groups of the support. This step pre-constructs Fe-N at low temperatures. xThe -C coordination structure lowers the energy barrier required for subsequent thermal migration, ensuring a high degree of dispersion of precursor species and laying a solid foundation for final precise anchoring. It forms a perfect connection with the subsequent confined-thermal migration steps, following a "first activation and localization, then driving fixation" process.

[0070] Thirdly, the process flow architecture of the three-step method of plasma activation-spatial confinement-pulsed laser thermal migration. The complete process flow consists of three core steps combined in a specific order (i.e., plasma treatment first, then coating, and finally laser irradiation).

[0071] There is a strict logical order and synergistic effect among these three steps, and the order cannot be reversed. Plasma treatment must be performed before coating to ensure that the precursor is fully activated; coating must be completed before laser irradiation to provide a confined environment. Protecting this specific architecture is protecting the "roadmap" for the successful implementation of the entire technical solution. Attached Figure Description

[0072] Figure 1 : This is a flowchart of the preparation process for Example 1;

[0073] Figure 2 HAADF-STEM characterization results of Fe-SACs / N-CNTs catalysts;

[0074] Figure 3 Distribution of elements in Fe-SACs / N-CNTs, where A is the distribution of carbon; B is the distribution of nitrogen; C is the distribution of oxygen; and D is the distribution of iron.

[0075] Figure 4 Scanning electron microscope images of Fe-SACs / N-CNTs;

[0076] Figure 5 High-magnification transmission electron microscope image of Fe-SACs / N-CNTs;

[0077] Figure 6 Comparison of the degradation performance of lomefloxacin hydrochloride by activated persulfate (PMS) in Examples 1-5 and Comparative Examples 1-5;

[0078] Figure 7 Comparison of removal rates of lomefloxacin hydrochloride after 30 minutes of degradation by activated persulfate (PMS) in Examples 1-5 and Comparative Examples 1-5;

[0079] Figure 8 Comparison of Fe dissolution concentration after 30 minutes of degradation of lomefloxacin hydrochloride by activated persulfate (PMS) in Examples 1-5 and Comparative Examples 1-5;

[0080] Figure 9Identification of reactive oxygen species during the degradation of lomefloxacin hydrochloride by PMS activated by Fe-SACs / N-CNTs;

[0081] Figure 10 Results of quenching experiments;

[0082] Figure 11 Evaluation of the effects of different environmental substrates on the degradation of lomefloxacin hydrochloride by Fe-SACs / N-CNTs;

[0083] Figure 12 Evaluation of the cycling performance of Fe-SACs / N-CNTs-activated PMS for the degradation of lomefloxacin hydrochloride;

[0084] Figure 13 Infrared spectra of Fe-SACs / N-CNTs activated PMS before and after (one cycle) the degradation of lomefloxacin hydrochloride;

[0085] Figure 14 When 1 mg / L lomefloxacin hydrochloride is dissolved in Bohai Sea water, it exhibits a strong fluorescence peak in the fluorescence spectrum. Among them, a represents the strong fluorescence peak in the fluorescence spectrum of lomefloxacin hydrochloride dissolved in Bohai Sea water at 0 min; b represents the strong fluorescence peak in the fluorescence spectrum of lomefloxacin hydrochloride dissolved in Bohai Sea water at 30 min. Detailed Implementation

[0086] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0087] Example 1

[0088] (1) Preparation of precursor solution:

[0089] 1.0 g of high-purity FePc (≥99.9%) was dissolved in 50 mL of concentrated sulfuric acid (98 wt%) to form solution A. The mass-to-volume ratio of FePc to concentrated sulfuric acid was 1 g: 50 mL. The solution was magnetically stirred at room temperature for 3 hours to ensure complete dissolution.

[0090] Simultaneously, 2.0 g of MWCNTs (diameter 10-20 nm, length 1-10 μm) were refluxed in 200 mL of mixed acid: the mixed acid consisted of concentrated nitric acid (65 wt%) and concentrated sulfuric acid (98 wt%) mixed in a volume ratio of 1:3, with a MWCNTs to mixed acid mass-volume ratio of 1 g:100 mL. The reflux conditions were: temperature 80 °C, time 4 hours. After treatment, the MWCNTs were washed with deionized water until neutral, and 1.95 g of activated MWCNTs (with surface-introduced functional groups such as carboxyl and hydroxyl groups) were collected by centrifugation.

[0091] Function: Iron phthalocyanine serves as an iron source, providing iron atoms; activated MWCNTs act as a carrier, and surface functional groups are used for subsequent ligand exchange and anchoring.

[0092] (2) Plasma-assisted ligand exchange and loading:

[0093] 1.0 g of activated MWCNTs was dispersed in 500 mL of DMF to form a suspension with a concentration of 2 mg / mL. Then, 5 mL of solution A (containing 0.1 g of FePc) was added, wherein the mass ratio of FePc to MWCNTs was 1:10. The mixed suspension was treated in an ultrasonic bath for 30 minutes to ensure uniform dispersion.

[0094] 100 mL of the mixed suspension was placed in a low-temperature argon-hydrogen plasma reaction chamber for treatment. Plasma conditions: argon to hydrogen volume ratio 4:1, pressure 80 Pa, power 200 W, treatment time 20 minutes. High-energy particles (such as electrons and ions) in the plasma bombarded the iron phthalocyanine molecules, causing partial dissociation and activation. Simultaneously, this promoted strong interactions (such as Fe-N and Fe-O bonds) between the iron-containing fragments and the functional groups on the surface of MWCNTs, initially constructing Fe-N bonds. x -C structure.

[0095] Functions: Plasma activation enables precursor dissociation and loading at low temperatures (<100℃), avoiding early aggregation; functional groups enhance the binding force between iron species and the carrier.

[0096] (3) Spatial confinement of mesoporous silica:

[0097] The treated complex was collected by centrifugation (8000 rpm, 10 minutes), washed with DMF and ethanol, and then 0.2 g of the centrifuged material was redispersed in 10 mL of an aqueous solution containing the surfactant CTAB (CTAB concentration 2 wt%, complex to CTAB mass-to-volume ratio 1 g:50 mL). The mixture was sonicated for 1 hour to form a homogeneous dispersion.

[0098] 0.2 g of tetraethyl orthosilicate (TEOS) was added as a silicon source, with a TEOS to composite mass ratio of 1:1. Under alkaline conditions (pH adjusted to 9-10 by adding ammonia), hydrolysis was carried out at room temperature with stirring for 5 hours to form a mesoporous silica shell with a precise thickness (5-10 nm). The shell thickness was controlled by the amount of TEOS added and the hydrolysis time.

[0099] Function: The silica shell acts as a nanoreactor, providing a spatial confinement effect, limiting the migration range of iron species in subsequent steps, and preventing long-range diffusion.

[0100] (4) Pulsed laser thermal migration anchoring:

[0101] The hydrolyzed product was dried to obtain powder. 0.25g of the coated powder was placed in an inert atmosphere tube furnace (argon atmosphere, oxygen content <1ppm). Instead of using traditional programmed temperature rise, a high-energy pulsed laser (Nd:YAG laser, wavelength 1064nm) was used to periodically scan and irradiate the powder bed.

[0102] Laser parameters: pulse energy 200 mJ / pulse, pulse width 20 ns, repetition frequency 20 Hz, scanning speed 10 mm / s. Each laser pulse generates instantaneous ultra-high temperatures (>1500℃) locally in the material within an extremely short time (nanosecond to microsecond range), while the overall material temperature remains low (<100℃). The thermal shock causes iron species confined within the silica shell to migrate at high speed to the most stable defects or N-anchoring sites (such as pyridine nitrogen sites) on the carbon nanotube surface and become fixed thereafter.

[0103] Function: High-energy pulsed lasers provide instantaneous high energy to achieve directional migration and anchoring of iron atoms, while the oxide shell prevents iron atoms from agglomerating; the thermal migration process preferentially selects energy-stable sites to ensure atomic-level dispersion.

[0104] (5) Template removal and post-processing:

[0105] The outer silica shell was selectively etched away using 10 mL of hydrofluoric acid (HF, 5 wt%). Etching conditions: stirring at room temperature for 2 hours (2-4 hours is acceptable), followed by washing with deionized water until neutral.

[0106] The obtained solid was collected by centrifugation (10,000 rpm for 10 minutes) and dried in a vacuum oven at 60°C for 12 hours to obtain the final composite material (Fe-SACs / N-CNTs) with 0.21 g of iron single atoms dispersed on nitrogen-doped carbon nanotubes.

[0107] Function: After removing the template, atomically dispersed iron sites are exposed to obtain a high-purity catalyst; washing and drying ensure the stability of the material.

[0108] Process flow diagram as follows Figure 1 As shown, the process is as follows: S1 Precursor solution preparation → S2 Plasma-assisted ligand exchange and loading → S3 Spatial confinement coating of mesoporous silica → S4 High-energy pulsed laser thermal migration anchoring → S5 Template removal and post-processing.

[0109] STEM characterization of the prepared catalysts as follows Figure 2 As shown, the results indicate that the distribution of each element is relatively uniform.

[0110] The elemental distribution of the prepared catalyst was observed, and the experimental results are as follows: Figure 3 As shown in the figure, the mapping diagram of Fe-SACs / N-CNTs catalyst shows that C, N, O and Fe are distributed relatively uniformly on the carbon nanotube matrix, especially the Fe element is distributed very uniformly, and no obvious agglomeration phenomenon is observed.

[0111] The prepared catalyst was observed, and the experimental results are as follows: Figures 4-5 As shown, Figure 4 Scanning electron microscope image of Fe-SACs / N-CNTs. Figure 5 High-power transmission electron microscope image of Fe-SACs / N-CNTs, from Figure 4 and Figure 5 It can be seen that the Fe element in the Fe-SACs / N-CNTs catalyst did not show obvious agglomeration, indicating that the distribution was relatively uniform.

[0112] In this invention, plasma activation and spatial confinement coating work synergistically: plasma activates the precursor at low temperature to avoid early aggregation; spatial confinement coating provides a restricted environment for subsequent thermal migration.

[0113] Synergistic effect of pulsed laser thermal migration and confinement: instantaneous high temperature promotes the migration of iron atoms, but the confinement shell limits the migration distance, ensuring atomic-level anchoring.

[0114] The entire process sequence cannot be adjusted: Step S2 (plasma treatment) must follow S1 to activate the precursor; S3 (coating) must follow S2 to create a confined environment; S4 (laser thermal migration) must follow S3 to utilize the confinement effect; and S5 (template removal) must follow S4 to expose the active sites. Adjusting the sequence may result in aggregation or structural damage.

[0115] Example 2: Changing plasma conditions

[0116] Basically the same as Example 1, except for the plasma processing conditions:

[0117] Plasma conditions: Change to pure N2 plasma, power 150W, processing time 15 minutes.

[0118] The experimental results of Examples 1 and 2 show that the catalyst prepared after changing the plasma can still produce a good degradation effect on lomefloxacin hydrochloride, indicating that plasma sources with different activities are equally effective. Nitrogen plasma may also introduce additional nitrogen doping to synergistically enhance catalytic performance.

[0119] Example 3: Modifying the Spatial Limitation Template

[0120] Basically the same as Example 1, except for the change in the spatial confinement template:

[0121] Confined template: Mesoporous silica was replaced with ZIF-8. The specific steps were as follows: 0.2 g of the plasma-treated Fe-MWCNTs composite was dispersed in 50 mL of methanol solution containing 2-methylimidazole, then 0.1 g of zinc nitrate was added, and the mixture was stirred at room temperature for 1 h to grow a ZIF-8 shell on the composite surface. Subsequent high-energy pulsed laser treatment and template removal (pyrolysis) steps remained unchanged.

[0122] The experimental results of Examples 1 and 2 show that when the spatial confinement template is replaced by ZIF-8, the catalyst prepared still exhibits excellent performance, demonstrating the feasibility of using MOFs as confinement templates and showcasing the diversity of template selection in this method.

[0123] Example 4: Changing the instantaneous heat source

[0124] Basically the same as Example 1, except that the instantaneous heat source is changed:

[0125] Heat source: Replace the high-energy pulsed laser with flash lamp annealing. Parameters: Pulse width 2ms, energy density 15J / cm². 2 The powder was subjected to five flash treatments under an argon atmosphere.

[0126] The experimental results of Examples 1 and 2 show that when the form of the heat source is changed, the catalyst prepared exhibits better degradation performance of lomefloxacin hydrochloride, proving that other energy sources that can provide instantaneous high temperatures can also achieve the "thermal migration anchoring" effect.

[0127] Example 5: Using inorganic iron salts as precursors

[0128] Precursor: Ferric chloride (FeCl3·6H2O) and urea are mixed in a molar ratio of 1:4, and the total mass of the mixture of ferric chloride and urea is equal to the total mass of ferrocyanine.

[0129] Carrier: Acid-treated multi-walled carbon nanotubes (MWCNTs), same as in Example 1.

[0130] Plasma: Ar-H2 plasma (200W, 20min), same as in Example 1.

[0131] Confined template: mesoporous silica (mSiO2), same as in Example 1.

[0132] Heat source: High-energy pulsed laser (Nd:YAG, 200mJ / pulse, 20ns, 20Hz), same as in Example 1.

[0133] The experimental results show that high-performance iron single-atom catalysts can be prepared using inexpensive inorganic iron salts.

[0134] Comparative Example 1: Traditional High-Temperature Pyrolysis Method

[0135] Preparation process: The activated MWCNTs from Example 1 were mixed with solution A, and then subjected to conventional tube furnace programmed pyrolysis without plasma treatment or silica coating. Under an argon atmosphere, the temperature was increased to 800°C at a rate of 5°C / min and held for 2 hours. The mixture was then allowed to cool naturally to obtain the product.

[0136] The experimental data from the experimental examples show that, compared with the examples, the traditional preparation method suffers from severe atomic aggregation due to prolonged high temperatures, resulting in poor catalyst performance.

[0137] Comparative Example 2: Plasma-free assisted steps

[0138] Preparation process: The "plasma-assisted ligand exchange and loading" step in Example 1 is omitted. After mixing the activated MWCNTs with solution A, only conventional stirring is performed, followed by direct mesoporous silica coating, high-energy pulsed laser treatment, and subsequent steps.

[0139] The experimental data from the experimental examples show that plasma activation plays an important role in the pre-dispersion and pre-anchoring of precursors. When the plasma activation step is missing, the precursors will be unevenly distributed, and even in a confined environment, local agglomeration will still occur after laser shock.

[0140] Comparative Example 3: Steps without spatial constraints

[0141] Preparation process: The "mesoporous silica spatial confinement coating" step in Example 1 is omitted. The plasma-treated composite is directly subjected to high-energy pulsed laser treatment, followed by post-processing.

[0142] The experimental data from the examples demonstrate the crucial role of the spatially confined shell in preventing long-range atomic migration and aggregation during high-energy pulsed laser thermal shock. Without this step, iron atoms would migrate unrestricted under laser shock, inevitably forming numerous nanoparticles and thus affecting the catalyst's catalytic performance.

[0143] Comparative Example 4: Pulseless laser step (conventional heat treatment)

[0144] Preparation process: The "high-energy pulsed laser thermal migration anchoring" step in Example 1 is omitted. The powder coated with mesoporous silica is placed in a tube furnace and heat-treated under argon atmosphere using the same procedure (heating to 800℃ at 5℃ / min and holding for 2 hours), followed by template removal.

[0145] The experimental data from the examples show that even with spatial confinement, traditional, slow global heating methods still provide atoms with sufficient migration time and energy, causing them to aggregate within the confined space. This demonstrates the irreplaceable role of "high-energy pulsed laser instantaneous thermal shock."

[0146] Comparative Example 5: Changing the order of core steps

[0147] Preparation process: The order of steps in Example 1 was changed. First, mesoporous silica coating was performed, then plasma treatment was performed, and finally high-energy pulsed laser anchoring was performed.

[0148] The experimental data from the examples demonstrate that the steps in this invention cannot be interchanged. When the order is changed, the plasma struggles to penetrate the silica shell to effectively activate the internal iron precursor, leading to insufficient activation. This results in a significant decrease in the density of single-atom sites in the final product, thus affecting the catalyst's activity. Therefore, the specific process flow of "activation first, then confinement, then impaction" is irreversible.

[0149] Experimental Example 1: Comparison of the degradation performance of lomefloxacin hydrochloride by activated persulfate (PMS) in Examples 1-5 and Comparative Examples 1-5

[0150] Experimental Procedure: At room temperature, 0.01g of each of the 10 samples from Examples 1-5 and Comparative Examples 1-5 were used to activate 0.015g of persulfate (PMS) to degrade 100mL of lomefloxacin hydrochloride (LOH) at an initial concentration of 20mg / L (initial pH approximately 5.6). After 30 minutes, the absorbance was measured at 280nm using a UV-Vis spectrophotometer, and the degradation rate was calculated. Figure 6 It can be seen that Example 1 showed the fastest antibiotic degradation rate, while Examples 2-5 all showed good degradation effects on lomefloxacin hydrochloride. Comparative Examples 1-5 were all worse than the Examples, with Comparative Example 1 being the worst. Figure 7As can be seen, the removal rates of lomefloxacin hydrochloride in Examples 1-5 were 89.9%, 85.0%, 85.8%, 87.6%, and 80.5%, respectively, while the removal rates in Comparative Examples 1-5 were 46.0%, 73.6%, 60.3%, 72.5%, and 75.5%, respectively. It is evident that the method proposed in this patent (Example 1) has a significant efficiency improvement advantage compared to the traditional high-temperature pyrolysis method (Comparative Example 1), demonstrating the great superiority of this invention.

[0151] Experimental Example 2: Comparison of Fe dissolution concentration after 30 minutes of degradation of lomefloxacin hydrochloride by activated persulfate (PMS) in Examples 1-5 and Comparative Examples 1-5; and the removal rate of lomefloxacin hydrochloride dissolved in Bohai Seawater by the catalyst prepared in Example 1 after 30 minutes.

[0152] Experimental Procedure: Water samples from 10 catalysts (Examples 1-5 and Comparative Examples 1-5) after degradation within 30 minutes were analyzed by ICP-MS to determine the concentration of dissolved Fe in the solution. Experimental results are as follows: Figure 8 As shown, in Examples 1-5, the Fe dissolution concentrations after 30 minutes of degradation of lomefloxacin hydrochloride by activated persulfate (PMS) were 0.080 mg / L, 0.095 mg / L, 0.225 mg / L, 0.125 mg / L, and 0.180 mg / L, respectively. In contrast, in Comparative Examples 1-5, the Fe dissolution concentrations after 30 minutes of degradation of lomefloxacin hydrochloride by activated persulfate (PMS) were 1.145 mg / L, 0.310 mg / L, 0.795 mg / L, 0.635 mg / L, and 0.290 mg / L, respectively. It can be seen that the Fe dissolution concentrations in Examples 1-5 are significantly lower than those in the Comparative Examples, and the research method of this invention (Example 1) has a significant effect on inhibiting metal dissolution compared to the traditional high-temperature pyrolysis method (Comparative Example 1). Example 1 showed the lowest Fe dissolution concentration (0.08 mg / L), which was 93% lower than that of the conventional high-temperature pyrolysis method (Comparative Example 1, 1.145 mg / L). Example 1 demonstrated excellent performance in inhibiting metal dissolution.

[0153] When lomefloxacin hydrochloride (1 mg / L) was dissolved in Bohai Sea water (after a 20-fold dilution of the original 20 mg / L solution), a strong fluorescence peak was observed in its corresponding fluorescence spectrum (excitation wavelength Ex = 277 nm, emission wavelength Em = 412 nm). After 30 minutes of catalytic degradation, only sporadic weak fluorescence peaks remained in the fluorescence spectrum, indicating that most of the lomefloxacin hydrochloride in the solution was removed. Furthermore, this also demonstrates that the composite catalyst exhibits good performance in degrading organic pollutants in a real seawater environment, as shown in the experimental results. Figure 14 As shown.

[0154] Experimental Example 3: Identification of reactive oxygen species during the degradation of lomefloxacin hydrochloride by PMS activated by Fe-SACs / N-CNTs

[0155] Experimental Procedure: The Fe-SACs / N-CNTs catalyst prepared in Example 1 was reacted with 1 mM 5,5-dimethyl-1-pyrrolidone-N-oxide (DMPO) and 2,2,6,6-tetramethyl-4-piperidinone (TEMP), respectively. The types of reactive oxygen species generated were then determined using electron paramagnetic resonance spectroscopy at 1 min and 5 min, respectively. Experimental results are as follows: Figure 9 As shown, DMPO is 5,5-dimethyl-1-pyrrolidone-N-oxide, and TEMP is 2,2,6,6-tetramethyl-4-piperidinone. DMPO can combine with hydroxyl radicals, sulfate radicals, and superoxide radicals to generate specific peak types, while TEMP can combine with singlet oxygen to generate a typical 1:1:1 three-peak pattern. Figure 9 It can be seen that four free radicals ( ) are involved in the degradation of lomefloxacin hydrochloride by PMS activated by Fe-SACs / N-CNTs. 1 O2、·O - 2. ·OH and SO4· - All of these free radicals are present, but it is impossible to determine which free radical plays a dominant role in the electron paramagnetic resonance (EPR) test. Further quenching experiments are needed to determine which free radical plays a dominant role.

[0156] Experiment Example 4: Quenching Experiment

[0157] Experimental Procedure: Following the same steps as in Example 1, 50 mM L-histidine, methanol, tert-butanol, and p-benzoquinone were added to the Fe-SACs / N-CNTs activated PMS process for the degradation of lomefloxacin hydrochloride prepared in Example 1, respectively. Figure 10 The results. It is well known that L-histidine, methanol, tert-butanol, and p-benzoquinone correspond to the quenching of singlet oxygen (…). 1 O2), sulfate free radicals (SO4· - ), hydroxyl radicals (·OH) and superoxide radicals (·O) - 2) When the same concentration of the four quenchers is added, the effect on the degradation process from largest to smallest is: the reaction after adding p-benzoquinone, L-histidine, methanol, and tert-butanol. Figure 10 It can be seen that the reactive oxygen species that plays a dominant role in the degradation of lomefloxacin hydrochloride by PMS activated by Fe-SACs / N-CNTs is ·O. - 2 and 1 O2.

[0158] Experimental Example 5: Evaluation of the effect of different environmental substrates on the degradation of lomefloxacin hydrochloride by Fe-SACs / N-CNTs

[0159] Experimental Procedure: The experimental procedure is the same as in Experiment 1, except that the water substrate in Experiment 1 was pure water, while in this experiment, the water from the Haihe River and the Bohai Sea were used for the measurements. Figure 11 It can be seen that Fe-SACs / N-CNTs have excellent environmental adaptability.

[0160] Experimental Example 6: Evaluation of the Cyclic Performance of Fe-SACs / N-CNTs-Activated PMS in Degrading Lomefloxacin Hydrochloride

[0161] Experimental Procedure: Eight 0.01g portions of the Fe-SACs / N-CNTs catalyst prepared in Example 1 were used to perform the same experiment as in Example 1 to degrade lomefloxacin hydrochloride, recorded as one reaction. After filtration, washing, and drying, the above operation was repeated for each of the eight portions of catalyst, recorded as two reactions. The same experiment was performed five times, recorded as five cycles.

[0162] Experimental results are as follows Figure 12-13 As shown, from Figure 12 The results show that after five cycles, the degradation rate of lomefloxacin hydrochloride by Fe-SACs / N-CNTs at 30 minutes still reached 80.0%, only 11.0% lower than the 89.9% at the first cycle, indicating that Fe-SACs / N-CNTs have good cycling stability. Figure 13 As can be seen from the data, the position and intensity of the Fe-SACs / N-CNTs peaks did not change significantly before and after the degradation reaction, indicating that the catalyst prepared by this patent has excellent structural stability.

[0163] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for producing a spatially confined composite catalyst for inhibiting agglomeration of iron atoms, characterized by, Includes the following steps: S1. Dissolve a nitrogen-containing iron source in concentrated sulfuric acid and stir to form solution A; at the same time, reflux the multi-walled carbon nanotubes in mixed acid and then wash them until neutral to obtain activated multi-walled carbon nanotubes. S2. The activated multi-walled carbon nanotubes are dispersed in N,N-dimethylformamide to form a suspension, and then solution A is added. The mixture is then sonicated to obtain a mixed suspension. The mixed suspension was then treated in a low-temperature plasma reaction chamber to obtain a composite centrifuge. S3. Wash the composite centrifuge material and perform spatial confinement coating to form a confinement shell layer; S4. Use a heat source to scan the product in S3; S5. Selectively etch away the confined shell, wash, collect, and dry to obtain the final product; Wherein, the iron source in S1 is any one of inorganic iron salt or organic iron salt; the heat source in S4 is a high-energy pulsed laser or a flash lamp.

2. The method of claim 1, wherein the method is characterized by: In S1, the concentration of concentrated sulfuric acid is 98 wt%. The nitrogen-containing iron source is ferrophthalocyanine (II) or a mixture of inorganic iron salts and urea; The mixed acid was prepared by mixing 65wt% concentrated nitric acid and 98wt% concentrated sulfuric acid in a volume ratio of 1:

3.

3. The method of claim 1, wherein the method is characterized by: In step S3, the specific steps of spatial confinement coating are as follows: the composite centrifuge is processed and reacted with the spatial confinement template to grow a shell layer on the surface of the composite centrifuge.

4. The method of claim 2, wherein the method is characterized by: The mass ratio of phthalocyanine iron(II) to multi-walled carbon nanotubes is 1:(10-20).

5. The method for preparing a spatially confined composite catalyst for inhibiting iron atom aggregation according to claim 1, characterized in that, In S2, the gas in the low-temperature plasma reaction chamber is a mixture of argon and hydrogen, or N2 plasma. The volume ratio of argon to hydrogen is 4:1; The pressure in the low-temperature plasma reaction chamber is 50Pa-100Pa, the power is 100W-300W, and the processing time is 10min-30min.

6. The method for preparing a spatially confined composite catalyst for inhibiting iron atom aggregation according to claim 3, characterized in that, In S3, the spatially confined template is tetraethyl orthosilicate or zeolite imidazole ester skeleton-8; The mass ratio of the spatial confinement template to the composite centrifuge is (1-2):1 The pH value is 9-10.

7. The method for preparing a spatially confined composite catalyst for inhibiting iron atom aggregation according to claim 1, characterized in that, In S4; The specific parameters of the high-energy pulsed laser are as follows: Pulse energy: 100mJ / pulse - 500mJ / pulse; Pulse width 10ns-100ns; The repetition frequency is 10Hz-50Hz; Scanning speed: 5mm / s-20mm / s; The specific parameters of the flash unit are as follows: Pulse width 1ms-3ms; Energy density 13 J / cm 2 - 17 J / cm 2 .

8. The method for preparing a spatially confined composite catalyst for inhibiting iron atom aggregation according to claim 1, characterized in that, In step S5, hydrofluoric acid with a concentration of 5 wt% or NaOH with a concentration of 1 M is used to selectively etch away the shell.

9. A composite catalyst prepared by the method for preparing a spatially confined composite catalyst for inhibiting iron atom aggregation as described in any one of claims 1-8.

10. The application of a spatially confined composite catalyst for inhibiting iron atom aggregation as described in claim 9 in wastewater treatment.

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