A heterogeneous photo-fenton iron monatomic catalyst, a preparation method and application thereof

Abstract

The present application belongs to the technical field of heterogeneous catalytic materials and its preparation and application, and particularly relates to a heterogeneous photo-Fenton iron monatomic catalyst, a preparation method and application thereof. The catalyst is composed of a graphite-like carbon nitride carrier containing sulfur doping and iron monatomic combined with the carrier, wherein the mass fraction of iron element in the catalyst is 0.1-3.0 wt.%. The preparation of the catalyst includes a sulfuric acid-induced precursor self-assembly process and an in-situ pyrolysis process, which is low in raw material cost, simple in operation, low in equipment requirement, environmentally friendly and can be popularized on a large scale. The highly dispersed Fe atomic catalytic active sites in the catalyst form stable chemical bonds with the sulfur-doped carbon nitride carrier with a porous structure, which not only improves the metal utilization rate, but also solves the problems of metal agglomeration and ion leaching. The catalyst can form an efficient photo-Fenton catalytic system in a low-concentration hydrogen peroxide solution, realizes efficient and rapid degradation of various kinds of organic pollutants, and has a broad application prospect.

Description

Technical Field

[0001] This invention belongs to the field of heterogeneous catalytic materials and their preparation and application technology, specifically relating to a heterogeneous photo-Fenton iron single-atom catalyst, its preparation method and application. Background Technology

[0002] With the rapid development of my country's economy, the processes of industrialization and urbanization are accelerating, undoubtedly placing enormous pressure on the environment. Water pollution, in particular, has become a major challenge in current environmental governance. Various recalcitrant organic pollutants in water bodies, such as antibiotics, organic dyes, and phenolic compounds, pose a serious threat to human health and the sustainability of the ecological environment. Conventional wastewater treatment processes such as coagulation-flocculation, sedimentation, adsorption, and membrane separation are insufficient to completely eliminate non-biodegradable organic compounds in the environment. In contrast, Fenton catalysis, as an advanced oxidation technology, has attracted considerable attention due to its wide applicable pH range, environmental friendliness, and versatility. Fenton catalysis typically utilizes iron-containing catalysts to promote the decomposition of hydrogen peroxide (H2O2), generating highly oxidizing hydroxyl radicals (·OH), thereby achieving the oxidative degradation of organic pollutants. Photo-Fenton catalysis combines the advantages of both photocatalysis and Fenton catalysis, not only improving the activation efficiency of H2O2 but also promoting the oxidation of Fe... 3+ / Fe 2+ The mutual conversion of these elements is crucial. Therefore, developing economical, efficient, and stable photo-Fenton catalysts will provide strong technical support for solving environmental pollution problems.

[0003] Traditionally prepared supported heterogeneous iron-containing catalysts are prone to iron ion leaching and nanoparticle aggregation during use, leading to a rapid decline in catalytic performance. Furthermore, the large size and uneven distribution of the supported nanoparticles result in low iron atom utilization. In recent years, single-atom metal catalysts have become a research hotspot in the field of catalysis due to their advantages such as high atom utilization, uniform distribution of active sites, high catalytic activity, and good stability. These novel catalysts, with their unique catalytic performance and ultra-high metal utilization, are gradually changing the design philosophy of traditional catalysts, providing new opportunities for the development of green catalysis technologies.

[0004] How to economically and conveniently prepare efficient and stable heterogeneous photo-Fenton iron single-atom catalysts to achieve efficient degradation of organic pollutants in water is an important technical problem that needs to be solved. Summary of the Invention

[0005] The purpose of this invention is to overcome the above-mentioned problems existing in the conventional technology and to provide a multiphase photo-Fenton iron single-atom catalyst, its preparation method and application.

[0006] To achieve the above-mentioned technical objectives and effects, the present invention is implemented through the following technical solution:

[0007] This invention provides a multiphase photo-Fenton iron single-atom catalyst, which includes a sulfur-doped graphitic carbon nitride support and iron single atoms bonded to the support; wherein the mass fraction of iron in the catalyst is 0.1 to 3.0 wt.%, and it can effectively catalyze the degradation of organic pollutants in water.

[0008] This invention also provides a method for preparing a multiphase photo-Fenton iron single-atom catalyst, which includes a sulfuric acid-induced precursor self-assembly process and an in-situ pyrolysis process. The specific operation steps are as follows:

[0009] 1) Weigh a certain amount of melamine and disperse it in water, then stir and dissolve it at 70-100℃ to obtain solution A;

[0010] 2) Add a certain amount of sulfuric acid to solution A and stir at 70-100℃ to form suspension B;

[0011] 3) Weigh a certain amount of iron salt and add it to suspension B. Continue stirring to dissolve the iron salt and obtain suspension C. Then, continue stirring at 70-100℃ until the solvent is evaporated. Grind the obtained solid thoroughly to obtain powder D.

[0012] 4) Place powder D in a covered crucible and calcine it in an inert atmosphere at 500-600℃ for 2-6 hours. Finally, allow it to cool naturally to room temperature to obtain the catalyst.

[0013] Further, in step 1), the mass ratio of melamine to water is 1 to 5:100.

[0014] Furthermore, in step 2), the sulfuric acid content in suspension B is 4.9–39.2 g·L⁻¹. -1 .

[0015] Further, in step 3), the iron salt is at least one of three iron-containing soluble salts: ferric chloride hexahydrate, ferric nitrate nonahydrate, and ferric sulfate.

[0016] Furthermore, in step 3), the iron content in the suspension C is 0.025–0.750 g·L⁻¹. -1 .

[0017] Further, in step 4), the inert atmosphere is one of N2, Ar, or He, and the calcination heating rate is 1–5 °C / min. -1 .

[0018] The present invention also provides an application of the catalyst in the catalytic degradation of organic pollutants in water. The catalyst is added to wastewater containing organic pollutants, and hydrogen peroxide is added as an oxidant. The hydrogen peroxide is catalytically activated under photo-assisted conditions to oxidize and degrade the organic pollutants in the water.

[0019] The beneficial effects of this invention are:

[0020] 1. The catalyst preparation method proposed in this invention uses low-cost and readily available raw materials with low metal loading, simple synthesis method, low equipment requirements, and is environmentally friendly, meeting the requirements of green chemistry. It is a single-atom synthesis method that can be mass-produced and has great application potential.

[0021] 2. The catalyst of this invention consists of atomically dispersed Fe catalytic sites and a porous graphitic carbon nitride support containing sulfur doping. Stable chemical bonds are formed between the Fe atoms and the carbon nitride support, which can better anchor the Fe catalytic sites. This not only greatly improves the metal utilization rate but also effectively solves the problems of metal agglomeration and ion leaching. Therefore, the catalyst of this invention has many advantages such as low cost, environmental friendliness, and good stability.

[0022] 3. The catalyst of this invention can form a highly efficient photo-Fenton catalytic system in a low-concentration hydrogen peroxide solution (4 mM), achieving rapid degradation of organic pollutants. Compared with catalysts supported on Fe2O3 nanoparticles, the catalyst of this invention has a higher Fe atom utilization rate.

[0023] 4. In the application of the catalyst for the catalytic degradation of organic pollutants, the catalyst of this invention requires a small amount of catalyst, can be continuously recycled, and the iron ion leaching is far lower than the EU standard of 2 mg·L⁻¹. -1 The environmental standards can be widely applied in fields such as environmental protection, chemical industry, and textiles.

[0024] 5. The catalyst of this invention exhibits high removal efficiency for persistent antibiotics that are difficult to degrade in water under normal temperature and pressure and simulated sunlight irradiation, and also shows good versatility for organic dyes and phenolic compounds.

[0025] Of course, any product implementing this invention does not necessarily need to achieve all of the above advantages at the same time. Attached Figure Description

[0026] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1The X-ray diffraction (XRD) patterns of the catalyst samples prepared in Example 1 and Comparative Examples 1-2 are shown below.

[0028] Figure 2 Scanning electron microscope (SEM) images of the catalyst samples prepared in Example 1 and Comparative Examples 1-2; where (a) CN, (b) S-CN, and (c) Fe1 / S-CN;

[0029] Figure 3 Characterization diagrams of the catalyst prepared in Example 1: (a) Transmission electron microscopy (TEM) image, (b) High resolution transmission electron microscopy (HRTEM) image, (c) High angle annular dark field (HAADF) image, and elemental distribution diagrams of C, N, Fe, O, and S.

[0030] Figure 4 X-ray photoelectron spectroscopy (XPS) spectra of the catalyst prepared in Example 1: (a) XPS full spectrum, (b) N1s spectrum, (c) Fe2p spectrum, (d) S2p spectrum;

[0031] Figure 5 The results of degradation of oxytetracycline hydrochloride (OTC) by various catalysts under photo-Fenton catalysis are as follows: (a) catalytic degradation results of catalysts with different Fe contents prepared in Examples 1-5, (b) catalytic degradation results of various catalysts prepared in Examples 1 and Comparative Examples 1-4, (c) recycling performance of the catalyst prepared in Example 1, and (d) iron ion leaching amount of the catalyst prepared in Example 1 before and after the cyclic catalytic reaction.

[0032] Figure 6 Example 1 shows the photo-Fenton catalytic degradation results of various organic pollutants, including: oxytetracycline hydrochloride (OTC), tetracycline hydrochloride (TC), ciprofloxacin (CIP), rhodamine B (RhB), methylene blue (MB), methyl orange (MO), phenol, and 2,4-dichlorophenol (2,4-DCP). Detailed Implementation

[0033] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. 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.

[0034] This invention provides a multiphase photo-Fenton iron single-atom catalyst, its preparation method, and its application. The catalyst comprises a sulfur-doped graphitic carbon nitride support and iron single atoms bonded to the support, wherein the theoretical mass fraction of iron in the catalyst is 0.1–3.0 wt.%. The catalyst preparation method of this invention uses low-cost, readily available raw materials, has a low metal loading, is simple to operate, requires minimal equipment, is environmentally friendly, meets green chemistry requirements, and is a scalable single-atom synthesis method. The catalyst consists of atomically dispersed Fe catalytic sites and a sulfur-doped porous graphitic carbon nitride support. Stable chemical bonds are formed between the Fe atoms and the carbon nitride support, which better anchors the Fe catalytic sites, significantly improving metal utilization and effectively solving the problems of metal agglomeration and ion leaching. The catalyst of this invention can form a highly efficient photo-Fenton catalytic system in low-concentration hydrogen peroxide solution, achieving rapid degradation of organic pollutants. It requires a small amount of catalyst, can be sustainably recycled, and exhibits iron ion leaching levels far below the EU standard of 2 mg / L. -1 The environmental standards can be widely applied in fields such as environmental protection, chemical industry, and textiles.

[0035] The specific implementation of the present invention is as follows:

[0036] Example 1

[0037] (1) Weigh 1.25g of melamine and disperse it in 45mL of deionized water. Stir and dissolve at 80℃ to obtain solution A;

[0038] (2) Add 5 mL of 2 mol·L to the above solution A. -1 Dilute sulfuric acid is stirred at 80°C to form suspension B;

[0039] (3) Weigh 60.5 mg of ferric chloride hexahydrate and add it to the above suspension B. Continue stirring to dissolve the ferric chloride hexahydrate to obtain suspension C. Then, continue stirring at 80°C until the solvent is evaporated. Grind the obtained solid thoroughly to obtain powder D.

[0040] (4) Place the above powder D in a covered crucible and incubate at 550°C in a N2 atmosphere at a rate of 2°C·min. -1 The catalyst was calcined at a heating rate of 2 h and then naturally cooled to room temperature to obtain the catalyst of this invention, denoted as Fe1 / S-CN (1.0% Fe), or simply Fe1 / S-CN.

[0041] Example 2

[0042] The difference between this embodiment and Example 1 is that the amount of ferric chloride hexahydrate in step (3) is changed to 6.0 mg, and the resulting catalyst is denoted as Fe1 / S-CN (0.1% Fe).

[0043] Example 3

[0044] The difference between this embodiment and Example 1 is that the amount of ferric chloride hexahydrate in step (3) is changed to 30.3 mg, and the resulting catalyst is denoted as Fe1 / S-CN (0.5% Fe).

[0045] Example 4

[0046] The difference between this embodiment and Example 1 is that the amount of ferric chloride hexahydrate in step (3) is changed to 90.8 mg, and the resulting catalyst is denoted as Fe1 / S-CN (1.5% Fe).

[0047] Example 5

[0048] The difference between this embodiment and Example 1 is that the amount of ferric chloride hexahydrate in step (3) is changed to 181.5 mg, and the resulting catalyst is denoted as Fe1 / S-CN (3.0% Fe).

[0049] Comparative Example 1

[0050] Weigh 1.25g of melamine and directly thaw it at 550℃ in a N2 atmosphere at a rate of 2℃·min. -1 The catalyst was calcined at a heating rate of 2 h for 2 h and the resulting catalyst was denoted as CN.

[0051] Comparative Example 2

[0052] The difference between this comparative example and Example 1 is that the amount of ferric chloride hexahydrate in step (3) is changed to 0 mg, and the resulting catalyst is denoted as S-CN.

[0053] Comparative Example 3

[0054] The difference between this comparative example and Example 1 is that the dilute sulfuric acid in step (2) is replaced with dilute hydrochloric acid, and the pH is controlled to be consistent with the added dilute sulfuric acid. The resulting catalyst is denoted as Fe1 / CN.

[0055] Comparative Example 4

[0056] The difference between this comparative example and Example 1 is that the amount of melamine and deionized water added in step (1) is replaced with the catalyst S-CN obtained in Comparative Example 2 and 20 mL of deionized water; the amount of sulfuric acid added in step (2) is replaced with 0 mL; the amount of ferric chloride hexahydrate added in step (3) is replaced with 55 mg; and the heat treatment conditions in step (4) are replaced with 500 °C and N2 atmosphere at 5 °C·min. -1 The Fe2O3 / S-CN catalyst was obtained by calcining at a heating rate of 30 min.

[0057] according to Figure 1The XRD patterns of the catalysts prepared in Example 1 and Comparative Examples 1-2 show that each catalyst sample exhibits diffraction peaks of graphitic carbon nitride (CN). The intensity of the CN diffraction peaks gradually decreases with the introduction of sulfuric acid and iron sources. Among them, the Fe1 / S-CN sample with a porous structure has the weakest diffraction peak intensity and no diffraction peaks of Fe species appear, indicating that the Fe atom loading is low and highly dispersed.

[0058] from Figure 2 The SEM images of the catalysts prepared in Example 1 and Comparative Examples 1-2 show that (a) the CN obtained by direct calcination is blocky, composed of densely packed nanosheets with a smooth, non-porous surface; (b) the S-CN sample shows a stacked structure with irregular pores; and (c) the Fe1 / S-CN sample shows a fluffy, sponge-like porous structure.

[0059] Figure 3 (a) and (b) show the TEM and HRTEM images of the Fe1 / S-CN catalyst prepared in Example 1. A clear pore structure can be observed, but no Fe-related lattice structure was observed. Figure 3 (c) indicates that C, N, Fe, O and S are uniformly distributed in the sample, indicating that Fe exists in the carbon nitride support in an atomically dispersed form.

[0060] Figure 4 The image shows the XPS spectrum of the Fe1 / S-CN sample prepared in Example 1. The full spectrum displays the XPS signals of C, N, Fe, O, and S elements, with Fe mainly present as Fe2+. 2+ The presence of the oxidized form and the fact that the S2p spectrum can be fitted to SO and CS bonds proves S doping.

[0061] Application Example 1

[0062] The catalysts prepared in Examples 1-5 and Comparative Examples 1-4 were applied to the photo-Fenton catalytic degradation of oxytetracycline hydrochloride (OTC), and the specific operation was as follows:

[0063] (1) Prepare 20 mg·L -1 The absorbance of the original OTC solution was measured at a wavelength of 353 nm using a UV spectrophotometer.

[0064] (2) Weigh 20 mg of photocatalyst and ultrasonically disperse it in 50 mL of a 20 mg·L⁻¹ solution. -1 A suspension was formed in an OTC aqueous solution. The suspension was sonicated for 10 min and then transferred to a dark room and stirred for 20 min. Samples were taken every 10 min, filtered through a 0.22 μm organic filter membrane, and the absorbance was measured using a UV spectrophotometer.

[0065] (3) Add hydrogen peroxide (H2O2) solution to the above suspension to make the initial concentration of H2O2 4 mM, and then use a 300W xenon lamp as the light source to provide simulated sunlight with a wavelength range of mainly 360-780 nm. The light power density irradiating the surface of the reaction solution is 200 mW·cm². -2 The photo-Fenton catalytic degradation of OTC was carried out. During the reaction, samples were taken every 5 minutes. The solutions were filtered through a 0.22 μm organic filter membrane, and the absorbance of residual OTC in the suspension was detected by a UV spectrophotometer.

[0066] Figure 5 The results shown are those of photo-Fenton catalytic degradation of OTC using catalysts prepared in Examples 1-5 and Comparative Examples 1-4. Figure 5 (a) shows that as the Fe content in the catalyst increases from 0.1 wt.% to 1.0 wt.%, the efficiency of photo-Fenton catalytic degradation of OTC gradually increases, and the removal rate of Fe1 / S-CN (1.0% Fe) is the highest, reaching 95.5% of the OTC degradation rate within 30 min. Figure 5 As shown in (b), compared with the catalyst samples prepared in each comparative example, the Fe1 / S-CN catalyst prepared in Example 1 has the best photo-Fenton catalytic degradation efficiency. Figure 5 (cd) shows the recycling performance of the Fe1 / S-CN catalyst in the photo-Fenton catalytic degradation of OTC. It can be seen that the catalyst maintains good catalytic performance after the fourth cycle, indicating good recyclability and stability. Furthermore, after calcination at 550℃ in a N2 atmosphere for 1 hour, it recovers its original catalytic activity, demonstrating its long-term usability. The iron ion leaching amount after each cycle, measured by atomic absorption spectrometry, is significantly lower than the EU environmental standard (2 mg·L⁻¹). -1 ).

[0067] Application Example 2

[0068] The photocatalyst prepared in Example 1 was applied to the photo-Fenton catalytic degradation of other organic pollutants.

[0069] (1) Prepare solutions with a concentration of 20 mg·L⁻¹. -1 The following organic pollutants in aqueous solutions were tested: tetracycline hydrochloride (TC), ciprofloxacin (CIP), rhodamine B (RhB), methylene blue (MB), methyl orange (MO), phenol, and 2,4-dichlorophenol (2,4-DCP). The absorbance of the original solutions was measured at wavelengths of 357 nm, 277 nm, 554 nm, 664 nm, and 460 nm using a UV spectrophotometer. The concentrations of phenolic compounds (phenol and 2,4-DCP) were determined using the 4-aminoantipyrine spectrophotometric method (standard HJ503-2009).

[0070] (2) Weigh 20 mg of photocatalyst and ultrasonically disperse it in 50 mL of the above-mentioned aqueous solutions of organic pollutants to form a suspension. After ultrasonicating the suspension for 10 min, transfer it to a dark room and stir for 20 min. Take a sample every 10 min, filter it through a 0.22 μm organic filter membrane, and determine the concentration of organic pollutants using an ultraviolet spectrophotometer.

[0071] (3) Add hydrogen peroxide (H2O2) solution to the above suspension to make the initial concentration of H2O2 4 mM, and then use a 300W xenon lamp as the light source to provide simulated sunlight with a wavelength range of mainly 360-780 nm. The light power density irradiating the surface of the reaction solution is 200 mW·cm². -2 The reaction was carried out by photo-Fenton catalysis to degrade organic pollutants. During the reaction, samples were taken every 5 minutes. The collected solutions were filtered through a 0.22 μm organic filter membrane, and the concentration of organic pollutants was determined by ultraviolet-visible spectrophotometry.

[0072] Figure 6 The results show the Fe1 / S-CN catalyst in the photo-Fenton catalytic degradation of various organic pollutants. After 30 minutes of irradiation, the removal efficiency of most organic pollutants reached over 80%. Extending the reaction time to 60 minutes further improved the degradation efficiency, with some organic pollutants completely degraded. This indicates that the Fe1 / S-CN catalyst can effectively degrade various types of organic pollutants and has good application potential.

[0073] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to specific implementations. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A multiphase photo-Fenton iron single-atom catalyst, characterized in that, The catalyst comprises a sulfur-doped graphitic carbon nitride support and iron single atoms bonded to the support; wherein the mass fraction of iron in the catalyst is 0.1~3.0 wt.%. The preparation method of this catalyst includes a sulfuric acid-induced precursor self-assembly process and an in-situ pyrolysis process. The specific operation steps are as follows: 1) Weigh a certain amount of melamine and disperse it in water, then stir and dissolve it at 70~100℃ to obtain solution A; 2) Add a certain amount of sulfuric acid to solution A and stir at 70~100℃ to form suspension B; 3) Weigh a certain amount of iron salt and add it to suspension B. Continue stirring to dissolve the iron salt and obtain suspension C. Then, continue stirring at 70~100℃ until the solvent is evaporated. Grind the obtained solid thoroughly to obtain powder D. 4) Place powder D in a covered crucible and calcine it in an inert atmosphere at 500~600℃ for 2~6 hours. Finally, allow it to cool naturally to room temperature to obtain the catalyst.

2. The catalyst according to claim 1, characterized in that, In step 1), the mass ratio of melamine to water is 1~5:

100.

3. The catalyst according to claim 1, characterized in that, In step 2), the sulfuric acid content in suspension B is 4.9~39.2 g·L⁻¹. -1 .

4. The catalyst according to claim 1, characterized in that, In step 3), the iron salt is at least one of three iron-containing soluble salts: ferric chloride hexahydrate, ferric nitrate nonahydrate, and ferric sulfate.

5. The catalyst according to claim 1, characterized in that, In step 3), the iron content in the suspension C is 0.025~0.750 g·L. -1 .

6. The catalyst according to claim 1, characterized in that, In step 4), the inert atmosphere is one of N2, Ar, or He, and the calcination heating rate is 1~5℃·min. -1 .

7. The application of the catalyst according to claim 1 in the catalytic degradation of organic pollutants in water, characterized in that, The catalyst was added to wastewater containing organic pollutants, and hydrogen peroxide was added as an oxidant. The hydrogen peroxide was catalytically activated under photo-assisted conditions to oxidize and degrade the organic pollutants in the water.

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