Monatomic iron-anchored hollow tubular carbon nitride catalyst and preparation method and application thereof

Abstract

This invention relates to the field of catalyst technology, specifically to a single-atom iron-anchored hollow tubular carbon nitride catalyst, its preparation method, and its applications. This invention achieves atom-level dispersion and stable anchoring of iron through a multi-step synergistic strategy involving the construction of a hollow tubular support, the introduction of nitrogen vacancies, surface functionalization modification, and iron-imidazolium coordination vacuum impregnation followed by segmented heat treatment. The catalyst exhibits excellent performance in activating persulfate under near-neutral conditions, achieving a 98.2% removal rate of triclocarban (a typical pollutant) and a 65.4% removal rate of total organic carbon within 60 minutes, with extremely low iron leaching. It combines high activity, excellent stability, and environmental compatibility, providing a highly efficient solution for advanced water treatment.

Description

Technical Field

[0001] This invention relates to the field of catalyst technology, and in particular to a single-atom iron-anchored hollow tubular carbon nitride catalyst, its preparation method, and its application. Background Technology

[0002] In the field of advanced oxidation technology, persulfate activation has attracted much attention due to its ability to generate highly oxidizing sulfate radicals, particularly suitable for the deep removal of recalcitrant organic pollutants from water. Iron-based catalysts are considered ideal for persulfate activation due to their low cost and environmental friendliness. Early research mainly focused on homogeneous iron salt catalytic systems. While these systems can efficiently activate persulfates under acidic conditions, under near-neutral or neutral pH conditions, iron ions readily hydrolyze to form ferric hydroxide precipitate, leading to a sharp decline in the efficiency of active species generation and rapid deactivation of the catalyst's effective components. More seriously, iron ions in homogeneous systems are difficult to recover, easily causing secondary pollution and limiting their application in sensitive water bodies such as drinking water treatment.

[0003] To address the challenge of catalyst recovery, research has shifted towards heterogeneous iron-based materials, such as nano-zero-valent iron, iron oxide, and their composites. These materials, through their solid-phase form, alleviate metal leaching to some extent, but their activity is highly dependent on the size and dispersion of the nanoparticles. During preparation and practical application, iron species are prone to migration and aggregation, forming larger nanoparticles or even bulk phases, leading to a sharp reduction in the number of active sites and decreased utilization. Furthermore, nanoparticles are easily detached from the support under long-term operation or hydraulic shear, and their stability remains a challenge. Especially in neutral water environments, the surface of nanoparticles is easily covered by naturally occurring organic matter or anions commonly found in water, further hindering their effective contact with persulfate and target pollutants, resulting in a decrease in activation efficiency.

[0004] To further improve the utilization efficiency of iron atoms, the concept of single-atom dispersed catalysis has been introduced into this field. This involves constructing Fe-N atoms on carbon-nitrogen materials. x Theoretically, coordination structures can maximize the exposure of iron atoms. However, existing supports mostly employ bulk or lamellar graphitic carbon nitride with limited specific surface area, whose dense structure severely restricts the mass transfer efficiency between reactants and products within the catalyst. During high-temperature heat treatment, iron precursors are prone to migration and aggregation due to the lack of sufficient anchoring sites and spatial confinement, making it difficult to obtain stable single-atom sites with high loading. When dealing with complex water bodies, trace organic molecules struggle to effectively diffuse to the active sites embedded within the support, resulting in unsatisfactory reaction rates and mineralization capabilities.

[0005] In summary, existing iron-based persulfate activation technologies, from homogeneous to heterogeneous phases and then to single-atom catalysis strategies, have consistently failed to effectively address the three core issues of activity, stability, and mass transfer efficiency. Developing a novel catalyst that combines high active site density, excellent structural stability, and unobstructed mass transfer channels under near-neutral conditions has become a key bottleneck for the practical application of this technology. Summary of the Invention

[0006] In view of this, the purpose of this invention is to propose a single-atom iron-anchored hollow tubular carbon nitride catalyst, its preparation method and application, in order to solve the problems of easy deactivation under near-neutral conditions, low iron atom utilization rate and large reaction mass transfer resistance of existing iron-based persulfate activated catalysts, which are difficult to meet the requirements of drinking water deep treatment for efficient and stable degradation of trace organic pollutants.

[0007] To achieve the above objectives, the present invention provides a method for preparing a single-atom iron-anchored hollow tubular carbon nitride catalyst, comprising the following steps:

[0008] (1) Melamine and cyanuric acid were dissolved in deionized water and mixed to form a precipitate. After solid-liquid separation, washing and drying, melamine-cyanuric acid precursor was obtained.

[0009] (2) The melamine-cyanuric acid precursor was mixed with sodium chloride, potassium chloride and ammonium chloride and ground. It was then heat-treated under a nitrogen atmosphere. The resulting solid was then crushed, washed with hot water to remove salt and dried to obtain a hollow tubular carbon nitride carrier.

[0010] (3) The hollow tubular carbon nitride carrier is added to potassium hydroxide aqueous solution for treatment. After solid-liquid separation, washing to neutrality and drying, it is heat-treated again under nitrogen atmosphere to obtain defective hollow tubular carbon nitride.

[0011] (4) Disperse the defective hollow tubular carbon nitride in tris(hydroxymethyl)aminomethane buffer, add dopamine hydrochloride under alkaline conditions and polymerize to form a coating layer, and obtain polydopamine-coated defective hollow tubular carbon nitride after solid-liquid separation, washing and drying.

[0012] (5) The diazonium salt solution is generated by diazotizing p-aminobenzenesulfonic acid. The diazonium salt solution is then coupled with the hollow tubular carbon nitride with defects coated with polydopamine to introduce sulfonic acid aryl groups. After solid-liquid separation, washing and drying, sulfonic acid aryl grafted polydopamine-coated hollow tubular carbon nitride with defects is obtained.

[0013] (6) Octadecylamine was introduced into and reacted with polydopamine-coated defect hollow tubular carbon nitride grafted with sulfonic acid aryl groups. After solid-liquid separation, washing and drying, double-grafted polydopamine-coated defect hollow tubular carbon nitride was obtained.

[0014] (7) Prepare an imidazole solution and a ferric chloride hexahydrate solution and mix them to obtain an iron-imidazole coordination solution. Then, the double-grafted polydopamine-coated hollow tubular carbon nitride is brought into contact with the iron-imidazole coordination solution and subjected to vacuum-backpressure cyclic impregnation. The solvent is then removed and the solution is dried to obtain an iron-containing precursor.

[0015] (8) The iron-containing precursor was subjected to segmental heat treatment and cooling under a nitrogen atmosphere, followed by acid washing, washing and drying to obtain a single-atom iron-anchored hollow tubular carbon nitride catalyst.

[0016] Preferably, in step (1), the mass ratio of melamine to cyanuric acid is 1:1.

[0017] Preferably, in step (2), the mass ratio of melamine-cyanuric acid precursor, sodium chloride, potassium chloride and ammonium chloride is 1:10:10:1.

[0018] Preferably, in step (2), the grinding time is 20-40 min.

[0019] Preferably, in step (2), the nitrogen flow rate during heat treatment under a nitrogen atmosphere is 180-220 mL / min, the heating rate is 1.5-2.5℃ / min, the heat treatment temperature is 530-570℃ and the holding time is 3-5 h; the hot water washing temperature is 75-85℃, the drying temperature is 75-85℃ and the drying time is 10-14 h.

[0020] Preferably, in step (3), the concentration of potassium hydroxide aqueous solution is 400-600 mmol / L, the treatment temperature is 55-65℃, and the mixture is stirred for 1.5-2.5 h.

[0021] Preferably, in step (3), the heating rate of the second heat treatment is 4-6℃ / min, the heat treatment temperature is 480-520℃ and the heat treatment is held for 1.5-2.5h.

[0022] Preferably, in step (4), the mass ratio of the hollow tubular carbon nitride in the defect to dopamine hydrochloride is 1.6-2.4:0.32-0.48.

[0023] Preferably, in step (5), the mass ratio of p-aminobenzenesulfonic acid to polydopamine-coated hollow tubular carbon nitride in the defects is 0.4-0.6:1.6-2.4.

[0024] Preferably, in step (6), the mass ratio of octadecylamine to polydopamine grafted with sulfonic acid aryl groups to the hollow tubular carbon nitride in the defect is 0.24-0.36:1.6-2.4.

[0025] Preferably, in step (7), the mass ratio of imidazole, ferric chloride hexahydrate and double-grafted polydopamine-coated hollow tubular carbon nitride in the defects is 0.08-0.12:0.024-0.036:1.6-2.4.

[0026] Preferably, in step (7), the vacuum-backpressure cycle impregnation is performed by: evacuating to -80±10kPa and maintaining it for 8-12 minutes, then introducing nitrogen to return to normal pressure, and the number of vacuum-backpressure cycles is 2-4.

[0027] Preferably, in step (8), the segmented heat treatment conditions are as follows: nitrogen flow rate 180-220 mL / min, temperature increased to 240-260℃ at 1.5-2.5℃ / min and held for 1.5-2.5h, then temperature increased to 500-540℃ at 4-6℃ / min and held for 1.5-2.5h before cooling.

[0028] Preferably, in step (8), the pickling is performed using a hydrochloric acid solution with a concentration of 80-120 mmol / L and a volume of 160-240 mL, and the pickling temperature is 20-30℃ with stirring for 1.5-2.5 h.

[0029] Furthermore, the present invention also provides a single-atom iron-anchored hollow tubular carbon nitride catalyst, which is obtained by the above-mentioned preparation method of the single-atom iron-anchored hollow tubular carbon nitride catalyst.

[0030] Preferably, the iron content of the single-atom iron-anchored hollow tubular carbon nitride catalyst is 0.5wt%-0.9wt%.

[0031] Preferably, the iron active sites are anchored to the defective hollow tubular carbon nitride support in an iron-nitrogen coordination structure.

[0032] Furthermore, the present invention also provides the application of a single-atom iron-anchored hollow tubular carbon nitride catalyst in activating persulfate to degrade organic pollutants in water.

[0033] Preferably, the organic pollutant is triclocarban.

[0034] The beneficial effects of this invention are:

[0035] This invention significantly improves the overall performance of the catalyst by combining a hollow tubular carbon nitride support with multi-level surface modification. The hollow tubular structure provides an ideal channel for one-dimensional mass transfer, greatly reducing the diffusion resistance between reactant and product molecules and ensuring high accessibility of active sites. By introducing abundant nitrogen vacancy defects on the support surface, a large number of highly active sites are created for subsequent metal anchoring, effectively suppressing the migration and aggregation tendency of iron species during heat treatment, and laying a solid foundation for the formation of a uniform and stable iron-nitrogen coordination structure.

[0036] The introduction of the polydopamine coating layer not only enhances the interfacial compatibility and adhesion between the support and subsequent functionalized components, ensuring the uniformity of the modification process, but also, as a nitrogen-carbon precursor, it can be further transformed into a highly conductive carbon layer during heat treatment, optimizing the electron transfer path around the active sites, thereby simultaneously enhancing the activity of the catalytic reaction and the long-term operational stability of the catalyst.

[0037] Before loading iron species, sulfonic acid aromatic molecules are grafted via diazotization, cleverly utilizing the strong hydrophilicity and potential coordination ability of the sulfonic acid groups. This design creates a unique interfacial microenvironment on the catalyst surface, which not only improves the catalyst's dispersibility in the aqueous phase and promotes the enrichment of persulfate ions at the solid-liquid interface, but also potentially modulates the electron cloud density of adjacent iron active centers through the electronic effects of sulfur species. This significantly enhances the efficiency of persulfate activation and the mineralization degree of target pollutants under neutral conditions.

[0038] The introduction of octadecylamine molecules, with their long-chain alkyl groups, creates moderately hydrophobic microdomains and steric hindrance effects in the catalyst precursor stage. This microenvironment regulation helps the iron-imidazolium coordination solution to penetrate and distribute more uniformly within the hollow lumen, avoiding excessive enrichment of the active component on the outer surface and promoting the loading of iron species onto the active anchoring sites within the lumen. In subsequent heat treatment, the decomposition of octadecylamine further contributes to the formation of a richer pore structure, further optimizing the catalyst's pore structure parameters.

[0039] A vacuum cyclic impregnation and segmented heat treatment process was employed to achieve the spatial confinement and stabilization of iron active centers. Pressure variations forced the active precursor solution into the depths of the cavity, ensuring uniform distribution of active sites and enrichment within the cavity. The segmented heating strategy allowed for precise control of the carbonization of organic components and the solidification of the iron-nitrogen coordination structure, avoiding structural damage and active component agglomeration caused by violent pyrolysis. Finally, a gentle acid wash effectively removed loosely bound iron species, resulting in a catalyst product with extremely low metal leaching rates, exhibiting excellent environmental compatibility and stability. Attached Figure Description

[0040] To more clearly illustrate the technical solutions in this invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below.

[0041] Figure 1 The image shown is aberration-corrected HAADF-STEM image of the single-atom iron-anchored hollow tubular carbon nitride catalyst obtained in Example 2 of this invention.

[0042] Figure 2The infrared spectra of the sulfonic acid aryl-grafted polydopamine-coated hollow tubular carbon nitride, the double-grafted polydopamine-coated hollow tubular carbon nitride, and the iron-containing precursor obtained in Example 2 of the present invention are shown.

[0043] Figure 3 The figures show the removal curves of triclocarban under near-neutral conditions for the embodiments and comparative examples of the present invention. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0045] Example 1:

[0046] Step S1: Weigh 8g of melamine and add it to 400mL of deionized water, and stir in a water bath at 85℃ for 50min; separately weigh 8g of cyanuric acid and add it to 400mL of deionized water, and stir in a water bath at 90℃ for 50min until completely dissolved; slowly mix the two hot solutions at 85℃ and continue stirring for 20min, then cool naturally to 20℃ and let stand for 1.5h to form a white precipitate, filter and wash twice with deionized water, and finally dry in a forced-air dryer at 75℃ for 10h to obtain the melamine-cyanuric acid precursor;

[0047] Step S2: Weigh 4g of melamine-cyanuric acid precursor, 40g of sodium chloride, 40g of potassium chloride and 4g of ammonium chloride and grind them in an agate mortar for 20min. Put the mixed powder into a covered alumina crucible and place it in a tube furnace. Under a nitrogen atmosphere, pass the powder through at 180mL / min and heat it to 530℃ at 1.5℃ / min. Hold the temperature for 3h and then let it cool naturally. After cooling, crush the solid and wash it three times with deionized water at 75℃. After filtration, dry it at 75℃ for 10h to obtain a hollow tubular carbon nitride support.

[0048] Step S3: Weigh 1.6 g of hollow tubular carbon nitride support and add it to 80 mL of potassium hydroxide aqueous solution (concentration 400 mmol / L). Stir at 55 °C for 1.5 h and then filter. Wash the filtrate with 1600 mL of deionized water until the pH of the filtrate is 7. Then dry it at 75 °C for 10 h. Place the dried solid in a tube furnace and heat it to 480 °C at 4 °C / min under a nitrogen atmosphere. Hold the temperature for 1.5 h and then cool to obtain defect-filled hollow tubular carbon nitride.

[0049] Step S4: Weigh 485 mg of tris(hydroxymethyl)aminomethane and add it to 400 mL of deionized water to prepare a buffer solution. Add hydrochloric acid aqueous solution (concentration 1 mol / L) dropwise to adjust the pH to 8.5. Weigh 1.6 g of defective hollow tubular carbon nitride and add it to the above buffer solution. Sonicate and disperse for 20 min. Then weigh 320 mg of dopamine hydrochloride and add it. Stir in an open container at 20 °C for 10 h. After filtration, wash with deionized water and anhydrous ethanol three times each. Dry at 55 °C for 10 h to obtain polydopamine-coated defective hollow tubular carbon nitride.

[0050] Step S5: Weigh 400 mg of p-aminobenzenesulfonic acid and add it to 16 mL of deionized water. Stir at 55 °C for 20 min, then add hydrochloric acid aqueous solution (concentration 1 mol / L) dropwise to adjust the pH to 3.0, and cool to 3 °C in an ice bath. Separately, take 5 mL of sodium nitrite aqueous solution (concentration 400 mmol / L) and add it to 7 mL of deionized water to prepare a sodium nitrite dilution. Add this dilution dropwise to the acidic p-aminobenzenesulfonic acid solution at 3 °C and keep it at this temperature for 25 min to generate a diazonium salt solution. At the same time, weigh 1.6 g of polydopamine-coated defective hollow tubular carbon nitride and add it to 160 mL of deionized water. The polydopamine-coated hollow tubular carbon nitride with sulfonic acid aryl grafts was ultrasonically dispersed in deionized water at 3℃ for 10 min. The diazonium salt solution was added dropwise to the dispersion, followed by the addition of potassium hydroxide aqueous solution (concentration 400 mmol / L) to adjust the pH of the system to 7.5 and stirring for 50 min. The temperature was then raised to 20℃ and stirring was continued for 2.5 h. After filtration, the polydopamine-coated hollow tubular carbon nitride with sulfonic acid aryl grafts was washed three times each with deionized water and anhydrous ethanol and dried at 55℃ for 10 h to obtain sulfonic acid aryl grafts.

[0051] Step S6: Weigh 240 mg of octadecylamine and add it to 24 mL of anhydrous ethanol. Stir at 45 °C for 20 min. Weigh 145 mg of tris(hydroxymethyl)aminomethane and add it to 120 mL of deionized water to prepare a buffer solution. Add hydrochloric acid aqueous solution (concentration 1 mol / L) dropwise to adjust the pH to 8.5. Weigh 1.6 g of sulfonic acid aryl-grafted polydopamine-coated hollow tubular carbon nitride and add it to the above buffer solution. Disperse it by sonication for 10 min. Then add the octadecylamine ethanol solution and stir at 45 °C for 5 h. After filtration, wash it three times with anhydrous ethanol and dry it at 55 °C for 10 h to obtain double-grafted polydopamine-coated hollow tubular carbon nitride.

[0052] Step S7: Weigh 80 mg of imidazole and add 40 mL of anhydrous ethanol and stir to dissolve; weigh 24 mg of ferric chloride hexahydrate and add 8 mL of anhydrous ethanol and stir to dissolve. Mix the two solutions and stir for 20 min to obtain an iron-imidazole complex solution; weigh 1.6 g of double-grafted polydopamine-coated hollow tubular carbon nitride with defects and add it to the above complex solution and stir for 20 min to form a uniform suspension. Then place the suspension in a vacuum dryer and evacuate to -70 kPa and hold for 8 min. Then introduce nitrogen gas to return to normal pressure. Repeat the vacuum-return cycle twice and continue stirring at 20 °C for 3 h. Finally, evaporate under reduced pressure at 55 °C to remove the solvent and dry for 10 h to obtain the iron-containing precursor.

[0053] Step S8: The iron-containing precursor was placed in a quartz boat and then placed in a tube furnace. Nitrogen gas was introduced at a rate of 180 mL / min, and the temperature was increased to 240℃ at a rate of 1.5℃ / min and held for 1.5 h. The temperature was then increased to 500℃ at a rate of 4℃ / min and held for 1.5 h before cooling. After cooling, the obtained solid was weighed and added to 160 mL of hydrochloric acid solution (concentration 80 mmol / L). The solution was stirred at 20℃ for 1.5 h, filtered, washed three times with deionized water, and dried at 75℃ for 10 h to obtain a single-atom iron-anchored hollow tubular carbon nitride catalyst.

[0054] Example 2:

[0055] Step S1: Weigh 10g of melamine and add it to 500mL of deionized water, and stir in a 90℃ water bath for 60min; separately weigh 10g of cyanuric acid and add it to 500mL of deionized water, and stir in a 95℃ water bath for 60min until completely dissolved; slowly mix the two hot solutions at 90℃ and continue stirring for 30min, then cool naturally to 25℃ and let stand for 2h to form a white precipitate, filter, wash twice with deionized water, and finally dry in a forced-air dryer at 80℃ for 12h to obtain the melamine-cyanuric acid precursor;

[0056] Step S2: Weigh 5g of melamine-cyanuric acid precursor, 50g of sodium chloride, 50g of potassium chloride and 5g of ammonium chloride and grind them in an agate mortar for 30min. Put the mixed powder into a covered alumina crucible and place it in a tube furnace. Under a nitrogen atmosphere, pass the powder through at 200mL / min and heat it to 550℃ at 2℃ / min. Hold it at this temperature for 4h and then let it cool naturally. After cooling, pulverize the solid and wash it three times with deionized water at 80℃. After filtration, dry it at 80℃ for 12h to obtain a hollow tubular carbon nitride support.

[0057] Step S3: Weigh 2g of hollow tubular carbon nitride support and add it to 100mL of potassium hydroxide aqueous solution (concentration 500mmol / L). Stir at 60℃ for 2h and then filter. Wash the filtrate with 2000mL of deionized water until the pH of the filtrate is 7. Then dry it at 80℃ for 12h. Place the dried solid in a tube furnace and heat it to 500℃ at 5℃ / min under a nitrogen atmosphere. Hold it at the temperature for 2h and then cool it to obtain defect-filled hollow tubular carbon nitride.

[0058] Step S4: Weigh 606 mg of tris(hydroxymethyl)aminomethane and add it to 500 mL of deionized water to prepare a buffer solution. Add hydrochloric acid aqueous solution (concentration 1 mol / L) dropwise to adjust the pH to 9. Weigh 2 g of defective hollow tubular carbon nitride and add it to the above buffer solution. Sonicate and disperse for 30 min. Then weigh 400 mg of dopamine hydrochloride and add it. Stir in an open container at 25 °C for 12 h. After filtration, wash with deionized water and anhydrous ethanol three times each. Dry at 60 °C for 12 h to obtain polydopamine-coated defective hollow tubular carbon nitride.

[0059] Step S5: Weigh 500 mg of p-aminobenzenesulfonic acid and add it to 20 mL of deionized water. Stir at 60 °C for 30 min, then add hydrochloric acid aqueous solution (concentration 1 mol / L) dropwise to adjust the pH to 3.2, and cool to 5 °C in an ice bath. Separately, take 6 mL of sodium nitrite aqueous solution (concentration 500 mmol / L) and add it to 8 mL of deionized water to prepare a sodium nitrite dilution. Add this dilution dropwise to the acidic p-aminobenzenesulfonic acid solution at 5 °C and keep it at this temperature for 30 min to generate a diazonium salt solution. At the same time, weigh 2 g of polydopamine-coated defective hollow tubular carbon nitride and add it to 200 mL of water. The polydopamine-coated hollow tubular carbon nitride with sulfonic acid aryl grafts was ultrasonically dispersed in deionized water at 5℃ for 15 min. The diazonium salt solution was added dropwise to the dispersion, followed by the addition of potassium hydroxide aqueous solution (concentration 500 mmol / L) to adjust the pH of the system to 8 and stirring for 60 min. The temperature was then raised to 25℃ and stirring was continued for 3 h. After filtration, the carbon nitride was washed three times each with deionized water and anhydrous ethanol and dried at 60℃ for 12 h to obtain sulfonic acid aryl grafted polydopamine-coated hollow tubular carbon nitride with defects.

[0060] Step S6: Weigh 300 mg of octadecylamine and add 30 mL of anhydrous ethanol, stirring at 50 °C for 30 min; weigh 182 mg of tris(hydroxymethyl)aminomethane and add 150 mL of deionized water to prepare a buffer solution, and add hydrochloric acid aqueous solution (concentration 1 mol / L) to adjust the pH to 9; weigh 2 g of sulfonic acid aryl-grafted polydopamine-coated hollow tubular carbon nitride and add it to the above buffer solution, sonicating for 15 min, then add the octadecylamine ethanol solution and stir at 50 °C for 6 h, filter, wash 3 times with anhydrous ethanol, and dry at 60 °C for 12 h to obtain double-grafted polydopamine-coated hollow tubular carbon nitride;

[0061] Step S7: Weigh 100 mg imidazole and add 50 mL of anhydrous ethanol and stir to dissolve; weigh 30 mg ferric chloride hexahydrate and add 10 mL of anhydrous ethanol and stir to dissolve. Mix the two solutions and stir for 30 min to obtain an iron-imidazole complex solution; weigh 2 g of double-grafted polydopamine-coated hollow tubular carbon nitride with defects and add it to the above complex solution and stir for 30 min to form a uniform suspension. Then place the suspension in a vacuum dryer and evacuate to -80 kPa and hold for 10 min. Then introduce nitrogen gas to return to normal pressure. Repeat the vacuum-re-pressure cycle 3 times and continue stirring at 25 °C for 4 h. Finally, evaporate under reduced pressure at 60 °C to remove the solvent and dry for 12 h to obtain the iron-containing precursor.

[0062] Step S8: The iron-containing precursor was placed in a quartz boat and then placed in a tube furnace. Nitrogen gas was introduced at a rate of 200 mL / min, and the temperature was increased to 250 °C at a rate of 2 °C / min and held for 2 h. The temperature was then increased to 520 °C at a rate of 5 °C / min and held for 2 h before cooling. After cooling, the obtained solid was weighed and added to 200 mL of hydrochloric acid solution (concentration 100 mmol / L). The solution was stirred at 25 °C for 2 h, filtered, washed three times with deionized water, and dried at 80 °C for 12 h to obtain a single-atom iron-anchored hollow tubular carbon nitride catalyst.

[0063] Example 3:

[0064] Step S1: Weigh 12g of melamine and add it to 600mL of deionized water, and stir in a water bath at 95℃ for 70min; separately weigh 12g of cyanuric acid and add it to 600mL of deionized water, and stir in a water bath at 100℃ for 70min until completely dissolved; slowly mix the two hot solutions at 95℃ and continue stirring for 40min, then cool naturally to 30℃ and let stand for 2.5h to form a white precipitate, filter and wash twice with deionized water, and finally dry in a forced-air dryer at 85℃ for 14h to obtain the melamine-cyanuric acid precursor;

[0065] Step S2: Weigh 6g of melamine-cyanuric acid precursor, 60g of sodium chloride, 60g of potassium chloride and 6g of ammonium chloride and grind them in an agate mortar for 40min. Put the mixed powder into a covered alumina crucible and place it in a tube furnace. Under a nitrogen atmosphere, pass the powder through at 220mL / min and heat it to 570℃ at 2.5℃ / min. Hold the temperature for 5h and then let it cool naturally. After cooling, crush the solid and wash it three times with deionized water at 85℃. After filtration, dry it at 85℃ for 14h to obtain a hollow tubular carbon nitride support.

[0066] Step S3: Weigh 2.4 g of hollow tubular carbon nitride support and add it to 120 mL of potassium hydroxide aqueous solution (concentration 600 mmol / L). Stir at 65 °C for 2.5 h, filter, and wash with 2400 mL of deionized water until the pH of the filtrate is 7. Then dry at 85 °C for 14 h. Place the dried solid in a tube furnace and heat it to 520 °C at 6 °C / min under a nitrogen atmosphere. Hold at the temperature for 2.5 h and then cool to obtain defect-laden hollow tubular carbon nitride.

[0067] Step S4: Weigh 727 mg of tris(hydroxymethyl)aminomethane and add it to 600 mL of deionized water to prepare a buffer solution. Add hydrochloric acid aqueous solution (concentration 1 mol / L) dropwise to adjust the pH to 9.5. Weigh 2.4 g of defective hollow tubular carbon nitride and add it to the above buffer solution. Sonicate and disperse for 40 min. Then weigh 480 mg of dopamine hydrochloride and add it. Stir in an open container at 30 °C for 14 h. After filtration, wash with deionized water and anhydrous ethanol three times each. Dry at 65 °C for 14 h to obtain polydopamine-coated defective hollow tubular carbon nitride.

[0068] Step S5: Weigh 600 mg of p-aminobenzenesulfonic acid and add it to 24 mL of deionized water. Stir at 65 °C for 40 min, then add hydrochloric acid aqueous solution (concentration 1 mol / L) dropwise to adjust the pH to 3.4, and cool to 7 °C in an ice bath. Separately, take 7 mL of sodium nitrite aqueous solution (concentration 600 mmol / L) and add it to 9 mL of deionized water to prepare a sodium nitrite dilution. Add this dilution dropwise to the acidic p-aminobenzenesulfonic acid solution at 7 °C and keep it at this temperature for 35 min to generate a diazonium salt solution. At the same time, weigh 2.4 g of polydopamine-coated defective hollow tubular carbon nitride and add it to 240 mL of deionized water. The polydopamine-coated hollow tubular carbon nitride with sulfonic acid aryl grafts was ultrasonically dispersed in deionized water at 7℃ for 20 min. The diazonium salt solution was added dropwise to the dispersion, followed by the addition of potassium hydroxide aqueous solution (600 mmol / L) to adjust the pH of the system to 8.5 and stirring for 70 min. The temperature was then raised to 30℃ and stirring was continued for 3.5 h. After filtration, the carbon nitride was washed three times each with deionized water and anhydrous ethanol and dried at 65℃ for 14 h to obtain sulfonic acid aryl grafted polydopamine-coated hollow tubular carbon nitride with defects.

[0069] Step S6: Weigh 360 mg of octadecylamine and add it to 36 mL of anhydrous ethanol. Stir at 55 °C for 40 min. Weigh 218 mg of tris(hydroxymethyl)aminomethane and add it to 180 mL of deionized water to prepare a buffer solution. Add hydrochloric acid aqueous solution (concentration 1 mol / L) dropwise to adjust the pH to 9.5. Weigh 2.4 g of sulfonic acid aryl-grafted polydopamine-coated hollow tubular carbon nitride and add it to the above buffer solution. Disperse by sonication for 20 min. Then add the octadecylamine ethanol solution and stir at 55 °C for 7 h. After filtration, wash three times with anhydrous ethanol and dry at 65 °C for 14 h to obtain double-grafted polydopamine-coated hollow tubular carbon nitride.

[0070] Step S7: Weigh 120 mg imidazole and add 60 mL of anhydrous ethanol and stir to dissolve; weigh 36 mg ferric chloride hexahydrate and add 12 mL of anhydrous ethanol and stir to dissolve. Mix the two solutions and stir for 40 min to obtain an iron-imidazole complex solution; weigh 2.4 g of double-grafted polydopamine-coated hollow tubular carbon nitride with defects and add it to the above complex solution and stir for 40 min to form a uniform suspension. Then place the suspension in a vacuum dryer and evacuate to -90 kPa and hold for 12 min. Then introduce nitrogen gas to return to normal pressure. Repeat the vacuum-recompression cycle 4 times and continue stirring at 30 °C for 5 h. Finally, evaporate under reduced pressure at 65 °C to remove the solvent and dry for 14 h to obtain the iron-containing precursor.

[0071] Step S8: The iron-containing precursor was placed in a quartz boat and then placed in a tube furnace. Nitrogen gas was introduced at a rate of 220 mL / min, and the temperature was increased to 260℃ at a rate of 2.5℃ / min and held for 2.5 h. The temperature was then increased to 540℃ at a rate of 6℃ / min and held for 2.5 h before cooling. After cooling, the obtained solid was weighed and added to 240 mL of hydrochloric acid solution (concentration 120 mmol / L). The solution was stirred at 30℃ for 2.5 h, filtered, washed three times with deionized water, and dried at 85℃ for 14 h to obtain a single-atom iron-anchored hollow tubular carbon nitride catalyst.

[0072] Parameter variation range (Examples 1-3):

[0073] Step S1: Melamine dosage 8-12g; deionized water volume 400-600mL; melamine dissolution temperature 85-95℃; stirring time 50-70min; cyanuric acid dosage 8-12g; deionized water volume 400-600mL; cyanuric acid dissolution temperature 90-100℃; stirring time 50-70min; mixing temperature 85-95℃; mixing and stirring time 20-40min; cooling to 20-30℃; standing time 1.5-2.5h; forced-air drying temperature 75-85℃; forced-air drying time 10-14h;

[0074] Step S2: 4-6g of melamine-cyanuric acid precursor; 40-60g of sodium chloride; 40-60g of potassium chloride; 4-6g of ammonium chloride; grinding time 20-40min; nitrogen flow rate 180-220mL / min; heating rate 1.5-2.5℃ / min; heat treatment temperature 530-570℃; holding time 3-5h; washing water temperature 75-85℃; drying temperature 75-85℃; drying time 10-14h.

[0075] Step S3: 1.6-2.4 g of hollow tubular carbon nitride support; 80-120 mL of potassium hydroxide aqueous solution; 400-600 mmol / L concentration of potassium hydroxide aqueous solution; treatment temperature 55-65℃; treatment time 1.5-2.5 h; 1600-2400 mL of deionized water for washing; drying temperature 75-85℃; drying time 10-14 h; heat treatment heating rate 4-6℃ / min; heat treatment temperature 480-520℃; holding time 1.5-2.5 h.

[0076] Step S4: Tris(hydroxymethyl)aminomethane dosage 485-727 mg; buffer volume 400-600 mL; pH 8.5-9.5; defect-hollow tubular carbon nitride dosage 1.6-2.4 g; ultrasonic dispersion time 20-40 min; dopamine hydrochloride dosage 320-480 mg; open stirring temperature 20-30℃; open stirring time 10-14 h; drying temperature 55-65℃; drying time 10-14 h.

[0077] Step S5: Use 400-600 mg of p-aminobenzenesulfonic acid; 16-24 mL of deionized water; stirring temperature 55-65℃; stirring time 20-40 min; pH 3.0-3.4; cool to 3-7℃ in an ice bath; use 5-7 mL of sodium nitrite aqueous solution; sodium nitrite aqueous solution concentration 400-600 mmol / L; use 7-9 mL of deionized water; diazotization reaction temperature 3-7℃; diazotization reaction time 25-35 min; poly(aminobenzenesulfonic acid) The dosage of dopamine-coated defective hollow tubular carbon nitride is 1.6-2.4 g; the volume of deionized water used for dispersion is 160-240 mL; the dispersion temperature is 3-7℃; the ultrasonic dispersion time is 10-20 min; the pH is 7.5-8.5; the concentration of potassium hydroxide aqueous solution is 400-600 mmol / L; the stirring time is 50-70 min; the temperature is raised to 20-30℃; the stirring time is continued for 2.5-3.5 h; the drying temperature is 55-65℃; and the drying time is 10-14 h.

[0078] Step S6: 240-360 mg of octadecylamine; 24-36 mL of anhydrous ethanol; stirring temperature 45-55℃; stirring time 20-40 min; 145-218 mg of tris(hydroxymethyl)aminomethane; 120-180 mL of buffer solution; pH 8.5-9.5; 1.6-2.4 g of sulfonic acid aryl-grafted polydopamine coating the defective hollow tubular carbon nitride; ultrasonic dispersion time 10-20 min; stirring temperature 45-55℃; stirring time 5-7 h; drying temperature 55-65℃; drying time 10-14 h.

[0079] Step S7: Imidazole dosage 80-120 mg; anhydrous ethanol volume 40-60 mL; ferric chloride hexahydrate dosage 24-36 mg; anhydrous ethanol volume 8-12 mL; mixing and stirring time 20-40 min; double-grafted polydopamine coating of defective hollow tubular carbon nitride dosage 1.6-2.4 g; stirring time 20-40 min; vacuuming to -90 to -70 kPa; holding time 8-12 min; vacuum-backpressure cycles 2-4 times; continuing stirring at 20-30℃; continuing stirring for 3-5 h; reduced pressure evaporation temperature 55-65℃; drying time 10-14 h.

[0080] Step S8: Nitrogen flow rate 180-220 mL / min; first stage heating rate 1.5-2.5℃ / min; first stage temperature 240-260℃; first stage holding time 1.5-2.5 h; second stage heating rate 4-6℃ / min; second stage temperature 500-540℃; second stage holding time 1.5-2.5 h; hydrochloric acid solution volume 160-240 mL; hydrochloric acid solution concentration 80-120 mmol / L; acid washing stirring temperature 20-30℃; acid washing stirring time 1.5-2.5 h; drying temperature 75-85℃; drying time 10-14 h.

[0081] Comparative Example 1:

[0082] The difference between Comparative Example 1 and Example 2 is that 5g of ammonium chloride is not added in step S2; the other conditions are the same as in Example 2.

[0083] Comparative Example 2:

[0084] The difference between Comparative Example 2 and Example 2 is that the hollow tubular carbon nitride support obtained in step S2 is directly used as the starting solid for subsequent step S4-S8; the other conditions are the same as in Example 2.

[0085] Comparative Example 3:

[0086] The difference between Comparative Example 3 and Example 2 is that 400 mg of dopamine hydrochloride is not added in step S4; the other conditions are the same as in Example 2.

[0087] Comparative Example 4:

[0088] The difference between Comparative Example 4 and Example 2 is that the defective hollow tubular carbon nitride coated with polydopamine obtained in step S4 is directly used as the starting solid for subsequent step S6-S8; the other conditions are the same as in Example 2.

[0089] Comparative Example 5:

[0090] The difference between Comparative Example 5 and Example 2 is that the sulfonic acid aryl-grafted polydopamine-coated hollow tubular carbon nitride obtained in step S5 is directly used as the starting solid for subsequent step S7-S8; the other conditions are the same as in Example 2.

[0091] Comparative Example 6:

[0092] The difference between Comparative Example 6 and Example 2 is that in step S7, after obtaining the iron-imidazolium coordination solution and weighing 2g of double-grafted polydopamine-coated hollow tubular carbon nitride to be added to the coordination solution and stirred for 30min to form a uniform suspension, the suspension is not placed in a vacuum dryer to be evacuated to -80kPa and held for 10min, then nitrogen is introduced to return to normal pressure and the evacuation-re-pressure cycle is repeated 3 times. Instead, the suspension is directly stirred at 25°C for 4h. Subsequently, the solvent is removed by vacuum evaporation at 60°C and dried for 12h to obtain the iron-containing precursor. The remaining conditions are the same as in Example 2.

[0093] Comparative Example 7:

[0094] The difference between Comparative Example 7 and Example 2 is that the stage of holding at 250°C for 2 hours in step S8 is omitted; after cooling, the catalyst is still obtained by adding 200 mL of hydrochloric acid solution (concentration 100 mmol / L), stirring at 25°C for 2 hours, filtering, washing with deionized water 3 times, and drying at 80°C for 12 hours; the remaining conditions are the same as in Example 2.

[0095] Performance testing:

[0096] Sample preparation: Catalysts were prepared according to the steps of the examples and comparative examples. After step S8 and drying for 12 hours, each sample was cooled to room temperature in a desiccator, ground for 2 minutes using an agate mortar, and passed through a 100-mesh sieve to obtain a powder sample with uniform particle size. All solid characterization tests were performed directly using this powder. The triclocarban simulated water sample used for the catalytic reaction test was prepared as follows: 20 mg of triclocarban was weighed and added to 20 mL of anhydrous ethanol, and sonicated for 10 minutes to obtain a 1 g / L stock solution. 20 mL of this stock solution was added to 198... A simulated water sample with an initial concentration of 10 mg / L triclocarban was obtained by adding 0 mL of deionized water. The pH was adjusted to 7 by adding hydrochloric acid aqueous solution (concentration 1 mol / L) or potassium hydroxide solution (concentration 500 mmol / L). 200 mg of the corresponding sample catalyst was added to the water sample and stirred for 10 min to reach adsorption-desorption equilibrium. Then, 400 mg of potassium peroxymonosulfate complex salt (potassium peroxymonosulfate content 44%) was added and stirred at 25 °C. Unless otherwise specified, each test was performed in triplicate and the average value was used for the result summary.

[0097] Specific surface area and pore structure: 0.20 g of powder sample was placed in a specific surface area test sample tube and degassed under vacuum at 200℃ for 6 h. Subsequently, nitrogen adsorption-desorption isotherm tests were performed at liquid nitrogen temperature. The specific surface area was calculated using the gas adsorption BET method within the relative pressure range of 0.05-0.30. The total pore volume was converted from the adsorption amount at a relative pressure of 0.99. The average pore diameter was calculated using the BJH model of the desorption branch. The results are shown in Table 1.

[0098] Aberration-corrected transmission electron microscopy characterization: The catalyst prepared in Example 2 was characterized using aberration-corrected transmission electron microscopy in HAADF mode. The results are as follows: Figure 1 As shown.

[0099] Infrared spectroscopy characterization: The sulfonic acid aryl-grafted polydopamine-coated defective hollow tubular carbon nitride, the double-grafted polydopamine-coated defective hollow tubular carbon nitride, and the iron-containing precursor prepared in Example 2 were mixed with dry potassium bromide at a mass ratio of 1 mg:100 mg and then compressed into tablets. Infrared spectroscopy was used to analyze the mixture at 4000 cm⁻¹. -1 -400cm -1 Spectra were acquired within the range, with a resolution of 4 cm⁻¹. -1 The scan was performed 32 times; the results are as follows. Figure 2 As shown.

[0100] Iron content in the catalyst and iron leaching amount in the reaction solution: 50 mg of each powder sample was weighed and added to 10 mL of hydrochloric acid solution (concentration 1 mol / L). The mixture was digested in an 80℃ water bath for 2 h. After cooling, the volume was adjusted to 50 mL and filtered. The iron content was then determined. The iron content was quantified by inductively coupled plasma atomic emission spectrometry and expressed as a mass fraction. After 60 min of catalytic reaction, the reaction solution was filtered through a 0.45 μm filter membrane and acidified with hydrochloric acid solution (concentration 1 mol / L) to a pH less than 2. The iron ion concentration was then determined and quantified by inductively coupled plasma atomic emission spectrometry. The results are shown in Table 1.

[0101] Reaction rate and removal rate of triclocarban removal under near-neutral conditions: Using the catalysts obtained in the examples and comparative examples, a 2L system was established under the conditions described in the sample preparation section: initial triclocarban concentration 10 mg / L, pH 7, catalyst dosage 200 mg, potassium persulfate complex salt dosage 400 mg, reaction temperature 25℃, and reaction time 60 min. At t = 0, 5, 10, 20, 30, 45, and 60 min, 10 mL samples were taken respectively, and 200 mg of sodium thiosulfate pentahydrate was immediately added to terminate the reaction. After filtration, the triclocarban concentration was measured, and a removal curve was plotted. The triclocarban concentration was determined using liquid chromatography-mass spectrometry (LC-MS / MS) corresponding to the organic matter index in the standard test methods for drinking water to establish an external standard curve. The standard curve concentration points were set to 0, 0.5, 1, 2, 5, 10, and 20 mg / L, and the correlation coefficient was calculated. t Calculate the removal rate η = (C0 - C t ) / C0×100%, and simultaneously ln(C0 / C t A linear fit was performed on t to obtain the apparent rate constant k (min). -1 The results are shown in Table 1.

[0102] Total organic carbon removal rate and mineralization capacity: In the same reaction system for removing triclocarban under near-neutral conditions, samples were taken at t=0 min and t=60 min, and 200 mg of sodium thiosulfate pentahydrate was added to terminate the reaction. The total organic carbon was then measured using a total organic carbon analyzer. The total organic carbon removal rate was calculated as ρ = (TOC0 - TOC) / (TOC0 - TOC0). t The mineralization capacity was calculated using 0.05 / TOC0×100%; the results are shown in Table 1.

[0103]

[0104] Data Analysis:

[0105] As can be seen from the data in Examples 1-3 in Table 1, the single-atom iron-anchored hollow tubular carbon nitride catalyst prepared in this invention exhibits a high specific surface area and suitable pore structure parameters, while maintaining a low level of iron leaching in the reaction solution. This allows for rapid removal of triclocarban under near-neutral conditions while maintaining good total organic carbon removal capacity. The possible reasons are: the hollow tubular framework provides a one-dimensional mass transfer channel and enhances site exposure; the defect structure and polydopamine coating form a stable confinement layer, which facilitates the in-situ conversion of the iron-imidazolium coordination precursor into a dispersed iron-nitrogen coordination structure during segmented heat treatment; sulfonic acid aryl grafting improves interfacial wetting and participates in electronic structure regulation, enabling more efficient activation of the potassium peroxymonosulfate composite salt at the solid-liquid interface; and the microenvironment and spatial barrier introduced by octadecylamine further inhibit external surface enrichment and promote porosity. Therefore, the pore structure, interfacial chemistry, and iron coordination state form a synergistic match on the same support, simultaneously improving activity and stability.

[0106] As can be seen from the data in Table 1 for Example 2 and Comparative Example 1, the absence of ammonium chloride in step S2 significantly restricts the pore structure and specific surface area, leading to a decrease in the efficiency of subsequent interface modification and iron anchoring. The removal of triclocarban and total organic carbon is difficult to achieve the combined level of Example 2. This is because ammonium chloride promotes the formation of cavities and channels during heat treatment. Its absence results in denser pore walls, making it more difficult for polydopamine coating, sulfonic acid aryl grafting, and iron-imidazole coordination impregnation to penetrate the inner cavity, resulting in uneven site distribution and increased mass transfer resistance.

[0107] As can be seen from the data in Example 2 and Comparative Example 2 in Table 1, omitting the defect construction step causes a simultaneous decrease in reaction rate and mineralization capacity. The main reason is that defect sites are key anchoring points for the fixation and thermal conversion of iron-imidazolium coordination precursors. Insufficient defects weaken the formation and stability of the iron-nitrogen coordination structure, and some iron species are more likely to be in a weakly bound state, thereby reducing the interfacial activation efficiency and increasing the leaching risk.

[0108] As can be seen from the data in Example 2 and Comparative Example 3 in Table 1, although the samples may still maintain a high specific surface area without polydopamine coating, the removal rate and mineralization capacity do not increase accordingly, and iron leaching is significantly increased, showing a mismatch between structural parameters and stability. This is because polydopamine provides nitrogen-containing functional groups and an adhesion layer, enhances the effectiveness of sulfonic acid aryl grafting, and forms a coordination and confinement environment during the impregnation stage; after the removal of these groups, iron species are more likely to accumulate and dissolve on the outer surface, leading to a decrease in the utilization rate of active sites. Therefore, an unpredictable synergistic site-fixing effect exists between polydopamine and the defective hollow tubular framework.

[0109] As can be seen from the data in Table 1 for Example 2 and Comparative Example 4, omitting the sulfonic acid aryl grafting decreases the reaction rate and total organic carbon removal. This is because the sulfonic acid aryl group improves surface wetting and interfacial enrichment, making the potassium peroxymonosulfate complex salt more easily activated at the solid-liquid interface. Simultaneously, its electronic effect helps regulate the electronic environment around the iron-nitrogen coordination structure. Without this step, even with a relatively high iron content, it is difficult to form an efficient interfacial reaction microenvironment.

[0110] As can be seen from the data in Example 2 and Comparative Example 5 in Table 1, without the introduction of octadecylamine, the removal and mineralization capacity of triclocarban decreased while iron leaching increased, indicating that octadecylamine affects the spatial distribution and stabilization process of iron species. This may be because the long-chain structure of octadecylamine forms a microenvironment and spatial barrier before impregnation, promoting more complete entry of the iron-imidazole coordination solution into the hollow tube and inhibiting enrichment on the outer surface; its decomposition during the segmented heat treatment process may also contribute to porosity and defects. In the absence of octadecylamine, iron is more likely to aggregate on the outer surface and form weak binding sites, thereby reducing oxidation utilization and amplifying leaching.

[0111] As can be seen from the data in Example 2 and Comparative Example 6 in Table 1, after the vacuum-backpressure cycle was removed, iron leaching increased and mineralization capacity decreased. This is because the pressure cycle can drive the iron-imidazolium coordination solution into the lumen and pores, achieving enrichment and uniform distribution within the lumen; without it, iron is more likely to remain on the outer surface and form an easily soluble enriched structure, making the interfacial reaction microenvironment unstable and hindering the mineralization process.

[0112] As can be seen from the data in Example 2 and Comparative Example 7 in Table 1, omitting the low-temperature heat treatment weakens the reaction rate and mineralization capacity, and is accompanied by increased iron leaching. This is because the low-temperature stage facilitates the gradual carbonization and cross-linking of the polydopamine, sulfonic acid aryl, and octadecylamine layers, first forming a stable confined network, and then promoting the in-situ transformation of the iron-imidazolium coordination structure into dispersed iron-nitrogen coordination sites at the high-temperature stage. If the temperature is directly raised to high, the pyrolysis is too rapid, easily triggering iron migration and aggregation, producing weakly bound iron and amplifying the leaching risk. Therefore, the combination of segmented heat treatment and dilute hydrochloric acid washing has a synergistic stabilizing effect.

[0113] from Figure 1 It can be seen that the uniformly distributed bright spots are signals of high-Z element iron, and their size is close to that of dots, indicating that iron species are anchored on the coordination sites of the carbon nitride framework in a highly dispersed single-atom form; the density of bright spots in different regions is basically the same, indicating that the preparation method can achieve uniform loading on the entire hollow tubular framework.

[0114] from Figure 2 It can be seen that all three samples maintained typical characteristics. Infrared signature of the skeleton, including 1630cm -1 Nearby C=N stretching vibrations and 810 cm -1 The presence of the triazine ring breathing peak indicates that the defective hollow tubular carbon nitride backbone structure was completely preserved during the multi-step modification process; in the polydopamine-coated sample grafted with sulfonic acid aryl groups, the peaks at 1185 and 1035 cm⁻¹ were observed. -1 A pair of strong S=O stretching vibration peaks appeared at 2920 and 2850 cm⁻¹, confirming that the sulfonic acid group had been successfully introduced into the surface; after further introduction of octadecylamine, peaks at 2920 and 2850 cm⁻¹ were observed. -1 -CH2- stretching vibration and 1465, 720cm -1 The characteristic peaks were significantly enhanced, indicating that the long-chain alkyl groups were effectively fixed on the organic coating layer; in the iron-containing precursor, the above-mentioned CH and S=O characteristic peaks still existed, and the 1120 cm⁻¹ peak was also significantly enhanced. -1 New CN / C=N vibrational peaks appear on both sides and at 580 cm⁻¹ -1 The presence of Fe-N / Fe-O coordination vibration signals nearby indicates that the Fe-imidazolium coordination structure has been formed.

[0115] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of the different aspects of the invention as described above, which are not provided in detail for the sake of brevity.

Claims

1. A method for preparing a single-atom iron-anchored hollow tubular carbon nitride catalyst, characterized in that, Includes the following steps: (1) Melamine and cyanuric acid were dissolved in deionized water and mixed to form a precipitate. After solid-liquid separation, washing and drying, melamine-cyanuric acid precursor was obtained. (2) The melamine-cyanuric acid precursor was mixed with sodium chloride, potassium chloride and ammonium chloride and ground. It was then heat-treated under a nitrogen atmosphere. The resulting solid was then crushed, washed with hot water to remove salt and dried to obtain a hollow tubular carbon nitride carrier. (3) The hollow tubular carbon nitride carrier is added to potassium hydroxide aqueous solution for treatment. After solid-liquid separation, washing to neutrality and drying, it is heat-treated again under nitrogen atmosphere to obtain defective hollow tubular carbon nitride. (4) Disperse the defective hollow tubular carbon nitride in tris(hydroxymethyl)aminomethane buffer, add dopamine hydrochloride under alkaline conditions and polymerize to form a coating layer, and obtain polydopamine-coated defective hollow tubular carbon nitride after solid-liquid separation, washing and drying. (5) The diazonium salt solution is generated by diazotizing p-aminobenzenesulfonic acid. The diazonium salt solution is then coupled with the hollow tubular carbon nitride with defects coated with polydopamine to introduce sulfonic acid aryl groups. After solid-liquid separation, washing and drying, sulfonic acid aryl grafted polydopamine-coated hollow tubular carbon nitride with defects is obtained. (6) Octadecylamine was introduced into and reacted with polydopamine-coated defect hollow tubular carbon nitride grafted with sulfonic acid aryl groups. After solid-liquid separation, washing and drying, double-grafted polydopamine-coated defect hollow tubular carbon nitride was obtained. (7) Prepare an imidazole solution and a ferric chloride hexahydrate solution and mix them to obtain an iron-imidazole coordination solution. Then, the double-grafted polydopamine-coated hollow tubular carbon nitride is brought into contact with the iron-imidazole coordination solution and subjected to vacuum-backpressure cyclic impregnation. The solvent is then removed and the solution is dried to obtain an iron-containing precursor. (8) The iron-containing precursor was subjected to segmental heat treatment and cooling under a nitrogen atmosphere, followed by acid washing, washing and drying to obtain a single-atom iron-anchored hollow tubular carbon nitride catalyst. In step (5), the mass ratio of p-aminobenzenesulfonic acid to polydopamine-coated hollow tubular carbon nitride in defects is 0.4-0.6:1.6-2.4; in step (6), the mass ratio of octadecylamine to sulfonic acid-based aryl-grafted polydopamine-coated hollow tubular carbon nitride in defects is 0.24-0.36:1.6-2.4; in step (7), the mass ratio of imidazole, ferric chloride hexahydrate to double-grafted polydopamine-coated hollow tubular carbon nitride in defects is 0.08-0.12:0.024-0.036:1.6-2.

4.

2. The method for preparing a single-atom iron-anchored hollow tubular carbon nitride catalyst according to claim 1, characterized in that, In step (1), the mass ratio of melamine to cyanuric acid is 1:

1.

3. The method for preparing a single-atom iron-anchored hollow tubular carbon nitride catalyst according to claim 1, characterized in that, In step (2), the mass ratio of melamine-cyanuric acid precursor, sodium chloride, potassium chloride and ammonium chloride is 1:10:10:

1.

4. The method for preparing a single-atom iron-anchored hollow tubular carbon nitride catalyst according to claim 1, characterized in that, In step (2), the nitrogen flow rate during heat treatment under a nitrogen atmosphere is 180-220 mL / min, the heating rate is 1.5-2.5℃ / min, the heat treatment temperature is 530-570℃ and the holding time is 3-5 h; the hot water washing temperature is 75-85℃, the drying temperature is 75-85℃ and the drying time is 10-14 h.

5. The method for preparing a single-atom iron-anchored hollow tubular carbon nitride catalyst according to claim 1, characterized in that, In step (3), the heating rate of the second heat treatment is 4-6℃ / min, the heat treatment temperature is 480-520℃ and the heat treatment is held for 1.5-2.5h.

6. The method for preparing a single-atom iron-anchored hollow tubular carbon nitride catalyst according to claim 1, characterized in that, In step (4), the mass ratio of the hollow tubular carbon nitride in the defect to dopamine hydrochloride is 1.6-2.4:0.32-0.

48.

7. The method for preparing a single-atom iron-anchored hollow tubular carbon nitride catalyst according to claim 1, characterized in that, In step (7), the vacuum-backpressure cycle impregnation is performed by: evacuating to -80±10kPa and maintaining it for 8-12 minutes, then introducing nitrogen to return to normal pressure, and repeating the vacuum-backpressure cycle 2-4 times.

8. The method for preparing a single-atom iron-anchored hollow tubular carbon nitride catalyst according to claim 1, characterized in that, In step (8), the segmented heat treatment conditions are as follows: nitrogen flow rate 180-220 mL / min, temperature increased to 240-260℃ at 1.5-2.5℃ / min and held for 1.5-2.5h, then temperature increased to 500-540℃ at 4-6℃ / min and held for 1.5-2.5h before cooling.

9. A single-atom iron-anchored hollow tubular carbon nitride catalyst, characterized in that, It is obtained by the preparation method of the single-atom iron-anchored hollow tubular carbon nitride catalyst according to any one of claims 1-8.

10. The use of the single-atom iron-anchored hollow tubular carbon nitride catalyst of claim 9 in activating persulfate to degrade organic pollutants in water.

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