Co@C / FHP catalyst, preparation method and application thereof

Abstract

The application belongs to the technical field of catalytic dye degradation, and particularly relates to a Co@C / FHP catalyst and a preparation method and application thereof. The preparation method comprises the following steps: dissolving Co(NO3)2.6H2O and terephthalic acid in DMF, adding fruit hair of Platanus (FHP), carrying out hydrothermal reaction, washing and drying, and then calcining under N2 atmosphere to obtain the Co@C / FHP catalyst. In the application, FHP is used as a carrier, Co-MOF is in-situ grown on the surface of the carrier, FHP is carbonized into a porous carbon carrier after pyrolysis, and Co-MOF is converted into metal cobalt nanoparticles wrapped by a carbon layer. The catalyst has the advantages of high dispersion degree of active sites, good stability and good conductivity, and can efficiently activate persulfate to degrade organic pollutants.

Description

Technical Field

[0001] This invention belongs to the field of catalytic dye degradation technology, and specifically relates to a Co@C / FHP catalyst, its preparation method, and its application. Background Technology

[0002] Advanced oxidation processes (AOPs) are based on the generation of highly oxidizing free radicals (such as sulfate radicals SO42-). - • and hydroxyl radicals (·OH) can effectively degrade organic pollutants, among which the activation of persulfate (PMS) is a current research hotspot.

[0003] Cobalt (Co)-based catalysts are among the most effective homogeneous catalysts for activating PMS, but they suffer from problems such as easy leaching, secondary pollution, and difficult recovery. Immobilizing cobalt species on a support to prepare heterogeneous catalysts is an ideal solution. Metal-organic frameworks (MOFs), due to their high specific surface area and tunable structure, can serve as ideal precursors. Carbon-coated metal nanoparticles can be prepared through high-temperature pyrolysis, which can effectively prevent the leaching and aggregation of cobalt particles while utilizing the excellent conductivity of carbon materials to promote catalytic reactions.

[0004] However, traditional MOF-derived carbon materials are prone to particle aggregation during pyrolysis, leading to a reduction in active sites. Therefore, developing a heterogeneous catalyst that can highly disperse and stabilize cobalt active sites, and which is simple to prepare and inexpensive, is of great significance for advancing the practical application of PMS activation technology. Summary of the Invention

[0005] The first objective of this invention is to provide a method for preparing a Co@C / FHP catalyst, comprising the following steps:

[0006] S1. Dissolve Co(NO3)2·6H2O and 0.4 mmol of terephthalic acid in DMF, stir at room temperature to dissolve, add fruit hair of Platanus orientalis (FHP), stir to disperse evenly, and then transfer to a reaction vessel for hydrothermal reaction.

[0007] S2. The obtained product was centrifuged at 8000 rpm for 10 min, the supernatant was discarded, and the product was washed once with DMF and then twice with anhydrous ethanol. The supernatant was discarded, and the product was dried in a vacuum drying oven at 80℃ for 24 h to obtain Co-MOF.

[0008] S3. Place the above product in a tube furnace and calcine it under N2 atmosphere. The product is the Co@C / FHP catalyst.

[0009] Furthermore, the molar ratio of Co(NO3)2·6H2O to terephthalic acid is 1.5:1.

[0010] Furthermore, the hydrothermal reaction conditions were 120℃ for 12 hours.

[0011] Furthermore, the calcination conditions were: calcination at 700-900℃ for 3 hours, with a heating rate of 5℃ / min. Temperatures exceeding 900℃ would damage the carbon support structure, weakening its ability to fix and disperse cobalt particles.

[0012] A second objective of this invention is to provide a Co@C / FHP catalyst prepared by the aforementioned method. The catalyst uses FHP pyrolysis products to form a carbon support. The Co-MOF undergoes pyrolysis, where the ligands are carbonized to form a carbon shell (Co@C) encapsulating cobalt nanoparticles, and the central cobalt ions are reduced to metallic cobalt nanoparticles.

[0013] A fourth objective of this invention is to provide the application of the catalyst in the degradation of various organic pollutants by activating PMS.

[0014] Furthermore, the organic pollutant is one of Ponceau 2R, tetracycline, and Rhodamine B.

[0015] Beneficial technical effects of the present invention:

[0016] This invention innovatively grows cobalt-based metal-organic frameworks (Co-based MOFs) in situ on the surface of the velvety hairs of Platanus orientalis fruit, and prepares a Co@C / FHP composite catalyst with a core-shell heterostructure through a controlled calcination process. The dual role of the FHP framework and the MOF precursor effectively prevents the aggregation of cobalt nanoparticles during high-temperature processing, exposing more active sites. The carbon shell and carbon support work together to firmly fix the cobalt particles, preventing them from being lost during the reaction, thus allowing the catalyst to maintain high activity even after 12 cycles. The entire Co@C / FHP composite catalyst is a conductive carbon network, facilitating rapid electron transfer to the cobalt active sites, thereby efficiently activating PMS. In other words, FHP and MOF, through high-temperature pyrolysis, together "transform" into a synergistic, high-performance catalytic system.

[0017] Thanks to the tandem regulation effect of the fruit villi (FHP) of Platanus orientalis, this catalyst can effectively modulate the d-band center position of cobalt species, significantly accelerate the directional transfer of electrons to PMS, and exhibit excellent catalytic performance in the degradation of typical organic pollutants such as Rhodamine B and tetracycline.

[0018] The Co@C / FHP-800 catalyst (calcined at 800℃) prepared in this invention exhibits a degradation rate of up to 99% within 4 minutes when activating PMS to degrade Ponceau 2R, far superior to samples prepared at 700℃ and 900℃, demonstrating optimal catalytic activity. After 12 consecutive cycles, the degradation rate of Ponceau 2R remains above 94.3%, and XRD patterns show no change in the catalyst's crystal structure before and after the reaction, proving its extremely high stability. This catalyst not only exhibits efficient degradation of azo dyes (Ponceau 2R, Rhodamine B) but also demonstrates excellent degradation ability for antibiotics (tetracycline), achieving a degradation rate of up to 90% within 10 minutes, indicating broad applicability. Attached Figure Description

[0019] Figure 1 The XRD patterns are those of Co-MOF / FHP after calcination at 700, 800 and 900 °C in a nitrogen atmosphere.

[0020] Figure 2 The image shows a scanning electron microscope image of Co@C / FHP-800 (a) and the distribution diagrams of the three elements C, Co, and O (bd).

[0021] Figure 3 Transmission electron microscopy image (a) of Co@C / FHP-800 and magnified view (b) of the lattice spacing corresponding to the (111) crystal plane of Co.

[0022] Figure 4 The catalytic degradation curve of Ponceau Red dye by Co@C / FHP is shown.

[0023] Figure 5 XRD patterns of Co@C / FHP-800, the catalyst with the best activity, before and after the catalytic reaction of Ponceau Rx.

[0024] Figure 6 The figure shows the effect of the optimal catalyst Co@C / FHP-800 on 13 cycles of Ponceau Red.

[0025] Figure 7 The catalytic degradation diagram of tetracycline and rhodamine B by Co@C / FHP-800, the catalyst with the best activity. Detailed Implementation

[0026] Example 1: Preparation of Co@C / FHP-700

[0027] Dissolve 0.6 mmol Co(NO3)2·6H2O and 0.4 mmol H2BDC (terephthalic acid) together in 50 mL of DMF solution and stir at room temperature. Add 40 mg FHP (fruit hairs of Platycodon grandiflorus), stir to disperse evenly, and then transfer to a 100 mL reaction vessel and hydrothermally heat in an oven at 120 °C for 12 h.

[0028] The obtained product was centrifuged at 8000 rpm for 10 min, the supernatant was discarded, and the product was washed once with DMF, then twice with anhydrous ethanol. The supernatant was discarded, and the product was dried in a vacuum drying oven at 80 °C for 24 h. The product was then placed in a tube furnace and calcined at 700 °C for 3 h under a N2 atmosphere (heating rate of 5 °C / min). The product was designated Co@C / FHP-700.

[0029] Example 2 Preparation of Co@C / FHP-800

[0030] Dissolve 0.6 mmol Co(NO3)2·6H2O and 0.4 mmol H2BDC (terephthalic acid) together in 50 mL of DMF solution and stir at room temperature. Add 40 mg FHP (fruit hairs of Platycodon grandiflorus), stir to disperse evenly, and then transfer to a 100 mL reaction vessel and hydrothermally heat in an oven at 120 °C for 12 h.

[0031] The obtained product was centrifuged at 8000 rpm for 10 min, the supernatant was discarded, and the product was washed once with DMF, then twice with anhydrous ethanol. The supernatant was discarded, and the product was dried in a vacuum drying oven at 80 °C for 24 h. The product was then placed in a tube furnace and calcined at 800 °C for 3 h under a N2 atmosphere (heating rate of 5 °C / min). The product was designated Co@C / FHP-800.

[0032] Example 3 Preparation of Co@C / FHP-900

[0033] Dissolve 0.6 mmol Co(NO3)2·6H2O and 0.4 mmol H2BDC (terephthalic acid) together in 50 mL of DMF solution and stir at room temperature. Add 40 mg FHP (fruit hairs of Platycodon grandiflorus), stir to disperse evenly, and then transfer to a 100 mL reaction vessel and hydrothermally heat in an oven at 120 °C for 12 h.

[0034] The obtained product was centrifuged at 8000 rpm for 10 min, the supernatant was discarded, and the product was washed once with DMF, then twice with anhydrous ethanol. The supernatant was discarded, and the product was dried in a vacuum drying oven at 80 °C for 24 h. The product was then placed in a tube furnace and calcined at 900 °C for 3 h under a N2 atmosphere (heating rate of 5 °C / min). The product was designated Co@C / FHP-900.

[0035] The Co@C / FHP-700, Co@C / FHP-800, and Co@C / FHP-900 obtained in Examples 1-3 were characterized as follows:

[0036] Figure 1 The XRD patterns of Co-MOF / FHP after calcination at 700, 800 and 900 °C in a nitrogen atmosphere are shown, corresponding to PDF cards 15-0806 for Co and 26-1079 for C.

[0037] No obvious C-attributed peaks were observed on the Co@C / FHP-700 catalyst, while peaks at approximately 26° on the (002) crystal plane of C were observed on both Co@C / FHP-800 and Co@C / FHP-900 catalysts. This indicates that FHP undergoes carbonization under a high-temperature inert atmosphere. Highly carbonized materials exhibit superior electrical conductivity, which can enhance the activity of the catalyst.

[0038] Figure 2 a is a STEM image of Co@C / FHP-800. The image shows that Co@C particles are attached to the carbonized FHP surface, and the elements are evenly distributed. Figure 2 bd). Figure 3 a is a transmission electron microscope image of Co@C / FHP-800, with the magnified portion corresponding to the lattice spacing of the (111) crystal plane of Co. Figure 3 b) is consistent with the XRD pattern results.

[0039] Example 4

[0040] Catalyst degradation wastewater test:

[0041] Five mg of Co@C / FHP-700, Co@C / FHP-800, and Co@C / FHP-900 were respectively added as catalysts to 100 mL of a 50 mg / L Ponceau 2R azo dye solution. The solution was incubated in a 30°C water bath at 300 rpm for 20 min. PMS was then added to initiate the reaction. Every 0.5 min, 3 mL of water was taken and ascorbic acid was added to quench the free radical reaction. The concentrations were determined using a UV-Vis spectrophotometer after filtration. Results are shown in [link to results]. Figure 4 Co@C / FHP-700 degrades 82% of azo dyes within 4 minutes. Co@C / FHP-800 degrades 99% of azo dyes within 4 minutes. Co@C / FHP-700 degrades 93% of azo dyes within 4 minutes. The degradation rate constants of Co@C / FHP-700, Co@C / FHP-800, and Co@C / FHP-900 are shown in Table 1.

[0042] Table 1. Effect of different calcination temperatures on the rate constant of Ponceau degradation.

[0043] Different calcination temperatures Rate constant / min Co@C / FHP-700 0.405 Co@C / FHP-800 1.213 Co@C / FHP-900 0.704

[0044] Figure 5 The XRD patterns of the optimally active catalyst, Co@C / FHP-800, before and after the catalytic reaction with Ponceau Rx show no change in peak activity. This indicates that the catalytic experiment does not affect the catalyst material itself, and it can be recycled.

[0045] After the initial degradation experiment, 3.0 mL of a 1667 mg / L Ponceau Rx solution was added again to the original Co@C / FHP-800 reaction system (to bring the Ponceau Rx concentration in the reaction system to 50 mg / L). PMS was then added to initiate the reaction, and the mixture was stirred at 300 rpm with a magnetic stirrer. At 3.0 min, 3 mL of the suspension was taken and ascorbic acid was added to quench the free radical reaction. Following the above steps, the catalyst was subjected to 12 cycles of use testing, i.e., the 13th Ponceau Rx degradation test. The degradation rate of Ponceau Rx still reached 94.3%. The results are shown below. Figure 6 .

[0046] Example 5

[0047] 5 mg of Co@C / FHP-800 was added as a catalyst to 100 mL of a 20 mg / L tetracycline solution. The mixture was incubated in a 30°C water bath and stirred at 300 rpm for 20 min. PMS was then added to initiate the reaction. Every 0.5 min, 3 mL of water was taken and ascorbic acid was added to quench the free radical reaction. The concentration was determined using a UV-Vis spectrophotometer after filtration through a filter membrane.

[0048] Example 6

[0049] 5 mg of Co@C / FHP-800 was added as a catalyst to 100 mL of a 30 mg / L Rhodamine B solution. The mixture was incubated in a 30°C water bath and stirred at 300 rpm for 20 min. PMS was then added to initiate the reaction. Every 0.5 min, 3 mL of water was taken and ascorbic acid was added to quench the free radical reaction. The solution was filtered through a membrane and the concentration was determined using a UV-Vis spectrophotometer.

[0050] The results of Examples 5 and 6 are shown in Figure 7 Co@C / FHP-800 exhibits extremely high degradation efficiency for the dye molecule Rhodamine B, achieving a degradation rate of 100% within 3 minutes. While its final degradation efficiency for the antibiotic tetracycline is also high (90%), it requires a longer reaction time (10 minutes). In summary, Co@C / FHP-800 can effectively activate PMS and rapidly degrade two different types of organic pollutants.

Claims

1. A Co@C / FHP catalyst, characterized in that: The catalyst forms a carbon support using FHP pyrolysis products. Co-MOF undergoes pyrolysis, where the ligands are carbonized to form a carbon shell that encapsulates cobalt nanoparticles, and the cobalt ions at the metal center are reduced to metallic cobalt nanoparticles. The preparation method of the Co@C / FHP catalyst includes the following steps: S1. Dissolve 0.6 mmol Co(NO3)2·6H2O and 0.4 mmol terephthalic acid in DMF and stir at room temperature. Add 40 mg of fruit hairs FHP from Platycodon grandiflorus and stir to disperse evenly. Then transfer to a reaction vessel for hydrothermal reaction. The hydrothermal reaction conditions are 120℃ for 12 h. S2. The obtained product was centrifuged at 8000 rpm for 10 min, the supernatant was discarded, and the product was washed once with DMF and then twice with anhydrous ethanol. The supernatant was discarded, and the product was dried in a vacuum drying oven at 80℃ for 24 h to obtain Co-MOF. S3. Place the above product in a tube furnace and calcine it under N2 atmosphere. The product is the Co@C / FHP catalyst. The calcination conditions are: calcination at 800℃ for 3 hours, with a heating rate of 5℃ / min.

2. The application of the Co@C / FHP catalyst as described in claim 1 in the degradation of organic pollutants by activated PMS, characterized in that: The organic pollutant is one of Ponceau 2R, tetracycline, and Rhodamine B.

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