Transition metal cluster-single atom complex catalyst and application thereof

Abstract

The application discloses a transition metal cluster-single atom composite catalyst, wherein transition metals are loaded on the surface of a carbon layer of a fixed carrier in the form of clusters and single atoms, and the fixed carrier is prepared by pyrolysis of a metal-organic framework assembled by taking zirconium ions as metal centers and organic ligands (HOOC)CH(NH2)-(X1)m-(X2)n-(X3)p-COOH. The composite catalyst anchors transition metals by the coordination of amino groups on the ligand branch, can generate metastable persulfate species with stronger oxidation capacity, can shorten the mass transfer distance between pollutants and active species, and significantly accelerates the degradation kinetics rate. The application can efficiently degrade organic pollutants in water based on a non-radical path, and can effectively avoid the free radical quenching effect caused by inorganic salts, and thus is especially suitable for salt-containing wastewater treatment.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of water treatment, and particularly relates to a transition metal cluster-single atom composite catalyst and application thereof in efficient activation of persulfate to degrade toxic organic pollutants in salt-containing wastewater. TECHNICAL BACKGROUND

[0002] In recent years, toxic organic pollutants such as antibiotics and volatile phenols contained in wastewater have caused serious threats to water ecological safety. Although Fenton oxidation technology has been widely used in organic wastewater treatment, anions existing in salt-containing wastewater can severely consume hydroxyl radicals generated in the reaction, thereby greatly reducing the operation efficiency of the Fenton method. Therefore, it is urgent to develop new oxidation technologies to achieve efficient control of toxic organic pollutants in salt-containing organic wastewater.

[0003] Heterogeneous persulfate (PS)-based advanced oxidation technology has advantages such as wide pH application range and reusable catalyst compared with traditional Fenton technology. Single atom catalyst (SAC) reduces the active site size to atomic level, and the unsaturated coordination structure of the metal and the theoretically 100% atom utilization rate make it show significantly improved catalytic activity in activating PS to degrade organic matter. Zirconium-based metal organic framework can stabilize metal atoms through coordination anchoring and micropore confinement effect, and is an excellent precursor for synthesizing SAC. Chinese patent CN113198511B discloses a nitrogen-doped carbon-supported Fe-Co bimetallic single atom catalyst for efficiently activating persulfate and a preparation method thereof. The catalyst loaded with Fe-Co bimetallic single atoms is prepared by taking UIO-66-NH2(Zr) as a carrier, and the degradation rate of sulfamethoxazole by the catalyst through activation of PS is 96.8% within 6 min; however, a large amount of N,N-dimethylformamide (DMF) organic solvent is used in the synthesis process, and the ligand 2-amino terephthalic acid is expensive, which is not conducive to the green and economic synthesis of SAC.

[0004] In addition, due to the single active site of SAC and low metal loading, it is easy to be limited by adsorption correlation, which makes it difficult to further improve the catalytic activity, so the catalyst coexisting with nanoclusters and single atoms has attracted widespread attention. Wang et al. (Applied Catalysis B: Environmental, 2023, 329, 122569) used zinc ions as metal active centers and 2-methyl imidazole as organic ligands to form ZIF-8, and then adjusted the content of Zn / Co to control the size of the atomic center of the catalyst. With the increase of cobalt content, cobalt single atoms are easy to aggregate to form cobalt nanoparticles during high-temperature calcination due to high energy, and it is difficult to maintain the coexistence state of nanoclusters and single atoms. Mo et al. (PNAS, 2023, 120, 2300281120) successfully constructed Fe ACs and Fe-N4 composite active sites using TiO2 as a carrier. However, after 5 cycles of reaction, the removal rate of tetracycline decreased from 90.81% to 76.53%, and the reaction process was affected by the coexisting inorganic anions.

[0005] In summary, the carrier has an important influence on the preparation of catalysts coexisting with nanoclusters and single atoms, but the research on this is still limited. Therefore, there is an urgent need to develop efficient and stable catalysts coexisting with nanoclusters and single atoms to achieve the degradation of toxic organic pollutants in salt-containing organic wastewater. SUMMARY

[0006] In order to overcome the above-mentioned deficiencies in the use and technology of existing heterogeneous transition metal catalysts, the purpose of the present application is to provide a transition metal cluster-single atom composite catalyst and its application.

[0007] The metal-organic framework formed by using zirconium ions as metal centers and low-valence nitrogen-containing organic ligands is used to adsorb transition metal ions by the coordination action of the amino group on the ligand branch and then calcined at high temperature to prepare a transition metal cluster-single atom composite catalyst. This method is low in price, safe and economical, and can be applied to efficiently degrade toxic organic pollutants in salt-containing wastewater.

[0008] To achieve the above-mentioned purpose, the present application provides the following technical solutions:

[0009] A transition metal cluster-single atom complex catalyst, transition metal is loaded on the surface of carbon layer of fixed carrier in the form of cluster and single atom, the fixed carrier is metal-organic framework (Zr-DAAMOF) pyrolyzed by assembling zirconium ion as metal center and organic ligand (HOOC)CH(NH2)-(X1)m-(X2)n-(X3)p-COOH, wherein X1, X2, X3 are the same or different, selected from -CH2-, -S-, -S-S- or -O- substituted with one or more of H, C1-C6 alkyl, C1-C6 alkoxy, hydroxyl, amino, halogen, nitro, m, n, p are the same or different, selected from 0, 1 or 2.

[0010] Preferably, the transition metal is selected from one or more of cobalt, iron, copper and manganese.

[0011] Preferably, the organic ligand is selected from one or more of alpha amino acids with two carboxyl functional groups, such as aspartic acid, glutamic acid and cystine.

[0012] The complex catalyst described in the application is prepared by the following method:

[0013] S1. The metal-organic framework Zr-DAAMOF assembled by zirconium ion as metal center and organic ligand (HOOC)CH(NH2)-(X1)m-(X2)n-(X3)p-COOH is stirred in transition metal ion aqueous solution, washed with water and dried to obtain Zr-DAA MOF adsorbed with transition metal ions;

[0014] S2. The Zr-DAA MOF adsorbed with transition metal ions is calcined in inert gas to obtain the transition metal cluster-single atom complex catalyst derived from Zr-DAA MOF.

[0015] Preferably, the mass concentration ratio of Zr-DAA MOF to transition metal ions in step S1 is 1:10-10:1.

[0016] Preferably, the Zr-DAA MOF in step S1 is obtained by the following method: aspartic acid and zirconium salt are dissolved in water, heated to reflux at 100-200℃ for 1-8h; the collected product is washed with water and dried to obtain Zr-DAAMOF; the molar concentration ratio of aspartic acid to zirconium salt is 1:5-5:1; the zirconium salt is zirconium tetrachloride or zirconium oxychloride.

[0017] Preferably, the mass concentration of Zr-DAA MOF in transition metal ion aqueous solution in step S1 is 1-5g / L; the stirring time is 1-12h; the drying temperature is 60-80℃ and the time is 24-80h.

[0018] Preferably, the transition metal ions in step S1 are one or more of cobalt ions, iron ions, copper ions, and manganese ions, and the concentration is 1-30 mmol / L.

[0019] Preferably, the inert gas in step S2 is nitrogen or argon; the calcination temperature is 600-900℃, the calcination time is 1-8h, and the heating rate is 1-10℃ / min.

[0020] Another object of the present application is to provide the use of the composite catalyst in a heterogeneous advanced oxidation process.

[0021] A specific application of the present application is to use the composite catalyst to activate persulfate to degrade toxic organic pollutants in wastewater, and the organic pollutants are selected from one or more of tetracycline, rhodamine B, bisphenol A, and phenol.

[0022] The persulfate is one or more of potassium peroxymonosulfate, sodium peroxymonosulfate, potassium persulfate, and sodium persulfate.

[0023] Further, the wastewater can also contain inorganic salts, and the anions of the inorganic salts are selected from one or more of chloride ions, sulfate ions, bicarbonate ions, and dihydrogen phosphate ions.

[0024] Preferably, the concentration of the inorganic salt ions in the water body is 0.1-600mmol / L.

[0025] Preferably, the mass ratio of the Zr-DAAMOF-derived transition metal cluster-single atom composite catalyst, persulfate, and organic pollutants is 1-5:2-10:1.

[0026] Compared with the prior art, the present application has the following advantages:

[0027] (1) The present application first uses Zr-DAAMOF as a porous carbon precursor to prepare a transition metal cluster-single atom composite catalyst, and the organic ligand does not contain a benzene ring or a heterocycle, but is a short-chain aliphatic hydrocarbon ligand, which forms a metal-organic framework with zirconium having a small pore size. Therefore, the distance between the transition metal ions adsorbed into the Zr-DAAMOF is shorter than that between the metal ions in the MOF containing a benzene ring or a heterocycle, and it is easier for them to approach each other to form metal-metal bonds during pyrolysis, thereby generating clusters. At the same time, due to the micropore confinement or coordination anchoring effect, part of the metals are distributed as single atoms, thereby forming a spatially adjacent cluster and single atom coexisting structure.

[0028] (2) The atomic cluster formed in situ by the catalyst prepared by the method can transfer electrons from the carbon carrier to the single atom, which causes the local electron density of the single atom site to increase, so that the PS adsorbed on the single atom site obtains more electrons, the activation degree is improved, and a metastable PS species with stronger oxidation capacity is generated; and the catalyst has a porous structure and a large specific surface area, which is beneficial to the rapid enrichment of various toxic organic pollutants, so that the pollutants and the metastable PS react on the surface of the catalyst, the mass transfer distance between the pollutants and the active species is greatly shortened, and the degradation kinetic rate is significantly accelerated.

[0029] (3) The Zr-DAA MOF derived transition metal cluster-single atom composite catalyst prepared by the method is suitable for a high-salt environment, does not generate free radicals in the process of efficiently activating persulfate, and can fundamentally avoid the inhibition of the catalytic reaction by inorganic salts in the environment through the free radical quenching effect, thereby improving the utilization rate of PS. In addition, the high-concentration inorganic salt ions in seawater can react with the metastable PS, further enriching the types of active species, thereby strengthening the oxidation of organic matter, and thus being suitable for the rapid removal of toxic organic pollutants in seawater and other high-salt water bodies. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 It is a spherical aberration-corrected scanning transmission electron microscope (AC-STEM) image of the transition metal cluster-single atom composite catalyst of the present application.

[0031] Figure 2 It is an effect diagram of the activation of persulfate by different catalysts in the present application to degrade tetracycline.

[0032] Figure 3 It is an effect diagram of the activation of persulfate by the transition metal cluster-single atom composite catalyst of the present application to degrade tetracycline in the presence of 600 mmol / L different inorganic salts.

[0033] Figure 4 It is an effect diagram of the continuous operation of a column reactor by the transition metal cluster-single atom composite catalyst of the present application to degrade tetracycline in different water environments. DETAILED DESCRIPTION

[0034] In order to make the purpose and advantages of the present application more clear and explicit, the present application will be specifically described below in combination with examples. It should be understood that the following text is only used to describe one or several specific embodiments of the present application, and does not strictly limit the specific protection scope claimed by the present application.

[0035] Example 1

[0036] A preparation method of a Zr-DAA MOF derived transition metal cluster-single atom composite catalyst, the specific steps of which are as follows:

[0037] S1. 14 g of aspartic acid and 11.65 g of zirconium tetrachloride were dispersed in 50 mL of ultrapure water, respectively, and then mixed and stirred at 25 °C for 15-30 min until dissolved, and then the resulting mixed solution was heated to reflux at 120 °C for 4 h. The white solid product was collected by centrifugation and washed with water three times, and dried at 60 °C under vacuum for 24 h to obtain the Zr-DAA MOF precursor.

[0038] S2. 500 mg of the Zr-DAA MOF precursor obtained in step S1 was dispersed in 90.4 mL of ultrapure water, and the pH of the solution was adjusted to 5.00-6.00, then 9.6 mL of 125 mmol / L CoCl2·6H2O aqueous solution was added to make the concentration of cobalt ions 12 mmol / L, and stirred at 25 °C for 4 h. The pink precipitate product was collected by centrifugation and dried at 60 °C under vacuum for 24 h after washing with water to obtain the Zr-DAA MOF adsorbed with cobalt ions.

[0039] S3. The Zr-DAA MOF adsorbed with cobalt ions obtained in step S2 was placed in a crucible, covered with a lid and transferred to a tube furnace, and calcined at 900 °C for 2 h at a rate of 5 °C / min under the protection of argon inert atmosphere. After the reaction was completed, the tube furnace was naturally cooled to room temperature to obtain a Zr-DAA MOF derived transition metal cluster-single atom composite catalyst.

[0040] The aberration-corrected scanning transmission electron microscopy (AC-STEM) image of the Zr-DAA MOF derived transition metal cluster-single atom composite catalyst obtained in step S3 of the example is shown in Figure 1 It can be seen that cobalt nanoclusters coexist with single atoms on the surface of the catalyst, the catalyst has a porous structure and a large specific surface area (329.64 m 2 / g), and the cobalt loading is 1.12 wt%.

[0041] Example 2

[0042] Tetracycline is widely used in medicine and animal husbandry as a broad-spectrum antibiotic, and its residues in environmental water pose a great threat to human health and the ecological environment. In this example, the Zr-DAA MOF derived transition metal cluster-single atom composite catalyst obtained in Example 1 was used to activate the potassium peroxymonosulfate composite salt to test its degradation performance on tetracycline. The specific experimental conditions were as follows: 10 mg of catalyst was placed in 100 mL of tetracycline solution, the concentration of tetracycline was 20 mg / L, the initial pH was 4.55 and the pH was not adjusted during the experiment, and the experimental temperature was 25 °C. After the catalyst was ultrasonically dispersed for 20 min, it was magnetically stirred for 10 min to reach adsorption-desorption equilibrium, then 0.4 mL of 20 g / L potassium peroxymonosulfate composite salt solution was added to initiate the reaction, and the degradation results are shown inFigure 2 The degradation rate of tetracycline is 97.5% within 10 minutes under the same experimental conditions as in Example 2, which verifies the high efficiency of the catalyst.

[0043] Example 3

[0044] The same as Example 1, except that the organic ligand used in step S1 is glutamic acid.

[0045] The degradation rate of tetracycline is 97.5% within 10 minutes under the same experimental conditions as in Example 2, which verifies the high efficiency of the catalyst.

[0046] Example 4

[0047] The same as Example 1, except that:

[0048] In step S2, CoCl2·6H2O is replaced by FeCl3·6H2O. 9.6 mL of FeCl3·6H2O aqueous solution with a concentration of 125 mmol / L is added to make the concentration of iron ions 12 mmol / L.

[0049] The degradation rate of tetracycline is 97.5% within 10 minutes under the same experimental conditions as in Example 2, which verifies the high efficiency of the catalyst.

[0050] Example 5

[0051] The same as Example 2, except that the persulfate salt used is potassium persulfate.

[0052] The degradation rate of tetracycline is 97.5% within 10 minutes under the same experimental conditions as in Example 2, which verifies the high efficiency of the catalyst.

[0053] Example 6

[0054] To test the degradation effect of the catalyst on different toxic organic pollutants, the same as Example 2, except that the organic pollutants are rhodamine B, bisphenol A and phenol, respectively. Under the same experimental conditions as in Example 2, the degradation rates of these three pollutants within 10 minutes are 100.0%, 99.8% and 97.6%, respectively, indicating that the catalyst has excellent removal effect on various toxic organic pollutants in water.

[0055] Example 7

[0056] To test the degradation effect of the catalyst on tetracycline in the presence of high concentration of inorganic salts, the treatment method is the same as Example 2, except that Cl - , SO4 2- , HCO3 - and H2PO4 -The inorganic salt concentration was 600 mmol / L. The results are shown in Figure 3 Table 1. The degradation rates of tetracycline within 10 min were 100.0%, 94.1%, 100.0%, and 96.4%, respectively, indicating that the catalyst can still efficiently remove tetracycline under the coexistence of high concentrations of inorganic salts; due to the high concentrations of Cl- and HCO3 - The remaining persulfate can activate active chlorine species, carbonate radicals, and hydroxyl radicals to promote the degradation of tetracycline.

[0057] Example 8

[0058] To evaluate the application potential of the catalyst in actual water bodies, 10 mg / L tetracycline solutions were prepared as water samples A using ultrapure water, tap water, Yangshan Lake water, and Bohai water as solvents, respectively; 0.2 g / L potassium hydrogen persulfate composite salt solution B was prepared using ultrapure water as a solvent; and a column reactor (Ф20 x 200 mm) was built using 100 mg of the catalyst as a filler. Solution A and solution B were introduced into the column reactor at a flow rate of 0.5 mL / min by using a peristaltic pump for reaction, and a constant-temperature circulating water tank was used to maintain the temperature of the column reactor at 25°C, with a hydraulic retention time of 62.8 min; the water body treated by the column catalyst reactor was introduced into an automatic partial collector at a flow rate of 1.0 mL / min by using a peristaltic pump. The results are shown in Figure 4 Table 2. The zero-discharge times of tetracycline in ultrapure water, tap water, Yangshan Lake water, and Bohai water were as long as 315 h, 300 h, 312 h, and 410 h, respectively. The column reactor showed stronger ability to completely degrade tetracycline in Bohai water, corresponding to Example 10, in which high concentrations of chloride ions and bicarbonate ions promoted the degradation of tetracycline, indicating that the catalytic system constructed in the application can successfully achieve efficient degradation of toxic organic pollutants in high-salt water bodies while having good anti-interference ability.

[0059] Comparative Example 1

[0060] To prove that the cobalt doping in the transition metal cluster-single atom composite catalyst derived from the Zr-DAA MOF has a promoting effect on the catalytic activity of the catalyst, a catalyst without loading transition metal was prepared, and the difference in catalytic effect thereof and the catalyst obtained in Example 1 was compared. The preparation method was the same as that in Example 1, except that no cobalt source was added in step S2. The degradation results are shown in Figure 2 Table 3. Under the same experimental conditions as in Example 2, the degradation rate of tetracycline within 10 min of the obtained catalyst was 54.1%.

[0061] Comparative Example 2

[0062] The same as Example 1, except that:

[0063] The organic ligand used in step S1 is 2,2'-dipyridyl-5,5'-dicarboxylic acid, and the solvent is N,N-dimethylformamide. 0.16 g of 2,2'-dipyridyl-5,5'-dicarboxylic acid and 0.24 mL of triethylamine were dissolved in 40 mL of DMF solution, 0.15 g of ZrCl4 and 11 mL of acetic acid were dissolved in 40 mL of DMF solution, and then the two DMF solutions were mixed and heated at 85°C for 24 h. The obtained product was washed with DMF and methanol by centrifugal ultrasonic washing for several times, and then dried at 25°C under vacuum for 24 h to obtain the zirconium-based metal organic framework precursor.

[0064] The degradation rate of the obtained catalyst to tetracycline under the same experimental conditions as in Example 2 was 30.1% within 10 min.

[0065] Comparative Example 3

[0066] The same as in Example 1, except that the organic ligand used in step S1 is 5-amino isophthalic acid.

[0067] The degradation rate of the obtained catalyst to tetracycline under the same experimental conditions as in Example 2 was 42.5% within 10 min.

[0068] The above describes the embodiments of the present application in detail in combination with the examples, but the present application is not limited to the above-described embodiments. For those skilled in the art, after learning the contents described in the present application, they can make some equivalent changes and substitutions without departing from the principles of the present application, and these equivalent changes and substitutions should also be considered as falling within the protection scope of the present application.

Claims

1. A transition metal cluster-single atom composite catalyst, characterized in that... Transition metals are supported on the carbon layer surface of a fixed support in the form of clusters and single atoms. The fixed support is obtained by pyrolysis of a metal-organic framework assembled with zirconium ions as the metal center and organic ligands. The organic ligands are selected from one or more of aspartic acid, glutamic acid, and cystine. The composite catalyst is prepared by the following method: S1. The metal-organic framework formed by assembling zirconium ions as the metal center and organic ligands is stirred in an aqueous solution of transition metal ions, washed with water and dried to obtain the metal-organic framework that adsorbs transition metal ions. S2. Calcining the metal-organic framework that adsorbs transition metal ions in an inert gas yields a transition metal cluster-single-atom composite catalyst.

2. The composite catalyst according to claim 1, characterized in that... The transition metal is selected from one or more of cobalt, iron, copper, and manganese.

3. The composite catalyst according to claim 1, characterized in that: In step S1, the mass concentration ratio of the metal-organic framework to the transition metal ion is 1:10-10:

1.

4. The application of the composite catalyst according to any one of claims 1-3 in heterogeneous advanced oxidation processes.

5. The application according to claim 4, characterized in that... The composite catalyst activates persulfate to degrade toxic organic pollutants in wastewater.

6. The application according to claim 5, characterized in that... The persulfate is one or more of potassium peroxymonosulfate, sodium peroxymonosulfate, potassium peroxymonosulfate, and sodium peroxymonosulfate.

7. The application according to claim 5, characterized in that... The wastewater contains inorganic salts, and the inorganic salt anions are selected from one or more of chloride ions, sulfate ions, bicarbonate ions, and dihydrogen phosphate ions.

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