A carbide supported cobalt catalyst, its preparation method and application

Abstract

The application provides a carbide-supported cobalt catalyst and a preparation method and application thereof, and the obtained carbide-supported cobalt catalyst has high catalytic activity. In the application, MAX is used as raw material, and a cobalt catalyst is anchored on an MXene carrier in the process of etching MXene by molten salt. The carbide-supported cobalt catalyst has a special flower-shaped or accordion-shaped structure, so that the specific surface area is large and more catalyst loading sites are provided, which is beneficial to the activation of PMS by cobalt and the degradation of organic pollutants.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of environmental purification materials, and particularly relates to a carbide-supported cobalt catalyst and a preparation method and application thereof. BACKGROUND

[0002] Advanced oxidation processes (AOPs) based on hydroxyl radicals (OH·) and sulfate radicals (SO4 ·- ) are currently considered as an effective method for treating refractory organic pollutants. Common transition metals such as Ni, Fe, Co and their compounds are excellent activators of peroxy monosulfate (PMS).

[0003] MXene is a general term for a large class of new two-dimensional transition metal nitrides / carbides. MXene is usually obtained by selective etching of the "A" site element in MAX. The preparation method of MXene can be divided into two kinds: fluorine-containing etching and fluorine-free etching. Compared with the more dangerous hydrofluoric acid etching method, the anion obtained by thermal decomposition of Lewis acid salt at high temperature can also react with A-type atoms to remove them. This etching method is safe and mild, and the surface terminal groups of MXene are controllable, which is more suitable for loading single atoms. The active cations in the molten salt oxidize the A site elements (such as Al) to form a new molten salt, and the metal cations are reduced to a metal state and anchored on the surface of MXene. The molten salts that can be used as etchants in the current reports include chloride salts represented by ZnCl2, CoCl2, and CuCl2, other halide molten salts such as CuBr2 and CuI2, and their binary or ternary mixtures. In order to promote the etching of A, alkali metal chlorides such as NaCl and KCl can also be used as fluxing agents. At present, the research on using CaCl 2、 MgCl2 and other alkaline earth metal chlorides as fluxing agents is less, especially the one-step molten salt etching of molybdenum-based MAX to simultaneously prepare carbide-supported cobalt catalysts has not been reported. SUMMARY

[0004] The present application aims to provide a carbide supported cobalt catalyst and its preparation method and application, which has the characteristics of high catalytic activity. The present application uses MAX as raw material, CaCl2 or MgCl2 as molten salt etchant, and can realize functionalization in the process of obtaining MXene by molten salt thermal decomposition. The double metal chloride salt not only removes the A type atom, but also fixes Co on the MXene carrier. The obtained catalyst selects CaCl2 or MgCl2 as etchant, and fully utilizes the advantages of metal chloride salt. The addition of CaCl2 or MgCl2 is beneficial to the dispersion of Co, which makes Co more stably fixed on MXene, enhances the activation of PMS, and reduces the leaching of Co. The catalyst uses high-stability MXene as a catalytic platform, activates PMS by using single-atom sites, and has excellent catalytic performance, which can effectively purify pollutants in wastewater.

[0005] In order to achieve the above-mentioned purpose, the technical scheme of the present application is as follows:

[0006] In the first aspect, the present application provides a carbide supported cobalt catalyst, which is prepared by the following method:

[0007] (1) The MAX phase is ground in a marver mortar; the MAX phase is one or both of Mo2TiAlC2 and Mo3AlC2 (preferably Mo2TiAlC2);

[0008] (2) In the ground MAX phase powder of step (1), a cobalt source and a chloride salt are added, and the mixture is ground to obtain a mixed powder; the amount ratio of the MAX phase, the cobalt source and the chloride salt is 0.5 mmol:0.0125-0.25 mmol:0.25-1 mmol (preferably 0.5 mmol:0.125 mmol:0.5 mmol)

[0009] (3) The mixed powder of step (2) is transferred to an alumina crucible with a lid, and is loaded into a tube furnace, and is calcined at 750-800℃ for 4-6h under nitrogen protection (preferably the calcination temperature is 750℃, and the preferred calcination time is 6h), and is naturally cooled in the tube furnace to obtain a calcined carbide supported cobalt catalyst;

[0010] (4) The calcined carbide supported cobalt catalyst obtained in step (3) is poured into an appropriate amount of deionized water, and is uniformly dispersed by ultrasonic, and is washed several times by centrifugation, and is dried at 40-80℃ for 12-24h (preferably the drying temperature is 60℃, and the preferred drying time is 24h) to obtain the catalyst.

[0011] Further, the cobalt source in step (2) is inorganic cobalt salt CoCl2·6H2O.

[0012] Further, the chlorinated salt in step (2) is one or more of CaCl2, MgCl2·6H2O mixed in any ratio.

[0013] Further, the heating rate in step (3) is 2-5℃ / min (preferably 5℃ / min).

[0014] In another aspect, the present application provides a use of a carbide-supported cobalt catalyst in activating persulfate (PMS) to degrade organic pollutants.

[0015] Further, the organic pollutants are one or more of fluorouracil, metronidazole, sulfamethoxazole, perfluorooctanoic acid, norfloxacin mixed. In an embodiment of the present application, the organic pollutants used are fluorouracil.

[0016] Since the catalytic degradation function of the carbide-supported cobalt catalyst in the present application is achieved by activating PMS, the present application team can foresee that any organic pollutants that can be degraded by PMS are within the protection scope of the present application.

[0017] The specific application mode is: uniformly disperse the carbide-supported cobalt catalyst in the aqueous solution of the organic pollutants, then add persulfate and stir, so as to realize the degradation process.

[0018] Further, the concentration of the organic pollutants in the aqueous solution of the organic pollutants is 10-50mg / L.

[0019] Further, the persulfate is one or a mixture of both of peroxymonosulfate and peroxodisulfate; in an embodiment of the present application, it is potassium monopersulfate.

[0020] Further, the mass value range of the catalyst is 0.5-1g / L based on the volume of the aqueous solution of the organic pollutants.

[0021] Further, the mass value range of the persulfate is 0.5-1g / L based on the volume of the aqueous solution of the organic pollutants.

[0022] Compared with the prior art, the present application has the following beneficial effects:

[0023] 1. The molten salt as the reaction medium can provide a good molybdenum carbide generation and Co catalyst loading environment, and can effectively reduce the oxidation of MAX and the leaching of Co catalyst in the etching process.

[0024] 2. The mixture of cobalt source and chlorinated salt can firmly anchor the Co catalyst on the molybdenum / titanium carbide carrier with the assistance of the chlorinated salt.

[0025] 3. In addition to the attempt of CaCl2 as flux, another alkaline earth metal chloride (MgCl2) was chosen. The mixed molten salt etchant composed of calcium chloride or magnesium chloride with a small amount of cobalt chloride can successfully etch MAX phase and form Co catalyst support through one-step calcination.

[0026] 4. The main phase of the carbide supported cobalt catalyst in the present application is Mo2C, and the morphology is three-dimensional flower-like. This unique flower-like structure makes it have a larger specific surface area and more catalyst loading sites.

[0027] 5. The main phase of the carbide supported cobalt catalyst in the present application is Ti3C2, which is derived from MXene phase as a substrate by high-temperature molten salt method (CoCl2 / CaCl2 mixed molten salt) etching MAX phase. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 are different scale SEM images of the catalysts prepared in Example 2, Example 4 and Comparative Example 3. Among them, a, b are Example 2 (Mo-Co / 4 Ca-750 ), c is Example 4 (Mo-Co / 40 Mg-750 ), d is Comparative Example 3 (Ti-Co / 20 Ca-750 ).

[0029] Figure 2 are XRD patterns of the catalyst Mo-Co / 4 Ca-750 prepared in Example 2, the catalyst Mo-Co / 40 Mg-750 prepared in Example 4, and the catalyst Ti-Co / 20 Ca-750 prepared in Comparative Example 3. DETAILED DESCRIPTION

[0030] Example 1

[0031] Take 0.5mmol Mo2TiAlC2, 0.25mmol CoCl2·6H2O, 0.25mmol CaCl2, put them into an agate mortar and grind them thoroughly, transfer the mixed powder into an alumina crucible with a cover, load it into a tube furnace, under nitrogen protection, heat it to 750℃ at a rate of 5℃ / min, keep it for 6h, after cooling to room temperature, add deionized water, repeat the washing for 4 times, dry it at 60℃ for 24h, and the sample is recorded as Mo-Co / 2 Ca / 2-750 .

[0032] Example 2

[0033] Take 0.5 mmol Mo2TiAlC2, 0.125 mmol CoCl2·6H2O, 0.5 mmol CaCl2 into the agate mortar and grind thoroughly, transfer the mixed powder into the alumina crucible with cover, load into the tube furnace, set the heating gradient at 5 ℃ / min under nitrogen protection, the reaction temperature is 750 ℃, heat for 6 h, add deionized water after cooling to room temperature, repeat washing for 4 times, dry at 60 ℃ for 24 h, and the catalyst sample is recorded as Mo-Co / 4 -1 . Ca-750 .

[0034] Example 3

[0035] Take 0.5 mmol Mo2TiAlC2, 0.125 mmol CoCl2·6H2O, 1 mmol CaCl2 into the agate mortar and grind thoroughly, transfer the mixed powder into the alumina crucible with cover, load into the tube furnace, set the heating gradient at 5 ℃ / min under nitrogen protection, the reaction temperature is 750 ℃, heat for 6 h, add deionized water after cooling to room temperature, repeat washing for 4 times, dry at 60 ℃ for 24 h, and the catalyst sample is recorded as Mo-Co / 4 -1 . 2Ca-750 .

[0036] Example 4

[0037] Take 0.5 mmol Mo2TiAlC2, 0.0125 mmol CoCl2·6H2O, 0.5 mmol MgCl2·6H2O into the agate mortar and grind thoroughly, transfer the mixed powder into the alumina crucible with cover, load into the tube furnace, set the heating gradient at 5 ℃ / min under nitrogen protection, the reaction temperature is 750 ℃, heat for 6 h, add deionized water after cooling to room temperature, repeat washing for 4 times, dry at 60 ℃ for 24 h, and the catalyst sample is recorded as Mo-Co / 4 -1 . Mg-750 .

[0038] Example 5

[0039] Take 0.5 mmol Mo2TiAlC2, 0.25 mmol CoCl2·6H2O, 0.25 mmol CaCl2 into the agate mortar and grind thoroughly, transfer the mixed powder into the alumina crucible with cover, load into the tube furnace, set the heating gradient at 5 ℃ / min under nitrogen protection, the reaction temperature is 550 ℃, heat for 6 h, add deionized water after cooling to room temperature, repeat washing for 4 times, dry at 60 ℃ for 24 h, and the catalyst sample is recorded as Mo-Co / 2 -1 . Ca / 2-550 .

[0040] Comparative Example 1

[0041] Take 0.5mmol Mo2TiAlC2, 0.25mmol CoCl2·6H2O, and 0.25mmol CaCl2 and grind them thoroughly in an agate mortar. Transfer the mixed powder into a covered alumina crucible and place it in a tube furnace. Under nitrogen protection, set the heating gradient to 5℃ / min. -1 The reaction temperature was 850 ° C, heated for 6 h, cooled to room temperature, added with deionized water, washed 4 times, and dried at 60 ° C for 24 h. The catalyst sample was recorded as Mo-Co / 2 Ca / 2-850 .

[0042] Comparative Example 2

[0043] Take 1mmol Ti3AlC2, 0.5mmol CoCl2·6H2O, and 0.5mmol CaCl2 and grind them thoroughly in an agate mortar. Transfer the mixed powder into a covered alumina crucible and place it in a tube furnace. Under nitrogen protection, set the heating gradient to 5℃ / min. -1 The reaction temperature was 750℃, heated for 6h, cooled to room temperature, added with deionized water, washed 4 times, and dried at 60℃ for 24h. The catalyst sample was recorded as Ti-Co / 2 Ca / 2-750 .

[0044] Comparative Example 3

[0045] Take 1mmol Ti3AlC2, 0.05mmol CoCl2·6H2O, and 1mmol CaCl2 and grind them thoroughly in an agate mortar. Transfer the mixed powder into a covered alumina crucible and place it in a tube furnace. Under nitrogen protection, set the heating gradient to 5℃ / min. -1 The reaction temperature was 750℃, heated for 6h, cooled to room temperature, added with deionized water, washed 4 times, and dried at 60℃ for 24h. The catalyst sample was recorded as Ti-Co / 20 Ca-750 .

[0046] Comparative Example 4

[0047] Take 1mmol Ti3AlC2, 0.025mmol CoCl2·6H2O, and 1mmol CaCl2 and grind them thoroughly in an agate mortar. Transfer the mixed powder into a covered alumina crucible and place it in a tube furnace. Under nitrogen protection, set the heating gradient to 5℃ / min. -1 The reaction temperature was 750℃, heated for 6h, cooled to room temperature, added with deionized water, washed 4 times, and dried at 60℃ for 24h. The catalyst sample was recorded as Ti-Co / 40 Ca-750 .

[0048] Comparative Example 5

[0049] Take 0.5mmol Mo2TiAlC2, 0.125mmol cobalt phthalocyanine, and 0.5mmol CaCl2 and grind them thoroughly in an agate mortar. Transfer the mixed powder into a covered alumina crucible and place it in a tube furnace. Under nitrogen protection, set the heating gradient to 5℃ / min. -1 The reaction temperature was 750 ° C, heated for 6 h, cooled to room temperature, added with deionized water, washed 4 times, and dried at 60 ° C for 24 h. The catalyst sample was recorded as Mo-Co T / 4 Ca-750 .

[0050] Comparative Example 6

[0051] Take 0.5mmol Mo2TiAlC2, 0.0125mmol cobalt phthalocyanine, and 0.5mmol MgCl2·6H2O and grind them thoroughly in an agate mortar. Transfer the mixed powder into a covered alumina crucible and place it in a tube furnace. Under nitrogen protection, set the heating gradient to 5℃ / min. -1 The reaction temperature was 750 ° C, heated for 6 h, cooled to room temperature, added with deionized water, washed 4 times, and dried at 60 ° C for 24 h. The catalyst sample was recorded as Mo-Co T / 40 Mg-750 .

[0052] Application comparison experiment

[0053] 1. Catalytic degradation test of organic matter: A 20 mg / L fluorouracil solution was prepared to simulate an organic pollutant. 25 mg of each sample of the embodiment and the comparative example was placed in 50 mL of the fluorouracil solution. 25 mg of potassium persulfate (PMS) was added. A small amount of the solution was filtered 5 min, 10 min, and 30 min after the reaction. The absorbance of the residual fluorouracil in the filtered solution was measured using an ultraviolet spectrophotometer. The degradation rate of the sample for fluorouracil was calculated, as shown in Table 1.

[0054] 2. Co ion leaching test: 5 mL of the filtered degradation reaction solution was taken to test the Co ion leaching concentration. The results are shown in Table 1.

[0055] Table 1 Sample degradation rate data

[0056]

[0057]

[0058] 1. The degradation data of fluorouracil in Examples 1-5 show that the catalysts prepared in the present invention have excellent catalytic performance and ideal Co ion leaching concentration. The catalytic performance is higher than 85%, and the Co ion leaching concentration is lower than 5.

[0059] 2. It can be seen from Example 1 and Example 5, Comparative Example 1 that the catalysts prepared at different temperatures all have high degradation efficiency, and when the temperature is too high (850℃) or too low (550℃), the cobalt ion leaching level of the catalyst obtained under the corresponding conditions will increase, and the most suitable temperature is 750-800℃.

[0060] 3. It can be seen from Examples 1-3 that when the content of cobalt chloride is appropriately reduced and the content of calcium chloride is increased, the flower-shaped molybdenum carbide-based catalyst prepared in the application still maintains high catalytic activity and low cobalt ion leaching level.

[0061] 4. It can be seen from Example 2 and Example 4 that when MAX is Mo2TiAlC2, both calcium chloride and magnesium chloride can ensure that the catalyst prepared in the application can efficiently degrade fluorouracil.

[0062] 5. It can be seen from Example 1 and Comparative Example 2 that when calcium chloride is selected as a fluxing agent and the MAX phase is changed from Mo2TiAlC2 to Ti3AlC2, the catalytic performance of the prepared catalyst is still high, but the cobalt ion leaching is significantly increased.

[0063] 6. It can be seen from Example 2 and Comparative Example 5 that both CoCl2·6H2O and cobalt phthalocyanine used in the application can ensure high catalytic activity of the catalyst prepared in the application, but CoCl2·6H2O can significantly reduce the cobalt ion leaching level.

[0064] 7. It can be seen from Comparative Examples 2-4 that when MAX is Ti3AlC2, calcium chloride can also be used as a fluxing agent to help transition metal cobalt to exhibit catalytic activity and activate PMS to degrade fluorouracil, but the cobalt ion leaching concentration is high or the catalytic performance is low.

[0065] 8. It can be seen from Example 4 and Comparative Example 6 that CoCl2·6H2O can effectively improve the catalytic performance of the catalyst compared with cobalt phthalocyanine.

[0066] Figure 1 are different scale SEM images of the catalysts prepared in Example 2, Example 4, and Comparative Example 3. Among them, a, b are Mo-Co / 4 Ca-750 , c is Mo-Co / 40 Mg-750 , d is Ti-Co / 20 Ca-750 . From the SEM images, it can be seen that the morphology of Mo-Co / 4 Ca-750 is three-dimensional flower-shaped. Mo-Co / 40 Mg-750 and Ti-Co / 20 Ca-750The layered accordion-like morphology of MXene is still maintained. It is illustrated that the catalysts in the application take MXene as a carrier, effectively disperse and anchor cobalt atoms by CaCl2 or MgCl2, have high degradation rate of organic pollutants, low cobalt leaching and good stability.

[0067] Figure 2 XRD patterns of the catalyst Mo-Co / 4 Ca-750 prepared in Example 2, the catalyst Mo-Co / 40 Mg-750 prepared in Example 4 and the catalyst Ti-Co / 20 Ca-750 prepared in Comparative Example 3. It can be illustrated from the XRD patterns that the phases of the catalysts prepared in Example 2 and Example 4 are Mo2C, and the phase of the catalyst prepared in Comparative Example 3 is Ti3C2. It is illustrated that the application selects CaCl2, MgCl2 and other alkaline earth metal chlorides as fluxing agents, and forms a mixed salt etchant with cobalt chloride, which can successfully etch MAX and obtain the corresponding MXene phase.

[0068] In summary, the application uses MAX as raw material, CaCl2 or MgCl2 as molten salt etchant, and the addition of CaCl2 or MgCl2 is beneficial to the dispersion of Co under a specific mixing ratio and temperature, so that Co is more stably fixed on MXene, which enhances the activation of PMS and reduces the leaching of Co. Especially for molybdenum-based MAX, a three-dimensional flower-like structure is formed after preparation, which further significantly improves the catalytic performance of the molybdenum-based catalyst.

Claims

1. A method for preparing a carbide-supported cobalt catalyst, characterized in that: The following steps are involved: (1) fully grinding the MAX phase; the MAX phase is one or two of Mo2TiAlC2 and Mo3AlC2; (2) adding a cobalt source and a chloride salt to the MAX phase fine powder ground in step (1), and grinding them thoroughly to obtain a mixed powder; the amount ratio of the MAX phase to the cobalt source and the chloride salt is 0.5:0.0125-0.25:0.25-1; the cobalt source is an inorganic cobalt salt CoCl2·6H2O; and the chloride salt is one or more of CaCl2 and MgCl2·6H2O mixed in any proportion; (3) The mixed powder in step (2) was transferred to a covered alumina crucible, placed in a tube furnace, and calcined at 550-800° C. for 4-6 h under nitrogen protection, and naturally cooled in the tube furnace to obtain a calcined carbide-supported cobalt catalyst.

2. The method according to claim 1, characterized in that The MAX phase is Mo2TiAlC2.

3. The method according to claim 1, characterized in that The usage ratio of the MAX phase, the cobalt source, and the chloride salt is 0.5:0.125:0.

5.

4. The method according to claim 1, wherein In step (3), the calcination temperature is 750° C. and the calcination time is 6 h.

5. The method according to claim 1, wherein Also includes a cleaning step: (4) Pour the carbide-supported cobalt catalyst obtained by calcining in step (3) into an appropriate amount of deionized water, disperse it evenly by ultrasonication, wash it by centrifugation several times, and dry it at 40-80°C for 12-24h.

6. A carbide-supported cobalt catalyst prepared by the method for preparing a carbide-supported cobalt catalyst according to any one of claims 1 to 5, wherein the carbide-supported cobalt catalyst is in a flower-like or accordion-like shape.

7. Use of the carbide-supported cobalt catalyst according to claim 6 in activating persulfate to degrade organic pollutants.

8. The use according to claim 7, characterized in that The organic pollutants are a mixture of one or more of fluorouracil, metronidazole, sulfamethoxazole, perfluorooctanoic acid, and norfloxacin.

9. The use according to claim 7, characterized in that The persulfate is one of peroxymonosulfate and peroxydisulfate or a mixture of the two.

10. The use according to claim 7, characterized in that Based on the volume of the aqueous solution of organic pollutants, the mass of the catalyst is in the range of 0.5-1 g / L.

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