Preparation method and application of ferrocobalt spinel catalyst for treating wastewater

Abstract

The invention relates to the technical field of water treatment, in particular to a preparation method and application of a ferrocobalt spinel catalyst for treating wastewater. The preparation method of the cobalt-iron spinel catalyst for treating the wastewater comprises the following steps: mixing an inorganic trivalent iron salt and a cobalt-based organic ligand, grinding, calcining, cooling, carrying out secondary grinding, carrying out suction filtration, cleaning, drying, and carrying out tertiary grinding, so as to prepare the cobalt-iron spinel catalyst for treating the wastewater. According to the invention, the characteristic that the spinel structure has a multi-way electron transfer structure is utilized, and the cobalt-iron bimetallic oxide with the spinel structure and multiple exposed active sites is synthesized, so that the performance of the activated PMS for degrading organic pollutants is improved. According to the method, the precursor formed by co-grinding the inorganic ferric salt and the cobalt-based organic ligand is calcined and can be converted into the ferrocobalt bimetallic oxide with a spinel structure, and then the high-activity catalyst capable of efficiently activating PMS to degrade organic pollutants is obtained.

Description

Technical Field

[0001] The present application relates to the technical field of water treatment, and in particular to a preparation method and application of a cobalt-iron spinel catalyst for treating wastewater. Background Art

[0002] Wastewater usually contains a large amount of difficult-to-biodegrade organic residues, so conventional sewage treatment processes cannot effectively remove them. These organic substances enter the water environment with the discharge of sewage treatment facilities, and will show certain biological toxicity to animals, plants, and environmental microorganisms, and will be further transmitted and spread through the water cycle and food chain, posing a great threat to human water safety and health. Therefore, there is still an urgent need for treatment technology for difficult-to-biodegrade organic pollutants in wastewater.

[0003] PMS (persulfate, HSO 5 - ) can produce active oxygen species with high redox potential (such as sulfate radicals and hydroxyl radicals, etc.) under the activation of the catalyst. These active oxygen species can quickly degrade and mineralize organic pollutants, and the reaction products of these active oxygen species are mostly common anions in water bodies, etc., with low secondary pollution risk. Therefore, advanced oxidation technology based on PMS is an efficient, reliable and easy-to-operate wastewater treatment method.

[0004] At present, many catalysts have been developed and used for PMS activation. However, the preparation steps of high-performance catalysts are mostly cumbersome. At the same time, the preparation of catalysts should take into account the cost issue, which is an important factor limiting the practical application of water treatment technology. From the perspective of raw material cost, the price of transition metals and their metal oxides is relatively low, and they have high catalytic activity, which has obvious advantages.

[0005] In recent years, nano-sized cobalt oxide catalysts have been found to have excellent catalytic activity. Theoretical studies have shown that cobalt oxide directly activates PMS through electron transfer between exposed solid-phase Co(II)-OH sites and PMS molecules or oxygen vacancies to produce active oxygen species with high redox potentials, thereby achieving rapid degradation of organic pollutants. Among them, cobalt-based bimetallic oxide catalysts with spinel structures have the advantages of rich electron transfer pathways, stable structure, safety and reliability, and low price, and are ideal catalyst materials for actual wastewater treatment. However, the preparation steps of existing cobalt-based bimetallic oxide catalysts are cumbersome and complicated, which is not conducive to large-scale implementation, limiting the large-scale practical application of such catalysts, and the catalytic activity needs to be further improved. Summary of the invention

[0006] In view of the above-mentioned shortcomings of the prior art, the present invention provides a preparation method of a cobalt-iron spinel catalyst for treating wastewater and its application, so as to improve the catalytic activity while simplifying the preparation steps.

[0007] To achieve the above objectives, the scheme of this application is as follows:

[0008] In a first aspect, the present invention provides a method for preparing a cobalt-iron spinel catalyst for treating wastewater, the method for preparing the cobalt-iron spinel catalyst for treating wastewater comprising the following steps:

[0009] The inorganic trivalent iron salt and the cobalt-based organic ligand are mixed, ground, calcined, cooled, ground twice, filtered, washed, dried, and ground three times to obtain the cobalt-iron spinel catalyst for treating wastewater.

[0010] Optionally, the inorganic ferric iron salt is selected from at least one of ferric chloride (including hydrate), ferric sulfate (including hydrate) and ferric nitrate (including hydrate).

[0011] Optionally, the inorganic ferric iron salt is selected from ferric nitrate.

[0012] Optionally, the cobalt-based organic ligand is selected from at least one of Co-1,3,5-benzenetricarboxylic acid (Co-BTC), Co-2,5-thiophenedicarboxylic acid (Co-CP) and Co-zeolite imidazolate framework 67 (Co-ZIF67).

[0013] Optionally, the cobalt-based organic ligand is selected from Co-zeolite imidazolate framework 67.

[0014] Optionally, the molar ratio of the inorganic trivalent iron salt to the cobalt-based organic ligand is 0.5-2:1, preferably 0.8-2:1.

[0015] Optionally, the calcination temperature is 300-500° C., preferably 350-500° C.; the calcination time is 1-4 h, preferably 1.5-4 h.

[0016] Optionally, during the calcination process, the heating rate is 2-5°C / min, preferably 2.5-5°C / min.

[0017] Optionally, the drying temperature is 50-80°C, preferably 55-80°C.

[0018] In a second aspect, the present application also provides a product for treating wastewater, comprising a cobalt-iron spinel catalyst prepared according to the method described above.

[0019] Beneficial effects of the present invention:

[0020] The present application utilizes the characteristics of the spinel structure with a multi-pathway electron transfer structure to synthesize a spinel-structured cobalt-iron bimetallic oxide with multiple exposed active sites, thereby improving the performance of activated PMS in degrading organic pollutants.

[0021] The present application calcines a precursor formed by co-grinding an inorganic trivalent iron salt and a cobalt-based organic ligand to convert it into a cobalt-iron bimetallic oxide with a spinel structure, thereby obtaining a highly active catalyst that can efficiently activate PMS to degrade organic pollutants.

[0022] The present application selects a specific cobalt-based organic ligand (Co-ZIF67) and utilizes the characteristics of Co-ZIF67 such as high specific surface area, rich pore structure and periodic network structure. Therefore, after the inorganic trivalent iron salt is mixed and calcined with it, more Co and Fe sites can be exposed and evenly distributed. At the same time, its rich pore structure is still retained, which is beneficial to the mass transfer of PMS molecules to the active sites, thereby improving the performance of the catalyst in activating PMS to degrade organic pollutants.

[0023] The preparation method of the present application is simple to operate and easy to realize large-scale production.

[0024] The catalyst of the present application is highly efficient in treating refractory organic pollutants in wastewater, and the products are mainly water and carbon dioxide, with little secondary pollution.

[0025] The catalyst of the present application can be used to treat wastewater containing refractory organic pollutants, and is particularly suitable for deep treatment of wastewater to achieve effective removal of refractory organic pollutants. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The X-ray diffraction pattern of the catalyst prepared in Example 1, the abscissa is 2θ, and the ordinate is intensity;

[0027] Figure 2 is a scanning electron microscope scan of the catalyst prepared in Example 1;

[0028] Figure 3 The degradation curves of Rhodamine B degraded by activated PMS of the catalysts prepared in Example 1, Comparative Example 1 and Comparative Example 2 are shown. DETAILED DESCRIPTION

[0029] The following will describe the embodiments of the present invention with reference to the accompanying drawings and preferred embodiments. Those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be understood that the preferred embodiments are only for illustrating the present invention, not for limiting the scope of protection of the present invention.

[0030] In the following description, numerous details are discussed to provide a more thorough explanation of embodiments of the present invention; however, it is apparent to one skilled in the art that embodiments of the present invention may be practiced without these specific details.

[0031] Example 1

[0032] A method for preparing a cobalt-iron spinel catalyst, comprising the following specific steps:

[0033] S1. 0.668 g of cobalt nitrate and 2.242 g of 2-methylimidazole were added to 100 mL of methanol, mechanically stirred for 30 min to accelerate dissolution, and allowed to stand for 24 h to obtain a purple suspension;

[0034] The purple suspension was placed in a centrifuge and centrifuged at 10,000 rpm for 20 min, the supernatant was discarded, and the solid obtained by centrifugation was washed with methanol;

[0035] The washed solid was dried in an oven at 70°C and ground to obtain a ZIF67 powder sample.

[0036] S1. 2.0355 g ZIF67 powder sample was placed in a mortar, and then 7.3528 g ferric nitrate nonahydrate was added to the mortar, and the mixture was thoroughly stirred and ground with the ZIF67 powder for 30 min;

[0037] Subsequently, the mixed powder was transferred into a quartz boat and placed in a tube furnace, and the temperature was raised to 400°C at a heating rate of 2°C / min, and the mixture was calcined at 400°C for 120 min, and then naturally cooled to room temperature.

[0038] S2. After cooling to room temperature, the solid was repeatedly washed with pure water to remove residual ions, and then filtered through a 0.22 μm filter membrane. The washed solid was placed in an oven and dried at 60 ° C;

[0039] The dried solid was ground into powder to obtain the sample Z-CoFe 2 O 4 .

[0040] The sample prepared in this example was subjected to X-ray diffraction (XRD) using an X-ray diffractometer. The results are as follows: Figure 1 shown.

[0041] The sample prepared in this embodiment was scanned using a scanning electron microscope, and the results are as follows: Figure 2 shown.

[0042] Depend on Figure 1 It can be seen that by observing the crystallization peak, it can be confirmed that the crystallization peak of the sample prepared in this embodiment is similar to that of CoFe 2 O 4 Most of the characteristic peaks of the XRD spectrum standard card (PDF 22-1086) are the same, indicating that the present application successfully prepared the cobalt-iron bimetallic oxide with a spinel structure.

[0043] Depend on Figure 2 It can be seen that the sample prepared in this embodiment has a nano morphology and a nano particle structure.

[0044] Comparative Example 1

[0045] The difference between this comparative example and Example 1 is:

[0046] S1. Place 2.0355 g of ZIF67 powder sample in a quartz boat, then place the quartz boat in a tube furnace, heat it to 400°C at a heating rate of 2°C / min, calcine at 400°C for 120 min, and cool it naturally to room temperature.

[0047] That is, no ferric nitrate nonahydrate was added in this comparative example.

[0048] Comparative Example 2

[0049] A method for preparing a stone catalyst, comprising the following specific steps:

[0050] 2.6193 g of cobalt nitrate hexahydrate was placed in a mortar, and then 7.3528 g of ferric nitrate nonahydrate was added to the mortar and mixed with the cobalt nitrate hexahydrate, and then ground for 30 minutes to obtain a mixed powder;

[0051] Subsequently, the mixed powder was transferred into a quartz boat and placed in a tube furnace, and the temperature was raised to 400°C at a heating rate of 2°C / min, and the mixture was calcined at this temperature for 120 min, and then naturally cooled to room temperature.

[0052] S2. After cooling to room temperature, the solid was repeatedly washed with pure water to remove residual ions, and then filtered through a 0.22 μm filter membrane. The washed solid was placed in an oven and dried at 60 ° C;

[0053] The dried solid was ground into powder to obtain the sample CoFeO x .

[0054] That is, the difference between this comparative example and Example 1 is that ZIF-67 is replaced by cobalt nitrate hexahydrate.

[0055] Performance Testing

[0056] The performance of the samples prepared in Example 1 and Comparative Examples 1-2 in activating PMS to degrade organic pollution was tested, and the specific steps were as follows:

[0057] Weigh 20 mg of the sample to be tested and add it to a beaker containing 60 mL of pure water. Ultrasonicate for about 30 seconds to evenly disperse the catalyst.

[0058] Then, 40 mL of 40 mg / L Rhodamine B (RhB) solution was added to the beaker and stirred for 30 min.

[0059] 46.5 mg of potassium monopersulfate Oxone complex salt (47 wt % PMS) was weighed and added to the above solution to start the reaction, and then the timing was started. Samples were taken at 0 min, 2.5 min, 5 min, 10 min and 15 min, and the concentration of rhodamine B (RhB) in the system was determined by spectrophotometry. The results are shown in Table 1 and Figure 3 shown.

[0060] Table 1 Test results

[0061] Time (min) <![CDATA[Z-CoFe 2 O 4 (Example 1)]]> <![CDATA[Z-CoO x (Comparative Example 1)]]> <![CDATA[CoFeO x (Comparative Example 2)]]> 0 10mg / L 10mg / L 10mg / L 2.5 6.0mg / L 8.4mg / L 8.6mg / L 5 2.7mg / L 7.5mg / L 7.6mg / L 10 0.5mg / L 6.2mg / L 6.3mg / L 15 0.3mg / L 5.2mg / L 5.2mg / L

[0062] From Table 1 and Figure 3 It can be seen that compared with 0 min, the concentration of rhodamine B in Example 1 was significantly reduced at 2.5 min, 5 min, 10 min and 15 min. Figure 1 From the results, it can be seen that the present application utilizes the characteristics of the spinel structure with multi-pathway electron transfer structure to synthesize a spinel-structured cobalt-iron bimetallic oxide with multiple exposed active sites, thereby improving the performance of activated PMS in degrading organic pollutants.

[0063] From Table 1 and Figure 3It can be seen that at 2.5min, 5min, 10min and 15min, compared with Comparative Example 1 (no nonahydrated ferric nitrate) and Comparative Example 2 (ZIF-67 is replaced by hexahydrated cobalt nitrate), the concentration of rhodamine B in Example 1 (with nonahydrated ferric nitrate, using ZIF-67) is significantly reduced. The results show that the present application can convert the precursor formed by co-grinding the inorganic trivalent iron salt and the cobalt-based organic ligand into a cobalt-iron bimetallic oxide with a spinel structure by calcining, thereby obtaining a highly active catalyst capable of efficiently activating PMS to degrade organic pollutants; the present application selects a specific cobalt-based organic ligand (Co-ZIF67), and utilizes Co-ZIF67 to have the characteristics of high specific surface area, rich pore structure and periodic network structure, so that after the inorganic trivalent iron salt is mixed and calcined, more Co and Fe sites can be exposed and evenly distributed, and its rich pore structure is still retained, which is beneficial to the mass transfer of PMS molecules to the active sites, thereby improving the performance of the catalyst in activating PMS to degrade organic pollutants.

[0064] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the technology may modify or change the above embodiments without violating the spirit and scope of the present invention. Therefore, all equivalent modifications or changes made by a person of ordinary skill in the art without departing from the spirit and technical ideas disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A method for preparing a cobalt-iron spinel catalyst for treating wastewater, characterized in that: The preparation method of the cobalt-iron spinel catalyst for treating wastewater comprises the following steps: The inorganic trivalent iron salt and the cobalt-based organic ligand are mixed, ground, calcined, cooled, ground twice, filtered, washed, dried, and ground three times to obtain the cobalt-iron spinel catalyst for treating wastewater.

2. The preparation method according to claim 1, characterized in that The inorganic ferric iron salt is selected from at least one of ferric chloride, ferric sulfate and ferric nitrate.

3. The preparation method according to claim 2, characterized in that: The inorganic ferric iron salt is selected from ferric nitrate.

4. The preparation method according to claim 1, characterized in that: The cobalt-based organic ligand is selected from at least one of Co-1,3,5-benzenetricarboxylic acid, Co-2,5-thiophenedicarboxylic acid and Co-zeolite imidazolate framework 67.

5. The preparation method according to claim 4, characterized in that: The cobalt-based organic ligand is selected from Co-zeolite imidazolate framework 67.

6. The preparation method according to claim 1, characterized in that: The molar ratio of the inorganic trivalent iron salt to the cobalt-based organic ligand is 0.5-2:

1.

7. The preparation method according to claim 1, characterized in that: The calcination temperature is 300-500°C, and the calcination time is 1-4h.

8. The preparation method according to claim 1, characterized in that: During the calcination process, the heating rate is 2-5°C / min.

9. The preparation method according to claim 1, characterized in that: The drying temperature is 50-80°C.

10. A product for treating wastewater, characterized in that The invention comprises a cobalt-iron spinel catalyst prepared according to the method according to any one of claims 1 to 9.

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