Preparation method of cobalt-based oxide catalyst and application of cobalt-based oxide catalyst in recycling of plastic wastes

Abstract

The invention discloses a preparation method of a cobalt-based oxide catalyst and application of the cobalt-based oxide catalyst in recycling of plastic wastes. The preparation method comprises the following steps: firstly, carrying out two-step stirring to obtain a precursor uniformly loaded on foamed nickel, and further carrying out heat treatment on the precursor to obtain the cobalt-based oxide CoOx / NF material. The preparation process has the characteristics of mild reaction conditions (normal pressure and low temperature), simplicity and convenience in operation, low raw material cost and the like. The current density of the synthesized CoOx / NF catalyst reaches 100 mAcm <-2 > under the voltage of 1.35 V vs.RHE, and meanwhile, the CoOx / NF catalyst has relatively high Faraday efficiency and shows good catalytic performance; meanwhile, the catalyst can efficiently catalyze ethylene glycol or waste PET plastic derived ethylene glycol to be converted into high-added-value formic acid, an efficient and economical solution is provided for resource utilization of plastic waste, and the catalyst has a remarkable industrial application prospect.

Description

Technical Field

[0001] The present invention belongs to the field of electrocatalytic technology and resource recycling, and specifically relates to a method for preparing a cobalt-based oxide catalyst and its application in the resource utilization of plastic waste. By catalytically oxidizing ethylene glycol derived from waste PET plastic to produce high-value-added formic acid, the resource upgrading of waste plastic is achieved. Background Art

[0002] The massive accumulation of plastic waste poses a serious threat to the ecological environment. Alkaline hydrolysis of discarded PET plastic to produce ethylene glycol not only recycles waste resources but also allows for the electrocatalytic oxidation of ethylene glycol to produce high-value chemicals. Ethylene glycol has a unique structure, possessing two reactive hydroxyl groups. Electrocatalytic oxidation of ethylene glycol requires only a very low overpotential, offering significant advantages over the oxygen evolution reaction in water splitting. The products of electrocatalytic oxidation of ethylene glycol vary depending on the catalyst used, typically producing a C1 product (formic acid) or a C2 product (glycolic acid), depending on whether the C-C bond is preserved or broken. Precious metal catalysts (such as Pt and Pd) are commonly used in electrocatalytic ethylene glycol oxidation, producing glycolic acid. They exhibit high reactivity (Faraday efficiency >90%), but their raw materials are scarce and costly, and intermediates produced during the reaction are easily adsorbed on the catalyst surface, leading to poisoning and inactivation of the precious metal catalyst and poor stability. The development of efficient, low-cost, and easily scalable catalytic materials is a key topic in current catalysis research.

[0003] Organic metal frameworks (MOFs), prepared by combining transition metals with organic ligands, are rich in dispersed active sites, possess abundant pore structures, and possess superior surface areas, making them highly valuable for use as catalysts. Transition metal oxides, with their excellent redox properties, abundant raw material resources, and low production costs, have demonstrated significant advantages in the field of plastic waste recycling.

[0004] Existing methods for preparing metal-organic framework (MOF)-derived catalysts often use hydrothermal methods, which are complex and pose safety risks. For example, the nickel-cobalt bimetallic oxide, nitrogen-oxygen co-doped carbon material, and CdS photocatalytic material disclosed in CN110327962A improves photocatalytic hydrogen production performance, but is not applicable to the field of plastic recycling and the synthesis steps are cumbersome. Therefore, there is an urgent need to develop a simple, low-cost, efficient and stable non-precious metal catalyst to address the technical bottleneck of ethylene glycol electrocatalytic oxidation in plastic recycling. Summary of the Invention

[0005] Based on the shortcomings of the prior art, the present invention aims to provide a method for preparing a cobalt-based oxide catalyst and its application in the recycling of plastic waste. The synthesis method is simple, the raw materials are cheap and easy to obtain, and the synthesized CoO xThe / NF material is evenly loaded on nickel foam and has rich and dispersed oxidation active sites, which significantly improves the catalytic activity. It also produces high-value chemical formic acid during the electrocatalytic oxidation of ethylene glycol derived from waste PET plastic, which is of great economic value.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] In one aspect, the present invention provides a method for preparing a cobalt-based oxide, comprising the following steps:

[0008] (1) Dissolving a cobalt metal salt and a ligand in ultrapure water, respectively, and ultrasonically obtaining a cobalt metal salt solution and a ligand solution, respectively, and pouring the ligand solution into the cobalt metal salt solution and mixing evenly to obtain a mixed solution; placing the pretreated nickel foam into the mixed solution and stirring at room temperature; after the mixture is completed, taking out the nickel foam, rinsing it with ultrapure water, and drying it to obtain a precursor ZIF-L(Co) / NF;

[0009] (2) adding cobalt chloride hexahydrate to anhydrous ethanol and ultrasonically dissolving it to obtain a blue solution; placing the ZIF-L(Co) / NF obtained in step (1) in the blue solution and stirring it; after the stirring is completed, taking out the ZIF-L(Co) / NF, rinsing it with ethanol and then drying it to obtain the Co-LDH / NF material;

[0010] (3) The Co-LDH / NF material obtained in step (2) is heat-treated under an atmosphere to obtain the cobalt oxide.

[0011] The size of the nickel foam described in step (1) above is 2 cm × 3 cm;

[0012] The cobalt metal salt described in the above step (1) is cobalt nitrate hexahydrate, and the ligand is 2-methylimidazole.

[0013] The mass ratio of the cobalt metal salt to the ligand in the above step (1) is 1:2.257.

[0014] The pretreatment method of the nickel foam after the pretreatment described in the above step (1) is: soaking in acetone, ultrapure water, ethanol, and ultrapure water in sequence for ultrasonic treatment for a total of five minutes, and then blowing dry after treatment.

[0015] The stirring time in the above step (1) is 4 hours.

[0016] The concentration of cobalt chloride hexahydrate in the blue solution in step (2) is 0.025M.

[0017] The stirring time in the above step (2) is 30 min.

[0018] The temperature of the heat treatment in the above step (3) is 300-400°C, the time is 2h, and the heating rate of the heat treatment is 5°C / min.

[0019] The atmosphere described in the above step (3) is N2 atmosphere.

[0020] On the other hand, the present invention also provides a cobalt oxide prepared by the above method.

[0021] In another aspect, the present invention also provides use of the cobalt oxide prepared by the above method in the electrocatalytic oxidation of ethylene glycol.

[0022] In another aspect, the present invention also provides the use of the cobalt oxide prepared by the above method in recycling plastic waste.

[0023] In another aspect, the present invention further provides a method for electrocatalytic oxidation of ethylene glycol, the specific operations being:

[0024] The cobalt oxide catalyst obtained by the above preparation method is used as the working electrode, the Pt sheet is used as the counter electrode, the Ag / AgCl electrode is used as the reference electrode, and the alkaline solution is used as the electrolyte solution. The electrocatalytic oxidation reaction is carried out under applied voltage. The electrolyte solution is a KOH solution of ethylene glycol.

[0025] In another aspect, the present invention also provides a method for recycling plastic waste, which comprises the following steps:

[0026] The cobalt oxide catalyst obtained by the above preparation method is used as the working electrode, the Pt sheet is used as the counter electrode, the Ag / AgCl electrode is used as the reference electrode, and the alkaline solution is used as the electrolyte solution. An electrocatalytic oxidation reaction is carried out under applied voltage, and the electrolyte solution is used to discard PET plastic to obtain an alkaline hydrolyzate.

[0027] The specific treatment method of the alkaline hydrolysis of the waste PET plastic is as follows:

[0028] Add PET plastic to KOH solution, place in an oil bath at 80°C and stir for 24 hours to obtain an alkaline hydrolyzate, which is an electrolyte solution containing ethylene glycol.

[0029] The plastic waste PET includes but is not limited to PET bottles, films and fibers.

[0030] The applied voltage is 1.4-1.7 V vs. RHE.

[0031] During the above reaction, the current density reached 100 mA cm at a voltage of 1.35 V vs. RHE. -2 The Faradaic efficiency can reach 92% at a voltage of 1.44V vs. RHE.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] (1) The present invention prepares rod-shaped Co-LDH / NF materials by simply stirring the solution, and further heat treatment can obtain dense needle-shaped CoO rich in active sites. x The material, namely cobalt oxide catalyst, has good electrocatalytic activity for ethylene glycol oxidation.

[0034] (2) The cobalt oxide catalyst prepared in the present invention has a current density of 461.2 mA cm-2 at 1.44 V vs. RHE and a formic acid Faradaic efficiency of 92%, which remains above 85% after 10 cycles.

[0035] (3) The present invention replaces precious metal catalysts with non-precious metals, reducing raw material costs by 70%, while achieving high-value conversion of PET waste. Under normal circumstances, PET-derived ethylene glycol from plastic waste is upgraded to high-value-added chemical formic acid, thereby protecting the environment and generating greater economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 The CoO synthesized in Examples 1 and 3 of the present invention and Comparative Example 1 is shown. x / X-ray diffraction (XRD) patterns of NF materials;

[0037] Figure 2 The following are the precursors involved in the embodiments of the present invention and the CoO synthesized in the embodiments and comparative examples. x Scanning electron microscope (SEM) images of / NF materials;

[0038] Figure 3 The CoO synthesized in Example 3 of the present invention is shown. x Energy dispersive X-ray spectroscopy (EDS) diagram of -3 / NF material.

[0039] Figure 4 The CoO synthesized in Examples 1-3 and Comparative Examples 1-2 of the present invention is shown. x Polarization curve of NF material applied to oxidation reaction;

[0040] Figure 5 For Example 3 and Comparative Example 3 of the present invention, the synthesized CoO x -3 / NF materials were applied to electrocatalytic ethylene glycol oxidation (EGOR) and oxygen evolution reaction (OER), respectively.

[0041] Figure 6 The CoO synthesized in Example 3 of the present invention is shown. x Faradaic efficiency of the electrocatalytic oxidation of ethylene glycol to formate by -3 / NF materials at different voltages;

[0042] Figure 7 The CoO synthesized in Example 3 of the present invention is shown. x Faradaic efficiency of -3 / NF material for producing formic acid after cyclic experiments of electrocatalytic oxidation of ethylene glycol at a voltage of 1.44 V vs. RHE.

[0043] Figure 8 The ethylene glycol solution after the hydrolysis of plastic waste PET in Example 4 of the present invention is shown. 1 H NMR spectrum.

[0044] Figure 9 Shown is a chronoamperometric curve of the electrocatalytic oxidation of ethylene glycol obtained from the degradation of PET in Example 4 of the present invention, with the voltage set to 1.45 V vs. RHE. DETAILED DESCRIPTION

[0045] The following is an explanation of the implementation details of the technical solution of the present invention in conjunction with the accompanying drawings and examples. It should be noted that the operation procedures involved in this embodiment are all carried out according to conventional methods unless otherwise specified; the chemical reagents and experimental materials used can be purchased through conventional commercial channels unless otherwise specified.

[0046] Example 1

[0047] S1. Surface pretreatment of nickel foam (2 cm × 3 cm) was performed by ultrasonic cleaning with acetone, deionized water, and anhydrous ethanol for 5 min each, with the solvent changed after each cleaning step to remove surface impurities. Finally, the foam was thoroughly rinsed with deionized water and dried for later use.

[0048] S2. 1.3137 g of 2-methylimidazole was dissolved in 40 mL of deionized water to prepare solution A. 0.5821 g of cobalt nitrate hexahydrate (Co(NO3)2·6H2O) was dissolved in 40 mL of deionized water to obtain solution B. Solution B was poured into solution A and stirred at room temperature to form a homogeneous reaction system. The pretreated nickel foam was immersed in the mixture, stirred for 4 h, removed, rinsed with deionized water, and dried with cold air to obtain ZIF-L(Co) / NF.

[0049] S3. Dissolve 0.6 g of cobalt chloride hexahydrate (CoCl2·6H2O) in 100 mL of anhydrous ethanol to form a cobalt source solution. Vertically immerse the ZIF-L(Co) / NF in the solution and stir at room temperature for 30 min. After the reaction, rinse with anhydrous ethanol and transfer to a vacuum drying oven at 60°C for 6 h to obtain a Co-LDH / NF material.

[0050] S4. The organic metal framework Co-LDH / NF material obtained in S3 was placed in a tube furnace and heated to 300°C at a heating rate of 5°C / min under N2 atmosphere and kept warm for 2h. After cooling to room temperature, CoOx -1 / NF.

[0051] The prepared CoO x Electrochemical testing was performed in an H-type electrolytic cell using a Pt / NF electrode as the working electrode, a Pt sheet as the counter electrode, and an Ag / AgCl electrode as the reference electrode. The working and reference electrodes served as anodes, with 1 M KOH solution and 0.1 M ethylene glycol solution as the electrolyte. The counter electrode served as cathode, with 1 M KOH solution as the electrolyte. Constant voltage testing was performed at 1.44 V vs. RHE.

[0052] Example 2

[0053] The difference from Example 1 is:

[0054] S4. The organic metal framework Co-LDH / NF material obtained in S3 was placed in a tube furnace, heated to 350°C at a heating rate of 5°C / min under N2 atmosphere and kept warm for 2h. After cooling to room temperature, CoO x -2 / NF.

[0055] The rest is the same as Example 1.

[0056] The prepared CoO x Electrochemical testing was performed in an H-type electrolytic cell using a -2 / NF electrode as the working electrode, a Pt sheet as the counter electrode, and an Ag / AgCl electrode as the reference electrode. The working and reference electrodes served as anodes, with 1 M KOH solution and 0.1 M ethylene glycol solution as the electrolyte. The counter electrode served as the cathode, with 1 M KOH solution as the electrolyte. Constant voltage testing was performed at 1.44 V vs. RHE.

[0057] Example 3

[0058] The difference from Example 1 is:

[0059] S4. The organic metal framework Co-LDH / NF material obtained in S3 was placed in a tube furnace and heated to 400°C at a heating rate of 5°C / min under N2 atmosphere and kept warm for 2h. After cooling to room temperature, CoO x -3 / NF.

[0060] The rest is the same as Example 1.

[0061] The prepared CoO xElectrochemical tests were performed in an H-type electrolytic cell using a Pt / AgCl electrode as the working electrode, a Pt sheet as the counter electrode, and a Ag / AgCl electrode as the reference electrode. The working and reference electrodes served as anodes, with 1 M KOH solution and 0.1 M ethylene glycol solution as the electrolytes. The counter electrode served as the cathode, with 1 M KOH solution as the electrolyte.

[0062] When performing constant voltage testing, the voltage is set to 1.44V vs. RHE.

[0063] Example 4

[0064] The difference from Example 3 is:

[0065] 2 g of waste PET plastic was added to 40 mL of 1.5 M KOH solution, placed in an oil bath at 80° C. and stirred for 24 h. After the reaction was completed, the clear solution obtained obtained an electrolyte containing ethylene glycol.

[0066] The prepared CoO x -3 / NF was used as the working electrode, Pt sheet as the counter electrode, and Ag / AgCl electrode as the reference electrode. The electrochemical test was carried out in a single cell using the ethylene glycol solution obtained by alkaline hydrolysis of the above-mentioned PET as the electrolyte solution, and the voltage was set to 1.45 V vs. RHE.

[0067] Comparative Example 1

[0068] The difference from Example 1 is:

[0069] S4. The organic metal framework Co-LDH / NF material obtained in S3 was placed in a tube furnace and heated to 500°C at a heating rate of 5°C / min under N2 atmosphere and kept warm for 2h. After cooling to room temperature, CoO x -4 / NF.

[0070] The rest is the same as Example 1.

[0071] The prepared CoO x Electrochemical tests were performed in an H-type electrolytic cell using a Pt / AgCl electrode as the working electrode, a Pt sheet as the counter electrode, and a Ag / AgCl electrode as the reference electrode. The working and reference electrodes served as anodes, with 1 M KOH solution and 0.1 M ethylene glycol solution as the electrolytes. The counter electrode served as the cathode, with 1 M KOH solution as the electrolyte.

[0072] Comparative Example 2

[0073] The difference from Example 1 is:

[0074] S4. The organic metal framework Co-LDH / NF material obtained in S3 was placed in a tube furnace and heated to 200°C at a heating rate of 5°C / min under N2 atmosphere and kept warm for 2h. After cooling to room temperature, CoO x -5 / NF.

[0075] The rest is the same as Example 1.

[0076] The prepared CoO x Electrochemical tests were performed in an H-type electrolytic cell using a Pt / AgCl electrode as the working electrode, a Pt sheet as the counter electrode, and a Ag / AgCl electrode as the reference electrode. The working and reference electrodes served as anodes, with 1 M KOH solution and 0.1 M ethylene glycol solution as the electrolytes. The counter electrode served as the cathode, with 1 M KOH solution as the electrolyte.

[0077] Comparative Example 3

[0078] The preparation method of the catalyst is the same as that of Example 2, except that:

[0079] The prepared CoO x Electrochemical tests were performed in an H-type electrolytic cell using a Pt / AgCl electrode as the working electrode, a Pt sheet as the counter electrode, and a Ag / AgCl electrode as the reference electrode. The working and reference electrodes served as anodes, the counter electrode served as cathode, and 1 M KOH solution was used as the electrolyte on both sides.

[0080] according to Figure 1 It can be seen that the CoO synthesized in Examples 1-3 and Comparative Examples 1-2 x / NF As the heat treatment temperature increases, the crystallinity of the synthesized sample becomes better. If the temperature is too low (such as in Comparative Example 2), the sample will have poor crystallinity, resulting in poor performance; but if the temperature is too high (such as in Comparative Example 1), the CoO x The Co in the catalyst is reduced, resulting in the appearance of Co atoms, which affects the surface structure of the catalyst.

[0081] according to Figure 2 It can be seen that the precursors involved in the examples (ZIF-L(Co) / NF, Co-LDH / NF) and the CoO synthesized in the examples x / NF materials, Figure a shows ZIF-L(Co) / NF densely grown in sheet form on nickel foam support, Figure b shows Co-LDH / NF material in rod form and also uniformly loaded. Figure c shows CoO in Example 1 x -1 / NF is irregular flake and Figure e is CoO in Comparative Example 1 x -4 / NF is a disordered dendritic shape; Figure d is the CoO in Example 3 x-3 / NF has a dense needle shape, a larger specific surface area, and abundant active sites, making it more advantageous for electrocatalytic oxidation of ethylene glycol.

[0082] according to Figure 3 It can be seen that the CoO synthesized in Example 3 of the present invention x -3 / NF material has uniform distribution of cobalt and oxygen elements.

[0083] according to Figure 4 It can be seen that the CoO synthesized in Examples 1-3 of the present invention and Comparative Examples 1-2 x / NF materials are used in the electrocatalytic performance of oxidation reactions. x -1 / NF can achieve a current density of 123.88 mA cm at a voltage of 1.45 V vs. RHE. -2 ; CoO in Example 2 x -2 / NF can achieve a current density of 271 mA cm at a voltage of 1.45 V vs. RHE. -2 ; CoO in Example 3 x -3 / NF can achieve a current density of 461.2 mA cm at a voltage of 1.45 V vs. RHE. -2 ; CoO in Comparative Example 1 x -4 / NF can achieve a current density of 55.6 mA cm at a voltage of 1.45 V vs. RHE. -2 ; CoO in Comparative Example 2 x -5 / NF can achieve a current density of 31.84 mA cm at a voltage of 1.45 V vs. RHE. -2 .

[0084] according to Figure 5 It can be seen that Example 3 of the present invention and Comparative Example 3 synthesized CoO x The NF materials were applied to electrocatalytic ethylene glycol oxidation (EGOR) and oxygen evolution reaction (OER), respectively. The onset potential of EGOR is much lower than that of OER. In Example 3, the current density can reach 450 mA cm at a voltage of 1.43 V vs. RHE. -2 , while the current density of comparative example 3 reaches the same level at a voltage of 1.67V vs. RHE.

[0085] according to Figure 6 It can be seen that the CoO synthesized in Example 3 of the present invention x When the -3 / NF material is used to electrocatalyze the oxidation of ethylene glycol to produce formate at different voltages, the Faradaic efficiency exceeds 92% at a voltage of 1.44 V vs. RHE.

[0086] according to Figure 7 It can be seen that the CoO synthesized in Example 3 of the present invention xThe -3 / NF material electrocatalytically oxidizes ethylene glycol to produce formic acid after a cyclic experiment at a voltage of 1.44 V vs. RHE, so that the Faradaic efficiency can still remain above 85% after ten cycle experiments.

[0087] according to Figure 8 It can be seen that the solutes in the solution obtained after alkaline hydrolysis of PET plastic in Example 4 of the present invention are terephthalic acid and ethylene glycol. (DMSO is a reference added later)

[0088] according to Figure 9 It can be seen that in Example 4 of the present invention, ethylene glycol derived from PET is used as the electrolyte solution, CoO x Partial chronoamperometric curves of the catalytic upgrading of ethylene glycol to high-value chemicals using α-thiazolyl-3 / NF as the working electrode.

[0089] The synthesis method of the present invention has a low threshold for preparation and operation, simple steps, low cost and easy access to non-precious metals, and the synthesized CoO based on the metal organic framework x The NF material has a large specific surface area and abundant active sites, demonstrating excellent catalytic activity. It has been applied to the electrocatalytic oxidation of ethylene glycol, upgrading it to the high-value chemical formic acid, with a Faradaic efficiency exceeding 92%.

[0090] Obviously, the described embodiments are only individual embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other implementations obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

Claims

1. A method for preparing a cobalt-based oxide, characterized in that: The steps include: (1) Dissolving a cobalt metal salt and a ligand in ultrapure water, respectively, and ultrasonically obtaining a cobalt metal salt solution and a ligand solution, respectively, and pouring the ligand solution into the cobalt metal salt solution and mixing evenly to obtain a mixed solution; placing the pretreated nickel foam into the mixed solution and stirring at room temperature; after the mixture is completed, taking out the nickel foam, rinsing it with ultrapure water, and drying it to obtain a precursor ZIF-L(Co) / NF; (2) adding cobalt chloride hexahydrate to anhydrous ethanol and ultrasonically dissolving it to obtain a blue solution; placing the ZIF-L(Co) / NF obtained in step (1) in the blue solution and stirring it; after the stirring is completed, taking out the ZIF-L(Co) / NF, rinsing it with ethanol and then drying it to obtain the Co-LDH / NF material; (3) The Co-LDH / NF material obtained in step (2) is heat-treated under an atmosphere to obtain the cobalt oxide catalyst.

2. The preparation method according to claim 1, wherein: The cobalt metal salt described in step (1) is cobalt nitrate hexahydrate, and the ligand is 2-methylimidazole.

3. The preparation method according to claim 1, wherein: The mass ratio of the cobalt metal salt to the ligand in step (1) is 1:2.

257.

4. The preparation method according to claim 1, wherein: The pretreatment method of the nickel foam after the pretreatment described in step (1) is: soaking in acetone, ultrapure water, ethanol, and ultrapure water in sequence for ultrasonic treatment for a total of five minutes, and then blowing dry after treatment.

5. The preparation method according to claim 1, wherein: The concentration of cobalt chloride hexahydrate in the blue solution described in step (2) is 0.025M.

6. The preparation method according to claim 1, characterized in that: The temperature of the heat treatment in step (3) is 300-400°C, the time is 2h, and the heating rate of the heat treatment is 5°C / min.

7. A cobalt-based oxide prepared by the preparation method according to any one of claims 1 to 6.

8. Use of the cobalt-based oxide prepared by the preparation method according to any one of claims 1 to 6 in the recycling of plastic waste.

9. Use of the cobalt-based oxide prepared by the preparation method according to any one of claims 1 to 6 in the catalytic oxidation of ethylene glycol.

10. A method for recycling plastic waste, characterized in that: The specific operations are: The cobalt-based oxide prepared by the preparation method according to any one of claims 1 to 7 is used as a working electrode, a Pt sheet is used as a counter electrode, an Ag / AgCl electrode is used as a reference electrode, and an alkaline solution is used as an electrolyte solution, and an electrocatalytic oxidation reaction is carried out under applied voltage; The alkaline solution is prepared by alkaline hydrolysis of waste PET plastics, and the preparation method is as follows: Add PET plastic to KOH solution, place in an oil bath at 80°C and stir for 24 hours to obtain a clear solution, which is the electrolyte solution containing ethylene glycol.

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