A graphite-supported manganese dioxide catalyst for waste lithium batteries, its preparation method and application

Abstract

The present invention discloses a graphite-supported manganese dioxide catalyst for waste lithium batteries, its preparation method and application; first, wet ball milling is carried out on waste graphite powder, and then the obtained activated graphite is dispersed into a mixed solution of KMnO 4 and MnSO 4 , and hydrothermal reaction is carried out at 120-180 °C for 8-20 h to obtain the graphite-supported manganese dioxide catalyst for waste lithium batteries; this catalyst enhances the catalytic activity of formaldehyde at room temperature. The non-metallic and metal doped atoms contained in the graphite of waste lithium batteries not only provide a large number of defect sites for anchoring manganese dioxide, generating highly dispersed and activity-enhanced manganese dioxide active sites for improving the catalytic performance of formaldehyde; at the same time, the formation of manganese dioxide promotes the exfoliation of graphite, further expanding the surface area of the graphite of waste lithium batteries, and in turn affecting the final growth morphology of manganese dioxide, greatly increasing the active area, thereby realizing the enhancement of formaldehyde catalytic activity.

Description

Technical Field

[0001] The present invention belongs to the field of environmental protection technologies, and particularly relates to a graphite-supported manganese dioxide catalyst for waste lithium batteries, a preparation method thereof, and an application in enhancing the catalytic oxidation of formaldehyde. Background Art

[0002] Formaldehyde (HCHO) is a colorless and easily soluble irritating gas, and has been identified as a Class I carcinogen by the International Agency for Research on Cancer (IARC). Acute poisoning by formaldehyde is manifested as irritation to the skin and mucous membranes. Long-term exposure to formaldehyde can reduce the respiratory function of the body, the information integration function of the nervous system, and affect the immune response of the body, and also has toxic effects on the cardiovascular system, endocrine system, digestive system, reproductive system, and kidneys. When the formaldehyde concentration reaches 0.1 mg / m 3 , there will be a feeling of discomfort in the pharynx. When the concentration reaches 0.5 mg / m 3 , it will irritate the eyes and cause tearing. When it reaches 0.6 mg / m 3 , it will cause serious conditions such as sore throat, nausea, vomiting, and pulmonary edema. When it reaches 30 mg / m 3 , it may lead to the death of people.

[0003] The main source of formaldehyde is the glue used for bonding artificial boards (there are also melamine-based glues and MDI glues, which do not contain formaldehyde but are expensive and not popular). Generally, it is urea-formaldehyde resin with formaldehyde as the main component. With decoration, artificial boards enter the home, and formaldehyde is also brought into the home and released. Secondly, coatings, paints, textile fabrics such as soft furnishings, wallpaper, wall covering, artificial leather products, etc. will all release formaldehyde. The residual and unreacted formaldehyde in the boards will gradually be released into the surrounding environment, which is the main body of indoor formaldehyde pollution. The release period of formaldehyde is as long as 3 to 15 years. If not effectively treated, it will cause great harm to human health.

[0004] At present, the methods for removing indoor formaldehyde are mainly divided into three categories: ventilation method, adsorption method, and chemical method. Due to limitations such as ventilation facilities and outdoor environment, increasing ventilation is not a long-term effective method for controlling indoor formaldehyde concentration. The adsorption method has the problem of adsorption saturation. After saturation, it will release formaldehyde into the room and cannot remove formaldehyde in a long-term manner. In the chemical method, the common ones are photocatalytic method and catalytic oxidation method. Among them, the photocatalytic method cannot be widely promoted due to its excessive dependence on ultraviolet light; the catalytic oxidation method can completely oxidize and decompose formaldehyde into CO 2 and H 2 O, and has strong oxidizing properties. Transition metal oxides are a type of catalyst for the chemical catalytic oxidation of formaldehyde, but the high-temperature catalytic environment and slow catalytic reaction rate are still problems to be solved.

[0005] Under the important strategic guidance of environmental governance and social sustainable development, the recycling of waste lithium batteries has attracted great attention. The negative electrode of a lithium battery is composed of a copper foil coated with an anode material mainly composed of graphite, and the graphite therein accounts for about 12 - 21 wt%. The waste graphite negative electrode not only contains heteroatoms such as sulfur and nitrogen, but also contains metal atoms such as nickel, cobalt, iron, manganese, lithium, and copper, which can provide a large number of defect sites for use as a regeneration catalyst. Therefore, it is of great significance to improve the catalytic activity of formaldehyde at room temperature by compounding the graphite of waste lithium batteries with oxides for chemical catalysis of formaldehyde. Summary of the Invention

[0006] In view of the deficiencies and problems to be solved in the above-mentioned prior art, the present invention provides a waste lithium battery graphite-supported manganese dioxide catalyst, its preparation method, and its application in enhancing the catalytic oxidation of formaldehyde. The catalyst of the present invention can improve the catalytic activity of formaldehyde at room temperature.

[0007] The technical solution of the present invention is as follows:

[0008] A preparation method of a waste lithium battery graphite-supported manganese dioxide catalyst, comprising the following steps:

[0009] (1) Pretreatment: Put the waste graphite powder into a ball mill for wet ball milling to obtain activated graphite;

[0010] The waste graphite powder is recycled from waste lithium batteries, and various types of lithium-ion batteries on the market can be used; the waste graphite powder is derived from the black powder in the dry process of the waste lithium-ion battery recycling process, which has undergone discharging, crushing, incineration, and screening. Since it is relatively completely separated from other substances in the dry process, it can be directly used as a raw material without further impurity removal;

[0011] Specifically, the operation method of wet ball milling is: put the waste graphite powder into a ball mill tank, pour in deionized water, stir evenly, and then carry out wet ball milling. After the ball milling is completed, filter and dry to obtain activated graphite;

[0012] Preferably, the mass-volume ratio of the waste graphite powder to deionized water is 50:800, g / mL;

[0013] The ball milling speed is 200 - 1000 rpm, preferably 500 - 800 rpm; the ball milling time is 2 - 10 h, preferably 2 - 4 h;

[0014] (2) Hydrothermal synthesis: Disperse the activated graphite obtained in step (1) into a mixed solution of KMnO 4 and MnSO 4 , stir evenly, seal, and then heat to 120 - 180 °C for hydrothermal reaction for 8 - 20 h. After that, cool to room temperature, filter, wash, and dry to obtain the waste lithium battery graphite-supported manganese dioxide catalyst;

[0015] Preferably, the mass-volume ratio of the activated graphite to the mixed solution of KMnO 4 and MnSO 4 is 3-8:150, g / mL; preferably 5:150, g / mL;

[0016] Preferably, the temperature of the hydrothermal reaction is 150 °C and the time is 12 h;

[0017] The molar ratio of KMnO 4 and MnSO 4 is (1-10):1, preferably 3:1;

[0018] The total amount of KMnO 4 and MnSO 4 can indirectly regulate the loading amount of MnO 2 The loading amount of MnO 2 is 1%-30%, preferably 17%;

[0019] The total amount of KMnO 4 and MnSO 4 is determined according to the loading amount of MnO 2 , the amount of waste graphite powder used and formula (a);

[0020] 2KMnO 4 +3MnSO 4 +2H 2 O = 5MnO 2 +2H 2 SO 4 (a).

[0021] The present invention relates to a waste lithium battery graphite-supported manganese dioxide catalyst prepared by the above method; in this catalyst, manganese dioxide has a birnessite-type structure.

[0022] The waste lithium battery graphite-supported manganese dioxide catalyst described in the present invention can be used for catalytic oxidation at room temperature to remove formaldehyde, and the specific steps are as follows:

[0023] (1) Pretreatment for formaldehyde removal experiment: The formaldehyde purification experiment is carried out in a closed experimental chamber with a volume of 100 L. The closed chamber consists of a chamber body, a cover body and a sealing clamp; before the experiment, the inner wall of the experimental chamber is wiped with distilled water. After cleaning the experimental chamber, wait for the inner wall to dry and then close the chamber body to measure the air in the chamber. The formaldehyde concentration is measured using a British PPM HTV-M formaldehyde analyzer. The experiment can be carried out only after the measured formaldehyde concentration is lower than 0.08 ppm;

[0024] (2) The experimental test steps are as follows: Weigh the graphite-supported manganese dioxide catalyst from waste lithium batteries and place it in a small fan. After spreading it evenly, put it into a formaldehyde test chamber together with a formaldehyde tester, and immediately cover the lid and seal it well. Conduct the corresponding experiment at room temperature. Use a syringe to inject the formaldehyde solution into the heating plate from the plug hole, plug the plug hole, and when the reading on the formaldehyde tester is stable, turn on the fan and record the formaldehyde concentration at each point every 10 minutes.

[0025] Among them, the dosage of the graphite-supported manganese dioxide catalyst from waste lithium batteries is 1 - 5 g, preferably 1.5 g.

[0026] The initial concentration of formaldehyde gas is 0.2 - 1 ppm, preferably 0.5 ppm.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] In the present invention, waste lithium battery graphite and manganese dioxide are compounded by an in-situ synthesis method, and waste lithium battery graphite and manganese dioxide complement each other during the hydrothermal process: the non-metallic and metal-doped atoms contained in waste lithium battery graphite not only provide a large number of defect sites for anchoring manganese dioxide, generating highly dispersed and enhanced-activity manganese dioxide active sites for improving formaldehyde catalytic performance; at the same time, the formation of manganese dioxide promotes the exfoliation of graphite, further expanding the surface area of waste lithium battery graphite, and in turn affecting the final growth morphology of manganese dioxide, greatly increasing the active area, thereby achieving enhanced formaldehyde catalytic activity. Description of the Drawings

[0029] Figure 1 SEM image (a) of C@17%MnO in Example 1 of the present invention 2 and SEM image (b) of AG@17%MnO in Example 4. 2

[0030] Figure 2 Efficiency graph of the graphite-supported manganese dioxide catalyst from waste lithium batteries prepared in Example 1 of the present invention for highly efficient oxidation and removal of formaldehyde at room temperature.

[0031] Figure 3 Efficiency graph of the graphite-supported manganese dioxide catalyst from waste lithium batteries prepared in Example 4 of the present invention for highly efficient oxidation and removal of formaldehyde at room temperature.

[0032] Figure 4 C@17%MnO in Example 1 of the present invention 2 , AG@17%MnO in Example 4 2 and N 2 adsorption-desorption characterization graphs of waste graphite powder C and activated waste graphite powder AG.

[0033] Figure 5C@17% MnO in Example 1 of the present invention 2 and AG@17% MnO in Example 4 2 as well as the pore size distribution diagrams of waste graphite powder C and activated waste graphite powder AG.

[0034] Figure 6 C@17% MnO in Example 1 of the present invention 2 and AG@17% MnO in Example 4 2 and AC@17% MnO in Example 5 2 Efficiency diagrams of the catalysts for highly efficient oxidation and removal of formaldehyde at room temperature. Detailed implementation manners

[0035] The present invention will be further described in detail below in conjunction with examples and drawings, but the protection scope of the present invention is not limited thereto.

[0036] The waste graphite powder used in the following examples comes from Zhejiang Tianneng New Materials Co., Ltd., and its metal content is shown in Table 1:

[0037] Table 1 Metal content table of waste graphite

[0038]

[0039] The specific surface area, pore volume and average pore diameter data of the relevant materials involved in the examples are shown in Table 2:

[0040] Table 2 Specific surface area, pore volume, average pore diameter data of waste graphite loaded with MnO 2 before and after ball milling

[0041]

[0042] Example 1

[0043] Using untreated waste graphite powder as the carrier, a waste lithium battery graphite supported manganese dioxide catalyst was prepared by changing the manganese dioxide loading amount, which was specifically realized through the following synthesis steps:

[0044] Disperse 5 g of untreated waste graphite powder into a solution (150 mL) with a molar ratio of 3:1 of KMnO 4 : MnSO 4 , and adjust KMnO 4 and MnSO 4The total amount was used to control the loadings of manganese dioxide at 0%, 1%, 7%, 13%, 17%, and 25% respectively. Stir for 5 min at 25 °C in a constant-temperature heating magnetic stirrer, then pour it into a 200 mL hydrothermal reactor, seal it, and react at 150 °C for 12 h. After the reaction, wait for the hydrothermal reactor to cool to room temperature, filter the precipitate, wash it with deionized water, and then put the filtered solid into an oven and dry it at 70 °C to obtain waste lithium battery graphite-supported manganese dioxide catalysts with different manganese dioxide loadings (denoted as C, C@1%MnO 2 , C@7%MnO 2 , C@13%MnO 2 , C@17%MnO 2 and C@25%MnO 2 ) in sequence.

[0045] Figure 1 Figure a in shows the SEM image of the waste lithium battery graphite (without pretreatment)-supported manganese dioxide catalyst prepared when the manganese dioxide loading is 17%. It can be seen that it is mainly composed of regularly shaped nanosheets. Compared with the bulk structure, the sheet structure will expose more active sites.

[0046] The application of the above waste lithium battery graphite-supported manganese dioxide catalysts with different manganese dioxide loadings in the efficient oxidation and removal of formaldehyde at room temperature is realized through the following steps:

[0047] Weigh 1.5 g of the waste lithium battery graphite-supported manganese dioxide catalyst and place it in a small fan. After spreading it evenly, put it into a formaldehyde test chamber together with a formaldehyde tester, and immediately cover the lid and seal it well. Conduct the corresponding experiment at room temperature. Use a syringe to inject a quantitative formaldehyde solution into the heating plate from the plug hole and plug the plug hole. When the reading on the formaldehyde tester stabilizes at 0.5 ppm, turn on the fan and record the formaldehyde concentration at each point every 10 min.

[0048] The test results show that when the MnO 2 loading is 17%, the formaldehyde removal rate is the best, and the formaldehyde removal rate within 1 h is 80.04% (see Figure 2 ). During the hydrothermal reaction process, when the manganese dioxide loading increases to a certain value, the waste graphite will react with KMnO 4 to generate the corresponding MnO 2 . In the one-step hydrothermal method, to obtain the MnO 2 morphology with the best formaldehyde removal performance, the pH of the solution during the reaction is relatively important. When the waste graphite participates in the reaction, it will cause different changes in the pH value of the solution, resulting in possible differences in the morphology of the generated MnO 2 . Therefore, it shows that different raw material ratios will result in different morphologies of MnO 2Meanwhile, metal atoms such as nickel, cobalt, iron, manganese, lithium, and copper in waste graphite (see Table 1) also participate in the reaction during hydrothermal treatment, forming more active sites on the material surface.

[0049] Example 2

[0050] Using untreated waste graphite powder as the carrier, prepare the waste lithium battery graphite-supported manganese dioxide catalyst by changing the ratio of KMnO 4 and MnSO 4 The specific synthesis steps are as follows:

[0051] Disperse 5 g of untreated waste graphite powder into solutions with molar ratios of 1:1, 2:1, 3:1, and 4:1 of KMnO 4 :MnSO 4 The loading amount of MnO 2 is 17%. Stir at 25 °C for 5 min in a constant-temperature heating magnetic stirrer, then pour it into a 200 mL hydrothermal reactor, seal it, and react at 150 °C for 12 h. After the reaction, wait for the hydrothermal reactor to cool to room temperature, filter the precipitate, wash it with deionized water, and then put the filtered solid into an oven and dry it at 70 °C to obtain the waste graphite-supported manganese dioxide.

[0052] The application of the waste lithium battery graphite-supported manganese dioxide catalyst prepared when the ratio of the above KMnO 4 and MnSO 4 is 4:1 in efficiently oxidizing and removing formaldehyde at room temperature, and the test method is the same as that in Example 1.

[0053] The test results show that when the ratio of KMnO 4 and MnSO 4 is 4:1, the formaldehyde removal rate within 1 h is 79.60%.

[0054] Example 3

[0055] Using pretreated waste graphite powder as the carrier, prepare the waste lithium battery graphite-supported manganese dioxide catalyst by changing the rotation speed of the ball mill. The specific synthesis steps are as follows:

[0056] (1) Put 50 g of waste graphite powder into the ball mill tank, then pour 800 mL of deionized water into the tank, stir the waste graphite powder and deionized water evenly, and the rotation speeds of the ball mill are 200 rpm, 400 rpm, 600 rpm, and 800 rpm respectively. The ball milling time is 2 h to obtain activated graphite under different ball milling conditions.

[0057] (2) Disperse 5 g of pretreated waste graphite powder into a solution with a molar ratio of 3:1 of KMnO 4 :MnSO 4In the solution of, MnO 2 The loading amount of is 17%. Stir at 25 °C for 5 min in a constant-temperature heating magnetic stirrer, then pour it into a 200 mL hydrothermal reactor, seal it and react at 150 °C in an oven for 12 h. After the reaction, wait for the hydrothermal reactor to cool to room temperature, filter the precipitate, wash it with deionized water, and then put the filtered solid into a vacuum oven and dry it at 70 °C to obtain the spent lithium battery graphite-supported manganese dioxide catalyst material.

[0058] The application of the spent lithium battery graphite-supported manganese dioxide catalyst prepared at different ball milling speeds above in efficiently oxidizing and removing formaldehyde at room temperature, and the test method is the same as that in Example 1.

[0059] The test results show that when the rotation speed of the ball mill is 400 rmp, the formaldehyde removal rate within 1 h is 84.31%.

[0060] Example 4

[0061] Using the pretreated spent graphite powder as the carrier, prepare the spent lithium battery graphite-supported manganese dioxide catalyst by changing the ball milling time of the ball mill, which is specifically realized through the following synthesis steps:

[0062] (1) Put 50 g of spent graphite powder into the ball mill tank, then pour 800 mL of deionized water into the tank, stir the spent graphite powder and deionized water evenly. Put 5 g of spent graphite powder into the ball mill, the rotation speed of the ball mill is 600 rpm, and the ball milling time is 2 h (the obtained material is denoted as AG@17% MnO 2 ), 4 h, 6 h, and 8 h to obtain activated graphite under different ball milling conditions.

[0063] (2) Disperse 5 g of pretreated spent graphite powder into a solution with a molar ratio of 3:1 of KMnO 4 : MnSO 4 In the solution of, the loading amount of MnO 2 is 17%. Stir at 25 °C for 5 min in a constant-temperature heating magnetic stirrer, then pour it into a 200 mL hydrothermal reactor, seal it and react at 150 °C in an oven for 12 h. After the reaction, wait for the hydrothermal reactor to cool to room temperature, filter the precipitate, wash it with deionized water, and then put the filtered solid into a vacuum oven and dry it at 70 °C to obtain the spent lithium battery graphite-supported manganese dioxide catalyst material.

[0064] Figure 1 What is shown in b is the SEM image of the spent lithium battery graphite (pretreated)-supported manganese dioxide catalyst prepared when the ball milling time is 2 h. It can be seen that it has a typical birnessite-type layered structure. Perform specific surface area and pore size distribution characterization on it (see Figure 4 , Figure 5As can be clearly seen from Table 2, it has a large specific surface area (27.62 m 2 / g) and a rich mesoporous structure, which is very helpful for the absorption and diffusion of formaldehyde gas molecules.

[0065] The application of the prepared spent lithium battery graphite-supported manganese dioxide catalyst at different ball milling times for the efficient oxidation and removal of formaldehyde at room temperature was tested in the same way as in Example 1.

[0066] The test results show that when the ball milling time of the ball mill is 2 h, the formaldehyde removal rate within 1 h is 97.58% (see Figure 3 ).

[0067] Example 5

[0068] A commercial activated carbon (from Pomelo Activated Carbon Co., Ltd.) was used as the carrier to prepare the manganese dioxide-supported catalyst, which was specifically realized through the following synthesis steps:

[0069] (1) Put 50 g of commercial activated carbon into the ball milling tank, then pour 800 mL of deionized water into the tank, stir the commercial activated carbon and deionized water evenly, the rotation speed of the ball mill is 600 rpm, and the ball milling time is 2 h to obtain activated carbon (AC).

[0070] (2) Disperse 5 g of the pretreated activated carbon into a solution with a molar ratio of 3:1 of KMnO 4 : MnSO 4 , the loading amount of MnO 2 is 17%, stir at 25 °C for 5 min in a constant temperature heating magnetic stirrer, then pour it into a 200 mL hydrothermal kettle, seal it and react at 150 °C in an oven for 12 h. After the reaction, wait for the hydrothermal kettle to cool to room temperature, filter the precipitate, wash it with deionized water, and then put the filtered solid into a vacuum oven and dry it at 70 °C to obtain the commercial activated carbon-supported manganese dioxide catalyst material (denoted as AC@17% MnO 2 ).

[0071] In this experiment, commercial activated carbon with an iodine value of 800 was used for comparison instead of pure graphite because: the adsorption performance of activated carbon is better and more common, and it is more suitable to be used as a pure adsorbent for comparison. Figure 6 The figure shows the efficiency of different composite materials for the efficient oxidation and removal of formaldehyde at room temperature. It can be seen that the activated spent lithium battery graphite-supported manganese dioxide catalyst containing metal elements (AG@17% MnO 2 ) has significantly higher formaldehyde removal efficiency at room temperature than the activated pure activated carbon-supported manganese dioxide catalyst (AC@17% MnO 2), which also proves that the metal elements naturally present in waste graphite have a promoting effect on the removal of formaldehyde at room temperature by the waste lithium battery graphite-supported manganese dioxide catalyst prepared subsequently.

Claims

1. A preparation method of a graphite-supported manganese dioxide catalyst for waste lithium batteries, comprising the following steps: (1) Pretreatment: Put waste graphite powder into a ball mill for wet ball milling to obtain activated graphite; (2) Hydrothermal synthesis: Disperse the activated graphite obtained in step (1) into a mixed solution of KMnO 4 and MnSO 4 . Stir evenly, seal, heat to 120 - 180 °C for hydrothermal reaction for 8 - 20 h, then cool to room temperature, filter, wash, and dry to obtain the waste lithium battery graphite-supported manganese dioxide catalyst described above.

2. The preparation method of the graphite-supported manganese dioxide catalyst for waste lithium batteries according to claim 1, characterized in that, in step (1), the operation method of wet ball milling is: put waste graphite powder into a ball milling tank, pour in deionized water, stir evenly and then carry out wet ball milling. After ball milling is completed, filter and dry to obtain activated graphite; The mass-volume ratio of waste graphite powder to deionized water is 50:800, g / mL; The ball milling speed is 200 - 1000 rpm; the ball milling time is 2 - 10 h.

3. The preparation method of the graphite-supported manganese dioxide catalyst for waste lithium batteries according to claim 1, characterized in that, In step (2), the mass-volume ratio of the activated graphite to the mixed solution of KMnO 4 and MnSO 4 is 3-8:150, g / mL.

4. The preparation method of the graphite-supported manganese dioxide catalyst for waste lithium batteries according to claim 1, characterized in that, In step (2), the molar ratio of KMnO 4 and MnSO 4 is (1 to 10):

1.

5. The preparation method of the graphite-supported manganese dioxide catalyst for waste lithium batteries according to claim 1, characterized in that, The prepared graphite-supported manganese dioxide catalyst MnO for waste lithium batteries 2 The loading amount is 1% to 30%.

6. A graphite-supported manganese dioxide catalyst for waste lithium batteries prepared by the preparation method according to any one of claims 1 - 5.

7. Application of the graphite-supported manganese dioxide catalyst for waste lithium batteries according to claim 6 in catalytic oxidation for removing formaldehyde at room temperature.

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