Method for preparing functionalized carbon dots from spent aluminum electrolysis cathode

Abstract

The application relates to a method for preparing functionalized carbon dots from electrolytic aluminum waste cathodes, which comprises the following steps: electrolytic aluminum waste cathodes are activated by ball milling with thiourea or L-cysteine to obtain activated mixed powders; the activated mixed powders are added into an alkaline solution, then a hydrothermal reaction is carried out in a sealed reaction container, and solid-liquid separation is carried out to obtain co-doped electrolytic aluminum cathode carbon powder; the co-doped electrolytic aluminum cathode carbon powder is added into a mixed solution of concentrated nitric acid and concentrated sulfuric acid, a hydrothermal reaction is carried out in a sealed reaction container, then solid-liquid separation is carried out, a first filtrate is collected, the first filtrate is neutralized with a hot alkaline solution, solid-liquid separation is carried out, a second filtrate is collected, then dialysis is carried out with a dialysis bag, and drying is carried out to obtain functionalized carbon dots; the method can effectively convert electrolytic aluminum waste cathodes into functionalized carbon dots, avoids pollution of the environment by electrolytic aluminum waste cathodes, and realizes conversion of electrolytic aluminum waste cathodes into high-value functionalized carbon dots while removing impurities.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of recycling of waste cathode for electrolytic aluminum, and more particularly to a method for preparing functionalized carbon dots from waste cathode for electrolytic aluminum. BACKGROUND

[0002] Aluminum metal is widely used in various fields. China's aluminum output and capacity has been ranked first in the world for many years. In industry, the main production method of aluminum is in electrolytic cell, which is produced by electrolysis of molten alumina and cryolite (Na3AlF6). In this process, the cathode is a key component, which will gradually consume and eventually become unusable, forming waste cathode, as the electrolytic aluminum process continues. Waste cathode is mainly composed of carbon powder, fluoride (Na3A1F6, NaF and CaF2), unreacted alumina and some impurities, among which the electrolytic aluminum cathode carbon powder is the main component. However, due to the presence of harmful substances such as fluoride, recycling and processing is difficult and costly, and waste cathode carbon is considered a hazardous waste. The carbon powder in the electrolytic aluminum waste cathode contains carbon materials that have not been fully utilized, and through effective recycling and processing, production costs can be reduced. Recycling and reusing the carbon powder in the waste cathode not only protects the environment, but also improves production efficiency. The fluorine element in the waste cathode itself is expected to be doped into the electrolytic aluminum cathode carbon powder through technical means, and if these electrolytic aluminum waste cathodes are efficiently and harmlessly treated and converted into higher value nitrogen, sulfur and fluorine doped functionalized carbon dots, the economic benefits of recycling electrolytic aluminum waste cathodes will be further improved, and environmental pollution will be avoided. SUMMARY

[0003] Based on the above technical problems existing in the prior art, the present application provides a method for preparing functionalized carbon dots from waste cathode for electrolytic aluminum, which adds thiocyanate or L-cysteine in the traditional alkali leaching process of waste cathode for electrolytic aluminum to realize the doping of N, S and F heteroatoms, and uses a concentrated nitric acid / concentrated sulfuric acid mixed solution with strong oxidizing property to replace hydrochloric acid in the step of removing CaF2 in the traditional acid leaching of waste cathode for electrolytic aluminum, so as to realize the oxidation cutting of doped electrolytic aluminum cathode carbon powder into high value functionalized carbon dots.

[0004] In order to achieve the above purpose, the technical scheme of the present application is as follows:

[0005] A method for preparing functionalized carbon dots from waste cathode for electrolytic aluminum, comprising the following steps:

[0006] S1, mixing and ball milling the waste cathode for electrolytic aluminum with thiocyanate or L-cysteine to obtain activated mixed powder;

[0007] S2, adding the mixed powder into an alkali solution, dispersing uniformly, and then performing hydrothermal reaction in a sealed reaction container;

[0008] S3, after the reaction is completed, cooling to room temperature, solid-liquid separation, collection of nitrogen sulfur fluorine co-doped electrolytic aluminum cathode carbon powder is obtained;

[0009] S4, the nitrogen sulfur fluorine co-doped electrolytic aluminum cathode carbon powder obtained in step S3 is added to a mixed solution of concentrated nitric acid and concentrated sulfuric acid, uniformly dispersed, and then subjected to hydrothermal reaction in a sealed reaction vessel;

[0010] S5, after the reaction is completed, cooling to room temperature, solid-liquid separation, collection of the first filtrate;

[0011] S6, a hot base solution is added to the first filtrate obtained in step S5 to make the solution neutral, and after the reaction is completed, cooling to room temperature, solid-liquid separation, collection of the second filtrate;

[0012] S7, the collected second filtrate is dialyzed with a dialysis bag, and then the obtained liquid is dried to obtain nitrogen sulfur fluorine co-doped functionalized carbon dots.

[0013] In some embodiments, in step S1, the mass ratio of thiourea or L-cysteine to the electrolytic aluminum waste cathode is 0.5-1.5:1, and the ratio of the beads to the material is 1:15-20.

[0014] In some embodiments, in step S1, during the ball milling process, the ball milling speed is 200-600 rpm / min; the ball milling time is 6-10 h.

[0015] In some embodiments, in step S2, the base includes at least one of lithium hydroxide, sodium alkoxide, potassium alkoxide, and quaternary ammonium base. In some embodiments, in step S2, the concentration of the base solution is 0.5-2 mol / L, the hydrothermal reaction temperature is 90-180℃, and the reaction time is 6-24 h.

[0016] In some embodiments, in step S2, the solid-liquid ratio of the mixed powder and the base solution is 1g:5-40mL.

[0017] In some embodiments, in step S4, in the mixed solution, the volume ratio of concentrated nitric acid to concentrated sulfuric acid is 1:1-4; the solid-liquid ratio of the nitrogen sulfur fluorine co-doped electrolytic aluminum cathode carbon powder and the mixed solution is 1g:20-70mL; the hydrothermal reaction temperature is 120-140℃; and the reaction time is 6-12 h.

[0018] In some embodiments, in step S6, the hot base includes at least one of sodium bicarbonate solution, potassium bicarbonate solution, sodium hydroxide solution, potassium hydroxide solution, magnesium carbonate solution, lithium carbonate solution, ammonia, lithium hydroxide solution, sodium alkoxide solution, potassium alkoxide solution, quaternary ammonium base solution, magnesium hydroxide solution, and zinc hydroxide solution.

[0019] In some embodiments, in step S6, the temperature of the hot alkali solution is 60-90 DEG C, and the concentration of the hot alkali solution is a saturated concentration at the set temperature.

[0020] Compared with the prior art, the application has the following advantages:

[0021] The inventors have found that, in the traditional alkali leaching process of electrolytic aluminum waste cathode, the addition of thiourea or L-cysteine can simultaneously achieve the dissolution and removal of impurities such as Al2O3 and SiO2, and can achieve the doping of N, S and F impurities by utilizing the fluorine impurities in the cathode powder, without the need for an acid leaching step to remove CaF2, thereby simplifying the impurity removal process, and directly reacting the obtained doped electrolytic aluminum cathode carbon powder with a mixed solution of concentrated nitric acid / concentrated sulfuric acid having strong oxidizing property, which not only removes the F element in the remaining fluorine-containing solid waste CaF2 by converting it into HF, but also realizes the high-value conversion of the electrolytic aluminum waste cathode into functional carbon dots.

[0022] The method of the application solves the problem of difficult recycling of electrolytic aluminum waste cathodes, avoids the solid waste pollution of electrolytic aluminum waste cathodes to the environment, provides a new raw material source for the preparation of functional carbon dots, and greatly improves the economic benefits of recycling electrolytic aluminum waste cathodes. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 TEM image of the functional carbon dot material prepared in Example 1 of the application;

[0024] Figure 2 HRTEM image of the functional carbon dot material prepared in Example 1 of the application;

[0025] Figure 3 XRD image of the functional carbon dot material prepared in Example 1 of the application. DETAILED DESCRIPTION

[0026] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the application. However, it will be apparent to one skilled in the art that the application can be practiced without the specific details set forth in this description. In other instances, well-known methods have not been described in detail in order to avoid unnecessarily obscuring the application.

[0027] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description herein is for describing particular embodiments only and is not intended to be limiting of the application.

[0028] Example 1

[0029] The application discloses a method for preparing functionalized carbon dots from waste cathodes of electrolytic aluminum.

[0030] After 2g of waste cathodes of electrolytic aluminum and 1g of thiourea are ball milled at a rotating speed of 500rpm / min for 8h, activated mixed powder is obtained; the activated mixed powder is added into 50ml of a lithium hydroxide solution with a concentration of 1mol / L to uniformly disperse the powder, so that a first mixed solution is obtained; then the first mixed solution is transferred into a sealed high-pressure reaction kettle, heated to 100 DEG C, and subjected to hydrothermal reaction for 24h; after the reaction is completed, the temperature is cooled to room temperature, centrifugation or suction filtration is performed, solid-liquid separation is performed, a solution containing NaAl(OH)4, [Al(OH)6] 3- , [Al2(OH) 10 ] 4- , Na2SiO3 impurities is removed, and nitrogen-sulfur-fluorine co-doped electrolytic aluminum cathode carbon powder is collected; 1g of the nitrogen-sulfur-fluorine co-doped electrolytic aluminum cathode carbon powder is added into a mixed solution of concentrated nitric acid and concentrated sulfuric acid (the volume ratio of the concentrated nitric acid to the concentrated sulfuric acid is 1:2, and the total solution volume is 60ml) to uniformly disperse the electrolytic aluminum cathode carbon powder, so that a second mixed solution is obtained; then the second mixed solution is subjected to hydrothermal reaction for 7h in a sealed high-pressure reaction kettle, heated to 130 DEG C; after the reaction is completed, the temperature is cooled to room temperature in a fume hood, HF gas generated is removed, centrifugation or suction filtration is performed, solid-liquid separation is performed, and a first filtrate is collected; saturated sodium hydroxide hot solution (60 DEG C) is added into the first filtrate until the first filtrate is neutral, and then the temperature is cooled, centrifugation or suction filtration is performed, solid-liquid separation is performed, and a second filtrate is collected; the collected second filtrate is subjected to dialysis with a dialysis bag, and the obtained liquid is dried to obtain functionalized carbon dots.

[0031] The functionalized carbon dot material is subjected to TEM testing and XRD testing, and the detection results are shown in Figure 1 , Figure 2 and Figure 3 . Wherein, Figure 1 is a TEM image of the functionalized carbon dot material, Figure 2 is an HRTEM image of the functionalized carbon dot material, Figure 3 is an XRD image of the functionalized carbon dot material.

[0032] As shown in Figure 1 , the functionalized carbon dot material obtained in the embodiment has a particle size of 3-10nm, is uniformly distributed, and has no obvious agglomeration phenomenon.

[0033] As shown in Figure 2 , the HRTEM image shows that the functionalized carbon dots have obvious graphitized lattices.

[0034] As shown in Figure 3As shown, the functionalized carbon dots prepared from the electrolytic aluminum waste cathode disappear the diffraction peak at 26.6° compared with the electrolytic aluminum waste cathode, which indicates that the two-dimensional structure of the electrolytic aluminum cathode carbon powder is destroyed, the electrolytic aluminum cathode carbon powder is successfully exfoliated to synthesize the functionalized carbon dots, and the peaks belonging to Na3AlF6, SiO2, NaF and CaF2 impurity phases in the electrolytic aluminum waste cathode have been removed.

[0035] Example 2

[0036] A method for preparing functionalized carbon dots from an electrolytic aluminum waste cathode, comprising the following steps:

[0037] After ball milling 2g of electrolytic aluminum waste cathode and 1.5g of L-cysteine at a speed of 500rpm / min for 8h, an activated mixed powder is obtained; the obtained activated mixed powder is added into 50ml of lithium hydroxide solution with a concentration of 1mol / L to make the powder uniformly dispersed, to obtain a first mixed solution; then the first mixed solution is transferred into a sealed high-pressure reaction kettle, heated to 180℃, and hydrothermal reaction is carried out for 24h; after the reaction is completed, it is cooled to room temperature, centrifuged or suction filtered, and solid-liquid separation is carried out to remove the solution containing NaAl(OH)4, [Al(OH)6] 3- , [Al2(OH) 10 ] 4- , Na2SiO3 impurities, and the nitrogen-sulfur-fluorine co-doped electrolytic aluminum cathode carbon powder is collected; 1g of the nitrogen-sulfur-fluorine co-doped electrolytic aluminum cathode carbon powder is added into a mixed solution of concentrated nitric acid and concentrated sulfuric acid (the volume ratio of concentrated nitric acid to concentrated sulfuric acid is 1:2, and the total solution volume is 60ml) to make the electrolytic aluminum cathode carbon powder uniformly dispersed, to obtain a second mixed solution; then the second mixed solution is heated to 130℃ in a sealed high-pressure reaction kettle, and hydrothermal reaction is carried out for 7h; after the reaction is completed, it is cooled to room temperature in a fume hood, the generated HF gas is removed, centrifuged or suction filtered, and solid-liquid separation is carried out, and the first filtrate is collected; saturated sodium hydroxide hot solution (60℃) is added to the first filtrate until the first filtrate is neutral, and after cooling, centrifugation or suction filtration is carried out, solid-liquid separation is carried out, and the second filtrate is collected; the collected second filtrate is dialyzed with a dialysis bag, and the obtained liquid is dried to obtain functionalized carbon dots.

[0038] It is detected that the functionalized carbon dots obtained by the method of the present application have a particle size of 3-9nm, and are uniformly distributed without obvious agglomeration.

[0039] Comparative Example 1

[0040] A method for preparing heteroatom-doped carbon powder from an electrolytic aluminum waste cathode, comprising the following steps:

[0041] After ball milling 2 g of used electrolytic aluminum cathode and 1 g of thiourea at a rotation speed of 500 rpm / min for 8 h, activated used electrolytic aluminum cathode powder was obtained; the activated used electrolytic aluminum cathode powder was added into 50 ml of 1 mol / L lithium hydroxide alkaline solution to uniformly disperse the powder, and then the mixed solution was heated to 100 DEG C in a sealed high-pressure reaction kettle to perform hydrothermal reaction for 24 h; after the reaction was completed, the temperature was cooled to room temperature, centrifugation or suction filtration was performed, solid-liquid separation was performed, and a solution containing NaAl(OH)4, [Al(OH)6] 3- 、[Al2(OH) 10 ] 4- 、Na2SiO3 impurities was removed, and doped cathode electrolytic aluminum cathode carbon powder was collected; 1 g of the doped cathode electrolytic aluminum cathode carbon powder was added into 60 ml of 1 mol / L hydrochloric acid to uniformly disperse the cathode electrolytic aluminum cathode carbon powder, and then the mixed solution was heated to 130 DEG C in a sealed high-pressure reaction kettle to perform hydrothermal reaction for 7 h; after the reaction was completed, the temperature was cooled to room temperature in a fume hood, HF gas generated was removed, centrifugation or suction filtration was performed, solid-liquid separation was performed, and electrolytic aluminum cathode carbon powder after the reaction was collected.

[0042] The method of the present comparative example cannot obtain functionalized carbon dots by removing CaF in the doped electrolytic aluminum cathode carbon powder with hydrochloric acid.

[0043] The technical features of the above-described embodiments can be combined in any manner, and to make the description concise, all possible combinations of the technical features in the above-described embodiments are not described, however, as long as the combinations of the technical features do not exist, they should be considered as the scope of the present disclosure.

[0044] The above-described embodiments only express several embodiments of the present disclosure, and the description is relatively specific and detailed, but it should not be understood as a limitation on the scope of the patent. It should be pointed out that for ordinary skilled persons in the art, without departing from the concept of the present disclosure, a number of modifications and improvements can be made, which are within the scope of the present disclosure. Therefore, the protection scope of the present patent should be subject to the appended claims.

Claims

1. A method for preparing functionalized carbon dots from spent aluminum electrolysis cathode, characterized in that, The method comprises the following steps: S1, mixing and ball-milling the electrolytic aluminum waste cathode with thiourea or L-cysteine to obtain activated mixed powder; S2, adding the mixed powder into an alkali solution and uniformly dispersing, and then performing hydrothermal reaction in a sealed reaction container; S3, after the reaction is completed, cooling to room temperature, solid-liquid separation, and collecting nitrogen-sulfur-fluorine co-doped electrolytic aluminum cathode carbon powder; S4, adding the nitrogen-sulfur co-doped electrolytic aluminum cathode carbon powder obtained in step S3 into a mixed solution of concentrated nitric acid and concentrated sulfuric acid, uniformly dispersing, and then performing hydrothermal reaction in a sealed reaction container; S5, after the reaction is completed, cooling to room temperature, solid-liquid separation, and collecting a first filtrate; S6, adding a hot alkali solution into the first filtrate obtained in step S5 to neutralize the solution, after the reaction is completed, cooling to room temperature, solid-liquid separation, and collecting a second filtrate; S7, dialyzing the collected second filtrate with a dialysis bag, drying the obtained liquid, and obtaining nitrogen-sulfur-fluorine co-doped functionalized carbon dots; In step S1, the mass ratio of thiourea or L-cysteine to electrolytic aluminum waste cathode is 0.5-1.5:1, and the ratio of beads to material is 1:15-20.

2. The method of claim 1, wherein the functionalized carbon dots are prepared from spent aluminum electrolysis cathodes. In step S1, during the ball-milling process, the ball-milling rotation speed is 200-600 rpm / min, and the ball-milling time is 6-10 h.

3. The method of claim 1, wherein the functionalized carbon dots are prepared from spent aluminum electrolysis cathodes. In step S2, the alkali includes at least one of lithium hydroxide, sodium alkoxide, potassium alkoxide, and quaternary ammonium base.

4. The method of claim 1, wherein the functionalized carbon dots are prepared from spent aluminum electrolysis cathodes. In step S2, the concentration of the alkali solution is 0.5-2 mol / L, the hydrothermal reaction temperature is 90-180℃, and the reaction time is 6-24 h.

5. The method of claim 1, wherein the functionalized carbon dots are prepared from spent aluminum electrolysis cathodes. In step S2, the solid-liquid ratio of the mixed powder to the alkali solution is 1 g:5-40 mL.

6. The method of claim 1, wherein the functionalized carbon dots are prepared from spent aluminum electrolysis cathodes. In step S4, in the mixed solution, the volume ratio of concentrated nitric acid to concentrated sulfuric acid is 1:1-4, the solid-liquid ratio of nitrogen-sulfur-fluorine co-doped electrolytic aluminum cathode carbon powder to the mixed solution is 1 g:20-70 mL, the hydrothermal reaction temperature is 120-140℃, and the reaction time is 6-12 h.

7. The method of claim 1, wherein the functionalized carbon dots are prepared from spent aluminum electrolysis cathodes. In step S6, the hot alkali includes at least one of sodium bicarbonate solution, potassium bicarbonate solution, sodium hydroxide solution, potassium hydroxide solution, magnesium carbonate solution, lithium carbonate solution, ammonia water, lithium hydroxide solution, sodium alkoxide solution, potassium alkoxide solution, quaternary ammonium base solution, magnesium hydroxide solution, and zinc hydroxide solution.

8. The method of claim 1, wherein the functionalized carbon dots are prepared from the electrolytic aluminum cathode carbon powder. In step S6, the temperature of the hot alkali solution is 60-90℃, and the concentration of the hot alkali solution is the saturated concentration at the set temperature.

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