Method for preparing carbon quantum dots from waste polyurethane

Abstract

The invention provides a method for preparing carbon quantum dots from waste polyurethane, and belongs to the technical field of carbon materials. The method for preparing the carbon quantum dots from the waste polyurethane comprises the following steps: mixing the waste polyurethane with water, and carrying out hydrothermal reaction to obtain the carbon quantum dots, the temperature of the hydrothermal reaction is 100-260 DEG C, and the time of the hydrothermal reaction is 8-24 hours. The waste polyurethane is used as a carbon source and a nitrogen source, the carbon quantum dots with excellent optical performance and stability are prepared under specific hydrothermal reaction conditions, and meanwhile, the waste polyurethane is adopted, so that the additional value can be increased, and the cost of the carbon quantum dots can be reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of carbon materials, and in particular relates to a method for preparing carbon quantum dots by using waste polyurethane. Background Art

[0002] The unique photoluminescence properties of carbon quantum dots have made them widely used in biosensing, metal ion detection, photoelectrocatalysis, food quality analysis and anti-counterfeiting. At present, carbon quantum dots mainly use glucose as a carbon source, which is relatively expensive.

[0003] Polyurethane is widely used due to its excellent physical and chemical properties. With the continuous increase in polyurethane production, waste polyurethane is gradually increasing. At present, waste polyurethane is mainly incinerated, which will release many harmful substances and bring a heavy burden to the environment. Therefore, how to increase the added value of waste polyurethane while reducing costs on the basis of ensuring the performance of carbon quantum dots has become a technical problem that needs to be solved urgently in this field. Summary of the invention

[0004] The purpose of the present invention is to provide a method for preparing carbon quantum dots using waste polyurethane. The method provided by the present invention can not only increase the added value of waste polyurethane, but also reduce the cost of carbon quantum dots while ensuring the performance of carbon quantum dots.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The invention provides a method for preparing carbon quantum dots by using waste polyurethane, comprising: mixing the waste polyurethane and water, performing a hydrothermal reaction, and obtaining carbon quantum dots; the temperature of the hydrothermal reaction is 100-260° C., and the time of the hydrothermal reaction is 8-24 hours.

[0007] Preferably, the particle size of the waste polyurethane is ≤100 mesh.

[0008] Preferably, the mass ratio of the waste polyurethane to water is 1:(10-100).

[0009] Preferably, the mass ratio of the waste polyurethane to water is 1:(25-50).

[0010] Preferably, the temperature of the hydrothermal reaction is 130-250° C., and the time of the hydrothermal reaction is 10-20 h.

[0011] Preferably, after the hydrothermal reaction is completed, filtration, dialysis and drying are further performed in sequence.

[0012] Preferably, the dialysis time is 12 to 48 hours.

[0013] Preferably, the drying includes pre-freezing and freeze-drying. The temperature of pre-freezing is -25 to -20 °C, and the time of pre-freezing is 10 to 15 h; the temperature of freeze-drying is -70 to -55 °C, and the time of freeze-drying is 2 to 4 d.

[0014] The present invention also provides carbon quantum dots prepared by the method according to the above technical solution.

[0015] The present invention also provides the application of the carbon quantum dots according to the above technical solution in biological imaging, sensors and photocatalysis.

[0016] In the present invention, waste polyurethane is used as a carbon source and a nitrogen source, and through specific hydrothermal reaction conditions, carbon quantum dots with excellent optical properties and stability are prepared. At the same time, the use of waste polyurethane can not only increase the added value, but also reduce the cost of carbon quantum dots. The experimental results show that the quantum yield of the carbon quantum dots provided by the present invention is 3.72 to 5.81%, and the fluorescence intensity is relatively high. Description of the Drawings

[0017] Figure 1 Process flow chart for preparing carbon quantum dots in Example 1;

[0018] Figure 2 Photo of the aqueous solution prepared from the carbon quantum dots prepared in Example 3 under sunlight irradiation;

[0019] Figure 3 Photo of the aqueous solution prepared from the carbon quantum dots prepared in Example 3 under ultraviolet light irradiation;

[0020] Figure 4 Fluorescence spectra of the carbon quantum dots prepared in Comparative Example 1 and Examples 5 to 9. Detailed Description of the Invention

[0021] The present invention provides a method for preparing carbon quantum dots using waste polyurethane, including: mixing waste polyurethane and water, and performing a hydrothermal reaction to obtain carbon quantum dots.

[0022] The present invention has no special limitation on the sources of each raw material, and commercially available products well-known to those skilled in the art can be used.

[0023] In the present invention, the particle size of the waste polyurethane is preferably ≤100 mesh. Limiting the particle size of the waste polyurethane within the above range is beneficial to the subsequent hydrothermal reaction.

[0024] In the present invention, when the particle size of the waste polyurethane does not meet the above requirements, it is preferably to crush and screen the waste polyurethane in sequence. The present invention has no special limitation on the operations of crushing and screening, as long as the particle size of the waste polyurethane meets the above requirements.

[0025] In the present invention, the waste polyurethane preferably includes at least one of rigid polyurethane foam, flexible polyurethane foam, polyurethane elastomer, spandex material and leather. Using waste polyurethane as the carbon precursor in the present invention can further utilize the waste polyurethane, thereby realizing the high-value utilization of waste; at the same time, it has its own carbon source and nitrogen source, and there is no need to additionally add a catalyst, a carbon source and a nitrogen source.

[0026] In the present invention, the mass ratio of the waste polyurethane to water is preferably 1:(10 - 100), more preferably 1:(20 - 80). As an embodiment, the mass ratio of the waste polyurethane to water can be 1:25, 1:30, 1:40, 1:50, 1:60 or 1:70. Limiting the mass ratio of the waste polyurethane to water within the above range in the present invention can further improve the degree of the hydrothermal reaction.

[0027] The present invention has no special limitation on the mixing of the waste polyurethane and water, and the technical solutions for preparing the mixed material well-known to those skilled in the art can be adopted.

[0028] In the present invention, the temperature of the hydrothermal reaction is 100 - 260 °C, preferably 130 - 250 °C; the time of the hydrothermal reaction is 8 - 24 h, preferably 10 - 20 h. Limiting the temperature and time of the hydrothermal reaction within the above range in the present invention can accelerate the hydrolysis of the waste polyurethane, promote the hydrothermal reaction, and produce carbon quantum dots with good water solubility, uniform size distribution and high yield.

[0029] As an embodiment, the temperature of the hydrothermal reaction can be 140 °C, 150 °C, 160 °C, 170 °C, 180 °C, 190 °C, 200 °C, 210 °C, 220 °C, 230 °C or 240 °C; the time of the hydrothermal reaction is 11 h, 12 h, 13 h, 14 h, 15 h, 16 h, 17 h, 18 h or 19 h.

[0030] After the hydrothermal reaction is completed, the present invention preferably filters, dialyzes and dries the product obtained from the hydrothermal reaction in sequence to obtain carbon quantum dots.

[0031] The present invention has no special limitation on the operation of the filtration, and the insoluble carbon can be removed by the operation well-known to those skilled in the art.

[0032] In the present invention, the dialysis is preferably carried out using a dialysis bag; the cut-off molecular weight of the dialysis bag is preferably ≥ 3500 Da; the dialysis time is preferably 12 - 48 h; deionized water is changed every 2 - 8 h during dialysis. The present invention can remove the over-decomposed small molecules by dialysis.

[0033] As an implementation method, the dialysis time can be 15 to 45 h, or can also be 20 to 30 h; deionized water is changed every 3 to 6 h during dialysis.

[0034] In the present invention, the drying preferably includes pre-freezing and freeze-drying; the temperature of the pre-freezing is preferably -25 to -20 °C, more preferably -23 to -22 °C; the time of the pre-freezing is preferably 10 to 15 h, more preferably 12 to 14 h; the temperature of the freeze-drying is preferably -70 to -55 °C, more preferably -65 to -60 °C; the time of the freeze-drying is preferably 2 to 4 days, more preferably 3 days; the pressure of the freeze-drying is preferably 15 to 25 Pa, more preferably 20 Pa.

[0035] The present invention uses waste polyurethane as a carbon source and a nitrogen source, and through specific hydrothermal reaction conditions, carbon quantum dots with uniform size, good water solubility, excellent fluorescence intensity, fluorescence quantum yield and blue light emission are prepared; and the operation is simple, the cost is low and it is environmentally friendly, realizing the efficient utilization of waste materials.

[0036] The present invention also provides carbon quantum dots prepared by the method of the above technical solution.

[0037] The present invention also provides the application of the carbon quantum dots of the above technical solution in bioimaging, sensors and photocatalysis.

[0038] The present invention has no special limitation on the operation of the application, and the application operations well-known to those skilled in the art can be adopted.

[0039] Next, the technical solutions in the present invention will be clearly and completely described in conjunction with the embodiments in the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present invention without creative efforts shall fall within the protection scope of the present invention.

[0040] The preparation methods of the waste polyurethane used in Comparative Example 1 and Examples 1 to 4 are as follows:

[0041] The waste polyurethane foam of the insulation layer of the prefabricated directly buried insulating pipe produced by Sanjie Energy Saving New Materials Co., Ltd. is mechanically crushed into a size of 0.5 mm, and then passed through a 100-mesh sieve to obtain waste polyurethane with a particle size ≤ 100 mesh.

[0042] Example 1

[0043] The preparation method of the carbon quantum dots is as follows:

[0044] The waste polyurethane was mixed with deionized water at a mass ratio of 1:30 by stirring for 30 min, then placed in a 100 mL high-pressure reactor, and hydrothermally reacted at 100 °C for 8 h. Then, suction filtration was carried out, and it was placed in a dialysis bag with a molecular weight cut-off of 3500 Da for dialysis for 48 h. During this period, deionized water was changed every 6 h. Subsequently, it was pre-frozen at -22 °C for 12 h, and then freeze-dried in a vacuum freeze dryer at -60 °C and a pressure of 20 Pa for 2 d to obtain carbon quantum dots.

[0045] The carbon quantum dots prepared in Example 1 can emit short-wavelength blue fluorescence at 443 nm under the excitation of 365 nm, have certain excitation dependence and good water solubility, and the quantum yield is 4.1% (using the fluorescence quantum yield method, with reference substance quinine sulfate as the standard, and calculating the relative quantum yield through fluorescence intensity and absorbance, the same below).

[0046] The process flow chart for preparing carbon quantum dots in Example 1 is as Figure 1 shown.

[0047] From Figure 1 it can be seen that in the present invention, the waste polyurethane is first mechanically pulverized, then sieved, and then hydrothermally reacted, suction filtered, washed, and dried in sequence to obtain carbon quantum dots.

[0048] Example 2

[0049] The preparation method of carbon quantum dots is as follows:

[0050] The waste polyurethane was mixed with deionized water at a mass ratio of 1:40 by stirring for 30 min, then placed in a 100 mL high-pressure reactor, and hydrothermally reacted at 170 °C for 10 h. Then, suction filtration was carried out, and it was placed in a dialysis bag with a molecular weight cut-off of 3500 Da for dialysis for 48 h. During this period, deionized water was changed every 6 h. Subsequently, it was pre-frozen at -22 °C for 12 h, and then freeze-dried in a vacuum freeze dryer at -60 °C and a pressure of 20 Pa for 2 d to obtain carbon quantum dots.

[0051] The carbon quantum dots prepared in Example 2 can emit short-wavelength blue fluorescence at 443 nm under the excitation of 365 nm, have certain excitation dependence and good water solubility, and the quantum yield is 5.65%.

[0052] Example 3

[0053] The preparation method of carbon quantum dots is as follows:

[0054] The waste polyurethane and deionized water were mixed at a mass ratio of 1:50 by stirring for 30 min, and then placed in a 100 mL high-pressure reactor for hydrothermal reaction at 240 °C for 12 h. Then, filtration was carried out, and then it was dialyzed in a dialysis bag with a molecular weight cut-off of 3500 Da for 48 h, during which deionized water was changed every 6 h. Subsequently, it was pre-frozen at -22 °C for 12 h and then freeze-dried in a vacuum freeze dryer at -60 °C and a pressure of 20 Pa for 2 d to obtain carbon quantum dots.

[0055] The carbon quantum dots prepared in Example 3 can emit short-wavelength blue fluorescence at 443 nm under excitation at 365 nm, have certain excitation dependence and good water solubility, and the quantum yield is 5.81%.

[0056] The photograph of the aqueous solution prepared from the carbon quantum dots prepared in Example 3 under sunlight irradiation is as Figure 2 shown.

[0057] The photograph of the aqueous solution prepared from the carbon quantum dots prepared in Example 3 under ultraviolet light irradiation is as Figure 3 shown.

[0058] From Figure 2 and 3 it can be seen that the carbon quantum dots have obvious blue fluorescence under ultraviolet light irradiation.

[0059] Example 4

[0060] The preparation method of the carbon quantum dots is as follows:

[0061] The waste polyurethane and deionized water were mixed at a mass ratio of 1:60 by stirring for 30 min, and then placed in a 100 mL high-pressure reactor for hydrothermal reaction at 260 °C for 14 h. Then, filtration was carried out, and then it was dialyzed in a dialysis bag with a molecular weight cut-off of 3500 Da for 48 h, during which deionized water was changed every 6 h. Subsequently, it was pre-frozen at -22 °C for 12 h and then freeze-dried in a vacuum freeze dryer at -60 °C and a pressure of 20 Pa for 2 d to obtain carbon quantum dots, denoted as PU CQDs.

[0062] The carbon quantum dots prepared in Example 4 can emit short-wavelength blue fluorescence at 443 nm under excitation at 365 nm, have certain excitation dependence and good water solubility, and the quantum yield is 4.53%.

[0063] Through the above experimental research and data analysis, when the mass ratio of waste polyurethane to deionized water is 1:50, the fluorescence yield of the carbon quantum dots prepared by hydrothermal reaction at a temperature of 240 °C for 12 h is relatively high.

[0064] Comparative Example 1

[0065] The preparation method of carbon quantum dots is as follows:

[0066] Waste polyurethane and deionized water were mixed at a mass ratio of 1:50 and stirred for 30 min. Then, potassium hydroxide was added as a catalyst, and the mixture was placed in a 100 mL autoclave and hydrothermally reacted at 240 °C for 12 h. Then, filtration was carried out, and the product was dialyzed in a dialysis bag with a molecular weight cut-off of 3500 Da for 48 h, during which deionized water was changed every 6 h. Subsequently, it was pre-frozen at -22 °C for 12 h and then freeze-dried in a vacuum freeze dryer at -60 °C and a pressure of 20 Pa for 2 d to obtain carbon quantum dots, denoted as KOH-PU CQDs.

[0067] The carbon quantum dots prepared in Comparative Example 1 can emit short-wavelength blue fluorescence at 443 nm under the excitation of 365 nm, showing certain excitation dependence and good water solubility. However, the fluorescence intensity and fluorescence quantum yield are not high, and the quantum yield is only 0.6%.

[0068] Example 5

[0069] The preparation method of carbon quantum dots is as follows:

[0070] The polyurethane foam from a discarded Midea freezer was mechanically crushed into a size of 0.5 mm and then passed through a 100-mesh sieve to obtain waste polyurethane with a particle size ≤ 100 mesh. Subsequently, waste polyurethane and deionized water were mixed at a mass ratio of 1:50 and stirred for 30 min. Then, the mixture was placed in a 100 mL autoclave and hydrothermally reacted at 240 °C for 12 h. Then, filtration was carried out, and the product was dialyzed in a dialysis bag with a molecular weight cut-off of 3500 Da for 48 h, during which deionized water was changed every 6 h. Subsequently, it was pre-frozen at -22 °C for 12 h and then freeze-dried in a vacuum freeze dryer at -60 °C and a pressure of 20 Pa for 2 d to obtain carbon quantum dots, denoted as H-PU CQDs.

[0071] The carbon quantum dots prepared in Example 5 can emit short-wavelength blue fluorescence at 448 nm under the excitation of 365 nm, showing certain excitation dependence and good water solubility. The average particle size is 3.3 nm, the size distribution is narrow, the fluorescence intensity is significantly improved, which is 7.83 times that of the carbon quantum dots in Comparative Example 1, and the quantum yield is 4.76%.

[0072] Example 6

[0073] The preparation method of carbon quantum dots is as follows:

[0074] The polyurethane soft foam from waste sofas was mechanically crushed into a size of 0.5 mm, then passed through a 100-mesh sieve to obtain waste polyurethane with a particle size ≤ 100 mesh. Subsequently, the waste polyurethane and deionized water were mixed by stirring for 30 min at a mass ratio of 1:50, then placed in a 100 mL high-pressure reactor and hydrothermally reacted at 240 °C for 12 h. Then, filtration was carried out, and then it was placed in a dialysis bag with a molecular weight cut-off of 3500 Da and dialyzed for 48 h, during which the deionized water was changed every 6 h. Subsequently, it was pre-frozen at -22 °C for 12 h and then freeze-dried in a vacuum freeze dryer at -60 °C and a pressure of 20 Pa for 2 d to obtain carbon quantum dots, denoted as R-PU CQDs.

[0075] The carbon quantum dots prepared in Example 6 can emit short-wavelength blue fluorescence at 454 nm under the excitation of 365 nm, have certain excitation dependence and good water solubility, with an average particle size of 2.8 nm, a narrow size distribution, and a significantly improved fluorescence intensity, which is 8.34 times that of the carbon quantum dots in Comparative Example 1, and the quantum yield is 5.36%.

[0076] Example 7

[0077] The preparation method of the carbon quantum dots is as follows:

[0078] The polyurethane sole material was mechanically crushed into a size of 0.5 mm, then passed through a 100-mesh sieve to obtain waste polyurethane with a particle size ≤ 100 mesh. Subsequently, the waste polyurethane and deionized water were mixed by stirring for 30 min at a mass ratio of 1:50, then placed in a 100 mL high-pressure reactor and hydrothermally reacted at 240 °C for 12 h. Then, filtration was carried out, and then it was placed in a dialysis bag with a molecular weight cut-off of 3500 Da and dialyzed for 48 h, during which the deionized water was changed every 6 h. Subsequently, it was pre-frozen at -22 °C for 12 h and then freeze-dried in a vacuum freeze dryer at -60 °C and a pressure of 20 Pa for 2 d to obtain carbon quantum dots, denoted as S-PU CQDs.

[0079] The carbon quantum dots prepared in Example 7 can emit short-wavelength blue fluorescence at 452 nm under the excitation of 365 nm, have certain excitation dependence and good water solubility, with an average particle size of 3.5 nm, a narrow size distribution, and a significantly improved fluorescence intensity, which is 7.34 times that of the carbon quantum dots in Comparative Example 1, and the quantum yield is 4.47%.

[0080] Example 8

[0081] The preparation method of the carbon quantum dots is as follows:

[0082] First, lay the leather flat, then cut a sample of appropriate size, and then scrape the surface layer with a blade. The scraped debris is mechanically pulverized into a size of 0.5 mm, and then passed through a 100-mesh sieve to obtain waste polyurethane with a particle size ≤ 100 mesh. Subsequently, the waste polyurethane and deionized water are mixed at a mass ratio of 1:25 and stirred for 30 min, then placed in a 100 mL high-pressure reactor and hydrothermally reacted at 240 °C for 12 h, then filtered by suction, and then placed in a dialysis bag with a cut-off molecular weight of 3500 Da for dialysis for 48 h. During this period, deionized water is changed every 6 h. Subsequently, it is pre-frozen at -22 °C for 12 h, and then freeze-dried in a vacuum freeze dryer at -60 °C and a pressure of 20 Pa for 2 d to obtain carbon quantum dots, denoted as P-PU CQDs.

[0083] The carbon quantum dots prepared in Example 8 can emit short-wavelength blue fluorescence at 448 nm under the excitation of 365 nm, have certain excitation dependence and good water solubility, with an average particle size of 4.1 nm, a narrow size distribution, and a significantly improved fluorescence intensity, which is 6.12 times that of the carbon quantum dots in Comparative Example 1, and the quantum yield is 3.72%.

[0084] Example 9

[0085] The preparation method of carbon quantum dots is as follows:

[0086] Lay the spandex material from the fabric flat, cut a sample of appropriate size and mechanically pulverize it into a size of 0.5 mm, and then pass through a 100-mesh sieve to obtain waste polyurethane with a particle size ≤ 100 mesh. Subsequently, the waste polyurethane and deionized water are mixed at a mass ratio of 1:50 and stirred for 30 min, then placed in a 100 mL high-pressure reactor and hydrothermally reacted at 240 °C for 12 h, then filtered by suction, and then placed in a dialysis bag with a cut-off molecular weight of 3500 Da for dialysis for 48 h. During this period, deionized water is changed every 6 h. Subsequently, it is pre-frozen at -22 °C for 12 h, and then freeze-dried in a vacuum freeze dryer at -60 °C and a pressure of 20 Pa for 2 d to obtain carbon quantum dots, denoted as A-PU CQDs.

[0087] The carbon quantum dots prepared in Example 9 can emit short-wavelength blue fluorescence at 448 nm under the excitation of 365 nm, have certain excitation dependence and good water solubility, with an average particle size of 3.8 nm, a relatively wide size distribution, and a significantly improved fluorescence intensity, which is 6.83 times that of the carbon quantum dots in Comparative Example 1, and the quantum yield is 4.19%.

[0088] Compared with the carbon quantum dots added with a catalyst in Comparative Example 1, its quantum yield is significantly improved.

[0089] The fluorescence spectra of the carbon quantum dots prepared in Comparative Example 1 and Examples 5 - 9 are as Figure 4 shown.

[0090] From Figure 4 It can be seen that, compared with the carbon quantum dots added with the catalyst, its fluorescence intensity is significantly improved; the catalyst provides an alkaline condition for the hydrothermal system and promotes the hydrolysis of waste polyurethane. However, if the dosage of the added catalyst is too much, the particles of the carbon quantum dots may be too fine, resulting in a decrease in the fluorescence yield. Without adding the catalyst is more convenient, and at the same time, the fluorescence yield of the carbon quantum dots is relatively high.

[0091] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing carbon quantum dots using waste polyurethane, comprising: The waste polyurethane is mixed with water and subjected to a hydrothermal reaction to obtain carbon quantum dots; the temperature of the hydrothermal reaction is 100 to 260° C. and the time of the hydrothermal reaction is 8 to 24 hours.

2. The method according to claim 1, characterized in that: The particle size of the waste polyurethane is ≤100 meshes.

3. The method according to claim 1, characterized in that The mass ratio of the waste polyurethane to water is 1:(10-100).

4. The method according to claim 1 or 3, characterized in that: The mass ratio of the waste polyurethane to water is 1:(25-50).

5. The method according to claim 1, characterized in that The temperature of the hydrothermal reaction is 130-250° C., and the time of the hydrothermal reaction is 10-20 hours.

6. The method according to claim 1, characterized in that After the hydrothermal reaction is completed, the steps of filtering, dialysis and drying are performed in sequence.

7. The method according to claim 6, characterized in that The dialysis time is 12 to 48 hours.

8. The method according to claim 6, characterized in that The drying includes pre-freezing and freeze drying. The pre-freezing temperature is -25 to -20°C and the pre-freezing time is 10 to 15 hours. The freeze drying temperature is -70 to -55°C and the freeze drying time is 2 to 4 days.

9. Carbon quantum dots prepared by the method according to any one of claims 1 to 8.

10. Use of the carbon quantum dots according to claim 9 in biological imaging, sensors and photocatalysis.

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