Preparation method of cuprous oxide quantum dots

Abstract

This invention relates to a method for preparing cuprous oxide quantum dots, comprising the following steps: all steps are carried out at a temperature of 5℃-40℃: (1) copper salt is added to deionized water and ultrasonically stirred to obtain solution A; (2) a dispersant is dissolved in a special solution and stirred to form solution B; (3) solution A from step (1) is added to solution B from step (2), and after mixing, ultrasonic treatment is performed for more than 30 minutes to obtain solution C; (4) the pH value of solution C in step (3) is adjusted to 10-12 using sodium hydroxide solution; (5) a reducing agent is slowly added dropwise to the mixed solution, and the solution gradually changes color. This method simultaneously completes the nucleation and dispersion of quantum dots, simplifying the quantum dot dispersion steps; it enhances the stability of cuprous oxide quantum dots and solves the problem of the difficulty in stably preserving cuprous oxide quantum dots.

Description

Technical Field

[0001] This invention relates to the field of nanomaterials technology, specifically to a method for preparing cuprous oxide quantum dots. Background Technology

[0002] Cuprous oxide (Cu2O), a typical p-type semiconductor material, has shown great potential in many fields due to its narrow bandgap of 2.1 eV, high absorption coefficient in the visible light region, and low cost. When the size of cuprous oxide is shrunk to the quantum dot (1-50 nm) level, the resulting quantum confinement effect can significantly enhance the separation efficiency of photogenerated carriers and expand the photoresponse range, making it a promising candidate for applications in solar cells, photocatalysis, and sensors.

[0003] Existing Cu2O quantum dots are prone to aggregation due to their high surface energy, leading to a reduction in active sites, intensified recombination of photogenerated carriers, increased particle size, and decreased dispersibility, ultimately weakening their photocatalytic activity and long-term stability. For example, patent (CN113651353A) involves rapidly heating the pressed copper sheet in a muffle furnace at 500-1000 ℃ and then quenching it. Although the steps are short, they are energy-intensive, and the quenching process carries the risk of thermal shock and oxidation runaway. Furthermore, the product lacks surface protectants, resulting in significant aggregation. To suppress aggregation, patent (CN119114074A) uses TiO2 and other supports for mechanical grinding and loading. While this can improve the dispersibility to some extent, the supports may shield the active sites on the Cu2O surface, and it is difficult to separate high-purity quantum dots from the composite system. At the same time, reducing agents such as hydrazine hydrate still need to be added during the grinding process, and the safety risks are not fundamentally eliminated. Patent (CN102139909A) synthesizes a cuprous oxide powder larger than 800 nm. Although the method is similar to this invention, it does not synthesize well-dispersed quantum dots, and the reaction temperature is between 50℃ and 80℃. This invention, however, provides a controllable preparation of dispersed cuprous oxide quantum dots. The preparation process has strict requirements on the concentration of the copper source (0.02 M), the reaction temperature (<40℃), the concentration of the dispersant, and the dropping rate of the reducing agent to ensure uniform particle size and controllable morphology of the prepared sample. In summary, existing technologies generally suffer from shortcomings such as "complex processes, harsh conditions, low product purity, significant safety hazards, and high costs," or problems with poor performance due to excessively large particle sizes. Therefore, a new method with mild conditions, simple steps, and the ability to obtain highly dispersed and high-purity Cu₂O quantum dots independently has been developed. Summary of the Invention

[0004] To overcome the four major drawbacks of existing technologies—high temperature and high pressure, agglomeration and inactivation, difficult purification, and carrier interference—this invention provides a room-temperature (5–40 °C) green colloidal chemical method that achieves the nucleation, growth, and surface coating of Cu₂O quantum dots in one step through continuous injection of a reducing agent. This method requires no external loading medium; agglomeration is suppressed solely by the in-situ steric hindrance of dispersants such as CMC / PVP. The resulting colloid retains ≥90% absorbance within 72 hours and can be directly stored or used in the dark. This process eliminates the need for high temperature and high pressure, uses deionized water / ethylene glycol as the primary solvent, and allows for the selection of low-toxicity ascorbic acid or sodium borohydride as the reducing agent. This eliminates energy consumption and safety hazards while significantly reducing production costs. It simultaneously solves the problems of agglomeration, high temperature, pollution, and carrier shielding, laying an irreplaceable technical foundation for the safe, large-scale preparation and efficient photocatalytic application of cuprous oxide quantum dots.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for preparing cuprous oxide quantum dots utilizes sodium carboxymethyl cellulose (CMC) and other substances as dispersants and stabilizers, and ethylene glycol and other substances as antioxidants. Sodium borohydride and other substances are slowly added dropwise as reducing agents to complete the nucleation and growth of cuprous oxide quantum dot nuclei.

[0007] The cuprous oxide quantum dots of the present invention include the following steps.

[0008] All steps were performed at temperatures between 5°C and 40°C.

[0009] (1) Add copper salt to deionized water and mix thoroughly by ultrasonic stirring to obtain solution A;

[0010] (2) Dissolve the dispersant in a specially prepared solution and stir until homogeneous to form solution B;

[0011] (3) Add solution A from step (1) to solution B from step (2), mix, and sonicate for more than 30 minutes to obtain solution C;

[0012] (4) Use sodium hydroxide solution to adjust the pH of solution C in step (3) above to 10-12;

[0013] (5) Add a reducing agent solution such as sodium borohydride slowly dropwise into the solution prepared in step (4) at a rate of 10 mL / min to 0.1 mL / min. The solution gradually changes color, and cuprous oxide quantum dots are obtained.

[0014] In step (1), the copper salt is one or more of copper sulfate pentahydrate, copper acetate, and copper chloride. The concentration of the copper salt is 0.02 mol / L to 0.00002 mol / L.

[0015] In step (2), the dispersant is one or more of sodium carboxymethyl cellulose, polyvinylpyrrolidone, and sodium alginate. The special solution is a mixture of deionized water and ethylene glycol, or a mixture of them at a volume ratio of 10:1 to 1:10. The concentration of the dispersant is 0.1-1.0 wt%.

[0016] In step (3), the volume ratio of solution A to solution B is 1:1 to 10:1.

[0017] In step (4), the concentration of sodium hydroxide solution is 0.01 mol / L-2 mol / L.

[0018] In step (5), the reducing agent is one or more of sodium borohydride, ascorbic acid, and glucose. The concentration of the reducing agent is 0.2 mol / L to 0.00002 mol / L, and the molar ratio of copper salt to reducing agent is 1:0.125 to 1:20. The rate of addition of the reducing agent is 10 mL / min to 0.1 mL / min.

[0019] Store the prepared colloidal solution away from light. The colloidal solution can be used directly in liquid applications. If a solid form is required, it is recommended to use freeze-drying (lyophilization) and store it in an inert atmosphere, avoiding mechanical grinding.

[0020] In this invention, the dispersant primarily forms a steric hindrance layer (such as PVP) through molecular chain entanglement and utilizes ionized carboxyl groups (such as CMC) to generate electrostatic repulsion, effectively inhibiting quantum dot aggregation. The dispersant concentration needs to be controlled between 0.1 and 1.0 wt%: below 0.1 wt%, the molecular chain density is insufficient, and quantum dots aggregate due to van der Waals forces; above 1.0 wt%, the solution viscosity increases, hindering mass transfer, leading to uneven reaction and excessively large particle size distribution differences. Multiple dispersants exhibit complementary mechanisms of action: CMC primarily relies on electrostatic repulsion (-COO⁻ ionization), while PVP depends on long-chain steric hindrance. Composite dispersants (such as CMC+PVP) synergistically enhance the effect; the electrostatic layer strengthens the charge repulsion, and the long chains thicken the steric hindrance layer, further enhancing stability.

[0021] In this invention, the choice of the reducing agent dropping rate directly affects the reduction activity and the nucleation-growth kinetics of cuprous oxide quantum dots. Strong reducing agents (such as NaBH4) need to be added slowly (0.1–1 mL / min) to avoid local supersaturation that could trigger explosive nucleation; weak reducing agents (such as ascorbic acid) can be added at a moderately faster rate (1–10 mL / min) to regulate growth through the slow release of reducing potential. If the dropping rate is >10 mL / min, local enrichment of the reducing agent will lead to non-uniform nucleation, irregular morphology, wide quantum dot size distribution, high surface defect density, weakened quantum confinement effect, and reduced light absorption efficiency. If the rate is <0.1 mL / min, Ostwald ripening will occur, small particles will dissolve, large particles will grow abnormally, and the particle size will increase by more than 100%, even exceeding 50 nm. By controlling the dropping rate (0.1–10 mL / min), the local reducing agent concentration can be precisely adjusted to maintain the dynamic balance between nucleation and growth, ensuring uniform quantum dot size, controllable morphology, and excellent optical properties.

[0022] Cuprous oxide quantum dots of different sizes prepared under different conditions in this method have different colors.

[0023] Cuprous oxide quantum dots of different sizes exhibit different colors, which is essentially due to changes in energy level structure caused by the quantum confinement effect: the smaller the quantum dot size, the larger the band gap, the shorter the wavelength of absorbed light, and the color of transmitted light shifts towards yellow-green; the larger the size, the smaller the band gap, the longer the wavelength of absorbed light, and the color of transmitted light shifts towards pale red.

[0024] When the Cu₂O particle size is between 1 and 50 nm, electron movement is confined to the nanoscale space, leading to energy level splitting. The band gap (Eg) increases as the particle size decreases, causing the light absorption threshold to shift towards shorter wavelengths.

[0025] In one embodiment of the present invention, the copper source in step (1) is copper acetate, the dispersant in step (2) is CMC, and the antioxidant is ascorbic acid. The resulting cuprous oxide quantum dot solution is pale red.

[0026] In one embodiment of the present invention, the copper source in step (1) is copper sulfate pentahydrate, the dispersant in step (2) is CMC, and the antioxidant is ethylene glycol. The resulting cuprous oxide quantum dot solution is pale yellow.

[0027] In one embodiment of the present invention, the copper source in step (1) is 0.0002 mol / L copper sulfate pentahydrate, the dispersant in step (2) is CMC, and the antioxidant is ethylene glycol. The molar ratio of the reducing agent to the copper source is 4:1, and the resulting cuprous oxide quantum dot solution is yellow-green.

[0028] According to this invention, the process does not require high temperature, high pressure, or toxic reagents. This effectively ensures experimental safety and environmental friendliness, and helps save energy. It is easy to store and facilitates large-scale synthesis.

[0029] This patent employs the aluminum foil method for preparing SEM samples. The aluminum foil method is a technique used in scanning electron microscopy (SEM) sample preparation, suitable for processing small-sized samples and improving sample dispersibility and conductivity. The sample preparation using the aluminum foil method in this patent mainly includes the following steps: First, 50 μL of colloidal quantum dot solution is dropped onto an aluminum foil sheet (1×1 cm²). 2 Next, the aluminum foil was placed in a freeze dryer and dried for 24 hours. Finally, the dried sample was adhered to the SEM sample stage for observation. This method can effectively avoid the aggregation of quantum dots caused by traditional baking or grinding, and maintain the original dispersed state. Attached Figure Description

[0030] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0031] Figure 1 Scanning electron microscope images of cuprous oxide with an average particle size of 15 nm were prepared for Example 2 of this invention.

[0032] Figure 2 This is a scanning electron microscope image of cuprous oxide after drying, prepared by the aluminum foil method in Example 2 of this invention. The small white dots are cuprous oxide quantum dots.

[0033] Figure 3 This is the X-ray diffraction (XRD) pattern of Example 2 in this invention.

[0034] Figure 4 The UV-Vis spectra of cuprous oxide quantum dots of different colors in this invention show that there is a significant blue shift compared to the non-quantum dot cuprous oxide suspension.

[0035] Figure 5 The images shown in Examples 1-3 of this invention depict cuprous oxide quantum dot samples of different colors, illustrating that cuprous oxide quantum dots of different sizes will exhibit different colors. When the quantum dot size decreases, the effective band gap Eg increases due to the quantum confinement effect. The greater the ability to excite or recombine electron-hole pairs, according to the photon energy formula E = hc / λ, the greater the energy E, the shorter the corresponding wavelength λ, and the color will tend towards blue-green.

[0036] Figure 6 The results show the UV stability test results of the sample in Example 2 over time (72 h).

[0037] Figure 7 The image shows the sample from Comparative Example 2. Detailed Implementation

[0038] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided below.

[0039] The present invention will be described in detail below using specific embodiments:

[0040] Example 1

[0041] The experimental environment was set at 25°C, protected from light, and the magnetic stirrer was set at 2000 rpm.

[0042] Dissolve 10 mg of copper sulfate pentahydrate in 50 mL of deionized water. Stirring is performed to prepare a clear solution A.

[0043] Dissolve 0.25 g of CMC in 50 mL of ethylene glycol. After stirring until well dispersed, prepare a pale white solution B.

[0044] Solutions A and B are ultrasonically stirred for 60 minutes to form solution C, which is white at this point.

[0045] The pH was adjusted to 11.5 by adding 0.2 mol / L sodium hydroxide solution dropwise. During the addition process, the mixed solution gradually turned milky white.

[0046] After thorough mixing, a 0.004 mol / L sodium borohydride solution was slowly added dropwise at a rate of 0.5 mL / min. After the addition was complete, sonication was continued, and the solution gradually turned pale yellow. The obtained cuprous oxide quantum dots had a particle size of 15 ± 3 nm.

[0047] Example 2

[0048] Weigh 0.0005 mol of copper acetate and dissolve it in 10 mL of deionized water to obtain solution A.

[0049] To prepare a 0.7% (w / v) CMC solution: Dissolve 0.35 g of CMC in 50 mL of ethylene glycol and sonicate for 30 min to obtain solution B.

[0050] Solution A was added to solution B, and the mixture was magnetically stirred for 15 minutes and then sonicated for 30 minutes to obtain mixed solution C.

[0051] Adjust the pH of solution C to 12.0 by adding 0.2 mol / L NaOH solution dropwise.

[0052] Dissolve 0.0006 mol of ascorbic acid in 10 mL of water (reducing agent solution), add it dropwise to solution C at a rate of 2 mL / min, and stir continuously for 10 min.

[0053] After sealing, the reaction was continuously stirred at 40°C until the solution turned light red, and the particle size of the obtained cuprous oxide quantum dots was 30±5nm.

[0054] Example 3

[0055] Dissolve 125 mg of copper sulfate pentahydrate in 50 mL of deionized water. Stir well to prepare a pale blue solution A.

[0056] Dissolve 0.5g of CMC in 50 mL of deionized water. Stir until homogeneous, then ultrasonically disperse to prepare solution B.

[0057] Solution B is slowly added to solution A under vigorous stirring to form a mixed solution C.

[0058] Dissolve 50 mg of ascorbic acid in 100 mL of deionized water and add to solution C.

[0059] Adjust the pH of solution C to 11 using 0.2 mol / L sodium hydroxide solution.

[0060] 10 mg of sodium borohydride was dissolved in 10 mL of deionized water to prepare solution D. Solution D was added dropwise to mixed solution C at a rate of 1 mL / min. After reacting for 12 h, the solution turned green and the particle size of the obtained cuprous oxide quantum dots was 8 ± 2 nm.

[0061] Example 4

[0062] Experimental temperature 5℃

[0063] Weigh 25 mg of copper sulfate pentahydrate and dissolve it in 50 mL of deionized water. Stir magnetically until completely dissolved to obtain a transparent solution A.

[0064] Weigh 50 mg of CMC and dissolve it in 50 mL of ethylene glycol. Disperse the solution by sonication for 30 min to obtain solution B.

[0065] Solution A is slowly added to solution B, and the mixture is magnetically stirred for 15 minutes and then sonicated for 30 minutes to form a mixed solution C.

[0066] Add 0.01 mol / L sodium hydroxide solution dropwise to adjust the pH of the solution to 11.0 (the solution turns milky white during the dropwise addition process).

[0067] Prepare a 0.02 mol / L sodium borohydride solution (10 mL) and add it dropwise to solution C at a rate of 0.1 mL / min. Continue stirring until the solution turns pale yellow (about 100 min). The resulting cuprous oxide quantum dots have a particle size of 13±3 nm.

[0068] Example 5

[0069] Weigh 0.5 mg of copper acetate and dissolve it in 10 mL of deionized water. Stir to dissolve and obtain solution A.

[0070] Weigh 50 mg PVP and 50 mg CMC and dissolve them in 50 mL of deionized water. Disperse the solutions by sonication for 30 min to obtain solution B.

[0071] Dissolve 50 mg of ascorbic acid in 10 mL of deionized water and store in the dark to obtain solution C (antioxidant).

[0072] Add solution A to solution B, stir magnetically for 15 minutes, then add solution C and continue stirring for 10 minutes.

[0073] Add 1.0 mol / L sodium hydroxide solution dropwise to adjust the pH to 10.5.

[0074] 0.036 mg of glucose was dissolved in 10 mL of water and added dropwise to the mixture at a rate of 1 mL / min. After 2 h of reaction, the solution turned blue-green, and the resulting cuprous oxide quantum dots had a particle size of 9 ± 3 nm.

[0075] Example 6

[0076] Weigh 67 mg of copper chloride and dissolve it in 50 mL of deionized water. Stir to dissolve and obtain solution A.

[0077] Weigh 500 mg of sodium alginate and dissolve it in 50 mL of ethylene glycol. Disperse the solution by sonication for 30 min to obtain solution B.

[0078] Add solution A to solution B, stir magnetically for 20 min, and then sonicate for 30 min.

[0079] Add 2 mol / L sodium hydroxide solution dropwise to adjust the pH to 12.0.

[0080] Prepare a 0.2 mol / L ascorbic acid solution (10 mL), add it dropwise to the mixture at a rate of 10 mL / min, and stir for 15 min. The solution turns orange-red, and the size of the cuprous oxide quantum dots generated is 35±4 nm.

[0081] Example 7

[0082] Experimental temperature 40℃

[0083] Weigh 12.5 mg of copper sulfate pentahydrate and dissolve it in 50 mL of deionized water. Stir to dissolve and obtain solution A.

[0084] Weigh 250 mg CMC and 250 mg PVP and dissolve them in 50 mL of deionized water. Disperse the solutions by sonication for 30 min to obtain solution B.

[0085] Add solution A to solution B and stir magnetically for 15 minutes.

[0086] Add 100 mg of ascorbic acid (antioxidant) and continue stirring for 10 min.

[0087] Add 1 mol / L sodium hydroxide solution dropwise to adjust the pH to 11.0.

[0088] Prepare a 0.0002 mol / L sodium borohydride solution (10 mL), add it dropwise at a rate of 0.5 mL / min, and after 24 h of reaction, the solution turns yellow-green, and the size of the cuprous oxide quantum dots produced is 10 ± 3 nm.

[0089] Unless otherwise specified, the entire reaction in the above embodiments was carried out at a constant temperature of 25 °C. All obtained samples were stored at low temperature and protected from light.

[0090] Comparative Example 1

[0091] Prepare a blue solution by dissolving 1.25 g of copper sulfate pentahydrate in 50 mL of deionized water and stirring the solution vigorously.

[0092] Dissolve 0.6 g of CMC in 50 mL of deionized water, and then add the solution to a copper sulfate solution. A white solution is obtained.

[0093] Dissolve ascorbic acid (0.9 g) and sodium hydroxide (0.4 g) in 100 mL of deionized water, and add the resulting solution to the previous solution.

[0094] Finally, an aqueous solution (50 mL) of sodium borohydride (0.4 g) was prepared and mixed into the solution under continuous stirring to form a dark green aqueous solution.

[0095] When the dark green solution is cooled for 12 hours, the solution turns into a dark yellow, opaque solution.

[0096] In this comparative example, the copper salt concentration exceeded the scope of the claims, and the reducing agent drop rate was not controlled, leading to quantum dot preparation failure or agglomeration, and the failure of colloidal protection.

[0097] Comparative Example 2

[0098] Experimental environment: Room temperature (25℃), protected from light, magnetic stirrer at 2000 rpm

[0099] Weigh 125 mg of copper sulfate pentahydrate (CuSO4·5H2O) and dissolve it in 80 mL of deionized water. Stir magnetically until completely dissolved.

[0100] Adjust the pH to 11 using 0.1 mol / L sodium hydroxide solution.

[0101] Prepare 10 mL of 0.005 mol / L sodium borohydride solution and add it dropwise to the above solution at a rate of 1 mL / min.

[0102] The solution was observed to turn yellow rapidly, and a yellowish-brown precipitate appeared after standing for 120 minutes.

[0103] After standing in the dark for 24 hours, the solution showed obvious stratification, with the upper clear liquid and the lower yellow-brown precipitate clearly distinguishable and obvious agglomeration observed.

[0104] This comparative example did not use a dispersant, which resulted in cuprous oxide growing too fast, becoming too large, and agglomerating.

[0105] Stability test: Since the optimal embodiment is Example 2, the stability test was performed to characterize the cuprous oxide quantum dots prepared under the conditions of Example 2.

[0106] Using the absorbance decay rate at 250 nm and 470 nm as indicators, the absorbance retention rate within 72 hours is ≥90%; using the absorbance at 700 nm as an indicator of colloidal turbidity, the change range within 72 hours is <5%.

[0107] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for preparing cuprous oxide quantum dots, characterized in that, Includes the following steps: All steps were performed at temperatures between 5°C and 40°C. (1) Add copper salt to deionized water and mix thoroughly by ultrasonic stirring to obtain solution A; wherein the concentration of copper salt is 0.00002 mol / L-0.02 mol / L; (2) Dissolve the dispersant in a specially prepared solution and stir until homogeneous to form solution B, wherein the concentration of the dispersant is 0.1-1.0 wt%; (3) Add solution A from step (1) to solution B from step (2), mix, and sonicate for more than 30 minutes to obtain solution C, wherein the volume ratio of solution A to solution B is 1:1 to 10:

1. (4) Adjust the pH of solution C in step (3) above to 10-12 using sodium hydroxide solution, wherein the concentration of sodium hydroxide solution is 0.01 mol / L-2 mol / L; (5) The reducing agent is slowly added dropwise to the solution prepared in step (4) at a rate of 0.1 mL / min to 10 mL / min. The solution gradually changes color, and the concentration of the reducing agent is 0.00002 mol / L to 0.2 mol / L. The molar ratio of copper salt to reducing agent is 1:0.125-1:20; Cuprous oxide quantum dots were obtained.

2. The preparation method according to claim 1, characterized in that, In step (1), the copper salt is one or more of copper sulfate pentahydrate, copper acetate, and copper chloride.

3. The preparation method according to claim 1, characterized in that, In step (2), the dispersant is one or more of sodium carboxymethyl cellulose, polyvinylpyrrolidone, and sodium alginate.

4. The preparation method according to claim 1, characterized in that, In step (2), the special solution is either deionized water or ethylene glycol, or a mixture of them in a volume ratio of 10:1 to 1:

10.

5. Cuprous oxide quantum dots prepared by any one of claims 1-4.

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