A Ga / Zn bimetallic doped nitrogen-doped carbon quantum dot solution and preparation method thereof

Abstract

The present invention belongs to the field of carbon quantum dots, and specifically relates to a Ga / Zn bimetallic doped nitrogen-doped carbon quantum dot solution and a preparation method thereof. The present invention adopts Ga / Zn / N three elements to co-dope CDs, adjusts the N element doping amount to improve the quantum yield of CDs, and adopts zinc and gallium ions with ionic radii of 74 picometers and 62.5 picometers, respectively, to co-dope N‑CDs to achieve the regulation of multiple molecules occupying orbits in N‑CDs. In addition, in the preparation process of carbon quantum dots, the use of traditional chemicals is avoided. Instead, rice bran, which is common in nature, is used to extract hemicellulose therein, and rice bran hemicellulose is used as a carbon source precursor. The preparation and doping of carbon quantum dots are achieved by a one-step hydrothermal method. This preparation method of Ga / Zn co-doped N‑CDs based on a green carbon source precursor is expected to achieve further application of CDs in the fields of optoelectronics and catalysis.

Description

Technical Field

[0001] The present invention belongs to the field of carbon quantum dots, and in particular relates to a Ga / Zn bimetallic doped nitrogen-doped carbon quantum dot solution and a preparation method thereof. Background Art

[0002] Carbon quantum dots (CDs), as a new type of fluorescent material, have good biocompatibility and low biotoxicity, and have great application prospects in biomedicine, sensing, optoelectronic devices, and fine chemicals.

[0003] Since Xu et al. accidentally produced carbon quantum dots in an experiment in 2004, research on carbon quantum dots has developed rapidly, gradually replacing traditional heavy metal quantum dots. However, general research has shown that compared with traditional quantum dots, the fluorescence quantum yield of carbon quantum dots is lower, and the luminescence mechanism is unclear.

[0004] Improving the fluorescence properties of carbon quantum dots (CQDs) has become a research hotspot in recent years. Studies have demonstrated that nitrogen atom doping can effectively enhance the fluorescence intensity of CDs, while the introduction of metal ions can modulate the band structure and enhance carrier and energy level transitions within CDs. Furthermore, metal ions can chelate with amino and carboxyl groups on the CDs' surfaces, preventing excessive loss of surface functional groups during carbonization or pyrolysis.

[0005] At present, some reports have studied the preparation and application of metal ion-doped CDs and metal ion / N co-doped CDs, but there are still few reports on the use of bimetallic / N element three-phase doped CDs in the fields of optoelectronics and catalysis. Summary of the Invention

[0006] In order to solve the above-mentioned technical problems, this application provides the following technical solutions:

[0007] The present invention uses Ga / Zn / N three elements to co-dope CDs, adjusts the N element doping amount to improve the quantum yield of CDs, and uses zinc and gallium ions with ionic radii of 74 picometers and 62.5 picometers, respectively, to co-dope N-CDs to achieve the regulation of orbital occupation by multiple molecules within N-CDs.

[0008] Furthermore, the preparation of carbon quantum dots avoids the use of traditional chemicals. Instead, hemicellulose extracted from rice bran, a common source in nature, is used as a carbon source precursor. This method for preparing Ga / Zn co-doped N-CDs, based on a green carbon source precursor, is expected to further the application of CDs in optoelectronics and catalysis.

[0009] The present invention provides a method for preparing a Ga / Zn bimetallic doped nitrogen-doped carbon quantum dot solution, comprising the following steps:

[0010] S11: dispersing rice bran hemicellulose in water to obtain an aqueous solution of a carbon source precursor;

[0011] S12: adding a nitrogen source solvent and a metal salt to the aqueous solution of the carbon source precursor and dispersing the mixture to obtain a precursor solution; the metal salt is selected from zinc salt and gallium salt;

[0012] S13: reacting the precursor solution at 200-260° C. for 4-36 hours to obtain a reaction solution;

[0013] S14: Cooling the reaction solution to room temperature and then purifying it to obtain the carbon quantum dot solution.

[0014] Preferably, the preparation method of the rice bran hemicellulose is as follows:

[0015] S21: grinding rice bran into 40-60 mesh size, adding alkaline solution and mixing, heating at 75-85° C. for 100-140 min, and filtering to obtain rice bran powder filtrate;

[0016] S22: adjusting the pH of the rice bran powder filtrate in step S21 to 5.4-5.6 with acetic acid and then centrifuging;

[0017] S23: concentrating the rice bran powder filtrate after centrifugation at 30-80° C. to obtain a concentrated solution;

[0018] S24: adding ethanol to the concentrated solution, filtering, and freeze-drying to obtain the rice bran hemicellulose.

[0019] Furthermore, in step S24, ethanol is added and the mixture is allowed to stand for 20-28 hours.

[0020] Furthermore, in step S24, ethanol is added in two times; the volume ratio of the ethanol added in the two times is 2:5.

[0021] Furthermore, in step S24, filtration is performed using an organic filter membrane with a pore size of 0.22 μm.

[0022] Preferably, the dispersion method is ultrasonic dispersion.

[0023] Preferably, the nitrogen source solvent is selected from N,N-dimethylformamide, N,N-dimethylacetamide, N,N-dimethylacetoacetamide, N-methylpyrrolidone or formamide.

[0024] The metal salt is selected from zinc chloride and gallium chloride.

[0025] Preferably, the concentration of nitrogen in the precursor solution is 3×10 -3 mol / 15mL to 20×10 -2 mol / 15mL.

[0026] Preferably, the concentration of zinc ions in the precursor solution is 7×10 -3 mol / 15mL to 14.67×10 -3 mol / 15mL; the concentration of gallium ions is 10.5×10 -3 mol / 15mL to 21.01×10 -3 mol / 15mL.

[0027] Preferably, in step S14, purification is performed by dialysis using a 500-5000Da dialysis bag for 24-72 hours.

[0028] The present invention also provides a Ga / Zn bimetallic doped nitrogen-doped carbon quantum dot solution prepared by the above preparation method.

[0029] The technical solution of the present invention has the following advantages over the prior art:

[0030] Advantages of rice bran hemicellulose:

[0031] 1. It avoids the environmental pollution and chemical toxicity problems caused by the use of chemical substances as precursors in the traditional preparation process of carbon quantum dots;

[0032] 2. Rice bran is a grain processing by-product with high output but low comprehensive utilization value. It is very easy to obtain in nature. Rice bran hemicellulose has a wide range of physiological functions and is very environmentally friendly to both the human body and nature.

[0033] Rice bran hemicellulose is primarily composed of monosaccharides, which possess numerous functional groups such as carboxyl and hydroxyl groups within their molecules. These groups play a key role in enriching the molecular and defect states on the surface of CDs, thereby influencing their fluorescence efficiency. Furthermore, during the preparation of metal-doped N-CDs, these functional groups can chelate with metal ions, and this coordination plays a key role in the optical stability of the CDs. Therefore, based on chemical structural analysis, using rice bran hemicellulose as the carbon source for Ga / Zn dual-doped N-CDs, thereby yielding CDs with high optical performance, offers significant advantages.

[0034] Reasons for using Ga / Zn / N three-phase co-doped CDs:

[0035] (1) N-doping can effectively improve the quantum yield of CDs;

[0036] (2) Each ion doped in N-CDs will generate a corresponding new HOMO energy level. The ionic radius of gallium ions is 74 picometers, and the ionic radius of zinc ions is 62.5 picometers. The doping of these two ions will show a gradient change in the formation of new energy levels, which can further realize the adjustability of electronic transitions, thereby changing its optical and electrical properties, and further expanding its application in the fields of optoelectronics and catalysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 These are transmission electron microscope images of carbon quantum dots; the main image is a transmission electron microscope image of carbon quantum dots, and the inner image is a high-magnification transmission electron microscope image of carbon quantum dots.

[0038] Figure 2 This is the particle size distribution diagram of carbon quantum dots.

[0039] Figure 3 This is the infrared analysis diagram of carbon quantum dots; in the figure, ν is stretching vibration and δ is in-plane shear vibration.

[0040] Figure 4 Fluorescence spectra of pure carbon quantum dots, Zn-doped carbon quantum dots, N-doped carbon quantum dots, and Ga / Zn / N co-doped carbon quantum dots prepared from rice bran hemicellulose.

[0041] Figure 5 This is a graph showing the quantum yield of N-doped carbon quantum dots and Ga / Zn / N co-doped carbon quantum dots as a function of the molar amount of N element. DETAILED DESCRIPTION

[0042] The present invention will be further described below with reference to the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it. However, the embodiments are not intended to limit the present invention.

[0043] Example 1 Extraction of rice bran hemicellulose

[0044] First, grind the rice bran with a micro plant grinder to obtain 40-60 mesh rice bran powder.

[0045] 20g of absolute dry rice bran powder was placed in a reactor. A 65g / L KOH solution was then added to the reactor at a liquid-to-liquid ratio of 1:12. The reactor was sealed and placed in a rotary evaporator, heated to 80°C, and then held at this temperature for 120 minutes. After cooling, the filtrate was filtered using filter paper and filter cloth. Glacial acetic acid was added dropwise to the filtrate until the pH reached 5.5. The resulting liquid phase was then centrifuged and concentrated to 20-30mL by rotary evaporation in a 35°C water bath under a vacuum of 0.08MPa. Finally, 80mL and 200mL of ethanol were added to the concentrate in two portions. The solution was allowed to stand for 24 hours before being filtered through a 0.22μm organic filter membrane. The filter membrane and solid phase were transferred to a weighing bottle, refrigerated for 5 hours, and then freeze-dried for 24 hours to obtain hemicellulose powder.

[0046] Example 2 Preparation steps of carbon quantum dots

[0047] (1) dispersing rice bran hemicellulose in ultrapure water and ultrasonically dispersing the resultant to obtain an aqueous solution of a carbon source precursor;

[0048] (2) Add N,N-dimethylformamide, zinc chloride and gallium chloride used as doping to step (1), and ultrasonically disperse to obtain a precursor solution; the concentration of nitrogen in the precursor solution is 10×10 -2 mol / 15mL; the concentration of zinc ions is 10×10 -3 mol / 15mL; the concentration of gallium ions is 15×10 -3 mol / 15mL.

[0049] (3) The precursor solution prepared in step (2) was transferred to a reactor and sealed; the reaction was carried out at 230°C for 20 hours, naturally cooled to room temperature, and then dialyzed with a 2000Da dialysis bag for 48 hours to obtain a carbon quantum dot solution.

[0050] Example 3 Preparation steps of carbon quantum dots

[0051] (1) dispersing rice bran hemicellulose in ultrapure water and ultrasonically dispersing the resultant to obtain an aqueous solution of a carbon source precursor;

[0052] (2) Add N,N-dimethylacetamide, zinc chloride and gallium chloride used as doping to step (1), and ultrasonically disperse to obtain a precursor solution; the concentration of nitrogen in the precursor solution is 20×10 -3 mol / 15mL; the concentration of zinc ions is 14.67×10 -3 mol / 15mL; the concentration of gallium ions is 21.01×10 -3 mol / 15mL.

[0053] (3) The precursor solution prepared in step (2) was transferred to a reactor and sealed; the reaction was carried out at 200°C for 4 hours, and the mixture was naturally cooled to room temperature. The carbon quantum dot solution was then dialyzed with a 500Da dialysis bag for 24 hours.

[0054] Example 4 Preparation steps of carbon quantum dots

[0055] (1) dispersing rice bran hemicellulose in ultrapure water and ultrasonically dispersing the resultant to obtain an aqueous solution of a carbon source precursor;

[0056] (2) Add N,N-dimethylacetoacetamide, zinc chloride and gallium chloride used as doping to step (1), and ultrasonically disperse to obtain a precursor solution; the concentration of nitrogen in the precursor solution is 3×10 -3 mol / 15mL; the concentration of zinc ions is 7×10 -3 mol / 15mL; the concentration of gallium ions is 10.5×10 -3 mol / 15mL.

[0057] (3) The precursor solution prepared in step (2) was transferred to a reactor and sealed; the reaction was carried out at 260°C for 36 hours, naturally cooled to room temperature, and then dialyzed with a 5000Da dialysis bag for 72 hours to obtain a carbon quantum dot solution.

[0058] Effect evaluation 1

[0059] The particle size and dispersion were tested by HRTEM;

[0060] Transmission electron microscope (TEM): A Tecnai G2 F20 model from FEI (USA) was used. The scanning transmission resolution of this TEM can reach 0.2 nm; the magnification range is 25X to 1,000,000X, and the acceleration voltage is 80 kV to 200 kV.

[0061] Fluorescence spectroscopy was used to detect the fluorescence PL performance. Fluorescence spectrophotometer (PL): PL spectra were obtained using a fluorescence spectrometer from JY, France. The instrument uses an ozone-free Xe lamp as a light source and can excite and emit light with a wavelength of 200-950 nm with a wavelength accuracy of ±0.5 nm.

[0062] UV-vis spectroscopy was used to detect its absorption properties;

[0063] Ultraviolet-visible spectrophotometer (UV-Vis): The instrument is Lambda 750 ultraviolet / visible ( / near infrared) spectrophotometer produced by PerkinElmer, and the standard wavelength range of the instrument is 190 to 3300 nm.

[0064] The performance tests of PL and UV were integrated, and the quantum yield was calculated using quinine sulfate as the standard dye.

[0065] Quantum yield calculation: Using 1N sulfuric acid solution of quinine sulfate as the standard (quantum yield: 45%), the quantum yield of carbon quantum dots was determined using the following formula:

[0066]

[0067] Where Q is the quantum yield, I is the integrated fluorescence emission area, A is the optical density, n is the refractive index, and R is a known standard fluorescent dye. To prevent the influence of solution self-absorption on the calculation of fluorescence quantum yield, the optical absorption value of the tested sample is usually kept below 0.1. The excitation and emission widths of the sample fluorescence spectrum are both set to 0.25.

[0068] Infrared analysis was used to detect the distribution of surface groups.

[0069] Fourier transform infrared / Raman spectrometer (FT-IR): The instrument is a Nicolet 6700 FT-IR and NXR FT-Raman Module from the United States, with an excitation wavelength of 1064 nm and a resolution of 4 cm -1 Use KBr powder to press the pellet. After applying the liquid sample onto the KBr pellet, irradiate it with an infrared lamp for a few minutes, remove the solvent, and perform infrared analysis.

[0070] Compared with the carbon quantum dots obtained directly from rice bran hemicellulose without any doping, the quantum yield of the prepared carbon quantum dots doped with N can be increased by 20%; the quantum yield of the carbon quantum dots obtained by Ga / Zn co-doped N-CDs can be increased by up to 80%.

[0071] As the N element doping content gradually increases, the quantum yield of N-CDs shows a trend of first increasing and then decreasing; after Ga / Zn co-doping N-CDs, the quantum yield change law remains the same.

[0072] Figure 1 The transmission electron microscope image of a typical carbon quantum dot is shown in Figure 2. As can be seen from the figure, the obtained carbon quantum dots show good monodispersity. Through data statistical software analysis, it can be concluded that the particle size distribution of carbon quantum dots is in the range of 1.75nm to 3.85nm, with an average particle size of 2.75±0.68nm. Figure 2 shown. Figure 1 The inner figure is a high-magnification transmission electron microscope of carbon quantum dots, from which we can see that the carbon quantum dots have an obvious lattice configuration, and the lattice spacing is between 0.22 and 0.23 nm, corresponding to the (100) plane of graphite carbon atoms.

[0073] Figure 3 This is the FT-IR characterization of carbon quantum dots.-1 and 1397cm -1 The strong absorption peaks at ν and ν correspond to the antisymmetric stretching vibration peaks of (-COO-) bonds. as (-COO-) and symmetrical stretching vibration peak ν s (-COO-). Located at 2794cm -1 , 1468cm -1 and 1068cm -1 Corresponding to the antisymmetric stretching vibration ν of (-CH2) as (-CH2-), (-CH2) in-plane shear vibration δ(-CH2-), and (-CN-) stretching vibration ν(-CN-). Located at 1100cm -1 and 1250cm -1 The absorption band in the range is derived from the stretching vibration ν(-CO-) of the carboxyl group. Located at 3000cm -1 to 3750cm -1 The strong and broad absorption peaks at indicate the presence of stretching vibration peaks of -OH and -NH bonds. Infrared spectroscopy results show that the surface of the prepared carbon quantum dots has abundant carboxyl, carbonyl, hydroxyl and amino groups.

[0074] Figure 4 The fluorescence spectra of pristine carbon quantum dots (pure CDs, PCDs for short), Zn-doped carbon quantum dots (Zn / CDs), N-doped carbon quantum dots (N / CDs), and Ga / Zn / N three-phase co-doped carbon quantum dots (Ga / Zn / N / CDs) are shown. Figure 4The fluorescence emission peak of the original carbon quantum dots is located at 446 nm. However, after chemical doping, the peak undergoes a significant blue shift, with N / CDs and Zn / CDs shifting to 438 nm and Ga / Zn / N / CDs to 437 nm. At the same volume concentration, the fluorescence intensities of the four different carbon quantum dots vary significantly. Metallic Zn doping decreases the fluorescence intensity by 28%, while N doping increases it by 20%. Ga / Zn / N triple-codoped CDs enhance the fluorescence intensity by 80%. The experimental results indicate that simple Zn doping quenches the fluorescence of the CDs, while N doping enhances their fluorescence performance. Further metal ion doping of the N / CDs further enhances their fluorescence performance. This is likely due to the formation of more amino and other functional groups on the CDs' surfaces, which contribute lone pairs of electrons to the occupied π orbitals within the CDs, altering the HOMO energy level and band gap width of the original CDs. Edge doping increases the number of photoexcited electrons in the CDs' emission transition channels, thereby improving the probability of radiative transitions and the fluorescence intensity. When Ga / Zn metal ions are further doped on the basis of N / CDs, the different ions generate new and different HOMO energy levels within the CDs, further enriching their internal radiative energy transfer and thus having a greater impact on the fluorescence properties.

[0075] In order to further analyze the effects of different chemical doping on the fluorescence properties of CDs, the present invention systematically analyzes the changes in the quantum yield of a series of doped quantum dots, such as Figure 5 The results show that when the total volume is 15 mL, the molar amount of N element doping is 3*10 -3 -20*10 -2 In the mol range, the fluorescence quantum yield of N / CDs increases first and then decreases with the molar amount of N. Ga / Zn / N / CDs exhibits the same relationship, indicating that N plays a primary role in the chemical doping process. The variation of quantum yield y with N doping amount x can be expressed in Equation 2, with the various parameters shown in Table 1.

[0076] y=y0+A*exp(-0.5*((xx c ) / w)^2) Formula 2;

[0077] Among them, y represents the quantum yield of carbon quantum dots, x represents the molar amount of N element per 15mL, yo, A, x c and w are the coefficients in the fitting formula.

[0078] Table 1 Quantum yield variation coefficients of N-doped carbon quantum dots and Ga / Zn / N-doped carbon quantum dots

[0079] <![CDATA[y0]]> A <![CDATA[x c ]]> w N-doped carbon quantum dots 5.81 1.83 0.088 0.039 Ga / Zn / N doped carbon quantum dots 6.01 5.13 0.082 0.033

[0080] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A method for preparing a Ga / Zn bimetallic doped nitrogen-doped carbon quantum dot solution, characterized in that: The steps include: S11: dispersing rice bran hemicellulose in water to obtain an aqueous solution of a carbon source precursor; S12: adding a nitrogen source solvent and a metal salt to the aqueous solution of the carbon source precursor and dispersing the mixture to obtain a precursor solution; the metal salt is selected from zinc salt and gallium salt; the nitrogen source solvent is selected from N,N-dimethylformamide, N,N-dimethylacetamide, N,N-dimethylacetoacetamide, N-methylpyrrolidone or formamide; S13: reacting the precursor solution at 200-260° C. for 4-36 hours to obtain a reaction solution; S14: Cooling the reaction solution to room temperature and then purifying it to obtain the Ga / Zn bimetallic doped nitrogen-doped carbon quantum dot solution.

2. The preparation method according to claim 1, wherein The preparation method of described rice bran hemicellulose is as follows: S21: grinding rice bran into 40-60 mesh size, adding alkaline solution, mixing, heating at 75-85° C. for 100-140 min, and filtering to obtain rice bran powder filtrate; S22: adjusting the pH of the rice bran powder filtrate in step S21 to 5.4-5.6 with acetic acid and then centrifuging; S23: concentrating the rice bran powder filtrate after centrifugation at 30-80° C. to obtain a concentrated solution; S24: adding ethanol to the concentrated solution, filtering, and freeze-drying to obtain the rice bran hemicellulose.

3. The preparation method according to claim 2, wherein In the step S24, ethanol is added and the mixture is allowed to stand for 20-28 hours.

4. The preparation method according to claim 2, wherein In step S24, filtration is performed using an organic filter membrane with a pore size of 0.22 μm.

5. The preparation method according to claim 1, wherein The dispersion methods are all ultrasonic dispersion.

6. The preparation method according to claim 1, wherein The concentration of nitrogen in the precursor solution is 3×10 -3 mol / 15mL to 20×10 -2 mol / 15mL.

7. The preparation method according to claim 1, wherein In the precursor solution, the concentration of zinc ions is 7×10 -3 mol / 15mL to 14.67×10 -3 mol / 15mL; the concentration of gallium ions is 10.5×10 -3 mol / 15mL to 21.01×10 - 3 mol / 15mL.

8. The preparation method according to claim 1, wherein In step S14, purification is performed by dialysis using a 500-5000 Da dialysis bag for 24-72 h.

9. A Ga / Zn bimetallic doped nitrogen-doped carbon quantum dot solution prepared by the preparation method according to any one of claims 1 to 8.

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