A method for preparing boron-doped graphene oxide quantum dots emitting cyan fluorescence

Abstract

This invention discloses a method for preparing boron-doped graphene oxide quantum dots emitting cyan fluorescence. The method involves reacting VXC-72 conductive carbon black with concentrated nitric acid at high temperature; after the reaction, the reactants are deacidified; the deacidified reactants are diluted and then filtered to obtain a graphene oxide quantum dot solution; the solution is dried to extract the graphene oxide quantum dots; the extracted graphene oxide quantum dots are uniformly mixed with boron oxide and subjected to thermal annealing in a horizontal tube furnace; the resulting mixture is dissolved in water, filtered using a membrane filter, and dialyzed; finally, a combination of freeze-drying and vacuum drying is used to obtain boron-doped graphene oxide quantum dots. The boron-doped graphene oxide quantum dots prepared by this method emit cyan fluorescence under 365nm wavelength excitation light, providing a novel preparation method for graphene oxide quantum dots with specific luminescent properties.

Description

Technical Field

[0001] This invention relates to the field of graphene quantum dot technology, specifically to a method for preparing boron-doped graphene oxide quantum dots that emit cyan fluorescence. Background Technology

[0002] Cyan photoluminescent nanomaterials have recently attracted significant attention due to their wide range of applications in the visible spectrum, such as biomedicine, environmental monitoring, lighting, displays, and optical communications. In recent years, graphene quantum dots (GQDs) have become a research hotspot due to their excellent optical properties, stability, low toxicity, biocompatibility, and broad applications.

[0003] Graphene quantum dots with a large number of oxygen-containing functional groups are called graphene oxide quantum dots, abbreviated as GOQDs. Research shows that doping with heteroatoms is an effective strategy for modulating the photoluminescence of graphene quantum dots. Researchers have modulated the photoluminescence properties of graphene quantum dots by doping them with heteroatoms such as nitrogen, sulfur, fluorine, and chlorine. Currently, various graphene quantum dots with emission wavelengths in the ultraviolet, blue, green, yellow, and red ranges have been developed using different methods. However, research on the cyan fluorescence of graphene quantum dots is still limited, which significantly impacts their widespread application. Summary of the Invention

[0004] The purpose of this invention is to address the aforementioned problems by providing a boron-doped graphene oxide quantum dot that emits cyan fluorescence and its preparation method. The boron-doped graphene oxide quantum dot obtained by the preparation method of this invention emits cyan fluorescence at an emission peak position of 490 nm under 365 nm excitation light, thus achieving the objective of preparing a graphene oxide quantum dot that emits cyan fluorescence.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A method for preparing boron-doped graphene oxide quantum dots that emit cyan fluorescence includes the following steps:

[0007] (1) Conductive carbon black and concentrated nitric acid are used as raw materials and strong oxidants. After mixing and stirring evenly, the mixture is reacted at a temperature of 135-155℃ for 22-26 hours.

[0008] (2) Deacidify the sample after the reaction in step (1);

[0009] (3) Disperse the sample after deacidification in step (2) into deionized water, first place it in an ultrasonic cleaner for ultrasonic treatment, then place the ultrasonic solution in a high-speed centrifuge for centrifugation, take the upper dispersion, add deionized water to the dispersion, first use a 220nm filter membrane for preliminary filtration, and then use a 25nm filter membrane for further filtration to obtain graphene oxide quantum dot solution.

[0010] (4) The graphene oxide quantum dot solution obtained in step (3) is concentrated using a rotary evaporator, and the concentrated solution is placed in a freeze dryer for freeze vacuum drying to obtain fluffy graphene oxide quantum dots, abbreviated as GOQDs.

[0011] (5) Weigh the graphene oxide quantum dots obtained in step (4), and then weigh the boron oxide, with the mass ratio of graphene oxide quantum dots to boron oxide being 1:10.

[0012] Mix the two ingredients thoroughly in a mortar, then place them in a small crucible and put them in a quartz tube. Place the quartz tube in a horizontal tube furnace equipped with temperature and gas flow control devices, and introduce argon gas to react at high temperature.

[0013] After the reaction, the tube furnace was cooled to room temperature, the resulting mixture was dissolved in water, and then filtered through a 220 nm filter membrane to remove large insoluble particles. The mixture was then purified by dialysis using a dialysis membrane with a molecular weight cutoff of 2000 Da to obtain a boron-doped graphene quantum dot solution.

[0014] (6) The solution after dialysis in step (5) is placed in a freeze dryer for freeze vacuum drying, and boron-doped graphene oxide quantum dots emitting cyan fluorescence are finally obtained, abbreviated as BGOQDs.

[0015] In this invention, preferably, the conductive carbon black in step (1) is VXC-72 conductive carbon black, and its weight-to-volume ratio with concentrated nitric acid is 1g:80-120ml, and the mass fraction of concentrated nitric acid is 68%.

[0016] In this invention, preferably, the acid removal process described in step (2) involves first placing the sample in a rotary evaporator to initially remove residual concentrated nitric acid. To further remove a small amount of residual concentrated nitric acid, the sample is then placed in an open-type vacuum tube furnace equipped with a quartz tube for heating and acid removal, while argon gas is introduced into the open-type vacuum tube furnace.

[0017] In this invention, preferably, the rotary evaporator operates at a temperature of 70–90°C and performs 3–5 repeated rotary evaporations; the open-type vacuum tube furnace operates at a temperature of 200–230°C and the argon flow rate is set to 50–70 ml / min.

[0018] In this invention, preferably, the centrifuge in step (3) has a rotation speed of 12000-14000 r / min and a centrifugation time of 15-30 min.

[0019] In this invention, preferably, the ultrasonic treatment time in step (3) is 12 to 20 minutes.

[0020] In this invention, preferably, the freeze dryer described in steps (4) and (6) operates at a freezing temperature of -70 to -30°C, freezes for 8 to 12 hours, and vacuums for 32 to 48 hours.

[0021] In this invention, preferably, the working procedure of the horizontal reaction tube furnace in step (5) is as follows: Ar gas is continuously introduced into one end of the tube furnace at a flow rate of 50-70 ml / min, and the tail gas is treated at the other end. At the same time, the reaction temperature in the tube furnace is raised from room temperature (25°C) to 300-400°C at a rate of 4-6°C / min for 50-80 minutes, and then continuously kept at 300-400°C for 2-4 hours.

[0022] In this invention, preferably, the dialysis purification in step (5) is carried out at a working temperature of 20-25°C for 22-26 hours.

[0023] Another objective of this invention is to provide boron-doped graphene oxide quantum dots that emit cyan fluorescence, prepared using the above-described method.

[0024] The beneficial effects of this invention are:

[0025] 1. This invention provides a method for synthesizing boron-doped graphene oxide quantum dots based on VXC-72 conductive carbon black as the carbon source and boron oxide as the boron doping source. Concentrated nitric acid is used as a strong oxidant, and deionized water and argon are used as auxiliary materials. This method uses readily available and low-cost raw materials, has a simple process flow, a short production cycle, and uses environmentally friendly and non-toxic materials, ensuring safety for organisms and the environment.

[0026] 2. The boron-doped graphene oxide quantum dots prepared by the method of the present invention have the advantages of simple process and short cycle, and the process parameters can be flexibly adjusted according to production needs;

[0027] 3. The boron-doped graphene oxide quantum dots prepared by the method of this invention exhibit a cyan fluorescence emission peak at 490 nm under 365 nm excitation light, with a maximum blue shift of 35.5 nm in photoluminescence, providing an effective route for preparing cyan fluorescent graphene oxide quantum dots. These quantum dots have potential application value in the cyan light field and in biomedical fields such as fluorescent probes and cell imaging. Attached Figure Description

[0028] Figure 1 The photoluminescence color and photoluminescence emission spectrum of the boron-doped graphene oxide quantum dots (BGOQDs360) emitting cyan fluorescence prepared in Example 1 are shown.

[0029] Figure 2 These are transmission electron microscope (TEM) images and size distribution diagrams of the graphene oxide quantum dots (GOQDs) and the boron-doped graphene oxide quantum dots (BGOQDs360) emitting cyan fluorescence prepared in Example 1.

[0030] Figures 2(a) and 2(b) show TEM images of GOQDs and BGOQDs360, respectively, and Figures 2(c) and 2(d) show the size distribution of GOQDs and BGOQDs360.

[0031] Figure 3 The Raman spectra of graphene oxide quantum dots (GOQDs) and boron-doped graphene oxide quantum dots (BGOQDs) prepared in Examples 1-4 are shown. Figure 3 (a) Fourier transform infrared spectroscopy analysis Figure 3 (b);

[0032] Figure 4 The images show X-ray photoelectron spectroscopy (XPS) analysis results of the graphene oxide quantum dots (GOQDs) and boron-doped graphene oxide quantum dots (BGOQDs) prepared in Examples 1-4.

[0033] Figure 5 These are the photoluminescence emission spectra of the graphene oxide quantum dots (GOQDs) and boron-doped graphene oxide quantum dots (BGOQDs) prepared in Examples 1-4.

[0034] Figure 6 These are the normalized focusing spectra, photoluminescence colors, and UV-Vis absorption spectra of the graphene oxide quantum dots (GOQDs) and boron-doped graphene oxide quantum dots (BGOQDs) prepared in Examples 1-4. Detailed Implementation

[0035] To enable those skilled in the art to better understand the methods of this application, the technical solutions of this application are clearly and completely described below through embodiments. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this application. Example 1

[0036] A method for preparing boron-doped graphene oxide quantum dots that emit cyan fluorescence includes the following steps:

[0037] (1) Weigh 5g of VXC-72 conductive carbon black and place it in a 1000ml round-bottom flask; then measure 500ml of concentrated nitric acid with a mass fraction of 68%, and add it to the round-bottom flask as a strong oxidant. Mix the VXC-72 conductive carbon black and stir evenly with a glass rod; place a magnetic stir bar in the round-bottom flask containing the sample, place the round-bottom flask in a heat-collecting constant-temperature magnetic stirrer, adjust the rotation speed of the magnetic stir bar to 25r / s, set the heating temperature of the heat-collecting constant-temperature magnetic stirrer to 140℃, and the reaction time to 24h. The heat-collecting constant-temperature magnetic stirrer contains dimethyl silicone oil. Connect the heat-collecting constant-temperature magnetic stirrer to a low-temperature constant-temperature stirring reaction bath, which is used to cool the refluxed concentrated nitric acid.

[0038] (2) Add deionized water to the sample after the reaction in step (1) to dilute it. Place the round-bottom flask in a rotary evaporator and perform rotary evaporation on the sample in a water bath at 80°C. Repeat the rotary evaporation three times to initially remove most of the residual concentrated nitric acid. To further remove a small amount of residual concentrated nitric acid, add deionized water to the obtained sample to dilute it. Then place the mixed solution in a quartz boat and slowly place the quartz boat into an open vacuum tube furnace equipped with a quartz tube. Set the heating temperature of the open vacuum tube furnace to 230°C and the heating time to 3 hours. At the same time as heating, introduce argon gas into the open vacuum tube furnace and set the argon gas flow rate to 50 ml / min.

[0039] (3) Disperse the sample obtained after deacidification in step (2) into 400ml of deionized water and place it in an ultrasonic cleaner for 15min. Divide the solution into 8 centrifuge tubes of 100ml each and place them in a high-speed centrifuge. Set the centrifuge speed to 12000r / min and centrifuge for 15min. After centrifugation, take the upper dispersion and add 500ml of deionized water to the dispersion. Perform vacuum filtration on it. First, use a 220nm filter membrane for preliminary vacuum filtration, and then use a 25nm filter membrane for further vacuum filtration to obtain graphene oxide quantum dot solution.

[0040] (4) The graphene oxide quantum dot solution obtained in step (3) is concentrated using a rotary evaporator. The 300ml solution after concentration is divided into 6 evaporating dishes. A layer of qualitative filter paper is placed on the evaporating dishes and then placed in a freeze dryer at -70℃. After freezing for 12 hours, the freeze dryer is then vacuumed for 48 hours to obtain fluffy graphene oxide quantum dots, abbreviated as GOQDs.

[0041] (5) Weigh 0.1g of graphene oxide quantum dots obtained in step (4), weigh 1g of boron oxide, mix the two in a mortar, put them in a small crucible, and place them in a quartz tube. Place the quartz tube in a horizontal reaction tube furnace equipped with temperature and airflow control devices. Set the working program of the tube furnace, continuously introduce Ar gas into one end of the tube furnace at a flow rate of 50ml / min, and treat the tail gas at the other end. At the same time, raise the reaction temperature in the tube furnace from room temperature 25℃ to 360℃ at a rate of 5℃ / min for 67 minutes, and then keep it at 360℃ for 2 hours.

[0042] After the reaction was completed, the horizontal tube furnace containing the sample was allowed to cool naturally. The crucible containing the oxide mixture was removed, and the resulting mixture was dissolved in water and then filtered through a 220 nm filter membrane to remove large insoluble particles. Then, the mixture was purified by dialysis using a dialysis membrane with a molecular weight cutoff of 2000 Da at an operating temperature of 25 °C for 24 h to obtain a boron-doped graphene oxide quantum dot solution.

[0043] (6) Dilute the obtained solution with deionized water, cover the small quartz cup with a layer of qualitative filter paper, place the small quartz cup in a freeze dryer at -70℃, freeze for 12 hours, and then vacuum for 48 hours to finally obtain boron-doped graphene oxide quantum dots that emit cyan fluorescence, abbreviated as BGOQDs 360 (the number represents the holding annealing temperature).

[0044] The photoluminescence color and photoluminescence emission spectrum of the boron-doped graphene oxide quantum dots (BGOQDs360) emitting cyan fluorescence prepared in Example 1 are as follows: Figure 1 As shown. Example 2

[0045] Repeat steps (1) to (4) of Example 1 to obtain fluffy graphene oxide quantum dots, abbreviated as GOQDs;

[0046] (5) Weigh 0.1g of graphene oxide quantum dots obtained in step (4), weigh 1g of boron oxide, mix the two in a mortar, put them in a small crucible, and place them in a quartz tube. Place the quartz tube in a horizontal reaction tube furnace equipped with temperature and airflow control devices. Set the working program of the tube furnace, continuously introduce Ar gas into one end of the tube furnace at a flow rate of 50ml / min, and treat the tail gas at the other end. At the same time, raise the reaction temperature in the tube furnace from room temperature 25℃ to 340℃ at a rate of 5℃ / min for 63 minutes, and then keep it at 340℃ for 2 hours.

[0047] After the reaction was completed, the horizontal tube furnace containing the sample was allowed to cool naturally. The crucible containing the oxide mixture was removed, and the resulting mixture was dissolved in water and then filtered through a 220 nm filter membrane to remove large insoluble particles. Then, the mixture was purified by dialysis at 25 °C for 24 hours using a dialysis membrane with a molecular weight cutoff of 2000 Da to obtain a boron-doped graphene oxide quantum dot solution.

[0048] (6) Dilute the obtained solution with deionized water, cover the small quartz cup with a layer of qualitative filter paper, place the small quartz cup in a freeze dryer at -70℃, freeze for 12 hours, and then vacuum for 48 hours to finally obtain boron-doped graphene oxide quantum dots that emit blue-green fluorescence, abbreviated as BGOQDs 340 (the number represents the holding annealing temperature). Example 3

[0049] Repeat steps (1) to (4) of Example 1 to obtain fluffy graphene oxide quantum dots, abbreviated as GOQDs;

[0050] (5) Weigh 0.1g of graphene oxide quantum dots obtained in step (4), weigh 1g of boron oxide, mix the two in a mortar, put them in a small crucible, and place them in a quartz tube. Place the quartz tube in a horizontal reaction tube furnace equipped with temperature and airflow control devices. Set the working program of the tube furnace, continuously introduce Ar gas into one end of the tube furnace at a flow rate of 50ml / min, and treat the tail gas at the other end. At the same time, raise the reaction temperature in the tube furnace from room temperature 25℃ to 320℃ at a rate of 5℃ / min for 59 minutes, and then keep it at 320℃ for 2 hours.

[0051] After the reaction was completed, the horizontal tube furnace containing the sample was allowed to cool naturally. The crucible containing the oxide mixture was removed, and the resulting mixture was dissolved in water and then filtered through a 220 nm filter membrane to remove large insoluble particles. Then, the mixture was purified by dialysis at 25 °C for 24 hours using a dialysis membrane with a molecular weight cutoff of 2000 Da to obtain a boron-doped graphene oxide quantum dot solution.

[0052] (6) Dilute the obtained solution with deionized water, cover the small quartz cup with a layer of qualitative filter paper, place the small quartz cup in a freeze dryer at -70℃, freeze for 12 hours, and then vacuum for 48 hours to finally obtain boron-doped graphene oxide quantum dots that emit water green fluorescence, abbreviated as BGOQDs 320 (the number represents the holding annealing temperature). Example 4

[0053] Repeat steps (1) to (4) of Example 1 to obtain fluffy graphene oxide quantum dots, abbreviated as GOQDs;

[0054] (5) Weigh 0.1g of graphene oxide quantum dots obtained in step (4), weigh 1g of boron oxide, mix the two in a mortar, put them in a small crucible, and place them in a quartz tube. Place the quartz tube in a horizontal reaction tube furnace equipped with temperature and airflow control devices. Set the working program of the tube furnace, continuously introduce Ar gas into one end of the tube furnace at a flow rate of 50ml / min, and treat the tail gas at the other end. At the same time, raise the reaction temperature in the tube furnace from room temperature 25℃ to 300℃ at a rate of 5℃ / min for 55 minutes, and then keep it at 300℃ for 2 hours.

[0055] After the reaction was completed, the horizontal tube furnace containing the sample was allowed to cool naturally. The crucible containing the oxide mixture was removed, and the resulting mixture was dissolved in water and then filtered through a 220 nm filter membrane to remove large insoluble particles. Then, the mixture was purified by dialysis at 25 °C for 24 hours using a dialysis membrane with a molecular weight cutoff of 2000 Da to obtain a boron-doped graphene oxide quantum dot solution.

[0056] (6) Dilute the obtained solution with deionized water, cover the small quartz cup with a layer of qualitative filter paper, place the small quartz cup in a freeze dryer at -70℃, freeze for 12 hours, and then vacuum for 48 hours to finally obtain boron-doped graphene oxide quantum dots that emit yellow-green fluorescence, abbreviated as BGOQDs 300 (the number represents the holding annealing temperature).

[0057] II. Performance Testing

[0058] 1. Transmission electron microscopy (TEM) analysis was performed on the graphene oxide quantum dots and boron-doped graphene oxide quantum dots prepared in Example 1, and their size distribution was described. Figures 2(a) and 2(b) show the TEM images of GOQDs and BGOQDs360, respectively. Figures 2(c) and 2(d) show the size distribution of GOQDs and BGOQDs360. The diameter ranges of GOQDs and BGOQDs360 are approximately 0.9–2.2 nm and 1.40–2.90 nm, respectively. Calculations show that the average diameter of GOQDs is approximately 1.38 nm, and the average diameter of BGOQDs360 is approximately 1.99 nm.

[0059] 2. Raman and Fourier transform infrared spectroscopy analyses were performed on the graphene oxide quantum dots (GOQDs) and boron-doped graphene oxide quantum dots (BGOQDs) prepared in Examples 1-4. Figure 3(a) shows the Raman spectra of GOQDs and BGOQDs. The D peak and G peak of GOQDs are located at 1390 cm⁻¹. -1 and 1616 cm -1 The blue peak of BGOQDs shifted to 1396 cm⁻¹. -1 The G peak redshifted to 1607 cm. -1 This may be due to lattice distortion caused by the formation of BC bonds. The ID / IG ratio of BGOQDs (0.97-0.98) is higher than that of GOQDs (0.93), indicating higher disorder. Fourier transform infrared spectroscopy analysis, Figure 3(b), shows that GOQDs and BGOQDs exhibit higher disorder in the 3300-3700 cm⁻¹ range. -1 There is a broad absorption band, attributed to the -OH stretching vibration. The -COOH vibration band of GOQDs is at 1447 cm⁻¹. -1 Almost disappeared, while the C=C vibration band of BGOQDs is at 1617 cm. -1 The enhancement indicates a decrease in oxygen content and the restoration of C=C bonds. BGOQDs at 1041 cm⁻¹ -1 1112 cm -1 and 1390 cm -1 The appearance of new bands is attributed to the extension of BOH, BC and OB, respectively, indicating the presence of boron doping.

[0060] 3. X-ray photoelectron spectroscopy analysis was performed on the graphene oxide quantum dots (GOQDs) and boron-doped graphene oxide quantum dots (BGOQDs) prepared in Examples 1-4. Figure 4(a) shows that GOQDs are mainly composed of C1s (285 eV) and O1s (532 eV), while... Figure 4 (b) shows that BGOQDs exhibit a B1s peak at 192 eV, confirming boron doping.

[0061] Table 1

[0062]

[0063] As shown in Table 1, with increasing annealing temperature, the carbon content in BGOQDs increases while the oxygen content decreases. The boron content is adjustable, ranging from 0.31 to 1.08 at.%. This indicates that the increase in boron doping level is accompanied by a decrease in oxygen content. It is speculated that during annealing, oxygen functional groups on GOQDs are removed by releasing CO2 and CO, while B atoms are incorporated into the lattice of GOQDs.

[0064] Figure 4(c) shows the high-resolution C1s spectra of GOQDs and BGOQDs. A CC peak was observed at 284.8 eV. Furthermore, peaks at 289.12, 286.59, 288.48, and 285.45 eV correspond to OC=O, COC, C=O, and C=C, respectively. Peaks at 284.15 and 290.45 eV correspond to BC and COB bonds, respectively.

[0065] Figure 4(d) shows the high-resolution B1s spectrum of BGOQDs. The high-resolution B1s spectrum can be decomposed into four peaks, corresponding to BC3 (189.68 eV), BC2O (190.59 eV), BCO2 (191.35 eV), and B2O3 (192.45 eV), respectively. Furthermore, as the annealing temperature increases from 300 °C to 360 °C, the peaks of some chemical bonds shift. This shift is likely due to heteroatoms donating electrons to C atoms, resulting in an increase in the electron cloud density on the C atoms. These findings clearly demonstrate the successful incorporation of B atoms into the lattice of GOQDs.

[0066] Table 2

[0067]

[0068] Table 2 lists the chemical group content of GOQDs and BGOQDs. Compared with GOQDs, the content of COC and C=C bonds in BGOQDs is slightly increased, while the content of C=O and OC=O bonds is significantly decreased. This indicates that most of the oxygen-containing functional groups are pyrolyzed or converted into thermally stable phenolic hydroxyl, ether, and carbonyl groups. However, the C / C bond content in BGOQDs decreases from 43.51 at.% in GOQDs to 39.78, 32.09, 29.24, and 27.04 at.% in BGOQDs300, BGOQDs320, BGOQDs340, and BGOQDs360, respectively, from 0 at.% to 4.14, 5.67, 11.32, and 15.56 at.%. This indicates that the breaking of C=C bonds in GOQDs promotes the formation of BC bonds between B atoms in boron oxide and carbon atoms in GOQDs. We hypothesize that the introduction of boron during thermal annealing reduces C=C bonds in various samples, while high temperatures convert C=C to C=C, which then breaks to form BC bonds. Furthermore, fluctuations in COC bond content are inversely proportional to fluctuations in COB bond content. This may be because COC in the samples represents edge epoxy and ether groups, while surface epoxy groups are unstable and easily break during annealing, leading to the formation of COB bonds with B atoms.

[0069] 4. Photoluminescence emission spectra of the graphene oxide quantum dots (GOQDs) and boron-doped graphene oxide quantum dots (BGOQDs) prepared in Examples 1-4 were analyzed. It is well known that fluorescent carbon materials typically exhibit excitation-dependent photoluminescence (PL) behavior. Figure 5(ae) shows the PL behavior of GOQDs and BGOQDs. As shown in Figure 5(a), when the excitation wavelength varied from 330 nm to 450 nm, GOQDs exhibited excitation-independent PL behavior, with the emission peak consistently located at 525.5 nm. In contrast, as shown in Figure 5(be), BGOQDs exhibited different focusing behaviors at the same excitation wavelength. The focusing emission peaks of BGOQDs300, BGOQDs320, BGOQDs340, and BGOQDs360 were located at 507.8, 504.3, 495.3, and 490.0 nm, respectively.

[0070] 5. The graphene oxide quantum dots (GOQDs) and boron-doped graphene oxide quantum dots (BGOQDs) prepared in Examples 1-4 were characterized by concentrated light spectrum normalization and UV-Vis absorption spectroscopy. Figure 6As shown in (a), the focused spectra of GOQDs and BGOQDs were normalized under 360 nm light illumination. The emission peak of BGOQDs was significantly bluer than that of GOQDs. Figure 6 (c) shows that the photoluminescence blue shift of BGOQDs increases with increasing annealing temperature, with a maximum blue shift of 35.5 nm for BGOQDs360. Since the CB content in BGOQDs increases with increasing annealing temperature, the PL blue shift may be related to CB bonds. Analysis indicates that the PL blue shift is consistent with the increasing CB content, suggesting that BC bonds may be the cause of the PL blue shift. UV-Vis absorption spectroscopy reveals the optical properties of the samples. Figure 6 (b) shows that both GOQDs and BGOQDs have an absorption peak at 300 nm. Figure 6 In (d), under 365nm ultraviolet light irradiation, GOQDs exhibit yellow fluorescence, while BGOQDs emit different colors, namely yellow-green, aqua-green, cyan-green, and cyan, indicating that boron doping can effectively modulate the optical properties of GOQDs.

[0071] The above description is a detailed description of the preferred embodiments of the present invention. However, the embodiments are not intended to limit the scope of the patent application of the present invention. All equivalent changes or modifications made under the technical spirit of the present invention should fall within the patent scope covered by the present invention.

Claims

1. A method for preparing boron-doped graphene oxide quantum dots emitting cyan fluorescence, characterized in that, Includes the following steps: (1) Conductive carbon black and concentrated nitric acid are used as raw materials and strong oxidants. The two are mixed and stirred evenly, and then reacted at a temperature of 135-155℃ for 22-26 hours. (2) Deacidify the sample after the reaction in step (1); (3) Disperse the sample after deacidification in step (2) into deionized water, first place it in an ultrasonic cleaner for ultrasonic treatment, then place the ultrasonic solution in a high-speed centrifuge for centrifugation, take the upper dispersion, add deionized water to the dispersion, first use a 220nm filter membrane for preliminary filtration, and then use a 25nm filter membrane for further filtration to obtain graphene oxide quantum dot solution. (4) The graphene oxide quantum dot solution obtained in step (3) is concentrated using a rotary evaporator, and the concentrated solution is placed in a freeze dryer for freeze vacuum drying to obtain fluffy graphene oxide quantum dots, abbreviated as GOQDs. (5) Weigh the graphene oxide quantum dots obtained in step (4), and then weigh the boron oxide. The mass ratio of graphene oxide quantum dots to boron oxide is 1:

10. Mix the two ingredients thoroughly in a mortar, then place them in a crucible and then in a quartz tube. Place the quartz tube in a horizontal tube furnace equipped with temperature and gas flow control devices, and introduce argon gas to react at high temperature. After the reaction, the tube furnace was cooled to room temperature, the resulting mixture was dissolved in water, and then filtered through a 220 nm filter membrane to remove large insoluble particles. The mixture was then purified by dialysis using a dialysis membrane with a molecular weight cutoff of 2000 Da to obtain a boron-doped graphene quantum dot solution. (6) The solution after dialysis in step (5) is placed in a freeze dryer for freeze vacuum drying, and boron-doped graphene oxide quantum dots emitting cyan fluorescence are finally obtained, abbreviated as BGOQDs; The working procedure of the horizontal reaction tube furnace in step (5) is as follows: Ar gas is continuously introduced into one end of the tube furnace at a flow rate of 50-70 ml / min, and the tail gas is treated at the other end. At the same time, the reaction temperature in the tube furnace is raised from room temperature (25°C) to 340-360°C at a rate of 4-6°C / min for 50-80 minutes, and then held at 340-360°C for 2-4 hours. The dialysis purification described in step (5) is carried out at a working temperature of 20-25°C for 22-26 hours. The conductive carbon black mentioned in step (1) is VXC-72 conductive carbon black, and its weight-to-volume ratio with concentrated nitric acid is 1g:80-120ml, with a mass fraction of 68% for concentrated nitric acid.

2. The preparation method according to claim 1, characterized in that: The acid removal process described in step (2) involves first placing the sample in a rotary evaporator to initially remove residual concentrated nitric acid. To further remove a small amount of residual concentrated nitric acid, the sample is then placed in an open vacuum tube furnace equipped with a quartz tube for heating and acid removal, while argon gas is introduced into the open vacuum tube furnace.

3. The preparation method according to claim 2, characterized in that: The rotary evaporator operates at a temperature of 70–90°C and undergoes 3–5 repeated rotary evaporations; the open-type vacuum tube furnace operates at a temperature of 200–230°C and is set with an argon flow rate of 50–70 ml / min.

4. The preparation method according to claim 1, characterized in that: The centrifuge speed in step (3) is 12000-14000 r / min, and the centrifugation time is 15-30 min.

5. The preparation method according to claim 1, characterized in that: The ultrasonic treatment time in step (3) is 12 to 20 minutes.

6. The preparation method according to claim 1, characterized in that: The freeze dryer described in steps (4) and (6) operates at a freezing temperature of -70 to -30°C, a freezing time of 8 to 12 hours, and a vacuuming time of 32 to 48 hours.

7. The boron-doped graphene oxide quantum dots emitting cyan fluorescence prepared by the preparation method according to any one of claims 1 to 6, characterized in that: The boron-doped graphene oxide quantum dots emit cyan fluorescence at a peak position of 490 nm when irradiated with 365 nm excitation light.

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