Preparation method of boron-doped graphene oxide quantum dots emitting cyan fluorescence

Abstract

The invention discloses a preparation method of boron-doped graphene oxide quantum dots emitting cyan fluorescence, which comprises the following steps: reacting VXC-72 conductive carbon black with concentrated nitric acid at high temperature; after the reaction, carrying out deacidification treatment; diluting the deacidified reactant, and performing suction filtration to obtain a graphene oxide quantum dot solution; drying the solution to extract graphene oxide quantum dots; uniformly mixing the extracted graphene oxide quantum dots with boron oxide, performing thermal annealing treatment by adopting a horizontal tubular furnace, dissolving the treated mixture in water, performing suction filtration by using a filter membrane, and performing dialysis; and finally, performing combined treatment of freezing and vacuum drying to obtain the boron-doped graphene oxide quantum dots. The boron-doped graphene oxide quantum dot prepared by the method disclosed by the invention can emit cyan fluorescence under the irradiation of exciting light with the wavelength of 365 nm, and a new preparation method is provided for preparing the graphene oxide quantum dot with a specific luminescence characteristic.

Description

Technical Field

[0001] The invention relates to the technical field of graphene quantum dots, and in particular to a method for preparing boron-doped graphene oxide quantum dots that emit cyan fluorescence. Background Art

[0002] Cyan photoluminescent nanomaterials have attracted great attention recently due to their wide applications in the visible spectrum, such as biomedicine, environmental detection, lighting, display and optical communication. In recent years, graphene quantum dots, abbreviated as GQDs, have become a hot topic of research due to their excellent optical properties, stability, low toxicity, biocompatibility and wide range of applications.

[0003] Graphene quantum dots with a large number of oxygen-containing functional groups are called graphene oxide quantum dots, abbreviated as GOQDs in English. Studies have shown that doping with heteroatoms is an effective strategy to regulate the photoluminescence of graphene quantum dots. Researchers have regulated the photoluminescence properties of graphene quantum dots by doping heteroatoms such as nitrogen atoms, sulfur atoms, fluorine atoms, and chlorine atoms into graphene quantum dots. Currently, various graphene quantum dots with emission wavelengths in the ultraviolet, blue, green, yellow, and red ranges have been developed through different methods. However, there are few studies on the cyan fluorescence of graphene quantum dots, which has a great impact on the widespread application of graphene quantum dots. Summary of the invention

[0004] The object of the present invention is to provide a boron-doped graphene oxide quantum dot emitting cyan fluorescence and a preparation method thereof in view of the above-mentioned problems. The boron-doped graphene oxide quantum dot obtained by the preparation method of the present invention emits cyan fluorescence at an emission peak position of 490 nm under 365 nm excitation light, thereby achieving the purpose of preparing a graphene oxide quantum dot emitting cyan fluorescence.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is as follows: A method for preparing boron-doped graphene oxide quantum dots that emit cyan fluorescence comprises the following steps: (1) Conductive carbon black and concentrated nitric acid are used as raw materials and strong oxidant, mixed and stirred evenly, and reacted at a temperature of 135 to 155°C for 22 to 26 hours; (2) subjecting the sample after the reaction in step (1) to deacidification; (3) dispersing the sample after acid removal in step (2) into deionized water, first placing it in an ultrasonic cleaner for ultrasonic treatment, then placing the sonicated solution in a high-speed centrifuge for centrifugal treatment, taking the upper layer of the dispersion, adding deionized water to the dispersion, first performing preliminary filtration using a 220 nm filter membrane, and then further filtration using a 25 nm filter membrane to obtain a graphene oxide quantum dot solution; (4) concentrating the graphene oxide quantum dot solution obtained in step (3) using a rotary evaporator, placing the concentrated solution in a freeze dryer for freeze vacuum drying, and obtaining fluffy graphene oxide quantum dots, abbreviated as GOQDs; (5) weighing the graphene oxide quantum dots obtained in step (4), and then weighing boron oxide, wherein the mass ratio of graphene oxide quantum dots to boron oxide is 1:10; The two are placed in a mortar and mixed evenly, then placed in a small crucible and placed in a quartz tube. The quartz tube is placed in a horizontal reaction tube furnace equipped with a temperature and gas flow control device, and argon gas is introduced to react at high temperature; After the reaction, the tube furnace was cooled to room temperature, and the obtained mixture was dissolved in water, and then filtered with a 220 nm filter membrane to remove large insoluble particles. Then, the mixture was dialyzed and purified using a dialysis membrane with a molecular weight cutoff of 2000 Da to obtain a boron-doped graphene quantum dot solution; (6) placing the dialyzed solution in step (5) in a freeze dryer for freeze vacuum drying, and finally obtaining boron-doped graphene oxide quantum dots (BGOQDs) emitting cyan fluorescence.

[0006] In the present invention, preferably, the conductive carbon black in step (1) is VXC-72 conductive carbon black, and the weight volume ratio of the conductive carbon black to concentrated nitric acid is 1 g: 80-120 ml, and the mass fraction of concentrated nitric acid is 68%.

[0007] In the present invention, preferably, in the deacidification treatment described in step (2), the sample is first placed in a rotary evaporator to preliminarily remove residual concentrated nitric acid. In order 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 deacidification, and argon gas is introduced into the open vacuum tube furnace.

[0008] In the present invention, preferably, the operating temperature of the rotary evaporator is 70-90°C, and the rotary evaporation is repeated 3-5 times; the operating temperature of the open vacuum tube furnace is 200-230°C, and the flow rate of argon is set to 50-70 ml / min.

[0009] In the present invention, preferably, the rotation speed of the centrifuge in step (3) is 12000-14000 r / min, and the centrifugation time is 15-30 min.

[0010] In the present invention, preferably, the ultrasonic treatment time in step (3) is 12 to 20 minutes.

[0011] In the present invention, preferably, the freezing working temperature of the freeze dryer in steps (4) and (6) is -70 to -30°C, the freezing working time is 8 to 12 hours, and the vacuuming time is 32 to 48 hours.

[0012] In the present invention, preferably, the working procedure of the horizontal reaction tube furnace in step (5) is to continuously introduce Ar gas at one end of the tube furnace at a flow rate of 50 to 70 ml / min, and to perform tail gas treatment at the other end, while raising the reaction temperature in the tube furnace from room temperature 25°C to 300 to 400°C at a rate of 4 to 6°C / min for 50 to 80 minutes, and then to keep the temperature at 300 to 400°C for 2 to 4 hours.

[0013] In the present invention, preferably, the dialysis purification in step (5) has an operating temperature of 20 to 25° C. and a working time of 22 to 26 hours.

[0014] Another object of the present invention is to provide boron-doped graphene oxide quantum dots emitting cyan fluorescence prepared by the above preparation method.

[0015] The beneficial effects of the present invention are: 1. The present invention provides a method for synthesizing boron-doped graphene oxide quantum dots based on VXC-72 conductive carbon black as a carbon source and boron oxide as a doping boron source, using concentrated nitric acid as a strong oxidant, and deionized water and argon as auxiliary materials. The raw materials used in this method are easy to obtain and low in cost, the process flow is simple, the production cycle is short, and the materials used are environmentally friendly and non-toxic, safe for organisms and the environment; 2. The boron-doped graphene oxide quantum dots prepared by the method of the present invention have the characteristics of simple process and short cycle, and the process parameters can be flexibly adjusted according to production needs; 3. The boron-doped graphene oxide quantum dots prepared by the method of the present invention exhibit a cyan fluorescence emission peak at 490nm under 365nm excitation light irradiation, and the maximum blue shift of photoluminescence is 35.5nm, which provides an effective way to prepare cyan fluorescent graphene oxide quantum dots. These quantum dots have potential application value in the field of cyan light and biomedical fields such as fluorescent probes and cell imaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] 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; Figure 2 The transmission electron micrograph and size distribution diagram of the graphene oxide quantum dots (GOQDs) and the boron-doped graphene oxide quantum dots (BGOQDs360) emitting cyan fluorescence prepared in Example 1; Figures 2(a) and 2(b) show the TEM images of GOQDs and BGOQDs360, respectively, and Figures 2(c) and 2(d) show the size distribution of GOQDs and BGOQDs360; Figure 3 The Raman spectra of graphene oxide quantum dots (GOQDs) and boron-doped graphene oxide quantum dots (BGOQDs) prepared in Examples 1 to 4 are shown in FIG. Figure 3 (a) Fourier transform infrared spectroscopy analysis Figure 3 (b); Figure 4 It is an X-ray photoelectron spectroscopy analysis diagram of graphene oxide quantum dots (GOQDs) and boron-doped graphene oxide quantum dots (BGOQDs) prepared in Examples 1 to 4; Figure 5 are photoluminescence emission spectra of graphene oxide quantum dots (GOQDs) and boron-doped graphene oxide quantum dots (BGOQDs) prepared in Examples 1 to 4; Figure 6 It is an analysis chart of normalized focusing spectra, photoluminescence colors, and ultraviolet-visible absorption spectra of graphene oxide quantum dots (GOQDs) and boron-doped graphene oxide quantum dots (BGOQDs) prepared in Examples 1 to 4. DETAILED DESCRIPTION

[0017] In order to enable those skilled in the art to better understand the method of the present application, the technical solution of the present application is clearly and completely described below through embodiments. Obviously, the described embodiments are only embodiments of a part of the present application, not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work should fall within the scope of protection of the present application. Example 1

[0018] A method for preparing boron-doped graphene oxide quantum dots that emit cyan fluorescence comprises the following steps: (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%, add it into the round-bottom flask as a strong oxidant, mix the VXC-72 conductive carbon black and stir it evenly with a glass rod; put a magnet in the round-bottom flask containing the sample, place the round-bottom flask in a thermal-collecting constant-temperature heating magnetic stirrer, adjust the speed of the magnet to 25r / s, set the heating temperature of the thermal-collecting constant-temperature heating magnetic stirrer to 140°C, and the reaction time is 24h. The thermal-collecting constant-temperature heating magnetic stirrer contains dimethyl silicone oil, and the thermal-collecting constant-temperature heating magnetic stirrer is connected to a low-temperature constant-temperature stirring reaction bath, which is used to cool and reflux the volatilized concentrated nitric acid; (2) adding deionized water to dilute the sample after the reaction in step (1), placing the round-bottom flask in a rotary evaporator, and performing rotary evaporation on the sample in a water bath at 80° C., and performing rotary evaporation three times using the rotary evaporator to preliminarily remove most of the residual concentrated nitric acid; in order to further remove a small amount of residual concentrated nitric acid, diluting the obtained sample with deionized water, and then placing the mixed solution in a quartz boat, and slowly placing the quartz boat in an open vacuum tube furnace equipped with a quartz tube, setting the heating temperature of the open vacuum tube furnace to 230° C., the heating time to 3 h, and while heating, introducing argon gas into the open vacuum tube furnace, and setting the flow rate of argon gas to 50 ml / min; (3) dispersing the sample obtained after deacidification in step (2) into 400 ml of deionized water, placing it in an ultrasonic cleaner for 15 min; dividing the solution evenly into 8 100 ml centrifuge tubes, placing them in a high-speed centrifuge, setting the speed of the centrifuge to 12000 r / min, centrifuging for 15 min, taking the upper layer of the dispersion after the centrifugation, adding 500 ml of deionized water to the dispersion, filtering it, first using a 220 nm filter membrane for preliminary filtration, and then using a 25 nm filter membrane for further filtration to obtain a graphene oxide quantum dot solution; (4) The graphene oxide quantum dot solution obtained in step (3) is concentrated by a rotary evaporator, and 300 ml of the concentrated solution is evenly divided into 6 evaporating dishes, and the evaporating dishes are covered with a layer of qualitative filter paper, and then the evaporating dishes are placed in a freeze dryer at -70°C, and after freezing for 12 hours, vacuuming for 48 hours to obtain fluffy graphene oxide quantum dots, abbreviated as GOQDs in English; (5) Weigh 0.1 g of the graphene oxide quantum dots obtained in step (4), and then weigh 1 g of boron oxide, place the two in a mortar and mix them evenly, then 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 a temperature and airflow control device for reaction, set the working program of the tube furnace, and continuously introduce Ar gas at one end of the tube furnace at a flow rate of 50 ml / min. The other end is well treated for exhaust gas, and at the same time, the reaction temperature in the tube furnace is raised from room temperature 25°C to 360°C at a rate of 5°C / min for 67 minutes, and then continuously kept warm at 360°C for 2 hours; After the reaction, the horizontal reaction tube furnace containing the sample was cooled naturally, and the small crucible containing the oxidation mixture was taken out. The obtained mixture was dissolved in water, and then filtered with a 220 nm filter membrane to remove large insoluble particles. Then, the mixture was dialyzed and purified for 24 hours at a working temperature of 25°C using a dialysis membrane with a molecular weight cutoff of 2000Da to obtain a boron-doped graphene oxide quantum dot solution; (6) The obtained solution was diluted with deionized water, and a layer of qualitative filter paper was covered on a small quartz cup. The small quartz cup was placed in a freeze dryer at -70°C. After freezing for 12 hours, the cup was vacuumed for 48 hours to finally obtain boron-doped graphene oxide quantum dots emitting cyan fluorescence, which are abbreviated as BGOQDs 360 (the number indicates the insulation annealing temperature).

[0019] 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 shown. Example 2

[0020] Repeat steps (1) to (4) of Example 1 to obtain fluffy graphene oxide quantum dots, abbreviated as GOQDs; (5) Weigh 0.1 g of the graphene oxide quantum dots obtained in step (4), and then weigh 1 g of boron oxide, place the two in a mortar and mix them evenly, then 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 a temperature and airflow control device for reaction, set the working program of the tube furnace, and continuously introduce Ar gas at one end of the tube furnace at a flow rate of 50 ml / min. The other end is well treated for exhaust gas, and at the same time, the reaction temperature in the tube furnace is raised from room temperature 25°C to 340°C at a rate of 5°C / min for 63 minutes, and then continuously kept warm at 340°C for 2 hours; After the reaction, the horizontal reaction tube furnace containing the sample was cooled naturally, and the small crucible containing the oxidation mixture was taken out. The obtained mixture was dissolved in water, and then filtered with a 220 nm filter membrane to remove large insoluble particles. Then, the mixture was dialyzed and purified for 24 hours at a working temperature of 25°C using a dialysis membrane with a molecular weight cutoff of 2000Da to obtain a boron-doped graphene oxide quantum dot solution; (6) The obtained solution was diluted with deionized water, and a layer of qualitative filter paper was covered on a small quartz cup. The small quartz cup was placed in a freeze dryer at -70°C. After freezing for 12 hours, the cup was vacuumed for 48 hours to finally obtain boron-doped graphene oxide quantum dots emitting cyan fluorescence, abbreviated as BGOQDs 340 (the number indicates the insulation annealing temperature). Example 3

[0021] Repeat steps (1) to (4) of Example 1 to obtain fluffy graphene oxide quantum dots, abbreviated as GOQDs; (5) Weigh 0.1 g of the graphene oxide quantum dots obtained in step (4), and then weigh 1 g of boron oxide, place the two in a mortar and mix them evenly, then 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 a temperature and airflow control device for reaction, set the working program of the tube furnace, and continuously introduce Ar gas at one end of the tube furnace at a flow rate of 50 ml / min. The other end is well treated for exhaust gas, and at the same time, the reaction temperature in the tube furnace is raised from room temperature 25°C to 320°C at a rate of 5°C / min for 59 minutes, and then continuously kept warm at 320°C for 2 hours; After the reaction, the horizontal reaction tube furnace containing the sample was cooled naturally, and the small crucible containing the oxidation mixture was taken out. The obtained mixture was dissolved in water, and then filtered with a 220 nm filter membrane to remove large insoluble particles. Then, the mixture was dialyzed and purified for 24 hours at a working temperature of 25°C using a dialysis membrane with a molecular weight cutoff of 2000Da to obtain a boron-doped graphene oxide quantum dot solution; (6) The obtained solution was diluted with deionized water, and a layer of qualitative filter paper was covered on a small quartz cup. The small quartz cup was placed in a freeze dryer at -70°C. After freezing for 12 hours, the cup was vacuumed for 48 hours to finally obtain boron-doped graphene oxide quantum dots emitting water green fluorescence, which are abbreviated as BGOQDs 320 (the number indicates the insulation annealing temperature). Example 4

[0022] Repeat steps (1) to (4) of Example 1 to obtain fluffy graphene oxide quantum dots, abbreviated as GOQDs; (5) Weigh 0.1 g of the graphene oxide quantum dots obtained in step (4), and then weigh 1 g of boron oxide, place the two in a mortar and mix them evenly, then 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 a temperature and airflow control device for reaction, set the working program of the tube furnace, and continuously introduce Ar gas at one end of the tube furnace at a flow rate of 50 ml / min. The other end is well treated for exhaust gas, and at the same time, the reaction temperature in the tube furnace is raised from room temperature 25°C to 300°C at a rate of 5°C / min for 55 minutes, and then continuously kept warm at 300°C for 2 hours; After the reaction, the horizontal reaction tube furnace containing the sample was cooled naturally, and the small crucible containing the oxidation mixture was taken out. The obtained mixture was dissolved in water, and then filtered with a 220 nm filter membrane to remove large insoluble particles. Then, the mixture was dialyzed and purified for 24 hours at a working temperature of 25°C using a dialysis membrane with a molecular weight cutoff of 2000Da to obtain a boron-doped graphene oxide quantum dot solution; (6) The obtained solution was diluted with deionized water, and a layer of qualitative filter paper was covered on a small quartz cup. The small quartz cup was placed in a freeze dryer at -70°C. After freezing for 12 hours, the cup was vacuumed for 48 hours to finally obtain boron-doped graphene oxide quantum dots emitting yellow-green fluorescence, which are abbreviated as BGOQDs 300 (the number indicates the insulation annealing temperature).

[0023] 2. Performance Test

[0024] 1. The graphene oxide quantum dots and boron-doped graphene oxide quantum dots prepared in Example 1 were analyzed by transmission electron microscopy 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 diameters of GOQDs and BGOQDs360 range from about 0.9 to 2.2 nm and 1.40 to 2.90 nm, respectively. It was calculated that the average diameter of GOQDs was about 1.38 nm, and the average diameter of BGOQDs360 was about 1.99 nm.

[0025] 2. The graphene oxide quantum dots (GOQDs) and boron-doped graphene oxide quantum dots (BGOQDs) prepared in Examples 1 to 4 were analyzed by Raman spectroscopy and Fourier transform infrared spectroscopy. 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 and 1616 cm -1, while the D peak of BGOQDs blue shifted to 1396 cm -1 , the G peak red-shifted to 1607 cm -1 , which may be due to the formation of BC bonds leading to lattice distortion. 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 have a high density of 3300-3700 cm -1 There is a broad absorption band, which is attributed to the -OH stretching vibration. The -COOH vibration band of GOQDs is at 1447 cm -1 The C=C vibration band of BGOQDs is at 1617 cm -1 The enhancement of BGOQDs at 1041 cm -1 , 1112 cm -1 and 1390 cm -1 The appearance of new bands, attributed to BOH, BC and OB stretching, respectively, indicates the presence of boron doping.

[0026] 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 to 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 have a B1s peak at 192 eV, confirming the doping of boron atoms.

[0027] Table 1

[0028] As shown in Table 1, with the increase of annealing temperature, the carbon content in BGOQDs increases while the oxygen content decreases, and the B 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 the annealing process, the oxygen functional groups on GOQDs are removed by releasing CO2 and CO, and the B atoms are integrated into the lattice of GOQDs.

[0029] Figure 4(c) shows the high-resolution C1s spectra of GOQDs and BGOQDs. A CC peak was observed at 284.8 eV, and the peaks at 289.12, 286.59, 288.48, and 285.45 eV correspond to OC=O, COC, C=O, and C=C, respectively. The peaks at 284.15 and 290.45 eV are BC bonds and COB bonds, respectively.

[0030] 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). In addition, as the annealing temperature increases from 300 °C to 360 °C, the peaks of some chemical bonds shift. This shift may be due to the heteroatoms donating electrons to C atoms, resulting in an increase in the electron cloud density on the C atoms. These findings clearly indicate that B atoms are successfully incorporated into the lattice of GOQDs.

[0031] Table 2

[0032] Table 2 lists the chemical group contents of GOQDs and BGOQDs. Compared with GOQDs, the contents of COC bonds and C=C bonds in BGOQDs increased slightly, while the contents of C=O bonds and OC=O bonds decreased significantly. This indicates that most of the oxygen-containing functional groups were pyrolyzed or converted into thermally stable phenolic hydroxyl groups, ethers, and carbonyl groups. However, the CC bond content in BGOQDs decreased from 43.51 at.% in GOQDs to 39.78, 32.09, 29.24, and 27.04 at.% in BGOQDs300, while the CB bond content in BGOQDs300, BGOQDs320, BGOQDs340, and BGOQDs360 increased from 0 at.% to 4.14, 5.67, 11.32, and 15.56 at.%, respectively. This suggests that the breaking of CC bonds in GOQDs promotes the formation of BC bonds between B atoms in boron oxide and carbon atoms in GOQDs. We speculate that the introduction of boron during thermal annealing reduces CC bonds in various samples, while high temperature converts CC to C=C, which then breaks to form BC bonds. In addition, the fluctuation of COC bond content is inversely proportional to the fluctuation of COB bonds. This may be because COC in the samples represents the epoxy and ether groups at the edge, while the surface epoxy groups are unstable and easily broken during annealing, resulting in the formation of COB bonds with B atoms.

[0033] 4. The photoluminescence emission spectra of the graphene oxide quantum dots (GOQDs) and boron-doped graphene oxide quantum dots (BGOQDs) prepared in Examples 1 to 4 were analyzed. It is well known that fluorescent carbon materials usually exhibit PL behavior related to excitation. Figure 5 (ae) shows the PL behavior of GOQDs and BGOQDs. As shown in Figure 5 (a), when the excitation wavelength changes from 330 nm to 450 nm, GOQDs show PL behavior independent of excitation, and the emission peak is always at 525.5 nm. In contrast, as shown in Figure 5 (be), BGOQDs exhibit different focusing behaviors at the same excitation wavelength. The focusing emission peaks of BGOQDs300, BGOQDs320, BGOQDs340 and BGOQDs360 are located at 507.8, 504.3, 495.3 and 490.0 nm, respectively.

[0034] 5. The graphene oxide quantum dots (GOQDs) and boron-doped graphene oxide quantum dots (BGOQDs) prepared in Examples 1 to 4 were subjected to normalized focusing spectra and UV-visible absorption spectra characterization. Figure 6 As shown in (a), the normalized emission spectra of GOQDs and BGOQDs under 360 nm light irradiation. The emission peak of BGOQDs is significantly bluer than that of GOQDs. Figure 6 (c) shows that the photoluminescence blue shift of BGOQDs increases with increasing annealing temperature, and the maximum blue shift of BGOQDs360 is 35.5 nm. Since the CB content in BGOQDs increases with increasing annealing temperature, the PL blue shift may be related to the CB bond. Analysis shows that the PL blue shift is consistent with the trend of increasing CB content, suggesting that the BC bond may be the cause of the PL blue shift. The UV-visible absorption spectrum reveals the optical properties of the sample. Figure 6 (b) shows that both GOQDs and BGOQDs have absorption peaks at 300 nm. Figure 6 In (d), under 365nm ultraviolet light, GOQDs exhibit yellow fluorescence, while BGOQDs emit different colors, namely yellow-green, aqua, cyan and cyan, indicating that boron doping can effectively adjust the optical properties of GOQDs.

[0035] The above description is a detailed description of the preferred feasible embodiments of the present invention, but the embodiments are not intended to limit the scope of the patent application of the present invention. All equivalent changes or modified changes completed under the technical spirit suggested by 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: The following steps are involved: (1) Conductive carbon black and concentrated nitric acid are used as raw materials and a strong oxidant, the two are mixed and stirred evenly, and then reacted at a temperature of 135 to 155° C. for 22 to 26 hours; (2) subjecting the sample after the reaction in step (1) to deacidification; (3) dispersing the sample after acid removal in step (2) into deionized water, first placing it in an ultrasonic cleaner for ultrasonic treatment, then placing the sonicated solution in a high-speed centrifuge for centrifugal treatment, taking the upper layer of the dispersion, adding deionized water to the dispersion, first performing preliminary filtration using a 220 nm filter membrane, and then further filtration using a 25 nm filter membrane to obtain a graphene oxide quantum dot solution; (4) concentrating the graphene oxide quantum dot solution obtained in step (3) using a rotary evaporator, placing the concentrated solution in a freeze dryer for freeze vacuum drying, and obtaining fluffy graphene oxide quantum dots, abbreviated as GOQDs; (5) weighing the graphene oxide quantum dots obtained in step (4), and then weighing boron oxide, wherein the mass ratio of the graphene oxide quantum dots to the boron oxide is 1:10; The two are placed in a mortar and mixed evenly, then placed in a crucible and placed in a quartz tube, the quartz tube is placed in a horizontal reaction tube furnace equipped with a temperature and airflow control device, and argon gas is introduced to react at high temperature; After the reaction, the tube furnace was cooled to room temperature, and the obtained mixture was dissolved in water, and then filtered with a 220 nm filter membrane to remove large insoluble particles. Then, the mixture was dialyzed and purified using a dialysis membrane with a molecular weight cutoff of 2000 Da to obtain a boron-doped graphene quantum dot solution; (6) placing the dialyzed solution in step (5) in a freeze dryer for freeze vacuum drying, and finally obtaining boron-doped graphene oxide quantum dots (BGOQDs) emitting cyan fluorescence.

2. The preparation method according to claim 1, characterized in that: The conductive carbon black in step (1) is VXC-72 conductive carbon black, and the weight volume ratio of VXC-72 conductive carbon black to concentrated nitric acid is 1g:80-120ml, and the mass fraction of concentrated nitric acid is 68%.

3. The preparation method according to claim 1, characterized in that: In the deacidification treatment described in step (2), the sample is first placed in a rotary evaporator to preliminarily 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 deacidification, while argon gas is introduced into the open vacuum tube furnace.

4. The preparation method according to claim 3, characterized in that: The working temperature of the rotary evaporator is 70-90° C., and the rotary evaporation is repeated 3-5 times; the working temperature of the open vacuum tube furnace is 200-230° C., and the flow rate of argon is set to 50-70 ml / min.

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

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

7. The preparation method according to claim 1, characterized in that: The freezing working temperature of the freeze dryer in steps (4) and (6) is -70 to -30°C, the freezing working time is 8 to 12 hours, and the vacuum working time is 32 to 48 hours.

8. The preparation method according to claim 1, characterized in that: The working procedure of the horizontal reaction tube furnace in step (5) is to continuously introduce Ar gas at one end of the tube furnace at a flow rate of 50 to 70 ml / min, and to perform tail gas treatment at the other end. At the same time, the reaction temperature in the tube furnace is raised from room temperature 25°C to 300 to 400°C at a rate of 4 to 6°C / min for 50 to 80 minutes, and then maintained at 300 to 400°C for 2 to 4 hours.

9. The preparation method according to claim 1, characterized in that: The dialysis purification in step (5) has an operating temperature of 20 to 25° C. and a working time of 22 to 26 hours.

10. The boron-doped graphene oxide quantum dots emitting cyan fluorescence prepared by the preparation method according to any one of claims 1 to 9, characterized in that: The boron-doped graphene oxide quantum dots emit cyan fluorescence at an emission peak position of 490 nm under irradiation with 365 nm excitation light.

Images