Molybdenum-nitrogen co-doped carbon quantum dot and application thereof

Abstract

The invention relates to the technical field of carbon nanomaterials, particularly discloses a molybdenum-nitrogen co-doped carbon quantum dot, and also discloses application of the molybdenum-nitrogen co-doped carbon quantum dot. The molybdenum-nitrogen co-doped carbon quantum dot provided by the invention is synthesized by taking L-arginine, a molybdenum source and 1-pyrenecarboxaldehyde as precursors through a one-step hydrothermal method. The molybdenum-nitrogen co-doped carbon quantum dot provided by the invention has obvious advantages in detection of Cr2O7 < 2-> and luteolin, and can also be applied to fluorescent ink.

Description

Technical Field

[0001] The present invention relates to the technical field of carbon nanomaterials, and particularly relates to a molybdenum and nitrogen co-doped carbon quantum dot, and also relates to its application. Background Art

[0002] Carbon quantum dots (CDs), also known as carbon dots, are a class of zero-dimensional carbon nanomaterials with remarkable fluorescence properties. Due to their extremely small size, carbon quantum dots have relatively special size quantization and quantum confinement effects, such as the dependence of the excitation wavelength, and have advantages such as low toxicity, good biocompatibility, and excellent chemical stability.

[0003] Research has found that doping CDs with metal atoms is a way to change the physical and chemical properties of carbon dots. Like non-metal doping, it has the advantages of improving the fluorescence quantum yield of carbon quantum dots, red-shifting their emission wavelength, increasing their stability, etc. It can even endow CDs with rich active sites, improve their optoelectronic efficiency, and improve their abilities for catalysis, acting as a contrast agent for magnetic resonance imaging, etc. However, current reports mainly focus on CDs doped with non-metal atoms (such as N, B, P, and S). Most metal atoms have limitations such as toxicity, low biocompatibility, and high cost, which makes the research on CDs doped with them relatively less, and the existing reports mainly focus on limited metal ions (such as Co, Cu, Fe, Ni, and Zn).

[0004] Therefore, the present invention aims to develop a new type of carbon quantum dot, namely molybdenum and nitrogen co-doped carbon quantum dot, and further study its properties and applications. Summary of the Invention

[0005] The main technical problem to be solved by the present invention is to provide a molybdenum and nitrogen co-doped carbon quantum dot, and the application of the prepared molybdenum and nitrogen co-doped carbon quantum dot.

[0006] To solve the above technical problem, the technical solution adopted by the present invention is: A molybdenum and nitrogen co-doped carbon quantum dot is prepared by a method including the following steps:

[0007] S1: Mix L-arginine, a molybdenum source, 1-pyrenecarboxaldehyde with a solvent, place it in an autoclave for hydrothermal reaction. After the reaction is completed, centrifuge the obtained reaction system, and take the supernatant obtained by separation, that is, a solution containing molybdenum and nitrogen co-doped carbon quantum dots is obtained;

[0008] S2: Dialyze the solution containing molybdenum and nitrogen co-doped carbon quantum dots obtained by treating in step S1 using a dialysis bag. The liquid in the bag obtained is freeze-dried into a solid to prepare molybdenum and nitrogen co-doped carbon quantum dots (Mo,N-CDs).

[0009] As an embodiment of the present invention, the mass ratio of L-arginine, molybdenum source, and 1-pyrenecarboxaldehyde is: L-arginine∶molybdenum source∶1-pyrenecarboxaldehyde = (0.1 - 0.5)∶(0.2 - 0.4)∶(0.01 - 0.03).

[0010] Preferably, the mass ratio of L-arginine, molybdenum source, and 1-pyrenecarboxaldehyde is: L-arginine∶molybdenum source∶1-pyrenecarboxaldehyde = (0.1 - 0.5)∶(0.2 - 0.4)∶(0.01 - 0.02).

[0011] More preferably, the mass ratio of L-arginine, molybdenum source, and 1-pyrenecarboxaldehyde is: L-arginine∶molybdenum source∶1-pyrenecarboxaldehyde = (0.1 - 0.3)∶(0.3 - 0.4)∶(0.01 - 0.02).

[0012] Even more preferably, the mass ratio of L-arginine, molybdenum source, and 1-pyrenecarboxaldehyde is: L-arginine∶molybdenum source∶1-pyrenecarboxaldehyde = 0.3∶0.3∶(0.01 - 0.02).

[0013] As an embodiment of the present invention, the molybdenum source is molybdic acid, sodium molybdate, or ammonium molybdate, preferably ammonium molybdate.

[0014] As an embodiment of the present invention, the solvent is water.

[0015] As an embodiment of the present invention, the temperature of the hydrothermal reaction is 180 - 200 °C. The reaction time of the hydrothermal reaction is 3 - 5 hours.

[0016] Preferably, the temperature of the hydrothermal reaction is 190 °C. The reaction time of the hydrothermal reaction is 4 hours.

[0017] As an embodiment of the present invention, the cut-off molecular weight of the dialysis bag is 1000 Daltons.

[0018] As an embodiment of the present invention, in step S1, after mixing L-arginine, molybdenum source, 1-pyrenecarboxaldehyde with the solvent, it is ultrasonically treated and then placed in an autoclave for hydrothermal reaction. Among them, the ultrasonic treatment time is 3 - 8 minutes.

[0019] As an embodiment of the present invention, in step S1, the obtained reaction system is cooled to room temperature (15 - 35 °C) and then centrifuged.

[0020] As an embodiment of the present invention, in step S1, the rotation speed of centrifugation is 15,000 rpm, and the centrifugation is carried out for 10 - 20 minutes.

[0021] The present invention also provides the molybdenum and nitrogen co-doped carbon quantum dots of the present invention in Cr 2 O 72- Applications in detection.

[0022] The present invention also provides the application of the molybdenum and nitrogen co-doped carbon quantum dots described in the present invention in the detection of luteolin.

[0023] The present invention also provides the application of the molybdenum and nitrogen co-doped carbon quantum dots described in the present invention in fluorescent inks, which has a fluorescent anti-counterfeiting effect.

[0024] The molybdenum and nitrogen co-doped carbon quantum dots provided by the present invention are synthesized by a one-step hydrothermal method using L-arginine, a molybdenum source, and 1-pyrenecarboxaldehyde as precursors. The molybdenum and nitrogen co-doped carbon quantum dots (Mo,N-CDs) provided by the present invention are doped with molybdenum metal. Molybdenum has an affordable price, high biocompatibility, good stability, and can be uniformly degraded. More importantly, the intake of molybdenum element at a low concentration has many benefits for the human body: such as maintaining the body's resistance, preventing anemia, kidney stones, heart diseases, etc., and has a positive effect on protecting the genetic material of cells and reducing the toxicity of carcinogens to genes.

[0025] The Mo,N-CDs provided by the present invention emit cyan fluorescence at 494 nm under a handheld 365 nm ultraviolet light, and have a high fluorescence quantum yield (FLQY). Research shows that Mo,N-CDs exhibit excellent pH stability, thermal stability, salt tolerance, and photobleaching resistance. More importantly, Cr 2 O 7 2- and luteolin can selectively and instantaneously quench the fluorescence of Mo,N-CDs, with high sensitivity, a wide linear range, and good linear correlation, and can be used to construct a rapid detection platform for Cr 2 O 7 2- and luteolin. In addition, the detection of Cr 2 O 7 2- in actual water samples and luteolin in drugs was also studied, and all showed acceptable recovery rates, with a relative standard deviation of less than 5%, and a short response time (<10 seconds). Mo,N-CDs will have great application value in environmental water monitoring and drug quantitative analysis, etc.

[0026] The Mo,N-CDs provided by the present invention have the advantage of high fluorescence quantum yield at a wavelength of 365 nm, making it have good application prospects in anti-counterfeiting. It is found that using Mo,N-CDs as fluorescent inks shows excellent anti-counterfeiting effects. Brief Description of the Drawings

[0027] Figure 1 is the TEM image of the Mo,N-CDs prepared in Example 1 of the present invention;

[0028] Figure 2 It is the particle size distribution histogram of Mo,N-CDs prepared in Example 1 of the present invention;

[0029] Figure 3 It is the HRTEM image (high-resolution TEM image) of Mo,N-CDs prepared in Example 1 of the present invention;

[0030] Figure 4 It is the X-ray diffraction pattern of Mo,N-CDs prepared in Example 1 of the present invention;

[0031] Figure 5 It is the Fourier transform infrared spectroscopy (FTIR) image of Mo,N-CDs prepared in Example 1 of the present invention;

[0032] Figure 6 It is the X-ray photoelectron spectroscopy (XPS) image of Mo,N-CDs prepared in Example 1 of the present invention;

[0033] Figure 7 It is the ultraviolet-visible light absorption, fluorescence excitation and emission spectroscopy images of Mo,N-CDs prepared in Example 1 of the present invention;

[0034] Figure 8 It is the comparison image of the photo of Mo,N-CDs prepared in Example 1 of the present invention under sunlight (left) and 365 nm ultraviolet light (right);

[0035] Figure 9 It is the fluorescence emission spectroscopy image of Mo,N-CDs prepared in Example 1 of the present invention at different excitation wavelengths;

[0036] Figure 10 It is the fluorescence intensity image of Mo,N-CDs prepared in Example 1 of the present invention at 494 nm;

[0037] Figure 11 It is the fluorescence intensity value image of Mo,N-CDs prepared in Example 1 of the present invention at different temperatures;

[0038] Figure 12 It is the fluorescence intensity value image of Mo,N-CDs prepared in Example 1 of the present invention at different pH values;

[0039] Figure 13 It is the fluorescence intensity value image of Mo,N-CDs prepared in Example 1 of the present invention at different NaCl concentrations;

[0040] Figure 14 It is the fluorescence emission spectroscopy image of Mo,N-CDs obtained in Application Example 1 of the present invention containing different concentrations of Cr 2 O 7 2- ;

[0041] Figure 15 It is the fluorescence spectrogram of Mo,N-CDs containing different ions obtained in Application Example 1 of the present invention;

[0042] Figure 16 It is in the absence and presence of Cr in Application Example 1 of the present invention 2 O 7 2- Under the circumstances, the fluorescence intensity diagram of Mo,N-CDs;

[0043] Figure 17 It is the titration linear diagram obtained in Application Example 1 of the present invention;

[0044] Figure 18 It is the fluorescence emission spectrogram of Mo,N-CDs containing different concentrations of luteolin obtained in Application Example 2 of the present invention;

[0045] Figure 19 It is the fluorescence spectrogram of Mo,N-CDs containing different compounds obtained in Application Example 2 of the present invention;

[0046] Figure 20 It is the fluorescence intensity diagram of Mo,N-CDs in the absence and presence of luteolin in Application Example 2 of the present invention;

[0047] Figure 21 It is the titration linear diagram obtained in Application Example 2 of the present invention;

[0048] Figure 22 It is a photograph of hand-drawn on test paper using Mo,N-CDs as a fluorescent ink under sunlight (left) and 365 nm ultraviolet light (right) in Application Example 3 of the present invention. Detailed implementation manners

[0049] The technical solution of the present invention will be described in detail below through specific examples. The following examples are intended to further illustrate the content of the present invention in detail, rather than limiting the scope of protection of the claims of the present invention.

[0050] In the following examples and comparative examples, when not specifically stated, the reagents used are all commercially available products.

[0051] Example 1

[0052] This example provides a molybdenum-nitrogen co-doped carbon quantum dot, and the preparation steps are as follows:

[0053] S1: Mix L-arginine (0.3 g), ammonium molybdate (0.3 g), 1-pyrenecarboxaldehyde (0.02 g) with pure water (12.5 mL), perform ultrasonic treatment for 5 minutes, then transfer it into a 25 mL Teflon liner, and seal it in a stainless steel autoclave. Heat and react at 190 °C for 4 hours; after the reaction is completed, let the resulting reaction system cool naturally to room temperature (about 25 °C), then centrifuge at 15,000 rpm for 15 minutes for separation, and take the separated supernatant to obtain an aqueous solution containing molybdenum and nitrogen co-doped carbon quantum dots (i.e., Mo,N-CDs aqueous solution);

[0054] S2: Dialyze the Mo,N-CDs aqueous solution obtained in step S1 with a dialysis bag for 24 hours. The cut-off molecular weight of the dialysis bag is 1000 daltons. The liquid in the bag is freeze-dried in a freeze dryer for 12 hours to make a solid powder, thus obtaining molybdenum and nitrogen co-doped carbon quantum dots Mo,N-CDs.

[0055] Example 2

[0056] This example provides a kind of molybdenum and nitrogen co-doped carbon quantum dots. The difference in the preparation steps from Example 1 is only that the dosage of L-arginine is adjusted to 0.1 g, and the others remain unchanged, obtaining molybdenum and nitrogen co-doped carbon quantum dots Mo,N-CDs.

[0057] Example 3

[0058] This example provides a kind of molybdenum and nitrogen co-doped carbon quantum dots. The difference in the preparation steps from Example 1 is only that the dosage of L-arginine is adjusted to 0.5 g, and the others remain unchanged, obtaining molybdenum and nitrogen co-doped carbon quantum dots Mo,N-CDs.

[0059] Example 4

[0060] This example provides a kind of molybdenum and nitrogen co-doped carbon quantum dots. The difference in the preparation steps from Example 1 is only that the dosage of ammonium molybdate is adjusted to 0.2 g, and the others remain unchanged, obtaining molybdenum and nitrogen co-doped carbon quantum dots Mo,N-CDs.

[0061] Example 5

[0062] This example provides a kind of molybdenum and nitrogen co-doped carbon quantum dots. The difference in the preparation steps from Example 1 is only that the dosage of ammonium molybdate is adjusted to 0.4 g, and the others remain unchanged, obtaining molybdenum and nitrogen co-doped carbon quantum dots Mo,N-CDs.

[0063] Example 6

[0064] This example provides a molybdenum-nitrogen co-doped carbon quantum dot. The preparation steps are only different from those of Example 1 in that the amount of 1-pyrenecarboxaldehyde is adjusted to 0.01 g, and the others remain unchanged, obtaining the molybdenum-nitrogen co-doped carbon quantum dot Mo,N-CDs.

[0065] Example 7

[0066] This example provides a molybdenum-nitrogen co-doped carbon quantum dot. The preparation steps are only different from those of Example 1 in that the amount of 1-pyrenecarboxaldehyde is adjusted to 0.03 g, and the others remain unchanged, obtaining the molybdenum-nitrogen co-doped carbon quantum dot Mo,N-CDs.

[0067] Example 8

[0068] This example provides a molybdenum-nitrogen co-doped carbon quantum dot. The preparation steps are only different from those of Example 1 in that the reaction conditions in the stainless steel autoclave are changed to heating reaction at 180 °C for 4 hours, and the others remain unchanged, obtaining the molybdenum-nitrogen co-doped carbon quantum dot Mo,N-CDs.

[0069] Example 9

[0070] This example provides a molybdenum-nitrogen co-doped carbon quantum dot. The preparation steps are only different from those of Example 1 in that the reaction conditions in the stainless steel autoclave are changed to heating reaction at 200 °C for 4 hours, and the others remain unchanged, obtaining the molybdenum-nitrogen co-doped carbon quantum dot Mo,N-CDs.

[0071] Example 10

[0072] This example provides a molybdenum-nitrogen co-doped carbon quantum dot. The preparation steps are only different from those of Example 1 in that the reaction conditions in the stainless steel autoclave are changed to heating reaction at 190 °C for 3 hours, and the others remain unchanged, obtaining the molybdenum-nitrogen co-doped carbon quantum dot Mo,N-CDs.

[0073] Example 11

[0074] This example provides a molybdenum-nitrogen co-doped carbon quantum dot. The preparation steps are only different from those of Example 1 in that the reaction conditions in the stainless steel autoclave are changed to heating reaction at 190 °C for 5 hours, and the others remain unchanged, obtaining the molybdenum-nitrogen co-doped carbon quantum dot Mo,N-CDs.

[0075] Example 12

[0076] This example provides a molybdenum-nitrogen co-doped carbon quantum dot. The preparation steps are only different from those of Example 1 in that ammonium molybdate is changed to molybdic acid, and the others remain unchanged, obtaining the molybdenum-nitrogen co-doped carbon quantum dot Mo,N-CDs.

[0077] Example 13

[0078] This example provides a molybdenum-nitrogen co-doped carbon quantum dot. The difference in the preparation steps from Example 1 is only that ammonium molybdate is replaced with sodium molybdate, and the others remain unchanged, obtaining molybdenum-nitrogen co-doped carbon quantum dots Mo,N-CDs.

[0079] Comparative Example 1

[0080] This comparative example provides a molybdenum-nitrogen co-doped carbon quantum dot. The difference in the preparation steps from Example 1 is only that 1-pyrenecarboxaldehyde is not added in the reaction raw materials, and the others remain unchanged. The specific preparation process is as follows:

[0081] S1: Mix L-arginine (0.3 g), ammonium molybdate (0.3 g) with pure water (12.5 mL), perform ultrasonic treatment for 5 minutes, then transfer it into a 25 mL Teflon inner liner, and then seal it into a stainless steel autoclave, and heat and react at 190 °C for 4 hours; after the reaction is completed, the obtained reaction system is naturally cooled to room temperature (about 25 °C), and then centrifuged at 15,000 rpm for 15 minutes for separation. Take the separated supernatant to obtain an aqueous solution containing molybdenum-nitrogen co-doped carbon quantum dots (i.e., Mo,N-CDs aqueous solution);

[0082] S2: Dialyze the Mo,N-CDs aqueous solution obtained in step S1 with a dialysis bag for 24 hours. The cut-off molecular weight of the dialysis bag is 1000 daltons. The liquid in the bag obtained is freeze-dried in a freeze dryer for 12 hours to make a solid powder, that is, molybdenum-nitrogen co-doped carbon quantum dots Mo,N-CDs are prepared.

[0083] The fluorescence intensities of the Mo,N-CDs prepared in the above examples and comparative examples were detected using a fluorescence spectrophotometer, and the results are shown in Table 1 below.

[0084] Table 1

[0085]

[0086] It can be seen from the results in Table 1 that when preparing molybdenum-nitrogen co-doped carbon quantum dots Mo,N-CDs, if 1-pyrenecarboxaldehyde is not added, the fluorescence intensity of the obtained Mo,N-CDs is very low, and when the added amount of 1-pyrenecarboxaldehyde is relatively large, such as the amount of 1-pyrenecarboxaldehyde in Example 7 is 0.03 g, the fluorescence intensity of the prepared molybdenum-nitrogen co-doped carbon quantum dots Mo,N-CDs is also relatively low. When the molybdenum source is molybdic acid or sodium molybdate, the fluorescence intensity of the obtained Mo,N-CDs is also relatively low. Therefore, the molybdenum source is preferably ammonium molybdate.

[0087] Experimental Example 1

[0088] The Mo,N-CDs provided in Example 1 were characterized.

[0089] The obtained TEM image and particle size distribution histogram are shown in Figure 1 and Figure 2 respectively, and the HRTEM image is shown in Figure 3 as shown, and the X-ray diffraction (XRD) pattern is shown in Figure 4 as shown.

[0090] From Figure 1 and Figure 2 , it can be seen that Mo,N-CDs are nearly spherical in shape with an average particle size of 1.7 nm. Figure 3 It shows that Mo,N-CDs have a lattice fringe carbon core structure with about 0.15 nm. Figure 4 A broad peak is shown at approximately 24.2°, corresponding to the (002) peak of graphite. In summary, these results are consistent with the characteristics of carbon dots.

[0091] The Fourier transform infrared spectroscopy (FTIR) pattern of Mo,N-CDs provided in Example 1 is shown in Figure 5 as shown, and the X-ray photoelectron spectroscopy (XPS) is shown in Figure 6 as shown. Figure 5 , Figure 6 The results show that molybdenum and nitrogen elements are successfully doped into the synthesized carbon dots.

[0092] Experimental Example 2

[0093] The optical properties of Mo,N-CDs provided in Example 1 were studied. The fluorescence spectrum was measured by a Hitachi F-7000 instrument with a slit width of 5 / 5 nm, an excitation wavelength of 365 nm, and an emission wavelength of 494 nm.

[0094] The optical properties of Mo,N-CDs provided in Example 1 were studied by ultraviolet-visible absorption and fluorescence spectroscopy. The ultraviolet-visible light absorption, fluorescence excitation, and emission spectra of Mo,N-CDs are shown in Figure 7 as shown. The fluorescence excitation and emission spectra show that the maximum excitation / emission wavelength of Mo,N-CDs is 365 / 494 nm.

[0095] The aqueous solution of Mo,N-CDs is colorless under sunlight and shows cyan fluorescence under 365 nm ultraviolet light. The comparison diagram of the photo of Mo,N-CDs under sunlight (left) and 365 nm ultraviolet light (right) is shown in Figure 8 .

[0096] The fluorescence emission spectra of Mo,N-CDs at different excitation wavelengths are shown in Figure 9 . When the excitation wavelength increases from 355 nm to 435 nm, the fluorescence emission peak of Mo,N-CDs hardly changes, showing emission characteristics independent of the excitation wavelength.

[0097] Under continuous excitation at 365 nm, the fluorescence intensity of Mo,N-CDs at 494 nm is shown in Figure 10 the figure. The fluorescence intensity values of Mo,N-CDs at different temperatures are shown in Figure 11 the figure. The fluorescence intensity values of Mo,N-CDs at different pH values are shown in Figure 12 the figure. The fluorescence intensity values of Mo,N-CDs at different NaCl concentrations are shown in Figure 13 the figure. Under continuous excitation at 365 nm for 90 min, different incubation temperatures (5 - 85 °C), pH values (3 - 12), and different NaCl concentrations (0 - 100 mM), the fluorescence intensity of Mo,N-CDs did not change significantly, indicating that Mo,N-CDs have excellent photobleaching resistance, thermal stability, pH stability, and salt tolerance.

[0098] Using quinine sulfate as a reference, the fluorescence quantum yield (FLQY) of Mo,N-CDs was calculated to be 41.5%, showing a high fluorescence quantum yield.

[0099] Application Example 1

[0100] Dichromate ion (Cr 2 O 7 2- ) is a dangerous oxyanion that is highly destructive to the environment and organisms. With its wide application in the chemical industry (electroplating, metallurgy, paint, and leather tanning), Cr 2 O 7 2- has become the most common heavy metal pollutant in water. Therefore, accurate detection of Cr 2 O 7 2- in water is crucial for environmental water monitoring and biological health.

[0101] The following experiments were carried out using the Mo,N-CDs provided in Example 1. Specifically, the Mo,N-CDs aqueous solution obtained by the treatment in step S1 of Example 1 was used for the experiment. The excitation and emission slits of the following fluorescence spectra were both 5.0 nm, and the excitation wavelength / emission wavelength was 365 / 494 nm.

[0102] Experiment 1

[0103] Take 500 μL of the Mo,N-CDs aqueous solution obtained by the treatment in step S1 of Example 1 and dilute it with pure water (3.0 mL) to prepare a dilution;

[0104] Add Cr 2 O 7 2-, formulated into a series of solutions containing different concentrations of Cr 2 O 7 2- . After that, they were further made up to 5.0 mL with pure water respectively to obtain test solutions. The concentration of Cr 2 O 7 2- in the test solutions was in the range of 0 - 200 μM.

[0105] The fluorescence intensity of the test solutions was measured, and the measurement was repeated 3 times. The fluorescence emission spectra of Mo, N-CDs containing different concentrations of Cr 2 O 7 2- are shown in Figure 14 . As can be seen from Figure 14 , the fluorescence intensity of Mo, N-CDs gradually decreases with the increase in the content of Cr 2 O 7 2- .

[0106] Experiment 2

[0107] Take 500 μL of the Mo, N-CDs aqueous solution obtained by the treatment in step S1 of Example 1 and dilute it with pure water (3.0 mL) to prepare a dilution;

[0108] Add Cr 2 O 7 2- to the dilution to formulate a solution containing Cr 2 O 7 2- . After that, it was further made up to 5.0 mL with pure water to obtain a test solution. The concentration of Cr 2 O 7 2- in the test solution was 100 μM;

[0109] Add aqueous solutions containing one of the following cations to the dilution. The addition amount of each cation aqueous solution was 50 μL, and the concentration of the cation in the cation aqueous solution was 10 mM. After that, it was further made up to 5.0 mL with pure water to obtain a test solution; the cations were respectively: Ag + , Al 3+ , Ba 2+ , Ca 2+ , Cd 2+ , Cr 3+ , Cu 2+ , Hg 2+ , K + , Mg 2+ , Na + , NH 4 +, Ni 2+ , Sn 2+ , Zn 2+ ;

[0110] Add an aqueous solution containing one of the following anions to the diluent. The addition amount of each aqueous anion solution is 50 μL, and the concentration of the anion in the aqueous anion solution is 10 mM. Then, further dilute to 5.0 mL with pure water to obtain a test solution. The anions are: Br - , Cl - , ClO 4- , CO 3 2- , F - , I - , NO 3- , PO 4 3- and SO 4 2- .

[0111] Take 500 μL of the Mo,N-CDs aqueous solution obtained by the treatment in step S1 of Example 1 and dilute it to 5.0 mL with pure water as a blank control solution.

[0112] Use a fluorescence spectrophotometer to measure the fluorescence intensities of the above test solutions and the blank control solution, and repeat 3 times. The fluorescence spectra of Mo,N-CDs containing different ions are shown in Figure 15 . As can be seen from Figure 15 , Cr 2 O 7 2- significantly quenched the fluorescence of Mo,N-CDs, while other ions hardly changed the fluorescence of Mo,N-CDs.

[0113] Further research was carried out on the response time. The fluorescence intensities of the above blank control solution and the test solution with a Cr 2 O 7 2- concentration of 100 μM were detected respectively. The fluorescence intensity diagrams of Mo,N-CDs (λex = 365 nm, λem = 494 nm) in the absence and presence of Cr 2 O 7 2- are shown in Figure 16 . Figure 16 It shows that Cr 2 O 7 2- can quench the fluorescence of Mo,N-CDs instantaneously, and the response time is less than 10 seconds.

[0114] Experiment 3

[0115] Determination of the quenching efficiency, from F / F 0 Determination was carried out by plotting the quenching efficiency against Cr 2 O 7 2- concentration (0 - 50 μM) to obtain a titration linear graph, as Figure 17 shown, the linear equation is:

[0116] F / F 0 = -0.0086C (Cr 2 O 7 2- ) + 0.9904, and the correlation coefficient is R 2 = 0.9956;

[0117] indicating excellent linearity, which is beneficial for the detection of actual samples.

[0118] Its detection limit (LoD) is 0.96 μM, calculated by the (3σ / k) method, where σ is the standard deviation of the blank sample (n = 10), and k is the slope of the linear calibration curve.

[0119] The detection range of Mo,N-CDs is 0 - 50 μM, and the detection limit is 0.96 μM.

[0120] Through the above experiments, it can be shown that Mo,N-CDs exhibit rapid response, wide linear range, acceptable detection limit (<WHO is 50 μg / L), etc. for Cr 2 O 7 2- . Therefore, Mo,N-CDs are expected to be used for the rapid quantitative analysis of Cr 2 O 7 2- in aqueous solutions.

[0121] Experiment 4

[0122] Detect Cr 2 O 7 2- in actual samples, the method is as follows:

[0123] The actual samples selected for the determination of Cr 2 O 7 2- are tap water, lake water, and C'estbon bottled drinking water respectively (where the tap water comes from laboratory water, the C'estbon bottled drinking water is purchased from a local supermarket, and the lake water is collected from Tianyi Lake of Henan University of Chinese Medicine).

[0124] Centrifuge the above actual water samples at 8000 rpm for 20 min and filter them through a 0.22 μm microporous membrane. Then, add different amounts of Cr 2 O7 2- (The concentration of Cr 2 O 7 2- added to the water sample is shown in Table 2 specifically), and a test sample solution is prepared. The fluorescence intensity of the test sample solution is measured using a fluorescence spectrophotometer, and the recovery rate and relative standard deviation (RSD) are calculated. All measurements are repeated 3 times. The test results are shown in Table 2.

[0125] Table 2

[0126]

[0127] As can be seen from Table 2, the recovery rates of Cr 2 O 7 2- in tap water, lake water, and bottled drinking water are 96 - 110%, and the relative standard deviation (RSD) is less than 2.5%. Therefore, Mo,N-CDs can be used as a "switch" to detect Cr 2 O 7 2- in the field of water quality monitoring.

[0128] Application Example 2

[0129] Luteolin (3,4,5,7-tetrahydroxyflavone) is a natural flavonoid compound with various pharmacological effects such as antibacterial, anti-inflammatory, and antioxidant effects. Therefore, the detection of luteolin has important practical significance in pharmaceutical analysis.

[0130] The following experiment was carried out using the Mo,N-CDs provided in Example 1. Specifically, the Mo,N-CDs aqueous solution obtained by treating in step S1 of Example 1 was used for the experiment. The excitation and emission slits of the following fluorescence spectra are both 5.0 nm, and the excitation wavelength / emission wavelength is both 365 / 494 nm.

[0131] Experiment 5

[0132] Take 500 μL of the Mo,N-CDs aqueous solution obtained by treating in step S1 of Example 1 and dilute it with pure water (3.0 mL) to prepare a dilution;

[0133] Add luteolin to the dilution to prepare a series of solutions containing different concentrations of luteolin, and then further dilute them to 5.0 mL with pure water respectively to obtain test solutions. The concentration of luteolin in the test solutions is in the range of 0 - 100 μM.

[0134] The fluorescence intensity of the test solutions was measured and repeated 3 times. The fluorescence emission spectra of Mo,N-CDs containing different concentrations of luteolin are shown in Figure 18 as shown. FromFigure 18 It can be seen that the fluorescence intensity of Mo,N-CDs gradually decreases with the increase in the content of luteolin.

[0135] Experiment 6

[0136] Take 500 μL of the Mo,N-CDs aqueous solution obtained by the treatment in step S1 of Example 1 and dilute it with pure water (3.0 mL) to prepare a dilution;

[0137] Add luteolin to the dilution to prepare a solution containing luteolin, and then further make up the volume to 5.0 mL with pure water to obtain a test solution. The concentration of luteolin in the test solution is 50 μM;

[0138] Add aqueous solutions containing one of the following compounds to the dilution: glutathione (GSH), glucose (Glucose), L-arginine (L-Arg), L-cysteine (L-Cys), L-glutamic acid (L-Glu), nicotinamide (Nicotinamide), ascorbic acid (AA), citric acid (CA), urea (Urea). The addition amount of each aqueous solution is 25 μL, and the concentration of the compound in the aqueous solution is 10 mM. Then further make up the volume to 5.0 mL with pure water to obtain a test solution;

[0139] Take 500 μL of the Mo,N-CDs aqueous solution obtained by the treatment in step S1 of Example 1 and dilute it to 5.0 mL with pure water as a blank control solution.

[0140] Use a fluorescence spectrophotometer to measure the fluorescence intensities of the above test solutions and the blank control solution, and repeat 3 times. The fluorescence spectra of Mo,N-CDs containing different compounds are shown in Figure 19 as shown. From Figure 19 It can be seen that luteolin significantly quenches the fluorescence of Mo,N-CDs, while other compounds can hardly change the fluorescence of Mo,N-CDs.

[0141] The response time was further studied. The fluorescence intensities of the above blank control solution and the test solution with a luteolin concentration of 50 μM were detected respectively. In the absence and presence of luteolin, the fluorescence intensity diagrams of Mo,N-CDs (λex = 365 nm, λem = 494 nm) are shown in Figure 20 as shown, Figure 20 indicating that luteolin can instantly quench the fluorescence of Mo,N-CDs, and the response time is less than 10 seconds.

[0142] Experiment 7

[0143] Determination of the quenching efficiency. From F / F 0Determination was carried out, and a titration linear graph was obtained by plotting the quenching efficiency against the luteolin concentration (0 - 45 μM), as Figure 21 shown. The linear equation is:

[0144] F / F 0 = -0.0129C (luteolin) + 0.9920, and the correlation coefficient is R 2 = 0.9992;

[0145] indicating excellent linearity, which is beneficial for the detection of actual samples.

[0146] Its limit of detection (LoD) is 0.64 μM, calculated by the (3σ / k) method, where σ is the standard deviation of blank samples (n = 10), and k is the slope of the linear calibration curve.

[0147] The detection range of Mo,N-CDs is 0 - 45 μM, and the limit of detection is 0.64 μM.

[0148] The above experiments can show that Mo,N-CDs exhibit characteristics such as a rapid response to luteolin and a low limit of detection. Therefore, Mo,N-CDs are expected to be used for the rapid quantitative analysis of luteolin.

[0149] Experiment 8

[0150] The luteolin in actual samples was detected as follows:

[0151] Duyiwei capsules were purchased from a local pharmacy. 10 capsules were taken, the weight of the powder was weighed after removing the capsule shells, and then one-tenth of the mass of Duyiwei powder was accurately weighed. Then it was dissolved in 20 mL of pure water under ultrasonic assistance; then it was centrifuged at 8000 rpm for 20 minutes, and the supernatant was taken. The supernatant was filtered through a 0.22 μM microporous membrane to remove insoluble substances to obtain a sample solution. The sample solution was diluted with pure water to maintain the concentration of the working solution within the linear range. Then different amounts of luteolin were added to the above working solution (the specific concentrations of luteolin added to the working solution are shown in Table 3), and a sample solution to be measured was prepared. The fluorescence intensity of the sample solution to be measured was measured using a fluorescence spectrophotometer, and the recovery rate and relative standard deviation (RSD) were calculated. All measurements were repeated 3 times. The detection results are shown in Table 3.

[0152] Duyiwei tablets (5 mg per tablet) were purchased from a local pharmacy. After thoroughly crushing 10 tablets into fine powder, the average weight was calculated, and an amount of Duyiwei powder equivalent to the mass of one Duyiwei tablet was precisely weighed. The Duyiwei powder was dissolved in 20 mL of pure water under ultrasonic assistance; then, it was centrifuged at 8000 rpm for 20 minutes, and the supernatant was taken. The supernatant was filtered through a 0.22 μM microporous membrane to remove insoluble substances, obtaining a sample solution. The sample solution was diluted with pure water to maintain the concentration of the working solution within the linear range. Then, different amounts of luteolin were added to the above working solution (the specific concentrations of luteolin added to the working solution are shown in Table 3), preparing a sample solution to be measured. The fluorescence intensity of the sample solution to be measured was determined using a fluorescence spectrophotometer, and the recovery rate and relative standard deviation (RSD) were calculated. All measurements were repeated 3 times. The test results are shown in Table 3.

[0153] Table 3

[0154]

[0155] As can be seen from Table 3, the recovery rates of luteolin in Duyiwei capsules and Duyiwei tablets are 93 - 105%, and the relative standard deviation (RSD) is less than 3.5%. Therefore, Mo,N-CDs can be used as a sensor for detecting luteolin with a "switch" in the field of drug analysis.

[0156] Application Example 3

[0157] The following experiments were carried out using the Mo,N-CDs provided in Example 1.

[0158] Due to the stable optical properties and relatively high FLQY value (fluorescence quantum yield) of Mo,N-CDs, Mo,N-CDs have potential application prospects in anti-counterfeiting.

[0159] Specifically, the aqueous solution of Mo,N-CDs obtained by the treatment in step S1 of Example 1 was used for the experiment. As Figure 22 shown, two pictures were hand-drawn directly using the aqueous solution of Mo,N-CDs as fluorescent ink on test paper. The two pictures were hardly visible under sunlight, but showed obvious cyan fluorescence under 365 nm ultraviolet light, and the cyan fluorescence completely disappeared with the removal of the 365 nm ultraviolet light. Its fluorescence could be maintained for several months (under 365 nm ultraviolet light irradiation), which showed good fluorescence anti-counterfeiting effects. At the same time, it indicated that Mo,N-CDs had high-quality information encryption and decryption effects, and the fluorescent ink based on Mo,N-CDs had better durability and reliability.

[0160] The simple synthesis, high quantum yield, stable optical properties, and fast response of Mo,N-CDs make Mo,N-CDs promising as a rapid detection platform for environmental water monitoring and drug quantitative analysis, and have great application value in environmental water monitoring, drug quantitative analysis, etc.

[0161] The above are only embodiments of the present invention, and do not limit the patent scope of the present invention. Any equivalent transformation made using the content of the specification of the present invention, directly or indirectly applied in other related technical fields, is included in the patent protection scope of the present invention.

Claims

1. A molybdenum-nitrogen co-doped carbon quantum dot, characterized in that: Prepared by a method comprising the following steps: S1: L-arginine, a molybdenum source, 1-pyrene formaldehyde and a solvent are mixed and placed in an autoclave for hydrothermal reaction. After the reaction is completed, the reaction system is centrifuged and separated, and the supernatant obtained is obtained to obtain a solution containing molybdenum and nitrogen co-doped carbon quantum dots; S2: The solution containing molybdenum and nitrogen co-doped carbon quantum dots obtained in step S1 is dialyzed using a dialysis bag, and the liquid in the bag is freeze-dried into a solid to obtain molybdenum and nitrogen co-doped carbon quantum dots.

2. The molybdenum-nitrogen co-doped carbon quantum dots according to claim 1, characterized in that: The mass ratio of L-arginine, molybdenum source and 1-pyrene carboxaldehyde is: L-arginine: molybdenum source: 1-pyrene carboxaldehyde = (0.1-0.5): (0.2-0.4): (0.01-0.03); Preferably, L-arginine: molybdenum source: 1-pyrene carboxaldehyde = (0.1-0.5): (0.2-0.4): (0.01-0.02); More preferably, L-arginine: molybdenum source: 1-pyrene carboxaldehyde = (0.1-0.3): (0.3-0.4): (0.01-0.02); More preferably, L-arginine: molybdenum source: 1-pyrenecarboxaldehyde = 0.3: 0.3: (0.01-0.02).

3. The molybdenum-nitrogen co-doped carbon quantum dots according to claim 1 or 2, characterized in that: The molybdenum source is molybdic acid, sodium molybdate or ammonium molybdate, preferably ammonium molybdate.

4. The molybdenum-nitrogen co-doped carbon quantum dots according to any one of claims 1 to 3, characterized in that: The solvent is water.

5. The molybdenum-nitrogen co-doped carbon quantum dots according to claim 4, characterized in that: The temperature of the hydrothermal reaction is 180-200° C.; and / or the reaction time of the hydrothermal reaction is 3-5 hours.

6. The molybdenum-nitrogen co-doped carbon quantum dots according to claim 5, characterized in that: The temperature of the hydrothermal reaction is 190° C.; and / or, the reaction time of the hydrothermal reaction is 4 hours.

7. The molybdenum-nitrogen co-doped carbon quantum dots according to claim 1, characterized in that: The molecular weight cut-off of the dialysis bag is 1000 Daltons.

8. The molybdenum-nitrogen co-doped carbon quantum dots according to any one of claims 1 to 7 are prepared in Cr2O7 2- Application in detection.

9. Use of the molybdenum-nitrogen co-doped carbon quantum dots according to any one of claims 1 to 7 in the detection of luteolin.

10. Use of the molybdenum-nitrogen co-doped carbon quantum dots according to any one of claims 1 to 7 in fluorescent ink.

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