A green room-temperature phosphorescent carbon dot and a preparation method thereof

Abstract

The application provides a green room-temperature phosphorescence (RTP) carbon dot (CD) in the technical field of luminescent carbon materials and a preparation method thereof, solves the problems of complex preparation process, high cost and great toxicity of traditional phosphorescence materials, and uses economical arginine, phosphoric acid and boric acid to prepare the RTP CDs material through a simple one-step hydrothermal method; under ultraviolet light, the CDs present blue fluorescence; after the ultraviolet light is removed, the phosphorescence CDs are green and still last for about 12s, and the dense cross-linking structure and the effect of multi-atom co-doping endow the CDs with excellent optical performance.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of luminescent carbon materials, and particularly relates to a green room-temperature phosphorescence (RTP) carbon dot (CD) doped with nitrogen (N), phosphorus (P) and boron (B) and a preparation method thereof. BACKGROUND

[0002] In recent years, due to the development of science and technology, anti-counterfeiting materials cannot meet the needs of social development, and it is urgent to develop efficient anti-counterfeiting materials. Fluorescent materials have been studied in depth in the field of anti-counterfeiting applications. However, similar emission characteristics can be obtained by using certain substitutes or simply mixing different fluorescent materials, thereby showing poor anti-counterfeiting performance. In the field of anti-counterfeiting materials, room-temperature phosphorescence (RTP) materials have always been a hotspot in the field of anti-counterfeiting applications. After the external excitation light source is turned off, the RTP material will have residual light, while the fluorescent material will be immediately extinguished. This characteristic makes the RTP material difficult to be counterfeited. RTP materials are widely used in anti-counterfeiting. The most common RTP materials are traditional rare earth metal complexes and organic compounds. However, due to the high cost of production, non-renewable resources, complex preparation process and high toxicity, the development of traditional phosphorescent materials is limited. Therefore, it is urgent to develop optical anti-counterfeiting materials with excellent optical performance, green environmental protection, low cost and simple preparation.

[0003] Carbon dots (CDs) as a new material, in the development momentum in recent years. Because of CDs low cost, small toxicity, excellent optical performance and excellent biocompatibility, etc. and received widespread attention, in the field of anti-counterfeiting, optical devices, sensing and biological cell imaging, etc. CDs is a kind of zero-dimensional carbon nanomaterial with spherical or core-shell structure, including carbon nanodots (CNDs), carbon quantum dots (CQDs), carbon polymer dots (CPDs), etc. However, single fluorescent CDs in anti-counterfeiting will be limited due to the interference of the object itself fluorescence, and the fluorescence lifetime is relatively short, limiting the application of CDs material. In the patent "a kind of solar light excitation room temperature phosphorescence carbon point@alumina composite material and its preparation method (application publication number CN 117903795 A)", two-step method is used to prepare and high temperature heating with muffle furnace, the present invention is relatively simple one-step hydrothermal doping multi-atom method and the temperature is not high, low energy consumption and relatively safe. And the phosphorescence lifetime of CDs in the patent "a kind of time response color changing phosphorescence carbon dot ink and its preparation method and application (application publication number CN 112500740 A)" is less than 0.4 s, and the afterglow time is only 0.9 s, which is difficult to distinguish with naked eye, and the phosphorescence lifetime of the present invention is 0.9 s, and the afterglow time can be up to 12 s. Finally, the patent "a kind of phosphorescence carbon point-metal organic framework composite material and its preparation method and application (application publication number CN 114381261 A)" adopts two-step method to invent RTP CDs, and the maximum afterglow time is 9 s, and the preparation method of the present invention is simple and the afterglow time of RTP CDs is relatively long, which is 12 s. In short, the preparation method of the present invention is simple, environmentally friendly, low energy consumption and relatively safe, and has excellent optical performance.

[0004] The present application uses arginine, phosphoric acid and boric acid as raw materials, forms a network structure through intermolecular crosslinking, carbonizes into CDs as the temperature rises, the covalent bond and hydrogen bond generated by crosslinking restricts molecular vibration and rotation, stabilizes the triplet exciton, reduces non-radiative transition, and co-dopes N, P and B atoms to promote intersystem crossing (ISC) of exciton from the lowest singlet state to the lowest triplet state, thereby promoting the generation of RTP. The RTP CDs of the present application provide a way for preparing luminescent carbon materials and show great application potential. SUMMARY

[0005] The present application is aimed at the problems of high cost, complex preparation process and high toxicity of traditional phosphorescent materials, and provides a simple, low-cost, environmentally friendly and excellent green room temperature phosphorescent CDs preparation method. By changing the amount of raw materials, reaction temperature, and selecting the optimal reaction conditions, CDs materials with phosphorescence and fluorescence dual luminescence are obtained. The one-step hydrothermal method used in the reaction makes the whole preparation process simple and environmentally friendly.

[0006] A green room temperature phosphorescent carbon dot and a preparation method thereof, comprising the following steps:

[0007] Step one, taking 1.3936 g arginine, different volumes of phosphoric acid and 1 g boron-containing substance, sequentially adding into a beaker containing 20 mL solvent, stirring the solution to clear and transparent by magnetic stirring;

[0008] Step two, transferring the mixed solution prepared in step one into a polytetrafluoroethylene high-pressure reaction kettle, and then placing it in a muffle furnace to react at high temperature for a certain time;

[0009] Step three, taking the brownish yellow liquid obtained after step two reaction, filtering the carbon residue with a 0.22 μm filter membrane, then transferring the brownish yellow transparent solution into a glass culture dish and placing it in an oven for drying at 180℃ for 6 h, grinding the finally obtained solid into powder with a mortar, and then collecting the CDs.

[0010] Further, the volume of phosphoric acid in step one is 525, 800, 1050 and 1315 μL.

[0011] Further, the solvent in step one is one of water, ethanol and N, N-dimethylformamide (DMF).

[0012] Further, the boron-containing substance in step one is one of boric acid (H3BO3) and boron oxide (B2O3).

[0013] Further, the reaction temperature in step two is set to 180℃, 200℃, 220℃ and 240℃.

[0014] Further, the reaction time in step two is set to 6 h, 8 h and 10 h.

[0015] Compared with the prior art, the method has the following advantages:

[0016] (1) The CDs are prepared by one-step hydrothermal method, which is simple in process technology and green in environment protection.

[0017] (2) The prepared CDs have fluorescence and phosphorescence dual light emitting effect.

[0018] (3) The phosphorescence lifetime of the CDs is long and the phosphorescence afterglow time in dark environment can reach 12 s.

[0019] (4) The problems of complex preparation process, high toxicity and high cost of traditional phosphorescent materials are solved. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1is a TEM image and a particle size distribution chart of CDs in Example 2 of the present application;

[0021] Figure 2 is an FTIR spectrum chart of CDs in Example 2 of the present application;

[0022] Figure 3 is an XRD spectrum chart of CDs in Example 2 of the present application;

[0023] Figure 4 is a phosphorescence lifetime decay chart of CDs in Example 2 of the present application;

[0024] Figure 5 is a luminescence condition of CDs powder in Example 2 of the present application. DETAILED DESCRIPTION

[0025] The specific embodiments provided by the present application are as follows:

[0026] A green room temperature phosphorescent carbon dot and a preparation method thereof, comprising the following specific steps:

[0027] 1) Take 1.3936 g of arginine, (525, 800, 1050 and 1315 μL, preferably 800 μL) of phosphoric acid and 1 g of boric acid (the optimal molar ratio is 1:1.5:2), and add them into a beaker containing 20 mL of ultrapure water in sequence, and stir the solution to be clear and transparent by magnetic stirring;

[0028] 2) Transfer the mixed solution prepared in step 1) into a polytetrafluoroethylene high-pressure reaction kettle, and then place it in a muffle furnace, and heat it at (180, 200, 220 and 240℃, preferably 220℃) for 8 h;

[0029] 3) Take out the brown-yellow liquid obtained after the reaction in step 2), filter it with a 0.22 μm filter membrane to remove carbon residue, then transfer the brown-yellow transparent solution into a glass culture dish, and place it in an oven at 180℃ for drying for 6 h, and then collect the CDs after grinding the finally obtained solid into powder.

[0030] The morphology and dispersity of the CDs prepared by the present application are detected by a transmission electron microscope (TEM); the molecular structure and functional groups of the CDs are analyzed by a Fourier transform infrared spectrometer (FTIR); the crystal structure of the CDs is analyzed by an X-ray diffractometer (XRD); in order to study the luminescent performance of the CDs, the phosphorescent intensity of different CDs is tested by a fluorescence spectrophotometer, and the room temperature phosphorescent lifetime of the CDs is tested by a FLS1000 steady-state transient fluorescence spectrometer.

[0031] To achieve the above-mentioned technologies, the present application is described below in combination with embodiments of the present application, through the drawings and examples. However, the described embodiments of the present application are only part of the embodiments, not all embodiments. Improved technical solutions and methods of the present application all belong to the protection scope of the present application.

[0032] The preparation processes are basically the same, and the only difference is that the volume of phosphoric acid in step 1) is changed.

[0033] Take 1.3936 g of arginine, different volumes of phosphoric acid as shown in Table 1, and 1 g of boric acid, and add them into a beaker containing 20 mL of ultrapure water in turn, and stir the solution to be clear and transparent with a magnetic stirrer;

[0034] 2) Transfer the mixed solution prepared in step 1) to a polytetrafluoroethylene high-pressure reaction kettle, and then place it in a muffle furnace for heating reaction at 220°C for 8 h;

[0035] 3) Take out the brown-yellow liquid obtained after step 2) reaction, filter it with a 0.22 μm filter membrane to remove carbon residue, then transfer the brown-yellow transparent solution to a glass culture dish, and place it in an oven at 180°C for drying for 6 h. After the final solid is ground into powder with a mortar, CDs are collected. Then the phosphorescent performance of different CDs prepared is tested.

[0036] Table 1 Specific implementation schemes of Examples 1-4

[0037] Example Boric acid mass (g) Molar ratio of raw materials Phosphorescence intensity (a.u.) 1 1 1:1:2 5379 2 1 1:1.5:2 8105 3 1 1:2:2 7603 4 1 1:2.5:2 7347

[0038] As can be seen from Examples 1-4, when the precursor ratio is changed, the phosphorescent intensity of the CDs shows a trend of first increasing and then decreasing, and when the volume of phosphoric acid is 800 μL and the optimal molar ratio is 1:1.5:2, the phosphorescent intensity of the CDs is the strongest and the luminescent performance is the best.

[0039] The preparation processes are basically the same, and the only difference is that the reaction temperature in step 2) is changed.

[0040] 1) Take 1.3936 g of arginine, 800 μL of phosphoric acid and 1 g of boric acid (molar ratio 1:1.5:2), and add them into a beaker containing 20 mL of ultrapure water in turn, and stir the solution to be clear and transparent with a magnetic stirrer;

[0041] 2) Transfer the mixed solution prepared in step 1) to a polytetrafluoroethylene high-pressure reaction kettle, and then place it in a muffle furnace for heating reaction at different reaction temperatures as shown in Table 2 for 8 h;

[0042] 3) The brownish yellow liquid obtained from step 2) was taken out and filtered with a 0.22 μm filter membrane to remove carbon residue, then the brownish yellow transparent solution was transferred to a glass culture dish and dried in an oven at 180 °C for 6 h. The final obtained solid was ground into powder with a mortar and then collected to obtain CDs. The phosphorescent performance of different CDs prepared was tested.

[0043] Table 2 Specific embodiments of Examples 5-8

[0044] Example Reaction temperature (°C) Phosphorescence intensity (a.u.) 5 180 6790 6 200 7159 7 220 8105 8 240 6129

[0045] From Examples 5-8, it can be seen that when the reaction temperature is changed, the phosphorescent intensity of CDs shows a trend of first increasing and then decreasing, and when the reaction temperature is 220 °C, the phosphorescent intensity reaches the highest and the luminescent performance is optimal.

[0046] The morphology characteristics and dispersibility of the CDs prepared in Example 2 were characterized by TEM. As can be seen from the TEM image of part (a) of FIG. 6, Figure 1 the CDs prepared are spherical nanoparticles and have good dispersibility. From the particle size distribution graph of part (b) of FIG. 6, Figure 1 it can be seen that the particle size distribution of the CDs is relatively uniform, and the average particle size is calculated to be 4.08 nm.

[0047] The chemical structure of the CDs was analyzed by FTIR in Example 2. As can be seen from FIG. 7, Figure 2 the wide absorption peak at 3100-3550 cm -1 is due to the stretching vibration of N-H and O-H. The wide absorption peak at 2550-3000 cm -1 is due to the stretching vibration of C-H. The peak at 1660 cm -1 is due to the stretching vibration of C=O. An absorption band is observed at 1450 cm -1 , which is related to the stretching vibration of C-N and B-O. Two smaller absorption peaks at 1190 cm -1 and 1140 cm -1 , a weak absorption peak at 884 cm -1 is due to the stretching vibration of P=O and P-N, respectively. The small absorption peak at 812 cm -1 and the strong absorption peak at 950 cm -1 are characteristic peaks of B-O and B-C stretching vibration, respectively. Finally, the absorption peak at 502 cm -1 indicates the presence of phosphate in the CDs. All the FTIR results show that arginine successfully reacts with phosphoric acid and boric acid, and the surface of the prepared CDs has rich heteroatom functional groups.

[0048] The crystal structure of the CDs was analyzed by XRD for Example 2. As shown in Figure 3 a broad diffraction peak centered at 22.3° appeared, indicating that the prepared CDs were amorphous carbon structure.

[0049] The room temperature phosphorescence lifetime of the CDs was tested for Example 2. As shown in Figure 4 the average phosphorescence lifetime of the CDs was 902 ms after the decay was fitted by three exponentials, which belonged to the long lifetime of RTP CDs.

[0050] The luminescence of the CDs powder was observed for Example 2. As shown in Figure 5 the invented CDs emitted green afterglow for about 12 s after the UV light was turned off.

[0051] From the test results, the hydrothermal method prepared doped with multiple atoms RTP CDs has high phosphorescence intensity and afterglow time in the aspect of luminescence, which shows that the doping of nitrogen, phosphorus and boron atoms has a positive effect on the phosphorescence performance, and at the same time, the hydrogen bond and chemical bond generated by the reaction between various substances weaken the molecular vibration and rotation, and promote the ISC process.

[0052] In summary, the RTP CDs material prepared by one-step hydrothermal method heating arginine, phosphoric acid and boric acid has the performance of visible luminescence for 12 s. The cross-linking effect generated in the reaction process provides a stable and rigid environment for the CDs, which inhibits the non-radiative transition, and the doping of nitrogen, phosphorus and boron atoms makes the intersystem crossing easier, and the above reasons make the invented room temperature phosphorescence CDs have excellent luminescence performance, which can be applied to information encryption and anti-counterfeiting and other aspects. The invention shows an environmentally friendly and simple preparation method of room temperature phosphorescence material, which provides a new idea for the preparation of luminescent carbon nanomaterials.

Claims

1. A method for preparing green room temperature phosphorescent carbon dots, characterized in that: The following steps are involved: 1) Add 1.3936 g of arginine, 525 μL, 800 μL, 1050 μL, or 1315 μL of phosphoric acid, and 1 g of boric acid to a beaker containing 20 mL of water. Stir magnetically until the solution becomes clear. 2) transferring the mixed solution prepared in step 1) into a polytetrafluoroethylene autoclave, and then placing it in a muffle furnace and reacting it at a temperature of 180° C. to 240° C. for 8 hours; 3) The brown-yellow carbon dot liquid obtained in step 2) was removed and filtered through a 0.22 μm filter membrane to remove carbon residue. The brown-yellow transparent solution was then transferred to a glass petri dish and dried in an oven at 180°C for 6 h. The resulting solid was ground into a powder using a mortar and collected for later use.

2. The preparation method according to claim 1, wherein: In step 1), the volume of phosphoric acid is 800 μL. At this time, the molar ratio of arginine, phosphoric acid and boric acid is 1:1.5:

2.

3. The preparation method according to claim 1, wherein: In step 2), the temperature is 220° C. and the reaction time is 8 h.

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