Preparation method of plant-based carbon nanometer luminescent material taking pomegranate peel as raw material and application thereof

Abstract

The application discloses a preparation method of plant-based carbon nanometer luminescent material taking pomegranate peel as raw material and application thereof, and first takes the pomegranate peel as the raw material, reasonably dopes N, P and B elements through a hydrothermal method, and prepares the carbon nanometer luminescent material, which has excellent phosphorescence characteristics, is efficient in fingerprint display, and shows good prospects in fingerprint detection; the carbon nanometer luminescent material prepared by the application has high phosphorescence intensity and excellent luminescence characteristics, emits bright blue fluorescence under the irradiation of a 365nm ultraviolet lamp, and emits brown-yellow phosphorescence when the lamp is turned off, so that the carbon nanometer luminescent material also shows good prospects in anti-fake application.

Description

Technical Field

[0001] This invention relates to the field of carbon nanomaterials luminescent technology, and in particular to a method for preparing plant-based carbon nanomaterials luminescent materials using pomegranate peel as raw material and their application. Background Technology

[0002] Luminescent carbon nanomaterials have attracted increasing attention due to their excellent optical properties, good biocompatibility, low toxicity, and low cost. Phosphorescent carbon nanomaterials are a new type of long-lived luminescent nanomaterial that continues to emit light even after the excitation source is cut off. This luminescence property can effectively avoid interference from background fluorescence in analytical detection, and they also have advantages such as inexpensive and widely available raw materials and simple synthesis processes. They have already shown significant advantages in fields such as anti-counterfeiting, information encryption, sensors, bioimaging, and light-emitting diodes. With the deepening of carbon material research, green, inexpensive, environmentally friendly, and readily available starting materials have attracted widespread attention from researchers. Natural plants, as a renewable resource, contain abundant carbon sources and other organic matter, and have great potential in carbon material synthesis. Moreover, due to the diversity of natural plants, carbon materials synthesized using different plants may exhibit different optical properties and application potential. However, the specific mechanisms and potential applications of plant-based carbon nanomaterial synthesis still require further exploration and research. Currently, the yield and quantum yield of plant- and polymer-based luminescent carbon nanomaterials are generally low, limiting their further practical applications. Therefore, it is necessary to design effective synthesis methods to improve the yield and quantum yield of carbon nanomaterials. Heteroatom doping is one of the main methods for regulating the luminescent properties of carbon nanomaterials. By doping with different elements to modulate the energy levels of carbon nanomaterials, changes in their photoelectric properties can be induced, opening up possibilities for different applications of carbon nanomaterials.

[0003] Due to the uniqueness and immutability of fingerprints, fingerprint recognition analysis has become the most mainstream and convenient method of personal identification. Fingerprint analysis is a preferred method for identifying individuals in the forensic field, and it is one of the authentication technologies used. Chemical imaging can clearly and intuitively describe the distribution of different components in a substance, thus the imaging of latent fingerprints has attracted widespread attention from researchers worldwide. In actual case analysis, fingerprints are easily left on smooth substrate surfaces, such as plastic and glass. In fact, these left fingerprints are difficult to observe under bright conditions, which undoubtedly increases the difficulty of solving cases. Therefore, fingerprint extraction and visualization are particularly important. Traditional fingerprint development methods are relatively complex to operate, and some chemical reagents are toxic and corrosive. Therefore, it is essential to explore a novel, non-toxic, and environmentally friendly material. In recent years, information security and anti-counterfeiting have attracted attention, such as in passports and product labels. In technologies such as coding and texture mapping, luminescent materials have gained attention due to their variety and ease of use. Traditional anti-counterfeiting marks, such as laser anti-counterfeiting labels and watermarks, have played an important role for a certain period of time, but their anti-counterfeiting performance is challenged as counterfeiting technology continues to advance. Therefore, it is necessary to develop materials with special properties to create higher-level anti-counterfeiting marks to meet the growing demand for product anti-counterfeiting.

[0004] Therefore, it is evident that developing novel carbon materials and exploring their applications in fields such as fingerprint display and anti-counterfeiting marking has significant theoretical and practical value. Summary of the Invention

[0005] Therefore, based on the above background, this invention provides a method for preparing plant-based carbon nano-luminescent materials using pomegranate peel as raw material and its application. This invention is the first to use common organic waste pomegranate peel as a carbon source and successfully prepare carbon nano-luminescent materials by doping with N, P, and B elements. The preparation process is simple.

[0006] The technical solution provided by this invention is as follows: A method for preparing a plant-based carbon nanotube luminescent material using pomegranate peel as raw material includes the following steps: S1: After drying the pomegranate peel, grind it into pomegranate peel powder; S2: Take the pomegranate peel powder, phosphoric acid, urea and boric acid from step S1, mix them together, add deionized water, mix evenly, and heat at 200℃ or above for 2-4 hours under sealed conditions. Grind the product into nanoscale powder to prepare N, P and B doped plant-based carbon nanoluminescent materials.

[0007] Preferably, in step S2, for every 1000 ml of deionized water, take: 5-20g of pomegranate peel powder; Urea 100-1000g; Boric acid 2-15g; 40-200ml of phosphoric acid; The mass concentration of the phosphoric acid is 80-90%.

[0008] Preferably, in step S2, for every 1000 ml of deionized water, take: 5g of pomegranate peel powder; 600g of urea; 15g of boric acid; 80ml of phosphoric acid.

[0009] Based on the same inventive concept, this invention also provides a method for preparing plant-based carbon nanomaterials with pomegranate peel as raw material.

[0010] Based on the same inventive concept, the present invention also provides the application of the plant-based carbon nanoluminescent material in fingerprint detection and / or as a latent fingerprint developer.

[0011] Based on the same inventive concept, the present invention also provides a fingerprint detection method, comprising the following steps: ① The powdered plant-based carbon nano-luminescent material is evenly sprinkled on the surface of the object where the latent fingerprint is located, and then the excess powder is gently blown away. ②The surface of the object containing the latent fingerprint is irradiated with a 364nm ultraviolet lamp. The fingerprint surface produces bright white visible light, and an image with a clear latent fingerprint is obtained.

[0012] Furthermore, the object is a permeable or non-permeable material with a rough or smooth surface.

[0013] Furthermore, the objects include objects made of glass, marble, leather, metal, wood, plastic, and ceramics, or banknotes, coins, and bank cards.

[0014] Based on the same inventive concept, this invention also provides the application of the aforementioned plant-based carbon nanotube luminescent material in the manufacture of anti-counterfeiting labels for products.

[0015] Furthermore, it serves as an anti-counterfeiting mark by being embedded in the product's packaging, label, or the product itself.

[0016] The beneficial effects achieved by this invention are as follows: This invention is the first to use pomegranate peel as raw material and prepare carbon nanotube luminescent material by hydrothermal method and reasonable doping with N, P and B elements. It has high efficiency in fingerprint display and shows good prospects in fingerprint detection. This invention rationally sets the carbon, nitrogen, phosphorus, and boron sources, resulting in carbon nanotube luminescent materials with high phosphorescence intensity and excellent luminescence properties. Under 365nm ultraviolet light, they emit bright blue fluorescence, and when the light is off, they emit brownish-yellow phosphorescence, making them promising for anti-counterfeiting applications.

[0017] The preparation method of this invention is simple, the materials are widely available and inexpensive, and the carbon nanomaterials prepared are low in toxicity and high in safety, belonging to green and safe materials. Attached Figure Description

[0018] Appendix Figure 1 An electron microscope image of pomegranate peel powder (pomegranate peel powder) according to an embodiment of the present invention.

[0019] Appendix Figure 2 Electron micrographs of N, P, and B doped plant-based carbon nanomaterials according to an embodiment of the present invention.

[0020] Appendix Figure 3 The X-ray diffraction (XRD) patterns of N, P, B doped plant-based carbon nanoluminescent material (2) and pomegranate peel powder (1) in this embodiment of the invention are shown.

[0021] Appendix Figure 4 XPS spectra of pomegranate peel powder (1) and N, P, B doped pomegranate peel powder carbon nanoluminescent material (2) in this embodiment of the invention.

[0022] Appendix Figure 5 The XPS C1s spectrum of pomegranate peel powder is shown in the embodiment of the present invention.

[0023] Appendix Figure 6 The C1s (a), N1s (b), P2p (c), and B1s (d) spectra of XPS of N, P, and B doped plant-based carbon nanoluminescent materials according to embodiments of the present invention are shown.

[0024] Appendix Figure 7 The infrared spectra of N, P, B doped plant-based carbon nanoluminescent material (2) and pomegranate peel powder (1) are from an embodiment of the present invention.

[0025] Appendix Figure 8 The phosphorescence spectrum of pomegranate peel powder carbon nanotube luminescent material in an embodiment of the present invention.

[0026] Appendix Figure 9 The phosphorescence lifetime of the pomegranate peel powder carbon nanotube luminescent material in this embodiment of the invention.

[0027] Appendix Figure 10 The phosphorescence spectrum of the N, P, and B doped plant-based carbon nanomaterials according to an embodiment of the present invention is shown.

[0028] Appendix Figure 11 The phosphorescence lifetime of the N, P, and B doped plant-based carbon nanomaterials in this embodiment of the invention is given.

[0029] Appendix Figure 12 The fingerprint development results of N, P, and B doped plant-based carbon nanofibers in this embodiment of the invention on a marble matrix under sunlight (a), with a 365nm ultraviolet lamp on (b), and with a 365nm ultraviolet lamp off (b).

[0030] Appendix Figure 13 The fingerprint development results of N, P, and B doped plant-based carbon nanofibers in this embodiment of the invention on a can substrate under sunlight (a), with a 365nm ultraviolet lamp on (b), and with a 365nm ultraviolet lamp off (b).

[0031] Appendix Figure 14 The fingerprint development results of N, P, and B doped plant-based carbon nanofiber luminescent materials in this embodiment of the invention on a leather matrix under sunlight (a), with a 365nm ultraviolet lamp on (b), and with a 365nm ultraviolet lamp off (b).

[0032] Appendix Figure 15 The fingerprint development results of N, P, and B doped plant-based carbon nanofiber luminescent materials in this embodiment of the invention on plastic under sunlight (a), with a 365nm ultraviolet lamp on (b), and with a 365nm ultraviolet lamp off (b).

[0033] Appendix Figure 16 The fingerprint development results of N, P, and B doped plant-based carbon nanofibers in this embodiment of the invention on a banknote substrate under sunlight (a), with a 365nm ultraviolet lamp on (b), and with a 365nm ultraviolet lamp off (b).

[0034] Appendix Figure 17 The N, P, and B doped plant-based carbon nanofibers used in this invention are used as developers on a banknote substrate under 365nm ultraviolet light to develop fingerprints and obtain primary, secondary, and tertiary feature maps of latent fingerprints.

[0035] Appendix Figure 18 The N, P, B doped plant-based carbon nanotube luminescent material of this invention was used to create an anti-counterfeiting pattern (b) tiger using N, P, B doped pomegranate peel powder carbon nanotubes under sunlight, with a 365nm ultraviolet lamp turned on and off.

[0036] Appendix Figure 19 (b) Sunflower pattern was created using N, P, B doped plant-based carbon nanotube luminescent materials in this embodiment of the invention under sunlight, with a 365nm ultraviolet lamp turned on and off. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] This invention utilizes pomegranate peel as a raw material to prepare plant-based carbon nanomaterials. Pomegranate peel is rich in organic components such as sugars, cellulose, and tannins. These organic compounds can serve as carbon sources under high-temperature reaction conditions, forming the carbon framework structure of carbon nanomaterials through a carbonization process. Urea serves as a nitrogen source, and during the reaction, nitrogen atoms can be doped into the carbon nanomaterial framework. The high-temperature reaction causes urea to decompose, allowing nitrogen atoms to bind into the carbon nanomaterial structure through chemical bonding, thereby altering the electronic structure and chemical properties of the carbon nanomaterials and enhancing their luminescence properties. For boron and phosphorus doping, boron and phosphorus atoms enter the carbon nanomaterial structure during synthesis. These heteroatoms (nitrogen, boron, and phosphorus) can introduce defects into the crystal lattice of carbon nanomaterials, adjusting their energy level structure and thus altering their optical, electrical, and other physicochemical properties, such as affecting their emission wavelength and quantum yield. Plant-based carbon nanomaterials doped with nitrogen alone, nitrogen and phosphorus, and nitrogen, boron, and phosphorus are prepared respectively.

[0039] Raw materials for preparation: urea, analytical grade, purchased from Tianjin Tianli Chemical Co., Ltd.; boric acid, analytical grade, purchased from Harbin Chemical Reagent Factory; phosphoric acid, analytical grade, Tianjin Fuyu Fine Chemical Co., Ltd.

[0040] Characterization instruments and their characterization methods: The morphology of the product was characterized using a JOEL 2100f transmission electron microscope (JOEL Ltd., Japan) (ethanol dispersion, microgrid sample preparation); the phosphorescence spectrum of the product was characterized using an FLS1000 steady-state-transient fluorescence spectrometer (Edinburgh, UK); the infrared spectrum analysis of the product was performed using Fourier transform infrared spectroscopy (FT-IR) on a TENSOR27 instrument from Bruke GmbH, Germany; the crystal structure of the product was characterized using a SmartLab X-ray powder diffractometer (Rigaku, Japan); X-ray photoelectron spectroscopy (XPS) was obtained using a PHI5000Versa Probe instrument from UlVAC-PHI GmbH, Japan. Phosphorescence photography was performed using a WFH-204BS portable ultraviolet analyzer from Hangzhou Qiwei Instrument Co., Ltd.; the high-temperature reaction was carried out in a DHG-9075A forced-air drying oven from Shanghai Yiheng Scientific Instrument Co., Ltd.

[0041] (1) Preparation of pomegranate peel powder (pomegranate powder carbon nanotube luminescent material): Wash and peel the pomegranates, then place the fresh pomegranate peels in a forced-air drying oven and heat at 80℃ for 5 hours. After heating, allow them to cool naturally to room temperature, then grind the dried pomegranate peels into nano-sized pomegranate peel powder.

[0042] (2) Plant-based carbon nanomaterials ①Preparation of nitrogen-doped plant-based carbon nanomaterials with luminescent properties i) Weigh out 1.0g, 3.0g, 6.0g, and 10.0g of urea-pomegranate peel powder respectively and place them into four identical 100ml beakers. Then, add 50mg of pomegranate peel powder to each beaker, label them, and add 10ml of deionized water to each beaker. Mix well to obtain a suspension. To prevent the deionized water from evaporating too quickly, cover the top of the beakers with aluminum foil and place them in a forced-air drying oven at 200℃ for 3 hours. After heating, allow them to cool naturally to room temperature, and then grind the resulting product in a mortar to obtain a uniform powder.

[0043] Fluorescence spectroscopy was used to detect the phosphorescence intensity of the four nitrogen-doped plant-based carbon nanomaterials prepared above. The results showed that the nitrogen-doped plant-based carbon nanomaterials prepared had the strongest phosphorescence intensity when the amount of pomegranate peel powder was 50 mg and the amount of urea was 6.0 g.

[0044] (ii) Take four 6.0g portions of urea and place them into four identical 100ml beakers. Then, take 50mg, 100mg, 150mg, and 200mg of pomegranate peel powder respectively and add them to the four beakers. Label each beaker. Add 10ml of deionized water to each of the four beakers and mix thoroughly to obtain a dispersion. To prevent the deionized water from evaporating too quickly, cover the top of the beakers with aluminum foil and place them in a forced-air drying oven at 200℃ for 3 hours. After heating, allow them to cool naturally to room temperature. Grind the resulting product in a mortar and pestle to obtain a uniform powder.

[0045] The phosphorescence intensity of the four nitrogen-doped carbon materials prepared above was detected by fluorescence spectroscopy. It was shown that the nitrogen-doped plant-based carbon nanomaterials prepared had the strongest phosphorescence intensity when the amount of urea was 6.0 g and the amount of pomegranate peel powder was 50 mg.

[0046] Using 6.0g of urea and 50mg of pomegranate peel powder, nitrogen-phosphorus-doped plant-based carbon nanomaterials or nitrogen-boron-doped plant-based carbon nanoluminescent materials were prepared by adding phosphoric acid or boric acid, respectively.

[0047] ②Preparation of nitrogen and phosphorus-doped plant-based carbon nanomaterials with luminescent properties Take 0.4 ml, 0.8 ml, 1.0 ml, and 2.0 ml of phosphoric acid solution (85% mass concentration) and add them to four identical 100 ml beakers, respectively. Then, add 6.0 g of urea and 50 mg of pomegranate peel powder to each beaker, and label each beaker. Add 10 ml of deionized water to each of the four beakers to obtain aqueous solutions. To prevent the deionized water from evaporating too quickly, cover the top of the beakers with aluminum foil and place them in a forced-air drying oven at 200°C for 3 hours. After heating, allow them to cool naturally to room temperature, and then grind the resulting product in a mortar to obtain a uniform powder.

[0048] Fluorescence spectroscopy was performed on the phosphorescence intensity of the four groups of nitrogen-phosphorus-doped carbon materials prepared above. It was shown that the nitrogen-phosphorus-doped plant-based carbon nanomaterials with the strongest phosphorescence intensity were obtained when the amount of urea was 6.0 g, the amount of pomegranate peel powder was 50 mg, and the amount of phosphoric acid was 0.8 ml.

[0049] ③ Nitrogen-boron-doped plant-based carbon nanomaterials with luminescent properties Take 25 mg, 50 mg, 100 mg, and 150 mg of boric acid respectively and add them to four identical 100 ml beakers. Then, add 6.0 g of urea and 50 mg of pomegranate peel powder to each beaker, and label each beaker. Add 10 ml of deionized water to each of the four beakers to obtain aqueous solutions. To prevent the deionized water from evaporating too quickly, cover the top of the beakers with aluminum foil and place them in a forced-air drying oven at 200°C for 3 hours. After heating, allow them to cool naturally to room temperature, and then grind the resulting products in a mortar to obtain a uniform powder.

[0050] Fluorescence spectroscopy was performed on the phosphorescence intensity of the four groups of nitrogen-boron-doped carbon materials prepared above. It was shown that the nitrogen-boron-doped plant-based carbon nanomaterials with the strongest phosphorescence intensity were obtained when the amount of urea was 6.0 g, the amount of pomegranate peel powder was 50 mg, and the amount of boric acid was 150 mg.

[0051] ④ Nitrogen, phosphorus, and boron doped plant-based carbon nanomaterials Weigh out four groups of phosphoric acid and boric acid: 0.8 ml of phosphoric acid and 50 mg of boric acid; 0.8 ml of phosphoric acid and 100 mg of boric acid; and 1.2 ml of phosphoric acid and 150 mg of boric acid. Add each of these four groups of phosphoric acid and boric acid to four identical 100 ml beakers. Then, add 6.0 g of urea and 50 mg of pomegranate peel powder to each beaker, label each beaker, and add 10 ml of deionized water to each beaker to obtain an aqueous solution. To prevent the deionized water from evaporating too quickly, cover the top of the beakers with aluminum foil and place them in a forced-air drying oven at 200°C for 3 hours. After heating, allow them to cool naturally to room temperature, then grind the resulting products in a mortar and pestle to obtain a uniform powder.

[0052] Fluorescence spectroscopy was performed on the phosphorescence intensity of the four groups of nitrogen, phosphorus, and boron doped carbon materials prepared above. The results showed that the nitrogen, phosphorus, and boron doped plant-based carbon nanomaterials with the strongest phosphorescence intensity were obtained when the amount of urea was 6.0 g, the amount of pomegranate peel powder was 50 mg, the amount of boric acid was 150 mg, and the amount of phosphoric acid was 0.8 ml.

[0053] By employing single-factor analysis and orthogonal experiments, the nitrogen-phosphorus-boron-doped plant-based carbon nanoluminescent material with the strongest phosphorescence intensity performance was identified.

[0054] The pomegranate peel powder prepared above, and the nitrogen, phosphorus, and boron doped plant-based carbon nanoluminescent material (i.e., N, P, B doped plant-based carbon nanoluminescent material) prepared by using 6.0 g of urea, 50 mg of pomegranate peel powder, 150 mg of boric acid, and 0.8 ml of phosphoric acid were characterized. The results are shown below.

[0055] (1) TEM analysis (see appendix) Figure 1 and attached Figure 2 ) Appendix Figure 1 Figure 1 shows an electron microscope (EM) image of pomegranate peel powder carbon nanoparticle luminescent material. As can be seen from the image, the surface structure of the material is relatively uniform, with densely distributed nanoparticles averaging 18 nm in size. There are no obvious large aggregates, forming a relatively uniform microstructure. Figure 2 shows an EEM image of N, P, and B doped plant-based carbon nanoparticle luminescent material. The particle size is 25 nm. The introduction of N, P, and B atoms alters the growth pattern of the carbon nanostructure. The image shows some relatively obvious cluster structures and irregularly shaped particle aggregates. The electronic structures of N, P, and B atoms differ from those of carbon atoms, causing changes in the local electron cloud distribution, leading to the aggregation of atoms in these regions, forming clusters and irregular particle aggregation areas.

[0056] (2) XRD analysis (see appendix) Figure 3 ) Appendix Figure 3 These are the X-ray diffraction (XRD) spectra of N, P, and B-doped plant-based carbon nanomaterials and pomegranate powder carbon nanomaterials. Curve 1 shows broad and low diffraction peaks without obvious sharp and high-intensity characteristic peaks in the 10–30°C range. oA broad, diffuse peak is observed within the range. This broad, diffuse peak indicates an amorphous or poorly crystallized substance. For the dried pomegranate powder sample, the internal atomic arrangement lacks long-range order, and there is no large amount of regularly arranged crystal structure. Curve 2 shows a non-sharp and very strong diffraction peak around 30°, with some relatively weaker small peaks to its left. This is a typical characteristic of highly crystalline substances. Doping with N, P, and B atoms promotes crystal growth, making the atomic arrangement more ordered and causing the crystal to grow in a specific direction, thus producing such a diffraction peak. The amorphous state of the pomegranate powder carbon nanotube luminescent material contrasts sharply with the high crystallinity of the N, P, and B-doped carbon nanotube luminescent material; their diffraction peaks and crystal structures are different. The luminescent properties of the N, P, and B-doped plant-based carbon nanotube luminescent material are superior to those of the pomegranate powder carbon nanotube luminescent material.

[0057] (3) XPS analysis (see appendix) Figure 4 To be continued Figure 6 ) XPS comparative analysis of dried pomegranate powder and N, P, and B doped plant-based carbon nanomaterials can clarify the regulatory mechanism of the doping process on the chemical state and phosphorescence properties of the materials. Figure 4 XPS full-spectrum comparisons of N, P, and B-doped plant-based carbon nanomaterials (Sample 2) and undoped pomegranate powder carbon nanomaterials (Sample 1) are presented. The spectrum of Sample 2 clearly shows characteristic peaks of C1s, N1s, B1s, and P2p, indicating that N, P, and B elements were successfully introduced into the carbon matrix, signifying the successful synthesis of the carbon nanomaterial.

[0058] Figure 5 The C1s spectrum of the pomegranate powder carbon nanotube luminescent material is mainly CC / CH (284.65 eV), and contains CO (286.27 eV), C=O (287.83 eV) and carboxylic acid groups (289.10 eV), indicating that the natural components of pomegranate peel are rich in oxygen-containing organic matter such as polysaccharides and polyphenols, which provide active sites for subsequent doping.

[0059] Figure 6The C1s spectrum shows a slight shift of the CC / CH peak to 284.44 eV after doping, with the addition of a new peak at 285.15 eV (CN / CP / CB bond), confirming the successful insertion of N, P, and B into the carbon framework. Simultaneously, the intensity of the carboxylic acid peak (289.45 eV) increases, possibly related to the oxidation of some carbon matrix during doping. The B1s spectrum shows boron existing in the forms of BN / BC (191.45 eV) and BP (189.19 eV), indicating that boron forms a cooperative bond structure with the carbon matrix and phosphorus atoms. However, the residual BO peak (193.51 eV) suggests the need to optimize synthesis conditions to reduce surface oxidation. The coexistence of pyridine nitrogen (399.63 eV) and NP / NB bond (400.47 eV) in the N1s spectrum indicates that nitrogen not only participates in the conjugated structure to enhance rigidity but also forms chemical bonds with phosphorus and boron. However, the dominant P=O / phosphate characteristic peaks (133.65 / 134.49 eV) in the P2p spectrum indicate a high degree of oxidation during phosphorus doping, resulting in insufficient formation of reduced PC / PB bonds. The chemical state of phosphorus can be further controlled through reducing atmosphere annealing or precursor optimization. In summary, N, P, and B co-doping successfully constructed a multi-component heteroatom-modified carbon nanomaterial system. Its rigid conjugated structure and heavy atom microenvironment provide favorable conditions for phosphorescence emission, enabling a synergistic enhancement of phosphorescence lifetime and quantum yield.

[0060] (4) Infrared analysis (see appendix) Figure 7 ) Appendix Figure 7 These are the infrared spectra of N, P, and B-doped plant-based carbon nanomaterials and pomegranate powder carbon nanomaterials. The spectra are in the range of 1000–1200 cm⁻¹. -1 In the absorption peaks, both pomegranate powder carbon nanotube luminescent materials and N, P, and B doped plant-based carbon nanotube luminescent materials exhibit absorption peaks, all corresponding to CO bond stretching vibrations. However, in pomegranate powder carbon nanotube luminescent materials, this absorption peak originates more from the COC bonds of polysaccharides and the CO bonds of alcohols and phenols in the pomegranate powder; the absorption peaks of N, P, and B doped plant-based carbon nanotube materials become broader and more irregular, with a reduced peak height. The introduction of heteroatoms alters the electron cloud density and chemical composition around the CO bonds. The chemical bonding environment causes differences in the position or intensity of the absorption peak compared to garnet powder carbon nanotube luminescent materials, resulting in a shift in the absorption peak wavenumber. (1200~1500 cm⁻¹) -1The absorption peaks may be related to OC or CN bond vibrations. Besides polysaccharides, some lignin components in pomegranate peel contain ether bonds. The absorption peaks of N, P, and B-doped plant-based carbon nanotube luminescent materials become broad and irregular, with a reduced peak height. The introduction of heteroatoms alters the electron cloud density and chemical bonding environment around the CO bond, leading to differences in absorption peak position or intensity compared to pomegranate powder carbon nanotube luminescent materials, thus causing a shift in absorption peak wavenumber. The presence of heteroatoms in N, P, and B-doped plant-based carbon nanotube luminescent materials introduces new chemical bonds. For example, at 850 cm⁻¹... -1 The nearby location corresponds to the stretching vibration of PO, at 1200cm. -1 The surrounding area corresponds to the stretching vibration of BO. 1200~1500cm -1 The absorption peaks may be related to OC or CN bond vibrations. Besides polysaccharides, some lignin components in pomegranate peel contain ether bonds. (2800~3000 cm⁻¹) -1 The absorption peak at 3200-3500 cm⁻¹ corresponds to the saturated CH bonds in the oils, waxes, and polysaccharides of pomegranate powder carbon nanotube luminescent materials. The absorption peak intensity and peak height of N, P, and B-doped plant-based carbon nanotube luminescent materials are slightly enhanced, indicating that other atoms alter the chemical environment of the saturated hydrocarbon groups, affecting the electron cloud distribution of carbon atoms. -1 Among the absorption peaks, the absorption peaks of pomegranate powder carbon nanotube luminescent materials are sharper, possibly due to the vibration of residual water -OH groups or amino-containing compound -NH groups. The position, intensity, and shape of the absorption peaks of pomegranate powder carbon nanotube luminescent materials match the chemical bond characteristics of components such as polysaccharides, organic acids, flavonoids, and proteins in pomegranate.

[0061] (5) Optical characterization (see appendix) Figure 8 To be continued Figure 11 ) Figure 8 The experiment demonstrates the excitation of pomegranate powder carbon nanotube luminescent materials by 240 nm light. The optimal excitation wavelength was 261 nm, and the optimal emission wavelength was 471 nm. This reflects the differences in the material's ability to absorb and emit fluorescence with excitation light of different wavelengths. Figure 9 To illustrate the lifetime of garnet phosphorescent materials, the phosphorescence lifetime is calculated using the following formula based on a three-exponential fit of its phosphorescence lifetime decay curve:

[0062] Where B and τ represent the exponential factor and lifetime, respectively. The calculated lifetime parameter Tau1 of this garnet phosphorescent material is 485.44 ms, meaning that the time required for its luminescence intensity to decay to its initial value is approximately 485.44 ms.

[0063] Figure 10The experiment demonstrated the excitation of N, P, and B-doped plant-based carbon nanomaterials with 240 nm light. The optimal excitation wavelength was 276 nm, and the optimal emission wavelength was 518 nm. Figure 11 To determine the phosphorescence lifetime of N, P, and B doped garnet powder carbon nanotube luminescent materials, the phosphorescence lifetime was calculated using a three-exponential fit of its phosphorescence lifetime decay curve. The results yielded two lifetime parameters: Tau1 was 278.79 ms and Tau2 was 793.13 ms, indicating that its luminescence decay process involves at least two different mechanisms.

[0064] (6) Application of N, P and B doped plant-based carbon nanomaterials in fingerprint detection and anti-counterfeiting labeling.

[0065] ① Application of N, P, B-doped plant-based carbon nanomaterials in fingerprint detection (see...) Figures 12 to 16 ) The N, P, and B doped plant-based carbon nanotube luminescent material prepared in this invention (using 6.0g of urea, 50mg of pomegranate peel powder, 150mg of boric acid, and 0.8ml of phosphate to prepare the N, P, and B doped plant-based carbon nanotube luminescent material) can be used to reveal latent fingerprints on various objects. Fingerprints contain various secretions and residues, such as amino acids and oils. Carbon nanotube materials can interact with these components and adsorb onto the surface of the fingerprint ridges. Due to the phosphorescent properties of the N, P, and B doped plant-based carbon nanotube material of this invention, the carbon material emits phosphorescence under light excitation of a specific wavelength, thus clearly displaying the fingerprint ridges. Furthermore, it possesses high sensitivity and high security, playing an important role in the field of crime scene investigation, helping police obtain fingerprint evidence from various object surfaces, such as glass, metal, and plastic.

[0066] By applying N, P, and B-doped plant-based carbon nanomaterials to different substrates (marble, aluminum cans, leather, plastic, and banknotes) and comparing them with traditional fingerprint display technologies, the application potential of plant-based carbon nanomaterials in criminal investigation and security fields can be highlighted. The specific morphology of fingerprints can be clearly seen on all five substrates.

[0067] Figure 17This image shows the primary, secondary, and tertiary feature maps of fingerprints and latent fingerprints developed on a banknote substrate under a 365nm ultraviolet lamp using N, P, and B-doped plant-based carbon nanotube luminescent materials as a developer. Fingerprint features are mainly divided into three levels: the first level refers to the overall flow of the fingerprint line; the second level refers to the detailed features of the fingerprint line; and the third level refers to the microscopic features of the fingerprint line, such as sweat pores, the edge morphology of the ridges, and fine dots. Figure (a) shows that in the development using N, P, and B-doped plant-based carbon nanotube luminescent materials, the termination point, center point, and bifurcation point of the primary feature of the latent fingerprint can be clearly distinguished. Figure (b) shows that when the material is developed, the bridges, lakes, islands, and burrs of the secondary features are excellent, with clear and complete shapes, making it very easy to find the relevant features. At present, the application of fingerprints in the field of forensic science is relatively traditional, and fingerprint identification is mainly carried out by comparing the morphology of the primary and secondary features, that is, the specific pattern and detailed feature points of the fingerprint. Third-level fingerprint features are more microscopic and have higher utilization value, but they are more difficult to distinguish than first- and second-level features. As shown in Figure (c), when this material is developed, the sweat pores and ridge edge features (texture morphology) of the third-level features can be clearly collected, which can serve as a powerful auxiliary tool.

[0068] ② Application of N, P, B-doped plant-based carbon nanomaterials in fingerprint detection (see...) Figures 17 to 18 ) As shown in the figure, N, P, and B doped plant-based carbon nanotube luminescent materials (prepared with 6.0g urea, 50mg pomegranate peel powder, 150mg boric acid, and 0.8ml phosphoric acid) can be marked or embedded in product packaging, labels, or the product itself using specific techniques. Because the optical properties of N, P, and B doped plant-based carbon nanotube luminescent materials are determined by their complex internal structure and composition, they are difficult for criminals to easily imitate. Furthermore, they exhibit good stability and can maintain their optical properties under certain environmental conditions; therefore, these optical signals can be used as anti-counterfeiting markers. Figure 17 and Figure 18 As shown, N, P, and B-doped plant-based carbon nanotube luminescent materials were used to draw "tiger" and "sunflower" patterns on cardboard. Under ultraviolet light with a wavelength of 365 nm, both the "tiger" and "sunflower" exhibited bright white fluorescence. After the ultraviolet light source was turned off, brownish-yellow "tiger" and "sunflower" patterns appeared, indicating that the prepared carbon nanotube phosphorescent material has good anti-counterfeiting effects.

[0069] The N, P, and B doped plant-based carbon nanotube luminescent materials prepared in this invention use pomegranate peel as raw material, which is widely available and relatively environmentally friendly. In large-scale production applications, costs can be effectively controlled through optimization of the synthesis process. The N, P, and B doped plant-based carbon nanotube luminescent materials prepared in this invention exhibit blue fluorescence and brownish-yellow room-temperature phosphorescence characteristics when a 365 nm ultraviolet lamp is turned on and off, respectively. These characteristics are well-suited for fingerprint detection and anti-counterfeiting image creation, providing a basis for widespread application in fields requiring high-security anti-counterfeiting, such as currency, bills, high-end product packaging, and certificates, ensuring the authenticity and security of products.

[0070] The present invention and its embodiments have been described above. This description is not restrictive, and the embodiments shown are only one of the embodiments of the present invention. The actual structure is not limited to this. In conclusion, if those skilled in the art are inspired by this description and design similar structures and embodiments without departing from the spirit of the present invention, they should all fall within the protection scope of the present invention.

Claims

1. A method for preparing plant-based carbon nanotube luminescent materials using pomegranate peel as raw material, characterized in that, The steps include the following: S1: After drying the pomegranate peel, grind it into pomegranate peel powder; S2: Take the pomegranate peel powder, phosphoric acid, urea and boric acid from step S1, mix them together, add deionized water, mix evenly, and heat at 180-220℃ or above for 2-4 hours under sealed conditions. Grind the product evenly to prepare N, P and B doped plant-based carbon nanomaterials.

2. The method for preparing plant-based carbon nanotube luminescent materials using pomegranate peel as raw material according to claim 1, characterized in that, In step S2, for every 1000 ml of deionized water, take: 5-20g of pomegranate peel powder; Urea 100-1000g; Boric acid 2-15g; 40-200ml of phosphoric acid solution; The mass concentration of the phosphoric acid is 80-90%.

3. The method for preparing plant-based carbon nanotube luminescent materials using pomegranate peel as raw material according to claim 2, characterized in that, In step S2, for every 1000 ml of deionized water, take: 5g of pomegranate peel powder; 600g of urea; 15g of boric acid; 80 ml of phosphoric acid solution.

4. The plant-based carbon nano-luminescent material prepared by the method for preparing a plant-based carbon nano-luminescent material using pomegranate peel as raw material as described in any one of claims 1 to 3.

5. The application of the plant-based carbon nanoluminescent material according to claim 4 in fingerprint detection and / or as a latent fingerprint developer.

6. A fingerprint detection method, characterized in that, The steps include the following: ① The plant-based carbon nano-luminescent material of claim 4 in powder form is evenly sprinkled on the surface of the object where the latent fingerprint is located, and then the excess powder is gently blown away. ②The surface of the object containing the latent fingerprint is irradiated with a 365nm ultraviolet lamp. The fingerprint surface produces bright blue visible light, and an image with a clear latent fingerprint is obtained.

7. The fingerprint detection method according to claim 6, characterized in that, The object is a permeable or non-permeable material with a rough or smooth surface.

8. A fingerprint detection method according to claim 6, characterized in that, The objects include objects made of glass, marble, metal, leather, wood, plastic and ceramics, or banknotes, coins and bank cards.

9. The application of the plant-based carbon nanotube luminescent material according to claim 4 in the manufacture of anti-counterfeiting labels for products.

10. The application according to claim 9, characterized in that, It serves as an anti-counterfeiting mark by being embedded in the product's packaging, label, or the product itself.

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