Preparation method and application of stimuli-responsive wide-gamut color-changing phosphorescent carbon dots

Abstract

The invention discloses a preparation method and application of stimuli-responsive wide-gamut color-changing phosphorescent carbon dots, and the preparation method comprises the following steps: S1, at 180-250 DEG C, taking levofloxacin and acid as reaction raw materials, and carrying out hydrothermal reaction in an aqueous solution for 1-8 hours; s2, cooling a reaction product obtained by the hydrothermal reaction, and performing centrifugal separation to obtain a reactant solution; and S3, drying the obtained reactant solution to obtain the stimuli-responsive wide-color-gamut color-changing phosphorescent carbon dots. The preparation method of the stimuli-responsive wide-gamut color-changing phosphorescent carbon dots is simple, the raw materials are wide in source and easy to obtain, the reaction conditions are mild, the yield is high, and the carbon dots are green, pollution-free, low in toxicity and suitable for batch production; the stimuli-responsive wide-color-gamut color-changing phosphorescent carbon dot material fills the blank of wide-color-gamut color-changing phosphorescent carbon dot materials, solves the problem that stimuli-responsive wide-color-gamut color-changing phosphorescent carbon dots are difficult to prepare, and can be used for phosphorescent color display, advanced information encryption and food freshness monitoring.

Description

Technical Field

[0001] The invention belongs to the field of luminescent material preparation, and specifically relates to a phosphorescent carbon dot and a preparation method and application thereof. Background Art

[0002] Stimuli-responsive luminescent materials are one of the frontiers in the field of stimuli-responsive materials, and have broad application potential in information storage, optical devices, pressure sensors, chemical and biological sensors, molecular recognition and labeling, etc. Compared with short-lived fluorescence, long-lived room temperature phosphorescence (RTP) exhibits richer stimuli-responsive characteristics (such as luminescence color, intensity and lifetime), making it more advantageous for application in various fields. Traditional room temperature phosphorescent materials are mostly inorganic or organic complexes containing heavy metals, which often have disadvantages such as poor processing performance, high energy consumption for preparation, and high toxicity, making them difficult to be applied in practice.

[0003] As an emerging photofunctional nanomaterial, carbon dots have a unique biocompatibility and excellent long-lifetime room temperature phosphorescence performance due to their structure consisting of sp2 / sp3 carbon core and functional group shell. They have shown broad application prospects in the field of room temperature phosphorescence. Over the past few decades, long-lifetime room temperature phosphorescent carbon dots with high efficiency (phosphorescence quantum yield up to 50%), full spectrum, and long life (visible afterglow within 1 hour) have been synthesized, and their phosphorescence performance is comparable to that of traditional phosphorescent materials. However, there are still few reports on stimuli-responsive color-changing long-lifetime room temperature phosphorescent carbon dots, especially wide color gamut color-changing phosphorescent carbon dots. Summary of the invention

[0004] Purpose of the invention: To address the problems of existing carbon dot materials such as narrow phosphorescent color-changing range and difficulty in stimulus-responsive color-changing, which are not conducive to practical applications, the present invention provides a stimulus-responsive wide-color-range color-changing phosphorescent carbon dot and its preparation method and application.

[0005] Technical solution: To achieve the above invention purpose, the present invention adopts the following technical solution: a method for preparing stimulus-responsive wide color gamut color-changing phosphorescent carbon dots, comprising the following steps: S1, using levofloxacin and acid as reaction materials, a hydrothermal reaction is carried out in an aqueous solution at 180-250°C for 1-8h; S2, cooling the reaction product obtained by hydrothermal reaction and centrifuging to obtain a reactant solution; S3, the obtained reactant solution is dried to obtain stimulus-responsive wide color gamut color-changing phosphorescent carbon dots.

[0006] Furthermore, the acid is phosphoric acid, phytic acid or styrene sulfonic acid.

[0007] Furthermore, in step S2, the centrifugal speed is 6000-9000 r / min, the centrifugal time is 2-20 min, the dialysis bag molecular weight is selected to be 500 Da, and the dialysis time is 12 h.

[0008] Furthermore, the ratio of the mass of levofloxacin to the volume of the acid and the solvent water is in the range of 1:1-10:200-1000.

[0009] The present invention also provides the application of the stimulus-responsive wide color gamut color-changing phosphorescent carbon dots in phosphorescent color display and advanced information encryption.

[0010] The present invention also provides the use of the stimulus-responsive wide-color-gamut color-changing phosphorescent carbon dots in visual monitoring of food freshness.

[0011] Furthermore, the stimulus-responsive wide color gamut color-changing phosphorescent carbon dots are made into an aqueous solution, and ink is injected into the aqueous solution to obtain stimulus-responsive wide color gamut color-changing phosphorescent carbon dot ink, which is then printed to form a barcode label and stored with seafood or meat products to display their freshness.

[0012] Beneficial effects: Compared with the prior art, the present invention has the following advantages: (1) The present invention uses small molecules containing heteroatoms such as O, N, and P as raw materials and synthesizes a new stimulus-responsive wide color gamut color-changing phosphorescent carbon dot material by a one-step hydrothermal method. The material preparation method is simple, the raw materials used for synthesis are widely available and easy to obtain, the reaction conditions are mild, the yield is high, and it is green and pollution-free, low in toxicity, and suitable for mass production.

[0013] (2) The present invention fills the gap in carbon dot materials with stimulus-responsive color-changing phosphorescent light. The prior art cannot achieve wide color-range color-changing phosphorescent light emission from carbon dots, especially near-infrared phosphorescent light emission in the presence of water. The prepared carbon dot surface contains a large number of phosphate groups, and the carbon core has a certain lattice structure. The acid-induced protonation of the phosphate groups on the surface of the carbon dots, and the strong electron-withdrawing ability induces the red shift of the phosphorescent wavelength of the carbon dots to the orange region; at the same time, the self-assembly induced by hydrogen bonds leads to the enlargement of the conjugated system, thereby achieving near-infrared phosphorescent light emission from the carbon dots. The carbon core luminescent center is protected by the surface groups of the self-assembled carbon dots, and can still emit high-intensity near-infrared phosphorescent light even in water conditions. Based on the above effects, the stimulus-responsive wide color-range color-changing phosphorescent light of the carbon dots is achieved, solving the problem of the difficulty in preparing stimulus-responsive wide color-changing phosphorescent carbon dots. Based on the pH color-changing characteristics, the carbon dots can be used for food freshness monitoring. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a Fourier transform infrared spectrum of the stimulus-responsive wide color gamut color-changing phosphorescent carbon dots according to an embodiment of the present invention.

[0015] Figure 2This is a zeta potential diagram of the stimulus-responsive wide color gamut color-changing phosphorescent carbon dot aqueous solution at different pH values ​​according to an embodiment of the present invention.

[0016] Figure 3 This is a TEM image of the stimulus-responsive wide-color-gamut color-changing phosphorescent carbon dots according to an embodiment of the present invention.

[0017] Figure 4 1 and 2 are long-lifetime phosphorescence emission spectra of the embodiments of the present invention under different excitations, wherein: (a) is the G-carbon dot@paper complex, (b) is the O-carbon dot@paper complex, and (c) is the NIR-carbon dot@paper complex.

[0018] Figure 5 It is a comparison chart of the color change recoverability of the G-carbon dot@paper composite, O-carbon dot@paper composite, and NIR-carbon dot@paper composite in the embodiments of the present invention.

[0019] Figure 6 The diagram shows the application effects of stimulus-responsive wide color gamut color-changing phosphorescent carbon dots according to an embodiment of the present invention, wherein: (a) is the application in phosphorescent colorful display and advanced information encryption; and (b) is the application in food freshness monitoring. DETAILED DESCRIPTION

[0020] The present invention is further explained below in conjunction with the accompanying drawings and specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention. After reading the present invention, various equivalent forms of modifications to the present invention by those skilled in the art all fall within the scope defined by the claims attached to this application. Example

[0021] 0.1 g of levofloxacin, 2 mL of phosphoric acid and 10 mL of deionized water were taken into a beaker, and ultrasonically dissolved at an ultrasonic power of 60 w and room temperature to form a uniform mixed solution. The uniform solution was charged into a 50 mL polytetrafluoroethylene high-temperature reactor and placed in an oven for hydrothermal carbonization reaction (reaction temperature 200 ° C, reaction time 3 h). After cooling to room temperature, a centrifuge (centrifugal speed 8000 r / min, centrifugal time 5 min) was used to remove large particle precipitation to obtain a dark brown carbon dot solution. The solution pH was adjusted to 7 to obtain a phosphorescent carbon dot solution with stimulus-responsive wide color gamut color change (named G-carbon dot solution). Further, an appropriate amount of H3PO4 was added to the above G-carbon dot solution, and the pH was adjusted to 2 to obtain an O-carbon dot solution.

[0022] Figure 1This is the Fourier transform infrared spectrum of stimulus-responsive widened color gamut phosphorescent carbon dots. It can be seen from the figure that both carbon dots contain the same stretching vibration bands, which proves that they have similar chemical compositions. Compared with G-carbon dots, the stretching vibration of P-OH at 2700cm-1 in the Fourier transform infrared spectrum of O-carbon dots increases, indicating the protonation of PO groups under acidic conditions.

[0023] Figure 2 Figure 2 is the zeta potential diagram of the stimulus-responsive wide-color gamut color-changing phosphorescent carbon dots aqueous solution. At pH 7, the surface zeta potential of the G-carbon dot solution is negative, at -24.6 mV, attributed to the deprotonation of the phosphate groups. This high zeta potential can inhibit particle aggregation through electrostatic repulsion. When the pH is reduced to 2, the surface zeta potential decreases to 0.38 m V due to the enhanced protonation of the phosphate groups, resulting in the aggregation of the carbon dots.

[0024] Figure 3 This is a TEM image of stimulus-responsive color-changing phosphorescent carbon dots. As can be seen from the figure: the carbon dots synthesized under neutral conditions show good dispersion, almost uniform size, and a diameter range of about 2-6nm. The transition from monodisperse spherical particles to aggregates was observed in the TEM images from G-carbon dots to O-carbon dots. At the same time, the corresponding high-resolution TEM images show that the lattice spacing of G-carbon dots and O-carbon dots is 0.21 nm, corresponding to the (100) crystal plane in the graphite structure, indicating that the two carbon dots have a certain lattice structure. Example

[0025] The dark brown carbon dot solution in Case 1 was freeze-dried to obtain a high-purity carbon dot powder, which was then dissolved in deionized water to disperse evenly to form a uniform solution (solution concentration of 1.5 mg / ml). The pH of the solution was adjusted to neutral by adding an appropriate amount of sodium hydroxide, and the filter paper was soaked in the neutral carbon dot solution and allowed to stand for 5 minutes. The filter paper was then taken out and dried at 90°C to obtain a filter paper with a responsive stimulus function (named G-carbon dot@paper complex). Under ultraviolet light, an obvious green phosphorescence was exhibited. Then, the G-carbon dot@paper complex was placed in a phosphoric acid atmosphere (named O-carbon dot@paper complex), and the green phosphorescence suddenly turned into a mixed emission of yellow and near-infrared. In addition, after adding an acidic aqueous solution to the G-carbon dot@paper complex (named NIR-carbon dot@paper complex, such as using a hydrochloric acid aqueous solution to adjust the pH and apply water stimulation), the phosphorescence immediately red-shifted by 225 nm, and the emission color changed from green to near-infrared.

[0026] Figure 4The following are photos of G-Cdot@paper complex, O-Cdot@paper complex, and NIR-Cdot@paper complex after ultraviolet excitation at 395 nm and the long-life phosphorescence emission spectra under different excitations. As can be seen from the figure: G-Cdot@paper complex exhibits obvious green phosphorescence with an emission peak wavelength of 525nm, and its emission peak is less dependent on the excitation wavelength, which means that the carbon dots have a single phosphorescence center. For O-Cdot@paper complex, the green phosphorescence suddenly turns into a mixed emission of yellow and near-infrared. Its phosphorescence spectrum is also independent of excitation, but there is a main emission peak at 580nm and a tail at 700-800nm, which means that there may be multiple phosphorescence centers. It is worth noting that when the O-Cdot@paper complex is activated by water, the orange phosphorescence peak at 580 nm almost disappears, and only the near-infrared phosphorescence peak at 750nm (NIR-Cdot@paper complex) is observed, and the emission intensity does not decrease significantly.

[0027] Figure 5 The color recovery of G-Cdot@paper composite, O-Cdot@paper composite and NIR-Cdot@paper composite. As shown in the figure, G-Cdot@paper composite shows obvious green afterglow, O-Cdot@paper composite shows orange afterglow, and NIR-Cdot@paper composite shows near-infrared phosphorescence. Green, orange and NIR phosphorescence can be reversibly converted to each other by adding appropriate amount of acid or alkali, as well as water or dry treatment. Even after multiple acid-base or dry-wet treatments, the sample still retains green (525nm), orange (580nm) and NIR (750nm) phosphorescence emissions under 395nm light excitation, and the photoluminescence intensity does not decrease significantly. Example

[0028] The stimulus-responsive wide color gamut color-changing phosphorescent carbon dots obtained in Examples 1 and 2 are used in phosphorescent color display, advanced information encryption, and food freshness detection.

[0029] By injecting the stimuli-responsive wide color gamut phosphorescent carbon dot solution into an inkjet printer, a maple leaf pattern was printed on A4 using O-carbon dot ink, and the stimuli-responsive color-changing phosphorescent properties of carbon dots were used to demonstrate their potential applications in phosphorescent color display and advanced information encryption.

[0030] like Figure 5 As shown: The printed maple leaf pattern shows green long-lifetime room temperature phosphorescence under 365nm ultraviolet light. However, when the printed pattern is exposed to hydrogen chloride atmosphere for a short time, the long-lifetime room temperature phosphorescence color of the maple leaf pattern changes from green to orange. After spraying a small amount of water on the pattern, deep red-near infrared phosphorescence dominates.

[0031] like Figure 6As shown in (a), an aqueous solution of O-carbon dots is used as ink to print 2D codes onto A4 paper treated with other pH-independent green long-lifetime room-temperature phosphorescent carbon dots. Due to the interference of background green phosphorescence, the 2D code is invisible to the naked eye under 395nm ultraviolet light. However, when placed in a hydrogen chloride atmosphere, the 2D code becomes recognizable after irradiation with 365nm ultraviolet light, so that the corresponding information can be read. Importantly, the decrypted code can be erased by wetting with sodium hydroxide solution. This shows the great potential of carbon dot ink in the field of phosphorescent color display and advanced information encryption.

[0032] like Figure 6 (b) shows: the freshness of shrimps is assessed by using smart label barcodes prepared by stimuli-responsive wide color gamut color-changing phosphorescent carbon dots. Animal products, including seafood and meat, produce considerable amounts of volatile organic amines. The activity of intrinsic enzymes and external microorganisms causes changes in pH, and the long-life room temperature phosphorescence emission wavelength of the stimuli-responsive wide color gamut color-changing phosphorescent carbon dots is affected by pH, so smart label barcodes can be used to assess the freshness of shrimps. The biogenic amines produced during the shrimp spoilage process will change the color of the barcode pattern from orange to green, making it unreadable by the machine and unsuitable for sale due to the interference of the surrounding green phosphorescence. After storage at 4℃ and 30℃ for 24h, the barcode of the shrimp stored at 4℃ was readable, indicating that the shrimp meat maintained good freshness and had market value, while the barcode of the shrimp stored at 30℃ was missing, indicating spoilage and unsuitable for sale. This result confirms that the synthesized carbon dots can be used as editable smart label barcodes for monitoring food freshness.

[0033] The above descriptions are only some embodiments of the present invention. It should be pointed out that, for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing stimulus-responsive wide color gamut color-changing phosphorescent carbon dots, characterized in that The following steps are involved: S1, using levofloxacin and acid as reaction materials, a hydrothermal reaction is carried out in an aqueous solution at 180-250°C for 1-8h; S2, cooling the reaction product obtained by hydrothermal reaction and centrifuging to obtain a reactant solution; S3, the obtained reactant solution is dried to obtain stimulus-responsive wide color gamut color-changing phosphorescent carbon dots.

2. The method for preparing stimulus-responsive wide color gamut color-changing phosphorescent carbon dots according to claim 1, characterized in that: The acid is phosphoric acid, phytic acid or styrene sulfonic acid.

3. The method for preparing stimulus-responsive wide color gamut color-changing phosphorescent carbon dots according to claim 1, characterized in that: In step S2, the centrifugal speed is 6000-9000 r / min, the centrifugal time is 2-20 min, the molecular weight of the dialysis bag is selected to be 500 Da, and the dialysis time is 12 h.

4. The method for preparing stimulus-responsive wide color gamut color-changing phosphorescent carbon dots according to claim 1, characterized in that: The ratio of the mass of levofloxacin to the volume of the acid and the solvent water is in the range of 1:1-10:200-1000.

5. Application of the stimulus-responsive wide color gamut color-changing phosphorescent carbon dots prepared by the method of any one of claims 1 to 4 in phosphorescent color display and advanced information encryption.

6. Use of the stimulus-responsive wide-color-gamut color-changing phosphorescent carbon dots prepared by the method of any one of claims 1 to 4 in visual monitoring of food freshness.

7. The application of the stimulus-responsive wide color gamut color-changing phosphorescent carbon dots in visual detection of food freshness according to claim 6, characterized in that: The stimulus-responsive wide color gamut color-changing phosphorescent carbon dots are made into an aqueous solution, and ink is injected into the aqueous solution to obtain stimulus-responsive wide color gamut color-changing phosphorescent carbon dots ink, which is then printed to form a barcode label and stored with seafood or meat products to display their freshness.

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