CN111073393B - Dual anti-counterfeiting fluorescent ink and preparation method and application thereof - Google Patents

Dual anti-counterfeiting fluorescent ink and preparation method and application thereof Download PDF

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CN111073393B
CN111073393B CN201911376801.7A CN201911376801A CN111073393B CN 111073393 B CN111073393 B CN 111073393B CN 201911376801 A CN201911376801 A CN 201911376801A CN 111073393 B CN111073393 B CN 111073393B
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citric acid
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CN111073393A (en
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曾劲松
李鹏飞
陈克复
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South China University of Technology SCUT
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    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
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    • C09D11/03—Printing inks characterised by features other than the chemical nature of the binder
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    • C09D11/00—Inks
    • C09D11/02—Printing inks
    • C09D11/10—Printing inks based on artificial resins
    • C09D11/106—Printing inks based on artificial resins containing macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds
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    • C09D11/00—Inks
    • C09D11/02—Printing inks
    • C09D11/14—Printing inks based on carbohydrates

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Abstract

The invention discloses a double anti-counterfeiting fluorescent ink and a preparation method and application thereof. The method comprises the following steps: reacting citric acid hexahydrate, ethylenediamine, ytterbium chloride hexahydrate, erbium chloride hexahydrate and water to obtain doped carbon quantum dots; mixing and reacting rare earth doped carbon dots, dialdehyde nanofibril cellulose, 2-methylpyridine-N-borane and sodium acetate-glacial acetic acid buffer solution to obtain a Yb/Er-carbon dot-nanocellulose composite material; mixing the Yb/Er-carbon dot-nano cellulose composite material, polyvinyl alcohol, methylene blue, sodium stearate, urea and water to obtain the dual anti-counterfeiting fluorescent ink. The method is green, environment-friendly and low-toxicity, the synthesis method is simple and convenient, two kinds of blue and green fluorescence can be emitted, compared with the traditional fluorescent ink, the added nanofibrillar cellulose has great improvement on the rheological property and the thixotropic property of the water-based ink, has certain competitive advantage compared with the same type of products, and can be used for important information security anti-counterfeiting application.

Description

Dual anti-counterfeiting fluorescent ink and preparation method and application thereof
Technical Field
The invention belongs to the field of printing ink, and particularly relates to dual anti-counterfeiting fluorescent printing ink as well as a preparation method and application thereof. In particular to rare earth element doped carbon quantum dot grafted nanofibril cellulose-based fluorescent ink, a preparation method and anti-counterfeiting application thereof.
Background
In the information age, counterfeiting is a great challenge to human property and even personal safety. Therefore, there is an increasing demand for anti-counterfeit technology to ensure the security and integrity of important information (such as banknotes, important documents, brands, etc.). In recent years, anti-counterfeiting technologies based on various complex anti-counterfeiting mechanisms, such as marks, bar codes, thermal imaging, fluorescence detection, and the like, have been rapidly developed. Wherein, the fluorescent ink is used as a simple and effective anti-counterfeiting technologyPlays an irreplaceable role in protecting information safety, and is widely applied to various industries. At present, the traditional luminescent materials, including metal quantum dots such as rare earth materials, CdS, ZnS, CdTe and other photochromic compounds, usually exhibit monochromatic luminescent properties under the excitation of ultraviolet light (UV) and near infrared light (NIR), and have single anti-counterfeiting performance and certain toxicity. The carbon quantum dots serve as a new subclass of nano materials, have photoluminescence Performance (PL) and up-conversion luminescence performance (UCPL), have the advantages of good optical stability, electrical conductivity, simple and convenient preparation process, high quantum yield and the like, and compared with the traditional metal quantum dots, the carbon quantum dots are more and more concerned due to low toxicity, good biocompatibility and reproducibility, and are widely applied to various fields such as fluorescence anti-counterfeiting, biological imaging, drug delivery, photocatalysis, sensor probes, supercapacitors and the like. However, many scientific problems of carbon quantum dots remain to be further studied, such as low yield, low quantum yield, and single luminescence behavior of hydrothermal synthesis. Many studies have shown that doping heteroatoms in carbon quantum dots is an effective method to increase its quantum yield and improve the fluorescence properties. Er3+The ions have larger Stokes displacement and linear emission in a near infrared region, and have special up-conversion luminescence property. Thus, Er3+It is significant to dope into carbon quantum dots so that they have more complex luminescence behavior. Meanwhile, Er3+The luminescence of ions requires a sensitizer, whereas Yb3+Near 980nm, has more Ln than other Ln3+More ion-rich absorption cross section, and Yb3+Energy separation between ground state and unique excited state and Er3+The energy difference of the Yb is well matched, which is beneficial to the Yb3+Transfer energy to Er3+The up-conversion luminescence is enhanced, so that the modified carbon dots have dual luminescence properties of photoluminescence and stable up-conversion luminescence.
Cellulose is one of the most abundant renewable biological resources on earth, and is almost considered to be one of the most promising materials. Nanocellulose, including nanocellulose (CNF), nanocellulose crystals (CNC) and Bacterial Cellulose (BC), can be separated from plant fibers by different preparation methods. CNF is a rod-like or filamentous material, tens of nanometers in diameter and several micrometers in length, which is separated from plant fibers by enzymatic or mechanical treatment. Compared with cellulose, the cellulose modified polyester has the properties of larger specific surface area, special rheological property, a large amount of hydroxyl groups which are easy to modify, higher mechanical modulus and the like. The rheological and thixotropic properties of conventional aqueous inks are very similar to those of nanofibrillar cellulose. At the beginning of the shearing, the viscosity is rapidly reduced to a lower level, and at the end of the shearing, the viscosity is rapidly restored to a higher level, the rheological property of the aqueous ink is consistent with the characteristic of a pseudoplastic fluid, and the attempt of adding the nanofibrillar cellulose in the aqueous ink is undoubtedly helpful for improving the overall rheological property of the aqueous ink and has important significance for improving the service performance of the ink.
The Chinese patent application with the application number of 201611177038.1 discloses a water-based fluorescent anti-counterfeiting ink based on carbon quantum dots and a preparation method thereof. The Chinese patent application with the application number of 201710335455.2 discloses a dual-mode luminescent ink and a preparation method thereof, wherein beta-NaYF 4 particles are combined with carbon quantum dots to obtain the dual-fluorescent ink in ultraviolet and near infrared regions, but the dual-mode luminescent ink is strict in synthesis conditions, high in cost and complex in operation. Therefore, it is necessary to develop an aqueous ink which is easy to handle, has high quantum yield and can improve rheological properties.
Disclosure of Invention
In order to overcome the defects and shortcomings in the prior art, the invention aims to provide a preparation method of dual anti-counterfeiting fluorescent ink.
The invention also aims to provide the dual anti-counterfeiting fluorescent ink prepared by the method.
The invention aims to provide application of the dual anti-counterfeiting fluorescent ink.
The purpose of the invention is realized by the following technical scheme:
a preparation method of dual anti-counterfeiting fluorescent ink comprises the following steps:
(1) uniformly mixing citric acid hexahydrate, ethylenediamine, ytterbium chloride hexahydrate, erbium chloride hexahydrate and water, then reacting for 3-10 hours at 120-180 ℃, cooling and dialyzing to obtain rare earth doped carbon dots;
(2) uniformly mixing the rare earth doped carbon dots, dialdehyde nanofibrillar cellulose, 2-methylpyridine-N-borane and a sodium acetate-glacial acetic acid buffer solution, stirring at room temperature for 12-48 hours, dialyzing, and centrifugally washing to obtain the Yb/Er doped carbon dot grafted nanofibrillar cellulose composite material;
(3) uniformly mixing 0.1-1.5% of Yb/Er doped carbon quantum dot grafted nanofibril cellulose composite material, 3-6% of polyvinyl alcohol, 10-14% of methylene blue, 0.5-1% of sodium stearate, 0.2-0.6% of urea and the balance of water in percentage by mass, stirring at 60-80 ℃ until the materials are completely dissolved, and performing vacuum suction for 0.5-2 hours to obtain the dual anti-counterfeiting fluorescent ink;
and (3) the total mass of the Yb/Er doped carbon quantum dot grafted nanofibril cellulose composite material, polyvinyl alcohol, methylene blue, sodium stearate, urea and water is 100%.
Preferably, the mole ratio of the citric acid hexahydrate to the ethylenediamine in the step (1) is 1: 3-1: 5; yb in the ytterbium chloride hexahydrate3+Er in erbium chloride hexahydrate3+In a molar ratio of 5: 1-10: 1; the Yb in the citric acid hexahydrate and the ytterbium chloride hexahydrate3+Is 1: 1-3: 1, the mass ratio of citric acid to water is 1: 10-3: 10.
preferably, the cutting molecular weight of the dialysis bag used in the dialysis in the step (1) is 200, and the dialysis time is 12-36 h.
Preferably, the preparation method of the dialdehyde nanofibrillar cellulose in the step (2) comprises the following steps: adding citric acid-sodium hydroxide buffer solution into paper pulp, soaking for 1-5 hours, adding cellulose endonuclease, reacting for 1-3 hours, grinding for 5-15 times, adding cellulose endonuclease, reacting for 1-3 hours, grinding for 5-10 times, adding sodium periodate, stirring at 50-70 ℃ in a dark place for 2-5 hours, adding ethylene glycol to terminate the reaction, centrifuging, and collecting precipitates to obtain the dialdehyde nanofibrillar cellulose.
More preferably, the paper pulp is obtained by soaking an absolutely dry wood pulp board in water for 6-24 hours and then pulping for 1-2 hours.
The wood pulp board is a needle-leaf wood pulp board, and pulping is carried out by a groove type pulping machine.
More preferably, the concentration of the paper pulp is 2-10%, wherein the mass-to-liquid ratio of the oven-dried fibers to the citric acid-sodium hydroxide buffer solution is (10-30) g:1ml, the molar ratio of citric acid to sodium hydroxide in the citric acid-sodium hydroxide buffer solution is 1: 1-1: 3, and the total concentration of citric acid and sodium hydroxide in the citric acid-sodium hydroxide buffer solution is 50 mmol/L.
More preferably, the first addition of the endo-cellulose is 10-20 mg/g of oven dry fiber, and the second addition of the endo-cellulose is 5-15 mg/g of oven dry fiber.
More preferably, the refining is carried out by an ultrafine particle mill; the mass ratio of the added sodium periodate to the oven-dried fiber is 3: 1-1: 1, and the liquid-mass ratio of the added ethylene glycol to the oven-dried fiber is (20-80) ml:1g of the total weight of the composition.
Preferably, the molar ratio of amine groups in the rare earth-doped carbon dots to aldehyde groups in the dialdehyde nanofibrillar cellulose in the step (2) is 5: 1-10: 1; the molar ratio of the 2-methylpyridine-N-borane to aldehyde groups in the dialdehyde nanofibrillar cellulose is 2: 1-4: 1.
preferably, the mass-to-liquid ratio of the rare earth doped carbon dots to the sodium acetate-glacial acetic acid buffer solution in the step (2) is (1-5) g:1ml, wherein the mass-to-liquid ratio of sodium acetate to glacial acetic acid buffer solution in the sodium acetate-glacial acetic acid buffer solution is (1-3) g:1 ml.
Preferably, the centrifugal washing in step (2) is carried out until the washed supernatant is colorless and does not emit fluorescence under the irradiation of ultraviolet light.
Preferably, the dialdehyde-based nanofibrillar cellulose in the step (2) has the length of 650-1250 nm, the diameter of 25-65nm and the length-diameter ratio of 10-50.
Preferably, the rotating speed of the stirring in the step (3) is 800-1500 r/min, and the stirring time is 1-2 hours.
The double anti-counterfeiting fluorescent ink prepared by the method.
The application of the double anti-counterfeiting fluorescent ink is disclosed.
Preferably in the field of security and anti-counterfeiting. The field of security anti-counterfeiting is security anti-counterfeiting of bank notes, important documents, certificates and brands.
Compared with the prior art, the invention has the following advantages and beneficial effects:
(1) according to the preparation method provided by the invention, the raw materials for preparing the carbon quantum dots and the nanofibril cellulose are renewable resources, and the preparation method has the advantages of environmental friendliness, low toxicity, sustainability and the like.
(2) The Yb/Er-doped carbon quantum dot grafted nanofibril cellulose-based fluorescent ink disclosed by the invention is endowed with two stable up-conversion luminescence characteristics of rare earth elements on the basis of the traditional photoluminescence characteristics of the carbon quantum dots, and can respectively emit strong blue and green fluorescence under the irradiation of 370nm ultraviolet light and 980nm near-infrared light, so that the double anti-counterfeiting effect is obvious.
(3) Compared with the same type of ink, the Yb/Er doped carbon quantum dot grafted nanofibril cellulose-based fluorescent ink increases nanofibril cellulose as a carrier of modified carbon quantum dots, and the special rheological property and thixotropic property of the nanocellulose solution can also improve the rheological property of the water-based ink, so that the water-based ink is easy to disperse, is beneficial to rapid forming and improves the quality of printed matters.
(4) The preparation method provided by the invention has the advantages of simple synthesis conditions, convenience in operation and low cost, and has certain competitive advantages compared with the same type of products.
Drawings
FIG. 1 is a comparison of fluorescence intensity of carbon quantum dots of comparative example 1 and doped carbon quantum dots of example 6.
FIG. 2 shows the emission spectra of the doped carbon quantum dots prepared in example 6 at excitation wavelengths of 370nm and 980 nm.
Fig. 3 is a particle size distribution of the doped carbon quantum dots prepared in example 6.
Figure 4 is the diameter of nanofibrillar cellulose of example 6.
FIG. 5 is an Atomic Force Microscope (AFM) profile of the Yb/Er-carbon quantum dots of example 6.
FIG. 6 is a TEM topography of the nanofibrillar cellulose of example 6.
FIG. 7 is a graph of the thixotropic properties of the ink of comparative example 2 without nanofibrillar cellulose added.
FIG. 8 is a graph of the thixotropic properties of the ink with nanofibrillar cellulose added to example 6.
Detailed Description
The present invention will be described in further detail with reference to examples and drawings, but the embodiments of the present invention are not limited thereto.
Those who do not specify specific conditions in the examples of the present invention follow conventional conditions or conditions recommended by the manufacturer. The raw materials, reagents and the like which are not indicated for manufacturers are all conventional products which can be obtained by commercial purchase.
The dimensions of the nanofibrillar cellulose used in the examples and comparative examples of the present application are: the length is 650-1250 nm, the diameter is 25-65nm, and the length-diameter ratio is 10-50. The pulp concentration refers to mass concentration.
Example 1
The embodiment provides a rare earth element and carbon quantum dot grafted nanofibril cellulose-based fluorescent ink and a preparation method thereof.
(1) Preparing rare earth doped carbon dots: the molar ratio of citric acid hexahydrate to ethylenediamine is 1:3, the molar ratio of ytterbium chloride hexahydrate to erbium chloride hexahydrate is 5:1, and Yb in citric acid hexahydrate and ytterbium chloride hexahydrate3+The raw materials with the molar ratio of 1:1 and the mass ratio of the citric acid to the water of 1:10 and 10ml of distilled water are sequentially added into a 100ml beaker, continuously stirred for 15min at room temperature and uniformly mixed; then transferring the mixed solution into a hydrothermal reaction kettle with polytetrafluoroethylene as a lining, heating to 120 ℃ in an oil bath, and continuously reacting for 3 hours; and then cooling the product to room temperature, dialyzing the product in a dialysis bag (200 cut-off molecular weight) for 12 hours, and collecting the product for later use to obtain the rare earth doped carbon quantum dots.
(2) Preparing dialdehyde nanofibril cellulose: adding distilled water into the completely dried needle-leaved wood pulp board, and soaking for 6 hours; pulping for 1 hour by using a groove type pulping machine; adding a citric acid-sodium hydroxide buffer solution (the total concentration of citric acid and sodium hydroxide in the citric acid-sodium hydroxide buffer solution is 50mmol/L, the molar ratio of citric acid to sodium hydroxide is 1:1, and the mass-to-liquid ratio of the oven-dried fibers in the paper pulp to the citric acid-sodium hydroxide buffer solution is 10g:1ml) into the pulp with the pulp concentration of 2%, and soaking for 1 hour. Subsequently, the pulp was added with 10mg/g of endocellulase at the first time to the oven dried fiber, reacted for 1 hour, and ground 5 times with an ultra-fine grain grinder. And adding 5mg/g of cellulose endonuclease into the paper pulp for the second time, reacting for 1 hour, and grinding for 5 times by using an ultramicron grinder to prepare the nanofibrillar cellulose. Subsequently, sodium periodate (the mass ratio of the amount of sodium periodate to the absolutely dry fibers was 3:1) was added to the nanofibrillar cellulose, and the mixture was stirred at 50 ℃ for 2 hours in the dark. Finally, the reaction was terminated by the addition of ethylene glycol (20 ml of ethylene glycol was added to the oven dried fibers in a liquid-to-mass ratio of 20ml:1 g). The mixture was centrifuged several times to remove excess chemicals and the recovered precipitate was defined as dialdehyde nanofibrillar cellulose.
(3) Preparing a Yb/Er doped carbon quantum dot grafted nanofibril cellulose composite material: mixing the rare earth doped carbon quantum dots prepared in the step (1) with the dialdehyde nanofibrillar cellulose prepared in the step (2) in a beaker, wherein the molar ratio of amine groups in the rare earth doped carbon quantum dots to aldehyde groups in the dialdehyde nanofibrillar cellulose is 5:1, then adding 2-methylpyridine-N-borane and a sodium acetate-glacial acetic acid buffer solution (the mass-to-liquid ratio of the rare earth doped carbon dots to the sodium acetate-glacial acetic acid buffer solution is 1g:1ml, and the mass-to-liquid ratio of the sodium acetate in the sodium acetate-glacial acetic acid buffer solution is 1g:1ml), wherein the molar ratio of 2-methylpyridine-N-borane to aldehyde groups in the dialdehyde nanofibrillar cellulose is 2:1, placing the mixed solution into a closed container, and continuously stirring for 24 hours at room temperature. Subsequently, the mixture was dialyzed and centrifuged to remove the remaining raw materials and byproducts until the washed supernatant was colorless and free from fluorescence under uv irradiation.
(4) Preparing dual anti-counterfeiting fluorescent ink: and (2) sequentially adding 0.1% of Yb/Er-carbon dot-nano cellulose composite material prepared in the step (3), 3% of polyvinyl alcohol, 10% of methylene blue, 0.5% of sodium stearate, 0.2% of urea and 86.2% of distilled water into a container by mass percent, slowly stirring to fully swell the Yb/Er-carbon dot-nano cellulose composite material, then heating to 60 ℃, continuously stirring to fully dissolve the Yb/Er-carbon dot-nano cellulose composite material at the rotating speed of 800r/min, finally performing vacuum suction for 0.5 hour, and collecting the finally obtained solution to obtain the ink.
Example 2
The embodiment provides a rare earth element and carbon quantum dot grafted nanofibril cellulose-based fluorescent ink and a preparation method thereof.
(1) Preparing rare earth doped carbon dots: the molar ratio of citric acid hexahydrate to ethylenediamine is 1:5, the molar ratio of ytterbium chloride hexahydrate to erbium chloride hexahydrate is 10:1, and Yb in citric acid hexahydrate and ytterbium chloride hexahydrate3+The raw materials with the molar ratio of 3:1 and the mass ratio of citric acid to water of 3:10 and 10ml of distilled water are sequentially added into a 100ml beaker, continuously stirred for 15min at room temperature and uniformly mixed; then transferring the mixed solution into a hydrothermal reaction kettle with polytetrafluoroethylene as a lining, heating to 180 ℃ in an oil bath, and continuously reacting for 10 hours; and then cooling the product to room temperature, dialyzing the product in a dialysis bag (200 cut-off molecular weight) for 36 hours, and collecting the product for later use to obtain the rare earth doped carbon quantum dots.
(2) Preparing dialdehyde nanofibril cellulose: adding distilled water into the completely dried needle-leaved wood pulp board, and soaking for 24 hours; pulping for 2 hours by using a groove type pulping machine; adding a citric acid-sodium hydroxide buffer solution (the total concentration of citric acid and sodium hydroxide in the citric acid-sodium hydroxide buffer solution is 50mmol/L, the molar ratio of citric acid to sodium hydroxide is 1:3, and the mass-to-liquid ratio of the oven-dried fibers in the paper pulp to the citric acid-sodium hydroxide buffer solution is 30g:1ml) into the pulp with the pulp concentration of 10%, and soaking for 5 hours. Subsequently, the pulp was added with the amount of the endo-cellulose enzyme of 20mg/g oven-dried fiber for the first time, reacted for 3 hours, and ground 15 times with an ultra-fine grain grinder. Adding 15mg/g of cellulose endonuclease into the pulp for the second time, reacting for 3 hours, and grinding for 10 times by using an ultramicron grinder. Then, sodium periodate (the mass ratio of the amount of sodium periodate added to the absolutely dry state was 1:1) was added to the slurry, and the mixture was stirred at 70 ℃ for 5 hours in the dark. Finally, the reaction was terminated by the addition of ethylene glycol (the liquid to mass ratio of ethylene glycol to oven dried fiber was 80: 1). The mixture was centrifuged several times to remove excess chemicals and the recovered precipitate was defined as dialdehyde nanofibrillar cellulose.
(3) Preparing a Yb/Er doped carbon quantum dot grafted nanofibril cellulose composite material: mixing the rare earth doped carbon quantum dots prepared in the step (1) with the dialdehyde nanofibrillar cellulose prepared in the step (2) in a beaker, wherein the molar ratio of amine groups in the rare earth doped carbon quantum dots to aldehyde groups in the dialdehyde nanofibrillar cellulose is 10:1, then adding 2-methylpyridine-N-borane and a sodium acetate-glacial acetic acid buffer solution (the mass-to-liquid ratio of the rare earth doped carbon dots to the sodium acetate-glacial acetic acid buffer solution is 5g:1ml, and the mass-to-liquid ratio of the sodium acetate in the sodium acetate-glacial acetic acid buffer solution is 3g:1ml), wherein the molar ratio of 2-methylpyridine-N-borane to aldehyde groups in the dialdehyde nanofibrillar cellulose is 4:1, placing the mixed solution in a closed container, and continuously stirring for 48 hours at room temperature. Subsequently, the mixture was dialyzed and centrifuged to remove the remaining raw materials and byproducts until the washed supernatant was colorless and free from fluorescence under uv irradiation.
(4) Preparing dual anti-counterfeiting fluorescent ink: and (2) sequentially adding 1.5% of the Yb/Er-carbon dot-nano cellulose composite material prepared in the step (3), 6% of polyvinyl alcohol, 14% of methylene blue, 1% of sodium stearate, 0.6% of urea and 76.9% of distilled water into a container by mass percent, slowly stirring to fully swell the Yb/Er-carbon dot-nano cellulose composite material, heating to 80 ℃, continuously stirring at the rotating speed of 1500r/min to fully dissolve the Yb/Er-carbon dot-nano cellulose composite material, finally performing vacuum suction for 2 hours, and collecting the finally obtained solution to obtain the prepared ink.
Example 3
The embodiment provides a rare earth element and carbon quantum dot grafted nanofibril cellulose-based fluorescent ink and a preparation method thereof.
(1) Preparing rare earth doped carbon dots: the molar ratio of citric acid hexahydrate to ethylenediamine is 1:4, the molar ratio of ytterbium chloride hexahydrate to erbium chloride hexahydrate is 8:1, and the molar ratio of citric acid hexahydrate to erbium chloride hexahydrateYb in ytterbium chloride hydrate3+The raw materials with the molar ratio of 2:1 and the mass ratio of the citric acid to the water of 1:5 and 10ml of distilled water are sequentially added into a 100ml beaker, continuously stirred for 15min at room temperature and uniformly mixed; then transferring the mixed solution into a hydrothermal reaction kettle with polytetrafluoroethylene as a lining, heating to 160 ℃ in an oil bath, and continuously reacting for 6 hours; and then cooling the product to room temperature, dialyzing the product in a dialysis bag (200 cut-off molecular weight) for 36 hours, and collecting the product for later use to obtain the rare earth doped carbon quantum dots.
(2) Preparing dialdehyde nanofibril cellulose: adding distilled water into the completely dried needle-leaved wood pulp board, and soaking for 12 hours; pulping for 2 hours by using a groove type pulping machine; adding a citric acid-sodium hydroxide buffer solution (the total concentration of citric acid and sodium hydroxide in the citric acid-sodium hydroxide buffer solution is 50mmol/L, the molar ratio of citric acid to sodium hydroxide is 2:1, and the mass-to-liquid ratio of the oven-dried fibers in the paper pulp to the citric acid-sodium hydroxide buffer solution is 20g:1ml) into the slurry with the pulp concentration of 5%, and soaking for 2 hours. Subsequently, the pulp was added with the amount of the endo-cellulose enzyme 15mg/g oven dried fiber for the first time, reacted for 1 hour, and ground 10 times with an ultra-fine grain grinder. Adding cellulose endonuclease with the amount of 8mg/g oven dry fiber into the paper pulp for the second time, reacting for 2 hours, and grinding for 8 times by using an ultramicron grinder to prepare the nanofibrillar cellulose. Next, sodium periodate (the mass ratio of the amount of sodium periodate added to the absolutely dry state was 2:1) was added to the nanofibrillar cellulose, and the mixture was stirred at 60 degrees celsius for 4 hours in the dark. Finally, the reaction was terminated by the addition of ethylene glycol (the ratio of the amount of ethylene glycol added to the liquid mass of the oven-dried fibers was 40ml:1 g). The mixture was centrifuged several times to remove excess chemicals and the recovered precipitate was defined as dialdehyde nanofibrillar cellulose.
(3) Preparing a Yb/Er doped carbon quantum dot grafted nanofibril cellulose composite material: mixing the carbon quantum dots prepared in the step (1) and the dialdehyde nano-cellulose prepared in the step (2) in a beaker, wherein the molar ratio of amine groups in the rare earth doped carbon quantum dots to aldehyde groups in the dialdehyde nano-fibril cellulose is 7:1, adding 2-methylpyridine-N-borane and a sodium acetate-glacial acetic acid buffer solution (the mass-to-liquid ratio of the rare earth doped carbon dots to the sodium acetate-glacial acetic acid buffer solution is 3g:1ml, and the mass-to-liquid ratio of the sodium acetate to the glacial acetic acid buffer solution is 2g:1ml), wherein the molar ratio of the 2-methylpyridine-N-borane to the aldehyde groups in the dialdehyde nano-cellulose is 3:1, placing the mixed solution in a closed container, and continuously stirring at room temperature for 18 hours. Subsequently, the mixture was dialyzed and centrifuged to remove the remaining raw materials and byproducts until the washed supernatant was colorless and free from fluorescence under uv irradiation.
(4) Preparing dual anti-counterfeiting fluorescent ink: and (2) sequentially adding 1% of the Yb/Er-carbon dot-nano cellulose composite material prepared in the step (3), 4% of polyvinyl alcohol, 12% of methylene blue, 0.8% of sodium stearate, 0.3% of urea and 81.9% of distilled water into a container by mass percent, slowly stirring to fully swell the Yb/Er-carbon dot-nano cellulose composite material, then heating to 70 ℃, continuously stirring at the rotating speed of 1200r/min to fully dissolve the Yb/Er-carbon dot-nano cellulose composite material, finally performing vacuum suction for 0.5 hour, and collecting the finally obtained solution to obtain the prepared ink.
Example 4
The embodiment provides a rare earth element and carbon quantum dot grafted nanofibril cellulose-based fluorescent ink and a preparation method thereof.
(1) Preparing rare earth doped carbon dots: the molar ratio of citric acid hexahydrate to ethylenediamine is 1:3, the molar ratio of ytterbium chloride hexahydrate to erbium chloride hexahydrate is 6:1, and Yb in citric acid hexahydrate and ytterbium chloride hexahydrate3+The raw materials with the molar ratio of 3:2 and the mass ratio of citric acid to water of 1:4 and 10ml of distilled water are sequentially added into a 100ml beaker, continuously stirred for 15min at room temperature and uniformly mixed; then transferring the mixed solution into a hydrothermal reaction kettle with polytetrafluoroethylene as a lining, heating to 130 ℃ in an oil bath, and continuously reacting for 8 hours; and then cooling the product to room temperature, dialyzing the product in a dialysis bag (200 cut-off molecular weight) for 16 hours, and collecting the product for later use to obtain the rare earth doped carbon quantum dots.
(2) Preparing dialdehyde nanofibril cellulose: adding distilled water into the completely dried needle-leaved wood pulp board, and soaking for 18 hours; pulping for 1.5 hours by using a groove type pulping machine; adding a citric acid-sodium hydroxide buffer solution (the total concentration of citric acid and sodium hydroxide in the citric acid-sodium hydroxide buffer solution is 50mmol/L, the molar ratio of citric acid to sodium hydroxide is 1:3, and the mass-to-liquid ratio of the oven-dried fibers in the paper pulp to the citric acid-sodium hydroxide buffer solution is 15g:1ml) into the pulp with the pulp concentration of 3%, and soaking for 4 hours. Subsequently, the pulp was added with 12mg of endo-cellulose per g of oven-dried fiber for the first time, reacted for 2.5 hours, and ground 8 times with an ultra-fine grinder. Adding 10mg/g of cellulose endonuclease into the paper pulp for the second time, reacting for 2.5 hours, and grinding for 6 times by using an ultramicron grinder to prepare the nanofibrillar cellulose. Subsequently, sodium periodate (the mass ratio of the amount of sodium periodate added to the oven-dried fibers was 2.5:1) was added to the nanofibrillar cellulose, and the mixture was stirred at 55 ℃ for 2.5 hours in the dark. Finally, the reaction was terminated by the addition of ethylene glycol (the ratio of the amount of ethylene glycol added to the liquid mass of the oven-dried fibers was 60ml:1 g). The mixture was centrifuged several times to remove excess chemicals and the recovered precipitate was defined as dialdehyde nanofibrillar cellulose.
(3) Preparing a Yb/Er doped carbon quantum dot grafted nanofibril cellulose composite material: mixing the carbon quantum dots prepared in the step (1) and the dialdehyde nano-fibril cellulose prepared in the step (2) in a beaker, wherein the molar ratio of amine groups in the rare earth doped carbon quantum dots to aldehyde groups in the dialdehyde nano-fibril cellulose is 6:1, then adding 2-methylpyridine-N-borane and a sodium acetate-glacial acetic acid buffer solution (the mass-to-liquid ratio of the rare earth doped carbon dots to the sodium acetate-glacial acetic acid buffer solution is 4g:1ml, and the mass-to-liquid ratio of the sodium acetate in the sodium acetate-glacial acetic acid buffer solution is 2.5g:1ml), wherein the molar ratio of the 2-methylpyridine-N-borane to the aldehyde groups in the dialdehyde nano-fibril cellulose is 2:1, placing the mixed solution in a closed container, and continuously stirring for 40 hours at room temperature. Subsequently, the mixture was dialyzed and centrifuged to remove the remaining raw materials and byproducts until the washed supernatant was colorless and free from fluorescence under uv irradiation.
(4) Preparing dual anti-counterfeiting fluorescent ink: and (2) sequentially adding 0.8% of the Yb/Er-carbon dot-nano cellulose composite material prepared in the step (3), 4% of polyvinyl alcohol, 10% of methylene blue, 0.6% of sodium stearate, 0.6% of urea and 84% of distilled water into a container by mass percent, slowly stirring to fully swell the composite material, then heating to 80 ℃, continuously stirring to fully dissolve the composite material under the condition that the rotating speed is 1000r/min, finally performing vacuum suction for 1.5 hours, and collecting the finally obtained solution, namely the prepared ink.
Example 5
The embodiment provides a rare earth element and carbon quantum dot grafted nanofibril cellulose-based fluorescent ink and a preparation method thereof.
(1) Preparing rare earth doped carbon dots: the molar ratio of citric acid hexahydrate to ethylenediamine is 1:4, the molar ratio of ytterbium chloride hexahydrate to erbium chloride hexahydrate is 9:1, and Yb in citric acid hexahydrate and ytterbium chloride hexahydrate3+The raw materials with the molar ratio of 1.5:1 and the mass ratio of the citric acid to the water of 1:10 and 10ml of distilled water are sequentially added into a 100ml beaker, continuously stirred for 15min at room temperature and uniformly mixed; then transferring the mixed solution into a hydrothermal reaction kettle with polytetrafluoroethylene as a lining, heating to 160 ℃ in an oil bath, and continuously reacting for 6 hours; and then cooling the product to room temperature, dialyzing the product in a dialysis bag (200 cut-off molecular weight) for 12 hours, and collecting the product for later use to obtain the rare earth doped carbon quantum dots.
(2) Preparing dialdehyde nanofibril cellulose: adding distilled water into the completely dried needle-leaved wood pulp board, and soaking for 10 hours; pulping for 1.5 hours by using a groove type pulping machine; adding a citric acid-sodium hydroxide buffer solution (the total concentration of citric acid and sodium hydroxide in the citric acid-sodium hydroxide buffer solution is 50mmol/L, the molar ratio of citric acid to sodium hydroxide is 1:2, and the mass-to-liquid ratio of the oven-dried fibers in the paper pulp to the citric acid-sodium hydroxide buffer solution is 20g:1ml) into the pulp with the pulp concentration of 7%, and soaking for 3 hours. Subsequently, the pulp was added with the amount of the endo-cellulose enzyme 15mg/g oven dried fiber for the first time, reacted for 2 hours, and ground with an ultra-fine grinder 12 times. Adding cellulose endonuclease 7mg/g oven dry fiber into the pulp for the second time, reacting for 2 hr, and grinding with ultramicron grinder for 8 times to obtain nanofibrillar cellulose. Subsequently, sodium periodate (the mass ratio of the amount of sodium periodate to the absolutely dry fibers was 2:1) was added to the nanofibrillar cellulose, and the mixture was stirred at 65 ℃ for 3 hours in the dark. Finally, the reaction was terminated by the addition of ethylene glycol (the ratio of the amount of ethylene glycol added to the liquid mass of the oven-dried fibers was 30ml:1 g). The mixture was centrifuged several times to remove excess chemicals and the recovered precipitate was defined as dialdehyde nanofibrillar cellulose.
(3) Preparing a Yb/Er doped carbon quantum dot grafted nanofibril cellulose composite material: mixing the carbon quantum dots prepared in the step (1) and the dialdehyde nano-cellulose prepared in the step (2) in a beaker, wherein the molar ratio of amine groups in the rare earth doped carbon quantum dots to aldehyde groups in the dialdehyde nano-fibril cellulose is 10:1, adding 2-methylpyridine-N-borane and a sodium acetate-glacial acetic acid buffer solution (the mass-to-liquid ratio of the rare earth doped carbon dots to the sodium acetate-glacial acetic acid buffer solution is 2g:1ml, and the mass-to-liquid ratio of the sodium acetate to the glacial acetic acid buffer solution is 3g:1ml), wherein the molar ratio of the 2-methylpyridine-N-borane to the aldehyde groups in the dialdehyde nano-cellulose is 2:1, placing the mixed solution in a closed container, and continuously stirring at room temperature for 36 hours. Subsequently, the mixture was dialyzed and centrifuged to remove the remaining raw materials and byproducts until the washed supernatant was colorless and free from fluorescence under uv irradiation.
(4) Preparing dual anti-counterfeiting fluorescent ink: and (2) sequentially adding 1.4% of the Yb/Er-carbon dot-nano cellulose composite material prepared in the step (3), 6% of polyvinyl alcohol, 14% of methylene blue, 0.7% of sodium stearate, 0.4% of urea and 77.5% of distilled water into a container by mass percent, slowly stirring to fully swell the Yb/Er-carbon dot-nano cellulose composite material, then heating to 70 ℃, continuously stirring to fully dissolve the Yb/Er-carbon dot-nano cellulose composite material at the rotating speed of 1300r/min, finally performing vacuum suction for 1.5 hours, and collecting the finally obtained solution to obtain the ink.
Example 6
The embodiment provides a rare earth element and carbon quantum dot grafted nanofibril cellulose-based fluorescent ink and a preparation method thereof.
(1) Preparing rare earth doped carbon dots: the molar ratio of citric acid hexahydrate to ethylenediamine is 1:5, the molar ratio of ytterbium chloride hexahydrate to erbium chloride hexahydrate is 8:1, and Yb in citric acid hexahydrate and ytterbium chloride hexahydrate3+The raw material with the molar ratio of 1:1 and the mass ratio of citric acid to water of 2:10, and 10ml of distilled water were sequentially added into a 100ml beaker and continuously stirred at room temperatureMixing for 15 min; then transferring the mixed solution into a hydrothermal reaction kettle with polytetrafluoroethylene as a lining, heating to 150 ℃ in an oil bath, and continuously reacting for 5 hours; and then cooling the product to room temperature, dialyzing the product in a dialysis bag (200 cut-off molecular weight) for 24 hours, and collecting the product for later use to obtain the rare earth doped carbon quantum dots.
(2) Preparing dialdehyde nanofibril cellulose: adding distilled water into the completely dried needle-leaved wood pulp board, and soaking for 12 hours; pulping for 1 hour by using a groove type pulping machine; adding a citric acid-sodium hydroxide buffer solution (the total concentration of citric acid and sodium hydroxide in the citric acid-sodium hydroxide buffer solution is 50mmol/L, the molar ratio of citric acid to sodium hydroxide is 1:2, and the mass-to-liquid ratio of the oven-dried fibers in the paper pulp to the citric acid-sodium hydroxide buffer solution is 10g:1ml) into the pulp with the pulp concentration of 7%, and soaking for 2 hours. Subsequently, the pulp was added with the amount of the endo-cellulose enzyme of 13mg/g oven-dried fiber for the first time, reacted for 2 hours, and ground 10 times with an ultra-fine grain grinder. Adding 10mg/g of cellulose endonuclease into the paper pulp for the second time, reacting for 1.5 hours, and grinding for 8 times by using an ultramicron grinder to prepare the nanofibrillar cellulose. Subsequently, sodium periodate (the mass ratio of the amount of sodium periodate to the absolutely dry fibers was 2:1) was added to the nanofibrillar cellulose, and the mixture was stirred at 65 ℃ for 3 hours in the dark. Finally, the reaction was terminated by the addition of ethylene glycol (the ratio of the amount of ethylene glycol added to the liquid mass of the oven-dried fibers was 60ml:1 g). The mixture was centrifuged several times to remove excess chemicals and the recovered precipitate was defined as dialdehyde nanofibrillar cellulose.
(3) Preparing a Yb/Er doped carbon quantum dot grafted nanofibril cellulose composite material: mixing the carbon quantum dots prepared in the step (1) and the dialdehyde nano-cellulose prepared in the step (2) in a beaker, wherein the molar ratio of amine groups in the rare earth doped carbon quantum dots to aldehyde groups in the dialdehyde nano-fibril cellulose is 9:1, adding 2-methylpyridine-N-borane and a sodium acetate-glacial acetic acid buffer solution (the mass-to-liquid ratio of the rare earth doped carbon dots to the sodium acetate-glacial acetic acid buffer solution is 2g:1ml, and the mass-to-liquid ratio of the sodium acetate to the glacial acetic acid buffer solution is 2g:1ml), wherein the molar ratio of the 2-methylpyridine-N-borane to the aldehyde groups in the dialdehyde nano-cellulose is 4:1, placing the mixed solution in a closed container, and continuously stirring at room temperature for 24 hours. Subsequently, the mixture was dialyzed and centrifuged to remove the remaining raw materials and byproducts until the washed supernatant was colorless and free from fluorescence under uv irradiation.
(4) Preparing dual anti-counterfeiting fluorescent ink: and (2) sequentially adding 1.4% of the Yb/Er-carbon dot-nano cellulose composite material prepared in the step (3), 6% of polyvinyl alcohol, 13% of methylene blue, 1% of sodium stearate, 0.2% of urea and 78.4% of distilled water into a container by mass percent, slowly stirring to fully swell the composite material, then heating to 80 ℃, continuously stirring at the rotating speed of 1500r/min to fully dissolve the composite material, finally performing vacuum suction for 1 hour, and collecting the finally obtained solution, namely the prepared ink.
Comparative example 1
(1) Preparing the carbon quantum dots: adding citric acid hexahydrate and ethylenediamine at a molar ratio of 1:5 into distilled water (10 ml, the mass ratio of citric acid to water is 2:10) to form a transparent solution, continuously stirring at room temperature for 15min, and uniformly mixing; then transferring the mixed solution into a hydrothermal reaction kettle with polytetrafluoroethylene as a lining, heating to 150 ℃ in an oil bath, and continuously reacting for 5 hours; the product was then cooled to room temperature, dialyzed in dialysis bag (200 cut molecular weight) for 24 hours, and collected for future use to yield carbon quantum dots.
(2) Preparing dialdehyde nanofibril cellulose: adding distilled water into the completely dried needle-leaved wood pulp board, and soaking for 12 hours; pulping for 1 hour by using a groove type pulping machine; adding a citric acid-sodium hydroxide buffer solution (the total concentration of citric acid and sodium hydroxide in the citric acid-sodium hydroxide buffer solution is 50mmol/L, the molar ratio of citric acid to sodium hydroxide is 1:2, and the mass-to-liquid ratio of the oven-dried fibers in the paper pulp to the citric acid-sodium hydroxide buffer solution is 10g:1ml) into the pulp with the pulp concentration of 7%, and soaking for 2 hours. Subsequently, the pulp was added with the amount of the endo-cellulose enzyme of 13mg/g oven-dried fiber for the first time, reacted for 2 hours, and ground 10 times with an ultra-fine grain grinder. Adding 10mg/g of cellulose endonuclease into the paper pulp for the second time, reacting for 1.5 hours, and grinding for 8 times by using an ultramicron grinder to prepare the nanofibrillar cellulose. Subsequently, sodium periodate (the mass ratio of the amount of sodium periodate to the absolutely dry fibers was 2:1) was added to the nanofibrillar cellulose, and the mixture was stirred at 65 ℃ for 3 hours in the dark. Finally, a proper amount of ethylene glycol (the liquid-mass ratio of the added amount of the ethylene glycol to the absolutely dry fiber is 60ml:1g) is added to stop the reaction. The mixture was centrifuged several times to remove excess chemicals and the recovered precipitate was defined as dialdehyde nanofibrillar cellulose.
(3) Preparing a Yb/Er doped carbon quantum dot grafted nanofibril cellulose composite material: mixing the carbon quantum dots prepared in the step (1) and the dialdehyde nano-cellulose prepared in the step (2) in a beaker, wherein the molar ratio of amine groups in the rare earth doped carbon quantum dots to aldehyde groups in the dialdehyde nano-fibril cellulose is 9:1, adding 2-methylpyridine-N-borane and a sodium acetate-glacial acetic acid buffer solution (the mass-to-liquid ratio of the rare earth doped carbon dots to the sodium acetate-glacial acetic acid buffer solution is 2g:1ml, and the mass-to-liquid ratio of the sodium acetate to the glacial acetic acid buffer solution is 2g:1ml), wherein the molar ratio of the 2-methylpyridine-N-borane to the aldehyde groups in the dialdehyde nano-cellulose is 4:1, placing the mixed solution in a closed container, and continuously stirring at room temperature for 24 hours. Subsequently, the mixture was dialyzed and centrifuged to remove the remaining raw materials and byproducts until the washed supernatant was colorless and free from fluorescence under uv irradiation.
(4) Preparing the carbon quantum dot-based anti-counterfeiting fluorescent ink: according to the mass percentage, 1.4% of the carbon quantum dot-nano cellulose composite material prepared in the step (1), 6% of polyvinyl alcohol, 13% of methylene blue, 1% of sodium stearate, 0.2% of urea and 78.4% of distilled water are sequentially added into a container, slowly stirred to be fully swollen, then heated to 80 ℃, continuously stirred to be fully dissolved under the condition that the rotating speed is 1500r/min, finally vacuum suction is carried out for 1 hour, and the finally obtained solution is collected, namely the prepared ink.
Comparative example 2
(1) Preparing rare earth doped carbon dots: the molar ratio of citric acid hexahydrate to ethylenediamine is 1:5, the molar ratio of ytterbium chloride hexahydrate to erbium chloride hexahydrate is 8:1, and Yb in citric acid hexahydrate and ytterbium chloride hexahydrate3+Is in a molar ratio of 1:1,sequentially adding raw materials with the citric acid-water mass ratio of 2:10 and 10ml of distilled water into a 100ml beaker, continuously stirring for 15min at room temperature, and uniformly mixing; then transferring the mixed solution into a hydrothermal reaction kettle with polytetrafluoroethylene as a lining, heating to 150 ℃ in an oil bath, and continuously reacting for 5 hours; and then cooling the product to room temperature, dialyzing the product in a dialysis bag (200 cut-off molecular weight) for 24 hours, and collecting the product for later use to obtain the rare earth doped carbon quantum dots.
(2) Preparing dual anti-counterfeiting fluorescent ink: and (3) sequentially adding 1.4% of Yb/Er-carbon point, 6% of polyvinyl alcohol, 13% of methylene blue, 1% of sodium stearate, 0.2% of urea and 78.4% of distilled water, which are obtained in the step (3), into a container by mass percent, slowly stirring to fully swell the mixture, then heating to 80 ℃, continuously stirring to fully dissolve the mixture under the condition that the rotating speed is 1500r/min, finally performing vacuum suction for 1 hour, and collecting the finally obtained solution, namely the prepared ink.
Comparative example 3
(1) Preparing rare earth doped carbon dots: the molar ratio of citric acid hexahydrate to ethylenediamine is 1:5, the molar ratio of ytterbium chloride hexahydrate to erbium chloride hexahydrate is 8:1, and Yb in citric acid hexahydrate and ytterbium chloride hexahydrate3+The raw materials with the molar ratio of 1:1 and the mass ratio of citric acid to water of 2:10 and 10ml of distilled water are sequentially added into a 100ml beaker, continuously stirred for 15min at room temperature and uniformly mixed; then transferring the mixed solution into a hydrothermal reaction kettle with polytetrafluoroethylene as a lining, heating to 150 ℃ in an oil bath, and continuously reacting for 5 hours; and then cooling the product to room temperature, dialyzing the product in a dialysis bag (200 cut-off molecular weight) for 24 hours, and collecting the product for later use to obtain the rare earth doped carbon quantum dots.
(2) Preparing dialdehyde nanofibril cellulose: adding distilled water into the completely dried needle-leaved wood pulp board, and soaking for 12 hours; pulping for 1 hour by using a groove type pulping machine; adding a citric acid-sodium hydroxide buffer solution (the total concentration of citric acid and sodium hydroxide in the citric acid-sodium hydroxide buffer solution is 50mmol/L, the molar ratio of citric acid to sodium hydroxide is 1:2, and the mass-to-liquid ratio of the oven-dried fibers in the paper pulp to the citric acid-sodium hydroxide buffer solution is 10g:1ml) into the pulp with the pulp concentration of 7%, and soaking for 2 hours. Subsequently, the pulp was added with the amount of the endo-cellulose enzyme of 13mg/g oven-dried fiber for the first time, reacted for 2 hours, and ground 10 times with an ultra-fine grain grinder. Adding 10mg/g of cellulose endonuclease into the paper pulp for the second time, reacting for 1.5 hours, and grinding for 8 times by using an ultramicron grinder to prepare the nanofibrillar cellulose. Subsequently, sodium periodate (the mass ratio of the amount of sodium periodate to the absolutely dry fibers was 2:1) was added to the nanofibrillar cellulose, and the mixture was stirred at 65 ℃ for 3 hours in the dark. Finally, a proper amount of ethylene glycol (the liquid-mass ratio of the added amount of the ethylene glycol to the absolutely dry fiber is 60ml:1g) is added to stop the reaction. The mixture was centrifuged several times to remove excess chemicals and the recovered precipitate was defined as dialdehyde nanofibrillar cellulose.
(3) Preparing a Yb/Er doped carbon quantum dot grafted nanofibril cellulose composite material: mixing the carbon quantum dots prepared in the step (1) and the dialdehyde nano-cellulose prepared in the step (2) in a beaker, wherein the molar ratio of amine groups in the rare earth doped carbon quantum dots to aldehyde groups in the dialdehyde nano-fibril cellulose is 9:1, adding 2-methylpyridine-N-borane and a sodium acetate-glacial acetic acid buffer solution (the mass-to-liquid ratio of the rare earth doped carbon dots to the sodium acetate-glacial acetic acid buffer solution is 2g:1ml, and the mass-to-liquid ratio of the sodium acetate to the glacial acetic acid buffer solution is 2g:1ml), wherein the molar ratio of the 2-methylpyridine-N-borane to the aldehyde groups in the dialdehyde nano-cellulose is 4:1, placing the mixed solution in a closed container, and continuously stirring at room temperature for 24 hours. Subsequently, the mixture was dialyzed and centrifuged to remove the remaining raw materials and byproducts until the washed supernatant was colorless and free from fluorescence under uv irradiation.
(4) Preparing dual anti-counterfeiting fluorescent ink: and (2) sequentially adding 3% of the Yb/Er-carbon dot-nano cellulose composite material prepared in the step (3), 6% of polyvinyl alcohol, 13% of methylene blue, 1% of sodium stearate, 0.2% of urea and 76.8% of distilled water into a container by mass percent, slowly stirring to fully swell the Yb/Er-carbon dot-nano cellulose composite material, heating to 80 ℃, continuously stirring at the rotating speed of 1500r/min to fully dissolve the Yb/Er-carbon dot-nano cellulose composite material, finally performing vacuum suction for 1 hour, and collecting the finally obtained solution, namely the prepared ink.
FIG. 1 is a comparison of fluorescence intensities of carbon quantum dots and doped carbon dots, and it can be seen that the fluorescence intensity of the carbon dots doped with rare earth elements is greatly improved.
FIG. 2 shows emission spectra of the doped carbon quantum dots prepared in example 6 at excitation wavelengths of 370nm and 980nm, respectively, from which it can be seen that an emission peak appears at 440nm under the excitation of ultraviolet wavelength of 370nm, resulting in blue fluorescence emission; under the excitation of near infrared wavelength of 990nm, an emission peak appears at 550nm, and green fluorescence emission is obtained.
FIG. 3 is a graph showing the particle size distribution of the doped carbon quantum dots obtained in example 6, wherein the particle size of the doped carbon quantum dots is 3.3nm-5.4nm, and the average particle size is 4.36 nm.
FIG. 4 shows the diameter of nanofibrillar cellulose of example 6, from which it can be seen that the diameter of nanofibrillar cellulose is between 25 and 65nm and the average diameter is 44.42 nm.
FIG. 5 is an Atomic Force Microscope (AFM) profile of Yb/Er-carbon quantum dots in example 6, which shows that the doped carbon quantum dots are small nano-circular particles with relatively uniform size distribution.
FIG. 6 is a TEM (transmission electron microscopy) topographical view of the nanofibrillar cellulose of example 6, which shows that the prepared nanofibrillar cellulose exhibits certain fibrillation properties.
Fig. 7 is a thixotropic performance of the ink without nanocellulose addition in comparative example 2, where low shear 1: rate 2s-160s in total, simulating the time when the ink is static; high shear 2: rate 1000s-115s total, simulating a scraper passage; low shear 3: rate 2s-1Total 35s, simulating the re-formation of the ink after printing. As can be seen, the ink without the nanofibrillar cellulose added has the viscosity which does not change with the change of the shear rate, shows the properties of the typical Newtonian fluid, and is not friendly to the water-based ink.
Fig. 8 is a graph of the thixotropic properties of the ink of example 6 with nanofibrillar cellulose added, where low shear 1: rate 2s-160s total, simulating ink restWhen the current is running; high shear 2: rate 1000s-115s total, simulating a scraper passage; low shear 3: rate 2s-1Total 200s, simulating the re-formation of ink after printing. As can be seen from the figure, after the nano-fibril cellulose is added, the ink shows a certain shear thinning performance, becomes a typical non-Newtonian fluid, and when the ink is subjected to high-speed shear, the viscosity of the ink is reduced, the fluidity of the ink is good, and the ink is easy to transfer; and when the ink is transferred onto the paper sheet, the external force disappears suddenly, the viscosity is increased suddenly, and the ink is protected from overflowing to the surrounding area, so that the ink has good print on the paper sheet.
For the ink prepared in the comparative example 3 when the amount of Yb/Er-carbon dot-nanocellulose composite material used was 3%, the ink was very likely to fall off when printed on plastic during printing, because the nanofibrillar cellulose was added in a large amount, and many hydroxyl groups on the surface adsorbed many pigments, which were not tightly bonded to the plastic surface, which was very disadvantageous for printing operations.
The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, combinations, and simplifications are intended to be included in the scope of the present invention.

Claims (7)

1. A preparation method of dual anti-counterfeiting fluorescent ink is characterized by comprising the following steps:
(1) uniformly mixing citric acid hexahydrate, ethylenediamine, ytterbium chloride hexahydrate, erbium chloride hexahydrate and water, then reacting for 3-10 hours at 120-180 ℃, cooling and dialyzing to obtain rare earth doped carbon dots;
(2) uniformly mixing the rare earth doped carbon dots, dialdehyde nanofibrillar cellulose, 2-methylpyridine-N-borane and a sodium acetate-glacial acetic acid buffer solution, stirring at room temperature for 12-48 hours, dialyzing, and centrifugally washing to obtain the Yb/Er doped carbon dot grafted nanofibrillar cellulose composite material;
(3) uniformly mixing 0.1-1.5% of Yb/Er doped carbon quantum dot grafted nanofibril cellulose composite material, 3-6% of polyvinyl alcohol, 10-14% of methylene blue, 0.5-1% of sodium stearate, 0.2-0.6% of urea and the balance of water in percentage by mass, stirring at 60-80 ℃ until the materials are completely dissolved, and performing vacuum suction for 0.5-2 hours to obtain the dual anti-counterfeiting fluorescent ink;
the total mass of the Yb/Er doped carbon quantum dot grafted nanofibril cellulose composite material, polyvinyl alcohol, methylene blue, sodium stearate, urea and water in the step (3) is 100 percent;
the mole ratio of the citric acid hexahydrate to the ethylenediamine in the step (1) is 1: 3-1: 5; yb in the ytterbium chloride hexahydrate3+Er in erbium chloride hexahydrate3+In a molar ratio of 5: 1-10: 1; the Yb in the citric acid hexahydrate and the ytterbium chloride hexahydrate3+Is 1: 1-3: 1, the mass ratio of the citric acid hexahydrate to the water is 1: 10-3: 10.
2. the method for preparing a dual anti-forgery fluorescent ink according to claim 1, wherein the molar ratio of the amine group in the rare earth-doped carbon dots to the aldehyde group in the dialdehyde nanofibrillar cellulose in the step (2) is 5: 1-10: 1; the molar ratio of the 2-methylpyridine-N-borane to aldehyde groups in the dialdehyde nanofibrillar cellulose is 2: 1-4: 1.
3. the preparation method of the dual anti-counterfeiting fluorescent ink according to claim 1 or 2, wherein the mass-to-liquid ratio of the rare earth doped carbon dot and the sodium acetate-glacial acetic acid buffer solution in the step (2) is (1-5) g:1ml, wherein the mass-to-liquid ratio of sodium acetate to glacial acetic acid buffer solution in the sodium acetate-glacial acetic acid buffer solution is (1-3) g:1 ml.
4. The preparation method of the dual anti-counterfeiting fluorescent ink according to claim 3, wherein the preparation method of the dialdehyde nanofibrillar cellulose in the step (2) comprises the following steps of: adding citric acid-sodium hydroxide buffer solution into paper pulp, soaking for 1-5 hours, adding cellulose endonuclease, reacting for 1-3 hours, grinding for 5-15 times, adding cellulose endonuclease, reacting for 1-3 hours, grinding for 5-10 times, adding sodium periodate, stirring at 50-70 ℃ in a dark place for 2-5 hours, adding ethylene glycol to terminate the reaction, centrifuging, and collecting precipitates to obtain the dialdehyde nanofibrillar cellulose.
5. The preparation method of the dual anti-counterfeiting fluorescent ink according to claim 4, wherein the amount of the endonuclease cellulose added for the first time is 10-20 mg/g of oven dry fibers, and the amount of the endonuclease cellulose added for the second time is 5-15 mg/g of oven dry fibers; the mass ratio of the added sodium periodate to the oven-dried fiber is 3: 1-1: 1, and the liquid-mass ratio of the added ethylene glycol to the oven-dried fiber is (20-80) ml:1g of the total weight of the composition.
6. The preparation method of the dual anti-counterfeiting fluorescent ink according to claim 4, wherein the mass concentration of the paper pulp is 2-10%, and the mass-to-liquid ratio of the absolutely dry fibers to the citric acid-sodium hydroxide buffer solution is (10-30) g:1ml, the molar ratio of citric acid to sodium hydroxide in the citric acid-sodium hydroxide buffer solution is 1: 1-1: 3, and the total concentration of citric acid and sodium hydroxide in the citric acid-sodium hydroxide buffer solution is 50 mmol/L.
7. The preparation method of the dual anti-counterfeiting fluorescent ink according to claim 3, wherein the cut-off molecular weight of a dialysis bag used in the dialysis in the step (1) is 200, and the dialysis time is 12-36 h; the dialdehyde-based nanofibril cellulose in the step (2) has the length of 650-1250 nm, the diameter of 25-65nm and the length-diameter ratio of 10-50; and (3) stirring at the rotating speed of 800-1500 r/min for 1-2 hours.
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