Preparation of fluorescent silver nanocluster composite material and application of fluorescent silver nanocluster composite material in fluorescent ink

Abstract

The invention discloses preparation of a fluorescent silver nanocluster composite material and application of the fluorescent silver nanocluster composite material in fluorescent ink. The preparation method comprises the following steps: by taking renewable resource cellulose powder as a raw material, carrying out acid hydrolysis and formylation treatment to prepare formyl modified cellulose nanocrystals; and uniformly mixing a silver source and a protective ligand, adding the aldehyde group modified cellulose nanocrystal as a stabilizer and a reducing agent, and preparing the aldehyde group modified cellulose nanocrystal-based fluorescent silver nanocluster composite material in an ultraviolet radiation manner. The composite material has a good photoluminescence characteristic, can emit orange red fluorescence under the irradiation of 365nm ultraviolet light, has a remarkable anti-counterfeiting effect, and can be used for preparing fluorescent ink, anti-counterfeiting printing, decorative printing and dyeing and the like.

Description

Technical Field

[0001] The present invention relates to the field of preparation of fluorescent ink, and in particular to the preparation of a fluorescent silver nanocluster composite material and the application of the same in fluorescent ink. Background Art

[0002] In the digital economy, the intersection of commodity circulation and information security has become a global issue. With the continuous advancement of counterfeiting technology, traditional anti-counterfeiting methods have gradually exposed the flaws of easy imitation and one-way verification in key areas such as food and drug traceability, financial instrument authentication, and intellectual property protection. To address this challenge, traditional methods such as holograms, watermarks, and gravure printing have emerged. However, with the research and development of precious metal nanoclusters over the past 20 years, silver nanoclusters, as a new type of photoluminescent material, are expected to drive the continuous development of security printing inks due to their unique physical, chemical, and optical properties. Current mainstream fluorescent inks rely on the photoluminescence effect of rare earth complexes or organic dyes. While they can achieve basic encryption functions, they are relatively easy to be cracked by skilled counterfeiters and cannot meet the stringent material stability and multi-level encryption requirements of high-security scenarios. Developing new fluorescent inks with silver nanoclusters close to the Fermi wavelength (<2nm) will help break through existing technological barriers and build the next generation of intelligent anti-counterfeiting systems.

[0003] As the renewable bio-based material with the greatest potential for large-scale application, cellulose can be processed in various ways to produce functionalized forms such as cellulose nanocrystals (CNCs), bacterial cellulose (BC), and cellulose nanofibrils (CNFs). CNCs, which almost exclusively possess crystalline regions, are often spindle-shaped, with fiber diameters ranging from 5nm to 50nm and lengths from 100nm to 500nm. They possess high specific surface area, high hydrophilicity, a high Young's modulus, and an ultrafine structure, making them suitable for modification and use as a reducing agent in the preparation of silver nanoclusters. Furthermore, their rheological properties are consistent with those of pseudoplastic fluids, facilitating the subsequent preparation of inks.

[0004] Although the current fluorescent ink system has achieved functional expansion through multiple synthesis pathways and component design, it is subject to common defects such as dependence on toxic solvents, complicated synthesis procedures and complex processes. The problem of insufficient anti-photobleaching performance is particularly prominent, which seriously restricts large-scale production and long-term anti-counterfeiting applications. For example, the Chinese patent application with application number 202411194531.9 discloses a nanoparticle, its preparation method and fluorescent ink use. It mainly uses polyacrylic acid to modify the surface of lanthanide rare earth-doped NaYF4 upconversion nanoparticles, but its preparation steps are relatively cumbersome and its practical application potential is general. The Chinese patent with patent number 201910839403.8 discloses a method for preparing a cellulose nanocrystal-loaded silver nanocluster composite material. It mainly uses ferric chloride to catalyze the hydrolysis of bleached wood pulp with citric acid to prepare citric acid-modified CNC, and prepares silver nanoclusters by light induction, but the addition of catalysts during its preparation does not conform to the direction of green chemistry. Chinese patent No. 202211265820.4 discloses a high-stability silver nanocluster fluorescent probe and its preparation method and application. Silver nanoclusters are synthesized by mixing aldehyde-modified nanocellulose solution, silver ammonia solution and penicillamine solution for the detection of heavy metal ions; Chinese patent No. 202211266642.7 discloses the preparation of a silver nanocluster fluorescent composite membrane and its application in the detection of heavy metals. Silver nanocluster micelles are obtained by mixing aldehyde-modified nanocellulose solution, silver ammonia solution and glutathione solution and stirring them thoroughly to obtain silver nanocluster micelles, and the silver nanocluster micelles are evenly mixed with glucose solution to obtain a composite membrane; however, these two preparation methods use natural ripening at room temperature and rely only on aldehyde groups to complete the reaction, which has the problems of low efficiency, low fluorescence intensity, short fluorescence lifetime and low quantum yield.

[0005] Given the application potential of silver nanoclusters in biosensors, cell imaging, and catalytic conversion, scholars are working hard to expand the application of silver nanoclusters. However, there are currently no reports on the preparation of silver nanocluster fluorescent inks using ultraviolet irradiation in conjunction with aldehyde-modified cellulose nanocrystals as reducing agents and stabilizers. Summary of the Invention

[0006] The primary purpose of the present invention is to overcome the shortcomings and deficiencies of the prior art and to provide a method for preparing an aldehyde-modified cellulose nanocrystal-based fluorescent silver nanocluster composite material.

[0007] The second object of the present invention is to provide an aldehyde-modified cellulose nanocrystal-based fluorescent silver nanocluster composite material prepared by the method.

[0008] The third object of the present invention is to provide an application of the aldehyde-modified cellulose nanocrystal-based fluorescent silver nanocluster composite material.

[0009] A fourth object of the present invention is to provide a method for preparing silver nanocluster fluorescent ink.

[0010] The fifth object of the present invention is to provide silver nanocluster fluorescent ink prepared by the method.

[0011] A sixth object of the present invention is to provide applications of the silver nanocluster fluorescent ink.

[0012] The purpose of the present invention is achieved through the following technical solutions:

[0013] A method for preparing an aldehyde-modified cellulose nanocrystal-based fluorescent silver nanocluster composite material comprises the following steps:

[0014] (1) hydrolyzing cellulose powder with acid to obtain cellulose nanocrystals, and then performing an aldehyde treatment to obtain aldehyde-modified cellulose nanocrystals;

[0015] (2) stirring and mixing the silver source and the protective ligand uniformly, then adding the aldehyde-modified cellulose nanocrystals (as a stabilizer and a reducing agent) obtained in step (1) and continuing to stir and mix uniformly, then using ultraviolet irradiation to perform ultraviolet irradiation under stirring conditions, and finally dialyzing to obtain an aldehyde-modified cellulose nanocrystal-based fluorescent silver nanocluster composite material; wherein the molar ratio of the silver source (calculated as the molar mass of silver nitrate), the protective ligand and the aldehyde content in the aldehyde-modified cellulose nanocrystals is 10:(5-9):(1-9).

[0016] The particle size of the cellulose powder in step (1) is 25 to 65 μm, preferably 25 μm.

[0017] The acid described in step (1) is one or more of sulfuric acid, phosphoric acid, hydrochloric acid and nitric acid; preferably sulfuric acid; more preferably an aqueous sulfuric acid solution with a concentration of 62 to 65% by mass; and even more preferably an aqueous sulfuric acid solution with a concentration of 64% by mass.

[0018] The mass ratio of the cellulose powder to the acid in step (1) is 1:(5-20); preferably 1:10.

[0019] The acid hydrolysis in step (1) is preferably achieved by the following steps: adding cellulose powder to an acid solution, performing acid hydrolysis at 50°C to 60°C under stirring conditions, cooling after hydrolysis, adding water for precipitation, centrifugation for washing, and dialysis to obtain cellulose nanocrystals.

[0020] The acid hydrolysis time is 40 to 60 minutes, preferably 50 minutes.

[0021] The stirring speed is 200 rpm to 800 rpm, preferably 500 rpm.

[0022] The cooling time is 1 to 4 hours, preferably 2 hours.

[0023] The precipitation is carried out by adding 5 to 15 times the volume of deionized water; preferably, 10 times the volume of deionized water is added for precipitation.

[0024] The centrifugation is achieved by the following steps: the centrifuge speed is 8000-1000 rpm (preferably 8000 rpm), the centrifugation time is 5-10 min (preferably 8 min), after each centrifugation, the supernatant is poured out and deionized water is added, and this is repeated three or more times, and the supernatant after the fourth time is taken.

[0025] The dialysis is performed using a dialysis bag with a molecular weight cut-off of 8000 to 14000 Da until the pH value of the solution is 7.

[0026] The dialysate used in the dialysis is ultrapure water or deionized water.

[0027] The size of the cellulose nanocrystals described in step (1) is: length ≤ 600 nm, diameter ≤ 20 nm; preferably: length 100-600 nm, diameter 2-20 nm; more preferably: length 200-400 nm, diameter 2-20 nm; further preferably: length 200-300 nm, diameter 4-10 nm; further preferably: length 300 nm, diameter 8 nm.

[0028] The aldehyde treatment described in step (1) is preferably achieved by the following steps: mixing cellulose nanocrystals with periodate, reacting in a water bath at 50°C to 60°C under a protective gas atmosphere, adding ethylene glycol to terminate the reaction after the reaction is completed, and dialyzing to obtain aldehyde-modified cellulose nanocrystals.

[0029] The periodate is preferably sodium periodate. After the periodate is added, the reaction can be carried out with or without light shielding during stirring; preferably, the reaction is carried out in the dark.

[0030] The mass ratio of the cellulose nanocrystals to periodate is 1:(1-3); preferably 1:1.5.

[0031] The protective gas is preferably nitrogen.

[0032] The water bath reaction is carried out under stirring conditions at a rotation speed of 200 rpm to 800 rpm (preferably 200 rpm to 600 rpm; more preferably 600 rpm).

[0033] The water bath reaction time is 4 to 6 hours.

[0034] The amount of ethylene glycol used is 0.1 to 0.2 times the volume of the reaction system.

[0035] The dialysis is performed using a dialysis bag with a molecular weight cutoff of 8000 to 14000Da; preferably, the dialysis is performed using a dialysis bag with a molecular weight cutoff of 8000 to 14000Da for more than 72 hours.

[0036] The dialysate used in the dialysis is ultrapure water or deionized water.

[0037] The size of the aldehyde-modified cellulose nanocrystals described in step (1) is: length ≤ 500 nm, diameter ≤ 20 nm; preferably: length 100-500 nm, diameter 2-16 nm; more preferably: length 200-400 nm, diameter 2-16 nm; more preferably: length 200-300 nm, diameter 4-8 nm; further preferably: length 200 nm, diameter 6 nm.

[0038] The aldehyde content of the aldehyde-modified cellulose nanocrystals in step (1) is 1 to 10 mmol / g, preferably 10 mmol / g.

[0039] The silver source described in step (2) is at least one of silver nitrate and silver ammonia solution; preferably silver ammonia solution.

[0040] The silver ammonia solution is preferably prepared by the following method: slowly adding an aqueous ammonia solution with a concentration of 25-28% by mass to a 100 mmol / L silver nitrate solution until the brown precipitate produced by the initial addition of the ammonia solution becomes transparent.

[0041] The protective ligand in step (2) is one or more of reduced glutathione, mercaptonicotinic acid, oxidized glutathione and mercaptosuccinic acid; preferably reduced glutathione.

[0042] The molar ratio of the silver source (calculated as molar mass of silver nitrate), the protective ligand and the aldehyde content in the aldehyde-modified cellulose nanocrystals described in step (2) is preferably 10:9:9.

[0043] In step (2), the silver source and the protective ligand are first blended and stirred, and then the aldehyde-modified cellulose nanocrystals are added and stirred evenly. This is necessary in order to allow the protective ligand to preferentially wrap the silver source. The stirring and mixing are carried out at room temperature (25-30°C).

[0044] The stirring and mixing conditions in step (2) are: a rotation speed of 600 to 1500 rpm, and a time of 1 to 60 min; preferably, a rotation speed of 600 to 1500 rpm, and a time of 5 to 20 min; more preferably, a rotation speed of 1000 rpm, and a time of 10 min.

[0045] The power of the ultraviolet irradiation in step (2) is 16 to 64 W, preferably 48 W.

[0046] The wavelength of the ultraviolet radiation in step (2) is 254 nm to 365 nm, preferably 365 nm.

[0047] The ultraviolet irradiation time in step (2) is 1 to 360 minutes, preferably 40 to 180 minutes, and more preferably 60 minutes.

[0048] In step (2), the stirring speed for ultraviolet irradiation under stirring conditions is 800 to 1200 rpm, preferably 1000 rpm.

[0049] The dialysis described in step (2) is performed using a dialysis bag with a molecular weight cutoff of 8000 to 14000Da; preferably, the dialysis is performed using a dialysis bag with a molecular weight cutoff of 8000 to 14000Da for 12 to 36 hours; more preferably, the dialysis is performed using a dialysis bag with a molecular weight cutoff of 8000 to 14000Da for 24 hours.

[0050] The dialysate used for the dialysis described in step (2) is ultrapure water or deionized water.

[0051] An aldehyde-modified cellulose nanocrystal-based fluorescent silver nanocluster composite material is prepared by any of the methods described above.

[0052] Application of the aldehyde-modified cellulose nanocrystal-based fluorescent silver nanocluster composite material in the preparation of fluorescent ink.

[0053] A silver nanocluster fluorescent ink comprises the following components by mass percentage: 10-25% polyethylene glycol, 5-15% anhydrous ethanol, 2-8% glycerol and the balance aldehyde-modified cellulose nanocrystal-based fluorescent silver nanocluster composite material.

[0054] In the silver nanocluster fluorescent ink, the total mass of the aldehyde-modified cellulose nanocrystal-based fluorescent silver nanocluster composite material, polyethylene glycol, anhydrous ethanol and glycerol is 100%.

[0055] The polyethylene glycol is preferably polyethylene glycol 4000.

[0056] The silver nanocluster fluorescent ink preferably comprises the following components, calculated by mass percentage: 25% polyethylene glycol, 15% anhydrous ethanol, 5% glycerol and the remainder aldehyde-modified cellulose nanocrystal-based fluorescent silver nanocluster composite material.

[0057] The preparation method of the silver nanocluster fluorescent ink comprises the following steps: uniformly mixing polyethylene glycol, anhydrous ethanol, glycerol and an aldehyde-modified cellulose nanocrystal-based fluorescent silver nanocluster composite material, and stirring until completely dissolved to obtain the silver nanocluster fluorescent ink.

[0058] The stirring conditions are: a rotation speed of 200 to 800 rpm, and a stirring time of 8 to 24 hours; preferably: a rotation speed of 600 to 800 rpm, and a stirring time of 24 hours.

[0059] The stirring until the mixture is completely dissolved is carried out at room temperature (25-30° C.).

[0060] The silver nanocluster fluorescent ink is used in anti-counterfeiting printing, decorative printing and dyeing, or the preparation of information anti-counterfeiting products.

[0061] The anti-counterfeiting printing includes screen printing, lithography, gravure printing and inkjet printing.

[0062] The information anti-counterfeiting product can be applied to the field of security and anti-counterfeiting, including but not limited to the security information anti-counterfeiting of banknotes, important certificates, legal documents and branded goods.

[0063] The present invention has the following advantages and effects compared to the prior art:

[0064] (1) The preparation method provided by the present invention uses renewable resources (cellulose powder) as raw materials to prepare aldehyde-modified cellulose nanocrystals. The raw materials have biodegradable properties, and the preparation method exhibits advantages such as environmental friendliness, low biotoxicity and sustainability.

[0065] (2) In the silver nanocluster fluorescent ink prepared by the present invention, the silver nanoclusters have good photoluminescence properties and emit strong orange-red fluorescence under 365nm ultraviolet light, with significant anti-counterfeiting effect; in addition, the special rheological and thixotropic properties of the aldehyde-modified cellulose nanocrystals not only improve the rheological properties of the ink, but also effectively improve the dispersion uniformity of the ink and significantly improve the rapid prototyping efficiency, thereby enhancing the printability and the apparent quality of the finished product.

[0066] (3) The silver nanocluster fluorescent ink prepared by the present invention has uniform texture and small particle size, which can meet the relevant industry performance standards. It avoids the shortcomings of traditional fluorescent inks such as containing radioactive elements, slight toxicity and being environmentally unfriendly, and achieves the advantages of high fluorescence intensity, good color rendering performance, beautiful printed patterns and strong resistance to light bleaching.

[0067] (4) The ink of the present invention is used to produce anti-counterfeiting products, and has the technical characteristics of simple process, excellent information concealment, and excellent detectability. It has a wide range of printing suitability and is compatible with various printing process systems such as screen printing, lithography, gravure printing and inkjet printing, and has good potential for industrial promotion. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] Figure 1 This is a scanning tunneling electron microscopy image of the aldehyde-modified cellulose nanocrystal-based fluorescent silver nanocluster composite material provided in Example 6 of the present invention.

[0069] Figure 2 This is a transmission electron microscopy image of the aldehyde-modified cellulose nanocrystal-based fluorescent silver nanocluster composite material provided in Example 6 of the present invention.

[0070] Figure 3 This is a particle size distribution diagram of silver nanoclusters in the aldehyde-modified cellulose nanocrystal-based fluorescent silver nanocluster composite material provided in Example 6 of the present invention.

[0071] Figure 4 This is a fluorescence excitation and emission spectrum diagram of the aldehyde-modified cellulose nanocrystal-based fluorescent silver nanocluster composite material provided in Example 6 of the present invention.

[0072] Figure 5 This is a physical picture of the aldehyde-modified cellulose nanocrystal-based fluorescent silver nanocluster composite material provided in Example 6 of the present invention and Comparative Examples 1 to 4 observed under ultraviolet light irradiation (365nm, 48W) (under a black background).

[0073] Figure 6 This is a graph showing the thixotropic performance test results of the cellulose nanocrystal-based fluorescent silver nanocluster composite ink without the addition of aldehyde-modified cellulose nanocrystals in Comparative Example 5 of the present invention.

[0074] Figure 7 This is a graph showing the thixotropic performance test results of the silver nanocluster fluorescent ink in Example 6 of the present invention.

[0075] Figure 8 These are actual screen-printed images of the silver nanocluster fluorescent ink in Example 6 of the present invention; wherein, a is under visible light; b to d are actual digital images under ultraviolet light irradiation (365 nm, 48 W) after screen printing. DETAILED DESCRIPTION

[0076] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention. It should be understood that the specific embodiments described are only used to explain the present application and are not intended to limit the present application. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the art. In the embodiments of the present invention, those without specific conditions are carried out according to conventional conditions or the conditions recommended by the manufacturer. The raw materials, reagents, etc. used without indicating the manufacturer are conventional products that can be purchased commercially.

[0077] The size of the aldehyde-modified cellulose nanocrystals used in the examples and comparative examples of the present application is: 100 to 500 nm in length and 2 to 16 nm in diameter. They are prepared by the following method:

[0078] (1) Cellulose powder (25 μm to 65 μm, preferably 25 μm, purchased from Shanghai MacLean Biochemical Technology Co., Ltd.) was added to a 62-65% by mass aqueous solution of sulfuric acid (preferably 64% by mass) and mixed uniformly, wherein the mass ratio of cellulose powder to sulfuric acid aqueous solution was 1:5-1:20 (preferably 1:10). Hydrolysis was carried out at 55°C for 50 min (stirring speed was 200 rpm to 800 rpm; preferably 500 rpm), cooled for 1-4 h (preferably 2 h), and 10 times the volume of deionized water was added for precipitation. The mixture was then centrifuged at a speed of 8000 rpm for 8 min. After each centrifugation, the supernatant was discarded and deionized water was added. This was repeated three times. The fourth supernatant was taken for use. The mixture was dialyzed using a dialysis bag with a molecular weight cutoff of 8000-14000 Da to a solution pH of 7. The dialyzate was ultrapure water to obtain cellulose nanocrystals. The cellulose nanocrystals had a size of 100-600 nm in length and 2-20 nm in diameter.

[0079] (2) Cellulose nanocrystals and sodium periodate were reacted in a nitrogen-protected water bath at a mass ratio of 1:1.5 at 50°C for 4 to 6 hours (reaction speed 200 to 600 rpm), and 0.1 times the volume of ethylene glycol was added to terminate the reaction. The cellulose nanocrystals were dialyzed again for 72 hours using a dialysis bag with a molecular weight cutoff of 8000 to 14000 Da. The dialysate was ultrapure water, and aldehyde-modified cellulose nanocrystals rich in aldehyde groups at the C2 and C3 sites were obtained, with an aldehyde content of 10 mmol / g.

[0080] The fluorescence intensity involved in the examples and comparative examples of the present invention was measured by fluorescence spectrometer, and the fluorescence lifetime was measured by transient fluorescence spectrometer (all results were repeated three times).

[0081] The relative quantum yields involved in the examples and comparative examples of the present invention were measured by ultraviolet and fluorescence spectrometers using a sulfo-Cy5 fluorescent dye (1 μg / mL of Cy5 carboxylic acid has an absorbance of 0.012 and a quantum yield of 28%) as a control, and were calculated using the following formula (repeated three times):

[0082] Yu=(Ys*Fu*As) / (Fs*Au);

[0083] Yu, Ys: fluorescence quantum yields of the analyte and reference standard substances;

[0084] Fu, Fs: integrated fluorescence intensity of the test substance and reference substance;

[0085] Au, As: are the absorbances of the incident light of the test substance and the reference substance at the excitation wavelength (A=εbc) (the absorbances As and Au are lower than 0.05).

[0086] The water used in the examples and comparative examples of the present invention is ultrapure water.

[0087] Unless otherwise specified, the room temperature described in the examples and comparative examples of the present invention is 25-30°C.

[0088] The silver ammonia solution (Ag(NH3)2OH) involved in the embodiments and comparative examples of the present invention is obtained by reacting silver nitrate and ammonia water. The specific method is as follows: 100 mmol / L silver nitrate solution is prepared, and an ammonia aqueous solution with a mass fraction of 25-28% is slowly added thereto until the brown precipitate produced when the ammonia water is just started to be added becomes transparent, indicating that the preparation of the silver ammonia solution (Ag(NH3)2OH) is complete.

[0089] Example 1

[0090] This embodiment provides a method for preparing a silver nanocluster fluorescent ink, which specifically includes the following steps:

[0091] (1) At room temperature, silver ammonia solution (silver source) and reduced glutathione (protective ligand) were mixed and stirred for 15 minutes (speed 1000 rpm), and then aldehyde-modified cellulose nanocrystals (stabilizer and reducing agent) were added and continued to stir evenly (according to the molar ratio of silver ammonia solution (calculated as silver nitrate molar mass): reduced glutathione: aldehyde-modified cellulose nanocrystals (calculated as aldehyde content) was 10:5:3). The mixture was irradiated with an ultraviolet lamp (365 nm, 48 W) for 40 minutes under stirring (speed 1000 rpm), and dialyzed for 24 hours using a dialysis bag with a molecular weight cutoff of 8000-14000 Da (dialysis fluid was ultrapure water) to obtain an aldehyde-modified cellulose nanocrystal-based fluorescent silver nanocluster composite material.

[0092] (2) 10% polyethylene glycol 4000, 5% anhydrous ethanol, 2% glycerol and the remainder aldehyde-modified cellulose nanocrystal-based fluorescent silver nanocluster composite material were mixed uniformly by mass percentage, and stirred at 200 rpm for 8 h at room temperature until completely dissolved to obtain silver nanocluster fluorescent ink.

[0093] The fluorescence emission peak of the aldehyde-modified cellulose nanocrystal-based fluorescent silver nanocluster composite material is around 585 nm. When observed under ultraviolet light (365 nm, 48 W) against a black background, it exhibits a weak orange-red fluorescence with a fluorescence intensity of 5.15×10 6 The relative quantum yield is 11.41% and the fluorescence lifetime is 2.893ns.

[0094] Example 2

[0095] This embodiment provides a method for preparing a silver nanocluster fluorescent ink, which specifically includes the following steps:

[0096] (1) At room temperature, silver ammonia solution (silver source) and reduced glutathione (protective ligand) were mixed and stirred for 20 min (speed 1000 rpm), and then aldehyde-modified cellulose nanocrystals (stabilizer and reducing agent) were added and continued to stir evenly (according to the molar ratio of silver ammonia solution (calculated as silver nitrate molar mass): reduced glutathione: aldehyde-modified cellulose nanocrystals (calculated as aldehyde content) was 10:5:5). The mixture was irradiated with an ultraviolet lamp (365 nm, 48 W) under stirring (speed 1000 rpm) for 60 min, and dialyzed for 24 h using a dialysis bag with a molecular weight cutoff of 8000-14000 Da (dialysis fluid was ultrapure water) to obtain an aldehyde-modified cellulose nanocrystal-based fluorescent silver nanocluster composite material.

[0097] (2) 15% polyethylene glycol 4000, 10% anhydrous ethanol, 3% glycerol and the remainder aldehyde-modified cellulose nanocrystal-based fluorescent silver nanocluster composite material were mixed uniformly by mass percentage, and stirred at 300 rpm for 10 h at room temperature until completely dissolved to obtain silver nanocluster fluorescent ink.

[0098] The fluorescence emission peak of the aldehyde-modified cellulose nanocrystal-based fluorescent silver nanocluster composite material is around 602 nm. When observed under ultraviolet light (365 nm, 48 W) against a black background, it exhibits orange-red fluorescence with a fluorescence intensity of 6.18×10 6 The relative quantum yield is 12.43% and the fluorescence lifetime is 3.006ns.

[0099] Example 3

[0100] This embodiment provides a method for preparing a silver nanocluster fluorescent ink, which specifically includes the following steps:

[0101] (1) At room temperature, silver ammonia solution (silver source) and reduced glutathione (protective ligand) were mixed and stirred for 20 min (speed 1000 rpm), and then aldehyde-modified cellulose nanocrystals (stabilizer and reducing agent) were added and continued to stir evenly (according to the molar ratio of silver ammonia solution (calculated as silver nitrate molar mass): reduced glutathione: aldehyde-modified cellulose nanocrystals (calculated as aldehyde content) was 10:7:1). The mixture was irradiated with an ultraviolet lamp (365 nm, 48 W) for 120 min under stirring (speed 1000 rpm), and dialyzed for 24 h using a dialysis bag with a molecular weight cutoff of 8000-14000 Da (dialysis fluid was ultrapure water) to obtain an aldehyde-modified cellulose nanocrystal-based fluorescent silver nanocluster composite material.

[0102] (2) 15% polyethylene glycol 4000, 15% anhydrous ethanol, 6% glycerol and the remainder aldehyde-modified cellulose nanocrystal-based fluorescent silver nanocluster composite material were mixed uniformly by mass percentage, and stirred at 400 rpm for 14 h at room temperature until completely dissolved to obtain silver nanocluster fluorescent ink.

[0103] The fluorescence emission peak of the aldehyde-modified cellulose nanocrystal-based fluorescent silver nanocluster composite material is around 583 nm. When observed under ultraviolet light (365 nm, 48 W) against a black background, it exhibits orange-red fluorescence with a fluorescence intensity of 5.25×10 6 The relative quantum yield is 12.52% and the fluorescence lifetime is 3.325ns.

[0104] Example 4

[0105] This embodiment provides a method for preparing a silver nanocluster fluorescent ink, which specifically includes the following steps:

[0106] (1) At room temperature, silver ammonia solution (silver source) and reduced glutathione (protective ligand) were mixed and stirred for 20 min (speed 1000 rpm), and then aldehyde-modified cellulose nanocrystals (stabilizer and reducing agent) were added and continued to stir evenly (according to the molar ratio of silver ammonia solution (calculated as silver nitrate molar mass): reduced glutathione: aldehyde-modified cellulose nanocrystals (calculated as aldehyde content) was 10:7:5). The mixture was irradiated with an ultraviolet lamp (365 nm, 48 W) under stirring (speed 1000 rpm) for 160 min, and dialyzed for 24 h using a dialysis bag with a molecular weight cutoff of 8000-14000 Da (dialysis fluid was ultrapure water) to obtain an aldehyde-modified cellulose nanocrystal-based fluorescent silver nanocluster composite material.

[0107] (2) 20% polyethylene glycol 4000, 15% anhydrous ethanol, 5% glycerol and the remainder aldehyde-modified cellulose nanocrystal-based fluorescent silver nanocluster composite material were mixed uniformly by mass percentage, and stirred at 500 rpm at room temperature for 12 h until completely dissolved to obtain silver nanocluster fluorescent ink.

[0108] The fluorescence emission peak of the aldehyde-modified cellulose nanocrystal-based fluorescent silver nanocluster composite material is around 601 nm. When observed under ultraviolet light (365 nm, 48 W) against a black background, it exhibits orange-red fluorescence with a fluorescence intensity of 7.23×10 6 The relative quantum yield is 13.45% and the fluorescence lifetime is 3.579ns.

[0109] Example 5

[0110] This embodiment provides a method for preparing a silver nanocluster fluorescent ink, which specifically includes the following steps:

[0111] (1) At room temperature, silver ammonia solution (silver source) and reduced glutathione (protective ligand) were mixed and stirred for 5 min (speed 1000 rpm), and then aldehyde-modified cellulose nanocrystals (stabilizer and reducing agent) were added and continued to stir evenly (according to the molar ratio of silver ammonia solution (calculated as silver nitrate molar mass): reduced glutathione: aldehyde-modified cellulose nanocrystals (calculated as aldehyde content) was 10:7:7). The mixture was irradiated with an ultraviolet lamp (365 nm, 48 W) under stirring (speed 1000 rpm) for 180 min, and dialyzed for 24 h using a dialysis bag with a molecular weight cutoff of 8000-14000 Da (dialysis fluid was ultrapure water) to obtain an aldehyde-modified cellulose nanocrystal-based fluorescent silver nanocluster composite material.

[0112] (2) 25% polyethylene glycol 4000, 10% anhydrous ethanol, 6% glycerol and the remainder aldehyde-modified cellulose nanocrystal-based fluorescent silver nanocluster composite material were mixed uniformly by mass percentage, and stirred at 700 rpm at room temperature for 18 h until completely dissolved to obtain silver nanocluster fluorescent ink.

[0113] The fluorescence emission peak of the aldehyde-modified cellulose nanocrystal-based fluorescent silver nanocluster composite material is around 590 nm. When observed under ultraviolet light (365 nm, 48 W) against a black background, it appears orange-red with a fluorescence intensity of 8.15×10 6 The relative quantum yield is 13.88% and the fluorescence lifetime is 3.689ns.

[0114] Example 6

[0115] This embodiment provides a method for preparing a silver nanocluster fluorescent ink, which specifically includes the following steps:

[0116] (1) At room temperature, silver ammonia solution (silver source) and reduced glutathione (protective ligand) were mixed and stirred for 10 min (speed 1000 rpm), and then aldehyde-modified cellulose nanocrystals (stabilizer and reducing agent) were added and continued to stir evenly (according to the molar ratio of silver ammonia solution (calculated as silver nitrate molar mass): reduced glutathione: aldehyde-modified cellulose nanocrystals (calculated as aldehyde content) was 10:9:9). The mixture was irradiated with an ultraviolet lamp (365 nm, 48 W) for 60 min under stirring (speed 1000 rpm), and dialyzed for 24 h using a dialysis bag with a molecular weight cutoff of 8000-14000 Da (dialysis fluid was ultrapure water) to obtain an aldehyde-modified cellulose nanocrystal-based fluorescent silver nanocluster composite material.

[0117] (2) 25% polyethylene glycol 4000, 15% anhydrous ethanol, 5% glycerol and the remainder aldehyde-modified cellulose nanocrystal-based fluorescent silver nanocluster composite material were mixed uniformly by mass percentage, and stirred at 800 rpm at room temperature for 24 h until completely dissolved to obtain silver nanocluster fluorescent ink.

[0118] The fluorescence emission peak of the aldehyde-modified cellulose nanocrystal-based fluorescent silver nanocluster composite material is around 688 nm. When observed under ultraviolet light (365 nm, 48 W) against a black background, it exhibits orange-red fluorescence with a fluorescence intensity of 1.87 × 10 7 The relative quantum yield is 14.5% and the fluorescence lifetime is 3.984ns.

[0119] Comparative Example 1

[0120] This comparative example provides a method for preparing a silver nanocluster ink, which specifically comprises the following steps:

[0121] (1) At room temperature, silver ammonia solution (silver source) and reduced glutathione (protective ligand) were mixed and stirred for 10 minutes (speed 1000 rpm), and then aldehyde-modified cellulose nanocrystals (stabilizer and reducing agent) were added and continued to stir evenly (according to the molar ratio of silver ammonia solution (calculated as silver nitrate molar mass): reduced glutathione: aldehyde-modified cellulose nanocrystals (calculated as aldehyde content) was 10:1:1). The mixture was irradiated with an ultraviolet lamp (365 nm, 48 W) under stirring (speed 1000 rpm) for 180 minutes, and dialyzed for 24 hours using a dialysis bag with a molecular weight cutoff of 8000-14000 Da (dialysis fluid was ultrapure water) to obtain an aldehyde-modified cellulose nanocrystal-based silver nanocluster composite material.

[0122] (2) 25% polyethylene glycol 4000, 15% anhydrous ethanol, 5% glycerol and the remainder aldehyde-modified cellulose nanocrystal-based fluorescent silver nanocluster composite material were mixed uniformly by mass percentage, and stirred at 800 rpm at room temperature for 24 h until completely dissolved to obtain silver nanocluster ink.

[0123] The aldehyde-modified cellulose nanocrystal-based silver nanocluster composite material has no fluorescence emission peak and has no color when observed against a black background under ultraviolet light (365 nm, 48 W).

[0124] Comparative Example 2

[0125] This comparative example provides a method for preparing a silver nanocluster ink, which specifically comprises the following steps:

[0126] (1) At room temperature, silver ammonia solution (silver source) and reduced glutathione (protective ligand) were mixed and stirred for 10 minutes (speed 1000 rpm), and then aldehyde-modified cellulose nanocrystals (stabilizer and reducing agent) were added and continued to stir evenly (according to the molar ratio of silver ammonia solution (calculated as silver nitrate molar mass): reduced glutathione: aldehyde-modified cellulose nanocrystals (calculated as aldehyde content) was 10:3:1). The mixture was irradiated with an ultraviolet lamp (365 nm, 48 W) under stirring (speed 1000 rpm) for 180 minutes, and dialyzed for 24 hours using a dialysis bag with a molecular weight cutoff of 8000-14000 Da (the dialysate was ultrapure water) to obtain an aldehyde-modified cellulose nanocrystal-based silver nanocluster composite material.

[0127] (2) 25% polyethylene glycol 4000, 15% anhydrous ethanol, 5% glycerol and the remainder aldehyde-modified cellulose nanocrystal-based fluorescent silver nanocluster composite material were mixed uniformly by mass percentage, and stirred at 800 rpm at room temperature for 24 h until completely dissolved to obtain silver nanocluster ink.

[0128] The aldehyde-modified cellulose nanocrystal-based silver nanocluster composite material has no fluorescence emission peak and has no color when observed against a black background under ultraviolet light (365 nm, 48 W).

[0129] Comparative Example 3

[0130] This comparative example provides a method for preparing a silver nanocluster fluorescent ink, which specifically comprises the following steps:

[0131] (1) At room temperature, silver ammonia solution (silver source) and reduced glutathione (protective ligand) were mixed and stirred for 10 min (rotation speed 1000 rpm), and then aldehyde-modified cellulose nanocrystals (stabilizer and reducing agent) were added and continued to stir evenly (according to the molar ratio of silver ammonia solution (calculated as silver nitrate molar mass): reduced glutathione: aldehyde-modified cellulose nanocrystals (calculated as aldehyde content) was 10:9:9). The mixture was naturally aged at room temperature for 24 h and dialyzed for 24 h using a dialysis bag with a molecular weight cutoff of 8000-14000 Da (the dialysate was ultrapure water) to obtain an aldehyde-modified cellulose nanocrystal-based fluorescent silver nanocluster composite material.

[0132] (2) 25% polyethylene glycol 4000, 15% anhydrous ethanol, 5% glycerol and the remainder aldehyde-modified cellulose nanocrystal-based fluorescent silver nanocluster composite material were mixed uniformly by mass percentage, and stirred at 800 rpm at room temperature for 24 h until completely dissolved to obtain silver nanocluster fluorescent ink.

[0133] The fluorescence emission peak of the aldehyde-modified cellulose nanocrystal-based fluorescent silver nanocluster composite material is around 671 nm. When observed under ultraviolet light (365 nm, 48 W) against a black background, it exhibits a weak orange-red fluorescence with a fluorescence intensity of 5.53 × 10 4 The relative quantum yield is 8.5% and the fluorescence lifetime is 1.688ns.

[0134] Comparative Example 4

[0135] This comparative example provides a method for preparing a silver nanocluster fluorescent ink, which specifically comprises the following steps:

[0136] (1) At room temperature, silver ammonia solution (silver source) and reduced glutathione (protective ligand) were mixed and stirred for 10 min (rotation speed 1000 rpm), and then aldehyde-modified cellulose nanocrystals (stabilizer and reducing agent) were added and continued to stir evenly (according to the molar ratio of silver ammonia solution (calculated as silver nitrate molar mass): reduced glutathione: aldehyde-modified cellulose nanocrystals (calculated as aldehyde content) was 10:5:3). The mixture was naturally aged at room temperature for 24 h and dialyzed for 24 h using a dialysis bag with a molecular weight cutoff of 8000-14000 Da (the dialysate was ultrapure water) to obtain an aldehyde-modified cellulose nanocrystal-based fluorescent silver nanocluster composite material.

[0137] (2) 25% polyethylene glycol 4000, 15% anhydrous ethanol, 5% glycerol and the remainder aldehyde-modified cellulose nanocrystal-based fluorescent silver nanocluster composite material were mixed uniformly by mass percentage, and stirred at 800 rpm at room temperature for 24 h until completely dissolved to obtain silver nanocluster fluorescent ink.

[0138] The fluorescence emission peak of the aldehyde-modified cellulose nanocrystal-based fluorescent silver nanocluster composite material is around 658 nm. When observed under ultraviolet light (365 nm, 48 W) against a black background, it exhibits a weak orange-red fluorescence with a fluorescence intensity of 2.21×10 4 The relative quantum yield is 6.5% and the fluorescence lifetime is 1.362ns.

[0139] Comparative Example 5

[0140] This comparative example provides a method for preparing an ink, which specifically comprises the following steps:

[0141] 25% polyethylene glycol 4000, 15% anhydrous ethanol, 5% glycerol and the balance ultrapure water were mixed uniformly by mass percentage, and stirred at 800 rpm at room temperature for 24 h until completely dissolved to obtain an ink without fluorescent silver nanoclusters.

[0142] Effect embodiment

[0143] 1. For the convenience of comparison, Examples 1 to 6 and Comparative Examples 1 to 5 are listed in Table 1.

[0144] From the comparison of Example 6 with Comparative Examples 3 and 4, it can be seen that the UV-synergistic aldehyde-modified cellulose nanocrystals can greatly improve the fluorescence intensity, quantum yield and fluorescence lifetime, which are extremely beneficial for its application as a silver nanocluster fluorescent ink.

[0145] Table 1

[0146]

[0147] 2. The inks prepared in Examples 1 to 6 and Comparative Examples 1 to 5 were subjected to the following tests:

[0148] (1) The scanning tunneling electron microscopy image of the aldehyde-modified cellulose nanocrystal-based fluorescent silver nanocluster composite material prepared in Example 6 of the present invention is as follows: Figure 1 As shown in the figure, the prepared silver nanoclusters are evenly attached to the aldehyde-modified cellulose nanocrystals. Figure 2 As shown in the figure, the prepared silver nanoclusters have uniform size and good dispersion. Figure 3As shown in the figure, the particle size of silver nanoclusters is between 1 and 3 nm, with an average particle size of 1.94 nm. The fluorescence excitation and emission spectra are shown in the figure. Figure 4 As shown in the figure, it can be seen that the excitation wavelength of the prepared aldehyde-modified cellulose nanocrystal-based fluorescent silver nanocluster composite material is 512nm, and the emission wavelength is 688nm, which belongs to orange-red fluorescence emission.

[0149] (2) The actual images of the aldehyde-modified cellulose nanocrystal-based fluorescent silver nanocluster composite materials prepared in Example 6 of the present invention and Comparative Examples 1 to 4 observed under ultraviolet light irradiation (365nm, 48W) are as follows: Figure 5 As shown: it can be clearly observed that comparative examples 1 and 2 have no fluorescence generation, and comparative examples 3 and 4 have weak fluorescence intensity.

[0150] (3) The thixotropic performance of the ink sample prepared without adding aldehyde-modified cellulose nanocrystals in Comparative Example 5 of the present invention was tested, wherein the low shear γ1 was set to 2s -1 The rate lasts for 60s to simulate the static state of ink; high shear γ2 is taken for 1000s -1 The rate lasts for 20s, simulating the shear environment of the scraper channel; the third stage low shear γ3 recovery 2s -1 The rate was set at 105s to simulate the structural reformation of the ink after printing. The experiment was repeated three times. Figure 6 As shown in the curve, the first low-shear stage occurs from 0 to 60 seconds, followed by a high-shear phase from 60 to 80 seconds, and a return to the third low-shear phase from 80 to 185 seconds. Ink samples without aldehyde-modified cellulose nanocrystals exhibit no significant viscosity fluctuations with shear rate, exhibiting typical Newtonian fluid characteristics. This rheological property is unsuitable for water-based ink systems.

[0151] (4) The silver nanocluster fluorescent ink prepared in Example 6 of the present invention was subjected to a thixotropic performance test, wherein the test parameters were set as follows: low shear γ1 with 2s -1 The speed was run for 60s to simulate the static state, and the high shear γ2 was run for 1000s -1 The speed runs for 20s to simulate the scraper shear environment, and the low shear γ3 runs for 2s -1 The speed was 105s to simulate the post-printing structural reformation process. The experiment was repeated three times. Figure 7 As shown: The test curve shows that the ink with the addition of aldehyde-modified cellulose nanocrystals exhibits significant shear thinning behavior and presents typical non-Newtonian fluid characteristics: when the ink is subjected to high-speed shear, the viscosity decreases, and good fluidity is obtained to achieve efficient transfer; and when it is transferred to the surface of the substrate and the external shear force disappears, the ink viscosity quickly recovers, effectively preventing the ink from diffusing to the surrounding area, ensuring the formation of clear and regular printing marks on the paper surface.

[0152] (5) The actual screen printing of the silver nanocluster fluorescent ink in Example 6 of the present invention is shown in the figure below. Figure 8 As shown: it can be clearly observed that the printed pattern is clear and the fluorescent anti-counterfeiting effect is good, which proves the practical application potential of the present invention in security anti-counterfeiting ink.

[0153] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A method for preparing an aldehyde-modified cellulose nanocrystal-based fluorescent silver nanocluster composite material, characterized in that: The following steps are involved: (1) hydrolyzing cellulose powder with acid to obtain cellulose nanocrystals, and then performing an aldehyde treatment to obtain aldehyde-modified cellulose nanocrystals; (2) stirring and mixing the silver source and the protective ligand uniformly, then adding the aldehyde-modified cellulose nanocrystals obtained in step (1) and continuing to stir and mix uniformly, then using ultraviolet irradiation to irradiate the mixture under stirring conditions, and finally dialyzing to obtain an aldehyde-modified cellulose nanocrystal-based fluorescent silver nanocluster composite material; wherein the molar ratio of the silver source, the protective ligand and the aldehyde content in the aldehyde-modified cellulose nanocrystals is 10:5-9:1-9.

2. The preparation method according to claim 1, wherein: The silver source in step (2) is at least one of silver nitrate and silver ammonia solution; The protective ligand in step (2) is one or more of reduced glutathione, mercaptonicotinic acid, oxidized glutathione and mercaptosuccinic acid.

3. The preparation method according to claim 1, wherein: The power of the ultraviolet irradiation in step (2) is 16 to 64 W; The wavelength of the ultraviolet irradiation in step (2) is 254 nm to 365 nm; The ultraviolet irradiation time in step (2) is 1 to 360 minutes.

4. The preparation method according to claim 3, wherein: The power of the ultraviolet irradiation in step (2) is 48W; The wavelength of the ultraviolet irradiation in step (2) is 365 nm; The ultraviolet irradiation time in step (2) is 40 to 180 minutes.

5. The preparation method according to claim 1, wherein: The particle size of the cellulose powder in step (1) is 25 to 65 μm; The acid in step (1) is one or more of sulfuric acid, phosphoric acid, hydrochloric acid and nitric acid; The mass ratio of the cellulose powder to the acid in step (1) is 1:5-20; The size of the cellulose nanocrystals in step (1) is: length ≤ 600 nm, diameter ≤ 20 nm; The size of the aldehyde-modified cellulose nanocrystals in step (1) is: length ≤ 500 nm, diameter ≤ 20 nm; The aldehyde content of the aldehyde-modified cellulose nanocrystals in step (1) is 1 to 10 mmol / g; In step (2), the stirring speed of the ultraviolet irradiation is 800 to 1200 rpm under stirring conditions; The dialysis in step (2) is performed using a dialysis bag with a molecular weight cut-off of 8000 to 14000 Da; In step (2), the dialysate used for dialysis is ultrapure water or deionized water.

6. An aldehyde-modified cellulose nanocrystal-based fluorescent silver nanocluster composite material, characterized by: It is prepared by the method according to any one of claims 1 to 5.

7. Use of the aldehyde-modified cellulose nanocrystal-based fluorescent silver nanocluster composite material according to claim 6 in the preparation of fluorescent ink.

8. A silver nanocluster fluorescent ink, characterized in that: The composition comprises the following components by mass percentage: 10-25% polyethylene glycol, 5-15% anhydrous ethanol, 2-8% glycerol, and the balance is the aldehyde-modified cellulose nanocrystal-based fluorescent silver nanocluster composite material according to any one of claims 1 to 5; The polyethylene glycol is further polyethylene glycol 4000.

9. The method for preparing the silver nanocluster fluorescent ink according to claim 8, wherein: The following steps are involved: Polyethylene glycol, anhydrous ethanol, glycerol and aldehyde-modified cellulose nanocrystal-based fluorescent silver nanocluster composite material are evenly mixed and stirred until completely dissolved to obtain silver nanocluster fluorescent ink.

10. Use of the silver nanocluster fluorescent ink according to claim 8 in anti-counterfeiting printing, decorative printing and dyeing, or preparation of information anti-counterfeiting products, characterized in that: The anti-counterfeiting printing includes at least one of screen printing, lithography, gravure printing and inkjet printing.

Images