Regenerated cellulose fluorescent sensing membrane material as well as preparation method and application thereof

Abstract

The invention discloses a regenerated cellulose fluorescent sensing film material as well as a preparation method and application thereof, and belongs to the fields of a biomass functional material preparation technology and food safety detection. The vinyl COFs with the pH response performance are prepared by taking a monomer containing an active methylene hydrogen structure and an aldehyde group monomer as raw materials and trifluoroacetic acid or potassium hydroxide as a catalyst through a Knoevenagel condensation reaction under a solvothermal condition. Meanwhile, a regenerated cellulose fluorescent sensing membrane material is prepared by combining the cellulose and regenerated cellulose through hydrogen-bond interaction, can be used as a high-sensitivity fluorescent sensor for pH and NH3, and has the advantages of being green, pollution-free, high in sensitivity, stable in response characteristic and the like. According to the present invention, the combination of the regenerated cellulose and the COF material is achieved, the preparation strategy based on the biomass-based renewable fluorescence sensing platform is provided, and the biomass-based renewable fluorescence sensing platform is innovatively used in the food spoilage monitoring field.

Description

Technical Field

[0001] The present invention belongs to the fields of biomass functional material preparation technology and food safety detection, and specifically relates to a regenerated cellulose fluorescent sensing membrane material and a preparation method and application thereof. Background Art

[0002] The information disclosed in this background technology section is only intended to enhance understanding of the overall background of the invention and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to those skilled in the art.

[0003] Against the backdrop of rapid industrial development, pH and NH3 testing are crucial in environmental safety, industrial production, and food safety. pH is a key parameter reflecting the acidity and alkalinity of water, soil, and atmosphere, while NH3, as a common harmful pollutant, not only affects pollution control but is also released during food storage, posing a serious threat to food safety.

[0004] However, existing pH and NH3 detection methods (such as pH meters, chromatography, electrochemistry, and biological methods) have limitations that hinder their application in food safety and are difficult to use for food spoilage monitoring. Therefore, the development of green and efficient pH-responsive and NH3 detection platforms that can be applied to food spoilage monitoring is an urgent issue. Summary of the Invention

[0005] To address the shortcomings of the existing technology, the present invention provides a regenerated cellulose fluorescent sensing membrane material, its preparation method, and its application. Specifically, vinyl COFs are synthesized via a Knoevenagel condensation reaction. These COFs are then incorporated into the hydrogen-bonded network of regenerated cellulose to prepare a cellulose-based porous membrane material. This material has been applied to the study of highly sensitive fluorescence responses for pH, NH3, and food spoilage monitoring.

[0006] The present invention uses monomers containing active methylene hydrogen structures and aldehyde monomers as raw materials, trifluoroacetic acid or potassium hydroxide as catalyst, and prepares vinyl COFs with pH-responsive properties through Knoevenagel condensation reaction under solvent thermal conditions. At the same time, it is combined with regenerated cellulose through hydrogen bonding to prepare a regenerated cellulose fluorescent sensing membrane material, which can be used as a highly sensitive fluorescent sensor for pH and NH3, and has the advantages of being green and pollution-free, highly sensitive, and having stable response characteristics. The present invention realizes the combination of regenerated cellulose and COF materials for the first time, proposes a preparation strategy based on a biomass-based renewable fluorescent sensing platform, and innovatively applies it to the field of food spoilage monitoring. The research results can provide theoretical support for the application of biomass-based composite materials in related fields.

[0007] In order to achieve the above object, the technical solution of the present invention is: In its first aspect, the present invention provides a regenerated cellulose fluorescent sensing membrane material comprising regenerated cellulose and vinyl COFs, with the mass ratio of regenerated cellulose to vinyl COFs being 50:1 to 100:1. A low vinyl COF content can affect sensing efficiency and detection range, hindering both data measurement and visual observation.

[0008] In the present invention, vinyl COFs and regenerated cellulose are blended in a homogeneous state, and subsequent infrared spectroscopy proves that the two are connected by hydrogen bonding. SEM proves that vinyl COFs and regenerated cellulose have an intertwined binding morphology. Therefore, the two are bound by hydrogen bonding, electrostatic attraction, van der Waals forces, etc.

[0009] The color of the regenerated cellulose fluorescent sensing membrane material is yellow or light yellow.

[0010] In the present invention, the regenerated cellulose membrane alone has no fluorescence properties; the vinyl COFs alone can be used to detect pH, and there is data to support its ability to respond to acidic and alkaline gases such as NH3 and HCl.

[0011] In a second aspect, the present invention provides a method for preparing the above-mentioned regenerated cellulose fluorescent sensing membrane material, comprising the following steps: The vinyl COFs dispersion and the cellulose solution are mixed and regenerated in a regeneration bath to obtain a mixed slurry of regenerated cellulose and vinyl COFs. The mixed slurry is filtered and dried.

[0012] In the preparation process, two monomers are connected via a carbon-carbon double bond through a condensation reaction, wherein the condensation reaction includes a Knoevenagel condensation reaction.

[0013] In one or more embodiments, vinyl covalent organic framework materials, namely vinyl COFs, are prepared using monomers containing active methylene hydrogen structures and aldehyde monomers as raw materials, using a solvent thermal method or a mechanical grinding method in the presence of a catalyst.

[0014] Furthermore, the monomer containing an active methylene hydrogen structure is one or more of 2,4,6-trimethyl-1,3,5-triazine (TMT; C6H9N3; CAS: 823-94-9), 2,5-dimethylpyrazine (C6H8N2; CAS: 123-32-0), and 2,4,6-tricyano-1,3,5-trimethylbenzene (C9H9N3; CAS: 1206-85-5).

[0015] Furthermore, the aldehyde monomer is terephthalaldehyde (TA; C8H6N2; CAS: 623-27-8), 4,4'-biphenyldicarboxaldehyde (BA; C 14 H10 O2; CAS: 66-98-8), 3,3'-dimethoxy-[1,1'-biphenyl]-4,4'-dicarbaldehyde (DHBA; C 16 H 14 O4; CAS: 27343-98-2), [1,1':4',1''-terphenyl]-4,4''-dicarboxaldehyde (TD; C 20 H 14 O2; CAS: 62940-38-9), trimesaldehyde (C9H6O3; CAS: 3163-76-6), 1,3,5-tris(4'-formylphenyl)benzene (C 27 H 18 O3; CAS: 118688-53-2), 1,3,5-triazine-2,4,6-tricarbaldehyde (C6H3N3O3, CAS: 1210045-03-6), 2,4,6-tris(4-formylphenyl)-1,3,5-triazine (C 24 H 15 N3O3; CAS: 443922-06-3) or more.

[0016] Furthermore, the catalyst is trifluoroacetic acid or potassium hydroxide.

[0017] Furthermore, the molar ratio of the monomer containing an active methylene hydrogen structure, the aldehyde monomer, and the catalyst is (0.2-0.6):(0.4-0.8):(0.4-0.8).

[0018] In one or more embodiments, the specific steps of the solvothermal method are as follows: a monomer containing an active methylene hydrogen structure, an aldehyde monomer, and a solvent are mixed, and the mixture is treated under an ultrasonic environment so that the monomer is fully dissolved in the solvent. A catalyst is then added, and the ultrasonic treatment is continued. The mixture is rapidly frozen in a liquid nitrogen bath, degassed through multiple freeze-thaw cycles, sealed under vacuum, and heated to react under certain conditions. The yellow precipitate is collected by vacuum filtration, and washed with N,N-dimethylformamide and tetrahydrofuran in sequence to remove unreacted precursors. Finally, the mixture is dried.

[0019] Before adding the catalyst, ultrasonic treatment is performed for 5 to 20 minutes as long as the monomer is fully dissolved in the solvent. After adding the catalyst, ultrasonic treatment is performed for 15 to 40 minutes as long as the catalyst is fully mixed.

[0020] Furthermore, the solvent used in the solvothermal method is one or more of n-butanol, tetrahydrofuran, N,N-dimethylformamide, o-dichlorobenzene, 1,4-dioxane, and dimethyl sulfoxide. For example, if the solvent is a mixed solution of n-butanol and o-dichlorobenzene, the volume ratio thereof is (8-14):(4-7). The ratio of the aldehyde monomer to the solvent is (100-150 mg):(10-20 mL), preferably (110-130 mg):(15-20 mL).

[0021] Furthermore, the solvothermal reaction temperature is 100-140°C, specifically 100°C, 110°C, 120°C, 130°C, or 140°C. The reaction time is 48-80 hours, specifically 48 hours, 36 hours, 40 hours, 50 hours, 60 hours, 70 hours, 72 hours, 74 hours, or 80 hours, preferably 70-74 hours. Under appropriate reaction conditions, the formation of vinyl COFs is more favorable.

[0022] Furthermore, the grinding conditions of the mechanical grinding method are grinding at room temperature for 5 to 20 minutes, specifically 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes, 10 minutes, 12 minutes, 14 minutes, 15 minutes, 16 minutes, 18 minutes, 20 minutes, etc. The most preferred grinding condition is 10 minutes.

[0023] In one or more embodiments, the vinyl COF dispersion and the cellulose solution are uniformly mixed under stirring or ultrasound. The stirring or ultrasound time is not specifically limited, as long as sufficient mixing is achieved and uniform mixing is achieved. For example, ultrasound can be performed for 10 to 40 minutes. Specifically, the stirring or ultrasound time can be 10 minutes, 20 minutes, 30 minutes, or 40 minutes.

[0024] In one or more embodiments, vinyl COFs are dispersed in an alcohol solvent to obtain a vinyl COFs dispersion. The alcohol is ethanol. The concentration of the vinyl COFs dispersion is 0.1 to 10 mg / mL. Specifically, it may be 0.1 mg / mL, 1 mg / mL, 2 mg / mL, 3 mg / mL, 4 mg / mL, 5 mg / mL, 6 mg / mL, 7 mg / mL, 8 mg / mL, 9 mg / mL, or 10 mg / mL. Preferably, it may be 5 to 10 mg / mL.

[0025] In one or more embodiments, the cellulose raw material and the solvent are mixed in a certain proportion, and the cellulose is dissolved in the solvent to obtain a cellulose solution.

[0026] The cellulose raw material is one or more of microcrystalline cellulose, pulp fiber, cotton fiber, and ramie fiber.

[0027] The solvent is one or more of NaOH / urea (NaOH / Ur), quaternary ammonium salt (such as tetramethylammonium hydroxide, etc.) / water, choline hydroxide / urea (ChOH / Ur), and choline hydroxide / urea / zinc glycinate (ChOH / Ur / ZG) systems.

[0028] The mass ratio of NaOH to urea in NaOH / Ur is 1:1 to 2:1. The dissolution temperature is -12°C to -8°C, and the dissolution time is 20 to 60 minutes. The dissolution temperature of NaOH / Ur can be -12°C, -10°C, or -8°C. The dissolution time can be 20 minutes, 30 minutes, 40 minutes, 50 minutes, or 60 minutes.

[0029] The mass ratio of the quaternary ammonium salt to water in the quaternary ammonium salt / water is 1:1 to 2:1. The dissolution temperature is 20 to 60°C, and the dissolution time is 60 to 120 minutes. The dissolution temperature of the quaternary ammonium salt / water can be 20°C, 30°C, 40°C, 50°C, or 60°C. The dissolution time can be 60 minutes, 70 minutes, 80 minutes, 90 minutes, 100 minutes, 110 minutes, or 120 minutes.

[0030] The mass ratio of choline hydroxide to urea in ChOH / Ur is 1:1 to 4:1. The dissolution temperature is 30°C to 60°C, and the dissolution time is 20 to 60 minutes. The dissolution temperature of ChOH / Ur can be 30°C, 40°C, 50°C, or 60°C. The dissolution time can be 20 minutes, 30 minutes, 40 minutes, 50 minutes, or 60 minutes.

[0031] The mass ratio of choline hydroxide, urea, and zinc glycinate in ChOH / Ur / ZG is 2:1:0.25% to 2:1:1.25%. The dissolution temperature is 30-60°C, and the dissolution time is 20-50 minutes. The dissolution temperature of ChOH / Ur / ZG can be 30°C, 40°C, 50°C, or 60°C. The dissolution time can be 20 minutes, 30 minutes, 40 minutes, or 50 minutes.

[0032] Different systems require different dissolution temperatures and dissolution times. Within the appropriate conditions, cellulose can be well dissolved in the solvent to obtain a transparent and uniform cellulose solution.

[0033] The mass ratio of the cellulose raw material to the solvent is 1:100-8:100, and specifically can be 1:100, 2:100, 3:100, 4:100, 5:100, 6:100, 7:100 or 8:100, and can be preferably 2:100-3:100. Alternatively, the mass concentration of the cellulose solution is 1-5 wt%, and specifically can be 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt% or 5 wt%.

[0034] The ratio of the vinyl COFs dispersion liquid to the cellulose solution is (1-10 mL):(5-15 g), and preferably (2-6 mL):(8-12 g). Specifically, it can be 2 mL:10 g, 4 mL:10 g, 4 mL:12 g, etc.

[0035] Alternatively, the mass ratio of the vinyl COFs dispersion liquid to the cellulose solution is 10:1-50:1, such as 40:1.

[0036] In one or more embodiments, the solvent of the regeneration bath is an alcohol aqueous solvent, and the volume ratio of alcohol to water is (0.8-1.2):(0.8-1.2). Preferably, it is 1:1. The temperature is room temperature.

[0037] During the regeneration in the regeneration bath, ultrasonic treatment is performed for 0.8-2 h to ensure complete regeneration of the cellulose.

[0038] In one or more embodiments, the solid content of the mixed slurry of the regenerated cellulose and the vinyl COFs is 1-5%, and specifically can be 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5% or 5%. Preferably, it is 1-3%.

[0039] In one or more embodiments, the filtration and drying method is not specifically limited. For example, the filtration is vacuum filtration. The drying includes but is not limited to hot pressing or air drying.

[0040] The vinyl COFs and the cellulose in the present application are blended in a homogeneous system, and therefore the filtration is to ensure uniform mixing of the vinyl COFs and the regenerated cellulose. Coating can also achieve a similar effect, but is contrary to the preparation method in the present application, and coating cannot ensure close combination of the vinyl COFs and the regenerated cellulose, and is prone to shedding of the vinyl COFs, affecting the stability of the product.

[0041] As a preferred embodiment, the preparation method of the regenerated cellulose fluorescent sensing film material is as follows: S1: Using monomers containing active methylene hydrogen structures and aldehyde monomers as raw materials, the two monomers are connected through carbon-carbon double bonds through Knoevenagel condensation reaction under the catalysis of trifluoroacetic acid or potassium hydroxide, and covalent organic framework materials (COFs) are prepared by solvent thermal or mechanical grinding method.

[0042] S2: Mixing the cellulose raw material and the solvent in a certain proportion, dissolving the cellulose in the solvent, and obtaining a transparent and uniform cellulose solution.

[0043] S3: The COFs are ultrasonically dispersed in a predetermined amount of ethanol to prepare a COF dispersion of a specific concentration. This dispersion is then uniformly mixed with a cellulose solution in a specific proportion under stirring or ultrasound to form a stable mixed system. This mixed solution is then regenerated in an ethanol regeneration bath. A mixed slurry of regenerated cellulose and COFs is then obtained through washing, filtration, or dialysis.

[0044] S4: Use mechanical stirring or high-pressure homogenization to evenly disperse the mixed slurry of regenerated cellulose and COFs, vacuum filter to obtain membrane sheets of uniform size and quantity, and obtain a light yellow regenerated cellulose fluorescent sensing membrane material by hot pressing or air drying.

[0045] In a third aspect, the present invention provides applications of the regenerated cellulose fluorescent sensing membrane material in pH detection, NH3 detection, and food spoilage monitoring, including colorimetric detection and / or fluorescence intensity detection.

[0046] In a fourth aspect, the present invention provides a biomass-based renewable fluorescent sensor or sensing platform, which comprises the above-mentioned regenerated cellulose fluorescent sensing membrane material.

[0047] In a fifth aspect, the present invention provides a method for pH detection, the specific method comprising: The dispersion of the regenerated cellulose fluorescent sensing membrane material is mixed with solutions at different pH values, and the pH value is detected by using the change in fluorescence intensity; or the regenerated cellulose fluorescent sensing membrane material is placed in solutions at different pH values, and the pH value is detected by colorimetry.

[0048] The method for detecting pH using changes in fluorescence intensity involves measuring a linear curve between fluorescence intensity and pH using a fluorescence spectrophotometer, and using this curve as a standard for pH detection. The excitation wavelength for pH detection is 420-450 nm. As the pH value changes from acid to alkaline at pH values ​​between 1 and 14, the fluorescence intensity gradually increases.

[0049] In a sixth aspect, the present invention provides a method for detecting NH3, which uses the above-mentioned regenerated cellulose fluorescent sensing membrane material, and the specific method includes: The regenerated cellulose fluorescent sensing membrane material was acidified in an acid vapor atmosphere and purged with N2. The acidified regenerated cellulose fluorescent sensing membrane material was placed in a vapor atmosphere of ammonia with different concentration gradients. After standing, it was taken out and purged with N2. The fluorescence intensity-NH3 concentration linear curve was measured by a fluorescence spectrophotometer and the curve was used as a standard for detecting NH3 concentration. Alternatively, the regenerated cellulose fluorescent sensor membrane material is placed in an atmosphere of ammonia vapor with varying concentration gradients and detected by colorimetric visual inspection. The colorimetric visual inspection method for NH3 detection is as follows: under ultraviolet light, the membrane material exhibits a color change from dark red to blue-green in an acidic to alkaline gas environment. Under natural light, the regenerated cellulose fluorescent sensor membrane material exhibits a color change from orange-red to yellow in an acidic to alkaline gas environment, thereby enabling colorimetric visual determination of gas pH.

[0050] Among them, the pH of air in a normal environment is pH≈6-7. In the process of detecting using changes in fluorescence intensity, the purpose of acidification is to detect trace amounts of NH3.

[0051] As the concentration of ammonia increases, the fluorescence intensity becomes stronger.

[0052] The sample was then acidified in an acid vapor atmosphere for 1–5 minutes. The sample was allowed to rest for 1–10 minutes. Each N2 purge was performed for 50–80 seconds to remove residual acid vapor or ammonia vapor. The excitation wavelength was 410–430 nm. The detection limit for NH3 was less than 5 ppb.

[0053] In a seventh aspect, the present invention provides a method for visually monitoring food spoilage, which uses the above-mentioned regenerated cellulose fluorescent sensing membrane material, and the specific method includes: The regenerated cellulose fluorescent sensing membrane material is placed in a sealed container containing food. The color change of the membrane material and the change in the fluorescence intensity of the membrane are used to judge the degree of food spoilage through colorimetric visual inspection and NH3 concentration.

[0054] Furthermore, the color change of the membrane material is specifically as follows: in the initial state, the color of the membrane is orange, and as the standing time increases, the freshness of the food decreases, and the color of the membrane gradually changes to yellow.

[0055] Furthermore, the specific method of judging the degree of food spoilage by NH3 concentration is as follows: as the standing time increases, the freshness of the food decreases and the fluorescence intensity of the membrane gradually becomes stronger.

[0056] One or more of the above technical solutions have the following advantages or beneficial effects: (1) The cellulose-based fluorescent sensing material prepared by the method has the advantages of greenness, non-pollution, high sensitivity and stable response characteristics.

[0057] (2) The regenerated cellulose fluorescent sensing film material prepared by the method can realize high-sensitivity response to pH and NH3, and has the advantages of greenness and non-pollution, and can be used for colorimetric visual observation and fluorescence intensity change determination in food spoilage monitoring.

[0058] (3) Under irradiation of ultraviolet light, the regenerated cellulose fluorescent sensing film material presents color change from dark red to blue-green in an acidic to alkaline gas environment, and under irradiation of natural light, the regenerated cellulose fluorescent sensing film material presents color change from orange red to yellow in an acidic to alkaline gas environment, so that colorimetric visual observation of gas acidity and alkalinity can be realized. The fluorescence intensity of the film material gradually increases with the gradual change from acid to base under pH=1-14.

[0059] (4) With the increase of the concentration of ammonia water, the fluorescence intensity of the regenerated cellulose fluorescent sensing film material is stronger. The minimum detection limit of NH3 is lower than 5ppb. When the film material is applied to visual monitoring of food spoilage, the color change of the film material is as follows: the color of the film is orange in the initial state, and with the extension of the standing time, the freshness of the food decreases, and the color of the film gradually changes to yellow. The specific method for judging the spoilage degree of the food by the concentration of NH3 is as follows: with the extension of the standing time, the freshness of the food decreases, and the fluorescence intensity of the film gradually increases. BRIEF DESCRIPTION OF DRAWINGS

[0060] The drawings accompanying the specification of the present application serve to provide further understanding of the present application, and the illustrative embodiments of the present application and their descriptions serve to explain the present application, and do not constitute an improper limitation on the present application.

[0061] Figure 1 Figure 1 is a monomer structure diagram of the vinyl COFs of the present application; wherein (a) is an aldehyde monomer capable of reacting with the monomer in (b), (b) is a monomer containing active methylene hydrogen structure capable of reacting with the monomer in (a), (c) is an aldehyde monomer capable of reacting with the monomer in (d), and (d) is a monomer containing active methylene hydrogen structure capable of reacting with the monomer in (c); Figure 2 The infrared and XRD spectra of the vinyl COFs prepared in Example 1 of the present invention; wherein (a) is the XRD spectrum and (b) is the infrared spectrum; Figure 3 The infrared and XRD spectra of the regenerated cellulose fluorescent sensing membrane material prepared in Example 1 of the present invention; wherein (a) is the infrared spectrum and (b) is the XRD spectrum; Figure 4 UV spectra of vinyl COFs prepared in Example 1 and Example 2 of the present invention; Figure 5 The pH response performance of the vinyl COFs prepared in Examples 1 and 2 of the present invention; wherein (a) is TMT-TA-COF, (b) is TMT-BA-COF, (c) is TMT-DHBA-COF, and (d) is TMT-TD-COF; Figure 6 The recycling performance of the vinyl COFs prepared in Example 1 of the present invention; wherein (a) is a pH-fluorescence intensity linear relationship diagram, and (b) is the recycling performance; Figure 7 The NH3 response performance and recycling performance of the regenerated cellulose fluorescent sensing membrane material prepared in Example 1 of the present invention; wherein (a) is a graph showing the change in fluorescence intensity at different wavelengths, (b) is a graph showing the change in fluorescence intensity at different NH3 concentrations, and (c) is the recycling performance; Figure 8 This is a diagram showing the color change of the regenerated cellulose fluorescent sensing membrane material prepared in Example 1 of the present invention in different acidic and alkaline environments; Figure 9 Macroscopic images of the regenerated cellulose fluorescent sensing film material prepared in Example 1 of the present invention sensing the changes in the freshness of fresh shrimp and pork within 0 to 3 hours; wherein, (a) is a macroscopic image of the changes in the freshness of fresh shrimp, and (b) is a macroscopic image of the changes in the freshness of pork. DETAILED DESCRIPTION

[0062] Terminology Notes: Vinyl COFs: Vinyl covalent organic frameworks (COFs) are prepared using monomers containing active methylene hydrogen structures and aldehyde monomers as raw materials, using a solvent thermal method or mechanical grinding method in the presence of a catalyst. For example, the TMT-TA-COF prepared in Example 1 is formed by the condensation of 2,4,6-trimethyl-1,3,5-triazine (TMT) and terephthalaldehyde (TA).

[0063] RCF membrane: refers to regenerated cellulose membrane.

[0064] RCF / TMT-TA-COF membrane refers to the regenerated cellulose / TMT-TA-COF membrane prepared in Example 1; TMT-TA-COF: vinyl COFs prepared from monomer 2,4,6-trimethyl-1,3,5-triazine (TMT) and monomer terephthalaldehyde (TA).

[0065] TMT-BA-COF: vinyl COFs prepared from monomers 2,4,6-trimethyl-1,3,5-triazine (TMT) and 4,4'-biphenyldicarboxaldehyde (BA).

[0066] TMT-DHBA-COF: vinyl COFs prepared from the monomers 2,4,6-trimethyl-1,3,5-triazine (TMT) and 3,3'-dimethoxy-[1,1'-biphenyl]-4,4'-dicarbaldehyde (DHBA).

[0067] TMT-TD-COF: vinyl COFs prepared from the monomer 2,4,6-trimethyl-1,3,5-triazine (TMT) and the monomer [1,1':4',1''-terphenyl]-4,4''-dicarboxaldehyde (TD).

[0068] In the present invention, unless otherwise specified, other test materials and instruments and equipment are conventional test materials in this field and can be purchased through commercial channels.

[0069] Existing pH and NH₃ detection methods, such as pH meters, chromatography, electrochemistry, and biological methods, have limitations, and most are not conducive to food safety, making them difficult to apply to food spoilage monitoring. Covalent organic frameworks (COFs) are crystalline porous polymers connected by covalent bonds, characterized by a well-ordered pore structure and flexibly tunable chemical properties. Vinyl-containing COFs exhibit unique fluorescence response properties and hold great potential for applications in pH detection and gas sensing, demonstrating superior chemical stability and more efficient conjugated electron delocalization. Cellulose, the most abundant natural polymer on Earth, offers numerous advantages, including strong plasticity, biodegradability, and low cost. Its unique hydrogen-bonded network structure, as a matrix for composite materials, imparts excellent mechanical strength, flexibility, and biocompatibility. Combining cellulose with COFs to create bio-friendly composite bio-based fluorescent sensors holds great promise. Therefore, the present invention proposes a regenerated cellulose fluorescent sensing membrane material and its preparation method and application, which realizes the combination of regenerated cellulose and vinyl COFs material, and can be used for high-sensitive fluorescence detection and colorimetric detection of pH, NH3 and food spoilage monitoring.

[0070] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0071] Example 1 A method for preparing a regenerated cellulose fluorescent sensing membrane material for pH and NH3 detection comprises the following steps: (1) Monomer TMT (102.4 mg, 0.4 mmol), TA (78.8 mg, 0.6 mmol), n-butanol (11.2 mL), and o-dichlorobenzene (5.6 mL) were added to a 25 mL pressure bottle and treated under ultrasonic conditions for 10 min to fully dissolve the monomer in the solvent. Then, catalyst KOH (33.6 mg, 0.6 mmol) was added and ultrasonic treatment was continued for 20 min. The pressure bottle was quickly frozen at 77 K in a liquid nitrogen bath, degassed through three freeze-thaw cycles, sealed under vacuum, and reacted at 120°C for 72 h. The yellow precipitate was collected by vacuum filtration and washed with N,N-dimethylformamide and tetrahydrofuran in sequence to remove unreacted precursors. Finally, it was vacuum dried at 80°C overnight.

[0072] (2) Pulp cellulose was dissolved in ChOH / Ur / ZG solution (solid-to-liquid ratio of 1:50, mass ratio of ChOH / Ur / ZG of 2:1:0.25%) to obtain a transparent and uniform cellulose solution. Subsequently, 10 g of cellulose solution (2 wt%) and 4 mL of TMT-TA-COF (5 mg mL -1 )-ethanol dispersion and sonicated for 20 minutes for thorough mixing. A 100 mL water / ethanol (1:1, v:v) solution was added to the sonicated dispersion as a regeneration bath. Ultrasonication was continued for 1 hour to completely regenerate the cellulose, resulting in a self-assembled regenerated cellulose / TMT-TA-COF slurry with a 2% solids content. 15 g of the regenerated cellulose / TMT-TA-COF slurry was filtered to form a membrane, which was then hot-pressed and dried at 80°C for 10 minutes to obtain a regenerated cellulose fluorescent sensing membrane material.

[0073] Figure 1 is a monomer type used to prepare vinyl covalent organic framework materials, wherein n=0, 1, 2, 3 or 4. Figure 1 (a) Monomer and Figure 1 The monomers in (b) can react; Figure 1 (c) Monomer and Figure 1 The monomers in (d) can react.

[0074] The XRD pattern of TMT-TA-COF is as follows Figure 2(a) As shown. TMT-TA-COF has a strong diffraction peak at 2θ=5º (red curve), which is attributed to the 100 crystal plane, indicating that TMT-TA-COF has good crystallinity; in addition, TMT-TA-COF has characteristic peaks at 8.02º, 9.33º, 11.87º and 24º, which are attributed to the (110), (200), (210) and (001) crystal planes, respectively. The structural simulation of TMT-TA-COF was performed using Material Studio software. After comparison, it was found that the XRD results of TMT-TA-COF were highly consistent with the PXRD spectrum of the simulated AA stacking model ( Figure 2 (a), black curve), indicating that the 2D layers in TMT-TA-COF are arranged in an AA stacking manner.

[0075] FTIR spectra of TMT-TA-COF and its monomers are shown in Figure 2. Figure 2 As shown in (b), the 1629 cm -1 The peak at 975 cm is the characteristic peak of C=C. -1 The peak at 1689 cm in TA is the out-of-plane bending vibration peak of CH of trans-substituted olefins, which proves the formation of the conjugated system of COF materials. -1 The characteristic peak of CO in the aldehyde group disappears after the formation of COF, and the characteristic peak of C=C in TMT shifts, which proves the successful preparation of TMT-TA-COF.

[0076] Figure 3 The peak intensity of the infrared curve of the regenerated cellulose / TMT-TA-COF film in (a) at 2θ=12.5° increases, and the area of ​​the crystalline region increases, indicating that the presence of TMT-TA-COF affects the arrangement of regenerated cellulose and improves the overall crystallinity of the material. Figure 3 (b) XRD patterns of the regenerated cellulose membrane and the regenerated cellulose / TMT-TA-COF membrane. As shown in the figure, the regenerated cellulose membrane and the regenerated cellulose / TMT-TA-COF membrane exhibit diffraction peaks at 2θ = 12.2°, 20°, and 21.5°, which are typical of type II cellulose crystals, proving that the regenerated cellulose was successfully prepared. The XRD curve of the regenerated cellulose / TMT-TA-COF membrane exhibits a clear crystalline peak at 2θ = 5°, which is attributed to the 100 peak plane of TMT-TA-COF, demonstrating the successful bonding of TMT-TA-COF with regenerated cellulose.

[0077] Example 2 TMT-BA-COF, TMT-DHBA-COF, and TMT-TD-COF were successfully prepared by the same COF synthesis method as in Example 1, and their pH response properties were tested. Specifically: To a 25 mL pressure bottle, monomers TMT (102.4.0 mg, 0.4 mmol), BA (126.1 mg, 0.6 mmol) or DHBA (162.2 mg, 0.6 mmol) or TD (171.8 mg, 0.6 mmol), n-butanol (11.2 mL), and o-dichlorobenzene (5.6 mL) were added. The monomers were fully dissolved in the solvent under ultrasonication for 10 min. Catalyst KOH (33.6 mg, 0.6 mmol) was then added and ultrasonication continued for 20 min. The pressure bottle was rapidly frozen in a liquid nitrogen bath at 77 K, degassed through three freeze-thaw cycles, sealed under vacuum, and reacted at 120°C for 72 h. The yellow precipitate was collected by vacuum filtration and washed sequentially with N,N-dimethylformamide and tetrahydrofuran to remove unreacted precursors. Finally, the solution was dried under vacuum at 80°C overnight.

[0078] Application Example 1 The pH response performance and recycling performance of the COFs prepared in Example 1 and Example 2 are measured, comprising the following steps: (1) pH response performance test: The fluorescence spectra of TMT-TA-COF, TMT-BA-COF, TMT-DHBA-COF and TMT-TD-COF in different acidic and alkaline liquid environments were tested using a fluorescence spectrophotometer. Taking TMT-TA-COF as an example, specifically, 5 mg of TMT-TA-COF powder was dispersed in 10 mL of ethanol and ultrasonicated for 1 h to prepare a concentration of 0.5 mg mL -1 Then, 10 μL of TMT-TA-COF ethanol dispersion was mixed with 990 μL of phosphate buffer (0.1 mol·L -1 ) were mixed to obtain TMT-TA-COF dispersions with different pH values ​​(0.005 mg mL -1 When testing the fluorescence spectrum, 2 mL of TMT-TA-COF dispersion was placed in a quartz cuvette with light permeable on all four sides. The sample was measured using the maximum absorption wavelength of the UV-visible spectrum as the excitation wavelength, and the fluorescence spectra of TMT-TA-COF ethanol dispersions at different pH values ​​were recorded.

[0079] Figure 4 This is the UV spectrum of vinyl COFs. The figure shows the maximum excitation wavelengths of the four COFs.

[0080] (2) pH Cyclic Response Performance Test: The pH value of the TMT-TA-COF ethanol dispersion was adjusted using acetic acid solution and NaOH solution, and the cyclic response performance of TMT-TA-COF to pH value was measured. Specifically, the pH value of the TMT-TA-COF ethanol dispersion was cycled between 1 and 14 for 5 times, and the fluorescence intensity of the TMT-TA-COF ethanol dispersion at pH = 1 and pH = 14 in each cycle was measured. The average value of three measurements for each group was used to evaluate its cyclic response performance.

[0081] pass Figure 5 and Figure 6 It can be seen that the material has obvious changes in fluorescence intensity for solutions with pH = 1 ~ 14, and has a good linear relationship when pH = 3 ~ 14. , The material also showed excellent reusability during pH detection, with no significant change in fluorescence intensity after five cycles.

[0082] Application Example 2 The NH3 response performance and recycling performance of the regenerated cellulose fluorescent sensing membrane material prepared in Example 1 are measured, comprising the following steps: (1) NH3 response performance test of the membrane: Before detecting NH3 gas, the regenerated cellulose fluorescent sensing membrane material was immersed in HCl solution (10 mol·L -1 The membrane was acidified in an atmosphere of HCl vapor (100 μg / ml) for 3 minutes, followed by a 30-second N2 purge to remove residual HCl vapor. The acidified regenerated cellulose / TMT-TA-COF membrane was then exposed to NH3 vapor from NH3·H2O solutions of varying concentrations for 5 minutes. The membrane was then removed and purged with N2 gas for 30 seconds to remove residual NH3 vapor. Fluorescence spectra of the regenerated cellulose fluorescent sensing membrane were recorded at an excitation wavelength of 420 nm.

[0083] (2) Test of the NH3 cycle response performance of the membrane: The regenerated cellulose fluorescent sensing membrane material treated with NH3 vapor was fumigated with HCl solution and then recycled to detect the same concentration of NH3. The fluorescence intensity of the regenerated cellulose fluorescent sensing membrane material in each cycle was measured. Each group was measured three times and the average value was taken to evaluate the cyclic response performance of the regenerated cellulose fluorescent sensing membrane material to NH3.

[0084] pass Figure 7 It can be seen that the material has excellent response performance to NH3 and has a good linear relationship when the NH3 concentration is 2~50 ppb. , The fluorescence intensity gradually increased with the increase of NH3 concentration. The membrane material also showed excellent reusability in the process of NH3 detection. After 5 cycles, the fluorescence intensity range decreased slightly.

[0085] In the detection of NH3, under the irradiation of ultraviolet light (420 nm excitation wavelength), the regenerated cellulose fluorescent sensing membrane material shows a color change from dark red to blue-green in an acidic to alkaline gas environment; under the irradiation of natural light, the regenerated cellulose fluorescent sensing membrane material shows a color change from orange-red to yellow in an acidic to alkaline gas environment. Figure 8 shown.

[0086] Application Example 3 The application of the regenerated cellulose fluorescent sensing membrane material prepared in Example 1 in the field of food spoilage monitoring includes the following steps.

[0087] Fresh shrimp and pork were placed in a transparent PC box that had been sterilized at high temperature. The regenerated cellulose / TMT-TA-COF membrane was fixed to the top of the box lid with transparent tape. The box was then sealed and the color changes of the regenerated cellulose / TMT-TA-COF membrane were observed and recorded at regular intervals to determine the degree of spoilage.

[0088] Depend on Figure 9 As can be seen, for fresh shrimp and pork, the membrane initially appears orange. After one hour of stabilization, some of the membrane turns yellow, indicating the beginning of a change in freshness. After three hours, the membrane has essentially turned yellow, indicating that the food's freshness has decreased over time. Therefore, the membrane can intuitively reflect the changes in freshness of fresh shrimp and pork over time through color changes, enabling visual detection of food freshness.

[0089] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A regenerated cellulose fluorescent sensing membrane material, characterized in that: The components of the regenerated cellulose fluorescent sensing membrane material include regenerated cellulose and vinyl COFs, wherein the mass ratio of regenerated cellulose to vinyl COFs is 50:1 to 100:1; Using monomers containing active methylene hydrogen structures and aldehyde monomers as raw materials, vinyl covalent organic framework materials, namely vinyl COFs, are prepared by solvent thermal method or mechanical grinding method under the action of catalyst; The monomer containing an active methylene hydrogen structure is one or more of 2,4,6-trimethyl-1,3,5-triazine, 2,5-dimethylpyrazine, and 2,4,6-tricyano-1,3,5-trimethylbenzene; The aldehyde monomer is one or more of terephthalaldehyde, 4,4'-biphenyldicarboxaldehyde, 3,3'-dimethoxy-[1,1'-biphenyl]-4,4'-dicarboxaldehyde, [1,1':4',1''-terphenyl]-4,4''-dicarboxaldehyde, trimesic acid, 1,3,5-tris(4'-formaldehyde phenyl)benzene, 1,3,5-triazine-2,4,6-tricarboxaldehyde, and 2,4,6-tris(4-formaldehyde phenyl)-1,3,5-triazine; The catalyst is trifluoroacetic acid or potassium hydroxide.

2. A method for preparing the regenerated cellulose fluorescent sensing membrane material according to claim 1, characterized in that: The following steps are involved: The vinyl COFs dispersion and the cellulose solution are mixed and regenerated in a regeneration bath to obtain a mixed slurry of regenerated cellulose and vinyl COFs. The mixed slurry is filtered and dried.

3. The preparation method according to claim 2, characterized in that Using monomers containing active methylene hydrogen structures and aldehyde monomers as raw materials, vinyl covalent organic framework materials, namely vinyl COFs, are prepared by solvent thermal method or mechanical grinding method under the action of catalyst; The monomer containing an active methylene hydrogen structure is one or more of 2,4,6-trimethyl-1,3,5-triazine, 2,5-dimethylpyrazine, and 2,4,6-tricyano-1,3,5-trimethylbenzene; The aldehyde monomer is one or more of terephthalaldehyde, 4,4'-biphenyldicarboxaldehyde, 3,3'-dimethoxy-[1,1'-biphenyl]-4,4'-dicarboxaldehyde, [1,1':4',1''-terphenyl]-4,4''-dicarboxaldehyde, trimesic acid, 1,3,5-tris(4'-formaldehyde phenyl)benzene, 1,3,5-triazine-2,4,6-tricarboxaldehyde, and 2,4,6-tris(4-formaldehyde phenyl)-1,3,5-triazine; The catalyst is trifluoroacetic acid or potassium hydroxide; The molar ratio of the monomer containing active methylene hydrogen structure, the aldehyde monomer and the catalyst is (0.2-0.6):(0.4-0.8):(0.4-0.8).

4. The preparation method according to claim 3, characterized in that The specific steps of the solvothermal method are as follows: a monomer containing an active methylene hydrogen structure and an aldehyde monomer are mixed with a solvent, treated under an ultrasonic environment to fully dissolve the monomer in the solvent, a catalyst is then added, the ultrasonic treatment is continued, the mixture is rapidly frozen in a liquid nitrogen bath, degassed through multiple freeze-thaw cycles, sealed under vacuum, heated under certain conditions for reaction, a yellow precipitate is collected by vacuum filtration, and washed with N,N-dimethylformamide and tetrahydrofuran in sequence to remove unreacted precursors, and finally dried to obtain the product; The solvent used in the solvothermal method is one or more of n-butanol, tetrahydrofuran, N,N-dimethylformamide, o-dichlorobenzene, 1,4-dioxane, and dimethyl sulfoxide; The ratio of aldehyde monomer to solvent is (100-150 mg):(10-20 mL); The reaction temperature of the solvothermal method is 100~140℃, and the reaction time is 48~80 h; Alternatively, the grinding conditions of the mechanical grinding method are grinding at room temperature for 5 to 20 minutes.

5. The preparation method according to claim 2, characterized in that Vinyl COFs are dispersed in an alcohol solvent to obtain a vinyl COFs dispersion; The concentration of vinyl COFs dispersion was 0.1–10 mg / mL; Alternatively, a cellulose raw material and a solvent are mixed in a certain proportion, so that the cellulose is dissolved in the solvent to obtain a cellulose solution; The cellulose raw material is one or more of microcrystalline cellulose, pulp fiber, cotton fiber, and ramie fiber; The solvent is one or more of NaOH / urea, quaternary ammonium salt / water, choline hydroxide / urea, and choline hydroxide / urea / zinc glycinate systems; The mass ratio of NaOH to urea in NaOH / urea is 1:1~2:1; the dissolution temperature is -12~-8℃, and the dissolution time is 20~60 min; The mass ratio of quaternary ammonium salt to water in quaternary ammonium salt / water is 1:1~2:1; the dissolution temperature is 20~60℃, and the dissolution time is 60~120 min; The mass ratio of choline hydroxide to urea in the choline hydroxide / urea is 1:1 to 4:1; the dissolution temperature is 30 to 60°C; and the dissolution time is 20 to 60 minutes. The mass ratio of choline hydroxide, urea, and zinc glycinate in the choline hydroxide / urea / zinc glycinate is 2:1:0.25% to 2:1:1.25%; the dissolution temperature is 30 to 60°C, and the dissolution time is 20 to 50 minutes; The mass ratio of the cellulose raw material to the solvent is 1:100 to 8:100; The ratio of vinyl COFs dispersion and cellulose solution is (1~10 mL):(5~15 g); Alternatively, the solvent of the regeneration bath is an alcohol-water solvent, and the volume ratio of alcohol to water is (0.8-1.2):(0.8-1.2); when regenerating in the regeneration bath, ultrasonication should be performed for 0.8-2 h; The solid content of the mixed slurry of regenerated cellulose and vinyl COFs is 1~5%.

6. Use of the regenerated cellulose fluorescent sensing membrane material according to claim 1 or the regenerated cellulose fluorescent sensing membrane material obtained by the preparation method according to any one of claims 2 to 5 in pH detection, NH3 detection and food spoilage monitoring.

7. A biomass-based renewable fluorescent sensor or sensing platform, characterized in that: The invention comprises the regenerated cellulose fluorescent sensing membrane material according to claim 1 or the regenerated cellulose fluorescent sensing membrane material obtained by the preparation method according to any one of claims 2 to 5.

8. A method for pH detection, characterized in that, The regenerated cellulose fluorescent sensing membrane material according to claim 1 or the regenerated cellulose fluorescent sensing membrane material obtained by the preparation method according to any one of claims 2 to 5 is used, and the method comprises: The dispersion of regenerated cellulose fluorescent sensing membrane material is mixed with solutions at different pH values, and the pH value is detected by using the change of fluorescence intensity. Alternatively, the regenerated cellulose fluorescent sensing membrane material is placed in solutions with different pH values, and the pH value is detected using a colorimetric method.

9. A method for detecting NH3, characterized in that: The method uses the regenerated cellulose fluorescent sensing membrane material according to claim 1 or the regenerated cellulose fluorescent sensing membrane material obtained by the preparation method according to any one of claims 2 to 5, and the specific method includes: The regenerated cellulose fluorescent sensing membrane material was acidified in an acid vapor atmosphere and purged with N2. The acidified regenerated cellulose fluorescent sensing membrane material was placed in a vapor atmosphere of ammonia with different concentration gradients. After standing, it was taken out and purged with N2. The fluorescence intensity-NH3 concentration linear curve was measured by a fluorescence spectrophotometer and the curve was used as a standard for detecting NH3 concentration. Alternatively, the regenerated cellulose fluorescent sensing membrane material is placed in a vapor atmosphere of ammonia water with different concentration gradients and detected by colorimetric method.

10. A visual monitoring method for food spoilage, characterized in that: The method uses the regenerated cellulose fluorescent sensing membrane material according to claim 1 or the regenerated cellulose fluorescent sensing membrane material obtained by the preparation method according to any one of claims 2 to 5, and the specific method includes: The regenerated cellulose fluorescent sensing membrane material is placed in a sealed container containing food. The color change of the membrane material and the change in the fluorescence intensity of the membrane are used to determine the degree of food corruption through colorimetric detection and NH3 concentration.

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