A regenerated cellulose fluorescent sensing membrane material and a preparation method and application thereof

Abstract

The application discloses a regenerated cellulose fluorescent sensing film material and a preparation method and application thereof, and belongs to the fields of biomass functional material preparation technology and food safety detection. The application uses monomers containing active methylene hydrogen structure and aldehyde monomers as raw materials, uses trifluoroacetic acid or potassium hydroxide as a catalyst, and prepares vinyl COFs with pH response performance through a Knoevenagel condensation reaction under a solvent thermal condition. Meanwhile, the regenerated cellulose fluorescent sensing film material is prepared by combining regenerated cellulose and the vinyl COFs through hydrogen bond action, and 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 characteristics and the like. The application realizes the combination of regenerated cellulose and the COF material, proposes a preparation strategy based on a biomass-based renewable fluorescent sensing platform, and innovatively applies the fluorescent sensing platform to the field of food spoilage monitoring.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of biomass functional material preparation technology and food safety detection, and particularly relates to a regenerated cellulose fluorescent sensing film material and a preparation method and application thereof. BACKGROUND

[0002] The information disclosed in this Background section is only for the purpose of increasing an understanding of the general background of the application and does not necessarily constitute an admission or a recognition that the information forms part of the prior art already known to a person of ordinary skill in the art.

[0003] Under the background of rapid industrial development, pH and NH3 detection are crucial in environmental safety, industrial production, and food safety, among others. pH is a key parameter of the acid-base degree of water bodies, soil, and atmosphere, while NH3, as a common harmful pollutant, not only affects pollution control but also is released during food storage.

[0004] However, existing pH and NH3 detection methods (such as pH meter method, chromatography, electrochemical method, and biological method) have limitations, which are not conducive to food safety applications and are difficult to be used for food spoilage monitoring. Therefore, developing a green and efficient pH response and NH3 detection platform that can also be applied to food spoilage monitoring is an important problem to be solved at present. SUMMARY

[0005] To solve the problems of the prior art, the present application aims to provide a regenerated cellulose fluorescent sensing film material and a preparation method and application thereof. Specifically, a vinyl COF is synthesized through Knoevenagel condensation reaction, and then introduced into the hydrogen bond network of regenerated cellulose to prepare a cellulose-based porous film material, which is applied to high-sensitivity fluorescent response research for pH, NH3, and food spoilage monitoring.

[0006] The present application uses monomers containing active methylene hydrogen structure and aldehyde monomers as raw materials, and trifluoroacetic acid or potassium hydroxide as catalyst to prepare a vinyl COF with pH response performance through Knoevenagel condensation reaction under solvent thermal conditions. At the same time, it is combined with regenerated cellulose through hydrogen bond to prepare a regenerated cellulose fluorescent sensing film material, which can be used as a high-sensitivity fluorescent sensor for pH and NH3, and has the advantages of green and non-polluting, high sensitivity, and stable response characteristics. The present application first realizes the combination of regenerated cellulose and COF material, proposes a preparation strategy based on 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] To achieve the above-mentioned purposes, the technical solutions of the present application are as follows:

[0008] In a first aspect, the present application provides a regenerated cellulose fluorescent sensing film material, which comprises regenerated cellulose and vinyl COFs, and the mass ratio of the regenerated cellulose and the vinyl COFs is 50:1-100:1. When the content of the vinyl COFs is too low, the sensing efficiency and the detection range will be affected, and the data determination and naked eye observation will be affected.

[0009] In the present application, the vinyl COFs and the regenerated cellulose are blended in a homogeneous state, and the subsequent infrared spectrum proves that the two are connected through hydrogen bonding, and the SEM proves that the vinyl COFs and the regenerated cellulose have an interlaced and entangled combination form, so the two are combined through hydrogen bonding, electrostatic attraction, van der Waals force and the like.

[0010] The regenerated cellulose fluorescent sensing film material is yellow or light yellow in color.

[0011] In the present application, the regenerated cellulose film alone has no fluorescent property; the vinyl COFs alone can be used for detecting pH, and there is data support proving that it has the response ability to acid and alkaline gases such as NH3 and HCl.

[0012] In a second aspect, the present application provides a preparation method of the regenerated cellulose fluorescent sensing film material, comprising the following steps:

[0013] The vinyl COFs dispersion liquid and the cellulose solution are mixed, regenerated in a regeneration bath, and a mixed slurry of regenerated cellulose and vinyl COFs is obtained, which is filtered and dried to obtain the regenerated cellulose fluorescent sensing film material.

[0014] In the preparation process, the two monomers are connected through carbon-carbon double bond through condensation reaction, and the condensation reaction includes Knoevenagel condensation reaction.

[0015] In one or more embodiments, the vinyl COFs is prepared by using a monomer containing an active methylene hydrogen structure and an aldehyde monomer as raw materials, using a solvent thermal method or a mechanical grinding method under the action of a catalyst.

[0016] Further, 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).

[0017] Further, the aldehyde monomer is one or more of terephthaldehyde (TA; C8H6N2; CAS: 623-27-8), 4,4'-biphenyldialdehyde (BA; C 14 H 10 O2; CAS: 66-98-8), 3,3'-dimethoxy-[1,1'-biphenyl]-4,4'-dialdehyde (DHBA; C 16 H 14 O4; CAS: 27343-98-2), [1,1':4',1''-terphenyl]-4,4''-dialdehyde (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-tricarboxaldehyde (C6H3N3O3, CAS: 1210045-03-6), 2,4,6-tris(4-formylphenyl)-1,3,5-triazine (C 24 H 15 N3O3; CAS: 443922-06-3).

[0018] Further, the catalyst is trifluoroacetic acid or potassium hydroxide.

[0019] Further, 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).

[0020] In one or more embodiments, the specific steps of the solvothermal method are as follows: the monomer containing active methylene hydrogen structure and the aldehyde monomer are mixed with a solvent, treated under ultrasonic conditions to make the monomers fully dissolved in the solvent, then the catalyst is added, ultrasonic treatment is continued, rapid freezing is performed through a liquid nitrogen bath, degassing is performed through multiple freeze-thaw cycles, sealing is performed under vacuum, heating reaction is performed under certain conditions, yellow precipitates are collected through vacuum filtration, and N,N-dimethylformamide and tetrahydrofuran are used for washing in sequence to remove unreacted precursors, and finally, drying is performed to obtain the product.

[0021] Before the catalyst is added, ultrasonic treatment is performed for 5-20 min, as long as the monomers are fully dissolved in the solvent. After the catalyst is added, ultrasonic treatment is performed for 15-40 min, as long as the catalyst is fully mixed.

[0022] Further, the solvent used in the solvothermal method is one or more of n-butanol, tetrahydrofuran, N,N-dimethylformamide, o-dichlorobenzene, 1,4-dioxane, dimethyl sulfoxide. For example, the solvent is a mixed solution of n-butanol and o-dichlorobenzene, and the volume ratio is (8-14):(4-7). The ratio of aldehyde-based monomer to solvent is (100-150 mg):(10-20 mL), preferably (110-130 mg):(15-20 mL).

[0023] Further, the reaction temperature of the solvothermal method is 100-140°C, and can be specifically 100°C, 110°C, 120°C, 130°C or 140°C. The reaction time is 48-80h, and can be specifically 48h, 36h, 40h, 50h, 60h, 70h, 72h, 74h or 80h, preferably 70-74h. Under suitable reaction conditions, the formation of vinyl COFs is more beneficial.

[0024] Further, the grinding conditions of the mechanical grinding method are room temperature grinding for 5-20min, and can be specifically 5min, 6min, 7min, 8min, 9min, 10min, 12min, 14min, 15min, 16min, 18min, 20min, etc. The most preferred is 10min.

[0025] In one or more embodiments, the vinyl COFs dispersion and the cellulose solution are uniformly mixed under the action of stirring or ultrasonic. The time of stirring or ultrasonic is not specifically limited, as long as sufficient mixing is achieved, and the embodiment of uniform mixing is achieved. For example, ultrasonic is performed for 10-40min. Specifically, it can be 10min, 20min, 30min, 40min.

[0026] In one or more embodiments, the 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 0.1-10mg / mL. Specifically, it can be 0.1mg / mL, 1mg / mL, 2mg / mL, 3mg / mL, 4mg / mL, 5mg / mL, 6mg / mL, 7mg / mL, 8mg / mL, 9mg / mL or 10mg / mL. It can be preferably 5-10mg / mL.

[0027] In one or more embodiments, the cellulose raw material is mixed with the solvent in a certain ratio to dissolve the cellulose in the solvent to obtain a cellulose solution.

[0028] The cellulose raw material is one or more of microcrystalline cellulose, pulp fiber, cotton fiber, ramie fiber.

[0029] 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), choline hydroxide / urea / zinc glycinate (ChOH / Ur / ZG) system.

[0030] The mass ratio of NaOH and urea in NaOH / Ur is 1:1-2:1. The dissolution temperature is -12--8℃, and the dissolution time is 20-60 min. The dissolution temperature of NaOH / Ur can be specifically -12℃, -10℃ or -8℃. The dissolution time can be specifically 20 min, 30 min, 40 min, 50 min or 60 min.

[0031] The mass ratio of quaternary ammonium salt and 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 dissolution temperature of quaternary ammonium salt / water can be specifically 20℃, 30℃, 40℃, 50℃ or 60℃. The dissolution time can be specifically 60 min, 70 min, 80 min, 90 min, 100 min, 110 min or 120 min.

[0032] The mass ratio of choline hydroxide and urea in ChOH / Ur is 1:1-4:1. The dissolution temperature is 30-60℃, and the dissolution time is 20-60 min. The dissolution temperature of ChOH / Ur can be specifically 30℃, 40℃, 50℃ or 60℃. The dissolution time can be specifically 20 min, 30 min, 40 min, 50 min or 60 min.

[0033] The mass ratio of choline hydroxide, urea and zinc glycinate in ChOH / Ur / ZG is 2:1:0.25%-2:1:1.25%. The dissolution temperature is 30-60℃, and the dissolution time is 20-50 min. The dissolution temperature of ChOH / Ur / ZG can be specifically 30℃, 40℃, 50℃ or 60℃. The dissolution time can be specifically 20 min, 30 min, 40 min or 50 min.

[0034] Different systems require different dissolution temperatures and dissolution times. Within the appropriate condition range, the cellulose can be well dissolved in the solvent to obtain a transparent and uniform cellulose solution.

[0035] 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%.

[0036] 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.

[0037] Alternatively, the mass ratio of the vinyl COFs dispersion liquid to the cellulose solution is 10:1-50:1, such as 40:1.

[0038] 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.

[0039] During the regeneration in the regeneration bath, ultrasonic treatment is performed for 0.8-2 h to ensure complete regeneration of the cellulose.

[0040] 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%.

[0041] In one or more embodiments, the filtration and drying methods are not specifically limited. For example, the filtration is vacuum filtration. The drying includes but is not limited to hot pressing or air drying.

[0042] 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.

[0043] As a preferred embodiment, the preparation method of the regenerated cellulose fluorescent sensing film material is as follows:

[0044] S1: Covalent organic frameworks (COFs) are prepared by Knoevenagel condensation reaction of monomers containing active methylene hydrogen structure and aldehyde monomers through carbon-carbon double bond under the catalysis of trifluoroacetic acid or potassium hydroxide, and by solvent thermal or mechanical grinding method.

[0045] S2: Cellulose raw materials are mixed with solvents in a certain proportion to dissolve the cellulose in the solvent to obtain a transparent and uniform cellulose solution.

[0046] S3: COFs are dispersed in a certain amount of ethanol by ultrasonic treatment to prepare a COFs dispersion liquid with a specific concentration. The dispersion liquid is uniformly mixed with the cellulose solution in a certain proportion under stirring or ultrasonic assistance to form a stable mixed system. The mixed solution is subjected to regeneration treatment in an ethanol regeneration bath, and then a mixed pulp of regenerated cellulose and COFs is obtained through steps such as washing, filtering or dialysis.

[0047] S4: The mixed pulp of regenerated cellulose and COFs is uniformly dispersed by mechanical stirring method or high-pressure homogenization method, and vacuum filtration is performed to obtain membrane pieces with uniform size and consistent quantity. A light yellow regenerated cellulose fluorescent sensing membrane material is obtained by hot pressing or air drying.

[0048] In a third aspect, the application provides applications of the above-mentioned regenerated cellulose fluorescent sensing membrane material in pH detection, NH3 detection and food spoilage monitoring. The applications include colorimetric method detection and / or fluorescence intensity method detection.

[0049] In a fourth aspect, the application provides a biomass-based renewable fluorescent sensor or sensing platform, which comprises the above-mentioned regenerated cellulose fluorescent sensing membrane material.

[0050] In a fifth aspect, the application provides a method for pH detection, which specifically comprises:

[0051] The dispersion liquid of the above-mentioned regenerated cellulose fluorescent sensing membrane material is mixed with a solution with different pH values, and the change in fluorescence intensity is used to detect the pH value; or the above-mentioned regenerated cellulose fluorescent sensing membrane material is placed in a solution with different pH values, and the colorimetric method is used to detect the pH value.

[0052] The method for detecting the pH value by using the change in fluorescence intensity is that a fluorescence intensity-pH value linear curve is measured by a fluorescence spectrophotometer, and the curve is used as a standard for detecting the pH value. The excitation wavelength for pH detection is 420-450 nm. With the gradual change from acid to base under pH = 1-14, the fluorescence intensity gradually increases.

[0053] In a sixth aspect, the application provides a method for NH3 detection, which uses the above-mentioned regenerated cellulose fluorescent sensing membrane material, and specifically comprises:

[0054] The regenerated cellulose fluorescent sensing film material is acidified in an acid vapor atmosphere, N2 is blown, the acidified regenerated cellulose fluorescent sensing film material is placed in a vapor atmosphere of ammonia water with different concentration gradients, and after standing, it is taken out and blown with N2. The fluorescence intensity-NH3 concentration linear curve is measured by a fluorescence spectrophotometer, and the curve is used as a standard for detecting the concentration of NH3.

[0055] Alternatively, the regenerated cellulose fluorescent sensing film material is placed in a vapor atmosphere of ammonia water with different concentration gradients, and the colorimetric method is used for detection. Under the irradiation of ultraviolet light, the film material presents a color change from dark red to blue-green in an acidic to alkaline gas environment, and under the irradiation of natural light, the regenerated cellulose fluorescent sensing film material presents a color change from orange red to yellow in an acidic to alkaline gas environment, so that the colorimetric visual determination of the acidity and alkalinity of the gas can be realized.

[0056] In the normal environment, the air pH is about 6-7, and the purpose of acidification is to detect trace amounts of NH3 in the process of detecting the change in fluorescence intensity.

[0057] As the concentration of ammonia water increases, the fluorescence intensity becomes stronger.

[0058] Further, the acidification in the acid vapor atmosphere is 1-5 min. The standing time is 1-10 min. Each time N2 is blown, the blowing time is 50-80 s to remove the residual acid vapor or ammonia vapor. The excitation wavelength is 410-430 nm. The minimum detection limit of NH3 is lower than 5 ppb.

[0059] In a seventh aspect, the application provides a visual monitoring method for food spoilage, which uses the regenerated cellulose fluorescent sensing film material described above, and the specific method comprises:

[0060] The regenerated cellulose fluorescent sensing film material is placed in a sealed container containing food, and the color change of the film material and the change in fluorescence intensity of the film are used to determine the degree of food spoilage by colorimetric visual observation and NH3 concentration.

[0061] Further, the color change of the film material is that the film color is orange in the initial state, and as the standing time increases, the freshness of the food decreases, and the color of the film gradually changes to yellow.

[0062] Further, the specific method for determining the degree of food spoilage by NH3 concentration is that as the standing time increases, the freshness of the food decreases, and the fluorescence intensity of the film gradually increases.

[0063] One or some of the above technical solutions have the following advantages or beneficial effects:

[0064] (1) The present application takes regenerated cellulose as the skeleton, introduces COFs containing vinyl into the hydrogen bond network thereof, and prepares a yellowish cellulose-based fluorescent sensing material. Specifically, the present application takes monomers containing active methylene hydrogen structure and aldehyde monomers as raw materials, takes trifluoroacetic acid or potassium hydroxide as a catalyst, and prepares vinyl COFs with pH response performance through Knoevenagel condensation reaction under solvothermal conditions. Meanwhile, the regenerated cellulose fluorescent sensing film material is prepared by combining the vinyl COFs with regenerated cellulose through hydrogen bond interaction, and can be used as a high-sensitivity fluorescent sensor for pH and NH3, and has the advantages of green, non-pollution, high sensitivity, stable response characteristics, etc.

[0065] (2) The regenerated cellulose fluorescent sensing film material prepared in the present application can realize high-sensitivity response to pH and NH3, and has the advantages of green and non-pollution, and can be used for colorimetric visual observation and dual determination of fluorescence intensity change in food spoilage monitoring.

[0066] (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. With the gradual change of the film material from acid to base under pH=1~14, the fluorescence intensity gradually becomes stronger.

[0067] (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: in the initial state, the color of the film is orange, 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 NH3 concentration is as follows: with the extension of the standing time, the freshness of the food decreases, and the fluorescence intensity of the film gradually becomes stronger. BRIEF DESCRIPTION OF DRAWINGS

[0068] The drawings accompanying the specification of the present application form a part thereof, serve to provide further understanding of the present application, and together with the specification explain the present application. The use of the same reference numerals in different drawings indicates similar or identical components.

[0069] Figure 1 It is a monomer structure schematic 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).

[0070] Figure 2 Infrared, XRD patterns of the vinyl COFs prepared in Example 1 of the present application; wherein (a) is the XRD pattern, (b) is the infrared pattern;

[0071] Figure 3 Infrared, XRD patterns of the regenerated cellulose fluorescent sensing film material prepared in Example 1 of the present application; wherein (a) is the infrared pattern, (b) is the XRD pattern;

[0072] Figure 4 Ultraviolet spectrum of the vinyl COFs prepared in Example 1 and Example 2 of the present application;

[0073] Figure 5 pH response performance of the vinyl COFs prepared in Example 1 and Example 2 of the present application; wherein (a) is TMT-TA-COF, (b) is TMT-BA-COF, (c) is TMT-DHBA-COF, (d) is TMT-TD-COF;

[0074] Figure 6 Cyclic use performance of the vinyl COFs prepared in Example 1 of the present application; wherein (a) is the pH-fluorescence intensity linear relationship diagram, (b) is the cyclic use performance;

[0075] Figure 7 NH3 response performance and cyclic use performance of the regenerated cellulose fluorescent sensing film material prepared in Example 1 of the present application; wherein (a) is the fluorescence intensity change diagram under different wavelengths, (b) is the fluorescence intensity change diagram under different NH3 concentrations, (c) is the cyclic use performance;

[0076] Figure 8 Color change diagram of the regenerated cellulose fluorescent sensing film material prepared in Example 1 of the present application in different acid-base environments;

[0077] Figure 9 Macroscopic pictures of the regenerated cellulose fluorescent sensing film material prepared in Example 1 of the present application sensing the freshness degree change of fresh shrimps and pork within 0~3 h; wherein (a) is the macroscopic picture of the freshness degree change of fresh shrimps, (b) is the macroscopic picture of the freshness degree change of pork. DETAILED DESCRIPTION

[0078] TERMS EXPLANATION:

[0079] Vinyl COFs: refers to vinyl covalent organic framework materials. In the present application, vinyl covalent organic framework materials are prepared by using monomers containing active methylene hydrogen structure and aldehyde group monomers as raw materials, solvent thermal method or mechanical grinding method under the action of catalyst, namely vinyl COFs. For example, TMT-TA-COF prepared in Example 1 is formed by condensation of monomer 2,4,6-trimethyl-1,3,5-triazine (TMT) and monomer terephthaldehyde (TA).

[0080] RCF film: refers to regenerated cellulose film.

[0081] RCF / TMT-TA-COF film refers to the regenerated cellulose / TMT-TA-COF film prepared in Example 1.

[0082] TMT-TA-COF: vinyl COFs prepared from monomer 2,4,6-trimethyl-1,3,5-triazine (TMT) and monomer terephthaldehyde (TA).

[0083] TMT-BA-COF: vinyl COFs prepared from monomer 2,4,6-trimethyl-1,3,5-triazine (TMT) and monomer 4,4'-diphenyl aldehyde (BA).

[0084] TMT-DHBA-COF: vinyl COFs prepared from monomer 2,4,6-trimethyl-1,3,5-triazine (TMT) and monomer 3,3'-dimethoxy-[1,1'-biphenyl]-4,4'-dialdehyde (DHBA).

[0085] TMT-TD-COF: vinyl COFs prepared from monomer 2,4,6-trimethyl-1,3,5-triazine (TMT) and monomer [1,1':4',1''-terphenyl]-4,4''-dialdehyde (TD).

[0086] In the present application, unless otherwise specified, other test materials and instruments and equipment are conventional test materials in the art, which can be purchased through commercial channels.

[0087] In view of the limitations of existing pH and NH3 detection methods such as pH meter method, chromatography method, electrochemical method and biological method, and the fact that most of the detection methods are not conducive to food safety, it is difficult to apply them to the field of food spoilage monitoring. Covalent organic framework material (COF) is a crystalline porous polymer connected by covalent bonds, which has a regular and ordered pore structure and can be flexibly controlled in chemical properties. Vinyl-containing COF materials have unique fluorescence response performance and great application potential in the field of pH detection and gas sensing, and exhibit more excellent chemical stability and more efficient conjugated electron delocalization characteristics. Cellulose, as the most abundant natural polymer on earth, has many advantages such as strong plasticity, biodegradability and low cost. Its unique hydrogen-bonded network structure as a composite material base endows it with excellent mechanical strength, flexibility and biocompatibility. It is of great prospect to combine cellulose with COF to prepare a biocompatible composite bio-based fluorescent sensor. Therefore, the present application proposes a regenerated cellulose fluorescent sensing film material and its preparation method and application, which realizes the combination of regenerated cellulose and vinyl COF material, and can be used for high-sensitivity fluorescence detection and colorimetric detection of pH, NH3 and food spoilage monitoring.

[0088] In order for those skilled in the art to more clearly understand the technical solutions of the present application, the technical solutions of the present application will be described in detail below in combination with specific examples.

[0089] Example 1

[0090] A method for preparing a regenerated cellulose fluorescent sensing film material for pH and NH3 detection, comprising the following steps:

[0091] (1) Add monomers 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) into a 25 mL pressure bottle, treat under ultrasonic environment for 10 min to make the monomers fully dissolved in the solvent, then add catalyst KOH (33.6 mg, 0.6 mmol), continue to treat under ultrasonic environment for 20 min, quickly freeze the pressure bottle at 77 K by liquid nitrogen bath, degas by three freeze-thaw cycles, seal under vacuum, and place in 120℃ condition for 72 h. Collect the yellow precipitate by vacuum suction filtration, and wash with N,N-dimethylformamide and tetrahydrofuran in sequence to remove unreacted precursors, and finally dry at 80℃ under vacuum overnight.

[0092] (2) The cellulose from the pulp was dissolved in a ChOH / Ur / ZG solution (solid-liquid ratio 1:50, ChOH / Ur / ZG mass ratio 2:1:0.25%) to obtain a clear and homogeneous cellulose solution. Then, 10 g of the cellulose solution (2 wt%) was mixed with 4 mL of TMT-TA-COF (5 mg·mL⁻¹). -1 The ethanol dispersion was mixed and ultrasonicated for 20 min to ensure thorough mixing. A 100 mL water / ethanol (1:1, v:v) solution was added to the ultrasonicated dispersion as a regeneration bath, and ultrasonication continued for 1 h to completely regenerate the cellulose, yielding a self-assembled regenerated cellulose / TMT-TA-COF slurry with a solid content of 2%. 15 g of the regenerated cellulose / TMT-TA-COF slurry was taken, filtered to form a membrane, and hot-pressed and dried at 80℃ for 10 min to obtain the regenerated cellulose fluorescent sensing membrane material.

[0093] Figure 1 Let n be the monomer type used to prepare vinyl covalent organic framework materials, where n = 0, 1, 2, 3, or 4. Figure 1 The monomers in (a) and Figure 1 The monomers in (b) can react; Figure 1 The monomers in (c) and Figure 1 The monomers in (d) can react.

[0094] The XRD pattern of TMT-TA-COF is as follows: Figure 2 As shown in (a), TMT-TA-COF exhibits a strong diffraction peak (red curve) at 2θ=5º, which is assigned to the 100 crystal plane, indicating that TMT-TA-COF has good crystallinity. Furthermore, TMT-TA-COF shows characteristic peaks at 8.02º, 9.33º, 11.87º, and 24º, which are assigned to the (110), (200), (210), and (001) crystal planes, respectively. Structural simulation of TMT-TA-COF was performed using Material Studio software. Comparison revealed that the XRD results of TMT-TA-COF highly agree with the PXRD spectrum of the simulated AA packing model. Figure 2 (a), the black curve), indicates that the 2D layers in TMT-TA-COF are arranged in an AA stacking manner.

[0095] FTIR spectra of TMT-TA-COF and its monomers are as follows: Figure 2 As shown in (b), 1629 cm in TMT-TA-COF -1 The peak at 975 cm⁻¹ is a characteristic peak of C=C. -1 The peak at 1689 cm⁻¹ corresponds to the out-of-plane bending vibration of CH in trans-substituted olefins, confirming the formation of the conjugated system in the COF material. Furthermore, the peak at 1689 cm⁻¹ in TA...-1 The characteristic peak of C-O in aldehyde group disappeared after the formation of COF, and the characteristic peak of C=C in TMT shifted, which proved the successful preparation of TMT-TA-COF.

[0096] Figure 3 The infrared curve of regenerated cellulose / TMT-TA-COF film in (a) showed an increase in peak intensity at 2θ = 12.5°, and the crystalline region area increased, indicating that the presence of TMT-TA-COF affected the arrangement of regenerated cellulose and improved the crystallinity of the whole material. Figure 3 (b) is the XRD pattern of regenerated cellulose film and regenerated cellulose / TMT-TA-COF film. As can be seen from the figure, regenerated cellulose film and regenerated cellulose / TMT-TA-COF film show diffraction peaks at 2θ = 12.2°, 20° and 21.5°, which belong to the typical cellulose crystal form II, proving that regenerated cellulose is successfully prepared, and the XRD curve of regenerated cellulose / TMT-TA-COF film has a clear crystalline peak at 2θ = 5°, which belongs to the 100 peak surface of TMT-TA-COF, proving the successful combination of TMT-TA-COF and regenerated cellulose.

[0097] Example 2

[0098] Through the same synthesis method of COFs as in Example 1, TMT-BA-COF, TMT-DHBA-COF and TMT-TD-COF were successfully prepared, and their pH response properties were tested. Specifically:

[0099] Into a 25 mL pressure-resistant bottle, monomer 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, and the monomers were fully dissolved in the solvent under ultrasonic treatment for 10 min, then catalyst KOH (33.6 mg, 0.6 mmol) was added, and ultrasonic treatment was continued for 20 min, the pressure-resistant bottle was quickly frozen at 77 K by liquid nitrogen bath, degassed by three freeze-thaw cycles, sealed under vacuum, and placed in a 120°C environment for 72 h. The yellow precipitate was collected by vacuum filtration and washed with N,N-dimethylformamide and tetrahydrofuran in turn to remove unreacted precursors, and finally dried at 80°C under vacuum overnight.

[0100] Application Example 1

[0101] The determination of the pH response performance and its recycling performance of the COFs prepared in Example 1 and Example 2 includes the following steps:

[0102] (1) pH response performance test: The fluorescence spectra of TMT-TA-COF, TMT-BA-COF, TMT-DHBA-COF and TMT-TD-COF in different acid-base liquid environments were tested by 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 an ultrasonic treatment was performed for 1 h to prepare a TMT-TA-COF ethanol dispersion solution with a concentration of 0.5 mg·mL -1 . Subsequently, 10 μL of the TMT-TA-COF ethanol dispersion solution was mixed with 990 μL of phosphate buffer solution with different pH values (0.1 mol·L -1 ), to obtain TMT-TA-COF dispersions with different pH values (0.005 mg·mL -1 ). When testing the fluorescence spectrum, 2 mL of the TMT-TA-COF dispersion was placed in a four-side light-transmitting quartz cuvette, and the fluorescence spectrum of the TMT-TA-COF ethanol dispersion with different pH values was recorded by taking the ultraviolet-visible spectrum maximum absorption wavelength as the excitation wavelength.

[0103] Figure 4 is the ultraviolet spectrum of the vinyl COF, and it can be seen from the figure that the maximum excitation wavelength of the four COFs.

[0104] (2) pH cycle response performance test: The pH value of the TMT-TA-COF ethanol dispersion solution was adjusted by using acetic acid solution and NaOH solution, and the cycle response performance of TMT-TA-COF to the pH value was determined. Specifically, the pH value of the TMT-TA-COF ethanol dispersion solution was cyclically changed between 1 and 14 for 5 times, and the fluorescence intensity of the TMT-TA-COF ethanol dispersion solution at pH=1 and pH=14 in each cycle was determined, and the average value of three determinations was taken to evaluate the cycle response performance.

[0105] It can be seen from Figure 5 and Figure 6 that the material has obvious fluorescence intensity change to the solution with pH=1-14, has good linear relationship at pH=3-14, , and the material shows excellent reusability in the pH detection process, and the fluorescence intensity does not change obviously after 5 cycles.

[0106] Application Example 2

[0107] The determination of the NH3 response performance and the cycle use performance of the regenerated cellulose fluorescent sensing film material prepared in Example 1 includes the following steps:

[0108] (1) Test of NH3 response performance of the film: Before detecting NH3 gas, the regenerated cellulose fluorescent sensing film material was acidized in an HCl steam atmosphere of HCl solution (10 mol·L -1 ) for 3 min, and then purged with N2 gas for 30 s to remove residual HCl steam. The acidized regenerated cellulose / TMT-TA-COF film was placed in NH3 steam of different concentrations of NH3·H2O solution for 5 min, and then taken out and purged with N2 gas for 30 s to remove residual NH3 steam. The fluorescence spectrum of the regenerated cellulose fluorescent sensing film material was recorded under an excitation wavelength of 420 nm.

[0109] (2) Test of NH3 cycle response performance of the film: The regenerated cellulose fluorescent sensing film material treated by NH3 steam was fumigated by HCl solution, and then recycled to detect NH3 of the same concentration, and the fluorescence intensity of the regenerated cellulose fluorescent sensing film material in each cycle was measured three times to obtain an average value, so as to evaluate the cycle response performance of the regenerated cellulose fluorescent sensing film material to NH3.

[0110] By Figure 7 It can be seen that the material has excellent response performance to NH3, and has a good linear relationship when the concentration of NH3 is 2-50 ppb, , . It is shown that the fluorescence intensity gradually increases with the increase of the concentration of NH3. And the film material shows excellent reusability in the process of NH3 detection, and the fluorescence intensity range slightly decreases after 5 cycles.

[0111] In the detection of NH3, the regenerated cellulose fluorescent sensing film material presents color change from dark red to blue-green in the acidic to alkaline gas environment under the irradiation of ultraviolet light (excitation wavelength of 420 nm); the regenerated cellulose fluorescent sensing film material presents color change from orange red to yellow in the acidic to alkaline gas environment under the irradiation of natural light, as shown in Figure 8 .

[0112] Application Example 3

[0113] The application of the regenerated cellulose fluorescent sensing film material prepared in Example 1 in the field of food spoilage monitoring includes the following steps.

[0114] Fresh shrimp and pork were placed in a transparent PC box sterilized by high-temperature sterilization, and the regenerated cellulose / TMT-TA-COF film was fixed on the top of the box cover with transparent tape, and then the box was sealed and placed, and the color change of the regenerated cellulose / TMT-TA-COF film was observed and recorded every certain period of time to determine the degree of spoilage.

[0115] From Figure 9It can be seen that for the fresh shrimp and pork, the film is orange in the initial state, and after standing for 1 h, part of the film turns yellow, indicating that the reaction of freshness change begins; after standing for 3 h, the film basically turns yellow, indicating that the freshness of the food decreases over time. Therefore, the film can intuitively reflect the change of the freshness of the fresh shrimp and pork within a certain time through the color change, thereby realizing the visual detection of the freshness of the food.

[0116] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. Use of a regenerated cellulose fluorescent sensing membrane material in pH detection, NH3 detection and food spoilage monitoring, characterized in that, The components of the regenerated cellulose fluorescent sensing film material include regenerated cellulose and vinyl COFs, wherein the mass ratio of the regenerated cellulose and the vinyl COFs is 50:1 to 100:1; The vinyl COFs are prepared by using one or more of monomers 2,4,6-trimethyl-1,3,5-triazine, 2,5-dimethylpyrazine and 2,4,6-tricyano-1,3,5-trimethylbenzene and an aldehyde-based monomer as raw materials, under the action of a catalyst, by using a solvothermal method or a mechanical grinding method; The aldehyde-based monomer is one or more of p-phenylenediformde, 4,4'-diphenyldiformde, 3,3'-dimethoxy-[1,1'-biphenyl]-4,4'-diformde, [1,1':4',1''-terphenyl]-4,4''-diformde, trimesic aldehyde, 1,3,5-tris(4'-formylphenyl)benzene, 1,3,5-triazine-2,4,6-triformaldehyde and 2,4,6-tris(4-formylphenyl)-1,3,5-triazine; The catalyst is trifluoroacetic acid or potassium hydroxide; The preparation method of the regenerated cellulose fluorescent sensing film material includes the following steps: The vinyl COFs dispersion liquid and the cellulose solution are mixed, regenerated in a regeneration bath, and a mixed pulp of regenerated cellulose and vinyl COFs is obtained, which is filtered, dried and obtained. The specific steps of the solvothermal method are as follows: one or more of monomers 2,4,6-trimethyl-1,3,5-triazine, 2,5-dimethylpyrazine and 2,4,6-tricyano-1,3,5-trimethylbenzene and an aldehyde-based monomer and a solvent are mixed, the monomers are fully dissolved in the solvent under ultrasonic treatment, then a catalyst is added, ultrasonic treatment is continued, rapid freezing is performed through a liquid nitrogen bath, degassing is performed through multiple freezing-melting cycles, sealing is performed under vacuum, heating is performed under certain conditions, yellow precipitates are collected through vacuum filtration, and N,N-dimethylformamide and tetrahydrofuran are used for washing in sequence to remove unreacted precursors, and finally, drying is performed. The reaction temperature of the solvothermal method is 100-140 DEG C, and the reaction time is 48-80 h. The regenerated cellulose fluorescent sensing film material is placed in a steam atmosphere of ammonia water with different concentration gradients, and colorimetric detection is performed; the method for detecting NH3 by using colorimetric detection is that, under the irradiation of ultraviolet light, the film material presents a color change from dark red to blue-green in an acidic to alkaline gas environment, and under the irradiation of natural light, the regenerated cellulose fluorescent sensing film material presents a color change from orange red to yellow in an acidic to alkaline gas environment, so that colorimetric detection of the acidity and alkalinity of the gas can be realized. The degree of food spoilage is determined by colorimetric detection and NH3 concentration, and the color change of the film material is as follows: in the initial state, the color of the film is orange, as the standing time is prolonged, the freshness of the food decreases, and the color of the film gradually changes to yellow.

2. Use according to claim 1, characterized in that, 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 and solvent is (100-150 mg):(10-20 mL); Or, the grinding condition of mechanical grinding method is normal temperature grinding for 5-20 min.

3. Use according to claim 1, characterized in that, The vinyl COFs is dispersed in alcohol solvent to obtain a vinyl COFs dispersion liquid; The concentration of the vinyl COFs dispersion liquid is 0.1-10 mg / mL; Or, the cellulose raw material is mixed with the solvent in a certain ratio to dissolve the cellulose 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 system; The mass ratio of NaOH and urea in NaOH / urea is 1:1-2:1; the dissolution temperature is-12 to-8℃, and the dissolution time is 20-60 min; The mass ratio of quaternary ammonium salt and 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 and urea in choline hydroxide / urea is 1:1-4:1; the dissolution temperature is 30-60℃, and the dissolution time is 20-60 min; The mass ratio of choline hydroxide, urea, and zinc glycinate in choline hydroxide / urea / zinc glycinate is 2:1:0.25%-2:1:1.25%; the dissolution temperature is 30-60℃, and the dissolution time is 20-50 min; The mass ratio of the cellulose raw material and the solvent is 1:100-8:100; The ratio of the vinyl COFs dispersion liquid and the cellulose solution is (1-10 mL):(5-15 g); Or, 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); during regeneration in the regeneration bath, ultrasonic treatment is performed for 0.8-2 h; The solid content of the mixed slurry of regenerated cellulose and vinyl COFs is 1-5%.

4. A method of pH detection, characterized by, The method uses the regenerated cellulose fluorescent sensing film material in the application of any one of claims 1-3, and the method comprises: Mixing a dispersion liquid of the regenerated cellulose fluorescent sensing film material and solutions with different pH values to detect the pH value by using the change of fluorescence intensity; Or, placing the regenerated cellulose fluorescent sensing film material in solutions with different pH values to detect the pH value by using colorimetric method.

5. A method of NH3 detection, characterized in that, The method uses the regenerated cellulose fluorescent sensing film material in the application of any one of claims 1-3, and the method comprises: Acidifying the regenerated cellulose fluorescent sensing film material in an acid steam atmosphere, purging with N2, placing the acidified regenerated cellulose fluorescent sensing film material in a steam atmosphere of ammonia water with different concentration gradients, taking out after standing, purging with N2, and measuring the fluorescence intensity-NH3 concentration linear curve by a fluorescence spectrophotometer to use the curve as a standard for detecting the concentration of NH3; Or, placing the regenerated cellulose fluorescent sensing film material in a steam atmosphere of ammonia water with different concentration gradients and detecting by using colorimetric method. The method for detecting NH3 by colorimetric method is that the film material presents color change from dark red to blue-green in acid to alkaline gas environment under ultraviolet light, and the regenerated cellulose fluorescent sensing film material presents color change from orange red to yellow in acid to alkaline gas environment under natural light, so that the colorimetric visual determination of gas acidity and alkalinity can be realized.

6. A method of visual monitoring of food spoilage, characterized in that, The application adopts the regenerated cellulose fluorescent sensing film material in the application of any one of claims 1-3, and the specific method comprises: The regenerated cellulose fluorescent sensing film material is placed in a sealed container containing food, and the color change of the film material and the change of the fluorescence intensity of the film are used to detect the spoilage degree of the food by colorimetric visual method and NH3 concentration. The color change of the film material is that the color of the film is orange in the initial state, and the color of the film gradually changes to yellow as the standing time is prolonged and the freshness of the food decreases.

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