Preparation method and application of cellulose-based porous structural color sensing material

Abstract

The present application relates to a preparation method of cellulose-based porous structural color sensing material, characterized by the following steps: 1) preparation of cellulose-based pre-liquid; 2) preparation of pre-formed pore structure; 3) preparation of cellulose nanocrystal cross-linked network system material; and 4) preparation of cellulose-based porous structural color sensing material. The present application uses biomass material cellulose nanocrystal combined with directional freezing strategy to prepare porous structural color sensing material, which is simple, efficient, environmentally friendly, environmentally friendly, easy to industrialize; the porous structural color sensing material can be used as a core component of a sensor for detecting various solvents or gases, which makes up for the disadvantages of low reaction sensitivity, long detection time, inaccurate results, unstable repeated use and other disadvantages of the currently used gas / liquid detector, and has great application potential in the fields of colorimetric sensor, optical device, anti-counterfeiting and the like.

Description

Technical Field

[0001] This invention belongs to the field of sensor materials technology, specifically relating to a method for preparing and applying a cellulose-based porous color sensor material. Background Technology

[0002] In environmental monitoring, industrial production, food processing, and biomedicine, the detection and sensing of moisture and solvents are crucial. Structural colors—derived from interference, diffraction gratings, scattering, and photonic crystals in sensing materials—can be used to control the color changes of sensing materials within the visible light range by manipulating their micro / nanostructure. These stimulus-responsive structural color films can be synthesized from various materials. However, their complex fabrication processes, slow response times, and high costs make them unsuitable for all situations. Therefore, a low-cost, simple, rapid, and highly sensitive sensing material is needed for the detection of organic solvents or gases.

[0003] Cellulose, as the most abundant biopolymer on Earth, possesses remarkable properties such as non-toxicity, high modulus, hydrophilicity, biocompatibility, and biodegradability. Cellulose nanocrystals (CNCs), a nanoscale material derived from cellulose, can be obtained by hydrolyzing natural cellulose sources (wood, cotton, membranes, bacteria, etc.) with sulfuric acid, and then self-assemble into chiral nematic liquid crystals during solvent evaporation. Due to the balanced interaction between the electrostatic repulsion of sulfate groups and the hydrogen bonds of CNCs, a long-range ordered structure is formed. This chiral nematic structure is easily modulated by environmental stimuli, leading to reversible changes in structural color. Therefore, CNC sensing materials have been widely used as stimulus-responsive photonic materials for physical or chemical sensing. Some polymers, such as polyethylene glycol, polyacrylic acid, polyacrylamide, and polyvinylpyrrolidone, can be used as functional agents and plasticizers in CNC composites. When exposed to organic solvents, including ketones and alcohols, the state (volume, conformation, etc.) of the added polymer changes, leading to an increase in the distance between the CNC multilayer structures, resulting in color changes observable to the naked eye.

[0004] While the addition of these polymers can enable CNC to produce structural color changes in response to organic solvents, their response speed is slow, mostly limited to a single solvent and almost unresponsive to gases. Therefore, a strategy is needed to improve the response speed and enable responses to multiple solvents or gases. Directional cryo-casting is a convenient method for producing porous structures by unidirectional freezing of colloidal nanoparticle suspensions combined with ice template removal, showing great potential in manufacturing materials with highly complex structures. Therefore, based on the directional cryo-photopolymerization strategy, cellulose-based porous structural color sensing materials were prepared for the detection and sensing of various solvents or gases. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing and applying a cellulose-based porous color sensing material.

[0006] The technical problem solved by this invention is achieved through the following technical solution:

[0007] A method for preparing a cellulose-based porous color sensing material, characterized in that the method comprises the following steps:

[0008] 1) Preparation of cellulose-based presol: Cellulose nanocrystals, photopolymers, photoinitiators and solvents are mixed in a certain proportion to form a cellulose-based presol;

[0009] 2) Preparation of preformed pore structure: The above cellulose-based pre-liquid is evaporated to a suitable concentration and directional freezing is performed to control the arrangement and growth direction of ice crystals. The preformed pore structure of the sensing material is formed through the occupancy effect of ice crystals.

[0010] 3) Preparation of cellulose nanocrystal cross-linked network system material: The pre-formed porous structure after directional freezing is placed under ultraviolet light for complete polymerization to prepare cellulose nanocrystal cross-linked network system material that has been positioned by ice crystals;

[0011] 4) Preparation of cellulose-based porous color sensing material: The obtained cellulose nanocrystal cross-linked network system material with ice crystal positioning is dried to obtain cellulose-based porous color sensing material.

[0012] Furthermore, in the cellulose-based pre-liquid of 1), the oven-dry weight of cellulose nanocrystals is 3% to 10% of the weight of the cellulose-based pre-liquid, the weight of the photopolymer is 1% to 5% of the weight of the cellulose-based pre-liquid, and the weight of the photoinitiator is 1% to 4% of the oven-dry weight of the photopolymer.

[0013] Furthermore, the solution concentration of the photopolymer in 1) is 15% to 25%.

[0014] Moreover, the photopolymer in 1) is one or more of acrylamide, acrylic acid, N-isopropylacrylamide, and polyethylene glycol diacrylate.

[0015] Moreover, the photoinitiator in 1) is one or more of HMPP1173, HMPP2959, HMPP4265, HMPP500, and HMPP819DW.

[0016] Moreover, the directional freezing in 2) is one or more of unidirectional freezing, bidirectional freezing, radial freezing, external magnetic field controlled freezing, and electric field controlled freezing.

[0017] Moreover, the suitable concentration obtained by evaporating the cellulose-based pre-liquid in 2) is 18wt% to 40wt%.

[0018] Moreover, the irradiation time of ultraviolet light in 3) is 30s to 30min.

[0019] Moreover, the drying process in 4) is one or more of the following: room temperature drying, vacuum freeze drying, and heating drying.

[0020] Application of a cellulose-based porous color sensing material in the detection and sensing of liquid and gas phase solvents.

[0021] The advantages and beneficial effects of this invention are as follows:

[0022] This invention prepares porous color sensing materials by using biomass cellulose nanocrystals combined with a directional freezing strategy. The preparation method is simple, efficient, environmentally friendly, and easy to industrialize. The porous color sensing materials prepared by this invention can be used as core components of sensors for the detection of various solvents or gases, overcoming the shortcomings of existing gas / liquid detectors on the market, such as low response sensitivity, long detection time, inaccurate results, and instability with repeated use. Moreover, the preparation method is simple, biocompatible, green and biodegradable, low in cost, and convenient to use, showing great application potential in colorimetric sensors, optical devices, anti-counterfeiting and other fields. Attached Figure Description

[0023] Figure 1 This is a flowchart illustrating the preparation process of the present invention;

[0024] Figure 2 This is the ultraviolet spectrum of the cellulose-based porous color sensing material prepared according to the present invention;

[0025] Figure 3 This is a physical image of the cellulose-based porous color sensing material prepared according to the present invention;

[0026] Figure 4 This is a scanning electron microscope image of the cellulose-based porous color sensing material prepared in this invention.

[0027] Figure 5 The image shows the ethanol solvent response UV spectrum of the cellulose-based porous color sensing material prepared in this invention.

[0028] Figure 6 This is a photograph of the color change of the cellulose-based porous color sensing material prepared in this invention in response to different concentrations of ethanol gas. Detailed Implementation

[0029] The present invention will be further described in detail below through specific embodiments. The following embodiments are merely descriptive and not limiting, and should not be used to limit the scope of protection of the present invention.

[0030] Example 1

[0031] like Figure 1 As shown, a method for preparing a cellulose-based porous color sensing material is innovative in that the preparation method comprises the following steps:

[0032] 1) Cotton was hydrolyzed with 64% concentrated sulfuric acid for 1-5 hours. After hydrolysis, the supernatant was obtained by repeated centrifugation. The aqueous suspension obtained by dialyzing the supernatant for several days was rotary evaporated. After the concentration was adjusted to a suitable level, it was put into a headspace bottle and placed in a refrigerator for future use.

[0033] 2) Mix 6 wt% cellulose nanocrystals, 15 wt% polyethylene glycol diacrylate, and 2 wt% photoinitiator HMPP1173 until homogeneous to form a cellulose-based presol.

[0034] 3) Pour the cellulose-based pre-liquid into a polytetrafluoroethylene culture dish and allow it to evaporate naturally to 26 wt% at room temperature. Then place it on a directional freezing substrate constructed of liquid nitrogen and copper sheets for directional freezing.

[0035] 4) The directionally frozen sample was polymerized under a UV lamp for 100 seconds. After the sample was polymerized, it was placed at room temperature until the moisture inside the film was completely dried, thus obtaining a cellulose-based porous color sensing material.

[0036] Example 2

[0037] The difference from Example 1 is that: the cellulose-based pre-liquid was poured into a polytetrafluoroethylene petri dish and naturally evaporated to 24 wt% at room temperature. Then, it was placed on a directional freezing substrate constructed of liquid nitrogen and copper sheets for directional freezing. The directionally frozen sample was polymerized under a UV lamp for 120 seconds. After the sample polymerization was completed, it was placed at room temperature until the moisture inside the film was completely dried, thus obtaining a cellulose-based porous color sensing material.

[0038] Example 3

[0039] The difference from Example 1 is that the cellulose-based pre-liquid was poured into a polytetrafluoroethylene petri dish and allowed to evaporate naturally to 28 wt% at room temperature. Then it was placed on a directional freezing substrate constructed of liquid nitrogen and copper sheets for directional freezing.

[0040] The cellulose-based porous color sensing materials prepared through the three examples showed relatively small differences in detection and sensing of liquid and gaseous solvents. Therefore, Example 1 was used for analysis.

[0041] like Figure 2 , Figure 3As shown, the images are the ultraviolet spectrum and physical image of the cellulose-based porous structured color sensing material prepared by Example 1 of this invention. The two images show that the cellulose-based porous structured color sensing material prepared by this invention is located in the blue region of the visual spectrum. Therefore, when used for the detection and sensing of liquid and gaseous solvents, it has a wide range of color changes and is easier to observe visually.

[0042] like Figure 4 The image shown is a SEM image of the cellulose-based porous color sensing material prepared according to Example 1 of this invention. A layered "pore" structure is observed in the cross-section, proving that the cellulose-based porous color sensing material was successfully prepared according to this invention. Subsequently, this sensing material was used for the detection of ethanol liquid, as shown... Figure 5 As shown, this is the real-time response UV spectrum of ethanol. Under the stimulation of liquid ethanol, the porous structure inside the cellulose-based color film rapidly absorbs the ethanol, causing a change in its internal pitch. Furthermore, over time, the internal pitch continuously increases, resulting in a redshift and thus exhibiting a dynamic color change visible to the naked eye.

[0043] Cellulose-based porous structured color sensing materials can be used for the detection of methanol liquid. Under the stimulation of methanol liquid, the "pore" structure inside the cellulose-based porous structured color film rapidly absorbs the methanol liquid, thereby causing changes in the internal structure of the structured color sensing material, which in turn shows a color change visible to the naked eye. Moreover, the color change rate caused by methanol is much different from that caused by ethanol. Therefore, this cellulose-based porous structured color film can be used for the response of various solvents and gases.

[0044] Cellulose-based porous structured color sensing materials can be used to detect water vapor. When stimulated by water vapor, the "pores" inside the cellulose-based porous structured color film rapidly absorb water vapor, thereby causing changes in the internal structure of the structured color sensing material, which in turn shows a color change visible to the naked eye.

[0045] like Figure 6 As shown, this is a physical image of the color change of the cellulose-based porous color sensing material obtained by Example 1 of this invention in response to different concentrations of ethanol gas. Based on the ratio of water to ethanol, 0%, 20%, 40%, 60%, 80%, and 100% concentrations of ethanol were prepared and atomized using a humidifier. This was used to illustrate the color response of the cellulose-based porous color sensing material to different concentrations of ethanol gas. During this stimulus-response process, as... Figure 6 As shown, significant color changes can be observed with the naked eye over time.

[0046] In summary, the cellulose-based porous color sensing material prepared by this invention can be used to respond to a variety of solvents and gases, and is simple to prepare and bio-friendly, showing good application prospects in environmental monitoring, industrial production, food processing and biomedicine.

[0047] Although embodiments and drawings of the present invention have been disclosed for illustrative purposes, those skilled in the art will understand that various substitutions, variations and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the scope of the present invention is not limited to the contents disclosed in the embodiments and drawings.

Claims

1. A method for preparing a cellulose-based porous color sensing material, characterized in that: The steps of the method are as follows: 1) Preparation of cellulose-based presol: cellulose nanocrystals, photopolymers, photoinitiators and solvents are mixed in a certain proportion to form a cellulose-based presol; 2) Preparation of preformed pore structure: The above cellulose-based pre-liquid is evaporated to a suitable concentration of 18wt%~40wt%, and directional freezing is performed to control the arrangement and growth direction of ice crystals. The preformed pore structure of the sensing material is formed through the occupancy effect of ice crystals. 3) Preparation of cellulose nanocrystal cross-linked network system material: The pre-formed porous structure after directional freezing is placed under ultraviolet light for complete polymerization to prepare cellulose nanocrystal cross-linked network system material that has been positioned by ice crystals; 4) Preparation of cellulose-based porous color sensing material: The obtained cellulose nanocrystal cross-linked network system material with ice crystal positioning is dried to obtain cellulose-based porous color sensing material.

2. The method for preparing the cellulose-based porous color sensing material according to claim 1, characterized in that: In the cellulose-based pre-liquid of 1), the oven-dry weight of cellulose nanocrystals is 3% to 10% of the weight of the cellulose-based pre-liquid, the weight of the photopolymer is 1% to 5% of the weight of the cellulose-based pre-liquid, and the weight of the photoinitiator is 1% to 4% of the oven-dry weight of the photopolymer.

3. The method for preparing the cellulose-based porous color sensing material according to claim 1, characterized in that: The concentration of the photopolymer solution in 1) is 15%~25%.

4. The method for preparing the cellulose-based porous color sensing material according to claim 1, characterized in that: The photopolymer in 1) is one or more of acrylamide, acrylic acid, N-isopropylacrylamide, and polyethylene glycol diacrylate.

5. The method for preparing the cellulose-based porous color sensing material according to claim 1, characterized in that: The photoinitiator in 1) is one or more of HMPP1173, HMPP2959, HMPP4265, HMPP500, and HMPP819DW.

6. The method for preparing the cellulose-based porous color sensing material according to claim 1, characterized in that: In the second part, directional freezing is one or more of the following: unidirectional freezing, bidirectional freezing, radial freezing, external magnetic field controlled freezing, and electric field controlled freezing.

7. The method for preparing the cellulose-based porous color sensing material according to claim 1, characterized in that: The irradiation time of ultraviolet light in 3) is 30s~30min.

8. The method for preparing the cellulose-based porous color sensing material according to claim 1, characterized in that: The drying process in 4) is one or more of the following: room temperature drying, vacuum freeze drying, and heat drying.

9. The application of the cellulose-based porous color sensing material prepared by the method according to any one of claims 1 to 8 in the detection and sensing of liquid and gas phase solvents.

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