CN109054805B - Preparation method of fluorescent cholesteric cellulose nanocrystal film with acid-base gas response - Google Patents
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Abstract
The invention discloses a preparation method of a fluorescent cholesteric cellulose nanocrystal film with acid-base gas response, which comprises the following steps of 1) preparing a cellulose nanocrystal suspension; 2) synthesizing an AIE organic small molecule fluorescent material; 3) preparing AIE fluorescent suspension; 4) mixing the cellulose nanocrystal suspension with an AIE organic micromolecule fluorescent material, magnetically stirring, and performing ultrasonic treatment; 5) and carrying out evaporation induction co-assembly process to obtain the fluorescent cellulose film with the cholesteric phase structure. The invention solves the problem of phase separation of the cellulose nanocrystals and the non-water-soluble organic small molecule fluorescent material, so that the cholesteric phase structure is retained, and the fluorescent color film with the periodic structure is successfully prepared. The composite film with both fluorescence characteristic and cholesteric phase structure shows the change of various optical characteristics of fluorescence, visible light and circularly polarized light under acid and alkaline atmosphere, can be accurately and efficiently applied to acid and alkaline gas detection, and can be recycled.
Description
Technical Field
The invention belongs to the technical field of optics and composite materials, relates to a gas response and recyclable high-efficiency sensor, and particularly relates to preparation of a cholesteric cellulose nanocrystal film sensitive to acid and alkaline gases and having a fluorescence characteristic.
Background
With the rapid development of industrialization, various toxic and harmful gases and polluted dust are discharged into the atmosphere, which causes great harm to human and environment. Among them, the harm of acid-base exhaust gas is particularly serious, which is generated in many industries. Highly volatile gases such as hydrochloric acid, ammonia gas, etc. have also been environmental concerns worldwide, and are therefore important for routine monitoring of acid and base gases.
Known conventional electrochemical gas sensors typically use metal oxides and conductive polymers as sensing materials due to the high sensitivity and selective detection characteristics of such materials. However, many such sensors are complex and expensive to operate, which limits their effective implementation and development. Therefore, the development of a gas response sensor with the characteristics of easy operation, high sensitivity, low price, stable circulation and environmental friendliness is urgently needed.
Cellulose is the most abundant natural renewable polymer on the earth, Cellulose Nanocrystal (CNC) lyotropic cholesteric liquid crystal can be formed after treatment of acid hydrolysis and the like, after evaporation, drying and film formation, the cholesteric structure of the cellulose is still retained, the characteristic of photonic crystal is shown, light with specific wavelength can be selectively reflected, and the characteristic can be applied to the sensing field. The organic small-molecule fluorescent materials are various in types, the structures are easy to adjust, the photoelectric properties can be changed, some organic fluorescent materials have strong responsiveness to acid and alkali, for example, acid gas can cause fluorescence quenching of certain organic fluorescent small molecules, and therefore the organic small-molecule fluorescent materials have good application prospects in the aspect of gas detection.
Unlike the traditional single-property fluorescence detector in patent CN102702558B, the photonic crystal property of the cholesteric phase structure of the CNC film is organically combined with the fluorescence property of the organic small molecule fluorescent material, so that the processability and applicability of the organic small molecule fluorescent material are improved, and at the same time, the material is endowed with more accurate detectability. The compatibility of the precursor with the matrix material is a problem to be solved in the preparation of the composite material. Unlike fluorescent materials such as carbon quantum dots, rare earth up-conversion luminescent materials and plasmon gold nanoparticles which are easily soluble in water, most organic small-molecule fluorescent materials are only soluble in organic solvents, and CNC suspension exists in a water phase system, if CNC and the organic small-molecule fluorescent materials are simply mixed together, a phase separation phenomenon will occur. And a method of transferring CNC into an organic solvent by using a solvent substitution method and mixing with an organic small molecule fluorescent material is generally used, and a method of grafting an organic fluorescent small molecule to the surface of CNC by chemical modification is also used. Both methods are complicated, time and labor consuming, and the cholesteric structure is difficult to preserve after mixing. Therefore, the problem to be solved is to ensure that the CNC can still complete self-assembly while the organic small-molecule fluorescent material exists.
Disclosure of Invention
Aiming at the problems of complex sensor operation and high cost caused by single characteristic of a fluorescence detection sensor in the prior art, the invention aims to provide a preparation method of a fluorescence cholesteric cellulose nanocrystal film with acid-base gas response, and prepare a fluorescence cholesteric CNC film which can realize detection of various optical characteristics of acid-base gas and can be recycled. The sensor has high sensitivity, and can realize accurate detection of acid and alkaline gases.
The technical scheme adopted by the invention is as follows:
a preparation method of a fluorescent cholesteric cellulose nanocrystal film with acid-base gas response specifically comprises the following steps:
1) treating cellulose by a sulfuric acid hydrolysis method or a TEMPO oxidation method to prepare a CNC suspension;
preparing a nanocellulose lyotropic Nx-LCs suspension by a sulfuric acid hydrolysis method: mixing microcrystalline cellulose powder and 64% sulfuric acid according to the mass fraction of 1 g: mixing 17.5ml of the mixture, heating, stirring at 40-50 ℃ for reaction for 0.5-1.5h, adding a large amount of deionized water to stop the reaction, removing excessive acid in the solution by centrifugation and dialysis, performing ultrasonic treatment on the solution by adopting high-power ultrasonic waves, and concentrating to obtain nano-cellulose lyotropic Nx-LCs suspension with different pitches; the power range of the high-power ultrasonic treatment is 100-1200W, the working frequency range is 21-25KHz, the time range is 1-180min, and the diameter of the amplitude transformer is 2-30 mm;
2) aggregation-induced emission (AIE) organic small-molecule fluorescent materials (9,10-bis (2-phenyl-2- (2-pyridyl)) vinyl anthracene (9,10-bis ((E) -2-phenyl-2- (pyridine-2-yl) vinyl) anthrene, BPP2VA), 9,10-bis (p-pyridylvinyl) anthracene ((9,10-bis ((E) -2- (pyridine-4-yl) vinyl) anthrene, BP4VA), tetraphenylethyleneoxazolidine (TPE-OX) and the like) are synthesized by chemical reaction, and the AIE organic small-molecule fluorescent materials are dissolved in respective good solvents and are prepared into a concentration of 10-3A mol/L solution;
3) transferring a certain amount of the solution prepared in the step 2), dropwise adding the solution into a certain amount of deionized water, magnetically stirring for a period of time, and after uniformly mixing, forming stable nano aggregates by the AIE fluorescent micromolecules in water to prepare an AIE fluorescent suspension;
4) according to different mixing proportions of the CNC suspension and the AIE organic micromolecule fluorescent material, dropwise adding a certain amount of the CNC suspension prepared in the step 1) into the AIE fluorescent suspension prepared in the step 3), magnetically stirring for a period of time, and regulating and controlling the screw pitch of the cholesteric phase structure through ultrasonic treatment after uniform and stable mixing;
5) placing the mixed suspension prepared in the step 4) in a polystyrene dish, standing at normal temperature, performing evaporation induction co-assembly process, and obtaining the fluorescent cellulose film with the cholesteric phase structure after 3-5 days.
Further, there are various AIE organic small molecule fluorescent materials in step (2), such as spiropyran or spirooxazine compounds, which are any one of (9,10-bis (2-phenyl-2- (2-pyridyl)) vinylanthracene, 9,10-bis (p-pyridylvinyl) anthracene, and tetraphenylethyleneoxazolidine.
Further, in the magnetic stirring process in the step (3), small magnetons with the diameter of 5mm and the length of 10mm are selected, and the magnetic stirring speed in the process is accurately controlled within the range of 500-1500rpm, so as to prevent the fluorescent substances from being separated out and hanging on the wall of the container; the magnetic stirring time was controlled until a significant tyndall was observed.
Further, in the magnetic stirring process in the step (4), small magnetons with the diameter of 5mm and the length of 10mm are selected, the magnetic stirring speed range in the process is accurately controlled to be 500-1500rpm, and the magnetic stirring time is controlled to prevent phase separation.
Further, the ultrasonic treatment in the step (4) is carried out under the conditions of an ice-water bath environment and 60W power for 1-15 min.
Further, the fluorescent cellulose composite film prepared in the step (5) is placed in a volatile acid atmosphere, the color of the film is changed due to the change of the thread pitch of the cholesteric phase structure, and the fluorescence intensity is weakened; under the alkaline atmosphere, the change of the thread pitch of the cholesteric phase structure causes the color of the film to be recovered, and the corresponding ultraviolet visible spectrum and the fluorescence spectrum are regularly changed.
Furthermore, the acid gas is any one of volatile acid nitric acid, formic acid, acetic acid, trifluoroacetic acid or hydrobromic acid.
Further, the alkaline gas is any one of volatile alkaline ammonia water, diethylamine or triethylamine.
Further, the thin composite cholesteric phase structure of the fluorescent cellulose prepared in the step (5) has a photon forbidden band effect, and the change of the thread pitch can cause the change of circularly polarized light.
Further, the addition amount of the AIE organic small molecule fluorescent material solution in the step (4) is in the range of 100-.
Further, the solid content of the CNC added in the step (4) is in a range of 0.1-0.3g, and the optimal addition amount is between 0.15-0.2g, which is determined based on the amount (3-10g) of the deionized water in the suspension, so that the CNC is too little to form a film, and too much film is too thick to influence the fluorescence effect.
The invention has the beneficial effects that:
in the invention, an AIE organic small molecular fluorescent material is selected, aiming at preventing aggregation induced quenching (ACQ) phenomenon after drying and film forming, and well solving the phase separation problem of two-phase substances by accurately and reasonably controlling the proportion and mixing conditions of CNC and the organic small molecular fluorescent material. In the high-speed stirring process, the dropwise added organic fluorescent small molecule solution can be quickly dispersed in water, and the large centrifugal force effectively avoids the agglomeration of the organic fluorescent small molecules, so that the organic fluorescent small molecules can stably exist in an aqueous phase system. After the CNC suspension is added, the two substances are further enabled to rapidly move in water by high-speed stirring, and the whole system is filled, so that the aggregation and the layering of the two substances are effectively avoided. Compared with the method for preparing the fluorescent cellulose by grafting the fluorescent group on the cellulose molecular chain through chemical modification, the method is more environment-friendly and simpler. The prepared composite film shows a periodic spiral structure and also shows fluorescence. The two characteristics enable the composite film to show the change of fluorescence and visible light at the same time under acid and alkaline atmosphere, and the photon forbidden band effect specific to the cholesteric phase structure can also cause the change of circularly polarized light. Therefore, the composite film has various optical characteristics, so that the composite film can be accurately and efficiently applied to acid and alkali gas detection.
Drawings
FIG. 1 is a molecular structure diagram of acid-base gas sensitive AIE organic small molecule fluorescent materials BPP2VA, BP4VA and TPE-OX.
FIG. 2 is a polarization microscope photograph of the CNC/BPP2VA fluorescent composite film having a cholesteric phase structure of example 1.
FIG. 3 is a graph of the fluorescence spectra of the CNC/BPP2VA composite film in hydrochloric acid atmosphere of example 1 at different times.
FIG. 4 is a graph of the fluorescence spectra of the CNC/BPP2VA composite film recovered under the triethylamine atmosphere in example 1 at different times.
FIG. 5 is a UV-Vis spectrum of the CNC/BPP2VA composite film in hydrochloric acid atmosphere of example 1 at different times.
FIG. 6 is a UV-Vis spectrum of the original CNC/BPP2VA composite film of example 1 and the recovered CNC/BPP2VA composite film under triethylamine atmosphere.
Figure 7 digital photograph of CNC/BPP2VA composite film prepared by direct blending process in comparative example 1.
Detailed Description
The present invention is further illustrated by the following examples, but the scope of the present invention is not limited to the following examples.
Example 1:
a preparation method of a fluorescent cholesteric cellulose nanocrystal film with acid-base gas response comprises the following steps:
1) preparing a CNC suspension: 10g of Whatman CF11 cellulose powder and 175mL of a 64 w% sulfuric acid solution were each charged into a round-bottomed flask, and the reaction was magnetically stirred at 45 ℃ for 1 hour and quenched by adding 1L of deionized water. Standing for 1 day, pouring out supernatant, centrifuging the lower layer turbid solution at 10000rpm for multiple times, collecting the upper layer turbid solution, and placing into a container with molecular weight cutoff of 1.4 × 104Is disclosedDialyzing the bag to remove redundant free acid in the suspension, and dialyzing for 15 days until the CNC suspension is neutral for later use;
2) preparation of BPP2 VA: adding anthracene (38.0mmol), paraformaldehyde (200.0mmol), zinc chloride (51.4mmol) and 1, 4-dioxane (80.0ml) into a single-neck round-bottom flask in sequence according to a determined proportion, dropwise adding a certain amount of concentrated hydrochloric acid, carrying out reflux reaction at 50 ℃ for 3 hours to obtain 9,10-bis (chloromethyl) anthracene, reacting the 9,10-bis (phosphonyl) anthracene with triethyl phosphite to obtain 9,10-bis (phosphonyl) anthracene, mixing the product (2.1mmol) with 2-benzoylpyridine (8.4mmol), potassium tert-butoxide (17.8mmol) and tetrahydrofuran (80.0ml), and carrying out reaction treatment to obtain yellow powder BPP2 VA;
3) the fluorescent material BPP2VA prepared above is dissolved in good solvent tetrahydrofuran, and the concentration is 10- 3A mol/L solution for later use;
4) 200 μ L of the prepared BPP2VA solution was pipetted and added dropwise to 4g of deionized water. To avoid precipitation, the process requires precise control of the magnetic stirring speed (1000rpm) to uniformly disperse the fluorescent material, and selection of appropriate sized magnetons to prevent the fluorescent material from precipitating and hanging on the vessel wall. Stirring for 10min, and after uniformly mixing, the BPP2VA fluorescent micromolecules form stable nano aggregates in water, and an obvious Tyndall phenomenon can be observed;
5) according to a certain mixing ratio of CNC and BPP2VA fluorescent micromolecules, 1g of 15 wt% CNC suspension is dropwise added into the suspension prepared in the step 4). This process also requires precise control of the magnetic stirring speed (1000rpm), which is a critical step to prevent phase separation from occurring. Stirring for 10min, and regulating and controlling the pitch of the cholesteric phase structure by ultrasonic treatment for different time after uniform and stable mixing;
6) 4.5g of the CNC/BPP2VA mixed suspension obtained in step 5) was placed in a 38mm polystyrene dish and allowed to stand at 25 ℃ to ensure that the evaporation-induced co-assembly process was carried out and that a fluorescent cellulose film having a cholesteric structure was obtained after about 3 days.
7) The CNC/BPP2VA composite film is placed in hydrochloric acid atmosphere, the color of the film is changed due to the change of the thread pitch of the cholesteric phase structure, the fluorescence intensity is weakened and can be restored in triethylamine atmosphere, and the corresponding ultraviolet visible spectrum and the fluorescence spectrum can regularly change. Furthermore, since the cholesteric structure has a photon forbidden band effect, a change in the pitch also causes a change in the circularly polarized light.
The product film prepared in example 1 was observed by polarization microscopy to have a distinct characteristic fingerprint texture, indicating that it has a cholesteric phase structure, as shown in figure 2.
The product film prepared in example 1 has a significantly reduced fluorescence intensity and a certain red shift of the fluorescence emission peak with time under the hydrochloric acid atmosphere, as shown in fig. 3.
The recovery of the product film prepared in example 1 in the presence of triethylamine after the acid gas treatment was observed to gradually increase the fluorescence intensity with time, as shown in fig. 4.
The product film prepared in example 1 has red shift of ultraviolet absorption peak with time under hydrochloric acid atmosphere, which shows that the color of the film is changed due to the change of the screw pitch, as shown in fig. 5.
The product film prepared in example 1 was treated with acid gas and then recovered under triethylamine atmosphere, and the ultraviolet absorption peak returned to the original position, indicating that the color of the film was recovered to the original state, as shown in fig. 6.
Example 2:
this example is the same as example 1, except that the AIE organic small molecule fluorescent material used may also be spiropyran or spirooxazine compounds responding to acid and alkaline gases, including BP4VA, TPE-OX, etc.
Example 3:
this example is the same as example 1, except that the acid gas used may also be a volatile acid such as nitric acid, formic acid, acetic acid, trifluoroacetic acid and hydrobromic acid.
Example 4:
this example is the same as example 1, except that the basic gas used may also be a volatile base such as ammonia.
Example 5:
this example is the same as example 1, except that the CNC suspension was prepared using TEMPO oxidation, see chinese patent: the preparation method in CN106317423A comprises the steps of hydrolyzing cotton cellulose microcrystals with 4mol/L hydrochloric acid to obtain a cellulose suspension with reduced size, oxidizing the cellulose suspension obtained after the hydrolysis with a TEMPO-NaBr-NaClO system, centrifuging, dialyzing and concentrating to obtain a CNC suspension with a certain concentration.
It is reported that the adsorption capacity of the TEMPO oxidized CNC to the fluorescent material is enhanced, and the luminescence property is improved.
Example 6:
this example is the same as example 1, except that the amount of BPP2VA solution added dropwise in step 4) can be in the range of 100-. When the amount of the fluorescent substance added is too small, the intensity of the fluorescent substance is too weak, and when the amount of the fluorescent substance added is too large, the cholesteric structure is destroyed.
Example 7:
the present embodiment is the same as embodiment 1, except that the magnetic stirring speed in step 4) is in the range of 500-1500rpm, the phase separation is easy to occur when the speed is too slow, the fluorescent small molecules will not form nano aggregates in water, and the fluorescent small molecules will be separated out and suspended on the wall of the container when the speed is too fast.
Example 8:
this example is the same as example 1 except that the added CNC solid content in step 5) ranges from 0.1 to 0.3g, the optimum addition amount is between 0.15 and 0.2 g. When the amount is too small, the film is not easily formed, and when the amount is too large, the fluorescent effect may be affected.
Comparative example 1:
dissolving organic fluorescent material BPP2VA in organic solvent (tetrahydrofuran or dimethylformamide) to obtain a solution with a concentration of 10-3And (3) mixing 300 mu L of the prepared solution with 5g of CNC suspension with the mass fraction of 3% of the prepared solution in mol/L, selecting small magnetons with the diameter of 5mm and the length of 10mm, controlling the speed of magnetic stirring to be 1000rpm, stirring for 10min, and performing ultrasonic treatment for 10min under the power of 60W in an ice-water bath. The observation shows that the two-phase material has obvious componentsLayer phenomenon, the fluorescent substance BPP2VA precipitated, indicating that the two-phase substance was phase separated and co-assembly could not be achieved. In the film formed by evaporation drying, the CNC and BPP2VA distribution was very uneven, and the fluorescent substance was precipitated and attached to the film surface, as shown in fig. 7.
The above description is not meant to be limiting, it being noted that: it will be apparent to those skilled in the art that various changes, modifications, additions and substitutions can be made without departing from the true scope of the invention, and these improvements and modifications should also be construed as within the scope of the invention.
Claims (9)
1. A preparation method of a fluorescent cholesteric cellulose nanocrystal film with acid-base gas response is characterized by comprising the following steps:
1) treating cellulose by a sulfuric acid hydrolysis method or a TEMPO oxidation method to prepare a cellulose nanocrystal suspension;
2) synthesizing the AIE organic micromolecule fluorescent material through chemical reaction, dissolving the AIE organic micromolecule fluorescent material in respective good solvent to prepare the AIE organic micromolecule fluorescent material with the concentration of 10-3A mol/L solution;
3) transferring a certain amount of the solution prepared in the step 2), dropwise adding the solution into a certain amount of deionized water, magnetically stirring for a period of time, and after uniformly mixing, forming stable nano aggregates by the AIE fluorescent micromolecules in water to prepare an AIE fluorescent suspension;
4) according to the volume ratio of the cellulose nanocrystal suspension to the AIE fluorescent suspension of 1: 5-1:6, dropwise adding a certain amount of the cellulose nanocrystal suspension prepared in the step 1) into the AIE fluorescent suspension prepared in the step 3), magnetically stirring for a period of time, and regulating and controlling the screw pitch of the cholesteric phase structure by ultrasonic treatment after uniform and stable mixing;
5) placing the mixed suspension prepared in the step 4) in a polystyrene dish, standing at normal temperature, performing evaporation induction co-assembly process, and obtaining the fluorescent cellulose film with the cholesteric phase structure after 3-5 days.
2. The method for preparing a fluorescent cholesteric cellulose nanocrystal film with acid-base gas response according to claim 1, wherein the AIE organic small molecule fluorescent material in step (2) is any one of 9,10-bis (2-phenyl-2- (2-pyridyl)) vinyl anthracene, 9,10-bis (p-pyridylvinyl) anthracene and tetraphenylethyleneoxazolidine.
3. The preparation method of the fluorescent cholesteric cellulose nanocrystal film with acid-base gas response according to claim 1, wherein in the step (3), small magnetons with the diameter of 5mm and the length of 10mm are selected during the magnetic stirring, and the speed of the magnetic stirring during the process is precisely controlled within the range of 500-1500rpm to prevent the fluorescent substances from being separated out and hanging on the wall of the container; the magnetic stirring time was controlled until a significant tyndall was observed.
4. The method for preparing a fluorescent cholesteric cellulose nanocrystal film with acid-base gas response according to claim 1, wherein in the step (4), a small magneton with a diameter of 5mm and a length of 10mm is selected during the magnetic stirring, the magnetic stirring speed in the process is accurately controlled within a range of 500-1500rpm, and the magnetic stirring time is controlled to prevent phase separation.
5. The method for preparing the fluorescent cholesteric cellulose nanocrystal film with acid-base gas response according to claim 1, wherein the ultrasonic treatment in the step (4) is carried out under the following conditions: ice water bath environment, 60W power, time 1-15 min.
6. The method for preparing a fluorescent cholesteric cellulose nanocrystal film with acid-base gas response according to claim 1, wherein the fluorescent cellulose composite film prepared in the step (5) is placed in a volatile acid atmosphere, the color of the film is changed due to the pitch change of the cholesteric phase structure, and the fluorescence intensity is weakened; under the alkaline atmosphere, the change of the thread pitch of the cholesteric phase structure causes the color of the film to be recovered, and the corresponding ultraviolet visible spectrum and the fluorescence spectrum are regularly changed.
7. The method for preparing the fluorescent cholesteric cellulose nanocrystal film with acid-base gas response according to claim 6, wherein the acid gas is any one of volatile acid nitric acid, formic acid, acetic acid, trifluoroacetic acid or hydrobromic acid.
8. The method for preparing the fluorescent cholesteric cellulose nanocrystal film with acid-base gas response according to claim 6, wherein the basic gas is any one of volatile basic ammonia, diethylamine or triethylamine.
9. The method for preparing the fluorescent cholesteric cellulose nanocrystal film with acid-base gas response according to claim 1, wherein the fluorescent cellulose composite thin cholesteric structure prepared in the step (5) has a photon forbidden band effect, and the change of the helical pitch can cause the change of circularly polarized light.
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| CN104017129A (en) * | 2014-05-30 | 2014-09-03 | 吉林大学 | Fluorescence functional polymer nanometer microsphere with dual responsiveness to temperature and pH, preparing method and applications |
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| 纤维素纳米晶胆甾相液晶传感膜;王硕;《中国优秀硕士学位论文全文数据库 工程科技Ⅰ辑》;20170215;第30 页 * |
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