CN109897317B - Cellulose nanocrystal-rare earth complex-polyvinyl alcohol composite hydrogel fluorescent probe and preparation method and application thereof - Google Patents
Cellulose nanocrystal-rare earth complex-polyvinyl alcohol composite hydrogel fluorescent probe and preparation method and application thereof Download PDFInfo
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Abstract
The invention belongs to the field of polymer composite materials, and discloses a cellulose nanocrystal-rare earth complex-polyvinyl alcohol composite hydrogel fluorescent probe, and a preparation method and application thereof. Research shows that the fluorescent probe-rare earth europium complex is well constructed in the cross-linked reversible hydrogel, so that the heavy metal ions in the water environment can be conveniently, quickly and sensitively detected, and the problem that the conventional fluorescent probe is inconvenient to carry is solved. The hydrogel fluorescent probe has a good application prospect in the aspect of detecting heavy metal ions in a water environment.
Description
Technical Field
The invention belongs to the field of polymer composite materials, and relates to a cellulose nanocrystal-rare earth complex-polyvinyl alcohol composite hydrogel fluorescent probe, and a preparation method and application thereof.
Background
The fluorescence probe method is a rapid detection method, takes rare earth complex as a fluorescence indicator, and the electrons are mainly in a high excited state energy level, so that the fluorescence emission peak is mainly concentrated in high energy level transition, and qualitative or quantitative analysis of metal ions is realized through the fluorescence intensity or the fluorescence peak displacement change. The method is convenient, simple and easy to operate, has the advantages of good selectivity, high sensitivity and the like, and is commonly used for real-time detection and in-situ detection of heavy metal ions.
The hydrogel is a high molecular material which is formed by chemically bonding or physically winding and crosslinking high molecular polymers, takes water as a dispersion medium and has a three-dimensional network structure. The smart hydrogel is a hydrogel having responsiveness to a stimulus of an external environment, wherein the hydrogel having an ion recognition response function is a member of a family of smart hydrogels. By utilizing the fluorescence property of the rare earth nanocrystals, the composite hydrogel with fluorescence characteristic is synthesized and can be used for detecting metal ions in water environment. Polyvinyl alcohol is one of the most important water-soluble polymers, has degradability, nontoxicity and biocompatibility, has a large number of hydroxyl groups on a molecular chain, and can form hydrogel through physical or chemical crosslinking. However, the hydrogel using polyvinyl alcohol as a matrix has a low strength and poor toughness, and has disadvantages in physical and mechanical properties, and thus cannot be industrially applied.
Because the cellulose nanocrystal and the polyvinyl alcohol have similar polarity and good interface compatibility, the performance of the cellulose nanocrystal/polyvinyl alcohol composite material has great research value. The cellulose nanocrystal is an ideal polyvinyl alcohol hydrogel reinforcing material, and compared with other reinforcing phases, the cellulose nanocrystal has extremely high strength and large length-diameter ratio, and can form a net structure in a matrix material as a reinforcing body to improve the material performance. The cellulose nanocrystal/polyvinyl alcohol composite gel not only maintains the biocompatibility of the traditional polyvinyl alcohol hydrogel, but also has the advantages of the mechanical properties of the cellulose nanocrystal, such as high tensile strength, toughness and high elastic modulus.
At present, no report exists that the rare earth complex is well constructed in the hydrogel, and the heavy metal ions in the water environment can be conveniently, rapidly and sensitively detected. At present, no cellulose nanocrystal-rare earth complex-polyvinyl alcohol composite hydrogel fluorescent probe with good mechanical property and capable of detecting heavy metal ions exists in the market.
Disclosure of Invention
The invention aims to provide a cellulose nanocrystal-rare earth complex-polyvinyl alcohol composite hydrogel fluorescent probe.
The invention also aims to provide a preparation method of the composite hydrogel fluorescent probe.
The invention further aims to provide application of the composite hydrogel fluorescent probe in detection of heavy metal ions in water environment. The portability of the solid-state fluorescent probe and the rapidness and accuracy of detecting the heavy metal in a liquid environment are realized simultaneously by crosslinking the reversible fluorescent probe.
The purpose of the invention is realized by the following technical scheme:
a cellulose nanocrystal-rare earth complex-polyvinyl alcohol composite hydrogel fluorescent probe is prepared by the following steps:
a. preparing cellulose nanocrystalline CNC;
b. preparation of rare earth Complex Eu (DPA)3；
c. To cellulose nanocrystal CNC and rare earth complex Eu (DPA)3And adding polyvinyl alcohol powder and a cross-linking agent into the mixed suspension, and stirring to form gel, thereby obtaining the cellulose nanocrystal-rare earth complex-polyvinyl alcohol composite hydrogel fluorescent probe.
Further, the preparation method of the cellulose nanocrystalline CNC (computer numerical control) (the cellulose raw material is delignified plant fiber, and is preferably bleached wood pulp fiber or absorbent cotton) in the step a adopts a chemical combination mechanical treatment method, and the specific steps comprise:
(1) chemical treatment method:
1) preparing a sulfuric acid solution with the mass fraction of 50-70% for later use;
2) heating the prepared sulfuric acid solution in an oil bath to 40-50 ℃ stably and stirring continuously;
3) when the temperature of sulfuric acid is constant, mixing delignified plant fibers and a sulfuric acid solution according to the mass ratio of 1: 10-1: 40, wherein the delignified plant fibers are preferably bleached wood pulp fibers or absorbent cotton fibers; stirring is continuously carried out in the process; during the process of adding the delignified plant fiber, the delignified plant fiber is not poured on the cup wall and the stirring paddle, so that impurities generated in the subsequent transfer process are prevented; after the lignin-removed plant fiber is added, continuously heating and stirring for 1-3 hours;
4) pouring the obtained suspension into a beaker, adding distilled water, standing, pouring out supernatant liquor, and repeating the operation for washing for multiple times; pouring the suspension into a dialysis bag, and dialyzing in running water to be neutral;
(2) mechanical treatment method:
and (3) in an ice water bath, ultrasonically treating the cellulose for 20-50 min under the power of 300-500W to strip the cellulose into cellulose nanocrystals, namely preparing the cellulose nanocrystal CNC suspension, and storing the prepared cellulose nanocrystal suspension in a refrigerator for later use.
Further, the preparation of the rare earth complex in the step b comprises the following steps:
(1) weighing 2, 6-dipicolinic acid and europium nitrate hexahydrate in a round-bottom flask in a molar ratio of 2: 1-4: 1, dissolving the 2, 6-dipicolinic acid and europium nitrate hexahydrate in 10-40 ml of absolute ethyl alcohol in a mass ratio of 1: 200-1: 800;
(2) adding 3-5 drops of ammonia water solution into the system to adjust the pH to 7;
(3) placing the round-bottom flask containing the mixture solution into a reflux device, heating and refluxing for 1-2 hours at 70-90 ℃, and cooling to room temperature;
(4) collecting the obtained precipitate, washing with distilled water twice, vacuum filtering to remove excessive water to obtain white powder containing europium fluorescent substance, i.e. rare earth complex Eu (DPA)3。
Further, the preparation method of the cellulose nanocrystal-rare earth complex-polyvinyl alcohol composite hydrogel fluorescent probe in the step c comprises the following steps:
(1) adding rare earth complex Eu (DPA) into cellulose nanocrystalline CNC suspension with solid content of 0.1-2%3And polyvinyl alcohol powder, and mechanically stirring for 30-70 min at the temperature of 80-95 ℃ in a water bath, wherein the mass ratio of the solid content of the cellulose nanocrystalline CNC suspension to the polyvinyl alcohol is 1: 2-1: 10, and the mass ratio of the rare earth complex to the polyvinyl alcohol is 1: 200-1: 2000;
(2) when the temperature is stable, adding a borate cross-linking agent, continuously stirring until gel is formed, and completely cooling to obtain the cellulose nanocrystal-rare earth complex-polyvinyl alcohol composite hydrogel fluorescent probe. Wherein the mass ratio of the borate crosslinking agent to the polyvinyl alcohol is 1: 2-1: 6.
The preparation method of the cellulose nanocrystal-rare earth complex-polyvinyl alcohol composite hydrogel fluorescent probe is characterized by comprising the following steps:
a. preparing cellulose nanocrystalline CNC;
b. preparation of rare earth Complex Eu (DPA)3；
c. To cellulose nanocrystal CNC and rare earth complex Eu (DPA)3And adding polyvinyl alcohol powder and a cross-linking agent into the mixed solution, and stirring to form gel, thereby obtaining the cellulose nanocrystal-rare earth complex-polyvinyl alcohol composite hydrogel fluorescent probe.
Further, the method for preparing the cellulose nanocrystalline CNC in the step a is characterized by adopting a chemical combination mechanical treatment method, and comprises the following specific steps:
(1) chemical treatment method:
1) preparing a sulfuric acid solution with the mass fraction of 50-70% for later use;
2) heating the prepared sulfuric acid solution in an oil bath to 40-50 ℃ stably and stirring continuously;
3) when the temperature of sulfuric acid is constant, mixing delignified plant fibers and a sulfuric acid solution according to the mass ratio of 1: 10-1: 40, wherein the delignified plant fibers are preferably bleached wood pulp fibers or absorbent cotton fibers; stirring is continuously carried out in the process; during the process of adding the delignified plant fiber, the delignified plant fiber is not poured on the cup wall and the stirring paddle, so that impurities generated in the subsequent transfer process are prevented; after the lignin-removed plant fiber is added, continuously heating and stirring for 1-3 hours;
4) pouring the obtained suspension into a beaker, adding distilled water, standing, pouring out supernatant liquor, and repeating the operation for washing for multiple times; pouring the suspension into a dialysis bag, and dialyzing in running water to be neutral;
(2) mechanical treatment method:
and (3) in an ice water bath, ultrasonically treating the cellulose for 20-50 min under the power of 300-500W to strip the cellulose into cellulose nanocrystals, namely preparing the cellulose nanocrystal CNC suspension, and storing the prepared cellulose nanocrystal suspension in a refrigerator for later use.
Further, the preparation of the rare earth complex in the step b comprises the following steps:
(1) weighing 2, 6-dipicolinic acid and europium nitrate hexahydrate in a round-bottom flask in a molar ratio of 2: 1-4: 1, dissolving the 2, 6-dipicolinic acid and europium nitrate hexahydrate in 10-40 ml of absolute ethyl alcohol in a mass ratio of 1: 200-1: 800;
(2) adding 3-5 drops of ammonia water solution into the system to adjust the pH to 7;
(3) placing the round-bottom flask containing the mixture solution into a reflux device, heating and refluxing for 1-2 hours at 70-90 ℃, and cooling to room temperature;
(4) collecting the obtained precipitate, washing with distilled water twice, vacuum filtering to remove excessive water to obtain white powder containing europium fluorescent substance, i.e. rare earth complex Eu (DPA)3。
Further, the preparation method of the cellulose nanocrystal-rare earth complex-polyvinyl alcohol composite hydrogel fluorescent probe in the step c comprises the following steps:
(1) adding rare earth complex Eu (DPA) into cellulose nanocrystalline CNC suspension with solid content of 0.1-2%3And polyvinyl alcohol powder, and mechanically stirring for 30-70 min at the temperature of 80-95 ℃ in a water bath, wherein the mass ratio of the solid content of the CNC to the polyvinyl alcohol is 1: 2-1: 10, and the mass ratio of the rare earth complex to the polyvinyl alcohol is 1: 200-1: 2000;
(2) when the temperature is stable, adding a borate cross-linking agent, continuously stirring until gel is formed, and completely cooling to obtain the cellulose nanocrystal-rare earth complex-polyvinyl alcohol composite hydrogel fluorescent probe. Wherein the mass ratio of the borate crosslinking agent to the polyvinyl alcohol is 1: 2-1: 6.
The application of the cellulose nanocrystal-rare earth complex-polyvinyl alcohol composite hydrogel fluorescent probe in detecting heavy metal ions in water environment.
The technical scheme of the invention has the following beneficial effects:
in the research, a rare earth complex is dispersed into hydrogel taking polyvinyl alcohol/borate as a matrix, and cellulose nanocrystalline CNC hydrolyzed by sulfuric acid is taken as a reinforcing material, so that the remaining CNC and 2, 3-pyridine europium dicarboxylate Eu (DPA) are obtained3The cellulose nanocrystal-rare earth complex-polyvinyl alcohol composite hydrogel fluorescent probe material has respective advantages and characteristics. The material may have a variety of advantageous properties.
1. The hydrogel is a high molecular material with a three-dimensional network structure and takes water as a dispersion medium, has biocompatibility and degradability, and introduces natural biomass material cellulose and nontoxic and harmless polyvinyl alcohol into the hydrogel, so that secondary pollution is avoided.
2. Hydrogen bond association is realized between the CNC and the polyvinyl alcohol through a chemical crosslinking method, a 3D network structure is constructed in the colloid, and nano reinforcement is realized;
3. the new-generation hydrogel fluorescent probe prepared by the invention has good mechanical property and excellent fluorescence property. In practical use, the hydrogel probes of the present invention are more portable than liquid fluorescent probes. However, the fluorescence intensity of the liquid measured by the existing fluorescence spectrophotometer on the market is more accurate, and the error caused by the influence of the thickness of the sample on the measured fluorescence intensity of the solid is larger. The hydrogel prepared by the invention has the advantages that the crosslinking of the hydrogel is reversible, the hydrogel is changed into a liquid state again after being stirred by adding water, the fluorescence intensity of the liquid is directly measured, and the defect of large error of the fluorescence intensity of a solid measured by a fluorescence spectrophotometer is overcome. The method is simple to operate, and meanwhile, the accuracy of the measurement result is guaranteed. The new generation of hydrogel fluorescent probe can realize the in-situ detection of the heavy metal ions in the water environment, is convenient and sensitive, and provides an effective new way for the detection of the heavy metal ions in the water environment. The portability of the solid-state fluorescent probe and the rapidness and accuracy of detecting the heavy metal in a liquid environment are realized simultaneously by crosslinking the reversible fluorescent probe.
4. Realization of Eu (DPA)3The dual functions of (1): within the addition range of the hydrogel, the hydrogel plays a role in fluorescence and undergoes a complex reaction with heavy metal ions such as copper ions and the like so as to quench fluorescence, so that the hydrogel disclosed by the inventionCan be used for detecting heavy metals, and has higher sensitivity. On the other hand, Eu (DPA)3As the reinforcing phase has two hydroxyl groups, the hydroxyl groups of the gel matrix polyvinyl alcohol and the nanocellulose form hydrogen bonds, so that the mechanical property of the hydrogel is improved, and the mechanical strength of the hydrogel is improved.
Drawings
FIG. 1 is a stress-strain plot of the hydrogels of examples 7-9.
FIG. 2 is a stress-strain diagram of the hydrogel fluorescent probes of examples 4-6 and 9.
FIG. 3 shows fluorescence intensities of hydrogel fluorescent probes of examples 1 to 6.
FIG. 4 shows the fluorescence intensity of the fluorescent probe of example 5 in solutions of copper ions of different concentrations.
FIG. 5 is the fluorescence quenching method for detecting Cu in example 52+The linear relationship of (c).
FIG. 6 shows the fluorescence intensities of the fluorescent probe of example 5 in the copper ion solution and the coexisting ion solution.
FIG. 7 is an infrared spectrum test chart of the hydrogel fluorescent probe of example 5, example 7 and example 9.
Fig. 8 is an SEM image of the porous aerogel formed after lyophilization of the hydrogel sample of example 5.
Detailed Description
The invention will be further illustrated with reference to the following specific examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Furthermore, it should be understood that various changes or modifications can be made by those skilled in the art after reading the teaching of the present invention, and these equivalents also fall within the scope of the claimed invention.
Abbreviations in the following examples:
polyvinyl alcohol is abbreviated as PVA, an English name of Borax as a cross-linking agent is Borax, and the invention takes initial letters of PVA and Borax, namely PB represents polyvinyl alcohol hydrogel;
CNC is cellulose nanocrystalline;
Eu(DPA)3simplified to Eu3+。
Example 1 preparation of cellulose nanocrystal-rare earth complex-polyvinyl alcohol composite hydrogel fluorescent probe PB-CNC-Eu3+I (CNC concentration 0.5 wt%, Eu)3+0.001g)
Firstly, preparing the cellulose into CNC by chemical combination mechanical treatment, wherein the specific method comprises the following steps:
(1) chemical treatment method:
1) preparing a sulfuric acid solution with the mass fraction of 60% for later use;
2) heating the prepared sulfuric acid solution in an oil bath to be stable to 45 ℃ and continuously stirring;
3) when the temperature of the sulfuric acid is constant, carefully adding the cotton fibers into the sulfuric acid according to the mass ratio of 1:20, and continuously stirring in the process; in the process of adding the cotton fiber, the cotton fiber is not required to be poured on the cup wall and the stirring paddle, so that impurities generated in the subsequent transfer process are prevented; after the cotton fibers are added, continuously heating and stirring for 2 hours;
4) pouring the obtained suspension into a beaker, adding distilled water, standing, pouring out supernatant liquor, and repeating the operation for washing for multiple times; pouring the suspension into a dialysis bag, and dialyzing in running water to be neutral;
(2) mechanical treatment method:
and (3) in an ice water bath, ultrasonically treating the cellulose for 30min under the power of 400W to strip the cellulose into cellulose nanocrystals, namely preparing a cellulose nanocrystal CNC suspension, and storing the prepared cellulose nanocrystal suspension in a refrigerator for later use.
Step two, preparing the rare earth complex, which comprises the following specific steps:
(1) 50.1mg of 2, 6-pyridinedicarboxylic acid and 44.6mg of europium nitrate hexahydrate were weighed into a round-bottomed flask, and 25ml of absolute ethanol was added.
(2) And adding 3-5 drops of ammonia water solution into the system to adjust the pH value to 7.
(3) The round-bottom flask with the mixture solution was placed in a reflux apparatus and heated to reflux at 85 ℃ for 1.5 hours and cooled to room temperature.
(4) Washing the collected precipitate with distilled water twice, vacuum filtering with vacuum pump to remove excessive water and obtain europium-containing fluorescent materialWhite powders of photophobic substances, i.e. rare-earth complexes Eu (DPA)3。
Step three, chemically crosslinking polyvinyl alcohol to prepare the cellulose nanocrystal-rare earth complex-polyvinyl alcohol composite hydrogel fluorescent probe named as PB-CNC-Eu3+-I, specific method steps comprising:
(1) adding 2g of polyvinyl alcohol powder into 100mL of CNC suspension with solid content of 0.5%, and mechanically stirring for 50min at 90 ℃ in water bath;
(2) adding 0.001g of rare earth complex Eu (DPA)3Then stirring is continued;
(3) when the temperature is stable, 0.4g of borax as a cross-linking agent is added, the stirring is continued until gel is formed, and the PB-CNC-Eu is obtained after complete cooling3+I (CNC concentration 0.5 wt%, Eu)3+0.001g)。
Example 2 preparation of cellulose nanocrystal-rare earth complex-polyvinyl alcohol composite hydrogel fluorescent probe PB-CNC-Eu3+II (CNC concentration 0.5 wt%, Eu)3+0.006g)
Firstly, preparing the cellulose into CNC by chemical combination mechanical treatment, wherein the specific method comprises the following steps:
(1) chemical treatment method:
1) preparing a sulfuric acid solution with the mass fraction of 60% for later use;
2) heating the prepared sulfuric acid solution in an oil bath to be stable to 45 ℃ and continuously stirring;
3) when the temperature of the sulfuric acid is constant, carefully adding the cotton fibers into the sulfuric acid according to the mass ratio of 1:20, and continuously stirring in the process; in the process of adding the cotton fiber, the cotton fiber is not required to be poured on the cup wall and the stirring paddle, so that impurities generated in the subsequent transfer process are prevented; after the cotton fibers are added, continuously heating and stirring for 2 hours;
4) pouring the obtained suspension into a beaker, adding distilled water, standing, pouring out supernatant liquor, and repeating the operation for washing for multiple times; pouring the suspension into a dialysis bag, and dialyzing in running water to be neutral;
(2) mechanical treatment method:
and (3) in an ice water bath, ultrasonically treating the cellulose for 30min under the power of 400W to strip the cellulose into cellulose nanocrystals, namely preparing a cellulose nanocrystal CNC suspension, and storing the prepared cellulose nanocrystal suspension in a refrigerator for later use.
Step two, preparing the rare earth complex, which comprises the following specific steps:
(1) 50.1mg of 2, 6-pyridinedicarboxylic acid and 44.6mg of europium nitrate hexahydrate were weighed into a round-bottomed flask, and 25ml of absolute ethanol was added.
(2) And adding 3-5 drops of ammonia water solution into the system to adjust the pH value to 7.
(3) The round-bottom flask with the mixture solution was placed in a reflux apparatus and heated to reflux at 85 ℃ for 1.5 hours and cooled to room temperature.
(4) Collecting the precipitate, washing with distilled water twice, vacuum filtering to remove excessive water to obtain white powder of europium-containing fluorescent substance, i.e. rare earth complex Eu (DPA)3。
Step three, chemically crosslinking polyvinyl alcohol to prepare the cellulose nanocrystal-rare earth complex-polyvinyl alcohol composite hydrogel fluorescent probe named as PB-CNC-Eu3+-II, specific process steps comprising:
(1) adding 2g of polyvinyl alcohol powder into 100mL of CNC suspension with solid content of 0.5%, and mechanically stirring for 50min at 90 ℃ in water bath;
(2) adding 0.006g of rare earth complex Eu (DPA)3Then stirring is continued;
(3) when the temperature is stable, 0.4g of borax as a cross-linking agent is added, the stirring is continued until gel is formed, and the PB-CNC-Eu is obtained after complete cooling3+II (CNC concentration 0.5 wt%, Eu)3+0.006g)。
Example 3 preparation of cellulose nanocrystal-rare earth complex-polyvinyl alcohol composite hydrogel fluorescent probe PB-CNC-Eu3+-III (CNC concentration 0.5 wt%, Eu)3+0.01g)
Firstly, preparing the cellulose into CNC by chemical combination mechanical treatment, wherein the specific method comprises the following steps:
(1) chemical treatment method:
1) preparing a sulfuric acid solution with the mass fraction of 60% for later use;
2) heating the prepared sulfuric acid solution in an oil bath to be stable to 45 ℃ and continuously stirring;
3) when the temperature of the sulfuric acid is constant, carefully adding the cotton fibers into the sulfuric acid according to the mass ratio of 1:20, and continuously stirring in the process; in the process of adding the cotton fiber, the cotton fiber is not required to be poured on the cup wall and the stirring paddle, so that impurities generated in the subsequent transfer process are prevented; after the cotton fibers are added, continuously heating and stirring for 2 hours;
4) pouring the obtained suspension into a beaker, adding distilled water, standing, pouring out supernatant liquor, and repeating the operation for washing for multiple times; pouring the suspension into a dialysis bag, and dialyzing in running water to be neutral;
(2) mechanical treatment method:
and (3) in an ice water bath, ultrasonically treating the cellulose for 30min under the power of 400W to strip the cellulose into cellulose nanocrystals, namely preparing a cellulose nanocrystal CNC suspension, and storing the prepared cellulose nanocrystal suspension in a refrigerator for later use.
Step two, preparing the rare earth complex, which comprises the following specific steps:
(1) 50.1mg of 2, 6-pyridinedicarboxylic acid and 44.6mg of europium nitrate hexahydrate were weighed into a round-bottomed flask, and 25ml of absolute ethanol was added.
(2) And adding 3-5 drops of ammonia water solution into the system to adjust the pH value to 7.
(3) The round-bottom flask with the mixture solution was placed in a reflux apparatus and heated to reflux at 85 ℃ for 1.5 hours and cooled to room temperature.
(4) Collecting the precipitate, washing with distilled water twice, vacuum filtering to remove excessive water to obtain white powder of europium-containing fluorescent substance, i.e. rare earth complex Eu (DPA)3。
Step three, chemically crosslinking polyvinyl alcohol to prepare the cellulose nanocrystal-rare earth complex-polyvinyl alcohol composite hydrogel fluorescent probe named as PB-CNC-Eu3+-iii, specific process steps comprising:
(1) adding 2g of polyvinyl alcohol powder into 100mL of CNC suspension with solid content of 0.5%, and mechanically stirring for 50min at 90 ℃ in water bath;
(2) adding 0.01g of rare earth complex Eu (DPA)3Then stirring is continued;
(3) when the temperature is stable, 0.4g of borax as a cross-linking agent is added, the stirring is continued until gel is formed, and the PB-CNC-Eu is obtained after complete cooling3+-III (CNC concentration 0.5 wt%, Eu)3+0.01g)。
Example 4 preparation of cellulose nanocrystal-rare earth complex-polyvinyl alcohol composite hydrogel fluorescent probe PB-CNC-Eu3+IV (CNC concentration 1 wt%, Eu)3+0.001g)
Firstly, preparing the cellulose into CNC by chemical combination mechanical treatment, wherein the specific method comprises the following steps:
(1) chemical treatment method:
1) preparing a sulfuric acid solution with the mass fraction of 60% for later use;
2) heating the prepared sulfuric acid solution in an oil bath to be stable to 45 ℃ and continuously stirring;
3) when the temperature of the sulfuric acid is constant, carefully adding the cotton fibers into the sulfuric acid according to the mass ratio of 1:20, and continuously stirring in the process; in the process of adding the cotton fiber, the cotton fiber is not required to be poured on the cup wall and the stirring paddle, so that impurities generated in the subsequent transfer process are prevented; after the cotton fibers are added, continuously heating and stirring for 2 hours;
4) pouring the obtained suspension into a beaker, adding distilled water, standing, pouring out supernatant liquor, and repeating the operation for washing for multiple times; pouring the suspension into a dialysis bag, and dialyzing in running water to be neutral;
(2) mechanical treatment method:
and (3) in an ice water bath, ultrasonically treating the cellulose for 30min under the power of 400W to strip the cellulose into cellulose nanocrystals, namely preparing a cellulose nanocrystal CNC suspension, and storing the prepared cellulose nanocrystal suspension in a refrigerator for later use.
Step two, preparing the rare earth complex, which comprises the following specific steps:
(1) 50.1mg of 2, 6-pyridinedicarboxylic acid and 44.6mg of europium nitrate hexahydrate were weighed into a round-bottomed flask, and 25ml of absolute ethanol was added.
(2) And adding 3-5 drops of ammonia water solution into the system to adjust the pH value to 7.
(3) The round-bottom flask with the mixture solution was placed in a reflux apparatus and heated to reflux at 85 ℃ for 1.5 hours and cooled to room temperature.
(4) Collecting the precipitate, washing with distilled water twice, vacuum filtering to remove excessive water to obtain white powder of europium-containing fluorescent substance, i.e. rare earth complex Eu (DPA)3。
Step three, chemically crosslinking polyvinyl alcohol to prepare the cellulose nanocrystal-rare earth complex-polyvinyl alcohol composite hydrogel fluorescent probe named as PB-CNC-Eu3+-iv, specific method steps comprising:
(1) adding 2g of polyvinyl alcohol powder into 100mL of CNC suspension with the solid content of 1%, and mechanically stirring for 50min at 90 ℃ in water bath;
(2) adding 0.001g of rare earth complex Eu (DPA)3Then stirring is continued;
(3) when the temperature is stable, 0.4g of borax as a cross-linking agent is added, the stirring is continued until gel is formed, and the PB-CNC-Eu is obtained after complete cooling3+-IV (CNC concentration 1 wt%, Eu)3+0.001g)。
Example 5 preparation of cellulose nanocrystal-rare earth complex-polyvinyl alcohol composite hydrogel fluorescent probe PB-CNC-Eu3+-V (CNC concentration 1 wt%, Eu)3+0.006g)
Firstly, preparing the cellulose into CNC by chemical combination mechanical treatment, wherein the specific method comprises the following steps:
(1) chemical treatment method:
1) preparing a sulfuric acid solution with the mass fraction of 60% for later use;
2) heating the prepared sulfuric acid solution in an oil bath to be stable to 45 ℃ and continuously stirring;
3) when the temperature of the sulfuric acid is constant, carefully adding the cotton fibers into the sulfuric acid according to the mass ratio of 1:20, and continuously stirring in the process; in the process of adding the cotton fiber, the cotton fiber is not required to be poured on the cup wall and the stirring paddle, so that impurities generated in the subsequent transfer process are prevented; after the cotton fibers are added, continuously heating and stirring for 2 hours;
4) pouring the obtained suspension into a beaker, adding distilled water, standing, pouring out supernatant liquor, and repeating the operation for washing for multiple times; pouring the suspension into a dialysis bag, and dialyzing in running water to be neutral;
(2) mechanical treatment method:
and (3) in an ice water bath, ultrasonically treating the cellulose for 30min under the power of 400W to strip the cellulose into cellulose nanocrystals, namely preparing a cellulose nanocrystal CNC suspension, and storing the prepared cellulose nanocrystal suspension in a refrigerator for later use.
Step two, preparing the rare earth complex, which comprises the following specific steps:
(1) 50.1mg of 2, 6-pyridinedicarboxylic acid and 44.6mg of europium nitrate hexahydrate were weighed into a round-bottomed flask, and 25ml of absolute ethanol was added.
(2) And adding 3-5 drops of ammonia water solution into the system to adjust the pH value to 7.
(3) The round-bottom flask with the mixture solution was placed in a reflux apparatus and heated to reflux at 85 ℃ for 1.5 hours and cooled to room temperature.
(4) Collecting the precipitate, washing with distilled water twice, vacuum filtering to remove excessive water to obtain white powder of europium-containing fluorescent substance, i.e. rare earth complex Eu (DPA)3。
Step three, chemically crosslinking polyvinyl alcohol to prepare the cellulose nanocrystal-rare earth complex-polyvinyl alcohol composite hydrogel fluorescent probe named as PB-CNC-Eu3+V, specific method steps comprising:
(1) adding 2g of polyvinyl alcohol powder into 100mL of CNC suspension with the solid content of 1%, and mechanically stirring for 50min at 90 ℃ in water bath;
(2) adding 0.006g of rare earth complex Eu (DPA)3Then stirring is continued;
(3) when the temperature is stable, 0.4g of borax as a cross-linking agent is added, the stirring is continued until gel is formed, and the PB-CNC-Eu is obtained after complete cooling3+V (CNC concentration 1 wt%, Eu)3+0.006g)。
Example 6 preparation of cellulose nanocrystal-rare earth complex-polyvinyl alcohol composite hydrogel fluorescent probe PB-CNC-Eu3+-Ⅵ(CNC concentration 1 wt%, Eu3+0.01g)
Firstly, preparing the cellulose into CNC by chemical combination mechanical treatment, wherein the specific method comprises the following steps:
(1) chemical treatment method:
1) preparing a sulfuric acid solution with the mass fraction of 60% for later use;
2) heating the prepared sulfuric acid solution in an oil bath to be stable to 45 ℃ and continuously stirring;
3) when the temperature of the sulfuric acid is constant, carefully adding the cotton fibers into the sulfuric acid according to the mass ratio of 1:20, and continuously stirring in the process; in the process of adding the cotton fiber, the cotton fiber is not required to be poured on the cup wall and the stirring paddle, so that impurities generated in the subsequent transfer process are prevented; after the cotton fibers are added, continuously heating and stirring for 2 hours;
4) pouring the obtained suspension into a beaker, adding distilled water, standing, pouring out supernatant liquor, and repeating the operation for washing for multiple times; pouring the suspension into a dialysis bag, and dialyzing in running water to be neutral;
(2) mechanical treatment method:
and (3) in an ice water bath, ultrasonically treating the cellulose for 30min under the power of 400W to strip the cellulose into cellulose nanocrystals, namely preparing a cellulose nanocrystal CNC suspension, and storing the prepared cellulose nanocrystal suspension in a refrigerator for later use.
Step two, preparing the rare earth complex, which comprises the following specific steps:
(1) 50.1mg of 2, 6-pyridinedicarboxylic acid and 44.6mg of europium nitrate hexahydrate were weighed into a round-bottomed flask, and 25ml of absolute ethanol was added.
(2) And adding 3-5 drops of ammonia water solution into the system to adjust the pH value to 7.
(3) The round-bottom flask with the mixture solution was placed in a reflux apparatus and heated to reflux at 85 ℃ for 1.5 hours and cooled to room temperature.
(4) Collecting the precipitate, washing with distilled water twice, vacuum filtering to remove excessive water to obtain white powder of europium-containing fluorescent substance, i.e. rare earth complex Eu (DPA)3。
Step three, chemically crosslinking polyethyleneEnol, and the prepared cellulose nanocrystal-rare earth complex-polyvinyl alcohol composite hydrogel fluorescent probe is named as PB-CNC-Eu3+-vi, the specific process steps comprising:
(4) adding 2g of polyvinyl alcohol powder into 100mL of CNC suspension with the solid content of 1%, and mechanically stirring for 50min at 90 ℃ in water bath;
(5) adding 0.01g of rare earth complex Eu (DPA)3Then stirring is continued;
(6) when the temperature is stable, 0.4g of borax as a cross-linking agent is added, the stirring is continued until gel is formed, and the PB-CNC-Eu is obtained after complete cooling3+VI (CNC concentration 1% by weight Eu)3+0.01g)。
Example 7 preparation of comparative, polyvinyl alcohol composite hydrogel PB
Step one, preparing hydrogel by chemically crosslinking polyvinyl alcohol/borax, namely PB, and the specific method comprises the following steps:
(1) adding 2g of polyvinyl alcohol powder into 100mL of deionized water, and mechanically stirring for 50min in a water bath at 90 ℃;
(2) and when the temperature is stable, adding 0.4g of borax as a cross-linking agent, continuously stirring until gel is formed, and completely cooling to obtain the PB hydrogel.
Example 8 preparation of cellulose nanocrystal-polyvinyl alcohol composite hydrogel for control PB-CNC-I (CNC suspension solid content 0.5%)
Firstly, preparing the cellulose into CNC by chemical combination mechanical treatment, wherein the specific method comprises the following steps:
(1) chemical treatment method:
1) preparing a sulfuric acid solution with the mass fraction of 60% for later use;
2) heating the prepared sulfuric acid solution in an oil bath to be stable to 45 ℃ and continuously stirring;
3) when the temperature of the sulfuric acid is constant, carefully adding the cotton fibers into the sulfuric acid according to the mass ratio of 1:20, and continuously stirring in the process; in the process of adding the cotton fiber, the cotton fiber is not required to be poured on the cup wall and the stirring paddle, so that impurities generated in the subsequent transfer process are prevented; after the cotton fibers are added, continuously heating and stirring for 2 hours;
4) pouring the obtained suspension into a beaker, adding distilled water, standing, pouring out supernatant liquor, and repeating the operation for washing for multiple times; pouring the suspension into a dialysis bag, and dialyzing in running water to be neutral;
(2) mechanical treatment method:
and (3) in an ice water bath, ultrasonically treating the cellulose for 30min under the power of 400W to strip the cellulose into cellulose nanocrystals, namely preparing a cellulose nanocrystal CNC suspension, and storing the prepared cellulose nanocrystal suspension in a refrigerator for later use.
Step two, preparing the cellulose nanocrystal-polyvinyl alcohol composite hydrogel by chemical crosslinking, namely named as PB-CNC-I, and the specific method comprises the following steps:
(1) adding 2g of polyvinyl alcohol powder into 100ml of 0.5% CNC suspension, carrying out water bath at 90 ℃, and mechanically stirring for 50 min;
(2) and when the temperature is stable, adding 0.4g of borax as a cross-linking agent, continuously stirring until gel is formed, and completely cooling to obtain the PB-CNC-I.
Example 9 preparation of cellulose nanocrystal-polyvinyl alcohol composite hydrogel PB-CNC-II (CNC suspension solid content 1%)
Firstly, preparing the cellulose into CNC by chemical combination mechanical treatment, wherein the specific method comprises the following steps:
(1) chemical treatment method:
1) preparing a sulfuric acid solution with the mass fraction of 60% for later use;
2) heating the prepared sulfuric acid solution in an oil bath to be stable to 45 ℃ and continuously stirring;
3) when the temperature of the sulfuric acid is constant, carefully adding the cotton fibers into the sulfuric acid according to the mass ratio of 1:20, and continuously stirring in the process; in the process of adding the cotton fiber, the cotton fiber is not required to be poured on the cup wall and the stirring paddle, so that impurities generated in the subsequent transfer process are prevented; after the cotton fibers are added, continuously heating and stirring for 2 hours;
4) pouring the obtained suspension into a beaker, adding distilled water, standing, pouring out supernatant liquor, and repeating the operation for washing for multiple times; the suspension was poured into dialysis bags and dialyzed to neutrality in running water.
(2) Mechanical treatment method:
and (3) in an ice water bath, ultrasonically treating the cellulose for 30min under the power of 400W to strip the cellulose into cellulose nanocrystals, namely preparing a cellulose nanocrystal CNC suspension, and storing the prepared cellulose nanocrystal suspension in a refrigerator for later use.
Step two, preparing the cellulose nanocrystal-polyvinyl alcohol composite hydrogel by chemical crosslinking, namely named as PB-CNC-II, and the specific method comprises the following steps:
(1) adding 2g of polyvinyl alcohol powder into 100mL of 1% CNC suspension, and mechanically stirring for 50min at 90 ℃ in water bath;
(2) and when the temperature is stable, adding 0.4g of borax as a cross-linking agent, continuously stirring until gel is formed, and completely cooling to obtain the PB-CNC-II.
Example 10 application of hydrogel to detection of heavy metal ions in water environment
1g of PB-CNC-Eu is taken3+The hydrogel was added to 10mL of deionized water and stirred until completely dissolved.
1g of PB-CNC-Eu is taken3+The hydrogel is dissolved in 10g of aqueous solution containing copper ions with different concentrations, the concentration of the copper ions is 10-6mol/L、10-5mol/L、2×10-5mol/L、3×10-5mol/L、4×10-5mol/L。
The fluorescence intensity of the solution was measured on an LS 55 fluorescence spectrophotometer (Perkin Elmer) with an excitation wavelength of 285nm, an emission wavelength of 610-640nm, a slit of 2.5nm, and a scanning speed of 200 (FIG. 5).
Example 11 application of hydrogel to detection of heavy metal ions in aqueous environment
1g of PB-CNC-Eu is taken3+The hydrogel was added to 10mL of deionized water and stirred until completely dissolved.
1g of PB-CNC-Eu is taken3+The hydrogel was dissolved in 10g 10-6mol/L copper ion solution.
1g of PB-CNC-Eu is taken3+The hydrogel was dissolved in 10g 10-6mixed solution with copper and cadmium ions coexisting in mol/L.
The fluorescence intensity of the solution was measured on an LS 55 fluorescence spectrophotometer (Perkin Elmer) with an excitation wavelength of 285nm, an emission wavelength of 610-640nm, a slit of 2.5nm, and a scanning speed of 200 (FIG. 6).
FIG. 1 shows the compression property test of PB prepared in example 7, PB-CNC-I prepared in example 8, and PB-CNC-II hydrogel prepared in example 9. it can be seen that at 40%, the compressive strength of PB hydrogel is the smallest, the compressive strength of PB-CNC-I is about 2 times that of PB, and the compressive strength of PB-CNC-II is about 6 times that of PB. The compression strength of the hydrogel matrix can be obviously improved by adding the CNC, and the compression strength is better when the solid content of the CNC is 1%;
FIG. 2 is PB-CNC-Eu prepared in example 43-IV PB-CNC-Eu prepared in example 53+-V, PB-CNC-Eu prepared in example 63+Compression Property test of the hydrogel of PB-CNC-II prepared in example 9, it can be seen from the figure that Eu was added3+Thereafter, the compression resistance of the hydrogel was further enhanced as compared with that of PB-CNC-II prepared in example 9, and PB-CNC-Eu3-Ⅳ、PB-CNC-Eu3+-Ⅴ、PB-CNC-Eu3+VI compressive strength increases in turn, indicating an increase in Eu (DPA)3The amount of the hydrogel fluorescent probe can effectively improve the compressive strength of the hydrogel fluorescent probe.
FIG. 3 is PB-CNC-Eu prepared in example 13-I PB-CNC-Eu prepared in example 23-II PB-CNC-Eu prepared in example 33-III PB-CNC-Eu prepared in example 43-IV PB-CNC-Eu prepared in example 53+-V, PB-CNC-Eu prepared in example 63+-fluorescence intensity of VI hydrogel. From the graph, the fluorescence intensity of the sample was determined in accordance with Eu (DPA)3Increases, and beyond the optimum range, the fluorescence intensity begins to decrease. The addition of TOCN had little effect on the fluorescence intensity.
FIG. 4 is PB-CNC-Eu prepared in example 53+-V fluorescence intensity in solutions of copper ions added at different concentrations. The fluorescence emission peak is generated near 620nm and mainly consists of high energy level5D→7The F transition occurs. The phenomenon of fluorescence quenching is obvious after soaking copper ions due to Cu2+Can be effectively coordinated with rare earth complex, and electrons or energy in molecules are transferred to cause fluorescenceAnd (6) quenching. The cellulose nanocrystal-rare earth complex-polyvinyl alcohol composite hydrogel fluorescent probe can be used for detecting heavy metal ions in water environment. When the concentration of copper ions is 10-6At mol/L, the detection can still be accurate.
FIG. 5 is PB-CNC-Eu prepared in example 53+-V hydrogel fluorescent probe (PB-CNC-Eu)3+) Relative fluorescence intensities of (A) and (B) of (B) are Δ F and lnC (Cu)2+) The linear regression equation of the experimental treatment method is 0.1366x +2.0253 and the linear correlation coefficient R2 is 0.9201 in example 10. Shows that the prepared fluorescent probe can be used for Cu2+And (5) carrying out quantitative detection.
FIG. 6 is PB-CNC-Eu prepared in example 53+-V addition of 10-6mol/L copper ion solution and 10-6mixed solution with copper and cadmium ions coexisting in mol/L. Respectively named PB-CNC-Eu3+-Cu and PB-CNC-Eu3+-Cu-Cd. The experimental treatment was carried out as described in example 11, shown by the scheme PB-CNC-Eu3+The fluorescence intensity of the-Cu-Cd is lower, which indicates that the detection of the copper ions is influenced by the coexisting metal ions, and the hydrogel fluorescent probe prepared by the invention can effectively detect various heavy metals in a complex water environment.
FIG. 7 is the PB hydrogel prepared in example 7, the PB-CNC-II hydrogel prepared in example 9, and the PB-CNC-Eu prepared in example 53+-infrared spectrogram of V hydrogel fluorescent probe. Through the test of chemical functional groups, PB is found to be 1429cm-1The absorption peak is asymmetric stretching vibration of B-O-C, and the vibration is 845cm-1661cm from-1The absorption peaks are respectively the tensile vibration of B-O and B-O-B, and the cross-linking of PVA and borax is verified. PB hydrogel, PB-CNC-II hydrogel and PB-CNC-Eu3+The hydrogel was at 3326cm due to the stretching vibration of O-H bonds-1A broader absorption peak appears nearby, and PB-CNC-Eu3+The peak intensity of the hydrogel is higher than that of PB-TOCN hydrogel and PB hydrogel, and hydrogen bonds are formed among CNC, PVA, rare earth complexes and borax. In conclusion, CNC and rare earth complex and polyvinyl alcohol are subjected to cross-linking reaction under the action of a cross-linking agent borax to generate hydrogen bond combination to form a three-dimensional network structure, so that hydrogel is kept relatively highGood stability.
FIG. 8 is PB-CNC-Eu prepared in example 53+SEM images of porous aerogels formed after lyophilization of hydrogel samples-v. The result shows that the porous structure of the cellulose nanocrystal-rare earth complex-polyvinyl alcohol composite hydrogel fluorescent probe forms a stable three-dimensional network structure.
Claims (11)
1. A cellulose nanocrystal-rare earth complex-polyvinyl alcohol composite hydrogel fluorescent probe is characterized in that the hydrogel is prepared by the following method:
a. preparing cellulose nanocrystalline CNC;
b. preparation of rare earth Complex Eu (DPA)3；
c. To cellulose nanocrystal CNC and rare earth complex Eu (DPA)3Adding polyvinyl alcohol powder and a cross-linking agent into the mixed suspension, and stirring to form gel, thereby obtaining the cellulose nanocrystal-rare earth complex-polyvinyl alcohol composite hydrogel fluorescent probe; wherein the mass ratio of the borate crosslinking agent to the polyvinyl alcohol is 1: 2-1: 6.
2. The cellulose nanocrystal-rare earth complex-polyvinyl alcohol composite hydrogel fluorescent probe as claimed in claim 1, wherein the preparation method of the cellulose nanocrystal CNC in step a adopts a chemical combination mechanical treatment method, and the specific steps include:
(1) chemical treatment method:
1) preparing a sulfuric acid solution with the mass fraction of 50-70% for later use;
2) heating the prepared sulfuric acid solution in an oil bath to 40-50 ℃ stably and stirring continuously;
3) when the sulfuric acid temperature is constant, the delignified plant fiber: mixing sulfuric acid solutions according to the mass ratio of 1: 10-1: 40; stirring is continuously carried out in the process; during the process of adding the delignified plant fiber, the delignified plant fiber is not poured on the cup wall and the stirring paddle, so that impurities generated in the subsequent transfer process are prevented; after the lignin-removed plant fiber is added, continuously heating and stirring for 1-3 hours;
4) pouring the obtained suspension into a beaker, adding distilled water, standing, pouring out supernatant liquor, and repeating the operation for washing for multiple times; pouring the suspension into a dialysis bag, and dialyzing in running water to be neutral;
(2) mechanical treatment method:
and (3) in an ice water bath, ultrasonically treating the cellulose for 20-50 min under the power of 300-500W to strip the cellulose into cellulose nanocrystals, namely preparing the cellulose nanocrystal CNC suspension, and storing the prepared cellulose nanocrystal suspension in a refrigerator for later use.
3. The cellulose nanocrystal-rare earth complex-polyvinyl alcohol composite hydrogel fluorescent probe as claimed in claim 2, wherein the delignified plant fiber is bleached wood pulp fiber or absorbent cotton fiber.
4. The cellulose nanocrystal-rare earth complex-polyvinyl alcohol composite hydrogel fluorescent probe as claimed in claim 1, wherein the rare earth complex preparation in step b comprises the steps of:
(1) weighing 2, 6-dipicolinic acid and europium nitrate hexahydrate in a round-bottom flask in a molar ratio of 2: 1-4: 1, dissolving the 2, 6-dipicolinic acid and europium nitrate hexahydrate in 10-40 ml of absolute ethyl alcohol in a mass ratio of 1: 200-1: 800;
(2) adding 3-5 drops of ammonia water solution into the system to adjust the pH = 7;
(3) placing the round-bottom flask containing the mixture solution into a reflux device, heating and refluxing for 1-2 hours at 70-90 ℃, and cooling to room temperature;
(4) collecting the obtained precipitate, washing with distilled water twice, vacuum filtering to remove excessive water to obtain white powder containing europium fluorescent substance, i.e. rare earth complex Eu (DPA)3。
5. The cellulose nanocrystal-rare earth complex-polyvinyl alcohol composite hydrogel fluorescent probe of claim 1, wherein the preparation method of the cellulose nanocrystal-rare earth complex-polyvinyl alcohol composite hydrogel fluorescent probe in step c comprises the following steps:
(1) to the direction ofAdding a rare earth complex Eu (DPA) into a cellulose nanocrystalline CNC suspension with a solid content of 0.1-2%3And polyvinyl alcohol powder, and mechanically stirring for 30-70 min at 80-95 ℃ in a water bath, wherein the mass ratio of the solid content of the CNC to the polyvinyl alcohol is 1: 2-1: 10, and the mass ratio of the rare earth complex to the polyvinyl alcohol is 1: 200-1: 2000;
(2) when the temperature is stable, adding a borate cross-linking agent, continuously stirring until gel is formed, and completely cooling to obtain the cellulose nanocrystal-rare earth complex-polyvinyl alcohol composite hydrogel fluorescent probe.
6. The preparation method of the cellulose nanocrystal-rare earth complex-polyvinyl alcohol composite hydrogel fluorescent probe as claimed in claim 1, characterized in that the method comprises the following steps:
a. preparing cellulose nanocrystalline CNC;
b. preparation of rare earth Complex Eu (DPA)3；
c. To cellulose nanocrystal CNC and rare earth complex Eu (DPA)3Adding polyvinyl alcohol powder and a cross-linking agent into the mixed suspension, and stirring to form gel, thereby obtaining the cellulose nanocrystal-rare earth complex-polyvinyl alcohol composite hydrogel fluorescent probe; wherein the mass ratio of the borate crosslinking agent to the polyvinyl alcohol is 1: 2-1: 6.
7. The preparation method according to claim 6, wherein the preparation method of the cellulose nanocrystalline CNC in the step a adopts a chemical combination mechanical treatment method, and the specific steps comprise:
chemical treatment method:
1) preparing a sulfuric acid solution with the mass fraction of 50-70% for later use;
2) heating the prepared sulfuric acid solution in an oil bath to 40-50 ℃ stably and stirring continuously;
3) when the sulfuric acid temperature is constant, the delignified plant fiber: mixing sulfuric acid solutions according to the mass ratio of 1: 10-1: 40; stirring is continuously carried out in the process; during the process of adding the delignified plant fiber, the delignified plant fiber is not poured on the cup wall and the stirring paddle, so that impurities generated in the subsequent transfer process are prevented; after the lignin-removed plant fiber is added, continuously heating and stirring for 1-3 hours;
4) pouring the obtained suspension into a beaker, adding distilled water, standing, pouring out supernatant liquor, and repeating the operation for washing for multiple times; pouring the suspension into a dialysis bag, and dialyzing in running water to be neutral;
(2) mechanical treatment method:
and (3) in an ice water bath, ultrasonically treating the cellulose for 20-50 min under the power of 300-500W to strip the cellulose into cellulose nanocrystals, namely preparing the cellulose nanocrystal CNC suspension, and storing the prepared cellulose nanocrystal suspension in a refrigerator for later use.
8. The method of claim 7, wherein the delignified plant fiber is preferably bleached wood pulp fiber or cotton wool fiber.
9. The method according to claim 6, wherein the rare earth complex is prepared in the step b by a method comprising:
(1) weighing 2, 6-dipicolinic acid and europium nitrate hexahydrate in a round-bottom flask in a molar ratio of 2: 1-4: 1, dissolving the 2, 6-dipicolinic acid and europium nitrate hexahydrate in 10-40 ml of absolute ethyl alcohol in a mass ratio of 1: 200-1: 800;
(2) adding 3-5 drops of ammonia water solution into the system to adjust the pH = 7;
(3) placing the round-bottom flask containing the mixture solution into a reflux device, heating and refluxing for 1-2 hours at 70-90 ℃, and cooling to room temperature;
(4) collecting the obtained precipitate, washing with distilled water twice, vacuum filtering to remove excessive water to obtain white powder containing europium fluorescent substance, i.e. rare earth complex Eu (DPA)3。
10. The preparation method according to claim 6, wherein the preparation method of the cellulose nanocrystal-rare earth complex-polyvinyl alcohol composite hydrogel fluorescent probe in the step c comprises the following steps:
(1) to cellulose nano-particles with solid content of 0.1-2%Adding rare earth complex Eu (DPA) into crystal CNC suspension3And polyvinyl alcohol powder, and mechanically stirring for 30-70 min at 80-95 ℃ in a water bath, wherein the mass ratio of the solid content of the CNC to the polyvinyl alcohol is 1: 2-1: 10, and the mass ratio of the rare earth complex to the polyvinyl alcohol is 1: 200-1: 2000;
(2) when the temperature is stable, adding a borate cross-linking agent, continuously stirring until gel is formed, and completely cooling to obtain the cellulose nanocrystal-rare earth complex-polyvinyl alcohol composite hydrogel fluorescent probe.
11. The application of the cellulose nanocrystal-rare earth complex-polyvinyl alcohol composite hydrogel fluorescent probe in claim 1 in detection of heavy metal ions in water environment.
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