CN112225913B - Preparation method of nano-cellulose/acrylamide/graphene oxide self-healing hydrogel - Google Patents

Preparation method of nano-cellulose/acrylamide/graphene oxide self-healing hydrogel Download PDF

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CN112225913B
CN112225913B CN202011156568.4A CN202011156568A CN112225913B CN 112225913 B CN112225913 B CN 112225913B CN 202011156568 A CN202011156568 A CN 202011156568A CN 112225913 B CN112225913 B CN 112225913B
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graphene oxide
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万才超
张陆雨
吴义强
魏松
刘心怡
田文燕
程文杰
苏嘉慧
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Central South University of Forestry and Technology
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Abstract

A preparation method of nano-cellulose/acrylamide/graphene oxide self-healing hydrogel relates to a preparation method of hydrogel. The invention solves the problems of low mechanical strength, poor dye adsorption effect, incapability of recycling and self-healing of the existing cellulose hydrogel. The preparation method comprises the following steps: firstly, removing lignin; secondly, preparing cellulose dispersion liquid; thirdly, preparing a nano-cellulose-graphene oxide mixed solution; fourthly, preparing the hydrogel. The preparation method is used for preparing the nano-cellulose/acrylamide/graphene oxide self-healing hydrogel.

Description

Preparation method of nano-cellulose/acrylamide/graphene oxide self-healing hydrogel
Technical Field
The invention relates to a preparation method of hydrogel.
Background
Cellulose can be isolated from biomass resources (including plants, microorganisms, animals) that are abundant in nature. In the case of plant cellulose, cellulose is often combined with hemicellulose, pectin and lignin as the main structural components of the plant cell wall, except for a small part which is present in a highly pure form (e.g. cotton fiber, kapok fiber). Lignocellulose is a cellulose resource generated by trees through photosynthesis, and the content of cellulose in wood is about 40-50%. Lignocellulose is widely stored in wood fibers in wood cell walls, and the wood fibers serving as raw materials of traditional forestry engineering and wood processing industry have the problems of excess capacity, low added value and the like. Meanwhile, under the circumstances that petroleum resources are gradually exhausted and environmental pollution is more and more serious, green biomass resources such as lignocellulose and the like are receiving new attention from the scientific community and the industrial community. Therefore, the intensive processing technology of lignocellulose is developed, the development of novel cellulose-based functional materials with environmental protection, high performance and high added value is enhanced, the application value of lignocellulose is improved, the development trend of global economy, energy and new materials is met, and the demand of renewable resource strategy in China is met. As a material having high water absorption and high water retention, hydrogels are widely used in various fields such as: facial mask, antipyretic patch, analgesic patch, humidity control agent, thickener, agricultural film, building condensation preventing agent, petrochemical water shutoff agent, crude oil or finished oil dehydrating agent, mining dust suppressant, food preservative, drug carrier, etc. The hydrogel is a colloidal substance that is connected to each other by a high molecular substance to form a network structure. Since some hydrophilic groups are usually present on the hydrogel polymer, and thus can absorb a large amount of water, these solvents are locked in the gel network structure to form the hydrogel. Compared with the traditional hydrogel derived from petrochemical resources, the hydrogel synthesized by taking cellulose as the main raw material has the advantages of renewable raw materials, natural degradation of products and the like. However, due to the enhancement effect of the hydrogen bond network formed among the hydroxyl groups on the cellulose molecular chain on the rigidity of the cellulose molecular chain, the synthesized cellulose hydrogel generally has the defects of poor flexibility (fragility), single shape, incapability of healing, incapability of recycling and the like. These disadvantages make the cellulose hydrogels mechanically weak and unusable in harsh environments. The defects of single shape and lack of material healing capacity seriously restrict the service life and the application range and do not have the function of changing according to special requirements, and the defects undoubtedly limit the application of the cellulose hydrogel in various fields. In addition, the unmodified cellulose hydrogel has a weak adsorption effect on pollutants such as dyes, and the application potential of the unmodified cellulose hydrogel as an adsorption material is significantly limited.
Disclosure of Invention
The invention provides a preparation method of a nano-cellulose/acrylamide/graphene oxide self-healing hydrogel, aiming at solving the problems of low mechanical strength, poor dye adsorption effect, incapability of recycling and self-healing of the existing cellulose hydrogel.
A preparation method of nano-cellulose/acrylamide/graphene oxide self-healing hydrogel comprises the following steps:
firstly, delignification:
firstly, preparing a cellulose raw material into powder;
② soaking the powder material in NaOH and Na 2 SO 3 Heating the mixed solution for 1 to 10 hours in a water bath kettle at the temperature of between 90 and 100 ℃, and then pouring out waste liquid to obtain NaOH and Na 2 SO 3 The treated powder material;
the NaOH and the Na 2 SO 3 The mixed solution of (a) is NaOH solution with the concentration of 0.01mol/L to 10mol/L and Na with the concentration of 0.01mol/L to 10mol/L 2 SO 3 The solution is prepared by mixing (0.1-10) by volume ratio of 1;
③ mixing NaOH and Na 2 SO 3 Boiling the treated powder with deionized water for 0.5-5 h, and then pouring out waste liquid;
fourthly, replacing deionized water, repeating the step one until the waste liquid is colorless, and then washing by using the deionized water as a washing liquid at normal temperature until the washing liquid is neutral to obtain preliminarily washed powder;
fifthly, soaking the powder after the primary cleaning in the solution with the concentration of 0.1 mol/L-5 mol/L of H 2 O 2 Heating the solution for 0.5 to 10 hours at the temperature of between 90 and 100 ℃, washing the solution with deionized water at normal temperature, and finally freeze-drying the solution to obtain lignin-removed powder;
secondly, preparing a nano cellulose dispersion liquid:
uniformly dispersing the delignified powder in ionized water, carrying out ultrasonic treatment for 60-300 min under the conditions that the power is 200-500W and the temperature is 0-30 ℃, placing the upper layer of flocculent liquid in a centrifugal machine after ultrasonic treatment, and centrifuging for 1-10 min under the condition that the rotating speed is 2000-10000 r/min to obtain a nano-cellulose dispersion liquid;
the volume ratio of the mass of the delignified powder to the deionized water is 1g (100-1000) mL;
thirdly, preparing a nano cellulose-graphene oxide mixed solution:
adding graphene oxide into the nano-cellulose dispersion liquid, and carrying out ultrasonic treatment for 1-200 min under the conditions that the ultrasonic power is 200-500W and the temperature is 0-30 ℃ to obtain a nano-cellulose-graphene oxide mixed solution;
the volume ratio of the mass of the graphene oxide to the volume of the nano-cellulose dispersion liquid is 1g (100-1000) mL;
fourthly, preparing the hydrogel:
sequentially adding acrylamide, acrylic acid and N-N-methylene bisacrylamide into a nano cellulose-graphene oxide mixed solution, stirring for 30-200 min under the conditions of nitrogen, stirring speed of 2-50 r/s and room temperature, then adding potassium persulfate, stirring for 0.5-30 min under the conditions of nitrogen, stirring speed of 2-50 r/s and room temperature to obtain a mixed solution, pouring the mixed solution into a mold, standing for 30-200 min under the condition of 40-100 ℃, taking out a sample, and obtaining the nano cellulose/acrylamide/graphene oxide self-healing hydrogel;
the mass ratio of the nano-cellulose-graphene oxide mixed solution to the acrylamide is 100 (5-15); the mass ratio of the nano-cellulose-graphene oxide mixed solution to acrylic acid is 100 (0.1-1); the mass ratio of the nano-cellulose-graphene oxide mixed solution to the N-N-methylene bisacrylamide is 100 (0.05-0.1); the mass ratio of the nano-cellulose-graphene oxide mixed solution to the potassium persulfate is 100 (0.1-1).
The invention has the beneficial effects that:
firstly, the original shape can be recovered within 1s after the nanocellulose/acrylamide/graphene oxide hydrogel prepared by the invention is deformed twice. The mechanical property is good, the tensile modulus is 0.61MPa, and the elastic modulus is 2.42 MPa.
Under the condition that no healing agent or stimulation is used, the nano-cellulose/acrylamide/graphene oxide hydrogel prepared by the method can repair mechanical damage in the gel, inhibit damage propagation, recover the integrity of a network, prolong the service life of the material, remarkably improve the safety of the material and optimize the economic benefit; the gel can automatically heal only by contacting the cut surfaces together at room temperature, and the surfaces can be completely restored after contacting for 5 min.
And thirdly, due to the electrostatic action, the hydrogen bond and the pi-pi bond interaction between Sudan IV cations and negative charges (oxidized graphene and acrylamide), the nano-cellulose/acrylamide/oxidized graphene hydrogel prepared by the invention has the effect of strongly adsorbing the Sudan IV dye, and the adsorption efficiency of the nano-cellulose/acrylamide/oxidized graphene hydrogel prepared by the invention can reach 93% after adsorbing the Sudan IV dye for 6 hours.
Fourthly, the nano-cellulose/acrylamide/graphene oxide hydrogel prepared by the method can still keep more than 92% of adsorption efficiency after 5 times of adsorption of Sudan IV dye.
The invention provides a preparation method of nano-cellulose/acrylamide/graphene oxide self-healing hydrogel.
Drawings
Fig. 1 is an SEM image of a nanocellulose/acrylamide/graphene oxide self-healing aerogel prepared in example one;
fig. 2 is an absorption spectrum of the self-healing nanocellulose/acrylamide/graphene oxide hydrogel prepared in the first embodiment for adsorbing sudan iv dye, wherein 1 is sudan iv original dye, 2 is adsorbing for 1.5h, 3 is adsorbing for 3h, 4 is adsorbing for 4.5h, and 5 is adsorbing for 6 h;
fig. 3 is a stress-strain graph of a nanocellulose/acrylamide/graphene oxide self-healing aerogel prepared in example one;
fig. 4 is an absorbance curve of the nanocellulose/acrylamide/graphene oxide hydrogel prepared in the first example for 6 hours of adsorbing sudan iv dye in the fifth cycle, 1 is sudan iv raw dye, and 2 is 6 hours of adsorbing sudan iv dye in the fifth cycle;
fig. 5 is an image of the preparation of self-healing hydrogels of nanocellulose/acrylamide/graphene oxide with different shapes according to the first embodiment;
fig. 6 is an image of an elliptical nanocellulose/acrylamide/graphene oxide self-healing hydrogel prepared in accordance with example one;
fig. 7 is an image of the elliptical nanocellulose/acrylamide/graphene oxide self-healing hydrogel prepared in the first example stretched to 2-fold deformation;
fig. 8 is an image of the elliptical nanocellulose/acrylamide/graphene oxide self-healing hydrogel prepared in the first example after being stretched to 2 times deformation and loosened for 1 s;
fig. 9 is an optical picture of the heart-shaped nanocellulose/acrylamide/graphene oxide self-healing hydrogel prepared in the first example cut into two pieces;
fig. 10 is an optical image of the self-healing hydrogel of cardiac nanocellulose/acrylamide/graphene oxide prepared in the first example after cutting for 5min after self-healing.
Detailed Description
The first embodiment is as follows: the preparation method of the nano-cellulose/acrylamide/graphene oxide self-healing hydrogel comprises the following steps:
firstly, delignification:
firstly, preparing a cellulose raw material into powder;
② soaking the powder material in NaOH and Na 2 SO 3 Heating the mixed solution for 1 to 10 hours in a water bath kettle at the temperature of between 90 and 100 ℃, and then heating the mixed solutionThe waste liquid is poured out to obtain NaOH and Na 2 SO 3 The treated powder material;
the NaOH and the Na 2 SO 3 The mixed solution of (a) is NaOH solution with the concentration of 0.01mol/L to 10mol/L and Na with the concentration of 0.01mol/L to 10mol/L 2 SO 3 The solution is prepared by mixing (0.1-10) by volume ratio of 1;
③ mixing NaOH and Na 2 SO 3 Boiling the treated powder with deionized water for 0.5-5 h, and then pouring out waste liquid;
fourthly, replacing deionized water, repeating the first step until waste liquid is colorless, and then washing by using the deionized water as washing liquid at normal temperature until the washing liquid is neutral to obtain preliminarily washed powder;
fifthly, soaking the powder after primary cleaning in H with the concentration of 0.1-5 mol/L 2 O 2 Heating the solution for 0.5 to 10 hours at the temperature of between 90 and 100 ℃, washing the solution with deionized water at normal temperature, and finally freeze-drying the solution to obtain lignin-removed powder;
secondly, preparing a nano cellulose dispersion liquid:
uniformly dispersing the delignified powder in ionized water, carrying out ultrasonic treatment for 60-300 min under the conditions that the power is 200-500W and the temperature is 0-30 ℃, placing the upper layer of flocculent liquid in a centrifugal machine after ultrasonic treatment, and centrifuging for 1-10 min under the condition that the rotating speed is 2000-10000 r/min to obtain a nano-cellulose dispersion liquid;
the volume ratio of the mass of the delignified powder to the deionized water is 1g (100-1000) mL;
thirdly, preparing a nano cellulose-graphene oxide mixed solution:
adding graphene oxide into the nano-cellulose dispersion liquid, and carrying out ultrasonic treatment for 1-200 min under the conditions that the ultrasonic power is 200-500W and the temperature is 0-30 ℃ to obtain a nano-cellulose-graphene oxide mixed solution;
the volume ratio of the mass of the graphene oxide to the volume of the nano-cellulose dispersion liquid is 1g (100-1000) mL;
fourthly, preparing the hydrogel:
sequentially adding acrylamide, acrylic acid and N-N-methylene bisacrylamide into a nano cellulose-graphene oxide mixed solution, stirring for 30-200 min under the conditions of nitrogen, stirring speed of 2-50 r/s and room temperature, then adding potassium persulfate, stirring for 0.5-30 min under the conditions of nitrogen, stirring speed of 2-50 r/s and room temperature to obtain a mixed solution, pouring the mixed solution into a mold, standing for 30-200 min under the condition of 40-100 ℃, taking out a sample, and obtaining the nano cellulose/acrylamide/graphene oxide self-healing hydrogel;
the mass ratio of the nano-cellulose-graphene oxide mixed solution to the acrylamide is 100 (5-15); the mass ratio of the nano-cellulose-graphene oxide mixed solution to acrylic acid is 100 (0.1-1); the mass ratio of the nano-cellulose-graphene oxide mixed solution to the N-N-methylene bisacrylamide is 100 (0.05-0.1); the mass ratio of the nano-cellulose-graphene oxide mixed solution to the potassium persulfate is 100 (0.1-1).
The beneficial effects of the embodiment are as follows:
firstly, after the nanocellulose/acrylamide/graphene oxide hydrogel prepared by the embodiment is deformed twice, the original shape can be recovered within 1 s. The mechanical property is good, the tensile modulus is 0.61MPa, and the elastic modulus is 2.42 MPa.
Under the condition that no healing agent or stimulation is used, the nano-cellulose/acrylamide/graphene oxide hydrogel prepared by the embodiment can repair mechanical damage in the gel, inhibit damage propagation, recover the integrity of a network, prolong the service life of the material, remarkably improve the safety of the material and optimize the economic benefit; the gel can automatically heal as long as the cut surfaces are contacted together at room temperature, and the surfaces are completely self-repaired after 5min of contact.
And thirdly, due to the electrostatic action, the hydrogen bond and the pi-pi bond interaction between Sudan IV cations and negative charges (oxidized graphene and acrylamide), the nano-cellulose/acrylamide/oxidized graphene hydrogel prepared by the embodiment has the effect of strongly adsorbing the Sudan IV dye, and the adsorption efficiency of the nano-cellulose/acrylamide/oxidized graphene hydrogel prepared by the embodiment can reach 93% after adsorbing the Sudan IV dye for 6 hours.
Fourthly, the nano-cellulose/acrylamide/graphene oxide hydrogel prepared by the embodiment can still maintain the adsorption efficiency of more than 92% after adsorbing the sudan IV dye for 5 times.
The second embodiment is as follows: the first difference between the present embodiment and the specific embodiment is: the particle size of the powder in the first step is 0.1-2 mm. The rest is the same as the first embodiment.
The third concrete implementation mode: the present embodiment differs from the first or second embodiment in that: the cellulose raw material in the first step is bamboo, Barlow or absorbent cotton. The other is the same as in the first or second embodiment.
The fourth concrete implementation mode: the difference between this embodiment mode and one of the first to third embodiment modes is: when the cellulose raw material is bamboo wood or balsa wood, the preparation of the cellulose raw material into powder in the first step is to cut the powder into square slices along the growth direction, and then to grind the slices; when the cellulose raw material is absorbent cotton, the step I of preparing the cellulose raw material into powder material specifically comprises the step of crushing and grinding the cellulose raw material. The others are the same as the first to third embodiments.
The fifth concrete implementation mode: the difference between this embodiment and one of the first to fourth embodiments is: in the first step, the powder after the preliminary cleaning is soaked in H with the concentration of 2.5 mol/L-5 mol/L 2 O 2 Heating the solution for 1-10 h at the temperature of 95-100 ℃, then washing the solution with deionized water at normal temperature, and finally freeze-drying the solution to obtain the delignified powder. The rest is the same as the first to fourth embodiments.
The sixth specific implementation mode: the difference between this embodiment and one of the first to fifth embodiments is: and step two, uniformly dispersing the delignified powder in ionized water, carrying out ultrasonic treatment for 240-300 min under the conditions that the power is 200-400W and the temperature is 25-30 ℃, placing the upper layer of flocculent liquid in a centrifugal machine after ultrasonic treatment, and centrifuging for 5-10 min under the condition that the rotating speed is 3500-10000 r/min to obtain the nano-cellulose dispersion liquid. The rest is the same as the first to fifth embodiments.
The seventh embodiment: the difference between this embodiment and one of the first to sixth embodiments is: the volume ratio of the mass of the delignified powder in the step two to the volume of the deionized water is 1g (500-1000) mL. The others are the same as the first to sixth embodiments.
The specific implementation mode is eight: the present embodiment differs from one of the first to seventh embodiments in that: and step three, adding graphene oxide into the nano-cellulose dispersion liquid, and carrying out ultrasonic treatment for 60-200 min under the conditions that the ultrasonic power is 200-400W and the temperature is 25-30 ℃ to obtain the nano-cellulose-graphene oxide mixed liquid. The rest is the same as the first to seventh embodiments.
The specific implementation method nine: the present embodiment differs from the first to eighth embodiments in that: the volume ratio of the mass of the graphene oxide to the volume of the nano-cellulose dispersion liquid in the third step is 1g (750-1000) mL. The others are the same as in the first to eighth embodiments.
The detailed implementation mode is ten: the present embodiment differs from one of the first to ninth embodiments in that: and step four, sequentially adding acrylamide, acrylic acid and N-N-methylene bisacrylamide into the nano-cellulose-graphene oxide mixed solution, stirring for 120-200 min under the conditions of nitrogen, stirring speed of 10-50 r/s and room temperature, then adding potassium persulfate, stirring for 10-30 min under the conditions of nitrogen, stirring speed of 10-50 r/s and room temperature to obtain a mixed solution, pouring the mixed solution into a mold, standing for 60-200 min under the condition of temperature of 60-100 ℃, taking out a sample, and obtaining the nano-cellulose/acrylamide/graphene oxide self-healing hydrogel. The other points are the same as those in the first to ninth embodiments.
The following examples were used to demonstrate the beneficial effects of the present invention:
the first embodiment is as follows:
a preparation method of nano-cellulose/acrylamide/graphene oxide self-healing hydrogel comprises the following steps:
firstly, delignification:
cutting a cellulose raw material into square slices along the growth direction of bamboos, and then grinding the slices to obtain powder;
② soaking the powder material in NaOH and Na 2 SO 3 Heating in 100 deg.C water bath for 5 hr, and discharging waste liquid to obtain NaOH and Na 2 SO 3 The treated powder material;
the NaOH and the Na 2 SO 3 The mixed solution of (a) is a NaOH solution with a concentration of 2.5mol/L and Na with a concentration of 0.4mol/L 2 SO 3 The solution is mixed according to the volume ratio of 1: 1;
③ mixing NaOH and Na 2 SO 3 Boiling the treated powder with deionized water for 30min, and pouring out waste liquid;
fourthly, replacing deionized water, repeating the step one until the waste liquid is colorless, and then washing by using the deionized water as a washing liquid at normal temperature until the washing liquid is neutral to obtain preliminarily washed powder;
fifthly, dipping the powder after the primary cleaning in H with the concentration of 2.5mol/L 2 O 2 Heating the solution for 1h at 100 ℃, washing the solution with deionized water at normal temperature, and finally freeze-drying the solution to obtain lignin-removed powder;
secondly, preparing a nano cellulose dispersion liquid:
uniformly dispersing the delignified powder in ionized water, carrying out ultrasonic treatment for 240min under the conditions of 200W of power and 25 ℃, placing the upper layer flocculent liquid in a centrifugal machine after ultrasonic treatment, and centrifuging for 10min under the condition of 3500r/min of rotating speed to obtain a nano-cellulose dispersion liquid;
the volume ratio of the mass of the delignified powder to the deionized water is 1g:1000 mL;
thirdly, preparing a nano cellulose-graphene oxide mixed solution:
adding graphene oxide into the nano-cellulose dispersion liquid, and carrying out ultrasonic treatment for 60min under the conditions that the ultrasonic power is 200W and the temperature is 25 ℃ to obtain a nano-cellulose-graphene oxide mixed liquid;
the volume ratio of the mass of the graphene oxide to the volume of the nano-cellulose dispersion liquid is 1g:750 mL;
fourthly, preparing the hydrogel:
sequentially adding acrylamide, acrylic acid and N-N-methylene bisacrylamide into a nano cellulose-graphene oxide mixed solution, stirring for 120min under the conditions of nitrogen, stirring speed of 10r/s and room temperature, then adding potassium persulfate, stirring for 10min under the conditions of nitrogen, stirring speed of 10r/s and room temperature to obtain a mixed solution, pouring the mixed solution into a mold, standing for 60min under the condition of temperature of 60 ℃, taking out a sample, and obtaining nano cellulose/acrylamide/graphene oxide self-healing hydrogel;
the mass ratio of the nano-cellulose-graphene oxide mixed solution to the acrylamide is 100: 11.67; the mass ratio of the nano-cellulose-graphene oxide mixed solution to the acrylic acid is 100: 0.4; the mass ratio of the nano-cellulose-graphene oxide mixed solution to the N-N-methylene bisacrylamide is 100: 0.06; the mass ratio of the nano-cellulose-graphene oxide mixed solution to the potassium persulfate is 100: 0.13.
The particle size of the powder in the first step is 0.1-2 mm.
The cellulose raw material in the first step is bamboo.
And step four, pouring the mixed solution into moulds with different shapes.
Freezing the nanocellulose/acrylamide/graphene oxide self-healing hydrogel prepared in the first embodiment at-20 ℃ for 24 hours, then vacuum-drying for 48 hours to obtain the nanocellulose/acrylamide/graphene oxide self-healing aerogel, and performing SEM test and stress-strain test on the aerogel.
Fig. 1 is an SEM image of a nanocellulose/acrylamide/graphene oxide self-healing aerogel prepared in example one; as can be seen from the figure, a graphene oxide wrinkled film can be observed, and the addition of graphene oxide adds oxygen-containing functional groups, thereby enhancing electrostatic action, hydrogen bonding and pairing action, resulting in high healing efficiency.
The nano-cellulose/acrylamide/graphene oxide self-healing hydrogel prepared in the first embodiment is used for adsorbing Sudan IV dye, and the specific adsorption method is that 1g of hydrogel is placed into 50mL of Sudan IV dye, and the Sudan IV dye is placed into a UV tester every 90min to test an absorption spectrum, wherein the absorption spectrum is tested for four times and the total time is 6 hours.
Fig. 2 is an absorption spectrum of the self-healing nanocellulose/acrylamide/graphene oxide hydrogel prepared in the first embodiment for adsorbing sudan iv dye, wherein 1 is sudan iv original dye, 2 is adsorbing for 1.5h, 3 is adsorbing for 3h, 4 is adsorbing for 4.5h, and 5 is adsorbing for 6 h; according to the figure, the adsorption performance of the nanocellulose/acrylamide/graphene oxide self-healing hydrogel for 6h is about 93%.
Fig. 3 is a stress-strain curve diagram of a nano-cellulose/acrylamide/graphene oxide self-healing aerogel prepared in example one; the hydrogen bond formed between acrylamide and cellulose, the dispersion of graphene oxide in an acrylamide matrix and the addition of a polymer can enable the nanocellulose/acrylamide/graphene oxide self-healing aerogel to generate excellent stretching capacity.
Stress-strain testing was performed on the nanocellulose/acrylamide/graphene oxide self-healing aerogel prepared in example one, and the nanocellulose/acrylamide/graphene oxide self-healing aerogel prepared in example one: the elastic modulus is 2.42MPa, the elongation at break is 16.19 percent, and the tensile strength is 0.61 MPa.
The method for circularly adsorbing sudan IV dye by utilizing the nano-cellulose/acrylamide/graphene oxide self-healing hydrogel prepared in the first embodiment comprises the following steps: a. putting 1g of hydrogel into 50mL of Sudan IV dye for adsorption for 6h, and testing an absorption spectrum in a UV tester; b. soaking the hydrogel adsorbed with the dye in alcohol for 6 hours; c. and (3) putting the soaked sample into the dye, repeating the step a for 5 times to perform a cycle test, and repeating the step a for 5 times to obtain a test result shown in figure 4.
FIG. 4 is an absorbance curve of the hydrogel adsorbing Sudan IV dye for 6 hours in the fifth cycle, wherein 1 is Sudan IV original dye, and 2 is the nano-cellulose/acrylamide/graphene oxide hydrogel prepared in the first example; it can be seen from the figure that the adsorption rate of the nanocellulose/acrylamide/graphene oxide hydrogel can be maintained at about 92.4% after adsorbing the dye for 5 times. The reduced rate of adsorption compared to the first time may be due to the surface active sites being occupied, resulting in a reduced effective area for the surface to adsorb dye.
Fig. 5 is an image of the preparation of self-healing hydrogels of nanocellulose/acrylamide/graphene oxide with different shapes according to the first embodiment; therefore, the defect that the shape of the cellulose hydrogel is single is overcome.
Fig. 6 is an image of an elliptical nanocellulose/acrylamide/graphene oxide self-healing hydrogel prepared in accordance with example one; fig. 7 is an image of the stretched to 2-fold deformation of the elliptical nanocellulose/acrylamide/graphene oxide self-healing hydrogel prepared in example one; fig. 8 is an image of the elliptical nanocellulose/acrylamide/graphene oxide self-healing hydrogel prepared in the first example after being stretched to 2 times deformation and released for 1 s. Therefore, the original shape of the nanocellulose/acrylamide/graphene oxide hydrogel can be recovered within 1s after twice deformation.
The heart-shaped nanocellulose/acrylamide/graphene oxide self-healing hydrogel prepared in example one was cut into two pieces, and the cut surfaces were contacted together at room temperature for 5 min. Fig. 9 is an optical picture of the heart-shaped nanocellulose/acrylamide/graphene oxide self-healing hydrogel prepared in the first example cut into two pieces; fig. 10 is an optical image of the heart-shaped nanocellulose/acrylamide/graphene oxide self-healing hydrogel prepared in the first example after being cut and automatically healed for 5 min; as can be seen, the cut surfaces contacted together at room temperature healed automatically, and after 5min contact, the surface healed completely.

Claims (1)

1. A preparation method of a nano-cellulose/acrylamide/graphene oxide self-healing hydrogel is characterized by comprising the following steps:
firstly, delignification:
cutting a cellulose raw material into square slices along the growth direction of bamboos, and then grinding the slices to obtain powder;
② soaking the powder material in NaOH and Na 2 SO 3 Heating in 100 deg.C water bath for 5 hr, and discharging waste liquid to obtain NaOH and Na 2 SO 3 The treated powder material;
the NaOH and the Na 2 SO 3 The mixed solution of (a) is a NaOH solution with a concentration of 2.5mol/L and Na with a concentration of 0.4mol/L 2 SO 3 The solution is mixed according to the volume ratio of 1: 1;
③ mixing NaOH and Na 2 SO 3 Boiling the treated powder with deionized water for 30min, and pouring out waste liquid;
fourthly, replacing deionized water, repeating the step one until the waste liquid is colorless, and then washing by using the deionized water as a washing liquid at normal temperature until the washing liquid is neutral to obtain preliminarily washed powder;
fifthly, soaking the powder after primary cleaning in H with the concentration of 2.5mol/L 2 O 2 Heating the solution for 1h at 100 ℃, washing the solution with deionized water at normal temperature, and finally freeze-drying the solution to obtain lignin-removed powder;
secondly, preparing a nano-cellulose dispersion liquid:
uniformly dispersing the delignified powder in deionized water, carrying out ultrasonic treatment for 240min under the conditions of 200W of power and 25 ℃, placing the upper-layer flocculent liquid in a centrifugal machine after ultrasonic treatment, and centrifuging for 10min under the condition of 3500r/min of rotating speed to obtain a nano-cellulose dispersion liquid;
the volume ratio of the mass of the delignified powder to the deionized water is 1g:1000 mL;
thirdly, preparing a nano-cellulose-graphene oxide mixed solution:
adding graphene oxide into the nano-cellulose dispersion liquid, and carrying out ultrasonic treatment for 60min under the conditions that the ultrasonic power is 200W and the temperature is 25 ℃ to obtain a nano-cellulose-graphene oxide mixed liquid;
the volume ratio of the mass of the graphene oxide to the volume of the nano-cellulose dispersion liquid is 1g:750 mL;
fourthly, preparing the hydrogel:
sequentially adding acrylamide, acrylic acid and N, N' -methylene bisacrylamide into a nano cellulose-graphene oxide mixed solution, stirring for 120min under the conditions of nitrogen, stirring speed of 10r/s and room temperature, then adding potassium persulfate, stirring for 10min under the conditions of nitrogen, stirring speed of 10r/s and room temperature to obtain a mixed solution, pouring the mixed solution into a mold, standing for 60min under the condition of temperature of 60 ℃, taking out a sample, and obtaining the nano cellulose/acrylamide/graphene oxide self-healing hydrogel;
the mass ratio of the nano-cellulose-graphene oxide mixed solution to the acrylamide is 100: 11.67; the mass ratio of the nano-cellulose-graphene oxide mixed solution to the acrylic acid is 100: 0.4; the mass ratio of the nano-cellulose-graphene oxide mixed solution to the N, N' -methylene bisacrylamide is 100: 0.06; the mass ratio of the nano-cellulose-graphene oxide mixed solution to the potassium persulfate is 100: 0.13;
the particle size of the powder in the first step is 0.1-2 mm;
the cellulose raw material in the first step is bamboo wood;
and step four, pouring the mixed solution into moulds with different shapes.
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