CN112851976B

CN112851976B - Preparation method of cellulose-based hydrogel for dye degradation

Info

Publication number: CN112851976B
Application number: CN202110247334.9A
Authority: CN
Inventors: 林鹿; 闫贵花; 曾宪海; 孙勇; 唐兴
Original assignee: Xiamen University
Current assignee: Xiamen University
Priority date: 2021-03-05
Filing date: 2021-03-05
Publication date: 2021-12-21
Anticipated expiration: 2041-03-05
Also published as: CN112851976A

Abstract

The invention discloses a preparation method of cellulose-based hydrogel for dye degradation, which comprises the steps of carrying out carboxylation on dialdehyde cellulose obtained after sodium periodate oxidation, then obtaining ammoniated cellulose by utilizing ammoniation reaction of the cellulose glycolate and dopamine, then depositing palladium nanoparticles on the surface of the ammoniated cellulose by utilizing a deposition method, forming the cellulose deposited with the nanoparticles into hydrogel by utilizing a simple polymerization method, and finally carrying out surface modification on the obtained hydrogel to enable the hydrogel to have the potential of long-term underwater application. The method has the advantages of mild reaction conditions, simple operation and less pollution, solves the problems of difficult recovery and long-term underwater application of common degradation materials, widens the application approach of cellulose, and has extremely high potential value.

Description

Preparation method of cellulose-based hydrogel for dye degradation

Technical Field

The invention belongs to the field of natural high polymer materials, and particularly relates to a preparation method of cellulose-based hydrogel for dye degradation.

Background

Hydrogels have attracted a great deal of interest in the fields of tissue engineering, chemical engineering, biomedicine, etc., where their use underwater is a widespread and indispensable requirement. Scientists have studied the underwater application of multifunctional hydrogel in water purification, organic matter adsorption and degradation and the like. However, it is difficult to maintain the mechanical properties and stability of the hydrogel itself because the hydrogel greatly weakens the intermolecular van der Waals forces when fully immersed in a body of water (Ma Y., Advanced Materials,2018,30(30): 1801595; Chakma, P., Angewandte Chemie International Edition,2019,58, 9682-. More seriously, the complicated water environment, especially the water containing more metal ions, can cause the structural change of the hydrogel due to the deposition phenomenon of a large amount of salt, which not only affects the working efficiency of the hydrogel, but also greatly reduces the cycle life of the hydrogel (Liu, J., J.Mater.Chem.A 2017,5, 4163-4171). This further increases the economic cost, and is a problem to be solved urgently at present.

To address these challenges, mussel inspired Polydopamine (PDA) based hydrogels are a typical example of a super tough hydrogel made from catechol chemistry that can be used in an aqueous environment (Cholewinski, A., mater. horiz.2019,6, 285-78293; North, M.A., ACS appl. mater. Inter.2017,9, 7866-7872). The hydrogel can effectively improve underwater mechanical property due to the formation of covalent bond/non-covalent bond in the system, and is an effective means for realizing strong mechanical property and self-healing property. However, pure PDA functionalized hydrogels generally do not meet the actual mechanical property requirements, and excessive oxidation of the catechol group leads to deterioration of the mechanical properties of the hydrogel, which is critical to control the degree of oxidation of the catechol group (Ponzio, F.et al, chem.Mater.2016,28, 4697-4705). On the other hand, in order to prevent the destruction of the hydrogel internal structure by salt deposition, a chemically stable membrane must be assembled so that different ions and species selectively pass (Lee, H.A., Accounts chem.Res.2019,52, 704-.

In order to solve the problems that the mechanical property of hydrogel is poor when the hydrogel works underwater and the influence of a severe water environment on the hydrogel structure is solved, a cellulose modification method is adopted, so that cellulose becomes a structure with a surface rich in phenolic hydroxyl, Pd nanoparticles are attracted to be deposited on the surface of the structure to serve as a catalyst for dye degradation, and the Pd nanoparticles are fixed in the hydrogel so as to be recycled. And the surface modification of the hydrogel by the graphene oxide makes metal ions difficult to enter the hydrogel, so that the damage of the metal ions to the internal result of the hydrogel in the dye degradation process is reduced, and multiple advantages of high efficiency, repeatability and economy pursued by dye wastewater treatment are realized.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provides a preparation method of cellulose-based hydrogel for dye degradation. FIG. 1 shows a schematic diagram of the reaction process of the preparation process of cellulose-based hybrid loaded with palladium nanoparticles (Pd NPs) according to the present invention. After dialdehyde cellulose is further oxidized by sodium chlorite, aldehyde group is further oxidized into carboxyl; and grafting dopamine to the surface of dialdehyde cellulose under the catalysis of sodium borohydride. Then, adding palladium chloride to react to generate Pd NPs; the negatively charged carboxyl groups can attract the positively charged Pd (II) through electrostatic interaction, and meanwhile, the aldehyde groups and partial hydroxyl groups are used as reducing agents, so that Pd NPs are distributed on the surface (note that the scheme 1 is shown by taking the example 1 as an example).

Therefore, the technical scheme provided by the invention is as follows:

a method for preparing cellulose-based hydrogel for dye degradation, comprising the following steps:

1) fully mixing cellulose and periodate in a water system, stirring in a dark place, washing with deionized water, and dialyzing to obtain cellulose; heating and dissolving the obtained dialdehyde cellulose in water, centrifuging, and concentrating to obtain dialdehyde cellulose aqueous solution. Preferably, the ratio of cellulose, periodate and deionized water is 1.0 g: 0.3-2.0 g: 50-200 ml; the reaction temperature is 25-75 ℃, and the reaction time is 6-64 h; the reaction temperature of the obtained dialdehyde cellulose dissolved in water is 60-120 ℃; more preferably, the ratio of cellulose, periodate, deionized water is 1.0 g: 2.0 g: 100 ml; the reaction temperature is 65 ℃, and the reaction time is 6 hours; the reaction temperature of the obtained dialdehyde cellulose dissolved in water is 100 ℃. Wherein the periodate is sodium periodate.

2) Taking the dialdehyde cellulose aqueous solution obtained in the step 1) and NaClO₂Mixing, adjusting pH to 5.5-6.0, and adding reducing agentPart of the aldehyde groups on the cellulose are carboxylated to form a carboxylated cellulose derivative.

3) Adding dopamine into the carboxylated cellulose derivative solution obtained in the step 2), reacting at room temperature, adding a reducing agent under vigorous stirring, and stirring for 1 h. And dialyzing and purifying to obtain the cellulose derivative rich in phenolic hydroxyl.

4) PdCl₂Adding the obtained product into the cellulose derivative obtained in the step 3), heating and continuously stirring for reaction, and then dialyzing and purifying to obtain the cellulose derivative with uniformly loaded Pd nanoparticles.

5) Stirring a propenyl monomer, sodium alginate, an initiator and the Pd-loaded cellulose derivative obtained in the step 4), and pouring the mixed solution into a mould; and then placing the mould at a certain temperature to polymerize the mould, thus obtaining the cellulose-based hydrogel. Preferably, the weight ratio of the acrylamide to the sodium alginate to the ammonium persulfate to the obtained Pd-loaded cellulose derivative is 8-12: 1-3: 0.05-0.2: 0.4-1.2, preferably 10: 2: 0.1: 0.8;

6) immersing the cellulose-based hydrogel obtained in the step 5) in a graphene oxide solution, then adding a mixed solution of poly-N-isopropylacrylamide and an initiator, and standing for a period of time to obtain the surface-modified hydrogel.

7) The hydrogel obtained in 6) is used for the degradation of dyes in wastewater.

In a preferred embodiment of step 1 of the present invention, the dialdehyde cellulose in step 2) is reacted with NaClO₂The pH value of the mixed solution is 5.5-6.0; the reducing agent may be potassium borohydride, sodium cyanoborohydride.

In a preferred embodiment of the present invention, the reaction time of dopamine and carboxylated cellulose in step 3) is 12-24 h; the reducing agent may be potassium borohydride, sodium cyanoborohydride.

In a preferred embodiment of the invention, the PdCl of step 4) is₂The reaction temperature of the cellulose derivative and the cellulose derivative is 60-100 ℃, and the stirring time is 2-5 h; preferably, the reaction temperature is 80-100 ℃, and the stirring time is 3-4 h.

In a preferred embodiment of the present invention, the vinyl monomer of step 5) is acrylamide or acrylic acid. The initiator is ammonium persulfate or potassium persulfate. The stirring temperature of the mixed solution is 20-30 ℃, and the gel polymerization temperature is 50-70 ℃.

In a preferred embodiment of the present invention, the method of step 6) is characterized in that: the initiator is ammonium persulfate or potassium persulfate; the standing temperature is 60 ℃, and the standing time is 2 h.

In a preferred embodiment of the present invention, the method of step 7) is characterized in that: the degradation dyes aimed at by the method are Congo red and methylene blue.

The invention has the beneficial effects that: firstly, the cellulose used by the invention is cheap and easily available, is a renewable biomass energy source widely existing in the nature, and greatly reduces the cost of raw materials. And the cellulose-based hydrogel obtained in the invention is different from the defects of difficult recovery, environmental pollution and the like of the conventional underwater material, is an environment-friendly material, is easy to recover and has better degradability. And thirdly, the cellulose-based hydrogel obtained by the invention can still keep the structural integrity under severe water environment due to the coating of the modified graphene oxide film, realizes the long-term underwater recycling, and has extremely high development value.

Drawings

FIG. 1 is a schematic flow chart of the preparation of cellulose-based hybrid loaded with palladium nanoparticles (Pd NPs) (taking example one as an example). Wherein: dialdehyde cellulose (DAC), oxidized dialdehyde cellulose (DACO), Polydopamine (PDA), and cellulose-based composites loaded with Pd NPs (DACO-PDA @ PdNPs) were prepared as in example one.

Figure 2 internal SEM topography of a formed hydrogel after lyophilization. As can be seen from the figure, the composite hydrogel has an interwoven ultrafine fiber structure inside.

FIG. 3 SEM (left) and TEM (right) images of Pd NPs supported on the surface of a prepared DACO-PDA fiber. As can be seen from the SEM (left) and TEM (right) images, the Pd NPs are randomly distributed on the surface of the cellulose material, and the particle size ranges from 15 to 40 nm.

FIG. 4 compares the tensile stress-strain curves of various hydrogels. As can be seen, the hydrogel prepared in the first example can withstand higher tensile stress. The addition of DACO-PDA @ Pd NPs prepared in example one significantly improved the strength of the hydrogel compared to pure PAA and SA hydrogels. Wherein SA is sodium alginate gel, PAA is polyacrylic acid, DPA is hydrogel without sodium alginate (DACO-PDA-PAA @ Pd NPs), and DPAS is prepared (DACO-PDA-PAA-SA @ Pd NPs) composite hydrogel.

Figure 5 example 5 cycle tensile load-unload curve for a hydrogel prepared as described above. As can be seen, the load-unload compression curve after 5 cycles remained almost unchanged, indicating that the prepared hydrogel had good recovery ability.

FIG. 6 is a cyclic compressive stress-strain curve for various hydrogels. As can be seen, the hydrogel prepared can withstand higher tensile stress. The addition of the DACO-PDA @ Pd NPs obtained in example one significantly improved the strength of the hydrogel compared to the pure PAA and SA hydrogels. Wherein SA is sodium alginate gel, PAA is polyacrylic acid, DPA is hydrogel without sodium alginate (DACO-PDA-PAA @ Pd NPs), and DPAS is prepared (DACO-PDA-PAA-SA @ Pd NPs) composite hydrogel.

Figure 7 example a crack recovery test of the hydrogel prepared. As can be seen, when the cut hydrogel was left to stand for a certain period of time (2 hours), the cracks of the hydrogel gradually disappeared. The prepared hydrogel has good self-repairing performance.

Figure 8 example a tensile image of the as-prepared hydrogel and a self-healing 2h tensile image of the hydrogel after cutting (left), and tensile stress-strain curves of the original hydrogel and the healing hydrogel after healing for 2h (right). In the self-repaired hydrogel, a remarkable stretching mode can be observed at a fracture part, but the fracture does not occur. From the viewpoint of tensile properties, the cut hydrogel was recovered for 2 hours (about 90% of the original) after self-healing.

Fig. 9 example a uv-vis spectrum of a hydrogel degraded Congo Red (CR) prepared. As can be seen from the figure, NaBH was observed as the reaction proceeded₄To CR solutionAnd (4) continuously decoloring, wherein the decoloring rate can reach about 98 percent after about 20 min.

FIG. 10 example one hydrogel prepared as a result of undergoing a continuous 5 cycle process on the degradation effect of CR. As can be seen, the degradation of the hydrogel for CR was reduced from 20min for the first cycle to 23min for the 5 th cycle, indicating the reusability of the prepared hydrogel.

FIG. 11 is a graph showing the results of Congo Red (CR) treatment of a body of water using the hydrogel prepared in the first example. As can be seen, the appearance of the monomeric structure demonstrates that the CR is degraded.

Figure 12 example six the uv-vis spectrum of the hydrogel degraded Methylene Blue (MB). As can be seen from the figure, in the presence of the hydrogel, the MB solution is decolorized within 3.5min, and the decolorization rate can reach 99%.

Figure 13 example six hydrogel prepared as a result of going through 5 consecutive cycles of the process on MB degradation effect. As can be seen from the figure, the degradation of the hydrogel to CR is shortened from 3.5min in the first period to 4min in the 5 th period, and the degradation rates reach 99%, which indicates the reusability of the prepared hydrogel.

FIG. 14 is a graph showing the results of Methylene Blue (MB) treatment in a water body using the hydrogel prepared in example six. The results show that Methylene Blue (MB) is degraded.

Detailed Description

The technical solution of the present invention is further illustrated and described by the following detailed description. FIG. 1 shows a schematic flow chart of the preparation of cellulose-based hybrid loaded with palladium nanoparticles (Pd NPs) by way of example one.

Example 1

1) The proportion of cellulose, sodium periodate and deionized water is 1.0 g: 2.0 g: 100 ml; the reaction temperature is 65 ℃, and the reaction time is 6 hours; the reaction temperature of the obtained dialdehyde cellulose dissolved in water is 100 ℃.

2) Taking the dialdehyde cellulose aqueous solution (20mL) obtained in the step 1) and 0.4g NaClO₂Mix well and adjust the pH to 5.6 in NaBH₄Under the action of the carboxylic acid, partial aldehyde groups on the cellulose are made to be carboxylic acid, and a carboxylic acid cellulose derivative is formed.

3) 0.2g dopamine was added to the carboxylated cellulose derivative solution (2.3 wt%, 10mL) obtained in step 2), reacted at room temperature for 12h, then 0.05g NaBH was added with vigorous stirring₄And stirring for 1 hour. And dialyzing and purifying to obtain the cellulose derivative rich in phenolic hydroxyl.

4) PdCl₂Hydrochloric acid solution (0.18g PdCl)₂Dissolved in 50mL of 20mM HCl) was added to the cellulose derivative (2.0 wt%, 10mL) obtained in step 3), and the reaction was carried out at 80 ℃ with continuous stirring for 3 hours, followed by purification by dialysis to obtain a cellulose derivative in which Pd nanoparticles were uniformly supported.

5) 2.0g of acrylamide, 0.4g of sodium alginate, 0.02g of ammonium persulfate and 0.16g of Pd-loaded cellulose derivative obtained in the step 4), stirring the mixed solution at 20 ℃, and pouring the mixed solution into a mold; and then standing the mould at 60 ℃ for 2h for polymerization to obtain the cellulose-based hydrogel.

6) Immersing the cellulose-based hydrogel obtained in the step 5) in a graphene oxide solution (0.1 wt%), then adding a mixed solution of 0.2g of poly-N-isopropylacrylamide and 10mg of ammonium persulfate, and standing the mixture at 60 ℃ for 2 hours to obtain the surface-modified hydrogel.

The tensile strength of the hydrogel prepared by the embodiment is 240kPa, and the ductility can reach 1700%; the tensile strength can be recovered to be nearly 95% within 2h after the cutting; the Congo red degrading agent is used for degrading Congo red in waste water, and the degradation rate reaches 98% within 20 minutes. Figure 2 shows the internal SEM topography of the formed hydrogel after lyophilization. As can be seen from the figure, the composite hydrogel has an interwoven ultrafine fiber structure inside.

Example 2

1) The method is carried out according to the corresponding steps in the first embodiment.

2) The procedure was carried out as described in example one, except that the pH was 6.0.

3) The procedure was repeated as described in example one, except that the carboxylated cellulose derivative solution was used in an amount of 2.0% by weight, 10 mL.

4) The procedure was repeated in accordance with the procedure described in example one, except that the reaction was carried out at 80 ℃ for 3 hours with continuous stirring.

5) And (4) carrying out the corresponding steps in the first example to obtain the cellulose-based hydrogel.

6) And (3) carrying out the corresponding steps in the first example to obtain the surface modified hydrogel.

The tensile strength of the hydrogel prepared by the embodiment is 170kPa, and the ductility can reach 1400%; the tensile strength can be recovered to nearly 83% within 2h after cutting; the Congo red degrading agent is used for degrading Congo red in wastewater, and the degradation rate reaches 97% within 15 minutes.

Example 3

Steps 1) to 6) were carried out according to the corresponding steps in example one, except that in step 2) the pH was 5.8.

The tensile strength of the hydrogel prepared by the embodiment is 220kPa, and the ductility can reach 1500%; the tensile strength can be restored to nearly 90% within 2h after cutting; the Congo red degrading agent is used for degrading Congo red in wastewater, and the degradation rate reaches 98% within 15 minutes.

Example 4

2) The procedure is as in example one except that the catalyst is KBH₄。

3) The procedure is as in example one except that the catalyst is KBH₄。

4) The method is carried out according to the corresponding steps in the first embodiment.

The tensile strength of the hydrogel prepared by the embodiment is 230kPa, and the ductility can reach 1700%; the tensile strength can be restored to nearly 96% within 2h after cutting; the Congo red degrading agent is used for degrading Congo red in wastewater, and the degradation rate reaches 99% within 20 minutes.

Example 5

Steps 1) to 6) were carried out according to the corresponding steps in example one, except that in step 3) the reaction time was 24 hours.

The tensile strength of the hydrogel prepared by the embodiment is 240kPa, and the ductility can reach 1730%; the tensile strength can be restored to nearly 93 percent within 2 hours after the cutting; the Congo red degrading agent is used for degrading Congo red in waste water, and the degradation rate reaches 99% within 18 minutes.

Example 6

Steps 1) to 6) were carried out according to the corresponding steps in example one, except that in step 3) the reaction time was 6 hours.

The tensile strength of the hydrogel prepared by the embodiment is 120kPa, and the ductility can reach 800%; the tensile strength can be restored to nearly 60% within 2h after cutting; the material is used for degrading methylene blue in wastewater, and the degradation rate reaches 99% within 3 minutes.

Example 7

Steps 1) to 6) were carried out according to the corresponding steps in example one, except that in step 4) the reaction conditions were: the reaction was carried out at 100 ℃ with constant stirring for 3 h.

The tensile strength of the hydrogel prepared by the embodiment is 230kPa, and the ductility can reach 1800%; the tensile strength can be restored to nearly 96% within 2h after cutting; the material is used for degrading methylene blue in wastewater, and the degradation rate reaches 99% within 2.5 minutes.

Example 8

Steps 1) to 6) were carried out according to the corresponding steps in example one, except that in step 6) the conditions for gel formation were: continuously stirring at 50 ℃ for reacting for 3h to obtain the cellulose-based hydrogel.

The tensile strength of the hydrogel prepared by the embodiment is 240kPa, and the ductility can reach 1600%; the tensile strength can be restored to nearly 94% within 2h after cutting; the material is used for degrading methylene blue in wastewater, and the degradation rate reaches 97 percent within 2 minutes.

Example 9

Steps 1) to 6) were carried out according to the corresponding steps in example one, except that in step 6) the conditions for gel formation were: continuously stirring at 60 ℃ for reacting for 4h to obtain the surface modified hydrogel.

The tensile strength of the hydrogel prepared by the embodiment is 240kPa, and the ductility can reach 1500%; the tensile strength can be restored to nearly 93 percent within 2 hours after the cutting; the material is used for degrading methylene blue in wastewater, and the degradation rate reaches 99% within 2.5 minutes.

Example 10

Steps 1) to 6) were carried out according to the corresponding steps in example one, except that in step 6) the conditions for gel formation were: continuously stirring at 50 ℃ to react for 4h, thus obtaining the surface modified hydrogel.

The tensile strength of the hydrogel prepared by the embodiment is 245kPa, and the ductility can reach 1550%; the tensile strength can be restored to nearly 96% within 2h after cutting; the material is used for degrading methylene blue in wastewater, and the degradation rate reaches 99% within 2.5 minutes.

Examples of Performance test

Taking the first embodiment as an example, the related performance test is performed. The results are as follows.

The cellulose-based hybrid prepared in the first example was subjected to Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM) experiments according to a conventional method. FIG. 3 shows SEM (left) and TEM (right) images of Pd NPs supported on the surface of DACO-PDA fiber prepared in example one. As can be seen from the SEM (left) and TEM (right) images, the Pd NPs are randomly distributed on the surface of the cellulose material, and the particle size ranges from 15 to 40 nm.

The hydrogel prepared in the first example was subjected to a tensile property test in a conventional manner. FIG. 4 compares the tensile stress-strain curves of various hydrogels. As can be seen, the hydrogel prepared in the first example can withstand higher tensile stress. The addition of DACO-PDA @ Pd NPs prepared in example one significantly improved the strength of the hydrogel compared to pure PAA and SA hydrogels. Wherein SA is sodium alginate gel, PAA is polyacrylic acid, DPA is hydrogel without sodium alginate (DACO-PDA-PAA @ Pd NPs), and DPAS is prepared (DACO-PDA-PAA-SA @ Pd NPs) composite hydrogel.

The hydrogel prepared in the first example was subjected to a tensile property test in a conventional manner. Figure 5 example 5 cycle tensile load-unload curve for a hydrogel prepared as described above. As can be seen, the load-unload compression curve after 5 cycles remained almost unchanged, indicating that the prepared hydrogel had good recovery ability.

The hydrogel prepared in the first example was subjected to a compression property test in a conventional manner. FIG. 6 is a cyclic compressive stress-strain curve for various hydrogels. As can be seen, the hydrogel prepared can withstand higher tensile stress. The addition of the DACO-PDA @ Pd NPs obtained in example one significantly improved the strength of the hydrogel compared to the pure PAA and SA hydrogels. Wherein SA is sodium alginate gel, PAA is polyacrylic acid, DPA is hydrogel without sodium alginate (DACO-PDA-PAA @ Pd NPs), and DPAS is prepared (DACO-PDA-PAA-SA @ Pd NPs) composite hydrogel.

And (3) carrying out a self-repairing performance experiment on the hydrogel prepared in the first embodiment according to a conventional method. Figure 7 example a crack recovery test of the hydrogel prepared. As can be seen, when the cut hydrogel was left to stand for a certain period of time (2 hours), the cracks of the hydrogel gradually disappeared. The prepared hydrogel has good self-repairing performance.

And (3) carrying out a self-repairing performance experiment on the hydrogel prepared in the first embodiment according to a conventional method. Figure 8 example a tensile image of the as-prepared hydrogel and a self-healing 2h tensile image of the hydrogel after cutting (left), and tensile stress-strain curves of the original hydrogel and the healing hydrogel after healing for 2h (right). In the self-repaired hydrogel, a remarkable stretching mode can be observed at a fracture part, but the fracture does not occur. From the viewpoint of tensile properties, the cut hydrogel was recovered for 2 hours (about 90% of the original) after self-healing.

Application example

The hydrogels prepared in the first and sixth examples were used as examples for carrying out the degradation experiments. The results are as follows.

Congo Red (CR) adsorption degradation experiments were performed using the hydrogel prepared in example one, according to conventional methods. FIG. 9 UV-Vis spectra of degradation CR of the hydrogel as prepared in the first example. As can be seen from the figure, NaBH was observed as the reaction proceeded₄The CR solution is continuously decolorized, and after about 20min, the decolorization rate can reach about 98 percent.

The hydrogel prepared in the first example was used for the CR adsorption degradation experiment according to the conventional method. FIG. 10 example one hydrogel prepared as a result of undergoing a continuous 5 cycle process on the degradation effect of CR. As can be seen, the degradation of the hydrogel for CR was reduced from 20min for the first cycle to 23min for the 5 th cycle, indicating the reusability of the prepared hydrogel.

The solution obtained after degradation of the hydrogel CR prepared in the first example was subjected to liquid phase-mass spectrometry (LC-MS) in accordance with a conventional method. FIG. 11 is a graph showing the results of Congo Red (CR) treatment of a body of water using the hydrogel prepared in the first example. As can be seen, the appearance of the monomeric structure demonstrates that the CR is degraded.

The Methylene Blue (MB) adsorption degradation experiment was carried out using the hydrogel prepared in example VI in a conventional manner. Figure 12 uv-vis spectra of the hydrogels prepared in example six degraded MB. As can be seen from the figure, in the presence of the hydrogel, the MB solution is decolorized within 3.5min, and the decolorization rate can reach 99%.

The hydrogel prepared in example six was used for MB adsorption degradation experiments according to the conventional method. Figure 13 example six hydrogel prepared as a result of going through 5 consecutive cycles of the process on MB degradation effect. As can be seen from the figure, the degradation of the hydrogel to CR is shortened from 3.5min in the first period to 4min in the 5 th period, and the degradation rates reach 99%, which indicates the reusability of the prepared hydrogel.

The solution obtained after degrading MB of the hydrogel prepared in example six was subjected to liquid phase-mass spectrometry (LC-MS) in accordance with a conventional method. FIG. 14 is a graph showing the results of Methylene Blue (MB) treatment in a water body using the hydrogel prepared in example six. The results show that Methylene Blue (MB) is degraded.

Claims

1. A preparation method of cellulose-based hydrogel for dye degradation is characterized by comprising the following steps: the method comprises the following steps:

1) fully mixing cellulose and periodate in a water system, stirring in a dark place, washing with deionized water, and dialyzing to obtain cellulose; heating and dissolving the obtained dialdehyde cellulose in water, centrifuging, and concentrating to obtain dialdehyde cellulose aqueous solution;

2) taking the dialdehyde cellulose aqueous solution obtained in the step 1) and NaClO₂Fully mixing, adjusting pH to 5.0-6.5, and carboxylating part of aldehyde groups on cellulose under the action of a reducing agent to form a carboxylated cellulose derivative;

3) adding dopamine into the carboxylated cellulose derivative solution obtained in the step 2), and then adding a reducing agent under stirring for stirring; dialyzing and purifying to obtain a cellulose derivative rich in phenolic hydroxyl;

4) PdCl₂Adding the obtained product into the cellulose derivative obtained in the step 3), heating and continuously stirring the obtained product for reaction, and then carrying out dialysis and purification to obtain the cellulose derivative uniformly loaded with Pd nanoparticles;

5) stirring a mixed solution of acrylamide, sodium alginate, ammonium persulfate and the Pd-loaded cellulose derivative obtained in the step 4), and pouring the mixed solution into a mould for polymerization to obtain cellulose-based hydrogel;

6) immersing the cellulose-based hydrogel obtained in the step 5) in a mixed solution of graphene oxide, poly N-isopropylacrylamide and an initiator, and standing to obtain the graphene-based hydrogel.

2. The method of claim 1, wherein: in the step 1), the proportion of the cellulose, periodate and deionized water is 1.0 g: 0.3-2.0 g: 50-200 ml; the reaction temperature is 25-75 ℃, and the reaction time is 6-64 h; the heating temperature of the obtained dialdehyde cellulose dissolved in water is 60-120 ℃; wherein the periodate is sodium periodate.

3. The method of claim 2, wherein: in the step 1), the proportion of the cellulose, periodate and deionized water is 1.0 g: 2.0 g: 100 ml; the reaction temperature is 65 ℃, and the reaction time is 6 hours; the heating temperature of the obtained dialdehyde cellulose dissolved in water is 100 ℃.

4. The method of claim 1, wherein: dialdehyde cellulose and NaClO in the step 2)₂The pH value of the mixed solution is 5.5-6.0; the reducing agent is potassium borohydride, sodium borohydride or sodium cyanoborohydride.

5. The method of claim 1, wherein: the reaction time in the step 3) is 12-24 h; the reducing agent is potassium borohydride, sodium borohydride or sodium cyanoborohydride.

6. The method of claim 1, wherein: the PdCl in step 4)₂The reaction temperature of the cellulose derivative and the cellulose derivative is 60-100 ℃, and the stirring time is 2-5 h.

7. The method of claim 6, wherein: the PdCl in step 4)₂The reaction temperature of the cellulose derivative and the cellulose derivative is 80-100 ℃, and the stirring time is 3-4 h.

8. The method of claim 1, wherein: in the step 5), the weight ratio of the acrylamide, the sodium alginate, the ammonium persulfate and the obtained Pd-loaded cellulose derivative is 8-12: 1-3: 0.05-0.2: 0.4-1.2.

9. The method of claim 7, wherein: in the step 5), the weight ratio of the acrylamide, the sodium alginate, the ammonium persulfate and the obtained Pd-loaded cellulose derivative is 10: 2: 0.1: 0.8.

10. the method of claim 1, wherein: in the step 5), the stirring temperature of the mixed solution is 20-30 ℃, and the gel polymerization temperature is 50-70 ℃.

11. The method of claim 1, wherein: the initiator in the step 6) is ammonium persulfate or potassium persulfate; the standing temperature is 60 ℃, and the standing time is 2 h.

12. The production method according to any one of claims 1 to 11, characterized in that: the degradation dye is Congo red or methylene blue.