Preparation method and multifunctional application of polyethyleneimine / MIL-101 (Cr) modified nanocellulose composite aerogel

Abstract

The application discloses a preparation method of nanocellulose / polyethyleneimine / MIL-101(Cr) composite porous material for efficiently capturing dyes and heavy metal ions in wastewater. First, Cr(NO3)3.9H2O is selected as a metal ion source, H2BDC is selected as an organic ligand, and water is selected as a solvent, and MIL-101(Cr) powder without fluorine is prepared through a hydrothermal synthesis method; then, CNF is selected as a green polymer matrix, PEI is selected as a functional reagent, and MIL-101(Cr) nano-filler is simply complexed with a crosslinking agent to prepare a series of new nanocellulose / polyethyleneimine / MIL-101(Cr) aerogels which are uniform and low in density, can efficiently absorb organic dyes and heavy metal ions in wastewater, and have a synergistic effect on simultaneously absorbing dyes and heavy metal ions in a binary system. The raw materials in the application are derived from biomass, have the advantages of biodegradability and good biocompatibility, and have the characteristics of easy availability, simple preparation method, short operation process, recyclability, environmental protection and economy. The application has a good application prospect in wastewater treatment and other industries.

Description

Technical Field

[0001] This invention belongs to the field of novel adsorbent materials in the biomass chemical industry, and relates to the preparation technology of nanocellulose / polyethyleneimine / MIL-101(Cr) composite aerogel and its multifunctional application in water treatment. Background Technology

[0002] Water is the source of life, playing an irreplaceable role in maintaining ecosystems and in human production and daily life. However, with the acceleration of urbanization and industrialization, water pollution has become a serious global environmental problem. Many industrial pollutants, such as Congo Red, Acid Blue 92, and Methyl Orange, are organic pollutants and Ni... 2+ Heavy metal ions released into water bodies cause serious harm to the environment and aquatic life. Therefore, developing efficient water pollutant removal technologies has become an important research direction in the current environmental field.

[0003] The removal of organic dyes and heavy metal ions from water by adsorption has attracted widespread attention due to its advantages such as simple operation and wide applicability. The core of this approach lies in developing highly efficient adsorption materials. Currently, activated carbon, inorganic porous materials, and metal-organic frameworks (MOFs) are widely used for the adsorption of dyes and heavy metal ions. Among them, MOFs, with their tunable structure, large adsorption capacity, and high removal efficiency, show significant potential. MIL-101(Cr), as a typical MOF material, possesses excellent specific surface area, abundant pore structure, good adsorption performance, and water stability, showing promising application prospects in the treatment of waterborne pollutants. However, the preparation of this material often requires the use of toxic and corrosive hydrofluoric acid, posing environmental risks and safety concerns. Therefore, it is necessary to actively seek alternative synthesis methods that do not rely on this toxic acid. Furthermore, existing methods often face challenges such as low reproducibility, limited scalability, and potential framework degradation under operating conditions. This highlights the necessity of improving synthesis strategies and further exploring the adsorption characteristics of MIL-101(Cr).

[0004] Cellulose nanofibers, as the most abundant renewable nanomaterials in nature, possess unique properties, including excellent environmental friendliness, biodegradability, and ease of chemical modification due to the abundance of hydroxyl groups. In the field of water treatment, CNF-based aerogels have become a key research area. Polyethyleneimine (PEI), a water-soluble cationic polyelectrolyte, has been widely used for the adsorption of dyes and heavy metal ions due to its abundant amino groups. PEI exhibits high affinity for various dyes, making it suitable as a complexing agent for removing pollutants from wastewater; this capability has the potential to expand the application range of aerogels. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing nanocellulose / polyethyleneimine / MIL-101(Cr) for the synergistic adsorption of dyes and heavy metal ions. Fluorine-free MIL-101(Cr) is rapidly synthesized using Cr(NO3)3·9H2O as the metal ion source, H2BDC as the organic ligand, and water as the solvent. Combining this with nanocellulose / polyethyleneimine provides more adsorption sites, increasing the dye adsorption capacity. Simultaneously, the modified nanocellulose-based composite material, with its abundant nanoporous structure and rich nitrogen / oxygen functional groups, achieves selective adsorption of Congo red. This adsorbent uses inexpensive raw materials, has a simple reaction process, and the material is green, biodegradable, and exhibits highly efficient dye adsorption performance.

[0006] The technical solution of this invention: a method for preparing nanocellulose / polyethyleneimine / MIL-101(Cr) for synergistic adsorption of dyes and heavy metal ions, characterized by the following steps:

[0007] 1) A certain amount of a mixture of Cr(NO3)3·9H2O and H2BDC was dispersed in deionized water, and the resulting dark purple mixture was ultrasonically treated.

[0008] 2) Place the mixed solution from step 1) into the liner of the reactor and transfer it to an oven for reaction. Cool to room temperature and remove.

[0009] 3) The reaction product from step 2) was washed sequentially with DMF and anhydrous ethanol by heating and reflux to remove unreacted BDC linkers.

[0010] 4) The product obtained in step 3) was vacuum dried overnight to obtain green powder MIL-101(Cr).

[0011] 5) Weigh a certain amount of nanocellulose suspension into a beaker, then add a certain amount of polyethyleneimine, a certain amount of MIL-101 powder and 1 mol / L ECH.

[0012] 6) Stir in an oil bath at 70℃ for 6 hours, then cool to room temperature. Place in a polytetrafluoroethylene cylindrical mold and freeze-dry to obtain nanocellulose / polyethyleneimine / MIL-101(Cr) aerogel.

[0013] 2. The nanocellulose / polyethyleneimine / MIL-101(Cr) composite aerogel according to claim 1, characterized in that: the molar ratio of Cr(NO3)3·9H2O and H2BDC in step 1) is 1:1.

[0014] 3. The nanocellulose / polyethyleneimine / MIL-101(Cr) composite aerogel according to claim 1, characterized in that: the reaction temperature in the oven in step 2) is 220°C and the reaction time is 8h.

[0015] 4. The nanocellulose / polyethyleneimine / MIL-101(Cr) composite aerogel according to claim 1, characterized in that: the amount of DMF and anhydrous ethanol used in step 3) is 20 mL, the reflux temperature of DMF is 150 °C, and the reflux temperature of anhydrous ethanol is 60 °C.

[0016] 5. The nanocellulose / polyethyleneimine / MIL-101(Cr) composite aerogel according to claim 1, characterized in that: the vacuum drying temperature in step 4) is 150°C and the drying time is 12h.

[0017] 6. The nanocellulose / polyethyleneimine / MIL-101(Cr) composite aerogel according to claim 1, characterized in that: the mass percentage concentration of the nanocellulose suspension in step 4) is 3%; the Mw of the polyethyleneimine in step 5) is 800; the mass ratio of nanocellulose to added PEI is 2:1; and the mass ratio of nanocellulose to added MIL-101(Cr) is 4:1 to 1:4.

[0018] 7. The nanocellulose / polyethyleneimine / MIL-101(Cr) composite aerogel according to claim 1, characterized in that: the freeze-drying conditions in step 6) are freeze-drying at -70℃ for 24h.

[0019] Beneficial effects: Compared with the prior art, the significant advantages of the present invention are:

[0020] 1) This invention addresses the problems of low adsorption efficiency of Congo red in current aerogel materials, poor reusability of MOF materials, and the use of toxic and corrosive hydrofluoric acid in the synthesis process. It proposes a method to rapidly synthesize fluorine-free MIL-101(Cr) and composite it with nanocellulose. By adjusting the amount of MOF, composite aerogels with different pore sizes can be obtained. The hydrothermal synthesis method involved is simple and highly controllable.

[0021] 2) This invention has the characteristics of being degradable, biocompatible, having excellent mechanical properties, and having mild reaction conditions.

[0022] 3) This technology is simple to operate, has low economic cost, strong processability, is universally applicable, and is easy to scale up for production.

[0023] 4) The aerogel material synthesized in this invention can efficiently adsorb CR or Ni. 2+ It also has a synergistic effect on the simultaneous adsorption of dyes and heavy metal ions. Attached Figure Description

[0024] Figure 1 This is a photograph of a nanocellulose / polyethyleneimine / MIL-101(Cr) composite aerogel.

[0025] Figure 2 This is a scanning electron microscope (SEM) image of the nanocellulose / polyethyleneimine / MIL-101(Cr) composite aerogel.

[0026] Figure 3 This is a graph showing the adsorption capacity of Congo red under different MOF loadings in nanocellulose / polyethyleneimine / MIL-101(Cr) composite aerogels.

[0027] Figure 4 This is a graph showing the adsorption capacity of different dyes on the nanocellulose / polyethyleneimine / MIL-101(Cr) composite aerogel.

[0028] Figure 5 This is a graph showing the adsorption capacity of different heavy metal ions for the nanocellulose / polyethyleneimine / MIL-101(Cr) composite aerogel.

[0029] Figure 6 It is a nanocellulose / polyvinyl alcohol / UIO-66-NH2 composite aerogel in mono- and binary systems (CR / Ni 2+ The removal rate comparison chart in )

[0030] Figure 7 It is Congo Red or Ni in nanocellulose / polyvinyl alcohol / UIO-66-NH2 composite aerogel. 2+ Adsorption cycle diagram Detailed Implementation

[0031] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to specific examples. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0032] Implementation Case 1

[0033] 1) Preparation of MIL-101(Cr): A hydrothermal synthesis method was used. A mixture of Cr(NO3)3·9H2O (800 mg, 2.0 mmol) and H2BDC (332 mg, 2.0 mmol) was dissolved in deionized water (10 mL). The mixture was stirred at room temperature for 30 min, and the resulting deep purple mixture was sonicated for 10 min. The final mixture (precursor solution) was placed in a 50 mL hydrothermal reactor liner, heated to 220 °C and maintained for 8 h. Then, the hydrothermal reactor was slowly cooled to room temperature, and the green powder was collected by centrifugation. The crude product was centrifuged to remove unreacted white needle-like crystals, i.e., unreacted terephthalic acid, to obtain a green precipitate. 20 mL of DMF was added, and the mixture was heated to reflux at 150 °C with stirring and centrifugation to remove any unreacted BDC linkers. 20 mL of ethanol was added, and the mixture was heated to reflux at 60 °C with stirring and centrifugation to replace the DMF molecules present in the pores. The resulting green MIL-101(Cr) was then vacuum dried at 150°C overnight for 12 hours to evaporate and remove ethanol.

[0034] 2) Preparation of nanocellulose / polyethyleneimine / MIL-101(Cr) composite aerogel: 6.67 g of nanocellulose suspension (3% by mass) was weighed and placed in a beaker. Then, 0.1 g of polyethyleneimine, 0.05 g of MIL-101(Cr) powder, and 1 mol / L ECH were added dropwise to the nanocellulose. The mass ratio of nanocellulose to MIL-101(Cr) was 4:1. The mixture was stirred in an oil bath at 70 °C for 6 h, and then cooled to room temperature. The resulting product was placed in a polytetrafluoroethylene cylindrical mold and freeze-dried to obtain the final nanocellulose / polyethyleneimine / MIL-101(Cr) aerogel.

[0035] Implementation Case 2

[0036] 1) Preparation of MIL-101(Cr): A hydrothermal synthesis method was used. A mixture of Cr(NO3)3·9H2O (800 mg, 2.0 mmol) and H2BDC (332 mg, 2.0 mmol) was dissolved in deionized water (10 mL). The mixture was stirred at room temperature for 30 min, and the resulting deep purple mixture was sonicated for 10 min. The final mixture (precursor solution) was placed in a 50 mL hydrothermal reactor liner, heated to 220 °C and maintained for 8 h. Then, the hydrothermal reactor was slowly cooled to room temperature, and the green powder was collected by centrifugation. The crude product was centrifuged to remove unreacted white needle-like crystals, i.e., unreacted terephthalic acid, to obtain a green precipitate. 20 mL of DMF was added, and the mixture was heated to reflux at 150 °C with stirring and centrifugation to remove any unreacted BDC linkers. 20 mL of ethanol was added, and the mixture was heated to reflux at 60 °C with stirring and centrifugation to replace the DMF molecules present in the pores. The resulting green MIL-101(Cr) was then vacuum dried at 150°C overnight for 12 hours to evaporate and remove ethanol.

[0037] 2) Preparation of nanocellulose / polyethyleneimine / MIL-101(Cr) composite aerogel: 6.67 g of nanocellulose suspension (3% by mass) was weighed and placed in a beaker. Then, 0.1 g of polyethyleneimine, 0.1 g of MIL-101(Cr) powder, and 1 mol / L ECH were added dropwise to the nanocellulose. The mass ratio of nanocellulose to MIL-101(Cr) was 2:1. The mixture was stirred in an oil bath at 70 °C for 6 h, and then cooled to room temperature. The resulting product was placed in a polytetrafluoroethylene cylindrical mold and freeze-dried to obtain the final nanocellulose / polyethyleneimine / MIL-101(Cr) aerogel.

[0038] Implementation Case 3

[0039] 1) Preparation of MIL-101(Cr): A hydrothermal synthesis method was used. A mixture of Cr(NO3)3·9H2O (800 mg, 2.0 mmol) and H2BDC (332 mg, 2.0 mmol) was dissolved in deionized water (10 mL). The mixture was stirred at room temperature for 30 min, and the resulting deep purple mixture was sonicated for 10 min. The final mixture (precursor solution) was placed in a 50 mL hydrothermal reactor liner, heated to 220 °C and maintained for 8 h. Then, the hydrothermal reactor was slowly cooled to room temperature, and the green powder was collected by centrifugation. The crude product was centrifuged to remove unreacted white needle-like crystals, i.e., unreacted terephthalic acid, to obtain a green precipitate. 20 mL of DMF was added, and the mixture was heated to reflux at 150 °C with stirring and centrifugation to remove any unreacted BDC linkers. 20 mL of ethanol was added, and the mixture was heated to reflux at 60 °C with stirring and centrifugation to replace the DMF molecules present in the pores. The resulting green MIL-101(Cr) was then vacuum dried at 150°C overnight for 12 hours to evaporate and remove ethanol.

[0040] 2) Preparation of nanocellulose / polyethyleneimine / MIL-101(Cr) composite aerogel: 6.67 g of nanocellulose suspension (3% by mass) was weighed and placed in a beaker. Then, 0.1 g of polyethyleneimine, 0.2 g of MIL-101(Cr) powder, and 1 mol / L ECH were added dropwise to the nanocellulose. The mass ratio of nanocellulose to MIL-101(Cr) was 1:1. The mixture was stirred in an oil bath at 70 °C for 6 h, and then cooled to room temperature. The resulting product was placed in a polytetrafluoroethylene cylindrical mold and freeze-dried to obtain the final nanocellulose / polyethyleneimine / MIL-101(Cr) aerogel.

[0041] Implementation Case 4

[0042] 1) Preparation of MIL-101(Cr): A hydrothermal synthesis method was used. A mixture of Cr(NO3)3·9H2O (800 mg, 2.0 mmol) and H2BDC (332 mg, 2.0 mmol) was dissolved in deionized water (10 mL). The mixture was stirred at room temperature for 30 min, and the resulting deep purple mixture was sonicated for 10 min. The final mixture (precursor solution) was placed in a 50 mL hydrothermal reactor liner, heated to 220 °C and maintained for 8 h. Then, the hydrothermal reactor was slowly cooled to room temperature, and the green powder was collected by centrifugation. The crude product was centrifuged to remove unreacted white needle-like crystals, i.e., unreacted terephthalic acid, to obtain a green precipitate. 20 mL of DMF was added, and the mixture was heated to reflux at 150 °C with stirring and centrifugation to remove any unreacted BDC linkers. 20 mL of ethanol was added, and the mixture was heated to reflux at 60 °C with stirring and centrifugation to replace the DMF molecules present in the pores. The resulting green MIL-101(Cr) was then vacuum dried at 150°C overnight for 12 hours to evaporate and remove ethanol.

[0043] 2) Preparation of nanocellulose / polyethyleneimine / MIL-101(Cr) composite aerogel: 6.67 g of nanocellulose suspension (3% by mass) was weighed and placed in a beaker. Then, 0.1 g of polyethyleneimine, 0.4 g of MIL-101(Cr) powder, and 1 mol / L ECH were added dropwise to the nanocellulose. The mass ratio of nanocellulose to MIL-101(Cr) was 1:2. The mixture was stirred in an oil bath at 70 °C for 6 h, and then cooled to room temperature. The resulting product was placed in a polytetrafluoroethylene cylindrical mold and freeze-dried to obtain the final nanocellulose / polyethyleneimine / MIL-101(Cr) aerogel.

[0044] Implementation Case 5

[0045] 1) Preparation of MIL-101(Cr): A hydrothermal synthesis method was used. A mixture of Cr(NO3)3·9H2O (800 mg, 2.0 mmol) and H2BDC (332 mg, 2.0 mmol) was dissolved in deionized water (10 mL). The mixture was stirred at room temperature for 30 min, and the resulting deep purple mixture was sonicated for 10 min. The final mixture (precursor solution) was placed in a 50 mL hydrothermal reactor liner, heated to 220 °C and maintained for 8 h. Then, the hydrothermal reactor was slowly cooled to room temperature, and the green powder was collected by centrifugation. The crude product was centrifuged to remove unreacted white needle-like crystals, i.e., unreacted terephthalic acid, to obtain a green precipitate. 20 mL of DMF was added, and the mixture was heated to reflux at 150 °C with stirring and centrifugation to remove any unreacted BDC linkers. 20 mL of ethanol was added, and the mixture was heated to reflux at 60 °C with stirring and centrifugation to replace the DMF molecules present in the pores. The resulting green MIL-101(Cr) was then vacuum dried at 150°C overnight for 12 hours to evaporate and remove ethanol.

[0046] 2) Preparation of nanocellulose / polyethyleneimine / MIL-101(Cr) composite aerogel: 6.67 g of nanocellulose suspension (3% by mass) was weighed and placed in a beaker. Then, 0.1 g of polyethyleneimine, 0.8 g of MIL-101(Cr) powder, and 1 mol / L ECH were added dropwise to the nanocellulose. The mass ratio of nanocellulose to MIL-101(Cr) was 1:4. The mixture was stirred in an oil bath at 70 °C for 6 h, and then cooled to room temperature. The resulting product was placed in a polytetrafluoroethylene cylindrical mold and freeze-dried to obtain the final nanocellulose / polyethyleneimine / MIL-101(Cr) aerogel.

[0047] The composite aerogels with different MIL-101(Cr) ratios prepared in Examples 1, 2, 3, 4, and 5 are labeled as CMP-1, CMP-2, CMP-3, CMP-4, and CMP-5, respectively.

[0048] Finally, it should be noted that the above description of the disclosed embodiments enables those skilled in the art to implement or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novelty disclosed herein.

Claims

1. A method for preparing nanocellulose / polyethyleneimine / MIL-101(Cr) for synergistic adsorption of dyes and heavy metal ions, characterized in that: Fluorine-free MIL-101(Cr) was rapidly synthesized using Cr(NO3)3·9H2O as the metal ion source, H2BDC as the organic ligand, and water as the solvent. This was then combined with nanocellulose / polyethyleneimine and freeze-dried to prepare a series of nanocellulose / polyethyleneimine / MIL-101(Cr) compounds. The preparation process included the following steps: 1) A certain amount of a mixture of Cr(NO3)3·9H2O and H2BDC was dispersed in deionized water, and the resulting dark purple mixture was ultrasonically treated. 2) Place the mixed solution from step 1) into the liner of the reactor and transfer it to an oven for reaction. Cool to room temperature and remove. 3) The reaction product from step 2) was washed sequentially with DMF and anhydrous ethanol by heating and reflux to remove unreacted BDC linkers. 4) The product obtained in step 3) was vacuum dried overnight to obtain green powder MIL-101(Cr). 5) Weigh a certain amount of nanocellulose suspension into a beaker, then add a certain amount of polyethyleneimine, a certain amount of MIL-101 powder and 1 mol / L ECH. 6) Stir in an oil bath at 70℃ for 6 hours, then cool to room temperature. Place in a polytetrafluoroethylene cylindrical mold and freeze-dry to obtain nanocellulose / polyethyleneimine / MIL-101(Cr) aerogel.

2. The nanocellulose / polyethyleneimine / MIL-101(Cr) composite aerogel according to claim 1, characterized in that: The molar ratio of Cr(NO3)3·9H2O and H2BDC mentioned in step 1) is 1:

1.

3. The nanocellulose / polyethyleneimine / MIL-101(Cr) composite aerogel according to claim 1, characterized in that: The reaction temperature in the oven described in step 2) is 220°C, and the reaction time is 8 hours.

4. The nanocellulose / polyethyleneimine / MIL-101(Cr) composite aerogel according to claim 1, characterized in that: In step 3), the amounts of DMF and anhydrous ethanol used are both 20 mL. The reflux temperature for DMF is 150 °C, and the reflux temperature for anhydrous ethanol is 60 °C.

5. The nanocellulose / polyethyleneimine / MIL-101(Cr) composite aerogel according to claim 1, characterized in that: The vacuum drying temperature described in step 4) is 150℃, and the drying time is 12h.

6. The nanocellulose / polyethyleneimine / MIL-101(Cr) composite aerogel according to claim 1, characterized in that: The nanocellulose suspension mentioned in step 4) has a mass percentage concentration of 3%. The polyethyleneimine M mentioned in step 5) w The mass ratio of nanocellulose to added PEI is 2:

1. The mass ratio of nanocellulose to added MIL-101(Cr) is 4:1 to 1:

4.

7. The nanocellulose / polyethyleneimine / MIL-101(Cr) composite aerogel according to claim 1, characterized in that: In step 6), the freeze-drying conditions are -70℃ for 24 hours.

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