Preparation method and application of cellulose-based composite material

Abstract

The invention discloses a preparation method and application of a cellulose-based composite material, and belongs to the technical field of environment functional composite materials. The preparation method comprises the following steps: preparing lignin nanocellulose by adopting a p-toluenesulfonic acid / formic acid catalytic acid treatment method, introducing N, N '-methylenebisacrylamide as a physical cross-linking agent, uniformly loading polydopamine on a lignin nanocellulose skeleton through continuous stirring, centrifuging the obtained brownish black turbid liquid, washing with water and alcohol for several times, and drying to obtain the lignin nanocellulose composite material. The polydopamine-lignin nanocellulose composite material is obtained. A simple bionic modification strategy is adopted, the preparation process is simple, the cost of raw materials is low, the problems that cellulose lacks active groups, water stability is poor and the like are solved, and the PDA-LCNF composite material with high adsorption capacity and good environmental stability is successfully constructed. When the initial concentrations of copper and tetracycline are 0.05 mmol / L and 0.1 mmol / L respectively and the pH value of an initial solution is 5.0, the adsorption capacities of the composite material to copper and tetracycline respectively reach 0.178 mmol / g and 0.431 mmol / g.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of environmental functional composite materials, and particularly relates to a cellulose-based composite material and a preparation method thereof, which is mainly applied to copper and tetracycline wastewater treatment. BACKGROUND

[0002] Copper and tetracycline, as additives for promoting animal growth and disease treatment, are widely added to feed. Most of the copper and tetracycline cannot be effectively absorbed by animals and enters the natural environment with excrement. When the two pollutants coexist in water bodies, they can form more stable and more toxic complexes, leading to the increasingly prominent problem of copper and tetracycline combined pollution. The treatment technologies for copper and tetracycline combined pollution in water bodies mainly include physical methods (such as adsorption method, membrane separation method), biological methods (such as fixed microorganism treatment method, anaerobic-aerobic combined process) and chemical methods (such as electrochemical method, chlorination method, advanced oxidation technology). Among them, the adsorption method is concerned due to its advantages of high efficiency, controllable cost, simple operation and low risk of secondary pollution.

[0003] Cellulose is the most abundant natural polysaccharide in nature, which is favored due to its high aspect ratio, rich surface functional groups, excellent mechanical properties, good water stability and environmental friendliness. Lignin nanocellulose (LCNF) as a new type of nanomaterial realizes the comprehensive utilization of lignocellulose biomass, avoiding the waste of resources and environmental pollution caused by lignin separation in the traditional pulping process. LCNF not only inherits the high specific surface area and rich reaction sites of cellulose nanofiber, but also has strong hydrophobicity, high surface polarity and pollutant binding potential due to the high cross-linking of lignin as a phenolic polymer. However, pure LCNF has limited selective adsorption capacity for copper ions and tetracycline and other combined pollutants in water bodies due to the relatively single type of surface functional groups, and still needs effective functional modification.

[0004] In order to break through the above bottleneck, the biomimetic surface functionalization strategy provides a key technical path. Polydopamine (PDA) as a biomimetic material inspired by mussel foot protein has rich active functional groups (such as o-diphenol, amino / imino), which can form a uniform coating layer on almost all material surfaces. The introduction of PDA has a dual effect: on the one hand, it provides a large number of adsorption sites for surface functionalization of materials; on the other hand, its unique active functional groups can produce hydrogen bonds and electrostatic attraction with copper and tetracycline molecules. In addition, the presence of PDA can also enhance its stability, thereby improving the anti-interference ability in complex water environment.

[0005] Against this backdrop, this study developed a general and efficient strategy to successfully load PDA onto a three-dimensional LCNF framework through a simple physical crosslinking and biomimetic modification process, constructing a PDA-LCNF composite material with excellent adsorption performance. This composite material can effectively remove copper and tetracycline from water simultaneously while maintaining good structural stability. This study further explored the reusability of the composite material and its synergistic adsorption mechanism for pollutants.

[0006] In the prior art, there are some achievements in the preparation methods of polydopamine (PDA)-lignin nanocellulose (LCNF) composite materials. For example, Chinese Patent No. 202510515293.5, published on June 20, 2025, discloses a patent document entitled "An Efficient Preparation Method of Nanocellulose". This patent uses straw as raw material to prepare nanocellulose using a deep eutectic solvent method. Purification is required during the preparation process, wasting lignin resources in the cellulose. Chinese Patent Application No. 202410762871.0, published on October 11, 2024, discloses a patent document entitled "An Aerogel Gas Sensing Material Containing Lignin Nanocellulose and Its Preparation Method". This patent uses an acidic eutectic solvent method to prepare lignin-containing nanocellulose. This material has good flexibility and biodegradability, but its stability in water limits its adsorption performance if developed as an adsorbent for pollutants. Patent application number 202410234052.9, published on May 17, 2024, discloses a patent document entitled "A method and application for preparing lignin-containing nanocellulose filaments from bagasse using acidified alcohols". This patent involves first mixing dried bagasse with acidified alcohol reagents and then preparing the final product by high-pressure homogenization. This method retains the amphiphilic properties of lignin, and the resulting lignin-containing nanocellulose has excellent emulsifying properties at low lignin content. However, its adsorption performance for pollutants in water is currently unknown if it is developed as an adsorbent for adsorbing pollutants. Chinese patent application number 202410506450.1, published on December 24, 2024, discloses a patent document entitled "A polydopamine-nanocellulose composite aerogel material and its preparation method and application". This patent prepares a polydopamine-nanocellulose composite aerogel material by freeze-drying polydopamine and quaternary ammonium salt modified nanocellulose. This method attempts to address the problems of difficult recycling and high cost of nanocellulose powder. It is used to adsorb microplastics and has a good adsorption and removal effect on microplastics in natural aquatic environments, but its adsorption and removal capacity for copper and tetracycline is unknown.

[0007] Several patent documents already exist for the adsorption and removal of copper and tetracycline from water. For example, Chinese Patent Application No. 202410323544.5, published on May 28, 2024, discloses a patent entitled "Preparation of Peanut Shell Biochar and its Adsorption Method for Copper and Nickel Ions in Electroplating Wastewater"; and Chinese Patent Application No. 202410501489.4, published on August 6, 2024, discloses a patent entitled "A Steel Slag-Based Molecular Sieve Adsorption Material in..." The patent documents mentioned above mainly focus on the adsorption and removal of copper ions from wastewater; Chinese patent application number 202111230288.8, published on May 24, 2024, entitled "Preparation method of a composite adsorbent for removing tetracycline from wastewater"; and Chinese patent application number 202111427480.6, published on January 28, 2022, entitled "Application of nylon 6 / chitosan-Fe nanofiber composite material in the adsorption of tetracycline". These patents primarily address the adsorption and removal of single pollutants such as copper and tetracycline in water, but do not cover binary composite pollutants. Summary of the Invention

[0008] To overcome the problems of insufficient synergistic removal capacity of existing adsorbents for copper and tetracycline, waste of lignin resources in traditional biomass materials, and poor stability of materials in complex aquatic environments, this invention provides a polydopamine (PDA) modified lignin nanocellulose (LCNF) composite material and its preparation method. The aim is to effectively integrate the skeletal advantages of LCNF with the multifunctional properties of PDA, providing a novel solution for the efficient and selective removal of copper and tetracycline complex pollution in water bodies.

[0009] To solve the above problems, the present invention adopts the following technical solution.

[0010] This invention provides a method for preparing a cellulose-based composite material, specifically comprising the following steps:

[0011] (1) Mix the cellulose of *Ulva prolifera* with water to form a suspension, and stir magnetically until evenly dispersed; add p-toluenesulfonic acid (p-TsOH), formic acid (FA), H2O and HCl and stir until completely mixed, then react in a water bath; after the reaction is complete, put the mixture directly into a centrifuge tube and centrifuge at a certain speed; wash the precipitate with deionized water until neutral to obtain lignin nanocellulose (LCNF); the mass ratio of toluenesulfonic acid, formic acid and H2O is 3:5:2;

[0012] (2) Add lignin nanocellulose to deionized water to form a lignin nanocellulose colloidal solution, then add it to a flask and stir magnetically; then add N,N'-methylenebisacrylamide (MBA) to the lignin nanocellulose solution and stir vigorously to dissolve it; after dissolving, add polydopamine (PDA) and stir to form a homogeneous mixture; finally, place it at room temperature to form a composite material; put the synthesized composite material into deionized water to remove unreacted chemicals; finally freeze-dry to obtain polydopamine-lignin nanocellulose; the mass ratio of polydopamine to lignin nanocellulose is 5:1~1:20.

[0013] As an optimization, in step (1), the HCl mass concentration is 2%, and the water bath reaction refers to reacting in a water bath at 80°C for 3 hours.

[0014] As an optimization, in step (2), the mass ratio of polydopamine to lignin nanocellulose is 1:10.

[0015] The cellulose-based composite material obtained by the above preparation method is polydopamine-lignin nanocellulose (PDA-LCNF).

[0016] The polydopamine-lignin nanocellulose (PDA-LCNF) composite material obtained by the above preparation method can be used in the removal of copper and tetracycline from water.

[0017] This invention first uses p-toluenesulfonic acid (p-TsOH) / formic acid (FA) catalytic acid treatment to prepare lignin nanocellulose (LCNF), introduces N,N'-methylenebisacrylamide (MBA) as a physical crosslinking agent, and continuously stirs to uniformly load polydopamine (PDA) onto the LCNF framework. The resulting brown-black suspension is centrifuged and then washed several times with water and alcohol to obtain a PDA-LCNF composite material.

[0018] The adsorption mechanism of PDA-LCNF on copper and tetracycline in water may be as follows: First, copper ions and tetracycline molecules in the solution are attracted to the surface of the PDA-LCNF composite material with opposite charges through electrostatic interaction; then, copper and tetracycline diffuse into the interior of the material through the three-dimensional porous network structure; finally, the abundant functional groups on the surface and inside of PDA-LCNF form hydrogen bonds with copper and tetracycline molecules and are electrostatically attracted.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0020] (1) The present invention adopts a simple biomimetic modification strategy, the preparation process is simple and the raw material cost is low, which improves the problems of lack of active groups and poor water stability of cellulose, and successfully constructs a PDA-LCNF composite material with both high adsorption capacity and good environmental stability.

[0021] (2) The present invention uses LCNF (containing lignin nanocellulose) as a base, which is greener and cheaper, and realizes the resource utilization of waste; it avoids the waste problem of lignin being separated as waste in traditional processes, and utilizes all components of lignin cellulose.

[0022] (3) This invention uses PDA for functionalization. The biomimetic modification of PDA provides more universal catechol and amino functional groups, and the interaction mechanism with pollutants is richer.

[0023] (4) The present invention targets the tetracycline and copper complex pollution that is common in the environment, rather than targeting only a single pollutant (tetracycline or copper).

[0024] (5) This invention is a non-biological adsorption process, which is not strictly limited by biological conditions such as bacterial activity, temperature, and pH, and has a wider range of applications. The multiple functional groups of the PDA in this invention can simultaneously and effectively act on heavy metal ions (Cu²⁺) and organic macromolecules (tetracycline), achieving synergistic removal of complex pollutants. When the initial concentrations of copper and tetracycline are 0.05 mmol / L and 0.1 mmol / L, respectively, and the initial solution pH is 5.0, the adsorption capacities of the PDA-LCNF composite material for copper and tetracycline reach 0.178 mmol / g and 0.431 mmol / g, respectively. Attached Figure Description

[0025] Figure 1 The flowcharts are for the preparation of Examples 1-5 and Comparative Example 1.

[0026] Figure 2 SEM characterization images of the composite materials prepared in Examples 1-5 and Comparative Examples 1-2 (where a is PDA, b is LCNF, c is PDA-LCNF (5:1), d is PDA-LCNF (1:1), e is PDA-LCNF (1:5), f is PDA-LCNF (1:10) and g is PDA-LCNF (1:20)).

[0027] Figure 3 The images show the FTIR characterization of the composite materials obtained in Examples 1-5 and Comparative Examples 1-2.

[0028] Figure 4 The images show the XRD characterization patterns of the composite materials obtained in Examples 1-5 and Comparative Examples 1-2.

[0029] Figure 5This is a comparison chart showing the adsorption capacity of PDA-LCNF composite materials with different mass ratios (5:1, 1:1, 1:5, 1:10, 1:20) prepared according to the preparation methods shown in Examples 1-5, and the adsorption capacity of LCNF prepared in the comparative example and purchased PDA for copper and tetracycline in water. Detailed Implementation

[0030] The technical solution of the present invention will be further described in detail below with reference to specific embodiments, but this is not intended to limit the present invention.

[0031] Example 1

[0032] This embodiment provides a method for preparing PDA-LCNF (the mass ratio of polydopamine PDA to lignin nanocellulose LCNF is 5:1), the method comprising the following steps:

[0033] (1) Preparation of lignin nanocellulose: 1.50 g (dry weight) of *Ulva prolifera* cellulose and water were mixed to form a suspension in a certain proportion and magnetically stirred until evenly dispersed. 50 g of p-TsOH / FA / H2O (mass ratio 3:5:2) and 2% HCl were added and stirred for 10 min until completely mixed. Then, the mixture was reacted in a water bath set at 80℃ for 3 h. The mixture was directly placed into a centrifuge tube and centrifuged at 8000 rpm for 5 min. The precipitate was washed with deionized water until neutral to obtain lignin nanocellulose LCNF.

[0034] (2) Preparation of PDA-LCNF: 60 g of LCNF colloidal solution (0.75 g of LCNF added to deionized water) was added to a 250 mL flask and magnetically stirred. Then, 0.18 g of MBA was added to the LCNF solution and stirred vigorously to dissolve it. After dissolution, 3.75 g of PDA was added and stirred for 30 minutes to form a homogeneous mixture. Finally, the mixture was left at room temperature for 6 h to form a composite material. The synthesized composite material was placed in deionized water to remove unreacted chemicals. Finally, the PDA-LCNF composite material was obtained by freeze-drying.

[0035] Example 2

[0036] This embodiment provides a method for preparing a PDA-LCNF composite material (the mass ratio of polydopamine PDA to lignin nanocellulose LCNF is 1:1), the method comprising the following steps:

[0037] (1) The preparation of lignin nanocellulose is the same as that described in step (1) of Example 1.

[0038] (2) The preparation of the PDA-LCNF composite material is the same as in step (2) of Example 1. The difference is that 0.75 g of polydopamine PDA is added.

[0039] Example 3

[0040] This embodiment provides a method for preparing a PDA-LCNF composite material (the mass ratio of polydopamine PDA to lignin nanocellulose LCNF is 1:5), the method comprising the following steps:

[0041] (1) The preparation of lignin nanocellulose is the same as that described in step (1) of Example 1.

[0042] (2) The preparation of the PDA-LCNF composite material is the same as in step (2) of Example 1. The difference is that 0.15 g of polydopamine PDA is added.

[0043] Example 4

[0044] This embodiment provides a method for preparing a PDA-LCNF composite material (the mass ratio of polydopamine PDA to lignin nanocellulose LCNF is 1:10), the method comprising the following steps:

[0045] (1) The preparation of lignin nanocellulose is the same as that described in step (1) of Example 1.

[0046] (2) The preparation of PDA-LCNF composite material is the same as that described in step (2) of Example 1.

[0047] Example 5

[0048] This embodiment provides a method for preparing a PDA-LCNF composite material (the mass ratio of polydopamine PDA to lignin nanocellulose LCNF is 1:20), the method comprising the following steps:

[0049] (1) The preparation of lignin nanocellulose is the same as that described in step (1) of Example 1.

[0050] (2) The preparation of the PDA-LCNF composite material is the same as in step (2) of Example 1. The difference is that 0.0375 g of polydopamine PDA is added.

[0051] Comparative Example 1:

[0052] This comparative example provides a method for preparing lignin-cellulose nanofibers (LCNF), the method comprising the following steps:

[0053] The preparation of lignin nanocellulose is the same as described in step (1) of Example 1.

[0054] Comparative Example 2:

[0055] This comparative example provides a method for directly using commercially available polydopamine (PDA) as an adsorbent. The PDA was purchased from Aladdin and has a purity of ≥98%.

[0056] The above Examples 1-5 and Comparative Examples 1-2 were characterized by SEM. Figure 1 It is known that when the PDA loading is high, excessive deposition leads to particle stacking, obscuring the LCNF fiber structure and blocking the interstitial spaces. Conversely, at lower ratios, the PDA no longer forms distinct spheres, but instead forms a uniform coral-like coating on the fiber surface. Furthermore, as... Figure 2 As shown, the Fourier transform infrared (FTIR) spectrum of LCNF exhibits characteristics corresponding to cellulose (3300-3340 cm⁻¹). -1 (broadband OH stretching vibration) and lignin (1595 cm) -1 The characteristic peak bands (at the aromatic C=C skeleton vibration) are prominent in the FTIR spectrum of PDA, which is located at 3200-3400 cm⁻¹. -1 The broadband OH stretching vibration peak at 1600 cm⁻¹ and the peak at 1600 cm⁻¹ -1 The peak originates from the aromatic C=C skeleton vibration of the main chain. Figure 3 XRD characterization showed that LCNF exhibited characteristic peaks at 2θ = 16.5° and 22.2°, corresponding to the (110) and (200) crystal planes of cellulose, respectively. PDA is a completely amorphous polymer, and XRD testing did not reveal any sharp crystalline peaks, but only showed extremely broad diffuse peaks typically concentrated in the 20°-30° range.

[0057] PDA-LCNF composite materials with different mass ratios (5:1, 1:1, 1:5, 1:10, and 1:20) prepared by the methods shown in Examples 1-5 above, as well as LCNF prepared in the comparative example and purchased PDA, were subjected to copper and tetracycline adsorption experiments. The adsorbent dosage was 0.1 g / L. Copper and tetracycline wastewater were prepared using copper chloride dihydrate and tetracycline hydrochloride, with a tetracycline to copper molar ratio of 2:1 and concentrations of 0.05 mmol / L and 0.1 mmol / L, respectively. The reaction was carried out at pH 5, temperature 25℃, and time 12 h. The remaining concentrations of copper and tetracycline were then measured, and the adsorption capacity was calculated. The experimental results are as follows: Figure 4 As shown, after 12 hours of adsorption, the adsorption of each material tended to be saturated. The PDA-LCNF composite material with a mass ratio of 1:10 showed the best adsorption effect, with adsorption capacities of 0.178 mmol / g for copper and 0.431 mmol / g for tetracycline.

[0058] Test data show that the PDA-LCNF obtained in Examples 1-5 of this invention has a very significant adsorption efficiency for copper and tetracycline in water (as shown in Table 1).

[0059] Table 1. Experimental results of copper and tetracycline adsorption in different embodiments

[0060] Example 1 Example 2 Example 3 Example 4 Example 5 Comparative Example 1 Comparative Example 2 Adsorbed amount of copper (mmol / g) 0.097 0.104 0.117 0.178 0.145 0.095 0.024 Adsorbed amount of tetracycline (mmol / g) 0.234 0.251 0.283 0.431 0.351 0.229 0.058

Claims

1. A method for the production of a cellulose-based composite material, characterized in that It comprises the following steps: (1) mixing Enteromorpha cellulose and water to form a suspension, stirring by magnetic force until evenly dispersed; adding p-toluenesulfonic acid, formic acid, H2O and HCl, stirring until completely mixed, then water bath reaction; after the reaction is completed, the mixture is directly placed in a centrifuge tube, and centrifuged at a speed; the precipitate is washed with deionized water until neutral, to obtain lignin nanocellulose; The mass ratio of toluenesulfonic acid, formic acid and H2O is 3:5:2; (2) adding lignin nanocellulose into deionized water to form a lignin nanocellulose colloidal solution, then adding into a flask, and stirring by magnetic force; then, adding N, N'-methylenebisacrylamide into the lignin nanocellulose solution, and stirring to dissolve; after dissolving, adding polydopamine and stirring to form a uniform mixture; finally, placing at room temperature to form a composite material; placing the synthesized composite material into deionized water to remove unreacted chemicals; and finally freeze-drying to obtain polydopamine-lignin nanocellulose; The mass ratio of polydopamine and lignin nanocellulose is 5:1-1:

20.

2. A process for the production of a cellulose-based composite material according to claim 1, characterized in that In step (1), the mass concentration of HCl is 2%, and the water bath reaction refers to reaction in a water bath at 80℃ for 3h.

3. A method of producing a cellulose-based composite material according to claim 1, characterized by, In step (2), the mass ratio of polydopamine and lignin nanocellulose is 1:

10.

4. The cellulose-based composite material obtained by the production method according to any one of claims 1 to 3, characterized by, The cellulose-based composite material is polydopamine-lignin nanocellulose.

5. Use of the cellulose-based composite material according to claim 4 in removing copper and tetracycline from water bodies.

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