Cellulose-based composite gel with catalytic degradation performance and preparation method thereof

Abstract

The invention belongs to the technical field of composite materials, and particularly relates to cellulose-based composite gel with catalytic degradation performance and a preparation method. According to the gel, microcrystalline cellulose serves as a framework, a three-dimensional network structure is formed through crosslinking of epoxy chloropropane and polyethyleneimine, and a Zn5 (OH) 8Cl2. H2O layer and metal copper particles are loaded on the surface in sequence. The preparation method comprises the steps of cellulose dissolution, amination crosslinking, alkali treatment of loaded zinc compounds, copper ion adsorption, in-situ reduction and the like. The obtained gel has a 11-14 nm mesoporous structure, the degradation rate of 300 mg / L Congo red under visible light is larger than 90%, the performance retention rate is larger than 93% after the gel is recycled for 3 times, and the technical problems that existing cellulose gel is low in photocatalytic activity and poor in cycling stability are solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of composite materials, and particularly relates to a cellulose-based composite gel with catalytic degradation performance and a preparation method. BACKGROUND

[0002] Cellulose-based aerogels have attracted much attention in the field of pollutant treatment due to their environmental-friendly and degradable characteristics. Traditional methods endow photocatalytic performance by loading metal oxides, but there are problems of weak visible light response and high carrier recombination rate. Although noble metals are introduced to improve performance, it leads to a sharp increase in cost and a decrease in cycle stability.

[0003] In the prior art, cellulose gels loaded with basic zinc chloride have adsorption capacity, but their wide band gap in the layered structure can only utilize ultraviolet light, and the photo-generated electron-hole pairs are prone to recombination. Although copper can broaden the light response range, direct loading leads to particle agglomeration, resulting in a decrease in active sites. Therefore, how to construct a stable copper-zinc synergistic catalytic system is still a technical bottleneck to be broken through. SUMMARY

[0004] This section aims to summarize some aspects of the embodiments of the present application and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the abstract and title of the specification to avoid obscuring the purpose of this section, abstract and title, and such simplifications or omissions cannot be used to limit the scope of the present application.

[0005] In view of the problems in the prior art, the present application is proposed by the present inventors.

[0006] Therefore, the purpose of the present application is to overcome the deficiencies in the prior art and provide a cellulose-based composite gel with catalytic degradation performance and a preparation method.

[0007] To solve the above technical problems, the present application provides the following technical solutions: a cellulose-based composite gel with catalytic degradation performance, which is composed of the following components:

[0008] A network skeleton of amine groups formed by cross-linking microcrystalline cellulose with epichlorohydrin and polyethyleneimine;

[0009] Zn(OH)Cl·HO layers uniformly loaded on the surface of the skeleton, with a loading amount of 10-30wt% of the mass of the skeleton;

[0010] Metal copper particles dispersed on the Zn(OH)Cl·HO layers, with a particle size of 50-200nm and a loading amount of 1-10wt% of the total mass of the gel;

[0011] The specific surface area of the gel is 40-100m 2 / g, pore size distribution of 11-14 nm, and porosity of 85-92%.

[0012] As a preferred scheme of the catalytic degradation performance of the cellulose-based composite gel, the polyethyleneimine has a polymerization degree of 5000-8000, and the mass ratio of the epichlorohydrin to the cellulose is 0.2-0.5:1.

[0013] A preparation method of the catalytic degradation performance of the cellulose-based composite gel, comprising the following steps:

[0014] (1) Dissolution: ZnCl and HO are mixed into a molten salt aqueous solution at a molar ratio of 3:1, and microcrystalline cellulose is added, and the solution is stirred and dissolved at 80±2℃ for 30 min to form a transparent solution;

[0015] (2) Crosslinking: epichlorohydrin is added to the solution of step (1), and the reaction is carried out at 60±2℃ for 1 h, and then a polyethyleneimine solution with a mass fraction of 5% is added, and the reaction is continued for 1 h;

[0016] (3) Molding: the mixed solution is injected into a mold, and after gelation at room temperature, it is immersed in a 1wt% glutaraldehyde solution, and solidified at 60±2℃ for 3 h;

[0017] (4) Zinc loading: the gel is immersed in a 1wt% NaOH solution for 120 min, and washed with deionized water until neutral;

[0018] (5) Copper loading: immersed in a 1-10wt% copper nitrate solution for 12 h, and then immersed in a 1mol / L NaBH solution after taking out, and reduced at 60±2℃ for 30 min;

[0019] (6) Post-treatment: washed with deionized water until the conductivity is less than 20μS / cm, and freeze-dried for 24 h.

[0020] As a preferred scheme of the preparation method of the catalytic degradation performance of the cellulose-based composite gel, the mass ratio of the microcrystalline cellulose to ZnCl in step (1) is 1:8-1:12.

[0021] As a preferred scheme of the preparation method of the catalytic degradation performance of the cellulose-based composite gel, the addition amount of the polyethyleneimine solution in step (2) is 0.5-1mL per gram of cellulose.

[0022] As a preferred scheme of the preparation method of the catalytic degradation performance of the cellulose-based composite gel, the concentration of the copper nitrate solution in step (5) is 5-10wt%, and the reduction reaction is carried out under nitrogen protection.

[0023] The application of the cellulose-based composite gel with catalytic degradation performance in the photocatalytic degradation of organic dyes, wherein the degradation object is an azo dye.

[0024] The application of the cellulose-based composite gel with catalytic degradation performance in the photocatalytic degradation of organic dyes, wherein the dye is Congo red, and the degradation condition is that the xenon lamp light intensity is 300 W, and the initial concentration of the dye is less than or equal to 300 mg / L.

[0025] The application of the cellulose-based composite gel with catalytic degradation performance in the photocatalytic degradation of organic dyes, wherein the degradation process conforms to a pseudo-first-order kinetic model, and the rate constant k is greater than or equal to 0.023 min-1.

[0026] The application of the cellulose-based composite gel with catalytic degradation performance in the photocatalytic degradation of organic dyes, wherein the degradation rate of the dye is maintained at more than 93% after the cellulose-based composite gel is used for three cycles.

[0027] The cellulose-based composite gel with catalytic degradation performance has the following advantages: a three-level ordered structure of a cellulose network-zinc compound layer-copper particles is constructed; the cellulose cross-linked network provides mechanical support; the zinc compound layer serves as an electron transport bridge; the copper particles act as visible light capture centers; and the three components are combined to realize efficient carrier separation; the narrow band gap characteristics of the copper particles extend the light response range to more than 500 nm; the zinc compound layer fixes the copper particles to prevent them from falling off, thereby improving the cycle stability by two times; the mesoporous structure accelerates the diffusion of dye molecules, and the degradation rate is close to 100% under a high concentration of 200 mg / L; and the preparation process does not require noble metals, and the basic zinc chloride is generated in situ to reduce the cost. DETAILED DESCRIPTION

[0028] In order to make the above objectives, characteristics and advantages of the present application more apparent and comprehensible, the specific embodiments of the present application will be described in detail below with reference to the embodiments of the present application.

[0029] In the following description, a large number of specific details are set forth in order to facilitate a thorough understanding of the present application, but the present application can also be implemented in other ways different from the description, and those skilled in the art can make similar generalizations without departing from the connotation of the present application, so the present application is not limited by the specific embodiments disclosed below.

[0030] Secondly, the "one embodiment" or "embodiment" referred to herein means that a specific feature, structure or characteristic can be included in at least one implementation of the present application. The "in one embodiment" appearing in different places in the specification does not mean the same embodiment, nor does it mean an embodiment that is separate or selectively excluded from other embodiments.

[0031] Embodiment 1

[0032] The embodiment provides a cellulose-based composite gel with catalytic degradation performance and a preparation method.

[0033] Specifically, the raw materials and the process are as follows:

[0034] Cellulose dissolution: ZnCl and deionized water are mixed at a molar ratio of 3:1 to form a molten salt aqueous solution in an 80°C oil bath. Microcrystalline cellulose (mass ratio of 1:10 to ZnCl) is added, and stirring is performed at a speed of 500 rpm for 30 minutes until the turbid suspension is converted into a uniform transparent solution.

[0035] Amino crosslinking: epoxy chloropropane (addition amount: 0.5 mL per gram of cellulose) is added to the above solution, and reaction is performed at 60±2°C for 60 minutes. Further, 5wt% polyethyleneimine solution (polymerization degree 6000, addition amount: 2 mL per gram of cellulose) is added, and reaction is continuously performed for 60 minutes to form a viscous sol.

[0036] Gel solidification: the sol is injected into a 60mm-diameter glass culture dish, and gelation is performed at room temperature for 30 minutes. The gel is transferred into a 1wt% glutaraldehyde solution, and oscillation is performed at 60±2°C for 3 hours to complete crosslinking and solidification.

[0037] Zinc copper loading: the solidified gel is immersed in a 1wt% NaOH solution for 120 minutes, and then washed with water until neutral. Further, the gel is transferred into a 1wt% copper nitrate solution for 12 hours, and then taken out and placed in a 1mol / L NaBH solution, and reduction is performed at 60±2°C under nitrogen protection for 30 minutes.

[0038] Post-processing: the gel is washed with flowing deionized water until the conductivity is less than 20μS / cm, pre-frozen at-50°C for 12 hours, and vacuum freeze-dried for 24 hours to obtain a porous composite gel (labeled as RC3P5G-120-Cu1).

[0039] Key phenomena and parameter control:

[0040] Dissolution stage: the solution changes from turbidity to transparency in the 80°C oil bath, and the viscosity significantly increases;

[0041] Crosslinking process: the sol flowability decreases after the addition of PEI, and a self-supporting gel is formed after standing at room temperature;

[0042] Reduction stage: the gel changes from light blue (Cu2) to brown red (Cu), which proves the generation of copper particles.

[0043] Performance verification:

[0044] Structural characterization: SEM shows that 50-100nm copper particles are attached to the surface of the Zn(OH)Cl·HO layered structure; XRD patterns show that Zn(OH)Cl·HO characteristic peaks appear at 12.3°, 24.6° and 33.5°, and Cu(111) crystal face peaks appear at 43.3°.

[0045] Photocatalytic performance: 0.1 g of the gel was added to 100 mL of a 200 mg / L Congo red solution, and irradiated with a xenon lamp (300 W, λ≥420 nm) for 60 minutes, with a degradation rate of 85.46%.

[0046] Cyclic stability: the degradation rate remained 82.5% after repeated use for 3 times, and the copper particles did not fall off significantly (verified by SEM).

[0047] Example 2

[0048] The present embodiment provides a cellulose-based composite gel with catalytic degradation performance and a preparation method thereof.

[0049] Improved technical features:

[0050] Improved copper source concentration: the concentration of copper nitrate solution was increased to 5 wt%, and the remaining steps were the same as in Example 1 to obtain sample RC3P5G-120-Cu5.

[0051] Improved reduction process: nitrogen gas was introduced (flow rate 0.5 L / min) during the NaBH reduction stage, and the reduction time was extended to 40 minutes to inhibit copper oxidation.

[0052] Improved drying process: gradient freeze-drying was used: -20°C for 2 h→-50°C for 10 h→vacuum drying to reduce pore collapse.

[0053] Improved effect: increased loading: EDX analysis showed that the Cu element content was 4.7 wt% (2.1 wt% in Example 1);

[0054] Improved photocatalytic efficiency: the 200 mg / L Congo red degradation rate was increased to 88.09% in 60 minutes, and the pseudo-first-order kinetic constant k was 0.00905 min -1 ;

[0055] Pore structure advantage: BET specific surface area 99.18 m 2 / g, average pore size 11.58 nm (41.49 m2 / g and 13.62 nm in Example 1), and more developed mesoporous structure.

[0056] Example 3

[0057] The present embodiment provides a cellulose-based composite gel with catalytic degradation performance and a preparation method thereof.

[0058] Process adjustment and application verification:

[0059] High concentration of copper loading: the concentration of copper nitrate solution was increased to 10 wt%, and the reduction time was adjusted to 45 minutes (NaBH concentration remained 1 mol / L).

[0060] Dye degradation test: 0.1 g of the gel (RC3P5G-120-Cu10) was added into 100 mL of 300 mg / L Congo red solution:

[0061] Dark adsorption for 30 min: 38.2% of dye removal (adsorption dominated);

[0062] Xenon lamp illumination for 60 min: total removal rate reached 90.3%, half-life t / = 29.6 min.

[0063] Cyclic performance verification: degradation rate remained 93.47% after repeated use for 3 times, BET test showed that the specific surface area decreased from 72.04 m 2 / g to 68.21 m 2 / g (only 5.3% loss).

[0064] Key mechanism embodiment: adsorption-degradation synergy: high specific surface area (72.04 m 2 / g) accelerates dye enrichment, and copper particles generate hot electrons to degrade dyes under visible light excitation;

[0065] Structural stability: Zn(OH)Cl·HO layer fixes copper particles, and no obvious agglomeration is observed by SEM after recycling.

[0066] The core innovation of the present application is to construct a "cellulose network-zinc compound layer-copper particle" three-level ordered structure, which solves the dual bottlenecks of low photocatalytic activity and poor cyclic stability of traditional cellulose gels. Cellulose is crosslinked with epichlorohydrin and PEI to form a three-dimensional network, and the rich hydroxyl and amine groups on its surface provide anchoring sites for zinc compound loading. When the gel is immersed in NaOH solution, Zn2+ is directionally converted into Zn(OH)Cl·HO layered crystals in an alkaline environment. This process is not simply deposited, but grown in situ on the cellulose molecular chain through ion exchange, forming a tightly bound catalytic matrix.

[0067] The key role of the zinc compound layer lies in its dual functional characteristics: as an anionic clay, it provides high adsorption capacity, and as a wide-bandgap semiconductor (~3.4 eV), it forms a type II heterojunction with the narrow-bandgap copper particles. Under visible light excitation, the photo-generated electrons from the copper particles can be quickly transferred to the conduction band of the zinc compound, while the holes in the valence band of the zinc compound are filled by electrons, which effectively suppresses the recombination of carriers. Electron microscopy observation shows that the copper particles are mainly embedded in the edge of the zinc compound layer, and the edge loading mode greatly improves the efficiency of interfacial electron transfer.

[0068] The introduction of copper breaks through the performance limitations of traditional cellulose-based catalysts. Compared with noble metals, the d-electron orbital characteristics of copper produce a strong localized surface plasmon resonance effect (LSPR) in the visible light region of 500-600 nm wavelength, and the high-energy hot electrons excited by the effect are transferred to the dye molecules through the heterojunction interface, triggering a free radical chain reaction. It is particularly noteworthy that the Cu-O-Zn bond (verified by XPS) between the copper particles and the zinc compound significantly improves the structural stability, making the cycle performance more than three times higher.

[0069] The optimization of the mesoporous structure solves the mass transfer limitations of high-concentration dye systems. By controlling the crosslinking density and freeze-drying parameters, the gel forms 11-14 nm through channels (determined by the BJH method), which is just larger than the size of Congo red molecules (~2.6 nm) and smaller than the light wavelength, ensuring the free diffusion of dye molecules and multiple reflections of photons in the channels. The nitrogen adsorption curve shows the IV isotherm characteristics, confirming the existence of ink bottle-shaped pores, and the capillary force generated by the narrow neck and wide cavity of the pores can accelerate the enrichment of dyes to active sites.

[0070] In terms of practical application, the composite gel exhibits significant technological breakthroughs. Traditional catalysts are often deactivated due to active site saturation in high-concentration systems of >200 mg / L, while the present invention achieves dynamic balance through a dual-active-center design (zinc compound adsorption center + copper particle catalytic center): the zinc layer quickly adsorbs dye molecules around the copper particles, which are then immediately degraded in situ, forming an adsorption-degradation synergistic cycle. This self-cleaning mechanism allows the gel to maintain an efficiency of more than 90% at a limit concentration of 300 mg / L. More importantly, the entire preparation process uses an aqueous system, avoiding organic solvent pollution, and the raw material cost is only 5-7% of that of noble metal catalysts, making it have potential for industrialization.

[0071] In summary, the present invention successfully realizes the transformation of cellulose-based materials from adsorbents to high-efficiency photocatalysts through structural design at the molecular level. The three-level synergistic system not only solves the band matching problem, but also optimizes the mass transfer path at the mesoscale, providing a new paradigm for the development of biomass-based environmental functional materials.

[0072] It should be noted that the above examples are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the present invention, and they should be included in the scope of the claims of the present invention.

Claims

1. A cellulose-based composite gel with catalytic degradation properties, characterized in that: It is composed of the following components: The aminated network skeleton is formed by cross-linking microcrystalline cellulose with epichlorohydrin and polyethyleneimine; The Zn(OH)Cl·HO layer is uniformly loaded on the surface of the skeleton, with a loading amount of 10-30wt% of the skeleton mass; The metallic copper particles dispersed on the Zn(OH)Cl·HO layer have a particle size of 50-200 nm and a loading amount of 1-10 wt% of the total mass of the gel; The specific surface area of ​​the gel is 40-100m 2 / g, pore size distribution is 11-14nm, and porosity is 85-92%.

2. The cellulose-based composite gel with catalytic degradation properties according to claim 1, characterized in that: The polymerization degree of the polyethyleneimine is 5000-8000, and the mass ratio of epichlorohydrin to cellulose is 0.2-0.5:

1.

3. A method for preparing a cellulose-based composite gel with catalytic degradation performance according to any one of claims 1-2, characterized in that: The following steps are involved: (1) Dissolution: ZnCl and HO were prepared into a molten salt solution at a molar ratio of 3:1, microcrystalline cellulose was added, and stirred and dissolved at 80 ± 2 °C for 30 min to form a transparent solution; (2) Cross-linking: epichlorohydrin was added to the solution of step (1), and the reaction was carried out at 60±2°C for 1 hour. Then, a 5% by mass polyethyleneimine solution was added and the reaction was continued for 1 hour. (3) Molding: The mixed solution was injected into the mold, gelled at room temperature, and then immersed in a 1 wt% glutaraldehyde solution and cured at 60 ± 2 °C for 3 h; (4) Zinc loading: The gel was immersed in 1 wt% NaOH solution for 120 min and then washed with deionized water until neutral; (5) Copper loading: Immerse in 1-10 wt% copper nitrate solution for 12 h, remove and immerse in 1 mol / L NaBH solution, and reduce at 60 ± 2 °C for 30 min; (6) Post-treatment: Wash with deionized water until the conductivity is less than 20 μS / cm, and freeze-dry for 24 h.

4. The method for preparing a cellulose-based composite gel with catalytic degradation performance according to claim 3, characterized in that: In step (1), the mass ratio of microcrystalline cellulose to ZnCl is 1:8-1:

12.

5. The method for preparing a cellulose-based composite gel with catalytic degradation performance according to claim 3, characterized in that: The amount of polyethyleneimine solution added in step (2) is 0.5-1 mL per gram of cellulose.

6. The method for preparing a cellulose-based composite gel with catalytic degradation performance according to claim 3, characterized in that: In step (5), the concentration of the copper nitrate solution is 5-10 wt %, and the reduction reaction is carried out under nitrogen protection.

7. Use of a cellulose-based composite gel with catalytic degradation performance according to any one of claims 1-2 in photocatalytic degradation of organic dyes, characterized in that: The degradation target is azo dyes.

8. Use of a cellulose-based composite gel with catalytic degradation performance in photocatalytic degradation of organic dyes as claimed in claim 7, characterized in that: The dye is Congo red, and the degradation conditions are: xenon lamp illumination intensity of 300W, and initial dye concentration ≤300mg / L.

9. Use of a cellulose-based composite gel with catalytic degradation performance in photocatalytic degradation of organic dyes as claimed in claim 8, characterized in that: The degradation process conforms to the pseudo-first-order kinetic model, with a rate constant k≥0.023min -1 .

10. Use of a cellulose-based composite gel with catalytic degradation performance as claimed in claim 9 in photocatalytic degradation of organic dyes, characterized in that: After three cycles of use, the dye degradation rate remained above 93%.