Three-dimensional composite adsorption material, preparation method and application thereof

Abstract

This invention relates to the field of adsorption materials technology, specifically to a three-dimensional composite adsorption material, its preparation method, and its application. The material comprises alkylated lignin / cellulose carbon fibers, organic polymers, modified attapulgite, and modified carbide slag. Alkylated lignin / cellulose carbon fibers serve as the three-dimensional structural matrix. The organic polymer, through a specific chemical reaction, links linear polymer chains into a three-dimensional network structure, forming a hydrogel or porous polymer. Modified attapulgite and modified carbide slag increase the specific surface area of ​​the material. By utilizing the natural network of biomass and the cross-linked framework of the polymer, and through the construction of mineral nanostructures, a leap from single-component to high-performance three-dimensional composite adsorption materials is achieved.

Description

Technical Field

[0001] This invention relates to the field of three-dimensional composite material technology, and more specifically, to a three-dimensional composite adsorption material, its preparation method, and its application. Background Technology

[0002] Lignin and cellulose are the most abundant renewable biomass resources on Earth. Because their molecular chains contain a large number of active groups (such as hydroxyl and carboxyl groups), they can bind with pollutants such as heavy metal ions, making them ideal raw materials for preparing green and efficient adsorbents.

[0003] Traditional adsorbent materials (such as powdered activated carbon and bentonite) suffer from drawbacks such as insufficient exposure of adsorption sites, slow ion diffusion rates, and difficulties in solid-liquid separation. Whether activated carbon, ordinary biochar, or nanoscale inorganic minerals (such as unmodified attapulgite and carbide slag powder), although they have large specific surface areas and numerous adsorption sites, they are easily dispersed in actual water bodies, making them difficult to recover through simple solid-liquid separation after adsorption, easily causing secondary pollution. Traditional polymer materials are difficult to degrade, and while synthetic organic adsorbents (such as polypropylene and polyurethane foam) are easy to recover, most are not biodegradable. Unmodified natural cellulose contains a large number of hydrophilic hydroxyl groups (-OH) on its surface, causing it to easily swell excessively in water, resulting in a significant decrease in mechanical strength.

[0004] Three-dimensional composite adsorbent materials significantly improve specific surface area and porosity by constructing a three-dimensional interconnected porous network structure, providing richer accessible active sites for adsorbates and accelerating mass transfer rates. However, nanocellulose is prone to aggregation, leading to unstable cross-linked networks. Furthermore, hydrophilic minerals are difficult to disperse and recover, and biochar is brittle, affecting the pore uniformity and mechanical strength of the final material. Summary of the Invention

[0005] This invention provides a three-dimensional composite adsorbent material, its preparation method, and its application. By grafting maleic anhydride onto the surface of cellulose through a chemical reaction, not only can a large number of carboxyl groups (-COOH) for adsorbing heavy metals be introduced, but the interfacial compatibility between biomass and hydrophobic polymer matrix can also be significantly improved, and the material can be endowed with hydrophobic properties.

[0006] In a first aspect, the present invention provides a method for preparing a three-dimensional composite adsorbent material, comprising the following steps: (1) Preparation of alkylated lignin / cellulose carbon fiber: 1,8-dibromooctane was used as an alkylating agent to modify sulfate lignin to prepare alkylated lignin, which was then blended with cellulose in a certain proportion. The carbon fiber precursor was obtained by electrospinning. The carbon fiber precursor was pre-oxidized at a temperature of 120~200℃ and then carbonized. The carbonization was carried out under nitrogen protection and the temperature was raised to 550~850℃ to obtain alkylated lignin / cellulose carbon fiber. (2) Preparation of modified attapulgite: Using natural attapulgite as raw material, organic modification was carried out by hexadecyltrimethylammonium bromide and β-cyclodextrin to obtain modified attapulgite; (3) Preparation of modified carbide slag: Bentonite and carbide slag are mixed, Na2CO3 is added as a binder, and the mixture is granulated by calcination to obtain modified carbide slag. (4) Maleic anhydride was added to alkylated lignin / cellulose carbon fibers, heated, and attached to porous organic polymers through esterification under the action of a catalyst. Modified attapulgite and modified carbide slag were then added to obtain a three-dimensional composite adsorbent material.

[0007] Preferably, in step (1), the mass ratio of the alkylated lignin to cellulose is 3~5:1~3.

[0008] Preferably, in step (1), the amount of 1,8-dibromooctane added as an alkylating agent is 3% to 8%.

[0009] Preferably, in step (2), the mass ratio of the natural attapulgite, hexadecyltrimethylammonium bromide and β-cyclodextrin is 5~8:1~3:1.

[0010] Preferably, in step (3), the mass ratio of bentonite to carbide slag is 1~2:2~3, and the amount of Na2CO3 added is 8%~12% of the mass of carbide slag.

[0011] Preferably, in step (3), the calcination temperature is 650~800℃ and the calcination time is 1~2h.

[0012] Preferably, in step (4), the heating temperature is 75~125℃, and the catalyst is 4-dimethylaminopyridine.

[0013] Preferably, in step (4), the mass ratio of the alkylated lignin / cellulose carbon fiber to maleic anhydride is 1:18~25.

[0014] Secondly, the present invention provides a three-dimensional composite adsorbent material prepared by the above-described preparation method.

[0015] Thirdly, the present invention provides a three-dimensional composite adsorption material for adsorbing heavy metal ions in wastewater.

[0016] In summary, the present invention has the following beneficial effects: 1. This invention uses 1,8-dibromooctane for alkylation modification, which can specifically alter the chemical structure of lignin. This modification can lower the glass transition temperature of lignin, enhance its flexibility and thermal stability, making it more suitable for electrospinning and subsequent heat treatment processes. Lignin itself is rich in aromatic rings and easily forms a graphite-like blocky structure during carbonization; while cellulose can form an isotropic structure during carbonization activation, which helps to build an ordered carbon skeleton. The combination of these two, along with modified attapulgite and modified carbide slag, readily forms a rich multi-level pore structure including micropores and mesopores within the material. This high specific surface area and porous nature are the core advantages of this adsorbent material for capturing pollutants.

[0017] 2. In this invention, carbon fibers formed from alkylated lignin / cellulose through electrospinning, pre-oxidation, and high-temperature carbonization are used to prepare continuous nano- or micron-sized fibers. These fibers intertwine to naturally form a three-dimensional spatial network skeleton with high porosity. This three-dimensional porous structure not only provides a huge specific surface area but also provides convenient channels for the transport and diffusion of pollutants. Based on the carbon fiber skeleton, various functional components are grafted and loaded through chemical means to form a complex surface structure. Maleic anhydride is grafted onto the carbon fiber surface through esterification, forming a porous organic polymer layer, which not only increases the porosity of the material but also provides abundant chemical reaction active sites. Organically modified attapulgite provides an organic-inorganic hybrid interface and, together with granular modified carbide slag, provides alkalinity and adsorption sites, serving as a functional filler and being uniformly composited in this three-dimensional polymer / carbon fiber network. Maleic anhydride and carbon fiber precursor form strong chemical bonds through esterification. Modified attapulgite and modified carbide slag are fixed in the pores and surface of the three-dimensional skeleton by physical filling, coating or embedding through processes such as mixing, calcination and granulation.

[0018] 3. In this invention, modification introduces a large number of hydrophobic organic functional groups onto the surface of attapulgite, enabling the originally hydrophilic natural mineral to more effectively adsorb heavy metal ions from water. β-Cyclodextrin possesses a unique cylindrical cavity structure that is hydrophilic on the outside and hydrophobic on the inside. This structure acts like a miniature molecular capsule, allowing heavy metal ions to be encapsulated within its hydrophobic cavity through host-guest interactions. This encapsulation not only increases the adsorption capacity but also endows the material with the selective recognition ability for specific organic molecules. Simultaneously, the encapsulated pollutant molecules are more stable within the cavity and less prone to desorption, thereby improving the overall adsorption efficiency of the material. Hexadecyltrimethylammonium bromide primarily adsorbs heavy metal ions through electrostatic interactions, while β-cyclodextrin encapsulates heavy metal ions through the cavity. The combination of these two organic molecules allows for intercalation and loading, further improving the pore structure and specific surface area of ​​natural attapulgite, exposing more active adsorption sites. This dual modification principle achieves complementary advantages. Natural attapulgite provides a framework with high specific surface area and mechanical support; the introduction of hexadecyltrimethylammonium bromide improves its surface properties and expands its pore structure, making it easier to adsorb heavy metal ions; while the introduction of β-cyclodextrin utilizes its cavity structure to further enhance its ability to capture and embed organic molecules. The resulting modified attapulgite mainly serves as a functional filler for efficiently adsorbing heavy metal ions in three-dimensional composite adsorption materials.

[0019] 5. In this invention, the Na2CO3 added to the modified calcium carbide slag not only acts as an excellent binder, aiding in particle formation, but also participates in the reaction as a modifier. It synergistically interacts with the calcium source in the calcium carbide slag, optimizing the pore structure of the material and promoting mineral phase transformation during calcination, thereby enhancing the overall adsorption and mineralization performance of the particles. Through calcination, not only are moisture and impurities removed from the raw materials, but the specific surface area and total pore volume of the composite particles are also significantly increased, forming a rich porous structure on the particle surface. This optimized porous structure provides more active sites and reaction channels for heavy metal ions. These composite particles can not only neutralize acidic wastewater by releasing alkalinity, but also efficiently adsorb and fix heavy metal ions in wastewater using the ion exchange capacity of bentonite and the precipitation effect of calcium carbide slag, further achieving the removal and mineralization recovery of heavy metals.

[0020] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and do not limit the scope of protection of the present invention. Detailed Implementation

[0021] The present invention will be further described in detail below with reference to the embodiments. It should be noted that: unless otherwise specified, the conditions in the following embodiments are carried out according to conventional conditions or the conditions recommended by the manufacturer. Unless otherwise specified, the raw materials used in the following embodiments can be obtained from commercially available sources.

[0022] The applicant of this invention has discovered that three-dimensional composite adsorbent materials, by constructing a three-dimensional interconnected porous network structure, significantly improve specific surface area and porosity, providing richer accessible active sites for adsorbates and accelerating mass transfer rates. However, nanocellulose is prone to aggregation, leading to instability in the cross-linked network and affecting the pore uniformity and mechanical strength of the final material.

[0023] To address the above problems, this invention provides a method for preparing a three-dimensional composite adsorbent material, comprising the following steps: (1) Preparation of alkylated lignin / cellulose carbon fiber: 1,8-dibromooctane was used as an alkylating agent to modify sulfate lignin to prepare alkylated lignin, which was then blended with cellulose in a certain proportion. The carbon fiber precursor was obtained by electrospinning. The carbon fiber precursor was pre-oxidized at a temperature of 120~200℃ and then carbonized. The carbonization was carried out under nitrogen protection and the temperature was raised to 550~850℃ to obtain alkylated lignin / cellulose carbon fiber. In this embodiment, a flexible spacer group is introduced. 1,8-Dibromooctane, a long-chain bifunctional reagent, is linked to the phenolic hydroxyl groups of lignin via ether bonds. This is equivalent to introducing flexible C8 carbon chains between the rigid aromatic rings of lignin, greatly increasing the flexibility and entanglement ability of the lignin molecular chains. This allows them to be uniformly stretched during electrospinning to form continuous, defect-free nanofibers. The two bromine end groups of dibromooctane can react with two different lignin molecules, playing a role in mild cross-linking. This cross-linking network effectively prevents fiber melting or collapse during subsequent pre-oxidation and carbonization processes, maintaining the integrity of the fiber morphology.

[0024] (2) Preparation of modified attapulgite: Using natural attapulgite as raw material, organic modification was carried out by hexadecyltrimethylammonium bromide and β-cyclodextrin to obtain modified attapulgite; In this embodiment, cetyltrimethylammonium bromide and β-cyclodextrin are used for dual organic modification. The long-chain alkyl group (hexadecyl) can enter the pores and interlayers of attapulgite through ion exchange, transforming the originally hydrophilic mineral surface into a hydrophobic / oleophilic one. This greatly improves the compatibility and dispersibility of attapulgite in the organic polymer matrix, prevents nanorod aggregation, and allows it to be uniformly interwoven in the fiber network, thus playing a role in reinforcement and toughening. After β-cyclodextrin is grafted onto the surface of attapulgite, it is equivalent to adding countless tiny "molecular capsules" to the material. These cavities can specifically capture organic pollutants in water through host-guest interactions.

[0025] (3) Preparation of modified carbide slag: Bentonite and carbide slag are mixed, Na2CO3 is added as a binder, and the mixture is granulated by calcination to obtain modified carbide slag. In this embodiment, the modified particles combine the interlayer micropores of bentonite, the packing pores of carbide slag, and the pores generated during calcination, forming a multi-level pore network that facilitates the rapid diffusion of pollutants. This further achieves functional complementarity: carbide slag provides high alkalinity and abundant calcium-based active sites for the chemical precipitation of phosphates, fluorides, etc.; bentonite provides excellent cation exchange capacity for the adsorption of heavy metals.

[0026] (4) Maleic anhydride was added to alkylated lignin / cellulose carbon fibers, heated, and attached to porous organic polymers through esterification under the action of a catalyst. Modified attapulgite and modified carbide slag were then added to obtain a three-dimensional composite adsorbent material.

[0027] In this embodiment, maleic anhydride is used as a molecular bridge. Under heating and catalysis, its anhydride groups undergo esterification with the hydroxyl groups on the surface of carbon fibers and porous organic polymers. This chemical bond connection is much stronger than ordinary physical doping, forming a highly cross-linked, water-resistant three-dimensional network, preventing the material from disintegrating during adsorption.

[0028] Optionally, in one embodiment, the mass ratio of the alkylated lignin to cellulose is 3~5:1~3, which can be one or any two of the following: 3:1, 4:1, 5:1, 3:2, 5:2, 5:3, 4:3, and the amount of the 1,8-dibromooctane alkylating agent added is 3%~8%, which can be one or any two of the following: 3%, 4%, 5%, 6%, 7%, 8%.

[0029] Optionally, in one embodiment, the mass ratio of the aforementioned natural attapulgite, hexadecyltrimethylammonium bromide, and β-cyclodextrin is 5-8:1-3:1, and can be any one or both of the following: 5:1:1, 6:1:1, 7:1:1, 8:1:1, 5:2:1, 5:3:1, 7:2:1, 7:3:1, 8:3:1. This ensures that the modified product retains the original excellent nanorod-like crystal structure and mechanical strength of attapulgite, and maximizes its interfacial compatibility with the organic polymer matrix without sacrificing mineral porosity.

[0030] Optionally, in one embodiment, the mass ratio of bentonite to calcium carbide slag is 1-2:2-3, which can be one or any two of 1:2, 1:3, 2:2, 2:3. The amount of Na2CO3 added is 8%-12% of the mass of calcium carbide slag, which can be one or any two of 8%, 9%, 10%, 11%, 12%. The calcium carbide slag occupies a slightly higher proportion in the formulation. As an industrial solid waste rich in calcium hydroxide, it can remove phosphates and fluorides from wastewater and has a pH-regulating effect. The higher proportion ensures that the particles have sufficient alkaline sites and calcium-based active components, guaranteeing excellent chemical precipitation and ion exchange capabilities.

[0031] Optionally, in one embodiment, the calcination temperature is 650~800℃, which can be any one or any two of 650℃, 700℃, 750℃, and 800℃, and the calcination time is 1~2h, which can be any one or any two of 1h, 1.5h, and 2h. At the high temperature of 650~800℃, the layered crystal structure of montmorillonite, the main component of bentonite, undergoes partial destruction and reorganization. This thermal activation breaks the originally stable crystal lattice, greatly increasing the chemical reactivity of components such as silicon and aluminum. The activated silicon and aluminum components can more rapidly undergo deep solid-phase reactions with the calcium components in the carbide slag and the binder Na2CO3, generating more cementing calcium silicate (CSH) and other hydraulic minerals, which not only enhance the strength of the particles but also provide a material basis for the subsequent slow release of alkalinity in water. At this temperature, the micro-powder inside the particles undergoes local melting and adhesion, forming an extremely strong ceramicized skeleton. After 1-2 hours of sintering, the resulting granules have extremely high wear resistance and compressive strength. In actual wastewater treatment, they can withstand strong hydraulic shear and friction, completely avoiding the powdering and breakage that are common in ordinary granulation, and greatly extending the service life of the material.

[0032] Optionally, in one embodiment, the heating temperature is 75~125℃, which can be one or any two of the following values: 75℃, 80℃, 85℃, 90℃, 95℃, 100℃, 105℃, 110℃, 115℃, 120℃, and 125℃. Within this temperature range, on the one hand, it is higher than the melting point of maleic anhydride (approximately 53℃), ensuring that the reactants are in a molten or well-flowing state, facilitating mass transfer; on the other hand, it is much lower than the thermal decomposition temperature of lignin, cellulose, and porous organic polymers. This further prevents damage to the skeletal structure. If the temperature is too high, it can not only lead to carbonization or degradation of biomass fibers but may also destroy the microporous structure of porous polymers. This temperature range ensures that the esterification reaction proceeds at a reasonable rate while perfectly preserving the original excellent properties of each component. The catalyst mentioned above is 4-dimethylaminopyridine. Under the catalysis of 4-dimethylaminopyridine, maleic anhydride can rapidly and uniformly form strong ester bonds between carbon fibers and porous polymers. This chemical bonding is much stronger than simple physical blending, giving the final material excellent structural integrity and water resistance.

[0033] Optionally, in one embodiment, the mass ratio of the alkylated lignin / cellulose carbon fibers to maleic anhydride is 1:18~25, which can be one or any two of the following: 1:18, 1:19, 1:20, 1:21, 1:22, 1:23, 1:24, 1:25. This ensures that every reactive hydroxyl group on the carbon fiber and porous polymer skeleton can be fully esterified and modified, resulting in a final material with extremely high ion exchange capacity and heavy metal removal rate. At this ratio, the excess maleic anhydride is no longer just a bridge connecting the carbon fiber and the polymer, but actually acts as a crosslinking agent and compatibilizer for the entire composite system. It can undergo mild polymerization under the action of a catalyst, or deeply graft with the porous organic polymer to form a dense, active coating rich in carboxyl groups. This coating can more firmly encapsulate and anchor the modified attapulgite and modified carbide slag in the three-dimensional network, greatly improving the integrity and anti-leakage ability of the material.

[0034] In this invention, the abundant maleic anhydride grafted onto the carbon fiber and polymer backbone provides a high density of carboxyl groups (-COOH), which can strongly chelate heavy metal ions such as lead, cadmium, and copper. The β-cyclodextrin cavity encapsulation effect on the modified attapulgite, combined with the hydrophobic distribution effect of the long chain of hexadecyltrimethylammonium bromide and the huge specific surface area of ​​the porous organic polymer, can efficiently remove recalcitrant organic pollutants such as dyes, antibiotics, and phenols from water. The modified carbide slag particles provide abundant calcium-based active sites and a local alkaline microenvironment, which can efficiently remove phosphates, fluorides, etc. from wastewater through chemical precipitation. The three-dimensional macroporous network formed by freeze-drying, the mesopores of the porous organic polymer, and the micropores of attapulgite / carbide slag constitute a perfect multi-level porous system. This structure greatly reduces water flow resistance, allowing pollutant molecules to rapidly diffuse from the macroscopic water body to every active site inside the material, significantly shortening the time required to reach adsorption equilibrium and improving wastewater treatment efficiency. The resulting three-dimensional composite adsorbent material ultimately presents as a macroscopic block, sponge, or granular morphology. After treating the wastewater, there is no need to consume high-energy centrifugal or precision membrane filtration equipment. Solid-liquid separation can be achieved simply by scooping out the wastewater, ordinary filtration, or direct filling into a fixed bed.

[0035] Example Example 1 A method for preparing a three-dimensional composite adsorbent material includes the following steps: (1) Preparation of alkylated lignin / cellulose carbon fibers: Sulfate lignin was added to the solvent N,N-dimethylformamide, and 1,8-dibromooctane was used as the alkylating agent to modify the sulfate lignin. The reaction temperature was 80℃, the reaction time was 12h, and alkylated lignin was prepared under pH=8 conditions. The alkylated lignin was then blended with cellulose in a certain proportion and a solution was prepared in the solvent N,N-dimethylformamide. Carbon fiber precursors were prepared by electrospinning under the conditions of a solution concentration of 10%, an electrostatic voltage of 20kV, and a receiving distance of 15cm. The carbon fiber precursors were pre-oxidized at a temperature of 180℃, and then carbonized at a temperature of 550℃ under nitrogen protection to obtain alkylated lignin / cellulose carbon fibers. The mass ratio of alkylated lignin to cellulose was 3:1; the amount of 1,8-dibromooctane added as the alkylating agent was 5% of the mass of sulfate lignin.

[0036] (2) Preparation of modified attapulgite: 7g of natural attapulgite was crushed and ground, passed through a 200-mesh sieve, dispersed in deionized water, and ultrasonically dispersed for 30min to fully debind it. 2mL of hydrochloric acid was added dropwise to adjust the pH to acidic. The mixture was stirred at 60℃ for 1.5h, filtered and washed until neutral, and dried at 60℃ to obtain acidified attapulgite. Hexadecyltrimethylammonium bromide was dissolved in an ethanol / water mixture and stirred continuously at 60℃ until completely dissolved to form a clear and transparent solution. β-cyclodextrin was weighed and dissolved in warm water at 60℃. The pretreated attapulgite dispersion was placed in a three-necked flask. Under high-speed stirring, hexadecyltrimethylammonium bromide solution was slowly added dropwise while maintaining the reaction temperature at 60℃. The mixture was stirred continuously for 2h. Subsequently, the prepared β-cyclodextrin solution was slowly added dropwise to the above mixture. The reaction was continued at 60℃ with stirring for 6 hours, allowing β-cyclodextrin to be loaded onto the surface of the attapulgite modified with hexadecyltrimethylammonium bromide through physical adsorption or hydrogen bonding. After the reaction was complete, the mixture was filtered. The filter cake was washed 3-5 times alternately with warm water and a small amount of anhydrous ethanol to thoroughly remove unreacted CTAB and β-cyclodextrin. The resulting solid product was dried to constant weight in an oven at 80℃ to obtain modified attapulgite; the mass ratio of natural attapulgite, hexadecyltrimethylammonium bromide, and β-cyclodextrin was 7:2:1.

[0037] (3) Preparation of modified carbide slag: Carbide slag and bentonite were dried in an oven at 105℃ to constant weight. The dried raw materials were taken out, ground and passed through a 100-mesh sieve. The bentonite and carbide slag were mixed and Na2CO3 was added as a binder. The three powders were poured into a mixer or mortar and thoroughly dry-mixed. A suitable amount of deionized water was slowly added. The moistened material was made into uniform wet granules by extrusion granulation or manual sieving. The wet granules were pre-dried at 80℃ for 2 hours. The pre-dried granules were placed in a muffle furnace or calcining kiln with a heating rate of 10℃ / min. Granulation was carried out by calcination to obtain modified carbide slag. The mass ratio of bentonite to carbide slag was 2:3, and the amount of Na2CO3 added was 10%. The calcination temperature was 650℃ and the calcination time was 2 hours.

[0038] (4) N,N-dimethylformamide was added to alkylated lignin / cellulose carbon fibers as a reaction solvent and p-toluenesulfonic acid was used as a catalyst. The amount of alkylated lignin / cellulose carbon fibers was about 5% of the mass of the alkylated lignin / cellulose carbon fibers. The alkylated lignin / cellulose carbon fibers, maleic anhydride, and catalyst 4-dimethylaminopyridine were added to a three-necked flask and heated to 85°C. The reaction was carried out by stirring in the dark. The carbon fibers were first carboxylated and then grafted onto the porous organic polymer polyacrylamide through esterification. The amount of polyacrylamide added was 2% of the mass of the carbon fibers. After the reaction was completed, the carbon fibers were repeatedly washed with ethanol and deionized water to remove unreacted maleic anhydride and catalyst. After drying, carboxylated porous carbon fibers were obtained. Modified attapulgite and modified carbide slag were added to deionized water and ultrasonically dispersed for 60 min to form a uniform and stable inorganic mineral suspension. Carboxylated porous carbon fibers were dispersed in water, and an inorganic mineral suspension was added to form a three-dimensional network hydrogel. The three-dimensional network hydrogel was pre-frozen to -80°C, and then dried in a vacuum freeze dryer for 24 hours. After the ice crystals sublimated, a rich porous structure was left, ultimately yielding a fluffy three-dimensional composite adsorption aerogel / scaffold material. The mass ratio of alkylated lignin / cellulose carbon fibers to maleic anhydride was 1:22.

[0039] Example 2 The difference from Example 1 is that in step (1), the carbon fiber precursor is pre-oxidized at a temperature of 120°C and then carbonized. The carbonization process is carried out under nitrogen protection and the temperature is raised to 750°C.

[0040] Example 3 The difference from Example 1 is that in step (1), the mass ratio of alkylated lignin to cellulose is 5:2.

[0041] Example 4 The difference from Example 1 is that in step (1), the amount of 1,8-dibromooctane added as an alkylating agent is 8%.

[0042] Example 5 The difference from Example 1 is that in step (2), the mass ratio of natural attapulgite, hexadecyltrimethylammonium bromide and β-cyclodextrin is 8:3:1.

[0043] Example 6 The difference from Example 1 is that in step (3), the mass ratio of bentonite to carbide slag is 1:2, and the amount of Na2CO3 added is 12%.

[0044] Example 7 The difference from Example 1 is that in step (3), the calcination temperature is 800°C and the calcination time is 1 hour.

[0045] Example 8 The difference from Example 1 is that in step (4), the heating temperature is 105°C.

[0046] Example 9 The difference from Example 1 is that in step (4), the mass ratio of alkylated lignin / cellulose carbon fiber to maleic anhydride is 1:20.

[0047] Comparative Example 1 The difference from Example 1 is that no alkylated lignin was added to the carbon fiber precursor.

[0048] Comparative Example 2 The difference from Example 1 is that no modified carbide slag was added.

[0049] Comparative Example 3 The difference from Example 1 is that no modified attapulgite was added.

[0050] Comparative Example 4 The difference from Example 1 is that maleic anhydride was not added to the alkylated lignin / cellulose carbon fibers.

[0051] Comparative Example 5 The difference from Example 1 is that the modified carbide slag is replaced with conventional activated carbon.

[0052] Comparative Example 6 The difference from Example 1 is that the modified attapulgite is replaced with ordinary attapulgite.

[0053] Performance testing: 1. Specific surface area and pore size BET test: Sample pretreatment: Weigh 100 mg of dried sample (powder or small pieces) and place it into a sample tube. Connect the sample tube to the degassing station and heat under vacuum conditions, usually set at 120°C, for 6 hours to thoroughly remove adsorbed moisture and impurities from the sample surface.

[0054] Adsorption test: Transfer the pretreated sample tube to the analysis station and immerse it in a liquid nitrogen Dewar flask (-196℃). The instrument will automatically introduce high-purity nitrogen gas and measure the adsorption and desorption of nitrogen gas under different relative pressures (P / P0), generating adsorption-desorption isotherms.

[0055] Data analysis: Using the instrument's software, the specific surface area (m² / g) of the material is calculated using the BET model, and the total pore volume is calculated using the BJH or NLDFT model.

[0056] 2. Adsorption capacity and adsorption isotherm test: Solution preparation: Accurately prepare a series of Pb solutions with initial concentrations of 20, 40, and 60 mg / L. 2+ Cd 2+ Cu 2+ Simulated wastewater solution.

[0057] Adsorption reaction: Weigh 2g of the same mass of the dried composite material and add it to an Erlenmeyer flask containing 50 mL of the above solutions of different concentrations.

[0058] Isothermal oscillation: Place the conical flask in an isothermal oscillator and oscillate at a set temperature of 25°C and a rotation speed of 150 rpm until adsorption reaches equilibrium, which usually takes 24 hours.

[0059] Concentration determination: After the reaction is complete, the supernatant is filtered, and the remaining Pb in the filtrate is determined using atomic absorption spectrometry (AAS) or inductively coupled plasma mass spectrometry (ICP-MS). 2+ Cd 2+ Cu 2+ concentration.

[0060] Results Calculation: The equilibrium adsorption capacity was calculated using the formula qe = (C0 - Ce) × V / m. Where qe is the equilibrium adsorption capacity (mg / g), C0 and Ce are the initial and equilibrium concentrations (mg / L), respectively, V is the solution volume (L), and m is the adsorbent mass (g).

[0061] 3. Cyclic Regeneration Performance Test: Adsorption and desorption: First, saturate the material with adsorption as described above. Then, immerse the saturated material in a 0.1 mol / L dilute hydrochloric acid solution and shake for several hours to desorb the adsorbed heavy metal ions.

[0062] Cyclic operation: Wash the desorbed material with deionized water until neutral, dry it, and reuse it in the next round of adsorption experiments. Repeat the "adsorption-desorption-washing" process for 5 cycles, record the adsorption capacity each time, and calculate the capacity retention rate.

[0063] 4. Adsorption performance test of cationic dyes in wastewater The pH of the wastewater was adjusted to 5. 2g of the same mass of the dried composite material was weighed and added to 50 mL of the treated wastewater. The removal rate of methylene blue by the three-dimensional composite adsorbent material within 30 minutes was calculated.

[0064] Table 1 Performance Test Results As shown in Table 1, the three-dimensional composite adsorbent material prepared in Example 1 exhibits excellent adsorption performance when applied to the adsorption of heavy metal ions in wastewater. This indicates that the abundant carboxyl groups (-COOH) introduced by maleic anhydride provide rich chemisorption sites; the porous organic polymer and attapulgite provide a large physical adsorption specific surface area. The robust three-dimensional cross-linked network prevents the loss of active components, and the introduction of carbide slag and attapulgite enhances the overall framework's resistance to swelling and aging.

[0065] Comparing Examples 1 and 2, it is evident that the temperatures of both the pre-oxidation and carbonization stages directly affect the degree of cross-linking and the formation of the carbon skeleton in the carbon fiber precursor. The core purpose of pre-oxidation is to induce a thermal cross-linking reaction in the precursor fibers, forming a heat-resistant trapezoidal structure to prevent melting or breakage during subsequent high-temperature carbonization. The carbonization stage involves transforming the pre-oxidized fibers into carbon-rich materials under an inert atmosphere (nitrogen). The temperature at this stage directly determines the degree of graphitization, pore structure, and conductivity of the carbon material.

[0066] Comparing Example 1 and Example 3, it can be seen that the mass ratio of alkylated lignin to cellulose further affects the adsorption performance of the three-dimensional composite adsorbent material. Lignin and cellulose do not simply react independently during pyrolysis, but rather exhibit a significant synergistic effect.

[0067] As can be seen from the comparison between Example 1 and Example 4, the amount of 1,8-dibromooctane added as an alkylating agent further affects the adsorption performance of the three-dimensional composite adsorbent material. The amount added not only determines the number of long-chain alkyl groups grafted onto lignin, but also affects the cross-linking between lignin molecules, significantly improving the specific surface area and porosity.

[0068] Comparing Example 1 and Example 5, it can be seen that the mass ratio of natural attapulgite, hexadecyltrimethylammonium bromide, and β-cyclodextrin improves the compatibility and dispersibility of attapulgite in the organic polymer matrix, further affecting the adsorption performance.

[0069] Comparing Example 1 and Example 6, it can be seen that the mass ratio of bentonite to carbide slag affects the ion exchange capacity and further affects the adsorption performance.

[0070] Comparing Example 1 and Example 7, it can be seen that the mass ratio of bentonite to carbide slag and the amount of Na2CO3 added provide excellent cation exchange capacity and further affect the adsorption performance.

[0071] Comparing Example 1 and Example 8, it can be seen that the heating temperature at which maleic anhydride is added to alkylated lignin / cellulose carbon fibers affects the degree of esterification reaction between maleic anhydride and the hydroxyl groups on the surface of carbon fibers and porous organic polymers, further affecting the adsorption performance.

[0072] Comparing Example 1 and Example 9, it can be seen that the mass ratio of alkylated lignin / cellulose carbon fiber to maleic anhydride is such that excess maleic anhydride is no longer just a bridge connecting carbon fiber and polymer, but actually acts as a crosslinking agent and compatibilizer for the entire composite system, further affecting the adsorption performance.

[0073] As can be seen from the comparison between Example 1 and Comparative Example 1, carbon fibers formed by electrospinning, pre-oxidation and high-temperature carbonization of alkylated lignin / cellulose can be used to prepare nanoscale or microscale continuous fibers. These fibers intertwine with each other and naturally form a three-dimensional spatial network skeleton with high porosity. This three-dimensional porous structure not only provides a huge specific surface area, but also provides a convenient channel for the transport and diffusion of pollutants.

[0074] As can be seen from the comparison between Example 1 and Comparative Example 2, the Na2CO3 added to the modified carbide slag is not only an excellent binder that helps the particles to form, but also a modifier that participates in the reaction. It can work synergistically with the calcium source in the carbide slag to optimize the pore structure of the material and promote the transformation of mineral phases during the calcination process, thereby improving the overall adsorption performance of the particles.

[0075] As can be seen from the comparison between Example 1 and Comparative Example 3, the modification can introduce a large number of hydrophobic organic functional groups on the surface of attapulgite, which enables the originally hydrophilic natural mineral to more effectively adsorb heavy metal ions in the water.

[0076] As can be seen from the comparison between Example 1 and Comparative Example 4, maleic anhydride was grafted onto the surface of the carbon fiber through esterification reaction, forming a porous organic polymer layer, which not only increased the pore structure of the material, but also provided abundant chemical reaction active sites.

[0077] As can be seen from the comparison between Example 1 and Comparative Example 5, the modified calcium carbide slag particles combine the interlayer micropores of bentonite, the stacking pores of calcium carbide slag, and the pores generated by calcination, forming a multi-level pore network that is conducive to the rapid diffusion of pollutants.

[0078] As can be seen from the comparison between Example 1 and Comparative Example 6, the use of cetyltrimethylammonium bromide and β-cyclodextrin for dual organic modification greatly improves the compatibility and dispersibility of attapulgite in the organic polymer matrix, prevents the agglomeration of nanorods, and enables them to be uniformly interwoven in the fiber network, thereby playing a role in strengthening and toughening.

[0079] The above description is merely an exemplary embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing a three-dimensional composite adsorbent material, characterized by, Includes the following steps: (1) Preparation of alkylated lignin / cellulose carbon fiber: 1,8-dibromooctane was used as an alkylating agent to modify sulfate lignin to prepare alkylated lignin, which was then blended with cellulose in a certain proportion. The carbon fiber precursor was obtained by electrospinning. The carbon fiber precursor was pre-oxidized at a temperature of 120~200℃ and then carbonized. The carbonization was carried out under nitrogen protection and the temperature was raised to 550~850℃ to obtain alkylated lignin / cellulose carbon fiber. (2) Preparation of modified attapulgite: Using natural attapulgite as raw material, organic modification was carried out by hexadecyltrimethylammonium bromide and β-cyclodextrin to obtain modified attapulgite; (3) Preparation of modified carbide slag: Bentonite and carbide slag are mixed, Na2CO3 is added as a binder, and the mixture is granulated by calcination to obtain modified carbide slag. (4) Maleic anhydride was added to alkylated lignin / cellulose carbon fibers, heated, and attached to porous organic polymers through esterification under the action of a catalyst. Modified attapulgite and modified carbide slag were then added to obtain a three-dimensional composite adsorbent material.

2. The method for preparing the three-dimensional composite adsorbent material according to claim 1, characterized in that, In step (1), the mass ratio of alkylated lignin to cellulose is 3~5:1~3.

3. The method for preparing the three-dimensional composite adsorbent material according to claim 1, characterized in that, In step (1), the amount of 1,8-dibromooctane added as an alkylating agent is 3% to 8%.

4. The method of claim 1, wherein the three-dimensional composite adsorbent material is prepared by a process comprising: In step (2), the mass ratio of the natural attapulgite, hexadecyltrimethylammonium bromide and β-cyclodextrin is 5~8:1~3:

1.

5. The method for preparing the three-dimensional composite adsorbent material according to claim 1, characterized in that, In step (3), the mass ratio of bentonite to carbide slag is 1~2:2~3, and the amount of Na2CO3 added is 8%~12% of the mass of carbide slag.

6. The method for preparing the three-dimensional composite adsorbent material according to claim 1, characterized in that, In step (3), the calcination temperature is 650~800℃ and the calcination time is 1~2h.

7. The method for preparing the three-dimensional composite adsorbent material according to claim 1, characterized in that, In step (4), the heating temperature is 75~125℃, and the catalyst is 4-dimethylaminopyridine.

8. The method for preparing the three-dimensional composite adsorbent material according to claim 1, characterized in that, In step (4), the mass ratio of the alkylated lignin / cellulose carbon fiber to maleic anhydride is 1:18~25.

9. A three-dimensional composite adsorbent material prepared by the preparation method according to any one of claims 1 to 8.

10. The three-dimensional composite adsorbent material according to claim 9 is used to adsorb heavy metal ions in wastewater.

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