Sepiolite composite materials, preparation methods and their application in leather tanning wastewater

Abstract

This invention belongs to the field of water treatment agent technology, and discloses a sepiolite composite material, its preparation method, and its application in leather tanning wastewater. The sepiolite composite material includes: a sepiolite carrier; a quaternary ammonium salt molecular layer gradient-anchored on the surface of the sepiolite carrier, wherein the quaternary ammonium salt molecular layer includes dodecyltrimethylammonium chloride and hexadecyltrimethylammonium chloride; and β-cyclodextrin molecules bound to the surface of the quaternary ammonium salt molecular layer through intermolecular forces. This invention successfully constructs a dual-functional interface on the sepiolite surface, possessing both a "broad-spectrum hydrophobic adsorption domain" (quaternary ammonium salt layer) and a "specific molecular recognition domain" (cyclodextrin layer). This design overcomes the limitations of single modified materials, achieving a synergistic effect of graded capture and synergistic locking of oily contaminants, significantly improving the overall adsorption performance and selectivity of the composite material in complex systems.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of water treatment agents, in particular to a sepiolite composite material, a preparation method and application thereof in tannery soaking waste liquid. BACKGROUND

[0002] With the increasingly stringent environmental requirements and the deepening of the resource concept, industrial wastewater treatment has developed from simple pollutant removal to component recovery and recycling. Tannery soaking waste liquid is complex in composition, containing a large amount of oil, surfactant, protein hydrolysate and inorganic salt, etc. Among them, oil is the key component causing subsequent treatment load and pollution, while surfactant and protein hydrolysate are beneficial components required in the soaking process and have recycling value. Therefore, developing a material capable of selectively separating oil and retaining beneficial components is a core challenge to realize the resource recycling of the waste liquid.

[0003] As a natural fibrous chain-layered silicate mineral, sepiolite is widely used as an adsorbent carrier due to its large specific surface area, abundant surface silicon hydroxyl groups and good chemical stability. To improve its affinity for organic pollutants, the prior art usually uses cationic surfactants (such as hexadecyl trimethyl ammonium chloride, CTAC) for organic modification. The modified sepiolite can effectively adsorb oil, but its hydrophobic surface is uniform, lacks selectivity for oil molecules of different chain lengths and polarities, and will indiscriminately adsorb surfactants in the demulsified wastewater, resulting in loss of beneficial components and inability to achieve selective separation.

[0004] Cyclodextrin can form inclusion compounds with molecules of specific size due to its unique hydrophobic cavity structure, and is often used for molecular recognition and selective adsorption. However, direct loading of cyclodextrin on sepiolite often has problems such as weak binding force, easy falling off and low utilization rate of inclusion sites. Although existing technologies use cross-linking agents for fixation, the cross-linking process may block the cyclodextrin cavity, affecting its inclusion ability and introducing secondary pollution risk.

[0005] In view of this, the present application is proposed. SUMMARY

[0006] The present application aims to at least solve one of the above technical problems, and provides a sepiolite composite material, a preparation method and application thereof in tannery soaking waste liquid.

[0007] To achieve the above-mentioned purpose, the first technical solution adopted by the present application is:

[0008] A sepiolite composite material comprises:

[0009] A sepiolite carrier;

[0010] A gradient anchoring quaternary ammonium salt molecular layer on the surface of the sepiolite carrier, the quaternary ammonium salt molecular layer comprising dodecyltrimethylammonium chloride and hexadecyltrimethylammonium chloride;

[0011] β-cyclodextrin molecules are bound to the surface of the quaternary ammonium salt molecular layer through intermolecular forces.

[0012] Preferably, the dodecyltrimethylammonium chloride and hexadecyltrimethylammonium chloride form a gradient distribution from the pore opening to the inside of the pore within the sepiolite carrier.

[0013] Preferably, the mass percentage concentration of hexadecyltrimethylammonium chloride is 0.5~0.8wt%, and the mass percentage concentration of dodecyltrimethylammonium chloride is 2.0~2.2wt%.

[0014] Preferably, the mass ratio of sepiolite to quaternary ammonium salt is 10:1 to 15:1, and the mass ratio of β-cyclodextrin to sepiolite is 1:8 to 1:12.

[0015] Preferably, the surface of the sepiolite composite material is further coated with a cross-linked polymer shell.

[0016] The second technical solution adopted in this invention is:

[0017] The preparation method of sepiolite composite material includes the following steps: acidifying sepiolite with hydrochloric acid solution, washing and drying to obtain acidified sepiolite;

[0018] The acidified sepiolite was first reacted with a hexadecyltrimethylammonium chloride solution at a first temperature to obtain a suspension; then a dodecyltrimethylammonium chloride solution was added to the suspension, and a second reaction was carried out at a second temperature. After the reaction was completed, the mixture was separated into solid and liquid phases and dried to obtain gradient-modified sepiolite.

[0019] The gradient-modified sepiolite was subjected to a third reaction with a β-cyclodextrin solution, which caused the cyclodextrin to bind to its surface through intermolecular forces. After solid-liquid separation and drying, the sepiolite composite material was obtained.

[0020] Preferably, the first temperature is room temperature, and the second temperature is 60~65℃.

[0021] The third technical solution adopted in this invention is:

[0022] A method for preparing sepiolite composite materials with a surface coated with a cross-linked polymer shell includes the following steps:

[0023] The sepiolite composite material was prepared using the second technical solution.

[0024] Sepiolite composite material, styrene, crosslinking agent and emulsifier are emulsified at high speed in an aqueous phase to form an emulsion;

[0025] An initiator is added to the emulsion to carry out an emulsion polymerization reaction, thereby forming a cross-linked polymer shell on the surface of the sepiolite composite material.

[0026] The reaction product was subjected to solid-liquid separation, washing, and drying to obtain a sepiolite composite material coated with a cross-linked polymer shell.

[0027] Preferably, the crosslinking agent is N,N'-methylenebisacrylamide; the emulsifier is a compound system of sodium dodecyl sulfate and polyvinyl alcohol.

[0028] The fourth technical solution adopted in this invention is:

[0029] The application of sepiolite composite material in the selective separation of oil components in leather soaking wastewater: the sepiolite composite material preferentially adsorbs oil while retaining surfactants and protein hydrolysates in the wastewater.

[0030] Preferably, the oil comprises at least one of free fatty acids, monoglycerides, diglycerides, and triglycerides.

[0031] The fifth technical solution adopted in this invention is:

[0032] A method for recycling waste liquid from leather tanning includes the following steps:

[0033] Sepiolite composite material was added to leather soaking waste liquid, stirred and adsorbed, and grease was selectively removed;

[0034] Solid-liquid separation yields regenerated sepiolite composite material and purified waste liquid desorbed from oil;

[0035] The purified waste liquid is reused in the leather soaking process.

[0036] Preferably, after obtaining the regenerated sepiolite composite material and the purified waste liquid desorbed from the grease, the method further includes a regeneration step of washing and drying the regenerated sepiolite composite material, and reusing the regenerated sepiolite composite material in a selective grease removal step.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] 1. This invention successfully constructs a dual-functional interface on the surface of sepiolite, possessing both a "broad-spectrum hydrophobic adsorption domain" (quaternary ammonium salt layer) and a "specific molecular recognition domain" (cyclodextrin layer). This design overcomes the limitations of single modified materials, achieving a synergistic effect of hierarchical capture and synergistic locking of oily contaminants, and significantly improving the overall adsorption performance and selectivity of the composite material in complex systems.

[0039] 2. The sepiolite composite material provided by this invention, based on the multiple sieving principles of size matching, hydrophobicity differences, and chemical affinity, can achieve precise differentiation of different components. Its gradient hydrophobic microenvironment can effectively capture oil molecules of different chain lengths; while the cavity inclusion effect of cyclodextrin specifically targets free fatty acids and small molecule glycerides. More importantly, it can effectively repel excessively large or hydrophilic surfactant micelles, protein hydrolysates, and inorganic salt ions, thereby efficiently removing oils while fully retaining the beneficial components with reuse value in the waste liquid (surfactant retention rate >90%), laying the foundation for the direct reuse of waste liquid.

[0040] 3. In the sepiolite composite material provided by this invention, cyclodextrin is directly fixed to the quaternary ammonium salt modified interface through intermolecular forces (such as hydrogen bonds), avoiding the use of chemical crosslinking agents. This not only maintains the integrity and high inclusion efficiency of the cyclodextrin cavity but also ensures the stability of the interface layer. The composite material is easy to regenerate and can be reused after simple washing. After 10 consecutive uses, its adsorption capacity decay rate is less than 7%, resulting in low operating costs and environmental friendliness.

[0041] 4. This invention not only provides a high-performance composite material, but also pioneers a new process for the resource-based treatment of leather tanning soaking wastewater. Through the selective separation effect of this material, the purified wastewater can be reused in the soaking process, while the recovered grease can also be utilized as a resource, truly realizing "turning waste into treasure." This solves the problems of resource waste and high costs in traditional treatment methods, and has significant economic and environmental benefits. Detailed Implementation

[0042] The technical solutions of the present invention will be clearly and completely described below with reference to embodiments and comparative examples. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0043] The first embodiment of the present invention provides a sepiolite composite material, comprising:

[0044] sepiolite carrier;

[0045] A gradient anchoring quaternary ammonium salt molecular layer on the surface of the sepiolite carrier, the quaternary ammonium salt molecular layer comprising dodecyltrimethylammonium chloride and hexadecyltrimethylammonium chloride;

[0046] β-cyclodextrin molecules are bound to the surface of the quaternary ammonium salt molecular layer through intermolecular forces.

[0047] The sepiolite composite material provided in this invention uses sepiolite fibrous chain layered silicate nanofibers as the core carrier, with abundant silanol and aluminol hydroxyl groups on its surface providing active sites for subsequent functionalization. Utilizing the differences in molecular size, diffusion rate, and hydrophobicity between hexadecyltrimethylammonium chloride (CTAC, long chain) and dodecyltrimethylammonium chloride (DTAC, short chain), a stepwise reaction strategy is employed to perform gradient modification, forming an ordered gradient distribution within the sepiolite channels: DTAC molecules are small and diffuse quickly, preferentially occupying the pore opening region; CTAC molecules are large and have strong hydrophobic interactions, more easily migrating into the depths of the channels, ultimately forming a gradient microenvironment of "short-chain hydrophobic at the pore opening - long-chain hydrophobic within the pore." The short-chain region (DTAC-dominated): enriches and preferentially adsorbs relatively polar, short-chain lipid molecules (such as short-chain fatty acids); the long-chain region (CTAC-dominated): strongly captures non-polar, long-chain lipid molecules (such as triglycerides) through strong hydrophobic interactions. This structure allows oil molecules of different chain lengths and polarities to find the most suitable binding sites, thereby greatly improving the adsorption capacity and rate, and realizing the "hierarchical capture" of mixed oils.

[0048] β-Cyclodextrin (β-CD) is firmly "locked" onto the interface by forming a dense network of hydrogen bonds between its hydroxyl groups on the outer edge and the remaining silanol groups on the surface of sepiolite modified with quaternary ammonium salts. The hydrophobic cavity of β-CD (with an inner diameter of approximately 0.6~0.8 nm) can specifically recognize and include matching hydrophobic molecules. It can precisely include free fatty acids (FFA) and small hydrophobic fragments such as monoglycerides (MAG) and diglycerides (DAG) produced after the hydrolysis of fats and oils, forming stable inclusion complexes, thereby achieving "precise locking" and preventing their desorption.

[0049] In summary, quaternary ammonium salt gradients anchor on the sepiolite surface, forming hydrophobic-hydrophilic microdomains that preferentially adsorb lipids while repelling proteins and water-soluble surfactants. β-cyclodextrin binds through intermolecular forces, forming a complete cavity structure that can encapsulate lipid molecules. β-cyclodextrin can dynamically adjust its conformation to adapt to different lipid molecules. Furthermore, the intermolecular forces are reversible, allowing for dissociation and recombination under specific conditions, which is beneficial for the adsorption-desorption cycle. If β-cyclodextrin is covalently fixed to sepiolite, the cavity may be partially obscured or its orientation restricted, leading to a decrease in inclusion efficiency. Moreover, the chemical bonds are essentially irreversible and difficult to break once formed.

[0050] It should be noted that in the above gradient modification stages, only cationic surfactants such as CTAC and DTAC can be used sequentially for modification. This is because sepiolite has a natural porous structure (pore size of approximately 0.36 × 1.06 nm) and a negatively charged surface, making it suitable for cationic quaternary ammonium salts (such as CTAC and DTAC) to gradually enter the pores through ion exchange and hydrophobic interactions, forming a gradient distribution from the pore opening to the inside of the pore. Anionic surfactants, such as sodium dodecyl sulfate (SDS), are difficult to enter the pores due to charge repulsion, easily accumulating at the pore opening, clogging the pores, and disrupting the gradient structure. This manifests as a significant decrease in specific surface area, pore volume, adsorption rate, equilibrium adsorption capacity, and lack of selectivity for oil removal.

[0051] Because sepiolite has a special fibrous structure and micropores, it requires sufficient quaternary ammonium salt molecules to fill the pores and form a gradient distribution. Long-chain quaternary ammonium salts occupy the pore openings first, and short-chain quaternary ammonium salts enter the pores later, forming a gradient from the outside to the inside. At the same time, because CTAC has a longer carbon chain than DTAC, it has greater steric hindrance. Therefore, the amount and concentration of CTAC and DTAC should be such that a gradient can be formed, and the concentration of CTAC should be lower.

[0052] As examples, the mass percentage concentration of hexadecyltrimethylammonium chloride is 0.5~0.8wt%, and the mass percentage concentration of dodecyltrimethylammonium chloride is 2.0~2.2wt%; the mass ratio of sepiolite to quaternary ammonium salt is 10:1~15:1; and the mass ratio of hexadecyltrimethylammonium chloride to dodecyltrimethylammonium chloride is 2:1~3:1.

[0053] The dosage and concentration of β-cyclodextrin can be adjusted by those skilled in the art based on the specific surface area and pore volume of sepiolite. The concentration range of β-CD is generally controlled between 0.5 and 2.0 g / L. Too low a concentration will result in insufficient adsorption capacity for oils and decreased selectivity, while too high a concentration will cause β-CD to easily aggregate, reducing the actual usable active sites. In some preferred embodiments, the mass ratio of β-cyclodextrin to sepiolite is 1:8 to 1:12.

[0054] In some preferred embodiments, the surface of the sepiolite composite material is further coated with a cross-linked polymer shell. This polymer shell has a polystyrene backbone, cross-linked with N,N'-methylenebisacrylamide (MBA) to form a three-dimensional network structure, in which β-cyclodextrin is distributed as a functional side chain or graft unit, providing selective adsorption sites. This cross-linked polymer shell enhances stability and service life, ultimately forming a core-shell composite material with sepiolite as the core and polymer as the shell. The cross-linked polymer shell encapsulates the functionalized sepiolite core, preventing the internal quaternary ammonium salts and cyclodextrin from detaching and being lost during mechanical stirring, hydraulic scouring, or regeneration. This significantly improves the material's mechanical strength and chemical stability, enabling it to withstand multiple adsorption-desorption cycles, which is crucial for the material's practical engineering applications.

[0055] The second embodiment of the present invention provides a method for preparing sepiolite composite material, comprising the following steps: acidifying sepiolite with hydrochloric acid solution, and then washing and drying to obtain acidified sepiolite;

[0056] The acidified sepiolite was first reacted with a hexadecyltrimethylammonium chloride solution at a first temperature to obtain a suspension; then a dodecyltrimethylammonium chloride solution was added to the suspension, and a second reaction was carried out at a second temperature. After the reaction was completed, the mixture was separated into solid and liquid phases and dried to obtain gradient-modified sepiolite.

[0057] The gradient-modified sepiolite was subjected to a third reaction with a β-cyclodextrin solution, which caused the cyclodextrin to bind to its surface through intermolecular forces. After solid-liquid separation and drying, the sepiolite composite material was obtained.

[0058] In this embodiment, the specific surface area and pore structure of sepiolite are increased through acidification pretreatment, followed by gradient anchoring modification using CTAC and DTAC: DTAC molecules occupy the pore openings first due to their small size and fast diffusion, while CTAC molecules migrate preferentially into the depth of the pores due to their larger size and stronger hydrophobic effect; with the help of differences in molecular size, restricted diffusion, and negative potential gradient on the inner surface of the pores, an ordered gradient distribution of "short chains at the pore openings - long chains inside the pores" is formed.

[0059] The specific preparation methods for acidified sepiolite described above are commonly used techniques in this field and do not require special limitations. To fully expose the buried active sites, ultrasonic treatment can also be performed after acidification.

[0060] In some preferred embodiments, the first temperature is room temperature, and the second temperature is 60~65°C.

[0061] As a specific implementation method, the preparation method of sepiolite composite material is as follows:

[0062] Pretreated sepiolite was obtained by acidifying sepiolite with hydrochloric acid at a concentration of 2-3 mol / L, a reaction temperature of 70-80℃, and a reaction time of 4-5 h.

[0063] The pretreated sepiolite was dispersed in a hexadecyltrimethylammonium chloride solution and magnetically stirred at room temperature and 200-300 rpm for 2-3 hours to obtain a suspension.

[0064] Dodecyltrimethylammonium chloride solution was added to the suspension, the temperature was raised to 60-65℃ and stirred for 6-7 hours to obtain a mixture. After centrifugation, the liquid was retained, washed and vacuum dried to obtain gradient modified sepiolite (G-Sep).

[0065] G-Sep was dispersed in water, ultrasonically treated, and then mixed with a β-cyclodextrin solution. The mixture was stirred at 50-60℃ for 4-5 hours to obtain an inclusion complex. The inclusion complex was separated by centrifugation and then freeze-dried to obtain the sepiolite composite material CD-G-Sep.

[0066] The third embodiment of the present invention provides a method for preparing a sepiolite composite material with a cross-linked polymer shell on its surface, comprising the following steps:

[0067] The sepiolite composite material was prepared using the method of the second embodiment.

[0068] Sepiolite composite material, styrene, crosslinking agent and emulsifier are emulsified at high speed in an aqueous phase to form an emulsion;

[0069] An initiator is added to the emulsion to carry out an emulsion polymerization reaction, thereby forming a cross-linked polymer shell on the surface of the sepiolite composite material.

[0070] The reaction product was subjected to solid-liquid separation, washing, and drying to obtain a sepiolite composite material coated with a cross-linked polymer shell.

[0071] In some preferred embodiments, the mass ratio of sepiolite composite material to styrene is 1:1 to 1:3; the mass percentage of crosslinking agent relative to styrene is 2 to 5 wt%, and the mass percentage of emulsifier relative to styrene is 1 to 3 wt%.

[0072] In some preferred embodiments, the crosslinking agent is N,N'-methylenebisacrylamide; the emulsifier is a compound system of sodium dodecyl sulfate and polyvinyl alcohol, wherein the mass ratio of sodium dodecyl sulfate to polyvinyl alcohol is preferably 1:2 to 1:4; and the initiator is potassium persulfate, wherein the mass percentage of potassium persulfate relative to styrene is 0.6 to 1.2 wt%.

[0073] In some preferred embodiments, the high-speed emulsification is performed at a rotation speed of 8000~15000 rpm for 3~8 minutes at a temperature of room temperature~30°C.

[0074] The fourth embodiment of the present invention provides the application of sepiolite composite material in the selective separation of oil components in leather soaking wastewater. The sepiolite composite material can preferentially adsorb oil while retaining surfactants and protein hydrolysates in the wastewater.

[0075] During application, the quaternary ammonium salt layer of the sepiolite composite material is responsible for rapidly adsorbing large amounts of oils, especially large molecules (such as triglycerides) that cannot be accommodated by the β-CD cavity. The cyclodextrin layer is responsible for specifically encapsulating small molecule fragments. The two layers are spatially adjacent, enabling a synergistic process of "adsorption-breakdown-re-encapsulation" of oil molecules, significantly improving the overall removal efficiency.

[0076] Understandably, the sepiolite composite material provided by the present invention can be applied not only to tanning soaking wastewater, but also to other wastewater containing oils. The sepiolite composite material can selectively adsorb oil components.

[0077] In the above applications, sepiolite composite materials repel non-target components through multiple mechanisms: (1) Size exclusion: The micelle size (usually >10 nm) formed by surfactants in water is much larger than the cavity entrance of β-CD (~0.6 nm), and cannot be included. (2) Hydrophilic repulsion: Protein hydrolysates (peptides, amino acids) are hydrophilic and lack affinity for the hydrophobic quaternary ammonium alkyl chains and β-CD cavities, and will not be adsorbed. (3) Charge repulsion: The positively charged head groups of quaternary ammonium salts will repel inorganic cations (such as Na⁺) that are also positively charged; the negatively charged hydroxyl groups on the outer edge of β-CD will also repel inorganic anions (such as Cl⁻). Therefore, the salt is perfectly retained.

[0078] The embodiments of the present invention are capable of adsorbing common oils, including at least one of free fatty acids, monoglycerides, diglycerides and triglycerides.

[0079] The fifth embodiment of the present invention provides a method for the resource recycling of leather tanning soaking wastewater, comprising the following steps:

[0080] Sepiolite composite material was added to leather soaking waste liquid, stirred and adsorbed, and grease was selectively removed;

[0081] Solid-liquid separation yields regenerated sepiolite composite material and purified waste liquid desorbed from oil;

[0082] The purified waste liquid is reused in the leather soaking process.

[0083] In some preferred embodiments, after obtaining the regenerated sepiolite composite material and the purified waste liquid desorbed from the grease, the process further includes a regeneration step of washing and drying the regenerated sepiolite composite material, and reusing the regenerated sepiolite composite material in a selective grease removal step.

[0084] To make the technical solution of the present invention clearer, the sepiolite composite material, its preparation and properties are described in detail below through several specific embodiments.

[0085] Example 1: Preparation of sepiolite composite material

[0086] Sepiolite was added to a 2.3 mol / L HCl solution and stirred in a water bath at 78°C for 4.5 h. After filtration, washing, and drying for 12-16 h, it was ground and sieved to obtain acidified sepiolite. The acidified sepiolite was dispersed in an ethanol-water (1:1) solution and ultrasonically treated at an ultrasonic power of 400-500 W for 30-40 min. After centrifugation and vacuum drying, pretreated sepiolite was obtained.

[0087] Pretreated sepiolite was dispersed in a 0.6 wt% hexadecyltrimethylammonium chloride solution and magnetically stirred for 3 h at room temperature and 200-300 rpm to obtain a suspension. A 2.1 wt% dodecyltrimethylammonium chloride solution was slowly added to the suspension, and the mixture was then heated to 63 °C and stirred for 6 h to obtain a mixture. The mixture was centrifuged, washed, and vacuum dried at 50-60 °C to obtain gradient-modified sepiolite (G-Sep). The mass ratio of sepiolite to quaternary ammonium salt was 12:1, and the mass ratio of hexadecyltrimethylammonium chloride to dodecyltrimethylammonium chloride was 2.5:1.

[0088] G-Sep was dispersed in water and sonicated for 10-15 min. Then, 2.3 g / L β-CD solution (β-CD to sepiolite mass ratio of 1:10) was slowly added and stirred at 52℃ for 5 h. After centrifugation and freeze-drying, the sepiolite composite material CD-G-Sep was obtained.

[0089] Example 2 Preparation of sepiolite composite material

[0090] A cross-linked polymer shell was prepared based on the sepiolite composite material CD-G-Sep obtained in Example 1. The specific method is as follows:

[0091] Styrene, β-cyclodextrin, and potassium persulfate were mixed and then reacted at 78°C for 4 hours to obtain the St-β-CD prepolymer.

[0092] Sodium dodecyl sulfate was fully dissolved in deionized water, polyvinyl alcohol was added, and the mixture was heated and stirred at 75-85°C for 30-40 minutes. After cooling to room temperature, the pH was adjusted to 9 to obtain an emulsifier solution.

[0093] The CD-G-Sep prepared in Example 1 was added to an emulsifier solution and ultrasonically dispersed for 20-25 minutes at a power of 200-300W with an intermittent 5-second operation followed by a 2-second pause. Then, St-β-CD prepolymer was added under nitrogen protection, and the mixture was emulsified at high speed for 3-5 minutes. N,N'-methylenebisacrylamide was added, and emulsification was continued for 1-2 minutes. The temperature was raised to 75-80°C, and potassium persulfate and sodium bisulfite solutions were added under nitrogen protection. The mixture was then reacted at 300-350 rpm for 4-5 hours, cooled to room temperature, and centrifuged for 10 minutes. The centrifuged solution was washed and vacuum dried to obtain a sepiolite composite material with a cross-linked polymer shell.

[0094] Example 3: Preparation of sepiolite composite material

[0095] The preparation method is as described in Example 2, and the key parameters are as follows:

[0096] Sepiolite pretreatment: 2.0 mol / L HCl, 70℃ water bath for 4 hours;

[0097] Gradient modification: First, treat with 0.5 wt% CTAC for 2 h, then add 2.0 wt% DTAC and stir at 60℃ for 6 h; wherein, the mass ratio of sepiolite to quaternary ammonium salt is 10:1, and the mass ratio of hexadecyltrimethylammonium chloride to dodecyltrimethylammonium chloride is 2:1.

[0098] Cyclodextrin anchoring: β-CD concentration 2.0 g / L, β-CD to sepiolite mass ratio 1:8, stirred at 50°C for 4 h;

[0099] Prepolymer preparation: Reaction at 75℃ for 4 hours to obtain the final sepiolite composite material.

[0100] Example 4: Preparation of sepiolite composite material

[0101] The preparation method is as described in Example 2, and the key parameters are as follows:

[0102] Sepiolite pretreatment: 3.0 mol / L HCl, 80℃ water bath for 5 h;

[0103] Gradient modification: First, treat with 0.8 wt% CTAC for 3 h, then add 2.2 wt% DTAC and stir at 65℃ for 7 h; wherein, the mass ratio of sepiolite to quaternary ammonium salt is 15:1, and the mass ratio of hexadecyltrimethylammonium chloride to dodecyltrimethylammonium chloride is 3:1;

[0104] Cyclodextrin anchoring: β-CD concentration 2.5 g / L, β-CD to sepiolite mass ratio 1:12, stirred at 55°C for 5 h;

[0105] Prepolymer preparation: react at 80℃ for 5 h to obtain the final sepiolite composite material.

[0106] Example 5: Preparation of sepiolite composite material

[0107] The preparation method is as described in Example 2, and the key parameters are as follows:

[0108] Sepiolite pretreatment: 2.5 mol / L HCl, 75℃ water bath for 4.5 h;

[0109] Gradient modification: First, treat with 0.6 wt% CTAC (the mass ratio of sepiolite to quaternary ammonium salt is 12.5:1) for 2.5 h, then add 2.1 wt% DTAC and stir at 65℃ for 6.5 h; wherein, the mass ratio of sepiolite to quaternary ammonium salt is 12.5:1, and the mass ratio of hexadecyltrimethylammonium chloride to dodecyltrimethylammonium chloride is 2.5:1;

[0110] Cyclodextrin anchoring: β-CD concentration 2.25 g / L, β-CD to sepiolite mass ratio 1:10, stirred at 55°C for 4.5 h;

[0111] Prepolymer preparation: react at 80℃ for 4.5h to obtain the final sepiolite composite material.

[0112] Comparative Example 1

[0113] Raw sepiolite: Commercially purchased sepiolite is used directly, with only basic cleaning and drying processes performed.

[0114] Comparative Example 2

[0115] Compared with Example 1, the difference is that the cyclodextrin anchoring and emulsion polymerization steps are performed to prepare only gradient-modified sepiolite G-Sep.

[0116] Comparative Example 3

[0117] Compared with Example 1, the only difference is that only CTAC is used for modification, that is, DTAC in Example 1 is also replaced with an equal amount of CTAC, and 2.7 wt% CTAC is used for modification. The remaining steps and parameters are the same as in Example 1.

[0118] Comparative Example 4

[0119] Compared with Example 1, the only difference is that only DTAC is used for modification, that is, CTAC in Example 1 is also replaced with an equal amount of DTAC, and 2.7 wt% DTAC is used for modification. The remaining steps and parameters are the same as in Example 1.

[0120] Comparative Example 5

[0121] Compared with Example 1, the only difference is that CTAB is used for modification in both cases. Specifically, DTAC and CTAC in Example 1 are replaced with an equal amount of CTAB, and 2.7 wt% CTAB is used for modification. All other steps and parameters are the same as in Example 1.

[0122] Comparative Example 6

[0123] Compared with Example 1, the only difference is that the pretreated sepiolite is directly compounded with β-CD without the quaternary ammonium salt modification and emulsion polymerization steps.

[0124] Comparative Example 7: Traditional Crosslinked β-Cyclodextrin Composite Materials

[0125] Preparation of cross-linked β-CD polymer: β-cyclodextrin was dissolved in 50 mL of deionized water and stirred thoroughly until completely dissolved. The pH was adjusted to 11-12. Epichlorohydrin (β-CD:epicochlorohydrin molar ratio = 1:10) was slowly added dropwise under ice bath conditions. After stirring in the ice bath for 2 hours, the temperature was raised to 60°C and reacted for 6 hours. The pH was neutralized to 7-8, and small molecule impurities were removed by dialysis (dialysis bag molecular weight cutoff 3500 Da, dialysis for 48 hours). The cross-linked β-CD polymer was obtained by freeze drying.

[0126] Sepiolite pretreatment: 2.3 mol / L HCl, 78°C water bath for 4.5 hours, wash with deionized water until neutral, dry at 80°C for 12 hours;

[0127] Preparation of composite material: Pretreated sepiolite (2 g) was dispersed in deionized water (100 mL), sonicated for 15 minutes, crosslinked β-CD polymer (calculated based on β-CD content of 2.3 g / L) was added, stirred at 52°C for 5 hours to allow the polymer to adsorb on the surface of sepiolite, centrifuged (8000 rpm, 10 minutes), washed 3 times with deionized water, and vacuum dried at 80°C for 12 hours to obtain the final composite material.

[0128] Comparative Example 8

[0129] Compared with Example 1, the only difference is that CTAC and DTAC are mixed and added to the modification at one time, while the other steps and parameters are the same as in Example 1.

[0130] Comparative Example 9

[0131] Compared with Example 1, the only difference is that the order of CTAC and DTAC modification is reversed, with DTAC modification performed first and then CTAC modification performed. All other steps and parameters are the same as in Example 1.

[0132] Comparative Example 10

[0133] Compared with Example 1, the only difference is that dodecyltrimethylammonium chloride is replaced with an equal amount of sodium dodecyl sulfonate; all other steps and parameters are the same as in Example 1. Comparative Example 11

[0134] Compared with Example 1, the only difference is that only sodium dodecyl sulfonate is used for modification. That is, the treatment of hexadecyltrimethylammonium chloride and dodecyltrimethylammonium chloride in Example 1 is replaced by a one-time treatment of 2.7 wt% sodium dodecyl sulfonate. All other steps and parameters are the same as in Example 1.

[0135] Comparative Example 12

[0136] Compared with Example 1, the only difference is that the order of β-cyclodextrin treatment and quaternary ammonium salt gradient modification is changed, that is, β-cyclodextrin is grafted first, followed by quaternary ammonium salt gradient modification. All other steps and parameters are the same as in Example 1.

[0137] Comparative Example 13

[0138] Compared with Example 1, the only difference is that quaternary ammonium salt gradient modification and β-cyclodextrin treatment are performed simultaneously, while the other steps and parameters are the same as in Example 1.

[0139] Test case

[0140] The following experiments were conducted on the sepiolite materials prepared in the above embodiments and comparative examples:

[0141] 1. Measurement of adsorption capacity of mixed oils

[0142] The sepiolite material was dried in an oven at 105℃ for 2 hours, cooled to room temperature, and its initial mass m0 was recorded. 1.0 g of the dried sample was placed in a 50 mL beaker, and excess oil (approximately 15-20 g) was added to ensure complete immersion. The sample was shaken in a constant temperature water bath at 25℃ for 2 hours at 150 rpm. It was then allowed to stand for 30 minutes to allow for full adsorption. Excess oil was quickly filtered off using filter paper, and the oil-absorbed sample was transferred to a pre-weighed beaker. The total mass m1 after adsorption was recorded. The adsorption capacity was calculated using the formula: Adsorption capacity = (m1 – m0) / m0 (g oil / g adsorbent). The results are shown in Table 1.

[0143] Table 1 Comparison of adsorption capacity of mixed oils

[0144] .

[0145] 2. Selective adsorption test of long-chain fatty acids

[0146] A mixed fatty acid solution (n-hexane system) combining C8, C10, C12, C14, C16, and C18 was used as the adsorbate. The specific method is as follows: Each fatty acid was accurately weighed and prepared into a 100 mg / L n-hexane solution. 50 mg / L of heptadecanoic acid (internal standard) was added, bringing the total volume to 500 mL, and the solution was stored under nitrogen. 0.1 g of sepiolite sample was placed in a 25 mL stoppered conical flask, and 20 mL of the mixed fatty acid solution was added. The mixture was incubated at 25°C with shaking for 2 h, filtered through a 0.45 μm filter at 180 rpm, and the filtrate was collected. The concentration was determined using gas chromatography. The removal rate was calculated as: Removal rate (%) = (C0 - C) / C0 × 100%, where C0 is the initial concentration and C is the equilibrium concentration. The test results are shown in Table 2.

[0147] Table 2. Removal rate of long-chain fatty acids for each sample

[0148] .

[0149] 3. Comparison of Recycling Performance

[0150] First adsorption: 2.0 g of sepiolite sample was used for soybean oil adsorption, and the initial adsorption capacity was recorded as the 100% baseline value. Desorption and regeneration: The oil-absorbed sample was eluted with n-hexane at a solid-liquid ratio of 1:10, shaken at room temperature for 30 minutes, and the elution was repeated 3 times until the eluent was colorless. The eluent was then dried in a 105°C oven for 2 hours to constant weight. Cyclic test: The adsorption-desorption process was repeated, and tests were conducted after the 3rd, 5th, 7th, 10th, and 15th cycles. The adsorption capacity was measured and the retention rate was calculated each time. The retention rate was calculated using the formula: Retention rate (%) = Adsorption capacity in the nth cycle / Initial adsorption capacity × 100%. The results are shown in Table 3.

[0151] Table 3. Recycling performance of each sample

[0152] .

[0153] 4. β-CD shedding rate determination

[0154] The stability of β-cyclodextrin (β-CD) loaded on the surface of sepiolite composites during recycling was evaluated. The β-CD content in the regenerated eluent of the composites was quantitatively determined by high performance liquid chromatography (HPLC), and the single-cycle shedding amount and cumulative shedding rate were calculated.

[0155] Preparation of eluent samples: The sepiolite composite material was subjected to an adsorption-regeneration cycle experiment according to the method in "3. Comparison of Cyclic Performance" above. The eluent after each regeneration operation was collected, diluted to 100 mL, and filtered through a 0.22 μm filter membrane for testing.

[0156] HPLC analysis conditions: mobile phase: acetonitrile: water = 75:25 (v / v);

[0157] Standard curve preparation: Accurately weigh β-CD standard (purity ≥98%) and prepare a series of standard solutions with concentrations of 0.1, 0.5, 1.0, 2.0, 5.0, and 10.0 mg / L; under the above chromatographic conditions, inject the solutions sequentially from low to high concentration, record the peak area of ​​each concentration, and plot the concentration-peak area standard curve.

[0158] Analysis of the sample to be tested: After filtering the eluent sample prepared above through a 0.22 μm filter membrane, it was directly injected for analysis, and the chromatographic peak area with the retention time consistent with that of the standard was recorded;

[0159] Results Calculation: Based on the peak area of ​​the sample to be tested, the concentration of β-CD in the eluent was calculated by substituting it into the standard curve. The cumulative detachment rate was calculated using the following formula: Single detachment amount (mg) = Eluent concentration (mg / L) × Eluent volume (L); Cumulative detachment rate (%) = Σ Single detachment amount / Initial β-CD loading × 100%. The results are shown in Table 4.

[0160] Table 4 β-CD shedding rate of each sample

[0161] .

[0162] 5. Comparison of Adsorption Kinetic Constants

[0163] Prepare 12 identical 100mL Erlenmeyer flasks, add 1.0g of sepiolite sample and 20mL of soybean oil to each flask, and shake at a constant temperature (25°C, shaking speed 180 rpm). Take samples at preset time points (1, 3, 5, 10, 15, 30, 45, 60, 90, and 120 min). After sampling, quickly filter to separate the solid and liquid phases, weigh the mass change of the adsorbent, and calculate the instantaneous adsorption capacity qt. Fit the pseudo-second-order kinetic equation and use linear regression to obtain k2 (rate constant), qe (equilibrium adsorption capacity), and R. 2 (Goodness of fit), calculate the half-adsorption time: t1 / 2 = 1 / (k2qe). The pseudo-second-order kinetic equation is: t / qt = 1 / (k2qe) 2 ) + t / qe. The results are shown in Table 5.

[0164] Table 5 Adsorption kinetic constants for each sample

[0165] .

[0166] 6. Actual Treatment Effect of Tannery Wastewater: Wastewater Source and Composition: A tannery's soaking wastewater contains the following components: COD: 25000 mg / L; grease: 5000 mg / L; surfactant: 500 mg / L; protein: 1000 mg / L; chloride ions: 18500 mg / L; pH: 7.8. The COD of this wastewater needs to be reduced to below 3000 mg / L to be considered a purified solution.

[0167] Each sepiolite sample was added to the waste liquid, mechanically stirred at 120 rpm at 25°C for 2 hours, allowed to settle for 30 minutes, filtered through a 0.45 μm membrane, and the treated liquid was collected. The treated parameters were measured according to the corresponding methods, and the removal rate and retention rate were calculated. Removal rate (%) = (Cinitial - Ctreated) / Cinitial × 100%; Retention rate (%) = Ctreated / Cinitial × 100%. The results are shown in Table 6.

[0168] Table 6 Comparison of treatment effects for each sample

[0169] .

[0170] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A sepiolite composite, characterized by, Comprise: A sepiolite carrier; A gradient-anchored quaternary ammonium salt molecular layer on the surface of the sepiolite carrier, the quaternary ammonium salt molecular layer comprising dodecyltrimethylammonium chloride and hexadecyltrimethylammonium chloride, wherein the dodecyltrimethylammonium chloride preferentially occupies the orifice region of the sepiolite carrier, and the hexadecyltrimethylammonium chloride preferentially occupies the interior region of the channel of the sepiolite carrier; Beta-cyclodextrin molecules bound to the surface of the quaternary ammonium salt molecular layer by intermolecular forces.

2. The sepiolite composite according to claim 1, characterized in that, The mass percentage concentration of hexadecyltrimethylammonium chloride is 0.5-0.8wt%, and the mass percentage concentration of dodecyltrimethylammonium chloride is 2.0-2.2wt%.

3. The sepiolite composite according to claim 1, characterized in that, The mass ratio of sepiolite to quaternary ammonium salt is 10:1-15:1, and the mass ratio of beta-cyclodextrin to sepiolite is 1:8-1:

12.

4. The sepiolite composite according to any one of claims 1 to 3, characterized in that, The surface of the sepiolite composite material is further coated with a crosslinked polymer shell layer.

5. The method for preparing the sepiolite composite material according to any one of claims 1 to 3, characterized in that, Comprise the following steps: Acidifying the sepiolite with a hydrochloric acid solution, washing and drying to obtain acidified sepiolite; Carrying out a first reaction of the acidified sepiolite with a hexadecyltrimethylammonium chloride solution at a first temperature to obtain a suspension; then adding a dodecyltrimethylammonium chloride solution to the suspension, carrying out a second reaction at a second temperature, and after the reaction is completed, carrying out solid-liquid separation and drying to obtain gradient-modified sepiolite; Carrying out a third reaction of the gradient-modified sepiolite with a beta-cyclodextrin solution, allowing the cyclodextrin to bind to the surface thereof by intermolecular forces, and carrying out solid-liquid separation and drying to obtain the sepiolite composite material.

6. The method of claim 5, wherein the sepiolite composite is prepared by mixing the sepiolite and the at least one organic compound in a weight ratio of 1 : 0.1-10. The first temperature is room temperature, and the second temperature is 60-65℃.

7. The method of claim 4, wherein the sepiolite composite is prepared by the steps of: Comprise the following steps: Using the method of claim 5 or 6 to prepare the sepiolite composite material; forming an emulsion by high-speed emulsification of the sepiolite composite material, styrene, a crosslinking agent, and an emulsifier in an aqueous phase; adding an initiator to the emulsion to carry out emulsion polymerization, forming a crosslinked polymer shell layer on the surface of the sepiolite composite material; and carrying out solid-liquid separation, washing, and drying on the product after the reaction to obtain the sepiolite composite material coated with a crosslinked polymer shell layer.

8. Use of the sepiolite composite material according to any one of claims 1 to 4 for the selective separation of the grease components in the tannery effluent immersion waste liquid, characterized in that, The sepiolite composite material preferentially adsorbs oil and fat while retaining surfactants and protein hydrolysates in the waste liquid.

9. A method for resource recycling of tannery effluent, characterized in that, Comprise the following steps: adding the sepiolite composite material of any one of claims 1-4 to tanning immersion waste liquid, stirring and adsorbing to selectively remove oil and fat; carrying out solid-liquid separation to obtain regenerated sepiolite composite material and purified waste liquid from which oil and fat has been desorbed; and recycling the purified waste liquid to the tanning immersion process.