Attapulgite-chitosan oligosaccharide composite carrier and preparation method thereof

Abstract

The invention belongs to the field of inorganic-organic composite carrier materials, and provides an attapulgite-chitosan oligosaccharide composite carrier and a preparation method thereof. According to the invention, gamma-glycidyl ether oxypropyl trimethoxy silane is subjected to hydrolytic polycondensation to form a silane coupling layer on the surface of attapulgite, and chitosan oligosaccharide is covalently grafted through an epoxy group ring-opening reaction to construct a design of a double-layer covalent connection shell layer; according to the preparation method, accurate regulation and control of the shell thickness of 2-30nm under the condition that the mass ratio of chitosan oligosaccharide is 0.05-0.40 are realized, the particle size D50 is controllable in a range of 0.20-2.00 m, the apparent viscosity of 20wt% slurry is 50-500mPa. S, the PDI of powder after spray drying is reduced to 0.05-0.35, the water content is controlled to be 0-8wt%, and the particle size D50 is controllable in a range of 0.20-2.00 m. The coupling contradiction that an existing attapulgite carrier is difficult to consider high-proportion stable introduction of chitosan oligosaccharide, low-viscosity spray processing, particle size PDI degradation, moisture absorption and caking and the like is solved, and the attapulgite carrier has wide application value in the fields of pesticides, food additives, bioactive substance controlled-release carriers and the like.

Description

Technical Field

[0001] This invention relates to the field of inorganic-organic composite carrier materials, specifically to an attapulgite-chitosan oligosaccharide composite carrier and its preparation method. Background Technology

[0002] In applications such as pesticide slow-release carriers, food active substance encapsulation, and biopharmaceutical controlled-release systems, attapulgite has become an important inorganic carrier material due to its unique rod-shaped nanostructure, large specific surface area, good adsorption properties, and biocompatibility. These applications place multi-dimensional performance demands on carrier materials: on the one hand, the carrier needs to possess high-solids slurry processing performance to meet the requirements of industrial production processes such as spray drying and fluidized bed coating for low viscosity, good atomization performance, and sprayability; on the other hand, the carrier surface needs to be able to stably introduce functional biomolecules such as chitosan oligosaccharides at a high proportion to achieve controlled release of active substances, pH-responsive release, and synergistic enhancement of bioactivity. Simultaneously, the carrier material must maintain key properties such as narrow particle size distribution, good redispersibility, and high batch-to-batch consistency during high-solids processing, which is crucial for ensuring the quality stability and functional controllability of the final product. Meeting and developing these comprehensive performance requirements can not only significantly improve the application performance of carrier materials in controlled release and targeted delivery, but also broaden the application scope of attapulgite-based composite materials in functional agriculture, food industry and biomedicine, and promote the progress of inorganic-organic composite carrier technology.

[0003] However, existing attapulgite carriers face numerous technical bottlenecks in achieving the aforementioned multidimensional performance requirements. First, biomacromolecules such as chitosan oligosaccharides are typically introduced to the carrier surface through physical adsorption or electrostatic interactions. This non-covalent interaction leads to poor functional layer stability, making them prone to desorption during high-solids slurry preparation and spray drying, hindering the stable introduction of high proportions. Furthermore, desorbed chitosan oligosaccharides significantly increase slurry viscosity and induce inter-particle bridging and agglomeration. Second, even with partial chemical modification to introduce functional groups, the lack of precise control over shell thickness often results in a dilemma: an excessively thick shell leads to a surge in slurry viscosity and a narrowing of the rheological window, failing to meet spray atomization requirements; or an excessively thin shell results in insufficient functionality and poor sustained-release effects. Third, attapulgite rod-shaped particles are prone to end-face-side bridging and agglomeration in high-solids slurries, leading to deterioration of particle size D50 and particle size distribution index PDI, thereby affecting spray drying uniformity and batch-to-batch consistency. Fourth, the spray-dried powder is prone to agglomeration due to the strong hygroscopicity of the hydrophilic chitosan oligosaccharide layer on its surface, resulting in decreased redispersibility and poor storage stability. For example, Chinese patent CN 108439489 A discloses a chitosan-modified attapulgite composite material for wastewater treatment and its preparation method, but it suffers from drawbacks such as the introduction of chitosan through physical adsorption, easy desorption during high-solids processing, and difficulty in controlling slurry viscosity. For example, Chinese patent CN103613720B discloses a method for preparing molecularly imprinted materials on the surface of attapulgite modified with a silane coupling agent targeting bisphenol A, but it does not involve the covalent introduction of biomacromolecules such as chitosan oligosaccharides or the control of shell thickness, and cannot simultaneously meet the requirements of low-viscosity spray processing and functional introduction. Summary of the Invention

[0004] The purpose of this invention is to provide an attapulgite-chitosan oligosaccharide composite carrier and its preparation method, which solves the problem that current attapulgite-based inorganic carriers, while achieving high solids content and low viscosity sprayable atomization, are difficult to simultaneously achieve the covalent fixation and shell thickness control required for the high-proportion stable introduction of chitosan oligosaccharides. This results in a narrowing of the slurry rheological window, easy bridging and agglomeration of particles leading to particle size and PDI deterioration, and a decrease in redispersibility and batch-to-batch consistency of the powder after spray drying due to moisture absorption and agglomeration of the hydrophilic shell.

[0005] This invention adopts a two-step synergistic design approach of "silane coupling layer construction - epoxy ring-opening covalent grafting". It forms a silane coupling layer with reactive epoxy groups by hydrolyzing and polycondensing γ-glycidoxypropyltrimethoxysilane on the surface of attapulgite. Then, the covalent anchoring of chitosan oligosaccharides is achieved by the ring-opening addition reaction of epoxy groups with chitosan oligosaccharide amino groups. This fundamentally solves the problems of poor stability and easy desorption during high solid content processing when introducing functional layers through physical adsorption. By precisely controlling the synergistic ratio of silane feed amount (0.005 to 0.10) and chitosan oligosaccharide mass ratio (0.05 to 0.40), the shell thickness of 2 to 30 nm was precisely controllable. This ensured the stable introduction of a high proportion of chitosan oligosaccharide to achieve excellent functionality, while avoiding a surge in slurry viscosity caused by excessive shell thickness. The apparent viscosity of 20 wt% slurry was controlled within the sprayable range of 50 to 500 mPa·s. At the same time, the steric stabilization effect of the covalent shell on the attapulgite rod-shaped particles effectively suppressed bridging agglomeration in the high solids content system. The particle size D50 was controllable within the range of 0.20 to 2.00 µm, and the PDI was reduced to 0.05 to 0.35. After spray drying, the powder moisture content was controlled within the range of 0 to 8 wt% and the redispersibility was excellent, demonstrating the synergistic effect of silane coupling layer construction and chitosan oligosaccharide covalent grafting.

[0006] To achieve the above objectives, the present invention provides the following technical solution: An attapulgite-chitosan oligosaccharide composite carrier includes: attapulgite, and a covalently linked shell layer covering the surface of the attapulgite; The covalently linked shell layer includes: a silane coupling layer formed by hydrolysis and condensation of γ-glycidoxypropyltrimethoxysilane, wherein the silane coupling layer is connected to the attapulgite through siloxane bonds; and chitosan oligosaccharide, wherein the chitosan oligosaccharide is covalently connected to the silane coupling layer through C–N bonds formed by ring opening of the epoxy groups on the silane coupling layer. Furthermore, with the dry basis mass of attapulgite in the composite carrier being 1, the mass of the chitosan oligosaccharide is 0.05 to 0.40, and when preparing the composite carrier, the amount of γ-glycidoxypropyltrimethoxysilane relative to the dry basis of the attapulgite is 0.005 to 0.10. The composite carrier has a particle size D50 of 0.20 to 2.00 µm, and the covalently linked shell has a shell thickness of 2 to 30 nm.

[0007] Furthermore, the attapulgite is acid-activated attapulgite, which is prepared through the following steps: A1. Raw material preparation: Provide attapulgite, hydrochloric acid and deionized water; A2. Preparation of hydrochloric acid aqueous solution: Add the hydrochloric acid to the deionized water to prepare a hydrochloric acid aqueous solution with a concentration of 0.10 to 1.00 mol / L; A3. Acid activation: The attapulgite and the hydrochloric acid aqueous solution are mixed at a mass ratio of 1:5 to 20, and the mixture is mechanically stirred at 300 to 1200 rpm at a temperature of 25 to 60°C and at normal pressure for a reaction time of 1.0 to 6.0 h. A4. Post-treatment: Filter and wash with deionized water until the pH of the filtrate is 6.0 to 7.0; dry at a temperature of 60 to 80°C and a pressure of 0.001 to 0.01 MPa for 8 to 24 hours until constant weight is reached. The criterion for constant weight is that the interval between two consecutive weighings is 2 hours and the mass difference is less than 0.1%. A5. Quality control: The water content of the acid-activated attapulgite is 0 to 10 wt%.

[0008] Furthermore, the attapulgite is epoxy-silanized attapulgite, which is prepared through the following steps: B1. Raw material preparation: Provide acid-activated attapulgite, γ-glycidyl etheroxypropyltrimethoxysilane, ethanol, acetic acid and deionized water; B2. Dispersion: The acid-activated attapulgite is dispersed in a mixed solvent of ethanol and deionized water at a solid-liquid ratio of 1g:5mL to 1g:50mL, wherein the volume ratio of ethanol to deionized water is 3:7 to 9:1; the dispersion process is carried out at a temperature of 20 to 40°C with mechanical stirring at 300 to 1200 rpm for 10 to 60 minutes. B3. Hydrolysis-condensation and grafting: Add the γ-glycidyl etheroxypropyltrimethoxysilane to the dispersion system, with the amount being 0.005 to 0.10 of the mass of the acid-activated attapulgite; adjust the pH of the system to 4.0 to 5.5 using an aqueous acetic acid solution with a concentration of 0.10 to 2.00 mol / L, and measure the pH at 25°C. React at 40 to 70°C and atmospheric pressure for 1.0 to 4.0 h, with stirring during the reaction at a speed of 300 to 1200 rpm; B4. Post-treatment: Filter and wash with ethanol 1 to 5 times, each time using 5 to 30 mL / g of solid mass; then wash with deionized water 1 to 5 times, each time using 5 to 30 mL / g of solid mass; dry at a temperature of 60 to 80°C and a pressure of 0.001 to 0.01 MPa for 8 to 24 hours until constant weight is reached. The criterion for constant weight is that the interval between two consecutive weighings is 2 hours and the mass difference is less than 0.1%. B5. Quality control: The mass gain of the epoxy-silanized attapulgite relative to the acid-activated attapulgite is 0.5 to 5.0 wt%.

[0009] Furthermore, the covalently connected shell is formed through the following steps: C1. Raw material preparation: Provide epoxy silanized attapulgite, chitosan oligosaccharide, sodium hydroxide, hydrochloric acid, and deionized water; C2. Preparation of chitosan oligosaccharide solution: Dissolve the chitosan oligosaccharide in deionized water to prepare a chitosan oligosaccharide aqueous solution with a mass fraction of 0.5 to 5.0 wt%; the dissolution process of the chitosan oligosaccharide is carried out at a temperature of 20 to 60°C with mechanical stirring at 300 to 1200 rpm for a stirring time of 10 to 120 min. C3. Grafting reaction: Add the epoxy-silanized attapulgite to the chitosan oligosaccharide aqueous solution, such that the mass ratio of the chitosan oligosaccharide to the original attapulgite in the epoxy-silanized attapulgite is 0.05 to 0.40; adjust the pH of the system to 8.0 to 9.5 using a sodium hydroxide aqueous solution with a concentration of 0.10 to 5.00 mol / L, measure the pH at 25°C, and react for 1.0 to 6.0 h at a temperature of 40 to 60°C and atmospheric pressure. Stirring is performed during the grafting reaction at a stirring speed of 300 to 1200 rpm. C4. Post-treatment: Adjust the pH of the system to 6.0 to 8.0 using a 0.10 to 2.00 mol / L hydrochloric acid aqueous solution. The pH value is measured at 25°C. Filter and wash with deionized water 1 to 5 times, each time using 5 to 30 mL / g of the solid mass. Dry at 60 to 80°C and 0.001 to 0.01 MPa for 8 to 24 hours until constant weight is reached. The criterion for constant weight is that the interval between two consecutive weighings is 2 hours and the mass difference is less than 0.1%. C5. Quality control: The mass gain of the attapulgite-chitosan oligosaccharide composite carrier relative to the epoxy-silanized attapulgite is 5.0 to 25.0 wt%.

[0010] Furthermore, the zeta potential of the composite carrier was determined by the following method: the sample was dispersed in a 1 mmol / L KCl aqueous solution and measured at a temperature of 25°C; the zeta potential was -60 to -20 mV when the pH value was 7.0 to 9.0; and 20 to 60 mV when the pH value was 3.0 to 5.0; the molecular weight of the chitosan oligosaccharide was no greater than 2000 Da (number average molecular weight Mn); when the composite carrier was prepared into an aqueous slurry with a mass fraction of 20 wt%, the viscosity of the aqueous slurry was determined by the following method: at a temperature of 25°C and a shear rate of 100 s⁻¹. -1 The apparent viscosity was determined under the following conditions, wherein the apparent viscosity was 50 to 500 mPa·s.

[0011] Furthermore, the composite carrier is a powder, the powder has a PDI of 0.05 to 0.35, and the powder has a water content of 0 to 8 wt%.

[0012] As a concept of this invention, the present invention employs a three-step sequential modification design of "acid activation - epoxy silane grafting - chitosan oligosaccharide covalent anchoring" mainly to enhance the stable fixation ability of attapulgite carrier for chitosan oligosaccharides and the processing performance of high solids content slurries. The acid activation step selectively dissolves the surface of attapulgite with hydrochloric acid, removing metal ion impurities such as magnesium and aluminum from the octahedral layer, exposing more silanol active sites, providing a sufficient reaction interface for the firm anchoring of the subsequent silane coupling layer. At the same time, the acid activation process can also regulate the rod-shaped morphology and specific surface area of ​​attapulgite, so that it maintains good dispersibility in the particle size range of 0.20 to 2.00 µm. In the epoxy silane grafting step, γ-glycidoxypropyltrimethoxysilane is hydrolyzed under acidic conditions to generate silanol. Subsequently, stable Si-O-Si covalent bonds are formed through the condensation reaction of silanol with silanol on the surface of attapulgite, firmly anchoring the silane coupling layer to the surface of attapulgite. This silane coupling layer not only provides epoxy reaction sites required for subsequent covalent grafting of chitosan oligosaccharides, but also imparts certain hydrophobicity and steric hindrance effects to the surface of attapulgite through its organic segments. This helps to reduce the hydrogen bonding and electrostatic attraction between particles in high-solids slurry, thereby reducing slurry viscosity and inhibiting particle agglomeration. In the chitosan oligosaccharide covalent grafting step, under alkaline conditions, the amino groups on the chitosan oligosaccharide molecular chain nucleophilically attack the terminal epoxy groups of the silane coupling layer, and the epoxy ring opens to form a stable CN covalent bond, achieving permanent anchoring of chitosan oligosaccharide. By precisely controlling the synergistic ratio of silane feed amount (0.005 to 0.10) and chitosan oligosaccharide mass ratio (0.05 to 0.40), the shell thickness can be precisely controlled within the range of 2 to 30 nm. This ensures that the high proportion of chitosan oligosaccharide is introduced to endow the carrier with excellent pH-responsive release, synergistic bioactivity, and surface hydrophilic-hydrophobic balance, while avoiding the surge in slurry viscosity and the decline in spray atomization performance caused by excessive shell thickness. This keeps the apparent viscosity of the 20 wt% slurry within the sprayable window of 50 to 500 mPa·s. At the same time, the covalently linked shell does not detach during spray drying, ensuring batch-to-batch consistency and storage stability of the powder.

[0013] This invention also discloses a method for preparing the above-mentioned attapulgite-chitosan oligosaccharide composite carrier, comprising the following steps: S0. Starting material supply: Attapulgite, acid-activated attapulgite, or epoxy-silanized attapulgite is provided as the starting material; wherein, the acid-activated attapulgite and the epoxy-silanized attapulgite are intermediates, which are obtained by this method or provided directly as raw materials; S1. Acid activation: When the starting material is attapulgite, the attapulgite is mixed with an aqueous hydrochloric acid solution with a concentration of 0.10 to 1.00 mol / L at a mass ratio of 1:5 to 20, and the mixture is mechanically stirred at 300 to 1200 rpm at a temperature of 25 to 60°C and at normal pressure for a reaction time of 1.0 to 6.0 h. The mixture is then filtered and washed with deionized water until the pH of the filtrate is 6.0 to 7.0, and dried to obtain acid-activated attapulgite. S2. Epoxysilane Grafting: When the starting material is attapulgite or acid-activated attapulgite, the acid-activated attapulgite is dispersed in a mixed solvent of ethanol and deionized water at a solid-liquid ratio of 1 g:5 mL to 1 g:50 mL, wherein the volume ratio of ethanol to deionized water is 3:7 to 9:1; the dispersion process is carried out at a temperature of 20 to 40 °C with mechanical stirring at 300 to 1200 rpm for 10 to 60 min; γ-glycidoxypropyltrimethoxysilane is added, with the amount being 0.005 to 0.1% of the mass of the acid-activated attapulgite. 0; The pH of the system was adjusted to 4.0 to 5.5 using an aqueous acetic acid solution with a concentration of 0.10 to 2.00 mol / L. The pH was measured at 25°C. The reaction was carried out at 40 to 70°C and atmospheric pressure for 1.0 to 4.0 h. During the reaction, the mixture was stirred at a speed of 300 to 1200 rpm. The mixture was filtered and washed with ethanol 1 to 5 times, with each wash using 5 to 30 mL / g of the solid mass. The mixture was then washed with deionized water 1 to 5 times, with each wash using 5 to 30 mL / g of the solid mass. The mixture was dried to obtain epoxy-silanized attapulgite. S3. Covalent grafting of chitosan oligosaccharide: Chitosan oligosaccharide is dissolved in deionized water to obtain a chitosan oligosaccharide aqueous solution with a mass fraction of 0.5 to 5.0 wt%; the dissolution process of chitosan oligosaccharide is carried out at a temperature of 20 to 60°C with mechanical stirring at 300 to 1200 rpm for 10 to 120 min; epoxy silanized attapulgite is added so that the mass ratio of chitosan oligosaccharide to the original attapulgite in the epoxy silanized attapulgite is 0.05 to 0.40; the pH value of the system is adjusted to 8.0 to 9.5 using a sodium hydroxide aqueous solution with a concentration of 0.10 to 5.00 mol / L, the pH value is measured at a temperature of 25°C, and the reaction is carried out at a temperature of 40 to 60°C and atmospheric pressure for 1.0 to 6.0 h; the grafting reaction is carried out with stirring at a stirring speed of 300 to 1200 rpm; S4. Neutralization, washing and drying: The pH of the system was adjusted to 6.0 to 8.0 using a hydrochloric acid aqueous solution with a concentration of 0.10 to 2.00 mol / L. The pH was measured at 25°C. The system was filtered and washed with deionized water 1 to 5 times, with each wash using 5 to 30 mL / g of the solid mass. The system was then dried to obtain the attapulgite-chitosan oligosaccharide composite carrier. S5. Powdering: The attapulgite-chitosan oligosaccharide composite carrier obtained in step S4 is dispersed in deionized water to obtain a slurry with a mass fraction of 10 to 30 wt%; the slurry is spray-dried at an inlet air temperature of 120 to 180°C and an outlet air temperature of 60 to 100°C; the spray drying is carried out using a two-fluid nozzle or centrifugal atomization. When using a two-fluid nozzle, the atomization pressure is 0.10 to 0.60 MPa and the feed rate is 1 to 20 mL / min. When using centrifugal atomization, the atomizing disc speed is 5000 to 25000 rpm; the powder is allowed to stand for 1 to 24 hours until constant weight is reached. The criterion for constant weight is that the interval between two consecutive weighings is 2 hours and the mass difference is less than 0.1%. The standing process is carried out in an environment with a temperature of 20 to 30°C, normal pressure, and relative humidity not exceeding 30%; wherein, the PDI of the powder is 0.05 to 0.35.

[0014] Furthermore, during the dispersion process in step S2, the dispersion system is ultrasonically dispersed. The ultrasonic frequency of the ultrasonic dispersion is 20 to 40 kHz, the ultrasonic power is 100 to 500 W, and the ultrasonic time is 5 to 30 min. The ultrasonic dispersion is probe-type ultrasonic or ultrasonic bath ultrasonic. The ultrasonic dispersion mode is continuous or pulsed, and when it is pulsed, the duty cycle is 10% to 90%. During the ultrasonic dispersion process, the system temperature is controlled at 10 to 40°C.

[0015] Furthermore, the drying in steps S1, S2 and S4 is carried out at a temperature of 60 to 80°C and a pressure of 0.001 to 0.01 MPa for 8 to 24 hours until constant weight is achieved. The criterion for constant weight is that the interval between two consecutive weighings is 2 hours and the mass difference is less than 0.1%.

[0016] Furthermore, the moisture content of the powder obtained in step S5 is 0 to 8 wt%.

[0017] Furthermore, the particle size D50 of the attapulgite-chitosan oligosaccharide composite carrier was determined by the following method: the sample was dispersed in deionized water at a mass fraction of 0.01 to 0.10 wt%, and ultrasonically treated at a temperature of 25°C with an ultrasonic frequency of 20 to 40 kHz and an ultrasonic power of 100 to 500 W for 5 to 10 minutes. The volume median particle size was then measured using a laser particle size analyzer. The laser particle size analyzer was calculated using Mie theory, with a dispersion medium refractive index of 1.330, a sample refractive index of 1.50, and an absorption coefficient of 0.01. The average value was taken from three measurements.

[0018] Furthermore, the shell thickness of the covalently linked shell is determined by transmission electron microscopy, with a sample size of no less than 30 particles, and the average value is taken as the shell thickness; the accelerating voltage of the transmission electron microscope is 120 to 200 kV, and the magnification is ×50,000 to ×100,000; during sample preparation, the sample is dispersed in deionized water and dropped onto a copper grid covered with a carbon support film, and observed after negative staining with a 2 wt% phosphotungstic acid solution.

[0019] Furthermore, the water content of the acid-activated attapulgite was determined by drying at 105°C to constant weight.

[0020] Furthermore, in step A2, when preparing the hydrochloric acid aqueous solution, a hydrochloric acid aqueous solution with a concentration of 0.10 to 1.00 mol / L based on HCl is provided.

[0021] Furthermore, the ethanol mentioned in step B1 is anhydrous ethanol with a volume fraction ≥ 99.5 vol.

[0022] Furthermore, the number-average molecular weight Mn of the chitosan oligosaccharide was determined by gel permeation chromatography, and a standard curve was plotted using pullulan polysaccharide standards.

[0023] Furthermore, the PDI of the powder is determined by the following method: the powder is dispersed in deionized water at a mass fraction of 0.01 to 0.10 wt%, and then subjected to ultrasonic treatment at a temperature of 25°C with an ultrasonic frequency of 20 to 40 kHz and an ultrasonic power of 100 to 500 W for 5 to 10 minutes, followed by determination by dynamic light scattering method.

[0024] Furthermore, the moisture content of the powder was determined by drying at 105°C to constant weight.

[0025] Furthermore, the attapulgite-chitosan oligosaccharide composite support exhibits characteristic Si-O-Si absorption peaks in the infrared spectrum at wavenumbers of 1000 to 1150 cm⁻¹, indicating that the silane coupling layer forms silicon-oxygen bonds with the attapulgite.

[0026] Furthermore, after alkali extraction at pH 12, temperature 80°C, and time 2 hours, the desorption rate of chitosan oligosaccharide from the attapulgite-chitosan composite carrier was no higher than 20 wt%, indicating that chitosan oligosaccharide was covalently linked to the silane coupling layer.

[0027] Furthermore, the silicon content in the epoxy-silanized attapulgite was determined by X-ray fluorescence spectroscopy or inductively coupled plasma atomic emission spectrometry.

[0028] Furthermore, the reaction described in step B3 is carried out under nitrogen protection or in open air.

[0029] Furthermore, the grafting reaction described in step C3 is carried out under nitrogen protection or in open air.

[0030] As another aspect of this invention, the process combination of "powder spray drying - low-humidity settling post-treatment" is mainly used to enhance the particle size uniformity, low moisture content, and excellent redispersibility of the attapulgite-chitosan oligosaccharide composite carrier powder. In the spray drying step, the composite carrier is dispersed in deionized water to form a slurry of 10 to 30 wt%. It is then rapidly dried through a two-fluid nozzle or centrifugal atomization at an inlet air temperature of 120 to 180°C and an outlet air temperature of 60 to 100°C. The high-temperature inlet air provides sufficient drying driving force, enabling the slurry droplets to complete moisture evaporation in a very short time. Controlling the outlet air temperature within the range of 60 to 100°C avoids thermal degradation of chitosan oligosaccharides due to excessively high temperatures. At the same time, the rapid drying process inhibits secondary agglomeration between particles, reducing the PDI of the powder to 0.05 to 0.35. In the low-humidity settling post-treatment step, the spray-dried powder is settling in an environment with a temperature of 20 to 30°C and a relative humidity of no more than 30% for 1 to 24 hours until constant weight. This process allows the residual surface adsorbed water and pore water in the powder to slowly evaporate in equilibrium, and the final moisture content is controlled at 0 to 8 wt%. The low moisture content not only improves the storage stability and flowability of the powder, but also avoids interparticle hydrogen bond bridging and agglomeration caused by moisture absorption in the chitosan oligosaccharide hydrophilic layer, ensuring the excellent redispersibility and batch-to-batch consistency of the powder, enabling it to be quickly dispersed in aqueous systems and restored to a particle size range of 0.20 to 2.00 µm.

[0031] In this invention, the silane coupling layer and chitosan oligosaccharide exhibit a significant synergistic effect in the attapulgite composite carrier. The synergistic mechanism between the two in terms of low-viscosity sprayable processability and sustained-release functionality is as follows: The main function of the silane coupling layer is to firmly anchor organosilane molecules to the attapulgite surface through Si-O-Si covalent bonds. Its terminal epoxy groups serve as reaction sites for covalent grafting of chitosan oligosaccharide and also impart certain hydrophobicity and steric hindrance to the attapulgite surface through organic segments, thereby reducing hydrogen bonding and electrostatic attraction between particles in high-solids slurries, which significantly contributes to the low-viscosity performance of the slurry. The main function of chitosan oligosaccharide is to endow the carrier with sustained-release functional properties such as pH-responsive release, synergistic bioactivity, and surface hydrophilicity. The CN covalent bonds formed by the ring-opening reaction of its amino and epoxy groups ensure the permanent anchoring of the shell layer and have a decisive influence on functional stability. In improving the spray processability of low-viscosity slurries, the silane coupling layer, through the hydrophobicity and steric hindrance effect of its organic segments, weakens the end-to-side hydrogen bond bridging between attapulgite rod-shaped particles, reducing the yield stress and apparent viscosity of the slurry. Chitosan oligosaccharides, through covalent anchoring, avoid the desorption and thickening problems associated with physical adsorption. Simultaneously, the flexible conformation of its molecular chains provides additional steric stabilization in high-solids slurries. Together, these two components control the apparent viscosity of a 20wt% slurry within a sprayable window of 50 to 500 mPa·s. In improving sustained-release functionality, the stable chemical anchoring interface provided by the silane coupling layer ensures that chitosan oligosaccharides do not desorb under pH changes and long-term storage conditions, maintaining the functional stability of the carrier. The amino groups of chitosan oligosaccharides are protonated and positively charged under acidic conditions and deprotonated and negatively charged under alkaline conditions, endowing the carrier with pH-responsive release characteristics. Furthermore, the bioactivity of chitosan oligosaccharides synergistically enhances the effects of the loaded active substances. The synergistic effect of the silane coupling layer and chitosan oligosaccharide is also reflected in the precise control of the shell thickness. By optimizing the synergistic ratio of silane feed amount (0.005 to 0.10) and chitosan oligosaccharide mass ratio (0.05 to 0.40), the shell thickness can be controlled within the range of 2 to 30 nm. This ensures a high proportion of chitosan oligosaccharide to achieve excellent functionality while avoiding the surge in slurry viscosity and decline in spray atomization performance caused by excessive shell thickness, reflecting the synergistic design concept of structural control and performance balance. Currently, the understanding of the synergistic mechanism of silane coupling layer and chitosan oligosaccharide in composite carriers mainly focuses on covalent bonding and shell thickness control. Further systematic research is needed on the deeper synergistic mechanism of the two in high-solids slurry rheological behavior, particle evolution kinetics during spray drying, and powder redispersion mechanism.

[0032] Beneficial technical effects Achieving a high-proportion stable introduction and covalent fixation of chitosan oligosaccharides: A silane coupling layer is formed by hydrolysis and condensation of γ-glycidyl etheroxypropyltrimethoxysilane on the surface of attapulgite. Subsequently, a stable CN covalent bond is formed by the ring-opening reaction of epoxy groups with the amino groups of chitosan oligosaccharides, achieving permanent anchoring of chitosan oligosaccharides under conditions of a mass ratio of 0.05 to 0.40. This completely solves the technical bottleneck of easy desorption of chitosan oligosaccharides and poor stability of the functional layer in traditional physical adsorption methods during high solid content processing and spray drying. Alkali extraction experiments show that the desorption rate of chitosan oligosaccharides is no higher than 20 wt%, which is significantly better than the desorption rate of more than 60% of physical adsorption methods.

[0033] Achieving precise control of shell thickness and synergistic optimization of low-viscosity sprayable performance of slurry: By precisely controlling the synergistic ratio of silane feed amount (0.005 to 0.10) and chitosan oligosaccharide mass ratio (0.05 to 0.40), the shell thickness can be precisely controlled within the range of 2 to 30 nm. This ensures that the high proportion of chitosan oligosaccharide is introduced to endow the carrier with excellent functional properties such as pH-responsive release and synergistic bioactivity, while avoiding the problem of slurry viscosity surge caused by excessive shell thickness. This keeps the apparent viscosity of 20 wt% slurry within the sprayable window of 50 to 500 mPa·s, solving the technical problems of difficult shell thickness control and narrow slurry rheological window that cannot meet the requirements of spray atomization in the prior art.

[0034] Effectively suppressing particle bridging and agglomeration in high-solids-content systems and optimizing particle size distribution: The covalently linked silane coupling layer and chitosan oligosaccharide shell provide steric stabilization on the surface of attapulgite rod-shaped particles, weakening end-to-side hydrogen bond bridging and electrostatic attraction between particles. This effectively suppresses particle agglomeration during the preparation of high-solids-content slurries and spray drying, controlling the particle size D50 of the composite carrier within the range of 0.20 to 2.00 µm and reducing the particle size distribution index (PDI) to 0.05 to 0.35. This is significantly better than the wide distribution characteristic of traditional modified attapulgite carriers with a PDI greater than 0.50, ensuring batch-to-batch consistency and functional stability of the carrier material.

[0035] Significantly improves the storage stability and redispersibility of powders: The composite carrier is powdered through spray drying and then subjected to a low-humidity environment for post-treatment to control the moisture content to 0-8 wt%. The low moisture content avoids interparticle hydrogen bond bridging and agglomeration caused by moisture absorption in the hydrophilic layer of chitosan oligosaccharide. At the same time, the covalently linked shell does not desorb or undergo chemical degradation during storage, allowing the powder to quickly disperse and recover to its original particle size range in an aqueous system after long-term storage. The particle size D50 deviation after redispersibility is less than 5%, solving the industry problems of easy moisture absorption and agglomeration, poor redispersibility, and unstable batch-to-batch consistency of traditional modified attapulgite powders.

[0036] Expanding the application scope of attapulgite carriers in the field of controlled release: The composite carrier of this invention has multiple functional characteristics, including low viscosity and spray processability, stable introduction of chitosan oligosaccharides in a high proportion, pH-responsive release, and synergistic bioactivity. This makes it promising for applications in pesticide controlled-release formulations, food active substance encapsulation, and biopharmaceutical controlled-release systems. The pH-responsive characteristics imparted by chitosan oligosaccharides enable selective release of active substances in acidic or alkaline environments. The bioactivity of chitosan oligosaccharides can synergistically enhance the active substances loaded with the carrier, significantly improving the application value and market competitiveness of the carrier material. Attached Figure Description

[0037] Figure 1 This is a comparison of the Fourier transform infrared spectra of the attapulgite-chitosan oligosaccharide composite carriers of Example 1 and Comparative Example 8 of the present invention.

[0038] Figure 2 This is a comparison of the Si 2p high-resolution X-ray photoelectron spectroscopy (XPS) spectra of the attapulgite-chitosan oligosaccharide composite carriers of Embodiment 1, Comparative Example 5, and Comparative Example 8 of the present invention, showing the superimposed curves.

[0039] Figure 3 This is a comparison of the N1s high-resolution X-ray photoelectron spectroscopy (XPS) spectra of the attapulgite-chitosan oligosaccharide composite carriers of Embodiment 1, Comparative Example 5, and Comparative Example 8 of the present invention, showing the superposition of multiple curves.

[0040] Figure 4 This is a superimposed comparison of the laser particle size distribution curves of the attapulgite-chitosan oligosaccharide composite carriers in Embodiment 1, Comparative Example 2, and Comparative Example 5 of the present invention.

[0041] Figure 5 This is a comparison chart of the PDI values ​​of the attapulgite-chitosan oligosaccharide composite carriers measured by dynamic light scattering method in Examples 1, 2, and 5 of this invention.

[0042] Figure 6 This is a comparison of the viscosity-shear rate curves of 20wt% attapulgite-chitosan oligosaccharide composite slurry from Examples 1, 2, and 4 of the present invention, which are superimposed multiple curves. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Example

[0044] This embodiment provides a method for preparing an attapulgite-chitosan oligosaccharide composite carrier, comprising the following steps: S0. Provision of starting materials Attapulgite is provided as the starting material.

[0045] S1. Acid activation Attapulgite was mixed with a 0.50 mol / L hydrochloric acid aqueous solution at a mass ratio of 1:12 and reacted under mechanical stirring at 750 rpm at 45°C and normal pressure for 3.5 h. After the reaction, the mixture was filtered and washed with deionized water until the pH of the filtrate was 6.5. The washed solid was dried at 70°C and 0.005 MPa for 16 h until constant weight was reached. The criterion for constant weight was that the interval between two consecutive weighings was 2 h and the mass difference was less than 0.1%, thus obtaining acid-activated attapulgite. In this example, the water content of the acid-activated attapulgite was 5 wt%, determined by drying at 105°C to constant weight.

[0046] S2. Epoxysilane grafting The acid-activated attapulgite was dispersed in a mixed solvent of ethanol and deionized water at a solid-liquid ratio of 1 g:25 mL. In this embodiment, the volume ratio of ethanol to deionized water was 6:4, wherein the ethanol was anhydrous ethanol with a volume fraction ≥99.5 vol%. The dispersion process was carried out at 30°C with mechanical stirring at 750 rpm for 35 min. γ-glycidoxypropyltrimethoxysilane was added to the dispersion system, with the amount being 0.050 of the mass of the acid-activated attapulgite. The pH of the system was adjusted to 4.8 using a 1.00 mol / L aqueous acetic acid solution, and the pH was measured at 25°C. The reaction was carried out at 55°C and atmospheric pressure for 2.5 h, with stirring at 750 rpm during the reaction. After the reaction, the mixture was filtered and washed three times with ethanol (15 mL / g of solid mass each time), and then washed three times with deionized water (15 mL / g of solid mass each time). The washed solid was dried at 70°C and 0.005 MPa for 16 h until constant weight was achieved. The criterion for constant weight was that the interval between two consecutive weighings was 2 h and the mass difference was less than 0.1%, thus obtaining epoxy-silanized attapulgite. In this embodiment, the mass gain of epoxy-silanized attapulgite relative to acid-activated attapulgite was 2.5 wt%.

[0047] S3. Covalent grafting of chitosan oligosaccharides Chitosan oligosaccharide was dissolved in deionized water to prepare a 2.5 wt% chitosan oligosaccharide aqueous solution. In this embodiment, the dissolution process of chitosan oligosaccharide was carried out at 40°C with mechanical stirring at 750 rpm for 65 min. Epoxysilane-modified attapulgite was added to the chitosan oligosaccharide aqueous solution to achieve a mass ratio of chitosan oligosaccharide to the original attapulgite in the epoxysilane-modified attapulgite of 0.20. The pH of the system was adjusted to 8.8 using a 2.50 mol / L sodium hydroxide aqueous solution, and the pH was measured at 25°C. The reaction was carried out at 50°C and atmospheric pressure for 3.5 h, with stirring at 750 rpm during the grafting reaction.

[0048] S4. Neutralization, washing and drying After the reaction, the pH of the system was adjusted to 7.0 using a 1.00 mol / L hydrochloric acid aqueous solution at 25°C. The solution was filtered and washed three times with deionized water, each time using 15 mL / g of the solid mass. The washed solid was dried at 70°C and 0.005 MPa for 16 h until constant weight was reached. The criterion for constant weight was that the interval between two consecutive weighings was 2 h and the mass difference was less than 0.1%, yielding the attapulgite-chitosan oligosaccharide composite carrier. In this embodiment, the mass gain of the attapulgite-chitosan oligosaccharide composite carrier relative to epoxy-silanized attapulgite was 15.0 wt%.

[0049] S5. Powdering The attapulgite-chitosan oligosaccharide composite carrier obtained in step S4 was dispersed in deionized water to obtain a slurry with a mass fraction of 20 wt%. The slurry was spray-dried at an inlet air temperature of 150°C and an outlet air temperature of 80°C. In this embodiment, the spray drying was performed using a two-fluid nozzle with an atomizing pressure of 0.35 MPa and a feed rate of 10 mL / min. The spray-dried powder was allowed to stand for 12 h until constant weight was achieved. The criterion for constant weight was that the interval between two consecutive weighings was 2 h and the mass difference was less than 0.1%. The standing process was carried out in an environment with a temperature of 25°C, normal pressure, and a relative humidity of 15%.

[0050] Product Characterization The attapulgite-chitosan oligosaccharide composite carrier prepared in this embodiment includes attapulgite and a covalently linked shell layer coating the surface of the attapulgite. The covalently linked shell layer includes a silane coupling layer formed by hydrolysis and condensation of γ-glycidoxypropyltrimethoxysilane, which is connected to the attapulgite through siloxane bonds; and chitosan oligosaccharide, which is covalently connected to the silane coupling layer through C-N bonds formed by ring opening of the epoxy groups on the silane coupling layer. Taking the dry basis mass of attapulgite in the composite carrier as 1, the mass of chitosan oligosaccharide is 0.20. During the preparation of the composite carrier, the feed amount of γ-glycidoxypropyltrimethoxysilane relative to the dry basis mass of attapulgite is 0.050.

[0051] In this embodiment, the particle size D50 of the composite carrier is 1.00 μm. The particle size D50 was determined by the following method: the sample was dispersed in deionized water at a mass fraction of 0.05 wt%, and ultrasonically treated at 25°C with an ultrasonic frequency of 30 kHz and an ultrasonic power of 300 W for 8 min. The volume median particle size was then measured using a laser particle size analyzer. The laser particle size analyzer was calculated using Mie theory, with a refractive index of 1.330 for the dispersion medium, a refractive index of 1.50 for the sample, and an absorption coefficient of 0.01. Three measurements were taken and the average value was calculated.

[0052] In this embodiment, the covalently linked shell thickness was 15 nm. The shell thickness was measured using transmission electron microscopy (TEM), with a sample size of no less than 30 particles, and the average value was taken as the shell thickness. The TEM acceleration voltage was 160 kV, and the magnification was ×75,000. During sample preparation, the sample was dispersed in deionized water and dropped onto a copper grid coated with a carbon support film. After negative staining with a 2 wt% phosphotungstic acid solution, the sample was observed.

[0053] The zeta potential of the composite carrier in this embodiment was determined by the following method: the sample was dispersed in a 1 mmol / L KCl aqueous solution, and the measurement was performed at a temperature of 25°C. The zeta potential was -40 mV when the pH value was 8.0, and 40 mV when the pH value was 4.0.

[0054] In this embodiment, the number-average molecular weight (Mn) of chitosan oligosaccharide was 1200 Da, which was determined by gel permeation chromatography, and a standard curve was plotted using pullulan polysaccharide standard.

[0055] In this embodiment, when the composite carrier is prepared into an aqueous slurry with a mass fraction of 20 wt%, the viscosity of the aqueous slurry is determined by the following method: at a temperature of 25°C and a shear rate of 100 s⁻¹. -1 The apparent viscosity was measured under the following conditions, and the apparent viscosity was 250 mPa·s.

[0056] In this embodiment, the composite carrier is a powder with a PDI of 0.20. The PDI was determined by the following method: the powder was dispersed in deionized water at a mass fraction of 0.05 wt%, and then subjected to ultrasonic treatment at a temperature of 25°C, an ultrasonic frequency of 30 kHz, and an ultrasonic power of 300 W for 8 min. The PDI was then determined by dynamic light scattering method.

[0057] The moisture content of the powder in this embodiment is 4 wt%, which was determined by drying at 105°C to constant weight.

[0058] In this embodiment, the attapulgite-chitosan oligosaccharide composite carrier exhibits an infrared spectrum at a wavenumber of 1070 cm⁻¹. -1 The presence of characteristic Si-O-Si absorption peaks indicates that the silane coupling layer is connected to attapulgite by silicon-oxygen bonds.

[0059] In this embodiment, after alkali extraction of the attapulgite-chitosan oligosaccharide composite carrier at pH 12, temperature 80℃, and time 2 h, the desorption rate of chitosan oligosaccharide was 12 wt%, indicating that chitosan oligosaccharide is connected to the silane coupling layer through covalent bonds.

[0060] Features of Example 1: This example employs a preparation process with moderate temperature and reaction time. Acid activation was performed using 0.50 mol / L hydrochloric acid at 45°C for 3.5 h, epoxy silane grafting at 55°C for 2.5 h, and chitosan oligosaccharide grafting at 50°C for 3.5 h. The silane feed amount was 0.050, and the chitosan oligosaccharide feed amount was 0.20. The resulting composite carrier had a particle size D50 of 1.00 μm, a shell thickness of 15 nm, and a PDI of 0.20, exhibiting good dispersibility and moderate viscosity. This example's process is stable and reliable, suitable for applications requiring a balance between flowability and drug loading performance, such as drug sustained-release formulations, functional coating additives, and water treatment adsorption materials. Example

[0061] This embodiment provides a method for preparing an attapulgite-chitosan oligosaccharide composite carrier, comprising the following steps: S0. Provision of starting materials Attapulgite is provided as the starting material.

[0062] S1. Acid activation Attapulgite was mixed with a 0.30 mol / L hydrochloric acid aqueous solution at a mass ratio of 1:8 and reacted under mechanical stirring at 900 rpm at 35°C and normal pressure for 2.0 h. After the reaction, the mixture was filtered and washed with deionized water until the pH of the filtrate was 6.5. The washed solid was dried at 65°C and 0.003 MPa for 12 h to constant weight. The criterion for constant weight was that the interval between two consecutive weighings was 2 h and the mass difference was less than 0.1%, thus obtaining acid-activated attapulgite. In this example, the water content of the acid-activated attapulgite was 3 wt%, determined by drying at 105°C to constant weight.

[0063] S2. Epoxysilane grafting The acid-activated attapulgite was dispersed in a mixed solvent of ethanol and deionized water at a solid-liquid ratio of 1 g:15 mL. In this embodiment, the volume ratio of ethanol to deionized water was 7:3, wherein the ethanol was anhydrous ethanol with a volume fraction ≥99.5 vol%. In this embodiment, the dispersion process was carried out at 25°C with mechanical stirring at 900 rpm for 20 min.

[0064] During the dispersion process, the dispersion system was ultrasonically dispersed at a frequency of 30 kHz, a power of 300 W, and a duration of 15 min. In this embodiment, the ultrasonic dispersion was performed using a probe-type ultrasonic method in continuous mode, and the system temperature was controlled at 25°C during the ultrasonic dispersion process.

[0065] γ-glycidoxypropyltrimethoxysilane was added to the dispersion system in an amount equal to 0.030% of the mass of acid-activated attapulgite. The pH of the system was adjusted to 4.5 using a 0.50 mol / L aqueous acetic acid solution at 25°C. The reaction was carried out at 50°C and atmospheric pressure for 1.5 h with stirring at 900 rpm. After the reaction, the mixture was filtered and washed twice with ethanol (10 mL / g of solid mass each time), followed by two washes with deionized water (10 mL / g of solid mass each time). The washed solid was dried at 65°C and 0.003 MPa for 12 h until constant weight was reached. Constant weight was determined by a 2-h interval between two consecutive weighings and a mass difference of less than 0.1%, yielding epoxy-silanized attapulgite. In this example, the mass gain of epoxy-silanized attapulgite relative to acid-activated attapulgite was 1.5 wt%.

[0066] S3. Covalent grafting of chitosan oligosaccharides Chitosan oligosaccharide was dissolved in deionized water to prepare a 1.5 wt% aqueous solution. In this embodiment, the dissolution of chitosan oligosaccharide was carried out at 30°C with mechanical stirring at 900 rpm for 40 min. Epoxysilane-modified attapulgite was added to the chitosan oligosaccharide aqueous solution to achieve a mass ratio of chitosan oligosaccharide to the original attapulgite in the epoxysilane-modified attapulgite of 0.15. The pH of the system was adjusted to 8.5 using a 1.50 mol / L sodium hydroxide aqueous solution, and the pH was measured at 25°C. The reaction was carried out at 45°C and atmospheric pressure for 2.0 h, with stirring at 900 rpm during the grafting reaction.

[0067] S4. Neutralization, washing and drying After the reaction, the pH of the system was adjusted to 7.0 using a 0.50 mol / L hydrochloric acid aqueous solution at 25°C. The solution was filtered and washed twice with deionized water, each time using 10 mL / g of the solid mass. The washed solid was dried at 65°C and 0.003 MPa for 12 h until constant weight was reached. The criterion for constant weight was that the interval between two consecutive weighings was 2 h and the mass difference was less than 0.1%, yielding the attapulgite-chitosan oligosaccharide composite carrier. In this embodiment, the mass gain of the attapulgite-chitosan oligosaccharide composite carrier relative to epoxy-silanized attapulgite was 10.0 wt%.

[0068] S5. Powdering The attapulgite-chitosan oligosaccharide composite carrier obtained in step S4 was dispersed in deionized water to obtain a slurry with a mass fraction of 15 wt%. The slurry was spray-dried at an inlet air temperature of 135°C and an outlet air temperature of 70°C. In this embodiment, the spray drying was carried out by centrifugal atomization with a spinning disk speed of 15,000 rpm. The spray-dried powder was allowed to stand for 6 hours until constant weight was reached. The criterion for constant weight was that the interval between two consecutive weighings was 2 hours and the mass difference was less than 0.1%. The standing process was carried out in an environment with a temperature of 25°C, normal pressure, and a relative humidity of 20%.

[0069] Product Characterization The attapulgite-chitosan oligosaccharide composite carrier prepared in this embodiment includes attapulgite and a covalently linked shell layer coating the surface of the attapulgite. The covalently linked shell layer includes a silane coupling layer formed by hydrolysis and condensation of γ-glycidoxypropyltrimethoxysilane, which is connected to the attapulgite through siloxane bonds; and chitosan oligosaccharide, which is covalently connected to the silane coupling layer through C-N bonds formed by ring opening of the epoxy groups on the silane coupling layer. Taking the dry basis mass of attapulgite in the composite carrier as 1, the mass of chitosan oligosaccharide is 0.15, and the feed amount of γ-glycidoxypropyltrimethoxysilane relative to the dry basis of attapulgite is 0.030 during the preparation of the composite carrier.

[0070] In this embodiment, the particle size D50 of the composite carrier is 0.60 μm. The particle size D50 was determined by the following method: the sample was dispersed in deionized water at a mass fraction of 0.05 wt%, and ultrasonically treated at 25°C with an ultrasonic frequency of 30 kHz and an ultrasonic power of 300 W for 8 min. The volumetric median particle size was then measured using a laser particle size analyzer. The laser particle size analyzer was calculated using Mie theory, with a refractive index of 1.330 for the dispersion medium, a refractive index of 1.50 for the sample, and an absorption coefficient of 0.01. Three measurements were taken and the average value was calculated.

[0071] In this embodiment, the covalently linked shell thickness was 8 nm. The shell thickness was measured using transmission electron microscopy (TEM), with a sample size of no less than 30 particles, and the average value was taken as the shell thickness. The TEM acceleration voltage was 160 kV, and the magnification was ×75,000. During sample preparation, the sample was dispersed in deionized water and dropped onto a copper grid coated with a carbon support film. After negative staining with a 2 wt% phosphotungstic acid solution, the sample was observed.

[0072] The zeta potential of the composite carrier in this embodiment was determined by the following method: the sample was dispersed in a 1 mmol / L KCl aqueous solution, and the measurement was performed at a temperature of 25°C. The zeta potential was -35 mV when the pH value was 8.0, and 35 mV when the pH value was 4.0.

[0073] In this embodiment, the number-average molecular weight (Mn) of chitosan oligosaccharide was 800 Da, which was determined by gel permeation chromatography, and a standard curve was plotted using pullulan polysaccharide standard.

[0074] In this embodiment, when the composite carrier is prepared into an aqueous slurry with a mass fraction of 20 wt%, the viscosity of the aqueous slurry is determined by the following method: at a temperature of 25°C and a shear rate of 100 s⁻¹. -1 The apparent viscosity was measured under the following conditions, and the apparent viscosity was 120 mPa·s.

[0075] In this embodiment, the composite carrier is a powder with a PDI of 0.15. The PDI is determined by the following method: the powder is dispersed in deionized water at a mass fraction of 0.05 wt%, and then subjected to ultrasonic treatment at a temperature of 25°C with an ultrasonic frequency of 30 kHz and an ultrasonic power of 300 W for 8 min. The PDI is then determined by dynamic light scattering method.

[0076] The moisture content of the powder in this embodiment is 2 wt%, which was determined by drying at 105°C to constant weight.

[0077] In this embodiment, the attapulgite-chitosan oligosaccharide composite carrier exhibits an infrared spectrum at a wavenumber of 1070 cm⁻¹. -1The presence of characteristic Si-O-Si absorption peaks indicates that the silane coupling layer is connected to attapulgite by silicon-oxygen bonds.

[0078] In this embodiment, after alkali extraction of the attapulgite-chitosan oligosaccharide composite carrier at pH 12, temperature 80℃, and time 2 h, the desorption rate of chitosan oligosaccharide was 8 wt%, indicating that chitosan oligosaccharide is connected to the silane coupling layer through covalent bonds.

[0079] Example 2 Features: This example employs a low-temperature rapid reaction process. Acid activation is carried out at 35°C for 2.0 h, epoxy silane grafting is carried out at 50°C for 1.5 h with ultrasonic dispersion technology, and chitosan oligosaccharide grafting is carried out at 45°C for 2.0 h. The silane feed amount is 0.030, the chitosan oligosaccharide feed amount is 0.15, and the resulting composite carrier has a particle size D50 of 0.60 μm, a shell thickness of 8 nm, and a PDI of 0.15. The product of this example has a small particle size and excellent particle size uniformity, with a low apparent viscosity of 120 mPa·s, exhibiting excellent flow properties. This example is particularly suitable for applications requiring high dispersibility and low viscosity, such as high-solids content coating systems, fine ceramic slurries, inkjet printing inks, and oral immediate-release formulations requiring rapid release. Example

[0080] This embodiment provides a method for preparing an attapulgite-chitosan oligosaccharide composite carrier, comprising the following steps: S0. Provision of starting materials Attapulgite is provided as the starting material.

[0081] S1. Acid activation Attapulgite was mixed with a 0.75 mol / L hydrochloric acid aqueous solution at a mass ratio of 1:16 and reacted under mechanical stirring at 600 rpm at 55°C and normal pressure for 5.0 h. After the reaction, the mixture was filtered and washed with deionized water until the pH of the filtrate was 6.5. The washed solid was dried at 75°C and 0.007 MPa for 20 h until constant weight was reached. The criterion for constant weight was that the interval between two consecutive weighings was 2 h and the mass difference was less than 0.1%, thus obtaining acid-activated attapulgite. In this example, the water content of the acid-activated attapulgite was 7 wt%, determined by drying at 105°C to constant weight.

[0082] S2. Epoxysilane grafting The acid-activated attapulgite was dispersed in a mixed solvent of ethanol and deionized water at a solid-liquid ratio of 1 g:40 mL. In this embodiment, the volume ratio of ethanol to deionized water was 5:5, wherein the ethanol was anhydrous ethanol with a volume fraction ≥99.5 vol%. The dispersion process was carried out at 35°C with mechanical stirring at 600 rpm for 50 min. γ-glycidoxypropyltrimethoxysilane was added to the dispersion system, with the amount being 0.075 of the mass of the acid-activated attapulgite. The pH of the system was adjusted to 5.0 using a 1.50 mol / L aqueous acetic acid solution, and the pH was measured at 25°C. The reaction was carried out at 65°C and atmospheric pressure for 3.5 h, with stirring at 600 rpm during the reaction. After the reaction, the mixture was filtered and washed four times with ethanol (25 mL / g of solid mass each time), and then washed four times with deionized water (25 mL / g of solid mass each time). The washed solid was dried at 75°C and 0.007 MPa for 20 h until constant weight was achieved. The criterion for constant weight was that the interval between two consecutive weighings was 2 h and the mass difference was less than 0.1%, thus obtaining epoxy-silanized attapulgite. In this embodiment, the mass gain of epoxy-silanized attapulgite relative to acid-activated attapulgite was 4.0 wt%.

[0083] S3. Covalent grafting of chitosan oligosaccharides Chitosan oligosaccharide was dissolved in deionized water to prepare a 3.5 wt% aqueous solution. In this embodiment, the dissolution of chitosan oligosaccharide was carried out at 50°C with mechanical stirring at 600 rpm for 90 min. Epoxysilane-modified attapulgite was added to the chitosan oligosaccharide aqueous solution to achieve a mass ratio of chitosan oligosaccharide to the original attapulgite in the epoxysilane-modified attapulgite of 0.30. The pH of the system was adjusted to 9.0 using a 3.50 mol / L sodium hydroxide aqueous solution, and the pH was measured at 25°C. The reaction was carried out at 55°C and atmospheric pressure for 5.0 h, with stirring at 600 rpm during the grafting reaction.

[0084] S4. Neutralization, washing and drying After the reaction, the pH of the system was adjusted to 7.0 using a 1.50 mol / L hydrochloric acid aqueous solution at 25°C. The solution was filtered and washed four times with deionized water, each time using 25 mL / g of the solid mass. The washed solid was dried at 75°C and 0.007 MPa for 20 h until constant weight was reached. Constant weight was determined by an interval of 2 h between two consecutive weighings and a mass difference of less than 0.1%, yielding the attapulgite-chitosan oligosaccharide composite carrier. In this embodiment, the mass gain of the attapulgite-chitosan oligosaccharide composite carrier relative to epoxy-silanized attapulgite was 20.0 wt%.

[0085] S5. Powdering The attapulgite-chitosan oligosaccharide composite carrier obtained in step S4 was dispersed in deionized water to obtain a slurry with a mass fraction of 25 wt%. The slurry was spray-dried at an inlet air temperature of 165°C and an outlet air temperature of 90°C. In this embodiment, the spray drying was performed using a two-fluid nozzle with an atomizing pressure of 0.50 MPa and a feed rate of 15 mL / min. The spray-dried powder was allowed to stand for 18 h until constant weight was achieved. The criterion for constant weight was that the interval between two consecutive weighings was 2 h and the mass difference was less than 0.1%. The standing process was carried out in an environment with a temperature of 25°C, normal pressure, and a relative humidity of 10%.

[0086] Product Characterization The attapulgite-chitosan oligosaccharide composite carrier prepared in this embodiment includes attapulgite and a covalently linked shell layer coating the surface of the attapulgite. The covalently linked shell layer includes a silane coupling layer formed by hydrolysis and condensation of γ-glycidoxypropyltrimethoxysilane, which is connected to the attapulgite through siloxane bonds; and chitosan oligosaccharide, which is covalently connected to the silane coupling layer through C-N bonds formed by ring opening of the epoxy groups on the silane coupling layer. Taking the dry basis mass of attapulgite in the composite carrier as 1, the mass of chitosan oligosaccharide is 0.30. During the preparation of the composite carrier, the feed amount of γ-glycidoxypropyltrimethoxysilane relative to the dry basis mass of attapulgite is 0.075.

[0087] In this embodiment, the particle size D50 of the composite carrier is 1.50 μm. The particle size D50 was determined by the following method: the sample was dispersed in deionized water at a mass fraction of 0.05 wt%, and ultrasonically treated at 25°C with an ultrasonic frequency of 30 kHz and an ultrasonic power of 300 W for 8 min. The volume median particle size was then measured using a laser particle size analyzer. The laser particle size analyzer was calculated using Mie theory, with a refractive index of 1.330 for the dispersion medium, a refractive index of 1.50 for the sample, and an absorption coefficient of 0.01. Three measurements were taken and the average value was calculated.

[0088] In this embodiment, the covalently linked shell thickness was 22 nm. The shell thickness was measured using transmission electron microscopy (TEM), with a sample size of no less than 30 particles, and the average value was taken as the shell thickness. The TEM acceleration voltage was 160 kV, and the magnification was ×75,000. During sample preparation, the sample was dispersed in deionized water and dropped onto a copper grid coated with a carbon support film. After negative staining with a 2 wt% phosphotungstic acid solution, the sample was observed.

[0089] The zeta potential of the composite carrier in this embodiment was determined by the following method: the sample was dispersed in a 1 mmol / L KCl aqueous solution, and the measurement was performed at a temperature of 25°C. The zeta potential was -50 mV when the pH value was 8.0, and 50 mV when the pH value was 4.0.

[0090] In this embodiment, the number-average molecular weight (Mn) of chitosan oligosaccharide was 1600 Da, which was determined by gel permeation chromatography, and a standard curve was plotted using pullulan polysaccharide standard.

[0091] In this embodiment, when the composite carrier is prepared into an aqueous slurry with a mass fraction of 20 wt%, the viscosity of the aqueous slurry is determined by the following method: at a temperature of 25°C and a shear rate of 100 s⁻¹. -1 The apparent viscosity was measured under the specified conditions and was 380 mPa·s.

[0092] In this embodiment, the composite carrier is a powder with a PDI of 0.28. The PDI was determined by the following method: the powder was dispersed in deionized water at a mass fraction of 0.05 wt%, and then subjected to ultrasonic treatment at a temperature of 25°C with an ultrasonic frequency of 30 kHz and an ultrasonic power of 300 W for 8 min. The PDI was then determined by dynamic light scattering method.

[0093] The moisture content of the powder in this embodiment is 6 wt%, which was determined by drying at 105°C to constant weight.

[0094] In this embodiment, the attapulgite-chitosan oligosaccharide composite carrier exhibits an infrared spectrum at a wavenumber of 1070 cm⁻¹. -1 The presence of characteristic Si-O-Si absorption peaks indicates that the silane coupling layer is connected to attapulgite by silicon-oxygen bonds.

[0095] In this embodiment, after alkali extraction of the attapulgite-chitosan oligosaccharide composite carrier at pH 12, temperature 80℃, and time 2 h, the desorption rate of chitosan oligosaccharide was 15 wt%, indicating that chitosan oligosaccharide is connected to the silane coupling layer through covalent bonds.

[0096] Example 3 Features: This example employs a high-temperature, high-reaction process. Acid activation is performed using 0.75 mol / L hydrochloric acid at 55°C for 5.0 h. Epoxy silane grafting is performed at 65°C for 3.5 h, and chitosan oligosaccharide grafting is performed at 55°C for 5.0 h. The silane feed amount is 0.075, and the chitosan oligosaccharide feed amount is 0.30. The resulting composite carrier has a particle size D50 of 1.50 μm, a shell thickness of 22 nm, and a PDI of 0.28. The product of this example exhibits a large particle size and a thick shell, a high apparent viscosity of 380 mPa·s, a high chitosan oligosaccharide grafting amount, and a large absolute value of zeta potential, demonstrating excellent surface charge properties and drug loading capacity. This example is particularly suitable for applications requiring high drug loading and sustained-release performance, such as long-acting sustained-release drug carriers, heavy metal ion adsorbents, antibacterial coating materials, and biomedical tissue engineering scaffolds. Example

[0097] This embodiment provides a method for preparing an attapulgite-chitosan oligosaccharide composite carrier, comprising the following steps: S0. Provision of starting materials Attapulgite is provided as the starting material.

[0098] S1. Acid activation Attapulgite was mixed with a 0.90 mol / L hydrochloric acid aqueous solution at a mass ratio of 1:18 and reacted under mechanical stirring at 1000 rpm at 30°C and normal pressure for 1.5 h. After the reaction, the mixture was filtered and washed with deionized water until the pH of the filtrate was 6.8. The washed solid was dried at 78°C and 0.009 MPa for 10 h to constant weight. The criterion for constant weight was that the interval between two consecutive weighings was 2 h and the mass difference was less than 0.1%, thus obtaining acid-activated attapulgite. In this example, the water content of the acid-activated attapulgite was 1 wt%, determined by drying at 105°C to constant weight.

[0099] S2. Epoxysilane grafting The acid-activated attapulgite was dispersed in a mixed solvent of ethanol and deionized water at a solid-liquid ratio of 1 g:45 mL. In this embodiment, the volume ratio of ethanol to deionized water was 8:2, wherein the ethanol was anhydrous ethanol with a volume fraction ≥99.5 vol%. The dispersion process was carried out at 22°C with mechanical stirring at 1000 rpm for 15 min. γ-glycidoxypropyltrimethoxysilane was added to the dispersion system, with the amount being 0.088 of the mass of the acid-activated attapulgite. The pH of the system was adjusted to 4.2 using a 0.20 mol / L aqueous acetic acid solution, and the pH was measured at 25°C. The reaction was carried out at 68°C and atmospheric pressure for 1.2 h, with stirring at 1000 rpm during the reaction. After the reaction, the mixture was filtered and washed five times with ethanol (8 mL / g of solid mass each time), and then washed five times with deionized water (8 mL / g of solid mass each time). The washed solid was dried at 78°C and 0.009 MPa for 10 h until constant weight was achieved. The criterion for constant weight was that the interval between two consecutive weighings was 2 h and the mass difference was less than 0.1%, thus obtaining epoxy-silanized attapulgite. In this embodiment, the mass gain of epoxy-silanized attapulgite relative to acid-activated attapulgite was 4.5 wt%.

[0100] S3. Covalent grafting of chitosan oligosaccharides Chitosan oligosaccharide was dissolved in deionized water to prepare a 0.8 wt% aqueous solution. In this embodiment, the dissolution process was carried out at 55°C with mechanical stirring at 1000 rpm for 100 min. Before adding epoxy-silanized attapulgite to the aqueous solution, the solution was ultrasonically dispersed at a frequency of 38 kHz, a power of 450 W, and a duration of 8 min. In this embodiment, ultrasonic dispersion was performed in an ultrasonic bath using a pulsed dispersion mode with a duty cycle of 70%. The system temperature was controlled at 15°C during the ultrasonic dispersion process.

[0101] Epoxysilane-modified attapulgite was added to the ultrasonically treated chitosan oligosaccharide aqueous solution to achieve a mass ratio of chitosan oligosaccharide to the original attapulgite in the epoxysilane-modified attapulgite of 0.08. The pH of the system was adjusted to 9.3 using a 4.50 mol / L sodium hydroxide aqueous solution, and the pH was measured at 25℃. The reaction was carried out at 42℃ and atmospheric pressure for 5.5 h, with stirring at 1000 rpm during the grafting reaction.

[0102] S4. Neutralization, washing and drying After the reaction, the pH of the system was adjusted to 6.2 using a 1.80 mol / L hydrochloric acid aqueous solution at 25°C. The solution was filtered and washed five times with deionized water, each time using 8 mL / g of the solid mass. The washed solid was dried at 78°C and 0.009 MPa for 10 h until constant weight was reached. Constant weight was determined by a 2-h interval between two consecutive weighings and a mass difference of less than 0.1%, yielding the attapulgite-chitosan oligosaccharide composite carrier. In this embodiment, the mass gain of the attapulgite-chitosan oligosaccharide composite carrier relative to epoxy-silanized attapulgite was 6.5 wt%.

[0103] S5. Powdering The attapulgite-chitosan oligosaccharide composite carrier obtained in step S4 was dispersed in deionized water to obtain a slurry with a mass fraction of 12 wt%. The slurry was spray-dried at an inlet air temperature of 175°C and an outlet air temperature of 95°C. In this embodiment, the spray drying was carried out by centrifugal atomization with a spinning disk speed of 22,000 rpm. The spray-dried powder was allowed to stand for 2 hours until constant weight was reached. The criterion for constant weight was that the interval between two consecutive weighings was 2 hours and the mass difference was less than 0.1%. The standing process was carried out in an environment with a temperature of 28°C, normal pressure, and a relative humidity of 25%.

[0104] Product Characterization The attapulgite-chitosan oligosaccharide composite carrier prepared in this embodiment includes attapulgite and a covalently linked shell layer coating the surface of the attapulgite. The covalently linked shell layer includes a silane coupling layer formed by hydrolysis and condensation of γ-glycidoxypropyltrimethoxysilane, which is connected to the attapulgite through siloxane bonds; and chitosan oligosaccharide, which is covalently connected to the silane coupling layer through C-N bonds formed by ring opening of the epoxy groups on the silane coupling layer. Taking the dry basis mass of attapulgite in the composite carrier as 1, the mass of chitosan oligosaccharide is 0.08. When preparing the composite carrier, the feed amount of γ-glycidoxypropyltrimethoxysilane relative to the dry basis mass of attapulgite is 0.088.

[0105] The particle size D50 of the composite carrier in this embodiment is 1.80 μm. The particle size D50 was determined by the following method: the sample was dispersed in deionized water at a mass fraction of 0.05 wt%, and ultrasonically treated at 25°C with an ultrasonic frequency of 30 kHz and an ultrasonic power of 300 W for 8 min. The volume median particle size was then measured using a laser particle size analyzer. The laser particle size analyzer was calculated using Mie theory, with a refractive index of 1.330 for the dispersion medium, a refractive index of 1.50 for the sample, and an absorption coefficient of 0.01. Three measurements were taken and the average value was calculated.

[0106] In this embodiment, the covalently linked shell thickness was 5 nm. The shell thickness was measured using transmission electron microscopy (TEM), with a sample size of no less than 30 particles, and the average value was taken as the shell thickness. The TEM acceleration voltage was 160 kV, and the magnification was ×75,000. During sample preparation, the sample was dispersed in deionized water and dropped onto a copper grid coated with a carbon support film. After negative staining with a 2 wt% phosphotungstic acid solution, the sample was observed.

[0107] The zeta potential of the composite carrier in this embodiment was determined by the following method: the sample was dispersed in a 1 mmol / L KCl aqueous solution, and the measurement was performed at a temperature of 25°C. The zeta potential was -25 mV when the pH value was 8.0, and 25 mV when the pH value was 4.0.

[0108] In this embodiment, the number-average molecular weight (Mn) of chitosan oligosaccharide was 500 Da, which was determined by gel permeation chromatography, and a standard curve was plotted using pullulan polysaccharide standard.

[0109] In this embodiment, when the composite carrier is prepared into an aqueous slurry with a mass fraction of 20 wt%, the viscosity of the aqueous slurry is determined by the following method: at a temperature of 25°C and a shear rate of 100 s⁻¹. -1 The apparent viscosity was measured under the following conditions, and the apparent viscosity was 80 mPa·s.

[0110] In this embodiment, the composite carrier is a powder with a PDI of 0.08. The PDI was determined by the following method: the powder was dispersed in deionized water at a mass fraction of 0.05 wt%, and then subjected to ultrasonic treatment at a temperature of 25°C, an ultrasonic frequency of 30 kHz, and an ultrasonic power of 300 W for 8 min. The PDI was then determined by dynamic light scattering method.

[0111] The moisture content of the powder in this embodiment is 7 wt%, which was determined by drying at 105°C to constant weight.

[0112] In this embodiment, the attapulgite-chitosan oligosaccharide composite carrier exhibits an infrared spectrum at a wavenumber of 1070 cm⁻¹. -1 The presence of characteristic Si-O-Si absorption peaks indicates that the silane coupling layer is connected to attapulgite by silicon-oxygen bonds.

[0113] In this embodiment, after alkali extraction of the attapulgite-chitosan oligosaccharide composite carrier at pH 12, temperature 80℃, and time 2 h, the desorption rate of chitosan oligosaccharide was 6 wt%, indicating that chitosan oligosaccharide is connected to the silane coupling layer through covalent bonds.

[0114] Example 4 Features: This example employs multi-parameter boundary region process conditions. Acid activation involves a short reaction of 0.90 mol / L hydrochloric acid at 30°C for 1.5 h. Epoxy silane grafting is carried out rapidly at 68°C for 1.2 h with a silane feed amount of 0.088. Chitosan oligosaccharide grafting involves a long reaction of a 0.8 wt% low-concentration solution at 42°C for 5.5 h with a chitosan oligosaccharide feed amount of 0.08. The resulting composite carrier has a particle size D50 of 1.80 μm, a shell thickness of 5 nm, and a PDI of 0.08, exhibiting excellent particle size uniformity. The product of this example features a relatively large particle size and a thin shell, a low apparent viscosity of 80 mPa·s, and a small chitosan oligosaccharide molecular weight of 500 Da, demonstrating a unique combination of properties. This embodiment is particularly suitable for applications requiring large particle carriers and low chitosan oligosaccharide loading, such as rheology modifiers for architectural coatings, retention aids for paper fillings, thickeners for oil drilling fluids, and slow-release carriers for pesticides.

[0115] Comparative Example 1: Basically the same as Example 1, except that the mass ratio of chitosan oligosaccharide to attapulgite is 0.03, and the amounts of other components and preparation conditions remain unchanged.

[0116] Comparative Example 2: Basically the same as Example 1, except that the mass ratio of chitosan oligosaccharide to attapulgite is 0.45, and the amounts of other components and preparation conditions remain unchanged.

[0117] Comparative Example 3: Basically the same as Example 1, except that the amount of γ-glycidoxypropyltrimethoxysilane relative to the dry basis of attapulgite is 0.003, while the amounts of other components and preparation conditions remain unchanged.

[0118] Comparative Example 4: Basically the same as Example 1, except that the amount of γ-glycidoxypropyltrimethoxysilane relative to the dry basis of attapulgite is 0.12, while the amounts of other components and preparation conditions remain unchanged.

[0119] Comparative Example 5: Basically the same as Example 1, except that no acid activation treatment was performed, and untreated attapulgite was directly used for epoxy silane grafting, while other conditions remained unchanged.

[0120] Comparative Example 6: Basically the same as Example 1, except that the pH value of the chitosan oligosaccharide grafting reaction was adjusted to 6.5, while other conditions remained unchanged.

[0121] Comparative Example 7: Basically the same as Example 1, except that the temperature of the chitosan oligosaccharide grafting reaction was 25°C, while other conditions remained unchanged.

[0122] Comparative Example 8: It is basically the same as Example 1, except that the chitosan oligosaccharide is introduced by physical adsorption rather than covalent grafting. Specifically, the chitosan oligosaccharide solution is mixed with acid-activated attapulgite and then dried directly, omitting the epoxy silane grafting step, while other conditions remain unchanged.

[0123] Performance testing: The test subject was an aqueous slurry based on an attapulgite-chitosan oligosaccharide composite carrier. The purpose of the test was to evaluate the rheological properties of the composite carrier under high solids content conditions and to verify its low-viscosity sprayability. The test principle involved using a rotational rheometer to measure the apparent viscosity at different shear rates, and then using the viscosity-shear rate curve to determine the slurry's flow behavior and sprayability. The experimental method involved preparing a slurry by dispersing the composite carrier at 20 wt% in deionized water, and measuring the apparent viscosity using a rotational rheometer at 25°C. The shear rate range during the measurement was 1 to 1000 s⁻¹. -1 Viscosity values ​​were recorded 30 seconds after each shear rate point stabilized, with a shear rate of 100 s⁻¹ selected. -1 The viscosity value is used as the apparent viscosity characteristic parameter. The standard reference is GB / T 9751 or similar rheological testing standards. Key parameters include test temperature 25±0.5℃, solid content 20±0.2 wt%, and shear rate 100 s⁻¹. -1 Data processing involved performing three parallel tests on each sample, calculating the mean ± standard deviation, and plotting the viscosity-shear rate curve.

[0124] The test subject was attapulgite-chitosan oligosaccharide composite carrier powder. The purpose of the test was to evaluate the particle size distribution and uniformity of the composite carrier and to verify the particle size control effect after spray drying. The test principle was to use a laser particle size analyzer based on Mie scattering theory to determine the volume median particle size (D50) and particle size distribution index (PDI) to characterize particle size and distribution uniformity. The experimental method involved dispersing the sample at 0.05 wt% in deionized water and ultrasonically treating it at 25℃ for 8 minutes at a frequency of 30 kHz and a power of 300 W. The laser particle size analyzer was then used to measure the particle size. The instrument parameters were set as follows: dispersion medium refractive index 1.330, sample refractive index 1.50, absorption coefficient 0.01. D10, D50, and D90 values ​​were measured, and PDI was calculated. Key parameters included test temperature 25℃, ultrasonic time 8 minutes, and sample concentration 0.05 wt%. The data processing method is to measure each sample three times and take the average value ± standard deviation. The PDI is calculated according to the formula (D90-D10) / (2×D50).

[0125] The test subject was an attapulgite-chitosan oligosaccharide composite carrier. The purpose of the test was to verify the stability of the chitosan oligosaccharide linked to the silane coupling layer via covalent bonds. The test principle involved treating the composite carrier under harsh conditions using an alkaline extraction method. The stability of the covalent bond was assessed by measuring the desorption rate of the chitosan oligosaccharide. The desorption rate of the covalently linked chitosan oligosaccharide should be significantly lower than that of the physically adsorbed one. The experimental method involved placing the composite carrier sample in a sodium hydroxide aqueous solution at pH 12 and treating it at 80℃ for 2 hours. The solid-liquid ratio was 1g:50mL. After treatment, the solid and filtrate were separated by filtration. The solid was washed with deionized water until neutral and then dried. The nitrogen content of the samples before and after treatment was determined using an elemental analyzer, and the chitosan oligosaccharide desorption rate was calculated based on the change in nitrogen content. The standard followed the reference material surface modification stability test method. Key parameters included pH 12, temperature 80℃, and treatment time of 2 hours. Data processing was performed as follows: desorption rate = (N% before treatment - N% after treatment) / N% before treatment × 100%. Each sample was tested in triplicate, and the average value ± standard deviation was taken.

[0126] The test subject was an attapulgite-chitosan oligosaccharide composite carrier. The purpose of the test was to determine the zeta potential of the composite carrier and evaluate its surface charge performance and dispersion stability. The test principle involved measuring the electrophoretic mobility of particles under an electric field using electrophoretic light scattering, and calculating the zeta potential using the Smoluchowski equation to characterize the particle surface charge density and electrostatic stability. The experimental method involved dispersing the sample in a 1 mmol / L KCl aqueous solution to prepare a dilute suspension. The zeta potential was measured using a Zetasizer nanoparticle size and potential analyzer at 25℃, with measurements taken at pH values ​​of 3.0, 5.0, 7.0, and 9.0. The pH value was adjusted using hydrochloric acid or sodium hydroxide solution. Key parameters included a test temperature of 25℃, a KCl concentration of 1 mmol / L, and a pH range of 3.0–9.0. Data processing involved performing five parallel tests at each pH value, automatically calculating the mean ± standard deviation, and plotting the zeta potential-pH curve.

[0127] The test subject was attapulgite-chitosan oligosaccharide composite carrier spray-dried powder. The purpose of the test was to evaluate the redispersibility of the powder and verify its resistance to moisture absorption and agglomeration after spray drying. The test principle was to evaluate the redispersibility and anti-agglomeration performance of the powder by measuring the deviation rate between the redispersed particle size in water and the particle size of the freshly prepared slurry. The experimental method involved placing the spray-dried powder at 25℃ and 60% relative humidity for 30 days. Powder samples before and after redispersing were then redispersed in deionized water at a mass fraction of 20 wt%. After ultrasonic treatment at 25℃ for 8 minutes, the D50 value was measured using a laser particle size analyzer. The particle size growth rate was calculated as (D50 after redispersing - D50 before redispersing) / D50 before redispersing × 100%. The standard referenced the powder dispersibility test method. Key parameters included the storage conditions of 25℃ / 60% relative humidity, the storage time of 30 days, and the redispersibility concentration of 20 wt%. Data processing was performed on each sample in three parallel tests, and the average value ± standard deviation was taken. A particle size growth rate of <10% was considered to indicate good redispersibility.

[0128] The test subject was an attapulgite-chitosan oligosaccharide composite carrier. The purpose of the test was to determine the shell thickness of the covalently linked shell layers and verify the controllability of the shell thickness. The test principle involved directly observing the core-shell structure of the composite carrier using a transmission electron microscope (TEM) and measuring the shell thickness using image analysis software. The experimental method involved dispersing the sample in deionized water and dropping it onto a copper grid coated with a carbon support film. After negative staining with a 2 wt% phosphotungstic acid solution, the sample was observed under a TEM with an accelerating voltage of 160 kV and a magnification of 75000. At least 30 particles were randomly selected, and the shell thickness of each particle was measured using ImageJ software. The average value was taken as the characteristic value of the shell thickness. The standard referenced the morphology characterization method for nanomaterials. Key parameters included an accelerating voltage of 160 kV, a magnification of 75000, and a sample size of ≥30. Data processing involved statistically analyzing the shell thickness of at least 30 particles and calculating the mean ± standard deviation.

[0129] Figure 1 This is a multi-curve overlay plot of Fourier transform infrared spectra. The characterization method was Fourier transform infrared spectroscopy, and the samples were Example 1 and Comparative Example 8. The fixed parameters were a test range covering wavenumbers from 1000 to 1150 cm⁻¹. -1 And 1650cm -1 The same spectral acquisition and normalization methods were used nearby, with the parameter change being the surface connectivity of the sample from covalently grafted in Example 1 to physically adsorbed in Comparative Example 8. Example 1 was measured at 1000 to 1150 cm⁻¹. -1 A more distinct Si-O-Si characteristic absorption band appears within the range, and at 1650 cm⁻¹... -1The difference in peak position and spectral shape compared to Comparative Example 8 indicates that there is a silane coupling layer on the surface of attapulgite forming a network of silicon-oxygen bonds and further chemically connecting with chitosan oligosaccharides. This results in a more stable and structurally consistent characteristic signal compared to the physically adsorbed sample, proving that the construction of the silane coupling layer and the subsequent reaction pathway are valid.

[0130] Figure 2 This is a multi-curve overlay of high-resolution Si 2p spectra in X-ray photoelectron spectroscopy (XPS). The characterization method was high-resolution Si 2p scanning using XPS, with samples being Example 1, Comparative Example 5, and Comparative Example 8. Fixed parameters included a Si 2p binding energy scan range of approximately 101 to 104 eV, employing the same energy step and background subtraction strategy. Variations included the pretreatment steps and connection methods: acid activation followed by epoxy silane grafting and chitosan oligosaccharide covalent grafting in Example 1; no acid activation conditions in Comparative Example 5; and physical adsorption conditions in Comparative Example 8. Example 1 exhibited a more stable peak shape and binding energy position in the Si 2p region, more consistent with the siloxane bond environment. Comparative Example 5 showed a relatively weaker peak shape and decreased consistency, while Comparative Example 8 lacked enhancement features related to the silane coupling layer. This indicates that acid activation helps form a more reliable siloxane bond anchoring interface and improves the degree of silane layer construction, thereby supporting the subsequent covalent connection and demonstrating the necessity and effectiveness of acid activation and silane coupling layer construction.

[0131] Figure 3 This is a multi-curve overlay of high-resolution N 1s X-ray photoelectron spectroscopy (XPS). The characterization method was high-resolution N 1s XPS scanning, and the samples were Example 1, Comparative Example 5, and Comparative Example 8. The N 1s binding energy scanning range was fixed at approximately 399 to 401 eV, and the same spectral processing procedure was used. The parameter change was that the nitrogen group introduction method of the samples changed from covalent grafting in Example 1 to physical adsorption in Comparative Example 8, and Comparative Example 5 was set as a control lacking acid activation. Example 1 showed peak characteristics in the 399 to 401 eV range that better matched the distribution of nitrogen chemical states after covalent bonding, and the peak composition was more concentrated compared to Comparative Example 8. The characteristics of Comparative Example 5 were relatively weakened and showed a trend of insufficient bonding. This indicates that the nitrogen groups of chitosan oligosaccharides in Example 1 existed in a more stable chemical state and chemically bonded to the coupling layer, making them less likely to exhibit free or reversible state characteristics compared to the physically adsorbed samples. This proves that the CN bond formation pathway is consistent and reproducible.

[0132] Figure 4The image shows a superposition of the particle size distribution curves from a laser particle size analyzer and the particle size distribution curves from the PDI (Potential Intensity Dispersion Index). The characterization method involved testing the particle size distribution using a laser particle size analyzer and outputting the intensity distribution curve. The samples were Example 1, Comparative Example 2, and Comparative Example 5. Fixed parameters included an aqueous dispersion medium, the same ultrasonic dispersion conditions and particle size calculation model, and measurements taken at the same temperature. Variations included the amount of chitosan oligosaccharide used and the pretreatment steps corresponding to the optimized formulation of Example 1, the higher amount of chitosan oligosaccharide in Comparative Example 2, and the absence of acid activation in Comparative Example 5. Example 1 showed a more concentrated particle size distribution and a weaker long tail. Comparative Example 2 showed significant widening and increased contribution from the high-particle-size side, while Comparative Example 5 exhibited a widening distribution trend. This indicates that excessive chitosan oligosaccharide or insufficient acid activation can induce bridging aggregation and distribution deterioration. The optimized process can suppress aggregation and form a more uniform dispersion system, demonstrating the rationality of the technical path to achieve a PDI of less than 0.35 and further optimization towards lower levels.

[0133] Figure 5 shows a comparison of PDI values ​​measured by dynamic light scattering. The characterization method was dynamic light scattering PDI determination, and the samples were Example 1, Comparative Example 2, and Comparative Example 5. Fixed parameters were obtained using the same dispersion and testing conditions, with fluctuations characterized by the mean and standard deviation of repeated measurements. Variable parameters were the amount of chitosan oligosaccharide used and whether the acid activation step was performed. The PDI of Example 1 (0.20±0.02) was significantly lower than that of Comparative Example 2 (0.38±0.04) and Comparative Example 5 (0.32±0.03). This indicates that excessive chitosan oligosaccharide usage significantly expands the particle size distribution and reduces system homogeneity. Simultaneously, lack of acid activation weakens the interface construction effect and causes a wider distribution. Optimized conditions achieve a narrower particle size distribution and higher batch-to-batch consistency, demonstrating the necessity of process window setting and proportion control.

[0134] Figure 6 This is a comparison of multiple curves superimposed on the viscosity-shear rate rheological profiles. The characterization method was rotational rheology determination of the apparent viscosity of a 20 wt% slurry at different shear rates. The samples were Example 1, Comparative Example 2, and Comparative Example 4. Fixed parameters were: slurry solid content 20 wt%, test temperature 25°C, and shear rates ranging from 1 to 1000 s. -1 And in 100s -1 Viscosity was used as a key comparison point. The varying parameters were the chitosan oligosaccharide and silane coupling agent amounts corresponding to the optimized ratios in Example 1, the higher chitosan oligosaccharide amount in Comparative Example 2, and the higher silane coupling agent amount in Comparative Example 4. Example 1 showed a viscosity of 100s. -1The viscosity of 250±15 mPa·s is significantly lower than that of Comparative Example 2 (520±30 mPa·s) and Comparative Example 4 (450±25 mPa·s), and the curve is in the lower viscosity range overall. This indicates that exceeding the range will cause the viscosity of the system to increase significantly and compress the processable window. The optimized formulation can still maintain a lower viscosity and has better atomization and processing adaptability under high solid content conditions, which proves that a low viscosity processing window can be obtained through parameter synergistic optimization.

[0135] Table 1 Performance Comparison Summary Table

[0136] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that any equivalent structural transformations made under the concept of the present invention and using the contents of the specification and drawings of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. An attapulgite-chitosan oligosaccharide composite carrier, characterized in that, include: Attapulgite, and a covalently bonded shell covering the surface of the attapulgite; The covalently linked shell layer includes: a silane coupling layer formed by hydrolysis and condensation of γ-glycidoxypropyltrimethoxysilane, wherein the silane coupling layer is connected to the attapulgite through siloxane bonds; and chitosan oligosaccharide, wherein the chitosan oligosaccharide is covalently connected to the silane coupling layer through C–N bonds formed by ring opening of the epoxy groups on the silane coupling layer. Furthermore, with the dry basis mass of attapulgite in the composite carrier being 1, the mass of the chitosan oligosaccharide is 0.05 to 0.40, and when preparing the composite carrier, the amount of γ-glycidoxypropyltrimethoxysilane relative to the dry basis of the attapulgite is 0.005 to 0.

10. The composite carrier has a particle size D50 of 0.20 to 2.00 µm, and the covalently linked shell has a shell thickness of 2 to 30 nm.

2. The attapulgite-chitosan oligosaccharide composite carrier according to claim 1, characterized in that, The attapulgite is acid-activated attapulgite, which is prepared by the following steps: A1. Raw material preparation: Provide attapulgite, hydrochloric acid and deionized water; A2. Preparation of hydrochloric acid aqueous solution: Add the hydrochloric acid to the deionized water to prepare a hydrochloric acid aqueous solution with a concentration of 0.10 to 1.00 mol / L; A3. Acid activation: The attapulgite and the hydrochloric acid aqueous solution are mixed at a mass ratio of 1:5 to 20, and the mixture is mechanically stirred at 300 to 1200 rpm at a temperature of 25 to 60°C and at normal pressure for a reaction time of 1.0 to 6.0 h. A4. Post-treatment: Filter and wash with deionized water until the pH of the filtrate is 6.0 to 7.0; dry at a temperature of 60 to 80°C and a pressure of 0.001 to 0.01 MPa for 8 to 24 hours until constant weight is reached. The criterion for constant weight is that the interval between two consecutive weighings is 2 hours and the mass difference is less than 0.1%. A5. Quality control: The water content of the acid-activated attapulgite is 0 to 10 wt%.

3. The attapulgite-chitosan oligosaccharide composite carrier according to claim 1, characterized in that, The attapulgite is epoxy-silanized attapulgite, which is prepared through the following steps: B1. Raw material preparation: Provide acid-activated attapulgite, γ-glycidyl etheroxypropyltrimethoxysilane, ethanol, acetic acid and deionized water; B2. Dispersion: The acid-activated attapulgite is dispersed in a mixed solvent of ethanol and deionized water at a solid-liquid ratio of 1g:5mL to 1g:50mL, wherein the volume ratio of ethanol to deionized water is 3:7 to 9:1; the dispersion process is carried out at a temperature of 20 to 40°C with mechanical stirring at 300 to 1200 rpm for 10 to 60 minutes. B3. Hydrolysis-condensation and grafting: Add the γ-glycidyl etheroxypropyltrimethoxysilane to the dispersion system, with the amount being 0.005 to 0.10 of the mass of the acid-activated attapulgite; adjust the pH of the system to 4.0 to 5.5 using an aqueous acetic acid solution with a concentration of 0.10 to 2.00 mol / L, and measure the pH at 25°C. React at 40 to 70°C and atmospheric pressure for 1.0 to 4.0 h, with stirring during the reaction at a speed of 300 to 1200 rpm; B4. Post-treatment: Filter and wash with ethanol 1 to 5 times, each time using 5 to 30 mL / g of solid mass; then wash with deionized water 1 to 5 times, each time using 5 to 30 mL / g of solid mass; dry at a temperature of 60 to 80°C and a pressure of 0.001 to 0.01 MPa for 8 to 24 hours until constant weight is reached. The criterion for constant weight is that the interval between two consecutive weighings is 2 hours and the mass difference is less than 0.1%. B5. Quality control: The mass gain of the epoxy-silanized attapulgite relative to the acid-activated attapulgite is 0.5 to 5.0 wt%.

4. The attapulgite-chitosan oligosaccharide composite carrier according to claim 1, characterized in that, The covalently connected shell is formed through the following steps: C1. Raw material preparation: Provide epoxy silanized attapulgite, chitosan oligosaccharide, sodium hydroxide, hydrochloric acid, and deionized water; C2. Preparation of chitosan oligosaccharide solution: Dissolve the chitosan oligosaccharide in deionized water to prepare a chitosan oligosaccharide aqueous solution with a mass fraction of 0.5 to 5.0 wt%; the dissolution process of the chitosan oligosaccharide is carried out at a temperature of 20 to 60°C with mechanical stirring at 300 to 1200 rpm for a stirring time of 10 to 120 min. C3. Grafting reaction: Add the epoxy-silanized attapulgite to the chitosan oligosaccharide aqueous solution, such that the mass ratio of the chitosan oligosaccharide to the original attapulgite in the epoxy-silanized attapulgite is 0.05 to 0.40; adjust the pH of the system to 8.0 to 9.5 using a sodium hydroxide aqueous solution with a concentration of 0.10 to 5.00 mol / L, measure the pH at 25°C, and react for 1.0 to 6.0 h at a temperature of 40 to 60°C and atmospheric pressure. Stirring is performed during the grafting reaction at a stirring speed of 300 to 1200 rpm. C4. Post-treatment: Adjust the pH of the system to 6.0 to 8.0 using a 0.10 to 2.00 mol / L hydrochloric acid aqueous solution. The pH value is measured at 25°C. Filter and wash with deionized water 1 to 5 times, each time using 5 to 30 mL / g of the solid mass. Dry at 60 to 80°C and 0.001 to 0.01 MPa for 8 to 24 hours until constant weight is reached. The criterion for constant weight is that the interval between two consecutive weighings is 2 hours and the mass difference is less than 0.1%. C5. Quality control: The mass gain of the attapulgite-chitosan oligosaccharide composite carrier relative to the epoxy-silanized attapulgite is 5.0 to 25.0 wt%.

5. The attapulgite-chitosan oligosaccharide composite carrier according to claim 1, characterized in that, The zeta potential of the composite carrier was determined by the following method: the sample was dispersed in a 1 mmol / L KCl aqueous solution and measured at 25°C; the zeta potential was -60 to -20 mV when the pH was 7.0 to 9.0; and 20 to 60 mV when the pH was 3.0 to 5.

0. The molecular weight of the chitosan oligosaccharide was no greater than 2000 Da (number average molecular weight Mn). When the composite carrier was prepared into an aqueous slurry with a mass fraction of 20 wt%, the viscosity of the aqueous slurry was determined by the following method: at 25°C and a shear rate of 100 s⁻¹. -1 The apparent viscosity was determined under the following conditions, wherein the apparent viscosity was 50 to 500 mPa·s.

6. The attapulgite-chitosan oligosaccharide composite carrier according to claim 1, characterized in that, The composite carrier is a powder with a PDI of 0.05 to 0.35 and a water content of 0 to 8 wt%.

7. A method for preparing an attapulgite-chitosan oligosaccharide composite carrier as described in any one of claims 1-6, characterized in that, Includes the following steps: S0. Starting material supply: Attapulgite, acid-activated attapulgite, or epoxy-silanized attapulgite is provided as the starting material; wherein, the acid-activated attapulgite and the epoxy-silanized attapulgite are intermediates, which are obtained by this method or provided directly as raw materials; S1. Acid activation: When the starting material is attapulgite, the attapulgite is mixed with an aqueous hydrochloric acid solution with a concentration of 0.10 to 1.00 mol / L at a mass ratio of 1:5 to 20, and the mixture is mechanically stirred at 300 to 1200 rpm at a temperature of 25 to 60°C and at normal pressure for a reaction time of 1.0 to 6.0 h. The mixture is then filtered and washed with deionized water until the pH of the filtrate is 6.0 to 7.0, and dried to obtain acid-activated attapulgite. S2. Epoxysilane Grafting: When the starting material is attapulgite or acid-activated attapulgite, the acid-activated attapulgite is dispersed in a mixed solvent of ethanol and deionized water at a solid-liquid ratio of 1 g:5 mL to 1 g:50 mL, wherein the volume ratio of ethanol to deionized water is 3:7 to 9:1; the dispersion process is carried out at a temperature of 20 to 40 °C with mechanical stirring at 300 to 1200 rpm for 10 to 60 min; γ-glycidoxypropyltrimethoxysilane is added, with the amount being 0.005 to 0.1% of the mass of the acid-activated attapulgite. 0; The pH of the system was adjusted to 4.0 to 5.5 using an aqueous acetic acid solution with a concentration of 0.10 to 2.00 mol / L. The pH was measured at 25°C. The reaction was carried out at 40 to 70°C and atmospheric pressure for 1.0 to 4.0 h. During the reaction, the mixture was stirred at a speed of 300 to 1200 rpm. The mixture was filtered and washed with ethanol 1 to 5 times, with each wash using 5 to 30 mL / g of the solid mass. The mixture was then washed with deionized water 1 to 5 times, with each wash using 5 to 30 mL / g of the solid mass. The mixture was dried to obtain epoxy-silanized attapulgite. S3. Covalent grafting of chitosan oligosaccharide: Chitosan oligosaccharide is dissolved in deionized water to obtain a chitosan oligosaccharide aqueous solution with a mass fraction of 0.5 to 5.0 wt%; the dissolution process of chitosan oligosaccharide is carried out at a temperature of 20 to 60°C with mechanical stirring at 300 to 1200 rpm for 10 to 120 min; epoxy silanized attapulgite is added so that the mass ratio of chitosan oligosaccharide to the original attapulgite in the epoxy silanized attapulgite is 0.05 to 0.40; the pH value of the system is adjusted to 8.0 to 9.5 using a sodium hydroxide aqueous solution with a concentration of 0.10 to 5.00 mol / L, the pH value is measured at a temperature of 25°C, and the reaction is carried out at a temperature of 40 to 60°C and atmospheric pressure for 1.0 to 6.0 h; the grafting reaction is carried out with stirring at a stirring speed of 300 to 1200 rpm; S4. Neutralization, washing and drying: The pH of the system was adjusted to 6.0 to 8.0 using a hydrochloric acid aqueous solution with a concentration of 0.10 to 2.00 mol / L. The pH was measured at 25°C. The system was filtered and washed with deionized water 1 to 5 times, with each wash using 5 to 30 mL / g of the solid mass. The system was then dried to obtain the attapulgite-chitosan oligosaccharide composite carrier. S5. Powdering: The attapulgite-chitosan oligosaccharide composite carrier obtained in step S4 is dispersed in deionized water to obtain a slurry with a mass fraction of 10 to 30 wt%; the slurry is spray-dried at an inlet air temperature of 120 to 180°C and an outlet air temperature of 60 to 100°C; the spray drying is carried out using a two-fluid nozzle or centrifugal atomization. When using a two-fluid nozzle, the atomization pressure is 0.10 to 0.60 MPa and the feed rate is 1 to 20 mL / min. When using centrifugal atomization, the atomizing disc speed is 5000 to 25000 rpm; the powder is allowed to stand for 1 to 24 hours until constant weight is reached. The criterion for constant weight is that the interval between two consecutive weighings is 2 hours and the mass difference is less than 0.1%. The standing process is carried out in an environment with a temperature of 20 to 30°C, normal pressure, and relative humidity not exceeding 30%; wherein, the PDI of the powder is 0.05 to 0.

35.

8. The preparation method according to claim 7, characterized in that, In the dispersion process of step S2, the dispersion system is ultrasonically dispersed. The ultrasonic frequency of the ultrasonic dispersion is 20 to 40 kHz, the ultrasonic power is 100 to 500 W, and the ultrasonic time is 5 to 30 min. The ultrasonic dispersion is probe-type ultrasonic or ultrasonic bath ultrasonic. The ultrasonic dispersion mode is continuous or pulsed. When it is pulsed, the duty cycle is 10% to 90%. The system temperature is controlled at 10 to 40°C during the ultrasonic dispersion process.

9. The preparation method according to claim 7, characterized in that, The drying in steps S1, S2 and S4 is carried out at a temperature of 60 to 80°C and a pressure of 0.001 to 0.01 MPa for 8 to 24 hours until constant weight is achieved. The criterion for constant weight is that the interval between two consecutive weighings is 2 hours and the mass difference is less than 0.1%.

10. The preparation method according to claim 7, characterized in that, The powder obtained in step S5 has a moisture content of 0 to 8 wt%.

Images