Preparation method of core-shell polymethyl methacrylate@TiO2@oxidized chitosan composite nanoparticles

Abstract

The present invention discloses a method for preparing core-shell polymethyl methacrylate (PMMA)@TiO2@oxidized chitosan composite nanoparticles. The method uses plant oil-based monomers methyl methacrylate and methacrylic acid as raw materials. Polymethyl methacrylate microspheres are prepared as the "core" via microwave irradiation miniemulsion polymerization. Anatase-phase nano-TiO2 sol is then added dropwise under ultrasonic action to electrostatically assemble onto the outer periphery of the PMMA microspheres as the "shell." Subsequently, an oxidized chitosan solution is added dropwise for hydrothermal reaction and electrostatic self-assembly onto the outer surface of the PMMA@TiO2 core-shell particles. The method is simple, low-cost, requires mild reaction conditions, and is environmentally friendly. The resulting core-shell composite nanoparticles exhibit broad-spectrum antibacterial, UV protection, and pollutant photodegradation properties, and have great potential for application in textiles and apparel, home textiles, biomedicine, and the environment.

Description

Technical Field

[0001] The invention relates to a method for preparing core-shell polymethyl methacrylate@TiO2@oxidized chitosan composite nanoparticles, belonging to the technical field of functional nanomaterial preparation. Background Art

[0002] Nano-TiO2 is considered to be the most commonly used photocatalytic material due to its strong photocatalytic ability, good chemical stability, safety, non-toxicity and low cost. The higher band gap energy (3.0-3.2eV) of nano-TiO2 makes its photogenerated carriers have higher energy, which can react with O2 and H2O adsorbed on the surface of TiO2 to generate a large number of active hydroxyl groups (·OH) and superoxide groups (·O2 - ) and other active groups, decomposing the surrounding pollutants and ultimately generating CO2 and H2O. Anatase nano-TiO2 has more serious lattice defects and more complex surface dislocations, with more "electron-hole" pairs on the surface, and its photocatalytic ability is more outstanding. However, due to its high surface energy and large specific surface area, nano-TiO2 is easy to agglomerate, and the photogenerated "electron-hole" is easy to recombine, resulting in poor adsorption capacity for organic pollutants. In addition, the large band gap causes the TiO2 light response range to be concentrated in the ultraviolet band [Johnson K E, Gakhar S, Deng Y, et al. Biomembrane-compatible sol-gel-derived photocatalytic titanium dioxide. ACS applied materials & interfaces, 2017, 9 (41): 35664-35672], which to some extent limits the practical application of TiO2.

[0003] A core-shell structure is an ordered nanoscale structure in which one nanomaterial uniformly encapsulates another nanomaterial through chemical bonds or other interactions. The composite material has a large "core" and a relatively thin and small "shell," with controllable nanoscale properties, coating morphology, and internal and external structures. Core-shell structures often offer enhanced performance or possess properties not possessed by individual materials. They are widely used in optical coatings, functional textiles, water purification, the food industry, and drug delivery [Li Y, Shen Q, Guan R, et al. AC@TiO2 yolk-shell heterostructure for synchronous photothermal-photocatalytic degradation of organic pollutants. Journal of Materials Chemistry C, 2020, 8:1025-1034]. In recent years, transparent composite films with a TiO2 core and a polystyrene (PS) shell have been prepared by mixing nano-TiO2 particles with styrene monomer, using cetyltrimethylammonium bromide (CTAB) as a surface modifier and benzoyl peroxide to initiate polymerization. These composite films, characterized by in-situ polymerization and spin coating, exhibit lower band gap energies and are therefore more suitable for photocatalytic applications. Core-shell (poly-L-lactic acid) PLLA@TiO2 fiber membranes have been successfully prepared via electrospinning / post-treatment. Acetone post-treatment induces crystallization of the PLLA chains, forming a unique porous structure that increases the specific surface area and exposes the TiO2 nanoparticles on the fiber surface. This reduces the core-shell nanomaterial's band gap energy to 3.03 eV, promoting the generation and transfer of reactive oxygen species and enhancing the composite's photocatalytic activity. However, these methods are complex, have long reaction cycles, and require the use of organic solvents, surfactants, cross-linking agents, and other reagents. Styrene monomer is toxic and irritating to the human body and harms the environment. At the same time, the core-shell structure of the composite material is unstable, which limits its scope of use [Chinese Invention Patent Publication Nos.: CN104477921A; CN112063040B; CN101328024B].

[0004] Chitosan, chemically known as (1,4)-2-amino-2-deoxy-β-D-glucose, is an alkaline polysaccharide obtained by deacetylation of chitin. It is also the second largest bioresource on Earth in terms of biosynthetic yield, second only to cellulose. It is widely used in water treatment, biomedical materials, food engineering, textile printing and dyeing, and other fields. However, there is a strong hydrogen bond between the hydroxyl and amino groups in the chitosan molecule, which makes chitosan difficult to dissolve in water and general solvents. It can only be dissolved in acidic solutions, which are volatile, difficult to recycle, highly corrosive, pollute the environment, and have certain toxicity to organisms. At the same time, the antibacterial activity of chitosan is easily affected by factors such as molecular weight, degree of deacetylation, and pH, which greatly limits the application of chitosan [Thakur VK, Thakur MK. Recent advances in graft co-polymerization and applications of chitosan: A Review. ACS Sustainable Chemistry &

[0005] Engineering,2014,2:2637-2652].

[0006] The present invention uses plant oil-based monomers methyl methacrylate and methacrylic acid as raw materials, and prepares polymethyl methacrylate (PMMA) microspheres as the "core" through microwave irradiation miniemulsion polymerization. Under the action of ultrasound, anatase-phase nano-TiO2 sol is added dropwise to electrostatically assemble on the periphery of the PMMA microspheres as the "shell". Then, oxidized chitosan solution is added dropwise for hydrothermal reaction and electrostatic self-assembly on the outside of the TiO2, thereby preparing core-shell composite nanoparticles with uniform particle size, strong stability, and high biological activity. Polymethyl methacrylate has extremely high transparency, which increases the utilization rate of visible light, and electrostatically adsorbs TiO2, preventing the agglomeration of nano-TiO2 particles. At the same time, the ester, carboxyl, aldehyde, and amino groups in PMMA and oxidized chitosan can respectively attract photogenerated holes and electrons in TiO2, effectively preventing the rapid recombination of the two and enhancing the photocatalytic reaction activity. With the development and utilization of plant oils, monomers such as methyl methacrylate and methacrylic acid are widely derived from renewable plant oil processing products, which have advantages in cost, "environmental protection", and safety. In addition, oxidized chitosan is an amphoteric polyelectrolyte, similar in structure to protein, and possesses excellent water solubility, biocompatibility, degradability, long-lasting antibacterial properties, reactivity, and safety and hygiene. The large number of polar groups, such as carboxyl, aldehyde, and amino groups, in the oxidized chitosan of the outermost layer of the core-shell composite nanoparticles readily react with fibers without the use of any chemical crosslinking agents, thereby imparting multiple functions to the textile material, including antibacterial and mite removal, virus killing, UV protection, dye-darkening, self-cleaning, and human affinity, while simultaneously avoiding the photocorrosion side effects of nano-TiO2 on the fiber matrix. The method of the present invention is simple and easy to implement, low in cost, with mild reaction conditions, and is environmentally friendly. The resulting core-shell composite nanoparticles have broad application prospects in the fields of textiles and clothing, home textiles, biomedicine, and the environment. Summary of the Invention

[0007] In view of the aforementioned problems in the prior art, the present invention aims to provide a method for preparing core-shell polymethyl methacrylate (PMMA)@TiO2@oxidized chitosan composite nanoparticles. The composite nanoparticles are prepared by microwave miniemulsion polymerization using polymethyl methacrylate (PMMA) microspheres as the "core." Under ultrasonic action, anatase-phase TiO2 sol is added dropwise to electrostatically assemble around the PMMA microspheres as the "shell." Subsequently, an oxidized chitosan solution is added dropwise for hydrothermal reaction and electrostatic self-assembly onto the TiO2 surface. The core-shell composite nanoparticles prepared by this method exhibit a stable structure, small particle size, uniform distribution, and controllable particle size. The method eliminates the use of organic solvents and aldehyde crosslinking agents, resulting in a simple, mild process. The nanoparticles exhibit environmentally friendly properties, broad-spectrum antibacterial and antiviral properties, UV protection, self-cleaning properties, and the ability to photodegrade pollutants.

[0008] To achieve the above object, the technical solutions adopted by the present invention are as follows:

[0009] A core-shell type polymethyl methacrylate@TiO2@oxidized chitosan composite nanoparticle is characterized in that: the composite nanoparticles are prepared from plant oil-based monomers methyl methacrylate and methacrylic acid as raw materials, polymethyl methacrylate (PMMA) microspheres are prepared by microwave radiation miniemulsion polymerization as the "core", anatase phase TiO2 sol is added dropwise under the action of ultrasound and electrostatically assembled on the periphery of the PMMA microspheres as the "shell", and then oxidized chitosan solution is added dropwise for hydrothermal reaction and electrostatic self-assembly on the outside of the polymethyl methacrylate@TiO2 (PMMA@TiO2) core-shell particles to obtain the composite nanoparticles.

[0010] Preferably, the mass ratio of methyl methacrylate to methacrylic acid is 1-10:1; the mass ratio of polymethyl methacrylate to anatase nano-TiO2 is 2-8:1; and the mass ratio of oxidized chitosan to PMMA@TiO2 core-shell particles is 1-8:1.

[0011] Preferably, the composite nanoparticles have a particle size range of 90 to 240 nm, a Zeta potential of 28.57 to 51.33 mV, and a monodispersity coefficient of 0.107 to 0.391.

[0012] Preferably, the nano-TiO2 is anatase-type, has an average particle size of 5 to 8 nm, and a Zeta potential of 24.45 to 36.28 mV; the viscosity-average molecular weight of the oxidized chitosan is 18,000 to 34,000, the degree of deacetylation is ≥88.57%, the carboxyl content at the C2 and C3 positions is 24.73 to 36.08%, and the aldehyde content at the C6 position is 51.69 to 74.32%; the structural formula of the oxidized chitosan is as follows:

[0013]

[0014] The method for preparing the core-shell polymethyl methacrylate@TiO2@oxidized chitosan composite nanoparticles of the present invention is carried out according to the following steps:

[0015] (1) dissolving methyl methacrylate monomer and methacrylic acid monomer in deionized water to prepare a solution A with a total mass concentration of 25-50%, adding an anionic surfactant to obtain a solution B, and using a high-speed shear emulsifier to shear and stir at 3500-6500 r / min for 3-10 minutes to obtain a uniformly dispersed milky white pre-emulsion; the mass concentration of the anionic surfactant in the solution B is 0.12-0.50%;

[0016] (2) adding 50 to 80 mL of deionized water to 30 mL of the pre-emulsion of step (1), introducing nitrogen for 15 to 30 min, then adding an initiator of ammonium persulfate or potassium persulfate to obtain a solution C, placing the solution in a microwave radiation reactor and reacting it at a stirring speed of 300 to 600 r / min for 3 to 6 h. After the reaction is completed, filtering it 3 to 5 times with a 500-mesh standard sieve to obtain a polymethyl methacrylate microsphere dispersion; the mass concentration of the initiator in the solution C is 0.15 to 0.35%;

[0017] (3) diluting the polymethyl methacrylate microsphere dispersion obtained in step (2) with deionized water to a mass concentration of 0.08-0.2%, adjusting the solution pH to 2.5-3.6 with a 0.05 mol / L dilute hydrochloric acid solution, and adding an anatase phase nano-TiO2 sol with a mass concentration of 0.06-0.15% dropwise at a rate of 1.6-3.2 mL / min using an automatic syringe, and then turning on a probe-type ultrasonic instrument at 160-380 W and 20-35° C. for 30-90 min to allow the negatively charged groups including the ester groups on the surface of the polymethyl methacrylate microspheres and the anions of the surfactant to interact with the positively charged nano-TiO2 particles by electrostatic force, thereby obtaining a polymethyl methacrylate@TiO2 core-shell microparticle dispersion;

[0018] (4) The oxidized chitosan powder is stirred and dissolved in a phosphate buffer solution with a pH of 5.2 to 6.4 to prepare an oxidized chitosan solution with a mass concentration of 0.6 to 1.5%, and then added dropwise to the polymethyl methacrylate@TiO2 core-shell microparticle dispersion of step (3), and the solution temperature is maintained at 60 to 85° C. for a hydrothermal reaction for 1 to 3 hours, so that the anions including the hydroxyl, aldehyde and carboxyl groups of the oxidized chitosan and the positively charged nano-TiO2 particles outside the polymethyl methacrylate@TiO2 core-shell microparticles are electrostatically attracted to each other, and further electrostatically self-assembled to form a core-shell polymethyl methacrylate@TiO2@oxidized chitosan composite nanoparticle dispersion;

[0019] (5) The composite nanoparticle dispersion obtained in step (4) is allowed to stand for 1 to 2 hours, then centrifuged in a high-speed refrigerated centrifuge and the supernatant is discarded, and a freeze-drying protective agent solution with a mass concentration of 0.5 to 1% is added, and after freeze-drying, a stable and uniform core-shell type polymethyl methacrylate@TiO2@oxidized chitosan composite nanoparticle powder is obtained.

[0020] Preferably, the anionic surfactant in step (1) is sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, sodium dodecylsulfonate or polyvinylpyrrolidone, and the viscosity-average molecular weight of the polyvinylpyrrolidone is 8000 to 36000.

[0021] Preferably, the microwave radiation power of the microwave reactor in step (2) is 320-600 W, and the microwave radiation temperature is 65-90° C.

[0022] Preferably, the temperature of the high-speed refrigerated centrifuge in step (5) is -15 to 5°C, and the rotation speed is 8500 to 12000 r / min.

[0023] Preferably, the freeze-drying protective agent in step (5) is selected from skim milk, pullulan, sucrose or glucose.

[0024] By optimizing the mass ratio of methyl methacrylate to methacrylic acid, the mass ratio of polymethyl methacrylate to anatase phase nano-TiO2, the mass ratio of oxidized chitosan to PMMA@TiO2 core-shell particles, the microwave radiation and probe-type ultrasonic treatment time, the amount of anionic surfactant and initiator, and the hydrothermal reaction temperature and time, a series of core-shell composite nanoparticle dispersions with different particle sizes can be obtained.

[0025] Compared with the prior art, the preparation principle and beneficial effects of the core-shell polymethyl methacrylate@TiO2@oxidized chitosan composite nanoparticles of the present invention are embodied in the following aspects:

[0026] 1. The present invention utilizes plant oil-based monomers methyl methacrylate and methacrylic acid as raw materials, which are abundant, renewable, and highly safe. Polymethyl methacrylate (PMMA) microspheres are prepared as "cores" through microwave irradiation miniemulsion polymerization. Miniemulsion polymerization disperses the monomer in tiny droplets in a continuous phase through mechanical action. A high-speed shear emulsifier is used to uniformly disperse the emulsifier, water, and monomer mixture to form submicron-sized monomer droplets. Miniemulsion polymerization has a clear monomer droplet nucleation mechanism. There are almost no micelles in the reaction polymerization system, which avoids the occurrence of micelle nucleation. The monomer droplet size range is relatively wide, ranging from tens to hundreds of nanometers. The addition of an emulsifier in miniemulsion polymerization increases the stability of the system. Compared with microemulsion polymerization, miniemulsion polymerization requires less surfactant. Since the nucleation stage of miniemulsion polymerization technology is longer, the particle nucleation process can be approximated as continuous nucleation. This nucleation method easily realizes continuous production in industry. At the same time, polymethyl methacrylate (PMMA) prepared by miniemulsion polymerization is the product of methyl methacrylate polymerization (acrylic (organic glass)), which has the advantages of high transparency, thermal stability, low cost, high Young's modulus and thermoplasticity. After PMMA is wrapped with nano-TiO2, polymethyl methacrylate@TiO2 core-shell nanoparticles are formed, which have strong stability, uniform particle size and high photocatalytic activity.

[0027] 2. The present invention adds an initiator, ammonium persulfate or potassium persulfate, to a plant oil-based monomer, methyl methacrylate, and a methacrylic acid emulsion under microwave irradiation conditions for polymerization reaction to obtain a polymethyl methacrylate microsphere dispersion. Due to the fast heating speed, short reaction time and good uniformity of microwave irradiation, the monomer methyl methacrylate can fully contact the active sites of methacrylic acid, significantly accelerating the miniemulsion polymerization reaction of the two monomers, effectively avoiding the formation of micelle nucleation and uneven emulsion caused by long-term treatment, making the nucleation size of monomer droplets small, and the polymerized microspheres uniform and stable, solving the shortcomings of the traditional water bath heating reaction process, such as long reaction cycle, low reaction rate, large monomer droplet size in the reaction solution, and micelle nucleation caused by uneven dispersion of tiny droplets in the aqueous phase. The polymethyl methacrylate (PMMA) microspheres polymerized by microwave irradiation miniemulsion have a stable structure, small size, large specific surface area, and strong electrostatic force on nano-TiO2.

[0028] 3. The present invention causes a polymethyl methacrylate microsphere dispersion and a titanium dioxide sol to undergo ultrasonic reaction under the action of a probe-type ultrasonic instrument, thereby electrostatically assembling them into core-shell nano-microspheres. In the probe-type ultrasonic chemical reaction, the multiple effects of ultrasound, such as dispersion, crushing, and activation, can promote both the homogeneous reaction of substances and the dispersion of nanoparticles. At the same time, ultrasound produces a cavitation effect, and cavitation bubbles will form, grow, and collapse in the reaction liquid. When the cavitation bubbles collapse, a high temperature of over 5000K and a high pressure of over 200 MPa are generated in a very short time and in a very small space of the cavitation bubbles. This provides an energy source for ultrasonic chemical synthesis and greatly accelerates the reaction. Ultrasound activates the electrostatic bonding between polymethyl methacrylate microspheres, surfactants, and nano-TiO2. The strong impact and cavitation of ultrasound dissociate water molecules adsorbed on the TiO2 surface to form hydroxyl groups, increasing the number of active groups on the TiO2 particle surface and promoting sonochemical crosslinking of the nano-TiO2 particles with the polymethyl methacrylate microspheres and surfactants, thereby forming uniformly sized and highly stable polymethyl methacrylate@TiO2 core-shell nanoparticles. Furthermore, the pH of the reaction solution, which is between 2.5 and 3.6 and below the isoelectric point of the TiO2 colloid (pH ≥ 4.0), renders the TiO2 nanoparticles positively charged. This significantly increases the electrostatic attraction and reaction efficiency of the positively charged TiO2 nanoparticles to the ester groups and anions of the surfactant on the negatively charged polymethyl methacrylate microspheres, thereby greatly improving the dispersibility of the nano-TiO2 particles and the coverage and stability of the polymethyl methacrylate microspheres.

[0029] 4. The present invention adds methacrylic acid monomer during the miniemulsion polymerization process. Methacrylic acid and methyl methacrylate have good compatibility, and the monomer droplets formed in the emulsion are small in size, which is conducive to the polymerization into polymethyl methacrylate microspheres with smaller particle sizes. In addition, the methacrylic acid monomer contains carboxyl groups with stronger polarity. The surface of the polymethyl methacrylate microspheres has a large content of negatively charged carboxyl groups. The negatively charged hydrophilic groups of the anionic surfactant and the positively charged TiO2 nanoparticles are electrostatically attracted to each other, which is conducive to the formation of stable core-shell polymethyl methacrylate@TiO2 nanoparticles.

[0030] 5. The present invention involves dropwise addition of an oxidized chitosan solution to a dispersion of polymethyl methacrylate@TiO2 core-shell microparticles to form core-shell polymethyl methacrylate@TiO2@oxidized chitosan composite nanoparticles via hydrothermal reaction and electrostatic self-assembly. This self-assembly method allows for the formation of ordered aggregates with specific structures and functions, without the need for surfactants or emulsifiers, offering advantages such as simplicity and controllability. The introduction of hydrophilic groups such as aldehyde and carboxyl groups into the oxidized chitosan molecules enhances the biocompatibility of the core-shell composite nanoparticles and their stability in aqueous solution, enabling the core-shell polymethyl methacrylate@TiO2@oxidized chitosan composite nanoparticles to exhibit long-lasting antibacterial, antiviral, UV-resistant, self-cleaning, and pollutant-photodegrading properties. Furthermore, oxidized chitosan exhibits environmentally friendly properties, broad-spectrum bactericidal activity, stable properties, non-toxicity, and safety. Hydrothermal crosslinking of the oxidized chitosan with the polymethyl methacrylate@TiO2 core-shell microparticles to form the composite nanoparticles further enhances their antibacterial and antiviral capabilities. At the same time, the pH value of the oxidized chitosan solution is 5.2 to 6.4, which is greater than the isoelectric point of the oxidized chitosan, pH = 4.9, making the oxidized chitosan molecules negatively charged, thereby enhancing the electrostatic interaction with nano-TiO2, and further electrostatically self-assembling the aldehyde, carboxyl, hydroxyl and other anions in the oxidized chitosan with the positively charged TiO2 nanoparticles outside the polymethyl methacrylate@TiO2 core-shell particles to form core-shell composite nanoparticles with small particle size, uniform distribution, good stability and high biological activity.

[0031] 6. The present invention uses water-soluble oxidized chitosan to coat the outside of polymethyl methacrylate@TiO2 core-shell particles. Oxidized chitosan selectively oxidizes the secondary hydroxyl groups at positions C2 and C3 in the chitosan molecule to carboxyl groups, and the primary hydroxyl group at position C6 to aldehyde groups, thereby maintaining the alkaline polysaccharide properties of chitosan and having the advantages of good water solubility, biocompatibility, degradability, reactivity, antibacterial properties, environmental friendliness, safety and hygiene, etc. Oxidized chitosan molecules contain negatively charged groups such as carboxyl, aldehyde and hydroxyl groups, which enhance the electrostatic attraction with positively charged TiO2 nanoparticles, facilitating the formation of core-shell composite nanoparticles with small particle size and strong stability. In addition, the aldehyde group at the C6 position of oxidized chitosan can rotate freely in spatial conformation, has low steric hindrance and high chemical activity, and is easy to contact and electrostatically bond with positively charged TiO2 nanoparticles, greatly improving the physicochemical stability and biological activity of the core-shell polymethyl methacrylate@TiO2@oxidized chitosan composite nanoparticles, making the nanoparticles smaller in size, more uniformly distributed and more widely used.

[0032] 7. The core-shell composite nanoparticles prepared by the present invention are obtained from plant oil-based monomers methyl methacrylate and methacrylic acid, nano-TiO2, and water-soluble oxidized chitosan as raw materials. They are obtained by microwave radiation miniemulsion polymerization and electrostatic assembly of nano-TiO2 under ultrasonic action, and then hydrothermal reaction and electrostatic self-assembly of oxidized chitosan molecules. The reaction process is simple, the preparation conditions are controllable, and no organic solvents and chemical cross-linking agents are used. It is green, environmentally friendly, safe and non-toxic, low in cost, and suitable for large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a schematic diagram of the preparation principle of the core-shell polymethyl methacrylate@TiO2@oxidized chitosan composite nanoparticles of the present invention.

[0034] Figure 2 This is a transmission electron microscope image of the core-shell composite nanoparticles of Example 2 of the present invention.

[0035] Figure 3 This is a transmission electron microscope image of the core-shell composite nanoparticles of Example 3 of the present invention.

[0036] Figure 4 It is a transmission electron microscope image of the core-shell composite nanoparticles of Comparative Example 2 of the present invention. DETAILED DESCRIPTION

[0037] The present invention will be further described below with reference to the accompanying drawings and examples. The reference examples described below are only for the purpose of explanation but not to limit the present invention in any form.

[0038] 1. Preparation of core-shell polymethyl methacrylate@TiO2@oxidized chitosan composite nanoparticles

[0039] Example 1

[0040] (1) Methyl methacrylate monomer and methacrylic acid monomer were dissolved in deionized water at a mass ratio of 8:1 to prepare a solution with a total mass concentration of 28%. An anionic surfactant polyvinylpyrrolidone with a viscosity-average molecular weight of 12,000 was added to adjust the mass concentration of the anionic surfactant polyvinylpyrrolidone in the solution to 0.16%. A high-speed shear emulsifier was used for shearing and stirring at 3,800 r / min for 5 minutes to obtain a uniformly dispersed milky white pre-emulsion.

[0041] (2) 50 mL of deionized water was added to 30 mL of the pre-emulsion of step (1), and nitrogen was introduced for 16 min. Then, ammonium persulfate as an initiator was added to make the mass concentration of the initiator in the solution 0.18%. The mixture was placed in a microwave radiation reactor with a power of 380 W and reacted at 70° C. at a stirring speed of 360 r / min for 3.5 h. After the reaction was completed, the mixture was filtered three times using a 500-mesh standard sieve to obtain a polymethyl methacrylate microsphere dispersion.

[0042] (3) The polymethyl methacrylate microsphere dispersion obtained in step (2) was diluted with deionized water to a mass concentration of 0.1%, and the solution pH was adjusted to 3.4 with a 0.05 mol / L dilute hydrochloric acid solution. An anatase phase nano-titanium dioxide sol with a mass concentration of 0.12% (average particle size of 6 nm, Zeta potential of 31.69 mV) was added dropwise at a rate of 2.1 mL / min using an automatic syringe to adjust the mass ratio of polymethyl methacrylate to anatase phase nano-TiO2 to 8:1. Then, a probe-type ultrasonicator was turned on and treated at 200 W at 25° C. for 45 min to allow the negatively charged groups such as the ester group on the surface of the polymethyl methacrylate microspheres and the anion of the surfactant polyvinyl pyrrolidone to interact with the positively charged nano-TiO2 particles with electrostatic force, thereby obtaining a polymethyl methacrylate@TiO2 core-shell particle dispersion.

[0043] (4) Chitosan oxide powder (viscosity-average molecular weight of 24,000, degree of deacetylation of 90.57%, C2 and C3 carboxyl content of 26.15%, C6 aldehyde content of 53.41%) was stirred and dissolved in a phosphate buffer solution of pH = 5.6 to prepare a solution with a mass concentration of 0.6%, and then added dropwise to the polymethyl methacrylate @ TiO2 core-shell microparticle dispersion of step (3) to make the mass ratio of chitosan oxide to PMMA @ TiO2 core-shell microparticles be 6:1. The solution temperature was maintained at 65 ° C for hydrothermal reaction for 2 h, so that the anions such as hydroxyl, aldehyde and carboxyl groups of chitosan oxide were electrostatically attracted to the positively charged nano-TiO2 particles outside the polymethyl methacrylate @ TiO2 core-shell microparticles, and further electrostatically self-assembled to form a core-shell polymethyl methacrylate @ TiO2 @ chitosan oxide composite nanoparticle dispersion.

[0044] (5) The core-shell composite nanoparticle dispersion obtained in step (4) was allowed to stand for 1 hour, and then centrifuged in a high-speed refrigerated centrifuge at a temperature of 3°C and a speed of 9200 r / min, and the supernatant was discarded. Then, a 0.6% mass concentration of a freeze-drying protective agent skim milk solution was added, and after freeze-drying, a stable and uniform core-shell polymethyl methacrylate@TiO2@oxidized chitosan composite nanoparticle powder was obtained, with a particle size range of 112 nm, a Zeta potential of 30.17 mV, and a monodispersity coefficient of 0.295.

[0045] Example 2

[0046] (1) Methyl methacrylate monomer and methacrylic acid monomer were dissolved in deionized water at a mass ratio of 6:1 to prepare a solution with a total mass concentration of 36%. Anionic surfactant sodium lauryl sulfate was added to adjust the mass concentration of the anionic surfactant sodium lauryl sulfate in the solution to 0.28%. A high-speed shear emulsifier was used to shear and stir at 4600 r / min for 6 minutes to obtain a uniformly dispersed milky white pre-emulsion.

[0047] (2) 60 mL of deionized water was added to 30 mL of the pre-emulsion of step (1), and nitrogen was introduced for 22 min. Then, ammonium persulfate as an initiator was added to make the mass concentration of the initiator in the solution 0.24%. The solution was placed in a microwave radiation reactor with a power of 460 W and reacted at 80° C. at a stirring speed of 450 r / min for 4 h. After the reaction was completed, the solution was filtered four times using a 500-mesh standard sieve to obtain a polymethyl methacrylate microsphere dispersion.

[0048] (3) The polymethyl methacrylate microsphere dispersion obtained in step (2) was diluted with deionized water to a mass concentration of 0.14%, and the solution pH was adjusted to 3.2 with a 0.05 mol / L dilute hydrochloric acid solution. An anatase phase nano-titanium dioxide sol with a mass concentration of 0.10% (average particle size of 5 nm, Zeta potential of 34.07 mV) was added dropwise at a rate of 2.5 mL / min using an automatic syringe to adjust the mass ratio of polymethyl methacrylate to anatase phase nano-TiO2 to 6:1. Then, a probe-type ultrasonicator was turned on at 260 W and 25° C. for 60 min to allow the negatively charged groups such as the ester group on the surface of the polymethyl methacrylate microspheres and the anion of the surfactant sodium dodecyl sulfate to interact with the positively charged nano-TiO2 particles with electrostatic force, thereby obtaining a polymethyl methacrylate@TiO2 core-shell particle dispersion.

[0049] (4) Chitosan oxide powder (viscosity-average molecular weight of 22,000, degree of deacetylation of 92.14%, carboxyl content at C2 and C3 of 30.25%, and aldehyde content at C6 of 65.08%) was stirred and dissolved in a phosphate buffer solution of pH = 5.6 to prepare a solution with a mass concentration of 1.0%, and then added dropwise to the polymethyl methacrylate @ TiO2 core-shell microparticle dispersion of step (3) to make the mass ratio of chitosan oxide to PMMA @ TiO2 core-shell microparticles 4:1. The solution temperature was maintained at 70°C for a hydrothermal reaction for 2 h, so that the anions such as hydroxyl, aldehyde and carboxyl groups of chitosan oxide were electrostatically attracted to the positively charged nano-TiO2 particles outside the polymethyl methacrylate @ TiO2 core-shell microparticles, and further electrostatically self-assembled to form a core-shell polymethyl methacrylate @ TiO2 @ chitosan oxide composite nanoparticle dispersion.

[0050] (5) The core-shell composite nanoparticle dispersion obtained in step (4) was allowed to stand for 1.5 hours, then centrifuged in a high-speed refrigerated centrifuge at a temperature of -1°C and a speed of 10,000 r / min and the supernatant was discarded. Then, a freeze-drying protective agent pullulan solution with a mass concentration of 0.8% was added, and after freeze-drying, a stable and uniform core-shell polymethyl methacrylate@TiO2@oxidized chitosan composite nanoparticle powder was obtained, with a particle size range of 168 nm, a Zeta potential of 37.06 mV, and a monodispersity coefficient of 0.213.

[0051] The transmission electron microscopy of the core-shell composite nanoparticles obtained in this example is as follows: Figure 2 As shown in the figure, the appearance is spherical with small particle size, the particles are evenly dispersed, and most of the nano-TiO2 particles have been electrostatically assembled on the surface of PMMA microspheres.

[0052] Example 3

[0053] (1) Methyl methacrylate monomer and methacrylic acid monomer were dissolved in deionized water at a mass ratio of 2:1 to prepare a solution with a total mass concentration of 40%. An anionic surfactant, sodium dodecylbenzenesulfonate, was added to adjust the mass concentration of the anionic surfactant, sodium dodecylbenzenesulfonate, in the solution to 0.36%. A high-speed shear emulsifier was used for shearing and stirring at 5400 r / min for 8 minutes to obtain a uniformly dispersed milky white pre-emulsion.

[0054] (2) 60 mL of deionized water was added to 30 mL of the pre-emulsion of step (1), and nitrogen was introduced for 25 min. Then, potassium persulfate as an initiator was added to make the mass concentration of the initiator in the solution 0.30%. The solution was placed in a microwave radiation reactor with a power of 520 W and reacted at 85° C. at a stirring speed of 500 r / min for 5 h. After the reaction was completed, the solution was filtered five times using a 500-mesh standard sieve to obtain a polymethyl methacrylate microsphere dispersion.

[0055] (3) The polymethyl methacrylate microsphere dispersion obtained in step (2) was diluted with deionized water to a mass concentration of 0.16%, and the solution pH was adjusted to 3.0 with a 0.05 mol / L dilute hydrochloric acid solution. An anatase phase titanium dioxide sol with a mass concentration of 0.08% (average particle size of 5 nm, Zeta potential of 34.07 mV) was added dropwise at a rate of 2.8 mL / min using an automatic syringe to adjust the mass ratio of polymethyl methacrylate to anatase phase nano-TiO2 to 4:1. Then, a probe-type ultrasonicator was turned on and treated at 30°C for 70 min at 300 W to allow the negatively charged groups such as the ester group on the surface of the polymethyl methacrylate microspheres and the anion of the surfactant sodium dodecylbenzenesulfonate to interact with the positively charged nano-TiO2 particles with electrostatic force to obtain a polymethyl methacrylate@TiO2 core-shell particle dispersion.

[0056] (4) Chitosan oxide powder (viscosity-average molecular weight of 18,000, degree of deacetylation of 91.52%, C2 and C3 carboxyl content of 34.19%, C6 aldehyde content of 70.36%) was stirred and dissolved in a phosphate buffer solution of pH = 6.0 to prepare a solution with a mass concentration of 1.2%, and then added dropwise to the polymethyl methacrylate @ TiO2 core-shell microparticle dispersion of step (3) to make the mass ratio of chitosan oxide to PMMA @ TiO2 core-shell microparticles 2:1. The solution temperature was maintained at 80 ° C for a hydrothermal reaction for 2.5 h, so that the anions such as hydroxyl, aldehyde and carboxyl groups of chitosan oxide were electrostatically attracted to the positively charged nano-TiO2 particles outside the polymethyl methacrylate @ TiO2 core-shell microparticles, and further electrostatically self-assembled to form a core-shell polymethyl methacrylate @ TiO2 @ chitosan oxide composite nanoparticle dispersion.

[0057] (5) The core-shell composite nanoparticle dispersion obtained in step (4) was allowed to stand for 2 hours, and then centrifuged in a high-speed refrigerated centrifuge at a temperature of -5°C and a speed of 11000 r / min, and the supernatant was discarded. Then, a freeze-drying protective agent glucose solution with a mass concentration of 0.8% was added, and after freeze-drying, a stable and uniform core-shell polymethyl methacrylate@TiO2@oxidized chitosan composite nanoparticle powder was obtained, whose particle size range was 208 nm, the Zeta potential was 46.37 mV, and the monodispersity coefficient was 0.134.

[0058] The transmission electron microscopy of the core-shell composite nanoparticles obtained in this example is as follows: Figure 3 As shown, the appearance is uniform spherical, the core-shell nanoparticles are well dispersed, the nano-TiO2 particles are completely electrostatically bonded to the surface of the PMMA microspheres, and there are basically no residual TiO2 particles around them. The core-shell structure of the composite nanoparticles is highly stable.

[0059] Example 4

[0060] (1) Methyl methacrylate monomer and methacrylic acid monomer were dissolved in deionized water at a mass ratio of 1:1 to prepare a solution with a total mass concentration of 45%. An anionic surfactant, sodium dodecylbenzenesulfonate, was added to adjust the mass concentration of the anionic surfactant, sodium dodecylbenzenesulfonate, in the solution to 0.42%. A high-speed shear emulsifier was used for shearing and stirring at 6000 r / min for 8 minutes to obtain a uniformly dispersed milky white pre-emulsion.

[0061] (2) 70 mL of deionized water was added to 30 mL of the pre-emulsion of step (1), and nitrogen was introduced for 25 min. Then, potassium persulfate as an initiator was added to make the mass concentration of the initiator in the solution 0.32%. The solution was placed in a microwave radiation reactor with a power of 560 W and reacted at 85° C. at a stirring speed of 540 r / min for 5 h. After the reaction was completed, the solution was filtered five times using a 500-mesh standard sieve to obtain a polymethyl methacrylate microsphere dispersion.

[0062] (3) The polymethyl methacrylate microsphere dispersion obtained in step (2) was diluted with deionized water to a mass concentration of 0.18%, and the solution pH was adjusted to 2.8 with a 0.05 mol / L dilute hydrochloric acid solution. An anatase phase titanium dioxide sol with a mass concentration of 0.08% (average particle size of 5 nm, Zeta potential of 34.07 mV) was added dropwise at a rate of 3.0 mL / min using an automatic syringe to adjust the mass ratio of polymethyl methacrylate to anatase phase nano-TiO2 to 2:1. Then, a probe-type ultrasonicator was turned on at 350 W and 30° C. for 80 min to allow the negatively charged groups such as the ester group on the surface of the polymethyl methacrylate microspheres and the anion of the surfactant sodium dodecylbenzenesulfonate to interact with the positively charged nano-TiO2 particles with electrostatic force to obtain a polymethyl methacrylate@TiO2 core-shell particle dispersion.

[0063] (4) Chitosan oxide powder (viscosity-average molecular weight of 18,000, degree of deacetylation of 91.52%, C2 and C3 carboxyl content of 34.19%, C6 aldehyde content of 70.36%) was stirred and dissolved in a phosphate buffer solution of pH = 6.2 to prepare a solution with a mass concentration of 1.2%, and then added dropwise to the polymethyl methacrylate @ TiO2 core-shell microparticle dispersion of step (3) to make the mass ratio of chitosan oxide to PMMA @ TiO2 core-shell microparticles 1:1. The solution temperature was maintained at 80 ° C for hydrothermal reaction for 3 h, so that the anions such as hydroxyl, aldehyde and carboxyl groups of chitosan oxide were electrostatically attracted to the positively charged nano-TiO2 particles outside the polymethyl methacrylate @ TiO2 core-shell microparticles, and further electrostatically self-assembled to form a core-shell polymethyl methacrylate @ TiO2 @ chitosan oxide composite nanoparticle dispersion.

[0064] (5) The core-shell composite nanoparticle dispersion obtained in step (4) was allowed to stand for 2 hours, then centrifuged in a high-speed refrigerated centrifuge at a temperature of -8°C and a speed of 11000 r / min and the supernatant was discarded. Then, a freeze-drying protective agent glucose solution with a mass concentration of 0.9% was added, and after freeze-drying, a stable and uniform core-shell polymethyl methacrylate@TiO2@oxidized chitosan composite nanoparticle powder was obtained, whose particle size range was 221 nm, the Zeta potential was 41.13 mV, and the monodispersity coefficient was 0.191.

[0065] Comparative Example 1

[0066] Preparation of core-shell composite nanoparticles (without microwave radiation reaction and probe-type ultrasonic instrument treatment):

[0067] (1) Methyl methacrylate monomer and methacrylic acid monomer were dissolved in deionized water at a mass ratio of 2:1 to prepare a solution with a total mass concentration of 40%. An anionic surfactant, sodium dodecylbenzenesulfonate, was added to adjust the mass concentration of the anionic surfactant, sodium dodecylbenzenesulfonate, in the solution to 0.36%. A high-speed shear emulsifier was used for shearing and stirring at 5400 r / min for 8 minutes to obtain a uniformly dispersed milky white pre-emulsion.

[0068] (2) 60 mL of deionized water was added to 30 mL of the pre-emulsion of step (1), and nitrogen was introduced for 25 min. Then, potassium persulfate as an initiator was added to make the mass concentration of the initiator in the solution 0.30%. The mixture was placed in an 85°C water bath and reacted at a stirring speed of 500 r / min for 5 h. After the reaction was completed, the mixture was filtered five times using a 500-mesh standard sieve to obtain a polymethyl methacrylate microsphere dispersion.

[0069] (3) The polymethyl methacrylate microsphere dispersion obtained in step (2) was diluted with deionized water to a mass concentration of 0.16%, and the solution pH was adjusted to 3.0 with a 0.05 mol / L dilute hydrochloric acid solution. An anatase phase titanium dioxide sol with a mass concentration of 0.08% (average particle size of 5 nm, Zeta potential of 34.07 mV) was added dropwise at a rate of 2.8 mL / min using an automatic syringe to adjust the mass ratio of polymethyl methacrylate to anatase phase nano-TiO2 to 4:1. The mixture was then treated at 30°C for 70 min under continuous stirring to allow the negatively charged groups such as the ester group on the surface of the polymethyl methacrylate microspheres and the anion of the surfactant sodium dodecylbenzenesulfonate to interact with the positively charged nano-TiO2 particles by electrostatic force, thereby obtaining a polymethyl methacrylate@TiO2 core-shell microparticle dispersion.

[0070] (4) Chitosan oxide powder (viscosity-average molecular weight of 18,000, degree of deacetylation of 91.52%, C2 and C3 carboxyl content of 34.19%, C6 aldehyde content of 70.36%) was stirred and dissolved in a phosphate buffer solution of pH = 6.0 to prepare a solution with a mass concentration of 1.2%, and then added dropwise to the polymethyl methacrylate @ TiO2 core-shell microparticle dispersion of step (3) to make the mass ratio of chitosan oxide to PMMA @ TiO2 core-shell microparticles 2:1. The solution temperature was maintained at 80 ° C for a hydrothermal reaction for 2.5 h, so that the anions such as hydroxyl, aldehyde and carboxyl groups of chitosan oxide were electrostatically attracted to the positively charged nano-TiO2 particles outside the polymethyl methacrylate @ TiO2 core-shell microparticles, and further electrostatically self-assembled to form a core-shell polymethyl methacrylate @ TiO2 @ chitosan oxide composite nanoparticle dispersion.

[0071] (5) The core-shell composite nanoparticle dispersion obtained in step (4) was allowed to stand for 2 hours, then centrifuged in a high-speed refrigerated centrifuge at a temperature of -5°C and a speed of 11,000 r / min and the supernatant was discarded. Then, a freeze-drying protective agent glucose solution with a mass concentration of 0.8% was added, and after freeze-drying, a stable and uniform core-shell polymethyl methacrylate@TiO2@oxidized chitosan composite nanoparticle powder was obtained, whose particle size range was 287 nm, the Zeta potential was 26.35 mV, and the monodispersity coefficient was 0.363.

[0072] Comparative Example 2

[0073] Preparation of core-shell composite nanoparticles (without adding anionic surfactant):

[0074] (1) Methyl methacrylate monomer and methacrylic acid monomer were dissolved in deionized water at a mass ratio of 2:1 to prepare a solution with a total mass concentration of 40%. A high-speed shear emulsifier was used to shear and stir at 5400 r / min for 8 minutes to obtain a uniformly dispersed milky white pre-emulsion.

[0075] (2) 60 mL of deionized water was added to 30 mL of the pre-emulsion of step (1), and nitrogen was introduced for 25 min. Then, potassium persulfate as an initiator was added to make the mass concentration of the initiator in the solution 0.30%. The solution was placed in a microwave radiation reactor with a power of 520 W and reacted at 85° C. at a stirring speed of 500 r / min for 5 h. After the reaction was completed, the solution was filtered five times using a 500-mesh standard sieve to obtain a polymethyl methacrylate microsphere dispersion.

[0076] (3) The polymethyl methacrylate microsphere dispersion obtained in step (2) was diluted with deionized water to a mass concentration of 0.16%, and the solution pH was adjusted to 3.0 with a 0.05 mol / L dilute hydrochloric acid solution. An anatase phase titanium dioxide sol with a mass concentration of 0.08% (average particle size of 5 nm, Zeta potential of 34.07 mV) was added dropwise at a rate of 2.8 mL / min using an automatic syringe to adjust the mass ratio of polymethyl methacrylate to anatase phase nano-TiO2 to 4:1. Then, a probe-type ultrasonicator was turned on and treated at 30°C for 70 min at 300 W to allow the negatively charged groups such as the ester group on the surface of the polymethyl methacrylate microspheres and the anion of the surfactant sodium dodecylbenzenesulfonate to interact with the positively charged nano-TiO2 particles with electrostatic force to obtain a polymethyl methacrylate@TiO2 core-shell particle dispersion.

[0077] (4) Chitosan oxide powder (viscosity-average molecular weight of 18,000, degree of deacetylation of 91.52%, C2 and C3 carboxyl content of 34.19%, C6 aldehyde content of 70.36%) was stirred and dissolved in a phosphate buffer solution of pH = 6.0 to prepare a solution with a mass concentration of 1.2%, and then added dropwise to the polymethyl methacrylate @ TiO2 core-shell microparticle dispersion of step (3) to make the mass ratio of chitosan oxide to PMMA @ TiO2 core-shell microparticles 2:1. The solution temperature was maintained at 80 ° C for a hydrothermal reaction for 2.5 h, so that the anions such as hydroxyl, aldehyde and carboxyl groups of chitosan oxide were electrostatically attracted to the positively charged nano-TiO2 particles outside the polymethyl methacrylate @ TiO2 core-shell microparticles, and further electrostatically self-assembled to form a core-shell polymethyl methacrylate @ TiO2 @ chitosan oxide composite nanoparticle dispersion.

[0078] (5) The core-shell composite nanoparticle dispersion obtained in step (4) was allowed to stand for 2 hours, and then centrifuged in a high-speed refrigerated centrifuge at a temperature of -5°C and a speed of 11000 r / min, and the supernatant was discarded. Then, a freeze-drying protective agent glucose solution with a mass concentration of 0.8% was added, and after freeze-drying, a stable and uniform core-shell polymethyl methacrylate@TiO2@oxidized chitosan composite nanoparticle powder was obtained, with a particle size range of 462 nm, a Zeta potential of 21.07 mV, and a monodispersity coefficient of 0.458.

[0079] The transmission electron microscopy of the core-shell composite nanoparticles obtained in this comparative example is as follows: Figure 4 As shown, the appearance is large spherical particles. Due to the lack of emulsification and electrostatic assembly of anionic surfactants, only a small amount of nano-TiO2 particles are electrostatically attracted to the surface of PMMA microspheres, and a large number of free TiO2 particles are distributed around them. The core-shell structure of the composite nanoparticles has poor stability.

[0080] 2. Testing the samples obtained in the above examples

[0081] Test Item 1: Particle size test of core-shell composite nanoparticles formed by adding different mass concentrations of anionic surfactant sodium dodecylbenzenesulfonate

[0082] The mass concentration of the anionic surfactant sodium dodecylbenzenesulfonate in step (1) of Example 3 was adjusted (0%, 0.16%, 0.28%, 0.36%, 0.48%), and the obtained core-shell composite nanoparticle dispersion was tested by dynamic light scattering (DLS). The test results are shown in Table 1.

[0083] Table 1 Average particle size of core-shell composite nanoparticles

[0084]

[0085] Analysis of the test data shown in Table 1 shows that when the anionic surfactant sodium dodecylbenzenesulfonate of the present invention is added to the pre-emulsion at different mass concentrations, the core-shell composite nanoparticles prepared have a smaller particle size, uniform size, low dispersion coefficient, and strong stability. Compared with the core-shell composite nanoparticles without the addition of the anionic surfactant, which have a particle size of 462 nm, the core-shell composite nanoparticles with the addition of the anionic surfactant have an average particle size of approximately 208 to 237 nm, a significantly smaller nanometer size, and a more uniform distribution. This indicates that the anionic surfactant can reduce the tension between the monomers methyl methacrylate and methacrylic acid and the aqueous phase interface, promote the formation of stable monomer droplets, and then the initiator triggers a continuous polymerization reaction within the monomer droplets, which further undergoes electrostatic self-assembly to form core-shell composite nanoparticles with smaller size, uniform particle size, strong stability, and high biological activity, which have a wide range of applications.

[0086] Test Item 2: Stability Test of Composite Nanoparticles

[0087] 10 mL samples of each of the core-shell composite nanoparticle dispersions from Comparative Examples 1-2 and Examples 2-4 were placed in 20 mL vials, sealed, and left at room temperature for 12 days. The average particle size and zeta potential of the core-shell composite nanoparticles were measured at the specified time intervals, and the appearance of each sample was compared. The test results are shown in Table 2.

[0088] Table 2 Changes in particle size and potential of core-shell composite nanoparticles before and after 12 days of standing

[0089]

[0090]

[0091] The data in Table 2 show that the present invention utilizes specific anionic surfactants to reduce the interfacial tension between the monomers methyl methacrylate and methacrylic acid and the aqueous phase, promoting the formation of stable monomer droplets. An initiator then initiates a continuous polymerization reaction within the monomer droplets, and through electrostatic self-assembly, the particle size and stability of the core-shell composite nanoparticles are significantly improved. The emulsification and electrostatic self-assembly effects of the anionic surfactant significantly influence the particle size, potential, stability, and functional effects of the core-shell composite nanoparticles. By optimizing the type and addition ratio of the anionic surfactant, the core-shell polymethyl methacrylate@TiO2@oxidized chitosan composite nanoparticles prepared by the present invention exhibit more ideal particle size, potential, and stability, as well as more durable and efficient functionality.

[0092] Test Item 3: Antibacterial Analysis of Core-Shell Polymethyl Methacrylate@TiO2@Oxidized Chitosan Composite Nanoparticles

[0093] The minimum inhibitory concentration (MIC) refers to the lowest concentration of an antimicrobial agent at which it inhibits microbial growth and is often used as an indicator of the antimicrobial activity of an antimicrobial agent. The lower the MIC value, the stronger the antimicrobial activity. Chitosan oxide with a viscosity-average molecular weight of 18,000, a degree of deacetylation of 91.52%, a carboxyl content of 34.19% at the C2 and C3 positions, and an aldehyde content of 70.36% at the C6 position was used. Core-shell polymethyl methacrylate@TiO2@chitosan oxide composite nanoparticle samples were obtained according to the methods of Examples 2, 3, and 4 and Comparative Examples 1 and 2. Culture solutions containing different concentrations of core-shell composite nanoparticles were prepared using the half-fold dilution method. The solution pH was adjusted to 5.0, and then bacterial solution was added and shaken for incubation. A control culture solution containing the same concentration of core-shell composite nanoparticle sample but without bacterial solution was used to determine the MIC by measuring its absorbance at 600 nm. The test results are shown in Table 3.

[0094] Analysis of the data in Table 3 shows that the minimum inhibitory concentrations of oxidized chitosan against Staphylococcus aureus and Escherichia coli under acidic conditions are 0.4 mg / mL and 1.0 mg / mL, respectively. The core-shell polymethyl methacrylate@TiO2@oxidized chitosan composite nanoparticles exhibit excellent antibacterial properties under acidic conditions, with MIC values ranging from 0.0125 to 0.25 mg / mL. In particular, the core-shell composite nanoparticles emulsified with the anionic surfactant sodium dodecylbenzenesulfonate in Example 3 exhibited MICs of 0.0125 mg / mL and 0.0313 mg / mL against Escherichia coli and Staphylococcus aureus, respectively, representing approximately 32 times the antibacterial activity of oxidized chitosan. This suggests that the emulsification and electrostatic self-assembly effects of the anionic surfactant facilitate the formation of small-sized and highly stable core-shell composite nanoparticles, further enhancing the antibacterial ability of the composite nanoparticles. In addition, compared with the Gram-positive bacteria S. aureus, the core-shell polymethyl methacrylate@TiO2@oxidized chitosan composite nanoparticles have stronger antibacterial ability against Gram-negative bacteria E. coli, which may be related to the presence of a thick layer of peptidoglycan in the cell wall of Staphylococcus aureus.

[0095] The nano-TiO2 particles in the core-shell composite nanomaterial undergo a photocatalytic reaction under ultraviolet light conditions to generate reactive oxygen species (ROS), mainly including superoxide ion radicals and hydroxyl radicals. These ROS substances can penetrate the bacterial cell wall and cell membrane, enter the bacteria, block their respiratory system and electron transport system, and cause cell death. At the same time, the amino groups in the oxidized chitosan in the outermost layer of the core-shell composite nanoparticles carry a positive charge in the acidic medium, forming polycations that act on the bacterial surface. Through strong and rapid charge interaction with the negatively charged phospholipids in the bacterial cell membrane, they cause cell membrane rupture and content outflow, ultimately leading to cell death. Therefore, the dual antibacterial activity of the core-shell polymethyl methacrylate@TiO2@oxidized chitosan composite nanoparticles further enhances their antibacterial properties.

[0096] Table 3 Minimum inhibitory concentration of oxidized chitosan and core-shell composite nanoparticles

[0097]

[0098] In summary, using methyl methacrylate and methacrylic acid monomers, products of vegetable oil processing, as raw materials, polymethyl methacrylate (PMMA) microspheres are prepared by microwave irradiation miniemulsion polymerization as the "core." Under the action of ultrasound, anatase-phase TiO2 sol is added dropwise for electrostatic assembly around the PMMA microspheres as the "shell." Then, an oxidized chitosan solution is added dropwise for hydrothermal reaction and electrostatic self-assembly on the outside of the TiO2 to form core-shell composite nanoparticles. The present invention has a fast reaction rate, a simple process, mild reaction conditions, and is environmentally friendly. The prepared core-shell composite nanoparticles have a stable structure, small size, uniform distribution, and controllable particle size. They are safe, hygienic, biodegradable, highly bioactive, and do not use organic solvents or aldehyde crosslinking agents. They are environmentally friendly, have broad-spectrum antibacterial and antiviral properties, are UV-resistant, self-cleaning, and can photodegrade pollutants. They have great application potential in the fields of textiles and clothing, home textiles, health care, daily chemicals, biomedicine, and environmental protection.

[0099] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A core-shell polymethyl methacrylate@TiO2@oxidized chitosan composite nanoparticle, characterized by: The composite nanoparticles are prepared using plant oil-based monomers methyl methacrylate and methacrylic acid as raw materials. Polymethyl methacrylate microspheres are prepared as the "core" by microwave irradiation miniemulsion polymerization. Anatase-phase nano-TiO2 sol is added dropwise under ultrasonic action and electrostatically assembled on the outer periphery of the polymethyl methacrylate microspheres as the "shell". Then, an oxidized chitosan solution is added dropwise and hydrothermally reacted and electrostatically self-assembled on the outer surface of the polymethyl methacrylate@TiO2 core-shell particles. The mass ratio of methyl methacrylate to methacrylic acid is 1 to 10:1; the mass ratio of polymethyl methacrylate to anatase nano-TiO2 is 2 to 8:1; the mass ratio of oxidized chitosan to the polymethyl methacrylate@TiO2 core-shell particles is 1 to 8:1; The preparation method of the core-shell polymethyl methacrylate@TiO2@oxidized chitosan composite nanoparticles is carried out according to the following steps: (1) dissolving methyl methacrylate monomer and methacrylic acid monomer in deionized water to prepare a solution A with a total mass concentration of 25-50%, adding an anionic surfactant to obtain a solution B, and using a high-speed shear emulsifier to shear and stir at 3500-6500 r / min for 3-10 minutes to obtain a uniformly dispersed milky white pre-emulsion; the mass concentration of the anionic surfactant in the solution B is 0.12-0.50%; the anionic surfactant is selected from sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, or sodium dodecylsulfonate; (2) adding 50 to 80 mL of deionized water to 30 mL of the pre-emulsion of step (1), introducing nitrogen for 15 to 30 min, then adding an initiator of ammonium persulfate or potassium persulfate to obtain a solution C, placing the solution in a microwave radiation reactor and reacting it at a stirring speed of 300 to 600 r / min for 3 to 6 h. After the reaction is completed, filtering it 3 to 5 times with a 500-mesh standard sieve to obtain a polymethyl methacrylate microsphere dispersion; the mass concentration of the initiator in the solution C is 0.15 to 0.35%; the microwave radiation power of the microwave reactor is 320 to 600 W, and the microwave radiation temperature is 65 to 90° C.; (3) diluting the polymethyl methacrylate microsphere dispersion obtained in step (2) with deionized water to a mass concentration of 0.08-0.2%, adjusting the solution pH to 2.5-3.6 with a 0.05 mol / L dilute hydrochloric acid solution, and adding an anatase phase nano-TiO2 sol with a mass concentration of 0.06-0.15% dropwise at a rate of 1.6-3.2 mL / min using an automatic syringe, and then turning on a probe-type ultrasonic instrument at 160-380 W and 20-35° C. for 30-90 min to allow the negatively charged groups including the ester groups on the surface of the polymethyl methacrylate microspheres and the anions of the surfactant to interact with the positively charged nano-TiO2 particles by electrostatic force, thereby obtaining a polymethyl methacrylate@TiO2 core-shell microparticle dispersion; (4) The oxidized chitosan powder is stirred and dissolved in a phosphate buffer solution with a pH of 5.2 to 6.4 to prepare an oxidized chitosan solution with a mass concentration of 0.6 to 1.5%, and then added dropwise to the polymethyl methacrylate@TiO2 core-shell microparticle dispersion of step (3), and the solution temperature is maintained at 60 to 85° C. for a hydrothermal reaction for 1 to 3 hours, so that the anions including the hydroxyl, aldehyde and carboxyl groups of the oxidized chitosan and the positively charged nano-TiO2 particles outside the polymethyl methacrylate@TiO2 core-shell microparticles are electrostatically attracted to each other, and further electrostatically self-assembled to form a core-shell polymethyl methacrylate@TiO2@oxidized chitosan composite nanoparticle dispersion; (5) The composite nanoparticle dispersion obtained in step (4) is allowed to stand for 1 to 2 hours, then centrifuged in a high-speed refrigerated centrifuge and the supernatant is discarded, and a freeze-drying protective agent solution with a mass concentration of 0.5 to 1% is added, and after freeze-drying, a stable and uniform core-shell type polymethyl methacrylate@TiO2@oxidized chitosan composite nanoparticle powder is obtained.

2. The core-shell polymethyl methacrylate@TiO2@oxidized chitosan composite nanoparticles according to claim 1, characterized in that: The composite nanoparticles have a particle size range of 90 to 240 nm, a Zeta potential of 28.57 to 51.33 mV, and a monodispersity coefficient of 0.107 to 0.

391.

3. The core-shell polymethyl methacrylate@TiO2@oxidized chitosan composite nanoparticles according to claim 1, characterized in that: The average particle size of the anatase phase nano-TiO2 is 5 to 8 nm, and the zeta potential is 24.45 to 36.28 mV; the viscosity-average molecular weight of the oxidized chitosan is 18,000 to 34,000, the degree of deacetylation is ≥88.57%, the carboxyl content at the C2 and C3 positions is 24.73 to 36.08%, and the aldehyde content at the C6 position is 51.69 to 74.32%. The structural formula of the oxidized chitosan is as follows:

4. The core-shell polymethyl methacrylate@TiO2@oxidized chitosan composite nanoparticles according to claim 1, characterized in that: The temperature of the high-speed refrigerated centrifuge in step (5) is -15 to 5° C., and the rotation speed is 8500 to 12000 r / min.

5. The core-shell polymethyl methacrylate@TiO2@oxidized chitosan composite nanoparticles according to claim 1, characterized in that: The freeze-drying protective agent in step (5) is selected from skim milk, pullulan, sucrose or glucose.

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