A pickering emulsion based on ring-shaped colloidal particles, its preparation method and application in bi-phase interface catalysis

Abstract

The application discloses a Pickering emulsion based on ring-shaped colloidal particles, a preparation method thereof and application thereof in biphasic interface catalysis. The Pickering emulsion is an oil-in-water emulsion, which comprises a water phase, an oil phase and ring-shaped colloidal particles. The oil phase is dispersed in the water phase in the form of small droplets. The ring-shaped colloidal particles are located at an oil-water interface or at the oil-water interface and the water phase, and the ring-shaped colloidal particles are assembled to form a monolayer structure on the oil-water interface. The Pickering emulsion is not only beneficial to the contact between reactants or between the reactants and a catalyst, but also can enhance the interface mass transfer rate, promote the product to rapidly diffuse from one phase to another phase, has advantages of high conversion rate, high catalytic efficiency, simple product separation and the like, and has an important application prospect in the field of interface catalysis.

Description

Technical Field

[0001] This invention belongs to the field of biphase interface catalysis, specifically relating to a Pickering emulsion based on cyclic colloidal particles, its preparation method, and its application in biphase interface catalysis. Background Technology

[0002] An emulsion is a system in which one phase is dispersed in the form of droplets within another immiscible phase, such as a water-in-oil emulsion or an oil-in-water emulsion. Due to the high surface energy between the two immiscible liquids, emulsion systems are generally considered thermodynamically unstable; therefore, emulsion formation often requires the addition of molecular surfactants or solid particles. Emulsions stabilized by solid particles are called Pickering emulsions. Compared to traditional surfactant-stabilized emulsions, Pickering emulsions exhibit many advantages, such as high anti-agglomeration properties, long-term stability, good biocompatibility, and tunable characteristics.

[0003] Oil-in-water pickering emulsions are a widely used system in industries such as food, cosmetics, catalysis, and coatings. Compared to organic solvents, water offers significant advantages as a continuous phase in certain reactions (such as hydrolysis and esterification) or applications because it is non-flammable, non-toxic, and inexpensive. Typically, oil-in-water pickering emulsions are stable because their oil-water interface contains a dense layer of particles that act as a spatial (mechanical) barrier to prevent droplet coalescence. However, this characteristic can sometimes be detrimental to mass release and interfacial catalysis. The dense solid particles covering the interface reduce the rate of mass diffusion and decrease the likelihood of reactants (in one phase) contacting the catalyst or other reactants (in another phase), thus leading to reduced catalytic efficiency.

[0004] For example, Frerelichowska et al. compared the release rates of caffeine in the aqueous phase of Pickering emulsions and surfactant-stabilized emulsions. Compared to surfactant-stabilized emulsions, the release rate of caffeine in Pickering emulsions was significantly slower, indicating that the dense silica particles at the emulsion droplet interface acted as a barrier to interfacial diffusion. (International Journal of Pharmaceutics 2009, 368, 7–15)

[0005] Simovic et al. also reported that silica particles assembled at the interface of oil-in-water Pickering emulsions slow down the release of lipophilic molecules (dibutyl phthalate) from the aqueous phase. (European Journal of Pharmaceutics and Bio-pharmaceutics 2007, 67(1), 39–47.)

[0006] One effective way to solve the above problems is to reduce the interfacial coverage of Pickering emulsions. For example, Gautier et al. prepared Pickering emulsions with low surface coverage by adjusting the pH of the system. However, they found that the stability of the Pickering emulsion decreased after reducing the interfacial coverage. This is not conducive to its application in the field of interfacial catalysis. (Phys.Chem.Chem.Phys.2007,9(48),6455.)

[0007] Li et al. stabilized a decane-water emulsion using polystyrene cylinders. When the particle concentration was insufficient, the polystyrene cylinders formed a network structure at the interface, resulting in low interface coverage. However, the authors did not further discuss the application prospects of this emulsion. (Journal of Colloid and Interface Science 2019, 552, 230–235.)

[0008] Nie et al. also prepared Pickering emulsions with low interfacial coverage by manipulating particle concentration or liquid flow rate using microfluidics. However, this method is time-consuming, complex, costly, and cannot be mass-produced, nor is it suitable for application in the field of interfacial catalysis. (J.Am.Chem.Soc.2008,130(49),16508–16509)

[0009] In previous work, the synthesis of Pickering emulsions with low interfacial coverage was often cumbersome, and the synthesis conditions were usually harsh, only achievable under specific pH or salt concentration conditions. How to prepare a widely applicable, highly stable emulsion with low interfacial coverage, and successfully apply it in the field of biphasic interfacial catalysis, has not yet been reported. This is also the technical problem that this invention aims to solve. Summary of the Invention

[0010] To address the aforementioned technical problems, this invention provides an oil-in-water Pickering emulsion, wherein droplets are covered by densely arranged monolayer of annular colloidal particles. Unlike traditional solid emulsifiers that almost completely occupy the emulsion interface, due to the unique cavity structure of the annular colloidal particles, the emulsion stabilized by these particles maintains emulsion stability while still possessing a very large free oil-water interface (approximately 80%). Furthermore, the annular colloidal particles are easily modified to achieve different interfacial activities, allowing the Pickering emulsion to adapt to various catalytic reactions.

[0011] The technical solution of the present invention is as follows:

[0012] A Pickering emulsion, wherein the Pickering emulsion is an oil-in-water emulsion comprising an aqueous phase, an oil phase, and cyclic colloidal particles; wherein the oil phase is dispersed in the aqueous phase in the form of small droplets; the cyclic colloidal particles are located at the oil-water interface, or at the oil-water interface and in the aqueous phase, and the cyclic colloidal particles are assembled at the oil-water interface to form a monolayer structure.

[0013] According to an embodiment of the invention, the Pickering emulsion may optionally include at least one of a reactant, a catalyst, and a stabilizer.

[0014] According to an embodiment of the present invention, the Pickering emulsion, by mass percentage, comprises at least: 10–99.9999 wt% aqueous solvent, 0.0001–20 wt% cyclic colloidal particles, 0–89.9999 wt% reactants, 0–89.9999 wt% catalyst, 0–80 wt% stabilizer, and the remainder being a solvent immiscible with water. Preferably, the mass percentage of the aqueous solvent in the Pickering emulsion is 10 wt%, 20 wt%, 30 wt%, 40 wt%, 50 wt%, 60 wt%, 70 wt%, 80 wt%, or 90 wt%. Preferably, the mass percentage of the cyclic colloidal particles in the Pickering emulsion is 1 wt%, 5 wt%, 10 wt%, 15 wt%, or 20 wt%. Preferably, the reactants in the Pickering emulsion are present in a mass percentage of 10 wt%, 20 wt%, 30 wt%, 40 wt%, 50 wt%, 60 wt%, 70 wt%, 80 wt%, or 90 wt%. Preferably, the catalyst in the Pickering emulsion is present in a mass percentage of 10 wt%, 20 wt%, 30 wt%, 40 wt%, 50 wt%, 60 wt%, 70 wt%, 80 wt%, or 90 wt%. Preferably, the stabilizer in the Pickering emulsion is present in a mass percentage of 10 wt%, 20 wt%, 30 wt%, 40 wt%, 50 wt%, 60 wt%, 70 wt%, or 80 wt%.

[0015] According to an embodiment of the present invention, the present invention does not specifically limit the content of the reactants, catalysts or stabilizers in the aqueous phase or oil phase, as long as a stable oil-in-water emulsion can be obtained.

[0016] According to an embodiment of the present invention, the volume ratio of the oil phase to the water phase is not specifically limited, as long as a stable oil-in-water emulsion can be obtained. For example, the volume ratio of the oil phase to the water phase can be 1:4000 to 4:1, such as 2:1, 1:100, or 1:1000.

[0017] According to an embodiment of the invention, the aqueous phase of the Pickering emulsion comprises an aqueous solvent, cyclic colloidal particles, and optionally at least one of reactants, catalysts, and stabilizers.

[0018] According to an embodiment of the present invention, the aqueous phase comprises, by mass percentage, at least: 10–99.9999 wt% aqueous solvent, 0.0001–20 wt% cyclic colloidal particles, 0–89.9999 wt% reactants, 0–89.9999 wt% catalyst, and 0–89.9999 wt% stabilizer.

[0019] According to an embodiment of the present invention, in the Pickering emulsion, the oil phase comprises a solvent that is immiscible with water.

[0020] According to embodiments of the present invention, the oil phase preferably comprises a solvent immiscible with water; and optionally comprises reactants, catalysts, and stabilizers.

[0021] According to an embodiment of the present invention, the oil phase comprises, by weight percentage: 0-100 wt% of a water-immiscible solvent, 0-100 wt% of reactants, 0-100 wt% of a catalyst, and 0-80 wt% of a stabilizer. Preferably, the oil phase comprises, by weight percentage: 0-90 wt% of a water-immiscible solvent, 0-10 wt% of reactants, 0-10 wt% of a catalyst, and 0-10 wt% of a stabilizer.

[0022] According to an embodiment of the present invention, the aqueous solvent is selected from at least one of water and ionic liquids. Preferably, the ionic liquid is selected from ionic liquids known in the art, and is preferably an ionic liquid that is immiscible with nonpolar solvents (e.g., solvents immiscible with water, such as alkanes) but miscible with water.

[0023] According to an embodiment of the present invention, the solvent immiscible with water is silicone oil, aliphatic ester, aromatic ester, aliphatic haloalkanes, aromatic hydrocarbons, aliphatic ethers, aromatic ethers, or alkanes (preferably C). 6-16 Alkanes), alcohols (preferably C) 6-16 Alcohols), petroleum hydrocarbons (preferably C) 22-50 A mixture of any one or at least two of petroleum hydrocarbons; preferably aromatic hydrocarbons, C 6-16 Alkanes, C 6-16 Any one of the alcohols.

[0024] According to an embodiment of the present invention, the material of the cyclic colloid particles is selected from at least one of inorganic substances, organic substances, and combinations of inorganic and organic substances. Preferably, the inorganic substance is selected from at least one or a combination of two or more of silicon dioxide, titanium dioxide, and iron oxide, with silicon dioxide being the most preferred. Preferably, the organic substance is selected from at least one or a combination of two or more of phenol-formaldehyde, resorcinol-formaldehyde, polyacrylamide, polystyrene, and polymethyl methacrylate, with resorcinol-formaldehyde resin being the most preferred.

[0025] According to an embodiment of the present invention, the annular colloidal particle is a hollow ring, and the diameter, height, or difference between the inner and outer diameters of the ring can be adjusted. Preferably, the diameter of the annular colloidal particle is 500nm to 5000nm, for example, 1000nm, 2000nm, 3000nm, or 4000nm. Preferably, the height of the annular colloidal particle is 100nm to 1000nm, for example, 200nm, 300nm, 400nm, 500nm, 600nm, 700nm, 800nm, or 900nm. Preferably, the difference between the inner and outer diameters of the annular colloidal particle is 10nm to 3000nm, for example, 50nm, 100nm, 500nm, or 2000nm.

[0026] According to embodiments of the present invention, the reactants are optional. Preferably, the reactants are selected from at least one of ester reactants, phenol reactants, alcohol reactants, acid reactants, and aldehyde reactants. Preferably, the ester reactants are selected from at least one of p-nitrobenzene palmitate, 4-nitrobenzenebutyrate, p-nitrobenzene hexanoate, 4-nitrobenzene decanoate, 4-nitrobenzene valerate, 4-nitrobenzene octanoate, 4-nitrobenzene laurate, 4-nitrobenzene salicylate, magnesium p-nitrobenzyl malonate monoester, and 4-nitrobenzene myristate. Preferably, the phenol reactants are selected from at least one of p-nitrophenol, p-aminophenol, and pyrogallol. Preferably, the alcohol reactants are selected from at least one of benzyl alcohol, 4-methoxybenzyl alcohol, 3-methylbenzyl alcohol, 3,5-dibenzyloxybenzyl alcohol, butanol, and hexanol. Preferably, the acid reactants are selected from at least one of formic acid, acetic acid, propionic acid, butyric acid, hexanoic acid, benzoic acid, salicylic acid, oxalic acid, etc. Preferably, the aldehyde reactants are selected from at least one of benzaldehyde, 2-fluorobenzaldehyde, 4-fluorobenzaldehyde, p-methylbenzaldehyde, p-methoxybenzaldehyde, sulphuraldehyde, pentanal, cinnamaldehyde, 3-(2-furanyl)propenal, etc.

[0027] According to embodiments of the present invention, the catalyst is an optional catalyst. Preferably, the catalyst is selected from at least one of metal catalysts, metal oxide catalysts, biocatalysts, acid catalysts, or base catalysts.

[0028] Preferably, the metal catalyst is selected from at least one of platinum, gold, palladium, iridium, silver, copper, rhodium, ruthenium, etc.

[0029] Preferably, the metal oxide catalyst is selected from at least one of copper oxide, iron oxide, tungsten oxide, titanium dioxide, cuprous oxide, zinc oxide, tin dioxide, etc.

[0030] Preferably, the biocatalyst is selected from lipase, hemoglobin, and catalase. Preferably, the lipase is selected from at least one of Candida antarcticis lipase A, Candida antarcticis lipase B, Candida pleurisy lipase, Pseudomonas cepacia lipase, Aspergillus oryzae lipase, Pseudomonas fluorescens lipase, and Aspergillus niger lipase.

[0031] Preferably, the acid catalyst is selected from at least one of hydrochloric acid, sulfuric acid, phosphoric acid, phosphotungstic acid, and boric acid.

[0032] Preferably, the alkaline catalyst is selected from at least one of ethylenediamine, triethylamine, ammonia, sodium carbonate, sodium hydroxide, and potassium hydroxide.

[0033] According to embodiments of the present invention, the stabilizer is an optional stabilizer. Preferably, it is selected from at least one of polyvinylpyrrolidone, sodium citrate, hexadecyltrimethylammonium bromide, tetramethylammonium hydroxide, tetramethylammonium bromide, and tetramethylammonium chloride.

[0034] The present invention also provides a method for preparing the above-mentioned Pickering emulsion, wherein the preparation method includes mixing an aqueous solvent, a solvent immiscible with water, and cyclic colloidal particles, and the emulsion obtained after emulsification is an oil-in-water Pickering emulsion.

[0035] Optionally, at least one of the reactants, catalysts, and stabilizers may be added during mixing.

[0036] According to an embodiment of the present invention, the preparation method specifically includes the following steps:

[0037] (1) Preparation of cyclic colloidal particles;

[0038] (2) Surface modification of cyclic colloidal particles to make them interfacially active: First, the cyclic colloidal particles in step (1) are hydrophilically treated to obtain hydrophilic cyclic colloidal particles; then the hydrophilic cyclic colloidal particles are dispersed in an organic solvent, and a hydrophobic agent is added to perform hydrophobic modification under stirring (e.g., magnetic stirring) to obtain cyclic colloidal particles with interfacial activity.

[0039] (3) Preparation of oil-in-water Pickering emulsion: The interfacially active cyclic colloidal particles are dispersed in an aqueous solvent, and then mixed with a water-immiscible solvent to emulsify and prepare an oil-in-water Pickering emulsion.

[0040] According to an embodiment of the present invention, in step (1), the preparation method of the cyclic colloidal particles is as follows: a composite droplet is prepared by using monodisperse polymer spheres, a cyclic colloidal precursor (such as a silicon precursor or a carbon precursor) is mixed with the dispersion of the composite droplet, the cyclic colloidal precursor is reacted using the composite droplet as a template (selectively coating material on the outside of the polymer disk), and after removing the template, cyclic colloidal particles are obtained.

[0041] According to an embodiment of the present invention, the composite droplet has a sandwich structure, with a polymer disk (such as a polystyrene disk) in the middle and hemispherical droplet caps of nonpolar alkanes (such as decane) at both ends. The two symmetrical hemispherical droplet caps sandwich the polymer disk in the middle to form a sandwich structure, so that the surface of the composite droplet has a "patch" structure. The middle surface of the composite droplet is the side of the polymer disk, and the two ends are the surfaces of the two nonpolar alkane spherical caps.

[0042] According to an embodiment of the present invention, in step (1), a sandwich-structured composite droplet is used as a template, and the cyclic colloidal precursor (e.g., tetraethyl orthosilicate) grows selectively only on the side of the polymer disk. After the composite droplet is removed, cyclic colloidal particles (e.g., cyclic silica particles) are obtained.

[0043] According to an embodiment of the present invention, the sandwich-structured composite droplet can be prepared using methods known in the art.

[0044] According to a preferred embodiment of the present invention, in step (1), polymer balls can be dispersed and polymerized in methanol, water, and nonpolar alkanes to prepare the sandwich-structured composite droplets.

[0045] According to an exemplary embodiment of the present invention, a method for preparing sandwich-structured composite droplets is as follows: polymer spheres, initiator, stabilizer, acrylate monomers, and nonpolar alkanes are reacted in a mixed solvent of methanol and water to prepare sandwich-structured composite droplets.

[0046] According to an embodiment of the present invention, in step (2), the hydrophilic treatment specifically includes: dispersing the cyclic colloidal particles in a strong oxidizing agent (e.g., hydrogen peroxide), then slowly adding a concentrated acid (e.g., 98 wt% sulfuric acid), and completing the hydrophilic treatment under magnetic stirring in a water bath. Preferably, after the hydrophilic treatment, the hydrophilic cyclic colloidal particles are dispersed with an aqueous solvent, centrifuged, and washed. Preferably, the aqueous solvent includes water and alcohols, such as water and ethanol.

[0047] According to an embodiment of the present invention, in step (2), the strong oxidant is, for example, hydrogen peroxide, preferably 30 wt% hydrogen peroxide. Preferably, the present invention does not specifically limit the amount of the strong oxidant used, for example, the volume is 3 to 36 mL, preferably 9 to 18 mL.

[0048] According to an embodiment of the present invention, in step (2), the temperature of the hydrophilic treatment is 20 to 100°C, preferably 60 to 90°C; the time of the hydrophilic treatment is 0.1 to 48 hours, preferably 1 to 6 hours.

[0049] According to an embodiment of the present invention, in step (2), the organic solvent is selected from at least one or a combination of two or more of toluene, alcohol solvents and alkane solvents, preferably toluene.

[0050] According to an embodiment of the present invention, in step (2), the hydrophobic agent is selected from silane coupling agents.

[0051] According to an embodiment of the present invention, in step (2), the silane coupling agent is selected from silane coupling agents containing alkyl, vinyl, amino, phenyl, epoxy, mercapto, methacryloyloxy, or other groups. Preferably, the silane coupling agent is phenyltrimethoxysilane, methyltrimethoxysilane, butyltrimethoxysilane, or dichlorodimethoxysilane.

[0052] According to an embodiment of the present invention, in step (2), the mass-to-volume ratio of the hydrophilic cyclic colloidal particles to the silane coupling agent is 80 mg:(0.001-2) μL, preferably 80 mg:(0.01-1.5) μL, for example 80 mg:0.02 μL, 80 mg:0.10 μL, 80 mg:0.20 μL, or 80 mg:1.00 μL.

[0053] According to the embodiment of the present invention, in step (2), the hydrophobic modification conditions can be selected from those known in the art, and the present invention does not make specific limitations.

[0054] According to an embodiment of the present invention, in step (2), after the hydrophobic modification is completed, the interfacially active cyclic colloidal particles are dispersed and washed by centrifugation with water and ethanol.

[0055] According to an embodiment of the present invention, in step (2), after obtaining the cyclic colloidal particles with interfacial activity, a drying process can also be performed.

[0056] According to an embodiment of the present invention, in step (2), the grafting density of the interfacially active cyclic colloidal particles is no greater than 1.5 nm. -2 For example, 0.35nm -2 0.54nm -2 0.76nm -2 1.35nm-2 In this invention, the grafting density refers to the number of hydrophobic agent molecules per square nanometer area on the cyclic colloidal particles.

[0057] According to embodiments of the present invention, the aqueous solvent has the meaning as described above, for example, selected from at least one of water and ionic liquids. Preferably, the ionic liquid is selected from ionic liquids known in the art, and is preferably an ionic liquid that is immiscible with nonpolar solvents (e.g., solvents immiscible with water, such as alkanes).

[0058] According to an embodiment of the present invention, in step (3), the water-immiscible solvent has the meaning as described above.

[0059] According to an embodiment of the present invention, in step (3), when dispersing the interfacially active cyclic colloidal particles in an aqueous solvent, or when mixing them with a solvent that is immiscible with water, reactants, catalysts and stabilizers may also be added.

[0060] According to an embodiment of the present invention, in step (3), the emulsification method is selected from homogenizer shear emulsification, ultrasonic emulsification or hand-crank emulsification.

[0061] The present invention also provides the application of the above-mentioned Pickering emulsion in biphasic interfacial catalysis.

[0062] According to embodiments of the present invention, the Pickering emulsion has the meaning as described above. Preferably, by mass percentage, the Pickering emulsion comprises at least: 10–99.9999 wt% aqueous solvent, 0.0001–20 wt% cyclic colloidal particles, 0–89.9999 wt% reactants, 0–89.9999 wt% catalyst, 0–80 wt% stabilizer, and the remainder being a solvent immiscible with water.

[0063] According to embodiments of the present invention, the biphase interface catalysis is, for example, at least one of the following: hydrolysis of ester reactants, reduction of phenol reactants, esterification of acid reactants and alcohol reactants, and oxidation of alcohol reactants and aldehyde reactants.

[0064] The present invention also provides a hydrolysis reaction of esters, wherein the Pickering composite emulsion is used as a catalyst platform in the hydrolysis reaction.

[0065] According to an embodiment of the present invention, the ester is p-nitrobenzene palmitate.

[0066] According to an embodiment of the present invention, the catalyst is Aspergillus oryzae lipase.

[0067] According to an embodiment of the present invention, the catalyst platform comprises an oil-in-water emulsion containing esters and a catalyst. Preferably, the oil-in-water emulsion containing esters and a catalyst is obtained by the following method: esters (such as p-nitrobenzene palmitate) are dissolved in a water-immiscible solvent, mixed with an aqueous dispersion of cyclic colloidal particles and an aqueous dispersion of a catalyst (such as an aqueous dispersion of Aspergillus oryzae lipase), and then emulsified.

[0068] According to an embodiment of the present invention, the hydrolysis reaction is carried out at 20–50°C.

[0069] The beneficial effects of this invention are:

[0070] By controlling the grafting density of cyclic colloidal particles, a Pickering emulsion with low interfacial coverage, stabilized by cyclic colloidal particles, was prepared. When the cyclic colloidal particles are arranged in a monolayer hexagonal close-packed structure at the interface, the free interface ratio of the emulsion is approximately 80% due to the unique cavity structure of the cyclic colloidal particles. Catalytic reactions based on this emulsion not only facilitate contact between reactants or between reactants and catalysts, but also enhance the interfacial mass transfer rate and promote the rapid diffusion of products from one phase to another. It exhibits advantages such as high conversion rate, high catalytic efficiency, and simple product separation, and has significant application prospects in the field of interfacial catalysis. Attached Figure Description

[0071] Figure 1 The image shows a scanning electron microscope (SEM) image of the silica cyclic colloidal particles prepared in Example 1, with a scale bar of 2 μm.

[0072] Figure 2 Thermogravimetric analysis (TGA) diagrams of the cyclic colloidal particles with different interfacial activities prepared in Example 1.

[0073] Figure 3 Optical microscope images of oil-in-water Pickering emulsions with different interfacial activities stable by cyclic colloidal particles in Example 1.

[0074] Figure 4 The images are optical micrographs of the oil-in-water Pickering emulsion stabilized by silica ring colloidal particles in Example 2, with scale bars of 100 μm (a) and 20 μm (b).

[0075] Figure 5 This is a schematic diagram illustrating the catalytic hydrolysis of p-nitrophenyl palmitate to p-nitrophenol in an oil-in-water Pickering emulsion stabilized by silica cyclic colloidal particles, as described in Example 2.

[0076] Figure 6 This is a kinetic curve of the hydrolysis of p-nitrophenyl palmitate to p-nitrophenol in an oil-in-water Pickering emulsion stabilized by silica cyclic colloidal particles, as shown in Example 2.

[0077] Figure 7 The image shows a scanning electron microscope (SEM) image of the silica spheres prepared in Comparative Example 1, with a scale bar of 500 nm.

[0078] Figure 8 The images show optical micrographs of the water-in-oil Pickering emulsion stabilized by silica spheres prepared in Comparative Example 1. The scale bars are 100 μm (a) and 20 μm (b).

[0079] Figure 9 The kinetic curve for the hydrolysis of p-nitrophenyl palmitate to p-nitrophenol in a silica-sphere-stabilized oil-in-water Pickering emulsion is shown in Comparative Example 1.

[0080] Figure 10 The images show optical micrographs of the oil-in-water Pickering emulsion in Comparative Example 2, where the cyclic colloidal particles are arranged into a tubular structure at the interface. The scale bars are 100 μm (a) and 20 μm (b).

[0081] Figure 11 The kinetic curve for the hydrolysis of p-nitrophenyl palmitate to p-nitrophenol in an oil-in-water Pickering emulsion in which cyclic colloidal particles are arranged in a tubular structure at the interface is shown in Comparative Example 2.

[0082] Figure 12 The kinetic curve of the hydrolysis of p-nitrophenyl palmitate to p-nitrophenol in a water-toluene biphase system is shown for Comparative Example 3. Detailed Implementation

[0083] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention, and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0084] Unless otherwise stated, the raw materials and reagents used in the following examples are commercially available products or can be prepared by known methods.

[0085] Example 1

[0086] The preparation method of a water-in-oil Pickering emulsion stabilized by cyclic colloidal particles includes the following steps:

[0087] 1) Dissolve 0.20 g of azobisisobutyronitrile (AIBN) and 3.78 g of polyvinylpyrrolidone (PVP) in 180.00 g of anhydrous ethanol. Add 22.00 mL of styrene to the solution, deoxygenate with nitrogen for 15 min, and magnetically stir at 70 °C for 8 h. Purify the polystyrene microspheres by centrifugation / redispersion cycles three times with ethanol, and then disperse them in 100.00 g of anhydrous ethanol. To modify the polystyrene microspheres, add 0.30 g of AIBN, 3.78 g of PVP, and 80.00 g of anhydrous ethanol to the 100.00 g polystyrene microsphere dispersion. Then, 300.00 μL of methacryloyloxyethyltrimethylammonium chloride aqueous solution (30 wt%), 6.00 mL of styrene, 6.00 mL of water, and 20.00 mL of anhydrous ethanol were added to the mixed solution. After deoxygenation under nitrogen for 15 min, the mixture was magnetically stirred at 70 °C for 1 h. The obtained particles were purified by sequential centrifugation / redispersion with ethanol and water. Finally, the particles were dispersed in water to obtain a modified polystyrene microsphere dispersion (23.5 wt%). The average particle size of the modified polystyrene microspheres was 1.22 ± 0.04 μm.

[0088] 0.10 g azobisisobutyronitrile (AIBN), 0.40 g polyvinylpyrrolidone (PVP), 32.00 g methanol, 4.25 g modified polystyrene microsphere dispersion, and 4.75 g water were ultrasonically mixed until homogeneous. Then, 1.21 g 2-ethylhexyl methacrylate was added and stirred at room temperature for 20 min. Next, 6.84 mL n-decane was added, the mixture was sealed, and nitrogen gas was purged to remove oxygen. The mixture was then sealed again and heated in a 60°C water bath with magnetic stirring for 10 h to obtain a sandwich-shaped composite droplet template. This sandwich-shaped composite droplet template was dispersed in a mixture of 121.20 g methanol and 20.88 g water and stirred at room temperature for 10 min. Then, 21.60 mL ammonia (28 wt%) and 9.6 mL tetraethyl orthosilicate were added. The mixture was reacted at room temperature for 6 h. The reaction solution was then washed with n-butanol by centrifugation, followed by centrifugation with tetrahydrofuran to remove the polystyrene core. Finally, the mixture was washed with ethanol and water by centrifugation to obtain an aqueous dispersion of silica ring-shaped colloidal particles.

[0089] The scanning electron microscope image of the silica cyclic colloidal particles prepared in step 1) is shown below. Figure 1 As shown in the figure, the inner diameter of the silica ring particles is 0.94±0.02μm, the outer diameter is 1.08±0.02μm, and the lateral height is 0.46±0.04μm.

[0090] 2) Surface hydrophobic modification of cyclic colloidal particles to make them interfacially active: a) First, the silica cyclic colloidal particles were hydrophilically treated with piranha acid. The specific method included: centrifuging the aqueous dispersion of silica cyclic colloidal particles obtained in step 1), discarding the supernatant, dispersing the precipitate in 9.00 mL of hydrogen peroxide (30 wt%), transferring the dispersion to a flask, and slowly adding 21.00 mL of sulfuric acid (98 wt%) to the flask under magnetic stirring. The mixture was then heated in a 90°C water bath under magnetic stirring for 3 h to obtain a reaction solution of hydrophilic silica cyclic colloidal particles. b) The above reaction solution of hydrophilic silica cyclic colloidal particles was poured into a 1:1 volume ratio ethanol / water mixture, and the mixture was dispersed and washed successively with water and ethanol by centrifugation, and finally dispersed in toluene. c) The hydrophilic silica cyclic particles were then modified with phenyltrimethoxysilane. The specific method included: dispersing approximately 80 mg of the hydrophilic silica cyclic particles in 12 mL of toluene, adding 0 μL, 0.02 μL, 0.10 μL, 0.20 μL, 1.00 μL, 2.00 μL, and 4.00 μL of phenyltrimethoxysilane respectively, and refluxing at 120 °C with magnetic stirring in an oil bath for 8 h. Then, the particles were dispersed and washed sequentially with toluene and ethanol by centrifugation, and finally dried in an oven to obtain unmodified silica cyclic particles with different interfacial activities, named R0, R1, R2, R3, R4, R5, and R6, respectively. The thermogravimetric diagrams of the cyclic particles with different interfacial activities prepared in this example are shown below. Figure 2 As shown in the figure. Based on the thermogravimetric analysis, the grafting densities of R1, R2, R3, R4, R5, and R6 are calculated to be 0.35 nm. -2 0.54nm -2 0.76nm -2 1.35nm -2 1.7nm -2 2.1nm -2 .

[0091] The silica cyclic colloidal particles with different interfacial activities were dispersed in water to achieve a concentration of 20 mg / mL. 400 μL of toluene was mixed with 800 μL of the aqueous dispersion of silica cyclic colloidal particles, and emulsified using a homogenizer at a shear rate of 14500 rpm / min for 2 min to obtain an oil-in-water Pickering emulsion. Optical microscopic images of the stable oil-in-water Pickering emulsions prepared by R1, R2, R3, R4, R5, and R6 are shown below. Figure 3 As shown in AF.

[0092] The results show that the grafting density of the cyclic colloidal particles affects their assembly structure at the interface. When the grafting density of the cyclic colloidal particles is no greater than 1.5 nm... -2At this time, the assembly structure of the cyclic colloidal particles at the interface is a single-layer hexagonal close-packed structure; as the grafting density of the cyclic colloidal particles increases to 1.7 nm... -2 At that time, the assembly structure of the cyclic colloidal particles at the interface gradually changes from a single-layer hexagonal close-packed structure to a coexistence of tubular and single-layer structures, and finally all of them become tubular structures.

[0093] Example 2

[0094] Catalytic hydrolysis of p-nitrophenyl palmitate to p-nitrophenol in an oil-in-water Pickering emulsion stabilized by cyclic colloidal particles includes the following steps:

[0095] 1) Dissolve 0.20 g of azobisisobutyronitrile (AIBN) and 3.78 g of polyvinylpyrrolidone (PVP) in 180.00 g of anhydrous ethanol. Add 22.00 mL of styrene to the solution, deoxygenate with nitrogen for 15 min, and magnetically stir at 70 °C for 8 h. Purify the polystyrene microspheres by centrifugation / redispersion cycles three times with ethanol, and then disperse them in 100.00 g of anhydrous ethanol. To modify the polystyrene microspheres, add 0.30 g of AIBN, 3.78 g of PVP, and 80.00 g of anhydrous ethanol to the 100.00 g polystyrene microsphere dispersion. Then, 300.00 μL of methacryloyloxyethyltrimethylammonium chloride aqueous solution (30 wt%), 6.00 mL of styrene, 6.00 mL of water, and 20.00 mL of anhydrous ethanol were added to the mixed solution. After deoxygenation under nitrogen for 15 min, the mixture was magnetically stirred at 70 °C for 1 h. The obtained particles were purified by sequential centrifugation / redispersion with ethanol and water. Finally, the particles were dispersed in water to obtain a modified polystyrene microsphere dispersion (23.5 wt%). The average particle size of the modified polystyrene microspheres was 1.22 ± 0.04 μm.

[0096] 0.10 g azobisisobutyronitrile (AIBN), 0.40 g polyvinylpyrrolidone (PVP), 32.00 g methanol, 4.25 g modified polystyrene microsphere dispersion, and 4.75 g water were ultrasonically mixed until homogeneous. Then, 1.21 g 2-ethylhexyl methacrylate was added and stirred at room temperature for 20 min. Next, 6.84 mL n-decane was added, the mixture was sealed, and nitrogen gas was purged to remove oxygen. The mixture was then sealed again and heated in a 60°C water bath with magnetic stirring for 10 h to obtain a sandwich-shaped composite droplet template. This sandwich-shaped composite droplet template was dispersed in a mixture of 121.20 g methanol and 20.88 g water and stirred at room temperature for 10 min. Then, 21.60 mL ammonia (28 wt%) and 9.6 mL tetraethyl orthosilicate were added. The mixture was reacted at room temperature for 6 h. The reaction solution was then washed with n-butanol by centrifugation, followed by centrifugation with tetrahydrofuran to remove the polystyrene core. Finally, the mixture was washed with ethanol and water by centrifugation to obtain an aqueous dispersion of silica ring-shaped colloidal particles.

[0097] 2) Surface hydrophobic modification of cyclic colloidal particles to make them interfacially active: a) First, the silica cyclic colloidal particles were hydrophilically treated with piranha acid. The specific method included: centrifuging the aqueous dispersion of silica cyclic colloidal particles obtained in step 1), discarding the supernatant, dispersing the precipitate in 9.00 mL of hydrogen peroxide (30 wt%), transferring the dispersion to a flask, and slowly adding 21.00 mL of sulfuric acid (98 wt%) to the flask under magnetic stirring. The mixture was then heated in a 90°C water bath under magnetic stirring for 3 h to obtain a reaction solution of hydrophilic silica cyclic colloidal particles. b) The above reaction solution of hydrophilic silica cyclic colloidal particles was poured into a 1:1 volume ratio ethanol / water mixture, and the mixture was dispersed and washed successively with water and ethanol by centrifugation, and finally dispersed in toluene. c) The hydrophilic silica cyclic particles were then modified with phenyltrimethoxysilane. The specific method included: dispersing approximately 80 mg of the hydrophilic silica cyclic particles in 12 mL of toluene, adding 0.2 μL of phenyltrimethoxysilane, refluxing in an oil bath at 120 °C with magnetic stirring for 8 h, then sequentially dispersing and washing with toluene and ethanol by centrifugation, and finally drying in an oven to obtain interfacially active silica cyclic particles. These interfacially active silica cyclic particles were then dispersed in water to a concentration of 20 mg / mL. In this example, the interfacially active silica cyclic particles were designated as R3 in Example 1, and their grafting density was 1.35 nm. -2 .

[0098] 40 mg of p-nitrophenyl palmitate was dissolved in 400 μL of toluene, and 800 μL of an aqueous dispersion of silica cyclic particles (20 mg / mL) was added. A Pickering emulsion was prepared by homogenization at 14500 rpm / min for 2 min. Subsequently, 8.18 mL of Aspergillus oryzae lipase aqueous dispersion (0.053 mg / mL, dispersed in phosphate buffer) was added, and the hydrolysis reaction was carried out under undisturbed conditions at 30 °C. At each given time point, 0.5 mL of the emulsion was taken for conversion analysis. The sampled emulsion was rapidly centrifuged at 5000 rpm / min for 2 min. After centrifugation, a clear emulsion layer and an aqueous layer were observed. 100 μL of the aqueous phase was taken from the aqueous layer and further diluted to 10 mL with 0.5 M sodium carbonate solution. The absorbance of the diluted sample was determined by UV-Vis spectroscopy, and the concentration of the product p-nitrophenol was analyzed using the absorption peak at 400 nm according to the standard curve. All reactions were repeated at least three times.

[0099] The optical microscope image of the oil-in-water Pickering emulsion stabilized by silica cyclic colloidal particles prepared in this embodiment is as follows: Figure 4 As shown, the results indicate that the average droplet size of the emulsion is 76±22μm; the silica ring particles are arranged in a hexagonal monolayer structure at the oil-water interface.

[0100] This embodiment illustrates the catalytic hydrolysis of p-nitrophenyl palmitate to p-nitrophenol in an oil-in-water Pickering emulsion stabilized by silica cyclic colloidal particles, as shown in the diagram. Figure 5 As shown in the figure. In this embodiment, the kinetic curve of the hydrolysis of p-nitrophenyl palmitate to p-nitrophenol in a Pickering emulsion stabilized by silica cyclic colloidal particles is shown in the figure. Figure 6 As shown in the figure. The results indicate that the conversion rate is greater than 80% after 1 hour of reaction and greater than 90% after 2 hours of reaction.

[0101] Comparative Example 1

[0102] The application of silica sphere-stabilized oil-in-water Pickering emulsions in the catalytic hydrolysis of p-nitrophenyl palmitate to p-nitrophenol includes the following steps:

[0103] 1) Silica spheres were synthesized according to a published method. 9.00 mL of tetraethyl orthosilicate and 180.00 mL of anhydrous ethanol were mixed in a 250 mL single-necked flask. A mixture of 15.40 mL of ammonia (25.0 wt%) and 4.46 mL of water was slowly added under magnetic stirring. The reaction was carried out at 30 °C for 12 h. The silica spheres were then purified by centrifugation / redispersion with water and ethanol sequentially.

[0104] The scanning electron microscope image of the silica spheres prepared in step 1) is shown below. Figure 7 As shown in the figure, the average diameter of the silica spheres is approximately 270 nm.

[0105] 2) Surface hydrophobic modification of silica spheres to enhance their interfacial activity. First, the silica spheres were hydrophilically treated with piranha acid. Specifically, the aqueous dispersion of silica spheres obtained in step 1) was centrifuged, the supernatant was discarded, and the precipitate was dispersed in 9.00 mL of hydrogen peroxide (30 wt%). The dispersion was transferred to a flask, and 21.00 mL of sulfuric acid (98 wt%) was slowly added to the flask under magnetic stirring. The mixture was heated in a 90°C water bath with magnetic stirring for 3 hours to obtain hydrophilic silica spheres. The reaction solution was then poured into a 1:1 ethanol / water mixture, and the mixture was washed sequentially by centrifugation with water and ethanol, finally dispersed in toluene. The hydrophilic silica spheres were then modified with phenyltrimethoxysilane. Specifically, approximately 160 mg of hydrophilic silica spheres were dispersed in 12.00 mL of toluene, and then 5.00 μL of phenyltrimethoxysilane was added. The mixture was refluxed at 120°C for 8 hours under magnetic stirring to obtain interfacially active silica spheres. These silica spheres were then dispersed in water to achieve a concentration of 20 mg / mL.

[0106] 3) Catalytic hydrolysis of p-nitrobenzene palmitate to p-nitrophenol was performed using a silica-sphere-stabilized oil-in-water Pickering emulsion. 40 mg of p-nitrobenzene palmitate was dissolved in 400 μL of toluene, and 800 μL of an aqueous dispersion of silica spheres was added. The mixture was emulsified using a homogenizer at a shear rate of 14500 rpm / min for 2 min to prepare a Pickering emulsion. Subsequently, 8.18 mL of Aspergillus oryzae lipase aqueous dispersion (0.053 mg / mL, dispersed in phosphate buffer) was added, and the hydrolysis reaction was carried out under undisturbed conditions at 30 °C. At each given time point, 0.5 mL of the emulsion was taken for conversion analysis. The sampled emulsion was rapidly centrifuged at 5000 rpm / min for 2 min. After centrifugation, a clear emulsion layer and an aqueous layer were observed. 100 μL of the aqueous phase was taken from the aqueous layer and further diluted to 10 mL with 0.5 M sodium carbonate solution. The absorbance of the diluted sample was determined by UV-Vis spectroscopy, and the concentration of the product p-nitrophenol was analyzed using the absorption peak at 400 nm according to the standard curve. All reactions were repeated at least three times.

[0107] The optical microscope image of the water-in-oil Pickering emulsion stabilized by silica spheres prepared in this embodiment is as follows: Figure 8 As shown, the results indicate that the average droplet size of the emulsion is 72 ± 18 μm, which is similar to the droplet size of oil-in-water Pickering emulsions stabilized by silica spheres.

[0108] The kinetic curves of the hydrolysis of p-nitrophenyl palmitate to p-nitrophenol in a silica-sphere-stabilized Pickering emulsion in this comparative example are shown in the figure below. Figure 9 As shown in the figure, the conversion rate was only 51% after 1 hour of reaction and only 72% after 2 hours of reaction.

[0109] Based on the conversion rate in the first 10 minutes, the specific activity of Aspergillus oryzae lipase in the water-in-oil Pickering emulsion with silica rings in Example 2 was 2.2 times that in the water-in-oil Pickering emulsion with silica spheres in Example 1. Since the droplet sizes of the silica sphere-based and silica ring-based stabilized Pickering emulsions are similar, it can be confirmed that the oil-water interface is larger in the silica monolayer ring-stabilized Pickering emulsion of the present invention, allowing the catalyst to achieve high conversion rates in a short reaction time.

[0110] Comparative Example 2

[0111] The application of oil-in-water Pickering emulsions stable when silica rings are arranged in a tubular structure at the interface in the catalytic hydrolysis of p-nitrophenyl palmitate to p-nitrophenol includes the following steps:

[0112] 1) Dissolve 0.20 g of azobisisobutyronitrile (AIBN) and 3.78 g of polyvinylpyrrolidone (PVP) in 180.00 g of anhydrous ethanol. Add 22.00 mL of styrene to the solution, deoxygenate with nitrogen for 15 min, and magnetically stir at 70 °C for 8 h. Purify the polystyrene microspheres by centrifugation / redispersion cycles three times with ethanol, and then disperse them in 100.00 g of anhydrous ethanol. To modify the polystyrene microspheres, add 0.30 g of AIBN, 3.78 g of PVP, and 80.00 g of anhydrous ethanol to the 100.00 g polystyrene microsphere dispersion. Then, 300.00 μL of methacryloyloxyethyltrimethylammonium chloride aqueous solution (30 wt%), 6.00 mL of styrene, 6.00 mL of water, and 20.00 mL of anhydrous ethanol were added to the mixed solution. After deoxygenation under nitrogen for 15 min, the mixture was magnetically stirred at 70 °C for 1 h. The obtained particles were purified by sequential centrifugation / redispersion with ethanol and water. Finally, the particles were dispersed in water to obtain a modified polystyrene microsphere dispersion (23.5 wt%). The average particle size of the modified polystyrene microspheres was 1.22 ± 0.04 μm.

[0113] 0.10 g azobisisobutyronitrile (AIBN), 0.40 g polyvinylpyrrolidone (PVP), 32.00 g methanol, 4.25 g modified polystyrene microsphere dispersion, and 4.75 g water were ultrasonically mixed until homogeneous. Then, 1.21 g 2-ethylhexyl methacrylate was added and stirred at room temperature for 20 min. Next, 6.84 mL n-decane was added, the mixture was sealed, and nitrogen gas was purged to remove oxygen. The mixture was then sealed again and heated in a 60°C water bath with magnetic stirring for 10 h to obtain a sandwich-shaped composite droplet template. This sandwich-shaped composite droplet template was dispersed in a mixture of 121.20 g methanol and 20.88 g water and stirred at room temperature for 10 min. Then, 21.60 mL ammonia (28 wt%) and 9.6 mL tetraethyl orthosilicate were added. The mixture was reacted at room temperature for 6 h. The reaction solution was then washed with n-butanol by centrifugation, followed by centrifugation with tetrahydrofuran to remove the polystyrene core. Finally, the mixture was washed with ethanol and water by centrifugation to obtain an aqueous dispersion of silica ring-shaped colloidal particles.

[0114] 2) Surface hydrophobic modification of cyclic colloidal particles to make them interfacially active: a) First, the silica cyclic colloidal particles were hydrophilically treated with piranha acid. The specific method included: centrifuging the aqueous dispersion of silica cyclic colloidal particles obtained in step 1), discarding the supernatant, dispersing the precipitate in 9.00 mL of hydrogen peroxide (30 wt%), transferring the dispersion to a flask, and slowly adding 21.00 mL of sulfuric acid (98 wt%) to the flask under magnetic stirring. The mixture was then heated in a 90°C water bath under magnetic stirring for 3 h to obtain a reaction solution of hydrophilic silica cyclic colloidal particles. b) The above reaction solution of hydrophilic silica cyclic colloidal particles was poured into a 1:1 volume ratio ethanol / water mixture, and the mixture was dispersed and washed successively with water and ethanol by centrifugation, and finally dispersed in toluene. c) The hydrophilic silica cyclic particles were then modified with phenyltrimethoxysilane. The specific method included: dispersing approximately 80 mg of the hydrophilic silica cyclic particles in 12 mL of toluene, adding 4 μL of phenyltrimethoxysilane, and refluxing in an oil bath at 120°C with magnetic stirring for 8 hours. The particles were then successively dispersed and washed with toluene and ethanol by centrifugation, and finally dried in an oven to obtain interfacially active silica cyclic particles. These interfacially active silica cyclic particles were then dispersed in water to a concentration of 20 mg / mL. In this comparative example, the interfacially active silica cyclic particles were designated as R6 in Example 1, with a grafting density of 2.1 nm. -2 .

[0115] 40 mg of p-nitrobenzene palmitate was dissolved in 400 μL of toluene. Then, 800 μL of an aqueous dispersion (20 mg / mL) of the interfacially active silica cyclic colloidal particles from the previous step was added. A Pickering emulsion was prepared by homogenization at 14500 rpm / min for 2 min. Subsequently, 8.18 mL of Aspergillus oryzae lipase aqueous dispersion (0.053 mg / mL, dispersed in phosphate buffer) was added, and the hydrolysis reaction was carried out under undisturbed conditions at 30 °C. At each given time point, 0.5 mL of the emulsion was taken for conversion analysis. The sampled emulsion was rapidly centrifuged at 5000 rpm / min for 2 min. After centrifugation, a clear emulsion layer and an aqueous layer were observed. 100 μL of the aqueous phase was taken from the aqueous layer and further diluted to 10 mL with 0.5 M sodium carbonate solution. The absorbance of the diluted sample was determined by UV-Vis spectroscopy, and the concentration of the product p-nitrophenol was analyzed using the absorption peak at 400 nm according to the standard curve. All reactions were repeated at least 3 times.

[0116] Optical microscopic images of the oil-in-water Pickering emulsion stabilized by silica cyclic colloidal particles prepared in this comparative example are shown below. Figure 10 As shown, the results indicate that the average droplet size of the emulsion is 75±17μm; the silica ring particles are arranged in a tubular structure at the oil-water interface.

[0117] In this comparative example, the kinetic curves for the hydrolysis of p-nitrophenyl palmitate to p-nitrophenol in a Pickering emulsion stabilized by silica cyclic colloidal particles are shown in the figure below. Figure 11 As shown in the figure. The results indicate that the conversion rate is greater than 80% after 1 hour of reaction and greater than 90% after 2 hours. Conversely, the conversion rate is only 53% after 1 hour and only 78% after 2 hours.

[0118] Based on the conversion rate in the first 10 minutes, the specific activity of Aspergillus oryzae lipase in the silica-ringed oil-in-water Pickering emulsion of Example 2 was 2.1 times that of the oil-in-water Pickering emulsion of Comparative Example 2. Although silica ring particles were also used in the emulsion of Comparative Example 2, and the droplet sizes were similar, the different grafting densities resulted in different structures assembled at the oil-water interface, leading to different interface coverage. When the silica was arranged in a single-layer hexagonal close-packed structure at the interface, the catalytic rate of Aspergillus oryzae lipase was faster. This demonstrates that the oil-water interface is larger in the silica-ringed Pickering emulsion stabilized by the present invention, allowing the catalyst to achieve high conversion rates in a short reaction time.

[0119] Comparative Example 3

[0120] Without preparing a Pickering emulsion, the hydrolysis of p-nitrophenyl palmitate to p-nitrophenol was directly catalyzed in a water-toluene biphase system. 2.25 mL of Aspergillus oryzae lipase aqueous solution (0.053 mg / mL, dispersed in phosphate buffer) was mixed with 0.64 mL of phosphate buffer solution in a 2 mL stoppered tube, followed by the addition of 110 μL of p-nitrophenyl palmitate toluene solution (100 mg / mL). The reaction was carried out at 30 °C. At each given time point, the stoppered tube was gently shaken to ensure uniform aqueous phase concentration. 100 μL of the aqueous phase was taken and diluted to 2.5 mL with sodium carbonate solution. The absorbance of the diluted sample was determined by UV-Vis spectroscopy, and the concentration of p-nitrophenol was analyzed using the absorption peak at 400 nm according to the standard curve. All reactions were repeated at least three times.

[0121] The kinetic curves for the hydrolysis of p-nitrophenyl palmitate to p-nitrophenol in a water-toluene biphase system of this comparative example are shown in the figure below. Figure 12 As shown in the figure, the conversion rate was only 7.3% after 1 hour of reaction, and only 12% after 2 hours.

[0122] Based on the conversion rate in the first 10 minutes, the specific activity of Aspergillus oryzae lipase in the silica-ringed oil-in-water Pickering emulsion of Example 2 was 17.43 times that in the water-toluene biphase system of Comparative Example 3. This further confirms that the oil-water interface is larger in the silica monolayer ring-stabilized Pickering emulsion of the present invention, and the catalyst can achieve high conversion rates in a short reaction time.

[0123] The exemplary embodiments of the present invention have been described above. However, the scope of protection of this application is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made by those skilled in the art within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A Pickering emulsion, characterized in that, The Pickering emulsion is an oil-in-water emulsion comprising an aqueous phase, an oil phase, and cyclic colloidal particles; wherein the oil phase is dispersed in the aqueous phase in the form of small droplets; the cyclic colloidal particles are located at the oil-water interface, or at the oil-water interface and in the aqueous phase, and the cyclic colloidal particles assemble at the oil-water interface to form a monolayer structure.

2. The Pickering emulsion according to claim 1, characterized in that, The Pickering emulsion may also optionally include at least one of reactants, catalysts, and stabilizers. Preferably, by mass percentage, the Pickering emulsion comprises at least: 10–99.9999 wt% aqueous solvent, 0.0001–20 wt% cyclic colloidal particles, 0–89.9999 wt% reactants, 0–89.9999 wt% catalyst, 0–80 wt% stabilizer, and the remainder being a solvent immiscible with water. Preferably, the aqueous phase of the Pickering emulsion contains an aqueous solvent, cyclic colloidal particles, and optionally at least one of reactants, catalysts, and stabilizers. Preferably, the aqueous phase comprises, by mass percentage, at least: 10–99.9999 wt% aqueous solvent, 0.0001–20 wt% cyclic colloidal particles, 0–90 wt% reactants, 0–90 wt% catalyst, and 0–80 wt% stabilizer. Preferably, the oil phase comprises a solvent immiscible with water; and optionally comprises reactants, catalysts, and stabilizers. Preferably, the oil phase comprises, by mass percentage: 0-100 wt% of a solvent immiscible with water, 0-100 wt% of reactants, 0-100 wt% of a catalyst, and 0-80 wt% of a stabilizer.

3. The Pickering emulsion according to claim 1, characterized in that, The aqueous solvent is selected from at least one of water and ionic liquid. Preferably, the water-immiscible solvent is any one or a mixture of at least two of the following: silicone oil, aliphatic ester, aromatic ester, aliphatic haloalkanes, aromatic hydrocarbons, aliphatic ethers, aromatic ethers, alkanes, alcohols, and petroleum hydrocarbons. Preferably, the material of the cyclic colloid particles is selected from at least one of inorganic substances, organic substances, and combinations of inorganic and organic substances. Preferably, the annular particles are hollow rings. Preferably, the reactants are optional reactants. Preferably, the catalyst is an optional catalyst. Preferably, the stabilizer is an optional stabilizer.

4. The method for preparing the Pickering emulsion according to any one of claims 1-3, characterized in that, The preparation method includes mixing an aqueous solvent, a water-immiscible solvent, and cyclic colloidal particles, and the resulting emulsion after emulsification is an oil-in-water Pickering emulsion. Optionally, at least one of the reactants, catalysts, and stabilizers may be added during mixing.

5. The preparation method according to claim 4, characterized in that, The preparation method specifically includes the following steps: (1) Preparation of cyclic colloidal particles; (2) Surface modification of cyclic colloidal particles to make them interfacially active: First, the cyclic colloidal particles in step (1) are hydrophilically treated to obtain hydrophilic cyclic colloidal particles; then the hydrophilic cyclic colloidal particles are dispersed in an organic solvent, and a hydrophobic agent is added for hydrophobic modification under magnetic stirring to obtain cyclic colloidal particles with interfacial activity. (3) Preparation of oil-in-water Pickering emulsion: The interfacially active cyclic colloidal particles are dispersed in an aqueous solvent, and then mixed with a water-immiscible solvent to emulsify and prepare an oil-in-water Pickering emulsion.

6. The preparation method according to claim 4 or 5, characterized in that, In step (1), the preparation method of the cyclic colloidal particles is as follows: composite droplets are prepared by using monodisperse polymer spheres, the cyclic colloidal precursor is mixed with the dispersion of the composite droplets, the cyclic colloidal precursor is reacted using the composite droplets as templates, and after removing the templates, cyclic colloidal particles are obtained.

7. The preparation method according to any one of claims 4-6, characterized in that, In step (2), the hydrophilic treatment specifically includes: dispersing the cyclic colloidal particles in a strong oxidant, then slowly adding concentrated acid, and completing the hydrophilic treatment under stirring. Preferably, in step (2), the temperature of the hydrophilic treatment is 20 to 100°C, and the time of the hydrophilic treatment is 0.1 to 48 hours. Preferably, in step (2), the organic solvent is selected from at least one or a combination of two or more of toluene, alcohol solvents and alkane solvents. Preferably, in step (2), the hydrophobic agent is selected from silane coupling agents. Preferably, in step (2), the silane coupling agent is selected from silane coupling agents containing alkyl, vinyl, amino, phenyl, epoxy, mercapto, methacryloyloxy, and other groups. Preferably, in step (2), the mass-to-volume ratio of the hydrophilic cyclic colloidal particles to the silane coupling agent is 80 mg:(0.001-2) μL. Preferably, in step (2), the grafting density of the interfacially active cyclic colloidal particles is no greater than 1.5 nm. -2 .

8. The preparation method according to any one of claims 4-7, characterized in that, In step (3), when dispersing interfacially active cyclic colloidal particles in an aqueous solvent, or when mixing them with a solvent that is immiscible with water, reactants, catalysts and stabilizers may also be added.

9. The application of the Pickering emulsion according to any one of claims 1-3 in biphasic interfacial catalysis. Preferably, the Pickering emulsion comprises at least the following by weight percentage: 10–99.9999 wt% aqueous solvent, 0.0001–20 wt% cyclic colloidal particles, 0–89.9999 wt% reactants, 0–89.9999 wt% catalyst, 0–80 wt% stabilizer, and the remainder being water-immiscible solvents.

10. A hydrolysis reaction of an ester, wherein the hydrolysis reaction uses the Pickering composite emulsion as described in any one of claims 1-3 as a catalyst platform. Preferably, the ester is p-nitrobenzene palmitate. Preferably, the catalyst is Aspergillus oryzae lipase. Preferably, the hydrolysis reaction is carried out at 20–50°C.

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