Method for asymmetrically assembling Janus microspheres in micro-droplets and application

Abstract

The invention discloses a method for asymmetrically assembling Janus microspheres in micro-droplets and application, and the method for assembling the Janus microspheres comprises the following steps: S1, preparing hydrophobic micron particles; s2, preparing hydrophilic nanoparticles; s3, performing asymmetric assembly in the micro-droplets to prepare Janus particles; and S3-2, preparation of the Janus microspheres. The microspheres prepared by the method are characterized in that hydrophilic nano-particles are distributed on one side of hydrophobic micro-particles, and the particle diameter is 0.1-10 microns; the self-propelled Janus microspheres are prepared by loading a MnO2 catalyst in situ on nano-particles which are asymmetrically distributed on the MnO2 catalyst. The Janus microsphere can be decomposed on one side of the microsphere in an H2O2 solution to generate oxygen, and the movement of the microsphere is promoted. The diffusion effect of the microspheres in a solution can be enhanced, and the catalytic and pollutant capturing and removing efficiency in the solution can be enhanced.

Description

Technical Field

[0001] This invention belongs to the field of Janus microsphere preparation technology, and in particular relates to a method and application of asymmetric assembly of Janus microspheres in microdroplets. Background Technology

[0002] Janus microspheres, named after the two-faced Roman god Janus, are biphasic colloids with two distinct chemical and physical aspects. Their tunable and controllable anisotropy in shape, chemistry, and characteristics (such as polarity and electro / magnetic properties) gives them unique behaviors and properties. These unique properties make them suitable for use as interface stabilizers, controllable pores in lipid membranes, and smart nanomaterials such as electronic devices and optical sensors. Janus microspheres have attracted considerable interest in emulsification, drug delivery, sensing, bioimaging, and catalysis. Based on morphology and size, Janus microspheres can be classified into granular, rod-shaped, or sheet-like forms. Among these Janus materials, Janus microspheres have been the most extensively studied and have been applied in drug delivery, catalysis, and environmental remediation.

[0003] Due to the unique advantages of Janus microspheres in a wide range of applications, developing simple, convenient, economical, and high-throughput preparation methods is essential for fabricating various Janus microspheres. Masking, also known as interface-selective modification or interface protection, is one of the most commonly used methods for preparing Janus particles. This involves immobilizing uniform particles on a solid substrate or interface, and then functionalizing one or both sides of the particles using masks, templates, and shadows of adjacent particles to prepare Janus particles. While this two-dimensional planar substrate or air-water interface synthesis strategy is very simple and offers many functionalization possibilities, it still limits the development of Janus particles in the submicron range. Furthermore, the number of Janus particles is limited to a few milligrams. Developing scalable technologies for preparing Janus microspheres will greatly enhance their application value.

[0004] Self-driving micromotors are a typical application of Janus microspheres. Micromotors are emerging materials that autonomously move in solution by converting energy input into mechanical work. They can be powered by various mechanisms, including bubble propulsion, self-electrophoresis, self-acoustic impedance, magnetic fields, and electric fields. Bubble-propelled micromotors have recently been shown to induce efficient fluid transport mixing, improve the yield of classical chemical processes, and show great promise in areas such as drug delivery and environmental remediation. However, large-scale fabrication methods for micromotors are currently lacking. Summary of the Invention

[0005] The first technical problem this invention aims to solve is to provide a method for asymmetric assembly of Janus microspheres in microdroplets. This method involves asymmetric assembly of initial particles with different properties (hydrophobic and hydrophilic) in a suspension within constructed microdroplets to obtain Janus microspheres, and is suitable for large-scale continuous preparation. The Janus microspheres obtained by this method consist of hydrophilic nanoparticles distributed on one side of hydrophobic micron-sized particles, with particle diameters ranging from 0.1 to 10 μm. Self-driven Janus microspheres are prepared by in-situ loading a MnO2 catalyst onto these asymmetrically distributed nanoparticles, enabling them to decompose in H2O2 solution on one side of the microspheres to generate oxygen, thus propelling the particles.

[0006] The second technical problem to be solved by this invention is to provide an application of self-driven Janus microspheres.

[0007] To solve the first technical problem mentioned above, the present invention adopts the following technical solution:

[0008] A method for asymmetric assembly of Janus microspheres in microdroplets, characterized by comprising the following steps:

[0009] S1. Prepare hydrophobic micron-sized particles;

[0010] S1-1: A suspension containing 30-200nm MOF nanoparticles and 0-3wt% 400nm PS spherical templates is ultrasonically treated for several seconds; then injected into a spray dryer at an inlet temperature of 50-150℃, an outlet temperature of 20-80℃, a compressed gas velocity of 538-1052L / h, a mixed liquid feed rate of 5-20mL / min, and a particle concentration of 0.5-5wt.%. The secondary porous MOF or MOF / PS composite spheres are collected in a collection container; subsequently, the MOF / PS is immersed in DMF and stirred at 80℃ for 1h to remove the PS template, yielding tertiary porous MOF microspheres. These microspheres are collected by centrifugation and further dried in a vacuum oven at 150℃ to obtain hydrophobic MOF microparticles.

[0011] The non-MOF hydrophobic micron particles were selected from commercially available sources;

[0012] S2. Prepare hydrophilic nanoparticles

[0013] S2-1, Adopting an improved method SiO2 nanoparticles prepared by the following method: Specifically, 12-14 mL TEOS, 570-575 mL ethanol and 23-27 mL H2O are added to a three-necked flask, and the mixture is shaken in a water bath at 38-42℃ for 8-12 minutes. Then, 45-50 mL ammonia is added, and the reaction is carried out for 3-5 hours. Then, 13-14 mL TEOS and 25-27 mL H2O are added, and the reaction is continued for 7-9 hours.

[0014] S2-2, Add 2.0-2.2 g of dopamine hydrochloride to the reaction solution and stir at room temperature for 7-9 h to obtain hydrophilic offset nanoparticles SiO2 / PDANPs;

[0015] Alternatively, commercially available hydrophilic nanoparticles can be used;

[0016] S3. Preparation of Janus particles by asymmetric assembly in microdroplets

[0017] S3-1. Select hydrophobic micron particles with a diameter of 1-10μm and hydrophilic offset nanoparticles with a diameter of 1-400nm as raw materials, adjust the ratio between the two, add distilled water to adjust the solid content of the dispersion to 1-10wt%, and stir to form a mixed liquid.

[0018] S3-2, Preparation of Janus microspheres: Asymmetric assembly of two particles with different properties is achieved by constructing microdroplets to form a confined space; methods for constructing microdroplets include Pickering emulsion method or spray drying method;

[0019] The conditions for the Pickering emulsion method are as follows: the oil phase and the mixed liquid obtained in step S3-1 are mixed and emulsified under a homogenizing device to form a Pickering emulsion. The water is removed by rotary evaporation, the particles are assembled in microdroplets, and Janus particles are obtained by multiple centrifugation and water washing.

[0020] The conditions for the spray drying method are as follows: the mixed liquid obtained in step S3-1 is fed into a spray dryer for spray drying. The inlet temperature of the spray dryer is 50-150℃ and the outlet temperature is 20-80℃. The compressed gas velocity of the spray dryer is 538-1052 L / h, and the feed velocity of the mixed liquid in the spray dryer is 5-20 mL / min. After the spray drying and separation are completed, Janus microspheres are collected in the collection chamber. The Janus microspheres are immersed in KMnO4, and MnO2 is loaded in situ on the asymmetrically distributed reducing nanoparticles to obtain Janus microspheres that can self-propel in H2O2.

[0021] Preferably, in step S1-1, the MOF nanoparticles are selected from one or more of UiO-66, ZIF-8, MOF-74, ZIF-68, MIL-101 or BUT-66.

[0022] Preferably, in step S1-1, the non-MOF hydrophobic microparticles are polymer microspheres selected from one or more monomers selected from styrene, styrene butyl acrylate, butyl acrylate, methacrylic acid, methyl methacrylate, butyl methacrylate, dimethyl methacrylate, dimethylaminoethyl methacrylate, acrylamine hydrochloride, acrylamide, n-butyl cyanoacrylate, isopropyl acrylamide, and vinylpyridine.

[0023] Preferably, in step S2-2, the commercially available hydrophilic nanoparticles include nanoparticles that are hydrophilic in themselves or after modification, such as Pt, Ag, SiO2, TiO2, CuO, ZnO, Fe3O4 or ZrO2 nanoparticles.

[0024] Preferably, in step S3-1, the diameter of the hydrophobic micron particles is 3-8 μm.

[0025] Preferably, in step S3-1, the diameter of the hydrophilic offset nanoparticles is 50-200 nm.

[0026] Preferably, in step S3-1, the ratio between the hydrophobic microparticles and the hydrophilic offset nanoparticles is 1 / 3 to 3 / 1.

[0027] Preferably, in step S3-1, the solid content in the mixed liquid is 2-5 wt%.

[0028] Preferably, in step S3-2, the microdroplet homogenization equipment for the Pickering emulsion method includes a stirred tank, an emulsifier, or a centrifuge; the rotational speed of the homogenization equipment is 1000-5000 r / min.

[0029] Preferably, in step S3-2, the inlet temperature of the spray dryer is 80-120℃ and the outlet temperature is 30-40℃;

[0030] Preferably, the compressed gas velocity of the spray dryer is 800-900 L / h;

[0031] Preferably, the feed rate of the mixed liquid in the spray dryer is 8.6-17.1 mL / min.

[0032] To solve the second technical problem mentioned above, the present invention adopts the following technical solution:

[0033] An application of the self-driven Janus microspheres prepared by the above method, wherein the Janus microspheres can enhance the diffusion effect in solution;

[0034] Preferably, the enhanced diffusion effect in the solution includes enhanced catalytic, adsorption, or pollutant capture effects in the solution.

[0035] Any range described in this invention includes the endpoint, any value between the endpoints, and any subrange consisting of the endpoint or any value between the endpoints.

[0036] Unless otherwise specified, all raw materials used in this invention can be obtained commercially, and the equipment used in this invention can be conventional equipment in the relevant field or refer to existing technology in the relevant field.

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

[0038] 1) This invention can shift the hydrophobic micron core to the surface of the water droplet in the microdroplet, while the hydrophilic particles are dispersed inside the water droplet. After the microdroplet is dried, Janus microspheres with nanoparticles aggregated on one side of the micron particles can be obtained, and self-propelled Janus microspheres can be directly obtained by in-situ loading of MnO2.

[0039] 2) Of the Janus microspheres prepared by this invention, ≥80% of the particles are Janus spherical with a particle size of 0.1-10 μm;

[0040] 3) This invention can achieve different MnO2 loading amounts in the later stage by changing the ratio of micron core particles to nano offset particles, so as to achieve different driving speeds of Janus microspheres in H2O2 solution.

[0041] 4) The method for preparing the Janus micromotor of the present invention has higher yield, lower cost, simple operation, and is easy to industrialize. Attached Figure Description

[0042] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0043] Figure 1 Schematic diagram of Janus microspheres prepared by spray drying;

[0044] Figure 2 The images show scanning electron microscope (SEM) images of the styrene core micron-sized particles and transmission electron microscope (TEM) images of SiO2 / PDA in Example 1.

[0045] Figure 3 This is a scanning electron microscope image of the Janus microspheres obtained by spray drying in Example 1;

[0046] Figure 4 The image shows a scanning electron microscope image of the MnO2 loaded in Example 1, along with its elemental distribution and X-ray photoelectron spectroscopy spectrum.

[0047] Figure 5 This is a comparison of the average motion speed of Janus microspheres with different SiO2 / PDA NPs loadings in Example 1 under 1% H2O2.

[0048] Figure 6 The adsorption effect of Janus particles on dyed oil droplets.

[0049] Figure 7 This is a scanning electron microscope image of the 66-micron particles with secondary pores UiO in Example 2;

[0050] Figure 8 This is a scanning electron microscope image of Janus microspheres with secondary pores UiO-66 micrometers in Example 2;

[0051] Figure 9 This is a motion trajectory diagram of Janus microspheres with secondary pores UiO-66 micrometers in Example 2 under 1% H2O2.

[0052] Figure 10 The images shown are scanning electron microscope (SEM) and transmission electron microscope (TEM) images of the three-level porous UiO-66 microspheres prepared in Example 3.

[0053] Figure 11 This is a scanning electron microscope image of the tertiary porous UiO-66 Janus microspheres prepared in Example 3;

[0054] Figure 12 The motion trajectory diagram of the tertiary porous UiO-66 Janus microspheres prepared in Example 3 under 1% H2O2;

[0055] Figure 13 The natural aquatic environment simulation system of sand and water designed in Example 3 and the performance of the micromotor in removing methyl orange in it;

[0056] Figure 14 This is a scanning electron microscope image of Janus particles obtained by the emulsifier in Example 4;

[0057] Figure 15 The image shows a scanning electron microscope (SEM) image of Janus prepared in Comparative Example 1.

[0058] Figure 16 The image shown is a scanning electron microscope image of Janus prepared in Comparative Example 2. Detailed Implementation

[0059] To more clearly illustrate the present invention, the following description, in conjunction with preferred embodiments, further clarifies the invention. Those skilled in the art should understand that the specific descriptions below are illustrative rather than restrictive, and should not be construed as limiting the scope of protection of the present invention.

[0060] As one aspect of the present invention, a method for asymmetric assembly of Janus microspheres in microdroplets is characterized by comprising the following steps:

[0061] S1. Prepare hydrophobic micron-sized particles;

[0062] S1-1: A suspension containing 30-200nm MOF nanoparticles and 0-3wt% 400nm PS spherical templates is ultrasonically treated for several seconds; then injected into a spray dryer at an inlet temperature of 50-150℃, an outlet temperature of 20-80℃, a compressed gas velocity of 538-1052L / h, a mixed liquid feed rate of 5-20mL / min, and a particle concentration of 0.5-5wt.%. The secondary porous MOF or MOF / PS composite spheres are collected in a collection container; subsequently, the MOF / PS is immersed in DMF and stirred at 80℃ for 1h to remove the PS template, yielding tertiary porous MOF microspheres. These microspheres are collected by centrifugation and further dried in a vacuum oven at 150℃ to obtain hydrophobic MOF microparticles.

[0063] The non-MOF hydrophobic micron particles were selected from commercially available sources;

[0064] S2. Prepare hydrophilic nanoparticles

[0065] S2-1, Adopting an improved method SiO2 nanoparticles prepared by the following method: Specifically, 12-14 mL TEOS, 570-575 mL ethanol and 23-27 mL H2O are added to a three-necked flask, and the mixture is shaken in a water bath at 38-42℃ for 8-12 minutes. Then, 45-50 mL ammonia is added, and the reaction is carried out for 3-5 hours. Then, 13-14 mL TEOS and 25-27 mL H2O are added, and the reaction is continued for 7-9 hours.

[0066] S2-2, Add 2.0-2.2 g of dopamine hydrochloride to the reaction solution and stir at room temperature for 7-9 h to obtain hydrophilic offset nanoparticles SiO2 / PDANPs;

[0067] Alternatively, commercially available hydrophilic nanoparticles can be used;

[0068] S3. Preparation of Janus particles by asymmetric assembly in microdroplets

[0069] S3-1. Select hydrophobic micron particles with a diameter of 1-10μm and hydrophilic offset nanoparticles with a diameter of 1-400nm as raw materials, adjust the ratio between the two, add distilled water to adjust the solid content of the dispersion to 1-10wt%, and stir to form a mixed liquid.

[0070] S3-2, Preparation of Janus microspheres: Asymmetric assembly of two particles with different properties is achieved by constructing microdroplets to form a confined space; methods for constructing microdroplets include Pickering emulsion method or spray drying method;

[0071] The conditions for the Pickering emulsion method are as follows: the oil phase and the mixed liquid obtained in step S3-1 are mixed and emulsified under a homogenizing device to form a Pickering emulsion. The water is removed by rotary evaporation, the particles are assembled in microdroplets, and Janus particles are obtained by multiple centrifugation and water washing.

[0072] The conditions for the spray drying method are as follows: the mixed liquid obtained in step S3-1 is fed into a spray dryer for spray drying. The inlet temperature of the spray dryer is 50-150℃ and the outlet temperature is 20-80℃. The compressed gas velocity of the spray dryer is 538-1052 L / h, and the feed velocity of the mixed liquid in the spray dryer is 5-20 mL / min. After the spray drying and separation are completed, Janus microspheres are collected in the collection chamber. The Janus microspheres are immersed in KMnO4, and MnO2 is loaded in situ on the asymmetrically distributed reducing nanoparticles to obtain Janus microspheres that can self-propel in H2O2.

[0073] According to certain embodiments of the present invention, in step S1-1, the MOF nanoparticles are selected from one or more of UiO-66, ZIF-8, MOF-74, ZIF-68, MIL-101 or BUT-66.

[0074] According to certain embodiments of the present invention, in step S1-1, the non-MOF hydrophobic microparticles are selected from polymer microspheres of one or more monomers selected from styrene, styrene butyl acrylate, butyl acrylate, methacrylic acid, methyl methacrylate, butyl methacrylate, dimethyl methacrylate, dimethylaminoethyl methacrylate, acrylamine hydrochloride, acrylamide, n-butyl cyanoacrylate, isopropyl acrylamide, and vinylpyridine.

[0075] According to certain embodiments of the present invention, in step S2-2, the commercially available hydrophilic nanoparticles include nanoparticles that are hydrophilic in themselves or after modification, such as Pt, Ag, SiO2, TiO2, CuO, ZnO, Fe3O4 or ZrO2 nanoparticles.

[0076] According to certain embodiments of the present invention, in step S3-1, the diameter of the hydrophobic microparticles is 3-8 μm.

[0077] According to certain embodiments of the present invention, in step S3-1, the diameter of the hydrophilic offset nanoparticles is 50-200 nm.

[0078] According to certain embodiments of the present invention, in step S3-1, the ratio between the hydrophobic microparticles and the hydrophilic offset nanoparticles is 1 / 3 to 3 / 1.

[0079] According to certain embodiments of the present invention, in step S3-1, the solid content in the mixed liquid is 2-5 wt%.

[0080] According to certain embodiments of the present invention, in step S3-2, the microdroplet homogenization equipment for the Pickering emulsion method includes a stirred tank, an emulsifier, or a centrifuge; the rotational speed of the homogenization equipment is 1000-5000 r / min;

[0081] According to certain embodiments of the present invention, in step S3-2, the inlet temperature of the spray dryer is 80-120°C and the outlet temperature is 30-40°C;

[0082] According to certain embodiments of the present invention, the compressed gas velocity of the spray dryer is 800-900 L / h;

[0083] According to certain embodiments of the present invention, the feed rate of the mixed liquid in the spray dryer is 8.6-17.1 mL / min.

[0084] As another aspect of the present invention, the present invention provides an application of a self-driven Janus microsphere prepared by the above method, wherein the Janus microsphere can enhance the diffusion effect in solution;

[0085] Preferably, the enhanced diffusion effect in the solution includes enhanced catalytic, adsorption, or pollutant capture effects in the solution.

[0086] Example 1

[0087] A method for preparing Janus microspheres by spray drying includes the following steps:

[0088] Step 1: Prepare a suspension of polystyrene core micron-sized particles

[0089] Commercially available hydrophobic polystyrene micron particles were obtained, and their scanning electron microscope images are shown below. Figure 2 a; Disperse it in water and sonicate for 10 minutes, then set aside;

[0090] Step 2: Preparation of SiO2 / PDA hydrophilic nanoparticles

[0091] Adopting improved SiO2 nanoparticles were prepared by a specific method. Specifically, 13 mL of TEOS, 571 mL of ethanol, and 25 mL of H2O were added to a three-necked flask and the mixture was shaken in a 40°C water bath for 10 minutes. Then, 47 mL of ammonia was added, and the reaction was allowed to proceed for 4 hours. Next, 13.4 mL of TEOS and 26 mL of H2O were added, and the reaction was continued for another 8 hours. Finally, 2.1 g of dopamine hydrochloride (DA) was added to the reaction solution, and the mixture was stored at room temperature for 8 hours to obtain SiO2 / PDA nanoparticles. The transmission electron microscopy (TEM) image is shown below. Figure 2b;

[0092] Step 3: Preparation of Janus particles by asymmetric assembly in spray-dried microdroplets

[0093] The solid content of the styrene microsphere aqueous dispersion was adjusted to 2 wt.% and the solid content of the SiO2 / PDA NPs aqueous dispersion was 0.2, 0.8, and 1.2 wt.%, respectively. Microdroplets were constructed using spray drying to create confined spaces for asymmetric assembly of the two types of particles with different properties. The above mixed liquid was fed into a spray dryer for spray drying. The inlet temperature of the spray dryer was 100℃ and the outlet temperature was 60℃. The compressed gas velocity of the spray dryer was 670 L / h, and the feed rate of the mixed liquid was 15 mL / min. After spray drying and separation, Janus microspheres were collected in the collection chamber, and their scanning electron microscopy results are shown below. Figure 3 ;

[0094] Step 4: Preparation of self-propelled Janus microspheres

[0095] Janus microspheres were immersed in KMnO4. The surface of SiO2 / PDA nanoparticles is rich in hydroxyl and amino groups, which can reduce KMnO4 in situ to form MnO2, thus obtaining self-propelled Janus microspheres.

[0096] Figure 4 The scanning electron microscope image of the self-propelled Janus microspheres shows the distribution of Mn elements and the X-ray photoelectron spectrum. It can be clearly seen that the Mn elements are attached to the SiO2 / PDA NPs and distributed on one side of the PS spheres, which proves that the Mn elements are mainly in the +4 valence and are mainly MnO2. Figure 5 Comparison of the average motion velocity of Janus microspheres with different SiO2 / PDA NPs loadings under 1% H2O2.

[0097] The lipophilic nature of polystyrene can be used for oil removal from water. Figure 6 The adsorption of stained oil phases by Janus microspheres was demonstrated, showing that oil droplets can be captured in water through self-driving.

[0098] Example 2

[0099] A method for preparing Janus UiO-66 microspheres by spray drying includes the following steps:

[0100] Step 1: Preparation of hydrophobic self-assembled secondary porous UiO-66 core micron-sized particles

[0101] The concentration of the 60nm UiO-66 nanoparticle suspension was adjusted to 3wt.%, and after ultrasonic treatment for several seconds, the feed was introduced at an inlet temperature of 110℃ and a feed rate of 22.5mL / min. -1Compressed air velocity 670 L / h -1 Under certain conditions, self-assembled secondary porous UiO-66 micrometer particles were obtained by injection into a spray dryer. Their scanning electron microscopy findings are shown below. Figure 7 ;

[0102] Step 2: Preparation of SiO2 / PDA hydrophilic nanoparticles

[0103] Adopting improved SiO2 nanoparticles were prepared by a specific method. Specifically, 13 mL of TEOS, 571 mL of ethanol, and 25 mL of H2O were added to a three-necked flask and the mixture was shaken in a 40°C water bath for 10 minutes. Then, 47 mL of ammonia was added, and the reaction was allowed to proceed for 4 hours. Next, 13.4 mL of TEOS and 26 mL of H2O were added, and the reaction was continued for another 8 hours. Finally, 2.1 g of dopamine hydrochloride (DA) was added to the reaction solution, and the mixture was stored at room temperature for 8 hours to obtain SiO2 / PDA nanoparticles.

[0104] Step 3: Preparation of Janus particles by asymmetric assembly in spray-dried microdroplets

[0105] The solid content of the secondary porous UiO-66 microsphere aqueous dispersion was adjusted to 2 wt.% and the solid content of the SiO2 / PDA NPs aqueous dispersion was adjusted to 1.2 wt.%. Microdroplets were constructed using spray drying to create confined spaces for asymmetric assembly of the two types of particles with different properties. The mixed liquid was fed into a spray dryer with an inlet temperature of 100°C and an outlet temperature of 60°C. The compressed gas velocity in the spray dryer was 670 L / h, and the feed rate of the mixed liquid was 15 mL / min. After spray drying and separation, Janus microspheres were collected in a collection chamber.

[0106] Step 4: Preparation of self-propelled Janus microspheres

[0107] Janus microspheres were immersed in KMnO4. The surface of SiO2 / PDA nanoparticles is rich in hydroxyl and amino groups, which can reduce KMnO4 in situ to form MnO2, thus obtaining self-propelled Janus microspheres.

[0108] Figure 7 The scanning electron microscope image of the self-propelled Janus microspheres clearly shows that the SiO2 / PDA NPs are distributed on one side of the UiO-66 microspheres. Figure 9 The trajectory diagram of UiO-66Janus microspheres under 1% H2O2.

[0109] These self-driven Janus MOF microspheres can enhance diffusion in solution and increase the rate of catalytic reactions.

[0110] Example 3

[0111] A method for preparing Janus UiO-66 microspheres by spray drying includes the following steps:

[0112] Step 1: Preparation of hydrophobic self-assembled tertiary porous UiO-66 core micron particles

[0113] A suspension of 60 nm UiO-66 and 400 nm PS was mixed and sonicated for several seconds, then injected into a spray dryer under the following conditions: inlet temperature 110℃, feed rate 22.5 mL min⁻¹, compressed air velocity 670 L h⁻¹, and particle concentration 3 wt.% (UiO-66 / PS = 3 / 2). The UiO-66 / PS composite spheres were collected in a collection container. Subsequently, 1 g of UiO-66 / PS was immersed in 80 mL of LDM and stirred at 80℃ for 1 h. The PS template was removed, yielding tri-porous UiO-66 microspheres. These microspheres were collected by centrifugation and further dried in a vacuum oven at 150℃. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images are shown below. Figure 10 ;

[0114] Step 2: Preparation of SiO2 / PDA hydrophilic nanoparticles

[0115] Adopting improved SiO2 nanoparticles were prepared by a specific method. Specifically, 13 mL of TEOS, 571 mL of ethanol, and 25 mL of H2O were added to a three-necked flask and the mixture was shaken in a 40°C water bath for 10 minutes. Then, 47 mL of ammonia was added, and the reaction was allowed to proceed for 4 hours. Next, 13.4 mL of TEOS and 26 mL of H2O were added, and the reaction was continued for another 8 hours. Finally, 2.1 g of dopamine hydrochloride (DA) was added to the reaction solution, and the mixture was stored at room temperature for 8 hours to obtain SiO2 / PDA nanoparticles.

[0116] Step 3: Preparation of Janus particles by asymmetric assembly in spray-dried microdroplets

[0117] The solid content of the tertiary porous UiO-66 microsphere aqueous dispersion was adjusted to 2 wt.% and the solid content of the SiO2 / PDA NPs aqueous dispersion was adjusted to 1.2 wt.%. Microdroplets were constructed using spray drying to create confined spaces for asymmetric assembly of the two types of particles with different properties. The mixed liquid was fed into a spray dryer with an inlet temperature of 100℃ and an outlet temperature of 60℃. The compressed gas velocity in the spray dryer was 670 L / h, and the feed rate of the mixed liquid was 15 mL / min. After spray drying and separation, Janus microspheres were collected in a collection chamber.

[0118] Step 4: Preparation of self-propelled Janus microspheres

[0119] Janus microspheres were immersed in KMnO4. The surface of SiO2 / PDA nanoparticles is rich in hydroxyl and amino groups, which can reduce KMnO4 in situ to form MnO2, thus obtaining self-propelled Janus microspheres.

[0120] Figure 11 The scanning electron microscope image of the self-propelled Janus microsphere clearly shows that the SiO2 / PDA NPs are distributed on one side of the tertiary porous UiO-66 microsphere.

[0121] Figure 12 The image shows the motion trajectory of a three-stage orifice UiO-66 Janus micromotor in 1% H2O2. To highlight its application scenario, a natural aquatic environment simulation system of sand and water was designed. Figure 13 It was discovered that the micromotor can easily pass through sand and gravel packing and efficiently adsorb and remove methyl orange pollutants from the aquatic environment.

[0122] Example 4

[0123] A method for preparing self-propelled Janus microspheres using an emulsifier includes the following steps:

[0124] Step 1: Prepare a suspension of polystyrene core micron-sized particles

[0125] Commercially available hydrophobic polystyrene micron particles were obtained, and their scanning electron microscope images are shown below. Figure 2 Disperse it in water and sonicate for 10 minutes, then set aside.

[0126] Step 2: Preparation of SiO2 / PDA hydrophilic nanoparticles

[0127] Adopting improved SiO2 nanoparticles were prepared by a specific method. Specifically, 13 mL of TEOS, 571 mL of ethanol, and 25 mL of H2O were added to a three-necked flask and the mixture was shaken in a 40°C water bath for 10 minutes. Then, 47 mL of ammonia was added, and the reaction was allowed to proceed for 4 hours. Next, 13.4 mL of TEOS and 26 mL of H2O were added, and the reaction was continued for another 8 hours. Finally, 2.1 g of dopamine hydrochloride (DA) was added to the reaction solution, and the mixture was stored at room temperature for 8 hours to obtain SiO2 / PDA nanoparticles.

[0128] Step 3: Asymmetric assembly of microdroplets in an emulsifier to prepare Janus particles.

[0129] The solid content of the polystyrene microsphere aqueous dispersion and the SiO2 / PDA NPs aqueous dispersion were adjusted to 1 wt.% and stirred to form a mixed liquid. 2 mL of the above mixture was added to 200 mL of sunflower seed oil containing 5 mL of Span 85, and stirred for 30 min at 4000 rpm in an emulsifier. The oil-water mixture was then subjected to rotary evaporation at 70°C to remove moisture, and Janus particles were obtained after three centrifugal washings. Scanning electron microscopy (SEM) results are shown below. Figure 14 As shown;

[0130] Step 4: Preparation of self-propelled Janus microspheres

[0131] Janus microspheres were immersed in KMnO4, and MnO2 was in situ loaded onto the asymmetrically distributed reducing nanoparticles to obtain self-propelled Janus microspheres.

[0132] Example 5

[0133] A method for preparing self-propelled Janus microspheres using hypergravity technology includes the following steps:

[0134] Step 1: Prepare a suspension of polystyrene core micron-sized particles

[0135] Commercially available hydrophobic polystyrene micron particles were obtained, and their scanning electron microscope images are shown below. Figure 2 Disperse it in water and sonicate for 10 minutes, then set aside.

[0136] Step 2: Preparation of SiO2 / PDA hydrophilic nanoparticles

[0137] Adopting improved SiO2 nanoparticles were prepared by a specific method. Specifically, 13 mL of TEOS, 571 mL of ethanol, and 25 mL of H2O were added to a three-necked flask and the mixture was shaken in a 40°C water bath for 10 minutes. Then, 47 mL of ammonia was added, and the reaction was allowed to proceed for 4 hours. Next, 13.4 mL of TEOS and 26 mL of H2O were added, and the reaction was continued for another 8 hours. Finally, 2.1 g of dopamine hydrochloride (DA) was added to the reaction solution, and the mixture was stored at room temperature for 8 hours to obtain SiO2 / PDA nanoparticles.

[0138] Step 3: Asymmetric assembly of Janus particles in emulsified microdroplets using a high-gravity machine

[0139] The solid content of the polystyrene microsphere aqueous dispersion and the SiO2 / PDA NPs aqueous dispersion were adjusted to 1 wt.% and stirred to form a mixed liquid. 2 mL of the above mixture was added to 200 mL of sunflower seed oil containing 5 mL of Span 85, and the mixture was circulated and stirred at 4000 rpm for 30 min using a centrifuge. Subsequently, the oil-water mixture was rotary evaporated at 70°C to remove moisture, and Janus particles were obtained after centrifugation and washing three times with water.

[0140] Step 4: Preparation of self-propelled Janus microspheres

[0141] Janus microspheres were immersed in KMnO4, and MnO2 was in situ loaded onto the asymmetrically distributed reducing nanoparticles to obtain self-propelled Janus microspheres.

[0142] Comparative Example 1

[0143] Example 1 was repeated, except that in step 3, the spray drying inlet temperature was 140°C. In this comparative example, the product did not form well-formed Janus microspheres; the SiO2 / PDA particles were uniformly distributed on the surface of the polystyrene spheres, as shown in the scanning electron microscope image below. Figure 15 As shown.

[0144] This shows that when the inlet temperature of the spray dryer is too high, good Janus microsphere particles cannot be formed.

[0145] Comparative Example 2

[0146] Example 1 was repeated, except that in step 3, the compressed air flow rate of the spray dryer was 450 L / h. The product of this comparative example did not form well-formed Janus microspheres; the SiO2 / PDA particles showed a tendency to shift in distribution, but the trend was not obvious. Its scanning electron microscope image is shown below. Figure 16 As shown.

[0147] This shows that when the compressed air velocity of the spray dryer is too low, good Janus microsphere particles cannot be formed.

[0148] Comparative Example 3

[0149] Repeat Example 1: The only difference is that in step 3, the stirring speed is 800 rpm. In this comparative example, due to the low stirring intensity, the microdroplets could not be formed uniformly, and the particles could not be successfully assembled to obtain Janus particles.

[0150] Therefore, it can be seen that when the stirring speed is too low in step 3, Janus microspheres cannot be successfully assembled.

[0151] Comparative Example 4

[0152] Repeat Example 1: The only difference is that when the inlet temperature is 40°C in step 3, the drying process is too slow, so that the moisture cannot be completely evaporated, the wet material enters the separation stage, and the product cannot be dried normally.

[0153] Comparative Example 5

[0154] Repeat Example 1: The only difference is that the feed rate of the spray dryer in step 3 is 21 mL / min. Because the feed rate is too fast, the moisture cannot be completely evaporated, the wet material enters the separation stage, cannot be dried normally, and the particles cannot be assembled.

[0155] Comparative Example 6

[0156] Repeat Example 1: The only difference is that in step 3, the compressed gas velocity of the spray dryer is 1574 L / h, and the diameter of the spray droplets is too small to complete the effective assembly of particles inside the droplets.

[0157] Comparative Example 7

[0158] Repeat Example 1: The only difference is that in step 3, the compressed gas velocity of the spray dryer is 439 L / h. Due to the low pressure, the efficiency of the liquid material being sprayed into droplets is too low, and it even flows down in streams, making it impossible to obtain micron-sized droplets and the particles cannot be assembled.

[0159] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is impossible to exhaustively list all embodiments here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A method for asymmetric assembly of Janus microspheres in microdroplets, characterized in that, Includes the following steps: S1. Prepare hydrophobic micron-sized particles; S1-1: A suspension containing 30-200nm MOF nanoparticles and 0-3wt% 400nm PS spherical templates is ultrasonically treated for several seconds; then injected into a spray dryer at an inlet temperature of 50-150℃, an outlet temperature of 20-80℃, a compressed gas velocity of 538-1052L / h, a mixed liquid feed rate of 5-20mL / min, and a particle concentration of 0.5-5wt.%. The secondary porous MOF or MOF / PS composite spheres are collected in a collection container; subsequently, the MOF / PS is immersed in DMF and stirred at 80℃ for 1h to remove the PS template, yielding tertiary porous MOF microspheres. These microspheres are collected by centrifugation and further dried in a vacuum oven at 150℃ to obtain hydrophobic MOF microparticles. The non-MOF hydrophobic micron particles were selected from commercially available sources; S2. Prepare hydrophilic nanoparticles S2-1, Adopting an improved method SiO2 nanoparticles prepared by the following method: Specifically, 12-14 mL TEOS, 570-575 mL ethanol and 23-27 mL H2O are added to a three-necked flask, and the mixture is shaken in a water bath at 38-42℃ for 8-12 minutes. Then, 45-50 mL ammonia is added, and the reaction is carried out for 3-5 hours. Then, 13-14 mL TEOS and 25-27 mL H2O are added, and the reaction is continued for 7-9 hours. S2-2, Add 2.0-2.2 g of dopamine hydrochloride to the reaction solution and stir at room temperature for 7-9 h to obtain hydrophilic offset nanoparticles SiO2 / PDANPs; Alternatively, commercially available hydrophilic nanoparticles can be used; S3. Preparation of Janus particles by asymmetric assembly in microdroplets S3-1. Select hydrophobic micron particles with a diameter of 1-10μm and hydrophilic offset nanoparticles with a diameter of 1-400nm as raw materials, adjust the ratio between the two, add distilled water to adjust the solid content of the dispersion to 1-10wt%, and stir to form a mixed liquid. S3-2, Preparation of Janus microspheres: Asymmetric assembly of two particles with different properties is achieved by constructing microdroplets to form a confined space; methods for constructing microdroplets include Pickering emulsion method or spray drying method; The conditions for the Pickering emulsion method are as follows: the oil phase and the mixed liquid obtained in step S3-1 are mixed and emulsified under a homogenizing device to form a Pickering emulsion. The water is removed by rotary evaporation, the particles are assembled in microdroplets, and Janus particles are obtained by multiple centrifugation and water washing. The conditions for the spray drying method are as follows: the mixed liquid obtained in step S3-1 is fed into a spray dryer for spray drying. The inlet temperature of the spray dryer is 50-150℃ and the outlet temperature is 20-80℃. The compressed gas velocity of the spray dryer is 538-1052 L / h, and the feed velocity of the mixed liquid in the spray dryer is 5-20 mL / min. After the spray drying and separation are completed, Janus microspheres are collected in the collection chamber. The Janus microspheres are immersed in KMnO4, and MnO2 is loaded in situ on the asymmetrically distributed reducing nanoparticles to obtain Janus microspheres that can self-propel in H2O2.

2. The method for asymmetric assembly of Janus microspheres in microdroplets according to claim 1, characterized in that: In step S1-1, the MOF nanoparticles are selected from one or more of UiO-66, ZIF-8, MOF-74, ZIF-68, MIL-101 or BUT-66.

3. The method for asymmetric assembly of Janus microspheres in microdroplets according to claim 1, characterized in that: In step S1-1, the non-MOF hydrophobic microparticles are selected from polymer microspheres of one or more monomers selected from styrene, styrene butyl acrylate, butyl acrylate, methacrylic acid, methyl methacrylate, butyl methacrylate, dimethyl methacrylate, dimethylaminoethyl methacrylate, acrylamine hydrochloride, acrylamide, n-butyl cyanoacrylate, isopropyl acrylamide, and vinylpyridine.

4. The method for asymmetric assembly of Janus microspheres in microdroplets according to claim 1, characterized in that: In step S2-2, the commercially available hydrophilic nanoparticles include nanoparticles that are hydrophilic in themselves or after modification, such as Pt, Ag, SiO2, TiO2, CuO, ZnO, Fe3O4 or ZrO2 nanoparticles.

5. The method for asymmetric assembly of Janus microspheres in microdroplets according to claim 1, characterized in that: In step S3-1, the diameter of the hydrophobic micron particles is 3-8 μm.

6. The method for asymmetric assembly of Janus microspheres in microdroplets according to claim 1, characterized in that: In step S3-1, the diameter of the hydrophilic offset nanoparticles is 50-200 nm.

7. The method for asymmetric assembly of Janus microspheres in microdroplets according to claim 1, characterized in that: In step S3-1, the ratio between the hydrophobic microparticles and the hydrophilic offset nanoparticles is 1 / 3 to 3 / 1.

8. The method for asymmetric assembly of Janus microspheres in microdroplets according to claim 1, characterized in that: In step S3-1, the solid content in the mixed liquid is 2-5 wt%.

9. The method for asymmetric assembly of Janus microspheres in microdroplets according to claim 1, characterized in that: In step S3-2, the homogenization equipment for the microdroplet structure of the Pickering emulsion method includes a stirred tank, an emulsifier, or a centrifuge; the rotation speed of the homogenization equipment is 1000-5000 r / min. Preferably, in step S3-2, the inlet temperature of the spray dryer is 80-120℃ and the outlet temperature is 30-40℃; Preferably, the compressed gas velocity of the spray dryer is 800-900 L / h; Preferably, the feed rate of the mixed liquid in the spray dryer is 8.6-17.1 mL / min.

10. The application of the self-propelled Janus microspheres prepared according to any one of claims 1-9, characterized in that, The Janus microspheres can enhance the diffusion effect in solution; Preferably, the enhanced diffusion effect in the solution includes enhanced catalytic, adsorption, or pollutant capture effects in the solution.

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