Nanosilica Janus particles with a narrow pH response range and a preparation method and application thereof

Abstract

This invention relates to Janus nano-silica particles with a narrow pH response range, their preparation method, and applications. The preparation method includes: preparing paraffin@SiO2 colloid; adding the obtained paraffin@SiO2 colloid to an alcohol-water system and adding γ-glycidoxypropyltrimethoxysilane for modification to obtain half-sided modified SiO2 particles; dispersing the modified particles in toluene solvent and adding octyltrimethoxysilane and triethylamine for hydrophobic modification to obtain the Janus nano-SiO2 particles with a narrow pH response range. This invention effectively achieves spatially selective modification of nano-SiO2, exposing one half of the surface and introducing highly reactive epoxy groups. These groups can react with various groups such as amino, carboxyl, or thiol groups, thereby introducing more functional molecules and broadening the application fields of the Janus nano-SiO2 particles.

Description

Technical Field

[0001] This invention belongs to the field of nanomaterials, specifically relating to a nano-silica Janus particle with a narrow pH response range, its preparation method, and its application. Background Technology

[0002] Pickering emulsions are emulsion systems stabilized by solid particles. Unlike traditional emulsions (usually stabilized by surfactants), the stabilization of picking emulsions primarily relies on the adsorption of solid particles at the oil-water interface. The solid particles stabilize the emulsion by reducing interfacial tension, forming a physical barrier, and preventing droplet coalescence. For applications like food storage, long-term emulsion stability is crucial. However, in other cases, such as petroleum recovery, heterogeneous catalysis, drug delivery, and sensing, only temporary stability is required. Traditional demulsification processes often introduce physical forces into the system, such as centrifugation, to destabilize the emulsion, leading to increased costs and operational complexity. Responsive picking emulsions, on the other hand, can reversibly change in response to external stimuli (pH, temperature, light, electric fields, magnetic fields, etc.), simplifying the demulsification process. pH-responsive systems are a simple and relatively easy-to-implement stimulus-response system. These emulsions are typically stabilized by solid particles with pH-responsive groups (amino, carboxyl, etc.) on their surface. The wettability of the particle surface changes with pH, ​​thus affecting the emulsion's properties. However, the current pH-responsive Pickering emulsions have too large a pH response range, requiring the addition of more acid or alkali to reduce the stability of the system. Too low or too high pH will affect the stability of enzymes in the Pickering emulsion system. Therefore, the preparation of an emulsifier with a narrower pH response range has a very broad application prospect.

[0003] Janus particles, named after the Janus deity, are a class of particles exhibiting chemical and geometric anisotropy. Different regions of a single particle display different properties and are arranged asymmetrically. Due to their unique structure and properties, Janus particles can reduce surface tension in oil-water systems, similar to surfactants. Compared to homogeneous solid particles, Janus particles can more easily adjust the distribution of hydrophilic and hydrophobic regions, altering their wettability at the oil-water interface and thus achieving specific functions. Summary of the Invention

[0004] To address the shortcomings and deficiencies of existing technologies, the primary objective of this invention is to provide a method for preparing nano-SiO2 Janus particles with a narrow pH response range.

[0005] Another object of the present invention is to provide nano-SiO2 Janus particles with a narrow pH response range obtained by the above method.

[0006] Another object of the present invention is to provide applications of the above-mentioned nano-SiO2 Janus particles having a narrower pH response range.

[0007] The objective of this invention is achieved through the following technical solution:

[0008] A method for preparing nano-SiO2 Janus particles with a narrow pH response range includes the following steps:

[0009] (1) Janus particles were prepared using the Pickering emulsion template method: nano-SiO2 was used as the emulsifier of the Pickering emulsion, solid paraffin was used as the oil phase, and water containing surfactant was used as the aqueous phase. The three were mixed and the entire system was heated to dissolve the solid paraffin and then homogenized to form the Pickering emulsion. The Pickering emulsion was cooled to room temperature and the oil phase was solidified. After filtration, washing, and drying, paraffin@SiO2 colloid was obtained.

[0010] (2) The obtained paraffin@SiO2 colloid was added to an alcohol-water system and γ-glycidoxypropyltrimethoxysilane was added for modification reaction. γ-glycidoxypropyltrimethoxysilane covalently binds to the hydroxyl groups exposed on the surface of SiO2. After the reaction was completed, the paraffin was dissolved in chloroform, washed with anhydrous ethanol, centrifuged, and dried to obtain half-modified SiO2 particles with hydroxyl groups on one half of the surface and epoxy groups on the other half of the surface.

[0011] (3) The half-sided modified SiO2 particles obtained in step (2) are dispersed in a solvent, and octyltrimethoxysilane and triethylamine are added for hydrophobic modification. After the reaction is completed, the particles are washed, centrifuged and dried to obtain the nano SiO2 Janus particles with a narrow pH response range.

[0012] Preferably, in step (1),

[0013] The nano-SiO2 is passed through Synthesis by method;

[0014] The nano-SiO2 has a particle size of 300-400 nm; the relatively uniform particle size of nano-SiO2 is beneficial for its stability at the oil-water interface.

[0015] The surfactant used is bis(dodecyl dimethyl)bromide (DDAB); the heating time and temperature are 30 min and 80 °C, respectively.

[0016] The nano-SiO2 is used as a solid particulate emulsifier in the Pickering emulsion. The amount of nano-SiO2 used is 0.5-1.0 parts by mass, which is 2%-4% of the total mass of the oil phase and the aqueous phase.

[0017] The mass ratio of the solid paraffin to water is in the range of 1:20-8:20; a more preferred mass ratio of the solid paraffin to water is 2:20-5:20.

[0018] The concentration of the surfactant in the aqueous phase is 60-200 mg / L;

[0019] The melting point of the solid paraffin is 52-64℃;

[0020] The homogenization speed is 14000-18000 rpm, and the homogenization time is 2-4 min;

[0021] The washing was performed with anhydrous ethanol, and the drying was carried out overnight at 60°C.

[0022] Preferably, in step (2),

[0023] The alcohol-water system is a 95% (by volume) ethanol solution;

[0024] The amount of paraffin@SiO2 colloid added is 1-3 parts by mass, and the amount of γ-glycidyl etheroxypropyltrimethoxysilane added is 0.5-1.5 parts by volume;

[0025] The modification reaction takes 6-24 hours and is carried out at a temperature of 25°C.

[0026] The washing was performed with anhydrous ethanol, and the drying was carried out overnight at 60°C.

[0027] Preferably, in step (3),

[0028] The amount of the half-sided modified SiO2 particles added is 0.05-0.2 parts by mass, the amount of the octyltrimethoxysilane added is 0.05-0.2 parts by volume, and the amount of the triethylamine added is 0.15 parts by volume.

[0029] The hydrophobic modification reaction time is 12-24 hours, and the temperature is 25℃.

[0030] The solvent is toluene;

[0031] The washing was performed with anhydrous ethanol, and the drying was carried out overnight at 60°C.

[0032] The nano-SiO2 Janus particles prepared by this invention have a stable Pickering emulsion that can be demulsified at pH 4-5.

[0033] The nano-SiO2 Janus particles prepared by this invention can be applied to fields such as biocatalysis, oil-water separation, and drug delivery.

[0034] This invention is based on the fact that surfactant-adsorbed nano-SiO2 can be well stabilized at the paraffin / water interface. Due to the high melting point of solid paraffin, a Pickering emulsion is prepared at a temperature above its melting point and then cooled to room temperature to solidify the paraffin. A portion of the nano-SiO2 stabilized at the oil-water interface is embedded in the paraffin, forming a paraffin@SiO2 colloid. The hydroxyl groups on the exposed aqueous side covalently bind to a silane coupling agent. The solid paraffin is then dissolved with chloroform. The surface hydroxyl groups of the embedded SiO2 are then modified with a hydrophobic silane coupling agent to obtain the Janus structure. The resulting nano-SiO2 Janus particles also have unreacted hydroxyl groups on their surface that can act as responsive groups, transitioning between protonated and deprotonated forms to alter the wettability of the particles. This allows the stable Pickering emulsion to respond to pH changes. Specifically, the nano-SiO2 Janus particles prepared in this invention are ultrasonically dispersed in an oil phase (e.g., ethyl acetate), and an equal volume of aqueous phase is added. After homogenization, a Pickering emulsion is formed. Hydrochloric acid is added to the obtained Pickering emulsion to make the pH 4-5. The water-in-oil emulsion will break down. Sodium hydroxide solution is added and the mixture is shaken and vibrated to reform the water-in-oil Pickering emulsion.

[0035] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0036] (1) By using the paraffin embedding method, the spatial selective modification of nano-SiO2 was effectively achieved, exposing half of the surface and introducing highly reactive epoxy groups. These groups can react with various groups such as amino, carboxyl or thiol groups, thereby introducing more functional molecules and broadening the application field of nano-SiO2 Janus particles.

[0037] (2) In the prior art, most pH-responsive particles use amino or carboxyl groups as responsive groups, while the present invention innovatively uses the hydroxyl groups on the surface of SiO2 particles as responsive groups. Its stable Pickering emulsion can demulsify in a narrower pH range (pH 4-5) compared to most pH-responsive Pickering emulsions (demulsification occurs at pH 2-3). Attached Figure Description

[0038] Figure 1 An optical microscope image of the nano-SiO2 stabilized Pickering emulsion template obtained in Example 1;

[0039] Figure 2 The image shown is a scanning electron microscope image of the paraffin@SiO2 colloid obtained in Example 1, where (b) is a magnified view of a portion of (a).

[0040] Figure 3 The figures show the Pickering emulsions stabilized by nano-SiO2 Janus particles obtained in Examples 1, 2, and 3, and their pH response. Examples 1, 2, and 3 in the figures represent Examples 1, 2, and 3, respectively. Detailed Implementation

[0041] The present invention will be further described in detail below with reference to embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto. All raw materials involved in the present invention can be purchased directly from the market. For process parameters not specifically specified, conventional techniques can be referred to.

[0042] In this invention, 1 part by mass = 1 part by volume = 1 g / mL.

[0043] Example 1

[0044] (1) Mix 180 mL of anhydrous ethanol, 10 mL of deionized water, and 15.4 mL of ammonia in a 250 mL Erlenmeyer flask for 5 minutes at 40 °C and 600 rpm. Then, slowly add 9.5 mL of TEOS. Incubate the resulting mixture at 40 °C and 350 rpm for 1 hour. Subsequently, collect silica nanoparticles (approximately 350 nm in diameter) by centrifugation (8000 rpm, 5 min), wash three times with anhydrous ethanol, and dry overnight at 60 °C.

[0045] (2) Janus particles were prepared using the Pickering emulsion template method. 0.5g of the nano-SiO2 synthesized in step (1) was used as the emulsifier for the Pickering emulsion, 3g of solid paraffin (melting point 52-54℃) was used as the oil phase, and 20mL of deionized water containing DDAB (its concentration in the aqueous phase was 60mg / L) was used as the aqueous phase. The entire system was heated in an 80℃ water bath for 30min to dissolve the solid paraffin, and then homogenized at 18000rpm for 2min using a high-speed homogenizer to form the Pickering emulsion. After cooling to room temperature and solidifying the oil phase, the mixture was filtered and dried to obtain paraffin@SiO2 colloid.

[0046] (3) Take 2g of paraffin@SiO2 colloid and add it to 20mL of 95% (volume) ethanol solution, and add 1mL of γ-glycidyl etheroxypropyltrimethoxysilane. React at 25℃ and 200rpm for 24h. After the reaction is completed, dissolve the paraffin in chloroform, centrifuge at 5000rpm for 5 minutes and wash 3 times with anhydrous ethanol. Dry at 60℃ overnight to obtain half-sided modified SiO2 particles with hydroxyl groups on one half and epoxy groups on the other half.

[0047] (4) Take 0.2g of the half-sided modified SiO2 particles obtained in step (3) and disperse them in 5mL of toluene. Add 0.2mL of octyltrimethoxysilane and 150μL of triethylamine. React at 25℃ and 200rpm for 24h. After the reaction is completed, centrifuge at 5000rpm for 5 minutes, wash three times with anhydrous ethanol, and dry at 60℃ overnight to obtain nano SiO2 Janus particles.

[0048] (5) Take 20 mg of nano SiO2 Janus particles obtained in step (4) and ultrasonically disperse them in 2 mL of ethyl acetate. Add an equal volume of aqueous phase and homogenize them by high-speed homogenizer at 18000 rpm for 2 min to form Pickering emulsion.

[0049] (6) Add 80 μL of 0.1 mol / L HCl to the Pickering emulsion obtained in step (5). At this time, the pH is about 5. After standing for 5 minutes, the water-in-oil emulsion breaks down. Add 80 μL of 0.1 mol / L NaOH solution and shake well to reform the water-in-oil Pickering emulsion.

[0050] Example 2

[0051] (1) Same as step (1) in Example 1.

[0052] (2) Janus particles were prepared using the Pickering emulsion template method. 0.7 g of nano-SiO2 synthesized in step (1) was used as the emulsifier for the Pickering emulsion, 4 g of solid paraffin (melting point 58-60℃) was used as the oil phase, and 20 mL of deionized water containing DDAB (its concentration in the aqueous phase was 80 mg / L) was used as the aqueous phase. The entire system was heated in an 80℃ water bath for 30 min to dissolve the solid paraffin, and then homogenized at 16000 rpm for 3 min using a high-speed homogenizer to form the Pickering emulsion. After cooling to room temperature and solidifying the oil phase, the mixture was filtered and dried to obtain paraffin@SiO2 colloid.

[0053] (3) Take 3g of paraffin@SiO2 colloid and add it to 20mL of 95% (volume) ethanol solution, and add 1.5mL of γ-glycidyl etheroxypropyltrimethoxysilane. React at 25℃ and 200rpm for 18h. After the reaction is completed, dissolve the paraffin in chloroform, centrifuge at 5000rpm for 5 minutes and wash 3 times with anhydrous ethanol. Dry at 60℃ overnight to obtain half-sided modified SiO2 particles with hydroxyl groups on one half and epoxy groups on the other half.

[0054] (4) Take 0.2g of the half-sided modified SiO2 particles obtained in step (3) and disperse them in 5mL of toluene. Add 0.2mL of octyltrimethoxysilane and 150μL of triethylamine. React at 25℃ and 200rpm for 18h. After the reaction is completed, centrifuge at 5000rpm for 5 minutes, wash three times with anhydrous ethanol, and dry at 60℃ overnight to obtain nano SiO2 Janus particles.

[0055] (5) Take 20 mg of nano SiO2 Janus particles obtained in step (4) and ultrasonically disperse them in 2 mL of ethyl acetate. Add an equal volume of aqueous phase and homogenize them by high-speed homogenizer at 16000 rpm for 3 min to form Pickering emulsion.

[0056] (6) Add 100 μL of 0.1 mol / L HCl to the Pickering emulsion obtained in step (5). At this time, the pH is about 4. After standing for 5 minutes, the water-in-oil emulsion breaks down. Add 100 μL of 0.1 mol / L NaOH solution and shake well to reform the water-in-oil Pickering emulsion.

[0057] Example 3

[0058] (1) Same as step (1) in Example 1.

[0059] (2) Janus particles were prepared using the Pickering emulsion template method. 1g of nano-SiO2 synthesized in step (1) was used as the emulsifier for the Pickering emulsion, 5g of solid paraffin (melting point 62-64℃) was used as the oil phase, and 20mL of deionized water containing DDAB (100mg / L in the aqueous phase) was used as the aqueous phase. The entire system was heated in an 80℃ water bath for 30min to dissolve the solid paraffin, and then homogenized at 14000rpm for 4min using a high-speed homogenizer to form the Pickering emulsion. After cooling to room temperature and solidifying the oil phase, the mixture was filtered and dried to obtain paraffin@SiO2 colloid.

[0060] (3) Take 1g of paraffin@SiO2 colloid and add it to 20mL of 95% (volume) ethanol solution, and add 0.5mL of γ-glycidyl etheroxypropyltrimethoxysilane. React at 25℃ and 200rpm for 12h. After the reaction is completed, dissolve the paraffin in chloroform, centrifuge at 5000rpm for 5 minutes and wash 3 times with anhydrous ethanol. Dry at 60℃ overnight to obtain half-sided modified SiO2 particles with hydroxyl groups on one half and epoxy groups on the other half.

[0061] (4) Take 0.05g of the half-sided modified SiO2 particles obtained in step (3) and disperse them in 5mL of toluene. Add 0.05mL of octyltrimethoxysilane and 150μL of triethylamine. React at 25℃ and 200rpm for 12h. After the reaction is completed, centrifuge at 5000rpm for 5 minutes, wash three times with anhydrous ethanol, and dry at 60℃ overnight to obtain nano SiO2 Janus particles.

[0062] (5) Take 20 mg of nano SiO2 Janus particles obtained in step (4) and ultrasonically disperse them in 2 mL of ethyl acetate. Add an equal volume of aqueous phase and homogenize them by high-speed homogenizer at 14000 rpm for 4 min to form Pickering emulsion.

[0063] (6) Add 100 μL of 0.1 mol / L HCl to the Pickering emulsion obtained in step (5). At this time, the pH is about 4. After standing for 5 minutes, the water-in-oil emulsion breaks down. Add 100 μL of 0.1 mol / L NaOH solution and shake well to reform the water-in-oil Pickering emulsion.

[0064] Comparison Case 1

[0065] (1) Same as step (1) in Example 1.

[0066] (2) Same as step (2) in Example 1.

[0067] (3) Take 2g of paraffin@SiO2 colloid and add it to 20mL of 95% (volume) ethanol solution, and add 1mL of 3-aminopropyltriethoxysilane. React at 25℃ and 200rpm for 24h. After the reaction is complete, dissolve the paraffin in chloroform, centrifuge at 5000rpm for 5 minutes and wash 3 times with anhydrous ethanol. Dry at 60℃ overnight to obtain half-sided modified SiO2 particles with hydroxyl groups on one half and amino groups on the other half.

[0068] (4) is the same as step (4) in Example 1.

[0069] (5) is the same as step (5) in Example 1.

[0070] (6) Add 200 μL of 0.1 mol / L HCl to the Pickering emulsion obtained in step (5). At this time, the pH is 2-3. After standing for 5 minutes, the water-in-oil emulsion breaks down. Add 200 μL of 0.1 mol / L NaOH solution and shake well to reform the water-in-oil Pickering emulsion.

[0071] Comparison Case 2

[0072] (1) Same as step (1) in Example 1.

[0073] (2) Same as step (2) in Example 1.

[0074] (3) Take 2g of paraffin@SiO2 colloid and add it to 20mL of 95% (volume) ethanol solution, and add 1mL of N-(β-aminoethyl)-γ-aminopropylmethyldimethoxysilane. React at 25℃ and 200rpm for 24h. After the reaction is complete, dissolve the paraffin in chloroform, centrifuge at 5000rpm for 5 minutes and wash 3 times with anhydrous ethanol. Dry at 60℃ overnight to obtain half-sided modified SiO2 particles with hydroxyl groups on one half and amino groups on the other half.

[0075] (4) is the same as step (4) in Example 1.

[0076] (5) is the same as step (5) in Example 1.

[0077] (6) Add 180 μL of 0.1 mol / L HCl to the Pickering emulsion obtained in step (5). At this time, the pH is 3. After standing for 5 minutes, the water-in-oil emulsion breaks down. Add 200 μL of 0.1 mol / L NaOH solution and shake well to reform the water-in-oil Pickering emulsion.

[0078] Comparison Case 3

[0079] (1) Same as step (1) in Example 1.

[0080] (2) Same as step (2) in Example 1.

[0081] (3) Take 2g of paraffin@SiO2 colloid and add it to 20mL of 95% (volume) ethanol solution, and add 0.1ml of γ-glycidyl etheroxypropyltrimethoxysilane. React at 25℃ and 200rpm for 24h. After the reaction is completed, dissolve the paraffin in chloroform, centrifuge at 5000rpm for 5 minutes and wash 3 times with anhydrous ethanol. Dry at 60℃ overnight to obtain half-sided modified SiO2 particles with hydroxyl groups on one half and amino groups on the other half.

[0082] (4) Take 0.2g of the half-sided modified SiO2 particles obtained in step (3) and disperse them in 5mL of toluene. Add 1mL of octyltrimethoxysilane and 150μL of triethylamine. React at 60℃ and 200rpm for 8h. After the reaction is completed, centrifuge at 5000rpm for 5 minutes, wash with anhydrous ethanol 3 times, and dry at 60℃ overnight to obtain nano SiO2 Janus particles.

[0083] (5) is the same as step (5) in Example 1.

[0084] (6) Add 200 μL of 0.1 mol / L HCl to the Pickering emulsion obtained in step (5). At this time, the pH is 2-3. After standing for 5 minutes, the water-in-oil emulsion did not break down. Adding more HCl solution did not cause the emulsion to break down.

[0085] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing nano-SiO2 Janus particles with a narrow pH response range, characterized in that, Includes the following steps: (1) Nano SiO2, solid paraffin and water containing surfactant are mixed and heated, and then homogenized to form Pickering emulsion; after cooling the Pickering emulsion to room temperature to solidify the oil phase, it is filtered, washed and dried to obtain paraffin@SiO2 colloid; (2) The obtained paraffin@SiO2 colloid was added to an alcohol-water system, and γ-glycidoxypropyltrimethoxysilane was added for modification. After the reaction was completed, the paraffin was dissolved in chloroform, washed, centrifuged and dried to obtain half-modified SiO2 particles with hydroxyl groups on one half of the surface and epoxy groups on the other half of the surface. The amount of γ-glycidoxypropyltrimethoxysilane added was 0.5-1.5 parts by volume. (3) The semi-modified SiO2 particles obtained in step (2) are dispersed in a solvent, and octyltrimethoxysilane and triethylamine are added for hydrophobic modification. After the reaction is completed, the particles are washed, centrifuged and dried to obtain the nano-SiO2 Janus particles with a narrow pH response range. The amount of octyltrimethoxysilane added is 0.05-0.2 parts by volume. The hydrophobic modification reaction time is 12-24 h and the temperature is 25 °C.

2. The preparation method according to claim 1, characterized in that, The particle size of the nano-SiO2 in step (1) is 300-400 nm; The surfactant mentioned in step (1) is bis(dodecyl)dimethylbromide; the heating time and temperature are 30 min and 80 °C, respectively.

3. The preparation method according to claim 1, characterized in that, In step (1), the mass of the nano-SiO2 is 2%-4% of the total mass of the oil phase and the aqueous phase; The mass ratio of the solid paraffin to water is 1:20-8:20; The concentration of the surfactant in water is 60-200 mg / L.

4. The preparation method according to claim 1, characterized in that, The melting point of the solid paraffin in step (1) is 52-64℃; The homogenization speed in step (1) is 14,000-18,000 rpm, and the homogenization time is 2-4 min.

5. The preparation method according to claim 1, characterized in that, The amount of paraffin@SiO2 colloid added in step (2) is 1-3 parts by mass.

6. The preparation method according to claim 1, characterized in that, The modification reaction in step (2) takes 6-24 hours and is carried out at a temperature of 25 °C.

7. The preparation method according to claim 1, characterized in that, In step (3), the amount of half-sided modified SiO2 particles added is 0.05-0.2 parts by mass, and the amount of triethylamine added is 0.15 parts by volume.

8. A nano-SiO2 Janus particle prepared by the preparation method according to any one of claims 1-7, characterized in that, Its stable Pickering emulsion can break down at pH 4-5.

9. The application of the nano-SiO2 Janus particles of claim 8 in the fields of biocatalysis, oil-water separation or drug delivery.

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