CN120460017A

CN120460017A - A Pickering emulsion of thiamine-functionalized graphene oxide, a preparation method thereof, and its application as a catalyst in Knoevenagel condensation reaction

Info

Publication number: CN120460017A
Application number: CN202510593731.XA
Authority: CN
Inventors: 刘大亮; 张坡; 宋智凝; 吴琼; 吴抒遥; 孟庆博; 张宇轩
Original assignee: Liaoning University
Current assignee: Liaoning University
Priority date: 2025-05-09
Filing date: 2025-05-09
Publication date: 2025-08-12

Abstract

The present invention relates to the technical field of emulsion preparation, and in particular to a Pickering emulsion of thiamine-functionalized graphene oxide, a preparation method thereof, and an application of the Pickering emulsion as a catalyst in a Knoevenagel condensation reaction. The thiamine-functionalized graphene oxide Pickering emulsion has good dispersibility in an aqueous phase, is not easy to agglomerate, can form an oil-in-water Pickering emulsion in a water-oil two-phase, and has uniform droplet size and good stability. The construction method of the Pickering emulsion catalytic system of the present invention is simple, low-cost, green and pollution-free, has good emulsion stability and excellent catalytic activity; and the catalyst is easy to separate and recycle, GO- _VB1 has good substrate adsorption capacity; and has stronger alkalinity; in the Knoevenagel condensation reaction, the yield of the target product is about 95% or more.

Description

Thiamine functionalized graphene oxide Pickering emulsion, preparation method thereof and application of thiamine functionalized graphene oxide Pickering emulsion as catalyst in Knoevenagel condensation reaction

Technical Field

The invention relates to the technical field of emulsion preparation, in particular to thiamine functionalized graphene oxide Pickering emulsion, a preparation method thereof and application of the thiamine functionalized graphene oxide Pickering emulsion serving as a catalyst in Knoevenagel condensation reaction.

Background

Pickering emulsion is a novel emulsion type with solid particles replacing the traditional surfactant stabilized emulsion system, and is more stable than common emulsion. The amphiphilic carbon nano material graphene oxide is used as an emulsifier, so that stability is higher when the emulsion is formed, strong van der Waals force exists between graphene sheets, aggregation is easy, the graphene can not be well dissolved in water, an organic solvent or common ionic liquid and the like, and the graphene oxide has poor effect with other mediums, so that the graphene serving as the emulsifier is limited in the related fields such as the formation and application of the emulsion. Compared with the spherical fixed particles, the graphene oxide is layered and can be covered on the surface of the sphere in a small amount, so that the dosage of the emulsifier can be reduced, and the cost is saved. Thiamine is a biological coenzyme, is greatly influenced by environment and self-properties, is easy to decompose and inactivate, and has biocompatibility. The thiamine modified by the chemical method is modified on the surface of the substrate, so that the stability, the recoverability and the recycling times of thiamine can be improved to a great extent.

Knoevenagel condensation is one of the most valuable reactions for forming carbon-carbon double bonds. The product has wide application in medicine, cosmetics, pesticide and biological industry or is valuable organic intermediate. The traditional homogeneous catalysis can also obtain better yield, such as organic amine, alkyl lithium reagent, solid alkali and the like, but the methods have some defects, such as difficult separation of a catalyst and a product, use of a toxic reagent, long reaction time, incapability of recycling the catalyst and the like, and the catalysis of a two-phase system has a limited reaction interface, so that mass transfer resistance between substrates is easy to cause, and the reaction is hindered. Additional surfactant and other methods are generally needed to improve the two-phase catalysis efficiency, but difficulties are brought to product separation. The Pickering emulsion catalysis technology is raised, a two-phase system emulsified by solid particles forms a Pickering emulsion which is stable in dynamics, the contact area of the catalyst and a substrate is increased under the condition that other reagents are not required to be added, the mass transfer resistance of the substrate is overcome, and the catalysis reaction rate is improved. Therefore, there is a need to develop a recoverable solid catalyst to stabilize Pickering emulsions and build Pickering emulsion interfacial catalyst systems. The literature reports that the method for preparing Pickering emulsion catalyst from amphiphilic GO-supported organosilane amine has obviously better catalytic activity to Knoevenagel reaction than common heterogeneous catalyst, but still has the defects of high reaction temperature (80 ℃), longer time, large catalyst dosage, less cycle number and the like.

Disclosure of Invention

In order to solve the problems, the invention aims to provide a preparation method of thiamine functionalized graphene oxide Pickering emulsion and application of the emulsion system in Knoevenagel condensation reaction.

The invention aims at:

the invention aims to provide a novel emulsion which does not contain any toxic materials, surfactant and toxic reagent, has good biological safety and strong biocompatibility, greatly enhances the stability of Pickering emulsion, and is applied to the construction of an emulsion catalytic system.

To achieve the above object, a first aspect of the present invention provides a method for preparing a Pickering emulsion using a substrate as a supported thiamine, and then constructing a Pickering emulsion catalyst system, the preparation method comprising:

the first step, pickering emulsion emulsifier/catalyst is prepared by the following steps:

1.1 Surface modified graphene oxide) is prepared:

(1) Under the ice bath condition, mixing graphite and potassium permanganate, adding 95% -98% of concentrated sulfuric acid and 45% -47% of phosphoric acid, fully mixing, removing the ice bath, heating the oil bath to 35 ℃ and stirring vigorously for 1h, and cooling to room temperature;

Further, the graphite powder is preferably natural flake graphite powder or colloidal graphite, and when the graphene oxide is prepared, the proportion of the graphite powder, the potassium permanganate, the concentrated sulfuric acid and the phosphoric acid is 1g:12g:92mL:12mL.

H ₂ O was added to the mixture, the temperature was raised to 90℃and reacted for 0.5H, then cooled to room temperature, H ₂ O and 30% H ₂O₂ were added to the suspension and stirring was continued for 1H, the color changed from brown to golden yellow.

GO was washed to neutrality by washing with hydrochloric acid solution to remove sulfate ions, and deionized water. After drying under vacuum, GO is obtained.

(2) Grinding and crushing the dried graphene oxide, taking a proper amount of the graphene oxide, placing the graphene oxide into a sample bottle, adding a proper amount of water, performing ultrasonic dispersion for 4 hours to obtain a graphene oxide suspension with a certain concentration, and sealing and preserving the graphene oxide suspension at normal temperature;

1.2 Preparation of thiamine functionalized graphene oxide (emulsifier/catalyst):

(1) Mixing thiamine (VB ₁), 95% ethanol and water, dropwise adding a 10% sodium hydroxide aqueous solution under ice bath condition, adjusting the pH value to 9-14, adding graphene oxide suspension, reacting at 80-90 ℃, stirring for reacting for 20 hours, centrifuging, washing with ethanol and deionized water to neutrality, and freeze-drying to obtain a VB ₁ modified graphene oxide composite material (GO-VB ₁);

Further, the ratio of VB ₁ to ethanol to water is 1g to 30mL to 5mL, and the concentration of the graphene oxide suspension is 1.5-5 mg/g.

Secondly, constructing a Pickering emulsion interface catalytic system, which comprises the following specific steps:

2.1 Dispersing the obtained GO-VB ₁ solid emulsifier catalyst in water, and performing ultrasonic treatment for 5min to prepare a dispersion liquid with the concentration of 0.5-4wt%.

2.2 2.1) Adding a water-immiscible organic solvent to the sample bottle (water: oil=2:1), and then vortex mixing for 5min to emulsify the above mixture to form a Pickering emulsion.

The Pickering emulsion interfacial catalysis system is constructed by fully dispersing GO-VB ₁ in a water phase, fully dissolving a water-soluble reactant (malononitrile) in the dispersion liquid to obtain a mixture A, fully dissolving an oil-soluble reactant (aromatic aldehydes) in an oil phase (toluene) to obtain a mixture B, combining the mixture A and the mixture B, and forming the Pickering emulsion interfacial catalysis system by intense vortex mixing. Standing in an oil bath pot at 25-50 ℃ for continuous reaction for 0.5-3h. The emulsifier is used in an amount of 0.005-0.025 g, the mol ratio of reactants is 1mmoL, and after the reaction is finished, the emulsion is broken by centrifugation to realize oil-water delamination, wherein the product is dissolved in an organic phase, and the catalyst is dispersed in a water phase. The product in the organic phase was detected by gas chromatography and the yield calculated, the catalyst in the aqueous phase being redispersible as dispersion a and recycled by repeating step 2.2. Wherein the reactant can be aromatic aldehydes (such as benzaldehyde) or active methylene compounds (such as malononitrile). The invention has the following beneficial effects:

(1) According to the invention, the thiamine modified graphene oxide is utilized to prepare the amphiphilic emulsifying catalyst, and the stable Pickering emulsion is prepared, no obvious sedimentation or deterioration is found after the Pickering emulsion is stored for 3 months at room temperature in a sealing way, no demulsification phenomenon is found after more than five months, and the water layer height after the emulsion layering is lower than about 10% of the total height, so that a foundation is laid for constructing an emulsion catalytic system.

(2) The catalytic active center of the emulsifier/catalyst is provided by VB ₁, the hydrophilic and hydrophobic properties of the GO surface are changed by adjusting the content of VB ₁, so that the property of Pickering emulsion is changed, the density, the distribution width and the size of liquid drops are improved, the compatibility of substrates is enhanced, and the catalytic activity of the emulsion is further improved.

(3) After intensive research, it is found that Pickering emulsion formed by using GO-VB ₁ in oil water under certain conditions has smaller droplet size (average size of 37 μm), larger droplet density and narrower distribution, and the emulsion has higher catalytic activity when being used for catalyzing Knoevenagel condensation reaction of malononitrile and benzaldehyde, and the yield of a target product is more than 95%.

(4) The emulsion prepared after the GO-VB ₁ is repeatedly used for many times has little change of the droplet size and the droplet distribution degree compared with the new catalyst, and still has higher catalytic activity.

Drawings

Fig. 1 is a transmission electron micrograph of a substrate GO of a stabilized Pickering emulsion.

FIG. 2 is a transmission electron microscope image of GO-VB ₁ composite nanoplatelets in a stable Pickering emulsion.

FIG. 3 is an IR spectrum of the GO-VB ₁ composite nanosheets provided by the embodiment of the invention.

Fig. 4 is an XPS spectrum of the GO-VB ₁ composite nano-sheet provided by the embodiment of the invention.

FIG. 5 is a physical image of an oil-in-water Pickering emulsion stabilized by GO-VB ₁.

FIG. 6 is a micrograph of a different ratio of oil-in-water Pickering emulsion stabilized by GO-VB ₁,

FIG. 6a is a microscopic image of an oil-in-water Pickering emulsion with a water-to-oil ratio of 1:1,

FIG. 6b is a micrograph of a 2:1 oil-in-water Pickering emulsion,

FIG. 6c is a micrograph of a water to oil ratio 3:1 oil-in-water Pickering emulsion,

FIG. 6d is a microscopic image of an oil-in-water Pickering emulsion with a water-to-oil ratio of 1:2,

FIG. 6e is a micrograph of a Pickering emulsion in water to oil ratio of 1:3.

FIG. 7 is a Pickering emulsion optical microscope picture (a) prepared from GO-VB ₁ and its corresponding emulsion droplet distribution map (b).

FIG. 8 is a photograph of an oil-in-water Pickering emulsion microscope stabilized by GO-VB ₁,

FIG. 8a is a Pickering emulsion microscope image of toluene as the oil phase;

FIG. 8b is a Pickering emulsion microscope image of n-hexane as the oil phase;

FIG. 8c is a Pickering emulsion microscope image of cyclohexane as the oil phase;

FIG. 8d is a Pickering emulsion microscope image of the oil phase methylene chloride;

FIG. 8e is a Pickering emulsion microscope photograph of an oil phase being ethyl acetate;

Fig. 8f is a Pickering emulsion microscope image of n-heptane as the oil phase.

FIG. 9 is a schematic representation of the reaction of benzaldehyde with malononitrile in a PEIC system.

Detailed Description

Preferred embodiments of the present invention will be described in more detail below. While the preferred embodiments of the present invention are described below, it should be understood that the present invention may be embodied in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. The invention is further illustrated and described below in connection with specific examples.

Example 1

Preparation of thiamine functionalized graphene oxide composite (GO-VB ₁):

(1) Preparation of graphene oxide nanosheets:

To a mixture of graphite flakes (2.0 g) and KMnO ₄ (75.9 mmol) was added concentrated H ₂SO₄/H₃PO₄ (92:12 mL) in an ice-water bath, and the suspension was stirred at 35℃for 1H, and after adding H ₂ O (160 mL), reacted at 90℃for 0.5H. When the suspension was cooled to room temperature, H ₂ O (150 mL) and 30% H ₂O₂ (30 mL) were poured into the suspension and stirring was continued for 1H, and the original graphene oxide was obtained after filtration. The graphene oxide was then washed several times by using 5% hydrochloric acid solution and deionized water. And drying under vacuum to obtain graphene oxide nano-sheets (GO), and observing the morphology of the graphene oxide nano-sheets through a Transmission Electron Microscope (TEM), wherein the morphology is shown in figure 1.

(2) Preparation of graphene oxide suspension:

And (3) placing the ground and crushed graphene oxide sheet powder (100 mg) into a sample bottle, adding proper deionized water, performing ultrasonic treatment at 25 ℃, wherein the ultrasonic power is 60-180W, and the ultrasonic treatment time is 50min, so as to obtain graphene oxide suspension (1.5 mg/mL), and sealing, preserving and waiting for use.

(3) Preparation of thiamine-functionalized graphene oxide (GO-VB ₁) composite material:

VB ₁ (0.5 g,1.48 mmol) was added to deionized water (5 mL) and 95% ethanol C ₂H₅ OH (30 mL), and the pH of the solution was adjusted (9-10) with 10% aqueous NaOH under ice-bath conditions. After the graphene oxide suspension (20 mL) obtained in step (2) was added to be suspended, the mixture was reacted at 70 ℃ for 24 hours. Centrifuging the mixture, washing the precipitate with deionized water for several times, and freeze-drying to obtain the target product, which is named as GO-VB ₁ -1.

For comparison, the amounts of VB ₁ were adjusted to 1.0g (2.96 mmol), 1.25g (3.71 mmol), 1.5g (4.45 mmol) and 1.75g (5.19 mmol), respectively. The corresponding targets are labeled as GO-VB ₁-2、GO-VB₁-3、GO-VB₁ -4 and GO-VB ₁ -5, respectively. The morphology and structure were characterized by TEM, IR and XPS, as shown in fig. 2,3 and 4.

Example 2

The preparation method of Pickering emulsion comprises the following steps:

Uniformly dispersing GO-VB ₁ (10 mg) obtained in the step (3) in the example 1 in an aqueous phase, mixing with toluene, regulating the water-oil ratio (the mass ratio of the aqueous phase to the oil phase) to be 1:1, 2:1, 3:1, 1:2 and 1:3, carrying out vortex mixing at 25 ℃, wherein the vortex mixing speed is 3000 (r/min), the vortex mixing time is 3min, obtaining Pickering emulsion (physical diagram (GO-VB ₁ -5, water: oil 2:1) stabilized on the basis of GO-VB ₁, as shown in figure 5), photographing by an optical microscope, observing the microstructure of emulsion drops, and when the oil-water ratio is 1:1, regulating the emulsion drop size to be nonuniform, and the emulsion drop size to be uniform (figure 6 a) when the oil-water ratio is 2:1, and the emulsion drop size to be uniform (figure 6 b) when the oil-water ratio is 3:1. The emulsion droplets are distributed sparsely and unevenly (fig. 6 c), relatively small and unevenly (fig. 6 d) when the oil-water ratio is 1:2, and relatively small and uneven in size (fig. 6 e) when the oil-water ratio is 1:3. From the above, it is found that the emulsion system obtained is preferable when the oil-water ratio is 2:1. As shown in fig. 6.

Emulsion Performance test (GO-VB ₁ -5):

The stable Pickering emulsion was formed using a water to oil ratio (2:1) as observed by light microscopy. The emulsion droplets were uniform in size and had an average size of about 37 μm, and no emulsion breaking or emulsifier sedimentation was observed in the room temperature environment for more than three days, as shown in FIG. 7. However, graphene oxide or thiamine alone is not stable when preparing Pickering emulsion as an emulsifier. The Pickering emulsion stabilized by pure graphene oxide can be stabilized for about five minutes at room temperature, and the Pickering emulsion cannot be formed by thiamine alone.

Example 3

The preparation method of the Pickering emulsion stabilized by GO-VB ₁ comprises the following steps:

Using GO-VB ₁ -4 (10 mg) as an example, it was sonicated in water (2 ml) to form a suspension. Subsequently, the different oil phases (toluene, n-hexane, cyclohexane, dichloromethane, ethyl acetate and n-heptane, 1 mL) were mixed with the suspension and vigorously vortexed to give an oil-in-water (O/W) Pickering emulsion. All emulsions were stored at room temperature (25 ℃) for a certain period of time and their microstructure was observed by light microscopy. The emulsion is prepared from toluene as an oil phase stable emulsion, relatively small emulsion drops and relatively uniform distribution (figure 8 a), the emulsion is prepared from n-hexane as an oil phase stable emulsion, the emulsion drops are different in size and are easy to coalesce and uneven in distribution (figure 8 b), the emulsion is prepared from cyclohexane as an oil phase stable emulsion, large in emulsion drops and easy to demulsify (figure 8 c), the emulsion is prepared from methylene dichloride as an oil phase stable emulsion, the emulsion is relatively sparse and uneven in distribution (figure 8 d), the emulsion is prepared from ethyl acetate as an oil phase stable emulsion, the emulsion drops are relatively small and uneven in distribution (figure 8 e), and the emulsion is prepared from n-heptane as an oil phase stable emulsion, the emulsion drops are different in size and uneven in distribution (figure 8 e) as shown in figure 8.

Example 4

The preparation method of Pickering emulsion interface catalytic system (PEIC) comprises the following steps:

A preparation method of a Pickering emulsion type functionalized catalyst utilizes GO composite material, toluene and water to form stable Pickering emulsion, and the emulsion catalyst system is used for catalyzing Knoevenagel condensation reaction of malononitrile and benzaldehyde at a mild temperature, and a PEIC system reaction schematic diagram is shown in figure 9.

(1) The GO-VB ₁ obtained in example 1 was dispersed in water to prepare a dispersion with a concentration of 0.5 wt%. 2mL of the dispersion was added to a sample bottle with 1mL of toluene and vortexed for 3min to form a Pickering emulsion.

(2) And (3) adding malononitrile (1 mmol), benzaldehyde (1 mmol) and vigorously shaking for 5min into the Pickering emulsion prepared in the step (1) to obtain the Pickering emulsion interface catalytic system. Followed by Knoevenagel condensation. The Knoevenagel condensation reaction conditions are that the reaction temperature is 40 ℃ and the reaction time is 30min, and the experimental results are shown in table 1.

TABLE 1

Claims

1. A thiamine-functionalized graphene oxide Pickering emulsion, characterized in that the preparation method comprises the following steps:

1) Grinding a certain amount of graphene oxide nanosheets, adding a certain amount of deionized water, and ultrasonically dispersing the mixture until a suspension A is formed;

2) Take a certain amount of thiamine, add a certain proportion of water and ethanol, and mix until a homogeneous solution B is formed;

3) After stirring the solution B obtained in step 2) uniformly, the pH of the mixed solution was adjusted with an alkaline solution until solution C was obtained;

4) After mixing solution A and solution C, stirring at a constant speed, and continuing the reaction at a certain temperature for a certain time; after the reaction is completed, centrifuging, washing with water and ethanol multiple times, and freeze-drying the resulting solid to obtain thiamine-functionalized graphene oxide GO- _VB1 ;

5) Preparation of oil-in-water Pickering emulsion: Add a certain proportion of GO-VB ₁ suspension and oil phase and vortex mix vigorously to form an oil-in-water (O/W) Pickering emulsion.

2. The Pickering emulsion of graphene oxide functionalized with thiamine according to claim 1, characterized in that in step 1), the ultrasonic dispersion is performed for 60 minutes.

3. The thiamine-functionalized graphene oxide Pickering emulsion according to claim 1, wherein in step 2), the volume ratio of water to ethanol is 5-10:10-40.

4 . The Pickering emulsion of graphene oxide functionalized with thiamine according to claim 1 , wherein in step 3), the pH of the mixed solution is 9-11.

5. The thiamine-functionalized graphene oxide Pickering emulsion according to claim 1, characterized in that in step 4), the reaction temperature is 50°C to 90°C, and the reaction time is 15 to 24 hours.

6. The thiamine-functionalized graphene oxide Pickering emulsion according to claim 1, wherein in step 5), the volume ratio of the GO- _VB1 suspension to the oil phase is (0.33-3):1.

7. The thiamine-functionalized graphene oxide Pickering emulsion according to claim 1, wherein in step 5), the oil phase is a hydrophobic oil, which is one or a mixture of any of toluene, n-hexane, cyclohexane, n-heptane, dichloromethane, ethyl acetate and decalin.

8. Use of any one of claims 1 to 7 of the thiamine-functionalized graphene oxide Pickering emulsion as a catalyst in a Knoevenagel condensation reaction.

9. The use according to claim 8, characterized in that the Knoevenagel condensation reaction is a Knoevenagel condensation reaction of malononitrile with benzaldehyde and its derivatives.