Method for preparing pickering miniemulsion and its catalytic application

Patent metadata

Field	Value
Publication number	US-12134087-B2
Application number	US-202318479002-A
Country	US
Kind code	B2
Filing date	Sep 30, 2023
Priority date	Oct 5, 2022
Publication date	Nov 5, 2024
Grant date	Nov 5, 2024

Abstract

A submicron-sized Pickering miniemulsion system stabilized by carbon quantum dots solid nanoparticles for biphasic catalysis is disclosed, which breaks the existing limits for homogenization of the immiscible biphasic system and overcomes the issues for big size of solid particles-stabilized emulsion droplets. A method for producing the carbon quantum dot-based catalysts and a process of establishing the Pickering miniemulsion system for biphasic reaction with enhanced catalytic efficiency are also disclosed. The carbon quantum dot-stabilized Pickering miniemulsion features a pH-responsive behavior, with a reversible transition between the emulsification and demulsification, triggering the easy & facile product separation and emulsifier/catalyst recycling in one reaction vessel.

First claim

What is claimed is:

1. A method for constructing a Pickering miniemulsion catalytic system, comprising the following steps:
step 1, preparing a Pickering miniemulsion catalyst/emulsifier, specifically comprising:
step 1.1, preparation of surface-modified carbon quantum dots:
adding citric acid and an amine compound to absolute ethanol, and modifying carbon dots by using the amine compound as a modifier and the citric acid as a carbon source, and heating for obtaining orange liquid; wherein 1.5-3 g of the citric acid and 0.1-4 g of the amine compound are added into every 25 mL of the absolute ethanol;
dispersing the orange liquid into sodium hydroxide (NaOH) aqueous solution dropwise, and stirring the NaOH aqueous solution added with the orange liquid at 35-50° C. for 24-48 h to obtain a dispersion; wherein a volume ratio of the NaOH aqueous solution to the orange liquid is 20:1; and
centrifuging the dispersion to obtain a supernatant, treating the supernatant with 500 Dalton (DA) dialysis membrane for 24-48 h to remove small molecular impurities and obtain yellow carbon dots solution; placing the yellow carbon dots solution in an environment below −10° C. until the yellow carbon dots solution is completely frozen, and then drying in a freeze dryer to obtain carbon dots solid powder with a size of 8-12 nm;
step 1.2, preparation of an emulsion catalyst:
adding the carbon dots solid powder and a metal salt into a mixed solution of water and ethanol and then stirring for 3-6 h to obtain a system; wherein 20-1000 mg of the carbon dots solid powder and 1-50 mg of the metal salt are correspondingly added into every 50 mL of the mixed solution of water and ethanol, and a volume ratio of the water to the ethanol in the mixed solution of water and ethanol is 1:4; after standing the system for 6-18 h, adding sodium borohydride (NaBH 4 ) aqueous solution dropwise into the system to perform reduction for 0.5-2 h until the system becomes a black suspension, and centrifuging the black suspension to obtain a solid emulsion catalyst; wherein 10 mL of the NaBH 4 aqueous solution with a concentration of 2 mg·mL −1 is correspondingly added to every 50 mL of the mixed solution of water and ethanol;

step 2, constructing the Pickering miniemulsion catalytic system, specifically comprising:
dispersing the obtained solid emulsion catalyst in water to prepare a dispersion A with a concentration of 0.05-5 wt %; adding the dispersion A to a vial with a water-immiscible organic solvent to obtain a mixture; wherein a volume ratio of the dispersion A to the organic solvent is 2:1; performing ultrasonic treatment on the mixture in the vial for 0.5-2 min, and then stirring the mixture for 10-20 min to emulsify the mixture and form a Pickering miniemulsion; and wherein a droplet size of the Pickering miniemulsion is in a range of 0.1-1 μm.

2. The method for constructing the Pickering miniemulsion catalytic system as claimed in claim 1 , wherein in step 1.1, the amine compound is one selected from the group consisting of dodecylamine, tetradecylamine, hexadecylamine, and octadecylamine.

3. The method for constructing the Pickering miniemulsion catalytic system as claimed in claim 1 , wherein in step 1.1, a centrifuging speed is in a range of 6000 rpm to 9000 rpm, and a centrifuging time is in a range of 5 min to 10 min; and
wherein in step 1.2, a centrifuging speed is in a range of 18000 rpm to 26000 rpm, and a centrifuging time is in a range of 15 min to 35 min.

4. The method for constructing the Pickering miniemulsion catalytic system as claimed in claim 1 , wherein in step 1.2, the metal salt is one selected from the group consisting of ruthenium chloride, palladium chloride and chloroplatinic acid.

5. The method for constructing the Pickering miniemulsion catalytic system as claimed in claim 1 , wherein in step 2, the organic solvent is one selected from the group consisting of toluene, cyclohexane, dichloromethane, ethyl acetate, and decalin.

6. An application method of the Pickering miniemulsion catalytic system constructed by the method as claimed in claim 1 , comprising:
applying the Pickering miniemulsion catalytic system in a biphasic catalytic reaction.

7. The application method as claimed in claim 6 , wherein the applying the Pickering miniemulsion catalytic system in a biphasic catalytic reaction, comprises:
adding a reactant and a water-soluble oxidant/reductant into the Pickering miniemulsion catalytic system, then uniformly stirring in an oil bath pot at 30-90° C. and reacting for 0.5-5 h; wherein a molar ratio of the reactant to the water-soluble oxidant/reductant is 1:3, and 2-10 mmol of the reactant are added into every 10 mL of the Pickering miniemulsion catalytic system; after the reacting, adding 1 M of inorganic acid solution dropwise into the Pickering miniemulsion catalytic system until demulsification and realizing oil-water stratification; wherein a product of the reacting is dissolved in an organic phase and a catalyst of the reacting is dispersed in a water phase, the product in the organic phase is detected by gas chromatography to obtain a yield, the water phase containing the catalyst is used as the dispersion A for repeated use in step 2; after adding several drops of NaOH solution (1 M) to tune a pH value to 10-11, the Pickering miniemulsion is regenerated by stirring; and the inorganic acid solution is one selected from the group consisting of hydrochloric acid, sulfuric acid, and nitric acid.

8. The application method as claimed in claim 7 , wherein the reactant comprises alcohol, olefin or a nitro compound; the water-soluble oxidant is hydrogen peroxide (H 2 O 2 ), and the reductant is NaBH 4 .

Assignees

• Univ Dalian Tech

Inventors

• Qiu Jieshan
• Yu Chang
• Ni Lin
• Wen Ji

Classifications

• C07C45/294 Primary

  with hydrogen peroxide · CPC title

• B01J37/343

  of ultrasonic wave energy · CPC title

• B01J37/16

  Reducing · CPC title

• B01J37/04

  Mixing {(B01J37/0009, B01J37/0018 take precedence)} · CPC title

• B01J37/0221

  of particles · CPC title