A method for preparing a carbon dot-based pH-responsive Pickering emulsion

Abstract

This invention discloses a method for preparing a carbon dot-based pH-responsive Pickering emulsion, belonging to the field of oil and gas field chemical agents technology. The preparation method includes: firstly, preparing carbon dot (CDs) nanoparticles using a solvothermal method, then modifying amino groups via hydrolysis for preliminary hydrophobic modification, and finally modifying the hydrophobic groups to form a pH-responsive amphiphilic Pickering emulsifier. This emulsion is added to a certain proportion of oil-water two-phase mixture and emulsified using a vortex mixer at a specific speed to obtain the final product. The emulsion of this invention not only exhibits good stability, but also allows for emulsification and demulsification under different pH conditions when a stable state is no longer required, and can be cycled more than three times. The Pickering emulsifier prepared by this invention is environmentally friendly, simple to prepare, and possesses excellent stability and pH responsiveness, making it worthy of widespread application.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas field chemical agents technology, specifically relating to a carbon point-stabilized pH-responsive Pickering emulsion and its preparation method. Background Technology

[0002] With the continuous development of my country's petroleum resources, the design of emulsifiers to stabilize emulsions and improve oil recovery has become increasingly important. Demulsification of the stabilized emulsion in the later stages of extraction for crude oil recovery is also a crucial step. When using traditional surfactants as emulsifiers, the stability of the emulsion is significantly reduced due to the influence of reservoir temperature, pressure, and salinity, making responsive demulsification difficult. Pickering emulsions prepared using nanoparticles modified with responsive groups as emulsifiers exhibit good stability and stimuli responsiveness, which can significantly improve crude oil recovery and solve the problem of difficult demulsification. Carbon dots, as nanoparticles, possess excellent photoelectric properties, good water solubility, low toxicity, and excellent biocompatibility, and have wide applications in environmental monitoring, photocatalysis, energy conversion devices, bioimaging, and nanomedicine. Therefore, this paper designs and synthesizes a pH-responsive carbon dot emulsifier, uses it to prepare emulsions, and studies the stability and responsiveness of the system. Summary of the Invention

[0003] The purpose of this invention is to provide a method for preparing a pH-responsive Pickering emulsion. This method stabilizes the Pickering emulsion by preparing carbon dots and modifying them with a pH-responsive surfactant, providing a reference for the chemical industry fields such as heavy oil gathering and transportation, emulsion polymerization, and enhanced oil recovery.

[0004] Its technical solutions include:

[0005] 1. A method for preparing a novel pH-responsive Pickering emulsifier, comprising the following steps:

[0006] (I) Carbon dot nanoparticles of suitable size were synthesized by a solvothermal method. The specific preparation process is as follows:

[0007] (1) Weigh 3.15g of citric acid and place it in a round-bottom flask. Add deionized water and ethylenediamine to the round-bottom flask in sequence, and stir ultrasonically for 1 hour to dissolve completely.

[0008] (2) The liquid is transferred to a reaction vessel for hydrothermal reaction. After the liquid cools, it is centrifuged to remove the large molecular insoluble substances and obtain the crude carbon dot product.

[0009] (3) The crude carbon dots were dialyzed for 72 hours and then dried in a freeze dryer to obtain carbon dots (CDs).

[0010] (ii) Modify the surface of CDs with amino groups to obtain CDs-NH2.

[0011] (1) Take 0.1g of CDs-NH2 nanoparticles into a round-bottom flask, add 80mL of anhydrous ethanol into the round-bottom flask, and sonicate for 20min.

[0012] (2) Add 300 μL of 3-aminopropyltriethoxysilane (APTES) to a round-bottom flask and heat and stir in an oil bath for 10 h at a temperature of 70 °C.

[0013] (3) After the reaction was completed, the CDs-NH2 nanoparticles were collected by centrifugation and washed three times with anhydrous ethanol. Then, the CDs-NH2 nanoparticles were placed in a vacuum oven and kept warm for 12 hours to dry.

[0014] (III) A pH-responsive carbon dot emulsifier (CDs-R) was obtained by modifying hydrophobic groups. The specific preparation process is as follows:

[0015] (1) Weigh out the amino-modified CDs-NH2 nanoparticles obtained in step three and mix them with cinnamaldehyde in methanol in a certain proportion.

[0016] (2) After the reaction was completed, the CDs-R nanoparticles were collected by centrifugation and washed three times with anhydrous ethanol. Then, the CDs-R nanoparticles were placed in a vacuum oven and kept warm for 12 hours to dry.

[0017] (iv) Preparation of Pickering Emulsion

[0018] (1) The CDs-R nanoparticles obtained in step three are added to a certain proportion of oil and water two phases and emulsified by vortex oscillator at a certain frequency to obtain the final product.

[0019] Furthermore, in steps (i) and (3), the dialysis bag specification is MW3500.

[0020] Furthermore, in steps (i) and (3), the freeze-drying time is 24 hours.

[0021] Furthermore, in steps (i) and (4), the particle size of the prepared CDs nanoparticles is 3nm-5nm.

[0022] Furthermore, in step (ii) (1), the ultrasonic power is 750W.

[0023] Furthermore, in steps (ii) and (3), the centrifugation speed is 10000 r / min, and the centrifugation is performed three times, with each centrifugation lasting 10 min.

[0024] Furthermore, in step (iv)(1), the vortex oscillator is subjected to high-speed shearing at a speed of 4000 rpm for 6 minutes and then left to stand.

[0025] Furthermore, in step (iv)(1), the ratio of oil phase to water phase is 3:1, 2:1, 1:1, 1:2, 1:3, and the emulsifier concentration is calculated according to the concentration in the water phase.

[0026] Furthermore, in step (iv)(1), the oil phase is toluene, n-heptane, or paraffin oil, and the volume fraction of the oil phase in the Pickering emulsion is 50%.

[0027] The advantages of this invention are:

[0028] (1) The experimental conditions of this invention are simple, the overall product is easy to prepare, and the cost is low.

[0029] (2) The surface-modified carbon dot nanoparticles have good stability on Pickering emulsion.

[0030] (3) The present invention is sensitive to pH stimulation response of Pickering emulsion formation, the response conditions are easy to control, and emulsification-demulsification is easy to achieve. Attached Figure Description

[0031] Figure 1 Infrared spectra of CDs, CDs-NH2 and CDs-R provided by the present invention.

[0032] Figure 2 The TEM spectrum of Fe3O4 and Fe3O4@SiO2 provided by this invention.

[0033] Figure 3 The XRD patterns of Fe3O4 and Fe3O4@SiO2 provided by this invention.

[0034] Figure 4 The contact angles of CDs, CDs-NH2 and CDs-R provided by the present invention.

[0035] Figure 5 Macroscopic images of Pickering emulsions at different carbon dot emulsifier concentrations provided for this invention.

[0036] Figure 6 Metallographic micrographs of Pickering emulsions at different concentrations of carbon dot emulsifiers provided by this invention.

[0037] Figure 7 Macroscopic photographs of Pickering emulsions with different oil-water ratios provided for this invention.

[0038] Figure 8 Metallographic micrographs of Pickering emulsions with different oil-water ratios provided for this invention.

[0039] Figure 9 The Zeta potential spectrum of the CDs-R emulsifier provided by this invention.

[0040] Figure 10 The pH response performance of the Pickering emulsion provided by this invention. Specific implementation methods

[0041] This invention proposes a novel method for preparing a pH-responsive Pickering emulsifier. To make the advantages and technical solutions of this invention clearer and more explicit, the invention will be described in detail below with reference to specific embodiments.

[0042] All the raw materials required for this invention can be purchased through commercial channels.

[0043] Example 1:

[0044] Weigh 3.15 g of citric acid and place it in a round-bottom flask. Add 30 mL of deionized water and 1 mL of ethylenediamine to the flask sequentially, and stir ultrasonically for 1 h to ensure complete dissolution. Transfer the liquid to a hydrothermal reactor and perform a hydrothermal reaction at 200 °C for 5 h. After cooling, centrifuge to remove large, poorly soluble molecules to obtain crude carbon dots. Dialyze the crude carbon dots to deionized water for 24 h to remove impurities. Use a MW3500 dialysis bag. After dialysis, freeze-dry the product for 48 h to obtain CDs.

[0045] Example 2:

[0046] 0.1 g of CDs nanoparticles were placed in a round-bottom flask. 30 mL of anhydrous ethanol was added to the flask, and the mixture was stirred and sonicated to dissolve. 2 mL of ammonia was added to the flask to provide an alkaline environment, and the mixture was sonicated for 15 min. After 15 min, 200 μL of 3-aminopropyltriethoxysilane (APTES) was added to the flask and sonicated for 30 min. After sonication, the mixture was mechanically stirred for 12 h. After the reaction was complete, the CDs nanoparticles were collected by centrifugation and washed five times with anhydrous ethanol. The obtained nanoparticles were then dried in a vacuum drying oven. After drying, CDs-NH2 nanoparticles were synthesized.

[0047] Example 3:

[0048] 0.1 g of nanoparticles were mixed with 800 μL of cinnamaldehyde in 30 mL of methanol and reacted with stirring for 12 h. After the reaction was completed, the CDs-NH2 nanoparticles were collected by centrifugation and washed five times with anhydrous ethanol. The obtained nanoparticles were then dried in a vacuum drying oven. After drying, the CDs-R emulsifier could be synthesized.

[0049] Example 4:

[0050] Measure 7 ml of deionized water into small reagent bottles using a graduated cylinder. Weigh out 0.007 g, 0.014 g, 0.021 g, 0.028 g, and 0.035 g of CDs-R emulsifier respectively and add them to the reagent bottles. After ultrasonic dispersion, add 7 ml of paraffin oil (water:oil = 1:1) to each bottle. Emulsify using a vortex mixer at 4000 rpm for 6 minutes to obtain a stable Pickering emulsion. The nanoparticle concentration is expressed relative to the aqueous phase. When the emulsion is used at low concentrations, a stable emulsion cannot be formed. As the concentration increases, the carbon dot emulsifier can uniformly cover the surface of the emulsion to form an emulsion.

[0051] Example 5:

[0052] 0.021 g of CDs-R emulsifier was added to a glass vial, along with a series of oil-water two-phase mixtures in different ratios (oil to water ratios of 3:1, 2:1, 1:1, 1:2, and 1:3). The mixture was emulsified using a vortex mixer at 4000 rpm for 6 minutes to obtain a stable Pickering emulsion. As the oil-water ratio decreased, the droplet size of the Pickering emulsion gradually decreased, and its stability increased.

[0053] Example 6:

[0054] pH response performance verification of Pickering emulsion. 0.021 g of CDs-R emulsifier was added to 7 mL of deionized water and dispersed evenly by ultrasonication. The solution was then transferred to a 30 mL glass vial containing 7 mL of paraffin oil and emulsified using a vortex mixer at 4000 rpm for 6 min to obtain a stable Pickering emulsion. Next, an appropriate amount of NaOH solution (0.1 mol / L) was added to the emulsion to adjust the pH to 9. The mixture was then shaken by hand for 1 min or ultrasonicated. After standing, the emulsion droplet size increased until demulsification occurred. Then, HCl solution (0.1 mol / L) was added, and the pH was adjusted to acidic by hand for 1 min or ultrasonication. The emulsion re-formed. This emulsification and demulsification process was repeated three times, and a stable emulsion was still obtained. However, with the increase in the number of cycles, it became increasingly difficult for the emulsion to form after demulsification, but the time required for demulsification gradually decreased.

[0055] Parts not described in detail in this embodiment and English abbreviations are common knowledge in this industry and can be found online, so they will not be described here. All the chemical reagents mentioned are available on the market.

[0056] For any parts not mentioned in this invention, existing technologies can be used as a reference.

[0057] It should be noted that any equivalent substitutions made by those skilled in the art based on the teachings of this invention should be within the scope of protection of this invention.

Claims

1. A method for preparing a carbon dot-based pH-responsive Pickering emulsion, comprising the following steps: (I) Carbon dot nanoparticles of suitable size were synthesized by a solvothermal method. The specific preparation process is as follows: (1) Weigh 3.15g of citric acid and place it in a round-bottom flask. Add 1mL of ethylenediamine and 30mL of deionized water to the round-bottom flask and stir with ultrasound until completely dissolved. (2) The liquid is transferred to a reaction vessel for hydrothermal reaction. After the liquid is cooled, it is centrifuged to remove the macromolecular insoluble substances and obtain the crude carbon dot product. (3) The crude carbon dot product was dialyzed to remove impurities, and then placed in a freeze dryer for drying. (II) The preparation process for generating amino-modified carbon dots CDs-NH2 by hydrolysis is as follows: (1) Take 0.1g of carbon nanoparticles into a round-bottom flask, add anhydrous ethanol into the round-bottom flask, and sonicate for 20min to dissolve them; (2) Add 400 μL of ammonia water to the round-bottom flask to provide an alkaline environment for the experiment. After 15 min, add 1000 μL of 3-aminopropyltriethoxysilane under microwave shaking. After sonication for 30 min, stir at room temperature for 12 h. (3) Centrifuge to remove excess reactants and wash five times with anhydrous ethanol. Place the obtained nanoparticles in a vacuum drying oven for drying. (III) Hydrophobic group modification, the specific preparation process is as follows: (1) Weigh 0.1g of the amino-modified CDs-NH2 nanoparticles obtained in step three and mix them with 800μL of cinnamaldehyde in 30mL of methanol; (2) After reacting for 12 hours under mechanical stirring, the product CDs-R was collected by centrifugation, washed five times with anhydrous ethanol, and then dried in a vacuum oven. (iv) Preparation of Pickering Emulsion (1) The CDs-R nanoparticles obtained in step 3 are added to oil-water two-phase mixtures with ratios of 3:1, 2:1, 1:1, 1:2, and 1:3, respectively. The emulsifier concentration is 0.3%, calculated according to the concentration in the aqueous phase. The mixture is emulsified by a vortex mixer at a certain speed to obtain the final product.

2. The method for preparing a carbon dot-based pH-responsive Pickering emulsion according to claim 1, characterized in that: In steps (i) and (2), the reaction temperature is 200℃ and the reaction time is 5h.

3. The method for preparing a carbon dot-based pH-responsive Pickering emulsion according to claim 1, characterized in that: In steps (i) and (3), the dialysis bag specification is MW3500, and the dialysis time is 72h.

4. The method for preparing a carbon dot-based pH-responsive Pickering emulsion according to claim 1, characterized in that: In step (ii) (1), the volume of anhydrous ethanol added is 30 mL.

5. The method for preparing a carbon dot-based pH-responsive Pickering emulsion according to claim 1, characterized in that: In step (ii) and (3), the centrifugation speed is 10000 r / min, and the centrifugation is performed three times, with each centrifugation lasting 10 min.

6. The method for preparing a carbon dot-based pH-responsive Pickering emulsion according to claim 1, characterized in that: In step (iv) (1), the average particle size of CDs-R nanoparticles is 3-5 nm, and the concentration used is 0.1% to 0.5% based on the aqueous phase.

7. The method for preparing a carbon dot-based pH-responsive Pickering emulsion according to claim 1, characterized in that: In step (iv)(1), the vortex oscillator emulsifies for 6 minutes at a speed of 4000 rpm.

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