Preparation method of carbon dot-based pH response type Pickering emulsion

Abstract

The invention discloses a preparation method of a carbon dot-based pH response type Pickering emulsion, and belongs to the technical field of oil and gas field chemical agents. The preparation method comprises the following steps: firstly, preparing carbon dot (CDs) nano-particles by adopting a solvothermal method, modifying amino by utilizing hydrolysis reaction to carry out primary hydrophobic modification, finally modifying hydrophobic groups to form an amphiphilic Pickering emulsifier with pH responsiveness, adding the amphiphilic Pickering emulsifier into an oil phase and a water phase in a certain proportion, and emulsifying at a certain rotating speed by virtue of a vortex oscillator. The emulsion provided by the invention not only has good stability, but also can realize emulsification-demulsification in different pH environments when the emulsion does not need to keep a stable state any more, and can be recycled for more than three times. The method for preparing the Pickering emulsifier is green and environment-friendly, the preparation method is simple, and the Pickering emulsifier has the characteristics of excellent stability, pH responsiveness and the like, and has popularization and application values.

Description

Technical Field

[0001] The invention belongs to the technical field of oil and gas field chemicals, and in particular relates to a carbon-dot-stabilized pH-responsive Pickering emulsion and a preparation method thereof. Background Art

[0002] With the continuous development of my country's oil resources, how to design emulsifiers to stabilize emulsions to improve their recovery rate has attracted more and more attention. Demulsification of the stable emulsion in the later stage of exploitation to recover crude oil is also an important step worthy of attention. When traditional surfactants are used as emulsifiers, the stability of the emulsion will be greatly reduced due to the influence of reservoir temperature, pressure, salinity, etc., and it is difficult to achieve responsive demulsification. Pickering emulsions prepared with nanoparticles modified with responsive groups as emulsifiers have good stability and stimulus responsiveness, which can greatly improve the recovery rate of crude oil and solve the problem of difficult demulsification. As nanoparticles, carbon dots have excellent photoelectric properties, good water solubility, low toxicity, excellent biocompatibility and other special properties. They are widely used in environmental monitoring, photocatalysis, energy conversion devices, bioimaging, nanomedicine and other fields. To this end, this paper designed and synthesized a pH-responsive carbon dot emulsifier, used it to prepare emulsions and study the stability and responsiveness of the system. Summary of the invention

[0003] The purpose of the present invention is to provide a method for preparing a pH-responsive Pickering emulsion, which stabilizes the Pickering emulsion by preparing carbon dots and modifying a pH-responsive surfactant thereon, thereby providing a certain reference for chemical 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) Synthesize carbon dot nanoparticles of appropriate size by solvothermal method. The specific preparation process is as follows:

[0007] (1) Weigh 3.15 g 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 h to completely dissolve it.

[0008] (2) The liquid is transferred to a reactor for hydrothermal reaction. After the liquid is cooled, it is centrifuged to remove the macromolecular insoluble substances to obtain a crude carbon dot product.

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

[0010] (ii) Modify the surface of CDs with amino groups to obtain CDs-NH 2 .

[0011] (1) Take 0.1gCDs-NH 2 The nanoparticles were placed in a round-bottom flask, 80 mL of anhydrous ethanol was added to the round-bottom flask, and ultrasonic treatment was performed for 20 min.

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

[0013] (3) After the reaction, CDs-NH 2 The nanoparticles were washed three times with anhydrous ethanol, and then the CDs-NH 2 The nanoparticles were placed in a vacuum oven and dried for 12 h.

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

[0015] (1) Weigh the amino-modified CDs-NH obtained in step 3 2 The nanoparticles were mixed with cinnamaldehyde in methanol at a certain ratio.

[0016] (2) After the reaction is completed, the CDs-R nanoparticles are collected by centrifugation and washed three times with anhydrous ethanol. The CDs-R nanoparticles are then placed in a vacuum oven for 12 hours for drying.

[0017] (IV) Preparation of Pickering emulsion

[0018] (1) Add the CDs-R nanoparticles obtained in step 3 to a certain proportion of oil and water phases, and oscillate and emulsify them at a certain frequency using a vortex oscillator to obtain the product.

[0019] Furthermore, in step (a) (3), the dialysis bag specification is MW3500.

[0020] Furthermore, in step (a) (3), the freeze-drying time is 24 hours.

[0021] Furthermore, in step (a) (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 step (ii) (3), the centrifugal speed is 10000 r / min, and the centrifugation is performed three times, each time for 10 minutes.

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

[0025] Furthermore, in step (iv) (1), the ratios of the oil phase to the water phase are 3:1, 2:1, 1:1, 1:2, and 1:3, respectively, 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 the present invention are:

[0028] (1) The experimental conditions of the present 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 in Pickering emulsion.

[0030] (3) The pH stimulus response of the present invention for Pickering emulsion formation is sensitive, the response conditions are well controlled, and emulsification-demulsification is easy to achieve. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 CDs, CDs-NH provided by the present invention 2 And the infrared spectrum of CDs-R.

[0032] Figure 2 The Fe provided by the present invention 3 O 4 ,Fe 3 O 4 @SiO 2 TEM spectrum of .

[0033] Figure 3 The Fe provided by the present invention 3 O 4 ,Fe 3 O 4 @SiO 2 XRD spectrum of .

[0034] Figure 4 CDs and CDs-NH provided by the present invention 2 And the contact angle of CDs-R.

[0035] Figure 5 Macroscopic photographs of Pickering emulsions at different carbon dot emulsifier concentrations provided by the present invention.

[0036] Figure 6 These are metallographic micrographs of Pickering emulsions at different carbon dot emulsifier concentrations provided by the present invention.

[0037] Figure 7 Macroscopic photos of Pickering emulsions at different oil-water ratios provided by the present invention.

[0038] Figure 8 Metallographic micrographs of Pickering emulsions at different oil-water ratios provided by the present invention.

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

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

[0042] The present invention proposes a method for preparing a novel pH-responsive Pickering emulsifier. In order to make the advantages and technical solutions of the present invention clearer and more specific, the present invention is described in detail below in conjunction with specific embodiments.

[0043] The raw materials required for the present invention can be purchased through commercial channels.

[0044] Embodiment 1:

[0045] Weigh 3.15g of citric acid and place it in a round-bottom flask. Add 30mL of deionized water and 1mL of ethylenediamine to the round-bottom flask in turn, and stir ultrasonically for 1h to completely dissolve it. Transfer the liquid to a hydrothermal autoclave and autoclave it at 200℃ for 5h for hydrothermal reaction. After the liquid is cooled, centrifuge to remove large molecular insoluble substances to obtain crude carbon dots. The crude carbon dots are dialyzed in deionized water for 24h to remove impurities. The dialysis bag specification is MW3500. After the dialysis is completed, put it into a freeze dryer and dry it for 48h to obtain CDs.

[0046] Embodiment 2:

[0047] Take 0.1g CDs nanoparticles in a round-bottom flask. Add 30mL of anhydrous ethanol to the round-bottom flask, stir and sonicate to dissolve it. Add 2mL of ammonia water to the round-bottom flask to provide an alkaline environment and sonicate for 15 minutes. After 15 minutes, add 200μL of 3-aminopropyltriethoxysilane (APTES) to the round-bottom flask and sonicate for 30 minutes. After the sonication, mechanically stir for 12 hours. After the reaction is completed, centrifuge to collect CDs nanoparticles, wash them five times with anhydrous ethanol, and place the obtained nanoparticles in a vacuum drying oven to dry. After drying, CDs-NH 2 Nanoparticles.

[0048] Embodiment 3:

[0049] 0.1 g of nanoparticles were mixed with 800 μL of cinnamaldehyde in 30 mL of methanol and reacted for 12 h under stirring. After the reaction, CDs-NH 2 The nanoparticles are washed with anhydrous ethanol five times, and the obtained nanoparticles are placed in a vacuum drying oven for drying. After drying, the CDs-R emulsifier can be synthesized.

[0050] Embodiment 4:

[0051] 7 ml of deionized water was measured with a measuring cylinder and added to a small reagent bottle. 0.007 g, 0.014 g, 0.021 g, 0.028 g, and 0.035 g of CDs-R emulsifier were weighed and added to the reagent bottle. After ultrasonic dispersion, 7 ml of paraffin oil (water: oil = 1: 1) was added. The vortex oscillator was used to emulsify at 4000 rpm for 6 minutes to obtain a stable Pickering emulsion. The concentration of nanoparticles is expressed relative to the aqueous phase. When the emulsion is used at a lower concentration, a stable emulsion cannot be formed. As the concentration increases, the carbon dot emulsifier can evenly cover the surface of the emulsion to form an emulsion.

[0052] Embodiment 5:

[0053] 0.021g CDs-R emulsifier was added to a glass vial, and a series of different ratios of oil and water phases (the ratio of oil phase to water phase was 3:1, 2:1, 1:1, 1:2, 1:3) were added at the same time, and a vortex shaker was used to emulsify at 4000rpm for 6min to obtain a stable Pickering emulsion. As the oil-water ratio decreased, the droplet size of the Pickering emulsion gradually decreased and the stability increased.

[0054] Embodiment 6:

[0055] Verification of pH response performance of Pickering emulsion. 0.021g CDs-R emulsifier was added to 7mL deionized water and dispersed evenly by ultrasound. Then the above solution was transferred into a 30mL glass vial containing 7mL paraffin oil and emulsified at 4000rpm for 6min using a vortex oscillator to obtain a stable Pickering emulsion. Then, an appropriate amount of NaOH solution (0.1mol / L) was added to the emulsion to adjust the pH to 9, and then the solution was shaken by hand for 1min or ultrasound was applied. After standing, the droplet size of the emulsion increased until demulsification occurred. Then, HCl solution (0.1mol / L) was added, and the solution was shaken by hand for 1min or ultrasound was applied to adjust the pH to acidic. The emulsion was formed again. After repeating the emulsification and demulsification process 3 times in the same way, a stable emulsion could still be obtained. However, as the number of cycles increased, the emulsion became increasingly difficult to form after demulsification, but the time required for demulsification gradually shortened.

[0056] The parts and English abbreviations not described in detail in this embodiment are common knowledge in the industry and can be searched on the Internet, so they are not described here one by one.

[0057] The parts not described in the present invention can be realized by referring to the prior art.

[0058] It should be noted that all equivalent substitutions made by those skilled in the art under the guidance of the present invention should be within the protection scope of the present invention.

Claims

1. A method for preparing a carbon dot-based pH-responsive Pickering emulsion, comprising the following steps: (I) Synthesize carbon dot nanoparticles of appropriate size by solvothermal method. The specific preparation process is as follows: (1) Weigh 3.15 g of citric acid and place it in a round-bottom flask. Add 1 mL of ethylenediamine and 30 mL of deionized water into the round-bottom flask and stir by ultrasonic to completely dissolve them. (2) The liquid is transferred to a reactor for hydrothermal reaction. After the liquid is cooled, it is centrifuged to remove the macromolecular insoluble substances to obtain a crude carbon dot product. (3) The crude carbon dot product is dialyzed to remove impurities and then placed in a freeze dryer for drying. (ii) The amino-modified carbon dots (CDs-NH2) were generated by hydrolysis reaction. The preparation process is as follows: (1) Take 0.1 g of carbon dot nanoparticles and place them in a round-bottom flask. Add anhydrous ethanol to the round-bottom flask and sonicate for 20 min 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 minutes, add 1000 μL of 3-aminopropyltriethoxysilane (APTES) under microwave oscillation, sonicate for 30 minutes, and stir at room temperature for 12 hours. (3) The excess reactants were removed by centrifugation, and the nanoparticles were washed with anhydrous ethanol five times. The obtained nanoparticles were placed in a vacuum drying oven for drying. (III) Hydrophobic group modification, the specific preparation process is as follows: (1) Weigh 0.1 g of the amino-modified CDs-NH2 nanoparticles obtained in step 3 and mix them with 800 μL of cinnamaldehyde in 30 mL of methanol. (2) After reacting for 12 h 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) Add the CDs-R nanoparticles obtained in step 3 to a certain proportion of oil and water phases, and emulsify them by vortexing at a certain speed to obtain the product.

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

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

6. The method for preparing a carbon dot-based pH-responsive Pickering emulsion according to claim 1, characterized in that: In the step (iii) (1), the hydrophobic group of the modified carbon dots is cinnamaldehyde.

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

8. The method for preparing a carbon dot-based pH-responsive Pickering emulsion according to claim 1, characterized in that: In the step (iv) (1), the ratios of the oil and water phases in the Pickering emulsion are 3:1, 2:1, 1:1, 1:2, and 1:3, respectively, and the emulsifier concentration is 0.3%, calculated based on the concentration in the water phase.

9. The method for preparing a carbon dot-based pH-responsive Pickering emulsion according to claim 1, characterized in that: In the step (iv) (1), the emulsification is carried out at 4000 rpm on a vortex shaker for 6 minutes.

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