An amphiphilic carbon dot, a rapid dispersion ultra-stable foam system and a preparation method thereof

Abstract

This invention provides an amphiphilic carbon dot, a rapidly dispersible, ultra-stable foam system, and its preparation method, belonging to the field of oilfield chemistry. The preparation method of the amphiphilic carbon dot includes: dissolving cholic acid in a first solvent to obtain a hydrophobic precursor solution; dissolving chitosan oligomers in a second solvent to obtain a hydrophilic precursor solution; mixing the hydrophobic and hydrophilic precursor solutions in a closed reactor, allowing it to stand for 5-10 minutes, and then performing staged microwave treatment: 180-220W for 1-3 minutes, 450-550W for 2-5 minutes, and 80-120W for 4-8 minutes; cooling the reaction solution to room temperature, and then filtering, dialyzing, and freeze-drying to obtain the amphiphilic carbon dot. This invention, through the synergistic effect of amphiphilic carbon dots and surfactants, can achieve rapid dispersion to form uniform foam and maintain foam stability for a long time in high-salt environments, meeting the application requirements in high-salt scenarios.

Description

Technical Field

[0001] This invention relates to the field of oilfield chemical technology, specifically to an amphiphilic carbon dot, rapidly dispersible, ultra-stable foam system and its preparation method. Background Technology

[0002] Foam fluids exhibit advantages in sealing and oil displacement due to their unique gas-liquid two-phase structure. At the microscopic level, foam systems significantly improve crude oil mobilization efficiency in matrix micropores by reducing interfacial tension and generating the Jamin effect. At the macroscopic level, the selective sealing characteristics and adaptive mobility control capabilities of foam in fracture-cavity systems allow displacing fluids to effectively redirect to unaffected areas, with field applications showing an increase in oil recovery of 8–15 percentage points. However, the thermodynamic instability of foam systems leads to rapid decay within the formation, limiting the effectiveness of foam applications, especially in high-salinity environments where stability is even worse.

[0003] Currently, polymers or nanoparticles are commonly used foam stabilizers. Polymer foams (such as HPAM) exhibit good mobility control and economic efficiency in low-to-medium temperature (<90℃) and fractured reservoirs by increasing liquid phase viscosity and forming elastic interfacial films, but they face problems such as insufficient stability in high-temperature and high-salinity environments and shear degradation. Nanoparticle foams (such as SiO2 and Al2O3), with their Pickering stabilization mechanism, demonstrate superior interfacial film strength and long-term stability in extreme conditions and large-scale caverns, but are limited by high cost and challenges in nanoparticle dispersibility. Under extreme reservoir conditions (high salinity >20×10⁻⁶), 4 Conventional polymers are prone to molecular chain breakage and interfacial film failure, leading to a sharp decline in foam stability. Furthermore, precipitated insoluble substances can clog oil flow channels, causing reservoir damage. During dynamic displacement, formation shearing can disrupt the polymer molecular network structure, shortening the half-life of the precipitate by more than 50%. Existing polymer systems are costly, and compatibility issues with formation fluids often result in adsorption losses exceeding 30%. In addition, polymer dissolution is time-consuming and labor-intensive, requiring a swelling-dissolution process and dedicated mother liquor tanks on-site, increasing cost and process complexity. The large-scale application of nanoparticle-stabilized foam systems still faces challenges such as poor nanoparticle dispersion stability, high synthesis costs, and the risk of formation retention (potentially clogging <100nm pores). Worm-like micelle stabilized foam systems suffer from problems such as high cost and sluggish dynamic response. To form stable worm-like micelles, high concentrations of surfactants are required, with dosages 3-5 times higher than those used in conventional foam flooding. In addition, expensive amphoteric surfactants are often used, which increases costs. Furthermore, their shear thinning-recovery behavior is time-dependent, making it difficult to match transient downhole flow conditions, leading to uncontrolled plugging-migration balance.

[0004] Therefore, developing a foam system that is fast-dispersing, temperature and salt resistant, highly stable and low-cost has important practical significance and application value. Summary of the Invention

[0005] In view of the technical problems existing in the background art, the present invention provides an amphiphilic carbon dot, a rapidly dispersible ultra-stable foam system and its preparation method, aiming to solve the technical problems of slow dispersion speed and poor temperature and salt resistance of existing foam systems.

[0006] In a first aspect, the present invention provides a method for preparing amphiphilic carbon dots, comprising the following steps: S1. Dissolve cholic acid in a first solvent to obtain a hydrophobic precursor solution; dissolve chitosan oligomers in a second solvent to obtain a hydrophilic precursor solution. S2. Mix the hydrophobic precursor solution and the hydrophilic precursor solution in a closed reactor, let stand for 5-10 minutes, and then perform staged microwave treatment: 180-220W for 1-3 minutes, 450-550W for 2-5 minutes, and 80-120W for 4-8 minutes. S3. After the reaction is complete, the reaction solution is cooled to room temperature, filtered, dialyzed, and freeze-dried to obtain amphiphilic carbon dots.

[0007] Preferably, the ratio of cholic acid to the first solvent is (10~100) mg: 5 mL; the first solvent includes a mixture of cyclohexane and ethyl acetate.

[0008] Preferably, the ratio of chitosan oligomer to the second solvent is (50~200) mg: 5 mL; the second solvent includes an aqueous acetic acid solution; and the molecular weight of the chitosan oligomer is ≤5000.

[0009] Preferably, the mass ratio of cholic acid to chitosan oligomer is 1:(1~3).

[0010] In a second aspect, the present invention provides an amphiphilic carbon dot, which is prepared by the preparation method described in the first aspect.

[0011] Thirdly, the present invention provides a rapidly dispersible ultra-stable foam system, comprising, by mass percentage, 0.05%~0.5% of the amphiphilic carbon dots described in the second aspect, 0.1%~2% of surfactant, and the balance being high-mineral water.

[0012] Preferably, the surfactant includes at least one of sodium dodecylbenzenesulfonate, lauryl glucoside, and cocamidopropyl betaine.

[0013] Preferably, the mineralization of high-mineral water is 150,000~210,000 mg / L.

[0014] Fourthly, the present invention provides a method for preparing a rapidly dispersed ultra-stable foam system, comprising the following steps: S1. Mix the amphiphilic carbon dots with high-mineral water and disperse them evenly to obtain an amphiphilic carbon dot dispersion. S2. Add surfactant to the amphiphilic carbon dot dispersion and disperse evenly to obtain a foam system solution; S3. Stir the foam system solution to generate foam, and obtain a rapidly dispersed and ultra-stable foam system.

[0015] Preferably, the stirring speed for stirring and foaming is 2000~4000 rpm, and the stirring time for stirring and foaming is 2~3 minutes.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The fast-dispersing ultra-stable foam system provided by the present invention has fast dispersibility. The hydrophilic-hydrophobic structure of the amphiphilic carbon dots Am-CD can reduce the gas-liquid interfacial tension, and its nanoscale size can quickly migrate to the interface, synergistically accelerating foam formation with surfactants; the stable foam system prepared by the present invention disperses quickly and can be dispersed rapidly with only industrial-grade stirring.

[0017] (2) The rapid dispersion ultra-stable foam system provided by this invention has excellent salt resistance: the hydrophilic groups on the surface of the amphiphilic carbon dots Am-CD can form coordination with salt ions, inhibiting the damage of the surfactant double layer by salt ions; at the same time, the dense adsorption layer formed by Am-CD at the interface can enhance the mechanical strength of the foam film and reduce liquid film drainage and gas diffusion; the liquid half-life of the foam system of this invention can reach 150~200min, which is 4~6 times that of the traditional particulate stable foam system (liquid half-life 30~60min). After aging in 210000mg / L brine at 110℃ for 30 days, the half-life can still reach more than 150min.

[0018] (3) The preparation process of the rapid dispersion ultra-stable foam system provided by the present invention is simple and green. The raw materials are derived from natural cholic acid / chitosan, and the energy consumption of the microwave method is significantly reduced compared with the hydrothermal method; Am-CD is prepared by microwave-assisted two-phase interface method, which has short reaction time, low energy consumption, and does not use toxic solvents; the preparation process of the foam system does not require complex equipment and is easy to scale up industrially.

[0019] (4) The rapid dispersion and ultra-stable foam system provided by this invention has wide applicability. This invention can be adapted to different high-salt scenarios by adjusting the composition and concentration of the system, and is compatible with a variety of surfactants. The formulation can be flexibly adjusted according to actual needs. Attached Figure Description

[0020] Figure 1 This is a transmission electron microscope image of the amphiphilic carbon dots Am-CD obtained in Example 1 of the present invention; Figure 2 This is a particle size distribution diagram of the amphiphilic carbon dots Am-CD obtained in Example 1 of the present invention; Figure 3 This is a photograph showing the changes of the foam system prepared in Example 3 of the present invention over time after aging. Detailed Implementation

[0021] The embodiments of the technical solution of the present invention will now be described in detail with reference to the accompanying drawings. These embodiments are merely illustrative of the technical solution of the present invention and are therefore intended to limit the scope of protection of the present invention.

[0022] To address the technical problems of slow dispersion speed and poor temperature and salt resistance stability in existing foam systems, this invention provides an amphiphilic carbon dot, a rapidly dispersed, ultra-stable foam system, and its preparation method. Through the synergistic effect of highly dispersed, temperature and salt resistant amphiphilic carbon dots (Am-CD) and surfactants, it is possible to achieve rapid dispersion to form uniform foam and maintain foam stability for a long time in high-salt environments, thus meeting the application requirements in high-salt scenarios.

[0023] In a first aspect, embodiments of the present invention provide a method for preparing amphiphilic carbon dots, comprising the following steps: S1. Dissolve cholic acid in a first solvent to obtain a hydrophobic precursor solution; dissolve chitosan oligomers in a second solvent to obtain a hydrophilic precursor solution. S2. Mix the hydrophobic precursor solution and the hydrophilic precursor solution in a closed reactor, let stand for 5-10 minutes, and then perform staged microwave treatment: 180-220W for 1-3 minutes, 450-550W for 2-5 minutes, and 80-120W for 4-8 minutes. S3. After the reaction is complete, the reaction solution is cooled to room temperature, filtered, dialyzed, and freeze-dried to obtain amphiphilic carbon dots.

[0024] In the technical solution of this invention, a staged microwave power control strategy is employed to achieve controllable carbonization of bile acids and chitosan oligomers. The first stage, low-power microwave treatment, utilizes the local heating effect of microwaves to induce self-assembly of bile acids and chitosan oligomers at the interface, forming an ordered molecular layer. The second stage increases the microwave power, triggering cross-linking and carbonization reactions in the self-assembled molecular layer at the interface, forming a carbon dot core structure. The third stage involves annealing with reduced power to passivate the active sites on the carbon dot surface, reduce aggregation, and further optimize the distribution of hydrophilic and hydrophobic groups. The static pretreatment ensures sufficient stratification of the two phases to form a clear interface, allowing the carbonization reaction to preferentially occur in the oil-water interface region, which is beneficial for generating uniformly sized and structurally regular amphiphilic carbon dots. The carbon dots obtained by this invention possess both hydrophilic and hydrophobic properties and can spontaneously orient themselves at the gas-liquid interface, effectively reducing interfacial tension.

[0025] Furthermore, in some embodiments, the ratio of cholic acid to the first solvent is (10~100) mg: 5 mL; the first solvent includes a mixture of cyclohexane and ethyl acetate.

[0026] Furthermore, in some embodiments, the volume ratio of cyclohexane to ethyl acetate is 3:1.

[0027] Furthermore, in some embodiments, the molecular weight of the chitosan oligomer is ≤5000.

[0028] Furthermore, in some embodiments, the ratio of chitosan oligomer to the second solvent is (50~200) mg: 5 mL; the second solvent includes an aqueous solution of acetic acid.

[0029] Furthermore, in some embodiments, the mass ratio of cholic acid to chitosan oligomer is 1:(1~3).

[0030] Furthermore, in some embodiments, the mass ratio of cholic acid to chitosan oligomer is 1:2.

[0031] Furthermore, in some embodiments, the staged microwave processing specifically includes: 200W processing for 2 minutes, 500W processing for 3 minutes, and 100W processing for 5 minutes.

[0032] Furthermore, in some embodiments, the molecular weight cutoff for dialysis is 500-2000 Da, and the dialysis time is 12-32 h.

[0033] Secondly, embodiments of the present invention provide an amphiphilic carbon dot, which is prepared by the preparation method described in the first aspect.

[0034] Thirdly, embodiments of the present invention provide a rapidly dispersible ultra-stable foam system, comprising, by mass percentage, 0.05%~0.5% of the amphiphilic carbon dots described in the second aspect, 0.1%~2% of surfactant, and the balance being high-mineral water.

[0035] In the technical solution of this invention embodiment, rapid dispersion and ultra-stable foam construction are achieved through the synergistic effect mechanism of amphiphilic carbon dots Am-CD and surfactants. The hydrophilic-hydrophobic structure of Am-CD can reduce the gas-liquid interfacial tension, and its nanoscale size can rapidly migrate to the interface, synergistically accelerating foam formation with surfactants; the hydrophilic groups on the surface of Am-CD can form coordination with salt ions, inhibiting the damage of salt ions to the electric double layer of surfactants; at the same time, the dense adsorption layer formed by Am-CD at the interface can enhance the mechanical strength of the foam film and reduce liquid film drainage and gas diffusion.

[0036] Furthermore, in some embodiments, the surfactant includes at least one of sodium dodecylbenzenesulfonate (SDBS), lauryl glucoside (APG), and cocamidopropyl betaine (CAB-35).

[0037] Furthermore, in some embodiments, the surfactant is lauryl glucoside (APG).

[0038] In the technical solution of this invention embodiment, extensive experiments have shown that when the surfactant is lauryl glucoside (APG), the synergistic effect with the amphiphilic carbon dot Am-CD is better.

[0039] Furthermore, in some embodiments, the mineralization of the high-mineral water is 150,000 to 210,000 mg / L.

[0040] Fourthly, embodiments of the present invention provide a method for preparing a rapidly dispersed ultra-stable foam system, comprising the following steps: S1. Mix the amphiphilic carbon dots with high-mineral water and disperse them evenly to obtain an amphiphilic carbon dot dispersion. S2. Add surfactant to the amphiphilic carbon dot dispersion and disperse evenly to obtain a foam system solution; S3. Stir the foam system solution to generate foam, and obtain a rapidly dispersed and ultra-stable foam system.

[0041] Furthermore, in some embodiments, the stirring speed for stirring and foaming is 2000~4000 rpm, and the stirring time for stirring and foaming is 2~3 min.

[0042] In the technical solution of this invention embodiment, amphiphilic carbon dots Am-CD are first dispersed in high-salt water to form a stable dispersion. Instant dispersion is achieved by utilizing the rapid affinity between the hydrophilic groups on the carbon dot surface and the aqueous phase, avoiding the problem of traditional nanomaterials requiring prolonged ultrasonication or high-speed shearing. Subsequently, a surfactant is added, and the surfactant molecules pre-assemble with Am-CD in the solution through hydrophobic interactions and hydrogen bonding, forming aggregate structures conducive to rapid foaming. Finally, gas is introduced through mechanical stirring to form a foam system with a high-strength interfacial film. This foam system, with its rapid dispersion characteristics, can be prepared on-site immediately, significantly simplifying the operation process; its ultra-stable properties ensure long-term effectiveness in underground high-temperature and high-salt environments; compared to traditional polymer foams, its injection performance is more stable; and compared to nanoparticle foams, this system disperses rapidly, reduces the risk of clogging, and is safer.

[0043] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0044] In the following embodiments of the present invention, the mineralization of the high-mineral water is 210,000 mg / L.

[0045] Example 1 The specific steps for preparing amphiphilic carbon dots (Am-CD) are as follows: (1) Preparation of precursor solution: Dissolve 50 mg of cholic acid in 5 mL of cyclohexane / ethyl acetate (3:1) and sonicate for 8 min until dissolved to obtain a clear hydrophobic phase solution; dissolve 100 mg of chitosan oligomer (molecular weight ≤5000) in 5 mL of 0.1 M acetic acid aqueous solution and stir for 18 min until the chitosan oligomer is completely dissolved to obtain a transparent hydrophilic phase solution.

[0046] (2) Construction of the two-phase system: The above hydrophobic phase solution and hydrophilic phase solution were added to a 25 mL polytetrafluoroethylene reaction vessel in sequence and allowed to stand for 8 min to form a clear liquid-liquid two-phase interface.

[0047] (3) Microwave reaction: After sealing the polytetrafluoroethylene reaction vessel, place it in a microwave reactor and process it according to the following three-stage procedure: ① First stage: Power 200W, time 2min. Utilizing the local heating effect of microwaves, bile acids and chitosan oligomers are self-assembled at the interface between the two phases to form an ordered molecular layer. ② Second stage: Power 500W, time 3min, increase microwave power to trigger cross-linking and carbonization reactions of interface self-assembly molecular layers to form carbon dot core structure; ③ Third stage: Power 100W, time 5min, reduce power for annealing treatment, passivate the active sites on the carbon dot surface, reduce agglomeration, and further optimize the distribution of hydrophilic-hydrophobic groups.

[0048] (4) Product purification: ①Collection by layer: After the microwave reaction is completed, the reaction solution is cooled to room temperature and naturally separated into layers (the upper layer is the organic phase and the lower layer is the aqueous phase containing Am-CD). The upper organic phase is removed by pouring and the lower aqueous phase is collected. ② Filtration: The collected aqueous phase is filtered through a 0.22μm nylon membrane to remove unreacted solid impurities; ③ Dialysis: Transfer the filtered solution to a dialysis bag with a molecular weight cutoff of 1000 Da, use deionized water as the dialysate, and dialyze at room temperature for 24 hours. Change the dialysate every 6 hours during the process to remove small molecule impurities. ④ Freeze-drying: The dialyzed solution was placed in a freeze dryer and freeze-dried at -50℃ and 0.1Pa for 24 hours to obtain yellow solid amphiphilic carbon dots Am-CD.

[0049] The transmission electron microscope (TEM) image of the amphiphilic carbon dot Am-CD prepared in this embodiment is shown below. Figure 1 As shown, Figure 2 The particle size distribution of the amphiphilic carbon dots Am-CD is shown, with a particle size of approximately 2.0 ± 0.8 nm.

[0050] The contact angle of the amphiphilic carbon dots Am-CD prepared in this embodiment was measured to be 15° in the aqueous phase and 110° in the oil phase, confirming its amphiphilicity.

[0051] The fluorescence quantum yield of this embodiment was found to be 62%.

[0052] Example 2 A method for preparing a rapidly dispersible ultrastable foam system, comprising the following specific steps: (1) Add 0.2g Am-CD to 99.3g of high mineral water and stir magnetically at 500rpm for 4min to obtain Am-CD dispersion; (2) Add 0.5g lauryl glucoside (APG) to the Am-CD dispersion and stir magnetically at 500rpm for 12min to form a uniform and transparent foam system solution; (3) Place the foam system solution in the Wu Yin mixer and stir at 3000 rpm for 3 min to obtain a uniform foam system.

[0053] Example 3 A method for preparing a rapidly dispersible ultrastable foam system, comprising the following specific steps: (1) Add 0.2g Am-CD to 98.8g of high mineral water and stir magnetically at 500rpm for 4min to obtain Am-CD dispersion; (2) Add 1.0 g lauryl glucoside (APG) to the Am-CD dispersion and stir magnetically at 500 rpm for 12 min to form a uniform and transparent foam system solution; (3) Place the foam system solution in the Wu Yin mixer and stir at 3000 rpm for 3 min to obtain a uniform foam system.

[0054] Example 4 A method for preparing a rapidly dispersible ultrastable foam system, comprising the following specific steps: (1) Add 0.2g Am-CD to 98.3g of high mineral water and stir magnetically at 500rpm for 4min to obtain Am-CD dispersion; (2) Add 1.5g lauryl glucoside (APG) to the Am-CD dispersion and stir magnetically at 500rpm for 12min to form a uniform and transparent foam system solution; (3) Place the foam system solution in the Wu Yin mixer and stir at 3000 rpm for 3 min to obtain a uniform foam system.

[0055] Example 5 A method for preparing a rapidly dispersible ultrastable foam system, comprising the following specific steps: (1) Add 0.2g Am-CD to 97.8g of high mineral water and stir magnetically at 500rpm for 4min to obtain Am-CD dispersion; (2) Add 2.0 g lauryl glucoside (APG) to the Am-CD dispersion and stir magnetically at 500 rpm for 12 min to form a uniform and transparent foam system solution; (3) Place the foam system solution in the Wu Yin mixer and stir at 3000 rpm for 3 min to obtain a uniform foam system.

[0056] Example 6 A method for preparing a rapidly dispersible ultrastable foam system, comprising the following specific steps: (1) Add 0.1g Am-CD to 98.9g of high mineral water and stir magnetically at 500rpm for 4min to obtain Am-CD dispersion; (2) Add 1.0 g lauryl glucoside (APG) to the Am-CD dispersion and stir magnetically at 500 rpm for 12 min to form a uniform and transparent foam system solution; (3) Place the foam system solution in the Wu Yin mixer and stir at 3000 rpm for 3 min to obtain a uniform foam system.

[0057] Example 7 A method for preparing a rapidly dispersible ultrastable foam system, comprising the following specific steps: (1) Add 0.3g Am-CD to 98.7g of high mineral water and stir magnetically at 500rpm for 4min to obtain Am-CD dispersion; (2) Add 1.0 g lauryl glucoside (APG) to the Am-CD dispersion and stir magnetically at 500 rpm for 12 min to form a uniform and transparent foam system solution; (3) Place the foam system solution in the Wu Yin mixer and stir at 3000 rpm for 3 min to obtain a uniform foam system.

[0058] Example 8 A method for preparing a rapidly dispersible ultrastable foam system, comprising the following specific steps: (1) Add 0.4g Am-CD to 98.6g of high mineral water and stir magnetically at 500rpm for 4min to obtain Am-CD dispersion; (2) Add 1.0 g lauryl glucoside (APG) to the Am-CD dispersion and stir magnetically at 500 rpm for 12 min to form a uniform and transparent foam system solution; (3) Place the foam system solution in the Wu Yin mixer and stir at 3000 rpm for 3 min to obtain a uniform foam system.

[0059] Example 9 A method for preparing a rapidly dispersible ultrastable foam system, comprising the following specific steps: (1) Add 0.2g Am-CD to 98.8g of high mineral water and stir magnetically at 500rpm for 4min to obtain Am-CD dispersion; (2) Add 1.0 g sodium dodecylbenzenesulfonate (SDBS) to the Am-CD dispersion and stir magnetically at 500 rpm for 12 min to form a uniform and transparent foam system solution; (3) Place the foam system solution in the Wu Yin mixer and stir at 3000 rpm for 3 min to obtain a uniform foam system.

[0060] Example 10 A method for preparing a rapidly dispersible ultrastable foam system, comprising the following specific steps: (1) Add 0.2g Am-CD to 98.8g of high mineral water and stir magnetically at 500rpm for 4min to obtain Am-CD dispersion; (2) Add 1.0 g cocamidopropyl betaine (CAB-35) to the Am-CD dispersion and stir magnetically at 500 rpm for 12 min to form a uniform and transparent foam system solution; (3) Place the foam system solution in the Wu Yin mixer and stir at 3000 rpm for 3 min to obtain a uniform foam system.

[0061] Comparative Example 1 The difference between this comparative example and Example 1 is that the carbon source is different. In step (1), cholic acid is replaced with stearic acid. Other conditions are the same as in Example 1. The resulting amphiphilic carbon dots are denoted as CDs-1.

[0062] Testing revealed that the amphiphilic carbon dots CDs-1 prepared in this comparative example had a particle size >2μm, indicating severe carbon dot aggregation.

[0063] Comparative Example 2 The difference between this comparative example and Example 1 is that in step (3), a constant power of 500W microwave is used for 10 minutes, while other conditions are the same as in Example 1.

[0064] Experimental results show that the product cannot be separated into layers, and the quantum yield drops to 28%.

[0065] Comparative Example 3 The difference between this comparative example and Example 2 is that the amphiphilic carbon dot Am-CD was not added. The remaining steps are the same as in Example 2, and the specific steps are as follows: Add 0.5g lauryl glucoside (APG) to 99.5g of high-quality mineral water and stir magnetically at 500rpm for 12min to form a homogeneous and transparent foam system solution; place the foam system solution in a Wu Yin mixer and stir at 3000rpm for 3min to obtain a uniform foam system.

[0066] Comparative Example 4 The difference between this comparative example and comparative example 3 is that 1.0g of lauryl glucoside (APG) was added to 99g of high-mineral water, while the rest was the same as comparative example 3.

[0067] Comparative Example 5 The difference between this comparative example and comparative example 3 is that 1.5g of lauryl glucoside (APG) was added to 98.5g of high-mineral water, while the rest was the same as comparative example 3.

[0068] Comparative Example 6 The difference between this comparative example and comparative example 3 is that 2.0g of lauryl glucoside (APG) was added to 98g of high-mineral water, while the rest was the same as comparative example 3.

[0069] Comparative Example 7 The difference between this comparative example and Example 3 is that lauryl glucoside (APG) was not added. The remaining steps are the same as in Example 3, as detailed below: Add 0.2g Am-CD to 99.8g of high-quality mineral water and stir magnetically at 500rpm for 4min to obtain a homogeneous and transparent foam system solution; place the foam system solution in a Wu Yin mixer and stir at 3000rpm for 3min to obtain a uniform foam system.

[0070] Comparative Example 8 The difference between this comparative example and Example 3 is that the amphiphilic carbon dots Am-CD are replaced with nano-silica, while the other steps are the same as in Example 3.

[0071] Comparative Example 9 The difference between this comparative example and Example 9 is that the amphiphilic carbon dot Am-CD was not added. The remaining steps are the same as in Example 9, and the specific steps are as follows: Add 1.0g sodium dodecylbenzenesulfonate (SDBS) to 99g of high-quality mineral water and stir magnetically at 500rpm for 12min to form a homogeneous and transparent foam system solution; place the foam system solution in a Wu Yin mixer and stir at 3000rpm for 3min to obtain a uniform foam system.

[0072] Comparative Example 10 The difference between this comparative example and Example 10 is that the amphiphilic carbon dot Am-CD was not added. The remaining steps are the same as in Example 2, and the specific steps are as follows: Add 1.0g of cocamidopropyl betaine (CAB-35) to 99g of high-quality mineral water and stir magnetically at 500rpm for 12min to form a homogeneous and transparent foam system solution; place the foam system solution in a Wu Yin mixer and stir at 3000rpm for 3min to obtain a uniform foam system.

[0073] Comparative Example 11 The difference between this comparative example and Example 3 is that the amphiphilic carbon dots Am-CD are replaced with the amphiphilic carbon dots prepared in Comparative Example 1, while the remaining steps are the same as in Example 3.

[0074] Performance testing 1. Performance evaluation of the foam system The dispersion time and liquid half-life of the foam systems obtained in Examples 2 to 10 and Comparative Examples 3 to 11 are shown in Table 1 below.

[0075] Table 1

[0076] The data in Table 1 show that the foam systems of the single-agent surfactants prepared in Comparative Examples 3-6 and 9-10 have extremely short liquid half-lives and poor stability.

[0077] The foam system prepared by single agent Am-CD in Comparative Example 7 has an extremely short liquid half-life and poor stability. The foam system prepared in the embodiments of the present invention exhibits a significant synergistic effect after being compounded with Am-CD and surfactants.

[0078] The data from Comparative Example 8 and Example 3 show that the amphiphilic carbon dots Am-CD prepared in this invention, compared with nano-silica, have a longer liquid separation half-life and a shorter dispersion time when combined with surfactants to form a foam system with superior performance.

[0079] The carbon dots used in Comparative Example 11 were prepared in Comparative Example 1, and their dispersion time was much longer than that in Example 3, indicating that the choice of carbon source has a crucial impact on dispersion performance. Am-CD prepared using cholic acid as a carbon source exhibits superior interfacial activity and dispersion ability. The core reason for choosing cholic acid over stearic acid in this invention lies in the difference in molecular structure. Stearic acid, as a flexible long-chain "head-to-tail" amphiphilic molecule, is prone to entanglement and aggregation due to hydrophobic interactions during microwave carbonization. In contrast, cholic acid has a rigid polycyclic steroidal framework, providing significant steric hindrance, effectively inhibiting aggregation during carbonization, thereby generating uniform nano-carbon dots. Furthermore, the unique "surface amphiphilicity" of cholic acid is retained after nucleation, allowing it to rapidly migrate to the gas-liquid interface and oriented, forming a dense composite film with the surfactant, thus significantly shortening the dispersion time and greatly improving foam stability.

[0080] 2. Evaluation of the temperature and salt resistance of the foam system Take the foam system solution prepared in Example 3, put the solution into an aging vessel and age it at 110°C for 30 days; take out the solution and put it into a high-speed stirrer and stir at 3000 rpm for 3 minutes to form a uniform foam system, and record its liquid half-life.

[0081] Physical images showing how the foam system changes over time are shown below. Figure 3 As shown, the half-life of the foam system can still reach 152 min, indicating that it has excellent temperature and salt resistance.

[0082] It should be noted that the present invention is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments that have the same structure and perform the same effects as the technical concept within the scope of the present invention are included within the scope of the present invention. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of the present invention, are also included within the scope of the present invention.

Claims

1. A method for preparing amphiphilic carbon dots, characterized in that, Includes the following steps: S1. Dissolve cholic acid in a first solvent to obtain a hydrophobic precursor solution; dissolve chitosan oligomers in a second solvent to obtain a hydrophilic precursor solution. S2. Mix the hydrophobic precursor solution and the hydrophilic precursor solution in a closed reactor, let stand for 5-10 minutes, and then perform staged microwave treatment: 180-220W for 1-3 minutes, 450-550W for 2-5 minutes, and 80-120W for 4-8 minutes. S3. After the reaction is complete, the reaction solution is cooled to room temperature, filtered, dialyzed, and freeze-dried to obtain amphiphilic carbon dots.

2. The method for preparing amphiphilic carbon dots according to claim 1, characterized in that, The ratio of cholic acid to the first solvent is (10~100) mg: 5 mL; And / or, the first solvent comprises a mixture of cyclohexane and ethyl acetate.

3. The method for preparing amphiphilic carbon dots according to claim 1, characterized in that, The ratio of chitosan oligomer to the second solvent is (50~200) mg: 5 mL; And / or, the second solvent comprises an aqueous solution of acetic acid; And / or, the molecular weight of the chitosan oligomer is ≤5000.

4. The method for preparing amphiphilic carbon dots according to claim 1, characterized in that, The mass ratio of the cholic acid to the chitosan oligomer is 1:(1~3).

5. An amphiphilic carbon dot, characterized in that, It is prepared by the method for preparing amphiphilic carbon dots according to any one of claims 1 to 4.

6. A rapidly dispersible, ultra-stable foam system, characterized in that, By mass percentage, it includes 0.05% to 0.5% of the amphiphilic carbon dots as described in claim 5, 0.1% to 2% of surfactant, and the balance being high mineral water.

7. The rapidly dispersible ultra-stable foam system according to claim 6, characterized in that, The surfactant includes at least one of sodium dodecylbenzenesulfonate, lauryl glucoside, and cocamidopropyl betaine.

8. The rapidly dispersible ultra-stable foam system according to claim 6, characterized in that, The mineralization of the high-mineral water is 150,000~210,000 mg / L.

9. The method for preparing the rapidly dispersed ultra-stable foam system according to any one of claims 6 to 8, characterized in that, Includes the following steps: S1. Mix the amphiphilic carbon dots with high-mineral water and disperse them evenly to obtain an amphiphilic carbon dot dispersion. S2. Add a surfactant to the amphiphilic carbon dot dispersion and disperse it evenly to obtain a foam system solution; S3. Stir the foam system solution to generate foam, thereby obtaining the rapidly dispersible ultra-stable foam system.

10. The method for preparing a rapidly dispersible ultra-stable foam system according to claim 9, characterized in that, The stirring speed for foaming is 2000~4000 rpm, and the stirring time for foaming is 2~3 min.

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