Green synthesis method and application of carbon dot cationic surfactant

Abstract

The application discloses a kind of green synthesis method and application of carbon dot cationic surfactant, it is related to functional nanomaterial preparation technical field, to make synthesis method more economical, green, simultaneously make product possess multiple functionality;The application includes with amino acid and citric acid as carbon source, with water as solvent, preparation fluorescent carbon quantum dots;According to fluorescent carbon quantum dots and long carbon chain primary amine mass ratio 1:0.1~1:1, amide reaction is carried out under the condition of stirring heating reflux in water, long carbon chain is introduced on the surface of carbon dot;The product is dried, and carbon dot cationic surfactant with surface activity and bacteriostasis is obtained;The synthesis method of the application is simple, raw material is renewable resource, is relatively cheap, does not need organic solvent in synthesis process, and there is no harmful product, green and environmental protection;The product prepared can significantly reduce water interfacial tension, also has bacteriostatic efficacy, simultaneously has fluorescence function.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of functional nanomaterial preparation, in particular to a green synthesis method of carbon dot cationic surfactant and application thereof. BACKGROUND

[0002] Carbon dots are a kind of nanomaterials with particle size less than 10 nm. They can be obtained from organic small molecules through hydrothermal, solvothermal or high-temperature pyrolysis. This kind of material has stable structure, contains a large number of hydrophilic groups on its surface, and also has certain chemical reactivity. It can be appropriately chemically modified to have certain specific functions.

[0003] Surfactants are an essential part of people's daily life. Surfactants can significantly change the interfacial state of the solution, can significantly reduce the surface tension of water, and also have emulsifying and foaming properties; among them, cationic surfactants also have certain antibacterial, antistatic and other properties. Traditional cationic surfactants mostly contain a specific quaternary ammonium structure (as a hydrophilic group). The synthesis of this specific quaternary ammonium structure requires the use of traditional organic synthesis methods, and a large amount of organic solvent may be used in the synthesis process, which may harm the environment. For example, the introduction of a long carbon chain into a tertiary amine structure (mostly using a halogenated hydrocarbon containing a long carbon chain as a quaternary ammonium reagent) requires a reaction in an organic solvent, which may harm the environment. In addition, a large amount of organic solvent is also required for the synthesis of tertiary amines.

[0004] Wang Liyan et al. synthesized an intermediate using substituted benzoyl chloride, long-chain primary amine (carbon number 12, 14 or 16), chloroacetyl chloride and N,N-dimethylethanolamine as raw materials, and dichloromethane as solvent, and then synthesized a series of quaternary ammonium salt cationic surfactants containing ester and amide groups using acetonitrile as solvent. The surface tension of the product with carbon number 16 was 41.44 mN / m, and the critical micelle concentration value reached 4.30 x 10 -5 mol / L; (Wang Liyan, Cheng Dayang, Duan Songyan, et al. Synthesis of quaternary ammonium salt cationic surfactants containing ester and amide groups. Chemical Research and Application [J], 2020, 32(12): 2182-2191).

[0005] Sun Yuhai et al. synthesized a series of new polymeric cationic surfactants using triethylenetetramine, epichlorohydrin, long-chain dimethyl tertiary amine (carbon number 12, 14 or 16) as raw materials, and anhydrous ethanol as solvent. The minimum surface tension reached 27.6 mN / m; (Sun Yuhai, Li Ximing, Wang Juan, et al. Preparation and properties of polymeric cationic surfactants. Fine Petroleum Chemical Industry [J], 2014, 31(5): 35-38).

[0006] Patent 202210976495.6 uses C1~C 18Alkyl tertiary amine, acid (HCl, HBr or HI), quaternary ammonium reagent (epichlorohydrin) as raw material, ethanol / ethyl acetate as solvent, quaternary ammonium reaction to obtain intermediate, then quaternary ammonium reaction with 4-methyl-1, 6 hexanediamine to prepare poly quaternary ammonium head group cationic oligomeric surfactant. The product has four quaternary ammonium head groups and two hydroxyl groups, and the minimum surface tension reaches 33.08 mN / m.

[0007] Patent 202110575948.X uses amino pyridine, alkyl acid chloride (carbon number is 1-20), halogenated alkane (carbon number is 1-20) as raw material, dichloromethane, acetone, acetonitrile and the like as solvent to prepare quaternary ammonium salt type cationic surfactant, and the minimum surface tension reaches 21.67 mN / m.

[0008] Patent 201910932428.2 uses N,N'-bis(3-dimethylaminopropyl)urea as raw material, bromotetradecane as quaternary ammonium reagent, and ethanol, acetone or acetonitrile as solvent to prepare carbamide-based gemini cationic surfactant, and the minimum surface tension reaches 37.54 mN / m. It can be used as a modifier of montmorillonite.

[0009] Patent 201710992717.2 reports a synthesis method of carbon dot quaternary ammonium salt cationic surfactant. Citric acid is used as carbon source, and diamino compound with primary amino group at one end and tertiary amino group at the other end is used as N source. Nitrogen-doped carbon dots are synthesized by hydrothermal method, which are used as raw material to react with normal halogenated hydrocarbon in ethanol aqueous solution to prepare carbon dot cationic surfactant, and the minimum surface tension reaches 32 mN / m.

[0010] In summary, at present, the preparation method of cationic surfactant is mainly traditional method. In these methods, organic solvent is needed as reaction medium, and some processes are relatively complex, the cost of raw materials is high, and some reactants are very unstable and easy to cause environmental harm. We have prepared cationic surfactant with carbon dots containing tertiary amine groups as raw material (patent 201710992717.2), but finally chlorinated hydrocarbon needs to be quaternized with carbon dots. Since chlorinated hydrocarbon has no water solubility, quaternization process must be carried out in organic solvent (ethanol); the surface of the synthesized carbon dots must contain tertiary amine groups, which react with long-chain chlorinated hydrocarbon to obtain carbon dot cationic surfactant. SUMMARY

[0011] The purpose of the present application is to provide a green synthesis method and application of carbon dot cationic surfactant, which has a more economical and green synthesis method, and the product has multiple functions.

[0012] To achieve the above purpose, the present application provides the following technical scheme: a green synthesis method of carbon dot cationic surfactant, comprising the following specific steps:

[0013] (1) taking amino acid and citric acid as carbon source, and water as solvent, fluorescent carbon quantum dots are prepared;

[0014] (2) under the condition of stirring and heating reflux in water, amide reaction is carried out according to the mass ratio of fluorescent carbon quantum dots to long carbon chain primary amine of 1:0.1-1:1, and long carbon chain is introduced on the surface of carbon dots;

[0015] (3) the product of step (2) is dried to obtain carbon dot cationic surfactant with surface activity and bacteriostasis.

[0016] Preferably, the amino acid is selected from any one or several of glycine, alpha-alanine, beta-alanine, L-arginine, D-arginine, L-histidine and D-histidine.

[0017] Preferably, the long carbon chain primary amine is a primary amine containing 8-14 carbon atoms, including n-octylamine, n-decylamine, n-dodecylamine and n-tetradecylamine, or isomers of these primary amines, or a combination of any of them.

[0018] Preferably, in the above step (1), the process of preparing fluorescent carbon quantum dots comprises: weighing a certain amount of amino acid, mixing with citric acid at a mass ratio of 1:0.5-1:5, dissolving the mixture in water, heating at 170-200 ℃ for 10-50 minutes, and reacting until the water is completely volatilized or being placed in a 60 ℃ oven for drying, and cooling to room temperature.

[0019] Preferably, in the above step (2), the process of amide reaction comprises: first dissolving the product of step (1) in water, heating to 60-90 ℃ and keeping the temperature, gradually adding long carbon chain primary amine under stirring condition, and continuing reflux for 1-5 hours until the reaction is completed, and at the end of the reaction, there is no excess oil on the surface of the solution.

[0020] Preferably, in the above step (3), the drying temperature is 60 ℃.

[0021] The present application provides another technical scheme: a carbon dot cationic surfactant prepared by the above green synthesis method.

[0022] The present application provides still another technical scheme: application of the above carbon dot cationic surfactant in reducing water surface tension, which can reduce the interfacial tension of water to below 30 mN / m at 298.15 K and critical micelle concentration.

[0023] The present application provides still another technical scheme: application of the above carbon dot cationic surfactant in inhibiting bacterial growth, which has a minimum inhibitory concentration of not more than 0.1 mg / ml for both escherichia coli and staphylococcus aureus.

[0024] The application further provides another technical scheme: application of the carbon dot cationic surfactant in a surfactant or bacteriostatic agent with fluorescence or fluorescent whitening function.

[0025] Compared with the prior art, the application has the following beneficial effects:

[0026] 1. The green synthesis method of the carbon dot cationic surfactant, first, carbon dots are prepared by pyrolysis of a water solution of raw materials, then, the carbon dots are used as raw materials, the long carbon chain is covalently connected to the carbon dots by an amide reaction between the carbon dots and the long carbon chain primary amine in an aqueous solution, the long carbon chain is introduced to the surface of the carbon dots, and the cationic surfactant with surface activity, bacteriostasis and fluorescent whitening is prepared, the synthesis process is simple and efficient, and the synthesis process route is completely different from that of the traditional cationic surfactant; compared with the traditional cationic surfactant, the raw materials used in the application are renewable resources and are relatively inexpensive.

[0027] 2. The green synthesis method of the carbon dot cationic surfactant, water is used as a solvent in the reaction process, no organic solvent is needed, and no harmful substances are generated, so the method is green and environmentally friendly.

[0028] 3. The carbon dot cationic surfactant obtained by the green synthesis method can significantly reduce the water interfacial tension, has bacteriostasis, has fluorescence, can play a fluorescent whitening role, can be widely applied to the fields of detergent manufacturing, metal corrosion inhibitor manufacturing, bactericide compounding manufacturing, bacteriostatic agent configuration, fluorescent whitening agent compounding and the like, and can also be used as a surfactant alone, especially in a scenario requiring the above-mentioned several uses, and has certain product competitiveness. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 is a reaction process schematic diagram of an embodiment of the application;

[0030] Figure 2 is a transmission electron microscope graph of the carbon dots and the carbon dot surfactant in Example 1, wherein Fig. (a) is the morphology of the carbon dots; Fig. (b) is the particle size distribution of the carbon dots, Fig. (c) is the morphology of the carbon dot surfactant, and Fig. (d) is the particle size distribution of the carbon dot surfactant;

[0031] Figure 3 is an infrared spectrum graph of the carbon dots and the carbon dot cationic surfactant in Example 1;

[0032] Figure 4 are X-ray photoelectron spectrograms of the carbon dots before and after the amide reaction in Example 1, Fig. (a) and (b) correspond to the C1s and N1s spectrograms of the carbon dots, respectively, and Fig. (c) and (d) correspond to the C1s and N1s spectrograms of the carbon dot surfactant, respectively.

[0033] Figure 5 is a plot of carbon dot cationic surfactant reducing water surface tension versus solution concentration in Example 2;

[0034] Figure 6 are photos of contact angle from left to right corresponding to pure water and carbon dot cationic surfactant concentration of 0.2, 1.0, 2.0, 5.0 and 10.0 mg / mL respectively prepared in Example 2;

[0035] Figure 7 is a plot of carbon dot cationic surfactant reducing water surface tension versus solution concentration in Example 3;

[0036] Figure 8 is a comparison of carbon dot cationic surfactant foamability and foam stability with dodecyltrimethylammonium chloride and sodium dodecylbenzenesulfonate in Example 6;

[0037] Figure 9 is a plot of Zeta potential of carbon dot and carbon dot cationic surfactant in Example 1;

[0038] Figure 10 is a plot of Zeta potential of carbon dot and carbon dot cationic surfactant in Example 3;

[0039] Figure 11 is a comparison of carbon dot cationic surfactant antibacterial property with carbon dot in Example 1; (a), (c) correspond to E. coli, (b), (d) correspond to S. aureus; (c) left is carbon dot, (c) right is carbon dot cationic surfactant, 1 to 6 correspond to concentration values of 0, 0.025, 0.05, 0.1, 0.2 and 0.4 mg / mL; (d) left is carbon dot, (d) right is carbon dot cationic surfactant, 1 to 6 correspond to concentration values of 0, 0.0125, 0.025, 0.05, 0.1 and 0.2 mg / mL.

[0040] Figure 12 is a comparison of carbon dot cationic surfactant antibacterial property with carbon dot in Example 2; (a), (c) correspond to E. coli, (b), (d) correspond to S. aureus; (c), (d) upper is carbon dot, (c), (d) lower is carbon dot cationic surfactant, 1 to 6 correspond to concentration values of 0, 0.025, 0.05, 0.1, 0.2 and 0.4 mg / mL.

[0041] Figure 13 is a fluorescence spectrum of carbon dot (left) and carbon dot surfactant (right) at different excitation wavelengths in Example 1. DETAILED DESCRIPTION

[0042] A green synthesis method of carbon dot cationic surfactant, comprising the following specific steps:

[0043] (1) Amino acid and citric acid are used as carbon sources, and water is used as a solvent to prepare fluorescent carbon quantum dots, wherein, by way of reference, the amino acid can be selected from any one or several of glycine, alpha-alanine, beta-alanine, L-arginine, D-arginine, L-histidine, and D-histidine, and in a more preferred embodiment, the mass ratio of the amino acid to the citric acid can be controlled to be 1:0.5-1:5, and the preparation process can be referred to as dissolving the carbon source in water, then transferring to an open stainless steel reaction dish, heating at 170-200 DEG C for 10-50 minutes, and reacting until the water is completely volatilized or being placed in a 60 DEG C oven for drying, and the product is generally sticky, and cooled to room temperature;

[0044] (2) Under the conditions of stirring and heating reflux in water, amide reaction is carried out according to the mass ratio of the fluorescent carbon quantum dots to the long carbon chain primary amine of 1:0.1-1:1, and long carbon chains are introduced onto the surface of the carbon dots, wherein, by way of reference, the long carbon chain primary amine uses a primary amine containing 8-14 carbon atoms, including n-octylamine, n-decylamine, n-dodecylamine, n-tetradecylamine, or isomers of these primary amines, or a combination of any of them, and the preparation process can be referred to as dissolving the carbon dots in water, heating to 60-90 DEG C and keeping the temperature, gradually adding the long carbon chain primary amine under stirring conditions, and continuing to reflux for 1-5 hours until the reaction is completed, and the judgment standard is that, by way of reference, there is no excess oil on the surface of the solution at the end of the reaction;

[0045] (3) The product of step (2) is dried to obtain a carbon dot cationic surfactant with surface activity and antibacterial activity, wherein the drying temperature can be controlled at 60 DEG C.

[0046] The carbon dot cationic surfactant prepared above has multiple uses, can reduce the interfacial tension of water to below 30 mN / m at 298.15 K and a critical micelle concentration, and has a minimum inhibitory concentration of not more than 0.1 mg / ml for both escherichia coli and staphylococcus aureus, and also has fluorescence or fluorescent whitening function.

[0047] The above embodiments are further illustrated by the following examples, and it should be noted that the following examples are only part of the examples of the present application and cannot represent the whole, therefore, they are only used for explanation and illustration, and cannot be regarded as absolute limitation, the specific steps, parameters, functions, etc. should be based on the above invention content and specific embodiments, and the scope of protection should be based on the claims.

[0048] Example 1

[0049] (1) 0.5 g of α-alanine was weighed and dissolved in 5 mL of distilled water, 0.6 g of citric acid was added, and after being uniformly mixed, it was transferred to a stainless steel reaction dish and reacted at 180°C for 20 min, cooled to room temperature and dried in a 60°C oven to obtain fluorescent carbon quantum dots;

[0050] (2) 0.4 g of n-dodecylamine was weighed and added to 15 mL of distilled water, and 0.5 g of carbon quantum dots in (1) was added, uniformly mixed, heated to reflux with stirring, reacted at 80°C for 2 h, cooled to room temperature and dried in a 60°C oven to obtain carbon quantum dot cationic surfactants with surface activity and antibacterial properties.

[0051] Example 2

[0052] (1) 1.2 g of glycine was weighed and dissolved in 5 mL of distilled water, 1.4 g of citric acid was added, and after being uniformly mixed, it was transferred to a stainless steel reaction dish and reacted at 180°C for 20 min, cooled to room temperature and dried in a 60°C oven to obtain fluorescent carbon quantum dots;

[0053] (2) 0.25 g of n-dodecylamine was weighed and added to 15 mL of distilled water, and 0.5 g of carbon quantum dots in (1) was added, uniformly mixed, heated to reflux with stirring, reacted at 85°C for 2 h, cooled to room temperature and dried in a 60°C oven to obtain carbon quantum dot cationic surfactants with surface activity and antibacterial properties.

[0054] Example 3

[0055] (1) 0.5 g of β-alanine was weighed and dissolved in 5 mL of distilled water, 0.6 g of citric acid was added, and after being uniformly mixed, it was transferred to a stainless steel reaction dish and reacted at 180°C for 23 min, cooled to room temperature and dried in a 60°C oven to obtain fluorescent carbon quantum dots;

[0056] (2) 0.2 g of n-dodecylamine was weighed and added to 15 mL of distilled water, and 0.5 g of carbon quantum dots in (1) was added, uniformly mixed, heated to reflux with stirring, reacted at 85°C for 1.5 h, cooled to room temperature and dried in a 60°C oven to obtain carbon quantum dot cationic surfactants with surface activity and antibacterial properties.

[0057] Example 4

[0058] (1) 0.5 g of L-arginine was weighed and dissolved in 5 mL of distilled water, 0.5 g of citric acid was added, and after being uniformly mixed, it was transferred to a stainless steel reaction dish and reacted at 170°C for 30 min, cooled to room temperature and dried in a 60°C oven to obtain fluorescent carbon quantum dots;

[0059] (2) Take 0.3 g of n-decylamine, add 15 mL of distilled water, add 0.5 g of carbon quantum dots in (1), mix well, heat under stirring to reflux, react at 70°C for 3 h, cool to room temperature and dry in a 60°C oven to obtain carbon quantum dot cationic surfactants with surface activity and bacteriostatic property.

[0060] Example 5

[0061] (1) Take 0.5 g of D-arginine, dissolve in 5 mL of distilled water, add 0.25 g of citric acid, mix well and transfer to a stainless steel reaction dish, react at 190°C for 25 min, cool to room temperature and dry in a 60°C oven to obtain fluorescent carbon quantum dots;

[0062] (2) Take 0.5 g of n-octylamine, add 15 mL of distilled water, add 0.5 g of carbon quantum dots in (1), mix well, heat under stirring to reflux, react at 60°C for 5 h, cool to room temperature and dry in a 60°C oven to obtain carbon quantum dot cationic surfactants with surface activity and bacteriostatic property.

[0063] Example 6

[0064] (1) Take 0.15 g of L-histidine, dissolve in 5 mL of distilled water, add 0.6 g of citric acid, mix well and transfer to a stainless steel reaction dish, react at 200°C for 15 min, cool to room temperature and dry in a 60°C oven to obtain fluorescent carbon quantum dots;

[0065] (2) Take 0.08 g of n-dodecylamine, add 15 mL of distilled water, add 0.5 g of carbon quantum dots in (1), mix well, heat under stirring to reflux, react at 65°C for 4.5 h, cool to room temperature and dry in a 60°C oven to obtain carbon quantum dot cationic surfactants with surface activity and bacteriostatic property.

[0066] Example 7

[0067] (1) Take 0.5 g of D-histidine, dissolve in 5 mL of distilled water, add 1.0 g of citric acid, mix well and transfer to a stainless steel reaction dish, react at 180°C for 28 min, cool to room temperature and dry in a 60°C oven to obtain fluorescent carbon quantum dots;

[0068] (2) Take 0.05 g of n-decylamine, add 15 mL of distilled water, add 0.5 g of carbon quantum dots in (1), mix well, heat under stirring to reflux, react at 80°C for 2.5 h, cool to room temperature and dry in a 60°C oven to obtain carbon quantum dot cationic surfactants with surface activity and bacteriostatic property.

[0069] Figure 1is a schematic diagram of the reaction process (taking the reaction of citric acid and α-alanine as an example) involved in the present application;

[0070] As shown in the figure, taking citric acid and an amino acid (α-alanine as an example) as raw materials, carbon dots containing high-reactivity carboxyl groups are prepared through pyrolysis reaction, and the carbon dot surface carboxyl groups are combined with long carbon chain primary amine (n-dodecylamine as an example) to obtain a cationic surfactant. It can occur surface adsorption on the surface of water, thus having a significant effect of reducing the surface tension of water.

[0071] Figure 2 is a transmission electron microscope image of the carbon dots and the carbon dot surfactant of Example 1;

[0072] Figure (a) is a carbon dot morphology image, and the inset is a high-resolution image of a single carbon dot with a lattice spacing of 0.20 nm; Figure (b) is a carbon dot particle size distribution graph, and most of the particle sizes are distributed in 1.0-2.1 nm. Figure (c) is a carbon dot surfactant morphology image, and Figure (d) is a carbon dot surfactant particle size distribution, most of the particle sizes are distributed in 1.7-2.9 nm. Obviously, the size is significantly increased, indicating that a chemical bond is formed between the alkyl chain and the carbon dot.

[0073] Figure 3 is an infrared spectrum of the carbon dots and the carbon dot cationic surfactant of Example 1;

[0074] In the figure: 1712 is the C=O stretching vibration peak of the carbon dot carboxyl group, indicating that the carbon dot surface contains carboxyl groups, and its reactivity is crucial for the generation of the surfactant, 3468 cm -1 and 3225 cm -1 absorption peaks are O-H stretching vibration peaks and N-H stretching vibration peaks in the carbon dot, which are both hydrophilic groups, giving the carbon dot good hydrophilicity; after amidation of the carbon dot, the C=O stretching vibration intensity decreases significantly, indicating the reaction between the carboxyl group and the primary amino group in n-dodecylamine; 2929 cm -1 and 2855 cm -1 are the anti-symmetric C-H stretching vibration peak and the symmetric stretching vibration peak of the introduced long carbon chain methylene group.

[0075] Figure 4 is an X-ray photoelectron spectroscopy graph of the carbon dot before and after amidation reaction in Example 1;

[0076] Figures (a) and (b) correspond to the C1s and N1s spectrograms of the carbon dot, respectively, (a) figure: 284.8, 285.3 and 286.7 eV correspond to C -C / C =C、 C -O and C =O, 288.6 eV corresponds to C=0, which means that the carbon dots surface contains a large number of carboxyl groups, and the presence of carboxyl groups is essential for the next step of amidation reaction; (b) figure shows that the carbon dot surface contains amino groups (400.3 eV) and protonated amino groups (401.3 eV), and the amino groups are derived from the amino acid raw material itself, and the protonation is due to the ionization of H + combined with the amino group; figures (c) and (d) correspond to the C1s and N1s spectra of the carbon dot surfactant, respectively, in figure (c): 284.7, 285.3, 286.5 and 288.5 eV still correspond to C -C / C = C, C -O, C = O and C OOH, but C -C / C = C content changes from 32.8% in (a) to 54.8% in (c), an increase of 22.0%; at the same time C OOH content changes from 24.3% in (a) to 17.3% in (c), a decrease of 7.0%, which means that the carboxyl groups on the surface of the carbon dots participate in the process of amidation reaction, resulting in a decrease in their content, also resulting in an increase in the C -C / C = C content on the surface of the carbon dots; in figure (d): 401.8 and 400.5 eV still belong to N H3 + and N H2, compared with (b) figure, obviously N H3 + content decreases, which means that due to the consumption of carboxyl groups on the surface of the carbon dots by the amidation reaction, the content of protonated N H3 + decreases; all of these show that the carboxyl groups on the surface of the carbon dots participate in the reaction with n-dodecylamine.

[0077] Figure 8 is the comparison of the foam property and foam stability of the carbon dot cationic surfactant in example 6 with dodecyltrimethylammonium chloride and sodium dodecylbenzenesulfonate; as can be seen from the figure, after the same intensity of oscillation, a large amount of foam appears above the carbon dot cationic surfactant solution; within 60 minutes, its foam volume is larger than that of the traditional cationic surfactant dodecyltrimethylammonium chloride and anionic surfactant sodium dodecylbenzenesulfonate. The picture in the upper right corner also shows that it has excellent foam property.

[0078] Figure 9 is the Zeta potential figure of the carbon dots and the carbon dot cationic surfactant in example 1;

[0079] From the figure: carbon dots surface with a small negative charge (-3.03 mV), and carbon dots cationic surfactant with positive charge (7.20 mV), proved that carbon dots after modification with n-dodecylamine with a large number of positive charge, belong to cationic surfactants.

[0080] Figure 10 is the Zeta potential diagram of carbon dots and carbon dots cationic surfactant in Example 3;

[0081] From the figure: carbon dots surface with a small negative charge (-0.077 mV), and carbon dots cationic surfactant with positive charge (9.26 mV), proved that carbon dots after modification with n-dodecylamine with a large number of positive charge, belong to cationic surfactants.

[0082] Example 8:

[0083] Surface tension determination: the maximum bubble method was used to determine the surface tension, at a certain temperature, the additional pressure of pure water was measured, and the additional pressure of 0.5, 1, 2, 4, 6, 8, 10 mg / mL sample was measured respectively. According to the principle of Laplace equation, the surface tension of the sample was calculated: surface tension (mN / m) = surface tension of pure water x additional pressure of sample / additional pressure of water; Figure 5 is the relationship diagram of carbon dots cationic surfactant reducing water surface tension and solution concentration in Example 2; from the figure, it can be seen that at 298.15 K, the critical micelle concentration (CMC) of the product is about 4.0 mg / mL, and the interfacial tension of water can be reduced to 29.7 mN / m. At the same temperature, sodium dodecylbenzenesulfonate can reduce the interfacial tension of water to 34.7 mN / m, obviously the performance of carbon dots cationic surfactant is better than that of sodium dodecylbenzenesulfonate. Figure 7 is the relationship diagram of carbon dots cationic surfactant reducing water surface tension and solution concentration in Example 3; from the figure, it can be seen that at 298.15 K, the critical micelle concentration (CMC) of the product is about 5.0 mg / mL, and the interfacial tension of water can be reduced to 29.2 mN / m.

[0084] Figure 6 is the contact angle photo of carbon dots surfactant solution droplets in Example 2; corresponding to the contact angle of pure water and carbon dots cationic surfactant with concentration of 0.2, 1.0, 2.0, 5.0 and 10.0 mg / mL in Example 2 respectively; from the figure, it can be seen that with the increase of the concentration of carbon dots cationic surfactant, the contact angle decreases significantly, and the change trend is the same as that of surface tension.

[0085] Example 9:

[0086] Bacteriostatic determination: E. coli and S. aureus were selected for the experiment, and the bacteria in the logarithmic growth phase were diluted to 2 x 10 6 CFU in liquid medium and incubated at 37°C, 220 rpm for several hours.

[0087] The absorbance of each well was measured at a wavelength of 600 nm after 18 h of incubation at a final concentration of 2-0.125 mg / mL (0.0125, 0.25, 0.5, 1, 2) of the sample in 100 μL of each well of a 96-well plate, with carbon quantum dots as the positive control and nutrient broth as the blank control. The bacteriostatic rate of the carbon quantum dot cationic surfactant was determined. Bacteriostatic rate (%) = (control count - experimental count) / control count x 100%.

[0088] Figure 11 is the bacteriostatic property of the carbon dot cationic surfactant in Example 1 compared with that of carbon dots;

[0089] As can be seen from the figure, the growth inhibition of E. coli and S. aureus of the carbon dots modified by n-dodecylamine was significantly enhanced. Figures (a) and (c) correspond to E. coli, and (b) and (d) correspond to S. aureus. Figure (c) on the left is carbon dots, and (c) on the right is carbon dot cationic surfactant. 1 to 6 correspond to the concentration values of 0, 0.025, 0.05, 0.1, 0.2 and 0.4 mg / mL. Figure (d) on the left is carbon dots, and (d) on the right is carbon dot cationic surfactant. 1 to 6 correspond to the concentration values of 0, 0.0125, 0.025, 0.05, 0.1 and 0.2 mg / mL. As shown in figures (a) and (b), the bacteriostatic rates at concentrations of 0.1 and 0.05 mg / mL were both more than 80%, while the carbon dots themselves had almost no bacteriostatic effect. Plate cloning experiments showed that the growth inhibition of E. coli and S. aureus at concentrations of 0.1 and 0.05 mg / mL was obvious, and the effective concentration was lower than the critical micelle concentration (4 mg / mL).

[0090] Figure 12 is the bacteriostatic property of the carbon dot cationic surfactant in Example 2 compared with that of carbon dots;

[0091] As can be seen from the figure: after the carbon dots are modified by n-dodecylamine, the growth inhibition effect of the carbon dots on E. coli and S. aureus is obviously enhanced, figures (a), (c) correspond to E. coli, (b), (d) correspond to S. aureus; on figures (c), (d) are carbon dots, (c), (d) below are carbon dot cationic surfactants, 1 to 6 correspond to concentration values of 0, 0.025, 0.05, 0.1, 0.2 and 0.4 mg / mL; as shown in figures (a) and (b), the bacteriostatic rates at a concentration of 0.1 mg / mL are all more than 80%, while the carbon dots themselves have almost no bacteriostatic effect; plate cloning experiments show that: at a concentration of 0.1 mg / mL, the growth inhibition effect on E. coli and S. aureus is obvious.

[0092] Example 10:

[0093] Figure 13 are fluorescence spectra of the carbon dots and the carbon dot surfactant in Example 1 under different excitation wavelengths, as can be seen from the left figure, under different excitation wavelengths, the fluorescence emission of the carbon dots is all at 422 nm; the right figure shows that the emission wavelength of the carbon dot surfactant is about 408 nm, which has a slight blue shift after modification, and the light-emitting characteristics of the carbon dots are consistent with the photoluminescence characteristics of the carbon dots reported in a large number of literatures.

[0094] Comparative Example:

[0095] The scheme of Example 4 in the invention patent with publication number CN112494517B and the name of a fluorescent antibacterial carbon dot, its preparation method and application is adopted, and the details are as follows:

[0096] (1) 200 mg of chitosan quaternary ammonium salt and 50 mg of citric acid are weighed and dispersed in 20 mL of ultrapure water, and then stirred under a magnetic stirrer to obtain a uniformly dispersed transparent solution.

[0097] (2) The transparent solution obtained in step (1) is transferred to a polytetrafluoroethylene reaction kettle, and reacted in an oven at 200℃ for 4h to obtain a carbon dot solution.

[0098] (3) The carbon dot solution obtained in step (2) is directly placed in a 500D dialysis bag and dialyzed for 24h, and then dried to obtain solid carbon dots.

[0099] It is tested that the product has an emission wavelength of 465 nm, a 100% minimum bacteriostatic concentration of 0.125 mg / ml for S. aureus, and it is known that chitosan quaternary ammonium salt itself has antibacterial properties, so the test results are not as good as those in Example 9 of the present application described above.

[0100] The above merely preferred embodiments of the present application, but the scope of protection of the present application is not limited thereto, any person skilled in the art within the scope of the present application disclosed in the technical range, can easily think of the changes or replacements, should be covered within the scope of protection of the present application. Therefore, the scope of protection of the present application should be limited to the scope of protection defined by the claims.

[0101] The present application is not detailed, are well known to those skilled in the art of the present technology.

Claims

1. A green synthesis method for a carbon dot cationic surfactant, characterized in that, The specific steps include the following: (1) Fluorescent carbon quantum dots were prepared using amino acids and citric acid as carbon sources and water as a solvent; (2) An amidation reaction was carried out in water under stirring and heating reflux conditions according to the mass ratio of fluorescent carbon quantum dots to long carbon chain primary amines of 1:0.1 to 1:1, so as to introduce long carbon chains on the surface of carbon dots. (3) Dry the product from step (2) to obtain a carbon dot cationic surfactant with surface activity and antibacterial properties; The amino acid is selected from any one or more of glycine, α-alanine, β-alanine, L-arginine, D-arginine, L-histidine, and D-histidine. The long-chain primary amine is a primary amine containing 8 to 14 carbon atoms, including n-octylamine, n-decylamine, n-dodecylamine, n-tetradecylamine, or any combination thereof; In step (1), the process of preparing fluorescent carbon quantum dots includes: weighing a certain amount of amino acids, mixing them with citric acid at a mass ratio of 1:0.5 to 1:5, dissolving the mixture in water, heating the mixture at 170 to 200°C for 10 to 50 minutes, reacting until the water is completely evaporated or drying it in an oven, and cooling it to room temperature. In step (2), the amidation reaction process includes: first dissolving the product of step (1) in water, heating to 60-90°C and maintaining the temperature, gradually adding long-chain primary amines under stirring, and continuously refluxing for 1-5 hours until the reaction ends. When the reaction ends, there is no excess oil on the surface of the solution.

2. The green synthesis method of a carbon dot cationic surfactant according to claim 1, characterized in that: In steps (1) and (3), the drying temperature is 60°C.

3. A carbon dot cationic surfactant prepared by the green synthesis method described in claim 1 or 2.

4. An application of the carbon dot cationic surfactant as described in claim 3 when it is necessary to reduce the surface tension of water, characterized in that: The carbon dot cationic surfactant can reduce the interfacial tension of water to below 30 mN / m at 298.15 K and the critical micelle concentration.

5. The application of the carbon dot cationic surfactant as described in claim 3 in inhibiting bacterial growth, characterized in that: The minimum inhibitory concentration of the carbon dot cationic surfactant against Escherichia coli and Staphylococcus aureus does not exceed 0.1 mg / ml.

6. The use of a carbon dot cationic surfactant as described in claim 3 in a surfactant requiring fluorescence or fluorescent whitening function or an antibacterial agent requiring fluorescence or fluorescent whitening function.

Images