An experimental method to analyze the assembly mechanism of carbon nanodots

Abstract

The present invention relates to the technical field of biomedical materials, and in particular to an experimental method for analyzing the assembly mechanism of carbon nanodots. The present invention discloses an experimental method for analyzing the assembly mechanism of carbon nanodots, comprising the steps of: (1) adding carbon nanodot assemblies to buffer systems of different pH values, molecular structures, and ionic strengths; (2) observing and recording the color change of the carbon nanodot assemblies, the position shift of the characteristic absorption peak of the ultraviolet-visible spectroscopic spectrum, and the change in the absorbance value of the characteristic absorption peak of the ultraviolet-visible spectroscopic spectrum; (3) analyzing the dissociation state of acidic functional groups and basic functional groups in different buffer systems using a pH calculation formula; (4) analyzing the depolymerization process of the carbon nanodot assemblies in combination with step (2) and step (3), and analyzing the assembly mechanism. The experimental and analytical methods designed by the present invention can be used to clarify the assembly mechanism of carbon nanodot assemblies constructed based on hydrogen bonds.

Description

Technical Field

[0001] This invention relates to the field of biomedical materials technology, and in particular to an experimental method for analyzing the assembly mechanism of carbon nanodots. Background Technology

[0002] Carbon nanodots, as a novel carbon-based nanomaterial, possess advantages such as high water solubility, good dispersibility, good biocompatibility, and ease of functionalization, and have been widely applied in various biomedical fields. However, carbon nanodots exhibit low photothermal conversion performance as photothermal conversion materials. Currently, the assembly effect of carbon nanodots can be used to enhance photothermal conversion efficiency. Studies have shown that the energy dissipation mode of carbon nanodots changes before and after assembly, resulting in a significant enhancement of the photothermal conversion performance of the assembled structure compared to free carbon nanodots. Among the assembly methods, non-covalent bonds are widely used due to their high efficiency and variety. However, developing an effective experimental and analytical method to elucidate the assembly mechanism of non-covalent assemblies remains another scientific problem that urgently needs to be solved. Summary of the Invention

[0003] To address the shortcomings of the existing technology, this invention provides an experimental method for analyzing the assembly mechanism of carbon nanodots.

[0004] The technical solution of the present invention to solve the above-mentioned technical problems is as follows:

[0005] An experimental method for analyzing the assembly mechanism of carbon nanodots includes the following steps:

[0006] (1) The carbon nanodot assemblies were added to buffer systems with different pH values, molecular structures and ionic strengths respectively;

[0007] (2) Observe and record the color change of the carbon nanodot assembly, the position shift of the characteristic absorption peak in the ultraviolet-visible spectrophotometer, and the change in the absorbance value of the characteristic absorption peak in the ultraviolet-visible spectrophotometer;

[0008] (3) In different buffer systems, the dissociation state of acidic and basic functional groups was analyzed using the pH calculation formula.

[0009] (4) Combine steps (2) and (3) to analyze the depolymerization process of the carbon nanodot assembly and analyze the assembly mechanism.

[0010] Furthermore, the molecular structure of the buffer system includes any one or more of sodium ions, potassium ions, hydrogen phosphate ions, dihydrogen phosphate ions, HEPES, Tris, or chloride ions.

[0011] Furthermore, the buffer system includes any one of the following: hydrochloric acid-urea (HCl-Urea) buffer system, hydroxyethylpiperazine ethanethioic acid (HEPES) buffer system, phosphate buffer system, or tris-hydroxymethylaminomethane hydrochloride (Tris-HCl) buffer system.

[0012] Furthermore, the pH value of the buffer system includes 2.5-3.5, 6.5-7.4, or 7.5-8.5.

[0013] Furthermore, the ionic strength of the buffer system is 0 mM-250 mM.

[0014] Furthermore, the shift in position of the characteristic absorption peak in the ultraviolet-visible spectrophotometer is a blue shift, and the blue shift range is 10nm-200nm.

[0015] Furthermore, the absorbance value of the characteristic absorption peak in the ultraviolet-visible spectrophotometer decreases, with a decrease range of 0.1-0.8.

[0016] Furthermore, the pH calculation formula is pH = pKa + lg([R - COO)). - ] / [R-COOH], where R-COOH is the acidic functional group in the carbon nanodot assembly, and Ka is the dissociation constant of the acidic functional group.

[0017] Furthermore, the dissociation state of the basic functional group is [H] dissociated from the acidic functional group. + ], buffer ions dissociated from [H] + The pH value of the buffer system is determined by the pH value of the buffer solution.

[0018] Furthermore, the characteristic absorption peak of the ultraviolet-visible spectrophotometer is the characteristic absorption peak in the range of 520 nm to 680 nm.

[0019] Compared with the prior art, the present invention has the following technical effects:

[0020] This invention establishes a complete analytical method by changing the pH, molecular structure, ionic strength, concentration, and ambient temperature of the buffer system. This method effectively elucidates the changes in solution color, UV-Vis spectra, and absorbance of the characteristic absorption peak at 680 nm in carbon nanodot assemblies, thereby analyzing the depolymerization process and elucidating the assembly mechanism. This invention provides a novel experimental and analytical method for clarifying the assembly mechanism of carbon nanodots, which can be widely applied to the study of various assembly systems and lays a solid foundation for the broad application of these systems. Attached Figure Description

[0021] Figure 1The following shows the effect of the HU system (pH=3.04) of Example 1 of the present invention on the stability of carbon nanodot assemblies: (a) color change of the carbon nanodot assembly solution at different time points under pH=3.04 conditions; (b) UV-Vis spectra of the carbon nanodot assembly solution at different time points under pH=3.04 conditions; (c) absorbance changes of the carbon nanodot assembly solution at A680nm at different time points under different pH conditions.

[0022] Figure 2 The following illustrates the effect of the HU system (pH = 7.04) of Example 2 of the present invention on the stability of carbon nanodot assemblies: (a) color changes of the carbon nanodot assembly solution at different time points under pH = 7.04 conditions; (b) UV-Vis spectra of the carbon nanodot assembly solution at different time points under pH = 7.04 conditions; (c) absorbance changes of the carbon nanodot assembly solution at A680nm at different time points under different pH conditions.

[0023] Figure 3 The following shows the effect of the HU system (pH=8.05) of Example 3 of the present invention on the stability of carbon nanodot assemblies: (a) color change of the carbon nanodot assembly solution at different time points under pH=8.05 conditions; (b) UV-Vis spectra of the carbon nanodot assembly solution at different time points under pH=8.05 conditions; (c) absorbance changes of the carbon nanodot assembly solution at A680nm at different time points under different pH conditions.

[0024] Figure 4 A schematic diagram showing the depolymerization of the carbon nanodot assembly of Example 1 of the present invention in the HU system (pH=3.04) is shown;

[0025] Figure 5 A schematic diagram showing the depolymerization of the carbon nanodot assembly of Example 2 of the present invention in the HU system (pH=7.04) is shown;

[0026] Figure 6 The diagram shows the depolymerization of the carbon nanodot assembly of Example 3 of the present invention in the HU system (pH=8.05). Detailed Implementation

[0027] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Although the description of the present invention is presented in conjunction with preferred embodiments, this does not mean that the features of the invention are limited to these embodiments. On the contrary, the purpose of describing the invention in conjunction with embodiments is to cover other options or modifications that may be derived based on the claims of the present invention. To provide a deep understanding of the invention, many specific details will be included in the following description. The invention may also be implemented without using these details. Furthermore, to avoid confusion or obscuring the focus of the invention, some specific details will be omitted in the description. It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0028] Preparation of carbon nanodot assemblies: Dissolve 0.75 g of citric acid monohydrate and 0.5 g of urea in 5 mL of deionized water and mix thoroughly; then place in a polytetrafluoroethylene autoclave and heat at 160 °C for 4 h; after the reaction is complete, the resulting blue solution is the carbon nanodot assembly solution to be analyzed.

[0029] Example 1

[0030] An experimental method for analyzing the assembly mechanism of carbon nanodots, comprising the following steps:

[0031] The carbon nanoparticle assembly prepared above was added to an HCl-Urea system with a pH of 3.04, and the final concentration was controlled at 320 μg / mL. The changes in solution color, UV-Vis spectrophotometry, and A680 absorbance of the carbon nanoparticle assembly at this pH value and 37℃ over time were observed. Figure 1 As shown, after analyzing and discussing the above results, a depolymerization diagram is drawn as follows. Figure 4 As shown.

[0032] Figure 1 The effect of the HU system on the stability of the carbon nanodot assembly in Example 1 is as follows: (a) The color change of the carbon nanodot assembly solution at different time points under pH = 3.04. As time increases, the solution changes from blue to dark brown; (b) The UV-Vis spectra of the carbon nanodot assembly solution at different time points under pH = 3.04. As time increases, the maximum absorption peak of the spectrum first shifts from 680 nm to 625 nm, then the absorbance (625 nm) decreases, then shifts from 625 nm to 560 nm, and finally the absorbance (560 nm) increases; (c) The change of absorbance at A680 nm of the carbon nanodot assembly solution at different time points under different pH conditions. From left to right, the pH values ​​are 3.04, 7.04 and 8.05, and the final concentration of the carbon nanodot assembly is 320 μg / mL.

[0033] At pH 3.04, by Figure 1 As can be seen from the color change of the solution in (a), the solution color changes from blue to dark brown, with the most significant color change occurring at 0.07 h, where the solution rapidly changes from blue to gray. Meanwhile, from... Figure 1 As shown in (b), the absorption peak undergoes a significant blue shift from 680 nm to 625 nm within 0.00 h to 0.02 h. Then, the absorbance (A625) decreases significantly between 0.02 h and 0.17 h, and finally, the absorption peak continues to blue shift from 625 nm to 560 nm between 0.17 h and 48.00 h, accompanied by an increase in absorbance (A560). Figure 1 As can be seen in (c), the absorbance at A680 decreases rapidly from 0h to 0.07h, from 2.0 to 0.4. Then, from 0.07h to 48.00h, the absorbance remains basically unchanged.

[0034] Meanwhile, the carbon nanodot assembly was added to a HU buffer system (pH 3.04) and placed at 37℃ for 48.00 h. The pH value of the solution was measured before and after the incubation. The results showed that the pH value of the assembly solution was 3.04 at 0.00 h, while it increased to 3.61 after 48.00 h.

[0035] The above results combined Figure 1 It can be observed that at pH 3.04, the solution color of the assembly changes from blue to dark brown, the absorption peak first shifts to blue (680nm-625nm), the absorbance (A625) then decreases, the absorption peak shifts to blue again (625nm-560nm), and the absorbance (A560) increases. Simultaneously, during the storage process, the pH of the assembly slightly increases with prolonged storage time, from 3.04 to 3.60. This fully demonstrates that during the depolymerization process of the assembly, the [H+] in the solution increases. + The pH value of the solution decreases, which in turn increases.

[0036] To explain the above results, this invention uses a pH calculation formula to analyze the change process of solution pH value, explore the depolymerization mechanism of the assemblies, and thus elucidate their assembly mechanism. In the HU buffer system, the urea carbon nanodots (R-NH2) in the assemblies can react with H+ in the solution. + The reaction produces R-NH3 + ,Right now Citric acid carbon nanoparticles (R-COOH) can dissociate to form R-COO. - and H + ,Right now Since there are no other ions in the HU buffer system that affect pH changes, it is only necessary to analyze the dissociation state of citric acid carbon dots (R-COOH) and the ionization state of urea carbon dots (R-NH2) in the assembly under different pH conditions. Since citric acid has three -COOH groups that can dissociate, there are three dissociation constants, namely pKa1 (3.15), pKa2 (4.76), and pKa3 (6.40). Because the solution pH is 3.04, which is less than the first dissociation constant pKa1 (3.15) of citric acid, and at the same time, the first dissociation constant pKa1 (3.15) of citric acid is within the solution pH change range (3.04 to 3.60), so, during the analysis of pH changes, taking 3.15 and 3.60 as the boundaries, it is divided into three different stages for separate analysis: 3.04 ≤ pH ≤ 3.15, 3.15 < pH < 3.6, and pH = 3.6. The specific analysis process is as follows:

[0037] ① 3.04 ≤ pH ≤ 3.15

[0038] 1) Dissociation state of citric acid carbon dots (R-COOH):

[0039] According to the pH calculation formula, assume:

[0040] pH = 3.10 (1),

[0041] pH = pKa1 + lg([R-COO - / [R-COOH]) (2),

[0042] In the formula: R-COOH = citric acid carbon dots, pKa1 = 3.15.

[0043] Substituting (1) into (2) gives: 3.10 = 3.15 + lg([R-COO - / [R-COOH]), lg([R-COO - / [R-COOH]) = -0.05 < 0, so, in the solution, [R-COO - < [R-COOH].

[0044] 2) Ionization state of urea carbon dots (R-NH2):

[0045] Since the solution pH = 3.04, in an acidic environment, [H + = 10 -3 M = 1 mM, [H + is relatively large, which causes the equilibrium to shift to the right. Therefore, the generation of R-NH3 + is determined by the H + concentration. In this invention, by calculating the H+ Based on the amount added, the remaining amount, and the amount consumed, deduce the concentration of [R-NH3] in the solution. + [] and [R-NH2]. Among them, H + The amount added includes H+ generated from the dissociation of R-COOH. + (H + 1) and the H in the added HCl solution + (H + 2). H + The remaining amount is the H+ remaining in the solution. + (H + 3) This brings the solution to a pH of 3.04. + The consumption amount refers to the amount of R-NH3 produced by the reaction with R-NH2. + H consumed + (H + 4). Four types of [H] + The calculation process for ] is as follows:

[0046] AR-COOH dissociates to produce H₂ + (H + 1):

[0047] By lg([R-COO) - From ] / [R-COOH])=-0.05, we can obtain:

[0048] [R-COO - ] / [R-COOH] = 10 -0.05 = 0.89 (3),

[0049] [R-COOH] + [R-COO - ] = 8.57 mM (4),

[0050] Substituting (3) into (4), we get [R-COOH] = 4.5 mM, [R-COO - ] = 4.07mM, according to the formula We can obtain: [H] + 1] = [R-COO - = 4.07mM.

[0051] B. The added HCl solution contains H + (H + 2): [HCl] = 12 mM, i.e., [H + 2] = 12mM.

[0052] C. Remaining H + (H + 3):

[0053] pH = -lg [H+ 3] (5),

[0054] pH = 3.04 (6),

[0055] (6) Substituting into (5), we get [H + 3] = 1mM.

[0056] DH + Consumption H + (H + 4):

[0057] Added amount = Remaining amount + Consumed amount, i.e., [H] + 1]+[H + 2]=[H + 3]+[H + 4], we can obtain:

[0058] [H + 4] = [H + 1]+[H + 2]-[H + 3]=4.07mM+12mM-1mM=15.07mM.

[0059] Due to the consumption of H + (H + 4) Used to generate NH3 + ,Right now therefore,

[0060] [R-NH3 + ] = [H + 4] = 15.07 mM (7),

[0061] The concentration of urea carbon nanoparticles in the reaction system was 20 mM, and the urea carbon nanoparticles only contained R-NH3. + Both R-NH2 and R-NH2 are in two states, therefore,

[0062] [R-NH3 + ]+ [R-NH2] = 20 mM (8),

[0063] Substituting (7) into (8), we get [R-NH2] = 20 - 15.07 = 4.93 mM.

[0064] It is worth noting that at this time, the [R-NH3] in the solution... + [R-NH2] = 15.07 mM, [R-NH3] = 4.93 mM, therefore, the concentration of [R-NH3] in the solution is... + [R-NH2].

[0065] In summary, when the pH of the solution is 3.04 ≤ pH ≤ 3.15, [R-COO- [R-COOH], [R-NH3] + [R-NH2].

[0066] 3) Based on the above ion changes, elucidate the depolymerization mechanism of the assembly:

[0067] The calculation results above show that when 3.04 ≤ pH ≤ 3.15, the [R-NH3] in the solution... + The presence of [R-NH2] indicates the presence of a large amount of R-NH3 in the assembly at this time. + The electrostatic repulsion caused by the positive charge leads to the urea carbon nanodots leaving the outer surface of the assembly, thereby breaking the hydrogen bonds between the urea carbon nanodots and the citric acid carbon nanodots, completely destroying the external structure of the assembly, and causing the assembly to depolymerize from the outside. Simultaneously, in the solution, [R-COOH]≥[R-COO] - The presence of a large amount of R-COOH can form stable hydrogen bonds within the assembly, ensuring the stability of the internal structure. The stability of the internal structure and the depolymerization of the external structure can be manifested as a significant blue shift in the UV-Vis absorption peak, from 680 nm to 625 nm.

[0068] ② 3.15 < pH < 3.60

[0069] 1) Dissociation state of citric acid carbon nanodots (R-COOH):

[0070] According to the pH calculation formula, assuming

[0071] pH = 3.20 (1),

[0072] pH = pKa1 + lg([R-COO)) - ] / [R-COOH]) (2),

[0073] In the formula: R-COOH = citric acid carbon nanoparticles, pKa1 = 3.15,

[0074] Substituting (1) into (2), we know that: 3.20 = 3.15 + lg([R-COO) - ] / [R-COOH]), lg([R-COO - ] / [R-COOH])=0.05>0, [R-COO - ]>[R-COOH].

[0075] 2) Ionization state of urea carbon nanodots (R-NH2):

[0076] By calculating H in the solution + Based on the amount added, the remaining amount, and the amount consumed, deduce the concentration of [R-NH3] in the solution.+ [] and [R-NH2]. Four types of [H] + The calculation process for ] is as follows:

[0077] AR-COOH dissociates to produce H₂ + (H + 1):

[0078] By lg([R-COO) - From ] / [R-COOH])=0.05, we can obtain,

[0079] [R-COO - ] / [R-COOH] = 10 0.05 = 1.12 (3),

[0080] [R-COOH] + [R-COO - ] = 8.57 mM (4),

[0081] Substituting (3) into (4), we get [R-COOH] = 4.04 mM, [R-COO - ] = 4.53mM, according to the formula We can obtain: [H] + 1] = [R-COO - = 4.53mM.

[0082] B. The added HCl solution contains H + (H + 2): [HCl] = 12 mM, i.e., [H + 2] = 12mM.

[0083] C. Remaining H + (H + 3):

[0084] pH = -lg [H + 3] (5),

[0085] pH = 3.20 (6),

[0086] (6) Substituting into (5), we get [H + 3] = 0.6mM.

[0087] DH + Consumption H + (H + 4):

[0088] Added amount = Remaining amount + Consumed amount, i.e., [H] + 1]+[H + 2]=[H + 3]+[H +4], it can be obtained that

[0089] [H + 4] = [H + 1] + [H + 2] - [H + 3] = 4.53 mM + 12 mM – 0.6 mM = 15.93 mM.

[0090] Since the consumed H + (H + 4) is used to generate NH3 + , that is Therefore,

[0091] [R-NH3 + = [H + 4] = 15.93 mM (7),

[0092] The concentration of urea carbon dots in the reaction system is 20 mM, and there are only two states of urea carbon dots, R-NH3 + and R-NH2. So,

[0093] [R-NH3 + + [R-NH2] = 20 mM (8),

[0094] Substituting (7) into (8) gives [R-NH2] = 20 - 15.93 = 4.07 mM.

[0095] It should be noted that at this time, [R-NH3 + = 15.93 mM in the solution, while [R-NH2] = 4.07 mM. Therefore, [R-NH3 + > [R-NH2].

[0096] In summary, when 3.15 < pH < 3.6 in the solution, [R-COO - > [R-COOH], [R-NH3 + > [R-NH2].

[0097] 3) Elucidate the disassembly mechanism of the assembly based on the above ion changes:

[0098] From the above calculation results, when 3.15 < pH < 3.6, [R-COO - > [R-COOH] in the solution, indicating that a large number of R-COO - appear in the assembly at this time, and R-COOH decreases significantly. The hydrogen bonds between citric acid carbon dots are broken, and the internal structure is damaged, causing the assembly to disassemble from the inside. After disassembly, the carbon dots surface has a large number of R-COO -The electrostatic repulsion caused by the negative charge allows carbon nanodots to exist freely in the solution. Therefore, the assemblies depolymerize from within, forming free carbon nanodots, which can be observed by the spectral absorbance (A). 625 A significant decrease in ).

[0099] ③ pH = 3.60

[0100] 1) Dissociation state of citric acid carbon nanodots (R-COOH):

[0101] According to the pH calculation formula,

[0102] When pH = 3.60 (1),

[0103] pH = pKa1 + lg([R-COO)) - ] / [R-COOH]) (2),

[0104] In the formula: R-COOH = citric acid carbon nanoparticles, pKa1 = 3.15,

[0105] Substituting (1) into (2), we know that: 3.60 = 3.15 + lg([R-COO) - ] / [R-COOH]), lg([R-COO - ] / [R-COOH])=0.45>0, [R-COO - ]>[R-COOH].

[0106] 2) Ionization state of urea carbon nanodots (R-NH2):

[0107] By calculating H in the solution + Based on the amount added, the remaining amount, and the amount consumed, deduce the concentration of [R-NH3] in the solution. + [] and [R-NH2]. Four types of [H] + The calculation process for ] is as follows:

[0108] AR-COOH dissociates to produce H₂ + (H + 1):

[0109] By lg([R-COO) - From ] / [R-COOH])=0.45, we can obtain,

[0110] [R-COO - ] / [R-COOH] = 10 0.45 = 2.82 (3),

[0111] [R-COOH] + [R-COO - ] = 8.57 mM (4),

[0112] Substituting (3) into (4), we get [R-COOH] = 2.24 mM, [R-COO - ] = 6.33mM, according to the formula We can obtain: [H] + 1] = [R-COO - = 6.33mM.

[0113] B. The added HCl solution contains H + (H + 2): [HCl] = 12 mM, i.e., [H + 2] = 12mM.

[0114] C. Remaining H + (H + 3):

[0115] pH = -lg [H + 3] (5),

[0116] pH = 3.60 (6),

[0117] (6) Substituting into (5), we get [H + 3] = 0.25mM.

[0118] DH + Consumption H + (H + 4):

[0119] Added amount = Remaining amount + Consumed amount, i.e., [H] + 1]+[H + 2]=[H + 3]+[H + 4], we can obtain

[0120] [H + 4] = [H + 1]+[H + 2]-[H + 3]=6.33mM+12mM–0.25mM=18.08m.

[0121] Due to the consumption of H + (H + 4) Used to generate NH3 + ,Right now We can obtain:

[0122] [R-NH3 + ] = [H + 4] = 18.08 mM (7),

[0123] The concentration of urea carbon nanoparticles in the reaction system was 20 mM, and the urea carbon nanoparticles only contained R-NH3. + Both R-NH2 and R-NH2 are in two states, therefore,

[0124] [R-NH3 + ] + [R-NH2] = 20 mM (8),

[0125] Substituting (7) into (8), we get [R-NH2] = 20 – 18.08 = 1.92 mM.

[0126] It is worth noting that at this time, the [R-NH3] in the solution... + [R-NH2] = 18.08 mM, while [R-NH3] = 1.92 mM. Therefore, the concentration of [R-NH3] in the solution is... + [R-NH2].

[0127] In summary, when the pH of the solution is 3.60, [R-COO - [R-COOH], [R-NH3] + [R-NH2].

[0128] 3) Based on the above ion changes, elucidate the depolymerization mechanism of the assembly:

[0129] The calculation results above show that when pH = 3.20, the [R-COO] in the solution... - [R-COO] = 4.53 mM, and at pH = 3.60, the concentration of [R-COO] in the solution is... - The concentration of [R-COO] was 6.33 mM, indicating that as pH increased, [R-COO]... - The concentration of [R-NH3] is gradually increasing. Meanwhile, at pH = 3.20, [R-NH3]... + The concentration of [R-NH3] was 15.93 mM, while at pH 3.60, the concentration of [R-NH3] in the solution was... + The concentration of [R-NH3] = 18.08 mM, indicating that as pH increases, [R-NH3]... + [R-NH3] is also gradually increasing. + ] and [R-COO -As it gradually increases, the electrostatic attraction between positive and negative charges gradually strengthens. When the role of hydrogen bonds in the solution is gradually replaced by the electrostatic attraction, it will cause the complete depolymerization of the original hydrogen-bond-mediated assembly, and at the same time form a new assembly mediated by electrostatic attraction. The hydrogen-bond-mediated assembly is composed of citric acid carbon nanodots and has larger particles. At this time, its maximum absorption peak is located at 625 nm, while the electrostatic-attraction-mediated assembly is formed by aggregating a small amount of free negatively charged citric acid carbon nanodots with a large number of positively charged urea carbon nanodots. It has smaller particles and its maximum absorption peak is located at 560 nm. Therefore, it shows that the spectral absorption peak blue-shifts from 625 nm to 560 nm. As - [R-COO 560 gradually increases, it will also cause the number of electrostatic-attraction-mediated assemblies to gradually increase, manifested as an increase in the spectral absorbance value (A - ). All in all, when the pH increases to 3.60, it will cause the gradual increase of [R-COO

[0130] (3) Explain the depolymerization mechanism of the assembly

[0131] As described above, in order to more intuitively express the depolymerization mechanism of carbon nanodot assemblies, we respectively show [R-COO - , [R-NH3 + and spectral changes under three pH environments. When 3.04 ≤ pH ≤ 3.15 in the solution, [R-COOH] > [R-COO - , [R-NH3 + > [R-NH2], and the spectral absorption peak blue-shifts (680 nm - 625 nm). When 3.15 < pH < 3.60 in the solution, [R-COO - > [R-COOH], [R-NH3 + > [R-NH2], and the spectral absorbance value (A 625 ) decreases. When the pH of the solution = 3.60, [R-COO - > [R-COOH], [R-NH3 + > [R-NH2], and the spectral absorption peak blue-shifts (625 nm - 560 nm) and the absorbance value (A 560 ) increases.

[0132] Figure 4 It is a schematic diagram of the decomposition of carbon nanodot assemblies in the HU buffer system of Example 1 under the pH 3.04 environment. Figure 4 The schematic diagram shows the depolymerization process of carbon nanodot assemblies in the pH 3.04 environment. As Figure 4As shown, in the initial state, the structure of the assembly is stabilized by two types of hydrogen bonds. The first is the hydrogen bond formed between the carboxyl groups of citric acid carbon dots, which is used to stabilize the internal structure of the assembly. The second is the hydrogen bond formed between the amino group of urea carbon dots and the carboxyl group of citric acid carbon dots, which is used to stabilize the external structure of the assembly. When the pH of the solution is within 3.04 ≤ pH ≤ 3.15, the amino group of urea carbon dots will ionize to generate R-NH3 + , resulting in an electrostatic repulsion between positive charges, which破坏了组装体的外部结构,使得组装体从外部解聚,从而导致光谱吸收峰蓝移(680nm移至625nm)。 When 3.15 < pH < 3.60, [R-COO - > [R-COOH] in the solution, resulting in an electrostatic repulsion between negative charges between citric acid carbon dots, which破坏了碳纳米点之间的原来的氢键,使得组装体从内部发生解聚,表现为光谱吸光值迅速降低(A 625 ). In addition, when pH = 3.20, [R-COO - = 4.53 mM, [R-NH3 + = 15.93 mM, and when the pH increases to 3.60, [R-COO - = 6.33 mM, [R-NH3 + = 18.08 mM, indicating that as the pH increases, both [R-COO - and [R-NH3 + are gradually increasing, resulting in a gradually increasing electrostatic attraction between positive and negative charges. When the role of hydrogen bonds in the solution is gradually replaced by the electrostatic attraction, the original hydrogen bond-mediated assembly is completely disassembled, and at the same time, a new assembly mediated by electrostatic attraction is formed. In addition, since the particles of the assembly mediated by electrostatic attraction are much smaller than the assembly mediated by hydrogen bonds, therefore, the spectral absorption peak blue-shifts from 625 nm to 560 nm. At the same time, as the pH further increases, [R-COO-] further increases, and the number of assemblies mediated by electrostatic attraction gradually increases,表现为光谱吸光值A 560 的升高。

[0133] Example 2

[0134] An experimental method for analyzing the assembly mechanism of carbon dots is as follows:

[0135] Add the above-prepared carbon dot assembly to the HCl-Urea system with a pH value of 7.04, and control its final concentration to be 320 μg / mL. Observe the changes in the solution color, ultraviolet-visible spectroscopy, and A680 absorbance value of the carbon dot assembly at 37 °C over time, as Figure 2 It should be noted that there are some unclear parts in the original text marked as "破坏了组装体的外部结构,使得组装体从外部解聚,从而导致光谱吸收峰蓝移(680nm移至625nm)。" and "破坏了碳纳米点之间的原来的氢键,使得组装体从内部发生解聚,表现为光谱吸光值迅速降低(A " which might need further clarification for a more accurate translation. The above translation tries to make sense based on the overall context but these parts seem a bit incomplete or unclear in the original.As shown, after analyzing and discussing the above results, a depolymerization diagram is drawn as follows. Figure 5 As shown.

[0136] Figure 2 The effect of the HU system (pH=7.04) on the stability of the carbon nanodot assembly in this embodiment is as follows: (a) The color change of the carbon nanodot assembly solution at different time points under pH=7.04 conditions, the solution changes from blue to dark blue as time progresses; (b) The UV-Vis spectra of the carbon nanodot assembly solution at different time points under pH=7.04 conditions, where the maximum absorption peak at 680nm decreases with time progresses, then shifts from 680nm to 575nm, and finally the absorbance at 575nm increases; (c) The change of absorbance at A680nm of the carbon nanodot assembly solution at different time points under different pH conditions, from left to right, the pH values ​​are 3.04, 7.04 and 8.05, and the final concentration of the carbon nanodot assembly is 320μg / mL.

[0137] At pH 7.04, by Figure 2 As can be seen from the color change of the solution in (a), the solution color changes from blue to dark purple, with the most significant color change occurring after 0.50 hours, rapidly changing from blue to purple. Meanwhile, from... Figure 2 As can be seen in (b), the spectral absorbance value (A) 680 The absorbance decreased slowly from 0.00h to 0.17h, followed by a rapid decrease from 0.17h to 1.00h. Then, a significant blue shift (680nm-575nm) occurred from 1.00h to 3.00h, and finally, the absorbance value (A) decreased from 3.00h to 48.00h. 575 (rises.) Figure 2 As can be seen from (c), A 680 The absorbance value decreased rapidly from 0.17h to 3.00h, from 2.0 to 0.8. Then, from 3h to 48h, the absorbance value remained basically unchanged (A). 680 =0.8).

[0138] Meanwhile, the carbon nanodot assembly was added to a HU buffer system (pH 7.04) and placed at 37°C for 48.00 h. The pH value of the solution was measured before and after the incubation. The results showed that the pH value of the assembly solution was 7.04 at 0.00 h, while it increased to 7.76 after 48.00 h.

[0139] The above results combined Figure 2 It can be seen that at pH 7.04, the solution color of the assembly changes from blue to deep purple, and the spectral absorbance (A) decreases. 680 The absorption peak first decreases, then blue-shifts (680nm-575nm) accompanied by an increase in absorbance (A).575 The pH of the assembly increased slightly during the storage process, from 7.04 to 7.76. This indicates that the depolymerization of the assembly reduces the pH of the [H+] in the solution. + This causes the pH value of the solution to increase.

[0140] To explain the above results, this invention uses a pH calculation formula to analyze the change process of solution pH value, explore the depolymerization mechanism of the assemblies, and thus elucidate their assembly mechanism. In the HU buffer system, the urea carbon nanodots (R-NH2) in the assemblies can react with H+ in the solution. + The reaction produces R-NH3 + ,Right now R-NH3 + Citric acid carbon nanodots (R-COOH) can dissociate to form R-COO. - and H + ,Right now Since the HU buffer system does not contain other ions affecting pH changes, we only need to analyze the dissociation state of citric acid carbon nanoparticles (R-COOH) and the ionization state of urea carbon nanoparticles (R-NH2) in the assembly under different pH conditions. Because the three dissociation constants of -COOH in citric acid are pKa1 = 3.15, pKa2 = 4.76, and pKa3 = 6.40, and because the pH of the solution in which the assembly is located is 7.04, which is a neutral environment, the dissociation of -COOH will only take a tertiary dissociation mode. Therefore, in the pH 7.04 system, this invention uses the tertiary dissociation constant of citric acid, pKa3 = 6.40, for subsequent analysis and discussion. Furthermore, considering that the spectral changes in the assembly are accompanied by pH changes during the depolymerization process, this invention approaches the analysis from the perspective of pH changes, examining the [R-COOH] dissociation process during assembly depolymerization. - ] and [R-NH3 + The pH value changes. Therefore, for ease of analysis, this invention divides the pH into two stages: 7.04 ≤ pH < 7.76 and pH = 7.76, for separate analysis. The specific analysis process is as follows:

[0141] ① 7.04 ≤ pH < 7.76

[0142] 1) Dissociation state of citric acid carbon nanodots (R-COOH):

[0143] According to the pH calculation formula, assuming when

[0144] pH = 7.04 (1),

[0145] pH = pKa3+ lg([R-COO) -] / [R-COOH]) (2),

[0146] In the formula: R-COOH = citric acid carbon nanoparticles, pKa3 = 6.40,

[0147] Substituting (1) into (2), we know that: 7.04 = 6.40 + lg([R-COO) - ] / [R-COOH]), [R-COO - ] / [R-COOH]=0.64>0, [R-COO - ]>[R-COOH].

[0148] 2) Ionization state of urea carbon nanodots (R-NH2):

[0149] Because the solution pH (7.04) is greater than the pKa3 value (6.40) of the citric acid carbon nanodots, the carboxyl group R-COOH of the citric acid carbon nanodots dissociates to form R-COO. - and H + ,Right now At the same time, the generated H + The amino group R-NH2 that causes urea carbon nanodots to ionize, i.e. This causes the equilibrium to shift to the right, thus indicating that the generated [R-NH3] + [H] + [By calculating H in the solution] + Based on the amount added, the remaining amount, and the amount consumed, deduce the concentration of [R-NH3] in the solution. + [] and [R-NH2]. Among them, H + The amount added includes H+ generated from the dissociation of R-COOH. + (H + 1) and the H in the added HCl solution + (H + 2). H + The remaining amount is the H+ remaining in the solution. + (H + 3) This brings the solution to a pH of 7.04. + The consumption amount refers to the amount of R-NH3 produced by the reaction with R-NH2. + H consumed + (H + 4). The specific calculation process is as follows:

[0150] AR-COOH dissociates to produce H₂ + (H + 1):

[0151] By lg([R-COO) -From ] / [R-COOH])=0.64, we can obtain,

[0152] [R-COO - ] / [R-COOH] = 10 0.64 = 4.36 (3),

[0153] [R-COOH] + [R-COO - ] = 8.57 mM (4),

[0154] Substituting (3) into (4), we get [R-COOH] = 1.60 mM, [R-COO - ] = 6.97mM, according to the formula We can obtain: [H] + 1] = [R-COO - = 6.97mM.

[0155] B. The added HCl solution contains H + (H + 2): [HCl] = 6mM, i.e., [H + 2] = 6mM.

[0156] C. Remaining H + (H + 3):

[0157] pH = -lg [H + 3] (5),

[0158] pH = 7.04 (6),

[0159] (6) Substituting into (5), we get [H + 3] = 10 -4 mM.

[0160] DH + Consumption H + (H + 4):

[0161] Added amount = Remaining amount + Consumed amount, i.e., [H] + 1]+[H + 2]=[H + 3]+[H + 4], we can obtain

[0162] [H + 4] = [H + 1]+[H + 2]-[H + 3] = 6.97mM + 6mM – 10 -4 mM = 12.97mM.

[0163] Due to the consumption of H + (H + 4) Used to generate NH3 + ,Right now We can obtain:

[0164] [R-NH3 + ] = [H + 4] = 12.97 mM (7),

[0165] The concentration of urea carbon nanoparticles in the reaction system was 20 mM, and the urea carbon nanoparticles only contained R-NH3. + Both R-NH2 and R-NH2 are in two states, therefore,

[0166] [R-NH3 + ] + [R-NH2] = 20 mM (8),

[0167] Substituting (7) into (8), we get [R-NH2] = 20 – 12.97 = 7.03 mM.

[0168] It is worth noting that at this time, the [R-NH3] in the solution... + The concentration of [R-NH3] is 12.97 mM, while [R-NH2] = 7.03 mM. Therefore, the concentration of [R-NH3] in the solution is... + [R-NH2].

[0169] In summary, when the pH of the solution is 7.04, [R-COO - [R-COOH], [R-NH3] + [R-NH2].

[0170] 3) Based on the above ion changes, elucidate the assembly depolymerization mechanism:

[0171] The calculation results above show that when 7.04 ≤ pH < 7.76, the [R-COO] in the solution... - The presence of [R-COOH] indicates the presence of a large amount of R-COO in the assembly at this point. - The electrostatic repulsion between negative charges causes the hydrogen bonds between citric acid carbon nanodots to break, disrupting the internal structure of the assembly and leading to depolymerization from the inside, as indicated by the spectral absorbance (A). 680 The decrease of [R-NH3] in the solution. At the same time, [R-NH3] in the solution... + The presence of [R-NH2] indicates that as the citric acid carbon nanodots depolymerize, R-NH2 in the solution reacts with a large amount of H+. + R-NH3 was generated +This generates electrostatic repulsion between positive charges, breaking the hydrogen bonds between urea carbon nanodots and citric acid carbon nanodots, causing urea molecules to detach from the surface of citric acid carbon nanodots, thus freeing the urea carbon nanodots in the solution.

[0172] ② pH = 7.76

[0173] 1) Dissociation state of citric acid carbon nanodots (R-COOH):

[0174] According to the pH calculation formula,

[0175] pH = 7.76 (1),

[0176] pH = pKa + lg([R-COO)) - ] / [R-COOH]) (2),

[0177] In the formula: R-COOH = citric acid carbon nanoparticles, pKa3 = 6.40,

[0178] Substituting (1) into (2), we know that: 7.76 = 6.40 + lg([R-COO) - ] / [R-COOH]), lg([R-COO - ] / [R-COOH])=1.36>0, [R-COO - ]>[R-COOH].

[0179] 2) Ionization state of urea carbon nanodots (R-NH2):

[0180] By calculating H in the solution + Based on the amount added, the remaining amount, and the amount consumed, deduce the concentration of [R-NH3] in the solution. + [R-NH2] and [R-NH2]. The specific calculation process is as follows:

[0181] AR-COOH dissociates to produce H₂ + (H + 1):

[0182] By lg([R-COO) - From ] / [R-COOH])=1.36, we can obtain,

[0183] [R-COO - ] / [R-COOH]= 10 1.36 = 22.91 (3),

[0184] [R-COOH] + [R-COO - ] = 8.57 mM (4),

[0185] Substituting (3) into (4), we get [R-COOH] = 0.36 mM, [R-COO - ] = 8.21mM, according to the formula We can obtain: [H] + 1] = [R-COO - =8.21mM.

[0186] B. The added HCl solution contains H + (H + 2): [HCl] = 6mM, i.e., [H + 2] = 6mM.

[0187] C. Remaining H + (H + 3):

[0188] pH = -lg [H + 3] (5),

[0189] pH = 7.76 (6),

[0190] (6) Substituting into (5), we get [H + 3] = 10 -5 mM.

[0191] DH + Consumption H + (H + 4):

[0192] Added amount = Remaining amount + Consumed amount, i.e., [H] + 1]+[H + 2]=[H + 3]+[H + 4], we can obtain

[0193] [H + 4] = [H + 1]+[H + 2]-[H + 3] = 8.21mM + 6mM – 10 -5 mM = 14.21mM.

[0194] Due to the consumption of H + (H + 4) Used to generate NH3 + ,Right now We can obtain:

[0195] [R-NH3 + ] = [H + 4] = 14.21 mM (7),

[0196] The concentration of urea carbon nanoparticles in the reaction system was 20 mM, and the urea carbon nanoparticles only contained R-NH3. + Both R-NH2 and R-NH2 are in two states, therefore,

[0197] [R-NH3 + ] + [R-NH2] = 20 mM (8),

[0198] Substituting (7) into (8), we get [R-NH2] = 20 – 14.21 = 5.79 mM.

[0199] It is worth noting that at this time, the [R-NH3] in the solution... + [R-NH2] = 14.21 mM, while [R-NH3] = 5.79 mM. Therefore, the concentration of [R-NH3] in the solution is... + [R-NH2].

[0200] In summary, when the pH of the solution is 7.76, [R-COO - [R-COOH], [R-NH3] + [R-NH2].

[0201] 3) Based on the above ion changes, elucidate the depolymerization mechanism of the assembly:

[0202] The calculation results above show that when the solution pH is 7.76, the [R-COO] in the solution... - [R-COOH], [R-NH3] + The presence of [R-NH2] indicates the presence of a large amount of R-NH3 in the solution. + and R-COO - And a large amount of R-NH3 + Can with R-COO - Aggregation occurs through electrostatic attraction between positive and negative charges. As hydrogen bonds in the solution are gradually replaced by electrostatic attraction, the original hydrogen-bonded assemblies completely depolymerize, forming new electrostatically mediated assemblies. The hydrogen-bonded assemblies consist of citric acid carbon nanodots, which are relatively large, and their maximum absorption peak is located at 680 nm. The electrostatically mediated assemblies, formed by the aggregation of a small number of free, negatively charged citric acid carbon nanodots by a large number of positively charged urea carbon nanodots, are smaller, and their maximum absorption peak is located at 575 nm. Therefore, the spectral absorption peak shifts from 680 nm to 575 nm. Simultaneously, when the solution pH is 7.04 ≤ pH < 7.76, the [R-COO] in the solution... - ]=6.97mM, [R-NH3 + [R-COO] = 12.97 mM. When the solution pH is 7.76, the concentration of [R-COO] in the solution is... -]=8.21mM, [R-NH3 + [R-COO] = 14.21 mM. Therefore, it can be seen that as the solution pH increases, [R-COO]... - ] and [R-NH3 + The increase in both values ​​leads to a gradual strengthening of the electrostatic attraction between positive and negative charges. This results in a greater number of electrostatically attracted assemblies, which can be reflected in higher spectral absorbance values ​​(A). 575 The increase of ) Furthermore, as electrostatic attraction gradually strengthens, electrostatically mediated assemblies completely replace hydrogen-bonded assemblies, leading to gradual system stability. Therefore, in A 680 The absorbance value change graph shows that the absorbance value remained basically stable within 3h-48h (A). 680 =0.8). In summary, R-COO - and R-NH3 + New assemblies form between these assemblies via electrostatic attraction, and the number of these new assemblies increases with increasing pH, which can be observed as a blue shift in the spectral absorption peak (680nm-575nm) and an increase in absorbance (A). 575 The increase of ).

[0203] Figure 5 This embodiment is a schematic diagram of the decomposition of carbon nanodot assemblies in the HU buffer system at pH 7.04. Figure 5 The schematic diagram illustrates the depolymerization process of carbon nanodot assemblies in an environment of pH 7.04. For example... Figure 5 As shown, in the initial state, the structure of the assembly is stabilized by two types of hydrogen bonds: the first type is the hydrogen bond formed between the carboxyl groups of citrate carbon nanodots, which stabilizes the internal structure of the assembly; the second type is the hydrogen bond formed between the amino groups of urea carbon nanodots and the carboxyl groups of citrate carbon nanodots, which stabilizes the external structure of the assembly. When the solution pH is 7.04 ≤ pH < 7.76, the [R-COO] in the solution... - The presence of [R-COOH] indicates the presence of a large amount of R-COO in the assembly at this point. - This generates electrostatic repulsion between negative charges, breaking the hydrogen bonds between citric acid carbon nanodots, thereby completely destroying the internal structure of the assembly and causing it to depolymerize from the inside, manifested as a decrease in spectral absorbance (A). 680 Meanwhile, in the solution [R-NH3] + The presence of [R-NH2] indicates that there is a large amount of R-NH3 in the solution at this time. + This generates electrostatic repulsion between positively charged particles, breaking the hydrogen bonds between urea carbon nanoparticles and citric acid carbon nanoparticles, thus freeing the urea carbon nanoparticles in the solution. When the solution pH is 7.76, a large amount of R-NH3 is present in the solution. + and R-COO - And a large amount of R-NH3+ Can with R-COO - Aggregation occurs through electrostatic attraction between positive and negative charges. As hydrogen bonds in the solution are gradually replaced by electrostatic attraction, the original hydrogen-bonded assemblies completely depolymerize, forming new electrostatically mediated assemblies. These electrostatically mediated assemblies are smaller than those mediated by hydrogen bonds, resulting in a blue shift of the spectral absorption peak from 680 nm to 575 nm. Simultaneously, as the solution pH increases to 7.76, [R-COO...] - ] and [R-NH3 + The increase in both values ​​leads to a gradual strengthening of the electrostatic attraction between positive and negative charges, resulting in a gradual increase in the number of electrostatically mediated assemblies, which can be reflected in the spectral absorbance (A). 575 The increase of ).

[0204] Example 3

[0205] An experimental method for analyzing the assembly mechanism of carbon nanodots, comprising the following steps:

[0206] The first step involved adding the prepared carbon nanoparticle assembly to an HCl-Urea system with a pH of 8.05, controlling the final concentration to 320 μg / mL. The changes in solution color, UV-Vis spectrophotometry, and A680 absorbance over time at this pH and 37°C were observed. Figure 3 As shown, after analyzing and discussing the above results, a depolymerization diagram is drawn as follows. Figure 6 As shown.

[0207] Figure 3 The effect of the HU system (pH=8.05) on the stability of the carbon nanodot assembly in this embodiment is as follows: (a) The color change of the carbon nanodot assembly solution at different time points under pH=8.05 conditions, the solution changes from blue to pale yellow as time progresses; (b) The UV-Vis spectra of the carbon nanodot assembly solution at different time points under pH=8.05 conditions, where the absorbance value of the maximum absorption peak at 680nm gradually decreases as time progresses; (c) The changes in the absorbance value of the carbon nanodot assembly solution at A680nm at different time points under different pH conditions, from left to right, the pH values ​​are 3.04, 7.04 and 8.05, and the final concentration of the carbon nanodot assembly is 320μg / mL.

[0208] At pH 8.05, by Figure 3 As shown in (a), the solution color changes from blue to light brown, with the most significant change occurring at 1.00 h, where the solution rapidly changes from blue to light blue. Meanwhile, from... Figure 3 As can be seen in (b), the spectral absorbance value (A) 680The absorption peak remained essentially unchanged between 0.00h and 1.00h, and decreased significantly between 1.00h and 48.00h without a blue shift. Figure 3 As can be seen from (c), A 680 The absorbance value decreased rapidly from 1 hour onwards, from 2.0 to 0.2.

[0209] Meanwhile, we added the carbon nanodot assembly to a HU buffer system (pH 8.05) and incubated it at 37°C for 48.00 h. The pH of the solution was measured before and after incubation. The results showed that the pH of the assembly solution was 8.05 at 0.00 h, but increased to 8.30 after 48.00 h.

[0210] The above results combined Figure 3 It can be seen that at pH 8.05, the solution color of the assembly changes from blue to light brown, and the spectral absorbance (A) decreases. 680 The pH only decreased, without a blue shift of the absorption peak. Meanwhile, during the storage process, the pH of the assembly slightly increased from 8.05 to 8.30, which fully demonstrates that the depolymerization of the assembly leads to an increase in [H+] in the solution. + The pH value of the solution decreases, which in turn increases.

[0211] To explain the above results, this invention uses a pH calculation formula to analyze the change process of solution pH value, explore the depolymerization mechanism of the assemblies, and thus elucidate their assembly mechanism. In the HU buffer system, the urea carbon nanodots (R-NH2) in the assemblies can react with H+ in the solution. + The reaction produces R-NH3 + ,Right now Citric acid carbon nanoparticles (R-COOH) can dissociate to form R-COO. - and H + ,Right now Since the HU buffer system does not contain other ions affecting pH changes, it is only necessary to analyze the dissociation state of citric acid carbon nanoparticles (R-COOH) and the ionization state of urea carbon nanoparticles (R-NH2) in the assembly under different pH conditions. Because the three dissociation constants of -COOH in citric acid are pKa1 = 3.15, pKa2 = 4.76, and pKa3 = 6.40, and the pH of the solution containing the assembly is 8.05, which is an alkaline environment, the dissociation of R-COOH will only occur via a tertiary dissociation mechanism. Therefore, in the pH 8.05 system, the tertiary dissociation constant of citric acid, pKa3 = 6.40, is used for subsequent analysis and discussion. Furthermore, considering that the spectral changes during the depolymerization process of the assembly are accompanied by pH changes, the analysis will focus on pH changes to examine the effects of [R-COOH] on the assembly's dissociation process. -] and [R-NH3 + The pH value changes. Therefore, for ease of analysis, the pH was divided into two stages: 8.05 ≤ pH < 8.30 and pH = 8.30, which were analyzed separately. The specific analysis process is shown below:

[0212] ① 8.05 ≤ pH < 8.30

[0213] 1) Dissociation state of citric acid carbon nanodots (R-COOH):

[0214] According to the pH calculation formula, assuming when

[0215] pH = 8.05 (1),

[0216] pH = pKa3 + lg([R-COO)) - ] / [R-COOH]) (2),

[0217] In the formula: R-COOH = citric acid carbon nanoparticles, pKa3 = 6.40,

[0218] Substituting (1) into (2), we know that: 8.05 = 6.40 + lg([R-COO) - ] / [R-COOH]), lg([R-COO - ] / [R-COOH])=1.65>0, [R-COO - ]>[R-COOH].

[0219] 2) Ionization state of urea carbon nanodots (R-NH2):

[0220] Because the solution pH (8.05) is greater than the pKa3 value (6.40) of the citric acid carbon nanodots, the carboxyl group R-COOH of the citric acid carbon nanodots dissociates to form R-COO. - and H + ,Right now At the same time, the generated H + The amino group R-NH2 that causes urea carbon nanodots to ionize, i.e. This causes the equilibrium to shift to the right, thus indicating that the generated [R-NH3] + [H] + [By calculating H in the solution] + Based on the amount added, the remaining amount, and the amount consumed, deduce the concentration of [R-NH3] in the solution. + [] and [R-NH2]. Among them, H + The amount added includes H+ generated from the dissociation of R-COOH. + (H + 1) and the H in the added HCl solution +(H + 2). H + The remaining amount is the H+ remaining in the solution. + (H + 3) This brings the solution to a pH of 8.05. + The consumption amount refers to the amount of R-NH3 produced by the reaction with R-NH2. + H consumed + (H + 4). The specific calculation process is as follows:

[0221] AR-COOH dissociates to produce H₂ + (H + 1):

[0222] By lg([R-COO) - From ] / [R-COOH])=1.65, we can obtain,

[0223] [R-COO - ] / [R-COOH] = 10 1.65 = 44.67 (3),

[0224] [R-COOH] + [R-COO - ] = 8.57 mM (4),

[0225] Substituting (3) into (4), we get [R-COOH] = 0.19 mM, [R-COO - ] = 8.38mM, according to the formula We can obtain: [H] + 1] = [R-COO - = 8.38mM.

[0226] B. The added HCl solution contains H + (H + 2): [HCl] = 0 mM, i.e., [H + 2] = 0mM.

[0227] C. Remaining H + (H + 3):

[0228] pH = -lg [H + 3] (5),

[0229] pH = 8.05 (6),

[0230] (6) Substituting into (5), we get [H + 3] = 10 -5 mM.

[0231] DH +Consumption H + (H + 4):

[0232] Added amount = Remaining amount + Consumed amount, i.e., [H] + 1]+[H + 2]=[H + 3]+[H + 4], we can obtain

[0233] [H + 4] = [H + 1]+[H + 2]-[H + 3]=8.38mM+0mM–10 -5 mM = 8.38mM.

[0234] Due to the consumption of H + (H + 4) Used to generate NH3 + ,Right now We can obtain:

[0235] [R-NH3 + ] = [H + 4] = 8.38 mM (7),

[0236] The concentration of urea carbon nanoparticles in the reaction system was 20 mM, and the urea carbon nanoparticles only contained R-NH3. + Both R-NH2 and R-NH2 are in two states, therefore,

[0237] [R-NH3 + ] + [R-NH2] = 20 mM (8),

[0238] Substituting (7) into (8), we get [R-NH2] = 20 – 8.38 = 11.62 mM.

[0239] It is worth noting that at this time, the [R-NH3] in the solution... + The concentration of [R-NH3] is 8.38 mM, while [R-NH2] = 11.62 mM. Therefore, the concentration of [R-NH3] in the solution is... + ]<[R-NH2].

[0240] In summary, when the pH of the solution is 8.05, [R-COO - [R-COOH], [R-NH3] + ]<[R-NH2].

[0241] ② pH = 8.30

[0242] 1) Dissociation state of citric acid carbon nanodots (R-COOH):

[0243] According to the pH calculation formula, when

[0244] pH = 8.30 (1),

[0245] pH = pKa3+ lg([R-COO) - ] / [R-COOH]) (2),

[0246] In the formula: R-COOH = citric acid carbon nanoparticles, pKa3 = 6.40,

[0247] Substituting (1) into (2), we know that: 8.30 = 6.40 + lg([R-COO) - ] / [R-COOH]), lg([R-COO - ] / [R-COOH])=1.90>0, [R-COO - ]>[R-COOH].

[0248] 2) Ionization state of urea carbon nanodots (R-NH2):

[0249] By calculating H in the solution + Based on the amount added, the remaining amount, and the amount consumed, deduce the concentration of [R-NH3] in the solution. + [R-NH2] and [R-NH2]. The specific calculation process is as follows:

[0250] AR-COOH dissociates to produce H₂ + (H + 1):

[0251] By lg([R-COO) - From ] / [R-COOH])=1.90, we can obtain,

[0252] [R-COO - ] / [R-COOH] = 10 1.90 = 79.43 (3),

[0253] [R-COOH] + [R-COO - ] = 8.57 mM (4),

[0254] Substituting (3) into (4), we get [R-COOH] = 0.11 mM, [R-COO - ] = 8.46mM, according to the formula We can obtain: [H] + 1] = [R-COO - = 8.46mM.

[0255] B. The added HCl solution contains H + (H+ 2): [HCl] = 0 mM, i.e., [H + 2] = 0mM.

[0256] C. Remaining H + (H + 3):

[0257] pH = -lg [H + 3] (5),

[0258] pH = 8.30 (6),

[0259] (6) Substituting into (5), we get [H + 3] = 10 -5 mM.

[0260] DH + Consumption H + (H + 4):

[0261] Added amount = Remaining amount + Consumed amount, i.e., [H] + 1]+[H + 2]=[H + 3]+[H + 4], we can obtain

[0262] [H + 4] = [H + 1]+[H + 2]-[H + 3]=8.46mM+0mM–10 -5 mM = 8.46mM.

[0263] Due to the consumption of H + (H + 4) Used to generate NH3 + ,Right now We can obtain:

[0264] [R-NH3 + ] = [H + 4] = 8.46 mM (7),

[0265] The concentration of urea carbon nanoparticles in the reaction system was 20 mM, and the urea carbon nanoparticles only contained R-NH3. + Both R-NH2 and R-NH2 are in two states, therefore,

[0266] [R-NH3 + ] + [R-NH2] = 20 mM (8),

[0267] Substituting (7) into (8), we get [R-NH2] = 20 – 8.46 = 11.54 mM.

[0268] It is worth noting that at this time, the [R-NH3] in the solution... + [R-NH2] = 8.38 mM, while [R-NH3] = 11.54 mM. Therefore, the concentration of [R-NH3] in the solution is... + ]<[R-NH2].

[0269] In summary, when the pH of the solution is 8.30, [R-COO - [R-COOH], [R-NH3] + ]<[R-NH2].

[0270] 3) Based on the above particle changes, elucidate the assembly depolymerization mechanism:

[0271] The calculation results above show that when the solution pH is 8.05 ≤ pH < 8.30, the [R-COO] in the solution... - ](8.38mM)>[R-COOH](0.19mM),[R-NH3 + [R-NH2] (8.38 mM) < [R-NH2] (11.38 mM), while when the solution pH = 8.30, the concentration of [R-COO2] in the solution is higher. - ](8.46mM)>[R-COOH](0.11mM),[R-NH3 + [R-NH2] (8.46 mM) < [R-NH2] (11.54 mM), indicating that as the pH of the solution increases, the concentration of [R-COO2] in the solution remains constant. - [R-COOH], [R-NH3] + ]<[R-NH2], and [R-COO - The levels of [R-COO] and [R-NH2] did not increase significantly, indicating that the solution states were similar throughout, therefore they were discussed together. When the solution pH was 8.05 ≤ pH ≤ 8.30, the [R-COO] level in the solution was... - The presence of [R-COOH] indicates the presence of a large amount of R-COO in the assembly at this point. - This generates electrostatic repulsion between negative charges, breaking the hydrogen bonds between citric acid carbon nanodots, thereby completely destroying the internal structure of the assembly and causing it to depolymerize from the inside, as indicated by the spectral absorbance (A). 680 The decrease of [R-NH3] in the solution. At the same time, [R-NH3] in the solution... + The presence of [R-NH2] indicates that the urea carbon nanoparticles in the solution are predominantly in the form of R-NH2. The abundance of R-NH2 allows for the formation of stable hydrogen bonds on the exterior of the assembly, ensuring the stability of the external structure and preventing a blue shift in the absorption peak. Conversely, the presence of abundant R-COO... - Unable to react with small amounts of R-NH3 +The aggregation of citric acid carbon nanodots through electrostatic attraction between positive and negative charges prevents the formation of new assemblies mediated by electrostatic attraction, allowing them to remain free in the solution. This is reflected in the spectral absorbance value (A). 680 The absorption peak decreases without a blue shift.

[0272] Figure 6 This is a schematic diagram of the decomposition of carbon nanodot assemblies in the HU buffer system of this embodiment at pH=8.05. Figure 6 The schematic diagram illustrates the depolymerization process of carbon nanodot assemblies in an environment of pH 8.05. For example... Figure 6 As shown, in the initial state, the structure of the assembly is stabilized by two types of hydrogen bonds: the first type is the hydrogen bond formed between the carboxyl groups of citrate carbon nanodots, which stabilizes the internal structure of the assembly; the second type is the hydrogen bond formed between the amino groups of urea carbon nanodots and the carboxyl groups of citrate carbon nanodots, which stabilizes the external structure of the assembly. When the solution has a pH of 8.05 ≤ pH ≤ 8.30, the [R-COO] in the solution... - The presence of [R-COOH] indicates the presence of a large amount of R-COO in the assembly at this point. - The electrostatic repulsion between negative charges leads to the breakage of hydrogen bonds between citric acid carbon nanodots, thereby completely destroying the internal structure of the assembly and causing it to depolymerize from the inside, manifested as a decrease in spectral absorbance (A). 680 Meanwhile, in the solution [R-NH3] + The presence of [R-NH2] indicates the presence of a large amount of R-NH2 in the solution. A large amount of R-NH2 can stabilize the external structure of the assembly, while a large amount of R-COO... - The inability to aggregate with large amounts of R-NH2 through electrostatic attraction between positive and negative charges prevents the formation of new electrostatically mediated assemblies, causing the citric acid carbon nanodots to remain free in the solution, resulting in a decrease in spectral absorbance (A). 680 (And the absorption peak does not undergo a blue shift.)

[0273] In summary, non-covalent assembly in the assembly effect has advantages such as high assembly efficiency and a wide range of bonding modes. However, how non-covalent bonds effectively assemble carbon nanodots during the synthesis process remains unclear. This invention takes hydrogen-bonded assemblies of carbon nanodots as an example. By changing the pH, molecular structure, ionic strength, concentration, and ambient temperature of the buffer solution, this invention designs and constructs an experimental method to analyze the assembly mechanism of carbon nanodots. It systematically elucidates the changes in solution color, UV-Vis spectrophotometry, and absorbance at A680, thereby analyzing the depolymerization process of the assemblies and elucidating their assembly mechanism. Taking the hydrochloric acid-urea (HCl-Urea) system as an example, the structure of the carbon nanodot assembly is stabilized by two types of hydrogen bonds: the first is the hydrogen bond formed between the carboxyl groups of citrate carbon nanodots, which stabilizes the internal structure of the assembly; the second is the hydrogen bond formed between the amino groups of urea carbon nanodots and the carboxyl groups of citrate carbon nanodots, which stabilizes the external structure of the assembly. This invention provides a novel experimental and analytical method for elucidating the assembly mechanism of carbon nanodots. It can be extended to the study of other assembly systems and lays a solid foundation for the widespread application of assembly systems.

[0274] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An experimental method for analyzing the assembly mechanism of carbon nanodots, characterized in that, Includes the following steps: (1) The carbon nanodot assemblies were added to buffer systems with different pH values, molecular structures and ionic strengths respectively; (2) Observe and record the color change of the carbon nanodot assembly, the position shift of the characteristic absorption peak in the ultraviolet-visible spectrophotometer, and the change in the absorbance value of the characteristic absorption peak in the ultraviolet-visible spectrophotometer; (3) In different buffer systems, the dissociation state of acidic and basic functional groups was analyzed using the pH calculation formula; (4) Combine steps (2) and (3) to analyze the depolymerization process of the carbon nanodot assembly and analyze the assembly mechanism; The molecular structure of the buffer system includes any one or more of sodium ions, potassium ions, hydrogen phosphate ions, dihydrogen phosphate ions, HEPES, Tris, or chloride ions. The pH calculation formula is: pH = pKa + lg([R-COO) / 2) - ] / [R-COOH], where R-COOH is the acidic functional group in the carbon nanodot assembly, and Ka is the dissociation constant of the acidic functional group.

2. The experimental method for analyzing the assembly mechanism of carbon nanodots according to claim 1, characterized in that, The buffer system includes any one of the following: hydrochloric acid-urea buffer system, hydroxyethylpiperazine ethanethioic acid (HEPES) buffer system, phosphate buffer system, or tris-hydroxymethylaminomethane hydrochloride (Tris-HCl) buffer system.

3. The experimental method for analyzing the assembly mechanism of carbon nanodots according to claim 1, characterized in that, The pH value of the buffer system includes 2.5-3.5, 6.5-7.4, or 7.5-8.

5.

4. The experimental method for analyzing the assembly mechanism of carbon nanodots according to claim 1, characterized in that, The ionic strength of the buffer system is 0 mM-250 mM.

5. The experimental method for analyzing the assembly mechanism of carbon nanodots according to claim 1, characterized in that, The shift in the position of the characteristic absorption peak in the ultraviolet-visible spectrophotometer is called a blue shift, and the blue shift range is 10 nm-200 nm.

6. The experimental method for analyzing the assembly mechanism of carbon nanodots according to claim 1, characterized in that, The absorbance value of the characteristic absorption peak in the ultraviolet-visible spectrophotometer decreases, ranging from 0.1 to 0.

8.

7. The experimental method for analyzing the assembly mechanism of carbon nanodots according to claim 1, characterized in that, The dissociation state of the basic functional group is formed by the dissociation of the acidic functional group [H]. + ], buffer ions dissociated from [H] + The pH value of the buffer system is determined by the pH value of the buffer solution.

8. The experimental method for analyzing the assembly mechanism of carbon nanodots according to claim 1, characterized in that, The characteristic absorption peak of the ultraviolet-visible spectrophotometer is located at 520 nm - 680 nm.

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