A water-sensitive carbon dot and its preparation method and application

Abstract

The present invention relates to water-sensitive carbon dots and a preparation method thereof, and relates to the field of carbon nanotechnology. The preparation method of the present invention is as follows: carbon source A and carbon source B are added to a solvent to obtain a mixed solution, the mixed solution is subjected to a hydrothermal reaction, the mixed solution is removed after the reaction is complete, the mixed solution is centrifuged to obtain a supernatant, the supernatant is mixed with water, and then centrifuged, and the filtrate is removed to obtain water-sensitive carbon dots. The present invention provides water-sensitive carbon dots, a preparation method thereof, and applications thereof. The water-sensitive carbon dots prepared by the present invention via a hydrothermal method have a simple preparation method and low cost. The water-sensitive carbon dots can be well dispersed in ethylene glycol and applied to detect the water content in ethylene glycol, thus having high practical value and good economic benefits.

Description

Technical Field

[0001] The present invention relates to the field of carbon nanotechnology, and in particular to water-sensitive carbon dots and a preparation method and application thereof. Background Art

[0002] Ethylene glycol (EG) is an important organic chemical raw material, primarily used in the production of polyester, antifreeze, and fine chemicals. Traditionally, EG is produced via the ethylene process, and its price is significantly affected by fluctuations in oil prices. With the development of the polyester industry, demand for EG has increased significantly. Currently, coal-based EG technology has captured a significant market share both domestically and internationally, and its market share is gradually expanding with the development of the coal chemical industry. Coal-to-EG technology primarily utilizes the oxalate hydrogenation process to produce EG. This reaction route differs from the traditional ethylene process, and side reactions generate new impurities. The emergence of these new impurities has had a significant impact on product purity, UV values, and even the downstream polyester industry, garnering widespread industry attention. Therefore, developing highly sensitive methods for detecting impurities in EG is of great significance and practical value.

[0003] However, existing standards for ethylene glycol purity and impurity testing only provide analytical methods for alcohols such as diethylene glycol, triethylene glycol, and tetraethylene glycol. Chromatographic methods have also been developed to detect impurities such as 1,2-butanediol, 1,4-butanediol, 1,2-hexanediol, and ethylene carbonate. However, these methods suffer from limited detectable impurities, high detection limits, and the need for expensive precision instrumentation, making them unable to meet the analytical needs of the polyester industry for ethylene glycol. Water has been shown to be an impurity that affects the UV value of coal-based ethylene glycol, but a simple, rapid, and efficient method for determining water content in ethylene glycol is lacking. Fluorescence detection methods based on specific fluorescent materials are widely used in environmental monitoring and sensing due to their fast response, high signal-to-noise ratio, and excellent sensitivity. Various methods for detecting water content in organic solvents based on fluorescent materials have been developed, but high-performance fluorescent materials suitable for water content detection in ethylene glycol are lacking.

[0004] Carbon dots (CDs) have attracted considerable attention in fields such as environmental monitoring, sensing, and cell imaging due to their unique physicochemical properties, including rich energy levels, tunable emission, good biocompatibility, and diverse luminescence patterns (DOI: 10.1016 / j.cej.2021.128999). Through heteroatom doping and surface functional group manipulation, CDs exhibit diverse luminescence properties, including excitation-dependent luminescence, excitation-independent luminescence, and aggregation-induced luminescence (AILE). Among them, AILE CDs can overcome the aggregation-induced luminescence quenching effect of CDs and have been widely used in solid-state luminescence. Therefore, their luminescence properties can be manipulated by adjusting the aggregation and dispersion state of AILE CDs (DOI: 10.1021 / acssuschemeng.0c08652). By altering the aggregation and dispersion state of AILE CDs with impurity solvents, CD fluorescence can be turned on and off, potentially enabling efficient quantitative analysis of impurity solvents. However, the luminescence of existing carbon dots is difficult to adjust due to the high viscosity of EG and the polyhydroxyl environment, which makes the development and design of carbon dots suitable for water content detection in EG still a challenge. Summary of the Invention

[0005] To address the above technical issues, the present invention provides water-sensitive carbon dots, their preparation method, and applications. The water-sensitive carbon dots are prepared by a simple, low-cost hydrothermal method. They can be well dispersed in ethylene glycol and applied to detect the water content in ethylene glycol, demonstrating high practical value and excellent economic benefits.

[0006] The technical solution of the present invention to solve the above technical problems is as follows:

[0007] The first object of the present invention is to provide a method for preparing water-sensitive carbon dots, comprising the following steps: adding carbon source A and carbon source B to a solvent to obtain a mixed solution, subjecting the mixed solution to a hydrothermal reaction, taking out the mixed solution after the reaction is completed, centrifuging the mixed solution to obtain a supernatant, mixing the supernatant with water and then centrifuging, removing the filtrate, and obtaining water-sensitive carbon dots.

[0008] The beneficial effects of the present invention are as follows: the present invention prepares water-sensitive carbon dots by a hydrothermal method, the preparation method is simple, the cost is low, the size distribution of the prepared carbon dots is uniform, and the preparation process is simple and easy to operate, which is conducive to large-scale production. It can be applied to the detection of water content in polyester-grade ethylene glycol, and has high practical value and good economic benefits.

[0009] Furthermore, the usage ratio of the carbon source A, the carbon source B, and the solvent is (0.1-0.3) mol: (0.1-0.3) mol: 50 mL.

[0010] Furthermore, the carbon source A includes at least one of citric acid and sodium citrate; and the carbon source B is 1,1'-binaphthyl-2,2'-diamine.

[0011] Preferably, the carbon source A is citric acid, and the carbon source B is 1,1'-binaphthyl-2,2'-diamine.

[0012] Furthermore, the solvent is glacial acetic acid.

[0013] The beneficial effect of adopting the above further scheme is: the present invention uses citric acid and 1,1'-binaphthyl-2,2'-diamine as starting materials, adopts a hydrothermal method to synthesize water-sensitive luminescent carbon dots, and uses them as fluorescent probes for detecting water content in ethylene glycol.

[0014] Furthermore, the centrifugal speed is 8000-10000 r / min, and the centrifugal time is 5-15 min.

[0015] Furthermore, the volume ratio of the supernatant to water is 1:(2-4).

[0016] The second object of the present invention is to provide a water-sensitive carbon dot.

[0017] Furthermore, the average particle size of the water-sensitive carbon dots is 2-4 nm.

[0018] The beneficial effects of adopting the above further scheme are: the carbon dots synthesized by the present invention have uniform size distribution, and the preparation process is simple and easy to operate, which is conducive to large-scale production.

[0019] The third object of the present invention is to provide an application of water-sensitive carbon dots, wherein the water-sensitive carbon dots are used as fluorescent probes for detecting the water content in ethylene glycol.

[0020] The present invention has the following beneficial effects: the carbon dots can be well dispersed in ethylene glycol. While the fluorescence of the carbon dots in ethylene glycol is weak, its intensity increases with increasing water content in the ethylene glycol solution, exhibiting a good linear relationship within the water content range of 0 to 0.284%, and exhibiting high detection sensitivity. Compared to other fluorescence detection methods, the present invention has a higher signal-to-noise ratio and higher detection sensitivity. It can be applied to the detection of water content in polyester-grade ethylene glycol, possessing high practical value and good economic benefits.

[0021] Furthermore, the detection of the water content in the ethylene glycol is a quantitative detection, and the volume fraction of water in the ethylene glycol is in the range of 0 to 0.284%. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The fluorescence excitation and emission spectra of the water-sensitive carbon dots in Example 1;

[0023] Figure 2is the UV-visible absorption spectrum of the carbon dots of Example 1;

[0024] Figure 3 This is a transmission electron microscopy image of the carbon dots of Example 3;

[0025] Figure 4 This is the particle size distribution diagram of the carbon dots in Example 3;

[0026] Figure 5 This is a high-resolution transmission electron microscopy image of the carbon dots of Example 3;

[0027] Figure 6 The full X-ray photoelectron spectrum and high-resolution C1s, N1s, and O1s images of the carbon dots of Example 3 are shown;

[0028] Figure 7 This is a graph showing the change in fluorescence intensity of the carbon dots in Example 3;

[0029] Figure 8 This is a linear fitting relationship diagram of the carbon dots in Example 3. DETAILED DESCRIPTION

[0030] The principles and features of the present invention are described below. The examples are only used to explain the present invention and are not intended to limit the scope of the present invention. Where specific techniques or conditions are not specified in the examples, the techniques or conditions described in the literature in this field or the product instructions are used. Where the manufacturers of the reagents or instruments used are not specified, they are all conventional products that can be purchased through regular channels.

[0031] Example 1: Preparation of water-sensitive carbon dots

[0032] (1) Add 50 mL of glacial acetic acid to a 100 mL beaker, then add 0.1 mol of citric acid and 0.1 mol of 1,1'-binaphthyl-2,2'-diamine, respectively, and stir magnetically for 5 min to obtain a colorless, clear mixed solution;

[0033] (2) The mixed solution was placed in a polytetrafluoroethylene-lined autoclave and reacted at 180°C for 10 h. After the reaction was completed, the mixture was centrifuged at 10,000 rpm and the supernatant was collected for later use.

[0034] (3) The supernatant and deionized water were mixed in a volume ratio of 1:3, and the precipitate was collected by centrifugation. The precipitate was freeze-dried in vacuum to obtain brown solid carbon dot powder.

[0035] The carbon dot powder prepared in Example 1 was dissolved in glacial acetic acid to obtain a colorless solution with a concentration of 8 mg / mL, which was used as a mother solution. The obtained mother solution was tested for fluorescence properties using a steady-state transient fluorescence spectrometer (FS5, Edinburgh, UK) and for UV-visible absorption spectrum using a UV-visible spectrophotometer (UV2600; Shimadzu). The results are shown in Figure 2. Figure 1 、 Figure 2 As shown:

[0036] Figure 1 The fluorescence excitation and emission spectra of the water-sensitive carbon dots prepared in Example 1 show that the water-sensitive carbon dots have weak fluorescence, with a maximum excitation wavelength of 340 nm and a maximum emission wavelength of 392 nm.

[0037] Figure 2 This is the UV-visible absorption spectrum of the water-sensitive carbon dots prepared in Example 1. The UV-visible absorption spectrum of the carbon dot solution has obvious absorption at around 240 nm and 350 nm.

[0038] Example 2: Preparation of water-sensitive carbon dots

[0039] (1) Add 40 mL of glacial acetic acid to a 100 mL beaker, then add 0.1 mol of citric acid and 0.1 mol of 1,1'-binaphthyl-2,2'-diamine, respectively, and stir magnetically for 5 min to obtain a colorless, clear mixed solution;

[0040] (2) The mixed solution was placed in a polytetrafluoroethylene-lined autoclave and reacted at 180°C for 10 h. After the reaction was completed, the mixture was centrifuged at 6000 r / min and the supernatant was collected for later use.

[0041] (3) The supernatant and deionized water were mixed in a volume ratio of 1:3, and the precipitate was collected by centrifugation. The precipitate was freeze-dried in vacuum to obtain brown carbon dot powder.

[0042] Example 3: Preparation of water-sensitive carbon dots

[0043] (1) Add 0.1 mol of citric acid, 0.1 mol of 1,1'-binaphthyl-2,2'-diamine, and 50 mL of glacial acetic acid to a 100 mL beaker and stir magnetically for 5 min to obtain a colorless, clear mixed solution;

[0044] (2) The mixed solution was placed in a polytetrafluoroethylene-lined autoclave and reacted at 180°C for 10 h. After the reaction was completed, the mixture was centrifuged at 8000 r / min and the supernatant was collected for later use;

[0045] (3) The supernatant and deionized water were mixed in a volume ratio of 1:3, and the precipitate was collected by centrifugation. The precipitate was freeze-dried in vacuum to obtain brown carbon dot powder.

[0046] The supernatant prepared in step (2) of Example 3 was subjected to high-resolution transmission electron microscopy testing. The results were as follows: Figure 3-5 As shown; the carbon dot powder obtained in step (3) of Example 3 was then taken and XPS test was performed using an X-ray photoelectron spectrometer (Kratos AXISUltra DLD, Kratos Analytical Ltd). The results are as follows Figure 6 As shown; the carbon dot powder prepared in Example 3 was dissolved in glacial acetic acid to obtain a colorless solution, which was used as a mother liquor (concentration of 8 mg / mL) for standby use. 200 μL of the mother liquor was added to 2.8 mL of polyester-grade ethylene glycol to obtain a colorless and transparent carbon dot ethylene glycol solution, and its fluorescence intensity was detected; 0-0.284% deionized water was then added to each solution, and the fluorescence performance was tested using a steady-state transient fluorescence spectrometer (FS5, Edinburgh, UK). The results are shown in FIG. Figure 7-8 shown.

[0047] Depend on Figure 3-8 We can get:

[0048] (1) Figure 3-5 As shown, the carbon dots obtained in Example 3 have a nearly spherical appearance (e.g. Figure 3 ), with an average particle size of about 2.75 nm (e.g. Figure 4 ), the interplanar spacing of carbon dots is 0.21 nm (such as Figure 5 ), which belong to the 100 crystal planes of graphitized carbon, proving that the prepared materials are carbon dots.

[0049] (2) Figure 6 As shown, the XPS spectrum of the carbon dot powder prepared in Example 3 shows that the carbon dots contain C (83.64%), N (8.96%), and O (7.41%) elements, and the high-resolution C1s, N1s, and O1s prove that the carbon dots contain a large number of hydroxyl, amino, and carbonyl functional groups.

[0050] (3) Figure 7-8 As shown in Figure 2, the maximum excitation wavelength is 340 nm, and the maximum emission wavelength is 392 nm. The fluorescence intensity of the carbon dot ethylene glycol solution increases significantly with the increase of water content. The optimal excitation wavelength is 340 nm, and the optimal emission wavelength is 392 nm (as shown in Figure 2). Figure 7 After adding 0-0.284% deionized water, the fluorescence intensity of the carbon dot ethylene glycol solution at an emission wavelength of 392 nm has a good linear relationship with different contents of deionized water. The fitting equation is y=0.513+1.726C(Water%), and the correlation coefficient R 2 =0.998(as Figure 8 ).

[0051] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. An application of water-sensitive carbon dots, characterized in that: Water-sensitive carbon dots were used as fluorescent probes to detect the water content in ethylene glycol. The detection of water content in the ethylene glycol is a quantitative detection, and the volume fraction of water in the ethylene glycol is in the range of 0 to 0.284%; The method for preparing water-sensitive carbon dots comprises the following steps: adding carbon source A and carbon source B to a solvent to obtain a mixed solution, subjecting the mixed solution to a hydrothermal reaction, removing the mixed solution after the reaction is completed, centrifuging the mixed solution to obtain a supernatant, mixing the supernatant with water and centrifuging the mixture, and removing the filtrate to obtain water-sensitive carbon dots; The carbon source A is at least one of citric acid and sodium citrate; and the carbon source B is 1,1'-binaphthyl-2,2'-diamine.

2. The use of a water-sensitive carbon dot according to claim 1, characterized in that: The usage ratio of the carbon source A, the carbon source B, and the solvent is (0.1-0.3) mol: (0.1-0.3) mol: 50 mL.

3. The use of water-sensitive carbon dots according to claim 2, characterized in that: The solvent is glacial acetic acid.

4. The use of water-sensitive carbon dots according to claim 1, characterized in that: The centrifugal speed is 8000-10000 r / min, and the centrifugal time is 5-15 min.

5. The use of water-sensitive carbon dots according to claim 1, characterized in that: The volume ratio of the supernatant to water is 1:(2-4).

6. The use of water-sensitive carbon dots according to claim 1, characterized in that: The average particle size of the water-sensitive carbon dots is 2-4 nm.

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