A method for preparing carbon quantum dot nanomaterials and its application

Abstract

This invention relates to the field of carbon quantum dot nanomaterials technology, and in particular to a method for preparing carbon quantum dot nanomaterials and their applications. The method includes the following steps: (1) mixing and pyrolyzing anhydrous citric acid and Na₂SO₄ to obtain a brownish-black solid; (2) dissolving the brownish-black solid in water, then adding NaOH solution dropwise and adjusting the pH to 7 to obtain a mixed solution; (3) adding ethanol to the mixed solution, stirring and mixing, allowing it to stand, taking the lower layer of black viscous liquid, diluting it with water, adding ethanol again and stirring, repeating this process multiple times, then adding the black viscous liquid dropwise to methanol to form a brown precipitate; filtering and washing with methanol, repeating the filtration process multiple times, and then vacuum drying the obtained solid to obtain carbon quantum dot nanomaterials. The method provided by this invention, by adding Na₂SO₄ to assist the pyrolysis of anhydrous citric acid, obtains carbon quantum dots rich in carboxyl groups, thereby improving the osmotic pressure and forward osmotic water absorption capacity of the carbon quantum nanomaterials.

Description

Technical Field

[0001] This invention relates to the field of carbon quantum dot nanomaterials technology, and in particular to a method for preparing carbon quantum dot nanomaterials and their applications. Background Technology

[0002] Forward osmosis, as a spontaneous membrane treatment technology, has promising applications. Forward osmosis water treatment technology mainly consists of three parts: a selectively permeable membrane, a feed solution, and a draw solution. In the forward osmosis water treatment process, selecting a draw solution with high osmotic pressure and easy separation is particularly important.

[0003] Carbon quantum dots possess excellent optical properties, good water solubility, low toxicity, environmental friendliness, wide availability of raw materials, low cost, and good biocompatibility, making them an excellent material for forward osmosis absorption solutions. However, existing methods for preparing carbon quantum dot materials result in low carboxyl groups in the carbon quantum dots, leading to low water absorption rates and hindering their practical applications. Therefore, this invention is proposed. Summary of the Invention

[0004] The first objective of this invention is to provide a method for preparing carbon quantum dot nanomaterials, wherein the carbon quantum dot nanomaterials prepared by this method contain abundant carboxyl groups. The second objective of this invention is to provide an application of carbon quantum dot nanomaterials as a water-absorbing liquid, exhibiting a high water-absorbing rate.

[0005] This invention provides a method for preparing carbon quantum dot nanomaterials, comprising the following steps:

[0006] (1) Citric acid pyrolysis: Anhydrous citric acid and Na2SO4 are mixed and pyrolyzed at 180-210℃ to obtain a brownish-black solid;

[0007] (2) Neutralization: Dissolve the brownish-black solid in water, then add NaOH solution dropwise and adjust the pH to 7 to obtain a mixed solution;

[0008] (3) Refining: Add ethanol to the mixed solution, stir and mix, let stand, take the lower layer of black viscous liquid, dilute with water, add ethanol and stir and mix again. Repeat this process several times, then add the black viscous liquid dropwise to methanol to form a brown precipitate; filter the brown precipitate and wash it with methanol. After repeated filtration, vacuum dry the obtained solid to obtain carbon quantum dot nanomaterials.

[0009] Preferably, the mass ratio of anhydrous citric acid to Na2SO4 in step (1) is 20:(0.1-1). More preferably, it is 20:1.

[0010] Preferably, the pyrolysis time in step (1) is 150-360 minutes. More preferably, it is 200 minutes.

[0011] Preferably, the concentration of the NaOH solution in step (2) is 8-10 mol / L. More preferably, it is 10 mol / L. The added NaOH solution can neutralize the carboxyl groups to form sodium carboxylate, resulting in faster dissolution, higher solubility, and higher osmotic pressure.

[0012] Preferably, the volume of water added in step (3) is 1-1.2 times the volume of the black viscous liquid.

[0013] Preferably, the carbon quantum dot nanomaterials prepared in step (3) have a size of 30-50 nm.

[0014] Preferably, the vacuum drying temperature in step (3) is 40-50℃.

[0015] This invention provides the application of carbon quantum dot nanomaterials obtained by the above preparation method as a forward osmosis draw solution.

[0016] In summary, compared with the prior art, the present invention has the following advantages:

[0017] The method for preparing carbon quantum dot nanomaterials provided by this invention involves adding Na2SO4 to assist in the pyrolysis of anhydrous citric acid, thereby obtaining carbon quantum dots rich in carboxyl groups. At the same time, some sulfate ions of Na2SO4 can also be loaded on the surface of carbon quantum dots, and the carboxyl groups hydrolyze. The sodium carboxylate formed therein hydrolyzes faster, providing osmotic pressure and improving the osmotic pressure and forward osmotic water absorption capacity of the carbon quantum nanomaterials. The water absorption rate is 1.57 times that of the commonly used 2 mol / L NaCl absorption solution.

[0018] The method for preparing carbon quantum nanomaterials provided by this invention is simple and easy to operate, with low raw material costs, and has the advantages of low toxicity and environmental friendliness. Attached Figure Description

[0019] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0020] Figure 1 The image shows the FTIR spectrum of the carbon quantum dot nanomaterials prepared in the embodiments of the present invention.

[0021] Figure 2 The images show the XRD patterns of carbon quantum dot nanomaterials prepared in the embodiments and comparative examples of the present invention; where (a) is the comparative example and (b) is the embodiment.

[0022] Figure 3The image shows a TEM image of the carbon quantum dot nanomaterials prepared in an embodiment of the present invention.

[0023] Figure 4 The images show the aqueous solution of carbon quantum dot nanomaterials prepared in various states according to embodiments of the present invention; wherein (a) is the aqueous solution of carbon quantum dot nanomaterials, (b) is under 365nm ultraviolet light irradiation, and (c) is under 365nm ultraviolet light irradiation with FeCl3 added.

[0024] Figure 5 This is a comparison chart showing the absorption rate of carbon quantum dot nanomaterials prepared in the embodiments and comparative examples of the present invention. Detailed Implementation

[0025] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0027] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the stated features. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified. Furthermore, the terms "installed," "connected," and "linked" should be interpreted broadly; for example, they may refer to a fixed connection, a detachable connection, or an integral connection; they may refer to a mechanical connection or an electrical connection; they may refer to a direct connection or an indirect connection through an intermediate medium; and they may refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0028] Example

[0029] A method for preparing carbon quantum dot nanomaterials, the specific process of which is as follows:

[0030] (1) Citric acid pyrolysis

[0031] Weigh 5g of Na2SO4 and 100g of anhydrous citric acid and add them to a 500mL beaker. Mix well, cover the beaker with a petri dish, and place it in an oven. Keep it at 200℃ for 200min to obtain a brownish-black solid through pyrolysis.

[0032] (2) Neutralization

[0033] Dissolve the brownish-black solid from step (1) in an appropriate amount of water, then add 10 mol / L NaOH solution dropwise to adjust the pH to 7, and obtain a mixed solution.

[0034] (3) Refined

[0035] Add ethanol to the mixed solution, stir and mix, let stand, remove the supernatant, keep the lower black viscous liquid, add an equal volume of water to the black viscous liquid to dilute, then add ethanol and stir to mix. Repeat this process 3-5 times to obtain a black viscous liquid.

[0036] A black, viscous liquid was added dropwise to methanol, forming a brown precipitate. The precipitate was filtered and then washed with methanol. This filtration process was repeated 2-3 times. The resulting solid was then vacuum-dried at 40°C for 12 hours to obtain carbon quantum dot nanomaterials. The added ethanol and methanol help remove adsorbed water from the material.

[0037] Comparative Example

[0038] A method for preparing carbon quantum dot nanomaterials is basically the same as the technical solution in the example, except that Na2SO4 is not added.

[0039] Figure 1 The images show the FTIR spectra of the carbon quantum dot nanomaterials prepared in the examples and comparative examples, compared with those obtained without Na2SO4 to promote citric acid pyrolysis. It can be seen that the overall peak shape of the carbon quantum dots prepared in the examples remains unchanged, with a peak at 1100 cm⁻¹. -1 The characteristic peaks on the left and right correspond to -SO3Na.

[0040] Figure 2 The XRD patterns of the carbon quantum dot nanomaterials prepared in the examples and comparative examples are shown. The overall characteristic peaks of the carbon quantum dot nanomaterials obtained by adding Na2SO4 to promote the pyrolysis of citric acid are characteristic peaks of Na2SO4, but there are also amorphous peaks of carbon quantum dots at an angle of about 30°, which can be equivalent to the combination of carbon quantum dots and Na2SO4.

[0041] Figure 3The image shown is a TEM image of the carbon quantum dot nanomaterials prepared in the example. It can be seen that the carbon quantum dots are uniformly dispersed and have a particle size of 30-50 nm.

[0042] The carbon quantum dot nanomaterials prepared in the examples were dissolved in water to prepare a 0.43 g / g carbon quantum dot solution. Figure 4 As shown in Figure (a); when placed under a 365nm ultraviolet lamp, it can be seen that it exhibits fluorescent properties, such as... Figure 4 As shown in Figure (b); FeCl3 was added to a 0.43 g / g carbon quantum dot solution (because Fe... 3+ When combined with carbon quantum dots, the fluorescence color changes, further indicating that it is a carbon quantum dot. When placed under 365nm ultraviolet light, the fluorescence color changes, as shown below. Figure 4 As shown in Figure (c).

[0043] The carbon quantum dot nanomaterials prepared in the examples and comparative examples were dissolved in water to prepare a 0.43 g / g carbon quantum dot solution. A 2M NaCl solution was also prepared. The absorption rate of the three solutions was tested, and the results are as follows: Figure 5 As shown.

[0044] The test was conducted using conventional methods in the field. An experimental setup was constructed, with a flat-plate forward osmosis membrane dividing the entire apparatus into two parts: one side containing a feed solution with lower osmotic pressure, and the other side containing a draw solution with higher osmotic pressure. Due to the selective permeability of the forward osmosis membrane, water from the lower osmotic pressure feed solution is drawn into the draw solution by the osmotic pressure difference between the two solutions. To ensure good flow of the solutions on both sides, a peristaltic pump was connected to each side. The flow pattern was co-current, with both solutions flowing from bottom to top for better contact. Seawater was used as the feed solution, and the flow rate of the draw solution was 25 cm / s. Figure 5 As can be seen, the absorption rate of the carbon quantum dot solution in both the examples and the comparative examples is greater than that of the 2 mol / L NaCl solution. Specifically, the absorption rate of the carbon quantum dot solution in the comparative example is 1.16 times that of the 2 mol / L NaCl solution, and the absorption rate of the carbon quantum dot solution in the examples is 1.57 times that of the 2 mol / L NaCl solution.

[0045] The method for preparing carbon quantum nanomaterials provided in this invention involves adding Na2SO4 to assist in the pyrolysis of anhydrous citric acid, thereby obtaining carbon quantum dots rich in carboxyl groups. This improves the osmotic pressure and forward osmotic water absorption capacity of the carbon quantum dots, and the water absorption rate is 1.57 times that of the commonly used 2 mol / L NaCl absorption solution.

[0046] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing carbon quantum dots nanomaterials, characterized in that, Includes the following steps: (1) Citric acid pyrolysis: Anhydrous citric acid and Na2SO4 are mixed and pyrolyzed at 180-210℃ to obtain a brownish-black solid; (2) Neutralization: Dissolve the brownish-black solid in water, then add NaOH solution dropwise and adjust the pH to 7 to obtain a mixed solution; (3) Refining: Add ethanol to the mixed solution, stir and mix, let stand, take the lower layer of black viscous liquid, dilute with water, add ethanol and stir and mix again. Repeat this process several times, then add the black viscous liquid dropwise to methanol to form a brown precipitate; filter the brown precipitate and wash it with methanol. Repeat the filtration process several times and then vacuum dry the obtained solid to obtain carbon quantum dot nanomaterials. In step (1), the mass ratio of anhydrous citric acid to Na2SO4 is 20:(0.1-1); The pyrolysis time in step (1) is 150-360 minutes; The concentration of the NaOH solution in step (2) is 8-10 mol / L; The carbon quantum dot nanomaterials prepared in step (3) have a particle size of 30-50 nm.

2. The production method according to claim 1, characterized by, The volume of water added in step (3) is 1-1.2 times the volume of the black viscous liquid.

3. The production method according to claim 1, characterized by, The vacuum drying temperature in step (3) is 40-50℃.

4. An application of carbon quantum dot nanomaterials obtained by any one of the preparation methods described in claims 1-3 as a forward osmosis draw fluid material.

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