Nitrogen and sulfur co-doped starch-based carbon microspheres with adjustable particle size and preparation method thereof

Abstract

The invention provides nitrogen and sulfur co-doped starch-based carbon microspheres with adjustable particle size and a preparation method thereof. The nitrogen-sulfur co-doped starch-based carbon microspheres with adjustable particle size are prepared by the preparation method, and the preparation method comprises the following steps: uniformly stirring and mixing starch, a surfactant and water to obtain a mixed solution, and then carrying out hydrothermal carbonization reaction; and after the hydrothermal carbonization reaction is finished, naturally cooling the mixture obtained by the reaction to room temperature, then carrying out separation treatment, repeatedly washing the solid obtained by separation with absolute ethyl alcohol and deionized water until the supernatant is colorless, and drying the obtained solid to obtain the nitrogen-sulfur co-doped starch-based carbon microspheres with adjustable particle sizes. Based on the simple hydrothermal carbonization reaction, the particle size of the starch-based carbon microspheres is accurately regulated and controlled by regulating and controlling parameters such as the raw material ratio, the preparation process is simple, the reaction conditions are mild and environmentally friendly, and the prepared material has wide application prospects in the fields of energy storage, adsorbents, catalyst carriers and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of preparation of novel carbon materials, and in particular relates to nitrogen-sulfur co-doped starch-based carbon microspheres with adjustable particle size and a preparation method thereof. Background Art

[0002] Carbon microspheres, due to their unique morphology, surface physicochemical properties, excellent chemical stability, and superior thermal and electrical conductivity, have found widespread application in catalyst supports, adsorbents, and energy storage applications. Carbon microspheres can be derived from a variety of raw materials, including coal and asphalt, polymers, and biomass. Biomass, in particular, has attracted significant attention due to its widespread availability, low cost, and environmentally friendly nature.

[0003] Hydrothermal carbonization is a promising method for producing biomass carbon microspheres. Traditional hydrothermal carbonization methods control the morphology and size of the carbon microspheres by manipulating the raw material concentration, reaction temperature, and reaction time, but the particle size adjustment range is limited, as exemplified by the method proposed in CN118004995A. Adding additives is also a method for manipulating the hydrothermal carbon microspheres, allowing for adjustments in surface properties, yield, size, and distribution. However, existing methods still exhibit issues such as poor sphericity and cross-linking and agglomeration, as exemplified by the method proposed in CN114105120A.

[0004] Therefore, it is particularly important to propose an efficient and simple preparation scheme for hydrothermal carbon microspheres with controllable particle size and good monodispersity.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] The object of the present invention is to provide a nitrogen-sulfur co-doped starch-based carbon microsphere with adjustable particle size and a preparation method thereof, so as to solve the above problems.

[0007] In order to achieve the above objectives, the present invention particularly adopts the following technical solutions:

[0008] The present invention first provides a method for preparing nitrogen-sulfur co-doped starch-based carbon microspheres with adjustable particle size, comprising:

[0009] The starch, surfactant and water are stirred and mixed to obtain a mixed solution, and then subjected to a hydrothermal carbonization reaction;

[0010] After the hydrothermal carbonization reaction is completed, the reaction mixture is naturally cooled to room temperature and then separated. The separated solid is repeatedly washed with anhydrous ethanol and deionized water until the supernatant is colorless. The obtained solid is dried to obtain the nitrogen-sulfur co-doped starch-based carbon microspheres with adjustable particle size.

[0011] The hydrothermal carbonization reaction satisfies one or more of the following conditions:

[0012] a. The hydrothermal carbonization reaction is carried out in a benchtop stainless steel reactor, with the volume of the mixed solution being 10% to 60% of the reactor volume; the monodispersity of the carbon spheres can be maintained by regulating the amount of reactants and controlling the reactor filling level;

[0013] b. The temperature of the hydrothermal carbonization reaction is 170 to 250°C, and the hydrothermal holding time is 1 to 24 hours;

[0014] c. The hydrothermal carbonization reaction is carried out under stirring conditions with a stirring rate of 0 to 800 rpm.

[0015] Optionally, the separation treatment is performed by a centrifuge, and the rotation speed of the centrifuge is 8000-12000 rpm, preferably 10000-12000 rpm;

[0016] Further optionally, the drying temperature is 60-90° C., and the drying time is 6-12 hours.

[0017] Preferably, the starch is selected from any one of corn starch, potato starch and sweet potato starch.

[0018] Preferably, the surfactant is a polyelectrolyte; further preferably, the surfactant includes one or more of cetyltrimethylammonium chloride, sodium polyacrylate, and polydiallyldimethylammonium chloride. Polydiallyldimethylammonium chloride has a large molecular weight and a strong positive charge, thus exerting steric hindrance and electrostatic repulsion to effectively inhibit the growth and cross-linking aggregation of carbon microspheres.

[0019] Preferably, in the step of stirring and mixing the starch, surfactant and water to obtain a mixed solution, L-cysteine is also added and stirred and mixed to obtain a mixed solution;

[0020] Optionally, the mass ratio of the starch, surfactant, L-cysteine and water is (0.05-0.5):(0.0002-0.004):(0.01-0.2):1; preferably, the mass ratio of the starch, surfactant, L-cysteine and water is (0.05-0.2):(0.0004-0.004):(0.01-0.1):1.

[0021] Preferably, the mixed solution further includes a dopant, specifically:

[0022] In the step of stirring and mixing the starch, surfactant and water to obtain a mixed solution, a certain amount of dopant is added and stirred and mixed to obtain a mixed solution;

[0023] Alternatively, in the step of stirring and mixing starch, surfactant, L-cysteine and water to obtain a mixed solution, a certain amount of dopant is further added and stirred and mixed to obtain a mixed solution.

[0024] The dopant is a compound containing an amino functional group;

[0025] Preferably, the dopant comprises any one or more of melamine, urea, L-leucine, and thiourea;

[0026] Further preferably, the mass ratio of the dopant to starch is (0-0.025):1.

[0027] The present invention also provides nitrogen-sulfur co-doped starch-based carbon microspheres with adjustable particle size, which are prepared by the preparation method.

[0028] The present invention adds an external additive to a traditional hydrothermal reaction system, and prepares heteroatom-doped carbon microspheres with adjustable particle size through the synergistic effect between L-cysteine and a surfactant, and further increases the nitrogen content through the rational use of a dopant. The present invention can achieve precise control of the particle size range of the carbon microspheres by adjusting the amount of L-cysteine and the surfactant. Within the amount range of L-cysteine and the surfactant specified in the present application, and under the premise of a high starch concentration, carbon microspheres with a particle size range of 182nm to 4.58μm can still be prepared. Furthermore, by adding a dopant, the dopant is used to generate a cross-linking reaction in the hydrothermal reaction to dope the carbon microspheres with nitrogen, which not only increases the nitrogen content of the carbon microspheres, but also improves the yield and thermal stability of the material.

[0029] The synergistic effect between the surfactant polyelectrolyte and L-cysteine used in the present invention can significantly improve the sphericity and monodispersity of carbon microspheres. The polyelectrolyte significantly inhibits the growth, agglomeration, and crosslinking of the carbon microspheres. The additional hydronium ions of L-cysteine catalyze the hydrothermal process, increasing the ball formation rate and increasing the size of the microspheres. Compared with the prior art using inorganic acids, L-cysteine has weaker acidity, resulting in carbon microspheres with better sphericity and smoother surfaces. The sphericity and monodispersity of the carbon microspheres can be significantly improved by adjusting the amounts of polyelectrolyte and L-cysteine used.

[0030] Beneficial effects of the present invention:

[0031] The present invention provides a method for preparing nitrogen-sulfur co-doped starch-based carbon microspheres with controllable particle size. The starch-based carbon microspheres are prepared by a green and mild hydrothermal carbonization method, while overcoming the shortcomings of traditional hydrothermal carbonization that are difficult to control the particle size and monodispersity of carbon microspheres. The method has the advantages of controllable particle size (182nm~4.58μm), good monodispersity, good sphericity and high yield, and a high content of nitrogen and controllable sulfur are doped in the carbon microspheres.

[0032] The present invention can prepare monodisperse carbon microspheres with controllable particle size under high starch concentration, solves the crosslinking and agglomeration of carbon microspheres caused by excessively high concentration, and maintains the dispersibility of the carbon microspheres while obtaining a high product yield. For example, corn starch, polydiallyl dimethyl ammonium chloride, L-cysteine and water in a mass ratio of 0.2:0.002:0.01:1 are stirred and uniformly mixed to obtain a mixed solution, and an appropriate amount of dopant is added. After the system is reacted at 220°C for only 4 hours, the yield reaches as high as 42.75%. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0034] Figure 1 This is a scanning electron microscope image of the carbon microspheres prepared in Example 1;

[0035] Figure 2 The average particle size distribution of carbon microspheres prepared in Example 1;

[0036] Figure 3 Graph showing the distribution and content of nitrogen and sulfur elements in the carbon microspheres prepared in Example 1;

[0037] Figure 4 This is a scanning electron microscope image of the carbon microspheres prepared in Comparative Example 1;

[0038] Figure 5 This is a scanning electron microscope image of the carbon microspheres prepared in Comparative Example 2;

[0039] Figure 6 This is a scanning electron microscope image of the carbon microspheres prepared in Comparative Example 3. DETAILED DESCRIPTION

[0040] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0041] Example 1

[0042] This embodiment provides a method for preparing nitrogen-sulfur co-doped starch-based carbon microspheres with adjustable particle size, which specifically includes:

[0043] Corn starch, polydimethylammonium chloride, L-cysteine and water in a mass ratio of 0.2:0.002:0.01:1 were stirred and uniformly mixed, and a dopant was added to obtain a mixed solution. The mass ratio of the dopant to corn starch was 0.0125:1. The mixed solution was then transferred to a 500 mL desktop stainless steel reactor for hydrothermal carbonization reaction, and the temperature was maintained at 220°C for 4 hours. After the hydrothermal treatment, the mixture was naturally cooled to room temperature and then removed and separated using a high-speed centrifuge. The obtained solid was repeatedly washed with deionized water and anhydrous ethanol until the supernatant was colorless. The obtained solid was placed in a drying oven and dried at 80°C for 12 hours to obtain nitrogen-sulfur co-doped starch-based carbon microspheres.

[0044] The average particle size of the nitrogen-sulfur co-doped starch-based carbon microspheres prepared in this example is about 185 nm, and the distribution is as follows: Figure 2 As shown in the scanning electron microscope image Figure 1 As shown, the carbon microspheres have good sphericity and monodispersity, and the yield reaches 40.85%.

[0045] The distribution and content of nitrogen and sulfur elements in the nitrogen-sulfur co-doped starch-based carbon microspheres prepared in this example are shown in Figure 2. Figure 3 As shown, Figure 3 The upper left figure shows the distribution of nitrogen. Figure 3 The upper right picture shows the distribution of sulfur. Figure 3 The lower left figure is the element content measurement result diagram; Figure 3 It can be seen that nitrogen and sulfur are evenly distributed on the carbon balls, and the nitrogen content and sulfur content are 3.13 at.% and 0.33 wt.%, respectively.

[0046] Example 2

[0047] This embodiment provides a method for preparing nitrogen-sulfur co-doped starch-based carbon microspheres with adjustable particle size, which specifically includes:

[0048] Corn starch, polydimethylammonium chloride, L-cysteine, and water in a mass ratio of 0.2:0.002:0.01:1 were stirred and mixed. The homogeneous mixture was transferred to a 500 mL benchtop stainless steel reactor for hydrothermal carbonization reaction, which was maintained at 220°C for 4 hours. After the hydrothermal treatment, the mixture was naturally cooled to room temperature and then removed and separated using a high-speed centrifuge. The resulting solid was repeatedly washed with deionized water and anhydrous ethanol until the supernatant was colorless. The resulting solid was placed in a drying oven and dried at 80°C for 12 hours to obtain nitrogen-sulfur co-doped starch-based carbon microspheres.

[0049] The average particle size of the nitrogen-sulfur co-doped starch-based carbon microspheres prepared in this example is about 182 nm. The particle size of the carbon microspheres without melamine addition is slightly reduced, the nitrogen content is reduced to 2.22 at.%, and the yield is reduced to 37.80%.

[0050] Example 3

[0051] This embodiment provides a preparation method for nitrogen-sulfur co-doped starch-based carbon microspheres with adjustable particle size, which specifically includes:

[0052] Corn starch, polydimethylammonium chloride, L-cysteine and water in a mass ratio of 0.2:0.002:0.1:1 were stirred and mixed, and the mixed solution was transferred to a 500 mL desktop stainless steel reactor for hydrothermal carbonization reaction, and the temperature was kept constant at 220°C for 4 hours. After the hydrothermal treatment, the mixture was naturally cooled to room temperature and then taken out and separated by a high-speed centrifuge. The obtained solid was repeatedly washed with deionized water and anhydrous ethanol until the supernatant was colorless. The obtained solid was placed in a drying oven and dried at 80°C for 12 hours to obtain nitrogen-sulfur co-doped starch-based carbon microspheres.

[0053] The average particle size of the nitrogen-sulfur co-doped starch-based carbon microspheres prepared in this example is about 4.58 μm. By increasing the amount of L-cysteine, its catalytic effect is enhanced, resulting in a significant increase in the particle size of the carbon microspheres.

[0054] Example 4

[0055] Corn starch, polydimethylammonium chloride, L-cysteine, and water were stirred in a mass ratio of 0.2:0.001:0.01:1, and the uniformly mixed solution was transferred to a 500 mL desktop stainless steel reactor for hydrothermal carbonization reaction, which was maintained at 220°C for 4 hours. After the hydrothermal treatment, the mixture was naturally cooled to room temperature and then removed and separated using a high-speed centrifuge. The resulting solid was repeatedly washed with deionized water and anhydrous ethanol until the supernatant was colorless. The resulting solid was placed in a drying oven at 80°C for 12 hours to obtain nitrogen-sulfur co-doped starch-based carbon microspheres.

[0056] The nitrogen-sulfur co-doped starch-based carbon microspheres prepared in this example had an average particle size of approximately 201 nm. Reducing the amount of polydiallyldimethylammonium chloride increased the particle size of the carbon microspheres. The steric hindrance and electrostatic repulsion of the polycationic electrolyte polydiallyldimethylammonium chloride inhibited the growth of the carbon microspheres. As the amount of polydiallyldimethylammonium chloride decreased, the inhibitory effect decreased, resulting in an increase in the size of the carbon microspheres.

[0057] Example 5

[0058] Corn starch, polydimethylammonium chloride, L-cysteine and water in a mass ratio of 0.2:0.002:0.01:1 were stirred and mixed, and the mixed solution was transferred to a 250 mL desktop stainless steel reactor for hydrothermal carbonization reaction, and the temperature was kept at 220 ° C for 4 hours. After the hydrothermal treatment, the mixture was taken out after natural cooling to room temperature and separated by a high-speed centrifuge. The obtained solid was repeatedly washed with deionized water and anhydrous ethanol until the supernatant was colorless; the obtained solid was placed in a drying oven and dried at 80 ° C for 12 hours to prepare nitrogen-sulfur co-doped starch-based carbon microspheres.

[0059] The average particle size of the nitrogen-sulfur co-doped starch-based carbon microspheres prepared in this example is about 213 nm; an increase in the filling amount increases the size of the carbon microspheres and improves the monodispersity.

[0060] Example 6

[0061] This embodiment provides a method for preparing nitrogen-sulfur co-doped starch-based carbon microspheres with adjustable particle size, which specifically includes:

[0062] Corn starch, polydimethylammonium chloride, L-cysteine and water in a mass ratio of 0.2:0.002:0.01:1 were stirred and mixed to obtain a mixed solution, and a dopant was added in a mass ratio of 0.025:1 to corn starch. The mixed solution was transferred to a 500 mL desktop stainless steel reactor for hydrothermal carbonization reaction and kept at a constant temperature of 220°C for 4 hours. After the hydrothermal treatment, the mixture was naturally cooled to room temperature and then taken out and separated by a high-speed centrifuge. The obtained solid was repeatedly washed with deionized water and anhydrous ethanol until the supernatant was colorless. The obtained solid was placed in a drying oven and dried at 80°C for 12 hours to obtain nitrogen-sulfur co-doped starch-based carbon microspheres.

[0063] The nitrogen-sulfur co-doped starch-based carbon microspheres prepared in this example had an average particle size of approximately 207 nm. The addition of melamine increased the particle size, raised the nitrogen content to 4.43 at.%, and increased the yield to 42.75%. Increasing the amount of dopant resulted in a more stable cross-linked structure in the sample, thereby improving the nitrogen content and yield of the material.

[0064] Comparative Example 1

[0065] This comparative example provides a method for preparing carbon microspheres, which specifically includes:

[0066] Corn starch and water in a mass ratio of 0.2:1 were stirred and mixed, and the uniformly mixed solution was transferred to a 500 mL desktop stainless steel reactor for hydrothermal carbonization reaction, and the temperature was maintained at 220°C for 4 hours. After the hydrothermal treatment, the mixture was naturally cooled to room temperature and then taken out and separated using a high-speed centrifuge. The obtained solid was repeatedly washed with deionized water and anhydrous ethanol until the supernatant was colorless. The obtained solid was placed in a drying oven and dried at 80°C for 12 hours to obtain carbon microspheres.

[0067] The scanning electron microscope image of the product obtained in Comparative Example 1 is as follows: Figure 4 As shown by Figure 4 It can be seen that the carbon microspheres prepared by conventional hydrothermal reaction of high concentration starch solution are severely cross-linked.

[0068] Comparative Example 2

[0069] This comparative example provides a method for preparing carbon microspheres, which specifically includes:

[0070] Corn starch, polydimethylammonium chloride, and water in a mass ratio of 0.2:0.002:1 were stirred and mixed, and the uniformly mixed solution was transferred to a 500 mL desktop stainless steel reactor for hydrothermal carbonization reaction, and the temperature was maintained at 220°C for 4 hours. After the hydrothermal treatment, the mixture was naturally cooled to room temperature and then taken out and separated using a high-speed centrifuge. The obtained solid was repeatedly washed with deionized water and anhydrous ethanol until the supernatant was colorless. The obtained solid was placed in a drying oven and dried at 80°C for 12 hours to obtain carbon microspheres.

[0071] The scanning electron microscope image of the product obtained in Comparative Example 2 is as follows: Figure 5 As shown by Figure 5 It can be seen that the carbon microspheres prepared in comparison 2 are small in size, poor in sphericity, and severely cross-linked.

[0072] Comparative Example 3

[0073] This embodiment provides a method for preparing nitrogen-sulfur co-doped starch-based carbon microspheres with adjustable particle size, which specifically includes:

[0074] Corn starch, polydimethylammonium chloride, L-cysteine and water in a mass ratio of 0.2:0.002:0.01:1 were stirred and mixed to obtain a mixed solution, and a dopant was added in a mass ratio of 0.0625:1 to corn starch. The mixed solution was transferred to a 500 mL desktop stainless steel reactor for hydrothermal carbonization reaction and kept at a constant temperature of 220°C for 4 hours. After the hydrothermal treatment, the mixture was naturally cooled to room temperature and then taken out and separated by a high-speed centrifuge. The obtained solid was repeatedly washed with deionized water and anhydrous ethanol until the supernatant was colorless. The obtained solid was placed in a drying oven and dried at 80°C for 12 hours to obtain nitrogen-sulfur co-doped starch-based carbon microspheres.

[0075] The difference from Example 1 is that the mass ratio of melamine to corn starch is 0.0625:1. The scanning electron microscope image of the product obtained in Comparative Example 3 is as follows: Figure 6 As shown by Figure 6 It can be seen that the sphericity of the carbon microspheres deteriorates and the particles are bonded and agglomerated. Therefore, it can be seen that the excessive increase in the amount of dopant and the excessive degree of cross-linking of the material cause the sphericity and dispersion of the carbon microspheres to deteriorate.

[0076] Please note that the technical features of the above embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification. The above embodiments only express several implementation methods of the present application. The description is relatively specific and detailed, but it cannot be understood as a limitation on the scope of the invention patent. It should be pointed out that for ordinary technicians in this field, without departing from the concept of this application, several variations and improvements can be made, which all fall within the scope of protection of this application. Therefore, the scope of protection of the patent in this application shall be based on the attached claims.

Claims

1. A method for preparing nitrogen-sulfur co-doped starch-based carbon microspheres with adjustable particle size, characterized in that: include: The starch, surfactant and water are stirred and mixed to obtain a mixed solution, and then subjected to a hydrothermal carbonization reaction; After the hydrothermal carbonization reaction is completed, the reaction mixture is naturally cooled to room temperature and then separated. The separated solid is repeatedly washed with anhydrous ethanol and deionized water until the supernatant is colorless. The obtained solid is dried to obtain the nitrogen-sulfur co-doped starch-based carbon microspheres with adjustable particle size.

2. The preparation method according to claim 1, characterized in that The starch is selected from any one of corn starch, potato starch and sweet potato starch.

3. The preparation method according to claim 1, characterized in that The surfactant is a polyelectrolyte; Preferably, the surfactant includes one or more of cetyltrimethylammonium chloride, sodium polyacrylate, and polydiallyldimethylammonium chloride.

4. The preparation method according to claim 1, characterized in that In the step of stirring and mixing starch, surfactant and water to obtain a mixed solution, L-cysteine is also added and stirred and mixed to obtain a mixed solution.

5. The preparation method according to claim 4, characterized in that The mass ratio of the starch, surfactant, L-cysteine and water is (0.05-0.5):(0.0002-0.004):(0.01-0.2):

1.

6. The preparation method according to claim 1, 4 or 5, characterized in that: The mixed solution also includes a dopant, specifically: In the step of stirring and mixing the starch, surfactant, and water to obtain a mixed solution, a certain amount of dopant is added and stirred and mixed to obtain a mixed solution; Alternatively, in the step of stirring and mixing starch, surfactant, L-cysteine and water to obtain a mixed solution, a certain amount of dopant is further added and stirred and mixed to obtain a mixed solution.

7. The preparation method according to claim 6, characterized in that The dopant is a compound containing an amino functional group; Preferably, the dopant includes any one or more of melamine, urea, L-leucine, and thiourea.

8. The preparation method according to claim 7, characterized in that The mass ratio of the dopant to the starch is (0-0.025):

1.

9. The preparation method according to claim 1, characterized in that The hydrothermal carbonization reaction satisfies one or more of the following conditions: a. The hydrothermal carbonization reaction is carried out in a desktop stainless steel reactor, and the volume of the mixed solution is 10% to 60% of the reactor volume; b. The temperature of the hydrothermal carbonization reaction is 170 to 250°C, and the hydrothermal holding time is 1 to 24 hours; c. The hydrothermal carbonization reaction is carried out under stirring conditions with a stirring rate of 0 to 800 rpm.

10. A nitrogen-sulfur co-doped starch-based carbon microsphere with adjustable particle size, characterized in that: The invention is prepared by the preparation method according to any one of claims 1 to 9.

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