A g-c3n4 material with high specific surface area and a preparation method thereof

Abstract

The application relates to the field of photocatalysis technology, in particular to a g-C3N4 material with high specific surface area and a preparation method thereof. The method comprises the following steps: (1) mixing a dispersion solvent with water to obtain a mixed solution M1; (2) mixing g-C3N4 raw materials with the mixed solution M1 to obtain a mixed solution M2; (3) homogenizing the mixed solution M2 to obtain a mixed solution M3; (4) washing and filtering the mixed solution M3, and drying the obtained solid phase to obtain the g-C3N4 material; the dispersion solvent is selected from the group consisting of ethanol, ethylene glycol, polyethylene glycol 200, polyethylene glycol 400, polyethylene glycol 1000, isopropyl alcohol, glycerol, ethanolamine and triethanolamine. The g-C3N4 material with high dispersion and high specific surface area is synthesized in one step by using a solvent-water system as a dispersant, using g-C3N4 as a dispersion raw material, adjusting the types of dispersants, the dispersion ratio and the homogenization process pressure, and using a high-pressure homogenization process. The g-C3N4 material has high application prospect and industrialization advantage in the field of photocatalysis technology.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of photocatalysis, in particular to a g-C3N4 material with high specific surface area and a preparation method thereof. BACKGROUND

[0002] g-C3N4 is a graphite-like layered 2D polymer semiconductor composed of triazine ring structural units. It has become an environmentally friendly inorganic non-metallic material that has attracted much attention due to its wear resistance, high temperature resistance, wide energy band gap and certain thermal conductivity. In particular, in the fields of water splitting for hydrogen production, photoelectrocatalytic reduction of CO2 and photocatalytic degradation of wastewater, g-C3N4 has shown great potential as a semiconductor / photocatalyst and carrier material.

[0003] However, although the method of preparing g-C3N4 material by thermal polymerization of melamine as raw material can produce g-C3N4 material with uniform sample and high yield, its specific surface area is small, which greatly limits its application in photocatalyst / catalyst carrier. In a heterogeneous reaction system, the specific surface area of the catalyst / catalyst carrier is closely related to its catalytic activity, because a larger specific surface area means that more reactant molecules can be adsorbed, promoting the diffusion of reactants / products and increasing the number of active sites, ultimately enhancing the catalytic activity.

[0004] In order to overcome this challenge, researchers have actively explored methods to increase the specific surface area of g-C3N4 material. Currently, soft and hard template methods, supramolecular self-assembly methods, recrystallization methods and the like are commonly used methods for preparing g-C3N4 material with high specific surface area. However, these methods have their own limitations. Soft template and supramolecular self-assembly methods require high equipment, materials and operation process, and have long preparation time; hard template method uses porous structure of silicon aluminum and other metal oxides as template, but the preparation process is complicated, has poor repeatability, and may cause pollution; recrystallization method involves the use of various solvents, removal and subsequent calcination and grinding process, also faces the problems of poor repeatability and pollution.

[0005] Therefore, how to develop an efficient and environmentally friendly method to prepare g-C3N4 material with high specific surface area is still the focus and challenge of current research. SUMMARY

[0006] In view of the above shortcomings, the purpose of the present application is to provide a simple method, a mild solvent and a good repeatability synthesis method to obtain g-C3N4 material with high specific surface area, effectively solving the problem of insufficient specific surface area of g-C3N4 material prepared by traditional thermal polymerization reaction of melamine as raw material.

[0007] The first aspect of the present application provides a preparation method of a g-C3N4 material with high specific surface area, the method comprising the following steps:

[0008] (1) mixing a dispersion solvent with water to obtain a mixed solution M1;

[0009] (2) mixing a g-C3N4 raw material with the mixed solution M1 to obtain a mixed solution M2;

[0010] (3) homogenizing the mixed solution M2 to obtain a mixed solution M3;

[0011] (4) washing and filtering the mixed solution M3, and drying the obtained solid phase to obtain the g-C3N4 material; wherein,

[0012] The dispersion solvent is selected from one or more of ethanol, ethylene glycol, polyethylene glycol 200, polyethylene glycol 400, polyethylene glycol 1000, isopropyl alcohol, glycerol, ethanolamine, and triethanolamine.

[0013] The second aspect of the present application provides a g-C3N4 material obtained by the above preparation method, the g-C3N4 material having a specific surface area of 24.3-102.4 m 2 / g.

[0014] Compared with the prior art, the present application has the following beneficial effects:

[0015] 1. The present application uses a solvent-water system with a certain proportion as a dispersant, and g-C3N4 with a certain particle size as a dispersed raw material. By adjusting the type and proportion of the dispersant, the process pressure, and using a high-pressure homogenization process, a highly dispersed g-C3N4 solution system is synthesized in one step.

[0016] 2. The present application uses a high-pressure homogenization delamination method. A high-pressure homogenizer is used to delaminate a g-C3N4 material with a certain concentration. Through high-pressure treatment, cavitation induced by micro-pore feeding, shearing and cavitation effect, a very strong impact force is generated to break and peel the g-C3N4 material into a dispersed structure with fewer layers.

[0017] 3. The g-C3N4 material treated by solvent-water system dispersion homogenization in the present application greatly improves the dispersibility and specific surface area of the g-C3N4 material in the solution through the hydrophilic groups on the edges of the layered two-dimensional structure and the steric hindrance effect of the dispersant in the solution, which prevents the g-C3N4 material from stacking again after homogenization treatment.

[0018] 4. The g-C3N4 material prepared by the present application has high specific surface area, simple preparation process, mild solvent, high application prospect and industrialization advantage. DETAILED DESCRIPTION

[0019] The specific embodiments of the present application are further illustrated below.

[0020] It is easily understood that, according to the technical solutions of the present application, a person skilled in the art can replace various structural modes and implementation modes with each other without changing the essential spirit of the present application. Therefore, the following specific embodiments are only exemplary illustrations of the technical solutions of the present application, and should not be considered as the whole or as a limitation or restriction on the technical solutions of the present application.

[0021] The first aspect of the present application provides a preparation method of a g-C3N4 material with high specific surface area, comprising the following steps:

[0022] (1) mixing a dispersion solvent with water to obtain a mixed solution M1;

[0023] (2) mixing a g-C3N4 raw material with the mixed solution M1 to obtain a mixed solution M2;

[0024] (3) homogenizing the mixed solution M2 to obtain a mixed solution M3;

[0025] (4) washing and filtering the mixed solution M3, and drying the obtained solid phase to obtain the g-C3N4 material; wherein,

[0026] The dispersion solvent is selected from ethanol, ethylene glycol, polyethylene glycol 200, polyethylene glycol 400, polyethylene glycol 1000, isopropyl alcohol, glycerol, ethanolamine, and triethanolamine.

[0027] In some embodiments, the dispersion solvent is preferably triethanolamine.

[0028] In some embodiments, in step (1), the mass ratio of the dispersion solvent to water is (1-10):(99-90);

[0029] Preferably, the mass ratio of the dispersion solvent to water is (5-10):(90-95).

[0030] In some embodiments, in step (1), the mixing is performed by ultrasonic stirring to uniformly disperse the dispersion solvent in water.

[0031] Further, the ultrasonic stirring time is 5-30 min, preferably 10-30 min.

[0032] Further, the ultrasonic stirring temperature is room temperature, for example, 20-30℃.

[0033] In some embodiments, in step (2), the g-C3N4 raw material is g-C3N4 prepared by thermal polymerization of melamine.

[0034] Further, the conditions of the thermal polymerization reaction include: temperature of 500-700℃, heating rate of 1-5℃ / min, and reaction time of 4-10h.

[0035] Further, the particle size of the g-C3N4 raw material is ≤300μm, preferably ≤100μm.

[0036] The inventors found that the g-C3N4 prepared by thermal polymerization reaction using melamine as raw material has triazine ring structure, however, the edge of the triazine ring structure in the g-C3N4 material is not complete, and there are a large number of amino groups (=NH, -NH2) on the edge, thus having certain hydrophilicity; meanwhile, for the plane of the triazine ring structure, the N atom in the middle of the plane is saturated and not connected to hydrophilic groups, thus having no hydrophilicity; therefore, the plane of the g-C3N4 material is hydrophobic while the edge is hydrophilic.

[0037] Meanwhile, similar to the structure of graphene with infinite extension of two-dimensional plane six-membered ring, the sheet layer of the g-C3N4 material also has Π-Π structure, which forms a whole through strong van der Waals force interaction and is difficult to peel off, thus having very small specific surface area.

[0038] In the present application, the inventors found through research that adding a suitable solvent / surfactant to form a mixed solution after mixing with water, and then dispersing the above g-C3N4 material in the mixed solution, and then performing high-pressure homogenization treatment on the mixed solution, can perform liquid phase exfoliation on the g-C3N4 material. Through the steric hindrance effect of adding the solvent / surfactant, the re-stacking of the two-dimensional layered structure of the triazine ring can be prevented, and the dispersibility and specific surface area of the g-C3N4 material in the solution can be effectively improved.

[0039] In some embodiments, in step (2), the mass ratio of the g-C3N4 raw material to the mixed solution M1 is (0.1-2):(99.9-98). When the g-C3N4 raw material is added to the mixed solution M1 at this ratio, no precipitation occurs after vigorous stirring for about 10min. If precipitation occurs, it indicates that too much g-C3N4 raw material is not conducive to subsequent homogenization operation.

[0040] Preferably, the mass ratio of the g-C3N4 raw material to the mixed solution M1 is (0.05-1.5):(99.95-98.5).

[0041] In some embodiments, in step (2), the mixing is performed by using ultrasonic stirring to uniformly disperse the g-C3N4 in the mixed solution M1, and the formed solution M2 is the raw material for homogenization treatment.

[0042] Further, the ultrasonic stirring time is 5-30 min, preferably 15-30 min.

[0043] Further, the ultrasonic stirring temperature is room temperature, for example 20-30℃.

[0044] In some embodiments, in step (3), the homogenization treatment can use a high-pressure homogenizer. The mixed solution M2 is loaded into the raw material bin of the high-pressure homogenizer. After being pressurized, the mixed solution M2 is converted into a high-energy water jet, and then enters the homogenization cavity of the high-pressure homogenizer for homogenization treatment to obtain the mixed solution M3. The high-pressure water flow is used as a carrier to transport the dispersed solution (i.e. the mixed solution M3) after homogenization treatment to the discharge port of the high-pressure homogenizer.

[0045] Further, the number of homogenization treatments is 1-30 times, preferably 25-30 times. The repeated homogenization treatment can obtain a highly dispersed M3 mixed solution. When the number of homogenization treatments exceeds 30 times, the dispersion degree of the M3 mixed solution is not obvious, and the marginal benefit decreases.

[0046] Further, the pressure of the homogenization treatment is 50-300 MPa, preferably 200-300 MPa. It is worth noting that when the pressure exceeds 300 MPa, the equipment requirements are extremely high. When the material is broken to a certain extent, it will not continue to become smaller due to the increase of pressure, but will tend to the minimum size of the material itself. Increasing the pressure only speeds up this process.

[0047] The present application uses a high-pressure homogenizer to strip the g-C3N4 material of a certain concentration. Through high-pressure treatment, cavitation, shearing and cavitation effect induced by micro-pore feeding, a strong impact force is generated to break and strip the g-C3N4 material into a dispersed structure with fewer layers.

[0048] As known to those skilled in the art, turbidity refers to the degree of hindrance to light passing through a solution, which is caused by the scattering of light by suspended matter and the absorption of light by solute molecules. In a dispersion system of a certain solvent, turbidity is considered as an intuitive response to the content, particle size and shape of the suspended matter. A key understanding is that under the condition that the dispersion system remains stable (i.e. no precipitation is generated), the degree of turbidity directly reflects the dispersion of the particles. The greater the turbidity, the more uniform the particle dispersion.

[0049] Therefore, in some embodiments, the present inventors use a simple method to evaluate the dispersion of g-C3N4 material in a solvent, i.e. to measure the turbidity after standing. When the measured turbidity value exceeds 1000, which is the upper limit of the instrument measurement, it can be considered that the turbidity of the suspension is extremely high, which indirectly indicates that the g-C3N4 material has achieved good dispersion in the solvent.

[0050] In some embodiments, in step (4), the washing can use deionized water and / or low alcohol.

[0051] In some embodiments, in step (4), the filtration is to separate the solid phase, i.e. the g-C3N4 material, in the mixed solution M3 using an ultrafiltration membrane.

[0052] Further, the pore size of the ultrafiltration membrane is 0.2-0.5 μm, preferably 0.2-0.3 μm.

[0053] In some embodiments, in step (4), the drying is freeze-drying. The reason for using freeze-drying is that the freeze-drying treatment can keep the sample chemical composition, physical properties, such as porous structure, etc. unchanged.

[0054] Further, the freeze-drying temperature is -40℃ to -80℃, and the pressure is 1-100 Pa.

[0055] The second aspect of the present application provides a g-C3N4 material prepared by the above method.

[0056] In some embodiments, the g-C3N4 material has a specific surface area of 24.3-102.4 m 2 / g.

[0057] In order to make the purpose, technical solutions and effects of the present application more clear and explicit, the preparation method of the present application will be described in detail through specific examples and comparative examples.

[0058] In the following examples and comparative examples, the g-C3N4 raw material is prepared by a melamine thermal polymerization process as follows: 50 g of melamine is ground and transferred to a muffle furnace, which is heated to 550℃ at a rate of 2℃ / min under nitrogen protection, and then kept at a constant temperature for 5 h to obtain g-C3N4. The sample is naturally cooled to room temperature and then taken out, crushed and sieved to obtain the g-C3N4 raw material used in the examples and comparative examples. Wherein, the g-C3N4 raw material with different particle sizes can be obtained by changing the mesh size of the sieve.

[0059] The specific surface area is determined by the BET method of the American Conda physical adsorption instrument through the N2 adsorption-desorption process.

[0060] Example 1 (A1)

[0061] (1) 5 g of triethanolamine and 95 g of deionized water are ultrasonically stirred at 25℃ for 10 min to obtain a mixed solution M1;

[0062] (2) 1 g of g-C3N4 raw material was added into the mixed solution M1 at 25°C, and ultrasonic stirring was performed for 15 min to obtain a mixed solution M2;

[0063] The particle size of the g-C3N4 raw material was D 90 = 75 μm.

[0064] (3) The mixed solution M2 was subjected to a homogenization treatment under a high-pressure homogenizer to obtain a highly dispersed mixed solution M3;

[0065] The pressure of the homogenization treatment was 241 MPa;

[0066] The number of times of the homogenization treatment was 25 times.

[0067] (4) The mixed solution M3 was washed with deionized water, and then filtered using an ultrafiltration membrane with a pore size of 0.30 μm, and the obtained aqueous solid phase was dried for 72 h to obtain a g-C3N4 sample;

[0068] The temperature of the drying was -60°C, and the pressure of the drying was 50 Pa.

[0069] The specific surface area of the g-C3N4 sample was 99.1 m 2 / g.

[0070] The particle size of the g-C3N4 sample was D 10 = 0.232 μm, D 50 = 0.356 μm, and D 90 = 1.662 μm.

[0071] Example 2 (A2)

[0072] The preparation process was performed with reference to Example 1, and the only difference was that:

[0073] In step (3), the pressure of the homogenization treatment was 138 MPa.

[0074] The specific surface area of the g-C3N4 sample was 58.9 m 2 / g.

[0075] Example 3 (A3)

[0076] The preparation process was performed with reference to Example 1, and the only difference was that:

[0077] In step (3), the pressure of the homogenization treatment was 276 MPa.

[0078] The specific surface area of the g-C3N4 sample was 102.4 m 2 / g.

[0079] Example 4 (A4)

[0080] The preparation process was carried out according to Example 1, except that:

[0081] In step (3), the number of homogenization treatments was 1.

[0082] The specific surface area of the g-C3N4 sample was 24.3 m 2 / g;

[0083] The particle size of the g-C3N4 sample was D 10 = 0.782 pm, D 50 = 6.14 pm, D 90 = 68.33 pm.

[0084] Example 5 (A5)

[0085] The preparation process was carried out according to Example 1, except that:

[0086] In step (3), the number of homogenization treatments was 15.

[0087] The specific surface area of the g-C3N4 sample was 67.1 m 2 / g;

[0088] The particle size of the g-C3N4 sample was D 10 = 0.293 pm, D 50 = 0.585 pm, D 90 = 2.983 pm.

[0089] Example 6 (A6)

[0090] The preparation process was carried out according to Example 1, except that:

[0091] In step (3), the number of homogenization treatments was 20.

[0092] The specific surface area of the g-C3N4 sample was 86.5 m 2 / g;

[0093] The particle size of the g-C3N4 sample was D 10 = 0.238 pm, D 50 = 0.374 pm, D 90 = 2.058 pm.

[0094] Example 7 (A7)

[0095] The preparation process was carried out according to Example 1, except that:

[0096] In step (3), the number of homogenization treatments was 30.

[0097] The specific surface area of the g-C3N4 sample is 101.8 m 2 / g;

[0098] The particle size of the g-C3N4 sample is D 10 = 0.227 pm, D 50 = 0.361 pm, D 90 = 1.512 pm.

[0099] Example 8 (A8)

[0100] The preparation process is carried out according to Example 1, and the only difference is that:

[0101] In step (1), the amount of triethanolamine added in the M1 solution is 1%.

[0102] The specific surface area of the g-C3N4 sample is 61.5 m 2 / g.

[0103] Example 9 (A9)

[0104] The preparation process is carried out according to Example 1, and the only difference is that:

[0105] In step (1), the amount of triethanolamine added in the M1 solution is 10%.

[0106] The specific surface area of the g-C3N4 sample is 101.7 m 2 / g.

[0107] Examples 10 to 17 (A10-A17)

[0108] The preparation process is carried out according to Example 1, and the only difference is that:

[0109] In step (1), the triethanolamine in the M1 solution is replaced with ethanolamine, glycerol, ethylene glycol, polyethylene glycol 200, polyethylene glycol 400, polyethylene glycol 1000, isopropyl alcohol, and ethanol, respectively.

[0110] The specific surface area of the g-C3N4 sample is 74.2 m 2 / g, 76.7 m 2 / g, 36.8 m 2 / g, 37.2 m 2 / g, 41.5 m 2 / g, 48.1 m 2 / g, 45.4 m 2 / g, 60.6 m 2 / g, respectively.

[0111] Comparative Example 1 (D1)

[0112] The g-C3N4 raw material was treated using a mortar to obtain a g-C3N4 sample.

[0113] The specific surface area of the g-C3N4 sample was 6.7 m 2 / g.

[0114] The particle size of the g-C3N4 sample was D 10 = 3.4 μm, D 50 = 26.78 μm, and D 90 = 110 μm.

[0115] Comparative Example 2 (D2)

[0116] The g-C3N4 raw material was treated using a pulverizer to obtain a g-C3N4 sample.

[0117] The specific surface area of the g-C3N4 sample was 18.1 m 2 / g.

[0118] The particle size of the g-C3N4 sample was D 10 = 2.28 μm, D 50 = 9.66 μm, and D 90 = 75 μm.

[0119] From the comparison of A1, A9-A16, it can be seen that the selected solvent in the prepared dispersion system solution has a significant effect on the homogenization process of the g-C3N4 sample. Among them, triethanolamine has the best effect, followed by ethanolamine, glycerol and ethanol, while isopropyl alcohol, ethylene glycol, polyethylene glycol 200, polyethylene glycol 400 and polyethylene glycol 1000 have little difference, which may be related to the hydrophilicity of the edge of the two-dimensional layered triazine ring structure of g-C3N4, the hydrophobicity of the interlayer plane structure, and the spatial structure of the solvent in the solution.

[0120] From the comparison of A1-A3, it can be seen that under the same number of homogenization (25 times), the homogenization pressure of A2 is 138 MPa, the specific surface area of the g-C3N4 product is 58.9 m 2 / g; the homogenization pressure of A1 is 241 MPa, the specific surface area of the g-C3N4 product is 99.1 m 2 / g; and the homogenization pressure of A3 is 276 MPa, the specific surface area of the g-C3N4 product is 102.4 m 2 / g. This shows that the homogenization pressure has a greater effect on the specific surface area of the g-C3N4 material. Within a certain range, the higher the pressure, the greater the specific surface area of the obtained g-C3N4 material.

[0121] A comparison of A1 and A4-A7 shows that, under the same homogenization pressure (241 MPa), A4 requires only one homogenization cycle, and its g-C3N4 product has a specific surface area of ​​24.3 m². 2 / g; A5 was homogenized 15 times, and its g-C3N4 product had a specific surface area of ​​67.1m². 2 / g; A6 was homogenized 20 times, and its g-C3N4 product had a specific surface area of ​​86.5m². 2 / g; A1 was homogenized 25 times, and its g-C3N4 product had a specific surface area of ​​99.1m². 2 / g; A7 was homogenized 30 times, and its g-C3N4 product had a specific surface area of ​​101.8m². 2 / g. This indicates that the number of homogenization cycles, within a certain range, promotes the dispersibility and specific surface area increase of g-C3N4 material. The more times the homogenization process is performed, the smaller the particle size of the g-C3N4 product becomes (significantly smaller than the sample obtained by using a mortar and pestle and a grinder), and the better the homogenization effect.

[0122] A comparison of Examples 1-16 and Comparative Examples 1-2 shows that, compared with traditional dry powder grinding and mechanical pulverization, the solution homogenization process of the present invention has better crushing and delamination effects. Considering the safety of the experiment, the service life of the equipment, and the experimental cost, the experimental conditions in Example 1 are more suitable for experimental scale-up research.

Claims

1. A method for preparing a g-C3N4 material with high specific surface area, characterized in that, The method comprises the following steps: (1) mixing a dispersion solvent with water to obtain a mixed solution M1; (2) mixing a g-C3N4 raw material with the mixed solution M1 to obtain a mixed solution M2; (3) homogenizing the mixed solution M2 to obtain a mixed solution M3; (4) washing and filtering the mixed solution M3, and drying the obtained solid phase to obtain the g-C3N4 material; the g-C3N4 material has a specific surface area of 58.9-102.4 m2 / g; wherein, 2 / g. The dispersion solvent is selected from one or more of glycerol, ethanolamine, and triethanolamine; The pressure of the homogenization treatment is 50-300 MPa.

2. The production method according to claim 1, characterized by, In step (1), the mass ratio of the dispersion solvent to water is (1-10):(99-90).

3. The production method according to claim 2, characterized by, The mass ratio of the dispersion system solvent to water is (5-10):(95-90).

4. The production method according to any one of claims 1 to 3, characterized by, In step (2), the g-C3N4 raw material is g-C3N4 prepared by thermal polymerization of melamine; wherein, The conditions of the thermal polymerization reaction include: a temperature of 500℃-700℃, a heating rate of 1-5 ℃ / min, and a reaction time of 4-10 h; The particle size of the g-C3N4 raw material is ≤300µm.

5. The preparation method according to claim 4, characterized in that, The particle size of the g-C3N4 raw material is ≤100µm.

6. The method of claim 1, wherein, In step (2), the mass ratio of the g-C3N4 raw material to the mixed solution M1 is (0.1-2):(99.9-98).

7. The preparation method according to claim 1, characterized in that, In step (2), the mass ratio of the g-C3N4 raw material to the mixed solution M1 is (0.05-1.5):(99.95-98.5).

8. The method of claim 1, wherein, In steps (1) and (2), the mixing is performed by ultrasonic stirring.

9. The production method according to claim 8, characterized by, The ultrasonic stirring time is 5-30 min; The ultrasonic stirring temperature is 20-30℃.

10. The production method according to any one of claims 1 to 3 and 5 to 9, characterized by, In step (3), the pressure of the homogenization treatment is 200-300 MPa.

11. The method of claim 10, wherein, In step (3), the number of homogenization treatments is 1-30 times.

12. The method of claim 11, wherein, The number of homogenization treatments is 20-30 times.

13. The production method according to claim 1, characterized by, In step (4), the filtration is performed using an ultrafiltration membrane with a pore size of 0.2-0.5µm.

14. The production method according to claim 1, characterized by, In step (4), the drying is performed by freeze-drying at a temperature of -40℃ to -80℃ and a pressure of 1-100 Pa.

15. A g-C3N4 material obtained by the method of any one of claims 1 to 14, having a specific surface area of 58.9 to 102.4 m2 / g. 2 / g.