A g-C3N4 porous fiber material and its preparation method and application

Abstract

The present invention belongs to the technical field of thermally conductive and wave-absorbing multifunctional materials, and discloses a g-C3N4 porous fiber material, its preparation method, and its application. The g-C3N4 porous fiber material prepared by the present invention using a liquid-phase acid precipitation-annealing process not only has a novel structure and formation mechanism, but also can be used to prepare a series of g-C3N4 porous fiber structures by regulating different cooling and annealing temperatures. The disclosed method is simple to operate and produces novel product morphology, overcoming the shortcomings of previous preparation processes, such as harsh reaction conditions, difficult to control reaction product morphology, and poor experimental reproducibility. It exhibits excellent wave-absorbing and thermal conductivity and has good potential for industrial application.

Description

Technical Field

[0001] The present invention belongs to the technical field of heat-conducting and wave-absorbing multifunctional materials, and relates to a preparation method of a g-C3N4 porous fiber material and its application in the field of wave absorption and heat conduction, sensors, supercapacitors, photocatalysis or lithium-ion batteries. Background Art

[0002] Graphitic carbon nitride (g-C3N4) has a structure similar to graphite, with an internal planar structure connected by triazine rings. Due to the difference in the conjugated structure of the triazine rings within it, it exhibits properties different from those of graphite. In its internal π-conjugated structure, electron motion is localized within the triazine rings, giving it semiconductor-like properties. Therefore, g-C3N4 has important applications in photocatalysis and water pollution control. Reduced graphene oxide (rGO) has reportedly shown good microwave absorption properties. Since g-C3N4 shares a similar structure to graphene, combining g-C3N4 with other magnetic metal particles also holds great potential in microwave absorption.

[0003] At the same time, the morphology has a significant influence on the properties of g-C3N4. Currently, the common morphologies of g-C3N4 include block, flake, spherical, tubular and porous morphologies. Among them, Chinese patent CN109607500A discloses a method for preparing g-C3N4 ultrathin nanosheets, which uses melamine as a precursor, undergoes a hydrothermal reaction, and is obtained through centrifugal washing, grinding, low-temperature drying, and high-temperature calcination. This method has a long reaction time and a cumbersome process; Chinese patent CN109529908A discloses a method for preparing porous g-C3N4 materials and their applications. This preparation method uses dicyandiamide as a raw material and urea as a template, and adopts microwave heating to prepare porous g-C3N4 materials, but its ultrasonication time is long and the morphology is irregular; Chinese patent CN111068733A discloses a method for preparing g-C3N4 nanoscrolls and their applications. This method requires multiple calcinations, has a long reaction time, and has low yield; Chinese patent CN110876954A discloses a foamed MXene / C3N4 / metal composite electrocatalyst and its preparation method, which has complex operation and high cost. Existing reports of g-C3N4 have mostly described flaky, tubular, spherical, and porous morphologies. Spherical forms generally require SiO2 as a hard template, making subsequent processing extremely difficult and dangerous. The aforementioned porous g-C3N4 fiber material has not been reported, and its production process is simple, using inexpensive and readily available raw materials.

[0004] Morphology has a great influence on g-C3N4 materials. As we all know, g-C3N4 is widely used in the field of catalysis. The size of the specific surface area is an important factor affecting the photocatalytic performance. The g-C3N4 obtained by the traditional thermal polycondensation method is generally blocky and has a small specific surface area. Therefore, spherical, lamellar, tubular, hollow, and porous structures can effectively increase the specific surface area of ​​the material, which can significantly improve the electron-hole separation efficiency, thereby improving its photocatalytic performance. At the same time, a large specific surface area is conducive to the loading of other metal particles, thereby giving g-C3N4 unique properties; and a regular morphology with a large specific surface area can greatly improve the performance of g-C3N4 materials.

[0005] Therefore, how to develop a g-C3N4 material with simple process, easy industrialization, controllable morphology and size, high specific surface area and excellent performance is an urgent problem to be solved by technicians in this field. Summary of the Invention

[0006] The purpose of the present invention is to provide a g-C3N4 porous fiber material and a preparation method thereof, which solves the problem of small specific surface area and poor performance of existing carbon materials. The g-C3N4 porous fiber material is simple to operate and has a novel product morphology. It overcomes the defects of harsh reaction conditions, difficult to control the morphology of reaction products, and poor experimental repeatability in previous preparation processes, and has good potential for industrial application.

[0007] In order to achieve the above-mentioned objectives, the first technical objective of the present invention is to provide a g-C3N4 porous fiber material, which is prepared by a liquid-phase acid precipitation-annealing process; the structure of the g-C3N4 porous fiber material is a porous fiber, and the average diameter of the g-C3N4 porous fiber material is 0.75~1.65μm, the average length is 15~35μm, and the atomic ratio of C / N in the g-C3N4 porous fiber material is 0.59~0.62.

[0008] Preferably, the liquid-phase acid precipitation-annealing process is as follows: melamine, ethylene glycol, nitric acid and water are mixed, stirred for reaction and then cooled, and uniform micro-nano fibers are precipitated by utilizing the principle that the solubility of melamine in cold nitric acid solution is much smaller than its solubility in ethylene glycol; then the mixture is washed and centrifuged multiple times with anhydrous ethanol to remove soluble organic solvents and water, and a precursor is obtained after drying; and finally annealing is performed, the precursor decomposes and polymerizes, and the g-C3N4 porous fiber material can be obtained.

[0009] The present invention discloses a g-C3N4 porous fiber material prepared by a liquid-phase acid precipitation-annealing process. The material not only has a novel structure and formation mechanism, but also can be used to prepare a series of g-C3N4 porous fiber materials by changing the volume ratio of a melamine solution to a nitric acid solution, different annealing temperatures, different cooling temperatures, and different cooling times. The prepared g-C3N4 porous fiber material has an average diameter of 0.75 to 1.65 μm and an average length of 15 to 35 μm. The g-C3N4 porous fiber material has the characteristics of being porous and having a large specific surface area. In the field of photocatalysis, the electron-hole separation efficiency can be effectively improved, and the photocatalytic performance can be optimized. At the same time, the high specific surface area can also be effectively compounded with other metal particles, giving the g-C3N4 porous fiber material unique properties, showing great potential in the field of wave absorption.

[0010] In addition, the g-C3N4 porous fiber material prepared by the present invention has excellent thermal conductivity and wave absorption properties, wherein the maximum effective bandwidth with a reflectivity of less than or equal to -10dB is 3.36 to 6.8GHz, the maximum absorption is -22.43 to -45.42dB, and the sample thickness is 1.7 to 3.0mm; when the filling ratio is 10 to 30%, the thermal conductivity is 1.387 to 2.147W / mK, and the electrical conductivity is 3.98×10 -3 ~4.75×10 -3 S / m.

[0011] The second technical purpose of the present invention is to provide a green and environmentally friendly method for preparing g-C3N4 porous fiber materials suitable for industrial production.

[0012] In order to achieve the above object, the present invention adopts the following technical solutions:

[0013] A method for preparing a g-C3N4 porous fiber material, the method specifically comprising the following steps:

[0014] (1) Weigh melamine, dissolve it in ethylene glycol, add a certain concentration of nitric acid solution, stir to react, and then cool;

[0015] (2) washing the uniform micro-nanofibers precipitated by cooling with anhydrous ethanol, centrifugally washing them multiple times and then drying them to finally obtain a precursor;

[0016] (3) The precursor is loaded into an ark, covered with a lid, and sealed with tin foil, placed in a tube furnace, and annealed under the protection of an inert gas to finally obtain the g-C3N4 porous fiber material.

[0017] By adopting the above technical solution, the beneficial effects of the present invention are as follows:

[0018] The preparation method disclosed in the present invention is simple to operate and has a novel product morphology, which overcomes the defects of harsh reaction conditions, difficult to control the morphology of reaction products, poor experimental repeatability and the like in previous preparation processes, and has good potential for industrial application.

[0019] Preferably, the concentration of the melamine is 0.06-0.18 mol / L; the concentration of the nitric acid solution is 0.12 mol / L; and the volume ratio of the nitric acid solution to the melamine solution is (0.92-1.71):1.

[0020] Furthermore, the cooling temperature in step (1) is -70 to 25° C., and the cooling time is 0.5 to 2 hours.

[0021] Preferably, the annealing temperature in step (3) is 450° C. to 600° C., the heating rate is 2 to 5° C. / min, and the annealing time is 1 to 4 hours.

[0022] Furthermore, the ark in step (3) is a high-temperature resistant jade or ceramic ark, and the inert gas is argon, nitrogen or a mixture thereof.

[0023] The third technical purpose of the present invention is to provide the application of the above-mentioned g-C3N4 porous fiber material in the field of microwave absorption, sensors, supercapacitors, photocatalysis or lithium-ion batteries.

[0024] It can be seen from the above technical solution that compared with the prior art, the present invention provides a g-C3N4 porous fiber material and its preparation method and application, which have the following excellent effects:

[0025] 1) The present invention uses ethylene glycol as a solvent to dissolve the nitrogen-containing organic substance melamine, and then adds a nitric acid solution to protonate it to obtain micro-nano fibers. A liquid-phase acid precipitation-annealing process is used to prepare g-C3N4 porous fibers with unique morphology. The average diameter of the fibers is 0.75 to 1.65 μm. The diameter, length, and shape of the g-C3N4 porous fiber materials are regulated by varying the volume ratio of the nitric acid solution to the melamine solution, varying the annealing temperature and time, and varying the cooling temperature and time.

[0026] 2) The g-C3N4 porous fiber material prepared by the present invention has a large specific surface area, a high dielectric constant and a certain conductivity. At the same time, the abundant defects in the structure of the porous fiber material also enhance the dielectric loss in wave absorption, giving the g-C3N4 porous fiber material unique properties and showing great potential in the field of wave absorption.

[0027] 3) The preparation method of the g-C3N4 porous fiber material described in the present invention is simple and unique, and the raw materials are cheap and easily available. The reaction process is simple, time-saving, energy-saving, low-risk, green and environmentally friendly, with good repeatability, low instrument precision requirements, and considerable output, and has good potential for industrial application. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0029] Figures 1 to 3 The phase and morphology of the product obtained in Example 1 of the present invention were measured under XRD, EDX and scanning electron microscope respectively.

[0030] Figures 4 to 6 They are the phase and morphology of the product obtained in Example 2 of the present invention measured under XRD, EDX and scanning electron microscope respectively.

[0031] Figures 7 to 9 They are the phase and morphology of the product obtained in Example 3 of the present invention measured under XRD, EDX and scanning electron microscope respectively.

[0032] Figures 10 to 12 They are the phase and morphology of the product obtained in Example 4 of the present invention measured under XRD, EDX and scanning electron microscope respectively.

[0033] Figures 13 to 15 They are the phase and morphology of the product obtained in Example 5 of the present invention measured under XRD, EDX and scanning electron microscope respectively.

[0034] Figure 16 The morphology of the product obtained in Example 6 of the present invention was measured under a scanning electron microscope.

[0035] Figure 17 The morphology of the product obtained in Example 7 of the present invention was measured under a scanning electron microscope.

[0036] Figure 18 The morphology of the product obtained in Example 8 of the present invention was measured under a scanning electron microscope.

[0037] Figure 19 The morphology of the product obtained in Example 9 of the present invention was measured under a scanning electron microscope.

[0038] Figure 20 The morphology of the product obtained in Example 10 of the present invention was measured under a scanning electron microscope.

[0039] Figure 21The morphology of the product obtained in Comparative Example 1 of the present invention was measured under a scanning electron microscope. DETAILED DESCRIPTION

[0040] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. 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 are within the scope of protection of the present invention.

[0041] The embodiments of the present invention disclose a g-C3N4 porous fiber material with simple process, controllable size and good microwave absorption properties, as well as a preparation method and application thereof.

[0042] For a better understanding of the present invention, the present invention is further specifically described below through the following examples, but it should not be understood as limiting the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above invention content are also considered to fall within the scope of protection of the present invention.

[0043] The technical solution of the present invention will be further described below in conjunction with specific embodiments.

[0044] Example 1

[0045] A method for preparing a porous g-C3N4 fiber material comprises the following steps:

[0046] 1.0 g of tricyanamide was dissolved in 35 mL of ethylene glycol and magnetically stirred at 25°C for 40 minutes to form a colorless solution; the solution was then cooled at room temperature for 2 hours to obtain micro-nanofibers; the uniform micro-nanofibers precipitated by cooling were washed with anhydrous ethanol, centrifuged and washed 7 times, and then dried to finally obtain a precursor; the precursor was loaded into an ark, covered with a lid, and wrapped with aluminum foil, placed in a tube furnace, annealed at 600°C (heating rate of 2°C / min) in an air atmosphere for 2 hours, and naturally cooled to room temperature to obtain a porous g-C3N4 fiber material.

[0047] The phase, composition and morphology of the obtained products measured by XRD, EDX and scanning electron microscopy are as follows: Figures 1 to 3 The product is a porous g-C3N4 fiber material with an average length of 23 μm, an average diameter of 0.75 μm, and a C / N atomic ratio of 0.59.

[0048] As shown in Table 1, the obtained porous g-C3N4 fiber material has excellent microwave absorption properties, including a maximum effective bandwidth of 6.4 GHz with a reflectivity of less than or equal to -10 dB, a maximum absorption of -27.56 dB, a thickness of 2.3 mm, a thermal conductivity of 2.147 W / mK, and an electrical conductivity of 4.75×10 -3 S / m.

[0049] Example 2

[0050] A method for preparing a porous g-C3N4 fiber material, with other conditions remaining unchanged, is provided with the annealing temperature being changed to 500°C based on Example 1.

[0051] The phase, composition and morphology of the obtained products measured by XRD, EDX and scanning electron microscopy are as follows: Figures 4-6 The product is porous g-C3N4 fibers with an average length of 35 μm, an average diameter of 1.65 μm, and a C / N atomic ratio of 0.62.

[0052] As shown in Table 1, the obtained porous g-C3N4 fiber material has excellent microwave absorption properties, including a maximum effective bandwidth of 5.76 GHz with a reflectivity of less than or equal to -10 dB, a maximum absorption of -22.65 dB, a thickness of 2.0 mm, a thermal conductivity of 1.573 W / mK, and an electrical conductivity of 4.27 × 10 -3 S / m.

[0053] Example 3

[0054] A method for preparing a porous g-C3N4 fiber material, with other conditions remaining unchanged, is provided with the annealing temperature being changed to 450°C based on Example 1.

[0055] The phase, composition and morphology of the obtained products measured by XRD, EDX and scanning electron microscopy are as follows: Figures 7-9 The product is a porous g-C3N4 fiber material with an average length of 31 μm, an average diameter of 1.55 μm, and a C / N atomic ratio of 0.61.

[0056] As shown in Table 1, the obtained porous g-C3N4 fiber material has excellent microwave absorption properties, including a maximum effective bandwidth of 6.8 GHz with a reflectivity of less than or equal to -10 dB, a maximum absorption of -45.42 dB, a thickness of 3.0 mm, a thermal conductivity of 1.387 W / mK, and an electrical conductivity of 3.98 × 10 -3 S / m.

[0057] Example 4

[0058] A method for preparing a porous g-C3N4 fiber material, with other conditions remaining unchanged, is provided with the cooling temperature changed to 0°C based on Example 2.

[0059] The phase, composition and morphology of the obtained products measured by XRD, EDX and scanning electron microscopy are as follows: Figures 10-12 The product is a porous g-C3N4 fiber material with an average length of 17 μm, an average diameter of 0.83 μm, and a C / N atomic ratio of 0.60.

[0060] As shown in Table 1, the obtained porous g-C3N4 fiber material has excellent microwave absorption properties, including a maximum effective bandwidth of 3.44 GHz with a reflectivity less than or equal to -10 dB, a maximum absorption of -34.14 dB, a thickness of 2.7 mm, a thermal conductivity of 1.590 W / mK, and an electrical conductivity of 4.29 × 10 -3 S / m.

[0061] Example 5

[0062] A method for preparing a porous g-C3N4 fiber material, with other conditions remaining unchanged, is provided with the cooling temperature being changed to -60°C based on Example 2.

[0063] The phase, composition and morphology of the obtained products measured by XRD, EDX and scanning electron microscopy are as follows: Figures 13-15 The product is a porous g-C3N4 fiber material with an average length of 15 μm, an average diameter of 0.80 μm, and a C / N atomic ratio of 0.61.

[0064] As shown in Table 1, the obtained porous g-C3N4 fiber material has excellent microwave absorption properties, among which the maximum effective bandwidth with a reflectivity of less than or equal to -10 dB is 3.36 GHz, the maximum absorption is -43.04 dB, the thickness is 2.5 mm, the thermal conductivity is 1.553 W / mK, and the electrical conductivity is 4.22×10 -3 S / m.

[0065] Example 6

[0066] A method for preparing a porous g-C3N4 fiber material, with other conditions remaining unchanged, is provided with the cooling time changed to 0.5 h based on Example 2.

[0067] The morphology of the product obtained under scanning electron microscopy is as follows Figure 16 The product is a porous g-C3N4 fiber material with an average length of 23 μm and an average diameter of 1.20 μm.

[0068] Example 7

[0069] A method for preparing a porous g-C3N4 fiber material, with other conditions remaining unchanged, is provided with the cooling time changed to 1 h based on Example 2.

[0070] The morphology of the product obtained under scanning electron microscopy is as follows Figure 17The product is a porous g-C3N4 fiber material with an average length of 28 μm and an average diameter of 1.40 μm.

[0071] Example 8

[0072] A method for preparing a porous g-C3N4 fiber material, with other conditions remaining unchanged, is provided with the volume of ethylene glycol changed to 50 mL based on Example 2.

[0073] The morphology of the product obtained under scanning electron microscopy is as follows Figure 18 The product is a porous g-C3N4 fiber material with an average length of 20 μm and an average diameter of 0.94 μm.

[0074] Example 9

[0075] A method for preparing a porous g-C3N4 fiber material, with other conditions remaining unchanged, is provided with the volume of ethylene glycol changed to 65 mL based on Example 2.

[0076] The morphology of the product obtained under scanning electron microscopy is as follows Figure 19 The product is a porous g-C3N4 fiber material with an average length of 15 μm and an average diameter of 0.80 μm.

[0077] Example 10

[0078] A method for preparing a porous g-C3N4 fiber material, with other conditions remaining unchanged, is annealed in an argon atmosphere based on Example 2.

[0079] The morphology of the product obtained under scanning electron microscopy is as follows Figure 20 The product is a porous g-C3N4 fiber material with an average length of 34 μm and an average diameter of 1.65 μm.

[0080] As shown in Table 1, the obtained g-C3N4 porous fiber material has excellent microwave absorption properties, including a maximum effective bandwidth of 3.84 GHz with a reflectivity of less than or equal to -10 dB, a maximum absorption of -22.43 dB, a thickness of 1.7 mm, a thermal conductivity of 1.569 W / mK, and an electrical conductivity of 4.28 × 10 -3 S / m.

[0081] The content of the present invention is not limited to the content of the above embodiments. The combination of one or more embodiments can also achieve the purpose of the present invention.

[0082] In order to further verify the excellent effect of the present invention, the inventors also conducted the following experiments:

[0083] Comparative Example 1:

[0084] A method for preparing a g-C3N4 bulk material, comprising the following steps:

[0085] Dissolve 3g of dicyandiamide in 75mL of deionized water and stir magnetically at 25℃ for 10min to form a colorless solution; then place the solution in a freeze drying oven and freeze it into a solid at -60℃, then freeze-dry it to obtain a dry gel; load the dry gel into an ark, cover it with a lid, and wrap it with aluminum foil, place it in a tube furnace, anneal it at 500℃ (heating rate of 5℃ / min) in an air atmosphere for 2h, and cool it naturally to room temperature; finally, soak the annealed product in water for 6h, centrifuge and wash it, and dry it at 60℃ to obtain a g-C3N4 bulk material. The morphology of the obtained product measured under a scanning electron microscope is as follows: Figure 21 shown.

[0086] As shown in Table 1, the obtained g-C3N4 bulk material has a thick sample and a narrow absorption bandwidth.

[0087] Table 1 shows the wave absorption and thermal conductivity properties of the products obtained in Examples 1 to 5, 10 of the present invention and Comparative Example 1.

[0088]

[0089] The above data show that the porous g-C3N4 fiber material prepared by the present invention can improve the thermal conductivity and wave absorption performance of the material. Among them, the effective bandwidth of the porous g-C3N4 fiber material is 3.36~6.8GHz, which is 1.20~2.43 times that of the g-C3N4 bulk material, and the wave absorption performance is significantly improved compared with the g-C3N4 bulk material; the electrical conductivity of the porous g-C3N4 fiber material is 3.98×10 -3 ~4.75×10 -3 S / m, which is 5.45 to 6.51 times that of g-C3N4 bulk material, and has a significant improvement in electrical conductivity compared with g-C3N4 bulk material; the thermal conductivity of porous g-C3N4 fiber material is 1.387 to 2.147 W / m·K, which is 6.08 to 9.42 times that of g-C3N4 bulk material, and has a significant improvement in thermal conductivity compared with g-C3N4 bulk material.

[0090] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A g-C3N4 porous fiber material, characterized in that The structure of the g-C3N4 porous fiber material is porous fiber; the average diameter of the g-C3N4 porous fiber material is 0.75-1.65 μm, the average length is 15-35 μm, and the atomic ratio of C / N in the g-C3N4 porous fiber material is 0.59-0.62; The g-C3N4 porous fiber material is prepared by a liquid phase acid precipitation-annealing process, and the liquid phase acid precipitation-annealing process specifically includes the following steps: (1) Melamine was dissolved in ethylene glycol, and then nitric acid solution was added and stirred, and cooled after the reaction; The concentration of the melamine is 0.06-0.18 mol / L, the concentration of the nitric acid solution is 0.12 mol / L; and the volume ratio of the nitric acid solution to the melamine solution is 0.92-1.71:1; (2) washing the micro-nanofibers precipitated by cooling in step (1) with anhydrous ethanol, centrifuging and washing for multiple times, and then drying to obtain a precursor; (3) The precursor is loaded into an ark, covered with a lid, and sealed with tin foil, and then placed in a tube furnace and annealed under inert gas protection to obtain the g-C3N4 porous fiber material; The annealing temperature is 450° C. to 600° C., the heating rate is 2° C. to 5° C. / min, and the annealing time is 1 to 4 hours.

2. A g-C3N4 porous fiber material according to claim 1, characterized in that: The g-C3N4 porous fiber material has excellent thermal conductivity and wave absorption properties, with a maximum effective bandwidth of 3.36 to 6.8 GHz and a maximum absorption of -22.43 to -45.42 dB less than or equal to -10 dB. The sample thickness is 1.7 to 3.0 mm. When the filling ratio is 10 to 30%, the thermal conductivity is 1.387 to 2.147 W / mK, and the electrical conductivity is 3.98×10 -3 ~4.75×10 -3 S / m.

3. The g-C3N4 porous fiber material according to claim 1, characterized in that: The cooling temperature in step (1) is -70°C to 25°C, and the cooling time is 0.5 to 2 hours.

4. An application of the g-C3N4 porous fiber material as claimed in claim 1 in the field of microwave absorption, sensors, supercapacitors, photocatalysis or lithium-ion batteries.

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