CN111392771B - Core-shell structure nitrogen-doped carbon-coated titanium dioxide microsphere composite material with controllable shell morphology and preparation and application thereof - Google Patents
Core-shell structure nitrogen-doped carbon-coated titanium dioxide microsphere composite material with controllable shell morphology and preparation and application thereof Download PDFInfo
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Abstract
The invention relates to a shell morphology controllable nitrogen-doped carbon-coated titanium dioxide microsphere composite material with a core-shell structure and a preparation method and application thereof. Compared with the prior art, the core-shell structure composite material provided by the invention has excellent electromagnetic wave loss capability in the frequency range of 2.0-18.0 GHz.
Description
Technical Field
The invention belongs to the technical field of functional material preparation, and relates to a shell-morphology-controllable nitrogen-doped carbon-coated titanium dioxide microsphere composite material with a core-shell structure, and preparation and application thereof.
Background
The modern scientific and technical level is increasing day by day, and advanced electronic products bring huge convenience to people, so that people are full of various novel electronic appliances in daily life and work, such as medical instruments, communication tools, 5G products and the like. However, the electromagnetic radiation generated by the electronic device during operation can cause problems of human tissue damage, signal interference distortion and the like, so the electromagnetic radiation has become another environmental safety pollution problem in the world. At present, experts have been working on the solution of electromagnetic pollution, wherein the coating of absorbing material is the focus of the current research. The electromagnetic wave absorption material utilizes the intrinsic or extrinsic property of matter to convert electromagnetic energy into other forms of energy for dissipation, and eliminates electromagnetic pollution in a manner of energy conversion. The loss mechanism of the wave-absorbing material to electromagnetic waves is mainly divided into magnetic medium dominant magnetization loss and dielectric loss controlled by dielectric medium and electric conductor. The dielectric loss type wave-absorbing material has the characteristics of small density, good weather resistance, strong performance and the like, and is widely applied to the wave-absorbing field. In addition, the core-shell structure composite material can adjust the impedance matching characteristic of substances, utilizes the synergistic effect among the components, and simultaneously has the interface polarization effect provided by heterogeneous contact, thereby promoting the wave absorbing performance of the composite material. Therefore, reasonably designing the microscopic morphology and preparing the dielectric loss type composite wave-absorbing material with good particle dispersibility is an important means for relieving electromagnetic pollution.
The semiconductor material titanium dioxide is often applied to the fields of catalysis, organic photoelectricity, energy and the like. Pure titanium dioxide has weak electromagnetic wave response capability in a frequency band of 2.0-18.0GHz due to lack of dielectric polarization loss and ferromagnetic resonance capability in the material. At present, the modification using titanium dioxide as a basic material is mainly based on methods of constructing polycrystalline phase, crystalline/amorphous interface or lattice defect to improve the microwave absorption performance, such as high-temperature high-pressure calcination, anodic oxidation, and the like. However, the above method generates additional energy consumption, and the product particles also have serious agglomeration phenomenon, thereby affecting the comprehensive properties of the material. Therefore, it is desired to develop a simpler and lower-consumption preparation method for improving the performance of the titanium dioxide-based wave-absorbing material.
Disclosure of Invention
The invention aims to overcome the defects in the prior art and provide a core-shell structure nitrogen-doped carbon-coated titanium dioxide microsphere composite material with a controllable shell shape, and preparation and application thereof.
Research shows that the surface of the high-conductivity carbon material has a serious reflection phenomenon, does not meet the impedance matching principle and is not beneficial to transmission of electromagnetic waves into a substance for loss, so that certain specific treatment is usually required when the high-conductivity carbon material is used in the field of microwave absorption, such as appearance design, improvement of magnetization loss by compounding with a magnetic medium or improvement of dielectric loss by compounding with a dielectric medium. Based on the method, a series of core-shell structure nitrogen-doped carbon-coated titanium dioxide microsphere composite materials with controllable shell morphology are prepared. By adjusting the carbon component of the precursor and the calcining temperature, the microstructure of the composite material can be greatly changed, and the structure can influence the electromagnetic parameters and the impedance matching characteristic of the material, so that the purpose of accurately regulating and controlling the wave absorption performance of the composite material is finally achieved. The titanium dioxide core particles provide a large amount of heterogeneous contact area, the carbon shell improves the conductivity loss performance of the composite material, and the cooperation and the compensation effect generated by combining the titanium dioxide core particles and the carbon shell promote the polarization loss and the conductivity loss of the composite material, so that the attenuation capacity of the composite material to electromagnetic waves is enhanced.
The invention adopts an efficient and simple liquid phase reaction method to synthesize the precursor bimetallic zeolite imidazole ester coated titanium dioxide microsphere. After calcination in an inert atmosphere, the product particles have good dispersibility and do not have obvious agglomeration phenomenon. Meanwhile, the core-shell structure nitrogen-doped carbon-coated titanium dioxide microsphere shows excellent comprehensive performance in the microwave absorption field.
The purpose of the invention can be realized by the following technical scheme:
one of the technical schemes of the invention provides a preparation method of a core-shell structure nitrogen-doped carbon-coated titanium dioxide microsphere composite material with a controllable shell morphology, which comprises the following steps:
(1) weighing ammonia water and deionized water, adding the ammonia water and the deionized water into a mixed solution of acetonitrile and absolute ethyl alcohol, stirring until the solution is uniform and transparent, adding tetrabutyl titanate serving as a titanium source, reacting, separating and drying to obtain amorphous titanium dioxide microspheres;
(2) dispersing amorphous titanium dioxide microspheres and polyvinylpyrrolidone into an anhydrous methanol solution, adding cobalt nitrate hexahydrate and zinc nitrate hexahydrate, and stirring to obtain a suspension A, wherein the polyvinylpyrrolidone in the system has the function of uniformly dispersing cobalt ions and zinc ions on the surfaces of the titanium dioxide microspheres; weighing 2-methylimidazole, dispersing in anhydrous methanol, dropwise adding into the suspension A, stirring for reaction, cleaning, separating and drying the obtained product to obtain precursor powder, wherein 2-methylimidazole in the system is used as an organic ligand and can be coordinated with cobalt ions and zinc ions to form a double-metal zeolite imidazolate microsphere shell, so that the shape of a subsequent carbon component shell can be regulated and controlled;
(3) weighing precursor powder, grinding the precursor powder and melamine, and calcining under the protection of argon to obtain the target product vermicular nitrogen-doped carbon-coated amorphous titanium dioxide microspheres, wherein the melamine in the system is used as a carbon source and can improve the stability of the core-shell structure nitrogen-doped carbon-coated titanium dioxide microsphere composite material under high-temperature calcination.
Further, in the step (1), the volume ratio of the addition amounts of ammonia water, deionized water, absolute ethyl alcohol, acetonitrile and tetra-n-butyl titanate is (0.2-0.6): (0.95-1.05): (148-152): (98-102): (4.8-5.2) and the concentration of the ammonia water is 25-28%.
Further, in the step (1), when tetra-n-butyl titanate is added, the dropping speed is controlled to be 10-15 drops/second;
after adding tetrabutyl titanate, the reaction temperature is 25 ℃ and the reaction time is 5-7 h.
Further, in the step (2), the addition amount ratio of the amorphous titanium dioxide microspheres, the polyvinylpyrrolidone, the cobalt nitrate hexahydrate, the zinc nitrate hexahydrate and the 2-methylimidazole is (76-84) mg: (0.9-1.1) g: (55-65) mg: (235-245) mg: (590-610) mg.
Further, in the step (3), the mass ratio of the precursor powder to the melamine is (95-105): (490-510);
the calcination process is specifically as follows: the temperature is controlled to be 600 +/-5 ℃ for 5 hours.
Further, the step (3) is replaced by: weighing precursor powder, grinding the precursor powder and melamine, and calcining at 800 +/-5 ℃ under the protection of argon gas to obtain the target product nitrogen-doped carbon/carbon nanotube coated rutile phase titanium dioxide microsphere. More preferably, the mass ratio of the precursor powder to the melamine is (95-105): (490-510).
Further, the step (3) is replaced by: weighing precursor powder and trihydroxymethyl aminomethane, dispersing in an anhydrous methanol solution to obtain a suspension B, adding dopamine hydrochloride into the suspension B, stirring for reaction, cleaning, separating, drying the obtained reaction product, placing under the protection of argon, and calcining to obtain the target product, namely the vesicular hollow structure nitrogen-doped carbon-coated rutile phase titanium dioxide microsphere.
Furthermore, the mass ratio of the precursor powder, the tris (hydroxymethyl) aminomethane and the dopamine hydrochloride is (290-310): (230-250): (290-310);
at this time, the calcination process is specifically controlled to be at 800 ± 5 ℃ for 5 hours.
The second technical scheme of the invention provides a core-shell structure nitrogen-doped carbon-coated titanium dioxide microsphere composite material with a controllable shell morphology, which is prepared by adopting the preparation method, wherein the composite material is a vermicular nitrogen-doped carbon-coated amorphous titanium dioxide microsphere, an outer shell layer is a vermicular nitrogen-doped carbon layer, and an inner core is amorphous titanium dioxide;
or the composite material is nitrogen-doped carbon/carbon nanotube coated rutile phase titanium dioxide microspheres, wherein the outer shell layer is a graphitized carbon shell composite carbon nanotube, and the inner core is rutile phase titanium dioxide nanoparticles;
or the composite material is a vesicle-shaped hollow structure nitrogen-doped carbon-coated rutile phase titanium dioxide microsphere, wherein the outer shell layer is a vesicle-shaped hollow structure graphitized carbon shell, and the inner core is rutile phase titanium dioxide particles.
The third technical scheme of the invention provides application of the core-shell structure nitrogen-doped carbon-coated titanium dioxide microsphere composite material with controllable shell morphology as a microwave absorbing material. The method can be used as an electromagnetic wave absorbing material, and comprises the following steps: the prepared composite material and the sliced paraffin were uniformly mixed in a mass ratio of 2: 3. The mixture was poured into an aluminum mold and pressed into a circular ring sample having an inner diameter of 3.0mm, an outer diameter of 7.0mm and a thickness of 2.0 mm. The complex relative permittivity and permeability in the range of 2.0-18.0GHz was tested using a vector network analyzer model N5230C.
Compared with the prior art, the core-shell structure nitrogen-doped carbon-coated titanium dioxide microsphere composite material prepared by the preparation method disclosed by the invention has the advantages that the appearance structure of the shell and the aggregation state of the core can be regulated and controlled. By regulating the types of the organic ligands and the calcining temperature, the prepared composite material can be vermicular, graphitized carbon shells/carbon nanotubes and vesicular hollow-structure graphitized carbon shells; the titanium dioxide core aggregation state can be amorphous nanoparticles, rutile phase nanoparticles, and rutile phase bulk particles.
According to the invention, the purpose of regulating and controlling the polarization loss and the conductivity loss capability of the composite material can be achieved by changing the appearance structure of the shell and the core accumulation state, and the attenuation performance of the composite material to electromagnetic waves is improved. The optimal reflection loss of the graphitized carbon shell/carbon nanotube coated rutile phase titanium dioxide microsphere composite material reaches-44.0 dB, and the maximum effective absorption frequency bandwidth is 5.4 GHz; in addition, the optimal reflection loss of the graphitized carbon shell coated rutile phase titanium dioxide microsphere composite material with the vesicular hollow structure reaches-24.3 dB, and meanwhile, the maximum effective absorption frequency bandwidth is 4.9 GHz. The composite material has excellent wave-absorbing performance, low preparation cost and high repeatability, and better meets the requirements of practical application.
The dielectric loss type nitrogen-doped carbon/titanium dioxide microsphere composite material provided by the invention has the characteristics of high absorption strength and wide response frequency band, and is probably caused by large-scale interface polarization between the core and the shell and a carrier rapid migration channel constructed between small-scale particles. The nitrogen-doped carbon/titanium dioxide microsphere composite material has good electromagnetic wave absorption performance, low material density and good application prospect, and is easy to prepare and simple.
Drawings
FIG. 1 is a scanning electron micrograph of each sample: (a) vermicular nitrogen-doped carbon-coated amorphous titanium dioxide microspheres; (b) coating rutile phase titanium dioxide microspheres with nitrogen-doped carbon/carbon nanotubes; (c) the nitrogen-doped carbon-coated rutile-phase titanium dioxide microsphere with the bubble-shaped hollow structure.
FIG. 2 is a transmission electron micrograph of each sample: (a) vermicular nitrogen-doped carbon-coated amorphous titanium dioxide microspheres; (b) coating rutile phase titanium dioxide microspheres with nitrogen-doped carbon/carbon nanotubes; (c) the nitrogen-doped carbon-coated rutile-phase titanium dioxide microsphere with the bubble-shaped hollow structure.
FIG. 3 is an X-ray diffraction spectrum of a core-shell structure nitrogen-doped carbon-coated titanium dioxide microsphere composite material with a controllable shell morphology.
Fig. 4 shows the values of the reflection loss for different thicknesses of the samples: (a) coating rutile phase titanium dioxide microspheres with nitrogen-doped carbon/carbon nanotubes; (b) the nitrogen-doped carbon-coated rutile-phase titanium dioxide microsphere with the bubble-shaped hollow structure.
FIG. 5 shows the relative complex dielectric constants of the respective samples: (a) the sum of real parts of relative complex dielectric constants; (b) relative complex dielectric constant imaginary part.
Fig. 6 is a graph of the samples of comparative example 1: (a) a transmission electron microscope image; (b) reflection loss values at different thicknesses.
Fig. 7 is a graph of the samples of comparative example 2: (a) a transmission electron microscope image; (b) reflection loss values at different thicknesses.
Fig. 8 is a graph of the samples of comparative example 3: (a) a transmission electron microscope image; (b) reflection loss values at different thicknesses.
Detailed Description
The invention is described in detail below with reference to the figures and specific embodiments. The present embodiment is implemented on the premise of the technical solution of the present invention, and a detailed implementation manner and a specific operation process are given, but the scope of the present invention is not limited to the following embodiments.
In the following examples, unless otherwise specified, the starting materials or the treatment techniques are all conventional and commercially available materials or conventional treatment techniques in the art.
Example 1:
preparing the vermicular nitrogen-doped carbon-coated amorphous titanium dioxide microspheres:
first, 0.40mL of ammonia water and 1.00mL of deionized water were measured and added to a mixed solution of 100mL of acetonitrile and 150mL of anhydrous ethanol, and the mixture was stirred at a constant temperature of 25 ℃ for 10 minutes to make the solution uniform and transparent. Subsequently, 5.0mL of tetra-n-butyl titanate was added dropwise to the above solution at a rate of 10 drops/sec, and the reaction was stirred at a constant temperature of 25 ℃ for 6 hours. After the reaction is finished, washing the reaction product for several times by using ethanol, centrifugally separating the product until the supernatant is colorless and transparent, and placing the obtained white slurry in a drying oven at 60 ℃ for vacuum drying to obtain white powder, namely the amorphous titanium dioxide microspheres.
Then, 0.08g and 1.0g of the above-prepared amorphous titania microspheres and polyvinylpyrrolidone (K15) were weighed out and placed in 100mL of an anhydrous methanol solution and ultrasonically dispersed for 45 minutes. Subsequently, 60mg of cobalt nitrate hexahydrate and 240mg of zinc nitrate hexahydrate were added thereto under constant temperature conditions at 25 ℃ and stirred for 6 hours, whereby suspension A was obtained. 600mg of 2-methylimidazole was further weighed and uniformly dispersed in 100mL of anhydrous methanol, added dropwise to suspension A and reacted for 45 minutes with stirring. After the reaction is finished, cleaning the product by using ethanol, centrifugally separating the product, placing the product at 60 ℃ and drying the product in vacuum to obtain light purple powder which is marked as a precursor double-metal zeolite imidazole ester coated amorphous titanium dioxide microsphere.
Finally, 100mg and 500mg of the precursor powder were weighed and placed in a mortar for grinding for 30 minutes. Placing the mixture into a high-temperature tube furnace, introducing argon, controlling the temperature to be 600 ℃ and calcining for 5 hours, wherein the heating rate is 5 ℃/min. Obtaining the product vermicular nitrogen-doped carbon-coated amorphous titanium dioxide microspheres.
Example 2:
preparing the nitrogen-doped carbon/carbon nanotube coated rutile phase titanium dioxide microspheres:
first, 0.40mL of ammonia water and 1.00mL of deionized water were measured and added to a mixed solution of 100mL of acetonitrile and 150mL of anhydrous ethanol, and the mixture was stirred at a constant temperature of 25 ℃ for 10 minutes to make the solution uniform and transparent. Subsequently, 5.0mL of tetra-n-butyl titanate was added dropwise to the above solution at a rate of 10 drops/sec, and the reaction was stirred at a constant temperature of 25 ℃ for 6 hours. After the reaction is finished, washing the reaction product for several times by using ethanol, centrifugally separating the product until the supernatant is colorless and transparent, and placing the obtained white slurry in a drying oven at 60 ℃ for vacuum drying to obtain white powder, namely the amorphous titanium dioxide microspheres.
Then, 0.08g of the titania microspheres prepared above and 1.0g of polyvinylpyrrolidone (K15) were weighed into 100mL of anhydrous methanol solution and ultrasonically dispersed for 45 minutes. Subsequently, 60mg of cobalt nitrate hexahydrate and 240mg of zinc nitrate hexahydrate were added thereto under constant temperature conditions at 25 ℃ and stirred for 6 hours, whereby suspension A was obtained. 600mg of 2-methylimidazole was further weighed and uniformly dispersed in 100mL of anhydrous methanol, added dropwise to suspension A and reacted for 45 minutes with stirring. After the reaction is finished, cleaning the product with ethanol, centrifugally separating the product, and vacuum-drying at 60 ℃ to obtain light purple powder which is marked as precursor bimetallic zeolite imidazole ester coated amorphous titanium dioxide microspheres.
Finally, 100mg and 500mg of the precursor powder were weighed and placed in a mortar for grinding for 30 minutes. Placing the mixture into a high-temperature tube furnace, introducing argon, controlling the temperature to be 800 ℃ and calcining for 5 hours, wherein the heating rate is 5 ℃/min. Obtaining the product nitrogen-doped carbon/carbon nanotube coated rutile phase titanium dioxide microspheres.
Example 3:
preparing nitrogen-doped carbon-coated rutile-phase titanium dioxide microspheres with bubble-shaped hollow structures:
first, 0.40mL of ammonia water and 1.00mL of deionized water were measured and added to a mixed solution of 100mL of acetonitrile and 150mL of anhydrous ethanol, and the mixture was stirred at a constant temperature of 25 ℃ for 10 minutes to make the solution uniform and transparent. Subsequently, 5.0mL of tetra-n-butyl titanate was added dropwise to the above solution at a rate of 10 drops/sec, and the reaction was stirred at a constant temperature of 25 ℃ for 6 hours. After the reaction is finished, washing the reaction product for a plurality of times by using ethanol, centrifugally separating the product until the supernatant is colorless and transparent, and placing the obtained white slurry in a drying oven at 60 ℃ for vacuum drying to obtain white powder, namely the amorphous titanium dioxide microspheres.
Then, 0.08g of the titania microspheres prepared above and 1.0g of polyvinylpyrrolidone (K15) were weighed into 100mL of anhydrous methanol solution and ultrasonically dispersed for 45 minutes. Subsequently, 60mg of cobalt nitrate hexahydrate and 240mg of zinc nitrate hexahydrate were added thereto under constant temperature conditions at 25 ℃ and stirred for 6 hours, whereby suspension A was obtained. 600mg of 2-methylimidazole was further weighed and uniformly dispersed in 100mL of anhydrous methanol, added dropwise to suspension A and reacted for 45 minutes with stirring. After the reaction is finished, cleaning the product with ethanol, centrifugally separating the product, and vacuum-drying at 60 ℃ to obtain light purple powder which is marked as precursor bimetallic zeolite imidazole ester coated amorphous titanium dioxide microspheres.
Finally, 300mg and 240mg of the precursor powder are weighed and uniformly dispersed in 200mL of anhydrous methanol solution, and the suspension is marked as suspension B. Then 300mg of dopamine hydrochloride is added into the suspension B, stirred and reacted for 4 hours, and the product is washed by methanol, centrifugally separated and dried in a vacuum oven at 60 ℃. Weighing 100mg of the dried powder, placing the powder into a high-temperature tube furnace, introducing argon, controlling the temperature to calcine for 5 hours at 800 ℃, and raising the temperature at a rate of 5 ℃/min to obtain the product of the nitrogen-doped carbon-coated rutile phase titanium dioxide microsphere with the vesicular hollow structure.
Comparative example 1:
compared to example 2, most of them are the same except that the melamine component is omitted in this example.
Comparative example 2:
compared to example 2, most of them are the same except that the calcination temperature in this example is changed to 900 ℃.
Comparative example 3:
compared to example 3, the same is for the most part, except that the calcination temperature in this example is changed to 900 ℃.
The microstructure of the core-shell structure nitrogen-doped carbon-coated titanium dioxide microsphere composite material with the controllable shell morphology in the embodiment is characterized by using a scanning electron microscope (SEM, Hitachi FE-SEM S-4800), and a powder sample is ultrasonically dispersed in ethanol and then dropped on a conductive silicon wafer to be dried for testing. The microstructure information of a series of composite materials is characterized by a transmission electron microscope (TEM, JEOL JEM-2100F), and a powder sample is ultrasonically dispersed in ethanol and then dropped on a carbon-supported copper net for drying to test. The X-ray diffraction spectra were measured on a bruker d8 Advance instrument. The complex relative permittivity and permeability in the range of 2.0-18.0GHz was tested using a vector network analyzer model N5230C.
Fig. 1 is a Scanning Electron Microscope (SEM) image of a series of core-shell structure nitrogen-doped carbon-coated titanium dioxide microsphere composites with controllable shell morphology synthesized by a control means, wherein fig. 1a is a microscopic morphology of a product calcined at 600 ℃ in an argon atmosphere in example 1, and the shell surface thereof is rough and is composed of a worm-like structure; if the calcination temperature is raised to 800 ℃, the outer shell of the final product is significantly changed, mainly consisting of carbon nanotubes and nitrogen-doped graphitized carbon, as shown in fig. 1b (i.e., the product obtained in example 2); if the precursor is etched with dopamine and then calcined at 800 ℃ in an argon atmosphere, the shell of the product is smooth and mainly composed of nitrogen-doped graphitized carbon, as shown in fig. 1c (i.e., the product obtained in example 3). The three groups of samples have uniform particle size distribution and good particle dispersibility.
Fig. 2 is a Transmission Electron Microscope (TEM) image of a series of core-shell structure nitrogen-doped carbon-coated titanium dioxide microsphere composites with controllable shell morphology, which are prepared in the above examples 1 to 3. As shown in fig. 2a, the outer carbon component is composed of discontinuous particles and has more voids, the morphology thereof is similar to a worm shape, the graphitization degree of the carbon component is lower, and the inner titanium dioxide core is still integral; as shown in fig. 2b, the shell has curved and elongated carbon nanotubes and contains metallic cobalt particles at the top, and a thin graphitized carbon layer is present on the surface of the core, and the inner titanium dioxide core has obvious granulation and is rutile phase; as shown in fig. 2c, the carbon shell is converted into a vesicular hollow structure of a vesicular bubble, the aggregation state of the inner titanium dioxide core is changed, and the micro particles are assembled into bulk particles. The core-shell structure was still maintained after calcination of the three groups of samples.
Fig. 3 is an X-ray diffraction (XRD) analysis of the core-shell structure nitrogen-doped carbon-coated titanium dioxide microsphere composite material with controllable shell morphology, which is prepared in the above examples 1 to 3. In the figure, the vermicular nitrogen-doped carbon-coated amorphous titanium dioxide microsphere composite material has a weak carbon peak (002) at the 2 theta (26.1 degrees), which indicates that the sample has low graphitization degree and the titanium dioxide is in an amorphous state. The diffraction peak positions of the nitrogen-doped carbon/carbon nanotube coated rutile phase titanium dioxide microsphere and the vesicle-shaped hollow structure nitrogen-doped carbon coated rutile phase titanium dioxide microsphere composite material are basically the same, wherein the diffraction peaks at the positions of 44.2 degrees, 51.5 degrees and 75.9 degrees correspond to (111), (200) and (220) crystal faces of face-centered cubic Co (JCPDS Card No. 15-0806); diffraction peaks at 27.5 °, 36.1 °, 41.2 °, 54.3 °, 69.0 ° and 69.8 ° with rutile phase TiO 2 The (110), (101), (111), (211), (301) and (112) crystal planes of (JCPDS Card No. 21-1276). XRD pattern analysis proves the component information of the composite material, and no obvious impurity and miscible phase exist.
FIG. 4 shows the reflection loss values of 2.0-18.0GHz frequency of the core-shell structure N-doped carbon-coated titanium dioxide microsphere composite materials with controllable shell morphology, which are prepared in the above examples 2-3, at a thickness of 1.0-5.0 mm. As shown in FIG. 4a, when the thickness of the sample is 3.0mm, the maximum reflection loss value of the nitrogen-doped carbon/carbon nanotube-coated rutile titanium dioxide microsphere reaches-44.0 dB. As shown in FIG. 4b, when the thickness of the sample is 5.0mm, the maximum reflection loss value of the nitrogen-doped carbon-coated rutile phase titanium dioxide microsphere with the vesicular hollow structure reaches-24.3 dB. In addition, by adjusting the thickness of the test sample, the effective response frequency bands of the two composites relate to C, X and the Ku wave band, which indicates that the composites have controllable harmonic characteristics. The core-shell structure nitrogen-doped carbon-coated titanium dioxide microsphere composite material with the controllable shell morphology simultaneously meets the practical application requirements of strong absorption, broadband response and low density, and is a potential high-efficiency wave-absorbing material.
FIG. 5 is a graph showing the real part of complex dielectric constant (ε') and the imaginary part of dielectric constant (ε ") of the core-shell structure N-doped carbon-coated titanium dioxide microsphere composite material with controllable shell morphology, which is prepared in the above examples 1 to 3, and is used to reveal the mechanism of excellent wave absorption performance. The wave absorbing performance of the composite material mainly derives from the conductivity loss and polarization loss capability. With the increase of the calcination temperature, the real part and the imaginary part of the complex dielectric constant are obviously increased, and the graphitization degree of the outer carbon shell enhances the conductivity loss of the composite material. And the nitrogen-doped carbon-coated rutile-phase titanium dioxide microspheres with the vesicle-shaped hollow structures have certain gaps, so that the complex dielectric constant is slightly reduced compared with the nitrogen-doped carbon/carbon nanotube-coated rutile-phase titanium dioxide microspheres. In addition, the large-scale heterogeneous contact of the small particles of the inner titanium dioxide core and the carbon component of the outer layer also enhances the polarization loss capability of the composite material and improves the wave-absorbing performance of the nitrogen-doped carbon/carbon nanotube coated rutile phase titanium dioxide microspheres.
FIG. 6 is a Transmission Electron Micrograph (TEM) of a comparative sample obtained in comparative example 1 and reflection loss values at a frequency of 2.0 to 18.0GHz at a thickness of 1.0 to 5.0 mm. As shown in FIG. 6a, the particle microspheres of comparative example 1 have a vesicular hollow structure, and the phase composition of the particle microspheres is rutile phase titanium dioxide. Compared with the example 2, the outer carbon shell of the comparative example 1 basically disappears due to the fact that no melamine is added, and the melamine can well protect the stability of the bimetallic zeolite imidazole ester in a high-temperature environment; meanwhile, the melamine provides enough carbon source, so that the carbon nano tube can be generated by catalysis in the presence of cobalt ions, and the conductive capability of the composite material is improved. Therefore, the melamine is a key component for preparing the nitrogen-doped carbon/carbon nanotube coated rutile phase titanium dioxide microsphere; as shown in fig. 6b, the wave-absorbing performance of the sample of comparative example 1 is poor, because the graphitized carbon shell and the disappearance of the carbon nanotubes affect the conductance loss and polarization loss of the material, and the two are the main loss mechanisms of the dielectric loss type wave-absorbing material, which further proves that the addition of melamine plays a key role in the wave-absorbing performance of the nitrogen-doped carbon/carbon nanotube-coated rutile phase titanium dioxide microsphere.
FIG. 7 is a Transmission Electron Micrograph (TEM) of a comparative sample obtained in comparative example 2 and reflection loss values at a frequency of 2.0 to 18.0GHz at a thickness of 1.0 to 5.0 mm. As shown in fig. 7a, the core particle size of the comparative example 2 sample was significantly increased and the number of outer graphitized carbon shells and carbon nanotubes was significantly reduced compared to example 2. Since the content of the carbon component is reduced due to an excessively high calcination temperature, the thickness of the carbon layer is reduced, which also results in a reduced restriction of the inner core, agglomeration of titanium dioxide particles and an increase in particle size. The proper calcination temperature interval is proved to be a key parameter for preparing the nitrogen-doped carbon/carbon nanotube coated rutile phase titanium dioxide microspheres; as shown in fig. 7b, too high calcination temperature results in the destruction of the morphology regularity of the composite particles, the deterioration of the dielectric capacity and the corresponding poor wave-absorbing performance. The calcination temperature is proved to be very important for the shape regularity and the wave-absorbing performance of the nitrogen-doped carbon/carbon nanotube coated rutile phase titanium dioxide microspheres.
FIG. 8 is a Transmission Electron Micrograph (TEM) of a comparative sample obtained in comparative example 3 above and reflection loss values at a frequency of 2.0 to 18.0GHz at a thickness of 1.0 to 5.0 mm. As shown in fig. 8a, the morphology of the particles of the sample of comparative example 3 is damaged due to the excessively high calcination temperature, the carbon shell of the vesicular hollow structure is broken and falls off, and the size of the titanium dioxide core particles is increased and gradually separated from the carbon shell. Compared with the example 3, the particle appearance is irregular, which shows that the calcination temperature is a key parameter for preparing nitrogen-doped carbon-coated rutile phase titanium dioxide microspheres with bubble-shaped hollow structures; as shown in fig. 8b, the wave-absorbing property of the sample of comparative example 3 is not ideal, and the compensatory effect of the core and the shell in the composite material disappears due to the destruction of the vesicular hollow core-shell structure. The calcination temperature is proved to be very important for the shape regularity and the wave-absorbing performance of the nitrogen-doped carbon-coated rutile phase titanium dioxide microsphere with the vesicular hollow structure.
Example 4:
compared to example 1, most of them are the same except that in this example:
the volume ratio of the addition amounts of ammonia water, deionized water, absolute ethyl alcohol, acetonitrile and tetra-n-butyl titanate is 0.2: 0.95: 148: 98: 4.8, the concentration of ammonia water is 25% -28%; when adding tetrabutyl titanate, the dropping speed is controlled at 10-15 drops/second, and after adding tetrabutyl titanate, the reaction temperature is 25 ℃ and the reaction time is 5-7 h;
the addition ratio of the amorphous titanium dioxide microspheres, polyvinylpyrrolidone, cobalt nitrate hexahydrate, zinc nitrate hexahydrate and 2-methylimidazole is 76 mg: 0.9 g: 55 mg: 235 mg: 590 mg;
the mass ratio of the precursor powder to the melamine is 95: 490, the calcination process is specifically as follows: the temperature is controlled to be 595 ℃ and the calcination is carried out for 5 hours.
Example 5:
compared to example 1, most of them are the same except that in this example:
the volume ratio of the addition amounts of ammonia water, deionized water, absolute ethyl alcohol, acetonitrile and tetra-n-butyl titanate is 0.6: 1.05: 152: 102: 5.2, the concentration of ammonia water is 25 to 28 percent; when adding tetrabutyl titanate, the dropping speed is controlled at 10-15 drops/second, and after adding tetrabutyl titanate, the reaction temperature is 25 ℃ and the reaction time is 5-7 h;
the addition ratio of the amorphous titanium dioxide microspheres, polyvinylpyrrolidone, cobalt nitrate hexahydrate, zinc nitrate hexahydrate and 2-methylimidazole is 84 mg: 1.1 g: 65 mg: 245 mg: 610 mg;
the mass ratio of the precursor powder to the melamine is 105: 510, in this case, the calcination process specifically comprises: the temperature was controlled to be 605 ℃ for 5 hours.
Example 6:
compared to example 2, most of them are the same except that in this example:
the precursor powder is directly calcined under the protection of argon, and the temperature is controlled at 795 ℃.
Example 7:
compared to example 2, most of them are the same except that in this example:
the precursor powder is directly calcined under the protection of argon, and the temperature is controlled at 805 ℃.
Example 8:
compared to example 3, most of them are the same except that in this example:
the mass ratio of the precursor powder, the trihydroxymethyl aminomethane and the dopamine hydrochloride is 290: 230: 290, and the calcination process is carried out at 795 ℃ for 5 hours.
Example 9:
compared to example 3, most of them are the same except that in this example:
the mass ratio of the precursor powder, the trihydroxymethylaminomethane and the dopamine hydrochloride is 310: 250: 310, the calcination process is specifically controlled at 805 ℃ for 5 hours.
The embodiments described above are described to facilitate an understanding and use of the invention by those skilled in the art. It will be readily apparent to those skilled in the art that various modifications to these embodiments may be made, and the generic principles described herein may be applied to other embodiments without the use of the inventive faculty. Therefore, the present invention is not limited to the above embodiments, and those skilled in the art should make improvements and modifications within the scope of the present invention based on the disclosure of the present invention.
Claims (6)
1. A preparation method of a core-shell structure nitrogen-doped carbon-coated titanium dioxide microsphere composite material with controllable shell morphology is characterized by comprising the following steps:
(1) measuring ammonia water and deionized water, adding the ammonia water and the deionized water into a mixed solution of acetonitrile and absolute ethyl alcohol, stirring until the solution is uniform and transparent, adding tetra-n-butyl titanate, reacting, separating and drying to obtain amorphous titanium dioxide microspheres;
(2) dispersing amorphous titanium dioxide microspheres and polyvinylpyrrolidone in an anhydrous methanol solution, adding cobalt nitrate hexahydrate and zinc nitrate hexahydrate, stirring to obtain a suspension A, weighing 2-methylimidazole, dispersing in anhydrous methanol, dropwise adding into the suspension A, stirring for reaction, cleaning, separating and drying the obtained product to obtain precursor powder;
(3) weighing precursor powder, mixing and grinding the precursor powder and melamine, and calcining for 5 hours at 600 +/-5 ℃ under the protection of argon gas to obtain a target product worm-shaped nitrogen-doped carbon-coated amorphous titanium dioxide microsphere;
in the step (1), the volume ratio of the addition amounts of ammonia water, deionized water, absolute ethyl alcohol, acetonitrile and tetra-n-butyl titanate is (0.2-0.6): (0.95-1.05): (148-152): (98-102): (4.8-5.2), wherein the concentration of ammonia water is 25% -28%;
in the step (1), when tetra-n-butyl titanate is added, the dropping speed is controlled to be 10-15 drops/second;
after tetra-n-butyl titanate is added, the reaction temperature is 25 ℃, and the reaction time is 5-7 h;
in the step (2), the adding amount ratio of the amorphous titanium dioxide microspheres, the polyvinylpyrrolidone, the cobalt nitrate hexahydrate, the zinc nitrate hexahydrate and the 2-methylimidazole is (76-84) mg: (0.9-1.1) g: (55-65) mg: (235-245) mg: (590-610) mg;
in the step (3), the mass ratio of the precursor powder to the melamine is (95-105): (490-510).
2. The preparation method of the core-shell structure nitrogen-doped carbon-coated titanium dioxide microsphere composite material with the controllable shell morphology according to claim 1, characterized in that in the step (3), the following steps are replaced: and (3) mixing and grinding the precursor powder and melamine, and calcining at 800 +/-5 ℃ under the protection of argon gas to obtain the target product nitrogen-doped carbon/carbon nanotube-coated rutile-phase titanium dioxide microspheres.
3. The preparation method of the core-shell structure nitrogen-doped carbon-coated titanium dioxide microsphere composite material with the controllable shell morphology according to claim 1, characterized in that in the step (3), the following steps are replaced: weighing precursor powder and trihydroxymethyl aminomethane, dispersing in an anhydrous methanol solution to obtain a suspension B, adding dopamine hydrochloride into the suspension B, stirring for reaction, cleaning, separating, drying the obtained reaction product, placing under the protection of argon, and calcining to obtain the target product, namely the vesicular hollow structure nitrogen-doped carbon-coated rutile phase titanium dioxide microsphere.
4. The preparation method of the core-shell structure nitrogen-doped carbon-coated titanium dioxide microsphere composite material with the controllable shell morphology according to claim 3, wherein the mass ratio of the precursor powder, the tris (hydroxymethyl) aminomethane and the dopamine hydrochloride is (290-310): (230-250): (290-310);
at this time, the calcination process is specifically to control the temperature to be 800 +/-5 ℃ for 5 hours.
5. A core-shell structure nitrogen-doped carbon-coated titanium dioxide microsphere composite material with a controllable shell morphology is prepared by the preparation method of any one of claims 1 to 4, and is characterized in that the composite material is a vermicular nitrogen-doped carbon-coated amorphous titanium dioxide microsphere, wherein the outer shell layer is a vermicular nitrogen-doped carbon layer, and the inner core is amorphous titanium dioxide;
or the composite material is nitrogen-doped carbon/carbon nanotube coated rutile phase titanium dioxide microspheres, wherein the outer shell layer is a graphitized carbon shell composite carbon nanotube, and the inner core is rutile phase titanium dioxide nanoparticles;
or the composite material is a vesicle-shaped hollow structure nitrogen-doped carbon-coated rutile phase titanium dioxide microsphere, wherein the outer shell layer is a vesicle-shaped hollow structure graphitized carbon shell, and the inner core is rutile phase titanium dioxide particles.
6. The core-shell structure nitrogen-doped carbon-coated titanium dioxide microsphere composite material with controllable shell morphology as claimed in claim 5, which is applied as a microwave absorbing material.
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| CN115725264B (en) * | 2022-10-25 | 2024-01-30 | 彗晶新材料科技(杭州)有限公司 | Mesoporous hollow core-shell structure, preparation method thereof, composite material and electronic device |
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