Preparation method of core-shell structured TiO2@N / C@Co / C composite microwave absorber

Abstract

This invention discloses a method for preparing a core-shell structured TiO2@N / C@Co / C composite microwave absorber. Specifically, the method involves: preparing MIL-125-NH2 powder using a microwave-assisted synthesis method; preparing MIL-125-NH2@ZIF-8 powder using an ultrasonic synthesis method; mixing the MIL-125-NH2@ZIF-8 powder with Co(NO3)2·6H2O, adding methanol for ultrasonic dispersion and stirring, and then carbonizing the resulting MIL-125-NH2@ZIF-8@ZIF-67 powder. This invention effectively improves the impedance matching of the microwave absorber by introducing a multi-component MOF, allowing incident electromagnetic waves to enter the composite absorber for dissipation and attenuation. Furthermore, the abundant heterogeneous interfaces in the core-shell structure can induce interfacial polarization losses, thereby increasing the absorption of electromagnetic waves.

Description

Technical Field

[0001] This invention belongs to the field of composite material preparation technology, specifically relating to a method for preparing a core-shell structured TiO2@N / C@Co / C composite microwave absorber. Background Technology

[0002] With the rapid development of 5G mobile communication technology, electronic devices are increasingly widely used in military, communication, and sensing fields. However, the accompanying electromagnetic radiation pollution not only affects the normal operation of nearby electronic devices but also poses a serious threat to human health. Therefore, it is urgent to develop high-performance electromagnetic wave absorbing materials with strong electromagnetic wave absorption performance, wide effective absorption bandwidth, low density, and thin thickness. In recent years, metal-organic framework (MOF) materials and their derivatives have shown great application potential in the field of electromagnetic wave absorption due to their high porosity, abundant active sites, and tunable physicochemical properties. However, pure MOF-derived absorbing materials often suffer from impedance mismatch and poor attenuation capabilities due to factors such as simple structure, single loss mechanism, and poor electromagnetic parameter performance, resulting in deteriorated electromagnetic wave absorption performance.

[0003] To enhance the electromagnetic wave absorption performance of MOF derivatives, the development of MOF-on-MOF structures has become an effective strategy. The construction of MOF-on-MOF structures not only significantly increases the heterogeneous interface of the material but also improves its dielectric properties and multiple reflection loss capability. The diversification of electromagnetic wave loss mechanisms and the synergistic effect of the heterogeneous interface contribute to its improved electromagnetic wave absorption performance. Therefore, composite absorbers designed based on MOF-on-MOF structures have broad application prospects in the field of electromagnetic wave absorption. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing a core-shell structured TiO2@N / C@Co / C composite microwave absorber, which solves the problems of poor electromagnetic wave absorption performance and narrow effective absorption bandwidth of existing microwave absorbers.

[0005] The technical solution adopted in this invention is a method for preparing a core-shell structured TiO2@N / C@Co / C composite microwave absorber, which is implemented according to the following steps:

[0006] Step 1: Prepare MIL-125-NH2 powder by microwave-assisted synthesis;

[0007] Step 2: Prepare MIL-125-NH2@ZIF-8 powder using ultrasonic synthesis method;

[0008] Step 3: Mix MIL-125-NH2@ZIF-8 powder with Co(NO3)2·6H2O, and add methanol solution for ultrasonic dispersion and stirring to obtain MIL-125-NH2@ZIF-8@ZIF-67 powder;

[0009] Step 4: Carbonize the MIL-125-NH2@ZIF-8@ZIF-67 powder to form a core-shell structured TiO2@N / C@Co / C composite microwave absorber.

[0010] The invention is further characterized in that,

[0011] Step 1 specifically involves:

[0012] Diaminoterephthalic acid was added to a mixed solution of DMF and methanol and ultrasonically dispersed for 10-20 min. Isopropyl titanate was added to the resulting solution and ultrasonically dispersed for 30-40 min to obtain a homogeneous mixed solution. The mixed solution was then subjected to microwave-assisted synthesis. The resulting suspension was then centrifuged and washed several times with DMF and methanol to obtain a MIL-125-NH2 dispersion. The dispersion was then vacuum dried to obtain MIL-125-NH2 powder.

[0013] The microwave-assisted synthesis temperature is 120-180℃, and the time is 0.5-4h; the centrifugation speed is 7500-8500r / min, and the centrifugation time is 5-8min; the vacuum drying temperature is 50-70℃, and the time is 10-14h.

[0014] Step 2 specifically involves:

[0015] Step 2.1: Add MIL-125-NH2 powder and 2-MI solid powder to methanol solution and ultrasonically disperse for 3-5 min to obtain a mixed solution;

[0016] Step 2.2: Add Zn(NO3)2·6H2O to the methanol solution and ultrasonically disperse for 3-5 min to obtain a Zn mixed solution;

[0017] Step 2.3: Under ultrasonic conditions, the Zn mixed solution from step 2.2 is rapidly added to the mixed solution from step 2.1, and then transferred to an ultrasonic cell disruptor for ultrasonication. After the reaction, the solution is stirred for 3-4 hours. The obtained mixture is washed several times with methanol to obtain a MIL-125-NH2@ZIF-8 dispersion, which is then vacuum dried to obtain MIL-125-NH2@ZIF-8 powder.

[0018] Step 3 specifically involves:

[0019] Step 3.1: Disperse the MIL-125-NH2@ZIF-8 powder from step 2 and the 2-MI solid powder in a methanol solution to obtain a mixed solution;

[0020] Step 3.2: Add Co(NO3)2·6H2O to the methanol solution and ultrasonically disperse for 3-5 min to obtain a uniformly dispersed Co mixed solution;

[0021] Step 3.3: Under ultrasonic conditions, the Co mixed solution from step 3.2 is rapidly added to the mixed solution prepared in step 3.1, ultrasonically dispersed for 30-40 min, and then stirred for 3-4 h;

[0022] Step 3.4: Wash the mixture obtained in step 3.3 several times with methanol to obtain the MIL-125-NH2@ZIF-8@ZIF-67 dispersion;

[0023] Step 3.5: Place the MIL-125-NH2@ZIF-8@ZIF-67 dispersion in a vacuum drying oven for vacuum drying to obtain MIL-125-NH2@ZIF-8@ZIF-67 powder.

[0024] In step 4, the carbonization conditions are as follows: nitrogen gas is introduced at a rate of 40-80 mL / s, the temperature is increased to 600-800℃ at a rate of 5℃ / min, held at this temperature for 2 hours, and finally cooled to room temperature at a rate of 5℃ / min.

[0025] The beneficial effects of this invention are that the introduction of a multi-component MOF effectively improves the impedance matching of the absorber, allowing as many incident electromagnetic waves as possible to enter the composite absorber for dissipation and attenuation. Furthermore, the abundant heterogeneous interfaces in the core-shell structure induce interfacial polarization losses, thereby enhancing electromagnetic wave absorption. Simultaneously, the complex structure traps electromagnetic waves within the absorber, resulting in multiple reflections and scattering losses. Benefiting from the synergistic effect of these advantages, the prepared TiO2@N / C@Co / C composite absorber exhibits excellent electromagnetic wave absorption performance, meeting the application requirements of next-generation electronic devices. Attached Figure Description

[0026] Figure 1 This is a morphological diagram of the disc-shaped MIL-125-NH2;

[0027] Figure 2 This is a topographic image of MIL-125-NH2@ZIF-8;

[0028] Figure 3 This is a topographic image of MIL-125-NH2@ZIF-8@ZIF-67;

[0029] Figure 4 This is a microstructure diagram of the TiO2@N / C@Co / C composite microwave absorber;

[0030] Figure 5 This is the XRD pattern of a core-shell structured TiO2@N / C@Co / C composite microwave absorber;

[0031] Figure 6 This is a graph showing the electromagnetic wave absorption performance of the core-shell structure TiO2@N / C@Co / C composite microwave absorber of Example 1;

[0032] Figure 7 This is a graph showing the electromagnetic wave absorption performance of the core-shell structure TiO2@N / C@Co / C composite microwave absorber of Example 2;

[0033] Figure 8 This is a graph showing the electromagnetic wave absorption performance of the core-shell structure TiO2@N / C@Co / C composite absorber of Example 3. Detailed Implementation

[0034] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0035] The preparation method of the core-shell structured TiO2@N / C@Co / C composite microwave absorber of the present invention is carried out according to the following steps:

[0036] Step 1: Prepare MIL-125-NH2 by microwave-assisted synthesis;

[0037] Diaminoterephthalic acid (BTC) was used as an organic linker and isopropyl titanate (TTIP) as a metal source. A mixed solution of N,N-dimethylformamide (DMF) and methanol was added in a certain proportion and ultrasonically dispersed. Subsequently, the mixed solution was transferred to a multifunctional microwave synthesizer and heated by microwave radiation to promote the reaction. The product was centrifuged, washed and vacuum dried to obtain MIL-125-NH2 powder.

[0038] Specifically, diaminoterephthalic acid (BTC) was added to a mixed solution of DMF and methanol and ultrasonically dispersed for 10-20 min to ensure complete dissolution. Isopropyl titanate was then added to the resulting solution and ultrasonically dispersed for 30-40 min to ensure complete dissolution, resulting in a homogeneous mixed solution. The mixed solution was then transferred to a multifunctional microwave synthesizer for microwave-assisted synthesis. Subsequently, the suspension obtained from the first step was centrifuged and washed several times with DMF and methanol to obtain a MIL-125-NH2 dispersion. The MIL-125-NH2 dispersion was then placed in a vacuum drying oven for vacuum drying to obtain a yellow MIL-125-NH2 powder.

[0039] The volume ratio of DMF to methanol is 1:1; the mass ratio of diaminoterephthalic acid to isopropyl titanate is 1.5-2.5:0.5-1.5; the microwave-assisted synthesis temperature is 120-180℃, and the time is 0.5-4h; the centrifugation speed is 7500-8500r / min, and the centrifugation time is 5-8min; the vacuum drying temperature is 50-70℃, and the time is 10-14h.

[0040] Step 2: Prepare MIL-125-NH2@ZIF-8 using ultrasonic synthesis method;

[0041] MIL-125-NH2 powder and 2-MI solid powder were ultrasonically dispersed in a methanol solution to obtain a mixed solution. Subsequently, Zn(NO3)2·6H2O was dissolved in methanol and combined with the mixed solution. The mixture was then ultrasonically dispersed and stirred in an ultrasonic cell disruptor to promote the formation of a two-component epitaxial MOF structure, thus obtaining MIL-125-NH2@ZIF-8. Specifically:

[0042] Step 2.1: Add MIL-125-NH2 powder and 2-methylimidazole (2-MI) solid powder to methanol solution, and ultrasonically disperse for 3-5 min to obtain a mixed solution;

[0043] The mass ratio of MIL-125-NH2 powder, 2-MI solid powder, and methanol is 0.8-1.2: 2.6-3.4: 0.8-1.2.

[0044] Step 2.2: Add Zn(NO3)2·6H2O to the methanol solution and ultrasonically disperse for 3-5 min to obtain a Zn mixed solution;

[0045] The mass ratio of Zn(NO3)2·6H2O to methanol is 9.5-10.5:0.5-1.5;

[0046] Step 2.3: Under ultrasonic conditions, the Zn mixed solution from Step 2.2 is rapidly added to the mixed solution from Step 2.1, and then transferred to an ultrasonic cell disruptor for ultrasonication to accelerate the reaction. After the reaction, the solution is placed on a magnetic stirrer and stirred continuously for 3-4 hours to ensure thorough mixing. The obtained mixture is washed several times with methanol to obtain a MIL-125-NH2@ZIF-8 dispersion. The MIL-125-NH2@ZIF-8 dispersion is placed in a vacuum drying oven for vacuum drying to obtain a pale yellow MIL-125-NH2@ZIF-8 powder.

[0047] The ultrasonic cell disruptor was set to 600W for 5-10 minutes to promote the uniform growth of ZIF-8 on the surface of MIL-125-NH2.

[0048] The centrifugation speed is 7500-8500 r / min, and the centrifugation time is 5-8 min; the vacuum drying temperature is 50-70℃, and the time is 10-14 h.

[0049] Step 3: Prepare MIL-125-NH2@ZIF-8@ZIF-67;

[0050] MIL-125-NH2@ZIF-8 powder was mixed with Co(NO3)2·6H2O, and then ultrasonically dispersed and stirred in a methanol solution to promote the epitaxial growth of ZIF-67 on the surface of MIL-125-NH2@ZIF-8; specifically:

[0051] Step 3.1: Disperse the MIL-125-NH2@ZIF-8 powder from step 2 and the 2-MI solid powder in a methanol solution to obtain a mixed solution;

[0052] The mass ratio of MIL-125-NH2@ZIF-8 powder, 2-MI solid powder, and methanol is 0.8-1.2:2.6-3.4:0.8-1.2;

[0053] Step 3.2: Add Co(NO3)2·6H2O to the methanol solution and ultrasonically disperse for 3-5 min to obtain a uniformly dispersed Co mixed solution;

[0054] The mass ratio of Co(NO3)2·6H2O to methanol is 9.5-10.5:0.5-1.5;

[0055] Step 3.3: Under ultrasonic conditions, rapidly add the Co mixed solution from step 3.2 to the mixed solution prepared in step 3.1, and ultrasonically disperse for 30-40 minutes to ensure uniform dispersion. Then place it on a magnetic stirrer and stir continuously for 3-4 hours to ensure complete reaction;

[0056] Step 3.4: Wash the mixture obtained in step 3.3 several times with methanol to obtain the MIL-125-NH2@ZIF-8@ZIF-67 dispersion;

[0057] The centrifugation speed is 7500-8500 r / min, and the centrifugation time is 5-8 min;

[0058] Step 3.5: Place the MIL-125-NH2@ZIF-8@ZIF-67 dispersion in a vacuum drying oven for vacuum drying to obtain light purple MIL-125-NH2@ZIF-8@ZIF-67 powder;

[0059] The vacuum drying temperature is 50-70℃, and the time is 10-14 hours.

[0060] Step 4: Carbonize the MIL-125-NH2@ZIF-8@ZIF-67 powder to transform the three-component MOF-on-MOF structure MIL-125-NH2@ZIF-8@ZIF-67 into a core-shell structure composite material, thus forming a core-shell structure TiO2@N / C@Co / C composite microwave absorber.

[0061] The carbonization conditions are as follows: nitrogen gas is introduced at a rate of 40-80 mL / s, the temperature is increased to 600-800℃ at a rate of 5℃ / min, held at the temperature for 2 hours, and finally cooled to room temperature at a rate of 5℃ / min.

[0062] Example 1

[0063] The preparation method of the TiO2@N / C@Co / C composite microwave absorber with core-shell MOF-on-MOF structure of the present invention is specifically implemented according to the following steps:

[0064] Step 1: Prepare MIL-125-NH2 using a microwave-assisted synthesis method; the specific steps are as follows:

[0065] Step 1.1: Add 0.3g of BTC to a mixed solution of 150mL DMF and 150mL methanol and sonicate for 10min to completely dissolve it.

[0066] Step 1.2: Add 0.15g of TTIP to the solution obtained in step 1.1, and sonicate for 30min to obtain a homogeneous mixed solution;

[0067] Step 1.3: The mixed solution is transferred to a multifunctional microwave synthesizer under magnetic stirring for microwave-assisted synthesis;

[0068] The microwave synthesizer was heated for 8 minutes to reach 120°C, with a maximum output power of 700W, and held at that temperature for 30 minutes to promote the formation of MIL-125-NH2.

[0069] Step 1.4: After the reaction is complete, wash the MIL-125-NH2 suspension with DMF and methanol by centrifugation at 7500 r / min for 8 min.

[0070] Step 1.5: Place the washed MIL-125-NH2 dispersion in a vacuum drying oven for drying to obtain MIL-125-NH2 powder.

[0071] The vacuum drying temperature is 50℃ and the time is 10 hours.

[0072] Step 2: Prepare MIL-125-NH2@ZIF-8 using ultrasonic synthesis; the specific steps are as follows:

[0073] Step 2.1: Add 0.1g of MIL-125-NH2 powder and 0.3g of 2-MI solid powder to 100mL of methanol solution and ultrasonically disperse for 3min.

[0074] Step 2.2: Add 3.0 g of Zn(NO3)2·6H2O to 300 mL of methanol solution and disperse by ultrasonication for 3 min;

[0075] Step 2.3: Under ultrasonic conditions, the solution obtained in step 2.2 is rapidly added to the mixed solution prepared in step 2.1, and then transferred to an ultrasonic cell disruptor for ultrasonication. After the reaction, the solution is placed on a magnetic stirrer and stirred continuously for 3 hours to ensure thorough mixing.

[0076] The ultrasonic cell disruptor was set to 600W for 5 minutes to promote the uniform growth of ZIF-8 on the surface of MIL-125-NH2.

[0077] Step 2.4: Wash the reaction mixture with methanol and centrifuge at 7500 r / min for 8 min.

[0078] Step 2.5: The washed MIL-125-NH2@ZIF-8 dispersion was vacuum dried at 50°C for 10 hours to obtain a light yellow MIL-125-NH2@ZIF-8 powder.

[0079] Step 3, prepare MIL-125-NH2@ZIF-8@ZIF-67, the specific steps are as follows:

[0080] Step 3.1: Take 0.3g of MIL-125-NH2@ZIF-8 powder prepared in step 2, mix it with 0.9g of 2-MI solid powder, and disperse it in 300mL of methanol solution;

[0081] Step 3.2: Add 1.5g of Co(NO3)2·6H2O to 150mL of methanol solution and sonicate for 3min to obtain a uniformly dispersed mixed solution.

[0082] Step 3.3: Under ultrasonic conditions, the solution obtained in step 3.2 is rapidly added to the mixed solution prepared in step 2.1, and then transferred to an ultrasonic cell disruptor for ultrasonication to accelerate the reaction. After the reaction, the solution is placed on a magnetic stirrer and stirred continuously for 3 hours to ensure thorough mixing.

[0083] The ultrasonic cell disruptor was set to 600W for 5 minutes.

[0084] Step 3.4: Wash the mixture obtained in step 3.3 several times with methanol to obtain the MIL-125-NH2@ZIF-8@ZIF-67 dispersion;

[0085] Step 3.5: The washed MIL-125-NH2@ZIF-8@ZIF-67 dispersion was vacuum dried at 50°C for 10 hours to obtain MIL-125-NH2@ZIF-8@ZIF-67 powder.

[0086] Step 4: Place the MIL-125-NH2@ZIF-8@ZIF-67 powder obtained in Step 3 into a tube furnace for carbonization treatment; the specific carbonization conditions are as follows: nitrogen gas is introduced at a rate of 80 mL / s, the temperature is increased to 800℃ at a rate of 5℃ / min, held at the temperature for 2 hours, and finally cooled to room temperature at a rate of 5℃ / min.

[0087] like Figure 6 As shown, the TiO2@N / C@Co / C composite microwave absorber prepared in Example 1 has a microwave absorption performance of -37.9dB, which is significantly improved compared with the microwave absorption performance of ZIF-8 derived magnetic carbon (-3.5dB) and ZIF-67 derived magnetic carbon (-21.8dB), and can meet its practical application requirements.

[0088] Example 2

[0089] The preparation method of the core-shell MOF-on-MOF structure TiO2@N / C@Co / C composite microwave absorber of the present invention is carried out according to the following steps:

[0090] Step 1: Prepare MIL-125-NH2 using a microwave-assisted synthesis method. The specific steps are as follows:

[0091] Step 1.1: Add 0.3g of BTC to a mixed solution of 150mL DMF and 150mL methanol and sonicate for 20min to completely dissolve it.

[0092] Step 1.2: Add 0.3g of TTIP to the solution obtained in step 1.1, and sonicate for 40min to obtain a homogeneous mixed solution;

[0093] Step 1.3: Transfer the mixed solution to a multifunctional microwave synthesizer under magnetic stirring for microwave-assisted synthesis.

[0094] The microwave synthesizer was heated for 8 minutes to reach 150°C, with a maximum output power of 700W, and held at that temperature for 2 hours to promote the formation of MIL-125-NH2.

[0095] Step 1.4: After the reaction is complete, wash the MIL-125-NH2 suspension with DMF and methanol by centrifugation at 8000 r / min for 5 min.

[0096] Step 1.5: Place the washed MIL-125-NH2 dispersion in a vacuum drying oven for drying to obtain yellow MIL-125-NH2 powder;

[0097] The vacuum drying temperature was 60℃ and the time was 12 hours.

[0098] Step 2, prepare MIL-125-NH2@ZIF-8; the specific steps are as follows:

[0099] Step 2.1: Mix 0.1g of MIL-125-NH2 powder with 0.3g of 2-MI solid powder, add to 100mL of methanol solution and ultrasonically disperse for 5min;

[0100] Step 2.2: Add 3.0 g of Zn(NO3)2·6H2O to 300 mL of methanol solution and sonicate for 5 min.

[0101] Step 2.3: Under ultrasonic conditions, the solution obtained in step 2.2 is rapidly added to the mixed solution prepared in step 2.1, and then transferred to an ultrasonic cell disruptor for ultrasonication. After the reaction, the solution is placed on a magnetic stirrer and stirred continuously for 4 hours to ensure thorough mixing.

[0102] The ultrasonic cell disruptor was set to 600W for 8 minutes to promote the uniform growth of ZIF-8 on the surface of MIL-125-NH2.

[0103] Step 2.4: Wash the reaction mixture with methanol and centrifuge at 800 r / min for 5 min.

[0104] Step 2.5: The washed MIL-125-NH2@ZIF-8 dispersion was vacuum dried to obtain a light yellow MIL-125-NH2@ZIF-8 powder;

[0105] The vacuum drying temperature was 60℃ and the time was 12 hours.

[0106] Step 3, prepare MIL-125-NH2@ZIF-8@ZIF-67; the specific steps are as follows:

[0107] Step 3.1: Take 0.3g of MIL-125-NH2@ZIF-8 powder prepared in step 2, mix it with 0.9g of 2-MI solid powder, and disperse it in 250mL of methanol solution;

[0108] Step 3.2: Take 1.5g of Co(NO3)2·6H2O and add it to 150mL of methanol solution. Disperse it by sonication for 5min to obtain a uniformly dispersed mixed solution.

[0109] Step 3.3: Under ultrasonic conditions, the solution obtained in step 3.2 is rapidly added to the mixed solution prepared in step 2.1, and then transferred to an ultrasonic cell disruptor for ultrasonication to accelerate the reaction rate. After the reaction, the solution is placed on a magnetic stirrer and stirred continuously for 4 hours to ensure thorough mixing.

[0110] The ultrasonic cell disruptor was set to 600W for 8 minutes.

[0111] Step 3.4: Wash the mixture obtained in step 3.3 several times with methanol to obtain the MIL-125-NH2@ZIF-8@ZIF-67 dispersion;

[0112] Step 3.5: The washed MIL-125-NH2@ZIF-8@ZIF-67 dispersion was vacuum dried at 60℃ for 12 hours to obtain light purple MIL-125-NH2@ZIF-8@ZIF-67 powder.

[0113] Step 4: Place the MIL-125-NH2@ZIF-8 powder obtained in Step 3 into a tube furnace for carbonization treatment;

[0114] The carbonization conditions were as follows: nitrogen gas was introduced at a rate of 80 mL / s, the temperature was increased to 800℃ at a rate of 5℃ / min, held at that temperature for 2 hours, and finally cooled to room temperature at a rate of 5℃ / min.

[0115] like Figure 7 As shown, the TiO2@N / C@Co / C composite microwave absorber prepared in Example 2 has a microwave absorption performance of -64.6dB, which is significantly improved compared with the microwave absorption performance of ZIF-8 derived magnetic carbon (-3.5dB) and ZIF-67 derived magnetic carbon (-21.8dB), and can meet its application in the next generation of high-performance fields.

[0116] Example 3

[0117] The preparation method of the core-shell MOF-on-MOF structure TiO2@N / C@Co / C composite microwave absorber of the present invention is carried out according to the following steps:

[0118] Step 1: Prepare MIL-125-NH2 using a microwave-assisted synthesis method. The specific steps are as follows:

[0119] Step 1.1: Add 0.3g of BTC to a mixed solution of 150mL DMF and 150mL methanol and sonicate for 20min to completely dissolve it.

[0120] Step 1.2: Add 0.45g of TTIP to the solution obtained in step 1.1, and sonicate for 30min to obtain a homogeneous mixed solution;

[0121] Step 1.3: Transfer the mixed solution to a multifunctional microwave synthesizer under magnetic stirring for microwave-assisted synthesis.

[0122] The microwave synthesizer was heated for 8 minutes to reach 180°C, with a maximum output power of 700W, and held at that temperature for 4 hours to promote the formation of MIL-125-NH2.

[0123] Step 1.4: After the reaction is complete, wash the MIL-125-NH2 suspension with DMF and methanol by centrifugation at 8000 r / min for 5 min.

[0124] Step 1.5: Place the washed MIL-125-NH2 dispersion in a vacuum drying oven for drying to obtain yellow MIL-125-NH2 powder;

[0125] The vacuum drying temperature is 70℃ and the time is 14 hours.

[0126] Step 2: Prepare MIL-125-NH2@ZIF-8 using ultrasonic synthesis; the specific steps are as follows:

[0127] Step 2.1: Mix 0.1g of MIL-125-NH2 powder with 0.3g of 2-MI solid powder, add to 100mL of methanol solution and ultrasonically disperse for 5min;

[0128] Step 2.2: Add 3.0 g of Zn(NO3)2·6H2O to 300 mL of methanol solution and sonicate for 5 min.

[0129] Step 2.3: Under ultrasonic conditions, the solution obtained in step 2.2 is rapidly added to the mixed solution prepared in step 2.1, and then transferred to an ultrasonic cell disruptor for ultrasonication. After the reaction, the solution is placed on a magnetic stirrer and stirred continuously for 4 hours to ensure thorough mixing.

[0130] The ultrasonic cell disruptor was set to 600W for 10 minutes to promote the uniform growth of ZIF-8 on the surface of MIL-125-NH2.

[0131] Step 2.4: Wash the reaction mixture with methanol and centrifuge at 8000 r / min for 5 min.

[0132] Step 2.5: The washed MIL-125-NH2@ZIF-8 dispersion was vacuum dried to obtain a light yellow MIL-125-NH2@ZIF-8 powder;

[0133] The vacuum drying temperature is 70℃ and the time is 14 hours.

[0134] Step 3, prepare MIL-125-NH2@ZIF-8@ZIF-67, the specific steps are as follows:

[0135] Step 3.1: Take 0.3g of MIL-125-NH2@ZIF-8 powder prepared in step 2, mix it with 0.9g of 2-MI solid powder, and disperse it in 250mL of methanol solution;

[0136] Step 3.2: Take 1.5g of Co(NO3)2·6H2O and add it to 150mL of methanol solution. Disperse it by sonication for 3min to obtain a uniformly dispersed mixed solution.

[0137] Step 3.3: Under ultrasonic conditions, the solution obtained in step 3.2 is rapidly added to the mixed solution prepared in step 2.1, and then transferred to an ultrasonic cell disruptor for ultrasonication to accelerate the reaction rate. After the reaction, the solution is placed on a magnetic stirrer and stirred continuously for 4 hours to ensure thorough mixing.

[0138] The ultrasonic cell disruptor was set to 600W for 10 minutes.

[0139] Step 3.4: Wash the mixture obtained in step 3.3 several times with methanol to obtain the MIL-125-NH2@ZIF-8@ZIF-67 dispersion;

[0140] Step 3.5: The washed MIL-125-NH2@ZIF-8@ZIF-67 dispersion was vacuum dried at 70℃ for 14 hours to obtain light purple MIL-125-NH2@ZIF-8@ZIF-67 powder.

[0141] Step 4: Place the MIL-125-NH2@ZIF-8 powder obtained in Step 3 into a tube furnace for carbonization treatment;

[0142] The carbonization conditions were as follows: nitrogen gas was introduced at a rate of 80 mL / s, the temperature was increased to 800℃ at a rate of 5℃ / min, held at that temperature for 2 hours, and finally cooled to room temperature at a rate of 5℃ / min.

[0143] like Figure 8As shown, the TiO2@N / C@Co / C composite microwave absorber prepared in Example 3 has a microwave absorption performance of -36.1dB, which is significantly improved compared with the microwave absorption performance of ZIF-8 derived magnetic carbon (-3.5dB) and ZIF-67 derived magnetic carbon (-21.8dB), and can meet its practical application requirements.

[0144] The main difference between Examples 1, 2, and 3 lies in the different amounts of 2-aminoterephthalic acid (BTC) and titanium tetraisopropanolate (TTIP) added during the preparation of MIL-125-NH2, which leads to the subsequent electromagnetic wave absorption performance. Obtaining excellent electromagnetic wave absorption performance usually requires good impedance matching and strong electromagnetic wave attenuation characteristics. Examples 1, 2, and 3 all exhibited relatively good electromagnetic wave absorption performance, at -37.9dB, -64.6dB, and -36.1dB, respectively. The excellent electromagnetic wave absorption performance of the examples is mainly attributed to the following aspects: (1) The establishment of the electromagnetic multi-loss mechanism improves the absorption efficiency while optimizing the impedance matching of the material, enabling electromagnetic waves to enter the composite absorber for dissipation and attenuation; (2) The construction of the core-shell structure introduces abundant heterogeneous interfaces, which can act as polarization centers to induce polarization losses (interface polarization, dipole polarization), thereby further dissipating electromagnetic waves; (3) The introduction of magnetic metals imparts magnetic loss to the composite absorber. Thanks to the synergistic effect of improved impedance matching and rich electromagnetic wave attenuation loss mechanisms (dielectric loss, magnetic loss, interface polarization loss, multiple reflection loss and dipole polarization loss), the prepared composite absorber exhibits excellent electromagnetic wave absorption performance.

[0145] The mechanism of action of the method in this invention is as follows: The core-shell MOF-on-MOF structured TiO2@N / C@Co / C composite absorber prepared in this invention exhibits excellent electromagnetic wave absorption performance, its advantages stemming from its unique microstructure and complex composition. This composite material significantly improves the internal dissipation and attenuation efficiency of electromagnetic waves by optimizing the impedance matching between electromagnetic waves and the material. In the MOF-on-MOF structure, the abundant heterogeneous interfaces between MOF layers and its complex chemical composition promote the occurrence of various electromagnetic wave dissipation mechanisms, including dielectric loss, magnetic loss, polarization loss, and multiple reflection loss. The synergistic effect of these mechanisms not only enhances the absorption efficiency but also expands the effective absorption frequency band.

[0146] Figures 1-4The images show SEM images of MIL-125-NH2, MIL-125-NH2@ZIF-8, MIL-125-NH2@ZIF-8@ZIF-67, and TiO2@N / C@Co / C formed after high-temperature heat treatment. Figure 1 The pancake-like structure of MIL-125-NH2 can be clearly observed, with uniform distribution and regular morphology, indicating the successful synthesis of pancake-like MIL-125-NH2. Figure 2 As can be seen, after ZIF-8 growth, MIL-125-NH2 maintained its original morphology without significant shape changes, indicating the structural stability of MIL-125-NH2. From... Figure 3 As can be seen, after in-situ growth of ZIF-67, ZIF-67 uniformly coats the surface of MIL-125-NH2, forming a typical core-shell structure. This MOF-on-MOF structure combines the characteristics of various heterogeneous MOFs, introducing multiple metal sources, increasing the specific surface area, enriching the porous structure, and providing abundant heterogeneous interfaces, all of which lay the foundation for the realization of high-performance electromagnetic wave absorbing materials. Figure 4 As can be seen, after high-temperature carbonization, the collapse of MOF materials and the formation of porous carbon structures further expand the cavities in the core and shell. This facilitates multiple reflections and scattering of electromagnetic waves within the material, thereby further dissipating electromagnetic waves. Furthermore, the newly introduced defects and heterogeneous interfaces during heat treatment establish multipolarization centers in the material, inducing polarization losses.

[0147] Figure 5 The images show the XRD patterns of the prepared TiO2@N / C and TiO2@N / C@Co / C materials. The XRD patterns reflect the crystal structure and phase composition of the materials. Analysis of the XRD patterns confirms the successful synthesis of the TiO2@N / C and TiO2@N / C@Co / C composite microwave absorbing materials.

[0148] The preparation method of the core-shell MOF-on-MOF structured TiO2@N / C@Co / C composite microwave absorber of the present invention adopts a strategy combining microwave-assisted synthesis and precipitation method. First, microwave synthesis precisely controls the synthesis of MIL-125-NH2 to ensure the uniformity and stability of the material's basic structure. Then, the complex MOF-on-MOF structure is gradually constructed using the precipitation method, and the effective combination of multi-component materials is achieved through precise control of chemical reactions. Finally, a heat treatment process is used to control the morphology and surface / interface defects of the material, further optimizing its electromagnetic wave absorption performance. This preparation method is simple, efficient, and suitable for large-scale production, providing an effective approach for the preparation of high-performance electromagnetic wave absorbing materials.

[0149] Core-shell MOF-on-MOF structured TiO2@N / C@Co / C composite microwave absorbers are particularly suitable for high-tech applications such as aerospace, electronic packaging, and next-generation electronic devices due to their superior electromagnetic wave absorption properties. This material can effectively reduce electromagnetic interference, improve the performance and stability of electronic devices, and also has significant value in electromagnetic compatibility and radiation protection.

Claims

1. A method for preparing a core-shell structured TiO2@N / C@Co / C composite microwave absorber, characterized in that, The specific steps are as follows: Step 1: Prepare MIL-125-NH2 powder by microwave-assisted synthesis; Step 2: Prepare MIL-125-NH2@ZIF-8 powder using ultrasonic synthesis; specifically: Step 2.1: Add MIL-125-NH2 powder and 2-MI solid powder to methanol solution and ultrasonically disperse for 3-5 min to obtain a mixed solution; Step 2.2: Add Zn(NO3)2·6H2O to the methanol solution and ultrasonically disperse for 3-5 min to obtain a Zn mixed solution; Step 2.3: Under ultrasonic conditions, the Zn mixed solution from step 2.2 is rapidly added to the mixed solution from step 2.1, and then transferred to an ultrasonic cell disruptor for ultrasonication. After the reaction, the solution is stirred for 3-4 hours. The obtained mixture is washed several times with methanol to obtain a MIL-125-NH2@ZIF-8 dispersion, which is then vacuum dried to obtain MIL-125-NH2@ZIF-8 powder. Step 3: Mix MIL-125-NH2@ZIF-8 powder with Co(NO3)2·6H2O, and add methanol solution for ultrasonic dispersion and stirring to obtain MIL-125-NH2@ZIF-8@ZIF-67 powder; specifically: Step 3.1: Disperse the MIL-125-NH2@ZIF-8 powder and 2-MI solid powder from step 2 in a methanol solution to obtain a mixed solution; Step 3.2: Add Co(NO3)2·6H2O to the methanol solution and ultrasonically disperse for 3-5 min to obtain a uniformly dispersed Co mixed solution; Step 3.3: Under ultrasonic conditions, the Co mixed solution from step 3.2 is rapidly added to the mixed solution prepared in step 3.1, ultrasonically dispersed for 30-40 min, and then stirred for 3-4 h; Step 3.4: Wash the mixture obtained in step 3.3 several times with methanol to obtain the MIL-125-NH2@ZIF-8@ZIF-67 dispersion; Step 3.5: Place the MIL-125-NH2@ZIF-8@ZIF-67 dispersion in a vacuum drying oven for vacuum drying to obtain MIL-125-NH2@ZIF-8@ZIF-67 powder; Step 4: Carbonize the MIL-125-NH2@ZIF-8@ZIF-67 powder to form a core-shell structured TiO2@N / C@Co / C composite microwave absorber.

2. The preparation method of the core-shell structured TiO2@N / C@Co / C composite microwave absorber as described in claim 1, characterized in that, In step 1, specifically: Diaminoterephthalic acid was added to a mixed solution of DMF and methanol and ultrasonically dispersed for 10-20 min. Isopropyl titanate was added to the resulting solution and ultrasonically dispersed for 30-40 min to obtain a homogeneous mixed solution. The mixed solution was then subjected to microwave-assisted synthesis. The resulting suspension was then centrifuged and washed several times with DMF and methanol to obtain a MIL-125-NH2 dispersion. The dispersion was then vacuum dried to obtain MIL-125-NH2 powder.

3. The preparation method of the core-shell structured TiO2@N / C@Co / C composite microwave absorber as described in claim 2, characterized in that, The microwave-assisted synthesis temperature is 120-180℃, and the time is 0.5-4h; the centrifugation speed is 7500-8500r / min, and the centrifugation time is 5-8min; the vacuum drying temperature is 50-70℃, and the time is 10-14h.

4. The preparation method of the core-shell structured TiO2@N / C@Co / C composite microwave absorber as described in claim 1, characterized in that, In step 4, the carbonization conditions are as follows: nitrogen gas is introduced at a rate of 40-80 mL / s, the temperature is increased to 600-800℃ at a rate of 5℃ / min, the temperature is maintained for 2 hours, and finally the temperature is reduced to room temperature at a rate of 5℃ / min.

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