Electromagnetic wave absorbing material and preparation method thereof

Abstract

The present invention belongs to the technical field of composite materials and provides an electromagnetic wave absorbing material and a preparation method thereof. The method comprises the following steps: mixing Cu2O powder, ammonium molybdate, thiourea and water and reacting them to obtain an electromagnetic wave absorbing material. In the present invention, an electromagnetic wave absorbing material with a high 1T phase ratio is prepared by a simple hydrothermal method using the principle of alkali ion intercalation, and the self-templated growth mechanism of MoS2 nanosheets is applied to Cu 2‑x The surface loading of the S hollow box avoids the problem of MoS2 transition agglomeration. The electromagnetic wave absorbing material prepared by the present invention has good dielectric loss and impedance performance and is an excellent lightweight electromagnetic wave absorber.

Description

Technical Field

[0001] The present invention relates to the technical field of composite materials, and in particular to an electromagnetic wave absorbing material and a preparation method thereof. Background Art

[0002] Graphene is considered a typical two-dimensional layered material. Due to its excellent physical and chemical properties, it is an ideal lightweight electromagnetic wave (EMW) absorber. Although the design of various types of graphene-based composite EMW absorbers is quite mature, its high cost limits its application. The development of practical absorbers is urgent to address the increasingly serious problem of electromagnetic pollution. Among alternative two-dimensional material candidates, the layered structure of MoS2, a typical representative of transition metal sulfides (TMDs), has been extensively studied due to its many interesting properties. In 2015, Ning et al. first reported the EMW absorption properties of MoS2 nanosheets prepared by a hydrothermal method. Subsequently, a number of MoS2-based composite absorbers have been reported, including composites of MoS2 with semiconductor materials, conductive materials, and ferromagnetic materials. The excellent dielectric loss capability and impedance matching characteristics make MoS2 a new type of EMW absorber.

[0003] Due to the different coordination patterns between transition metals and chalcogenides, TMDs typically exist in multiple forms. For MoS2, this structure typically exhibits two phases: a 2H phase with hexagonal coordination and a 1T phase with octahedral coordination, depending on the positions of the six S atoms surrounding the Mo atom. The crystal structure of a material plays a crucial role in determining its physical, chemical, and electronic properties, and thus, its intrinsic properties can be tuned by manipulating the crystal structure of MoS2. 2H-MoS2 has active sites located only at its edges, resulting in poor electron transport properties, which limits its applications in catalysis and electrochemistry. Fortunately, these issues can be overcome by converting it to the 1T phase. 1T-MoS2 exhibits excellent electronic, optical, and mechanical properties. By precisely tailoring the size of 1T-MoS2 nanosheets and rationally combining them with other functional materials, novel interfacial materials with unique crystal structures can be obtained. Given the superior properties of the 1T phase, phase manipulation of MoS2 holds promise as an effective approach to improving electromagnetic wave absorption.

[0004] Due to the metastability of 1T-MoS2, it is generally difficult to obtain in nature. Therefore, extensive research has been devoted to the targeted manipulation of 2H-MoS2 to generate 1T-MoS2, including techniques such as element doping, temperature regulation, pressure regulation, stress regulation, plasma / electron bombardment induction, and gas molecule induction. While significant progress has been achieved, many methods for improving the proportion of the 1T phase in MoS2 are plagued by high costs and complex procedures. Furthermore, due to van der Waals forces, layered MoS2 tends to aggregate and stack, resulting in a large dead volume that limits electromagnetic wave response.

[0005] Therefore, how to provide an electromagnetic wave absorbing material with low cost, simple preparation method and excellent electromagnetic wave absorbing performance has become a problem that needs to be solved urgently by those skilled in the art. Summary of the Invention

[0006] In view of this, the present invention provides an electromagnetic wave absorbing material and a preparation method thereof, the purpose of which is to solve the technical problems that the preparation method of the existing 1T-MoS2 material is complex, costly and has poor electromagnetic wave absorption performance.

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

[0008] The present invention provides a method for preparing an electromagnetic wave absorbing material, comprising the following steps:

[0009] The electromagnetic wave absorbing material is obtained by mixing Cu2O powder, ammonium molybdate, thiourea and water and reacting them.

[0010] Furthermore, the molar ratio of the Cu2O powder to ammonium molybdate is 3-4:0.25-1.

[0011] Furthermore, the Mo / S molar ratio of the ammonium molybdate and thiourea is 1:2-8.

[0012] Furthermore, the molar volume ratio of ammonium molybdate to water is 0.25-1 mmol:100-200 mL.

[0013] Furthermore, the reaction temperature is 160-240° C., and the reaction time is 20-30 h.

[0014] The present invention also provides an electromagnetic wave absorbing material prepared by the above preparation method.

[0015] It can be seen from the above technical solution that compared with the prior art, the beneficial effects of the present invention are as follows:

[0016] The electromagnetic wave absorbing material prepared by the present invention is a core-shell composite structure of MoS2 coated hollow Cu9S5 cubes prepared by a simple hydrothermal method. In an acidic environment, a large amount of NH4 +Inserted into the MoS2 interlayer, it has a high 1-T phase ratio. In addition, the self-templated growth mechanism of MoS2 nanosheets is applied to the surface loading of Cu2-xS hollow boxes, avoiding the problem of MoS2 transition agglomeration;

[0017] Due to the excellent properties of the hollow structure, a conductive network can be formed at a relatively low mass filling concentration. In addition, multiple dielectric loss mechanisms such as dipole polarization and interface polarization make the electromagnetic wave absorbing material prepared by the present invention have excellent electromagnetic wave absorption properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a diagram showing the crystal structure and morphology of the Cu2O powder used in Examples 1 to 3 of the present invention;

[0019] Figure 2 Cu 2-x S@MoS2-1、Cu 2-x S@MoS2-2 and Cu 2-x Microscopic morphology of S@MoS2-3;

[0020] Figure 3 Cu 2-x Schematic diagram of the synthesis process of S@1T-MoS2 hollow microbox;

[0021] Figure 4 a, b, c, and d are Cu 2-x XRD pattern, XPS pattern, Cu2p pattern and Mo3d pattern of S@MoS2;

[0022] Figure 5 The composition ratio of Cu9S5 and MoS2 in the products of Examples 1 to 3 is shown in FIG.

[0023] Figure 6 Cu 2-x Complex dielectric constant diagram of S@MoS2 sample with a filling ratio of 40wt%;

[0024] Figure 7 Cu 2-x Reflection loss evaluation diagram of S@MoS2 sample. DETAILED DESCRIPTION

[0025] The present invention provides a method for preparing an electromagnetic wave absorbing material, comprising the following steps:

[0026] The electromagnetic wave absorbing material is obtained by mixing Cu2O powder, ammonium molybdate, thiourea and water and reacting them.

[0027] In the present invention, the molar ratio of the Cu2O powder to ammonium molybdate is 3-4:0.25-1, preferably 3.2-3.6:0.4-0.8, and more preferably 3.5:0.5-0.6.

[0028] In the present invention, the Mo / S molar ratio of the ammonium molybdate and thiourea is 1:2-8, preferably 1:4-6.

[0029] In the present invention, the molar volume ratio of ammonium molybdate to water is 0.25-1 mmol:100-200 mL, preferably 0.4-0.8 mmol:120-180 mL, and more preferably 0.5-0.6 mmol:140-160 mL.

[0030] In the present invention, the reaction temperature is 160-240° C., preferably 200-220° C.; the reaction time is 20-30 h, preferably 24-26 h.

[0031] The present invention also provides an electromagnetic wave absorbing material prepared by the above preparation method.

[0032] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0033] Example 1

[0034] 3.5 mmol Cu2O powder, 0.25 mmol ammonium molybdate and thiourea were uniformly dissolved in 100 mL deionized water to obtain a mixed solution with an element ratio of Mo:S=1:4. The mixed solution was then reacted at 200°C for 24 hours. After the reaction was completed, it was collected by suction filtration, washed with deionized water three times, and vacuum dried at 60°C. The obtained product was recorded as Cu 2-x S@MoS2-1.

[0035] Example 2

[0036] 3.5 mmol Cu2O powder, 0.5 mmol ammonium molybdate and thiourea were uniformly dissolved in 100 mL deionized water to obtain a mixed solution with an element ratio of Mo:S=1:4. The mixed solution was then reacted at 200°C for 24 hours. After the reaction was completed, it was collected by suction filtration, washed with deionized water three times, and vacuum dried at 60°C. The obtained product was recorded as Cu 2-x S@MoS2-2.

[0037] Example 3

[0038] 3.5 mmol Cu2O powder, 1 mmol ammonium molybdate and thiourea were uniformly dissolved in 100 mL deionized water to obtain a mixed solution with an element ratio of Mo:S=1:4. The mixed solution was then reacted at 200°C for 24 hours. After the reaction was completed, it was collected by suction filtration, washed with deionized water three times, and vacuum dried at 60°C. The obtained product was recorded as Cu 2-x S@MoS2-3.

[0039] Figure 1 The figure is a diagram showing the crystal structure and morphology of the Cu2O powder used in Examples 1 to 3 of the present invention. Figure 1 It can be seen that the Cu2O powder has uniform particle size, smooth surface and good dispersibility, and its average size is about 1 μm.

[0040] Figure 2 Cu 2-x S@MoS2-1、Cu 2-x S@MoS2-2 and Cu 2-x The microscopic morphology of S@MoS2-3 shows that Cu 2-x S@1T-MoS2 presents a hollow structure. When the amount of ammonium molybdate and thiourea is low, some broken box particles can be observed, and the surface is slightly rough. As the amount of ammonium molybdate and thiourea increases, the surface gradually becomes smoother and the breakage rate of the box particles decreases, indicating that the MoS2 is evenly covered ( Figure 2 a1-c1). Cu was observed by TEM images. 2-x Shell state of S@1T-MoS2 hollow microbox ( Figure 2 a2-c2), it can be observed that the MoS2 nanosheets gradually grow thicker and longer with the increase of the amount of ammonium molybdate & thiourea, from the initial attachment growth to the final vertical growth on the surface of the box particles. In addition, Cu 2-x The size of the S@MoS2-3 microbox structure shrinks significantly ( Figure 2 a3-c3), which is related to the surface sulfidation of Cu2O and NH4 + It is related to the synergistic effect on the etching of Cu2O.

[0041] Figure 3 Cu 2-x Schematic diagram of the synthesis process of S@1T-MoS2 hollow microbox. Since the electronegativity of O is stronger than that of S, the O element in Cu2O is easily replaced by S. In addition, the NH4 + It can react with Cu2O to form copper ammonia complex, which is the etching process. The S element in the system and NH4 + If the sulfurization process is dominant, a solid Cu 2-xS cubes; if the etching process dominates, the cubes will completely dissociate into fragments. Therefore, the formation of a perfect hollow structure is the result of the competition between the sulfurization process and the etching process, which eventually tends to an equilibrium state. When the concentrations of ammonium molybdate and thiourea are low, the Cu 2-x S@MoS2-1 and Cu 2-x The morphology and size of S@MoS2-2 are similar to those of the original Cu2O cubes, indicating that the sulfurization process takes precedence over the etching process. After the sulfurization reaction occurs on the Cu2O surface, the residual Cu2O inside is immediately absorbed by NH4 + When the concentration of ammonium molybdate and thiourea is high, the Cu 2-x The size of S@MoS2-3 is significantly reduced, and the internal hollow part is transformed from a cube to a rounded cube, indicating that the etching process at this time occurs first before the sulfurization process, and the Cu2O surface sulfurization is completed in the subsequent etching process.

[0042] Figure 4 a, b, c, and d are Cu 2-x XRD spectrum, XPS spectrum, Cu2p spectrum and Mo3d spectrum of S@MoS2. Figure 4 As shown in a, the diffraction peaks of the prepared sample at 27.8°, 29.2°, 32.0°, 41.6° and 54.4° correspond to the (751), (911), (1000), (1081), (10100) and (1641) crystal planes of the PDF#09-0064 standard card, respectively, indicating that the obtained product is mainly cubic Cu9S5. When the concentrations of ammonium molybdate and thiourea are low, the prepared Cu 2-x The diffraction peak of S@MoS2-1 shows weak noise, which is caused by insufficient crystallinity. As the concentration of ammonium molybdate and thiourea increases, the diffraction peak becomes sharper and the crystallinity of the sample increases. 2-x S@MoS2-1 and Cu 2-x The reason why the diffraction peak of MoS2 is not observed in S@MoS2-2 is due to the low content of MoS2. When the concentrations of ammonium molybdate and thiourea are high, Cu 2-x S@MoS2-3 shows a sharp diffraction peak (red dot) at 9.6°, representing 1T-MoS2. XPS spectra are used to analyze the elemental composition of the sample. Figure 4 b shows the total spectrum of the three samples, where the presence of Cu, O, N, C, Mo, and S elements can be observed. As the concentrations of ammonium molybdate and thiourea increase, the relative signal intensities of the Mo3d orbital and the S2p orbital increase. The Cu2p spectrum is used to further analyze the chemical valence state of the Cu element ( Figure 4 c), where the two main peaks at 932.3eV and 952.0eV belong to Cu2p 3 / 2 and Cu2p1 / 2 , corresponding to Cu + And no independent satellite peaks were observed at 942.6eV and 962.2eV, indicating that there is almost no Cu in the product. 2+ The above proves that the chemical valence of Cu element is Cu + This is consistent with the valence characteristics of the product Cu9S5. 2-x The proportion of 1T phase in S@1T-MoS2 was calculated using the integral of Mo3d ( Figure 4 d) The 1T phase in Cu2-xS@MoS2-1 accounts for 79.2%, slightly lower than that of pure NH4 + -MoS2, which is the copper-ammonia complexation that consumes part of the NH4 + Due to.

[0043] In order to calculate the composition ratio of Cu9S5 and MoS2 in the products of Examples 1 to 3, EDS-mapping elements were used to quantitatively analyze Mo, N, Cu, and S. Figure 5 The colored dots in the figure confirm the uniformity of the distribution of Mo, N, Cu, and S elements. The atomic ratios of Cu, Mo, and S are consistent with the material combination of Cu9S5+MoS2. 2-x S@MoS2-1 and Cu 2-x The content of Mo element in S@MoS2-2 is low, which is the main reason why no MoS2 diffraction peak can be observed in the XRD pattern. When the concentration of ammonium molybdate and thiourea continues to increase, the loading amount of MoS2 on Cu9S5 continues to increase until Cu 2-x In S@MoS2-3, the ratio of Cu atoms to Mo atoms is close to 1:1, indicating that there is a large amount of MoS2 loading on Cu9S5.

[0044] Performance Testing

[0045] Figure 6 ab is Cu 2-x The complex dielectric constant of the S@MoS2 sample with a filling ratio of 40wt% can be observed to be significantly higher than that of NH4 + -MoS2-40wt%, indicating that these hollow core-shell particles can successfully form a conductive network at a lower filling ratio. Figure 6 As can be seen in a, with the increase of ammonium molybdate and thiourea concentrations, Cu 2-xThe increased proportion of MoS2 in S@MoS2 helps reduce the ε′ value. This reduction in ε′ improves the impedance matching between the dielectric and air, allowing more electromagnetic waves to enter the dielectric. However, at frequencies above 6 GHz, the ε″ value can be observed to decrease with increasing MoS2 loading. Although the 1T phase of MoS2 theoretically has very high conductivity, increasing the MoS2 loading will lead to a significant thickening of the core-shell particle shell and a decrease in the degree of hollowing. This decreases the volume concentration at the same filling mass, thereby weakening the product's dielectric loss capacity.

[0046] Cu 2-x The reflection loss of S@MoS2 was evaluated, and the results are as follows Figure 7 As shown in ac, Cu 2-x The electromagnetic wave absorption performance of S@MoS2 is significantly better than that of NH4 + -MoS2. Generally speaking, -10dB R L The value is regarded as the qualified electromagnetic wave absorption threshold, R L The frequency region below -10 dB is called the effective absorption band (EAB), which means that at least 90% of electromagnetic waves are lost. Figure 7 df detailed statistics of the minimum R in the range of 0 to 5 mm L The values ​​and their corresponding EAB show that with the increase of MoS2 loading, the absorption of electromagnetic waves by the samples shows an enhanced trend. 2-x S@MoS2-1 R at 1.9mm L min can reach -31dB, and the effective frequency range is 10.4GHz~13.4GHz; Cu 2-x S@MoS2-2 R at 3mm L min can reach -44.6dB, and the effective frequency range is 6.6GHz~9.6GHz; Cu 2-x S@MoS2-3 R at 2.1mm L The minimum value can reach -52.2dB, and the effective frequency range is 11.9GHz~16.6GHz. Therefore, no matter which sample, its R L min are far above the -10dB absorption standard. 2-x S@MoS2-3 has the most superior electromagnetic wave absorption performance because it has both wide bandwidth and strong absorption at 2.1 mm.

[0047] In summary, the present invention adopts a simple hydrothermal method to prepare the MoS2 coated hollow Cu9S5 cube core-shell composite structure, which is in an acidic environment with a large amount of NH4 +Inserted into the MoS2 interlayer, it has a high 1-T phase ratio. In addition, the self-templated growth mechanism of MoS2 nanosheets is applied to Cu 2-x The surface loading of S hollow boxes avoids the problem of transition agglomeration of MoS2. Due to the excellent characteristics of the hollow structure, a conductive network can be formed at a lower mass filling concentration. In addition, multiple dielectric loss mechanisms such as dipole polarization and interface polarization are also possible. 2-x S@MoS2 has excellent electromagnetic wave absorption properties. As the MoS2 loading increases, the impedance characteristics of the sample continue to optimize. 2-x S@MoS2-3 exhibits enhanced electromagnetic wave absorption performance, achieving a RL of -52.2 dB and an EAB of approximately 4.7 GHz at 2.1 mm.

[0048] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for preparing an electromagnetic wave absorbing material, characterized in that: The following steps are involved: The electromagnetic wave absorbing material is obtained by mixing Cu2O powder, ammonium molybdate, thiourea and water and reacting them; The molar ratio of the Cu2O powder to ammonium molybdate is 3-4:0.25-1; The Mo / S molar ratio of the ammonium molybdate and thiourea is 1:2-8; The reaction temperature is 160-240°C and the reaction time is 20-30h; The electromagnetic wave absorbing material has a core-shell composite structure of MoS2 coated hollow Cu9S5 cubes. In an acidic environment, a large amount of NH4 + Inserted into the MoS2 interlayer, it has a high 1-T phase ratio, and the self-templated growth mechanism of MoS2 nanosheets is applied to Cu 2-x The surface loading of S hollow boxes avoids the problem of transition agglomeration of MoS2.

2. The preparation method according to claim 1, characterized in that The molar volume ratio of the ammonium molybdate to water is 0.25-1 mmol:100-200 mL.

3. The electromagnetic wave absorbing material prepared by the preparation method according to claim 1 or 2.

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