Key Laboratory of Organosilicon Chemistry and Material Technology of Ministry of Education， College of Material， Chemistry and Chemical Engneering， Hangzhou Normal University， Hangzhou 311121， China
With the rapid development of communication and microelectronics technology， electromagnetic wave pollution has become an important issue affecting human health and the performance of microelectronic devices. Copper sulfide， as an important P-type semiconductor chalcogenide material， has become a research hotspot in the field of electromagnetic shielding materials in recent years due to its high carrier concentration， strong electronic polarization relaxation ability， excellent optoelectronic properties， and special nanostructure. This article will provide a tutorial review of the preparation of copper sulfide and copper sulfide based composite materials， as well as their latest application progress in the field of electromagnetic shielding materials.
Contents
1 Introduction
2 Synthesis and morphology control mechanisms of CuS nanomaterials
2.1 Hydrothermal method
2.2 Solvothermal method
2.3 Regulatory effects of surfactants and ligands
2.4 Fabrication of hollow-structured CuS nanomaterials
3 Electromagnetic absorption and shielding performance of pure-phase CuS nanomaterials
3.1 Principles of electromagnetic shielding
3.2 Electromagnetic absorption and shielding of pure-phase CuS nanomaterials
4 Preparation and electromagnetic shielding performance of CuS-based composite nanomaterials
With the rapid development of 5G communications, smart electronic devices, and aerospace technology, electromagnetic pollution has become increasingly prominent. This issue not only interferes with the stable operation of electronic components and threatens information transmission security but also poses potential hazards to human health. Therefore, developing high-performance electromagnetic shielding materials has become a critical challenge urgently needing resolution in the fields of materials science and electromagnetic protection.[1-3]. Although traditional metal-based electromagnetic shielding materials exhibit excellent shielding effectiveness, they suffer from inherent drawbacks such as high density, susceptibility to corrosion, and poor flexibility. Furthermore, their shielding mechanism relies primarily on electromagnetic wave reflection, which can cause secondary electromagnetic pollution, making them unable to meet the diverse modern requirements for lightweight, flexible, and green absorption-type shielding in electronic devices. In this context, researching new composite materials that combine lightweight, flexible, and easily processable characteristics with superior broadband wave-absorbing performance has become the core and frontier direction in the field of electromagnetic protection.
Currently, mainstream electromagnetic shielding materials mainly include metals and metal-based composites[4], carbon-based composites[5], MXene-based composites[6], etc. Most of these materials block electromagnetic wave propagation through physical isolation; their core limitation lies in the fact that electromagnetic wave energy is mostly reflected rather than effectively dissipated, easily causing secondary electromagnetic interference. Specifically, although metal materials exhibit high shielding effectiveness, they suffer from high density and poor corrosion resistance, with secondary reflection issues being particularly prominent; carbon-based materials possess significant lightweight advantages, but achieving high shielding effectiveness often requires a high filler loading, and their shielding performance tends to attenuate in high-frequency bands; MXene-based materials have excellent conductivity, yet they face problems such as high preparation costs and poor environmental stability, severely limiting their large-scale application. Unlike the aforementioned materials, absorption-type electromagnetic shielding materials can efficiently dissipate electromagnetic energy by converting it into heat and other forms through mechanisms such as dielectric loss and magnetic loss, fundamentally avoiding secondary electromagnetic interference. In recent years, semiconductor-based absorption-shielding composites, which combine absorption-dominated shielding characteristics with good comprehensive performance, have gradually become a research hotspot in this field.
In the design of high-performance electromagnetic wave absorbing-shielding composite materials, the electromagnetic properties, morphological structure, and compatibility with the matrix of functional fillers are the core factors determining the shielding effectiveness and comprehensive application performance of the composites. Copper sulfide (CuS), as a typical P-type semiconductor, has a bandgap width of 1.2~2.0 eV[7], its non-stoichiometric composition (Cu1-xS) and the coexistence of mixed Cu+/Cu2+ valence states within the crystal can induce the generation of high-concentration hole carriers (concentration up to 1021 cm-3)[8], endowing it with a metal-like conductivity of 102~103 S/cm, which imparts its unique "conductive-dielectric" dual-functional characteristics. Meanwhile, copper sulfide possesses features such as tunable microstructure and phase composition, simple preparation processes, and low cost, demonstrating irreplaceable advantages in the field of electromagnetic wave absorption and shielding.
In recent years, scholars both domestically and internationally have conducted extensive exploratory research on the controllable preparation of copper sulfide and its composite nanomaterials, their electromagnetic shielding mechanisms, and the applications of wave-absorbing composite materials, achieving significant progress. This paper will systematically review the current research status and development trends of copper sulfide-based nanomaterials in the field of wave-absorbing electromagnetic shielding composites by integrating existing research advances. First, it will elucidate strategies for the controllable preparation of CuS nanomaterials with different morphologies; second, it will briefly describe the electromagnetic shielding mechanisms and performance characteristics of copper sulfide nanomaterials, revealing the core principles of their wave absorption and shielding; third, it will categorically summarize research progress on copper sulfide-based composite nanomaterials, analyzing the design concepts, structure-activity relationships, and wave-absorbing shielding performance of core-shell structures, polymer composite films, fiber-based fabrics, binary/multinary, and multifunctional composite materials; finally, it will summarize the challenges faced by such materials in the field of wave absorption and shielding, as well as future development directions, aiming to provide theoretical support and technical reference for the development of a new generation of lightweight, flexible, wave-absorbing electromagnetic shielding composite materials.
2 Preparation and Morphology Control Mechanism of Copper Sulfide Nanomaterials
Currently, researchers have successfully constructed copper sulfide nanostructures with diverse morphologies, including nanospheres, nanorods, nanowires, nanosheets, nanotubes, nanoplates, flower-like structures, and nanobelts.[8-11]. The essence of this morphological diversity stems from the synergistic regulation of thermodynamic and kinetic factors during the synthesis process. Based on the physical state of the reaction system and the mechanism of mass transfer, mainstream preparation methods can be categorized into three types: liquid-phase, solid-phase, and gas-phase methods. Among these, the liquid-phase method, which generates copper sulfide through precipitation or coordination reactions between copper ions and sulfur sources in a liquid medium, offers significant advantages in the precise control of crystal morphology, microstructure, and particle size, making it the most widely applied approach.
Common liquid-phase synthesis strategies include hydrothermal/solvothermal methods, co-precipitation, sol-gel processes, and template-assisted growth, etc.[12-15]. Copper sulfide (CuS) is a hexagonal semiconductor composed of layered Cu+, S2-, and mobile Cu2+; its layered structure and differences in crystal plane energy result in significant anisotropic crystal growth. By regulating parameters such as the type and ratio of copper and sulfur sources, reaction temperature, time, pH, surfactants, organic ligands, and solvent polarity, effective control over nucleation, growth modes, crystallization behavior, and self-assembly processes can be achieved. Additionally, the Kirkendall effect[16-17], Ostwald ripening[18-19], or template-directed mechanisms[20-21]can be employed to construct hollow or hierarchical structures. This paper systematically elucidates the principles and mechanisms governing the regulation of CuS micro-morphology by integrating typical studies on hydrothermal/solvothermal and co-precipitation methods.
2.1 Hydrothermal method
The hydrothermal method typically involves mixing a copper source and a sulfur source in an aqueous solution, where high temperatures of 120–200 °C and autogenous pressure within a sealed autoclave promote the hydrolysis or decomposition of the sulfur source to release S2- ions, which subsequently combine with Cu2+ to form CuS[22]. The high-temperature and high-pressure environment facilitates enhanced anisotropic growth of CuS, thereby enabling the controlled preparation of complex micro/nanostructures.
The selection of copper and sulfur sources plays a decisive role in the final morphology of copper sulfide. Copper sources primarily influence nucleation and growth kinetics through solubility, hydrolysis behavior, anion type, and coordination ability. For example, copper sulfate (CuSO4) has high solubility, and SO42- exhibits weak coordination ability, allowing rapid release of Cu2+, increasing system supersaturation, promoting rapid nucleation and anisotropic growth, and facilitating the formation of nanosheets, nanoflowers, or spherical microstructures[23]. Copper nitrate (Cu(NO3)2) also possesses high solubility, and NO3- similarly shows weak coordination ability; however, its tendency to hydrolyze lowers the system pH, inhibiting sulfur source hydrolysis and slowing the reaction rate, while higher ionic strength may exacerbate particle aggregation[24]. In copper chloride (CuCl2), Cl- possesses certain coordination ability, capable of forming [CuCl4]2- complexes and selectively adsorbing onto specific crystal planes (such as the [001] plane), inhibiting growth in that direction and promoting two-dimensional extension. This is commonly used to prepare hexagonal nanosheets, nanodisks, or wire-like structures and represents a typical mechanism for synthesizing hexagonal CuS nanosheets via low-temperature solution methods[14]. In copper acetate (Cu(CH3COO)2), CH3COO⁻ exhibits strong coordination ability, buffering pH and slowing the release rate of Cu2+[25]. This anion-coordination-controlled slow-release effect reduces burst nucleation, favoring Ostwald ripening or directed assembly processes, thereby enabling the preparation of uniform nanospheres, porous microspheres, or monodisperse nanoparticles. Pradhan et al.[26] investigated the formation mechanism of nanotubes by adjusting reaction temperature, reaction time, precursor ratios, and anions. They found that the type of anion in the copper source significantly affects the morphology of copper sulfide; when the anions are NO3- and SO42-, nanotube formation is favored, whereas Cl- or OAc- favors the acquisition of sheet-like structures or CuS assembled from nanoparticles (Figure 1).
The regulation of copper sulfide nucleation and growth by sulfur sources mainly depends on their solubility in the solvent, decomposition mechanism, and S2- release kinetics. Different sulfur sources exhibit significant differences in the mechanism of releasing S2- under specific conditions. Inorganic sulfides (such as Na2S and K2S) directly dissociate into S2- in solution, with fast release rates enabling rapid nucleation[27-28]. In contrast, the reaction pathway of sodium thiosulfate strongly depends on the environmental pH. Under acidic conditions, thiosulfate disproportionates to generate elemental sulfur and sulfur dioxide; the elemental sulfur further reacts with water to produce H2S, and finally H2S reacts with Cu2+ to form CuS. Under this pathway, S2- is released rapidly, resulting in high supersaturation in the reaction system, which favors rapid nucleation and facilitates the formation of small-sized nanoparticles or hierarchical assembled structures. Under neutral or weakly alkaline conditions, thiosulfate first coordinates with Cu2+, then disproportionates into S2- and SO32-, after which S2- combines with Cu2+ to form CuS. Under this mechanism, the release of S2- is relatively moderate, offering strong controllability of the reaction.
Compared with inorganic sulfur sources, organic sulfur sources (such as thiourea, thioacetamide, etc.) need to gradually release S through hydrolysis reactions2-, their release kinetics are relatively slow, which is conducive to reducing the nucleation rate and promoting anisotropic crystal growth, thus can be used to prepare products with regular morphologies such as nanosheets and nanowires (Figure 2). For example, the hydrolysis of thiourea mainly occurs in alkaline environments, while thioacetamide can undergo hydrolysis under both acidic and neutral conditions; this characteristic provides more flexible options for finely controlling the morphology of copper sulfide in different reaction systems.
Xu et al.[29]Using copper nitrate as the copper source, thiourea as the sulfur source, and water as the solvent, they reacted at 150 °C for 6 h to prepare flower-like spherical nanostructures composed of thin nanosheets with a thickness of approximately 20 nm and a size of 2–3.5 μm. Davar et al.[30]Using copper nitrate as the copper source, thioacetamide as the sulfur source, and water as the solvent, they reacted at 150 °C for 6 h to prepare CuS microspheres self-assembled from nanosheets.
Grace et al.[31]Cylindrical copper sulfide self-assembled from nanosheets was prepared via a hydrothermal method at 150 °C for 24 h, using thiourea as the sulfur source and copper nitrate as the copper source. Under the same conditions, when sodium thiosulfate was used as the sulfur source, spherical copper sulfide with non-uniform sizes, also self-assembled from nanosheets, was obtained.
2.2 Solvothermal method
The solvothermal method is similar in principle to the hydrothermal method, but uses organic solvents (such as ethylene glycol, ethanol, DMF, DMSO, etc.) instead of water as the reaction medium, or partially mixed with water. Leveraging the high boiling point, higher viscosity, and coordination ability of organic solvents, this method can effectively regulate the diffusion rate of ions in the reaction system and their adsorption on specific crystal planes, thereby influencing nucleation and growth kinetics to achieve precise control over the micro-morphology of copper sulfide.
The polarity of the solvent effectively regulates the micro-morphology of copper sulfide by influencing factors such as the solubility of copper salts and sulfur sources, ion diffusion rates, and crystal facet growth kinetics[26]. Typically, high-polarity solvents (such as water) exhibit high reactant solubility, fast ion diffusion, and strong solvation effects, which facilitate isotropic growth to form small-sized nanoparticles or spherical aggregates; medium-polarity solvents (such as ethylene glycol) often selectively adsorb onto certain high-energy crystal facets, inhibiting their growth and promoting directional expansion along low-energy facets, thereby yielding nanorod or nanosheet structures; whereas low-polarity solvents restrict the decomposition of sulfur sources and the release rate of S2-, thereby delaying the nucleation process and favoring the formation of large-sized or specific-morphology crystals (Figure 3).
Using copper nitrate as the copper source and sodium thiosulfate as the sulfur source, pine needle-like copper sulfide nanomaterials assembled from regular hexagonal nanotubes can be prepared via a solution chemical method at 70 °C under conditions where the volume ratio of water to ethylene glycol is controlled at 1:3. The anisotropic growth of copper sulfide nuclei induced by hydrogen bonding between water and ethylene glycol makes a significant contribution to the formation of hexagonal copper sulfide nanotubes.[32]. Radhakrishnan et al.[33]Using copper acetate as the copper source and thiourea as the sulfur source, cauliflower-like, micro-flower-like, and interconnected network structures of copper sulfide nanoparticles were respectively prepared in water, ethanol, and a water-ethanol medium with a volume ratio of 1:1 by regulating solvent polarity via a solvothermal method at 160 °C for 16 h, without requiring any template or surfactant.
Zhao et al.[34]Using copper chloride as the copper source and thiourea as the sulfur source, under surfactant-free conditions in N,N-dimethylformamide (DMF), rose-like copper sulfide assembled from nanosheets was efficiently synthesized (diameter approximately 3~3.5 μm). The Cu2+-thiourea complex facilitates the growth of CuS crystals along the [001] plane to form hexagonal nanosheets. In the low-viscosity DMF medium, Ostwald ripening and oriented attachment act synergistically: small nanosheets dissolve and promote the growth of larger nanosheets through redeposition, while partially undiffused CuS monomers directionally attach to the [001] planes of the large nanosheets, forming "petal-like" secondary structures that ultimately self-assemble into rose-like CuS microflowers.
2.3 Regulatory effects of surfactants and ligands
If surfactants are introduced into the reaction system, they can achieve precise control over the morphology, size, and assembly behavior of copper sulfide through multiple mechanisms, including adsorption, spatial confinement (micelles or microemulsions), template guidance, and coordination regulation.
The regulation mechanisms of surfactants with different structures vary. For instance, cationic (CTAB) or anionic (SDS) surfactants can act as soft templates to guide the self-assembly of nanounits into hierarchical structures such as flower-like shapes, hollow spheres, or mesoporous forms. In contrast, nonionic (PVP) or polymeric (PEG) surfactants can coordinate with metal ions, regulate ion release rates, and provide steric hindrance effects to enhance colloidal stability, thereby achieving control over morphology uniformity and complexity. Xiao et al.[35]Using copper chloride as the copper source, sodium thiosulfate as the sulfur source, and sodium dodecyl sulfate (SDS) as the surfactant, cauliflower-like assembled morphologies of copper sulfide composed of interconnected nanoparticles were prepared via a solution chemistry method in an ethylene glycol-water mixed solvent (volume ratio 3:2) at 70 °C. Zhang et al.[36]Using copper sulfate as the copper source and sulfur powder as the sulfur source, flower-like hollow microspheres of copper sulfide assembled from nanosheets were prepared by reacting for 15 h at 160 °C in an ethylene glycol medium with the assistance of the cationic surfactant CTAB.
Yu et al.[37]used copper bromide (CuBr2) as the copper source and sulfur powder as the sulfur source to prepare vine-like copper sulfide nanofibers via a hydrothermal method. During the reaction, ascorbic acid first reduced Cu2+in situ to Cu+, which then formed stable Cu+-PEI complexes with branched polyethyleneimine (BPEI), subsequently reacting with sulfur powder to generate CuS. They found that the BPEI concentration and halide anions jointly determine the product morphology; by adjusting the BPEI dosage, the microscopic morphology of CuS can be reversibly switched between "vine-like nanofibers" and "hollow nanoparticles".
Xue et al.[38]Using copper nitrate as the copper source, donut-shaped, spherical, and flower-like copper sulfide crystals self-assembled from nanosheets were prepared by varying the medium (DMF and DMSO), sulfur source, and the presence or absence of a surfactant, with reactions conducted in an autoclave at 110–160 °C for 15–30 h. Using thiourea as the sulfur source and polyvinylpyrrolidone (PVP) as the surfactant in dimethyl sulfoxide (DMSO), donut-shaped copper sulfide (approximately 1.5 μm in diameter) was obtained. Using sulfur powder as the sulfur source in DMF, spherical copper sulfide was produced in the presence of PVP, while flower-like copper sulfide was obtained in the absence of a surfactant.
2.4 Preparation of hollow structure copper sulfide
The preparation of hollow copper sulfide is primarily based on principles such as template guidance, differential ion diffusion, and dissolution-redeposition, achieving structural cavitation by regulating nucleation, growth, and reaction processes. The core strategy involves the spatial confinement effects of hard/soft templates, utilizing Cu2+ and S2-diffusion rate asymmetry, or leveraging Ostwald ripening and selective etching to induce internal mass migration and external shell formation, ultimately obtaining copper sulfide materials with a hollow structure (Figure 4).
Zhu et al.[39]Based on the sacrificial template method, rapid and controllable preparation of CuS hollow spheres was achieved under mild conditions. In this method, copper sulfate serves as the copper source, thioacetamide as the sulfur source, and aggregates self-assembled from loose Cu2O nanoparticles act as sacrificial templates; hollow-structured CuS crystals were successfully constructed via the Kirkendall effect. By regulating the aggregation degree of Cu2O nanoparticles, the shell thickness of the resulting CuS hollow spheres can be precisely controlled. Compared with traditional methods that typically require high temperatures or long reaction times to consume dense templates, this strategy based on nanoparticle-assembled templates enables rapid and efficient preparation under mild conditions. Song Junwang et al.[40]Using [Cu(tu)]Cl·1/2H2O nanowires as self-sacrificing templates, porous copper sulfide nanotubes (PCSNTs) were prepared via solution chemistry at room temperature.
Thus, copper sulfide nanomaterials not only feature simple preparation processes and ease of industrial production; more importantly, their phase composition and three-dimensional microstructure can be flexibly regulated to achieve precise performance optimization according to practical application requirements, while maintaining good compatibility with polymer matrices. These characteristics lay an important foundation for their application in the field of wave-absorbing and electromagnetic shielding polymer nanocomposites.
3 Electromagnetic Wave Absorption and Shielding Properties of Pure Phase Copper Sulfide Nanomaterials
3.1 Principle of electromagnetic shielding
Typically, the shielding effect of materials on electromagnetic waves is primarily achieved through two core mechanisms: reflection and absorption (Figure 5), quantitatively described using power coefficients (reflection coefficient R, absorption coefficient A, and transmission coefficient T). The specific relationship is as follows:
wherePIis the input power incident on the material surface,PRis the reflected power at the material surface,PTis the transmitted power output from the material.
According to the Schelkunoff formula[41], the total shielding effectiveness (SE) is defined as the sum of reflection loss (SER), absorption loss (SEA), and internal multiple reflection loss (SEM):
$S{E}_{T}=S{E}_{R}+S{E}_{A}+S{E}_{M}$
based on the reflection theory of transmission lines, when the material satisfies the good conductor criterion (σ ≫ ωε), it can be approximately expressed as:
in the formula, σr is the relative conductivity, μr is the relative permeability, f is the electromagnetic wave frequency (Hz), t is the thickness of the shielding material (m), δ is the skin depth (m), r is the distance from the radiation source to the shielding material (m). As seen from the above calculation formulas, to achieve low reflection, it is necessary to reduce SER, which requires the material to possess moderate electrical conductivity σr and high magnetic permeability μr, optimizing impedance matching through their synergy to allow more electromagnetic waves to enter the material interior rather than being directly reflected. To achieve high absorption, it is necessary to maximize SEA, which requires the material to possess high electrical conductivity σr, high magnetic permeability μr and sufficient thickness t, efficiently dissipating electromagnetic energy through the synergistic effect of conduction loss and magnetic loss. For the multiple reflection correction term SEM, when the material thickness t is far greater than the skin depth δ, SEM ≈ 0, avoiding energy leakage caused by electromagnetic waves reflecting back and forth inside the material, ensuring that electromagnetic waves entering the material are primarily absorbed.
SE can be calculated from the scattering parameters measured by a vector network analyzer (Sparameters), and the calculation formula is as follows:
among them,SERdescribes the portion of electromagnetic wave energy that has entered the material and is lost due to reflection at internal interfaces,SEAcorresponds to the portion of this energy entering the interior that is lost due to absorption by the material itself.
SETfocuses on characterizing the material's comprehensive ability to block electromagnetic waves. When SET≥20 dB, corresponding to a total attenuation of electromagnetic waves by the material of ≥99%, it can be judged as having good electromagnetic shielding performance. When SET≥40 dB, the total attenuation corresponding to the material is ≥99.99%, which can be judged as having excellent electromagnetic shielding performance.
3.1.2 Reflection Loss (RL)
Reflection loss (RL) is a metric for measuring the attenuation of electromagnetic waves reflected at the material surface, describing how much of the energy incident on the material surface is reflected back. It is also expressed in decibels (dB), and its definition formula is as follows:
among them, Z0 is the free space wave impedance (approximately 377 Ω), Zin is the input characteristic impedance of the material, ε0 and μ0 are the permittivity and permeability of vacuum, respectively, εr and μr are the complex permittivity and complex permeability of the composite material in air, f is the electromagnetic wave frequency, c is the speed of light, d is the thickness of the composite material. As seen from the calculation formula, when Zin approaches Z0, impedance matching is achieved, allowing electromagnetic waves to efficiently enter the interior of the material. The real parts of the complex permittivity and complex permeability serve as characteristic parameters of the material's electromagnetic energy storage capacity; their reasonable adaptation can make Zin approach Z0, thereby minimizing the reflection of electromagnetic waves at the material surface. The imaginary parts of the complex permittivity and complex permeability are characteristic parameters of the material's ability to dissipate electromagnetic waves. A larger ε″ indicates more significant relaxation processes such as dipole relaxation and interfacial polarization under an alternating electric field, resulting in a higher efficiency of converting electromagnetic energy into thermal energy; a larger μ″ implies stronger magnetic loss mechanisms such as hysteresis loss and natural resonance, further dissipating electromagnetic wave energy. In addition, ε″ and μ″ also directly affect the magnitude of the complex variable inside the tanh function, thereby determining the attenuation amplitude of electromagnetic waves within the material.
RLcan also be calculated from the scattering parameters (S11) measured by a vector network analyzer using the following formula:
RLprimarily characterizes the surface energy dissipation properties of electromagnetic waves before entering the material. When RL ≤ -10 dB, the reflected energy from the material surface does not exceed 10% of the incident electromagnetic waves, indicating that the material possesses effective wave-absorbing performance. The frequency range capable of effectively absorbing electromagnetic waves at a specific thickness is defined as the Effective Absorption Bandwidth (EAB); the wider the interval, the stronger the adaptability of the material across wave-absorbing frequency bands. When RL ≤ -20 dB, the reflected energy is less than 1%, meaning over 99% of the incident electromagnetic waves are absorbed or transmitted by the material, achieving an excellent level of wave-absorbing performance. In practical analysis, attention must be paid to the RLand SERdifferences in their physical connotations. RL is directly related to impedance matching; the smaller its value, the weaker the reflection of incident electromagnetic waves by the material and the superior the wave-absorbing performance. Conversely, a larger value indicates stronger reflection and poorer wave-absorbing performance.
The essence of absorptive electromagnetic shielding is to attenuate and block incident electromagnetic waves through low reflection and high isolation, preventing them from entering the shielded area. It is generally required to exhibit low reflection (RL≤-10 dB) within the target frequency band to maximize the suppression of interface reflection and avoid secondary pollution; high isolation (total shielding effectiveness SE≥20 dB), which efficiently converts the energy of incident electromagnetic waves into heat and other forms for dissipation through mechanisms such as dielectric loss, magnetic loss, and polarization loss of the shielding material.
3.2 Wave Absorption-Shielding Mechanism and Performance of Pure Phase Copper Sulfide Nanomaterials
Combining the basic principles of wave absorption and electromagnetic shielding of materials, copper sulfide (CuS), as a typical class of P-type semiconductor dielectric wave-absorbing materials, possesses electromagnetic parameters (εr, μr, σr) with high tunability and strong designability of microstructure, among other prominent advantages. Through the synergistic regulation of impedance matching and dielectric loss, it provides important support for the development of high-performance electromagnetic protection materials characterized by "low reflection and high absorption".
From the perspective of phase composition, precise control over the copper-sulfur ratio, crystal structure, and lattice defect concentration enables the regulation of material conductivity (σr) and permittivity (εr), thereby optimizing the synergistic mechanism between impedance matching and dielectric loss. Research indicates that high-conductivity phases are more prone to forming rapid conduction currents under alternating electromagnetic fields, efficiently converting electromagnetic energy into Joule heat, thus achieving more effective electromagnetic energy dissipation through conduction losses.
He et al.[43]confirmed that, compared to Cu2S, CuS with superior conductivity exhibits better electromagnetic shielding performance. Two-dimensional copper sulfide nanosheets with CuS as the main phase and a thickness of only 20 nm can achieve a specific shielding effectiveness (SSE/t) of over 106 dB∙cm2/g, fully verifying the significant regulatory effect of phase composition on material loss strength (Figure 6). Taso et al.[44]found that, compared to CuₓS/polyaniline (PAN) composites where CuS, Cu1.75S, and Cu1.8S coexist in three phases, pure hexagonal CuS is more conducive to constructing an efficient conductive network, significantly reducing its volume resistivity. Consequently, the electromagnetic shielding effectiveness can be improved by 10~15 dB. In the frequency range of 30 MHz~1.5 GHz, thin (0.05~0.076 mm) single-phase CuS/PAN composite films can achieve a shielding effectiveness of 27~30 dB, far superior to multiphase coexistence systems.
Due to the high intrinsic electrical conductivity of copper sulfide (CuS), when it exists in the form of a dense bulk, incident electromagnetic waves tend to undergo strong reflection at the material surface due to impedance mismatch and the skin effect, making it difficult to simultaneously achieve high absorption and broadband performance. Therefore, its microstructure usually needs to be optimized and designed to effectively regulate its electromagnetic parameters and endow it with excellent wave-absorbing properties.Table 1summarizes the wave absorption and electromagnetic shielding performance data of pure-phase CuS nanomaterials with different morphologies (such as hollow hierarchical microspheres, flower-like hollow spheres, porous nanotubes, etc.) after compounding with paraffin or PVDF.
The number of interfaces and specific surface area of CuS nanomaterials are key factors regulating their wave absorption performance. A greater number of interfaces and larger specific surface area can significantly enhance interfacial polarization, dipole polarization effects, and multiple scattering capabilities of electromagnetic waves, thereby improving the dissipation efficiency of electromagnetic energy. Wang et al.[45]prepared three CuS samples with polyhedral hierarchical morphologies (S1, S2, and S3) using a wet chemical method. The microwave absorption properties of the composites obtained by compounding them with paraffin at a filling amount of 20 wt% varied (Figure 7). The study found that compared to the polyhedral structure samples S1 and S3, the symmetric hierarchical nanostructured CuS (S2), which possesses more polarization sites and scattering interfaces as well as a higher specific surface area, exhibited superior electromagnetic loss capability and wave absorption performance. When the thickness of this composite material was 3.5 mm, it achieved a minimum reflection loss of -76.4 dB at the 12.64 GHz frequency band, with an effective absorption bandwidth reaching 11.5 GHz (6.48~18 GHz), combining the dual excellent characteristics of strong absorption and broad bandwidth.
Constructing hollow, porous, and hierarchical composite structures is another important structural design strategy for optimizing the wave absorption and shielding performance of CuS. This approach can effectively reduce the equivalent dielectric constant while retaining the material's high dielectric loss characteristics, thereby improving impedance matching performance and reducing electromagnetic wave surface reflection losses. The advantages of such structures are fully demonstrated through specific cases.
The hierarchical hollow structure assembled from nanosheets features an internal cavity that induces multiple reflections and scattering of electromagnetic waves within the material, significantly extending the microwave propagation path and residence time. Meanwhile, the high specific surface area and secondary nanosheet structure increase the number of heterogeneous interfaces and strengthen the polarization relaxation process, thereby enhancing wave absorption performance. Zhang et al.[36]prepared flower-like CuS hollow microspheres. When compounded with paraffin at a filling ratio of 30 wt%, the resulting composite exhibited excellent microwave absorption performance. By adjusting the sample thickness (1.5–4.0 mm), the effective absorption bandwidth could be flexibly tuned within the range of 6.2–18.0 GHz. At a sample thickness of 1.8 mm, the minimum reflection loss reached -31.5 dB at 16.7 GHz, with an effective absorption bandwidth of 3.6 GHz (14.4–18.0 GHz), fully demonstrating the synergistic advantages of "path extension" and "loss enhancement" in the hollow structure (Figure 8). This research group[46]further employed an electrochemical displacement reaction to prepare hollow flower-like hierarchical CuS with similar morphology, and fabricated paraffin-based composite wave-absorbing materials with a filling ratio of 50 wt%. At a thickness of only 1.1 mm, the material achieved a minimum reflection loss of -17.5 dB within the 2–18 GHz frequency range, with an effective absorption bandwidth of 3.0 GHz. These results further confirm that the hollow flower-like hierarchical structure can effectively enhance the microwave absorption performance of materials by optimizing impedance matching and strengthening multiple scattering and interfacial polarization.
Hollow and porous structured CuS also exhibits outstanding performance in electromagnetic shielding. Its internal channels and cavities can reduce the equivalent dielectric constant and optimize impedance matching, while inducing multiple reflections and scattering of electromagnetic waves to achieve a shielding effect dominated by absorption. Furthermore, it offers the advantages of a large skin depth and the ability to realize deep-layer loss of electromagnetic waves. Wu, Xie, et al.[47]found that after compounding 30 wt% hollow Cu1.8S nanocubes with paraffin, samples with a thickness of 3 mm achieved an electromagnetic shielding effectiveness of over 45 dB in the 2–18 GHz range. The shielding mechanism is primarily based on absorption, which benefits from the deep attenuation of electromagnetic waves by the hollow structure (Figure 9). Similarly, wool-ball-shaped hollow copper sulfide/polyvinylidene fluoride (PVDF) composites exhibited an electromagnetic shielding effectiveness greater than 30 dB across the 2–18 GHz frequency range, with 86% of incident electromagnetic waves attenuated via absorption and a skin depth reaching the millimeter level.[24], demonstrating the significant role of hollow structures in enhancing absorption loss. Song Junwang et al.[40]prepared porous copper sulfide nanotubes (PCSNTs). Their porous structure not only reduced the equivalent dielectric constant and optimized impedance matching but also extended the propagation path of electromagnetic waves through the channels. When compounded with paraffin at a filling content of 60 wt%, they demonstrated extremely strong microwave absorption capability at a thickness of 2.2 mm, achieving a maximum reflection loss of -45.02 dB near 15.67 GHz and an effective absorption bandwidth of 4.75 GHz (13.25–18.00 GHz), fully verifying the enhancing effect of the porous structure on the wave-absorbing performance of CuS.
The design of high-efficiency CuS nano electromagnetic wave absorbing and shielding materials is a systematic engineering project involving multi-parameter synergistic optimization. It requires regulating the real parts of complex permittivity and complex permeability to achieve impedance matching, while modulating their imaginary parts and relative conductivity to enhance electromagnetic loss. Simultaneously, by integrating microstructural optimizations such as hollow, porous, and hierarchical structures, an optimal balance among impedance matching, electromagnetic loss, and structural design is sought, ultimately achieving comprehensive performance goals of wide-frequency absorption, strong attenuation, and lightweight characteristics.
4 Electromagnetic wave absorption properties of copper sulfide-based composite nanomaterials
Pure-phase copper sulfide nanomaterials primarily exhibit dielectric loss for electromagnetic attenuation, suffering from inherent drawbacks such as the absence of magnetic loss and a limited range for impedance matching regulation. Consequently, they struggle to meet the demands of complex scenarios for broadband, high-efficiency electromagnetic wave-absorbing materials. Constructing copper sulfide-based composite nanomaterials through composite modification evolves the paradigm from "single component-single loss" to "multi-element synergy-structural coupling." This approach enables synergistic dielectric-magnetic losses, optimizes impedance matching characteristics, and simultaneously expands the structural design space and functional diversity of the materials, representing a core strategy for enhancing the electromagnetic wave absorption performance of copper sulfide-based materials.
4.1 Core-shell structured CuS composite materials
The core-shell structure, through interface regulation and component synergy of the "core-shell," can precisely optimize the dielectric/magnetic properties and impedance matching of materials, representing a typical structural design form for copper sulfide-based composites. Studies have revealed the synergistic mechanisms between different core components (such as magnetic media and carbon materials) and the CuS shell, as well as their regulatory patterns on electromagnetic wave absorption performance. Shen Yong et al.[48-49]A core-shell structured CuS/PANI composite was prepared by coating polyaniline (PANI) onto the surface of flower-like CuS microspheres using an in-situ polymerization method. Testing the wave absorption properties of its paraffin composite revealed that, compared to pure CuS, this composite exhibited significant improvements in maximum electromagnetic shielding effectiveness and effective absorption bandwidth within the 2.6–3.0 GHz frequency range. Its maximum shielding effectiveness increased from 25.2 dB to 45.2 dB, suggesting that coating copper sulfide with polyaniline facilitates achieving characteristic impedance matching in the composite (Figure 10). When the mass ratio of CuS/PANI to paraffin was 2:8 (with a CuS mass fraction of 50%), the shielding effectiveness of a 3 mm thick pressed pellet reached 18 dB within the 300 kHz–3.0 GHz frequency range, with a maximum loss of -45.2 dB at approximately 2.78 GHz.
Liu et al.[50]used tetradecahedral Cu2O as a template to prepare hollow microspheres composed of a CuS and Mn(OH)2 double shell (CuS@Mn(OH)2) through coordination etching, precipitation, and sulfidation reactions. The outer shell of these hollow microspheres consists of low-conductivity, loose Mn(OH)₂, which facilitates electromagnetic wave entry into the absorber; the hollow structure optimizes impedance matching; and the numerous heterogeneous interfaces between the CuS inner shell and the Mn(OH)2 outer shell can induce strong interfacial polarization. This enables the double-shell hollow CuS@Mn(OH)2 microspheres to exhibit excellent electromagnetic wave absorption performance. Using paraffin as the matrix, at a filling ratio of 25 wt% and a sample thickness of 2.3 mm, the effective absorption bandwidth reaches 6.88 GHz (11.12–18 GHz). Similarly, they[51]also prepared hollow CuS@CoS2 nanoboxes with a double-shell structure using a similar method: the inner shell consists of CuS hollow boxes, while the outer shell is tightly coated with CoS2 nanosheets. Thanks to the synergistic effects of dipole polarization and interfacial polarization, multiple scattering, the hollow/core-shell structure, and good impedance matching, these hierarchical hollow nanoboxes demonstrate excellent microwave attenuation performance. At a filling ratio of 20 wt% and a thickness of 2.5 mm, the minimum reflection loss reaches -58.6 dB; at a filling ratio of 30 wt% and a thickness of 2.2 mm, the effective absorption bandwidth reaches 8.2 GHz.
The core-shell structure can significantly enhance the microwave absorption performance of CuS-based materials through mechanisms such as introducing heterogeneous interfaces, optimizing impedance matching, and enhancing polarization loss. This structural design provides an effective pathway for regulating the electromagnetic response of copper sulfide composite nanomaterials.
4.2 CuS/polymer composite membrane
By combining the flexibility, lightweight nature, and ease of processing of the polymer matrix with the high dielectric loss advantage of CuS, composite film materials possessing both excellent electromagnetic shielding/wave absorption performance and mechanical adaptability can be constructed, meeting the application requirements for flexible electronics, wearable devices, and lightweight electromagnetic protection scenarios.
Huang et al.[52]using CuSO4 as the copper source, NaHSO3 and Na2S2O3·5H2O as reducing agents and triethanolamine (TEA) as a chelating agent, a CuS/PAN composite film was prepared by in situ growth of CuS on the surface of PAN films via electroless plating. The study found that as the CuS coating thickness increased from 76 nm to 247 nm, the electromagnetic shielding effectiveness of the CuS/PAN composite film in the 30~1500 MHz frequency range improved from 10~12 dB to 25~27 dB (Figure 11).
Taso et al.[44]A simplified electroless plating process without sensitization or activation was employed to prepare PAN@CuₓS composite films on the PAN surface, and the regulation laws of the reducing agent on the phase composition and shielding performance were investigated. When using NaHSO3/Na2S2O3·5H2O as a composite reducing agent, the resulting coating consists of CuS, Cu1.75S, and Cu1.8S, forming a three-phase coexisting CuxS (CuxS-PAN); whereas when using only Na2S2O3·5H2O as the reducing agent, pure hexagonal phase CuS (CuS-PAN) can be obtained. The electrical conductivity and shielding performance of the two composite materials differ significantly. The volume resistivity of CuS-PAN is as low as 0.012 Ω·cm, which is only 1/1000 of that of CuₓS-PAN, with a corresponding EMI SE improvement of approximately 10~15 dB. In the frequency range of 30 MHz~1.5 GHz, the shielding effectiveness of CuS-PAN with a thickness of 0.05~0.076 mm can reach 27~30 dB, far exceeding the 15~17 dB of CuₓS-PAN, indicating that pure-phase CuS is more conducive to achieving high conductivity and efficient shielding.
Wu et al.[53]Dense, continuous CuS nanosheet layers with strong interfacial bonding were constructed on the surface of polyimide (PI) films using an in-situ growth method to obtain PI@CuS composite films. These composite films combine excellent electrothermal conversion, photothermal response, and mechanical properties, while also demonstrating superior electromagnetic shielding performance. With a thickness of only 80 μm, the PI@CuS film achieves an EMI SE of up to 57.1 dB in the 8–12.4 GHz frequency range and a tensile strength exceeding 90 MPa, showing great application potential in the field of high-strength flexible electromagnetic shielding.
The preparation process of CuS/polymer composite films is flexible and diverse. By regulating the phase composition, deposition thickness, and micro-morphology of copper sulfide, the dielectric properties and electromagnetic shielding performance of the composite films can be precisely optimized.
Fiber-based fabrics possess inherent advantages such as being lightweight, breathable, and flexibly weaveable. Composite fabrics constructed by combining CuS with a polymer fiber matrix not only exhibit absorption-dominated electromagnetic shielding performance but can also integrate multifunctional properties including electrothermal conversion, photothermal sterilization, UV resistance, and thermal management. They demonstrate broad application prospects in medical electronic devices, flexible wearable equipment, and personal protection, representing an important development direction for the new generation of flexible electromagnetic shielding materials.
In recent years, research work has loaded CuS onto polymer fibers via in-situ growth, blend spinning, or post-coating/impregnation methods[54-55]and cotton fibers[56], preparing various CuS-based composite fiber fabrics. These composite fibers contain abundant heterogeneous interfaces inside; by regulating the fiber microstructure, CuS loading morphology and content, component ratio, and interface bonding state, synergistic regulation of electromagnetic parameters can be achieved from aspects such as dielectric loss, interfacial polarization, multiple reflection, and scattering, thereby enhancing the wave absorption and shielding performance of the materials.
In-situ growth is the mainstream method for constructing high-performance CuS-based composite fabrics, enabling uniform and firm coating of CuS on fiber surfaces. Wang et al.[54]grown CuS nanosheets in-situ on dopamine (PDA)-modified spandex fabrics (SF) and coated them with a polydimethylsiloxane (PDMS) protective layer to produce multifunctional composite fabrics (PDMS@CuS@PSF). The CuS adhered tightly to the fiber surface in a sheet-like structure. The shielding effectiveness of the composite fabric increased with the thickness of CuS deposition, exceeding 46 dB in the X-band, with absorption loss being dominant. Wu et al.[55]used a similar method to attach flower-like copper sulfide nanosheets onto aramid fibers (AF). The resulting CuS@PDA/AF single-layer fabric achieved a shielding effectiveness close to 60 dB, while the double-layer fabric exceeded 100 dB. Over 90% of this contribution stemmed from absorption, realizing "low reflection, high absorption" green shielding, while also offering multifunctionality including UV resistance, flame retardancy, and antibacterial properties.
The hierarchical coaxial "core-shell" structure can further enhance interfacial polarization and impedance matching. Ding et al.[57]prepared a composite polyurethane fiber membrane with coaxial heterogeneous double conductive sheaths (PPUO@CuS) using electrospinning combined with sequential deposition. Introducing CuS nanosheet layers outside the PPy conductive layer creates more heterogeneous interfaces and enhances dielectric loss, increasing the X-band EMI SE from less than 30 dB (PPUO) to a maximum of 50.11 dB, an improvement of over 20 dB, demonstrating a significant synergistic enhancement effect of the components.
Through multi-component compounding and functional integration, CuS-based composite fabrics can achieve the integration of electromagnetic shielding, pressure sensing, and thermal management functions. Sun et al.[56]prepared MXene/CuS/cotton composite fabrics using a dip-coating and spray-coating process. Benefiting from the high conductivity of MXene, the high dielectric loss of CuS, and the synergistic effect of the continuous conductive network and porous structure constructed by the fabric, the fabric with a thickness of only 335 μm achieved an electrical conductivity of 121.3 S/m and an electromagnetic shielding effectiveness of 51.10 dB. It also possesses a high sensing sensitivity of up to -18.2 kPa-1within the pressure range of 1~4 kPa, demonstrating great application potential in wearable multifunctional electronic devices (Figure 12).
Park et al.[58]then performed electroless nickel plating on the CuS‑PAN surface to introduce magnetic loss and high-conductivity channels. When the nickel coating thickness was 12.3 μm, the EMI SE of Ni/CuS‑PAN fibers reached up to 45 dB in the 1.5~2.5 GHz frequency range, an increase of nearly 30 dB compared to the original CuS‑PAN fibers, indicating that combining a conductive metal layer with CuS can significantly enhance electromagnetic shielding performance.
In addition to traditional fabrics, nanofiber membranes also exhibit significant advantages in the field of lightweight electromagnetic shielding due to their high specific surface area and hierarchical porous structures. Wang et al.[59]prepared polyacrylonitrile (PAN) nanofiber membranes via air-spinning processes, followed by in-situ reactions to obtain ultra-low density (0.044 g/cm3), ultra-thin thickness (0.423 mm) three-dimensional flexible CuₓS/PAN nanofiber felts. This material achieves an EMI SE of 29~31 dB in the 500~3000 MHz frequency range, with a mass-normalized shielding effectiveness as high as 16655.92 dB cm2/g, far exceeding most CuS-based shielding materials, while also significantly improving heat resistance and water-wash durability.
CuS/polymer fiber-based electromagnetic shielding fabrics, through structural designs such as in-situ growth, electrospinning, and multi-layer coating, can fully leverage the flexibility advantages of the fiber matrix and the high dielectric loss characteristics of CuS to achieve absorption-dominated efficient electromagnetic shielding. By regulating the CuS morphology, loading amount, interface structure, and synergistic effects of multi-component systems, these materials can attain high shielding effectiveness while endowing them with features such as lightweight, flexibility, breathability, and multifunctional integration.
4.4 CuS-based binary composite materials
Composite CuS with a second component that complements it in electrical, magnetic, and dielectric properties, such as carbon materials, magnetic media, and metal compounds (Table 2), and optimize the regulation of electromagnetic parameters and impedance matching through precise design of hierarchical microstructures, leveraging the synergistic enhancement of loss mechanisms such as interfacial polarization, dipole polarization, and multiple scattering; this is an important approach to improving the electromagnetic wave attenuation and dissipation capabilities of CuS-based composite materials.
4.4.1 CuS binary composite system based on high conductivity synergy
The sandwich structure is a typical design that realizes the complementary advantages of CuS and carbon materials. Wang et al.[60]prepared RGO/CuS sandwich composites with CuS microspheres embedded between reduced graphene oxide (RGO) layers using an in-situ growth method. In this material, nanoscale CuS microspheres are uniformly anchored in a discrete "island-like" form between micrometer-scale RGO sheets, which not only effectively suppresses RGO stacking and maintains its high specific surface area, but also constructs efficient electron transport channels via the continuous three-dimensional RGO skeleton, providing a fast pathway for conductive loss (Figure 13). Meanwhile, the numerous heterogeneous interfaces formed between CuS and RGO can enhance the interfacial polarization effect, endowing the system with an additional polarization loss mechanism. When compounded with PVDF to obtain a flexible film, at a filler content of only 5 wt% and a thickness of 2.5 mm, the minimum reflection loss reaches -32.7 dB at 10.7 GHz, and the absorption performance can be regulated by adjusting the thickness.
Jiang et al.[61]Using moss-derived amorphous carbon (BC) as a substrate, flower-like CuS was uniformly attached to its surface via a hydrothermal method to prepare CuS/BC heterogeneous composite materials. In this material, the continuous conductive network and the CuS/BC heterogeneous interface significantly enhance interfacial polarization and relaxation polarization effects. Meanwhile, the three-dimensional structure with high specific surface area, constructed from wrinkled BC and flower-like CuS nanosheets, can further promote multiple scattering and energy dissipation of electromagnetic waves, making its wave absorption performance far superior to that of pure BC. Among them, CuS/BC-1 achieves a minimum reflection loss of -28.8 dB, with an effective absorption bandwidth covering the entire X band.
Xiang et al.[62]Using phallus fungus-derived porous carbon (PC, pore size 15~30 μm) as a carrier, hollow CuS micro-flowers were uniformly anchored on its surface via an ethylene glycol solvothermal method to prepare PC@CuS composites integrating microwave absorption, flame retardancy, and thermal infrared stealth functions. Relying on multi-component synergy and unique microstructures, the material establishes a microwave attenuation mechanism coupling multiple polarization, multiple reflection/scattering, and conduction losses, with absorption performance precisely tunable via carbonization temperature and filler content. In a paraffin composite with a 10 wt% filler loading, PC800@CuS achieves a minimum reflection loss of -61.5 dB and an ultra-wide effective absorption bandwidth of 7.8 GHz in the X-band.
In addition to carbon-based materials, conductive polymers and highly conductive dielectric MXenes can also form binary composite systems with CuS. Through component synergy and structural regulation, the microwave absorption performance of the materials is significantly enhanced. Sun et al.[63]employed a solvothermal method combined with self-assembly polymerization to construct a uniform PPy aerogel coating on the surface of hollow hierarchical CuS microspheres, yielding core-shell structured CuS@PPy composites. The thickness of the PPy coating could be regulated by adjusting the usage ratio of CuS to pyrrole monomers. Compared with pure CuS sheet-like microspheres and pure PPy, the wave absorption performance of this composite was significantly improved. Under optimal conditions, the paraffin composite of CuS@PPy achieved a maximum reflection loss (RL) of -52.85 dB within the 2–18 GHz frequency range at a thickness of 2.5 mm, with an effective absorption bandwidth broadened to 8.02 GHz (9.78–17.80 GHz). This performance enhancement is closely related to the increase in complex permittivity and the strengthened dielectric loss resulting from enhanced interfacial dielectric polarization.
Gu et al.[64]CuS nanoparticles with a diameter of 10~20 nm were loaded onto Ti3C2Tₓ MXene surfaces via a solvothermal method to construct a layered heterostructure CuS/Ti3C2Tx composite material. When compounded with paraffin as the matrix, this material exhibits excellent microwave absorption performance due to the combined effects of a three-dimensional conductive network, interfacial polarization, dipole polarization, and multiple scattering. At a filler content of 35 wt%, the minimum reflection loss reaches -45.3 dB at 7.3 GHz; with a thickness of only 2.0 mm, the effective absorption bandwidth can reach 5.2 GHz.
4.4.2 Magnetic medium/CuS binary composite system
Combining magnetic components with CuS can introduce magnetic loss and further optimize impedance matching. Dai et al.[65]Three-dimensional hierarchical porous CuS microparticles and magnetic NiCo2O4 nanospheres (particle size 30~65 nm) were separately compounded with 30 wt% paraffin and processed via molding to fabricate a bilayer structure with an upper layer of CuS and a lower layer of NiCo2O4. The reflection loss of this bilayer absorber significantly depends on the microstructure, thickness, and spatial arrangement of the absorbing fillers. When both layers have a thickness of 1 mm, the minimum reflection loss of the absorber reaches -33 dB at 11 GHz, fully demonstrating the significant enhancement of wave absorption performance achieved through structural design and component synergy.
Gu et al.[66]Using copper sulfate and sulfur powder as raw materials, and CTAB as a surfactant, Fe3O4nanoparticles were loaded onto the surface of CuS microspheres via a solvothermal method in ethylene glycol to prepare CuS/Fe3O4composites with a chicken-nugget-like morphology. In this material, the CuS microspheres are formed by the self-assembly of nanosheets into a wrinkled hierarchical structure, with Fe3O4nanoparticles uniformly distributed on them. Compared with pure Fe3O4and CuS, the heterostructure significantly enhances the microwave absorption performance (Fig. 14). The optimal sample CSF‑160, when compounded with 40 wt% paraffin, achieves a minimum reflection loss of -61.32 dB at 14.00 GHz with a thickness of 1.5 mm, and an effective absorption bandwidth of 4.15 GHz (12.72~16.87 GHz).
4.4.3 Metal sulfide/CuS binary composite system
Constructing a heterogeneous composite system of metal sulfides such as ZnS with CuS can optimize dielectric loss and impedance matching through crystal phase differences and interfacial effects, further expanding the performance regulation space of CuS-based microwave absorbing materials. Wang et al.[67]Using copper nitrate and zinc nitrate as raw materials and CTAB as a surfactant, a three-dimensional hierarchical nanocomposite (CZS, average particle size 3 μm) with ZnS particles embedded in CuS microspheres was prepared via a one-step hydrothermal method, wherein CuS exhibits a hexagonal phase and ZnS a tetragonal phase. Studies indicate that the Zn2+/Cu2+molar ratio significantly affects the material morphology and microwave absorption performance, with optimal performance achieved at a molar ratio of 0.3 (CZS0.3) (Figure 15). After compounding this sample with paraffin at a 20 wt% filling content, a reflection loss of -22.6 dB was achieved at 9.7 GHz with a thickness of 3 mm, and the effective absorption bandwidth reached 2.2 GHz (9.2~11.4 GHz).
Liu et al.[68]employed a cationic exchange reaction to load silver sulfide (Ag2S) nanoparticles onto the surface of copper sulfide (CuS) sheets, preparing CuS/Ag2S composites with tunable heterogeneous interfaces. By varying the Ag2S loading, the heterogeneous interface between Ag2S and CuS could induce strong dielectric resonance peaks and optimize impedance matching, thereby significantly enhancing electromagnetic wave absorption performance and causing the CuS/Ag2S composites to exhibit continuous dual absorption peaks. Under conditions of a filler content of 20 wt% and a coating thickness of 2.89 mm, the optimized CuS/Ag2S paraffin composites exhibited continuous dual absorption peaks, with reflection losses reaching -47.2 and -20.6 dB, respectively.
CuS-based binary composite materials, through compounding with single-functional components such as carbon materials and magnetic media, and leveraging precise structural designs like sandwich and heterogeneous layered structures, achieve synergistic enhancement of mechanisms including conductive loss, interfacial polarization loss, and multiple scattering. This significantly optimizes the impedance matching and microwave absorption performance of the materials, laying a foundation for performance regulation of copper sulfide-based composite systems. However, the loss mechanisms and functional integration of binary composite systems still have limitations. On this basis, introducing more functional components to construct multivariate composite systems and fully exploiting component synergy mechanisms represents another important pathway for enhancing microwave absorption performance.
4.5 CuS-based multi-component composite materials
Compared to binary composite systems, CuS-based multi-component composite materials (Table 3) can construct multiple loss mechanisms through multi-component synergy (such as dielectric-dielectric, dielectric-magnetic, carbon-magnetic-dielectric, etc.), further broadening the microwave absorption bandwidth and enhancing loss intensity.
Carbon materials, such as graphene oxide (GO), multi-walled carbon nanotubes (MWCNT), and porous carbon (PC), feature high conductivity, low density, and three-dimensional network structures. They can form efficient conductive pathways with CuS of various morphologies (e.g., microflowers, nanoparticles), combining the morphological advantages of CuS to enhance conduction loss and multiple electromagnetic wave scattering. Bose et al.[69]used copper chloride as the copper source and thiourea as the sulfur source to synthesize rGO-CuS composite nanomaterials by in situ growth of CuS microflowers on the surface of sheet-structured rGO via a hydrothermal method. Subsequently, these were compounded with MWCNTs and PVDF into films through melt blending and hot pressing. With an MWCNT content of 3 wt% and rGO@CuS content of 10 wt%, using the hybrid material rGO-CuS prepared under optimal conditions (6 h reaction time), the high specific surface area of CuS microflowers synergized with the two-dimensional sheet structure of rGO and the one-dimensional tubular structure of MWCNTs to create a hierarchical morphology. This effectively enhanced interfacial polarization and conduction loss, yielding performance significantly superior to that of physically blended systems (Figure 16). Under the optimal ratio, a 1 mm thick sample achieved a shielding effectiveness of 25 dB in the 12–18 GHz frequency range, with absorption loss accounting for 86% and a minimum skin depth of only 0.38 mm.
Sun et al.[70]A facile two-step method was employed to synthesize rGO/CuS/polypyrrole (PPy) nanocomposites with a sandwich structure. When the filler mass fraction was 10 wt%, the rGO/CuS/PPy paraffin composites exhibited enhanced electromagnetic wave absorption performance in terms of both effective absorption bandwidth and absorption intensity, achieving a minimum reflection loss (RL) of -49.11 dB and an effective absorption bandwidth of 4.88 GHz.
Cellulose nanofibers (CNFs) can interweave to form a natural porous network structure, uniformly attaching CuS and carbon materials onto the CNF surfaces and within their pores, thereby enabling the preparation of CuS-based porous composite materials. Such composites combine lightweight properties with excellent structural toughness, fully leveraging the synergistic advantages of the porous structure and multi-component composition to demonstrate superior electromagnetic wave absorption and shielding performance. Xu et al.[71]prepared a porous composite material (CNFs/RGO/CuS) composed of cellulose nanofibers (CNFs), flower-like copper sulfide, and reduced graphene oxide via a hydrothermal method. Benefiting from the synergistic effects of CNFs, RGO, and flower-like CuS, this three-dimensional porous structure exhibits favorable impedance matching and high attenuation constant characteristics, demonstrating excellent microwave absorption performance. At a thickness of 2.5 mm, the minimum reflection loss (RLmin) reached -49.71 dB, with an effective absorption bandwidth (EAB) of 5.30 GHz (10.40~15.70 GHz).
Based on CuS/carbon-based composites, further introducing magnetic ferrites can simultaneously endow the material with magnetic loss characteristics and effectively optimize its impedance matching performance. Liu et al.[72]first used a hydrothermal method to magnetically modify graphene oxide (GO) with NiFe2O4 nanoparticles (NiFe2O4/GO), and then employed a solvothermal method to grow CuS nanosheets in situ vertically on their surface to prepare NiFe2O4/GO@CuS ternary composite materials. By adjusting the amount of CTAB in the solvothermal reaction, three-dimensional hybrid nanostructures with different CuS nanosheet thicknesses and degrees of magnetic graphene coating were prepared. When the optimal composite material was mixed with paraffin at a mass ratio of 1:4, at a thickness of 2.5 mm, the maximum reflection loss reached -54.5 dB at 11.4 GHz, with an effective absorption bandwidth of 4.5 GHz. The wave absorption performance was significantly improved compared to GO and NiFe₂O₄/GO (Figure 17).
Using a stepwise solvothermal method, Wang et al.[73]in situ grew flower-like CuS microspheres on a reduced graphene oxide substrate modified with ZnFe₂O₄ nanoparticles (ZnFe2O4@RGO), fabricating a ternary composite material with a hierarchical structure: ZnFe2O4@RGO@CuS. Among them, ZnFe2O4consists of microspheres with a diameter of approximately 300 nm, while CuS forms flower-like microspheres of 1~2 μm through the self-assembly of nanosheets; this unique microstructure provides an important foundation for enhancing microwave absorption performance. After compounding the composite material with paraffin at a mass ratio of 1:4 for microwave absorption testing, ZnFe2O4@RGO achieved a maximum reflection loss of -30.5 dB at 13.5 GHz with a thickness of 2.5 mm, and an effective absorption bandwidth of 8.4 GHz (9.6~18 GHz). Upon introducing CuS microspheres, the microwave absorption performance of the ternary composite improved significantly; when the thickness was reduced to 2.2 mm, the maximum reflection loss reached as low as -55.4 dB at 14.6 GHz, while maintaining a broadband effective absorption of 7.5 GHz (10.5~18 GHz). On one hand, the three-dimensional flower-like structure of CuS can increase multiple reflections and scattering of electromagnetic waves, accelerating energy dissipation; on the other hand, it can form a synergistic effect with ZnFe2O4, and RGO, optimizing the material's impedance matching as well as its magnetic and dielectric loss capabilities, thereby strengthening the electromagnetic wave attenuation effect of the composite.
Carbon nanotubes, owing to their high conductivity and one-dimensional conductive network structure, often serve as ideal carriers to construct efficient microwave absorption systems with magnetic and dielectric components. Wei et al.[74]employed a stepwise solvothermal method to load magnetic CoFe2O4 microspheres with particle sizes of 60~100 nm and CuS nanoparticles onto the outer walls of multi-walled carbon nanotubes (MWCNTs), constructing a CuS/CoFe2O4/MWCNT nanocomposite with a "tube-sphere" hierarchical structure. Among them, CoFe2O4 is tightly bonded to MWCNTs and CuS via chemical bonds, forming a stable three-dimensional conductive-magnetic network. Theoretical calculations indicate that CuS can effectively reduce the electron transfer barrier of the system, promote the formation of directional charge transport channels, thereby regulating the electromagnetic parameters of the composite material, playing a key role in optimizing impedance matching and enhancing multi-mechanism synergistic loss. The microwave absorption performance was tested after mixing the composite material with paraffin at a mass ratio of 4:6. The optimal sample (CuS-1.5CoFe2O4/MWCNTs) achieved a maximum effective absorption bandwidth of 5.26 GHz at a matching thickness of 1.77 mm; when the thickness increased to 4.64 mm, the minimum reflection loss reached as low as -58.74 dB at 17.52 GHz, demonstrating significantly superior microwave absorption performance compared to the CoFe2O4/MWCNTs system.
Porous carbon (PC) features low density, high specific surface area, abundant pore structure, a three-dimensional interconnected skeleton, and good conductivity, making it an excellent microwave absorption medium. Its porous structure not only effectively reduces material density but also extends the electromagnetic wave transmission path, enhancing multiple scattering and energy dissipation. Based on this, Wu et al.[75]used copper sulfide/rice husk-based porous carbon (Cu7.2S4@RPC) as a carrier to prepare FeS2‑CuFeS2@RPC composite microwave absorption materials by adjusting the amounts of iron and sulfur sources. Under optimal conditions, the prepared FeS2‑CuFeS2@RPC‑3 achieved a minimum reflection loss of -42.30 dB at 15.11 GHz in the Ku band with a matching thickness of 1.7 mm; at a thickness of 1.9 mm, the maximum effective absorption bandwidth reached 5.78 GHz.
Conductive polymers combined with morphological designs such as core-shell and hierarchical structures can further enhance interfacial polarization, multiple scattering, and structural stability, achieving ultra-high absorption intensity when integrated with the unique morphology of CuS. Li et al.[76]employed a three-step "hydrothermal-solvothermal-in situ polymerization" method to construct a CuS/Fe3O4@PPy core-shell hierarchical structured composite material. The core of this composite consists of CuS microflowers with diameters of 2–4 μm, self-assembled from ultrathin nanosheets (featuring high specific surface area and a three-dimensional wrinkled structure); the intermediate layer comprises hollow Fe3O4nanoparticles with particle sizes of 180–220 nm, and the outermost layer is a continuous and dense PPy coating. When this composite material was uniformly blended with paraffin at a mass ratio of 3:7 for testing, the synergistic effect of the multi-level core-shell morphology and the various components enabled the material to achieve a minimum reflection loss of up to -74.12 dB at a thickness of 2.96 mm, while maintaining an effective absorption bandwidth of 4.6 GHz (13.4–18.0 GHz) at a thickness of 1.68 mm, thereby realizing the unification of strong absorption, broad bandwidth, and thin profile. The synergistic effects among the components are key to enhancing microwave absorption performance: the flower-like CuS microspheres self-assembled from nanosheets provide a continuous conductive skeleton, while the nanoscale Fe3O4hollow spheres attached to the exterior of the microspheres not only introduce magnetic loss but also, through their cavity structure, allow electromagnetic waves to penetrate and trigger multiple reflections and refractions; the PPy coating layer not only enhances the structural bonding strength of the composite material but also scatters microwaves and induces multiple refractions via its interlayer structure, thereby efficiently dissipating electromagnetic energy.
Graphitic carbon nitride (g-C3N4), as a typical dielectric microwave-absorbing material, possesses a unique π-π conjugated structure and abundant polar groups, enabling electromagnetic wave dissipation through polarization loss. Based on this, Zong et al.[77]prepared a nanocomposite of flower-like copper sulfide microspheres (CuS) and nano iron oxide (Fe3O4) attached to graphitic carbon nitride (g-C₃N₄) (CuS/g-C3N4/Fe3O4) via high-temperature calcination, hydrothermal treatment, and co-precipitation methods. When this composite was compounded with paraffin at a 50 wt% filling ratio, a sample with a thickness of 2.5 mm achieved a reflection loss of -41.2 dB at 13.7 GHz, with an effective absorption bandwidth of 8.6 GHz (9.4–18 GHz). Compared to single flower-like CuS microspheres, the introduction of the heterostructured g-C3N4and magnetic Fe3O4nanoparticles significantly improved the impedance matching and dielectric loss of the composite while increasing magnetic loss, thereby substantially enhancing its microwave absorption performance (Figure 18).
The synergistic introduction of magnetic components, conductive polymers, and carbon materials into the CuS-based system constructs diversified hybrid nanocomposites and hierarchical microstructures. Leveraging the dielectric properties of CuS, this achieves a synergistic enhancement of dielectric and magnetic losses, further optimizing wave absorption performance. Wang et al.[78]designed and prepared a quaternary CuS/RGO/PANI/Fe3O4composite material, systematically investigating the regulatory role of its hierarchical nanostructure. With CuS as the core dielectric component, the material relies on RGO sheets, a PANI conductive network, and Fe3O4magnetic particles to form a hierarchical heterogeneous structure, effectively suppressing agglomeration and constructing abundant heterogeneous interfaces. Compared with binary and ternary systems, the microwave absorption performance of this quaternary material is significantly improved. This is primarily attributed to the synergistic loss between CuS and other components, favorable impedance matching, and the multiple scattering and interfacial polarization enhancement provided by the hierarchical structure. At a coating thickness of 2.5 mm, the maximum reflection loss reaches -60.2 dB at 10.2 GHz, with an effective absorption bandwidth of 7.4 GHz (7.5–14.9 GHz). CuS-based multicomponent composites, by incorporating various functional components such as carbon materials, magnetic particles, and conductive polymers, combined with precise structural designs like core-shell, hierarchical, and porous architectures, have constructed loss systems featuring synergistic mechanisms such as dielectric-magnetic and carbon-magnetic-dielectric interactions. This not only achieves a significant improvement in absorption intensity and an effective broadening of the absorption frequency band but also optimizes the impedance matching characteristics of the materials, demonstrating superior comprehensive wave absorption performance compared to binary systems. With the diversification of functional requirements for materials in practical applications, integrating electromagnetic wave absorption properties with other functions such as thermal conductivity and photothermal conversion to develop CuS-based multifunctional composites has become an important development trend in this field.
4.6 CuS-based multifunctional composite materials
With the diversification of electromagnetic protection demands, CuS-based multifunctional composites that combine electromagnetic wave absorption properties with other functions, such as thermal conductivity, phase change, infrared stealth, antibacterial activity, flame retardancy, and photothermal conversion, have become a research hotspot. They are expected to be applied in photothermal conversion devices and thermal management of electronic equipment, showing promising application prospects in the design of wearable devices.
Cheng et al.[79]Stearic acid (SA) was encapsulated into a porous biochar (BC) skeleton via vacuum impregnation to obtain an energy storage matrix (SA/BC). Subsequently, flower-like CuS and ZnO particles were loaded onto a carbon mesh (CM) using a hydrothermal method to prepare a modified carbon mesh (E-CM). Finally, the E-CM was hot-pressed onto the top and bottom surfaces of the SA/BC to fabricate a multilayered multifunctional composite phase change material (E-SA/BC). This composite not only exhibits excellent thermal performance, photothermal conversion, and visible-light photocatalytic properties, but also demonstrates superior electromagnetic shielding performance due to the electric field generated by the CuS/ZnO heterostructure and the porous structure of the biochar. When the stearic acid content in the composite is 80%, it achieves a total shielding effectiveness exceeding 40 dB in the frequency range of 8.2–12.4 GHz.
Huang et al.[80]A double-layer flexible phase change composite membrane (MLPC) containing highly conductive copper sulfide and porous carbon was prepared using a combined strategy of hydrothermal method, vacuum impregnation, and vacuum filtration. One side of the composite membrane is rich in porous carbon, composed of porous carbon loaded with nickel-aluminum layered double hydroxides (MPC@NiAl-LDH), polyethylene glycol (PEG), and nanocellulose (CNF); the other side is rich in CuS, composed of CuS and CNF. Benefiting from the synergistic effects of structure and composition within the composite membrane, the prepared membrane possesses electromagnetic shielding, flame retardancy, high thermal conductivity, and efficient photothermal conversion properties. When the MPC@NiAl-LDH content is 15 wt%, its phase change enthalpy, thermal conductivity, electromagnetic shielding effectiveness, and electrical conductivity reach 146.8 J/g, 1.07 W/(m·K), 38.8 dB, and 126.4 S/m, respectively.
CuS-based multifunctional composite materials, through precise multilayer/bilateral structural design and multi-component synergistic regulation, have successfully achieved the efficient integration of electromagnetic shielding with phase change energy storage, photothermal conversion, and flame-retardant thermal conductivity functions, thereby better meeting the demands of diversified application scenarios such as thermal management for electronic devices and wearable equipment.
5 Conclusion and Outlook
In summary, copper sulfide (CuS), as a typical class of P-type semiconductors, demonstrates strong application potential in commercial aviation, stealth, and other target fields due to its simple synthesis process, unique micro-morphological structure, and excellent optoelectronic and microwave absorption properties. Benefiting from favorable skin depth and the ability to achieve efficient microwave attenuation through dual mechanisms of dielectric heating and polarization loss, this CuS nanocomposite is poised to replace traditional conductive or magnetic nanoparticles, offering novel technical pathways and options for the design and preparation of high-performance electromagnetic functional materials.
Currently, various methods have been developed for preparing CuS pure phases and composite nanomaterials with different phase compositions and morphologies. Researchers have successfully constructed diverse copper sulfide-based composite material systems, including core-shell structured composites, polymer composite membranes, and fiber-based textiles, by utilizing them as functional components. In-depth studies on their wave absorption and shielding properties have achieved significant progress, effectively expanding the application of CuS-based nanomaterials in the field of lightweight, flexible, and multifunctional wave-absorbing electromagnetic shielding composite materials.
Despite numerous breakthroughs in research, significant challenges remain: (1) Scalable preparation technologies are immature; existing methods for precise morphology control are mostly limited to small-batch laboratory synthesis, lacking green and low-cost mass production processes. (2) Research on long-term service reliability is insufficient, particularly regarding the reliability of electromagnetic shielding performance under complex operating environments such as humidity, high temperature, or UV radiation; specifically, the challenge of balancing multiple objectives with high stability has not yet been overcome. (3) Adaptability for practical applications needs improvement; the cost of multifunctional composite materials is relatively high, and integration with real-world scenarios requires further strengthening. Furthermore, research on performance in low-frequency bands (<6 GHz) and high-frequency millimeter waves (>18 GHz) remains scarce, making it difficult to meet the high-frequency protection requirements of 5G and subsequent communication technologies.
Research on copper sulfide-based electromagnetic wave absorption/shielding materials can be deeply explored from the following three aspects: (1) Green synthesis strategies: Develop template-free, low-energy-consumption green scalable synthesis technologies to achieve precise morphology control while balancing mass production; (2) Theoretical simulation and optimization: Combine first-principles calculations with machine learning to predict optimal material compositions and structures, strengthening multi-component synergistic design to break through bottlenecks in core performance synergistic optimization; (3) Multifunctional integration: While ensuring stability under operating conditions for electromagnetic wave absorption/shielding performance, endow materials with thermal conductivity, flame retardancy, or flexibility to meet the demands of electronic devices for multifunctional materials.
PDF
