Core–Shell Structure and Interaction Mechanism of γ‐MnO2 Coated Sulfur for Improved Lithium‐Sulfur Batteries

Lithium‐sulfur batteries have attracted worldwide interest due to their high theoretical capacity of 1672 mAh g^?1 and low cost. However, the practical applications are hampered by capacity decay, mainly attributed to the polysulfide shuttle. Here, the authors have fabricated a solid core–shell γ‐MnO₂‐coated sulfur nanocomposite through the redox reaction between KMnO₄ and MnSO₄. The multifunctional MnO₂ shell facilitates electron and Li⁺ transport as well as efficiently prevents polysulfide dissolution via physical confinement and chemical interaction. Moreover, the γ‐MnO₂ crystallographic form also provides one‐dimensional (1D) tunnels for the Li⁺ incorporation to alleviate insoluble Li₂S₂/Li₂S deposition at high discharge rate. More importantly, the MnO₂ phase transformation to Mn₃O₄ occurs during the redox reaction between polysulfides and γ‐MnO₂ is first thoroughly investigated. The S@γ‐MnO₂ composite exhibits a good capacity retention of 82% after 300 cycles (0.5 C) and a fade rate of 0.07% per cycle over 600 cycles (1 C). The degradation mechanism can probably be elucidated that the decomposition of the surface Mn₃O₄ phase is the cause of polysulfide dissolution. The recent work thus sheds new light on the hitherto unknown surface interaction mechanism and the degradation mechanism of Li‐S cells.     

Synthesis and microwave absorption enhancement of yolk–shell Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@C microspheres

Rational design on the microstructure of microwave-absorbing materials is paving the way for upgrading their performances in electromagnetic pollution prevention. In this study, a Fe₃O₄/C composite with unique yolk–shell microstructure (YS-Fe₃O₄@C) is successfully fabricated by a silica-assisted route. It is found that carbon shells in this composite can make up the shortages of Fe₃O₄ microspheres in dielectric loss ability, while they may more or less attenuate the intrinsically magnetic loss of Fe₃O₄ microspheres. The microwave absorption properties of YS-Fe₃O₄@C are evaluated in the frequency range of 2.0–18.0 GHz in terms of the measured complex permittivity and complex permeability. The results demonstrate that YS-Fe₃O₄@C can exhibit much better performance than bare Fe₃O₄ microspheres and individual carbon materials, as well as core–shell Fe₃O₄/C composite (CS-Fe₃O₄@C), where strong reflection loss and wide response bandwidth can be achieved simultaneously. With an absorber thickness of 2.0 mm, the maximum reflection loss is ?73.1 dB at 14.6 GHz and a bandwidth over ?10.0 dB is in the range of 12.3–18.0 GHz. It can be proved that the unique yolk–shell microstructure is helpful to reinforce the dielectric loss ability and create an optimized matching of characteristic impedance in the composite.     

Rational Design of Multifunctional Fe@γ‐Fe2O3@H‐TiO2 Nanocomposites with Enhanced Magnetic and Photoconversion Effects for Wide Applications: From Photocatalysis to Imaging‐Guided Photothermal Cancer Therapy

Titanium dioxide (TiO₂) has been widely investigated and used in many areas due to its high refractive index and ultraviolet light absorption, but the lack of absorption in the visible–near infrared (Vis–NIR) region limits its application. Herein, multifunctional Fe@γ‐Fe₂O₃@H‐TiO₂ nanocomposites (NCs) with multilayer‐structure are synthesized by one‐step hydrogen reduction, which show remarkably improved magnetic and photoconversion effects as a promising generalists for photocatalysis, bioimaging, and photothermal therapy (PTT). Hydrogenation is used to turn white TiO₂ in to hydrogenated TiO₂ (H‐TiO₂), thus improving the absorption in the Vis–NIR region. Based on the excellent solar‐driven photocatalytic activities of the H‐TiO₂ shell, the Fe@γ‐Fe₂O₃ magnetic core is introduced to make it convenient for separating and recovering the catalytic agents. More importantly, Fe@γ‐Fe₂O₃@H‐TiO₂ NCs show enhanced photothermal conversion efficiency due to more circuit loops for electron transitions between H‐TiO₂ and γ‐Fe₂O₃, and the electronic structures of Fe@γ‐Fe₂O₃@H‐TiO₂ NCs are calculated using the Vienna ab initio simulation package based on the density functional theory to account for the results. The reported core–shell NCs can serve as an NIR‐responsive photothermal agent for magnetic‐targeted photothermal therapy and as a multimodal imaging probe for cancer including infrared photothermal imaging, magnetic resonance imaging, and photoacoustic imaging.     

Hierarchical α‐MnO2 Nanowires@Ni1‐xMnxOy Nanoflakes Core–Shell Nanostructures for Supercapacitors

A facile two‐step solution‐phase method has been developed for the preparation of hierarchical α‐MnO₂ nanowires@Ni_1‐xMn_xO_y nanoflakes core–shell nanostructures. Ultralong α‐MnO₂ nanowires were synthesized by a hydrothermal method in the first step. Subsequently, Ni_1‐xMn_xO_y nanoflakes were grown on α‐MnO₂ nanowires to form core–shell nanostructures using chemical bath deposition followed by thermal annealing. Both solution‐phase methods can be easily scaled up for mass production. We have evaluated their application in supercapacitors. The ultralong one‐dimensional (1D) α‐MnO₂ nanowires in hierarchical core–shell nanostructures offer a stable and efficient backbone for charge transport; while the two‐dimensional (2D) Ni_1‐xMn_xO_y nanoflakes on α‐MnO₂ nanowires provide high accessible surface to ions in the electrolyte. These beneficial features enable the electrode with high capacitance and reliable stability. The capacitance of the core–shell α‐MnO₂@Ni_1‐xMn_xO_y nanostructures (x = 0.75) is as high as 657 F g^?1 at a current density of 250 mA g^?1, and stable charging‐discharging cycling over 1000 times at a current density of 2000 mA g^?1 has been realized.     

Magnetic Metal–Organic Frameworks: γ‐Fe2O3@MOFs via Confined In Situ Pyrolysis Method for Drug Delivery

A general one‐step in situ pyrolysis route for the construction of metal–organic frameworks encapsulating superparamagnetic γ‐Fe₂O₃ NPs dispersed in the confined cavities of MOFs homogeneously is described. The integration of γ‐Fe₂O₃ NPs or clusters into MOFs can endow these porous materials with superparamagnetic element. By the combination of the thermal stability of MOFs and pyrolysis of metal triacetylacetonate complex at matched conditions, the porous structure of MOFs are well maintained while the size‐induced superparamagnetic property of nano γ‐Fe₂O₃ is obtained. As a proof of concept, both the γ‐ Fe₂O₃@ZIF‐8 and γ‐Fe₂O₃@MIL‐53(Al) were successfully prepared, and the latter was chosen to demonstrate its potential drug delivery as a magnetic MOF.     

Multilayer Amorphous‐Si‐B‐C‐N/γ‐Al2O3/α‐Al2O3 Membranes for Hydrogen Purification

The hydrogen and carbon monoxide separation is an important step in the hydrogen production process. If H₂ can be selectively removed from the product side during hydrogen production in membrane reactors, then it would be possible to achieve complete CO conversion in a single‐step under high temperature conditions. In the present work, the multilayer amorphous‐Si‐B‐C‐N/γ‐Al₂O₃/α‐Al₂O₃ membranes with gradient porosity have been realized and assessed with respect to the thermal stability, geometry of pore space and H₂/CO permeance. The α‐Al₂O₃ support has a bimodal pore‐size distribution of about 0.64 and 0.045 µm being macroporous and the intermediate γ‐Al₂O₃ layer—deposited from boehmite colloidal dispersion—has an average pore‐size of 8 nm being mesoporous. The results obtained by the N₂‐adsorption method indicate a decrease in the volume of micropores—0.35 vs. 0.75 cm³ g^?1—and a smaller pore size ?6.8 vs. 7.4 Å—in membranes with the intermediate mesoporous γ‐Al₂O₃ layer if compared to those without. The three times Si‐B‐C‐N coated multilayer membranes show higher H₂/CO permselectivities of about 10.5 and the H₂ permeance of about 1.05 × 10^?8 mol m^?2 s^?1 Pa^?1. If compared to the state of the art of microporous membranes, the multilayer Si‐B‐C‐N/γ‐Al₂O₃/α‐Al₂O₃ membranes are appeared to be interesting candidates for hydrogen separation because of their tunable nature and high‐temperature and high‐pressure stability.     

Scalable Synthesis of Triple‐Core–Shell Nanostructures of TiO2@MnO2@C for High Performance Supercapacitors Using Structure‐Guided Combustion Waves

Core–shell nanostructures of metal oxides and carbon‐based materials have emerged as outstanding electrode materials for supercapacitors and batteries. However, their synthesis requires complex procedures that incur high costs and long processing times. Herein, a new route is proposed for synthesizing triple‐core–shell nanoparticles of TiO₂@MnO₂@C using structure‐guided combustion waves (SGCWs), which originate from incomplete combustion inside chemical‐fuel‐wrapped nanostructures, and their application in supercapacitor electrodes. SGCWs transform TiO₂ to TiO₂@C and TiO₂@MnO₂ to TiO₂@MnO₂@C via the incompletely combusted carbonaceous fuels under an open‐air atmosphere, in seconds. The synthesized carbon layers act as templates for MnO₂ shells in TiO₂@C and organic shells of TiO₂@MnO₂@C. The TiO₂@MnO₂@C‐based electrodes exhibit a greater specific capacitance (488 F g^?1 at 5 mV s^?1) and capacitance retention (97.4% after 10 000 cycles at 1.0 V s^?1), while the absence of MnO₂ and carbon shells reveals a severe degradation in the specific capacitance and capacitance retention. Because the core‐TiO₂ nanoparticles and carbon shell prevent the deformation of the inner and outer sides of the MnO₂ shell, the nanostructures of the TiO₂@MnO₂@C are preserved despite the long‐term cycling, giving the superior performance. This SGCW‐driven fabrication enables the scalable synthesis of multiple‐core–shell structures applicable to diverse electrochemical applications.     

Bifunctional Graphene/γ‐Fe2O3 Hybrid Aerogels with Double Nanocrystalline Networks for Enzyme Immobilization

Highly porous hosting materials with conducting (favorable to electron transfer) and magnetic (favorable to product separation) bicontinuous networks should possess great potentials for immobilization of various enzymes in the field of biocatalytic engineering, but the synthesis of such materials is still a great challenge. Herein, bifunctional graphene/γ‐Fe₂O₃ hybrid aerogels with quite low density (30–65 mg cm^?3), large specific surface area (270–414 m² g^?1), high electrical conductivity (0.5–5 × 10^?2 S m^?1), and superior saturation magnetization (23–54 emu g^?1) are fabricated. Single networks of either graphene aerogels or γ‐Fe₂O₃ aerogels are obtained by etching of the hybrid aerogels with acid solution or calcining of the hybrid aerogels in air, indicative of the double networks of the as‐synthesized graphene/γ‐Fe₂O₃ hybrid aerogels for the first time. The resulting bifunctional aerogels are used to immobilize β‐glucuronidase for biocatalytic transformation of glycyrrhizin into glycyrrhetinic acid monoglucuronide or glycyrrhetinic acid, with high biocatalytic activity and definite repeatability.     

Giant Magnetic Heat Induction of Magnesium‐Doped γ‐Fe2O3 Superparamagnetic Nanoparticles for Completely Killing Tumors

Magnetic fluid hyperthermia has been recently considered as a Renaissance of cancer treatment modality due to its remarkably low side effects and high treatment efficacy compared to conventional chemotheraphy or radiotheraphy. However, insufficient AC induction heating power at a biological safe range of AC magnetic field (H_appl·f_appl < 3.0–5.0 × 10⁹ A m^?1 s^?1), and highly required biocompatibility of superparamagnetic nanoparticle (SPNP) hyperthermia agents are still remained as critical challenges for successful clinical hyperthermia applications. Here, newly developed highly biocompatible magnesium shallow doped γ‐Fe₂O₃ (Mg_0.13‐γFe₂O₃) SPNPs with exceptionally high intrinsic loss power (ILP) in a range of 14 nH m² kg^?1, which is an ≈100 times higher than that of commercial Fe₃O₄ (Feridex, ILP = 0.15 nH m² kg^?1) at H_appl·f_appl = 1.23 × 10⁹ A m^?1 s^?1 are reported. The significantly enhanced heat induction characteristics of Mg_0.13‐γFe₂O₃ are primarily due to the dramatically enhanced out‐of‐phase magnetic susceptibility and magnetically tailored AC/DC magnetic softness resulted from the systematically controlled Mg²⁺ cations distribution and concentrations in octahedral site Fe vacancies of γ‐Fe₂O₃ instead of well‐known Fe₃O₄ SPNPs. In vitro and in vivo magnetic hyperthermia studies using Mg_0.13‐γFe₂O₃ nanofluids are conducted to estimate bioavailability and biofeasibility. Mg_0.13‐γFe₂O₃ nanofluids show promising hyperthermia effects to completely kill the tumors.     

Synthesis and microwave absorption property of ternary composites: polyaniline/CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript>/Ba<Subscript>3</Subscript>Co<Subscript>2</Subscript>Fe<Subscript>24</Subscript>O<Subscript>41</Subscript>

Polyaniline (PANI)/CoFe₂O₄/Ba₃Co₂Fe₂₄O₄₁ composite was prepared by an in-situ polymerization method. The phase structure, morphology and magnetic properties of the as-prepared PANI/CoFe₂O₄/Ba₃Co₂Fe₂₄O₄₁ composite were characterized by XRD, FT-IR, SEM, TEM, and VSM, respectively. The microwave absorption properties of the composite were investigated by using a vector network analyzer in the 2–18 GHz frequency range. The results show that the maximum reflection loss value of the PANI/CoFe₂O₄/Ba₃Co₂Fe₂₄O₄₁ composite reaches ?30.5 dB at 10.5 GHz with a thickness of 3 mm and the bandwidth of reflection loss below ?10 dB reaches up to 1.2 GHz. The excellent microwave absorption properties of the as-prepared PANI/CoFe₂O₄/Ba₃Co₂Fe₂₄O₄₁ composite due to the enhanced impedance match between dielectric loss and magnetic loss.     

Facile Synthesis of γ‐In2Se3 Nanoflowers toward High Performance Self‐Powered Broadband γ‐In2Se3/Si Heterojunction Photodiode

An effective colloidal process involving the hot‐injection method is developed to synthesize uniform nanoflowers consisting of 2D γ‐In₂Se₃ nanosheets. By exploiting the narrow direct bandgap and high absorption coefficient in the visible light range of In₂Se₃, a high‐quality γ‐In₂Se₃/Si heterojunction photodiode is fabricated. This photodiode shows a high photoresponse under light illumination, short response/recovery times, and long‐term durability. In addition, the γ‐In₂Se₃/Si heterojunction photodiode is self‐powered and displays a broadband spectral response ranging from UV to IR with a high responsivity and detectivity. These excellent performances make the γ‐In₂Se₃/Si heterojunction very interesting as highly efficient photodetectors.     

H+‐Insertion Boosted α‐MnO2 for an Aqueous Zn‐Ion Battery

Rechargeable Zn/MnO₂ batteries using mild aqueous electrolytes are attracting extensive attention due to their low cost, high safety, and environmental friendliness. However, the charge‐storage mechanism involved remains a topic of controversy so far. Also, the practical energy density and cycling stability are still major issues for their applications. Herein, a free‐standing α‐MnO₂ cathode for aqueous zinc‐ion batteries (ZIBs) is directly constructed with ultralong nanowires, leading to a rather high energy density of 384 mWh g^?1 for the entire electrode. Greatly, the H⁺/Zn²⁺ coinsertion mechanism of α‐MnO₂ cathode for aqueous ZIBs is confirmed by a combined analysis of in situ X‐ray diffractometry, ex situ transmission electron microscopy, and electrochemical methods. More interestingly, the Zn²⁺‐insertion is found to be less reversible than H⁺‐insertion in view of the dramatic capacity fading occurring in the Zn²⁺‐insertion step, which is further evidenced by the discovery of an irreversible ZnMn₂O₄ layer at the surface of α‐MnO₂. Hence, the H⁺‐insertion process actually plays a crucial role in maintaining the cycling performance of the aqueous Zn/α‐MnO₂ battery. This work is believed to provide an insight into the charge‐storage mechanism of α‐MnO₂ in aqueous systems and paves the way for designing aqueous ZIBs with high energy density and long‐term cycling ability.     

Graphene-enhanced microwave absorption properties of Fe3O4/SiO2 nanorods

Fe₃O₄/SiO₂/graphene composite composed of Fe₃O₄/SiO₂ core–shell nanorods and graphene nanosheets were synthesized by a facile wet chemical method. Structure and morphology studies reveal that the Fe₃O₄/SiO₂ nanorods with porous structure and large aspect ratio are densely wrapped by the graphene nanosheets. By changing the graphene content, the electromagnetic properties of the Fe₃O₄/SiO₂/graphene composite can be well tuned. When the weight ratio of Fe₃O₄/SiO₂ to graphene reaches an appropriate value, excellent microwave absorption performance is achieved due to the large electromagnetic losses and good impedance matching. The Fe₃O₄/SiO₂/graphene composite with graphene content of 5 wt.% shows the minimum reflection loss of −27.1 dB at 12.2 GHz when the coating layer thickness is only 1.5 mm.     

Enhanced electromagnetic wave absorption properties of polyaniline-coated Fe3O4/reduced graphene oxide nanocomposites

Fe₃O₄-reduced graphene oxide-polyaniline (Fe₃O₄–RGO–PANI) ternary electromagnetic wave absorbing materials were prepared by in situ polymerization of aniline monomer on the surface of Fe₃O₄–RGO nanocomposites. The morphology, structure and other physical properties of the nanocomposites were characterized by X-ray diffraction, transmission electron microscopy, vibration sample magnetism, etc. The electromagnetic wave absorbing properties of composite materials were measured by using a vector network analyzer. The PANI–Fe₃O₄–RGO nanocomposites demonstrated that the maximum reflection loss was ?36.5 dB at 7.4 GHz with a thickness of 4.5 mm and the absorption bandwidth with the reflection loss below ?10 dB was up to 12.0 GHz with a thickness in the range of 2.5–5.0 mm, suggesting that the microwave absorption properties and the absorption bandwidth were greatly enhanced by coating with polyaniline (PANI). The strong absorption characteristics of PANI–Fe₃O₄–RGO ternary composites indicated their potential application as the electromagnetic wave absorbing material.     

A wrinkle to sub-100 nm yolk/shell Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@SiO<Subscript>2</Subscript> nanoparticles

Yolk/shell nanoparticles (NPs), which integrate functional cores (likes Fe₃O₄) and an inert SiO₂ shell, are very important for applications in fields such as biomedicine and catalysis. An acidic medium is an excellent etchant to achieve hollow SiO₂ but harmful to most functional cores. Reported here is a method for preparing sub-100 nm yolk/shell Fe₃O₄@SiO₂ NPs by a mild acidic etching strategy. Our results demonstrate that establishment of a dissolution–diffusion equilibrium of silica is essential for achieving yolk/shell Fe₃O₄@SiO₂ NPs. A uniform increase in the silica compactness from the inside to the outside and an appropriate pH value of the etchant are the main factors controlling the thickness and cavity of the SiO₂ shell. Under our “standard etching code”, the acid-sensitive Fe₃O₄ core can be perfectly preserved and the SiO₂ shell can be selectively etched away. The mechanism of regulation of SiO₂ etching and acidic etching was investigated.

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Fe2O3–TiO2 Nano‐heterostructure Photoanodes for Highly Efficient Solar Water Oxidation

Harnessing solar energy for the production of clean hydrogen by photo­electrochemical water splitting represents a very attractive, but challenging approach for sustainable energy generation. In this regard, the fabrication of Fe₂O₃–TiO₂ photoanodes is reported, showing attractive performances [≈2.0 mA cm⁻² at 1.23 V vs. the reversible hydrogen electrode in 1 M NaOH] under simulated one‐sun illumination. This goal, corresponding to a tenfold photoactivity enhancement with respect to bare Fe₂O₃, is achieved by atomic layer deposition of TiO₂ over hematite (α‐Fe₂O₃) nanostructures fabricated by plasma enhanced‐chemical vapor deposition and final annealing at 650 °C. The adopted approach enables an intimate Fe₂O₃–TiO₂ coupling, resulting in an electronic interplay at the Fe₂O₃/TiO₂ interface. The reasons for the photocurrent enhancement determined by TiO₂ overlayers with increasing thickness are unraveled by a detailed chemico‐physical investigation, as well as by the study of photo­generated charge carrier dynamics. Transient absorption spectroscopy shows that the increased photoelectrochemical response of heterostructured photoanodes compared to bare hematite is due to an enhanced separation of photogenerated charge carriers and more favorable hole dynamics for water oxidation. The stable responses obtained even in simulated seawater provides a feasible route in view of the eventual large‐scale generation of renewable energy.     

Investigation of adjacent spacing dependent microwave absorption properties of lamellar structural Ti3C2Tx MXenes

Ti₃C₂Tx MXenes and their composites play a vital role in the research on microwave absorbing materials. Herein, the different interlamellar spaces of Ti₃C₂Tx MXene materials were prepared by an etching process. The dependence of the microwave absorbing properties of the Ti₃C₂Tx MXene nanosheets on different interlamellar spaces was studied. The complex permittivity, dielectric loss, impedance matching characteristic and the minimum reflection loss (RL) value with the variation in interlamellar space were systematically investigated. Results showed that 40% ratio paraffin-bonded composites (S3) have a strong electromagnetic wave absorption performance and large effective absorbing bandwidth. The maximum RL reaches −36.3 dB at 4.67 GHz with the thickness of 4.5 mm, ascribed to its a high dielectric loss and good impedance matching characteristics. The RL value of Ti₃C₂Tx MXenes is strongly dependent on the inter-lamellar space. The enhanced microwave absorption originates from the unique 2-D structure, good impedance matching characteristics, and enhanced space-charge polarization effects. This work provides a new avenue for exploring high-performance microwave absorbers based on MXene materials.     

Microstructure and microwave absorption properties of Fe3O4/dextran/SnO2 multilayer microspheres

Fe₃O₄/dextran/SnO₂ multilayer microspheres have been successfully designed and synthesized by solvothermal and hydrothermal reactions. Dextran worked as a linker between Fe₃O₄ core and SnO₂ shell. It can not only prevent the oxidation of Fe₃O₄ but also be carbonize to another absorber carbon black. The as-synthesized microspheres were about 320 nm in size and well-defined in shape. The maximum reflection loss of Fe₃O₄/dextran/SnO₂ microspheres and paraffin wax composites could reach 20.26 dB at 4.72 GHz, and the bandwidth with a reflection loss less than ? 10 dB was 4.86 GHz with 4 mm in thickness. The excellent microwave absorption properties of the composites were attributed to the special multilayer structures of Fe₃O₄/dextran/SnO₂ microspheres and the effective complementarity between dielectric loss and magnetic loss.     

The effect of polyethylenimine on the microwave absorbing properties of a hybrid microwave absorber of Fe3O4/MWNTs

The hybrid microwave absorber of Fe₃O₄/multi-walled carbon nanotubes (MWNTs)modified with polyethylenimine (PEI) polymers was fabricated by chemical co-precipitation. The structure and morphology of hybrids are characterized by X-ray diffraction, Fourier transform infrared spectroscopy, and transmission electron-microscopy (TEM). The effect of PEI on the distribution of Fe₃O₄ nanoparticles and the microwave absorbing properties of hybrid microwave absorber of Fe₃O₄/MWNTs were investigated. The TEM results show that Fe₃O₄ nanoparticles are attached homogeneously on MWNTs, which indicates that the adding of PEI is effective to control the distribution of Fe₃O₄ nanoparticles on the surface of MWNTs. The microwave absorbing properties results show that the maximum reflection loss (RL) of PEI modified Fe₃O₄/MWNTs hybrids is improved significantly, which is ?30.69 dB at 7.24 GHz and ?10 dB bandwidth is 1.84 GHz. However, the RL of the Fe₃O₄/MWNTs without PEI is ?21.96 dB at 7.02 GHz and ?10 dB bandwidth is 1.2 GHz.     

Boosted Interfacial Polarization from Multishell TiO2@Fe3O4@PPy Heterojunction for Enhanced Microwave Absorption

Core@shell structures have been attracting extensive attention to boost microwave absorption (MA) performance due to the unique interfacial polarization. However, it still remains a challenge to synthesize sophisticated 1D semiconductor‐based materials with excellent MA competence. Herein, a hierarchical cable‐like TiO₂@Fe₃O₄@PPy is fabricated by a sequential process of solvothermal treatment and polymerization. The complex permittivity of ternary composites can be optimized by tunable PPy coating thickness to improve the loss ability. The maximum reflection loss can reach ?61.8 dB with a thickness of 3.2 mm while the efficient absorption bandwidth can achieve over 6.0 GHz, which involves the X and Ku band at only a 2.2 mm thickness. Importantly, the heterojunction contacts constructed by PPy–Fe₃O₄ and Fe₃O₄–TiO₂ contribute to the enhanced polarization loss. Besides, the configuration of magnetic Fe₃O₄ sandwiched between dielectric TiO₂ and PPy facilitates the magnetic stray field to radiate into the TiO₂ core and out of the PPy shell, which significantly promotes magnetic–dielectric synergy. Electron holography validates the distinct charge distribution and magnetic coupling. The new findings might shed light on novel structures for functional core@shell composites and the design of semiconductor‐based materials for microwave absorption.