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Open Access Research Article Issue
Dielectric–magnetic manipulation of reduced graphene oxide permittivity for enhanced electromagnetic wave absorption
Journal of Advanced Ceramics 2024, 13(12): 1974-1984
Published: 28 December 2024
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Graphene is a promising electromagnetic wave absorption (EMWA) material because of its structural designability, controllable electromagnetic properties, and excellent stability. However, the impedance mismatch caused by high conductivity and dielectric properties has seriously hindered the application of graphene in the EMWA field. In this work, based on the dielectric dispersion behavior of ideal broadband absorption as a guide, a Fe microsheet/reduced graphene oxide (Fe/RGO) composite was prepared by simple hydrothermal and thermal reduction methods. The permittivity of RGO is optimized by adjusting the content of anisotropic Fe microsheets, and a balance between attenuation ability and impedance matching is achieved. Theoretical calculations and off-axis electron holography results reveal that the abundant polar sites and heterogeneous interfaces of Fe and RGO enhance the dipole and interface polarizations. The three-dimensional (3D) conductive network structure contributes to multiple reflections of incident electromagnetic waves and conduction loss. The natural and exchange resonances and eddy current loss caused by anisotropic Fe microsheets further increase magnetic loss. Based on the dielectric-magnetic loss mechanism and good impedance matching, Fe/RGO achieves a minimum reflection loss (RLmin) of −67.95 dB at 8.48 GHz and a maximum effective absorption bandwidth (EABmax) of 6.91 GHz (11.09–18 GHz) with a low filling content of 10 wt%. In addition, Fe/RGO has excellent radar stealth performance, with a radar cross section (RCS) of −31.21 dBm2 at 0°. Therefore, the proposed strategy and theoretical analysis provide a reference for the microstructure design, composition, and mechanism analysis of EMWA materials.

Research Article Issue
Hollow porous FeCo/Cu/CNTs composite microspheres with excellent microwave absorption performance
Nano Research 2024, 17(11): 9857-9864
Published: 03 September 2024
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Downloads:101

Magnetic/dielectric composite materials with numerous heterointerfaces are highly promising functional materials, which are widely applied in the fields of electromagnetic wave absorption. Constructing heterogeneous structure is beneficial to further enhance the microwave absorption performance of composite materials. However, the process of constructing multi-heterogeneous interfaces is extremely complex. In this work, hollow porous FeCo/Cu/CNTs composite microspheres are prepared by the simple spray drying method and subsequently two-step annealing treatment, which possess abundant heterogeneous interfaces, unique three-dimensional conductive network and magnetic coupling network. This unique structure is beneficial to improving the ability of dielectric loss and magnetic loss, and then achieving an excellent microwave absorption performance. The prepared FeCo/Cu/CNTs-1 composite microspheres maintain a minimum reflection loss (RL) of –48.1 dB and a maximum effective absorption bandwidth of 5.76 GHz at a thickness of 1.8 mm. Generally, this work provides a new idea for designing multi-heterogeneous of microwave absorbing materials.

Research Article Issue
Hollow FeCoNiAl microspheres with stabilized magnetic properties for microwave absorption
Nano Research 2024, 17(3): 2079-2087
Published: 26 January 2024
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Development of high-performance microwave absorption materials (MAM) with stabilized magnetic properties at high temperatures is specifically essential but remains challenging. Moreover, the Snoke's limitation restrains the microwave absorption (MA) property of magnetic materials. Modulating alloy components is considered an effective way to solve the aforementioned problems. Herein, a hollow medium-entropy FeCoNiAl alloy with a stable magnetic property is prepared via simple spray-drying and two-step annealing for efficient MA. FeCoNiAl exhibited an ultrabroad effective absorption band (EAB) of 5.84 GHz (12.16–18 GHz) at a thickness of just 1.6 mm, revealing an excellent absorption capability. Furthermore, the MA mechanism of FeCoNiAl is comprehensively investigated via off-axis holography. Finally, the electromagnetic properties, antioxidant properties, and residual magnetism at high temperatures of FeCoNiAl alloys are summarized in detail, providing new insights into the preparation of MAM operating at elevated temperatures.

Research Article Issue
Vortex tuning magnetization configurations in porous Fe3O4 nanotube with wide microwave absorption frequency
Nano Research 2022, 15(7): 6743-6750
Published: 26 April 2022
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The design and optimization of one-dimension (1D) magnetic material are of great importance for the energy conversion, storage and spin electron devices, which remain a huge challenge. Herein, 1D porous Fe3O4 nanotubes (NTs) have been fabricated via a combined process of electrospinning and calcination. In the electrospinning precursors, by regulating the content ratio between two types of polyvinyl pyrrolidone with different molecular weight, porous Fe3O4 NTs with vortex-domain configuration have been fabricated. Based on the unique 1D nanotube structure encapsulated with multi-domains, the composite Fe3O4 NTs exhibit high complex permeability (μʹ, μʺ) values, and hold both strong magnetic storage and dissipation capacity. Our Fe3O4 NTs exhibit excellent microwave absorption (MA) performance with the maximum reflection loss value of −57.1 dB and the efficient absorption bandwidth of 12.0 GHz. The generated magnetic vortices make the crucial contribution to the spin-wave resonance which improves the MA dissipation under high-frequency. Related magnetic flux line distribution and magnetic domain moment were confirmed by the electron holography and micro-magnetic simulation, respectively, providing the deep insight to the microwave absorption mechanism.

Research Article Issue
Dual strategy of modulating growth temperature and inserting ultrathin barrier to enhance the wave function overlap in type-II superlattices
Nano Research 2022, 15(6): 5626-5632
Published: 19 March 2022
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Maximizing wave function overlap (WFO) within type-II superlattices (T2SL) is demonstrated to be important for improving their photoelectric properties, such as optical transition strength and quantum efficiency, which, however, remains a great challenge for now. Herein, the dual strategy of modulating growth temperature and inserting ultrathin AlAs barrier into the AlSb layers is presented to enhance the WFO in InAs/AlSb T2SL. The charge distributions and strain states indicate that moderate growth temperature of 470 °C promotes the As–Sb exchange at AlSb-on-InAs (AOI) interfaces, which would introduce skew of energy band structure towards InAs-on-AlSb (IOA) interface. Such band structure could drive electrons and holes to the IOA interfaces simultaneously, thus resulting in the enhanced WFO. On this basis, insertion of relatively thick (0.3 nm) AlAs layers is found to squeeze more holes towards adjacent interfaces, boosting the WFO further. The InAs/AlSb superlattices with optimized WFO reveal better optical performance, where the peak intensity shows 50% improvement in the PL spectra than the original one. Moreover, a dual-miniband radiative transition mechanism appears in the InAs/AlSb superlattice with relatively thick AlAs intercalation, which helps broaden the wavelength range of the superlattice.

Open Access Rapid Communication Issue
Dual-surfactant templated hydrothermal synthesis of CoSe2 hierarchical microclews for dielectric microwave absorption
Journal of Advanced Ceramics 2022, 11(3): 504-514
Published: 11 February 2022
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Cobalt diselenide (CoSe2) hierarchical clew-like structure is synthesized via a dual-surfactant templated hydrothermal process, and for the first time, its microwave absorption capability has been established. Specifically, the as-synthesized hierarchical interconnected structure is assembled by numerous dense nanobelts. Meticulous tuning of the synthetic conditions which could influence the hierarchical architecture indicates that, in this system, cetyltrimethylammonium bromide (CTAB) plays a dominate role of "balling" while protonated diethylenetriamine (DETA) plays the role of "stringing" . As a novel absorbent, the microwave absorption performance of CoSe2 microstructure is evaluated in 2-18 GHz band. Particularly, 3D hierarchical CoSe2 microclews exhibit superior minimum reflection loss of -26.93 dB at 7.28 GHz and effective absorption bandwidth of 3.72 GHz, which are ~120% and ~104% higher than those of simple CoSe2 nanosheets, respectively. Such drastic enhancement could be attributed to the large specific surface area, and more dissipation channels and scattering sites enabled by the unique clew-like microstructure. The versatile dual-surfactant templated assembly of hierarchical CoSe2 microstructure, along with its appreciable dielectric microwave absorption performance, provides new inspirations in developing novel microwave absorbents for mitigation of electromagnetic pollution.

Open Access Research Article Issue
Unusual effects of vacuum annealing on large-area Ag3PO4 microcrystalline film photoanode boosting cocatalyst- and scavenger-free water splitting
Journal of Materiomics 2021, 7(5): 929-939
Published: 21 April 2021
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Ag3PO4 as a novel photoanode material, despite its arguably highest photoactivity, suffers for its poor light absorption and stability for photoelectrochemical (PEC) water oxidation. In this work, 4.5 × 4.5 cm2 Ag3PO4 microcrystalline films are grown via a room-temperature solution process, and vacuum annealing is proposed to solve the stability and light absorption issues. It is found that the major process below 400 ℃ of vacuum annealing is the |Recovery| process for Ag3PO4 microcrystals, when lattice defects and Ag0 surface species get reduced. Next, |Recrystallization| stage occurs at >400 ℃. The recovery of native defects of silver vacancies, with both density functional theory calculation and experimental results, could simultaneously improve the light absorption and catalytic activity of Ag3PO4. The 400 ℃-annealed Ag3PO4 photoanode, with enhanced light harvesting and crystal quality, exhibits 88% increase in (JlightJdark) value (1.94 mA cm−2) than non-annealed photoanode (1.03 mA cm−2). Moreover, it retains >99% current density after a 4000-s stability test. These results suggest that vacuum annealing can substantially improve the PEC performance of Ag3PO4 microcrystalline film photoanodes due to mitigated effects of native defects, improved light harvesting, and inhibited Ag3PO4 decomposition during water oxidation reaction.

Research Article Issue
Understanding the role of interface in advanced semiconductor nanostructure and its interplay with wave function overlap
Nano Research 2020, 13(6): 1536-1543
Published: 30 April 2020
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As the proportion of interfaces increases rapidly in nanomaterials, properties and quality of interfaces hugely impact the performance of advanced semiconductors. Here, the effect of interfaces is explored by comparatively studying two InAs/AlSb superlattices with and without the thin InAsSb layers inserted inside each InAs layers. Through strain mapping, it indicates that the addition of interfaces leads to an increase of local strain both near interfaces and inside layers. Meantime, owing to the creation of hole potential wells within the original electron wells, the charge distribution undergoes an extra electron-hole alternating arrangement in the structure with inserted layers than the uninserted counterpart. Such a feature is verified to enhance electron-hole wave function overlap by theoretical simulations, which is a must for better optical performance. Furthermore, with an elaborate design of the inserted layers, the wave function overlap could be boosted without sacrificing other key device performances.

Research Article Issue
Self-transforming ultrathin α-Co(OH)2 nanosheet arrays from metal-organic framework modified graphene oxide with sandwich-like structure for efficient electrocatalytic oxygen evolution
Nano Research 2020, 13(3): 810-817
Published: 26 February 2020
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Developing efficient and low-cost electrocatalysts for oxygen evolution reaction (OER) with high electrochemical activity and durability for diverse renewable and sustainable energy technologies remains challenging. Herein, an ultrasonic-assisted and coordination modulation strategy is developed to construct sandwich-like metal-organic framework (MOF) derived hydroxide nanosheet (NS) arrays/graphene oxide (GO) composite via one-step self-transformation route. Inducing from unsteady state, the dodecahedral ZIF-67 with Co2+ in tetrahedral coordination auto-converts into defect-rich ultrathin layered hydroxides with the interlayered ion NO3-. The self-transforming α-Co(OH)2/GO nanosheet arrays from ZIF-67 (Co(OH)2-GNS) change the coordination mode of Co2+ and bring about the exposure of more metal active sites, thereby enhancing the spatial utilization ratio within the framework. As monometal-based electrocatalyst, the optimized Co(OH)2-GNS exhibits remarkable OER catalytic performance evidenced by a low overpotential of 259 mV to achieve a current density of 10 mA·cm-2 in alkaline medium, even exceeding commercial RuO2. During the oxygen evolution process, electron migration can be accelerated by the interfacial/in-plane charge polarization and local electric field, corroborated by the off-axis electron holography. Density functional theory (DFT) calculations further studied the collaboration between ultrathin Co(OH)2 NS and GO, which leads to lower energy barriers of intermediate products and greatly promotes electrocatalytic property.

Research Article Issue
Hierarchical coupling effect in hollow Ni/NiFe2O4-CNTs microsphere via spray-drying for enhanced oxygen evolution electrocatalysis
Nano Research 2020, 13(2): 437-446
Published: 13 January 2020
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Design and fabrication of cost-effective transition metal and their oxides-based nanocomposites are of paramount significance for metal-air batteries and water-splitting. However, the traditional optimized designs for nanostructure are complicated, low-efficient and underperform for wide-scale applications. Herein, a novel hierarchical framework of hollow Ni/NiFe2O4-CNTs composite microsphere forcibly-assembled by zero-dimensional (0D) Ni/NiFe2O4 nanoparticle (< 16 nm) and one-dimensional (1D) self-supporting CNTs was fabricated successfully. Benefitted from the unique nanostructure, such monohybrids can achieve remarkable oxygen evolution reaction (OER) performance in alkaline media with a low overpotential and superior durability, which exceeds most of the commercial catalysts based on IrO2/RuO2 or other non-noble metal nanomaterials. The enhanced OER performance of Ni/NiFe2O4-CNTs composite is mainly ascribed to the increased catalytic activity and the optimized conductivity induced by the effects of strong hierarchical coupling and charge transfers between CNTs and Ni/NiFe2O4 nanoparticles. These effects are greatly boosted by the polarized heterojunction interfaces confirmed by electron holography. The density functional theory (DFT) calculation indicates the epitaxial Ni further enriches the intrinsic electrons contents of NiFe2O4 and thus accelerates absorption/desorption kinetics of OER intermediates. This work hereby paves a facile route to construct the hollow composite microsphere with excellent OER electrocatalytic activity based on non-noble metal oxide/CNTs.

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