Lightweight NiFe2O4 with controllable 3D network structure and enhanced microwave absorbing properties

Interconnected magnetic carbon@NixCo1-xFe2O4 nanospheres with core-shell structure: An efficient and thin electromagnetic wave absorber

The applications of cobalt ferrite and nickel ferrite composite materials on electromagnetic (EM) wave absorption are the research hotspot currently. However, the systematical comparison study between these two ferrites composites have rarely been carried out. Thus, the EM wave absorption performance of interconnected carbon@Ni_xCo_1-xFe₂O₄ composites with core-shell structures were investigated comprehensively in this work. A series of magnetic nanospheres including NiFe₂O₄, cobalt-doped nickel ferrite, nickel-cobalt ferrite, nickel-doped cobalt ferrite and CoFe₂O₄ were synthesized firstly, and then uniformly encapsulation by carbon rendered the corresponding C@Ni_xCo_1-xFe₂O₄ composites nanospheres. Synthesis reactions involved for C@Ni_xCo_1-xFe₂O₄ formation were investigated in detail, and afterwards their magnetic behavior, EM wave absorption performance and absorbing mechanism were thoroughly explored and analyzed. Results show that when nickel is dominant element and cobalt is doping element (Ni_0.75Co_0.25Fe₂O₄), the composite nanosphere exhibits optimum EM wave absorption performance. When the sample thickness is just 1.9 mm, its RL_min value can reach -51 dB, and the corresponding EAB width is 3.3 GHz. The synthesized C@Ni_0.75Co_0.25Fe₂O₄ can be qualified as an efficient and thin electromagnetic wave absorber, which is mainly attributed to its special structure, fair electromagnetic matching and impedance matching.

Alkaline steaming-assisted conversion: a new strategy for the synthesis of pure NiFe2O4 and CoFe2O4 spinel ferrite nanoparticles

A new strategy, the ‘alkaline steaming-assisted conversion route,’ has been developed to synthesize pure NiFe2O4 and CoFe2O4 nanoparticles by using ethylenediamine, together with ammonia, collectively as the alkaline steaming vapor.

General Synthesis of Two-Dimensional Porous Metal Oxides/Hydroxides for Microwave Absorbing Applications

Metal oxides/hydroxides with a two-dimensional (2D) porous structure have extensive applications in catalysis, microwave absorption, and energy storage fields due to their large specific surface areas, massive exposed active sites, and good structural integrities. Herein, a general surfactant-assisted vapor diffusion-deposition self-assembly method is developed to synthesize various 2D porous metal oxides/hydroxides. Benefiting from the structure-directing effect of surfactants and the precise tuning of nucleation and growth process that results from this vapor diffusion-deposition strategy, a 2D porous structure is constructed. To explore the advantages of such 2D porous structure, electromagnetic characteristics and absorbing properties of as-obtained materials are investigated. The minimum reflection loss (RL) of 2D porous NiFe₂O₄ is -23.1 dB at 6.4 GHz, and the effective absorption bandwidth (EAB) is 5.1 GHz. However, the minimum RL is only -15.0 dB at 8.7 GHz and the EAB is 3.9 GHz for NiFe₂O₄ particles. In addition, the as-obtained 2D porous NiFe₂O₄ exhibits superior absorbing properties compared with many previously reported nickel ferrites. Furthermore, the microwave absorbing mechanism of 2D porous NiFe₂O₄ is investigated.

A Facile Synthesis of NiFe-Layered Double Hydroxide and Mixed Metal Oxide with Excellent Microwave Absorption Properties

Microwave-absorbing materials have attracted increased research interest in recent years because of their core roles in the fields of electromagnetic (EM) pollution precaution and information security. In this paper, microwave-absorbing material NiFe-layered double hydroxide (NiFe-LDH) was synthesized by a simple co-precipitation method and calcined for the fabrication of NiFe-mixed metal oxide (NiFe-MMO). The phase structure and micromorphology of the NiFe-LDH and NiFe-MMO were analyzed, and their microwave-absorbing properties were investigated with a vector network analyzer in 2–18 GHz. Both NiFe-LDH and NiFe-MMO possessed abundant interfaces and a low dielectric constant, which were beneficial to electromagnetic wave absorption, owing to the synergistic effect of multi-relaxation and impedance matching. The optimum reflection loss (RL) of NiFe-LDH and NiFe-MMO was −58.8 dB and −64.4 dB, respectively, with the thickness of 4.0 mm in the C band. This work demonstrates that LDH-based materials have a potential application in electromagnetic wave absorption.

Advances of 3D graphene and its composites in the field of microwave absorption

The intensive progress of information technology increases the demand for urgent development of practical materials for microwave absorption (MA), meeting the general requirement "thin, wide, light and strong". In the past 6 years, graphene is of great interest for MA performance due to its unique properties such as high specific surface area, high electrical conductivity, strong dielectric loss, and low density. Taking in account that the structure of absorber plays a key role in MA performance, the attempts to produce an efficient microwave absorbing materials (MAMs) have led to 3D graphene - aerogels and foams - due to their extremely high porosity, large specific surface area, excellent mechanical properties with ability of compression and further maintaining the original shape, lightweight, reduced agglomeration of graphene sheets. All listed parameters enhance the impedance matching of MAMs, generate the synergistic loss effects, thereby improving the MA properties. The review describes the bases of MA theory and summarizes the recent achievements in the fabrication of pure 3D graphene networks and their composites with magnetic, ceramic nanoparticles and nanowires, polymers, MXenes, and multicomponent systems, directed to improve the impedance matching and generate loss mechanisms for the overall improvement of their performance as MAMs.

Two-dimensional MoS2 modified using CoFe2O4 nanoparticles with enhanced microwave response in the X and Ku band

A novel MoS₂/CoFe₂O₄ two-dimensional composite was designed, which showed ideal impedance matching and enhanced interface polarization.

Ordered mesoporous NiFe2O4 with ultrathin framework for low-ppb toluene sensing

Highly sensitive and selective detection against specific target gases, especially at low-ppb (part per billion) level, remain a great number of challenges in gas sensor applications. In this paper, we first present an ordered mesoporous NiFe₂O₄ for highly sensitive and selective detection against low-ppb toluene. A series of mesoporous NiFe₂O₄ materials were synthesized by templating from mesoporous silica KIT-6 and its framework thickness was reduced from 8.5 to 5 nm by varying the pore size of KIT-6 from 9.4 to 5.6 nm, accompanied with the increase of the specific surface area from 134 to 216 m² g^-1. The ordered mesoporous NiFe₂O₄ with both ultrathin framework of 5 nm and large specific surface area of up to 216 m² g^-1 exhibits a highest response (R_gas/R_air - 1 = 77.3) toward 1,000 ppb toluene at 230 °C and is nearly 7.3 and 76.7 times higher than those for the NiFe₂O₄ replica with thick framework and its bulk counterpart respectively, which also possesses a quite low limit of detection (<2 ppb), and good selectivity.

Economical synthesis of composites of FeNi alloy nanoparticles evenly dispersed in two-dimensional reduced graphene oxide as thin and effective electromagnetic wave absorbers

Developing electromagnetic wave absorbing materials prepared by a facile and economical way is a great challenge. Herein, we report a feasible route to synthesize a series of two-dimensional FeNi/rGO composites by a hydrothermal method followed by a carbonization process. The characterization confirms that nano-sized FeNi alloy nanoparticles are evenly supported onto graphene sheets without aggregation. The homogeneous dispersion of the nanoparticles may result from the introduction of glucose and the oxygen-containing groups on the surface of the graphene oxide. Measurements show that the microwave attenuation capability of the composites can be improved dramatically by adjusting the proportion of dielectric and magnetic components. Consequently, the two-dimensional magnetic material (FeNi/rGO-100) exhibits an excellent microwave absorption performance. In detail, the minimum reflection loss of −42.6 dB and effective bandwidth of 4.0 GHz can be reached with a thinner thickness of 1.5 mm. This study demonstrates that synergistic effects among the magnetic particles, reduced graphene oxide and amorphous carbon layers give rise to the highlighted microwave attenuation ability. Overall, the FeNi/rGO composite is a promising candidate to be used as a microwave absorber, and the feasible and economical method has shown potential application to construct multitudinous two-dimensional materials.

Two-dimensional magnetic FeNi/rGO composites with excellent microwave absorbing performance have been synthesized under the assistance of glucose.

Hierarchically structured magnesium based oxides: synthesis strategies and applications in organic pollutant remediation

In this highlight, we review the design and formation of MgO based hierarchical structures and cover some selected examples on their applications in adsorption of organic contaminants.