From VIB- to VB-Group Transition Metal Disulfides: Structure Engineering Modulation for Superior Electromagnetic Wave Absorption.

The laminated transition metal disulfides (TMDs), which are well known as typical two-dimensional (2D) semiconductive materials, possess a unique layered structure, leading to their wide-spread applications in various fields, such as catalysis, energy storage, sensing, etc. In recent years, a lot of research work on TMDs based functional materials in the fields of electromagnetic wave absorption (EMA) has been carried out. Therefore, it is of great significance to elaborate the influence of TMDs on EMA in time to speed up the application. In this review, recent advances in the development of electromagnetic wave (EMW) absorbers based on TMDs, ranging from the VIB group to the VB group are summarized. Their compositions, microstructures, electronic properties, and synthesis methods are presented in detail. Particularly, the modulation of structure engineering from the aspects of heterostructures, defects, morphologies and phases are systematically summarized, focusing on optimizing impedance matching and increasing dielectric and magnetic losses in the EMA materials with tunable EMW absorption performance. Milestones as well as the challenges are also identified to guide the design of new TMDs based dielectric EMA materials with high performance.

Achieving Superior Tensile Performance in Individual Metal-Organic Framework Crystals.

Rapid advances in the engineering application prospects of metal-organic framework (MOF) materials necessitate an urgent in-depth understanding of their mechanical properties. This work demonstrates unprecedented recoverable elastic deformation of Ni-tetraphenylporphyrins (Ni-TCPP) MOF nanobelts with a tensile strain as high as 14%, and a projected yield strength-to-Young's modulus ratio exceeding the theoretical limit (≈10%) for crystalline materials. Based on first-principles simulations, the observed behavior of MOF crystal can be attributed to the mechanical deformation induced conformation transition and the formation of helical configuration of dislocations under high stresses, arising from their organic ligand building blocks in the crystal structures. The investigations of the mechanical properties along with electromechanical properties demonstrate that MOF materials have exciting application potential for biomechanics integrated systems, flexible electronics, and nanoelectromechanical devices.

Multifunctional MoSe2 @MXene Heterostructure-Decorated Cellulose Fabric for Wearable Thermal Therapy.

A booming demand for wearable electronic devices urges the development of multifunctional smart fabrics. However, it is still facing a challenge to fabricate multifunctional smart fabrics with satisfactory mechanical property, excellent Joule heating performance, highly efficient photothermal conversion, outstanding electromagnetic shielding effectiveness, and superior anti-bacterial capability. Here, a MoSe2 @MXene heterostructure-based multifunctional cellulose fabric is fabricated by depositing MXene nanosheets onto cellulose fabric followed by a facile hydrothermal method to grow MoSe2 nanoflakes on MXene layers. A low-voltage Joule heating therapy platform with rapid Joule heating response (up to 230 °C in 25 s at a supplied voltage of 4 V) and stable performance under repeated bending cycles (up to 1000 cycles) is realized. Besides, the multifunctional fabric also exhibits excellent photothermal performance (up to 130 °C upon irradiation for 25 s with a light intensity of 400 mW cm-2 ), outstanding electromagnetic interference shielding effectiveness (37 dB), and excellent antibacterial performances (>90% anti-bacterial rate toward Escherichia coli, Bacillus subtilis, and Staphylococcus aureus). This work offers an efficient avenue to fabricate multifunctional wearable thermal therapy devices for mobile healthcare and personal thermal management.

Recent Advances in Design Strategies and Multifunctionality of Flexible Electromagnetic Interference Shielding Materials.

With rapid development of 5G communication technologies, electromagnetic interference (EMI) shielding for electronic devices has become an urgent demand in recent years, where the development of corresponding EMI shielding materials against detrimental electromagnetic radiation plays an essential role. Meanwhile, the EMI shielding materials with high flexibility and functional integrity are highly demanded for emerging shielding applications. Hitherto, a variety of flexible EMI shielding materials with lightweight and multifunctionalities have been developed. In this review, we not only introduce the recent development of flexible EMI shielding materials, but also elaborate the EMI shielding mechanisms and the index for "green EMI shielding" performance. In addition, the construction strategies for sophisticated multifunctionalities of flexible shielding materials are summarized. Finally, we propose several possible research directions for flexible EMI shielding materials in near future, which could be inspirational to the fast-growing next-generation flexible electronic devices with reliable and multipurpose protections as offered by EMI shielding materials.

Metal-Organic-Framework-Derived Ball-Flower-like Porous Co3O4/Fe2O3 Heterostructure with Enhanced Visible-Light-Driven Photocatalytic Activity.

A porous ball-flower-like Co3O4/Fe2O3 heterostructural photocatalyst was synthesized via a facile metal-organic-framework-templated method, and showed an excellent degradation performance in the model molecule rhodamine B under visible light irradiation. This enhanced photocatalytic activity can be attributed to abundant photo-generated holes and hydroxyl radicals, and the combined effects involving a porous structure, strong visible-light absorption, and improved interfacial charge separation. It is notable that the ecotoxicity of the treated reaction solution was also evaluated, confirming that an as-synthesized Co3O4/Fe2O3 catalyst could afford the sunlight-driven long-term recyclable degradation of dye-contaminated wastewater into non-toxic and colorless wastewater.

Giant magnetocaloric effect in nanostructured Fe-Co-P amorphous alloys enabled through pulse electrodeposition.

In this work, amorphous Fe-Co-P films prepared by electrodeposition are found to exhibit dense microstructures with amorphous grains. Through a pulse electrodeposition synthesis route, complex microstructures containing nano-sized grains are obtained in the amorphous alloy films. The nanostructured Fe-Co-P amorphous alloys show superior soft magnetic and magnetocaloric properties as compared with those of other iron-based soft magnetic amorphous alloys reported to date. The coercive field of samples can be as small as 1.6 Oe at room temperature. The magnetocaloric effect (MCE) of the ternary amorphous alloys has been investigated by evaluating the magnetic entropy changes, |ΔSM |, from their temperature-dependent magnetization behaviors. The |ΔSM| values are as high as 1.846 J kg-1 K-1 with an applied magnetic field of 10 kOe. With a temperature span of 90 K, the refrigerant capacity of samples can be as high as 118.64 J kg-1. The nanostructure enabled giant MCE in Fe-Co-P amorphous alloys is discussed.

Confinedly growing and tailoring of Co3O4 clusters-WS2 nanosheets for highly efficient microwave absorption.

Electromagnetic (EM) wave absorbing materials have been a research hotspot in materials science and related technical fields in recent years. Finding lightweight, efficient, and broadband electromagnetic wave absorbing materials has always been a very challenging subject. Herein, we successfully prepared Co3O4-WS2 hybrid nanosheets with heterostructures, which excellent combine the advantages of magnetic property of Co3O4 and dielectric property of WS2. By the electromagnetic synergy effect, maximum RL is up to -61.1 dB at 1.9 mm, and the bandwidth exceeds 5 GHz. Such highly efficient microwave absorption is attributed to not only the electromagnetic synergy effect, but the dipole polarization as well as conduction loss. These results show that the obtained Co3O4-WS2 is an excellent EM wave absorbing material and can be used as a candidate for advanced EM wave absorbing materials in the fields such as commerce, military and aerospace in future.

Nickel-metal-organic framework nanobelt based composite membranes for efficient Sr2+ removal from aqueous solution.

The sorption removal of radionuclides Sr2+ using a freestanding functional membrane is an interesting and significant research area in the remediation of radioactive wastes. Herein, a novel self-assembled membrane consisting of metal-organic framework (MOF) nanobelts and graphene oxides (GOs) are synthesized through a simple and facile filtration method. The membrane possesses a unique interwove morphology as evidenced from SEM images. Batch experiments suggest that the GO/Ni-MOF composite membrane could remove Sr2+ ions from aqueous solutions and the Sr2+ adsorption capacity and efficiency of the GO/Ni-MOF composite membrane is relevant to the MOF content in the composite. Thus, the dominant interaction mechanism was interface or surface complexation, electrostatic interaction as well as ion substitution. The maximum effective sorption of Sr2+ over GO/Ni-MOF membrane is 32.99% with 2 mg composite membrane containing a high content of Ni-MOF at 299 K in 100 mg/L Sr2+ aqueous solution. The FT-IR and XPS results suggest that the synergistic effect between GO and Ni-MOF is determinant in the sorption Sr2+ process. The GO/Ni-MOF composite membrane is demonstrated to have the advantages of efficient removal of Sr2+, low cost and simple synthesis route, which is promising in the elimination of radionuclide contamination.

Synergetic dielectric loss and magnetic loss towards superior microwave absorption through hybridization of few-layer WS2 nanosheets with NiO nanoparticles.

WS2 nanomaterials have attracted great attention in the field of electromagnetic wave absorption due to their high specific surface area, layered structure, and peculiar electronic properties. However, further improvements on their limited electromagnetic absorbing (EMA) capacity and bandwidth are urgently required for their practical application as EMA absorbents. In this work, WS2/NiO hybrids with heterostructures are prepared by a hydrothermal method and developed into EMA absorbents. The maximum reflection loss of the hybrids with 20% NiO loading could reach -53.31 dB at a thickness of 4.30 mm; the bandwidth with a reflection loss value of less than -10 dB is determined to be 13.46 GHz (4.54-18 GHz) when the thickness of the absorbent is between 3.5 and 5.5 mm. It is found that the enhanced EMA performance of WS2/NiO hybrids is caused by the addition of magnetic NiO, which could result in the interfaces between WS2 and NiO being responsible for the synergetic magnetic loss and dielectric loss in the hybrids. This work provides a new approach for the design of excellent EMA materials for practical applications.

Two-Dimensional Black Phosphorus Nanomaterials: Emerging Advances in Electrochemical Energy Storage Science.

Two-dimensional black phosphorus (2D BP), well known as phosphorene, has triggered tremendous attention since the first discovery in 2014. The unique puckered monolayer structure endows 2D BP intriguing properties, which facilitate its potential applications in various fields, such as catalyst, energy storage, sensor, etc. Owing to the large surface area, good electric conductivity, and high theoretical specific capacity, 2D BP has been widely studied as electrode materials and significantly enhanced the performance of energy storage devices. With the rapid development of energy storage devices based on 2D BP, a timely review on this topic is in demand to further extend the application of 2D BP in energy storage. In this review, recent advances in experimental and theoretical development of 2D BP are presented along with its structures, properties, and synthetic methods. Particularly, their emerging applications in electrochemical energy storage, including Li-/K-/Mg-/Na-ion, Li-S batteries, and supercapacitors, are systematically summarized with milestones as well as the challenges. Benefited from the fast-growing dynamic investigation of 2D BP, some possible improvements and constructive perspectives are provided to guide the design of 2D BP-based energy storage devices with high performance.

Corrigendum: Highly Ordered Mesoporous NiCo2O4 as a High Performance Anode Material for Li-Ion Batteries.

[This corrects the article DOI: 10.3389/fchem.2019.00521.].

Highly Ordered Mesoporous NiCo2O4 as a High Performance Anode Material for Li-Ion Batteries.

The controlled synthesis of highly ordered mesoporous structure has attracted considerable attention in the field of electrochemistry because of its high specific surface area which can contribute the transportation of ions. Herein, a general nano-casting approach is proposed for synthesizing highly ordered mesoporous NiCo2O4 microspheres. The as-synthesized mesoporous NiCo2O4 microsphere materials with high Brunner-Emmett-Teller (BET) surface area (~97.77 m2g-1) and uniform pore size distribution around 4 nm exhibited a high initial discharge capacity of ~1,467 mAhg-1, a good rate capability as well as cycling stability. The superior electrochemical performance was mainly because of the highly porous nature of NiCo2O4, which rendered volume expansion during the process of cycling and shortened lithium-ions transport pathways. These properties showcase the inherent potential for use of highly ordered mesoporous NiCo2O4 microspheres as a potential anode material for lithium-ion batteries in the future.

Self-Assembly Construction of WS2-rGO Architecture with Green EMI Shielding.

Accurately tailoring electromagnetic (EM) materials for achieving high-performance EM interference (EMI) shielding is significantly imperative with increasing EM pollution worldwide. Green EMI shielding materials are attracting extensive attention because of the less additional environmental hazard caused by the lower secondary reflection. However, the conflict between high efficiency and eco-friendly nature makes green EMI shielding still challenging. In this work, a new strategy of turning a guest into a host is developed for the first time, and a unique WS2-rGO architecture of mountain-like wall is constructed successfully achieving efficient and green EMI shielding. The shielding efficiency (SE) is over 20 dB in the investigated frequency range (2-18 GHz) and the maximum was 32 dB with an endearing green index (gs ≈ 1.0). The efficient and green EMI SE is ascribed to the multilevel structure and intrinsic dielectric properties of the WS2-rGO architecture, including the synergy of relaxation and conduction, multi-scattering between the interface and void, and the equivalent wedge effect. These results demonstrate that the WS2-rGO architecture is a promising candidate in EM transducers, microwave imaging, EM protection, and energy devices.

Light-weight and low-cost electromagnetic wave absorbers with high performances based on biomass-derived reduced graphene oxides.

Rational structure design of microwave absorption material is extremely significant from the perspectives of enhancing the electromagnetic microwave absorption (EMA) performance and adapting to cost-effective and sustainable industrial applications. Here, reduced graphene oxides (rGOs) with curl structures derived from corn stover are applied for the absorption of electromagnetic waves. The results suggest that biomass-rGO show the maximum reflection loss of -51.7 dB and an effective absorption bandwidth 13.5 GHz (4.5-18 GHz) at a thickness of 3.25 mm, implying the unique critical role of the microstructure in adjusting the EMA performance. Moreover, the successful conversion of waste biomass into widely used electromagnetic wave absorbing materials could solve the problems of environmental pollution caused by straw burning.

Nitrogen-Doped Graphene-Encapsulated Nickel-Copper Alloy Nanoflower for Highly Efficient Electrochemical Hydrogen Evolution Reaction.

Development of high-performance and low-cost nonprecious metal electrocatalysts is critical for eco-friendly hydrogen production through electrolysis. Herein, a novel nanoflower-like electrocatalyst comprising few-layer nitrogen-doped graphene-encapsulated nickel-copper alloy directly on a porous nitrogen-doped graphic carbon framework (denoted as Nix Cuy @ NG-NC) is successfully synthesized using a facile and scalable method through calcinating the carbon, copper, and nickel hydroxy carbonate composite under inert atmosphere. The introduction of Cu can effectively modulate the morphologies and hydrogen evolution reaction (HER) performance. Moreover, the calcination temperature is an important factor to tune the thickness of graphene layers of the Nix Cuy @ NG-NC composites and the associated electrocatalytic performance. Due to the collective effects including unique porous flowered architecture and the synergetic effect between the bimetallic alloy core and graphene shell, the Ni3 Cu1 @ NG-NC electrocatalyst obtained under optimized conditions exhibits highly efficient and ultrastable activity toward HER in harsh environments, i.e., a low overpotential of 122 mV to achieve a current density of 10 mA cm-2 with a low Tafel slope of 84.2 mV dec-1 in alkaline media, and a low overpotential of 95 mV to achieve a current density of 10 mA cm-2 with a low Tafel slope of 77.1 mV dec-1 in acidic electrolyte.

Lightweight and High-Performance Microwave Absorber Based on 2D WS2-RGO Heterostructures.

Two-dimensional (2D) nanomaterials are categorized as a new class of microwave absorption (MA) materials owing to their high specific surface area and peculiar electronic properties. In this study, 2D WS2-reduced graphene oxide (WS2-rGO) heterostructure nanosheets were synthesized via a facile hydrothermal process; moreover, their dielectric and MA properties were reported for the first time. Remarkably, the maximum reflection loss (RL) of the sample-wax composites containing 40 wt% WS2-rGO was - 41.5 dB at a thickness of 2.7 mm; furthermore, the bandwidth where RL < - 10 dB can reach up to 13.62 GHz (4.38-18 GHz). Synergistic mechanisms derived from the interfacial dielectric coupling and multiple-interface scattering after hybridization of WS2 with rGO were discussed to explain the drastically enhanced microwave absorption performance. The results indicate these lightweight WS2-rGO nanosheets to be potential materials for practical electromagnetic wave-absorbing applications.

Highly effective photocatalytic performance of {001}-TiO2/MoS2/RGO hybrid heterostructures for the reduction of Rh B.

Effective separation and rapid transfer of photogenerated electron-hole pairs are key features of photocatalytic materials with high catalytic activity, which could be achieved in co-catalysts. It is reported that the two-dimensional (2D) MoS2 is a promising co-catalyst due to its unique semi-conductive properties and graphene-like layered structure. However, the application of MoS2 as a co-catalyst is limited by its poor electrical conductivity. On the other hand, it is worth noting that TiO2 possesses reactive crystal facets, which is one of the dominant mechanisms for the separation of photogenerated electron-hole pairs. In this work, we prepared MoS2/RGO hybrids as co-catalysts which were doped to TiO2 with highly reactive {001} planes via the hydrothermal method. It was found that the {001}-TiO2/MoS2/RGO photocatalysts with 7 wt% MoS2/RGO co-catalyst show the highest photodegradation activity for the degradation of Rh B under visible light irradiation (λ > 400 nm), which could result from the synergy of the effective separation of electron-hole pairs by the {001} facets in TiO2 and the rapid transfer of electron-hole pairs in MoS2/RGO. The results show that the {001}-TiO2/MoS2/RGO hybrid is a low-cost and stable photocatalyst for the effective degradation of Rh B under visible light.

The effects of additions of two-dimensional graphitic-C3N4 on the negative electro-caloric effects in P(VDF-TrFE) copolymers.

In order to enhance and tune the electrocaloric effect (ECE) and ferroelectric responses, nanocomposites containing ferroelectric copolymer poly(vinylidene fluoride trifluoroethylene) and two-dimensional (2D) graphitic-C3N4 (g-C3N4) are synthesized. The effects of g-C3N4 on the ferroelectric-to-paraelectric phase transition of the copolymer are investigated by the differential scanning calorimetry (DSC), P-E hysteresis loop and dielectric spectrum measurements. The results indicate that the addition of 2D g-C3N4 in the ferroelectric copolymer is an effective approach in enhancing its dielectric and ferroelectric properties. Furthermore, the nanocomposites show the maximum absolute value of negative electrocaloric effect (ECE) of 5.4 K at 322 K under an electric field of 0.45 MV cm-1, which is much better than that of pristine copolymer. The negative ECE of the nanocomposites can be well explained by the Kauzmann theory. The low cost and enhanced negative ferroelectric properties of P(VDF-TrFE) make them more feasible over ceramics materials such as lead zirconate titanate (PZT) based ferroelectrics for applications in electrocaloric refrigeration.

Evolution of 3D nanoporosity and morphology in selectively dealloying ternary Au55Cu25Si20 metallic glass ribbon with enhanced alcohol electro-oxidation performance.

Current fabrication methods of nanoporous gold (NPG) mainly rely on dealloying Ag-Au binary crystalline precursors, typically Ag65Au35, with the "dealloying threshold" or "parting limit" above 55 at%. Here we report a simple chemical dealloying process, through selective dissolution of one element from a Au55Cu25Si20 metallic glass ribbon with low 'parting limit', and a novel peculiar three-dimensional 'cone shaped protrusion' nanoporous structure which has never been reported before. In this structure, a metastable gold silicide formed in the initial dealloying stage was decomposed into gold nanoparticles and amorphous SiOx in the later coarsening stage. Our finding provides insights into the underlying relationship between 'parting limit' and atomic level structure of metallic glass. Comprehensive discussions on the porosity evolution stages as well as the correlation between the porous 'cone shaped protrusion' development and potential energy landscape are made in this report. The fabricated 3D NPG also exhibited excellent electro-oxidation catalytic ability attributed to the high density of low-coordinated atomic sites provided by the gold particle inside of 'cone shaped protrusion'.

Unconventional Nickel Nitride Enriched with Nitrogen Vacancies as a High-Efficiency Electrocatalyst for Hydrogen Evolution.

Development of high-performance and cost-effective non-noble metal electrocatalysts is pivotal for the eco-friendly production of hydrogen through electrolysis and hydrogen energy applications. Herein, the synthesis of an unconventional nickel nitride nanostructure enriched with nitrogen vacancies (Ni3N1-x ) through plasma-enhanced nitridation of commercial Ni foam (NF) is reported. The self-supported Ni3N1-x /NF electrode can deliver a hydrogen evolution reaction (HER) activity competitive to commercial Pt/C catalyst in alkaline condition (i.e., an overpotential of 55 mV at 10 mA cm-2 and a Tafel slope of 54 mV dec-1), which is much superior to the stoichiometric Ni3N, and is the best among all nitride-based HER electrocatalysts in alkaline media reported thus far. Based on theoretical calculations, it is further verified that the presence of nitrogen vacancies effectively enhances the adsorption of water molecules and ameliorates the adsorption-desorption behavior of intermediately adsorbed hydrogen, which leads to an advanced HER activity of Ni3N1-x /NF.