Laser Precise Synthesis of Oxidation-Free High-Entropy Alloy Nanoparticle Libraries.

High-entropy alloy nanoparticles (HEA-NPs) show exceptional properties and great potential as a new generation of functional materials, yet a universal and facile synthetic strategy in air toward nonoxidized and precisely controlled composition remains a huge challenge. Here we provide a laser scribing method to prepare single-phase solid solution HEA-NPs libraries in air with tunable composition at the atomic level, taking advantage of the laser-induced metastable thermodynamics and substrate-assisted confinement effect. The three-dimensional porous graphene substrate functions as a microreactor during the fast heating/cooling process, which is conductive to the generation of the pure alloy phase by effectively blocking the binding of oxygen and metals, but is also beneficial for realizing accurate composition control via microstructure confinement-endowed favorable vapor pressure. Furthermore, by combining an active learning approach based on an adaptive design strategy, we discover an optimal composition of quinary HEA-NP catalysts with an ultralow overpotential for Li-CO2 batteries. This method provides a simple, fast, and universal in-air route toward the controllable synthesis of HEA-NPs, potentially integrated with machine learning to accelerate the research on HEAs.

Introducing VO2+ Group in Phosphomolybdic Acid and Supporting on MOF-808 for Efficient Oxidative Desulfurization.

Herein, by introducing a VO2+ group into the microstructure of phosphomolybdenic acid (PMA) and loading it onto MOF-808, a series of composite catalysts were obtained by reducing the V element with Vitamin C (ascorbic acid). V atoms exist in the secondary structural units of phosphomolybdic acid as [VO(H2O)5]H[PMo12O40]. Surprisingly, the VC-VO-PMA/MOF-808 completely removed DBT and 4,6-DMDBT from the simulated oil in 12 min. The EPR and XPS results verify the electronic structure and valence state of V4+ in the composites. The oxygen vacancy and V4+ generated by VC modification in VC-VO-PMA/MOF-808 have positive effects on the oxidation desulfurization (ODS) activity. Based on the design of the microstructure and electronic structure, this study provides a new paradigm for the development of readily available and efficient ODS catalysts.

Highly Efficient and Reusable Denitrogenation Adsorbent Obtained by the Fluorination of PMA-MIL-101.

A simple but efficient strategy to improve the ability of adsorptive denitrogenation (ADN) of MIL-101(M101) was studied by the in situ encapsulation of phosphomolybdic acid (PMA) and the subsequent purification of the as-synthesized product by the NH4F solution. After the NH4F treatment, the vast majority of PMA was removed, loss of organic ligand (BDC) was observed, and the fluorination of the hydroxyl group in the M101 structure occurred. The ADN activities of the Cr-MOF matrix composites before and after fluorination were studied in detail. The rest of PMA interacts strongly with M101 and assists the ADN activity. Coordination unsaturated metal sites (CUS) in M101 are formed after fluorination and also contribute to ADN activity. Further, fluoride anions replace most of the hydroxide groups in M101, which can promote the ADN of quinoline (QUI) and indole (IND) through an acid-base interaction and N-atom coordination with the CUS in M101. P-M101-F 5% exhibits the highest adsorptive capacity and excellent regeneration ability. Special emphasis in this work is placed on structure modulation (including PMA doping, CUS creation, and fluorination) of M101 for enhancing ADN activity, which provides a useful scaffold for future research in the rational design of MOF-based ADN catalysts.

Flexible N-doped carbon fibers decorated with Cu/Cu2O particles for excellent electromagnetic wave absorption.

Flexible N-doped carbon fibers decorated with Cu/Cu2O particles (NCF-Cu/Cu2O) are synthesized through electrospinning, preoxidation and carbonization processes in this work. The characterization results indicate that HKUST-1 is embedded in polyacrylonitrile (PAN) fibers, and a special structure in which Cu/Cu2O particles are strung together by carbon fibers is formed after preoxidation and carbonization. NCF-Cu/Cu2O is mixed with paraffin in different mass ratios (5%, 10%, 15%, 20% and 25%) to study electromagnetic (EM) wave absorption performance at frequencies from 2.0 GHz to 18.0 GHz. When the filling ratio is 10%, the maximum reflection loss (RL) value is -50.54 dB at 14.16 GHz with a thickness of 2.4 mm, and the maximum effective absorption bandwidth (EAB) value reaches 7.2 GHz (10.8 âˆ¼ 18.0 GHz) with a thickness of 2.6 mm. The NCF-Cu/Cu2O composite fibers exhibit strong absorption, broad bandwidth, low filling ratio and thin thickness, and the corresponding absorption mechanism is analyzed in detail. The excellent EM wave absorption performance is attributed to a suitable attenuation ability, good impedance matching, conductive loss, interfacial polarization, dipole polarization, multiple reflections and scattering. This work provides a research reference for the application of flexible carbon-based composite fibers in the field of EM wave absorption.

Core-shell CoFe2O4@C nanoparticles coupled with rGO for strong wideband microwave absorption.

Strong absorption and large bandwidth are two contributors to materials' absorbing performance. In this work, a series of multi-element core-shell magnetic nano-particle composite layered graphene absorbing materials CoFe2O4@C/rGO (CCr) were prepared by adjusting carbon shell thickness. The CCr at a low thickness achieved strong microwave absorption and a wide effective absorption bandwidth. Not only the core-shell structure of the magnetic nanoparticle CoFe2O4@C (CFO@C) increases the interface loss, but both the coating carbon shell and the core CoFe2O4 (CFO) are beneficial to improve impedance matching. Due to the synergistic effect of the dielectric and magnetic properties of graphene and ferrite, CCr possessed high absorption performance, and its minimum reflection loss reached (RLmin) -52.5 dB when the thickness was only 2 mm. At the same time, the effective absorption bandwidth (EAB) was 5.68 GHz when the thickness was only 1.7 mm. The chemically stable core-shell dielectric nanocomposite provided a new solution for preparing materials with excellent chemical structure and high absorbing properties.

Construction of hierarchical Co9S8@NiO synergistic microstructure for high-performance asymmetric supercapacitor.

Metal-organic frameworks (MOFs) become a research hot-spot owing to their unique properties originating from the ultra-high porosity and large specific surface area with highly accessible active sites. However, the electrochemical performance of a single component is unsatisfied when MOFs are applied as electrode material in a supercapacitor. In this work, the hierarchical hollow framework involving interconnected Co9S8 structure and NiO nanosheets (Co9S8@NiO) are successfully prepared by MOFs derived methods and proposed to electrode materials. As a result, the prepared Co9S8@NiO electrode materials exhibit a superior specific capacitance of 1627 F g-1 at a current density of 1 A g-1. Moreover, an assembled hybrid supercapacitor shows a high energy density of 51.65 Wh Kg-1 at a power density of 749.8 W Kg-1 as well as excellent long-term cycling stability with 81.79% capacity retention after 10,000 cycles. Meanwhile, we concluded that the marvelous electrochemical performance is closely associated with the unique structure of NiO, in particular, the nanosheet surface provides a superior specific surface area and rich accessible redox reaction sites, thus enlarged the contact between the surface and interface of the electrode material. Finally, two supercapacitor devices connected in series can light up four light-emitting diodes (LEDs) for about 30 min. Hence, the presented strategy represents a general route for supercapacitor electrode material with promising electrochemical performance, which can combine the MOFs template and other hierarchical nanosheets together.

Magnetic porous CoNi@C derived from bamboo fiber combined with metal-organic-framework for enhanced electromagnetic wave absorption.

In order to commit to the core concept of energy saving and emission reduction, the preparation of absorbing materials with sustainable development, light weight, strong absorption and wide absorption bandwidth has become an urgent problem that should be solved. As a natural product from nature, ubiquitous bamboo is combined with metal-organic framework on its surface through a simple chemical activation method is demostrated to be an effective method to prepare a composite absorbing material with amazing electromagnetic wave absorption. The prepared bamboo fiber/CoNi alloy (CN-ABF) reaches a minimum reflection loss of -75.19 dB at 11.12 GHz when the thickness is 2.66 mm, and the corresponding bandwidth is 4.56 GHz. The prepared CN-ABF greatly enhances the multi-polarity, dielectric loss, magnetic loss and impedance matching. Sustainable absorbing materials prepared by using biomass as a dielectric carbon-based recombined magnetic metal provide a good research strategy for improving the absorbing performance of materials.

Design and microwave absorption properties of thistle-like CoNi enveloped in dielectric Ag decorated graphene composites.

A novel hierarchical composites for coupling thistle-like CoNi with dielectric Ag decorated graphene in paraffin wax as high performance microwave absorber has been synthesized by a facile two-step strategy. The components, particle size, microstructure and morphology of the resulting composites are characterized by X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectra, scanning electron microscope, transmission electron microscopy and energy dispersive X-ray spectroscopy, etc. Due to the unique flower structure and good synergistic effect of dielectric loss and magnetic loss, thistle-like CoNi@dielectric Ag decorated graphene composites have showed glorious microwave absorption intensity and frequency width. The maximum reflection loss of -61.9 dB can be gained at 6.96 GHz, which has rarely been reported yet. In addition, the corresponding effective bandwidth with reflection loss less than -10 dB is 5.6 GHz ranging from 12.4 to 18 GHz at only 1.67 mm thickness. This highly efficient and broad band features endow thistle-like CoNi@dielectric Ag decorated graphene composites with promising applications in microwave absorption, electromagnetic shielding, information safety, direct broadcast satellite and military radar fields.

Enhanced microwave-absorption with carbon-encapsulated Fe-Co particles on reduced graphene oxide nanosheets with nanoscale-holes in the basal plane.

In this study, an Fe-Co alloy is coated with carbon and decorated on a holey reduced graphene oxide nanosheet (FeCo@C/HRGO) composite. The structure is synthesized using liquid-phase reduction and hydrothermal processes followed by high-temperature calcination. The FeCo@C/HRGO composite is identified and characterized using XRD, XPS, Raman spectroscopy, TEM, and SEM. This novel composite exhibits excellent electromagnetic-wave absorption properties. The maximum reflection loss for FeCo@C/HRGO reaches -76.6 dB at 16.64 GHz with a thickness of 1.7 mm. The RL below -10 dB reaches 14.32 GHz for a thickness of 1.7-5.0 mm. This confirms that microwave absorption of FeCo@C can be substantially improved upon decoration with HRGO nanosheets.

Novel nanocomposites of cobalt ferrite covalently-grafted on graphene by amide bond as superior electromagnetic wave absorber.

Unique covalently bonded cobalt ferrite (CoFe2O4)/graphene nanocomposites are successfully fabricated via an amino-ester-amide reaction process. The morphology, component, functional groups and electromagnetic properties are detected by Transmission Electron Microscope (TEM), Scanning Electron Microscope (SEM), X-ray Photoelectron Spectroscopy (XPS), Fourier Transform Infrared Spectra (FTIR), Vibrating Sample Magnetometer (VSM) and Vector Network Analyzer (VNA). Compared to non-covalently bonded nanocomposites, the covalently bonded CoFe2O4/graphene nanocomposites have outstanding electromagnetic wave absorption properties. We found that the maximum reflection loss value reached at -55.2 dB and the absorption bandwidth with reflection loss below -10 dB was about 5.4 GHz at 1.7 mm of thickness. The efficiency is attributed to the introduction of amide bonds in the nanocomposites. As a stable carrier channel, amide bonds can promote the migration rate of electrons and binding degree between CoFe2O4 and graphene nanosheets, which provide a crucial impact on electromagnetic parameters and polarization modes of materials, thus improving the absorption capacity of electromagnetic waves. It can be inferred that the nanocomposites have a broad application prospect in the field of electronic instruments, aerospace, military radars and national defense security fields.

Synthesis and microwave absorption enhancement of graphene@Fe3O4@SiO2@NiO nanosheet hierarchical structures.

Hierarchical structures of graphene@Fe3O4@SiO2@NiO nanosheets were prepared by combining the versatile sol-gel process with a hydrothermal reaction. Graphene@Fe3O4 composites were first synthesized by the reduction reaction between FeCl3 and diethylene glycol (DEG) in the presence of GO. Then, graphene@Fe3O4 was coated with SiO2 to obtain graphene@Fe3O4@SiO2. Finally, NiO nanosheets were grown perpendicularly on the surface of graphene@Fe3O4@SiO2 and graphene@Fe3O4@SiO2@NiO nanosheet hierarchical structures were formed. Moreover, the microwave absorption properties of both graphene@Fe3O4 and graphene@Fe3O4@SiO2@NiO nanosheets were investigated between 2 and 18 GHz microwave frequency bands. The electromagnetic data demonstrate that graphene@Fe3O4@SiO2@NiO nanosheet hierarchical structures exhibit significantly enhanced microwave absorption properties compared with graphene@Fe3O4, which probably originate from the unique hierarchical structure with a large surface area and high porosity.