An optimized impedance matching construction strategy: carbon nanofibers inlaid with Ni nanocrystals by electrospinning for high-performance microwave absorber.

With the widespread use of electronic goods, solving electromagnetic pollution has become one of the new challenges. Higher requirements for microwave-absorbing materials (MAM) have emerged to address this issue. The composite of carbon nanofiber (CNF) and magnetic nanoparticles is the material that effectively absorbs microwaves. This paper fabricated Ni/C nanofibers using a combination of electrospinning and high-temperature carbonization. With 50 wt% paraffin wax, Ni/C nanofibers demonstrated optimal microwave absorption capabilities. With a thickness of 3 mm, the minimum RL value can reach -30.6 dB, and the effective absorption bandwidth is 5.96 GHz. By encapsulating Ni nanoparticles in carbon nanofibers, the synergic interaction of dielectric and magnetic losses effectively meets the need for constant attenuation and impedance matching, and effectively improves microwave-absorbing properties. Hence, Ni/C nanofibers are promising for MAM application with excellent MA performance.

Toward Enhanced Electrochemical Performance by Investigation of the Electrochemical Reconstruction Mechanism in Co2V2O7 Hexagonal Nanosheets for Hybrid Supercapacitors.

As for hybrid supercapacitors, it is important to enhance the long cycling performance and high specific capacitance. In this paper, cobalt vanadate (Co2V2O7) hexagonal nanosheets on nickel foam are manufactured by a facile hydrothermal method and then transformed into numerous smaller size interconnected hierarchical nanosheets without any shape change via electrochemical reconstruction. Benefiting from the favorable architecture of hierarchical nanosheets via electrochemical reconstruction, the Co2V2O7 hexagonal nanosheet electrode exhibits a remarkable long cycling performance with 272% specific capacitance retention after 100,000 cycles at a current density of 5 A g-1 and then displays an increasing specific capacitance of 1834 F g-1 (tested at 1 A g-1). Furthermore, an aqueous hybrid supercapacitor device based on the Co2V2O7 hexagonal nanosheet electrode exhibits a high energy density of 35.2 Wh kg-1 at a power density of 1.01 kW kg-1 and an excellent cyclic stability with 71.4% capacitance retention after 10,000 cycles at 5 A g-1. These results offer a practicable pathway for enhancing the electrochemical properties of other metal oxides through electrochemical reconstruction.

The Simulation Design of Microwave Absorption Performance for the Multi-Layered Carbon-Based Nanocomposites Using Intelligent Optimization Algorithm.

The optimal design objectives of the microwave absorbing (MA) materials are high absorption, wide bandwidth, light weight and thin thickness. However, it is difficult for single-layer MA materials to meet all of these requirements. Constructing multi-layer structure absorbing coating is an important means to improve performance of MA materials. The carbon-based nanocomposites are excellent MA materials. In this paper, genetic algorithm (GA) and artificial bee colony algorithm (ABC) are used to optimize the design of multi-layer materials. We selected ten kinds of materials to construct the multi-layer absorbing material and optimize the performance. Two algorithms were applied to optimize the two-layer MA material with a total thickness of 3 mm, and it was found that the optimal bandwidth was 8.12 GHz and reflectivity was -53.4 dB. When three layers of MA material with the same thickness are optimized, the ultra-wide bandwidth was 10.6 GHz and ultra-high reflectivity was -84.86 dB. The bandwidth and reflectivity of the optimized material are better than the single-layer material without optimization. Comparing the GA and the ABC algorithm, the ABC algorithm can obtain the optimal solution in the shortest time and highest efficiency. At present, no such results have been reported.

Study on preparation, stability, thermal conductivity, and viscosity of silver nanoparticles-decorated three-dimensional graphene-like porous carbon hybrid nanofluids.

In the present study, a novel silver nanoparticles-decorated three-dimensional graphene-like porous carbon (Ag/3D GPC) nanocomposite has been synthesized via the method of carbonization and reduction of silver ions at the same time. This Ag/3D GPC nanocomposite possess an interconnected network of well crystalized and submicron-sized macropores with thin graphene walls of several nanometers, where silver nanoparticles distributing uniformly. The water based and ethylene glycol based Ag/3D GPC hybrid nanofluids have been prepared without any surfactant. The hybrid nanofluids with low concentration (<0.8 wt%) can be steadily dispersed for more than six months. The thermal conductivity enhancement for the nanofluids with 0.1 wt% can reach 10.3% and 8.8% at 25 °C compared with pure water and ethylene glycol, respectively. The viscosity of nanofluids is investigated, the temperature dependence of the dynamic viscosity obeys an Arrhenius-like behavior. The prepared Ag/3D GPC hybrid nanofluids with good stability and thermal conductivity are promisingly considered to be used in heat transfer field.

Investigation on Synthesis, Stability, and Thermal Conductivity Properties of Water-Based SnO2/Reduced Graphene Oxide Nanofluids.

With the rapid development of industry, heat removal and management is a major concern for any technology. Heat transfer plays a critically important role in many sectors of engineering; nowadays utilizing nanofluids is one of the relatively optimized techniques to enhance heat transfer. In the present work, a facile low-temperature solvothermal method was employed to fabricate the SnO2/reduced graphene oxide (rGO) nanocomposite. X-ray diffraction (XRD), thermogravimetric analysis (TGA), X-ray photoelectron spectroscope (XPS), Raman spectroscopy, and transmission electron microscopy (TEM) have been performed to characterize the SnO2/rGO nanocomposite. Numerous ultrasmall SnO2 nanoparticles with average diameters of 3-5 nm were anchored on the surface of rGO, which contain partial hydrophilic functional groups. Water-based SnO2/rGO nanofluids were prepared with various weight concentrations by using an ultrasonic probe without adding any surfactants. The zeta potential was measured to investigate the stability of the as-prepared nanofluid which exhibited great dispersion stability after quiescence for 60 days. A thermal properties analyzer was employed to measure thermal conductivity of water-based SnO2/rGO nanofluids, and the results showed that the enhancement of thermal conductivity could reach up to 31% at 60 °C under the mass fraction of 0.1 wt %, compared to deionized water.

Large-area aligned branched Cu(2)S nanostructure arrays: room-temperature synthesis and growth mechanism.

In this work, an effective approach to synthesize large-area Cu(2)S hierarchical nanotree arrays is presented: Cu nanowire arrays synthesized via template-assisted electrodeposition are used as precursors for the self-growth of branched Cu(2)S nanotree arrays by a gas-solid reaction in H(2)S atmosphere at room temperature. The branched Cu(2)S nanotrees with a high aspect ratio are vertically aligned over the Au film surface, forming a nanoscale 'forest'. Electron microscopy studies reveal that the treelike branched nanostructures are composed of an end-capped tubular Cu(2)S trunk and radially organized Cu(2)S nanorod branches over the trunk. A formation mechanism of the hollow trunk and the nanobranches is proposed on the basis of experimental observations.