Xian Jian

Facile Synthesis of Fe3O4/GCs Composites and Their Enhanced Microwave Absorption Properties

Graphene has good stability and adjustable dielectric properties along with tunable morphologies, and hence can be used to design novel and high-performance functional materials. Here, we have reported a facile synthesis method of nanoscale Fe3O4/graphene capsules (GCs) composites using the combination of catalytic chemical vapor deposition (CCVD) and hydrothermal process. The resulting composite has the advantage of unique morphology that offers better synergism among the Fe3O4 particles as well as particles and GCs. The microwave-absorbing characteristics of developed composites were investigated through experimentally measured electromagnetic properties and simulation studies based on the transmission line theory, explained on the basis of eddy current, natural and exchange resonance, as well as dielectric relaxation processes. The composites bear minimum RL value of -32 dB at 8.76 GHz along with the absorption bandwidth range from 5.4 to 17 GHz for RL lower than -10 dB. The better performance of the composite based on the reasonable impedance characteristic, existence of interfaces around the composites, and the polarization of free carriers in 3D GCs that make the as-prepared composites capable of absorbing microwave more effectively. These results offer an effective way to design high-performance functional materials to facilitate the research in electromagnetic shielding and microwave absorption.

Synthesis of high-purity CuO nanoleaves and analysis of their ethanol gas sensing properties

CuO nanocrystals with as-designed morphologies such as uniform quasi-spherical nanoparticles and high-purity nanoleaves were synthesized by adjusting the addition of sodium hydroxide and hydrazine hydrate in aqueous solution at room temperature (25 °C). The increase of sodium hydroxide would accelerate the reaction rate and favor the nucleation of CuO nanocrystals. The decrease of the surface energy will promote the oriented attachment of nanocrystallites along the [−111] direction into nanowires and the final formation of two dimensional (2D) nanoleaves. Increasing the quantity of hydrazine hydrate could decrease the solution system energy and promote the aggregation of CuO nanocrystals from 2D nanoleaves into 3D quasi-spherical nanoparticles. All the CuO nanocrystals with different morphologies were characterized via transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD). The CuO nanoleaves exhibit excellent gas sensing performance in response to ethanol, showing the strongest response value of 8.22 at 1500 ppm ethanol for ∼260 °C.

Heterostructured Nanorings of Fe-Fe3O4@C Hybrid with Enhanced Microwave Absorption Performance

Microwave absorption is a critical challenge with progression in electronics, where fine structural designing of absorbent materials plays an effective role in optimizing their microwave absorption properties. Here, we have developed Fe3O4@C (FC) and Fe-Fe3O4@C (FFC) hybrid nanorings via a hydrothermal method coupled with a chemical catalytic vapor deposition technique. FC and FFC hybrid nanorings have fine carbon coating while their size can easily be tunable in a certain range from 80-130 to 90-140 nm. The optimized FC and FFC hybrid nanorings bear minimum reflection loss (RL) values of -39.1 dB at 15.9 GHz and -32.9 dB at 17.1 GHz, respectively, whereas FFC shows an effective absorption bandwidth (RL values < -10 dB) ranged from 5.2 to 18 GHz. Such an enhanced microwave absorption performance of hybrid nanorings is mainly due to the suitable impedance characteristics, multilevel interfaces, and polarization features in nanorings. This work provides an approach to design hybrid materials having a complex structure to enhance the microwave absorption properties.

Preparation and microwave-absorbing property of BaFe12O19 nanoparticles and BaFe12O19/Fe3C/CNTs composites

BaFe12O19 ferrite was firstly prepared through a sol–gel auto-combustion process, and then BaFe12O19/Fe3C/CNTs composites were synthesized from the acetylene chemical vapor deposition process with the introducing of BaFe12O19 ferrite at 400–600 °C. The structure and morphology of the BaFe12O19 ferrite and BaFe12O19/Fe3C/CNTs composites were studied using X-ray diffraction, scanning electron microscopy, transmission electron microscopy and energy dispersive X-ray. The microwave-absorbing properties of pure BaFe12O19 and such composites were investigated in the frequency range of 2–18 GHz through the evaluation of the experimental data based on the transmission line theory. The reflection loss results showed that the microwave absorption of BaFe12O19/Fe3C/CNTs composites performed better as the reaction temperature increasing up to 500 °C, due to the generation of the high-purity helical CNTs. The composites obtained at 600 °C performed well in electromagnetic wave loss at low frequency, owing to effective interfacial polarizations and good dispersion of magnetic nanoparticles. The composites were very potential for lightweight and strong electromagnetic attenuation materials at relatively low frequency.

Facile Synthesis of Three-Dimensional Sandwiched MnO2@GCs@MnO2 Hybrid Nanostructured Electrode for Electrochemical Capacitors

Designable control over the morphology and structure of active materials is highly desirable for achieving high-performance devices. Here, we develop a facile microwave-assisted synthesis to decorate MnO2 nanocrystals on three-dimensional (3D) graphite-like capsules (GCs) to obtain sandwich nanostructures (3D MnO2@GCs@MnO2) as electrode materials for electrochemical capacitors (ECs). A templated growth of the 3D GCs was carried out via catalytic chemical vapor deposition and MnO2 was decorated on the exterior and interior surfaces of the GC walls through microwave irradiation to build an engineered architecture with robust structural and morphological stability. The unique sandwiched architecture has a large interfacial surface area, and allows for rapid electrolyte diffusion through its hollow/open framework and fast electronic motion via the carbon backbone. Furthermore, the tough and rigid nature of GCs provides the necessary structural stability, and the strong synergy between MnO2 and GCs leads to high electrochemical activity in both neutral (265.1 F/g at 0.5 A/g) and alkaline (390 F/g at 0.5 A/g) electrolytes. The developed hybrid exhibits stable capacitance up to 6000 cycles in 1 M Na2SO4. The hybrid is a potential candidate for future ECs and the present study opens up an effective avenue to design hybrid materials for various applications.

Space matters: Li+ conduction versus strain effect at FePO4/LiFePO4 interface

FePO4/LiFePO4 (FP/LFP) interfacial strain, giving rise to substantial variation in interfacial energy and lattice volume, is inevitable in the (de)lithiation process of LiFePO4, a prototype of Li ion batterycathodes. Extensive theoretical and experimental research has been focused on the effect of lattice strain energy on FP/LFP interface propagation orientation and cyclic stability of the electrode. However, the essential effect of strain induced lattice distortion on Li+ transport at the FP/LFP interface is typically overlooked. In this report, a coherent interface model is derived to evaluate quantitatively the correlation between FP/LFP lattice distortion and Li+conduction. The results illustrate that the effect of lattice strain on Li+conduction depends strongly on FP/LFP interface orientations. Lattice strain induces a 90% decrease of Li+conductivity in ac-plane oriented (de)lithiation at room temperature. The opposite effect of lattice strain on delithiation and lithiation for ab- and bc-orientations is elucidated. In addition, the effect of lattice strain tends to be more pronounced at a lower working temperature. This study provides an efficient platform to comprehend and manipulate Li+conduction in the charge and discharge of lithium ion batteries, the large-scale application of which is frequently challenged by limited in-cell ion conduction.

Enhancement in photoluminescence performance of carbon-decorated T-ZnO

The facile preparation of ZnO possessing high visible luminescence intensity remains challenging due to an unclear luminescence mechanism. Here, two basic approaches are proposed to enhance the luminescent intensity based on the theoretical analysis over surface defects. Based on the deduction, we introduce a methodology for obtaining hybrid tetrapod-like zinc oxide (T-ZnO), decorated by carbon nanomarterials on T-ZnO surfaces through the catalytic chemical vapor deposition approach. The intensity of the T-ZnO green emission can be modulated by topography and the proportion of carbon. Under proper experiment conditions, the carbon decorating leads to dramatically enhanced luminescence intensity of T-ZnO from 400 to 700 nm compared with no carbon decorated, which elevates this approach to a simple and effective method for the betterment of fluorescent materials in practical applications.

A novel strategy to motivate the luminescence efficiency of a phosphor: drilling nanoholes on the surface

A facile approach to fabricate nanoholes on the surface of a phosphor via a carbothermal reaction between C and BaMgAl10O17 was adopted. Drilling nanoholes greatly enhanced excitation light absorption and consequently increased the quantum efficiency, which provided new insight to help improve the luminescence efficiency of oxygen-containing phosphors.

Mechanistic study of graphitic carbon layer and nanosphere formation on the surface of T-ZnO

Graphitic carbon (GC) coatings on the surface of functional materials have received tremendous attention because of their significant effect on surface chemistry. Herein, we have explained the interactions of a carbon source (acetylene) on the surface of functional material (tetrapod-zinc oxide, T-ZnO) through Density Functional Theory (DFT) calculations. DFT studies suggested that the growth of GC in the catalytic chemical vapour deposition (CCVD) process follows two typical pathways: one is chemo/physioadsorption of acetelyne on the T-ZnO surface, and the second one is decomposition of acetylene on the T-ZnO surface to activate carbon atoms that are restructured to generate a GC layer on the T-ZnO surface. Therefore, such a growth through catalytic accumulation reaction of carbon species on the substrate surface is named as vapour-dissociation-solid (VDS) growth. To support our theoretical observation, the GCs on the surface of T-ZnO are grown using acetylene through CCVD, and the results strongly support the VDS growth mechanism. The varying conditions of the CCVD process results in two types of microstructures including a smooth GC coating on T-ZnO that can also yield functional hollow GC nanostructures through acid leaching of the metallic part and ZnC8 nanoparticles embedded in GC walls. The high resolution microscopic analyses confirm the existence of ZnC8 in the nanospheres with an average size of 5.36 nm, which authenticates the decomposition followed by the solid deposition to form the GC on the substrate surface and supports a unique VDS growth mechanism. Therefore, an in-depth study of the GC growth mechanism and its fine coating on complex structures will facilitate research in the prevention of metal oxidation and the design of novel active materials for sensors, environment, energy and medical applications.

Carbon-Based Electrode Materials for Supercapacitor: Progress, Challenges and Prospective Solutions

Carbon-based materials are typical and commercially active electrode for supercapacitors due to their advantages such as low cost, good stability and easy availability. In the light of energy storage, supercapacitors mechanism is classified into EDLCs (electrochemical double layer capacitors) and pseudocapacitors. Multidimensional carbon nanomaterials (active carbon, carbon nanotube, graphene, etc.), carbon-based composite and corresponding electrolyte are the critical and important factor in the eyes of researcher. In this minireview, we will discuss the storage mechanism and summarize recent developed novel carbon and carbon-based materials in supercapacitors. The techniques to design the novel nanostructure and high performance electrodematerials that facilitate charge transfer to achieve high energy and power densities will also be discussed.