Hejun Li

Facile synthesis of NiCo2O4@Polyaniline core–shell nanocomposite for sensitive determination of glucose

In this work, the core-shell structure of NiCo2O4@Polyaniline (NiCo2O4@PANI) nanocomposite is fabricated via a facile hydrothermal treatment followed by a post-Polyaniline (PANI) coating process. The synthesized materials are characterized by Transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Raman spectrometer. The biosensing properties of NiCo2O4@PANI composite and NiCo2O4 nanoparticles toward glucose are studied based on glassy carbon electrode. Electrochemical studies indicate that the obtained core-shell NiCo2O4@PANI composite shows higher electrocatalytic activity toward the oxidation of glucose, compared with NiCo2O4 nanoparticles. The enhanced performance is related to the core-shell structure of NiCo2O4@PANI composite and the outstanding conductivity of the polyaniline shell. At a potential of +0.5V, the NiCo2O4@PANI nanocomposite modified glass carbon electrode demonstrates a wide linear range up to 4.7350mM with sensitivity of 4.55mAmM(-1)cm(-2) and detection limit of 0.3833μM. It also shows significant electrochemical stability, good reproducibility and excellent selectivity. The results suggest that the NiCo2O4@PANI nanocomposite is a promising electrode material for electrochemical biosensor.

Carbon Nanotube–Multilayered Graphene Edge Plane Core–Shell Hybrid Foams for Ultrahigh‐Performance Electromagnetic‐Interference Shielding

Materials with an ultralow density and ultrahigh electromagnetic-interference (EMI)-shielding performance are highly desirable in fields of aerospace, portable electronics, and so on. Theoretical work predicts that 3D carbon nanotube (CNT)/graphene hybrids are one of the most promising lightweight EMI shielding materials, owing to their unique nanostructures and extraordinary electronic properties. Herein, for the first time, a lightweight, flexible, and conductive CNT-multilayered graphene edge plane (MLGEP) core-shell hybrid foam is fabricated using chemical vapor deposition. MLGEPs are seamlessly grown on the CNTs, and the hybrid foam exhibits excellent EMI shielding effectiveness which exceeds 38.4 or 47.5 dB in X-band at 1.6 mm, while the density is merely 0.0058 or 0.0089 g cm-3 , respectively, which far surpasses the best values of reported carbon-based composite materials. The grafted MLGEPs on CNTs can obviously enhance the penetration losses of microwaves in foams, leading to a greatly improved EMI shielding performance. In addition, the CNT-MLGEP hybrids also exhibit a great potential as nano-reinforcements for fabricating high-strength polymer-based composites. The results provide an alternative approach to fully explore the potentials of CNT and graphene, for developing advanced multifunctional materials.

SiC nanowire networks

Novel 2-D semiconductor SiC nanonetworks have been synthesized at relatively low-temperature via a new method (chemical vapor reaction approach) in a homemade graphite reaction cell. The mixture of milled Si and SiC powder and C,He were chosen as the starting materials. EDX, XRD and HRTEM indicated that the nanonetworks are formed by interconnecting nanowires. The nanowires with diameter of about 20-70 nm are single crystalline beta-SiC and the growth direction is along [111]. A growth mechanism of beta-SiC nanowire networks is discussed

Deposition mechanism of pyrolytic carbons at temperature between 800–1200 °C

Abstract The textures, growth features, microstructures and binding of carbon atoms of pyrolytic carbons prepared by chemical vapor deposition (CVD) at a temperature between 800–1200 °C on graphite substrate and carbon fibers were studied. The intermediate product phase of pyrolytic carbons was also investigated. Based on the present study a deposition model of viscous droplet was proposed in this paper. The viscous droplet here refers to all kinds of fine spheroids that are more or less viscous. The mechanism of the formation of three typical textures namely, smooth laminar, rough laminar and isotropic carbons can be satisfactorily explained by this model.

Carbon-Fiber Reinforced Paper-Based Friction Material: Study on Friction Stability as a Function of Operating Variables

Carbon-fiber-reinforced paper-based friction material (CFRPF), as a new type of wet friction material for automatic transmission, was prepared by a paper-making process. The frictional response of CFRPF is highly complex under a set of dynamically variable operating conditions. To better understand the effect of operating factors (braking pressure, rotating speed, oil temperature, and oil flow rate) on friction stability of the material, tests were carried out using a single ingredient experiment and the Taguchi method. Experimental results show that the braking stability and the dynamic friction coefficient (μ d ) decrease as braking pressure, rotating speed, oil temperature, and oil flow rate increase. The influence of braking pressure on μ d is largest among the four operating factors. μ d declines gradually during the first 3000 repeated braking cycles and changes very little subsequently due to the surface topography change in friction material.

Modification of multi-walled carbon nanotubes with cobalt phthalocyanine: effects of the templates on the assemblies

Cobalt phthalocyanine (CoPc) assemblies are prepared using several kinds of multiwalled carbon nanotube (MWCNT) templates by in situ solid synthesis in a muffle furnace. The products are characterized by infrared spectroscopy, scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and differential thermal analysis-thermogravimetry. The electrocatalytic activity of the obtained MWCNT-templated CoPc assemblies is measured by cyclic voltammograms in an oxygen-saturated 0.5 M H2SO4. The results show that the CoPc assemblies have several different structures: CoPc nanothreads supported by MWCNTs, nanocrystals mixed with MWCNTs and CoPc/MWCNT coaxial nanotubes. The size and the structure of CoPc assemblies are controlled by the interfacial interaction, including π–π interaction, hydrogen bond and coordinate bond, between CoPc and the MWCNTs, which strongly depend on the microstructure of the MWCNTs. Thermal analysis shows CoPc/MWCNT coaxial nanotubes exhibit higher thermal stability than the assemblies with the structure of CoPc nanothreads supported by MWCNTs and nanocrystals linked to MWCNTs. In addition, the cyclic voltammogram measurements show they display different electrochemical characteristics depending on their structures. CoPc/MWCNT assemblies with coaxial nanotube structure have better electrocatalytic activity to oxygen reduction than the others.

A Cr–Al–Si oxidation resistant coating for carbon/carbon composites by slurry dipping

A Si-Al-Ir oxidation resistant coating was prepared for SiC coated carbon/carbon composites by slurry dipping. The phase composition, microstructure and oxidation resistance of the as-prepared Si-Al-Ir coating were studied by XRD (X-ray difiraction), SEM (scanning electron microscopy), and isothermal oxidation test at 1773 K in air, respectively. The surface of the as-prepared Si-Al-Ir coating was dense and the thickness was approximately 100 „m. Its anti-oxidation property was superior to that of the inner SiC coating. The weight loss of SiC/SiAl-Ir coated carbon/carbon composites was less than 5 wt. pct after oxidation at 1773 K in air for 79 h. The local oxidation defects in the coating may result in the failure of the SiC/Si-Al-Ir coating.

Nitrogen-doped carbon nanotubes synthesized by pyrolysis of nitrogen-rich metal phthalocyanine derivatives for oxygen reduction

Two kinds of N-doped multiwalled carbon nanotubes (N-MWCNTs) S1 and S2 are prepared by pyrolysis of nitrogen-rich metal phthalocyanine derivatives, i.e. a mixture of metal tetrapyridinoporphyrazines (MTAPs, M = Fe2+, Ni2+) and tetrapyrazinoporphyrazines (MPTpzs) in a chemical vapour deposition furnace. The N-MWCNTs S1 and S2 have a straight structure and a high N/C atomic ratio. The ratios of N/C in S1 and S2 are 20.01% and 18.50%, respectively. The N atoms in S1 exhibit a uniform distribution, and the majority of N atoms are present in a pyridine type environment, while the N atoms in S2 are concentrated in certain areas, and are mainly in a graphite type environment. The electrocatalytic activities of the N-MWCNTs obtained are measured by the rotating disk electrode technique and cyclic voltammetry in an oxygen-saturated 0.1 M KOH solution. The results show that S1 exhibits a one-step, four-electron pathway for the reduction of oxygen (ORR), whereas S2 exhibits a two-step, two-electron process for ORR, S1 has much higher catalytic activity than S2.

Fabrication and Tribological Properties of B2O3 as Friction Reducing Coatings for carbon-carbon Composites

B2O3 lubricating coatings for the SiC coated C/C composites were prepared by a slurry brushing method. The morphologies, components, and structure of the as-prepared coatings were characterized by SEM and XRD. The friction coefficient of the coatings was also tested. The lubricating mechanism of the coating is discussed. Results show that the friction coefficient of the coatings is 0.06-0.08, which is less than that of the carbon/carbon composites (0.15-0.18). The decrease of the friction coefficient of C/C composites after adding a SiC/B2O coating is attributed to the formation of a lubricious layer of boric acid from the boron oxide after exposure to the moisture in air.

A Ti/Ti-Based-Metallic-Glass Interpenetrating Phase Composite with Remarkable Mutual Reinforcement Effect

A Ti/Ti-based-metallic-glass interpenetrating phase composite (IPC) was prepared by infiltrating the melt into the porous Ti skeleton. Porous Ti limits the shear band (SB) propagation and promotes the SB multiplication, leading to the improved ductility. Moreover, the interpenetrating phase structure shows a mutual reinforcement effect for both amorphous and crystalline phases, making IPC possess higher strength than that calculated by the models held for the conventional composites. This finding will suggest a new way for preparing composites with high strength and ductility.