Nacre-inspired Zirconia/Carbon Nanocomposites with High Strength and Toughness

Inspired by structures of natural shells,zirconia-carbon nanocomposites were obtained by using natural chitin from shrimp shells as templates via the sol-gel route in this study.Chitin was dispersed in the water and chelated with the zirconia precursors by amidogen.After a heat treatment for carbonization,nacre-like structures of carbon-zirconia nanocomposites were successfully synthesized.Due to the toughening mechanism of tetragonal zirconia,the mechanical properties of carbon-zirconia composites are further improved.The as-received zirconia/carbon nanocomposite with best mechanical property has a hardness of 5.88GPa and an elastic modulus of 80.6 GPa,which is even stronger than natural shells.This work might facilitate a versatile platform for developing green nanocomposites with reasonably good mechanical properties.

Preparation and Supercapacitive Properties of Fe_2O_3/Active Carbon Nanocomposites

Fe2O3/active carbon（Fe2O3/AC） nanocomposites were readily fabricated by pyrolyzing Fe3＋ impregnated active carbon in a nitrogen atmosphere. The as-prepared composites were studied by X-ray powder diffraction（XRD）, X-ray photoelectron spectroscopy（XPS） and transmission electron microscopy（TEM）. The capacitive property of the composites was investigated by cyclic voltammetry（CV） and galvanostatic charge-discharge test. Physical characterizations show that the γ-Fe2O3 fine grains dispersed in the AC well, with a mean size of 21.24 nm. Electrochemical tests in 6 mol/L KOH solutions indicate that the as-prepared nanocomposites exhibited improved capacitive properties. The specific capacitance（SC） of Fe2O3/AC nanocomposites was up to 188.4 F/g that was derived from both electrochemical double-layer capacitance and pseudo-capacitance, which was 78% larger than that of pristine AC. A symmetric capacitor with Fe2O3/AC nanocomposites as electrode showed an excellent cycling stability. The SC was only reduced by a factor of 9.2% after 2000 cycles at a current density of 1 A/g.

Monolithic metal-based/porous carbon nanocomposites made from dissolved cellulose for use in electrochemical capacitor

Porous metal-based carbon nanocomposites,with a monolithic shape,were prepared by a one-pot synthesis from dissolved cellulose and metallic salts using a simple,cheap,and environmentally friendly route.Their potential performances as electrochemical capacitors were tested with three metal precursors(M=Cu,Mn,and Fe)with two loadings and in an asymmetric cell for the Fe-based carbon material.Interestingly,here soluble metal precursors were not deposited on a hard cellulose template but mixed in a precooled concentrated NaOH solution where cellulose was previously dissolved,allowing for a good dispersion of the metallic species.After a freezing step where concomitant cellulose regeneration and pore ice-templating phenomena took place,followed by a carbonization step,the mixture led to a porous carbon monolith embedding well-dispersed metal-based nanoparticles having a diameter below 20 nm and present as metallic,oxide,or carbide phase(s)according to the element M.These materials were characterized by different physicochemical techniques and electrochemical tests.Their performances as supercapacitors are discussed in light of the specific behaviour of the metal-based phase and its influence on the carbon matrix properties such as mesopore formation and carbon graphitization.An asymmetric energy storage cell assembled with a Fe-based carbon electrode against a carbon xerogel electrode derived from a phenolic resin shows specific energy and power of 18.3 Wh kg^(−1)at 5 mA cm^(−2)and 1.6 kW kg^(−1)at 25 mA cm^(−2),respectively.

Dynamically observing the formation of MOFs-driven Co/N-doped carbon nanocomposites by in-situ transmission electron microscope and their application as high-efficient microwave absorbent

Metal-organic frameworks(MOFs)derived magnetic carbon-based nanocomposites have drawn widespread attentions due to the well distributed nanocrystals in carbon matrix.Dynamically observing the formation process is urgently needed.Herein,taking zeolitic imidazolate framework(ZIF)-67 as an example,the pyrolysis process is investigated by in-situ transmission electron microscopy(TEM)assisted with ex-situ characterizations.Co nanocrystals are evenly distributed in carbon at the initial stage of carbonization.By increasing pyrolysis temperature,the nanocrystals grow bigger and migrate to carbon surface.The carbon texture transfers from amorphous to crystalline at 600°C,and thoroughly converts at 800°C.In-situ heating TEM shows that more tiny Co nanocrystals move out from the carbon texture by increasing temperature from 700 to 800°C.At 1,000°C,some escaped tiny Co nanocrystals are volatilized and disappeared.The residual escaped Co nanocrystals catalyze the formation of carbon nanotubes(CNTs).Due to the synergistic effect between Co and carbon as well as porous structure,the nanocomposites show high-efficient microwave absorption performance,which can be tuned by pyrolysis temperature,heating rate,and mass fraction.When the mass fraction is 30 wt.%,the nanocomposites obtained at 600 or 700°C display remarkable microwave absorption with optimal reflection loss(RL)smaller than−70 dB and effective absorption band larger than 4.9 GHz.Combining the in-situ and ex-situ techniques,some key findings were observed:(1)graphitization of carbon;(2)volatilization of Co nanocrystals;(3)formation process of CNTs by Co catalyst.These findings are helpful to understand the formation of MOFs derived carbon-based composites and expand their practical applications,especially for microwave absorption.

Chemical, mechanical, and thermal expansion properties of a carbon nanotube-reinforced aluminum nanocomposite

In the present study,the chemical and mechanical properties and the thermal expansion of a carbon nanotube（CNT）-based crystalline nano-aluminum（nano Al） composite were reported.The properties of nanocomposites were tailored by incorporating CNTs into the nano Al matrix using a physical mixing method.The elastic moduli and the coefficient of thermal expansion（CTE） of the nanocomposites were also estimated to understand the effects of CNT reinforcement in the Al matrix.Microstructural characterization of the nanocomposite reveals that the CNTs are dispersed and embedded in the Al matrix.The experimental results indicate that the incorporation of CNTs into the nano Al matrix results in the increase in hardness and elastic modulus along with a concomitant decrease in the coefficient of thermal expansion The hardness and elastic modulus of the nanocomposite increase by 21%and 20%,respectively,upon CNT addition.The CTE of CNT/A1 nanocomposite decreases to 70%compared with that of nano Al.

Effect of carbon nanotube on physical and mechanical properties of natural fiber/glass fiber/cement composites

The objective of this investigation was to introduce a cement-based composite of higher quality. For this purpose new hybrid nanocomposite from bagasse fiber,glass fiber and multi-wall carbon nanotubes（MWCNTs）were manufactured. The physical and mechanical properties of the manufactured composites were measured according to standard methods. The properties of the manufactured hybrid nanocomposites were dramatically better than traditional composites. Also all the reinforced composites with carbon nanotube, glass fiber or bagasse fiber exhibited better properties rather than neat cement.The results indicated that bagasse fiber proved suitable for substitution of glass fiber as a reinforcing agent in the cement composites. The hybrid nanocomposite containing10 % glass fiber, 10 % bagasse fiber and 1.5 % MWCNTs was selected as the best compound.

Effect of the duty cycle of pulsed current on nanocomposite layers formed by pulsed electrodeposition

Nickel-tungsten/carbon nanotube nanocomposite layers with high content and uniform dispersion of carbon nanotubes were fabricated using pulsed electrodeposition technique.Nanocomposite layers were analyzed by scanning electron microscopy, atomic force microscopy, microhardness, and Tafel polarization tests.The effect of the duty cycle of pulsed current or concentration of carbon nanotubes in the metallic matrix on electrochemical and mechanical properties of obtained layers has been investigated.It has been shown that both the electrochemical and mechanical properties of nanocomposite layers that formed by pulsed current were improved significantly with respect to un-composed Ni-W layer.The results were not only concerned by the concentration of carbon nanotubes in the layer but also influenced by the distribution of nanoparticulates in the metallic matrix.

Enhancing electromagnetic wave absorption in carbon fiber using FeS_(2)nanoparticles

Carbon-based electromagnetic wave absorbing materials(absorbers)adhered with metallic sulfide nanoparticles of good electrical conductivity attract increasing researchers’attention.In this study,on the basis of carbon fiber(C_(f))@Fe_(3)O_(4) nanocomposites obtained by the electrostatic spinning and reflow method,C_(f)@FeS_(2)nanocomposite was successfully prepared during a further hydrothermal process.The products exhibit excellent electromagnetic wave absorption performances with a minimum reflection loss(RLmin)of-54.11 dB at 2.13 mm matching thickness.At the same time,the optimal effective absorption bandwidth(EAB)value of 6.04 GHz at a thickness of 1.98 mm covers the whole Ku band,suggesting its excellent electromagnetic wave absorption performances.In addition,the interlaced network structure constructed by carbon fiber,outstanding conductivity of FeS_(2)nanoparticles,and interfacial polarization from hetero-structure play significant parts in enhancing the electromagnetic parameters and absorption performances.All these results suggest that the C_(f)@FeS_(2)nanocomposites can be taken as a new electromagnetic wave-absorbing material under their low density,simple craft,and strong absorption characteristics.

Synthesis of a novel illite@carbon nanocomposite adsorbent for removal of Cr(Ⅵ)from wastewater

A novel illite@carbon（I@C） nanocomposite adsorbent has been synthesized via a facile hydrothermal carbonization process（HTC） using glucose as carbonaceous source and illite as the carrier.The morphology,microstructure and surface properties of the prepared nanocomposite adsorbent were analyzed by FESEM,TGA,XRD,FT-IR and Zeta potential measurements.Batch experiments were carried out on the adsorption of Cr（Ⅵ） to determine the adsorption properties of the composite.The adsorption of Cr（Ⅵ） onto the I@C nanocomposite was well described by the pseudo-second-order kinetic model and Langmuir isotherm.Compared with the illite and carbon material（SC） separately,the prepared I@C nanocomposite adsorbent exhibited enhanced adsorption performance for Cr（Ⅵ） with a maximum adsorption capacity of 149.25 mg/g,which was higher than that of most reported adsorbents.In addition,the adsorption process was spontaneous and endothermic based on the adsorption thermodynamics study.The adsorption of Cr（Ⅵ） by I@C was highly p H-dependent and the optimum adsorption occurred at p H 2.0.The Zeta potential analysis results indicated that the electrostatic interactions between anionic Cr（Ⅵ） and the positively charged surface of the adsorbent might be critical to the adsorption mechanism.This study demonstrated that the I@C nanocomposite should be a promising candidate for a low-cost,environmental friendly and highly efficient adsorbent for the removal of toxic Cr（Ⅵ） from wastewater.

A novel aluminum-carbon nanotubes nanocomposite with doubled strength and preserved electrical conductivity

Enhancing the mechanical strength of highly conductive pure metals usually causes significant reduction in their electrical conductivity.For example,introducing phase/matrix interfaces or more grain boundaries,are common and effective methods to strengthen metals.But it simultaneously increases the electron scattering at the interface,thus reducing the electrical conductivity.In this study,we demonstrate that pure aluminum(Al)/carbon nanotubes(CNTs)nanocomposites prepared by friction stir processing have successfully broken through these limitations.The yield strength and tensile strength of Al/CNTs nanocomposites have improved by 104.7%and 51.8%compared to pure Al,while the electrical conductivity remained comparable to that of pure Al.To explore the potential mechanisms,the interface between CNTs and Al was examined and characterized by transmission electron microscopy(TEM)and Raman spectroscopy.Little interfacial reaction compounds were present and no visible physical gaps were observed at CNTs and Al interfaces.We defined it as a clean and tightly bonded interface.Although the quantity of phase interface has increased,the electrical conductivity of the nanocomposite remains approximately unchanged.We attribute the preserved electrical conductivity to the clean and tightly bonded CNTs/Al interface in the nanocomposite.

Synthesis and Characterization of Magnetite/Carbon Nanocomposite Thin Films for Electrochemical Applications

Stable colloidal suspension of magnetite/starch nanocomposite was prepared by a facile and aqueous-based chemical precipitation method, Magnetite/carbon nanocomposite thin films were subsequently formed upon carbonization of the starch component by heat treatment under controlled conditions. The initial content of native sago starch as the carbon source was found to affect the microstructure and electrochemical properties of the resulted magnetite/carbon nanocomposite thin films, A specific capacitance of 124 F/g was achieved for the magnetite/carbon nanocomposite thin films as compared to that of 82 F/g for pure magnetite thin films in Na2SO4 aqueous electrolyte.

Superbroad-band actively tunable acoustic metamaterials driven from poly(ethylene terephthalate)/carbon nanotube nanocomposite membranes

Actively tunable acoustic metamaterials have attracted ever increasing attention.However,their tunable frequency range is quite narrow(tens of Hz)even under ultrahigh applied voltage(about 1,000 V).Here,we report a superbroad-band actively tunable acoustic metamaterials with the bandwidth over 400 Hz under a low voltage.In the actively tunable acoustic metamaterials,the acoustic membrane is a laminated nanocomposite consisting of a poly(ethylene terephthalate)(PET)and super-aligned carbon nanotube(CNT)drawn from CN T forest array.The laminated nanocomposite membrane exhibits adjustable acoustic properties,whose modulus can be adjusted by applying external electric field.The maximum frequency bandwidth of PET/CN T nanocomposite membrane reaches 419 Hz when applying an external DC voltage of 60 V.Our actively tunable acoustic metamaterials with superbroad-band and lightweight show very promising foreground in noise reduction applications.

LiMn_2O_4/CNTs and LiNi_(0.5)Mn_(1.5)O_4/CNTs Nanocomposites as High-Performance Cathode Materials for Lithium-Ion Batteries

The demand of higher energy density and higher power capacity of lithium（Li）-ion secondary batteries has led to the search for electrode materials whose capacities and performance are better than those available today. Carbon nanotubes（CNTs）, with their unique properties such as 1D tubular structure, high electrical and thermal conductivities, and extremely large surface area, have been used as materials to prepare cathodes for Li-ion batteries. The structure and morphology of CNTs were analyzed by X-ray diffraction（XRD）, scanning electron microscopy（SEM）, and transmission electron microscopy（TEM）. The functional groups on the purified CNT surface such as –COOH, –OH were characterized by Fourier Transform infrared spectroscopy. The electrode materials were fabricated from LiMn2O4（LMO）, doped spinel LiNi0.5Mn1.5O4, and purified CNTs via solid-state reaction. The structure and morphology of the electrode were characterized using XRD, SEM, and TEM. Finally, the efficiency of the electrode materials using CNTs was evaluated by cyclic voltammetry and electrochemical impedance spectroscopy.

Current challenge and perspective of PGM-free cathode catalysts for PEM fuel cells

To significantly reduce the cost of proton exchange membrane fuel cells, platinum-group metal （PGM）-free cathode catalysts are highly desirable. Current M-N-C （M： Fe, Co or Mn） catalysts are considered the most promising due to their encouraging performance. The challenge thus has been their stability under acidic conditions, which has hindered their use for any practical applications. In this review, based on the author＇s research experience in the field for more than 10 years, current challenges and possible solutions to overcome these problems were discussed. The current Edisonian approach （i.e., trial and error） to developing PGM-free catalysts has been ineffective in achieving revolutionary breakthroughs. Novel synthesis techniques based on a more methodolo- gical approach will enable atomic control and allow us to achieve optimal electronic and geometric structures for active sites uniformly dispersed within the 3D architec- tures. Structural and chemical controlled precursors such as metal-organic frameworks are highly desirable for making catalysts with an increased density of active sites and strengthening local bonding structures among N, C and metals. Advanced electrochemical and physical characterization, such as electron microscopy and X-ray absorption spectroscopy should be combined with first principle density functional theory （DFT） calculations to fully elucidate the active site structures.