Application of as-synthesized Co–Al layered double hydroxides for the preparation of the electroactive composites containing N-doped carbon nanotubes

A set of electrically conductive, porous and electrocatalytically active composites was prepared by catalytic chemical vapor deposition using Co–Al layered double hydroxides and acetonitrile. The effect of synthesis temperature, i.e. 600, 700 and 800 °C on their composition, structure and morphology was examined by means of X-ray diffraction, thermogravimetric analysis, X-ray photoelectron spectroscopy, nitrogen sorption and scanning electron microscopy. Electrochemical properties of the composites were evaluated by cyclic voltammetry (CV) in alkaline solution in the presence and absence of oxygen. The composites were composed of metallic cobalt, metal oxides and turbostratic/graphitic carbon. Graphite-like carbon was doped with nitrogen (according to XPS analysis N concentration is 2 at.%) and occurred as multi-walled carbon nanotubes with diameters ranging from 10 up to 55 nm. The composites were a mixture of compounds showing strongly temperature-dependent crystallinity therefore they showed various specific surface areas (125, 114 and 53 m² g^− 1) and different specific capacitances (9, 7 and 3 F g^− 1). The oxygen reduction peak in the CVs recorded in 0.1 M KOH was observed at − 0.26, − 0.28 and − 0.31 V versus Ag/AgCl/KCl_sat electrode for the samples prepared at 600, 700 and 800 °C, respectively.     

Fabrication of Nd-doped Ni–Zn ferrite/multi-walled carbon nanotubes composites with effective microwave absorption properties

The electromagnetic materials are featured by good magnetic permeability and dielectric constant characteristics, which are of significant importance in solving the pollution problem of electromagnetic. In this study, after the complete of the use of sol-gel method, argon gas was then introduced for calcination, and eventually a new type of MWCNTs/Ni_0.5Zn_0.5Nd_0.04Fe_1.96O₄ composites was synthesized after the above mentioned procedures. The synthesized MWCNTs were able to be adsorbed on the surface of Ni_0.5Zn_0.5Nd_0.04Fe_1.96O₄ and could form a good conductive work of 3D. Also, the effect of additional MWCNTs on microwave absorption properties of MWCNTs/Ni_0.5Zn_0.5Nd_0.04Fe_1.96O₄ composites were also observed in this study. The results indicate that the additional MWCNTs function to significantly improve the microwave absorption property of MWCNTs/Ni_0.5Zn_0.5Nd_0.04Fe_1.96O₄. Through altering the amount of MWCNTs, the microwave attenuation performance and impedance matching coefficient of this electromagnetic materials can be effectively improved. The S2 sample presented a minimum reflection loss of ?35.05 dB when its thickness reached 1.6 mm, meanwhile, the effective absorption bandwidth achieved 4.55 GHz. The prepared composites perform well in microwave absorption, which can attribute to the reasonable ratio of composites as well as its interaction with both of the magnetic and dielectric components. This research paved the way for novel ideas to be put in the electromagnetic absorption materials with high-efficient.     

Preparation and electrochemical properties of SiO2–non-graphitizable carbon composites as negative electrode materials for Li-ion batteries

SiO₂–non-graphitizable carbon composites were prepared by pyrolysis of a mixture of ethyl cellulose and nano-sized SiO₂. The composite electrode showed high reversibility in insertion and/or extraction reactions of Li ions at potentials below 1 V with little hysteresis after the 2nd cycle, whereas a large irreversible capacity was observed in the 1st cycle. This reversible capacity increased with increasing SiO₂ content above 5 wt%. Li ion transfer at the interface between a composite electrode and an electrolyte was studied by ac impedance spectroscopy. In the Nyquist plots, a semi-circle that was assigned to charge-transfer resistance (R _ct) because of Li ion transfer across the interface between the composite electrode and electrolyte appeared at potentials below 1 V. The values of R _ct decreased with increasing SiO₂ content. These results indicate that both a decrease in R _ct and an increase in reversible capacity can be achieved by use of SiO₂–non-graphitizable carbon composite electrodes; this would lead to Li-ion batteries with higher power and energy density.     

Fischer–Tropsch synthesis on mono- and bimetallic Co and Fe catalysts supported on carbon nanotubes

An extensive study of Fischer–Tropsch synthesis (FTS) on carbon nanotubes (CNTs)-supported bimetallic cobalt/iron catalysts is reported. Up to 4 wt.% of iron is added to the 10 wt.% Co/CNT catalyst by co-impregnation. The physico-chemical properties, FTS activity and selectivity of the bimetallic catalysts were analyzed and compared with those of 10 wt.% monometallic cobalt and iron catalysts at similar operating conditions (H₂/CO = 2:1 molar ratio, P = 2 MPa and T = 220 °C). The metal particles were distributed inside the tubes and the rest on the outer surface of the CNTs. For iron loadings higher than 2 wt.%, Co–Fe alloy was revealed by X-ray diffraction (XRD) techniques. 0.5 wt.% of Fe enhanced the reducibility and dispersion of the cobalt catalyst by 19 and 32.8%, respectively. Among the catalysts studied, cobalt catalyst with 0.5% Fe showed the highest FTS reaction rate and percentage CO conversion. The monometallic iron catalyst showed the minimum FTS and maximum water–gas shift (WGS) rates. The monometallic cobalt catalyst exhibited high selectivity (85.1%) toward C₅+ liquid hydrocarbons, while addition of small amounts of iron did not significantly change the product selectivity. Monometallic iron catalyst showed the lowest selectivity for 46.7% to C₅+ hydrocarbons. The olefin to paraffin ratio in the FTS products increased with the addition of iron, and monometallic iron catalyst exhibited maximum olefin to paraffin ratio of 1.95. The bimetallic Co–Fe/CNT catalysts proved to be attractive in terms of alcohol formation. The introduction of 4 wt.% iron in the cobalt catalyst increased the alcohol selectivity from 2.3 to 26.3%. The Co–Fe alloys appear to be responsible for the high selectivity toward alcohol formation.     

Phosphorus-doped Ni–Co sulfides connected by carbon nanotubes for flexible hybrid supercapacitor

As promising electrode materials for supercapacitors, nickel-cobalt bimetallic sulfides render the advantages of abundant redox reactions and inherently high conductivity. However, in general, unsatisfactory performance of low specific capacity, low rate capability, and fast capacity loss exist in Ni–Co sulfide electrodes. Herein, we rationally regulate phosphorus-doped nickel–cobalt sulfides (P-NCS) to enhance the electrochemical performance by gas–solid phosphorization. Moreover, carbon nanotubes (CNTs) as conductive additives are added to improve the cycle stability and conductivity and form the composite P-NCS/C/CNT. According to density functional theory, more electrons near the Fermi surface of P-NCS are demonstrated notionally than those of simple CoNi₂S₄. Electrochemical results manifest that P-NCS/C/CNT exhibits superior electrochemical performance, e.g., high specific capacity (932.0 C∙g^‒1 at 1 A∙g^‒1), remarkable rate capability (capacity retention ratio of 69.1% at 20 A∙g^‒1), and lower charge transfer resistance. More importantly, the flexible hybrid asymmetric supercapacitor is assembled using P-NCS/C/CNT and activated carbon, which renders an energy density of 34.875 W·h∙kg^‒1 at a power density of 375 W∙kg^‒1. These results show that as-prepared P-NCS/C/CNT demonstrates incredible possibility as a battery-type electrode for high-performance supercapacitors.     

Facile synthesis of hierarchical Co–Mo–O–S porous microspheres for high-performance supercapacitors

Transition metal oxides are considered promising functional materials for energy storage, but their poor conductivity and stability limits their application in energy storage devices. The conductivity and stability of transition metal oxides can be significantly improved by nanostructuring the material, and in this work we report a method for preparing porous Co–Mo–O–S microspheres. As a supercapacitor electrode, Co–Mo–O–S demonstrated a high capacitance of 1134 F g⁻¹ at 1 A g⁻¹ as well as a high rate capability. A hybrid supercapacitor composing Co–Mo–O–S vs reduced graphene oxide delivered a high energy density of 67.6 Wh kg⁻¹, which is much higher than most previously reported results. Therefore, Co–Mo–O–S are expected to be widely used in energy storage devices.     

Growth of carbon nanotubes on the surface of carbon fiber using Fe–Ni bimetallic catalyst at low temperature

This article provides a method for growing carbon nanotubes(CNTs) on carbon fibers(CFs) using iron and nickel as catalysts at low temperatures. This series of experiments was conducted in a vacuum chemical vapor deposition(CVD)furnace. It is found that Fe–Ni catalysts, which have a certain thickness and can be better combined with resins when manufacturing composite materials, are more ideal for the growth of CNTs than single metal catalysts. At the same time, it is proved that the CVD process worked best at 450 °C. The mechanical property test proved the reinforcing effect of CNTs on carbon fiber, the single-filament tensile strength of CFs obtained by using Fe–Ni catalyst at 450 °C was 11% higher than that of Desized CFs. The bonding strength of carbon fiber and resin has also been significantly improved. When synthesized at low temperature, CNTs exhibited a hollow multi-wall structure.     

Production and investigation of structure and properties of polyethylene–polylactide composites

Under conditions of shear deformations, low-density polyethylene (LDPE) and polylactide (PLA) composites are obtained in rotor disperser. The production of these composites allows one to use polymers derived from natural raw and to reduce the cost of the materials on their base. The addition of rigid PLA leads to increase in elastic modulus from 200 for LDPE to 1190 for LDPE–PLA (50:50 wt %) composites and in tensile strength from 13.3 for LDPE to 17.8 for LDPE–PLA. By differential scanning calorimetry method, it is shown that LDPE and PLA are incompatible. Using X-ray diffraction analysis, it is found that degree of crystallinity of composites decreases from 46.1 at 50:50 wt % to 36.9 at 80:20 wt % component ratios with the rise in LDPE content. Tests on fungus resistance show that the composites containing 50 wt % PLA are more resistant than the composites containing 30 wt % PLA. First by gel-permeation chromatography method, it is shown that composite degradation after exposure in soil is accompanied by the PLA chain scission and depolymerization with formation of monomers and dimers (M _w of PLA decreases from 118,860 to 80,100). The obtained composites can be applied as packaging materials. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47598.     

Interface microstructure and mechanical properties of Ni–Co–P alloy coatings modified carbon fibres reinforced 7075Al matrix composites

To optimize interface microstructure between 7075Al matrix and CFs, Ni–Co–P multi-component alloy coatings coated carbon fibres were prepared by electroless plating firstly and then Ni–Co–P coated CFs reinforced 7075Al matrix composites (CF/Al(Ni–Co–P)) with high relative density were fabricated by hot pressing sintering process. After modification of Ni–Co–P coatings, Al–Co–Ni Intermetallic compounds were formed stably between matrix and reinforcement because of the smaller mixing enthalpy values of Al–Co, Al–Ni and Co–Ni, which not only restrained the generation of Al₄C₃ but also improved interfacial bonding strength. Yield strength and ultimate tensile strength of CF/Al(Ni–Co–P) composites with 30 vol% CFs had maximum improvement compared with CF/Al(U) composites than other composites reinforced by 10 vol%, 20 vol% and 30 vol%CFs, which is up to 305.8 MPa and 668.7 MPa respectively, and the fracture mode of composites from accumulation fracture to non-accumulation fracture as the existence of Ni–Co–P coatings.     

Thermal,optical and dielectric properties of Zn–Al layered double hydroxide

Zn–Al–NO₃–layered double hydroxide (Zn–Al–NO₃–LDH) was prepared by the co-precipitation method at a constant pH of 7 and a ratio of Zn/Al = 4. A thermal treatment was performed for LDH at various temperatures. Powder XRD patterns showed that the layered structure of the LDH samples was stable below 200 °C, which was also confirmed by thermogravimetric (TGA) and differential thermal (DTA) analyses. Infrared spectra of the samples showed the characteristic peaks of LDH, and changes of these peaks were observed when thermal treatment was performed above 150 °C. Diffuse reflectance spectroscopy of the samples showed more than one energy gap at calcination temperatures below200 °C. In samples calcined at 200 °C and above only one energy gap was observed at approximately 3.3 eV. The photocatalytic activity was found to increase with the increase of the ZnO crystal size, which can be achieved by increasing the calcination temperature of the samples. Because of the presence of water molecules and anionic NO₃⁻ in the interlayer of the LDH, the dielectric response of the calcined LDH can be described by an anomalous low frequency dispersion using the second type of Universal Power Law for calcination temperatures below 200 °C. The dielectric response of the calcined LDH above 150 °C displays the dielectric relaxation behaviour of ZnO because of the formation of a ZnO phase in the LDH within this temperature range.     

Effect of carbon nanotubes additives on mechanical properties of WC–6Co cemented carbide

In order to increase the toughness of WC–6Co cemented carbide, different contents of carbon nanotubes (CNTs) were added to the WC–6Co alloy powder to prepare cemented carbide by low-pressure sintering. The results showed that some of the CNTs were embedded between the grains of WC–6Co cemented carbide, which would hinder the growth of WC grain boundary, thus leading to grain refinement. In addition, CNTs inhibited the formation of decarbonized phase and guided the deflection and bridge of crack to hinder the crack extension. With the increase of CNTs content, the density increased at first and then decreased, and the transverse fracture strength increased at first and then decreased. When the content was 0.2 wt.%, the alloy had the best performance. The density of the alloy was 99.67%; the transverse fracture strength was up to 2937.5 MPa, which is about 100% higher than that of cemented carbide without CNTs. The fracture toughness was 9.84 MPa m^1/2, and the hardness was 1924.8HV₃₀.     

Effect of activation on the carbon fibers from phenol–formaldehyde resins for electrochemical supercapacitors

Activated carbon fibers (ACF) are prepared from phenol–formaldehyde resin fibers through chemical activation and physical activation methods. The chemical activation process consisted of KOH, whereas the physical activation was performed by activation in CO₂. The characteristics of the electrochemical supercapacitors with carbon fibers without activation (CF), carbon fibers activated by CO₂ (ACF-CO₂), and carbon fibers activated by KOH (ACF-KOH) have been compared. The activated carbon fibers from phenol–formaldehyde resins present a broader potential range in aqueous electrolytes than activated carbon and other carbon fibers. Activation does not produce any important change in the shape of starting fibers. However, activation leads to surface roughness and larger surface areas as well as an adapted pore size distribution. The higher surface areas of fibers treated by KOH exhibited higher specific capacitances (214 and 116 F g⁻¹ in aqueous and organic electrolytes, respectively) and good rate capability. Results of this study suggest that the activated carbon fiber prepared by chemical activation is a suitable electrode material for high performance electrochemical supercapacitors.     

Modulation of electromagnetic absorption and shielding properties of geopolymer nanocomposites by designing core–shell structure of carbon nanotubes

In this work, an electromagnetic (EM) protective building material was developed by combining silica (SiO₂)-grafted carbon nanotubes (S@CNTs) with geopolymer (GeoP). The EM absorption and shielding properties of the GeoP nanocomposites were modulated by tailoring the SiO₂ shell thickness. With the increase in shell thickness, the attenuation coefficient decreased, while the impedance matching degree, which acted as a prerequisite for evaluating EM absorption performance, improved. As a result, the minimum reflection loss (RL_min) reached ?38.4 dB at 11.1 GHz and the effective absorption bandwidth of 3.4 GHz with a thickness of 2.9 mm was obtained. Practically, the electron transport capability was promoted with a thinner SiO₂ shell, leading to an improvement in electrical conductivity. As the conductivity increased, the EM interference shielding effectiveness (SE) increased to 11.0 dB, while the RL_min also increased to ?8.7 dB. Based on the underlying mechanism analysis, the strategy for modulating EM performance can be extended to other building materials.     

Synthesis,characterization, and electrical properties of polypyrrole–bimetallic oxide composites

In this study, polypyrrole (PPy) and its bimetallic oxide composites (PPy–V₂O₅–MnO₂) were synthesized via a modified chemical oxidation polymerization method in the aqueous medium with FeCl₃·6H₂O as an oxidant. The synthesized materials were characterized with various analytical techniques to investigate their structural, crystallographic, thermal, morphological, optical, and electrical properties. The Fourier transform infrared study confirmed the successful synthesis of the materials, whereas the X-ray diffraction analyses showed the amorphous and crystalline natures of the PPy and PPy–V₂O₅–MnO₂ composites, respectively. The bimetallic oxide content improved the thermal stability of the composites, as ratified by thermal analysis. The synthesized PPy had a globular and spongy nature, whereas the composites were mixtures of short and long rod-shaped particles. The bimetallic oxide blend enhanced the doping, surface area and semiconducting nature of composites, and lower electrical resistance compared with those of the PPy. The resistance of the synthesized materials depended on the V₂O₅–MnO₂ blend content in the composites and the temperature. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 47680.     

Preparation and characterization of novel polyethylene/carbon nanotubes nanocomposites with core–shell structure

Preparation of novel polyethylene/carbon nanotubes (CNTs) nanocomposites with core–shell structure was presented. The method involved in situ ethylene polymerization in which nanotube surface was treated with Grignard Agent, followed by reacting with active transition metal compound, TiCl₄. The multiwalled carbon nanotubes (MWCNTs) supported catalysts polymerize ethylene to form polymer nanocomposite. MWCNTs were homogeneously dispersed within polymer matrix, and as expected, the resultant nanocomposites featured core–shell structure which was confirmed by HRTEM. For the nanocomposite, the microscopic examination of the cryogenically fractured surface not only ensured a good distribution of carbon nano-particles in the PE matrix but also revealed the ductile-like fracture. The Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) were employed for the study of covalent sidewall functionalization and chemical bonding environment of MWCNTs, also indicated effective immobilization of titanium catalyst on the MWCNTs surface. The crystalline properties, dielectric property and thermal stability of the nanocomposites were determined by WAXD, impedance analyzer and TGA. The dielectric result showed a slight decline of the dielectric constant of the nanocomposites with increase of the polymerization time, and lower dielectric loss was also observed.     

Crystal structure and dielectric properties of barium titanate–kaolinite composites

Barium Titanate–Kaolinite composites were prepared systematically by conventional solid-state method. The crystal structure and dielectric properties of samples were investigated by XRD and dielectric measurements, respectively. XRD results show that new phase BaAl₂Si₂O₈ was formed as kaolinite added into BaTiO₃. The 10 wt% kaolinite addition led to a considerable reduction in sintering temperature and a strong densification. The dielectric constant of BaTiO₃–Kaolinite composites tended to be stable with increasing of kaolinite content.     

Interaction of carbon monoxide with Cu–Pd and Cu–Ni bimetallic clusters

Interaction of CO with Cu–Pd and Cu–Ni bimetallic clusters deposited on a ZnO substrate has been investigated by core-level spectroscopy. The surface reactivity of both these alloy clusters increases with the decrease in cluster size, giving rise to dissociative adsorption at small cluster size. The surface reactivity also increases with the increase in Pd or Ni content and the reactivity of the alloy clusters is unlike that of either component metal. Thus, dissociative adsorption occurs on small Cu–Pd clusters unlike on either Cu or Pd clusters of comparable size. The reactivity of the Cu–Ni clusters, on the other hand, falls somewhere between those of Cu and Ni clusters. This revised version was published online in August 2006 with corrections to the Cover Date.