Electrophoretic deposition of titania–carbon nanotubes nanocomposite coatings in different alcohols

The suspensions of titania nanoparticles in different alcohols (methanol, ethanol and butanol) were prepared using triethanolamine (TEA) as a dispersant. The optimum concentration of TEA was 16.67, 8 and 0.33 mL/L in methanol, ethanol and butanol, respectively. Two component suspensions of titania (20 g/L) and carbon nanotubes (CNTs) (0.1, 0.2, 0.5 and 1 g/L) were prepared in different alcohols without and with optimum concentration of TEA. The finer and positively charged titania nanoparticles were heterocoagulated on the surface of coarser and negatively charged CNTs and generated the titania–CNT composite particles with the net positive charge. In the presence of TEA, titania nanoparticles completely covered CNTs surface due to their higher positive surface charge. At same CNT concentration, the deposition rate was faster for suspensions with TEA additive due to the faster mobility of the composite particles. The photocatalysis efficiency of coatings for methylene blue degradation increased as CNTs were incorporated in their microstructure.     

Electrophoretic deposition of carbon nanotube–ceramic nanocomposites

The purpose of this paper is to present an up-to-date comprehensive overview of current research progress in the development of carbon nanotube (CNT)–ceramic nanocomposites by electrophoretic deposition (EPD). Micron-sized and nanoscale ceramic particles have been combined with CNTs, both multiwalled and single-walled, using EPD for a variety of functional, structural and biomedical applications. Systems reviewed include SiO₂/CNT, TiO₂/CNT, MnO₂/CNT, Fe₃O₄/CNT, hydroxyapatite (HA)/CNT and bioactive glass/CNT. EPD has been shown to be a very convenient method to manipulate and arrange CNTs from well dispersed suspensions onto conductive substrates. CNT–ceramic composite layers of thickness in the range <1–50 μm have been produced. Sequential EPD of layered nanocomposites as well as electrophoretic co-deposition from diphasic suspensions have been investigated. A critical step for the success of EPD is the prior functionalization of CNTs, usually by their treatment in acid solutions, in order to create functional groups on CNT surfaces so that they can be dispersed uniformly in solvents, for example water or organic media. The preparation and characterisation of stable CNT and CNT/ceramic particle suspensions as well as relevant EPD mechanisms are discussed. Key processing stages, including functionalization of CNTs, tailoring zeta potential of CNTs and ceramic particles in suspension as well as specific EPD parameters, such as deposition voltage and time, are discussed in terms of their influence on the quality of the developed CNT/ceramic nanocomposites. The analysis of the literature confirms that EPD is the technique of choice for the development of complex CNT–ceramic nanocomposite layers and coatings of high structural homogeneity and reproducible properties. Potential and realised applications of the resulting CNT–ceramic composite coatings are highlighted, including fuel cell and supercapacitor electrodes, field emission devices, bioelectrodes, photocatalytic films, sensors as well as a wide range of functional, structural and bioactive coatings.     

Asymmetric supercapacitor based on novel coal fly ash derived metal–organic frameworks as positive electrode and its derived carbon as negative electrode

Journal of Applied Electrochemistry - The paper presents a comparative study between aluminum fumarate metal–organic framework (Al-FumMOF) and a novel coal fly ash derived aluminum MOF...     

Densified multiwalled carbon nanotubes–titanium nitride composites with enhanced thermal properties

Densified multiwalled carbon nanotube (MWNT)–TiN composites with various MWNTs contents were successfully obtained through a spark plasma sintering (SPS) method. The thermal conductivity k was found to increase with the MWNT amount and temperature. In the presence of 5 wt% MWNTs, there was a 97% enhancement in k at 703 K compared with that of TiN. The high thermal conductivity of MWNTs, a good interfacial combination and a homogeneous dispersion of MWNTs are key issues to enhance the thermal conductivity of MWNT–TiN composites.     

Large third-order optical nonlinearity of ZnO–Bi2O3–B2O3 glass–ceramic containing Bi2ZnB2O7 nanocrystals

Homogeneous transparent optical glass–ceramics precipitated with unique nonlinear crystals are promising materials for photonic applications. We have utilized heat treatment method to prepare transparent ZnO–Bi₂O₃–B₂O₃ glass–ceramic containing Bi₂ZnB₂O₇ nonlinear nanocrystals. A large third-order nonlinear susceptibility χ⁽³⁾ of glass–ceramic is measured by Z-scan technique, which mainly attributed to unique [BiO₆] and [B₂O₅] units in Bi₂ZnB₂O₇ crystal structure and the quantum size effect of nanoparticles. The discovery is of great potential in the application of nonlinear optical integrated devices.     

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.     

Influence of adding multiwalled carbon nanotubes on the adhesive strength of composite epoxy/sol–gel materials

The tensile shear strength of a composite epoxy/sol–gel system modified with different ratios of multiwall carbon nanotubes (MWCNTs) was evaluated using a mechanical testing machine. The experimental results showed that the shear strength increased when lower than ~0.07 wt% of MWCNTs were added in the composite solution. The increase of the shear strength was attributed to both the mechanical load transfer from the matrix to the MWCNTs and the high specific surface area of this material that increased the degree of crosslinking with other inorganic fillers in the formulation. However, a decrease in the adhesive shear strength was observed after more than ~0.07 wt% MWCNTs were added to the composite. The reason for this may be related to the high concentration of MWCNTs within the matrix leading to excessively high viscosity, dewetting of the substrate surfaces, and reduced bonding of MWCNTs with the matrix, thereby limiting the strength. SEM observation of the fracture surfaces for composite epoxy/sol–gel adhesive materials with 0.01 wt% MWCNTs showed a mixed interfacial/cohesive fracture mode. This fracture mode indicated strong links at the adhesive/substrate interface, and interaction between CNTs and the matrix was achieved; therefore, adhesion performance of the composite epoxy/sol–gel material to the substrate was improved. An increase of a strong peak related to the C–O bond at ~1733 cm^?1 in the FTIR spectra was observed. This peak represented crosslinking between the CNT surface and the organosilica nanoparticles in the MWCNTs-doped composite adhesive. Raman spectroscopy was also used to identify MWCNTs within the adhesive material. The Raman spectra exhibit peaks at ~1275 cm^?1 and in the range of ~1549–1590 cm^?1. The former is the graphite G-band, while the latter is the diamond D-band. The D-band and G-band represent the C–C single bond and C=C double bond in carbon nanotubes, respectively.     

Microstructure and mechanical properties of multi-walled carbon nanotubes containing Al2O3–C refractories with addition of polycarbosilane

Carbon nanotubes (CNTs) are a promising reinforcement for fabricating Al₂O₃–C refractories. However, CNTs are prone to agglomerate or react with antioxidants or reactive gaseous phases such as Al (g), Si (g) and SiO (g), etc. at high temperatures. To overcome the problems above, polycarbosilane (PCS) and multi-walled carbon nanotubes (MWCNTs) were firstly mixed with micro-alumina powder in a liquid medium and then incorporated into Al₂O₃–C refractories. Then the microstructure and mechanical properties of Al₂O₃–C refractories fired in the temperature range from 800 °C to 1400 °C were investigated in this work. The results showed that the MWCNTs were well dispersed in the specimens with addition of PCS in contrast to the specimens without PCS due to the PCS adsorption on the surface of MWCNTs during the mixing process. And the mechanical properties, such as cold modulus of rupture (CMOR), flexural modulus (FM), forces and displacements of Al₂O₃–C refractories with PCS were much higher than those without PCS, which was attributed to more homogeneous dispersion of MWCNTs, more residual MWCNTs as well as different morphologies of ceramic whiskers. Meanwhile, the oxidation resistance of Al₂O₃–C refractories with PCS was improved greatly, which was supposed that the in situ formed SiC_xO_y coating prevented the oxidation of MWCNTs to some extent.     

Pressureless sintering of carbon nanotube–Al2O3 composites

Alumina ceramics reinforced with 1, 3, or 5 vol.% multi-walled carbon nanotubes (CNTs) were densified by pressureless sintering. Commercial CNTs were purified by acid treatment and then dispersed in water at pH 12. The dispersed CNTs were mixed with Al₂O₃ powder, which was also dispersed in water at pH 12. The mixture was freeze dried to prevent segregation by differential sedimentation during solvent evaporation. Cylindrical pellets were formed by uniaxial pressing and then densified by heating in flowing argon. The resulting pellets had relative densities as high as ～99% after sintering at 1500 °C for 2 h. Higher temperatures or longer times resulted in lower densities and weight loss due to degradation of the CNTs by reaction with the Al₂O₃. A CNT/Al₂O₃ composite containing 1 vol.% CNT had a higher flexure strength (～540 MPa) than pure Al₂O₃ densified under similar conditions (～400 MPa). Improved fracture toughness of CNT–Al₂O₃ composites was attributed to CNT pullout. This study has shown, for the first time, that CNT/Al₂O₃ composites can be densified by pressureless sintering without damage to the CNTs.     

Composites of V2O3–ordered mesoporous carbon as anode materials for lithium-ion batteries

The composites of V₂O₃–ordered mesoporous carbon (V₂O₃–OMC) were synthesized and used as anode materials for Li-ion intercalation. These materials exhibited large reversible capacity, high rate performance and excellent cycling stability. For instance, a reversible capacity of V₂O₃–OMC composites was 536 mA h g⁻¹ after 180 cycles at a current density of 0.1 A g⁻¹. The high electrochemical performance of the V₂O₃–OMC composites is attributed to the anchoring of nanoparticles on mesoporous carbon for improving the electrochemical active of V₂O₃ particles for energy storage applications in high performance lithium-ion batteries.     

Dielectric Relaxation in CaO–Bi2O3–B2O3 Glasses

Glasses in the system CaO–Bi₂O₃–B₂O₃ (in molar ratio) have been prepared using melt-quenching route. Ion transport characteristics were investigated for this glass using electric modulus, ac conductivity and impedance measurements. The ac conductivity was rationalized using Almond–West power law. Dielectric relaxation has been analyzed based on the behavior of electric modulus behavior. The activation energy associated with the electrical relaxation determined from the electric modulus spectra was found to be 1.76 eV, close to that the activation energy for dc conductivity (1.71 eV) indicating that the same species took part in both the processes. The stretched exponent β (0.5–0.6) is invariant with temperature for the present glasses.     

Viscous behaviour of Bi2O3–B2O3–ZnO glass composites with ceramic fillers

Abstract

Variation in the viscous flow behaviour, nature and extent of glass fluidity in glass/filler composites are addressed with respect to various factors such as filler type, content, size, density and migration distance. The characterisation of a glass (Bi₂O₃–B₂O₃–ZnO) composite consisting of two different fillers (cordierite and willemite) was determined using hot stage microscopy, a differential scanning calorimeter and a flow button test. The microstructure was analysed using a scanning electron microscope. The apparent viscosity of the glass composites increased on increasing concentration and density of the filler. The variation in the viscosity is due to the diffusion of the glass matrix through channels in the cordierite filler of the composite. Based on the calculated migration distance of the filler in the glass matrix, the present work suggests that the interfacial behaviour and the density of the filler play a significant role in determining the viscous flow of the glass composites.     

Ablation behavior of ZrB2–SiC protective coating for carbon/carbon composites

Ablation behavior of ZrB₂–SiC protective coating for carbon/carbon composites during oxyacetylene flame test at 2500 °C was investigated by analyzing the microstructure differentiation caused by the increasing intensity of ablation from the border to the center of the surface. After ablation, a continuous SiO₂ scale, a porous SiO₂ layer inlaid with fine ZrO₂ nuclei, and a continuous ZrO₂ scale respectively emerged in the border region, the transitional region, and the center region. In order to investigate the ablation microstructure in the initial stage, the sub-layer microstructure was characterized and found to be mainly formed by coral-like structures of ZrO₂, which showed huge difference with the continuous structure of ZrO₂ on the surface layer. A kinetic model concerning the thickness change induced by volatilization and oxidation during ablation was built to explain the different growth mechanisms of the continuous ZrO₂ scale and the coral-like ZrO₂ structure.     

Improved activity of a graphene–TiO2 hybrid electrode in an electrochemical supercapacitor

We present a simple and fast approach for the synthesis of a graphene–TiO₂ hybrid nanostructure using a microwave-assisted technique. The microstructure, composition, and morphology were characterized by X-ray diffraction, Fourier-transform infrared spectroscopy, Raman microscopy, X-ray photoelectron spectroscopy, and field-emission scanning electron microscopy. The electrochemical properties were evaluated using cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge–discharge tests. Structural analysis revealed a homogeneous distribution of nanosized TiO₂ particles on graphene nanosheets. The material exhibited a high specific capacitance of 165 F g⁻¹ at a scan rate of 5 mV s⁻¹ in 1 M Na₂SO₄ electrolyte solution. Theenhanced supercapacitance property of these materials could be ascribed to the increased conductivity of TiO₂ and better utilization of graphene. Moreover, the material exhibited long-term cycle stability, retaining ∼90% specific capacitance after 5000 cycles, which suggests that it has potential as an electrode material for high-performance electrochemical supercapacitors.     

Facile synthesis and characterization of conducting polymer-metal oxide based core-shell PANI-Pr2O–NiO–Co3O4 nanocomposite: As electrode material for supercapacitor

Metal oxide nanoparticles and their composites with conducting polymers, specifically Polyaniline (PANI) were utilized for fabricating nanoscale supercapacitor (SC) electrode materials. In the present study, we have synthesized pristine Pr₂O₃, NiO, Co₃O₄ nanoparticles, binary PANI-Pr₂O₃, PANI-NiO, PANI-Co₃O₄, ternary Pr₂O₃–NiO–Co₃O₄, and quaternary PANI-Pr₂O₃–NiO–Co₃O₄ spherical core-shell nanocomposite using co-precipitation and ultra-sonication methods. The grown samples were characterized with different analytical techniques. The XRD pattern revealed that the as-synthesized products were crystalline with Pr₂O₃ hexagonal phase, NiO cubic phase, and Co₃O₄ cubic phase in pure and nanocomposites. The Williamson-Hall, Scherrer, and size-strain plot methods were employed to study the crystalline development and contribution of micro-strain. FTIR pattern exhibited the metal-oxygen and PANI bond vibrations. FE-SEM images shown the spherical core-shell shape morphology of quaternary nanocomposite. EDX evident the presence of praseodymium, cobalt, and nickel in synthesized samples. UV–vis spectroscopy confirmed the absorption in the visible region. The IV graphs showed a higher conductivity of quaternary nanocomposite. The cyclic voltammetry results revealed that the quaternary nanocomposite has a higher specific capacitance 500 Fg^-1 as compared to binary nanocomposites 134 F g^?1 (PANI-Pr₂O₃), 143 F g^?1 (PANI-Co₃O₄), 256 F g^?1 (PANI-NiO), and PANI (90.8 F g^?1) at a scan rate of 5 m Vs^?1. The GCD results also showed that the quaternary nanocomposite has a higher specific capacitance of 905 F g^?1 at current density 1 A g^?1 with maximum energy density and power density of 87.99 kWhkg^-1 and 2.6 k W kg^?1_, respectively. The EIS curve also confirmed that the quaternary nanocomposite has a lower polarization resistance (R_p) and solution resistance (R_s). The higher capacitance of quaternary nanocomposite can facilitate ion transfer, and the formation of its core-shell structure flourish to enhance surface-dependent electrochemical properties. Furthermore, this study gives a novel research idea to manufacture electrode materials for supercapacitors.     

Nanocrystaline solid solution CeO2–Bi2O3

Nanocrystalline powders of solid solution CeO₂–Bi₂O₃ were synthesized by self-propagating room temperature reaction (SPRT) procedure with composition (Ce_1?xBi_xO_2?δ where the x = 0.1–0.5). X-ray diffraction analyses show that for x < 0.50 a solid solution with fluorite structure is formed. Rietveld's structure refinement method was applied to characterize prepared powders and its microstructure (size–strain). The lattice parameters increase according to Vegard's rule with increasing of Bi concentration. The average crystallite size is about 2–3 nm. Spectroscopic ellipsometry and Raman scattering measurements were used to characterize the samples at room temperature. The Raman measurements demonstrated electron molecular vibrational coupling and increase of oxygen vacancy concentration whereas increase of Bi content provokes a small decrease of optical absorption edge in comparison with pure ceria. Specific surface area of obtained powders was measured by Brunauer–Emmet–Teller (BET) method.     

The nickel–carbon asymmetric supercapacitor—Performance,energy density and electrode mass ratios

The performance of nickel hydroxide/carbon asymmetric supercapacitors has been studied with a range of positive and negative active material ratios. The utilisation of the nickel hydroxide electrode in asymmetric supercapacitors was found to be a function of the mass ratio of the positive and negative electrode materials and not independent as previously assumed. Previous models describing the behaviour of asymmetric supercapacitors assumed that the voltage swing was entirely due to the polarisable electrode. These models were found to be inadequate for describing the rate dependant charge/discharge behaviour of asymmetric supercapacitors. The mass ratio of the active materials was determined to be an important factor in predicting the observed behaviour and has been incorporated into an improved model.     

Fe3O4–carbon black nanocomposite as a highly efficient counter electrode material for dye-sensitized solar cell

Iron oxide–carbon black (Fe₃O₄–CB) nanocomposite has been proposed as a cost–effective alternative counter electrode (CE) to the conventional Pt in a dye sensitized solar cell (DSSC). The Fe₃O₄–CB nanocomposite at three different weight ratio (1:1, 1:2 and 2:1) was prepared by a simple solution mixing process and the material was characterized by Fourier transform infrared spectroscopy, X-ray diffraction, scanning and transmission electron microscopy techniques. The performance of the three Fe₃O₄–CB nanocomposite CEs was assessed with respect to Fe₃O₄, CB and Pt in a conventional DSSC consisting of N719 dye sensitized TiO₂ (P25) photoanode in contact with an electrolyte containing the I⁻/I₃⁻ redox couple. The electrocatalytic activities of the various CEs towards triiodide (I₃⁻) reduction were analyzed by cyclic voltammetry, electrochemical impedance spectroscopy and Tafel polarization analysis. The photocurrent voltage (J–V) characteristics of the DSSCs assembled with various counter electrodes were assessed at a light intensity of 80 mW cm⁻². The DSSC assembled with Fe₃O₄–CB nanocomposite (1:2) CE showed the best photovoltaic performance in terms of a high power conversion efficiency of 6.1% which is superior to that of sputtered Pt (4.1%). The simple preparation, excellent electrocatalytic activity and low-cost nature allow the Fe₃O₄–CB nanocomposite to be a promising alternative CE to Pt for use in DSSCs.