Prospective growth region for chemical vapor deposition synthesis of carbon nanotube on C–H–O ternary diagram

Chemical vapor deposition has become a standard process for synthesizing carbon nanotubes. Since the successful use of chemical vapor deposition for the first time, much effort has been expended into exploring various carbon sources that can be used to synthesize carbon nanotubes, such as methane, ethane, and ethanol. However, whole perspectives for suitable carbon sources have not been clear. In this study, we performed experiments in order to determine that the appropriate C–H–O components ratio in raw materials can be used to synthesize carbon nanotubes. We also examined a variety of raw materials in our newly developed round-trip-type vacuum furnace in order to determine whether they could be used to synthesize a carbon nanotube. We used Raman spectroscopy to identify the developed carbon nanotube, and we plotted the component ratios of effective and ineffective materials on a C–H–O ternary diagram; in this diagram, the growth region became highly apparent. It should be noted that for the growth of the carbon nanotube, this region should satisfy the equation O < C < (H + O) in molar ratio. Furthermore, it was observed that adjusting the component ratios by mixing raw materials did not cause an inconsistency in the growth region.     

Selective synthesis of single-walled carbon nanotubes on Fe–MgO catalyst by chemical vapor deposition of methane

The selective synthesis of single-walled carbon nanotubes (SWCNTs) with narrow chirality and diameter distribution by methane decomposition over Fe–MgO catalyst is reported. The catalyst was examined by nitrogen physisorption, X-ray diffraction, temperature programmed reduction, X-ray photoelectron spectroscopy, and UV–Vis diffuse reflectance spectroscopy to elucidate the structure and chemical state of the species responsible for SWCNT growth. High resolution electron microscopy, Raman and optical absorption spectroscopy, temperature programmed oxidation, energy dispersive X-ray spectroscopy and nitrogen physisorption were used to probe reaction selectivity, SWCNT chirality and diameter distribution, carbon yield and effectiveness of purification protocols. The yield of carbon increased with an increase in temperature, although SWCNTs selectivity decreased above the optimum synthesis temperature. Results established a clear link between the degree of dispersion of iron oxide species inside the MgO lattice and the catalyst selectivity for SWCNT growth.     

One-step synthesis of ternary MnO2–Fe2O3–CeO2–Ce2O3/CNT catalysts for use in low-temperature NO reduction with NH3

In this article, a facile one-step strategy for the synthesis of ternary MnO₂–Fe₂O₃–CeO₂–Ce₂O₃/carbon nanotubes (CNT) catalysts was discussed. The as-prepared catalysts exhibited 73.6–99.4% NO conversion at 120–180 °C at a weight hourly space velocity (WHSV) of 210 000 ml·g_cat^− 1·h^− 1, which benefited from the formation of amorphous MnO₂, Fe₂O₃, CeO₂, and Ce₂O₃, as well as high Ce^3 + and surface oxygen (O_ε) contents. The mechanism of formation of MnO₂–Fe₂O₃–CeO₂–Ce₂O₃/CNT catalysts was also proposed.     

One-step synthesis of pH-sensitive poly(Acrylamide-co-Sodium Acrylate) beads with core–shell structure

This work describes a novel one-step method to prepare poly(AMm-co-AAcNa) pH-sensitive hydrogel beads with core–shell structure induced by a spontaneous phase separation process during polymerization. In virtue of the phase separation process, polymers with high molecular weight separate to the core phase whereas monomers are left in the shell. This redistribution inside the droplets enables the polymerization environment change sharply to endow the beads with different network structure in core and shell. FTIR spectrum and EDS show that core and shell share identical composition; yet GPC exhibits a bimodal molecular weight distribution which lead to a conventional network in core but a rich-in-branch network in shell. This difference in structure results in mainly three discrepancies in performance. The level of volume change that the beads exhibit at about pH = 4 is much more intense for shell than for core; the swelling/shrinking kinetics of the core and shell indicates that shell responses about 30 times faster than core does; fitting of the absorbency capacity exhibited that the ones of the core and shell are about 67 g/g and 2126 g/g, respectively. A microfluidic device with co-axial channel structure is introduced in this fabrication. The hydrogel beads exhibited narrow size distribution and the diameter of core and shell could be freely controlled by the high controllability of microfluidic technology and by manipulating the phase separation process. In sum, this method impart us an easy and fast-running way to obtain hydrogel beads with core–shell structure, which has potential in various applications like optical material, lenses and sensors.     

Low-temperature growth of highly crystalline β-Ga2O3 nanowires by solid-source chemical vapor deposition

Growing Ga₂O₃ dielectric materials at a moderately low temperature is important for the further development of high-mobility III-V semiconductor-based nanoelectronics. Here, β-Ga₂O₃ nanowires are successfully synthesized at a relatively low temperature of 610°C by solid-source chemical vapor deposition employing GaAs powders as the source material, which is in a distinct contrast to the typical synthesis temperature of above 1,000°C as reported by other methods. In this work, the prepared β-Ga₂O₃ nanowires are mainly composed of Ga and O elements with an atomic ratio of approximately 2:3. Importantly, they are highly crystalline in the monoclinic structure with varied growth orientations in low-index planes. The bandgap of the β-Ga₂O₃ nanowires is determined to be 251 nm (approximately 4.94 eV), in good accordance with the literature. Also, electrical characterization reveals that the individual nanowire has a resistivity of up to 8.5 × 10⁷ Ω cm, when fabricated in the configuration of parallel arrays, further indicating the promise of growing these highly insulating Ga₂O₃ materials in this III-V nanowire-compatible growth condition.

PACS

77.55.D; 61.46.Km; 78.40.Fy     

One-step hydrothermal synthesis of hybrid core-shell Co3O4@SnO2–SnO for supercapacitor electrodes

We successfully synthesized a novel core-shell hybrid metal oxide via a simple one-step hydrothermal method without annealing. This composite of Co₃O₄ particles covered with SnO₂–SnO (Co₃O₄@SnO₂–SnO) predicted better performance compared to pure Co₃O₄, which strongly depends on the synthetic temperature. The Co₃O₄@SnO₂–SnO prepared at a temperature of 250 °C (labeled Co₃O₄@SnO₂–SnO-250) exhibited an outstanding specific capacitance of 325 F g⁻¹ under the current density of 1 A g⁻¹, which was much higher than those of Co₃O₄ (12.6 F g⁻¹) and other composites. Additionally, the sample also exhibited good cycle stability performance with a retention rate of 100% after 5000 cycles at a current density of 5 A g⁻¹. Through X-ray photoelectron spectroscopy analysis, the presumed mechanism was that Sn-O_x decreases the surface electron densities of Co₃O₄, which is beneficial to OH⁻ adsorption and specific capacitance improvement, and the synthetic temperature had a strong impact on the microstructure and thus on the surface electron densities. The most.obvious finding to emerge from this study is that the specific capacitance can be improved through adjusting the surface electron densities of transition metal oxides.     

Facile synthesis,antibacterial mechanisms and cytocompatibility of Ag–MnFe2O4 magnetic nanoparticles

Magnetic MnFe₂O₄ nanoparticles containing 0, 1 and 3 at.% silver, respectively were synthesized by one-pot sol-gel method for antibacterial applications in biomedical fields. Material characterizations indicate that MnFe₂O₄ begins crystallization at 134 °C and oxidation at 450 °C, the grain size and agglomeration degree increase with the silver content and silver exists as metallic state for the particles. The saturation magnetization decreases with the sintering temperature and slightly increases with the silver content, with the maximum of 50.0 emu/g obtained. Antibacterial tests by plate counting and PI-Hoechst 33342 staining suggest that the antibacterial activity of Ag–MnFe₂O₄ nanoparticles is silver content-dependent. Silver ions concentration measurement, β-galactosidase activity assay and transmission electron microscopic observation show that the antibacterial activity is dominated by the actions of the released silver ions, rather than the membrane cell impairment or reactive oxygen species-induced oxidative stress mechanism. MC3T3-E1 cell test demonstrates the best cytocompatibility of the nanoparticles with 3 at.% silver, which is likely related to the reduced cell endocytosis of the aggregated particles. The combination of magnetism, antibacterial activity and biocompatibility would make Ag–MnFe₂O₄ nanoparticles a potential multi-functional material in various biomedical applications.     

Preparation of Al2O3–ZrO2 nanocomposite films by laser chemical vapour deposition

Alumina (Al₂O₃)–zirconia (ZrO₂) nanocomposite films were prepared by laser chemical vapour deposition. α-Al₂O₃–ZrO₂ and γ-Al₂O₃–t-ZrO₂ nanocomposite films were prepared at 1207 and 1000 K, respectively. In the nanocomposite films, 10-nm-wide t-ZrO₂ nanodendrites grew inside the α- or γ-Al₂O₃ columnar grains. The γ-Al₂O₃–t-ZrO₂ nanocomposite films exhibited high nanoindentation hardness (28.0 GPa) and heat insulation efficiency (4788 J s^−1/2 m⁻² K⁻¹).     

Enhanced thickness uniformity of large-scale α-Ga2O3 epilayers grown by vertical hot-wall mist chemical vapor deposition

Smooth surface morphology and high thickness uniformity heteroepitaxy of corundum-structured (α-) gallium oxide (Ga₂O₃) crystalline thin films on 100-mm diameter c-plane sapphire substrates were successfully demonstrated using vertical hot-wall mist chemical vapor deposition (CVD). The growth rate and surface morphology of the epitaxial layers were numerically and experimentally found to be dependent on the diameter of the precursor-diluted microdroplets approaching the substrate surface. Since the microdroplet is gradually evaporated while traveling through the furnace, the growth variables such as temperature, mist-flow velocity, and substrate position were tuned to obtain a suitable diameter of microdroplets approaching the substrate. In this study, the diameter of the approaching microdroplet was ≈2 μm, which was optimal for the smooth surface (root mean square roughness ≈1 nm) of α-Ga₂O₃ epitaxial layers with a growth rate of ≈230 nm/h. Due to the even flow of mist in the vertical furnace, high thickness uniformity of the α-Ga₂O₃ epitaxial layer is guaranteed on large-scale substrates, with a standard deviation of thickness as small as 28 nm, paving the way for highly reliable Ga₂O₃-based electric and optoelectronic devices.     

Static magnetic field-assisted synthesis of Fe_3O_4 nanoparticles and their adsorption of Mn(Ⅱ) in aqueous solution

A facile method for synthesis of the magnetic Fe_3O_4 nanoparticles was introduced.Magnetic nanoparticles were prepared via co-precipitation method with(PMF) and without(AMF) 0.15 T static magnetic field.The effects of magnetic field on the properties of magnetic nanoparticles were studied by XRD,TEM,SEM,VSM and BET.The results showed that the magnetic field in the co-precipitation reaction process did not result in the phase change of the Fe_3O_4 nanoparticles but improved the crystallinity.The morphology of Fe_3O_4 nanoparticles was varied from random spherical particles to rod-like cluster structure.The VSM results indicated that the saturation magnetization value of the Fe_3O_4 nanoparticles was significantly improved by the magnetic field.The BET of Fe_3O_4nanoparticles prepared with the magnetic field was larger than the control by 23.5%.The batch adsorption experiments of Mn(Ⅱ) on the PMF and AMF Fe_3O_4 nanoparticles showed that the Mn(II) equilibrium capacity was increased with the pH value increased.At pH 8,the Mn(Ⅱ) adsorption capacity for the PMF and AMF Fe_3O_4 was reached at 36.81 and 28.36 mg·g~(-1),respectively.The pseudo-second-order model fitted better the kinetic models and the Freundlich model fitted isotherm model well for both PMF and AMF Fe_3O_4.The results suggested that magnetic nanoparticles prepared by the magnetic field presented a fairly good potential as an adsorbent for an efficient removal of Mn(Ⅱ) from aqueous solution.     

Fabrication of graphene nanosheet (GNS)–Fe3O4 hybrids and GNS–Fe3O4/syndiotactic polystyrene composites with high dielectric permittivity

Graphene nanosheet–Fe₃O₄ (GNS–Fe₃O₄) hybrids were obtained by a one-step solvothermal reduction of iron (III) acetylacetonate [Fe(acac)₃] and graphene oxide (GO) simultaneously, which had several advantages: (1) the Fe₃O₄ nanoparticles were firmly anchored on GNS surface even after mild ultrasonication; (2) the loading amount of Fe₃O₄ nanoparticles could be effectively controlled by changing the initial feeding weight ratio of Fe(acac)₃ to GO; (3) the Fe₃O₄ nanoparticles were homogeneously distributed on the GNS surface without much aggregation. Composites based on syndiotactic polystyrene (sPS) and GNS–Fe₃O₄ were prepared by a solution-blending method and the electric and dielectric properties of the resultant GNS–Fe₃O₄/sPS composites were investigated. The percolation threshold of GNS–Fe₃O₄ in the sPS matrix was determined to be 9.41 vol.%. Slightly above the percolation threshold with 9.59 vol.% of GNS–Fe₃O₄, the GNS–Fe₃O₄/sPS composite showed a high dielectric permittivity of 123 at 1000 Hz, which was 42 times higher than that of pure sPS. The AC electrical conductivity at 1000 Hz increased from 3.6 × 10⁻¹⁰ S/m for pure sPS to 2.82 × 10⁻⁴ S/m for GNS–Fe₃O₄/sPS composite containing 10.69 vol.% of GNS–Fe₃O₄, showing an obvious insulator-semiconductor transition.     

Thermodynamic calculations on the chemical vapor deposition of Si–C–N from the SiCl4–NH3–C3H6–H2–Ar system

Based on the Gibbs free energy minimum principle and Factsage software, the thermodynamic phase diagram for the SiCl₄–NH₃–C₃H₆–H₂–Ar system was calculated. The effects of temperature, dilution ratio of H₂, total pressure on product types and distribution regions of reacted solid products were discussed. The results show that: (1) The area of SiC–Si₃N₄ increases at first, then decreases with the rising of temperature and reaches the maximum value at 1273.15 K. (2) The ratio of C/Si is the main factor for the deposition of SiC in the double phase of SiC–Si₃N₄. (3) The preferred deposition conditions of Si₃N₄ are: T=1173.15 K, H₂:SiCl₄=10:1, and P_Total=0.01 atm. Taking the deposition of SiC into consideration, the deposition of Si₃N₄ influences the formation of Si–C–N directly. (4) According to the influencing factors of depositing SiC and Si₃N₄, the suitable parameter for Si–C–N deposition can be determined. (5) Through the experimental verification, it can be demonstrated that Si–C–N can be obtained by low-pressure chemical vapor deposition (CVD), its product being amorphous and mainly constituted by Si–N and Si–C bonds. The obtained Si–C–N ceramics can transform to α-Si₃N₄ and SiC nano-crystal when heat-treated at 1773.15 K in N₂ for 2 h.     

Isostructural organic–inorganic hybrids of P,P′-diphenyl-methylenediphosphinate (CH2(P(Ph)O2)2)2− with divalent transition metals

New organic–inorganic hybrid materials have been synthesized by reaction in water solution of manganese, cobalt or nickel acetates with P,P^′-diphenylmethylenediphosphinic acid and all the two-dimensional structure coordination polymers obtained have been found to be isomorphous.     

Large dielectric constants and good thermal stability of Nb2O5-doped BaTiO3–Bi(Mg1/2Ti1/2)O3 ceramics with core–shell structure

0.96BaTiO₃-0.04Bi(Mg_1/2Ti_1/2)O₃ (0.96BT-0.04BMT) + y wt.% Nb₂O₅ ceramics (0.0 ≤ y ≤ 2.0) were sintered at 1275 °C to fabricate a ceramic with a large ε_r for an X8R multilayer ceramic capacitor (MLCC). Addition of Nb₂O₅ afforded a core–shell structure, and the compositions of the core and shell regions were similar to those of BT and BT-BMT, respectively. The sample (y = 1.25) exhibited a large ε_r of 2285 with a good temperature stability satisfying the X8R specification because of a broad shell-region phase-transition peak at −17 °C and a decreased ε_r of the core-region phase-transition peak. The 0.1 wt% BaO–CaO–SiO₂ (BCS) was used to reduce the sintering temperature, and the 9-layered MLCC produced using a BCS-doped 0.96BT-0.04BMT + 1.25 wt% Nb₂O₅ ceramic at 1200 °C showed a large capacitance of 67 nF with a good temperature stability thus complying with EIA-X8R regulations.     

Possibility of Initiation of Combustion of CH4–O2 (Air) Mixtures with Laser‐Induced Excitation of O2 Molecules

The possibility of initiation of combustion of CH₄–O₂ mixtures with excitation of O₂ molecules to the states a¹_g and b¹⁺ _g by laser radiation with wavelengths of 1.268 m and 762 nm is considered. It is shown that excitation of O₂ molecules significantly decreases the induction period and ignition temperature because of accelerated formation of active atoms and radicals and intensification of the chain mechanism of the process. Even if the specific energy of laser radiation absorbed by the gas is low ( 0.1 eV per molecule), the ignition temperature of the CH₄–O₂ mixture with a ratio of 1:2 can be reduced from 1000 to 300 K.     

Sonochemical synthesis and characterization of magnetic separable Fe3O4–TiO2 nanocomposites and their catalytic properties

A novel sonochemical method is described for the preparation of Fe₃O₄–TiO₂ photocatalysts in which nanocrystalline titanium dioxide particles are directly coated onto a magnetic core. The Fe₃O₄ nanoparticles were partially embedded in TiO₂ agglomerates. TiO₂ nanocrystallites were obtained by hydrolysis and condensation of titanium tetraisopropyl in the presence of ethanol and water under high-intensity ultrasound irradiation. This method is attractive since it eliminated the high-temperature heat treatment required in the conventional sol–gel method, which is important in transforming amorphous titanium dioxide into a photoactive crystalline phase. In comparison to other methods, the developed method is simple, mild, green and efficient. The magnetization hysteresis loop for Fe₃O₄–TiO₂ nanocomposites indicates that the hybrid catalyst shows superparamagnetic characteristics at room temperature. Photocatalytic activity studies confirmed that the as-prepared nanocomposites have high photocatalytic ability toward the photodegradation of RhB solution. Furthermore, the photodecomposition rate decreases only slightly after six cycles of the photocatalysis experiment. Thus, these Fe₃O₄–TiO₂ nanocomposites can be served as an effective and conveniently recyclable photocatalyst.     

Al2O3–W nanocomposites obtained by colloidal processing and in situ synthesis of nano-metal particles

The preparation process and the properties of Al₂O₃-W nanocomposites obtained by gelcasting are reported. The novelty of the synthesis path is the formation of nano-tungsten particles in an in situ reduction of water-soluble precursor during pressureless sintering. The use of water-soluble salt as a tungsten precursor ensured highly homogenous distribution of reinforcing particles and good adhesion between ceramic and metal phases. The maximum content of tungsten in the composites was approximately 0.5 wt%. The size of the reinforcing particles was less than 100 nm. Presence of metallic tungsten and tungsten carbide (W₂C) in the composites lead to the improvement of mechanical parameters: an increase of hardness by about 10 % and of fracture toughness by about 20 %, compared to the reference sample of pure aluminum oxide.     

Preparation of Y1−x Yb x Ba2Cu3O7−y superconducting films by chemical vapor deposition

High Tc Y_1−x Yb _x Ba₂Cu₃O_7−y films were prepared on SrTiO₃(100) substrates by chemical vapor deposition method. Yb₁Ba₂Cu₃O_7−y films were obtained at higher oxygen partial pressure compared with Y₁Ba₂Cu₃O_7−y films at the same deposition temperature. Tc,o (R=0) decreased about 1.5 K when Y was fully substituted with Yb. The caxis lattice parameter of Y_1−x Yb _x Ba₂Cu₃O_7−y films also decreased as the amount of Yb(x) increased.