Single wall carbon nanohorns coated with anatase titanium oxide

Single wall carbon nanohorns (SWCNHs) were coated with anatase titanium oxide thin films by metal-organic chemical vapour deposition with titanium tetraisopropoxide Ti(OiPr)₄ as the precursor. The pristine SWCNHs and the new hybrid material SWCNHs/TiO₂ were characterized by transmission electron microscopy, Raman spectroscopy, X-ray diffraction, thermogravimetric thermal analysis and inductively coupled plasma-mass spectrometry, showing that the deposition process does not alter the typical structures of the SWCNHs. Finally, it is shown how the hydrophilic properties of the titanium oxide coating allowed a stable dispersion of SWCNHs/TiO₂ in water, opening new perspectives for water based nanofluids, biological sensing or drug delivery systems.     

Synthesis and characterization of carbon aerogels with different catalysts

Journal of Porous Materials - Carbon aerogels were synthesized by a sol–gel process by polycondensation of phloroglucinol, resorcinol and formaldehyde, using sodium hydroxide, calcium...     

Molybdenum doped carbon aerogels with catalytic potential

Mo-doped carbon aerogels were obtained in the polycondensation reaction of aqueous resorcinol and formaldehyde by adding Mo-salt at two different stages of the synthesis: (i) to the initial sol; (ii) by incipient wetting impregnation of the supercritically dried polymer gel. Molybdenum added during the polymerization yielded a more compact gel structure with practically no mesoporosity. With post-impregnation, by contrast, mesopores of diameter 3–15 nm were generated. Carbonization appreciably enhanced the microporous character of both samples, but in the mesopore range their pore size distribution was conserved. The Mo-content of the samples was also different: Mo was lost during the solvent exchange before the supercritical drying (i.e., the Mo failed to bind chemically to the polymer matrix). The residual Mo congregated into 25–60 nm bulk clusters of α-Mo₂C. In the other carbon aerogel, finely dispersed α-Mo₂C and η-Mo₃C₂ crystals formed, of size 8–20 nm. On the surface of both carbons the Mo formed oxides. In the model test reaction (acetic acid hydroconversion) the catalytic activity of both carbon aerogels was enhanced by molybdenum. The more open pore structure, higher concentration and finer Mo distribution, as well as its chemical form, may all be responsible for the greater conversion and higher value products obtained with the post-impregnated sample.     

Synthesis and characterization of Fe doped titanium dioxide nanopowders

Titanium dioxide nanopowders, doped with different amounts of Fe³⁺ ions (0.3-5 mass%), were synthesized by acid-catalyzed sol-gel method in a non-aqueous medium. The obtained powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy and determination of izoelectric points as well as particle diameters. Careful investigation of porous structure was provided by application of nitrogen adsorption-desorption method. Structure analysis showed that the obtained nanopowders exhibited the anatase crystal structure, independent of the amount of iron dopants. The presence of Fe³⁺ ions in anatase decreases the value of isoelectric point of undoped TiO₂. Unlike crystal structure, porosity parameters are strongly affected by the amount of iron ions incorporated in TiO₂ lattice. The mesoporosity of TiO₂ can be successfully controlled by changing the amount of iron dopants.     

Synthesis and characterization of monolithic carbon/silicon carbide composite aerogels

Resorcinol–formaldehyde/silica composite (RF/SiO₂) aerogels were synthesized using sol–gel process followed by supercritical CO₂ drying. Monolithic carbon/silicon carbide composite (C/SiC) aerogels were formed from RF/SiO₂ aerogels after carbothermal reduction. X-ray diffraction and transmission electron microscopy demonstrate that β-SiC was obtained after carbothermal reduction. Scanning electron microscopy and nitrogen adsorption/desorption reveal that the as-prepared C/SiC aerogels are typical mesoporous materials. The pore structural properties were measured by nitrogen adsorption/desorption analysis. The resulting C/SiC aerogels possess a BET surface area of 564 m²/g, a porosity of 95.1 % and a pore volume of 2.59 cm³/g. The mass fraction of SiC in C/SiC aerogels is 31 %.     

Morphology of heat-treated tunsgten doped monolithic carbon aerogels

The morphology of a tungsten-doped monolithic organic aerogel, prepared by the sol-gel method from the polymerisation of a resorcinol, formaldehyde and ammonium tungstate mixture, and of its carbonized derivatives at 500 and 1000 °C was studied by scanning and high-resolution electron microscopy. Tungsten influenced the surface morphology of the carbon aerogels. The tungsten-containing phase was homogeneously distributed in the organic aerogel and its heat treatment produced changes in the metal phase distribution throughout the pellets. Tungsten oxide particles of needle-like structure similar to hollow tubules were detected after heat treatments at different temperatures. In addition, particles of dendritic appearance, formed by tungsten carbide and an intermediate Magnelli phase, appeared when the heat treatment was carried out at 1000 °C.     

Synthesis and characterization of niobia-containing aerogels

Niobium ethoxide was used as a precursor either by itself to impregnate a silica aerogel or in conjunction with tetraethyl orthosilicate to produce a mixed oxide aerogel. In contrast with bulk niobia, niobia in these samples did not crystallize into the high-temperature form even after calcination at 1273 K. Niobia-silica interactions, which apparently stabilized niobia from crystallization, also introduced acidity as shown by n-butylamine titration and infrared study of pyridine adsorption. Furthermore, niobia on silica was found to have stronger Brönsted acid sites than niobia in silica, in agreement with previous observations on samples prepared with more conventional methods. All these samples were also active in the isomerization of 1-butene.     

Synthesis and characterization of phosphorus–nitrogen doped multiwalled carbon nanotubes

Phosphorus–nitrogen doped multiwalled carbon nanotubes (CN_xP_y) were prepared using a floating catalyst chemical vapor deposition method. Triphenylphosphine (TPP), as phosphorus (P) precursor, was used to control the structure of the CN_xP_y. Transmission electron microscope (TEM) observation indicated that with the increase of TPP amount, the outer diameter and wall thickness of the CN_xP_y gradually increased, while their inner diameter decreased. TEM and backscattered electron imaging revealed that structural changes of the nanotubes could be attributed to the shape change of the catalyst particles, from conical for nitrogen-doped carbon nanotubes (CN_x) to elongated for CN_xP_y, with the addition of TPP. X-ray photoelectron spectroscopy analysis demonstrated that the P content in CN_xP_y can reach as high as 1.9 at.%. Raman analysis indicated that CN_xP_y had a lower crystallinity than CN_x.     

Preparation and characterization of antibacterial silver-dispersed activated carbon aerogels

Silver-dispersed carbon aerogels (CAs) were obtained by direct immersion of organic aerogels prepared by ambient pressure drying technique in AgNO₃ aqueous solution and then carbonization. The effect of preparation conditions such as the resorcinol/catalyst ratio, the feed AgNO₃ concentration, the ratio of aerogel mass/solution volume, immersion time and carbonization temperature on the bulk density and silver content as well as the BET surface area of the dispersed CAs was studied. The dispersion and structure of silver nanoparticles in obtained materials were investigated by means of scanning electron microscopy, transmission electron microscopy and X-ray diffraction. The Ag-dispersed CAs prepared exhibit strong and long-term antibacterial activity.     

Synthesis and characterization of tanninsulfonic acid doped polyaniline–metal oxide nanocomposites

Composites of conducting polymers and metal oxides have a potential role in electronic devices because of their enhanced physical and electronic properties. An in situ synthesis of metal oxide nanocomposites of polyaniline (PANI) and tanninsulfonic acid doped PANI was carried out at ?10°C with two different ratios of aniline to sodium persulfate (oxidant) and the simultaneous incorporation of TiO₂, Al₂O₃, and ZnO nanopowders. The products were characterized by X‐ray diffraction (XRD), thermal analysis, spectroscopy, and electrical conductivity measurements. XRD and thermogravimetric analysis confirmed the presence of the metal oxide in the final product, whereas the spectroscopic characterization revealed interactions among the tannin, metal oxides, and PANI. The electrical properties were determined by four‐point‐probe bulk conductivity measurements. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Synthesis and characterization of titanium oxide nanotubes and its performance in epoxy nanocomposite coating

Titanium oxide nanotubes (TiO₂ nanotube, TNT) were prepared from hydrothermal treatment of TiO₂ particles in NaOH at 140 °C, followed by neutralization with HCl. The structure of the nanotubes was characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). TNT synthesized under the optimal conditions with approximately 10–20 nm wide, and several (100–200) of nanometers long. TNT is used as white pigment for two component epoxy-based coating. Ultrasonication followed by mechanical stirring has been applied for dispersion of TNT powder in an epoxy matrix. The resulting perfect dispersion of TNT particles in epoxy coating revealed by scanning electron microscopy (SEM) ensured white particles embedded in the epoxy matrix. The effects of TNT particle concentrations on thermal, mechanical and corrosion resistance of epoxy coatings composite were studied and compared to that of submicron particles. It was found that the TNT significantly enhances the heat resistance, the thermal stability and the glass transition temperature of epoxy resin. Epoxy/TNT nanocomposite with 5.0 wt.% TNT shows the highest thermal stability, the temperature of 50% weight loss increased from 365 to 378 °C, the amount of char yields or residues at 600 °C increased from 7.13 to 13.50 wt.%, respectively to 1.0 and 5.0 wt.% TNT. The glass transition temperature (Tg) increased from 182 to 220 °C too. The mechanical properties and corrosion resistance of epoxy resin greatly improved by using reinforcing TNT and this improvement increases with increase TNT wt.%.     

Synthesis and characterization of hexagonal BN-based aerogels for absorbing oils

Porous oil absorbents have been extensively studied in recent years. Boron nitride (BN) is an ideal inorganic material to withstand severe absorption conditions due to its excellent inertness and high-temperature resistance. A large challenge of BN aerogels is their high preparation costs due to requiring high temperatures and dangerous atmospheres. A facial synthesis of h-BN-based aerogels by the cast-freezing method is reported here, which has the advantages of producing a light and recyclable material (~0.035 g/ml) at a low cost and with low energy consumption. In this work, carboxymethylcellulose (CMC) is used as the compounder to interact with BN and form an aerogel that has controllable porosity (38–86 μm) and hydrophobicity (~140°). The porous structure, components, and reaction mechanisms are analyzed by SEM, XRD, mercury porosimetry, etc.. The pore distributions can be controlled by the concentrations of CMC and crosslinking agents. The intercalation effect on BN is carried out by CMC, which increases the specific surface area. Finally, the oil absorption performances are measured. The oil absorption capacity is up to 31.55 g/g (~97% ml/ml) because of the high specific surface area of the prepared material; additionally, the capacity of this material shows no obvious decrease after 6 cycles. Therefore, h-BN-based aerogels are expected to be applied in the oil absorption field and have the potential to be applied in the biochemical and nuclear fields.     

Synthesis and characterization of alternating copolymer from carbon dioxide and propylene oxide

High yield and pure zinc glutarate catalysts used for copolymerization of carbon dioxide and propylene oxide have been synthesized in different solvents by ultrasonic methodology. For the purposes of comparison, low‐yield zinc glutarates were also synthesized via mechanical stirring method with other synthetic conditions remaining unchanged. Fourier Transform Infrared Spectroscopy and wide‐angle X‐ray diffraction techniques confirmed the presence of high‐quality zinc glutarate catalysts. Accordingly, poly(propylene carbonate) (PPC) can be synthesized from carbon dioxide and propylene oxide using the zinc glutarate catalysts. It was confirmed that the as‐prepared PPC had an alternating copolymer structure together with high molecular weight. The thermal and mechanical properties of the obtained PPC copolymer were determined by means of differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and tensile test. DSC and TGA results showed that the PPC copolymer exhibited high glass transition temperature (39.39°C) and decomposition temperature (278°C) when compared to their corresponding values reported in the literature. Tensile test showed that the PPC film exhibited superior mechanical strength. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2327–2334, 2002     

Synthesis and optic properties of titanium dioxide nanostructures doped with alkali metals

The synthesis of nanotubes and faceted nanocrystals of titanium dioxide doped with alkali metals cations has been performed. It has been established that TiO₂ nanotubes with lengths of up to 100 nm and thicknesses of 50–500 nm obtained by solvothermal synthesis have an anatase structure in the direction of crystal growth. Faceted TiO₂ particles with sizes of 80–150 nm doped with Na and K cations (2–7 at % calculated to a yield of TiO₂ yield) preserve the anatase structure, whereas doping with Li induces the formation of a mixture of anatase and rutile. An analysis of the diffuse reflectance spectra showed that dopants had an insignificant effect on optic properties of TiO₂ nanoparticles. The high activity of these catalysts is explained by a decrease in the rate of recombination of charge carriers, rather than by the increase of their photo-generation yield.

     

Synthesis,characterization and evaluation of titanium carbonitride surface layers with varying concentrations of carbon and nitrogen

Titanium carbonitride (TiCN) surface layers were grown by direct exposure of Ti to a gas mixture of ammonia and methane at 1050 °C. TiC_xN_1?x coatings with varying C/N ratio were synthesized by appropriately changing the content of methane and ammonia in the reactive gas mixture. The resultant layers were subjected to various characterization and evaluation techniques to study the variation of properties with respect to change in C/N ratio. A systematic change in lattice parameter and microstructure was observed as a function of the composition of active gas mixture. Friction coefficient of TiC was found to be extremely low (0.078). Reaction mechanisms for the growth of TiN and TiC were found to be entirely different. The effect of composition of the gas mixture on growth kinetics of TiCN is elucidated.     

多元酸催化炭气凝胶的常压制备及表征

在多元有机酸催化和表面活性剂的作用下,间苯二酚和甲醛反应生成有机凝胶,经过常压干燥、高温炭化得到炭气凝胶。用扫描电镜(SEM)、X射线衍射(XRD)和亚甲基蓝吸附测试表征所制备的样品。结果表明,所制备的炭气凝胶属于非晶态物质,呈现均匀的球状结构,且微球内富含连通的电荷转移的孔道,其比表面积达到740m2/g。循环伏安扫描测试表明,所制备的炭气凝胶具有良好的电化学性能,有望成为超级电容器的电极材料。     

Synthesis and characterization of multiwalled carbon nanotubes-protoporphyrin IX composites using acid functionalized or nitrogen doped carbon nanotubes

In this research we describe the synthesis and characterization of composite materials based on multiwalled carbon nanotubes and protoporphyrin IX. We compare the results of using three types of carbon nanotubes: pristine (diameter < 10 nm), acid functionalized (diameter < 10 nm), and nitrogen doped carbon nanotubes (diameter ≈ 20 nm). Carbon nanotubes were mixed with protoporphyrin IX via two simple and straightforward methods using sonication, or heating-stirring. The characterization of the composites was done by Raman spectroscopy, field emission scanning electron microscopy, thermogravimetric analysis, ultraviolet-visible and fluorescence spectroscopy and infrared spectroscopy. A diversity of coatings of the nanotubes by protoporphyrin were obtained depending on the type of nanotube used or the method of synthesis. Some carbon nanotubes increased their diameter up to 40% after the reaction with protoporphyrin. Percentages by weight up to 20% of protoporphyrin were measured by thermogravimetric analysis. We obtained experimental evidences by different techniques of the electronic interaction and the formation of covalent bonds between both constituents, above all for the composites using nanotubes < 10 nm in diameter. Some of these evidences were ~ 98% of fluorescence quenching, reduction in the intensity of the absorption bands in ultraviolet visible spectroscopy, strong reduction in the intensity of some bands in Raman spectroscopy, red and blue shifts, as well as the presence of new absorption bands in infrared spectroscopy. Nitrogen doped carbon nanotubes showed low chemical reactivity to protoporphyrin IX, perhaps due to their lower acceptor character as they could have charge transfer from nitrogen dopants to the nanotube network, or because of their metallic character.     

Synthesis,purification and microstructural characterization of nickel doped carbon nanotubes for spintronic applications

The formation of nickel doped carbon nanotubes (Ni/CNTs), using the arc discharge method in open air deionized water is reported. The formation of Ni/CNTs was confirmed by Raman spectroscopy. Transmission Electron Microscopy (TEM) was used to examine the morphology of the system at different synthesis stages. Energy dispersion X-ray spectroscopy (EDX) was employed for elemental determination. According to the study, CNTs are self-assembled with the tangled carbonaceous system, with entanglement being overwhelming where metallic concentration is lower in the absence of acidic treatment.