Nanostructured TiO2-based mixed metal oxides prepared using microemulsions for carbon monoxide detection

Nanostructured powders of Nb-doped TiO₂ (TN) and SnO₂ mixed with Nb-doped TiO₂ in two different atomic ratios—10 to 1 (TSN 101) and 1 to 1 (TSN 11)—were synthesized using the reverse micelle microemulsion of a nonionic surfactant (brine solution/1-hexanol/Triton X-100/cyclohexane). The powders were characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). Thick films were fabricated for gas sensors and characterized by XRD analysis and field emission scanning electron microscopy (FE-SEM). The effects of the film morphology and firing temperature in the range 650–850 °C on CO sensitivity were studied. The best gas response, expressed as the ratio between the resistance in air and the resistance under gas exposure (R _air/R _gas), was measured for TSN 11 at 11 for 1,000 ppm CO exposure. All types of sensors showed good thermal stability. The electrochemical impedance spectroscopy (EIS) measurements were performed in different gas atmospheres (air, O₂, CO and NO₂) to better understand the electrical properties of the nanostructured mixed metal oxides.     

Recent Progress of Counter Electrodes in Nanocrystalline Dye-sensitized Solar Cells

Dye-sensitized solar cell （DSC） consists a combination of several different materials： photoanodes with nanoparticulated semiconductors, sensitizers, electrolytes and counter electrodes （CEs）. Each materials performs specific task for the conversion of solar energy into electricity. The main function of CE is to transfer electrons to the redox electrolyte and regenerate iodide ion. The work of CE is mainly focused on the studies of the kinetic performance and stability of the traditional CEs to improve the overall efficiency of DSC, seeking novel design concepts or new materials. In this review, the development and research progress of different CE materials and their electrochemical performance, and the problems are discussed.     

Catalytic chemical vapor deposition of carbon nanotubes using Ni-La-O precursors

Carbon nanotubes (CNT) are synthesized by catalytic chemical vapor deposition with different compositions of Ni-La-O catalyst precursors obtained by citric acid complexometry. Only two compounds: LaNiO₃ (perovskite-type crystal structure, hexagonal system) and La₂NiO₄ (spinel-type crystal structure, orthorhombic system) in the obtained Ni-La-O catalyst precursors have the ability to grow CNT. Moreover, CNT obtained with the two different crystal structure catalyst precursors have different characteristics: different yield, pattern and oxidation resistance performance.     

Preparation and properties of alumina-magnesia precast block for ladle lining

An alumina-magnesia precast block was prepared by using high-alumina fused corundum as aggregate, and fused magnesia, ultra-fine Al₂O₃ and SiO₂ powders as matrix materials. A small linear expansion for the precast block was achieved through spinel formation from the reaction of MgO with Al₂O₃ in the matrix. The precast block showed a lower apparent porosity, higher modulus of rupture and better slag corrosion resistance compared to the traditional Al₂O₃-MgO-C brick. In addition, the practical application of the precast block to the ladle lining proved it to possess a better thermal insulation which could effectively prevent the temperature drop of molten steel during the refining process. It can be considered that the alumina-magnesia precast block could possibly be applied as a new type of ladle lining material for the production of low-carbon and ultra-low-carbon steel.     

Synthesis of binary and triple carbon nanotubes over Ni/Cu/Al2O3 catalyst by chemical vapor deposition

Novel binary and triple carbon nanotubes (CNTs) with one common catalytic particle encapsulated have been synthesized using Ni/Cu/Al₂O₃ catalyst, which was produced by a sol-gel method. But when using Ni/Al₂O₃ as catalyst, a mass of common CNTs, that is, one CNT with one catalytic particle encapsulated, was obtained. The results showed that copper-element doping to the Ni/Al₂O₃ catalyst played a key role in the synthesis of CNTs, signifying a novel approach to modify the Ni/Al₂O₃ catalyst. Based on the transmission electron microscopy observations, a simple growth mechanism was developed to describe the growth of the binary or triple CNTs, which could be well explained by a diffusion segregation process.     

Growth of calcium carbonate on non-covalently modified carbon nanotubes

The crystallization of calcium carbonate was investigated on pristine and non-covalently modified carbon nanotubes (CNTs) using the vapor diffusion technique in a calcium chloride solution. Non-covalent modification was accomplished by treating the carbon nanostructures with the amphiphilic copolymer poly(isoprene-b-acrylic acid). Calcium carbonate crystals grown on the surface and in the interstitial channels of CNT buckypapers were observed in both cases. Scanning electron microscopy analysis of the untreated CNTs showed the characteristic rhombohedral morphology of calcite crystals, while in the case of modified material spherical and ellipsoidal crystals, consisted of nanocrystallites, were observed. X-ray diffraction analysis showed the presence of calcite crystals in both cases.     

A perspective on the optimisation of hard carbon and related coatings for engineering applications

Hard carbon coatings hold the key to improved performance for many types of products. However the achievement of these improvements requires the selection of the appropriate type of carbon coating and therefore the correct process and appropriate deposition parameters. The huge range of properties achievable in carbon coatings is mainly due to the ability of carbon to form different types of interatomic bonds, to take up different sites, and to adopt different structures. In addition to intrinsic material properties, other factors must also be considered for each application, such as the adhesion level achievable and coating cost. This complex situation explains why the number of applications for hard carbon films is still more limited than originally expected. Despite the considerable progress achieved during the last decade in hard coating technologies, practical results often appear conflicting, with differences in properties occurring even within the same types of coatings. Furthermore, the many different deposition systems and processes which have been developed introduce further complications in regard to (for example) achievable coating uniformity and deposition rates. Thus, there is often confusion in the use of certain fundamental principles, especially regarding the growth mechanisms and the effects which produce more dense homogeneous and stable coating materials. This is especially true for the improved properties of tetrahedral amorphous carbon films, which are different from previously reported diamond-like carbon materials, and can be created by adapting and improving existing industrial processes, to offer advantages compared to earlier coatings, and hence possibilities for important new applications. This paper discusses issues relating to intrinsic material properties, and practical aspects such as adhesion, to provide a framework for the development, selection and use of hard carbon coatings in practical situations.     

Electronic nature of vanadium nitride-carbon cluster composite materials obtained by the calcination of oxovanadylphthalocyanine

Calcination of oxovanadylphthalocyanine at 500-1000 °C under an argon atmosphere was performed. Elemental analyses, XRD and TEM measurements revealed that the calcined materials are composed of nano-sized vanadium nitride and carbon clusters. ESR spectral examinations suggested that the calcined materials have a photo-responsive charge separation feature. The decomposition of methylene blue and trimethylhydroquinone in the presence of the material calcined at 900 °C was accelerated by visible light irradiation. H₂ evolution was detected from a mixture of the calcined material and water under the visible light irradiation.     

High-aligned carbon nanotube film with netlike bulges

High-aligned carbon nanotubes film with netlike bulges made of catalyst particles has been synthesized on a silica wafer by pyrolyzing ferrocene/melamine mixtures. The structure and composition of carbon nanotubes are investigated by scanning electron microscopy, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and electron energy-loss spectroscopy (EELS). It is found that these nanotubes have uniform outer diameters of about 25 nm and lengths of about 40 μm. High-resolution TEM images show that each carbon nanotube is composed of graphite-like layers arranged in a stacked-cup-like structure. XPS spectrum shows that the crust covering the tops of the aligned carbon nanotube film consists of carbon, iron and ferric oxide. The EELS spectrum shows that these nanotubes are pure-carbon tubes. The formation mechanism of the netlike bulges has been provided.     

Fabrication of dye sensitized solar cell using TiO2 coated carbon nanotubes

We fabricated a dye sensitized solar cells (DSCs) using TiO₂ coated multi-wall carbon nanotubes (TiO₂-CNTs). Carbon nanotubes (CNTs) have excellent electrical conductivity and good chemical stability. We introduced CNTs in DSCs to improve solar cell performance through reduction of series resistance. TiO₂-CNTs were obtained by Sol-Gel method. Compared with a conventional TiO₂ cell, the TiO₂-CNTs content (0.1 wt.%) cell showed ∼ 50% increase in conversion efficiency, which is attributed to the increase in short circuit current density (J_sc). The enhancement in J_sc occurs due to improvement in interconnectivity between the TiO₂ particles and the TiO₂-CNTs in the porous TiO₂ film.