Marc Mamak

The synthesis, characterization and electrochemical behavior of the layered LiNi0.4Mn0.4Co0.2O2 compound

The mixed transition metal layered compound, LiNi0.4Mn0.4Co0.2O2, with the α-NaFeO2 layer structure has been synthesized and characterized. The optimum temperature of synthesis was found to be 800–900 °C. Rietveld refinement showed that cobalt suppresses transition metal ion migration into the Li sites whereas nickel promotes the migration. XPS analysis shows that the Co and about 20% of the Ni and Mn are in the 3+ oxidation state, while 80% of the Ni and Mn are in the 2+ and 4+ oxidation states, respectively. LiNi0.4Mn0.4Co0.2O2 shows Curie–Weiss paramagnetic behavior above 150 K, and the value of the Curie constant is consistent with the above oxidation states. In lithium electrochemical cells the composition LiNi0.4Mn0.4Co0.2O2 gave the highest reversible capacity among the studied compositions. It shows excellent rate capability, giving reversible capacities ranging from 180 to 155 mA h g−1 at current densities from 0.1 to 2.0 mA cm−2.

Pore architecture affects photocatalytic activity of periodic mesoporous nanocrystalline anatase thin films

We report the photocatalytic activity of periodic mesoporous nanocrystalline anatase thin films (denoted meso-nc-TiO2) using Methylene Blue (denoted MB) as a probe of pore architecture effects on reactivity. Specifically, 2D hexagonal and 3D cubic mesoporous nanocrystalline anatase thin films (denoted h-meso-nc-TiO2 and c-meso-nc-TiO2 respectively) annealed at different temperatures were investigated to reveal the effects of different pore architectures on the photocatalytic activity. The adsorption behavior of MB on the films annealed at the same temperature signaled that c-meso-nc-TiO2 has a larger accessible surface area but a lower adsorption surface affinity, compared to h-meso-nc-TiO2. In the case of the solid-state photodegradation of MB, the most efficacious photocatalyst was found to be c-meso-nc-TiO2 annealed at 450 °C. For MB in solution, a 400 °C annealed c-meso-nc-TiO2 was established to have the optimum photocatalytic activity among the samples investigated. The observed superior photocatalytic activity of c-meso-nc-TiO2 relative to both h-meso-nc-TiO2 and nc-TiO2 is believed to originate from the higher photoactivity of anatase nanocrystallites comprising the more open cubic framework. as well as geometrical advantages, such as a larger surface area and less obstructed 3D diffusion paths of guest molecules. It is concluded that the photocatalytic efficiency of periodic mesoporous nanocrystalline anatase thin films depends on the pore architecture.

Electroactive Mesoporous Yttria Stabilized Zirconia Containing Platinum or Nickel Oxide Nanoclusters: A New Class of Solid Oxide Fuel Cell Electrode Materials

The electroactivity of surfactant-templated mesoporous yttria stabilized zirconia, containing nanoclusters of platinum or nickel oxide, is explored by alternating current (AC) complex impedance spectroscopy. The observed oxygen ion and mixed oxygen ion–electron charge-transport behavior for these materials, compared to the sintered-densified non-porous crystalline versions, is ascribed to the unique integration of mesoporosity and nanocrystallinity within the binary and ternary solid solution microstructure. These attributes inspire interest in this new class of materials as candidates for the development of improved performance solid oxide fuel cell electrodes.

Thermal plasma synthesis of tungsten bronze nanoparticles for near infra-red absorption applications

A novel synthesis concept based on inductively coupled thermal plasma technology is presented for the continuous high throughput production of tungsten bronze nanoparticles with high purity and tunable composition. Tungsten bronzes in nanoparticle form are of renewed technical interest for use in applications such as IR curing of coatings and heat shielding filters since they exhibit a high extinction coefficient in the near IR region but with little impact on transparency or visible color.

Large scale production of high aspect ratio graphite nanoplatelets with tunable oxygen functionality

High aspect ratio graphite nanoplatelets with tunable oxygen functionality are prepared using a two-step scalable process consisting of expansion by thermal plasma processing followed by exfoliation with ultrasonic processing. The result of this process is graphite nanoplatelets in high yield with an average particle size distribution ranging from monolayer graphene up to 10 nm in thickness, 1 to 30 μm in length/width, and a tunable carbon to oxygen (C/O) ratio from 50 to 200 without requiring any special separation or isolation techniques such as sedimentation or centrifugation. It has been demonstrated for the first time that an intermediate level of oxygen functionalization improves the ability to exfoliate expanded graphite without having a detrimental effect on electrical conductivity.

Towards flexible inorganic ?mesomaterials?: one-pot low temperature synthesis of mesostructured nanocrystalline titaniaElectronic supplementary information (ESI) available: IR spectra and SEM image of mesoporous nanocrystalline titania. See http://www.rsc.org/suppdata/cc/b4/b403607g/

We hereby report a simple route for the low temperature synthesis of mesoporous nanocrystalline titania involving brief hydrothermal treatment of butanolic precursors and non-ionic tri-block-copolymer surfactant at 100 degrees C, followed by evaporation induced self assembly to make a crack-free flexible film. At no time in the film-forming process is a temperature of more than 120 degrees C reached, thereby permitting the use of substrates that are not stable to higher temperatures.

Practical solid oxide fuel cells with anodes derived from self-assembled mesoporous-NiO-YSZ

Solid oxide fuel cells comprised of an anode made from sintered and reduced mesoporous-NiO-YSZ are shown to provide stable current and power densities at the operating temperature of 800 degrees C and show better performance than cells with anode cermets made from mechanical mixtures of NiO and YSZ, attributable to the unique anode microstructure.

Making sense out of sulfated tin dioxide mesostructures

An in-depth investigation into the synthesis, characterization and sensor response of mesoporous SnO2 materials formed utilizing tin(IV) chloride, sodium dodecylsulfonate, and urea is described. The structures have been stabilized towards calcination by increasing the condensation of the tin oxide network utilizing urea as a slow-release base. PXRD, FT-Raman, N2 gas adsorption, thermal gravimetric analysis, and pyrolysis mass spectroscopy were used to monitor the two-step surfactant decomposition in which a sulfated tin oxide surface is formed followed by removal of the sulfate groups at elevated calcination temperatures. In situ a.c. impedance measurements of the materials in dry air and 2000 ppm carbon monoxide showed that the sensitivity of these materials towards carbon monoxide was inhibited by the presence of sulfate groups on the surface, whereas after the sulfate groups were removed the materials became much more sensitive towards carbon monoxide. These materials could find promising applications as gas-selective chemical sensors, super-acid catalysts, and anode materials for lithium battery applications.

NMe4V3O7: critical role of pH inhydrothermal synthesis of vanadium oxides

pH is critical in the formation of new mixed-valence vanadium oxides, NMe 4 V 3 O 7 , NMe 4 V 4 O 10 and the dioxide Li x V 2 O 4 ·H 2 O, with NMe 4 + cations or water molecules residing between vanadium oxide layers.

Evolution of nanocrystallinity in periodic mesoporous anatase thin films

Herein we report the first kinetic study of the intrachannel wall phase-transition of amorphous titania to nanocrystalline anatase for periodic mesoporous titania thin films, monitored by time-resolved in situ high-temperature X-ray diffraction. Structural transformations associated with the phase transition are further probed by high-resolution scanning electron microscopy and transmission electron microscopy. The model found to be most consistent with the kinetic data involves 1D diffusion-controlled growth of nanocrystalline anatase within the spatial confines of the channel walls of the mesostructure. The observation of anisotropic, rod-shaped anatase nanocrystals preferentially aligned along the channel axis implies that the framework of the liquid-crystal-templated mesostructure guides the crystal growth.