Surface characterization of acidic ceria-zirconia prepared by direct sulfation

Acidic ceria-zirconia (SCZ) solid acid catalysts with a nominal surface density of ca 2 SO₄²⁻/nm² were prepared by a simple route consisting in soaking high specific surface area Ce_xZr_1−xO₂ (with x = 0.21 and 0.69) mixed oxides solutions in 0.5 M sulphuric acid. Characterizations by TPD-MS, TP-DRIFTS and FT-Raman revealed that most of surface structures generated by sulfation are stable at least up to 700 °C under inert atmosphere and consist mainly as isolated sulfates located on defects or crystal planes and to a lesser extent as polysulfates. Investigations by pyridine adsorption/desorption have stated that: SCZ possess both strong Brønsted (B) and Lewis (L) acid sites, some of them being presumably superacidic; the B/L site ratio was found to be more dependent on the temperature and hydration degree than on the composition of the ceria-zirconia. By contrast, the reactivity of the parent Ce_xZr_1−xO₂ materials towards pyridine is mostly driven by redox properties resulting in the formation of Py-oxide with the participation of Lewis acid sites of moderate strength (cus Ce^x+ and Zr^x+ cations). Basicity studies by CO₂ adsorption/desorption reveal that SCZ surfaces are solely acidic whereas the number and strength of Lewis basic sites increases with the Ce content for the parent Ce_xZr_1−xO₂ materials.     

Crystal structure and physical properties of the quaternary manganese-bearing pavonite homologue Mn1.34Sn6.66Bi8Se20

The quaternary manganese tin bismuth selenide, Mn_1.34Sn_6.66Bi₈Se₂₀ was synthesized by combining constituent elements at 723 K. Single crystal structure determination revealed that Mn_1.34Sn_6.66Bi₈Se₂₀ is isostructural to the mineral pavonite, AgBi₃S₅, crystallizing in the monoclinic space group C2/m (#12) with a=13.648(3) Å; b=4.175(1) Å; c=17.463(4) Å; β=93.42(3)°. In the structure, two kinds of layered modules, denoted A and B, alternate along [0 0 1]. Module A consists of paired chains of face-sharing monocapped trigonal prisms (around Bi/Sn) separated by a single chain of edge-sharing octahedra (around Mn/Sn). Module B represents a NaCl-type fragment of edge-sharing [(Bi/Sn)Se₆] octahedra. Mn_1.34Sn_6.66Bi₈Se₂₀ is an n-type narrow gap semiconductor with E_g∼0.29 eV. At 300 K, thermopower, electrical conductivity and lattice thermal conductivity values are −123 μV/K, 47 S/cm and 0.6 W/m K, respectively. Mn_1.34Sn_6.66Bi₈Se₂₀ is paramagnetic at high temperatures and undergoes antiferromagnetic transition at T_N=10 K.     

The production of carbon nanotubes from carbon dioxide: challenges and opportunities

Recent advances in the production of carbon nanotubes (CNTs) are reviewed with an emphasis on the use of carbon dioxide (CO2) as a sole source of carbon. Compared to the most widely used carbon precursors such as graphite, methane, acetylene, ethanol, ethylene, and coal-derived hydrocarbons, CO2 is competitively cheaper with relatively high carbon yield content. However, CNT synthesis from CO2 is a newly emerging technology, and hence it needs to be explored further. A theoretical and analytical comparison of the currently existing CNT-CO2 synthesis techniques is given including a review of some of the process parameters (i.e., temperature, pressure, catalyst, etc.) that affect the CO2 reduction rate. Such analysis indicates that there is still a fundamental need to further explore the following aspects so as to realize the full potential of CO2 based CNT technology: (1) the CNT-CO2 synthesis and formation mechanism, (2) catalytic effects of transitional metals and mechanisms, (3) utilization of metallocenes in the CNT-CO2 reactions, (4) applicability of ferrite-organometallic compounds in the CNT-CO2 synthesis reactions, and (5) the effects of process parameters such as temperature, etc.     

Laser Micropatterning of Polylactide Microspheres into Neuronal-Glial Coculture for the Study of Axonal Regeneration

250,000 Americans suffer from spinal cord injury caused by vehicular, work, and sports related accidents^[1]. After injury to the spinal cord, axons do not have the capability of regenerating across the lesioned site. To understand the mechanisms of axon regeneration and to identify a better method of regeneration, a new technique for mimicking and studying the in vivo cellular environment is needed. To meet this goal, we have developed a laser cell micropatterning system that uses a weakly focused laser beam to pattern both biological cells and nonbiological particles for the study of various cell-cell-polymer interactions. Using this system, we have successfully copatterned neurons, glial cells, and polymer microspheres into a viable matrix. These copatterns allow us to study the effects nerve growth factor has, when released from a degradable polymer microsphere, on a single neuron within a specific arrangement of multiple cell types.