Adham R. Ramadan

Unique prokaryotic consortia in geochemically distinct sediments from Red Sea Atlantis II and discovery deep brine pools.

The seafloor is a unique environment, which allows insights into how geochemical processes affect the diversity of biological life. Among its diverse ecosystems are deep-sea brine pools - water bodies characterized by a unique combination of extreme conditions. The ‘polyextremophiles’ that constitute the microbial assemblage of these deep hot brines have not been comprehensively studied. We report a comparative taxonomic analysis of the prokaryotic communities of the sediments directly below the Red Sea brine pools, namely, Atlantis II, Discovery, Chain Deep, and an adjacent brine-influenced site. Analyses of sediment samples and high-throughput pyrosequencing of PCR-amplified environmental 16S ribosomal RNA genes (16S rDNA) revealed that one sulfur (S)-rich Atlantis II and one nitrogen (N)-rich Discovery Deep section contained distinct microbial populations that differed from those found in the other sediment samples examined. Proteobacteria, Actinobacteria, Cyanobacteria, Deferribacteres, and Euryarchaeota were the most abundant bacterial and archaeal phyla in both the S- and N-rich sections. Relative abundance-based hierarchical clustering of the 16S rDNA pyrotags assigned to major taxonomic groups allowed us to categorize the archaeal and bacterial communities into three major and distinct groups; group I was unique to the S-rich Atlantis II section (ATII-1), group II was characteristic for the N-rich Discovery sample (DD-1), and group III reflected the composition of the remaining sediments. Many of the groups detected in the S-rich Atlantis II section are likely to play a dominant role in the cycling of methane and sulfur due to their phylogenetic affiliations with bacteria and archaea involved in anaerobic methane oxidation and sulfate reduction.

Fabrication and Properties of Nylon-6/Layered Silicate Nanocomposites by Melt Blending

Polymer/clay nanocomposites currently attract immense interest from both research and industrial communities. By dispersing at the molecular level a tiny amount of clay within a polymeric matrix, a wide range of properties can be significantly improved. The efficiency of the clay (layered silicate) in improving the properties of the polymer materials is primarily determined by the degree of its dispersion in the polymer matrix. To promote the molecular and stable dispersion of the clay layers, the clays should be organically-modified with onium salts. In this work, nylon-6 nanocomposites based on two types of commercial organoclays were prepared by melt blending via single-screw extrusion. The good dispersion of clay in the nylon-6 nanocomposites was confirmed by X-ray diffraction and transmission electron microscopy. The influence of the dispersed nano-clay fillers on the thermal and mechanical properties of the resulting nanocomposites was characterized using thermogravimetric analysis and nanoindentation.Copyright

Surface and related studies in sulphated oxides of zirconium

Zirconium oxide superacids with different sulphate ion contents were prepared from Zr(SO4)2 using urea as precipitating agent. These oxides were subjected to different heating temperatures. Characterization was carried out by means of infrared spectroscopy, X-ray diffraction and nitrogen adsorption studies. The surface acidity was determined by the method described by Boehm [1]. Infrared results confirmed the presence of the sulphate ions and suggested the gradual lowering through heat-treatment of the symmetry of the sulphate ions by complex formation. Surface acidity was favored when the sulphate ions were in a bidentate state of ligation. The latter ligands seemed in turn to be stabilized by water. The strongest acidity was displayed in systems where a high concentration of bidentated sulphate ions was present in conjunction with high surface areas and micropore volumes.

Preparation and Characterization of Cobalt Aluminate Spinels CoAl2O4 Doped with Magnesium Oxide

Cobalt aluminate spinels were prepared from cobalt and aluminium nitrate solutions using sol–gel synthesis route by ammonium hydroxide precipitation. The gels were dried at 75°C, doped with different amounts of magnesium nitrate, and then calcined for 3 h at 650°C. Sample characterization was carried out by infrared spectroscopy, X-ray diffraction, scanning electron microscopy, nitrogen adsorption studies, thermogravimetry and by determining acid–base properties. This was carried out with the objective of elucidating the effect, if any, of the presence of the dopant on the spinel structure and properties. The spinel structure was clearly exhibited in all of the prepared samples which were predominantly mesoporous. None of the samples showed any acidic properties, i.e. they exhibited only basic properties. We found that doping with Mg resulted in a slightly increased disorder of cation distribution for those samples doped with higher amounts of Mg. Doping also led to a general increase in surface areas and the development of larger pores, as well as larger content of chemisorbed water.

Ion-Exchange and Adsorption Properties of Titania Gels Prepared from Titanous Chloride and Hydrogen Peroxide

A study was carried out of the uptake of Cu2+, Ni2+, Co2+ and Ca2+ cations by hydrous titanium oxides prepared at different pH values using titanous chloride as the starting material and hydrogen peroxide as the oxidizing agent. Characterization of the oxides was carried out by nitrogen adsorption and infrared studies. The oxides were found to be amphoteric in nature and exhibited an isoelectric point of 6.6. An attempt was made to elucidate the mechanism of cation uptake which does not entail a simple ion-exchange mechanism.

Sulphated Oxides of Titanium Prepared from Titanium Ethoxide: Surface and Related Properties

Titanium oxides, with moderately high surface areas exhibiting a mixed mesoporous/microporous texture, were prepared from titanium ethoxide. The porosity seemed to stem from the loss of volatile components from the inner coordination sphere of the titanium ions. After impregnation with sulphate groups, a general decrease in surface area was observed. This decrease was more drastic at higher temperatures when the sulphate ions are in a bidentate state of ligation. A high sulphate concentration led to a distinctive decrease in the total pore volume and to the loss of the microporous texture. Micropore blocking appeared to be due to the presence of the bidentate sulphate groups. The latter are responsible for the higher surface acidities displayed by the sulphated oxides.

Thermal stability of ion exchange and adsorption properties of titania gels prepared from titanous chloride and hydrogen peroxide

A comparative study of the uptake of the cations, Cu 2+ , Ni 2+ , Co 2+ and Ca 2+ by hydrous titanium oxides unheated and heat-treated at 400°C was carried out. The hydrous oxides were prepared at different pH values, using titanous chloride as starting material and hydrogen peroxide as oxidizing agent. Similarly to the unheated oxides, the heat-treated samples were found to be amphoteric in nature and exhibited an isolelectric point of ∼6.6. The total ion exchange capacity was found to generally decrease with heat treatment, so did the selectivity to a number of cations. Characterization of the samples by infrared and nitrogen adsorption studies were also carried out.