Development of composite adsorbents of carbon and intercalated clay for N2 and O2 adsorption: A preliminary study

Composite adsorbents of carbon and alumina intercalated montmorillonite were prepared and characterized by adsorption of N-2 and O-2 at various temperatures. The effects of pyrolysis, temperature, heating rate, subsequent degassing, and doping of cations and anions were investigated. The adsorption capacities of the composite adsorbents developed at higher temperatures (0 and -79 degrees C) are found to be larger than those of normal alumina pillared clays. The experimental results showed that the framework of these adsorbents is made of alumina particles and clay sheets while the pyrolyzed carbon distributes in the space of interlayers and interpillars. The pores between the carbon particles, clay sheets, and alumina pillars are very narrow with very strong adsorption forces, leading to enhanced adsorption capacities at 0 and -79 degrees C. The composite adsorbents exhibit features similar to those of carbonaceous adsorbents. Their pore structures, adsorption capacities, and selectivities to oxygen can be tailored by a controlled degassing procedure. Meanwhile, ions can be doped into the adsorbents to modify their adsorption properties, as usually observed for oxide adsorbents like zeolite and pillared clays. Such flexibility in pore structure tailoring is a potential advantage of the composite adsorbents developed for their adsorption and separation applications. (C) 1999 Academic Press.

Catalytic conversion to N2O to N2 over potassium catalyst supported on activated carbon

Catalytic conversion of N2O to N-2 With potassium catalysts supported on activated carbon (K/AC) was investigated. Potassium proves to be much more active and stable than either copper or cobalt because potassium possesses strong abilities both for N2O chemisorption and oxygen transfer. Potassium redispersion is found to play a critical role in influencing the catalyst stability. A detailed study of the reaction mechanism was conducted based upon three different catalyst loadings. It was found that during temperature-programmed reaction (TPR), the negative oxygen balance at low temperatures (< 50 degrees C) is due to the oxidation of the external surface of potassium oxide particles, while the bulk oxidation accounts for the oxygen accumulation at higher temperatures (below ca. 270 degrees C). N2O is beneficial for the removal of carbon-oxygen complexes because of the formation of CO2 instead of CO and because of its role in making the chemisorption of produced CO2 on potassium oxide particles less stable. A conceptual three-zone model was proposed to clarify the reaction mechanism over K/AC catalysts. CO2 chemisorption at 250 degrees C proves to be an effective measurement of potassium dispersion. (C) 1999 Academic Press.

The role of carbon surface chemistry in N2O conversion to N2 over Ni catalyst supported on activated carbon

The effect of acidic treatments on N2O reduction over Ni catalysts supported on activated carbon was systematically studied. The catalysts were characterized by N-2 adsorption, mass titration, temperature-programmed desorption (TPD), and X-ray photoelectron spectrometry (XPS). It is found that surface chemistry plays an important role in N2O-carbon reaction catalyzed by Ni catalyst. HNO3 treatment produces more active acidic surface groups such as carboxyl and lactone, resulting in a more uniform catalyst dispersion and higher catalytic activity. However, HCl treatment decreases active acidic groups and increases the inactive groups, playing an opposite role in the catalyst dispersion and catalytic activity. A thorough discussion of the mechanism of the N2O catalytic reduction is made based upon results from isothermal reactions, temperature-programmed reactions (TPR) and characterization of catalysts. The effect of acidic treatment on pore structure is also discussed. (C) 1999 Elsevier Science B.V. All rights reserved.

Effect of salinity on growth, pigmentation, N2 fixation and alkaline phosphatase activity of cultured Trichodesmium sp

Trichodesmium sp. isolated from the Great Barrier Reef lagoon was cultured in artificial seawater media containing a range of salinities. Trichodesmium sp. actively grew over a wide range of salinities (22 to 43 psu) and hence can be classed as euryhaline. Maximum growth occurred with salinities in the range 33 to 37 psu. Chl a content and alkaline phosphatase activity were found to increase with salinity over the range 22 to 43 psu, but the N-2 fixation rate was reduced at salinities below and above the range for maximum growth. Growth in media exhibiting maximum growth was characterised by well-dispersed cultures of filaments, while significant aggregations of filaments formed in other media. It is proposed that the tendency for Trichodesmium filaments to aggregate in media with salinities outside the range for maximum growth is an opportunistic response to a deficiency of cellular nitrogen, which results from the reduced N-2 fixation rates, and the aggregation occurs in order to enhance the uptake of combined N released within the aggregates and/or the N-2 fixation within the aggregates.

Factors affecting N2 fixation by the cyanobacterium Trichodesmium sp. GBRTRLI101

Various factors affecting N-2 fixation of a cultured strain of Trichodesmium sp. (GBRTRLI101) from the Great Barrier Reef Lagoon were investigated. The diurnal pattern of N2 fixation demonstrated that it was primarily light-induced although fixation continued to occur for at least 1 h in the dark in samples that had been actively fixing N-2. N-2 fixation was dependent on the light intensity and stimulated more by white light when compared with blue, green, yellow and red light whereas rates of N-2 fixation decreased most under red light. Inorganic phosphorous concentrations in the lower range of treatments up to 1.2 muM significantly stimulated N-2 fixation and further additions promoted little or no increase in N-2 fixation. Organic phosphorous (Na-glycerophosphate) also stimulated N-2 fixation rates. Added combined nitrogen (NH4+, NO3-, urea) of 10 muM did not inhibit N-2 fixation in short-term studies (first generation), however it was depressed in the long-term studies (fifth generation). (C) 2003 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.

Preparation and characterization of copper catalysts supported on mesoporous Al2O3 nanofibers for N2O reduction to N2

A series of mesoporous Al2O3 samples with different porous structures and phases were prepared and used as supports for Cu/Al2O3 catalysts. These catalysts were characterized by N-2 adsorption, NMR, TGA, XRD, and UV - vis spectroscopic techniques and tested for the catalytic reaction of N2O decomposition. The activity increased with the increasing calcination temperatures of supports from 450 to 900 degreesC; however, a further increase in calcination temperature up to 1200 degreesC resulted in a significant reduction in activity. Characterization revealed that the calcination temperatures of supports influenced the porous structures and phases of the supports, which in turn affected the dispersions, phases, and activities of the impregnated copper catalyst. The different roles of surface spinel, bulk CuAl2O4, and bulk CuO is clarified for N2O catalytic decomposition. Two mechanism schemes were thus proposed to account for the varying activities of different catalysts.

In vitro characterization of lamotrigine N2-glucuronidation and the lamotrigine-valproic acid interaction

Studies were performed to investigate the UDP-glucuronosyltransferase enzyme( s) responsible for the human liver microsomal N2-glucuronidation of the anticonvulsant drug lamotrigine ( LTG) and the mechanistic basis for the LTG-valproic acid ( VPA) interaction in vivo. LTG N2-glucuronidation by microsomes from five livers exhibited atypical kinetics, best described by a model comprising the expressions for the Hill ( 1869 +/- 1286 mu M, n = 0.65 +/- 0.16) and Michaelis-Menten ( Km 2234 +/- 774 mu M) equations. The UGT1A4 inhibitor hecogenin abolished the Michaelis-Menten component, without affecting the Hill component. LTG N2-glucuronidation by recombinant UGT1A4 exhibited Michaelis-Menten kinetics, with a K-m of 1558 mu M. Although recombinant UGT2B7 exhibited only low activity toward LTG, inhibition by zidovudine and fluconazole and activation by bovine serum albumin ( BSA) ( 2%) strongly suggested that this enzyme was responsible for the Hill component of microsomal LTG N2-glucuronidation. VPA ( 10 mM) abolished the Hill component of microsomal LTG N2-glucuronidation, without affecting the Michaelis-Menten component or UGT1A4-catalyzed LTG metabolism. K-i values for inhibition of the Hill component of LTG N2-glucuronidation by VPA were 2465 +/- 370 mu M and 387 +/- 12 mu M in the absence and presence, respectively, of BSA ( 2%). Consistent with published data for the effect of fluconazole on zidovudine glucuronidation by human liver microsomal UGT2B7, the Ki value generated in the presence of BSA predicted the magnitude of the LTG-VPA interaction reported in vivo. These data indicate that UGT2B7 and UGT1A4 are responsible for the Hill and Michaelis-Menten components, respectively, of microsomal LTG N2-glucuronidation, and the LTG-VPA interaction in vivo arises from inhibition of UGT2B7.

Hydrothermal Stability of Modified Silica Membranes for Gas Separation

A new class of hybrid molecular sieve silica (MSS) membranes is developed and tested against standard and organic templated membranes. The hybrid membrane is synthesized by the standard sol-gel process, integrating a template (methyltriethoxysilane - MTES) and a C6 surfactant (triethylhexylammonium bromide) into the silica film matrix. After hydro treatment under a relative humidity of 96% for 50h, the hybrid membrane shows no changes in its gas separation capabilities or energy of mobility. The structural characteristics and integrity of the hybrid membrane are retained due to a high concentration of organophilic functional groups and alkoxides observed using 29 Si NMR. In contrast, the structural integrity of the membranes prepared with non-templated films deteriorated during the hydro treatment due to a large percentage of silanol groups (Si-OH) which react with water. The hybrid membranes underwent a decrease in the H2/CO2 selectivity of only 1% whereas for the non-templated membrane a 21% decrease was observed. The transport mechanism of the hybrid membranes is activated as permeation increased with temperature. The activation energy for the permeation of H2 is positive while negative for CO2. The H2 permeation obtained was 3x 10 -8 mol.m -2 .s -1 .Pa -1 and permselectivities for H2/CO2 and H2/N2 varied between 1-7 and 31-34, respectively.

Effect of Mn deficiency and legume inoculation on rhizosphere pH in highly alkaline soils

Although plant growth is often limited at high pH, little is known about root-induced changes in the rhizospheres of plants growing in alkaline soils. The effect of Mn deficiency in Rhodes grass (Chloris gayana cv. Pioneer) and of legume inoculation in lucerne (Medicago sativa L. cv. Hunter River), on the rhizosphere pH of plants grown in highly alkaline bauxite residue was investigated. Rhizosphere pH was measured quantitatively, with a micro pH electrode, and qualitatively, with an agar/pH indicator solution. Manganese deficiency in Rhodes grass increased root-induced acidification of the rhizosphere in a soil profile in which N was supplied entirely as NO3-. Rhizosphere pH in the Mn deficient plants was up to 1.22 pH units lower than that of the bulk soil, while only 0.90 to 0.62 pH units lower in plants supplied with adequate Mn. When soil N was supplied entirely as NO3-, rhizosphere acidification was more efficient in inoculated lucerne (1.75 pH unit decrease) than in non-inoculated lucerne (1.16 pH unit decrease). This difference in capacity to lower rhizosphere pH is attributable to the ability of the inoculated lucerne to fix atmospheric N2 rather than relying on the soil N (NO3 ) reserves as the non-inoculated plants. Rhizosphere acidification in both Rhodes grass and lucerne was greatest in the meristematic root zone and least in the maturation root zone.

Determination of Ralstonia (Pseudomonas) solanacearum rDNA subgroups by PCR tests

Rapid and sensitive polymerase chain reaction (PCR) methods ape described for determination of the two 16 S rDNA subgroups of Ralstonia solanacearum, the causal agent of bacterial wilt. A third subgroup consisting of Indonesian R. solanacearum isolates belonging to Division II, the blood disease bacterium and Pseudomonas syzygii can also be identified. Primers were designed to sequences within R, solanacearum 16 S rDNA (equivalent to Escherichia coli 16 S rDNA positions 74-97, 455-475, 1454-1474), and the internal transcribed spacer region between the 16 S and 23 S rDNA genes. Different combinations of forward and reverse primers allowed selective PCR amplification of (a) R. solanacearum Division I (biovars 3, 4 and 5), (b) Division TI (biovars 1, N2, and 2) including the blood disease bacterium and P. syzygii, or (c) amplification of Division II only except for five biovar 1, 2 or N2 isolates of R. solanacearum from Indonesia, P. syzygii and the BDB. A total of 104 R. solanacearum, 14 blood disease bacterium and 10 P. syzygii isolates were tested. Simultaneous detection of species and subdivision was achieved by designing a multiplex PCR test in which a 288-base pair (bp) band is produced by all R. solanacearum isolates, and an additional 409-bp band in Division I strains.

Self-defocusing effects in an ethanol solution of chlorophyll

The thermally induced optical nonlinearity in a chlorophyll ethanol solution is examined. A theory is presented which shows good agreement with experiment. The theory models an optically thick but physically thin medium whose only heat transport mechanism is conduction. An average nz was found for the medium which corresponds well with previous results but the thermal medium is shown to be fundamentally different from a Kerr medium.