Search results for "surface area"
showing 10 items of 203 documents
Polymorphism, Metastable Species and Interconversion
2014
Abstract The natively unfolded peptide hormone glucagon forms fibrillar structures with amyloid properties. Here, we summarize past advances in glucagon fibrillation and combine them with recent new unpublished data to provide some more general conclusions on how glucagon fibrillation adapts to different physicochemical conditions such as high temperature, pressure, mechanical and chemical stress. Factors such as peptide concentration, accessible surface area, surface hydration of the glucagon molecular state, contact surface, temperature and ionic strength all contribute to fibrillar structure and stability. In addition to fundamental changes in secondary structure, glucagon fibril morphol…
Porous zirconia and titania as packing materials for high-performance liquid chromatography
1990
Abstract Porous amorphous zirconia (ZrO 2 ) and titania (TiO 2 ) packings were synthesized as rigid microparticulate beads by means of a sol—gel process. Sufficient rigidity and desired mesoporosity of the ZrO 2 and TiO 2 particles were achieved only by a gel hardening process, followed by heat treatment. The mean pore diameter, p d , the specific surface area, a s , and the specific pore volume, ν p , were controlled by the heat treatment. Typical values were p d = 8 nm, a s = 80 m 2 /g and ν p = 0.23 ml/g. ZrO 2 - and TiO 2 -based revesed-phase packings were prepared by subjecting the native materials to a specific activation process and reaction with octadecyltrimethoxysilane. Native ZrO…
Investigation of surface properties of lunar regolith: Part I
2007
This paper describes an initial investigation of the surface properties of three lunar soil samples from the Apollo 11, 12 and 16 missions, respectively. We report on density measurements using a helium pycnometer, adsorption isotherms of krypton applied for the determination of specific surface area of the samples and gravimetric measurement of the isotherms of water, heptane and octane. Electron-microscopic photographs are described and discussed.
Supported H3PW12O40 for 2-propanol (photo-assisted) catalytic dehydration in gas-solid regime: The role of the support and of the pseudo-liquid phase…
2016
Abstract Catalytic and photocatalytic 2-propanol dehydration was carried out by using a supported Keggin heteropolyacid H3PW12O40 (PW12). Binary materials were prepared by impregnation and/or solvothermal treatment by using commercial supports: SiO2 (Mallinckrodt), TiO2 (Evonik P25) and multiwall carbon nanotubes (Sunnano) or home solvothermically prepared SiO2 and TiO2. All the materials have been characterized by X-ray diffraction (XRD), scanning electron microscopy observations (SEM) coupled with EDX microanalysis, specific surface area measurements, diffuse reflectance spectroscopy (DRS), FTIR and Raman spectroscopy. (Photo)catalytic 2-propanol dehydration was studied in gas-solid regim…
A new microporous 12-ring zincosilicate THK-2 with many terminal silanols characterized by automated electron diffraction tomography.
2020
A newly synthesized microporous zincosilicate THK-2 (estimated structural composition: |(H2O)6.7(C6H13N)0.9|[Li0.5Zn3.1Si32O62.7(OH)9.3]) was characterized by single-crystal electron diffraction using the automated electron diffraction tomography (ADT) approach in combination with powder X-ray diffraction. The lattice constants and space group of as-synthesized THK-2 were a = 2.50377(7) nm, b = 1.43866(4) nm, c = 0.505369(8) nm, and Pccn (no. 56) with orthorhombic symmetry. Because the crystal lattice was almost identical to a hexagonal lattice (), the first several peaks in its powder X-ray diffraction data severely overlapped, which suppressed the structural information to decide the fram…
Photo-assisted degradation of 2-propanol in gas–solid regime by using TiO2 impregnated with heteropolyacid H3PW12O40
2009
Abstract Commercial and home prepared TiO2 samples impregnated with tungstophosphoric acid (H3PW12O40) were used for the photo-assisted degradation of 2-propanol in gas–solid regime. The characterization results evidenced a good coverage of the polyoxometalate (POM) onto the surface of TiO2 along with a marginal effect of the presence of the POM on the specific surface area, morphology and cristallinity of the samples. Propene was the main intermediate product revealed in 2-propanol photocatalytic degradation by using as photocatalysts the samples containing the POM, whereas propanone was mainly obtained when the photocatalysts was bare TiO2, both commercial or home prepared. Acetaldehyde w…
Effect of biochar on the physical and structural properties of a sandy soil
2019
Abstract Biochar application to soil can be considered as a means to improve soil quality, thereby optimizing irrigation management and reducing irrigation needs, especially in dryland regions. This paper is aimed at investigating the effect of biochar (BC) on a desert sandy soil (Al Foah, United Arab Emirates) in terms of bulk density, porosity, water retention, plant available water (AWmax), aggregate stability (AS) and specific surface area (BET-SSA). BC was produced from forest biomass (Italy). Soil water retention was measured by the High Energy Moisture Characteristic (HEMC) and by pressure plate measurements, by using BC fractions equal to 0 (soil only), 0.014, 0.091, 0.23, 0.33 and …
Effects of pyrolysis conditions on the porous structure development of date pits activated carbon
2012
International audience; Activated carbons were prepared from biomass of Algerian date pits for developing efficient and cheap adsorbents in the aim to remove heavy metals from waste water. Carbon adsorbents were obtained following two successive treatments: pyrolysis under dry nitrogen flow and physical activation under wet nitrogen flow. Pyrolysis process was optimized by varying some operating parameters such as temperature, nitrogen flow, heating rate and pyrolysis hold time in order to determine their effects on the porous structure development of date pits activated carbon. Chars obtained from pyrolysis process were activated with the same operating conditions (activation temperature o…
Some factors affecting the removal of lead(II) ions from aqueous solution by porous hydroxyapatite: relationships between surface and adsorption prop…
2006
A porous hydroxyapatite (p-HAp) was prepared and employed for the removal of lead(II) ions at different concentrations from aqueous solution to determine the adsorption properties of p-HAp and compare them with those of a commercial hydroxyapatite (CAp) sample. The kinetic data obtained indicated that the adsorption performances of the adsorbents depended both on their specific surface area and crystallinity. Complexation of the Pb(II) ion on the adsorbent surface favoured the dissolution of hydroxyapatites characterized by a Ca/Pb molar ratio in the 0.85–1.5 range. The maximum adsorption capacity of p-Hap for Pb(II) ions at 30 ± 2°C was 2.30 mmol/g relative to 1.38 mmol/g for the commercia…
La1-xSrxCo1-yFeyO3-delta perovskites: Preparation, characterization and solar photocatalytic activity
2015
Abstract LaCoO3 perovskites substituted by Sr at the A site and/or by Fe at the B site have been prepared by the citrate method. Characterizations by several techniques, such as specific surface area (BET method), XRD, TPR, SEM, UV–vis in DRS mode, XPS and TGA analyses, have been performed. The so prepared La1−xSrxCo1−yFeyO3−δ perovskites are semiconductor materials showing band gap energy values from 1.9 to 3.2 eV. They displayed solar photocatalytic activity for the 2-propanol degradation in gas–solid regime. The photocatalytic results suggest that the perovskites containing Fe are less active and the activity decreases by increasing the Fe content, however the presence of iron avoids the…