Search results for "surface area"

Arrangements de cercles sur une sphère: Algorithmes et Applications aux modèles moléculaires representés par une union de boules

2008

Since the early work of Richard et al., geometric constructions havebeen paramount for the description of macromolecules and macro-molecularassemblies. In particular, Voronoï and related constructions have beenused to describe the packing properties of atoms, to compute molecularsurfaces, to find cavities. This thesis falls in this realm, andafter a brief introduction to protein structure, makes fourcontributions.First, using the sweep line paradigm of Bentley and Ottmann, wepresent the first effective algorithm able to construct the exactarrangement of circles on a sphere. Moreover, assuming the circlesstem from the intersection between spheres, we present a strategy to reportthe covering …

Irreversible modifications of the porous microstructure of soluble anhydrite β-CaSO4 induced by hydration-dehydration cycles

2006

26 pages; The internal surface area of hexagonal (soluble) primary anhydrite CaSO4 produced by dehydration of gypsum decreases by about 70 % when the anhydrite is successively subjected to rehydration and dehydration at room temperature in humid air and in vacuum respectively. In the rehydration step, the hemihydrate is formed; its dehydration yields secondary anhydrite. Additional hydration-dehydration cycles in the same conditions have a much smaller effect. The first cycle also brings about a modification of the t-plot, which reveals that the micropores of primary anhydrite are irreversibly healed. Mercury intrusion porosimetry shows that the primary dehydration of gypsum also generates …

Nitrogen Adsorption on Graphene Sponges Synthesized by Annealing a Mixture of Nickel and Carbon Powders

2017

The present research has been supported by the National Research Programme for 2014–2017 “Multifunctional Materials and Composites, Photonics and Nanotechnologies”.

Carbons from second generation biomass as sustainable supports for catalytic systems

2018

Abstract In this study activated carbons were produced from the wood of three different wood species (pine, birch, spruce). The resulting activated carbons were characterized in bulk for ash content, carbon content (elemental analyses), specific surface area, and pore size distribution, and at the surface by measuring the autogenerated pH and studying their structure by XPS. All the samples presented high surface areas and appeared to be mesoporous materials (mesopores >80%). The carbons were then used as support for AuPt nanoparticles and tested in the liquid phase oxidation of glycerol (GLY) and in the hydrogenation of levulinic acid (LA), two important chemicals from cellulose-based biom…

2021

Amino acids with small side chains and motifs of small residues in a distance of four are rather abundant in human single-span transmembrane helices. While interaction of such helices appears to be common, the role of the small residues in mediating and/or stabilizing transmembrane helix oligomers remains mostly elusive. Yet, the mere existence of (small)xxx(small) motifs in transmembrane helices is frequently used to model dimeric TM helix structures. The single transmembrane helix of the human carbonic anhydrases XII contains a large number of amino acids with small side chains, and critical involvement of these small amino acids in dimerization of the transmembrane domain has been sugges…

Hybrid methacrylate monolithic columns containing magnetic nanoparticles for capillary electrochromatography

2015

Abstract Vinylized iron oxide magnetic nanoparticles (VMNPs) were incorporated into polymethacrylate monolithic columns to develop novel stationary phases with enhanced separation performance. The VMNPs were dispersed in a polymerization mixture containing gycidyl methacrylate and ethylene glycol dimethacrylate as monomers, cyclohexanol and 1-dodecanol as porogens and azobisisobutyronitrile as initiator. The stability of the VMNPs in the polymerization mixture was investigated at several VMNP contents. Using short UV-polymerization times, polymeric beds with homogenously dispersed VMNPs were obtained. The novel stationary phases were characterized by scanning electron microscopy. The chroma…

Effect of polystyrene coating on pore, structural and chromatographic properties of silica packings

1990

Abstract A series of mesoporous and macroporous silicas with a mean pore diameter (PD), between 6 and 200 nm were reacted with a copolymer of styrene and vinyl-methyldiethoxysilane. The mass load of coated silicas corresponded to the monolayer capacity of the polymer calculated on the basis of the molecular cross-sectional area, except for the two mesoporous silcias of PD = 6 and 7.5 nm. Depending on the pore size, changes occurred in the specific surface area, as, between the native and the coated product. A comparison of the specific pore volume, νp, of silicas before and after polymer immobilization indicated a major loss of νp for the two mesoporous silicas whereas this effect was much …

A novel approach to polymer-template mesoporous molecular sieves

2000

A novel synthesis route was developed to produce spherical silica particles. The synthesis is based on a modified Stoeber method and the room-temperature synthesis of MCM 41S-materials applying tetraethoxysilane, alcohol, water, ammonia and homopolymers as template. The specific surface area, the specific pore volume and the average pore diameter were varied in the following ranges: 5 – 1,000 m2/g; 0.1 – 1.0 cm3/g and 2-50 nm. With respect to catalytic applications hetero-atoms e.g. Al were incorporated into the silica framework.

Synthesis of high-surface area CeO2 through silica xerogel template: influence of cerium salt precursor”;

2010

Abstract Ceria nanosized oxides with high surface area were synthesized by means of a templating approach, using a porous silica xerogel with surface area as high as 718 m2/g. After impregnation of the silica template with the cerium salt solution and further calcination at 600 °C, the final ceria oxide was recovered by dissolving the silica framework in NaOH solution. The effect of cerium counteranion, nitrate or chloride, on the textural and reduction properties of the ceria oxide was examined. Characterizations by BET and pore size distribution, XRD, TPR and SEM/EDX techniques were performed. The silica xerogel templated approach resulted in the preparation of ceria with surface area of …

Experimental design approach in the synthesis of molecularly imprinted polymers specific for iprodione fungicide

2015

International audience; An experimental design (ED) approach was applied to study the weight of three factors in the synthesis of a molecularly imprinted polymer (MIP) specific for iprodione fungicide. The objective was to obtain a high specific polymer with the best performance of iprodione binding. Thirteen iprodione-imprinted polymers and 13 non-imprinted polymers (NIP) were synthesized according to ED having 3 influencing factors: the polymerization method, the crosslinker nature and the functional monomer type. For each factor, two levels were studied: bulk and precipitation polymerization for the first factor, trimethylolpropane trimethacrylate (TRIM) and ethylene glycol dimethacrylat…