A5044051503- Catalysis and Oxidation Reactions
- Catalytic Processes in Materials Science
- Metal-Organic Frameworks: Synthesis and Applications
- X-ray Diffraction in Crystallography
- Polyoxometalates: Synthesis and Applications
- Bone Tissue Engineering Materials
- Crystal Structures and Properties
- Chemical Synthesis and Characterization
- Crystallography and molecular interactions
- Oxidative Organic Chemistry Reactions
- Transition Metal Oxide Nanomaterials
- Zeolite Catalysis and Synthesis
- Mesoporous Materials and Catalysis
- Graph theory and applications
- Advanced NMR Techniques and Applications
- Catalysis and Hydrodesulfurization Studies
- Topological and Geometric Data Analysis
- History and advancements in chemistry
- X-ray Spectroscopy and Fluorescence Analysis
- Layered Double Hydroxides Synthesis and Applications
- Graph Theory and Algorithms
- Radioactive element chemistry and processing
- Digital Image Processing Techniques
- Vanadium and Halogenation Chemistry
- Dental Implant Techniques and Outcomes
Universidade Federal do Rio de Janeiro
2013-2023
Aix-Marseille Université
2009
Centro Brasileiro de Pesquisas Físicas
2009
Centre National de la Recherche Scientifique
1994-2009
Pontifical Catholic University of Rio de Janeiro
2007
Catalyse
1994
Military Institute of Engineering
1991-1992
Université de Technologie de Compiègne
1980
First-principles modeling combined with experimental methods were used to study hydroxyapatite in which Sr2+ is substituted for Ca2+. Detailed analyses of cation-oxygen bond distributions, cation-cation distances, and site 1-oxygen polyhedron twist angles made order provide an atomic-scale interpretation the observed structural modifications. Density functional theory periodic band-structure calculations indicate that Ca2+ substitution induces strong local distortion on lattice: nearest...
This communication briefly reviews why network topology is an important tool (for understanding, comparing, communicating, designing, and solving crystal structures from powder diffraction data) then discusses the terms of IUPAC project dealing with various aspects topology. One ambiguity in node assignment, this question addressed more detail. First, we define most approaches: "all node" deconstruction considering all branch points linkers, "single only components mixed, ToposPro "standard...
Characterization of lead substitution for calcium in hydroxyapatite (CaHA) is carried out, using experimental techniques and Density Functional theoretical (DFT) analyses. Theoretical modeling used to obtain information the Pb chemical environment occupancy at either Ca(I) or Ca(II) sites CaHA. Effects larger ionic radius Pb(+2) compared Ca(+2) are apparent embedded cluster calculations local bonding properties. DFT periodic planewave pseudopotential studies provide first-principles...
Gallium-modified ZSM5 zeolites, containing 2, 3, and 4 wt % Ga, were prepared by incipient wetness impregnation with gallium(III) nitrate solutions of HZSM5 samples SAR values 24 35. The modified zeolites subjected to two consecutive treatment cycles reduction in hydrogen reoxidation air. catalysts characterized nitrogen physical adsorption, 29Si 27Al MAS NMR, temperature-programmed reduction, desorption ammonia, X-ray absorption spectroscopy, infrared spectroscopy the OH stretching region...
Crystal-structure topologies, represented by periodic nets, are described labelled quotient graphs (or voltage graphs). Because the edge space of a finite graph is direct sum its cycle and co-cycle spaces, Euclidian representation derived net provided mapping basis spaces to set real vectors. The consistent if every mapped on own voltage. all outgoing edges at vertex may be chosen as generating space. embedding maps onto lattice L. By analogy, concept co-lattice L* defined image generators...
Right angle magnetron sputtering (RAMS) was used to produce hydroxyapatite (HA) film coatings on pure titanium substrates and oriented silicon wafer (Si(0 0 1)) with flat surfaces as well engineered having different forms. Analyses using synchrotron XRD, AFM, XPS, FTIR SEM EDS showed that as-sputtered thin consist of highly crystalline hydroxyapatite. The HA induced calcium phosphate precipitation when immersed in simulated body fluid, suggesting vivo bioactive behavior. In vitro...
The charge distribution (CHARDI) method is a self-consistent generalization of Pauling's concept bond strength which does not make use empirical parameters but exploits the experimental geometry coordination polyhedra building crystal structure. In two previous articles this series [Nespolo et al. (1999). Acta Cryst. B55, 902-916; Nespolo (2001). B57, 652-664], we have presented features and advantages approach its extension to distorted heterovalent hydrogen bonds. third article generalize...
Pyrite is a common sulfide mineral, which has arisen early interest by its euhedral shape and metallic glow similar to gold. However, it only in our century that we began understand pyrite crystal growth, considering the thermodynamic kinetic aspects of formation as function temperature concentration elements present medium. This article reports an analysis molecular mechanics 11 surfaces associated observed morphologies order explain growth natural synthesized minerals. The lowest surface...
Polycrystalline solid solutions of phosphate and vanadate calcium apatites were synthesized studied by XRD, XPS, 31P 51V NMR, FTIR UV spectroscopies. Homogeneous distributions vanadium within the surface obtained. While NMR spectra suggest an axial symmetry group, indicate distortion from essentially C3v in with low content to Cs for pure apatite, agreement site group hydroxyapatite. Refinements XRD pattern apatite Rietveld method confirm point attribution. Three oxygen bond lengths found...
A systematic study on cationic and anionic substitution in hydroxyapatite structures was carried out, with the aim of understanding impact ion exchange crystalline structure properties these materials. Lead vanadium were chosen for exchange, due to their known effects redox catalytic hydroxypatites. Hydroxyapatites variable Pb V contents, PbxCa10-x(VO4)y(PO4)6-y(OH)2 (x = 0, 2, 4, 6, 8 10 y 1; 0.5, 1, 3 6 x 10) synthesized characterized by NMR spectroscopy. Solid-state allowed an analysis...
In situ gallium K edge XAFS spectroscopy experiments were performed with GaZSM5 catalysts containing two different loadings (2 and 4%) under hydrogen or propane in the 703−823K temperature range. It was found that, irrespective of loading reducing gas, linear correlations between coordination numbers both first (Ga−O scattering legs) second (Ga−Ga spheres estimated from EXAFS degree reduction by XANES. The results showed that proceeds Ga3+ binuclear species 4-fold coordinated to oxygen an...
Substitution of cadmium into bulk hydroxyapatite Ca(10−x)Cdx(PO4)6(OH)2 (CdHA: x = 0.12, 1.3, 2.5) is studied by combining X-ray diffraction data from synchrotron radiation, Fourier transform infra-red spectroscopy (FTIR) and density functional theory (DFT) calculations. Energetic electronic analyses are carried out for several configurations Cd substitution Ca at both cationic sites. Rietveld analysis shows preferential occupation the Ca2 site cadmium. FTIR suggest a non-negligible covalent...
Local automorphisms in infinite graphs are defined as those for which the distance (in graph-theoretical sense) between any vertex and its image possesses an upper bound. Abelian subgroups of direction-preserving local without fixed point, so-called shift groups, used to determine quotient graph graphs. It is shown that group, closest topological analogue a translation group crystal structures, isomorphic C/C0 cycle space C by some subgroup C0, kernel. As main consequence, isomorphism class...
Alumina-supported zirconia catalysts, containing from 2.1 to 20.1 wt% ZrO2 and prepared by multiple incipient wetness impregnation using benzene solutions of zirconium acetylacetonate, were characterised the EXAFS technique. The results indicated that supported phase consists Zr4+ species do not have Zr as second neighbours, hexacoordinated oxide anions, suggesting these ions occupy octahedral positions in defective spinel structure γ-alumina support. In order test this hypothesis, an...