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An electron paramagnetic resonance (EPR) study has been carried out on the hybrid layered nanocomposite formed by TiO2 and myristic acid. The samples were characterized by means of X-ray diffractio...

Raman and NMR spectroscopies have long been employed in pursuing quantitative relationships between polymerization of silicate glasses and melts. However, varying assumptions and ambiguities have often meant structural models vary significantly depending on the probe used. This study investigates a 40BaO·60SiO2 glass to determine its polymerization using static and MAS 29Si NMR, and Raman spectroscopies to construct a coherent structural interpretation. The challenges and advantages of each technique are discussed as the structural model of 40BaO­60SiO2 glass required partial evidence derived from each of these spectroscopies. The Raman scattering cross sections for Q2 and Q3 were found to be 0.85 and 1.22, respectively. The Qn distribution was shown to be 3, 35, 57, 6% (±4%) for Q1 to Q4, respectively. This distribution yields a polymerization consistent with the stoichiometry, Ba0.66SiO2.66, having a O:Si ratio of 2.66. The agreement between all Qn distributions, the stoichiometry, the polymerization, and equilibria strongly indicate that this structural interpretation is robust.

The desire to harness solar energy to address current global environmental problems led us to investigate two-dimensional (2D) core–shell hybrid photocatalysts in the form of a 2D-TiO2–surfactant, mainly composed of fatty acids. The bulk products, prepared by two slightly different methods, consist of stacked host–guest hybrid sheets held together by van der Waals forces between alkyl carboxylate moieties, favoring the synergistic conjugation of the photophysical properties of the core and the hydrophobicity of the self-assembled surfactant monolayer of the shell. X-ray diffraction and the vibrational characteristics of the products revealed the influence of synthesis strategies on two types of supramolecular aggregates that differ in the core chemical structure, guest conformers of alkyl surfactant tails and type, and the bilayer and monolayer of the structure of nanocomposites. The singular ability of the TiO2 core to anchor carboxylate leads to commensurate hybrids, in contrast to both layered clay and layered double-hydroxide-based ion exchangers which have been previously reported, making them potentially interesting for modeling the role of fatty acids and lipids in bio-systems. The optical properties and photocatalytic activity of the products, mainly in composites with smaller bandgap semiconductors, are qualitatively similar to those of nanostructured TiO2 but improve their photoresponse due to bandgap shifts and the extreme aspect-ratio characteristics of two-dimensional TiO2 confinement. These results could be seen as a proof-of-concept of the potential of these materials to create custom-designed 2D-TiO2–surfactant supramolecular photocatalysts.

This paper presents a new mixed valence heptavanadate (NH4)2V7O16, obtained from a two-stage treatment in a single container of ammonium metavanadate with hexadecylamine in an acetic medium. The hydrolysis of the precursor under normal conditions leads to an intermediate, layered hybrid nanocomposite, V2O5/alkylamine, which after an in situ hydrothermal treatment is transformed almost quantitatively into an amine-free microcrystalline phase constituted by perfect square microparticles of (NH4)2V7O16. The analysis of composition, structure and morphology of the product points to a mixed valence vanadium oxide with a high content of V(IV) (approximately 73%). The microsquares have a tetragonal structure similar to that of BaV7O16, as well as to those proposed for the VOx/amine hybrid nanocomposite series: nanotubes, nano urchins and the compound (en)V7O16. The results suggest that all these phases belong to the V7O16 family, but that they differ in the amine content, the degree of reduction and the curvature of the network. The feasibility of obtaining flat nanostructures based on V7O16 without templates, beyond demonstrating the robustness of the structural unit V7O16 in networks with different degrees of reduction and curvatures, clarifies the role of alkylamines in this type of anti-entropic supramolecular process. First, the amine provides a stable platform that allows for an orderly reduction of the network under hydrothermal conditions and, when the medium favours the stability of the V–amine bond, the alkylamine contributes to the driving force that leads to the curving of the V–O network., This work was supported by the Universidad de Chile, Universidad Tecnológica Metropolitana, FONDECYT 1171803, Fund of Scientific and Technological Equipment, 2018, L318-03 UTEM, CMST Spanish MINECO projects PHENTOM (FIS2015-70862-P) and Severo Ochoa (SEV-2013-0295) and the CERCA Programme/Generalitat de Catalunya and Conicyt-Programa Fondequip SEM EQM (150101).

Reinforcing steel imported into Colombia from various countries, which does not meet the requirements of local building codes, hinders the compliance with the life safety limit state intended by the local building code. The results of a statistical analysis of the tensile mechanical properties that characterize the stress-strain curves of steel bars marketed in Bogota are presented and discussed. The experimental program was planned to provide statistics of the main mechanical properties of grade 60 steel bars with bar diameter ranging from 9.5 mm to 25.4 mm subjected to monotonic tension loading. The study comprises 85 monotonic tensile tests and 85 bending tests, including five specimens per diameter for each of three manufacturing companies evaluated. The measured results are compared with those reported by different studies conducted previously in Colombia, Mexico, Canada and the US. Characteristic graphical stress-strain curves are proposed for each diameter studied. These curves, along with the statistics reported for each bar diameter can be used for future analytical studies on the structural performance and reliability of reinforced concrete structures in central Colombia.

Dense microspheres consisting of poorly crystalline ReS 2 embedded in carbon were synthesized with a high yield via a facile one-pot solvothermal route, by reacting dirhenium decacarbonyl, elemental sulfur and an aromatic solvent (benzene, toluene or p-xylene) for 24 h at 180 °C. X-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray spectroscopy (EDS), Raman spectroscopy, and Fourier transform infrared spectroscopy (FT-IR) techniques were used to characterize the samples. The resulting microspheres were dense, with average diameters between 0.79 and 1.40 μm, had smooth surfaces and were constructed of ReS 2 sheet-like structures with 4.5–9.8 wt % of structural amorphous carbon, which is retained as a textural stabilizer after calcination at 800 °C. The synthesis was repeated using isopropanol and cyclohexane, whose products were agglomerated grains and botryoidal quasi-spherical particles, respectively. A possible formation mechanism of ReS 2 /C microspheres was preliminarily presented, in order to clarify the mechanistic differences between the rhenium carbonyl and other transition metal carbonyls used in similar syntheses.

Sulfides of molybdenum and rhenium poorly crystalline were prepared by solvothermal oxidative decarbonylation of the respective metal carbonyls with sulfur using p-xylene as solvent. The same reaction, but in presence of hexadecylamine (HDA), was used for preparing the nanocomposites MoS2/HDA and ReS2/HDA. The products were analyzed by X-ray diffraction analysis, scanning electron microscopy, atomic force microscopy, and Fourier-transform infrared spectroscopy. The products, MoS2 and ReS2, are structurally similar but morphologically different: small undefined particles (150–300 nm) and well-defined, almost perfect microspheres (0.4–2.8 μm), respectively. Preparations containing HDA lead to the corresponding layered nanocomposites. MoS2/HDA is a dark solid easily separable from the reaction mixture, while ReS2/HDA remains as a suspension in p-xylene, from which it is obtained by evaporating the solvent under vacuum. Both are layered species with basal spacing of 33.8 A (Mo) and 30.4 A (Re), respectively. ...

A novel hybrid nanocomposite constituted of single TiO nanosheets sandwiched between stearic acid self-assembled monolayers was synthesized and tested in the photodegradation of methylene blue under sunlight. The product showed better photocatalytic performance than anatase under similar conditions, which may be further improved through sensitization with cadmium sulfide., The authors acknowledge the Universidad Tecnologica Metropolitana, Universidad de Chile, FONDECT Grants 1151189 and 1131112, and CONICYT Grant FB0807 (CEDENNA).

The deposition of hybrid organic-inorganic nanocomposites of titanium dioxide--prepared by hydrolysis of titanium tretraisopropoxide modified through exchanging one of its ligands with a butinoxy-, octiloxy- or phenoxy-group--on a gold surface modified by a monolayer of decanethiol was studied using a Quartz Crystal Microbalance. The depositions, performed from a suspension in alcohol of the nanocomposites, consisting in titanium oxide bilayers hydrophobically functionalized, occurs by a spontaneous process 'layer by layer.' However the amount of deposited mass in a layer as well as the rates of deposition depend on the degree of aggregation of the nanocomposite in the suspension which is in turn determined by nature of the organic ligands.

Both low-dimensional bar-coded metal oxide layers, which exhibit molecular hinging, and free-standing organic nanostructures can be obtained from unique nanofibers of vanadium oxide (VO(x)). The nanofibers are successfully synthesized by a simple chemical route using an ethanolic solution of vanadium pentoxide xerogel and dodecanethiol resulting in a double bilayered laminar turbostratic structure. The formation of vanadium oxide nanofibers is observed after hydrothermal treatment of the thiol-intercalated xerogel, resulting in typical lengths in the range 2-6 microm and widths of about 50-500 nm. We observe concomitant hinging of the flexible nanofiber lamina at periodic hinge points in the final product on both the nanoscale and molecular level. Bar-coded nanofibers comprise alternating segments of organic-inorganic (thiols-VO(x)) material and are amenable to segmented, localized metal nanoparticle docking. Under certain conditions free-standing bilayered organic nanostructures are realized.

We have investigated the properties of films from polymer complexes obtained by the reaction of chitosan with poly(aminoproylethoxysiloxane) which are known to be constituted by molecularly compatibilized microdomains of the components. Specifically, we studied the influence that both, the acetylation degree the donor-acceptor activity of chitosan in the precursor solutions, have on the composition, thermal stability and morphology of the products. Comparison of the behaviour of two chitosans of similar molecular weight but different origin and acetylation degree, 12% and 17% respectively, shows that the latter is an important factor in stabilising the formation of chitosan aggregates in its solutions and films, thus making less efficient the formation of strong chitosan/polysiloxane interfaces. Dissolution of chitosan by microwave radiation improves polymer dissociation, thus increasing its donor-acceptor activity. That however also results, in this case, to disfavours strong hetero-polymer interfaces du...

Metal nanoparticles have attracted great interest particularly because of the size dependence of physical and chemical properties and its enormous technological potential. Although most pioneering advancements refers to gold and silver, more recently there is growing interest in nanoparticles of copper, mostly due to its relatively low cost, which could allow the use of these small metal objects in large-scale nanotechnology applications, for example, antiseptics materials and metallic inks. However, the manufacture of copper nanoparticles stable in air with controlled size and shape has been a major challenge because of the relatively high reactivity of this element. Great efforts in getting the basic knowledge and synthesis know-how has gone into finding better ways to produce particles protected against oxidation and selfaggregation under normal conditions. In this review article, we briefly discuss a number of selected papers and recent patents on procedures and other issues related to the fabrication of copper nanoparticles.

The effect of the neutral surfactant dodecylamine and octadecylamine on the synthesis of TiO2-based nanostructures by the treatment of anatase with NaOH under hydrothermal conditions in the temperature range 120-150 °C and different reaction times was investigated. The products analyzed by electron microscopy, X-ray diffraction, FT-IR and elemental analysis contains—depending of the amine, the temperature and the duration of the hydrothermal treatment—spherical and tubular species containing the acid H2Ti3O7. The formation of morphologically almost pure phases constituted by nanospheres and nanotubes were obtained at 130 °C after about 30 and 50 h respectively. Using dodecylamine, structurally fragile tubular amine containing nanocomposites are obtained, while in the case of the octadecylamine, notoriously stable purely inorganic nanotubes are formed. The role of the amine in these reactions is discussed.

The deposition of hybrid organic-inorganic nanocomposites of titanium dioxide--prepared by hydrolysis of titanium tretraisopropoxide modified through exchanging one of its ligands with a butinoxy-, octiloxy- or phenoxy-group--on a gold surface modified by a monolayer of decanethiol was studied using a Quartz Crystal Microbalance. The depositions, performed from a suspension in alcohol of the nanocomposites, consisting in titanium oxide bilayers hydrophobically functionalized, occurs by a spontaneous process 'layer by layer.' However the amount of deposited mass in a layer as well as the rates of deposition depend on the degree of aggregation of the nanocomposite in the suspension which is in turn determined by nature of the organic ligands.

Measurements of 1H and 13C Nuclear Magnetic Resonance (NMR) for the nanocomposite materials formed by the intercalation of hexadecylamine (HDA) in metal oxides (TiO2, V2O5 and MoO3), are reported. The 1H NMR spin-lattice relaxation in the rotating frame was described by using the spectral density due to Davidson and Cole, which incorporates a distribution of correlation times characterized by a width parameter ϵ. The fitting of the data was obtained for ϵ = 0.74, indicating that the correlation times are distributed over a narrow range in this system. High-resolution 13C NMR techniques were used to resolve the NMR lines of middle-chain methylene groups in the spectra and variable contact time cross-polarization {1H-}13C experiments were employed to analyze the reorientation dynamics of the CH3 and CH2 groups in the HDA chains.

Measurements of 1H and 13C Nuclear Magnetic Resonance (NMR) for the nanocomposite materials formed by the intercalation of hexadecylamine (HAD) in metal oxides (TiO2, V2O5, CrO3 and MoO3), are reported. The 1H NMR relaxation results reflects the complexity of the chain segments motions in these systems. The proton (and the carbon) mobility depends on the position in the HDA hydrocarbon chain to the restriction imposed by the anchoring of the head group. The nonexponential behavior of the proton magnetization is clearly a result of the anisotropic motion of the HDA chains. For most of the protons, the rate of motion is not fast enough to fulfill the condition for the nuclear spin-lattice relaxation (NSR) maximum in the laboratory frame but they fulfill the condition for the NSR in the rotating frame. The maximum at around 280 K reflects the relative lower mobility of the protons of the HDA chain inside the low-dimensional space of the metal oxide. The description of the segmental motion of long ch...