RESUMEN
A general bottom-up modeling strategy for gas sensor response to CO, O(2), H(2)O, and related mixtures exposure is demonstrated. In a first stage, we present first principles calculations that aimed at giving an unprecedented review of basic chemical mechanisms taking place at the sensor surface. Then, simulations of an operating gas sensor are performed via a mesoscopic model derived from calculated density functional theory data into a set of differential equations. Significant presence of catalytic oxidation reaction is highlighted.
RESUMEN
Full NMR characterization of ZnO nanoparticles (NPs) stabilized by various amines (hexadecylamine, dodecylamine, and octylamine) in C(7)D(8) demonstrated that the surface of this apparently simple system was very complex. Using different NMR spectroscopic techniques ((1)H, PGSE-NMR, diffusion-filtered (1)H NMR, NOESY, ROESY), we observed at least three different modes of interaction of the amines at the surface of the NPs, in thermodynamic equilibrium with the free amines, the relative populations of which varied with their concentration. The first mode corresponded to a strong interaction between a small amount of amine and the ZnO NPs (k(desorp)≈13 s(-1)). The second mode corresponded to a weak interaction between the amines and the surface of the ZnO NPs (k(off(2))≈50-60 s(-1)). The third, and weakest, mode of interaction corresponded to the formation of a second ligand shell by the amine around the NPs that was held together through van der Waals interactions (k(off(1))≈25×10(5) s(-1)). The second and third modes were in fast exchange on the NMR timescales with the free amines. The strongly interacting amines at the NPs surface (first mode) were in slow exchange with the other modes. A complex hydrogen-bonding network at the NPs surface was also observed, which did not only involve the coordinated amine but also THF and water molecules that remained from the synthesis.
RESUMEN
The self-organization in solution of ZnO nanocrystals into superlattices is monitored by dynamic light scattering. When long-alkyl-chain amines or carboxylic acids are used as stabilizing ligands, no organization is observed. In contrast, when binary mixtures of long-alkyl-chain amines and carboxylic acids are used, the presence of a thermodynamic equilibrium between free and organized ZnO nanoparticles is detected in THF or toluene. The superlattices of organized ZnO nanoparticles are independently observed by TEM and SEM. The coordination mode of the ligands at the surface of the ZnO nanoparticles is evidenced by NMR studies. The presence of ion-paired ammonium carboxylate surrounding the surface of ZnO nanoparticles appears to be a necessary requirement to govern this reversible organization. This is substantiated by the absence of organization of ZnO nanoparticles when either a solvent of high dielectric constant, such as acetone, or a strong hydrogen-bond acceptor is used.
RESUMEN
Spontaneous decomposition of [In(η5 -C5 H5 )] in the presence of poly(vinyl pyrrolidone) or trioctylphosphane oxide (TOPO) as a stabilizer gave monodisperse indium nanoparticles with a mean diameter of about 5-6 nm. In the case of TOPO, self-organization of the nanoparticles in two- and three-dimensional superlattices is observed.
Asunto(s)
Coloides/química , Nanopartículas del Metal/química , Nanopartículas/química , Óxidos/química , Óxido de Zinc/química , Ácidos Carboxílicos/química , Cristalización , Ligandos , Microscopía Electrónica de Rastreo , Microscopía Electrónica de Transmisión , Nanotecnología/instrumentación , Nanotecnología/métodos , Tamaño de la Partícula , SolventesRESUMEN
The reduction of [Pt(COD)(CH3)2] with CO in the presence of hexadecylamine (HDA) and oleic acid (OlAc) leads to amine carbonylation and formation of an air-stable colloidal solution of N,N'-bis(hexadecyl)urea-stabilized Pt(0) nanoparticles. These air-stable colloidal solutions can be used to form thin films of Pt nanoparticles on a silicon substrate.