Structure of extremely nanosized and confined In-O species in ordered porous materials

Perturbed-angular correlation, x-ray absorption, and small-angle x-ray scattering spectroscopies were suitably combined to elucidate the local structure of highly diluted and dispersed InOₓ species confined in the porousof the ZSM5 zeolite. This novel approach allow us to determined the structure of extremely nanosized In-O species exchanged inside the 10-atom-ring channel of the zeolite, and to quantify the amount of In₂O₃ crystallites deposited onto the external zeolite surface.Facultad de Ciencias Exacta

Nanoespecies de Co depositadas en silicatos mesoporosos MCM-41 altamente ordenados como prometedores materiales para novedosas aplicaciones: caracterización superficial

Silicatos Co/MCM-41 se sintetizaron por el método de impregnación húmeda. La naturaleza de las especies de Co fue inferida por DRX, TEM, XPS, XANES y medidas de ZFC/FC. La presencia de óxidos de Co (clusters y nanopartículas de Co3O4) dentro de los canales fue evidenciada por TEM, XPS y XANES. La relación Co/Si superficial (XPS) fue notablemente menor que la correspondiente relación Co/Si bulk (ICP), dando otra evidencia de la presencia del Co en los canales de la matriz. Por TEM y DRX se observaron nanopartículas de Co3O4 de pequeño tamaño segregadas en la superficie externa de los sólidos con altas cargas de metal. Las curvas de ZFC y FC para la muestra Co/M(2,5) permitieron asignar su comportamiento superparamagnético a la presencia de clusters y nanopartículas de Co3O4 que crecen en el interior de los mesoporos de la estructura MCM-41. Los análisis presentados indican que el sólido con propiedades estructurales y magnéticas optimizadas resultaría un material interesante para utilizarse en el campo de la liberación controlada de fármacos.Co-modified MCM-41 molecular sieves were synthesized by wet impregnation method. The nature and location of the different Co species were inferred by XRD, TEM, XPS, XANES and ZFC/FC. The presence of Co oxide species (clusters and Co3O4 nanoparticles) inside the channels could be evidenced by TEM, XPS and XANES. The surface Co/Si atomic ratios (XPS) were notably lowers than the corresponding bulk Co/Si ratios (ICP), indicating that the Co atoms are mostly incorporated inside the mesopore channels of the matrix. Nevertheless, by TEM and XRD, Co3O4 nanoparticles of small size segregated on the external surface were observed for the higher metal loadings. The ZFC and FC curves for the Co/M(2.5) sample allowed to assign its superparamagnetic behavior to the presence of clusters and Co3O4 nanoparticles of very small size that grow inside the MCM-41 mesopores. The analyses presented in this work indicate that the sample with improved structural and magnetic properties would result an attractive porous solid for drug hosting, to be applied in the field of the controlled release of medicaments.Instituto de Física La Plat

Sunlight active g-C3N4-based Mn+ (M[dbnd]Cu, Ni, Zn, Mn) – promoted catalysts: Sharing of nitrogen atoms as a door for optimizing photo-activity

In this work we analyze the photocatalytic performance of Mn+ (M[dbnd]Cu, Ni, Zn, Mn) - g-C3N4 materials in toluene photo-oxidation under UV and Sunlight-type illumination conditions. The characterization of the solids showed that Cu and Mn containing samples have an oxide type environment, while Ni has a hydroxide type and Zn shows an oxynitride type local order. The photo-activity of the samples under UV and sunlight excitation(s) was evaluated in terms of activity and selectivity, and the subsequent calculation of the quantum efficiency. Optimum activity was obtained with the Zn-containing catalyst. The charge carrier(s) handling and fate through interfaces and recombination was measured and correlated with the structural characterization of the solids. This indicates that the interface contact between the Zn oxynitride and carbon nitride components has significant influence in charge carrier processes and it is at the core of the good photocatalytic properties owned by this sample.Fil: Muñoz Batista, Mario J.. Universidad de Granada; España. Consejo Superior de Investigaciones Científicas; España. Instituto de Catálisis y Petroleoquímica; EspañaFil: Andrini, Leandro Ruben. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Requejo, Félix G.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Gómez Cerezo, Maria N.. Consejo Superior de Investigaciones Científicas; España. Instituto de Catálisis y Petroleoquímica; EspañaFil: Fernández García, Marcos. Consejo Superior de Investigaciones Científicas; España. Instituto de Catálisis y Petroleoquímica; EspañaFil: Kubacka, Anna. Consejo Superior de Investigaciones Científicas; España. Instituto de Catálisis y Petroleoquímica; Españ

Outstanding nobility observed in Cu5 clusters reveals the key role of collective quantum effects

21 pags., 5 figs.Subnanometer-sized metal clusters often feature a molecule-like electronic structure, which makes their physical and chemical properties significantly different from those of nanoparticles and bulk material. Considering potential applications, there is a major concern about their thermal stability and susceptibility towards oxidation. Cu clusters of only 5 atoms (Cu5 clusters) are first synthesized in high concentration using a new-generation wet chemical method. Next, it is shown that, contrary to what is currently assumed, Cu5 clusters display nobility, beyond resistance to irreversible oxidation, at a broad range of temperatures and oxygen pressures. The outstanding nobility arises from an unusual reversible oxidation which is observed by in situ X-ray Absorption Spectroscopy and X-ray Photoelectron Spectroscopy on Cu5 clusters deposited onto highly oriented pyrolitic graphite at different oxygen pressures and up to 773 K. This atypical property is explained by a theoretical approach combining different state-of-the-art first principles theories. It reveals the essential role of collective quantum effects in the physical mechanism responsible for the nobility of Cu5 clusters, encompassing a structural ‘breathing’ through concerted Cu–Cu elongations/contractions upon O2 uptake/release, and collective charge transfer as well. A predictive phase diagram of their reversible oxidation states is also delivered, agreeing with the experimental observations. The collective quantum effects responsible of the observed nobility are expected to be general in subanometer-sized metal clusters, pushing this new generation of materials to an upper level.This work has been partly supported by the European Union’s Horizon 2020 Research and Innovation Programme un-der Grant Agreement No. 825999; the Spanish Agencia Estatal de Investigación (AEI) and the Fondo Europeo de Desarrollo Regional (FEDER, UE) under Grant No. MAT2016-75354-P; the Austrian Science Fund (FWF) under Grant P29893-N36; the CMST COST Action CM1405 “Molecules in Motion” (MOLIM); the Xunta de Galicia, Spain (Grupos Ref. Comp.ED431C 2017/22 and AEMAT ED431E 2018/08); Obra Social Fundación La Caixa: Ref.LCF/PR/PR12/11070003; ANPCyT PICT (2017-1220 and 2017-3944) and UNLP (Project11/X790), Argentina.N