A convenient synthesis of highly luminescent lanthanide 1D-zigzag coordination chains based only on 4,4′-bipyridine as connector

The coordination polymers View the MathML source·C7H8 (Ln = Eu, β-dik = dbm, tta, hfac; Ln = Tb; β-dik = dbm; Hdbm = dibenzoylmethane, Htta = thenoyltrifluoroacetone, Hhfac: hexafluoroacetylacetone) were easily assembled in mild conditions and high yields starting from the anhydrous lanthanide β-diketonates as nodes and 4,4′-bipyridine (bpy) as connector. X-ray single crystal studies have shown zigzag extended chains where lanthanide centres are 8-coordinated in a distorted square-antiprismatic geometry. Photoluminescence studies show bright red europium emission and spectral features dependent on the topology of the polymeric chains

An easily recoverable and recyclable homogeneous polyester-based Pd catalytic system for the hydrogenation of α,β-unsaturated carbonyl compounds

Homogeneous catalysis is an efficient tool to carry out hydrogenation processes but the major drawback is represented by the separation of the expensive catalyst from the product mixture. In this view we prepared a polyester-based Pd catalytic system that offers the advantages of both homogenous and heterogeneous catalyses: efficacy, selectivity and recyclability. Here its application in the hydrogenation of selected alpha,beta-unsaturated carbonyl compounds is described

Oxide-oxide galvanic displacement reactions: Effect of the concentration of the ions released by the sacrificial oxide

Abstract Galvanic displacement reactions between a solid oxide and a dissolved metal cation are interesting processes for the preparation of oxide nanoparticles or electrocatalytic layers consisting of secondary mixed oxides. Their mechanism is not yet fully clarified. The composition of the secondary mixed oxides and their growth rate depend on many physical and chemical variables. In the present study, we have focused on the effects of the concentration of the ions released from the sacrificial oxide to the solution, when they are intentionally added to reaction media. We have studied the displacement of sacrificial PbO2 by either Mn2+ or Co2+ cations in acetate solution that contained variable concentrations of Pb2+, using electrochemical methods, SEM-EDS and XPS. The evolution of the open circuit potential of the systems was monitored during the reactions. We have found that, for both divalent cations, increasing concentrations of Pb2+ ions in the acetate solutions caused the formation of mixed oxides richer in Pb. Effects on growth rate and equilibrium potential were different for Mn2+ and Co2+

New insights into the dynamics that control the activity of ceria-zirconia solid solutions in thermochemical water splitting cycles

The reactivity of a ceria-rich Ce0.85Zr0.15O2 solid solution toward the thermochemical water splitting process (TWS) was studied over repeated H2/H2O redox cycles. The structural and surface modifications after treatment at high temperature under air or N2 atmospheres were characterized by high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and positron annihilation lifetime spectroscopy (PALS). Samples treated under nitrogen resulted more active due to phase segregation with formation of a zirconyl oxynitride phase in catalytic amount. Insertion of N3- into the structure contributes to an increase in the numbers of oxygen vacancies that preferably arrange in large clusters, and to the stabilization of Ce3+ centers on the surface. In comparison, treatment under air resulted in a different arrangement of defects with less Ce3+ and smaller and more numerous vacancy clusters. This affects charge transfer and H-coupling processes, which play an important role in boosting the rate of H2 production. The behavior is found to be only slightly dependent on the starting ceria-zirconia composition, and it is related to the development of a similar surface heterostructure configuration, characterized by the presence of at least a ceria-rich solid solution and a (cerium-doped) zirconyl oxynitride phase, which is supposed to act as a promoter for TWS reaction. The above findings confirm the importance of a multiphase structure in the design of ceria-zirconia oxides for water splitting reaction and allow a step forward to find an optimal composition. Moreover, the results indicate that doping with nitrogen might be a novel approach for the design of robust, thermally resistant, and redox active materials.Postprint (author's final draft

Copper single-atoms embedded in 2D graphitic carbon nitride for the CO2 reduction

AbstractWe report the study of two-dimensional graphitic carbon nitride (GCN) functionalized with copper single atoms as a catalyst for the reduction of CO2 (CO2RR). The correct GCN structure, as well as the adsorption sites and the coordination of the Cu atoms, was carefully determined by combining experimental techniques, such as X-ray diffraction, transmission electron microscopy, X-ray absorption, and X-ray photoemission spectroscopy, with DFT theoretical calculations. The CO2RR products in KHCO3 and phosphate buffer solutions were determined by rotating ring disk electrode measurements and confirmed by 1H-NMR and gas chromatography. Formate was the only liquid product obtained in bicarbonate solution, whereas only hydrogen was obtained in phosphate solution. Finally, we demonstrated that GCN is a promising substrate able to stabilize metal atoms, since the characterization of the Cu-GCN system after the electrochemical work did not show the aggregation of the copper atoms

Hydrodechlorination of Aroclor 1260 in aqueous two-phase mixture catalyzed by biogenerated bimetallic catalysts

The PCBs are known recalcitrant and toxic pollutants and significant values of contamination could be found in water. PCBs can be hydrodechlorinated using Pd-based catalysts and hydrogen, but the research to identify more efficient heterogeneous catalysts, able to work in an aqueous phase, less sensible to deactivation and easily removable at the end of the treatment, remains a considerable interesting goal. A strain of Klebsiella oxytoca, DSM 29614, known to produce a specific exopolysaccaride (EPS), was grown in different media with sodium citrate or with sodium citrate plus ferric citrate, as sole energy and carbon sources under anaerobic conditions. The cultures were amended with 50 mg of palladium as Pd(NO3)2 to generate Pd-EPS (Pd content 13%) or FePd-EPS (Pd content 8.4%; Fe 7.4%) species which were secreted from the cells, isolated by treatment with a cold ethanol solution (70%) and dried under vacuum as powders. The catalytic ability of these mono- and bi-metallic species was tested in the hydrodechlorination reaction of the Aroclor 1260 PCBs mixture under aqueous biphasic conditions. Here we demonstrate that the degree of PCBs hydrodechlorination is dependent by the nature of catalyst and of base used to neutralize HCl produced, the bimetallic species being more active and an organic base resulting more effective. Working with a substrate/catalyst 8/1 molar ratio, at 3 MPa H2 and 60°C in 20 h a significant removal of highly chl orinated PCBs was obtained under the best conditions. The result seems promising for remediation of groundwater contaminated with PCBs

An easily recoverable and recyclable homogeneous polyester-based Pd catalytic system for the hydrogenation of alpha,beta-unsaturated carbonyl compounds

Abstract Homogeneous catalysis is an efficient tool to carry out hydrogenation processes but the major drawback is represented by the separation of the expensive catalyst from the product mixture. In this view we prepared a polyester-based Pd catalytic system that offers the advantages of both homogenous and heterogeneous catalyses: efficacy, selectivity and recyclability. Here its application in the hydrogenation of selected α,β-unsaturated carbonyl compounds is described.Homogeneous catalysis is an efficient tool to carry out hydrogenation processes but the major drawback is represented by the separation of the expensive catalyst from the product mixture. In this view we prepared a polyester-based Pd catalytic system that offers the advantages of both homogenous and heterogeneous catalyses: efficacy, selectivity and recyclability. Here its application in the hydrogenation of selected alpha,beta-unsaturated carbonyl compounds is described. (C) 2015 Elsevier B.V. All rights reserved

Origin of the unusual ground-state spin S = 9 in a Cr10 single-molecule magnet

The molecular wheel [Cr10(OMe)20(O2CCMe3)10], abbreviated {Cr10}, with an unusual intermediate total spin S = 9 and non-negligible cluster anisotropy, D/kB = −0.045(2) K, is a rare case among wheels based on an even number of 3d-metals, which usually present an antiferromagnetic (AF) ground state (S = 0). Herein, we unveil the origin of such a behavior. Angular magnetometry measurements performed on a single crystal confirmed the axial anisotropic behavior of {Cr10}. For powder samples, the temperature dependence of the susceptibility plotted as χT(T) showed an overall ferromagnetic (FM) behavior down to 1.8 K, whereas the magnetization curve M(H) did not saturate at the expected 30 μB/fu for 10 FM coupled 3/2 spin Cr3+ ions, but to a much lower value, corresponding to S = 9. In addition, the X-ray magnetic circular dichroism (XMCD) measured at high magnetic field (170 kOe) and 7.5 K showed the polarization of the cluster moment up to 23 μB/fu. The magnetic results can be rationalized within a model, including the cluster anisotropy, in which the {Cr10} wheel is formed by two semiwheels, each with four Cr3+ spins FM coupled (JFM/kB = 2.0 K), separated by two Cr3+ ions AF coupled asymmetrically (J23/kB = J78/kB = −2.0 K; J34/kB = J89/kB = −0.25 K). Inelastic neutron scattering and heat capacity allowed us to confirm this model leading to the S = 9 ground state and first excited S = 8. Single-molecule magnet behavior with an activation energy of U/kB = 4.0(5) K in the absence of applied field was observed through ac susceptibility measurements down to 0.1 K. The intriguing magnetic behavior of {Cr10} arises from the detailed asymmetry in the molecule interactions produced by small-angle distortions in the angles of the Cr–O–Cr alkoxy bridges coupling the Cr3+ ions, as demonstrated by ab initio and density functional theory calculations, while the cluster anisotropy can be correlated to the single-ion anisotropies calculated for each Cr3+ ion in the wheel.The authors acknowledge financial support from the Spanish Agencia Estatal de Investigación, through Projects MAT2017-83468-R (AEI/FEDER, UE) and PID2020-115159GB-I00/AEI/10.13039/501100011033, Aragonese Project RASMIA E12_20R (co-funded by Fondo Social Europeo) and of the European Union FEDER (ES). Also University of Padova Grants P-DISC#09BIRD2019-UNIPD SMOW.Peer reviewe

A new biogenerated Rh-based catalyst for aqueous biphasic hydroformylation

A new bio-generated rhodium based system embedded in a peculiar polysaccharide matrix (Rh-EPS), was obtained and purified from cultures of bacterial cells of Klebsiella oxytoca DSM 29614. The product was analyzed with different techniques to obtain information on its structure-property correlation. In order to determine its catalytic activity and selectivity in the aqueous biphasic hydroformylation some olefins were chosen as model substrates, obtaining fine-good results.A new bio-generated rhodium based system embedded in a peculiar polysaccharide matrix (Rh-EPS), was obtained and purified from cultures of bacterial cells of Klebsiella oxytoca DSM 29614. The product was analyzed with different techniques to obtain information on its structure-property correlation. In order to determine its catalytic activity and selectivity in the aqueous biphasic hydroformylation some olefins were chosen as model substrates, obtaining fine-good results

Sol-gel synthesis and characterisation of ZnO-based nanosystems

Semiconductor nanoclusters embedded in thin coatings of transparent and homogeneous silica glasses are suitable materials for the development of optical devices. The optical properties of such systems are strongly dependent on the elemental composition and the morphology of the coatings as well as on the nanocluster size distribution, their mutual interactions and the interactions with the host matrix. To achieve a good control over film composition and morphology the sol-gel route was used. The sol-gel synthesis. of ZnO nanocrystals embedded in silica has been faced by the study of the gel-derived binary system ZnO-SiO2. The dip-coating procedure from alcoholic solutions containing tetraethoxysilane [Si(OC2H5)(4), TEOS] and zinc acetate [Zn(CH3,COO),(2)] was adopted. Zinc oxide nanograins have been generated in silica by hydrolysis of TEOS and the zinc salt and subsequent thermal annealing of the coatings. The system evolution under thermal treatment was studied by X-ray photoelectron spectroscopy, X-ray diffraction, transmission electron microscopy, UV-Vis absorption spectroscopy and secondary-ion mass spectrometry