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Well-defined colloidal-stable citrate-stabilized Au/CeO2 hybrid nanocrystals (NCs) with coherent quasi-epitaxial interfaces and unprecedented control of their architectural and morphological characteristics have been synthesized via a novel and straightforward seeded-growth aqueous approach. The synthetic strategy, based on the identification of the experimental conditions under which the heterogeneous nucleation and growth processes of CeO2 onto presynthesized Au are controlled, allows for the fine adjustment of each individual domain in the structure, particularly the size of the Au core (from 5 to 100 nm), the thickness of the CeO2 shell (from 5 to 20 nm), and the growth mode of CeO2 onto Au NCs (from core@shell to heterodimer, clover- and star-like structures). This morphological control is achieved by the rational use of sodium citrate, which plays multiple key roles, as a reducer and stabilizing agent in the preparation of Au NCs, and as a complexing agent of Ce3+ for its controlled oxidation and hydrolysis during the subsequent CeO2 deposition. The resultant Au/CeO2 NCs remain stable and well-dispersed in water, allowing us to study the impact of fine variations of the NC structure on the underlying optical response. This level of morphological control, as well as the ease by which such well-defined nanostructures are produced, opens new opportunities for systematically investigating the interactions between individual components in designing more advanced complex NCs. Remarkably, because no organic solvents are used and no toxic waste is formed during the reaction, the proposed synthesis method can be defined as sustainable, viable, and cost-effective., We acknowledge financial support from the Spanish MINECO (MAT2015-70725-R, ENE2017-85087-C3), MICINN (RTI2018-099965-B-I00), and from the Catalan Agencia de Gestió d’Ajuts Universitaris i de Recerca (AGAUR) (2017-SGR-1431, 2017-SGR-327). Financial support from the HISENTS (685817) Project financed by the European Community under H20202 Capacities Programme is gratefully acknowledged. N.G.B. acknowledges financial support by MINECO through the Ramon y Cajal program (RYC-2012-10991). ICN2 is supported by the Severo Ochoa program from Spanish MINECO (grant no. SEV-2017-0706) and is funded by the CERCA Programme/Generalitat de Catalunya. Part of the present work has been performed in the framework of the Universitat Autonoma de Barcelona Degree and Ph.D. program.

Au-coated magnetic-core nanocomposites with diameters of ∼100 nm were synthesized by the biphasic reduction of Au3+ onto the surface of organosilane-stabilized Co nanoparticles of ∼12 nm in diameter via an iterative gold reduction. The shell consists initially of Au seeds of ∼3 nm in diameter, which can be later grown to form partially fused ∼6 nm Au NPs. A detailed investigation by transmission electron microscopy, scanning electron microscopy, UV–vis, dynamic light scattering, ζ-potential, X-ray diffraction, inductively coupled plasma mass spectrometry, and superconducting quantum interference device magnetometry was performed in order to elucidate the morphology and properties of these nanocomposites. These novel nanoarchitectures, which could be transferred into aqueous phase by means of an amphiphilic polymer, showed low cytotoxicity on human HepG2 cells and presented relaxivity in MRI contrast enhancement experiments.

Multicomponent metal-oxide nanoparticles are appealing structures from applied and fundamental viewpoints. The control on the synthetic parameters in colloidal chemistry allows the growth of complex nanostructures with novel morphologies. In particular, the synthesis of biphase metal-oxide hollow nanoparticles has been reported based on galvanic replacement using an organic-based seeded-growth approach, but with the presence of HO. Here we report a novel route to synthesize either fully dense or hollow core/shell metal-oxide nanoparticles (MnO/FeO) by simply adding or not oxidants in the reaction. We demonstrate that the presence of oxidants (e.g., O carried by the not properly degassed HO or (CH)NO) allows the formation of hollow structures by a galvanic reaction between the MnO and FeO phases. In particular, the use of (CH)NO as oxidant allows for the first time a very reliable all-organic synthesis of hollow MnO/FeO nanoparticles without the need of water (with a somewhat unreliable oxidation role). Oxidants permit the formation of MnO/FeO hollow nanoparticles by an intermediate step where the MnO/MnO seeds are oxidized into MnO, thus allowing the Mn → Mn reduction by the Fe ions. The lack of proper oxidative conditions leads to full-dense onion-like core/shell MnO/MnO/FeO particles. Thus, we show that the critical step for galvanic replacement is the proper seed oxidation states so that their chemical reduction by the shell ions is thermodynamically favored., Financial support from the 2014-SGR-1015, MAT2010-20616-C02, MAT2013-48628-R, MAT2013-41506, and CSD2009-00013 projects is acknowledged. ALO acknowledges the Juan de la Cierva Program (MINECO IJCI-2014-21530). ICN2 acknowledges support from the Severo Ochoa Program (MINECO, Grant SEV-2013-0295).

A low-temperature route to pure CoO nanoparticles based on the oxidative decarbonylation of dicobalt octacarbonyl promoted by amine oxides is presented. The small size of the resulting particles (∼1.7 nm) leads to spontaneous nanoparticle aggregation. Magnetic measurements show a bimodal behavior with two distinct blocking temperatures, which can be ascribed to the individual CoO nanoparticles and to narrowly size-dispersed aggregates.

Industrial catalysts often consist of transition metals supported on microporous or mesoporous high surface area oxides and are prepared by techniques such as impregnation and ion adsorption. In standard fabrication processes the metal particle size is not well-controlled. In this paper we report a new synthetic route for the production of catalyst materials with more precise control of the metal particle size. Gold nanoparticles encapsulated in mesoporous silica (MCM-41 and MCM-48) served as a model system, although the techniques described are applicable to a wide variety of metals and oxide supports. The samples were characterized by a combination of low-angle powder X-ray diffraction, transmission electron microscopy, N2 porosimetry, infrared spectroscopy, and X-ray absorption near-edge spectroscopy. The results show that the MCM-41 and MCM-48 structures retain their long-range order when metal particles are added; in addition, the size of the channels increases monotonically with metal loading. X-ray...

Highly monodisperse sodium citrate-coated spherical silver nanoparticles (Ag NPs) with controlled sizes ranging from 10 to 200 nm have been synthesized by following a kinetically controlled seeded-growth approach via the reduction of silver nitrate by the combination of two chemical reducing agents: sodium citrate and tannic acid. The use of traces of tannic acid is fundamental in the synthesis of silver seeds, with an unprecedented (nanometric resolution) narrow size distribution that becomes even narrower, by size focusing, during the growth process. The homogeneous growth of Ag seeds is kinetically controlled by adjusting reaction parameters: concentrations of reducing agents, temperature, silver precursor to seed ratio, and pH. This method produces long-term stable aqueous colloidal dispersions of Ag NPs with narrow size distributions, relatively high concentrations (up to 6 × 1012 NPs/mL), and, more important, readily accessible surfaces. This was proved by studying the catalytic properties of as-synthesized Ag NPs using the reduction of Rhodamine B (RhB) by sodium borohydride as a model reaction system. As a result, we show the ability of citrate-stabilized Ag NPs to act as very efficient catalysts for the degradation of RhB while the coating with a polyvinylpyrrolidone (PVP) layer dramatically decreased the reaction rate., We acknowledge financial support from Spanish MICINN (MAT2012-33330). N.G.B. thanks the Spanish MICINN for the financial support through the Juan de la Cierva program and the European Commission for the Career Integration Grants (CIG)-Marie Curie Action. We also acknowledge financial support from the EU-FP7 project QualityNano.

Multifunctional hybrid nanoparticles comprising two or more entities with different functional properties are gaining ample significance in industry and research. Due to its combination of properties, a particularly appealing example is Au-FeO composite nanoparticles. Here we present an in-depth study of the synthesis of Au-FeO heterostructured nanocrystals (HNCs) by thermal decomposition of iron precursors in the presence of preformed 10 nm Au seeds. The role of diverse reaction parameters on the HNCs formation was investigated using two different precursors: iron pentacarbonyl (Fe(CO)) and iron acetylacetonate (Fe(acac)). The reaction conditions promoting the heterogeneous nucleation of FeO onto Au seeds were found to significantly differ depending on the precursor chosen, where Fe(acac) is considerably more sensitive to the variation of the parameters than Fe(CO) and more subject to homogeneous nucleation processes with the consequent formation of isolated iron oxide nanocrystals (NCs). The role of the surfactants was also crucial in the formation of well-defined and monodisperse HNCs by regulating the access to the Au surface. Similarly, the variations of the [Fe]/[Au] ratio, temperature, and employed solvent were found to act on the mean size and the morphology of the obtained products. Importantly, while the optical properties are rather sensitive to the final morphology, the magnetic ones are rather similar for the different types of obtained HNCs. The surface functionalization of dimer-like HNCs with silica allows their dispersion in aqueous media, opening the path to their use in biomedical applications.