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J Hazard Mater

Air-stable bimetallic spherically shaped Fe-Ni and Fe-Co magnetic nanoparticles (MNPs), having an average size of 15 nm and core-shell structure, were synthesized by a simple wet chemical method under ambient conditions. For the first time, sodium borohydride reduction method, commonly applied for the syntheses of metal nanoparticles, was used for the preparation of well-defined Fe-Ni and Fe- Co nanoalloys, avoiding exploitation of any organic solvent. This approach allows a large scale production of nanoparticles specifically stabilized by an iron oxyhydroxide shell without a need of secondary functionalization. Transmission electron microscopy, X-ray powder diffraction, X-ray fluorescence, magnetization, and M?ssbauer data demonstrate a core- shell nature of the as-synthesized nanoparticles. The nanoparticle core is of metallic origin and is inhomogeneous at the atomic level, consisting of iron-rich and iron-poor alloy phases. The composition of the shell is close to the ferrihydrite and its role lies in prevention of oxidation-induced degradation of nanoparticle properties. The core is ferromagnetic at and below room temperature, experiencing superparamagnetic relaxation effects due to a reduced size of nanoparticles, whereas the shell is completely superparamagnetic at 300 K and magnetically orders below?25 K. Both developed types of magnetic nanoalloys exhibit a strong magnetic response under applied magnetic fields with a high magnetization values achievable at relatively low applied magnetic fields. Beside this, the highly biocompatible chemical composition of the nanoparticle shell and ability of its chemical modification by substitution or addition of other ions or molecules further empower the application potential of these MNPs, especially in the field of biomedicine. © Springer Science+Business Media B.V. 2012. Journal of Nanoparticle Research

Single-atom catalysts (SACs) aim at bridging the gap between homogeneous and heterogeneous catalysis. The challenge is the development of materials with ligands enabling coordination of metal atoms in different valence states, and preventing leaching or nanoparticle formation. Graphene functionalized with nitrile groups (cyanographene) is herein employed for the robust coordination of Cu(II) ions, which are partially reduced to Cu(I) due to graphene-induced charge transfer. Inspired by nature’s selection of Cu(I) in enzymes for oxygen activation, this 2D mixed-valence SAC performs flawlessly in two O2-mediated reactions: the oxidative coupling of amines and the oxidation of benzylic CH bonds toward high-value pharmaceutical synthons. High conversions (up to 98%), selectivities (up to 99%), and recyclability are attained with very low metal loadings in the reaction. The synergistic effect of Cu(II) and Cu(I) is the essential part in the reaction mechanism. The developed strategy opens the door to a broad portfolio of other SACs via their coordination to various functional groups of graphene,as demonstrated by successful entrapment of FeIII/FeII single atoms to carboxy-graphene.