The use of multifunctional nanoparticles (NPs), usually in the range of 3–100 nm, with their newly discovered properties – such as superparamagnetic (SPM) behaviour, enhancement of activity and ...selectivity in catalytic processes and localised surface plasmon resonance (LSPR) – offers new technical possibilities for biomedical applications such as magnetic hyperthermia (MH), plasmonic photothermal therapy (PPTT) and enhanced magnetic resonance imaging (MRI). In addition, the small size of NPs presents a unique opportunity to interfere, in a highly localised and specific way, with natural processes involving viruses, bacteria or cells and allows interference in the development of complex diseases like many types of cancer and neuropathies (Alzheimer's, Parkinson's, Kreutzer–Jacobs'). The design of biological applications based on MH is a chemical challenge and core@shell structures are most often used to endow NPs with multifunctional abilities. The success of such MH‐based biological applications depends on the magnetic functionality of the core as well as the properties of the surface shell in direct interaction with the biological medium. In this review we will describe the most important methodologies developed to synthesise magnetic core@shell nanostructures and their MH applications.
Hierarchical core–shell architectures based on magnetic cores decorated with several agents (polymers, drugs, proteins, etc.) allow for multipurpose applications including magnetic hyperthermia, magnetic resonance imaging (MRI) or tissue engineering within a single design. The designed criteria emerge from the interaction of the nano–bio interface, and the planned therapeutic applications.
Nitride coatings are increasingly demanded in the cutting- and machining-tool industry owing to their hardness, thermal stability and resistance to corrosion. These properties derive from strongly ...covalent bonds; understanding the bonding is a requirement for the design of superhard materials with improved capabilities. Here, we report a pressure-induced cubic-to-orthorhombic transition at approximately 1 GPa in CrN. High-pressure X-ray diffraction and ab initio calculations show an unexpected reduction of the bulk modulus, K0, of about 25% in the high-pressure (lower volume) phase. Our combined theoretical and experimental approach shows that this effect is the result of a large exchange striction due to the approach of the localized Cr:t3 electrons to becoming molecular-orbital electrons in Cr-Cr bonds. The softening of CrN under pressure is a manifestation of a strong competition between different types of chemical bond that are found at a crossover from a localized to a molecular-orbital electronic transition.
An ab initio study of the interaction of O2, the most abundant radical and oxidant species in the atmosphere, with a Cu5 cluster, a new generation atomic metal catalyst, is presented. The open-shell ...nature of the reactant species is properly accounted for by using the multireference perturbation theory, allowing the experimentally confirmed resistivity of Cu5 clusters toward oxidation to be investigated. Approximate reaction pathways for the transition from physisorption to chemisorption are calculated for the interaction of O2 with quasi-iso-energetic trapezoidal planar and trigonal bipyramidal structures. Within the multireference approach, the transition barrier for O2 activation can be interpreted as an avoided crossing between adiabatic states (neutral and ionic), which provides new insights into the charge-transfer process and gives better estimates for this hard to localize and therefore often neglected first intermediate state. For Cu5 arranged in a bipyramidal structure, the O–O bond cleavage is confirmed as the rate-determining step. However, for planar Cu5, the high energy barrier for O2 activation, related to a very pronounced avoided crossing when going from physisorption to chemisorption, determines the reactivity in this case.
Nitride coatings are increasingly demanded in the cutting- and machining-tool industry owing to their hardness, thermal stability and resistance to corrosion. These properties derive from strongly ...covalent bonds; understanding the bonding is a requirement for the design of superhard materials with improved capabilities. Here, we report a pressure-induced cubic-to-orthorhombic transition at -1GPa in CrN. High-pressure X-ray diffraction and ab initio calculations show an unexpected reduction of the bulk modulus, K(0), of about 25% in the high-pressure (lower volume) phase. Our combined theoretical and experimental approach shows that this effect is the result of a large exchange striction due to the approach of the localized Cr:t(3) electrons to becoming molecular-orbital electrons in Cr-Cr bonds. The softening of CrN under pressure is a manifestation of a strong competition between different types of chemical bond that are found at a crossover from a localized to a molecular-orbital electronic transition.
Reducing the size from the bulk material to nanoparticles produces a scaling behavior in physical properties in the later ones, due to the large surface-to-volume fraction. By further size reduction, ...entering into the subnanometric cluster region, physical properties are largely affected by strong quantum confinement. These quantum size effects (HOMO-LUMO gap), the small size and the specific geometry award subnanometric clusters with totally new and fascinating properties, including cluster photoluminescence, enhanced catalytic activity, etc. In this review, we report an introduction to the physical properties of clusters based on the jellium model; the controlled synthesis by microemulsion methods and the catalytic properties in different areas as heterogeneous catalysis, photocatalysis or electrocatalysis among others.
A comparative study on different bimetallic nanocatalysts prepared from microemulsions using a one-pot method has been carried out. The analysis of experimental observations, complemented by ...simulation studies, provides detailed insight into the factors affecting nanoparticle architecture: (1) The metal segregation in a bimetallic nanocatalysts is the result of the combination of three main kinetic parameters: the reduction rate of metal precursors (related to reduction standard potentials), the material intermicellar exchange rate (determined by microemulsion composition), and the metal precursors concentration; (2) A minimum difference between the reduction standard potentials of the two metals of 0.20 V is needed to obtain a core-shell structure. For values ∆ε0 smaller than 0.20 V the obtaining of alloys cannot be avoided, neither by changing the microemulsion nor by increasing metal concentration; (3) As a rule, the higher the film flexibility around the micelles, the higher the degree of mixture in the nanocatalyst; (4) A minimum concentration of metal precursors is required to get a core-shell structure. This minimum concentration depends on the microemulsion flexibility and on the difference in reduction rates.
Emerging contaminants (ECs) represent a wide range of compounds, whose complete elimination from wastewaters by conventional methods is not always guaranteed, posing human and environmental risks. ...Advanced oxidation processes (AOPs), based on the generation of highly oxidizing species, lead to the degradation of these ECs. In this context, TiO2 and ZnO are the most widely used inorganic photocatalysts, mainly due to their low cost and wide availability. The addition of small amounts of nanoclusters may imply enhanced light absorption and an attenuation effect on the recombination rate of electron/hole pairs, resulting in improved photocatalytic activity. In this work, we propose the use of silver nanoclusters deposited on ZnO nanoparticles (ZnO–Ag), with a view to evaluating their catalytic activity under both ultraviolet A (UVA) and visible light, in order to reduce energetic requirements in prospective applications on a larger scale. The catalysts were produced and then characterized by scanning electron microscopy (SEM), X-ray diffractometry (XRD) and inductively coupled plasma-optical emission spectrometry (ICP-OES). As proof of concept of the capacity of photocatalysts doped with nanoclusters, experiments were carried out to remove the azo dye Orange II (OII). The results demonstrated the high photocatalytic efficiency achieved thanks to the incorporation of nanoclusters, especially evident in the experiments performed under white light.
An ab initio study of the interaction of O
, the most abundant radical and oxidant species in the atmosphere, with a Cu
cluster, a new generation atomic metal catalyst, is presented. The open-shell ...nature of the reactant species is properly accounted for by using the multireference perturbation theory, allowing the experimentally confirmed resistivity of Cu
clusters toward oxidation to be investigated. Approximate reaction pathways for the transition from physisorption to chemisorption are calculated for the interaction of O
with quasi-iso-energetic trapezoidal planar and trigonal bipyramidal structures. Within the multireference approach, the transition barrier for O
activation can be interpreted as an avoided crossing between adiabatic states (neutral and ionic), which provides new insights into the charge-transfer process and gives better estimates for this hard to localize and therefore often neglected first intermediate state. For Cu
arranged in a bipyramidal structure, the O-O bond cleavage is confirmed as the rate-determining step. However, for planar Cu
, the high energy barrier for O
activation, related to a very pronounced avoided crossing when going from physisorption to chemisorption, determines the reactivity in this case.
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