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We present experimental intrinsic loss power (ILP) values, measured at an excitation frequency of 1 MHz and at relatively low field amplitudes of 3.4–9.9 kA/m, as a function of the mean core diameter, for selected magnetic nanoparticles (MNPs). The mean core sizes ranged from ca. 8 nm to 31 nm. Transmission electron microscopy indicated that those with smaller core sizes (less than ca. 22 nm) were single-core MNPs, while those with larger core sizes (ca. 29 nm to 31 nm) were multi-core MNPs. The ILP data showed a peak at core sizes of ca. 20 nm. We show here that this behaviour correlates well with the predicted ILP values obtained using either a non-interacting Debye model, or via dynamic Monte-Carlo simulations, the latter including core-core magnetic interactions for the multi-core particles. This alignment of the models is a consequence of the low field amplitudes used. We also present interesting results showing that the core-core interactions affect the ILP value differently depending on the mean core size.

One of the ultimate goals of nanocrystal self-assembly is to transform nanoscale building blocks into a material that displays enhanced properties relative to the sum of its parts. Herein, we demonstrate that 1D needle shaped assemblies composed of Fe3-delta O4 nanocubes display a significant augmentation of the magnetic susceptibility and dissipation as compared to OD and 2D systems. The performance of the nanocube needles is highlighted by a colossal anisotropy factor defined as the ratio of the parallel to the perpendicular magnetization components. We show that the origin of this effect cannot be ascribed to shape anisotropy in its classical sense; as such, it has no analogy in bulk magnetic materials. The temperature-dependent anisotropy factors of the in- and out-of-phase components of the magnetization have an extremely strong particle size dependence and reach values of 80 and 2500, respectively, for the largest nanocubes in this study. Aided by simulations, we ascribe the anisotropy of the magnetic susceptibility, and its strong particle-size dependence to a synergistic coupling between the dipolar interaction field and a net anisotropy field resulting from a partial texture in the 1D nanocube needles.

Electrochemistry can bring important contributions to current applications, such as organic synthesis or wastewater treatment. In an environmental context, electrochemical processes are interesting substitutes to the conventional wastewater treatment techniques (STEP). In this work, we have studied different types of electrodes, in order to develop a predictive model, so as to propose an electrode concept suitable for these two processes. The metal support/conducting oxide electrodes can behave in two distinct ways. The electrode can be active, and thereby directly take part to the oxidation of the organic product, or it can be inert and oxidise the organics through hydroxyl radicals produced during water electrolysis. We have studied the behavior of several electrodes, such as Ti/IrO2, Ti/CoMn204, Ti/SnO2-Sb2O5, Ti/PbO2, Pb/PbO2, Ti/PbO2-Bi2O5, Ti/IrO2/PbO2 and Pt (massive electrode) during electrochemical oxidation processes. The analysis of the formation of hydroxyl radicals showed a strong •OH formation for inert electrodes (PbO2, PbO2-Bi2O5, SnO2-Sb2O5), whereas the •OH formation was lower in case of active electrodes (IrO2, Pt). The electrochemical oxidation of phenol allowed us to show the efficiency and the features of two different types of electrodes. Ti/IrO2 selectively oxidises phenol into intermediate products, where Pb/PbO2 leads to total oxidation (combustion) of phenol to CO2. Finally, the formation of a polymer film at the surface of the electrodes was clearly shown by cyclic voltametry and oxygen evolution measurements. This film was shown to have a passivation effect on the Ti/CoMn2O4 electrode, and lead to a considerable decrease of its efficiency., Dans le cadre d'applications actuelles, comme la synthèse de produits organiques ou le traitement des eaux résiduaires, l'électrochimie peut apporter d'importantes contributions. Dans un contexte environnemental, les procédés électrochimiques représentent une palliatif intéressant pour les techniques classiques (STEP) d'épuration des eaux polluées. Dans ce travail, nous avons étudié différents types d'électrodes, afin d'établir un modèle prédictif permettant de proposer un concept d'électrode pouvant satisfaire à ces deux procédés. Il faut distinguer, pour les électrodes dites de type métal support/oxyde conducteur, deux cas extrêmes de comportement lors de procédés d'oxydation électrochimique. Dans un des cas, l'électrode est active et participe de façon indirecte à l'oxydation du produit organique. Dans l'autre cas, l'électrode est inerte et participe à l'oxydation par l'intermédiaire des radicaux hydroxyles, formés pendant l'électrolyse de l'eau. Nous avons étudié le comportement de différentes électrodes, comme Ti/IrO2, Ti/CoMn2O4, Ti/SnO2Sb2O5, Ti/PbO2, Pb/PbO2, Ti/PbO2-Bi2O5, Ti/IrO2/PbO2 et platine (électrode massive) lors de procédés d'oxydation électrochimique. L'analyse de la formation des radicaux hydroxyles, par la méthode du "spin-trapping", a montré une forte production de •OH pour les électrodes à caractère inerte (PbO2, PbO2-Bi2O5, SnO2-Sb2O5) et une faible production pour les électrodes à caractère actif (IrO2, Pt). L'oxydation électrochimique du phénol nous a permis de mettre en évidence l'efficacité et le caractère de deux types différents d'électrodes. Ti/IrO2 engendre une oxydation sélective (conversion) du phénol en produits intermédiaires, alors que Pb/PbO2 provoque l'oxydation complète (combustion) du phénol en CO2. Finalement, des mesures par voltamétrie cyclique et par le dégagement d'oxygène ont permis d'étudier la formation d'un film de polymères qui se dépose à la surface des électrodes. L'apparition de ce film a démontré son effet de pa