Influence of the hierarchical architecture of multi-core iron oxide nanoflowers on their magnetic properties.

Magnetic properties of superparamagnetic iron oxide nanoparticles are controlled mainly by their particle size and by their particle size distribution. Magnetic properties of multi-core iron oxide nanoparticles, often called iron oxide nanoflowers (IONFs), are additionally affected by the interaction of magnetic moments between neighboring cores. The knowledge about the hierarchical structure of IONFs is therefore essential for understanding the magnetic properties of IONFs. In this contribution, the architecture of multi-core IONFs was investigated using correlative multiscale transmission electron microscopy (TEM), X-ray diffraction and dynamic light scattering. The multiscale TEM measurements comprised low-resolution and high-resolution imaging as well as geometric phase analysis. The IONFs contained maghemite with the average chemical composition [Formula: see text]-Fe[Formula: see text]O[Formula: see text]. The metallic vacancies located on the octahedral lattice sites of the spinel ferrite structure were partially ordered. Individual IONFs consisted of several cores showing frequently a specific crystallographic orientation relationship between direct neighbors. This oriented attachment may facilitate the magnetic alignment within the cores. Individual cores were composed of partially coherent nanocrystals having almost the same crystallographic orientation. The sizes of individual constituents revealed by the microstructure analysis were correlated with the magnetic particle sizes that were obtained from fitting the measured magnetization curve by the Langevin function.

Redox Polyelectrolytes with pH-Sensitive Electroactive Functionality in Aqueous Media.

A framework of ferrocene-containing polymers bearing adjustable pH- and redox-active properties in aqueous electrolyte environments was developed. The electroactive metallopolymers were designed to possess enhanced hydrophilicity compared to the vinylferrocene (VFc) homopolymer, poly(vinylferrocene) (PVFc), by virtue of the comonomer incorporated into the macromolecule, and could also be prepared as conductive nanoporous carbon nanotube (CNT) composites that offered a variety of different redox potentials spanning a ca. 300 mV range. The presence of charged non-redox-active moieties such as methacrylate (MA) in the polymeric structure endowed it with acid dissociation properties that interacted synergistically with the redox activity of the ferrocene moieties to impart pH-dependent electrochemical behavior to the overall polymer, which was subsequently studied and compared to several Nernstian relationships in both homogeneous and heterogeneous configurations. This zwitterionic characteristic was leveraged for the enhanced electrochemical separation of several transition metal oxyanions using a P(VFc0.63-co-MA0.37)-CNT polyelectrolyte electrode, which yielded an almost twofold preference for chromium as hydrogen chromate versus its chromate form, and also exemplified the electrochemically mediated and innately reversible nature of the separation process through the capture and release of vanadium oxyanions. These investigations into pH-sensitive redox-active materials provide insight for future developments in stimuli-responsive molecular recognition, with extendibility to areas such as electrochemical sensing and selective separation for water purification.

Magnetic/flow controlled continuous size fractionation of magnetic nanoparticles using simulated moving bed chromatography.

The use of magnetic nanoparticles shows a steadily increasing technical importance. Particularly in medical technology disciplines such as cancer treatment, the potential of these special particles is increasing rapidly. Magnetic nanoparticles are particles with a submicron size, and consist mostly of magnetite-containing composites. An important quality parameter of such particles is a particle size distribution as narrow as possible, which can only be obtained to a certain degree by synthesis. Apart from ultracentrifugation, there are so far only methods on an analytical scale to narrow the size distribution as a post-processing step. We present a method based on magnetic chromatography, by which high separation efficiencies at yields of up to 99.9% are achieved. The novel technique is based on a competition between the magnetic interaction of the nanoparticles and the separation matrix, as well as the hydrodynamic forces. Furthermore, the method is extended using a continuous mode, namely simulated moving bed chromatography, to obtain potent space-time yields of up to 2.94 g/(L*h). For those reasons, this novel continuous magnetic chromatography method offers high potential for large-scale refinement of magnetic nanoparticles while fulfilling sophisticated quality criteria for high-technology applications.