Secondary structural, superparamagnetic Fe3O4 microparticles with an average diameter of 280 nm have been successfully synthesized by using a one-step hydrothermal method. The size of the primary nanograins has been controlled from 5.9 to 21.5 nm by varying the sodium acrylate/sodium acetate weight ratios. The magnetic properties of the Fe3O4 microparticles have been characterized at room temperature, whereas the saturation magnetization values of the Fe3O4 microparticles increase with increasing grain sizes. Magnetic resonance imaging reveals that Fe3O4 microparticle with larger grain size yields higher molar T 2 relaxation rate. A plausible growth mechanism of the particles is proposed, and the role of sodium acrylate and sodium acetate for tuning the grain size of the particles has been discussed. Additionally, the size of the secondary structural Fe3O4 particles can also be continuously controlled from 6 to 170 nm by varying the volume ratio of ethylene glycol/diethylene glycol in a bisolvent system. The described method presents the synthesis of secondary structural nanomaterials with tunable sizes, grain sizes, and different magnetic responses.

We report a new method to synthesize magnetically responsive Fe3O4@polyaniline@Au nanocomposites. The superparamagnetic Fe3O4@polyaniline with well-defined core/shell nanostructure has been synthesized via an ultrasound-assisted in situ surface polymerization method. The negatively charged Au nanoparticles with a diameter of about 4 nm have been effectively assembled onto the positively charged surface of the as-synthesized Fe3O4@polyaniline core/shell microspheres via electrostatic attraction. The morphology, phase composition, and crystallinity of the as-prepared nanocomposites have been characterized by transmission electron microscopy (TEM) and powder X-ray diffraction (XRD). The central Fe3O4 cores are superparamagnetic at room temperature with strong magnetic response to externally applied magnetic field, thus providing a convenient means for separating the nanocomposite from solution. As-prepared inorganic/organic nanocomposite can be used as a magnetically recoverable nanocatalyst for the reduction of a selected substrate.

This article features both molecular and supramolecular chemistry involving: i) stimuli‐induced nanoscale movements within mechanically interlocked molecules; ii) the fabrication of mesoporous silica substrates; and iii) the integration of the mechanically interlocked molecular/supramolecular actuators to act as gatekeepers at the entrances to the silica nanopores into which guest dye molecules can be uploaded and released on demand from the mesoporous silica substrates. The supramolecular actuators are based on two [2]pseudorotaxanes—that is, 1:1 complexes that can be dissociated by external inputs, such as acid/base cycles, electrons, and light. The molecular actuators are based on bistable [2]rotaxanes and can be operated mechanically by using either redox chemistry or electrochemistry. After these pseudorotaxanes and bistable rotaxanes have been attached covalently to the orifices of the silica nanopores, stimuli‐controlled mechanical movements within these mechanically interlocked molecules can be harnessed to close and open the nanopores. Therefore, these mechanically interlocked molecules have been employed as nanovalves for controlled sequestering and release of guest dye molecules into and out of the mesoporous silica substrates. These actuators can be regarded as the prototypes of highly controllable drug‐delivery systems.

Monodispersed ferrite nanospheres were synthesized in an ethylene glycol/diethylene glycol (EG/DEG) binary solvent by using poly(vinylpyrrolidone) (PVP) as the surfactant. Particle size control can be attained by careful adjustment of the V EG /V DEG ratio. Different from previous reports, the magnetic studies of our iron ferrite (Fe 3 O 4 ) nanospheres with various sizes from 20 to 300 nm reveal that they exhibit a similar magnetic saturation (M s ) value. In particular, both the ferromagnetic and superparamagnetic Fe 3 O 4 nanospheres with similar M s can be selectively obtained by varying the H 2 O concentration in the reaction system. The magnetic resonance imaging (MRI) characterization indicates that the as-prepared superparamagnetic Fe 3 O 4 and ZnFe 2 O 4 nanospheres possess a T 2 relaxivity range that can be used as potential MRI contrast agents.