Anisotropic magnetic nanoparticles: A review of their properties, syntheses and potential applications

Modern trends in the greener synthesis and fabrication of inorganic, organic and coordination compounds, materials, nanomaterials, hybrids and nanocomposites are discussed. Green chemistry deals with synthesis procedures according to its classic 12 principles, contributing to the sustainability of chemical processes, energy savings, lesser toxicity of reagents and final products, lesser damage to the environment and human health, decreasing the risk of global overheating, and more rational use of natural resources and agricultural wastes. Greener techniques have been applied to synthesize both well-known chemical compounds by more sustainable routes and completely new materials. A range of nanosized materials and composites can be produced by greener routes, including nanoparticles of metals, non-metals, their oxides and salts, aerogels or quantum dots. At the same time, such classic materials as cement, ceramics, adsorbents, polymers, bioplastics and biocomposites can be improved or obtained by cleaner processes. Several non-contaminating physical methods, such as microwave heating, ultrasound-assisted and hydrothermal processes or ball milling, frequently in combination with the use of natural precursors, are of major importance in the greener synthesis, as well as solventless and biosynthesis techniques. Non-hazardous solvents including ionic liquids, use of plant extracts, fungi, yeasts, bacteria and viruses are also discussed in relation with materials fabrication. Availability, necessity and profitability of scaling up green processes are discussed.

https://royalsocietypublishing.org/doi/pdf/10.1098/rsos.191378

Greener synthesis of chemical compounds and materials

Magnetic collection of the microalgae Chlorella sp. from culture media facilitated by low-gradient magnetophoretic separation is achieved in real time. A removal efficiency as high as 99% is accomplished by binding of iron oxide nanoparticles (NPs) to microalgal cells in the presence of the cationic polyelectrolyte poly(diallyldimethylammonium chloride) (PDDA) as a binder and subsequently subjecting the mixture to a NdFeB permanent magnet with surface magnetic field ≈6000 G and magnetic field gradient <80 T m(-1) . Surface functionalization of magnetic NPs with PDDA before exposure to Chlorella sp. is proven to be more effective in promoting higher magnetophoretic removal efficiency than the conventional procedure, in which premixing of microalgal cells with binder is carried out before the addition of NPs. Rodlike NPs are a superior candidate for enhancing the magnetophoretic separation compared to spherical NPs due to their stable magnetic moment that originates from shape anisotropy and the tendency to form large NP aggregates. Cell chaining is observed for nanorod-tagged Chlorella sp. which eventually fosters the formation of elongated cell clusters.

Rapid Magnetophoretic Separation of Microalgae

Stimuli-responsive materials can sense specific environmental changes and adjust their physical properties in a predictable manner, making them highly desired components for designing novel sensors, intelligent systems, and adaptive structures. Magnetically responsive structures have unique advantages in applications, as external magnetic stimuli can be applied in a contactless manner and cause rapid and reversible responses. In this Perspective, we discuss our recent progress in the design and fabrication of nanostructured materials with various optical responses to externally applied magnetic fields. We demonstrate tuning of the optical properties by taking advantage of the magnetic fields’ abilities to induce magnetic dipole–dipole interactions or control the orientation of the colloidal magnetic nanostructures. The design strategies are expected to be extendable to the fabrication of novel responsive materials with new optical effects and many other physical properties.

Magnetically Responsive Nanostructures with Tunable Optical Properties

Studies of Fe3O4-chitosan nanoparticles prepared by co-precipitation under the magnetic field for lipase immobilization

A series of Fe3O4 particle chains with an average particle diameter of 150 nm and different lengths were synthesized by using the self-assembly method at reduced temperature in different synthesizing magnetic fields. The influence of synthesizing magnetic field on the properties of the magnetite particle chains was studied by structural analyses, magnetometry measurement, and ferromagnetic resonance. A uniaxial magnetic anisotropy in the saturation field (Hs), hysteresis loop, and ferromagnetic resonance were observed to increase with increasing synthesizing field. The saturation magnetization and g-factor were found to increase slightly with increasing synthesizing field. The demagnetizing fields and demagnetizing factors were determined from the experimental data of magnetometry measurement, ferromagnetic resonance, and also numerical calculation, which agreed reasonably well. It was found that the magnetization non-uniformity in the chains and the magnetostatic interaction among the chains have an impo...

H. R. Zhai

Papers

The Shape Anisotropy in the Magnetic Field-Assisted Self-Assembly Chain-like Structure of Magnetite