Tailoring of magnetite powder properties for enhanced phosphate removal: Effect of PEG addition in the synthesis process

This study demonstrates that PEG-assisted hydrothermal synthesis provides a convenient and eco-friendly route to fabrication of mesoporous magnetite with enhanced capacity for phosphate removal, excellent potential for magnetic separation and good reusability. Adsorption of phosphate onto 4 laboratory prepared magnetite powders was investigated in a systematic manner. Powders were synthesized in poly(ethylene) glycol-free or assisted conditions (PEGs 400 and 20,000 at varied PEG/water ratio), and characterized in terms of crystalline structure, and magnetic, morphological, textural, and acid-base properties. PEG acted as a powerful pore forming agent, the PEG/water ratio being the key factor in developing the surface area and mesoporosity of magnetite. Uptake capacity for phosphates increased with an increase in surface area and pore volume. PEG 20,000 at a ratio of 3:1 gave the best result. This mesoporous (D-max = 11 nm), nano-scale ( lt 10 nm) magnetite was ca. 9 times more efficient than nonporous micrometric powder derived from PEG-free synthesis (Langmuir maximum capacity, q(m) = 26.2 vs. 3.0 mg g(-1)). The adsorption was pH-dependent, in accord with variations in zeta potential of magnetite. Opposite shifts of isoelectric point and point of zero charge confirmed specific adsorption of phosphates at water/magnetite interface which proceeded via replacement of surface hydroxyls and sulfates

Copper-based magnetic catalysts for alkyne oxidative homocoupling reactions

We successfully prepared copper-based magnetic catalysts combining copper oxide and magnetite nanoparticles. These systems are active and selective in the oxidative homocoupling reaction of phenylacetylene in the absence of an external base. These systems are particularly interesting since the addition of an external base induces copper leaching by production of soluble molecular copper-base complexes. Some of these systems were also supported on oxidized few layer graphene to investigate a potential role of this support. We discover that this supported system is three times more active than the other ones. We propose that the role of graphene support is to improve catalyst dispersion, but also to provide a favorable micro-environment around the active phase via a pre-adsorption of the substrate on the support, which affords a substrate rich micro-environment around the active particles. Recycling experiments show that the graphene-supported systems cannot be recycled, while the other ones can. This result could be explained by a competitive pre-adsorption between the substrate and the product of the reaction on the surface of the support

Magnetic field-induced self-assembly of iron oxide nanocubes

Self-assembly of inorganic nanoparticles has been studied extensively for particles having different sizes and compositions. However, relatively little attention has been devoted to how the shape and surface chemistry of magnetic nanoparticles affects their self-assembly properties. Here, we undertook a combined experiment-theory study aimed at better understanding of the self-assembly of cubic magnetite (Fe3O4) particles. We demonstrated that, depending on the experimental parameters, such as the direction of the magnetic field and nanoparticle density, a variety of superstructures can be obtained, including one-dimensional filaments and helices, as well as C-shaped assemblies described here for the first time. Furthermore, we functionalized the surfaces of the magnetic nanocubes with light-sensitive ligands. Using these modified nanoparticles, we were able to achieve orthogonal control of self-assembly using a magnetic field and light

Field-induced self-assembly of iron oxide nanoparticles investigated using small-angle neutron scattering

The magnetic-field-induced assembly of magnetic nanoparticles (NPs) provides a unique and flexible strategy in the design and fabrication of functional nanostructures and devices. We have investigated the field-induced self-assembly of core–shell iron oxide NPs dispersed in toluene by means of small-angle neutron scattering (SANS). The form factor of the core–shell NPs was characterized and analyzed using SANS with polarized neutrons. Large-scale aggregates of iron oxide NPs formed above 0.02 T as indicated by very-small-angle neutron scattering measurements. A three-dimensional long-range ordered superlattice of iron oxide NPs was revealed under the application of a moderate magnetic field. The crystal structure of the superlattice has been identified to be face-centred cubic