Tailoring the Synthesis of LnF₃ (Ln = La–Lu and Y) Nanocrystals via Mechanistic Study of the Coprecipitation Method

Here, 15 LnF₃ nanocrystals are synthesized using coprecipitation method with citrate stabilization to allow the fast, easy, and reproducible synthesis of several nanoscaled structures in water. General trends related to the behavior of LnF₃ nanocrystals are highlighted due to their broad range of application in several fields (e.g., medical applications). The same nature for all Ln³⁺ cations is expected due to the internal role of f orbitals. However, we found that the use of different lanthanide elements is crucial in the final size, shape, assembly, and crystalline structure. In addition, the decrease of the cation size of the lanthanide series changes the behavior of these compounds, resulting in hexagonal, orthorhombic, and cubic crystalline structures. In addition, we are able to tune the cubic crystalline phase to pure orthorhombic by modifying the pH of the system using HBF₄ instead of tetramethylammonium citrate. Via ¹¹B NMR, we demonstrated the mechanism of HBF₄ as fluorinating agent if an additional source of F^– is not added during the synthesis. ¹H NMR and IR techniques were performed to unravel the picture of the surface chemistry of the two representative metal cations (Y and La). Finally, HRTEM and SAED were performed to uncover the shape of the obtained nanocrystals and the preferential orientation of the assembled particles, giving crucial information on the involved mechanisms. This study reveals not only the dependence of the crystalline structure on the used metal and pH but also ability to achieve LnF₃ assembled particles depending on the final shape and temperature

Kinetics of Low Field Gradient Magnetophoresis in the Presence of Magnetically Induced Convection

Previous work (Leong et al. <i>Soft Matter</i> <b>2015</b>, <i>11</i>, 6968) has demonstrated, by using both experiments and simulations, that a magnetic field gradient can induce substantial convective currents during magnetophoresis of superparamagnetic nanoparticles in the solution. This effect substantially enhances the efficiency of low gradient magnetic separation (LGMS) processes. Throughout the LGMS process, this circulating flow plays a dominant role in homogenizing the nanoparticle solution and enhancing the vertical motion of particles. Here we perform a detailed quantitative study of the factors affecting the kinetics of LGMS in the presence of magnetically induced convection. In particular, we have found that the magnetophoretic collection rate of magnetic nanoparticles in LGMS is solely determined by the magnetic field gradient at the surface of contact of the dispersion cuvette with the magnet (denoted as the “collection plane of particles” in this work) and the area of this surface. Surprisingly, the kinetics of LGMS is independent of the magnetic field distribution across the solution subjected to magnetophoresis as long as magnetically induced convection is present. These conclusions are of crucial relevance in the design of low gradient magnetic separators for engineering applications

Highly Fluorescent Silicon Nanocrystals Stabilized in Water Using Quatsomes

Fluorescent silicon (Si) nanocrystals (2.8 nm diameter) were incorporated into surfactant assemblies of cetyltrimethylammonium bromide (CTAB) and cholesterol, called quatsomes. In water, the quatsome-Si nanocrystal assemblies remain fluorescent and well-dispersed for weeks. In contrast to Si nanocrystals, alkanethiol-capped gold (Au) nanocrystals do not form stable dispersions in water with quatsomes. Cryogenic transmission electron microscopy (cryo-TEM) confirmed that the Si nanocrystal-quatsome structures do not change over the course of several weeks. The long-term stability of the Si nanocrystal-quatsome assemblies, their fluorescence, and biocompatibility makes them attractive candidates for medical applications

Pressure-Responsive, Surfactant-Free CO₂‑Based Nanostructured Fluids

Microemulsions are extensively used in advanced material and chemical processing. However, considerable amounts of surfactant are needed for their formulation, which is a drawback due to both economic and ecological reasons. Here, we describe the nanostructuration of recently discovered surfactant-free, carbon dioxide (CO₂)-based microemulsion-like systems in a water/organic-solvent/CO₂ pressurized ternary mixture. “Water-rich” nanodomains embedded into a “water-depleted” matrix have been observed and characterized by the combination of Raman spectroscopy, molecular dynamics simulations, and small-angle neutron scattering. These single-phase fluids show a reversible, pressure-responsive nanostructuration; the “water-rich” nanodomains at a given pressure can be instantaneously degraded/expanded by increasing/decreasing the pressure, resulting in a reversible, rapid, and homogeneous mixing/demixing of their content. This pressure-triggered responsiveness, together with other inherent features of these fluids, such as the absence of any contaminant in the ternary mixture (<i>e</i>.<i>g</i>., surfactant), their spontaneous formation, and their solvation capability (enabling the dissolution of both hydrophobic and hydrophilic molecules), make them appealing complex fluid systems to be used in molecular material processing and in chemical engineering