Saturation magnetisation as an indicator of the disintegration of barium hexaferrite nanoplatelets during the surface functionalisation.

Barium hexaferrite nanoplatelets (BHF NPLs) are permanent nanomagnets with the magnetic easy axis aligned perpendicular to their basal plane. By combining this specific property with optimised surface chemistry, novel functional materials were developed, e.g., ferromagnetic ferrofluids and porous nanomagnets. We compared the interaction of chemically different phosphonic acids, hydrophobic and hydrophilic with 1-4 phosphonic groups, with BHF NPLs. A decrease in the saturation magnetisation after functionalising the BHF NPLs was correlated with the mass fraction of the nonmagnetic coating, whereas the saturation magnetisation of the NPLs coated with a tetraphosphonic acid at 80 °C was significantly lower than expected. We showed that such a substantial decrease in the saturation magnetisation originates from the disintegration of BHF NPLs, which was observed with atomic-resolution scanning transmission electron microscopy and confirmed by a computational study based on state-of-the-art first-principles calculations. Fe K-edge XANES (X-ray absorption near-edge structure) and EXAFS (Extended X-ray absorption fine structure) combined with Fourier-transformed infrared (FTIR) spectroscopy confirmed the formation of an Fe-phosphonate complex on the partly decomposed NPLs. Comparing our results with other functionalised magnetic nanoparticles confirmed that saturation magnetisation can be exploited to identify the disintegration of magnetic nanoparticles when insoluble disintegration products are formed.

ZnO and reduced graphene oxide electrodes for all-in-one supercapacitor devices.

Reduced graphene oxide/zinc oxide (rGO/ZnO) hybrid nanocomposites were prepared from synthesized GO and high energy ball milled (HEBM) ZnO for supercapacitor electrodes. Evolution of intrinsic point defects and defect-induced morphological, structural and size-dependent properties of rGO/ZnO hybrid nanocomposites were investigated using electron paramagnetic resonance (EPR) spectroscopy. CV, PEIS and GCPL techniques were employed to investigate the electrochemical behavior of the electrode materials and the effects of defects on the electrochemical performance of the electrodes by using the standard two-electrode cell in a 6 M KOH electrolyte. Analyses of the obtained CV and impedance profiles have shown the pseudocapacitive and EDLC-type contributions in the supercapacitors. Cycling stabilities were evaluated using galvanostatic charge-discharge curves at current densities between 0.10 and 2.40 A g-1. The capacitance retention of all electrodes was found to be 100% after 30 cycles at 0.30 A g-1. The electrochemical analyses revealed that the incorporation of ZnO that is rich in core defects improved the charge transfer performance and ion diffusion of the rGO electrode.

Synthesis and Morphological Control of VO2 Nanostructures via a One-Step Hydrothermal Method.

The morphology of nanostructures is a vital parameter to consider in components comprised of materials exhibiting specific functionalities. The number of process steps and the need for high temperatures can often be a limiting factor when targeting a specific morphology. Here, we demonstrate a repeatable synthesis of different morphologies of a highly crystalline monoclinic phase of vanadium dioxide (VO2(M)) using a one-step hydrothermal method. By adjusting the synthesis parameters, such as pH, temperature, and reducing agent concentration in the precursor, VO2 nanostructures with high uniformity and crystallinity are achieved. Some of these morphologies were obtained via the choice of the reducing agent that allowed us to skip the annealing step. Our results indicate that the morphologies of the nanostructures are very sensitive to the hydrazine hydrate (N2H4.H2O) concentration. Another reducing agent, dodecylamine, was used to achieve well-organized and high-quality VO2(M) nanotubes. Differential scanning calorimetry (DSC) experiments revealed that all samples display the monoclinic-to-tetragonal structural transition (MTST) regardless of the morphology, albeit at different temperatures that can be interpreted as the variations in overheating and undercooling limits. VO2(M) structures with a higher surface to volume ratio exhibit a higher overheating limit than those with low ratios.

Iron oxide nanoparticles based magnetic luminescent quantum dots (MQDs) synthesis and biomedical/biological applications: A review.

Combination of quantum dots (QDs) and magnetic nanoparticles (MNPs) as magnetic quantum dots (MQDs) has a broad range of applications as multifunctional nanoscale devices in biological imaging, medical nano-diagnostics and nanomedicine. MQDs derived from iron oxide nanoparticles and QDs possess excellent superparamagnetic and fluorescent properties, respectively making them multifunctional nanoprobes because of their; (a) strong magnetic strength with tunable functionality, such as rapid and simple magnetic separation, (b) intense and stable fluorescence from QDs combined with tunable biological functionality upon QDs' bio-activation, and (c) imaging/visualization by simple ultraviolet light exposure. These excellent features of MQD nanoprobes enable them to be used for magnetic resonance imaging (MRI) as contrast agents, nano-diagnostic systems for Point-of-Care (PoC) disease diagnosis, theranostics nanorobots and in other bio-medical applications. Most of MQDs are derived from iron based MNPs because of their abundancy, superparamagnetic properties, low cost and easy to synthesize. In this review, we present different methods employed for chemical synthesis of MQDs derived from iron oxide MNPs, their major chemical compositions and important parameters, such as precursor compositions, quantum yield and magnetic properties. The review also summarizes the most frequently used MQDs in applications such as bio-imaging, drug delivery, biosensor platforms and finally ends with future prospects and considerations for MQDs in biomedical applications.

Synergy of nano-ZnO and 3D-graphene foam electrodes for asymmetric supercapacitor devices.

Two kinds of electrode materials were produced to fabricate asymmetric supercapacitor devices: (i) Highly defective, n-type wide bandgap semiconductor ZnO nanocrystalline electrodes below 50 nm were synthesized with the aid of the high energy ball milling technique. (ii) Flexible 3D-graphene foams were synthesized via the chemical vapor deposition technique. Extensive defect structure analysis was performed via enhanced characterization techniques mainly the spectroscopy ones: electron paramagnetic resonance (EPR), Raman, and photoluminescence (PL). Compared to bulk ZnO electrodes the nanoscale ZnO electrodes revealed a dramatic increase of defect concentration. The surface defect plays a crucial role in the electrochemical performance of supercapacitor devices. Strong decreases in charge transfer resistance were observed for the smallest crystallite size which is 15 nm. This work also shows that synthesis, controlling the defect structures, electronic and electrical characterization and the device production are extremely important to obtain high performance faradaic asymmetric supercapacitors.

Electrospun Nanofibers With pH-Responsive Coatings for Control of Release Kinetics.

Functional and stimuli-responsive nanofibers with an enhanced surface area/volume ratio provide controlled and triggered drug release with higher efficacy. In this study, chemotherapeutic agent Rose Bengal (RB) (4,5,6,7-tetrachloro-2', 4',5',7'-tetraiodofluoresceindisodium)-loaded water-soluble polyvinyl alcohol (PVA) nanofibers were synthesized by using the electrospinning method. A thin layer of poly(4-vinylpyridine-co-ethylene glycol dimethacrylate) p(4VP-co-EGDMA) was deposited on the RB-loaded nanofibers (PVA-RB) via initiated chemical vapor deposition (iCVD), coating the fiber surfaces to provide controllable solubility and pH response to the nanofibers. The uncoated and [p(4VP-co-EGDMA)-PVA] coated PVA-RB nanofiber mats were studied at different pH values to analyze their degradation and drug release profiles. The coated nanofibers demonstrated high stability at neutral and basic pH values for long incubation durations of 72 h, whereas the uncoated nanofibers dissolved in <2 h. The drug release studies showed that the RB release from coated PVA-RB nanofibers was higher at neutral and basic pH values, and proportional to the pH of the solution, whereas the degradation and RB release rates from the uncoated PVA-RB nanofibers were significantly higher and did not depend on the pH of environment. Further analysis of the release kinetics using the Peppas model showed that while polymer swelling and dissolution were the dominant mechanisms for the uncoated nanofibers, for the coated nanofibers, Fickian diffusion was the dominant release mechanism. The biocompatibility and therapeutic efficiency of the coated PVA-RB nanofibers against brain cancer was investigated on glioblastoma multiforme cancer cells (U87MG). The coated PVA nanofibers were observed to be highly biocompatible, and they significantly stimulated the ROS production in cells, increasing apoptosis. These promising results confirmed the therapeutic activity of the coated PVA-RB nanofibers on brain cancer cells, and encouraged their further evaluation as drug carrier structures in brain cancer treatment.