Microwave Synthesis of Poly(Acrylic) Acid-Coated Magnetic Nanoparticles as Draw Solutes in Forward Osmosis.

Polyacrylic acid (PAA)-coated magnetic nanoparticles (MNP@PAA) were synthesized and evaluated as draw solutes in the forward osmosis (FO) process. MNP@PAA were synthesized by microwave irradiation and chemical co-precipitation from aqueous solutions of Fe2+ and Fe3+ salts. The results showed that the synthesized MNPs have spherical shapes of maghemite Fe2O3 and superparamagnetic properties, which allow draw solution (DS) recovery using an external magnetic field. Synthesized MNP, coated with PAA, yielded an osmotic pressure of ~12.8 bar at a 0.7% concentration, resulting in an initial water flux of 8.1 LMH. The MNP@PAA particles were captured by an external magnetic field, rinsed in ethanol, and re-concentrated as DS in repetitive FO experiments with deionized water as a feed solution (FS). The osmotic pressure of the re-concentrated DS was 4.1 bar at a 0.35% concentration, resulting in an initial water flux of 2.1 LMH. Taken together, the results show the feasibility of using MNP@PAA particles as draw solutes.

Superparamagnetic Fe3O4@CA Nanoparticles and Their Potential as Draw Solution Agents in Forward Osmosis.

In this study, citric acid (CA)-coated magnetite Fe3O4 magnetic nanoparticles (Fe3O4@CA MNPs) for use as draw solution (DS) agents in forward osmosis (FO) were synthesized by co-precipitation and characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), dynamic light scattering (DLS), transmission electron microscopy (TEM) and magnetic measurements. Prepared 3.7% w/w colloidal solutions of Fe3O4@CA MNPs exhibited an osmotic pressure of 18.7 bar after purification without aggregation and a sufficient magnetization of 44 emu/g to allow DS regeneration by an external magnetic field. Fe3O4@CA suspensions were used as DS in FO cross-flow filtration with deionized (DI) water as FS and with the active layer of the FO membrane facing the FS and NaCl as a reference DS. The same transmembrane bulk osmotic pressure resulted in different water fluxes for NaCl and MNPs, respectively. Thus the initial water flux with Fe3O4@CA was 9.2 LMH whereas for 0.45 M NaCl as DS it was 14.1 LMH. The reverse solute flux was 0.08 GMH for Fe3O4@CA and 2.5 GMH for NaCl. These differences are ascribed to a more pronounced internal dilutive concentration polarization with Fe3O4@CA as DS compared to NaCl as DS. This research demonstrated that the proposed Fe3O4@CA can be used as a potential low reverse solute flux DS for FO processes.

Synthesis of Poly-Sodium-Acrylate (PSA)-Coated Magnetic Nanoparticles for Use in Forward Osmosis Draw Solutions.

The synthesis of magnetic nanoparticles (MNPs) coated with hydrophilic poly-sodium-acrylate (PSA) ligands was studied to assess PSA-MNP complexes as draw solution (DS) solutes in forward osmosis (FO). For MNP-based DS, the surface modification and the size of the MNPs are two crucial factors to achieve a high osmolality. Superparamagnetic nanoparticles (NP) with functional groups attached may represent the ideal DS where chemical modifications of the NPs can be used in optimizing the DS osmolality and the magnetic properties allows for efficient recovery (DS re-concentration) using an external magnetic field. In this study MNPs with diameters of 4 nm have been prepared by controlled chemical co-precipitation of magnetite phase from aqueous solutions containing suitable salts of Fe2+ and Fe3+ under inert atmosphere and a pure magnetite phase could be verified by X-ray diffraction. Magnetic colloid suspensions containing PSA-coated MNPs with three different molar ratios of PSA:MNP = 1:1, 1:2 and 1:3 were prepared and assessed in terms of osmotic pressure, aggregation propensity and magnetization. Fourier Transform Infrared Spectroscopy (FTIR) confirmed the presence of PSA on coated MNPs and pristine PSA-MNPs with a molar ratio PSA:MNP = 1:1 exhibited an osmotic pressure of 30 bar. Molar ratios of PSA:MNP = 1:2 and 1:3 lead to the formation of less stabile magnetic colloid solutions, which led to the formation of aggregates with larger average hydrodynamic sizes and modest osmotic pressures (5.5 bar and 0.2 bar, respectively). After purification with ultrafiltration, the 1:1 nanoparticles exhibited an osmotic pressure of 9 bar with no aggregation and a sufficient magnetization of 25 emu/g to allow for DS regeneration using an external magnetic field. However, it was observed that the amount of PSA molecules attached to the MNPs decreased during DS recycling steps, leaving only strong chelate-bonded core-shell PSA as coating on the MNPs. This demonstrates the crucial role of MNP coating robustness in designing an efficient MNP-based DS for FO.

Monolithic Magneto-Optical Nanocomposites of Barium Hexaferrite Platelets in PMMA.

The incorporation of magnetic barium hexaferrite nanoparticles in a transparent polymer matrix of poly(methyl methacrylate) (PMMA) is reported for the first time. The barium hexaferrite nanoplatelets doped with Sc(3+), i.e., BaSc0.5Fe11.5O12 (BaHF), having diameters in the range 20 to 130 nm and thicknesses of approximately 5 nm, are synthesized hydrothermally and stabilized in 1-butanol with dodecylbenzenesulfonic acid. This method enables the preparation of monolithic nanocomposites by admixing the BaHF suspension into a liquid monomer, followed by in-situ, bulk free-radical polymerization. The PMMA retains its transparency for loadings of BaHF nanoparticles up to 0.27 wt.%, meaning that magnetically and optically anisotropic, monolithic nanocomposites can be synthesized when the polymerization is carried out in a magnetic field. The excellent dispersion of the magnetic nanoparticles, coupled with a reasonable control over the magnetic properties achieved in this investigation, is encouraging for the magneto-optical applications of these materials.

The magnetic and colloidal properties of CoFe2O4 nanoparticles synthesized by co-precipitation.

Magnetic CoFe(2)O(4) nanoparticles were synthesized by co-precipitation at 80 °C. This co-precipitation was achieved by the rapid addition of a strong base to an aqueous solution of cations. The investigation of the samples that were quenched at different times after the addition of the base, using transmission electron microscopy (TEM) coupled with energy-dispersive X-ray spectroscopy (EDXS) and X-ray powder diffractometry, revealed the formation of a Co-deficient amorphous phase and Co(OH)(2), which rapidly reacted to form small CoFe(2)O(4) nanoparticles. The nanoparticles grew with the time of aging at elevated temperature. The colloidal suspensions of the nanoparticles were prepared in both an aqueous medium and in a non-polar organic medium, with the adsorption of citric acid and ricinoleic acid on the nanoparticles, respectively. The measurements of the room-temperature magnetization revealed the ferrimagnetic state of the CoFe(2)O(4) nanoparticles, while their suspensions displayed superparamagnetic behaviour.

Synthesis of chromium-nickel nanoparticles prepared by a microemulsion method and mechanical milling.

A chemical and a physical method have been applied for the preparation of chromium-nickel alloy nanoparticles. These particles were designed to be used for controlled magnetic hyperthermia applications. Microemulsions with Ni2+ and Cr3+ and/or NaBH4 as precursors were prepared using the isooctane/CTAB, n-butanol/H2O system. The samples of CrxNi1-x nanoparticles with the desired composition were obtained after the reduction of their salts with NaBH4 and afterwards heat treated in a TGA in a N2 atmosphere at various temperatures. The CrxNi1-x materials were also prepared by mechanical milling. Utilizing a ball-to-powder mass ratio of 20 : 1 and selecting the proper alloy compositions we were able to obtain nanocrystalline CrxNi1-x particles. Thermal demagnetization in the vicinity of the Curie temperature of the nanoparticles was studied using a modified TGA-SDTA method. The alloy's phase composition, size and morphology were determined with XRD measurements and TEM analyses.

Ferromagnetism in suspensions of magnetic platelets in liquid crystal.

More than four decades ago, Brochard and de Gennes proposed that colloidal suspensions of ferromagnetic particles in nematic (directionally ordered) liquid crystals could form macroscopic ferromagnetic phases at room temperature. The experimental realization of these predicted phases has hitherto proved elusive, with such systems showing enhanced paramagnetism but no spontaneous magnetization in the absence of an external magnetic field. Here we show that nanometre-sized ferromagnetic platelets suspended in a nematic liquid crystal can order ferromagnetically on quenching from the isotropic phase. Cooling in the absence of a magnetic field produces a polydomain sample exhibiting the two opposing states of magnetization, oriented parallel to the direction of nematic ordering. Cooling in the presence of a magnetic field yields a monodomain sample; magnetization can be switched by domain wall movement on reversal of the applied magnetic field. The ferromagnetic properties of this dipolar fluid are due to the interplay of the nematic elastic interaction (which depends critically on the shape of the particles) and the magnetic dipolar interaction. This ferromagnetic phase responds to very small magnetic fields and may find use in magneto-optic devices.

A facile route to the synthesis of coated maghemite nanocomposites for hyperthermia applications.

CM-dextran-covered maghemite particles for applications in magnetic hyperthermia treatments were synthesized and their physical, magnetic and morphological properties were examined. Magnetic fluids were prepared and their heating properties in an alternating magnetic field were studied. The results reveal that the particle size and the thickness of the carboxy-methyl-dextran (CM-dextran) coatings have a decisive influence on the heating properties: specific absorption rate (SAR). The majority of the magnetic dissipation comes from the Neel relaxation, while the Brown contribution is small. A thermal steady state at the selected temperature (42 °C) can be achieved using synthesized maghemite particles with proper particle morphology and by controlling the magnetic field intensity or the frequency.

Colloidal stability of oleic- and ricinoleic-acid-coated magnetic nanoparticles in organic solvents.

The colloidal stability of oleic- and ricinoleic-acid-coated nanoparticles in organic solvents with dielectric constants ε(r) ranging from 2.0 to 9.8 was studied. Although the acids are structurally similar, there is an OH group in the ricinoleic acid's tail, a marked improvement in the colloidal stability of the ricinoleic-acid-coated magnetic nanoparticles in moderately polar organic solvents and monomer methyl methacrylate was observed as a result. The bonding of both acids provokes a significant change in the surface properties of the iron-oxide nanoparticles. A clear shift from a strong electron-donor to a weak electron-donor was confirmed with the bonding of the oleic acid. The effect of ricinoleic acid bonding is even more dramatic: a clear shift toward a weak electron-acceptor is evident. A detailed analysis of the total energy of interaction, including the vOCG theory, between two particles was used to describe the different behaviors of the coated nanoparticles. In the case of the oleic acid nanoparticles in an apolar medium, such as decane, a small net attraction of ∼0.84k(B)T, which is insufficient to cause nanoparticles agglomeration, exists. In polar media the net attraction is larger than 1.5k(B)T, resulting in precipitation of the oleic-acid-coated nanoparticles. The same findings apply to the ricinoleic-acid-coated nanoparticles, but only when dispersed in the apolar medium. In the polar medium an additional repulsion due to polar solvation forces exists, resulting in a decrease of the net attraction to as low as ∼0.14k(B)T.

A sonochemical method for the preparation of cadmium sulfide and cadmium selenide nanoparticles in aqueous solutions.

Sonochemistry is a branch of chemistry where sound energy in the form of ultrasound is used to influence the course of reactions. A short-term, local increase in temperature occurs when the solutions and suspensions are irradiated by ultrasound. This happens because the substance absorbs the ultrasound waves. The purpose of this research was the synthesis of CdS and CdSe nanoparticles. We used cadmium sulfate hydrate (CdSO(4).8/3H(2)O), elemental S and Se. Aqueous solutions of NaOH, Na(2)SO(3) and EDTA were used as the solvents. During the syntheses, we used a direct immersion ultrasound probe by vibracell. The device operates with a constant frequency of 20 kHz, with the possibility to change the amplitude and with it the input of energy to the time unit. The products were characterized by X-ray powder diffraction (XRD), thermal analyses (TGA, SDTA) and TEM analyses.

Barium hexaferrite suspensions for electrophoretic deposition.

In this investigation we have looked at the preparation of barium hexaferrite suspensions, with the stability of the magnetic barium hexaferrite particles being increased by the addition of a surfactant, dodecylbenzylsulfonic acid (DBSA). The influence of the solubility DBSA in different solvents and its adsorption onto the surfaces of particles with different sizes were determined from zeta-potential measurements. The most suitable and stable suspensions of barium hexaferrite particles, regardless of their sizes, were obtained in 1-butanol, and these were then used for a subsequent electrophoretic deposition. The microstructures of the deposits were examined with electron microscopy. The thickness and density of the deposits as a function of the electric field, the zeta-potential, the particle size, and the separation distance between the electrodes were investigated. The thickness of the deposits was found to increase with the increasing zeta-potential of the suspension and with the increasing separation distance between the electrodes. Denser deposits were obtained from the suspensions of smaller particles that had narrower particle size distributions.

Sonochemical synthesis of nanocrystalline mercury sulfide, selenide and telluride in aqueous solutions.

Nanocrystalline mercury chalcogenides HgE (E=S, Se, Te) were synthesized in a single step by a convenient, simple sonochemical method. Mercury nitrate, Hg(NO3)2, dissolved in 0.1 M ethylenediamine tetraacetic acid (EDTA), was used as the source of mercury and elemental chalcogenes, dissolved in a NaOH solution, as the sources of chalcogenide. The products were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDAX). The synthesis procedure is simple and uses less toxic reagents than the previously reported methods. The results showed that the complexing agent EDTA plays a crucial role in the process.

Reverse micelles: inert nano-reactors or physico-chemically active guides of the capped reactions.

Reverse micelles present self-assembled multi-molecular entities formed within specific compositional ranges of water-in-oil microemulsions. The structure of a reverse micelle is typically represented as nano-sized droplet of a polar liquid phase, capped by a monolayer of surfactant molecules, and uniformly distributed within a non-polar, oil phase. Although their role in serving as primitive membranes for encapsulation of primordial self-replicating chemical cycles that anticipated the very origins of life has been proposed, their first application for 'parent(hesis)ing' chemical reactions with an aim to produce 'templated' 2D arrays of nanoparticles dates back to only 25 years ago. Reverse micelles have since then been depicted as passive nano-reactors that via their shapes template the growing crystalline nuclei into narrowly dispersed or even perfectly uniform nano-sized particles. Despite this, numerous examples can be supported, where from deviations from the simple unilateral correlations between size and shape distribution of reverse micelles and the particles formed within may be reasonably implied. A rather richer, dynamical role of reverse micelles, with potential significance in the research and design of complex, self-assembly synthesis pathways, as well as possible adoption of their application as an aspect of biomimetic approach, is suggested herein.