Core-shell Magnetite Research Articles

Novel dispersed magnetite core–shell nanogel polymers as corrosion inhibitors for carbon steel in acidic medium

Novel core–shell preparing poly(2-acrylamido-2-methylpropane sulfonic acid) (PAMPS) and copolymers with acrylic acid (AA) or acrylamide (AM) magnetic nanogels with controllable particle size produced via free aqueous polymerization at room temperature have been developed for the first time. The crosslinking polymerization was carried out in the presence of N,N′-methylenebisacrylamide (MBA) as a crosslinker, N,N,N′,N′-tetramethylethylenediamine (TEMED) and potassium peroxydisulfate (KPS) as redox initiator system. The structure and morphology of the magnetic nanogels were characterized by Fourier transform infrared spectroscopy (FTIR), transmission and scanning electron microscopy (TEM and SEM). The effectiveness of the synthesized compounds as corrosion inhibitors for carbon steel in 1 M HCl was investigated by various electrochemical techniques such as potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The results showed enhancement in inhibition efficiencies with increasing the inhibitor concentrations and temperatures. The results showed the nanogel particles act as mixed inhibitors. Adsorption of nanogel particles was found to fit the Langmuir isotherm and was chemisorption.

Synthesis and micellization of polydimethylsiloxane– carboxy-terminated poly(ethylene oxide) graft copolymer in aqueous and organic media and its application for the synthesis of core-shell magnetite particles

AbstractAn amphiphilic graft copolymer having an average of 7-8 carboxyesterterminated poly(ethylene oxide) grafted sequences on each polydimethylsiloxane main chain was obtained by a multistep procedure. Through fluorescence, surface tension and laser diffractometry methods the graft copolymer was proved to undergo micellization in aqueous media. In water, the critical micellization concentrations (CMC) are dependent on pH. Two CMC values were established for pH = 4, i.e. CMC1 = 1.01 g/L and CMC2 = 1.73 g/L corresponding to the transition from single chain to multiple chain micelles and to intermicellar aggregation, respectively. Between CMC1 and CMC2, the dimensions of micelles increased from 18 nm to 46 nm. The graft copolymer was proved to efficiently act as surfactant in the preparation of magnetite particles with a hydrophobic siloxane shell.

Magnetic nanoparticle detection using nano-SQUID sensors

We demonstrate detection of a single core-shell magnetite–silica nanoparticle (outer diameter ∼120 nm, moment ∼104μB) using an Nb dc superconducting quantum interference device (SQUID) with the loop size of 350 nm operational at T < 10 K. The system noise was minimized down to 0.2 µΦ0 Hz−1/2 using a cryogenic SQUID series array pre-amplifier. Initial measurements of an individual magnetic nanoparticle were performed and a clear change of the noise spectra of the nano-SQUID was detected at low frequencies in the presence of the nanoparticle. Similar behaviour was confirmed with an FePt nanoparticle with a larger magnetic moment (diameter ∼150 nm, moment ∼106μB). Thus, we demonstrate a magnetic sensor based on a dc nano-SQUID and enabling detection of small moments (potentially down to a few electron spins). Such a sensor is of considerable significance for nanomagnetic metrology and quantum information processing based on spin systems.

Preparation of Magnetic Silica Nanoparticle-Supported Iron Tetra-Carboxyl Phthalocyanine Catalyst and its Photocatalytic Properties

Iron tetra-carboxyl phthalocyanine (TCFePc) was covalently immobilized to the surface of core-shell magnetite silica nanoparticles (NPs) as facilely separated supported catalyst, namely P-M SiO(2) NPs, for catalyzing the degradation of organic pollutants in aqueous solution under visible light irradiation. X-ray diffraction, transmission electron microscopy (TEM), scanning electron microscopy (SEM), superconducting quantum interference device (SQUID), and ultraviolet-visible (UV-Vis) spectroscopy were used to characterize the sample. The photocatalytic activity of P-M SiO(2) NPs was determined using rhodamine B (RhB) and methyl orange (MO) as the objective decomposition substances. The results revealed that the novel supported catalyst exhibited good catalytic activity over a wide pH range, and the degradation rate of RhB and MO is up to 90% during 120 min of reaction. Moreover, it is noteworthy that the catalyst can be easily separated using an external magnetic field and employed directly for the next round of reaction.

One-step synthesis of superparamagnetic monodisperse porous Fe3O4 hollow and core-shell spheres

Monodisperse hollow and core-shell magnetite (Fe3O4) spheres have been prepared by a simple one-pot method based on hydrothermal treatment of FeCl3, citrate, polyacrylamide and urea. The as-prepared samples have been characterized using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, nitrogen adsorption-desorption isotherms, superconducting quantum interference device magnetometer. The results of control experiments reveal that citrate and polyacrylamide are crucial for the formation of spherical product and the well known Ostwald ripening process is responsible for the transformation from solid spheres to hollow and core-shell spheres. The hollow and core-shell magnetite spheres are porous and highly water soluble. They exhibit superparamagnetic properties with relatively high saturation magnetization at room temperature. The superparamagnetic properties, high magnetization, high water solubility, together with the hollow interiors will render them ideal candidates for various biomedical applications.

Rapid magnetic-mediated solid-phase extraction and pre-concentration of selected endocrine disrupting chemicals in natural waters by poly(divinylbenzene- co-methacrylic acid) coated Fe 3O 4 core-shell magnetite microspheres for their liquid chromatography–tandem mass spectrometry determination

A new Fe 3O 4/poly(divinylbenzene- co-methacrylic acid) core-shell magnetite microspheric material have been successfully developed as magnetic-mediated solid-phase extraction micro-particle sorbent in dispersion mode (MM-SPE-MP) for the determination of selected estrogenic endocrine disrupting chemicals (EDCs), namely: estrone (E1), 17β-estradiol (E2), estriol (E3), 17α-ethynylestradiol (EE2) and bisphenol-A (BPA), in natural water, via quantification by HPLC tandem mass spectrometry. The magnetite Fe 3O 4 core of this MM-SPE-MP sorbent was fabricated by a solvothermal approach and the thin layer of amphipolar poly(divinylbenzene- co-methacrylic acid) (pDVB-MAA) coating was established via suspension polymerization. The resultant core-shell MM-SPE-MP sorbent material was characterized by electron microscopy, X-ray diffraction and Fourier-transformed infrared spectroscopy. Particle size distribution of the core-shell microspheres was within the range 300–700 nm in diameter and the thickness of the pDVB-MAA coating was ca. 10 nm. This magnetite microspheric material can be easily dispersed in aqueous samples and retrieved by the application of external magnetic field via a small piece of permanent magnet. The MM-SPE-MP process for the selected estrogenic EDCs involved the dispersion of the core-shell microspheric sorbent in water samples with sonication, followed by magnetic aided retrieval of the sorbent and solvent (methanol) desorption of extracted EDCs for LC–MS/MS analysis. Partition equilibrium for all the selected EDCs onto this MM-SPE-MP sorbent was achieved within 15 min. Recoveries of the EDCs were in ranges of 56–111%. Analytes with smaller K OW value showed relatively lower recovery (and relatively longer equilibration time for partitioning). Method detection limits achieved were found to be 1–36 pg ml −1 ( n = 3), while the repeatability was 6–34% ( p < 0.05, n = 3). This work demonstrates the usefulness of MM-SPE-MP in the rapid and highly sensitive monitoring of trace organic contaminants in natural waters.

Influence of Silica-Derived Nano-Supporters on Cellobiase After Immobilization

Core shell magnetite nanoparticle (CSMN) was successfully synthesized with diameter around 125 nm according to the determination with scanning electronic microscopy. SBA-15 with diameter around 31 nm was synthesized in our previous work as another supporter for immobilized degradation enzymes. The aim of this study was to investigate the influence of silica-derived nano-supporters on cellobiase after immobilization. With covalent method, glutaraldehyde was introduced to immobilize cellobiase. The immobilized enzyme efficiency, specific activity, and its characterization, including optimum pH, pH stability, optimum temperature for enzyme reaction, and enzyme thermal stability were investigated. Results show that the method of enzyme immobilization on both nano-supporters could improve cellobiase stability under low pH and high temperature conditions compared with the free enzyme. In the aspect of immobilization efficiency, SBA had higher amount of bounded protein than that of CSMN, but had lower specific enzyme activity than CSMN, assumably due to the change in silica surface properties caused by process of supporter synthesis.

Synthesis of magnetite core–shell nanoparticles by surface-initiated ring-opening polymerization of l-lactide

Fe 3O 4–polylactide (PLA) core–shell nanoparticles were perpared by surface functionalization of Fe 3O 4 nanoparticles and subsequent surface-initiated ring-opening polymerization of l-lactide. PLA was directly connected onto the magnetic nanoparticles surface through a chemical linkage. Fourier transform infrared (FT-IR) spectra directly provided evidence of the PLA on the surface of the magnetic nanoparticles. Transmission electron microscopy images (TEM) showed that the magnetic nanoparticles were coated by PLA with a 3-nm-thick shell. The amount of grafted polymer determined by thermal gravimetric analysis was ∼13.3% by weight. X-ray diffraction (XRD) patterns of as-prepared core–shell nanoparticles showed the same structure (spinel cubic lattice type) to that of the bare core materials with similar intensity of the corresponding peaks, and that the polymer coating was amorphous. The particles could be stably dispersed in chloroform for several weeks. The prepared Fe 3O 4–PLA core–shell nanoparticles were superparamagnetic behavior with a saturation magnetization value nearly identical to that of the bare magnetic nanoparticles, rendering the Fe 3O 4–PLA nanoparticles for potential applications in both the material technology and biomedical fields.