Oleic Acid-coated Fe3O4 Nanoparticles Research Articles

Synthesis of varied oleic acid-coated Fe3O4 nanoparticles using the co-precipitation technique for biosensor applications

This study successfully synthesized oleic acid (OA)-coated Fe3O4 nanoparticles using the coprecipitation method for the needs of biosensor applications, as shown through the characterization of structure and morphology using XRD and TEM. This observation used 0.75 ml of OA (Fe3O4-OA(0.75)) and 1.25 ml of OA (Fe3O4-OA(1.25). A decrease in particle size distribution from 18.55 nm to 16.30 nm was observed, which means a reduction in agglomeration and increased dispersibility. Vibrating Sample Magnetometer (VSM) observations showed that the saturation magnetization of Fe3O4 particles modified with OA decreased from 47.71 emu/g to 45.90 emu/g at Fe3O4-OA(0.75) and decreased again to 42.29 emu/g at Fe3O4-OA(1.25). But they all show soft ferromagnetic properties with very low coercivity, making them suitable for Giant Magnetoresistance (GMR) biosensor applications. A series of concentrations in ethanol solution were performed to evaluate the detection sensitivity of GMR for these pure and oleic acid-modified Fe3O4 samples. Concentrations of 2, 5, 10, 15, 25, and 35 mg/ml were integrated at 2 μL each onto the surface of the GMR chip. A decrease in sensitivity was observed due to the change in saturation. Pure Fe3O4 with a sensitivity of 5.07 mV (mg/ml) decreased to 4.49 mV (mg/ml) and 3.35 mV (mg/ml) after oleic acid coating. Thus, although adding a proportional amount of oleic acid can slightly decrease the saturation magnetization, it can be a valuable method for applications such as GMR biosensors that demand high dispersibility and sensitivity that remains strong.

The Effect of a DC Magnetic Field on the AC Magnetic Properties of Oleic Acid-Coated Fe3O4 Nanoparticles.

The AC magnetic properties of a sample of Fe3O4 nanoparticles coated with oleic acid have been investigated with the help of AC susceptibility measurements. In particular, several DC magnetic fields have been superimposed on the AC field, and their effect on the magnetic response of the sample has been analysed. The results show the presence of a double peak structure in the imaginary component of the complex AC susceptibility measured as a function of the temperature. A preliminary evaluation of the Mydosh parameter for both peaks gives the information that each one of them is associated with a different state of interaction between nanoparticles. The two peaks evolve both in amplitude and position when the intensity of the DC field is changed. The field dependence of the peak position shows two different trends, and it is possible to study them in the framework of the currently existing theoretical models. In particular, a model of non-interacting magnetic nanoparticles has been used to describe the behaviour of the peak at lower temperatures, whereas the behaviour of the peak at higher temperatures has been analysed in the framework of a spin-glass-like model. The proposed analysis technique can be useful for the characterisation of magnetic nanoparticles used in several types of applications, such as biomedical and magnetic fluids.

Fabrication of porous polymer particles containing BiVO4 and Fe3O4 nanoparticles using block copolymer as porogen for effective dye removal

Hybrid porous particles (HPPs) of poly(methyl methacrylate-divinylbenzene) P(MMA-DVB) containing a visible light-photocatalyst bismuth vanadate (BiVO4) and magnetite (Fe3O4) nanoparticles (NPs) were synthesized and employed as a reusable material for effective dye removal. The porous structure increasing the surface to volume ratio and high water diffusivity of HPPs, prepared via the microsuspension iodine transfer polymerization, was generated by using poly(methacrylic acid)-block-poly(MMA-3-[trimethoxysilyl] propyl methacrylate) (PMAA-b-P(MMA-MPS)) as porogen. The block copolymer also acting as a surface modifier of BiVO4 NPs allowed the encapsulation of this photocatalyst together with oleic acid coated Fe3O4 NPs in spherical HPPs. The fabricated HPPs could efficiently remove methylene blue (MB) up to 235 mg/g-BiVO4 based on the adsorption and photocatalytic degradation mechanism caused by the particle porosity and BiVO4 NPs, respectively. Moreover, the incorporated Fe3O4 NPs provided the magnetic separation ability of the HPPs for their reusability up to 5 cycles with a high MB removal performance of > 86. These HPPs would be good candidates for effective dye removal in contaminated water

Rheological Tunable Magnetic Fluids with Long-Term Stability.

Magnetic fluids have advantages such as flow ability and solid-like property in strong magnetic fields, but have to suffer from the tradeoff between suspension stability and flow resistance. In this work, a thermal/photo/magnetorheological water-based magnetic fluid is fabricated by using oleic acid-coated Fe3 O4 (Fe3 O4 @OA) nanoparticles as the magnetic particles and the amphiphilic penta block copolymer (PTMC-F127-PTMC)-based aqueous solution as the carrier fluid. Due to the hydrophobic self-assembly between Fe3 O4 @OA and PTMC-F127-PTMC, the Newtonian-like magnetic fluid has outstanding long-term stability and reversible rheological changes between the low-viscosity flow state and the 3D gel structure. In the linear viscoelastic region, the viscosity exhibits an abrupt increase from below 0.10Pa s at 20°C to ≈1.3×104 Pa s at 40°C. Benefitting from the photothermal and magnetocaloric effects of the Fe3 O4 @OA nanoparticles, the rheological change process also can be controlled by near infrared light and alternating magnetic field, which endows the magnetic fluid with the applications in the fields of mobile valves, moveable switches, buffer or damping materials in sealed devices, etc.

Probing the Interactions between Pickering Emulsion Droplets Stabilized with pH-Responsive Nanoparticles.

The presence and adsorption of particles at the oil/water interface play a critical role in stabilizing Pickering emulsions and affecting their bulk behavior. For water-in-oil (W/O) and oil-in-water (O/W) Pickering emulsions with pH-responsive nanoparticles, their interaction forces and stabilization mechanisms at the nanoscale have not been reported. Herein, the Pickering emulsions formed by oil/water mixtures under different pH values with bilayer oleic acid-coated Fe3O4 nanoparticles (Fe3O4@2OA NPs) were characterized using microscopy imaging and zeta potential and interfacial tension (IFT) measurements. The interaction forces between formed emulsion droplets were quantified using an atomic force microscope (AFM) drop probe technique. A W/O emulsion formed at pH 2 and 4 is mainly stabilized by the steric barrier formation of confined particle layers (with Fe3O4@2OA NPs and aggregates). At pH 9 and 11, an O/W emulsion is formed, and its stabilization mechanism is mainly due to relatively low IFT, strong electrostatic repulsion due to carboxyl groups, and steric repulsion from confined nanoparticles and aggregates, leading to a stable confined thin water film. Increasing the maximum loading force and dwelling time enhances the confinement of Fe3O4@2OA particles and aggregates at the oil/water interface. This work provides useful insights into the interaction and stabilization mechanisms of Pickering emulsions with stimuli-responsive interface-active particles.

Oriented layered assemblies of graphene nanosheets/Fe3O4 nanoparticles as a superior anode material for lithium ion batteries

The development of more effective electrodes for lithium ion batteries requires increasing the specific surface area and improving the reversible capacity of the materials. We prepared a hybrid multilayer film consisting of graphene oxide (GO) nanosheets and iron oxide (Fe3O4) nanoparticles assembled using the Langmuir-Schaefer (LS) technique. The GO-Fe3O4 hybrid monolayer is formed by ligand exchange between GO suspended in the subphase and oleic acid-coated Fe3O4 nanoparticles dispersed at the liquid-gas interface. Transmission electron microscopy (TEM) and grazing incidence small angle X-ray scattering (GISAXS) results indicate that the GO-Fe3O4 composite monolayer at the interface possesses closely packed hexagonal structure of the Fe3O4 nanoparticles with high coverage upon monolayer compression. The multilayer GO-Fe3O4 hybrid materials were prepared by repeated LS deposition, exhibiting high reversible capacity (~600 mAh g−1) and superior cycle stability over 1000 cycles.

An efficient approach for the synthesis of magnetic separable Fe3O4@TiO2 core-shell nanocomposites and its magnetic and photocatalytic performances

A convenient and efficient approach for the synthesis of Fe3O4@TiO2 nanocomposites with core-shell structure has been demonstrated. It takes four steps for synthesis process. Oleic acid-coated monodisperse Fe3O4 nanoparticles are obtained firstly, and surface modified Fe3O4 nanoparticles are followed to proceed. Then Fe3O4@TiO2 core-shell nanocomposites are subsequently synthesized using tetrabutyl titanate (TBOT) as titanium source and some polar aprotic solvents used as the mixed solvents. The obtained core-shell structure is composed of a central Fe3O4 nanoparticle core with sequential TiO2 surface, whereas the outer TiO2 coating was useful for the degradation of organic contaminants. Different core-shell nanocomposites in different polar solution are obtained. Shell thickness of Fe3O4@TiO2 nanocomposites could be adjusted rationally by changing synthetic conditions. The measurements of the magnetic properties demonstrate that the Fe3O4@TiO2 core-shell nanocomposites exhibit magnetic behavior at room temperature. The degradation of methylene blue solution was also explored.

Ferrofluids for Active Shock Absorbers

This paper deals with synthesis and characterization of a ferrofluid and examining its suitability for developing a damper whose damping behavior can be controlled by applying magnetic field. In particular, ferrofluids, consisting of oleic acid coated Fe3O4 nanoparticles dispersed in kerosene, have been synthesized and characterized. Oleic acid coated nanoparticles of Fe3O4 have been characterized using XRD, TEM and FTIR. These studies show that sizes of particles are in range of 6 to17 nm and oleic acid is adsorbed on the surface of above particles. The role of damping medium on the damping behavior of a damper has been studied by carrying out studies with several different liquids. The effect of magnetic field on the damping behavior of ferrofluid based damper has also been studied. It is seen that damping ratio depends on the viscosity of damping medium. In particular, it is seen that damping ratio of a ferrofluid based damper increases on application of magnetic field. However, the sensitivity of damping ratio to the magnetic field has been found to be different for different ferrofluids. It seems, magnetic moment or size of the particle plays an important role in deciding the sensitivity of the damper. No attempt has been made to improve the sensitivity of the damper by optimizing various parameters. All the same, present studies provide a proof of concept for smart shock absorber.

Evidence of particle-particle interaction quenching in nanocomposite based on oleic acid-coated Fe3O4 nanoparticles after over-coating with essential oil extracted from Croton cajucara Benth

This study reports on the synthesis and characterization of oleic acid (OA)-coated Fe3O4 nanoparticles (Fe3O4@OA) and AO plus essential oil (EO)-coated Fe3O4 nanoparticles (Fe3O4@OA/EO). The EO was extracted from Croton cajucara Benth (CCB) leaves; a plant from the Brazilian Amazon region. Structural and morphological characterizations were carried out using X-ray diffraction (XRD) and transmission electron microscopy (TEM) images, respectively. Additionally, thermogravimetric analysis and magnetization measurements (hysteresis cycle, zero field-cooled-ZFC, field-cooled-FC, and AC susceptibility) were used to assess thermal and magnetic properties of the as-fabricated samples. Rietveld refinement of XRD pattern confirmed the formation of magnetite phase with no extra phases, whereas TEM images revealed spherically-shaped nanoparticles in the Fe3O4@OA and (Fe3O4@OA/EO) samples with a mean physical size of 8.5 nm and 10.1 nm, respectively. ZFC and FC curves revealed the occurrence of blocked/frozen state below the maximum peak (Tmax) at ∼81 K and ∼40 K for the Fe3O4@OA and (Fe3O4@OA/EO) samples, respectively. Moreover, low-temperature AC susceptibility vs. T curves recorded in the range of 0.2–1000 Hz showed that the OA coating of the Fe3O4 nanoparticles leads to a spin-glass-like behavior credited to the strong particle-particle interactions; meanwhile, the double layer (AO + EO) coating of the Fe3O4 nanoparticles remarkably quenches the particle-particle interaction leading to a superparamagnetic-like behavior.

Ferrofluid synthesis using oleic acid coated Fe3O4 nanoparticles dispersed in mineral oil for heat transfer applications

Ferrofluids are stable dispersion of iron oxide nanoparticles in a carrier fluid which find potential applications in heat transfer. Fe3O4 nanoparticles of mean size in the range of 5–10 nm were synthesized using conventional co-precipitation method. This work deals with the synthesis of ferrofluids using mineral oil as a carrier fluid and oleic acid coated Fe3O4 nanoparticles as dispersed phase. Morphology (shape and size) and crystallinity of the synthesized nanoparticle is captured using TEM and XRD. Oleic acid coating on nanoparticle is probed using FTIR for confirming the stability of ferrofluid. Thermal properties of mineral oil based ferrofluid with varying concentration of nanoparticles are evaluated in terms of thermal conductivity. It was found that the thermal conductivity of ferrofluid increases upto 2.5% (w/v) nanoparticle loading, where a maximum enhancement of ∼51% in thermal conductivity was recorded as compared to the base fluid.

Ionic liquid enhanced magnetic solid-phase extraction of phthalate esters in food samples with oleic acid coated-Fe3O4 nanoparticles prior to HPLC

ABSTRACTA novel method based on ionic liquid enhanced magnetic solid-phase extraction (MSPE) coupled with high-performance liquid chromatography (HPLC) for the separation/analysis of phthalate esters (PAEs) in food samples was established. 1-hexyl-3-methylimidazoliu-hexafluorophosphate ([C6MIM][PF6]) was used to coat oleic acid Fe3O4 nanoparticles with core–shell structures to prepare MSPE agents (Fe3O4@OA@IL). The main parameters affecting the extraction efficiency of PAEs were studied. Under the optimal conditions, the calibration curves were linear in the range of 5–5000 ng mL−1 (R2 = 0.9972–0.9998) of four PAEs. The limit of detections (LODs) and relative standard deviations (RSDs, n = 5) of the method were 1.27–2.95 ng mL−1 and 3.9–5.3%, respectively.

Large-Scale, Facile Transfer of Oleic Acid-Stabilized Iron Oxide Nanoparticles to the Aqueous Phase for Biological Applications.

Fe3O4 nanoparticles synthesized via thermal decomposition in the organic phase have attracted tremendous research interest because of their unique morphology, size dispersion, and crystallinity. However, their poor water dispersibility strongly limited their development in biomedical applications. Therefore, a phase-transfer strategy through which hydrophobic nanoparticles with good performance in the aqueous phase can be obtained is an extremely critical issue. Herein, we present a large-scale, facile, highly efficient strategy for the phase transfer of oleic acid-coated Fe3O4 nanoparticles via a reverse-micelle-based oxidative reaction. The reverse micelle system improves the efficiency of the interface oxidative reaction and prevents the aggregation of nanoparticles during the reaction, facilitating the transfer of Fe3O4 nanoparticles from the organic phase to the aqueous phase. The transferred Fe3O4 nanoparticles are used as a T2 contrast agent to perform magnetic resonance imaging of CNE2 cells (nasopharyngeal carcinoma cell line). In addition, the free carboxyl groups on the surface of transferred nanoparticles can also be programmed to permit the conjugation of other molecules, in turn allowing nanoparticles to be extended in biological targeting or biological recognition applications. Therefore, this strategy offers a promising platform for the large-scale, highly efficient phase transfer of oleic acid-capped nanoparticles and may become a new paradigm to promote the development of diverse nanoparticles for widespread biomedical applications.

Recyclable magnetic-Pickering emulsion liquid membrane for extracting phenol compounds from wastewater

A Pickering emulsion liquid membrane (PELM) stabilized by oleic acid-coated Fe3O4 nanoparticles has been prepared and used to extract phenolic compound from wastewater. Compared to traditional emulsion liquid membrane (ELM), nano-Fe3O4 particle-stabilized PELM can be easily demulsified after extraction under magnetic field, which could greatly improve the reutilization of oil phase and reduce the energy consumption of ELM operation. Practically, our PELM contains tri-n-butyl phosphate as a carrier, corn oil as a liquid membrane, and sodium hydroxide as a stripping agent. The stability of Pickering emulsion was investigated under different homogenization speeds and characterized by centrifugal stability method. Reutilization of emulsifier and oil phase exhibited comparable extraction efficiency after three cycles of remediation, and no significant change on the particle property was observed.

Magnetic boron specific chelating microsphere by dispersion polymerisation for boron adsorption

Magnetic poly(glycidylmethacrylate) microspheres were prepared by dispersion polymerisation in the presence of oleic acid coated Fe3O4 nanoparticles and modified by N-methyl-D-glucamine for the fabrication of magnetic boron specific chelating microspheres. The structure and properties of obtained microspheres were analysed by scanning electron microscopy, Fourier transform infrared spectroscopy and vibrating sample magnetometer. The utility efficiency of monomer reached 60% under an optimum dropwise feeding process. The magnetic microspheres are ∼1 μm in size, and superparamagnetic nanoparticles have a saturation magnetisation of 17.1 emu g− 1 and a Fe3O4 content of 28 wt.%. The resultant boron specific chelating sorbent presents an adsorption capacity of 0.43 mmol g− 1 in the optimum conditions. Fast separation by magnetic field makes the prepared microspheres useful for the purification of boron contaminated water. These microspheres will exhibit strong potential in the treatment of boron contaminated water by rapid cost efficient separation under external magnetic field.

Polymer-coated magnetic nanospheres for preconcentration of organochlorine and pyrethroid pesticides prior to their determination by gas chromatography with electron capture detection

Magnetic polymer nanospheres were prepared and used as adsorbents for the extraction of organochlorine and pyrethroid pesticides from water samples. The adsorbents were synthesized by miniemulsion polymerization of N-vinylimidazole and divinylbenzene and simultaneous encapsulation of oleic acid-coated Fe3O4 nanoparticles. Following desorption with ethyl acetate, the target analytes β-hexachlorocyclohexane, δ-hexachlorocyclohexane, p,p’-DDE, heptachlor, trans-chlordan, cis-chlordan, bifenthrin, β-cypermethrin, δ-methrin, λ-cyhalothrin and esfenvalerate were determined by gas chromatography with electron capture detection. Desorption conditions, extraction times and sample volume were screened by Plackett-Burman design and optimized by Box-Behnken design. Under the optimum conditions, the organochlorines can be quantified in the 20 to 400 ng L−1 concentration range, and the pyrethroids in the 400 to 4000 ng L−1 concentration range. The recoveries of organochlorines and pyrethroids from spiked real water samples are between 77.6 and 97.3 %, with relative standard deviations between 0.9 and 10.0 %. The method for magnetic solid phase extraction described here is fast, simple and friendly to the environment.

Imaging and Chemotherapeutic Comparisons of Iron Oxide Nanoparticles Chemically and Physically Coated with Poly(ethylene glycol)-<I>b</I>-Poly(<I>ε</I>-caprolactone)-<I>g</I>-Poly(acrylic acid)

We designed a new copolymer, poly(ethylene glycol)-block-poly(ε-caprolactone)-graft-poly(acrylic acid) (PAA-PEC), which could be chemically and physically coated onto iron oxide (Fe3O4) nanoparticles for theranostic applications. The chemically PAA-PEC-coated Fe3O4 nanoparticles (PAA-PEC-IO) were prepared using the carboxylic groups of PAA-PEC to bind the Fe3O4 nanoparticles during a co-precipitation reaction. Because of the amphiphilic properties of PAA-PEC, the compound self-assembled into a core-shell structure. The hydrophobic oleic acid-coated Fe3O4 nanoparticles could then be physically encapsulated inside the hydrophobic core of PAA-PEC (PAA-PEC-OA-IO) using an emulsion technique. A similar amount of iron content was controlled in both the PAA-PEC-IO and PAA-PEC-OA-IO (-23%). The particle diameters, morphologies, superparamagnetism, drug loading efficiency, and transversal relaxivity (r2) were studied and compared between the two magnetic nanoparticles. All results displayed the chemically-synthesized PAA-PEC-IO nanoparticles had higher potential than did the physically-synthesized PAA-PEC-OA-IO as an MRI contrast agent and a drug delivery carrier. Rodamine123-linked PAA-PEC-IO (PAA-PEC-IO-Rh123) was used as a molecular probe. Flow cytometric diagrams indicated that cellular internalization of PAA-PEC-IO occurred primarily through clathrin-mediated endocytosis.

Magnetic polar post-cross-linked resin and its adsorption towards salicylic acid from aqueous solution

A novel magnetic polar post-cross-linked resin M-PMD-P-A was prepared, characterized and evaluated for its adsorption towards salicylic acid from aqueous solution. M-PMD-P-A was prepared using suspension polymerization of methyl acrylate (MA) and divinylbenzene (DVB) with addition of oleic acid-coated Fe3O4 nanoparticles, followed by a Friedel–Crafts reaction and an amination reaction. The results indicated that M-PMD-P-A had a large equilibrium capacity towards salicylic acid, and both of the Langmuir and Freundlich models were appropriate for fitting the equilibrium data. The breakthrough capacity at C/C0=0.05 and saturated capacity at C/C0=0.95 of salicylic acid on M-PMD-P-A were measured to be 45.65 and 62.25mg/mL wet resin, respectively. A mixture desorption solvent containing 0.01mol/L of NaOH (w/v) and 20% of ethanol (v/v) could regenerate the resins completely and the resins exhibited good reusability.

Temperature dependent light transmission in ferrofluids

We investigate the influence of temperature on the magnetic field induced light transmission in a kerosene based ferrofluid containing oleic acid coated Fe3O4 nanoparticles, where the direction of propagation of light is parallel to the direction of the external magnetic field. At a fixed temperature the transmitted light intensity is found to monotonically increase with incident wavelength due to reduced extinction efficiency at higher wavelength. The transmitted intensity decreases with external magnetic field due to enhanced scattering from the field induced linear chain like structures along the direction of the external magnetic field and due to the build-up of standing waves inside the scattering medium. The extinction of the field induced transmitted light intensity is found to occur at a lower external field as the sample temperature is lowered. The rate of extinction of normalized transmitted light intensity decreased linearly with increasing sample temperature due to slower field induced aggregation kinetics because of an increased Brownian motion of the suspended nanoparticles and a reduced coupling constant. The observed temperature dependent magneto-optical properties of magnetic nanofluids can be exploited for applications in optical devices.

Phosphatidylcholine-coated iron oxide nanomicelles for in vivo prolonged circulation time with an antibiofouling protein corona.

We report the synthesis of micellar phosphatidylcholine-coated superparamagnetic iron oxide nanoparticles as a new long circulation contrast agents for magnetic resonance imaging. Oleic acid-coated Fe3 O4 nanoparticles were first prepared through thermal degradation and then encapsulated into small clusters with a phosphatidylcholine coating to obtain hydrophilic nanomicelles. A thorough characterization confirmed the chemical nature of the coating and the excellent colloidal stability of these nanomicelles in aqueous media. Magnetization and relaxivity properties proved their suitability as magnetic resonance imaging (MRI) contrast agent and in vitro cell viability data showed low toxicity. Vascular lifetime and elimination kinetics in the liver were assessed by blood relaxometry and by in vivo MRI in rats and compared with "control" particles prepared with a polyethylene glycol derivative. These micellar particles had a lifetime in blood of more than 10 h, much longer than the control nanoparticles (≈2 h), which is remarkable considering that the coating molecule is a small biocompatible zwitterionic phospholipid. The protein corona was characterized after incubation with rat serum at different times by high-throughput proteomics, showing a higher proportion of bound apolipoproteins and other dysopsonins for the phosphatidylcholine particles. The antibiofouling properties of this corona and its resistance to the adsorption of proteins corroborate the observed enhanced stability and prolonged systemic circulation.

Preparation and Characterization of Magnetic Microspheres with an Epoxy Group Coating and Their Applications for Lipase Immobilization

Magnetic microspheres coated with epoxy groups (Ep) were prepared by suspension polymerization of glycidyl methacrylate (GMA) and styrene (St) in the presence of oleic acid-coated Fe3O4 (OA-Fe3O4) nanoparticles, using ethylene glycol dimethacrylate (EGDMA) as a cross-link reagent. The resulting magnetic microspheres were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and vibrating sample magnetometry (VSM). It was verified that the magnetic microspheres had small diameters of 10–30 μm, as well as having super paramagnetism with a saturation magnetization of 10.5 emu/g. Porcine pancreas lipase (PPL) was selected as a model enzyme to be covalently immobilized (IPPL) on the magnetic microspheres via the reactive Ep; they had an activity yield up to 58.6%, when the protein loading reached 55.4 mg/g supports. In addition, the resulting immobilized lipases exhibited a better thermal stability, temperature and pH endurance than that of the free ones. In particular, an excellent reusability of IPPL, which could meet industrial requirements, was achieved.