Synthesis of graphene nanosheets modified with the Fe3O4@ phenol formaldehyde resin or PFR nanoparticles for their application in bio‐imagine and thermal treatment

Two different types of graphene‐based composites have been synthesized with simple assays. The multifunctional composites were obtained through loading Fe₃O₄@phenol formaldehyde resin (PFR) nanoparticles (NPs) synthesized with Fe₃O₄ NPs, hexamethylene‐tetramine, and phenol onto the surface of graphene oxide sheets in the presence of coupling agent. The Fe₃O₄@PFR loaded graphene oxide composites bring several merits. It prevents PFR NPs aggregation due to the existed graphene oxide but also endows the composites photothermal conversion property. Furthermore, the graphene‐wrapped PFR composites were prepared by mixing oxide graphene and PFR NPs at 110 °C by means of the good reduction of the hydroxyl group on the surface of PFR NPs to graphene. Under the assistance of chitosan, a building block consists of graphene‐wrapped PFR composites could be obtained. Thus, an ideal method may be developed to synthesize graphene‐wrapped PFR composites for constructing building blocks. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45007.     

Preparation of stable magnetic nanofluids containing Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@PPy nanoparticles by a novel one-pot route

Stable magnetic nanofluids containing Fe₃O₄@Polypyrrole (PPy) nanoparticles (NPs) were prepared by using a facile and novel method, in which one-pot route was used. FeCl₃·6H₂O was applied as the iron source, and the oxidizing agent to produce PPy. Trisodium citrate (Na₃cit) was used as the reducing reagent to form Fe₃O₄ NPs. The as-prepared nanofluid can keep long-term stability. The Fe₃O₄@PPy NPs can still keep dispersing well after the nanofluid has been standing for 1 month and no sedimentation is found. The polymerization reaction of the pyrrole monomers took place with Fe³⁺ ions as the initiator, in which these Fe³⁺ ions remained in the solution adsorbed on the surface of the Fe₃O₄ NPs. Thus, the core-shell NPs of Fe₃O₄@PPy were obtained. The particle size of the as-prepared Fe₃O₄@PPy can be easily controlled from 7 to 30 nm by the polymerization reaction of the pyrrole monomers. The steric stabilization and weight of the NPs affect the stability of the nanofluids. The as-prepared Fe₃O₄@PPy NPs exhibit superparamagnetic behavior.     

Ultrafine palladium nanoparticle-bonded to polyetheylenimine grafted reduced graphene oxide nanosheets: Highly active and recyclable catalyst for degradation of dyes and pigments

Much attention has been increasingly focused on the applications of noble metal nanoparticles (NPs) for the catalytic degradation of various dyes and pigments in industrial wastewater. We have demonstrated that Pd NPs/Fe₃O₄-PEI-RGO nanohybrids exhibit high catalytic activity and excellent durability in reductive degradation of MO, R6G, RB. Specific surface area was successfully prepared by simultaneous reduction of Pd(OAc)₂ chelating to PEI grafted graphene oxide nanosheets modified with Fe₃O₄. The as-prepared Pd NPs/Fe₃O₄-PEI-RGO nanohybrids were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, high-resolution TEM and energy dispersive X-ray spectroscopy, and UV-lambda 800 spectrophotometer, respectively. The catalytic activity of Pd NPs/Fe₃O₄-PEI-RGO nanohybrids to the degradation of MO, R6G, RB with NaBH4 was tracked by UV-visible spectroscopy. It was clearly demonstrated that Pd NPs/Fe₃O₄-PEI-RGO nanohybrids exhibited high catalytic activity toward the degradation of dyes and pigments, which could be relevant to the high surface areas of Pd NPs and synergistic effect on transfer of electrons between reduced graphene oxide (RGO), PEI and Pd NPs. Notably, Pd NPs/Fe₃O₄-PEI-RGO nanohybrids were easily separated and recycled thirteen times without obvious decrease in system. Convincingly, Pd NPs/Fe₃O₄-PEI-RGO nanohybrids would be a promising catalyst for treating industrial wastewater.     

The attachment of Fe3O4 nanoparticles to graphene oxide by covalent bonding

Hybrids of graphene oxide (GO) nanosheets and surface-modified Fe₃O₄ nanoparticles (NPs) were fabricated by a two-step process. First, Fe₃O₄ was modified by tetraethyl orthosilicate and (3-aminopropyl) triethoxysilane to introduce amino groups on its surface. Second, the amino groups of Fe₃O₄ were reacted with the carboxylic groups of GO with the aid of 1-ethyl-3-(3-dimethyaminopropyl)carbodiimide and N-hydroxysuccinnimide to form a GO-Fe₃O₄ hybrid. The attachment of Fe₃O₄ NPs on the GO nanosheet surface was confirmed by transmission electron microscopy and Fourier-transform infrared spectroscopy. The adsorption capacity of GO-Fe₃O₄ for methylene blue and neutral red cationic dyes was as high as 190.14 and 140.79 mg/g, respectively. The GO-Fe₃O₄ hybrids could be reduced to form graphene-Fe₃O₄ hybrids by using NaBH₄ as reducing agent and be used to prepare magnetic GO films.     

Magnetically Separable Fe3O4 Nanoparticles-Decorated Reduced Graphene Oxide Nanocomposite for Catalytic Wet Hydrogen Peroxide Oxidation

Fe₃O₄ nanoparticles-decorated reduced graphene oxide magnetic nanocomposites (Fe₃O₄/rGO NCs) were prepared by a facile one-step strategy, and further used as heterogeneous Fenton-like catalysts for catalytic wet hydrogen peroxide oxidation (CWHPO) of methylene blue (MB) at 25 °C and atmospheric pressure. The effects of variables such as the Fe₃O₄/rGO with the mass ratio of rGO, initial pH, MB concentration and H₂O₂ dosage were investigated. The Fe₃O₄/rGO NCs with rGO mass ratio of 10.0 wt % showed the highest H₂O₂-activating ability, which was six-fold than that of pure Fe₃O₄ nanoparticles (NPs). The resulting catalysts demonstrated high catalytic activity in a broad operation pH range from 5 to 9, and still retained 90.5 % catalytic activity after reuse in five cycles. Taking advantage of the combined benefits of rGO and magnetic Fe₃O₄ NPs, these Fe₃O₄/rGO NCs were confirmed as an efficient heterogeneous Fenton-like catalyst for CWHPO to treat organic pollutants. And a reasonable catalytic mechanism of Fe₃O₄/rGO NCs was proposed to interpret the degradation process.     

Preparation and characterization of conductive and magnetic PPy/Fe3O4/Ag nanocomposites

In this article, conductive and magnetic nanocomposites composed of polypyrrole (PPy), magnetite (Fe₃O₄) nanoparticles (NPs), silver (Ag) NPs, have been successfully synthesized with a two step process. First, the PPy/Fe₃O₄ was prepared by the ultrasonic in situ polymerization. Next, the PPy/Fe₃O₄/Ag was synthesized through the electrostatic adsorption. The products were characterized by fourier‐transform infrared (FTIR) spectroscopy, Scanning electron microscopy (SEM), Thermogravimetric (TG), conductivity and magnetization analysis, and the results showed that the Ag NPs with the good conductivity coated uniformly on the surface of PPy/Fe₃O₄ and improved the conductivity of PPy/Fe₃O₄/Ag composites. In addition, as compared with PPy/Fe₃O₄, PPy/Fe₃O₄/Ag composites also have the excellent electro‐magnetic property and enhanced thermostability. POLYM. COMPOS., 35:450–455, 2014. © 2013 Society of Plastics Engineers     

Preparation and characterization of spindle-like Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> mesoporous nanoparticles

Magnetic spindle-like Fe₃O₄ mesoporous nanoparticles with a length of 200 nm and diameter of 60 nm were successfully synthesized by reducing the spindle-like α-Fe₂O₃ NPs which were prepared by forced hydrolysis method. The obtained samples were characterized by transmission electron microscopy, powder X-ray diffraction, attenuated total reflection fourier transform infrared spectroscopy, field emission scanning electron microscopy, vibrating sample magnetometer, and nitrogen adsorption-desorption analysis techniques. The results show that α-Fe₂O₃ phase transformed into Fe₃O₄ phase after annealing in hydrogen atmosphere at 350°C. The as-prepared spindle-like Fe₃O₄ mesoporous NPs possess high Brunauer-Emmett-Teller (BET) surface area up to ca. 7.9 m² g^-1. In addition, the Fe₃O₄ NPs present higher saturation magnetization (85.2 emu g^-1) and excellent magnetic response behaviors, which have great potential applications in magnetic separation technology.     

Magnetic resonance imaging of glioma with novel APTS-coated superparamagnetic iron oxide nanoparticles

We report in vitro and in vivo magnetic resonance (MR) imaging of C6 glioma cells with a novel acetylated 3-aminopropyltrimethoxysilane (APTS)-coated iron oxide nanoparticles (Fe₃O₄ NPs). In the present study, APTS-coated Fe₃O₄ NPs were formed via a one-step hydrothermal approach and then chemically modified with acetic anhydride to generate surface charge-neutralized NPs. Prussian blue staining and transmission electron microscopy (TEM) data showed that acetylated APTS-coated Fe₃O₄ NPs can be taken up by cells. Combined morphological observation, cell viability, and flow cytometric analysis of the cell cycle indicated that the acetylated APTS-coated Fe₃O₄ NPs did not significantly affect cell morphology, viability, or cell cycle, indicating their good biocompatibility. Finally, the acetylated APTS-coated Fe₃O₄ nanoparticles were used in magnetic resonance imaging of C6 glioma. Our results showed that the developed acetylated APTS-coated Fe₃O₄ NPs can be used as an effective labeling agent to detect C6 glioma cells in vitro and in vivo for MR imaging. The results from the present study indicate that the developed acetylated APTS-coated Fe₃O₄ NPs have a potential application in MR imaging.     

Highly selective purification of ferulic acid from wheat bran using deep eutectic solvents modified magnetic nanoparticles

Fe₃O₄ nanoparticles (Fe₃O₄NPs) were prepared by chemical coprecipitation. Deep eutectic solvents (DESs) (ChCl/glycol, 1/2, n/n) were used to modify Fe₃O₄NPs. The obtained Fe₃O₄NPs and DESs–Fe₃O₄NPs were applied for purification of ferulic acid from wheat bran by magnetic solid-phase extraction (MSPE). The satisfactory extraction recoveries for ferulic acid (88.7%) were obtained by changing different washing and eluted solvents. The recovery of the proposed method at three spiked level analysis was 77.9–97.5%, with the relative standard deviation less than 4.5%. DESs–Fe₃O₄NPs showed good performance for ferulic acid and the proposed approach might offer a novel method for purifying complex samples.     

Graphene non-covalently tethered with magnetic nanoparticles

We describe a novel approach for coupling pristine graphene with superparamagnetic iron oxide nanoparticles to create dispersed, magnetically responsive hybrids. The magnetic iron oxide (Fe₃O₄) nanoparticles are synthesized by a co-precipitation method using ferric (Fe³⁺) and ferrous (Fe²⁺) salts and then grafted with polyvinylpyrrolidone (PVP). These PVP-grafted Fe₃O₄ nanoparticles are then used to stabilize colloidal graphene in water. The PVP branches non-covalently attach to the surface of the pristine graphene sheets without functionalization or defect creation. These Fe₃O₄–graphene hybrids are stable against aggregation and are highly responsive to external magnetic fields. These hybrids can be freeze-dried to a powder or magnetically separated from solution and still easily redisperse while retaining magnetic functionality. At all stages of synthesis, the Fe₃O₄–graphene hybrids display no coercivity after being brought to magnetic saturation, confirming superparamagnetic properties. Microscopy and light scattering data confirm the presence of pristine graphene sheets decorated with Fe₃O₄ nanoparticles. These materials show promise for multifunctional polymer composites as well as biomedical applications and environmental remediation.     

Synthesis and strengthened microwave absorption properties of three-dimensional porous Fe3O4/graphene composite foam

The three-dimensional porous Fe₃O₄/graphene composite foam as a new kind of absorbing composite with electrical loss and magnetic loss was successfully synthesized by a facile method. Fe₃O₄ was evenly attached on structure of graphene sheets which overlapped with each other to form three-dimensional porous graphene foam. The results revealed that when the mass ratio of graphene oxide (GO) and Fe₃O₄ was 1:1, the Fe₃O₄/graphene composite foam possessed the best absorption properties: the minimum reflection loss was up to ??45.08?dB when the thickness was 2.5?mm and the bandwidth below ??10?dB was 6.7?GHz when the content of the composite foam absorbents was just 8%. The micron-sized three-dimensional porous structure provided more propagation paths, enhancing the energy conversion of incident electromagnetic waves. The addition of Fe₃O₄ contributed to improving the impedance matching performance and magnetic loss. The three-dimensional porous Fe₃O₄/graphene composite foam was a kind of high-efficiency wave absorber, providing a new idea for the development of microwave absorbing materials.     

One-pot method fabrication of superparamagnetic sulfonated polystyrene/Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>/graphene oxide micro-nano composites

In this work, using monodispersed sulfonated polystyrene (SPS) microspheres as carriers, FeCl₃·6H₂O and FeSO₄·7H₂O as precursors, NaOH as precipitant in the presence of graphene oxide (GO), SPS/Fe₃O₄/GO micro-nano composites were fabricated by a simple one-pot method employing an inverse coprecipitation in-situ compound technology. The SPS/Fe₃O₄/GO micro-nano composites were characterized by scanning electron microscopy, transmission electron microscopy, X-ray powder diffractometer, Fourier transform infrared spectroscopy, nitrogen adsorption/desorption isotherms and vibrating sample magnetometer. The results show that the SPS/Fe₃O₄/GO micro-nano composites were fabricated with SPS as core, GO and Fe₃O₄ nanoparticles as shell. The SPS/Fe₃O₄/GO micro-nano composites had larger BET specific surface area, average pore width and micropore volume than the pure SPS microspheres. Meanwhile, the SPS/Fe₃O₄/GO micro-nano composites had superparamagnetism and hydrophilic property. The saturation magnetization (M_s) of the SPS/Fe₃O₄/GO micro-nano composites was 10.86 emu/g, which was enough to ensure the convenient magnetic separation of solid and liquid phase.     

Synthesis of ultrathin carbon dots-coated iron oxide nanocubes decorated with silver nanoparticles and their excellent catalytic properties

A facile ultrasonic method has been successfully developed for the fabrication of multifunctional Fe₃O₄@carbon dot/Ag (Fe₃O₄@C-dot/Ag) nanocubes (NCs), and the resulting materials are well characterized using transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FTIR), Vibrating sample magnetometer (VSM) and fluorescence measurements. The Ag nanoparticles (NPs) are uniform and well dispersed on the surface of Fe₃O₄@C-dot, while maintaining the shape and the size of the core-shell Fe₃O₄@C-dot NCs. In addition, its catalytic activities are evaluated by measuring the reduction of p-nitroaniline (p-NA) and crystal violet (CV), and the composite materials exhibit excellent catalytic activity towards reduction of p-NA and CV dye, which is superior to most reported catalysts. The good catalytic performance of Fe₃O₄@C-dot/Ag NCs may be attributed to the specific characteristics of its nanostructure and the synergistic effect on the delivery of electrons between Ag NPs and Fe₃O₄@C-dot NCs. Furthermore, the as-prepared catalysts also show good activity for the reduction of other nitrobenzene analogs. The effect of solvent and reducing agent was also studied on the catalytic activity of Fe₃O₄@C-dot/Ag NCs. Most importantly, the Fe₃O₄@C-dot/Ag catalyst shows excellent recycling stabilities, which can be potentially applied in the fields of catalysis and green chemistry.     

One-step hydrothermal synthesis and enhanced microwave absorption properties of Ni0.5Co0.5Fe2O4/graphene composites in low frequency band

Ni_0.5Co_0.5Fe₂O₄/graphene composites were synthesized successfully via one-step hydrothermal method. The crystal structure, morphology and corresponding elemental distribution, electromagnetic parameters and microwave absorption performances of the as-prepared composites were measured by XRD, SEM, TEM and VNA, respectively. The results indicated that the microwave absorbing performance can be obviously enhanced through the addition of graphene in a suitable range, the magnetic loss plays a dominant contribution for the microwave absorption of composites. The maximum reflection loss of ?30.92?dB at 0.84?GHz with a ?10?dB bandwidth over the frequency range of 0.58–1.19?GHz is obtained when the composite contains 12?wt% graphene and the thickness of sample is 4?mm. This investigation presents a simple method to prepare Ni_0.5Co_0.5Fe₂O₄/graphene composites with excellent microwave absorption performance in the low frequency band of 0.1–3?GHz.     

Influence of Fe3O4 nanoparticles decoration on dye adsorption and magnetic separation properties of Fe3O4/rGO nanocomposites

Magnetite (Fe₃O₄) nanoparticles were prepared by solvothermal method and its composites with reduced graphene oxide namely FG1, FG2, and FG3 (changing magnetite precursor loading 0.1, 0.5, and 1 respectively) were used as adsorbents for the removal of methyl violet (MV) dye. The structural and morphological results confirm that rGO sheets were decorated with Fe₃O₄ and it ensures the variation of active sites toward dye removal property. The maximum adsorption capacity obtained for FG2 was 196 mg/g. The adsorption isotherms and kinetics better fit Langmuir and pseudo-second-order kinetic model for FG1 and FG2. Increasing of Fe₃O₄ loading on rGO reduces the dye adsorption sites and too low Fe₃O₄ loading affects the magnetic separation. The optimal loading of Fe₃O₄ on rGO is important parameter for the adsorption process and fast separation of adsorbent.     

Bimagnetic hard/soft and soft/hard ferrite nanocomposites: Structural,magnetic and hyperthermia properties

Recent studies show that the chemical composition and shape of magnetic nanoparticles (NPs) play an important role in their properties. In particular, the bimagnetic NPs display useful and in many cases, more interesting properties than single-phase NPs. In this work, we prepared Fe₃O₄ and CoFe₂O₄ cube-like NPs and bimagnetic hard/soft (CoFe₂O₄/Fe₃O₄) and soft/hard (Fe₃O₄/CoFe₂O₄) nanocomposites (core/coating) using a facile and eco-friendly co-precipitation method that allows the synthesis of the cube-like NPs at temperatures near room temperature. The phase purity and the crystallinity of the NPs with a spinel structure were confirmed by the X-ray diffraction and infrared spectra techniques. Transmission electron microscopy (TEM) images revealed that the NPs have a cubic-like shape with an average dimension of 20 nm. Energy dispersive X-ray analysis, Mössbauer spectroscopy and SQUID magnetic measurements indicated the co-existence of Fe₃O₄ and CoFe₂O₄ phases in nanocomposites. In addition, the hysteresis loops exhibited a single-phase behavior in the nanocomposites that indicates there is a good exchange-coupling interaction between the hard and soft magnetic phases. The CoFe₂O₄/Fe₃O₄ nanocomposites presented a larger saturation magnetization than the CoFe₂O₄ NPs that is effective for their use in magnetic hyperthermia. Finally, we studied the hyperthermia properties of samples in an alternating magnetic field with a frequency of 276 kHz and field amplitude of 13.9 kA/m. Our results showed that magnetic hyperthermia efficiency simultaneously depends on the composition of samples along with magnetic anisotropy and saturation magnetization.     

Enhanced Cycle Stability of Magnetite/Carbon Nanoparticles for Li Ion Battery Electrodes

We demonstrate a facile synthesis of monodisperse magnetite (Fe₃O₄) nanoparticles (NPs) via a simple wet chemical route at 180°C using oleylamine (C₁₈H₃₇N), which serves as a solvent, ligand, and surfactant. The particles have a narrow size distribution centered at about 10 nm. To provide better electron conductivity and structural stability, the as‐synthesized particles are given a carbon nanocoating by pyrolysis of the residual surfactant on their surface. This pyrolysis forms a uniform thin nanocoating on each particle, and a core/shell Fe₃O₄/carbon NP network was thus obtained. The core/shell Fe₃O₄/carbon electrode shows better reversible capacity, cycle life, and rate capability than a bare Fe₃O₄ NP electrode because of its efficient electron transport and stress relaxation provided by the thin carbon layer.     

Electrochemically exfoliated graphene oxide/iron oxide composite foams for lithium storage,produced by simultaneous graphene reduction and Fe(OH)3 condensation

We describe the production of graphene-based composites for energy storage, obtained by a combination of electrochemical and solution processing techniques. Electrochemically exfoliated graphene oxide sheets (EGO) are produced using an original setup that allows fast expansion of graphite flakes and efficient exfoliation of expanded graphite via an electrochemical route. The sheets are deposited on a sacrificial nickel foam together with an iron hydroxide colloidal precursor. Calcination treatment simultaneously renders the EGO foam conductive and transforms Fe(OH)₃ into hematite (α-Fe₂O₃), yielding a nanoporous Fe₂O₃ layer on the surface of the mesoporous EGO foam, creating an ideal structure for lithium storage. The obtained graphene/metal oxide hybrid is a continuous, electrically conductive three-dimensional (3D) composite featuring a hierarchical meso–nano porous structure. A systematic study of these composites, varying the Fe₂O₃:EGO ratio, is then performed to maximize their performance as nanostructured electrodes in standard coin cell batteries.     

A nano-Fe3O4 material coated with AM/AMPS copolymer for viscosity enhancement at harsh reservoir conditions

A Fe₃O₄ nonaparticles coated with acrylamide/2-acrylamido-2-methyl-1-propanesulfonic acid copolymer(Fe₃O₄-Polymer NPs) was synthesized by emulsion polymerization. The structure of Fe₃O₄-Polymer NPs was then characterized by infrared spectroscopy, thermo-gravimetric analysis, and scanning electron microscopy. Meanwhile, the rheological properties of Fe₃O₄-Polymer NPs solution were systematically studied. The results showed that when dosage of hydrophobic Fe₃O₄-Oleic NPs is 10%, the synthesized Fe₃O₄-Polymer NPs was with the best viscosity enhancement performance, and the maximum saturation magnetization could reach to 20.0 emu/g. The apparent viscosity value of 5000 mg/L magnetic nano-composite solution was 154.6 mPa·s at 30°C. It shows strong viscosity enhancement ability and good temperature performance. Hence, it has great application potential in well stimulation of medium and high temperature oil and gas reservoirs.     

Synthesis of magnetic citric‐acid‐functionalized graphene oxide and its application in the removal of methylene blue from contaminated water

A magnetic nanocomposite of citric‐acid‐functionalized graphene oxide was prepared by an easy method. First, citric acid (CA) was covalently attached to acyl‐chloride‐functionalized graphene oxide (GO). Then, Fe₃O₄ magnetic nanoparticles (MNPs) were chemically deposited onto the resulting adsorbent. CA, as a good stabilizer for MNPs, was covalently attached to the GO; thus MNPs were adsorbed much more strongly to this framework and subsequent leaching decreased and less agglomeration occurred. The attachment of CA onto GO and the formation of the hybrid were confirmed by Fourier transform infrared spectroscopy, scanning electron microscopy, X‐ray diffraction spectrometry and transmission electron microscopy. The specific saturation magnetization of the magnetic CA‐grafted GO (GO‐CA‐Fe₃O₄) was 57.8 emu g^?1 and the average size of the nanoparticles was found to be 25 nm by transmission electron microscopy. The magnetic nanocomposite was employed as an adsorbent of methylene blue from contaminated water. The adsorption tests demonstrated that it took only 30 min to attain equilibrium. The adsorption capacity in the concentration range studied was 112 mg g^?1. The GO‐CA‐Fe₃O₄ nanocomposite was easily manipulated in an external magnetic field which eases the separation and leads to the removal of dyes. Thus the prepared nanocomposite has great potential in removing organic dyes. © 2014 Society of Chemical Industry