Synthesis and Characterization of the Superparamagnetic Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>/Ag Nanocomposites

The study of superparamagnetic Fe₃O₄/Ag nanocomposites have received great research attention due to their wide range of potential applications in biomedicine. In this report, an easy microemulsion reaction was employed to synthesis Fe₃O₄/Ag nanocomposites with self-aggregated branch like nanostructures. The Fe₃O₄ nanoparticles were initially prepared and subsequently AgNO₃ was reduced as Ag by chemical reduction method. The results showed that the average size of the Fe₃O₄/Ag nanocomposites were in the range of 10 ± 2 nm. These nanoparticles were self-aggregated as a branch like nanostructure. The optical properties of Fe₃O₄ nanoparticles were modified with surface plasmon resonance of Ag nanoparticles. The observed saturation magnetization of superparamagnetic Fe₃O₄/Ag nanocomposites were 40 emu/g.     

Ag nanoparticles decorated Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>/chitosan nanocomposite: synthesis,characterization and application toward electrochemical sensing of hydrogen peroxide

We studied a rapid, sensitive and selective amperometric sensor for determination of hydrogen peroxide by electrodeposited Ag NPs on a modified glassy carbon electrode (GCE). The modified GCE was constructed through a step by step modification of magnetic chitosan functional composite (Fe₃O₄–CH) and high-dispersed silver nanoparticles on the surface. The resulted Ag@Fe₃O₄–CH was characterized by various analytical methods including Fourier transform infrared spectroscopy, X-ray diffraction, transmission electron microscopy, scanning electron microscopy and cyclic voltammetry. The proposed sensor employed Ag@Fe₃O₄–CH/GCE as the working electrode with a linear current response to the hydrogen peroxide concentration in a wide range from 0.01 to 400 µM with a low limit of detection (LOD = 0.0038 µM, S/N = 3). The proposed sensor showed superior reproductivity, sensitivity and selectivity for the detection of hydrogen peroxide in environmental and clinical samples.     

The hemoglobin-modified electrode with chitosan/Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanocomposite for the detection of trichloroacetic acid

A hemoglobin (Hb)-modified electrode based on chitosan/Fe₃O₄ nanocomposite coated glassy carbon has been constructed for trichloroacetic acid (TCA) detection. The structure of chitosan/Fe₃O₄ nanocomposite was investigated using energy-dispersive X-ray analysis (EDS) and X-ray diffraction (XRD) patterns. The electron transfer rate constant (k _s) of Hb was estimated for as high as 3.12 s^?1. The immobilized Hb exhibited excellent electro-catalytic activity toward the reduction of TCA. The response current regressed to the concentration of TCA within the range of 5.70 μM to 205 μM with a detection limit of 1.9 μM (S/N = 3).     

Graphene oxide/Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@polythionine nanocomposite as an efficient sorbent for magnetic solid-phase extraction followed by high-performance liquid chromatography for the determination of duloxetine in human plasma

Herein, an efficient graphene oxide/Fe₃O₄@polythionine (GO/Fe₃O₄/PTh) nanocomposite sorbent was introduced for magnetic solid-phase extraction combined with high-performance liquid chromatography–ultraviolet detection of duloxetine (DLX) in human plasma. To prepare the sorbent, an oxidative polymerization of thionine on the surface of magnetic GO was utilized while PTh was simply used as a surface modifier to improve extraction efficiency. Transmission electron microscopy, scanning electron microscopy, X-ray diffraction, energy-dispersive X-ray analysis, vibrating sample magnetometry, Fourier transform-infrared spectroscopy and Brunauer–Emmett–Teller technique were applied to characterize the prepared nanoparticles. Firstly, effective parameters controlling the performance of the extraction process were evaluated in detail and optimized. Under the optimized conditions, calibration curve showed linearity in the range of 2–2500 ng mL^?1 with regression coefficient corresponding to 0.998. Limits of detection (LOD, S/N = 3) and quantification (LOQ, S/N = 10) were 0.5 and 2 ng mL^?1, respectively. Reasonable intra-assay (3.5–4.5%, n = 6) and inter-assay (3.8–6.7%, n = 9) precision represented acceptable performance of the procedure. The applicability of the method was successfully extended to the determination of DLX in human plasma after oral administration of 60 mg single dose of the drug and finally some pharmacokinetic data was achieved.     

Controlled synthesis and enhanced bacteriostatic activity of Mg(OH)<Subscript>2</Subscript>/Ag nanocomposite

Silver nanoparticles have good sterilization performance due to their small size and large specific surface area, while the small size also brings about reunification and reduces the sterilization activity. To resolve the problem, magnesium hydroxide [Mg(OH)₂] microsphere was designed as a supported material to load silver particles on its surface. Mg(OH)₂ microspheres were successfully synthesized under the control of a biotemplate of eggshell membrane. X-ray diffraction, thermal gravimetric analysis/differential scanning calorimetry, and transmission electron microscopy were performed to characterize the Mg(OH)₂ microspheres. The results indicate that the Mg(OH)₂ microspheres of average size ~ 2 μm were formed from nanoflakes. The silver nanoparticles were loaded on the surface of Mg(OH)₂ microspheres to form Mg(OH)₂/Ag nanocomposite, which exhibited enhanced antibacterial effect compared to that of silver nanoparticles. The enhanced antibacterial mechanism was investigated in detail.     

Highly sensitive simultaneous quantification of buprenorphine and norbuprenorphine in human plasma by magnetic solid-phase extraction based on P<Emphasis Type="Italic">p</Emphasis>PDA/Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanocomposite and high-performance liquid chromatography

A rapid and sensitive method based on magnetic solid-phase extraction coupled to high-performance liquid chromatography with ultraviolet detection was developed for the simultaneous determination of buprenorphine (BPN) and its major metabolite, norbuprenorphine (N-BPN), in human plasma samples. Poly (para-phenylenediamine)-modified Fe₃O₄ nanoparticles (PpPDA/Fe₃O₄) were synthesized and used as a magnetic adsorbent for the extraction and preconcentration of BPN and N-BPN in biological samples. The synthesized nanocomposites were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy and vibrating sample magnetometery. An isocratic separation was achieved on a Nova-Pak C18 reversed-phase column using a mobile phase consisting phosphate buffer (pH 3.4) and acetonitrile (50:50, v/v) at a flow rate of 1.0 mL min^?1. The detection was conducted at 280 nm. Under the optimum conditions, the calibration curves for BPN and N-BPN were linear in the ranges 3.0–150.0 and 1.0–120.0 ng mL^?1, respectively. The sensitivity was also high with limit of detection of 0.8 and 0.3 ng mL^?1 for BPN and N-BPN in plasma, respectively. The method was successfully applied to the extraction and determination of BPN and N-BPN in human plasma samples with an average recovery of 98.10 and 96.41%, respectively.     

Facile ultrasonic-assisted preparation of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>/Ag<Subscript>3</Subscript>VO<Subscript>4</Subscript> nanocomposites as magnetically recoverable visible-light-driven photocatalysts with considerable activity

In this work, a facile ultrasonic-assisted method was applied for preparation of Fe₃O₄/Ag₃VO₄ nanocomposites with different compositions. The as-prepared products were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy-dispersive analysis of X-rays, UV–Vis diffuse reflectance spectroscopy, Fourier transform infrared spectroscopy, and vibrating sample magnetometery. Photocatalytic degradation of rhodamine B under visible-light irradiation was investigated, and it was found that weight ratio of Fe₃O₄–Ag₃VO₄ has significant influence on the photocatalytic activity and the nanocomposite with 1:4 weight ratio of Fe₃O₄–Ag₃VO₄ has superior activity. In addition, the nanocomposite showed great activities in degradations of methylene blue and fuchsine, which are comparable with activity of the pure Ag₃VO₄. More importantly, this nanocomposite displayed remarkable saturation magnetization, leading to easily and quickly separation of its suspension from treated system by applying a magnetic field.     

Enhanced electrochemical properties of Li<Subscript>2</Subscript>ZnTi<Subscript>3</Subscript>O<Subscript>8</Subscript>/C nanocomposite synthesized with phenolic resin as carbon source

Li₂ZnTi₃O₈/C nanocomposite has been synthesized using phenolic resin as carbon source in this work. The structure, morphology, and electrochemical properties of the as-prepared Li₂ZnTi₃O₈ samples were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), Raman spectroscopy (RS), galvanostatic charge–discharge, and AC impedance spectroscopy. SEM images show that Li₂ZnTi₃O₈/C was agglomerated with a primary particle size of ca. 40 nm. TEM images reveal that a homogeneous carbon layer (ca. 5 nm) formed on the surface of Li₂ZnTi₃O₈ particles which is favorable to improve the electronic conductivity and inhibit the growth of Li₂ZnTi₃O₈ during annealing process. The as-prepared Li₂ZnTi₃O₈/C composite with 6.0 wt.% carbon exhibited a high initial discharge capacity of 425 and 159 mAh g^?1 at 0.05 and 5 A g^?1, respectively. At a high current density of 1 A g^?1, 95.5 % of its initial value is obtained after 100 cycles.     

A Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@SiO<Subscript>2</Subscript>@graphene quantum dot core-shell structured nanomaterial as a fluorescent probe and for magnetic removal of mercury(II) ion

The authors describe the synthesis of a multifunctional nanocomposite with an architecture of type Fe₃O₄@SiO₂@graphene quantum dots with an average diameter of about 22 nm. The graphene quantum dots (GQDs) were covalently immobilized on the surface of silica-coated magnetite nanospheres via covalent linkage to surface amino groups. The nanocomposite displays a strong fluorescence (with excitation/emission peaks at 330/420 nm) that is fairly selectively quenched by Hg²⁺ ions, presumably due to nonradiative electron/hole recombination annihilation. Under the optimized experimental conditions, the linear response to Hg²⁺ covers the 0.1 to 70 μM concentration range, with a 30 nM lower detection limit. The high specific surface area and abundant binding sites of the GQDs result in a good adsorption capacity for Hg²⁺ (68 mg?g^?1). The material, due to its superparamagnetism, can be separated by using a magnet and also is recyclable with EDTA so that it can be repeatedly used for simultaneous detection and removal of Hg²⁺ from contaminated water.

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Graphical abstract A schematic view of preparation process for the Fe₃O₄@SiO₂@graphene quantum dots nanocomposite (denoted as Fe₃O₄@SiO₂@GQDs). The graphene quantum dots were covalently immobilized on the surface of silica-coated magnetite nanospheres (Fe₃O₄@SiO₂) via covalent linkage to surface amino groups.

     

Influence of pressure on the electrical and electrochemical behaviour of high-temperature steam electrolyser La<Subscript>0.6</Subscript>Sr<Subscript>0.4</Subscript>Co<Subscript>0.2</Subscript>Fe<Subscript>0.8</Subscript>O<Subscript>3</Subscript> anode

This paper is dedicated to the impact of pressure on the electrochemical behaviour of LSCF (La_1-xSr_xCo_yFe_1-yO_3-δ) anode in high-temperature electrolysers. This study was carried out with symmetrical cells associating LSCF electrodes to a 3YSZ (yttrium-stabilised zirconia) electrolyte. Impedance spectroscopy measurements were performed using a three-electrode configuration, at temperature as high as 700 to 800 °C, in a pressure range from 1 to 30 bar. A clear improvement in terms of electrode resistance decrease is highlighted, mainly due to faster oxygen adsorption/desorption kinetics and a better supply of gas to electrochemical reaction sites. Other assumptions were considered and analysed, such as the impact of pressure on LSCF electrical conductivity and on the mechanical contacts. Thus, three contributions were determined as limiting steps at low pressure, up to 5 bar, whilst for higher pressure, the optimised conditions in operation are reached. This study completes a previous one related to a modelling approach.     

Facile synthesis of Fe@Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> core-shell nanowires as O<Subscript>2</Subscript> electrode for high-energy Li-O<Subscript>2</Subscript> batteries

Fe@Fe₂O₃ core-shell nanowires were synthesized via the reduction of Fe³⁺ ions by sodium borohydride in an aqueous solution with a subsequent heat treatment to form Fe₂O₃ shell and employed as a cathode catalyst for non aqueous Li-air batteries. The synthesized core-shell nanowires with an average diameter of 50–100 nm manifest superior catalytic activity for oxygen evolution reaction (OER) in Li-O₂ batteries with the charge voltage plateau reduced to ～3.8 V. An outstanding performance of cycling stability was also achieved with a cutoff specific capacity of 1000 milliampere hour per gram over 40 cycles at a current density of 100 mA g^?1. The excellent electrochemical properties of Fe@Fe₂O₃ as an O₂ electrode are ascribed to the high surface area of the nanowires’ structure and high electron conductivity. This study indicates that the resulting iron-containing nanostructures are promising catalyst in Li-O₂ batteries.     

Visible-light-driven photocatalysis of heterostructure Ag/Bi<Subscript>2</Subscript>WO<Subscript>6</Subscript> nanocomposites and their photocatalytic degradation of dye under visible light irradiation

Ag/Bi₂WO₆ nanocomposites were successfully synthesized by a combination of hydrothermal method and ultrasonic vibration. The phases, vibration modes, constituents and morphologies were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, field emission scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. The visible-light-driven photocatalytic activitiy of 0–10 wt% Ag/Bi₂WO₆ samples was studied by determining the photodegradation of rhodamine B under xenon lamp. In this research, 10 wt% Ag/Bi₂WO₆ nanocomposites exhibit the highest efficiency and have the promising photocatalytic properties for waste water treatment.     

Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>/rice husk-based maco-/mesoporous carbon bone nanocomposite as superior high-rate anode for lithium ion battery

Rice husks (RHs), a kind of biowastes, are firstly hydrothermally pretreated by HCl aqueous solution to achieve promising macropores, facilitating subsequently impregnating ferric nitrate and urea aqueous solution, the precursor of Fe₃O₄ nanoparticles. A Fe₃O₄/rice husk-based maco-/mesoporous carbon bone nanocomposite is finally prepared by the high-temperature hydrothermal treatment of the precursor-impregnated pretreated RHs at 600 °C followed by NaOH aqueous solution treatment for dissolving silica and producing mesopores. The macro-/mesopores are able to provide rapid lithium ion-transferring channels and accommodate the volumetric changes of Fe₃O₄ nanoparticles during cycling as well. Besides, the macro-/mesoporous carbon bone can offer rapid electron-transferring channels through directly fluxing electrons between Fe₃O₄ nanoparticles and carbon bone. As a result, this nanocomposite delivers a high initial reversible capacity of 918 mAh g^?1 at 0.2 A g^?1 and a reversible capacity of 681 mAh g^?1 remained after 200 cycles at 1.0 A g^?1. The reversible capacities at high current densities of 5.0 and 10.0 A g^?1 still remain at high values of 463 and 221 mAh g^?1, respectively.     

Synthesis,Characterization and Photocatalytic Application of TiO<Subscript>2</Subscript>/SnO<Subscript>2</Subscript> Nanocomposite Obtained Under Non-thermal Plasma Condition at Atmospheric Pressure

A plasma-assisted synthesis of TiO₂/SnO₂ nanocomposite is described. In this approach, a precursor containing a mixture of [TiCl₃ and SnCl₂] exposed to electric discharge was oxidized by plasma-generated reactive species (HO^·/H₂O = 2.85 eV/SHE). SnO₂ microstructures with a diameter of 10–40 µm were coated by thin layers TiO₂ nanorods with mean diameter of 6–8 nm. The obtained TiO₂/SnO₂ nanocomposite was characterized by transmission and scanning electron microscopy, X-ray diffraction and Fourier transform infrared. TiO₂/SnO₂ nanocomposite was found to be a promising new material for the photocatalytic discoloration of aqueous Remazol Brilliant Blue-R dye under daylight and UVA light sources, due to the combined effects of large specific surface area and heterojunction which efficiently separates the electron–hole pairs delaying the charge recombination. The leaching test indicated that the nanocomposite is stable easily reusable.     

Magnetic carbon nitride nanocomposites as enhanced peroxidase mimetics for use in colorimetric bioassays,and their application to the determination of H<Subscript>2</Subscript>O<Subscript>2</Subscript> and glucose

Graphite-like carbon nitride ? Fe₃O₄ magnetic nanocomposites were synthesized by a chemical co-precipitation method. The nanocomposites were characterized by transmission electron microscopy, X-ray diffraction, FTIR spectroscopy, X-ray photoelectron spectroscopy and magnetization hysteresis loops. The nanocomposites exhibit enhanced peroxidase-like activity (compared to that of graphite-like carbon nitride or Fe₃O₄ NPs). More specifically, they are capable of catalyzing the oxidation of different peroxidase substrates (such as TMB, ABTS or OPD) by H₂O₂ to produce the typical color reactions (blue, green or orange). The nanocomposites retain their magnetic properties and can be separated by an external magnet. On the basis of these findings, a highly sensitive and selective method was applied to the determination of H₂O₂ and glucose (by using glucose oxidase). It was successfully applied to the determination of glucose in (spiked) human serum. Compared to other nanomaterial-based peroxidase mimetics, the one described here provides distinctly higher sensitivity for both H₂O₂ and glucose, with detection limits as low as 0.3 μM and 0.25 μM, respectively.

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Graphical abstract The magnetic carbon nitride nanocomposite exhibits enhanced peroxidase-like activity that is much larger than that of graphite-like carbon nitride or Fe₃O₄ NPs alone. This finding was applied to design a highly sensitive and selective colorimetric assay for H₂O₂ and glucose.

     

Voltammetric determination of vitamin B<Subscript>6</Subscript> (pyridoxine) at a graphite screen-printed electrode modified with graphene oxide/Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@SiO<Subscript>2</Subscript> nanocomposite

The preparation and study of electrochemical properties of a graphite screen-printed electrode (SPE) modified with the GO/Fe₃O₄@SiO₂ (GO is graphene oxide) nanocomposites are described. The morphologies of the GO/Fe₃O₄@SiO₂ nanocomposites were examined by scanning electron microscopy. The electrochemical oxidation of vitamin B₆ (pyridoxine) on SPE modified with the GO/Fe₃O₄@SiO₂ nanocomposite was investigated by cyclic voltammetry, differential pulse voltammetry, and chronoamperometry. Under optimum conditions (pH 7.0), the vitamin B₆ oxidation at the surface of the modified SPE occurs at a potential about 190 mV less positive than that at the unmodified SPE. A linear voltammetric response for vitamin B₆ was obtained in the concentration range 1.0?10 ⁶—9.0?10 ⁴ mol L^–1 with a detection limit of 5.2?10 ⁷ mol L^–1 using differential pulse voltammetry. The developed sensor was also successfully applied for determination of trace level of vitamin B₆ in both the standard vitamin B₆ sample and biological samples (urine).     

Photo-fenton refreshable Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@HCS adsorbent for the elimination of tetracycline hydrochloride

A yolk–shell-structured sphere composed of a superparamagnetic Fe₃O₄ core and a carbon shell (Fe₃O₄@HCS) was etched from Fe₃O₄@SiO₂@carbon by NaOH, which was synthesized through the layer-by-layer coating of Fe₃O₄. This yolk–shell composite has a shell thickness of ca. 27 nm and a high specific surface area of 213.2 m² g^?1. Its performance for the magnetic removal of tetracycline hydrochloride from water was systematically examined. A high equilibrium adsorption capacity of ca. 49.0 mg g^?1 was determined. Moreover, the adsorbent can be regenerated within 10 min through a photo-Fenton reaction. A stable adsorption capacity of 44.3 mg g^?1 with a fluctuation <10% is preserved after 5 consecutive adsorption–degradation cycles, demonstrating its promising application potential in the decontamination of sewage water polluted by antibiotics.     

Thermal oxide synthesis and characterization of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanorods and Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> nanowires

Fe₃O₄ nanorods and Fe₂O₃ nanowires have been synthesized through a simple thermal oxide reaction of Fe with C₂H₂O₄ solution at 200–600°C for 1 h in the air. The morphology and structure of Fe₃O₄ nanorods and Fe₂O₃ nanowires were detected with powder X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The influence of temperature on the morphology development was experimentally investigated. The results show that the polycrystals Fe₃O₄ nanorods with cubic structure and the average diameter of 0.5–0.8 μm grow after reaction at 200–500°C for 1 h in the air. When the temperature was 600°C, the samples completely became Fe₂O₃ nanowires with hexagonal structure. It was found that C₂H₂O₄ molecules had a significant effect on the formation of Fe₃O₄ nanorods. A possible mechanism was also proposed to account for the growth of these Fe₃O₄ nanorods. Supported by the Fund of Weinan Teacher’s University (Grant No. 08YKZ008), the National Natural Science Foundation of China (Grant No. 20573072) and the Doctoral Fund of Ministry of Education of China (Grant No. 20060718010)     

Enhancement of thermoelectric performance of Na<Subscript>x</Subscript>Co<Subscript>2</Subscript>O<Subscript>4</Subscript> with Ag dispersion by precipitation from Ag<Superscript>+</Superscript> aqueous solution

Thermoelectric Na_xCo₂O₄/Ag composites were synthesized by citric acid complex (CAC) method and Ag precipitation from CH₃COOAg aqueous solution on the Na_xCo₂O₄ powders. Effects of the synthesis process on microstructure and thermoelectric performance of Na_xCo₂O₄/Ag composites were investigated. When the Na_xCo₂O₄ CAC powders were dipped in CH₃COOAg aqueous solution and dried, fine Ag particles less than around 300 nm in size were precipitated on the surface of Na_xCo₂O₄ powders. After the subsequent sintering process, the flaky Ag phase, the length and thickness of which were up to 5 and 1 μm, respectively, existed along interfaces between Na_xCo₂O₄ grains. The sizes of Ag particles obtained in this study were found to be smaller than those of the conventionally prepared Na_xCo₂O₄/Ag composites. The fine dispersion of Ag grains was effective for suppressing the increase in thermal conductivity due to the addition of metallic phase, Ag, and for improving the thermoelectric performance of Na_xCo₂O₄/Ag composites, suggesting that the synthesis technique composed of the CAC method and Ag precipitation from CH₃COOAg aqueous solution is significantly important process for thermoelectric Na_xCo₂O₄/Ag composites.     

In situ crystalline investigation of sol–gel deposited barium stannate (Ba<Subscript>x</Subscript>SnO<Subscript>2+y</Subscript>; x:y ≈ 1:1) nanoparticles in alkaline medium

Fine layers of barium stannate nanoparticles have been synthesized by sol–gel technique with tin chloride pentahydrate (SnCl₄·5H₂O) and barium sulphate (BaSO₄). Physico-chemical properties of barium stannate, Ba_xSnO_2+y; x:y ≈ 1:1 were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy and UV–Visible spectrophotometry technique. A growth mechanism based on the combination of particle sticking and molecule level heterogeneous growth is proposed. It has been found that the particle size of all the samples was distributed in the range 3.0–6.5 ? while optical absorption spectrum indicates that Ba_xSnO_2+y nanoparticles have a direct band gap of 3.9 eV.