Electrochemical characterization and reactivity of Pt nanoparticles supported on single-walled carbon nanotubes

Carbon nanotubes have been proposed as advanced metal catalyst support for electrocatalysis. In this paper, Pt nanoparticles supported on single-walled carbon nanotubes (SWCNTs)-Pt, were prepared using a solid-state reaction between the SWCNTs and two different Pt precursors, bis(dibenzylideneacetone)platinum [Pt(DBA)₂] or tri(dibenzylideneacetone)platinum [Pt(DBA)₃]. TEM images of the samples show Pt nanoparticles with a particle size around 2.5 nm with a high degree of dispersion on the SWCNTs. A detailed electrochemical characterization of the surface of the samples including irreversibly adsorbed adatoms of Bi and Ge as probe reactions has been carried out. It has been stated that SWCNTs-Pt samples subjected to the classical electrochemical activation induce a serious sintering of the Pt nanoparticles.     

Low temperature synthesis of monolithic mesoporous magnetite nanoparticles

Magnetite nanoparticles are commonly used for drug delivery, as MRI contrast agents, and as adsorbents for the removal of heavy metal cations from waste water. The smaller the particle sizes the higher the efficiency of these particles in these applications. Different methods have been explored for the preparation of magnetic nanoparticles with this size limitation. Co-precipitation is one of the most versatile methods in this regard, and is characterized by the ability of preparation of a high yield of nanoparticles. Control of the particle size distribution, phase purity and type of porosity of the formed magnetite nanoparticles has been always considered a challenge. In the current study, magnetite mesoporous nanoparticles with an average particle size of 55 nm were prepared in pre-adjusted highly alkaline aqueous media at relatively low temperatures. Phase purity of the deposited magnetite was confirmed by X-ray diffraction (XRD) and thermogravimetric analysis (TGA). Scanning (SEM) and transmission electron microscopy (TEM) graphs showed homogenously dispersion of spherical magnetite nanoparticles. Agglomeration of the mesoporous nanoparticles took place forming clusters with unified pore size distribution due to the homogenous particle size distribution. Magnetic susceptibility measurements at room temperature confirmed the magnetization characteristics of the nanoparticles.     

Reductant-free synthesis of magnetoplasmonic iron oxide-gold nanoparticles

Stable suspensions of spherical 10–15 nm superparamagnetic iron oxide nanoparticles (SPIONs) have been synthetized by co-precipitation, stabilized with citric acid, surface functionalized with aminopropyltriethoxysilane (APTES) and finally decorated with ultra-small gold nanoparticles (GNPs) by in situ reduction of a soluble gold salt (HAuCl₄), obtaining well dispersed SPIONs-GNPs colloids.The morphology, size and stability of the SPIONs-GNPs suspensions have been controlled by adjusting the molar ratio of the reagents (Fe/HAuCl₄ and Fe/APTES). The synthesis route differs from that typically found in literature, using tunable chelating layer modifications (such as citric acid and –NH₂ groups) of the magnetic core, depositing GNPs on the amine-functionalized iron oxide surface without the use of a specific reducing agent, and tuning the process pH and temperature. An explanation of how the different chemical species involved in the synthesis route could be responsible for the reducing action has been provided. The SPIONs-GNPs colloids have been characterized after each synthesis step by Transmission Electron Microscopy (TEM), Scanning Transmission Electron Microscopy (STEM), energy-dispersive X-ray spectroscopy (EDXS), Fourier transform infrared spectroscopy (FTIR), ζ Potential measurements, magnetic measurements with a vibrating-sample magnetometer (VSM) and UV–VIS spectroscopy. The SPIONs-GNPs colloids showed magnetoplasmonic behaviors since they maintained the plasmonic properties of GNPs and the superparamagnetic response of iron oxide NPs.     

Electrochemical synthesis and characterization of polyaniline thin film and polyaniline powder

The polyaniline thin film electrode and powder have been synthesized on graphite electrodes from 0.5 M hydrochloric acid solution under galvanostatic conditions. The water insoluble and acetone soluble polyaniline mass fractions of the powder, as well as the polymerization efficiency, based on the emeraldine salt have been determined. The morphology of the obtained emeraldine salt powder has been investigated by the optical microscopy.     

Photocatalytic,magnetic, and electrochemical properties of La doped BiFeO3 nanoparticles

We successfully prepared La_1?xBi_xFeO₃ (L_xB_1?xFO, x?=?0.01–0.1) nanoparticles using a sol-gel technique, and studied their photocatalytic, magnetic, and electrochemical properties. Structural refinement studies of the prepared nanoparticles revealed a gradual structural transition from rhombohedral to orthorhombic. The average grain size was observed to decrease with increasing the concentration of La. The photocatalytic degradation of Rhodamine B (RhB) in the presence of the prepared nanoparticles was studied under visible light irradiation. The L_0.06B_0.94FO nanoparticles showed higher degradation efficiency compared to pure BiFeO₃ (BFO) nanoparticles. Magnetic studies showed that La doping improved the magnetization of BFO due to the reduction in grain size and destruction of cycloid coupling of spins. Higher specific capacitance values were obtained for La doped BFO (LBFO) nanoparticles compared to BFO nanoparticles. A maximum specific capacitance of 219?F?g^?1 was obtained at a current density of 1?A?g^?1 for LBFO nanoparticles.     

Microwave assisted hydrothermal synthesis of (Fe,Co)3O4 nanoparticles in the presence of surfactants and effects of Co/Fe ratio on microstructure and magnetism

Microstructure and magnetic properties of nanoparticles can be tailored by optimising the synthesis procedure and changing chemical composition. In this study, a two-step procedure, i.e., coprecipitation in the presence of PEG 300 followed by microwave assisted (MW) hydrothermal synthesis, was introduced to obtain Co_xFe_3-xO₄ (x?=?0, 0.1 and 0.2) nanoparticles. It was found that with the increase of Co content, particle/crystallite size increased, with significant change of coercivity (H_c). The mixed samples of Co_xFe_3-xO₄ (x?=?0.1 and 0.2) were magnetically harder in comparison with Fe₃O₄. Тhe H_c of Fe₃O₄ was 91?Oe, while for Co_0.10Fe_2.90O₄ and Co_0.20Fe_2.80O₄, H_c was 256?Oe and 1070?Oe, respectively. Saturation magnetisation (M_s) of mixed samples also increased up to 6% compared to Fe₃O₄. A special effort was devoted to study the effects of introducing different surfactants (PEG 300, PEG 4000 or SDS) during the synthesis procedure in order to improve morphological and microstructural properties of CoFe₂O₄ nanoparticles. The influence of surfactants on physical/chemical properties of nanoparticles is discussed.     

Microwave-assisted solution combustion synthesis of Fe3O4 powders

Magnetite (Fe₃O₄) powders were synthesized by solution combustion method at different fuel to oxidant ratios (ϕ = 0.5, 0.75, 1 and 1.5) using conventional and microwave ignition. The ignition method and fuel content affected the phase evolution, microstructure and magnetic properties of Fe₃O₄ powders as characterized by X-ray diffractometry, infrared spectroscopy, N₂ adsorption–desorption, electron microscopy and vibrating sample magnetometry techniques. Single phase Fe₃O₄ powders were only obtained using conventional ignition at ϕ value of 1, while the impurity phases such as α-Fe₂O₃ and FeO together with Fe₃O₄ phase were formed by microwave ignition. The bulky microstructure of conventionally combusted powders with specific surface area of 71.5 m²/g was transformed to disintegrated structure (76.5 m²/g) by microwave heating. The microwave combusted powders showed the highest saturation magnetization of 86.5 emu/g at ϕ value of 0.5 and the lower coercivity than that of conventionally combusted powders at all ϕ values, due to their larger particles.     

One-step synthesis and characterization of polyelectrolyte-protected gold nanoparticles through a thermal process

Polyelectrolyte-protected gold nanoparticles have been facilely obtained by heating an amine-containing polyelectrolyte/HAuCl₄ aqueous solution without the additional step of introducing other reducing agents. All experimental data indicate that different initial molar ratio of polyelectrolyte to gold can lead to the formation of dispersed nanoparticles, quasi one-dimensional aggregates of nanoparticles or bulk metal deposits. More importantly, the growth kinetics of gold particles thus formed can be tuned by changing the initial molar ratio of polyelectrolyte to gold.     

Characterization by electrochemical impedance spectroscopy of magnetite nanoparticles supported on carbon paste electrode

Magnetite nanoparticles were supported on carbon paste electrode and characterized by low scan rate voltammetry and electrochemical impedance spectroscopy (EIS) to obtain mechanistic information related to its oxidation and reduction in acid media.The voltammograms showed only one reduction and one oxidation peak for the supported magnetite, which were attributed to formation of ferrous ion and ferric oxide, respectively. Both peaks are fairly wide, indicating complex mechanisms.Using EIS, a mechanism showing up to three time constants, capacitive all of them, was evidenced, both in anodic and cathodic domain. These were attributed to charge transfer at the highest frequencies, adsorption of generated species at intermediate frequencies, and proton adsorption at low frequencies. Discussion about the nature of the adsorbed species and the concerned mechanism for each domain is developed.     

Electrochemical synthesis of melanin free-standing films

Free-standing melanin films were successfully synthesised electrochemically from dopa. The optimum synthetic conditions such as pH, concentration and current were determined, and it was found that free-standing films could only be formed when ITO glass electrodes were used. The films were analysed by solid state NMR and XPS which showed the presence of indolic moieties characteristic of melanin-type macromolecules. The film showed higher conductivity than chemically synthesised melanin previously reported in literature and also exhibited photoconductivity.     

Influence of carbon chain length on the synthesis and yield of fatty amine-coated iron-platinum nanoparticles

Iron oxide nanoparticles are among the most widely used and characterized magnetic nanoparticles. However, metal alloys such as superparamagnetic iron-platinum particles (SIPPs), which have better magnetic properties, are receiving increased attention. Scalable techniques to routinely synthesize SIPPs in bulk need further study. Here, we focus on the role played by the fatty amine ligand in the formation of the bimetallic FePt nanocrystal. More specifically, we compare the effect of varying lengths of fatty amine ligands on the shape, structure, uniformity, composition, and magnetic properties of the SIPPs. We synthesized SIPPs by employing a ‘green’ thermal decomposition reaction using fatty amine ligands containing 12 to 18 carbons in length. Greater fatty amine chain length increased the polydispersity, particle concentration, iron concentration, and the stability of the SIPPs. Additionally, longer reflux times increased the diameter of the particles, but decreased the iron concentration, suggesting that shorter reaction times are preferable. Fourier transform infrared spectroscopy of the SIPPs indicates that the ligands are successfully bound to the FePt cores through the amine group. Superconducting quantum interference device magnetometry measurements suggest that all of the SIPPs were superparamagnetic at room temperature and that SIPPs synthesized using tetradecylamine had the highest saturation magnetization. Our findings indicate that the octadecylamine ligand, which is currently used for the routine synthesis of SIPPs, may not be optimal. Overall, we found that using tetradecylamine and a 30-min reflux reaction resulted in optimal particles with the highest degree of monodispersity, iron content, stability, and saturation magnetization.

PACS

81.07.-b; 75.75.Fk; 61.46.Df     

In vitro bonelike apatite formation on magnetite nanoparticles after a calcium silicate treatment: Preparation,characterization and hemolysis studies

Bioactive magnetite nanoparticles were prepared successfully by coating magnetite nanoparticles with CaSiO₃ followed by their immersion in simulated body fluid. The Fe₃O₄ nanoparticles (5–10 nm) were synthesized by a co-precipitation technique. In order to prepare core–shell nanocomposites, the nanoparticles were soaked for 1 h in a calcium silicate solution that had been aged for 24 h before using it. The samples were dried in air and then immersed in SBF at 37 °C for 1, 3 and 7 days. The analyses of the samples after the biomimetic process revealed the formation of a bonelike apatite layer on all the samples tested and not a significant change was observed on their original magnetic behavior. Hemolysis test, evaluated as release of hemoglobin, revealed that all the samples showed no hemolytic effects up to 3 mg/ml, indicating no damage of the red blood cell membranes. These bioactive, hemocompatible and superparamagnetic particles may be potential materials for bone cancer treatment by hyperthermia.     

Catechin-capped gold nanoparticles: green synthesis,characterization, and catalytic activity toward 4-nitrophenol reduction

An eco-friendly approach is described for the green synthesis of gold nanoparticles using catechin as a reducing and capping agent. The reaction occurred at room temperature within 1 h without the use of any external energy and an excellent yield (99%) was obtained, as determined by inductively coupled plasma mass spectrometry. Various shapes of gold nanoparticles with an estimated diameter of 16.6 nm were green-synthesized. Notably, the capping of freshly synthesized gold nanoparticles by catechin was clearly visualized with the aid of microscopic techniques, including high-resolution transmission electron microscopy, atomic force microscopy, and field emission scanning electron microscopy. Strong peaks in the X-ray diffraction pattern of the as-prepared gold nanoparticles confirmed their crystalline nature. The catalytic activity of the as-prepared gold nanoparticles was observed in the reduction of 4-nitrophenol to 4-aminophenol in the presence of NaBH₄. The results suggest that the newly prepared gold nanoparticles have potential uses in catalysis.     

Effects of pH value on the microstructure and magnetic properties of solution combusted Fe3O4 powders

Magnetite (Fe₃O₄) powders were prepared by solution combustion synthesis method using conventional and microwave ignition at various pH values of starting solution, adjusted by NH₄OH. The chelated species in dried gels were predicted by theoretical calculations and Fourier transform infrared spectroscopy. The combustion reaction rate strongly depended on pH values as investigated by thermal analysis. Phase evolution and structure characterized by X-ray diffraction method showed single phase and well-crystalline Fe₃O₄ powders which were achieved using conventional ignition at pH ≥ 7. However, the microwave ignition led to the formation of impure FeO phase together with Fe₃O₄. The microwave combusted powders exhibited the disintegrated structure in comparison with the bulky microstructure for conventionally combusted powders, as observed by scanning electron microscopy. Magnetic properties of the as-combusted powders studied by vibration sample magnetometry showed the highest saturation magnetization of 81.3 emu/g for conventional ignition at pH of 7, due to the high purity and large crystallite size.     

Self-assembled gold nanoparticles modified ITO electrodes: The monolayer binder molecule effect

The fabrication of gold attached organosilane-coated indium tin oxide Au_NPs-MPTMS/ITO and Au_NPs-APTES/ITO electrodes [MPTMS = 3-(mercaptopropyl)-trimethoxysilane, APTES = 3-(aminopropyl)-triethoxysilane, ITO = indium tin oxide] was carried out making use of a well-known two-step procedure and the role played by the -SH and -NH₂ functional groups in the two electrodes has been examined and compared using different techniques. Information about particle coverage and inter-particle spacing has been obtained using trasmission electron microscopy (TEM), scanning electron microscopy (SEM) and atomic force microscopy (AFM) whereas, bulk surface properties have been probed with UV-vis spectroscopy, CV and electrochemical impedance spectroscopy (EIS). The catalytic activity of the two electrodes has been evaluated studying the electrooxidation of methanol in alkaline conditions. The results obtained show that the NH₂ functionality in the APTES binder molecule favours the formation of isle-like Au nanoparticle aggregates that lead to both a higher electron transfer and electrocatalytic activity.     

Electrochemical synthesis of bismuth molybdates with controllable composition and their photocatalytic performance

Bismuth molybdate photocatalysts were controllably prepared via an electrochemical approach at room temperature. The composition and optical property of each product were determined according to the NaOH and Na₂MoO₄ quantities in the electrolyte. Pure Bi_3.64Mo_0.36O_6.55 was prepared at a NaOH concentration range of 0.2‐0.8 mol L^?1, whereas the Bi_3.64Mo_0.36O_6.55/Bi₁₄MoO₂₄ composite was obtained in an electrolyte containing 0.4 mol L^?1 NaOH and 0.5 mol L^?1 Na₂MoO₄. The results of rhodamine B degradation under visible light indicated that Bi_3.64Mo_0.36O_6.55 nanoparticles with a size of 10‐50 nm displayed the best photocatalytic efficiency, which was considerably higher than that of composite one and bulk Bi_3.64Mo_0.36O_6.55.     

Magnetic and morphological characterization of Bi2Fe4O9 nanoparticles synthesized via a new reverse chemical co-precipitation method

Nano-sized Bi₂Fe₄O₉ (BFO) was successfully synthesized using a new reverse chemical co-precipitation method at different pH values of 8–12. These powders were examined by x-ray diffractometery (XRD), thermogravimetrical differential thermal analysis (TG-DTA), field emission scanning electron microscopy (FESEM) and vibrating sample magnetometery (VSM). The XRD analysis showed the formation of pure phase Bi₂Fe₄O₉ at calcination temperature over 700 ℃. The TG-DTA curves indicated the crystallization temperature of 617 ℃ for the Bi₂Fe₄O₉ sample. The FESEM micrographs revealed a precipitates agglomeration, which is related to the nature of the chemical co-precipitation method and free surface energy of nanoparticles. Furthermore, the particle size of the powder samples increased from 43 to 131 nm as the pH value increased from 8 to 12, respectively. Also, the morphological change from nearly cubic to rod-like shape in the nanoparticles was observed by increasing the pH value. The M-H curves of the as-prepared powders confirmed the antiferromagnetic behavior in all samples. Uncompensated spins from the surface led to the appearance of saturation magnetization in the Bi₂Fe₄O₉ nanoparticles. Besides, a decrease in the particles size resulted in more uncompensated spins, thereby improving the saturation and remnant magnetization from M_s = 0.35 emu/g and M_r = 0.010 emu/g for pH = 12 to M_s = 1.15 emu/g and M_r = 0.042 emu/g for pH = 8. Furthermore, as the pH values increase the coercive fields firstly rise up to 196 Oe for pH = 9 and then decrease to 151 for pH = 12.     

Microwave-assisted synthesis and characterization of bioactive chitosan scaffolds doped with Au nanoparticles for mesenchymal stem cells culture

In this work we present a novel strategy for chitosan-based scaffolds. Chitosan is a versatile biopolymer obtained from waste biomass known of its favorable biological properties. Thus it can replace other polymers in the preparation of bioactive scaffolds. To increase its durability chitosan can be crosslinked into form of the hydrogel yet application of toxic crosslinkers may lead to loss of biocompability. Mesenchymal stem cells can be used in cell therapy for advanced wound treatment. However their culture requires special biomaterials application. In this article a novel microwave-assisted synthesis method for bioactive chitosan scaffolds is presented.     

Preparation of biocompatible magnetite-PLGA composite nanoparticles using supercritical fluid extraction of emulsions

We report a new strategy for the production via supercritical fluid extraction of emulsion of biocompatible magnetic nanocomposite particles made of magnetite nanocrystals dispersed in a poly(lactic-co-glycolic) acid (PLGA) matrix. Ricinoleic acid-stabilized magnetic nanocrystals have been prepared via coprecipitation of two iron salts in alkaline environment, and subsequently dispersed in a solution of PLGA in dichloromethane. The obtained oil phase has then been dispersed in an aqueous solution of polyvinyl alcohol (PVA) in order to obtain a kinetically stable oil-in-water miniemulsion. The solvent was finally extracted via supercritical fluid extraction of emulsions. The continuous extraction of dichloromethane by means of supercritical CO₂ leads directly to a stable suspension of magnetite-PLGA composite nanoparticles in water. The influence of those parameters affecting the final particle size distribution and morphology, primarily emulsifier amount and magnetite content, has been investigated, so as to optimize the process. Analysis of the products, performed through light scattering and electron microscopy, indicates that narrower size distributions are obtained with larger amounts of emulsifier and lower amounts of magnetite. The morphology of the particles tends to be of Janus type, with the magnetite accumulated on one hemisphere of the particle. The proposed approach is suitable for the preparation of large quantities of high-quality magnetite-PLGA composite nanoparticles for biomedical applications.     

Electrochemical self-assembly synthesis of zinc oxide nanoparticles and lamellar-structured organic/inorganic hybrids by electrodeposition in surfactant solution

A cathodic electrodeposition was potentiostatically performed in an anionic surfactant solution under various electrodeposition conditions to investigate the influence of the condition on the structure of electrodeposited products, c-axis oriented ZnO films, ZnO nanoparticles shaped like ellipsoidal grains, and lamellar-structured organic/inorganic hybrids. The single phase of the ZnO nanoparticles was obtained only at a specific electrodeposition condition which was confirmed to be the boundary condition for two phases of the c-axis oriented ZnO and the lamellar hybrids. The origin of synthesis of the ZnO nanoparticles is probably a competitive formation reaction between the products of the two phases.