In situ thermolysis of magnetic nanoparticles using non-hydrated iron oleate complex

A novel strategy for the fabrication of nanostructured materials based on preparation of metallic surfactants is presented and some examples are demonstrated in this article. The suggested synthetic procedure of metal oleate is universal, potentially able to produce bulk quantities, and can be applicable to the synthesis of other metal oxide and metal nanoparticles. In general, organometallic compounds are quite expensive and are mostly classified as a highly toxic substance. In this study, we used simple, inexpensive, and eco-friendly approaches to prepare the metallic surfactants. As an example, non-hydrated iron oleate (FeOl) complexes are prepared as precursors for the in situ-fabricated superparamagnetic iron oxide nanoparticles (SPIONs) by thermolysis. The different coordination of the non-hydrated FeOl complexes are directly relating to the competition between nucleation and crystal growth. The in situ preparation of SPIONs involves the reaction of metal nitrate and carboxylic acid at 120 °C to synthesize the non-hydrated FeOl complexes and following the thermolysis of FeOl at 300 °C in non-coordination solvent. The coordination modes and distinct thermal behaviors of intermediates non-hydrated FeOl complexes are comparatively investigated by means of thermo-analytic techniques complimented by differential scanning calorimetry, thermal gravimetric analysis (TGA) and infrared spectroscopy (FTIR). The potential chemical structures of non-hydrated FeOl and their reaction mechanism by thermolysis were elucidated. The resulting lipid-coated SPIONs were characterized by transmission electron microscope, FTIR, differential temperature analysis, and TGA. These data suggested a bimodal interaction of organic shell and nanoparticle surface, with chemically absorbed inner layer and physically absorbed outer layer of carboxylic acid.     

Surface functionalization of carbon nanofibers by sol-gel coating of zinc oxide

In this paper the functional carbon nanofibers were prepared by the carbonization of ZnO coated PAN nanofibers to expand the potential applications of carbon nanofibers. Polyacrylonitrile (PAN) nanofibers were obtained by electrospinning. The electrospun PAN nanofibers were then used as substrates for depositing the functional layer of zinc oxide (ZnO) on the PAN nanofiber surfaces by sol-gel technique. The effects of coating, pre-oxidation and carbonization on the surface morphology and structures of the nanofibers were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) and Scanning electron microscopy (SEM), respectively. The results of SEM showed a significant increase of the size of ZnO nanograins on the surface of nanofibers after the treatments of coating, pre-oxidation and carbonization. The observations by SEM also revealed that ZnO nanoclusters were firmly and clearly distributed on the surface of the carbon nanofibers. FTIR examination also confirmed the deposition of ZnO on the surface of carbon nanofibers. The XRD analysis indicated that the crystal structure of ZnO nanograins on the surface of carbon nanofibers.     

Characterization of surfaces by soft X-ray spectroscopy

Soft X-ray spectroscopy has important capabilities for investigating the surface region of metals and alloys. By calibrating the changes in the soft X-ray emission bands from both the metal and the oxygen, it is possible to determine the oxide thickness, the degree of oxidation, the element in the alloy with which the oxygen has combined, the relative amounts of alloying elements in the surface oxide, and the oxide state of a substrate metal that has a protective coating. For Ti-6Al-4V alloys there was an increase in surface oxygen after prebond treatment which was due to a change in the degree of oxidation rather than in oxide thickness, and the oxygen was combined with the titanium in the surface oxide. The oxygen K intensity distribution, from aluminum that was given a surface chromate treatment, showed that the oxygen is combined with the chromium. In Fe-Cr alloys there is an increase in the amount of chromium combined with oxygen relative to bulk chromium with decreasing chromium content. The oxide surface of steel with a 50 Å metal protective coating was reduced when the oxide of the protective metal coating had a heat formation greater than that of the iron oxide.     

Dendronization of gold and CdSe/cdS (core-shell) quantum dots with tomalia type, thiol core, functionalized poly(amidoamine) (PAMAM) dendrons

Poly(amidoamine) (PAMAM) dendrimers containing disulfide cores (i.e., cystamine) and possessing carboxylic acid or hydroxyl terminal groups were reduced with dithiothreitol (DTT) to yield single site, thiol core, functionalized PAMAM dendron reagents. These thiol functionalized dendron reagents were used to surface modify (dendronize) both gold nanoparticles, as well as CdSe/CdS (core-shell) quantum dots (QDs). Dendronization involved self-assembly of the focal point thiol functional dendrons at the metal interface of both gold and CdSe/CdS QDs by ligand exchange of protective surfactants used for their synthesis. The synthesis, characterization and preliminary luminescence studies of these new dendritic hybrids are reported.     

Charging and stabilization of Pd atoms and clusters on an electron-rich MgO surface

We report density functional theory calculations on the interaction of Pd atoms and small Pd clusters with an electron-rich MgO surface. This surface can be generated by forming a specific kind of defects, named (H⁺)(e⁻) centers, using well known chemical recipes. By deposition of gas-phase Pd atoms on the properly functionalized MgO surface, one can generate collections of small Pd cluster anions with peculiar chemical properties. The (H⁺)(e⁻) centers act as nucleation sites for diffusing Pd atoms and favor the formation of small, thermally stable clusters. The presence of an extra charge on the metal cluster results in a large vibrational red-shift of adsorbed CO molecules. The present results intend to stimulate experimental work to produce stable metal cluster anions on the surface of an ionic oxide.     

Electrospun precursor carbon nanofibers optimization by using response surface methodology

Ultrafine fibers were electrospun from Polyacrylonitrile and N,N-dimethylformamide solution to be used as a precursor for carbon nanofibers. An electrospinning set-up was used to collect fibers with diameter ranging from 104 nm to 434 nm. Morphology of fibers and its distribution were investigated by varying Berry's number, charge density, spinning angle, spinneret diameter and collector area. A more systematic understanding of process parameters was obtained and a quantitative relationship between electrospinning parameters and average fiber diameter was established by using response surface methodology. It was concluded that; Berry's number, charge density and spinneret diameters played an important role to the diameter of nanofibers and its standard deviation. Spinning angle and collector area had no significant impact. Based on response surface methodology the optimum Polyacrylonitrile average fiber diameter of 280 nm and 28 nm standard deviation, were collected at 1.6 kV/cm charge density, 8 Berry's number and 0.9 mm spinneret diameter.     

Tracing locations of new coating material during spark anodizing of titanium

The growth of anodic coatings on titanium, under sparking conditions, is investigated in tracer experiments, using alkaline silicate and phosphate electrolytes. Coatings are formed sequentially in each electrolyte, with phosphorus and silicon located by energy-dispersive X-ray analysis and glow discharge optical emission spectroscopy. The coatings, containing anatase, rutile and amorphous oxide, with incorporated phosphorus and silicon species, are shown to grow by discrete thickening at sites of dielectric breakdown. New material is found near the metal, within the coating bulk and at the coating surface. Approximately 10–30% of the new material is located near to the coating surface and about 40–60% near to the metal. The findings are attributed to the formation of breakdown channels allowing access of electrolyte species to the inner parts of the coating and to subsequent rapid formation of coating material, under high temperatures, associated with increased local current density, and high pressures, associated with volume constraints on oxide growth and gas generation.     

Nucleation of single-walled carbon nanotubes

The nucleation pathway for single-wall carbon nanotubes on a metal surface is demonstrated by a series of total energy calculations using density functional theory. Incorporation of pentagons at an early stage of nucleation is energetically favorable as they reduce the number of dangling bonds and facilitate curvature of the structure and bonding to the metal. In the presence of the metal surface, nucleation of a closed cap or a capped single-wall carbon nanotube is overwhelmingly favored compared to any structure with dangling bonds or to a fullerene.     

Functionalization of carbon nanofibers with elastomeric block copolymer using carbodiimide chemistry

Surface functionalization of carbon nanofibers (CNFs) with aminopropyl terminated polydimethylsiloxane [(PDMS-NH₂)] and other organic diamines was achieved using carbodiimide chemistry. The carbodiimide chemistry provides faster reaction rate so that the reaction occurs at lower temperature compared to amidation and acylation-amidation chemistry. CNF functionalized with PDMS-NH₂ fibers were further functionalized with oligomer of polyimide (6FDA-BisP) using imidization reaction. The formation of block copolymer on the surface of CNF is proposed as an effective method to engineer the interphase between the fiber and the polymer, which is essential to modulate and enhance the properties of the nanocomposite. The efficiency of the carbodiimide chemistry to functionalize amine terminated groups on CNF and the functionalization of block copolymer was characterized using thermal gravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS) and UV-vis spectroscopy.     

Fabrication and Optimization of Poly(vinyl alcohol)/Zirconium Acetate Electrospun Nanofibers Using Taguchi Experimental Design

This paper presents an investigation regarding poly(vinyl alcohol)/zirconium acetate (organic–inorganic) (PVA/Zrace) nanofibers prepared by electrospinning which could be used as a precursor for fabricating ceramic metal oxide nanofibers. The effect of some processing variables, including polymer solution concentration, tip to collector distance and applied voltage of electrospinning, and the amount of Zrace and their interactions, on the diameter of the nanofibers were studied. Taguchi experimental design and a statistical analysis (ANOVA) were employed and the relationship between experimental conditions and yield levels determined. It was concluded that to obtain a narrow diameter distribution as well as maximum fiber fineness, a polymer concentration of 10 wt%, tip to collector distance of 18 cm and applied voltage of 20 kV variables were the optimum. Furthermore, it was also concluded that the ratio of Zrace (6 g) to PVA solution (10% wt) played an important role for achieving the minimum fiber diameter. Under these optimum conditions, the diameters of the electrospun composite fibers ranged from 86 nm to 381 nm with a diameter average of 193 nm. The experiments were done with Qualitek-4 software with “smaller is better” as the quality characteristics. The optimized conditions showed an improvement in the fibers diameter distribution and the average fibers diameter showed good resemblance with the result predicted using the Taguchi method and the Qualitek-4 software. The ANOVA results showed that all factors had significant effects on the fibers diameter and distribution, but the effect of PVA concentration and zirconium acetate were more significant than the other factors.     

Chemical treatment of TiO2-based coatings formed by plasma electrolytic oxidation in electrolyte containing nano-HA, calcium salts and phosphates for biomedical applications

TiO₂-based coatings were formed on titanium alloy by plasma electrolytic oxidation (PEO) in an electrolyte containing nano-HA, calcium salts and phosphates. Bioactive surface was formed after chemical treatment (NaOH aqueous solution) of the PEO coating. The surface of the PEO coating was mainly composed of Ti, O, Ca and P showing anatase and rutile; while that of the chemically treated PEO (CT-PEO) coating mainly contains Ti, O, Ca and Na showing anatase, rutile and amorphous phase. And the chemically treated surface exhibits dissolution of P and introduction of Na during the chemical treatment process. The chemical treatment has no effect on the chemical states of Ca and Ti of the PEO coating. In addition, the surface constituents of the CT-PEO coating show a uniform distribution near its surface with increasing depth. When incubated in a simulated body fluid for 7 and 14 days, the PEO coating does not exhibit apatite-forming ability; however, apatite was successfully deposited on the CT-PEO coating after 7 days probably due to the formation of hydroxyl functionalized surface, enhancing the heterogeneous nucleation of apatite. The addition of nano-HA in the electrolyte has effects on the surface character and apatite-forming ability of the PEO coating; however, it has no obvious influence on those of the CT-PEO coatings.     

Production and Characterization of Zirconia (ZrO2) Ceramic Nanofibers by Using Electrospun Poly(Vinyl Alcohol)/Zirconium Acetate Nanofibers as a Precursor

Zirconia (ZrO₂) inorganic ceramic nanofibers were produced using electrospinning of the poly(vinyl alcohol)/zirconium acetate as a precursor followed by calcinating and sintering to decompose the polymer and turn the metal salt (zirconium acetate) into the metal oxide. Characterization of the nanofibers, including polymer thermal decomposition, chemical and crystal structure, phase transformations, and fiber morphology were investigated by simultaneous thermal analysis (STA), thermomechanical analysis (TMA), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and field emission scanning electron microscopy (FESEM). The results showed that the polymer decomposition started at 250°C and zirconia nanofibers with different phases (tetragonal and monoclinic) were obtained by the calcination of the precursor nanofibers at various temperatures between 500°C and 1100°C. The initially crystallized zirconia phase, which formed at 500°C, was tetragonal and with increasing calcination temperature, zirconia nanofibers with increasing amount of monoclinic phase were formed. Consequently, at 1100°C, the tetragonal phase disappeared and was transformed to the monoclinic phase of the zirconia completely. Increasing the calcination temperature caused the fiber average diameter decrease and grain growth took place due to the removal of the polymer and organic groups; neighboring grains sintered to each other and formed fibers with a high aspect ratio. At 1100°C the grains size was about the same as the fiber diameter.     

Heterogeneous nucleation on cleavage steps: I. Theory

A theory of the nucleation kinetics of clusters formed on the cleavage steps of a substrate surface during metal deposition is presented. The spatial distribution of clusters along steps is shown to evolve with time in a shape-preserving way. As a consequence it has been possible to derive an expression for the linear number density of clusters as a function of substrate temperature, deposition rate and the duration of the deposition.     

Preparation and characterization of boron nitride coatings on carbon fibers from borazine by chemical vapor deposition

Boron nitride (BN) coatings were deposited on carbon fibers by chemical vapor deposition (CVD) using borazine as single source precursor. The deposited coatings were characterized by scanning electron microscopy (SEM), Auger electron spectroscopy (AES), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy. The effect of temperatures on growth kinetics, morphology, composition and structure of the coatings was investigated. In the low temperature range of 900 °C-1000 °C, the growth rate increased with increasing temperature complying with Arrhenius law, and an apparent active energy of 72 kJ/mol was calculated. The coating surface was smooth and compact, and the coatings uniformly deposited on individual fibers of carbon fiber bundles. The growth was controlled by surface reaction. At 1000 °C, the deposition rate reached a maximum (2.5 μm/h). At the same time, the limiting step of the growth translated to be mass-transportation. Above 1100 °C, the growth rate decreased drastically due to the occurrence of gas-phase nucleation. Moreover, the coating surface became loose and rough. Composition and structure examinations revealed that stoichiometric BN coatings with turbostratic structure were obtained below 1000 °C, while hexagonal BN coatings were deposited above 1100 °C. A penetration of carbon element from the fibers to the coatings was observed.     

Structural investigation of n-hexadecanoic acid multilayers on mica surface: Atomic force microscopy study

The structure of n-hexadecanoic acid (HA) multilayers formed by spreading an ethanol solution containing this molecule onto a freshly cleaved mica surface has been studied by atomic force microscopy (AFM). AFM images of multilayers obtained with different coating time showed that HA molecules first formed some sporadic domains on mica surface. With the proceeding of the coating process, these domains gradually enlarged and coalesced, until formed a continuous film finally. It was observed that HA molecules were always adsorbed on mica surface with tilted even-numbered layers structure. The height of the repeated tilted bilayer film was measured to be approximately 3.8 ± 0.2 nm, which implied a ∼60° tilt molecular conformation of the HA bilayers on mica surface. Phase image confirmed that the HA multilayers terminated with the hydrophilic carboxylic acid groups. The formation mechanism of the HA multilayers was discussed in detail. Thus, resulted hydrophilic surfaces are of special interest for further study in biological or man-made member systems.     

Fabrication and characterization of bismuth oxide–holmia nanofibers and nanoceramics

In this article, a novel and simple method to produce both boron doped and undoped holmia stabilized bismuth oxide nanoceramic materials has been put forward. Boron doped and undoped poly (vinyl alcohol)/bismuth–holmia acetate nanofibers were produced using the electrospinning technique and were calcined at 850 °C afterward in order to obtain nanopowder. The characteristics of the nanofibers were investigated with FT-IR, XRD, and SEM. XRD analyses showed that boron undoped holmia stabilized bismuth oxide nanopowders have the face-centered cubic structure (δ-phase), and that the incorporation of boron atoms into the composite prevents the nucleus formation and turns the structure into a more amorphous glassy form. The SEM micrographs of the fibers showed that the addition of boron results in the formation of cross-linked bright-surfaced fibers. The average fiber diameters for electrospun boron doped and undoped PVA/Bi–Ho acetate nanofibers were calculated using the ImageJ software as 102 nm and 171 nm, respectively.     

Characterization of oxide coatings formed on tantalum by plasma electrolytic oxidation in 12-tungstosilicic acid

Oxide coatings were formed on tantalum by plasma electrolytic oxidation (PEO) process in 12-tungstosilicic acid. The PEO process can be divided into three stages with respect to change of the voltage-time response. The contribution of electron current density in total current density during anodization results in the transformation of the slope of voltage-time curve. The surface morphology, chemical and phase composition of oxide coatings were investigated by AFM, SEM-EDX, XRD and Raman spectroscopy. Oxide coating morphology is strongly dependent of PEO time. The elemental components of PEO coatings are Ta, O, Si and W. The oxide coatings are partly crystallized and mainly composed of WO₃, Ta₂O₅ and SiO₂. Raman spectroscopy showed that the outer layer of oxide coatings formed during the PEO process is silicate tungsten bronze.     

Modification of surface properties of electrospun polyamide nanofibers by means of a perfluorinated acridine

Polyamide 6 (PA6) nanofibers were prepared from formic acid solutions by using electrospinning technique. The fibers were smooth, defects free and with diameters smaller than 200 nm. Small amounts of a perfluorinated acridine were added as dopant to the feed solution to modify the wettability of the fibers. The effect of doping on the contact angle values is well apparent. The contact angle values go from 50° of pure PA6 to 120° when 6% of acridine is added. A comparison between fibers and films of pure and doped polyamide 6 was carried out in order to determine the effect of morphology on wettability. Thermal annealing near the T_g of the polymer promoted the segregation of the molecules to the surface, reaching contact angles of 131° with smaller amounts (4%) of acridine. The surface segregation was also promoted by time aging.     

Substrate‐Induced Synthesis of Nitrogen‐Doped Holey Graphene Nanocapsules for Advanced Metal‐Free Bifunctional Electrocatalysts

The development of efficient metal‐free electrocatalysts for oxygen electrocatalysis is of great significance for various energy conversion devices. Herein, novel nitrogen‐doped holey graphene nanocapsules (NHGNs) are reported prepared by self‐assembly of graphene oxide nanosheets on the surface of amino‐functionalized silica template and NH₃ activation with simultaneously enhanced nitrogen doping and etching of nanopores in graphene, followed by template etching. The silica template is demonstrated to show a substrate‐enhanced effect on nitrogen doping and etching of nanopores in graphene based on density functional theory calculations. Benefiting from the large surface area, unique pore distribution, and high surface functionality of nitrogen doping, the resulting NHGNs exhibit superior bifunctional electrocatalytic activity and durability for both oxygen reduction reaction and oxygen evolution reaction, which is similar to that of the commercial Pt/C and RuO₂ electrocatalysts, respectively. This work presents an advance in developing new nitrogen‐doped graphene species for highly efficient metal‐free electrocatalysis.     

Growth of thin silver films on silicon oxide pretreated by low temperature argon plasma

In the present study, we investigate the influence of low energy ion bombardment on nucleation and growth of thin silver films on silicon oxide by in situ photoelectron spectroscopy (PES) combined with specific resistivity measurements. Thermally grown thin silicon oxide films were exposed to a low temperature argon plasma for different time intervals resulting in changes in surface chemical composition as monitored by angle-resolved X-ray photoelectron spectroscopy (ARXPS). We demonstrate that irradiation of the oxide surface with low energy ions results in substantially changed nucleation of silver. Furthermore, silver films deposited on plasma treated oxide tend to have lower resistivity which is attributed to the effect of reduced grain boundary and surface roughness.