Growth of uniform lath-like α-(Fe,Al)OOH and disc-like α-(Fe,Al)2O3 nanoparticles in a highly alkaline medium

The effects of aluminium (Al³⁺)-dopant on the precipitation of uniform lath-like α-FeOOH particles, the obtention and growth of α-(Fe,Al)OOH and α-(Fe,Al)₂O₃ solid solutions, particle size and shape were investigated using X-ray powder diffraction, Mössbauer and Fourier transform infrared spectroscopies, field emission scanning electron microscopy and energy dispersive X-ray spectroscopy. Acicular α-FeOOH particles, precipitated in a highly alkaline medium with the addition of tetramethylammonium hydroxide (TMAH), were used as reference material. The influence of Al-dopant was investigated by adding varying amounts of Al³⁺ ions to the initial FeCl₃ solution. In the presence of lower concentrations of aluminium ions (up to 11.11 mol%) α-(Fe,Al)OOH as a single phase was formed, whereas higher concentrations led to an additional obtention and growth of α-(Fe,Al)₂O₃. Al-for-Fe substitution in the α-FeOOH and α-Fe₂O₃ structures was confirmed by a decrease in the unit-cell dimensions, a decrease in the hyperfine magnetic field and an increase in the wave number of the infrared absorption bands. The presence of lower concentrations of aluminium ions (up to 11.11 mol%) in the precipitation system did not affect the size and shape of the α-(Fe,Al)OOH particles, whereas higher concentrations influenced a decrease in the length and aspect ratio. In the presence of 42.86 mol% Al³⁺ ions fairly uniform disc-shaped α-(Fe,Al)₂O₃ were formed.     

Facile synthesis of air-stable Prussian white microcubes via a hydrothermal method

Air-stable Prussian white (PW) microcubes were fabricated by the slow dissociation of K₄[Fe(CN)₆] under hydrothermal condition without the protection of inert atmosphere. Mössbauer spectra and Fourier transform infrared (FT-IR) spectrum were used to characterize the composition of PW. X-ray diffraction (XRD) identified the obtained PW was monoclinic, and the purity was high. Scanning electron microscopy (SEM) images indicated the cubes were composed by solid cubes and hollow cubes. The shape of crystals strongly depended on the concentration of K₄[Fe(CN)₆], the hydrothermal temperature as well as the reaction duration. The lower concentration and lower temperature resulted in perfect cubic crystals, while the higher concentration or the higher temperature resulted in irregular cubic crystals. After exposing in air for 2 months, no oxidation of PW occurred. To explain the formation of the PW microcubes, a layer-by-layer growth mechanism was put forward based on the low dissociation rate of K₄[Fe(CN)₆]. The partially solubility of PW in water caused the formation of hollow cubes.     

Femtosecond laser synthesis of bimetallic Pt-Au nanoparticles

Bimetallic Pt-Au nanoparticles were successfully synthesized by irradiating the metal precursor solution with high intensity femtosecond laser. The intense optical field created by femtosecond laser pulse induced the production of highly charged ions and molecules due to the optical decomposition of metal precursor molecules. Further collisions with molecules result in subsequent growth of the nuclei and codeposition of Pt and Au atoms on the nuclei to form the larger ones. The method is a simple, easy-to-control and environmentally benign process. The average size and morphology of bimetallic nanoparticles were examined by transmission electron microscope. The compositional distributions of Pt and Au of individual Pt-Au nanoparticles were examined by X-ray energy dispersive spectroscopy (EDS).     

Tin dioxide nanoparticles: Reverse micellar synthesis and gas sensing properties

Tin dioxide (SnO₂) nanoparticles have been synthesized by reverse micellar route using cetyltrimethyl ammoniumbromide (CTAB) as the surfactant. Monophasic tin dioxide (SnO₂) was obtained using NaOH as the precipitation agent at 60 °C, however, when liquor NH₃ was used as precipitating agent then crystalline SnO₂ nanoparticles are obtained at 500 °C. SnO₂ prepared using NaOH show crystallite size of 4 and 12 nm after heating at 60 and 500 °C respectively using X-ray line broadening studies. Transmission electron microscopy (TEM) studies show agglomerated particles of sizes 70 and 150 nm, respectively. The grain size was found to be 6-8 nm after heating the precursor obtained (using liquor NH₃) at 500 °C by X-ray line broadening and the TEM studies. Dynamic light-scattering (DLS) studies show the aggregates of SnO₂ nanoparticles with uniform size distribution. Mössbauer studies show an increase of s-electron density at the Sn sites compared to bulk SnO₂ and a finite quadrupole splitting indicative of lowering of symmetry around tin atoms. The gas sensing characteristics have also been investigated using n-butane which show high sensitivity and fast recovery time.     

Facile synthesis of prickly CoNi microwires

Novel prickly CoNi microwires have been successfully synthesized via a hydrothermal synthetic route. The samples prepared at 120 °C for 6 h were made up of large-scale wire-like assemblies with the diameter of about 3 μm and length up to several dozens microns. These wires exhibited hierarchical structure, which was constructed by thornlike crystals with the length of 300-500 nm. The morphology of the wires could be adjusted by the NaOH contents in the system. The magnetic hysteresis measurement revealed that the CoNi microwires displayed ferromagnetic behaviors with a saturation magnetization (Ms) of 83.90 emu/g and a coercivity (Hc) of 119.1 Oe.     

Crystal structure and magnetic property of Nd doped BiFeO3 nanocrytallites

Bi_1-xNd_xFeO₃ (BNFO_x, x = 0-0.15) nano-crystallites were successfully synthesised by solution combustion technique. Neodymium substitution has changed the rhombohedral symmetry of BiFeO₃ to the triclinic and reduced the impurity phase. The average particle size found to vary from 74 to 26 nm when Nd concentration was increased from x = 0 to 0.15. The change in the symmetry is also confirmed by Raman spectra of nanocrystallite samples. The value of remnant magnetization has improved due to the continuing collapse of the space-modulated spin structure of BNFO_x. Long-range ferromagnetic ordering in BNFO_x at room temperature was also confirmed from Mössbauer spectra.     

Solution assisted laser ablation synthesis of discrete aluminum nanoparticles

Discrete aluminum nanoparticles with an average particle size of 21 nm have been prepared by laser ablation of a metallic aluminum target submerged in dry tetrahydrofuran in the presence of 0.001 M oleic acid as a stabilizing ligand. The particles display high solubility and minimal aggregation while the absence of oleic acid leads to highly aggregated particles and a broader particle size distribution. O/Al ratios obtained from EDS analysis suggest that the particles produced are primarily metallic aluminum with minimal oxide content.     

Mössbauer spectroscopy study on the corrosion inhibition of carbon steel in hydrochloric acid solution

The effect of ammonium polymolybdate (APM) on the corrosion of carbon steel in a solution of 1 M HCl was studied by weight loss and Mössbauer spectrometry. Inhibition efficiencies (P) have been obtained from weight measurement. The inhibition efficiencies increased with increase APM concentration. Mössbauer spectrometry shows that a superficial compound is formed on the electrode surface as a result of corrosion.     

Mechanical alloying synthesis of carbon nanotubes in the presence of AlFe small clusters

Carbon nanotubes and small metallic particles (1-3 nm) have been obtained using mechanical alloying techniques. High resolution electron microscope (HREM) techniques have been employed for the structural characterization of the small metallic particles and for the carbon multiwalled nanotubes. Theoretical simulations based on molecular dynamics and quantum mechanic calculations have been used to get insights on the experimental structural results.     

The Structure and Magnetic Properties of Fe-Si-Cu-Nb-B Powder Prepared by Mechanochemical Way

We have studied the influence of the long-term (1700 h) milling on the structure and magnetic properties of Fe_73.5Si_13.5Cu₁Nb₃B₉ powder prepared in a vibratory mill. Three samples (in amorphous state, partially crystallized state, and mixed of pure elements) of the same chemical content were prepared. We found that the structure and magnetic properties significantly depend on the milling time. The coercivity of the sample prepared from pure elements monotonously increases with increased milling time. The coercivity of the samples milled from the ribbon increases to its maximum for milling time of 800 h and then decreases.     

Tensile fracture behavior of aging hardened Mg-1Ca and Mg-1Ca-1Zn alloys

The tensile properties and fracture characteristics of the peak-aged Mg-1.0 wt.% Ca and Mg-1.0 wt.% Ca-1.0 wt.% Zn alloys, have been investigated in the temperature range 295-450 K. In this temperature range the tensile strength of the Mg-1Ca alloy linearly diminishes by 20%. However the drop in the tensile strength for the Mg-1Ca-1Zn alloy is smaller. The results indicate that the precipitates formed in the Mg-1Ca-1Zn alloy retain their strengthening potential up to ~ 450 K. Microstructure observations using scanning electron microscopy revealed that the failure mode for both alloys is transgranular combined with intergranular rupture, irrespective of the treatment and test temperature. The fractography analyses showed that the transgranular fracture changed from quasi-cleavage to dimple rupture with increasing temperature.     

Reduction and adsorption of Pb in aqueous solution by nano-zero-valent iron—A SEM, TEM and XPS study

This study reports the synthesis, characterisation and application of nano-zero-valent iron (nZVI). The nZVI was produced by a reduction method and compared with commercial available ZVI powder for Pb²⁺ removal from aqueous phase. Comparing with commercial ZVI, the laboratory made nZVI powder has a much higher specific surface area. XRD patterns have revealed zero-valent iron phases in two ZVI materials. Different morphologies have been observed using SEM and TEM techniques. EDX spectrums revealed even distribution of Pb on surface after reaction. The XPS analysis has confirmed that immobilized lead was present in its zero-valent and bivalent forms. ‘Core-shell’ structure of prepared ZVI was revealed based on combination of XRD and XPS characterisations. In addition, comparing with Fluka ZVI, this lab made nZVI has much higher reactivity towards Pb²⁺ and within just 15 min 99.9% removal can be reached. This synthesized nano-ZVI material has shown great potential for heavy metal immobilization from wastewater.     

Magnetic structure of the modulated martensite phase in Ni-Mn-Ga ferromagnetic shape memory alloys

The magnetic structure of the seven layered (7 M) modulated martensite phases in Mn-rich Ni-Mn-Ga alloys was studied using Mössbauer spectroscopy. The Mössbauer results clearly demonstrate that in contrast to the non-modulated tetragonal structure two new magnetic sublattices exists for the 7 M orthorhombic martensite phase. Based on the unit cell symmetry and atomic coordination, the additional magnetic sublattices have been assigned to the Ni site. The variation in the magnetic properties of the martensite phases has been related to the underlying magnetic structure.     

NiMn2−xFexO4 prepared by a reverse micelles method as conversion anode materials for Li-ion batteries

Synthesis by reverse micelles was used to produce NiMn_2−xFe_xO₄ with nanometric particle sizes for their use as conversion anode materials for lithium ion batteries. The hydroxide precursor was characterized by infrared spectroscopy and the decomposition was followed by thermal analysis. Cation distribution in the spinel structure of pristine samples was evaluated by Mössbauer spectroscopy evidencing that octahedral Fe³⁺ is substituted by Mn³⁺ ions in NiMnFeO₄. Capacity values of 750 mA h g⁻¹ were retained for 50 cycles for NiMnFeO₄ and NiFe₂O₄, respectively. A good kinetic response was observed in NiMnFeO₄ at 2C.     

Synthesis of nanostructured Ag–Cu alloy ultra-fine particles

We report Ag–Cu solid solution formation by chemical reduction of silver and copper salts in aqueous medium. Depending on the proportion of silver and copper salts taken, varied degrees of solid solubility in the Ag–Cu system are observed. In most systems, we have got hexagonal Ag(rich)-2H phase in addition to Ag-rich face centered cubic one. It seems that the formation of Cu-rich phase is facilitated by the presence of Ag(rich)-2H phase.     

Moderate temperature synthesis of single-walled carbon nanotubes on alumina supported nickel oxide catalyst

A simple nickel oxide catalyst has been developed in synthesizing single-walled carbon nanotubes (SWNTs) at moderate temperature. The catalyst used in the experiment was without a preceding reduction in hydrogen flow. The synthesis of SWNTs was performed at a temperature of 700 °C, which represents a moderate reaction temperature. The presence of SWNTs on the catalyst was confirmed by transmission electron microscope (TEM) and Raman spectroscope. The Raman spectrum shows a strong intensity at the radial breathing mode, indicating that the occurrence of SWNTs was dominant. Raman data further reveals that the synthesized SWNTs had the diameters in the range from 0.58 to 2.02 nm.     

An investigation on the fracturing behavior of bulk metallic glass with large plasticity

A bulk metallic glass (BMG) with large plasticity was prepared and its fracturing behavior was observed at a strain rate larger than ∼ 10^− 3 s^− 1 under uniaxial compression. Even in this strain rate condition, the BMG still exhibits an excellent plastic deformability. The BMG exhibits a large elastic limitation of about 2.43% for engineering strain and 2.46% for true strain. The engineering and true plastic strains are 3.05% and 3.18%, respectively, and the maximum compressive strength is 1810 MPa. High dense shear bands appear in the outer surfaces of the failed BMG, of which the fracture surface exhibits melting and subsequently tearing-up signs with low vein height and small droplet, orientating significantly. The fracture angle is about 54°, deviating from the theoretical fracture angle by 9°. These may be related to the unique performance characteristics and the micro-structure of the BMG.     

Facile solution synthesis and characterization of porous cubic-shaped superstructure of ZnAl2O4

Porous and cubic-shaped superstructure of ZnAl₂O₄ was successfully synthesized by a facile wet chemical solution-phase method. The structural properties of the samples were systematically investigated by X-ray powder diffraction (XRD), Brunauer-Emmet-Teller (BET), scanning electron microscopy (SEM), energy-dispersive spectra (EDS), and Fourier transform infrared spectroscopy (FT-IR) techniques. The characterization results revealed that the structure of the cubic-shaped ZnAl₂O₄ was an inverse spinel structure. The sample prepared by a solution-phase chemical method has a higher surface area and monomodal pore size distributions. Furthermore, the valence states and the surface chemical compositions of ZnAl₂O₄ were further identified by X-ray photoelectron spectroscopy (XPS). This study provides a simple method to prepare cubic-shaped ZnAl₂O₄ in large scale, which broadens their practical applications.     

Morphology controllable synthesis of TiO2 by a facile hydrothermal process

Titanium dioxide nanoparticles were prepared via a facile hydrothermal approach with titanium tetrabutoxide as a precursor under strongly acidic condition. The transmission electron microscopy results showed that novel flower-like, leaf-like, and rod-like TiO₂ nanoscale materials could be easily obtained by tailoring the concentration of the precursor and the reaction temperature. And the analysis from X-ray diffraction revealed that all the as-prepared products under different experimental conditions possessed a mixed crystal phase of anatase and rutile. The reasons for the phase formation were discussed. Larger proportion of rutile phase should be ascribed to the strongly acidic conditions. The growth mechanisms of TiO₂ nanostructures with various morphologies were also proposed.     

One-step synthesis of reduced graphite oxide–silver nanocomposite

Here, a general approach for the preparation of reduced graphite oxide (rGO)–silver nanocomposite has been investigated. Graphite oxide (GO) sheets are used as the nanoscale substrates for the formation of rGO–silver composite. GO sheets and Ag ions can be reduced at the same time, under a mild condition using l-ascorbic acid (l-AA) as reducing agent. This simple approach should find practical applications in the production of rGO–silver nanocomposite. The SEM analysis indicates that the silver particles are dispersed on graphene sheets. Raman signals of rGO in the composite are increased by the attached silver nanoparticles, displaying surface-enhanced Raman scattering activity. The degree of enhancement can be adjusted by varying the quantity of silver nanoparticles in the composite. In addition, antibacterial activity of the composite against Escherichia coli was evaluated using zone of inhibition. Composites with Ag clearly showed antibacterial activity against E. coli. While GO alone has almost no effect against this bacteria.