Experimental and theoretical study on the β-FeOOH nanorods: growth and conversion

This study presents an experimental and theoretical study on the growth of monodispersed akaganéite (β-FeOOH) nanorods with tunable aspect ratios (longitudinal to transversal) under mild conditions (80 °C, aqueous solution). The synthesis of β-FeOOH nanorods is highly influenced by the presence of salt ions, and thus, the effect of various anions (e.g., NO₃ ⁻, SO₄ ²⁻, F⁻, Cl⁻, and Br⁻) were investigated on the microstructure, morphology, and size of the nanoparticles. It was found that these anions could interact strongly or weakly with the FeO₆ octahedral unit in the ferric oxyhydroxides, hence greatly affect the morphology, crystallization, and structure of the iron oxide/oxyhydroxide nanoparticles under the reported conditions. Moreover, these nanorods could be converted into magnetite (Fe₃O₄) through the reduction of hydrazine, which provides a new template approach to prepare magnetite nanorods with shape and size control at ambient conditions. The microstructure, composition, and structural transformation of the as-synthesized nanoparticles were characterized by various techniques, such as transmission electron microscopy (TEM and HRTEM), X-ray diffraction (XRD), and energy dispersive spectroscopy (EDS). The possible formation and growth mechanism of akaganéite nanorods were discussed. Finally, the influence of anions on the β-FeOOH(100), (110), and (001) surfaces was further understood by theoretical simulations (e.g., molecular dynamics method).     

干斜压大气拉格朗日原始方程组的半解析解法和非线性密度流数值试验

以差分方程代替微分方程给大气原始方程组求解带来了诸多难以解决的问题, 对于(半)拉格朗日模式来说质点轨迹的计算与Helmholtz方程的求解是两大难题. 本文通过对气压变量代换, 并在积分时间步长内将原始方程组线性化, 近似为常微分方程组, 求出方程组的半解析解, 再采用精细积分法求解半解析解. 半解析方法可同时计算风、气压和位移, 无需求解Helmholtz方程, 质点的位移采用积分风的半解析解得到, 相比采用风速外推的计算方法, 半解析方法更科学合理. 非线性密度流试验检验表明: 半解析模式能够清晰地模拟Kelvin-Helmholtz 切变不稳定涡旋的发生和发展过程; 模拟的气压场和风场环流结构与标准解非常相似, 且数值解是收敛的, 同时, 总质量和总能量具有较好的守恒性. 试验初步证明了采用半解析方法求解大气原始方程组是可行的, 为大气数值模式的构建提供了一个新的思路.     

Ochres from rituals of prehistoric human funerals at the Toca do Enoque site, Piau��, Brazil

The archaeological site known as Toca do Enoque (geographical coordinates, 09° 14?? 65.3?? S 43° 55?? 62.5?? W) is a rock shelter located in the Serra das Andorinhas (Serra das Confusões National Park), rural area of the city of Guaribas, state of Piauí, Brazil. Several rupestrian paintings (anthropomorphic and zoomorphic motifs along with some pure graphisms), predominantly in red, are found on the sandstone walls. Charcoals, lithic materials, necklaces with teeth, animal bones, gastropod shells, ochres and human skeletons (dated from 6,220 ± 40 to 6,610 ± 40 years before present, BP) were identified in recent excavations in this shelter. Red and yellow ochre samples were collected from prehistoric funeral structures and analyzed with powder X-ray diffractometry, Fourier-transform infrared spectroscopy and ⁵⁷Fe transmission Mössbauer spectroscopy at 298 K and 80 K. Mössbauer data indicate that the red ochre do contain predominantly hematite (??-Fe₂O₃) whereas goethite (??-FeOOH) is the major mineral in the yellow ochre.     

Preparation,characterization, magnetic property,and Mössbauer spectra of the β-FeOOH nanoparticles modified by nonionic surfactant

β-FeOOH nanoparticles have been prepared in a microemulsion system with nonionic surfactant polyoxyethylene(4)nonylphenylether CH₃(CH₂)₈C₆H₄O(CH₂OCH₂)₄H. The powder X-ray diffraction, infrared spectra, and transmission electron microscopic images indicate that the products are 20–30 nm length nanorods with a crystal structure belonging to monoclinic β-FeOOH and lattice parameters of a=0.9981, b=0.2948, c=1.0485 nm and β=92.26°. The size and shapes of β-FeOOH nanoparticles can be manipulated by the surfactant. The modified β-FeOOH nanoparticles are paramagnetic at room temperature and may be antiferromagnetic or weakly ferrimagnetic at lower temperatures. The ⁵⁷Fe Mössbauer spectra show that the magnetic structure transforms below 150 K and two kinds of Fe–O octahedra exist in the lattice of the modified β-FeOOH nanoparticles. The numbers of each kind of Fe–O octahedra are not the same at room temperature or at low temperatures.     

In situ formation of magnetic–luminescent, bi-functional, polymer-stabilized cerium sulfide nanoparticles

Polymer-stabilized paramagnetic and fluorescent rare-earth metal sulfide (cerium sulfide, Ce₂S₃) nanoparticles have been synthesized by using an ??in situ polymerization and composite formation?? (IPCF) technique (Mallick et al. in J. Appl. Phys. 106:074303, 2009) at room temperature. Encapsulated cerium sulfide nanoparticles showed photoluminescence when excited with laser irradiation. The composite material exhibited a paramagnetic behavior due to the in situ formation of magnetic Ce³⁺ ionic species at the reaction condition.     

Efficient fluorescence of dissolved CaF2:Tb and CaF2:Ce, Tb nanoparticles through surface coating sensitization

Oleic acid (OA)-modified CaF₂:Tb³⁺ nanoparticles with various Tb³⁺ concentrations and CaF₂:Ce³⁺, Tb³⁺ nanoparticles were synthesized. The as-prepared nanoparticles were shown to be well dissolved in some common organic solvents, such as chloroform and toluene. The nanoparticles were characterized by Fourier transform infrared spectroscopy (FT-IR), X-Ray diffraction (XRD) and transmission electron microscopy (TEM). The investigation of fluorescence properties of CaF₂:Tb³⁺ nanoparticles showed that the Tb³⁺ ions could be sensitized efficiently by the surface coating of OA and CaF₂:Tb³⁺ nanoparticles with 10 mol% Tb³⁺ concentrations possess the highest emission intensity. The comparison of emission for CaF₂:Ce³⁺, Tb³⁺ and CaF₂:Tb³⁺ (10 mol%) nanoparticles revealed that the emission intensity of the former is about 4.5 times as strong as that of the latter.     

Avidin conjugation to up-conversion phosphor NaYF4:Yb3+, Er3+ by the oxidation of the oligosaccharide chains

NaYF₄:Yb³⁺, Er³⁺ nanoparticles were successfully prepared by a polyol process using diethyleneglycol (DEG) as solvent. After being functionalized with SiO₂–NH₂ layer, these NaYF₄:Yb³⁺, Er³⁺ nanoparticles can conjugate with activated avidin molecules (activated by the oxidation of the oligosaccharide chain). The as-formed NaYF₄:Yb³⁺, Er³⁺ nanoparticles, NaYF₄:Yb³⁺, Er³⁺ nanoparticles functionalized with amino groups, avidin conjugated amino-functionalized NaYF₄:Yb³⁺, Er³⁺ nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), atomic force microscopy (AFM), Fourier transform infrared (FT-IR), UV/Vis absorption spectra, and up-conversion luminescence spectra, respectively. The biofunctionalization of the NaYF₄:Yb³⁺, Er³⁺ nanoparticles has less effect on their luminescence properties, i.e., they still show the up-conversion emission (from Er³⁺, with ⁴S_3/2 → ⁴I_15/2 at ~540 nm and ⁴F_9/2 → ⁴I_15/2 at ~653 nm), indicative of the great potential for these NaYF₄:Yb³⁺, Er³⁺ nanoparticles to be used as fluorescence probes for biological system.     

Preparation of α-Fe2O3 nanoparticles by high-energy ball milling

α-Fe₂O₃ nanoparticles were prepared by high-energy ball milling using α-FeOOH as raw materials. The prepared samples were characterized by transmission electron microscopy (TEM), Mössbauer spectroscopy, X-ray diffraction (XRD) and differential thermal analysis–thermogravimetric analysis (DTA–TGA). The results showed that after 90 h milling α-Fe₂O₃ nanoparticles were obtained, and the particle size is about 20 nm. The mechanism of reaction during milling is supposed that the initial α-FeOOH powder turned smaller and smaller by the high-speed collision during ball milling, later these particles turned to be superparamagnetic, at last these superparamagnetic α-FeOOH particles were dehydrated and transformed into α-Fe₂O₃.     

Enhanced electrochemical performance of La- and Zn-co-doped LiMn2O4 spinel as the cathode material for lithium-ion batteries

We report on the nanoparticle uptake into MCF10A neoT and PC-3 cells using flow cytometry, confocal microscopy, SQUID magnetometry, and transmission electron microscopy. The aim was to evaluate the influence of the nanoparticles?? surface charge on the uptake efficiency. The surface of the superparamagnetic, silica-coated, maghemite nanoparticles was modified using amino functionalization for the positive surface charge (CNPs), and carboxyl functionalization for the negative surface charge (ANPs). The CNPs and ANPs exhibited no significant cytotoxicity in concentrations up to 500???g/cm³ in 24?h. The CNPs, bound to a plasma membrane, were intensely phagocytosed, while the ANPs entered cells through fluid-phase endocytosis in a lower internalization degree. The ANPs and CNPs were shown to be co-localized with a specific lysosomal marker, thus confirming their presence in lysosomes. We showed that tailoring the surface charge of the nanoparticles has a great impact on their internalization.     

Mössbauer spectroscopy of frozen solutions as a stepwise control tool in preparation of biocompatible humic-stabilized feroxyhyte nanoparticles

Mössbauer spectroscopy of frozen aqueous solutions was demonstrated as an efficient stepwise control technique in the new one-pot synthesis of biocompatible feroxyhyte (δ ^′-FeOOH) nanoparticles in situ stabilized by humic substances. Formation of ultradispersed Fe(OH)₂ as an intermediate product and its interaction with humic substances were ascertained. The interaction of the surface of Fe(OH)₂ with humic substances was considered as a starting point in the mechanism of in situ stabilization and further growth control of humic-stabilized feroxyhyte nanoparticles.     

The study of novel Fe3O4@γ-Fe2O3 core/shell nanomaterials with improved properties

The surface structure of the iron oxide nanoparticles obtained by the co-precipitation method has been investigated, and a thin layer of α-FeOOH absorbed on surface of the nanoparticle is confirmed by analyses of Fourier transform infrared (FTIR), X-ray photoelectron spectra (XPS) and surface photovoltage spectroscopy (SPS). After annealed at 400 °C, the α-FeOOH can be converted to γ-Fe₂O₃. The simple-annealed procedure resulted in the formation of Fe₃O₄@γ-Fe₂O₃ core/shell structure with improved stability and a higher magnetic saturation value, and also the simple method can be used to obtain core/shell structure in other similar system.     

Energy migration toward a dye in nanoparticles from complexes with short fluorescent state lifetimes

We have studied regular features of the fluorescence sensitization (cofluorescence) of coumarin 30 and rhodamine 6G introduced into nanoparticles from complexes Ln(PhBTA)₃phen, where PhBTA is p-phenylbenzoyltrifluoroacetone and Ln is a triply charged Pr, Nd, Sm, Eu, Er, or Yb ion, which absorbs in the fluorescence range of ligands of complexes and dyes. We show that both the cofluorescence intensities (I _cofl) of rhodamine 6G in nanoparticles from Sm and Eu complexes and the behavior of intensity I _cofl on the content of rhodamine 6G coincide with the corresponding data obtained for nanoparticles from La and Lu complexes doped with rhodamine 6G molecules. A considerable decrease in I _cofl of rhodamine 6G is observed only in nanoparticles from complexes Nd(PhBTA)₃phen. In nanoparticles from Pr, Nd, Sm, Eu, Er, and Yb complexes doped with coumarin 30, it has been observed that, depending on the choice of the central ion, I _cofl of coumarin 30 is 2 to 80 times lower compared to I _cofl of the dye in nanoparticles from La and Lu complexes. A separate analysis of the influence of these ions on the energy transfer from complexes to coumarin 30 and on the fluorescence intensity of coumarin 30 incorporated into nanoparticles from these ions showed that a decrease in I _cofl of coumarin 30 by a factor of 2?C20 occurs due to the reduction of ??_fl of ligands of complexes under the influence of the interaction with Pr, Nd, Sm, Eu, Er, and Yb ions. Since ??_fl of complexes La(PhBTA)3phen is ??2 ps, while that of complexes Gd(PhBTA)3phen is ??1 ps, then, in nanoparticles with a maximal decrease in I _cofl of coumarin 30, ??_fl of complexes is reduced to ??0.1 ps. It has been found that, in nanoparticles from complexes with this ??_fl, energy migration over complexes takes place. However, as distinct from nanoparticles from La, Lu, and Y complexes, the free path length of singlet excitons in nanoparticles from complexes of absorbing ions is smaller than the nanoparticle size.     

Simulating physiological conditions to evaluate nanoparticles for magnetic fluid hyperthermia (MFH) therapy applications

Magnetite nanoparticles with high self-heating capacity and low toxicity characteristics are a promising candidate for cancer hyperthermia treatment. In order to achieve minimum dosage to a patient, magnetic nanoparticles with high heating capacity are needed. In addition, the influence of physiological factors on the heat capacity of a material should be investigated in order to determine the feasibility. In this study, magnetite nanoparticles coated with lauric acid were prepared by co-precipitation of Fe³⁺:Fe²⁺ in a ratio of 2:1, 5:3, 3:2, and 4:3, and the pH was controlled using NaOH. Structural and magnetization characterization by means of X-ray diffractometry (XRD) and a superconducting quantum interference device (SQUID) revealed that the main species was Fe₃O₄ and further showed that most of the nanoparticles exhibited superparamagnetic properties. All of the magnetic nanoparticles showed a specific absorption rate (SAR) increase that was linear with the magnetic field strength and frequency of the alternating magnetic field. Among all, the magnetic nanoparticles prepared in a 3:2 ratio showed the highest SAR. To further test the influence of physiological factors on the 3:2 ratio magnetic nanoparticles, we simulated the environment with protein (bovine serum albumin, BSA), blood sugar (dextrose), electrolytes (commercial norm-saline) and viscosity (glycerol) to examine the heating capacity under these conditions. Our results showed that the SAR value was unaffected by the protein and blood sugar environments. On the other hand, the SAR value was significantly reduced in the electrolyte environment, due to precipitation and aggregation with sodium ions. For the simulated viscous environment with glycerol, the result showed that the SAR values reduced with increasing glycerol concentration. We have further tested the heating capacity contribution from the Néel mechanism by trapping the magnetic nanoparticles in a solid form of polydimethylsiloxane (PDMS) to eliminate the heating pathway due to a Brownian motion. We measured the heating capability and determined that 47% of the total heat generated by the magnetic nanoparticles was from the Néel mechanism contribution. For evaluating magnetic nanoparticles, this method provides a fast and low cost method for determining qualitative and quantitative information measurement for the effect of physiological interference and could greatly reduce the cost and time by in vitro or animal test.     

Increasing the stability of DNA-functionalized gold nanoparticles using mercaptoalkanes

In this work, the stability of DNA functionalized gold nanoparticles was examined in relation to their size, temperature, as well as the presence of mono- and bivalent ions. Furthermore, we report on the stabilizing effect of an additional post-functionalization with mercaptoalkanes, optionally bearing triethylene glycol (TEG) units. Although such so-called backfilling molecules are commonly used for planar gold surfaces, they have rarely been reported in combination with DNA-functionalized nanoparticles. Our results show that, conform the DLVO theory, smaller citrate-capped gold nanoparticles were more stable towards higher concentrations of salt. Citrate nanoparticles of 30 nm in size were only stable in sodium chloride concentrations up to ~0.05 M and up to 45 °C. The stability of these uncoated nanoparticles was even lower when bivalent salts were used (i.e. <2 × 10⁻⁴ M). Immobilization of DNA on these nanoparticles, on the other hand, improved the stability in salt solutions with at least one order of magnitude. The additional use of backfilling molecules stabilized the gold nanoparticles even further, without negatively affecting the DNA hybridization efficiency. DNA functionalization also had a positive impact on the thermal stability of the nanoparticles. Unfortunately, this beneficial effect was not observed after a subsequent backfilling step.

     

Mössbauer analysis on the magnetic properties of Fe–Co nanoparticles synthesized by chemical vapor condensation process

The magnetic properties of Fe–Co nanoparticles synthesized by chemical vapor condensation (CVC) process were investigated. Effect of CVC processing variables on the magnetic properties was analyzed in detail, using Mössbauer spectroscopy, XRD, BET and HRTEM. The synthesized particles were nearly spherical, and their surfaces were identified to be -FeOOH, γ-FeOOH and Fe₃O₄, but not -Fe₂O₃. The magnetic properties were strongly influenced by CVC processing parameters. The increase of cobalt content had changed the magnetic property of the sample. However, when the decomposition temperature and the oxygen content in the carrier gas (Ar) were increased, the magnetic property reduced with decreasing the average particle size. Increasing the vacuum pressure in the chamber resulted in that the magnetic field reinforced with the increase of average particle size.     

Investigation of Rust Formed on Steel Surfaces and Related Oxyhydroxides

In order to indentity the corrosion products formed on steel surfaces from ⁵⁷Fe Mössbauer spectroscopy, detailed Mössbauer parameters have been determined for various kinds of iron-oxyhydroxides: -FeOOH, -FeOOH, -FeOOH and -FeOOH. ⁵⁷Fe Mössbauer measurements of the iron oxyhydroxides indicate the following results. Fe occupies a single site in -FeOOH, but below the Néel temperature as at e.g., 300 K the Mössbauer spectrum is always broad, showing a distribution of the strength of the magnetic exchange interactions. Its shape depends on the grain-size and synthetic methods of the specimen. Fe occupies 3 sites in -FeOOH. High-purity reagents of -FeOOH always contain small amounts of -FeOOH and their Néel temperatures depend on the synthetic methods of the specimen. Mössbauer spectroscopy of the synthetic -FeOOH shows very broad distribution of the hyperfine magnetic fields.     

Atmospheric corrosion in the Gulf of México

The corrosion products on steels exposed at two sites in Campeche, México and one site at Kure Beach, USA, have been investigated to determine the extent to which different marine conditions and exposure times control the oxide formation. The corroded coupons were analyzed by Mössbauer, Raman and infrared spectroscopy as well as X‐ray diffraction, in order to completely identify the oxides and map their location in the corrosion coating. The coating compositions were determined by Mössbauer spectroscopy using a new parameter, the relative recoilless fraction (F-value) which gives the atomic fraction of iron in each oxide phase from the Mössbauer sub‐spectral areas. For short exposure times, less than three months, an amorphous oxyhydroxide was detected after which a predominance of lepidocrocite (γ-FeOOH), and akaganeite (β-FeOOH) were observed in the corrosion coatings with the fraction of the later phase increasing at sites with higher atmospheric chloride concentrations. The analysis also showed that small clusters of magnetite (Fe₃O₄), and maghemite (γ(Fe₂O₃), were seen in the micro-Raman spectra but were not always identified by Mössbauer spectroscopy. For longer exposure times, goethite (α-FeOOH), was also identified but little or no β-FeOOH was observed. It was determined by the Raman analysis that the corrosion products generally consisted of inner and outer layers. The protective layer, which acted as a barrier to slow further corrosion, consisted of the α-FeOOH and nano-sized γ-Fe₂O₃ phases and corresponded to the inner layer close to the steel substrate. The outer layer was formed from high γ-FeOOH and low α-FeOOH concentrations.     

Oleic acid coating on the monodisperse magnetite nanoparticles

Monodisperse magnetite nanoparticles provide a more factual model to study the interface interactions between the surfactants and magnetic nanoparticles. Monodisperse magnetite nanoparticles of 7 and 19 nm coated with oleic acid (OA) were prepared by the seed-mediated high temperature thermal decomposition of iron(III) acetylacetonate (Fe(acac)₃) precursor method. Fourier transform infrared spectra (FTIR) and X-ray photoelectron spectroscopy (XPS) reveal that the OA molecules were adsorbed on the magnetic nanoparticles by chemisorption way. Analyses of transmission electron microscopy (TEM) shows the OA provided the particles with better isolation and dispersibility. Thermogravimetric analysis (TGA) measurement results suggest that there were two kinds of different binding energies between the OA molecules and the magnetic nanoparticles. The cover density of OA molecules on the particle surface was significantly various with the size of magnetite nanoparticles. Magnetic measurements of the magnetite nanoparticles show the surface coating reduced the interactions among the nanoparticles.     

Mössbauer and XRD analysis of corrosion products on weathering steel treated by wet-dry cycles using various solutions

Weathering steels (COR-TEN) were corroded by wet-dry cycles using a splay of various solutions in a laboratory. Corrosion products on weathering steel were characterized by X-ray diffractometry and Mössbauer spectrometry at room and low temperatures. Fine α-FeOOH, γ-FeOOH and γ-Fe ₂ O ₃ are fundamentally formed in various atmospheric conditions. β-FeOOH is additionally formed under the existence of chloride ions, but not formed when sulfate ions are coexisting. Spraying a NaF solution prevents the progress of corrosion.     

Size control synthesis of starch capped-gold nanoparticles

Metallic gold nanoparticles have been synthesized by the reduction of chloroaurate anions [AuCl₄]⁻ solution with hydrazine in the aqueous starch and ethylene glycol solution at room temperature and at atmospheric pressure. The characterization of synthesized gold nanoparticles by UV–vis spectroscopy, high resolution transmission electron microscopy (HRTEM), electron diffraction analysis, X-ray diffraction (XRD), and X-rays photoelectron spectroscopy (XPS) indicate that average size of pure gold nanoparticles is 3.5 nm, they are spherical in shape and are pure metallic gold. The concentration effects of [AuCl₄]⁻ anions, starch, ethylene glycol, and hydrazine, on particle size, were investigated, and the stabilization mechanism of Au nanoparticles by starch polymer molecules was also studied by FT-IR and thermogravimetric analysis (TGA). FT-IR and TGA analysis shows that hydroxyl groups of starch are responsible of capping and stabilizing gold nanoparticles. The UV–vis spectrum of these samples shows that there is blue shift in surface plasmon resonance peak with decrease in particle size due to the quantum confinement effect, a supporting evidence of formation of gold nanoparticles and this shift remains stable even after 3 months.