Sol-gel synthesis of iron(III) oxyhydroxide nanostructured monoliths using Fe(NO3)3·9H2O/CH3CH2OH/NH4OH ternary system

Iron(III) oxyhydroxide xerogels were prepared through sol-gel technology, using iron(III) nitrate nonahydrate as precursor, ethanol as solvent and ammonium hydroxide as gelation agent. This base is used for propylene oxide substitution, which was the gelation agent in previous works. Synthesis of a gel using NH₄OH as a gelation agent is an innovative result with this type of precursor, since with metal salts the addition of a strong base commonly results in precipitation of the solid. The gel synthesis was achieved by controlling the base addition time. The dried material has a residual amount of organic impurities, in contrast with the significant amount detected in xerogels prepared using propylene oxide. The iron phase prevailing in the produced xerogels can be defined as γ-FeO(OH) (lepidocrocite), according to FTIR and Mössbauer analyses. The xerogels are formed by large clusters of well connected nanocrystallites of this phase. XRD revealed a crystalline phase retained inside the iron oxyhydroxide amorphous structure, which corresponds to NH₄NO₃ and results from the combination of NO₃⁻ and NH₄⁺ ions in solution. The produced xerogel has a promising composition to be an oxidizing composite for the energetic materials area.     

Mössbauer investigations of iron phases of the workable glass ceramic ilmavit(R)40

In the castings of the workable glass ceramic ilmavit(R)40, the precipitation form of the different oxidic iron species of the crystalline and amorphous phases occuring in the structure is dependent on the cooling rate. The distribution of the existing iron species along the cross-section of the casting is not constant. It is assumed that the concentration gradient of the secondary magnetite over the cross-section of the casting originates from the predominant incorporation of the Fe(II) into the sodium fluorine phlogopite (SFP) at low cooling rates and consequently its non-availability for the secondary crystallization of magnetite in the rest glass phase. The Fe(III) not bound in the magnetite remains primarily solved in the rest glass phase.     

Morphological and textural characterization of functionalized particulate silica xerogels

The functionalization of xerogels for use in chromatography and catalysis was carried out by solubilization of amorphous silica using a soxhlet extractor. Xerogels were prepared by sol-gel method using tetraethoxysilane, TEOS, ethanol, and water in a 1/3/10 molar ratio with HCl and HF as catalysts. The samples were prepared in monolithic form and dried at 70 °C and 550 °C for 1 h each. After functionalization, changes in textural and morphological characteristics of xerogels were investigated by means of nitrogen gas adsorption, positron annihilation lifetime spectroscopy (PALS), and scanning electron microscopy (SEM). As the analysis methods are based on different physical principles, the results are complementary, leading to a good knowledge of the texture of the samples studied.     

Photophysical Properties of Rare Earth (Eu<Superscript>3+</Superscript>, Sm<Superscript>3+</Superscript>, Tb<Superscript>3+</Superscript>) Complex Covalently Immobilized in Hybrid Si-O-B Xerogels

The molecular linkage (phenSi) from functionalized 5-amino-1,10-phenanthroline (PhenNH₂) by 3-(triethoxysilyl)-propyl isocyanate (TESPIC) is to construct the rare earth (Sm³⁺, Eu³⁺, Tb³⁺) center covalently immobilized in the hybrid xerogels of Si-O-B through the cohydrolysis and copolycondensation process between different alkoxide precursors of them (tetraethoxysilane (TEOS), tri-n-butylborate (TBB)). NMR, FTIR and ultraviolet absorption are measured to confirm the obtained materials. X-ray diffraction patterns revealed the hybrid materials are amorphous. Scanning electronic microscopy images show the stripe microstructure without phase separation phenomenon in the obtained hybrid materials. The covalently bonded Si-O-B hybrid xerogel presents the similar photoluminescent behavior to the pure Si-O-Si hybrid xerogels, which indicates that Si-O-B hybrid xerogel is a suitable system for the luminescence of RE³⁺.     

Mössbauer spectroscopy in studying magnetite formed by iron- and sulfate-reducing bacteria

The kinetics of iron mineral formation by thermophilic dissimilatory iron reducing bacteria using Fe(III) amorphous hydroxide and acetate CH₃COO^? as an electron acceptor and donor, respectively, was investigated by Mössbauer spectroscopy. The effects of various physical and chemical conditions and the presence of an inert organic substance on the formation of biogenic minerals were considered. The production of magnetite due to microbial sulfate reduction by hyperthermophilic dissimilatory sulfate-reducing microorganisms was investigated by Mössbauer spectroscopy methods.     

Reduction of amorphous Fe(III)-hydroxide by binary microbial culture, a Mössbauer study

Mössbauer investigations between 4.5 and 300 K of iron minerals formed during the growth of the binary culture containing two anaerobic alkaliphilic bacteria-dissimilatory iron-reducing Geoalkalibacter ferrihydriticus (strain Z-0531) and organotrophic Anaerobacillus alkalilacustre (strain Z- 0521), have been carried out. Mannitol (2 g/l) as the sole substrate with amorphous Fe(III) hydroxide at final concentration 10 or 100 mM were added to the mineral medium. The formation of siderite and probable magnetite or a mixture of magnetite and maghemite were observed.     

Behavior of Prussian blue-based materials in presence of ammonia

Prussian blue and related materials, usually considered that behave as a zeolite for ammonia adsorption, when hydrated are unstable in the presence of this gaseous species. They remain stable only in the anhydrous form. In the decomposition products ammonium hexacyanometallates and an XRD amorphous iron(III) oxyhydroxide are detected. The crystallization and adsorbed water present in these solid materials participates in a decomposition reaction to give NH₄⁺ and OH⁻. The very basic OH⁻ anion removes the iron(III) cations from the complex to form Fe(OH)₃ and finally FeOOH, while the formed NH₄⁺ appears as the salt of the complex anion. As reference reactions, the interaction of ammonia with ferrocyanic acid and ferric chloride, both in solid state, were studied where crystalline ammonium ferrocyanide and ammonium chloride, respectively, are formed.     

Mössbauer and EXAFS studies of amorphous iron produced by thermal decomposition of carbonyl iron in liquid phase

Decomposition of iron carbonyl Fe(CO)₅ and Fe₂(CO)₉ in liquid phase gave amorphous and crystalline iron powders in the absence and presence of catalyst, respectively. The hyperfine fields were large in amorphous phases prepared from Fe(CO)₅ than from Fe₂(CO)₉. Crystalline iron, iron carbide and a trace amount of Fe₃O₄ were detected in the decomposition products of the amorphous phase prepared from Fe(CO)₅, and iron carbide was mainly included in the decomposition products of the amorphous phase prepared from Fe₂(CO)₉.     

Mössbauer spectroscopic study of the early crystallization stage of iron(III) hydroxide particles

Mössbauer spectroscopy was used to investigate the early aging stage of iron(III) hydroxide sols prepared by oxidation of Fe(CO)₅ in ethanolic solution, followed by vacuum drying at room temperature. One sample was composed of amorphous particles, while two other samples were partially crystallized, either as a result of solvent change or of spontaneous aging. The main results of Mössbauer measurements in the 80–320 K temperature range are: (a) partially crystallized particles exhibit a strong, S-shaped temperature dependence of the quadrupole splitting, in contrast to a weak and linear variation for amorphous particles; (b) the recoilless fraction temperature dependence is affected by vibration of the particles as a whole, with an effective force constant which is smaller for crystallized particles than for amorphous ones. Furthermore, the former exhibit anf-factor discontinuity near 0°C, which is attributed to melting of a surface layer built up during the crystallization process.     

Application of M?ssbauer spectroscopy to the study of tannins inhibition of iron and steel corrosion

The inhibitory effect of tannins was investigated using, among others, potentiodynamic polarizations and Mössbauer spectroscopy. These techniques confirmed that the nature, pH and concentration of tannic solution are of upmost importance in the inhibitory properties of the solutions. It is observed that at low tannin concentration or pH, both, hydrolizable and condensed tannins, effectively inhibit iron corrosion, due to the redox properties of tannins. At pH ?? 0, Mössbauer spectra of the frozen aqueous solutions of iron(III) with the tannin solutions showed that iron is in the form of a monomeric species [Fe(H₂O)₆]^3?+?, without coordination with the functional hydroxyl groups of the tannins. The suspended material consisted of amorphous ferric oxide and oxyhydroxides, though with quebracho tannin partly resulted in complex formation and in an iron (II) species from a redox process. Other tannins, such as chestnut hydrolysable tannins, do not complex iron at this low pH. Tannins react at high concentrations or pH (3 and 5) to form insoluble blue?Cblack amorphous complexes of mono-and bis-type tannate complexes, with a relative amount of the bis-ferric tannate generally increasing with pH. Some Fe^2?+? in the form of hydrated polymeric ferrous tannate could be obtained. At pH 7, a partially hydrolyzed ferric tannate complex was also formed. The latter two phases do not provide corrosion protection. Tannin solutions at natural pH react with electrodeposited iron films (approx. 6 ??m) to obtain products consisting only on the catecholate mono-complex of ferric tannate. Some aspects of the mechanism of tannins protection against corrosion are discussed.     

Mössbauer spectroscopic characterization of iron methyl pyropheophorbide a and its derivatives

Two kinds of iron chlorophylls, i.e. (methyl pyropheophorbide a)iron(III) chloride and its bis-pyridine adduct, were prepared and characterized by⁵⁷Fe Mössbauer spectroscopy. (Methyl pyropheophorbide a)iron(III) chloride gave an asymmetric quadrupole-split doublet typical of high-spin iron(III) chlorophylls, while its bis-pyridine adduct showed a symmetric quadrupole-split doublet characteristic of low-spin iron(II) chlorophylls. The isomer shift and quadrupole splitting obtained for (methyl pyropheophorbide a)iron(III) chloride and its bis-pyridine adduct have led to the following conclusions. The substitution of the bulky phytyl group for the methyl group hardly affects the electronic state of the iron(II,III) ion, but the elimination of the methoxycarbonyl group increases the planarity of the macrocyclic chlorin ligand.     

Poly(3-Hydroxybutyrate) Matrices Modified with Iron(III) Complexes with Tetraphenylporphyrin. Analysis of the Structural Dynamic Parameters

The effect of small additions of the iron(III) complex with tetraphenylporphyrin (0–5%) on the structure and properties of ultrathin fibers based on poly(3-hydroxybutyrate) (PHB) was studied by differential scanning calorimetry (DSC), X-ray diffraction analysis (XRD), EPR probe method, and scanning electron microscopy. When tetramethylporphyrin was added to the PHB fibers, the crystallinity significantly increased, and the molecular mobility in the amorphous regions of the polymer decreased. The thermal treatment of the fibers (annealing at 140°C) led to significantly increased crystallinity and decreased molecular mobility in the amorphous regions of the PHB fibers. The addition of tetramethylporphyrin to the PHB fibers led to a sharp decrease in crystallinity. Ozonolysis of the fibers at small treatment times caused a considerable decrease in their molecular mobility (to 5 h), while prolonged ozonolysis led to increased mobility. The obtained fibrous materials have bactericidal properties and will find use in the development of antibacterial and antitumor therapeutic systems.     

Eu掺杂SiO2纳米基质的发光特性

采用溶胶-凝胶(sol-gel)法制备了Eu掺杂的SiO₂干凝胶,分别用光致发光(PL)光谱、透射电镜(TEM)、扫描电镜(SEM)、红外吸收(IR)谱等分析手段对样品进行了表征,研究了SiO₂的基质中Eu³⁺、Eu²⁺的发光特性以及退火温度对发射光谱的影响,并对其发光机理进行了分析。结果表明,样品掺杂均匀,颗粒尺寸大约在50~80 nm,硼(B)离子进入SiO₂网格,成为了基质的一部分,改变了基质的网络结构。当采用258 nm激发样品时,随着退火温度的升高,红光发射强度先增强后减弱。对于经800 ℃退火处理的样品红光发射最强,出现了576 nm(⁵D₀ →⁷F₀),620 nm(⁵D₀ →⁷F₂),658 nm(⁵D₀ →⁷F₃)3条谱线,其中主峰位于 620 nm红光发射,对应于Eu³⁺离子的⁵D₀ →⁷F₂超灵敏跃迁,进一步说明B离子参与到基质中,形成了Si—O—B键,导致Eu³⁺离子所处配位环境的对称性降低,从而有利于Eu³⁺离子的特征发射;当采用271 nm激发样品时,随着退火温度的升高,蓝光发射强度先增强后减弱,经850 ℃退火的样品400~500 nm蓝光发射最强,归属于Eu²⁺的5d→4f的跃迁发射,证明在铝离子(Al³⁺)存在的情形下,在高温退火过程中Al³⁺部分取代Si⁴⁺形成AlO^-₄基团,掺杂Eu³⁺填补AlO^-₄基团附近的空位,增加了Eu³⁺周围的AlO^-₄四面体中氧原子的电子给予能力,使得Eu³⁺还原成Eu²⁺,从而得到了较强的蓝光发射。但是,当退火温度达到900 ℃时,由于稀土离子发生位置的迁移形成团簇红光和蓝光都明显地降低。     

Investigation of the evolution of the hydrated zirconia mesostructure at different stages of heat treatment

The mesostructure of amorphous xerogels based on hydrated zirconia ZrO₂ and its evolution at different stages of heat treatment have been investigated using the small-angle neutron scattering method. A correlation function of the nuclear scattering amplitude density has been obtained from experimental neutron scattering cross sections, and the characteristic radii of ZrO₂ nanoparticles and their specific surface areas have been determined. The influence of the annealing temperature on the fractal properties of the zirconia surface has been elucidated.     

Methyl orange adsorption by microporous and mesoporous TiO2-SiO2 and TiO2-SiO2-Al2O3 composite xerogels

We investigate the adsorption behavior of methyl orange (MO) on composite xerogels. Mesoporous TiO₂-SiO₂ and TiO₂-SiO₂-Al₂O₃ xerogels are prepared by hydrolysis of tetraethyl orthosilicate (TEOS), tetrabutyl orthotitanate (TBOT), and AlCl₃ ·6H₂O using HCl as a catalyst and cetyltrimethylammonium bromide (CTAB) as a templating agent. The corresponding microporous xerogels are also prepared without addition of CTAB. These xerogels are then characterized by XRD, FTIR, and BET.We find that MO is adsorbed by the mesoporous xerogels in acidic solutions, showing Langmuir type adsorption isotherms. We also find that the adsorption decreases with increasing temperature. It is suggested that adsorption exhibits a sieve effect and that MO is adsorbed through electrostatic attraction and hydrogen bonding between MO and the xerogels.     

小角x射线散射方法研究甲基改性氧化硅干凝胶的孔结构

以正硅酸乙酯［Si(OC2H5)4，TEOS］为前驱体制备SiO2悬浮液，分别以甲基三乙氧基硅烷［CH3Si(OC2H5)3，MTES］和二甲基二乙氧基硅烷［(CH3)2Si(OC2H5)2，DDS］为前驱体制备硅氧烷聚合物溶液，通过混合法得到两种不同的甲基改性氧化硅凝胶-测量了凝胶的散射强度，计算了凝胶的孔径分布、平均孔径DSAXS、界面层厚度E等参数，结合氮气吸附实验，分析了凝胶的孔结构-发现SiO2一次簇团被MTES聚合物或DDS聚合物连接为二次簇团时产生微孔，同时甲基随聚合物连接于凝胶骨架上形成与 关键词： 小角x射线散射 甲基改性氧化硅 干凝胶 孔结构     

一阶导数光谱法同时测定石英砂中铁和铝的研究

研究了在pH＝6.0的HAc-NaAc缓冲体系中，Al(Ⅲ)和Fe(Ⅲ)分别与乙二醇二乙醚二氨基四乙酸（EGTA），邻苯三酚红（PR），溴化十六烷基吡啶（CPB）形成的四元络合物的性质，利用一阶导数光谱法对微量铁和铝进行了同时测定，测定的变异系数分别为4.5%和1.1%，加标回收率分别为93－98％和95－102％,方法可用于石英砂中微量铁和铝的测定。     

Phase-controlled preparation of iron (oxyhydr)oxide nanocrystallines for heavy metal removal

Obtaining cost-effective iron (oxyhydr)oxide nanocrystallines is the essential prerequisite for their future extensive applications in environmental remediation, such as the removal of heavy metals from contaminated waters. Here, various phases of iron (oxyhydr)oxide nanocrystallines were simply synthesized from the phase-controlled transformation of amorphous hydrous ferric- or ferrous-oxide in thermal solution with a certain ethanol/water ratio and with the presence of oleic acid. According to this method, goethite nanorods in diameter of 3–4 nm, hematite nanocubes sized 20–30 nm, and magnetite nanoparticles in diameter of 6–7 nm were successfully obtained. The final products of this transformation can be conveniently controlled by adjusting the reaction parameters, such as pH, temperature, and ethanol/water ratio. Due to the enhanced specific surface area and probably the modifications of the surface structure of nanocrystallines, the as-synthesized goethite nanorods and magnetite nanoparticles demonstrated extremely strong As(III) affinity, with 5.8 and 54 times of As(III) adsorption, respectively, higher than the micron-sized relatives. The cost-effective feature of as-synthesized nanocrystallines and their remarkably enhanced affinity toward arsenic made them potentially applicable for the removal of arsenic and such like heavy metals from the contaminated environment.     

In situ observation of carbon-nanopillar tubulization caused by liquidlike iron particles

The tubulization process of amorphous carbon nanopillars was observed in situ by transmis-sion electron microscopy. Amorphous carbon nanopillars were transformed into graphitic tubules by annealing at 650-900 degrees C in the presence of iron nanoparticles. A molten catalyst nanoparticle penetrated an amorphous carbon nanopillar, dissolving it, and leaving a graphite track behind. An iron nanoparticle moved with its shape changing like an earthworm. We concluded that the tubulization mechanism is a solid-(quasiliquid)-solid mechanism where the carbon phase transformation is a kind of liquid phase graphitization of amorphous carbon catalyzed by liquefied metal-carbon alloy nanoparticles.     

SiO2干凝胶中CdS量子点的光致发光性质

以正硅酸乙酯(TEOS)为SiO2的前驱物,硝酸镉为镉源,硫脲为硫源,用溶胶-凝胶法制备了CdS量子点掺杂的SiO2干凝胶,利用XRD、紫外-可见吸收光谱、光致发光谱对其性质进行研究.样品的测试结果表明在SiO2干凝胶的网状结构中形成了CdS量子点,平均粒径为5.1 nm.SiO2凝胶中CdS吸收峰位置明显蓝移.在一定...