Fe(II)-induced transformation from ferrihydrite to lepidocrocite and goethite

The transformation of Fe(II)-adsorbed ferrihydrite was studied. Data tracking the formation of products as a function of pH, temperature and time is presented. The results indicate that trace of Fe(II) adsorbed on ferrihydrite can accelerate its transformation obviously. The products are lepidocrocite and/or goethite and/or hematite, which is different from those without Fe(II). That is, Fe(II) not only accelerates the transformation of ferrihydrite but also leads to the formation of lepidocrocite by a new path. The behavior of Fe(II) is shown in two aspects—catalytic dissolution-reprecipitation and catalytic solid-state transformation. The results indicate that a high temperature and a high pH(in the range from 5 to 9) are favorable to solid-state transformation and the formation of hematite, while a low temperature and a low pH are favorable to dissolution-reprecipitation mechanism and the formation of lepidocrocite. Special attentions were given to the formation mechanism of lepidocrocite and goethite.     

Optical and photocatalytic properties of single crystalline ZnO at the air-liquid interface by an aminolytic reaction

Crystalline flowerlike ZnO was synthesized by an aminolytic reaction at the air-liquid interface in an aqueous media at an alkaline pH. A thin visible film was formed at the air-liquid interface by self-assembly of flowerlike ZnO. Diffraction studies show rearrangement of the single crystalline units at the air-liquid interface leading to the formation of nanobelts. These nanobelts overlap systematically to form petals of the flowerlike structure; individual petals get curved with time. Each nanobelt is found to be single crystalline and can be indexed as the hexagonal ZnO phase. The organic product formed in the aminolytic reaction and dissolution-reprecipitation mechanism is the driving force for the formation of flowerlike ZnO at the air-liquid interface. A clear relationship between the surface, photocatalytic, and photoluminescent properties of ZnO is observed. The flowerlike structure exhibits a blue shift (3.56 eV) in the band emission as compared to bulk ZnO (3.37 eV). The photodegradation of methylene blue over the flowerlike ZnO catalyst formed at the air-liquid interface and in the sediments shows enhanced photocatalytic activity. The sub-bands formed due to surface defects facilitate separation of charge carriers increasing their lifetime, leading to enhanced photocatalytic activity of flowerlike ZnO.     

Effect of hydroxyl group position and system parameters on the features of hydroxystearic Acid monolayers

The characteristic features of hydroxystearic acid monolayers OH-substituted in the mid position of the alkyl chain deviate considerably from those of the usual nonsubstituted stearic acid. The phase behavior, domain morphology, and two-dimensional lattice structure of 9-, 11-, and 12-hydroxystearic acids are studied, using pi-A isotherms, Brewster angle microscopy (BAM), and grazing incidence X-ray diffraction (GIXD), to obtain detailed information on the effect of the exact position of the OH-substitution. The pi-A isotherms of all three hydroxyoctadecanoic acids have an extended flat plateau region, the extension of which only slightly decreases with the increase of temperature. At the same temperature, the extension of the plateau region increases and the plateau pressure decreases from 9-hydroxyoctadecanoic acid to 12-hydroxyoctadecanoic acid. The absolute -DeltaH and -DeltaS values for the phase transition increase slightly from 9-hydroxyoctadecanoic acid to 12- hydroxyoctadecanoic acid and indicate differences in the ordering of the condensed phase under consideration of the special reorientation mechanism of these bipolar amphiphiles at the fluid/condensed phase transition. The morphology of the condensed phase domains formed in the fluid/condensed coexistence region is specific for the position of the OH-substitution of the alkyl chain, just as the lattice structures of the condensed monolayer phase. 11-hydroxyoctadecanoic acid monolayers form centered rectangular lattices with the chain tilt toward the NNN (next nearest neighbor) direction, and 12-hydroxyoctadecanoic acid monolayers have an oblique lattice over the entire pressure range. A special feature of 9-hydroxystearic acid monolayers is the phase transition between two condensed phases observed in the pi-A isotherm of 5 degrees C at approximately 18 mN/m, where the centered rectangular lattice shows a NNN/NN transition. The morphology of the condensed phase domains formed in the fluid/condensed coexistence region, just as the lattice structures of the condensed monolayer phase, reveal the high specifity of the monolayer feature of the bipolar hydroxystearic acids OH-substituted in the mid position.     

On the Reactivity of Silver Electrodes in a Chlorine Radiofrequency Plasma — Plasma Oxidation vs. Thermal Oxidation

The plasma‐electrochemical growth of an ion‐conducting film by the oxidation of a metal in an electronegative plasma is investigated and compared with results from thermal oxidation. As model system we studied the oxidation kinetics of silver electrodes in a Cl₂ rf plasma. The electrochemical control of the reaction by external currents through the product layer using the plasma as a fluid electrode was achieved. Both potentiostatic and galvanostatic control of the reaction was applied. The morphology of the product layer and its temporal evolution was investigated using SEM. A formation of silver chloride surface patterns in the oxidation process takes place if a simple stability criterion is not fulfilled. Specific surface morphologies were found under different experimental conditions. The morphology of the product layer is influenced by the external electric current and the substrate temperature. The influence of the plasma phase on the thermodynamics and kinetics of the oxidation process is discussed. The role of excited plasma species, the electrical charging of the surface and radiation from the plasma are taken into account.     

Use of Alkaline Degradation for the Analysis of Dihydrotriazines via High Pressure Liquid Chromatography

Abstract

An HPLC method is described for the determination of 4,6-diamino-1,2-dihydro-2,2-dimethyl-1-(3′,4′-dichlorobenzyloxy)-1,3,5-triazine hydrochloride (WR 38839). The procedure required the isomerization of the drug sample by alkaline treatment with sodium hydroxide, as the parent compound was retained by the column. The reaction product of the drug was analyzed by HPLC using a strong cation exchange resin as the stationary phase and glycine buffer, pH 10.4 as the mobile phase. The product was isolated and identified by TLC, UV, IR, mass spectroscopy and elemental analysis. The postulated mechanism indicates that this would be a general analytical method for dihydrotriazine compounds. This technique, developed for the assay of the dihydrotriazine in an aqueous system, was successfully applied to rat urine samples spiked with the drug.     

Synthesis of nanocrystalline zinc sulfide in a non-aqueous system by gamma-irradiation

Summary Gamma-irradiation has been applied to synthesize nanocrystalline ZnS with average size of 38 nm in a non-aqueous system at room temperature by utilizing homogeneous release of S^2- ions from the decomposition of carbon disulfide under γ-irradiation. The structure, morphology, size and optical properties have been studied by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), ultraviolet-visible spectrometer (UV-visible). The product containing zinc ions and the sulfur source has been characterized as β-ZnS, sphalerite phase, with spherical morphology and with a diameter average size of about 38 nm.The possible mechanism of formation of the product is suggested in accord with the experiment.     

Highly-crystallized quaternary chalcopyrite nanocrystals via a high-temperature dissolution-reprecipitation route

Quaternary chalcopyrite (Cu(2)CoSnS(4), Cu(2)ZnSnS(4)) nanocrystals displaying high crystallization and controlled morphology were synthesized via a high-temperature growth regime achieved by dissolution-reprecipitation of tailored ultrafine precursors in the temperature range 400-500 °C.     

微流控技术在纳米合成中的应用

微流控技术具有微型化、集成化的特点,且所合成产物形貌和单分散性好,已经越来越多的被应用于纳米材料的合成中。 本文对微流体技术在纳米材料合成中的应用做了系统的阐述。 对微流控芯片中流体流动、混合机理进行了介绍,并详细介绍了微流控芯片的制作工艺,展望了微流体技术在合成纳米材料中应用前景。     

立方相KNb0.77Al0.23O2.77的水热合成与输运性质研究

用水热法合成了立方相KNb_0.77Al_0.23O_2.77通过调整初始铌源和反应介质的KOH浓度,还得到了正交相钙钛矿和一新相化合物.立方相产物采用XRD、DSC和XPS进行表征.低于1000℃的热处理不能导致立方KNb_0.77Al_0.23O_2.77发生结构相变.阻抗谱测量结果表明,离子输运机制归属于小极化子.而正交的同组分样品结构不稳定,在高温发生结构相变,导致电导率不连续.水热法得到的立方KNb_0.77Al_0.23O_2.77可望成为新一代电解质材料.     

Suppression of the reversible thermal behavior of the layered double hydroxide (LDH) of Mg with Al: stabilization of nanoparticulate oxides

The layered double hydroxide of Mg with Al decomposes below 600 degrees C with the loss of nearly 48% mass, resulting in the formation of an oxide residue having the rock salt structure and nanoparticulate morphology. However, this product reconstructs back into the parent LDH, owing to its compositional and morphological metastability. The oxide can be kinetically stabilized within an amorphous phosphate network built up through an ex situ reaction with a suitable phosphate source such as (NH4)H2PO4. This oxide transforms into a thermodynamically more stable phase with a spinel structure on soaking in an aqueous medium. The oxide residue has a nanoparticulate morphology as revealed by the Scherrer broadening of the Bragg reflections as well as by electron microscopy. This work shows that the hydroxide reconstruction reaction and spinel formation are competing reactions. Suppression of the former catalyzes spinel formation as the excess free energy of the metastable oxide residue is unlocked to promote the diffusion of Mg2+ ions from octahedral to tetrahedral sites, which is the essential precondition to the formation of a normal spinel. This reaction taking place as it does at ambient temperature and in solution helps in the retention of a nanostructured morphology for the spinel. Another way of stabilizing the oxide is by incorporating the thermally stable borate anion into the LDH. This paves the way for an in situ reaction between the cations of the host LDH and the borate guest. The in situ reaction directly leads to the formation of an oxide with a spinel structure.     

心磷脂蓝莓类结构的形成和演化

用共聚焦显微镜和光学显微镜研究了NaCl溶液中心磷脂蓝莓类结构的形成和演化过程. 研究发现, 在NaCl溶液(浓度0.005~0.25 mol/L)中, 心磷脂海绵相的表面首先生成半球形的层状相微结构元胞, 并逐渐呈蜂窝状六角密堆积排列. 溶液中NaCl浓度的轻微增加驱使层状相与海绵相的界面由表面向海绵相内部扩散, 溶液中微弱流场的存在也会影响微结构元胞的形貌, 最终形成蜂窝样网状结构、 蓝莓样包状结构和蓝莓样球状结构, 统称蓝莓类结构. 由于心磷脂在线粒体内膜的拓扑结构转变中具有重要作用, 因此相转变及微结构形态演化的研究有助于进一步理解其在线粒体功能发挥中的作用机理.     

Selected-control hydrothermal synthesis and formation mechanism of monazite- and zircon-type LaVO(4) nanocrystals

Selective-controlled structure and shape of LaVO(4) nanocrystals were successfully synthesized by a simple hydrothermal method without the presence of catalysts or templates. It was found that tuning the pH of the growth solution was a crucial step for the control of the structure transformation, that is, from monoclinic (m-) to tetragonal (t-) phase, and morphology evolution of LaVO(4) nanocrystals. Further studies demonstrated that the morphology of the product had a strong dependence on the initial lanthanum sources. In the La(NO(3))(3) or LaCl(3) reaction system, pure t-LaVO(4) nanorods with uniform diameters about 10 nm could be obtained. But when using La(2)(SO(4))(3) as the lanthanum source, we can get t-LaVO(4) nanowiskers with broomlike morphology. The detailed systematic study had shown that a special dissolution-recrystallization transformation mechanism as well as an Ostwald ripening process was responsible for the phase control and anisotropic morphology evolution of the LaVO(4) nanocrystals. As a result, the controlled synthesis of m- and t-LaVO(4) not only has great theoretical significance in studying the polymorph control and selective synthesis of inorganic materials but also benefits the potential applications based on LaVO(4) nanocrystals owing to the unusual luminescent properties induced by structural transformation.     

Identification of major metabolites in rat urine and plasma of N(6) -(4-hydroxybenzyl) adenine riboside by LC/MS/MS

N(6) -(4-hydroxybenzyl) adenine riboside, a novel neuroprotective compound found in Gastrodia elata at trace level, is regarded as a potential drug for the treatment of neural degenerative disease. To understand the metabolism of this compound, the metabolites in rat urine and plasma of N(6) -(4-hydroxybenzyl) adenine riboside were analyzed by HPLC-ESI-MS/MS after oral administration of this compound. Beside the parent compound, six phase I metabolites and four phase II metabolites in urine were detected by scanning all possible metabolites in extracted ion chromatograms mode. By comparing their product ion spectra and retention times with those of parent compound, these metabolites were identified and proved to be mainly formed via hydrolysis or hydroxylation in phase I, N-sulfation or N-glucuronidation in phase II or their combinations. Similarly, the parent compound, one phase I metabolite and two phase II metabolites were also identified in rat plasma. Therefore, the in vivo metabolic pathways of N(6) -(4-hydroxybenzyl) adenine riboside in rat were proposed.     

The effect of the second phase inversion on microstructures in phase inversion EVAL membranes

There were many discussions in the literature describing the membrane formation mechanism for the phase inversion process such as liquid–liquid demixing or crystallization, but few references described the phenomena after the event of the phase inversion process. The purpose of this work is to illustrate the effect of the second phase inversion on membrane structures when the first phase inversion has occurred. Analysis showed the second phase inversion (crystallization or liquid–liquid demixing) may be preceded by the first phase inversion (liquid–liquid demixing only) during poly (ethylene-co-vinyl alcohol) (EVAL) membrane formation. Therefore, we can make membranes combined with macrovoids (the first phase inversion) and particulate morphology (the second phase inversion) from experiments in this work. As a result, the concept the membrane morphology only influenced by the liquid–liquid demixing is misleading and the second phase inversion must be considered as a possible and important mechanism.     

Kinetics of heterogeneous free-radical polymerization of vinylidene chloride

Poly(vinylidene chloride) precipitates as a crystalline phase during the polymerization reaction. Under the conditions studied, this phase is made up of complex particles with a lamellar substructure. The detailed morphology is very sensitive to reaction medium. The morphology developed by particles formed during polymerization of vinylidene chloride in dioxane suggests a mechanism of polymerization followed by crystallization. The morphology observed in mass polymerization suggests that both processes occurs simultaneously. Kinetic data, however, suggest a solid-phase reaction mechanism for both cases. The results are analyzed by comparison with a model that takes into account the solid-phase morphology. The theoretical analysis is consistent with experimental results if it is assumed that polymerization occurs on the edges of the lamellar crystals.     

Modeling and simulation of morphology variation during the solidification of polymer melts with amorphous and semi‐crystalline phases

The solidification of polymer melts in practical processing such as extrusion, injection molding and blow molding can significantly influence the inner structure and performance of final products. The investigation of its mechanism has both scientific and industrial interests. In the study, the three‐dimensional mathematical model is developed for the simulation of morphology variation in the solidification of polymer melts with amorphous and semi‐crystalline phases. The amorphous phase is simulated as the finite extensible nonlinear elastic dumbbell with a peterlin closure approximation (FENE‐P) fluid and the semi‐crystalline phase is approximated as rigid rods that grow and oriented in the flow field. The model of amorphous phase and semi‐crystalline phase are coupled through the stress and momentum balance and the feedback of crystallinity to the system relaxation time. The evolution of crystallization kinetics process are described by using a set of Schneider equation that discriminating the relative roles of the thermal and the flow effect on the crystallization behavior. With the standard Galerkin formulation adopted as basic computational framework, the discrete elastic viscous stress splitting algorithm in cooperating with the streamline upwinding approach serves as a relatively robust numerical scheme by using penalty finite element–finite difference simulation with a decoupled solving algorithm. The proposed mathematical model and numerical method have been successfully applied to the investigation of solidification of polymer melts in the extrusion process. The variations of orientation and crystallization morphology during the solidification process are further discussed. Copyright © 2014 John Wiley & Sons, Ltd.     

Effects of synthesis parameters on the microstructure and phase structure of porous 316L stainless steel supported TiO2 membranes

Porous stainless steel (PSS) supported TiO₂ membrane was synthesized from colloidal TiO₂ sol by the sol–gel technique. Morphology and phase structure of the obtained membranes were regulated through optimizing the synthesis parameters including organic binders, aging periods of the parent sol and concentrations of the casting solutions as well as the sintering temperatures. Polyvinyl alcohol (PVA) 1750 was found to be feasible to fabricate TiO₂ membrane with relatively flat surface and homogeneous morphology without crack. The aging period of the parent sol, which was revealed to be very important to the morphology of the particles deposited in the membranes on PSS, was decided to be 24 h. The concentration, under which the membranes could avoid macro-pores and have a uniform thickness of approximately 8 μm, was regulated to 0.0036 mol/l. Besides, a homogeneous microstructure with grain sizes of 0.08–0.2 μm was obtained in the membrane with a pure rutile phase when sintered at 850 °C. The obtained PSS supported TiO₂ membrane with homogeneous microstructure and rutile phase may be very promising for practical applications.     

Dissipative particle dynamics simulation study of the bilayer-vesicle transition

A bilayer structure is an important immediate for the vesicle formation. However,the mechanism for the bilayer-vesicle transition remains unclear. In this work,a dissipative particle dynamics(DPD) simulation method was employed to study the mechanism of the bilayer-vesicle transition. A coarse-grained model was built based on a lipid molecule termed dimyristoylphosphatidylcholine(DMPC). Simulations were performed from two different initial configurations:a random dispersed solution and a tensionless bilayer. It was found that the bilayer-vesicle transition was driven by the minimization of the water-tail hydrophobic interaction energy,and was accompanied with the increase of the position entropy due to the redistribution of water molecules. The bulk pressure was reduced during the bilayer-vesicle transition,suggesting the evolved vesicle morphology was at the relatively low free energy state. The membrane in the product vesicle was a two-dimensional fluid. It can be concluded that the membrane of a vesicle is not interdigitated and most of the bonds in lipid chains are inclined to orient along the radical axis of the vesicle.     

Soft or hard ionization of molecules in helium nanodroplets? An electron impact investigation of alcohols and ethers

Electron impact (70 eV) mass spectra of a series of C1-C6 alcohols encased in large superfluid liquid helium nanodroplets (approximately 60,000 helium atoms) have been recorded. The presence of helium alters the fragmentation patterns when compared with the gas phase, with some ion product channels being more strongly affected than others, most notably cleavage of the C(alpha)-H bond in the parent ion to form the corresponding oxonium ion. Parent ion intensities are also enhanced by the helium, but only for the two cyclic alcohols studied, cyclopentanol and cyclohexanol, is this effect large enough to transform the parent ion from a minor product (in the gas phase) into the most abundant ion in the helium droplet experiments. To demonstrate that these findings are not unique to alcohols, we have also investigated several ethers. The results obtained for both alcohols and ethers are difficult to explain solely by rapid cooling of the excited parent ions by the surrounding superfluid helium, although this undoubtedly takes place. A second factor also seems to be involved, a cage effect which favors hydrogen atom loss over other fragmentation channels. The set of molecules explored in this work suggest that electron impact ionization of doped helium nanodroplets does not provide a sufficiently large softening effect to be useful in analytical mass spectrometry.     

水冷壁气流床气化炉灰渣结构分析

在管式电炉还原性气氛下,对煤灰进行1 300℃和1 400℃的高温热处理。同时,在小型膜式水冷壁气流床气化炉热模装置中进行煤气化实验。利用XRD、SEM和EDS等方法,考察了热处理后灰渣与煤气化所得炉渣的表面形态、内部微观结构、矿物组成等结构特性,并对管式电炉内进行灰渣热处理实验的可行性进行评估。结果表明,热处理温度和灰渣流动温度对灰渣的结构具有重大影响,热处理温度高于灰渣流动温度约10℃时,灰渣中含有大量矿物晶体且表面形态粗糙,内部微观结构凹凸不平,灰渣难于流动;热处理温度高于灰渣流动温度约100℃时,渣中大部分矿物晶体已变成无定形的玻璃体物质,灰渣表面及内部微观结构变得光滑均匀。采用管式电炉模拟气化炉内灰渣氛围,研究气化炉操作温度对灰渣结构的影响,具有一定的可行性。