Spherical Precursor Research Articles

Sacrificed template synthesis of Li1.2Ni0.13Co0.13Mn0.54O2 spheres for lithium-ion battery cathodes

Porous and solid Li1.2Ni0.13Co0.13Mn0.54O2 spheres have been prepared by spherical Ni0.13Co0.13Mn0.54(CO3)0.8 and MnO2-sacrificed templates route. X-ray diffraction profiles show two kinds of Li1.2Ni0.13Co0.13Mn0.54O2 spheres have good layered structure with solid solution characteristic. Scanning electron microscope images reveal that the porous Li1.2Ni0.13Co0.13Mn0.54O2 spheres obtained from spherical carbonate precursor are composed of well-defined primary nanoparticles. These nanoparticles have the size of 100–300 nm, and some porous structure can be observed among these particles on the surface. The solid spheres obtained from MnO2 are made of tightly clustered nanoparticles. As lithium-ion battery cathodes, the porous spheres exhibit a high initial discharge capacity of 255.7 mAh g−1 at 0.1 C between 2.0 and 4.8 V. After 50 cycles, a discharge capacity of 177.7 mAh g−1 could be retained at 0.5 C. Even at high charge–discharge rate of 5 C (1,000 mA g−1), 121.4 mAh g−1 can be reached. But the solid spheres only deliver initial discharge capacity of 159.9 mAh g−1 at 0.1 C. Anyway, the different electrochemical performances of two samples should be attributed to the use of different sacrificed templates.

Preparation and Mechanism of Spherical [Ni1/3Co1/3Mn1/3]Ox Precursors for Li [Ni1/3Co1/3Mn1/3]O2 by an Ultrasonic Atomization Method

The spherical precursors - [Ni1/3Co1/3Mn1/3]Ox and Li [Ni1/3Co1/3Mn1/3]O2 were synthesized by an ultrasonic atomization method via two routes. The [Ni1/3Co1/3Mn1/3]Ox and Li [Ni1/3Co1/3Mn1/3]O2 powders were characterized by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). The experimental results show that the initial concentration of the raw solution would affect the size of precursor [Ni1/3Co1/3Mn1/3]Ox particles. The Li [Ni1/3Co1/3Mn1/3]O2 particles which were prepared from the mixture of LiNO3 and [Ni1/3Co1/3Mn1/3]Ox were much larger than the precursor particles and those prepared from the LiNO3-[Ni1/3Co1/3Mn1/3]Ox may maintain the size of the precursor particles.

Axon Outgrowth: Motor Protein Moonlights in Microtubule Sliding

Neurons develop from small, spherical precursors into the largest, most asymmetric of all metazoan cells by extending thin axonal processes over enormous distances. Although the forces for this extension have been unclear, recent work shows that the initial axonal extension may involve an unexpected mechanism: sliding of microtubules, driven by a motor protein previously thought to be deployed only in organelle transport.

Tailored synthesis of Ni0.25Mn0.75CO3 spherical precursors for high capacity Li-rich cathode materials via a urea-based precipitation method

This study develops a urea-based homogeneous precipitation method to synthesize spherical carbonate precursors (Ni0.25Mn0.75CO3) for the Li-rich layered cathode material Li(Ni0.2Li0.2Mn0.6)O2. The structure and morphology of the precursor particles were tailored by controlling of urea concentration, reaction temperature and time. Combined with XRD, SEM, and particle size analysis, the optimized conditions for synthesizing desired stoichiometric Ni0.25Mn0.75CO3 were obtained. We also investigated the processes of nucleation and growth of precursors. The obtained spherical Li(Ni0.2Li0.2Mn0.6)O2 delivers discharge capacity of 237 mAh g−1 at the initial cycle and 253 mAh g−1 after 50 cycles.

Orbit/CLASP Is Required for Germline Cyst Formation through Its Developmental Control of Fusomes and Ring Canals in Drosophila Males

Orbit, a Drosophila ortholog of microtubule plus-end enriched protein CLASP, plays an important role in many developmental processes involved in microtubule dynamics. Previous studies have shown that Orbit is required for asymmetric stem cell division and cystocyte divisions in germline cysts and for the development of microtubule networks that interconnect oocyte and nurse cells during oogenesis. Here, we examined the cellular localization of Orbit and its role in cyst formation during spermatogenesis. In male germline stem cells, distinct localization of Orbit was first observed on the spectrosome, which is a spherical precursor of the germline-specific cytoskeleton known as the fusome. In dividing stem cells and spermatogonia, Orbit was localized around centrosomes and on kinetochores and spindle microtubules. After cytokinesis, Orbit remained localized on ring canals, which are cytoplasmic bridges between the cells. Thereafter, it was found along fusomes, extending through the ring canal toward all spermatogonia in a cyst. Fusome localization of Orbit was not affected by microtubule depolymerization. Instead, our fluorescence resonance energy transfer experiments suggested that Orbit is closely associated with F-actin, which is abundantly found in fusomes. Surprisingly, F-actin depolymerization influenced neither fusome organization nor Orbit localization on the germline-specific cytoskeleton. We revealed that two conserved regions of Orbit are required for fusome localization. Using orbit hypomorphic mutants, we showed that the protein is required for ring canal formation and for fusome elongation mediated by the interaction of newly generated fusome plugs with the pre-existing fusome. The orbit mutation also disrupted ring canal clustering, which is essential for folding of the spermatogonia after cytokinesis. Orbit accumulates around centrosomes at the onset of spermatogonial mitosis and is required for the capture of one of the duplicated centrosomes onto the fusome. Moreover, Orbit is involved in the proper orientation of spindles towards fusomes during synchronous mitosis of spermatogonial cysts.

The Growth of Bismuth Sulfide Nanorods from Spherical-Shaped Amorphous Precursor Particles under Hydrothermal Condition

A surfactant/solid-template-free hydrothermal process has been developed for the synthesis of single-crystalline nanorods of bismuth sulfide (Bi2S3) using triethanolamine as a complexing agent for the Bi3+ ions and elemental sulfur, solubilized in monoethanolamine, as the sulfur source. X-ray diffraction and morphological studies of a series of samples synthesized at different reaction conditions suggest that the growth of nanorods occurred at the expense of the low-crystalline spherical precursor particles of aminium compounds of bismuth sulfide or bismuth sulfate formed at room temperature. In the process, the reaction condition is optimized for obtaining crystalline nanorods of pure Bi2S3 with high aspect ratio. From the XRD, XPS, and HRTEM analysis of the samples, the growth of nanorods was assessed to be due to the cooperative effects of solid-solution-solid transformation and controlled oriented attachment. The hydrothermal process parameters and the presence of water in the reaction system have been found to play a crucial role in the formation of high aspect ratio nanorods. The optical band gap of the synthesized sample at optimized conditions is found to be 1.46 eV as calculated from its diffused reflectance spectrum at room temperature.

Fabrication of high tap density LiFe0.6Mn0.4PO4/C microspheres by a double carbon coating–spray drying method for high rate lithium ion batteries

Spherical LiFe0.6Mn0.4PO4/C particles with high tap density were successfully synthesized by sintering spherical precursor powders prepared by a modified spray drying method with a double carbon coating process. The obtained secondary spheres were made of carbon-coated nanocrystallines (∼100 nm), exhibiting a high tap density of 1.4 g cm−3. The LiFe0.6Mn0.4PO4/C microspheres had a reversible capacity of 160.2 mAh g−1 at 0.1C, and a volume energy density of 801.5 Wh L−1 which is nearly 1.4 times that of their nano-sized counterparts. This spherical material showed remarkable rate capability by maintaining 106.3 mAh g−1 at 20C, as well as excellent cycleablity with 98.9% capacity retention after 100 cycles at 2C and 200 cycles at 5C. The excellent electrochemical performance and processability of the LiFe0.6Mn0.4PO4/C microspheres make them very attractive as cathode materials for use in high rate battery application.

Synthesis of beta-SiC powder from alkoxide precursor and study of its sintering behaviour

In this study, β-SiC powder was prepared using a pyrolysed spherical precursor derived from the hydrolysis mixture of phenyltrimethoxysilane and tetraethyl orthosilicate. Before the pyrolysed experiment, an alkoxide precursor was characterised using 29Si solid nuclear magnetic resonance, Fourier transform infrared spectroscopy and thermogravimetric analysis. The alkoxide precursor was heated at 1800°C for 4 h under an Ar atmosphere. To examine the pyrolysed residue after heat treatment, the sample was collected and analysed with X-ray diffraction. The X-ray diffraction results for the sample show diffraction peaks at ∼35, 60 and 73°, which correspond to the β-SiC phase. According to the results of chemical analysis, the SiC content of the powder that was prepared at 1800°C was determined to be 99·4%. The sintering behaviour of the prepared β-SiC powder was examined using B4C and C as sintering additives in the temperature range of 1900–2200°C.

Synthesis of Monodispersed Spherical Yttrium Aluminum Garnet (YAG) Powders by a Homogeneous Precipitation Method

Monodispersed yttrium aluminum garnet (YAG) powders have been synthesized via homogeneous precipitation method from the mixed solutions of yttrium nitrate, aluminum nitrate, and ammonium aluminum sulfate using urea as the precipitant. The molar ratio of aluminum nitrate to ammonium aluminum sulfate has a significant effect on morphology and particle size of the precursor powders. It was found that spherical precursor particles can be obtained when the ratio is 1:1. During the homogeneous precipitation process, aluminum ions precipitate first and form monodispered spherical powders, and then yttrium ions precipitate onto the surface of the existing spheres. Monodispersed spherical YAG particles with 500 nm in diameter were obtained by calcining the precursor powder at 1100°C for 5 h. The so‐prepared monodispersed spherical Nd:YAG powders have good sinterability, and can be sintered into transparent ceramics by vacuum sintering at 1650°C for 3.5 h.

Synthesis of spinel LiMn2O4 microspheres with durable high rate capability

Spinel LiMn2O4 microspheres with durable high rate capability were synthesized by a facile route using spherical MnCO3 precursors as the self-supported templates, combined with the calcinations of LiNO3 at 700 °C for 8 h. The spherical MnCO3 precursors were obtained from the control of the crystallizing process of Mn2+ ions and NH4HCO3 in aqueous solution. The effects of the mole ratio of the raw materials, reaction time, and reaction temperature on the morphology and yield of the MnCO3 were investigated. The as-synthesized MnCO3 and LiMn2O4 microspheres were characterized by powder X-ray diffractometry (XRD) and scanning electron microscopy (SEM). Galvanostatic charge/discharge tests indicate that the spinel LiMn2O4 microspheres deliver a discharge capacity of 90 mA·h/g at 10C rate show good capacity retention capability (75% of their initial capacity after 800 cycles at 10C rate). The durable high rate capability suggests that the as-synthesized LiMn2O4 microspheres are promising cathode materials for high power lithium ion batteries.

Precipitation of barite by marine bacteria: A possible mechanism for marine barite formation

Barite (BaSO 4 ) is found throughout the ocean, yet seawater is undersaturated with respect to barite, and organisms that could account for the abundance of barite have not yet been identifi ed. The mechanism for barite formation in seawater is not fully understood. Here we show that marine bacteria have the ability to precipitate barite through a metabolically mediated biomineralization process. We precipitated barite in laboratory experiments in the presence of several strains of marine bacteria grown on yeast media enriched with barium (Ba); barite did not precipitate under identical conditions in killed-bacteria controls. The crystals develop from amorphous, phosphorous-rich spherical precursors with fi brous internal textures, common in bacterial mineral precipitation. Bacterial mediation of barite precipitation can explain the distribution of barite in the water column and the occurrence of barite crystals in organic-rich sinking aggregates where bacteria are concentrated. This fi nding has implications for the use of barite and Ba proxies in paleoceanographic research.

Porous Mn2O3 microsphere as a superior anode material for lithium ion batteries

Porous Mn2O3 microspheres have been synthesized by morphology-controlled decomposition of spherical MnCO3 precursors at 600 °C. The porous Mn2O3 microspheres show a good rate capability and a high specific capacity of 796 mA h g−1 after 50 cycles.

Microwave synthesis of spherical spinel LiNi0.5Mn1.5O4 as cathode material for lithium-ion batteries

Spinel LiNi0.5Mn1.5O4 cathode material with excellent electrochemical performance was synthesized through microwave heat treatment using spherical (Ni0.25Mn0.75)3O4 precursor which was prepared by a co-precipitation method. Compared with the conventional heat treatment in a muffle furnace, the microwave approach not only diminished the impurity level but also reduced the sizes of primary particles. These characters led to increase in discharge capacity and rate capability of LiNi0.5Mn1.5O4. In this study, it was found that the microwave co-precipitation method was fairly effective for further solving the problem of cycling performance, when the microwave irradiation was introduced in. The LiNi0.5Mn1.5O4 cathode material synthesized by this method delivered a discharge capacity of 142mAhg−1 at 0.1C rate (corresponding to 97% of the theoretical capacity), and had a capacity retention of 97% after the 50th cycle at room temperature, showing an improved electrochemical performance.

Synthesis and electrochemical properties of LiMn2O4 and LiCoO2-coated LiMn2O4 cathode materials

The synthesis of spinel LiMn2O4 material by a spherical MnO2 precursor route is reported in this paper. Hydrothermal and solid-state reactions were adopted to investigate the effects of synthetic methods on the morphologies and electrochemical characteristics of the LiMn2O4 products, respectively. LiCoO2-coated LiMn2O4 microspheres were also prepared by a sol–gel route based on the as-prepared LiMn2O4 microspheres. The products were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectrum (EDX), and inductively-coupled plasma emission spectrograph (ICP-ES). The results show that LiMn2O4 octahedrons can be obtained under hydrothermal conditions while LiMn2O4 microspheres can be prepared by the solid-state reaction. Electrochemical characterization reveals that the resulting LiMn2O4 microspheres and LiCoO2-coated LiMn2O4 microspheres display much better cycling properties than those of LiMn2O4 octahedrons.

Well-ordered spherical LiNi xCo (1−2 x) Mn xO 2 cathode materials synthesized from cobolt concentration-gradient precursors

Spherical Ni x Co (1−2 x) Mn x (OH) 2 ( x = 0.333, 0.4, 0.416, 0.45) precursors with Co concentration-gradient were prepared by co-precipitation from sulfate solutions using NaOH and NH 4OH as precipitation and complexing agents. Then, well-ordered spherical LiNi x Co (1−2 x) Mn x O 2 was synthesized by sintering the mixture of as-prepared precursor and Li 2CO 3 at 950 °C for 16 h in air. EDXS results indicated that the concentration of cobalt decreased gradually inside out of the spherical precursor particle, and it was uniform in spherical LiNi x Co (1−2 x) Mn x O 2 particle obtained by sintering with Li 2CO 3. According to Rietveld refinement of XRD patterns, the LiNi x Co (1−2 x) Mn x O 2 synthesized from Co gradient precursor showed lower degree of cation disorder than that prepared from conventional precursor. The well-ordered LiNi x Co (1−2 x) Mn x O 2 from Co gradient precursor delivered much better high-rate capability than conventional one. The decrease of cation disorder of LiNi x Co (1−2 x) Mn x O 2 is attributed to the cobalt-rich in core of the precursor particles. Both abundant Co 3+ and Li + can restrain cation mixing effectively. Since Li + needs long time to reach core during calcining, cobalt-rich in core of the precursor particle is very important for restraining cation mixing. Concentration-gradient precursor is helpful to prepare well-ordered LiNi x Co (1−2 x) Mn x O 2 with good high-rate capability, and the total content of expensive and toxic cobalt does not need to be increased.

Rapid Microwave Synthesis of Porous TiO2 Spheres and Their Applications in Dye-Sensitized Solar Cells

Porous anatase TiO2 spheres with sizes ranging from 150 to 250 nm were synthesized by a rapid microwave treatment of spherical titanium glycolate precursors preformed via an ethylene glycol-mediated sol–gel process. The effects of various experimental conditions on the formation of titanium glycolate precursors and final TiO2 spheres were investigated. A dye-sensitized solar cell (DSSC) assembled with the as-synthesized porous TiO2 spheres as photoanodes exhibits a 5% energy conversion efficiency, which is almost 40% higher than that made of the standard commercial Degussa P25 TiO2 nanopowders.

Microemulsion synthesis and photocatalytic activity of visible light-active BiVO4 nanoparticles

A water-in-oil microemulsion made up of a cyclohexane/n-hexyl alcohol/Polyethylene glycol tertoctylphenyl/aqueous solution including Bi3+ and VO3+ ions yields the spherical BiVO4 precursors with the size from 5 to 300 nm. Well-crystallized monoclinic scheelite BiVO4 particles with nanometer or micrometer size are fabricated in control by heating microemulsion precursors under various temperatures. The corresponding nucleation and growth process of as-prepared samples has also been investigated via TEM, which demonstrates the detailed morphological evolution of nuclei inside the precursors. As-prepared BiVO4 photocatalysts exhibit enhanced photocatalytic activity under visible-light irradiation in comparison with the bulk BiVO4 prepared by solid-state reaction. The highest RB degrading efficiency of 98% in 180 min under visible-light irradiation is observed for the sample calcined at 600 °C.

Evolution of Local Structure in Geopolymer Gels: An In Situ Neutron Pair Distribution Function Analysis

Geopolymer cement is fast becoming a technologically important alternative to ceramics and traditional cement. However, the amorphous nature of the phases which participate in the molecular processes occurring during evolution of geopolymer gel has made nanoscale research challenging. Here, for the first time, the local structural correlations of metakaolin‐based geopolymer gel have been elucidated using in situ neutron pair distribution function analysis, following the structural changes occurring due to dissolution and repolymerization molecular processes. Over the initial 17 h of reaction, the subtle structural changes observed predominantly relate to dissolution of the initial metakaolin precursor before formation of the gel. After 90 days the gel has formed and has transitioned from the initially formed geopolymer structure (gel 1) to a more stable and more ordered state (gel 2), via an increase in cross‐linking within the geopolymer gel. Through analysis of precursor dissolution behavior in different activator solutions, the impact of morphology on the rate of dissolution has been postulated, with layered precursors (metakaolin) shown to behave differently than spherical precursors (fly ash) depending on the type of activator solution used. Hence, this investigation reveals the important structural changes occurring during synthesis of this new class of low‐temperature ceramics.

Studies on the Catalyzing Transesterification of Soybean Oil with Methanol for Biodiesel Using a Novel Porous CaO Microsphere Catalyst

A novel porous CaO microsphere catalyst was synthesized by calcining spherical CaCO3 precursor which was prepared easily by mixing CaCl2 with Na2CO3. After characterized by scanning electron microscope and X-ray diffraction analysis, the synthesized CaO was studied on Studies on the catalyzing transesterification of soybean oil with methanol for biodiesel. The effects of calcining temperature, reaction time and temperature, amounts of catalyst and methanol on the catalytic activity of CaO microsphere had been evaluated by catalyzing transesterification of soybean oil with methanol for biodiesel. It expressed excellent catalytic activity with a transesterification yield of more than 98% at 65 °C in one hour with 3 wt% of CaO microsphere calcined at 800 °C.

Size-controlled synthesis of monodispersed mesoporous α-Alumina spheres by a template-free forced hydrolysis method

We demonstrated the formation of monodispersed spherical aluminum hydrous oxide precursors with tunable sizes by controlling the variables of a forced hydrolysis method. The particle sizes of aluminum hydrous oxide precursors were strongly dependent on the molar ratio of the Al(3+) reactants (sulfates and nitrates). In addition, the systematic phase and morphological evolutions from aluminum hydrous oxide to γ-alumina (Al(2)O(3)) and finally to α-Al(2)O(3) through thermal dehydrogenation were characterized by X-ray powder diffraction (XRD), field-emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM). After annealing the amorphous aluminum hydrous oxide in air at 900 °C and 1100 °C for 1 h, we observed complete conversion to phase-pure γ- and α-Al(2)O(3), respectively, while maintaining monodispersity (125 nm, 195 nm, 320 nm, and 430 nm diameters were observed). Furthermore, both γ- and α-Al(2)O(3) were found to be mesoporous in structure, providing enhanced specific surface areas of 102 and 76 m(2) g(-1), respectively, based on the Brunauer-Emmett-Teller (BET) measurement.