Arresting butterfly-like intermediate nanocrystals of beta-Co(OH)2 via ethylenediamine-mediated synthesis

A synthesis of beta-Co(OH)2 nanocrystalline materials has been investigated with the assistance of chelating agent ethylenediamine. By controlling precipitation processes, various forms of beta-Co(OH)2 crystallites can be prepared at different stages. The crystallite morphologies include two-dimensional hexagonal sheet platelets, one-dimensional nanorods, and butterfly-like nanocrystallite intermediates. In particular, a triangular construction unit for beta-Co(OH)2 crystallites has been revealed with the ethylenediamine mediation in the synthesis. With the successful arrest of these butterfly-like intermediate crystallites, especially of linearly aligned "butterflies", the formation mechanism of one-dimensional nanorods or nanoribbons has been experimentally explained. The chemical composition of solution precursors and resultant beta-Co(OH)2 crystallites has been analyzed with UV-vis/FTIR/CHN /XRD/TGA/TEM/SAED methods. The relationships among various observed crystallite morphologies have also been discussed on the basis of the experimental findings.     

Cosynthesis, coexistence, and self-organization of alpha- and beta-cobalt hydroxide based on diffusion and reaction in organic gels

We report the cosynthesis of highly stable laminated single crystal alpha- and beta-Co(OH) 2 using the reaction and diffusion of a hydroxide solution into a gel containing Co(II). The obtained alpha-Co(OH) 2, which is known to be thermodynamically unstable and transforms in a short period of time to the beta form, has been stabilized in the gel medium for weeks. The system also exhibits Liesegang banding where complicated spatial dynamics during the formation of the two polymorphs are shown to take place.     

Synthesis and exfoliation of Co2+-Fe3+ layered double hydroxides: an innovative topochemical approach

This paper describes a topochemical synthetic approach to Co2+-Fe3+ layered double hydroxides (LDHs). Micrometer-sized hexagonal platelets of brucite-like Co2/3Fe1/3(OH)2 were first prepared by a homogeneous precipitation of an aqueous solution of divalent cobalt and ferrous ions through hexamethylenetetramine (HMT) hydrolysis under a nitrogen gas atmosphere. A subsequent oxidative intercalation process, by the action of iodine (I2) in chloroform (CHCl3), transformed the precursory brucite-like Co2+-Fe2+ hydroxides into hydrotalcite-like Co2+-Fe3+ LDHs, in which the oxidization of Fe2+ into Fe3+ induced positive charges to the octahedral hydroxyl layers while anions (I-) were intercalated into the interlayer space. Co2+-Fe3+ LDHs inherited the high crystallinity and hexagonal platelet morphology from their brucite-like precursor due to the topotactic nature of the transformation, which was verified by abundant microscopic and spectroscopic characterizations. After a normal ion-exchange process, Co2+-Fe3+ LDHs accommodating perchlorate anions were exfoliated into unilamellar nanosheets in formamide by an ultrasonic treatment.     

The formation mechanism of a textured ceramic of thermoelectric [Ca2CoO3](0.62)[CoO2] on beta-Co(OH)2 templates through in situ topotactic conversion

We investigated the formation mechanism of thermoelectric [Ca(2)CoO(3)](0.62)[CoO(2)] (CCO) on beta-Co(OH)(2) templates with maintained orientations by identifying the intermediate phases and specifying the relationship between their crystallographic orientations. We mixed beta-Co(OH)(2) templates with the complementary reactant CaCO(3) and prepared a compact by tape casting, with the developed (001) plane of the templates aligned along the casting plane. High-temperature XRD of the compact revealed that beta-Co(OH)(2) decomposed into Co(3)O(4) by 873 K, and Co(3)O(4) reacted with CaO to form CCO by 1193 K via the formation of the newly detected intermediate phase beta-Na(x)()CoO(2)-type Ca(x)()CoO(2) at 913-973 K. Pole figure measurements and SEM and TEM observations revealed that the relationship between the crystallographic planes was (001) beta-Co(OH)(2)//{111} Co(3)O(4)//(001) Ca(x)()CoO(2)//(001) CCO. The crystal structures of the four materials possess the common CoO(2) layer (or similar), which is composed of edge-sharing CoO(6) octahedra, parallel to the planes. The cross-sectional HRTEM analysis of an incompletely reacted specimen showed transient lattice images from Ca(x)()CoO(2) into CCO, in which every other CoO(2) layer of Ca(x)()CoO(2) was preserved. Thus, it was demonstrated that a textured CCO ceramic is produced through a series of in situ topotactic conversion reactions with a preserved CoO(2) layer of its template.     

双注-水热法制备高分散氢氧化镁纳米片

本工作以氯化镁、氢氧化钠为原料，氯化钠为衬底溶液，探讨了采用双注-水热法制备高分散氢氧化镁纳米片的可行性。结果表明：采用双注方式或提高衬底溶液氯化钠浓度均有利于降低反应体系过饱和度，改善常温产物的结晶性和分散性；对常温合成的氢氧化镁进行水热处理可进一步提高产物的结晶度，形成形貌规则、粒径分布窄、分散良好的氢氧化镁纳米片。     

Preparation and characterization of nanostructured Ni(OH)2 and NiO thin films by a simple solution growth process

Nanostructured Ni(OH)2 thin films were prepared by a simple solution growth process with F(-) and NH3 used as Ni2+ coordination agents, and ammonia hydroxide solution used as OH(-) supplier to accelerate the hydrolyzation of nickel complex species. The results showed Ni(OH)2 thin films were constructed mainly with hexagonal beta-Ni(OH)2 nanorods; the F(-) and NH3 in reactive solutions played important roles in the film growth process; and solution pH had great influence on the morphologies of thin films, which was explained by the competition of Ni(OH)2 nucleation and growth in solutions. NiO crystallinity thin films were obtained by annealing Ni(OH)2 thin films at 400 degrees C for 2 h and the morphologies of the Ni(OH)2 thin films were sustained well during the annealed process.     

新方法合成规则六角片状层状双金属氢氧化物

探索了一种合成规则的层状双金属氢氧化物(简称LDHs)六角纳米片的新方法,该方法基于传统的共沉淀法,并借鉴了尿素法的优点。 系统研究了沉淀剂、反应溶剂、反应时间和沉淀剂滴加速率对最终得到的粒子结晶度和形貌的影响。 研究结果表明,采用NH4OH为沉淀剂,以乙醇/水混合溶液为溶剂得到的LDHs纳米粒子结晶度高,晶型发育完美,呈现规则的六角片状,单分散性良好,粒径介于100~250 nm之间。 乙醇的加入一方面减慢了NH4OH电离出OH-的速率,降低了溶液过饱和度;另一方面,乙醇分子包裹在LDHs粒子周围,其表面的羟基起到了空间位阻作用,阻止粒子之间的团聚。 最佳反应时间既要保证LDHs晶粒的充分发育和成长,又要防止粒子之间的团聚。反应时间较短(1 h)时,晶粒发育不完全,粒子呈现不规则的六角片形;反应时间较长(4 h)时,LDHs粒子出现了六角片状重叠现象;只有当反应时间适中(3 h),LDHs粒子因晶胞生长充分而粒径分布均匀,并呈现规则六角片状。 沉淀剂滴加速率的不同会改变体系的过饱和度,从而影响LDHs粒子的形貌,滴加速率较低(0.025 mL/s)时,得到的粒子形貌规则、单分散性良好,且随着滴加速率的降低,粒子粒径逐渐增大。     

水热-固相热解法制备不同形貌的四氧化三钴纳米微粉

以氨水和氢氧化钾水溶液为沉淀剂,利用沉淀-固相热解法和中压水热-固相热解法,制备了不同形貌的Co₃O₄纳米微粉.在水热条件下,得到了立方和六角片状的Co₃O₄微粉,采用XRD和TEM等手段跟踪反应过程并表征产物,在此水热反应体系中影响产物Co₃O₄形貌的主要因素是pH值和NO₃^-.     

二甲基甲酰胺中电沉积制备钐钴合金

稀土;恒电位电沉积;柠檬酸;二甲基甲酰胺中电沉积制备钐钴合金     

微/纳米六方β-Co(OH)_2水热法制备及影响因素

在无模板和表面活性剂的水热条件下,调节反应参数,可以得到一致的片状六方相β-Co(OH)2和多层片状的β-Co(OH)2微/纳米材料.合适的反应条件下,可以制备一致的结晶性好的单片状六方相β-Co(OH)2.用X射线衍射(XRD)、场发射扫描电镜(FESEM)、透射电镜(TEM)、高分辨透射电镜(HRTEM)以及选区电子衍射(SAED)等对反应产物进行了结构和形貌的表征.结果显示,Co(NO3)2的起始浓度、反应温度及溶液成分(异丙醇的加入)对反应产物的形貌结构有着重要的影响.     

Preparation and formation process of Ni2+–Fe3+ CO32− LDHs materials with high crystallinity and well-defined hexagonal shapes

A new complexing agent assisted homogeneous precipitation technology was successfully developed to synthesize Ni²⁺–Fe³⁺ CO₃^2? LDHs materials with crystallinity and well-defined hexagonal shape [1]. By using urea as hydrolysis agent and trisodium citrate as complexing agent, Ni²⁺–Fe³⁺ CO₃^2? LDHs with different ratios of Ni²⁺/Fe³⁺ were prepared under optimized reaction conditions, and their formation process was discussed on the basis of the experimental results. Ni²⁺–Fe³⁺ CO₃^2? LDHs thin hexagonal nanoplates with high crystallinity were obtained for from the ratios of Ni²⁺/Fe³⁺ = 3 and 4, while Ni²⁺–Fe³⁺ CO₃^2? LDHs material from Ni²⁺/Fe³⁺ = 2 could not be obtained due to the formation of impurity β-Ni(OH)₂. The as-prepared Ni²⁺–Fe³⁺ CO₃^2? LDHs materials were completely converted to Cl^? LDHs materials by treating with a NaCl–HCl mixed solution, showing a good anion exchange property. Sodium fluoride, tartarate and trisodium citrate with different molecular structures were chosen as a complexing agent to investigate their effect on the crystalline and shape of the as-prepared materials. Not only had the molecular structure of the complexing agents but also the amount had an obvious effect in the formation of the as-prepared materials. Trisodium citrate played a key role for the formation of Ni²⁺–Fe³⁺ CO₃^2? LDHs materials with high crystalline and well-defined hexagonal shapes, which made the pH deposition range of Fe(OH)₃ increase due to the formation of metal ligand [Fe(C₆H₄O₇)₂]^5? when the pH of the reaction system was above 8. The formed metal ligand [Fe(C₆H₄O₇)₂]^5? changed the translation process of Fe(OH)₃ with Ni²⁺ ions, which reacted with free Ni²⁺ ions and formed Ni²⁺–Fe³⁺ CO₃^2? LDHs materials with high crystallinity and well-defined hexagonal shapes.     

Synthesis, morphology, structure, and magnetic characterization of layered cobalt hydroxyisocyanates

New layered pink cobalt hydroxyisocyanates have been prepared by controlled hydrolysis of aqueous solutions of CoCl2.6H2O. Co(OH)(1.4)(NCO) 0.6.0.6H 2O ( 1) is formed when urea is used as the hydrolysis agent and mannitol as the stabilizer, while Co(OH)(1.25)(NCO)(0.75).0.2H2O ( 2) is formed when the hydrolysis agent is changed to hexamethylenetetramine and NaOCN is added to the solution. IR spectroscopy of 1 and 2 indicates that the OCN (-) is N-bonded to Co (2+). The X-ray powder data for 1 could be indexed using an intergrowth model consisting of both rhombohedral ( R3 m (166); a = 3.2031(1) A, c = 23.6876(11) A, hydrotalcite-like, 3 R 1) and hexagonal ( P 63/ mmc (194); a = 3.2005(2) A, c = 15.8303(5) A, Manasseite-like, 2H1) polytypes. Rietveld refinement of the X-ray powder data was performed using a two polytype model and 30% random substitution of the OH (-) ions by OCN (-). Although it is less crystalline, the XRD data for 2 can be indexed using a rhombohedral-symmetry cell with unit cell parameters, a = 3.158 A and c = 21.57 A. Both 1 and 2 exhibit magnetically ordered ground states with a saturation magnetization of ca. 2.0 mu B. The magnetization data is consistent with 3D ferromagnetic ordering of edge-share octahedral-Co (2+) layers with effective spin S' = 1/2.     

Synthesis of High Dispersion and Uniform Nano-sized Flame Retardant-Used Hexagonal Mg(OH)<Subscript>2</Subscript>

Nanosized dispersive flake-like magnesium hydroxide (Mg(OH)₂) had been prepared by a hydrothermal method. In the process, when the surfactant polyvinyl pyrrolidone was added, high dispersion, small particle size and large specific surface area of hexagonal crystal magnesium hydroxide was obtained by ultrasonic dispersion and temperature program. The flame retardant of Mg(OH)₂ was systematically explored by scanning electron microscope (SEM), transmission electron microscopy, X-ray diffraction, BET analysis and thermo-gravimetric analysis tests. SEM showed the formation of uniform and small size magnesium hydroxide particle with hexagonal nanoscale. Under the optimized conditions, high nano-sized hexagonal Mg(OH)₂ was acquired with a mean particle size of 134 nm and a specific surface area of 26.66 m²/g. According to TGA results, the sample’s decomposition temperature was 626.9 K, which was consistent with the reported literature. It is vitally prospected that the prepared hexagonal Mg(OH)₂ is to be applied to the industry as a flame retardant.     

Synthesis and characterization of mesoporous silica from selectively acid-treated saponite as the precursors

Mesoporous silicas were synthesized by hydrothermal treatment of selectively acid-treated saponite (an ideal structural formula: Na(1/3)Mg(3)(Si(11/3)Al(1/3))O(10)(OH)(2)), having a 2:1 type layered structure as the silica source and its porous properties were examined and compared with that from kaolinite (an ideal structural formula: Al(2)Si(2)O(5)(OH)(4)), having a 1:1 type layered structure. Synthetic saponite was selectively leached in H(2)SO(4) solutions with various concentrations (0.05-1 M) at 70 degrees C for 0.5 h. The resulting products (precursors) were mixed with cetyltrimethylammonium bromide (CTABr), NaOH and H(2)O, hydrothermally treated at 110 degrees C and removed the CTABr by calcining at 560 degrees C. A hexagonal mesoporous phase was obtained with higher Si/(Al(+Mg)) ratios of the resulting precursors. The XRD patterns of these products show the peaks assigned by a hexagonal lattice with a(0)=4.0-4.6 nm and the crystallinity becomes higher with higher Si/(Al(+Mg)) ratios of the precursors. The specific surface area (S(BET)) values of the present mesoporous silicas range from 800 to 1100 m(2)/g at CTABr/precursor=0.1 and although they are not as high as those from precursors prepared from calcining and acid-treatment of kaolinite (1420 m(2)/g), they are increased to 1400-1500 m(2)/g by increasing the ratio CTABr/precursor 0.2. The reason for the difference in the optimum preparation conditions between saponite and kaolinite may be attributed to the difference in the linkage of the SiO(4) tetrahedra in these precursors (i.e. layered or framework structures), which result in great differences in the selective leaching rates and structures of the resulting silica-rich products.     

Cobalt-catalyzed hydrogen desorption from the LiNH2-LiBH4 system

A doping of 5 wt% CoCl2 considerably decreases the dehydrogenation temperature of a mixture of LiNH2 and LiBH4. More that 8 wt% of hydrogen can be released at ca. 155 degrees C. X-Ray absorption near edge structure (XANES) spectroscopy indicated the formation of metallic Co after ball milling CoCl2 with LiNH2 and LiBH4. Extended X-ray absorption fine structure (EXAFS) spectroscopy measurements revealed that Co particles have poor crystallinity and are finely dispersed in the sample, which could lead to a high catalytic efficiency.     

Reactions of trivacant Wells-Dawson heteropolytungstates. Ionic strength and Jahn-Teller effects on formation in multi-iron complexes

Reaction of alpha-P(2)W(15)O(56)(12-) and Fe(III) in a saturated NaCl solution produces a trisubstituted Wells-Dawson structure with three low-valent metals, alpha-(Fe(III)Cl)(2)(Fe(III)OH(2))P(2)W(15)O(59)(11-) (1). Dissolution of this species into 1 M NaBr (Br(-) is non-coordinating) gives the triaquated species alpha-(Fe(III)OH(2))(3)P(2)W(15)O(59)(9-) (2). Ionic strength values of 1 M or greater are necessary to avoid decomposition of 1 or 2 to the conventional sandwich-type complex, alpha beta beta alpha-(Fe(III)OH(2))(2)Fe(III)(2)(P(2)W(15)O(56))(2)(12-) (3). If the pH is greater than 5, a new triferric sandwich, alpha alpha beta alpha-(NaOH(2))(Fe(III)OH(2))Fe(III)(2)(P(2)W(15)O(56))(2)(14-) (4), forms rather than 3. Like the previously reported Wells-Dawson-derived sandwich-type structures with three metals in the central unit ([TM(II)Fe(III)(2)(P(2)W(15)O(56))(P(2)TM(II)(2)W(13)O(52))],(16-) TM = Cu, Co), this complex has a central alpha-junction and a central beta-junction. Thermal studies suggest that 4 is more stable than 3 over a wide range of temperatures and pH values. The intrinsic Jahn-Teller distortion of d-electron-containing metal ions incorporated into the external sites of the central multi-metal unit impacts the stoichiometry of their incorporation (with a consequent change in the inter-POM-unit connectivity, where POM = polyoxometalate). Reaction of non-distorting Ni(II) with the diferric lacunary sandwich-type POM alpha alpha alpha alpha-(NaOH(2))(2)Fe(III)(2)(P(2)W(15)O(56))(2)(16-) (5) produces alpha beta beta alpha-(Ni(II)OH(2))(2)Fe(III)(2)(P(2)W(15)O(56))(2)(14-) (6), a Wells-Dawson sandwich-type structure with two Ni(II) and two Fe(III) in the central unit. All structures are characterized by (31)P NMR, IR, UV-vis, magnetic susceptibility, and X-ray crystallography. Complexes 4 and 6 are highly selective and effective catalysts for the H(2)O(2)-based epoxidation of alkenes.     

A facile and green synthesis route to C@LaCO3OH core-shell microspheres using colloidal carbonaceous spheres as template and its by-products as carbon source

C@LaCO₃OH core-shell microspheres have been synthesized by a hydrothermal method using colloidal carbonaceous spheres (CCSs) as template and its by-products as reactant without any other precipitating agent added in the reaction system. The FT-IR and XRD results indicated the successful formation of the well-crystallized LaCO₃OH shell with hexagonal crystal structure on the CCSs’ surface. The morphology and qualitative elemental chemical analysis were characterized by SEM, TEM, and EDS. The effects of co-solvent on the crystallinity of the LaCO₃OH shell were also studied. In addition, PL result showed one emission band centered at 421 nm (λ_ex = 365 nm) of the C@LaCO₃OH microspheres. The UV–visible spectrum was also employed to investigate the optical property of the products. Further, a possible formation mechanism of the core-shell structure was proposed.     

Surfactant-assisted alignment of ZnO nanocrystals to superstructures

Self-organization of ZnO nanoparticles into various superstructures (sheet, platelet, ring) has been achieved with the assistance of micelles formed by surfactant cetyltrimethylammonium bromide (CTAB) under one-pot condition. The CTAB-modified zinc hydroxy double salt (Zn-HDS) mesocrystals act as intermediates to form ZnO hexagonal superstructures at temperatures as low as 50 degrees C. The decomposition temperature of Zn-HDS mesocrystals is much lower than that of the corresponding bulk crystals because the organic additive CTAB effectively decreases the degree of crystallinity. Taking advantage of temperature-induced phase transformation of micelles, two-stage self-organization can form ZnO platelets and ring mesocrystals, that is, ZnO ellipsoidal superstructures formed through vertical attachment on (0001) facets of basic units can further assemble to form ZnO platelets and rings through vertical attachment on (0001) facets of ZnO ellipsoidal superstructures. The structural transformation of micelles as shape templates can offer a new route for self-assembly of nonspherical colloids into three-dimensional photonic crystals. ZnO sheet, ring, and platelet mesocrystals with a high population of polar Zn-(0001) plane are expected to have high photocatalytic activity.     

PREPARATION AND STRUCTURE OF Na[Et_4N][Co_4 (SC_2H_4OH)_10]

<正> Anaerobic reaction of CoCl2.6H2O with NaSCH2CH2OH and Et4NBr gave compound Na(EtaN)[Co4 (SC2H4OH)10] which crystallized in monoclinic space group P21/c with an adamantane-like core structure for Co4(u-S)6.The anion contains a tetrahedron of four Co(Ⅱ) atoms intercalating with an octahedron of the S atoms from six 2-hydroxyethanethiolato bridging ligands.     

Adding water to sugar: a spectroscopic and computational study of alpha- and beta-phenylxyloside in the gas phase

The gas phase structures of phenyl alpha- and beta-d-xylopyranoside (alpha- and beta-pXyl) and their mono-hydrates have been investigated using a combination of resonant two-photon ionization (R2PI), ultra-violet hole-burning and resonant infrared ion dip spectroscopy, coupled with density functional theory (DFT) and ab initio computation. The hole-burning experiments indicate the population of a single conformer only, in each of the two anomers. Their experimental and calculated infrared spectra are both consistent with a conformational assignment corresponding to the computed global minimum configuration. All three OH groups are oriented towards the oxygen atom (O1) on the anomeric carbon atom to form an all trans(ttt) counter-clockwise chain of hydrogen bonds. The mono-hydrates, alpha- and beta-pXyl(H(2)O) each populate two distinct structures in the molecular beam environment, with the water molecule inserted between OH4 and OH3 or between OH3 and OH2 in alpha-pXyl(H2O), and between OH2 and O1 in either of two alternative orientations, in beta-pXyl(H2O). In all of the mono-hydrated xyloside complexes, the water molecule inserts into the weakest link of the sugar molecules' hydrogen-bonded chain of hydroxy groups, creating a single extended chain, strengthened by co-operativity. The all-trans configuration of the xylose moiety is retained and the mono-hydrate structures correspond to those calculated to lie at the lowest relative energies.