Enhanced proton conductivity of polymer electrolyte membrane doped with titanate nanotubes

Nafion-titanate nanotubes composite membranes were prepared through a casting process. With the addition of 5 wt.%, the nanotubes were homogenously distributed in Nafion solution. The formed composite membrane showed a comparable mechanical strength to Nafion membrane. The proton conductivity of the composite membrane without external humidification is higher than that of the Nafion membrane, reaching 0.034 Scm^?1 and 0.01 Scm^?1 at 100 °C and 120 °C, respectively. The improved proton conductivity was attributed to the great water retention ability of the doped nanotubes.     

Hydrothermal synthesis of perovskite nanotubes

A low-temperature hydrothermal reaction has been utilized to generate crystalline barium titanate and strontium titanate nanotubes, which have been characterized by means of X-ray diffraction and transmission electron microscopy, coupled with energy dispersive X-ray analysis.     

Large-scale synthesis of sodium and potassium titanate nanobelts

A low-temperature solution-based synthetic method was developed for the large-scale synthesis of one-dimensional nanostructures of alkali titanates. Two kinds of highly pure ribbonlike titanates were synthesized successfully in gram quantities without introducing any templates or catalysts. The structure and composition of the titanates were characterized by XRD, HRTEM, and EDX. The chemical and physical properties were preliminarily characterized, and some distinctive properties were observed.     

Co掺杂的OMS-2纳米纤维的合成研究

以KMnO4、MnSO4、Co (NO3)2?6H2O和HNO3为反应原料,采用水热法合成了一系列掺杂过渡金属Co的氧化锰八面体分子筛(OMS-2),采用X-射线衍射(XRD),扫描电镜(SEM),傅里叶红外光谱(FT-IR),低温氮气物理吸脱附和H2程序升温还原(H2-TPR)对样品进行了表征,研究了Co的掺杂对OMS-2分子筛的结构、形貌和氧化还原性质等的影响,并对该系列催化剂进行了CO氧化性能评价。结果表明,掺杂的Co并未改变OMS-2的晶体结构,并高分散在OMS-2骨架结构中;掺杂Co的OMS-2分子筛的形貌发生了由纳米短棒向纳米纤维的转变。不仅如此,Co的掺杂增加了活性氧物种的移动性,改善了OMS-2分子筛的催化CO氧化性能。     

Bulk synthesis of single-crystalline magnesium oxide nanotubes

Crystalline tubular magnesium oxide nanostructures were obtained through carbon-thermal evaporation of a MgO powder. Gallium oxide was added into the mixture of MgO and carbon. The reduction of gallium oxide by carbon resulted in gallium vapor at high temperatures. Condensed gallium droplets catalyzed the anisotropic growth of tubular MgO nanostructures in situ. The products were characterized by X-ray powder diffraction technique, scanning electron microscopy, and high-resolution microscopy. All the analyses indicated that the prepared tubular MgO nanostructures are, in fact, single crystals.     

Toward a more environmentally benign synthesis of doped barium titanate

Abstract

Barium titanate is one of the most thoroughly studied members of the perovskite family due to its prominent place in the electroceramic industry. To be used as a capacitor at room temperature, a high-dielectric constant is needed which is achieved through doping. The focus of this research was to develop a more environmentally benign alternative to the doping of barium titanate. The barium source was barium titanyl catecholate, Ba[Ti(cat)₃] (aq) and the doping sources were strontium oxalate (SrC₂O₄) and strontium carbonate (SrCO₃). The doping strategies included a solid-state synthetic pathway as well as microwave- and centrifuge-assisted methods which both employed water as the only solvent. The last two benign by design methods were tested with respect to their thermodynamic control over barium-to-strontium stoichiometric ratios. These methods of doping proved to be more environmentally friendly and economical while combining green chemistry and materials science.     

水热法制备磷酸镍及其光催化性能评价

采用水热合成法以Ni(NO3)2·6H2O为镍源、KH2PO4为磷源合成了磷酸镍,并详细研究了用水热法合成磷酸镍过程中Ni/P摩尔比、晶化温度及溶液酸碱度对磷酸镍光催化降解染料亚甲基蓝的影响,优化了合成条件。通过X-射线粉末衍射(XRD)、扫描电子显微镜(SEM)、红外吸收光谱(FT-IR)、紫外-可见漫反射光谱(UV-Vis DRS)和热重-差热(TG-DTA)和N2吸附等技术对其晶相组成、表面形貌、官能团结构、光吸收特性、热稳定性和比表面积进行了表征。合成材料通过对亚甲基蓝的光催化降解性能进行评价,当制备条件Ni/P摩尔比为3:2、反应温度为110℃、p H为碱性时晶化36 h合成的材料其光催化性能最佳。     

Layer-by-layer assembled multilayer films of titanate nanotubes, Ag- or Au-loaded nanotubes, and nanotubes/nanosheets with polycations

Aqueous suspensions of hydrothermally synthesized titanate nanotubes and poly(diallyldimethylammonium chloride) (PDDA) have been employed to fabricate multilayer films on various substrates in a layer-by-layer fashion. Atomic force microscopy displays the dense coverage of the substrate surface by the nanotubes. UV-vis absorption spectroscopy confirms the consecutive growth of PDDA/nanotube layer pairs. Single crystalline Ag and Au nanoparticles with narrow size distribution spatially correlating with the nanotubes have been obtained by treating the nanotubes with AgNO(3) or HAuCl(4) aqueous solution followed by chemical reduction. The noble metal nanoparticles show a strong surface plasmon absorption band. A multilayer film construction of the noble-metal-loaded nanotubes has also been achieved. This process has been further extended to the heteroassembly of nanotubes/nanosheets in different layer sequences.     

Layered hydroxide nickel benzoates: Hydrothermal synthesis, structure characterization, and exfoliation reaction

Mussel adhesive proteins have received considerable attention due to their ability to bind strongly to many surfaces under water. Key structural features of these proteins include a large number of 3,4-dihydroxyphenyl-L-ALANIN (DOPA) and positively charged lysine residues. We elucidate the effects of solution pH, in the pH range 3-9, on adsorption kinetics, adsorbed amount, and layer structure on silicon oxynitride by employing Dual Polarization Interferometry. As a comparison, the cationic globular protein lysozyme was also investigated. The zeta-potential of the silicon oxynitride substrate was determined as a function of pH, and the isoelectric point was found to be below pH 3. Mefp-1 is positively charged at pH<10, and thus, the protein is expected to have an electrostatic attraction for the surface at all pH values investigated. The adsorbed amount and the initial adsorption rate were found to increase with solution pH, and no significant desorption occurred due to rinsing with pure water. The layer thickness after rinsing was 3-4 nm, except at pH 3, where the adsorption was limited to a small amount. Covalent cross-linking of the Mefp-1 layer with NaIO(4) resulted in a small but significant compaction and increase in refractive index of the layer. The results are discussed in terms of the role of DOPA and electrostatic interactions for the adsorption of Mefp-1 to silicon oxynitride.     

Hydrothermal synthesis of single-crystalline anatase TiO2 nanorods with nanotubes as the precursor

Preparation of anatase TiO2 nanorods from solutions in the absence of surfactants or templates has rarely been reported. The present work has found that hydrothermal treatment of titanate nanotube suspensions under an acidic environment resulted in the formation of single-crystalline anatase nanorods with a specific crystal-elongation direction. The nanotube suspensions were prepared by treatment of TiO2 in NaOH, followed by mixing with HNO3 to different pH values. The crystal size of the anatase nanoparticles obtained from the hydrothermal treatment increased with the pH of the suspensions, and nanorods with an aspect ratio up to 6 and a long axis along the anatase [001] were obtained at a pH slightly less than 7. A mechanism for the tube-to-rod transformation has been proposed on the basis of the crystalline structures of the tubes and rods. The local shrinkage of the tube walls to form anatase crystallites and the subsequent oriented attachment of the crystallites have been suggested to be the key steps involved in the nanorod formation.     

Hydrothermal synthesis,crystal structure,and properties of a novel magnesium phosphonate with a 1D chain structure

A novel 1D chain magnesium phosphonate with a 1D channel system along the c-axis, [Mg(H₄L)(H₂O)₃]_n (1) (H₄L^2-=HN(CH₂PO₃H)₃)^2-, has been synthesized under hydrothermal condition using triphosphonate ligand. The MgO₆ polyhedra and NC₃ planes are connected by phosphonate groups to form a 1D chain. The chains are interlinked by hydrogen bonds into 2D layers. Adjacent layers are further linked via hydrogen bonds to build a 3D network structure. The luminescent property of complex 1 has been also studied. For the complex 1, a blue fluorescent emission band with a maximum peak at 460 nm was observed.     

Electrochemical capacitance of nickel oxide nanotubes synthesized in anodic aluminum oxide templates

Nickel oxide (NiO) nanotubes for supercapacitors were synthesized by chemically depositing nickel hydroxide in anodic aluminum oxide templates and thermally annealing at 360 °C. The synthesized nanotubes have been characterized by scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. The capacitive behavior of the NiO nanotubes was investigated by cyclic voltammetry, galvanostatic charge–discharge experiment, and electrochemical impedance spectroscopy in 6 M KOH. The electrochemical data demonstrate that the NiO nanotubes display good capacitive behavior with a specific capacitance of 266 F g⁻¹ at a current density of 0.1 A g⁻¹ and excellent specific capacitance retention of ca. 93% after 1,000 continuous charge–discharge cycles, indicating that the NiO nanotubes can become promising electroactive materials for supercapacitor.     

Hydrothermal synthesis of simonkolleite microplatelets on nickel foam-graphene for electrochemical supercapacitors

Nickel foam-graphene (NF-G) was synthesized by chemical vapour deposition followed by facial in situ aqueous chemical growth of simonkolleite (Zn₅(OH)₈Cl₂·H₂O) under hydrothermal conditions to form NF-G/simonkolleite composite. X-ray diffraction and Raman spectroscopy show the presence of simonkolleite on the NF-G, while scanning and transmission electron microscopies show simonkolleite micro-plates like structure evenly distributed on the NF-G. Electrochemical measurements of the composite electrode give a specific capacitance of 350 Fg^?1 at current density of 0.7 Ag^?1 for our device measured in three-electrode configuration. The composite also shows a rate capability of ~87 % capacitance retention at a high current density of 5 Ag^?1, which makes it a promising candidate as an electrode material for supercapacitor applications.     

Preparation, characterization and thermal dehydration kinetics of titanate nanotubes

Titanate nanotubes were synthesized utilizing the hydrothermal method using titanium dioxide nanoparticles. The experiments were carried out considering the process as a function of reaction temperature, time, NaOH concentration and the acidity of the washing solution. The formation of titanate nanotubes was shown to be affected strongly by variations in any parameter. The optimum conditions for the synthesis of titanate nanotubes were determined to be a reaction temperature of 190 °C, and a reaction time of 12 h, using 10 M NaOH concentration and the washing solution to have a pH of 5.5. In addition, thermogravimetric analysis (TG/DTG) was used to investigate the thermal behaviour and dehydration kinetics of titanate nanotubes. In order to better understand their thermal behaviour, the thermal analysis of bulk hydrogen trititanate was performed. The values of the apparent activation energies of the first and second dehydration stages for titanate nanotubes were 81.44 ± 15.85 and 82.69 ± 7.46 kJ mol^?1, respectively. The values of the apparent activation energies of the first, second and third dehydration stages for bulk hydrogen trititanate were 115.93 ± 5.40, 137.58 ± 6.47 and 138.97 ± 8.47 kJ mol^?1, respectively.     

Green synthesis of hydrotalcite from untreated magnesium oxide and aluminum hydroxide

The influence of reaction temperature and time on the hydrothermal dissolution-precipitation synthesis of hydrotalcite was investigated. Untreated MgO, Al(OH)₃ and NaHCO₃ were used. An industrially beneficial, economically favourable, environmentally friendly, zero effluent synthesis procedure was devised based on green chemistry principles, in which the salt-rich effluent typically produced was eliminated by regenerating the sodium bicarbonate in a full recycle process. It was found that the formation of hydromagnesite dominates at low temperatures independent of reaction time. With an increase in reaction time and temperature, hydromagnesite decomposes to form magnesite. At low temperatures, the formation of hydrotalcite is limited by the solubility of the Al(OH)₃. To achieve a hydrotalcite yield of 96%, a reaction temperature of 160°C for 5?h is required. A yield higher than 99% was achieved at 180°C and 5?h reaction time, producing an layered double hydroxide with high crystallinity and homogeneity.     

Synthesis and characterization of ion-exchangeable titanate nanotubes

Titanate nanotubes were synthesized under hydrothermal conditions. The optimized synthesis (100-180 degrees C, longer than 48 h), thermal and hydrothermal stability, ion exchangeability and consequent magnetic and optical properties of the titanate nanotubes were systematically studied in this paper. First, nanotubes with monodisperse pore-size distribution were prepared. The formation mechanism of the titanate nanotubes was also studied. Second, the thermal and hydrothermal stability were characterized with X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), Fourier transform infrared (FTIR), and Raman spectroscopy. Results showed that sodium ions played a significant role in the stability of the frameworks. Third, the selective ion exchangeability was demonstrated with a series of ions. The ion substitution also enlarged the BET surface area of the titanate nanotubes to 240 m(2) x g(-1). Combination of these two features implied that these nanotubes might be functionalized by substitution of different transitional-metal ions and consequently used for selective catalysis. Magnetism, photoluminescence, and UV/Vis spectra of the substituted titanate nanotubes revealed that the magnetic and optical properties of the nanotubes were modifiable.     

Hydrothermal synthesis of nickel hydroxide nanostructures in mixed solvents of water and alcohol

Nickel hydroxide nanosheets and flowers have been hydrothermally synthesized using Ni(CH₃COO)₂·4H₂O in mixed solvents of ethylene glycol (EG) or ethanol and deionized water at 200 °C for different time. The phase and morphology of the obtained products can be controlled by adjusting the experimental parameters, including the hydrothermal time and the volume ratio of water to EG or ethanol. The possible reaction mechanism and growth of the nanosheets and nanoflowers are discussed based on the experimental results. Porous nickel oxide nanosheets are obtained by heating nickel hydroxide nanosheets in air at 400 °C. The products were characterized by using various methods including X-ray diffraction (XRD), fourier transform infrared (FTIR), transmission electron microscopy (TEM), selected-area electron diffraction (SAED), field emission scanning electron microscopy (FESEM). The electrochemical property of β-Ni(OH)₂ nanosheets was investigated through the cyclic voltammogram (CV) measurement.     

Synthesis of complex hydroxo salts of magnesium, nickel, cobalt, aluminum, and bismuth and oxide catalysts on their base

Synthesis methods have been developed for the precursors of oxide catalysts that include the combination of magnesium nickel cobalt aluminum hydroxocarbonate, with a layered hydrotalcite-type structure and decavanadate and paramolybdate ions in the anion layers, and bismuth hydroxocarbonate. On the base of these precursors, multicomponent oxide catalysts have been manufactured for the oxidative dehydrogenation (OD) of light alkanes. Some of these catalysts showed high selectivities and high product yields in the conversion of ethane to ethylene.     

Reaction of nickel,cobalt, and ferric acetylacetonates with aluminum hydroxide

Conclusions Fe, Co, and Ni acetylacetonates react with boehmite aluminum hydroxide upon its formation in a mother liquor containing aluminum alcoholate with separation of mixed metal-containing complexes from solution.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1898–1900, August, 1988.The authors express their gratitude to T. I. Khomenko for taking the diffuse reflection spectra and a discussion of the results.