Simultaneous phase- and size-controlled synthesis of TiO(2) nanorods via non-hydrolytic sol-gel reaction of syringe pump delivered precursors

The simultaneous phase- and size-controlled synthesis of TiO(2) nanorods was achieved via the non-hydrolytic sol-gel reaction of continuously delivered two titanium precursors using two separate syringe pumps. As the injection rate was decreased, the length of the TiO(2) nanorods was increased and their crystalline phase was simultaneously transformed from anatase to rutile. When the reaction was performed by injecting titanium precursors contained in two separate syringes into a hot oleylamine surfactant solution with an injection rate of 30 mL/h, anatase TiO(2) nanorods with dimensions of 6 nm (thickness) x 50 nm (length) were produced. When the injection rate was decreased to 2.5 mL/h, star-shaped rutile TiO(2) nanorods with dimensions of 25 nm x 200 nm and a small fraction of rod-shaped anatase TiO(2) nanorods with dimensions of 9 nm x 100 nm were synthesized. Pure star-shaped rutile TiO(2) nanorods with dimensions of 25 nm x 450 nm were synthesized when the injection rate was further decreased to 1.25 mL/h. The simultaneous phase transformation and length elongation of the TiO(2) nanorods were achieved. Under optimized reaction conditions, as much as 3.5 g of TiO(2) nanorods were produced. The TiO(2) nanorods were used to produce dye-sensitized solar cells, and the photoconversion efficiency of the mixture composed of star-shaped rutile TiO(2) nanorods and a small fraction of anatase nanorods were comparable to that of Degussa P-25.     

The thermal decomposition of metal ethylenediamine oxalate complexes

The thermal dehydration and deamination of some ethylenediamine complexes of Zn, Cd, Cu, Ni and Co oxalate were studied by TGA, DTA, DSC, reflectance spectroscopy, and by GE. The tris(amine) complexes deaminated to mono(amine) compounds which then decomposed directly to the metal oxide. The kinetics and heats of dehydration and deamination of several of the complexes were determined.     

Preparation of mixed-ligand complexes of nickel via thermal decomposition

If heated to around 270° in argon, [Ni(HSal)₂] (H₂Sal=salicylic acid) gives off gaseous H₂Sal and forms [NiSal], which reacts with monoprotic ligands HL (e.g. 8-hydroxyquinoline) to form mixed-ligand complexes [NiHSalL], or with diprotic ligands H₂L' (e.g. quadratic acid) to form dinuclear complexes [HSalNiL'NiHSal].

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Zusammenfassung Die Komplexverbindung [Ni(HSal)₂] spaltet beim Erhitzen auf 270 °C in Argon Salicylsäure ab und liefert [NiSal], das mit Monoproton-Liganden HL (z. B. 8-Hydroxychinolin) zu Gemischtliganden-Komplexen [NiHSalL], mit Zweiprotonen-Liganden H₂L' (z. B. Quadratsäure) dagegen Zweikernkomplexe [HSalNiL'NiHSal] bildet.

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[Ni(HSal)₂] 270°, [NiSal], HL (., 8-) [NiHSalL] H₂L [HSalNiLNiHSal].

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The preparative and thermoanalytical part of this work was performed by C. Gribi, D. Noukakis and M. Piccand, who also drew the Figures.

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This research was supported by the Swiss National Science Fundation, grant No. 2.053-0.99.     

Solution-phase synthesis of single-crystalline iron phosphide nanorods/nanowires

A solution-phase route for the preparation of single-crystalline iron phosphide nanorods and nanowires is reported. We have shown that the mixture of trioctylphosphine oxide (TOPO) and trioctylphosphine (TOP), which are commonly used as the solvents for semiconductor nanocrystal synthesis, is not entirely inert. In the current process, TOP, serving as phosphor source, reacts with Fe precursors to form FeP nanostructures with large aspect ratios. In addition, the experimental results show that both TOP and TOPO are necessary for the formation of FeP nanowires and their ratio appears to control the morphology of the produced FeP structures. A possible growth mechanism is discussed.     

Formation of perovskite phase mixed metal oxides via thermal decomposition of metal-organic complexes with bifunctional ligands

Single-source metal precursors designed to form crystalline perovskite phase mixed metal oxides at low temperatures have been synthesized using -hydroxycarboxylates and alkoxides as ligands. Divalent salts of Ba, Sr, Ca and Pb, [A(O₂CCR₂OH)₂], R = H, Me, were formed from the reaction between ACO₃ and HO₂CCR₂OH in which the hydroxyl group is free to react with metal alkoxide compounds B(OR)₄ where B=Ti, Zr, Sn. These compounds react to eliminate two equivalents of alcohol producing precursors with fixed stoichiometry as shown by the equation: A(O₂CCR₂OH)₂+B(OR)₄ A(O₂CCR₂O)₂B(OR)₂+2HOR. The reaction product is only slightly soluble in pyridine, however upon hydrolysis these compounds form clear solutions from which yellow powders can be isolated by removal of the solvent. Thermolysis of these powders in the temperature range 300–350°C yields perovskite ABO₃. Aqueous solutions of these powders can also be used to form sub-micron sized particles of ABO₃ materials via aerosol processing techniques. In control experiments it was shown that Pb(O₂CCH₂OPh)₂ does not react with metal alkoxide compounds. As a result perovskite PbTiO₃ is not formed below 550°C. Solutions for spin coating thin films can be formed by dissolution of the powder in ethanol, but the crystallization behavior is quite different compared to the bulk powders.     

Fabrication of CoO nanorods via thermal decomposition of CoC2O4 precursor

Cobalt oxide (CoO) nanorods were synthesized by annealing CoC₂O₄ precursor. The nanorods were identified by Transmission electron microscopy (TEM), X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and other methods. The results showed that the nanorods are composed of cubic CoO with diameter of 10–80 nm, and lengths ranging from 1 to 3 μm. The mechanism of formation of CoO nanorods was also discussed.     

Preparation of transition metal complexes of strongly basic ligands by thermal decomposition

The usual stoichiometry of metal salicylates, 2-oxy-3-naphtholates, anthranilates and salicylaldoximates is M²⁺(HL⁻)₂.xH₂O. Heating such a solid in an inert atmosphere causes proton transfer between the two HL⁻-ligands and the following reaction takes place: M(HL)₂(s) → ML(s) + H₂L(g). The new complex ML(s) (e.g. zincsalicylate) reacts with solid or dissolved monoprotic ligands HL' (e.g. 8-hydroxyquinoline) to form the mixed complex (e.g. zinc-salicylate-oxyquinolate) in excellent yield.     

Influence of encapsulation on the mechanism of thermal decomposition of hexacyanotransition metal complexes

It has been established that, in contrast to the pure substances, the thermal decomposition of hexacyanotransition metal complexes, encapsulated in the large cavities of faujasite, occurs by a hydrolytic mechanism. The composition of the gaseous products of the thermal decomposition depend on the characteristics of the localization of the cations in the inclusion compounds. L. V. Pisarzhevskii Institute of Physical Chemistry, National Academy of Sciences of Ukraine, 31 Prospekt Nauki, Kiev 252039, Ukraine. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 35, No. 2, pp. 107–112, March–April, 1999.     

热解单源前驱体方法可控制备纳米金属硫化物

本文简要综述了本研究组近年来在利用热解单源前驱体合成方法制备纳米金属硫化物方面的相关工作．通过采用不同的反应前驱体,改变反应时间、反应温度,选择不同的表面配体分子及反应溶剂等手段实现了对纳米金属硫化物形貌、尺寸、组成和晶相的精确调控．除了对合成方法和过程进行介绍外,本文还简要讨论了具有特定形貌的金属硫化物的形成机理,并对几类典型硫化物的应用研究进行了总结．     

Kinetics of thermal decomposition of trivalent metal complexes with all-cis-1,2,3,4-cyclopentane tetracarboxylic acid

All-cis-1, 2, 3, 4-cyclopentane tetracarboxylic acid forms 11 complexes with metals like Al(III), Y(III) and Ga(III), and have been isolated in solid state from the aqueous solutions. Thermogravimetry of these complexes supports the probable formulae assigned on the basis of elemental analysis. Kinetics of some of the thermal decompositions have been studied. Various kinetic parameters such as apparent activation energy, order of decomposition, frequency factor and activation entropy have been evaluated and the former two constants have been compared by two methods and are in reasonable agreement with each other.

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Zusammenfassung All-cis-l,2,3,4-Cyclopentantetracarbonsäure bildet 11 Komplexe mit Metallen wie Al(III), Y(III) und Ga(III). Sie wurden in festem Zustand aus den wässerigen Lösungen isoliert. Die Thermogravimetrie dieser Komplexe unterstützt die wahrscheinlichen Formeln, welche den Verbindungen auf Grund der Elementaranalyse Zugeschrieben worden sind. Die Kinetik einiger dieser thermischen Zersetzungen wurde untersucht. Verschiedene kinetische Parameter, wie die scheinbare Aktivierungsenergie, die Ordnung der Zersetzung, der Frequenzfaktor und die Aktivierungsentropie wurden bewertet und die ersten beiden Konstanten mittels zweier Methoden verglichen und in guter Übereinstimmung mit einander gefunden.

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Résumé L'acide all-cis-l,2,3,4-cyclopentanetétracarboxylique forme des complexes 11 avec les métaux tels que Al(III), Y(III) et Ga(III) et a été isolé à l'état solide à partir des solutions aqueuses. La thermogravimétrie de ces complexes vient à l'appui des formules probables établies par l'analyse élémentaire. La cinétique de la décomposition thermique de plusieurs d'entre eux a été étudiée. Divers paramètres cinétiques comme l'énergie d'activation, l'ordre de la décomposition, le facteur de fréquence et l'entropie d'activation ont été évalués. La comparaison des deux premières constantes obtenues par deux méthodes différentes montre une très bonne concordance des valeurs.

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--1,2,3,4- 1(III), (III) Ga(III) 11, . , . . , , , , , .

     

A contribution to the thermal decomposition of salts and metal complexes of 1,1-dithiolates

Summary The thermal decomposition of salts and metal complexes (binary and mixed ligand) of dithiocarbamates, xanthates, dithiocarbazates and dithiophosphates has been studied thermogravimetrically. The activation energies of decomposition for some of them were calculated adopting the Coats and Redfern equation. In most cases the binary complexes decompose in a single sharp stage whereas the mixed ligand complexes are characterised by decompositions having more than one stage.     

Studies on the thermal decomposition of some metal complexes of 5,5′-methylendisalicylhydroxamic acid

The thermal behaviour of the chelates of 5,5′-methylendisalicylhydroxamic acid with Pb(II), Zn(II), Ni(II), Cd(II), Fe(III), Cr(III), Al(III), Ti(IV), V(V), Mo(VI) and Cu(II) has been studied by thermogravimetry (TG), differential thermal analysis (DTA), IR spectroscopy and X-ray diffraction.The compounds decompose through three major steps, dehydration, transformation of the anhydrous hydroxamates to intermediate N-hydroxylactams, which decompose to yield metal oxides as the final products.     

State of components in group IV A metal modified nickel catalysts prepared via decomposition of metal complexes

The dispersity and state of components in (M+Ni)/SiO₂ catalysts (M=Ge, Sn, Pb), prepared via the reduction of anchored complexes, have been studied by chemisorption and electron microscopy. High dispersity of metallic particles (6Å) has been revealed. According to Mössbauer spectroscopy, in (Ni+Sn)/SiO₂ catalysts reduced at 873 K, a partial reduction of Sn to the metallic state is observed.

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(M+Ni)/SiO₂ ( M=Ge, Sn, Pb), , , - . 873 ° K (Sn+Ni)/SiO₂ , , , 6 Å.

     

Factors influencing the thermal decomposition of transition metal complexes with 2-OH-aryloximes under nitrogen

Summary The thermal behavior of copper(II), nickel(II) and palladium(II) complexes with two anionic varieties of 2-OH-aryloximes (ox), [M(ox)₂] (2-hydroxypropiophenonoxime and 2-hydroxy-4-methoxy-benzophenonoxime) was studied by using simultaneous TG/DTG-DTA technique under nitrogen in the temperature range 40-700°C. The behavior was compared with that in static air, which had been previously studied. It was found that the metal, the substituents on the ligand and the heating rate influenced their thermal decomposition. The thermal stability of the complexes with the same ligand depended on the metallic cation, following the order Pd(II)>Ni(II)>Cu(II). It also depended on the type of ligand, increasing with bulky substituents on the oximic carbon and the benzene ring. The sample mass almost did not affect their decomposition mode. The residues at 700°C of all complexes consisted of a carbonaceous oxide, determined by energy dispersive spectrometry (EDS) and IR spectroscopy     

Templated synthesis of metal nanorods in silica nanotubes

We report a general method for the synthesis of noble metal nanorods, including Au, Ag, Pt, and Pd, based on their seeded growth in silica nanotube templates. The controlled growth of the metals occurs exclusively on the seeds inside the silica nanotubes, which act as hard templates to confine the one-dimensional growth of the metal nanorods and define their aspect ratios. This method affords large quantities of noble metal nanorods with well-controlled aspect ratios and high yield, which may find wide use in the fields of nanophotonics, catalysis, sensing, imaging, and biomedicine.     

Selected-control synthesis of metal phosphonate nanoparticles and nanorods

By surfactant-assisted methods, nanoscale Co(O3PC6H5).H2O species of different morphologies, namely, nanoparticles and nanorods, have been successfully synthesized and characterized. Upon removal of the organic part of the compound, peculiar Co2P2O7 porous nanorods formed.     

Preparation of palladium catalysts via thermal decomposition of supported Pd(O) complexes

Heat treatment of the Pd(O) complex of dibenzylidenacetone on carbon supports was found to afford formation of more uniform Pd particles and an equal or higher activity of samples in hydrogenation of hexene and nitrobenzene compared to conventional methods of catalyst preparation from PdCl₂.

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, Pd(O) Pd , PdCl₂.

     

Thermal decomposition of metal complexes with thioureas

Thermal decomposition of methyl and dimethylthiourea complexes of several transition metals and of cadmium complexes with several thioureas and ureas were studied by thermogravimetric analysis in air and vacuum and stability relations established. In vacuum, dimethylthiourea complexes decompose to a mixture of metal chloride and sulfide; the organic products include dimethylthiourea, methylisothiocyanate, HCl and polymerized material. In air, intermediates are formed in which part of the organic ligand is retained followed by complete decomposition to inorganic salts at higher temperatures. The intermediate contains little sulfur and appears to be a substituted urea compound.     

Kinetics of thermal decomposition of metal acetates

The acetates of magnesium, nickel, copper, manganese, sodium and barium were subjected to thermal decomposition by means of thermogravimetric techniques (TG) under a constant flow of nitrogen. The decompositions occurred in steps and the kinetics of every set of reactions was determined by the Coats and Redfern method. These results were analysed to establish the decomposition kinetics and hence to calculate activation energies. The activation energies were also determined by applying the Horowitz-Hugh method, which yielded similar results.

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Zusammenfassung Mittels TG in konstantem Stickstoffstrom wurde die thermische Zersetzung von Magnesium-, Nickel-, Kupfer-, Mangan-, Natrium- und Bariumazetat untersucht. Es erfolgte eine schrittweise Zersetzung, die Kinetik für jede der Reaktionen wurde mit Hilfe der Methode von Coats und Redfern bestimmt. Diese Ergebnisse wurden genutzt, um die Kinetik der Zersetzung und anschlie\end die Aktivierungsenergien festzustellen. Ähnliche Werte für die Aktivierungsenergien erhielt man auch mit Hilfe der Methode von Horowitz Hugh.