Growth and Characterization of Graphene Layers on Different Kinds of Copper Surfaces.

Graphene films were grown by chemical vapor deposition on Cu foil. The obtained samples were characterized by Raman spectroscopy, ellipsometry, X-ray photoelectron spectroscopy and electron back-scatter diffraction. We discuss the time-dependent changes in the samples, estimate the thickness of emerging Cu2O beneath the graphene and check the orientation-dependent affinity to oxidation of distinct Cu grains, which also governs the manner in which the initial strong Cu-graphene coupling and strain in the graphene lattice is released. Effects of electropolishing on the quality and the Raman response of the grown graphene layers are studied by microtexture polarization analysis. The obtained data are compared with the Raman signal of graphene after transfer on glass substrate revealing the complex interaction of graphene with the Cu substrate.

Solid-Phase Quasi-Intramolecular Redox Reaction of [Ag(NH3)2]MnO4: An Easy Way to Prepare Pure AgMnO2.

Two monoclinic polymorphs of [Ag(NH3)2]MnO4 containing a unique coordination mode of permanganate ions were prepared, and the high-temperature polymorph was used as a precursor to synthesize pure AgMnO2. The hydrogen bonds between the permanganate ions and the hydrogen atoms of ammonia were detected by IR spectroscopy and single-crystal X-ray diffraction. Under thermal decomposition, these hydrogen bonds induced a solid-phase quasi-intramolecular redox reaction between the [Ag(NH3)2]+ cation and MnO4- anion even before losing the ammonia ligand or permanganate oxygen atom. The polymorphs decomposed into finely dispersed elementary silver, amorphous MnOx compounds, and H2O, N2 and NO gases. Annealing the primary decomposition product at 573 K, the metallic silver reacted with the manganese oxides and resulted in the formation of amorphous silver manganese oxides, which started to crystallize only at 773 K and completely transformed into AgMnO2 at 873 K.

Effect of Different Anions Upon the WO3 Morphology and Structure.

In this study the effects of various anions (SO2-4, ClO-4 and PO3-4) were investigated on the hydrothermal treatment of WO3 from Na2WO4 and HCl at 180 and 200 °C. The products were analyzed by XRD and SEM. With the usage of SO2-4 the obtained product was hexagonal (h-) WO3 in the form of nanorods at both temperatures. Applying ClO-4 resulted in a mixture of WO3·0.33H2O and small amount of m-WO3 at 180 °C and pure WO3·0.33H2O at 200 °C. The morphology was consisted of cuboid shapes arranged into spherical structures at 180 °C and longitudinal ones at 200 °C. By the application of PO3-4 no product formed at either temperature. Using the combination of SO2-4, and ClO-4 the product was h-WO3 at both 180 and 200 °C with rod-like crystals; thus, the effect of ClO-4 was overdominated by the SO2-4ions. Utilization of PO3-4 together with SO2-4, and/or ClO-4 resulted again in no product, meaning that adding PO3-4 to the reaction mixture completely blocks the hydrothermal formation of solid products by forming water soluble phosphotungstic acids.

Unexpected Sequential NH3/H2O Solid/Gas Phase Ligand Exchange and Quasi-Intramolecular Self-Protonation Yield [NH4Cu(OH)MoO4], a Photocatalyst Misidentified before as (NH4)2Cu(MoO4)2.

[NH4Cu(OH)MoO4] as active photocatalyst in the decomposition of Congo Red when irradiated by UV or visible light has been prepared in an unusual ammonia/water ligand exchange reaction of [tetraamminecopper(II)] molybdate, [Cu(NH3)4]MoO4. [Cu(NH3)4]MoO4 was subjected to moisture of open air at room temperature. Light blue orthorhombic [Cu(NH3)(H2O)3]MoO4 was formed in 2 days as a result of an unexpected solid/gas phase ammonia-water ligand exchange reaction. This complex does not lose its last ammonia ligand on further standing in open air; however, a slow quasi-intramolecular (self)-protonation reaction takes place in 2-4 weeks, producing a yellowish-green microcrystalline material, which has been identified as a new compound, [NH4Cu(OH)MoO4], ( a = 10,5306 Å, b = 6.0871 Å, c = 8.0148 Å, ß = 64,153°, C2, Z = 4). Mechanisms are proposed for both the sequential ligand exchange and the self-protonation reactions supported by ab initio quantum-chemical calculations and deuteration experiments as well. The [Cu(NH3)(H2O)3]MoO4 intermediate transforms into NH4Cu(OH)(H2O)2MoO4, which loses two waters and yields [NH4Cu(OH)MoO4]. Upon heating, both [Cu(NH3)4]MoO4 and [Cu(NH3)(H2O)3]MoO4 decompose, losing three NH3 and three H2O ligands, respectively, and stable [Cu(NH3)MoO4] is formed from both. The latter can partially be hydrated in boiling water into [NH4Cu(OH)MoO4. This compound can also be prepared in pure form by boiling the saturated aqueous solution of [Cu(NH3)4]MoO4. All properties of [NH4Cu(OH)MoO4] match those of the active photocatalyst described earlier in the literature under the formulas (NH4)2[Cu(MoO4)2] and (NH4)2Cu4(NH3)3Mo5O20.

Effect of pH in the Hydrothermal Preparation of Bi2WO6 Nanostructures.

In this study, Bi2WO6 was prepared by the hydrothermal method. The effects of reaction temperature (150/170/200 °C) and reaction time (6/12/24 h) were investigated. The role of strongly acidic pH (1 >) and the full range between 0.3 and 13.5 were studied first. Every sample was studied by XRD and SEM; furthermore, the Bi2WO6 samples prepared at different temperatures were examined in detail by EDX and TEM, as well as FT-IR, Raman and UV-vis spectroscopies. It was found that changing the temperature and time slightly influenced the crystallinity and morphology of the products. The most crystallized product formed at 200 °C, 24 h. The pure, sheet-like Bi2WO6, prepared at 200 °C, 24 h, and 0.3 pH, gradually transformed into a mixture of Bi2WO6 and Bi3.84W0.16O6.24 with increasing pH. The nanosheets turned into a morphology of mixed shapes in the acidic range (fibers, sheets, irregular forms), and became homogenous cube- and octahedral-like shapes in the alkaline range. Their band gaps were calculated and were found to vary between 2.66 and 2.59 eV as the temperature increased. The specific surface area measurements revealed that reducing the temperature favors the formation of a larger surface area (35.8/26/21.6 m2/g belonging to 150/170/200 °C, respectively).

Cu-doped resorcinol-formaldehyde (RF) polymer and carbon aerogels.

Introduction of transition metal salt(s) onto the surface of porous carbons may increase the selectivity and/or efficiency of these adsorbents in catalysis or separation. Carbon aerogels with low pressure drop are particularly suited for these applications. Moreover the sol-gel process used in the synthesis of the resorcinol-formaldehyde polymer gel (RF) precursors offers an extra opportunity for introducing metal ions. Salts of different metals modify both the macroscopic texture and the porosity, depending on the synthesis protocol. In this paper we show, by means of low temperature nitrogen adsorption measurements and SEM, as well as small- and wide-angle X-ray scattering (SAXS and WAXS), how the addition of copper acetate at three different stages influences not only the specific surface area but also the resulting overall structure over a wide range of length scales. Posttreatment in either the polymer or the carbon aerogel stage provides a means of adjusting the copper content. While the Cu-containing carbon aerogels differ mainly in their micropore volume but not in the width of the distribution, their pore size window in the mesopore range can be tuned between 50 and 400 A by the protocol of Cu addition. The synthesis protocol also determines the chemical form of the copper.

Atomic layer deposition of tungsten(III) oxide thin films from W2(NMe2)6 and water: precursor-based control of oxidation state in the thin film material.

The atomic layer deposition of W2O3 films was demonstrated employing W2(NMe2)6 and water as precursors with substrate temperatures between 140 and 240 degrees C. At 180 degrees C, surface saturative growth was achieved with W2(NMe2)6 vapor pulse lengths of >/=2 s. The growth rate was about 1.4 A/cycle at substrate temperatures between 140 and 200 degrees C. Growth rates of 1.60 and 2.10 A/cycle were observed at 220 and 240 degrees C, respectively. In a series of films deposited at 180 degrees C, the film thicknesses varied linearly with the number of deposition cycles. Time-of-flight elastic recoil analyses demonstrated stoichiometric W2O3 films, with carbon, hydrogen, and nitrogen levels between 6.3 and 8.6, 11.9 and 14.2, and 4.6 and 5.0 at. %, respectively, at substrate temperatures of 160, 180, and 200 degrees C. The as-deposited films were amorphous. Atomic force microscopy showed root-mean-square surface roughnesses of 0.7 and 0.9 nm for films deposited at 180 and 200 degrees C, respectively. The resistivity of a film grown at 180 degrees C was 8500 microhm cm.