E. Reguera

Colloidal Photonic Crystal Pigments with Low Angle Dependence

Poly(methyl methacrylate) (PMMA)-based colloidal photonic crystals have an incomplete photonic band gap (PBG) and typically appear iridescent in the visible range. As powders, synthetic PMMA opals are white, but when infiltrated with carbon black nanoparticles, they exhibit a well-defined color that shows little dependence on the viewing angle. The quantity of black pigment determines the lightness of the color by controlling scattering. The combined effects of internal order within each particle and random orientation among the particles in the powder are responsible for this behavior. These pigments were employed as paints, using a mixture of polyvinyl acetate as a binder and deionized water as the solvent, and were applied to wood and paper surfaces for color analysis.

Mechanochemical reactions in alkali halide pressed disks

Mechanochemical reactions that take place when milling and pressing analytes with KBr to form a disk suitable for IR spectral work are reviewed. The topic is extended to other alkali halides matrices. The literature from 1952 is surveyed from an analytical point of view. Several reactions are discussed at length with emphasis on the nature of the products. The mechanism and the factors affecting the mechanochemical changes are discussed in detail for copper sulphate, alkaline and transition metal ferricyanides, and Ag, Hg and Pb salts.

Study of the linkage isomerization process in hexacyanometallates

Abstract The linkage isomerism in several transition metal hexacyanometallates was studied by Mossbauer, IR and XRD techniques. Ferrous chromicyanide and manganicyanide transform into Cr3+ ferrocyanide and Mn2+ ferrocyanide, respectively, through an unstable intermediate ferric salt produced by the mean of an electron transfer which reduces the inner cation to CrII and MnII.

Instantaneous Synthesis of Stable Zerovalent Metal Nanoparticles under Standard Reaction Conditions

In this report is discussed a novel, easy, and general synthesis method to prepare zerovalent iron (ZVI) and copper (ZV Cu) nanoparticles (NPs), from colloid dispersions in an environmental friendly organic solvent, ethylene glycol (EG). Conventional metallic salts are used as nanoparticle precursors; sodium borohydride (NaBH4) is the reducing agent, and triethylamine (TEA) is used as the nanoparticle stabilizer. The chemical changes take place instantaneously under normal reaction conditions. Small iron (alpha-Fe0 phase) and copper (fcc phase) NPs with average diameters of 10.2 +/- 3.3 and 9.5 +/- 2.5 nm, respectively, were obtained. In both cases, the experimental evidence reveals the absence of any metal oxide shell coating the particle surfaces, and their powders remain stable, under aerobic conditions at least for 3 weeks. ZVI NPs were characterized by X-RD, Mössbauer, and Raman spectroscopies and by EELS coupled to HR-TEM. Otherwise, copper NPs were characterized by X-RD, Z-contrast, and HR-TEM. This synthesis pathway is particularly suitable for large-scale and high-quality zerovalent metallic nanoparticle (ZV M NP) production due to its simple process and low cost.

The existence of ferrous ferricyanide

Evidence in the literature on the synthesis of ferrous ferricyanide is critically discussed. Pyrolysis and pressure effects on Prussian Blue lead to ferrous ferrocyanide together with decomposition by-products, and not to ferrous ferricyanide. The latter compound could be a precursor in the formation of Turnbulls Blue or an excited state of Prussian Blue, but it is not a stable chemical species.

Proton transfer in the solid state: Reactions of organic acids and amines

Grinding of crystalline organic acids and amines leads to proton transfer with ammonium salt formation or to hydrogen bonded complexes. Formation of amides is not achieved with these reagents even under strong impact. The mechanochemical processes were monitored by IR spectroscopy. Thirteen acids and four amines covering a wide range of acidity, basicity and hardness were employed.

Petroleum solid adherence on tubing surface

Blocking of the crude oil flow is induced occasionally by the presence of a black layer of material adhered along the internal walls of petroleum wells. A piece of tubing with a significant amount of organic material, collected from a Mexican oil well, was analyzed by Mossbauer Spectroscopy (MS), X-ray Diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIRS). At room temperature, a fraction of the adherence detaches easily off from the tubing surface, but part of it remains firmly adhered. Non-stoichiometric iron oxides (oxidized magnetite or maghemite) and iron sulfides (pyrrhotite) and also small amounts of iron hydroxides and organic material were found on the tubing surface with adhered-material. This suggests a competitive adsorption of sulfur atoms and hydroxyl groups from petroleum, on the surface iron sites. Finally, the organic material, which contains alkyl chains and aromatic rings, is adsorbed non-dissociatively on the modified surface but only in the presence of non-stoichiometric iron sulfide.

Modification of the magnetic properties in molecular magnets based on Prussian blue analogues through adsorbed species

The interaction of guest molecules (H2O, N2 ,C O 2, ethanol, methanol) with the metal ions at the pore surface in porous molecular magnets (M3(Fe(CN)6)2·xH2O, M = Mn, Co, Ni, Cu) was studied by x-ray diffraction, together with Mossbauer and magnetic data. These compounds can be dehydrated at relatively low temperature, usually below 100 ◦ C. On the removal of water a cell contraction of about 4% of the cell volume is observed. This corresponds to a shortening of the metal-metal distance and to a strengthening for the metal-metal interaction through the CN bridge groups. In these materials the outer metal (M) is always found at the pore surface and the guest-host interactions modify the electronic structure of the host solid. Such interactions and their effect on the material electronic structure were studied by Mossbauer spectroscopy for the guest molecules mentioned. The most pronounced metal- metal charge overlapping was observed for the host solid free of adsorbed species. When the guest molecules were absorbed the observed changes in the solid electronic structure followed the order N2 ∼ CO2 < ethanol < methanol < water. The most pronounced effect on the solid properties was observed for water, the most polar molecule within these guest species. The magnetic properties were evaluated for anhydrous and hydrated samples. The highest Curie temperature (TC )a nd Curie-Weiss(θCW) constant values were found for the anhydrous solids, when the metal at the pore surface only interacts with the CN bridge groups. This corresponds to an increase in the charge delocalization among metal centres on the removal of water, an effect already detected by x-ray diffraction and Mossbauer data. Since, during the water adsorption and desorption processes, the cell symmetry is preserved, such changes for the TC and θCW values cannot be ascribed to a variation in the linearity of the overlapping path. The observed effects are common to all the

Evaluation of cadmium hexacianoferrate(III) as a microporous material

The properties of cadmium hexacyanoferrate(III), Cd3[Fe(CN)6]2, as a microporous material were evaluated from adsorption data of CO2, N2 and water vapor. The adsorption isotherms were interpreted according to the Dubinin– Radushkevich and Dubinin–Astakhov models. The adsorbate–adsorbent interactions during the activation and the adsorption processes were monitored by XRD, IR and M€ossbauer techniques where the adsorption of propanol, ethanol and diethyl ether was also considered. As a measure of the adsorbate–adsorbent interactions, calculations of the adsorption isosteric heats were also carried out. 2002 Published by Elsevier Science Inc.

MÖSSBAUER AND INFRARED SPECTROSCOPIC STUDIES OF NOVEL MIXED VALENCE STATES IN COBALTOUS FERROCYANIDES AND FERRICYANIDES

Novel mixed valence states have been obtained by the treatment of cobaltous ferrocyanides (Co+2FeII) and ferricyanides (Co+2FeIII) in an ozone flow. The CN stretching bands occur at 2085 cm−1 for Co+2FeII and at 2160 cm−1 for Co+2FeIII. After the ozonization process of Co+2FeII, an intense band approximately at 2125 cm−1 is detected. This intermediate band must correspond to a mixed valence state of the type: FeII−CN−Co2+−NC−FeIII Mössbauer spectra recorded “in situ” during the ozonization of Co+2FeII show the presence of two components: a doublet with isomer shift and quadrupole splitting values close to the cobalti ferricyanide and a very broad line for the mixed valence state. From the Mössbauer and infrared spectra of the aged samples of the Co+2FeII after ozonization, a relaxation process to the initial state of the samples is observed but the mixed valence state is stable.