Bismuth Oxide Nanoparticles Partially Substituted with EuIII, MnIV, and SiIV: Structural, Spectroscopic, and Optical Findings.

Interest in nanostructured partially substituted bismuth oxides has been increasing over the last years. Research on new synthesis methods, properties, and possible uses for these oxides is needed. The objective of this paper is to synthesize ß-Bi2O3, ß-Bi2O3:Eu3+, ß-Bi2O3:Mn4+, Bi12Bi0.8O19.2, Bi12Bi0.8O19.2/Li+, Bi12MnO20, and Bi12SiO20 nanoparticles and to investigate their structural, spectroscopic, and optical changes. Some of the causes that generated their properties are also discussed. These materials are important because the doping or partial substitution of bismuth oxide with these cations (Eu3+, Mn4+, and Si4+) modifies some properties such as optical absorption, reactivity toward CO2, among others. X-ray diffraction (in powders), high-resolution transmission electron microscopy, Fourier transform infrared (FTIR), resonance Raman scattering, diffuse reflectance, and solid-state magic-angle-spinning 29Si NMR were used for the characterization of the synthesized materials. We found that partial substitution of yellow Bi12Bi0.8O19.2 with Mn4+ and Si4+ changed the color to green and whitish, respectively. New bands in the Raman scattering and FTIR spectra of these oxides are deeply discussed. Raman scattering spectroscopy was a valuable and reliable technique to detect the Eu3+ and Mn4+ cations as dopants in the bismuth oxides. The 29Si chemical shift (δ) in Bi12SiO20 was -78.16 ppm, whereas in SiO2, it was around -110 ppm. This considerable shift in Bi12SiO20 occurred because of an increased shielding of the Si nucleus in the Si(O)4 tetrahedron. This shielding was provided by the low-electronegativity and highly polarizable Bi cations. The isovalent doping of ß-Bi2O3 nanoparticles with Eu3+ enhanced their thermal stability over 400 °C. Variation in the optical absorption and reactivity toward the acidic CO2 molecule of the partially substituted bismuth oxides was explained on the basis of the optical basicity and ionic-covalent parameter concepts. Some possible uses for the synthesized oxides are suggested.

Easy synthesis of high-purity BiFeO3 nanoparticles: new insights derived from the structural, optical, and magnetic characterization.

Synthesis of high-purity BiFeO3 is very important for practical applications. This task has been very challenging for the scientific community because nonstoichiometric Bi(x)Fe(y)O(z) species typically appear as byproducts in most of the synthesis routes. In the present work, we outline the synthesis of BiFeO3 nanostructures by a combustion reaction, employing tartaric acid or glycine as promoter. When glycine is used, a porous BiFeO3 network composed of tightly assembled and sintered nanocrystallites is obtained. The origin of high purity BiFeO3 nanomaterial as well as the formation of other byproducts is explained on the basis of metal-ligand interactions. Structural, morphological, and optical analysis of the intermediate that preceded the formation of porous BiFeO3 structures was accomplished. The thorough characterization of BiFeO3 nanoparticles (NPs) included powder X-ray diffraction (XRD); scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM); thermogravimetric analysis (TGA); UV-vis electronic absorption (diffuse reflectance mode), Raman scattering, Mössbauer, and electron paramagnetic resonance (EPR) spectroscopies; and vibrating sample magnetometry (VSM). The byproducts like ß-Bi2O3 and 5 nm Bi2Fe4O9 NPs were obtained when tartaric acid was the promoter. However, no such byproducts were formed using glycine in the synthesis process. The average sizes of the crystallites for BiFeO3 were 26 and 23 nm, for tartaric acid and glycine promoters, respectively. Two band gap energies, 2.27 and 1.66 eV, were found for BiFeO3 synthesized with tartaric acid, obtained from Tauc's plots. A remarkable selective enhancement in the intensity of the BiFeO3 A1 mode, as a consequence of the resonance Raman effect, was observed and discussed for the first time in this work. For glycine-promoted BiFeO3 nanostructures, the measured magnetization (M) value at 20,000 Oe (0.64 emu g(-1)) was ∼5 times lower than that obtained using tartaric acid. The difference between the M values has been associated with the different morphologies of the BiFeO3 nanostructures.

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.

New insights on molybdenum suboxide: nature of carbons in isomerization reactions.

MoO3 transformations under isomerization process conditions were studied. The products obtained after different times under stream (H2/n-heptane mixture, 18.5 bar, at 370 degrees C) were characterized by X-ray diffraction, Raman spectroscopy, thermal analysis, and high-resolution transmission electron microscopy (HRTEM). Theoretical quantum calculations were carried out with the aim of understanding the paradox of the real active phase in isomerization reactions. Theoretical calculations predict the existence of a metallic-like MoO phase with a structure that matches the X-ray diffraction experimental results. From experimental and simulated HRTEM images it was possible to identify the presence of small MoO cubic crystallites inside MoOx matrix phases. These results also support the previously proposed idea that isomerization reactions take place as a result of the existence of a bifunctional catalyst. The Raman and thermo-programmed oxidation (TPO) analyses show the existence of at least two types of carbonaceous deposits which tend to increase its ordering with the increase of time under stream. The carbon K edge in electron energy loss spectroscopy (EELS) of a sample after 24 h under stream shows that these carbonaceous deposits consist of a mixture of sp2- and sp3-hybridized carbons.

Synthesis and characterization of RuS2 nanostructures.

Small naked ruthenium sulfide nanoparticles (NPs) with narrow size distribution (2.5 +/- 0.4 nm of diameter) were synthesized in DMSO colloidal dispersions, under mild reaction conditions and using commercial RuCl3 as precursor. To test the chemical reactivity with soft and hard bases, fresh presynthesized RuS2 colloids were mixed with triethylamine (N(Et)3) and ammonium tetrathiomolybdate ((NH4)2MoS4) dimethyl sulfoxide solutions. Naked N(Et)3 and [MoS4](2-)-capped RuS2 nanoparticle colloids were characterized using UV-visible electronic absorption and emission spectroscopies and high-resolution transmission electron microscopy (HR-TEM). It has also been shown that capped RuS2-[MoS4]2- nanoparticles yield MoO3 crystalline matrix by means of HR-TEM experiments. The emission spectra of RuS2 and N(Et)3-RuS2 dispersions show that both nanosized materials have strong fluorescence. The existence of the ruthenium precursor species in solution was established by cyclic voltammetry. Moreover, naked RuS2 NPs were mixed with a chemical mixture with composition similar to gasoline (dibenzothiophene (Bz2S, 400 ppm), hexane, and toluene (55:45% v/v)). The reaction mixture consisted of two phases; in the polar phase, we found evidences of a strong interaction of Bz2S and toluene with the naked RuS2 NPs. We have also obtained self-organized thin films of capped N(Et)3- and RuS2-[MoS4]2- nanoparticles. In both cases, the shape and thickness of the resulting thin films were controlled by a dynamic vacuum procedure. The thin films have been characterized by atomic force microscopy, scanning electron microscopy, HR-TEM, energy dispersion spectroscopy, X-ray diffraction, and absorbance and fluorescence spectroscopies.

Tio2-dopamine complex implanted unilaterally in the caudate nucleus improves motor activity and behavior function of rats with induced hemiparkinsonism.

Parkinson's disease (PD) is characterized by malfunction of dopaminergic systems, and the current symptomatic treatment is to replace lost dopamine. For investigating mechanisms of pathogenesis and alternative treatments to compensate lack of dopamine (DA) activity in PD, the 6-hydroxydopamine (6-OHDA)-lesioned rat model of PD has been useful, these animals display apomorphine-induced contralateral rotational behavior, when they are examined after lesion. The purpose of this study was to assess Titania-dopamine (TiO2-DA) complexes implanted on the caudate nucleus for diminishing motor behavior alterations of the 6-OHDA rat model. Rats with 6-OHDA unilateral lesions received TiO2 alone or TiO2-DA implants, and were tested for open field (OF) gross motor crossing and rearing behaviors, and apomorphine-induced rotation (G) behavior. TiO2 complex have no effects on rearing OF and G behaviors, and a significant reducing effect on crossing motor behavior of normal rats compared to control non-treated rats throughout 56 days of observation. Interestingly, TiO2-DA treatment significant recovered motor crossing and rearing behaviors in 6-OHDA-lesioned rats, and diminished the G behaviors during 56 days of examination. Additionally, in the 6-OHDA-lesioned rats TiO2 treatment had a moderate recovering effect only on crossing behavior compared to lesioned non treated rats. Our results suggest that continuous release of dopamine in the caudate nucleus from TiO2-DA complex is capable of reversing gross motor deficits observed in the 6-OHDA-lesioned rat model of PD. Thistype of delivery system of DA represents a promising therapy for PD in humans.