Patricia Santiago-Jacinto

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 β-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 Taucs 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.

Synthesis and Thermal Behavior of Metallic Cobalt Micro and Nanostructures

In this contribution, a comparative study of metallic cobalt micro and nanoparticles obtained in solution by four different chemical routes is reported. Classic routes such as borohydride reduction in aqueous media and the so-called polyol methodology were used to obtain the cobalt nanostructures to be studied. Using CTAB as surfactant, cobalt hollow nanostructures were obtained. The use of strong reducing agents, like sodium borohydride, favors the formation of quasi-monodispersed nanoparticles of about 2 nm size but accompanied with impurities; for hydrazine (a mild reducer), nanoparticles of larger size are obtained which organize in spherical microagglomerates. Valuable information on the particles thermal stability and on nature of the species anchored at their surface was obtained from thermogravimetric curves. The samples to be studied were characterized from UV-vis, IR, X-ray diffraction, and electron microscopy images (scanning and transmission).

Gold nanoparticles conjugated to benzoylmercaptoacetyltriglycine and l-cysteine methylester

Benzoyl-protected mercaptoacetyltriglycine, a synthetic precursor used in the preparation of Technetium-99m-mercaptoacetyltriglycine, a radiopharmaceutical for renal tubular function and L-cysteine methylester, a small, non-zwitterionic amino acid derivative, were used as capping agents of gold nanoparticles obtained by borohydride reduction method. The capped gold nanoparticles composites were prepared from aqueous solutions and characterized by UV-Vis, infrared and Raman spectra and Transmission Electron Microscopy images. The presence of the ligands and its different binding mode to the particles as a consequence of the benzoyl-protection of the thiol group in benzoyl-protected mercaptoacetyltriglycine were evidenced from infrared and Raman spectra. The stability on aging in water solution of the formed composites is discussed from the obtained UV-Vis spectra.

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 β-Bi2O3, β-Bi2O3:Eu3+, β-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 β-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.