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 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.

Iron oxide nanoparticles are promising materials for many technological and environmental applications due to their versatile functionalization and magnetic properties that allow a facile remote control, separation and analyte recovery. In this contribution, the results of gold(III) sorption by naked and DMSA-capped (DMSA = m-2,3,dimercapto succinic acid) magnetite nanoparticles are discussed. Magnetite nanoparticles of 8 nm diameter were first synthesized by thermal decomposition of iron(III) oleate followed by a ligand exchange reaction to substitute oleic acid (OA) molecules by DMSA. Such systems of coated magnetite nanoparticles were characterized with Fourier transform infrared (FT-IR), X-ray diffraction (XRD), transmission electron microscopy (TEM) and magnetic measurements. FT-IR spectroscopy suggests that in Fe 3 O 4 @DMSA the organic coating is not homogeneous and it interacts with surface iron cations either through the carboxylate groups (by forming bridging bidentate complexes) or through disulfide bonds after oxidation of thiol groups. The magnetic measurements show that the nanoparticles are in the superparamagnetic range at room temperature despite the presence of dipolar interactions. The gold(III) adsorption isotherms for both bare Fe 3 O 4 and Fe 3 O 4 @DMSA nanoparticles were fitted with the Langmuir and Freundlich models. The better fit for the second model suggests the heterogeneous nature of the surface and the multilayer nature of gold adsorption. XPS spectra reveal that the adsorption of Au(III) ions comprises mostly its reduction to Au 0 by disulfide groups, although there is a fraction of these gold ions that is reduced directly onto the bare surface of the iron oxide leading to Fe(II) oxidation. According to the recorded optical absorption spectra, gold clusters of metallic character are also formed at the nanoparticle surface, a fraction of them forming subnanometer aggregates. The magnetic recovery of gold by this nanosystem could be extendable to other heavy metals.

A novel and easy synthesis pathway to synthesize small ZnO nanoparticles with a narrow size distribution is reported. The synthesis implies the simple dissolution of a zinc carboxylate hydrated salt (cyclohexanebutyrate or acetate) in a polar basic aprotic solvent as dimethyl sulfoxide (DMSO) or N,N‘-dimethylformamide (DMF) at room temperature. It is necessary to control the water content and temperature to ensure the reproducibility. The hydrolysis of zinc carboxylates allows the formation of ZnO nanoparticles of different sizes, depending on reaction conditions. Solvent basicity and the interaction of DMSO−H2O play crucial roles on the hydrolysis mechanism. The stability and the optical properties of the ZnO colloids were monitored by UV−visible electronic absorption and emission spectroscopies. From an HR-TEM study it was established that low concentration (2 × 10-4 M) of zinc cyclohexanebutyrate and zinc acetate afforded ZnO nanocrystallites of (2.12 nm, SD = 0.76) and (3.0 nm, SD = 0.5), average size, respectively. ZnO nanocrystals with rock salt structure coexist with wurtzite structure when zinc cyclohexanebutyrate is used as the starting salt. Dynamic light backscattering size measurements of ZnO nanoparticles were accomplished in DMSO colloid dispersions, resulting in the detection of small individual nanoparticles and assemblies of nanoparticles. Powder X-ray diffraction spectroscopy was used to accomplish the nanoparticle characterization, of DMF dispersions. Experimental results show that cyclohexanebutyrate acts as a more effective capping agent than acetate. Low concentration (2 × 10-4 M) colloidal ZnO dispersions in DMSO did not show any flocculation or red shift in two months, probably due to the concatenated dynamic stabilizing action of carboxylate ions and solvent molecules. The ZnO colloids in DMF are not stable and readily precipitate; moreover, nanoparticles in this solvent tend to adhere to glass walls, which allows production of ZnO films.

This report outlines the synthesis of zerovalent bismuth nanoparticle (ZV-Bi NP) colloidal dispersions, in dimethyl sulfoxide. For the general preparation pathway of these colloids, a commercial bismuth(III) salt and also a conventional reducing agent were used. All reactions took place immediately and under mild conditions. Stable, for more than three months, under room conditions, ZV-Bi NP colloids are obtained when using sodium citrate and a deficit of the reducing agent respect to the bismuth salt. This reaction mixture yields small, well-faceted, and also quasi-spherical crystalline particles, with an average size of 3.3 nm, SD of 1.0 nm, determined by HR-TEM. These are the smallest ZV-Bi NPs, synthesized by a fast and straightforward colloidal method, found in the literature. Indirect and direct energy gaps were discovered in the near-infrared spectral range (1400–1600 nm) of the ZV-Bi NPs, indicating the displacement of the conduction and valence bands due to the strong quantum confinement; bulk bismuth itself is a semimetal. This is the first time that energy gaps of quantum confined ZV-Bi NPs are found at room conditions. The dry ZV-Bi NP powders that precipitated from the colloids are totally stable in storage, at room conditions, for more than three years.

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.