Solvothermal synthesis of lanthanide-functionalized graphene oxide nanocomposites

We propose a facile approach to the preparation of graphene oxide (GO) composites with lanthanide (Ln) oxide/hydroxide nanoparticles (Ln = La, Eu, Gd, Tb) under relatively mild conditions by two different procedures of solvothermal synthesis. The mechanism of GO-Ln nanocomposite formation is thought to involve the initial coordination of Ln3+ ions to the oxygen-containing groups of GO as nucleation sites, followed by f Ln2O3 and Ln(OH)3 nanoparticle growth. The nanocomposites obtained preserve the intrinsic planar honeycomb-like structures of graphene as proven by the typical G and D bands in the Raman spectra. Fourier-transform infrared and X-ray photoelectron spectroscopy confirm the interaction between oxygen-containing groups of GO and Ln ions. The size and distribution of Ln oxide/hydroxide nanoparticles on GO sheets, estimated from scanning and transmission electron microscopy images, vary broadly for the different lanthanides. The size can span from sub-nm dimensions for Eu oxide to more than 10 μm for Eu hydroxide nanoparticles. The most homogeneous distribution of Ln oxide/hydroxide nanoparticles was found in La-containing composites. Thermogravimetric analysis demonstrated that all the GO-Ln nanocomposites are thermally less stable, by up to 30 °C than pristine GO.</p

Eco-friendly synthesis of graphene oxide–palladium nanohybrids

Nanostructured hybrids of graphene oxide and palladium were fabricated by means of one-step solvent-free gas phase treatment of graphene oxide with the aliphatic amines 1-octadecylamine and 1,8-diaminooctane, followed by in situ decoration with palladium in the liquid medium using palladium chloride as the precursor and citric acid as a mild and environmentally friendly stabilizing and reducing agent. The proposed synthesis method represents an eco-friendly alternative for obtaining nanohybrids of graphene oxide and palladium nanoparticles under mild conditions. Spectroscopic studies evidenced -COOH group derivatization of graphene due to the amidation reaction; transmission electron microscopy demonstrated the formation of nanometer-sized crystalline palladium particles and evidenced that the diamine-functionalization results in a larger particle sizes than observed for monoamine- or non-functionalized substrates. The hybrids obtained have a slightly lower thermal stability than pristine graphene oxide.</p

Solvothermal Synthesis of Rare Earth Bisphthalocyanines

Rare earth bisphthalocyanines (MPc2) are of particular interest because of their behavior as single-molecular magnets, which makes them suitable for applications in molecular spintronics, high-density data storage and quantum computation. Nevertheless, MPc2 are not commercially available, and the synthesis routes are mainly focused on obtaining substituted phthalocyanines. Two preparation routes depend on the precursor: synthesis from phthalonitrile (PN) and the metalation of free or dilithium phthalocyanine (H2Pc and Li2Pc). In both options, byproducts such as free-base phthalocyanine and in the first route additional PN oligomers are generated, which influence the MPc2 yield. There are three preparation methods for these routes: heating, microwave radiation and reflux. In this research, solvothermal synthesis was applied as a new approach to prepare yttrium, lanthanum, gadolinium and terbium unsubstituted bisphthalocyanines using Li2Pc and the rare earth(III) acetylacetonates. Purification by sublimation gave high product yields compared to those reported, namely 68% for YPc2, 43% for LaPc2, 63% for GdPc2 and 62% for TbPc2, without any detectable presence of H2Pc. Characterization by infrared, Raman, ultraviolet–visible and X-ray photoelectron spectroscopy as well as elemental analysis revealed the main featuresof the four bisphthalocyanines, indicating the success of the synthesis of the complexes.</p

N-doped carbon nanofibers from pyrolysis of free-base phthalocyanine

Heating free-base phthalocyanine (H2Pc) at around 450 °C under static vacuum results in the formation of a nonvolatile carbonaceous material through oxidative pyrolysis. We used a number of instrumental techniques to characterize its morphology and chemical composition. According to electron microscopy observations, the dominating morphology is fibrous. The estimated length of individual fibers, which appear as rather homogeneous and continuous structures, is several micrometers, with diameters of roughly 200 nm. According to elemental analysis estimates, the per cent contribution of carbon remains approximately the same as in pristine H2Pc, but about 5.4 at% of nitrogen is substituted by oxygen. Spectroscopic measurements suggest that the oxygen is incorporated into nanofiber structure in the form of different functionalities containing C]O and C–OH bonds. Raman spectroscopy revealed an approximately equal contribution due to sp3 and sp2 -hybridized carbon atoms, which would made one to expect that the thermal stability of nanofibers must be similar to that of defect-containing nanotubes, graphene oxide and nanodiamond. Nevertheless, according to thermogravimetric curves obtained, nanofibers are at least as thermally stable as graphene and defect-free nanotubes. Density functional theory calculations were employed to suggest possible initial steps of H2Pc oxidative pyrolysis leading to the formation of nanofibers.Financial support from the National Autonomous University of Mexico (grant DGAPA-IN101118, FTIR and Raman spectroscopic measurements; DGAPA-IN203219, SEM and EDS characterization) and from the National Council of Science and Technology, Mexico (CONACYT, grant 250655) is greatly appreciated. L. M. B.-P. is grateful to the Doctorate Degree Program in Chemical Sciences of UNAM and to CONACyT for PhD scholarshi

Lanthanide-modified graphene oxide and nanodiamond materials and their cytotoxicity

Integrating lanthanide elements with carbon-based nanomaterials results in the creation of hybrid materials and nanocomposites with unique properties. We report a functionalization approach free of organic solvents for modifying graphene oxide (GO) and nanodiamond (ND) with various lanthanides (La(III), Ce(III), Eu(III), Gd(III), Tb(III) and Ho(III)). The aqueous-phase impregnation with their acetates was followed first by drying at 80 °C and then by heating at 300 °C for 2 h in air conditions. Scanning electron microscopy revealed that after the initial drying, the samples exhibited the presence of larger lanthanide-containing particles, whereas after the heating at 300 °C they became indistinguishable, and thus the lanthanide species became more homogeneously distributed throughout GO and ND. The toxicity, which is commonly associated with the presence of lanthanides, was evaluated in terms of the ability to inhibit the proliferation of COS-7 monkey kidney cell cultures. Most composites demonstrated a dose-dependent toxicity, with significantly lower cytotoxic effects compared to both the thermally treated GO and ND, as well as the pristine GO. The composites functionalized with gadolinium were among the least toxic at the maximum tested concentration (100 µg/ml). The ND-based composites were not cytotoxic at 50 µg/ml, the lowest tested concentration.</p