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.