# Influence of Content and Type of Lanthanide on the Structure of Ln2O3-Covered Carbon Nanoflakes: The EPR and XPS Study

## TL;DR

This study examines how different lanthanide elements affect the structure of Ln2O3-coated carbon nanoflakes using EPR and XPS techniques.

## Contribution

The paper reveals how lanthanide content and type influence paramagnetic centers in carbon nanoflakes.

## Key findings

- Ln3+ ions reduce the number of unpaired electrons in carbon nanoflakes.
- C–O–Ln bonds likely form during Ln3+ impregnation.
- Oxidized CNFs show two types of paramagnetic centers.

## Abstract

Synthesized Ln2O3 (Ln = La, Nd or Gd) nanoparticles with sizes of 1–3 nm, 5–6 nm and 10–15 nm were stabilized by carbon nanoflakes (CNFs). The weight content of Ln2O3 in the Ln2O3/CNF composites was 20–50 wt. %, which makes these composites potentially suitable for practical use as computed tomography and magnetic resonance imaging contrast agents. The structure of CNFs and Ln2O3/CNF composites was investigated by X-ray diffraction data, X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR). The EPR spectra of raw CNFs were silent. The oxidation of the CNF surface resulted in the appearance of paramagnetic centers associated with two types of unpaired electrons in the carbon support. After impregnation of the CNFs with the Ln3+ ion solution, the number of unpaired electrons was reduced, presumably due to the formation of C–O–Ln bonds. All Ln3+ ions changed the composites’ EPR spectra by reducing the number of unpaired electrons in the CNF structure.