Synthesis and characterization of arsenic-doped cysteine-capped thoria-based nanoparticles

Thoria materials have been largely used in the nuclear industry. Nonetheless, fluorescent thoria-based nanoparticles provide additional properties to be applied in other fields. Thoria-based nanoparticles, with and without arsenic and cysteine, were prepared in 1,2-ethanediol aqueous solutions by a simple precipitation procedure. The synthesized thoria-based nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (ED-XRS), Raman spectroscopy, Fourier transform infrared (FT-IR) spectroscopy and fluorescence microscopy. The presence of arsenic and cysteine, as well as the use of a thermal treatment facilitated fluorescence emission of the thoria-based nanoparticles. Arsenic-doped and cysteine-capped thoria-based nanoparticles prepared in 2.5 M 1,2-ethanediol solutions and treated at 348 K showed small crystallite sizes and strong fluorescence. However, thoria nanoparticles subjected to a thermal treatment at 873 K also produced strong fluorescence with a very narrow size distribution and much smaller crystallite sizes, 5 nm being the average size as shown by XRD and TEM. The XRD data indicated that, even after doping of arsenic in the crystal lattice of ThO2, the samples treated at 873 K were phase pure with the fluorite cubic structure. The Raman and FT-IR spectra shown the most characteristics vibrational peaks of cysteine together with other peaks related to the bonds of this molecule to thoria and arsenic when present.