RESUMO
Carbon nano-onions (CNOs), in their spherical or polyhedral forms, represent an important class of nanomaterials, due to their peculiar physical and electrochemical properties. Among the different methods of production, arc discharge between graphite electrodes sustained by deionized water is one of the most promising to obtain good quality CNOs in gram quantities. We applied the method with the aim to optimize the production of CNOs, using an innovative experimental arrangement. The discharges generate dispersed nanomaterials and a black hard cathodic deposit, which were studied by transmission electron microscopy-high-resolution TEM, scanning electron microscopy, Raman, thermogravimetric analysis and energy-dispersive x-ray spectroscopy. A simple mechanical grinding of the deposits permitted us to obtain turbostratic polyhedral CNOs that exhibited higher stability towards burning in air, compared to CNOs found in water. We propose a mechanism for the formation of the CNOs present in the deposit, in which the crystallization is driven by a strong temperature gradient existing close to the cathode surface at the beginning of the process, and subsequently close to the deposit surface whenever it is growing.
RESUMO
We present a study of adsorption of Cresyl Violet (CV) in aqueous solution on sonicated Graphite Oxide (sGO). For comparison, we also show adsorption results of Methylene Blue (MB) and Acridine Orange (AO) performed in the same conditions. The adsorbent was synthesized by the Tour's method followed by washing in water and ethanol and sonication, without any reduction, and studied by Raman, IR, UV-Vis, SEM and TEM techniques. Our results show that adsorption fits the pseudosecond order model for the three dyes, and that the adsorption quantity for CV is 125.0 mg g-1, while for MB and AO is 123.3 and 94.6 mg g-1 respectively.
