Hydrothermal Synthesis of Nanohybrid Gr-CeO2
Microscopy and Microanalysis
Nanohybrids (NHs) materials are a conjugation of metal oxides with a carbonaceous coating or doping. These combinations have been pursued to enhance the original oxide performance and/or incorporate multifunctional properties. NHs have emerged as a new class of compounds that are interesting in diverse areas such as: chemistry, physics, material sciences, biology and medicine . When CeO2 and Graphite are conjugated, the resulting properties are expected to be different, for cases when one or
... more of the components properties will become dominant. This can be a function of the conjugation or the synthesis procedure. Such changes may be manifested in their resultant size, shape, crystalline structure, surface chemistry, etc. Natural graphite flakes (-10 mesh, 99.9% purity from Alfa Aesar Co.) was used in this work as raw material. Graphite was processed in a high-energy SPEX 8000M mill. The balls to powder ratio was kept 5 to 1 (in weight). Milling was accomplished after a period of 8h under an inert argon atmosphere. Ceria synthesis was performed mixing 2.0 mg of chelating agent (citric acid, C6H8O7) and 2.0 g of Ce (NO3)3·6H2O in 75 mL ethanol/water solution 9:1 (in volume). The Nanohybrid Gr-CeO2 (NH Gr-CeO2) was prepared by mixing the above solution with the milled graphite following this route: 1.0 mg of graphite was added in the solution; the mixture was sonicated for 0.5h and heated at 160°C for 24 h. After cooling, the solid sample was filtered, washed, dried and calcined at 500°C for 2h, under a protective argon atmosphere to avoid graphite oxidation. The microstructural characterization was carried out through two electron microscopes: a Hitachi TEM model 7700 and a Jeol SEM model JSM-7201F. XRD studies were performed using a Bruker diffractometer model D8 Advance. Fig. 1 presents two SEM images of CeO2 and NH Gr-CeO2, where one can notice a coral-like structure in both cases, the observed particles exhibiting a low agglomeration after graphite addition. Fig. 2 (a-b) displays SEM micrographs and EDS elemental analyses of products. There is an important concentration of carbon in the NH Gr-CeO2 sample. Based on XRD studies, the mean crystallite size was calculated using the Scherrer equation, the determined values for CeO2 and NH Gr-CeO2 were 14 nm and 11 nm, respectively. In Fig. 2c we observe nanoparticles of CeO2 with sizes lower than 20 nm, which agrees with the XRD results. As was described, the citric acid was used as a chelating agent to inhibit growth and to reduce agglomeration of the particles [2,3]. Fig. 2d shows graphite sheets decorated with CeO2 nanoparticles on their surface. These particles were homogeneously distributed. Fig. 2e presents a STEM/EDS elemental mapping, which confirms the presence of carbon as a main component of the prepared NH Gr-CeO2.