Fan Bingbing

Structural Evolution during the Oxidation Process of Graphite

The structural evolution during the oxidation process of graphite by a modified Hummers method is investigated. The graphite oxide (GO) composition, disorder parameter, and structures are confirmed by means of x-ray diffraction, Fourier transform infrared spectroscopy, Raman, and scanning electron microscope techniques. Results show that: Hydroxyl, carboxyl and ether groups are present in the low-temperature oxide (at 0°C); and the degree of oxidation is increased with a longer oxidation time. The middle-temperature oxidation (35°C) is a transitory stage with a slight change to the GO structures. While for the high-temperature oxidation (95°C), the hydroxyl, carboxyl and epoxide functional groups are largely originated on the GO flakes. Hydroxyl groups are transformed into more epoxide groups with longer oxidation time, and at the same time, ether groups are eliminated, leading to defects (such as holes) on the GO flakes.

Ground States of Silicon-Multisubstituted Fullerene: First-Principles Calculations and Monte Carlo Simulations

We present a systematical study on the possible stable structures of C60−xSix(x = 1−12) fullerenes using first-principles calculations combined with Monte-Carlo simulations. The initial fullerenes randomly substituting with silicon atoms are firstly generated and then their total energies are calculated quickly. The ground-state structures are found by the annealing process where Si atoms exchange their positions with C atoms. The stable structures are finally obtained through first-principles calculations with high precision. For the cases with a small amount of Si atoms (x≤4), results similar to those report previously are achieved. Some new stable Si-doped fullerenes with more Si atoms are also predicated. The results show that Si atoms in the C60−xSix(x≤4) fullerenes have a trend of segregation with C atoms. The minimum-energy structure changes from a chemical unstable state to a chemical stable state when x≥8.