Jiarong Niu

Modifying graphite oxide nanostructures in various media by high-energy irradiation

The alterations of GO nanostructures after γ-ray irradiation in water, air and styrene with an absorbed dose of 200 kGy are systematically investigated. The interlayer structures of the ultimate products are confirmed to be remarkably different from each other due to the distinct changes of functional groups on single-sheets in various media. After irradiation in water, oxygen groups in graphite oxide are shown to be obviously decreased owing to the generation of reductive radicals by the decomposition of water molecules, which is reflected in the decrease of graphite oxide interlayer spacing. The interlayer distance of graphite oxide irradiated in air is found to be significantly increased, which may be attributed to the increase of the hydroxyl groups and the topological defects. However, the graphite oxide seems to be mainly exfoliated and functionalized by the intercalation of the monomers and the grafting of polystyrene chains when irradiated in styrene. It is expected that γ-ray irradiation in different media should be a promising strategy for manipulating nanostructures and properties of graphite oxide for improving its applicability in fields of composites, catalysts and sensors.

TiO2 seeded on nitrogen-doped porous carbon nanofibers for superior electrochemical performance as freestanding anodes of lithium-ion batteries

Fibrous mats piled by nitrogen-doped porous carbon nanofibers with seeded TiO2 are fabricated and punched directly into circles as lithium-ion battery anodes. The seeding structure is composed of semi-wrapped TiO2 nanoparticles on carbon nanofibers (CNFs) coated with a thin layer of carbon. Synchronously, pores with various widths are formed on CNFs. As a freestanding anode, an initial discharge capacity of 615 mAh g-1 with a coulombic efficiency of 56% is reached, and 322 mAh g-1 is obtained after 100 cycles at a current density of 100 mA g-1. This is assigned to the increasing number of active sites for the lithium ion from pores with various widths and improved conductivity originating from nitrogen doping. Superior rate performance (179 mAh g-1 at the current density of 2000 mA g-1) under various current densities compared with that of other counterparts is attributed to the structural stability originating from the seeding structure with the help of the C-O-Ti bond. An additional 800 cycles are displayed at the current density of 2000 mA g-1, and superior stability is also exhibited.