Vanadium Compounds And Their Hybrid With Graphene: Synthesis And New Property

The goal of this dissertation is trying to resolve the basical problems in new resources of energy and materials, and develop new micro-nanostructure materials with advanced features. By understanding the crystal structure of the target products, new vanadium oxides and their graphene-based hybrids was designed and developed via a simple solvethermal method. On the basis of the detailed microscopic crystal structures, the electronic structure and the related property of the vanadium oxides and their graphene-based hybrid was analysised, based on the unique property, the products was developed for their new application in electronic devices and new resources of energy active anode materials for aqueous lithium ion batteries, and the corresponding structure-property relationship have been also investigated. The details are summarized briefly as follows:1. We successfully synthesized a new lithium vanadate (LiVO)-graphene alternate intercalated hybrid which adopts a ABAB... stacking pattern. Taking graphene as the starting material, the hybrid was synthesized via a simple solvethermail method. The intercalated LiVO-graphene hybrid was then exfoliated into ultrathin nanosheets after ultrasound treatment. The ultrathin LiVO-graphene nanosheets have a peculiar structure which has a quasi-"rock chair confugiration", the theoretical calculation revealed that the carrier type of the graphene layer could be altered the position of the lithium ions embedded between the graphene layer and vanadate layer. Based on this property, the hybrid nanosheets were assembled into a transistion for electrical modulation through the movement of the embedded lithium ions by the application of external electric field.2. We synthesized a ferromagnetic semiconductor silver vanadium oxide (Ag1.2V3O8) nanorings for the first time. The nanorings are achieved by polarization-induced self-coiling of in situ formed Ag1.2V3O8 nanobelts, which are synthesized by hytrothermal method. Not as a tranditional ferromagnetic material, the Ag1.2V3O8 nanorings have weak ferromagnetism. The NEXAFS spectra and the density functional calculations clearly reveal that the electron transfer originates from the hybridization of the doped Ag+ and V4+ atoms, causing ordering of the magnetic moments that give rise to the intrinsic ferromagnetism of the Ag1.2V3O8 structure. Magnetic nanoring structures are attractive for spintronic devices due to their unique attributes of well-defined and reproducible magnetic states originating from their characteristic geometry.3. To study the mechanism of the magnetic entropy change and to develop new materials with magnetocaloric effect, we successfully synthesized a new vanadium oxide-graphene alternate intercalated hybrid using a solvethermal method, accompanied by abrupt change in magnetic susptibility, conductivity and transmittance in the mid-infraed region. We found that the vanadium oxide of the hybrid have the VO framework similar to monolayered VO2(B) with some modification. The modified structure of the VO layer was comfirmed by the EXAFS spectra which revealed that the final VO layer have a structure similar with VO2(R) with a zigzag V-V chain with a new isometric bond length analogous to the linear V-V chain with the isometric bond length of 2.88A in VO2(R). A reversible first order phase transition was observed, which may be the result of the similar arrangement of V-V chain by formation of V-V pairs at low temperature as in the transition from V02(R) to V02(M). The abrupt magnetic susceptibility change accompanied with the reversible phase transition caused large magnetic entropy change. Since the large magnetic entropy change is related to the magnetocaloric effect, so the magnetocaloric effect was observed across the phase transition, the large magnetic entropy change may be the result of the synergistic reaction of the magnetic entropy change and the purely magnetic induced magnetic entropy change.4. To solve the basic capacity and cyclicity problem of the aqueous lithium ion batteries, we synthesized a lithium vanadate (LiV2O5) as the cathode material of the aqueous lithium ion battery, and the graphite as the anode material, to investigate the charge-discharge reaction mechanism of the aqueous lithium ion battery for the first time. By carefully analysis the electrode materials at different charge-discharge state, the mechanism of the battery was proposed and the reason for capacity fading was also deduced. This aqueous lithium ion battery show preferable capacity and cyclicity, and provide resolution for improving the performance of the aqueous lithium ion batteries.