Study On Preparation, Structure And Properties Of Low-dimensioned Vanadium Oxide Nanomaterials

In the dissertation the low-dimensioned vanadium oxide nanomaterials such as vanadium oxide nanotubes(VONTs), vanadium dioxide nanorods and LJMVO4 nanomaterials were chosen as the objects of study. Modem testing methods were used to study the preparation, structure and properties of low-dimensioned vanadium oxide nanomaterials. The obtained main results are as follows:(1) Vanadium oxide nanotubes: (1) Vanadium oxide nanotubes with length of 1-10 m, inner diameter of 10~30 nm, outer diameter of 50~100nm and the diameter of the namotube bundles of 200~300nm were synthesized in a Theological self-assembled methods, which open a way which synthesizes low-dimensioned inorganic nanostructure in a low-cost and high-control way. Based on the mechanism of "rolling" and "bending", the growth model of 3-2-1 D(R) and 3-2-lD(B) are built. (2) The first charge and discharge capacity for VONTs is 200 and 185mAh/g, respectively, evidently higher than other cathode materials, which is attributed to more intercalation space and better thermodynamic intercalation sites for Li+ in the nanotubes. The dicharge capacity decrease to 120mAh/g after 10 cycles because of the presence of residual organic template. (3) Mo doping changes the growth dynamics of the nanotubes, and results in bigger interlayer spacing and shorter diffusivity distance and enhanced electrochemical performances. The heat treatment in inert atmosphere makes the nanotubes have stabler structure and better cycling properties. Laser is used to remove the residual organic template to improve the electrochemical performance. PEO is inserted in the tubes, which takes up some space and leads to the decrease of the capacity, but the PEO insertion can form the partial preferential direction of the nanotube bundles and shield the electrostatic interaction between V2O5 interlayer and Li+ ions to improve the transition and the insertion/extraction reversibility of Li+. The molar ratio of VONTs to carbon materials have great effect on the electrochemical capacity. When the ratio is 4:3 and 4:1, the attained discharge capacity is 185 and 383mAh/g, respectively. The topological substitution of the residual amine with Mn2+ stabilize the structure the nanotubes, and decrease the loss of capacity in the process of cycle. (4) The well-resolved photoluminescence band at 450-550 nm is discovered in VONTs, which is attributed to the transitions from the lowest vibrational level of excited triplet Ti(V4+-O-) to the various vibrational levels of the ground state So(V5+=O2-) and belongs to the mechanism of charge transition. The intensity of photoluminescence spectrum of nanotubes increases with Mo doping and shifts to 455nm. The coupling effect and quantum limiting effect between Mo and nanotube lead to red shift of absorption edge. (5) There are abundant defects on the nanotube surface and the surface states are easily formed, VONTs exhibit stronger optical limiting property based on TPA and better infrared radiation property based on two phonon combination radiation mechanism. And this infrared radiation property isimproved with Mo doping resulting in decreased symmetry of crystal lattice vibration.(2) VO2 nanorods: The VO2 (B) nanords with length of l~2um, nanorod diameter of 30~60nm, and the diameter of the nanorod bundles of 100~300nm were synthesized for the first time by V2O5 and CTAB in a Theological self-assembled methods. The formation of VO2 (B) nanorods is "face landing" self-assembled process. The as-synthesized VO2 (B) nanorods was treated by H2O2 and CTAB solution and VO2 (M) nanorods were attained through phase transfer process of VO2(B)-VO2 (R)-VO2(M). (2) The initial charge and discharge capacity of VO2(B) nanorods is 254.08 and 247.60mAh/g, respectively. The efficiencies of first 35 cycles exceed to 97.4%. (3) Mo doping reduces the phase separation during deep discharge and supports structure, resulting in improved electrochemical performance. (4) For VO2(M) nanorods, the transition temperature is 65 C and the hysteresis loop width is 8C. The active energy of...