Preparation And Characterization Of Vanadium Dioxide With Different Phases And Morphologies

Vanadium dioxide?VO₂?been widely used in fields of energy smart,Li/Na ion batteries,industrial catalysis,etc.,due to their unique optical/electronic properties.The most emphasis and difficulty are the regulation of performance parameters and development of exceptional function,which is depended on the preparation method reaction condition.Base on the structure analysis and the theoretical guidance of VO₂,this dissertation is arm to develop novel synthesis routes to obtain VO₂ nanomaterials with well-defined shape,size and morphology.And the valuable exploration of their novel structures,sizes and catalytic activity in ammonia oxidation process have been investigated.The main contents and results are listed as follows:Firstly,hedgehog-like VO₂?B?with surface area of 7.03 m2·g-1 has been obtained from the decomposition of VOC₂O₄ under hydrothermal method,without any additives or templates.The influences of structure and morphology have been investigated by controlling the content of oxalic acid,water,and vanadium.The ammonia oxidation results show that,the productivity,conversion and selectivity of 3,4-chlorotoluene?3,4-DCT?were 75.5%,92.5%,81.6%,respectively,which are higher than that of commercial V2O5 or some vanadium compound oxides.Secondly,six-arms star-like VO₂?B?with surface area of 112.10 m2·g-1 and 111.59 m2·g-1 have been obtained from the systems of VOC₂O₄-H₂C₂O₄ and NH₄VO₃-H₂C₂O₄,respectively,by using low temperature hydrothermal reaction.The influences of structure and morphology have been investigated by controlling the content of oxalic acid,water,and vanadium,and the possible formation process was proposed and explained reasonable.The ammonia oxidation results show that,the productivity,conversion and selectivity of 3,4-DCT were?68.3%?89.4%?76.2%?and?70.6%?90.3%?78.2%?,respectively,indicating that VO₂ with similar shapes and morphologies exhibited the same catalytic activity.However,compared with hedgehog-like VO₂?B?,the six-arms star-like VO₂?B?had lower catalytic activity even its surface area is much higher,indicating morphology has great influence on the catalytic activity.Finally,six-arms star-like VO₂?M?with surface area of 112.10 m2·9-1 and 111.59 m2·g-1 have been obtained from a new intermedium VO₂?M?-H₂O by dehydration in heat treatment.And the VO₂?M?H₂O was obtained from the systems of VOC₂O₄-H₂C₂O₄ and NH₄VO₃-H₂C₂O₄,respectively.The dehydration and crystallization of VO₂?M?·xH₂O has been investigated by combining the TGA and DSC thermal analysis for the first time.The ammonia oxidation results show that,the productivity,conversion and selectivity of 3,4-DCT were 63.4%,95.0%,66.7%,respectively,which is slightly lower than that of star-like VO₂?B?.The six-arms star-like VO₂?M?has narrow thermal hysteresis width around 3.4 0C,indicating that the obtained sample is high sensitivity materials to be used in high sensitivity of smart optical and electrical switchers.Thus it can be seen that the properties of VO₂ are depended on its shapes and morphologies.And the synthesis method and condition control are the key to change these parameters,which is the foundation to develop and apply the specific properties of VO₂.