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Metal Orthovanadates MVO4 (M=La, Sm, Bi) Nanomaterials: Hydrothermal Synthesis and Characterization

Author: Sun
Tutor: ZhengWenJun
School: Nankai University
Course: Materials Physics and Chemistry
Keywords: nanomaterials metal orthovanadates hydrothermal synthesis ionic liquid surfactant
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Type: PhD thesis
Year: 2010
Downloads: 219
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Abstract


Over the past few years, metal orthvanadates nanomaterials have exhibited promising applications in batteries, catalysis, sensing, optics, and magnetism because of their size-dependent properties comparing with their bulk counterparts. Preparation of nanostructures with well-defined size, morphology, dimension through novel synthesis approaches and investigations of their formation mechanism should be a key precondition to pave the way to the real applications. Moreover, ionic liquids and surfactants as functional solvents have been attracted great attention to prepare inorganic nanomaterials. In this dissertation, ionic liquid and surfactant-assisted synthesis of lanthanum orthovanadate (LaV04), samarium orthovanadate (SmVO4), and bismuth orthovanadate (BiV04) nanostructures along with their formation mechanisms and novel properties have been studied. The main content is as follows:(1) Ultralong monoclinic (m-) LaVO4 nanowires were synthesized from the reaction of hexagonal (h-) La(OH)3 nanowires and VO3- via topotactic transformation in an ionic liquid-assisted hydrothermal system. It was found that ionic liquid 1-butyl-3-methylimidazolium bromide ([BMIM]Br) can effectively influent the morphology of h-La(OH)3 one-dimensional nanostructures through the adsorbing model of [BMIM]Br on the (010) plane, which controlled the oriented growth along the [001] direction. After the results were systematically analyzed from products obtained by modifying the reaction time, topotactic transformation from h-La(OH)3 through the diffusion of VO3- ions to m-LaVO4 is proposed to explain the growth mechanism of m-LaV04 nanowires. This research indicates that topotactic transformation may allow the design and fabrication of metal vanadates with 1D shape from the corresponding metal hydroxide, and could be extended to the synthesis of nanoscale compounds with multicomponent and complex structures.(2) The synthesis of ultrathin SmVO4 nanosheets through a simple and facile ionic liquid-assisted hydrothermal approach and their application in luminescence properties were reported. The amount of ionic liquid, pH value and synthesizing temperature played crucial roles in controlling the structure and morphology of as-prepared samples. Particularly, ionic liquid [BMIM]Br can effectively control the shape of t-SmVO4 nanostructures by adsorption on the (001) plane of the crystals, resulting in their preferential growth along the [100] and [010] directions via hydrogen bond-co-π-πstack interaction. Based on the experimental results, a dissolution-recrystallization process was reasonably proposed to understand the formation mechanism of t-SmV04 nanosheets. In addition, the as-prepared t-SmV04 nanosheets have the luminescent performance related to electron transition.(3) BiVO4 micro/nanomaterials with different morplogies were synthesized by ionic liquid and surfactant-assisted hydrothermal methods. The studies on the crystal growth reveal the relationship between the structures and ionic liquid/surfactant.

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