Solution Synthesis And Property Studies On Hierarchical Tungstenic Nanomaterials

Nanomaterials have attracted much attention from people due to theirextensively applicable prospects. With the alternation of dimension andshape, nanomaterials have gone great changes in physical,chemical andelectronic properties. So, more efforts have been devoted to the synthesis ofone dimensional (1D) nanowires, nanotubes, nanorods and two dimensional(2D)nanoplates, nanodiscs and so forth. Now, integrating ofnanorod/nanowire/nanoplate as building blocks into hierarchicalsuperstructures has been successfully performed. Nanoassembly is animportant process for fabrication of functional electronic and photonicnanodevices. These novel assembled structures offer opportunities fordiscovering exciting new properties of materials, and are useful forfabricating complex nanodevices.As important wide gap semiconductors, tungsten oxides and tungstenoxide hydrate have many outstanding properties. They have variedapplications in many areas, especially photocatalysts, smart windows, gassensors. However, major factors impacting materials nature are their shapesand structures. Hence, it is vital for studying on synthesis and structure ofWO₃ nanomaterials. We report a novel synthesis of WO₃·H₂O nanocrystalsunder relative mild conditions to synthesize square nanoplates, nanoflowersand ewalnut-lik hierarchical nanomaterials. We systematically examined thereaction parameters on the evolvement of WO₃·H₂O nanomaterials inaqueous phase, and we found that different hierarchical structure ofWO₃·H₂O had great influences on the degradation of Rhodamine B. Thethesis work contains three parts:First, we synthesized WO₃·H₂O nanoplates and nanoflowers with help ofoxalic acid.We studied the influences of temperature, time, adding style,type and amount of additive on the final samples. As a result, we found thatoxalic acid (H₂C₂O₄) played a key role for the assembly of the products.When H₂C₂O₄/Na₂WO₄=0.25:1, monodisperse nanoplates were obtained,which have an average size of 150 nm with thickness of about 25 nm; AsH₂C₂O₄/Na₂WO₄ ratio reached 1.5:1 by increasing the H₂C₂O₄ amount, rectangular nanoplates started to organize into hierarchical structures ofnanoflowers. UV–vis detection was also made on the samples with variedamount of H₂C₂O₄, and the mechanism of oxalic acid was analyzed. Wefound that the carboxyl group of oxalic acid is the most important factor.Second, We added Ba²⁺ to the experimental system, BaWO₄ formed asintermediate substance,and the walnut-like and flower-like WO₃·H₂Onanostructures were synthesized by morphology heredity of BaWO₄. Weexamined the impact of Ba²⁺amount, ways of reactant adding, acidity,temperature, time and type of surfactants on the purity and morphology ofthe WO₃·H₂O products. The results showed that the assembly degree and thepurity of WO₃·H₂O can be controlled through Ba²⁺amount and pH value, themechanism concerning this part of work was also discussed.Samples with different assemble degree were chosen to performadsorption and degradation of RhB under simulant visible light. The resultsshowed that the degree of assembly was higher, the adsorption anddegradation of Rhodamine B was greater, and its influence factors werefurther examined.