Liquid phase syntheses of niobium oxide and zinc oxide with controlled morphology

Abstract

Development on the synthesis approaches for controlling morphology of nanomaterials would implement to new advanced materials for many interesting applications in the future. Two main synthesis goals presented in this research were controlling mesoporosity and shape of metal oxide. Niobium oxide with mesoporosity and nanocrystalline zinc oxide with anisotropic shape were representatives for each synthesis goal and the syntheses were based on wet chemistry. Using high drying temperature, the longer ethylene oxide chain of the triblock copolymer enhanced the well organization of the mesostructure and the mesoporous niobium oxides obtained after template removal were well-organized. The hydrothermal aging at 110°C showed significantly enlarged mesoporous size and surface area, with distinct structural development pathway of niobium skeleton which showed potentially enhanced Lewis acidity. An amount of water in the system was also found to affect the properties observed. Too large or an absence of water did not give the distinct observations and the surface area and pore sizes were lower. Fine tuning of the pore sizes in the range of 3-7 nm was attained by making use of dialysis process. The procedure gave precipitates form of mesostructured oxide and shortened the long drying time required in the normally non-dialyzed method. The mesoporous niobium oxide, after calcinations at 500°C, possessed surface area in the range of 120-170 m2/g under the concentrations employed. The strategy to the adjusted textural properties of all the mesoporous niobium oxide samples were mainly based on the modification of the triblock copolymer micelles and the intrinsic sol-gel chemistry of the niobium moieties. In nanocrystalline zinc oxide syntheses, solvothermal process in the absence of hydroxyl group gave highest aspect ratio of 1-dimensional nanorod. The morphology of the products was related to dielectric constant of the solvents and the nuclei formation and growth rate of crystal were affected by the reagents.