Preparation And Characterization Of Hierarchical Three-Dimensional Metal Oxide Nanostructures And Bamboo-Like Carbon Nanotubes

Currently,the study on hierarchical three-dimensional nanostructures assembled by low-dimensional nanostructures as building units is a hot area in research of nanostructures and nanomaterials.To explore new synthesis methods and research on physico-chemical properties of hierarchical three-dimensional nanostructures is of great significance for better understanding of their self-assembly behavior.Carbon nanotubes(CNTs) with novel morphology represent potential values in many application areas because of their particular structures and morphology.Fabrication of dominant and high proportion CNTs with novel morphology may promote further research of their physico-chemical properties and application performance.The preparations of a series of hierarchical three-dimensional metal oxide nanostructures such asα-Fe₂O₃ spheres,TiO₂ spheres,hollow TiO₂ and walnut-like CeO₂ and bamboo-like carbon nanotubes have been achieved adopting new,facile, and environmentally friendly methods.The structure,morphology,magnetic,optical properties and photocatalytic activity of the products are systematically characterized by X-ray diffraction(XRD),transmission electron microscopy(TEM),field emission scanning electron microscopy(FESEM),high resolution transmission electron microscopy(HRTEM),selected area electron diffraction(SAED),Raman spectroscopy,nitrogen sorption analysis,thermogravimetry(TG),differential scanning calorimetry(DSC),UV-Vis diffuse relectance spectroscopy(UV-Vis DRS), UV-Vis absorption spectroscopy(UV-Vis),photoluminescence(PL) spectroscopy and physical property measurement system(PPMS).The hierarchical sphericalα-Fe₂O₃ nanostructures have been prepared by polyacrylamide(PAM)-assisted microwave heating reflux as well as calcination process.The hierarchical sphericalα-Fe₂O₃ nanostructures are assembled by nanoparticles,exhibit mesoporous structures,display a remanent magnetization of 0.08947 emu g^-1 and a coercivity of 2 301.5 Oe in 300 K.PAM plays an important role in the formation of the hierarchical sphericalα-Fe₂O₃ nanostructures.The hierarchical spherical TiO₂,nanostructures assembled by nanoparticles as building units have been prepared via PAM-assisted hydrothermal route using TiCl₃ as Ti source.The hierarchical spherical TiO₂ nanostructures remain with dominant anatase phase and partial rutile phase,exhibit mesoporous structures and display red shift in UV-Vis DRS.The hierarchical spherical TiO₂ nanostructures have preferable photocatalytic activity in the photodegradation of methyl orange(MO) in aqueous solution under UV light.The role of PAM in the prepration of the hierarchical spherical TiO₂ nanostructures was discussed.The hierarchical hollow TiO₂ nanostructures have been prepared via a facile hydrothermal route using TiCl₃ as Ti source,H₂O₂ as oxidation agent and KBF₄ as mineralizer through template-free synthesis strategy.The hierarchical hollow TiO₂ nanostructures are assembled by nanoparticles,possess anatase phase and mesoporous structure.Control experiments show that the hierarchical hollow TiO₂ nanostructures formed in accordance with the Oswald ripening.Synergy of H₂O₂ and KBF₄ in the formation of the hierarchical hollow TiO₂ nanostructures plays an important role.The hierarchical hollow TiO₂ nanostructures exhibit better photocatalytic activity in the photodegradation of MO in aqueous solution under UV light.The hierarchical walnut-like mesocrystal CeOHCO₃ nanostructures with hexagonal phase have been prepared via a hydrothermal route usingβ-cyclodextrin as assistant agent.The hierarchical walnut-like CeOHCO₃ nanostructures are assembled by nanoparticles as building units,exhibit monodisperse characteristic and single-crystalline nature.In the formation process,unique crystal phase and morphology transitions of CeOHCO₃ nanostructures occurred.β-cyclodextrin plays an important role in the formation of the hierarchical walnut-like CeOHCO₃ nanostructures.The CeOHCO₃ nanostructures with hexagonal phase show an evident PL property.The mesocrystal CeO₂ nanostructures with unchanged monodisperse walnut-like morphology and single-crystalline nature are obtained after thermal conversion of the hierarchical walnut-like mesocrystal CeOHCO₃ nanostructures.The CeO₂ nanostructures display mesoporous structure,strong absorption phenomenon in UV light region with clear red shift.The CNTs with dominant bamboo-like morphology were obtained by chemical vapor deposition over Cu/Al₂O₃ catalyst using ethanol as carbon source under atmospheric pressure.The majority bamboo-like structure obviously differs from the past situation in which generally a mixture of bamboo-like and conventional straight CNTs was obtained.Control experiments show that 800℃is the optimum temperature for the growth of bamboo-like CNTs with higher quality.The combination of Cu/Al₂O₃ catalyst and ethanol played a critical role in the growth of bamboo-like CNTs.The possible causes of the formation of bamboo-like morphology were also discussed.