Morphosynthesis Of Hierarchical Nanostructures And Their Applications

In recent years,the chemical construction and patterning of inorganic materials with complex multi-dimentional and hierarchical nanostructures is an important development in the science of organized matter.Materials with such structures exhibit distinguishable electric,magnetic,optical,thermodynamic and mechanical properties,which become the foundamental for design and investigation novel nanodevices,therefore,excite considerable research interest of chemistry,physics, and biology etcetera.The objective of this dissertation is to explore new avenue for the solution-phase fabrication of hierarchical nanostructures and the investigation into their applications.Some simple and effective technologies have been developed for assembling highly ordered functional structures.The main parts of the results are summarized below:(1) Ferric phosphate hydroxide with novel core/shell structure has been successfully synthesized via a surfactant-assisted etching in biomimetic mineralization process.Such a structure shows an impressive surface curvature,and represents a new kind of material with hollow interior in the family of various micro/nanostructures.The formation process involves adsoption of surfactant and H⁺ induced etching in {001} facet of ferric phosphate hydroxide.By optimization the kinetic parameters,the structure is controllable and can be achived in largescale.(2) A facile hydrothermal route to fabricate Bi₂S₃ nanobelts in large scale with unique highly oriented {001} surfaces has been proposed.The growth mechanism follows two-stage crystallization with initial bubble-template growth and a subsequent anisotropic growth process,which is obviously different from previous reports for fabricating 1D micro/nanostructures.Because the work function is an important parameter for the surface and applied to the investigation of many surface phenomena,the work function of Bi₂S₃ at the highly oriented {001} surfaces is calculated using a density functional theory based on the planewave method, implemented in the Vienna ab initio simulation package.The high work function of 4.93 eV at the highly oriented {001} surfaces of Bi₂S₃ microbelts contributes to the potential application for anode materials and understanding the field-emission characteristics and photoelectrochemical behaviors.(3) Bi₂S₃ networks can be constructed via a one-pot hydrothermal process, where the intermediates show two kinds of assembly behaviour:symmetric growth and oriented attachment along a specific plane.Furthermore,the current method avoids high temperature and template,thus may be easily to extend to other sulfide systems and could be used for device integration.The as-prepared 2D network structure shows great potential in building novel field emission devices and is of potential technological importance,especially for nanoelectronics and optoelectronics.(4) Hyperbranehed monoclinic BiVO₄(h-BiVO₄) consisted of four trunks with branches distributed on opposite sides has been synthesized in large scale and with good uniformity by a surfactant-free hydrothermal route.Through the observation of the intermediates at an early stage of the reaction process,it can be seen that h-BiVO₄ has different growth rates along a,b,and c axes.Based on crystal structure analysis and experimental results,h-BiVO₄ shows preferential growth along[100] direction,and subsequently along[010]and[001]directions.As-synthesized h-BiVO₄ exhibits excellent photocatalytic ability in the photodegradation of RB solution under visible light irradiation.Electrochemical measurements predict that h-BiVO₄ possesses high sensitivity to formaldehyde and ethanol gases,favorable discharge capacity,and capacity retention,which suggest its potential applications in building sensing devices and anode materials for lithium-ion batteries.(5) The natural phenomenon that calcium carbonate secretion in coral tissues falls at night or in darkness and rises during the day illumines us to glean some clues that the light irradiation,either directly or indirectly,should be of contribution to the mineralization of natural minerals.This paper describes the bio-inspired synthesis of self-assembled witherite hierarchical architectures originating from the photolysis of living matters,pyruvic and barbituric acid as examples.Most of the witherite architectures have seldom been reported up-to-date.Furthermore,the witherite crystals which are obtained in the absence of commonly used polymers or surfactants show impressive hierarchical order and mesoscale assembly. Investigation into the architecture formation process suggests that the adsorbate effect caused by low molecular weight ions such as CH₃COO^- under UV-irradiation have a remarkable kinetic effect on crystallization,particularly with regard to polymorph selectivity and habit modification.Inasmuch the avoidance of extra additives and different kinds of matrices can achieved through such a process,this method provides the possibility to utilize such carbonates to serve as PCM supporter in future "smart" wall.