Syntheses And Properties Of Nanomaterials With Stepped Structures On Surfaces

Stepped structure is a kind of planar defect and formed on grain surface during crystal growth,which is constructed by step edges,terraces and kinks.It not only changes the surface topography of a material on micro-and nano-scale,but also leads to unusual surface physical and chemical properties?such as molecular adsorption/desorption,surface energy and electron behaviors?of a material because of the low atomic coordination on its step edge and kink sites.Then,an easy and feasible way to create stepped structures will help us to realize the physical and chemical properties of stepped structures on different materials and to improve the performance of these materials and even develop novel applications.Up to now,many methods/strategies have been developed to synthesize materials with stepped structures.Most of them are based on classical crystal growth pathway,e.g.spiral growth,2D-nucleation and epitaxial growth.Usually,they need an accurate control of supersaturation or crystallographically matched materials as substrates,in which the reaction setups are high-cost and the stepped structures can't be prepared massively.Recently,a nonclassical crystal growth pathway based on self-assembly of nanoparticles has been accepted and studied by more and more researchers.They have suggested and proven that nanoparticles can grow through the oriented attachment and form planar defects,which provides the possibility to create stepped structures.However,the oriented attachment needs the crystallographic alignment of the adjacent nanoparticles through the collision and rotation process deriving from Brownian motion,which is random and uncontrollable.In this study,a novel strategy based on oriented attachment is proposed to create stepped structures by using mesocrystals as the precursors.In this method,mesocrystals were synthesized through a topotactic transformation process which is considered as a“bottom-up”process.Then,the crystallographically aligned nanoparticles of mesocrystals can skip over the collision and rotation process and meet the requirement for the formation of stepped structures.By using this strategy,we successfully synthesized the HA and anatase TiO₂ with stepped structures,respectively.?1?For the HA,CaHPO₄ was prepared by chemical precipitation method.Then,the mesocrystalline HA was obtained via a topotactic transformation reaction from CaHPO₄ to HA in hot alkaline aqueous solution.Lastly,the HA with stepped structures was synthesized by sintering the mesocrystalline HA.?2?For the anatase TiO₂,NH₄TiOF₃ was prepared by chemical precipitation method.Then,the NH₄TiOF₃ was sintered at a lower temperature to obtain mesocrystalline TiO₂ via a topotactic transformation reaction.Lastly,the TiO₂ with stepped structures was synthesized by sintering the mesocrystalline TiO₂ at a higher temperature.In addition,disorderly aligned nanocrystalline HA and monocrystalline HA were synthesized and used as the control groups.The results indicate that the crystallographic alignment of the nanoparticles of mesocrystals is essential to the formation of the stepped structures.We also tried to prepare mesocrystals composed of nanoparticles with different orderliness or size by changing the topotactic transformation conditions.The results reveal that the decrease of orderliness of nanoparticles will hinder the formation of stepped structures and the stepped structures are not stable if the nanoparticles are too small.A possible formation mechanism of the stepped structures is proposed,which is based on the evolution of the grain morphology,the grain growth rate curve and the DSC thermograms during sintering process.Besides,for the properties of materials with stepped structures,we evaluated the visible light photocatalytic activities of the anatase TiO₂ with stepped structures and investigated the adhesion and proliferation of BMSCs on HA surface with stepped structures.?1?In this study,we tried to give anatase TiO₂ materials the visible light photocatalytic ability by creating stepped structures on their{001}facets.The results of TEM,AFM,XRD,SEM and XRS indicate that the visible light photocatalytic activity is induced by the stepped structures on exposed{001}facets instead of introducing impurities during the processes of preparation and sintering.This strategy based on adjusting surface morphology increases the visible light photocatalytic ability of pure TiO₂ materials without sacrificing UV light photocatalytic ability.We also evaluated the photocatalytic activities of the samples under multiple light sources.The results indicate that the stepped structures on exposed{001}facets not only improve the photocatalytic performance of TiO₂ under outside solar light but also expand the range of indoor applications of TiO₂.?2?In this study,HA dishes with different density of stepped structures on surface were synthesized.The results of immunofluorescence staining and cell proliferation tests indicate that the stepped structures on HA surface significantly inhibit the adhesion and proliferation of BMSCs.The effect is highly related with the density of the stepped structures on HA surfaces.Normally,HA is considered as a bioactive material and widely used in bone repair.However,the biocompatibility of HA is influenced by the stepped structures on HA surface.The results not only show that the micro/nano structures on HA surface have a significant impact on BMSCs'cell behavior,but also laid the foundation for the further detailed study.