Study Of The Crystallization Behavior Of Several Sn-based Nanomaterials And Their Applications

Precisely controlling the growth of nanocrystals at the mesoscopic scale,understanding the relationship between micro-crystalline structure and macro-performance parameters,and on this basis,realizing the optimization design of nanomaterials are the promising research field in nanoscience and nanotechnology.As crystal nucleation and growth determines the final structure and properties of materials,the study of basic rules of crystal growth is of great significance to both perfect crystallographic theory and direct the design of nanomaterials and functional applications.In this paper we studied the crystallization behavior of several Sn-based materials in solution phase,aiming at exploring the influence of external conditions on the processes of nanocrystals growth by combining high-resolution electron microscopy with a series of characterization methods.Considering the crystal structural characteristics,the further nanostructural optimization and design were made for the applications in gas sensor and lithium-ion battery,and some related problems in practical applications were solved.Specific contents and results are as follows:（1）Three different ZnSn（OH）₆morphologies（nanocube,nanosphere and nanooctahedron）were synthesized by chemical co-precipitation method with the addition of surfactant dopamine,and the correlation between crystal shapes and micro-defects was investigated by combing positron annihilation lifetime spectra（PALS）,energy dispersive X-ray diffraction（XRD）,X-ray photoelectron spectroscopy（XPS）and ultraviolet visible light absorption spectroscopy（UV-Vis）.In addition,we investigated the positron annihilation behavior in nanostructured ZnSn（OH）₆and carried on qualitatively and quantitatively analysis to crystal vacancy defects.The results show that as crystal morphology gradually transform from cube to sphere and to octahedron,the type of defects remain unchanged but the oxygen vacancy concentration increases,and the band-gap decreases,successively.We demonstrate a Ostwald ripening process that transforming solid nanospheres into hollow one.When used as the gas sensing material,the hollow structure shows a high sensing selectivity for formaldehyde,fast response/recovery performance and good stability.（2）Based on the non-classical crystallization theory,we demonstrate an organic-inorganic cocrystallization growth mode for driving the self-assembly of two-dimensional（2D）building blocks.Taking 2D-layered SnS₂as experimental model,and through one-pot facile solvothermal approach,the nanocrystal growth and evolutionprocess under different conditions were investigated.It was found that attractive interactions between 2D building blocks and surfactant sodium dodecylbenzene sulfonate（SDBS）during initial stage of crystallization are crucial to realize the twist growth of SnS₂.Our experiment results reveal that the high pressure in reaction system can both reduce the critical nucleus radius and enhance the adsorption energy of SDBS molecules on the SnS₂{001}facets,which makes massive molecules attach onto the surface of atomically thin nanosheets.These surface-attached molecules not only play an important role in preventing nanocrystals growth,but also act as structural directing agent for driving atomically thin nanosheet units to crystallize into molecules-intercalated nanosheet aggregates.When reacted at200℃,guest molecules are locally intercalated in between the SnS₂layers,which altering the interactions of adjacent layers,thus inducing the twist of 2D atomic layers and formation of moirépattern.When the reaction temperature increases to 260℃,guest molecules are intercalated between the adjacent layers in 2D-carbon monolayer form.It was found that with the prolonging of the reaction time,further crystallograpically fusion can occur,which altering the interactions of SnS₂atomic layers during the coalescence of small-grain-size 2D domains due to insertion of foreign molecules,leading to interlayer rotation and moirésuperlattices formation.This work uncovers an interesting organic-inorganic cocrystallization growth mode from the molecular level,and provides a novel pathway for large-scale fabricating the moirésuperlattices.（3）This organic-inorganic cocrystallization mode can be extended to synthesize hybrid SnSe₂/C superstructures with flower-like morphology and hybrid SnS/C superstructure with ribbon-like morphology.The growth and evolution of such organic-inorganic hybrid superstructure can be divided into three steps:in the initial nucleation stage,massive molecules in solution phase can attach onto the surface of2D nucleus to form organic adsorption layer.During the subsequent growth stage,these atomically thin nanosheet units covered with organic adsorption layer are co-assembled to form three-dimensional（3D）hierarchical structure,in which the molecular organics either cover onto the lattice surface or imbedded within the lattice.As the reaction time was further prolonged,crystal growth can be dominated by Oswald ripening mechanism.Subsequent pyrolysis and pickling can completely remove the SnSe₂or SnS components,leaving conformal carbon nanoflowers and nanoribbons behind.（4）Based on the above chapters,we synthesized several nanostructured Sn-based materials,including SnS₂,SnO₂and Sn/SnO₂@G-PPy nanocomposites,and compared their lithium storage behavior.And on this basis we then designed hybrid SnS/FeCl₃@FeNSC nanocomposite with flower-like morphology,in which uniformly-dispersed SnS and FeCl₃quantum sheets are confined in the ultrathin Fe-N-S co-doped carbonaceous network.Benefiting from the unique structural features,the resultant nanohybrids exhibited the brilliant rate performance,high initial Coulomb efficiency and long-durable stability during high-rate cycling.In addition,the electrode shows an obvious adversely capacity growth,which was discussed in detail.