| Metallomesogens have aroused considerable interest over the past decades owing to their combining the physical properties exhibited by metal coordination complexes with liquid crystallity of organic ligands.Such as they may possess diverse molecular structures and shapes,various metal color,optics,electronic,and magnetic properties compared with organic liquid crystals(LC).Therefore,as a class of functional liquid crystalline materials,metal lomesogens bear a wide application prospect.On the other hand,due to a series of novel physical and chemical properties different from bulk materials,nanomaterials have exhibited broadly potential applications in the fields such as energy conversion and storage,biological medical diagnosis,catalysis,photoelectronic materials.Nevertheless,the character and application of nanomaterials are heavily dependent on their morphology and size.Although a wide variety of methods have been developed for obtaining nanomaterials,controlled synthesis of nanomaterials has always been the hotspot and challenging work of scientific research.Korgel and co-workers have done a lot of pioneering research work for synthesis of size-and shape-controlled metal sulfide nanocrystals through solventless thermolysis of metal alkylthiolate precursors.And on this basis,some researchers put forward a new structure-controlling solventless method of converting solid layered precursors to layered nanoproducts.Based on the particular correlation between the structure of precursors and the shape of relevant nanoproducts,we introduced azobenzene mesogens to the metal alkylthiolate precursors,which can induce more ordered self-assembly structures owing to the p-p stacking of azobenzene mesogens.With the appropriate design of metallomesogen precursors,size-and shape-controlled nanomaterials can be achieved through solventless thermolysis method,further for possible applications in electrode materials for lithium ion batteries(LIBs).In this thesis,azobenzene-containing thiol ligands with fixed spacer length and different length alkoxy tails,denoted as 2-C1 and 2-C10 respectively,and their corresponding tin thiloates,denoted as 2-C1-Sn and 2-C10-Sn respectively,have been successfully synthesized and fully confirmed by1H NMR,FT-IR.Their thermal properties,phase behavior and self-assembled structures have been systematically investigated by combination of DSC,POM and SAXS/WAXS.It is worthwhile to note from DSC and POM that tin thiloates possessed more stable and persistent mesogenic phase compared with their corresponding azobenzene-containing thiol ligands.2-C1 and 2-C1-Sn only showed mesogenic phase in the cooling process with narrow mesophase temperature range,belonging to monotropic LC.While 2-C10 and 2-C10-Sn exhibited reversible mesogenic phases during both heating and cooling process,showing enantiotropic LC behaviors.Both 2-C10 and 2-C10-Sn exhibited stable and persistent mesophase and their phase behaviors were further affected by two factors:flexible molecular stretch and arrangement benefiting from the soft long alkoxy tails.The metallomesogen 2-C10-Sn presented highly ordered layered structures in the crystalline state with more than seven orders reflection fringes in the low-angle region and retained lamellar mesophase untill higher temperature.Herein,SnS nanocomposites encapsulated with in situ N-doped carbon layer,denoted as 1-SnS@N/C and 10-SnS@N/C,were prepared via a simple solventless pyrolysis process of tin thiolate precursors 2-C1-Sn and 2-C10-Sn,which served as Sn,S,N,and C sources simultaneously.First,we determined the best pyrolysis temperature by TGA analyses and took a systematic research on crystal structure,elemental composition,morphology and structure of thus prepared nanocomposites.XRD patterns showed that all the diffraction peaks can be easily attributed to orthorhombic SnS crystal(JSPDS card No.39-0354)and no diffraction signals belonging to carbon were detected,indicating the amorphous nature of carbon.XPS demonstrated the existence of elements O,Sn,N,C,S in the as-prepared SnS nanocomposites and EDX of 10-SnS@N/C further illustrated the uniform distribution of all elements and verified the formation of SnS nanocrystals since the molar ratio of Sn to S was 1:1.Finally,the morphology and structure of prepared nanocomposites were characterized via TEM.Uniform distribution of SnS nanocrystals encapsulated in the carbon layer with small particle size have been clearly seen from TEM analysis of 10-SnS@N/C.Combining with the above results,the formation of SnS nanocomposites encapsulated with in situ N-doped carbon layer have been confirmed through solventless pyrolysis process of tin thiolates metallomesogens as precursors.The electrochemical behavior of the as-prepared nanocomposites 1-SnS@N/C and 10-SnS@N/C was preliminary investigated as anodes of LIBs.It turned out that the performance of 10-SnS@N/C was better than 1-SnS@N/C,even after 90 cycles,the discharge and charge capacity still maintained 493.4 mAh g-1 and 477.9 mAh g-1 respectively,higher than 372 mAh g-1 of commercial graphite electrodes.The excellent battery performance originated from the particular morphology and structure of 10-SnS@N/C,with N-doped carbon layer,small size of SnS nanoparticles and uniform distribution,which effectively prevented the pulverization of electrodes,poor electrical conductivity and aggregation of nanocrystals.2-C10-Sn precursor exhibited a persistent layered structure from crystalline solid to mesophase at higher temperature owing to flexible molecular stretch and arrangement benefiting from the interplay of azobenzene mesogen p-p stacking and the soft long alkoxy tails,the special structure could induce the formation of uniform distribution of ultrasmall SnS nanocrystals in carbon layer.Such universal,moderate and effective method for preparation of SnS nanomaterials can be extended to synthesis of other metal thiolates.During the process of solventless pyrolysis,precursors served as source of all elements,with no need for other raw materials.Particular morphology of nanomaterials could be obtained through one-step thermal reduction of precursor with designed structure.This method focuses on in-situ thermal reduction,which is different from the uneven traditional carbon coating on the surface of nanomaterials.By controlling the proper pyrolysis condition,uniform N-doped carbon surface can be achieved,which may boost extensive fascinating development and applications of advanced nanocomposites as next generation electrode materials of LIBs. |
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