Solution-Based Controllable Synthesis Of Metal Cyanamides Nanostructures And Energy-Related Applications

Metal cyanamides（M_χ（NCN）_γ）as a new family of pseudochalcogenides with linear and conjugated[NCN]^2-anions,possess the spacious crystal structure,the unique electronic structure and novel physicochemical properties,becoming a rising research hotspot.Among them,cyanamides nanocrystals（NCs）with high specific surface area and abundant reaction sites have shown promising application potential in energy storage and photocatalysis.However,little systematic work has been reported towards controllable synthesis of cyanamides nanomaterials.The main challenges are how to precisely control the nucleation and growth of cyanamides to further regulate the sizes,morphology,compositions,structures and physicochemical properties,which may work to achieve structure-activity relationship study and design specific functional materials.Then,the complex crystal structure of cyanamides;the narrow precursor selection of[NCN]^2-and difficulties in intermediate forming with the surfactants in the reaction create immense barriers for applying the conventional strategies to realize the controllable synthesis.In this thesis,researches on solution-based morphological regulation routes of cyanamides are carried out.Based on the crystal structures of cyanamides,the anisotropic[NCN]^2-directed fast nucleation and selective growth route on cyanamides NCs is raised;The strategies for the kinetical structure regulation and thermodynamic phase control is developed;The multi-dimensional cyanamides NCs and their hierarchical nanostructures are achieved;The energy-related applications for cyanamides nanomaterials are preliminary explored.The major results are shown as follows:（1）Anisotropic[NCN]^2-directed morphological regulation route on the synthesis of multi-dimensional cyanamides NCs is raised.Taking Ag₂NCN as a case,based on the anisotropy of[NCN]^2-and its oriented binding behaviors created unique unit,the selective growth of Ag₂NCN NCs was kinetically controlled to get nanorods,nanowires and nanosheets while the Ag₃PO₄ and Ag₂S only obtained nanoparticles with isotropic PO₄^3-and S^2-.Then,the anisotropic[N（CN）₂]^-can help to obtain Ag[N（CN）₂]nanorods and nanosheets in a similar strategy illustrating the universality of morphology-directing effect for anisotropic anions.Above all,this strategy creates an inspiring route for the controllable synthesis of complex ions containing compounds.（2）The General fabrication strategy for kinetically controlled two dimensional cyanamides nanosheets is developed.Based on the quasi-layered structure for cyanamides and[NCN]^2-directed morphology regulation route,the confined growth of cyanamides was realized to obtain two-dimensional single crystalline nanosheets by bonding metal cations with oxygen-containing functional groups on GO planes.The ultrathin nanosheets were prepared as Mn NCN,Cd NCN,Pb NCN,（Bi O）₂NCN and Zn NCN with kinetical-structure regulation.Among them,the thickness of Mn NCN nanosheets is about 1.4 nm,corresponding to single unit cell height in direction c.Then,Mn NCN nanosheets exhibit great electrochemical performance with the high capacity about 931 m Ah g^-1 and striking stability as anode in LIB superior than the capacity(200m Ah g^-1)of Mn NCN microcrystals,illustrating the good potential in energy storage.（3）The thermodynamic phase selectivity of VIII cyanamides and their new mechanism in energy storage are achieved.The preparation of cyanamides depends on high-temperature solid-state reactions,and it is difficult to obtain most known compounds by low-temperature liquid-phase reactions.Taking VIII cyanamides as the case,the deprotonation reaction of cyanamide was designed to enhance the concentration of[NCN]^2-.After side reactions’inhibition,the thermodynamic equilibrium was promoted to synthesize Fe NCN,Co NCN and Ni NCN NCs based on the chemical equilibrium.Then,Fe NCN NCs has a specific capacity of 1244 m Ah g^-1as anode,beyond the theoretical value of conversion reaction(559 m Ah g^-1).The mechanism study illustrated that unsaturated bonds in[NCN]^2-anions have the ability to connect extra Li⁺,demonstrating the great application potential of VIII cyanamides in energy storage.（4）The anion exchange reactions for cyanamides-based hierarchical nanostructures are designed.Based on the spacious structure and extraordinary stability in ions exchange for cyanamides,the anion exchange reactions were regulated to realize the controllable transformation of single crystalline nanostructure.Cd NCN NCs are chosen to perform precise anion exchange with chalcogenide anions,achieving the hierarchical nanostructures（core-shell,hollow,solid）at desired reaction stage.Trigonal Cd NCN transformed into cubic Cd Se claims the retention of the cationic sublattice.The products keep the morphology and crystallinity of synthons,breaking down the conventional concept about anion exchange reactions.The obtained Cd NCN@Cd S nanocrystals realized the effective carriers’separation efficiency,exhibiting the superior photocatalytic degradation activity than the pure Cd NCN and Cd S NCs.