Study On The Controllable Syntheses And Properties Of ?-?-? Bismuth-Based Mutinary Chalcogenide Nanocrystals

?-?-? Bismuth-based multinary chalcogenides nanomaterials containing green,non-toxic,earth abundant and low-price elements,with the unique characteristics and advantages of high conductivity,multiple active sites and narrow band gaps,biological non-toxicity,high X-ray attenuation coefficient and high light absorption coefficient,have been widely applied in the fields of energy storage and conversion,catalysis and biomedicine etc.The synthesis of bismuth-based multinary chalcogenides nanomaterials is the basis for its effective development and utilization.At present,the study on bismuth-based nanomaterials is still in its infancy and it is necessary to conduct in-depth research and understanding of the growth mechanism of these nanocrystals.So that,to come up with efficient and controllable synthesis strategies.Here,we reveal the growth mechanism of the ?-?-? family nanocrystals.Based on this,a series of bismuth-based multinary chalcogenides nanomaterials have been synthesized.At the same time,phase separation has been effectively avoided and products with controllable sizes and morphologies have been obtained.Finally,we explored the applications of these obtained nanomaterials.Here,it is the first time for bismuth-based multinary chalcogenides nanomaterials to be applied as anodes for potassium-ion batteries(KIBs).In the study,we found that in-situ exsolution of superior conductive metallic Ag/Cu was introduced during the electrochemical reactions.The special synergistic effect of the in-situ reduced Ag/Cu effectively improves the specific capacity and cycle stability of KIBs.Our research offer the supplements for controllable synthesis of bismuth-based nanocrystals and provides the fundamental of design and preparation for this family.Simultaneously,the applications have been further expanded,providing new nanomaterials and strategies for the design and selection for electrodes of ion batteries.The first chapter introduces the colloidal synthesis and growth mechanism of metal chalcogenide nanocrystals,the research progress and applications of bismuth-based multinary chalcogenides nanocrystals and the significance of the selected topics.In the second chapter,we use S/octadecene as sulfur source to synthesize Cu-Bi-S nanocrystals by hot-injection method,and successfully prepared two-phase high bismuth content Cu_1.57Bi_4.57S₈ and Cu_2.93Bi_4.89S₉ new nanocrystals and Cu₃BiS₃nanocrystals.In the experiment,we use the Bi-S molecular bonds of Bi₂S₃ nano-seeds to fatter Bi³⁺,in order to prevent strong oxidizing Bi³⁺from being reduced to metallic bismuth.Besides,to obtain three pure phases of Cu-Bi-S nanocrystals by adjusting the ratio of different Cu_2-xS seeds to Bi₂S₃ seeds.We have studied and revealed the growth mechanism of Cu-Bi-S system:m Cu_2-xS+n Bi₂S₃?Cu-Bi-S.This study established an effective method for synthesizing multinary chalcogenides nanocrystals of high Bi content.In the third chapter,we use N,N'-diphenylthiourea as the sulfur source to prepare Cu₃BiS₃ nanocrystals of different sizes and morphologies by hot-injection method.High reactive N,N'-diphenylthiourea can balance the relative reactivity of different metal precursors,thereby preventing Bi³⁺from being reduced to metallic state.In addition,we successfully used simple anions to bond with Bi³⁺generating intermediates and control the releasing rate of Bi³⁺through the precipitation and dissolution equilibrium of Bi OCl,and then adjusted the nucleation rate to control the growth of ternary Cu₃BiS₃nanocrystals.This anion control method opens a new way for the synthesis of multinary chalcogenide nanocrystals.Besides,we explored the potassium ion battery performance of ternary Cu₃BiS₃ nanocrystals for the first time.We found that Cu₃BiS₃ nanocrystals can reach a specific capacity of 400 m Ah g^-1 at a current density of 0.5 A g^-1.In the fourth chapter,we synthesize a new type of octahedral AgBiS₂ nanocrystals using N,N'-diphenylthiourea as the sulfur source and AgBiS₂ nanocrystals were applied as anode material for potassium-ion batteries for the first time.We discovered that the in-situ exsolution of Ag from the AgBiS₂ nanomaterial anode plays a key role in promoting high-performance potassium-ion batteries.Besides,a mixed electrochemical reaction of replacement/conversion/alloying occurred in the entire potassium-ion battery(more than two):AgBiS₂-Ag/Bi-KBi₂-K₃Bi₂-K₃Bi.We found that the conductivity of the electrode gradually increased with the exsolution of Ag from the matrix,which spontaneously promoted the anode electrochemical reaction of K⁺cycle.The battery provides a high reversible capacity of 420 m A h g^-1 at the current density of 0.5 A g^-1and 210 m A h g^-1 at 5 A g^-1 as well as 300 cycles long cycle stability.These discoveries open new directions for the design and development of high-performance electrode materials for KIBs.In the fifth chapter,a one-pot colloidal chemistry method is used to prepare AgBiSe₂ nanocrystals with a sub-oriented rock-salt cubic structure and an intermediate rhombohedral structure that are stable at room temperature.We found that when the amount of oleylamine in the system is excessive,product will be an intermediate rhombohedral phase AgBiSe₂;when the amount of oleylamine is not sufficient,theproduct will be the sub-substituted rock-salt cubic phase AgBiSe₂.The phase transformation of nanocrystals can be achieved by adjusting the amount of oleylamine.In the experiment,it was also found that the formation of the rhombohedral phase requires large numbers of Ag defects to achieve the orderly transformation of atoms.In this way,this method of ligands stablized metastable and mesophase nanocrystals can be further extended to the synthesis of more inorganic nanomaterials.Finally,we studied the potassium ion battery performance of AgBiSe₂ nanomaterials.At the current density is 0.5 A g^-1,it can reach a specific capacity of 350 m Ah g^-1,showing good potential as anode materials for potassium ion batteries.The sixth chapter is the summary and outlook of the referred research systems in this dissertation.Based on current research results and experience,the synthesis methods involved in the paper can be extended to more systems,and the potential applications of bismuth-based multinary chalcogenides nanomaterials can be further explored.In summary,in this thesis we use colloidal chemistry method to synthesize bismuth-based multinary chalcogenides nanocrystals and apply them as potassium-ion anodes.Use precursor seed control,anion bonding control,chemical component control,surface crystal facet ligand control and other means to prepare ?-?-? semiconductor nanocrystals with various components and morphologies.The study on the growth mechanism,internal structure,material characteristics and application of the semiconductor nanocrystals and the exploration of the actual nucleation growth process of different precursors of the multi-system,will be of the chemical synthesis fundamental for composition of non-toxic and earth-abundant multinary chalcogenides nanocrystals.Application design and expansion provide the basis for chemical preparation.It provides a new idea for the controllable synthesis of bismuth-based nanomaterials.