Investigations On The Preparation Of[023]-Ta₃N₅ And [110]-Al₂O₃ Oriented Nanostructures Through Endotaxial Transformation

As the basis and material carrier,the exploration and utilization of new materials are vital for the development of human society.Because the properties of materials are closely related to their size and shape,some unique properties would emerge as the sizes of the materials were decreased to the nanoscale,which enables nanomaterials to a series of important applications in various fields.Owing to the anisotropic properties of crystal materials,the construction or fabrication of nanostructures with preferential orientations or ordered structures can not only retain the unique properties of nanomaterials,but also exhibit macro-anisotropic properties originated from the ordered arrangement of anisotropic nanomaterials,which can greatly enhance the device performances and exhibit great potentials in the field of energy conversion and storage,biological detection,catalysis,etc.However,with the decrease in the size of nanomaterials,the degree of order also decreases,which makes it a great challenge to construct or fabricate nanostructures with preferential orientations or ordered structures.Although great efforts and progress have been made in the past few decades,various strategies and methods have been developed to fabricate nanostructures with preferential orientations and ordered structures.It still remains a great challenge on preparing or constructing some specific nanomaterials,i.e.,nitrides or oxynitrides,with ordered or preferential orientations.According to our previous work,we fabricated[100]-TaON nanostructures by employing(012)-LiTaO3 single crystal as a substrate through an endotaxial transformation mechanism for the first time.And the[100]-TaON photoanode exhibit greatly enhanced performances owing to the unique ordered nanostructure.However,as a new mechanism to prepare ordered nanostructures with preferential orientations,the present investigations on the new endotaxial transformation mechanism are preliminary.And the versatility and universality of the endotaxial transformation mechanism to prepare other ordered nanostructures is awaited to be further verification.Therefore,in this thesis,we investigated the fabrication of Ta3Ns andα-Al2O3 nanostructures with preferential orientations by using KTaO3 and LiAlO2 single crystals as the substrates on the basis of the unique endotaxial transformation mechanism.Based on the investigations of the endotaxial transformation mechanism,we also propose a new method to separate the Li and Co elements from LiCoO2 through a CCl4 assisted high temperature annealing treatment.The main contents of the thesis are listed as follows.In Chapter 1,we first introduced the development of nanomaterials and nanotechnology briefly.Then,we summarized and reviewed the strategies to construct or fabricate ordered nanostructures with preferential orientations.At last,we proposed the main contents of this thesis.In Chapter 2,on the basis of our previous work,we first analyzed the crystal structure and the Ta atomic arrangement in both KTaO3 and Ta3N5.Then,we chose(100)-KTaO3 single crystal as the substrate,and prepared[023]-oriented Ta3Ns through a CCl4 assisted nitridation process.And the growth process and the transformation mechanism have been systematically investigated.In Chapter 3,we extended the endotaxial transformation mechanism to the fabrication of metal oxide nanostructures.[110]-oriented α-Al2O3 nanostructures have been fabricated by using(100)-LiAlO2 single crystal as a substrate through a high temperature annealing process assisted with CCl4.And this result demonstrated that the endotaxial transformation is a versatile strategy,which can not only fabricate nitrides nanostructures with preferential orientations,but also be used to fabricate metal oxide nanostructures.In Chapter 4,based on the investigations on the endotaxial transformation mechanism,we proposed a new method to separate and recycle Li and Co elements in LiCoO2 nanomaterials by high temperature annealing treatment with the assistance of CCl4.In Chapter 5,we summarized the main contents of this thesis and proposed the main conclusions and findings of this work.Then,we made a plan to address the remaining problems.