Laser-induced Synthesis Of Hybrid Metal Nanometerials In Liquid And Their Optical Properties

Metal nanocomposites not only embrace the inherent small-sized effect,surface effect,quantum size effect,macroscopic quantum tunneling effect and dielectric limit effect,but also demonstrate efficient light,electricity,catalysis and ultra-sensitive sensing and other properties due to the unique the unique inter-metallic synergies among different metals.Compared with the nanomaterials which possess smooth surface and solid body,the hollow porous nanocomposites have a greater specific surface area.The core-shell structure which can produce a peculiar micro "wrap"effect is endowed with excellent physical or chemical performances.In order to effectively mediate the synthesis of hollow porous structure of metal nanomaterials,exploring a simple,environmentally friendly,efficient and low cost method is meaningful to the basic research and promotes the field of applied research to achieve a breakthrough in the crucial part of the progress.Compared with traditional methods(template method,thermal evaporation method,hydrothermal method,etc.),the pulsed laser can produce the ultra-fast interaction between the high powder laser beam and materials,as well as a unique thermodynamic non-equilibrium state by laser ablation makes the metal element instantaneous gasification to high energy state,and then the metal composite nanomaterials are formed due to rapid cooling crystallization.Laser liquid phase ablation induced nanomaterials synthesis technology is a simple,efficient and environment friendly technology,which isn't necessary to provide templates,high temperature and high pressure harsh experimental conditions and complex chemical auxiliary reagents,laying the foundation for the needed efficient controllable synthesis of hollow porous nanomaterials.In this thesis,we study the fabrication of ultra-fine hollow porous TiO2 nanomaterials and two kinds of ZnS/Zn nanocomposites with different structures by pulsed laser liquid ablation technology,and explore the controllable synthesis mechanism.Based on the previous work,we study the outstanding property via photocatalytic degradation of Cr(?)using ZnS/Zn nanocomposites with different structures under the visible light condition.We respectively focus on the surface of Ti/Al alloy by nanosecond pulse laser ablation in water and ammonium hydroxide to synthesize hybrid metal nanomaterials,working at wavelength of 1064nm,and have researched the process of growth of hollow porous Ti02 nanomaterials,which is synthesized alkaline solution.In deionized water,we synthesize spherical-shaped TiO2/Al(OH)3 nanocomposite materials,however,a series of hollow porous TiO2 nanomaterials which has different morphology and size are fabricated by changing ammonium hydroxide in ammonium hydroxide.As for the ammonia concentration increasing to 1/3,the average diameter of the hollow porous TiO2 nanomaterials decrease from 300nm to 9.2nm,the shell thickness decrease from 60nm to 2.8nm.The study indicate that alkaline solution can improve the degree of decomposition of the Al(OH)3 material in original TiO2/Al(OH)3 composite material which is fabricated in ablation of Ti/Al alloy,due to the ultra-rapid alkaline etching in nucleation and crystallization process,finally,the ultrafine and hollow porous Ti02 nanomaterials are synthesized.When raising PH value,we find that there are obvious changes in hollow area and porous shell.Base on the ultra-rapid alkaline etching in laser ablation process for the composites containing amphoteric hydroxides,alkaline solution is expected to provide a new idea for the controlled synthesis of hollow porous composite nanomaterials.ZnS/Zn nanocomposites are developed by 1064 nm pulse laser ablation Zn metal in a solution containing thioacetamide(TAA),hydrochloric acid(HCl)and hexadecyl trimethyl ammonium bromide(CTAB),we fabricate ZnS/Zn core-shell nano-(?)composites and hollow porous nanocomposites under low(<5?L)and enough(10?L)HCl,respectively.The acid plays a critical role in the formation of porous surface structures.The TAA can be hydrolyzed in weak acidic solution to provide sulfur sources,therefore we can get pure ZnS/Zn core-shell nanocomposites.Increasing the acidity of the solution,the pre-synthesized ZnS/Zn core-shell structure is chemically etched to synthesize hollow porous nanocomposites.The as-prepared porous ZnS/Zn nanocomposites show excellent photo-catalytic activity in reduction of aqueous Cr(VI)under visible-light irradiation.Under the same experimental conditions,the hollow porous ZnS/Zn nanocomposites can reduce 97%Cr(VI)in the solution within 15 min,while the core-shell nanomaterials require 50 min.The high efficiency in reduction of Cr(VI)is mainly due to the fact that the porous structure of the nanocomposites not only increases the contact area between the material and Cr(VI)but also reduces energy gap.Due to the etching in nucleation and crystallization in the process of laser ablation,acidity plays an important role in the formation of hollow porous configurations,which is helpful to promote the study of high efficiency photocatalytic degradation.