Study On Controlled Synthesis And Growth Mechanism Of CdS Micro/Nanomaterials

As the intersection of material science and nanotechnology, nanomaterials are also the most basic and active area of nanotechnology and have intense influence on the development of economy and society.Due to these special properties--small size effect,surface effect and quantum size effect,etc,which differ from bulk substances and single molecular, nanomaterials have great potential applications in many fields such as electronics,solar cell,ceramics,biology and medicine.The fabrication of nanomaterials and nanostructures goes deeper with the understanding of their unique properties and the study on nanomaterials application.Among nanomaterials with different morphology,the synthesis of 1D and special morphology nanomaterials will be the key problem for the application in nanodevice,photocatalyzer and sensor and will be the emphases of nanomaterials research for a long time.CdS is a typical wide band gap semiconductor ofâ…¡-â…¥group with excellent physiochemical properties and is widely used in piezoelectricity-crystal,windows-materials and laser-materials,etc.With the development of nanomaterials,many different morphology CdS nanomaterials have been fabricated.CdS nanomaterials have excellent properties and have great potential applications in photocatalyzer,solar cell,LED,biolabel,LCD display and sensor.Although there is great progress in the synthesis of CdS nanomaterials in the past decades,there are still some problems.Now controlling effectively the morphology and microstructure of CdS nanomaterials and exploring the growth mechanism are still challenging work for researchers.This thesis is interested in CdS nanomaterials and emphasizes the synthesis and morphological control of CdS nanomaterials.1D or special morphology CdS nanomaterials were synthesized using the appropriate starting reagents,assistant reagents and reaction routs.The products were characterized by different technologies.In order to control effectively the structure,morphology and size of products,the influence of experimental parameters on the morphology of products was studied.The growth mechanisms were also explored.The main contents of this thesis are summarized as follows.(1)CdS nanowires have been synthesized using poly(vinyl alcohol)as soft-template.In the reaction system,poly(vinyl alcohol)forms molecular network in solution,which can prevent the aggregation of CdS particles.At the same time,ethylenediamine guides the 1D growth of CdS particles.Finally, CdS nanowires are obtained.The influence of manner of poly(vinyl alcohol) added on the morphology of products was also studied.In order to simplify the route and increase the application feasibility of this route,we substituted poly(ethylene glycol)for poly(vinyl alcohol)to improve the route.(2)Using L-cysteine as sulfur source and ethylenediamine as solvent, large quantities of CdS nanowires have been synthesized via one-step solvothermal route.The influence of experimental parameters on the morphology of CdS products was studied systematically.A growth mechanism of CdS nanowires was proposed.In the reaction system,Cd-cysteine complex plays an important role in adjusting the rate of S^2-releasing,the peptide formed from L-cysteine and ethylenediamine can serve as directing molecule for the growth of CdS nanowires.(3)3D urchin-like CdS microparticles or CdS nanowires have been synthesized via a simple solvothermal process without any additives.3D urchin-like CdS microparticles or CdS nanowires can obtained respectively by just adjusting the amount of added TGA,so CdS product can be morphology controlled.The growth mechanism was explored based on the results of comparative experiments.In the reaction system,the initial CdS particles aggregate with each other,and then the aggregations change into regular sphere-like aggregation generally.With effect of ethylenediamine,the adjacent particles in aggregations grow into nanorods,and the 3D urchin-like CdS microparticles are formed.(4)Novel dumbbell-like and necklace-like CdS microparticles were synthesized through a facile one-step hydrothermal route.The influence of reaction time,polymer kind,the amount of added polymer,sulfur source and reaction temperature on the morphology of CdS product was studied systematically.A nonequilibrium-equilibrium transfer growth mechanism was proposed.(5)Well-dispersed homogeneous CdS nanomaterial has been synthesized via thermal decomposition of precursor.In the thermal decomposition process of Cd-TGA complex,the formed CdS was wrapped and dispersed by glucose, which effectively prevent the aggregation of CdS.Then glucose was decomposed and carbonized,so CdS particles were wrapped by carbon,carbon also prevent the aggregation while the crystallinity of CdS particles is improved at high temperature.Finally,well-dispersed and high crystallinity CdS particles were obtained after carbon was oxidized.This thesis developed and improved the preparation methods of CdS nanomaterial.The preparation methods can be applied to preparing other nanomaterials.The experimental results are the basis of the application and development of CdS nanomaterials.