Preparation And Growth Mechanism Invistigation Of Cu₂O And Cu₂O/Ag Nanostructure

Cu₂O,Ag and their composites are important inorganic functional materials and due to their excellent properities,have been widely used in photocatalysis,solar cell and sensing.The morphology of Cu₂O is crucial to not only the direct applications of it,but also the synthesis of Cu₂O-based composite with novel structure.To better utilize Cu₂O,Surfactant is commonly used to control its morphology.But generally there is more than one type of ion or molecule that exists in the precursor and functions as surfactant.Thus,it is necessary to analyze the effect of individual ion surfactant on the morphology.Recently many researchers reported Cu₂O/Ag composite.On the contrary,the self-assembly growth of Ag nanostructures by Cu₂O has been scarcely reported and consequently the corresponding growth mechanism was not deeply researched.Therefore a further study is needed.Meanwhile,when using Cu₂O to grow Ag nanowires,the capability of controlling their orientation is very fascinating,because aligned one dimentional?1D?material array commonly exhibits better or novel performance in various applications.Heretofore great efforts have been made to devise synthesis methods of aligned 1D material array.The"grow-in-place" method is promosing candidate as it provides facile control over the 1D material array.But unfortunately researchers have reported only a few successful syntheses based on this strategy up to now.Therefore it is still appealing to.expand the applications of this strategy.From the above discussion,in this paper I synthesized concave apex-truncated Cu₂O microcrystal and analysed its growth process.The influence of ion surfactant on the morphology of Cu₂O was explored by centrifugation.Furthermore,this paper also extensively studied the effect of various parameters on the morphology of Ag nanostructures synthesized by using metal oxide,Cu₂O,as reductant and,based on the observation,proposed the corresponding growth mechanism.Finally,this paper reported a "grow-in-place" method that guided grew aligned Ag nanowires on curved substrate,PET,by Galvanic Replacement.The details are discussed below.1)The nucleation stage of Cu₂O crystal is long,and therefore its growth process is consistent with the sol-gel growth mode instead of Lamer mode.The decrease of growth speed in the the later stage of growth process make the octahedra Cu₂O develope concave apex-truncated octahedra morphology.By centrifuging the Cu?OH?2 gel,the ions are separated from it and it is discovered that OH-initiate the reduction and SO42-plays a crucial role in developing the Cu₂O crystal into octahedra morphology.This centrifugation method can be extended to organic surfactant,PVP.Experiment results shows that a competition for adsorbing on Cu₂O {111} faceto occurs between different surfactant,OH-,SO42-and NO₃-,which,on the other hand,have different power in controlling the morphology of Cu₂O.2)In AgNO₃ solution,Cu₂O microcrystals isotropically release Cu₂O nanoparticles,which diffuse around the Cu₂O microcrystal and,seveing as growth substrate and redutant,galvanic replace Ag+ into Ag nanostructures.Therefore the GR has a localized nature and consequently spontaneous nucleation occurs,leading to the interrupted features in the synthesized Ag nanostructures.High Ag+ concentration arouse the MS instability,which make Ag+ transfers not only to the growth front but also to the sides of it.This promotes the lateral growth of the growth front,and in the end results in Ag dendrite.Real-time observation of the growth of Ag nanowires illustrates that the growth speed fluctuates around the average speed?74 nm/s?,which shows no decrease with the growth procceding.The developing nanowires contain incompletely oxidized Cu₂O.Thus,post-cystallization occurs after the growth process ends.The size of Cu₂O microcrystal exerts limited influence on the morphology of Ag nanostructure.Compared with {111} facet of Cu₂O,{100} facet releases much smaller amount of Cu₂O nanoparticles,which leads to a great difference between the morphology of Ag nanostructures synthesized by Cu₂O cube and that by Cu₂O cube-octahedra and octahedra.More specifically,the reaction of GR by cube mainly occurs in the vicinity of the cube.The concentration of Ag+ influcences the reaction speed and diffusion speed of Ag+,which determines the morphology of synthesized Ag nanostructures.On the other hand,light irridition,heating and stirring the precursor solution increase the reaction or growth speed,and thereby modifying the morphology of the synthesized Ag nanostructures.3)The surface energy of Ag nanowires exposed to the solution is higher that attached on the substrate.Therefore,because the Ag nanowires extending in parallel with the curvature axis expose less proportion of surface than those following different directions,they tend to grow along the axis direction.When the curvature is reduced,the difference in surface energy between different directions is enlarged and correspondingly the Ag nanowire array will be more aligned.A second growth of Ag nanowire in different dirction produce Ag nanowire network.This novel method of guided can potentially be applied in different situations,for example,aligned Ag nanowire array has been successfully synthesized by using Zn microcrystal?substitute Cu₂O microcrystal?as reductant or PS?substitute PET?as growth substrate.