Study On The Synthesis And Growth Mechanism Of Silver Nanowires By Cl~- And Br~- Controlled By Polyol Method

Silver nanowires?AgNWs?have received extensive attention in many different fields,due to their unique structure and excellent electronic,catalytic,optical and other related properties.Their good electrical conductivity and flexibility are considered as The best alternative to traditional rigid ITO transparent electrodes,but large-scale industrial production cannot be achieved due to higher production costs and lower yields.In this work,silver nanowires were prepared by polyol method using NaCl and KBr composite metal salts as the mediator.Silver nitrate was used as the silver source,ethylene glycol was used as the reducing agent and solvent,and polyvinylpyrrolidone was used as the growth directing agent.SEM and XRD were used.The surface morphology,phase structure,optical properties,microstructure and chemical state of the obtained silver nanowires were analyzed by UV-vis,TEM and XPS.The effects of various reaction variables on the formation and morphology of silver nanowires were tested.The optimized experimental procedure was obtained:when the reaction temperature was 160?,the ethylene glycol preheating temperature was 175?,and the molar ratio of PVP to AgNO₃ was obtained.When the concentration of AgNO₃ is 0.1 mM,the concentration of NaCl is 0.4 mM,and the stirring speed is 300 rpm,silver nanowires having uniform diameter,high aspect ratio and high yield can be obtained.The main phase of the obtained impurities is a face-centered cubic silver structure and a small amount of AgCl,which can create a nucleation site for the nucleation of the silver crystal nucleus.The molecular weight of PVP has a decisive influence on the formation of silver nanowires.The small molecular weight PVP cannot form silver nanowires.The critical average molecular weight of silver nanowires formed in this system is about 24000.As the average molecular weight of PVP increases,the length of silver nanowires increases.The ratio of diameter to diameter is obviously increased.When the molecular weight is 1,300,000,silver nanowires with an aspect ratio of more than 1000 can be obtained.The carbonyl oxygen of PVP interacts with the silver atom on the surface of the silver wire to reduce the electron cloud density of the carbonyl oxygen atom,and preferentially adsorbs at?100?.The crystal face inhibits its lateral growth.The growth process of silver nanowires is mainly divided into:reduction,nucleation,growth and coarsening.A large number of decahedral twin nucleus and single crystal nucleus can be observed in the system after 5 minutes of complete dropping of silver nitrate into the reaction solution.The decahedral seed crystals are anisotropically grown to form silver nanowires with a growth direction of[110].Adding NaCl as a control agent in the reaction system can reduce the reaction rate and stabilize the aggregation of silver nuclei.When the NaCl concentration is 0.4 mM,silver nanowires with good uniformity can be obtained.Adding trace amounts of KBr to the system can significantly reduce the diameter of silver nanowires.By increasing the aspect ratio,silver nanowires with a diameter of less than 30 nm can be obtained by process adjustment,but the yield is low,and Br^-does not change the crystal structure of the silver nanowires;the energy spectrum analysis by transmission electron microscopy shows that the surface of the silver nanowires A small amount of bromine is used to simulate the adsorption of Br^-on different crystal faces of Ag.It is found that Br^-selectively adsorbs on the surface of Ag,and its adsorption energy on the?100?plane is significantly higher than that of the?111?plane.Therefore,Br^-may adsorb on the?100?plane,inhibiting its lateral growth,thereby reducing the diameter of the silver wire.