Size Control Of The Citrate Caped Spherical Silver Nanoparticles In Hydrolyzing Conditions

Metal nanoparticles are intensively studied in recent decades due to its unique optical properties. electromagnetic properties, chemical and catalytic properties, thermal properties. And one of them. the silver nanoparticles besides having metal nanoparticles's unique properties, still have good thermal and electric conductivity and antibacterial property. And it is the most cheap metal in precious metals family that can be used for mass production, and has certain practical value and the economyBecause of the silver nanoparticles has a strong surface plasmon resonance absorption in visible area. near infrared area. so that it has a wide range of applications in the chemical and biological sensors. molecular imaging. surface enhanced Raman (SERS). Great efforts have been devoted to control over the size and shape of silver nanoparticles since it is well documented that their properties are both size-and shape-dependent.A variety of silver nanoparticles with different shapes such as nanodisk, nanoprism. nanoflower, nanowire and nanorod have been successfully prepared. Synthetic method is different, but can be roughly divide it into microwave method. electrochemical measurements.the research and chemical reduction method. Compared with traditional heating mode. the microwave method has fast heating. heated evenly. accurate temperature control etc. Characteristics. The electrochemical preparation of the nano particles has the advantage of mild. easy to control. and environmental pollution and so on. But now the most studied is chemical reduction method. Such as sodium borohydride, hydrazine. ascorbic acid, sodium citrate are commonly used as reducing agents. Sodium borohydride is too difficult to regulate its activity, so this method is difficult to control the synthesis of nanoparticles.and it is usually used for synthesis of spherical nano particles below 10nm; But sodium citrate is an active weak reducing agent, so the synthesized nanoparticles are more commonly dispersed. While reducing activity between in the reducing agent such as hydrazine hydrate. ascorbic acid and other reducing agents can chang the nanoparticles size by changing the concentration or pH.Since citrate has a good biocompatibility and can be easily exchanged with other ligand, for reference prepared by sodium citrate reduction of silver nanoparticles can be applied to biological systems. But because of its weak reduction, the ultimately prepared nanoparticles are polydisperse. At present, we can preare the shape uniform nano-particles by seed growth or stepwise reduction method, but the seed growth method is tedious, the stepwise reduction method can not achieve size control. Therefore, in this paper is mainly based on stepwise reduction method, by adjusting the number of nucleation reaction, to achieve the size control of spherical particles.The traditional sub-step nucleation selected pH values is less than 10. but due to the reduction capacity of sodium citrate is limited, it can not control the number of nuclear. So in the second chapter, we quantitative analysis the process of the system of the first pH values greater than 10.At last we determine the response to this condition can be divided into three stages, namely, a single in the first stage is the rapid consumption period, some of the silver ions at this time is hydrolysis, while the other part of the silver ions are reduced nuclear; in the second stage is a single consumption plateau, when the amount of silver ions that is reduced from the system and silver hydroxide solution from the same amount of silver ions is a balanced process; and the third stage, but also a rapid consumption of single process, this time silver hydroxide solution is completely dissociated, silver ions is only reducted. We also study the factors that affect the hydrolysis, from the side is confirmed the occurrence of complexation with silver ions and sodium citrate. Finally, according to different pH values of the first phase of the response have different concentrations of silver ions is reduced, that generate different numbers of nuclear, we can adjust the spherical silver nanoparticles in the size range of 87nm～150nm by step by step reduction method using high pH. as nuclear, low pH values (pH=6.1) prepared under Slow growth...