Synthesis Of Monodispersed Silver And Copper Nanoparticles Via Chemical Reduction Methods

As a new kind of advanced functional materials, silver and copper nanoparticles with unique physical and chemical properties, have received considerable attention, because they are widely used in optical materials, catalyst materials, antibacterial materials, biological sensor materials, coating, battery electrode materials, anti-static materials, and superconductiong materials, etc. Generally speaking, the properties as well as the corresponding applications of the silver and copper nanoparticles are mostly dependent on the size, size distribution, shape and stability of the metal nanoparticles. Apparently, accurate and controllable synthesis of silver and copper nanoparticles has been and continues to be one of the hot topics in research of nano materials. The precise controllable synthesis of silver and copper nanoparticles allows not only to investigate unusual properties of metal nanoparticles but also to adjust their physical and chemical properties as desired. Firstly, the preparations as well as the properties of silver and copper nanoparticles are introduced in brief. Particularly, the green synthesis of silver nanoparticles is discussed in detail. The shortcomings of relevant research fields in silver and copper nanoparticles are also pointed out. Subsequently, the research on the controlled synthesis of silver and copper nanoparticles are performed, such as preparation of monodispersed silver and copper nanoparticles via chemical reduction method, syntheisis of small sized silver nanoparticles by green method. Furthermore, the preliminary studies of their applications are carried out. The research work maily includes the following aspects:Syntheis of silver and copper nanoparticles via traditional methods:(1)Silver nanoparticles with narrow distribution were prepared by using lauric acid as capping agents, hydrazine hydrate as reducing agents, and silver ammonia as silver source. Lauric acid, was firstly dissolve in water in presence of ammonia and then can serve as capping agents to synthesize silver nanoparticles. The results show that the lauric acid can combine with silver ions to form a complex compound, which decrease reducing rate of silver and hence reduce the size of silver nanoparticles. The mass ratio of lauric acid to silver nitrate and the reaction temperature have great influence on the size of the synthesized silver nanoparticles. Well-dispersed silver nanoparticles with an average diameter of8nm are obtained when the mass ratio of lauric acid to silver nitrate is1.2:1, and the reaction temperature is room temperature. The HRTEM and XRD reflect the high crystallinity of the silver nanoparticles.(2) Poly-acrylic acid ammonium (PAA-NH4) is water-soluble polymer surfactant, which can be served as capping agents to prepare metal nanoparticles. In the synthesis process, silver nitrate or silver ammonia is used as silver source, and hydrazine hydrate or glucose is acted as reducing agents. The results reveal that small sized silver nanoparticles can be obtaind by using silver ammonia as silver source, and hydrazine hydrate as redcuing agents. Furthermore, the amounts of capping agents play an important role in the formation of silver nanoparticles. Approximately spherical, uniform silver nanoparticles with an average size of10nm are obtained when the weight ratio of poly-acrylic acid ammonium to silver nitrate3:2.(3) Silver nanoparticles with narrow distribution from3-15nm are prepared by using stearic acid and hydrazine hydrate as capping agents and reducing agents respectively. In the synthesis process, the stearic acid is dissolved in water by heating the mixture of stearic acid and ammonia water, and hence the stearic can be served as capping agents in the preparation of silver nanoparticles. In the system, the size of the silver nanoparticles can be adjusted by controlling the reaction parameters. The effect of reaction temperature and the weight ratio of stearic acid to silver nitrate, ammonia water on the size of silver nanoparticles are investigated.(4) A simple method was put forward for the preparating colloid copper nanoparticles in aqueous solution using gum acacia, hydrazine hydrate and copper sulfate as capping agents, reducing agents and copper precursor, respectively, without any inert gas. The formation of copper nanoparticles is confirmed by its characteristic surface Plasmon absorption peak at604nm in UV-vis spectra. The SEM and TEM images reveal that the synthesized copper spherical particles are distributed uniformly with a narrow distribution from3-9nm. The average diameter of the copper nanoparticles is5nm. The XRD and HRTEM demonstrate that the obtained metal nanoparticles are single crystalline copper nanoparticles. The FT-IR dates suggest that the copper nanoparticles are coated with gum acacia. The growth process of metal nanoparticles is monitored by the UV-vis spectra. The effects of gum acacia and hydrazine hydrate amounts on the size of nanoparticles are investigated by TEM images and UV-vis spectra. The formation mechanism of copper nanoparticles is also discussed.Synthesis of silver nanoparticles by green methods:(1)A simple and environmentally friendly method is developed for preparing colloidal silver nanoparticles in aqueous solution using hydroxyl propyl methy cellulose (HPMC) or sodium alginate (NaAlg) as capping agents respectively. In this method, glucose and silver nitrate are used as reducing agents and silver precursor respectively. The TEM images demonstrate that the HPMC capped silver nanoparticles are from3-17nm, and the NaAlg capped silver nanoparticles are from3-12nm. The XRD and HRTEM reveal that the metal particles obtained by HPMC or NaAlg are single crystalline silver nanoparticles. The UV-vis spectra show that the concentration of silver nitrate and glucose, the reaction time and temperature have a great effect on the size of silver nanoparticles.(2) Gum acacia is also used to prepare silver nanoparticles. In this method, small and monodispersed silver nanoparticles are simply obtained by heating silver nitrate and gum acacia in aqueous solution. The gum acacia is served as reducing agent as well as capping agent. The synthesized silver particles are single crystalline single crystalline silver nanoparticles with a narrow distribution from2-20nm. The effects of the silver nitrate concentration, gum acacia amount, reaction time and temperature on the particles size are discussed. (3) Small size and monodispersed silver nanoparticles are prepared at room temperature by using osmanthus fragrans extract and silver nitrate solution as raw materials, without adding any other reducing agents and capping agents. In the synthesis process, the color the solution are changed from colorless to yellow, indicating the formation of silver nanoparticles.The formation of silver nanoparticles also confirmed by its characteristic surface plamon absorption peak at440nm in UV-vis spectra. The TEM and SEM show that the as-synthesized silver nanoparticles are distributed uniformly with a narrow distribution from2-30nm. The HRTEM and XRD results demonstrated that the obtained metal particles are single crystalline silver nanoparticles. The effects of silver nitrate concentration and osmanthus fragrans extract amount on the particles size are investigated.(4) Semen cassiae extract are also ued for the green synthesis of silver nanoparticles at room temperature in silver nitrate solution. The semen cassiae extract are acted as reducing agent as well as capping agent. The obtained silver nanoparticles are spherical in shape with a size distribution from2-35nm. The XRD and HRTEM confirm the highly crystallinity of silver nanoparticles. The effect of reaction time and semen cassiae extract amount on the particles size are studied. The results show that the higher amount of the semen cassiae extract, the yields and bigger size of silver nanoparticles are formed. Gradually longer reaction time, increase the corresponding particles size. The as synthesized silver nanoparticles are tested against Escherichia coli and the obtained data are indicative of good antibacterial properties of the materials.