Study On The Preparation Of Silver Nanoparticles By Chemical Reduction Using Sodium Hypophosphite In Solution

Silver is a cheaper kind of noble metals. It is widely used as optics materials, ornamental materials, conducting electricity and transmitting heat materials, catalysts, and medicine materials, etc. Because of their unique properties of volume effect, the surface effect, the quantum dimension effect and macro-quantum tunnel effect, the silver nanoparticles have a lot of the specicific usages such as the special functions in superconductive, chemistry, optics, medicine and antimicrobial etc. Therefore silver nanoparticles are materials with good prospect.There are many methods of preparation of silver nanoparticles, and in which the chemical reduction in liquid phase is the method we often use in present laboratory and in industry, because this method has many advantages. First, the process conditions are easily controlled. Second, the method does not need advanced equipments. Third, the sliver nanoparticles distribute narrowly and it can be produced efficiently. And because of its advantages, the method suits for large-scale production of silver nanoparticles.In this paper, the silver colloids were prepared by the chemical reduction in liquid phase using silver nitrate, sodium hypophosphite (as reducer), sodium hexametaphosphate (as disperser), and polyvinylpyrrolidone (as protective agent). Through controlling reaction condition, the spheroid, dispersible and the stable silver colloids were prepared. The affecting characters of colloid were researched such as temperature, the proportion of reactions (n(NaH₂PO₂)/n(AgNO₃), m([NaPO₃]₆)/m(AgNO₃),etc.), pH of solution. Comparing to the results of experiments, the better condition of preparation of sliver colloid was summarized. A dispersible and stable silver colloid was synthesized at 50 ℃, c(AgNO₃)=1.0 mol/L, c(NaH₂PO₂ H₂O)=0.1 mol/L, the dosage of Na₂PO₄is two and half time of theoretical dosage, m(PVP)/m(AgNO3) = 1.0-1.2, m([NaPO3]6)/ m(AgNO3)= 0.1- 0.2, pH=l², the reaction time is about 1 hour. The nanosized silver colloid is brown .And the morphology and structure of synthesized silver colloid was characterized on transmission electron microscopy (TEM). The result shows that the morphology of Ag particles is spherical and the mean size is about 7-10 nm.In order to solve the problem of separating silver solid nanoparticles from colloid, which was synthesized through reduction in solution, the characters of silver nanosized colloid were researched. Zeta potentials of colloid in different pH were measured, and the relationships between colloid's pH and the average size of sliver particles were shown. And some alkaline agents such as ammonia, organic alkaline agent, flocculation agent, and admixture agent were used to adjust the pH of colloid. The relation between pH and agglomeration of silver colloid was investigated. The concentration, particle size distribution, dispersibility and morphology of silver nanoparticles were studied. The results show that silver particle size was controlled by adjusting pH of colloid with 5wt% ammonia. Average size of silver nanoparticles from 30 tolOO nm were produced by controlling pH=3⁶. The structure, morphology, purity and concentration of silver powders were characterized using XRD, TEM, FT1R, LPSA and AAS. The results also show that the silver particles appear spheroid, with good dispersibility, arrow size contribution, and the average diameter about 35 nm (pH³). Furthermore, smaller silver powders were produced through separated by admixture agent. After purified, cleaned, and dryness, these silver powders are proved without Ag2O and organic group by XRD, FTIR and ASS etc. The purity of silver powder is about 96%, and there is trace impurity. The morphology of the silver particles appears spheroid, with good dispersibility, arrow size contribution, and the average size is about 10-20 nm.Two antioxidants (oleic acid and 1,2,3-benzotriazole) on affecting anti-oxygenation of silver powders were compared. And both antioxidants are good for avoiding the silver powders oxidated. But 1,2,3-benzotriazole is easy to dissolved in the water, so it is more practical and after dryness the silver powders have good character.The dispersibility and purity of three samples, which were dried by three methods such as nature dryness, vacuum dryness and vacuum freezing evaporation, were compared. The results show that the silver powders are not oxygenated with three dryness methods, and the silverpowders dried with vacuum freezing evaporation have best dispersibility. The vacuum dryness is efficient and the silver nanoparticles dried with vacuum dryness are purer.To decrease the coagulation of silver particles, penetrating agent T as dispersant to soak and disperse conglomeration of silver particles. Comparing with water and ethanol, the penetrating agent T is the best dispersant to silver powders. And the silver nanosize colloid which was dispersed again with the penetrating agent T was stabile after a long time (more than 14 days).In this paper, process to produce concentrated silver colloid was studied. When the concentration of silver particles in colloid is less 50 g/L or so, the silver nanosized colloid has good stability, and the average size of silver particles is less 10 nm. When the amount of volume is about 1.5 L, the stable and dispersed silver colloid can still be sythesized. So it was confirmed that scale-up experimentation recur and with good stability.By optimizing the whole process of preparation, three kinds of nanosized silver products were produced. They are silver nanosized colloid, silver nanoparticles l*and silver nanoparticles 2*.Through testing, different productions technological parameter were listed. From the social situation demands, the paper discussed the process of reclaiming castoff of silver.Also, some antibacterial experiments were made to test the antimicrobial ability of silver nanoparticles made by us, and silver nanoparticles were added to paint to make antibacterial coating. Some antibacterial experiments results show that doping silver coating kill and restrain virus well. And when concentration of silver nanoparticles gets to 0.02wt%, above 90% virus can be killed.