Synthesis, Characterization And Modification Of Silver Nanopaticles By OIL-Water Interface Method

As an advanced functional material, oil-soluble silver nanoparticles have been widely used as catalytic materials, cryogenic superconducting materials, biosensor materials, microelectronic materials, and antibacterial materials. The capability of silver nanoparticles is dependent on their structure, shape, size, size distribution and the chemi-physical environment. Generally, these properties can be affected by employing different synthetic techniques. Thus, it is necessary to study the nucleation and growth mechanism of the silver nanoparticles. In this work, well-dispersed silver nanoparticles were synthesized by oil-water interface method. Compared with other methods, it had many advantages, such as, simple operation, mild reaction conditions, controllable particle size, available reactants, low cost and high efficiency. To optimize the synthesis of silver nanoparticles, the effects of organic solvents, surfactant concentration, pH, the concentration ratio of different reactants, reaction temperature, reaction time and reaction system were discussed in detail. Furthermore, hydrophobic silver nanoparticles, modified by alpha cyclodextrins, have been successfully transferred into water.The main research results of this paper can be briefly described as follows:(1) Silver nanoparticles of face centered cubic crystalline were successfully synthesized by oil-water interface method. The obtained well-dispersed products were of neat morphology and even size. TEM images showed that the mean size of the products was8.4±1.1nm while UV-Vis spectrum displayed that the absorption peak was at408nm or so. (2) Using different characterization methods, the optimum reaction conditions about synthesis of silver nanoparticles were concluded in the following:using the toluene as organic phase,7.5mL oleic acid as surfactant (the total volume of oil and water is165mL), sodium borohydride as reducing agent, pH value for8.0and the reaction time for two hours. Besides, the volume ratio between oil and water phases was1:1while the ratio of [Ag+]:[BH4-] was1:3.(3) The possible formation mechanism of monodispersed particles prepared in oil-water interface was deduced in this paper. The probable process was that reactants dispersing in two phase firstly diffused onto the oil-water interface and the adsorption of surfactants on the nuclei took place upon the nucleation occurred.(a) The rapid adsorption showed that the nuclei generated from the oil-water interface were capped by surfactants swiftly and then the nanoparticles entered into the oil phase spontaneously, resulting in the inhibition of the particle growth. Therefore, the monodispersed silver nanoparticles were obtained easily. Meanwhile, higher the reaction temperature was, easier the surfactants reached the interface to cap the nuclei, and the adsorption mainly displayed in the fast way in this situation.(b)The slow adsorption showed that the lower the concentration of surfactants, the slower adsorption to the interface of the nuclei the surfactants showed. The particles didn’t enter into the oil phase until the adsorption of surfactants to the nucleus increased to sufficient quantity, and the particles continued growing as the new reactants deposited onto the nuclei, therefore the final particles might have various dimensions and the polydispersed silver nanoparticles would be obtained. Therefore, the absorption velocity of surfactants to the nuclei was the key factor which determined the dispersion of silver nanoparticles. In this work, we adopted the proper concentration of reactants and surfactant at the temperature of100℃in preparing silver nanoparticles, then the adsorption mainly displayed in the fast way under these conditions and the products had the good monodispcrsion.(4) Hydrophobic silver nanoparticles, modified by alpha cyclodextrin, have been successfully transferred into water. The results showed that this method could transfer silver nanoparticles dispersed in cyclohexane completely into water in48h. And after modification by alpha cyclodextrin, UV-Vis spectrum showed that the adsorption peak of silver nanoparticles became redshift, from408nm to413nm. TEM image displayed that no obvious shape or size change was found between the sample before and after phase transfer. Meanwhile, when the concentration of oil-soluble silver nanoparticles was0.5g/L, the influence of alpha cyclodextrins concentration was also discussed for the transferring efficiency of the hydrophobic silver nanoparticles. The results showed that when the concentration of the alpha cyclodextrins was7mM, and surface modification of silver nanoparticles reached saturation. UV-Vis spectrum displayed that ultraviolet absorption strength of silver nanoparticles in the water was the highest. demonstrating the best transfer. After modification by alpha cyclodextrins, the hydrophilic products can be further applied to biological marker, biological monitoring, catalysis, etc.