Preparation And Morphology Control Of Gold Nanoparticles

The present work is to develop an aqueous-phase method to synthesize gold nanoparticles with different shapes,characterize their crystalline structure,size,shape,and optical properties with TEM,SEM,XRD,and UV-Vis,analyze the mechanism of the formation of different-shape gold nanoparticles.The main results are outlined as follows:(1) Structure and spectroscopic study of single-crystal gold nanoplates synthesized by low-temperature chemical reducingIn this work,gold nanoplates were successfully synthesized from the reduction of HAuCl₄ by ascorbic acid,in the presence of poly(vinyl pyrrolidone)(PVP).The morphologies and structure of the products were characterized by TEM,HRTEM and UV-vis spectrum. TEM images indicate nanoplates were fcc single crystals with average edge length of 600 nm. For the first time,their UV-vis spectrum not only show a strong absorption peak and a weak absorption peak centered at～975 nm and～580nm,which originated from in-plane dipole resonance and out-of-plane dipole resonance respectively,but also show two quadrupole resonances which appeared at 740nm and 835nm.A preliminary growth mechanism is also proposed to explain the formation of nanoplates.It is believed that PVP induced different growth rate of various facets of nuclei.(2) Nitric Acid Induced Seed-Mediated Growth of Gold Nanobelts and Their Spectroscopic StudiesSingle-crystal gold nanobelts were successfully synthesized by a seed-mediated growth method in the presence of nitric acid.The morphologies and structures of the products were characterized by TEM,HRTEM and UV-vis spectrum.TEM images indicated nanobelts were dominant morphology with perfect fcc single-crystal structure.Their absorption spectra show a strong longitudinal surface plasma resonance(SPR) band and a weak transverse SPR band centered at～975 nm and～550 nm,respectively.A possible growth mechanism were also proposed to explain the formation of nanobelts,dipole-dipole interaction between adjacent nanoplates was regarded as driving force to assemble plates into belts.It is believed that nitric acid plays an important role in the formation of nanobelts.(3) Self-assembly gold nanoparticle synthesized by low-temperature chemical reducing systemThe gold nanoparticles were fabricated tentatively by the reduction of HAuCl₄ with AA in the presence of CTAB as a stabilizing agent in NaOH solution.The products were characterized by TEM and UV-vis spectrum.TEM images indicate diameter of nanoparticles is about 60～100nm.UV-vis spectrum show a strong absorption peak centered at 522～or～589nm.