SYNTHESIS AND OPTICAL PROPERTIES OF NANOCOMPOSITES BASED ON LIQUID CRYSTAL WITH BIMETALLIC Au + Ag NANOPARTICLES OF ALLOY TYPE.

Abstract

In this work, we have carried out a research which aimed to obtain complex nanoparticles of noble metals Au + Ag in the form of bimetallic alloys. Bimetallic nanoparticles were synthesized directly in a liquid-crystalline cadmium caprylate melt in an argon atmosphere in the temperature range of mesophase existence by the simultaneous chemical reduction of cations of gold (Au3+) and silver (Ag+) from their compounds, tetrachloroaurate acid (H[AuCl4]×3Н2О) and silver  nitrate AgNO3, respectively.   The effect of synthesis duration (3 and 5 hours) on the spectral behavior of binary nanoparticles have been studied. It has been shown that when the synthesis duration is 3 h, mainly homogeneous bimetallic alloys are obtained, and when it is 5 h, both homogeneous and gradient alloys can be obtained. The absorption spectra of homogeneous alloys are characterized by the presence of one surface plasmon resonance (SPR) peak, which occupies an intermediate position relative to the SPR peaks for monometallic nanoparticles, i.e. between 425 and 560 nm. When forming heterogeneous alloys, which are formed in the molar ratio range where the amount of silver ions predominates, the absorption spectra exhibit two SPR peaks which relate to nanoparticles with different metallic silver content. The formation of metallic nanoparticles containing different metals may be due both to the different mobility of noble metals ions in the liquid crystal matrix and to the different rate of rearrangement of metals in the new formed heteronanoparticle.   It has been found by electron spectroscopy and transmission electron microscopy that the nanoparticles in this matrix have mostly a spherical shape with a mean diameter of 15 nm. The possibility of the fine control of the position of SPR peak of bimetallic nanoparticles in a liquid crystal matrix over a wide optical range   of  422–580 nm is shown.