2.2.2.2. Indigo dye modified with silver nanoparticles. Silver nanoparticles were prepared in-situ during the synthesis of indigo dye. Nanoparticles were obtained based on a chemical reduction method in aqueous phase. Silver nitrate was used as a source of silver ions and tannic acid served as a reducing and stabilizing factor. The aim was to produce three dye materials differing by silver concentration in relation to the theoretical mass of indigo dye (1.3 g). 3.0 g of 2-Nitrobenzaldehyde was dissolved in 9.0 cm3 acetone. In the next step, an aqueous solution of silver nitrate (V) and an aqueous solution of tannic acid were added to the previously prepared solution. Their total volume was equal to
the volume of water used in the reference indigo dye production process. Subsequent steps were the same as that used for obtaining pure indigo. The filtrates were subjected to spectrophotometric analysis (UV–vis) and to inductively coupled plasma with optical emission spectrometry (ICP-OES). UV–vis analyses were performed using Rayleigh UV1800 spectrophotometer. ICP-OES analysis were conducted on Plasm 40 apparatus by Perkin Elmer Co. In order to
confirm the presence of silver nanoparticles in the modified dye, the dried products were analyzed by scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS) and by FT-IR. EDS analysis were performed using 1430 VP microscope by LEO Electron Microscopy Ltd. equipped with EDS spectrophotometer and using the HITACHI S-4700 NORAN Vantage microscope equipped with system for microanalysis. Table 1 presents the parameters of the processes used to obtain indigo dye modified with silver nanoparticles. It also displays in detail the nominal concentration of silver in relation to the theoretical mass of indigo dye (CAg(ind-Ag)), the volume of silver nitrate aqueous solution (VAgNO3(ind-Ag)), the volume of tannic acid aqueous solution (Vtan(ind-Ag)), concentrations of silver nitrate aqueous solution