Preparation of indigo dye
2.2.2.1. Reference indigo dye. In order to obtain indigo dye, approx. 3.0 g of 2-Nitrobenzaldehyde was dissolved in 9.0 cm3 acetone. In the next step, 8.0 cm3 of deionized water was added to previously prepared solution under continuous stirring. Next, 15.0 cm3 of aqueous solution of sodium hydroxide at a concentration of 1 mol/dm3 was dropped into the mixture. The stirring was turned off and the mixture was left for approximately 10 min. The crystallized dye was filtered under reduced pressure with a filter with a pore diameter of 0.2 m. The precipitate was washed with 20.0 cm3 of deionized water and 15.0 cm3 of ethyl alcohol. Subsequently, it was left to dry at room temperature. The resulting dye, which served as reference material, was analyzed by scanning electron microscopy (SEM) and by Fourier transform infrared spectroscopy (FT-IR). FT-IR analysis were performed using Nicolet 380 spectrophotometer by Nicolet Co.