POLLUTION_CONTROL_IN_DYE_INDUSTRY-_22-04-09.ppt

POLLUTION CONTROL IN DYE INDUSTRY K.Suthagar National Centre for Catalysis Research Introduction A dye can generally be described as a colored substance that has an affinity to the substrate to which it is being applied. The dye is generally applied in an aqueous solution, and may require a mordant to improve the fastness of the dye on the fiber Both dyes and pigments appear to be colored because they absorb some wavelengths of light preferentially. In contrast with a dye, a pigment generally is insoluble, and has no affinity for the substrate. Electronic excitation energies σ → σ* π → π* n → σ* n → π* aromatic π → aromatic π* Chromophore: it is a functional groups which are unsaturated and they cause a compound to become coloured. Examples of chromophores are –N=N-, -C=C-, -C=N- and -C=O. 1. Transitions involving σ, π, and n electrons 2. Transitions involving charge-transfer electrons 3. Transitions involving d and f electrons Auxochrome Auxochromes are groups that does not impart color to the compound but increase the color of the compound. Functional groups such as hydroxyl (–OH), amino ( -NH2), nitro (-NO2), alkyl (-R), —OH, —OR, —NH2, —NHR, —NR2, —SH are common examples for auxochrome. The effect of the auxochrome is due to its ability to extend the conjugation of a chromophore by the sharing of non-bonding electrons. Bathochromic Effect Hypsochromic shift Hyperchromic Effect Hypochromic Effect Pictorial representation of bathochromic shift and hypsochromic shift in the absoption spectra Typical data on some chromophre CLASSIFICATION OF DYES Acid Dyes These are generally applied to textile fibers from dye baths containing acid. Most have one or two sodium sulfonate (–SO3Na) groups which are water soluble and capable of bonding with fibers having cationic sites. They give a wide range o