Abstract
Among the different substances containing organic compounds, dyes are considered the most important class, and they are now an essential requirement in the modern world, mostly in the textile industries. In addition to the textile colouring, they are used in automobile, leather, paints, paper industries, etc., but their importance in the textile industries is maximum. Because of huge demand of dye, the production of a variety of dyes with advanced properties has drastically increased. Since dyes are complex aromatic organic compounds containing conjugated double bonds, they are highly toxic to the biological community of the world. In this chapter, more emphasis is given for synthesis technologies of various kinds of dyes, different kinds of hazardous pollutants generated from the dyeing industries, and their environmental impact along with the implementation of the technology developed to reduce the pollutant and its effect to our sustainable environment. Hence, more focus has to be given for manufacturing and application of dyes from renewable natural resources.
TopIntroduction
The chemical substances or the materials which are fastness to water, light, heat, moisture, dilute acids, alkalis and used for imparting colour in the materials like paper, textiles, lather etc.is known as dye. The dyes may be natural or synthetic which mostly dispersed in the liquid phase and produces paints, inks or it may be blended with other materials and enhances the colour and beauty of the manufactured products. Dyes are mainly organic aromatic complex compounds, whereas the pigments are organic or inorganic compounds, but both are given bright colour when imparted on any materials or textiles simultaneously. Dyes and colours both are different in natures. The colour is not resistant to acids, alkalis sunlight, water and all other environmental factors and is directly related to the structure of the molecules of the dye. The colour imparted by dyes is due to the following reasons.
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Due to absorption of visible light in the range of 400-700 nm
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It contains chromophore groups within its molecules, which are the colour imparting groups.
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Contains alternate single and double bond with the conjugated system in its molecular structure
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The stabilization of the dye is due to resonance within the aromatic ring of the molecule of the dye i.e. the migration of conjugated electrons will occur within the alternating single and double bond. If any of the features among these is not found, then the dye losses its property of imparting colour. Most of the dyes contain chromophores along with another group known as auxochrome, which has the property of enhancing the efficiency of auxochrome.(L.A. Thi et. al. 2018)
Examples: The groups like carboxylic, sulphonic, hydroxyl etc. are not responsible for imparting colour but if it is present in the molecule of the dye it can influence imparted colour i.e. shifting of the colour of the colorant present in the dye.
Key Terms in this Chapter
Degassing: The emission of gases from a planet either directly during volcanism or May indirectly during weathering of ignited rocks on a plane surface is known as degassing.
Hydrophilic: It literally means water loving (i.e., it is the property of more favourable interaction with water and forms hydrogen bonding with the molecules interact with water).
Anaerobic: The process of treatment of water by using anaerobic bacteria in the absence of oxygen or air and converting the COD or organic matters in to simple biogas is known as anaerobic treatment.
Hydrophobic: It literally means water hating (i.e., the property of molecules not interacting with water).
Aerobic: The treatment of water or waste water effluents by using aerobic bacteria in the presence of oxygen or air is termed as aerobic treatment process.
Anoxic: It is the process which is mainly used for removal of nitrogen from the waste water effluents by the process of denitrification in which the nitrogenous compounds present in the effluents converted into nitrate which is again converted into free nitrogen gas and nitrous oxide.
Biological Oxygen Demand (BOD): The amount of dissolve oxygen required during a specified period of incubation (5 days) for complete biochemical oxidation of organic matter present inside the water bodies at a temperature of 25 o C is known as biological oxygen demand.
Chemical Oxygen Demand (COD): The amount of dissolve oxygen necessary for complete biodegradation of chemically oxidizable substances present inside the water bodies is known as chemical oxygen demand.