24 - Mechanistic aspects and rate-limiting steps in green synthesis of metal and metal oxide nanoparticles and their potential in photocatalytic degradation of textile dye

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The industrially developed countries possibly raising the rate of pollution in order to increase their economic activity, causing the environmental damage to a greater extent. More specifically the enormous quantity of water used by the textile industry hence, producing a significant amount of liquid effluent pollutants for processing of fabrics and generating toxic dyes to the environment. Annually the environment is discharged with near about 50,000 tons of synthetic dyes whic cause momentous water pollution worldwide. Various chemical, physical, and biological methods have been used for the reduction of these dyes from textile waste water which is not only costly and time-consuming but has problems in proper disposals. To conquer these problems, the photocatalytic degradation of dyes has been achieved by green-synthesized metal and metal oxide nanoparticles. The green approach of nanoparticle synthesis has gained more attention by researchers because of its nontoxic, ecofriendly, biocompatible, and for its sustainable nature. Hence, the destructive effects of traditional nanoparticle synthesis have replaced by mechanistic and rate-limiting green approach. Recently, the nanoparticles are vastly applied in various biomedical fields and also in photocatalysis process. The nanoparticles also show its application as catalyst, bioimaging, sensors, antioxidants, biotransformation, fuel cells, antimicrobial agents, etc. due to its free radical scavenging nature and smaller size. Recently, the attracting function of nanoparticle is the possible alternative to photocatalytic degradation of toxic chemicals or dyes than that of traditional methods. In this process, the UV–visible light along with catalysts is exposed to the pollutants or toxic chemicals for its degradation, which is inexpensive and there is no chance of formation of polycyclic compounds. In this chapter, we emphasized on the mechanistic green synthesis process of metal and metal oxide (Ag, Au, CuO, ZnO, etc.) nanoparticles using natural extract. We have also explored the possible role of reducing agent from various phytochemicals (i.e., flavonoids, alkaloids, terpenoids, amides, and aldehydes) and other biological components to determine the rate-limiting steps during green synthesis with its biophysical characterization and possible photocatalytic degradation of dyes from textile industry. Hope the present work shall explore new possibilities in safe degradation of textile dyes and reduce the water pollution to a greater extent.