Role of Black Tea in the Advancement of Nanotechnology: A Critical Review.

Black tea (BTE), a well-used beverage, has immense applications in nanotechnology. The extract of black tea can perform as a reducing and capping agent for forming metal and metal oxide nanoparticles (NPs). Though many metal nanoparticles are reported to be formed employing black tea extract, Ag- and Fe-based nanoparticles are mostly found in the literature. Among the different constituents of BTE extract, catechin and epigallocatechin gallate are responsible for the passivation of the nanoparticles due to the oxidation of the polyphenol moiety. Such nanoparticles, being capped with BTE, exhibit direct and indirect applications, including anticancer, antifungal, cytotoxicity, cell viability, Aflatoxins B1 adsorption, and dye removal applications. BTE is a natural reducing and capping agent that produces zero-valent metal nanoparticles. However, ZnO and CuO nanoparticles are also found in the literature due to subsequent oxidation of the zero-valent metalized surface. We included the synthesis, applications, and mechanistic details of nanoparticles passivated with BTE. Moreover, we summarized the effect of components in nanotechnological applications. As BTE is nontoxic, its involvement makes the process green and warrants a detailed review for the young researcher in nanotechnology. No review article is available regarding the nanometric application of BTE, justifying our present Review's novelty and originality.