## 2 Utilization of Various Nano-Modified Coatings for Corrosion Mitigation
### Plant Extract and Natural Source-Based Nanoc coatings  
The examination of the utilization of nanotechnology in various biological phenomena is known as nanobiotechnology, which is the fusion of biology and nanotechnology [73; 79]. Making biocompatible, environmentally safe, and biologically active NNs and NPs is another focus of nanobiotechnology. The production of natural and non-hazardous additives has proven crucial owing to the toxicity and expensive price of synthetic additives. The efficacy of nanocoatings is being improved by adding organic elements like plant extracts as \"green\" additions. Plant extracts are employed as coating framework additives because they are eco-benign, non-hazardous, inexpensive, effortlessly accessible, and heavy metal-free. They come from the plants' stems, leaves, branches, fruit, and seeds [80; 81; 82]. They contain bioactive components with antioxidants that may aid in improving nanocoatings' characteristics. In an experiment, as a capping and reducing reagent, [PERSON] et al. [5] used an extract from the leaves of _Abutilon indicum_ (L.) Sweet to create chromium oxide (Cr\({}_{2}\)O\({}_{3}\)) NPs. The NPs' sizes varied between 17 and 42. Utilizing a live/dead staining approach and agar well penetration, the antibacterial and anticorrosion efficacy of the green-produced NPs was assessed using four distinct bacterial strains, including _S. aureus_, _E. coli_, _B. subtilis_, and _B. bronchiseptica_. By observing a color alteration after the introduction of a metal salt precursor to the leaf extract, the formation of Cr\({}_{2}\)O\({}_{3}\) NPs was optically observed. The reaction mixture's color shift from red to black signified the production of Cr\({}_{2}\)O\({}_{3}\) NPs. The surface plasmon resonance (SPR) process on the NPs' interface was responsible for this color change. To decrease and stabilize the metal ions to nano size, certain phytocompounds may function as ligands and establish chelates with various metal ions. After dissolving in H\({}_{2}\)O, chromium sulfate salt (Cr\({}_{2}\)(SO\({}_{4}\))\({}^{3}\)) transforms into readily floating ions. Owing to a lack of electrons, the readily floating Cr\({}^{3+}\) ions are drawn to the phytomolecules of the plant (polyphenols, etc.). As a consequence, metallic ions and phytomolecules within plants produce chelate complexes when O\({}_{2}\) is used as the donor and Cr\({}^{3+}\) as the acceptor in the donor-acceptor mechanism (Figure 9). This causes flavonoids, polyphenols, etc. to oxidize and change into the keto state (Figure 9). On either end, the adjacent tannins, alkaloids, flavonoids, and other plant phytomolecules stabilize Cr\({}^{3+}\) while reducing it to the zero-valent isotope Cr\({}^{0}\). They easily oxidize throughout air drying and carbonization to become Cr\({}_{2}\)O\({}_{3}\) NPs covered in _Abutilon Indicum phytomolecules_ (L.) Sweet leaf infusion. [PERSON] et al. [71] used _Delonix elata_ leaf extract as a capping and reducing reagent to produce nickel oxide NPs (NiO NPs) in an environmentally friendly way utilizing ultrasonic waves. Utilizing SEM and Brunauer-Emmett-Teller examination, the phase formation, crystalline nature, physical and thermal durability, and surface area of the synthesized NiO NPs were examined. When contrasted to the other three electrolyte media, the NiO NP-coated Zn metal sheets demonstrated outstanding corrosion-inhibition behaviors. They demonstrated an 88.6% increase in resistance to corrosion in 1 M H\({}_{2}\)SO\({}_{4}\), compared to improvements of 75.74%, 68.4%, and 56.8% in the corrosion resistance in 1 M HCl, 3.5% NaCl, and 6 M KOH media, correspondingly. Moreover, in 1 M HCl, 3.5% NaCl, 6 M KOH, and 1 M H\({}_{2}\)SO\({}_{4}\) environments, NiO NP-coated Mg metal plates showed good corrosion-prevention efficacy of 71.9%, 61.1%, 55.9%, and 79.5%. The Tafel curve demonstrated that the generated large surface region and mesoporous NiO NPs effectively reduce the corrosive character of Mg and Zn sheets under all electrolytes, particularly in acidic media. [PERSON] et al.