**1. Introduction**

The advanced technological application demands value-added materials of requisite surface properties. In most of the cases, the metallic materials are employed as prime part of the instrument/device. But after certain period of repeated use, passivation/inactiveness of the surface has been realized. This is mainly due to the corrosion of the metallic surface. Corrosion is nothing but the physicochemical interaction of a metal surface with the surrounding environment leading to change the original properties of that metal. Further it impairs the function of the metal as well as the environment and the technical equipment of which these form a part. Therefore methods/technologies are strictly indispensable to protect the metal surface from the detrimental effect of the environment as well as to preserve its integrity. Although many technological prospects have been formulated, still now focus is given on the development of methods for surface modification/functionalization of materials. The definition of surface modification/functionalization directs the employment of a procedure to introduce new properties to an existing material to fulfil the requirement for a particular application. These techniques have been used from the ancient times aiming for an improved response of a material when it interacts with the environment. After the evolution of nanoscale materials and nanotechnology, this functionalization is performed in either by manipulating the material composition in molecular level or by making an optimized coating onto the material surface. Basically the surface modification is performed by applying advanced coatings onto the material surface. These coatings offer an efficient physical barrier clogging the approach of corrosive species to the metal surface, thereby lengthening the lifetime of the equipment. Additionally these coatings are capable to suppress the corrosion process, if the protective barrier is disrupted by any means. Hence these corrosion protective materials require the use of anticorrosion pigments or corrosion inhibitors which will protect the underlying metallic surface. Further the thickness of coating and optimization of the number of layers strictly depends on the application for which it is intended. Generally the thickness varies from micro to millimetres, and the number of layers varies according to the targeted application. Each of the layers is designed to aim specific functionalities like as adhesive to the metal surface or in between the metal and other coating layers, corrosion inhibitor, water-repellent, antifouling/wear resistive agent, etc.

From the heritage of mankind, animal fat, gelatins, beeswax, clay minerals, and different vegetable oils have been employed as the coating material to protect the surface of metallic articles from corrosion, to retain brightness, for lubrication, etc. [1]. Later on with the passage of time, the boost on nanomaterials and nanotechnology developed many advanced routes for surface coating, but still now some of the ancient coating materials are in use. Afterwards the chromate-based surface treatments are developed and show efficient corrosion protective properties; however the use of hexavalent chromium is imposed legislatively (because of its carcinogenic properties) in most of the areas excluding the aerospace industries. Therefore more focus has been paid to design advanced, nontoxic (low-volatility,

organic, hexavalent chromium- and isocyanate-free compounds), and low-cost coatings for corrosion protection. In this regard, many of the nanomaterial-based coatings (organic, inorganic, or composites) have been formulated and demonstrated successfully.
