Sustainable Corrosion Protection of Steel Using Plant Extracts: A Review of Neem, Cashew, and Ziziphus-Derived Inhibitors

Abstract

The increasing demand for environmentally benign corrosion protection methods has led to the exploration of plant-based (green) corrosion inhibitors over toxic and non-renewable synthetic chemicals. This study presents a comprehensive review of empirical studies reported on the application of plant extracts to prevent corrosion of mild and carbon steels in acidic and saline media. Special emphasis is placed on the extracts from Azadirachta indica (neem), Anacardium occidentale (cashew) and Ziziphus species because of their availability, richness in phytochemicals and proven inhibitory performance. A critical review of published studies utilising gravimetric, electrochemical, surface analytical and computational techniques was performed. The results suggest that inhibition efficiencies higher than 80-90% are generally achievable under optimised conditions and adsorption of phytochemicals such as polyphenols, alkaloids, tannins, flavonoids and phenolic lipids is the dominant mechanism. Most of the extracts are mixed type inhibitors following Langmuir, Temkin or Freundlich adsorption isotherms with physisorption and chemisorption processes. Despite their efficacy challenges exist regarding extract stability, standardisation and long-term performance. In general, the review confirms the huge potential of neem, cashew and Ziziphus based inhibitors for sustainable corrosion control in industrial applications.