Green Corrosion Inhibitors from Natural Sources and Biomass Wastes

Abstract

Over the past decade, green chemistry has been emphasizing the importance of protecting the environment and human health in an economically beneficial manner aiming at avoiding toxins and reducing wastes. The field of metallic materials degradation, generally faced by using toxic compounds, found a fertile research field in green chemistry. In fact, the use of inhibitors is a well-known strategy when metal corrosion needs to be prevented, controlled, or retarded. Green inhibitors are biodegradable, ecologically acceptable and renewable. Their valorization expands possible applications in industrial fields other than ‘waste to energy’ in the perspective of circular economy. Although lot of experimental work has been done and many research papers have been published, the topic of green inhibitors is still an open issue. The great interest in the field expanded the research, resulting in high numbers of tested molecules. However, the most frequently adopted approaches are conventional and, hence, not suitable to fully characterize the potential efficacy of inhibitors. All the mentioned aspects are the object of the present review and are meant as a constructive criticism to highlight the weak points of the green inhibitors field as to re-evaluate the literature and address the future research in the field that still lacks rationalization.

Biosurfactants: Eco-Friendly and Innovative Biocides against Biocorrosion

“…This has prompted the search for green corrosion inhibitors as eco-friendly. There are several papers that describe the use of natural resources, ranging from waste materials to plant extracts, as green corrosion inhibitors [1][2][3][4][5][6].…”

Green Corrosion Inhibitors from Agri-Food Wastes: The Case of Punica granatum Extract and Its Constituent Ellagic Acid. A Validation Study

“…The circular economy finds application in many fields. In the corrosion science, it has been causing an escalation of scientific papers aimed to find green corrosion inhibitors as alternatives to the more common, but toxic and harmful, ones (e.g., chromium and molybdenum compounds, nitrites, amines) [2][3][4][5]. Corrosion inhibitors are compounds that, directly added in a small concentration into the aggressive solution with which the metal is in contact, slow down the irreversible interfacial reaction, i.e., corrosion process, based on the concomitant advent of an oxidation reaction (i.e., metal dissolution) and a reduction one (typically, hydrogen evolution or oxygen reduction) [6].…”

“…This "green turn" must surely receive praise but it is to be worth noting also the other side of the medal. A critical revision of the open literature concerning green corrosion inhibitors brings up to a constructive critique [3]. First of all, only a few works actually deal with extracts from natural residues, by-product or biomass wastes [3].…”

Inclusion of 5-Mercapto-1-Phenyl-Tetrazole into β-Cyclodextrin for Entrapment in Silane Coatings: An Improvement in Bronze Corrosion Protection

“…In this research, the effective formation and the stability of a complex between β-CD and 5-mercapto-1-phenyl-tetrazole (MPT) ( Figure 1) were assessed. Among non-toxic corrosion inhibitors [24][25][26], MPT was chosen because of its outstanding inhibiting properties towards copper and bronze corrosion [27][28][29]. Its complex with β-CD was incorporated in a 3-mercapto-propyltrimethoxy-silane (PropS-SH) coating, and the protectiveness of the obtained coating was assessed on bronze during both immersions in concentrated acid rain and exposures to alternated acid rain spray.…”