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Euterpe oleracea Mart. (Arecaceae) is an endogenous palm tree from the Amazon region. Its seeds correspond to 85% of the fruit’s weight, a primary solid residue generated from pulp production, the accumulation of which represents a potential source of pollution and environmental problems. As such, this work aimed to quantify and determine the phytochemical composition of E. oleracea Mart. seeds from purple, white, and BRS-Pará açaí varieties using established analytical methods and also to evaluate it as an eco-friendly corrosion inhibitor. The proanthocyanidin quantification (n-butanol/hydrochloric acid assay) between varieties was 6.4–22.4 (w/w)/dry matter. Extract characterization showed that all varieties are composed of B-type procyanidin with a high mean degree of polymerization (mDP ≥ 10) by different analytical methodologies to ensure the results. The purple açaí extract, which presented 22.4% (w/w) proanthocyanidins/dry matter, was tested against corrosion of carbon steel AISI 1020 in neutral pH. The crude extract (1.0 g/L) was effective in controlling corrosion on the metal surface for 24 h. Our results demonstrated that the extracts rich in polymeric procyanidins obtained from industrial açaí waste could be used to inhibit carbon steel AISI 1020 in neutral pH as an abundant, inexpensive, and green source of corrosion inhibitor.

Cocos nucifera L. is a palm tree (Arecaceae) with a high economic value. The coconut husk fibers are nonedible, thick, and abrasion-resistant and correspond up to 85% of biomass discarded as solid waste residue. Therefore, the husk fibers are an underexploited byproduct with a high content of extractives of unreported nature. Two varieties of C. nucifera L. husk extracts were investigated to uncover bioactive metabolites and their possible application as a green corrosion inhibitor for carbon steel AISI 1020 under neutral pH conditions. The chemical analysis indicated 3% (w/w) of proanthocyanidins in the husk fibers with a high B-type procyanidin content. The husk fibers’ crude extract showed promising results as an eco-friendly corrosion inhibitor for carbon steel AISI 1020 under neutral pH conditions. Although it formed a film on the metal surface in all tested concentrations (0.4, 0.8, 1.2, and 1.6 g L –1 ), the highest protective efficiency was shown at a concentration of 1.2 g L –1 , determined by electrochemical techniques and mass loss. This was the first comprehensive report on coconut husk fibers’ chemical composition, which was similar between the two varieties with potential for industrial application.

This work aims to analyze, through weight loss and X-ray photoelectron spectroscopy (XPS) methods, the inhibitive films of 1-hydroxyethane-1,1-diphosphonic acid (1-hydroxyethylidene-1,1-diphosphonic acid, HEDP) and zinc(II) ions formed on AISI 1020 carbon steel when immersed in solutions containing 30 ppm of chloride ions, 50 ppm of HEDP, and three different concentrations of zinc(II) ions (14, 20, and 30 ppm). Moreover, the results of the experimental surface analyses were compared to molecular modeling studies of the proposed HEDP-Fe(III)/Zn(OH) 2 /HEDP-Zn(II) protective film. The film presented dissimilar structures responsible for the different levels of metallic protection for each particular zinc(II) concentration. In general, the increase in Zn(II) concentration leads to more compact and adherent film formation, with decreased corrosion rates of carbon steel.

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