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Developing a sustainable and environmentally friendly inhibitor remains an essential and challenging goal for corrosion control. Here, different extracts from the same biomass (Juçara - Euterpe edulis) were applied as a new inhibitor for mild steel in different corrosive medium: 1 mol L−1HCl (pH 0) and simulated CO2-saturated formation water (pH 5). Depending on the extraction process, the anticorrosive capacity of extracts may increase, a fact verified in gravimetric tests, reaching 94.4% maximum inhibition efficiency for the acidic medium (1000 mg L−1of Juçara pulp in 48 h of immersion) and 86.1% inhibition efficiency for the saline medium (600 mg L−1of Juçara pulp extract assisted by ultrasound in 24 h of immersion). Gravimetric tests, electrochemical tests, and surface and biochemical characterization analyses were carried out to better understand these extracts' performance. This work provides an interesting application of the same biomass effectively acting in different corrosive medium, depending on the extraction method.

In this work, an endogenous self-doping N,P,S-CQDs was synthesized by the acid hydrolysis of pumpkin seeds (Cucurbita maxima)and its performance as a corrosion inhibitor was evaluated. Mild steel (MS) is one of the most used materials in the industry; however, it has low corrosion resistance in acidic environments. Pumpkin is cultivated worldwide, and this compositional characteristic makes pumpkin seeds a great alternative as a raw material to produce CQDs. The results show that endogenous self-doping CQD was successfully obtained with a size distribution smaller than 10 nm. The N,P,S-CQDs presented 91.3% at 60 ppm and 94.6% at 10 ppm as maximum inhibition efficiency after 2 and 24 h immersion, respectively. Activation energy studies, XPS analysis, and isotherm studies show that the inhibition mechanism occurs through physical interaction. These results show an excellent alternative for using pumpkin seeds (Cucurbita maxima), an agroindustry waste, as a corrosion inhibitor.

The soybean (Glycine Max) meal extracts inhibitory action, the aqueous extract by infusion (AE), its high molecular weight fraction (HMWF) and the aqueous extract by infusion of a commercially isolated soy protein (CIP) towards the mild steel corrosion in 0.5 mol L−1H2SO4was investigated by weight loss measurements, electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization curves. Additionally, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) were used, respectively, to characterize morphologically and chemically the surface. The total content of proteins in the different extracts was determined by a quantitative method, the Biuret methods, as well as by two qualitative methods, the nuclear magnetic resonance (NMR) and sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis (SDS-PAGE). The AE, its HMWF and CIP extracts acted as good corrosion inhibitors, reaching inhibition efficiencies of 85.2%, 88.7% and 94.8% for 800 mg L−1, respectively, from the jcorrdata. The polarization curves show that these extracts act as mixed-type inhibitor with predominantly cathodic characteristics. The adsorption of components from AE, its HMWF, and CIP on the mild steel surface follows the Langmuir adsorption isotherm. The SEM results indicate that the surface was covered by the inhibitor and the XPS analyses confirm chemical interactions between the extracts components and the mild steel surface. The results obtained with HMWF from AE and CIP suggest that the proteins are probably responsible for the inhibitory action.