The corrosion inhibition of mild steel by aqueous extract of cumaru (Dipteryx odorata) seeds and its high molecular weight fraction (HMWF) was investigated in 1 mol L-1 HCl solution. The study was carried out through gravimetric essays, open circuit potential measurements, anodic and cathodic polarization curves and electrochemical impedance analyses, as well as morphological analysis of the mild steel by scanning electron microscopy. Gravimetric tests showed that the inhibition efficiency (IE) increased with immersion time and inhibitor concentration, reaching 98% of IE using 100 mg L-1 of the HMWF, after 6 h immersion time. The activation energy (Ea) increased with the addition of both inhibitors which characterizes a physical adsorption of the constituents of the aqueous extract of cumaru on the metal surface. Polarization curves indicated that both aqueous cumaru seeds extract and its HMWF act as mixed-type inhibitor. Impedance results showed a decrease in double layer capacitance (Cdl) and an increase in charge transfer resistance (Rct) evidencing a typically screening effect. The adsorption of molecules present in the aqueous extract of cumaru followed the Langmuir isotherm. The aqueous cumaru seeds extract was characterized by Fourier transform infrared spectroscopy (FTIR), 1H, 13C and 2D nuclear magnetic resonance (NMR).

Abstract The present work aims to study the aqueous cotton seeds extract as a natural inhibitor of the corrosion of mild steel in 1 mol L−1 HCl using gravimetric tests, potentiodynamic polarization curves, electrochemical impedance measurements and surface morphological analysis by scanning electron microscopy (SEM). The aqueous cotton seed extract acted as a good corrosion inhibitor reaching an inhibition efficiency of 95.7% after 24 h of immersion for 800 mg L−1 inhibitor concentration. For the gravimetric tests varying the temperature, a decrease of the activation energy (Ea) was observed, suggesting a chemical adsorption on the surface of the metal. 400 mg L−1 of the high molecular weight fraction isolated from the total extract showed inhibition efficiency equal to 800 mg L−1 of the total extract, 97.3% and 94.2% from electrochemical impedance and polarization curves data, respectively, suggesting that the macromolecules present a fundamental participation in the inhibitive process.

Abstract An electrochemical sensor based on a modified glassy carbon electrode (GCE) with reduced graphene oxide and Ni-Au nanoparticles (Ni(OH)2/AuNp/rGO/GCE) was developed for the determination of ethylene glycol. The graphene oxide was reduced electrochemically at the electrode surface by chronoamperometry, the gold nanoparticles were deposited by chronopotentiometry while the nickel hydroxide nanoparticles were deposited by cyclic voltammetry. The characterization of graphene oxide was performed by Raman spectroscopy, X-ray diffraction (XRD) and transmission-mode scanning electron microscopy (TSEM), while the modified electrodes were characterized by scanning electron microscopy (SEM) and electron dispersive spectroscopy (EDS) analysis. The determination of ethylene glycol was performed by cyclic voltammetry due to the regeneration of the active sites, preventing loss of the sensor signal. The modified GCE with rGO and Ni(OH)2/AuNp showed a good performance obtaining a linear range of 0.24 to 1.4 mmol L-1 with a correlation coefficient of 0.9903, limits of detection and quantification (49 and 162 µmol L-1, respectively) and high stability with 500 continuous analysis cycles.

The present work studied aqueous extracts of castor beans as a natural inhibitor of the corrosion of mild steel in 1 M HCl using gravimetric tests, potentiodynamic polarization curves, linear polarization method, electrochemical impedance measurements, surface analysis by scanning electron microscopy (SEM) and chemical characterization by Fourier transform infrared spectroscopy (FTIR). Gravimetric tests showed that inhibition efficiency (IE) increased with immersion time and concentration of the extract, reaching 97.8% in the presence of 800 mg L−1 inhibitor after 24 h immersion time. For the gravimetric tests varying the temperature, a decrease of the activation energy (Ea) was observed, suggesting chemical adsorption of extract components on the metal surface. The extracts from the castor beans acted as a good corrosion inhibitor, and the macromolecules present in the high molecular weight fraction (HMWF) have a fundamental participation in this process since it presented 93.7% of IE for 200 mg L−1.

Abstract The projections for the global energy demand have been one of our society’s greatest challenges, which has contributed significantly to the search for new sources of energy, among which biodiesel stands out and, consequently, the development of methods for quality assurance is essential to ensure its technological demand. In this context, a stable sensor based on graphene oxide and gold nanoparticles was developed for glycerol analysis. The electrochemically deposited gold nanoparticles presented the best results with a peak current (Ip) four times greater than the chemically produced gold nanoparticles. The combination of glassy carbon electrode with electrochemically reduced graphene and electrochemically deposited gold nanoparticles (GCE-ErGO-EAuNp) resulted in an efficient sensor to detect glycerol, promoting an Ip increase. The proposed non-enzymatic method showed a linear response in the concentration range of 1.0 x 10-3 to 1.0 x 10-2%(w/w) with a good determination coefficient (r2 = 0.9989), limits of detection and quantification at 1.2 x 10-4% and 4.0 x 10-4%(w/w), respectively, with a repeatability of (RSD% ranged from 0.36% to 2.78%), intermediate precision and recovery of (99.3% to 104.4%) and excellent stability of 700 continuous analysis cycles.

The present work aims at studying the preconcentration of Cu2+ ions by solid phase extraction using SiO2/Al2O3/TiO2 ternary oxide as adsorbent material. This methodology consists of the affinity of the analyte for the adsorbent material and its subsequent elution with the least amount of solvent. Subsequently, the aqueous phase containing the extracted analyte was collected and analyzed by square wave anodic stripping voltammetry (SW-ASV). For the applied solid phase extraction (SPE) methodology, a complete factorial design was carried out with 3 variables at 2 levels (pH, elution flow rate and analyte concentration) to optimize the extraction conditions. The results showed that at pH 9, the SiO2/Al2O3/TiO2 oxide presents excellent Cu2+ adsorption capacity with recovery values between 81.0 and 104% for this pH range. The limit of detection (LOD) and limit of quantification (LOQ) values were determined to be 1.71 and 5.64 µg L-1, respectively. The study of recovery for SPE method revealed results of 102 and 103%.

The use of corrosion inhibitors is one of the most common methods to combat acid corrosion. The current studies aim to apply natural products as corrosion inhibitors, once the most used compounds are mostly toxic to the environment and to humans. The present paper purposes the application of an aqueous extract of agro-industrial waste (AEAW) to inhibit the corrosion of stainless steel AISI 304 in sulfuric acid. Gravimetric and electrochemical experiments were performed. The gravimetric experiments revealed that the extract acts as an inhibitor for stainless steel, showing inhibitory efficiency up to 81.6%. The electrochemical tests show that the AEAW makes the steel surface more noble. The extract acts by adsorption in the metallic surface, following a Temkin isotherm. The results indicate that the AEAW is a promising substitute of conventional organic compounds as a corrosion inhibitor to AISI 304 stainless steel in sulfuric acid.

The corrosion inhibition of mild steel in 1 mol L−1HCl by barley grains and malting process residue extracts was investigated by weight loss measurements, polarization curves, electrochemical impedance measurements and scanning electron microscopy. The inhibition efficiency exceeded 92% in the presence of 100 mg L−1 extracts after 24 h immersion time for both extracts. The Ea decreased with the addition of the extracts, characterizing the chemical adsorption by the molecules present in the extracts on the surface.The high molecular weight fraction isolated from the barley grain extract also showed high inhibition efficiency, suggesting that macromolecules are probably responsible for the inhibitory action.