The purification of used oils and their introduction into production cycles lead to reduction in environmental contamination. A simulation was conducted to study the thermal degradation of sunflower ...oil under varying temperatures over time. In the purification process of used cooking oil, an adsorption technique using zeolite and eggshell as an adsorbent (5, 10, 20, and 30 g/100 mL used oil) was applied. To optimize purification, different doses of thermally and chemically activated adsorbents were used, at different temperatures (30 and 80 °C). Therefore, this study was conducted in batch operations to determine the effect of suitable adsorption for a contact time of the adsorbent of 2 h. In comparison, the purification of used vegetable oils was achieved using a saline solution. The adsorption capacity was evaluated by determining the physicochemical parameters of the oils before and after purification. The characterization of natural adsorbents was carried out using scanning electron microscopy (SEM) and X-ray fluorescence spectrometry (XRF). The results showed that the adsorbent in a dose of 30 g of zeolite activated with NaOH and heat-treated eggshell, respectively, exhibited a larger surface area and greater adsorption capacity. Adsorption increased with contact time. The FT-IR spectra of the oils showed the IR bands at 1097, 1160, and 1237, corresponding to the presence of the ester C-O-, 1743 for C=O ester, 2853, 2922 for (CH2, CH3), and 3008 for (C=C). The acidity and peroxide values decreased with increasing dose and contact time with zeolite or eggshell. Together, our result strongly suggests that natural adsorbents contribute to the purification of used oils.
The purpose of this study was to review the physicochemical characterization of Romanian honey and propolis and their antifungal effect on different strains. As an indicator of environmental ...pollution, lead exceeded the allowed limits in two study areas. The relationship between the acidity and electrical conductivity of polyfloral honey and the antioxidant activity with the total content of phenolics and flavonoids was investigated. The antifungal activity of 13 polyfloral honey and propolis samples from North-West and Central Romania and 12 samples from Alba County was investigated against six fungal strains: Aspergillus niger, Aspergillus flavus, Candida albicans, Penicillium chrysogenum, Rhizopus stolonifer, Fusarium oxysporum. All honey and propolis samples exhibited an antifungal effect. The most sensitive strains were P. chrysogenum and R. stolonifer for honey and P. chrysogenum and F. oxisporumn for propolis. A two-way analysis of variance was used to evaluate the correlations between the diameter of the inhibition zones for the strains and the propolis extracts. Statistical analysis demonstrated that the diameter of the inhibition zone was influenced by the strain type and the geographical origin of honey and propolis. Pearson’s correlation coefficient shows a significant positive linear relationship between the diameter of the inhibition zone and the flavonoid and phenol concentration of honey and propolis, respectively.
The dissolution of the main metals (Cu, Zn, Sn, Pb and Fe) found in waste printed circuit boards (WPCBs) was investigated by electrochemical corrosion measurements (potentiodynamic polarization and ...electrochemical impedance spectroscopy (EIS)) in different bromide-based systems that could be used as lixiviants in hydrometallurgical route of metals recovery. The analysis of the corrosion products was carried out by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) measurements. All measurements showed that the addition of bromine in the electrolyte favors to great extents the dissolution process of all studied metals as compared to bromine-free electrolytes. In the investigated experimental conditions, the highest dissolution rates of the metals were obtained in acidic KBr solution containing 0.01 mol/L bromine and they decreased in the following order: Zn >> Sn > Pb > Fe > Cu. The XRD and XPS chemical assessment allowed the identification of the dissolution products formed on the metallic surfaces after exposure to the electrolytes. They consisted mainly of oxides in the case of Cu, Zn, Sn and Fe, while the presence of PbBr2 was also noticed on the lead surface. Based on the results of EIS and surface investigations, several models explaining the corrosion behavior of the metals were proposed and discussed. The obtained results demonstrate that all studied metals could be successfully leached using brominated solutions, providing a viable alternative for the selective and efficient recovery of the base metals from WPCBs through a multi-step hydrometallurgical processing route.
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•Propolis is an efficient green corrosion inhibitor for bronze surface.•The inhibitive effectiveness of propolis on bronze is time-dependent.•The main organic constituents of propolis ...sample were identified by HPLC-DAD.•The adsorption of propolis on bronze surface obeys Langmuir isotherm.
In the present work, the inhibitive action of natural propolis on bronze corrosion in a weakly acidic solution containing Na2SO4 and NaHCO3 at pH 5 was evaluated using multiscale electrochemical techniques, namely potentiodynamic polarization, electrochemical impedance spectroscopy and scanning vibrating electrode technique measurements. The major constituents of propolis were identified by HPLC. Surface characterization was performed by SEM-EDX and AFM analysis. Experiments were performed as a function of the propolis concentration and immersion time in the corrosive electrolyte. The obtained results showed that propolis presents good anticorrosive properties on bronze, acting as a mixed-type inhibitor, but its protective effectiveness is time-dependent. The highest inhibiting efficiency of 98.9% was obtained in the presence of 100ppm propolis, after about 12h of exposure to inhibitor-containing electrolyte through the stabilization of Cu2O on the bronze surface. The inhibitive properties of propolis on bronze corrosion are likely due to the adsorption of its main constituents (flavonoids and phenolic compounds), through the oxygen atoms in their functional groups and aromatic rings, which have been evidenced by FT-IR spectra. The adsorption of propolis on bronze was found to follow Langmuir adsorption isotherm.
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•Horse-chestnut extract (HCE) applied on bronze for corrosion protection.•HCE addition decreased corrosion current and enhanced the surface film resistance.•The best protection was ...achieved after 14 h in a solution containing 0.5 g L−1 HCE.•HCE-bronze interaction arises from physisorption described by Langmuir isotherm.•Novel analytical methodology for SECM kinetic study on inhibitor adsorption.
Horse-chestnut ethanolic extract was tested as potential corrosion inhibitor of bronze in simulated acid rain. The extract was analysed by FTIR, GC–MS and HPLC-PDA, and its anti-corrosion behaviour studied using a multiscale electrochemical approach by polarization curves, EIS and scanning electrochemical microscopy, along with SEM-EDS. 94 % inhibition efficiency was attained by developing a surface physisorbed film. A novel methodology for kinetic evaluation of dynamic adsorption of inhibitive species on metal surface is proposed using SECM, achieving good agreement with results from conventional electrochemical techniques. Excellent adsorption-desorption kinetic constants (ka = 0.102 s−1 mol−1 L; kd = 3.33 × 10-5 s−1) were determined.
In the present paper, the inhibition performance of benzydamine hydrochloride drug, commercially named Tantum Rosa on copper was investigated in 3.5 wt.% NaCl solution. Potentiodynamic polarization, ...electrochemical impedance spectroscopy, scanning electron microscopy and energy dispersive X-ray spectroscopy were employed. The electrochemical results revealed that Tantum Rosa acts as a mixed-type inhibitor on the copper corrosion and its protective effectiveness is concentration and time-dependent. The inhibiting efficiency of Tantum Rosa was improved with the increase in the drug concentration and reached the maximum value of 91.5% at 5 mM. The inhibitive effect of Tantum Rosa was afforded to its spontaneous adsorption on the copper surface, through combined physical and chemical processes, according to Langmuir adsorption isotherm. The time-weakening of the inhibitor film stability leaded to a progressive decay of the inhibition ability of Tantum Rosa at prolonged exposure. SEM-EDX analysis confirmed that the surface morphology of copper was significantly improved in the presence of the inhibitor.
•Copper protection in 3.5 wt.%NaCl by 5-(4-pyridyl)-1,3,4-oxadiazole-2-thiol (PyODT).•High inhibitive efficacy of PyODT on Cu corrosion was reached at long exposure.•A uniform and compact inhibitor ...film was formed on copper surface.•Interaction between Cu and PyODT proceeded through thiol and oxadiazole groups.•Machine learning algorithms and Raman data were firstly applied in corrosion study.
An oxadiazole derivative with functional groups favouring its adsorption on copper surface, namely 5-(4-pyridyl)-1,3,4-oxadiazole-2-thiol, has been explored as potential inhibitor of copper corrosion in 3.5 wt.% NaCl. Electrochemical evaluation by electrochemical impedance spectroscopy, potentiodynamic polarization and SVET reveals high inhibition efficiencies. Surface microscopy inspection and spectroscopic analysis by Raman, SEM-EDX and XPS highlight the formation of a compact barrier film responsible for long-lasting protection, that is mainly composed of the organic molecules. Machine learning algorithms used in combination with Raman spectroscopy data were applied successfully for the first time in corrosion studies to allow discrimination between corroded and inhibitor-protected metal surfaces. Quantum Chemistry calculations in aqueous solution and Molecular Dynamic studies predict a strong interaction between copper and the thiol group and an extensive coverage of the metal surface, responsible for the excellent protection against corrosion.
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► Phenothiazine derivatives are efficient inhibitors for bronze corrosion. ► Potentiodynamic polarization and EIS were used to elucidate inhibition mechanism. ► Adsorption of phenothiazine ...derivatives on bronze surface obeys Langmuir isotherm. ► A correlation between energy gaps and inhibition efficiencies values was obtained.
Four phenothiazine derivatives have been tested as inhibitors for bronze corrosion in a solution containing Na2SO4 and NaHCO3 (pH 5).
Electrochemical investigations (potentiodynamic polarisation and impedance measurements) revealed that all phenothiazine derivatives exert a protective effect against bronze corrosion and, in some cases their inhibition efficiency exceeds 90% at concentration level as low as 75μM. An adherent layer of organic molecules chemisorbed on bronze surface is responsible for the protective effect of the investigated compounds. Adsorption of phenothiazine derivatives on bronze obeys Langmuir isotherm. Correlation between quantum chemical calculations and inhibition efficiency of the investigated compounds was discussed using DFT method.
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•New organic coatings for patinated bronze protection were tested in simulated rain.•Time-degradation of the coatings based on nitrocellulose lacquer was monitored by EIS.•Addition of ...organic inhibitors into lacquer enhance its protective properties.•MAT-added coating offers the highest long-lasting protection to patinated bronzes.•FTIR spectra evidenced interactions between inhibitor and lacquer functional groups.
In the present work, the efficiency and time-degradation of new protective organic coatings for artificially patinated bronze based on nitrocellulose lacquer containing thiadiazole derivatives (2-mercapto-5-amino-1,3,4-thiadiazole and 2-mercapto-5-methyl-1,3,4-thiadiazole) as corrosion inhibitors were investigated. The samples were intermittently exposed to a solution simulating an urban rain (pH 5) and their behaviour was monitored for nearly three months by electrochemical impedance spectroscopy (EIS) measurements.
Optical microscopy examination of cross sections of bronze samples covered with patina and nitrocellulose lacquer, without and with inhibitors, was used to determine the thickness of the coatings. Fourier transformed infrared spectroscopy (FT-IR) was employed to put on evidence the chemical interactions between the organic inhibitors and nitrocellulose lacquer functional groups.
The best results were achieved in the presence of 2-mercapto-5-amino-1,3,4-thiadiazole into the nitrocellulose lacquer coating, which offers the highest long-lasting protection to patinated bronzes, without changing the visual appearance of the bronze surfaces covered with patina. This approach proved to be a promising alternative to benzotriazole in the development of highly protective coatings for patinated bronzes.
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