4-(Pyridin-4-yl)thiazol-2-amine as an efficient non-toxic inhibitor for mild steel in hydrochloric acid solutions

A novel eco-friendly corrosion inhibitor, namely, 4-(pyridin-4-yl)thiazol-2-amine (PTA), was synthesized and evaluated as a corrosion inhibitor for mild steel in 1 M HCl solution. Its inhibition effect against mild steel corrosion was investigated via weight loss methods, electrochemical measurements, and surface analyses. The experimental results showed that PTA is an effective corrosion inhibitor for mild steel in an acid medium, and the maximum inhibition efficiency reached 96.06% at 0.2 mM concentration. Polarization studies showed that PTA acted as a mixed inhibitor. The sorption behavior on the steel surface complies with the Langmuir adsorption isotherm, exhibiting both physisorption and chemisorption. The constitution and characteristic of the protective layer on the steel surface were verified using scanning electron microscopy (SEM)/energy-dispersive X-ray spectroscopy (EDX) and UV-Vis spectroscopy. Quantum chemistry calculations were used to study the relationship between the inhibition efficiency and molecular structure of the inhibitor.

The corrosion inhibition performance and mechanism of 4-(pyridin-4-yl)thiazol-2-amine toward mild steel in hydrochloric acid were studied for the first time.     

Understanding the adsorption performance of two glycine derivatives as novel and environmentally safe anti-corrosion agents for copper in chloride solutions: experimental,DFT, and MC studies

The inhibition impacts of two non-toxic glycine derivatives, namely, bicine (N,N-bis(2-hydroxyethyl)glycine) and tricine (N-(tri(hydroxymethyl)methyl) glycine) on copper corrosion were investigated in 3.5% NaCl solutions. Surprisingly, there is no report on using bicine and/or tricine as corrosion inhibitors for Cu and its alloys in a seawater-like environment. The effects of bicine and tricine on the corrosion behavior of Cu in 3.5% NaCl were examined using the open circuit potential, Tafel polarization, and AC spectroscopy (EIS) techniques. The corrosion rate decreased as a function of the inhibitor dose. The Tafel and EIS parameters showed that the inhibitors decreased both the anodic and cathodic corrosion currents and inhibited the charge transfer process by adsorption on the Cu surface. The inhibition property was attributed to the adsorption of inhibitor molecules with the Langmuir model. Tricine showed a superior inhibition performance of more than 98% at a concentration of ∼5 mmol L⁻¹. The free energy of adsorption data revealed physical adsorption. The outcomes of Monte Carlo simulations and theoretical studies well supported the experimental data.

The inhibition impacts of two non-toxic glycine derivatives, namely, bicine (N,N-bis(2-hydroxyethyl)glycine) and tricine (N-(tri(hydroxymethyl)methyl) glycine) on copper corrosion were investigated in 3.5% NaCl solutions.     

A combination of experiment and theoretical methods to study the novel and low-cost corrosion inhibitor 1-hydroxy-7-azabenzotriazole for mild steel in 1 M sulfuric acid

1-Hydroxy-7-azabenzotriazole (HOAT) was explored via experimental and theoretical computation methods as a corrosion inhibitor for mild steel in 1 M sulfuric acid. These data indicate that HOAT has good ability to suppress corrosion of the mild steel, with ideal agreement with between experimental and computational results. Besides, the electrochemical experiments show that HOAT is a mixed-type corrosion inhibitor for mild steel in 1 M H₂SO₄. Furthermore, HOAT adsorption on the surface of steel conforms to the Langmuir isotherm model. Finally, computational simulation was executed to deeply investigate the mechanism to HOAT inhibition corrosion of steel.

1-Hydroxy-7-azabenzotriazole (HOAT) was explored via experimental and theoretical computation methods as a corrosion inhibitor for mild steel in 1 M sulfuric acid.     

Functional polyaspartic acid derivatives as eco-friendly corrosion inhibitors for mild steel in 0.5 M H2SO4 solution

To improve the corrosion inhibition efficiency of eco-friendly polyaspartic acid (PASP) for mild steel in acidic solutions, PASP/N-(3-aminopropyl)imidazole (PD-1) and PASP/N-(3-aminopropyl)-imidazole-co-n-dodecylamine (PD-2) were chemically synthesized by the facile ring-opening reaction of polysuccinimide. Inhibition efficiencies of PD-1 and PD-2 for mild steel in a 0.5 M H₂SO₄ solution were investigated by electrochemical measurements (electrochemical impedance and polarization) and the weight loss method. In comparison with PASP, PD-1 and PD-2 show improved inhibition efficiencies due to the functional groups. In particular, PD-2 shows superior corrosion inhibition capacity, and the efficiency is up to 94% at a relatively low concentration of 100 mg L⁻¹ at 298 K, as determined by potentiodynamic polarization measurements. Surface analysis of mild steel with PD-2 as an inhibitor clearly indicates that the inhibitor molecules adsorb on the steel surface and efficiently inhibit the corrosion of mild steel. The present work provides very meaningful results in designing and preparing new polymer inhibitors with high inhibition efficiency.

To improve the corrosion inhibition efficiency of polyaspartic acid (PASP) for mild steel in acidic solutions, PASP/N-(3-aminopropyl)imidazole (PD-1) and PASP/N-(3-aminopropyl)-imidazole-co-n-dodecylamine (PD-2) were synthesized.     

The inhibition of mild steel corrosion in 0.5 M H2SO4 solution by radish leaf extract

The inhibitory effect of radish leaf extract (RLE) on mild steel corrosion in 0.5 M H₂SO₄ was studied by the weight loss method and the electrochemical method. The results demonstrated that the efficiency of inhibition increased with an increase in the concentration of RLE and decreased with an increase in temperature. The inhibition performance reached 93% with 300 mg L⁻¹ at 298 K. RLE behaved as a mixed-type inhibitor based on the cathode. The inhibition mechanism involved the adsorption of the active ingredients of RLE on the mild steel surface to prevent corrosion. The adsorption followed the Langmuir adsorption isotherm, and physical and chemical adsorption coexisted. The results were supported by SEM, quantum chemical calculations, FTIR and UV-visible spectroscopy analyses.

The inhibitory effect of radish leaf extract (RLE) on mild steel corrosion in 0.5 M H₂SO₄ was studied by the weight loss method and the electrochemical method.     

Synthesis and characterization of novel dicarbohydrazide derivatives with electrochemical and theoretical approaches as potential corrosion inhibitors for N80 steel in a 3.5% NaCl solution

Two novel ethanoanthracene-11,12-dicarbohydrazide derivatives N′¹¹,N′¹²-bis((Z)-4-hydroxybenzylidene)-9,10-dihydro-9,10-ethanoanthracene-11,12-dicarbohydrazide (H₂HEH) and N′¹¹,N′¹²-bis((Z)-4-methoxybenzylidene)-9,10-dihydro-9,10-ethanoanthracene-11,12-dicarbohydrazide (H₂MEH) were synthesized and characterized by FT-IR spectroscopy, electronic spectra, and NMR spectroscopy. These two derivatives as novel anticorrosion inhibitors for N80 steel in a 3.5% NaCl solution were studied using electrochemical techniques including potentiodynamic polarization (PP), electrochemical impedance spectroscopy (EIS), and electrochemical frequency modulation (EFM). Corrosion parameters and adsorption isotherms were determined from current–potential diagrams (i.e., Tafel slopes). The impact of temperature and inhibitor concentration on the corrosion performance was studied using the PP method. The PP results suggested mixed-type inhibitors. The inhibition prohibition increased and decreased when the dose was increased and the temperature was increased, respectively. The adsorption of the hydrazides on the N80 exterior followed the Langmuir isotherm. The maximum inhibition proficiency for H₂MEH and H₂HEH were 93.3% and 92.2%, respectively, at 1 × 10⁻⁴ M. Moreover, the investigated surface was studied with the synthesized compounds through X-ray photoelectron spectroscopy (XPS) to confirm the construction of an adsorbed shielding barrier. An evident association was established between the corrosion inhibition proficiency and theoretical variables acquired using the density functional theory (DFT) method and Monte Carlo (MC) simulations. The experimental data were in good agreement with the theoretical results.

Two novel dicarbohydrazide derivatives (H₂HEH) and (H₂MEH) were synthesized and tested as corrosion inhibitors for N80 steel in 3.5% NaCl solution via electrochemical and theoretical approaches.     

Experimental and theoretical investigations of four amine derivatives as effective corrosion inhibitors for mild steel in HCl medium

Four amine derivative compounds were synthesized: 2-[(phenylamino)methyl]phenol, 2-{[(4-hydroxyphenyl)amino]methyl}phenol, 2-[(2-hydroxybenzyl)amino]benzonitrile and 2-{[(3-chlorophenyl)amino]methyl}phenol. The structure of the organic molecules was confirmed by FT-IR, ¹³C NMR and ¹H NMR spectroscopy analyses. Their corrosion inhibition performances on mild steel in 1 M HCl were investigated using electrochemical measurements and surface analysis. Scanning electron microscopy analysis confirms the presence on the mild steel surface of a protective film of the as-prepared organic compounds, which depends on the substituent groups. Moreover, density functional theory and molecular dynamics simulation were employed in order to determine the adsorption mechanism and the position of amine derivative molecules towards the mild steel surface in an aggressive solution and to confirm the electrochemical results. The inhibition efficiency (IE) decreases with a decrease in concentration and the adsorption obeyed the Langmuir isotherm. The substitution of the OH group on the aromatic ring by Cl or CN increases IE to 90.23 and 92.56%, respectively. Molecular dynamics simulations attested that the four molecules were adsorbed on the Fe (110) surface in a flat position in the presence of water and HCl with high interaction between the different groups of the inhibitors and mild steel surface.

Four amine derivative compounds were synthesized and used as organic corrosion inhibitors.     

The synergistic influence of polyethyleneimine-grafted graphene oxide and iodide for the protection of steel in acidizing conditions

Herein, graphene oxide (GO) was chemically functionalized with polyethyleneimine (PEI) in a single step to obtain PEI-GO, which was characterized via FTIR spectroscopy, SEM, and TEM. Additionally, for the first time, PEI-GO was employed for the corrosion mitigation of carbon steel in a solution of 15% HCl. The corrosion performance of the inhibitor was evaluated by utilizing weight loss tests, electrochemical measurements with impedance analysis, electrochemical frequency modulation, and potentiodynamic polarization studies. Thorough surface analysis was performed using 3D profilometry and static water contact angle measurements. PEI-GO was adsorbed on the steel surface and showed mixed-type corrosion inhibition behavior with the prevalence of cathodic characteristics. Additionally, potassium iodide was incorporated in the acid solution as a synergistic agent to enhance the corrosion inhibition behavior of PEI-GO. The obtained results showed that PEI-GO alone provided a high corrosion inhibition efficiency of 88.24% at a temperature of 65 °C and in the presence of KI, it showed an I.E. of 95.77% due to their synergistic effect. These interesting results demonstrate that PEI-GO can act as a potential corrosion inhibitor in acidizing conditions. The DFT-based computational studies showed that the inhibitor functioned in both its neutral and protonated forms.

Herein, graphene oxide (GO) was chemically functionalized with polyethyleneimine (PEI) in a single step to obtain PEI-GO, which was characterized via FTIR spectroscopy, SEM, and TEM.     

Analysis of effect of oil and S2− impurities on corrosion behavior of 16Mn steel for storage tanks by electrochemical method

Corrosion is a common problem of storage tanks, and different storage media and impurities have different effects on the corrosion behavior of steel used for tanks. In this paper, electrochemical impedance spectroscopy (EIS) and polarization curves were used to study the corrosion behavior of 16Mn steel in 3.5% sodium chloride solution after immersion in heavy oil, diesel oil and gasoline, considering the influence of the main impurities, S²⁻, on the corrosion process. The results showed that the self-corrosion current density of 16Mn steel in the solution after the immersion in gasoline was higher than that in heavy oil and diesel oil, due to the higher dissolved oxygen concentration promoting the cathodic reaction. The comparison of blank sample in 3.5% sodium chloride solution and the immersed samples showed that the corrosion rate of the 16Mn steel decreased in the presence of an oil film on the surface of the steel. With the increase of S²⁻ concentration in the oil, the corrosion rate of 16Mn steel tended to be stable after it gradually increased. This was mainly related to the composition of FeS and FeS_1−x in the sulfide film formed on the surface of the steel as well as the change of the lattice structure.

Corrosion is a common problem of storage tanks, and different storage media and impurities have different effects on the corrosion behavior of steel used for tanks.     

Synthesis,characterization and electrochemical analysis of cysteine modified polymers for corrosion inhibition of mild steel in aqueous 1 M HCl

Butler''s cyclopolymerization protocol was used to synthesize homo and copolymers of cysteine residues and diallyldimethylammonium chloride (DADMAC) using water as a solvent and excellent yields were obtained. The structural composition of the polymers was determined using nuclear magnetic resonance (NMR) and Fourier-transform infrared (FT-IR) spectroscopies. The thermal stability of the synthesized polymers was determined using thermogravimetric analysis (TGA). The corrosion efficiencies and adsorption characteristics of these polymers on mild steel were evaluated using gravimetric weight loss and potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS). The copolymers of cysteine residues and DADMAC exhibited excellent inhibition efficiencies in arresting mild steel corrosion in 1 M hydrochloric acid (HCl) at 60 °C. The best fitted Langmuir, Temkin and Freundlich adsorption isotherms suggested that the adsorption process occurs through chemisorption and physisorption. The surface morphology of mild steel in the presence or absence of polymers was determined using atomic force microscopy (AFM), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS). This systematic study might provide a way to design new inhibitor compounds that could be beneficial in the field of biomedical science as well as for anti-corrosion applications.

Mild steel framework embedded in corrosion inhibiting structural motifs.     

Preparation of epoxy/ZrO2 composite coating on the Q235 surface by electrostatic spraying and its corrosion resistance in 3.5% NaCl solution

The epoxy coating containing ZrO₂ nanoparticles modified with 3-aminopropyltriethoxysilane (APTES) was prepared by electrostatic spraying on the surface of Q235 mild steel. The effect of the concentration of APTES-modified ZrO₂ nanoparticles on the corrosion resistance of epoxy coating was characterized and tested by FTIR spectroscopy, scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). The results show that nano ZrO₂ was successfully modified by a silane coupling agent. By adding an appropriate amount of APTES to modify nano ZrO₂ in epoxy coating could significantly improve the corrosion resistance of the Q235 surface. When the mass fraction of nano ZrO₂ is 2%, the composite coating shows the highest impedance value of about 1.0 × 10⁵ Ω cm² to achieve the best corrosion resistance.

Epoxy/ZrO₂ composite coating was prepared by electrostatic spraying. The best corrosion resistance in 3.5% NaCl solution was observed using 2 wt% ZrO₂.     

Green inhibitor of carbon steel corrosion in 1 M hydrochloric acid: Eruca sativa seed extract (experimental and theoretical studies)

The adsorption activity and inhibition effect of Eruca sativa seed extract as a green inhibitor for the dissolution of carbon steel in 1 M hydrochloric acid solution were investigated. In this study, we used a chemical technique (gravimetric method), electrochemical techniques, electrical frequency modulation (EFM), electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization techniques, and theoretical studies. In addition to these techniques, we examined the surface morphology of the carbon steel utilizing different methods. The measurements of the polarization technique indicate that this extract acts as a mixed-type inhibitor. Thermodynamic parameters were calculated and discussed. The adsorption of Eruca sativa seed extracts on the alloy obeys the Langmuir and Henry adsorption isotherms. The extract gives an excellent inhibition efficiency 94.8% by a gravimetric method at 0.3 g L⁻¹ from the extract. The relationship between the calculated % IE from experiments and the theoretical studies was established.

The adsorption activity and inhibition effect of Eruca sativa seed extract as a green inhibitor for the dissolution of carbon steel in 1 M hydrochloric acid solution were investigated.     

Interfacial interaction study of EDTA with the defect structure of Fe3−δO4 passive film in an aggressive alkaline medium based on the lattice theory of point defects

Despite extensive research on the matter of corrosion inhibition efficiency, the interactions between the defect structure of the passive layer and the inhibitor molecules still remain poorly understood. In this study, the corrosion inhibition mechanism of ethylenediamine-tetraacetic acid as a carboxylate-based organic inhibitor on steel specimens in simulated concrete pore solution was studied. The point defect model was used to describe the response of the passive oxide film on the steel surface to the perturbation caused by the addition of the carboxylate compound. The electrochemical behavior of the steel specimens was evaluated through open circuit potential, electrochemical impedance spectroscopy and potentiodynamic analysis. The reduction in efficiency outside the optimal concentrations was discussed from an electrochemical point of view. We suggest that the performance of the inhibitor is highly dependent on the positively charged entities on the passive layer including anion vacancies and interstitial cations. To further investigate the physicochemical behavior of the organic molecules, density functional theory and adsorption isotherms were applied. The topography and morphology of the surface were analyzed through scanning electron microscopy. To confirm the inhibitive effect of EDTA, the elements and chemical bonds present on the surface were characterized via X-ray photoelectron spectroscopy. The surface analysis confirmed that the addition of EDTA formed a network of chemical bonds, which significantly hindered the corrosion phenomenon.

Despite extensive research on the matter of corrosion inhibition efficiency, the interactions between the defect structure of the passive layer and the inhibitor molecules still remain poorly understood.     

A novel l-histidine based ionic liquid (LHIL) as an efficient corrosion inhibitor for mild steel

A novel l-histidine based ionic liquid (LHIL) was developed and successfully synthesized. Its structure was confirmed by Fourier-transform infrared spectroscopy, UV-vis spectroscopy, X-ray photoelectron spectroscopy, ¹H-NMR and high-resolution mass spectrometry. The outstanding corrosion inhibition effect of the LHIL on mild steel in 1 M hydrochloric acid was thoroughly evaluated by Tafel plots, electrochemical impedance spectroscopy, and localized electrochemical strategies. The results revealed that the corrosion of mild steel was effectively suppressed by the adsorption of LHIL on its surface, and the best inhibition efficiency reached 98.8%. The adsorption behavior of LHIL on steel obeyed the Langmuir adsorption isotherm, which involved both chemisorption and physisorption. Theoretical calculations indicated the strong chemisorption of LHIL on steel, as proved by the low energy gap (ΔE = 0.0522 eV) and high binding energy (E_binding = 303.47 kcal mol⁻¹), which clearly confirmed the effectiveness of LHIL for steel protection.

A novel l-histidine based ionic liquid (LHIL) was developed and successfully synthesized.     

Corrosion inhibition on mild steel in 1 M HCl solution by Cryptocarya nigra extracts and three of its constituents (alkaloids)

Corrosion inhibition effect of the crude extracts (hexane, dichloromethane, methanol) from the bark of Cryptocarya nigra and three alkaloids named N-methylisococlaurine 1, N-methyllaurotetanine 2 and atherosperminine 3 isolated from the Cryptocarya nigra dichloromethane extract (CNDE) were investigated for mild steel corrosion in 1 M HCl solution. An electrochemical impedance study showed that CNDE and 2 reduced the corrosion significantly through a charge transfer mechanism with inhibition efficiency of 91.05% and 88.05%, respectively. Potentiodynamic polarization data indicated that CNDE acted through anodic type inhibition while 2 was a mixed type inhibitor with predominant anodic effectiveness. ΔG_ads values calculated from the Langmuir adsorption isotherm plots for CNDE (−28.2 kJ mol⁻¹) and 2 (−13.2 kJ mol⁻¹) suggested that they adsorbed on the mild steel surface via a physisorption mechanism. Scanning electron microscopy micrographs and elemental composition studies confirmed the formation of a protective film over the metal surface. Wastewater quality parameters of all the inhibitors demonstrated good biodegradability as their values were within the permissible limits to discharge for irrigation and horticultural uses.

Staggered and systematic arrangement of N-methyllaurotetanine 2 on the MS surface.     

The co-adsorption of thymohydroquinone dimethyl ether (THQ) and coumarin present in the aqueous extract of Ayapana triplinervis on mild steel and its protection in hydrochloric acid up to 323 K: computational and physicochemical studies

This study evaluates the corrosion inhibition property of the aqueous and alcoholic leaf extracts of the medicinal plant Ayapana triplinervis. The major components in the extracts are thymohydroquinone dimethyl ether (THQ) and coumarin. It is clear from the weight-loss studies that the water extract of the leaves (AYW) is superior to the alcoholic extract (AYA) in terms of offering corrosion inhibition. The 96% efficiency of 4% (v/v) AYW in 0.5 N HCl at room temperature changes to 84.62% at 323 K. The mixed-type inhibition behaviour of AYW shows slight dominance in the anodic direction. Studies suggest the multilayer adsorption of phytochemicals on the metal surface and that the adsorption follows the Temkin model. Theoretical studies using DFT and BIOVIA Materials Studio investigations establish THQ as a good inhibitor with high adsorption characteristics. Even though the concentration of coumarin in the extract is low, its presence in the extract facilitates the adsorption of THQ on the metal surface, which is evident from the MD simulation study. The changes in the surface topography and elemental composition of the metal specimen in the inhibited and uninhibited solution are monitored by SEM and EDX spectral studies. XPS data support the presence of both THQ and coumarin on the metal surface and the existence of co-ordinate bonding between the metal''s d orbital and the O atoms of THQ. Theoretical and experimental studies support the mixed mode of adsorption of THQ as physisorption followed by chemisorption.

This study evaluates the corrosion inhibition property of the aqueous and alcoholic leaf extracts of the medicinal plant Ayapana triplinervis.     

Aizoon extract as an eco-friendly corrosion inhibitor for stainless steel 430 in HCl solution

Aizoon extract is used as an eco-friendly anti-corrosive material for stainless steel 430 (SS430) in a 2 M hydrochloric acid solution. Many strategies were utilized to estimate the mitigation efficacy such as mass reduction (MR), electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization (PDP). The inhibition percentage (%I) increases by increasing the concentration of Aizoon and reaches 95.8% at 300 ppm and 298 K, while it lowers by raising the temperature, reaching 85.6% at 318 K. Tafel curves demonstrated that Aizoon extract is a mixed type inhibitor with an excellent ability to inhibit the cathodic reaction. Adsorption of the Aizoon extract on an SS430 surface is regulated by the Langmuir adsorption model. The value is is −20.9 kJ mol⁻¹ at 298 K indicating that the adsorption is of mixed type affecting both cathodic and anodic reactions. Thermodynamic factors for adsorption and activation processes were estimated and discussed. The adsorption of Aizoon extract on the SS430 surface was tested utilizing Fourier transform infrared spectroscopy (FTIR) and scanning electron microscope (SEM) techniques. The Nyquist curves confirmed that Aizoon extract prohibits the disintegration of SS430 in an acid medium without changing the dissolution reaction mechanism. The theoretical calculations showed that Aizoon extract is considered as an excellent corrosion inhibitor. The experimental data were supported by theoretical evaluations.

Aizoon extract is used as an eco-friendly anti-corrosive material for stainless steel 430 (SS430) in 2 M hydrochloric acid solution.     

Experimental and theoretical investigation on corrosion inhibitive properties of steel rebar by a newly designed environmentally friendly inhibitor formula

In order to mitigate the corrosion of steel rebar in concrete, a new environmentally friendly corrosion inhibitor formula (WKI) was designed and the corrosion inhibitive effects of WKI on steel rebar were studied by gravimetric method, electrochemical impendence spectroscopy (EIS), potentiodynamic polarization and Mott–Schottky scanning in simulated concrete pore solution. Furthermore, surface analysis and quantum chemical calculations were conducted in order to illustrate the corrosion inhibitive mechanism. The results indicate that WKI exhibits excellent corrosion inhibitive activities on steel rebar in simulated concrete pore solution. By the presence of WKI, local corrosion was significantly suppressed and no pitting could be detected during the whole experimental period. The total corrosion resistance was increased from 5469 Ω cm² to 64 440 Ω cm² and the corrosion current density was reduced from 3.23 μA cm⁻² to 0.21 μA cm⁻² for the sample immersed in the corrosion medium for 7 d with WKI. The corrosion potential of the steel rebar electrode moved to a higher level and the charge transfer resistance increased, indicating that the anti-corrosion properties of the steel rebar were enhanced. The corrosion inhibitive mechanism of WKI can be attributed to the fact that it can promote the formation of a passive film and reduce its defect concentration via its adsorption and interaction with the metal surface, consequently inhibiting the corrosion of steel rebar caused by chloride ions.

A new corrosion inhibitor formula was designed and the inhibitive mechanism was analyzed based on HSAB theory and the PDM model.     

Sub–acute oral toxicity study of methanol leaves extract of Catharanthus roseus in rats

ObjectiveTo examine the sub-acute (14 d) oral toxic effects of methanol leaves extract of Catharanthus roseus (C. roseus) (Family: Apocynaceae) on liver and kidney functions in Sprague Dawley (SD) rats.MethodsTwenty four female SD rats were used throughout the experiment. The first group was orally treated with distilled water and served as control, whereas the remaining three groups were orally treated with single dose daily of 0.1 g/kg, 0.5 g/kg, 1 g/kg of C. roseus extract, respectively for 14 d. Cage-side observations were done daily. Any animal died during the experiment was dissected for gross organ examination. Body weight changed, food consumption and water intake were recorded weekly. Blood was collected via cardiac puncture on day-15 and used for determination of serum levels of aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase, creatinine and urea. The relative organ weights were also measured. All results were expressed as mean ± S.E.M and analysed using Dunnett's test. The level of significance was set at P<0.05 when compared to the control group.ResultsRepeated oral administration of 0.5 g/kg and 1 g/kg of methanol leaves extract of C. roseus caused mortality and diarrhoea in rats after few days of treatment. There were no significant changes observed in serum biochemical markers, body weight changed, water and food intake and relative organ weight in rats treated with a single dose daily of 0.1 g/kg of C. roseus extract treatment for 14 d when compared to control group.ConclusiondsFourteen days repeated oral administration of 0.1 g/kg of methanol leaves extract of C. roseus was safe in female SD rats without causing any significant damages to liver and kidney.     

Efficient corrosion inhibition by sugarcane purple rind extract for carbon steel in HCl solution: mechanism analyses by experimental and in silico insights

Sugarcane purple rind ethanolic extract (SPRE) was evaluated as an efficient corrosion inhibitor for carbon steel (C-steel) in 1 M HCl solution. Dynamic weight loss, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and frequency modulation (EFM) measurements were employed to evaluate the anticorrosive efficiency of SPRE, which was further validated by morphological and wettability analyses. The results of the weight loss tests showed that the inhibition efficiency (η_w) for C-steel in HCl solution increased with an increase in the concentration of SPRE. An increase in temperature moderately impaired the anticorrosive efficacy of SPRE. The maximum η_w of 96.2% was attained for C-steel in the inhibition system with 800 mg L⁻¹ SPRE at 298 K. The polarization curves indicated that SPRE simultaneously suppressed the anodic and cathodic reactions for C-steel in HCl solution, which can be categorized as a mixed-type corrosion inhibitor with a predominant anodic effect. The corrosion current density (i_corr-P) was monotonously reduced with an increase in the concentration of SPRE. The charge transfer resistance (R_ct) was enhanced for C-steel in the inhibition solution with a restrained capacitive property due to the adsorption of SPRE. A high temperature caused partial desorption of SPRE on the C-steel surface and a slight increase in i_corr-P and decrease in R_ct. However, SPRE still fully maintained its morphology and wettability at 328 K. The electrochemical kinetics of C-steel in HCl solution without and with SPRE was also supported by EFM spectra. The adsorption of SPRE conformed to the Langmuir isotherm and increased the corrosion activation energy of C-steel. Complementing the experimental observations, calculations based on density functional theory indicated that the hydroxyl-substituted pyran moiety on the carthamin (CTM) and anthocyanin (ATC) constituents in SPRE hardly contributed to its reactive activity due to their adsorption processes. Therefore, CTM and ATC exhibited imperfect parallel adsorption on the Fe (100) plane according to the molecular dynamics simulation, while anthoxanthin (ATA) and catechinic acid (CCA) constituents exhibited a flat orientation on the iron surface.

The anticorrosive mechanism of extracted components from sugarcane purple rind for carbon steel in HCl solution is clarified by weight loss, electrochemical and theoretical (novel DFT calculation and molecular dynamics simulation) analyses.