Influence of 5-chloro and 5-methyl benzotriazole on the corrosion of copper in acid solution: an experimental and a theoretical approach

The inhibition of copper corrosion in aerated 0.1 mol l⁻¹ hydrochloric acid solutions was studied using electrochemical polarization in the presence of different concentrations of benzotriazole and its two derivatives, 5-chloro and 5-methyl benzotriazole. The inhibition efficiencies obtained from cathodic Tafel plots increased markedly with increase in the additive concentration. Benzotriazole and 5-methyl-benzotriazole were found to be cathodic type corrosion inhibitors for concentrations higher than 10⁻⁴ mol l⁻¹ . However, the 5-chloro-benzotriazole was found to be a mixed inhibitor for concentrations up to 10⁻³ mol l⁻¹, above this concentration the inhibitor behaves as an anodic type inhibitor. The inhibitors are physisorbed on the copper surface following a Langmuir’s isotherm. The inhibition efficiencies depended on the inhibitor concentration and follows the order 5-chloro-benzotriazole > 5-methyl-benzotriazole > 1-H-benzotriazole. From the theoretical calculations, the change in the inhibition mechanism observed for 5-chloro-benzotriazole at concentrations higher than 10⁻³ mol l⁻¹ is associated with the electronic acceptor characteristic of chloro, which increases the benzotriazole acidity allowing the formation of CuBTA.     

Determination of the stability constant for acetic acid in synthetic seawater media at various temperatures and salinities

The stability constant (association constant) for acetic acid in synthetic seawater was determined for salinities in the range 5 to 40, in 0.4M and 0.7M ionic strength sodium chloride and at temperatures between 5 and 45°C. The minimum in the log K₁ vs. temperature curve is displaced towards higher temperatures as the ionic strength of NaCl increases. For synthetic seawater solutions, H is independent of temperature but does depend on salinity.     

Ceratonia siliqua extract as a green corrosion inhibitor for copper and brass in nitric acid solutions

ABSTRACT

The influence of extract of ceratonia siliqua extract on the corrosion of copper and brass in aqueous 1 M nitric acid was examined by weight loss, potentiodynamic polarization, electrochemical impedance spectroscopy and electrochemical frequency modulation techniques. The surface morphology was analyzed using scanning electron microscope and energy dispersive X-ray techniques. Potentiodynamic polarization curves indicated that the plant extract behaves as cathodic inhibitor. The results indicate that the extract solution of the plant could serve as an effective inhibitor for the corrosion of copper and brass in nitric acid media. As temperature increases, percentage of inhibition decreases. The degree of surface coverage of the adsorbed inhibitor was determined by weight-loss technique, and it was found that the results obeyed the Langmuir adsorption isotherm.     

Utilisation of liquid chromatography in aquatic photodegradation studies of pesticides: A comparison between distilled water and seawater

Summary The advantages of liquid chromatography with diode array and mass spectrometric detection are described for the direct characterization of the photodegradation products of Fenitrothion, Atrazine and Diuron in distilled water and artifical seawater samples. The photodegradation (UV >290 nm) of the herbicides Atrazine and Diuron was examined in distilled water and in artificial seawater containing humic acids. Major photodegradation products were hydroxyatrazine and Monuron, respectively. The results showed a faster degradation in seawater as compared to distilled water for Atrazine whereas for Diuron a quenching effect was observed thus retarding photodegradation. The photodegradation of Fenitrothion was also investigated. For this pesticide, hydrolysis predominates in seawater and photolysis is very slow in distilled water, so that acetone was needed as photosensitizer.Presented at the 5th International Symposium on Environmental Pollution and its Impact on Life in the Mediterranean Region, Blanes, Spain, 2–6 October, 1989.     

Analysis of corrosion scales formed on steel at high temperatures in hydrocarbons containing model naphthenic acids and sulfur compounds

Corrosive naphthenic acids and sulfur compounds in crude oils present a major challenge for refineries from a corrosion perspective. Although it is accepted that some sulfur compounds may form protective FeS scales on the metal surface and deter corrosion, attempting to correlate the characteristics of FeS scale with its protective properties has not been successful. Given the complex chemical compositions of real crudes, model sulfur compound and model naphthenic acids were used to mimic the corrosion by crude fractions in the present study. The iron sulfide scale formed by the model sulfur/acid compounds was challenged by naphthenic acids under high‐velocity conditions to examine its protectiveness against corrosion. Moreover, the scale was analyzed with transmission electron microscope/energy dispersive X‐ray spectroscopy technique, and a layer of iron oxide formed on the 5Cr steel was found when naphthenic acids were present in the solution. The iron oxide layer appeared to be important for maintaining protection against naphthenic acid corrosion, and further analysis revealed that it was composed of magnetite. Copyright © 2015 John Wiley & Sons, Ltd.     

4-phenyl-decahydro-1H-1,5-benzodiazepin-2-one as novel and effective corrosion inhibitor for carbon steel in 1 M HCl solution: A combined experimental and empirical studies

The heterocyclic system, namely 4-phenyl-decahydro-1H-1,5-benzodiazepin-2-one (POBZ) was inspected as a corrosion inhibitor of carbon steel (CS) in a 1 M HCl medium through electrochemical impedance spectroscopy (EIS), potentiodynamic polarization measurements (PDP), and scanning electron microscopy (SEM). The experimental data indicate that the inhibiting action augments with augmenting POBZ amount and reduces with augmenting temperature. The inhibiting action efficiency of 90.98% is obtained with 0.001 M at 303 K. The potentiodynamic polarization (PDP) results mentioned that the POBZ is of mixed type. The adsorption of POBZ on the CS followed Langmuir isotherm. SEM exams affirmed that the steel surface is smooth in presence of POBZ. In light of the calculations of density functional theory (DFT) and molecular dynamics simulation, the mechanism of POBZ inhibitory activity was addressed.     

Coconut coir dust extract: a novel eco-friendly corrosion inhibitor for Al in HCl solutions

Abstract

Corrosion inhibition of aluminium in 1 M HCl by coconut coir dust extract (CCDE) was studied using weight loss and hydrogen evolution techniques at 30 and 60°C. It was found that the studied extract exhibits a very good performance as inhibitor for aluminium corrosion in 1 M HCl. Results show that the inhibition efficiency increases with increasing temperature and concentration of the extract. Inhibitive effect was afforded by adsorption of the extracts' components which was found to accord with Langmuir adsorption isotherm. Inhibition mechanism is deduced from the temperature dependence of the inhibition efficiency and was further corroborated by the values of activation parameters obtained from the experimental data.     

Thermodynamics of the dissociation of 2-aminopyridinium ion in synthetic seawater and a standard for pH in marine systems

Buffer solutions composed of 2-aminopyridinium chloride and 2-aminopyridine in synthetic seawater are useful as a supplement to buffers of Tris (pH 8.2) and Bis (pH 8.8) in standardizing measurements of hydrogen ion concentration (pm _H or pH(SWS)) in oceanography. The dissociation constant of 2-amino-pyridinium ion over the range of salinities (S) from 30 to 40 has now been determined from the emf of cells without liquid junction at eight temperatures (T) from 278.15 to 313.15 K. The results fit the equation pK=2498.31/T–15.3274+2.4050 lnT+S(0.012928–2.9417×10^–5T) with a standard deviation of 0.0023. Thermodynamic constants for the dissociation process and standard reference values of pm _H and pH(SWS) were derived from the data. The pm _H of the buffer consisting of 2-aminopyridinium chloride and 2-aminopyridine (each 0.04 molal) in synthetic seawater of salinity 35 varies from 7.356 at 278.15 K to 6.601 at 313.15 K.     

Potentiometric stripping analysis and anodic stripping voltammetry for measurement of copper(II) and lead(II) complexation by fulvic acid: A comparative study

The utility of potentiometric stripping analysis (PSA) for studying the interaction of fulvic acid with Cu^II and Pb^II at pH 1.8 and 4.8 was assessed. The impact of fulvic acid on both the deposition and stripping steps was considered. In contrast to results obtained by anodic stripping voltammetry, fulvic acid influenced both these steps in PSA, and to different degrees. Surface active substances have been claimed to have self-compensatory effects in PSA; this work shows that this is not valid for heterogenous natural complexants such as fulvic acid.     

Synthesis and characterization of some binuclear metal complexes with a pentadentate azodye ligand: An experimental and theoretical study

A novel series of binuclear complexes with Mn(II), Co(II), Ni(II), Cu(II), Zn(II), and Cd(II) ions derived from a pentadentate azo dye ligand (H₃L) was synthesized and structurally investigated by various physicochemical analyses, namely, scanning electron microscopy, transmission electron microscopy, NMR, UV–visible spectroscopy, and Electron-Spin Resonance (ESR) studies. The infrared spectral data revealed characteristic bands due to ν(N=N) and ν(C=O) at 1606 and 1631 cm⁻¹ in the free ligand. However, their positions shifted and appeared at ~1564 and ~1592 cm⁻¹ on coordination, suggesting the involvement of carbonyl oxygen and azo nitrogen in complex formation. The spectral data suggested octahedral geometry for the complexes. The kinetic parameters such as order and activation energy were determined from the thermal decomposition values. X-ray powder diffraction analysis showed the orthorhombic nature of the cadmium complex. Furthermore, Density functional theory (DFT) calculations were also recorded to describe the insight bonding. The synthesized compounds were tested for in vitro antibacterial activity against K. aerogenes, S. aureus, B. acidoterrestris, E. coli, and V. cholerae strains by the cup-plate method. In addition, the interactions that occurred in the protein–ligand complexes have been predicted by docking analysis.     

Copper phosphonates with dinuclear and layer structures: a structural and magnetic study

Hydrothermal reactions of copper (II) nitrate with 1-hydroxycyclohexanephosphonic acid [C₆H₁₀(OH)PO₃H₂] or Δ¹-cyclohexenephosphonic acid [C₆H₉PO₃H₂] have resulted in three new copper phosphonates, namely, Cu(C₆H₁₀(OH)PO₃)(H₂O)₂ (1), Cu(C₆H₁₀(OH)PO₃) (2) and Cu(C₆H₉PO₃)(H₂O) (3). Compound 1 has a dinuclear structure in which two {CuO₅} square pyramids are bridged by two {CPO₃} tetrahedra through corner sharing. The dimers are connected through intermolecular hydrogen bonds, forming supramolecular layers. Both compounds 2 and 3 show layer structures typical for metal mono-phosphonates, in which the inorganic metal-containing layers are separated by cyclohexane or cyclohexene groups. The magnetic studies show that ferromagnetic interactions are mediated between copper centers in compound 1. In compounds 2 and 3, antiferromagnetic interactions are dominant.     

Experimental,DFT studies and molecular dynamic simulation on the corrosion inhibition of carbon steel in 1 M HCl by two newly synthesized 8-hydroxyquinoline derivatives

In the present work, two new 8-hydroxyquinoline derivatives namely, 5-(((2-hydroxybenzylidene)amino)methyl) 8-hydroxyquinoline [HBMQ] and 5-(((4-chlorobenzylidene)amino)methyl) 8-hydroxyquinoline [CBMQ] were synthesized and investigated as corrosion inhibitors against the dissolution of carbon steel (C38 steel) in 1 M HCl. These compounds were obtained with high yield, and their structures were characterized by nuclear magnetic resonance spectroscopy (NMR) and elemental analysis. Gravimetric, electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (PDP), and surface morphology analyses utilizing scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) were used to quantify inhibitory performance. The adsorption process of inhibitory compounds was then demonstrated using quantum mechanics approaches such as Density Functional Theory (DFT) and Molecular Dynamic Simulation (MD). Based on EIS results, the investigated derivatives effectively inhibit the degradation of C38 steel over the entire concentration range with a maximum efficiency of 91.9% and 88.0% for [CBMQ] and [HBMQ], respectively, at 10^?3 M. In addition, the PDP studies revealed that [HBMQ] and [CBMQ] compounds acted according to a mixed-type mechanism. Moreover, the adsorption mechanism follows the Langmuir isotherm model. The quantum theoretical study by DFT and MD simulation confirmed the experimental results.     

Boric acid: a novel and safe catalyst for aza-Michael reactions in water

Boric acid efficiently catalyzes the conjugate addition of aliphatic amines to α,β-unsaturated compounds to produce β-amino compounds, with great alacrity and excellent yields, in water under mild conditions. Aromatic amines do not participate effectively in the reaction.     

Determination of trace elements in seawater by electrothermal atomic absorption spectrometry with and without a preconcentration step

The determination of the trace metals Cd, Pb and Cu in seawater by electrothermal atomic absorption spectrometry (ETA-AAS) has been investigated. A combination of the platform with mixed palladium nitrate-magnesium nitrate as matrix modifier and Zeeman background correction allows Cd an Pb to be determined by aqueous standard calibration in appropriately diluted seawater samples. Copper can be determined in undiluted seawater samples without chemical modification using a standard additions method. Detection limits (3) of 2.97,5.27 and 1.1 gl^–1 are obtained for Cd, Pb and Cu respectively. A Kelex-100 impregnated silica C18 material (Kelex 100-C18) has been tried and has proved to be effective as a column packing for extraction/preconcentration of these metals from seawater. Using the column extraction method, the sensitivity of the graphite furnace technique is enhanced 50-fold using a 10 l injection volume. Thus, the determination of the studied three metals in seawater at the ng.l^–1 level could be achieved.     

Xanthione: A new and effective corrosion inhibitor for mild steel in sulphuric acid solution

The adsorption and inhibition effect of xanthione (XION) on mild steel in 0.5 M H₂SO₄ at 303–333 K were studied using gravimetric and UV–visible spectrophotometric methods. The results obtained show that XION acts as an effective corrosion inhibitor for mild steel in sulphuric acid and inhibition efficiency reaches 98.0% at a very low inhibitor concentration of 10 μM. Inhibition efficiency was found to increase with increase in XION concentration but decreased with temperature suggesting physical adsorption mechanism. Arrhenius law and its transition equation lead to estimate the activation parameters of the corrosion process. XION inhibits the corrosion of mild steel effectively at moderate temperature and adsorbs according to the Langmuir isotherm. Thermodynamic parameters governing the adsorption process have been calculated and discussed. The UV–visible absorption spectra of the solution containing the inhibitor after the immersion of mild steel specimen indicate the formation of a XEN–Fe complex. Attempt to correlate the molecular structure to quantum chemical indices was made using density functional theory (DFT).     

Copper(I) oxide and benzoic acid ‘on water’: a highly practical and efficient catalytic system for copper(I)-catalyzed azide-alkyne cycloaddition

A simple combination of Cu₂O and PhCO₂H ‘on H₂O’ has been developed as a highly practical and efficient catalytic system for copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC). It not only provides a further evidence for the strategy of carboxylic acids-promoted CuAAC, but also offers significant advantages to CuAAC because Cu₂O is one of the most stable and cheapest Cu(I) sources; PhCO₂H is one of the structurally simplest bidentate ligands; and water is the most ‘green’ solvent.     

Copper(II) complexes of tridentate selenobisphenolate ligand in mixed ligand environments: Synthesis, crystal structure, EPR and electrochemical studies

A series of square-pyramidal copper(II) complexes, [Cu(L^Se)(N^∧N)] (H₂L^Se = seleno-bisphenolate; N^∧N = bipyridyl, phenanthroline or N,N-dimethylethylenediamine) have been synthesized and characterized by elemental analyses, magnetic measurements, IR, EPR, and electronic spectral studies. Single crystal X-ray structures of [Cu(L^Se)(bpy)]·H₂O (2), [Cu(L^Se)(phen)]·CH₂Cl₂ (3) and [Cu(L^Se)(N,N-Me₂en)] (4) showed that all the complexes have approximately square-pyramidal geometry. In complexes 2 and 3, the square plane is occupied by O(1), O(2), N(1) and N(2) and the apical position by Se atom of L^{Se 2−} ligand. The asymmetric unit of complex 4 contains two crystallographically independent discrete molecules A and B with CuN₂OSe chromophore comprising the square plane and the axial position being occupied by another phenolate oxygen atom. Complexes 2, 3 and 4 are found to be paramagnetic and EPR parameters extracted are: g_∥ = 2.232, g_⊥ = 2.069; 〈g_eff〉 = 1.95; and g_∥ = 2.232, g_⊥ = 2.083 for complexes 2, 3 and 4, respectively. Both the complexes 2 and 4 show three reduction processes: (a) a quasi-reversible reduction of Cu^II to Cu^I, (b) an irreversible reduction of Cu^I to Cu⁰ with the release of free ligand, and (c) a reduction process occurs at this coordinated ligand. They also show a well-defined quasi-reversible oxidation of Cu^II to Cu^III and an irreversible oxidation peak at ∼1.30 and 1.40 V vs. Ag/AgCl for 4 and 2, respectively, with no cathodic counterpart, and were attributed to the oxidation of the metal coordinated ligand.     

Mixed metal fluorides as doped Lewis acidic catalyst systems: a comparative study involving novel high surface area metal fluorides

MF₃-doped/MgF₂ systems with enhanced Lewis acidity are reported, which are obtained either by the conventional aqueous route of co-precipitation or, by a novel non-aqueous soft chemistry route. The latter gives outstanding high surface areas and exhibits potent Lewis acid catalyst behaviour. The doped solid metal fluorides with dopant metals such as Ga, In, Fe, V are discussed in terms of the modified Tanabe model, which is adopted for metal fluoride systems. The two doped but differently prepared systems are analysed according to their surface characteristics by BET surface area, pore-size distribution and XPS/XAES as well as for the solid state structure by scanning electron microscopy (SEM), XRD and -MAS-NMR. The surface properties were evaluated by photoacoustic IR-spectroscopy of pyridine adsorbates and selected catalytic reactions.The exemplarily investigated GaF₃-doped/MgF₂ system reveals modified intrinsic properties of the solid mixture culminating in very high surface areas of a structurally distorted mesoporous solid and electrostatic charge rearrangements causing increased Lewis acid sites.     

Determination of iron in seawater by electrothermal atomic absorption spectrometry and atomic fluorescence spectrometry: A comparative study

Two methods available for direct determination of total Fe in seawater at low concentration level have been examined: electrothermal atomization atomic absorption spectrometry (ETAAS) and electrothermal atomization laser excited atomic fluorescence spectrometry (ETA-LEAFS). In a first part, we have optimized experimental conditions of ETAAS (electrothermal program, matrix chemical modification) for the determination of Fe in seawater by minimizing the chemical interference effects and the magnitude of the simultaneous background absorption signal. By using the best experimental conditions, a detection limit of 80 ng L⁻¹ (20 μL, 3σ) for total Fe concentration was obtained by ETAAS. Using similar experimental conditions (electrothermal program, chemical modification), we have optimized experimental conditions for the determination of Fe by LEAFS. The selected experimental conditions for ETA-LEAFS: excitation wavelength (296.69 nm), noise attenuation and adequate background correction led to a detection limit (3σ) of 3 ng L⁻¹ (i.e. 54 pM) for total Fe concentration with the use a 20 μL seawater sample. For the two methods, concentration values obtained for the analysis of Fe in a NASS-5 (0.2 μg L⁻¹) seawater sample were in good agreement with the certified values.