In this study, leaves extract of Arbutus unedo L. plant was used as a green corrosion inhibitor of mild steel in hydrochloric acid. The aqueous extract is rich in polyphenol and in particular ...flavonoid compounds as determined by the quantitative aluminum chloride colorimetric method. The n-butanol extract shows the highest concentration of total phenol and total flavonoid contents with 219.46 GAE mg/g extract and 174.66 mg QE/g of dry extract, respectively. Electrochemical impedance spectroscopy and potentiodynamic polarization were used as experimental measurements to confirm the anti-corrosion performances of the extract of plant leaves at different temperatures. The addition of extract plant even at low concentration increases significantly the inhibition efficiency with a maximum of 91.72% at 298 K for 0.5 g/L of leaves extract. Surface analysis was performed to attest the presence of the protected film on the surface of mild steel in HCl solution. The calculated ΔG0ads value (−24.441 kJ/mol) confirmed a spontaneous mixed chemical and physical adsorption of leaves extract compounds on the metal surface. The pKa analysis attested that the two leaves extract compounds, quercetin and catechin, exist in the neutral form in an acidic environment. Moreover, density functional theory and molecular dynamic simulation were also conducted to support the high inhibition efficiency results obtained by the experimental tests and to propose the adsorption mechanism.
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•Leaves extract of Arbutus unedo L. plant was used as efficient corrosion inhibitor.•Adsorption of the leaves extract on mild steel surface obeys Langmuir's isotherm.•Quantum chemical parameters were in good correlation with electrochemical results.•MD simulation showed that quercetin molecule was adsorbed spontaneously on parallel to the metal surface.
The CuBi2O4/TiO2 heterojunction was tested with success for the photo-catalytic reduction of chromate ions under sunlight. CuBi2O4, prepared by nitrate process, was characterised ...photo-electrochemically. The oxide is stable against photo corrosion by consumption of holes in presence of oxalic acid. The light absorption promotes electrons in the conduction band of the sensitizer (CuBi2O4) with a very negative potential (−1.74 VSCE) to participate in the exchange of the electron with HCrO4−. The enhanced activity is due to electron injection of activated CuBi2O4 into TiO2-CB (−0.97 VSCE). The band gap of the semiconductor CuBi2O4 is 1.50 eV with a direct optical transition. This compound is a p-type semiconductor with a flat band potential of −0.39 VSCE and activation energy of 0.18 eV. The electrochemical impedance spectroscopy was undertaken to study the semiconductor/electrolyte interfacial phenomena. The photoactivity on the heterojunction is strongly enhanced. A remarkable performance is obtained in less than 4 h for a concentration of 30 mg in (Cr (VI)) at pH ∼ 4 and a dose of 1 mg/mL; a 98% reduction has been obtained. The kinetic of chromate photoreduction is well described by the Langmuir-Hinshelwood model. The chromate elimination obeys to a pseudo-first order kinetic with an apparent rate constant of 0.014 min−1.
•In this work, the photocatalytic reduction of chromate using a new hetero-system CuBi2O4/TiO2 was studied.•The cathodic photocurrent is characteristic of p-type semiconductor. The flat band potential was determined from the Mott-Schottky characteristic.•The photocatalytic activity of the p-n hetero-system is much better than those of TiO2 or CuBi2O4 under the same conditions.•In less than 4 h and at pH∼ 4, 98% reduction was obtained for a concentration of 30 mg/L.•The experimental data fit adequately the Langmuir-Hinshelwood model. The reduction obeys to a first order kinetics.
In this work, a Discrete Element Method (DEM)-based numerical model has been developed in C++ program, which enables to simulate the crack propagation of plasma-sprayed Al2O3 coatings thus enabling ...to predict their failure. DEM-based approach is combined with the image analysis procedure applied on two-dimensional (2D) cross-section images of as-sprayed coatings. This procedure allows to build up the model of the coating microstructure taking into account defects which can be regarded as pores and cracks. Pores are then discriminated from cracks and these latter are in turn categorized into two types intra- and inter-splat cracks which have been considered in the simulations of crack propagation. Results indicate that the Young's modulus of as-sprayed coatings depends strongly on the geometric features of the porosity, namely the shape and the distribution. The simulation results on crack propagation exhibit that the generation of cracks which begin inside the splat due to the intra-splat cracks yield large cracks which propagate vertically until to reach the surface of the coating, while inter-splat cracks located at the interface between splats evolve by creating a bifurcation through an interlinking mechanism with other cracks.
•A numerical tool has been developed to study the mechanical behavior of plasma-sprayed alumina coatings.•This numerical tool is based on the discrete element method and enables to simulate the crack propagation.•The crack propagation located at the splat interface evolves by creating a bifurcation through an interlinking mechanism.•The fracture strength depends on the local properties of microstructure defects.
Nanocrystalline lithium manganese oxide (LiMn2O4), synthesized by the sol-gel method, crystallizes in the spinel structure. The physical, electrical, and photoelectrochemical properties were studied ...for the photocatalytic degradation of methyl orange, a toxic compound, under solar irradiation. The diffuse reflectance spectrum allowed the direct band gap (1.99 eV) to be calculated. The Fourier transform IR spectrum contained all the characteristic peaks of the spinel LiMn2O4, which exhibited n-type behavior. The thermal evolution of the electrical conductivity exhibited an Arrhenius-type behavior with an activation energy of 0.27 eV. The Mott-Schottky curve allowed the determination of the flat band potential (−0.24 V vs. the saturated calomel electrode) as well as the carrier density (1.78 × 1021 cm−3). The detoxification of water containing methyl orange with LiMn2O4 as a photocatalyst was successfully completed. Total degradation for an initial concentration of 10−4 M methyl orange at pH ∼3 and 25 °C was obtained in less than 5 h under solar irradiation. No adsorption was obtained in the dark in the presence of LiMn2O4.
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•The physical, optical, and photoelectrochemical properties of LiMn2O4 prepared by the sol-gel method were studied.•The photocatalytic activity of LiMn2O4 under sunlight was tested for the first time for the degradation of methyl orange.•The energy diagram of LiMn2O4 was established regarding the different characterizations performed.•The photocurrent is characteristic of an n-type semiconductor. The flat band potential was determined from the Mott-Schottky curve.•In less than 2 h and at pH∼ 3, 50% degradation of methyl orange was obtained.
Gadolinium cuprate Gd2CuO4 was synthesized by nitrate route and its physical and electrochemical properties were investigated for the first time. The cuprate was characterized by X-ray diffraction ...(XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The Diffuse reflectance infrared Fourier transform (DRIFT) spectrum confirms the characteristic peaks of Gd2CuO4 while the Brunauer-Emmett-Teller (BET) measurement gave a specific surface area of 20.45 m2 g−1. An optical gap of 1.41 eV was obtained from the diffuse reflectance (DR) and the transition is directly allowed. The electrical conductivity indicated semiconducting behavior with activation energy of 0.1 eV that correlates with the formal valence of copper. Indeed, the insertion of oxygen into the layered crystal lattice induces p-conductivity with mixed valences Cu3+/2+ and mechanism conduction by small polaron hopping. The carrier density (1.17 1019 cm−3) and flat potential (Efb = −0.33 VSCE) were determined from the (capacitance−2 – potential) characteristic. The conduction band (−1.64 VSCE), positioned at 3.11 eV below vacuum, is made up of Gd3+: (5d, 6s) hybridized orbital while the valence band (−0.23 VSCE/4.52 eV) derives mostly from Cu2+: 3d orbital.
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•The gadolinium cuprate Gd2CuO4 was prepared by nitrate route.•Gadolinium cuprate crystallizes in a K2NiF4-type structure with space group 14/mmm.•The optical band gap is directly allowed with a value of 1.41 eV.•The insertion of oxygen into the layered crystal lattice induces p-conductivity.•The position of the conduction and valence bands are proposed.
Context and results
In this study, the heterojunction Cu
2
O/TiO
2
is used for the degradation of a cationic dye, Rhodamine B, under solar light irradiation over a wide pH range. The physical and ...optical properties of both semiconductors Cu
2
O and TiO
2
are correlated with the photo-electrochemical characterization to establish the energy diagram of the heterojunction Cu
2
O/TiO
2
. X-ray diffraction, UV–visible, SEM, EDX, and BET analyses are conducted for both photocatalysts. The band gap (E
g
) of 3.26 eV is obtained for TiO
2
with an indirect optical transition. In the case of Cu
2
O, the transition is directly allowed at 2.05 eV. According to the BET analysis, the specific surface area of TiO
2
particles is higher (82.65 m
2
g
−1
) than that of Cu
2
O (29.81 m
2
g
−1
). The flat band potentials, determined from the Mott-Schottky plots, are 0.3 and − 0.32 V
SCE
for TiO
2
and Cu
2
O, respectively. The photocatalytic activity is directly proportional to the mass ratio, and the best result is obtained for the mass ratio 1:1 of Cu
2
O/TiO
2
.
Computational and theoretical techniques
Furthermore, a theoretical study is conducted by using density functional theory to optimize the structure, reactivity sites of the RhB molecule, and physical parameters like the energy of the frontier molecular orbitals and electronegativity and to predict the proposed mechanism of RhB degradation as well as its intermediates. Also, molecular dynamics simulation is used to determine the adsorption behavior of RhB on TiO
2
(101) and Cu
2
O (111) surfaces. The ecotoxicity evaluation showed that degradation products have significantly lower acute toxicity than RhB.
The semiconducting properties of La
2
CuO
4
prepared by a chemical route are investigated for the first time by the photo-electrochemical technique. The optical gap is found to be 1.27 eV and the ...transition is directly allowed. p-Type conductivity is demonstrated from the Mott–Schottky plot in alkaline KOH solution (0.1 M), extrapolation of the linear region to the potential axis gives a flat band potential of −0.41 V
SCE
, a holes density of 1.75 × 10
19
cm
−3
and a space-charge region of 18 nm. The electrochemical impedance spectroscopy, measured over the frequency range (1 mHz–10
5
Hz), reveals the predominance of the bulk contribution with a constant phase element. The energy diagram shows the feasibility of La
2
CuO
4
for the H
2
evolution under visible light. The best performance occurs at pH 12.5 in the presence of S
2
O
3
2
−
as holes scavenger. A liberation rate of 20.6 μmol mn
−1
(g catalyst)
−1
is obtained under full light (29 mW cm
−2
).
•Antioxidant activity were explored of three natural flavonoid compounds of Arbutus unedo L. plant.•The HO at 4′ site displays the best stability.•HAT mechanism is most favorable in the gas and ...benzene phases.•SPLET mechanism is the thermodynamically preferred pathway in polar media.•B-ring of the three flavonoid compounds is the active center for the antioxidant activity.
In this work, the antioxidant activity, free radical-scavenging capacity, molecular geometry and intramolecular hydrogen bonding interaction were explored for three natural flavonoid compounds of Arbutus unedo L. plant, Fisetin (3,3′,4′,7-tetrahydroxy flavone), Catechin (Flavan-3,3′,4′,5,7-pentol) and Apigenin (4′,5,7-trihydroxy flavone). Three potential mechanisms of antioxidant activity, hydrogen atom transfer (HAT), single electron transfer-proton transfer (SET-PT) and sequential proton loss electron transfer (SPLET), have been explored. The physicochemical parameters (BDE, IP, PA, PD, ETE, HOMO and LUMO), as well spin density distribution, were calculated in different solvents. The mechanisms involved in the radical scavenging activity, taking into account the position of the most active OH hydroxyl group, are in accordance with the experimental tests. HAT mechanism is most favorable in the gas phase and benzene solvent. B-ring of the three flavonoids is the active center for the antioxidant activity. Fisetin presents the best antioxidant activity with high free radical scavenging capacity followed by Catechin and Apigenin, respectively.
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