We describe a combined electrochemical and first principle density functional study to probe the corrosion inhibiting and adsorption behavior of methionine (Met) and phenylalanine (Phe) on polycrystalline and nanocrystalline iron in acid media. Met functioned as a better inhibitor for both Fe microstructures, and was more favorably adsorbed on the nanocrystalline surface. The nanocrystalline surface however diminished adsorption of Phe. The comparable values of our computed physisorption energies (−94.2 kcal mol⁻¹ and −86.6 kcal mol⁻¹ for Phe and Met respectively) as well as the stable adsorption orientations of both molecules on Fe suggest a controlling influence of a soft epitaxial adsorption mechanism in which C, N, O, S atoms of the molecules align with epitaxial grooves on the Fe lattice. The significant contribution of physisorptive interactions also correlates with the similarity in experimental inhibition efficiencies on polycrystalline Fe (Phe = 73% and Met = 82%), though for Met the thiol group imparts an added ability for covalent interaction with Fe, which accounts for the higher efficiency. Furthermore, we have related the diminished inhibition efficiency of Phe on the nanocrystalline Fe surface to disruption of the epitaxial patterns on the lattice as the surface becomes increasingly defective, leading to weaker adsorption. The improved efficiency of Met on the nanocrystalline surface is related to scaling up of the covalent interactions around defect sites. Our theoretical conclusions are validated by the consistency with our experimental findings.

The effect of temperature (from 288 to 308 K) and concentration of sulfide ions (up to 40 ppm) on the corrosion behavior of AISI 304L and AISI 316L stainless steels in seawater was studied with measurements of open-circuit potential, linear and potentiodynamic polarization, and electrochemical impedance spectroscopy. An increase in temperature and pollutant concentration negatively affects the corrosion stability of stainless steels at the open circuit (the resistance, compactness, and thickness of the surface layer decrease and the corrosion current increases), in the passive region (the passivation current increases, the depassivation potential decreases, and the passive potential region narrows), and in the transpassive potential region (the rate of metal dissolution increases). The occurrence of pitting corrosion on the surface of the samples was confirmed with optical microscopy and a non-contact 3D profilometer. A few large pits (depth 80–100 μm and width 100 μm) were formed on the surface of AISI 304L steel, while several smaller pits (depth 40–50 μm and width 50 μm) were formed on the surface of AISI 316L steel. With increasing temperature and sulfide ion concentration, the width, depth, and density of the pits increased on both steel samples. In the studied temperature and concentration range of sulfide ions, the AISI 316L steels exhibited higher corrosion resistance. Overall, the influence of sulfide ions on steel corrosion was more pronounced than the influence of temperature.

The inhibition capacity of Brassica oleracea (BO) extract on the corrosion of pipeline steel in 0.5M H2SO4 was evaluated using electrochemical techniques. The results showed an excellent inhibition efficiency which increased with initial increase in extract concentration and temperature to a point and decreased with further increase in BO extract concentration and temperature. Mixed inhibition behaviour was proposed for the action of BO. The unique behaviour of BO was attributed to the organic entities present in the extract.

The potential of Calcinated and uncalcinated zinc oxide as effective Photocatatlyst for the degradation of malachite green dye, MG from aqueous medium using UV light has been identified. The photocatalysts were characterized using scanning electron microscope, SEM and x-ray diffraction, XRD. The SEM investigations of the calcinated ZnO revealed highly dispersed nanomaterials and the particles were of nanometer size in agreement with the XRD result. The uncalcinated zinc oxide, ZnO revealed some pronounced nanoparticles. The degradation of MG by the photocatalyst was found to be influenced by adsorbent loading and irradiating time. The optimum degradation was obtained at 0.5g catalyst loading of both calcinated and uncalcinated zinc oxide which is 98.48% and 96.31 % respectively at 150 minutes. The degradation kinetics conformed to the pseudo-first-order kinetic model. The present study showed that calcinated and uncalcinated zinc oxide ZnO can be effectively used as efficient photocatalyst for the degradation of Malachite green dyes from aqueous solutions and effluents.

The influence of composition and surface microstructure on the corrosion behavior of low carbon steel specimens from Nigeria (NCS) and China (CCS) in a 0.5 M H₂SO₄ environment has been investigated using electrochemical techniques and surface probe techniques. The corrosion inhibition performance of Chrysophyllum albidum extract (CA) and synergistic iodide additives (KI) were assessed as well. The obtained results reveal that NCS was more susceptible to corrosion in uninhibited 0.5 M H₂SO₄ solution than CCS, which presented a more positive surface charge. CA inhibited the corrosion of both specimens, yielding maximum inhibition efficiencies of 89.6% and 48.5% for NCS and CCS, respectively, which were further increased to 93.9% and 98.9% on introduction of iodide ions. The corrosion and corrosion inhibition behavior of the carbon steel specimens were influenced by the metal composition and microstructure.

A Ni–Al composite was electrodeposited on Ni substrate and its corrosion characteristic was investigated after 72 hr. immersion in 2M NaCl solution, compared with a pure Ni coating. A corrosion product layer could be formed on Ni–Al composite surface during this immersion time which, however, was characterized by high porosity and charge percolation both at the corrosion product layer–solution interface and the substrate–solution interface, based on EIS characterization. This phenomenon greatly decreased the corrosion potential and increased both cathodic and anodic current densities in the active region, as well as the passive current density in the passive potential range, during polarization of the composite. Although a continuous Al³⁺ ions supply to the passivation front was suspected based on longer passivation potential of the Ni–Al composite, the chloride ions simultaneously adsorb and consume the Al₂O₃ leading to serious cracking and localized collapse of the corrosion product layer, as confirmed by SEM. This conferred lower corrosion resistance on the Ni–Al composite, relative to the pure Ni coating, in the 2M NaCl solution.