The effect of ethylenediaminetetraacetic acid (EDTA) as a capping agent on the structure, morphology, optical, and magnetic properties of nickel oxide (NiO) nanosized particles, synthesized by coprecipitation method, was investigated. Nickel chloride hexahydrate and sodium hydroxide (NaOH) were used as precursors. The resultant nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). XRD patterns showed that NiO have a face-centered cubic (FCC) structure. The crystallite size, estimated by Scherrer formula, has been found in the range of 28–33 nm. It is noticed that EDTA-capped NiO nanoparticles have a smaller size than pure nanoparticles. Thus, the addition of 0.1 M capping agent EDTA can form a nucleation point for nanoparticles growth. The optical and magnetic properties were investigated by Fourier transform infrared spectroscopy (FTIR) and UV-vis absorption spectroscopy (UV) as well as electron paramagnetic resonance (EPR) and magnetization measurements. FTIR spectra indicated the presence of absorption bands in the range of 402–425 cm⁻¹, which is a common feature of NiO. EPR for NiO nanosized particles was measured at room temperature. An EPR line withgfactor ≈1.9–2 is detected for NiO nanoparticles, corresponding to Ni²⁺ions. The magnetic hysteresis of NiO nanoparticles showed that EDTA capping recovers the surface magnetization of the nanoparticles.

The inhibitive mechanism, thermodynamics, and adsorptive properties of thiobarbituric acid (TBA) and thiourea (TU) on the corrosion of mild steel in 0.5 M HNO₃ solution have been investigated using potentiodynamic, electrochemical impedance spectroscopy techniques, and quantum chemical calculations. Both inhibitors showed good inhibition efficiency in nitric acid solution. TU was the most effective inhibitor and its inhibition efficiency increases with increasing concentration to attain 99% at 6 × 10⁻³ mol · L⁻¹ at 30°C. Theoretical fitting of different isotherms, Langmuir, Flory–Huggins, Temkin, and the kinetic-thermodynamic models were tested to clarify the nature of inhibitors adsorption on mild steel surface. The obtained experimental data fitted all the applied adsorption isotherms except Langmuir. The thermodynamic activation parameters were determined to provide evidence of the inhibitory effect of TBA and TU. To determine the surface charge at the steel surface in nitric acid solution the potential of zero charge was measured using AC measurements at different potentials. Quantum chemical parameters were calculated and explained. The data clarified that the inhibition of steel in nitric acid by TU or TBA takes place through physicochemical adsorption mechanism.

The inhibitive action of plant leaf extracts, Crataegus oxyacantha (Hawthorn) and Prunus Avium (Sweet Cherry) on the corrosion of mild steel in 0.5 M HCl solution was investigated using open circuit potential-time measurements (OCP), potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. Functional groups of these plants’ leaf extracts and their absorption bands were identified by Fourier transform infrared spectroscopy (FTIR) and Ultra-Violet Spectrophotometer (UV), respectively. The leaf extracts showed good inhibition efficiency in hydrochloric acid solution. Potentiodynamic polarization curves revealed that Crataegus oxyacantha and Purnus Avium plants leaves extracts acted as mixed type inhibitors. Theoretical fitting of different isotherms, Langmuir, Florry–Huggins and the kinetic–thermodynamic models was tested to describe the mode of inhibitors’ adsorption on mild steel surface. UV spectra proved that the inhibiting action takes place through simple physical adsorption of the extracts molecules on mild steel surface.

The thermodynamic, inhibitive and synergistic properties of Fragaria ananassa (strawberry) and Cucurbita pepo L (zucchini) leaf extracts on the corrosion of mild steel in Hydrochloric acid solutions were examined by potentiodynamic polarization curves measurements and electrochemical impedance spectroscopy (EIS) technique as well as optical photographic study. Fourier transform infrared spectroscopy (FTIR) and UV-Spectroscopy were applied to predict the possible functional groups and constituents of both leaf extracts. Potentiodynamic polarization curves proved that Fragaria ananassa and Cucurbita pepo L leaf extracts act as mixed type inhibitors for mild steel in 0.5 M HCl solutions. Impedance plots indicated that the corrosion process occurred under activation control. Thermodynamic parameters proved that the formation of the activated complex is an endothermic association instead of a dissociation step. The inhibitive efficiency of these leaf extracts relies on their physical adsorption on the metal surface rather than the complexation with Fe²⁺ ions. Cucurbita pepo L leaf extract is more efficient than Fragaria ananassa as a corrosion inhibitor for mild steel in 0.5 M HCl. The synergistic effect between both extracts may be due to co-adsorption between their molecules, which could be either competitive or co-operative adsorptions. The synergistic parameter value S was higher than unity indicating a cooperative synergistic effect.