Adsorption isotherm models are an important tool for describing interaction of corrosion inhibitors with metal surfaces which they are aimed to protect. In this paper, key adsorption isotherms used in corrosion inhibition studies have been reviewed. We have examined how some deductions on the nature of metal-corrosion inhibitor interactions are obtained from certain parameters and interpreted to characterize the adsorption of the corrosion inhibitors and their mechanisms of inhibition. More attention is paid to their applications and the useful information that may be derived from them than on their background and derivation. Efforts have also been made to identify some limitations (where applicable) and/or discrepancies in usage of some models in reporting experimental findings. Informed by some inconsistencies observed from some literature reports, critical suggestions on appropriate approaches to collection and processing of data for fitting into these isotherms have been made. This paper will be a beneficial secondary source of information to readers and invaluable reference material to experts and future researchers in the subject area.

Ethanolic extracts of olive leaves (OLE) in the presence of TiCl₄ solution was used to form OLE – Ti nanoparticles composite (OLE-Nano). The particle size of Ti nanoparticles in the composite was determined using particle sizer and the nanoparticles were characterized using UV–vis, FTIR, SEM/EDAX and XRD techniques. Results show that the particles were around 70–74 nm in size and show maximum absorption around 420 nm. Prominent FTIR peaks correspond to C=C, N–H, O–H and C=O functionalities. XRD spectrum shows four distinctive diffraction peaks at 27.42°, 36.07°, 41.23°, and 54.30° corresponding to lattice plane value indexed at (101), (104), (200) and (211) planes of face centered cubic (FCC). The anticorrosion property of the OLE-Nano for mild steel in 1 M HCl at 30–60 °C was assessed using weight loss and electrochemical techniques complemented by surface analysis of the corroded steel specimen in the absence and presence of OLE – Nano with SEM and AFM. Results obtained show that OLE inhibited the acid corrosion of mild steel and the inhibition performance was enhanced in the presence of Ti nanoparticles. The corrosion inhibition effect was found to be concentration and temperature dependent. The inhibition efficiency of the OLE and OLE-Nano were 83.5 and 94.3% respectively at 30 °C but decreased to 51.7 and 85.4% at 60 °C respectively. The OLE-Nano adsorbed on mild steel surface by physical adsorption mechanism as predicted by Langmuir adsorption isotherm model. Potentiodynamic polarization results show that OLE-Nano behaves as mixed type inhibitor.