Abstract
The adsorption isotherm model best fit of the methanol leaf extract of Securinega virosa as corrosion inhibitor for the corrosion of mild steel in 2 M HCl medium was determined with the assistance of the Adejo-Ekwenchi adsorption isotherm. The corrosion inhibition study was carried out using the weight loss method at the temperature range of 301 K to 313 K. The inhibition efficiency, %IE, of the extract was found to increase with increase in both concentration and temperature. On the account of, R2 this adsorption process well fitted into Langmuir, Freundlich, Temkin isotherm, Flory-Huggins and Adejo-Ekwenchi models. However, through the parameter b of the Adejo-Ekwenchi isotherm, which clearly shows the adsorption process to be chemisorption, the best isotherm fit for the extract has been resolved to be the Langmuir isotherm and Temkin isotherm models.
Highlights
Adsorption, the accumulation onto the surface of a solid or a liquid by gas or liquid molecules, is a process which is present in many physical, biological and chemical systems [1, 2]
Securinega virosa leaves were collected within the premises of Benue State University, Makurdi-Nigeria, rinsed with distilled water, air dried for 40 days under shade and size-reduced with a pestle and mortal in the Chemistry Department of the same University. 20 g of the powdered leaves was soaked in 200 mL of 98% methanol (BDH Chemicals Ltd, Pool, England) in a 500 mL volumetric flask for 48 hours, with occasional shaking
The increase in the %IE with rise in temperature is suggestive of chemisorption [19]
Summary
Adsorption, the accumulation onto the surface of a solid or a liquid (adsorbent) by gas or liquid molecules (adsorbate), is a process which is present in many physical, biological and chemical systems [1, 2]. Adsorption isotherm is usually described by an isotherm equation whose parameters express the surface properties and affinity of the adsorbate and from which the mechanism of the adsorption process can be deduced [6]. The fitness of adsorption data into an isotherm has largely been determined through the value of the regress coefficient, R2 , while the Gibb’s free energy, ΔGads , value has, usually, been employed to ascertain whether the process is physisorption or chemisorption. There exist ambiguity in the use R2 and ΔGads as sole criteria for the determination of isotherm best fit of adsorption process. In this research the adsorption isotherm best fit for methanolic leaf extract of Securinega virosa as a green corrosion inhibitor of corrosion of mild steel in HCl was determined, largely, through the use of a new proposed twoparameter Adejo-Ekwenchi isotherm
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