J. Nig. Soc. Phys. Sci. 4 (2022) 740 Journal of the Nigerian Society of Physical Sciences Cathodic corrosion inhibition of Steel by Musa paradisiaca leave extract Titus O. Martinsa, Edwin A. Ofudjea,∗, Abimbola A. Ogundiranb, Ojo A. Ikeoluwab, Osipitan A. Oluwatobib, Ezekiel F. Sodiyaa, Opeyemi Ojoa aDepartment of Chemical Sciences, Mountain Top University, Prayer City, Ogun State, Nigeria bDepartment of Chemical Sciences, Tai Solarin University of Education, Ijebu-Ode, Ogun State Abstract It is reported here that the phytochemicals present on the surface of the Musa paradisiaca (MPL) prevent water and other corroding agents from having direct access to the surface of mild steel. These phytochemicals were extracted from the MPL using 70% Ethanol solution and Weight Loss experiment was carried out with variation of temperature, time and concentration HCl and that of the MPL extract in % v/v. The inhibitive effect of M. paradisiaca leaves of mild steel in aqueous solutions of Hydrochloric acid were investigated at 25, 35, 45 and 60 oC being immersed simultaneously and independently in the acid medium over a period of 12, 24, 48, and 72 hours. A protecting film appeared on the metal surface by the MPL extract via electron donation, hence, acting as the cathode. The temperature and immersion time were inversely proportional to inhibition efficiency while concentration of MPL is directly proportional. FT-IR of the extract showed oxygen and nitrogen containing functional groups which are the general characteristics of a typical corrosion inhibitor, while the Gas Chromatography–Mass Spectrometry (GC–MS) investigation revealed different biomolecules thus suggesting that the plant extract consists of different molecules. DOI:10.46481/jnsps.2022.740 Keywords: Corrosion, corrosion inhibitor, desorption, green chemistry, M. paradisiaca, mild steel Article History: Received: 27 March 2022 Received in revised form: 25 June 2022 Accepted for publication: 09 September 2022 Published: 05 November 2022 c© 2022 The Author(s). Published by the Nigerian Society of Physical Sciences under the terms of the Creative Commons Attribution 4.0 International license (https://creativecommons.org/licenses/by/4.0). Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Communicated by: E. A. Emile 1. Introduction Corrosion of metals has been around us even before indus- tries came to existence and the need for the prevention or cure has been a major problem. Aggressive acids such as HCl are frequently utilized to eliminate mild scale and rust found in iron and steel in chemical industries [1]. These inhibitors were utilized by the industries for their anti-corrosive properties but ∗Corresponding author tel. no: +234(0)8060981250 Email address: eaofudje@mtu.edu.ng (Edwin A. Ofudje) they cause some adverse effects on the environment. This has resulted in the synthesis of corrosion inhibitors that are envi- ronmentally affable and are called Organic Corrosion Inhibitors (OCI) [2]. Corrosion Inhibition can be carried out by the use of organic or inorganic approach. The organic approach is also known as Green Corrosion Inhibition which is one of the best- known corrosion safety techniques [3-5]. The use of extract of natural product as inhibitor of corrosion was first evidence in 1930 whilst extracts from Chelidonium majus and some other plants were utilized in Sulfuric acid, H2SO4 medium for the first time [6-7]. With this, there is no or minimal amount of 1 Martins et al. / J. Nig. Soc. Phys. Sci. 4 (2022) 740 2 pollution caused and it is cost efficient since these are extracts from plants that can be easily isolated. Organic compounds with effective corrosion inhibitors of- ten contain conjugated systems, and conjugated aliphatic bonds due to the presence of lone pairs of electrons (N, O, S and P), in aromatic rings, and pi-electrons, often have ionizable parts which are either hydrophilic or hydrophobic in nature [6, 8-10]. More research and developments are emerging in the study of natural corrosion inhibitors as need for environmen- tally friendly inhibitors are gaining ground. For example, Cr2O3 which is insoluble in aqueous media that span across acidic and basic pH range and its susceptible to the underlying metal, it may serve as a barrier to corrosion [11]. Hexavalent chromium has shown to persuade irrevocable health challenges through skin irritation, nose, throat and eye and most importantly raises the alarm of lung cancer [12]. For application in coatings and primers, a comparable universal anti-corrosion compound has yet to be found, so that the need for chromate substitutes and ways of deployment of corrosion protection spans many indus- tries. Drugs had been studied as corrosion inhibitor at some time [13]. Over the decades, green chemistry has shown how basic scientific approaches can benefit from the conservation of the human health and that of the environment by combining ar- eas such as polymers [14-15]. Awareness to corrosion and the adaptation of fast, appropriate and accurate control measures holds the key in the eradication of corrosion failures. Hete- rocyclic molecules show essential behaviour as anti-corrosion owning to the available of sulfur, oxygen, and nitrogen atoms in either open or in their ring structure. However, no much works had provided detailed study on the mechanism of corro- sion inhibition by these heteroatoms or heterocyclic molecules. In this work, extracted phytochemicals from MPL were used as green corrosion inhibition to decrease the rate of corrosion of steel in acidic medium. GC-MS and FT-IR investigations were carried out to examine the composition of the corrodent. The concept of Crystal Field splitting was deployed to provide lucid interpretation of the corrosion mechanism. Isotherms and ther- modynamics were deployed to investigate corrodent sorption onto the steel surface. 2. Materials and Methods 2.1. Preparation of Metal Coupons The specimen of mild steel was sliced into rectangular coupons by lathe machine into dimension of 20.21 mm by 14.63 mm. The coupons with its edge were polished with emery paper of 600 grades. The thickness was examined with Mitutoyo brand of analog micrometer screw gauge and the dimension by Mitu- toyo digital venier gauge. The surface of the coupons was de- grease through immersion in absolute ethanol and then removed for rinse with double distilled water and acetone and thereafter stored in moisture free desiccators before use [16]. 2.2. Preparation of Plant Extract and Cold Extraction Process Fresh Musa Paradisiaca leaves (MPL) were gathered in large quantities, selected from around same source, to ensure no con- taminated leaves of different plant or specie. The impurities as- sociated with the leaves were removed through tap water wash- ing and thereafter air-dried to constant weight. It was shred- ded into smaller pieces to increase drying rate and thereafter dried for 3 weeks. Using 70% ethanol for solvent extraction at room temperature, the pulverized sample of MPL was soaked for 48 hours until a dark-green color was observed indicating that extraction has taken place. The darkish-green solution was filtered out which contains the plant extract while the residue is the chaff from pulverized leaves. The procedure was repeated on the chaff to ensure maximum extraction. The filtrate was re- fluxed to ensure homogeneity of the sample. The concentration of the extract of plants was carried out using a Rotary Evapora- tor which removes solvents from the extract thereby making it slurry. The concentrated and purified extract was then stored in desiccator. 2.3. Plant Extract Structural Elucidation 2.3.1. Gas Chromatography Mass - Spectroscopy (GC-MS) In- vestigation A 7820A gas chromatograph coupled to 5975C inert mass spectrometer was used for this analysis. Scanning of poten- tial compounds was at 2.62 s/scan rate and was recognized by comparing detected spectral data with NIST 14 Mass Spectral Library standard [17]. 2.3.2. FT-IR Analysis The functional group evaluation was done using Fourier transform infrared spectroscopy (FT-IR) model 8400S (Shimadzu, Japan). A mortar and pestle were used to mixed the MLP and KBr in the ratio of 1:99% and pestle and compressed into pel- lets. The FT-IR spectrums were determined from 400 cm−1 to 4000 cm−1 at a resolution and times scanning of 4 and 64 re- spectively. 2.3.3. Weight Loss Experiments Mild steel of 20.21 mm by 14.63 mm were used for weight loss measurement. The total geometric of the coupon’s surface area available to the corroding agent was about 295.67 mm2 and average weight of coupons was 13.18 to 15.61 grams. The weighed coupons were immersed in 20 mL sample bottles con- taining concentration of corroding agent, HCl to that of the ex- tract (Musa paradisiaca) as: 20:0 v/v, 15:5 v/v, 10:10 v/v, 5:15 v/v at 25 ± 2 oC and 60 oC consecutively for 72 hrs. This pro- cedure is repeated further for 1.0 M and 2.0 M of HCl at 60 oC. Experiment on weight loss was used to estimate the inhibition efficiency, rate of corrosion and also the half-life of the metal coupon. 3. Results and Discussion 3.1. Fourier Transform Infrared (FT-IR) Analysis Investigation on the various functional groups in the plant extract was determined using FT-IR. In the FT-IR spectra shown in Figure1 below, it revealed absorption bands belonging to the N-H and O-H bands which occured between 3325 - 3567 2 Martins et al. / J. Nig. Soc. Phys. Sci. 4 (2022) 740 3 Figure 1. Musa Paradisiacal Leaves FT-IR spectrum cm−1, while the C-H stretching vibrations was noted between 2378 - 2987 cm−1. The vibration of C=C stretching occured at around 1645 cm−1, while that corresponding to C-N vibration stretching was observed at 1248 cm−1. The absorption vibra- tions which occurred between 1098 and 1102 cm−1 are due to C-O functional group. FT-IR of the extract showed that oxygen and nitrogen atoms were present in the plant extracts which is the general characteristics of a typical corrosion inhibitor. Ta- ble 1 shows the different functional groups present on the plant extract. Table 1. Musa Paradisiacal Leaves Extract FT-IR Analysis Wave number (cm−1) Vibration mode 3325 - 3567 O-H and N-H 2987 C-H 2378 C-H 1645 C=C 1462 Methyl C-H 1248 C-N 1098 - 1102 C-O GC–MS examination of the corrosion inhibitor revealed dif- ferent biomolecules thus suggesting that the plant extract con- sists of different molecules as listed in Table 2 with the mi- crogram shown in Figure 2. As identified from the GC-MS analysis, the compounds which could be responsible for the weight loss are 6-Amino-1,3,5-triazine-2,4(1H,3H)- dione, 9- Octadecenamide, (Z)- Ole amide, Polygalitol, Cyclotetrasilox- ane, octamethyl-, Thiophene, 2,3-dihydro- and Ginsenol repec- tively. It should be noted that O, N or S and/or p-electrons are present in most of the biomolecules identified from the ex- tracts of the plant. From the GC-MS investigation, the com- pound which mostly has more inhibition is Ginsenol with time retention of 24.063. The inhibition of the rate of corrosion by MPL extract could be assigned to the presence of these phyto- chemicals which are made up of S, N, O, and other heteroatoms in their structures which are responsible for donating electrons to inhibit the corrosion process and thus serving as adsorption points on the surface of the metal. 3.2. Weight Loss Determination of Extract Inhibition The metal weight loss during the experiment can be calcu- lated as shown in equation 1 [18]: ∆W = (Wi − W j)g (1) Given that ∆W is the coupon weight loss, the initial coupon weight is denoted as Wi, the final coupon weight is given as W f . The corrosion rate is estimated as: CR,ρ = Weight Loss (S ur f ace Area) × T ime = ∆Wt S (2) where CR= ρ and is corrosion rate gcm−2 min−1 or gcm−2 hr−1, ∆W is weight loss, S is Surface area, and t is immersion period. The inhibition efficiency can be obtained by using equation 3a or 3b I.E.% = [ Wu − Wi Wu ] × 100 (3a) I.E.% = [ ρ1 −ρ2 ρ1 ] × 100 (3b) such that I.E. is Inhibition Efficiency, Wu is Weight of unin- hibited mild steel surface, Wi = Weight of inhibited mild steel surface, ρ1 is rate of rate of uninhibited corrosion, and ρ2 is the rate of inhibited corrosion. For calculating Percentage extract yield, %E xtraction Y ield = W1 − W2 W1 × 100 (4) where W1 is weight of extract before extraction and W2 is weight of extract after extraction. Surface coverage determination for Isotherm calculations is given as: θ = I.E 100 (5) given θ is the surface coverage and I.E. is Inhibition Efficiency. 3.3. Effect of MPL extract Concentration The MPL extract concentration is the variation in volume of the corrodent to the acid used, HCl, to make a volume of 20 mL. The experiment indicates a reduction in rate at which cor- rosion occur, thereby increasing inhibition efficiency (Figure 3). This also was calculated by comparing a medium with only the acidic medium and another containing the MPL extract, even with temperature variation, the result was still relative. It was established that the best inhibition efficiency was gotten from 5-15% v/v which is 5 mL of the acid and 15 mL of the plant ex- tract. And the highest corrosion rate was seen on 20-0% v/v. As shown in Figure 3 below, the corrosion rate is inversely propor- tional to the concentration of the MPL extraction. Moreover, corrosion rate is the inverse of inhibition efficiency. 3 Martins et al. / J. Nig. Soc. Phys. Sci. 4 (2022) 740 4 Figure 2. GC-MS Chromatogram of MPL extract Table 2. Molecules extracted from the GC-MS Chromatogram of MPL Retention Name Formula Molecular Estimated time Weight Conc. (g.mol−1) 6.841 6-Amino-1,3,5-triazine- C3H4N4O2 127.29 27 2,4(1H,3H)-dione 6.841 9-Octadecenamide, (Z)- C18H35NO 281.477 98 Ole amide 12.726 Polygalitol C6H12O5 164.16 49 9.324 Cyclotetrasiloxane, C8H24O4Si4 296.6152 87 octamethyl- 8.475 Thiophene, 2,3-dihydro- C4H6S 86.16 50 24.063 Ginsenol C15H26O 222.3663 38 3.4. Effect of Immersion Time The variation of inhibition performance of Musa paradisi- acal leave extract as well as the corrosion rate with immersion time at concentration of 5-15% v/v is shown Figure 4. It was observed that the corrosion rate increases with the immersion time until 72 hour. A best immersion time of 12 hours was perceived for the whole concentration gradient of the inhibitor. Marginal inhibition sets in after the 48 hours due to desorption which occurs with prolonged exposure of the inhibitor to the acid medium, the corrosion rate tend to decline more rapidly than normal. And I.E. was noticed to have decreased with in- creased immersion time, this phenomenon could be blamed on desorption of the plant extract which initially prevent corrosion from taking place and also, at initial stage of the immersion, the inhibitory efficiency of the active components of the plant is high but as the reaction proceed, these active components are used up or destroyed; thus giving rise to increase in corrosion rate. More also, the presence of the corroding agent over long time made the corrosion abundant. Not forgetting that adsorp- tion is by Van der Waal forces of attraction, and they are eas- ily reversible [19], by stress. This stress may include pressure, temperature, current, etc. but on this case, it is caused by tem- perature and long exposure to the corroding agent. According to Ascencio et al. [20], he reported the influence of immersion time on corrosion mechanism and there is an inclination from this study. 4 Martins et al. / J. Nig. Soc. Phys. Sci. 4 (2022) 740 5 Figure 3. Effect of Musa paradisiaca concentration on the inhibition efficiency and corrosion rate Figure 4. Effect of time of immersion 3.5. Effect of Temperature Inhibitors desorption or decomposition of the inhibitor with increase in temperature are some of the changes that occur on the metal surface [21-23]. Variation in CR at different con- centration of MPL extract was examined, while putting into constant immersion time at 12 hours and concentration as in- dicated in Figure 5. It was observed that inhibitor efficiency (IE) decreased with a rise in temperature and the best inhibitor efficiency obtained at a temperature of 25 oC. The reduction in IE may be as a result of desorption at higher temperatures of the molecules of inhibitors from the surface of the metal [24- 25]. Corrosion rate (CR) rises as temperature rose which is as a result of desorption of bio-molecules of MPL extract from the surface of the metal, resulting in greater portions of the surface of the metal being exposed to acidic medium. An increase in temperature also brings about increase in weight loss and in- crease in corrosion rate, CR [24, 26]. When the inhibitor cov- ers the surface of the metal, it hinders corrosion process to set in since the surface of the metal has been coated with the in- hibitor. It takes time for the inhibition coating to wear off and consequently, this slows down corrosion [27]. But when tem- Figure 5. Effect of Temperature perature increases, it causes the inhibitor to desorb from the surface of the metal thereby, causing a sharp rise in corrosion rate, and resulting in the decrease of the inhibitory efficiency. The reduction in the physical adsorption at higher temperature agrees that inhibition on the metal surface is physical in nature. Table 3 shows that the MPL compete favorably well with other plant extracts in literature. 3.6. Thermodynamic Study Thermodynamic properties such as activation energy (Ea), free energy change (∆G), entropy change (∆S ) and enthalpy change (∆H) were estimated to further examine the impact of temperature on the inhibitory efficiency of the inhibitor. The Arrhenius equation was used to estimate the activation energy: logCR = logA − Ea 2.303R · 1 T (6) Such that CR denotes corrosion rate, the activation energy is given as Ea, the molar gas constant is represented as R and T stands for temperature. Then, the slope of the graph of logCR against 1/T is shown in Figure 6 from where the activation en- ergy was determined as presented in Table 4. The activation energy determined is 0.014 kJ/mol/K. All chemical reactions need a minimum amount of energy for the reaction to proceed which is known as activation energy. Low activation energy im- plies that the reaction is likely to occur spontaneously or with- out the intervention of catalyst or increase in temperature and thus favours the inhibition process. The ∆H and ∆S estimated are listed in presented in Table 4 using the slope and intercept of equation 7. ln( CR T ) = ln( R Nh ) + ∆S θ R − ∆Hθ RT (7) Such that h is the Planck’s constant, Avogadro’s number is given as N, R, T and CR are as previously defined above. The free en- ergy change is concerned with how feasible and spontaneously a reaction will occur and this was obtained using equation 3 below: ∆G = −RT ln(55.5K) (8) 5 Martins et al. / J. Nig. Soc. Phys. Sci. 4 (2022) 740 6 Table 3. Comparative inhibition efficiencies as reported in literature with MLP Plants Inhibition References Efficiency (%) Neem ark extract 91.73 Desai [28] Leaves extract of 97 Abiola et al. [29] Gossipium Seed extract of 94 Abiola et al. [29] Gossipium Khillah seed 71 El-Etre [30] (Ammi visnaga) Justicia gendarussa 93 Satapathy et al. [31] Pennyroyal oil 80 Bouyanzer et al. [32] Occidimum 69 Oguzie [33] Leaves of ankado 90.09 Desai [34] ark extract Adathoda vasica 98.1 Shyamala and Kasthuri [35] Eclipta alba 99.6 Shyamala and Kasthuri [35] Centella asiatica 85 Shyamala and Kasthuri [35] Bitter leaf 90 Caroline et al. [36] root extract Cassia italica 87.4 Al-Otaibi et al. [37] Tripleurospermum 83.4 Al-Otaibi et al. [37] auriculatum Artemisia sieberi 86.2 Al-Otaibi et al. [3] Gentian olivieri extract 93 Evrim et al. [38] extract Musa paradisiacal 99.3 Present study leave extract and K was estimated as: K = θ C(1 − θ) . (9) All the parameters in equation 9 above are as previously de- fined above. A negative value of ∆G was obtained, showing that it is a spontaneous reaction. This is also used to determine the pathway of the experiment to either be physical adsorption or chemisorption. If ∆G is negative, then the process is more of physical adsorption, while a positive value of ∆G or rela- tively higher is chemisorption [39]. From this study, value of ∆G from the study of MPL extract inhibit on mild steel ranges between -5.57 and -4.96 kJmol−1 which further indicate that the reaction pathway of corrosion is somewhat physical adsorption. Since Van der Waal force is responsible for adsorption, the pro- cess happens spontaneously i.e. it requires no activation energy. Enthalpy, on the other hand is seen to be positive, depicting an endothermic reaction. Corrosion is known to be exothermic re- action, because it increases with increase in temperature and this temperature comes from the surrounding. The value of en- thalpy obtained from this study is 6.72 kJmol−1 K−1. This indi- cates that the inhibition process of the metal surface by the in- hibitor (MPL) is endothermic in nature. It has been noted from Figure 6. A plot to determine Activation Energy Figure 7. A plot to determine entropy and enthalpy experiment that positive enthalpy (endothermic) value and low entropy (-) is best for inhibition which is in line with what was observed in this study and that a rise in temperature reduces in- hibition and increase the corrosion rate [27]. Entropy depicts the degree of disorderliness of a slope and this is brought about by high temperature that causes the molecule to move randomly due to gained energy which explains desorbing of the MPL ex- tract from the surface of the metal and this will leads to low in- hibitor efficiency. Thus, a relatively low temperature is required for an effective and efficient inhibition process. So, for corro- sion process, it always leads to the evolution of heat, while for the adsorption of inhibitor onto the metal surface, the process is always endothermic because higher temperature will results in desorption of the inhibitor from the surface. So, while corrosion is favoured by exothermic process, inhibition process (adsorp- tion on metal surface) is favoured by endothermic process. 3.7. Inhibitor Mechanism It is important to note that steel is an alloy of carbon and iron where the carbon atom is bonded to iron to reduce corro- sion and the formation of steel is a function of Fe − C phase present i.e., Ferrite (αFe), Austenite (γFe), Cementite (Fe3C), 6 Martins et al. / J. Nig. Soc. Phys. Sci. 4 (2022) 740 7 Table 4. Thermodynamic properties of Musa paradisiacal Temperature ∆G ∆H ∆S Ea (K) (kJ/mol) (kJ/mol) (kJ/mol) (kJ/mol) 298 -5.57 308 -5.10 6.72 -197.53 0.014 318 -4.99 333 -4.96 Pearlite (αFe+Fe3C) [40]. The bonding of C with Fe in Ce- mentite made the 3d6 electrons of Fe to remain in t2g that is low spin [41]. Consequently, the four electrons of the carbon are made readily available to the eg-orbital for bonding. The fer- rite regions are the most reactive site and tend to corrode easily [42]. The iron particles become oxidized in water when they are lost to the water’s acidic electrolytes, resulting in the formation of Fe2+. The formed Fe ion at the anode migrates to the cath- ode. The hydroxyl ions formed from reaction of the hydrogen ion produced with oxygen react with Fe+ to produce hydrous iron oxide (FeOH), also which is often called rust [43]. When inhibitors are added into corrosive medium in minute quantity, they retard the corrosion process. The inhibition of corrosion process is successful when Fe2+ is stabilized from further oxidation to Fe3+. Either physical adsorption or chemisorp- tion is the process through which inhibitors should readily be adsorbed to the metal surface so as to be an effective shield op- posing the metal corrosion [44]. The inhibitor group’s physic- ochemical properties, like the functional group, the donor atom electronic density and molecular structure depend primarily on one of these adsorption processes. Corrosion inhibition mecha- nism is also accomplished in aromatic rings, nitrogen and oxy- gen containing molecules which donate their lone pair of elec- trons to the metal and thus favoring the uptake of these molecules onto the surface of the metal [45]. Furthermore, molecules hav- ing large structure occupy a larger surface area and thus devel- oping a protective coating. Plantain leaves on this note have inhibitive properties as they have been identified by GC-MS analysis to contain compounds such as 6-Amino-1,3,5-triazine- 2,4(1H,3H)- dione, 9-Octadecenamide, (Z)- Ole amide, Poly- galitol, Cyclotetrasiloxane, octamethyl-, Thiophene, 2,3-dihydro- and Ginsenol which contain elements such as O, N or S which serves as electrons donors. These molecules of inhibitors con- tain strong ligands such as CN−, N H3−, OCN −, S CN−, etc, which causes low spin forcing the 3d6 electrons into t2g orbital (dxy, dxz and dyz). The degree of splitting is the inverse of the strength of ligands. This disrupts the degeneracy and in- creasing the energy of the eg orbital which allows for the donat- ing of electron by the ligand to the empty eg orbital (d x2 − y2 and dz2) [46]. When this donated electron by the inhibitor molecules or ions (ligand) is dative covalent bond between the inhibitor and metal, weak bond or Van der Waal force of attrac- tion is produced, which is physical adsorption (physical adsorp- tion). While an ionic bonding gives rise to chemisorption due to strong electrostatic bond created [47]. Figure 8. Fe2+ ion and Energy levels of d orbital in octahedral field (Low spin) Figure 9. Isotherm plot of Langmuir isotherm 3.8. Isotherms Study Adsorption isotherm can reveal information relating to the adsorption mechanism, surface coverage, and adsorption equi- librium constant. To verify the isotherm, the linear relation that exists between θ and C was established using the value of the correlation coefficients (R2) of Langmuir isotherm as illustrated in equation 10: log C θ = logC − logb, (10) where b stands for inhibitor adsorption equilibrium constant. Figure 9 depicts the plots of logC/θ against the inhibitor con- centrations (C) at 303 K. From the calculated value of corre- lation coefficients (R2) which is 0.971, it can be said that the Langmuir isotherm can also be deployed to explain the inhi- bition process which assumed a physical reaction with weak intermolecular forces. 4. Conclusion This work examined the potency of leaf extract of Musa paradisiaca (MP) as inhibitor against the corrosion of mild steel 7 Martins et al. / J. Nig. Soc. Phys. Sci. 4 (2022) 740 8 in acidic medium. An immersion period of 12 hours was per- ceived as the best performance for MPL for the whole concen- tration of the inhibitor examined. Inhibitor efficiency (IE) re- duced with rise in temperature. The reduction in I.E. is as a result of desorption of the molecule of the inhibitor at higher temperatures from the surface of the metal. The reaction at the surface of the metal by the extract is endothermic with the pos- itive enthalpy obtained from this study as 6.72 kJ/mol/K, sug- gesting a mix adsorption process but having chemical adsorp- tion predominate on the surface of the metal. The value of ∆G obtained from the study of MPL extract inhibit on mild steel in HCl ranges between -5.57 and -4.96 kJmol−1 which further in- dicated that the reaction pathway is achieved by adsorption on the surface at the studied temperatures. From the experimental result gathered, it can be concluded that the plant leaf extract of MP inhibitor extracted is efficient in inhibiting steel. Acknowledgments We sincerely appreciate staff of Central Laboratory, Moun- tain Top University for their support during sample analysis. References [1] I. B. Obot, N. O. Obi-Egbedi, & S. A. Umoren, “Adsorption Character- istics and Corrosion Inhibitive Properties of Clotrimazole for Aluminium Corrosion in Hydrochloric Acid”, Intern. J. Electrochem. 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