J. Nig. Soc. Phys. Sci. 5 (2023) 1386 Journal of the Nigerian Society of Physical Sciences Experimental and computational studies of the corrosion inhibitive effects of Zingiber officinale rhizomes on mild steel corrosion in acidic solutions C. B. Adindua,∗, S. C. Nwanonenyib, C. B. C. Ikpaa aDepartment of Chemistry, Imo State University, P.M.B 2000 Owerri, Imo State, Nigeria bDepartment of Polymer and Textile Engineering, Federal University of Technology, P.M.B.1526, Owerri, Nigeria Abstract The study investigates the anticorrosion potentials of Zingiber officinale (ZO) on mild steel induced in 1.0 M HCl and 0.5 M H2SO4 acid solu- tion respectively using structural characterization (gas chromatography-mass spectroscopy, GC-MS and Fourier transform infrared spectroscopy, FTIR) and electrochemical (electrochemical impedance spectroscopy, EIS and potentiodynamic polarization, PDP) techniques respectively and theoretical simulations. The structural characterization was performed to identify chemical constituents and functional groups present in the plant extract whereas electrochemical techniques and theoretical computations were used to examine the anticorrosion potentials of the extract and validate the experimental results. The GC-MS result revealed the presence of twenty-three (23) compounds within the extract and out of which three (1-(1,5-dimethyl-4-hexenyl)-4-methyl-, dodecanoic acid and 9-Octadecenoic acid (Z)-2-hydroxy-1-(hydroxymethyl)ethyl ester) were selected for computational simulation and the results of FTIR revealed the presence of the following functional groups (O–H, C=C, C=O, C–C and C–H) in the ZO extract. The results of EIS revealed that extract of ZO exhibited corrosion inhibition efficieny of 82.7% and 93.6 % for mild steel in 1 M HCl and 0.5 M H2SO4 solution respectively at maximum inhibitor concentration of 1000 mg/L for mild steel. Also, PDP results revealed that ZO extract functioned as mixed inhibitor because both the anodic and cathodic reaction process was altered. The quantum chemical calculation results revealed that 9- Octadecenoic acid (Z)-2-hydroxy-1-(hydroxymethyl) ethyl ester had a good energy gap (∆E) compared to other two compounds, indicating its better adsorption interaction with the metal surface in sulfuric acid environment. This was further confirmed by its good adsorption energy of -355.55 Kcal/mol with mild steel surface in H2SO4 environment compared with -167.81Kcal/mol in HCl environment from the molecular dynamic simulation. DOI:10.46481/jnsps.2023.1386 Keywords: Zingiber officinale, solvation molecules, corrosion, molecular dynamic simulation, inhibition efficiency Article History : Received: 06 February 2023 Received in revised form: 19 May 2023 Accepted for publication: 12 June 2023 Published: 23 August 2023 © 2023 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: K. Sakthipandi ∗Corresponding author tel. no: +234 7030676855 Email address: blessingojiegbe@yahoo.com ( C. B. Adindu ) 1. Introduction Corrosion of component tools and parts made of metallic alloys in different service environments and its control is a vital research area and requires adequate attention due to its utmost importance in industrial and engineering sectors. Thus, 1 Adindu et al. / J. Nig. Soc. Phys. Sci. 5 (2023) 1386 2 purified metals together with their alloys possess some inherent features and exhibit outstanding performances in different service environment to ensure sustainable economy. Corro- sion of metals is an unpreventable phenomenon caused by unfavourable interactions between the metal substrate and its environment surrounding and the interaction is electrochemical in nature involving anodic and cathodic process. Metals and their alloys are indispensible materials for the design and fabri- cations of water treatments plants, heat exchangers, dye-bath, drill bits, food processing equipment, hollow pipes for fluid transportation, distribution and storage, etc. filter membrane, etc. However, it is observed over time that scales of inorganic materials or products develop on the internal walls of these components and reduced the efficiency or productivity. On the other, removing these unwanted products via acid cleaning or acidizing process with dilute mineral acids (hydrogen chloride and sulphuric acid) is ideal but significant corrosion effects are introduced on the metal surface on the process. The resultant effects of metal corrosion are enormous; it causes tremendous damage to life-span and integrity of industrial tools of metallic component especially in oil and gas sectors and other chemical processing industries [1-3], creates pollution problems which poses great health challenge to man and his environment and results to waste of economic resources in routine corrective and preventive maintenance and material loss. Thus, identifying the possible solution to mitigate these problems associated with metal corrosion is imperative and highly efficient corrosion inhibitors from organic sources together with computational modeling techniques possess all it will take to achieve this feat. Many researchers in the field of corrosion of metals and their inhibition have reported the use of several methods to combat the problem of corrosion of metals in different service environment [4]. One of such methods is the use of material regarded as corrosion inhibitor and it is not a complex technique neither does it requires much training during application. Corrosion inhibitor is a material capable of reducing the corrosive effect of any corrodent system when added in a little amount or quantity. Many corrosion inhibitors in use during metal corrosion and its control are sourced from either organic or synthetic background with little or no modification. Chromates, some imidazole based inhibitors, etc. are typical examples of corrosion inhibitor from synthetic sources with effective performance but the application of these inhibitors are currently restricted due to their toxicity and other environmental issues. Over time, the use of extracts from various plant leaves, bark, root, etc. has received detailed attention as anti-corrosion material. Some of these natural materials particularly plant materials, proteins, biopolymer and amino acids have been re- ported to function as effective corrosion preventing additives [5- 10]. Plant materials are viewed to contain rich chemical com- pounds that can be extracted by simple methods and some of these chemicals are known to resemble the synthetic organic corrosion retarding compounds and have been proven to func- tion as effective as their synthetic counterparts. These mate- rials have at different proportions hetero atoms which contain sulphur, nitrogen and oxygen in a conjugation as well as dou- ble bond and aromatic ring in their chemical structures [11-20]. It is believed that these functional groups within the chemical structure of inhibitor play significant roles in corrosion, adsorp- tion and inhibition. Zingiber officinale (ginger) plays a very important role in medicinal science and it has high medicinal value due to its antifungal, anti-bacterial and other nutritional benefits. Thus, it has been in use in many parts of the world as remedy and cure for many known diseases [21-22]. This study is aimed at investigating the corrosion inhibitive effects of ZO ethanol extract on mild steel corrosion in acidic solutions using experimental and theoretical studies respectively. The essence of employing the computational study in the study is to unravel the correlation existing between the inhibitor efficiency and their electronic molecular structures. Furthermore, the work seeks to widen the application of ginger as eco-friendly corro- sion inhibitor for mild steel protection [23-25]. 2. EXPERIMENTAL SECTION 2.1. Preparation of materials The metal used for the research was mild steel low carbon grade with the following composition: 0.05%C, 0.36%P, 0.03%Si, 0.6%Mn and 98.96%Fe. The metal coupons were cut to 3 x 3 x 0.14 cm using mechanical cutter, cleaned, polished with fine emery paper (1000 and 1200 grade) degreased and prepared as earlier described in our previous work [26]. Zinbiber officinale rhizomes tuber used was obtained from harvested samples kept at Agricultural farm store in Imo state polytechnic Umuagwo, Imo State and identified at Crop Science Laboratory, Federal University of Technology Owerri, Imo state. The ZO tuber foreskin was washed thoroughly with water to remove dirts, pealed to remove the thick back, sliced into pieces, dried thoroughly, pulverized to fine powder particle, stored in an air tight container and kept for corrosion studies. The prepared ZO sample (50 g) was introduced in 500 ml of absolute ethanol in a beaker and allowed to stand for 72 h and kept in an aerated condition. The mixture was thoroughly filtered with filter paper and the solution obtained was used to prepared inhibited solution for corrosion studies. The stock blank of 1 M HCl and 0.5 M H2SO4 acid solu- tion respectively was prepared using dilution serial principle whereas the inhibited solutions were prepared by introducing 200 and 1000 mg of ZO extract respectively into 1 L of 1 M HCl and 0.5 M H2SO4 acid solution, respectively. The prepared ZO extract sample was concentrated with rotary evaporator and subjected for functional group exam- ination and analysis in a Fourier transform infrared (FTIR) spectrophotometer (Nicolet Magna-IR 560 model)[28]. Also, the prepared ZO powdered sample was subjected to Gas chromatography-mass spectrophotometer, GC-MS 2 Adindu et al. / J. Nig. Soc. Phys. Sci. 5 (2023) 1386 3 (19091S-433UI model) for examination and analysis. The HP- 5ms Ultra Inert 0◦C - 325◦C: with dimension 30 m × 250 µm × 0.25 µm was used for the GC-MS analysis, at the gas Chro- matography section, the oven temperature was 50 oC, held for 120 secs raised to 180 oC at a rate of 50 oC/min the final tem- perature was 325 oC with injection volume of 10 µL and 7.3614 psi pressure. The carrier gas was Helium with flow rate of 0.97414 mL/min, For mass Spectrometer part. The solvent was methanol and the scanning was at 40-650 m/z the result ob- tained was compared with NIST mass spectral library search program. 2.2. Electrochemical experiments (a) Electrochemical experiments were done using direct current voltammetry (VERSASTAT 400) advanced electro- chemical workstation. The corrosion cell is made of cylindrical glass and contains three conventional electrodes namely [7]; working electrode (mild steel coupon), graphite rod (counter electrode) and reference electrode (saturated calomel electrode). The working electrode, a mild steel coupon of dimension 1.5 cm × 1.5 cm was affixed in polytetrafluoroethy- lene (PTFE) rods using epoxy resin in a way that just one of its surfaces of area 1 cm 2 was exposed to test solution under evaluation. The electrochemical workstation, central processing system, monitor and electrolytic cell terminals were connected tightly with luggin capillaries. Open circuit potential (OCP) was performed for the test solution to achieve steady state potential at 1800 secs and 303 K before the EIS and PDP experiments commenced. The measurements were performed at the end of 1800 secs in an aerated environment and stagnant test solution. Polarization curves were determined from the scanning electrode potential of -250 mV to +250 mV versus corrosion potential (Ecorr) at a scan rate of 0.33 mV/s [29] while linear polarization segments of cathodic and anodic curves were extrapolated to determine corrosion current densities (icorr) using V3 studio software. Electrochemical impedance measurements were undertaken at corrosion potential (Ecorr) at a frequency range of 10 m Hz to 100 kHz and amplitude of perturbation of 5 mV. Electrochemi- cal data were analyzed using the ZSim Win 3.10 software mod- eling package. The experimental measurements (i.e both EIS and PDP) were repeated three different times to ensure repro- ducibility of results. EIS measurement was performed to mon- itor the effect of thin film of the active inhibitor components adsorbed on the metal surface while PDP measurement was per- formed to proof evidence of effect of inhibitor on cathodic and anodic partial reactions and this assists to classify whether the inhibitor acts as cathodic, anodic or mixed type inhibitor. 2.3. Theoretical computations The results of corrosion studies revealed that ethanol ZO extract retarded the corrosion of mild steel in the different acid solution medium studied and theoretical computations was used to validate the experimental results. The theoretical studies pro- vide evidence of chemical parameters within the inhibitor struc- tures that are responsible for the corrosion inhibition and also give information on the adsorption energy between the corro- sion inhibitor species and metal surface. Molecular geometries and electron distributions influencing corrosion inhibition prop- erties of some materials known had been previously evaluated using density functional theory [30 - 32]. Structures of the most three (3) active constituents of the ginger rhizomes were se- lected from the GC-MS results and modeled. The theoretical calculation was done with Material Studio software Accelrys (7.0 version) within the framework of density functional theory (DFT) tools (quantum chemical computation and molecular dy- namic simulation) from the molecular point of view. 3. RESULTS AND DISCUSSION 3.1. Sample characterization 3.1.1. FTIR Result The FTIR characterization was performed to ascertain the functional groups present in the extract of ZO which may have facilitated its adsorption on the mild steel surface. The re- sult obtained is presented in Figure 1. The prominent peaks observed in the Figure include; a strong and broad hydrogen bonded (O – H) stretching band at 3272.6 cm-1, the strong band at 1640.0 cm-1 may be assigned to C = C and C = O stretch- ing vibrations which may be due to the presence of conjugation in the chemical constituents of the ZO powder and the band at 1408.6 cm-1 which corresponds to the C – H bending bands of CH2 and CH3 groups and the absorption bands at 1043.7 – 1084.7 cm-1 which may be assigned to C – O functional group [34]. The FTIR result revealed that the extract contain func- tional groups which may facilitate the effectiveness of the ex- tract to adsorb and interact with the mild steel surface. As a result, protection of the metal surface may be as a result of the adsorption of these functional groups present in the ZO powder [35]. Figure 1: FTIR image of ZO powder 3.1.2. GC-MS Results The active phytochemical components of ZO [36] were re- vealed in the Gas Chromatography-Mass Spectroscopy result presented in Table 1 and Figures 2 & 3. The peaks were identified by comparing their retention times with those found in (NIST-MS) library. Compounds with less than 4 % area 3 Adindu et al. / J. Nig. Soc. Phys. Sci. 5 (2023) 1386 4 peak were not included in the presented result. Benzene, 1- (1,5-dimethyl-4-hexenyl)-4-methyl-, Dodecanoic acid and 9- Octadecenoic acid (Z)-2-hydroxy-1-(hydroxymethyl) ethyl es- ter were selected for the computational studies. 3.2. Electrochemical Results Potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) experiments were carried out to understand the effect of ZO extract on the corrosion of mild steel in acidic environments. The concentrations of the ZO ex- tract chosen for the experiment were 200 and 1000 mg/L re- spectively and the plots of OCP obtained in 1.0 M HCl and 0.5 M H2SO4 environments are presented in Figure 4 (a & b). 3.2.1. Electrochemical impedance spectroscopy results Impedance experiments were undertaken on mild steel in the selected acid solutions in the presence and absence of ZO inhibitor at two concentrations. The Nyquist and Bode plots re- spectively for mild steel corrosion in 1 M HCl and 0.5 M H2SO4 acid solution respectively are presented in Figures 5 (a & b) and 6 (a & b) respectively while the electrochemical parameters from the EIS experiments are presented in Table 2. The Nyquist plot can be seen to show a single depressed semicircle in the re- gion of high frequency for all the systems studied equivalent to one time constant found in the bode graphs. In the Nyquist plot, the high frequency that intercepts with the real axis in named the solution resistance (Rs) whereas the low frequency that in- tercept with the real axis is called the charge transfer resistance (Rct) [37]. The impedance results were fitted into an equivalent circuit model Rs (QdlRct) to get the impedance data presented in Table 2 and Qdl is the double layer capacitance. This equiva- lent circuit has been previously used to model impedance result [38-39] for mild steel corrosion in acidic media. The solution resistance in the equivalent circuit was shorted by a constant phase element (CPE) which was subsequently connected par- allel to the charge transfer resistance (Rct). The pure capacitor was replaced in the equivalent circuit to account for the devi- ations from ideal dielectric behavior which may arise from the dissimilar nature of the electrode surfaces. The electrochemical impedance response of the constant phase element is given in equation (1): ZCPE = Q −1 (Jω−n) . (1) Here Q is the CPE constant, n is the CPE exponent, J an imag- inary number which is equivalent to (-1)1/2 and ω is the angular frequency in s-1 (ω = 2π f ), f is the frequency in Hz. The in- hibition efficiencies presented in Table 2 from the impedance response were estimated according to the equation (2): I E% = ( 1 − Rct, bl Rct, in ) × 100, (2) where Rct,bl represents charge transfer resistance in the absence of the inhibitor and Rct, in represents charge transfer resistance when the inhibitor was added. The results presented in Table 2 shows that Rct values increased with increase in the concen- tration of the ZO inhibitor whereas the Qdl values decreased as the ZO concentration increased, the former action indicated that anticorrosion process is experienced whereas the later showed that the ZO extract actually adsorbed on the mild steel surface. 3.2.2. Potentiodynamic Polarization (PDP) Results The mechanisms of the partial anodic and cathodic half cor- rosion reactions as well as the effect of ZO on either reactions were studied with the aid potentiodynamic polarization experi- mental techniques. Figure 7 shows the PDP plots for mild steel corrosion in (a) 1 M HCl solution and (b) 0.5 M H2SO4 acid solutions with and without ZO inhibitor and Table 3 shows the PDP parameters for mild steel corrosion in the presence and ab- sence of the inhibitor. The result in Table 3 shows that the ad- dition of the inhibitor reduced the anodic and also the cathodic half corrosion reactions while shifting the corrosion reaction potential (Ecorr)towards the negative value as well as reducing both the anodic and cathodic current densities in both acidic environments. These effects showed that ZO functioned as a mixed type corrosion inhibitor for mild steel in both acidic so- lutions. The corrosion inhibition efficiencies (IE%) reported for ZO were estimated from the current densities without (icorr,bl) and with (icorr,inh) ZO inhibitor according to the equation (3): IE% = ( 1 − icorr, inh icorr, bl ) × 100. (3) The (I E%) values shown in Table 3 are remarkably high indi- cating that ZO is a good anti-corrosion material. 3.3. Theoretical computational results 3.3.1. Quantum chemical computation: Exact experimental identification of contributions of the in- dividual constituents of the bulk extract to the overall corrosion inhibition has been hindered as a result of the complex nature of the plant extract, we therefore rely on quantum chemical computations as well as molecular dynamic simulations to ascertain the individual contributions of three selected major constituents of ZO extract to the experimentally observed corrosion inhibition effects. The molecular structures of ben- zene, 1-(1,5-dimethyl-4-hexenyl)-4-methyl- (α-Curcumene), dodecanoic acid (Lauric acid) and 9-Octadecenoic acid (Z)-, 2-hydroxy-1-(hydroxymethyl)ethyl ester present in the ZO were optimized with the density functional theory electronic program DMol3 utilizing a Mulliken population analysis [40, 41). Electronic condition for the simulation are restricted spin polarization by the DND basis set and the Perdew–Wang (PW) local correlation density functional, Further calculation was achieved to obtain the quantum chemical parameters such as the lowest unoccupied molecular orbital energy (ELUMO) the highest occupied molecular orbital energy (EHOMO), energy gap (∆E), absolute hardness (η), chemical softness (σ), the fraction of electrons that were transferred from inhibitor molecule to the metal surface (∆N) and fukui functions. To mimic the extraction medium, these calculations were done in the presence of ethanol as the solvated medium using LDA and PWC functional. 4 Adindu et al. / J. Nig. Soc. Phys. Sci. 5 (2023) 1386 5 Table 1: Some of the active components of ZO from the GC-MS result Peak No. Retention Time Name of compound Molecular weight (g/mol) Molecular for- mular Area percent 11 16.6262 Benzene, 1-(1,5-dimethyl-4- hexenyl)-4-methyl- 202.3352 C15H22 4.1746 13 17.0368 1,3-Cyclohexadiene, 5-(1,5- dimethyl-4-hexenyl)-2-methyl-, (Zingiberene) 204.3511 C15H24 4.6564 18 19.6874 Dodecanoic acid (Lauric acid) 200.32 C12H24O2 5.414 23 23.8033 Tetradecanoic acid 228.37 C14H28O2 5.2783 35 27.7678 n-Hexadecanoic acid 256.40 C16H32O2 4.6996 41 29.9013 9,17-Octadecadienal, (Z)- 264.40 C18H32O 5.0745 55 32.8447 9-Octadecenoic acid (Z)-, 2- hydroxy-1-(hydroxymethyl)ethyl ester 356.50 C21H40O4 16.4469 Figure 2: GC-MS microgram of ZO powder 5 Adindu et al. / J. Nig. Soc. Phys. Sci. 5 (2023) 1386 6 Figure 3: Mass spectra and molecular structures of the some ZO constituents Table 2: Electrochemical impedance parameters for mild steel corrosion with and without ZO System Rs (ω cm2 ) Rct (Ω cm2) N Qdl (µF cm -2) IE% 1 M HCl 1.67 104 0.88 91.7 200 mg/L ZO 1.78 286 0.89 38.9 63.6 1000 mg/L ZO 1.81 602 0.89 22.3 82.7 0.5 M H2SO4 2.87 8.4 0.84 258.8 200 mg/L ZO 3.16 40 0.89 153.6 79 1000 mg/L ZO 3.26 132 0.89 61.5 93.6 Table 3: Potentiodynamic polarization parameters for mild steel corrosion with and without ZO inhibitor System Ecorr (mV vs SCE) Icorr (µA/cm2) ba (mV dec-1 ) bc (mV dec-1 ) IE% 1 M HCl -471.3 649.4 126.3 168.5 200 mg/L ZO -477 224.5 112.7 123.2 65.4 1000 mg/L ZO -474.3 109.6 104.8 116.9 83.1 0.5 M H2SO4 -500 2940 136.7 208.5 200 mg/L ZO -506 1476 123.5 194.7 49.8 1000 mg/L ZO -509 756.9 114.3 186.2 74.3 6 Adindu et al. / J. Nig. Soc. Phys. Sci. 5 (2023) 1386 7 Figure 4: Graph of open circuit potential for mild steel in (a) 1 M HCl (b) 0.5 M H2SO4 in the presence and absence of ZO. The simulation results including the optimized structure, frontier orbitals (HOMO and LUMO orbital), the Fukui in- dices (f+ and f-) and the electron density are shown in Figure 8 while the quantum chemical parameters such as HOMO energy (EHOMO), LUMO energy (ELUMO), energy gap, (∆E = (ELUMO - (EHOMO), electron charge transfer (∆N), absolute hardness (η), absolute electronegativity (χ) and absolute softness(η) are pre- sented in Table 4. High values of EHOMO indicate the ability of an inhibitor to donate electron the unoccupied d-orbital of the metal. Similarly, low value of the energy gap shows that the energy needed to remove the lowest occupied orbital will be small indicating that the corrosion retardation will be high. Ac- cordingly, f-values show the reactivity relating to electrophilic attack while the corresponding f+ values indicate the reactivity in relation to nucleophilic attack or the ability of the metal to at- tract electron. The ionization potential (I) and electron affinity (A) are, respectively, related to the HOMO and LUMO energies as shown in equations (4) and (5): I = −EHOMO (4) A = −ELUMO. (5) The quantification of the electron charge transfer (∆N) from the electron rich inhibitor to the surface of the metal was done according to equation (6): ∆N = χmetal −χinh 2 (ηmetal + ηinh) , (6) Figure 5: Nyquist and Bode plots for mild steel corrosion without and with the ZO extract in 0.5 M H2SO4 where χmetal and χinh /represent the absolute electronegativity of the metal and inhibitor respectively whereas ηmetal and ηinh are the absolute hardness of metal and inhibitor respectively. The tabulated values of ∆N were accordingly computed using theo- retical values of 7 eV/mol for χmetal and θ eV/mol for ηmetal [41]. It has been previously reported that values of ∆N relate well with binding energies of corrosion inhibitors with high values favoring stronger adsorption of the inhibitor on the metal sur- face [42]. The values of η, χ and σ reported in Table 4 are computed according to equations (7)-(9): η = I − A 2 (7) χ = I + A 2 (8) σ = 1 η . (9) Accordingly our obtained results fall within the range of values already reported for some organic corrosion inhibitors 7 Adindu et al. / J. Nig. Soc. Phys. Sci. 5 (2023) 1386 8 Figure 6: (a) Nyquist and (b) Bode plots for mild steel in 1.0 M HCl in the presence and absence of ZO extract [42]. The low value of ∆E obtained for 9-Octadecenoic acid (Z)-, 2-hydroxy-1-(hydroxymethyl)ethyl ester suggests that it must have interacted more covalently with the metal surface than the other constituents studied showing that it might have contributed more to the observed inhibiting property exhibited by the extract. 3.3.2. Molecular dynamic simulation results Molecular dynamic simulation was performed on the three compounds previously selected using the forcite quench tool of Material Studio. The molecular structures were first subjected to geometric optimization using a maximum iteration of 1000 and energy of 0.01 Kcal/mol. Modeling was achieved using the Condensed phase Optimized Molecular Potentials for Atom- istic Simulation Studies (COMPASS) force field including smart algorithm. The temperature was maintained at 298K using the Andersen thermostat having NVE microcanonical Figure 7: Potentiodynamic polarization plots for mild steel corrosion in (a) 1 M HCl and (b) 0.5 M H2SO4 solutions ensemble, 1fs step time and 5ps total simulation time were used and the number of steps were 5000. The Fe (110) slab was chosen for the simulation with a simulation box of dimension 30 × 25 × 29 Å and periodic boundary conditions to simulate representative section of the interface [36].The simulation box consist of Fe (1 1 0), electrolytic systems [(H2O, H3O+, Cl-) and (H2O, H3O+ and SO4-)] and inhibitor molecules. The configuration of the lower layer of the Fe slab was constraint to the lager position, although the other degrees of freedom were relaxed before the optimization of the Fe (1 1 0) was done which was further increased to 12 × 8 supercell. Quenching was done every 250 steps. The results of interaction mechanism between the inhibitor and the metal surface in the presence of the following molecules H2O, H3O+, Cl- and SO4- performed with molecular dynamic simulation are presented in Figure 9, Figure 10 and Table 4. 8 Adindu et al. / J. Nig. Soc. Phys. Sci. 5 (2023) 1386 9 Figure 8: Electronic properties of benzene, 1-(1,5-dimethyl-4-hexenyl)-4- methyl,dodecanoic acid and 9-Octadecenoic acid (Z)-2-hydroxy-1- (hydroxymethyl)ethyl ester The results in Figure 8 and 9 show that the inhibitor maintained a flat-lying adsorption orientation on the surface of the metal as a result of the delocalization of the electron density all over the molecule. This type of orientation is known to improve close contact between the inhibitor and the metal surface. In other to study the effect of the different acid corrodent on the adsorption energy, the solvation particles H2O, H3O+, Cl-) and H2O, H3O+ and SO4-)] were packed into the simulation box using the amor- phous cell tool of the material studio 7.0 modeling and simula- tion software. The level of interaction between each inhibitor molecule and the metal surface was quantified by evaluating the energy of interaction energy equation (10): Interaction Energy = Etotal− ( EFe+solvation particles − Einhibitor ) ,(10) where Etotal, EFe+solvent particles and EInhibitor corresponds to the total energy of the Fe (110)/EFe+solvent particles couple, Energy of the Fe slab in addition to the solvent particles and the en- ergy of the inhibitor molecule respectively, the solvation par- ticles refer to either H2O, H3O+, Cl-) and H2O, H3O+ and SO4-, a negative value of the interaction energy is an indication that the molecule possess a stable adsorption structure, all the molecules studied showed negative values which accounts for 9 Adindu et al. / J. Nig. Soc. Phys. Sci. 5 (2023) 1386 10 Table 4: Calculated quantum chemical properties for the most stable configurations of the selected ZO constituents Quantum chemical parameter Benzene, 1-(1,5- dimethyl-4-hexenyl) -4-methyl- Dodecanoic acid 9-Octadecenoic acid (Z)-, 2-hydroxy-1- (hydroxymethyl) ethyl ester EHOMO (eV) -5.0347 -5.7252 -3.3152 ELUMO (eV) -1.7278 -2.0098 -2.9711 Energy gap (∆E) 3.3069 3.7154 0.3440 Electron charge transfer (∆N) 1.0943 0.8431 11.2051 Absolute hardness (η) 1.65375 1.8577 0.1721 Absolute electroneg- ativity (χ) 3.3813 3.8675 3.1432 Absolute softness (σ) 0.6048 0.5383 5.8106 Interaction energy (Kcal/mol) HCl -117.82 -172.46 -167.81 H2SO4 -167.98 -145.35 -355.55 Figure 9: Depiction of the side and top views revealing suitable configurations for adsorption of ZO constituents on Fe (110) surface in H2SO4 solution the inhibition efficiencies obtained in the experimental results.. The large interaction energy (-355.5Kcal/mol) observed for 9- Octadecenoic acid (Z)-, 2-hydroxy-1-(hydroxymethyl)ethyl es- ter 0.5 M H2SO4 mirrors its ability to adsorb better on the metal surface than the other constituents which agrees with the quan- tum chemical computation result. 4. CONCLUSION The corrosion inhibition study revealed that the ethanol ex- tract of Zingiber officinale efficiently inhibited the corrosion of Figure 10: Depiction of the side and top views revealing suitable configurations for adsorption of ZO molecules on Fe (110) surface in 1.0 M HCl acid solution mild steel induced on 1.0 M HCl and 0.5 M H2SO4 acid solu- tion respectively. The PDD results showed that Zingiber offic- inale is a mixed type corrosion inhibitor for mild steel in both acidic solutions while EIS results revealed that Zingiber offic- inale adsorbed on the surface of mild steel indicating the evi- dence of metal protection. Also, GC-MS results revealed that extract of Zingiber officinale contains twenty-three (23) com- pounds of which three (3) compounds namely; Benzene, 1- (1,5-dimethyl-4-hexenyl)-4-methyl-, Octadecanoic acid and 9- Octadecenoic acid (Z)-, 2-hydroxy-1-(hydroxymethyl)ethyl es- ter were used for computational studies. Quantum chemical calculation results revealed the positions of quantum chemical descriptors and indicators respectively of the active inhibitor 10 Adindu et al. / J. Nig. Soc. Phys. Sci. 5 (2023) 1386 11 molecule while the molecular dynamic simulation results pro- vided the binding energy of interaction between the active in- hibitor molecule and metal surface. Finally, it observed that extract of ZO exhibited effective corrosion inhibition of mild steel induced in HCl and H2SO4 acid solution due to presence of active inhibitive molecule presence in ZO extract. 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