Synergetic Effect of Potassium Iodide and Miana ( Coleus scutellaroides (L.) Benth. ) Leaves Extract on Mild Steel in HCl Medium

Due to its low carbon content, mild steel is prone to corrosion. Therefore, corrosion inhibitors are needed to decrease the corrosive rate of mild steel. This research aims to investigate the influence of adding potassium iodide to Miana leaves extract ( Coleus scutellaroides (L.) Benth.) (MLE) on the corrosion rate of mild steel, identify the type of adsorption, synergistic effects and characterize the surface of mild steel both before and after the addition of potassium iodide. The weight loss method is employed to test the corrosion rate, and the type of adsorption is identified through thermodynamic calculations. Surface characterization is evaluated using Fourier Transform Infrared (FTIR) and Scanning Electron Microscopy (SEM). As potassium iodide is added, the weight loss findings show an increase in inhibitory efficiency. When potassium iodide concentration was 0.4 g/L and temperature was 30°C, the maximum inhibitory efficiency was attained, which was 92.784%. Characterization analysis indicates the interaction between potassium iodide and MLE with the surface of mild steel. This research has not been explored yet and is expected to provide information on the use of potassium iodide and MLE as environmentally friendly corrosion inhibitors.


INTRODUCTION
Corrosion plays a significant role in various industrial applications such as acid settling, chemical cleaning, water treatment, and oil well evacuation.It is responsible for causing severe issues that lead to financial losses and environmental hazards.Acidic solutions, such as HCl, H2SO4, and H3PO4, are frequently employed in various industrial processes, including those that involve metal corrosion through dissolution, descaling, and oil evaporation (Khadiri et al., 2021;Saraswat & Yadav, 2021).
Since mild steel is inexpensive, has key mechanical properties, is widely available, and is used in infrastructure (buildings and bridges), well covers, and oil and gas transportation pipelines, it is one of the most important structural materials.Nonetheless, in an acidic environment, mild steel is more prone to corrosion.To keep mild steels free of corrosion, it is necessary to apply a corrosion inhibitor that is considered affordable, user-friendly, biodegradable, and practical.Currently, a lot of research has been developed on corrosion inhibitors using plant extracts.This development aims to reduce the use of synthetic inhibitors that are toxic in nature (Bhardwaj et al., 2021;Saraswat & Yadav, 2021).
Plant extracts are potentially corrosion inhibitors because they contain active compounds such as polyphenols, amino acids or alkaloids.The π and heteroatom bonds of these active Hydrogen: Jurnal Kependidikan Kimia, December 2023, 11(6) |836 substances can interact with steels through absorption or reception of electron pairs.This interaction results in the formation of coordinating bonds or polar covalent bonds that can prevent corruption (Marzorati et al., 2019).
Miana leaves (Coleus scutellarioides (L.) Benth.), a plant with a longstanding history in traditional medicine, contain alkaloids, flavonoids, terpenoids, and tannins known for their medicinal properties (Astuti et al., 2019;Salimi, 2021).These compounds have demonstrated corrosion inhibition capabilities, as evidenced by previous research (Benghalia et al., 2019;Chapagain et al., 2022).Plant extracts have also been demonstrated to work synergistically with other compounds (such halide salts) to increase the effectiveness of corrosion inhibition in acidic conditions.effect synergy for halides in the following order: I − >Br − >F − >Cl − .The combination of iodide and organic inhibitors can enhance the effectiveness of inhibiting mild steel corrosion in harsh settings, as iodide ions have advantages such bigger atomic sizes and simpler polarisation.Studies by Pramudita et al. (2019) and El-katori et al. (2020) highlight the positive impact of potassium iodide on inhibition efficiency.
The purpose of this work is to assess the effectiveness of potassium iodide and MLE and synergistic effects, offering valuable perspectives on strategies to inhibit corrosion in mild steel exposed to acidic conditions.This study tackles the issue by specifically investigating how potassium iodide and MLE synergistically affect HCl media, with the goal of proposing practical approaches for inhibiting corrosion in applications involving mild steel.

Tools and Materials
The equipment used in this research includes a water bath

Weight Loss Method
Before conducting weight loss measurements, the mild steel is prepared.Specimens of mild steel with dimensions of 3 x 2 cm and a thickness of 1 mm are prepared.The surface of the mild steel is smoothed using iron sandpaper, then rinsed with deionized water and acetone.The cleaned mild steel is dried using an oven and weighed, with the recorded weight being the initial weight (W1) (Untari et al., 2020).
The corrosion rate determination based on the weight loss method involves immersing mild steel in a 50 mL solution of corrosive medium, 1 M HCl, with the addition of MLE at 6 g/L and varying iodide concentrations (0; 0.1; 0.2; 0.3; 0.4) g/L.The immersion is conducted at different temperatures: 30, 40, 50, and 60°C for a duration of 7 hours using a water bath.The mild steel is then cleaned, rinsed, and dried.After completing these steps, the mild steel is weighed, and the ultimate weight (W2) is indicated by the recorded weight (Untari et al., 2020).
The corrosion rate and inhibition efficiency with respect to the addition of various EDM concentrations to mild steel can be examined based on the weight loss data.The following formulas can be used to determine the inhibition efficiency and corrosion rate (Verma et al., 2017;Wahyuni et al., 2022).Determination of corrosion rate can be executed by formula (1).

A×t
(1) Hydrogen: Jurnal Kependidikan Kimia, December 2023, 11(6) |837 Where, Vcorr is the corrosion rate (mg/cm 2 hour), W1 is the weight of mild steel before immersion (mg), W2 is the weight of mild steel after immersion (mg), A is the surface area (cm 2 ), t is the immersion time (hours).From equation ( 1), the degree of surface coverage (θ) and inhibition efficiency (EI) can be calculated by formula ( 2) and (3).(2) Where, θ is the degree of surface coverage, EI is the inhibition efficiency, V1 is the corrosion rate before immersion (mg/cm 2 hour), and V2 is the corrosion rate after immersion (mg/cm 2 hour).

Fourier-Transform Infrared Spectroscopy (FTIR) Analysis
Mild steel is immersed in a corrosive medium of 1 N HCl with the presence of MLE at a concentration of 6 g/L for a duration of 6 days.Measurements are also conducted on the MLE at a concentration of 6 g/L, combined with iodide at 0.4 g/L, and a concentrated extract of the inhibitor at 6 g/L.After immersion, the mild steel is dried, and the layer adhering to the mild steel surface is obtained by scraping off this layer.Subsequently, Fourier Transform Infrared (FTIR) measurements are performed (Untari et al., 2020).

Surface Morphology Analysis (SEM)
Surface morphology analysis is conducted through Scanning Electron Microscopy (SEM) to investigate the structural characteristics of mild steel.The process involves immersing the mild steel in a corrosive medium of 1 N HCl for 6 days, both with and without the presence of MLE at a concentration of 6 g/L, and with the addition of iodide at 0.4 g/L.Subsequently, the mild steel is retrieved, dried, and subjected to surface analysis using Scanning Electron Microscopy (SEM).Comparative analysis is also performed on mild steel without immersion.The SEM analysis allows for the examination of surface topography, the identification of corrosion products, and the assessment of the effectiveness of the MLE in mitigating corrosion.This detailed examination provides valuable insights into the structural changes and corrosion mechanisms occurring at the surface of the mild steel under different experimental conditions (Untari et al., 2020).

Weight Loss Considerations
Figure 1 shows how adding different potassium iodide concentrations to MLE can successfully lower the corrosion rate and raise the inhibition efficiency.This is explained by the simultaneous electrostatic interactions-mediated adsorption of iodide ions and secondary metabolites from the MLE on the mild steel surface.A protective layer that guards against corrosion reactions forms on the mild steel surface as a result of this adsorption process.Thus, adding potassium iodide greatly improves mild steel's resistance to corrosion and makes it more resilient to the harm that corrosion in an HCl medium can do (Priya et al., 2018;Shamnamol et al., 2020).
In contrast, the rate of corrosion tends to increase while the efficiency of inhibition diminishes with increasing temperature.This is because the mild steel surface has EDM chemicals desorbing on it, which eventually speeds up the corrosion process (Sait et al., 2021).With an inhibitory efficiency of 92.784%, the lowest corrosion rate is measured at a concentration of 0.4 g/L of MLE at 30°C, or 0.095 mg/cm²hour.

Isotherm Adsorption
Adsorption isotherms provide an explanation for the inhibitor's interaction with the mild steel surface.The Langmuir adsorption isotherm seems to be the most appropriate among the several investigated adsorption isotherm models, including Temkin, Freundlich, and Langmuir.The coefficient of determination (R2) numbers getting close to one clearly show this.The following is the Langmuir isotherm equation as shown in formula (4) (Febriani et al., 2022).
Where C is the inhibitor concentration (g/L), θ is the degree of surface coverage, and Kads is the adsorption equilibrium constant.This proves that in 1 M HCl, MLE and potassium iodide follows the Langmuir adsorption isotherm (Untari et al., 2020).
The value of Kads is obtained from the intercept of the straight line equation in Figure 2. The Kads values are related to the strength of MLE and potassium iodide adsorption on the surface of mild steel.Table 2 shows that the highest Kads value is at a temperature of 303 K, indicating that the highest inhibition efficiency is achieved at that temperature (Thakur & Kumar, 2021).The determination of ∆G o ads can be calculated from the Kads values obtained from equation (4).
Where C H 2 O is the water concentration (1000 g/L), and R is the molar gas constant (8.314J mol⁻¹K⁻¹).The obtained value of the Gibbs free energy of adsorption (ΔGads) is negative, indicating that the MLE adsorption process on the mild steel surface occurs spontaneously.A substance is classified as physical adsorption (physisorption) if its ΔGads value is less than -20 kJ/mol.ΔGads value of greater than -40 kJ/mol indicates chemical adsorption, often known as chemisorption.Table 2 shows ΔG ads value between -32 and -34 kJ/mol, indicating a combination of chemical and physical adsorption, rather chemisorption.Chemical absorption takes place at this point as a result of the formation of a chemical link between the inhibitor and the surface of the mild steel, creating a coordinating covalent bond.(Indah & Safnowandi, 2020; Untari et al., 2020;Wan et al., 2021).
The value of ∆G o ads can be used to determine enthalpy (∆H o ads) and entropy (∆S o ads) calculated by the equation ( 6) (Stiadi et al., 2020).
Where ΔHads is the enthalpy of adsorption (kJ mol⁻¹), ΔGads is the Gibbs free energy (kJ mol⁻¹), ΔSads is the entropy of adsorption (J mol⁻¹), and T is the temperature (K).According to the research findings, the adsorption of MLE molecules and potassium iodide on the mild steel surface is exothermic, or releases heat, as indicated by the negative value of ΔHads.There is more disorder in the solution when ΔSads is positive (Untari et al., 2020;Wan et al., 2021).

Thermodynamic Parameters Activation
The activation energy (Ea) of mild steel corrosion can be found using the Arrhenius equation ( 7) (Emriadi et al., 2021).
Where A is frequency factor, Ea is is the activation energy (kJmol -1 ), and T is temperature (K).
Figure 3 shows the graph of Arrhenius ln V corr versus 1/T for mild steel in a solution of 1 M HCl both with and without potassium iodide at different concentrations.The straight-line equation's slope value in Figure 3 yields the value of E a .Table 3 illustrates that an increase in potassium iodide concentration in HCl 1 M solution results in a corresponding increase in Ea.According to the results, the value of Ea was 35.196 kJ/mol when potassium iodide was not added.Ea will, however, rise in value when potassium iodide is added.At 0.4 g/L, the maximum value of Ea is 57.545 kJ/mol.When MLE and potassium iodide were included in the table, the Ea value was larger than when neither was present.From the data above, it can be seen that there is a strong inhibition of compounds in MLE and potassium iodide, namely an increase in energy barrier in the corrosion process and an electrostatic reaction occurs from adsorption inhibitors on the surface of mild steel (physiosorption) (Pramudita et al., 2019).The values of enthalpy (∆H * ) and entropy (∆S * ) can be calculated using the Arrhenius equation (Emriadi et al., 2018): Where N is the avogadro number (6.023x10 23 ), h is Planck's constant (6.63x10-34), (∆S * ) is the change in entropy (Jmol -1 K −1 ), and (∆H * ) is the enthalpy change (Jmol -1 K −1 ).
The value of ∆H* is obtained positive (+) which indicates that the corrosion reaction that occurs is included in endothermic reactions.A negative sign (-) in the value of ∆S* indicates that the formation of activated complexes in the determination of reaction rate involves an association mechanism.Increasingly negative values as concentration increases indicate decreased randomness behavior and increased inhibitory efficiency (Emembolu & Igwegbe, 2022;Untari et al., 2020).

Synergetic Effect
When KI is added, the inhibitory efficiency is higher than when MLE is used alone.The following formula is used to calculate the synergistic effect: P1+2 = (P1 + P2) -(P1 .P2) (9) Where, S is synergism, P1 is the surface coverage of iodide ions, P2 is the surface coverage of MLE, P'1+2 are the surface coverage of ion iodides and MLE.If S = 1 indicates that the inhibitor molecules do not interact and absorb individually on the metal contact.Furthermore, a synergistic impact is indicated by S > 1, whereas an antagonistic effect is indicated by S < 1 (Djellab, 2018;Pramudita et al., 2019).The resultant S value is more than 1, as Table 4.7 demonstrates.This suggests the occurrence of a synergistic effect, wherein cation adsorption on the anion layer that forms the protective layer is followed by anions chemically adsorbed on the metal surface (Pramudita et al., 2019).

FTIR Analysis
FTIR analysis was conducted to identify functional groups that play a role in corrosion inhibition.Several compounds commonly used as corrosion inhibitors include flavonoids, alkaloids, saponins, triterpenes, tannins, and phenolics.These compounds have polar functional groups, which have free electron pairs and π bonds capable of donating electrons, forming complex compounds (Riastuti et al., 2022;Zakeri et al., 2022).
The spectrum results in Figure 4 (a) represent the spectrum of pure MLE.The spectrum results show the presence of several functional groups in the MLE.The O-H group is observed at the wavenumber of 3365.08 cm -1 , aliphatic C-H groups at wavenumbers 2921.53 cm -1 and 2855.72 cm -1 , aromatic C=C group at wavenumbers 1606.52 cm -1 and 1539.29 cm -1 , alkane C-H group at 1393.02 cm -1 , and C-O group at wavelengths 1252.47 cm -1 and 1040.49cm -1 (Astuti et al., 2021).The results indicate the presence of hydroxyl (-OH) functional groups bound to the aromatic ring, suggesting the presence of organic compounds such as flavonoids, phenolics, cresol, and other organic compounds.The high corrosion inhibition efficiency obtained using MLE in a 1 M HCl solution is associated with the presence of hydroxyl functional groups that can form complex compounds with mild steel, inhibiting corrosion (Ogunleye et al., 2020;Wijayanti et al., 2023).

CONCLUSION
The study found that potassium iodide and MLE can be used as environmentally friendly corrosion inhibitors.The synergistic effects resulting from the interaction of potassium iodide and MLE can increase the inhibition efficiency to 92.784% at 30 °C at a concentration of 0.4 g/L which is the highest inhibiting efficiency.The pattern of adsorption without and with the presence of potassium iodide follows Langmuir's isothermal pattern.The interaction between MLE, potassium iodide, and mild steel surfaces is demonstrated by changes in the wavenumber seen in the FTIR measurement.SEM morphological examination of a mild steel surface revealed that potasium iodide and MLE have been absorbed on the surface of mild steel forming a protective layer.The current research findings emphasize the notable advantages of including potassium iodide into corrosion inhibitors derived from natural sources, resulting in a reduction in the quantity of extract utilized.The researcher hopes that future studies can utilize different types of leaves and various mediums.

Figure 1 .
Figure 1.The Influence of Various Concentrations of Potassium Iodide on the Corrosion Rate (Vcorr) and Inhibition Efficiency (%IE) in 1 M HCl

Figure 2 .
Figure 2. The Langmuir adsorption isotherm graph for the corrosion of mild steel with MLE and potassium iodide in a 1 M HCl solution Figure 2 shows the linear relationship of C/θ vs. C, obtained from the equation of a straight line.The coefficient of determination (R2) values obtained from equation (4) are close to 1.This proves that in 1 M HCl, MLE and potassium iodide follows the Langmuir adsorption isotherm(Untari et al., 2020).

Figure 3 .
Figure 3. Arrhenius plots for the corrosion of mild steel in a 1 M HCl solution without and with the addition of MLE and potassium iodide at various concentrations

Figure 4
Figure 4 (b) and Figure 4 (c) indicates a shift in the absorption band of functional groups compared to.These wavenumber shifts indicate interactions between MLE and potassium iodide with the surface of mild steel(Khadom et al., 2022).

Table 1 .
Thermodynamic parameters for the adsorption of EDM on mild steel in a 1 M HCl solution at each temperature based on the results of the Langmuir isotherm

Table 3 .
The value of the synergetic effect of MLE with potassium iodide at a temperature of 30 o C