1 Introduction

Corrosion is a natural process that takes place when a substance, often an alloy or a metal, degrades over time under the effect of an external factor. Metals are subject to this phenomenon and become more stable chemical compounds, such as oxides, sulfides, and chlorides. These metals are immersed in assorted applications, the most important of which are power generation, construction, and oil refineries. Some chemical practices such as pickling and cleaning are also often resorted to releasing oxides, impurities, as well as deposits from metals, so hydrochloric acid is typically utilized for this purpose [1,2,3,4]. As a result of such direct processing, the acidic environment causes surface damage, equipment breakdowns, and environmental and financial losses. Among the adequate and approved means of protecting equipment and ensuring its long-term durability is the usage of corrosion inhibitors [5, 6].

Organic compounds that include heterocyclic atoms such as nitrogen (N), oxygen (O), and sulfur (S) along with aromatic scaffolds are deemed to be efficacious anticorrosive inhibitors [7,8,9,10,11,12,13]. The availability of π electrons, the large size, the number of heteroatoms, and other properties influence the strength of inhibition of these organic molecules [14,15,16]. These molecules adsorb through the interaction of an unshared pairs of heterocyclic atoms with empty d-orbitals of the metal, developing a protective layer that prevents further damage to the metal [17,18,19]. Although there are several organic compounds that are efficacious against corrosion, researchers continue to prioritize the search for new inhibitors so that they are non-toxic, economically viable, and effective even when present in extremely low concentrations [20].

Pyrazine is one prominent heterocyclic organic substance that is being closely studied owing to its several uses. Pyrazine and its analogs are employed in industries, such as food flavoring [21], drugs [22, 23], and agro-based compounds [24]. Furthermore, since pyrazines are often employed as flavoring ingredients in food, they are both cost-effective and ecologically benign. However, several investigations have demonstrated that certain pyridazine derivatives are efficient against metal corrosion in acidic environments [25,26,27]. There have been no reports of pyridazinone analogs functioning as inhibitors of carbon steel corrosion in an acidic environment. As a consequence, the application of pyridazinone derivatives as corrosion inhibitors for carbon steel might be explored further.

The aim objective of this study is to evaluate the anti-corrosion performance of a novel pyridazinone analog (Fig. 1); 4-benzyl-2-(3-(4-fluorophenyl)-2-oxopropyl)-6-phenylpyridazin-3(2H)-one (BOPP), as an inhibitor of (CR/S) corrosion in 1-M HCl employing PDP, EIS SEM and EDX, UV–Visible, and contact angle techniques. The influence of temperature on the anti-corrosion effectiveness of BOPP was also scrutinized employing the PDP method. In addition, DFT was employed for insight into the adsorption mechanism of the potential activity center. MD simulation was employed to assess their corresponding corrosion effectiveness from a theoretical standpoint.

Fig. 1
figure 1

BOPP molecular structure

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2 Experimental

2.1 CR/S and Medium

The constituent chemical elements (% by weight) of the (CR/S) employed as the working electrode are 0.37 C%, 0.230 Si%, 0.680 Mn%, 0.016 S%, 0.077 Cr%, 0.011 Ti%, 0.059 Ni%, 0.009 Co%, 0.160 Cu%, and the remaining portion of iron. For electrochemical tests, the substrates were encased in epoxy, leaving an exposed area of 1 cm2. The steel substrates were cleaned with purified water and degreased with acetone after being rubbed with SiC paper ranging in grades from 180 to 1200. The practical medium was 1-M HCl, which was made by dissolving 37% commercial HCl. About the solubility, BOPP is completely soluble in 1-M HCl. The corrosive medium containing the inhibitor was also prepared by dissolving the required amounts of BOPP directly in 1 M HCl to prepare concentrations of 10−3, 10−4, 10−5, and 10−6 M.

2.2 Inhibitor

The selection of BOPP as a corrosion inhibitor was adopted because it has many N, F, and O atoms, a planar structure, double bonds, and is easy to prepare.

2.3 Electrochemical Inspections

All assays were undertaken at an electrochemical workstation (PGZ 100) and monitored by a personal computer equipped with VoltaMaster 4 software. However, the electrochemical assessments were all realized in a three-electrode cell, incorporating (CR/S) as the working electrode, a platinum counter electrode, and a mercury-mercurous chloride reference electrode. After 1/2 h of exposure in the corrosive medium, a stable open-circuit potential was reached, and EIS experiments took place at OCP with frequencies ranging from 105 to 10−2 Hz and an amplitude of 5 mV. Finally, PDP tests were conducted from − 800 to − 100 mV at an average sweep speed of 5 × 10−1 mV/s.

Equations (1) and (2) serve their purpose to calculate the inhibition effectiveness of the BOPP on the basis of EIS and PDP data, respectively [28]:

$$\eta_{i} (\% ) = \left( {\frac{{R_{{{\text{Pf}}}} - R_{{{\text{Pi}}}} }}{{R_{{{\text{Pi}}}} }}} \right) \times 100$$
(1)

In the preceding equation, \(R_{{{\text{Pi}}}}\) and \(R_{{{\text{Pf}}}}\) correspond to the polarization resistances of the uninhibited and inhibited conditions, respectively.

$$\eta_{p} (\% ) = \left( {\frac{{i_{i} - i}}{{i_{i} }}} \right) \times 100$$
(2)

In the preceding equation, \(i\) and \(i_{i}\) denote the polarization resistances of the uninhibited and inhibited conditions, respectively.

We utilized findings that had previously been published [29] on the impact of both temperature and concentration for the 1-M HCl medium in the absence of the inhibitor in the electrochemical and surface assessments (SEM–EDX) since we worked under identical conditions.

2.4 UV–Visible Assessments

The BOPP's UV–Visible spectrum was initially recorded after it was dissolved in 1-M HCl. For 72 h, a (CR/S) substrate with a pre-treated surface was placed in the BOPP’s acidic medium. The inhibited acidic medium was then put through another UV–visible examination.

2.5 Surface and Contact Angle Assessments

To gather further insight into BOPP adsorption, the SEM–EDX technique was utilized after submerging for 24 h in the lack and presence of 10−3 M BOPP. The contact angle analysis was registered using an optical tensiometer with theta flow (Biolin Scientific).

2.6 DFT and MDs

The comprehension of the molecular-level characteristics and active sites of corrosion inhibitor molecules, as well as the energetics of the adsorption process on the BOPP molecule with the (CR/S) surface, was elucidated through the application of DFT and MD simulations.

2.6.1 DFT Computation

To establish a correlation between the anticipated inhibitory effectiveness through experimentation and chemical reactivity indices, the DFT method was employed. The Gaussian 09 package [30], utilizing the three-parameter Becke, Lee–Yang–Parr (B3LYP) functional [31] and the 6-31G + (d, p) basis sets [32], was employed to optimize the molecular structure of the studied inhibitor (BOPP) and their protonated forms within an aqueous medium. The optimization process included an exploration of various electronic properties, encompassing geometric parameters, frontier molecular orbitals (EHOMO and ELUMO), and global reactivity biological descriptors [33].

By extracting energy values from the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO), essential global chemical descriptors were derived. These descriptors encompassed gap energy (ΔE = ELUMO − EHOMO), ionization energy (I = − EHOMO), electronic affinity (A = − ELUMO), electronegativity (χ = (I + A)/2), hardness (η = (I − A)/2), and softness (σ = 1/η).

2.6.2 MD Simulation

The interaction of a neutral and protonated BOPP molecule with the CR/S surface was studied using MD modeling. The Forcite module from BIOVIA Material Studio 8.0 software was used in this simulation. The simulation approach began with the import of the Fe metal, which was then cleaved into six layers along the (110) plane. The Fe surface was then extended to a (12 × 12) supercell to create a large surface zone for inhibitor–Fe interactions. The Fe (110) design was chosen as the initial layer of the simulation box, measuring 35.25 × 35.25 × 70.43 A3. Then, the second layer contains one BOPP molecule (neutral or protonated form), H2O molecules, and H3O+ and Cl− ions. In this investigation, the crystal plane (110) in pure iron was employed to imitate our inhibitor’s adhesion properties. Previous theoretical investigations of corrosion inhibitor adsorption on a (CR/S) substrate made extensive use of this crystal plane [34, 35]. All simulations were performed at 303 K, 400-ps simulation duration, and 1.0-fs time step using the COMPASS force field and periodic boundary conditions in the NVT ensemble [36]. This force field (i.e., COMPASS) has been used in examinations of both inorganic and organic systems because it can accurately predict a variety of gas-/condensed-phase properties of different substances [37, 38]. After the MD simulation was successfully completed, the radial distribution function (RDF) was calculated from the trajectory of the simulation results to predict the type of adsorption of the BOPP molecule (neutral and protonated form) onto the Fe (110) plane, which could be chemisorption, physisorption, or both.

3 Results and Discussion

3.1 Open-Circuit Potential (OCP) and PDP Assessments

Figure 2a shows the diagram of the OCP of the (CR/S) electrode at 303 K in 1-M HCl with and without BOPP. It could be observed from OCP curves that the allowed time (1800 s) was sufficient to reach stable interface conditions. However, it can be found that the open-circuit potential is shifted in a more positive direction after the addition of BOPP. This implies that the kinetics of the anodic reaction of (CR/S) (steel dissolution) in 1-M HCl were influenced more strongly in the presence of BOPP. This may be due to the immediate formation of the protective layer of the BOPP on the (CR/S) surface, thereby protecting it from corrosive ions [39].

Fig. 2
figure 2

a OCP curves for (CR/S) in 1-M HCl with and without BOPP at 303 K. b PDP graphical representations for (CR/S) in the 1-M HCl medium and with BOPP

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Figure 2b outlines the PDP profiles of (CR/S) in 1-M HCl medium consisting of various amounts of BOPP. Table 1 conveys the inhibition efficiency as well as the electrochemical traits derived from the extrapolation approach, which include corrosion current density (icorr), corrosion potential (Ecorr), Tafel cathodic (βc), and anodic (βa). It is clear from Fig. 2b that the cathodic and anodic current densities are considerably reduced when BOPP is introduced into the 1-M HCl and the change in cathodic current densities with BOPP concentrations is more pronounced, which suggests that BOPP significantly inhibits both anodic metal dissolution and cathodic hydrogen evolution reactions. It is also observed that the cathodic curves give rise to Tafel lines that are nearly parallel. This feature indicates that the introduction of BOPP does not modify the hydrogen evolution mechanism, and most likely the reduction of hydrogen ions on the (CR/S) surface is mainly through a charge transfer mechanism [40]. In fact, the active sites of the (CR/S) surface available for H+ ions are reduced, while the actual reaction mechanism remains unaltered. However, the anodic curves of (CR/S) in 1-M HCl in the presence of BOPP show that this inhibitor has little effect, especially at high concentrations, at a potential higher than – 260 mV/SCE. At this potential, steel dissolution appears to occur, leading to desorption of the inhibiting layer. In this case, the desorption rate of BOPP is greater than its adsorption rate [40, 41]. In addition, the Ecorr is shifted toward the anodic direction in the presence of BOPP, and the shift in Ecorr (i.e., ΔEcorr = 59.7 mV) among without and with the inhibitor is less than 85 mV [42]. These findings indicated that BOPP can be categorized as a mixed-type inhibitor with predominantly anodic effects.

Table 1 Electrochemical variables for (CR/S) in the 1-M HCl medium and with BOPP
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Inspection of Table 1 reveals that the icorr values appreciably diminished in the presence of BOPP, and the ηp (%) rose with the growth of the concentration of inhibitor. This can be attributed to the adsorption of BOPP molecules on the (CR/S) surface, thereby forming a barrier film and diminishing the corrosion rates of the (CR/S). The presence of BOPP causes the values of βc to rise. The βc changes imply that they have an effect on the kinetics of the hydrogen evolution process. This reveals that the energy barrier for proton discharge has grown, resulting in less gas evolution [43]. Furthermore, the βa values were reduced with the inclusion of BOPP, suggesting that BOPP impacted the anodic mechanism. Because the BOPP species adhered to the metal surface and reduced the active sites of the (CR/S) surface, this behavior indicated the formation of a protective covering [44]. Furthermore, the nitrogen and oxygen atoms of BOPP may contribute to the formation of the BOPP–Fe(II) complex, which serves as a barrier preventing (CR/S) dissolution [45]. BOPP’s high inhibitory value, reaching 95.7% at 0.001 M, is a consequence of its huge size, its abundance of heteroatoms, as well and the conjugated system formed by consecutive C=C double bonds at the pyridazine rings.

In some recent papers, one can find a few pyridazine derivatives tested for corrosion inhibition of carbon steel. This family of inhibitors has demonstrated a middle-to-good ability to inhibit carbon steel corrosion. A comparison with other pyridazine derivatives for a concentration of 10−3 M in 1-M HCl against carbon steel corrosion is given in Table 2. These results revealed that BOPP exhibited better corrosion inhibition behavior than similar-type compounds previously published under identical test conditions (Table 2) [46,47,48,49,50,51,52].

Table 2 Comparison of the inhibition efficiency derived from PDP measurements of BOPP with other similar structure inhibitors at 10−3 M
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3.2 EIS Assessments

Figure 3a shows that the Nyquist plots for (CR/S) in an acidic medium containing BOPP are similar, with just one capacitive loop matching the charge transfer resistance and double-layer capacitance at the (CR/S)/medium interface throughout the corrosion process [53]. Similar capacitive loops might imply that the charge transfer mechanism controls the electrode reactions, either in the absence or with BOPP [54]. However, the capacitive loop dilates apparently in the presence of BOPP, suggesting that the inhibitor has a significant inhibitory impact. The impedance rises with BOPP concentration due to the increased surface covering of BOPP molecules. Furthermore, the Nyquist plots revealed a slightly depressed capacitive loop, which is ascribed to the heterogeneity inherent to the surface of solid electrodes during corrosion and is commonly referred to as dispersion effects [55].

Fig. 3
figure 3

Nyquist (a) and Bode (b) plots for (CR/S) in the 1-M HCl medium and with BOPP

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For the Bode plots, the existence of a single-phase peak shows that the dissolution of the (CR/S) mainly occurs by a single charge transfer mechanism. However, the magnitude of impedance and phase angle rise with the concentration of the BOPP, revealing the formation of the protective film. The protective inhibitor film on the (CR/S) surface acts as an active barrier to the corrosive ions of 1-M HCl. In addition, the successive increase of the maximum phase angle values toward the ideal capacitive behavior (-90°) (it increased from 55.31° for 1-M HCl to 59.38°, 62.11°, 66.41°, and 70.94° with adding 10−6, 10−5, 10−4, and 10−3 M of BOPP, respectively) may be demonstrated by slowing down the rate of dissolution with time, which reflects the inhibitive action of BOPP [55]. The values of the impedance plot slope (Fig. 3b) for middle-frequency ranges are inferior to − 1, which is assigned to the frequency dispersion of interfacial impedance [56].

The Randles circuit (RC) diagram offered in Fig. 4 is applied to fitting the EIS outcomes using or without BOPP. The RC consists of medium resistance (Rs), polarization resistance (Rp), and a constant phase element (CPE). However, CPE was employed in the equivalent circuit instead of double-layer capacitance (Cdl) to improve EIS data fit [56]. Figure 3 shows an excellent relationship between theoretical results (red lines) and experimental results (geometric symbols), indicating that the selected RC is appropriate for fitting the Nyquist plots. There is a high correspondence between the experimental and fitted results, which is demonstrated by the minimal chi-squared fit (χ2 ≈ 10−3) displayed in Table 3. The formula for computing CPE impedance is as follows [56, 57]:

$$Z_{CPE} = \left( {\frac{1}{{Q\left( {i\omega } \right)^{n} }}} \right)$$
(3)
Fig. 4
figure 4

RC employed to fit EIS data

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Table 3 EIS variables for (CR/S) in the 1-M HCl medium and with BOPP
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In the aforementioned formula, Q symbolizes the magnitude of the CPE, i symbolizes the imaginary element, ω symbolizes the angular frequency, and n symbolizes the deviation factor.

As a result, the Cdl is computed using the equation that comes next [57]:

$$C_{dl} = \left( {QR_{p}^{1 - n} } \right)^{1/n} = Q\left( {\omega_{\max } } \right)^{n - 1}$$
(4)

The findings presented in Table 3 demonstrate that the Rp values in the presence of BOPP are higher than those in 1-M HCl medium. The rise in Rp values is due to the development of an insulating protective layer at the (CR/S)/medium interface. With increasing BOPP concentration, the Rp value rises, while the CPE (Q) falls, indicating an augmentation in the electrical double-layer thickness [58]. The double-layer forming among the charged (CR/S) surface and the medium can be considered as an electrical capacitor. The adsorption of the BOPP reduces the (CR/S)/medium electrical capacity by displacing the water molecules and other ions that were initially adsorbed on the surface. The decreasing value of Cdl implies that the BOPP substances operate via adsorption on the steel/medium interface, showing a drop in the local dielectric constant and/or an increase in the thickness of the electrical double layer [59]. The value of n is proportional to the roughness of the surface. Surface roughness often rises as the value of n decreases [60]. The observation reveals that the values on n when BOPP is present are greater (0.880 for BOPP) than when it is not present, indicating that the adsorption of BOPP onto the (CR/S) surface causes an improvement in surface smoothness when BOPP is present. Consequently, when BOPP concentration rose, the ηi (%) values also rose, peaking at 89.9% for 0.001-M BOPP. The results of this study validated that the addition of BOPP to a 1-M HCl medium effectively prevented steel corrosion. Last but not least, it is noteworthy to see that the ηi (%) values collected using the PDP (Table 1) and the EIS measurements (Table 3) are parallel and complementary.

3.3 Adsorption Isotherms

Organic substances have been demonstrated to suppress metallic corrosion by adsorbing to the metal’s surface and acting as a replacement for the water molecules that would otherwise adsorb on the metal surface, as explained in reference [61]. Several attempts have been made to fit θ and inhibitor concentration (C) values to adsorption isotherms, including Langmuir, Temkin, Frumkin, Freundlich, Flurry Hugging, and El-Awady, as displayed in Fig. 5. The correlation coefficient (R2) and slope values of the straight lines depicted in Fig. 5 are relatively close to unity for Freundlich and Flurry Hugging isotherms, while for Langmuir, they are equal to unity. Consequently, the Langmuir adsorption isotherm shows the best potential adsorption model of the BOPP molecules on the (CR/S) surface in 1-M HCl, which can be formulated as follows [63]:

$$\frac{C}{\theta } = \frac{1}{K} + C$$
(5)
Fig. 5
figure 5

Isotherms plot for (CR/S) corrosion in 1-M HCl medium with BOPP

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In the preceding formula, the terms θ and K denote the degree of surface coverage (θ = ηi/100) and the equilibrium constant.

However, the subsequent formula employed to connect K to standard free energy \(\left( {\Delta G_{{{\text{ads}}}} } \right)\) is as follows [61]:

$$\Delta G_{{{\text{ads}}}} = - RT \, \ln \left( {55.5{\text{ K}}} \right)$$
(6)

where the abbreviations for the gas constant, absolute temperature, and water content, respectively, are R, T, and 55.5.

As indicated in Table 4, the K value was computed by deploying the intercepts in Fig. 5. Elevated K value for BOPP provides more effective adsorption and, therefore, better anti-corrosion performance [62]. Additionally, the \(\Delta G_{{{\text{ads}}}}^{{}}\) is negative, implying a spontaneous adsorption process and considerable interaction among the pyridazone analog and the (CR/S) surface. \(\Delta G_{{{\text{ads}}}}^{{}}\) is a widely accepted way of assessing adsorption on solid surfaces. Physisorption (intermolecular forces among inhibitor and Fe atoms on the steel surface) can be identified by values under − 20 kJ/mol, whereas chemisorption (the development of coordination bonds between the inhibitor molecules and Fe atoms on the steel surface) is denoted by values above − 40 kJ/mol [62]. QBPA has a \(\Delta G_{{{\text{ads}}}}^{{}}\) greater than − 40 kJ/mol, suggesting that it is predominantly adsorbed on the (CR/S) surface by chemisorption.

Table 4 The computed \(\Delta G_{{{\text{ads}}}}\) and K of BOPP on the (CR/S) surface
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3.4 Influence of Temperature

A variation in temperature (T) might hasten the corrosion of (CR/S) in acid medium, affecting the inhibitory potential of BOPP. As a result, the PDP technique was applied to evaluate the performance of BOPP in reducing (CR/S) corrosion in HCl medium at temperatures ranging from 303 to 333 K, as pictured in Fig. 6, and Table 5 summarizes the pertinent metrics that were extracted. It is noticeable that the icorr readings have augmented for both mediums (inhibited and uninhibited), whereas the augmentation in the presence of BOPP in the medium is significantly lower than without it, suggesting that the BOPP has severely inhibited the corrosion reaction of (CR/S). At more raised temperatures, ηp (%) falls since the duration period between BOPP’s adsorption and desorption over the (CR/S) surface shortens as a consequence of the long period that the metal surface is exposed to the acidic medium [63]. The faster rate of hydrogen gas evolution at the cathode is another factor contributing to the drop in ηp (%) at high temperatures. The comparatively tiny performance variance at temperature ranges of 11% demonstrates that the BOPP is moderately temperature dependent.

Fig. 6
figure 6

PDP charts for (CR/S) in the 1-M HCl medium and with BOPP at multiple temperatures

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Table 5 PDP variables for (CR/S) in the 1-M HCl medium and with BOPP at multiple temperatures
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Using the Arrhenius and associated alternate-form equations, which are outlined below, we could examine how temperature affects corrosion rate, activation energy (\({E}_{a}\)), activation enthalpy (\(\Delta {H}_{a}\)), and activation entropy (\(\Delta {S}_{a}\)) [64, 65]:

$$\ln \,i_{{{\text{corr}}}} = \frac{{ - E_{a} }}{R} \times \left( \frac{1}{T} \right) + \ln \,A$$
(7)
$$\ln \left( {\frac{{i_{{{\text{corr}}}} }}{T}} \right) = \left( {\ln \left( \frac{R}{Nh} \right) + \frac{{\Delta S_{a} }}{R}} \right) - \left( {\frac{{\Delta H_{a} }}{R} \times \frac{1}{T}} \right)$$
(8)

The terms, \(A\) stands for the Arrhenius factor, \(N\) stands for the Avogadro number, and \(h\) stands for the Planck’s constant.

Charting ln icorr vs. 1000/Τ results in a line that is straight and whose slope is equivalent to \(-\frac{{E}_{a}}{R}\), as noticed in Fig. 7a and mentioned in Table 6. Table 6 makes it evident that the free acid’s \({E}_{a}\) (35.4 kJ/mol) is lower than that of the BOPP molecules (71.3 kJ/mol), indicating that the adsorption happens to be physical and revealing that there is more energy barrier to the corrosion process when BOPP is present. The rise in \({E}_{a}\) in the presence of BOPP is interpreted as first forming a greater energy barrier for the process of corrosion, implying that the adsorbed layer on the (CR/S) interface prevents the charge/mass transfer reaction from happening on the surface, and secondly, a drop-in rate of (CR/S) dissolution in the presence of BOPP due to the development of a metal–inhibitor complex [66].

Fig. 7
figure 7

Arrhenius (a) and alternative Arrhenius (b) plots for (CR/S) in the 1-M HCl medium and with BOPP at multiple temperatures

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Table 6 \(\Delta {S}_{\text{a}}\), \(\Delta {H}_{\text{a}}\), and \({E}_{\text{a}}\) for (CR/S) in 1-M HCl medium and with BOPP at multiple temperatures
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Charting ln icorr/T vs.1000/Τ results in a line that is straight and whose slope is equivalent to \(-\frac{{\Delta H}_{\text{a}}}{R}\) and its intercept is equivalent to \(\text{ln}\left(\frac{R}{Nh}\right)+\left(-\frac{{\Delta S}_{\text{a}}}{R}\right)\) as noticed in Fig. 7b and mentioned in Table 6.

The fact that \(\Delta {H}_{a}\) is positive means the (CR/S) dissolving process is endothermic. However, the presence of BOPP raised the value of \(\Delta {H}_{a}\), suggesting that (CR/S) dissolving is difficult owing to BOPP adsorption at the steel–medium interface [67]. The medium containing BOPP had a higher \(\Delta {S}_{a}\) value than the medium without it. This is due to the competing adsorption of BOPP molecules and water molecules on the steel surface, which causes a rise in chaos [68].

3.5 MEB and EDX Assessments

Figure 8 depicts the surface shape changes of (CR/S) in acidic medium containing and not containing the BOPP. A close examination of Fig. 8a revealed that the surface of polished steel had some scratches generated by mechanical polishing. The contact of the substrate with the acid medium resulted in extensive degradation of the (CR/S) and the formation of several corrosion remnants on the surface (Fig. 8b), which were artifacts of accelerated corrosion. On the other hand, the presence of BOPP resulted in a considerable improvement in the surface morphology of the substrate, as illustrated in Fig. 8c, owing to the BOPP adsorption that shields the surface from acid corrosion.

Fig. 8
figure 8

SEM & EDX micrographs of (CR/S) surface: subsequent to polishing (a), BOPP-free (b), and BOPP-containing medium (c)

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The left side of Fig. 8 portrays EDX spectra for (CR/S) subsequently a 24-h exposure to the acid medium containing BOPP and without it. The characteristic peaks of (CR/S) components like Cu, Mn, Ni, and Fe can be viewed in Fig. 8a. The EDX spectrum for the substrate after soaking in the acidic medium (Fig. 8b) provides signals for the chlorine and oxygen which are components of 1-M HCl, in addition to the iron oxide signals, demonstrating that corrosion products amass on the steel surface. When introducing BOPP (Fig. 8c), the associated peaks for the oxide of corrosion products were significantly reduced, and those for chlorine completely disappeared. This demonstrates the BOPP’s capacity to reduce (CR/S) corrosion.

Table 7 indicates that the percentage atomic content of chlorine ions (Cl−) in the absence of BOPP is 46.30%, while it was zero in its presence. The absence of Cl− ions in the presence of BOPP suggests that this latter one can be deposited on the (CR/S) surface, providing protection against attack by Cl− ions. The percentage atomic content of iron (Fe) for (CR/S) immersed in 1 M HCl is 36.6%. However, when BOPP is dipped in 10−3 M of BOPP, it increases to 89.9%. This increase suggests that the presence of BOPP hinders the dissolution reaction of (CR/S) in 1-M HCl. Additionally, the percentage atomic content of oxygen (O) significantly decreases from 50.7 to 3.7%. These findings confirm the presence and formation of a protective film of BOPP on the (CR/S) surface in 1-M HCl.

Table 7 The percentage atomic and weight contents of elements of the (CR/S) surface in the absence and presence of BOPP obtained from EDX spectra
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3.6 Contact Angle Assessments

Contact angle measurements may assess the existence of a protective layer on the steel surface as well as its physical characteristics. The obtained findings are displayed in Fig. 9a and b, where we can observe that the substrate submerged in the acidic medium had the lowest contact angle (25.35°). This might be because of the hydrophilic character of the surface, which makes the water droplet fall easily on the surface. But in return, the presence of BOPP caused a considerable shift in the contact angle (40.17°), demonstrating the existence of the hydrophobic coating on the surface.

Fig. 9
figure 9

The contact angle of (CR/S) surfaces after soaking in both BOPP-free (a) and BOPP-containing medium (b)

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3.7 UV–Visible Assessments

Figure 10 illustrates the UV–Vis spectra of BOPP solubilized in 1-M HCl prior to and subsequent to 72 h of soaking in (CR/S). Prior to (CR/S) soak, the absorption spectrum of BOPP reveals bands at 213 nm, 255 nm, and 380 nm, which correspond to n–π⁎, π–π⁎, and intramolecular charge transfers, respectively. Subsequent to (CR/S) soaking, there were visible variations in the absorption spectrum of BOPP and the absorbance of the bands at 255 and 380 nm augmented, whereas the band at 213 nm vanished. The development of the Fe-metal-BOPP complex is responsible for the changes in the spectra of the mediums prior to subsequent steel soaks [68].

Fig. 10
figure 10

UV–Visible spectra of BOPP solubilized in acidic medium prior to (CR/S) soaking (a) and subsequent to (CR/S) soaking (b)

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3.8 Molecular Simulations

In the presence of a corrosive environment, particularly under acidic conditions, an organic inhibitor has the capability to uptake one or more protons, influencing its behavior in such media. The heteroatoms within this inhibitor play a crucial role in its reactivity, leading to the formation of a more electronegative (attractive) cationic state. The Marvinsketch software can theoretically be employed to precisely identify the attack site(s) capable of accepting the more mobile H+ protons from an acidic medium. Figure 11 illustrates the variation in the percentage of protonation for each form relative to pH. As depicted in this figure, three protonation forms exist, with the neutral form (A) representing the chemical reactivity of BOPP.

Fig. 11
figure 11

The electronic distribution within the BOPP structure

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Figure 12 shows the optimized structure of the molecule and their protonated forms, the distribution of the HOMO and LUMO orbitals, and the molecular electrostatic potential (MEP). The HOMO electron for the form A of the molecule cloud is distributed over the molecule except for the benzyl ring bearing the fluorine atom and the benzyl ring linked to the C50 atom. In contrast, in the protonated forms of the molecules (B and C), the distribution of the HOMO electron is inversely distributed compared to form A. The LUMO electron for neutral and protonated forms of the molecule cloud is also distributed over the molecule except for the benzyl ring bearing the fluorine atom and the benzyl ring linked to the C50 atom. The molecular electrostatic potential (MEP) awards minutiae on a substance’s reactive sites. On the blue MEP zones, positive potential values reveal lowly electron density areas that are more appropriate for nucleophilic attack. On the other hand, since the red MEP zones contain negative potential values, they indicate regions that are more suited for electrophilic attack, while the green MEP zones exhibit a neutral potential. Established on MEP analysis, the BOPP compound has a red zone with negative potentials focused on the oxygen atoms O19 and O24 of ketone (carbonyl) groups in forms A and C, implying that they are the two sites most vulnerable to electrophilic attack. The blue area reveals that the hydrogen atoms in the benzyl rings of the molecule are vulnerable to nucleophilic attack because it is situated close to them. In contrast, the fluorine atom is close to the center of the green zone for the neutral form, which indicates a neutral potential.

Fig. 12
figure 12

a The optimized structure at the B3LYP/6–31 + G(d,p) level of DFT calculations in aqueous phase, b the contour plots of FMO, and c the MEP maps for the investigated compound (BOPP) and their protonated forms

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Table 8 summarizes the quantum parameters corresponding to the BOPP molecule and their protonated forms. The neutral form A exhibits the lowest energy level among the three forms, indicating its superior stability compared to the protonated forms B and C. As a result, form A is considered the most stable configuration due to its lower energy state. It is noted that this molecule exhibits a rather high gap energy value (3.525 eV) which indicates that it is stable, hard, and has low chemical reactivity. This stability is also confirmed by the negative value of the chemical potential Pi (− 4.738 eV) and the value of the hardness η (1.762 eV) which affirms the resistance of the electron cloud to deformation. The high value of electronegativity χ (4.738 eV) gives this molecule the property of behaving as a Lewis acid and also shows its attractive effect. In addition, it is shown that this molecule behaves as a strong electrophile since the high value of its electrophilicity index ω (6.369 eV). The chemical softness σ which describes the ability of this molecule to accept electrons has a value of 0.567 eV.

Table 8 Quantum parameters of the BOPP in gas phase at B3LYP/6–31 + G(d,p) level of DFT calculations
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The MD approach was used to get a further understanding of the adsorption of the BOPP molecule (neutral and protonated form) on the (CR/S) surface (substrate) in an HCl environment. The most stable side- and top-view adsorption configurations of neutral (BOPP) and protonated (BOPPH+) inhibitor forms on a Fe surface are shown in Fig. 13 and their associated energies [energy interaction (Einteraction) and energy binding (Ebinding)] are listed in Table 9. As shown in these configurations, both BOPP and BOPPH+ structures are adsorbed near and parallel above the iron surface (Fig. 13). These adsorption topologies give higher coverage of the iron surface due to the number of active sites (heteroatoms/C=C bonds) in neutral (BOPP) and protonated (BOPPH+) inhibitor forms. It is important to note that the higher negative value of Einteraction and a higher positive value of Ebinding indicate spontaneity and a robust interaction process between the inhibitor molecule and the metal surface, as well as better inhibition effectiveness [69,70,71]. The MD simulation results show that the Einteraction values for BOPP and BOPPH+ with the Fe surface are – 9209 kcal/mol and – 9217 kcal/mol, respectively. Furthermore, Ebinding = 9209 kcal/mol for BOPP and Ebinding = 9217 kcal/mol for BOPPH+. Higher negative interaction and higher positive binding energies suggest that both neutral and protonated forms of our inhibitor act on the iron metallic surface in a sustained and spontaneous manner, with higher inhibition efficiency. These results are compatible with DFT calculations and experimental results.

Fig. 13
figure 13

The final snapshots of BOPP and BOPPH + over the Fe (110) surface obtained from MD simulations

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Table 9 Calculated values of Einteraction and Ebinding (all in kcal/ mol) obtained from MD simulations of neutral and protonated BOPP compound onto the Fe (1 1 0)
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One way to guarantee that the elements contain the least amount of energy feasible is to monitor any temperature changes that occur during the MD simulation run. For an equilibrium contact with a certain temperature requirement, the temperature distribution generated by MD simulation should be restricted to 5 to 15% [72]. The temperature curves that have been obtained by MD at 303 K for the BOPP/Fe (110) and BOPPH+/Fe (110) systems are displayed in (Fig. 14). The MD simulation appears to have been successful based on the slight temperature changes that occurred, indicating that all systems have reached their equilibrium states.

Fig. 14
figure 14

Temperature equilibrium curves for BOPP/BOPPH+ on the Fe (110) obtained from MD simulations

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To investigate the affinity of both neutral and protonated (BOPP /BOPPH+) forms of our inhibitor toward the iron adsorbent further, radial distribution function analysis (RDF) closely examines the type of bonds produced at the inhibitor/Fe–substrate interface [73]. Using MD simulation trajectories, RDF was analyzed for both inhibitory (neutral and protonated) forms. In general, the interactions between an inhibitor and iron atoms are significant and can be determined by comparing the first notable peaks in the RDF curves. If the peak appears at 1–3.5 Å, it indicates a short bond length, which corresponds to chemisorption, whereas peaks longer than 3.5 Å are connected with physical interactions [74]. Figure 15 depicts the RDF findings for the BOPP and BOPPH+ structures. The first notable peak for both inhibitor types is found at a distance less than 3.5, especially 1.03 Å for BOPP and 1.01 Å for BOPPH+.

Fig. 15
figure 15

The RDFs of BOPP and BOPPH+ over the Fe (110) surface obtained from MD simulations

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As shown in Fig. 15, the initial peak for both structures is less than 3.55 Å, and subsequent peaks outside of 3.5 Å are attributed to physical interactions. These are the most important interactions of the simulated neutral and protonated forms of the title molecule on the first layer of Fe atoms, demonstrating that the BOPP and BOPPH+ forms of our inhibitor do indeed inhibit the disintegration of the tested metal.

4 Conclusion

Spectroscopic, electrochemical, and theoretical assessments were employed to scrutinize the anti-corrosion ability of pyridazinone (BOPP) against (CR/S) corrosion in an acidic medium. We might outline the following conclusions:

  • The pyridazinone displays high inhibitory efficacy for the corrosion of (CR/S) in 1-M HCl medium. The inhibitory performance rises with a rise in BOPP amount and marginally reduces with temperature. The greatest inhibitory effectiveness was recorded at about 95.7% for 0.001 M at 303K.

  • BOPP functions as a mixed-type inhibitor, suppressing both anodic and cathodic corrosion.

  • UV–Visible tests demonstrated that chemical interactions between BOPP and iron occur in (CR/S).

  • BOPP could chemisorb on the (CR/S) surface following the Langmuir isotherm model.

  • The measured increase in contact angle in hydrophobicity on the surface (CR/S) supported the formation of a protective layer, which was confirmed by MEB and EDX.

  • Based on DFT modeling, BOPP is a good potential candidate for inhibiting corrosion on Fe metal surfaces.

  • Through molecular dynamics simulations, the chemical inhibitor BOPP was shown to generate a corrosion-resistant interfacial layer on the metal surface. This finding validates our previous investigations into the inhibitory effectiveness of our corrosion inhibitor.

  • In conclusion, there could be an interesting set of future research such as conducting long-term corrosion tests to assess the tolerance of BOPP and its continued effectiveness over long periods of exposure. Also, synergistic effects can be studied when combined with other corrosion inhibition strategies, such as coatings and surface modifications. In addition, its toxicity and environmental impact must be assessed to ensure safe handling and disposal. Moreover, the possibility of its practical production can be explored and experimental or industrial experiments conducted to assess its feasibility before it is widely marketed.