Utilizing birch leaf extract in pickling liquid as a sustainable source of corrosion inhibitor for pipeline steel

This study set out to determine the effectiveness of birch leaves extract (BLE) as a corrosion inhibitor against X52 pipeline steel in the pickling solution. Chemical and electrochemical techniques, as well as scanning electron microscope (SEM), Fourier-transform infrared (FT-IR), and adsorption isotherms were used in the research. Various triterpenoids, including betulin, betulinic acid, oleanolic acid, sitosterol, and kaempferol, are unquestionably involved in the corrosion inhibition mechanism, according to the high-performance-liquid-chromatography (HPLC) analysis. The 95% efficiency of the produced BLE extract (at optimum concentration 400 mg L−1) significantly reduced the corrosion rate of X52 pipeline steel in the pickling solution. The adsorption of BLE extract molecules on the X52-steel surface was demonstrated by SEM and FT-IR analysis. The adsorption activity follows the Langmuir adsorption theory.

Birch leaves powder was delivered by an Egyptian herbal family group. For 5 h, 25 g of birch leaves powder was refluxed in 100 ml of the stock mixture (70% C 2 H 5 OH + 10% ethyl acetate + 20% distilled H 2 O) at 358 K. Following that, the refluxed mixture was filtered using a separator funnel. The mixture was then concentrated in a rotary vacuum evaporator and dried in a pressure dry oven at 333 K for 24 h. Lastly, the precipitate was left to dry in a desiccator. Liquid chromatography (shimadzu co. japan) and FTIR (Perkinelme co.) were used to determine the major components of BLE extract. The BLE extract is completely soluble in pickling solution.
Corrosion rate tests. Both chemical and electrochemistry approaches were used to assess the corrosion rates of the X52-steel in testing solutions.
Weight loss assessments were taken by weighing the dry X52-steel (dimension 3.0 × 3.0 × 0.1 cm) on an electronic balance and immersing it in testing solutions for 5.0 h. The weight loss was estimated by subtracting the weight of the sample before and upon immersion in the investigated solutions.
The electrochemical investigations were conducted using a Gamry 3000 electrochemical station outfitted with a standard three-electrode setup. The working electrode was an X52-steel piece (electrode area = 0.445 cm −2 ), the counter electrode was a platinum plate, and the reference electrode was a saturated calomel electrode (SCE). The tests were conducted out in a temperature-controlled water bathtub. On the E OCP , electrochemical impedance spectroscopy (EIS) was used. A 10 mV peak-to-peak sinusoidal wave in the frequency region of 100,000-0.01 Hz was used. Gamry's software was used to fit and analyze the EIS data. Surface characterization. SEM (ZEISS/EVO) equipped with an EDX analyzer was used to examine the morphologies of X52-steel surfaces in pickling solutions.
The FT-IR spectrum of BLE extract is presented in Fig. 3. A broad band at 3375 cm −1 assigned to hydrogenbonded O-H stretching, the bands at 1684, 1528, 1453, 1267, 1250, 1170, 730, and 686 cm −1 are due to C=O, C=C, C-C, C-H in-plane bending, C-H out plane bending, C-O-C stretch, aromatic bending zone, and ring deformation out of the plane, respectively.

Weight loss study.
Weight loss studies were done to examine the influence of BLE extract on X52-steel corrosion in pickling solution (1.0 M HCl). Different doses of the BLE extract were injected into the experimental solution for an estimation of the inhibition activity, and the test was conducted at temperatures of 298 K. Table 1 displays the results. The next formulas are used to compute the experiment variables of corrosion rate (v), inhibition efficiency (η W %), and surface coverage (θ) [20][21][22] .   www.nature.com/scientificreports/ where W = weight loss, S = total surface area of X52-steel, t = immersion time, v 0 and v are the corrosion rate without and with BLE extract, respectively. According to Table 1, raising the concentration of BLE extract decreases the corrosion rate, increases the inhibitor effectiveness, and increases the coverage, indicating that an increase in the BLE extract concentration leads to a higher degree of adsorption 23 . The inhibitor power of BLE extract increases to 94.4% when the concentration approaches 300 mg L −1 , confirming that BLE extract is an efficient inhibitor of X52-steel corrosion in the pickling solution. When the concentration of BLE extract approaches 400 mg L −1 , there is no appreciable decrease in corrosion rate.
The open circuit potential (OCP) vs. time for different BLE extract concentrations is depicted in Fig. 4. They have been compared to a blank curve produced under comparable environments. The OCP is clearly balanced after 30 min, as shown in Fig. 4, and the process also seems to have achieved steady state. The change of the curve towards the negative potential area caused by the high concentrations of BLE extract (100 mg L −1 ) in the solution showed that BLE extract has an impact on cathodic reaction.
The polarization curves for X52-steel corrosion in pickling solution (1.0 M HCl) with and without varying concentrations of BLE extract at 298 K and a scan rate of 0.125 mV s −1 are seen in Fig. 5. Table 2 shows the electrochemical variables of corrosion potential (E corr ), corrosion current density (j corr ), Tafel slopes (βa, β c ), assessed using Tafel extrapolation, as well as the inhibition efficiency (η j %) calculation by the following formula 24 .  www.nature.com/scientificreports/ where the j corr(0) is the corrosion current density without BLE extract. Table 2 clearly shows that as the content of BLE extract grew, the inhibition efficiency (η j %) improved while the value of corrosion current density (j corr ) reduced rapidly, particularly at higher concentrations. Table 2 illustrates that the change values of E corr versus blank solution were less than 85 mV, revealing that the BLE extract becomes a mixed-type inhibitor 25,26 . The fact that the injection of BLE extract has no strong influence on the Tafel slopes (a, c) implies that the BLE extract's inhibitor has no direct impact on the corrosion mechanism 27,28 .
Once the BLE extract concentration was raised to 400 mg L −1 , the η j % value attained 95.1%, indicating that the BLE extract has a strong anti-corrosion ability.

EIS study.
To verify the polarization results, impedance tests for X52-steel corrosion in pickling solution (1.0 M HCl) with and without BLE extract were investigated (see Fig. 6). The Nyquist plot (Fig. 6a) reveals a depressing capacitive circle, and as the BLE extract concentration increases, the size of the capacitive circle expands, implying that the BLE extract significantly restricts charge transfer between the pickling solution and X52-steel 29 . Furthermore, the fact that the pattern of the impedance spectra does not vary with the presence of BLE extract implies that the addition of the BLE extract does not affect the corrosion mechanism [30][31][32] . Figure 6b depicts phase angle plots for X52-steel corrosion in pickling solution (1.0 M HCl) with various concentrations of BLE extract. The phase angle plot demonstrates a growing trend as the concentration of BLE extract increases. The results revealed that increasing the BLE extract content up to 400 mg L −1 strengthened the protective barrier qualities of the BLE extract layer 33 . The appearance of a high and low-frequency plateau can be seen in the Bodemodulus graphs (Fig. 6c). The radii of the capacitive semicircles and the values of the low-frequency plateau are both consistent.
The equivalent circuit type with and without BLE extract can be seen in Fig. 7 by fitting the results were significant, which includes the solution resistance (R S ), and polarization resistance (R p ). Furthermore, CPE is a constant phase that represents the double layer capacitance (C dl ) at the contact of the X52-steel and pickling solution. To produce a more precise fit of the experimental given data, CPE was incorporated 34 . Equation (7) provided estimates for the C dl values.  where the R p(0) is the polarization resistance without BLE extract. Table 3 displays that as the concentration of BLE extract rose, the values of R p increased and C dl decreased, implying that the production of a protective film on the X52-steel surface can lead to the creation of a more uniform protective layer to delay the transmission of corrosive species. Furthermore, when compared to the blank experiment, the value of CPE with various BLE extract concentrations drops dramatically, which is believed to be due to the BLE extract molecules going to replace the water molecules adsorbed on the X52-steel surface, indicating a thicker layer between X52-steel and solution 35 .
The equivalent circuit fitted is valid based on the obtained minimum goodness of fit (chi-square = χ 2 ) value. Table 3 reveals that the values of n (surface heterogeneity) rise in comparison to the control solution, which can be attributed to the adsorbed BLE extract molecules' ability to form more homogeneous surface species.   Adsorption isotherms. To establish relevant insights on the interaction of BLE extract and X52-steel surfaces, adsorption isotherms are used. Based on the adsorption concept, the replacement of BLE extract molecules BLE (sol) for water molecules occurs during the adsorption of BLE extract on X52-steel surfaces 36 : As a result, the data collected from the weight loss approach (see Table 1) was used to simulate four isotherms: Langmuir, Freundlich, Temkin, and Frumkin. The Langmuir isotherm, which may be described by Eq. (10), is the result that best fits.
where C inh = BLE extract concentration, K ads = constant equilibrium of adsorption.
The model using Langmuir isotherm is shown in Fig. 8. The adsorption activity follows the Langmuir adsorption theory, as indicated by the correlation coefficient (R 2 > 0.97), establishing a protecting mono-layer of BLE extract molecules on the X52-steel surface.
Indeed, merely using R 2 values to fit experimental data to the Langmuir adsorption is insufficient. This issue could be overcome by including a "dimensionless separation constant," (K L ) (see Eq. 11) 37 .
The adsorption operation is regarded favourable since the values of K L are less than one (see Table 4), and the experimental results satisfy the Langmuir adsorption isotherm.
The small K ads value (0.0124 L/mg) validates BLE extract's physical adsorption activity 38 . Because the molecular mass of BLE extract molecules is uncertain, it is not feasible to assess the free standard adsorption energy, as stated by numerous other studies 39 .  www.nature.com/scientificreports/ Surface morphologies. SEM was used to examine the surface morphology of X52-steel surfaces that had been immersed in the pickling solution for 5.0 h without and with (400 mg L −1 ) BLE extract. The pickling solution significantly damages the surface of the X52-steel surface, as seen in Fig. 9a: pores form on the X52-steel surface plate, which is accompanied by surface roughness. SEM images of specimens dipped in BLE extracttreated BLE extract, on the other hand, reveal a better uniform and clean texture (Fig. 9b). We analyzed the FT-IR spectra of the scratched layer generated on the X52-steel surface upon electrode soaking in pickling solution including 400 mg L −1 of BLE extract to reveal the adsorption procedure of BLE extract molecules on the X52-steel surface (Fig. 10). The adsorption of BLE extract molecules on the X52-steel surface is recognized by matching the FT-IR spectra in Figs. 3 and 10. The majority of the typical bands in Fig. 3 are found at comparable frequencies in Fig. 10, but with different signal strengths. This variance might be caused by the interaction of certain bioactive constituents of BLE extract molecules with the X52-steel, which results in the formation of a protective layer 40 .
Inhibition mechanism. The various data (chemical and electrochemical techniques, SEM, FT-IR, and adsorption isotherms) demonstrate that the adsorption of bioactive chemical constituents in the BLE extract is the principal cause of corrosion protection of the X52-steel in the pickling solution. The HPLC examination identified several triterpenoids (betulin, betulinic acid, oleanolic), sitosterol, and kaempferol that are likely participating in the corrosion inhibition process. These molecules have O-bearing groups which possess a high binding affinity for Fe on the surface of X52-steel. Besides, the binding of aromatic rings, these molecules are attached through physisorption at the steel surface via partial exchange of O electrons and the creation of double bonds 41 . The organic compound-adsorbed layer acts as a shield between the metallic surface and the pickling solution 42,43 . The majority of the chemicals contained in BLE extract in 1.0 M HCl are neutral or cationic compounds. X52-steel, on the other hand, is expected to be positively chargeable in 1.0 M HCl. As a result, at 1.0 M HCl, the X52-steel surface will initially bind anionic ions that may cover the surface; however, in a second stage,  www.nature.com/scientificreports/ the association of these anionic charges can assist in the adsorption of BLE cationic compounds. Because the organic molecules in BLE extract have greater dipole moments than water, they readily substitute water molecules at the surface of the X52-steel 44 . Table 5 compares the current study's findings to previous work done by other researchers and demonstrates that the BLE extract can be highly efficient anti-corrosive agents at lower dosages 14,15,39,45,46 .

Conclusions
In pickling solution, BLE extract indicates an effective inhibitor for corrosion of X52 pipeline steel. The presence of triterpenoids (betulin, betulinic acid, oleanolic), sitosterol, and kaempferol were identified by the chromatogram. The physisorption of the compounds included in the BLE extract is the cause of inhibition. These compounds protect the surface of X52-steel sheets, minimizing pickling solution corrosive damage. The EIS plots imply that the inhibitory effect improves with rising BLE dosage: the R ct increases significantly while the CPE declines dramatically. Importantly, the polarization findings show that the BLE extract acts as a mixed inhibitor. The adsorption activity of BLE extract is consistent with the Langmuir adsorption theory, as evidenced by SEM and FTIR spectra. This research opens up a new avenue for environmentally corrosion inhibitors (i.e. BLE extract).for pipe steel that must be cleaned using acid chemicals.

Data availability
The datasets used and/or analysed during the current study available from the corresponding author on reasonable request.