article · Scientific Reports
Verbena officinalis leaf extract was tested as a corrosion inhibitor for carbon steel exposed to a 0.5 M sulphuric acid solution. Evaluation using mass loss, potentiodynamic polarisation, electrical impedance spectroscopy, atomic force microscopy, and X-ray photoelectron spectroscopy demonstrated the extract's protective capabilities. Adding the extract increased the activation energy of the corrosion process, reaching a peak of 49.9 kJ mol-1 at a concentration of 1000 mg L-1. Negative free energy values indicated that the extract molecules spontaneously form a stable adsorbed layer on the metal surface, conforming to the Langmuir adsorption isotherm model. Electrical impedance spectroscopy revealed a maximum inhibition efficiency of 91.1% at a concentration of 1000 ppm. Furthermore, polarisation data confirmed that the plant extract functions as a mixed-type inhibitor, simultaneously suppressing anodic and cathodic corrosion reactions.
Carbon steel is widely used across infrastructure and manufacturing but degrades rapidly when exposed to aggressive acidic conditions. Plant-derived substances offer a potential route to replacing toxic synthetic chemical inhibitors with plant-based alternatives. Demonstrating that Verbena officinalis leaf extract can significantly reduce steel degradation in sulphuric acid provides experimental support for developing cleaner protective treatments in industrial acid environments.
The work points towards potential applications in steel pickling, acid cleaning, and industrial acid handling systems where carbon steel requires corrosion protection. Likely end users include industrial maintenance engineers and protective chemical formulators. However, this remains early-stage laboratory research based on electrochemical and surface characterisation, with no real-world pilot testing or scale-up processing evaluated in the abstract.
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Abstract In the present work, Verbena Officinalis (VO) leaf extract was used as potential corrosion inhibitor for the corrosion of carbon steel (CS) in 0.5 M H 2 SO 4 medium. Further, the corrosion inhibiting nature of VO leaf extract towards the CS was evaluated using mass loss (ML), potentiodynamic polarization (PDP), electrical impedance spectroscopy (EIS) and surface morphological analyses using atomic force microscope (AFM) and X-ray photoelectron spectroscopy (XPS) techniques. Calculation of activation energy $$\left( {{\text{E}}_{{\text{a}}}^{*} } \right)$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mfenced> <mml:mmultiscripts> <mml:mtext>E</mml:mtext> <mml:mrow> <mml:mtext>a</mml:mtext> </mml:mrow> <mml:mrow> <mml:mrow/> <mml:mo>∗</mml:mo> </mml:mrow> </mml:mmultiscripts> </mml:mfenced> </mml:math> using Arrhenius equation shows the increase in activation energy when adding the VO leaf extract in 0.5 M H 2 SO 4 medium and the maximum activation energy ( $${\text{E}}_{{\text{a}}}^{*}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mtext>E</mml:mtext> <mml:mrow> <mml:mtext>a</mml:mtext> </mml:mrow> <mml:mrow> <mml:mrow/> <mml:mo>∗</mml:mo> </mml:mrow> </mml:mmultiscripts> </mml:math> = 49.9 kJ mol −1 ) was observed for 1000 mg L −1 VO leaf extract in acid medium. The negative free energy values suggested the spontaneous and the stability of the adsorbed layer of VO leaf extract on the CS surface. Using EIS measurements, high percent inhibitory effectiveness of 91.1% for 1000 ppm solutions was achieved. With an increase in VO leaf extract dose, the double layer capacitance (C dl ) values fall while the values of charge transfer (R ct ) increase. This showed that a protective layer of VO leaf extract on CS surface was formed. The polarization curves showed that the VO leaf extract acts as a mixed-type inhibitor. It is discovered that the adsorption of VO leaf extract molecules adhering to the CS surface followed the Langmuir isotherm. The anti-corrosion action of VO leaf extract is fully demonstrated by some surface techniques.
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DOI: 10.1038/s41598-024-65266-z
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