Zinc oxide nanoparticles made with Bauhinia purpurea leaf extract showed high reported corrosion inhibition in a laboratory comparison of two synthesis routes. At 100 parts per million (ppm), the sol-gel condition had a reported inhibition efficiency of 97.7% in potentiodynamic polarization (PDP), compared with 94.1% for co-precipitation. PDP is the electrochemical test used here to report corrosion current density and inhibition efficiency. The route ranking changed in electrochemical impedance spectroscopy (EIS), a separate electrochemical readout: co-precipitation was reported at 99% inhibition and sol-gel at 98%.
The PDP current-density readings matched that ordering: 50 µA cm−2 for co-precipitation and 19.4 µA cm−2 for sol-gel at 100 ppm. Current density is the corrosion-related electrical signal reported for the coupon, so the lower sol-gel value was consistent with its higher PDP inhibition percentage. The close but opposing results make the route comparison more nuanced than a simple overall ranking.
A narrow laboratory comparison
The experiment used cylindrical carbon-steel coupons with a reported surface area of 1 cm² and a diameter of 10 mm. The researchers compared zinc oxide nanoparticles made by co-precipitation and sol-gel synthesis. The formulations were tested in 1 M hydrochloric acid at 50, 75 and 100 ppm. Those details define the setting in which the inhibition figures were obtained.
The electrochemical work used a three-electrode cell. The protocol recorded open-circuit potential before PDP and performed EIS at open-circuit potential, with repeated EIS experiments averaged. Alongside those measurements, the reported characterization included Fourier-transform infrared spectroscopy (FTIR), ultraviolet-visible spectroscopy (UV-vis), scanning electron microscopy and energy-dispersive spectroscopy (SEM/EDS), and X-ray photoelectron spectroscopy (XPS). In ordinary terms, the electrochemical tests supplied the corrosion-inhibition readings, while the other methods examined the nanoparticles and surfaces.
Dissolved iron fell in the inhibitor tests
A separate chemical measurement pointed in the same direction. Atomic absorption spectroscopy (AAS) reported 3.45 mg L−1 of dissolved iron in the blank condition. At 100 ppm, the reported dissolved-iron concentration was 0.83 mg L−1 for co-precipitation and 0.73 mg L−1 for sol-gel. Both inhibitor conditions were therefore associated with less iron in solution than the blank, with sol-gel showing the lower of the two treated values.
What the measurements can support
The authors interpret the electrochemical, iron-dissolution and surface findings as consistent with adsorption of leaf phytochemicals and zinc oxide nanoparticles onto the steel. In that interpretation, the adsorbed material forms a protective organic-inorganic film. They classify the inhibitor as mixed-type and report Langmuir adsorption behavior, based on the way the data fit that model. These are the authors' explanations of the combined measurements; the reported tests do not by themselves establish a definitive molecular mechanism or a universal route winner.
The reach of the result is narrower than the percentages may suggest. The evidence is limited to laboratory carbon-steel coupon tests in 1 M HCl, using the three reported nanoparticle concentrations. It does not show how stable the proposed film would be during long-term practical service, whether the route ranking would persist with other steel grades or acid conditions, or whether the material is environmentally safe, biodegradable, non-toxic or cheaper. No human, animal or field-structure evidence is part of this study.
For materials researchers, the result is best read as a laboratory proof of concept: under the tested setup, the leaf-mediated ZnO nanoparticles were associated with high electrochemical inhibition readings and lower dissolved-iron readings than the blank. Broader testing would need to check other steels, acid conditions and longer exposures, as well as whether the route-dependent pattern persists. Until then, co-precipitation and sol-gel both show strong reported performance under the specified conditions, but the two electrochemical tests do not produce a definitive overall route winner.
Paper data and sources
Original title: Corrosion inhibition evaluation of Bauhinia purpurea extract mediated ZnO nanoparticles for carbon steel in acidic environment.
Authors: O Swathy, S Shanmuga Priya, Meghana K Navada, Lavanya Mulky
Journal/Repository: Discover nano
Status: Peer-reviewed
First online: 2026-08-21
DOI: 10.1186/s11671-026-04826-w
Original paper · Full text