Berberine as a natural source inhibitor for mild steel in 1 M H2SO4

Berberine was abstracted from coptis chinensis and its inhibition efficiency on corrosion of mild steel in 1 M H₂SO₄ was investigated through weight loss experiment, electrochemical techniques and scanning electronic microscope (SEM) with energy disperse spectrometer (EDS). The weight loss results showed that berberine is an excellent corrosion inhibitor for mild steel immersed in 1 M H₂SO₄. Potentiodynamic curves suggested that berberine suppressed both cathodic and anodic processes for its concentrations higher than 1.0 × 10⁻⁴ M and mainly cathodic reaction was suppressed for lower concentrations. The Nyquist diagrams of impedance for mild steel in 1 M H₂SO₄ containing berberine with different concentrations showed one capacitive loop, and the polarization resistance increased with the inhibitor concentration rising. A good fit to Flory-Huggins isotherm was obtained between surface coverage degree and inhibitor concentration. The surface morphology and EDS analysis for mild steel specimens in sulfuric acid in the absence and presence of the inhibitor also proved the results obtained by the weight loss and electrochemical experiments. The correlation of inhibition effect and molecular structure of berberine was then discussed by quantum chemistry study.