Insight into the Anticorrosion Properties of Stephania kwangsiensis Root Extracts as High-Efficiency Eco-Friendly Inhibitors for Carbon Steel in HCl Medium.

In the present study, Stephania kwangsiensis root extracts (SKRE) were first investigated as an innovative, environmentally friendly corrosion inhibitor for Q235 steel in 1 M HCl medium by combining experimental measurements and theoretical calculations. It is indicated that the SKRE inhibitor, which represses both cathodic and anodic reactions, serves as a mixed type inhibitor. The corrosion inhibition efficiency (IE) at 100 mg/L SKRE exceeds 99% when using electrochemical techniques, demonstrating a preeminent anticorrosion capability in acid environments. The IE could still be beyond 92% after 5 days of immersion, suggesting an excellent long-term stability of the SKRE inhibitor. A considerably high IE (more than 98%) could also be achieved at various temperatures. The main active component, cepharanthine (CEPT), adsorbs on the steel surface in a parallel configuration. The presence of isoquinoline rings, dioxole rings, benzene rings, and oxygen atoms could donate profuse π-electrons and lone pair electrons to metals, which facilitates the stable adsorption of SKRE onto the steel surface.