Exploring the role of N-S codoped carbon dots for enhanced corrosion inhibition of carbon steel in sulfuric acid

In the present work, nitrogen-doped carbon dots (N-CDs) and nitrogen-sulphur codoped carbon dots (NS-CDs) have been used as corrosion inhibitors for carbon steel in 0.5 M H₂SO₄. The evaluation was carried out by using weight-loss studies, electrochemical assessments, and surface morphology analyses. Although a decrease in the N content in NCDs is marked by an increase in the corrosion inhibition efficiency, the results exhibited significantly higher corrosion inhibition rates with codoped NS-CDs as compared to N-CDs, evidenced by their inhibition efficiency values (98 % vs. 88 %). In addition, NS-CDs not only revealed an increase in the charge transfer resistance value, rising from 50 to 4964 ohm cm², the corrosion current density exhibited a significant decrease (∼10⁻³ mA/cm²). The significant improvements were attributed to the formation of dense adsorption films and the hydrophobic properties of NS-CDs on the steel surface, leading to formation of an effective barrier against corrosion. In addition, the carbon dots that behaved as a mixed type of inhibitors (with predominant cathodic effect), were adsorbed onto the steel surface according to a Langmuir adsorption isotherm and the mechanism of inhibition is attributed to physicochemical adsorption dominated by physical interactions. The high efficiency accompanied by low corrosion current density indicates reduced corrosion rate that in turn can be beneficial in several applications, as it contributes in enhanced durability and structural sturdiness of the material.