Effect of Sulfonamide Functionalization on the Corrosion Inhibition Efficiency of Chitosan for Carbon Steel in 1.0 m <scp>HCl</scp> : Experimental and Computational Approaches

ABSTRACT This study successfully synthesized and evaluated a novel, eco‐friendly corrosion inhibitor based on chitosan functionalized with a quinoxaline moiety (DQDS). A series of modified chitosan sulfonamide inhibitors (CH‐DQDS1, CH‐DQDS2, CH‐DQDS3) was synthesized by reaction of chitosan with varying molar ratios of quinoxaline sulfonyl chloride under mild conditions (room temperature, stirring). In a corrosive solution of 1.0 M HCl, the samples were determined to be effective corrosion inhibitors for carbon steel. The most effective inhibitor (CH‐DQDS3) achieved a high inhibition efficiency of 91.36% at 400 ppm. Adsorption of inhibitors onto the surface of the steel occurs via a combination of physical and chemical interactions (mixed type), as confirmed by strongly negative Gibbs free energy values (Δ G °ads = −30 to −36 kJ mol −1 ), indicating a spontaneous process. Electrochemical Impedance Spectroscopy (EIS) demonstrated an increase in charge transfer resistance corresponding to the concentration of the inhibitor, as well as the modified chitosan sulfonamide samples exhibiting a higher capacitive semicircle and higher inhibition efficiency percentage than the native chitosan. SEM‐MAP and atomic force microscope (AFM) analyses provided visual confirmation of the creation of a protective adsorbed film. AFM specifically showed a dramatic reduction in surface roughness (from 852 to 210 nm) due to the inhibitor's protective action. Quantum chemical calculations, molecular dynamics (MD), and Monte Carlo simulations provided atomistic insights into the adsorption mechanism at the steel/solution interface. Lastly, the incorporation of the quinoxaline moiety significantly enhanced Chitosan's corrosion inhibition properties. Future work will focus on optimizing the molecular structures and testing performance in more complex, real‐world corrosive environments.