Sustainable novel chitosan sulfonamides conjugated with a phthalazine derivative for enhanced corrosion inhibition in acidic environments.

Chitosan, a biopolymer material, has shown great promise as a biodegradable corrosion inhibitor. Herein, this research details the synthesis of new chitosan sulfonamide conjugates by coupling chitosan with 1,4-phthalazinedione sulfonyl chloride (DEPS) at various molar ratios to create enhanced, eco-friendly corrosion inhibitors (CHDEPS1-3). The modifications increased the biopolymer's crystallinity, peaking at 79.80% for CHDEPS3 compared to 64% for native chitosan. The protective performance of the inhibitors on carbon steel in an acidic medium was assessed using electrochemical tests, weight loss measurements, and surface characterization. The findings were highly positive, especially with CHDEPS3 demonstrating a superior inhibition efficiency of 95.38% at a concentration of 400 ppm. Atomic Force Microscopy (AFM) confirmed the formation of a protective adsorbed layer, which reduced the steel's average surface roughness from 852.05 nm to just 36.78 nm. Theoretical analysis, including quantum chemical calculations, molecular dynamics, and Monte Carlo simulations, elucidated the adsorption mechanism. The potentiodynamic polarization data and significantly negative Gibbs free energy values (ΔG: -30.04 to -35.75 kJ mol-1) confirmed a spontaneous, mixed physical-chemical adsorption process, occurring via the formation of Fe-N and Fe-O bonds at the steel/solution interface. The study concludes that the insertion of the phthalazine moiety successfully enhanced the inhibitor's electrostatic effect, hydrophobicity, and overall efficiency by promoting robust interfacial adsorption.