Picolinoyl N4-Phenylthiosemicarbazide-Modified ZnAl and ZnAlCe Layered Double Hydroxide Conversion Films on Hot-Dip Galvanized Steel for Enhancing Corrosion Protection in Saline Solution

ZnAl and ZnAlCe layered double hydroxide (LDH) conversion layers modified with picolinoyl N4-phenylthiosemicarbazide (HL) are fabricated on hot-dip galvanized steel (HDG) to improve corrosion protection. X-ray diffraction (XRD) confirms that HL molecules are not intercalated within the LDH interlayers, whereas Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and energy-dispersive X-ray spectroscopy (EDS) analyses reveal their surface adsorption. Moreover, scanning electron microscopy (FE-SEM) observations reveal that HL modification induces changes in surface morphology. After 168 h in 0.1 M NaCl, the LDH structure remains intact, and N and S signals are still detected, confirming the persistence of both the LDH layer and adsorbed HL molecules under corrosive conditions. During 168 h immersion in NaCl, electrochemical measurements indicate that the modified LDH layers exhibit higher corrosion resistance than the unmodified ones, with the ZnAlCe LDH/HL coating providing the most effective protection.