Comparative investigation of corrosion inhibition performance and mechanism of TU and p-TTU on CRS in H2SO4 solution

• p-TTU exhibits superior inhibition efficiency (97.97%) over TU (93.64%) for steel in 0.5 M H2SO4. • A multi-scale mechanism from molecular electron distribution to macroscopic protective film is fully elucidated. • Combined DFT/MD simulations reveal p-TTU's stronger adsorption energy and faster adsorption kinetics. • The benzene ring in p-TTU is identified as the key structural feature governing its enhanced performance. • The adsorption mode shifts from localized (TU) to multi-point anchoring (p-TTU) due to the phenyl group. The inhibition mechanism of thiourea derivatives remains inadequately understood due to their strong dependence on molecular structure and corrosive environment. The corrosion inhibition performance and mechanism of thiourea (TU) and 1-p-tolylthiourea (p-TTU) for steel in 0.5 M H 2 SO 4 were systematically investigated using an integrated methodology combining density functional theory (DFT), molecular dynamics (MD) simulations, and experimental validation. The results demonstrate that both inhibitors exhibit remarkable efficiency, reaching 93.64% (TU) and 97.97% (p-TTU) at 50 mg L –1 , with p-TTU maintaining superior performance even at elevated temperature (323 K). The outstanding efficacy of p-TTU originates from its benzene ring, which optimizes electron density distribution, reduces the energy gap, and strengthens physical adsorption capability. This molecular advantage yields a significantly more negative adsorption energy for p-TTU (–581.7 kJ mol –1 ) compared to TU (–241.5 kJ mol –1 ), enabling faster adsorption and formation of a denser protective film that effectively suppresses steel corrosion in sulfuric acid.