HNP-PhOH as a Potential Inhibitor of Aluminium Corrosion in 1M H₂SO₄: Experimental and Quantum Chemical Studies

This study investigated the corrosion-inhibition behaviour of HNP-PhOH for pure aluminium in 1 M H₂SO₄ using gravimetric measurements and density functional theory (DFT). Mass-loss experiments were conducted over 298–338 K at different HNP-PhOH concentrations. The results showed that inhibition efficiency increased with inhibitor concentration but decreased with temperature. At 298 K, 1 mM HNP-PhOH produced the highest recorded inhibition efficiency of 100%, whereas the efficiency at the same concentration decreased to 69.30% at 338 K. Adsorption behaviour was assessed using several isotherms, and the modified Langmuir model provided the best description of the experimental data. Thermodynamic adsorption and activation parameters were calculated to evaluate the adsorption process. The Adejo–Ekwenchi isotherm indicated contributions from both physisorption and chemisorption. Quantum-chemical calculations were performed at the B3LYP/6-311G(d,p) level to evaluate global and local molecular descriptors relevant to the interaction of HNP-PhOH with aluminium. The calculated descriptors included frontier molecular orbital energies, energy gap, dipole moment, electronegativity, hardness, softness, electrophilicity, electron-transfer fraction, and Fukui functions. The theoretical analysis identified probable reactive sites and supported the experimentally observed inhibitory behaviour. Overall, HNP-PhOH inhibited aluminium corrosion under the investigated acidic conditions, although its inhibition efficiency decreased as temperature increased. The findings provide mutually supportive experimental and theoretical evidence for the observed inhibition behaviour within the conditions examined.