Corrosion inhibition potentials of ampicillin for mild steel in hydrochloric acid solution

Ampicillin [(2S,6R)-6-(2-(aminomethyl)benzamido)-3,3-dimethyl-7-oxo-4-thia-1-azabicyclo(3.2.0) heptanes-2-carboxylic acid], an antibiotic drug was investigated as corrosion inhibitor for mild steel in HCl using gravimetric method. The results obtained showed that various concentrations of ampicillin studied inhibited the corrosion of mild steel in solutions of HCl. The inhibition efficiency increased with increase in the concentrations of ampicillin and decreased with increase in temperature of which the inhibitor of concentration 5 × 10−3 M at 30 °C had the highest inhibition efficiency of 75.85%. Its adsorption was found to be physical, exothermic and spontaneous as confirmed by values of activation energy and free energy of adsorption (around −20 kJ mol−1 for adsorption and below 80 kJ mol−1 for activation energy) and also fitted the Langmuir adsorption model. Quantum chemical calculations results show that ampicillin possesses a number of active centers concentrated mainly on the nitrogen atoms and the neighboring C atoms. The HOMO and LUMO plots of ampicillin further present ampicillin as an effective corrosion inhibitor.