Experimental and Theoretical Investigations on Copper Corrosion Inhibition by Cefixime Drug in 1M HNO₃Solution

Cefixime, a third-generation semi-synthetic cephalosporin antibiotic was used as a copper corrosion inhibitor in 1M HNO3 solution. The study was conducted through the weight loss technique at 298 - 318 K and theoretical studies based on quantum chemistry. The studied drug inhibited the corrosion of copper in 1M HNO3 over the cefixime concentration range (0.02 - 2 mM). The inhibition efficiency increased with an increase in the inhibitor concentration to reach 91.07% at 2 mM, but decreased with an increase in temperature. The thermodynamic functions related to the adsorption of cefixime on the copper surface and that of the metal dissolution were computed and analyzed. The results point out spontaneous adsorption, mainly through a physisorption mechanism following Langmuir adsorption isotherm model and an endothermic dissolution process. Quantum chemical calculations were also performed at B3LYP level with 6-31G (d, p) basis set and lead to molecular descriptors such as EHOMO (energy of the highest occupied molecular orbital), ELUMO (energy of the lowest unoccupied molecular orbital), ΔE (energy gap) and μ (dipole moment). The global reactivity descriptors such as χ (electronegativity), χ (global hardness), S (global softness), and ω (electrophilicity index) were derived using Koopman’s theorem and analyzed. The local reactivity parameters, including Fukui functions and dual descriptors were determined and discussed. Experimental and theoretical results were found to be in good agreement.

Electrochemical Study of the Synergistic Effect of Two Copper Corrosion Inhibitors, Nicotinic Acid (NAC) and Nicotinamide (NAM) in Two Different Media

Inhibitive properties of NAC and NAM as well as their mixture have been investigated in two different corrosive media through potentiodynamic polarization and electrochemical impedance spectroscopy at 298 K. These electrochemical measurements indicate that the inhibition efficiency increases with the concentration for each of the inhibitors used separately as well as for their mixture. In both cases, the combination behaves as mixed type inhibitor with a great cathodic tendency. NaCl 3.5% highlights an antagonist effect of NAM which reduces the effectiveness of NAC whereas HNO3 1M shows a synergistic effect between them.