Sodium dodecylsulfate–benzotriazole synergistic effect as an inhibitor of processes on copper ∣ chloridric acid interfaces

The copper ∣ hydrochloric acid interface has been studied in the presence of sodium dodecylsulfate (SDS), benzotriazole (BTAH) and SDS+BTAH mixtures. Polarization curves have shown that SDS exerts little effect as an inhibitor on the anodic dissolution of copper either in the absence or in the presence of BTAH. On the other hand SDS acts as an inhibitor for the H+/H2 reaction over the entire range of negative overpotentials and promotes significant synergism on the inhibitive action of BTAH. ‘In situ’ Raman spectra show that SDS adsorbs on the copper surface through both moieties, the non-polar aliphatic chain and the polar head. At negative overpotentials SDS promotes the BTAH adsorption on the copper surface. The adsorption equilibrium constant (Kads) calculated from a Langmuir isotherm model at a constant negative overpotential is about 104 dm3 mol−1, and it depends on the potential. The Langmuir model was applied considering n active sites per SDS molecule, according to the results previously observed in sulfuric medium. Kads increases and n decreases as the potential becomes more positive suggesting a charge effect on the surfactant adsorption.