Quantification of the Adsorption Kinetics of a Model Corrosion Inhibitor on Gold Using QCM-D

In the present study, a quartz crystal microbalance with dissipation monitoring (QCM-D) was used to investigate the adsorption of a model corrosion inhibitor compound, tetradecyldimethylbenzylammoniumbromide (BDA-C14), on gold electrode. Sauerbrey’s equation was used to analyze the equilibrated normalized frequency change for estimation of the adsorbed mass and adsorbed layer thickness at different bulk inhibitor concentrations after careful validation. The average adsorbed layer thickness for BDA-C14 at tested experimental conditions lie in the range of 1 nm to 1.4 nm. Time-dependent part of the frequency change was analyzed using Langmuir adsorption isotherm to calculate the kinetic constants (kA = 0.075±0.02 mM–1·s–1, kD = 0.0023±0.0007 s–1, and KAD = 32.2 mM–1). Equilibrium surface coverage (θeq) was estimated at each bulk inhibitor concentration tested: 0.69 for 25 ppm(w), 0.74 for 50 ppm(w), and 0.91 for 100 ppm(w). Some theoretical calculations are also shown explaining the use of known molecular geometry and adsorption kinetics information from QCM-D analysis to reasonably speculate the predominant adsorbed layer configuration. A conscious effort is made to state and validate each assumption made for the analysis of the experimental results.