Adsorption Mechanism of Nicotinic Acid onto a Passive Iron Surface

Abstract

Cyclic voltammetry and in situ Raman spectroscopy were used to determine the adsorption mechanism of nicotinic acid onto passive iron film surface. Its ability to form a surface complex tends to stabilize the interstitial Fe II in Fe III states and results in the progressive development of an insoluble film. Furthermore, an analytical investigation using a rotating electrochemical quartz crystal microbalance (rEQCM) showed that the adsorption isotherms of nicotinic acid onto iron in the active and passive states followed Langmuir-Freundlich behavior from which the adsorption constant, standard free energy of adsorption, and heterogeneity could be calculated. The organic molecules attach to the film surface by chemisorption and the interstitial cations are fixed in the octahedral sites giving stable nanocrystals. These assumptions were confirmed by scanning electron microscopy (SEM) and attenuated total reflection transform infrared (ATR FTIR) spectroscopy.