Kinetics and thermodynamics analysis of the polybenzimidazole adsorption onto carbon materials using adsorption isotherm measurements

Abstract

The surface modification of carbon materials is an effective method for enhancing the properties of carbon-based functional materials; particularly, the use of a polymer coating is advantageous owing to its intactness and simplicity. Polybenzimidazole (PBI) has been used to modify carbon surfaces, yet its adsorption behavior has not been thoroughly examined. In this study, the adsorption kinetics and thermodynamics of PBI adsorption on various types of carbon black with different surface morphologies and chemical compositions were analyzed via isotherm measurements. To determine the effects of the polymer, its adsorption behavior was compared to that of the PBI monomer (1,3-bis(1H-benzo[d]imidazol-2-yl)benzene (referred to as the PBI-unit)). The surface adsorption of PBI was slower than that of the PBI-unit; however, PBI exhibited a greater adsorption capacity. The PBI adsorption is an entropy-driven process, whereas PBI-unit adsorption is enthalpy-driven. The adsorption of PBI was more thermodynamically favorable on carbon surfaces with higher crystallinity (lower oxygenation) owing to the easier detachment of solvent molecules from the carbon surface, leading to a higher adsorption constant.