Multicomponent adsorption of chlorhexidine gluconate in presence of a cationic surfactant: Role of electrostatic interactions and surface complexation

The modified competitive Langmuir-like model and the LeVan-Vermeulen model are applied for the adsorption of chlorhexidine gluconate and cetrimide (present in various antiseptic solutions) using Granular Activated Carbon (GAC). Parameters of each of these models are estimated using NAG E04USA subroutine, based on minimizing the sum of squares (SSQ). The GACs are physically and chemically characterized. A good fit for the Langmuir adsorption isotherm, for both the pure components, confirms the applicability of both the multicomponent adsorption isotherm models. Kinetic study, pore and film diffusion modelling are also applied. The goodness of the fits in the pseudo-second order model and the film diffusion model helps conclude that film diffusion is the rate controlling step for the adsorption of chlorhexidine gluconate and cetrimide by GAC after around 15 h. The surface remaining negative beyond the pHpzc(=2.185), a pH of approximately 7–8 is maintained for all the experiments of batch adsorption. This helps in much larger adsorption of cetrimide, which exists as cetrimonium ion in the model antiseptic solution. Results demonstrate that specific chemical interactions between chlorhexidine gluconate and surface functional groups, in combination with electrostatic forces, play the major role in the adsorption mechanism.