In vitro adsorption kinetic model of phenobarbital onto powdered seeds of Garcinia kola

The in vitro adsorption kinetics of phenobarbital on Garcinia kola seed powder was investigated. Batch adsorption experiment to determine effects of adsorbent dose (0.1 to 2.0 g), adsorbate concentration (50 to 200 ppm), contact time (20 to 300 min) and temperature (298 to 318 K) was conducted. Adsorption data were subjected to different experimental and theoretical adsorption kinetic models (first order, second order, Elovich equation and modified Freundlich). The adsorption rate constants obtained from the best fit model were used to determine the activation energy, Ea from the Arrhenius equation. The studies showed that adsorption of phenobarbital onto powdered G. kola seed followed second order kinetics with adsorption rate constant (0.174 to 2.156 g mg-1 min-1) at 298 to 318 K with good correlation coefficient (0.909 to 0.951). The adsorption equilibrium was attained after 4 h with different equilibrium concentration (0.0902, 0.0864 and 0.0968 mg/ml) at 298, 308 and 318 K, respectively. Intra-particle adsorption model revealed three stages of adsorption with different Kiads which implied that intra-particle diffusion could not be the only factor controlling phenobarbital adsorption onto G. kola seed. Arrhenius plot gave Ea of 99.435 KJ mol-1 and frequency factor of 5.25 × 1016. In conclusion, adsorption of phenobarbital followed strictly second order kinetic model and its overdose and/or poisoning could be effectively managed with G. kola seed powder.   Key words: Kinetic model, adsorption, Garcinia kola, Arrhenius equation, phenobarbital.