Removal of cyanocobalamine from aqueous solution using mesoporous activated carbon

The adsorption of cyanocobalamine was studied using coal-based mesoporous activated carbon (AC). The ACs tested showed a comparable pore volume, around 0.5 cm3 g−1, but different contribution of mesopores ranging from 0.53 to 0.82 cm3 g−1. The adsorption of cyanocobalamine was carried out in slightly alkaline solution in static conditions. Three kinetic models including a first-order Lagergren model, a pseudo-second-order model, and an intraparticle diffusion model were applied to describe the kinetics and mechanism of adsorption. The adsorption of cyanocobalamine on mesoporous carbons followed the pseudo-second-order model. The diffusion of cyanocobalamine molecule within smaller mesopores was identified to be the rate-limiting step. The analysis of adsorption equilibrium data indicates that the adsorption of cyanocobalamine better fits the Langmuir equation than the Freundlich equation. The Langmuir adsorption capacity of the carbon is strongly related to the degree of mesoporosity development. Among ACs tested, the carbon with the highest mesopore volume and mesopore width of 10–50 nm shows the greater ability to remove cyanocobalamine from aqueous solution. The effect of pore-size distribution on the kinetics and mechanism of adsorption has been discussed.