2-Mercaptobenzimidazole-functionalized chitosan for enhanced removal of methylene blue: Batch and column studies

Chitosan functionalized with 2-mercaptobenzimidazole (2-MBI) (i.e. 2-MBI@Chit) shows high sorption capacity (i.e., 1.28 mmol MB g(-1)) for methylene blue (MB) (at pH close to 9.3). Sorption is weakly decreased (by less than 25%) by high NaCl concentration (up to 45 g L-1). The sorption (slightly endothermic) is fitted by the Langmuir equation. The kinetic profile is fitted by the pseudo-first order rate equation (PFORE): equilibrium reached within 90 min of contact. The resistance to film diffusion is minimized when setting agitation speed at 200 rpm. Dye desorption is successfully achieved (up to 94.5%) using 0.8 M HCl; desorption kinetics is little slower than the sorption step. The loss in sorption capacity at the fifth sorption/desorption cycle does not exceed 5%. Yoon-Nelson, Bohart-Adams, and bed-depth service time equations are used for analyzing the breakthrough in fixed-bed columns. At the exhaustion of the column, the sorption capacity approaches the maximum sorption capacity in batch: all the reactive groups remain accessible in dynamic sorption mode. The dye is efficiently recovered from spiked seawater and the sorption performance is depreciated by less than 16% while comparing tap water and seawater under selected experimental conditions.

Automated summary

Chitosan functionalized with 2-mercaptobenzimidazole shows high sorption capacity for methylene blue, which remains stable even at high NaCl concentration. The sorption process follows Langmuir equation, and the efficiency of adsorption and desorption can be influenced by agitation speed and HCl concentration.