Adsorption of Cu2 + and methylene blue on dodecyl sulfobetaine surfactant-modified montmorillonite

The dodecyl sulfobetaine surfactant-modified montmorillonite (Mt-SB12) was synthesized using montmorillonite (Mt) and dodecyl sulfobetaine surfactant. The as-prepared material was used as adsorbent for removal of Cu2 + and methylene blue (MB) in single and binary systems. In the single systems, the results showed that the kinetics of adsorption followed the linear pseudo-second-kinetic model. The results of interlayer diffusion indicated that MB had higher diffusion rate than Cu2 +. For the Mt-SB12, the isotherm results showed that MB adsorption followed the Langmuir and Cu2 + adsorption followed the Freundlich isotherm. The adsorption capacities for Cu2 + and MB at 298 K and pH 5 were (10.2 and 254.0) mg/g, respectively. For the Mt, Cu2 + and MB adsorptions both followed the Langmuir. The adsorption capacities for Cu2 + and MB at 298 K and pH 5 were (9.5 and 150.2) mg/g, respectively. So the dodecyl sulfobetaine surfactant-modified Mt is more beneficial to adsorb MB than Mt. Dubinin–Radushkevitch (D–R) equation indicated Cu2 + and MB adsorptions were chemical ion exchange adsorption and adsorption thermodynamics showed they were spontaneous and endothermic processes. In binary systems, Cu2 + and MB showed competitive adsorption. The adsorption capacity of Cu2 + or MB would be decreased with the increased concentration of another adsorbate. Mt-SB12 exhibited relative higher affinity and selectivity to MB.