Acetone fractionation: a simple and efficient method to improve the performance of lignin for dye pollutant removal.

In this work, it was found that the adsorption capacity of lignin to cationic dye (methylene blue, MB) from aqueous solution could be significantly improved by simple acetone fractionation. The removal efficiency of MB by acetone insoluble kraft lignin (AIKL) was 10 times that of unfractionated kraft lignin (KL). And the maximum capacity of AIKL could reach up to 623.4 mg g. And the high removal rate could be achieved even at low concentrations. The effects of ionic strength, temperature, adsorbent dosage were systematically investigated. Adsorption kinetics showed the adsorption behavior obeyed the pseudo-second-order kinetic model. The equilibrium data was more consistent with the Langmuir isotherm model. Thermodynamic analyses proved that the adsorption was a spontaneous and endothermic physisorption process. In addition, the reasons for the enhanced adsorption effect by fractionation were clarified based on characterization by FT-IR. The enhancement of π-π interaction between AIKL and MB caused by fractionation plays an important role in the adsorption process.