Preparation of lignin-based porous carbon as an efficient absorbent for the removal of methylene blue

• Hierarchical LPC showed a high specific surface area up to 3382.32 m 2 /g. • The maximum adsorption capacity of MB by the LPC was as high as 1119.18 mg/g. • The adsorption kinetic was in well agreement with pseudo-second-order model. • Langmuir isotherm model fitted well to the adsorption experimental data. • The LPC exhibited the outstanding selective adsorption property to cationic dyes. Lignin is the most abundant renewable aromatic polymer in the world, but its complex structure makes it difficult for efficient utilization. In this study, lignin-based porous carbon (LPC) was prepared through hydrothermal treatment and KOH activation and then used as an adsorbent for the adsorption of methylene blue (MB). The influence of contact time, initial MB concentration, solution pH and adsorption selectivity on adsorption performance was explored. Hierarchical LPC showed a high specific surface area up to 3382.32 m 2 /g and a large number of active sites. The maximum adsorption capacity of MB was as high as 1119.18 mg/g. The adsorption kinetic was in well agreement with pseudo-second-order model. Langmuir isotherm model fitted well to the adsorption experimental data. The maximum adsorption capacity calculated from Langmuir isotherm model (1119.65 mg/g) approached the experimental result. Moreover, the LPC exhibited the outstanding selective adsorption property to cationic dyes, where the adsorption capacities of malachite green and rhodamine B were 2467.30 mg/g and 1657.82 mg/g, respectively. In addition to electrostatic interaction due to the negatively charged surface of LPC, hydrogen bonding and π - π stacking interactions were responsibility for the adsorption mechanism. On account of low-cost, excellent adsorption properties and favorable reusability, the LPC has the promising potential as a lignin-based absorbent for removing cationic dyes in wastewater treatment.