A sustainable lignin-clay nano-absorbent for highly efficient methylene blue removal

Water pollution caused by toxic dyes such as methylene blue (MB) has become a bottleneck for recycling or reusing enormous industrial wastewater. Designing a green and cost-effective bio-absorbent for the highly efficient removal of MB from wastewater is crucial but remains a great challenge. In this study, abundant, inexpensive, and environmentally benign lignin and bentonite were used as starting materials, and quaternary and amphiphilic lignin as a network macromolecule was designed to be inserted into the galleries of the stacked bentonite clay to prepare lignin-bentonite nanohybrids. The specific surface area of the modified nano-absorbent was significantly increased to 45.60 m²/g and owned a type II-like isothermal mechanism. The absorbent showed a maximum removal of MB of 99.7 % at neutral pH and room temperature with a maximum adsorption capacity of 822.22 mg/g, demonstrating the potential of an excellent adsorbent. The MB adsorption process fits well with both Langmuir and Freundlich isotherm models, the adsorption mechanism includes strong electrostatic attraction between absorbent and MB, and physical adsorption in a complicated monolayer and multiple macroporous structures. This study leverages the economic and environmental benefits of lignin and bentonite clay to prepare a cost-effective bio-absorbent for efficient removal of MB from aqueous solutions.