Centrifugally spun lignin fibers with high Cr(Ⅵ) adsorption capacity

Due to its structural cohesiveness, lignin is unable to construct an efficient adsorption structure and exhibits poor adsorption capacity of heavy metal ions. Most of the current studies have been conducted to improve the adsorption performance of lignin by functionalization or construction of spatial network structure to change the aggregation state of lignin. However, this did not develop the adsorption capacity of lignin itself and the enhancement is quite dependent on the introduced materials. In this study, lignin fibers were prepared by facile centrifugal spinning method to expose more effective adsorption sites, and the corresponding Cr(VI) adsorption capacity was improved. The further enhancement of the Cr(VI) adsorption capacity of lignin fibers can be achieved by the formation of porous structure via adding sodium dodecyl sulfate and then dissolving it in aqueous solution during adsorption. The obtained lignin fibers exhibited maximum Cr(VI) adsorption capacity of 339.0 mg/g, which is quite higher than that of modified lignin in previous studies. As-prepared lignin fibers showed monolayer adsorption and chemical adsorption which mainly included reduction, electrostatic attraction, complexation, π-cation interaction, and pore filling. These results are useful for the application of lignin adsorbent materials in wastewater treatment.