Weaving Hyper‐crosslinked Polymer from Alkaline Lignin for Adsorption of Organic Dyes from Wastewater

Abstract Lignin is widely found in nature and attracts increasing concern as the renewable carbon material. In this work, hyper‐crosslinked lignin was successfully prepared and applied for adsorbing dyes such as rhodamine B (RhB), methylene blue (MB) and Congo Red (CR) in wastewater. The characteristics of the alkaline lignin and hyper‐crosslinked lignin were identified by Fourier transform infrared spectroscopy (FT‐IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and N 2 adsorption and desorption measurements. The results show that the hyper‐crosslinked lignin is composed of uniform and porous nanoparticles with smaller size as compared to the sheet and‐ block structure of alkaline lignin. The specific surface area and pore structure of the hyper‐crosslinked lignin have been greatly optimized, while retaining the functional groups on the surface of the alkali lignin. The Brunner‐Emmet‐Teller (BET) surface area of the hyper‐crosslinked lignin reaches up to 402.8 m 2 ⋅ g −1 , and the adsorption capacity of RhB is up to 1332 mg ⋅ g −1 . The isotherm model and thermodynamic results indicate that the adsorption process conforms to the Langmuir model, mainly showing a single‐layer spontaneous chemical endothermic process. In addition, HCP−L showed good selective adsorption performance for cationic dyes with the adsorption amounts of 228 mg ⋅ g −1 for MB, while that of the anionic dye CR (89 mg ⋅ g −1 ) was comparatively low. The adsorption mechanism was hydrogen bonding and π‐π stacking in addition to the electrostatic effect caused by the negative charge on the surface of HCP−L.