Application of lignin adsorbent in wastewater Treatment: A review

Lignin as a naturally synthesized polymer widely existing in plant cell walls, is characterized by extensive sources, environmental protection and abundant functional groups. In recent years, many scholars have obtained various lignin-derived adsorption materials with excellent properties by modifying, carbonizing and compositing of lignin, which have a wide application prospect in the field of wastewater treatment. In this review, the modification methods of lignin adsorbents are introduced in detail, such as surface modification with N, O and S functional groups and composite modification, etc. The thermodynamic and kinetic models of lignin-based adsorbent adsorption process are summarized, and the adsorption mechanisms such as electrostatic attraction, π-π complexation and hydrogen-bond interaction are listed. The application of lignin-based adsorbents to the treatment of wastewater containing heavy metal ions, inorganic anions, organic dyes and drugs is reviewed. Finally, the current problems and future research directions of lignin-derived adsorbents are summarized and prospected. To achieve controllable preparation and large-scale production of lignin-derived adsorbents, and to improve the applicability of adsorbents in the actual environment are the main research contents in the future.