Biomitigation of noxious metal ions using engineered lignin-based nanocomposites for sustainable environment

Given the inclusion of high amounts of harmful metals in industrial effluent, it is causing significant health concerns. The extraction of such metals remains a major global concern, and in this context, creating lignin-incorporated composites using additional components has gained attention due to their substantial surface area and the high number of pores in their structures, significant reactive properties, and low ability to get dissolved in water. We present here the ability to adsorb several lignin-based nanocomposites containing a range of components such as sawdust, bentonite, polyacrylic acid, and others for heavy metal extraction. Initially, this review examines the sources of heavy metal pollution and their associated health and environmental risks. Subsequently, lignin's sources, chemical structure, and properties are presented. The latest developments in lignin-based nanohybrids for the adsorptive removal of several heavy metals, including Pb(II), Ar(V), Cu(II), and Cr(VI), are then covered. Primarily, the synthesis methods involving modifications and chemical functionalization for improved structural and chemical alterations and surface characteristics such as surface area, pore volume, and adsorptive removal capability are explained and compared. In addition, the most suitable isotherms and kinetic models are discussed. Following that, the regeneration capabilities of various lignin-based nanohybrids are described. Lastly, the challenges and research gaps, and suggestions for further research and development are provided. This review reveals that lignin-based nanocomposites are a great option for removing heavy metals from effluents when combined with additional substances such as sawdust, bentonite, polyacrylic acid, and so on.